RESUMO
Ag-containing ZnO/ ß-Ga2O3 semiconductor, which exhibit reduced bandgap, increased light absorption, and hydrophilicity, have been found to be useful for photocatalytic CO2 reduction and N2 fixation by water. The charge-separation is facilitated by the new interfaces and inherent vacancies. The Ag@GaZn demonstrated the highest photocurrent response, about 20- and 2.27-folds that of the Ga and GaZn samples, respectively. CO, CH4, and H2 formed as products for photo-reduction of CO2. Ag@GaZn catalyst exhibited the highest AQY of 0.121 % at 400 nm (31.2 W/m2). Also, Ag@GaZn generated 740 µmolg-1 of NH4+ ions, which was about 18-folds higher than Ga sample. In situ DRIFTS for isotopic-labelled 13CO2 and 15N2 reaffirmed the photo-activity of as-synthesized catalysts. Density functional theory provided insight into the relative affinity of different planes of heterostructures towards H2O, CO2 and N2 molecules. The structure-photoactivity rationale behind the intriguing Ag@GaZn sample offers a fundamental insight into the role of plasmonic Ag and design principle of heterostructure with improved photoactivity and stability.
RESUMO
When two semiconductors are electronically coupled, their photocatalytic performance can be greatly enhanced. Herein, we formed a heterostructure between Cu2O and SnS2/SnO2 nanocomposite using a solvothermal reactor, which reduced CO2 by H2O at ambient conditions to produce CO, H2, and CH4. With inclusion of Cu2O, apparent quantum yield, a measure of photoactivity, has increased from 7.16% to 8.62%. Also, the selectivity of CH4 over CO was approximately 1.8-times higher than that of SnS2/SnO2. Interestingly, the as-synthesized catalysts were able to fix N2 to NH3 under light illumination at ambient conditions. Dissecting the mechanism into basic steps, it is shown that oxygen vacancies within the catalysts act as trapping sites for photo-induced charge carriers which strongly influenced the reactivity and selectivity of product. Additionally, oxygen vacancies act as active sites to chemisorb nitrogen molecules, which follow associative steps to generate NH3. In absence of sacrificial agent, the NH4+ generation rate was66.35µmol.g-1h-1 for Cu2O/SnS2/SnO2, which is 1.9-fold higher than SnS2/SnO2. Formation of a p-n heterojunction between Cu2O and SnS2/SnO2 nanocomposite offered favorable photoreductive potentials and high stability, mainly owing to their intimate interfacial contact. The results clearly illustrate a promising strategy to use oxygen vacancies rich heterostructure for wide application in photocatalysis.
RESUMO
The high de-/hydrogenation temperature of magnesium hydride is still a challenge in solid-state hydrogen storage system for automobiles applications. To improve the hydrogenation properties of MgH2, we select activated carbon/charcoal (AC) as a catalyst. A systematic investigation was performed on the hydrogen storage behaviors of MgH2 and MgH2 - 5 wt% AC nanocomposites, which were prepared by a high-energy planetary ball mill. These synthesized nanocomposites were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) for phase identification, surface morphology and microstructural analysis. The pressure-composition-temperature (PCT) isotherm investigation shows the maximum hydrogen storage capacity ~ 6.312 wt% for MgH2-AC nanocomposites, while 3.417 wt% for MgH2 at 300 °C. The onset temperature for MgH2-AC nanocomposites is shifted towards lower side than the 50 h milled MgH2. The HRTEM study show the activated carbon helps to reduce oxygen from MgO phase in MgH2, so that significantly improvement achieved in the absorption capacity and kinetics also for the MgH2-AC nanocomposites. The presence of ß- and γ-phases of MgH2 in MgH2-AC nanocomposites also supports the high hydrogenation properties and with the support of XRD data.