Chemistry

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2,2-Dithiobis(benzothiazole) complexes (Cd and Ni): Precursors to nanoparticles and electrochemical properties and interactions with Rhodamine B
(Vaal University of Technology, 2021-10-13) Mabaso, Busisiwe Dagracia; Moloto, N., Prof.; Moloto, M. J., Prof.
The ligand 2, 2-dithiobisbenzothiazole and it metal complexes have been a subject of interest in various fields but they have found to exhibit remarkable and prevalent biological and pharmacological activities. The ligand tends to coordinate to complexes through the sulfur atom and hence the metal-sulphide bond are good precursor to generate metal sulfide nanoparticles using single-source precursor route. The complexes are generally prepared by reflux for 1 to 2 hours depending on the solvent used to produce very stable solid products and some form in crystalline form. All the prepared nickel and cadmium complexes were characterized using techniques such as elemental analyzer, IR, 13C NMR spectroscopy and thermogravimatric analysis. The data obtained from the spectroscopic analysis was consistent of the coordination of the ligand with the metal ions through the sulphur atoms of the 2,2-dithiobisbenzothiazole moiety. The thermal analysis of the prepared complexes gave a final residue of metal sulphide for both metal complexes. Characterization techniques showed the formation of bidentate complexes for both nickel complex and cadmium complex. The prepared complexes were then used to synthesize metal sulphide nanoparticles .The nanoparticles were prepared by thermal decomposition method of the single source precursor in a solution of oleylamine (OLA). Two different parameters were investigated temperature and time to study their effect on the size and shape of the nanoparticles. The synthesized nanoparticles were characterized using techniques such as UV-Vis spectroscopy, photoluminescence spectroscopy, and X-ray diffraction analysis and transmission electron microscopy. The temperatures of the reaction have a significant effect on the rate of the reaction that will affect the size and shape of the nanoparticles. This effect was confirmed by the optical properties of the synthesized nanoparticles prepared at different reaction temperatures. The spectra shows that absorption maximum and band edge shift to lower wavelength as the temperature of reaction was progressively increased. This trend is associated to the decrease in particles size of the prepared nanoparticles. TEM images further confirmed that the particles size of the prepared nanoparticles was progressively decreased as the temperature was increased. The time of the reaction is one of the most significant factors in the synthesis of the nanoparticles. The investigation of the time of the reaction yield results that depicted that with increase in time of the reaction, the band edge increases, but relatively at short wavelength to the bulk. Hence, the band edges of the nanoparticles were blue shifted significantly to the bulk. The results show that with an increase in the time of the reaction, the nanoparticles increases in their size due to Ostwald ripening. The optimum complexes and optimum nanoparticles were used to further study their electrochemical properties using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) graphs were fitted using the randles circuit and they confirm that the NiS nanoparticles GCE greatly increase the electron transfer rate, probably due to the nanostructured surface property of the NiS nanoparticles. Differential pulse voltammetry (DPV) was used to study the electrochemical behavior and the DPV showed that the current response of Rhb was higher for the optimum temperature NiS nanoparticles compared to all the materials used. There was an increase in the Rhb current response with an increase in pH and pH 7 was used as the optimum pH when Ni- complex was used as a modifier and pH 8 was used as optimum when NiS nanoparticles were used as a modifier. Effect of concentration showed that the NiS nanoparticles for the optimum temperature had a wide linear range and a low detection limit. The method has good accuracy, acceptable precision, and reproducibility. This method provides a novel electrochemical method for determination of RhB.
Adsorption and Photodegradation of Molasses Wastewater using TiO2-ZnO Hybrid Nanocatalysts Supported on Activated Carbon and Silica
(Vaal University of Technology, 2017-03) Otieno, Benton Onyango; Naidoo, E. B., Prof.; Aoyi, Ochieng, Prof.
There is an increasing use of composite materials in photo-catalysed remediation of wastes such as molasses wastewater (MWW), which is characterised by high organic load and a dark brown colour caused by biorecalcitrant melanoidin compounds. This study was carried out to determine the photocatalytic efficiency of a TiO2-ZnO hybrid supported onto activated carbon (AC) and silica for the remediation of MWW. Immobilisation of ZnO onto synthesised TiO2 formed TiO2-ZnO, which was then supported onto AC and silica, to give TiO2-ZnO/AC and TiO2-ZnO/Silica composites, respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX) and Fourier Transform Infrared (FTIR) spectroscopies, and transmission electron microscopy (TEM), revealed the successful hybridisation of TiO2 and ZnO, and the subsequent support of the hybrid onto AC and silica. Thermal stability of the synthesised composite catalysts was studied by differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). Photoluminescence (PL) spectroscopy further revealed a restrained electron-hole pair recombination resulting from both the successful formation of a heterojunction in the hybrid, and the introduction of electron accepting AC support. Introduction of a silica support on the other hand increased the rate of recombination resulting in reduced quantum efficiency of the TiO2-ZnO/Silica composite, hence AC was adopted as the ideal support material for this study. Photodegradation was monitored in terms of colour and total organic carbon (TOC) reductions, and nitrate formation. It was observed that the TiO2-ZnO hybrid, due to its desirable optical properties, had better activity than the respective oxides (TiO2 and ZnO). On supporting the hybrid onto AC, both adsorption and photocatalytic activities were further enhanced with improved overall colour removal of 86% from 68%. Photodegradation followed pseudo-first order rection model, with the rate constant (𝑘𝑎𝑝𝑝) decreasing from 0.0701 to 0.0436 min-1 with increased MWW initial concentration from 3000 to 6000 ppm. Formation of nitrates confirmed a reductive pathway for the degradation of melanoidins. The UV-photodegradation process was found to be 33-fold less energy intensive for colour reduction as compared to TOC reduction, with energy demands of 35 and 1183 kWh/m3, respectively. Sorption of MWW onto TiO2-ZnO/AC fitted well with the Freundlich isotherm and were found to be endothermic in nature with physisorption being the rate determining step. An optimum pH of 5 for the degradation process was determined. The robustness of the composite TiO2-ZnO/AC photocatalyst was revealed by its high reusability up to four cycles.
Adsorption of Cr(VI) by iron oxide functionalized polyethyleneimine (PEI) coated activated carbon-silica composites
(Vaal University of Technology, 2020-12-14) Qhubu, Mpho Cynthia; Nomngongo, P. N., Prof.; Pakade, V. E., Prof.
Water scarcity due to limited resources and pollution of the little available water by organic and inorganic contaminants remains as one of the critical issues of the 21st century. Several treatment methods have been developed, with some being used successfully at industrial scale but many challenges including secondary sludge generation, high operation costs, high maintenance costs and high energy input were observed. In this study, the adsorption process was explored as an effective means for the removal of Cr(VI) ions from aqueous solution due to its economic feasibility and use of abundantly available adsorbents. Amongst the many available adsorbents, this work focused on exploring functionalized activated carbons (ACs) as adsorbents for Cr(VI) ions due to their favorable adsorption characteristics which involve large surface area, high porosity, and high radiant stability. The iron oxide functionalized polyethyleneimine activated carbon-silica composites were prepared through co-precipitation of Fe(II) and Fe(III) over Macadamia activated carbon to form the AC-Fe3O4 co-shell which was reacted with tetraethylorthosilicate (TEOS) and the polyethyleneimine (PEI). The different adsorbents prepared were labelled AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI. The adsorbents were further characterized using elemental analysis (CHNS), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), transmission electron spectroscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FTIR displayed successful attachment of Fe3O4 and SiO2 with bands at 404 and 786 cm-1 being assigned to the asymmetric vibration of Fe-O and Si-O-Si while the asymmetric stretch of Si-OH is observed at 1066 cm-1. XRD showed the presence of magnetite particles in the adsorbents confirmed by the JCPDS 00-019-0629. EDS revealed the presence of Fe, Si, and N atoms which can relate to successful incorporation of the desired functional groups. Each of these materials were evaluated for their Cr(VI) ion removal through batch adsorption experiments where one parameter at a time was varied while all others were fixed. The parameters investigated included the effect of pH, contact time, initials Cr(VI) concentration, adsorbent dosage concentration and temperature. The optimum conditions were obtained at pH 3, initial concentration 2.5 mg/L, contact time of 120 min for AC-Fe3O4-SiO2-PEI. The optimization of each parameter was done in order to determine the conditions in which the adsorbents work best in the uptake of Cr(VI). All the three studied adsorbents showed acceptable adsorption performance for the removal of Cr(VI) from aqueous solutions. Adsorption isotherms studied confirmed that the adsorption data in all the three adsorbents fitted well into the Langmuir isotherm, demonstrating a homogeneous monolayer coverage. Regarding the kinetic studies, the adsorption data were best described by the pseudo-second order rate model with R2 values of 0.974, 0.974 and 0.962 for AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI, respectively. The adsorption capacity observed from the present study (6.62, 3.92 and 5.48 for AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI, respectively) were satisfactory and suitable as compared to those reported in literature. Thermodynamics data of the adsorption processes revealed a feasible spontaneous endothermic adsorption process which also confirmed that the reaction process occurred through chemisorption.
