Volatile-Organic-Compound-Intercepting Solar Distillation Enabled by a Photothermal/Photocatalytic Nanofibrous Membrane with Dual-Scale Pores

Synergistic enhancement of hydrophobic n-hexane biodegradation in a biotrickling filter: Role of hydrophilic VOCs in mass transfer and extracellular polymeric secretion

Volatile organic compounds (VOCs) emitted from the pharmaceutical industry, such as n-hexane, dichloromethane (DCM), and N, N-dimethylacetamide (DMAC), pose significant environmental and health risks. This study evaluates the performance of a bamboo charcoal-based bio-trickling filter (BTF) in removing these VOCs, comparing two systems: BTF-a, treating only n-hexane, and BTF-b, treating a mixture of n-hexane, DCM, and DMAC. After 26 days of operation at an n-hexane concentration of 100 mg m-3, BTF-b achieved a removal efficiency (RE) of 87.25 % for n-hexane, significantly higher than the 62 % in BTF-a, showcasing the synergistic effects of multi-component VOCs. As the DMAC concentration increased from 100 mg L-1 to 500 mg L-1, the RE of n-hexane improved from 65.93 % to 82.08 %, with a significant enhancement in the mass transfer coefficient (KLa) from 1.75 × 10-6 to 6.34 × 1-5 s-1, demonstrating the positive promotional effect of DMAC on n-hexane biodegradation. Conversely, high DCM concentrations (750 mg m-3) reduced the RE of n-hexane to 58.57 % due to substrate competition. The extracellular proteins (PN) content rose from 16.76 mg g-1 to 18.73 mg g-1. Microbial analysis after 220d operation revealed the enrichment of Mycobacterium (57.67 %) and Hyphomicrobium (5.38 %), key genera involved in VOCs biodegradation. Metabolic pathway analysis showed n-hexane and DMAC were transformed into intermediates, including hexanoic acid and acetic acid, demonstrating both pollutant removal and resource recovery potential. These findings highlight the synergistic role of hydrophilic VOCs, which are more hydrophilic than n-hexane, in promoting the biodegradation of hydrophobic pollutants, as well as the feasibility of BTF for treating multi-component VOCs.

Green Upcycling of Crop Residue into Activated Carbon in Designing Photothermal/Adsorptive Membrane for Solar-Driven Desalination and Simultaneous Volatile Organic Compound Removal

The growing freshwater scarcity and decline in air quality pose serious threats to the natural biosphere and human well-being. Developing functional materials for water purification through upcycling agricultural waste like crop residues, which are often burned in open fields and cause air pollution, offers an eco-friendly and sustainable solution for the global freshwater crisis. Solar-driven interfacial water evaporation (SIWE) presents a green and efficient method for freshwater production from seawater/wastewater. However, the presence of volatile organic compounds (VOCs) in wastewater limits its practicality as they co-evaporate with water molecules, leading to secondary pollution. Herein, we report a three-layered photothermal/adsorptive membrane (PCP-m), in which crop residue-derived activated carbon (CRAC) is sandwiched between a PVDF support and a PVA hydrogel layer, exhibiting desalination and simultaneous removal of VOCs like phenol, p-nitrophenol, and p-cresol. Under 1 sun illumination, PCP-m achieves an evaporation efficiency of 86.4% and maintains it even at higher intensities. The PVA hydrogel layer in PCP-m promotes mechanical strength, leaching resistance, and stability in harsh chemical conditions while ensuring even water distribution for Marangoni-driven site-specific salt rejection, enabling effective long-term desalination. Moreover, the superior VOC capturing capacity of CRAC enables PCP-m to achieve exceptional VOC removal efficiency (>95%) for phenol, even at high concentrations (100 mg L-1) or higher solar intensity (3 kW m-2). This work presents an efficient and environmentally conscious strategy for seawater desalination and simultaneous VOC removal through SIWE.

A Multistage Wastewater Purification System for the Effective Removal and Conversion of Water-Soluble VOCs: Leveraging White-Body Photothermal Evaporators

A novel multistage wastewater purification and conversion system (MWPCS) was designed to effectively remove and convert water-soluble dinitrotoluene (DNT). The MWPCS comprises a unique configuration, including the U-shaped solar evaporator (U-SE) with a white body, a polyelectrolyte multilayer (PEM)-coated roof dome, and a catalytic filter. The U-SE achieved a DNT removal efficiency (RE) of 78.5%, constituting the first stage of purification. Upon integration of the PEM-coated roof dome, the RE increased to 84.7%, representing the second purification capability of MWPCS. Additionally, the catalytic filter facilitated the conversion of toxic DNT into valuable diaminotoluene (DAT) with a conversion rate of 94.2%, marking the third purification stage of MWPCS. The U-SE with a white body exhibited a water evaporation rate of 2.17 kg/m2 h, which decreased to 1.37 kg/m2 h within the dome. However, with improved ventilation provided by the dome with holes, the evaporation rate increased to 1.85 kg/m2 h. A high water evaporation rate-based MWPCS is anticipated to be a multistage wastewater purification system capable of effectively removing and converting water-soluble DNT.

Surface Oxygen Vacancy Engineering for Enhanced Volatile Organic Compounds Removal in Solar-Interfacial Water Evaporation

Solar-interfacial water-vapor conversion has emerged as a promising method for clean water production, particularly in water-scarce regions, but a major challenge is the volatile organic compounds (VOCs) along with water vapor, leading to polluted condensed water. This study introduces a novel design strategy that leverages surface oxygen vacancies (OVs) in photocatalysts to maximize both oxygen (O2) utilization from the air and photocarrier efficiency at the air-water interface, building upon previous research that demonstrated that oxygen concentration at the interface can be significantly higher than that in bulk water. By enhancing oxygen adsorption and facilitating charge carrier separation, OVs significantly improve reactive oxygen species (ROS, including ·O2- and ·OH) generation and overall photocatalytic activity. As a demonstration, the surface OVs-engineered BiOCl-based photocatalytic solar interfacial evaporator demonstrated a 3.41-fold increase in VOC (phenol) removal efficiency compared to a conventional system, achieving over 99.6% VOC removal in condensed water and maintaining a high water vapor generation flux of 1.90 kg/m2/h. This innovative design was further validated using ZnO-based photocatalysts, demonstrating the broad applicability of OV-engineering in interfacial systems. By fully utilizing both the high oxygen content at the air-water interface and improving photocarrier dynamics, this approach represents a significant advancement in photocatalytic water treatment technologies, offering a scalable and highly efficient solution for VOC removal and clean water production.

