Self-cleaning catalytic membrane for water treatment via an integration of Heterogeneous Fenton and membrane process

MnOOH/carbon-based reactive electrochemical membrane for aqueous organic pollutants decontamination

The electrochemical filtration process (ECFP), which integrates the benefits of membrane separation with electrochemical advanced oxidation, exhibits significant potential for water decontamination. A key aspect in realizing practical applications of ECFP lies in the development of cost-effective, high-performance reactive electrochemical membranes (REM). In this work, a novel carbon-based REM (MCM-30) was prepared by coating the low-cost coal-based carbon membrane (CM) with MnOOH nano-catalyst through a simple and environmentally friendly electrochemical deposition method. Results indicated that the nano-MnOOH catalyst significantly improved the hydrophilicity and electrochemical properties of the CM, thereby enhancing its permeability and removal efficiency towards bisphenol A (BPA). The effects of deposition time, applied voltages, flow rates, electrolyte concentrations, and water matrixes on BPA removal efficiency were systematically investigated. Under optimal conditions, 30 min deposition, 2.0 V applied voltage, 2 mL min-1 flow rate, 0.1 mol L-1 Na2SO4 electrolyte concentration, the BPA removal efficiency of the MCM-30 reached to over 95%, which is much higher than that of the CM. The improved water treatment performance of MCM-30 during the electrochemical filtration could be attributed to the enhancement in both direct and indirect oxidation owing to the nano MnOOH deposition. Furthermore, the MCM-30 is recyclable and can be applied across various water backgrounds and pollutant types.

Self-Cleaning Antifouling Membrane Engineered by Oxygen-Activated MOF-Derived Catalysts for Efficient Organic Wastewater Treatment

Utilizing membrane separation technology has displayed promising application potential for removing synthetic dyes; however, membrane performance tends to decline over time due to fouling caused by feed solution contaminants, leading to decreased separation efficiency and shortened membrane lifespan. Therefore, improving the antifouling properties of membranes is critical to ensure the long-term efficiency of water treatment systems. In this work, a high-performance catalyst, CuZn@ZC, with remarkable oxygen activation activity, was successfully prepared and subsequently integrated onto the membrane surface via simple pumping filtration, resulting in self-cleaning membranes with superior antifouling capabilities. The results indicated that zero-valence copper containing CuZn@ZC can rapidly and efficiently remove a wide range of dyes under mild natural conditions, accompanied by strong 1O2 and •O2- signals detected in electron paramagnetic resonance spectra. When applied to membrane surfaces, the modified membrane exhibited excellent antifouling and filtration properties, which showed high flux recovery ratios and a superior rejection rate for cationic dyes, attributed to the participation of ROS generated by the activation of natural dissolved oxygen. Moreover, the membrane still retained its structural stability and environmental compatibility during prolonged operation, which is beneficial for advancing the development of sustainable membrane filtration technologies.

Facile Preparation of Sulfonated Polysulfone Composite Membranes with High Hydrophilicity and Visible-Light Driving Self-Cleaning Performance

The photo-Fenton reaction can efficiently degrade organic pollutants and thus is applied intensively for clearing out membrane fouling. However, the pollutant removal efficiency is greatly limited by the redox cycle rate of Fe2+/Fe3+ and the rapid recombination rate of the photogenerated electrons and holes. In order to overcome these drawbacks, a sulfonated polysulfone composite membrane was designed and prepared by incorporating titanium dioxide (TiO2) nanoparticles into a sulfonated polysulfone membrane and sequentially forming β-FeOOHs on the membrane surface. It was found that the synergy of TiO2 and β-FeOOH enhanced the hydrophilicity and improved the pure water flux of the composite membrane. As a result, the composite membrane exhibited superior separation performance for methylene blue and rhodamine B cationic dyes. The rejection rate was larger than 99.5%, and the pure water flux was larger than 125.7 L m-2 h-1, largely surpassing that of nanofiltration membranes. Meanwhile, the composite membrane exhibited an excellent self-cleaning performance, achieving a flux recovery rate over 99.7% after visible-light driving Fenton reaction treatment. The rejection rate still remained above 97.2% after 5 cycles of filtration and recovery, indicating the strong treatment ability of the membrane for dye wastewater.

