Fundamentals and applications of photocatalytic CO2 methanation

Rapid construction of nickel phyllosilicate with ultrathin layers and high performance for CO2 methanation

The traditional techniques for the synthesis of nickel phyllosilicates usually time-consuming and energy-intensive, which often lead to the formation of layers with excessive thickness due to uncontrolled crystal growth. In order to overcome these challenges, this work introduces a microwave-assisted synthesis strategy to facilitate the synthesis of Ni-phyllosilicate-based catalysts within an exceptionally short duration of only five minutes, attaining a peak temperature of merely 102 °C. To enhance the specific surface area and to increase the exposure of active sites, an investigation was conducted involving three surfactants. The employment of hexadecyl trimethyl ammonium bromide (CTAB) has yielded remarkable results, with an ultrahigh specific surface area reaching 535 m2 g-1 and an ultrathin lamellar thickness of 1.43 nm. The catalyst exhibited an impressive CO2 conversion of 81.7 % at 400 °C, 60 L g-1 h-1, 0.1 MPa. It also demonstrated a substantial turnover frequency for CO2 (TOFCO2) of 5.4 ± 0.1 × 10-2 s-1, alongside a relatively low activation energy (Ea) of 80.74 kJ·mol-1. Moreover, the catalyst maintained its high stability over a period of 100 h and displayed high resistance to sintering. To further elucidate growth temperature gradient of the catalyst and concentration gradient of the materials involved, COMSOL Multiphysics (COMSOL) simulations were effectively utilized. In conclusion, this work breaks the limitation associated with traditional, laborious synthesis methods for Ni-phyllosilicates, which can produce materials with high surface area and thin-layer characteristics.

Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Efficient integration of covalent triazine frameworks (CTFs) for augmented photocatalytic efficacy: A review of synthesis, strategies, and applications

Heterogeneous photocatalysis emerges as an exceptionally appealing technological avenue for the direct capture, conversion, and storage of renewable solar energy, facilitating the generation of sustainable and ecologically benign solar fuels and a spectrum of other pertinent applications. Heterogeneous nanocomposites, incorporating Covalent Triazine Frameworks (CTFs), exhibit a wide-ranging spectrum of light absorption, well-suited electronic band structures, rapid charge carrier mobility, ample resource availability, commendable chemical robustness, and straightforward synthetic routes. These attributes collectively position them as highly promising photocatalysts with applicability in diverse fields, including but not limited to the production of photocatalytic solar fuels and the decomposition of environmental contaminants. As the field of photocatalysis through the hybridization of CTFs undergoes rapid expansion, there is a pressing and substantive need for a systematic retrospective analysis and forward-looking evaluation to elucidate pathways for enhancing performance. This comprehensive review commences by directing attention to diverse synthetic methodologies for the creation of composite materials. And then it delves into a thorough exploration of strategies geared towards augmenting performance, encompassing the introduction of electron donor-acceptor (D-A) units, heteroatom doping, defect Engineering, architecture of Heterojunction and optimization of morphology. Following this, it systematically elucidates applications primarily centered around the efficient generation of photocatalytic hydrogen, reduction of carbon dioxide through photocatalysis, and the degradation of organic pollutants. Ultimately, the discourse turns towards unresolved challenges and the prospects for further advancement, offering valuable guidance for the potent harnessing of CTFs in high-efficiency photocatalytic processes.

High-Entropy Oxides: A New Frontier in Photocatalytic CO2 Hydrogenation

Herein, we investigate the potential of nanostructured high-entropy oxides (HEOs) for photocatalytic CO2 hydrogenation, a process with significant implications for environmental sustainability and energy production. Several cerium-oxide-based rare-earth HEOs with fluorite structures were prepared for UV-light driven photocatalytic CO2 hydrogenation toward valuable fuels and petrochemical precursors. The cationic composition profoundly influences the selectivity and activity of the HEOs, where the Ce0.2Zr0.2La0.2Nd0.2Sm0.2O2-δ catalyst showed outstanding CO2 activation (14.4 molCO kgcat-1 h-1 and 1.27 mol CH 3 OH kgcat-1 h-1) and high methanol and CO selectivity (7.84% CH3OH and 89.26% CO) under ambient conditions with 4 times better performance in comparison to pristine CeO2. Systematic tests showed the effect of a high-entropy system compared to midentropy oxides. XPS, in situ DRIFTS, as well as DFT calculation elucidate the synergistic impact of Ce, Zr, La, Nd, and Sm, resulting in an optimal Ce3+/Ce4+ ratio. The observed formate-routed mechanism and a surface with high affinity to CO2 reduction offer insights into the photocatalytic enhancement. While our findings lay a solid foundation, further research is needed to optimize these catalysts and expand their applications.

Noble-Metal-Free High-Entropy Alloy Nanoparticles for Efficient Solar-Driven Photocatalytic CO2 Reduction

Metal nanoparticle (NP) cocatalysts are widely investigated for their ability to enhance the performance of photocatalytic materials; however, their practical application is often limited by the inherent instability under light irradiation. This challenge has catalyzed interest in exploring high-entropy alloys (HEAs), which, with their increased entropy and lower Gibbs free energy, provide superior stability. In this study, 3.5 nm-sized noble-metal-free NPs composed of a FeCoNiCuMn HEA are successfully synthesized. With theoretic calculation and experiments, the electronic structure of HEA in augmenting the catalytic CO2 reduction has been uncovered, including the individual roles of each element and the collective synergistic effects. Then, their photocatalytic CO2 reduction capabilities are investigated when immobilized on TiO2. HEA NPs significantly enhance the CO2 photoreduction, achieving a 23-fold increase over pristine TiO2, with CO and CH4 production rates of 235.2 and 19.9 µmol g-1 h-1, respectively. Meanwhile, HEA NPs show excellent stability under simulated solar irradiation, as well high-energy X-ray irradiation. This research emphasizes the promising role of HEA NPs, composed of earth-abundant elements, in revolutionizing the field of photocatalysis.

A Solar to Chemical Strategy: Green Hydrogen as a Means, Not an End

Green hydrogen is the key to the chemical industry achieving net zero emissions. The chemical industry is responsible for almost 2% of all CO2 emissions, with half of it coming from the production of simple commodity chemicals, such as NH3, H2O2, methanol, and aniline. Despite electrolysis driven by renewable power sources emerging as the most promising way to supply all the green hydrogen required in the production chain of these chemicals, in this review, it is worth noting that the photocatalytic route may be underestimated and can hold a bright future for this topic. In fact, the production of H2 by photocatalysis still faces important challenges in terms of activity, engineering, and economic feasibility. However, photocatalytic systems can be tailored to directly convert sunlight and water (or other renewable proton sources) directly into chemicals, enabling a solar-to-chemical strategy. Here, a series of recent examples are presented, demonstrating that photocatalysis can be successfully employed to produce the most important commodity chemicals, especially on NH3, H2O2, and chemicals produced by reduction reactions. The replacement of fossil-derived H2 in the synthesis of these chemicals can be disruptive, essentially safeguarding the transition of the chemical industry to a low-carbon economy.

