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Small: Ag2S CDs p-n heterojunction promotes selective oxidation of alcohols

wallpapers News 2020-12-04
The selective oxidation of

alcohols is of great significance in the fields of synthetic chemistry fine chemical industry. Traditional thermal catalytic oxidation usually requires noble metal catalysts (supported Au PD etc.) the reaction conditions are harsh (strong oxidant high temperature high pressure etc.) which will cause resource waste excessive oxidation. Photocatalytic oxidation of alcohols to aldehydes by light energy is an ideal way. Although much progress has been made in light driven selective oxidation of alcohols in the past few years most of them still need precious metal additives (PT Au Ru etc.) the efficiency selectivity still need to be improved. It is necessary to design more efficient photocatalysts. In recent years Mott Schottky junctions or different types of semiconductor heterojunctions (N-N p-n P-P junctions) composed of metals semiconductors or semiconductor semiconductors have helped to regulate electron density thus promoting photogenerated charge separation transfer. For example p-n junction can form a strong embedded field at the interface which can achieve efficient charge separation in the process of hydrogen evolution show excellent catalytic activity. However their potential in organic synthesis has not been fully explored.

CDs materials are commonly used as photocatalysts because of their good light trapping ability. However precious metal promoters (AU Pt etc.) are usually needed to improve the photocatalytic activity. Inspired by the above Xie Wei research group of Nankai University prepared Ag2S CDs nanojunctions by seed growth method as noble metal free photocatalysts for selective oxidation of alcohols at room temperature. HRTEM shows that the lattice mismatch between Ag2S CDs is only 2.7%. Photoelectrochemical tests show that Ag2S CDs exhibit the characteristics of p-type n-type semiconductors respectively. Compared with CDs etched by top the carrier concentration of p-n nanojunction increases significantly which indicates that more carriers can be generated in p-n junction to drive the chemical reaction. The energy b structure of p-n junction is thermodynamically feasible to drive alcohol oxidation O2 reduction. The results show that the catalytic activity of p-n nanojunctions is much better than that of single component Ag2S CDs mechanical mixed catalysts. The quantum yields at 380 nm 420 nm can reach 59.6% 36.9%. Photoelectrochemical fluorescence measurements show that the p-n nanojunction exhibits much better charge separation transfer performance than its single component CDs. The close contact lattice matching between Ag2S CDs reduce the carrier transport barrier enhance the charge separation. The control experiments showed that photogenerated electrons holes were involved in the catalytic oxidation process at the same time. Electrons activated O2 in the air to produce the species of reactive oxygen species while holes were involved in the activation of alcohol substrate molecules to form activated intermediates which further reacted with · O2 − to produce aldehyde products H2O2. Using p-n junction as catalyst a series of benzyl alcohols pyridine alcohols biomass alcohols were selectively oxidized at room temperature with air as oxygen source. Almost no acid products were produced. The mass reaction rate of the catalyst was better than that of most noble metal Semiconductor Photocatalysts reported in the literature. The utilization of p-n junction provides a new opportunity for high performance catalytic oxidation under mild conditions.

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