Regulating charge transfer for enhanced PAA activation over sulfur-doped magnetic CoFe2O4: A novel strategy for simultaneous micropollutants degradation and bacteria inactivation.

Micropollutants and bacteria are prevalent pollutants in wastewater, posing significant risks to ecosystems and human health. As peracetic acid (PAA) is being increasingly used as a disinfectant, activation of PAA by low-cost and high-performance activators is a promising strategy for wastewater treatment. In this study, the sulfur-doped magnetic CoFe2O4 (SCFO) is successfully developed for efficient PAA activation to simultaneously decontaminate and disinfect wastewater. PAA/SCFO-0.3 exhibits exceptional performance, degrading 100 % of 8 µM sulfamethoxazole (SMX) with a first-pseudo reaction rate of 1.275 min-1, and achieving 5.3-log inactivation of Escherichia coli (E. coli) within 3 min at a PAA dosage of 0.2 mM and catalyst dosage of 0.025 g/L (initial pH 6.5). Scavenging experiments and electron paramagnetic resonance (EPR) analysis identify CH3C(O)O• and CH3C(O)OO• as the dominant reactive species for SMX degradation. The sulfur species in SCFO-0.3 facilitate Co2+ regeneration and regulate charge transfer, promoting PAA activation for SMX degradation. Moreover, the PAA/SCFO-0.3 system demonstrates operational feasibility over a broad range of water matrices and has excellent stability and reusability (maintaining 93 % removal of SMX after 5 cycles), demonstrating its potential for industrial applications. This study provides insights into enhancing PAA activation through sulfur doping in transition metal catalysts and highlights the practical applicability of the PAA/SCFO-0.3 system as an advanced alternative to conventional disinfection for simultaneous decontamination and disinfection in wastewater.

Directional Separation of Highly Reductive Electrons to the Reactive Center in a Magnetic S-Scheme ZnFe2O4/A-MoS2 Heterojunction for Enhanced Peroxymonosulfate Activation toward Pharmaceuticals and Personal Care Product Removal.

Pharmaceuticals and personal care products (PPCPs) are ubiquitous in sewage, adversely affecting ecosystems and human health. In this study, an S-scheme magnetic ZnFe2O4/ammoniated MoS2 (ZnFe2O4/A-MoS2) heterojunction as a visible-light-driven PMS activator for PPCP degradation was developed. ZnFe2O4/A-MoS2 achieves improved photocatalytic activity because the construction of S-scheme heterojunction promotes the separation of the highly reductive photogenerated electrons. The optimized photocatalyst (10%-ZnFe2O4/A-MoS2, 0.2 g/L) achieved 100% removal of 2 ppm carbamazepine (CBZ) within 2.5 min at a PMS dosage of 0.5 mM (initial pH 7.0). Mechanistic investigation revealed that the separated electrons to the ZnFe2O4 reactive center of the heterojunction facilitated PMS activation and generated SO4·- as the dominant reactive species for CBZ degradation. The system exhibited excellent practicability in various samples of actual sewage, where most sewage components negatively impacted CBZ degradation. Further, the chloride ions in high-salinity sewage could be activated to generate additional reactive chlorine species for PPCP degradation. The heterojunction possesses outstanding reusability and stability in treating various water conditions. This work provides mechanistic and practical perspectives in developing novel S-type heterojunctions for recalcitrant pollutant treatment.

Solar-driven photocatalytic chlorine activation for the simultaneous degradation of pharmaceuticals and personal care products and the inactivation of Escherichia coli in drinking water.

Removal of pharmaceuticals and personal care products (PPCPs) is often inefficient during conventional water treatment, posing threats to human health. Herein, we have developed a novel solar/TiO2/chlorine system upgraded from chlorine disinfection for the simultaneous degradation of PPCPs and the inactivation of Escherichia coli from drinking water. The addition of 100 µM of chlorine to the photocatalytic process considerably enhanced the degradation efficiency of PPCPs and demonstrated excellent disinfecting abilities, as confirmed by a 4.7 × increase in the carbamazepine degradation rate constant coupled with a 3.2-log (99.94%) reduction of E. coli cells within 1 min. Photoinduced charge pairs (hVB+ and eCB-) were identified for reactive species generation, and HO• and ClO• were the primary contributors to PPCPs degradation. The process exhibited satisfactory carbamazepine degradation efficiency in different water matrices and the cycling tests showed the TiO2 photocatalyst to be highly stable and reusable. Overall, our solar/TiO2/chlorine system is a potentially effective alternative to conventional drinking water treatment using chlorination.

Integrating Reactive Chlorine Species Generation with H2 Evolution in a Multifunctional Photoelectrochemical System for Low Operational Carbon Emissions Saline Sewage Treatment.

