Selahle, S. K.Madala, N. E.Mashele, Ntumbuko Tia2026-06-172026-06-172026-05-19Mashele, N.T. 2026. Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples. . .https://univendspace.univen.ac.za/handle/11602/3206M.Sc. in ChemistryDepartment of ChemistryWater pollution caused by persistent organic contaminants, such as antibiotics and pesticides, has become a critical global challenge, threatening aquatic ecosystems, human health, and sustainable water resources. Conventional treatment technologies, including advanced oxidation processes, membrane filtration, and chemical precipitation, often fail to completely remove these pollutants and are associated with high costs, energy intensity, and secondary pollution. To address these limitations, this study adopts a circular economy framework by transforming agricultural wastes such as palm fronds, corncobs, and sugarcane bagasse into silica-based magnetic nanocomposites (Fe3O4@SiO2), thereby converting low-value biomass into functional adsorbents while reducing waste disposal burdens. Guided by green chemistry principles, these cost-effective and eco-friendly materials are used for the extraction and adsorption of emerging pharmaceutical and pesticide contaminants from wastewater systems. The research begins with a comprehensive review of water pollution sources, and the environmental and health impacts of emerging pollutants. Antibiotics such as sulfonamides, and pesticides, like neonicotinoid insecticides, were identified as priority contaminants due to their persistence, toxicity, and widespread occurrence in aquatic environments. Agricultural waste valorization was explored as a sustainable solution, taking advantage of its high silica and carbon content to produce functional adsorbents with tailored surface properties. Two major experimental investigations were conducted. First, Fe3O4@SiO2 nanocomposites were prepared using silica (SiO2) extracted from palm fronds ash (PFA) and corncobs ash (CCA) via a sol-gel process and iron oxide (Fe3O4) synthesized using the co-precipitation method. The two nanocomposites were systematically compared based on comprehensive physicochemical characterization, including x-ray fluorescence spectroscopy (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses, to evaluate the influence of precursor biomass on material properties and performance. Palm frond-derived silica nanocomposite (Fe3O4@SiO2-PFA) exhibited superior physicochemical characteristics, including a higher BET surface area (191.984 m2/g) and pore volume (0.468 cm3/g), compared to the corncob-derived nanocomposite (Fe3O4@SiO2-CCA), which showed a surface area of 105.288 m2/g and pore volume of 0.406 cm3/g. Based on this comparative assessment, Fe3O4@SiO2-PFA was selected as the optimal material for subsequent adsorption and extraction studies. Consequently, Fe3O4@SiO2-PFA achieved higher extraction efficiencies for sulfonamide antibiotics, including sulfamethoxazole (SMX) and sulfamethazine (SMT). Dispersive magnetic solid-phase microextraction (DMSPME) coupled with HPLC-DAD yielded recoveries of 99.1–101%, low detection limits (0.028 μg/L for SMX and 0.035 μg/L for SMT), and adsorption capacities of 66.4 mg/g (SMX) and 55.3 mg/g (SMT). The adsorption behaviour suggested that electrostatic interactions and hydrogen bonding were the primary mechanisms, while π−π interactions may also contribute, particularly given the presence of aromatic structures in the target analytes and the surface heterogeneity of the biomass-derived composite. This interpretation was supported by pHpzc analysis (7.3–7.5) and isotherm modeling, with the Sips model providing the best fit (R2> 0.98), indicating heterogeneous adsorption sites. Kinetic evaluation confirmed rapid uptake behavior consistent with a pseudo-first-order model. The selected nanocomposite further demonstrated strong reusability over six adsorption cycles with minimal loss in extraction efficiency. Secondly, Fe3O4@SiO2, synthesized from sugarcane bagasse waste (SBW), was optimized for the removal of neonicotinoid insecticides, imidacloprid (IMD), and thiacloprid (THIA) from wastewater. Characterization confirmed high silica content and mesoporosity (BET surface area and pore volume: 115.855 m²/g and 0.358 cm3/g, respectively). Adsorption experiments revealed the dominance of the Langmuir isotherm (R2 > 0.99), indicating monolayer adsorption on a relatively homogeneous surface, with maximum capacities of 88.32 mg/g (IMD) and 82.30 mg/g (THIA). Kinetic studies were best described by the pseudo-second-order model (R2 > 0.98), suggesting that adsorption was governed by the availability of active sites rather than chemisorption. Thermodynamic analysis confirmed that the process was spontaneous and endothermic. Real wastewater tests demonstrated removal efficiencies exceeding 80%, validating the practical applicability of the developed adsorbent. Regeneration studies showed that Fe3O4@SiO2-SBW maintained high performance over multiple cycles, reinforcing its potential for sustainable water treatment.1 online resource (xvii, 164 leaves): color illustrationsenUniversity of VendaUCTDDissertationMashele NT. Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples. []. , 2026 [cited yyyy month dd]. Available from:Mashele, N. T. (2026). <i>Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples</i>. (). . Retrieved fromMashele, Ntumbuko Tia. <i>"Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples."