Flexible and Efficient Solar Thermal Generators Based on Polypyrrole Coated Natural Latex Foam for Multimedia Purification

Water scarcity has become a major global challenge in recent years needed to deal with urgently. Solar evaporation has emerged as a renewable energy source and a novel technique for clean water production and wastewater treatment. However, developing a high-performance, environment-friendly, and scalable solar evaporator remains a significant challenge. Herein, we developed a high-performance, self-floatable, environmentally friendly, and single-step manufacturing of a two-dimensional solar steam generator. The developed solar evaporator is composed of facile coating of Fe2O4@PPy nanoparticles (NPs) deposit on low-cost and commercially available super hydrophilic wood pulp sponge which offers a sustainable solution to the ever-growing issues of the energy and water crises. The as-prepared foam exhibits good wettability (zero contact angle), salt-resistance (3 g /180 minutes), low thermal conductivity (0.225 W m−1 K−1), and excellent light absorption of ∼95% due to the omnidirectional porous surface of Fe2O4@PPy NPs. The broadband solar absorption of Fe2O4@PPy solar evaporator is capable to transform into thermal energy (42.3 ˚C) and generate vapors (1.62 kg m-2 h-1) along with 93 % photothermal conversion efficiency under one sun (1 kW m-2). Furthermore, the presented prototype can be directly installed to purify various types of wastewaters with a high rejection ratio of heavy metal ions (nearly 100%). This simple fabrication process with renewable polymer resources and photothermal materials provides fundamental guidance and practical application value toward developing high-performance solar evaporation technologies for remote areas and individuals. Keywords: Fe2O4@PPy, solar steam generation, wood pulp, polypyrrole.

As a sustainable and clean water production technology, solar thermal water evaporation has been extensively studied in the past few years. One challenge is that upon operation, salt would form on surface of the solar absorbers leading to inefficient water supply and light absorption and thus much reduced water vaporization rate. To address this problem, a simple solar evaporator based on an array of aligned millineedles for efficient solar water evaporation and controlled site-specific salt formation is demonstrated. The maximum solar evaporation rate achieved is 2.94kg m-2 h-1 under one Sun irradiation in brine of high salinity (25wt% NaCl), achieving energy conversion efficiency of 94.5% simultaneously. More importantly, the spontaneously site-specific salt formation on the tips of millineedles endows this solar evaporator with salt harvesting capacity. Rationally separating the clean water and salt from brine by condensation and gravity assistance, this tip-preferential crystallization solar evaporator is not affected by the salt clogging compared with conventional 2D solar evaporators. This study provides new insights on the design of solar evaporators and advances their applications in sustainable seawater desalination and wastewater management.

3D porous materials are of great interest in many areas of study, but it is still difficult to prepare those with high elasticity and low thermal conductivity via facile methods. Here, superelastic laponite/silicone (LS) composite sponges with low thermal conductivity are prepared via a simple approach. The LS sponges were analyzed by various characterization methods. The content of laponite nanosheets in LS sponges has a great influence on the microstructure, comprehensive mechanical properties, and thermal conductivity. LS sponges feature (i) high mechanical strength, compressibility, and elasticity, (ii) excellent superhydrophobicity/superoleophilicity, and (iii) low thermal conductivity. Consequently, LS sponges could be used for water purification, for example, oil/water separation and solar-driven interfacial evaporation in combination with carbon nanotubes (CNTs). The LS/CNTs solar evaporator has a remarkable evaporation rate of 1.77 kg m-2 h-1 for the 3.5 wt % NaCl aqueous solution under 1 kW m-2 irradiation and high salt resistance. We foresee that this study will promote the development of new 3D porous materials and their applications.

Sustainable MXene/PDA hydrogel with core-shell structure tailored for highly efficient solar evaporation and long-term desalination

In situ generation of carbonized polyaniline nanowires on thermally-treated and electrochemically-etched carbon fiber cloth for high efficient solar seawater desalination

As a new family in carbon nanomaterials, carbon dots (CDs) are potential candidates for solar water evaporator, owing to their cost-effectiveness, non-toxicity, high solubility, and tunable optical properties. Despite such potentials, however, CDs mainly absorb solar spectrum in the ultraviolet region while their absorption in the visible region is limited, the characteristics that hinder their functionality in generating steam from solar energy. Herein, the optical and photothermal properties of CDs, derived from urea and citric acid, can be modulated by controlling their surface stoichiometry through varying the molar ratio of the precursors. Our approach is simple, fast, and highly scalable by utilizing a microwave irradiation technique. We found that increasing the nitrogen content results in broadening of the absorption spectra into the visible region due to more functional groups introduced on the CD surface that reduce the band gap, as confirmed both by X-ray photoelectron spectroscopy and theoretical calculation. Employing the CDs as photothermal materials in the volumetric solar evaporator, we demonstrate a remarkable evaporation efficiency of up to 70% along with a volumetric evaporation rate of 1.11 kg m–2 h–1 under 1 sun illumination, superior to direct bulk water heating. Furthermore, the CDs show excellent durability and stability, as demonstrated by their stable evaporation rate for 10 days, with no significant decrease in the optical and photothermal properties. This finding provides a pathway to design and functionalize CDs with controllable optical and photothermal properties for an efficient solar evaporation system.

