Black indium oxide a photothermal CO2 hydrogenation catalyst

Effect of reduction pretreatment on the structure and catalytic performance of Ir-In2O3 catalysts for CO2 hydrogenation to methanol

In2O3 has been found a promising application in CO2 hydrogenation to methanol, which is beneficial to the utilization of CO2. The oxygen vacancy (Ov) site is identified as the catalytic active center of this reaction. However, there remains a great challenge to understand the relations between the state of oxygen species in In2O3 and the catalytic performance for CO2 hydrogenation to methanol. In the present work, we compare the properties of multiple In2O3 and Ir-promoted In2O3 (Ir-In2O3) catalysts with different Ir loadings and after being pretreated under different reduction temperatures. The CO2 conversion rate of Ir-In2O3 is more promoted than that of pure In2O3. With only a small amount of Ir loading, the highly dispersed Ir species on In2O3 increase the concentration of Ov sites and enhance the activity. By finely tuning the catalyst structure, Ir-In2O3 with an Ir loading of 0.16 wt.% and pre-reduction treatment under 300°C exhibits the highest methanol yield of 146 mgCH3OH/(gcat·hr). Characterizations of Raman, electron paramagnetic resonance, X-ray photoelectron spectroscopy, CO2-temperature programmed desorption and CO2-pulse adsorption for the catalysts confirm that more Ov sites can be generated under higher reduction temperature, which will induce a facile CO2 adsorption and desorption cycle. Higher performance for methanol production requires an adequate dynamic balance among the surface oxygen atoms and vacancies, which guides us to find more suitable conditions for catalyst pretreatment and reaction.

Unraveling the molecular and growth mechanism of colloidal black In2O3-x

Black metal oxides with varying concentrations of O-vacancies display enhanced optical and catalytic properties. However, direct solution syntheses of this class of materials have been limited despite being highly advantageous given the different synthetic handles that can be leveraged towards control of the targeted material. Herein, we present an alternate colloidal synthesis of black In2O3-x nanoparticles from the simple reaction between In(acac)3 and oleyl alcohol. Growth studies by PXRD, TEM, and STEM-EDS coupled to mechanistic insights from 1H, 13C NMR revealed the particles form via two paths, one of which involves In0. We also show that variations in the synthesis atmosphere, ligand environment, and indium precursor can inhibit formation of the black In2O3-x. The optical spectrum for the black nanoparticles displayed a significant redshift when compared to pristine In2O3, consistent with the presence of O-vacancies. Raman spectra and surface analysis also supported the presence of surface oxygen vacancies in the as-synthesized black In2O3-x.

Photothermal CO2 Catalysis toward the Synthesis of Solar Fuel: From Material and Reactor Engineering to Techno-Economic Analysis

Carbon dioxide (CO2), a member of greenhouse gases, contributes significantly to maintaining a tolerable environment for all living species. However, with the development of modern society and the utilization of fossil fuels, the concentration of atmospheric CO2 has increased to 400 ppm, resulting in a serious greenhouse effect. Thus, converting CO2 into valuable chemicals is highly desired, especially with renewable solar energy, which shows great potential with the manner of photothermal catalysis. In this review, recent advancements in photothermal CO2 conversion are discussed, including the design of catalysts, analysis of mechanisms, engineering of reactors, and the corresponding techno-economic analysis. A guideline for future investigation and the anthropogenic carbon cycle are provided.

Engineering Photothermal Catalytic CO2 Nanoreactor for Osteomyelitis Treatment by In Situ CO Generation

Photocatalytic carbon dioxide (CO2) reduction is an effective method for in vivo carbon monoxide (CO) generation for antibacterial use. However, the available strategies mainly focus on utilizing visible-light-responsive photocatalysts to achieve CO generation. The limited penetration capability of visible light hinders CO generation in deep-seated tissues. Herein, a photothermal CO2 catalyst (abbreviated as NNBCs) to achieve an efficient hyperthermic effect and in situ CO generation is rationally developed, to simultaneously suppress bacterial proliferation and relieve inflammatory responses. The NNBCs are modified with a special polyethylene glycol and further embellished by bicarbonate (BC) decoration via ferric ion-mediated coordination. Upon exposure to 1064 nm laser irradiation, the NNBCs facilitated efficient photothermal conversion and in situ CO generation through photothermal CO2 catalysis. Specifically, the photothermal effect accelerated the decomposition of BC to produce CO2 for photothermal catalytic CO production. Benefiting from the hyperthermic effect and in situ CO production, in vivo assessments using an osteomyelitis model confirmed that NNBCs can simultaneously inhibit bacterial proliferation and attenuate the photothermal effect-associated pro-inflammatory response. This study represents the first attempt to develop high-performance photothermal CO2 nanocatalysts to achieve in situ CO generation for the concurrent inhibition of bacterial growth and attenuation of inflammatory responses.

