Metal-phenolic network coated cellulose foams for solar-driven clean water production

Gum Ghatti: A Comprehensive Review on Production, Processing, Remarkable Properties, and Diverse Applications

Gum ghatti, popularly known as Indian gum and obtained from Anogeissus latifolia, is a complex high-molecular-weight, water-soluble, and swellable nonstarch polysaccharide comprised of magnesium and calcium salts of ghattic acids and multiple monosugars. Unlike other nontimber forest produce, gums ghatti is a low-volume but high-value product. It has several applications and is widely used as food, in pharmaceuticals, and for wastewater treatment and hydrogel formation, and it has attracted a great deal of attention in the fields of energy, environmental science, and nanotechnology. Industrial applications of gum ghatti are primarily due to its excellent emulsification, stabilization, thickening, heat tolerance, pH stability, carrier, and biodegradable properties. However, utilization of gum ghatti is poorly explored and implemented due to a lack of knowledge of its production, processing, and properties. Nevertheless, there has been interest among investigators in recent times for exploring its production, processing, molecular skeleton, and functional properties. This present review focuses on production scenarios, processing aspects, structural and functional properties, and potential applications in the food, pharmaceuticals, nonfood, and other indigenous and industrial usages.

Waste Tea-Derived Theabrownins for Solar-Driven Steam Generation

Solar-driven seawater desalination has been considered an effective and sustainable solution to mitigate the global freshwater crisis. However, the substantial cost associated with photothermal materials for evaporator fabrication still hinders large-scale manufacturing for practical applications. Herein, we successfully obtained high yields of theabrownins (TB), which were oxidation polymerization products of polyphenols from waste and inferior tea leaves using a liquid-state fermentation strategy. Subsequently, a series of photothermal complexes were prepared based on the metal-phenolic networks assembled from TB and metal ions (Fe(III), Cu(II), Ni(II), and Zn(II)). Also, the screened TB@Fe(III) complexes were directly coated on a hydrophilic poly(vinylidene fluoride) (PVDF) membrane to construct the solar evaporation device (TB@Fe(III)@PVDF), which not only demonstrated superior light absorption property and notable hydrophilicity but also achieved a high water evaporation rate of 1.59 kg m-2 h-1 and a steam generation efficiency of 90% under 1 sun irradiation. More importantly, its long-term stability and exceptionally low production cost enabled an important step toward the possibility of large-scale practical applications. We believe that this study holds the potential to pave the way for the development of sustainable and cost-effective photothermal materials, offering new avenues for utilization of agriculture resource waste and solar-driven water remediation.

Synergistic Effect of Ti3C2Tx MXene Nanosheets and Tannic Acid-Fe3+ Network in Constructing High-Performance Hydrogel Composite Membrane for Photothermal Membrane Distillation

Photothermal membrane distillation (PMD) has emerged as a promising and sustainable approach for seawater desalination and wastewater purification. However, the wide application of the technique is severely impeded by low freshwater production and membrane fouling/wetting issues. Herein, we developed an advanced hydrogel-engineered membrane with simultaneously enhanced photothermal conversion capacity and desired fouling and wetting resistance for PMD. By the synergies of photothermal Ti3C2Tx MXene nanosheets and the tannic acid-Fe3+ network in the hydrogel, the membrane was endowed with excellent surface self-heating ability, yielding the highest freshwater production rate (1.71 kg m-2 h-1) and photothermal efficiency among the fabricated hydrogel composite membranes under 1 sun irradiation. Meanwhile, the PMD membrane could robustly resist oil-induced fouling and surfactant-induced wetting, significantly extending the membrane lifespan in treating contaminated saline water. Furthermore, when desalinating real seawater, the membrane exhibited superior durability with a stable vapor flux and excellent ion rejection (e.g., 99.24% for boron) for 100 h.