Conventional wastewater treatment plants (WWTPs) suffer from high carbon emissions and are inefficient in removing emerging organic pollutants (EOPs). Consequently, we have developed a low operational carbon emissions multifunctional photoelectrochemical (PEC) system for saline sewage treatment to simultaneously remove organic pollutants, ammonia, and bacteria, coupled with H2 evolution. A reduced BiVO4 (r-BiVO4) photoanode with enhanced PEC properties, ascribed to constructing sufficient oxygen vacancies and V4+ species, was synthesized for the aforementioned technique. The PEC/r-BiVO4 process could treat saline sewage to meet local WWTPs' discharge standard in 40 min at 2.0 V vs Ag/AgCl and completely degrade carbamazepine (one of EOPs), coupled with 633 µmol of H2 production; 93.29% reduction in operational carbon emissions and 77.82% decrease in direct emissions were achieved by the PEC/r-BiVO4 process compared with large-scale WWTPs, attributed to the restrained generation of CH4 and N2O. The PEC system activated chloride ions in sewage to generate numerous reactive chlorine species and facilitate •OH production, promoting contaminants removal. The PEC system exhibited operational feasibility at varying pH and total suspended solids concentrations and has outstanding reusability and stability, confirming its promising practical potential. This study proposed a novel PEC reaction for reducing operational carbon emissions from saline sewage treatment.

Different responses of gram-negative and gram-positive bacteria to photocatalytic disinfection using solar-light-driven magnetic TiO2-based material, and disinfection of real sewage.

A solar-light-driven magnetic photocatalyst, reduced-graphene-oxide/Fe,N-TiO2/Fe3O4@SiO2 (RGOFeNTFS), was developed for the photocatalytic disinfection of different strains of bacteria: gram-negative Escherichia coli (E. coli) and Salmonella typhimurium (S. typhimurium), and gram-positive Enterococcus faecalis (E. faecalis). The different responses of the bacteria during the reaction were investigated. Gram-positive E. faecalis was found to be more susceptible to photocatalytic disinfection and exhibited a higher leakage of intracellular components than the two gram-negative bacteria. The interactions between the bacteria and RGOFeNTFS were analyzed for Zeta potential, hydrophilicity and SEM. Under the experimental conditions, the opposite surface charges of the bacteria (negative Zeta potential) and RGOFeNTFS (positive Zeta potential) contribute to their interactions. With a more negative Zeta potential (than E. coli and E. faecalis), S. typhimurium interacts more strongly with RGOFeNTFS and is mainly attacked by •OH near the photocatalyst surface. E. coli and E. faecalis (with less negative Zeta potentials) interact less strongly with RGOFeNTFS, and compete for the dominant reactive species (•O2-) in the bulk solution. Therefore, the co-existence of bacteria significantly inhibits the photocatalytic disinfection of E. coli and E. faecalis, but insignificantly for S. typhimurium. Moreover, photocatalytic disinfection using RGOFeNTFS show potential for treating real sewage, which meets the local discharge standard (of E. coli) after a 60-min reaction. In real sewage, different bacteria are disinfected simultaneously.

N-doped graphitic C3N4 nanosheets decorated with CoP nanoparticles: A highly efficient activator in singlet oxygen dominated visible-light-driven peroxymonosulfate activation for degradation of pharmaceuticals and personal care products.

CoP nanoparticle-loaded N-doped graphitic C3N4 nanosheets (CoP/N-g-C3N4) were fabricated via a facile three-step method to degrade pharmaceuticals and personal care products (PPCPs) via a visible-light-driven (VLD) peroxymonosulfate (PMS) activation system. 2 ppm carbamazepine (CBZ) can be removed completely within 10 min by the VLD-PMS system with a kinetic constant of k = 0.29128 min-1, as 25.8 times compared to that under dark conditions (k = 0.01128 min-1). The experimental and theoretical results showed that the doped graphitic N atoms could modulate the electronic properties of the g-C3N4 nanosheets. Subsequently, the Density Functional Theory (DFT) explained that CoP showed preference to bonding with the nitrogen atoms involved in the newly formed NË­N bond, and the Co‒N bond dramatically enhanced the transfer of photo-generated electrons from the N-g-C3N4 nanosheets. Electron paramagnetic resonance (EPR) tests show that singlet oxygen (1O2) plays a leading role in this case. Moreover, PMS molecules are also tended to be absorbed onto the electron-deficient carbon atoms near the newly formed NË­N bonds for PMS reduction, synergistically enhancing the degradation efficiency for CBZ and benzophenone-3 (BZP). The newly established VLD-PMS activation system was shown to treat the actual sewage in Hong Kong sewage treatment plants (STPs) very well. This work supplements the fundamental theory of radical and non-radical pathways in the sulfate radical (SO4•-)-based advanced oxidation process (SR-AOP) for environmental cleanup purposes.

Scaled-up development of magnetically recyclable Fe3O4/La(OH)3 composite for river water phosphate removal: From bench-scale to pilot-scale study.

