Activation Of C-h Bond In Heterogeneous Photocatalysis And Its Application In Green Synthesis Of Fine Chemicals

The development of green chemistry and clean energy is the urgent task to ensure the sustainable development of human society.As an environmentally friendly catalytic process,heterogeneous photocatalysis has opened the curtain for the green synthesis of fine chemicals and clean energy production due to its advantages of simple reaction conditions,low energy consumption and easy separation.In addition,directly activating the most common C-H bond in organic molecules to construct C-C/C=N/C-S chemical bonds has become an attractive green synthesis approach.However,how to achieve C-H activation under mild,simple and non-noble metal conditions is still quite challenging.Therefore,the combination of heterogeneous photocatalysis and C-H activation to explore the synthesis of fine chemicals is a promising research area.（1）CdS with different morphologies were prepared by various methods,and S vacancies were introduced by calcination（Sv-CdS NRs）.SEM,TEM,HRTEM,XRD,XPS and EPR characterization showed that Sv-CdS NRs had rod-like morphology,hexagonal phase crystal plane and S-vacancies defect characteristics.The photoelectrochemical characterization showed that the formation of polarization dipole moment and internal polarization electric field in Sv-CdS NRs hexagonal crystal,which could promote the migration of photogenerated carriers.In the photocatalytic reaction of tetrahydrofuran（THF）with phenylacetylene,up to 95%conversion could be achieved with Sv-CdS NRs.The reaction mechanism was proposed based on electron,hole and radical capture experiments.In addition to the coupling reaction between oxygen-containing heterocycles and olefins/alkynes,Sv-CdS NRs could also construct C-C/C=N/C-S chemical bonds through C-H activation.For example,DMF sp³C-H could also be activated to form C-C bonds;benzylamine sp³C-H could be activated to construct C=N bonds accompanied by H₂generation;benzyl mercaptan S-H bonds and phenylacetylene/styrene C-H bonds could be activated to build C-S bonds;and benzene/toluene C-H bonds could be activated in the presence of CO₂to produce carboxylic acid.（2）CdSe QDs and spherical Si O₂ were prepared by using reflux method and Stober method,and CdSe QDs/B-Si O₂nanocomposite was constructed by electrostatic self-assembly.XRD,SEM,TEM and HRTEM confirmed that CdSe QDs/B-Si O₂had characteristics of spherical Si O₂,with average CdSe QDs particle size of 2.5 nm.FT-IR,XPS and other tests proved the electrostatic self-assembly of CdSe QDs and Si O₂by mercaptopropionic acid and branched polyethylene imine.Photoelectric tests,such as UV vis-DRS,EIS and transient photocurrent,showed that the introduction of Si O₂significantly improved the light absorption ability and the separation and electron-hole pairs transmission efficiency of CdSe QDs.The prepared CdSe QDs/B-Si O₂photocatalyst could efficiently realize the C-H activation of lignin oil and CO₂reduction to prepare fuel precursor and syngas（H₂+CO）for the first time under the mild conditions（visible light,green solvent H₂O and noble metal free）.The reaction mechanism was proposed with electron,hole and radical capture experiments.In this heterogeneous photocatalysis system,spherical Si O₂significantly enhanced the light absorption ability and the photogenerated carriers generation of CdSe QDs/B-Si O₂through near-field scattering.With UV vis-DRS,the solvent-assisted near-field scattering effect was demonstrated to play an important role in light absorption promotion.This study provided promising strategy for the synthesis of renewable fuels,which showed a bright prospect for the direct application of heterogeneous photocatalysis to the production of diesel precursors and clean energy.In summary,we designed and synthesized S vacancies enriched Sv-CdS NRs,and CdSe QDs/B-Si O₂photocatalytic nanocomposites.The photocatalysis materials exhibited excellent photocatalytic performance in the photocatalytic reaction,which included clean energy production and fine chemicals construction through heterogeneous photocatalytic C-H activation.The mechanism of these photocatalytic reactions was studied through a series of experiments and characterization.