Ultrahigh-flux and self-cleaning composite membrane based on BiOCl-PPy modified MXene nanosheets for contaminants removal from wastewater

Ti3C2Tx MXene-Based Hybrid Photocatalysts in Organic Dye Degradation: A Review

This review provides an overview of the fabrication methods for Ti3C2Tx MXene-based hybrid photocatalysts and evaluates their role in degrading organic dye pollutants. Ti3C2Tx MXene has emerged as a promising material for hybrid photocatalysts due to its high metallic conductivity, excellent hydrophilicity, strong molecular adsorption, and efficient charge transfer. These properties facilitate faster charge separation and minimize electron-hole recombination, leading to exceptional photodegradation performance, long-term stability, and significant attention in dye degradation applications. Ti3C2Tx MXene-based hybrid photocatalysts significantly improve dye degradation efficiency, as evidenced by higher percentage degradation and reduced degradation time compared to conventional semiconducting materials. This review also highlights computational techniques employed to assess and enhance the performance of Ti3C2Tx MXene-based hybrid photocatalysts for dye degradation. It identifies the challenges associated with Ti3C2Tx MXene-based hybrid photocatalyst research and proposes potential solutions, outlining future research directions to address these obstacles effectively.

Recent Advancement in Emerging MXene-Based Photocatalytic Membrane for Revolutionizing Wastewater Treatment

MXene-based photocatalytic membranes provide significant benefits for wastewater treatment by effectively combining membrane separation and photocatalytic degradation processes. MXene represents a pioneering 2D photocatalyst with a variable elemental composition, substantial surface area, abundant surface terminations, and exceptional photoelectric performance, offering significant advantages in producing high-performance photocatalytic membranes. In this review, an in-depth overview of the latest scientific progress in MXene-based photocatalytic membranes is provided. Initially, a brief introduction to the structure and photocatalytic capabilities of MXene is provided, highlighting their pivotal role in promoting the photocatalytic process. Subsequently, in pursuit of the optimal MXene-based photocatalytic membrane, critical factors such as the morphology, hydrophilicity, and stability of MXenes are meticulously taken into account. Various preparation strategies for MXene-based photocatalytic membranes, including blending, vacuum filtration, and dip coating, are also discussed. Furthermore, the application and mechanism of MXene-based photocatalytic membranes in micropollutant removal, oil-water separation, and antibacterial are examined. Lastly, the challenges in the development and practical application of MXene-based photocatalytic membranes, as well as their future research direction are delineated.

Photocatalytic PAN Nanofibrous Membrane through Anchoring a Nanoflower-Branched CoAl-LDH@PANI Heterojunction for Organic Hazards Degradation and Oil-Containing Emulsified Wastewater Separation

The synergistic treatment of oily wastewater containing organic hazards and emulsified oils remains a big challenge for membrane separation technology. Herein, the photocatalytic membrane, which combined the physical barrier and catalytic oxidation-driven degradation functionality, was fabricated via anchoring a nanoflower-branched CoAl-LDH@PANI Z-scheme heterojunction onto a porous polyacrylonitrile mat and using tannic acid as an adhesive. The assembly of such a Z-scheme heterojunction offered the superior photocatalytic degradation performance of soluble dyes and tetracycline (up to 94.3%) to the membrane with the improved photocatalytic activity of 2.33 times compared with the CoAl-LDH@pPAN membrane. Quenching experiments suggested that the •O2- was the most reactive oxygen species in the catalytic reaction system of the composite membrane. The greatly enhanced photocatalytic activity was attributed to the effective inhibition of photogenerated hole-electron combination using PANI as a carrier, with charge transferring from LDH to PANI. The possible photocatalytic degradation mechanism was proposed based on VB-XPS, electron spin resonance spectroscopy, and DRS technologies, which was confirmed by density functional theory calculation. Meanwhile, benefiting from the superhydrophilic/oleophobic feature and low oil adhesion, the membrane exhibited high permeability for isooctane emulsion (3990.39 L·m-2·h-1), high structure stability, and satisfactory cycling performance. This work provided a strategy to develop superwetting and photocatalytic composite membranes for treating complex multicomponent pollutants in the chemical industry.

