科研之友
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摘要
Photo-corrosion is one of the major obstacles for CdS application in wet chemical fields, and atomic layer deposition (ALD) has been proposed as an effective way to suppress the corrosion. Here, prior to ALD coating, CdS, one facilely corrosive photocatalyst, was synthesized via hydrothermal synthesis to access the fundamental corrosion mechanism and the according corrosive sites. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrated that the failure of catalytic decomposition of methylene blue originated from the formation of soluble CdSO4 by oxidizing S2- of as-prepared CdS. High resolution transmission electron microscopy (HRTEM) further identified the active sites in the V-shaped regions of CdS nanoparticles, confirmed by the simulated electric field distribution. To rationally coat oxides on CdS, the right candidates and their thicknesses have been considered by our tunneling model with transfer matrix method based on quantum mechanism, upon which the thickness of protective layer should be less than 0.5 nm to maintain a high tunneling probability, and thus one cycle of ALD TiO2 or Al2O3 was proposed to passivate the CdS powder to balance the carrier transportation and corrosion suppression. Based on HRTEM results, we found that the active V-shaped region was covered by ALD oxides (TiO2 or Al2O3). For each case, no soluble CdSO4 has been found before and after photocatalytic reactions based XPS measurements. Importantly, we noticed that with the passivation of one cycle of ALD, the catalyst's lifetime was elongated up to > 14 times higher than that of the as-prepared CdS.
