Photocatalytic selective organic transformations provide an efficient synthetic alternative for several industrially relevant chemicals using solar rather than thermal energy. However, in most cases, photocatalytic organic reaction systems involve only reductive or oxidative pathways with the aid of sacrificial reagents as efficient electron acceptors or donors, thus limiting the economic added value. Recently, merging selective organic reductions and oxidations in a dual-functional photocatalytic reaction system has been put forward to tackle this limitation. In this coupled reaction system, both the photogenerated electrons and holes can be simultaneously utilized to generate value-added products, make the overall process more valuable from the economic perspective. In this review, the development of dualfunctional photocatalytic organic synthesis is systemically summarized. Particular emphasis is paid to merging selective organic oxidation and reduction reactions and coupling selective organic transformations with chemical fuel generation (e.g., H2, CO). Also, a personal perspective on future developments in this field is provided. Although still in its infancy, it is expected that this dual-functional technology offers opportunities to develop the next-generation selective organic transformation processes that meet the stringent economic, societal, and ecological expectations.
TiO 2 @Co-C 3 N 4 nanorod arrays were prepared by drop coating and hydrothermal method. The Photoelectrochemical (PEC) performance of TiO 2 @Co-C 3 N 4 nanorod arrays can be tuned by the amount of Co-C 3 N 4 coated. When the amount of Co-C 3 N 4 reached about 0.75 μg/cm 2 , the PEC performance of TiO 2 @Co-C 3 N 4 reached the maximum. The results show that the photocurrent density of TiO 2 @Co-C 3 N 4 nanorod array reaches 1.79 mA/cm 2 at 1.23 V RHE , which is about 2.3 times of that from TiO 2 @g-C 3 N 4 . And the PEC device has good stability and the photocurrent density remains no decline after 10 hours of continuous operation. Co atoms coordinated with g-C 3 N 4 could act as a co-catalyst for water oxidation, and a possible mechanism is proposed for water oxidation based on careful analysis of the detailed results. The holes photogenerated by excited electrons oxidize Co atoms from Co II to Co III and Co IV , and then these high-valence cobalt species accelerate the kinetics of water oxidation. In addition, Co-C 3 N 4 not only can promote the charge transfer but also improve the overall energy conversion efficiency of the PEC device.
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