Ag/AgBr/AgVO3 Photocatalyst-Embedded Polyacrylonitrile/Polyamide/Chitosan Nanofiltration Membrane for Integrated Filtration and Degradation of RhB

Critical review on emerging photocatalytic membranes for pollutant removal: From preparation to application

Due to synergistically enhanced separation and degradation performances, photocatalytic membranes offer an environmentally friendly and energy-sustainable method for water purification. However, a comprehensive review on preparation and application of photocatalytic membranes is still lacking. Systematically comparing different photocatalytic membrane fabrication methods and revealing the underlying mechanisms of their respective applications are of particular interest. In this review, we first discuss the common preparation methods for photocatalytic membranes in detail, focusing on the main approaches to improve their photocatalytic performance. We elucidate the mechanisms of photocatalytic membrane-based degradation processes, and describe some representative applications of photocatalytic membranes in water treatment. At the same time, the influencing factors that are critical for achieving high removal efficiency are also proposed. In the end, the practical applications and the perspectives for future studies and implementation of photocatalytic membranes are evaluated. This review will serve as a summary to advance researchers' understanding of the advantages of photocatalytic membranes, with the ultimate goal of achieving large-scale relevant applications of photocatalytic membranes in water treatment.

Ultrahigh antifouling ultrafiltration membrane based on Ag NPs photoreduction modified PVP/BiOCl nanoflower for efficient membrane fouling removal

Polyethersulfone (PES) is widely used as an ultrafiltration (UF) membrane material in industrial production due to its excellent performance. However, its inherent hydrophobicity leads to severe membrane fouling issues during practical operation. In this study, focusing on the fouling issues of PES UF membrane, bismuth oxychloride (BiOCl) was chosen as the main nanomaterial. Ag NPs were introduced via photoreduction into BiOCl at the optimal ratio of polyvinylpyrrolidone (PVP) and BiOCl (wt%-0.3:100), resulting in the synthesis of Ag@BiOCl nanoparticles. These nanoparticles were then blended into the PES casting solution and fabricated into composite UF membranes using the reverse thermally induced phase separation (RTIPS) method. Analysis of UV-vis characterization results revealed that the introduction of Ag NPs widened the visible light absorption range of the composite material from 414.30 nm to 508.62 nm. PL spectroscopy results indicated that Ag NPs effectively inhibited the recombination of photogenerated electron-hole pairs, significantly enhancing the photocatalytic activity of Ag@BiOCl. Additionally, the introduction of Ag NPs induced the generation of oxygen vacancies (OVs) on the surface of the composite membrane. Under visible light, the contaminated composite membrane drove the OVs in the photocatalytic material to generate hot electrons (h+-e-). These h+-e- promoted the generation of more active oxygen species, thereby improving the efficiency of membrane fouling removal. The optimal membrane in the PES/Ag@BiOCl series, AGMC5-2 exhibited a pure water flux of 3960.43 L m-2 h-1, a humic acid (HA) rejection rate of 95.00%, and a flux recovery rate of 85.98%. The antibacterial rates against E. coli and S. aureus were 79.07% and 82.33%, respectively. In this study, the PES/Ag@BiOCl composite membrane demonstrated outstanding pure water flux, excellent pollutant rejection rates, significant self-cleaning, and antibacterial properties, effectively addressing membrane fouling issues caused by the inherent hydrophobicity of PES. The successful preparation of the PES/Ag@BiOCl composite membrane lays the foundation for the application of photocatalytic membranes in the field of water treatment.

