Bioinspired 1T-MoS2-based aerogel beads for efficient freshwater harvesting in harsh environments

Freshwater scarcity is one of the most critical issues worldwide, particularly in arid regions, stemming from population growth and climate change. Inspired by the hydrophilic bump structures of desert beetles, 1T-MoS2-based aerogel beads with porous structures and CaCl2-crystal loading (termed as MoAB-m@CaCl2-n) were prepared for freshwater harvesting. Metallic-phase MoS2 nanospheres exhibit excellent photothermal conversion abilities, facilitating solar-driven water desorption and evaporation. Owing to the synergistic effect of its localized surface features, hydrophilic groups, and dispersive CaCl2 particles, MoAB-2@CaCl2-2 efficiently harvests water from atmosphere with a superior moisture adsorption capacity (0.18-0.82 g g-1) at a wide range of relative humidity (10 %-70 %). Under one-sun illumination, MoAB-2@CaCl2-2 demonstrates an outstanding solar-driven water evaporation rate of 2.25 kg m-2h-1. The water evaporation rate from soil (water content = 20 %) is 1.19 kg m-2h-1, which is sufficient for sustainable freshwater generation from the soil in arid regions. More importantly, the multifunctional MoAB-2@CaCl2-2-based homemade freshwater generation prototype delivers a certain amount of water harvesting (0.99 g g-1 day-1) on a rainy day and provides an impressive daily freshwater yield (53.7 kg m-2) under natural sunlight. The integrated device exhibits excellent efficiency and practicality and offers a feasible method for freshwater harvesting in harsh environments.

A PAM hydrogel surface-coated hydroponic bamboo evaporator with efficient thermal utilization for solar evaporation

Solar-driven interfacial water purification emerges as a sustainable technology for seawater desalination and wastewater treatment to address the challenge of water scarcity. Currently, the energy losses via radiation and convection to surrounding environment minimize its energy efficiency. Therefore, it is necessary to develop strategies to minimize the heat losses for efficient water purification. Here, a novel evaporator was developed through the in situ gelation of PAM hydrogel on the surface carbonized hydroponic bamboo (PSC) to promote energy efficiency. The inherent porous and layered network structures of bamboo, in synergy with the functional hydration capacity of PAM hydrogel, facilitated adequate water transportation, while reducing evaporation enthalpy. The PAM hydrogel firmly covered on the photothermal layer surface effectively minimized the radiation and convection heat losses, while further harvesting those thermal energy that would otherwise dissipate into the surrounding environment. The reduced thermal conductivity of PSC served as a thermal insulator as well, obstructing heat transfer to bulk water and thus diminishing conduction losses. Consequently, the rational designed PSC could efficiently convert solar energy to purified water, leading to the evaporation of 2.09 kg m-2 h-1, the energy efficiency of 87.6 % under one sun irradiation, and yielding 9.6 kg m-2 fresh water over 11 h outdoor operation. Moreover, the PSC also performs excellent salt rejection, and long-term stability at outdoor experiment. These results demonstrated high and stable solar evaporation performance could be achieved if turning heat losses into a way of extra energy extraction to further enhance the evaporation performance. This strategy appears to be a promising strategy for effective thermal energy management and practical application.

Janus membranes derived from multi-shelled hollow spheres coated electrospun PVA membranes as phase change composites for photothermal conversion

The development and preparation of multifunctional photothermal conversion materials has far-reaching significance for the utilization of solar energy resources in response to the energy crisis. Herein, we propose a Janus membrane for interfacial solar evaporation and phase change energy storage. The membranes were fabricated via combining the PVA film with multi-shelled hollow spheres (MHS). The membranes have asymmetric wettability, that is, one side is hydrophilic and the other side is hydrophobic. The as-resulted membranes obtain outstanding light absorption without further processing. According to these two advantages, the membranes were applied to solar evaporation. The evaporation rate of the membrane is 1.41 kg*m-2h-1 and the evaporation efficiency is 92.4 % under 1sun irradiation. Moreover, the membrane prepared by impregnating 1-Hexadecanamine (HDA) into MHS possesses excellent tensile strength (2.21 MPa) and photothermal conversion ability. The light-to-thermal conversion efficiency can reach 81.9 % under 1sun irradiation. Therefore, the membranes have broad application prospects in the field of photothermal conversion.

