Selective Visible Light-Driven Conversion Of Alcohols By ?-Cyclodextrin Decorated CdS Nanocrystal

Selective conversion of alcohols into corresponding target products and hydrogen under the action of catalyst and visible light has wide application prospects.The reported photocatalytic alcohol oxidation systems have the following disadvantages:?1?poor reaction activity and selectivity of photocatalyst in aqueous medium;?2?unsatisfied stability of the photocatalyst and the additional participation of noble/non-noble metals to act as a co-catalyst.Benefitting from the host-guest interactions between?-cyclodextrin??-CD?and hydrophobic substrates,we modified?-CD to the surface of CdS nanocrystals to construct a cyclodextrin-modified CdS nanocrystals composite system?CdS-CD?,which was subsequently employed to the selective conversion of alcohols under visible-light irradiation in water.The host-guest interaction between?-CD and alcohols can enrich them on the surface of CdS nanocrystal,thereby improving the catalytic oxidation efficiency and selectivity.The main research details include the following parts:1?The?-mercaptocyclodextrin?SH-?-CD?and oleic acid capped CdS nanocrystals?CdS-OA?were used to construct CdS-CD through ligands exchange reaction and the host-guest interactions between?-CD and alcohol molecules were explored.The binding interactions between?-CD and model substrates?benzyl alcohol and 1-phenylethanol?were investigated by ¹H NMR experiments.The bonding ratio and binding constants between?-CD and model substrates were investigated by Job plot and UV titration experiments.The results show that both of the bonding ratio were 1:1,and the corresponding binding constants were146 M^-11 and 160 M^-1.2?The application of CdS-CD in the selective conversion of alcohols under visible light driven were studied.Just through changing the concentration of the alcohols,CdS-CD can convert different alcohol molecules into vicinal diols/aldehyde ketone compounds and hydrogen with high selectivity.The specific contents are as follows:?1?Optimize the substrate concentration of alcohols by concentration gradient experiment.The results show that the optimum concentrations for the products of vicinal diols and benzaldehyde are 0.3 M and 0.001 M,respectively;?2?Under the condition of alcohol concentration of 0.3 M,the catalytic activity of CdS-CD for the catalytic conversion of different alcohols to vicinal diols was studied.The results indicate that CdS-CD possesses high catalytic activity and selectivity for benzyl alcohol,1-phenylethanol,2-methylbenzyl alcohol,3-methylbenzyl alcohol,4-methylbenzyl alcohol,2-furan methanol,2-thiophene methanol,3-pyridinemethanol and4-chlorobenzyl alcohol;?3?The catalytic activity of CdS-CD for catalytic conversion of different alcohols to aldehydes or ketones was studied under the condition of alcohol concentration of 0.001 M.The results showed that CdS-CD exhibited high conversion and selectivity for benzyl alcohol,1-phenylethanol,2-methylbenzyl alcohol,3-methylbenzyl alcohol,4-methylbenzyl alcohol,2-thiophene methanol,and 2-furan methanol.These results indicate that the modification of cyclodextrin to the surface of CdS nanocrystals can not only improve the stability of CdS nanocrystals in water,but also significantly improve the selectivity and activity of CdS nanocrystals for the conversion of alcohols.3?The kinetic isotope experiment?KIE?,electron paramagnetic resonance spectroscopy?EPR?and guest competition experiments were conducted to clarify and propose the possible reaction mechanism,which was a free radical reaction process promoted by the host-guest interactions.