Solar-driven desalination using salt-rejecting plasmonic cellulose nanofiber membrane.

Solar-driven steam generation is a promising, renewable, effective, and environment-friendly technology for desalination and water purification. However, steam generation from seawater causes severe salt formation on the photothermal material, which hinders long-term and large-scale practical applications. In this study, we develop salt-rejecting plasmonic cellulose-based membranes (CMNF-NP) composed of an optimized ratio of Au/Ag nanoparticles, cellulose micro/nanofibers, and polyethyleneimine for efficient solar-driven desalination. The CMNF-NP exhibits a water evaporation rate of 1.31 kg m-2h-1 (82.1% of solar-to-vapor conversion efficiency) for distilled water under 1-sun. The CMNF-NP shows a comparable evaporation rate for 3.5 wt% brine, which has been maintained for 10 h; the evaporation rate of the filter paper-based counterpart severely decreases because of salt-scaling. The efficient salt-rejecting capability of the CMNF-NP membrane is attributed to the compact structure and electrostatic repulsion of cationic ions of salt that originate from cellulose nanofibers and the amine-functionalized polymer, polyethyleneimine, as a structural binder. This simple fabrication method of casting the CMNF-NP solution on the substrate followed by drying allows a facile coating of a highly efficient and salt-rejecting photothermal membrane on various practical substrates.

Photothermal Fabrics for Efficient Oil-Spill Remediation via Solar-Driven Evaporation Combined with Adsorption.

Oil spill rapidly destroys aquatic system and threatens humans, requiring fast and efficient remedy for removal of oil. The conventional remedy employs water-floating oil adsorbents whose volume should be large enough to accommodate all oil ingredients. Here, we suggest a new concept for efficient oil-spill remediation, which combines solar-driven evaporation of light oil components and simultaneous adsorption of heavy oil components, namely, solar-driven evaporation of oil combined with adsorption (SEOA). To design photothermal oil absorbents for the efficient SEOA, we designed carbonaceous fabrics with high photothermal heating performance and oil-adsorption capacity by carbonizing nonwoven cotton fabrics. For three model organic solvents of octane, decane, and dodecane floating on water, the fabrics, respectively, accelerated the evaporation in factors of 2.0, 4.4, and 2.3 through photothermal heating under simulated sunlight condition. For the 1.18 mm thick crude oil floating on water, 70 and 77 wt % of crude oil were evaporated within 2 and 16 h, respectively, with the photothermal fabrics, whereas only 22 and 34 wt % was evaporated in the absence of the fabrics, indicating the dramatic enhancement of oil removal by solar-driven evaporation. The remaining heavy oil components were accommodated in the pores of the fabrics, removal of which showed an additional 18 wt % reduction; that is, a total 95 wt % of the crude oil was removed. The oil-treatment capacity is as high as 110 g g-1, which has never been achieved with conventional oil adsorbents to the best of our knowledge. We believe that our combinatorial SEOA approach potentially contributes to minimizing the environmental disaster through a fast and efficient oil-spill remediation.

Cheap, facile, and upscalable activated carbon-based photothermal layers for solar steam generation.

Solar-to-steam generation characterized by nanostructured photothermal materials and interfacial heating is developed based on various carbon nanostructures such as graphene, reduced graphene oxide, CNT, or their combinations. However, multiple and sophisticated synthetic steps are required to generate macroscopic porosity in photothermal devices for the efficient mass transport of water and generated steam. Additionally, the fabrication of photothermal layers on a practical scale constitutes the main hurdle for real applications toward solar-driven desalination. Herein, we report on the development of highly efficient photothermal layers with a commercially available low-cost material, activated carbon (AC), by using facile filtration and spray coating methods, which lead to the generation of intraparticle porous structure without any additional processing. The AC-based photothermal layers generated 1.17 kg m-2 h-1 of steam under 1 sun, and 4.7 wt% of polyethyleneimine coating on AC enhanced steam generation by 8.5% under 1 sun, corresponding to 1.27 kg m-2 h-1 of the water evaporation rate and 85.66% of the photothermal conversion efficiency. This was due to improvements in light absorption and water uptake properties with the additional advantage of mechanical robustness. The outdoor solar-to-steam generation test with the spray-coated A4-sized photothermal layer in conjunction with the desalination test demonstrated the potential for practical desalination application with upscalability.

Black Diatom Colloids toward Efficient Photothermal Converters for Solar-to-Steam Generation.

Steam generation from solar power using converters has attracted significant research attention in recent years as an alternative form of energy conversion from solar energy. Rationally designed photothermal converters are essential to increase the efficiency of steam generation. Here, we propose a novel colloidal type of photothermal converter based on a frustule skeleton, which is a naturally designed colloid containing through-pore structures. Several coating processes were used to provide broadband absorption, magnetic, and water-floating properties without deteriorating pore structures, through vapor deposition polymerization of polypyrrole, weak base treatment, and additional vapor deposition polymerization of polystyrene. The prepared colloidal photothermal converter showed superior efficiency for steam generation under sunlight irradiation.

Electrostatic Stabilized InP Colloidal Quantum Dots with High Photoluminescence Efficiency.

Electrostatically stabilized InP quantum dots (QDs) showing a high luminescence yield of 16% without any long alkyl chain coordinating ligands on their surface are demonstrated. This is achieved by UV-etching the QDs in the presence of fluoric and sulfuric acids. Fluoric acid plays a critical role in selectively etching nonradiative sites during the ligand-exchange process and in relieving the acidity of the solution to prevent destruction of the QDs. Given that the InP QDs show high luminescence without any electrical barriers, such as long alkyl ligands or inorganic shells, this method can be applied for QD treatment for application to highly efficient QD-based optoelectronic devices.