Harnessing renewable solar energy for solar desalination shows great promise for addressing freshwater scarcity. However, conventional solar desalination suffers from low photothermal conversion and excessive heat dissipation, limiting its practicality for meeting water demand. Interfacial solar steam generation (ISSG) has emerged to address these limitations, leveraging advances in photothermal absorber materials, structural design, and thermal management. The photothermal material (PTM) plays a crucial role as it facilitates the conversion of solar energy into localized heat energy, leading to water evaporation within a localized high-temperature zone.1 In this talk, we present unique photothermal absorber materials that are not common for ISSG, such as bismuth copper oxysulfide (BiCuSO; BCSO), silicon (Si), and red phosphorus (RP), exhibiting broad light absorption, low thermal conductivity, and high heat localization. 2–5 We employed a mechanochemical activation method to regulate particle size and surface defects simultaneously, thus enhancing the optical, thermal, and photothermal properties. Utilizing the 1D water path architecture, we achieved an outstanding water evaporation rate of 2.2 (photothermal efficiency: 107.9%), 1.77 (96%), and 1.75 kg/m2·h (94.0%) using Si, BCSO, and RP absorber materials, respectively, under 1 sun illumination (100 mW/cm2). Furthermore, our photothermal absorbers demonstrated excellent ion rejection capabilities when subjected to continuous measurement for 50 h with both seawater and industrial wastewater. The emerging interface solar-driven steam generation technology promises to meet future human needs for freshwater, energy, and environmental sustainability. Keywords: Photothermal materials; Mechanochemical activation; Defect control; Interfacial solar desalination; Wastewater purification.

Flexible hierarchical polypyrrole-coated Cu-BTC MOFs photothermal textile for efficiently solar water evaporation and wastewater purification

An efficient interfacial solar evaporator featuring a hierarchical porous structure entirely derived from waste cotton

A loofah-based all-day-round solar evaporator with phenolic lignin as the light-absorbing material for a highly efficient photothermal conversion

Wood-based solar steam evaporators have been attracting increasing interest due to their great potential for addressing water scarcity by utilizing sustainable materials and energy. However, engineering a 3D porous structure within the wood lumens and its effect on solar vapor evaporation have not yet been well explored. Here, a natural wood-based solar evaporator with hierarchical pores is fabricated by assembling polyvinyl alcohol within the lumens through an ice-templating approach. The polyvinyl alcohol porous network is engineered from vertically aligned microchannels to dendritically bridged pores with a narrowed size of a few micrometers and significantly increased surface area. Although the formation of plenty of microscopic channels increases the capillary force in comparison to the native wood lumen, the morphology change induces a high tortuosity factor of the porous structure, resulting in a reduced water transportation rate as well as an increased contact angle. On the other hand, the high surface area of the engineered wood lumens and the good hydrophilicity of the filled polyvinyl alcohol improve the ratio of the formed intermediate water, contributing to reduced vaporization enthalpy. Consequently, by using polydopamine as the photothermal material, the hierarchically structured polyvinyl alcohol-wood solar evaporator exhibits an evaporation rate of 1.6 kg m-2 h-1 under 1 sun irradiation and a high solar evaporation efficiency of up to 107%, which are higher than most of the reported natural-wood-based solar evaporators. Moreover, by exploring the correlation between porous morphology and performance, it has been found that the polyvinyl alcohol-wood composite not only presents an inexpensive and sustainable evaporator but also provides guidelines for designing high-performance steam generation devices.

Facile preparation of polydimethylsiloxane/carbon nanotubes modified melamine solar evaporators for efficient steam generation and desalination

A solar evaporator that utilizes solar radiation energy can be a renewable approach to deal with energy crisis and fresh water shortage. In this study, a solar evaporator was prepared by assembling composite carbonized wood of Melaleuca Leucadendron L. and biobased hydrogel. The multilayer MXene (Ti3C2Tx) was embedded in the scaffolding structure of the wood to form composite carbonized wood, where the loose and ordered scaffolding structure of the carbonized wood significantly improves the efficiency of water transportation with increased capillary force. The MXene adsorbed in the carbonized wood has high binding energy with water molecules, leading to reduction of vaporization enthalpy and contact angle. Moreover, the addition of MXene can improve the light absorbance, especially for the infrared and ultraviolet light bands. The hydrogel was fabricated by crosslinking konjac glucomannan and sodium alginate polysaccharides with Ca2+, and it has a lower thermal conductivity than water and improves the evaporation efficiency by regulating the temperature distribution and concentrating the heat on the surface of the evaporator. This solar evaporator has an evaporation rate of 3.71 kg·m-2·h-1 and an evaporation efficiency of 129.64% under 2 sun illumination and is available to generate an open-circuit voltage of 1.8 mV after a 20 min hydrovoltaic, demonstrating a high performance and versatility. Also, experiments and numerical simulation were carried out to understand the mechanism and design principles of this solar evaporators.

Review on the recent development and applications of three dimensional (3D) photothermal materials for solar evaporators

Solar photothermal water evaporation technology has attracted attention owing to its promising applications in wastewater treatment and desalination for producing clean water. However, high-performance solar evaporators are still limited by the complex manufacturing process, less flexibility, intolerance to salt, high cost, and low water evaporation efficiency. In this study, composite fibre paper composed of waste tissue paper, aramid nanofibers, and polyaniline was prepared to produce clean water. The evaporator was designed to pump water through a cotton wick to the composite paper, which reduced heat loss and avoided the deposition of salt on the surface. The use of waste tissue paper solves the problem of waste disposal, increases the commercial value of waste tissue, and reduces production costs. The composite fibre paper exhibited broad-band light absorption of an average of 96%. The average evaporation rate of the solar evaporator was 1.43 kg m−2 h−1, and the photothermal conversion efficiency was 98.33% under 1 sun illumination. This solar evaporator is easily fabricated and is cost-effective, demonstrating the enormous potential for real-world wastewater treatment and desalination to produce clean water.