Interfacial electron transfer from nonstoichiometric cadmium sulfide nanoparticles to free and complexed copper(II) ions in 2-propanol

Abstract

The interactions of free and complexed copper ions (Cu(ClO4)2, Cu(acac)2, and CuTPP) with the surface of nonstoichiometric CdS nanoparticles were monitored by EPR spectroscopy, recombination luminescence quenching and UV/VIS absorption spectroscopy. It was found that formation of a surface S-Cu bond takes place both in the case of Cu(ClO4)2 (free Cu2+ ions) and Cu(acac)2. This process is accompanied by thermal (dark) reduction of Cu2+ to Cu+, formation of a new energy level in the semiconductor bandgap and quenching of the original recombination luminescence of the nanoparticles. The quenching data obey a static interaction model, which confirms binding of copper ions onto the surface of CdS nanoparticles. In addition, Cu(acac)2 molecules can interact with Cd2+ ions on the surface of CdS, leading to a less effective quenching of the recombination luminescence of CdS, compared to that by free copper ions. In contrast to the behavior of Cu(ClO4)2 and Cu(acac)2, copper(II) tetraphenylporphyrin does not interact directly with the surface of CdS nanoparticles, leading to a very negligible quenching of the recombination luminescence of CdS (e tr − /h tr + ) nanoparticles.