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Synergistic Interaction of Ionic Liquid Grafted Poly(vinylidene Fluoride) and Carbon Nanotubes to Construct Water Treatment Membranes with Multiple Separation Properties

In this study, the dual strategy of 1-butyl-3-vinylimidazolium bromide ionic liquid (IL) grafting and carbon nanotubes (CNTs) nanocomposition was applied to modify poly(vinylidene fluoride) (PVDF)-based membranes. The highly hydrophilic/oleophobic and fouling-resistant PVDF-g-IL/CNTs membranes with excellent separation efficiency were obtained by the nonsolvent-induced phase separation method with ethanol-water mixed solution as the coagulation bath. The grafted IL not only generated hydrophilic groups on PVDF chains but also acted together with the CNTs to induce the formation of hydrophilic β-crystalline phase of PVDF, which significantly improved the hydrophilicity and pore structure of the modified PVDF membranes. As a result, the pure water flux of the optimal membrane increased up to 294.2 L m-2 h-1, which was 5.2 times greater than that of the pure PVDF membrane. Simultaneously, the electrostatic interaction of the positive IL and the integration of CNTs enhanced adsorption sites of the membranes, producing exceptional retention and adsorption of dye wastewater and oil-water emulsion. This study presents a straightforward and efficient approach for fabricating PVDF separation membranes, which have potential applications in the purification of various polluted wastewater.

Electrostatic deposition of TiO2 nanoparticles on porous wood veneer for improved membrane filtration performance and antifouling properties

Wood has been a promising water purifier material on account of its abundant natural transport channels, easy processing, and renewability, which is mainly focused on its utilization in growth direction for effective separation.Wood veneer manufacured from raw wood block has a reversed-tree pore structure, and possesses advantages of low cost, easy fabrication, material saving, and abundant sources. To realize its functionalization and practicable application for membrane separation, modification of wood veneer is prerequisite. Herein, thin wood veneer with disparate utilization direction of wood was developed to design filter membrane loading TiO₂ nanoparticles for treatment of dye wastewater. Wood veneer with reversed-tree transport pathways exhibits unique porous structure, and filtering direction and wood growth direction is almost orthogonal generated numerous sinuous channels. Thereout, sufficient area for loading TiO₂ nanoparticles and contacting pollutants as well as appropriate water transport pathways at significantly shrinking thickness of wood (the thickness of 0.2 mm) can be provide by these sinuous channels. TiO₂ nanoparticles was first modified by (3-Aminopropyl)triethoxysilane with high positive charge, and immobilized on negatively charged wood surface through atmospheric impregnation via strong electrostatic attractive interaction. Vast quantities of exposed TiO₂ nanoparticles on wood cell lumens significantly enhance the adsorption ability for dye contaminants, resulting in a high membrane separation performance. The flux of TiO₂/wood veneer membrane can achieve high level of 636.94 L/(m²h) with considerable methylene blue removal of 99.9% at 0.01 MPa. Meanwhile, it shows good cycling stability as well as decent flexibility and excellent mechanical strength. Moreover, the designed membrane with photocatalytic function of TiO₂ also displays impressive decontaminated and recycling ability. The flux can recover its pre-recession level after 10 h light irradiation. The designed TiO₂/wood veneer with simple preparation process and excellent water treatment capacity exhibits promising results for practical wastewater treatment.

Simultaneous Nitrite Resourcing and Mercury Ion Removal Using MXene-Anchored Goethite Heterogeneous Fenton Composite

The integrated system of gas-phase advanced oxidation process combined with sulfite-based wet absorption process is a desirable method for simultaneous removal of SO₂, NO, and Hg⁰, but due to the enrichment of nitrite and Hg²⁺, resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional β-FeOOH@MXene heterogeneous Fenton material, of which the crystalline phase, morphology, structure, and composition were revealed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, and transmission electron microscopy. It exhibits excellent performance on nitrite oxidation (99.5%) and Hg²⁺ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg²⁺ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and β-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe₂O₃ into β-FeOOH in the hydrothermal method and greatly reduced its monomer size; (ii) the introduced ≡Ti(III)/≡Ti(II) accelerated the regeneration of ≡Fe(II) via rapid electron transfer, thereby improving the heterogeneous Fenton reaction; and (iii) MXene strongly immobilized β-FeOOH to greatly inhibit Fe-leaching. HO^•, ^•O₂^--, and ¹O₂ were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO₂^- oxidation in the descending order HO^• > ¹O₂ > ^•O₂^-. Quantum chemical calculations revealed that ^•OH-induced oxidation of NO₂^- or HNO₂ was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg²⁺ removal mechanism, with Hg₂Cl₂, HgCl₂, and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg²⁺.

Iron-containing poly(ionic liquid) membranes: a heterogeneous Fenton reaction and enhanced anti-fouling ability

Iron-containing poly(ionic liquid) membranes were prepared by Cu(0)-mediated reversible deactivation radical polymerization, which was achieved to catalyze a heterogeneous Fenton reaction and realize self-cleaning of the membrane surface.