High-performance and scalable contactless solar evaporation with 3D structure

Solar evaporation is a sustainable pathway for diverse water treatment technologies. The contactless evaporation stands out for its superior anti-contamination property. However, the evaporation performance is significantly limited by the non-contact heat transport, which is more pronounced in scalable applications with suppressed vapor escaping and tilted solar irradiation. Here, we propose a high-performance contactless solar evaporation design with three-dimensional (3D) solar-heating and vapor-escaping structure. Our theoretical analysis reveals that mass transport is the true bottleneck of contactless solar evaporation in scalable application, and can be significantly improved by our 3D design. A laboratory solar evaporation rate of 1.03 kg m-2 h-1 was demonstrated with our 3D design, which was 110% higher than the conventional design. Owing to the enhanced solar harvesting and transport, an average evaporation rate of 1.21 kg m-2 h-1 was demonstrated in outdoor field test with dilute solar flux of 589.98 W m-2. The scalability of 3D design was proved by the minimal difference (3%) in natural seawater evaporation performance between the small and large 3D devices. This work provides a robust, high-performance, and scalable solution for solar evaporation, especially for those scenarios with limited tolerance for contamination.

Dynamic Regulation of Hydrogen Bonding Networks and Solvation Structures for Synergistic Solar-Thermal Desalination of Seawater and Catalytic Degradation of Organic Pollutants

Although solar steam generation strategy is efficient in desalinating seawater, it is still challenging to achieve continuous solar-thermal desalination of seawater and catalytic degradation of organic pollutants. Herein, dynamic regulations of hydrogen bonding networks and solvation structures are realized by designing an asymmetric bilayer membrane consisting of a bacterial cellulose/carbon nanotube/Co2(OH)2CO3 nanorod top layer and a bacterial cellulose/Co2(OH)2CO3 nanorod (BCH) bottom layer. Crucially, the hydrogen bonding networks inside the membrane can be tuned by the rich surface -OH groups of the bacterial cellulose and Co2(OH)2CO3 as well as the ions and radicals in situ generated during the catalysis process. Moreover, both SO42- and HSO5- can regulate the solvation structure of Na+ and be adsorbed more preferentially on the evaporation surface than Cl-, thus hindering the de-solvation of the solvated Na+ and subsequent nucleation/growth of NaCl. Furthermore, the heat generated by the solar-thermal energy conversion can accelerate the reaction kinetics and enhance the catalytic degradation efficiency. This work provides a flow-bed water purification system with an asymmetric solar-thermal and catalytic membrane for synergistic solar thermal desalination of seawater/brine and catalytic degradation of organic pollutants.

A 2.5-Dimensional biomimetic dual-functional bifacial-evaporator for high efficient evaporation and water purification

Nowadays, solar-driven interfacial steam generation (SISG) is a sustainable and green technology for mitigating the water shortage crisis. Nevertheless, SISG is suffering from the enrichment of volatile organic compounds in condensate water and non-volatile organic compounds in feed water in practical applications. Herein, taking inspiration from nature, a dual-functional bifacial-CuCoNi (Bi-CuCoNi) evaporator with a special biomimetic urchin-like microstructure was successfully prepared. The unique design with 2.5-Dimensional bifacial working sides and urchin-like light absorption microstructure provided the Bi-CuCoNi evaporator with remarkable evaporation performance (1.91 kg m-2 h-1 under 1 kW m-2). Significantly, due to the urchin-like microstructure, the adequately exposed catalytic active sites enabled the Bi-CuCoNi/peroxydisulfate (PDS) system to degrade non-volatile organic pollutants (removal rate of 99.3 % in feed water, close to 100 % in condensate water) and the volatile organic pollutants (removal rate of 99.1 % in feed water, 98.2 % in condensate water) simultaneously. Moreover, the Bi-CuCoNi evaporator achieved non-radical pathway degradation at whole-stages. The dual-functional evaporator successfully integrated advanced oxidation processes (AOPs) into SISG, providing a new idea for high-quality freshwater production from polluted wastewater. ENVIRONMENTAL IMPLICATION: Inspired by nature, a dual-functional bifacial CuCoNi evaporator with a special biomimetic urchin-like microstructure formed by CuCoNi oxide nanowires grown on nickel foam by the hydrothermal synthesis method was successfully prepared. The prepared Bi-CuCoNi evaporator can effectively degrade organic pollutants in feed water and condensate water simultaneously during SISG, thus generating high-quality fresh water. Meanwhile, the health risks associated with the accumulation of organic pollutants in water during traditional SISG were reduced via green and sustainable way. The spatial 2.5-Dimensional structural design of Bi-CuCoNi provided new insights for achieving efficient water evaporation and fresh water generation from various polluted wastewater.

An in-depth study of integrating cascaded photocatalytic H2O2 generation and activation with solar-driven interfacial evaporation for in-situ organic contaminant remediation

Integrating cascaded photocatalytic H2O2 generation and subsequent activation of H2O2 (into ·OH radicals) with solar-driven interfacial evaporation techniques offers an effective and sustainable approach for in-situ treating water contaminated with organic substances. Unlike traditional water-dispersed catalysts, the interfacial evaporation approach presents unique challenges in photocatalytic reactions. We explored these dynamics using an AgI/PPy/MF interfacial photothermal set, achieving H2O2 production efficiency (approximately 1.53 mM/g/h) - three times higher than submerged counterparts. This efficiency is attributed to exceptional solar light absorption (about 95 %), a significant surface photothermal effect (raising temperatures by approximately 36 °C), and enhanced oxygen availability (38 times more than in water), all characteristic of the interfacial system. The in-situ activation of H2O2 into ·OH notably improves the degradation of organic pollutants, achieving up to 99 % removal efficiency. This comprehensive analysis highlights the potential of combining photocatalytic H2O2 processes with interfacial evaporation for efficiently purifying organically polluted water.

Photo-Fenton-Active MIL-88A/CNT-Based PVA Hydrogel for Solar-Driven Water Evaporation and Simultaneous Volatile Organic Compound Removal

Solar-driven interfacial water evaporation (SIWE) has emerged as a promising avenue for cost-effective freshwater production from seawater or wastewater. However, the simultaneous evaporation of volatile organic compounds (VOCs) presents a limitation for the widespread implementation of this technique. Thus, developing dual-functional evaporators capable of both desalining seawater and degrading VOCs is challenging. Herein, we fabricated an iron-based metal-organic framework MIL-88A/carbon nanotubes (CNTs) poly(vinyl alcohol) hydrogel (MCH) evaporator via the conventional freezing method for solar-driven seawater desalination and simultaneous photo-Fenton VOC degradation. Because of the superior photothermal conversion capability of CNTs, reduced thermal conductivity and water evaporation enthalpy within the hydrogel, and the photo-Fenton activity of rod-shaped MIL-88A, the MCH evaporator exhibits a higher evaporation rate of 2.26 kg m-2 h-1 under 1 sun illumination with simultaneous VOC degradation. The higher hydrophilicity and vertical channels in the MCH evaporator enable its self-salt cleaning ability, facilitating consistent seawater desalination, even in high salt concentrations up to 10 wt %. The synergistic effects of localized heating from CNTs and hydrogen peroxide activation through reactive sites of MIL-88A allow the MCH evaporator to degrade more than 93% of the added phenol during evaporation. This work presents a sustainable and efficient approach for solar-driven seawater desalination, offering simultaneous VOC degradation.