Adsorption of nitrate and fluoride anions from aqueous solutions using doped magnetite-pinecone nanocomposites
(Vaal University of Technology, 2022-03-23) Frans, Nonhlanhla; Ofomaja, A. E., Prof.; Akpotu, S., Dr.; Pholosi, A., Prof.
The increasing rate of pollutants, such as nitrate and fluoride from industrial and agricultural sources in the environment, especially in water bodies, is becoming alarming. Excessive nitrate and fluoride concentration in water cause environmental toxicity and hazard such as eutrophication and toxic, chronic illnesses such as methemoglobinemia. Hence, there is an urgent need to remove these pollutants from water. There have been a few successful strategies for the purification of pollutants contaminated water. Adsorption has been applied to remove pollutants from aqueous media due to its flexibility, ease of use, cost-effectiveness and ability to adsorb contaminants at low concentrations. Various adsorbents have been applied to remove nitrate and fluoride anions, and doped magnetic has shown to be effective in removing these anions. In this study, manganese doped magnetite coated pinecone (Mn-MNP-PCP) and lanthanum doped magnetite coated pinecone (La-MNP-PCP) nanocomposite were prepared using the co-precipitation method. Fourier Transform Infra-Red (FT-IR), Scanning electron microscopy (SEM), Energy-dispersive x-ray spectroscopy (EDS), Thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) were used to determine the surface groups, structure and morphology, chemical composition, thermal stability and phase determination (amorphous or crystalline) structure of the synthesised Mn-MNP-PCP and La-MNP-PCP adsorbents, respectively. In addition, batch adsorption experiments were conducted to evaluate the effects of solution pH, adsorbent dose, initial solution concentrations, contact time, adsorption kinetics, adsorption isotherm and the impact of co-existing anions on the adsorption of nitrate and fluoride ions. The mechanism of adsorption processes was also determined using equilibrium isotherm modelling results and thermodynamic parameters. The maximum adsorption capacity of Mn-MNP-PCP and La-MNP-PCP adsorbents for nitrate adsorption was 22.8 mg/g and 37.7 mg/g at solution pH 4, while the adsorption efficiency was 45.6% and 75.4%. Fluoride removal occurred at pH 2 with the adsorption capacity of 46.2 mg/g and 44.77 mg/g with the removal efficiency of 92.4 % and 89.6% on both Mn-MNP-PCP and La-MNP-PCP adsorbents. The optimum adsorbent dose for both Mn-MNP-PCP and La-MNP-PCP in the adsorption of nitrate and fluoride was 1 g/L. The optimum time for the uptake of nitrate and fluoride onto MNP-PCP and La-MNP-PCP was between 15 – 20 min. The competing phosphate and sulphate ions impacted the nitrate adsorption, while the presence of carbonate and chloride had positive nitrate adsorption onto both Mn-MNP-PCP and La-MNP-PCP nanocomposites. The decrease in nitrate adsorption may be attributed to the lower affinity of Mn-MNP-PCP and La-MNP-PCP for nitrate and a competition between the nitrate ions and co-existing anions for the active sites. The presence of all competitive ions decreased the fluoride adsorption onto Mn-MNP-PCP and La-MNP-PCP nanocomposites. The multi-valent anion with higher charge density have been reported to be more readily adsorbed than monovalent anion. The equilibrium data for nitrate and fluoride ions uptake was best described by Langmuir isotherm, which predicts the formation of ionic or covalent chemical bonds between the adsorbent and adsorbate. In the same vein, pseudo-second-order model is considerably suitable for nitrate and fluoride ions adsorption, which showed that their uptake was fast. Conclusively, La-MNP-PCP adsorbent is an effective adsorbent for nitrate adsorption, while Mn-MNP-PCP effectively trmoved fluoride ions from the aqueous solution.
Adsorption studies of toxic metal ions (Co(II), Ni(II), Cu(II), Cr(VI) and Pb(II)) and methylene blue using black cumin (Nigella sativa L.) seeds
(Vaal University of Technology, 2021) Thabede, P. M.; Xaba, T., Dr.; Naidoo, E. B., Prof.; Shooto, N. D., Dr.
High levels of pollutants in water are found to have poisonous effects on human health. Due to increasing awareness about the environment and strict environmental regulations, wastewater treatment has become a very important aspect of research. Thus, this makes the adsorption of pollutants an urgent matter. The aim of this research was to investigate the adsorption capacity of black cumin seeds in the removal of cobalt-Co(II), nickel-Ni(II), copper-(II), chromium-Cr(VI), lead-Pb(II), and methylene blue (MB) dye from aqueous solution. In this research work the black cumin seeds were reacted with sodium hydroxide (NaOH), hydrochloric acid (HCl), phosphoric acid (H3PO4), potassium permanganate (KMnO4) and sulfuric acid (H2SO4). Thereafter it was carbonized at 200 and 300 °C and functionalized with magnetite-sucrose nanoparticles and further carbonized at 600 °C to improve the adsorption capacity of the materials towards different pollutants. The seeds were characterized by scanning electron microscopy (SEM), thermogravimetric analyser (TGA), X-ray diffractometer (XRD), Brunauer, Emmett and Teller (BET) and Fourier transformed infrared (FTIR) spectroscopy. The SEM images showed that the surface morphology of the treated adsorbents was more porous and had cavities more than the starting material. The TGA profile showed a major weight loss between 198-487 °C which was due to disintegration of cellulose, lignin and hemicellulose. The XRD spectra of adsorbents showed broad peaks at 2θ value of 21° associated crystalline lignocellulose content. FTIR results showed that the adsorbents had functional groups such as hydroxyl (-OH), carboxyl (-COOH), amide (-NH) and carbonyl (-C=O). The BET surface area of pristine black cumin seeds was 2.7 m2/g and increased after treatment with KMnO4 and H3PO4 to 10.1 and 9.3 m2/g respectively. The surface area of the carbon black cumin seeds was 11.67 m2/g whilst the activation of carbon from black cumin seeds with 10 and 20% H2SO4 gave the surface area of 20.14 and 21.54 m2/g respectively. The seeds activated with 20% H2SO4 showed larger pore width of 7.13 nm compared to 6.81 and 3.78 nm after treatment with 10% H2SO4 and carbon black cumin seeds respectively. The results show that there is an increase in surface area and pore size for both 10 and 20% H2SO4 in comparison with carbon black cumin seeds. The adsorption of Co(II), Ni(II), Cu(II), Cr(VI) and Pb(II) and MB in the solution was investigated by studying the effect of initial concentration, contact time, temperature and pH. The batch adsorption experiments were conducted using different ion solution concentrations of 20, 40, 60, 80 and 100 mg/L, contact time was determined at intervals of 1, 5, 10, 15, 20, 30, 60, 90 and 120 min, while temperature was studied at 298, 303, 313, 333 and 353 K. On the other hand, the effect of pH on all solutions was studied at pH 1, 3,5,7 and 9. The results showed that the acid treated black cumin seeds (AT-BCS) and base treated black cumin seeds (BT-BCS) were successfully used for quaternary adsorption study of Cu(II), Co(II), Pb(II) and Ni(II) ions from aqueous solution. The results for the adsorbents indicated that the BT-BCS adsorbed more metals than AT-BCS and the UT-BCS. The maximum capacity for BT-BCS was 190.7 mg/g for Cu(II) whilst AT-BCS and UT-BCS showed capacities of 180.1 and 135 mg/g respectively for Pb(II). The uptake of Cr(VI) and Cd(II) ions onto pristine black seeds (PBS), KMnO4 black seeds (KMBS) and H3PO4 black seeds (H3BS) treated adsorbents showed that the trend for Cr(VI) ions was KMBS>H3BS>PBS with capacities of 16.12, 15.98 and 10.15 mg/g respectively. Meanwhile the adsorption of Cd(II) ions showed maximum capacities of 19.15, 19.09 and 16.80 mg/g for KMBS, H3BS and PBS respectively. Carbon from black cumin (CBC) seeds was modified with 10 % and 20 % sulfuric acid (H2SO4) then carbonized at 200 °C to obtain the activated adsorbents of ACBC-10 and ACBC-20. The new adsorbents were used for the adsorption of Cd(II) and methylene blue (MB). The adsorbents maximum trend for Cd(II) was ACBC-10>ACBC-20>CBC meanwhile the trend for methylene blue (MB) dye was ACBC-20>ACBC-10>CBC. The overall capacities showed that the prepared materials adsorbed more MB dye (16.42 mg/g) than Cd(II) ions (13.65 mg/g). The preparation of carbon from black cumin seeds (BCC) and activation with 10 and 20 % sulfuric acid (H2SO4) at 300 °C to obtain new