Piezo-photocatalysis for efficient charge separation to promote CO2 photoreduction in nanoclusters

Breaking the intrinsic activity barriers of bilayer metal oxides for catalytic CO2 reduction

The photocatalytic CO2 reduction reaction is severely limited by sluggish charge kinetics. To address this issue, a strategy utilizing non-metal-doped layered double hydroxide (LDH) has been developed to control the electronic structure of spindle-shaped nanoflowers, resulting in efficient photocatalytic CO2 reduction. The results demonstrate that the designed catalyst yields 263.16 μmol g-1 h-1 for the photoreduction of CO2 to CO. Furthermore, the in situ Fourier transform infrared spectrum (FT-IR) analysis demonstrate that the specific S-ligand (S-bridge) facilitates CO2 activation, ensuring the continuous production of *COOH. The hydrothermal-assisted ionic liquid method proposed in this study offers guidance for modifying catalysts.

Unraveling the pyridinic nitrogen vacancy in carbon nitride for photo-self Fenton-like purification of organic contaminants

This work reports a carbon nitride with pyridinic nitrogen-vacancy (N2CV-CN), which purifies organic contaminants via an in-situ photo-self Fenton-like reaction. Experiments and calculations demonstrated that the nitrogen-vacancy induces lone-paired (LP) and symmetry-unpaired electrons, promoting the formation of low-energy LP-π hybridized orbitals and helping to overcome the pairing energy required for oxygen to accept electrons. Furthermore, the nitrogen-vacancy accelerates film and intra-particle diffusion rates of organic contaminants on N2CV-CN, creating beneficial conditions for reactive oxide species to mineralize organic contaminants. Under sunlight and atmospheric oxygen, a photo-self Fenton-like reaction involving proton-coupled electron transfer occurred on the surface of N2CV-CN. Furthermore, by integrating photocatalysis with flocculation, about 99.1 % suspended substance, 45.5 % chemical oxygen demand, and 38.4 % biological oxygen demand were reduced from polluted river-water. Constructing N2CV-CN and understanding its crucial role offer theoretical and methodological insights into the in-situ purification of contaminated water bodies.

Regulating superstructures of conjugated polymers towards enhanced and stable photocatalytic hydrogen evolution via covalent crosslinking and complementary supramolecular self-assembly

The modulation of microstructures in conjugated polymers represents a viable strategy for enhancing photocatalytic efficiency, albeit hampered by complex processing techniques. Here, we present an uncomplicated, template-free method to synthesize polymeric photocatalysts, namely BCN(x)@PPy, featuring a hollow nanotube-nanocluster core-shell superstructure. This configuration is realized through intramolecular covalent crosslinking and synergistic intermolecular donor-acceptor (D-A) interactions between phenylene pyrene (PPy, D) nanotubes and poly([1,1'-biphenyl]-3-carbonitrile) (PBCN, A) nanoclusters. Interestingly, the optimized BCN2@PPy composite demonstrates remarkably enhanced performance for photocatalytic hydrogen evolution, with an efficiency of 14.7-fold higher than that of unmodified PPy nanotubes. Experimental and density functional theory calculations revealed that BCN(x)@PPy composites are conducive to shortening photogenerated exciton migration, facilitating charge separation and transfer, reducing nanoclusters aggregation or re-stacking, and providing sufficient catalytically active sites, all contributing to the heightened efficiency in photocatalysis. These insights underscore the potential for precise molecular adjustments in conjugated polymers, advancing artificial photosynthesis.

Fe-TiO2-x/TiO2 S-scheme homojunction for efficient photocatalytic CO2 reduction

CO2-to-high value-added chemicals via a photocatalytic route is of interest but strangled by the low efficiency. Herein, a novel Fe-TiO2-x/TiO2 S-scheme homojunction was designed and constructed by using a facile surface modification approach whereby oxygen vacancy (OV) and Fe introducing on the TiO2 nanorod surface. The as-synthesized Fe-TiO2-x/TiO2 S-scheme homojunction exhibits positive properties on promoting photocatalytic CO2 reduction: i) the nanorod structure provides numerous active sites and a radical charge transfer path; ii) the doped Fe and OV not only synergistically enhance light utilization but also promote CO2 adsorption; iii) the Fe-TiO2-x/TiO2 S-scheme homojunction benefits photoexcited charge separation and retains stronger redox capacity. Thanks to those good characters, the Fe-TiO2-x/TiO2 homojunction exhibits superior CO2 reduction performances with optimized CO/CH4 generation rates of 122/22 μmol g-1h-1 which exceed those of pure TiO2 by more than 9.4/7.3 folds and most currently reported catalytic systems. This manuscript develops a facile and universal approach to synthesize well-defined homojunction and may inspire the construction of other more high-efficiency photocatalysts toward CO2 reduction and beyond.

Na-Ru bimetallic functional sites promote photo-driven CO2 directed conversion into CH4

Recently, there has been a significant increase in interest in using photocatalysis for the energy conversion of polluting gases. In this research, sodium and ruthenium bimetallic functional sites co-modified bismuth tungstate (Ru/Na-Bi2WO6) nanoflower photocatalyst was synthesized via the hydrothermal method. The CO2 reduction products on the Bi2WO6 substrate were CO (1.66 μmol/g/h, 68 %) and CH4 (0.78 μmol/g/h, 32 %). After optimization, a significant change in the CO2 products of the Bi2WO6-based composite material was observed, with CO (0.61 μmol/g/h, 3.6 %) and CH4 (16.1 μmol/g/h, 96.4 %). Results showed that the dominance of CH4 as the main product in the Ru/Na-BWO system is attributed to the effective doping of Na, which generates impurity energy levels composed of oxygen vacancies, lowering the conduction band position of Bi2WO6, thereby suppressing CO generation, and enhancing CH4 selectivity by changing the CO2 activation pathway. The remarkable performance is ascribed to the synergized adsorption and activation of CO2 by the tandem Na+ sites and Ru0 sites. Specifically, the doped Na+ sites play a major role in promoting the adsorption CO2 molecules, while the Ru0 sites play a dominant role in facilitating the activation of the intermediates.

