Structure development of carbon-based solar-driven water evaporation systems

Vertical graphene nanoarray decorated with Ag nanoparticles exhibits enhanced antibacterial effects

Bacterial infection of biomedical implants is an important clinical challenge, driving the development of novel antimicrobial materials. The antibacterial effect of vertically aligned graphene as a nanoarray coating has been reported. In this study, vertically aligned graphene nanosheets decorated with silver nanoparticles were fabricated to enhance antibacterial effectiveness. Vertical graphene (VG) nanoflakes were synthesized by plasma-enhanced chemical vapor deposition (PECVD). Ag nanoparticles were attached to the surface of VG through using polydopamine and achieving a sustained release of Ag+. VG loaded with Ag nanoparticles (VGP/Ag) not only prevented bacterial adhesion for a long time, but also exhibited good biocompatibility. This work provides a new venue for designing antibacterial surfaces based on combination of graphene nanoarrays with other nanomaterials, and the results indicate that this approach could be very successful in preventing implant associated infections.

Green Synthesis of Polyurethane Sponge-Grafted Calcium Alginate with Carbon Ink Aerogel with High Water Vapor Harvesting Capacity for Solar-Driven All-Weather Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) technology is a new strategy for alleviating freshwater scarcity. Adsorbent materials with high hygroscopicity and high photothermal conversion efficiency are the key to AWH technology. Hence, in this study, a simple and large-scale preparation for a hygroscopic compound of polyurethane (PU) sponge-grafted calcium alginate (CA) with carbon ink (SCAC) was developed. The PU sponge in the SCAC aerogel acts as a substrate, CA as a moisture adsorber, and carbon ink as a light adsorber. The SCAC aerogel exhibits excellent water absorption of 0.555-1.40 g·g-1 within a wide range of relative humidity (40-80%) at 25 °C. The SCAC aerogel could release adsorbed water driven by solar energy, and more than 92.17% of the adsorbed water could be rapidly released over a wide solar intensity range of 1.0-2.0 sun. In an outdoor experiment, 57.517 g of SCAC was able to collect 32.8 g of clean water in 6 h, and the water quality meets the drinking water standards set by the World Health Organization. This study suggests a new approach to design promising AWH materials and infers the potential practical application of SCAC aerogel-based adsorbents.

Nonmetallic graphite for tumor magnetic hyperthermia therapy

Magnetic hyperthermia therapy (MHT) has garnered immense interest due to its exceptional spatiotemporal specificity, minimal invasiveness and remarkable tissue penetration depth. Nevertheless, the limited magnetothermal heating capability and the potential toxicity of metal ions in magnetic materials based on metallic elements significantly impede the advancement of MHT. Herein, we introduce the concept of nonmetallic materials, with graphite (Gra) as a proof of concept, as a highly efficient and biocompatible option for MHT of tumors in vivo for the first time. The Gra exhibits outstanding magnetothermal heating efficacy owing to the robust eddy thermal effect driven by its excellent electrical conductivity. Furthermore, being composed of carbon, Gra offers superior biocompatibility as carbon is an essential element for all living organisms. Additionally, the Gra boasts customizable shapes and sizes, low cost, and large-scale production capability, facilitating reproducible and straightforward manufacturing of various Gra implants. In a mouse tumor model, Gra-based MHT successfully eliminates the tumors at an extremely low magnetic field intensity, which is less than one-third of the established biosafety threshold. This study paves the way for the development of high-performance magnetocaloric materials by utilizing nonmetallic materials in place of metallic ones burdened with inherent limitations.

