Design、assembly And Photocatalytic Activity Of Porous G-C₃N₄-based Composite Photocatalysts

Graphitic carbon nitride（g-C₃N₄）is a metal-free organic photocatalyst,which exhibits a promising potential in practical application due to its many advantages,such as earth abundance,synthesis convenience,non-toxicity and structural stability in different environments.This dissertation focuses on the researches about design,preparation and photocatalytic activity of g-C₃N₄ based nanocomposites,including the emphasis on the structure modulation and performance optimization and construction of several g-C₃N₄ based photocatalysts with highly visible light response and excellent photo-stability on the basis of modified g-C₃N₄.Systematic characterizations were employed to investigate the phase structure,morphology,chemical composition,specific surface areas,photocatalytic performances and possible photocatalytic mechanism.The main contributions involved in this dissertation are as follows:1.Synthesis of Bi₂MoO₆/g-C₃N₄ nanocomposites and their photocatalytic performanceA series of Bi2Mo06/g-C₃N₄ heterojunction photocatalysts with different Bi₂MoO₆ mass ratio have been successfully fabricated by combination of a simple liquid chemisorptions and thermal treatment.The phase structure,microstructure morphology,light absorption properties,chemical elements and interaction were investigated in detail.The photocatalytic activity was evaluated by RhB degradation.The result indicates that 20 wt%Bi₂MoO₆/g-C₃N₄ exhibits highest photocatalytic efficiency for RhB degradation with constant rate of 0.108 min^-1,with nearly 2.63 and 5.40 fold enhancement in photocatalytic efficiency over pure g-C₃N₄ and Bi₂MoO₆.Also,20 wt%Bi₂MoO₆/g-C₃N₄ possesses excellent photo-stability during recycling runs.2.Synthesis of Bi₂WO₆ QDs/g-C₃N₄ nanocomposites and their photocatalytic activityThe hydrothermal route was employed to prepare Bi₂WO₆QDs/g-C₃N₄ nanocomposites by using C₁₈H₃₃O₂-as complex reagent.During photocatalytic RhB degradation,we found that g-C₃N₄ content in Bi₂WO₆ QDs/g-C₃N₄ nanocomposites has important effect on photocatalytic activity.The Bi₂WO₆QDs/g-C₃N₄ nanocomposites exhibit higher efficiency photocatalytic activity than others when 10 mg of g-C₃N₄ was added.The improved photocatalytic activity is dominated by heterogeneous interface constructed between Bi₂W0₆ QDs and g-C₃N₄ nanosheets,which affect the separation efficiency of photo-generated holes and electrons.Besides,series of sacrificial agents were used to quench the relevant active species during the photocatalytic process,revealing that ·O2-plays a key role in RhB degradation.By analyzing the band gaps and band potentials,we confirm that the Bi₂WO₆QDs/g-C3N;nanocomposites are Z-scheme photocatalyst.3.Synthesis of three-dimensional CdIn₂S₄/g-C₃N₄ nanocomposites and their photocatalytic activityThe CdIn₂S₄/g-C₃N₄ nanocomposites with different g-C₃N₄ content have been successfully fabricated by a simple one-pot route,wherein the mesoporous g-C₃N₄ nanosheets were in-situ self-wrapped onto CdIn₂S₄ nanosheets to construct binary photocatalysts with multi-dimensional interfacial contacts.Some measurements,including PL analysis,I-t plot and EIS spectroscopy,confirm that CdIn₂S₄/g-C₃N₄ nanocomposites possess the features of high separation efficiency of charge pairs.Besides,the analyses on crystalline phase,microstructure morphology,absorption properties and BET further verified that the effective charge separation between CdIn₂S₄ and g-C₃N₄ via heterogeneous contacts is an important factor in photocatalytic activity.The photocatalytic experiment reveals that optimum photocatalytic activity was presented towards 4-NA reduction using 50 wt%CdIn₂S₄/g-C₃N₄ as catalyst.The recycling reactions indicate that CdIn₂S₄/g-C₃N₄ nanocomposites,based on the construction of three-dimensional interface,not only improve the photocatalytic activity,but also strengthen the photo-stability.4.Ultrasound-assisted synthesis of Zn_o.2Cd_0.8S/P-C₃N₄ and their photocatalytic activityHighly-efficient visible light driven Zn_0.2Cd_0.8S/P-C₃N₄ heterostructure were successfully synthesized via ultrasound-assisted growth route by loading Zn_0.2Cd_0.8S solid solution on the surface of P-C₃N₄.And the as-obtained samples were systemically characterized by SEM,TEM,etc.Compared with pure Zn_0.2Cd_0.8S with agglomeration and bigger size,the as-prepared Zn_o.2Cd_0.8S/P-C₃N₄ nanocomposites were in-situ immobilized with homogeneously dispersed Zn_0.2Cd_0.8S NPs.Such result reveals that P-C₃N₄ serves as structural direction agent during Zn_0.2Cd_0.8S preparation.Obviously,this homogeneously dispersive loading-structure is certainly responsible for the enhancement of photocatalytic activity.Because of the synergistic effect between Zn_0.2Cd_0.8S and P-C₃N₄,the as-prepared binary Zn_0.2Cd_0.8S/P-C₃N₄ nanocomposites exhibit higher photocatalytic activities towards hydrogen evolution fro m water splitting and 4-N A reduction.5.Synthesis of P-C₃N₄/ZnIn₂S₄ nanocomposites and their photocatalytic activityWe rationally designed and fabricated P-C₃N₄/ZnIn₂S₄ nanocomposites by in situ immobilizing ZnIn₂S₄ nanosheets onto the surface of mesoporous P-C₃N₄ nanosheets in a mixed solvothermal environment.The as-fabricated P-C₃N₄/Znln2S4 nanocomposites were systematically characterized by analyzing the phase structure,chemical components,BET,photoelectrochemical properties and separation of charge carrier pairs.Their applications to the photoreduction of 4-nitroaniline and MO degradation were used to estimate the photocatalytic performance using P-C₃N₄/ZHIn2S4 nanocomposites with different P-C₃N₄ content.The 20 wt%P-C₃N₄/ZnIn₂S₄ heterostructures have been proven to be visible light responsive photocatalysts with higher photocatalytic efficiency than others.By combination of VB-XPS and UV-vis DRS,the transfer direction of photo-generated holes and electrons was investigated;Meanwhile,the possible photocatalytic mechanism was proposed to describe the photocatalytic process.