Solar-powered water evaporation — the extraction of vapour from liquid water using solar energy — provides the basis for the development of eco-friendly and cost-effective freshwater production. Liquid water consumes and carries energy, and, thus, plays an essential role in this process. As such, extensive experimental and theoretical studies have been focused on water management to achieve efficient solar vapour generation. Many innovative materials have been proposed to enable highly controllable and efficient solar-to-thermal energy conversion to address the challenges in the energy–water nexus from the microscale to the molecular level. In this Review, we summarize the fundamental principles of materials design for efficient solar-to-thermal energy conversion and vapour generation. We discuss how to integrate photothermal materials, nanostructures/microstructures and water–material interactions to improve the performance of the evaporation system via in situ utilization of solar energy. Focusing on materials science and engineering, we overview the key challenges and opportunities for nanostructured and microstructured materials in both fundamental research and practical water-purification applications. Materials engineering enables the control of water–material interactions in solar vapour generators, which aim to efficiently utilize solar energy for the cost-effective production of clean water. This Review discusses material-design principles for solar evaporators, spanning from macrostructures to molecular configurations.

Materials for solar-powered water evaporation

The development of fluorophores and molecular probes for the second near-infrared biological window (NIR-II, 1000–1700 nm) represents an important, newly emerging and dynamic field in molecular imaging, chemical biology and materials chemistry. Because of reduced scattering, minimal absorption and negligible autofluorescence, NIR-II imaging provides high resolution, a high signal-to-noise ratio, and deep tissue penetration capability. Among various state-of-the-art bioimaging modalities, one of the greatest challenges in developing novel probes is to achieve both high resolution and sensitivity. The chemical design and synthesis of NIR-II fluorophores suitable for multimodal imaging is thus emerging as a new and powerful strategy for obtaining high-definition images. NIR-II fluorophores may convert NIR-II photons into heat for photothermal therapy and be excited by NIR-II light to produce singlet oxygen for photodynamic therapy. The presence of simultaneous diagnostic and therapeutic capabilities in a single probe can be used for precise treatment. In this review, we have focused on recent advances in the chemical design and synthesis of NIR-II fluorophores from small organic molecules to organic and inorganic nanoparticles, and we have further discussed recent advances and key operational differences in reported NIR-II imaging systems and biomedical applications based on NIR-II imaging, such as multimodal imaging, photothermal and photodynamic therapy, guidance for intraoperative surgery, and drug delivery.

Crucial breakthrough of second near-infrared biological window fluorophores: design and synthesis toward multimodal imaging and theranostics

Photoelectrochemical sensing is an attractive tool for rapid and accurate monitor of chemical and biochemical mole-cules. Compared with conventional analysis techniques, photoelectrochemical sensing exhibits unique technique superiority and has become a hot topic in material chemis-try and analytical chemistry. This review provides an over-view of the important advances in the construction and application of photoelectrochemical sensing in recent year. In the first segment, we briefly introduce the general princi-ple and technical characteristic of photoelectrochemical sensing. In the subsequent sections, we primarily devote to elaborating the typical strategies of design and engineering photoactive materials for improve the light excitation as well as charge separation/transfer to modulate the perfor-mance of photoelectrochemical sensing system. Addition-ally, the current research status of photoelectrochemical sensing with a particular emphasis on the innovative sens-ing devices and detection modes for achieving specific sensing functions is describes in detail with the illustrative examples. Finally, the critical challenges on the journey to achieve real-life applications of photoelectrochemical sens-ing and the viable solutions for solving these problems as well as the future research perspectives are discussed.

Recent Advances in Photoelectrochemical Sensing: From Engineered Photoactive Materials to Sensing Devices and Detection Modes.

