Efficient photocatalytic H2production realized by MnxCd1-xSeIn situheterojunction

Fast recombination of photoinduced carriers inhibits the performance of photocatalysts. By constructing heterojunctions, built-in electric fields can be formed to separate electrons and holes and finally enhance the photocatalytic efficiency. Herein, a Mn_xCd_1-xSein situheterojunction was fabricated by a facile solvothermal method to draw upon this advantage. Absorption spectra show that the light absorption of CdSe raises up obviously after the doping of Mn²⁺. Best performance was achieved when the doping percent of Mn²⁺was 50%. This Mn_0.5Cd_0.5Se sample exhibits a 7.2 folds increase in hydrogen evolution against pure CdSe owing to the fast electron transportation. Moreover, it proves well stability in an 18 h cycling test and gains a 6.7% apparent quantum yield under 420 nm light. In summary, this work constructs anin situheterojunction to enhance the photocatalytic hydrogen evolution efficiency and sheds light on a feasible way for the application of photocatalysis.

Enhanced Photodegradation of p-Nitrobenzoic Acid by Binary Mixtures with Ba2+/TiO2 and MCM-41

A novel Ba(II)/TiO₂-MCM-41 composite was synthesized using binary mixtures with Ba²⁺/TiO₂ and MCM-41, and Ba²⁺ as a doping ion of TiO₂. The specific surface area and pore structure characterizations confirm that a mesoporous structure with a surface area of 341.2 m²/g and a narrow pore size distribution ranging from 2 to 4 nm was achieved using Ba(II)/TiO₂-MCM-41. Ba(II)/TiO₂ particles were synthesized into 10-15 nm particles and were well dispersed onto MCM-41. The diffraction peaks in the XRD patterns of TiO₂-MCM-41 and Ba(II)/TiO₂-MCM-41 were all attributed to anatase TiO₂. By taking advantage of MCM-41 and Ba²⁺, the photocatalytic performance of Ba(II)/TiO₂-MCM-41 was remarkably enhanced by suppressing its rutile phase, by lowering the band gap energy, and by facilitating the dispersion of TiO₂. Therefore, the photodegradation efficiencies of p-nitrobenzoic acid (4 × 10^-4 mol/L) by various photocatalysts (60 min) under UV light irradiation are arranged in the following order: Ba(II)/TiO₂-MCM-41 (91.7%) > P25 (86.3%) > TiO₂-MCM-41 (80.6%) > Ba(II)/TiO₂ (55.7%) > TiO₂ (53.9%). The Ba(II)/TiO₂-MCM-41 composite was reused for five cycles and maintained a high catalytic activity (73%).

From Macro to Mesoporous ZnO Inverse Opals: Synthesis, Characterization and Tracer Diffusion Properties

Oxide inverse opals (IOs) with their high surface area and open porosity are promising candidates for catalyst support applications. Supports with confined mesoporous domains are of added value to heterogeneous catalysis. However, the fabrication of IOs with mesoporous or sub-macroporous voids (<100 nm) continues to be a challenge, and the diffusion of tracers in quasi-mesoporous IOs is yet to be adequately studied. In order to address these two problems, we synthesized ZnO IOs films with tunable pore sizes using chemical bath deposition and template-based approach. By decreasing the size of polystyrene (PS) template particles towards the mesoporous range, ZnO IOs with 50 nm-sized pores and open porosity were synthesized. The effect of the template-removal method on the pore geometry (spherical vs. gyroidal) was studied. The infiltration depth in the template was determined, and the factors influencing infiltration were assessed. The crystallinity and photonic stop-band of the IOs were studied using X-Ray diffraction and UV-Vis, respectively. The infiltration of tracer molecules (Alexa Fluor 488) in multilayered quasi-mesoporous ZnO IOs was confirmed via confocal laser scanning microscopy, while fluorescence correlation spectroscopy analysis revealed two distinct diffusion times in IOs assigned to diffusion through the pores (fast) and adsorption on the pore walls (slow).