Hypercrosslinked Hydrogel Composite Membranes Targeted for Removal of Volatile Organic Compounds via Selective Solution-Diffusion in Membrane Distillation

Membrane distillation (MD) has attracted considerable interest in hypersaline wastewater treatment. However, its practicability is severely impeded by the ineffective interception of volatile organic compounds (VOCs), which seriously affects the product water quality. Herein, a hypercrosslinked alginate (Alg)/aluminum (Al) hydrogel composite membrane is facilely fabricated via Alg pregel formation and ionic crosslinking for efficient VOC interception. The obtained MD membrane shows a sufficient phenol rejection of 99.52% at the phenol concentration of 100 ppm, which is the highest rejection among the reported MD membranes. Moreover, the hydrogel composite membrane maintains a high phenol interception (>99%), regardless of the feed temperature, initial phenol concentration, and operating time. Diffusion experiments and molecular dynamics simulation verify that the selective diffusion is the dominant mechanism for VOCs-water separation. Phenol experiences a higher energy barrier to pass through the dense hydrogel layer compared to water molecules as the stronger interaction between phenol-Alg compared with water-Alg. Benefited from the dense and hydratable Alg/Al hydrogel layer, the composite membrane also exhibits robust resistance to wetting and fouling during long-term operation. The superior VOCs removal efficiency and excellent durability endow the hydrogel composite membrane with a promising application for treating complex wastewater containing both volatile and nonvolatile contaminants.

Interfacial Solar Evaporation: From Fundamental Research to Applications

In the last decade, interfacial solar steam generation (ISSG), powered by natural sunlight garnered significant attention due to its great potential for low-cost and environmentally friendly clean water production in alignment with the global decarbonization efforts. This review aims to share the knowledge and engage with a broader readership about the current progress of ISSG technology and the facing challenges to promote further advancements toward practical applications. The first part of this review assesses the current strategies for enhancing the energy efficiency of ISSG systems, including optimizing light absorption, reducing energy losses, harvesting additional energy, and lowering evaporation enthalpy. Subsequently, the current challenges faced by ISSG technologies, notably salt accumulation and bio-fouling issues in practical applications, are elucidated and contemporary methods are discussed to overcome these challenges. In the end, potential applications of ISSG, ranging from initial seawater desalination and industrial wastewater purification to power generation, sterilization, soil remediation, and innovative concept of solar sea farm, are introduced, highlighting the promising potential of ISSG technology in contributing to sustainable and environmentally conscious practices. Based on the review and in-depth understanding of these aspects, the future research focuses are proposed to address potential issues in both fundamental research and practical applications.

Super-hydrophilic LaCoO3/g-C3N4 nanocomposite coated beauty sponge for solar-driven seawater desalination with simultaneous volatile organic compound removal

Interfacial solar steam generation (ISSG) is emerging as a promising, environment-friendly solution for fulfilling freshwater and energy demands. However, a critical challenge for ISSG lies in the presence of harmful volatile organic compounds (VOCs) in the feedwater which are co-evaporated with water, leading to more enriched concentration in condensed water. Herein, lanthanum cobaltate-graphitic carbon nitride (LaCoO3/g-C3N4, LCO/g-CN) nanocomposite decorated beauty sponge (LCO/g-CN@BS) is proposed as an efficient photothermal/photocatalytic material for solar-driven seawater desalination and simultaneous VOC degradation. The hydrophobic surface of the beauty sponge after LCO/g-CN coating becomes super-hydrophilic, ensuring sufficient water supply and our LCO/g-CN@BS delivers an evaporation rate of 1.94 kg m-2 h-1 under 1 sun irradiation. This LCO/g-CN@BS shows excellent seawater desalination capacity with a self-cleaning ability when employed for saltwater purification for a salt (NaCl) concentration as high as 15 wt%. Moreover, fast photocarrier transfer between LCO and g-CN leads to enhanced photocatalytic degradation of over 90% of phenol simultaneously, which is about 60% for only an LCO-based beauty sponge. This work presents a promising approach to combining novel nanocomposites with microporous structures for efficient solar desalination, offering simultaneous VOC degradation.

Boosting the Viable Water Harvesting in Solar Vapor Generation: From Interfacial Engineering to Devices Design

Continuously increasing demand for the life-critical water resource induces severe global water shortages. It is imperative to advance effective, economic, and environmentally sustainable strategies to augment clean water supply. The present work reviews recent reports on the interfacial engineering to devices design of solar vapor generation (SVG) system for boosting the viability of drinkable water harvesting. Particular emphasis is placed on the basic principles associated with the interfacial engineering of solar evaporators capable of efficient solar-to-thermal conversion and resulting freshwater vapor via eliminating pollutants from quality-impaired water sources. The critical configurations manufacturing of the devices for fast condensation is then highlighted to harvest potable liquid water. Fundamental and practical challenges, along with prospects for the targeted materials architecture and devices modifications of SVG system are also outlined, aiming to provide future directions and inspiring critical research efforts in this emerging and exciting field.

Synchronizing Efficient Purification of VOCs in Durable Solar Water Evaporation over a Highly Stable Cu/W18O49@Graphene Material

Solar-driven clean water production is challenged by VOCs (volatile organic compounds), which pose health risks in distilled water. Herein, we developed a Cu/W18O49@Graphene photothermal-photocatalytic material addressing VOCs contamination. Plasmonic coupling between Cu and W18O49 enhances light absorption, and 1-2 layers of graphene encapsulation protects oxygen vacancies within W18O49 while facilitating hot electron extraction, effectively mitigating their ultrafast relaxation. Density functional theory calculations revealed enhanced VOCs adsorption on graphene. These synergies address oxygen vacancy decay in W18O49 and provide more active sites for gas-liquid-solid triphase photocatalytic reactions. Integrated with a three-dimensional floating evaporator substrate, the optimized Cu/W18O49@Graphene material achieved an effective water evaporation rate of 1.41 kg m-2 h-1 (efficiency of 88.6%), exceptional stability (>120 h), and remarkable 99% phenol removal under 1 sun irradiation (1 kW m-2). This work provides a promising solution to mitigate VOCs contamination in solar-driven water evaporation.

Environmental energy enhanced solar-driven evaporator with spontaneous internal convection for highly efficient water purification

Solar-driven interfacial evaporation for water purification is limited by the structural design of the solar evaporator and, more importantly, by the inability to separate the water from volatile organic compounds (VOCs) present in the water source. Here, we report a three-dimensional (3D) bifunctional evaporator based on N-doped carbon (CoNC/CF), which enables the separation of fresh water from VOCs by activating PMS during the evaporation process with a VOC removal rate of 99%. There is abundant van der Waals interaction between peroxymonosulfate (PMS) and CoNC/CF, and pyrrolic N is confirmed as the active site for binding phenol, thus contributing to the separation of phenol from water. With the advantageous features of sufficient light absorption, adequate water storage capacity, and spontaneous internal convection flow on its top surface, the 3D evaporator achieves a high evaporation rate under one sun (1 kW/m2) at 3.16 kg/m2/h. More notably, through careful structural design, additional energy from the environment and water can be utilized. With such a high evaporation rate and satisfactory purification performance, this work is expected to provide a promising platform for wastewater treatment.