Adsorptive removal and photocatalytic degradation of organic pollutants using metal oxides and their composites: A comprehensive review

Second near-infrared photothermal therapy (NIR-II PTT, 1000-1500 nm) has recently emerged as a new phototherapeutic modality with the advantages of deeper penetration, less energy dissipation and minimal normal-tissue toxicity over traditional first NIR PTT (750-1000 nm). However, suboptimal photothermal conversion and limited therapeutic efficacy remain the major challenges for NIR-II PTT. With the convergence in materials science, nanomedicine and biology, multifunctional NIR-II photothermal inorganic or organic materials have been extensively developed to combine NIR-II PTT with other therapeutic modalities for improved efficacies in treating life-threatening diseases including cancer and infection. This review summarizes the recent advances of NIR-II photothermal combinational theranostics pertinent to chemotherapy, immunotherapy, radiotherapy, and photodynamic, sonodynamic, chemodynamic, gene, gas, ionic, vascular and magnetothermal therapy. Potential obstacles and perspectives for future research and clinical translation of this new theranostic modality are also discussed.

Second near-infrared photothermal materials for combinational nanotheranostics

Nanostructured photothermal membranes hold great potential for solar-driven seawater desalination; however, their pragmatic applications are often limited by substantial salt accumulation. To solve this issue, we have designed and prepared flexible and washable carbon-nanotube-embedded polyacrylonitrile nonwoven fabrics by a simple electrospinning route. The wet fabric exhibits a strong photoabsorption in a wide spectral range (350-2500 nm), and it has a photoabsorption efficiency of 90.8%. When coated onto a polystyrene foam, the fabric shows a high seawater evaporation rate of 1.44 kg m-2 h-1 under simulated sunlight irradiation (1.0 kW m-2). With a high concentration of simulated seawater as the model, the accumulation of solid salts can be clearly observed on the surface of the fabric, resulting in a severe decay of the evaporation rate. These salts can be effortlessly washed away from the fabric through a plain handwashing process. The washing process has a negligible influence on the morphology, photoabsorption, and evaporation performance of the fabric, demonstrating good durability. More importantly, a larger fabric can easily be fabricated, and the combination of washable fabrics with various parallel PS foams can facilitate the construction of large-scale outdoor evaporation devices, conferring the great potential for efficient desalination of seawater under natural sunlight.

Flexible and Washable CNT-Embedded PAN Nonwoven Fabrics for Solar-Enabled Evaporation and Desalination of Seawater.

Continuously Producing Watersteam and Concentrated Brine from Seawater by Hanging Photothermal Fabrics under Sunlight

Recyclable CNT-coupled cotton fabrics for low-cost and efficient desalination of seawater under sunlight

Thiol-capped Bi nanoparticles as stable and all-in-one type theranostic nanoagents for tumor imaging and thermoradiotherapy.

Solar-driven seawater evaporation is usually achieved on floating evaporators, but the performances are substantially limited by high evaporation enthalpy, solid salt crystallization, and reduced evaporation due to inclined sunlight. To solve these problems, we fabricated hierarchical polyacrylonitrile@copper sulfide (PAN@CuS) fabrics and proposed a prototype of heliotropic evaporator. Hierarchical PAN@CuS fabrics show significantly decreased water-evaporation enthalpy (1956.32 kJ kg-1, 40 °C), compared with that of pure water (2406.17 kJ kg-1, 40 °C), because of the disorganization of the hydrogen bonds at the CuS interfaces. Based on this fabric, a heliotropic evaporation model was developed, where seawater slowly flows from high to low in the fabric. Under solar irradiation (1.0 kW m-2), this model exhibits a high-rate evaporation (∼2.27 kg m-2 h-1) and saturated brine production without solid salt crystallization. In particular, under inclined sunlight (angle range: from -90° to +90°), the heliotropic model retains an almost unchanged solar evaporation rate, whereas the floating model shows severe evaporation reduction (83.9%). Therefore, our study provides a strategy for reducing the evaporation enthalpy, maximally utilizing solar energy and continuous salt-free desalination.

Zixiao Liu

Papers

Flexible and Washable CNT-Embedded PAN Nonwoven Fabrics for Solar-Enabled Evaporation and Desalination of Seawater.

Continuously Producing Watersteam and Concentrated Brine from Seawater by Hanging Photothermal Fabrics under Sunlight

Recyclable CNT-coupled cotton fabrics for low-cost and efficient desalination of seawater under sunlight

Thiol-capped Bi nanoparticles as stable and all-in-one type theranostic nanoagents for tumor imaging and thermoradiotherapy.

Hierarchical Photothermal Fabrics with Low Evaporation Enthalpy as Heliotropic Evaporators for Efficient, Continuous, Salt-Free Desalination.