Distribution-according-to-work: Enhancing solar vapor generation of photothermal sponge by using cellulose-based water storage platform

Interfacial solar vapor generation (ISVG) has shown extraordinary promise in achieving high-efficiency water purification. However, the rapid water supply often leads to excessive water in the solar absorber, resulting in undesired heat loss and a decrease in evaporation rate. To tackle this issue, we developed a bio-based solar evaporator comprising cellulose-based water retention resin (CRR) and straw-derived photothermal sponge. CRR serves as an effective water storage platform with a high binding capacity for water molecules, preventing water from entering the absorber and reducing the water evaporation enthalpy. The water management of CRR confines the solar-to-vapor conversion to the interface between CRR and the photothermal sponge, thereby eliminating the adverse effects of excess water. Additionally, the ISVG process operates based on the principle of Distribution-according-to-work, meaning that the quantity of generated vapor depends on the evolution of the sponge structure. Optimal sponge configuration enables evaporation rates of 2.28 and 1.53 kg/m2/h under solar irradiation of 1.0 and 0.5 kW/m2, respectively. Additionally, the obtained evaporator is capable of producing 7.1 kg/m2/day of freshwater in outdoor experiment. This report proposes a novel approach to designing an ISVG device that incorporates effective water management strategy for achieving high-efficiency water purification in real-world scenarios.

Boosting interfacial solar steam generation by three-dimensional bilayer cellulose aerogels

Interfacial solar steam generation (ISSG) provides a sustainable approach of clean water production through desalination and water purification. It is still needed to pursue a fast evaporation rate, high-quality freshwater production, and low-cost evaporators. Herein, a three-dimensional (3D) bilayer aerogel was fabricated using cellulose nanofiber (CNF) as a skeleton filled with polyvinyl alcohol phosphate ester (PVAP), and carbon nanotubes (CNT) as a light absorbing material in the top layer. The CNF/PVAP/CNT aerogel (CPC) had broadband light absorption ability and exhibited an ultrafast water transfer rate. The lower thermal conductivity of CPC effectively confined the convert heat in the top surface and minimized heat loss. Additionally, a large amount of intermediate water caused by water activation decreased the evaporation enthalpy. Under 1 sun irradiation, the CPC-3 (3.0 cm height of CPC) achieved a high evaporation rate of 4.02 kg m-2 h-1 with an energy conversion efficiency of 125.1%. The additional convective flow and environmental energy made CPC achieve an ultrahigh evaporation rate of 11.37 kg m-2 h-1, surpassing 673% of the solar input energy. More importantly, the continuous solar desalination and higher evaporation rate (10.70 kg m-2 h-1) in seawater revealed that CPC was a promising candidate for practical desalination. Outdoor cumulative evaporation was up to 73.2 kg m-2 d-1 in weak sunlight and lower temperature, which would meet the daily drinking water demands of 20 people. The excellent cost-effectiveness of 1.085 L h-1 $-1 presented its potential for a wide range of practical applications, such as solar desalination, wastewater treatment, and metal extractions.

Gradient heating induced better balance among water transportation, salt resistance and heat supply in a high performance multi-functional solar-thermal desalination device

