g-C3N4/TiO2/ZnIn2S4 graphene aerogel photocatalysts with double S-scheme heterostructure for improving photocatalytic multifunctional performances

The construction of aerogel photocatalyst materials with heterostructure is a practical and effective strategy to remove heavy metal ions, degrade pollutants, and conduct hydrogen evolution reactions. Herein, the isoelectric point assisted calcination technique is used to prepare a g-C3N4/TiO2/ZnIn2S4 graphene aerogel (CTZA) photocatalyst with a double S-scheme heterostructure using graphene aerogel as carriers, which can improve photocatalytic multifunctional performances. Under simulated sunlight illumination, through the joint action of photocatalysis and adsorption, the reduction rate of Cr(VI) by CTZA composites reaches 98.3% within 70 min, and the degradation efficiency of methyl orange (MO) reaches 97.5% within 30 min, which are much higher than the photocatalytic performances of the single samples. The charge transfer mechanism of the double S-scheme heterostructure in the CTZA photocatalytic system is proposed and confirmed via the combination of the DFT theoretical calculations with a series of experiments. In addition, the CTZA photocatalyst also displays a high hydrogen evolution rate (6531.9 μmol g−1). The excellent photocatalytic performance of CTZA is mainly due to the advantages of both the heterojunction photocatalyst and the graphene aerogel framework. The formation of a double S-scheme heterostructure can more effectively reduce the recombination of photo-induced carriers and increase the reduction and oxidation abilities. The graphene aerogel skeleton provides more active sites, and the unique three-dimensional network provides abundant electron transport channels, which extend the lifetime of light and accelerate the transport rates of carriers. This study shows that the aerogel photocatalyst has potential applications in solving energy and environmental problems.