Research progress of industrial wastewater treatment technology based on solar interfacial adsorption coupled evaporation process

Solar interface evaporation is an effective method for the treatment of water that has low energy consumption. Adsorption is recognized to be one of the most stable wastewater treatment methods and is widely used. Combining solar interface evaporation with adsorption provides a novel and low-cost approach for the efficient removal of heavy metals and organic pollutants from industrial wastewater. This paper reviews the characteristics and application of some common wastewater treatment methods. The photothermal conversion and the conceptual design of interface evaporation combined with adsorption are introduced and the photo-thermal conversion and adsorption methods are discussed. The study provides a summary of recent studies and advancements in interfacial evaporation-coupled adsorption materials, which include hydrogels, aerogels, and biomass materials for adsorption, and carbon materials for photothermal conversion. Finally, the current challenges encountered in industrial wastewater treatment are outlined and its prospects are discussed. The aim of this review is to explore a wide range of possibilities with the interfacial evaporation-coupled adsorption method and propose a new low-cost and high-efficiency method for industrial wastewater treatment.

Simultaneous photothermal and photocatalytic MOF- derived C/TiO2 composites for high-efficiency solar driven purification of sewage

Solar-driven water evaporation is a promising technology of freshwater production to address the water scarcity. However, the photothermal material and the distilled water would be contaminated in the evaporation of wastewater including organic pollutants. In this work, MOF-derived C/TiO2 composites (carbonized UiO-66-NH2 (Ti)) with simultaneous photothermal and photocatalytic functions are designed for producing freshwater from sewage. With advantageous features of porous structure with large specific area, excellent sunlight absorption and super-hydrophilicity, the carbonized UiO-66-NH2 (Ti) layer exhibits high water evaporation efficiency of 94% under 1.0 sun irradiation. Meanwhile, the layer can simultaneously decompose the organic pollutants with degradation efficiency of 92.7% in the underlying water during solar-driven water evaporation. This bifunctional material will provide a new approach for solar-driven water evaporation and photocatalytic degradation of organic pollutant synergistically.

Ionization Engineering of Hydrogels Enables Highly Efficient Salt-Impeded Solar Evaporation and Night-Time Electricity Harvesting

Interfacial solar evaporation holds immense potential for brine desalination with low carbon footprints and high energy utilization. Hydrogels, as a tunable material platform from the molecular level to the macroscopic scale, have been considered the most promising candidate for solar evaporation. However, the simultaneous achievement of high evaporation efficiency and satisfactory tolerance to salt ions in brine remains a challenging scientific bottleneck, restricting the widespread application. Herein, we report ionization engineering, which endows polymer chains of hydrogels with electronegativity for impeding salt ions and activating water molecules, fundamentally overcoming the hydrogel salt-impeded challenge and dramatically expediting water evaporating in brine. The sodium dodecyl benzene sulfonate-modified carbon black is chosen as the solar absorbers. The hydrogel reaches a ground-breaking evaporation rate of 2.9 kg m-2 h-1 in 20 wt% brine with 95.6% efficiency under one sun irradiation, surpassing most of the reported literature. More notably, such a hydrogel-based evaporator enables extracting clean water from oversaturated salt solutions and maintains durability under different high-strength deformation or a 15-day continuous operation. Meantime, on the basis of the cation selectivity induced by the electronegativity, we first propose an all-day system that evaporates during the day and generates salinity-gradient electricity using waste-evaporated brine at night, anticipating pioneer a new opportunity for all-day resource-generating systems in fields of freshwater and electricity.

Multi-bioinspired hierarchical integrated hydrogel for passive fog harvesting and solar-driven seawater desalination

In recent years, with the outbreak and epidemic of the novel coronavirus in the world, how to obtain clean water from the limited resources has become an urgent issue of concern to all mankind. Atmospheric water harvesting technology and solar-driven interfacial evaporation technology have shown great potential in seeking clean and sustainable water resources. Here, inspired by a variety of organisms in nature, a multi-functional hydrogel matrix composed of polyvinyl alcohol (PVA), sodium alginate (SA) cross-linked by borax as well as doped with zeolitic imidazolate framework material 67 (ZIF-67) and graphene owning macro/micro/nano hierarchical structure has successfully fabricated for producing clean water. The hydrogel not only can reach the average water harvesting ratio up to 22.44 g g-1 under the condition of fog flow after 5 h, but also be capable of desorbing the harvested water with water release efficiency of 1.67 kg m-2 h-1 under 1 sun. In addition to excellent performance in passive fog harvesting, the evaporation rate over 1.89 kg m-2 h-1 is attained under 1 sun on natural seawater during long-term. This hydrogel indicates its potential in producing clean water resources in multiple scenarios in different dry or wet states, and which holds great promise for flexible electronic materials and sustainable sewage or wastewater treatment applications.

Effect of surface roughness on the solar evaporation of liquid marbles

HYPOTHESIS

Nanostructured materials are widely used for solar energy harvesting and conversion due to their excellent photothermal properties. It is generally accepted that the better the light absorption ability, the better the photothermal conversion efficiency.

EXPERIMENT

A series of experiments in solar evaporation of liquid marbles (LMs) by coating the droplets with Fe3O4, Ni nanoparticles (NPs) and carbon nanotubes (CNTs) are conducted.

