| Nowadays,energy scarcity and environmental pollution caused by the rapid consumption of fossil fuels have become major factors limiting sustainable economic and social development.Semiconductor photocatalysis technology is favored by researchers for its excellent performance in decomposing water to produce hydrogen,reducing carbon dioxide,converting organic matter and degrading pollutants.Among many semiconductor photocatalytic materials,graphitic carbon nitride(g-C3N4)materials have attracted much attention because of their low price,simple synthesis method,and tunable energy band structure.Currently,g-C3N4 is mainly prepared by direct thermal decomposition of urea,melamine,mono-and dicyandiamide,etc.However,the disadvantages such as relatively small specific area,many structural defects and insufficient photogenerated carrier separation ability limit the photocatalytic applications of these materials.To overcome these drawbacks,researchers have continuously optimized g-C3N4 from the materials perspective,including co-catalyst loading,defect modulation,morphology modulation,improving crystallinity and constructing heterojunctions.This thesis focuses on typical g-C3N4 nanosheets and highly crystalline g-C3N4.First,the application of the composites in photocatalytic selective oxidation of toluene was explored by constructing in situ heterojunctions of g-C3N4 nanosheets with non-lead perovskite.Secondly,the highly crystalline g-C3N4 was modified from the perspective of optimized precursor pretreatment to explore its application in photocatalytic hydrogen production.The experimental results showed that both modifications resulted in a significant improvement of the photocatalytic activity of the materials as follows:In the first chapter,the basic principles and application prospects of semiconductor photocatalysis are discussed,and some common semiconductor photocatalysts are summarized.The current research status of g-C3N4 materials,including the origin development,material properties and material applications,is further elaborated,while the problems and common modification strategies of g-C3N4 materials in photocatalytic applications are presented,which finally leads to the content and research significance of the selected topic of this thesis.In the second chapter,non-lead perovskite Cs2AgBiBr6(CABB)nanocrystals were grown in situ on flexible ultrathin carbon nitride sheets(UCNT),and the successful construction of heterojunctions was confirmed by a series of characterization means such as SEM,TEM,XRD and XPS.Further performance tests showed that through the synergistic effect of energy band engineering and size tuning,the composites could achieve efficient selective oxidation of the organic pollutant toluene with the products of high value-added benzaldehyde and benzyl alcohol.Meanwhile,the optimal loading of CABB on UCNT was preferentially obtained by adjusting the loading of CABB.Further reactive oxygen species capture experiments and in situ ESR tests were performed on the composites,which confirmed that superoxide radicals and photogenerated holes were the main substances involved in the activation of the C(sp3)-H bond of toluene in this photocatalytic reaction.In the third chapter,the tubular g-C3N4,named TCN,was first synthesized by the supramolecular self-assembly pretreatment method.Subsequently,the ionothermal method was adopted to collapse the tubular structure,and finally the small-sized sea urchin-like highly crystalline g-C3N4,named TCN-M,was formed.The characterization of sample morphology,specific surface area,light absorption ability and elemental analysis confirmed that the prepared TCN-M samples exhibit large specific surface area,high crystallinity and excellent light absorption ability at the same time.The high crystallinity implies that the material has few defects,which means that the electron-hole complex sites are limited,so TCN-M exhibits good photogenerated carrier separation ability and thus shows 70 and 1.8 times higher photocatalytic hydrogen production activity than that of bulk carbon nitride(BCN)and bulk molten salt carbon nitride(BCN-M).In addition,by introducing 0.5 M of K2HPO4 into the reaction system,a typical H+reduction cycle could be constructed,which further improved the catalytic performance of TCN-M.In the fourth chapter,we provide a comprehensive summary and outlook of the research content of this thesis. |
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