</i> ., , 2026.TY - Dissertation AU - Mashele, Ntumbuko Tia AB - Water pollution caused by persistent organic contaminants, such as antibiotics and pesticides, has become a critical global challenge, threatening aquatic ecosystems, human health, and sustainable water resources. Conventional treatment technologies, including advanced oxidation processes, membrane filtration, and chemical precipitation, often fail to completely remove these pollutants and are associated with high costs, energy intensity, and secondary pollution. To address these limitations, this study adopts a circular economy framework by transforming agricultural wastes such as palm fronds, corncobs, and sugarcane bagasse into silica-based magnetic nanocomposites (Fe3O4@SiO2), thereby converting low-value biomass into functional adsorbents while reducing waste disposal burdens. Guided by green chemistry principles, these cost-effective and eco-friendly materials are used for the extraction and adsorption of emerging pharmaceutical and pesticide contaminants from wastewater systems. The research begins with a comprehensive review of water pollution sources, and the environmental and health impacts of emerging pollutants. Antibiotics such as sulfonamides, and pesticides, like neonicotinoid insecticides, were identified as priority contaminants due to their persistence, toxicity, and widespread occurrence in aquatic environments. Agricultural waste valorization was explored as a sustainable solution, taking advantage of its high silica and carbon content to produce functional adsorbents with tailored surface properties. Two major experimental investigations were conducted. First, Fe3O4@SiO2 nanocomposites were prepared using silica (SiO2) extracted from palm fronds ash (PFA) and corncobs ash (CCA) via a sol-gel process and iron oxide (Fe3O4) synthesized using the co-precipitation method. The two nanocomposites were systematically compared based on comprehensive physicochemical characterization, including x-ray fluorescence spectroscopy (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses, to evaluate the influence of precursor biomass on material properties and performance. Palm frond-derived silica nanocomposite (Fe3O4@SiO2-PFA) exhibited superior physicochemical characteristics, including a higher BET surface area (191.984 m2/g) and pore volume (0.468 cm3/g), compared to the corncob-derived nanocomposite (Fe3O4@SiO2-CCA), which showed a surface area of 105.288 m2/g and pore volume of 0.406 cm3/g. Based on this comparative assessment, Fe3O4@SiO2-PFA was selected as the optimal material for subsequent adsorption and extraction studies. Consequently, Fe3O4@SiO2-PFA achieved higher extraction efficiencies for sulfonamide antibiotics, including sulfamethoxazole (SMX) and sulfamethazine (SMT). Dispersive magnetic solid-phase microextraction (DMSPME) coupled with HPLC-DAD yielded recoveries of 99.1–101%, low detection limits (0.028 μg/L for SMX and 0.035 μg/L for SMT), and adsorption capacities of 66.4 mg/g (SMX) and 55.3 mg/g (SMT). The adsorption behaviour suggested that electrostatic interactions and hydrogen bonding were the primary mechanisms, while π−π interactions may also contribute, particularly given the presence of aromatic structures in the target analytes and the surface heterogeneity of the biomass-derived composite. This interpretation was supported by pHpzc analysis (7.3–7.5) and isotherm modeling, with the Sips model providing the best fit (R2> 0.98), indicating heterogeneous adsorption sites. Kinetic evaluation confirmed rapid uptake behavior consistent with a pseudo-first-order model. The selected nanocomposite further demonstrated strong reusability over six adsorption cycles with minimal loss in extraction efficiency. Secondly, Fe3O4@SiO2, synthesized from sugarcane bagasse waste (SBW), was optimized for the removal of neonicotinoid insecticides, imidacloprid (IMD), and thiacloprid (THIA) from wastewater. Characterization confirmed high silica content and mesoporosity (BET surface area and pore volume: 115.855 m²/g and 0.358 cm3/g, respectively). Adsorption experiments revealed the dominance of the Langmuir isotherm (R2 > 0.99), indicating monolayer adsorption on a relatively homogeneous surface, with maximum capacities of 88.32 mg/g (IMD) and 82.30 mg/g (THIA). Kinetic studies were best described by the pseudo-second-order model (R2 > 0.98), suggesting that adsorption was governed by the availability of active sites rather than chemisorption. Thermodynamic analysis confirmed that the process was spontaneous and endothermic. Real wastewater tests demonstrated removal efficiencies exceeding 80%, validating the practical applicability of the developed adsorbent. Regeneration studies showed that Fe3O4@SiO2-SBW maintained high performance over multiple cycles, reinforcing its potential for sustainable water treatment. DA - 2026-05-19 DB - ResearchSpace DP - Univen LK - https://univendspace.univen.ac.za PY - 2026 T1 - Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples TI - Design of silica-based sustainable biomaterial adsorbents from agricultural waste for the microextraction and adsorptive removal of insecticides and antibiotics from wastewater samples UR - ER -