Titanium dioxide (TiO2) has been considered as one of the most promising photocatalysts nanomaterials and is being used in a variety of fields of energy and environment under sunlight irradiation via photocatalysis. Highly efficient photocatalytic materials require the design of the proper structure with excellent morphology, interfacial structures, optical and surface properties, etc. Which are the key points to realize effective light-harvesting for photocatalytic applications. Hierarchical TiO2 based nanoflower structures (i.e., 3D nanostructures) possess such characteristics and have attracted much attention in recent years. The uniqueness of TiO2 nanoflowers (NFs) with a coarse texture and arranged structures demonstrates higher photocatalytic activity. This review deals with the hydrothermal synthesis of 3D TiO2 NFs and effect of shape/size as well as various key synthesis parameters to improve their optoelectronic and photocatalytic properties. Furthermore, to improve their photocatalytic properties, various strategies such as doping engineering and heterojunction/nanocomposite formation with other functional nanomaterials have been discussed followed by their potential applications in photocatalytic degradation of various emerging pollutants discharged into the wastewater from various sources. Importance of such 3D nanoarchitecutres and future research in other fields of current interest in environments are discussed. 

TiO2 nanoflower photocatalysts: Synthesis, modifications and applications in wastewater treatment for removal of emerging organic pollutants.

Zeolitic imidazolate framework (ZIF‐8)‐derived single‐atom catalysts (SACs) are widely studied in many catalytic reactions such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and CO2 reduction reactions (CO2RR). Grinding procedures involved in the synthesis of ZIF‐8‐derived SACs could affect the catalytic performance but are less evaluated in the literature. Herein, a series of ZIF‐8‐derived cobalt SACs (C–Co–ZIFs) with different grinding processes to investigate the impact of the grinding degrees on the performance of the electrochemical reduction reaction of CO2 (ECO2RR) is presented. The moderate grinding process affords a boost in CO Faradaic efficiency (FE, around 15% higher than that of the original C–Co–ZIF) and the highest current densities among all the samples. The variations in the electronic structure of the Co active sites in the ground catalysts are confirmed by X‐Ray absorption spectroscopy (XAS) and X‐Ray emission spectroscopy (XES) for improved catalytic performance. The increased micropores in the moderately ground catalyst provide more exposed active sites while the increased meso‐ and macropores promote the mass transfer, benefiting the ECO2RR performance. It suggests that the impact of grinding processes on the synthesis of ZIF‐8‐derived SACs should be considered for the evaluation of the catalytic performance.

The Deep Understanding into the Promoted Carbon Dioxide Electroreduction of ZIF‐8‐Derived Single‐Atom Catalysts by the Simple Grinding Process

Photocatalysis is a promising route to utilize sunlight, which has been potentially used to solve energy as well as environmental problems with an emphasis on fundamental understanding and technological applications in society. Semiconductors are excellent photocatalysts but often show less efficient activities due to the fast recombination of photogenerated charge carriers and very slow kinetics of surface photochemical reactions. However, recent advancements show promising strategies to improve their photocatalytic activities, including surface modifications using suitable co-catalysts and the development of novel efficient photocatalysts. Graphene oxide (GO) is one of such nanomaterials which shows multifarious roles in photocatalysis with a great potential to act as an independent solar-driven sole photocatalyst. In this minireview, the photochemistry of GO has been discussed in view of its multifarious roles/mechanisms in improving the photocatalytic activity of metal oxide semiconductors, plasmonic nanomaterials, and also their nanocomposites. In addition, recent advancements and applications of such GO-based photocatalysts in photocatalytic degradation of organic dye pollutants, including engineering of GO as the sole photocatalyst, have been discussed. Furthermore, the challenges and future prospects for the development of GO-based photocatalysts are discussed.

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Mechanistic Insights into Graphene Oxide Driven Photocatalysis as Co-Catalyst and Sole Catalyst in Degradation of Organic Dye Pollutants

Designed TiS2 nanosheets efficient for electrocatalytic reductive amination of biomass-derived furfurals

Multi-metallic organic framework-derived materials for electrocatalytic CO2 reduction reaction

Electrochemical CO2 reduction reaction (ECO2RR) offers an opportunity to sustainably convert CO2 into value-added fuels and chemicals by using the electricity that could be generated by renewable energies. Recently, enormous efforts are focused on the development of metal-based catalysts for the selective ECO2RR with high efficiency. Multi-metallic catalyst design emerges as one of the most promising strategies for the promotion of the Faradaic efficiency (FE), the current density, and the lowering of the overpotential of the catalysts for ECO2RR. The synergistic effects of the different metal sites in the hybrid catalysts are of significance for the enhancement of the ECO2RR performance. This review summarizes the rational design of multi-metallic catalysts, including alloy, atomically dispersed multi-metallic sites, and others, along with the popular metal elements studied in multi-metallic catalysts to clarify the advantages of different metal elements for ECO2RR. The density functional theory (DFT) simulations and advanced in-situ characterizations that contribute to demystifying the synergies between metal elements are highlighted. Challenges and outlook concerning the catalyst design and reaction mechanism of multi-metallic catalysts for ECO2RR are also discussed.

Hangrong Chen

Papers

Multi-metallic catalysts for the electroreduction of carbon dioxide: Recent advances and perspectives