A Bioinspired Elastic Hydrogel for Solar-Driven Water Purification

A review of methods for mitigating microplastic contamination in biosolids from wastewater treatment plants before agricultural soil application

Wastewater treatment plants (WWTP) are recognized as major sources of microplastic (MP) particles in terrestrial environments, particularly in agricultural soils through biosolids application. While many reviews have focused on the distribution, detection, and mitigation of MPs in wastewater effluent to limit their discharge into oceans, our understanding of methods to mitigate biosolid contamination remains limited. This review focuses on methods for mitigating MPs contamination in biosolids at various intervention points, including sources, WWTP including the primary and secondary treatment stages where sludge is generated, and post-contamination. These methods are categorized as physical, physicochemical, and biological approaches, and their advantages and limitations are discussed. For instance, physicochemical methods, especially froth flotation, are cost-effective but are hindered by contaminants and reagents. Physical methods like microfibre filtration devices (MFD) are safe but their efficiency depends on the filter pore size and design. Biological methods, particularly microbial degradation, are limited by the varying efficiencies of microorganisms in breaking down MPs and the extended time required for their effective degradation. Other physical methods including dissolved air flotation, and ultrasonication already exist in WWTPs but may require retrofitting or optimization to enhance MP removal from biosolids. As each method inherently has limitations, the key to achieving MP-free biosolids, and thus preventing their release into agricultural soil, lies in integrating these methods through multi-coupling strategies.

Monolith floatable dual-function solar photothermal evaporator: efficient clean water regeneration synergizing with pollutant degradation

Meeting the growing demands of attaining clean water regeneration from wastewater and simultaneous pollutant degradation has been highly sought after. In this study, nanometric CuFe2O4 and plasmonic Cu were in situ confined into graphitic porous carbon nanofibers (CNF) through electrospinning and controlled graphitization, which were integrated onto a melamine sponge (S-FeCu/CNF) as a monolithic evaporator via a calcium ion-triggered network crosslinking method using sodium alginate (SA). This monolithic evaporator serves a dual purpose: harnessing solar-driven photothermal energy for water regeneration and facilitating synchronous contaminant mineralization through advanced oxidation processes (AOPs). The metal-modified FeCu/CNF graphitic porous carbon exhibited an enhanced light absorption property (≥95%) and was further securely anchored on the sponge by a calcium ion-triggered SA crosslinking technique, thereby efficiently restraining salt deposition. The FeCu/CNF evaporator demonstrated a solar-vapor conversion efficiency of 105.85% with an evaporation rate of 1.61 kg m-2 h-1 under one sun irradiation. The evaporation rate of the monolithic S-FeCu/CNF evaporator is close to 1.76 kg m-2 h-1, and an evaporation rate of 1.54 kg m-2 h-1 can be achieved even in 20% NaCl solution, with resistance to salt deposition and cycling stability. Synchronously, the monolithic D-S-FeCu/CNF evaporator also acts as a heterogeneous catalyst to activate peroxymonosulfate (PMS) and trigger rapid pollutant degradation, which also shows excellent catalytic cycling stability, producing clean water that satisfies the World Health Organization (WHO) standards. This work provides a potentially valuable solution for addressing desalination and wastewater treatment.

3D-printed controllable bio-accelerators with sustained release property to boost chromium (VI) inhibited denitrification recovery

Although soluble bio-accelerators have proven effective in mitigating Cr(VI) inhibition within denitrification system, issues persist in immobilizing bio-accelerators and making them slow-release for sustained regulation. In this study, a novel strategy was proposed to fabricate immobilized bio-accelerators with controlled structure, sustained release property by 3D printing technology. Notably, the sustained release of bio-accelerators from 3D-printed bio-accelerators (3DP-B) lasted for at least 144 h. Compared to control group, 3DP-B with basic components (3DP-BB) shortened the recovery time by 1.4 folds, and the COD and NO3--N removal efficiency was 36.5 % and 38.0 % higher than that of natural recovery. Correspondingly, the activity of key enzymes (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), electron transfer system activity and extracellular polymer substances of denitrification biofilm maintained at relatively high levels. Furthermore, introducing 60 mg·L-1 anthraquinone-2,6-disulfonate (AQDS) into the ink showed noticeable superiority on the bio-inhibition release over 1000 mg·L-1 AQDS. The released AQDS facilitated the electron transport capacity by 1.25 times compared with control group. The groundbreaking findings of this study could advance the development of 3D printing technology and utilization of bio-accelerators in the field of wastewater treatment.

Facile Formation of Multifunctional Biomimetic Hydrogel Fibers for Sensing Applications

To face the challenges in preparing hydrogel fibers with complex structures and functions, this study utilized a microfluidic coaxial co-extrusion technique to successfully form functional hydrogel fibers through rapid ionic crosslinking. Functional hydrogel fibers with complex structures, including linear fibers, core-shell structure fibers, embedded helical channels, hollow tubes, and necklaces, were generated by adjusting the composition of internal and external phases. The characteristic parameters of the hydrogel fibers (inner and outer diameter, helix generation position, pitch, etc.) were achieved by adjusting the flow rate of the internal and external phases. As biocompatible materials, hydrogel fibers were endowed with electrical conductivity, temperature sensitivity, mechanical enhancement, and freeze resistance, allowing for their use as temperature sensors for human respiratory monitoring and other biomimetic application developments. The hydrogel fibers had a conductivity of up to 22.71 S/m, a response time to respiration of 37 ms, a recovery time of 1.956 s, and could improve the strength of respiration; the tensile strength at break up to 8.081 MPa, elongation at break up to 159%, and temperature coefficient of resistance (TCR) up to -13.080% °C-1 were better than the existing related research.