Bioinspired Solar-Driven Osmosis for Stable High Flux Desalination

The growing global water crisis necessitates sustainable desalination solutions. Conventional desalination technologies predominantly confront environmental issues such as high emissions from fossil-fuel-driven processes and challenges in managing brine disposal during the operational stages, emphasizing the need for renewable and environmentally friendly alternatives. This study introduces and assesses a bioinspired, solar-driven osmosis desalination device emulating the natural processes of mangroves with effective contaminant rejection and notable productivity. The bioinspired solar-driven osmosis (BISO) device, integrating osmosis membranes, microporous absorbent paper, and nanoporous ceramic membranes, was evaluated under different conditions. We conducted experiments in both controlled and outdoor settings, simulating seawater with a 3.5 wt % NaCl solution. With a water yield of 1.51 kg m-2 h-1 under standard solar conditions (one sun), the BISO system maintained excellent salt removal and accumulation resistance after up to 8 h of experiments and demonstrated great cavitation resistance even at 58.14 °C. The outdoor test recorded a peak rate of 1.22 kg m-2 h-1 and collected 16.5 mL in 8 h, showing its practical application potential. These results highlight the BISO device's capability to address water scarcity using a sustainable approach, combining bioinspired design with solar power, presenting a viable pathway in renewable-energy-driven desalination technology.

Electrothermal interfacial evaporation through carbon-nanostructured composite membranes

High energy demand required in membrane distillation (MD) process to heat feed water and maintain the necessary temperature gradient across the membrane presents a challenge to widespread adoption of MD. In response to this challenge, surface heating membrane distillation (SHMD) has emerged as a promising solution. SHMD can employ solar or electrical energy to directly heat the membrane and feed, eliminating the need for an external heat source to heat feed water. In this study, we explore electrothermally-driven interfacial evaporation using a multi-walled carbon nanotube (MWCNT)-based composite membrane and further envision its utilization for high-efficient SHMD. Upon application of voltage, the resistance of the MWCNT leads to the conversion of electrical energy into heat, which is then uniformly transferred to feeds. The MWCNT-based composite membrane exhibited an evaporative water flux of up to 2.34 kg m-2h-1 with an associated energy efficiency of 61% and demonstrated outstanding localized surface heating performance. The employed membranes exhibited no significant variations in either resistance or surface temperature, regardless of the direction of the applied electric field. Energy parameters from the electrothermal membranes showed quantitative agreement with values reported for various electrothermal MD systems, suggesting the potential of the composite membranes in energy-efficient and cost-effective localized heating MD applications.

Carbonaceous Materials-Based Photothermal Process in Water Treatment: From Originals to Frontier Applications

The photothermal process has attracted considerable attention in water treatment due to its advantages of low energy consumption and high efficiency. In this respect, photothermal materials play a crucial role in the photothermal process. Particularly, carbonaceous materials have emerged as promising candidates for this process because of exceptional photothermal performance. While previous research on carbonaceous materials has primarily focused on photothermal evaporation and sterilization, there is now a growing interest in exploring the potential of photothermal effect-assisted advanced oxidation processes (AOPs). However, the underlying mechanism of the photothermal effect assisted by carbonaceous materials remains unclear. This review aims to provide a comprehensive review of the photothermal process of carbonaceous materials in water treatment. It begins by introducing the photothermal properties of carbonaceous materials, followed by a discussion on strategies for enhancing these properties. Then, the application of carbonaceous materials-based photothermal process for water treatment is summarized. This includes both direct photothermal processes such as photothermal evaporation and sterilization, as well as indirect photothermal processes that assisted AOPs. Meanwhile, various mechanisms assisted by the photothermal effect are summarized. Finally, the challenges and opportunities of using carbonaceous materials-based photothermal processes for water treatment are proposed.

Conductive Metal-Organic Framework Nanosheets Constructed Hierarchical Water Transport Biological Channel for High-Performance Interfacial Seawater Evaporation

Solar interfacial water evaporation shows great potential to address the global freshwater scarcity. Water evaporation being inherently energy intensive, Joule-heating assisted solar evaporation for addressing insufficient vapor under natural conditions is an ideal strategy. However, the simultaneous optimization of low evaporation enthalpy, high photothermal conversion, and excellent Joule-heating steam generation within a single material remain a rare achievement. Herein, inspired by the biological channel structures, a large-area film with hierarchical macro/microporous structures is elaborately designed by stacking the nanosheet of a conductive metal-organic framework (MOF), Ni3 (HITP)2 , on a paper substrate. By combining the above three features in one material, the water evaporation enthalpy reduces from 2455 J g-1 to 1676 J g-1 , and the photothermal conversion efficiency increases from 13.75% to 96.25%. Benefiting from the synergistic photothermal and Joule-heating effects, the evaporation rate achieves 2.60 kg m-2 h-1 under one sun plus input electrical power of 4 W, surpassing the thermodynamic limit and marking the highest reported value in MOF-based evaporators. Moreover, Ni3 (HITP)2 -paper exhibits excellent long-term stability in simulated seawater, where no salt crystallization and evaporation rate degradation are observed. This design strategy for nanosheet films with hierarchical macro/microporous channels provides inspiration for electronics, biological devices, and energy applications.