adsorbents namely (BCAC-10) and (BCAC-20) respectively was used for the adsorption of Pb(II) ions and MB dye from aqueous solution. The maximum adsorption of Pb(II) ions was 17.19, 17.71 and 17.98 mg/g onto BCC, BCAC-10 and BCAC-20 respectively. Whilst for MB dye it was 11.63, 12.71 and 16.85 mg/g onto BCC, BCAC-10 and BCAC-20 respectively. The utilization of pristine Nigella Sativa (PNS) and magnetite-sucrose functionalized Nigella Sativa (FNS) seeds as the adsorbents for the uptake of Cr(VI) and Pb(II) ions from synthetic wastewater revealed that the maximum adsorption capacities for Cr(VI) were 15.6 and 13.0 mg/g onto PNS and FNS composites respectively at pH 1. On the hand, the maximum sorption capacities for Pb(II) ions were 39.7 and 37.9 mg/g onto PNS and FNS respectively at pH 5. The sorption study of Cr(VI), Cd(II) ions and MB dye by pristine Nigella Sativa (PNS) seeds, defatted and carbonized Nigella Sativa seeds from aqueous solution was investigated. The PNS seeds were treated using acetone (then named ANS) and N,N dimethylformamide (named DNS). The defatted ANS and DNS adsorbents were carbonized at 600 °C and named CANS and CDNS. The results of pristine, defatted and carbonized seeds maximum capacities were compared with each other and found that CANS had highest adsorption capacity of 99.82 mg/g for MB, 96.89 mg/g for Cd(II) and 87.44 mg/g for Cr(VI) followed by CDNS with 93.90, 73.91 and 65.38 mg/g for MB, Cd(II) and Cr(VI) respectively. ANS capacities were 58.44, 45.28 and 48.96 mg/g whilst DNS capacities were 48.19, 32.69 and 34.65 mg/g for MB, Cd and Cr(VI) respectively. PNS had the lowest sorption capacities at 43.88, 36.01 and 19.84 mg/g for MB, Cd and Cr(VI) respectively. Therefore, this makes black cumin seeds a promising material for use in wastewater treatment to mitigate metal ions and dye pollution.
An adsorptive study of Pb(II), Cr(VI) ions and methylene blue dye by treated and untreated coral limestones in aqueous solution
(Vaal University of Technology, 2021) Nkutha, Cynthia Sibongile; Naidoo, E. B., Prof.; Shooto, N. D., Dr.
For centuries the contamination of surface water has been problematic, especially in third world countries whereby socio-economic issues are prevalent. With the development of various technologies for surface water rehabilitation, adsorption has been found to be the most viable due to its lower cost implications. As such the development of innovative adsorbents which are synergistic to the low cost method have been sought. Herein, the use of fossil coral limestone from Mauritius as adsorbents for the removal of Pb(II), Cr(VI) and methylene blue is presented. The pristine material (PCLS) was thermally treated by calcination to temperatures 800°C (CLS-800) and 900°C (CLS-900) and chemically treated by using an acid HCl (ACL) and base NaOH (BCL). The optimum conditions found for chemical and thermal treatment of the pristine material were used for the one pot synthesis of magnetite and maghemite calcium carbonate based nanocomposites. The pristine fossil coral limestones were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDS), X-ray fluorescence XRF), X-ray diffractometer (XRD), Brunauer, Emmett and Teller (BET) and Fourier transformed infrared (FTIR) spectroscopy, UV visible spectrophotometer (UV/vis) and Photolumiscent spectroscopy (PL). Surface morphology of the material was found to contain an interconnected framework of pores, with a surface area of 20.45 m2/g and pore with of 4.04 nm. Thermal treatment of the material was found to increase the surface area of the materials to 64.10 and 63.28 m2/g for CLS-800 and CLS-900. The surface morphology of the calcined materials compared to the pristine were fibrous like and irregularly shaped for CLS-800 and CLS-900 respectively. The FTIR revealed the dominant surface groups to be (-C-O) and (-C=O) asymmetric stretch of the in and out of plane bend of carbonate (-CO32-), with the composition of the material being 91.76 % (-CaO) and 3.32% SrO. The thermally treated materials also exhibited vibrations of asymmetric stretch, which are characteristics of the carbonates as with the pristine material. However, EDS of the pristine compared to that of the calcined materials show a decline in the carbon and oxygen content, due to calcination. The XRD analysis confirmed the orthorhombic structure of aragonite, while CLS-800 was rhombohedral calcite with newly developed (-CaO) peaks. CLS-900 showed complete removal of CaCO3 polymorphs with more (-CaO) peaks. The surface morphology of the chemically modified samples show irregularly shaped surface. The XRD analysis confirmed that chemical treatment did convert the materials to a different polymorph. The FTIR of the chemically modified materials compared to the pristine, were found to reveal a removal of the vibrations of the asymmetric stretch associated with carbonates. However, vibrations associated with (-CaO) were observed. The SEM of the nanocomposites was observed to deviate from sphericity with variable size distribution. The materials were both red and blue shifted due to their variable sizes. Their UV/vis revealed absorption bands in the visible region. The adsorption analysis was done by varying parameters such as time, pH, concentration and temperature. The data was such that the highest capacity for the pristine material was found to be 37.24, 39.26 and 69.42 mg/g for MB, Pb(II) and Cr(VI) respectively. The removal of MB and Pb(II) pollutants were due to physical adsorption, as observed from the good fitting to pseudo first order model (PFOM). The removal of Cr(VI) was due chemisorption and the good fit on pseudo second order model (PSOM). The adsorption process was supported on a heterogeneous surface whereby multilayer adsorption could occur. Adsorption was spontaneous and feasible, exothermic for MB and Pb(II) and endothermic for Cr(VI) at all the studied temperatures as observed from thermodynamics. The adsorption of methylene blue was found to be more favourable on adsorption compared to photo-degradation Chemical modification was observed to increase adsorption and the maximum removal capacities for PCLS, ACL and BCL for Cr(VI) ions were 69.42, 65.04, 64.88 mg/g, Pb(II) ions 39.36, 74.11, 78.34 mg/g and methylene blue 37.24, 46.28, 46.39 mg/g, respectively. Uptake of Cr(VI) and methylene blue on ACL and BCL was feasible on a heterogeneous surface whereby multilayer adsorption took place. Monolayer adsorption on a homogenous surface of ACL and BCL was observed for Pb(II) uptake. The uptake of Pb(II) was exothermic on PCLS and ACL while methylene blue only on PCLS. The adsorption of Cr(VI) ions onto PCLS, ACL and BCL and methylene blue dye onto ACL and BCL were endothermic in nature. The adsorption process was spontaneous and feasible at all the studied temperatures. Thermal modification further increased the adsorption uptake of the pollutants. The recorded uptake for Cr(VI) and Pb(II) were 99.12 and 98.42 mg/g onto CLS-800 and CLS-900, respectively. The adsorption process was found to be physisorption, due to the good fit on PFOM. In addition, the adsorption occurred on a heterogeneous surface whereby multilayer adsorption was possible. The removal of Cr(VI) was found to be exothermic for both the materials and Pb(II) was found to be endothermic. The materials were tested for their reusability to up to four cycles, whereby the removal on the fourth cycle were 16.87, 63.60, 73.13 mg/g for Cr(VI), 9.87, 64.19 and 70.95 mg/g for Pb(II) on PCLS, CLS-800 and CLS-900. While the leaching test for PCLS, CLS-800 and CLS-900 for the release of Ca2+ into solution was found to be within the permissible limits of world health organisation (WHO). The as synthesized nanocomposites increase adsorption of the pollutants. Maximum capacities were found to be 345.34, 388.31, 377.92 and 375.35 mg/g for Pb(II) onto magnetite-PCLS, magnetite-CLS, maghemite-PCLS and maghemite-CLS, respectively and 308.01, 335.3, 335.29 and 335.27 mg/g for Cr(VI) onto magnetite-PCLS, magnetite-CLS, maghemite-PCLS and maghemite-CLS, respectively. From the data it was observed that the maghemite samples were much more favourable for the removal of the pollutants. The removal was due to chemical adsorption, as observed from the good fit onto PSOM and intraparticle diffusion (IPD), whereby surface adsorption was the rate limiting step. The adsorption process was heterogeneous and multilayer, while thermodynamic data reveal that adsorption was spontaneous and favourable at the studied temperature.