Self-Adhesive, Stretchable, and Thermosensitive Iontronic Hydrogels for Highly Sensitive Neuromorphic Sensing-Synaptic Systems

Artificial sensory afferent nerves that emulate receptor nanochannel perception and synaptic ionic information processing in chemical environments are highly desirable for bioelectronics. However, challenges persist in achieving life-like nanoscale conformal contact, agile multimodal sensing response, and synaptic feedback with ions. Here, a precisely tuned phase transition poly(N-isopropylacrylamide) (PNIPAM) hydrogel is introduced through the water molecule reservoir strategy. The resulting hydrogel with strongly cross-linked networks exhibits excellent mechanical performance (∼2000% elongation) and robust adhesive strength. Importantly, the hydrogel's enhanced ionic conductance and heterogeneous structure of the temperature-sensitive component enable highly sensitive strain information perception (GFmax = 7.94, response time ∼ 87 ms), temperature information perception (TCRmax = -1.974%/°C, response time ∼ 270 ms), and low energy consumption synaptic plasticity (42.2 fJ/spike). As a demonstration, a neuromorphic sensing-synaptic system is constructed integrating iontronic strain/temperature sensors with fiber synapses for real-time information sensing, discrimination, and feedback. This work holds enormous potential in bioinspired robotics and bioelectronics.

Natural-inspired hierarchic double-Janus solar evaporator for stable clean water production from high-salinity emulsions

Interfacial solar evaporation shows great potential in clean water production, emulsions separation, and high-salinity brine treatment. However, it remains challenging for the evaporators to maintain a high evaporation rate in the high-salinity emulsions due to the co-pollution of salt and oil. Herein, we first proposed a hierarchic double-Janus solar evaporator (HDJE) with a hydrophobic salt-rejecting top layer and oil-rejecting bottom layer. Compared to the traditional one, HDJE could treat industrial high-salinity oil-in-water emulsions stably for over 70 h, with a stable average evaporation rate of 1.73 kg m-2 h-1 and a high purification efficiency of up to 99.8 % for oil and ions. It was also verified that HDJE could be used for high-efficiency purification of oily concentrated seawater outdoor. An average water production rate of 3.59 kg m-2 d-1 and a TOC removal ratio of over 98 % was obtained. In conclusion, this study provides a novel way to effectively dispose of high-salinity oily wastewater.

Rapid Preparation Triggered by Visible Light for Tough Hydrogel Sensors with Low Hysteresis and High Elasticity: Mechanism, Use and Recycle-by-Design

Hydrogels have emerged as promising candidates for flexible devices and water resource management. However, further applications of conventional hydrogels are restricted due to their limited performance and lack of a recycling strategy. Herein, a tough, flexible, and recyclable hydrogel sensor via a visible-light-triggered polymerization is rapidly created. The Zn2+ crosslinked terpolymer is in situ polymerized using g-C3N4 as the sole initiator to form in situ chain entanglements, endowing the hydrogels with low hysteresis and high elasticity. In the use phase, the hydrogel sensor exhibited high ion conductivity, excellent mechanical properties, fast responsiveness, high sensitivity, and remarkable anti-fatigue ability, making it exceptionally effective in accurately monitoring complex human movements. At the end-of-life (EOL), leveraging the synergy between the photodegradation capacity of g-C3N4 and the adsorption function of the hydrogel matrix, the post-consumer hydrogel is converted into water remediation materials, which not only promoted the rapid degradation of organic pollutants, but also facilitated collection and reuse. This innovative strategy combined in situ entangling reinforcement and tailored recycle-by-design that employed g-C3N4 as key blocks in the hydrogel to achieve high performance in the use phase and close the loop through the reutilization at EOL, highlighting the cost-effective synthesis, specialized structure, and life cycle management.

KOH Activated Carbon Coated 3D Wood Solar Evaporator with Highest Water Transport Height and Evaporation Rate for Clean Water Production

The water evaporation rate of 3D solar evaporator heavily relies on the water transport height of the evaporator. In this work, a 3D solar evaporator featuring a soil capillary-like structure is designed by surface coating native balsa wood using potassium hydroxide activated carbon (KAC). This KAC-coated wood evaporator can transport water up to 32 cm, surpassing that of native wood by ≈8 times. Moreover, under 1 kW m-2 solar radiation without wind, the KAC-coated wood evaporator exhibits a remarkable water evaporation rate of 25.3 kg m-2 h-1, ranking among the highest compared with other reported evaporators. The exceptional water transport capabilities of the KAC-coated wood should be attributed to the black and hydrophilic KAC film, which creates a porous network resembling a soil capillary structure to facilitate efficient water transport. In the porous network of coated KAC film, the small internal pores play a pivotal role in achieving rapid capillary condensation, while the larger interstitial channels store condensed water, further promoting water transport up more and micropore capillary condensation. Moreover, this innovative design demonstrates efficacy in retarding phenol from wastewater through absorption onto the coated KAC film, thus presenting a new avenue for high-efficiency clean water production.

Recent Advances of Bio-Based Hydrogel Derived Interfacial Evaporator for Sustainable Water and Collaborative Energy Storage Applications

Solar interfacial evaporation strategy (SIES) has shown great potential to deal with water scarcity and energy crisis. Biobased hydrogel derived interfacial evaporator can realize efficient evaporation due to the unique structure- properties relationship. As such, increasing studies have focused on water treatment or even potential accompanying advanced energy storage applications with respect of efficiency and mechanism of bio-based hydrogel derived interfacial evaporation from microscale to molecular scale. In this review, the interrelationship between efficient interfacial evaporator and bio-based hydrogel is first presented. Then, special attention is paid on the inherent molecular characteristics of the biopolymer related to the up-to-date studies of promising biopolymers derived interfacial evaporator with the objective to showcase the unique superiority of biopolymer. In addition, the applications of the bio-based hydrogels are highlighted concerning the aspects including water desalination, water decontamination atmospheric water harvesting, energy storage and conversion. Finally, the challenges and future perspectives are given to unveil the bottleneck of the biobased hydrogel derived SIES in sustainable water and other energy storage applications.