FINDINGS

Conversely, we found that the surface roughness of solar absorber plays a significant role in solar evaporation rather than the light absorption. The results disclose that the Fe3O4 NPs with the lowest absorptivity has the largest roughness on drop surface, while that of CNTs show the opposite properties. The evaporation dynamics of LMs are featured with dome or constant spherical collapse with different roughness. Such dynamic difference arises from the mechanical competition between the capillary force and interparticle interaction. Besides, the strong light-harvesting and near-field radiation enabled by the rough surfaces enhance the solar evaporation. The Fe3O4-LM shows the highest evaporation rate of 6.55 μg/s, which is 1.09 and 1.30 times larger than that of Ni-LM and CNT-LM, respectively. Numerical analysis reveals that the rough surface with stacking arrangement of NPs greatly enhances the light-induced electromagnetic field and heat concentration over the interface, leading to a plasmon-coupling boundary with high temperature for the fast evaporation. Uncovering these properties could be of much help for developments of heatable miniature evaporators or reactors and their counterparts, permitting a broad range of processes with precise temperature and kinetic control.

Biomass hydrogels combined with carbon nanotubes for water purification via efficient and continuous solar-driven steam generation

Solar vapor generation is a promising, environmentally friendly solution for water purification. The development and design of new materials and supporting devices for efficient energy conversion and clean water production are essential for the practical application of solar-driven desalination and water purification. In this study, an environmentally friendly and economical biomass hydrogel-based solar evaporator with a controllable shape was developed in a simple method by integrating carbon nanotubes (CNTs) into a sodium alginate (SA) hydrogel network. The evaporator had a high solar absorption rate (94.3%) and satisfactory hydrophilicity and could effectively avoid salt crystallization during the desalination process. This study took advantage of the aforementioned merits, and a high evaporation rate of 1.699 kg m^-2 h^-1 and a conversion efficiency of 86% were achieved under 1.0 sun irradiation. The evaporator could efficiently remove Na⁺, K⁺, Ca²⁺, and Mg²⁺ from seawater with a removal rate of up to 99.3% and a good decolorization effect on methylene blue (MB) and methyl orange (MO) dye wastewater, whose colour could be completely removed. This study provides a simple, practical, and economical method to prepare hydrogel-based evaporators that utilize abundant solar energy for large-scale desalination and wastewater treatment.

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.

A flexible and salt-rejecting electrospun film-based solar evaporator for economic, stable and efficient solar desalination and wastewater treatment

Recently, interfacial solar evaporation has been developed for water treatment. However, the high cost and low stability of solar evaporators significantly hinder their practical applications. In this study, layered graphene and polymethylmethacrylate were used to fabricate a composited film (GF) by electrospinning, which acted as a solar absorber. Together with a water transporter (polyurethane sponge) and a thermal insulator (polystyrene foam), the GF-based evaporator was constructed for solar distillation. Taking advantage of the porous three-dimensional structure of GF, the light path could be extended, rendering an efficient broadband solar absorption (92%). More importantly, although the content of layered graphene in the GF-based evaporator (1.75 g m^-2) was only 5.8-17.5% of that in the current reported graphene-based evaporators (10-30 g m^-2), a comparable water evaporation efficiency was acquired, which was induced by the much higher utilization efficiency of photothermal nanomaterials in the GF-based evaporator than that in the reported devices, ensuring its economic feasibility. Meanwhile, more than 99.9% heavy metal ions and 99.8% organic dye could be removed by the GF-based evaporator. Combining the merits of long-term and stable evaporation, salt rejection, and resistance to harsh environment, the GF-based evaporator was promising for freshwater recycling from both seawater and wastewater.

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

Solar driven interfacial evaporation has received extensive attention as a very promising desalination technique to solve the fresh water shortage crisis. However, salt-fouling and poor stability during long-term solar desalination seriously hinder applications of solar evaporators. In addition, most of the reported evaporators rely on expensive materials and complex preparation processes. Here, we report facile preparation of polydimethylsiloxane/carbon nanotubes (PDMS/CNTs) modified melamine solar evaporators for efficient steam generation and desalination. The elastic solar evaporators feature (i) macroporous network with rough skeleton owing to phase separation of PDMS, high solar absorbance (99%) and excellent photothermal performance, low thermal conductivity (0.032 W m^-1 K^-1), and (iii) unique wettability (hydrophobic upper surface and hydrophilic lower part). Consequently, the evaporators have an evaporation rate of 1.44 kg m^-2 h^-1 and a solar-to-vapor conversion efficiency of 84% for solar evaporation of deionized water under 1 sun illumination. Interestingly, the evaporators show similar solar evaporation performance for saline water compared to deionized water. Moreover, the evaporators show excellent salt-resistance and stability during long-term continuous solar desalination owing to rapid water replenishment in the evaporators. The evaporators may find practical applications in solar desalination because of the merits of the evaporators and the simple preparation method.