Alanine, aspartic acid and lactose-capped CuS, ZnS and FeS nanoparticles: synthesis, characterization and properties
(Vaal University of Technology, 2017) Mofokeng, Thapelo Prince; Shumbula, P. M., Dr.; Moloto, M. J., Prof.
Water soluble metal sulfide nanoparticles were successfully synthesized using an aqueous, simple and environmentally friendly synthetic method in the presence of ʟ-alanine, ʟ-aspartic acid and lactose, acting as both stabilizers and crystal growth modifiers. The structural and optical properties of the synthesized metal sulfide nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Ultraviolet-visible (UV-Vis) and photoluminescence spectroscopy. Colloidal method was employed in the synthesis of CuS, ZnS and FeS nanoparticles from metal chlorides as precursors and thioacetamide (TAA) as a sulphur source. The effect of temperature on the growth and solubility of nanoparticles was investigated. The absorption spectra of all samples prepared were blue shifted as compared to their bulk materials indicating small particles size. The morphologies and sizes of the nanoparticles were influenced by the variation of temperature and capping agent. TEM images revealed interesting changes in the morphology of CuS nanoparticles formed from various capping agents. By varying the temperature, ʟ-aspartic acid-capped CuS nanoparticles changed from rod-shaped particles to particles dominated with hexagonal shape. However, the morphologies of both ZnS and FeS nanoparticles were close to spherical shape and were unaffected by either change of temperature or capping agent. Water-solubility of bio-functionalized CuS, ZnS and FeS nanoparticles was investigated. Amongst the three capping agents used, ʟ-alanine (Ala) was found to be the most effective capping agent to render solubility of the nanoparticles. As the temperature was increased, the solubility of the particles also increased. Cytotoxicity and antimicrobial activity of ʟ-alanine-capped CuS and ZnS nanoparticles were investigated. The particles were less toxic at low to moderate concentrations and only induced toxicity at higher concentrations. Particles synthesized at 95 °C were less toxic compared to other nanoparticles (35 and 65 °C) for both two set of experiments, as informed by the CC50 values. Antimicrobial properties were tested using different strains of both positive and negative bacteria and fungi. It was found that Ala-capped CuS nanoparticles were more effective against the bacteria than Ala-capped ZnS nanoparticles.
Amino acid-capped metal selenide nanoparticles: their synthesis, characterization, optical and magnetic properties
(2018-04) Mokubung, Kopano Edward; Moloto, N; Moloto, M. J.
Quantum dots (QDs) have already proven features that can be considered to improve their properties for biological applications. Metal selenide nanoparticles possess semiconducting behaviors that can vary with structural and optical properties evolving from their synthesis. An aqueous medium through a simple, non-toxic and environmentally friendly colloidal route for the preparation of water-soluble CdSe, Cu2Se, FeSe semiconductor nanoparticles has been developed. Different capping molecules with multi-functional moieties (-COOH, -NH2 and -OH) namely, L-cysteine, L-glutamic acid and L-phenylalanine, have been employed in the preparation of cadmium selenide, copper selenide and iron selenide semiconductor nanoparticles as capping molecules. The synthesized metal selenide nanoparticles were characterized by Fourier Transform Infrared (FTIR), UV-Vis spectroscopy, Photoluminescence spectroscopy (PL), X-ray Diffraction (XRD), Vibrating Sample Magnetometer (VSM) and Transmission Electron Microscopy (TEM). The FTIR spectroscopy confirmed the binding moiety through the surface of the nanoparticles which is pH dependent. The XRD patterns confirmed a cubic phase of CdSe and Cu2Se while FeSe revealed a hexagonal phase for the synthesized nanoparticles. The optical absorption as a function of wavelength for the prepared nanoparticles at different temperature is investigated. The morphology of the nanoparticles dominated through this method was spherical in shape. Amino acids capped metal selenide nanoparticles were successfully synthesized by aqueous medium through a simple colloidal route. The absorption spectra of all samples prepared were blue shifted as compared to their bulk counterparts which signify quantum confinement effect. The optical absorption measurements show some dependency of the temperature values used in the synthesis of nanoparticles. The effect of temperature and pH on the growth and morphology of nanoparticles was investigated. X-ray diffraction patterns confirms the structure, single cubic and hexagonal phase for the synthesized nanoparticles. TEM studies of metal selenide nanoparticle show that particle size increases with the increase in reaction temperature. The vibrating sample magnetometer (VSM) shows almost linear without any hysteresis loop for copper selenide, which indicated the absence of magnetism and exhibits paramagnetic nature than diamagnetic properties while iron selenide revealed twofold ferromagnetic behavior in low fields and paramagnetic behavior in up fields.
Antimicrobial activity and dye photodegradation of titanium dioxide nanoparticles immobilized on polyacrylonitrile-cellulose acetate polymer blended nanofibers.
(Vaal University of Technology, 2019) Nkabinde, Sibongile Chrestina; Matabola, K. P., Dr.; Moloto, M. J., Prof.