Versatile GO/ANFs Aerogel for Highly Efficient Solar-Powered Water Purification in Wide Environments

Solar-driven interfacial evaporation is a very promising choice for producing clean water. Despite the considerable investigation of pure NaCl brine purification, solar-driven complex water purification, such as real-world seawater desalination as well as domestic and industrial wastewater treatment, has rarely been investigated, mainly due to its compositions being much more complicated than NaCl brine. Herein, we developed a graphene oxide/aramid nanofiber (GO/ANFs) aerogel by a freeze-drying process. The GO/ANFs aerogel combined opened porous microchannels, superhydrophilicity, anti-oil-fouling capacity, enhanced broad-spectrum light absorption (more than 92%), and good solar/heat management. These integrated properties enabled the GO/ANFs aerogel to be an advanced solar interfacial evaporator for efficient freshwater production with the characteristics of localized heat conversion, quick water transport, and salt crystallization inhibition, and the rate of steam production rate was as high as 2.25 kg m-2 h-1 upon exposure to 1 solar irradiation. Importantly, the high-water-vapor generation rate was maintained even under complicated conditions, including real-world seawater, dye water, emulsions, and corrosive liquid environments. Considering its promising adaptability to a wide range of environments, this work hopes to inspire the development of brine desalination, wastewater purification, clean water production, and solar energy utilization.

Nanocellulose-mediated conductive hydrogels with NIR photoresponse and fatigue resistance for multifunctional wearable sensors

The rapid development of hydrogels has garnered significant attention in health monitoring and human motion sensing. However, the synthesis of multifunctional conductive hydrogels with excellent strain/pressure sensing and photoresponsiveness remains a challenge. Herein, the conductive hydrogels (BPTP) with excellent mechanical properties, fatigue resistance and photoresponsive behavior composed of polyacrylamide (PAM) matrix, 2,2,6,6-tetramethylpiperidin-1-yloxy-oxidized cellulose nanofibers (TOCNs) reinforcement and polydopamine-modified black phosphorus (BP@PDA) photosensitizer are prepared through a facile free-radical polymerization approach. The PDA adhered to the BP surface by π-π stacking promotes the optical properties of BP while also preventing BP oxidation from water. Through hydrogen bonding interactions, TOCNs improve the homogeneous dispersion of BP@PDA nanosheets and the mechanical toughness of BPTP. Benefiting from the synergistic effect of PDA and TOCNs, the conductive BPTP integrates superior mechanical performances, excellent photoelectric response and photothermal conversion capability. The BPTP-based sensor with high cycling stability demonstrates superior strain sensitivity (GF = 6.0) and pressure sensing capability (S = 0.13 kPa-1) to monitor various human activities. Therefore, this work delivers an alternative construction strategy for generating high-performance conductive hydrogels as multifunctional wearable sensors.

An eco-friendly versatile superabsorbent hydrogel based on sodium alginate and urea for soil improvement with a synchronous chemical loading strategy

In this paper, an eco-friendly versatile superabsorbent material was designed for soil improvement, and a synchronous chemical loading strategy was proposed. In this strategy, urea not only acted as fertilizer but also acted as a crosslinker to construct an alginate network. The microstructure, chemical structure, thermal stability and composition of the obtained SA/urea hydrogel were characterized in detail. Adsorption behavior and application performance in agriculture were evaluated. The results demonstrated that urea had two different conformations in the network. The SA/urea hydrogel had abundant pore structures with excellent water absorption performance. It could not only improve the water retention capacity of soil but also release nitrogen, phosphorus and potassium elements with degradation for as long as 9 weeks. Moreover, the hydrogel could promote plant growth, increase the nutritional composition of plants and inhibit the accumulation of harmful nitrate in plants. With advantages, including biodegradability, high water absorption, controllable degradation, excellent water retention, sustained NPK release and improved plant nutrition value, the SA/urea hydrogel has great potential for soil improvement in agriculture as an eco-friendly versatile water retention agent and can be expected to extend to more fields as a novel superabsorbent material.

Hydrophobic Carbon Nitride Nanolayer Enables High-Flux Oil/Water Separation with Photocatalytic Antifouling Ability

Efficient oil/water separation tackles various issues in occasions of oil leakage and oil discharge, such as environmental pollution, recollection of the oil, and saving the water. Herein, a compact superhydrophobic/superoleophilic graphitic carbon nitride nanolayer coated on carbon fiber networks (CNBA/CF) is designed and synthesized for efficient gravity-driven oil/water separation. The CNBA/CF shows excellent oil absorption and an impressive oil/water filtration separation performance. The flux reaches the state-of-art value of 4.29 × 105 L/m2/h for dichloromethane with separation efficiency up to 99%. Successive oil absorption tests, long-term filtration separation, and harsh conditions experiments confirm the remarkable separation and chemical structure stability of the CNBA/CF filter. Besides, the CNBA/CF demonstrates good photocatalytic antifouling ability thanks to the extended visible light absorption and improved charge separation. This work combines the material surface wettability modulation with a photocatalytic self-cleaning property in the fabrication of efficient oil/water separation materials while overcoming the filter fouling issue.

