https://ir.unisa.ac.za/handle/10500/2738 2026-05-08T19:21:55Z https://ir.unisa.ac.za/handle/10500/31967 Synthesis of magnetic nanoadsorbents derived from maize waste and their application for the adsorptive removal of selected heavy metal ions from wastewater samples Mahlaule Glory, Louisah Mmabaki Over the past few years, heavy metal ion (HMI) pollution has become a crucial matter due to their threat to human health and ecological systems.,. Furthermore, HMIs have been reported to be hazardous, persistent, and in some of the global health organizations reports, they have been declared as carcinogens. These HMIs include Pb (II) and Cr (VI) and they are very reactive and highly oxidizing in nature. Thus, the need to remediate these HMIs from wastewater using magnetic nano adsorbents. In this study, three nano-adsorbents such as cellulose nano crystals (CNC), magnetite (M), and magnetic cellulose nanocrystal (MCNC) were synthesized for the removal of Pb (II) in wastewater. The magnetic cellulose nanocrystals (MCNCs) were synthesized using a co-precipitation method from the magnetite (Fe3O4) and cellulose nano crystals (CNCs) were used as a base for stability and easy dispersion of iron for the adsorptive removal of Pb (II) ions. Furthermore, to enhance the adsorption capacity and to improve selectivity of the CNC towards -targeting anionic Cr (VI) ions, the surface modification was conducted by crosslinking CNCs with 2,2,6,6-tetramethylpiperidinyloxy (TEMPO), thereby oxidising the material to form a bridge with the grafting of the polyethyleneimine (PEI). The surface of the CNC-TEMPO-PEI was further magnetised by introducing iron on to the surface material via a co-precipitation method. Fourier-transform infrared spectroscopic (FTIR) analysis revealed the presence of C=O, COOH, CH, OH and FeO stretching frequencies in MCNC, while powder X-ray diffraction (P-XRD) confirmed the formation of MCNC and the monoclinic type 1 cellulose with 1β lattice and magnetite cubic spinel phases of the CNC. Ultraviolet-visible spectroscopy (UV-Vis) showed the presence of both CNC and magnetite at 400 nm. The scanning electron microscopy (SEM) indicated a smooth fibroid surface of CNCs while magnetite (M) displayed 2 morphologies, the rod like and spherical morphology, indicating the presence of iron and oxygen. The MCNC were stable after 600 ⁰C as shown on the thermograms generated from the thermogravimetric analyser (TGA). Last, the Brunauer-Emmett-Teller (BET) displayed surface area, pore size and pore volume improvement of 56 m2/g, 98 Å and 0,1465 cm3/g. Å, respectively, for the MCNC. Following the characterization of the MCNCs nanocomposites, the material was used for adsorptive removal of Pb (II). It was discovered that for the Pb (II) removal efficiency was 97 % with an acceptable precision of ≤ 3 %. The highest efficiency was obtained at optimal conditions of 60 mg dosage, 0,1 ppm concentration within a rapid contact time of 5 min at a temperature of 60 ⁰C and at a pH of 6. These parameters were optimised by using multivariate optimization tools (Minitab) and were also validated against the magnetite and the CNC. A maximum adsorption capacity of MCNC was also obtained at 47,70 mg/g for Pb (II) and the material was re-used for up to 4 cycles. The results revealed that the reaction followed Freundlich isotherms and Pseudo First Order kinetic model with a regression coefficient of 0,98 and 0,96 respectively. The adsorption thermodynamics studies indicated a spontaneous process and an exothermic reaction. On the other hand, the MCNC-TEMPO-PEI was characterised with FTIR, P-XRD, TEM and SEM-EDS techniques. The FTIR confirmed a successful formation and the presence of COOH, OH, Fe-O band and NH2 groups on the nanocomposite. The P-XRD confirmed the crystal structure of CNC-TEMPO and the amorphous structure of both the CNC-TEMPO-PEI and the MCNC-TEMPO-PEI. The SEM-EDS results demonstrated the rod-like, oval and irregular cubic morphology for successful preparation of MCNC-TEMPO-PEI nanocomposite. The adsorption performance of MCNC-TEMPO-PEI on Cr (VI) ions was investigated by using univariate optimization tools. The MCNC-TEMPO-PEI was efficient at 5 ppm, using a 30 mg dosage at 25 ⁰C within the acidic conditions at pH 2 within a rapid contact time of 15 min. The optimised parameters were further validated using 5 various adsorbent materials and the results indicated that the MCNC-TEMPO-PEI was the most efficient by exhibiting