REN Gui-ping, SUN Man-yi, LU An-huai, LI Yan, DING Hong-rui*

(The Key Laboratory of Orogenic Belts and Crustal Evolution, Beijing Key Laboratory of Mineral Environmental Function, School of Earth and Space Sciences, Peking University, Beijing 100871, China)

Abstract: With the serious problems of environmental pollution, conversion of solar energy has caused widely attention in the fields of catalytic and environmental protection. Birnessite is one of the most common mineral distributed on earth. Nano-birnessite electrodes were synthesized quickly and effectively by electrochemical method in this paper. X-ray Diffraction(XRD) and Raman spectroscopy confirm that the electrode film has single mineral phase of birnessite. Atomic Force Microscope(AFM) was used to observe the morphology information of birnessite and which distributed irregular polygon lattice spaces. The film thickness of 0.5, 1.0, and 1.5 C birnessite electrodes approximately are 30, 200, and 450 nm, respectively. Moreover, the UV-Vis Diffuse Reflectance spectra illustrate the significant absorption of visible light from 300 to 600 nm. Tauc plots were used to extrapolating an allowed indirect band gap of 0.8－1.3 eV and an allowed direct band gap of 2.0－2.3 eV for electrodes. The flat band potential of three electrodes is 1.15 V and the carrier concentration are 3.26×1019, 4.63×1019, and 2.70×1020 cm-3 respectively evaluated by Mott-Schottky. In addition, the photocurrent density-time curves and LSV curves indicate that the electrodes have great photoelectrochemical activity. Furthermore, photoelectrocatalytic degradation of methyl orange with 5 mg/L concentration by three electrodes were investigated. Results show that degradation rate of methyl orange by 0.5, 1.0, and 1.5 Cbirnessite electrodes reach to 66.3%, 70.0%, and 67.5% respectively after 150 minunder a constant pre-pulsed potential of 1.0 V vs. SCE (Saturated Calomel Electrode). And fitting the first-order kinetics reaction model the constant of reaction rate k are 0.44 h-1,0.48 h-1, and 0.46 h-1 (R2> 0.996). In consequence, the electrochemically deposited nano-birnessite has the ability to degrade phenol and other organic pollution.

Keywords: birnessite; photoelectrochemistry; photocurrent; Methyl orange degradation

E-mail: dhr@pku.edu.cn

ACTA MINERALOGICA SINICA Vol. 37, No. 4, 2017, Page 373-379