Ling Meng1 , Zhiyu Ren1 , Wei Zhou1 , Yang Qu1 , and Guofeng Wang1 

ABSTRACT 

 An effective photocatalytic hydrogen production catalyst comprising MgTiO3/ MgTi2O5/TiO2 heterogeneous belt-junctions was prepared using magnesium ions by a thermally driven doping method. The tri-phase heterogeneous junction was confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The as-prepared MgTiO3/MgTi2O5/ TiO2 heterojunctions exhibited a very high photocatalytic hydrogen production activity (356.1 mol·g0.1gcat·h−1 ) and an apparent quantum efficiency (50.69% at 365 nm) that is about twice of that of bare TiO2 nanobelts (189.4 mol·g0.1gcat·h−1 ). Linear sweep voltage and transient photocurrent characterization as well as analysis of the electrochemical impedance spectra and Mott–Schottky plots revealed that the high photocatalytic performance is caused by the one-dimensional structure, which imparts excellent charge transportation characteristic, and the MgTiO3/MgTi2O5/TiO2 tri-phase heterojunction, which effectively drives the charge separation through the inherent electric field. This titanate-based tri-phase heterogeneous junction photocatalyst further enriches the catalyst system for photocatalytic hydrogen production.

Photocatalytic H2 production experiments 

 Photocatalytic evolution of H2 from water was conducted in an online photocatalytic hydrogen production system (AuLight, Beijing, China, CEL-SPH2N). A powder sample of the catalyst (0.1 g) was suspended in a mixture of 80 mL of distilled water and 20 mL of methanol in the cell using a magnetic stirrer. Pt-loaded photocatalysts were prepared using a known, standard, in situ photo-deposition method. For this, the photocatalyst powder was added to an aqueous methanol solution containing the required amount (1 wt.% of Pt) of H2PtCl6. The solution was illuminated for 3 h under simulated solar light, filtered, and then dried in a static oven at 80–100 ° C. Before the reaction, the mixture was deaerated by evacuation to remove any O2 and CO2 dissolved in the water. The reaction was carried out by irradiating the mixture with UV light from a 300 W Xe lamp with a UVREF reflection filter, which generates light with a wavelength of approximately 300–390 nm. Gas evolved only under photoirradiation and was analyzed using an online gas chromatograph.

Results and discussion

Figure 1 XRD spectra of the products prepared from different molar ratios of Ti and Mg. (PTBs = TiO2 nanobelts; MTB-1= Ti/Mg molar ratio of 1:1; MTB-2 = Ti/Mg molar ratio of 2:1; MTB-3 = Ti/Mg molar ratio of 3:1; MTB-4 = Ti/Mg molar ratio of 4:1; MTB-5 = Ti/Mg molar ratio of 5:1.)

Figure 4 (a) Relationship between H2 production and the Ti/Mg molar ratio, (b) photocatalytic H2 production curves for the different samples, and (c) cycle experiments on the PTB and MTB-4 samples.

Figure 5 (a) N2 adsorption–desorption isotherm curves and surface areas (inset) of the different samples, and (b) UV–vis absorption spectra of the PTBs and MTB-4

Figure 6 Photoelectrochemical properties of the samples: (a) chronoamperometry, (b) linear sweep voltammograms, (c) Nyquist plots of electrochemical impedance, and (d) Mott–Schottky plots.

Conclusions 

 In summary, we successfully synthesized MgTiO3/ MgTi2O5/TiO2 heterogeneous belt-junctions through hard template-based magnesium ions using a thermally driven doping method. The as-prepared MgTiO3/ MgTi2O5/TiO2 heterogeneous belt-junctions show enhanced photocatalytic hydrogen production activity as well as excellent stability. This study confirms that the heterojunctions of MgTiO3/MgTi2O5/TiO2 nanobelts effectively promote charge transfer, as demonstrated by PEC measurements. The electrons photo-induced on the magnesium titanate rapidly localize to the TiO2, which improves the hydrogen evolution ability of MTB with respect to that of pure TiO2 nanobelts. Our results suggest that the special belt-like structure enhances light utilization, effectively increases the number of catalyst surface active sites, and improves material transportation. It is believed that these research results provide useful information for the design of an optimal semiconductor that would combine the ability to dissociate water molecules with a proper band gap that absorbs UV–vis light while retaining high stability. Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 21471050, 21501052 and 21473051), the China Postdoctoral Science Foundation (No. 2015M570304), the Postdoctoral Science Foundation of