Advanced photocatalytic sterilization for recalcitrant Enterococcus sp. contaminated water by newly developed Z-scheme Bi2WO6 based composites under solar light

Efficient photodegradation of antibiotics by g-C3N4 and 3D flower-like Bi2WO6 perovskite structure: Insights into the preparation, evaluation, and potential mechanism

Antibiotics are emerging organic pollutants that have attracted huge attention owing to their abundant use and associated ecological threats. The aim of this study is to develop and use photocatalysts to degrade antibiotics, including tetracycline (TC), ciprofloxacin (CIP), and amoxicillin (AMOX). Therefore, a novel Z-scheme heterojunction composite of g-C3N4 (gCN) and 3D flower-like Bi2WO6 (BW) perovskite structure was designed and developed, namely Bi2WO6/g-C3N4 (BW/gCN), which can degrade low-concentration of antibiotics in aquatic environments under visible light. According to the Density Functional Theory (DFT) calculation and the characterization results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FITR), Scanning electron microscopy - energy spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), this heterojunction was formed in the recombination process. Furthermore, the results of 15 wt%-BW/gCN photocatalytic experiments showed that the photodegradation rates (Rp) of TC, CIP, and AMOX were 92.4%, 90.1% and 82.3%, respectively, with good stability in three-cycle photocatalytic experiments. Finally, the quenching experiment of free radicals showed that the holes (h+) and superoxide radicals (·O2-) play a more important role than the hydroxyl radicals (·OH) in photocatalysis. In addition, a possible antibiotic degradation pathway was hypothesized on the basis of High performance liquid chromatography (HPLC) analysis. In general, we have developed an effective catalyst for photocatalytic degradation of antibiotic pollutants and analyzed its photocatalytic degradation mechanism, which provides new ideas for follow-up research and expands its application in the field of antibiotic composite pollution prevention and control.

Harnessing the photocatalytic potential of bismuth ferrite-activated carbon nanocomposite (BFO-AC) for Staphylococcus aureus decontamination under visible light

In response to the escalating global issue of microbial contamination, this study introduces a breakthrough photocatalyst: bismuth ferrite-activated carbon (BFO-AC) for visible light-driven disinfection, specifically targeting the Gram-positive bacterium Staphylococcus aureus (S. aureus). Employing an ultrasonication method, we synthesized various BFO-AC ratios and subjected them to comprehensive characterization. Remarkably, the bismuth ferrite-activated carbon 1:1.5 ratio (BA 1:1.5) nanocomposite exhibited the narrowest band gap of 1.86 eV. Notably, BA (1:1.5) demonstrated an exceptional BET surface area of 862.99 m2/g, a remarkable improvement compared to pristine BFO with only 27.61 m2/g. Further investigation through FE-SEM unveiled the presence of BFO nanoparticles on the activated carbon surface. Crucially, the photocatalytic efficacy of BA (1:1.5) towards S. aureus reached its zenith, achieving complete inactivation in just 60 min. TEM analysis revealed severe damage and rupture of bacterial cells, affirming the potent disinfection capabilities of BA (1:1.5). This exceptional disinfection efficiency underscores the promising potential of BA (1:1.5) for the treatment of contaminated water sources. Importantly, our results underscore the enhanced photocatalytic performance with an increased content of activated carbon, suggesting a promising avenue for more effective microorganism inactivation.

Photocatalytic degradation of multiple-organic-pollutant under visible light by graphene oxide modified composite: degradation pathway, DFT calculation and mechanism

Wastewater containing antibiotics, organic dyes, and waterborne bacteria is a severe threat to human health and the environment. Amoxicillin has a slow metabolism rate in humans. Methylene blue is mutagenic and carcinogenic. In addition, Salmonella causes serious diarrhea. In this study, an effective 2D/2D photocatalyst with excellent elimination of these pollutants was fabricated by combining graphene oxide (GO), Bi2WO6, BiPO4 and Ag species. GO was applied at varying loading contents (0.8, 1.6, 2.4, 3.2 wt%) to improve the properties of the photocatalyst toward the removal of representative pollutants. The chemical structures, morphology, light absorption and charge mobility were investigated by different GO loading samples. The results indicated that when the wt% of GO was 2.4%, the photocatalyst showed excellent photocatalytic properties and removal rates for typical pollutants. Amoxicillin and methylene blue were mineralized into CO2, H2O, and small molecules, while Salmonella was disinfected with excellent photocatalytic efficiency. Furthermore, the possible photodecomposition pathways of amoxicillin and methylene blue were proposed by DFT calculations and intermediates identified by LCMS. The mechanism of the photocatalytic process was investigated by radical trapping experiments, ESR spectroscopy, and Motty-Schottky plots. The free radicals could be produced constantly during the photocatalytic process, leading to mineralization of amoxicillin and methylene blue, and disinfection of Salmonella. In this work, a new perspective on GO modified Bi2WO6 with different loading contents and the degradation pathways of antibiotics and dyes was proposed.