Solar-driven desalination (SDD) is a promising technology for addressing water scarcity. However, how to overcome the trade-off between water transportation and heat supply of the evaporator to achieve a high evaporation rate and good salt tolerance simultaneously remains a challenge. Here, a novel all-in-one multi-functional SDD evaporator undergoing gradient heating is used. This evaporator incorporates a hydrophilic PDA (polydopamine)@CNT(carbon nanotube)/PVA (polyvinyl alcohol) aerogel with vertically aligned structures as the water evaporation layer, enabling rapid water transportation. Surrounding the evaporation layer, there is a photothermal hydrophobic CCP (cotton/CNT/polydimethylsiloxane) film that serves as the heating layer, enhancing the heat supply to the evaporation layer. This innovative design strikes a favorable balance between water transportation and heat supply, facilitating high evaporation rates and good salt tolerance simultaneously, while also maximizing electricity generation. Due to the wettability difference between the evaporation layer (PVA aerogel) and heating layer (CCP film), a record stable temperature gradient of nearly 70 °C was formed between the CCP film and the PVA aerogel under 1 sun irradiation, so that heat on the high-temperature CCP film was continuously transferred to the low-temperature aerogel through its thermal conductive network, leading to a high evaporation rate of 6.96 kg m-2 h-1 under 1 sun irradiation in 5.0 wt% sodium chloride (NaCl) brine (higher than the world average seawater salinity (3.5 wt%)). Meanwhile, high flux directional flow of brine generated 130 mV stable voltage and 120 μA circuit current. Furthermore, the evaporator illustrates good stability for consecutive 7 days of testing and shows industry-leading comprehensive performance of SDD in actual use. More importantly, it was tested in real Bohai seawater under weak natural light, and fresh water generated can meet the recommended daily intake of water for 2.6 households and the simultaneously generated voltage reaches above 60 mV. In addition, the evaporator exhibits good adsorption capacity for heavy metals and dye molecules. This simple and universal solar evaporation structure is suitable for the assembly of gradient thermal structures for most solar thermal materials reported in the literature, which provides a new route for maximizing the use of solar energy for freshwater and electricity generation.

Waterwheel-inspired rotating evaporator for efficient and stable solar desalination even in saturated brine

Solar desalination is one of the most promising technologies to address global freshwater shortages. However, traditional evaporators encounter the bottleneck of reduced evaporation rate or even failure due to salt accumulation in high-salinity water. Inspired by ancient waterwheels, we have developed an adaptively rotating evaporator that enables long-term and efficient solar desalination in brines of any concentration. The evaporator is a sulphide-loaded drum-type biochar. Our experiments and numerical simulations show that this evaporator, thanks to its low density and unique hydrophilic property, rotates periodically under the center-of-gravity shift generated by salt accumulation, achieving self-removal of salt. This allows it to maintain a high evaporation rate of 2.80 kg m-2 h-1 within 24 h even in saturated brine (26.47%), which was not achieved previously. This proof-of-concept work therefore demonstrates a concentration- and time-independent, self-rotation-induced solar evaporator.

Ethyl cellulose composite membranes containing a 2D material (MoS2) and helical carbon nanotubes for efficient solar steam generation and desalination

With the increasing water consumption, water evaporators have been investigated for clean water production. Herein, the fabrication of electrospun composite membrane evaporators based on ethyl cellulose (EC), with the incorporation of light-absorption enhancers 2D MoS₂ and helical carbon nanotubes, for steam generation and solar desalination is described. Under natural sunlight, the maximum water evaporation rate was 2.02 kg m^-2 h^-1 with an evaporation efficiency of 93.2 % (1 sun) and reached 2.42 kg m^-2 h^-1 at 12:00 pm (1.35 sun). The composite membranes demonstrated self-floating on the air-water interface and minimal accumulation of superficial salt during the desalination process due to the hydrophobic character of EC. For concentrated saline water (21 wt% NaCl), the composite membranes maintained a relatively high evaporation rate of up to ~79 % compared to the freshwater evaporation rate. The composite membranes are robust due to the thermomechanical stability of the polymer even while operating under steam-generating conditions. Over repeated use, they exhibited excellent reusability with a relative water mass change of >90 % compared to the first evaporation cycle. Moreover, desalination of artificial seawater produced a lower cation concentration (~3-5 orders of magnitude) and thereby yielded potable water, indicating the potential for solar-driven freshwater generation.

