(Photo)Electrocatalytic CO2 Reduction at the Defective Anatase TiO2 (101) Surface

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.

Recent advances in metal halide perovskite based photocatalysts for artificial photosynthesis and organic transformations

Metal halide perovskites (MHP) emerged as highly promising materials for photocatalysis, offering significant advancements in the degradation of soluble and airborne pollutants, as well as the transformation of functional organic compounds. This comprehensive review focuses on recent developments in MHP-based photocatalysts, specifically examining two major categories: lead-based (such as CsPbBr3) and lead-free variants (e.g. Cs2AgBiX6, Cs3Bi2Br9 and others). While the review briefly discusses the contributions of MHPs to hydrogen (H2) production and carbon dioxide (CO2) reduction, the main emphasis is on the design principles that determine the effectiveness of perovskites in facilitating organic reactions and degrading hazardous chemicals through oxidative transformations. Furthermore, the review addresses the key factors that influence the catalytic efficiency of perovskites, including charge recombination, reaction mechanisms involving free radicals, hydroxyl ions, and other ions, as well as phase transformation and solvent compatibility. By offering a comprehensive overview, this review aims to serve as a guide for the design of MHP-based photocatalysis and shed light on the common challenges faced by the scientific community in the domain of organic transformations.

Electrocatalytic Reactions for Converting CO2 to Value-Added Products: Recent Progress and Emerging Trends

Carbon dioxide (CO₂) emissions are an important environmental issue that causes greenhouse and climate change effects on the earth. Nowadays, CO₂ has various conversion methods to be a potential carbon resource, such as photocatalytic, electrocatalytic, and photo-electrocatalytic. CO₂ conversion into value-added products has many advantages, including facile control of the reaction rate by adjusting the applied voltage and minimal environmental pollution. The development of efficient electrocatalysts and improving their viability with appropriate reactor designs is essential for the commercialization of this environmentally friendly method. In addition, microbial electrosynthesis which utilizes an electroactive bio-film electrode as a catalyst can be considered as another option to reduce CO₂. This review highlights the methods which can contribute to the increase in efficiency of carbon dioxide reduction (CO₂R) processes through electrode structure with the introduction of various electrolytes such as ionic liquid, sulfate, and bicarbonate electrolytes, with the control of pH and with the control of the operating pressure and temperature of the electrolyzer. It also presents the research status, a fundamental understanding of carbon dioxide reduction reaction (CO₂RR) mechanisms, the development of electrochemical CO₂R technologies, and challenges and opportunities for future research.

Ga and Zn increase the oxygen affinity of Cu-based catalysts for the CO x hydrogenation according to ab initio atomistic thermodynamics

The direct hydrogenation of CO or CO₂ to methanol, a highly vivid research area in the context of sustainable development, is typically carried out with Cu-based catalysts. Specific elements (so-called promoters) improve the catalytic performance of these systems under a broad range of reaction conditions (from pure CO to pure CO₂). Some of these promoters, such as Ga and Zn, can alloy with Cu and their role remains a matter of debate. In that context, we used periodic DFT calculations on slab models and ab initio thermodynamics to evaluate both metal alloying and surface formation by considering multiple surface facets, different promoter concentrations and spatial distributions as well as adsorption of several species (O*, H*, CO* and ) for different gas phase compositions. Both Ga and Zn form an fcc-alloy with Cu due to the stronger interaction of the promoters with Cu than with themselves. While the Cu-Ga-alloy is more stable than the Cu-Zn-alloy at low promoter concentrations (<25%), further increasing the promoter concentration reverses this trend, due to the unfavoured Ga-Ga-interactions. Under CO₂ hydrogenation conditions, a substantial amount of O* can adsorb onto the alloy surfaces, resulting in partial dealloying and oxidation of the promoters. Therefore, the CO₂ hydrogenation conditions are actually rather oxidising for both Ga and Zn despite the large amount of H₂ present in the feedstock. Thus, the growth of a GaO _x /ZnO _x overlayer is thermodynamically preferred under reaction conditions, enhancing CO₂ adsorption, and this effect is more pronounced for the Cu-Ga-system than for the Cu-Zn-system. In contrast, under CO hydrogenation conditions, fully reduced and alloyed surfaces partially covered with H* and CO* are expected, with mixed CO/CO₂ hydrogenation conditions resulting in a mixture of reduced and oxidised states. This shows that the active atmosphere tunes the preferred state of the catalyst, influencing the catalytic activity and stability, indicating that the still widespread image of a static catalyst under reaction conditions is insufficient to understand the complex interplay of processes taking place on a catalyst surface under reaction conditions, and that dynamic effects must be considered.

A Critical Review on Black Phosphorus-Based Photocatalytic CO2 Reduction Application

Energy shortages and greenhouse effects are two unavoidable problems that need to be solved. Photocatalytically converting CO₂ into a series of valuable chemicals is considered to be an effective means of solving the above dilemmas. Among these photocatalysts, the utilization of black phosphorus for CO₂ photocatalytic reduction deserves a lightspot not only for its excellent catalytic activity through different reaction routes, but also on account of the great preponderance of this relatively cheap catalyst. Herein, this review offers a summary of the recent advances in synthesis, structure, properties, and application for CO₂ photocatalytic reduction. In detail, the review starts from the basic principle of CO₂ photocatalytic reduction. In the following section, the synthesis, structure, and properties, as well as CO₂ photocatalytic reduction process of black phosphorus-based photocatalyst are discussed. In addition, some possible influencing factors and reaction mechanism are also summarized. Finally, a summary and the possible future perspectives of black phosphorus-based photocatalyst for CO₂ reduction are established.