S‑scheme heterojunction of thin-layer O-modified graphitic carbon nitride/cobalt porphyrin to promote photocatalytic CO2 conversion

The emissions of CO2 are increasing year by year, which have led to serious environmental problems. Converting CO2 into valuable fuels through photocatalysis is a promising strategy. In this research, oxygen atoms were successfully innovated into graphitic carbon nitride (CN). Additionally, cobalt porphyrin (CoTPP) was successfully loaded onto the modified carbon nitride (Co/CN). The generation of interfacial electric fields and bending bands between CN and CoTPP was demonstrated experimentally. The electrons in the CN and the holes in the CoTPP were combined to form a unique S-scheme heterojunction structure, and efficient separation of carriers was promoted. As a result, the CO conversion under visible light irradiation reached an impressive 100.70 μmol g-1 h-1. By integrating theoretical and experimental findings, this study underscores the critical role of catalyst design in enabling efficient photocatalytic CO2 reduction.

Nitrogen-functionalization of carbon materials for supercapacitor: Combining with nanostructure directly is superior to doping amorphous element

Just how heteroatomic functionalization enhances electrochemical capacity of carbon materials is a recent and widely studied field in scientific research. However, there is no consensus on whether combining with heteroatom-bearing nanostructures directly or doping amorphous elements is more advantageous. Herein, two kinds of porous carbon nanosheets were prepared from coal tar pitch through anchoring graphitic carbon nitride (PCNs/GCNs-5) or doping amorphous nitrogen element (PCNs/N). The structural characteristics and electrochemical properties of the two PCNs were revealed and compared carefully. It can be found that the amorphous nitrogen of PCNs/N will have a grievous impact on its carbon skeleton network, resulting in reduced stability in charge and discharge process, while the structural collapse of carbon network could be avoided in PCNs/GCNs-5 by the heteroatoms in the form of nanostructure. Particularly, PCNs/GCNs-5 exhibits extremely high specific capacity of 388 F g-1 at 1 A g-1, and splendid the capacitance retention rate of 98% after 10,000 cycles of charge and discharge, which are overmatch than the amorphous nitrogen doped carbon materials reported recently and PCNs/N. The combining strategy with nanostructure will inspire the design of carbon materials towards high-performance supercapacitor.

Recent developments in piezo-photocatalytic CO2 reduction: concepts, mechanism, and advances

Out of the high number of photocatalytic applications, CO2 reduction has proved to be quite a boon for the present world. Increasing CO2 emissions owing to fossil fuel usage has been a menace to our society. To date, many methods have been developed to redress the situation. One of them is photocatalysis, which has been a well-known branch of energy and environmental applications since 1972. This is due to its low energy consumption and green nature. In recent years, a new phenomenon has come into existence wherein a combination of mechanical energy and photocatalysis can increase the efficiency of any catalytic process. In this regard, this frontier article will discuss the recent developments in piezo-photocatalysis for CO2 reduction. The main focus will be understanding the underlying mechanisms of efficiency enhancements in photocatalytic systems. Initially, the mechanism of CO2 reduction and its current needs will be discussed in the introduction. Further, a collection of recent reports from the literature and various material systems will be discussed to gain insights into the latest developments in the area. Then, literature and references that are purely mechanism-based with deeper analysis will be discussed, along with crucial characterization techniques for piezo-photocatalysts. Many factors need to be factored in for a better understanding of piezo-photocatalysis, e.g., factors such as piezo energy source, material design, and CO2 adsorption, require more attention to increase the CO2 reduction capability of photocatalysts. Based on the discussions in this article, researchers will gain new perceptions on the combination of vibrational energy and light energy to enhance CO2 reduction yields. Moreover, this article can advance understanding of techniques such as Kelvin probe microscopy, the requirement of simulation studies, and CO2 reduction mechanisms to better understand the piezo behavior of materials and ways to improve them for maximum product yield.

Stacking Engineering of Heterojunctions in Half-Metallic Carbon Nitride for Efficient CO2 Photoreduction

Enhancing charge separation in semiconductor photocatalysts is a major challenge for efficient artificial photosynthesis. Herein, a compact heterojunction is designed by embedding half-metallic C(CN)3 (hm-CN) hydrothermally in BiOBr (BOB) as the backbone. The interface between hm-CN and BOB is seamless and formed by covalent bonding to facilitate the transmission of photoinduced electrons from BOB to hm-CN. The transient photocurrents and electrochemical impedance spectra reveal that the modified composite catalyst exhibits a larger electron transfer rate. The photocatalytic activity of hm-CN/BOB increases significantly as indicated by a CO yield that is about four times higher than that of individual components. Density-functional theory calculations verify that the heterojunction improves electron transport and decreases the reaction energy barrier, thus promoting the overall photocatalytic CO2 conversion efficiency. The half-metal nitride coupled semiconductor heterojunctions might have large potential in artificial photosynthesis and related applications.