the highest adsorption capacity of 4,4 mg/g with a 98% removal. The interaction between the MCNC-TEMPO-PEI and the Cr (VI) ions indicated a chemisorption of the electrostatic forces governing the magnetic and ionic exchange interaction between of the adsorbate and the analyte. The Langmuir adsorption isotherm displayed a correlation coefficient of 0,94 following the PSO kinetic model against the adsorptive removal of Cr (VI) ions. The thermodynamic interaction indicated a non-spontaneous endothermic reaction with a favourable reaction. The adsorbent could be reused at least 8 times with a removal efficiency above 75 %. The results revealed that the real wastewater samples analysed from this study did not contain Cr (VI) ion. Text in English 2024-05-01T00:00:00Z https://ir.unisa.ac.za/handle/10500/31883 Development of novel mesoporous magnetic adsorbents from industrial waste and their application for removal of lead and efavirenz in aqueous solutions Kgoedi, Thabang Industrial waste materials have garnered increased attention as viable adsorbents that could be used for the extraction of heavy metals and organic pollutants from wastewater. This is primarily due to their abundant availability in large quantities and economical cost-effectiveness. Coal fly ash, bottom ash, and fly ash are examples of industrial waste generated from coal combustion in power plants, while petroleum coke is derived from oil refineries. These waste materials contain diverse functional groups, including carbon, calcium oxide, silicon dioxide, aluminium oxide, and iron oxide, which makes them ideal for the remediation of wastewater. Previous research studies have indicated that modified industrial waste materials possess greater adsorption capabilities. As a result, this study sought to modify coal fly ash (RCFA), bottom ash (RBA), fly ash (RFA), and petroleum coke (RPC) by adding iron oxide (Fe3O4) nanoparticles. This modification enables easy separation with an external magnet and enhances their effectiveness in adsorbing lead and efavirenz. The following adsorbents Fe3O4@APC, Fe3O4@ACFA, Fe3O4@AFA, and Fe3O4@ABA were prepared in a two-step method. The first step was activation of the RPC, RBA, RFA, and RCFA with NaOH then followed by incorporating Fe3O4 nanoparticle. These mesoporous magnetic materials were successfully prepared and characterized using various techniques such as thermogravimetric analysis (TGA), scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDS), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller analysis (BET). The Langmuir, Temkin, and Freundlich isotherm models were applied to analyse the equilibrium data. The maximum adsorption capacities for obtained for lead were 48.8, 15.63, 12.16, and 270.27 mg/g for Fe3O4@ACFA, Fe3O4@AFA, Fe3O4@ABA, and Fe3O4@APC, respectively. The maximum adsorption capacities for efavirenz obtained were 25.38, 37.64, 13.07 and 76.54 mg/g Fe3O4@ACFA, Fe3O4@APC, Fe3O4@ABA, Fe3O4@AFA respectively. Based on the adsorption isotherms for lead ions, both Fe3O4@ACFA and Fe3O4@AFA, are best described by the Temkin isotherm while Fe3O4@ABA and Fe3O4@APC were best described by the Langmuir and Freundlich isotherm, respectively. Additionally, adsorption of efavirenz was best described by the Langmuir isotherm for all prepared adsorbents. viii The kinetic data were also evaluated for the lead and efavirenz which revealed that the pseudo-second-order equation provided the best correlation for both lead and efavirenz. Thermodynamic parameters suggest that the adsorption process is endothermic and spontaneous for lead. However, for efavirenz it behaved differently on various adsorbents, revealing non-spontaneous adsorption. The adsorption process for lead was endothermic for all adsorbents, whereas for efavirenz it was found to be endothermic for Fe3O4@APC and Fe3O4@ACFA adsorbents, while exothermic for Fe3O4@ABA and Fe3O4@AFA adsorbents. The findings demonstrate that Fe3O4@ACFA, Fe3O4@APC, Fe3O4@ABA, and Fe3O4@AFA possesses the potential to effectively remove lead ions and efavirenz from aqueous solutions. 