Olalekan C. Olatunde

The release of common medications and illegal drugs into the environment could be potentially harmful to the ecosystem and hamper the behavior and growth of plants and animals. These pollutants gain access to water through sewage and factory discharges and have been found to exceed safety limits in water bodies. Therefore, there is an urgent need for improved wastewater purification systems. In this study, semiconductor-based heterojunction photocatalyst CuInS₂/CeO₂, synthesized through a facile solvothermal process, was explored for the photocatalytic degradation of ciprofloxacin, commonly used antibiotics. Studies on the electronic properties of the heterojunction revealed interfacial characteristics that were suitable for enhanced charge carrier separation and transport and a potential S-scheme charge transfer mechanism. The heterojunction achieved ∼90% efficiency for the degradation of CIP compared to 60% and 12% reported for CeO₂ and CuInS₂, respectively. This shows an improvement in the activity, which results from the improved charge carrier properties of the heterojunction. Further investigation of the charge transfer mechanism through radical scavenging experiments identified ^•OH, O2^•-, and h⁺ as active species contributing to the catalyst's efficacy. Based on X-ray photoelectron spectroscopy analysis, a proposed S-scheme charge transfer mechanism was suggested for the CuInS₂/CeO₂ heterojunction. The findings indicate the potential of the CuInS₂/CeO₂ heterojunction as a promising photocatalyst for treating waste effluents from the pharmaceutical industry.

This study explores the microstructural, morphological, and optical properties of Fe₂O₃ nanoparticles synthesized from the pyrolysis of ZIF-8 like Fe-2-methyl imidazole (MIM) metal–organic frameworks (MOFs). Using X-ray diffraction (XRD) profile analysis methods, including the modified Scherrer, Williamson–Hall (W-H), size strain plot, and Halder-Wagner methods, the impact of annealing temperature on the microstructural parameters and crystal defects of the obtained Fe₂O₃ nanoparticles was investigated. The nanoparticles exhibited high crystallinity and a rhombohedral α-Fe₂O₃ phase. Morphological analysis through transmission electron microscopy (TEM) revealed distinct structural features, while UV–vis spectroscopy was employed to examine their optical properties. The results indicated that higher annealing temperatures enhance crystallinity, reduce defect density, and improve atomic mobility. This comprehensive analysis provides valuable insights into the synthesis-structure–property relationships of Fe₂O₃ nanoparticles, highlighting their potential applications in applications such as gas sensing and photocatalysis.

ZnO and TiO₂ nanoparticles were prepared through a plant-extract mediated hydrothermal synthesis. X-ray diffraction (XRD) study confirmed the crystalline nature and the phase characteristic of the obtained nanoparticles. X-ray diffraction profile analysis models such as Williamson–Hall analysis, size-strain plot and Rietveld analysis were further used in evaluating the microstructural parameters of the obtained materials. The calculated particle size for all the models was in great agreement, with values in the range of 55.46–87.6 nm recorded for ZnO, while for TiO₂, the crystallite size was in the range of 33.82–41.9 nm. The calculated crystal microstrain varied based on the model, while the stress in the ZnO and TiO₂ nanoparticles was evaluated at 3.8 and 13.7 MPa, respectively. Furthermore, TiO₂ nanoparticles had a higher energy density of 8.96 × 10^–8 KJ m⁻³ compared to 7.12 × 10^–8 KJ m⁻³ obtained for ZnO.

Photocatalysis has shown high potential in dealing with the ever-broadening problem of wastewater treatment, escalated by the increasing level of recalcitrant chemicals often referred to as emerging contaminants. In this study, the effect of support material on the photocatalytic activity of copper tin sulfide (Cu₃SnS₄) nanoparticles for the degradation of tetracycline as an emerging contaminant is presented. Graphene oxide, protonated graphitic carbon nitride, and a composite of graphitic carbon nitride and graphene oxide were explored as support materials for Cu₃SnS₄ nanoparticles. The nanoparticles were incorporated with the different carbonaceous substrates to afford graphene-supported Cu₃SnS₄ (GO-CTS), protonated graphitic carbon nitride-supported Cu₃SnS₄ (PCN-CTS), and graphene oxide/protonated graphitic carbon nitride-supported Cu₃SnS₄ (GO/PCN-CTS). Physicochemical, structural, and optical properties of the prepared nanocomposites were characterized using techniques such as Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis near infrared, and fluorescence spectrophotometry. The compositing of the Cu₃SnS₄ nanoparticles on the support materials was confirmed by the characterization techniques, and the optical properties of the composites were found to be influenced by the nature of the support material. The incorporation of CTS into the support materials resulted in a reduction in band gap energy with evaluated band gaps of 1.65, 1.46, 1.43 eV, and 1.16 eV. The reduction in band gap energy suggests the potential of the composites for enhanced photocatalytic activity. From the photocatalytic study, the degradation efficiency of tetracycline by CTS, PCN-CTS, GO-CTS, and PC/GO-CTS was 74.1, 85.2, 90.9, and 96.5%, respectively. All the composites showed enhanced activity compared to pristine CTS, and the existence of a synergy between GO and PCN when both were employed as support materials was observed. Based on the charge carrier recombination characteristics and the band edge potential calculations from the composites, a possible mechanism of action of each composite was proposed. This study therefore confirms the possibility of modulating the mechanism of action and subsequently the efficiency of semiconductor materials by altering the nature of the support material.

The incessant release of pharmaceuticals into the aquatic environment continues to be a subject of increasing concern. This is because of the growing demand for potable water sources and the potential health hazards which these pollutants pose to aquatic animals and humans. The inability of conventional water treatment systems to remove these compounds creates the need for new treatment systems in order to deal with these class of compounds. This review focuses on advanced oxidation processes that employ graphene-based composites as catalysts for the degradation of pharmaceuticals. These composites have been identified to possess enhanced catalytic activity due to increased surface area and reduced charge carrier recombination. The techniques employed in synthesizing these composites have been explored and five different advanced oxidation processes—direct degradation process, chemical oxidation process, photocatalysis, electrocatalyis processes and sonocatalytic/sono-photocatalytic processes—have been studied in terms of their enhanced catalytic activity. Finally, a comparative analysis of the processes that employ graphene-based composites was done in terms of process efficiency, reaction rate, mineralization efficiency and time required to achieve 90% degradation.