Robust ceramic-based graphene membrane for challenging water treatment with enhanced fouling and scaling resistance

Membrane fouling and scaling are two challenges for efficient treatment of hypersaline wastewater, greatly hindering separation performance and operation stability of desalination membranes. In this work, we report a smooth ceramic-based graphene desalination membrane, exhibiting enhanced anti-fouling and anti-scaling ability and operational performance for efficient treatment of both synthetic and real industrial wastewaters, outperforming polypropylene (PP) membrane. For treatment of hypersaline waters containing organic or inorganic substance, we demonstrate that the graphene membrane exhibits more stable water flux and almost complete salt rejection (>99.9%) during constant operation. Enhanced anti-fouling and desalination performance of graphene membrane could be attributed to the lower attractive interaction force with foulant (-4.65 mJ m-2), lower surface roughness (Ra = 2.2 ± 0.1 nm) and higher affinity with water than PP membrane. Furthermore, an anti-scaling mechanism enabled by graphene membrane is evidenced, with a highlight on the roles of smooth graphene surface with lower roughness, less nucleation sites and lower binding force with scaling crystals. Importantly, even for industrial petrochemical wastewater, such a graphene membrane also exhibits relatively more stable water flux and promising oil and ions rejection during long-term operation, outperforming PP membrane. This study further confirms a promising practical application potential of robust ceramic-based graphene membrane for efficient treatment of more challenging hypersaline wastewater with complicated compositions, which is not feasible by conventional desalination membranes.

A dual-functional hydrogel for efficient water purification: Integrating solar interfacial evaporation with fenton reaction

Solar interfacial evaporation is a potential technology to produce clean water due to its simplicity and being driven by renewable clean energy, but it still requires further development to break through the bottleneck of removing volatile organic compounds (VOCs), especially in wastewater treatment. Herein, we proposed a dual-functional hydrogel evaporator that coupled solar interfacial evaporation with Fenton reaction to simultaneously remove VOCs and non-volatile pollutants from water with low energy consumption and high efficiency. The evaporator was composed with β-FeOOH and polydopamine (PDA) on an electrospun nanofibrous hydrogel. Arising from the PDA with excellent photothermal properties, the evaporator revealed a high light absorption characteristics (∼90%) and photothermal efficiency (83.4%), which ensured a favorable evaporation rate of 1.70 kg m-2 h-1 under one solar irradiation. More importantly, benefited from the coupled Fenton reaction, the VOCs removal rate of β-FeOOH@PDA/polyvinyl alcohol nanofibrous hydrogel (β-FeOOH@PPNH) reached 95.8%, which was 6.5 times than that of sole solar interfacial evaporation (14.8%). In addition, the evaporator exhibited an outstanding non-volatile pollutant removal capability and stable removal performance for organic pollutants over a long period of operation. The prepared β-FeOOH@PPNH evaporator provides a promising idea for simultaneous removal of non-volatile pollutants and volatile pollutants performance in long-term water purification.

Photothermal-Photocatalytic CSG@ZFG Evaporator for Synergistic Salt Rejection and VOC Removal during Solar-Driven Water Distillation

Sunlight-driven interfacial photothermal evaporation has been considered as a promising strategy for addressing global water crisis. Herein, we fabricated a self-floating porous triple-layer (CSG@ZFG) evaporator using porous fibrous carbon derived from Saccharum spontaneum (CS) as a photothermal material. The middle layer of the evaporator is composed of hydrophilic sodium alginate crosslinked by carboxymethyl cellulose and zinc ferrite (ZFG), whereas the top hydrophobic layer consists of fibrous (CS) integrated benzaldehyde-modified chitosan gel (CSG). Water is transported to the middle layer through the bottom elastic polyethylene foam using natural jute fiber. Such a strategically designed three-layered evaporator exhibits a broad-band light absorbance (96%), excellent hydrophobicity (120.5°), a high evaporation rate of 1.56 kg m^-2 h^-1, an energy efficiency of 86%, and outstanding salt mitigation ability under the simulated sunlight of intensity 1 sun. Adding ZnFe₂O₄ nanoparticle as a photocatalyst has been proved to be capable of restricting the evaporation of volatile organic contaminants (VOCs) like phenol, 4-nitrophenol, and nitrobenzene to ensure the purity of evaporated water. Such an innovatively designed evaporator offers a promising approach for the production of drinking water from wastewater and seawater.

Topologically Porous Heterostructures for Photo/Photothermal Catalysis of Clean Energy Conversion

As a straightforward way to fix solar energy, photo/photothermal catalysis with semiconductor provides a promising way to settle the energy shortage and environmental crisis in many fields, especially in clean energy conversion. Topologically porous heterostructures (TPHs), featured with well-defined pores and mainly composed by the derivatives of some precursors with specific morphology, are a major part of hierarchical materials in photo/photothermal catalysis and provide a versatile platform to construct efficient photocatalysts for their enhanced light absorption, accelerated charges transfer, improved stability, and promoted mass transportation. Therefore, a comprehensive and timely review on the advantages and recent applications of the TPHs is of great importance to forecast the potential applications and research trend in the future. This review initially demonstrates the advantages of TPHs in photo/photothermal catalysis. Then the universal classifications and design strategies of TPHs are emphasized. Besides, the applications and mechanisms of photo/photothermal catalysis in hydrogen evolution from water splitting and CO_x hydrogenation over TPHs are carefully reviewed and highlighted. Finally, the challenges and perspectives of TPHs in photo/photothermal catalysis are also critically discussed.

Emerging Materials for Interfacial Solar-Driven Water Purification

Solar-driven water purification is considered as an effective and sustainable technology for water treatment using green solar energy. One major goal for practical applications is to improve the solar evaporation performance by the design of novel photothermal materials, with optimized heat localization and water transport pathways to achieve reduced energy consumption for water vaporization. Recently, some emerging materials like polymers, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and also single molecules were employed to construct novel solar evaporation systems. In this minireview, we present an overview of the recent efforts on materials development for water purification systems. The state-of-the-art applications of these emerging materials for solar-driven water treatment, including desalination, wastewater purification, sterilization and energy production, are also summarized.

Reduced graphene oxide/carbon nitride composite sponge for interfacial solar water evaporation and wastewater treatment

Interfacial solar-driven steam generation has been proposed as a cost-effective green sustainable technology to alleviate the freshwater crisis. However, the desire to produce clean water from water sources containing organic contaminants is still remains a challenge due to the limitations of the traditional wastewater treatment methods. Here, we constructed a g-C3N4-based composite sponge solar steam generator (rGCPP) by a simple hydrothermal reaction. Benefiting from its low cost and easy preparation, this evaporator can be expected to be a promising candidate for the alleviation of water shortages and water pollution in practical applications. By combination of the solar steam generation and the photocatalysis into the rGCPP-based interfacial solar-driven steam generation system, the resulted rGCPP-based solar steam generator performs outstanding solar absorption of 90.8%, which achieves high evaporation rate of 1.875 kg m-2 h-1 and solar-to-vapor efficiency of 81.07% under 1 sun irradiation. Meanwhile, organic pollutants in the water source can be completely removed by photocatalytic degradation and the degradation rates were measured to be 99.20% for methylene blue and 91.07% for rhodamine B, respectively. Consequently, the as-prepared composite sponge has promising applications in generating clean water and alleviating water pollution.