Concentrated solar CO2 reduction in H2O vapour with >1% energy conversion efficiency

H2O dissociation plays a crucial role in solar-driven catalytic CO2 methanation, demanding high temperature even for solar-to-chemical conversion efficiencies <1% with modest product selectivity. Herein, we report an oxygen-vacancy (Vo) rich CeO2 catalyst with single-atom Ni anchored around its surface Vo sites by replacing Ce atoms to promote H2O dissociation and achieve effective photothermal CO2 reduction under concentrated light irradiation. The high photon flux reduces the apparent activation energy for CH4 production and prevents Vo from depletion. The defects coordinated with single-atom Ni, significantly promote the capture of charges and local phonons at the Ni d-impurity orbitals, thereby inducing more effective H2O activation. The catalyst presents a CH4 yield of 192.75 µmol/cm2/h, with a solar-to-chemical efficiency of 1.14% and a selectivity ~100%. The mechanistic insights uncovered in this study should help further the development of H2O-activating catalysts for CO2 reduction and thereby expedite the practical utilization of solar-to-chemical technologies.

Surface CN bonds mediate photocatalytic CO2 reduction into efficient CH4 production in TiO2-decorated g-C3N4 nanosheets

Graphitic carbon nitride (g-C3N4, CN) has garnered considerable attention in the field of photocatalysis due to its favorable band gap and high specific surface area. However, its primary practical limitation lies in the strong radiative recombination of lone pair (LP) electronic states, leading to limited efficiency in separating photogenerated carriers and subsequently diminishing photocatalytic performance. In this study, we devised and synthesized a heterojunction photocatalytic system comprising TiO2 nanosheets supported on modified g-C3N4 (MCN), designated as MCN/TiO2. The presence of CN functional groups on the tri-s-triazine nitrogen captures photogenerated electrons by modifying LP electronic states, resulting in a reduction in the fluorescence emission intensity of g-C3N4. Simultaneously, it forms chemical bonds with the supported TiO2 nanosheets, creating an efficient electron transfer pathway for the accumulation of photogenerated electrons at the active Ti sites. Experimentally, the MCN/TiO2 photocatalytic system exhibited optimal performance in CO2 reduction. The CH4 production rate reached 26.59 μmol g-1 h-1, surpassing that of TiO2 and CN/TiO2 by approximately 8 and 3 times, respectively. Furthermore, this photocatalytic system demonstrated exceptional photostability over five cycles, each lasting 4 h. This research offers a valuable approach for the efficient separation and transfer of photogenerated carriers in composite materials based on g-C3N4.

Local Ordering, Distortion, and Redox Activity in (La0.75Sr0.25)(Mn0.25Fe0.25Co0.25Al0.25)O3 Investigated by a Computational Workflow for Compositionally Complex Perovskite Oxides

Mixing multiple cations can result in a significant configurational entropy, offer a new compositional space with vast tunability, and introduce new computational challenges. For applications such as the two-step solar thermochemical hydrogen (STCH) generation techniques, we demonstrate that using density functional theory (DFT) combined with Metropolis Monte Carlo method (DFT-MC) can efficiently sample the possible cation configurations in compositionally complex perovskite oxide (CCPO) materials, with (La0.75Sr0.25)(Mn0.25Fe0.25Co0.25Al0.25)O3 as an example. In the presence of oxygen vacancies (VO), DFT-MC simulations reveal a significant increase of the local site preference of the cations (short-range ordering), compared to a more random mixing without VO. Co is found to be the redox-active element and the VO is the preferentially generated next to Co due to the stretched Co-O bonds. A clear definition of the vacancy formation energy (Evf) is proposed for CCPO in an ensemble of structures evolved in parallel from independent DFT-MC paths. By combining the distribution of Evf with VO interactions into a statistical model, the oxygen nonstoichiometry (δ), under the STCH thermal reduction and oxidation conditions, is predicted and compared with the experiments. Similar to the experiments, the predicted δ can be used to extract the enthalpy and entropy of reduction using the van't Hoff method, providing direct comparisons with the experimental results. This procedure provides a full predictive workflow for using DFT-MC to obtain possible local ordering or fully random structures, understand the redox activity of each element, and predict the thermodynamic properties of CCPOs, for computational screening and design of these CCPO materials at STCH conditions.

Ni-Based Catalysts for CO2 Methanation: Exploring the Support Role in Structure-Activity Relationships

The catalytic hydrogenation of CO2 to methane is one of the highly researched areas for the production of chemical fuels. The activity of catalyst is largely affected by support type and metal-support interaction deriving from the special method during catalyst preparation. Hence, we employed a simple solvothermal technique to synthesize Ni-based catalysts with different supports and studied the support role (CeO2, Al2O3, ZrO2, and La2O3) on structure-activity relationships in CO2 methanation. It is found that catalyst morphology can be altered by only changing the support precursors during synthesis, and therefore their catalytic behaviours were significantly affected. The Ni/Al2O3 with a core-shell morphology prepared herein exhibited a higher activity than the catalyst prepared with a common wet impregnation method. To have a comprehensive understanding for structure-activity relationships, advanced characterization (e. g., synchrotron radiation-based XAS and photoionization mass spectrometry) and in-situ diffuse reflectance infrared Fourier transform spectroscopy experiments were conducted. This research opens an avenue to further delve into the role of support on morphologies that can greatly enhance catalytic activity during CO2 methanation.

Structural Heredity in Catalysis: CO2 Self-Selective CeO2 Nanocrystals for Efficient Photothermal CO2 Hydrogenation to Methane

The chemical inertness of CO2 molecules makes their adsorption and activation on a catalyst surface one of the key challenges in recycling CO2 into chemical fuels. However, the traditional template synthesis and chemical modification strategies used to tackle this problem face severe structural collapse and modifier deactivation issues during the often-needed post-processing procedure. Herein, a CO2 self-selective hydrothermal growth strategy is proposed for the synthesis of CeO2 octahedral nanocrystals that participate in strong physicochemical interactions with CO2 molecules. The intense affinity for CO2 molecules persists during successive high-temperature treatments required for Ni deposition. This demonstrates the excellent structural heredity of the CO2 self-selective CeO2 nanocrystals, which leads to an outstanding photothermal CH4 productivity exceeding 9 mmol h-1 mcat -2 and an impressive selectivity of >99%. The excellent performance is correlated with the abundant oxygen vacancies and hydroxyl species on the CeO2 surface, which create many frustrated Lewis-pair active sites, and the strong interaction between Ni and CeO2 that promotes the dissociation of H2 molecules and the spillover of H atoms, thereby greatly benefitting the photothermal CO2 methanation reaction. This self-selective hydrothermal growth strategy represents a new pathway for the development of effective catalysts for targeted chemical reactions.

Non-Photochemical Origin of Selectivity Difference between Light and Dark Catalytic Conditions

The interest in introducing light into heterogeneous catalysis is driven not only by the urgent need of replacing fossil energy but also by the promise of controlling product selectivity by light. The product selectivity differences observed in recent studies between light and dark reactions are often attributed to photochemical effects. Here, we report the discovery of a non-photochemical origin of selectivity difference, at essentially the same CO2 conversion rate, between photothermal and thermal CO2 hydrogenation reactions over a Ru/TiO2-x catalyst. While the presence of the photochemical effect from ultraviolet light is confirmed, it merely enhances the catalytic activity. Systematic investigation reveals that the gradual formation of an adsorbate-mediated strong metal-support interaction under catalytic conditions is responsible for the variation in the catalytic selectivity. We demonstrate that differences in product selectivity under light/dark reactions do not necessarily originate from photochemical effects. Our study refines the basis for determining photochemical effects and highlights the importance of excluding non-photochemical effects in mechanistic studies of light-controlled product selectivity.