Thermocatalytic Hydrogen Production from Water at Boiling Condition

Thermochemical water-splitting cycles are technically feasible for hydrogen production from water. However, the ultrahigh operation temperature and low efficiency seriously restrict their practical application. Herein, one-step and one-pot thermocatalytic water-splitting process is reported at water boiling condition catalyzed by single atomic Pt on defective In2O3. Water splitting into hydrogen is verified by D2O isotopic experiment, with an optimized hydrogen production rate of 36.4 mmol·h-1·g-1 as calculated on Pt active sites. It is revealed that three-centered Pt1In2 surrounding oxygen vacancy as catalytic ensembles promote the dissociation of the adsorbed water into H, which transfers to singlet atomic Pt sites for H2 production. Remaining OH groups on adjacent In sites from Pt1In2 ensembles undergoes O─O bonding, hyperoxide formation and diminishing via triethylamine oxidation, water re-adsorption for completing the catalytic cycle. Current work represents an isothermal and continuous thermocatalytic water splitting under mild condition, which can re-awaken the research interest to produce H2 from water using low-grade heat and competes with photocatalytic, electrolytic, and photoelectric reactions.

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.

Improved Charge Separation and CO2 Affinity of In2O3 by K Doping with Accompanying Oxygen Vacancies for Boosted CO2 Photoreduction

The CO2 photocatalytic conversion efficiency of the semiconductor photocatalyst is always inhibited by the sluggish charge transfer and undesirable CO2 affinity. In this work, we prepare a series of K-doped In2O3 catalysts with concomitant oxygen vacancies (OV) via a hydrothermal method, followed by a low-temperature sintering treatment. Owing to the synergistic effect of K doping and OV, the charge separation and CO2 affinity of In2O3 are synchronously promoted. Particularly, when P/P0 = 0.010, at room temperature, the CO2 adsorption capacity of the optimal K-doped In2O3 (KIO-3) is 2336 cm3·g-1, reaching about 6000 times higher than that of In2O3 (0.39 cm3·g-1). As a result, in the absence of a cocatalyst or sacrificial agent, KIO-3 exhibits a CO evolution rate of 3.97 μmol·g-1·h-1 in a gas-solid reaction system, which is 7.6 times that of pristine In2O3 (0.52 μmol·g-1·h-1). This study provides a novel approach to the design and development of efficient photocatalysts for CO2 conversion by element doping.

A nonmetallic plasmonic catalyst for photothermal CO2 flow conversion with high activity, selectivity and durability

The meticulous design of active sites and light absorbers holds the key to the development of high-performance photothermal catalysts for CO2 hydrogenation. Here, we report a nonmetallic plasmonic catalyst of Mo2N/MoO2-x nanosheets by integrating a localized surface plasmon resonance effect with two distinct types of active sites for CO2 hydrogenation. Leveraging the synergism of dual active sites, H2 and CO2 molecules can be simultaneously adsorbed and activated on N atom and O vacancy, respectively. Meanwhile, the plasmonic effect of this noble-metal-free catalyst signifies its promising ability to convert photon energy into localized heat. Consequently, Mo2N/MoO2-x nanosheets exhibit remarkable photothermal catalytic performance in reverse water-gas shift reaction. Under continuous full-spectrum light irradiation (3 W·cm-2) for a duration of 168 h, the nanosheets achieve a CO yield rate of 355 mmol·gcat-1·h-1 in a flow reactor with a selectivity exceeding 99%. This work offers valuable insights into the precise design of noble-metal-free active sites and the development of plasmonic catalysts for reducing carbon footprints.