The use of magnetic lanthanum-based materials for phosphate removal from river water has gained increasing attention. However, challenges to produce and use lanthanum-based materials in large-scale or pilot-scale studies remain. In this work, a kilogram-scale Fe3O4/La(OH)3 magnetically recyclable composite for removing phosphate from river water was developed through a low-temperature precipitation route. The composite was used to remove phosphate from river water at both bench- and pilot-scales. Based on the bench-scale tests, the developed Fe3O4/La(OH)3 composite was found to have excellent magnetic particle separation efficiency (>98%) and a sorption capacity of 11.77 mg/g for phosphate. A 1.0 g/L dosage of the composite in the river water sample was able to selectively reduce the phosphate level from 0.089 to 0.005 mg/L in 60 min over five consecutive adsorption cycles. At the pilot-scale, the Fe3O4/La(OH)3 composite only achieved 36.0% phosphate removal efficiency, which is considerably different from the bench-scale results over an operational time of five months and a total treatment volume of 300 m3. This significantly reduced removal efficiency is mainly attributable to turbidity, suspended solids, and organic matter in the river water and the deteriorated magnetic separation efficiency. This study revealed potential challenges and shed new insights on moving magnetic nanocomposite-based technology from the bench-scale to the pilot-scale, which can inspire new designs for the application of similar technology.

Visible-light-driven peroxymonosulfate activation in photo-electrocatalytic system using hollow-structured Pt@CeO2@MoS2 photoanode for the degradation of pharmaceuticals and personal care products.

In this study, we constructed an innovative photo-electrocatalysis-assisted peroxymonosulfate (PEC/PMS) system to degrade pharmaceuticals and personal care products (PPCPs). A hollow-structured photoanode (i.e., Pt@CeO2@MoS2) was specifically synthesized as a photoanode to activate PMS in the PEC system. As proof of concept, the Pt@CeO2@MoS2 photoanode exhibited superior degradation performance toward carbamazepine (CBZ) with PMS assistance. Specifically, the kinetic constant of PEC/PMS (k = 0.13202 min-1) could be enhanced about 87.4 times compared to that of the PEC system (0.00151 min-1) alone. The PMS activation mechanism revealed that the synergistic effect between the hollow material and the change of surface valence states (Ce3+ to Ce4+) and (Mo4+ to Mo6+) contribute to enhancing the degradation efficiency of the visible-light-driven PEC/PMS process. The scavenger testing and EPR showed that 1O2, O2•-, SO4•- and •OH play dominant roles in the SR-AOPs. Furthermore, the applicability of Pt@CeO2@MoS2 used in SR-AOPs was systematically investigated regarding of the reaction parameters and identification of intermediates and dominant radicals as well as the mineralization rate and stability. The outcomes of this study can provide a new platform for environmental remediation.

Visible-light-driven photoelectrocatalytic activation of chloride by nanoporous MoS2@BiVO4 photoanode for enhanced degradation of bisphenol A.

The massive emission of bisphenol A (BPA) has imposed adverse effects on both ecosystems and human health. Herein, nanoporous MoS2@BiVO4 photoanodes were fabricated on fluorine-doped tin oxide (FTO) substrates for photoelectrocatalytic degradation of BPA. The photocurrent density of the optimized photoanode (MoS2-3@BiVO4) was 5.4 times as that of BiVO4 photoanode at 1.5 V vs. Ag/AgCl under visible light illumination, which was ascribed to the reduced recombination of photogenerated charge carriers of the well-designed hybrid structure. 10 ppm of BPA could be completely degraded in 75 min by MoS2-3@BiVO4 photoanode, with a bias of 1.5 V vs. Ag/AgCl and 100 mM of NaCl as the supporting electrolyte. The electron paramagnetic resonance (EPR) and free radicals scavenging experiments confirmed that chlorine oxide radical (•ClO) played a dominant role in the degradation of BPA. 14 intermediates were detected and identified during photoelectrocatalytic degradation of BPA by MoS2-3@BiVO4 photoanode and 3 pathways were proposed based on the above intermediates. The hybrid film exhibited high stability and reusability, and promising application potential in photoelectrocatalytic degradation of organic pollutants in aqueous solution.

MoS2 decorated CdS hybrid heterojunction for enhanced photoelectrocatalytic performance under visible light irradiation.

Pervious photocatalysis application of nanostructured suspensions reveals high recombination rates of photogenerated electron-hole pairs, low recycling efficiency and secondary pollution problems. Herein, MoS2@CdS nanocomposites thin films on FTO (fluorine-doped tin oxide) substrates are fabricated using facile electrodeposition by decorating a layer of highly-active MoS2 cocatalyst on CdS film to optimize the interface modification. The hybrid film exhibits enhanced photoelectrocatalytic activity compared to pristine CdS film. The synthesized CdS exhibits a bandgap of 2.42 eV with the conduct band at ca. -0.25 V vs. RHE, while MoS2 reveals a bandgap of 1.73 eV with the valance band at ca. 1.59 V vs. RHE. The appropriate band alignment between the hybrid films favours the electrons transfer thus the charge recombination are suppressed. The MoS2@CdS film yields a highest photocurrent of 15.2 mA/cm2 at 0 V vs. Ag/AgCl under visible light illumination (λ ≧ 420 nm), exhibiting a 5.2 times enhancement as compared to that of CdS film (2.9 mA/cm2). The structural integration of MoS2 with CdS will be a promising strategy to develop a high-efficient and low-cost non-noble metal cocatalyst for solar energy conversion.