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

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.

Recent Progress on Solar-Driven Interfacial Evaporation for Resource Recovery and Pollutant Removal

Solar-driven interfacial evaporation (SDIE) has emerged as a transformative technology for clean water generation by localizing solar-thermal energy conversion at the air-liquid interface. Beyond water production, recent advancements reveal its potential as a pivotal platform for addressing the challenges in resource reclamation and environmental sustainability. Drawing inspiration from plant transpiration mechanisms, particularly ion-selective absorption, long-distance transport, and bioactive enrichment, this review systematically examines bioinspired SDIE architectures that synergistically integrate membrane separation, adsorption, and photocatalytic processes. The recent progress is summarized across three tiers: 1) structural biomimetics replicating natural plants, 2) functional hybridization coupling complementary purification mechanisms, and 3) hierarchical integration of multi-process cascades. The review highlights the recent progress in material innovation and structure design to expand its function. Furthermore, implementation frameworks addressing interfacial engineering, process optimization, and system durability are proposed to bridge lab-scale prototypes with practical applications. The future prospects are also outlined for multifunctional SDIE technologies to address water-energy-resource interdependency, advancing their role in sustainable environmental management.

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.

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.

Dynamic defects boost in-situ H2O2 piezocatalysis for water cleanup

Creating efficient catalysts for simultaneous H2O2 generation and pollutant degradation is vital. Piezocatalytic H2O2 synthesis offers a promising alternative to traditional methods but faces challenges like sacrificial reagents, harsh conditions, and low activity. In this study, we introduce a cobalt-loaded ZnO (CZO) piezocatalyst that efficiently generates H2O2 from H2O and O2 under ultrasonic (US) treatment in ambient aqueous conditions. The catalyst demonstrates exceptional performance with ~50.9% TOC removal of phenol and in situ generation of 1.3 mM H2O2, significantly outperforming pure ZnO. Notably, the CZO piezocatalyst maintains its H2O2 generation capability even after multiple cycles, showing continuous improvement (from 1.3 mM to 1.8 mM). This is attributed to the piezoelectric electrons promoting the generation of dynamic defects under US conditions, which in turn promotes the adsorption and activation of oxygen, thereby facilitating efficient H2O2 production, as confirmed by EPR spectrometry, XPS analysis, and DFT calculations. Moreover, the CZO piezocatalysts maintain outstanding performance in pollutant degradation and H2O2 production even after long periods of inactivity, and the deactivated catalyst due to metal ion dissolution could be rejuvenated by pH adjustment, offering a sustainable solution for wastewater purification.

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.

A novel, flexible porous nanofibrous hydrogel interfacial solar evaporator for highly efficient seawater and wastewater purification

Solar desalination is recognized as one of the eco-friendly and sustainable ways to alleviate the global freshwater crisis but still requires further research, especially in developing high-performance evaporators. Herein, we prepared an efficient carbon nanotubes (CNTs)@polyvinyl alcohol (PVA) nanofibrous hydrogel evaporator by electrospinning and subsequently chemical cross-linking treatment. Due to CNTs with good light absorption capacity, the evaporator exhibited an excellent light absorption capacity (>90%) throughout the full spectrum range (250-2500 nm). Meanwhile, the interconnected pores from electrospinning, as well as the intermediate water in the hydrogel, ensured the prepared evaporator with a favorable evaporation rate of up to 2.16 kg m^-2 h^-1 and photothermal conversion efficiency of ∼88.13% under one solar light intensity. For long-term seawater desalination, the CNTs@PVA nanofibrous hydrogel evaporator also presented superior salt resistance, durability and good self-cleaning properties. Besides, various non-volatile pollutants can be completely removed by the prepared evaporator during the wastewater purification. As a result, this work is considered to provide a new direction for developing high-performance evaporators to provide freshwater through seawater desalination and wastewater purification.