Efficient Thermal Management with Selective Metamaterial Absorber for Boosting Photothermal CO2 Hydrogenation under Sunlight

Photothermal catalytic CO2 hydrogenation is a prospective strategy to simultaneously reduce CO2 emission and generate value-added fuels. However, the demand of extremely intense light hinders its development in practical applications. Herein, this work reports the novel design of Ni-based selective metamaterial absorber and employs it as the photothermal catalyst for CO2 hydrogenation. The selective absorption property reduces the heat loss caused by radiation while possessing effectively solar absorption, thus substantially increasing local photothermal temperature. Notably, the enhancement of local electric field by plasmon resonance promotes the adsorption and activation of reactants. Moreover, benefiting from the ingenious morphology that Ni nanoparticles (NPs) are encapsulated by SiO2 matrix through co-sputtering, the greatly improved dispersion of Ni NPs enables enhancing the contact with reaction gas and preventing the agglomeration. Consequently, the catalyst exhibits an unprecedented CO2 conversion rate of 516.9 mmol gcat -1 h-1 under 0.8 W cm-2 irradiation, with near 90% CO selectivity and high stability. Significantly, this designed photothermal catalyst demonstrates the great potential in practical applications under sunlight. This work provides new sights for designing high-performance photothermal catalysts by thermal management.

Selective Gas-Phase Hydrogenation of CO2 to Methanol Catalysed by Metal-Organic Frameworks

Large scale production of green CH3 OH obtained from CO2 and green H2 is a highly wanted process due to the role of CH3 OH as H2 /energy carrier and for producing chemicals. Starting with a short summary of the advantages of metal-organic frameworks (MOFs) as catalysts in liquid-phase reactions, the present article highlights the opportunities that MOFs may offer also for some gas-phase reactions, particularly for the selective CO2 hydrogenation to CH3 OH. It is commented that there is a temperature compatibility window that combines the thermal stability of some MOFs with the temperature required in the CO2 hydrogenation to CH3 OH that frequently ranges from 250 to 300 °C. The existing literature in this area is briefly organized according to the role of MOF as providing the active sites or as support of active metal nanoparticles (NPs). Emphasis is made to show how the flexibility in design and synthesis of MOFs can be used to enhance the catalytic activity by adjusting the composition of the nodes and the structure of the linkers. The influence of structural defects and material crystallinity, as well as the role that should play theoretical calculations in models have also been highlighted.

Aggregate assembly of ferrocene functionalized indium-oxo clusters

In this study, we synthesized multi-nuclear indium oxide clusters (InOCs) using 1,1'-ferrocene dicarboxylic acid (H2FcDCA) as the chelating and surface protection ligand. The obtained clusters include the cubane-type heptanuclear InOCs ([In7]) and the sandwich-type thirteen-nuclear InOCs ([In13]). Notably, [In13] represents the highest nuclear number reported within the InOC family. In addition, the presence of labile coordination sites in these clusters allowed for structural modification and self-assembly. A series of [In7] clusters with adjustable band gaps have been obtained and the self-assembly of [In7] clusters resulted in the formation of an Fe-doped dimer, [Fe2In12], and an imidazole-bridged tetramer, [In28]. Similarly, in the case of [In13] clusters, the coordinated water molecules could be replaced by imidazole, methylimidazole, and even a bridged carboxylic acid, allowing the construction of one-dimensional extended structures. Additionally, part of the H2FcDCA could be substituted by pyrazole. This flexibility in replacing solvent molecules offered diverse possibilities for tailoring the properties and structures of the InOCs to suit specific applications.

Wettability Engineering of Solar Methanol Synthesis

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 μmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

rh-In2O3 Nanoparticles for Efficient Photocatalytic Degradation of Rifampin

Photodegradation, a widely accepted and promising technology, has gained significant attention for addressing the escalating concerns of environmental deterioration. In this article, rhombohedral corundum-type In2O3 nanocrystals were obtained from the transformation of InOOH via a simple calcining process. Under ultraviolet light irradiation, they showed higher photocatalytic activity in the decomposition of rifampin compared to that of the cubic phase In2O3 and P25-TiO2. Furthermore, the probable pathway and the feasible mechanism for the degradation of rifampin were also deeply explored and discussed.

Polarized Active Pairs at Grain Boundary Boost CO2 Chemical Fixation

The chemical fixation of CO2 as a C1 feedstock is considered one of the most promising ways to obtain long-chain chemicals, but its efficiency was limited by the ineffective activation of CO2. Herein, we propose a grain boundary engineering strategy to construct polarized active pairs with electron poor-rich character for effective CO2 activation. By taking CeO2 as a model system, we illustrate that the polarized "Ce4+-Ce3+-Ce4+" pairs at the grain boundary can simultaneously accept and donate electrons to coordinate with O and C, respectively, in CO2. By the combination of synchrotron radiation in situ technique and density functional theory calculations, the mechanism of the catalytic reaction has been systematically investigated. As a result, the CeO2 nanosheets with a rich grain boundary show a high DMC yield of 60.3 mmol/gcat with 100% atomic economy. This study provides a practical way for the chemical fixation of CO2 to high-value-added chemicals via grain boundary engineering.