All-in-one self-floating porous foams as robust heat-blocking layers for efficient photothermal conversion and solar desalination

Solar-driven interfacial evaporation is a highly efficient and ecofriendly technology for producing freshwater. Herein, self-floating plasmon Ag/black TiO2/carbon porous layered foams (Ag-BTCFs) were demonstrated as efficient solar-thermal convectors using freeze-drying cast-molding and high-temperature surface hydrogenation strategies. This all-in-one three-dimensional (3D) cross-linked self-floating porous layered foam material with full-spectrum absorption can fully harvest sunlight (∼95.45%) and effectively block heat transfer to its sublayer. The synergy of sufficient utilization of absorbed ultraviolet radiation by black TiO2 (b-TiO2), visible light absorption by Ag nanoparticles (Ag NPs) via localized surface plasmon resonance, and near-infrared absorption by layered-amorphous carbon can achieve full-solar-spectrum absorption to concentrate thermal energy. In addition to their synergistic effect, they are conducive to the relaxation of hot electrons when utilizing photogenerated holes to degrade pollutants in domestic wastewater. The steam generation efficiency of Ag-BTCFs is up to 1.79 kg m-2h-1 due to their solar energy conversion efficiency of 81.74% under 1 sun irradiation, which is five times higher than the evaporation rate of pure water. Notably, the material's efficient ion removal rate of 99.80% for solar desalination indicates its high potential for various applications. This strategy provides new insights for fabricating recyclable heat-blocking layer systems against thermal loss to enhance solar steam generation.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

Stable polyethylene glycol/biochar composite as a cost-effective photothermal absorber for 24 hours of steam and electricity cogeneration

Seawater desalination powered by solar energy is the most environmentally and economical solution in responding to the global water and energy crisis. However, solar desalination has been negatively impacted by intermittent sun radiation that alternates between day and night. In this study, sugarcane bagasse (SCB) was recycled via the pyrolysis process to biochar as a cost-effective solar absorber. Besides, polyethylene glycol (PEG) as a phase change material was encapsulated in the abundant pore structure of biochar to store the thermal energy for 24 hours of continuous steam generation. The BDB/1.5 PEG evaporator exhibited an evaporation rate of 2.11 kg m-2 h-1 (98.1% efficiency) under 1 sun irradiation. Additionally, the BDB/1.5 PEG evaporator incorporated by the TEC1-12706 module for continuous steam and electricity generation with a power density of 320.41 mW m-2. Moreover, 10 continuous hours of evaporation were applied to the composite demonstrating outstanding stability. The composite exhibited high water purification efficiency through solar desalination due to the abundant functional groups on the biochar surface. Finally, the resulting low-cost and highly efficient PCM-based absorber can be used on a wide scale to produce fresh water and energy.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Sulfonated PAM/PPy Cryogels with Lowered Evaporation Enthalpy for Highly Efficient Photothermal Water Evaporation