Unveiling Advancements: Trends and Hotspots of Metal-Organic Frameworks in Photocatalytic CO2 Reduction

Metal-organic frameworks (MOFs) are robust, crystalline, and porous materials featured by their superior CO2 adsorption capacity, tunable energy band structure, and enhanced photovoltaic conversion efficiency, making them highly promising for photocatalytic CO2 reduction reaction (PCO2RR). This study presents a comprehensive examination of the advancements in MOFs-based PCO2RR field spanning the period from 2011 to 2023. Employing bibliometric analysis, the paper scrutinizes the widely adopted terminology and citation patterns, elucidating trends in publication, leading research entities, and the thematic evolution within the field. The findings highlight a period of rapid expansion and increasing interdisciplinary integration, with extensive international and institutional collaboration. A notable emphasis on significant research clusters and key terminologies identified through co-occurrence network analysis, highlighting predominant research on MOFs such as UiO, MIL, ZIF, porphyrin-based MOFs, their composites, and the hybridization with photosensitizers and molecular catalysts. Furthermore, prospective design approaches for catalysts are explored, encompassing single-atom catalysts (SACs), interfacial interaction enhancement, novel MOF constructions, biocatalysis, etc. It also delves into potential avenues for scaling these materials from the laboratory to industrial applications, underlining the primary technical challenges that need to be overcome to facilitate the broader application and development of MOFs-based PCO2RR technologies.

High-Volumetric Density Atomic Cobalt on Multishell ZnxCd1-xS Boosts Photocatalytic CO2 Reduction

The volumetric density of the metal atomic site is decisive to the operating efficiency of the photosynthetic nanoreactor, yet its rational design and synthesis remain a grand challenge. Herein, we report a shell-regulating approach to enhance the volumetric density of Co atomic sites onto/into multishell ZnxCd1-xS for greatly improving CO2 photoreduction activity. We first establish a quantitative relation between the number of shell layers, specific surface areas, and volumetric density of atomic sites on multishell ZnxCd1-xS and conclude a positive relation between photosynthetic performance and the number of shell layers. The triple-shell ZnxCd1-xS-Co1 achieves the highest CO yield rate of 7629.7 μmol g-1 h-1, superior to those of the double-shell ZnxCd1-xS-Co1 (5882.2 μmol g-1 h-1) and single-shell ZnxCd1-xS-Co1 (4724.2 μmol g-1 h-1). Density functional theory calculations suggest that high-density Co atomic sites can promote the mobility of photogenerated electrons and enhance the adsorption of Co(bpy)32+ to increase CO2 activation (CO2 → CO2* → COOH* → CO* → CO) via the S-Co-bpy interaction, thereby enhancing the efficiency of photocatalytic CO2 reduction.

CO2 Enrichment Boosts Highly Selective Infrared-Light-Driven CO2 Conversion to CH4 by UiO-66/Co9S8 Photocatalyst

Photocatalytic CO2 reduction to high-value chemicals is an attractive approach to mitigate climate change, but it remains a great challenge to produce a specific product selectively by IR light. Hence, UiO-66/Co9S8 composite is designed to couple the advantages of metallic photocatalysts and porous CO2 adsorbers for IR-light-driven CO2-to-CH4 conversion. The metallic nature of Co9S8 endows UiO-66/Co9S8 with exceptional IR light absorption, while UiO-66 dramatically enhances its local CO2 concentration, revealed by finite-element method simulations. As a result, Co9S8 or UiO-66 alone does not show observable IR-light photocatalytic activity, whereas UiO-66/Co9S8 exhibits exceptional activity. The CH4 evolution rate over UiO-66/Co9S8 reaches 25.7 µmol g-1 h-1 with ca.100% selectivity under IR light irradiation, outperforming most reported catalysts under similar reaction conditions. The X-ray absorption fine structure spectroscopy spectra verify the presence of two distinct Co sites and confirm the existence of metallic Co─Co bond in Co9S8. Energy diagrams analysis and transient absorption spectra manifest that CO2 reduction mainly occurs on Co9S8 for UiO-66/Co9S8, while density functional theory calculations demonstrate that high-electron-density Co1 sites are the key active sites, possessing lower energy barriers for further protonation of *CO, leading to the ultra-high selectivity toward CH4.

Mechanism of photocatalytic CO2 methanation on ultrafine Rh nanoparticles

Selective hydrogenation of CO2 to yield CH4 relies on the appropriate catalysts that can facilitate the cleavage of CO bonds and dissociative adsorption of H2. Ultrafine Rh nanoparticles loaded on silica nanospheres were used as a class of photocatalysts to significantly improve the selectivity and reaction rate of producing CH4 from the mixture of CO2 and H2 under the illumination of a broadband visible light source. The intense light scattering resonances in the silica nanospheres generate strong electric fields near the silica surface to enhance the light absorption power in the supported ultrafine Rh nanoparticles, promoting the efficiency of hot electron generation in the Rh nanoparticles. The interaction of the hot electrons with the adsorbate species on the Rh nanoparticle surface weakens the C-O bond to facilitate the deoxygenation of CO2, favoring the production of CH4 with a unity selectivity at a faster rate in the presence of surface adsorbed hydrogen (H*). The systematic studies on reaction kinetics and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy under different conditions, including various temperatures, illumination powers, and feeding gas compositions, reveal the reaction mechanism responsible for CO2 methanation and the role of photoillumination.

Solar-Driven Continuous CO2 Reduction to CO and CH4 using Heterogeneous Photothermal Catalysts: Recent Progress and Remaining Challenges

The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.

Hydrogen Activation with Ru-PN3P Pincer Complexes for the Conversion of C1 Feedstocks

The hydrogenation of C1 feedstocks (CO and CO2) has been investigated using ruthenium complexes [RuHCl(CO)(PN3P)] as the catalyst. PN3P pincer ligands containing amines in the linker between the central pyridine donor and the phosphorus donors with bulky substituents (tert-butyl (1) or TMPhos (2)) are required to obtain mononuclear single-site catalysts that can be activated by the addition of KOtBu to generate stable five-coordinate complexes [RuH(CO)(PN3P-H)], whereby the pincer ligand has been deprotonated. Activation of hydrogen takes place via heterolytic cleavage to generate [RuH2(CO)(PN3P)], but in the presence of CO, coordination of CO occurs preferentially to give [RuH(CO)2(PN3P-H)]. This complex can be protonated to give the cationic complex [RuH(CO)2(PN3P)]+, but it is unable to activate H2 heterolytically. In the case of the less coordinating CO2, both ruthenium complexes 1 and 2 are highly efficient as CO2 hydrogenation catalysts in the presence of a base (DBU), which in the case of the TMPhos ligand results in a TON of 30,000 for the formation of formate.

Spin Polarization: A New Frontier in Efficient Photocatalysis for Environmental Purification and Energy Conversion

As a promising strategy to improve photocatalytic efficiency, spin polarization has attracted enormous attention in recent years, which could be involved in various steps of photoreaction. The Pauli repulsion principle and the spin selection rule dictate that the behavior of two electrons in a spatial eigenstate is based on their spin states, and this fact opens up a new avenue for manipulating photocatalytic efficiency. In this review, recent advances in modulating the photocatalytic activity with spin polarization are systematically summarized. Fundamental insights into the influence of spin-polarization effects on photon absorption, carrier separation, and migration, and the behaviors of reaction-related substances from the photon uptake to reactant desorption are highlighted and discussed in detail, and various photocatalytic applications for environmental purification and energy conversion are presented. This review is expected to deliver a timely overview of the recent developments in spin-polarization-modulated photocatalysis for environmental purification and energy conversion in terms of their practical applications.