Synergistic Modulation between Non-thermal and Thermal Effects in Photothermal Catalysis based on Modified In2O3

To promote the solar-energy cascade utilization, it is necessary to increase the thermal effect of irradiation in the catalytic reactions, while simultaneously augmenting the non-thermal effect, so as to fulfill photothermal coupling. Herein, the non-thermal and thermal effect of light radiation on the surface of In2O3-based catalysts are explored and enhanced by the modification of transition metals Fe and Cu. Optical characterizations combined with water-splitting experiments show that Fe doping greatly broadens the radiation response range and enhances the absorption intensity of semiconductors' intrinsic portion, and Cu doping facilitates the absorption of visible-infrared light. The concurrent incorporation of Fe and Cu offers synergistic benefits, resulting in improved radiation response range, carrier separation and migration, as well as higher photothermal temperature upon photoexcitation. Collectively, these advantages comprehensively enhance the photothermal synergistic water-splitting reactivity. The characterizations under variable temperature conditions have demonstrated that the reaction temperature exerts a significant influence on the process of radiation absorption and conversion, ultimately impacting the non-thermal effect. The results of DFT calculations have revealed that the increasing temperature directly impacts the chemical reaction by reducing the energy barrier associated with the rate-determining step. These findings shine new light on the fundamental mechanisms underlying non-thermal and thermal effect, while also imparting significant insights for photo-thermal-coupled catalyst designing.

Recent Advances of Indium Oxide-Based Catalysts for CO2 Hydrogenation to Methanol: Experimental and Theoretical

Methanol synthesis from the hydrogenation of carbon dioxide (CO₂) with green H₂ has been proven as a promising method for CO₂ utilization. Among the various catalysts, indium oxide (In₂O₃)-based catalysts received tremendous research interest due to the excellent methanol selectivity with appreciable CO₂ conversion. Herein, the recent experimental and theoretical studies on In₂O₃-based catalysts for thermochemical CO₂ hydrogenation to methanol were systematically reviewed. It can be found that a variety of steps, such as the synthesis method and pretreatment conditions, were taken to promote the formation of oxygen vacancies on the In₂O₃ surface, which can inhibit side reactions to ensure the highly selective conversion of CO₂ into methanol. The catalytic mechanism involving the formate pathway or carboxyl pathway over In₂O₃ was comprehensively explored by kinetic studies, in situ and ex situ characterizations, and density functional theory calculations, mostly demonstrating that the formate pathway was extremely significant for methanol production. Additionally, based on the cognition of the In₂O₃ active site and the reaction path of CO₂ hydrogenation over In₂O₃, strategies were adopted to improve the catalytic performance, including (i) metal doping to enhance the adsorption and dissociation of hydrogen, improve the ability of hydrogen spillover, and form a special metal-In₂O₃ interface, and (ii) hybrid with other metal oxides to improve the dispersion of In₂O₃, enhance CO₂ adsorption capacity, and stabilize the key intermediates. Lastly, some suggestions in future research were proposed to enhance the catalytic activity of In₂O₃-based catalysts for methanol production. The present review is helpful for researchers to have an explicit version of the research status of In₂O₃-based catalysts for CO₂ hydrogenation to methanol and the design direction of next-generation catalysts.

Selective CO2 Photoreduction to Acetate at Asymmetric Ternary Bridging Sites

Photoreduction of CO₂ is a promising strategy to synthesize value-added fuels or chemicals and realize carbon neutralization. Noncopper catalysts are seldom reported to generate C₂ products, and the selectivity over these catalysts is low. Here, we design rich-interface, heterostructured In₂O₃/InP (r-In₂O₃/InP) for highly competitive photocatalytic CO₂-to-CH₃COOH conversion with a productivity of 96.7 μmol g^-1 and selectivity > 96% along with water oxidation to O₂ in pure water (no sacrificial agent) under visible light irradiation. The hard X-ray absorption near-edge structure (XANES) shows that the formation of r-In₂O₃/InP with the isogenesis cation adjusts the coordination environment via interface engineering and forms O-In-P polarized sites at the interface. In situ FT-IR and Raman spectra identify the key intermediates of OCCO* for acetate production with high selectivity. Density functional theory (DFT) calculations reveal that r-In₂O₃/InP with rich O-In-P polarized sites promotes C-C coupling to form C₂ products because of the imbalanced adsorption energies of two carbon atoms. This work reports an interesting indium-based photocatalyst for selective CO₂ photoreduction to acetate under strict solution and irradiation conditions and provides significant insights into fabricating interfacial polarization sites to promote the process.