Synthesis of TiO2/RGO with plasmonic Ag nanoparticles for highly efficient photoelectrocatalytic reduction of CO2 to methanol toward the removal of an organic pollutant from the atmosphere

The synergistic photoelectrochemical (PEC) technology is a robust process for the conversion of CO₂ into fuels. However, designing a highly efficient UV-visible driven photoelectrocatalyst is still challenging. Herein, a plasmonic Ag NPs modified TiO₂/RGO photoelectrocatalyst (Ag-TiO₂/RGO) has been designed for the PEC CO₂ reduction into selective production of CH₃OH. HR-TEM analysis revealed that Ag and TiO₂ NPs with average sizes of 4 and 7 nm, respectively, were densely grown on the few-micron-sized 2D RGO nanosheets. The physicochemical analysis was used to determine the optical and textural properties of the Ag-TiO₂/RGO nanohybrids. Under VU-Vis light illumination, Ag-TiO₂/RGO photocathode possessed a current density of 23.5 mA cm^-2 and a lower electrode resistance value of 125 Ω in CO₂-saturated 1.0 M KOH-aqueous electrolyte solution. Catalytic studies showed that the Ag-TiO₂/RGO photocathode possessed a remarkable PEC CO₂ reduction activity and selective production of CH₃OH with a yield of 85 μmol L^-1 cm^-2, the quantum efficiency of 20% and Faradic efficiency of 60.5% at onset potential of -0.7 V. A plausible PEC CO₂ reduction mechanism over Ag-TiO₂/RGO photocathode is schematically demonstrated. The present work gives a new avenue to develop high-performance and stable photoelectrocatalyst for PEC CO₂ reduction towards sustainable liquid fuels production.

Fabrication of S-scheme CdS-g-C3N4-graphene aerogel heterojunction for enhanced visible light driven photocatalysis

Constructing S-scheme heterojunction photocatalysts reveals a greatly improved separation efficiency of photogenerated carriers and enhanced harvesting ability of solar energy in photocatalytic field. Herein, a ternary CdS-g-C₃N₄-GA heterojunction has been fabricated by a facile ultrasound strategy, which behaved as a S-scheme heterojunction with an intimate interface formed, and GA played as an electronic transportation platform to promote the separation of photo-induced charge carriers, which was certified through photoelectrochemical techniques. Density functional theory calculations revealed that the different component in ternary CdS-g-C₃N₄-GA heterojunction demonstrated an obvious difference of work function, resulting in the charge transfer from CdS to g-C₃N₄ through GA with S-scheme principle. In the optimized conditions, the S-scheme CdS-g-C₃N₄-GA heterojunction not only displayed greatly enhanced photocatalytic performances for degradation of dye and antibiotic wastewater, but also improved photocatalytic H₂ production activity. In addition, the photocatalytic mechanism and driving force of charge transfer and separation in S-scheme CdS-g-C₃N₄-GA heterojunction were studied. This study offers a feasible strategy to construct a ternary S-scheme heterojunction for environmental and energy photocatalysis.

Surface defects induced charge imbalance for boosting charge separation and solar-driven photocatalytic hydrogen evolution

Low charge separation efficiency of semiconductor materials is the main obstacle for high-performance photocatalyst. Herein, we report surface defects engineered uniform mesoporous TiO₂ nanospheres (DMTNSs) through surfactant-mediated self-assembly solvothermal approach combined with hydrogenation strategy to promote charge separation. The surface defects induced charge imbalance result in the formation of built-in field, which can promote photogenerated charge separation efficiently and be confirmed by experimental and density functional theory (DFT) calculations. Under AM 1.5G irradiation, the photocatalytic hydrogen evolution of DMTNSs is ~3.34 mmol h^-1 g^-1, almost 3.5 times higher than that of pristine non-defective TiO₂ nanospheres (0.97 mmol h^-1 g^-1), due to the engineered surface defects narrowing the bandgap (~3.01 eV) and inducing charge imbalance to boost spatial charge separation and extend visible-light response. The defect induced charge imbalance strategy opens a new valuable perspective for fabricating other high-efficient oxide photocatalysts.

Porous Copper/Zinc Bimetallic Oxides Derived from MOFs for Efficient Photocatalytic Reduction of CO2 to Methanol

A novel metal organic framework (MOF)-derived porous copper/zinc bimetallic oxide catalyst was developed for the photoreduction of CO2 to methanol at a very fast rate of 3.71 mmol gcat−1 h−1. This kind of photocatalyst with high activity, selectivity and a simple preparation catalyst provides promising photocatalyst candidates for reducing CO2 to methanol.

Size-dependent interaction of plasma with anatase TiO2 nanoparticles

We study the particle size distribution and phase changes of the anatase TiO2 nanopowder samples when they are subject to the plasma treatments of three different kinds of gases as nitrogen (N2), oxygen (O2), and argon (Ar). The plasma gas pressures vary as 0.1, 0.3, and 0.6 Torr. We demonstrate that the plasma treatments have an effect neither on the phase structure nor on the mean nanocrystalline size. The phase and size invariances of the samples are attributed to their nanoscale thermodynamic aspects. We find out that elevating the gas pressure in some cases creates fine-size amorphous nanoparticles with a narrow distribution. Our findings authenticate that plasma treatment affects the amorphous phase with etching particles down to a mean value of ∼3 nm. The small-angle X-ray scattering (SAXS) technique was utilized to obtain the size distribution of the nanoparticles, and the wide-angle X-ray scattering (WAXS) technique was used to probe the phase and size changes of the crystalline structure.