Solar-driven strongly coupled plasmonic Au nanoarrays on mesoporous silica nanodisks enable selective fungal and bacterial inactivation in well water

Well water is an important water source in isolated rural areas but easily suffers from microbial contamination. Herein, we anchored periodic Au nanoarrays on mesoporous silica nanodisks (Au-MSN) to fabricate a solar-driven nano-stove for well water disinfection. The solar/Au-MSN process completely inactivated 3.98, 6.55, 7.11 log10 cfu/mL, and 3.37 log10 pfu/mL of Aspergillus niger spores, Escherichia coli, chlorine-resistant Spingopyxis sp. BM1-1, and bacteriophage MS2 within 5 min, respectively. Moreover, the complete inactivation of various microorganisms (even at a viable but nonculturable state) was achieved in the flow-through reactor under natural solar light in real well water matrixes. Thorough characterizations and theoretical simulations verified that the densely anchoring strategy of Au-MSN's nanoarray worked on broadband absorption via the photon confinement effect, and trace amounts of Au can induce strong electromagnetic fields and collective localized heating. The resulting surge of 1O2 and heat synergically destroyed membranes, dysfunction cellular self-defense and metabolic system, induced intracellular oxidative stress, and ultimately inactivated microorganisms. Additionally, the 1O2-dominated oxidation and cell adhesion facilitated the selective disinfection in real well water matrixes. This study provides a cost-effective and practical solution for efficient well water disinfection, which assists isolated rural areas in getting safe drinking water.

Bromine Ion-Intercalated Layered Bi2WO6 as an Efficient Catalyst for Advanced Oxidation Processes in Tetracycline Pollutant Degradation Reaction

The visible-light-driven photocatalytic degradation of pharmaceutical pollutants in aquatic environments is a promising strategy for addressing water pollution problems. This work highlights the use of bromine-ion-doped layered Aurivillius oxide, Bi2WO6, to synergistically optimize the morphology and increase the formation of active sites on the photocatalyst's surface. The layered Bi2WO6 nanoplates were synthesized by a facile hydrothermal reaction in which bromine (Br-) ions were introduced by adding cetyltrimethylammonium bromide (CTAB)/tetrabutylammonium bromide (TBAB)/potassium bromide (KBr). The as-synthesized Bi2WO6 nanoplates displayed higher photocatalytic tetracycline degradation activity (~83.5%) than the Bi2WO6 microspheres (~48.2%), which were obtained without the addition of Br precursors in the reaction medium. The presence of Br- was verified experimentally, and the newly formed Bi2WO6 developed as nanoplates where the adsorbed Br- ions restricted the multilayer stacking. Considering the significant morphology change, increased specific surface area, and enhanced photocatalytic performance, using a synthesis approach mediated by Br- ions to design layered photocatalysts is expected to be a promising system for advancing water remediation.

Liquid exfoliation of bulk g-C3N5 to nanosheets for improved photocatalytic antibacterial activity

Liquid exfoliation of bulk g-C₃N₅ was applied to synthesize g-C₃N₅ nanosheets. In order to characterize the samples, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectra (XPS), UV-Vis absorption spectra (UV-Vis), and photoluminescence spectra (PL) were examined. g-C₃N₅ nanosheets exhibited enhanced performance in the inactivation of Escherichia coli (E. coli) with visible light irradiation relative to bulk g-C₃N₅ and promoted complete inactivation of E. coli within 120 min. h⁺ and •O₂^- were the principal reactive species in the antibacterial process. In the early stages, SOD and CAT played a defensive role in resisting oxidative damage of active species. With the prolonged light exposure time, the antioxidant protection system was overwhelmed leading to the destruction of the cell membrane. The leakage of cell contents such as K⁺, protein, and DNA caused bacterial apoptosis ultimately. The enhanced photocatalytic antibacterial performance of g-C₃N₅ nanosheets is ascribed to the stronger redox property by the upward shift of CB and downward shift of VB compared with bulk g-C₃N₅. On the other hand, larger specific surface area and better separation efficiency of photoinduced carriers are helpful to the improved photocatalytic performance. This study systematically revealed the inactivation process toward E. coli and expanded the application range of g-C₃N₅-based materials with abundant solar energy.

Construction of S-Scheme CuS/Bi5O7I Heterojunction for Boosted Photocatalytic Disinfection with Visible Light Exposure

In this paper, a novel S-scheme CuS/Bi5O7I heterojunction was successfully constructed using a two-step approach comprising the alkaline hydrothermal method and the adsorption–deposition method, and it consisted of Bi5O7I microrods with CuS particles covering the surface. The photocatalytic antibacterial effects on Escherichia coli (E. coli) were systematically examined with visible light exposure. The results suggested that the 3%-CuS/Bi5O7I composite showed the optimal antibacterial activity, completely inactivating E. coli (5 × 108 cfu/mL) in 180 min of irradiation. Moreover, the bacterial inactivation process was scientifically described. •O2− and h+ were the major active species for the inactivation of the bacteria. In the early stages, SOD and CAT initiated the protection system to avoid the oxidative destruction of the active species. Unfortunately, the antioxidant protection system was overwhelmed thereafter, which led to the destruction of the cell membrane, as evidenced by the microstructure changes in E. coli cells. Subsequently, the leakage of intracellular components including K+, proteins, and DNA resulted in the unavoidable death of E. coli. Due to the construction of the S-scheme heterojunction, the CuS/Bi5O7I composite displayed the boosted visible light harvesting, the high-efficiency separation of photogenerated electrons and holes, and a great redox capacity, contributing to an outstanding photocatalytic disinfection performance. This work offers a new opportunity for S-scheme Bi5O7I-based heterojunctions with potential application in water disinfection.