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.

Niche Applications of MXene Materials in Photothermal Catalysis

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis.

Comment on "CO2 Footprint of Thermal Versus Photothermal CO2 Catalysis"

The previously published report by Wang et al. provides universal equations for evaluating the net CO₂ emission via photothermal/thermal CO₂ hydrogenation reactions in batch and flow reactors, respectively. However, it remains to be discussed whether the original feed amount or feed rate of H₂ should be changed accordingly when the CO₂ reduction rate is selected as the variable to investigate the net CO₂ emission rate of the system. If not, the reaction would not be in accordance with the stoichiometric ratio, which is inconsistent with reality, bringing about the optimistic scenario in the assessment of CO₂ footprint. This work has taken the potential relationship between the original feed amount or feed rate of H₂ and CO₂ conversion rate into account. The effects of CO₂ conversion rate on the net CO₂ emission rate in the photothermal catalytic system are re-examined, the obtained trends exhibit more challenging preconditions to achieve net-zero carbon emission than those in the work by Wang et al. The quantitative results indicate that green hydrogen source is indeed vital for carbon neutrality in photothermal CO₂ catalysis. Here, the viewpoints will be worth considering and be seen as complementary to the proposed carbon emission assessment equations.

Photo-Induced Switching of CO2 Hydrogenation Pathway towards CH3 OH Production over Pt@UiO-66-NH2 (Co)

It is highly desired to achieve controllable product selectivity in CO₂ hydrogenation. Herein, we report light-induced switching of reaction pathways of CO₂ hydrogenation towards CH₃ OH production over actomically dispersed Co decorated Pt@UiO-66-NH₂ . CO, being the main product in the reverse water gas shift (RWGS) pathway under thermocatalysis condition, is switched to CH₃ OH via the formate pathway with the assistance of light irradiation. Impressively, the space-time yield of CH₃ OH in photo-assisted thermocatalysis (1916.3 μmol g_cat ^-1  h^-1 ) is about 7.8 times higher than that without light at 240 °C and 1.5 MPa. Mechanism investigation indicates that upon light irradiation, excited UiO-66-NH₂ can transfer electrons to Pt nanoparticles and Co sites, which can efficiently catalyze the critical elementary steps (i.e., CO₂ -to-*HCOO conversion), thus suppressing the RWGS pathway to achieve a high CH₃ OH selectivity.

Nanostructured Materials for Photothermal Carbon Dioxide Hydrogenation: Regulating Solar Utilization and Catalytic Performance

Converting carbon dioxide (CO₂) into value-added fuels or chemicals through photothermal catalytic CO₂ hydrogenation is a promising approach to alleviate the energy shortage and global warming. Understanding the nanostructured material strategies in the photothermal catalytic CO₂ hydrogenation process is vital for designing photothermal devices and catalysts and maximizing the photothermal CO₂ hydrogenation performance. In this Perspective, we first describe several essential nanomaterial design concepts to enhance sunlight absorption and utilization in photothermal CO₂ hydrogenation. Subsequently, we review the latest progress in photothermal CO₂ hydrogenation into C₁ (e.g., CO, CH₄, and CH₃OH) and multicarbon hydrocarbon (C₂₊) products. Finally, the relevant challenges and opportunities in this exciting research realm are discussed. This perspective provides a comprehensive understanding for the light-heat synergy over nanomaterials and instruction for rational photothermal catalyst design for CO₂ utilization.