Accelerating Charge Separation and CO2 Photoreduction in Aqueous Phase under Visible Light with Ru Nanoparticles Loaded on Ga-Doped NiTiO3 in a Batch Photoreactor

Titanate perovskite (ATiO3) semiconductors show prospects of being active photocatalysts in the conversion of CO2 to chemical fuels such as methanol (CH3OH) in the aqueous phase. Some of the challenges in using ATiO3 are limited light-harvesting capability, rapid bulk charge recombination, and the low density of catalytic sites participating in CO2 reduction. To address these challenges, Ga-doped NiTiO3 (GNTO) photocatalysts in which Ga ions substitute for Ti ions in the crystal lattice to form electron trap states and oxygen vacancies have been synthesized in this work. The synthesized GNTO was then loaded with Ru nanoparticles to accelerate charge separation and enable excellent CO2 photoreduction activity under visible light. CO2 photoreduction was conducted in a batch photoreactor charged with a 0.1 M NaHCO3 aqueous solution at room temperature and a 3.5 bar pressure using a 1.0 wt % Ru-GNTO photocatalyst to yield methanol at a rate of 84.45 μmol g-1 h-1. A small amount of methane was produced as a side product at 21.35 μmol g-1 h-1, which is also a fuel molecule. We attribute this high catalytic activity toward CO2 photoreduction to a synergistic combination of our novel heterostructured 1.0 wt % Ru-GNTO photocatalyst and the implementation of a pressurized photoreactor. This work demonstrates an effective strategy for metal doping with active nanospecies functionality to improve the performance of ATiO3 photocatalysts in valorizing CO2 to solar fuels.

Facile fabrication of Ni, Fe-doped δ-MnO2 derived from Prussian blue analogues as an efficient catalyst for stable Li-CO2 batteries

Rechargeable Li-CO2 batteries are regarded as an ideal new-generation energy storage system, owing to their high energy density and extraordinary CO2 capture capability. Developing a suitable cathode to improve the electrochemical performance of Li-CO2 batteries has always been a research hotspot. Herein, Ni-Fe-δ-MnO2 nano-flower composites are designed and synthesized by in situ etching a Ni-Fe PBA precursor as the cathode for Li-CO2 batteries. Ni-Fe-δ-MnO2 nanoflowers composed of ultra-thin nanosheets possess considerable surface spaces, which can not only provide abundant catalytic active sites, but also facilitate the nucleation of discharge products and promote the CO2 reduction reaction. On the one hand, the introduction of Ni and Fe elements can improve the electrical conductivity of δ-MnO2. On the other hand, the synergistic catalytic effect between Ni, Fe elements and δ-MnO2 will greatly enhance the cycling performance and reduce the overpotential of Li-CO2 batteries. Consequently, the Li-CO2 battery based on the Ni-Fe-δ-MnO2 cathode shows a high discharge capacity of 8287 mA h g-1 and can stabilize over 100 cycles at a current density of 100 mA g-1. The work offers a promising guideline to design efficient manganese-based catalysts for Li-CO2 batteries.

Sustainable all-weather CO2 utilization by mimicking natural photosynthesis in a single material

Solar-driven CO2 conversion into hydrocarbon fuels is a sustainable approach to synchronously alleviating the energy crisis and achieving net CO2 emissions. However, the dependence of the conversion process on solar illumination hinders its practical application due to the intermittent availability of sunlight at night and on cloudy or rainy days. Here, we report a model material of Pt-loaded hexagonal tungsten trioxide (Pt/h-WO3) for decoupling light and dark reaction processes, demonstrating the sustainable CO2 conversion under dark conditions for the first time. In such a material system, hydrogen atoms can be produced by photocatalytic water splitting under solar illumination, stored together with electrons in the h-WO3 through the transition of W6+ to W5+ and spontaneously released to trigger catalytic CO2 reduction under dark conditions. Furthermore, we demonstrate using natural light that CH4 production can persist at night and on rainy days, proving the accomplishment of all-weather CO2 conversion via a sustainable way.

Minimizing CO2 emissions by photocatalytic CO2 reduction to CH3OH over Li2MnO3/WO3 heterostructures under visible illumination

Photocatalytic CO2 reduction to valuable fuels has proved to be a favourable process to produce renewable energy and reduce CO2 emissions, which mostly depends on designing effective photocatalysts with the rapid separation rate of charge carriers. In this contribution, mesoporous n-n heterojunction Li2MnO3/WO3 nanocomposites were designed via a simplistic sol-gel process for CO2 reduction utilizing visible illumination (λ > 420 nm). XRD and TEM measurements confirmed the synthesized Li2MnO3/WO3 nanocomposite is a monoclinic structure, and its particle size is 25 ± 5 nm. The obtained Li2MnO3/WO3 exhibited narrower bandgap energy (1.74 eV), larger surface area (212 m2g-1), exceedingly visible absorbing, and lower recombination of electron and hole. The yield of CH3OH was determined about 198, 871, 1140, 1550 and 1570 mmolg-1 for bare WO3 and 5%, 10%, 15% and 20% Li2MnO3/WO3 nanocomposites, respectively. These results evidenced that the 15% Li2MnO3/WO3 photocatalyst exhibited the best reduction ability compared to other nanocomposites. The CO2 reduction over 15% Li2MnO3/WO3 photocatalyst achieved a maximal CO2 conversion with the substantially boosted CH3OH, i.e., 1550 mmolg-1 after 9 h, which was enhanced 7.8 folds great than of WO3 NPs. Mesoporous Li2MnO3/WO3 nanocomposites, in comparison with bare WO3 NPs, created more active sites for facilitating CO2 and had a specific electric field to more effectively separate charge carriers. The Li2MnO3/WO3 photocatalyst has superior photostability during the continuous reduction of CO2 for 45 h with no remarkable decrease. The possible direct S-scheme mechanism for electron transfer over Li2MnO3/WO3 photocatalyst with the enhanced CO2 reduction ability was discussed. The present work demonstrates an avenue for building highly effective heterostructure photocatalysts in solar-energy-induced potential applications.

Progress and Perspectives on Promising Covalent-Organic Frameworks (COFs) Materials for Energy Storage Capacity

In recent years, a new class of highly crystalline advanced permeable materials covalent-organic frameworks (COFs) have garnered a great deal of attention thanks to their remarkable properties, such as their large surface area, highly ordered pores and channels, and controllable crystalline structures. The lower physical stability and electrical conductivity, however, prevent them from being widely used in applications like photocatalytic activities and innovative energy storage and conversion devices. For this reason, many studies have focused on finding ways to improve upon these interesting materials while also minimizing their drawbacks. This review article begins with a brief introduction to the history and major milestones of COFs development before moving on to a comprehensive exploration of the various synthesis methods and recent successes and signposts of their potential applications in carbon dioxide (CO2 ) sequestration, supercapacitors (SCs), lithium-ion batteries (LIBs), and hydrogen production (H2 -energy). In conclusion, the difficulties and potential of future developing with highly efficient COFs ideas for photocatalytic as well as electrochemical energy storage applications are highlighted.

