A functional material for special scenarios, usually supplied as a colloidal dispersion or sol–gel precursor, with nanoparticles stabilised by ultrasonication or surface modification (e.g. PEG) for spray or dip coating. Its layered structure and surface acid sites (Brønsted and Lewis acids) make it a solid acid catalyst for esterification, alkylation and cracking, replacing conventional liquid acids to reduce corrosion and pollution. It is also used in catalysis (photocatalytic degradation, hydrogen production by water splitting), ion exchange and adsorption (capture of heavy metals and radionuclides), energy materials (proton-conducting membranes, lithium/sodium-ion batteries), biomedicine (drug release, antibacterial coatings) and polymer composite reinforcement.