Construction of BiOIO3/AgIO3 Z-Scheme Photocatalysts for the Efficient Removal of Persistent Organic Pollutants under Natural Sunlight Illumination

The efficient removal of persistent organic pollutants (POPs) in natural waters is vital for human survival and sustainable development. Photocatalytic degradation is a feasible and cost-effective strategy to completely disintegrate POPs at room temperature. Herein, we develop a series of direct Z-scheme BiOIO₃/AgIO₃ hybrid photocatalysts via a facile deposition-precipitation method. Under natural sunlight irradiation, the light intensity of which is ∼40 mW/cm², a considerable rate constant of 0.185 min^-1 for photodecomposing 40 mg/L MO is obtained over 0.5 g/L Bi@Ag-5 composite photocatalyst powder, about 92.5 and 5.3 times higher than those of pristine AgIO₃ and BiOIO₃. The photoactivity of Bi@Ag-5 for photodecomposing MO under natural sunlight illumination surpasses most of the reported photocatalysts under Xe lamp illumination. After natural sunlight irradiation for 20 min, 95% of MO, 82% of phenol, 78% of 2,4-DCP, 54% of ofloxacin, and 88% of tetracycline hydrochloride can be photodecomposed over Bi@Ag-5. Relative to the commercial photocatalyst TiO₂ (P25), Bi@Ag-5 exhibits greatly higher photoactivity for the treatment of MO-phenol-tetracycline hydrochloride mixture pollutants in the scale-up experiment of 500 mL of solution, decreasing COD, TOC, and chromaticity value by 52, 19, and 76%, respectively, after natural sunlight irradiation for 40 min. The photodegradation process and mechanism of MO have been systematically investigated and proposed. This work provides an archetype for designing efficient photocatalysts to remove POPs.

Atomically Precise Integration of Multiple Functional Motifs in Catalytic Metal-Organic Frameworks for Highly Efficient Nitrate Electroreduction

Ammonia production plays a central role in modern industry and agriculture with a continuous surge in its demand, yet the current industrial Haber-Bosch process suffers from low energy efficiency and accounts for high carbon emissions. Direct electrochemical conversion of nitrate to ammonia therefore emerges as an appealing approach with satisfactory sustainability while reducing the environmental impact from nitrate pollution. To this end, electrocatalysts for efficient conversion of eight-electron nitrate to ammonia require collective contributions at least from high-density reactive sites, selective reaction pathways, efficient multielectron transfer, and multiproton transport processes. Here, we report a catalytic metal-organic framework (two-dimensional (2D) In-MOF In8) catalyst integrated with multiple functional motifs with atomic precision, including uniformly dispersed, high-density, single-atom catalytic sites, high proton conductivity (efficient proton transport channel), high electron conductivity (promoted by the redox-active ligands), and confined microporous environments. These eventually lead to a direct and efficient electrochemical reduction of nitrate to ammonia and record high yield rate, FE, and selectivity for NH₃ production. A novel "dynamic ligand dissociation" mechanism provides an unprecedented working principle that allows for the use of a high-quality MOF crystalline structure to function as highly ordered, high-density, single-atom catalyst (SAC)-like catalytic systems and ensures the maximum utilization of the metal centers within the MOF structure. Further, the atomically precise assembly of multiple functional motifs within a MOF catalyst offers an effective and facile strategy for the future development of framework-based enzyme-mimic systems.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction

The photocatalytic CO₂ reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In₂O₃ plasmonic photocatalysts. The Ag-In₂O₃ compounds show remarkedly enhanced photocatalytic activity for CO₂ conversion to CO compared to pristine In₂O₃. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag-In₂O₃-10 is 1.56 μmol/g/h, achieving 5.38-folds higher than that of In₂O₃ (0.29 μmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In₂O₃ on Ag-In₂O₃ compounds. In Ag-In₂O₃ compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In₂O₃, resulting in the photocatalytic activity enhancement of Ag-In₂O₃ compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Elucidating CO2 Hydrogenation over In2 O3 Nanoparticles using Operando UV/Vis and Impedance Spectroscopies

In₂ O₃ has emerged as a promising catalyst for CO₂ activation, but a fundamental understanding of its mode of operation in CO₂ hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water-gas shift reaction (rWGSR) over In₂ O₃ nanoparticles, both at the surface and in the bulk. Based on temperature-dependent operando UV/Vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO₂ as the rate-determining step for the rWGSR. The results are consistent with redox processes, whereby hydrogen-containing surface species are shown to exhibit a promoting effect. Our findings demonstrate that oxygen/hydrogen dynamics, in addition to surface processes, are important for the activity, which is expected to be of relevance not only for In₂ O₃ but also for other reducible oxide catalysts.

