Abstract
Colloidal photocatalysts can utilize solar light for the conversion of CO2 to carbon-based fuels, but controlling the product selectivity for CO2 reduction remains challenging, in particular in aqueous solution. Here, we present an organic surface modification strategy to tune the product selectivity of colloidal ZnSe quantum dots (QDs) towards photocatalytic CO2 reduction even in the absence of transition metal co-catalysts. Besides H2, imidazolium-modified ZnSe QDs evolve up to 2.4 mmolCO gZnSe−1 (TONQD > 370) after 10 h of visible light irradiation (AM 1.5G, λ > 400 nm) in aqueous ascorbate solution with a CO-selectivity of up to 20%. This represents a four-fold increase in CO-formation yield and 13-fold increase in CO-selectivity compared to non-functionalized ZnSe QDs. The binding of the thiolated imidazolium ligand to the QD surface is characterized quantitatively using 1H-NMR spectroscopy and isothermal titration calorimetry, revealing that a subset of 12 to 17 ligands interacts strongly with the QDs. Transient absorption spectroscopy reveals an influence of the ligand on the intrinsic charge carrier dynamics through passivating Zn surface sites. Density functional theory calculations indicate that the imidazolium capping ligand plays a key role in stabilizing the surface-bound *CO2− intermediate, increasing the yield and selectivity toward CO production. Overall, this work unveils a powerful tool of using organic capping ligands to modify the chemical environment on colloids, thus enabling control over the product selectivity within photocatalyzed CO2 reduction.
Highlights
The sustainable generation of carbon neutral fuels is expected to play a critical role in the future energy supply
Having excluded a mechanism directly catalyzed by the MEMIligand, as well as the in uence of methyl-imidazolium halide (MEMI) on the intrinsic charge carrier dynamics in order to explain the enhanced CO formation activity promoted by MEMI, we explore secondarycoordination sphere effects of MEMI on quantum dots (QDs)-surface promoted CO2 reduction
We report a simple organic surface modi cation strategy to enhance the photocatalytic CO2 to CO reduction activity of inexpensive and benign ZnSe QDs
Summary
The sustainable generation of carbon neutral fuels is expected to play a critical role in the future energy supply. To rule out the possibility that the in uence of MEMI originates purely from the presence of a thiol group, we conducted a control experiment with a ligand consisting of a thiol with no additional functionality, 1-butanethiol (BuSH), which resulted in a similar product distribution compared to nonfunctionalized ZnSe (Fig. S12†).
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