Hydrogen peroxide treated g-C3N4 as an effective hydrophilic nanosheet for modification of polyethersulfone membranes with enhanced permeability and antifouling characteristics

Performance improvement of polyethersulfone membranes with Ti3AlCN MAX phase in the treatment of organic and inorganic pollutants

In this work, the hydrophobic polyethersulfone (PES) membrane was modified by incorporating Ti3AlCN MAX phase. Synthesis of Ti3AlCN MAX phase was performed using the reactive sintering method. The scanning electron microscopy (SEM) images showed a 3D compressed layered morphology for the synthesized MAX phase. The Ti3AlCN MAX phase was added to the casting solution, and the mixed-matrix membranes were fabricated by the non-solvent induced phase inversion method. The performance and antifouling features of bare and modified membranes were explored by pure water flux, flux recovery ratio (FRR), and fouling resistance parameters. Through the modification of membranes by introducing the Ti3AlCN MAX phase, the enhancement of these features was observed, in which the membrane containing 1 wt% of MAX phase showed 17.7 L/m2.h.bar of permeability and 98.6% for FRR. Also, the separation efficiency of all membranes was evaluated by rejecting organic and inorganic pollutants. The Ti3AlCN MAX membranes could reject 96%, 95%, and 88% of reactive blue 50, Rose Bengal, and azithromycin antibiotics, respectively, as well as 98%, 80%, 86%, and 36% of Pb2+, As5+, Na2SO4, and NaCl, respectively. Finally, the outcomes indicated the Ti3AlCN MAX phase was an excellent and efficient novel additive for modifying the PES membrane.

Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Modification of PAN electrospun nanofiber membranes with g-C3N4 nanotubes/carbon dots to enhance MBR performance

This study is dedicated to the enhancement of electrospun polyacrylonitrile (PAN) nanofiber membranes for their application in membrane bioreactor (MBR) processes. The improvement is achieved through the incorporation of graphitic carbon nitride nanotubes/carbon dots (g-C3N4 NT/CDs) and subsequent heat post-treatments at varying temperatures. Notably, the hot-pressing methodology effectively mitigates surface roughness and significantly reduces issues related to peeling during nanofiber experimentation. Our results demonstrate that the introduction of 0.5 wt% of g-C3N4 NT/CDs leads to a substantial enhancement in water flux. In particular, nanocomposite membranes subjected to hot-pressing at 90 °C for 10 min exhibited an impressive flux recovery ratio (FRR) of 70%. Furthermore, the heat-treated nanocomposite membranes exhibited remarkable antifouling properties and significantly reduced fouling rates when compared to their heat-treated bare counterparts. This study underscores the noteworthy potential of g-C3N4 NT/CDs-modified PAN nanofiber membranes to substantially elevate MBR performance, firmly positioning them as highly promising candidates for critical applications in the domains of water and wastewater treatment. However, it is imperative to underscore that the existing written material necessitates a comprehensive overhaul to align with the provided structural framework.

Construction of Pt@BiFeO3 Xerogel-Supported O-g-C3N4 Heterojunction System for Enhanced Visible-Light Activity towards Photocatalytic Degradation of Rhodamine B

Synthetic organic pigments from the direct discharge of textile effluents are considered as colossal global concern and attract the attention of scholars. The efficient construction of heterojunction systems involving precious metal co-catalysis is an effective strategy for obtaining highly efficient photocatalytic materials. Herein, we report the construction of a Pt-doped BiFeO₃/O-g-C₃N₄ (Pt@BFO/O-CN) S-scheme heterojunction system for photocatalytic degradation of aqueous rhodamine B (RhB) under visible-light irradiation. The photocatalytic performances of Pt@BFO/O-CN and BFO/O-CN composites and pristine BiFeO₃ and O-g-C₃N₄ were compared, and the photocatalytic process of the Pt@BFO/O-CN system was optimized. The results exhibit that the S-scheme Pt@BFO/O-CN heterojunction has superior photocatalytic performance compared to its fellow catalysts, which is due to the asymmetric nature of the as-constructed heterojunction. The as-constructed Pt@BFO/O-CN heterojunction reveals high performance in photocatalytic degradation of RhB with a degradation efficiency of 100% achieved after 50 min of visible-light irradiation. The photodegradation fitted well with pseudo-first-order kinetics proceeding with a rate constant of 4.63 × 10^-2 min^-1. The radical trapping test reveals that h⁺ and ^•O₂^- take the leading role in the reaction, while the stability test reveals a 98% efficiency after the fourth cycle. As established from various interpretations, the considerably enhanced photocatalytic performance of the heterojunction system can be attributed to the promoted charge carrier separation and transfer of photoexcited carriers, as well as the strong photo-redox ability established. Hence, the S-scheme Pt@BFO/O-CN heterojunction is a good candidate in the treatment of industrial wastewater for the mineralization of organic micropollutants, which pose a grievous threat to the environment.

