High-Index-Faceted NiS Confined in Sodium Alginate Aerogel Enhanced Photothermal Conversion for Water Purification

Solar-driven interfacial evaporation is widely viewed as a promising technology for seawater desalination and other wastewater purifications thanks to its low cost and environmentally friendly features. Here, we proposed high-index-faceted NiS (NiWO4-NiS) as a light absorbent for photothermal conversion. In water evaporation tests, the NiWO4-NiS flat membrane evaporator (NiWO4-NiS 2D evaporator) exhibited a markedly higher water evaporation rate than the ordinary NiS 2D evaporator. To disclose the reason, various characterizations were performed. UV–visible spectra confirmed a semiconductor character with band gap energies of 2.47 and 2.38 eV for NiS and NiWO4-NiS, respectively, in which a narrower band gap favored photothermal conversion by photothermal electronic excitation and localized surface plasmon resonance. The broad band spectra showed that NiWO4-NiS had stronger absorption and less reflectivity for light than NiS, which was more beneficial for effectively harvesting solar energy. The high-index-faceted NiS was confined in sodium alginate (SA) aerogel to form an interfacial water evaporator (NiWO4-NiS-aerogel 3D evaporator) and offered a far higher water evaporation rate than its corresponding NiWO4-NiS 2D evaporator. Under 1 sun, the NiWO4-NiS-aerogel 3D evaporator achieved a higher evaporation rate of 2.43 kg m–2 h–1 as well as an evaporation efficiency of 93.1% for pure water while the NiWO4-NiS 2D evaporator displayed an evaporation rate of 1.32 kg m–2 h–1 together with an evaporation efficiency of 80.6%. Furthermore, the NiWO4-NiS-aerogel 3D evaporator not only showed an excellent evaporation rate for seawater but also exhibited an excellent durability. In addition, for heavy-metal wastewater, the NiWO4-NiS-aerogel 3D evaporator also exhibited an excellent purification ability. More importantly, the water evaporation rate of the NiWO4-NiS-aerogel 3D evaporator achieved 1.54 kg m–2 h–1 under real solar irradiation during the outdoor test process, which outperformed most of the previous work. This work demonstrated that the high-index-faceted NiS possessed an excellent performance for light harvest, photothermal conversion, and water evaporation and presented a novel solution for seawater desalination and other wastewater purification.