Quantum Dots as Photocatalysts for Bicarbonate Reduction to Solar Fuels: Formate Production from CuS, CuInS 2 , and CuIn
- PDF / 945,966 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 84 Downloads / 186 Views
Downloaded from https://www.cambridge.org/core. HKUST Library, on 02 Jan 2019 at 09:37:08, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2018.646
Quantum Dots as Photocatalysts for Bicarbonate Reduction to Solar Fuels: Formate Production from CuS, CuInS2, and CuInS2/ZnS Hanqing Pan1, Ruwini Rajapaksha1, and Michael D. Heagy1 1 Department of Chemistry, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801
ABSTRACT
In this study, non-cadmium-based quantum dots were synthesized and used as catalysts for the photochemical reduction of bicarbonate to value-added formic acid. Three types of quantum dots (CuS, CuInS2, and CuInS2/ZnS) were chosen because of they feature environmentally benign properties, possess wide optical absorption, and exhibit excellent photocatalytic activity. All three photocatalysts exhibited excellent efficiency in the photo-reduction of bicarbonate to formic acid, with CuInS2/ZnS showing the highest photon to formate conversion efficiency of 6.07 ± 0.07%. We attribute these exceptional results to their smaller bandgap leading to enhanced visible light absorption and the application of an appropriate hole scavenger that prolongs photo-generated charge carrier separation. To the best of our knowledge, the application of quantum dots in photocatalysis is still quite limited; this report describes the highest apparent quantum efficiency (AQE) to date.
INTRODUCTION Quantum dots (QDs) are nanocrystals of a semiconductor possessing a diameter less than 10 nm.1 Quantum dots have unique optical and electronic properties which make them attractive materials for light emitting diodes (LEDs),2,3 solar cells,4,5 sensors,6,7 and biological imaging.8 Although II-VI Cd-based QDs have been widely used, such QDs are toxic to humans and the environment, moreover the inclusion of heavy metals can also limit their application.9 As an alternative, binary III-V and ternary I-III-VI compounds have been used as replacements to conventional Cd-based QDs. Ternary I-III-VI compounds such as CuInS2 (CIS), CuInSe2 (CISe), CuGaS2 (CGS), AgInS2 (AIS), and AgGaS2 (AGS) have been gaining more attention.9 These quantum dots are direct band gap semiconductors have lower toxicity, high absorption
Downloaded from https://www.cambridge.org/core. HKUST Library, on 02 Jan 2019 at 09:37:08, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2018.646
coefficients, are more stable, and maintain enhanced photoluminescence quantum yields (QY) up to ~80%.10 For example, CuInS2 QDs has a band gap of 1.53 eV, exhibits a high absorption coefficient (α = 5x105 cm-1) and long photoluminescence lifetimes.11 We hypothesize that these quantum dots would be suitable photocatalysts for bicarbonate reduction because the conduction band energies of CuS lies at -0.8 eV, which is above the reduction potential of CO2/HCOOH at -0.61 eV. The conduction band and reduction po
Data Loading...