Highly Efficient Continuous Flow Nanocatalyst Platform Constructed with Regenerable Bacterial Cellulose Loaded with Gold Nanoparticles and a Nanoporous Membrane

With the development of society and the growing concern about environmental issues, continuous flow catalytic reactors have gained significant interest due to their resource-efficient advantages over traditional batch devices. In this study, we employed a facile one-step in situ reduction approach to construct highly dispersed gold nanoparticles loaded on regenerable bacterial cellulose nanofiber (BCN) heterogeneous catalysts. These catalysts, in combination with a nanoceramic membrane with a pore size of 1 nm, formed a fully mixed system that was favorable for the efficient continuous flow catalysis of selective reduction reactions of nitrophenol. The reaction system demonstrated remarkable catalytic activity toward nitrophenol reduction reactions at low reductant dosages (<5 equiv), achieving over 95% conversion and 99% selectivity for the aniline product in 10 min under room temperature conditions. Furthermore, continuous flow operations maintained stable catalytic activity with minimal catalyst loss after a 120-h test and were 3 times more time-efficient than batch operations. Additionally, continuous monitoring could be conducted through ultraviolet (UV) spectroscopy. A highly efficient and environmentally friendly strategy was present for designing continuous flow reactions in future applications.

Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139-228 L·m-2·h-1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.

Exploring the potential of ZnO-Ag@AgBr/SBA-15 Z-scheme heterostructure for efficient wastewater treatment: synthesis, characterization, and real-world applications

This study reports on the synthesis and characterization of ZnO-Ag@AgBr/SBA-15 composites using natural halloysite clay from Yenbai Province, Vietnam, as a silica aluminum source. The synthesized materials demonstrated visible light absorption with a band gap energy range of 2.63-2.98 eV. The dual Z-scheme ZnO-Ag@AgBr/SBA-15 heterojunction exhibited superior catalytic performance compared to ZnO/SBA-15 and Ag@AgBr/SBA-15, owing to its improved electron transfer and reduced electron and hole recombination rate. In particular, the photocatalytic efficiency of ZnO-Ag@AgBr/SBA-15 was evaluated for the removal of harmful phenol red from wastewater under visible light irradiation. The photocatalytic process was optimized by varying the phenol red concentration, pH, and catalyst dosage, and showed that 98.8% of phenol red in 100 mL wastewater (pH = 5.5) can be removed using 40 mg of 20%ZnO-Ag@AgBr/SBA-15 within 120 min. Furthermore, the degradation pathway of phenol red was predicted using liquid chromatographic-mass spectrometry (LC-MS). Finally, the photocatalytic process was successfully tested using water samples collected from the four main domestic waste sources in Hanoi, including the To Lich River, the Hong River, the Hoan Kiem Lake, and the West Lake, demonstrating the high potential of the ZnO-Ag@AgBr/SBA-15 photocatalyst for phenol red degradation in real-world wastewater treatment applications.

Purification performance of modified polyacrylonitrile fiber-activated carbon fiber filter for heavy metal ions

A heavy metal ion adsorbent (HFPANF) with high surface area was obtained from polyacrylonitrile fibers with fibrillation and alkali hydrolysis, and an activated carbon fiber filter was prepared by using HFPANF as the binder. The surface area of polyacrylonitrile was 48.64 m²/g due to fibrillation, which also led to the carboxyl content of the HFPANF up to 3.4 mmol/g. Batch adsorption experiments on Cu²⁺ and Pb²⁺ showed that the adsorption capacities of HFPANF for Cu²⁺ and Pb²⁺ were 47.5 mg/g and 54.3 mg/g. The adsorption kinetics showed that the adsorption reached equilibrium at 90 min and that the adsorption followed the pseudo-second order model. It indicates that the adsorption process is chemisorption. HFPANF formed a single tooth chelate with Cu and a double tooth chelate with Pb. HFPANF-ACF filter was prepared by wet molding technique. When the HFPANF content was 30%, the filter reached a compressive strength of 15.37 MPa and its maximum flux was 180 L/h. 2.5 mg/L of Cu and Pb were used for dynamic adsorption experiments and the heavy metal removal rate was still above 95% after filtering 600 L. The pressure drop of HFPANF-ACF filter was much smaller compared with that of GAC filter due to the combined effect of fibrillated nanofibers and ACF, which can improve the filtration efficiency of the filter.