Ultrathin 2D ZnGa-borate-LDH nanosheets for boosting dye-sensitized photocatalytic coupled reaction of H2 production with pollutant degradation

Ultrathin 2D borate anions B4O5(OH)42- intercalated layered double hydroxide (ZnGa-BLDH) nanosheets (about 5–6 nm, 2–3 layers stacked), which construct a mesoporous structure, were prepared for efficient dye adsorption, photocatalytic dye degradation, and the dye-sensitized photocatalytic coupled reaction of pollutant degradation with hydrogen production. Because of its unique ultrathin 2D structure, ZnGa-BLDH shows significantly enhanced dye adsorption and photocatalytic performance. The process of CR photodegradation is in accord with the Langmuir-Hinshelwood model and the photocatalytic degradation rate constant k of ZnGa-BLDH (0.0262 min-1) is 2.6 and 6.0 times higher than that of ZnGa-CLDH (0.0099 min-1) and ZnGa-C-BLDH (0.0044 min-1), respectively. The photocatalytic coupled reaction can be achieved effectively on the ZnGa-BLDH nanosheets in the wastewater containing dye and TEOA for simultaneous hydrogen production and dye degradation under the effect of the dye sensitization on harvesting sunlight and promotion of the separation and transfer of e--h+ pairs. Upon light irradiation, the photogenerated electrons of ZnGa BLDH itself under UV light and the electrons on the conduction band of ZnGa-BLDH transferred from LUMO of excited CR* are captured by protons to produce hydrogen. Some holes on the valance band of ZnGa-BLDH can migrate to the HOMO of CR for dye degradation and some holes were consumed by TEOA. H2 production of ZnGa-BLDH-CR (32 μmol/h/g) is 2.6 and 2.5 times higher than that of carbonate anions intercalated LDH (ZnGa-CLDH-CR, 12.2 μmol/h/g) hexagonal nanosheets and borate anions B(OH)4- intercalated LDH (ZnGa-C-BLDH-CR, 12.6 μmol/h/g) hexagonal nanosheets obtained from ZnGa-CLDH, respectively. This work not only provides a strategy for the rational design and development of ultrathin 2D nanosheets, but also guides the development of a bifunctional system of organic pollutant degradation and hydrogen production.