Spinel-Oxide-Integrated BiVO4 Photoanodes with Photothermal Effect for Efficient Solar Water Oxidation

Spinel oxide materials have been widely used as oxygen evolution catalysts to enhance the photoelectrochemical (PEC) performance of photoelectrodes. Herein, we demonstrate that the water splitting efficiency of a photoanode can be further enhanced by introducing its photothermal effect. Under near-infrared radiation, the temperature of the NiCo₂O₄/BiVO₄ photoanode increases moderately, leading to improved water oxidation kinetics and charge transport simultaneously. With the assistance of the photothermal effect, the obtained photoanode reaches a photocurrent density of 6.20 mA cm^-2 at 1.23 V vs reversible hydrogen electrode. A series of spinel-type MCo₂O₄ oxides (M = Mn, Zn, Cu, and Fe) are deposited on the surface of the BiVO₄ photoanode to show similar photothermally enhanced PEC performance. The research discovery provides a way for improving the catalytic activity of photoanode materials with a photothermal effect, which may be applied to various fields of energy conversion, including CO₂ reduction, N₂ fixation, and pollutant degradation.

Trace Amount CoFe2O4 Anchored on a TiO2 Photocatalyst Efficiently Catalyzing O2 Reduction and Phenol Oxidation

Semiconducting TiO₂ is the most studied photocatalyst for organic oxidation by O₂. To accelerate the reaction, a cocatalyst for O₂ reduction or for organic oxidation is often used, but the bifunctional one is rare. Herein we report a spinel CoFe₂O₄ (CF) efficiently catalyzing O₂ reduction and phenol oxidation on TiO₂ in aqueous suspensions at pH 3-11. The composite materials (CF/TiO₂) were made by depositing 0-5 wt % CF onto TiO₂ through a hydrothermal method. Solid characterization showed that CF nanoparticles (5 nm) homogeneously distributed in CF/TiO₂, whereas the TiO₂ phase remained unchanged in crystal structure and crystallite size. For phenol oxidation under UV light, CF was nearly not active, but 0.01 wt % CF/TiO₂ was more active than TiO₂, by approximately a factor of 3.6. Such trend in activity among the catalysts was also observed from the photocatalytic reduction of O₂ to H₂O₂, from the electrochemical reduction of O₂, and from the photoelectrochemical oxidation of phenol and H₂O. An open-circuit potential and photoluminescence measurement suggest that there is an interfacial electron transfer from TiO₂ to CF, followed by O₂ reduction. Accordingly, a possible mechanism is proposed, involving CF catalysis for O₂ reduction and phenol oxidation. Then the mutual promotion between electron and hole transfer results in great enhancement in the efficiency of charge separation and hence in the rate of chemical reaction. Because spinel compounds have rich composition and unique structures, they are worthy of being further investigated as cocatalysts of a semiconductor photocatalysis.

Enhanced Visible-Light-Driven Photocatalytic Bacterial Inactivation by Ultrathin Carbon-Coated Magnetic Cobalt Ferrite Nanoparticles

Ultrathin hydrothermal carbonation carbon (HTCC)-coated cobalt ferrite (CoFe₂O₄) composites with HTCC coating thicknesses between 0.62 and 4.38 nm were fabricated as novel, efficient, and magnetically recyclable photocatalysts via a facile, green approach. The CoFe₂O₄/HTCC composites showed high magnetization and low coercivity, which favored magnetic separation for reuse. The results show that the close coating of HTCC on CoFe₂O₄ nanoparticles enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. The composites exhibited superior photocatalytic inactivation toward Escherichia coli K-12 under visible-light irradiation, with the complete inactivation of 7 log₁₀ cfu·mL^-1 of bacterial cells within 60 min. The destruction of bacterial cell membranes was monitored by field-effect scanning electron microscopy analysis and fluorescence microscopic images. The bacterial inactivation mechanism was investigated in a scavenger study, and ^•O₂, H₂O₂, and h⁺ were identified as the major reactive species for bacterial inactivation. Multiple cycle runs revealed that these composites had excellent stability and reusability. In addition, the composites showed good photocatalytic bacterial inactivation performance in authentic water matrices such as surface water samples and secondarily treated sewage effluents. The results of this work indicate that CoFe₂O₄/HTCC composites have great potential in large-scale photocatalytic disinfection operations.

The effect of fluorine doping on the photocatalytic properties of hematite for water splitting

Fluorine-doped hematite samples with different concentrations were successfully synthesized through a hydrothermal method to improve the water splitting properties.

Prussian blue analogue derived magnetic carbon/cobalt/iron nanocomposite as an efficient and recyclable catalyst for activation of peroxymonosulfate

A Prussian blue analogue, cobalt hexacyanoferrate Co₃[Fe(CN)₆]₂, was used for the first time to prepare a magnetic carbon/cobalt/iron (MCCI) nanocomposite via one-step carbonization of Co₃[Fe(CN)₆]₂. The resulting MCCI consisted of evenly-distributed cobalt and cobalt ferrite in a porous carbonaceous matrix, making it an attractive magnetic heterogeneous catalyst for activating peroxymonosulfate (PMS). As Rhodamine B (RhB) degradation was adopted as a model test for evaluating activation capability of MCCI, factors influencing RhB degradation were thoroughly examined, including MCCI and PMS dosages, temperature, pH, salt and radical scavengers. A higher MCCI dosage noticeably facilitated the degradation kinetics, whereas insufficient PMS dosage led to ineffective degradation. RhB degradation by MCCI-activated PMS was much more favorable at high temperatures and under neutral conditions. The presence of high concentration of salt slightly interfered with RhB degradation by MCCI-activated PMS. Through examining effects of radical scavengers, RhB degradation by MCCI-activated PMS can be primarily attributed to sulfate radicals instead of a combination of sulfate and hydroxyl radicals. Compared to Co₃O₄, a typical catalyst for PMS activation, MCCI also exhibited a higher catalytic activity for activating PMS. In addition, MCCI was proven as a durable and recyclable catalyst for activating PMS over multiple cycles without efficiency loss and significant changes of chemical characteristics. These features demonstrate that MCCI, simply prepared from a one-step carbonization of Co₃[Fe(CN)₆]₂ is a promising heterogeneous catalyst for activating PMS to degrade organic pollutants.

Facile synthesis of porous CoFe2O4 nanosheets for lithium-ion battery anodes with enhanced rate capability and cycling stability

Porous CoFe₂O₄ nanosheets are prepared via a low-cost and scalable process and are shown to be high-performance anode materials for lithium-ion batteries.