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

Abstract

We synthesized CuAlS 2 /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 CuAlS 2 /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 cm 2 above 1.8 eV), spatial proximity of both semiconductor components to the surface, as well as photochemical stability. CuAlS 2 /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 for a cocatalyst, promoter, or sacrificial reagent while maintaining large turnover numbers in excess of 7 × 10 4 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 short 550 fs electron dwell times in these structures. The high energy efficiency and the environmentally friendly composition of these materials suggest a future role in solar light harvesting.

Blue Light Emitting Defective Nanocrystals Composed of Earth‐Abundant Elements

“…[34,35] Here we report the synthesis of Cu-Al-S/ZnS NCs,which are largely unexplored apart from one report of efficient PL from Cd-containing Cu-Al-S NCs via non-defect states and another report of Cu-Al-S/ZnS NCs with ah exagonal ZnS shell with < 3%QY. [36,37] Through adifferent reaction scheme (i.e.temperature,time,shell precursor identity), we report PL properties that reflect the aforementioned reports for the core-only Cu-Al-S NCs for as ubstantially brighter Cu-Al-S/ ZnS NC product with cubic ZnS shells while also providing insights into the PL mechanism. Further,weprovide avariety of spectroscopic insights and theoretical calculations to understand the observed optical properties.…”

“…Here we report the synthesis of Cu‐Al‐S/ZnS NCs, which are largely unexplored apart from one report of efficient PL from Cd‐containing Cu‐Al‐S NCs via non‐defect states and another report of Cu‐Al‐S/ZnS NCs with a hexagonal ZnS shell with <3 % QY . Through a different reaction scheme (i.e.…”

Semiconductor Quantum Dots: An Emerging Candidate for CO2 Photoreduction

“…Semiconductor QDs composed of biocompatible, earth‐abundant elements are also employed as the photocatalysts to reduce salts of carbon dioxide under visible light: 2HCO 3 − → 2HCOO − + O 2 . For instance, CuAlS 2 /ZnS QDs had been confirmed as robust photocatalysts to achieve unprecedented photochemical activity of CO 2 reduction in the form of aqueous sodium bicarbonate without the need of an external cocatalyst, promoter or sacrificial reagent ( Figure ) . High‐resolution transmission electron microscopy (TEM) image as well as the corresponding selected area Fourier transform confirmed the structure of CuAlS 2 /ZnS core/shell QDs, where the CuAlS 2 core was completely embedded in the asymmetric ZnS shell (Figure c,d).…”

“…Here, we will mainly focus on how the unique properties of QDs and the interaction between QDs and cocatalysts would promote CO 2 photoreduction. Table 1 gave a detailed summary of the currently reported examples of utilization of QDs for CO 2 photoreduction . The recent advances of using semiconductor QDs in photocatalytic CO 2 reduction will be discussed in three categories: II–VI QDs, I–III–VI QDs and perovskite‐type QDs.…”

“…d) Fourier transform of the region marked in red in panel (c) showing coincidence of spots corresponding to ZnS[002] and CuAlS 2 [112] planes. Reproduced with permission . Copyright 2018, American Chemical Society.…”