The photoelectrocatalytic CO2 reduction on TiO2@ZnO heterojunction by tuning the conduction band potential

Cu2ZnSnS4 (CZTS) for Photoelectrochemical CO2 Reduction: Efficiency, Selectivity, and Stability

Massive emissions of carbon dioxide (CO2) have caused environmental issues like global warming, which needs to be addressed. Researchers have developed numerous methods to reduce CO2 emissions. Among these, photoelectrochemical (PEC) CO2 reduction is a promising method for mitigating CO2 emissions. Recently, Cu2ZnSnS4 (CZTS) has been recognized as good photocathode candidate in PEC systems for CO2 reduction due to its earth abundance and non-toxicity, as well as its favourable optical/electrical properties. The performance of PEC CO2 reduction can be evaluated based on its efficiency, selectivity, and stability, which are significantly influenced by the photocathode materials. As a result, researchers have applied various strategies to improve the performance of CZTS photocathodes, including band structure engineering and surface catalytic site engineering. This review provides an overview of advanced methods to enhance the PEC systems for CO2 reduction, focusing on CZTS.

Impact of structure, doping and defect-engineering in 2D materials on CO2 capture and conversion

2D material based strategies for adsorption and conversion of CO2 to value-added products.

Recent developments and challenges in practical application of visible-light-driven TiO2-based heterojunctions for PPCP degradation: A critical review

The ability of the TiO₂-based photocatalysis process to mineralize organic pollutants has attracted attention worldwide for the degradation of recalcitrant pharmaceuticals and personal care products (PPCPs). Nevertheless, (1) the limited exploitation of the solar spectrum, i.e., activation under UV light (only 2-3% of solar spectrum), and (2) the high recombination rate of photo-generated charge carriers, i.e., electrons and holes, have limited its application which can, however, be improved by developing a TiO₂-based heterojunction. The objective of this critical review paper is to discuss the recent developments (2009-2019) in visible-light-driven (VLD) TiO₂-based heterojunctions for PPCP degradation and their degradation mechanisms. Compared to the conventional heterojunctions, Schottky and Z-scheme heterojunctions, which are non-conventional heterojunctions, are found to be more effective for PPCP degradation due to their more efficient separation of charge carriers and the occurrence of redox reactions at a relatively higher redox potential. Furthermore, the enhancement strategies for the development of a VLD TiO₂-based heterojunction are also explored which can be achieved by selecting the (1) highly photocatalytically active {001} facet of anatase TiO₂, (2) synthesis methods governing the structural changes at the junction interface, and (3) heterojunction components which can efficiently generate the powerful •OH radicals. The challenges in practical applications are also discussed which include factors, viz., cost reduction, recycling, stability, byproducts analysis, evaluation of the environmental effectiveness, and reactor design and scale-up of the VLD TiO₂-based heterojunctions. Accordingly, the prospects of VLD TiO₂-based heterojunctions for PPCP degradation in real environmental applications are discussed.

Effective combination of CuFeO2 with high temperature resistant Nb-doped TiO2 nanotube arrays for CO2 photoelectric reduction

Herein, we report a simple approach to synthesize CuFeO₂/TNNTs photocathodes composed of high-temperature resistance n-type Nb-doped TiO₂ nanotube arrays (TNNTs) and p-type CuFeO₂ for CO₂ reduction. TNNTs were prepared by anodic oxidation on TiNb alloy sheets and CuFeO₂/TNNTs were then prepared by coating precursor liquid onto TNNTs followed by heat treatment in argon atmosphere. The microstructures of CuFeO₂/TNNTs and TNNTs before and after heat treatment were investigated by SEM and TEM. The phase compositions of CuFeO₂/TNNTs were studied by XRD and XPS, and the light absorption performance were tested by UV-vis diffuse reflectance spectrum. Results show that TNNTs exhibit a regular nanotube arrays structure and this structure is well remained after the calcination at 650 °C. In addition, TNNTs show similar semiconductor properties to n-type TiO₂, which enables them to be integrated with p-type CuFeO₂ to obtain composite photocathodes with a p-n junction. The synthesized CuFeO₂/TNNTs photocathode is well crystallized because no other crystalline iron or copper compounds are included in the prepared photocathode. Furthermore, the photocathode shows high light absorption and fast carrier transport due to the appropriate band gap and p-n junction. As a result, high photoelectrocatalytic CO₂ reduction performance with high selectivity to ethanol is obtained on this photocathode.

Fabrication of Opaline ZnO Photonic Crystal Film and Its Slow-Photon Effect on Photoreduction of Carbon Dioxide

Monodisperse ZnO particles with adjustable size have been produced on a large scale by two-step seeding-growth polyol reactions. Through spin coating of supersaturated ZnO/diethylene glycol solution and evaporation of solvent, opaline ZnO photonic crystal (PC) film with good crystallinity and uniform photonic structures can be prepared from these ZnO particles. Compared with a disorderly stacked ZnO film, the ZnO PC film shows a higher activity in photocatalytic reduction of CO₂ due to the generated slow photons at the edge of the photonic band gap and their promotion to the light absorption. When the electronic band gap of ZnO matches the red edge of the photonic band gap of ZnO PC, the enhancement factor of photocatalytic activity represented by CO evolution can be maximized to 2.64-fold in the current experiment. Compared to the traditional inverse opal photocatalysts, the opaline ZnO photocatalysts are prepared by simplified and scalable procedures, and they still possess the same enhancement in activity compared to ZnO without the photonic structure, which might be broadly used in solar energy utilization, environment protection, and many other green chemical processes in the future.