Metal-Free Photocatalytic CO2 Reduction to CH4 and H2 O2 under Non-sacrificial Ambient Conditions

Photocatalytic CO2 reduction to CH4 requires photosensitizers and sacrificial agents to provide sufficient electrons and protons through metal-based photocatalysts, and the separation of CH4 from by-product O2 has poor applications. Herein, we successfully synthesize a metal-free photocatalyst of a novel electron-acceptor 4,5,9,10-pyrenetetrone (PT), to our best knowledge, this is the first time that metal-free catalyst achieves non-sacrificial photocatalytic CO2 to CH4 and easily separable H2 O2 . This photocatalyst offers CH4 product of 10.6 μmol ⋅ g-1  ⋅ h-1 under non-sacrificial ambient conditions (room temperature, and only water), which is two orders of magnitude higher than that of the reported metal-free photocatalysts. Comprehensive in situ characterizations and calculations reveal a multi-step reaction mechanism, in which the long-lived oxygen-centered radical in the excited PT provides as a site for CO2 activation, resulting in a stabilized cyclic carbonate intermediate with a lower formation energy. This key intermediate is thermodynamically crucial for the subsequent reduction to CH4 product with the electronic selectivity of up to 90 %. The work provides fresh insights on the economic viability of photocatalytic CO2 reduction to easily separable CH4 in non-sacrificial and metal-free conditions.

Efficient Solar-Driven CO2 Methanation and Hydrogen Storage Over Nickel Catalyst Derived from Metal-Organic Frameworks with Rich Oxygen Vacancies

Solar-driven photothermal conversion of carbon dioxide (CO2 ) to methane (CH4 ) is a promising approach to remedy energy shortage and climate changes, where highly efficient photothermal catalysts for CO2 methanation urgently need to be designed. Herein, nickel-based catalysts (Ni/ZrO2 ) derived from metal-organic frameworks (MOFs) are fabricated and studied for photothermal CO2 methanation. The optimized catalyst 50Ni/ZrO2 achieves a stable CH4 production rate of 583.3 mmol g-1  h-1 in a continuous stability test, which is almost tenfold higher than that of 50Ni/C-ZrO2 synthesized via commercial ZrO2 . Physicochemical properties indicate that 50Ni/ZrO2 generates more tetragonal ZrO2 and possesses more oxygen vacancies (OVs) as well as enhanced nickel-ZrO2 interaction. As a result, 50Ni/ZrO2 exhibits the strong abilities of light absorption and light-to-heat conversion, superior adsorption capacities of reactants (H2 , CO2 ), and an intermediate product (CO), which finally boosts CH4 formation. This work provides an efficient strategy to design a photothermocatalyst of CO2 methanation through utilizing MOFs-derived support.

Unraveling Temperature-Dependent Plasma-Catalyzed CO2 Hydrogenation

Hydrogenation of carbon dioxide to value-added chemicals and fuels has recently gained increasing attention as a promising route for utilizing carbon dioxide to achieve a sustainable society. In this study, we investigated the hydrogenation of CO2 over M/SiO2 and M/Al2O3 (M = Co, Ni) catalysts in a dielectric barrier discharge system at different temperatures. We compared three different reaction modes: plasma alone, thermal catalysis, and plasma catalysis. The coupling of catalysts with plasma demonstrated synergy at different reaction temperatures, surpassing the thermal catalysis and plasma alone modes. The highest CO2 conversions under plasma-catalytic conditions at reaction temperatures of 350 and 500 °C were achieved with a Co/SiO2 catalyst (66%) and a Ni/Al2O3 catalyst (68%), respectively. Extensive characterizations were used to analyze the physiochemical characteristics of the catalysts. The results show that plasma power was more efficient than heating power at the same temperature for the CO2 hydrogenation. This demonstrates that the performance of CO2 hydrogenation can be significantly improved in the presence of plasma at lower temperatures.

WS2 supported PtOx clusters for efficient photocatalytic CO2 reduction: a DFT study

Platinum (Pt) nanoparticles/nanoclusters are some of the most efficient cocatalysts for photocatalytic CO2 reduction. Nevertheless, the produced CO can lead to a poisoning effect due to the strong adsorption strength of the Pt cocatalysts. Using density functional theory, PtOx clusters with variable sizes (Pt4O6, Pt5O8, Pt7O10, and Pt8O13) are selected to load on WS2 (PtOx-WS2) for photocatalytic CO2 conversion. The calculated results demonstrate that PtOx-WS2 are highly stable, and the electron-rich PtOx clusters are beneficial for the photocatalytic CO2 reduction. All the PtOx-WS2 catalysts exhibit efficient photocatalytic performance for CO2 reduction. Especially, Pt4O6-, Pt5O8-, and Pt8O13-WS2 have acceptable or ultra-low ΔGmax (ΔG for the rate-determining step) of 0.57, 0.23, and 0.48 eV to produce CH3OH, HCOOH, and CH4, respectively. The photocatalytic activities of PtOx-WS2 are correlated with the adsorption strength of the key intermediates, and the strong interactions between PtOx-WS2 and *COOH or *HCOO can lower the free energy changes for the first hydrogenation step. More importantly, PtOx-WS2 can also weaken the adsorption strength of *CO and *HCOOH, which are conducive to forming *CHO. This work gives an in-depth insight to design novel catalysts and promote their catalytic activity for photocatalytic CO2 reduction.

Advances in photothermal regulation strategies: from efficient solar heating to daytime passive cooling

Photothermal regulation concerning solar harvesting and repelling has recently attracted significant interest due to the fast-growing research focus in the areas of solar heating for evaporation, photocatalysis, motion, and electricity generation, as well as passive cooling for cooling textiles and smart buildings. The parallel development of photothermal regulation strategies through both material and system designs has further improved the overall solar utilization efficiency for heating/cooling. In this review, we will review the latest progress in photothermal regulation, including solar heating and passive cooling, and their manipulating strategies. The underlying mechanisms and criteria of highly efficient photothermal regulation in terms of optical absorption/reflection, thermal conversion, transfer, and emission properties corresponding to the extensive catalog of nanostructured materials are discussed. The rational material and structural designs with spectral selectivity for improving the photothermal regulation performance are then highlighted. We finally present the recent significant developments of applications of photothermal regulation in clean energy and environmental areas and give a brief perspective on the current challenges and future development of controlled solar energy utilization.

CO2 -Mediated Photocatalytic Chlorine Production Over Bismuth Oxychloride in Chloride Solution

As one of the most commonly bulky chemicals, chlorine is conventionally manufactured by electrolysis of NaCl solution in the chlor-alkali process, which requires a huge supply of electrical energy. The photocatalytic route to produce chlorine by using solar energy and NaCl solution offers a promising strategy to reduce energy consumption and bring economic benefits. Herein, it was found that the introduction of CO2 would enhance the productivity of Cl2 from 8.24 μmol⋅h-1 to 39.6 μmol⋅h-1 in NaCl solution over BiOCl. Experimental studies reveal that the CO2 species (CO3 2- ) entered into the crystal texture of BiOCl and the interlayer space between [Bi2 O2 ]2+ slabs were increased and distorted, accelerating the cycle of Cl species. Besides, the cycle of carbonate species also existed and accelerated the reaction efficiency of Cl- oxidation to Cl2 . This work provides a new feasible method of using abundant CO2 resources to accelerate the process of chlorine production via photocatalysis.

Solar Photocatalytic Activity of Ba-Doped ZnO Nanoparticles: The Role of Surface Hydrophilicity

Bare zinc oxide (ZnO) and Ba-doped ZnO (BZO) samples were prepared by using a simple precipitation method. The effects of Barium doping on the structural, morphological, and optoelectronic properties, as well as on the physico-chemical features of the surface were investigated and correlated with the observed photocatalytic activity under natural solar irradiation. The incorporation of Ba2+ ions into the ZnO structure increased the surface area by ca. 14 times and enhanced the hydrophilicity with respect to the bare sample, as demonstrated by infrared spectroscopy and contact angle measurements. The surface hydrophilicity was correlated with the enhanced defectivity of the doped sample, as indicated by X-ray diffraction, Raman, and fluorescence spectroscopies. The resulting higher affinity with water was, for the first time, invoked as an important factor justifying the superior photocatalytic performance of BZO compared to the undoped one, in addition to the slightly higher separation of the photoproduced pairs, an effect that has already been reported in literature. In particular, observed kinetic constants values of 8∙10-3 and 11.3∙10-3 min-1 were determined for the ZnO and BZO samples, respectively, by assuming first order kinetics. Importantly, Ba doping suppressed photocorrosion and increased the stability of the BZO sample under irradiation, making it a promising photocatalyst for the abatement of toxic species.