Eco-friendly photothermal hydrogel evaporator for efficient solar-driven water purification

The field of solar vapor generation has developed rapidly in recent years, but achieving the goals of a high evaporation rate, eco-friendliness and rapid preparation with low-cost raw materials is still a challenge. In this work, a type of photothermal hydrogel evaporator was prepared by blending eco-friendly poly(vinyl alcohol), agarose, Fe³⁺ and tannic acid (TA) together, in which the tannic acid-ferric ion (TA*Fe³⁺) complexes served as photothermal materials and effective gelators. The results indicate that the TA*Fe³⁺ complex exhibits excellent gelatinization ability and light-absorption performance, which leads to a compressive stress of 0.98 MPa at 80% strain and up to 85% light absorption ratio in the photothermal hydrogel. For interfacial evaporation, a high rate of 1.897 ± 0.11 kg·m^-2·h^-1 corresponding to an energy efficiency of 89.7 ± 2.73% under 1 sun irradiation is achieved. Moreover, the hydrogel evaporator exhibits high stability in a 12-hour test and a 20-cycle test without a decline in evaporation performance. The outdoor testing results show that the hydrogel evaporator can achieve an evaporation rate of > 0.70 kg/m² and effectively purify wastewater treatment and seawater desalination.

An injectable all-small-molecule dynamic metallogel for suppressing sepsis

All-small-molecule dynamic hydrogels have shown great promise in cell culture, tissue engineering, and controlled drug release. The further development of more kinds of all-small-molecule dynamic hydrogels is severely hindered by the lack of enough commensurate building blocks from nature and on the market. Inspired by the widely developed metal-organic framework structures, herein we report a facile fabrication of metallogels by direct gelation of small molecular compounds including aminoglycosides (AGs), 2,2'-bipyridine-4,4'-dicarboxaldehyde (BIPY), and metal ions via coordination interactions and Schiff base reactions. These prepared metallogels exhibited good biodegradability and biosafety, excellent conductivity, tunable mechanical properties and potent antibacterial activities both in vitro and in vivo. This study provides a new strategy for expanding the scope of all-small-molecule dynamic metallogels for various biomedical applications.

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.

Multi-Wavelength Light-Responsive Metal-Phenolic Network-Based Microrobots for Reactive Species Scavenging

Light-driven microrobots with different propulsion mechanisms have attracted great attention in microrobot synthesis and applications. However, current systems rely heavily on precious metals, using a complex synthesis process and limited working wavelength. It is therefore of great interest to fabricate microrobots that can be driven by multi-wavelength irradiation and with simple components. Here, metal-phenolic network (MPN)-based microrobots are synthesized using a sacrificial polystyrene bead template and an extra capping is added to regulate their symmetry. The hollow MPN microrobots with different layers of capping are capable of moving under both near-infrared (NIR) irradiation and ultraviolet (UV) irradiation, without fuel. The velocity of the microrobots under irradiation is altered by the thickness of the asymmetric capping and their motion could be manipulated remotely by switching the NIR or UV irradiation on and off. With light-driven mobility, the reactive oxygen and nitrogen species (RONS) scavenging activity of the microrobots is significantly increased. Therefore, this proposed microrobot system provides a synthesis strategy to develop asymmetric light-navigated microrobots for future medical treatment with tunable structure, multi-wavelength light-responsive mobility, and great RONS scavenging capacity.

A robust and 3D-printed solar evaporator based on naturally occurring molecules

The interfacial solar desalination has been considered a promising method to address the worldwide water crisis without sophisticated infrastructures and additional energy consumption. Although various advanced solar evaporators have been developed, their practical applications are still restricted by the unsustainable materials and the difficulty of precise customization for structure to escort high solar-thermal efficiency. To address these issues, we employed two kinds of naturally occurring molecules, tannic acid and iron (III), to construct a low-cost, highly efficient and durable interfacial solar evaporator by three-dimensional (3D) printing. Based on a rational structural design, a robust and 3D-printed evaporator with conical array surface structure was developed, which could promote the light harvesting capacity significantly via the multiple reflections and anti-reflection effects on the surface. By optimizing the height of the conical arrays, the 3D-printed evaporator with tall-cone structure could achieve a high evaporation rate of 1.96 kg m^-2 h^-1 under one sun illumination, with a photothermal conversion efficiency of 94.4%. Moreover, this evaporator was also proved to possess excellent desalination performance, recycle stability, anti-salt property, underwater oil resistance, as well as adsorption capacity of organic dye contaminants for multipurpose water purification applications. It was believed that this study could provide a new strategy to fabricate low-cost, structural regulated solar evaporators for alleviating the dilemma of global water scarcity using abundant naturally occurring building blocks.

