High-Index-Faceted\nNiS Confined in Sodium Alginate\nAerogel Enhanced Photothermal Conversion for Water Purification

Solar-driven interfacial evaporation is widely viewed\nas a promising\ntechnology for seawater desalination and other wastewater purifications\nthanks to its low cost and environmentally friendly features. Here,\nwe proposed high-index-faceted NiS (NiWO<sub>4</sub>-NiS) as a light\nabsorbent for photothermal conversion. In water evaporation tests,\nthe NiWO<sub>4</sub>-NiS flat membrane evaporator (NiWO<sub>4</sub>-NiS 2D evaporator) exhibited a markedly higher water evaporation\nrate than the ordinary NiS 2D evaporator. To disclose the reason,\nvarious characterizations were performed. UV–visible spectra\nconfirmed a semiconductor character with band gap energies of 2.47\nand 2.38 eV for NiS and NiWO<sub>4</sub>-NiS, respectively, in which\na narrower band gap favored photothermal conversion by photothermal\nelectronic excitation and localized surface plasmon resonance. The\nbroad band spectra showed that NiWO<sub>4</sub>-NiS had stronger absorption\nand less reflectivity for light than NiS, which was more beneficial\nfor effectively harvesting solar energy. The high-index-faceted NiS\nwas confined in sodium alginate (SA) aerogel to form an interfacial\nwater evaporator (NiWO<sub>4</sub>-NiS-aerogel 3D evaporator) and\noffered a far higher water evaporation rate than its corresponding\nNiWO<sub>4</sub>-NiS 2D evaporator. Under 1 sun, the NiWO<sub>4</sub>-NiS-aerogel 3D evaporator achieved a higher evaporation rate of\n2.43 kg m<sup>–2</sup> h<sup>–1</sup> as well as an\nevaporation efficiency of 93.1% for pure water while the NiWO<sub>4</sub>-NiS 2D evaporator displayed an evaporation rate of 1.32 kg\nm<sup>–2</sup> h<sup>–1</sup> together with an evaporation\nefficiency of 80.6%. Furthermore, the NiWO<sub>4</sub>-NiS-aerogel\n3D evaporator not only showed an excellent evaporation rate for seawater\nbut also exhibited an excellent durability. In addition, for heavy-metal\nwastewater, the NiWO<sub>4</sub>-NiS-aerogel 3D evaporator also exhibited\nan excellent purification ability. More importantly, the water evaporation\nrate of the NiWO<sub>4</sub>-NiS-aerogel 3D evaporator achieved 1.54\nkg m<sup>–2</sup> h<sup>–1</sup> under real solar irradiation\nduring the outdoor test process, which outperformed most of the previous\nwork. This work demonstrated that the high-index-faceted NiS possessed\nan excellent performance for light harvest, photothermal conversion,\nand water evaporation and presented a novel solution for seawater\ndesalination and other wastewater purification.