Achieving artificial carbon cycle via integrated system of high-emitting industries and CCU technology: Case of China

Process-related carbon emissions, which cannot be completely eliminated by the improvement of processes and energy structure, are recognized as an enormous challenge for in-depth decarbonization. To accelerate the achievement of carbon neutrality, the concept of 'artificial carbon cycle' is proposed based on the integrated system of process-related carbon emissions from high-emitting industries and CCU technology as a potential pathway towards a sustainable future. This paper conducts a systematic review on the integrated system with the case of China, which is the largest carbon-emitting and manufacturing country, to provide a clearer and more meaningful analysis. Multi-index assessment was used to organize the literature and draw the useful conclusion. Based on literature review, the high-quality carbon sources, reasonable carbon capture approaches and promising chemical products were identified and analyzed. Then the potential and practicability of the integrated system was further summarized and analyzed. Finally, key factors of future development including technology improvement, green hydrogen, clean energy and industrial cooperation were stressed to provide a theoretical reference for future researchers and policy makers.

Broadband and Spectrally Selective Photothermal Conversion through Nanocluster Assembly of Disordered Plasmonic Metasurfaces

Plasmonic metasurfaces have been realized for efficient light absorption, thereby leading to photothermal conversion through nonradiative decay of plasmonic modes. However, current plasmonic metasurfaces suffer from inaccessible spectral ranges, costly and time-consuming nanolithographic top-down techniques for fabrication, and difficulty of scale-up. Here, we demonstrate a new type of disordered metasurface created by densely packing plasmonic nanoclusters of ultrasmall size on a planar optical cavity. The system either operates as a broadband absorber or offers a reconfigurable absorption band right across the visible region, resulting in continuous wavelength-tunable photothermal conversion. We further present a method to measure the temperature of plasmonic metasurfaces via surface-enhanced Raman spectroscopy (SERS), by incorporating single-walled carbon nanotubes (SWCNTs) as an SERS probe within the metasurfaces. Our disordered plasmonic system, generated by a bottom-up process, offers excellent performance and compatibility with efficient photothermal conversion. Moreover, it also provides a novel platform for various hot-electron and energy-harvesting functionalities.

Photophysical Characterization of Ru Nanoclusters on Nanostructured TiO2 by Time-Resolved Photoluminescence Spectroscopy

Despite the promising performance of Ru nanoparticles or nanoclusters on nanostructured TiO₂ in photocatalytic and photothermal reactions, a mechanistic understanding of the photophysics is limited. The aim of this study is to uncover the nature of light-induced processes in Ru/TiO₂ and the role of UV versus visible excitation by time-resolved photoluminescence (PL) spectroscopy. The PL at a 267 nm excitation is predominantly due to TiO₂, with a minor contribution of the Ru nanoclusters. Relative to TiO₂, the PL of Ru/TiO₂ following a 267 nm excitation is significantly blue-shifted, and the bathochromic shift with time is smaller. We show by global analysis of the spectrotemporal PL behavior that for both TiO₂ and Ru/TiO₂ the bathochromic shift with time is likely caused by the diffusion of electrons from the TiO₂ bulk toward the surface. During this directional motion, electrons may recombine (non)radiatively with relatively immobile hole polarons, causing the PL spectrum to red-shift with time following excitation. The blue-shifted PL spectra and smaller bathochromic shift with time for Ru/TiO₂ relative to TiO₂ indicate surface PL quenching, likely due to charge transfer from the TiO₂ surface into the Ru nanoclusters. When deposited on SiO₂ and excited at 532 nm, Ru shows a strong emission. The PL of Ru when deposited on TiO₂ is completely quenched, demonstrating interfacial charge separation following photoexcitation of the Ru nanoclusters with a close to unity quantum yield. The nature of the charge-transfer phenomena is discussed, and the obtained insights indicate that Ru nanoclusters should be deposited on semiconducting supports to enable highly effective photo(thermal)catalysis.

Confining charge-transfer complex in a metal-organic framework for photocatalytic CO2 reduction in water

In the quest for renewable fuel production, the selective conversion of CO₂ to CH₄ under visible light in water is a leading-edge challenge considering the involvement of kinetically sluggish multiple elementary steps. Herein, 1-pyrenebutyric acid is post-synthetically grafted in a defect-engineered Zr-based metal organic framework by replacing exchangeable formate. Then, methyl viologen is incorporated in the confined space of post-modified MOF to achieve donor-acceptor complex, which acts as an antenna to harvest visible light, and regulates electron transfer to the catalytic center (Zr-oxo cluster) to enable visible-light-driven CO₂ reduction reaction. The proximal presence of the charge transfer complex enhances charge transfer kinetics as realized from transient absorption spectroscopy, and the facile electron transfer helps to produce CH₄ from CO₂. The reported material produces 7.3 mmol g^-1 of CH₄ under light irradiation in aqueous medium using sacrificial agents. Mechanistic information gleans from electron paramagnetic resonance, in situ diffuse reflectance FT-IR and density functional theory calculation.

Accessing parity-forbidden d-d transitions for photocatalytic CO2 reduction driven by infrared light

A general approach to promote IR light-driven CO2 reduction within ultrathin Cu-based hydrotalcite-like hydroxy salts is presented. Associated band structures and optical properties of the Cu-based materials are first predicted by theory. Subsequently, Cu4(SO4)(OH)6 nanosheets were synthesized and are found to undergo cascaded electron transfer processes based on d-d orbital transitions under infrared light irradiation. The obtained samples exhibit excellent activity for IR light-driven CO2 reduction, with a production rate of 21.95 and 4.11 μmol g-1 h-1 for CO and CH4, respectively, surpassing most reported catalysts under the same reaction conditions. X-ray absorption spectroscopy and in situ Fourier-transform infrared spectroscopy are used to track the evolution of the catalytic sites and intermediates to understand the photocatalytic mechanism. Similar ultrathin catalysts are also investigated to explore the generality of the proposed electron transfer approach. Our findings illustrate that abundant transition metal complexes hold great promise for IR light-responsive photocatalysis.

Advanced Catalyst for CO2 Photo-Reduction: From Controllable Product Selectivity by Architecture Engineering to Improving Charge Transfer Using Stabilized Au Clusters

Despite enormous progress and improvement in photocatalytic CO₂ reduction reaction (CO₂ RR), the development of photocatalysts that suppress H₂ evolution reaction (HER), during CO₂ RR, remains still a challenge. Here, new insight is presented for controllable CO₂ RR selectivity by tuning the architecture of the photocatalyst. Au/carbon nitride with planar structure (p Au/CN) showed high activity for HER with 87% selectivity. In contrast, the same composition with a yolk@shell structure (Y@S Au@CN) exhibited high selectivity of carbon products by suppressing the HER to 26% under visible light irradiation. Further improvement for CO₂ RR activity was achieved by a surface decoration of the yolk@shell structure with Au₂₅ (PET)₁₈ clusters as favorable electron acceptors, resulting in longer charge separation in Au@CN/Au_c Y@S structure. Finally, by covering the structure with graphene layers, the designed catalyst maintained high photostability during light illumination and showed high photocatalytic efficiency. The optimized Au@CN/Au_c /G Y@S structure displays high photocatalytic CO₂ RR selectivity of 88%, where the CO and CH₄ generations during 8 h are 494 and 198 µmol/gcat., respectively. This approach combining architecture engineering and composition modification provides a new strategy with improved activity and controllable selectivity toward targeting applications in energy conversion catalysis.

