Facile passivation of black phosphorus nanosheets via silica coating for stable and efficient solar desalination

Although black phosphorus (BP) exhibits an outstanding performance in various fields due to its superior properties, its practical applications are seriously challenged by its low stability in oxygenated and/or aqueous environments. Most current passivation techniques focus on protecting bulk BP and require special equipment or the use of organic solvents and metallic reagents. Here, we present a facile, eco-friendly, and universally applicable method for inactivating BP nanosheets. Upon the hydrolytic co-condensing of 3-aminopropyl-triethoxysilane (APTES) and methyltrithoxysilane (MTEOS), a hydrophobic shell was formed on the surface of BP (SiO2/BP-M), which retarded the degradation by preventing water from contacting the BP nanosheets. To expand the scope of applications, BP nanosheets were endowed with hydrophilicity by introducing a second hydrophilic silica shell layer (SiO2/BP-MT). Taking advantage of the broadband absorption and photothermal conversion capacity of BP, we constructed a solar desalination device using a SiO2/BP-MT film as a solar absorber along with a water transporter (non-textile) and thermal insulator (polystyrene foam). The SiO2/BP-MT film-based evaporator possessed a solar evaporation rate of 1.63 kg m−2 h−1 under one sun illumination and remained stable for at least 10 days, demonstrating that the silica coating was effective in prolonging the life-span of the BP nanosheets in an aqueous environment.