Ultra-high flux mesh membranes coated with tannic acid-ZIF-8@MXene composites for efficient oil-water separation

Oil/water separation has become a global concern due to the increasing discharge of multi-component harmful oily wastewater. Super wetting membranes have been shown to be an effective material for oil/water separation. Ultra-high flux stainless-steel meshes (SSM) with superhydrophilicity and underwater superoleophobicity were fabricated by tannic acid (TA) modified ZIF-8 nanoparticles (TZIF-8) and two-dimensional MXene materials for oil/water separation. The TZIF-8 increased the interlayer space of MXene, enhancing the flux permeation (69,093 L m-2h-1) and rejection of the composite membrane (TZIF-8@MXene/SSM). The TZIF-8@MXene/SSM membrane showed an underwater oil contact angle of 154.2°. The membrane maintained underwater superoleophobic after stability and durability tests, including various pH solutions, organic solvents, reusability, etc. In addition, the oil/water separation efficiency of TZIF-8@MXene/SSM membranes was higher than 99% after treatment in harsh conditions and recycling. The outstanding anti-fouling, stability, durability, and recyclability properties of TZIF-8@MXene/SSM membrane highlight the remarkable potential of membranes for complex oil/water separation process.

New directions on membranes for removal and degradation of emerging pollutants in aqueous systems

Emerging pollutants (EPs) refer to a group of non-regulated chemical or biological substances that have been recently introduced or detected in the environment. These pollutants tend to exhibit resistance to conventional treatment methods and can persist in the environment for prolonged periods, posing potential adverse effects on ecosystems and human health. As we enter a new era of managing these pollutants, membrane-based technologies hold significant promise in mitigating impact of EPs on the environment and safeguarding human health due to their high selectivity, efficiency, cost-effectiveness and capability for simultaneous separation and degradation. Moreover, these technologies continue to evolve rapidly with the development of new membrane materials and functionalities, advanced treatment strategies, and analyses for effectively treating EPs of more recent concerns. The objective of this review is to present the latest directions and advancements in membrane-based technologies for addressing EPs. By highlighting the progress in this field, we aim to share valuable perspectives with researchers and contribute to the development of future directions in sustainable treatments for EPs.

Construction of a Two-Dimensional GO/Ti3C2TX Composite Membrane and Investigation of Mg2+/Li+ Separation Performance

Graphene oxide (GO) two-dimensional (2D) membranes with unique layer structures and tunable layer spacing have special advantages and great potential in the field of water treatment. However, GO membranes face the issues of weak anti-swelling ability as well as poor permeability. We prepared GO/Ti3C2TX 2D composite membranes with 2D/2D structures by intercalating Ti3C2TX nanosheets with slightly smaller sizes into GO membranes. Ti3C2TX intercalation can effectively expand the layer spacing of GO, thereby substantially enhancing the flux of the composite membrane (2.82 to 6.35 L·m-2·h-1). Moreover, the GO/Ti3C2TX composite membrane exhibited a good Mg2+/Li+ separation capability. For the simulated brine, the separation factor of M2 was 3.81, and the salt solution flux was as high as 5.26 L·m-2·h-1. Meanwhile, the incorporation of Ti3C2TX nanosheets significantly improved the stability of GO/Ti3C2TX membranes in different pH environments. This study provides a unique insight into the preparation of highly permeable and ion-selective GO membranes.

Research on the Antibacterial Properties of MXene-Based 2D-2D Composite Materials Membrane

Novel MXene-based two-dimensional (2D) membranes are widely used for water purification due to their highly controllable structure and antibacterial properties. However, in the process of membrane separation, the problems of membrane fouling, especially biological fouling, limits the further application of MXene-based membranes. In this study, in order to improve the antibacterial and separation properties of membranes, three kinds of MXene-based 2D-2D composite membranes (M2~M4) were prepared using polyethersulfone (PES) as the substrate, which were GO@MXene, O-g-C₃N₄@MXene and BiOCl@MXene composite membranes respectively. The results showed that the antibacterial activity of M2~M4 against Escherichia coli and Staphylococcus aureus was further improved, especially the antibacterial ratio of M4 against Escherichia coli and Staphylococcus aureus was up to 50% and 82.4%, respectively. By comparing the surface morphology of MXene membrane and modified membrane treated bacteria through scanning electron microscopy (SEM), it was found that the cell density on modified membrane was significantly lower than that of pure MXene membrane.