Highly selective CO2 photoreduction to CO on MOF-derived TiO2

Metal-Organic Framework (MOF)-derived TiO2, synthesised through the calcination of MIL-125-NH2, is investigated for its potential as a CO2 photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH4. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH4. Over the range of experimental settings explored, the MOF-derived TiO2 displays high selectivity towards CO (98%), with only a small amount of CH4 (2%) being produced. This is notable when compared to other state-of-the-art TiO2 based CO2 photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO2 was found to have a peak production rate of 8.9 × 10-4 μmol cm-2 h-1 (2.6 μmol g-1 h-1) and 2.6 × 10-5 μmol cm-2 h-1 (0.10 μmol g-1 h-1) for CO and CH4, respectively. A comparison is made to commercial TiO2, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10-3 μmol cm-2 h-1 (5.9 μmol g-1 h-1), but a lower selectivity preference for CO (3 : 1 CH4 : CO) than the MOF-derived TiO2 material developed here. This paper showcases the potential for MIL-125-NH2 derived TiO2 to be further developed as a highly selective CO2 photoreduction catalyst for CO production.

Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ

Direct solar-driven methane (CH₄) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (W^δ+), stabilised over an oxygen-vacancy-rich WO₃, which enables exceptional photocatalytic CH₄ conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 μmol·g^-1 within 2 h, and the normalised mass activity of 8.5 × 10⁶ μmol·g^-1_Cu·h^-1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O₂, generating reactive •OOH radicals. In parallel, the adjacent W^δ+ species act as the hole acceptor and the preferred adsorption and activation site of H₂O to produce hydroxyl radicals (•OH), and thus activate CH₄ to methyl radicals (•CH₃). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process.

Investigating the interfacial properties of halide perovskite/TiOx heterostructures for versatile photocatalytic reactions under sunlight

Heterostructures of metal halide perovskites and TiO_x are efficient photocatalytic materials owing to the combination of the advantages of each compound, specifically the high absorption coefficients and long charge-carrier lifetimes of perovskites, and efficient photocatalytic activity of TiO_x. However, chemical reduction of CO₂ using PNC/TiO_x heterostructures without organic solvents has not been reported yet. Here, we report the first solvent-free reduction of CO₂ using amorphous TiO_x with embedded colloidal perovskite nanocrystals (PNCs). The combination was obtained by carrying out hydrolysis of titanium butoxide (TBOT) on the PNC surface without high-temperature calcination. We proposed a mechanism involving photoexcited electrons being transferred from PNCs to TBOT, enabling photocatalytic reactions using TiO_x under visible-light excitation. We demonstrated efficient visible-light-driven photocatalytic reactions at PNC/TiO_x interfaces, specifically with a CO production rate of 30.43 μmol g^-1 h^-1 and accelerated degradation of organic pollutants under natural sunlight. Our work has provided a simple path toward both efficient CO₂ reduction and photocatalytic degradation of organic dyes.

Surface plasmon-enhanced photo-driven CO2 hydrogenation by hydroxy-terminated nickel nitride nanosheets

The majority of visible light-active plasmonic catalysts are often limited to Au, Ag, Cu, Al, etc., which have considerations in terms of costs, accessibility, and instability. Here, we show hydroxy-terminated nickel nitride (Ni₃N) nanosheets as an alternative to these metals. The Ni₃N nanosheets catalyze CO₂ hydrogenation with a high CO production rate (1212 mmol g^-1 h^-1) and selectivity (99%) using visible light. Reaction rate shows super-linear power law dependence on the light intensity, while quantum efficiencies increase with an increase in light intensity and reaction temperature. The transient absorption experiments reveal that the hydroxyl groups increase the number of hot electrons available for photocatalysis. The in situ diffuse reflectance infrared Fourier transform spectroscopy shows that the CO₂ hydrogenation proceeds via the direct dissociation pathway. The excellent photocatalytic performance of these Ni₃N nanosheets (without co-catalysts or sacrificial agents) is suggestive of the use of metal nitrides instead of conventional plasmonic metal nanoparticles.

Fabrication of layered In2S3/WS2 heterostructure for enhanced and efficient photocatalytic CO2 reduction and various paraben degradation in water

Because of the excessive use of fossil fuels, CO₂ emissions into the environment are increasing. An efficient method of converting CO₂ to useful carbonaceous products in the presence of light is one way to address the issues associated with energy and environmental remediation. In₂S₃/WS₂ heterostructure has been fabricated using the efficient hydrothermal method. The results of structural, morphological, optical, and photo/electrochemical characterization confirm the formation of a hierarchical, layered heterostructure of type-II. Enhanced photocatalytic activity is observed in InS/WS heterostructure compared to pristine In₂S₃ and WS₂. InS/WS heterostructure exhibit higher photocatalytic activity than pure In₂S₃ and WS₂. For 12 h, photocatalytic CO₂ reduction produces 213.4 and 188.6 μmol of CO and CH₄, respectively. Furthermore, the photocatalytic ability of the synthesized materials to degrade different parabens (Methyl: MPB, Ethyl: EPB, and Benzyl: BPB) under visible radiation was evaluated. Under optimized conditions, the InS/WS heterostructure degraded 88.6, 90.4, and 95.8% of EPB, BPB, and MPB, respectively, in 90 min. The mechanism of photocatalysis was discussed in detail. MCF-7 cell viability was assessed and found to exhibit low mortality in InS/WS treated MPB aqueous solution. InS/WS heterostructure could improve the fabrication of more sulphide-based layered materials to combat environmental pollution.

A Cu medium designed Z-scheme ZnO-Cu-CdS heterojunction photocatalyst for stable and excellent H2 evolution, methylene blue degradation, and CO2 reduction

Solar photocatalysis has emerged as a pollution-free and inexhaustible technique that has been extensively researched in the domains of environmental remediation and energy production. Herein, we have integrated ZnO and CdS nanoparticles through Cu as a solid-state electron mediator to design a ZnO-Cu-CdS Z-scheme heterosystem via a sol-gel route and further tested this as a photocatalyst for dye degradation, H₂ evolution, and CO₂ reduction. Within 60 min of visible light exposure, about 97% of methylene blue (MB) is degraded with a degradation rate constant of 0.042 min^-1 for the ZnO_0.45Cu_0.1CdS_0.45 catalyst. The MB degradation with this catalyst is 84, 21, 4.8, and 2 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. The ZnO-Cu-CdS catalyst manifests an H₂ evolution efficiency of 5579 μmol h^-1 g^-1, which is 169, 41, 3.9, and 3.5 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. Using H₂ as a reducing agent, the CO production rate over the ZnO_0.45Cu_0.1CdS_0.45 catalyst reaches 770 μmol h^-1 g^-1, which is 3 and 1.8 times higher than those of ZnO_0.5CdS_0.5 and Cu_0.1ZnO_0.9 catalysts. Besides, the optimal CH₄ production rate over ZnO_0.45Cu_0.1CdS_0.45 reaches 890 μmol h^-1 g^-1. The improved photocatalytic response of the ZnO-Cu-CdS catalyst is assigned to the delayed recombination of photoexcited charge carriers through a Z-scheme charge transport mode, maintaining the photocarriers with strong redox potentials and the dual role of Cu to serve as a conductive bridge to accelerate the charge transfer rate and enhance the light absorption due to its SPR phenomenon. This research offers a promising strategy for developing binary/ternary Z-scheme heterojunction photocatalytic systems for different photocatalytic applications.