Water Harvesting Strategies through Solar Steam Generator Systems

Solar steam generator (SSG) systems have attracted increasing attention, owing to its simple manufacturing, material abundance, cost-effectiveness, and environmentally friendly freshwater production. This system relies on photothermic materials and water absorbing substrates for a clean continuous distillation process. To optimize this process, there are factors that are needed to be considered such as selection of solar absorber and water absorbent materials, followed by micro/macro-structural system design for efficient water evaporation, floating, and filtration capability. In this contribution, we highlight the general interfacial SSG concept, review and compare recent progresses of different SSG systems, as well as discuss important factors on performance optimization. Furthermore, unaddressed challenges such as SSG's cost to performance ratio, filtration of untreatable micropollutants/microorganisms, and the need of standardization testing will be discussed to further advance future SSG studies.

Supramolecular Engineering of Amorphous Porous Polymers for Rapid Adsorption of Micropollutants and Solar-Powered Volatile Organic Compounds Management

Freshwater shortage is becoming one of the most critical global challenges owing to severe water pollution caused by micropollutants and volatile organic compounds (VOCs). However, current purification technology shows slow adsorption of micropollutants and requires an energy-intensive process for VOCs removal from water. In this study, a highly efficient molecularly engineered covalent triazine framework (CTF) for rapid adsorption of micropollutants and VOC-intercepting performance using solar distillation is reported. Supramolecular design and mild oxidation of CTFs (CTF-OXs) enable hydrophilic internal channels and improve molecular sieving of micropollutants. CTF-OX shows rapid removal efficiency of micropollutants (>99.9% in 10 s) and can be regenerated several times without performance loss. Uptake rates of selected micropollutants are high, with initial pollutant uptake rates of 21.9 g mg^-1  min^-1 , which are the highest rates recorded for bisphenol A (BPA) adsorption. Additionally, photothermal composite membrane fabrication using CTF-OX exhibits high VOC rejection rate (up to 98%) under 1 sun irradiation (1 kW m^-2 ). A prototype of synergistic purification system composed of adsorption and solar-driven membrane can efficiently remove over 99.9% of mixed phenol derivatives. This study provides an effective strategy for rapid removal of micropollutants and high VOC rejection via solar-driven evaporation process.

A bionic solar-driven interfacial evaporation system with a photothermal-photocatalytic hydrogel for VOC removal during solar distillation

Solar-driven interfacial evaporation is a breakthrough water treatment method because it harvests solar energy for producing clean water. However, evaporated volatile organic compounds (VOCs) in distilled water are the greatest barrier to this technology. Herein, a bionic solar-driven interfacial evaporation system integrating photothermal and photocatalysis technology was developed based on a new combined material TiO₂/Ti₃C₂/C₃N₄/PVA (TTCP) hydrogel as an evaporator. Phenol-contaminated water, especially actual water (seawater, lake water and reclaimed water), is used to evaluate the water evaporation and VOC photocatalytic degradation performance. The results show that the evaporation rate of TTCP hydrogel was 1.54 kg m ^- 2h ^- 1 under 1 kW m ^- 2, and the removal efficiency of phenol ranged from 69.4% to 100% at different concentrations (1-50 mg/L) in source water. Particularly, the capacity of the bionic evaporator was first evaluated for different types of actual water. Despite the initial TOC (38.12-57.93 mg/L) and total dissolved solids (TDS, 1.35×10³-8.78×10⁴ mg/L) for seawater, lake water and reclaimed water being very different, the TDS was decreased by more than two orders of magnitude, below the US EPA drinking water standard (500 mg/L). The maximum TOC removal efficiency reached 80% under simulated sunlight (1 kW m ^- 2), which is comparable to the efficiency of the ultrafiltration technique previously reported except for seawater. Furthermore, real sunlight (average solar irradiation ∼0.82 kW m^{- 2}) was used to assess the practicability. The bionic evaporator can produce 0.72 kg m ^- 2h ^- 1 of vapor from reclaimed water and run with steadily efficient TDS and TOC removals, reaching 99% and 74%, respectively. This technology, as a small, decentralized water treatment method, is a good choice for remote and off-grid areas.

Inhibition of Phenol from Entering into Condensed Freshwater by Activated Persulfate during Solar-Driven Seawater Desalination

Recently, solar-driven seawater desalination has received extensive attention since it can obtain considerable freshwater by accelerating water evaporation at the air-water interface through solar evaporators. However, the high air-water interface temperature can cause volatile organic compounds (VOCs) to enter condensed freshwater and result in water quality safety risk. In this work, an antioxidative solar evaporator, which was composed of MoS₂ as the photothermal material, expandable polyethylene (EPE) foam as the insulation material, polytetrafluoroethylene (PTFE) plate as the corrosion resistant material, and fiberglass membrane (FB) as the seawater delivery material, was fabricated for the first time. The activated persulfate (PS) methods, including peroxymonosulfate (PMS) and peroxodisulfate (PDS), were applied to inhibit phenol from entering condensed freshwater during desalination. The distillation concentration ratio of phenol (R_D) was reduced from 76.5% to 0% with the addition of sufficient PMS or PDS, which means that there was no phenol in condensed freshwater. It was found that the Cl^- is the main factor in activating PMS, while for PDS, light, and heat are the dominant. Compared with PDS, PMS can make full utilization of the light, heat, Cl^- at the evaporator's surface, resulting in more effective inhibition of the phenol from entering condensed freshwater. Finally, though phenol was efficiently removed by the addition of PMS or PDS, the problem of the formation of the halogenated distillation by-products in condensed freshwater should be given more attention in the future.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg²⁺) has become a severe issue for human beings. Herein, a 3D-MoS₂ sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS₂ sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m^-2 h^-1 under sunlight irradiation and produces freshwater with Hg²⁺ under the WHO drinking water standard at 0.001 mg L^-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Self-Regulating Solar Steam Generators Enable Volatile Organic Compound Removal through In Situ H2O2 Generation

Interfacial solar steam generation for clean water production suffers from volatile organic compound (VOC) contamination during solar-to-steam conversion. Here, we present a solar steam generator based on the integration of melamine foam (MF), polydopamine (PDA), and Ag/AgCl particles. Together with the high photothermal conversion efficiency (ca. 87.8%, 1 kW/m²) achieved by the PDA thin film, the Ag/AgCl particles can efficiently activate the localized generation of H₂O₂ and •OH in situ, thus degrading the VOCs during the rapid vapor generation. The generation of H₂O₂ and •OH in situ also facilitates the creation of a buffer zone containing H₂O₂ and •OH for the rapid removal of organic pollutants in the surrounding water attracted to the solar vapor generator, demonstrating a self-cleaning steam generator toward various volatile compounds such as phenol, aniline, 2,4-dichlorophenol, and N,N-dimethylformamide in a wide range of concentrations.