Because of the increasing scarcity of water resources, the desalination of seawater by photothermal evaporation with harvested solar energy has gradually become a popular research topic. The interconnected macroporous cryogel prepared from polymerization and crosslinking below the freezing temperature of the reactant solution has an excellent performance in photothermal water evaporation after loading photothermal materials. In this study, polyacrylamide (PAM) cryogels were prepared by cryo-polymerization and sulfonated in an alkaline solution containing formaldehyde and Na₂SO₃. Importantly, the evaporation enthalpy of water in sulfonated PAM cryogel was reduced to 1187 J·g^-1 due to the introduction of sulfonate groups into PAM, which was beneficial to increase the photothermal evaporation rate and efficiency. The sulfonated PAM cryogels loaded with polypyrrole and the umbrella-shaped melamine foam substrate were combined to form a photothermal evaporation device, and the evaporation rate was as high as 2.50 kg·m^-2·h^-1 under one-sun radiation. Meanwhile, the evaporation rate reached 2.09 kg·m^-2·h^-1 in the 14 wt% high-concentration saline solution, and no salt crystals appeared on the surface of the cryogel after 5 h of photothermal evaporation. Therefore, it was evidenced that the presence of sulfonate groups not only reduced the evaporation enthalpy of water but also prevented salting-out from blocking the water delivery channel during photothermal evaporation, with a sufficiently high evaporation rate, providing a reliable idea of matrix modification for the design of high-efficiency photothermal evaporation materials.

A Novel Functionalized MoS2-Based Coating for Efficient Solar Desalination

Molybdenum disulfide (MoS₂) has emerged as a promising photothermal material for solar desalination. However, its limitation in integrating with organic substances constrains its application because of the lack of functional groups on its surface. Here, this work presents a functionalization approach to introduce three different functional groups (-COOH -OH -NH₂) on the surface of MoS₂ by combining them with S vacancies. Subsequently, the functionalized MoS₂ was coated on the polyvinyl alcohol-modified polyurethane sponge to fabricate a MoS₂-based double-layer evaporator through an organic bonding reaction. Photothermal desalination experiments show that the functionalized material has higher photothermal efficiency. The evaporation rate of the hydroxyl functionalized the MoS₂ evaporator evaporation rate is 1.35 kg m^-2 h^-1, and the evaporation efficiency is 83% at one sun. This work provides a new strategy for efficient, green, and large-scale utilization of solar energy by MoS₂-based evaporators.

3D carbonized grooved straw with efficient evaporation and salt resistance for solar steam generation

Solar steam generation (SSG) is considered an effective solution to the global shortage of freshwater resources. To solve the practical application challenges of SSG in remote outdoor environments where electricity is scarce, it is of great importance to developing new solar evaporators. In this study, a three-dimensional (3D) biochar solar evaporator based on carbonized grooved straw was prepared from agricultural waste corn straw, which had high solar energy conversion efficiency and excellent salt resistance. The existence of grooves increases the surface area to absorb more sunlight and makes the light multilevel reflection improve the evaporation rate. The excellent light absorption, super hydrophilic, and heat shielding properties of 3D carbonized grooved straw resulted in a good evaporation rate (1.57 kg⋅m^-2·h^-1) and energy efficiency (85.9%) under 1 sun irradiation. The 3D grooved biochar solar distiller also demonstrated efficient formation evaporation performance and excellent salt resistance in practical applications in seawater desalination and surface water purification. The 3D grooved biochar solar distiller prepared from agricultural waste has the advantages of being economical and environmentally friendly, with good application prospects.

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.

An Iron-NDC Framework with a Cage Structure and an Optothermal Conversion in NIR Window

Pursuing novel materials with efficient photothermal conversion under irradiation at the near-infrared region windows (NIR, 750-850 nm; NIR-I and NIR-II, 1000-1320 nm)) is of great importance due to their irreplaceable applications, especially in the biomedical field. Herein, on the basis of a coordination chemistry strategy, an iron-based metal-organic framework (MOF) of [N(CH₃)₄]₂[Fe₃(NDC)₄]·DMF·3H₂O (Fe-NDC, 1,4-H₂NDC = 1,4-naphthalenedicarboxylic acid, N(CH₃)₄⁺ = tetramethyl-ammonium, and DMF = N,N-dimethylformamide) was prepared and characterized. Due to the d-d transition effect introduced by coordination with the transition-metal ion of iron and the highly conjugated naphthalenic moiety in 1,4-H₂NDC, guaranteeing an energy transfer between iron and the organic module, Fe-NDC shows a remarkable broad absorption, which could be extended into the NIR-II section. As a result, Fe-NDC could be irradiated by NIR laser (both 808 and 1064 nm) to achieve photothermal conversion. This work sets a good example to inspire the future designation of NIR light-irradiated photothermal materials based on the first-row transition metals.