Light-Driven Reversible Hydrogen Storage in Light-Weight Metal Hydrides Enabled by Photothermal Effect

Requiring high temperature for hydrogen storage is the main feature impeding practical application of light metal hydrides. Herein, to lift the restrictions associated with traditional electric heating, light is used as an alternative energy input, and a light-mediated catalytic strategy coupling photothermal and catalytic effects is proposed. With NaAlH₄ as the initial target material, TiO₂ nanoparticles uniformly distribute on carbon nanosheets (TiO₂ @C), which couples the catalytic effect of TiO₂ and photothermal property of C, is constructed to drive reversible hydrogen storage in NaAlH₄ under light irradiation. Under the catalysis of TiO₂ @C, complete hydrogen release from NaAlH₄ is achieved within 7 min under a light intensity of 10 sun. Furthermore, owing to the stable catalytic and photothermal effect of TiO₂ @C, NaAlH₄ delivers a reversible capacity of 4 wt% after 10 cycles with a capacity retention of 85% under light irradiation only. The proposed strategy is also applicable to other light metal hydrides such as LiAlH₄ and MgH₂ , validating its universality. The concept of light-driven hydrogen storage provides an alternative approach to electric heating, and the light-mediated catalytic strategy proposed herein paves the way to the design of reversible high-density hydrogen storage systems that do not rely on artificial energy.

Aqueous transfer of colloidal metal oxide nanocrystals via base-driven ligand exchange

A general method is developed for removal of native nonpolar oleate ligands from colloidal metal oxide nanocrystals of varying morphologies and compositions. Ligand stripping occurs by phase transfer into potassium hydroxide solution, yielding stable aqueous dispersions with little nanocrystal aggregation and without significant changes to the nanomaterials' physical or chemical properties. This method enables facile fabrication of conductive films of ligand-free nanocrystals.

A Stacked Plasmonic Metamaterial with Strong Localized Electric Field Enables Highly Efficient Broadband Light-Driven CO2 Hydrogenation

Light utilization largely governs the performance of CO₂ photoconversion, whereas most of the materials that are implemented in such an application are restricted in a narrow spectral absorption range. Plasmonic metamaterials with a designable regular pattern and facile tunability are excellent candidates for maximizing light absorption to generate substantial hot electrons and thermal energy. Herein, a concept of coupling a Au-based stacked plasmonic metamaterial with single Cu atoms in alloy, as light absorber and catalytic sites, respectively, is reported for gas-phase light-driven catalytic CO₂ hydrogenation. The metamaterial structure works in a broad spectral range (370-1040 nm) to generate high surface temperature for photothermal catalysis, and also induces strong localized electric field in favor of transfer of hot electrons and reduced energy barrier in CO₂ hydrogenation. This work unravels the significant role of a strong localized electric field in photothermal catalysis and demonstrates a scalable fabrication approach to light-driven catalysts based on plasmonic metamaterials.

Thermoplasmonics in Solar Energy Conversion: Materials, Nanostructured Designs, and Applications

The indispensable requirement for sustainable development of human society has forced almost all countries to seek highly efficient and cost-effective ways to harvest and convert solar energy. Though continuous progress has advanced, it remains a daunting challenge to achieve full-spectrum solar absorption and maximize the conversion efficiency of sunlight. Recently, thermoplasmonics has emerged as a promising solution, which involves several beneficial effects including enhanced light absorption and scattering, generation and relaxation of hot carriers, as well as localized/collective heating, offering tremendous opportunities for optimized energy conversion. Besides, all these functionalities can be tailored via elaborated designs of materials and nanostructures. Here, first the fundamental physics governing thermoplasmonics is presented and then the strategies for both material selection and nanostructured designs toward more efficient energy conversion are summarized. Based on this, recent progress in thermoplasmonic applications including solar evaporation, photothermal chemistry, and thermophotovoltaic is reviewed. Finally, the corresponding challenges and prospects are discussed.

Light-Induced Synthesis of Oxygen-Vacancy-Functionalized Ni(OH)2 Nanosheets for Highly Selective CO2 Reduction