A Light-Permeable Solar Evaporator with Three-Dimensional Photocatalytic Sites to Boost Volatile-Organic-Compound Rejection for Water Purification

Solar-driven interfacial evaporation (SIE) is emerging as an energy-efficient technology to alleviate the global water shortages. However, there is a fatal disadvantage in using SIE, that is, the volatile organic compounds (VOCs) widely present in feedwater would concurrently evaporate and transport in distilled water, which threatens the water safety. Photocatalysis is a sustainable technology for pollution control, and after years of development, it has become a mature method. Considering the restriction by the insufficient reaction of the permeating VOCs on the two-dimensional (2D) light-available interface of conventional materials, a 3D photocatalytic approach can be established to boost VOC rejection for photothermal evaporation. In the present work, a light-permeable solar evaporator with 3D photocatalytic sites is constructed by a porous sponge decorated with BiOBrI nanosheets with oxygen-rich vacancies. The 3D microchannels in the evaporator provide a light-permeable path with the deepest irradiation depth of about 580 μm, and the reactive interface is increased by tens of times compared with the traditional 2D membrane, resulting in suppression of VOC remnants in distilled water by around four orders of magnitude. When evaporating river water containing 5 mg L^-1 extra added phenol, no phenol residues (below 0.001 mg/L) were detected in the produced freshwater. This development is believed to provide a powerful strategy to resolve the VOC bottleneck of SIE.

Metal-Organic Framework Composite Photothermal Membrane for Removal of High-Concentration Volatile Organic Compounds from Water via Molecular Sieving

Water-soluble volatile organic compounds (VOCs) are among the most difficult-to-treat species during wastewater treatment. The current purification and removal of high-concentration VOCs still rely on the energy-consuming distillation and high-pressure driven reverse osmosis technology. There is an urgent need for an advanced technology that can effectively remove high-concentration VOCs from water. Here, we report a metal-organic framework (MOF)/polyaniline (PANI) nanofiber array composite photothermal membrane for removal of high-concentration VOCs from water via molecular sieving during a solar-driven evaporation process. The modified zeolitic imidazole framework-8 (ZIF-8) layer grown on a PANI nanofiber array acts as a molecular sieving layer to evaporate water but intercept VOCs. The composite membrane exhibits high VOCs rejection and a high-water evaporation rate for water containing different concentrations of VOCs. When treating water containing VOCs with a concentration of up to 400 mg L^-1, the VOCs rejection rate is up to 99% and the water evaporation rate is 1.0 kg m^-2 h^-1 under 1 sun irradiation (1 kW m^-2). Our work effectively combines the molecular sieve effect with a solar-driven evaporation process, which provides an effective strategy for the treatment of water containing VOCs.

Armor-Structured Interconnected-Porous Membranes for Corrosion-Resistant and Highly Permeable Waste Ammonium Resource Recycling

Ammonium recovery from wastewater by gas-permeable membranes is promising but suffers from the tradeoff between membrane stability and permeability under harsh operating conditions. Chemical-resistant membranes display modest permeability due to the poor solubility and processibility; chemically active membranes are easier to be endowed with better permeability however hinder by instability. To resolve such a problem, we cleverly design a novel membrane configuration via one-step solution-electrospinning, with the chemical-active component (low-strength fluorine polymer) as the inner skeleton to construct interconnected porous structures and the chemical-resistant component (high-strength fluorine polymer) as the outer armor to serve as a protective layer. Due to the significantly enhanced mass transfer coefficient, the interconnected-porous armor-structured membrane exhibited much higher permeability for NH₄⁺-N recovery, which was 1.4 and 5 times that of the traditional PTFE membrane and PP membrane, respectively. Through long-term intermittent and consecutive experiments, the reusability and durability of the armor-structured nanofibrous membrane were verified. When treating actual hoggery wastewater with complicated water quality, the armor-structured nanofibrous membrane also displayed robust stable performance with excellent antiwettability. The mechanisms of membrane formation, corrosion resistance, and mass transfer were discussed in detail.

Inhibition of typical phenolic compounds entering into condensed freshwater by surfactants during solar-driven seawater distillation

Recently, solar-driven seawater desalination based on air-water interfacial heating has triggered significant research interest due to its high water evaporation rate, high photothermal conversion efficiency, low energy consumption, simple operation and low cost. However, as the air-water interface temperature reaches as high as 40-70 °C, volatile organic compounds (VOCs) will volatilize into the condensed desalinated water and results in the polluted freshwater. In this work, anionic, cationic, and nonionic surfactants were applied for the first time to inhibit the phenolic compounds such as phenol, p-methylphenol and p-chlorophenol entering into the condensed freshwater. Results showed that the concentration of phenol could be reduced by the addition of cetyl trimethyl ammonium bromide (CTAB). The phenol's distillation concentration ratio (R_D) reduced from 76% to 35% due to the electrostatic interaction and the micellar encapsulation between the CTAB and phenol. Moreover, parameters including CTAB dose, initial phenol concentration, solar intensity, pH, and salinity that affecting the R_D were also investigated. Finally, a real seawater solar-driven distillation experiment also revealed that the water quality of freshwater was improved by the addition of CTAB. This work revealed that the surfactants such as CTAB can be potentially used to inhibit VOCs entering into the condensed freshwater during solar-driven seawater distillation.

Towards sustainable saline agriculture: Interfacial solar evaporation for simultaneous seawater desalination and saline soil remediation

Interfacial solar steam generation is an efficient way to produce freshwater from saline water. This technology was further harnessed here for simultaneous saline soil remediation and enhanced agricultural sustainability. An interfacial solar evaporation and planting system was designed that uses treated seawater for saline soil washing and agricultural irrigation. In outdoor experiments the evaporator realized high freshwater production (10.95 kg m^-2 day^-1) with a soil washing efficiency 3 times greater than traditional distillation. Post treatment plant assays showed that initially highly saline soils could be restored to functional agricultural soils with germination rates of 65% after soil washing, where solar evaporation could continuously provide irrigation water for plant growth. This system is fully automated and uses only solar energy and seawater for saline soil remediation and irrigation. The development of this system provides a potentially useful solution to alleviate global problems associated with water scarcity, soil salinization, and desertification.

Bilayer rGO-Based Photothermal Evaporator for Efficient Solar-Driven Water Purification[ ] *

Interfacial evaporation has emerged as a promising approach to produce freshwater. However, an urgent concern is that, due to the illegal discharge of industrial wastewater, most water bodies are polluted by trace volatile organic compounds (VOCs), which are easily volatilized and enriched in the collected water during the interfacial evaporation process. Herein, a bilayer photothermal evaporator was reasonably designed for contaminated water purification. The bottom hydrophilic rGO-sodium alginate (SA) sheets purposefully disintegrate water transport channels, thus quickly removing VOCs through physical adsorption. The rGO-SA-TiO₂ upper layer sufficiently absorbs incident light and therefore persistently generates reactive oxidizing species to degrade upward VOCs. Notably, the oriented microchannels inside the evaporator allow sustained light reflections to improve the utilization of solar energy. The evaporation rate can reach 1.63 kg m^-2  h^-1 with a considerably high VOC removal efficiency of up to 96 %. Such an integrated bilayer evaporator provides an effective strategy to obtain clean water via solar distillation.

