Introduction

During the past decades, the photocatalytic hydrogenation technology of water has attracted increasing attention [1e3]. Among various photocatalysts [4e9], titanium dioxide (TiO2) is still one of the most promising candidates for H2 evolution in water because of its excellent photocatalytic property, high stability, nontoxicity and low cost [10e15]. However, pure titanium dioxide (for anatase TiO2) can only be excited by UV light with wavelengths less than 388 nm, which only accounts for 4% of the solar spectrum and limits the utilization of solar energy. In order to efficiently utilize solar energy, a great many of efforts have been made on extending the absorption of TiO2- based materials to visible light region. For instance, surface photosensitizaiton of TiO2 with dyes [16e21], doping of TiO2 with foreign ions (such as transition metals or noble metals) [22e26], coupling TiO2 with other narrow semiconductor [27e31]. Recently, TiO2 doping with nonmetal elements has been considered as an effective approach to extend the light adsorption of TiO2 to visible region [32e36]. From then on, many attempts have been done on nonmetal doped TiO2, such as N [37e39], C [40,41], B [42,43], F [44e46] and S [47,48], indicating that these TiO2-based catalysts exhibit relatively high visible-light photocatalytic activity due to narrowing the band gap. However, nonmetal doped TiO2 are usually synthesized below 500
C owing to the phase transformation from anatase to rutile above 500
C calcination temperature. In this case, the crystallinity of nonmetal doped TiO2 are relative low, implying the surface defects of TiO2 are relative much, which will reduce the activity of photocatalyst [49e51]. In this paper, a novel in-situ S-doped porous anatase TiO2 nanopillar is synthesized by a facile one-step thermal protection method. The obtained S-doped TiO2 can maintain anatase phase up to 700
C. The high crystallinity, porous structure and S introduction of TiO2 samples calcined at 700
C can increase its photocatalytic activity in the visible-light region. The final prepared S-doped porous anatase TiO2 nanopillar exhibits the excellent H2 evolution performance. 

The photocatalytic hydrogen evolution experiments were conducted in an online photocatalytic hydrogen evolution experiments were conducted in an online photocatalytic hydrogen generation system (AuLight, Beijing, CEL-SPH2N) at ambient temperature (20 ℃). Photocatalyst (100 mg) was suspended in a mixture of 80 mL of water and 20 mL of methanol in closed-gas circulation reaction cell by using a magnetic stirrer. Prior to the reaction, the mixture was deaerated by evacuation to remove O2 and CO2 dissolved in water. An AM 1.5 solar power system (solar simulator (Oriel, USA) equipped with an AM 1.5G filter (Oriel, USA)) was used as light irradiation source with bandpass filter (l ¼ 400 nm). Gas evolution was observed only under photoirradiation with a power density of 100 mW/cm2 , being analyzed by an on-line gas chromatograph (SP7800, TCD, molecular sieve 5 Å, N2 carrier, Beijing Keruida Limited)

Conclusions 

A novel in-situ S-doped porous anatase TiO2 nanopillar was successfully synthesized by a facile one-step thermal treatment method. The calcination temperature was a key parameter for its visible-light photocatalytic performance. The crystalline phase transformation from anatase to rutile of TiO2 could be inhibited at 700 ℃. T700 could obtain the optimum H2 evolution performance under visible-light irradiation. It could be attributed to the high anatase crystallinity, the S introduction and the porous structure of T700. Therefore, the facile synthesized porous anatase TiO2 nanopillars could be as promising photocatalytic hydrogen production materials in the future.