2024-02-01T00:00:00Z https://ir.unisa.ac.za/handle/10500/31645 Potential-dependent real-time multidrug sensing with screen printed manganese oxide electrode platform Mokaba, Pheladi Lizzy Emerging pollutants (EPs) provide a new global water quality concern, potentially posing a major damage to human health and the surrounding. Pharmaceuticals, extensively used in both human and veterinary medicine, have become pervasive environmental contaminants due to their continual release into sewage systems and subsequent ubiquity in various ecosystems. In the ambient matrix, they are often present in small amounts (ng/L to g/L) due to their stable composition and slightly elevated polarization. Traditional methods for detecting pharmaceutical compounds in water have long been hindered by their expense and complexity, making widespread implementation challenging. However, electrochemical sensors offer a promising solution to this problem. These sensors provide a cost-effective, portable, and user-friendly alternative to traditional analytical techniques. This research focuses on the development an electrochemical sensor using a screen-printed manganese oxide electrode platform for the potential-dependent analysis of multiple drugs, including sulfamethoxazole, carbamazepine, metoprolol, and ibuprofen. These substances are critical to monitor due to their widespread presence and potential health implications. The study leveraged the unique properties of MnO2 nanoparticles, such as their electrochemical activity, large surface area, and catalytic qualities, to enhance the sensitivity and functionality of screen-printed electrodes for the detection of these drugs. The MnO2 nanoparticles were characterized using a suite of techniques including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, small-angle X-ray scattering (SAXS), and Raman spectroscopy. The optical properties of MnO2NPs were investigated using UV/Vis spectroscopy, covering a wavelength range from 280 to 800 nm. This analysis revealed crucial information about the behaviour of MnO2NPs in response to light across different wavelengths. Specifically, the band gap of the MnO2NPs was determined to be 1.14 electron volts (eV) suggests that these nanoparticles possess favourable electrical and optical characteristics. A band gap of this magnitude indicates that MnO2NPs can effectively absorb light within a certain energy range, making them potentially useful in various applications such as photocatalysis, photovoltaics, and optical sensing. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to investigate the electrochemical behavior of both bare and MnO2NPs-modified screen-printed electrodes. A comparison between the two revealed significant differences in electron transfer kinetics. In the case of the bare electrode, EIS and CV analyses indicated slower electron transfer kinetics, as evidenced by a peak potential separation of 0.249 V in the CV curve. This separation reflects the energy barrier that electrons must overcome during the redox process. Conversely, for the MnO2NPs-modified SPCE, the peak potential dispersion was reduced to 0.269 V, suggesting faster electron transfer kinetics. This reduction in peak potential separation indicates a more efficient and rapid reaction occurring at the electrode surface, likely facilitated by the presence of MnO2NPs. The study investigated the influence of pH, scan speed, and electrolytes to identify optimal experimental conditions. Subsequently, under these ideal circumstances, the electrochemical characteristics of carbamazepine, sulfamethoxazole, ibuprofen, and metoprolol were assessed using differential pulse voltammetry. Calibration curves were constructed for each analyte of interest, enabling the determination of limit of detection. The results revealed limit of detection 0.0005 μM for CBZ, 0.0002 μM for SMX, 0.0004 μM for IBU, and 0.005 μM for MP. These values were derived from the extrapolation of calibration curves, which demonstrated linearity within the range of 0.010 to 0.006 μM. These limits of detection signify the lowest concentrations of each analyte that can be reliably detected and quantified using the DPV technique under the specified experimental conditions. Furthermore, the study conducted stability and interference investigations to evaluate the performance of the MnO2NPs/SPCE sensor under optimal conditions. These investigations demonstrated satisfactory performance, indicating the sensor's robustness and reliability in real-world applications. The effectiveness of the suggested sensor was validated through its successful application in analysing wastewater samples. This practical testing confirmed the sensor's ability to detect multiple drugs, highlighting its potential accurately and selectively. In conclusion, the study successfully developed an extremely accurate, precise, and selective MnO2NPs/SPCE sensor for the multidrug detection. By combining the advantages of MnO2 nanoparticles and screen-printed electrode technology, this sensor offers a cost-effective and efficient solution for environmental monitoring and pharmaceutical analysis. 