Efficient Atmospheric Water Harvesting of Superhydrophilic Photothermic Nanocapsule

Drought and water scarcity are two of the world's major problems. Solar-powered sorption-based atmospheric water harvesting technology is a promising solution in this category. The main challenge is to design materials with high water harvesting performance while achieving fast water vapor adsorption/desorption rates. Here, a superhydrophilic photothermic hollow nanocapsule (SPHN) is represented that achieves efficient atmospheric water harvesting in outdoor climates. In SPHN, the hollow mesoporous silica (HMS) is grafted with polypyrrole (PPy) and also loaded with lithium chloride (LiCl). The hollow structure is used to store water while preventing leakage. The hydrophilic spherical nanocapsule and the trapped water produce more free and weakly adsorbed water. Significantly lower the heat of desorption compared to pure LiCl solution. Such SPHN significantly improves the adsorption/desorption kinetics, e.g., absorbs 0.78-2.01 g of water per gram of SPHN at 25 °C, relative humidity (RH) 30-80% within 3 h. In particular, SPHN has excellent photothermal properties to achieve rapid water release under natural sunlight conditions, i.e., 80-90% of water is released in 1 h at 0.7-1.0 kW m-2 solar irradiation, and 50% of water is released even at solar irradiation as low as 0.4 kW m-2 . The water collection capacity can reach 1.2 g g-1 per cycle by using the self-made atmospheric water harvesting (AWH) device. This finding provides a way to design novel materials for efficient water harvesting tasks, e.g., water engineering, freshwater generator, etc.

Advances in photothermal regulation strategies: from efficient solar heating to daytime passive cooling

Photothermal regulation concerning solar harvesting and repelling has recently attracted significant interest due to the fast-growing research focus in the areas of solar heating for evaporation, photocatalysis, motion, and electricity generation, as well as passive cooling for cooling textiles and smart buildings. The parallel development of photothermal regulation strategies through both material and system designs has further improved the overall solar utilization efficiency for heating/cooling. In this review, we will review the latest progress in photothermal regulation, including solar heating and passive cooling, and their manipulating strategies. The underlying mechanisms and criteria of highly efficient photothermal regulation in terms of optical absorption/reflection, thermal conversion, transfer, and emission properties corresponding to the extensive catalog of nanostructured materials are discussed. The rational material and structural designs with spectral selectivity for improving the photothermal regulation performance are then highlighted. We finally present the recent significant developments of applications of photothermal regulation in clean energy and environmental areas and give a brief perspective on the current challenges and future development of controlled solar energy utilization.

Unusual Temperature Dependence of Water Sorption in Semicrystalline Hydrogels

Water vapor sorption is a ubiquitous phenomenon in nature and plays an important role in various applications, including humidity regulation, energy storage, thermal management, and water harvesting. In particular, capturing moisture at elevated temperatures is highly desirable to prevent dehydration and to enlarge the tunability of water uptake. However, owing to the thermodynamic limit of conventional materials, sorbents inevitably tend to capture less water vapor at higher temperatures, impeding their broad applications. Here, an inverse temperature dependence of water sorption in poly(ethylene glycol) (PEG) hydrogels, where their water uptake can be doubled with increasing temperature from 25 to 50 °C, is reported. With mechanistic modeling of water-polymer interactions, this unusual water sorption is attributed to the first-order phase transformation of PEG structures, and the key parameters for a more generalized strategy in materials development are identified. This work elucidates a new regime of water sorption with an unusual temperature dependence, enabling a promising engineering space for harnessing moisture and heat.

A melanin-inspired robust aerogel for multifunctional water remediation

Solar-driven vapor generation has emerged as a promising wastewater remediation technology for clean water production. However, the complicated and diversified contaminants in wastewater still restrict its practical applications. Herein, inspired by the melanin in nature, a robust aerogel was facilely fabricated for multifunctional water remediation via a one-pot condensation copolymerization of 5,6-dihydroxyindole and formaldehyde. Benefiting from the superhydrophilicity, underwater superoleophobicity, and synergistic coordination effects, the resulting aerogel not only showed excellent performances in underwater oil resistance and oil-water separation ability, but also removed organic dyes and heavy metal ions contaminants in wastewater simultaneously. Moreover, owing to its admirable light harvesting capacity and porous microstructure for fast water transportation, the aerogel-based evaporator exhibited an excellent evaporation rate of 1.42 kg m^-2 h^-1 with a 91% evaporation efficiency under 1 sun illumination, which can be reused for long-term water evaporation. Note that such a stable evaporation rate could be maintained even in wastewater containing complex multicomponent contaminants. Outdoor evaporation experiments for lotus pond wastewater under natural sunlight also proved its great potential in practical applications. All those promising features of this all-in-one melanin-inspired aerogel may provide new strategies for the development of robust photothermal devices for multifunctional solar-driven water remediation.

Quick-Release Antifouling Hydrogels for Solar-Driven Water Purification

Hydrogels are promising soft materials for energy and environmental applications, including sustainable and off-grid water purification and harvesting. A current impediment to technology translation is the low water production rate well below daily human demand. To overcome this challenge, we designed a rapid-response, antifouling, loofah-inspired solar absorber gel (LSAG) capable of producing potable water from various contaminated sources at a rate of ∼26 kg m^-2 h^-1, which is sufficient to meet daily water demand. The LSAG-produced at room temperature via aqueous processing using an ethylene glycol (EG)-water mixture-uniquely integrates the attributes of poly(N-isopropylacrylamide) (PNIPAm), polydopamine (PDA), and poly(sulfobetaine methacrylate) (PSBMA) to enable off-grid water purification with enhanced photothermal response and the capacity to prevent oil fouling and biofouling. The use of the EG-water mixture was critical to forming the loofah-like structure with enhanced water transport. Remarkably, under sunlight irradiations of 1 and 0.5 sun, the LSAG required only 10 and 20 min to release ∼70% of its stored liquid water, respectively. Equally important, we demonstrate the ability of LSAG to purify water from various harmful sources, including those containing small molecules, oils, metals, and microplastics.

