Construction of N, S codoped TiO2 NCs decorated TiO2 nano-tube array photoelectrode and its enhanced visible light photocatalytic mechanism

• N-S-TiO2/TiO2 nanotube electrodes were prepared combined anodization and ultrasonic.
• The photoelectrocatalytic properties of photoanodes were investigated in detail.
• The enhanced visible light photocatalytic mechanism was proposed.

In the present work, N, S codoped TiO2 nano-crystallites (NCs) decorated TiO2 nano-tube arrays (N-S-TiO2 NCs/TNTAs) photoelectrodes have been successfully constructed through anodization method, followed by evaporation induced self-assembly (EISA) strategy. The structures of N-S-TiO2 NCs/TNTAs samples were characterized by scanning electrons microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron microscopy (XPS). Results indicated that TNTAs was partly covered by N, S codoped TiO2 NCs. Meanwhile, N elements coexisted in the forms of substitutional N (Ti–N and N–Ti–O) and interstitial N (Ti–O–N) in TiO2, while S elements were also incorporated into the lattice of TiO2 through substituting titanium atom and coexisted in the cationic forms of S6+ and S4+. In addition, optical and photoelectrochemical (PECH) properties of the as-prepared N-S-TiO2 NCs/TNTAs samples were investigated through UV–vis light diffuse reflection spectroscopy (DRS), transient open circuit potential (OCP), photocurrent response (PCR) and electro-chemical impedance spectroscopy (EIS). Furthermore, photodecomposition performances were evaluated by the yield of OH radicals and photocatalytic (PC) degradation of methyl blue (MB) under Xenon lamp irradiation. All results showed that N-S-TiO2 NCs/TNTAs photoelectrode exhibited intense visible light absorption ranging from 400 to 700 nm, high transient photoinduced current of 0.115 mA cm−2, open circuit photovoltage of −0.312 mV cm−2, generation of hydroxyl radicals and PC efficiency of 59.7% for the degradation of MB. The enhanced PC performance could mainly be attributed to the decoration of N, S codoped TiO2 NCs, which could not only enhance the light absorption in visible region but also improve the transfer and separation efficiency of photoinduced charge carriers.