Feng Li1 ,Peihua Wangyang2 , Amir Zada1 ,Muhammad Humayun1 ,Binsong Wang1 * and Yang Qu1 *

Abstract:

Hierarchical Mn2O3 microspheres have been prepared via polyol-mediated solvothermal method. The as-prepared hierarchical microspheres is about 8-10 μm in diameter assembled with porous nanosheets which favors charge transport. The formation process has been studied which is to form nanosheet first and then to self-assemble and finally to grow spheres. The band structure of Mn2O3 microspheres is confirmed through XPS valence spectrum and UV-vis,verfiying that it is suitable for hydrogen reduction. The H2 production efficiency of hierarchical Mn2O3 microspheres is found to three time higher than that of Mn2O3 particles. The promoted photocatalytic hydrogen production efficiency could be attributed to the interesting hierarchical structure, large surface area and suitable band gap.

2. Experimental Section

2.4.Evaluation of photocatalytic activity

The photocatalytic H2 production experiment was conducted in an online photocatalytic H2 production system (AuLight, Beijing, CEL-SPH2N) at ambient temperature (20 ºC). In a typical experiment, 0.1 g of photocatalyst was suspended in a mixture of 80 mL distilled water and 20 mL methanol in the reaction cell by using a magnetic stirrer. 1 wt.% Pt loaded photocatalysts were prepared by known standard method of in-situ photodeposition method using H2PtCl6 aqueous solution. Prior to the reaction, the mixture was deaerated by evacuation to remove O2 and CO2 dissolved in water. The reaction was carried out by irradiating the mixture with visible light from a 300 W Xe lamp (AuLight, CEL-HXF300) with a UVCUT filter (AuLight, 400-780 nm). Gas evolution was observed only under photoirradiation, being analyzed by an on-line gas chromatograph (SP7800, TCD, molecular sieve 5 Å, N2 carrier, Beijing Keruida Limited).

Conclusions

 In summary, hierarchical Mn2O3 microspheres assembled with porous nanosheets have been prepared by solvothermal method. The self assemble process of the microsphere are studied. The band structure of Mn2O3 microspheres calculated from UV-vis and XPS valence spectra reveals that the conduction band is more negative and potentially much suitable for photocatalytic hydrogen production. The H2 production activity of hierarchical Mn2O3 microspheres and Mn2O3 particles is 74.24 and 25.36 μmol·g-1·h-1, respectively. The promoted photocatalytic hydrogen production activity may come from the interesting hierarchical structure and suitable band gap of Mn2O3 microspheres. This Mn2O3 microspheres photocatalyst give a new choice to prepare high efficiency photocatalysts for solar hydrogen production.

Figures caption: 

Fig. 1 XRD patterns of the prepared Mn2O3 precursor and products calcined at different temperature. 

Fig. 2 FT-IR spectrum of prepared Mn2O3 precursor. 

Fig. 3 SEM images of the precursor and hierarchical Mn2O3 microspheres. 

Fig. 4 The N2 adsorption-desorption isotherms of hierarchical Mn2O3 microspheres (black) and particles(red). 

Fig. 5 TEM (A, B) and HRTEM (C) images of the hierarchical Mn2O3 microspheres. 

Fig. 6 SEM images of the collected samples at different hydrothermal time intervals. (A) 1h, (B) 5 h and (C) 10 h, respectively. 

Fig. 7 UV-vis spectra (A), XPS valence band spectra (B) and Scheme of the band structures of Mn2O3 and MnO2. 

Fig. 8 Time course H2 production efficiency (A) and cycling tests of H2 production (B) of hierarchical Mn2O3 microspheres and Mn2O3 particles. 

Fig. 9 SEM image of Mn2O3 particles.