Electrospinning is a method that has gained more attention due to its capability in spinning a wide variety of polymeric fibers and nanoparticles embedded in polymer fibers. Polymer blending has been considered the most appropriate way for creating new materials with fused properties which improve poor chemical, mechanical, thermal and dynamic mechanical properties of each polymer. Hence, in this study, electrospinning technique was used to fabricate polyacrylonitrile (PAN) nanofibers at concentrations of (10, 12 and 14 wt%) and cellulose acetate (CA) nanofibers at concentrations of (14, 16 and 18 wt%). 10wt% of PAN and 16 wt% of CA were blended together and the optimum blend ratio was found to be 80/20 PAN/CA. TiO2 nanoparticles (0.2 and 0.4 wt%) were incorporated into CA nanofibers and (1, 2 and 3 wt%) were incorporated into PAN and PAN/CA blended polymers, respectively. Applied voltages of 20, 22 and 24 kV were varied at a spinning distance of 15cm and the optimum voltage for the fabrication of composite was 22 kV. The sol-gel method was used to synthesise the TiO2 nanoparticles at different calcination temperatures of 400, 500 and 600 ºC. The fabricated composite nanofibers were tested for antibacterial and photocatalytic activities. The synthesised nanomaterials were characterized using SEM, TEM, EDX, UV-Vis, PL, FTIR spectroscopy, XRD and TGA. The absorption and emission spectra illustrated the formation of TiO2 nanoparticles and the increase in absorption band edges. TEM showed the spherical morphology of the nanoparticles with average diameter of 12.2 nm for nanoparticles calcined at 500 ºC. SEM illustrated the diameter and morphology of the nanofibers and composites with the average diameter of 220, 338, 181, 250, 538, 294 nm for PAN, CA, PAN-TiO2, CA-TiO2, PAN/CA and PAN/CA-TiO2, respectively. XRD revealed anatase phase as the dominant crystalline phase of the synthesised nanoparticles. FTIR spectroscopy and EDX signified that the formation of composite nanofibers and the presence of TiO2 nanoparticles corresponded to the Ti-O stretching and Ti-O-Ti bands on the FTIR spectra. The antimicrobial activity of the composite nanofibers were tested against E. coli, S. aureus and C. albicans microorganisms. The photocatalytic activity of the nanomaterials was tested using methyl orange dye. PAN/CA-TiO2 composite nanofibers revealed the greatest antibacterial activity against selected microorganisms as compared to the other nanocomposites. PAN/CA-TiO2 nanocomposite (44%) showed greater rate of photodegradation of methyl orange than PAN-TiO2 nanofibers (28%) and TiO2 nanoparticles (12%) under visible light irradiation.
Antimicrobial activity of synthesized copper chalcogenides nanoparticles and plant extracts.
(2019-03) Mbewana, Nokhanyo; Mubiayi, Kalenga Pierre, Dr; Mthunzi, Fanyana, Dr; Moloto, Makwena Justice, Prof
Chemical precipitation method is the most widely used of all methods for preparing good quality semiconductor nanoparticles. Several conditions are optimized for producing the desired size and shape of particles. The parameters such as capping molecule, precursor concentration, time and temperature were investigated using the colloidal hot injection method. The effect of capping agent was the first parameter investigated in the synthesis of copper selenide, copper sulphide and copper oxide nanoparticles. The capping agents of interest in this study were oleylamine (OLA) and trioctylphosphine (TOP), due to their ability to act as reducing agents, surfactant, solvent and enhancement of colloidal stabilization. The use of oleylamine and trioctylphosphine were carried out at 220 °C for 30 minutes. The optical and structural properties of the yielded nanoparticles were characterize using UV/Vis spectroscopy, TEM and XRD and showed dependence on the type capping interactions from the two agents. Nanoparticles synthesized using TOP produced two phases whereas a single phase was observed from OLA as confirmed by XRD. OLA produced bigger particle sizes compared to TOP but with a wider variety of shapes. The wide variety of particle structures of OLA capped nanoparticles was advantageous since different types of bacteria were targeted in this work. Therefore, other synthetic parameters were investigated using OLA as both solvent and capping molecule. Precursor concentration ratio showed bigger effect in the size, and shape of the yielded nanoparticles. For copper selenide and copper sulphide (Cu: Se/ S), 1:1 concentration ratio gave the best optical and structural properties while copper oxide (CuO) nanoparticles demonstrated its best optical and structural properties in 2:1 ratio (Cu: O). Nonetheless, 1:1 precursor concentration ratio was used to optimise other parameters. Since reaction time has a profound effect on the nanocrystals size and shapes, the effect of reaction time in OLA was also investigated. The reaction time showed no effect on the phase composition of the synthesized copper sulphide, copper oxide and copper selenide nanoparticles. Reaction time of 30 minutes gave the best optical (the shape of the absorption band edge and emission maxima values) and structural (size distribution of particles) properties for CuSe and CuS compared to other reaction times (15 min, 45 and 60 min). 15 min reaction time gave the best optical and structural properties for copper oxide but nonetheless, 30 min was used as the optimum reaction time for further optimization. Temperature showed an effect in size, shape and the stoichiometry of the reaction. These effects were confirmed by the optical and structural properties of the synthesized nanoparticles. XRD patterns revealed some differences with the temperature change, indicating an effect on the phase composition of CuS and CuO but not on CuSe nanoparticles. CuSe and CuS nanoparticles synthesized at 220 °C gave the ideal optical and morphological features compared to other temperatures that were selected (160 ºC, 190 ºC and 240 ºC). Nonetheless, CuO revealed its best optical and structural properties at 160 ºC. 220 ºC was deduced to be the optimum temperature for the synthesis of these three materials under the synthetic conditions. The optimum parameter (220 ºC, 30 min and 1:1 ratio) were used to synthesize the three copper chalcogenides which were then tested against Gram-negative (E. coli and P. aeruginosa), Gram-positive (S. aureus and E. faecalis), and fungi (C. albicans). The plant species, Combretum molle and Acacia mearnsii were phytochemical screened for the presence of active organic compounds and the content of total phenols, flavonoids and antioxidants using different solvents. Both C. molle and A. mearnsii revealed the highest phenolic content in acetone extracts. C. molle revealed its highest flavonoid content in methanol extract and its highest free radical scavenging activity in acetone extract. Acetone extracts demonstrated the highest flavonoid content as well as the highest free radical scavenging activity of A. meansii. The solubility of copper chalcogenides and plant extract was tested in four different solvents and the solvent that demonstrated highest solubility was used for the coordination of the plant extract and copper chalcogenides. The plant extract coordinated nanoparticles were tested for their antibacterial and antifungal activity. Their results were compared to those of the active ingredient in their respective solvents from the medicinal plants as well as those of copper chalcogenides nanoparticles without plant extracts using diffusion disk and MICs methods. The synthesized nanoparticles showed better performance than plant extracts with copper oxide performing the best, followed by copper selenide and lastly by copper sulfide. The performance of plants extracts highly dependent on the solvent of extract with acetone showing the best performance for both C. molle and A. Mearnsii followed by ethanol. The addition of active ingredients from C. molle and A. mearnsii to the synthesized nanoparticles did not enhance the performance of these nanoparticles.
Assessment of carcinogenic PAHs, their oxy-derivatives and heavy metals in soil and sediments from coal mine in Witbank, Mpumalanga Province, South Africa
(Vaal University of Technology, 2022-11-14) Nqaba, Zoleka; Akpotu, S. O., Dr.; Okoli, P. C., Dr.; Pholosi, A., Dr.