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.

Gradient hydrogel actuator with fast response and self-recovery in air

The driving principle of a thermal-responsive hydrogel that loses water at high temperature and absorbs water at low temperature limits its application in an aqueous environment. Here, a gradient hydrogel actuator was developed by introducing sodium hyaluronate into poly(N-isopropylacrylamide) hydrogel by an asymmetric mold method. The hydrogel exhibited a fast response above the LCST in air and unusual self-recovery without the need for further temperature stimuli. The actuation behavior was related to conversion from free water to bound water and water retention within the gradient matrix. The self-recovery mechanism was explored. This work provides a new insight into designing bionic hydrogels applied in a non-aqueous environment.

A bioinspired antibacterial and photothermal membrane for stable and durable clean water remediation

Solar-driven steam generation has been considered as a prevalent and sustainable approach to obtain clean fresh water. However, the presence of microorganisms in seawater may cause the biofouling and degradation of polymeric photothermal materials and clog the channels for water transportation, leading to a decrease in solar evaporation efficiency during long-term usage. Herein, we have reported a facile strategy to construct a robust cellulose membrane device coated by tobramycin-doped polydopamine nanoparticles (PDA/TOB@CA). The PDA/TOB@CA membrane not only exhibited synergistic antibacterial behaviors with long-term and sustained antibiotic release profiles, but also achieved a high water evaporation rate of 1.61 kg m^-2 h^-1 as well as an evaporation efficiency of >90%. More importantly, the high antibacterial activity endowed the PDA/TOB@CA membrane with superb durability for stable reuse over 20 cycles, even in microbe-rich environments. Therefore, we envision that this study could pave a new pathway towards the design and fabrication of robust antibacterial and photothermal materials for long-term and stable clean water production.

Amphiphilic sodium alginate-polylysine hydrogel with high antibacterial efficiency in a wide pH range

Bacterial infection is a major pathological factor leading to persistent wounds. With the aging of population, wound infection has gradually become a global health-issue. The wound site environment is complicated, and the pH changes dynamically during healing. Therefore, there is an urgent need for new antibacterial materials that can adapt to a wide pH range. To achieve this goal, we developed a thymol-oligomeric tannic acid/amphiphilic sodium alginate-polylysine hydrogel film, which exhibited excellent antibacterial efficacy in the pH range from 4 to 9, achieving the highest achievable 99.993 % (4.2 log units) and 99.62 % (2.4 log units) against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, respectively. The hydrogel films exhibited excellent cytocompatibility, suggesting that the materials are promising as a novel wound healing material without the concern of biosafety.

Bacteria-Activated Dual pH- and Temperature-Responsive Hydrogel for Targeted Elimination of Infection and Improved Wound Healing

Antibacterial treatment that provides on-demand release of therapeutics that can kill a broad spectrum of pathogens while maintaining long-term efficacy and without developing resistance or causing side effects is urgently required in clinical practice. Here, we demonstrate the development of a multistimuli-responsive hydrogel, prepared by cross-linking N-isopropylacrylamide with acrylic acid and loaded with ultrasmall silver nanoparticles (AgNPs), offering the on-demand release of Ag⁺ ions triggered by changes in the wound microenvironment. We demonstrate that this dual-responsive hydrogel is highly sensitive to a typical wound pH and temperature change, evidenced by the restricted release of Ag⁺ ions at acidic pH (<5.5) while significantly promoting the release in alkaline pH (>7.4) (>90% release). The pH-dependent release and antibacterial effect show minimal killing at pH 4 or 5.5 but dramatically activated at pH 7.4 and 10, eliminating >95% of the pathogens. The in vivo antibacterial efficacy and safety showed a high potency to clear Staphylococcus aureus wound infection while significantly accelerating the wound healing rate. This multifunctional hydrogel presents a promising bacteria-responsive delivery platform that serves as an on-demand carrier to not only reduce side effects but also significantly boost the antibacterial efficiency based on physiological needs. It offers great potential to improve the way wound infections are treated with direct clinical implications, providing a single platform for long-lasting application in wound management.

Self-Propelled Structural Color Cylindrical Micromotors for Heavy Metal Ions Adsorption and Screening

Water contamination resulting from heavy metal ions (HMIs) poses a severe threat to public health and the ecosystem. Attempts are tending to develop functional materials to realize efficient and intelligent adsorption of HMIs. Herein, self-propelled structural color cylindrical micromotors (SCCMs) with reversible HMIs adsorption capacity and self-reporting property are presented. The SCCMs are fabricated by using platinum nanoparticles (Pt NPs) tagged responsive hydrogel of carboxymethyl chitosan (CMC) and polyacrylamide (PAM) to asymmetrically replicate tubular colloidal crystal templates (TCCTs). Owing to the self-propelled motion of the SCCMs, the enhancive ion-motor interactions bring significantly improved decontamination efficiency. Moreover, it is demonstrated that the SCCMs can realize quick and naked-eye-visible self-reporting during the adsorption/desorption process based on their responsive structure color variation and superior adsorption capacity. Thus, it is anticipated that such intelligent SCCMs can significantly facilitate the evolution of sensing assays and diverse environmental fields.

