Optimization of bamboo-based photothermal interfacial solar evaporator for enhancing water purification.

Although solar desalination is a promising approach for obtaining freshwater, its practical application encounters challenges in achieving efficient photothermal evaporation. Recent research has focused on novel configurations of solar absorbers with unique structural features that can minimize heat loss. High-efficiency interfacial solar steam generation (SSG) can be achieved by optimizing the design of the absorber to harness incident heat energy on the top interfacial surface and ensuring a continuous water supply through microchannels. Artificially nanostructured absorbers might have high solar absorptivity and thermal stability. However, the manufacturing of absorbers is expensive, and the constituting materials are typically non-biodegradable. The unique structural configuration of natural plant-based solar absorbers provides a major breakthrough in SSG. Bamboo, as a natural biomass, possesses exceptional mechanical strength and excellent water transport through vertically oriented microchannels. This study aimed to enhance the performance of SSG with a carbonized bamboo-based solar absorber (CBSA). To achieve this goal, we optimized the carbonization thickness of the absorber by varying the carbonization time. Furthermore, the height of the CBSA was varied from 5 to 45 mm to determine the optimal height for effective solar evaporation. Accordingly, the highest evaporation rate of 3.09 kg m-2 h-1 was achieved for the CBSA height of 10 mm and top-layer carbonization thickness of 5 mm. The cost-effectiveness, simple fabrication, and superior desalination performance of the CBSA demonstrate a strong potential for practical applications.

Conversion of Hazardous Diesel Soot Particles into a Novel Highly Efficient 3D Hydrogel for Solar Desalination and Wastewater Purification.

Diesel particulate matter (DPM) generated as vehicular exhaust is one of the main sources of atmospheric soot. These soot particles have been known to cause adverse health problems in humans and cause acute environmental problems. Despite great efforts for minimizing soot production, research on the disposal and recycling of inevitable diesel soot is scarce. However, DPM consists mainly of carbonaceous soot (DS) that can be easily utilized as a photothermal material for solar desalination. Recently, interfacial solar steam generation using three-dimensional (3D) structures has gained extensive attention. 3D-structured hydrogels have exhibited incredible performance in solar desalination owing to their tunable physicochemical properties, hydrophilicity, intrinsic heat localization, and excellent water transport capability. Herein, a novel DS-incorporated 3D polyvinyl alcohol (PVA)-based hydrogel is proposed for highly efficient solar desalination. The polymer network incorporated with purified DS (DSH) achieved an excellent evaporation rate of 3.01 kg m-2 h-1 under 1 sun illumination due to its vertically aligned water channels, hydrophilicity, and intrinsic porous structure. In addition, the DSH-PVA hydrogel could generate desalinated water efficiently (2.5 kg m-2 h-1) with anti-salt fouling properties. The present results would motivate the utilization and recycling of waste materials like DS as photothermal materials for efficient, low-cost, and sustainable solar desalination.

Highly Efficient and Salt-Rejecting Poly(vinyl alcohol) Hydrogels with Excellent Mechanical Strength for Solar Desalination.

Interfacial solar steam generation (ISSG)-based solar desalination has recently emerged as a promising solution to tackle the global issue of fresh water scarcity. However, the energy-intensive process of conventional vapor generation techniques limits its practical applications. Hydrogels with three-dimensional (3D) structures have been reported to alleviate this energy demand, but their applications in sustainable solar desalination are hindered by their poor mechanical stability. Herein, we propose a 3D poly(vinyl alcohol) (PVA)-based hydrogel with excellent mechanical strength for effective solar desalination. The dual polymer network hydrogel (PVA-agar) incorporated with multi-walled carbon nanotubes (MWCNTs) achieved a noticeable evaporation rate of 3.1 kg m-2 h-1 under 1 sun irradiation, owing to its broadband light absorption, intrinsic water channels, and microporous structure that help reduce the latent heat of vaporization. More importantly, the application of kosmotropic ammonium sulfate ions was found to greatly improve the mechanical strength of the hydrogels using a facile Hofmeister-assisted soaking method. Finally, the PVA-agar-MWCNT hydrogel was able to desalinate seawater efficiently (2.5 kg m-2 h-1) with self-cleaning capability of salt crystals. The salinity level of the desalinated water was also comparable to drinking clean water. The present results would pave the way for fabricating mechanically strong, hydrophilic, and highly efficient hydrogels for effective and sustainable solar desalination.

Adsorptive seawater desalination using MOF-incorporated Cu-alginate/PVA beads: Ion removal efficiency and durability.

With the worsening water scarcity problem, seawater desalination has been receiving gradually increasing attention. Ion adsorptive desalination was introduced as one of the seawater desalination techniques. In our previous study, metal-organic framework (MOF)-incorporated single-network alginate (MOF-Alg(Cu)) beads were used to adsorb ions in seawater. In the present study, MOF-incorporated Cu-based alginate/PVA hydrogel (MOF-Alg(Cu)/PVA) beads were fabricated to enhance the ion adsorption desalination technique. Cu-based MOFs were successfully synthesized in situ on an interpenetrating polymer network (IPN). Given that the IPN hydrogel beads have high stability, the amount of MOF particles extracted during the adsorption of ions is reduced. The fabricated MOF-Alg(Cu)/PVA beads exhibit efficient removal of dissolved ions in artificial seawater and NaCl solution with varied concentrations. The ion adsorption characteristics were evaluated on the basis of adsorption kinetics, adsorption isotherms, and dosage of adsorbent. The repeat cycle tests show that more than half of the ion removal efficiency was maintained after 10 cycle tests. The concentration of artificial seawater was reduced to 1500 ppm by employing MOF-Alg(Cu)/PVA beads through a multistage experiment. Compared with other seawater desalination techniques, the proposed adsorptive desalination technique using MOF-Alg(Cu)/PVA beads will pave the way for developing a new ecofriendly and energy-saving approach.