Abstract
The increasing presence of pharmaceutical contaminants in environmental water systems poses a significant threat to ecosystems and human health. Most commonly, pharmaceuticals pose a risk to aquatic organisms, such as fish, by affecting their ability to reproduce or change their behaviour. Non-steroidal anti-inflammatory drugs (NSAIDs) and antiretroviral drugs (ARVs) are among the most detected pharmaceuticals in wastewater treatment plants (WWTPs), especially in regions with high pharmaceutical consumption rates. A variety of methods used in WWTPs are not effective in removing some of the pharmaceuticals from water. Thus, the main aim of this study was to prepare, characterise, and apply magnetic nanomaterials (NMs) for the effective removal of pharmaceuticals from environmental water samples. Magnetic NMs were synthesised from waste materials as precursors using environmentally friendly and cost-effective methods. Nanomaterials have unique properties, and incorporating them with iron oxide (Fe₃O₄) nanoparticles (NPs) improve those properties, which are favourable in adsorption processes.
Easily available waste material, coal fly ash (CFA), was used as a precursor in the preparation of SiO2 NPs, and acid mine drainage (AMD) was also used as Fe₃O₄ NPs precursor. A Fe₃O₄@SiO2 nanocomposite was synthesised through the co-precipitation method. The SiO2 NPs, Fe3O4, Fe3O4@SiO2 nanocomposites exhibited the BET surface area, pore volume, and pore size of (SiO2–30 min: 3.7 m2/g, 0.21 cm3/g, 229 nm; SiO2–2 h: 10.6 m2/g, 0.23 cm3/g, 87.3 nm); Fe3O4: 90.8 m2/g, 0.27 cm3/g, and 12.1 nm; and (Fe3O4@SiO2–30 min: 37.7 m2/g, 0.19 cm3/g, 20.1 nm; Fe3O4@SiO2–2 h: 67.8 m2/g, 0.39 cm3/g, and 23.2 nm). The major functional groups (Si–O–Si and Fe–O) and Si, O, and Fe content from FTIR and EDS confirmed the successful preparation of the SiO2 NPs, Fe3O4 NPs, and Fe3O4@SiO2 nanocomposites. SEM results revealed sponge-like structures with SiO2–30 min particles dispersed and SiO2–2 h particles clustered. Observations also revealed tiny spherical Fe3O4 NPs and irregular in shape. Furthermore, the successful synthesis of Fe3O4@SiO2 nanocomposites was observed as the Fe3O4 NPs were incorporated into SiO2 NPs' pores. From TEM, SiO2–30 min and SiO2–2 h showed aggregated uniform rod-like structures; and Fe3O4 NPs were distributed evenly. It was observed that Fe3O4 NPs were embedded in the thin rod-like structures, which confirmed the successful synthesis of the Fe3O4@SiO2 nanocomposites. The crystalline nature of the SiO2 NPs, Fe3O4 NPs, and Fe3O4@SiO2 nanocomposites was observed from XRD. The
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Fe₃O₄@SiO2 nanocomposite was used as an adsorbent for the removal of diclofenac (DCF), a widely used NSAID that is frequently detected in various environmental water bodies. Batch experiments were conducted, and the effect of different factors, including the mass of adsorbent, pH, and sample volume, were systematically evaluated using central composite design (CCD). The adsorption process was monolayer and physisorption under optimum conditions, as described by the Langmuir and Dubinin–Radushkevich (D-R) isotherm model with an adsorption capacity of 55.7 mg/g. The kinetic data indicated a physisorption adsorption mechanism and best fitted the pseudo-first-order kinetic model. The adsorption process was confirmed to be spontaneous by the thermodynamic experimental data. Real water sample results revealed a maximum removal efficiency of 97.44%, respectively. This showed the effectiveness of Fe₃O₄@SiO2 nanocomposite in the removal of DCF from wastewater. Lastly, this adsorbent demonstrated high stability since it could be regenerated and reused over seven cycles.
Waste-derived carbon nanomaterial material, Fe₃O₄ NPs, and magnetic waste-derived carbon nanomaterial nanocomposite (Fe₃O₄@WDCNM) were synthesised from potato peels and AMD through the co-precipitation method. The materials exhibited the BET surface area, pore volume, and pore size of (WDCNM: 41.5 m2/g, 0.24 cm3/g, 56.4 nm), Fe3O4: 90.8 m2/g, 0.27 cm3/g, and 12.1 nm, and (Fe3O4@WDCNM: 54.6 m2/g, 0.17 cm3/g, 28.5nm). The synthesis of the WDCNM, Fe3O4 NPs, and Fe3O4@WDCNM nanocomposite was successfully confirmed by the primary functional groups including C≡C, C-O, and Fe–O as well as the C, O, and Fe content from FTIR and EDS. The WDCNM showed amorphous nature and crystalline nature of Fe3O4 NPs, and Fe3O4@WDCNM nanocomposite was observed from XRD. The SEM results revealed porous structures of WDCNM, and spherical Fe3O4 NPs in various sizes were observed. Fe3O4 NPs were incorporated into WDCNM's pores, indicating successful synthesis of Fe3O4@WDCNM nanocomposite. The observation from TEM displayed irregular and porous structures of WDCNM; and uniformly distributed spherical Fe3O4 NPs. The successful deposition of Fe3O4 NPs onto the surface of the WDCNM was confirmed in the formation of Fe3O4@WDCNM nanocomposite. The adsorption performance of Fe₃O₄@WDCNM material was investigated for the adsorptive removal of lamivudine (3TC) and zidovudine (AZT) from wastewater. Under optimum conditions, the adsorption process followed the Langmuir isotherm model, indicating monolayer adsorption and Dubinin–Radushkevich (D-R) isotherm model further confirmed that the mechanism was physisorption. The kinetic data best fitted the pseudo-first-order kinetic model and suggested a physisorption
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adsorption mechanism. The thermodynamics experimental data corroborated the spontaneous nature of the adsorption process. The isotherm, kinetic and thermodynamics studies' optimum conditions were used, and the Fe₃O₄@WDCNM nanocomposite was applied in real water samples to investigate its performance. The highest 3TC and AZT removal efficiency from real water samples was greater than 90%. Fe₃O₄@WDCNM nanocomposite was shown to be suitable for the removal of 3TC and AZT.