Design,Synthesis And Performance Of Novel Covalent Organic Frameworks Materials For Photocatalytic Organic Transformation

In recent years,photocatalytic reaction as a mild,environmentally friendly and green chemical process has attracted widespread attention in the scientific and industrial communities.However,the photocatalytic organic transformation still needs to be improved in terms of photocatalytic efficiency,selectivity and catalyst stability.Covalent organic frameworks（COFs）,as a new type of organic semiconductor that is sensitive to visible light and tunable band gap,have been reported more and more in the field of photocatalytic organic transformation.Therefore,this thesis works research on design of COFs-based photocatalysts and photocatalytic organic transformations.The main results are summarized as follows:1.A series of [3+3] covalent organic frameworks with similar 2-D hexagonal structure but different compositions were synthesized and employed as model materials for investigating the key factors affecting the photocatalytic properties in visible-light-driven reductive dehalogenation reaction and the aerobic cross-dehydrogenative coupling reaction.In comparison with-H and-CF₃,-OH substituent in the aromatic ring could narrow the band gap of the COFs and triazine skeleton in the framework usually boosts the photocatalytic activity.As a combined result of narrow band gap,efficient charge separation and high conductivity,the COFs possessing both-OH group and triazine skeleton show the highest activity in the photocatalytic reductive dehalogenation reaction.Notably,COFs could be readily retrieved and reproductive for several times without the loss of crystallinity.Our results may shed light on the design of efficient COFs-based semiconductors for photocatalytic organic transformations.2.QH-COF@TiO₂ and TiO₂@QH-COF（QH-COF:tetrahydroquinoline-linked COFs）core-shell structured heterojunctions were designed,prepared and used for photocatalytic oxidation of alcohols.The spatial location of two semiconductors either in the core or onto the shell was designed,and their corresponding photocatalytic performance has been well investigated.In the case of photocatalytic benzyl alcohol oxidation,the activity of QH-COF@Ti O₂（Ti O₂onto the shell）is almost triple higher than Ti O₂@QH-COF（Ti O₂in the core）（TOF:1.19 vs 0.44 mmol/g/h）,although both photocatalysts exhibit similar capability for light harvesting and charge separation.The higher photocatalytic activity of QH-COF@Ti O₂is due to its easier donation of electrons to O₂.We also demonstrate that QH-COF@Ti O₂can catalyze other organic transformations,for example,the visible-light photocatalytic aerobic cross-dehydrogenative coupling reactions.We provide a feasible method in synthesizing two single-component semiconductors synergy to enhance the properties of photocatalytic organic reactions.