Investigating the Control by Quantum Confinement and Surface Ligand Coating of Photocatalytic Efficiency in Chalcopyrite Copper Indium Diselenide Nanocrystals

Abstract

ABSTRACT:In the past few years, there has been an immense interest in the preparation of sustainable photocatalysts composed of semiconductor nanocrystals (NCs) as one of their component. We report here, for the first time, the effects of structural parameters of copper indium diselenide (CuInSe 2 ) NCs on visible light driven photocatalytic degradation of pollutants under homogeneous conditions. Ligand exchange reactions were performed replacing insulating, oleylamine capping with poly(ethylene glycol) thiols to prepare PEG-thiolate-capped, 1.8 to 5.3 nm diameter CuInSe 2 NCs to enhance their solubility in water. This unique solubility property caused inner-sphere electron transfer reactions (O 2 to O 2 −) to occur at the NCs surface allowing for sustainable photocatalytic reactions. Electrochemical characterization of our dissolved CuInSe 2 NCs showed that the thermodynamic driving force (-ΔG) for oxygen reduction, which increased with decreased NCs size, was the dominant contributor to the overall process when compared to the contribution light absorption and the coulombic interaction energies of electronhole pair (J e/h ). A two-fold increase in phenol degradation efficiency (from 30 to ~60%) was achieved by controlled variation of the diameter of CuInSe 2 NCs from 5.3 to 1.8 nm. The surface ligand dependency of photocatalytic efficiency was also investigated and a profound effect on phenol degradation was observed. Our PEG-thiolate-capped CuInSe 2 NCs showed photocatalytic activity towards other organic compounds, such as N, N-dimethyl-4-phenylenediamine, methylene blue, and thiourea, which showed decomposition under visible light.3

Electro‐photovoltaics of Polymer‐stabilized Copper–Indium Selenide Quantum Dot

“…In the Randles circuit diagram, R s describes the resistance of the solution with regards to the movement of electrons, R ct is the resistance charge transfer occurring at the surface of the modified GCE\G1PPT‐CuInSe 2 QD. CPE is considered to be the constant phase element (double layer capacitance) occurs when there is a fluctuation of current because of the adsorption of ions the electrode surface and W s is the Warburg impedance component arising from ion diffusion quotients [81]. The kinetic parameters obtained from fitting the EIS fitting of the G1PPT‐CuInSe 2 QD are shown in Table S‐1 ( ESM) .…”

Nonstoichiometric CuxInyS Quantum Dots for Efficient Photocatalytic Hydrogen Evolution

“…Cyclic voltammetry measurements indicated that the valence band edge ( E VB ) of Cu x In y S QDs (Cu/In=1:6) is about 1.05 V (Figure S8, vs. normal hydrogen electrode, NHE). In combination with the band‐gap data obtained from the absorption spectra, the conduction band edge ( E CB ) of Cu x In y S QDs (Cu/In=1:6) is approximately −1.15 V. This makes electron transfer from QDs to Ni 2+ /Ni 0 (−0.25 V vs. NHE) or Ni 2+ –GSH (−0.95 V vs. NHE, see below) thermodynamically possible.…”

Dual Role of Electron-Accepting Metal-Carboxylate Ligands: Reversible Expansion of Exciton Delocalization and Passivation of Nonradiative Trap-States in Molecule-like CdSe Nanocrystals

“…Surface ligands are generally introduced during the colloidal synthesis of nanocrystals; − however, most of the ligands, long-chain aliphatic amines and phosphines (neutral 2-electron donating L-type) , and long-chain aliphatic carboxylates and phosphonates (1-electron donating X-type), , are insulating in nature. Therefore, in order to enhance the electrochemical − and charge transport properties, ,− and biological imaging detection of nanocrystals, − postsynthetic surface ligand exchange is routinely carried out. The ligand exchange reaction strongly affects the emission properties (PLQY and PL lifetime) ,,− and excitonic absorption characteristics of nanocrystals. , Recently Weiss and co-workers, , our group, , and others have shown that postsynthetic ligand exchange of CdSe and/or CdS nanocrystals with X-type ligands induces the delocalization of quantum-confined holes causing a red-shift in the first excitonic absorption peak, which can be characterized as an “increase the confinement box size”. , However, such change in the optical properties was found to be irreversible.…”