Heat Transfer Characteristics of Carbon-Based Photothermal Superhydrophobic Materials with Thermal Insulation Micropores During Anti-icing/Deicing

Photothermal deicing is a noncontact, economically, efficient, and environmentally friendly melting/preventing ice method. Obtaining a cheap, easily fabricated material with high photothermal conversion and deicing efficiency is a challenge. Here, carbon-based photothermal superhydrophobic materials with thermal insulation micropores were prepared by using the salt-template. We demonstrate that the microholes array structure can enhance light absorption and hydrophobicity of the material, and the micropores structure can inhibit the heat transfer from the surface to the subcooled substrate, which synergistically greatly enhances the photothermal conversion. A heat transfer model was established to clarify the influence mechanisms of air cushion on interfacial heat transfer during the photothermal anti-icing and deicing process. The self-cleaning, flexibility, mechanical, and chemical stability tests show that the material has the potential for outdoor application. The prepared materials with high photothermal deicing efficiency provide a new way for the anti-icing and deicing of outdoor equipment.

Bio-Derived Photothermal Materials and Evaporators for Sustainable Solar Energy-Driven Water Process

Interfacial solar steam generation (ISSG) is considered as an excellent seawater desalination technology because of its electricity-independent nature, low cost, and portability. However, improving the water evaporation efficiency, simplifying the fabrication process, and reducing the overall cost of the evaporator are still challenging. Here, an efficient and sustainable solar water evaporator is fabricated with carbonized ginkgo biloba leaves as the structural basis of photothermal materials. The combination of the abundant capillary channels in ginkgo leaves paired with polyacrylamide (PAM) hydrogel accelerates water transportation and solar-driven evaporation. The fabricated evaporator shows excellent photothermal conversion capability and evaporates water at 2.39 kg m^-2 h^-1 under 1 sun irradiation. In addition, the device exhibits remarkable stability in simulated seawater and can effectively realize seawater desalination or sewage treatment. As a result, the system is promising for future highly efficient solar evaporation due to its environmental protection and low cost.

Enhanced Phase-Change Heat Transfer by Surface Wettability Control

The phase-change heat-transfer coefficient can be improved by several orders of magnitude through the design of micro-nanostructures on typical surfaces. However, with the rapid development of intelligent and integrated devices, there is an increasing desire to regulate the heat exchange form of the surface to adapt to various environmental requirements. This study concerns the design of a carbon nanotube array-based phase-change heat-transfer surface, which can switch its wettability between superhydrophobicity and superhydrophilicity. By installing this surface on a device that integrates boiling heat transfer and condensation heat transfer, the device can independently adjust the surface wettability for different heat-transfer requirements. As a result, this surface can enhance condensation heat-transfer coefficient over 90 % in the superhydrophobic state and enhance the boiling heat-transfer coefficient over 41 % in the superhydrophilic state. Surfaces with controllable wettability can aid development of a new generation of smart control technologies to actively regulate system and device temperatures.

Smart near infrared-responsive nanocomposite hydrogels for therapeutics and diagnostics

Nanocomposite (NC) hydrogels are emerging biomaterials that possess desirable and defined properties and functions for therapeutics and diagnostics. Particularly, nanoparticles (NPs) are employed as stimulus-transducers in NC hydrogels to facilitate the treatment process by providing controllable structural change and payload release under internal and external simulations. Among the various external stimuli, near-infrared (NIR) light has attracted considerable interest due to its minimal photo-damage, deep tissue penetration, low auto-fluorescence in living systems, facile on/off switch, easy remote and spatiotemporal control. In this study, we discuss four types of transducing nanomaterials used in NIR-responsive NC hydrogels, including metal-based nanoparticles, carbon-based nanomaterials, polydopamine nanoparticles (PDA NPs), and upconversion nanoparticles (UCNPs). This review provides an overview of the current progress in NIR-responsive NC hydrogels, focusing on their preparation, properties, applications, and future prospects.