Preparation, Characterization And Photocatalytic Activity Of Layered Double Hydroxide Supported-Bi₂O₃

New catalysts with high efficieney photocatalytic activity in the visible light, Bi2O3modification and Pd immobilization, layered double hydroxides (LDHs) as catalyst support were studied in this paper. A series of new visible light photocatalysts were synthesized by wet impregnation. The as-synthesized catalysts were characterized by several techniques. The adsorption kinetics, the equilibrium isotherm and the kinetics of photocatalytic reactions of MB were tested. With the supports of characterization analysis and the experimental results, the photodegration mechanism was also discussed. The main research contents and results are as follows:(1) A new series of visible light photocatalyst Bi2O3/LDHs were prepared with the Bi(NO3)3·5H2O and LDHs by employing ethylene glycol as the solvent. And the photocatalytic activities of Bi2O3/LDHs were improved by the surface modification with Pd. The as-synthesized catalysts were characterized by several techniques, such as the powder XRD, FTIR, UV-Vis, SEM, TEM, EDX, ICP and N2physisorption, to investigate their crystalline structure, morphology and textural properties.(2) Factors such as various LDHs, the molar ratio of Mg2+/Al3+, LDHs content, calcination temperature, Pd (Ⅱ) content that may affect photocatalytic activities of as-prepared catalysts were studied. Experiments were carried out as a function of contact time, pH, initial concentrations of methylene blue (MB) and the stability of the photocatalysts. And the photocatalytic activities of catalysts were evaluated by degradation of methylene blue (MB) in aqueous solution under visible light irradiation, which exhibited an efficient photocatalytic activity with90.6%of the degradation of MB (10mg/L) by Bi2O3/Mg3Al-LDH (calcination temperature500℃for5h) containing1.0wt%of Pd (Ⅱ) under visible-light irradiation for4h.(3) The equilibrium isotherms and kinetic models for the adsorption process under dark conditions were studied to evaluate the viability and effectiveness of this process. The kinetics of adsorption was shown to be suitably described by the pseudo-second-order kinetics model, and the calculated value of Ea was9.30kJ/mol, indicating diffusion controlled the process of MB removal. The experimental data obtained from isotherm studies well fitted the Langmuir isotherm model, indicating monolayer adsorption of the surface. Furthermore, the kinetics of photocatalytic reactions followed the first-order kinetic model at different condition in the reaction system.(4) With the supports of characterization analysis and the experimental results, the mechanism underlying the enhanced photocatalytic activity of Pd (Ⅱ)-Bi2O3/RLDH was also discussed, which reveals that the synergist effect of LDHs as adsorbent materials and OH group providers play a critical role in the degradation process.