RESUMO
The loading of cocatalysts is an effective approach to optimize the separation of carriers during photocatalytic processes. Among them, cocatalysts often work independently during the photocatalytic production of H2. However, an investigation of the synergistic effect of dual cocatalysts is beneficial for further promoting photocatalytic H2 production activity. In this work, dual cocatalyst Ni2P-NiS-modified TiO2 nanosheets were fabricated through a solvent evaporation method. The investigation indicates that Ni2P-NiS can widen the light absorption range and reduce the contact angle between TiO2 and water from 26.71 to 8.27°, which facilitates the adsorption of water molecules. Besides, the introduction of Ni2P-NiS can decrease the overpotential of H2 evolution and induce more electrochemically active surface area. The photocatalytic tests show that the H2 production rate of 15% Ni2P-NiS/TiO2 can reach up to 4891.6 µmol·g-1·h-1, which is 30.2, 4.4, and 1.3 times than pure TiO2 (161.8 µmol·g-1·h-1), 15% Ni2P/TiO2 (1112.1 µmol·g-1·h-1), and 15% NiS/TiO2 (3678.1 µmol·g-1·h-1), respectively. The enhancement mechanism of photocatalytic H2 production is attributed to the Schottky barrier effect between Ni2P-NiS nanoparticles and TiO2 nanosheets, which can enormously promote the interface charge separation and transfer, and enhance the kinetics of H2 production. This work provides a potential strategy for enhancement H2 production using appropriate dual cocatalyst-decorated semiconductor materials.
RESUMO
Exploiting efficient and stable photocatalysts is the primary goal of photocatalytic water splitting for H2 production. In this work, a sea urchin-like bimetallic NiCo2O4-decorated ZnIn2S4 heterojunction was fabricated via a solvent evaporation method. Investigation shows that the introduction NiCo2O4 can expand the UV-vis absorption range, enhance the absorption intensity, promote the charge separation, decrease the charge transfer resistance, induce more active sites, and decrease the H2 evolution overpotential of the composite. Besides, the charge transfer between NiCo2O4 and ZnIn2S4 follows a Z-scheme route based on the ËOH radical capture experiments; this can preserve the strong oxidation-reduction reaction ability of photogenerated electrons and holes, leading to a faster H2 evolution rate, which reaches 17.28 mmol g-1 h-1 over the 4.8%-NiCo2O4/ZnIn2S4 composite under 300 W Xe lamp irradiation in 20 vol% triethanolamine (TEOA) solution and is 3.0 times higher than that of ZnIn2S4. In addition, NiCo2O4/ZnIn2S4 also has excellent stability during 5 consecutive cycles. This work provides an effective method for constructing a highly effective Z-scheme heterojunction system for photocatalytic H2 production.
RESUMO
A new technology, a freeze-dissolving method, has been developed to isolate nanoparticles or ultrafine powder and is a more efficient and sustainable method than the traditional freeze-drying method. In this work, frozen spherical ice particles were produced with an aqueous solution of sodium bicarbonate or ammonium dihydrogen phosphate at various concentrations to generate nanoparticles of NaHCO3 or (NH4)(H2PO4). The freeze-drying method sublimates ice, and nanoparticles of NaHCO3 or (NH4)(H2PO4) in the ice templates remain. The freeze-dissolving method dissolves ice particles in a low freezing point solvent at temperatures below 0 °C, and then, nanoparticles of NaHCO3 or (NH4)(H2PO4) can be isolated after filtration. The freeze-dissolving method is 100 times faster with about 100 times less energy consumption than the freeze-drying method as demonstrated in this work with a much smaller facility footprint and produces the same quantity of nanoparticles with a more uniform size distribution.