All-Polymer and Self-Roughened Superhydrophobic PVDF Fibrous Membranes for Stably Concentrating Seawater by Membrane Distillation

Novel specially wettable membranes have been attracting significant attention for durable membrane distillation (MD). However, constructing a superhydrophobic interface often has to undergo complex modification procedures including roughness construction and hydrophobic modification. Herein, all-polymer and self-roughened superhydrophobic poly(vinylidene fluoride) fibrous membranes (PVDF FMs) with robustly stable pores were successfully constructed via electrospinning of fluorinated polyhedral oligomeric silsesquioxanes/PVDF (F-POSS/PVDF) emulsion solution in combination with hot-pressing. The comparative experiment reveals that proper hot-pressing, including adequate temperature and pressure, can help improve membrane pore stability by welding the intersecting fibers and increase the membrane surface hydrophobicity by transferring the inner fluorine chains to the outer fiber surface, simultaneously advancing membrane scaling and fouling resistance. Nevertheless, excessive temperature or pressure will destroy the interconnected pores and surface wettability of the PVDF FM. Significantly, the hot-pressing-treated F-POSS/PVDF FM shows a high water recovery (∼90%) and robust stability after five rounds of the concentration process toward concentrating natural seawater as a target. Thus, the all-polymer and self-roughened superhydrophobic PVDF FMs constructed via electrospinning combined with the thermal treatment have potential applications in concentrating hypersaline brines, which make up for the other membrane technology, including reverse osmosis and nanofiltration technologies that failed to concentrate hypersaline solutions.

Solar-Powered Sustainable Water Production: State-of-the-Art Technologies for Sunlight-Energy-Water Nexus

Alternative water resources (seawater, brackish water, atmospheric water, sewage, etc.) can be converted into clean freshwater via high-efficiency, energy-saving, and cost-effective methods to cope with the global water crisis. Herein, we provide a comprehensive and systematic overview of various solar-powered technologies for alternative water utilization (i.e., "sunlight-energy-water nexus"), including solar-thermal interface desalination (STID), solar-thermal membrane desalination (STMD), solar-driven electrochemical desalination (SED), and solar-thermal atmospheric water harvesting (ST-AWH). Three strategies have been proposed for improving the evaporation rate of STID systems above the theoretical limit and designing all-weather or all-day operating STID systems by analyzing the energy transfer of the evaporation and condensation processes caused by solar-thermal conversion. This review also introduces the fundamental principles and current research hotspots of two other solar-driven seawater or brackish water desalination technologies (STMD and SED) in detail. In addition, we also cover ST-AWH and other solar-powered technologies in terms of technology design, materials evolution, device assembly, etc. Finally, we summarize the content of this comprehensive review and discuss the challenges and future outlook of different types of solar-powered alternative water utilization technologies.

In Situ Three-Dimensional Welded Nanofibrous Membranes for Robust Membrane Distillation of Concentrated Seawater

Membrane distillation (MD) is a promising technology for treating the concentrated seawater discharged from the desalination process. Interconnected porous membranes, fabricated by additive manufacturing, have received significant attention for MD technology because of their excellent permeability. However, their poor hydrophobic durability induced by the deformation of pores constrains their water desalination performance. Herein, an in situ three-dimensional (3D) welding approach involving emulsion electrospinning is reported for fabricating robust nanofibrous membranes. The reported method is simple and effective for welding nanofibers at their intersections, and the reinforced membrane pores are uniform in the 3D space. The results show that the in situ 3D welded nanofibrous membrane, with a stability of 170 h and water recovery of 76.9%, exhibits better desalination performance than the nonwelded (superhydrophobic) nanofibrous membrane and the postwelded (superhydrophobic) nanofibrous membrane. Furthermore, the stability mechanism of the in situ 3D welded nanofibrous membrane and the two different wetting mechanisms of the nonwelded and postwelded nanofibrous membranes were investigated in the current work. More significantly, the in situ 3D welded nanofibrous membrane can further concentrate the actual concentrated seawater (121°E, 37°N) to crystallization, demonstrating its potential applications for the desalination of challenging concentrated seawater.

A Critical Review on Removal of Gaseous Pollutants Using Sulfate Radical-based Advanced Oxidation Technologies

Excessive emissions of gaseous pollutants such as SO₂, NO_x, heavy metals (Hg, As, etc.), H₂S, VOCs, etc. have triggered a series of environmental pollution incidents. Sulfate radical (SO₄•^-)-based advanced oxidation technologies (AOTs) are one of the most promising gaseous pollutants removal technologies because they can not only produce active free radicals with strong oxidation ability to simultaneously degrade most of gaseous pollutants, but also their reaction processes are environmentally friendly. However, so far, the special review focusing on gaseous pollutants removal using SO₄•^--based AOTs is not reported. This review reports the latest advances in removal of gaseous pollutants (e.g., SO₂, NO_x, Hg, As, H₂S, and VOCs) using SO₄•^--based AOTs. The performance, mechanism, active species identification and advantages/disadvantages of these removal technologies using SO₄•^--based AOTs are reviewed. The existing challenges and further research suggestions are also commented. Results show that SO₄•^--based AOTs possess good development potential in gaseous pollutant control field due to simple reagent transportation and storage, low product post-treatment requirements and strong degradation ability of refractory pollutants. Each SO₄•^--based AOT possesses its own advantages and disadvantages in terms of removal performance, cost, reliability, and product post-treatment. Low free radical yield, poor removal capacity, unclear removal mechanism/contribution of active species, unreliable technology and high cost are still the main problems in this field. The combined use of multiactivation technologies is one of the promising strategies to overcome these defects since it may make up for the shortcomings of independent technology. In order to improve free radical yield and pollutant removal capacity, enhancement of mass transfer and optimization design of reactor are critical issues. Comprehensive consideration of catalytic materials, removal chemistry, mass transfer and reactor is the promising route to solve these problems. In order to clarify removal mechanism, it is essential to select suitable free radical sacrificial agents, probes and spin trapping agents, which possess high selectivity for target specie, high solubility in water, and little effect on activity of catalyst itself and mass transfer/diffusion parameters. In order to further reduce investment and operating costs, it is necessary to carry out the related studies on simultaneous removal of more gaseous pollutants.