2024-02-23T00:00:00Z https://ir.unisa.ac.za/handle/10500/31639 Methods development for determination of neonicotinoid pesticides from selected vegetable oils using hplc-dad Victoria, Sengane Musiiwa The neonicotinoid pesticides (NEOs) have been used over the years for plant protection. The use of these NEOs on crops and oil seed plants has led to vegetable oil and crop produce contamination. The four selected NEOs for this study are acetamiprid, imidacloprid, thiacloprid and thiamethoxam. Their accumulation in oil crops is through absorption via roots and plant leaves. The presence of NEOs in the vegetable oils results in human health problems, hence there is a need for monitoring and control of their concentration levels present in agricultural products. Different organisations like World Health Organization (WHO), Codex Alimentarius Commission (CAC) and European Union (EU) have maximum residue limits set for NEOs in countries like Japan, China and US at less than 0.5 mg.kg-1. Different chromatographic techniques have been used for determination of NEOs in various sample matrices. The high-performance liquid chromatography with diode-array detection (HPLC-DAD) was among the most reported chromatographic techniques for detection of NEOs. However, due to the complexity of vegetable oils and the trace concentration levels of NEOs, sample preparation step is required prior to chromatographic detection. The solid phase extraction (SPE) and liquid-liquid extraction (LLE) methods are popular for extraction of various targeted analytes. However, these two extraction methods suffer from different limitations like use of large amount of organic solvents, tediousness, costly adsorbents and production of hazardous waste. Therefore, the aim of the study was to develop rapid, greener, and efficient extraction methods followed by HPLC-DAD analysis for determination NEOs in selected vegetable oils. The magnetic solid phase microextraction (MSPME) was the first extraction method to be investigated. A novel magnetic adsorbent (Fe3O4@Al2O3/AC) was synthesized using maize waste material and characterized using various techniques such Fourier transform infrared spectrometry (FTIR), Powdered X-ray diffraction (PXRD), Scanning electron microscope coupled to energy dispersive X-ray spectroscopy (SEM-EDS), Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM), and Ultraviolet visible spectroscopy (UV-Vis) to confirm the formation of the adsorbent material. The proposed MSPME method achieved high accuracy (80-119.21 %) and precision (≤10 %) for all the investigated NEOs. Furthermore, the obtained limit of detection (LOD) ranged from 0.5-1.76 ng.μL-1, limit of quantification (LOQ) ranged from 1.87-6.62 ng.μL-1, with satisfactory high 9 preconcentration factors (73.02-407) were comparable with literature reported studies. The Analytical GREEness calculator (AGREE) analysis confirmed the 0.54 greenness scale, suggesting that the MSPME was environmentally friendly. Deep eutectic solvent- dispersive liquid-liquid microextraction (DES-DLLME) was the second examined extraction method prior to chromatographic determination of NEOs in vegetable oils. The GREEness of the proposed DES-DLLME was attributed using “greener” more environmentally friendly solvent known as deep eutectic solvents. The method achieved good limit of detection (LOD) ranging from 0.4 to 4.95 ng. μL-1 and limit of quantification (LOQ) ranging from 1.43 to 9.7 ng.μL-1. The method also showed good accuracy (79-119.6 %) and precision (0.1 to 0.9 %). Method greenness was studied using the Analytical GREEness calculator (AGREE) in full tool and the greenness was 0.67 scale. The DLLME method has proved to be greener compared to the AGREE calculator as reported above. The method detection limits for MSPME were lower compared to that for DES-DLLME. The MSPME also shows the high preconcentration factors than the DES-DLLME. The accuracy for the DES-DLLME was good and higher compared to that for MSPME. Both the methods were conducted under room temperature. The precision for DES-DLLME was lower compared to that of MSPME which shows that DES-DLLME is more sensitive than the MSPME. 2024-02-29T00:00:00Z