Topographical Design and Thermal-Induced Organization of Interfacial Water Structure to Regulate the Wetting State of Surfaces

Smart surfaces with superhydrophobic/superhydrophilic characteristics can be controlled by external stimuli, such as temperature. These transitions are attributed to the molecular-level conformation of the grafted polymer chains due to the varied interactions at the interface. Here, tunable surfaces were prepared by grafting two well-known thermo-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(oligoethylene glycol)methyl ether acrylate (POEGMA₁₈₈) onto micro-pollen particles of uniform morphology and roughness. Direct Raman spectra and thermodynamic analyses revealed that above the lower critical solution temperature, the bonded and free water at the interface partially transformed to intermediate water that disrupted the "water cage" surrounding the hydrophobic groups. The increased amounts of intermediate water produced hydrogen bonding networks that were less ordered around the polymer grafted microparticles, inducing a weaker binding interaction at the interface and a lower tendency to wet the surface. Combining the roughness factor, the bulk surface assembled by distinct polymer-grafted-pollen microparticles (PNIPAM or POEGMA₁₈₈) could undergo a different wettability transition for liquid under air, water, and oil. This work identifies new perspectives on the interfacial water structure variation at a multiple length scale, which contributed to the temperature-dependent surface wettability transition. It offers inspiration for the application of thermo-responsive surface to liquid-gated multiphase separation, water purification and harvesting, biomedical devices, and printing.

Swelling Behaviour of Polystyrene Microsphere Enhanced PEG-Based Hydrogels in Seawater and Evolution Mechanism of Their Three-Dimensional Network Microstructure

To understand the microstructure evolution of hydrogels swollen in seawater, freeze-drying technology was used to fix and preserve the swollen three-dimensional microstructure. By this method, we revealed the swelling behavior of hydrogels in seawater, and elucidated the mechanism of the swelling process. Meanwhile, we also used Fourier-transform infrared spectroscopy; laser confocal microscopy; field emission scanning electron microscopy, and swelling performance tests to research the structure and properties of PS-PEG hydrogels, before and after seawater swelling, and analyzed the structure and properties of PEG-based hydrogels with different contents of polystyrene microspheres. Results showed that PS-PEG hydrogels went through three stages during the swelling process, namely ‘wetting-rapid swelling-swelling equilibrium’. Due to the capillary effect and hydration effect, the surface area would initially grow tiny pores, and enter the interior in a free penetration manner. Finally, it formed a stable structure, and this process varied with different content of polystyrene microspheres. In addition, with the increase of polystyrene microsphere content, the roughness of the hydrogel before swelling would increase, but decrease after swelling. Appropriate acquisition of polystyrene microspheres could enhance the three-dimensional network structure of PEG-based hydrogels, with a lower swelling degree than hydrogels without polystyrene microspheres.

Hierarchical Natural Pollen Cell-Derived Composite Sorbents for Efficient Atmospheric Water Harvesting

Freshwater scarcity is a critical challenge threatening human survival especially due to poverty and arid and off-grid regions. Sorption-based atmospheric water harvesting (AWH) has emerged as a promising strategy for clean water production. However, most of the high-capacity sorbents are limited by the poor sorption/desorption kinetics and uncontrollable liquid leakage problem. Inspired by the plant transpiration process, we develop an environmentally friendly LiCl@pollen cell-polypyrrole (LiCl@PC-PPy) composite sorbent by confining the LiCl hygroscopic agent in the cages of the PC-PPy. The composite sorbent exhibits much improved sorption/desorption kinetics owing to the hydrophilicity of the hierarchical porous structure of the pollen cells, which provides abundant water sorption active sites and diffusion pathways and forms a concave meniscus on cell skeletons to maximize the thermal utilization efficiency. Moreover, the big cavities of the PC-PPy cages can serve as a water reservoir to reduce liquid leakage. As a result, the sorbent can capture atmospheric water to 85% of its own weight under 60% relative humidity (RH) within 2 h and rapidly release the water within 1 h under weak light irradiation of 0.8 sun. As a proof-of-concept demonstration, the fabricated AWH device can absorb 1.55 gwater/gsorbent at night and collect 1.53 gwater/gsorbent of water in 1-day outdoor operation, and the collected water can meet the drinking water standards defined by the World Health Organization (WHO) and Environmental Protection Agency (EPA).

Adhesion behaviors of water droplets on bioinspired superhydrophobic surfaces

The adhesion behaviors of droplets on surfaces are attracting increasing attention due to their various applications. Many bioinspired superhydrophobic surfaces with different adhesion states have been constructed in order to mimic the functions of natural surfaces such as a lotus leaf, a rose petal, butterfly wings, etc. In this review, we first present a brief introduction to the fundamental theories of the adhesion behaviors of droplets on various surfaces, including low adhesion, high adhesion and anisotropic adhesion states. Then, different techniques to characterize droplet adhesion on these surfaces, including the rotating disk technique, the atomic force microscope cantilever technique, and capillary sensor-based techniques, are described. Wetting behaviors, and the switching between different adhesion states on bioinspired surfaces, are also summarized and discussed. Subsequently, the diverse applications of bioinspired surfaces, including water collection, liquid transport, drag reduction, and oil/water separation, are discussed. Finally, the challenges of using liquid adhesion behaviors on various surfaces, and future applications of these surfaces, are discussed.