Interfacial Solar Distillation for Freshwater Production: Fate of Volatile and Semivolatile Organic Contaminants

Interfacial solar distillation (ISD) is an approach with low cost and low energy demand useful for seawater desalination and freshwater production. However, the commercial potential of ISD for applications such as polluted seawater desalination or industrial wastewater reuse may be hindered by low rejection of volatile and semivolatile contaminants. For the first time, the results of this study showed that the transport (from bulk water (B) to distilled water (D)) of volatile and semivolatile contaminants during the solar desalination process was highly correlated with compound volatility (R² = 0.858). The obtained relationship was verified to be capable of predicting the distillation concentration ratio (C_D/C_B,0) of different contaminants (K_H = 6.29 × 10^-7-2.94 × 10^-4 atm·m³·mol^-1) during the ISD process. Compounds such as phenols, which have relatively high volatilization and condensation rates, deserve the most attention as potential contaminants in the distilled water. Meanwhile, other compounds that are more volatile than phenol condensed less in distilled water. Adding an activated carbon adsorbent or a photothermal oxidant is a promising strategy to effectively mitigate the distillation of contaminants and ensure water safety. These results fill the knowledge gap in understanding the transport of volatile and semivolatile compounds in ISD for the treatment of complex source waters.

A flexible and salt-rejecting electrospun film-based solar evaporator for economic, stable and efficient solar desalination and wastewater treatment

Recently, interfacial solar evaporation has been developed for water treatment. However, the high cost and low stability of solar evaporators significantly hinder their practical applications. In this study, layered graphene and polymethylmethacrylate were used to fabricate a composited film (GF) by electrospinning, which acted as a solar absorber. Together with a water transporter (polyurethane sponge) and a thermal insulator (polystyrene foam), the GF-based evaporator was constructed for solar distillation. Taking advantage of the porous three-dimensional structure of GF, the light path could be extended, rendering an efficient broadband solar absorption (92%). More importantly, although the content of layered graphene in the GF-based evaporator (1.75 g m^-2) was only 5.8-17.5% of that in the current reported graphene-based evaporators (10-30 g m^-2), a comparable water evaporation efficiency was acquired, which was induced by the much higher utilization efficiency of photothermal nanomaterials in the GF-based evaporator than that in the reported devices, ensuring its economic feasibility. Meanwhile, more than 99.9% heavy metal ions and 99.8% organic dye could be removed by the GF-based evaporator. Combining the merits of long-term and stable evaporation, salt rejection, and resistance to harsh environment, the GF-based evaporator was promising for freshwater recycling from both seawater and wastewater.

Constructing Mesoporous Adsorption Channels and MOF-Polymer Interfaces in Electrospun Composite Fibers for Effective Removal of Emerging Organic Contaminants

Recently, metal-organic framework (MOF)-based electrospun fibers have attracted considerable attention as adsorbents for organic contaminant removal from water. To prepare these fibers, two common strategies including blending electrospinning and surface coating are employed. However, fibers obtained from the two strategies still have some disadvantages, such as adsorption site blockage and unstable loading. Here, we constructed interconnected mesopores in the electrospun zeolitic imidazolate framework-8 (ZIF-8)/polyacrylonitrile (PAN) fibers with the assistance of poly(vinylpyrrolidone) to expose more adsorption sites of ZIF-8 and make ZIF-8 more stable. Moreover, the mesopores could also enhance the diffusion of contaminant molecules and create MOF-polymer interfaces in the fiber, which improve the adsorption rate and adsorption capacity, respectively. The obtained fibers were used to adsorb antibiotic tetracycline from water. Benefiting from the mesoporous adsorption channels and the MOF-polymer interface, porous ZIF-8/PAN fibers showed faster adsorption kinetics than ZIF-8/PAN blending fibers and larger adsorption capacity than ZIF-8-coated PAN fibers and ZIF-8/PAN blending fibers. The maximum adsorption capacity of porous ZIF-8/PAN fibers was 885.24 mg/g, which is close to that of pure ZIF-8. After 10 adsorption-desorption cycles, the removal efficiency was still above 97%. In addition, porous ZIF-8/PAN fibers could act as the membrane adsorbents to dynamically separate tetracycline with a treated capacity of 9.93 × 10³ bed volumes. These results demonstrate that our prepared porous ZIF-8/PAN fibers have great potential in antibiotic drug removal.

Photocatalytic reaction mechanisms at the gas–solid interface for environmental and energy applications

Five gas–solid photocatalytic reactions including the oxidation of NOx, VOCs and NH3, and reduction of CO2 and N2 are summarized. Besides, basic properties of gas molecules, their adsorption and activation, and various reaction pathways are analyzed.

Clean water generation through a multifunctional activated carbon-TiO2 interfacial solar distillation system

Solar distillation is emerging as an environmentally friendly and energy-effective technology for clean water generation. However, bulk water heating and the possibly complex composition of water matrices of source water could undermine the system efficacy. In this study, an interfacial evaporation device consisting of activated carbon combined with P25 TiO₂ as the top layer and polyethylene foam as the bottom layer (AC-P25/foam device) was established. With the excellent optical absorbance of AC and the heat localization effect contributed by the PE foam, the evaporation rate (r_evp) of the device (r_evp = 2.1 kg m⁻² h⁻¹) was improved by 209% and 71% compared with that of the water-only (r_evp = 0.68 kg m⁻² h⁻¹) and conventional evaporation (i.e., submerged AC-P25) systems (r_evp = 1.23 kg m⁻² h⁻¹), respectively. The reusability test showed the stable evaporation performance of AC-P25/foam within 7 cycles; this interfacial evaporation was also found to be less affected by suspended solids in water due to a reduction in the influence of light scattering. The AC-P25/foam device not only possessed photothermal ability for water distillation but was also able to prevent enrichment of volatile organic compounds (i.e., phenol) with ∼95% removal efficiency through adsorption and photocatalytic reactions under illumination. Additionally, an outdoor solar distillation test performed with synthetic saline water demonstrated the desalination ability of the AC-P25/foam device, with the concentrations of all ions in the distilled water ≤3.5 mg L⁻¹, far below the drinking water guideline value provided by the World Health Organization. The materials of the AC-P25/foam photothermal device are readily available and easily fabricated, showing the practical feasibility of this device for clean water generation.

The fabricated AC-P25/foam interfacial system possesses high water productivity, prevention of phenol enrichment and desalination ability in the solar distillation process.

Polymeric Membranes with Selective Solution-Diffusion for Intercepting Volatile Organic Compounds during Solar-Driven Water Remediation

Solar evaporation through a photothermal porous material provides a feasible and sustainable method for water remediation. Several photothermal materials have been developed to enhance solar evaporation efficiency. However, a critical limitation of current photothermal materials is their inability to separate water from the volatile organic compounds (VOCs) present in wastewater. Here, a microstructured ultrathin polymeric membrane that enables freshwater separation from VOC pollutants by solar evaporation with a VOC removal rate of 90%, is reported. The different solution-diffusion behaviors of water and VOCs with polymeric membranes facilitate their separation. Moreover, owing to increased light absorption, enlarged liquid-air interface, and shortened mass transfer distance, the microstructured and ultrathin configuration of the membrane helps to balance the tradeoff between permeation selectivity and water production capacity. The membrane is not only effective for evaporation of simulated volatile pollutants in a prototype, but can also intercept complex volatile organic contaminants in natural water sources and produce water that meets drinking-water standards. With practical demonstration and satisfactory purification performance, this work paves the way for practical application of solar evaporation for effective water remediation.