A Facile and Controllable Vapor-Phase Hydrothermal Approach to Anionic S2--doped TiO2 Nanorod Arrays with Enhanced Photoelectrochemical and Photocatalytic Activity.

Hai Yu,Gang He,Haocheng Yang,Zhaoqi Sun,Yanfen Wang,Yanmei Liu,Lei Yang,Miao Zhang

doi:10.3390/nano10091776

Abstract

Anionic S2−-doped TiO2 nanorod arrays (S2−-TiO2) were synthesized by a facile and controllable vapor-phase hydrothermal (VPH) approach based on the sulfur source of H2S gas. After the VPH treatment of TiO2 nanorod arrays (TNA), the isolated O2− species replaces the S2− ion in TiO2 (TiO2−xSx). The structural, morphological, optical, compositional, photocatalytic and photoelectrochemical (PEC) properties of the obtained samples were investigated in detail. It was found that S2−-TiO2 can enhance the separation rate of electron–hole pairs, improve the absorption of visible light, and augment the photocatalytic and photoelectrochemical properties. Anionic S2− doping can significantly adjust the absorption cut-off wavelength (409.5–542.5 nm) and shorten the bandgap (3.05-2.29 eV) of TNA. For the degradation of methylene orange (MO) under mercury lamp light, the 0.24 At%S2−-TiO2 (0.24S2−-TiO2) sample exhibited the best photogradation efficiency of 73% in 180 min compared to bare TiO2 (46%). The 0.24S2−-TiO2 showed the highest photocurrent of 10.6 μA/cm2, which was 1.73 times higher than that of bare TiO2 (6.1μA/cm2). The results confirmed that the visible light absorption, photocurrent and photocatalytic activity optimization of TNA are closely related not only to anionic S2−-doped but also different ratios of anionic S2−-doped. It is noteworthy that the VPH approach is very promising for applications in low cost and highly efficient ion doping into nanomaterials for energy devices.

Highlights

Since the 1970s, titanium dioxide (TiO2) has been recognized as a promising solar-driven photocatalyst due to its high availability, efficiency, excellent functionality, long-term stability, nontoxicity and low cost [1]
Many reports have indicated that using various ions (C, N, F, S, Fe, Co, Ag, Ni) doped into TiO2 narrows the bandgap of TiO2 and improves the photocatalytic activity of TiO2 under visible light [4,5,6,7,8]
MaterialsTetrabutyl titanate C16H36O4Ti, 37% hydrochloric acid (HCl), Ferrous sulfide (FeS), deionized water and absolute ethanol were used for the sample preparation

Summary

Introduction

Since the 1970s, titanium dioxide (TiO2) has been recognized as a promising solar-driven photocatalyst due to its high availability, efficiency, excellent functionality, long-term stability, nontoxicity and low cost [1]. There are two main problems in the application of TiO2: the low separation efficiency of photoinduced electron–hole pairs and the wide bandgap (3.0 eV for rutile and 3.2 eV for anatase) It can only use the ultraviolet region of solar light and photocatalytic activity is limited [1,2,3]. While experiments have confirmed that both (anionic or cationic) states of S ions are simultaneously doped into TiO2 nanotubes [2], only one chemical species of anionic S2−-doped TiO2 has rarely been observed in the experimental stage. To this extent, the main reason is that a single anionic S2− source is not easy to synthesize in the conventional experiment. In order to realize only one species of anionic S2−-doped TiO2, TNA with tiny size is selected by as the precursor, whose special structure made it possess a high reaction activity and facilitate the diffusion of S2− into TiO2 by the VPH method

Experimental

Photoelectrochemical and Photocatalytic Measurements

Results and Discussion

Photoresponse

Photocatalytic Activity Measurements