Defects Tune the Strong Metal-Support Interactions in Copper Supported on Defected Titanium Dioxide Catalysts for CO2 Reduction

A highly active and stable Cu-based catalyst for CO₂ to CO conversion was demonstrated by creating a strong metal-support interaction (SMSI) between Cu active sites and the TiO₂-coated dendritic fibrous nano-silica (DFNS/TiO₂) support. The DFNS/TiO₂-Cu10 catalyst showed excellent catalytic performance with a CO productivity of 5350 mmol g^-1 h^-1 (i.e., 53,506 mmol g_Cu^-1 h^-1), surpassing that of almost all copper-based thermal catalysts, with 99.8% selectivity toward CO. Even after 200 h of reaction, the catalyst remained active. Moderate initial agglomeration and high dispersion of nanoparticles (NPs) due to SMSI made the catalysts stable. Electron energy loss spectroscopy confirmed the strong interactions between copper NPs and the TiO₂ surface, supported by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy. The H₂-temperature programmed reduction (TPR) study showed α, β, and γ H₂-TPR signals, further confirming the presence of SMSI between Cu and TiO₂. In situ Raman and UV-vis diffuse reflectance spectroscopy studies provided insights into the role of oxygen vacancies and Ti³⁺ centers, which were produced by hydrogen, then consumed by CO₂, and then again regenerated by hydrogen. These continuous defect generation-regeneration processes during the progress of the reaction allowed long-term high catalytic activity and stability. The in situ studies and oxygen storage complete capacity indicated the key role of oxygen vacancies during catalysis. The in situ time-resolved Fourier transform infrared study provided an understanding of the formation of various reaction intermediates and their conversion to products with reaction time. Based on these observations, we have proposed a CO₂ reduction mechanism, which follows a redox pathway assisted by hydrogen.

UiO-66 MOF-Derived Ru@ZrO2 Catalysts for Photo-Thermal CO2 Hydrogenation

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO2 catalysts by controlled thermal treatment of zirconium-based MOF UiO-66 with ruthenium moieties. Ru3+ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 °C) to obtain ZrO2-derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO2 to CH4. Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO2 to H2 molar ratio) reactor at temperatures from 80 to 300 °C. Ru0.10@ZrO2 catalyst calcined at 600 °C was able to hydrogenate CO2 to CH4 with production rates up to 65 mmolCH4·gcat.–1·h–1, CH4 yield of 80% and nearly 100% selectivity at 300 °C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO2 conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO2 catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO2 for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO2 crystalline phase on the CH4 selectivity has been found, with monoclinic zirconia being much more selective to CH4 than its cubic allotrope.

Nickel-Laden Dendritic Plasmonic Colloidosomes of Black Gold: Forced Plasmon Mediated Photocatalytic CO2 Hydrogenation

In this work, we have designed and synthesized nickel-laden dendritic plasmonic colloidosomes of Au (black gold-Ni). The photocatalytic CO₂ hydrogenation activities of black gold-Ni increased dramatically to the extent that measurable photoactivity was only observed with the black gold-Ni catalyst, with a very high photocatalytic CO production rate (2464 ± 40 mmol g_Ni^-1 h^-1) and 95% selectivity. Notably, the reaction was carried out in a flow reactor at low temperature and atmospheric pressure without external heating. The catalyst was stable for at least 100 h. Ultrafast transient absorption spectroscopy studies indicated indirect hot-electron transfer from the black gold to Ni in less than 100 fs, corroborated by a reduction in Au-plasmon electron-phonon lifetime and a bleach signal associated with Ni d-band filling. Photocatalytic reaction rates on excited black gold-Ni showed a superlinear power law dependence on the light intensity, with a power law exponent of 5.6, while photocatalytic quantum efficiencies increased with an increase in light intensity and reaction temperature, which indicated the hot-electron-mediated mechanism. The kinetic isotope effect (KIE) in light (1.91) was higher than that in the dark (∼1), which further indicated the electron-driven plasmonic CO₂ hydrogenation. Black gold-Ni catalyzed CO₂ hydrogenation in the presence of an electron-accepting molecule, methyl-p-benzoquinone, reduced the CO production rate, asserting the hot-electron-mediated mechanism. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ hydrogenation took place by a direct dissociation path via linearly bonded Ni-CO intermediates. The outstanding catalytic performance of black gold-Ni may provide a way to develop plasmonic catalysts for CO₂ reduction and other catalytic processes using black gold.

Recent Trends in Plasmon-Assisted Photocatalytic CO2 Reduction

Direct photocatalytic reduction of CO₂ has become an highly active field of research. It is thus of utmost importance to maintain an overview of the various materials used to sustain this process, find common trends, and, in this way, eventually improve the current conversions and selectivities. In particular, CO₂ photoreduction using plasmonic photocatalysts under solar light has gained tremendous attention, and a wide variety of materials has been developed to reduce CO₂ towards more practical gases or liquid fuels (CH₄ , CO, CH₃ OH/CH₃ CH₂ OH) in this manner. This Review therefore aims at providing insights in current developments of photocatalysts consisting of only plasmonic nanoparticles and semiconductor materials. By classifying recent studies based on product selectivity, this Review aims to unravel common trends that can provide effective information on ways to improve the photoreduction yield or possible means to shift the selectivity towards desired products, thus generating new ideas for the way forward.

Toward a Comprehensive Understanding of Amorphous Photocatalysts: Fundamental Hypotheses and Applications in CO2 Photoreduction

In principle, photocatalytic activity can be precisely controlled with crystalline catalysts. However, an amorphous photocatalyst could be a viable candidate for CO₂ photoreduction to form value-added products. The amorphous phase is currently part of the crystalline material in several ongoing CO₂ photoreduction studies. Additionally, no study indicates the amorphous material required for overall CO₂ photoreduction. This perspective review article highlights fundamental assumptions that are necessary to gain insights and understand the effectiveness of amorphous photocatalysts for CO₂ photoreduction. We start with basic ideas and theories about these materials, including light harvesting, variable coordination number, and the interaction of CO₂ molecules with the amorphous catalytic surface. To understand the prospects of the amorphous photocatalyst, we explore machine learning with EXAFS. Furthermore, we discuss product selectivity and regeneration of photocatalysts in detail. Finally, we briefly review the work in progress on amorphous materials and compare it to that on crystalline ones.

Recent advances in structural engineering of photocatalysts for environmental remediation

Photocatalysis appears to be an appealing approach for environmental remediation including pollutants degradation in water, air, and/or soil, due to the utilization of renewable and sustainable source of energy, i.e., solar energy. However, their broad applications remain lagging due to the challenges in pollutant degradation efficiency, large-scale catalyst production, and stability. In recent decades, massive efforts have been devoted to advance the photocatalysis technology for improved environmental remediation. In this review, the latest progress in this aspect is overviewed, particularly, the strategies for improved light sensitivity, charge separation, and hybrid approaches. We also emphasize the low efficiency and poor stability issues with the current photocatalytic systems. Finally, we provide future suggestions to further enhance the photocatalyst performance and lower its large-scale production cost. This review aims to provide valuable insights into the fundamental science and technical engineering of photocatalysis in environmental remediation.