Solar-driven CO₂ reduction into fuels and chemicals has gained increasing attention in recent years. In this study, oxygen-vacancies-functionalized Ni(OH)₂ (OVs-Ni(OH)₂ ) nanosheets are synthesized by a photochemical method to serve as a catalyst for CO₂ reduction. Characterization reveals that COOH* is the key intermediate for CO₂ -to-CO photoreduction. Experimental results and theoretical calculations confirm that OVs modification can greatly modulate the interaction strength between the OVs-Ni(OH)₂ and CO₂ , while lowering the energy barrier for COOH* formation, thereby preferentially facilitating CO₂ reduction. As a result, the OVs-Ni(OH)₂ catalyst exhibits outstanding activity and selectivity for CO₂ -to-CO photoreduction with visible light. A CO evolution rate of 31.58 μmol h^-1 (0.35 mg catalyst, 90228 μmol h^-1  g^-1 ) with a selectivity of 98 % over OVs-Ni(OH)₂ was achieved, outperforming most analogous reported catalysts. Moreover, even under a low CO₂ concentration of 0.04 % (representative of the CO₂ concentration in air) and low reaction temperature (273 K, 0 °C), this catalyst can still trigger CO₂ reduction. This work provides a new method to synthesize OVs-Ni(OH)₂ catalysts for efficient CO₂ reduction and establishes a relationship between the OVs and the catalytic activity, which may guide the design of highly selective CO₂ reduction catalysts.

Photodriven CO2 Hydrogenation into Diverse Products: Recent Progress and Perspective

Converting CO2 into value-added chemicals through hydrogenation can optimize the energy structure dominated by fossil energy, effectively alleviate environmental problems, and achieve full utilization of carbon resources. However, the traditional CO2 hydrogenation reactions need to be carried out under high temperature and pressure, causing inevitable secondary pollution to the environment. A fundamental way to solve these problems is to use clean solar energy to convert CO2 into value-added chemicals and to establish an artificial carbon cycle process. In this Perspective, we highlight recent advances in photodriven CO2 conversion, including the reverse water-gas-shift reaction, methanation reaction, methanol synthesis reaction, and C2+ hydrocarbon synthesis reaction. Finally, we also discuss the challenges and future investigation opportunities for modulating the selective conversion of CO2. This Perspective offers guidance for the design of photodriven CO2 conversion or even the entire C1 catalyst chemistry for tuning product selectivity and activity.

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

Biodegradable Bismuth-Based Nano-Heterojunction for Enhanced Sonodynamic Oncotherapy through Charge Separation Engineering

Sonodynamic therapy is a noninvasive treatment method that generates reactive oxygen species (ROS) triggered by ultrasound, to achieve oxidative damage to tumors. However, methods are required to improve the efficiency of ROS generation and achieve continuous oxidative damage. A ternary heterojunction sonosensitizer composed of Bi@BiO_{2- x} @Bi₂ S₃ -PEG (BOS) to achieve thermal injury-assisted continuous sonodynamic therapy for tumors is prepared. The oxygen vacancy in BOS can capture hot electrons and promotes the separation of hot carriers on the bismuth surface. The local electric field induced by localized surface plasmon resonance also contributes to the rapid transfer of electrons. Therefore, BOS not only possesses the functions of each component but also exhibits higher catalytic activity to generate ROS. Meanwhile, BOS continuously consumes glutathione, which is conducive to its biodegradation and achieves continuous oxidative stress injury. In addition, the photothermal conversion of BOS under near-infrared irradiation helps to achieve thermal tumor damage and further relieves tumor hypoxia, thus amplifying the sonodynamic therapeutic efficacy. This process not only provides a strategy for thermal damage to amplify the efficacy of sonodynamic therapy, but also expands the application of bismuth-based heterojunction nanomaterials as sonosensitizers in sonodynamic therapy.

Thermo-photo catalysis: a whole greater than the sum of its parts

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.

Accessing Highly Efficient Photothermal Conversion with Stable Open-Shell Aromatic Nitric Acid Radicals

It is very challenging to prepare stable radicals as they are usually thermodynamically or kinetically unstable in air. Herein, a series of star-shaped aromatic nitric acid radicals were prepared via facile demethylation and consequent oxidation. As phenol radicals without steric hindrance group protection, they exhibit high electrochemical and thermal stability due to their rich resonance structures including closed-shell nitro-like and open-shell nitroxide structure with unpaired electrons delocalized in conjugated backbones. Among them, TPA-TPA-O₆ powder exhibited extremely wide absorption from 300 to 2000 nm covering the whole solar spectral irradiance, high photothermal conversion efficiency, and negligible photobleaching effect in seawater desalination. Under the irradiation of one sunlight, the water evaporation efficiency of TPA-TPA-O₆ is recorded to be as high as 89.41 % and the water evaporation rate is 1.293 kg m^-2  h^-1 , which represents the top performance in pure organic small molecule photothermal materials.