Efficient Photosynthesis of Organics from Aqueous Bicarbonate Ions by Quantum Dots Using Visible Light

Abstract

We synthesized CuAlS2/ZnS quantum dots (QDs) composed of biocompatible, earth abundant elements that can reduce salts of carbon dioxide under visible light. The use of an asymmetric morphology at a type-II CuAlS2/ZnS heterointerface balances multiple requirements of a photoredox agent by providing a low optical bandgap (~1.5 eV), a large optical cross section (>10-16 cm2 above 1.8 eV), spatial proximity of both semiconductor components to the surface as well as photochemical stability. CuAlS2/ZnS QDs thus have an unprecedented photochemical activity in terms of reducing carbon dioxide in the form of aqueous sodium bicarbonate under visible light, without the need of a co-catalyst, promoter or a sacrificial reagent while maintaining large turnover numbers in excess of 7x104 per QD. Devices based on these QDs exhibit energy conversion efficiencies as high as 20.2 ± 0.2%. These observations are rationalized through our spectroscopic studies that show a short 550 fs electron dwell times in these structures. T...