Preparation of Graphitic Carbon Nitride-based Photocatalytic Composites and Its Photocatalytic Hydrogen Evolution Properties

Author:Song Ting

Supervisor:zeng he ping


Degree Year:2019





Environmental issues and energy crises are now attracting more and more attention.Fossil fuel is one of the main factors that worsen the environment.It is manifested in:the greenhouse effect caused by the emission of carbon dioxide,the acid rain pollution caused by sulfur dioxide and the problem of PM2.5,so finding the clean and renewable energy desperately needed.Hydrogen(H2)has received much attention as one of the cleanest energy sources of the 21st century.Among the many preparation methods,photocatalytic H2 production is one of the best ways in the future.Since Wang Xinchen and others first reported graphitic carbon nitride(g-C3N4)for photocatalysis research in 2009,g-C3N4 has become the focus of research on photocatalytic materials.In this paper,the photocatalytic H2 production performance of g-C3N4 was studied,and its photocatalytic performance was improved by various control means.The details are as follows:(1)In chapter 3,photogenerated carriers possess high recombination efficiency in carbon nitride materials,which results in lower photocatalytic H2 evolution activity.By reviewing the literature,it was concluded that relying only on a structure-controlled technique was insufficient to reduce the combination of photogenerated carriers without introducing a foreign material or element.Hence,bulk-like g-C3N4[CN(B)],globe/strip-like g-C3N4[CN(G/S)],and globe/tree-like g-C3N4[CN(G/T)]were in situ obtained through a facile calcination method.Similar to platinum(Pt)as a cocatalyst,globe-like carbon nitride as a self-cocatalyst was found to improve the separation efficiency of photogenerated carriers effectively.Interestingly,the hollow-tree branch morphology of CN(G/T)effectively transmitted photogenerated holes,which thereby enhanced the photocatalytic H2 evolution activity.(2)In chapter 4,the photocatalytic capacity of conventional bulk g-C3N4,with its largeπ-πconjugated electronic system,is still constrained by theπ-πstacking interaction and small number of active sites.Hence,an uncomplicated postprocessing method to construct a differentπ-πconjugated electronic system of holey CN nanosheets using alkali etching of bulk CN(CN(B))at 300°C for 1 h has been developed.Among such compounds,the optimal alkali treatment bulk CN(CN 3(2))exhibits a suitable conjugated system and copious in-plane holes,and it retains the ability to absorb sunlight during alkali depolymerization.Compared to CN(B),the resultant CN 3(2)has a distensible bandgap of 2.66 eV associated with a much larger specific surface area of 265.2 m2 g-1.However,excessive alkali treatment significantly decreases the visible light absorbance and the photocatalytic properties of the CN nanosheet,which demonstrated that a suitableπ-πconjugated electronic system is very important in allowing the process to proceed.(3)In chapter 5,an uncomplicated vopor-polymerization strategy is used to obtain a novel sample of carbon-rich holey few-layer CN nanosheet with large domain size(S-ACN)using the oxygen in-situ regulation.Interestingly,the same preparation strategy synthesizes the carbon rich amorphous hollow-cubic CN materials(S-NCN)without the oxygen in-situ regulation.Consequently,the optimized S-ACN exhibits marked improvement in photocatalytic H2 evolution.(4)In chapter 6,a simple method was developed to manufacture reticulated carbon nitride materials(CN-4N).Utilizing the self-capturing property of CN-4N to capture black phosphorus quantum dots(BQ)uniformly dispersed in aqueous solution,BQ were successfully implanted in the interior surface of CN-4N to form a unique structure instead of the normal exterior surface contact pattern.The optimized CN-4N(BQ)showed good stability and achieved an excellent H2 production rate of13.83 mmol h-1 g-1,which was 3.3-and 35.5-fold higher than that of CN-4N and bulk CN(NCN),respectively.The experimental results illustrated that the greatly improved photocatalytic performance of CN-4N(BQ)was attributed to the joint actions of the abundant active sites provided by the ultra-porous structure,the excellent vis-NIR absorption capability,the spatially separated reactive sites for the redox reaction,and the greatly enhanced photoinduced electron-hole separation efficiency.(5)In chapter 7,efficient photocarrier transfer and sufficient light absorption play a crucial role in improving photocatalytic H2 evolution activity.Hence,we report a conceptual design of an ultrathin carbon nitride intraplane implanted with graphited carbon ring domain(CN-GP)via thermal polymerization of polyvinyl butyral and melamine membrane,displaying obvious disparities in the decoration type compared with the adsorption of graphene on the bulk g-C3N4 surface.This unique intraplane heterostructural CN-GP can greatly sheathe the visible/near-infrared light range,expedite electron-hole pair separation,and weaken the barrier of the photocarrier transfer through their suitable energy band structures and in-built electric fields.