Fossil fuels provide more than two-thirds of the world’s energy needs with a significant contribution from coal. Coal is referred to as “dirty energy” and it is still used as an energy source because of its vast availability and relatively low cost of production. In South Africa, Witbank mines in Mpumalanga province have the largest coal deposits, supplying power stations that generates 41% of the country’s electricity. Coal mining results in anthropogenic hazardous emissions such as slag waste and coal dust with high concentrations of organic and inorganic pollutants. Polycyclic Aromatic Hydrocarbons (PAHs) are emitted by incomplete coal combustion resulting into coal ash which can contain large quantities of heavy metals. PAHs and heavy metals are known to be major contributors to the environmental pollution due to their negative effects on human health and the ecosystem. As a result this study aims to investigate heavy metals, PAHs and their oxy-derivatives in areas affected by coal soil pollution in Mpumalanga. In this research, 132 soil and sediments samples were collected from 6 coal-containing areas in Mpumalanga (i.e. Greenside coal mine, Kriel power station, Klipfontein dam, Kriel dam, Middleburg dam, and Witbank dam) and these were investigated for their physiochemical properties (pH, TOC, TOM determined by pH electrochemical method and Walkerly Black Method), presence of heavy metals and organics (PAHs and oxy-PAHs). Soil and sediment samples were collected in both winter and summer seasons in 2019. Soil samples were characterised using FTIR and SEM-EDX spectroscopy for functional groups and determination of metal elements, respectively. Heavy metals present in the samples were investigated and the assessment of possible risks of exposure was studied. Heavy metals investigated included Zn, Cu, Co, Fe, Mn, Cr, and Pb. The coefficients of determination of the calibration standards for heavy metals were greater than 0.995 and the recovery values ranged between 75 - 105 %. For the organic pollutants, an extraction method was developed. Organic Pollutants analysed include naphthalene, acenapthene, fluorene, anthracene, pyrene, benzo(a)pyrene and 1,4-naphthalene. Samples were extracted using soxhlet and ultrasonic bath techniques and extracts were analysed using gas chromatography mass spectrometry (GC-MS). The GC-MS method developed was validated by inter-day and intra-day reproducibility of standards, recovery test, linearity of calibration method and limits of quantification and detection. Coefficient determination of the calibration standards were greater than 0.995 for PAHs and recovery values ranged between 60 - 86 %. All the heavy metals that were analysed were detected in all the samples. Generally, it was observed that Greenside and Kriel samples had higher metal concentration as compared to the dams (Klipfontein, Kriel, Middleburg and Witbank) and these had the following range: Fe > Mn > Cr > Pb > Cu > Co. The results for the organics followed a similar trend as the heavy metals, that is, samples from Greenside and Kriel had higher concentration of PAHs as compared to the samples from the dams (Flt > Pyr > Anthr> 1,4-napth > Nap > Flu> benzo(a)anthr > Acy). Based on the results, the concentrations of heavy metals and organics in soil were slightly higher than the World Health Organization limits for these pollutants. This is concerning because the studied areas include residential and agricultural communities. As a result, a continuous and routine monitoring of these pollutants is required to preserve the environment and the health of humans and animals living around the area.
Biodiesel Production by Transesterification of Waste Cooking Oil Using Modified Attapulgite.
(Vaal University of Technology, 2019-10) Mabungela, Ntandokazi; Viljoen, E., Dr.; Mtunzi, F., Prof.
Biodiesel has an ability to solve the problem associated with the use of fossil fuels as a source of energy. The aim of this study was to produce biodiesel from waste cooking oil (WCO) by transesterification, catalysed with potassium hydroxide (KOH) supported on attapulgite (ATP) clay as the heterogeneous catalyst. WCO was used on the basis that it is one of the cheapest feedstocks for biodiesel production, is readily available and can minimise environmental impact. ATP clay was first crushed and sieved to particle sizes of ≤ 90 μm and subsequently treated with hydrochloric acid (HCl) to remove impurities. The KOH supported ATP catalyst was prepared through ion exchange method by soaking ATP into KOH solution, dried in an oven and later calcined at 400 ℃ in a furnace. The prepared catalyst and ATP clay were characterised using Hammett indicator to determine the basic strength of the catalyst. XRF and EDX were used to determine the elemental composition of the catalyst whilst XRD was used to determine the crystallinity of the ATP after modification. The functional groups of ATP were determined by FTIR. BET was utilised to determine the changes on the surface area, pore volume and pore diameter of ATP and on the other hand, SEM was used to determine the morphological changes on the surface of ATP. The XRD, FTIR, BET AND SEM-EDX showed that addition of potassium caused changes on the surface of the ATP. The optimal conditions for the transesterification reaction of waste cooking oil with methanol were found to be oil-to-methanol molar ratio of 1:15, 3wt% catalyst amount, 65 ℃, 3 h of a reaction time, at 200 rpm stirring rate and 94 % biodiesel yield was obtained. After the catalyst was reuse three consecutive times, the decrease in biodiesel yield was observed (Figure 17) after each cycle. However, the 5MKOH/ATP catalyst is heterogeneous and can be used to transesterify WCO with good yield.
Cobalt and cadmium chalcogenide nanomaterials from complexes based on thiourea, urea and their alkyl derivatives : synthesis and characterization
(2015) Morifi, E. L.; Moloto, M. J.; Matabola, K. P.
Cadmium and cobalt complexes of urea and thiourea were synthesized using ethanol as a solvent. All complexes were refluxed at 70 - 80 °C, left to cool at room temperature, washed with methanol and acetone to remove impurities and dried at an open environment. The characterization of complexes was done using FTIR spectroscopy, elemental analysis and TGA. The complexes were found to coordination with the ligands through sulphur and oxygen atoms to the metal, instead of nitrogen. These were as results of wavelength shifting from high to low frequency from spectra of the complexes as compare to their free ligands. These observations make these complexes good candidates for the possible use in synthesis of metal sulphides or oxides nanoparticles. Thermogravimetric analyses of all the complexes were conducted to check the stability of use as precursors for nanoparticles at low and high temperature. A number of thiourea and urea complexes with cadmium and cobalt have been prepared and used in the preparation of metal sulphides/oxides nanoparticles. Complexes start to decompose at low temperature about 100°C and the last decomposition step was at about 800-900°C, which is convenient to thermal decomposition of precursors in the high boiling solvents or capping agent to prepare surface capped metal sulphides/oxides nanoparticles. The complexes were easy to synthesize, low cost and stable in air and were obtained in reasonable yields. All the complexes reported in this study have been used as single source molecular precursor in the preparation of cadmium oxide, cadmium sulphide, cobalt oxide, cobalt sulphide nanoparticles (normal) and as mixture of any two complexes to form core-shells nanoparticles. Quality nanoparticles synthesis requires three components: precursors, organic surfactants and solvents. The synthesis of the nanoparticles can be thought of as a nucleation event, followed by a subsequent growth period. Both the nucleation and growth rates were found to be dependent upon factors such as temperature, growth time, and precursor concentration. For a continuous flow system the residence time (at nucleation and growth conditions) was also found to be important. In order to separate the nucleation and growth events, injection techniques were employed to achieve rapid nucleation of nanoparticles with final size dictated by the growth temperature and/or residence time through the growth zone of the reaction system. Good crystalline normal nanoparticles were obtained from thermolysis of the precursors in hexadecylamine (HDA) as the capping agent at fixed concentrations, temperature and time. All nanoparticles showed a blue-shift in band edges with good photoluminescence behaviour which is red-shifted from their respective band edges and XRD patterns, the crystal structure are in hexagonal phase. The particles showed rods, spheres and hexagonal shapes. Nucleation and growth mechanism brings new avenue in nanostructures called core-shells, which have been reported to have improved luminescence, quantum yields, decreased fluorescence lifetimes, and benefits related to the tailoring of the relative band-gap positions between the two materials. In this study cadmium and cobalt complexes of urea and thiourea were separately dispersed in TOP and injected separately (allowing nucleation/core to occur, followed by the shell) in hot HDA at 180ºC for 1hour to yield core-shell nanoparticles. Parameters, such as concentration, temperature and capping molecule as factor affecting nucleation and growth of the core-shells were monitored. The core-shell nanoparticles were characterized by UV/Vis spectroscopy, XRD and TEM. We observed spherical, tripod, bipods, hexagonal and irregular shaped nanoparticle as the concentration of the precursors was increasing, however we were able to form core-shells nanoparticles in one set of experiment 1:3 CdS-CdO, which are assumed to be a reverse type I coreshells nanoparticles. Exciton absorption peaks at higher energy than the fundamental absorption edge of bulk indicate quantum confinement effect in nanoparticles as a consequence of their small size. XRD patterns, crystals range from hexagonal, cubic and mixture of hexagonal and orthorhombic. A low temperature studies were also conducted a mixture of hexagonal and sphererical shapes with sheets like onion morphology were observed.
Competitive biosorption of a mixture of cationic dyes from a multicomponent solution using modified pine cone powder
(Vaal University of Technology, 2012-07) Ngema, Silindile Lucia; Ofomaja, A. E., Dr.; Naidoo, E. B., Prof.