Enhanced water permeance and EDCs rejection using a UiO-66-NH2-predeposited polyamide membrane

Endocrine disrupting compounds (EDCs) have been increasingly detected in drinking water sources, and pose severe threat to human health. Polyamide (PA) based nanofiltration (NF) membrane has great potential for EDCs removal from water, but the removal of hydrophobic EDCs is not satisfying due to strong hydrophobic affinity. In this study, UiO-66-NH₂/PA membranes were prepared by predepositing hydrophilic UiO-66-NH₂ onto the substrate prior to interfacial polymerization. The UiO-66-NH₂ aggregates increased the permeable area and strengthened the "gutter effect". Therefore, the pure water flux of UiO-66-NH₂/PA increased by 115% compared with that of the thin-film composite (TFC) membrane, and its rejection of Na₂SO₄ was 96%. The hydrophilicity-enhanced PA film reduced its adsorption of EDCs and decreased the driving force for EDCs diffusion. Moreover, the UiO-66-NH₂-induced hydrophilic nanochannels, including the interfacial gaps between PA film and UiO-66-NH₂ aggregates, the gaps in UiO-66-NH₂ aggregates, and the inherent pores in UiO-66-NH₂ crystals, alleviated the hydrophobic affinity and effectively restricted EDCs diffusion. The rejection rates of methylparaben, propylparaben, bisphenol A, and benzylparaben by the optimal UiO-66-NH₂/PA were 50%, 67%, 75%, and 85%, respectively, and the water/benzylparaben selectivity was 4.4 times as high as that of TFC. The results demonstrate that incorporating hydrophilic metal-organic frameworks (MOFs) can improve the membrane hydrophilicity and create hydrophilic nanochannels, and is an effective strategy to enhance EDCs removal by nanofiltration.

Surface modification of commercial reverse osmosis membranes using both hydrophilic polymer and graphene oxide to improve desalination efficiency

Various methods have been applied to modify the surface of reverse osmosis (RO) membranes to modify the membrane performance to enhance the flux, rejection, and resistance to various factors of fouling. Hence, the main objective of the current study is to modify the surface of commercial RO membranes using the synergistic effect of the hydrophilic polymer and graphene oxide (GO). GO nanosheets were firstly synthesized by the modified hummer method, then characterized by FTIR, XRD, and SEM analyses. Then, the polyacrylic acid (PAA) was grafted on the membrane surface for membrane fabrication. Furthermore, effective factors of grafting such as monomer concentration, time, and temperature of polymerization were optimized. After that, different amounts of GO nanosheets were loaded in PAA optimized layer. Then, the effect of GO loading on the RO membrane structure and performance was investigated. The outcomes of membrane characterization demonstrated that modified RO membranes had a smoother surface, more negative surface charge, a little better hydrophilicity, and more thickness. Moreover, the results of PAA and GO optimization were shown that grafting 1.5 mM of PAA and loading 0.1 wt% of GO nanosheets give the best membrane performance. This membrane (GO 0.1@1.5M PAA/RO) between all modified membranes has the most water flux (37.1 L/m²h), the highest NaCl rejection (98%), and the best antifouling efficiency. Ultimately, it was concluded that the grafting of GO@PAA on the surface of a commercial RO membrane is an efficient approach for the enhancement of desalination and antifouling performance of this kind of membrane.

