Laccase enzymes from Rhus vernificera were covalently bound on hyperbranched polyethyleneimine/polyethersulfone (HPEI/PES) electrospun nanofibrous membranes and used for the removal of bisphenol A (BPA) from water. The laccase enzyme was anchored on the dendritic membranes through the abundant peripheral amine groups on the HPEI using glutaraldehyde as a crosslinker. The membranes were characterized with attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) and ultraviolet–visible spectroscopy and correlative light and electron microscopy (CLEM). Furthermore, contact-angle analyses, pure water flux measurements and rejection analyses were carried out. CLEM showed that the enzymes were uniformly dispersed on the nanofibres while SEM analysis revealed that the nanofibres had an average diameter of 354 ± 37 nm. EDS showed the presence of Cu, which is the active entity in laccase enzymes. The laccase-modified membranes were hydrophilic (50°–53° contact angle) and exhibited high BPA rejection of 89.6% as compared to the 52.4% demonstrated by pristine PES. The laccase-modified membranes also maintained a constant permeate flux (7.07 ± 5.54 L/m² h) throughout the filtration process. Recyclability studies indicated that the membranes still maintained a high BPA removal of up to 79% even after four filtration cycles.

Tungsten trioxide (WO₃) is a photocatalyst that has gained interest amongst researchers because of its non-toxicity, narrow band gap and superior charge transport. Due to its fast charge recombination, modification is vital to counteract this limitation. In this paper, we report on the fabrication of Mn-doped WO₃/SnS₂ nanoparticles, which were synthesised with the aim of minimising the recombination rates of the photogenerated species. The nanomaterials were characterised using spectroscopic techniques (UV-Vis-diffuse reflectance spectroscopy (DRS), Raman, XRD, photoluminescence (PL) and electrochemical impedance spectroscopy (EIS)) together with microscopic techniques (FESEM-EDS and high resolution transmission electron microscopy selected area electron diffraction (HRTEM-SAED)) to confirm the successful formation of Mn-WO₃/SnS₂ nanoparticles. The Mn-doped WO₃/SnS₂ composite was a mixture of monoclinic and hexagonal phases, confirmed by XRD and Raman analysis. The Mn-WO₃/SnS₂ heterojunction showed enhanced optical properties compared to those of the un-doped WO₃/SnS₂ nanoparticles, which confirms the successful charge separation. The Brunauer–Emmett–Teller (BET) analysis indicated that the nanoparticles were mesoporous as they exhibited a Type IV isotherm. These nanomaterials appeared as a mixture of rectangular rods and sheet-like shapes with an increased surface area (77.14 m²/g) and pore volume (0.0641 cm³/g). The electrochemical measurements indicated a high current density (0.030 mA/cm²) and low charge transfer resistance (157.16 Ω) of the Mn-WO₃/SnS₂ heterojunction, which infers a high charge separation, also complemented by photoluminescence with low emission peak intensity. The Mott–Schottky (M-S) plot indicated a positive slope characteristic of an n–n heterojunction semiconductor, indicating that electrons are the major charge carriers. Thus, the efficiency of Mn-WO₃/SnS₂ heterojunction photocatalyst was monitored for the degradation of chlorpyrifos. The effects of pH (3–9), catalyst loading (0.1–2 g) and initial chlorpyrifos concentration (100 ppb–20 ppm) were studied. It was observed that the degradation was purely due to photocatalysis, as no loss of chlorpyrifos was observed within 30 min in the dark. Chlorpyrifos removal using Mn-WO₃/SnS₂ was performed at the optimum conditions of pH = 7, catalyst loading = 1 g and chlorpyrifos concentration = 1000 ppb in 90 min. The complete degradation of chlorpyrifos and its major degradation by-product 3,5,6-trichloropyridin-2-ol (TCP) was achieved. Kinetic studies deduced a second order reaction at 209 × 10⁻³ M⁻¹s⁻¹.

Coal fly ash (CFA) has been extensively researched as an adsorbent for heavy metals, but its application is limited by its low adsorption capacity. The modification of CFA with hyperbranched polymers results in improved adsorption capacities. Hyperbranched polyethylenimine (HPEI) is a hyperbranched polymer containing NH₂ groups that can bind with heavy metal ions through complexation or electrostatic interactions. In this study, CFA-HPEI adsorbents with various HPEI loadings (1-5%) were prepared and evaluated for the removal of Cr(VI). The successful incorporation of HPEI onto CFA was confirmed using Fourier transform infrared, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The 3% CFA-HPEI loaded adsorbent resulted in optimum results when the effect of pH and adsorbent dosage was studied. The pseudo-second-order kinetics model best described the adsorption kinetics at an initial concentration of 20 mg/L. The Freundlich adsorption isotherm model best fitted the equilibrium adsorption data with a maximum adsorption capacity of 85.93 mg/g. The Cr-loaded adsorbent was reused as a photocatalyst to degrade methylene blue (MB) in the presence of visible light. The loaded adsorbent degraded 98.9% of MB (5 mg/L) within 180 min and was accompanied by compounds with m/z of 173 and 234, corresponding to the intermediate degradation of Azure A. The XPS analysis confirmed the coexistence of Cr(III) and Cr(VI) on the surface of the adsorbent. In addition, the loaded adsorbent exhibited good stability following MB degradation with no structural changes observed. Thus, CFA-HPEI adsorbents can be utilized as low-cost adsorbents for the remediation of toxic Cr(VI) from water and wastewater. The Cr-loaded CFA-HPEI adsorbent can be effectively reused as a photocatalyst, thus reducing environmental pollution.

Water pollution, resulting from the degradation of plastics into microplastics, exposes humans and other living organisms to contaminated drinking water. Microplastics are capable of adsorbing toxic heavy metals which are carcinogenic and may affect the reproductive functions of living organisms. Hence, this study focuses on the characterization and quantification of microplastics in water to raise the awareness and propose a method of dealing with this emerging pollutant in various aqueous environments. The microplastics were separated from water using polyvinylidene difluoride (PVDF) and PVDF modified with carbon nano-onions (CNOs). The PVDF exhibited the highest concentration of microplastics in the wastewater influent (140 ± 1.85 MP/L) compared to the effluent (8.8 ± 2.10 MP/L), tap water (6.5 ± 5.77 MP/L), and lake water (10 ± 2.65 MP/L). The stereo microscope displayed red, blue, and black colored plastics. The morphological properties were determined using SEM. ATR-FTIR, equipped with Spectrum 10 Spectroscopy Software was used to establish the presence of high-density polyethylene (50%), poly(1,4-butylene terephthalate) (16.6%), nylon 12 (16.6%), and cellulose (16.6%) in the influent. The quantification of heavy metals extracted from the microplastics indicated that the concentrations of As (1.759 to 8.699 mg/L), Cu (83.176 mg/L) and Zn (0.610 mg/L) were above the acceptable limits. Our work is beneficial for the development of a microplastics monitoring protocol for various municipalities. Water treatment plants may also include the treatment of microplastics in the influent and monitor the effluent before the water is released back into the environment.