Freshwater production via efficient oil-water separation and solar-assisted water evaporation using black titanium oxide nanoparticles

Fabrication of a multipurpose superhydrophobic mesh via modification of a galvanized steel mess using black titanium oxide nanoparticles and perfluorodecyltriethoxysilane is reported. Modified mesh exhibits superhydrophobicity with a water static contact angle of 157° ± 2 along with a tilt angle of 5° ± 1 and suitable chemical, thermal, mechanical stability, and self-cleaning ability. The droplet dynamic behavior of superhydrophobic mesh revels the impact velocity is 1.5 ms^-1 for splashing of the water droplet. The developed mesh is studied for freshwater generation from oily water and seawater via efficient oil-water separation and solar evaporation, respectively. A proficiency of 99% and 88% is achieved for oil-water separation from mixture and emulsion, respectively. Solar evaporation efficiency of 64% and 76% are recorded under low-intensity light (225 Wm^-2) and natural sunlight (591 Wm^-2), respectively, from distilled water. For seawater, the evaporation efficiency of 69% is achieved under natural sunlight. Present approach can be applied to any size and shape of the mesh and has great industrial applications.

Effect of sonication time on the evaporation rate of seawater containing a nanocomposite

Sonication time has a significant contribution to the stability and properties of nanofluids (mixtures of nanoparticles and a base fluid). Finding the optimum sonication time can help to save energy and ensure optimal design. The present study deals with the sonication time effect on the evaporation rate of seawater containing a nanocomposite (i.e., a mixture of multi-walled carbon nanotubes and graphene nanoplates). For indoor experiments, a solar simulator was employed as the radiation source. At first, the nanofluid with a concentration of 0.01% wt. was sonicated in an ultrasonic bath for different times of 30, 60, 90, 120, 180, 240 min, and the associated zeta potential values were recorded to evaluate the stability. Next, the best time function was used to appraise the effect of concentration variations (0.001, 0.002, 0.004, 0.01, 0.02 and 0.04% wt.) and the light intensities (1.6, 2.6, and 3.6 suns) on the rate of solar steam generation. The results indicate that for a concentration of 0.01% wt. and under 3.6 suns, the highest evaporation efficiency of 61.3% would be achieved at 120 min sonication time.

Accelerated solar steam generation for efficient ions removal

Solar-driven evaporation as a sustainable water purification technology exhibits great potential in solving the global water crisis. In this paper, a novel solar evaporator was successfully prepared with the reduced graphene oxide (rGO) and silver (Ag) nanowires as photothermal conversion media which were loaded into the sodium alginate (SA) hydrogel. It was found that the evaporation rate of the prepared evaporator reached 2.02 kg m^-2 h^-1 and the solar energy efficiency was 91% under one sun irradiation intensity. Furthermore, this novel solar evaporator exhibited expectant evaporation performance in the treatment of seawater and heavy metal sewage with excellent ion removal ability, with the removal efficiency of various ions higher than 99.9%. The ion-crosslinked SA hydrogel contained in the evaporator ensured the rejection of multivalentions based on the distribution of carboxylate anions, and the three-dimensional porous channel of the super-hydrophilic hydrogel provided the convenient path for the transport of water molecules and the escape of water vapor. The binary composition of rGO and silver nanowires enhanced the photothermal conversion and the thermal conductivity, which was beneficial to the stable supply of thermal energy for evaporation. The purpose of this paper is to provide reference for promoting the practical application of solar evaporation.

A novel composite hydrogel for solar evaporation enhancement at air-water interface

This paper reports a facile approach to synthesize a novel composite hydrogel with graphene oxide (GO), silica aerogel (SA), acrylamide (AM), and poly(vinyl alcohol) (PVA) through physical and chemical cross-linking method. The composite hydrogel (GO/SA PAM-PVA hydrogel) exhibits excellent solar evaporation property, good water transmission capacity, and floatability. The GO nanosheets dispersed homogeneously in the hydrogel could provide prominent photothermal conversion efficiency to heat water for evaporation. Excellent hydrophilicity of hydrogel promotes the water molecules transport from the bottom to the top of the hydrogel, which can increase evaporation efficiency. The SA in the hydrogel makes the GO/SA PAM-PVA hydrogel floatable, which is crucial for improving evaporation efficiency because evaporation occurs primarily at several molecular layers on the surface of the water. Furthermore, the self-cleaning ability derived from SA of the GO/SA PAM-PVA hydrogel surface provides a convenient recycling and reusing process for practical applications. The evaporation mass of seawater achieved by the GO/SA PAM-PVA hydrogel is 6 times higher than that of traditional process at an optical density of 2 kW m^-2 for 30 min. Meanwhile, the evaporation efficiency of GO/SA PAM-PVA hydrogel remains good during reuse.