| At present,semiconductor photocatalysis has attracted many attentions due to their wide applications in solving environmental pollution and energy crisis.However,the practical application of the traditional photocatalytic materials,especially TiO2,is subject to severe restrictions due to their wide band gap,low utilization of visible light,low quantum yield and the easy recombination of photogenerated electrons/holes.Therefore,it is necessary to discover new photocatalytic materials with low cost,high quantum efficiency,high utilization of visible light and high stability.Two-dimensional?2D?structured nanomaterials exhibit unique structure and performance characteristics that are different from the bulk material.2D nanomaterials have unique advantages and particularity as photocatalysts.As 2D layered material that has advantageous properties of suitable band-gap?2.7eV?,appropriate band edges,metal-free,non-toxicity,stability and low-cost,graphitic carbon nitride?g-C3N4?has great potential of practical utilization.This dissertation is devoted to developing g-C3N4-based photocatalysts with high photocatalytic activity and/or wide spectrum response by modulating the compositions and heterostructures according to the basic procedures of photocatalytic degradation of organic pollutants and photocatalytic H2 production.The modulation is based on the 2D structures and the surface properties,and the possible influencing factors of photocatalytic activity and spectral response of photocatalyst are discussed.1.A facile in-situ precipitation method is developed to synthesize ultrafine amorphous iron oxyhydroxide/ultrathin g-C3N4 nanosheets heterojunction composites.The amorphous iron oxyhydroxides possess ultrafine particle size and a wide range of visible light absorption.The ultrafine particles not only shorten the diffusion distance of photogenerated carriers,but also facilitate the formation of more heterojunctions with ultrathin g-C3N4 nanosheets.The photocatalytic activities are evaluated using rhodamine B,methylene blue and methyl orange as pollution models under visible light irradiation.Notably,the optimal photocatalytic activity of a-FeOOH/CNNS-800 composite is17.8 times higher than that of CNNS towards the degradation of rhodamine B under visible light.The outstanding photocatalytic activities are ascribed to the narrower band gap,the enhanced visible light absorbance,abundant heterojunction interfaces and the effective separation of the photogenerated charges driven by the matched band edge in the heterostructures.The facile and easy-to-extend synthesis method can be further expanded to synthesize other ultrafine semiconductors coupled with g-C3N4 for enhancing the photocatalytic activities.2.Highly dispersed metal?M=Ni,Co,Fe?phosphides modified g-C3N4 nanosheets?CNNS?were prepared through in-situ precipitation and solid/gas-phase phosphorization.The results confirm that metal phosphides?MPX?nanoparticles with high dispersion are well loaded on CNNS surface.This property well reveals the transfer path of photogenerated charges and the origin of high charge separation efficiency in photocatalytic reaction,thus yielding a remarkable catalytic activity.The apparent quantum efficiency?AQY?based on the NiPX/CNNS-900 is up to 6.61%at 400 nm while the H2 evolution rate boosts to 4068.84?mol·g-1·h-1,which is 50 times higher than that of pristine CNNS.The mechanism can be attributed to the highly dispersed MPX nanoparticles on the surface of CNNS,which act as effective active sites to promote the separation and migration of photogenerated carriers,leading to greatly increase in H2 production.This study is beneficial to further develop the high-efficient,low cost and environmentally-friendly CNNS-based photocatalytic materials for H2 production.3.Developing effective approaches for the preparation of 0D quantum dots/2D nanosheets nanocomposites is favorable for the heterogeneous catalysis,and this work is highly desirable but remains a great challenge.In addition,the development of noble-metal-free photocatalysts with high efficiency photocatalytic properties is critical to the development of photocatalytic technology.Herein,0D metal sulfide quantum dots/2D g-C3N4 nanosheet?Co3S4/CNNS?nanocomposites are synthesized by two-step method,including the ways of in-situ deposition and water bath.The highly dispersed Co3S4 quantum dots?2-4 nm?are uniformly and tightly fixed on the surface of CNNS,and Co3S4 quantum dots can be used as co-catalyst to effectively replace noble metals to enhance the photocatalytic performance of CNNS.The apparent quantum efficiency based on the Co3S4/CNNS-900 is up to 7.85%at 400 nm while the H2evolution rate is 20536.4?mol·g-1·h-1,which is 555 times of CNNS.The excellent photocatalytic performance is due to the highly dispersed Co3S4 quantum dots on the surface of2D CNNS,which facilitates the formation of more active sites,promotes the separation and migration of photogenerated carriers,shortens the migration distance of photogenerated carriers and eventually leads to an increase in its photocatalytic performance.4.2D/2D ultra-thin ZnIn2S4/protonated g-C3N4 nanocomposites?ZnIn2S4/pCN?are fabricated by electrostatic self-assembly strategy between negatively charged 2D ultra-thin ZnIn2S4 nanosheets and 2D protonated g-C3N4 nanosheets.The optimized ZnIn2S4/pCN?5:3?shows excellent photocatalytic activity toward H2 production(8601.16?mol·g-1·h-1)under visible light.In addition,ZnIn2S4/pCN also exhibits superior visible-light-driven photocatalytic tetracycline degradation efficiency,about4.13 and2.28 times higher than protonated g-C3N4and ultra-thin ZnIn2S4,respectively.The optimal ZnIn2S4/pCN?5:3?also has good photostability.The excellent photocatalytic activity of ZnIn2S4/pCN can be attributed to the unique 2D/2D heterojunctions,which are obtained by electrostatic self-assembly.The intimate interfacial contact and larger contact areas promote the separation and migration of photogenerated carriers,which contribute to the improvement of photocatalytic activity and photostability.Our research on the 2D/2D nanocomposites provides a scalable solution for the research of efficient and active photocatalysts. |
PDF Full Text Request