Fabrication of In-S-co-doped two-dimensional BiOCl coupling with surface hydroxylation toward simultaneously efficient charge separation and redox capability for photocatalytic water remediation

Tailoring energy band structure of bismuth oxychloride (BiOCl)-based photocatalysts by virtue of the metal and/or non-metal elements is one of the promising strategy to address environmental issues, especially plays a crucial role in water remediation. However, it still remains a great challenge to balance the light-harvesting and charge carriers separation. Herein, a feasible strategy was proposed for the simultaneous integration of energy-band modulation and surface hydroxylation to alleviate the as-mentioned contradiction and long-standing issues. By using a simple one-pot hydrothermal method, In-S-co-doped BiOCl photocatalyst coupling with surface hydroxylation (denoted as In/BOC-S-OH) was prepared by the simultaneous co-precipitation and ripening process and exhibited a good photocatalytic activity for removing tetracycline (TC) under visible light-irradiation than the counterparts of In-doped BiOCl (In/BOC), S-doped BiOCl (In/BOC-S) or surface -OH modification BiOCl (In/BOC-OH). Such satisfied photocatalytic efficiency benefits from the synergistic effect on the visible light capture, charge migration and separation associated with the introduction of intermediate energy levels and surface defect, respectively. Accompanying with the introduction of In and S hetero-atoms intercalation, both the potentials of valence and conduction bands were adjusted and the reduction of the bandgap could promote the capture of photons. Meanwhile, the powerful polarization effect associated with the non-uniform charge distribution could promote the special separation of carriers. More importantly, the surface defects induced by hydroxylation could act as traps for photogenerated electrons to stimulate the rapid separation of carriers, thereby causing the cleavage of antibiotics on the catalytic surface. This research offers a reliable strategy and promising scheme via effective solar energy conversion and charge carrier separation to advance photocatalytic wastewater remediation.

Simultaneous degradation and separation of antibiotics in sewage effluent by photocatalytic nanofiltration membrane in a continuous dynamic process

Bifunctional photocatalytic nanofiltration (PNF) membrane is increasingly concerned in practical micro-polluted water purification, but there are still several bottlenecks that inhibit its practicality. In this context, the feasibility of a novel metal-free and visible light-responsive surface-anchored PNF membrane for simultaneously removing target antibiotics in real sewage effluent in a continuous dynamic process was explored. The results showed that the optimal PNF-4 membrane was expectedly consisted of an inside tight sub-nanopore structured separation layer and an outside thinner, smoother, super hydrophilic mesoporous degradation layer, respectively. Consequently, the activated PNF-4 membrane could synergistically reduce trimethoprim and sulfamethoxazole concentrations to below two orders of magnitude, accompanying with almost constant high water permeability, suggesting that the hydrophilic modification of the mesoporous degradation layer basically offsets its inherent hydraulic resistance. Also, after repeating the fouling-physical rinsing process three times lasted for 78 h, only sporadic adherent contaminants remained onto the top surface, together with the minimal total and irreversible fouling ratios (as low as 7.2% and 1.2%, respectively), strongly demonstrated that PNF-4 membrane displayed good self-cleaning performance. Undoubtedly, this will significantly reduce its potential cleaning frequency and maintenance cost in long-term operation. Meanwhile, the acute and chronic biotoxicities of its permeate to Virbrio qinghaiensis sp. -67 were also reduced sharply to 2.22% and 0.45%, respectively. All of these evidences suggest that the dual functions of PNF-4 membrane are synergetic in an uninterrupted permeating process. It will provide useful insights for continuously enhancing the practicality and effectiveness of PNF membrane in actual micro-polluted water purification scenarios.

Recent advances and perspectives of emerging two-dimensional transition metal carbide/nitride-based materials for organic pollutant photocatalysis

This review outlines the fabrication strategies, morphological structures, electronic properties and applications of MXene based materials for photocatalysis in the treatment of recalcitrant organic pollutants (dyes, phenols, antibiotics and pharmaceuticals).