Impact of a new functionalization of multiwalled carbon nanotubes on antifouling and permeability of PVDF nanocomposite membranes for dye wastewater treatment

Here, novel hydroxyl and carboxyl functionalized multiwalled carbon nanotubes (AHF-MWCNT and ACF-MWCNT) were successfully synthesized and introduced for modification and antifouling improvement of the PVDF membrane. The blending effect of AHF-MWCNT and ACF-MWCNT on the morphology and surface properties of the PVDF membrane was explored by SEM, AFM, water contact angle, and zeta potential analysis. The results indicated that the membrane surface has become more hydrophilic, smoother as well more negative. In addition, the overall porosity and mean pore radius are increased by MWCNTs embedding. The filtration performance, antifouling and dye separation of the nanocomposite membranes were improved by adding any amounts of AHF-MWCNT and ACF-MWCNT in the PVDF membrane matrix. The carboxylic modification presented better performance than the hydroxyl functionalization. The 0.1 wt% ACF-MWCNT blended membrane presented an optimum performance with 46 L m^-2 h^-1 bar^-1 permeability, 93% FRR, and 97.3% dye rejection. Consequently, embedding functionalized MWCNT in the PVDF membrane matrix was led to improvement of membrane characteristics and enhancement of pure water flux, antifouling feature, and dye separation. So, the functionalized MWCNT could be a promising additive for the PVDF membrane modification.

Performance improvement of PES membrane decorated by Mil-125(Ti)/chitosan nanocomposite for removal of organic pollutants and heavy metal

The Mil-125(Ti)-CS nanocomposite was successfully synthesized and characterized by using scanning electron microscopy (SEM) images, Fourier-transform infrared (FTIR) analysis and X-ray diffraction (XRD). Then, to improve the membrane performance, the synthesized Mil-125(Ti)-CS nanocomposite was embedded into the polyethersulfone (PES) membrane matrix. The nanofiltration membranes were fabricated via phase inversion method. Presence of chitosan in the structure of Mil-125(Ti) has increased the compatibility of nanoparticles with the polymer and also improved the hydrophilicity of the resulted membranes. The water contact angle of bare membrane (58°) was reduced to 40° by blending of 1 wt% nanocomposite led to increasing the pure water flux. However, the incorporation of more than 1 wt% of the nanocomposite caused the accumulation of nanocomposites and this was reduced the pore radius and permeability. The membrane containing 1 wt% nanocomposite was displayed the highest flux recovery ratio (FRR) ∼ 98% in bovine serum albumin (BSA) filtration. The membranes containing Mil-125(Ti)-CS also showed good performance against fouling. The performance of membranes was evaluated by treatment of six reactive dyes, antibiotic (cefixime), heavy metal, NaCl and Na₂SO₄ solutions. Addition of Mil-125(Ti)-CS NPs at low concentrations resulted in membranes with high pure water flux, higher separation efficiency, and remarkable anti-fouling behavior.

Hyperbranched polyethylenimine functionalized silica/polysulfone nanocomposite membranes for water purification

Hyperbranched polyethyleneimine functionalized silica (PEI-SiO₂) nanoparticles with considerable hydrophilicity were synthesized and incorporated into a polysulfone (PSF)/dimethylacetamide (DMA)/polyvinylpyrrolidone (PVP) membrane casting solution in five different ratios to fabricate PEI-SiO₂/PSF nanocomposite membranes using nonsolvent-induced phase separation. The hydrophilic PEI-SiO₂ nanoparticles were characterized by TEM, FTIR, TGA, and XPS analyses. Morphology, water contact angles, mean pore sizes, overall porosity, tensile strengths, water flux, antifouling and the dye separation performances of the PEI-SiO₂/PSF membranes were also studied. The PEI-SiO₂ nanoparticles were uniformly dispersed in the PSF-based membranes, where a fall in the water contact angle was observed from 65.4° to 49.7° by addition of 2 wt% nanoparticles. The fouling resistance parameters of the PEI-SiO₂/PSF membranes were declined with an increase in the nanoparticle concentration, suggesting the superior hydrophilic nature of the PEI-SiO₂ nanoparticles. The permeability of the nanocomposite membranes was increased from 38.5 to 70 L m^-2 h^-1 bar^-1 by incorporation of 2 wt% PEI-SiO₂. Finally, improvements were observed in the flux recovery ratio (95.8%), Reactive Green 19 dye rejection (99.6%) and tensile strengths of the PEI-SiO₂/PSF membranes over the neat PSF and SiO₂/PSF membranes, which were used as controls. The results of this study demonstrate the promising application of PEI-SiO₂ nanoparticles in improving the separation and antifouling performances of the PSF membranes for water purification.