The biosorption of methyl violet and methylene blue onto modified pine cone powder was studied. Single and binary component systems studies were carried out for the biosorption of methyl violet and methylene blue onto raw, Fenton treated and acrylic acid grafted pine cone powder. Various experimental parameters were studied including initial dye concentration (200-900 mg/dm3), contact time, solution pH (4-12), mass of adsorbent (0.05-0.30g) and temperature (25-45 °C). Pseudo-first order and pseudo-second order equations were used to analyze the kinetic data. It was found that the data follow the pseudo -second order kinetic model for all temperature studied. The experimental data were analyzed using Langmuir and Freudlich isotherm model. The biosorption of methyl violet and methylene blue showed a better fit to Langmuir isotherm which properly describes the experimental data and that the sample surfaces are homogeneous. Various thermodynamic parameters, such as Gibbs energy (ΔG*), enthalpy change (ΔH*) and entropy change (ΔS*), were calculated which indicated the present system was spontaneous and exothermic process for methyl violet and methylene blue. It was found that enthalpy and entropy of acrylic acid grafted pine cone was higher as compared to raw and Fenton‘s reagent for methyl violet and methylene blue. Raw, Fenton treated and acrylic acid pine cone powder were characterized with Fourier transform infrared spectroscopy (FTIR), Ultraviolet-visible spectroscopy (UV-VIS), Thermogravimetic analysis (TGA/DTA), X-ray Diffraction (XRD) and Brauner, Emmett and Teller (BET). The following parameters were used to determine the surface properties of the grafted pine cone: change in H+ concentration and oxidation reduction potential (ORP), surface negative charge, bulk density and acid number measurements. The FTIR analysis confirmed the presence of the organic compounds on the raw, Fenton treated and acrylic acid grafted pine cone powder. The UV/VIS determined the percentage removal of dyes from aqueous solution in single and binary component systems by comparing the raw, Fenton treated and Acrylic acid grafted pine cone powder. Thermo gravimetric analysis confirmed the reactions which occur at the molecular level of the raw, Raw + KMnO4 and Fenton treated + KMnO4 pine cone powder materials. The second order derivative spectroscopy (SODS) was a suitable method for the analysis of the study of cationic dyes in binary solution. To determine the unknown concentrations of methyl violet and methylene blue dyes in binary solution using SODS, maximum wavelengths 561.8 nm and 623.1 nm were obtained. It was found that the percentage removal was higher for acrylic acid grafted pine cone than Fenton‘s treated and raw pine cone and treated samples adsorbed more methyl violet that methylene blue.
Copper oxide-carbon catalysts for the oxidation of methylene blue
(Vaal University of Technology, 2020) Makamu, Anza Reliance; Ofomaja, Prof.; Viljoen, E. L., Dr.
Organic water pollutants such as dyes are difficult to biodegrade. In this study Fenton, photo-Fenton and photocatalysis were used to degrade methylene blue dye in the presence of copper oxide catalysts. The copper oxide catalysts were prepared with a precipitation reduction method. The effect of different preparation parameters on the catalyst properties and catalytic activity were investigated. The reducing agents, ascorbic acid (ASC, C6H8O6), hydrazine (N2H4), sodium boron hydride (NaBH4) and glucose (C₆H₁₂O₆) could be used to obtain the desired Cu2O phase. ASC, N2H4 and NaBH4 were able to reduce copper (II) to copper (I) at room temperature whereas glucose required a higher reduction temperature. Stoichiometric amounts of the reducing agents ASC, N2H4 and glucose and double the stoichiometric amount of NaBH4 were required to obtain Cu2O. A further increase in the amounts of NaBH4 and N2H4 resulted in the formation of copper metal (Cu (0)). High amounts of ASC did not over-reduce the copper. ASC also functioned as capping molecule and anti-oxidant preventing the oxidation of the Cu2O to CuO in air after preparation. Hydrazine was thus not able to protect the Cu2O against oxidation. The SEM results showed that an increase in the amount of the precipitating agent, NaOH, resulted in an increase in the particle sizes. The particle shapes changed from spherical to cubic when a high amount of NaOH was used with hydrazine as reducing agent. Smaller particle sizes were obtained when CuCl2 was used instead of CuSO4 and Cu(NO3)2. Larger crystallites formed when the preparation temperature was increased from room temperature to 100°C with glucose as reducing agent. TEM and XRD analyses showed that the micro-particles seen in SEM analyses are made up of nano-particles. The catalysts were not active for photocatalysis which may be explained by the oxidation of these nano-particles to form the photocatalytic inactive CuO. The catalysts were shown to be active for Fenton and photo-Fenton degradation. The addition of graphene and activated carbon to the Cu2O catalysts were detrimental to the catalytic activity. The percentage degradation of methylene blue by the Fenton reaction increased with an increase in the BET surface area from 1.5 m2/g to 10 m2/g and a further increase in the surface area resulted in a decrease in the percentage degradation. A direct correlation between the Fenton catalytic activity and the pore size were found which indicate that the reaction was mass transfer limited.
Determination and removal of organochlorine pesticides by activated macadamia nutshell in water and sediment alongside Vaal River using GC-MS
(Vaal University of Technology, 2017-10) Phele, Mokete John; Rimayi, C.; Mthunzi, F., Dr.
A rapid and reliable method was developed and applied for the simultaneous determination of 15 organochlorine pesticides (OCPs) in water and sediment. OCPs are continually detected in the environment due to their increasing applications in agriculture and industry, their presence in the environment are not desirable since they are well known to have negative impact in humans and animals. Thus, there has been a continual demand to monitor the presence of OCPs within the environment. The analytical technique employed was gas chromatography equipped mass spectrometer (GC–MS). The correlation coefficients from linear regression for the analysed concentrations were >0.9998. The limits of detection (LODs) varied between 0.068 ppm for 4, 4-DDT and 0.021 ppm for endrin, and the limits of quantitation (LOQs) ranged from 0.06 to 0.23 ppm. The average recoveries varied between 92.08 and 99.71 %. Relative standard deviations (RSD %) ranged from 2.01 to 6.42 %. Sediment samples were extracted using accelerated solvent extraction (ASE), it was found that the limits of quantification ranged from 0.002 to 0.004 ppm, and the average recoveries were in the range 63.2 % - 96 % with standard deviations in the range 3 %-12 %. Macadamia nutshell was characterised using FTIR, spectroscopy and scanning electron microscope (SEM). The functional groups present were found to be O-H stretching vibration of hydrogen bonded hydroxyl groups, aliphatic C-H stretching vibration and C-OH stretching of phenolic groups. SEM image revealed that the material consisted of flaky long fold-like structure which are typical of plant materials.
Determination of the antibacterial, antioxidant activity, isolation and characterisation of active compounds from the leaves of Rhys Leptodictia plant
(2014-02) Matamela, Tshifhiwa; Myunzi, F. M.; Sipamla, A.
Rhus leptodictya commonly known as a mountain karee belongs to the family Anacadeceae and has been used since antiquity in tradition medicine. In the present study antimicrobial and antioxidant potentials of the leaves of Rhus leptodictya were studied, followed by isolation of at least one active compound which showed antibacterial and antioxidant potentials. Extractions were performed based on the polarity of the solvent used. The solvents used were hexane, dichloromethane, ethyl acetate, acetone and methanol. Dichloromethane was found to be extracting more compounds than the other used solvents. Thin layer chromatography (TLC) was used to determine the chemical composition of the extracts by employing different solvent systems. The results showed that, of the solvent systems used, namely ethyl acetate: methanol: water (EMW) 40: 5: 1; chloroform: ethyl acetate: formic acid (CEF) 5: 4: 1 and benzene: ethanol: ammonium hydroxide (BEA) 90:10:1, BEA produced better separations. To determine the antioxidant potential of the leaves, 2.2-diphenyl picrylhydrazyl (DPPH) was used. Different spot with different Rf values were found to be active by show of yellow colour on the TLC plate. The yellow colour is due to the proton gained by DPPH when it reacts with active compound. Bioutography results showed that different leaves were active against selected bacterium. Minimum inhibitory concentration studies showed that the methanol extract was more active against B.subtilis and S.pnuemonia at concentration less than 0.1 mg/ml respectively. Dichloromethane extract was found to be the least effective on S.pneumonia, as compared to the methanol, acetone and ethyl acetate extracts. In terms of the total activity, the ethyl acetate concentration showed better total activity than the other extracts studied in this research. A new compound 7, 8-trihydroxy-2-(4’hydroxy phenyl)-3-5-[5’’, 6’’-dihydroxy-2’’-O-(4’’’hydroxyphenyl)-4-1t-chromen-4’’-one]-41t-chromen-4-one was isolated and characterized by H1-NMR, C13-NMR, MS and IR. According to the literature search, this compound has never been isolated from any plant and it has showed both antioxidant and antibacterial activity.