Photothermal Aerogel Beads Based on Polysaccharides: Controlled Fabrication and Hybrid Applications in Solar-Powered Interfacial Evaporation, Water Remediation, and Soil Enrichment

Solar-powered interfacial evaporation has emerged as an innovative and sustainable technology for clean water production. However, the rapid, mass and shape-controlled fabrication of three-dimensional (3D) steam generators (SGs) for versatile hybrid applications remains challenging. Herein, composite aerogel beads with self-contained properties (i.e., hydrophilic, porous, photothermal, and durable) are developed and demonstrated for threefold hybrid applications including efficient solar-powered interfacial evaporation, water remediation, and controlled soil enrichment. The rational incorporation of selected polysaccharides enables us to fabricate bead-like aerogels with rapid gelation, continuous processing, and enhanced ion adsorption. The composite beads can attain a high water evaporation rate of 1.62 kg m-2 h-1 under 1 sun. Meanwhile, high phosphate adsorption capacity of over 120 mg g-1 is achieved in broad pH (2.5-12.4) and concentration (200-1000 mg L-1) ranges of phosphate solutions. Gratifyingly, we demonstrate the first example of recycling biomaterials from interfacial SGs for controlled nutrient release, soil enrichment, and sustainable agriculture. The phosphate-saturated beads can be gradually broken down in the soil. Macronutrients (N, P, and K) can be slowly released in 50 days, sustaining the plant germination and growth in a whole growth stage. This work shines light on the mass and controlled fabrication of aerogel beads based on double-network biopolymers, not merely scaling up solar-powered interfacial evaporation but also considering water remediation, waste material disposal, and value-added conversion.

Robust and multifunctional natural polyphenolic composites for water remediation

The scarcity of clean water has become a global environmental problem which constrains the development of public health, economy, and sustainability. In recent years, natural polyphenols have drawn increasing interests as promising platforms towards diverse water remediation composites and devices, owing to their abundant and renewable resource in nature, highly active surface chemistry, and multifunctionality. This review aims to summarize the most recent advances and highlights of natural polyphenol-based composite materials (e.g., nanofibers, membranes, particles, and hydrogels) for water remediation, by focusing on their structural and functional features, as well as their diversified applications including membrane filtration, solar distillation, adsorption, advanced oxidation processes, and disinfection. Finally, the future challenges in this field are also prospected. It is anticipated that this review will provide new opportunities towards the future development of natural polyphenols and other kinds of naturally occurring molecules in water purification applications.

Preparation and characterization of ZnO/graphene/graphene oxide/multi-walled carbon nanotube composite aerogels

ZnO/Graphene (G)/Graphene Oxide (GO)/Multi-walled Carbon Nanotube (MCNT) composite aerogels with a three-dimensional porous structure were prepared by the sol-gel method under average temperature and alkaline conditions, combined with freeze-drying process and heat treatment process. The photocatalytic degradation of Rhodamine B (RhB) was mainly studied. The scanning electron microscope (SEM) test results showed that the morphology uniformity of the ZnO/G/GO/MCNT composite aerogel was significantly enhanced, which effectively solving the agglomeration problem of MCNT and ZnO. The photocatalytic degradation test results of RhB show that due to the synergistic effect of physical adsorption and photocatalytic degradation, the total degradation efficiency of RhB by ZnO/G/GO/MCNT could reach 86.8%, which is 3.3 times higher than that of ZnO. In addition, the synergistic effect of ZnO and G effectively hinders the recombination of photo-generated electron-hole pairs and enhances photocatalytic activity. The ZnO/G/GO/MCNT composite aerogel can be applied in the visible light catalytic degradation of water pollution.