A cystine-modified TiO 2 visible-light photocatalyst was prepared by the sol-gel method and characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), and X-ray photoelectron spectroscopy (XPS). The XRD results showed the cystine-modified TiO 2 was in the anatase phase, but with reduced size. UV-Vis DRS indicated that cystine-modification could reduce the band gap of TiO 2 and enhance the absorption of visible light. The XPS spectra showed that the cystine-modified TiO 2 sample contained C, N, and S, and that some of the C, N, and S entered the TiO 2 lattice. The cystinemodified TiO 2 visible-light photocatalyst was added to a chitosan (CS) anionexchange layer to prepare PVA-CMC/modified TiO 2 -PVA-CS bipolar membrane (BPM; here, PVA denotes poly(vinyl alcohol), CMC denotes carboxymethylcellulose, and the solidus ''/'' denotes the interlayer) by a paste method. The membrane was characterized by determination of contact angle, J-V characteristics, and AC impedance spectroscopy, among other techniques. Experimental results showed that the cystine-modified TiO 2 visible-light photocatalyst was a better photocatalyst than TiO 2 for splitting of water at the interlayer of the BPM. The membrane impedance and trans-membrane voltage drop (IR drop) of the modified BPM clearly decreased under sunlight irradiation. At a current density of 60 mA/cm 2 , the cell voltage of the PVA-CMC/modified TiO 2 -PVA-CS BPM decreased by 0.9 V. Moreover, the hydrophilicity of the modified BPM was increased and its mechanical properties were improved.
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