Dual-Layer Multichannel Hydrogel Evaporator with High Salt Resistance and a Hemispherical Structure toward Water Desalination and Purification

Interfacial solar steam generation technology has been considered as one of the most promising methods for seawater desalination. However, in practical applications, salt precipitation on the evaporation surface reduces the evaporation rate and impairs long-term stability. Herein, a dual-layer hydrogel-based evaporator that contains a microchannel-structured water-supplying layer and a nanoporous light-absorbing layer was synthesized via sol-gel transition and "hot-ice" template methods. Contributed by the designed structure-induced accelerated salt ion exchange, the hemispherical dual-layer hydrogel evaporator showed excellent salt formation resistance property, as well as a high evaporation rate reaching 2.03 kg m^-2 h^-1 even under high brine concentration conditions. Furthermore, the hydrogel-based evaporator also demonstrated excellent ion rejection, high/low pH tolerance, and excellent purification properties toward heavy metals and organic dyes. It is believed that this type of dual-layer multichannel evaporator is promising to be used in seawater desalination, water pollution treatment, and other environmental remediation-related applications.

Ultrafast Solar-Vapor Harvesting Based on a Hierarchical Porous Hydrogel with Wettability Contrast and Tailored Water States

Optimizing the water bonding network in an evaporator is significant for efficient solar-driven vapor generation (SVG). Herein, we report a facile one-pot method to regulate the hydrated structure and wettability in a hierarchical porous hydrogel. An ovalbumin (OVA)-polyacrylamide hydrogel foam was fabricated in a cake-making fashion. Because of the enrichment of amphiphilic OVA at the interface, the hydrophobic walls of the air pores in the foam provide vaporization sites and help reduce parasitic heat loss, while the hydrophilic skeleton with the secondary pores effectively pumps capillary water. Notably, the proportion of intermediate water in the foam reaches 87.6% with the melting point as low as -10 °C. All these features contribute to an exceptional evaporation rate of 3.4-4.5 kg m^-2 h^-1 under 1 sun and robust SVG performances at high-humidity, weak sunlight, or cold weathers. The strategy of using amphiphilic molecules to optimize the hydrated structures both at the interface and in bulk promises the reasonable design of SVG materials with superior efficiency and weather adaptability.

Design of asymmetric-adhesion lignin-reinforced hydrogels based on disulfide bond crosslinking for strain sensing application

Soft and elastic polymer hydrogel materials are booming in the fields of wearable biomimetic skin, sensors, robotics, and bioelectrodes. Currently, many researchers are exploring new chemistries for the preparation of hydrogels to improve their performance. In the present study, we design and develop a strategy to prepare lignin reinforced hydrogels based on disulfide bond crosslinking mechanisms, and resultant hydrogels exhibit excellent stretchability, with tensile strain of up to 1085.4%, and high adhesion (with the highest T-peel strength of up to 432.2 N/m to pigskin). The underlying mechanism is based on the disulfide bonds that act as crosslinkers in the as-prepared hydrogel, and they can be easily cleaved and re-formed under mild conditions. Thanks to the presence of lignin, the as-obtained hydrogels also have excellent UV shielding effect. When assembled into a strain sensor, they can output stable and sensitive sensing signals, with gauge factor (GF) of 2.72 (strain: 0-72.8%). Furthermore, a simple and effective strategy to construct asymmetric adhesive hydrogels was adopted, which is based on directional soaking of the top portion of the hydrogel in a high-concentrated calcium chloride solution. The asymmetric hydrogel strain sensor transmits accurate and stable signals without the interference of various contaminants.

Nature-Inspired Polyethylenimine-Modified Calcium Alginate Blended Waterborne Polyurethane Graded Functional Materials for Multiple Water Purification

In recent years, natural disasters such as hurricanes and floods have become more frequent, which usually leads to the pollution of drinking water. Drinking contaminated water may cause public health emergencies. The demand for healthy drinking water in disaster-affected areas is huge and urgent. Therefore, it is necessary to develop a simple water treatment technology suitable for emergencies. Inspired by nature, a fractional spray method was used to prepare graded purification material under mild conditions. The material consists of a calcium alginate isolation layer and a functional layer composed of calcium alginate, polyethylenimine, and water-based polyurethane, which can purify complex pollutants in water such as heavy metals, oils, pathogens, and micro/nano plastics through percolation. It does not require additional energy and can purify polluted water only under gravity. A disposable paper cup model was also designed, which can be used to obtain purified water by immersing in polluted water directly without other filtering devices. The test report shows that the water obtained from the paper cup was deeply purified. This design makes the material user-friendly and has the potential as a strategic material. This discovery can effectively improve the safety of drinking water after disasters and improve people's quality of life.

Swelling and glyphosate-controlled release behavior of multi-responsive alginate-g-P(NIPAm-co-NDEAm)-based hydrogel

Intelligent controlled release systems (ICRS) displayed great achievement in agriculture by enhancing the utilization efficiency of agrochemicals. In this work, an intelligent graft copolymer (Alg-g-P(NIPAm-co-NDEAm)) with alginate (Alg) backbone and thermo-responsive poly(N-isopropyl acrylamide-co-N,N-diethylacrylamide) (P(NIPAm-co-NDEAm)) side chain was constructed as the matrix of ICRS through redox copolymerization, and its thermo-induced responsive property was studied. Then, the copolymer was mixed with a promising photothermal material semi-coke (SC) to form hydrogel beads (Ca-Alg-g-P(NIPAm-co-NDEAm)/SC) by ion crosslinking. The water absorbency of beads under different stimuli (pH, temperature, and light) presented outstanding responsive performance and the swelling mechanism was analyzed through coupling theory. Furthermore, the release of glyphosate (Gly) from Ca-Alg-g-P(NIPAm-co-NDEAm)/SC under environmental stimuli displayed regulatable behaviors. This multi-responsive hydrogel bead shows bright prospect in the sustainable advancement of crop production.