Determination of volatile organic compounds in ambient air by using thermal desorber, sorbent tubes, canister and GC-MS
(2009-06) Mkhwanazi, Sipho Sydney; Naidoo, E. B.; Niemandt, M. J.
The dissertation deals with volatile organic compounds that evaporate from the water-oil separate in the refinery, which causes bad odour around the neighbouring communities, the existence of these compounds are being identified and quantified in different seasons for the year. VOC are emitted whenever wastewater is exposed to the atmosphere. As such, emission points include open drains ditches, manhole sewer outfalls and surface fore bays, separators and treatment ponds. Refinery units such as reactors, fractionators are periodically shutdown and emptied for internal inspection and maintenance. The amount of VOC entering the wastewater is not monitored. The effluent water discharged from the refinery is not checked for the amount ofVOC present. The monitoring of the amount of VOC in wastewater stream may lead to a decrease in the emission. From the quantified results at different season, the summer session has the highest VOC emission due to the heat that causes more vapours. The preparation of a method for determination of VOC's in air presents many difficulties, because of their high volatilities and low concentrations in air. As well, the results of determination are affected by the properties of the sorbent used, mainly its sorption capacity, depending on the properties of the compound under determination. The methods for sampling and analytical procedures for the measurements of volatile organic compounds that are hazardous to air pollution are compendium method T0-14 and sorbent tube method compendium T0-17. Both methods (sorbent tube and canister) differ from each other in their extraction and detection techniques. The well suitable method for the VOC determination is canister method; this method gives more representative sample of the ambient monitoring of 24 hours, where as sorbent tube can do for 2 hours only. The canister method is more advantages due to the sample that will be still remaining for further analyses or re-check. The integrity of API water-oil separator has been improved to cause less evaporation during high temperature season. As the temperature drops from season to season, the VOC also comes down as its being seen in this study that on the winter results that all the VOC were below 90 1-lg/kg.
Development and optimization of selective leaching processes for the extraction of calcium from steel slag in view of sequestering carbon dioxide
(2013-05) Kotoane, Alice Mpho; Naidoo, E. B.; Doucet., Frederic J.
Several technologies are currently being developed to mitigate the greenhouse gas CO2. One of these promising processes is industrial mineral carbonation whereby alkaline industrial wastes are taken as raw material. The process is a multi-step process which involves the extraction of calcium from industrial alkaline wastes and the subsequent reaction of extracted calcium rich supernatant with CO2 at elevated pH to form stable carbonates. Steelmaking slags were selected from four different plants in SA and used for this investigation owing this to their high calcium content. The potentially-suitable four slags were selected on the basis of their Ca content and high chemical reactivity. The objective of this investigation was to develop a common leach process for all four steel slags to achieve a complete Ca extraction from slags. A Ca rich solution was carbonated to achieve a stable carbonate that can be used. Experiments were carried out using ammonium reagents and a hydroxide reagent to investigate their suitability for the rapid, selective extraction of calcium. Calcium was leached under different experimental conditions including varying leachant concentrations, temperatures and solid to liquid ratios. The slags exhibited contrasting reactive properties to different leachants, which can essentially be explained in terms of differences in mineralogical composition, hence mineral solubility characteristics. Leaching with 2M NH4NO3 aqueous solution at room temperature extraction efficiency increased with increasing concentration. The extent of extraction was different for the four slags. WMO5 showed a complete dissolution of Ca within 20 min of experiment. This difference is due to their different Ca-containing minerals. Same is observed with aqueous NH4CL but WMO5 did not reach a complete dissolution as with NH4NO3. Aqueous NaOH made it impossible for Ca extraction due to its high pH and upon slag addition it was more elevated. Increasing solid to liquid ratio had an influence in percentage slag loss. The pH of leach solution was elevated to 9 making it difficult to extract Ca. Under controlled conditions (pH kept under 1) optimal slag dissolution was achieved with traces of larnite and large amount of brownmillerite. The generated Ca-rich leachate was carbonated in a 600 ml reactor vessel with liquid CO2. A stable carbonate aggregate was produced.
Development of a sensitive electrochemical sensor based on carbon dots and graphitic carbon nitride for the detection of 2-chlorophenol and arsenic (III) in water
(Vaal University of Technology, 2021-02) Moundzounga, Theo Herman Gael; Oseghe, E. O., Dr.; Peleyeju, M. G., Dr.; Ofomaja, A. E., Prof.; Klink, M. J., Dr.
The presence of organic and inorganic pollutants in aqueous environments is one of the major challenges confronting man. It is therefore important to develop sensitive, versatile and cheap techniques for their detection. Arsenic (III), 2-chlorophenol (2-CP) and sulfamethoxazole (SMX) are priority pollutants that pose health threats to humans and animals. This study was thus aimed at exploring two promising carbon nanomaterials as electrode modifiers for the electrochemical sensing of arsenic (III), 2-CP and SMX in water. Glassy carbon electrode (GCE) was modified with a nanocomposite of carbon dots (CDs) and graphitic carbon nitride (g-C3N4) and used as a sensor for the analytes in aqueous media. The CDs was prepared by a facile one-pot hydrothermal method using pine cone as the carbon source; g-C3N4 and g-C3N4/CDs nanocomposite were prepared via the microwave irradiation heating method. CDs, g-C3N4 and g-C3N4/CDs were dropped-dried on the surface of bare GCE. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the prepared materials. GCE, g-C3N4/GCE, CDs/GCE and g-C3N4/CDs/GCE electrodes were electrochemically investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) using a ferrocyanide [Fe (CN) 6]3-/4- redox probe. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical behavior of arsenic (III), 2-CP and SMX on different electrodes (GCE, CDs/GCE, g-C3N4/GCE and g-C3N4/CDs/GCE) were investigated by differential pulse voltammetry (DPV) under optimized conditions in a phosphate buffer solution (pH 7.6, 6 and 5 for 2-CP, As (III) and SMX respectively). The results demonstrated that the g-C3N4/CDs/GCE electrode significantly enhanced the oxidation peak current of all three analytes. The detection sensitivity of the analytes was greatly improved, suggesting that this new modified electrode has great potential in the determination of trace level of arsenic (III), 2-CP and SMX in water. The oxidation peak currents displayed a linear relationship to concentrations for 2-CP (0.5 - 2.5 μM, R2=0.958, n=5), arsenic (III) (2 - 10 μM R2=0.978, n=5) and SMX (0.3 - 1.3 μM R2=0.9906, n=5). The detection limits of 0.62 μM, 1.64 μM and 0.10 μM were obtained for 2-CP, arsenic and SMX, respectively. Phenol and 4-chloro-3-methyl-phenol were found to interfere with the detection of 2-CP, while, Cu2+, Zn2+, Pb2+ and Cd2+ were the only significant ions that interfered with the electrochemical detection of arsenic (III). EDTA was used as a ligand to mask the interference effects of copper, cadmium, lead and zinc on arsenic sensing. The modified electrode (g-C3N4/CDs/GCE) was used to determine arsenic, 2-CP and SMX in spiked tap and effluent water samples by the standard addition method and the results showed percentage recoveries varying from 93-118% for 2-CP, 98-100% for arsenic and 80-105% for SMX. The outcomes of this study established that the nanocomposite material represents an easy and sensitive sensing platform for the monitoring of arsenic (III), 2-CP and SMX in aqueous media.

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