The interactions of free and complexed copper ions (Cu(C104)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(C104)2 (free Cu 2 ÷ ions) and Cu(acac)2. This process is accompanied by thermal (dark) reduction of Cu 2 + 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 Cd 2 ÷ 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(C104)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 (eft/hE ) nanoparticles.
The main analytical band of chromium, the Cr 2p band, is -30 eV away from the oxygen 0 1s band and so it superposes with the energy loss band (ELB), which is composed of energy loss peaks from inelastically scattered 1s electrons of oxygen (Fig. 1). During studies of chromium-containing catalysts it has been observed that, in the case of samples with low chromium content, Cr 2p binding energies (BE) are lower but full widths at half maximum (FWHM) are much larger than those expected for the Cr6+ oxide forms. This indicates a significant contribution from the ELB structure and the necessity to remove it.To illustrate the meaning of the problem and its solution, the usual XPS analysis can be compared with that after removal of the ELB for a sample of fused silica grafted to chromium oxide using Cr02C12 .l The chromium content was in the monolayer range.The elimination of the ELB was carried out as follows. In the 0 1s spectrum of a pure silica carrier recorded in an 85 eV wide scan (Fig. l), after Shirley's background subtraction, the ELB region was cut off and the band was fitted using a set of Gaussian-20% 2).
The photoreactivity of zinc tetraphenylporphyrin (ZnTPP) in the presence of photoexcited CdS nanoparticles and molecular oxygen in 2-propanol has been revisited. The photodecomposition of ZnTPP in 2-propanol, in the presence of CdS(e-CB/h+VB)and molecular oxygen, is linked to isopropyl free radicals formed by both hole transfer from CdS(h+VB)to(CH3)2CHOH and the reaction of superoxide ion(O2−)with 2-propanol. Isopropyl free radicals react with ZnTPP, leading to the formation ofZnTPP•−. Intermediate paramagnetic species monitored by EPR spectroscopy(g=2.0029,ΔH=5.7G)were characterized as superoxides formed in the reaction ofZnTPP•−withO2. Further transformations of such EPR-active species lead to the formation of diamagnetic intermediate photoproducts of ZnTPP observed by absorption and emission spectroscopy.
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