Chemical treatment of biomasswastes as carbon dot carriers for solar-driven water purification

A purely chemical method is demonstrated to treat a variety of biomass wastes for extracting cellulose nanofibrils (CNFs) with a consistent property. By hydrothermal reaction, carbon dots (CDs) can be easily grafted on the surface of CNFs to act as photo-thermal agents and enable fast water evaporation rate at 2.5 kg m^-2h^-1 with about 96.45% solar-to-vapor efficiency under one sun irradiation. This derives from good hydration ability of this system, which lowers the evaporation enthalpy. Moreover, this system not only adsorbs dye contaminants effectively by the formation of hydrogen bonds, but also possesses long-term antifouling solar desalination by means of rationally drilled millimeter-sized channels. Given the sustainable biomass resources and scalable fabrication process, this work offers a promising strategy towards construct low-cost evaporators with the excellent water purification performance.

Developing Flexible Quinacridone-Derivatives-Based Photothermal Evaporaters for Solar Steam and Thermoelectric Power Generation

Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air-water interface has attracted tremendous attention. In the process of converting solar energy into heat energy, photothermal materials play an essential role. Herein, a flexible solar-thermal material di-cyan substituted 5,12-dibutylquinacridone (DCN-4CQA)@Paper was developed by coating photothermal quinacridone derivatives on the cellulose paper. The DCN-4CQA@Paper combines desired chemical and physical properties, broadband light-absorbing, and shape-conforming abilities that render efficient photothermic vaporization. Notably, synergetic coupling of solar-steam and solar-electricity technologies by integrating DCN-4CQA@Paper and the thermoelectric devices is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas.

Biomimetic Design of Macroporous 3D Truss Materials for Efficient Interfacial Solar Steam Generation

Interfacial solar steam generation (ISSG) utilizing local heating technology for evaporation at the water-to-steam interface is drawing great attention because of its high efficiency of solar-thermal conversion for a sustainable and eco-friendly drinking water regeneration process. Here, inspired by the structure of penguin feathers and polar bear hairs that both have macropores to trap air for thermal insulation, we report a bionic solar evaporator (BSE) with macroporous skeleton for partial thermal management and macro patulous channels for abundant water transportation and rapid steam extraction. Meanwhile, the 3D hierarchical isotropic truss structures can induce multiple light reflections to enable omnidirectional light absorption, and bimodal pores facilitate ion diffusion to suppress salt deposits. This BSE exhibits an evaporation rate of 2.3 kg m^-2 h^-1 and efficiency of 93% under 1 sun. The multiple advantages of high efficiency and salt resistance make BSE available for future practical sewage purification and desalination applications.

Recent innovations in solar energy education and research towards sustainable energy development

The essential requirements of our everyday lives are fresh air, pure water, nourishing food, and clean energy in a most sustainable manner. The present review article concisely discusses recent innovations in solar energy education, research, and development toward providing clean and affordable energy and clean water to some extent. This article primarily addresses the Sustainable Development Goal 7 of the United Nations (SDG 7: Affordable and Clean Energy). Over the past few decades, many research activities have been carried out on solar energy conversion and utilization. The deployment of solar energy technologies has been witnessed to combat global warming and the betterment of the planet. Drivers and barriers to implementing solar energy systems from school to master's level through real-time deployments are discussed for further development and innovations. Mainly, expedited solar energy education and research are essential to improve solar energy utilization. The advancements in solar energy education and research towards sustainable energy development and circular economy are highlighted along with further directions required.

A Simple Polypyrrole/Polyvinylidene Fluoride Membrane with Hydrophobic and Self-Floating Ability for Solar Water Evaporation

The traditional hydrophobic solarevaporator is generally obtained through the modification of alkyl or fluoroalkyl on the photothermal membrane. However, the modified groups can easily be oxidized in the long-term use process, resulting in the poor salt resistance and stability of photothermal membrane. In order to solve this problem, a simple polypyrrole/polyvinylidene fluoride membrane, consisting of an intrinsic hydrophobic support (polyvinylidene fluoride) and a photothermal material (polypyrrole), was fabricated by ultrasonically mixing and immersed precipitation. This photothermal membrane showed good self-floating ability in the process of water evaporation. In order to further improve the photothermal conversion efficiency, a micropyramid structure with antireflective ability was formed on the surface of membrane by template method. The micropyramids can enhance the absorption efficiency of incident light. The water evaporation rate reached 1.42 kg m⁻² h⁻¹ under 1 sun irradiation, and the photothermal conversion efficiency was 88.7%. The hydrophobic polyvinylidene fluoride ensures that NaCl cannot enter into membrane during the evaporation process of the brine, thus realizing the stability and salt resistance of polypyrrole/polyvinylidene fluoride in 3.5%wt and 10%wt NaCl solution.

A smart enzyme reactor based on a photo-responsive hydrogel for purifying water from phenol contaminated sources

In this paper, a smart enzyme reactor (SER) was synthesized using immobilized tyrosinase (Tyr) in a photo-responsive hydrogel via a polydopamine-assisted self-assembly strategy for purifying water from phenol contaminated water. PDA was not only utilized as a binder between Tyr and the hydrogel to prevent the leakage of Tyr with relatively high enzymatic activity from the SER, but also acted as a light absorber to trigger the hydrophilic/hydrophobic switching of PNIPAm hydrogels to realize the efficient reclamation of clean water. Experimental results showed that the SER maintained a well-defined porous structure with excellent elasticity, which was beneficial for water transport and enzyme accessibility. And the stability and reusability of Tyr in the degradation of phenol were all improved. Furthermore, clean water could be reclaimed completely and facilely by light irradiation after enzymatic remediation in the SER.