Efficient capture of low-concentration carbon dioxide (CO2) requires chemisorbents that couple strong reactivity with long-term structural stability. Alkali metal oxides are promising candidates but suffer from rapid sintering that severely reduces accessible active sites. Here we develop a universal interfacial strategy that immobilizes Li2O, Na2O, and K2O as highly dispersed amorphous domains on hollow carbon spheres (named Li-HCS, Na-HCS, and K-HCS) forming robust M-O-C anchor sites. These interfacial structures prevent oxide migration, enhance surface basicity, and significantly strengthen CO2 binding. Among the alkali metal-loaded hollow carbon spheres, K-HCS exhibits the highest CO2 uptake (4.9 mmol g- 1 at 273 K and 1 bar), fastest adsorption kinetics (13.56 mol kg- 1 h- 1 at 313 K and 1 bar), and optimal low-pressure removal efficiency (44 % at 273 K and 0.15 bar). Density functional theory calculations further reveal a monotonic increase in adsorption strength and molecular activation from Li to Na to K, driven by enhanced electron donation and polarizability. This work establishes a broadly applicable route for stabilizing alkali metal oxides and provides mechanistic insights for advancing lowpressure CO2 capture materials.

The surfaces and interfaces of catalysts dictate activity, selectivity, and stability in heterogeneous catalysis, yet achieving atomic-level control over charge density flow and reaction energetics across these regions remains challenging. MXenes, a rapidly expanding family of two-dimensional transition-metal carbides, nitrides, and carbonitrides, offer an exceptional platform to address these challenges owing to their compositional tunability, rich surface terminations, and the strong influence of these groups on their physicochemical properties. Surface engineering provides the foundation for tailoring MXene reactivity, where controlled regulation of terminations, heteroatom doping, defect generation, and morphology enables precise tuning of active sites, adsorption energies, and redox potentials. Nevertheless, optimizing a single material may not provide sufficient control over surface charge dynamics and reaction energetics. For this reason, interface engineering that couples MXenes with metals, semiconductors, or carbon materials has become essential, as such heterostructures create Fermi-level equilibration, built-in electric fields, and orbital hybridization that govern charge transport and reshape catalytic pathways. Together, these hierarchical design strategies transform MXenes from simple conductive supports into dynamic catalytic mediators that bridge electro-, photo-, and thermocatalysis. This review summarizes recent progress in MXene surface and interface engineering, elucidates how atomic configurations regulate charge dynamics and catalytic behavior, and outlines design principles for programmable, self-adaptive, and stable MXene catalysts toward sustainable heterogeneous catalysis.

Photocatalytic reduction of CO2 into carbon-based fuels offers a viable approach for solar-to-chemical energy conversion but remains limited by inefficient charge separation and the intrinsic inertness of CO2. Overcoming these challenges requires rationally engineered heterostructures capable of simultaneously accelerating charge transport and activating CO2 molecules. Here, a well-defined Nb2C/Nb2O5-x hybrid photocatalyst is developed via controlled partial oxidation of Nb2C MXene. Comprehensive time-resolved and in situ spectroscopic analyses reveal a Schottky-governed interfacial charge-transfer pathway in which photogenerated holes in Nb2O5-x rapidly migrate to Nb2C for water oxidation, while electrons remain within the Nb2O5-x domains to drive CO2 reduction. The in situ-formed Nb2O5-x nanodomains contain abundant oxygen vacancies that act as electron-storing centers, extending carrier lifetimes, enhancing CO2 adsorption and bending, and lowering the free-energy barrier of the rate-determining step during the CO2 conversion. The metallic Nb2C substrate provides high conductivity and generates a pronounced photothermal effect under illumination, locally elevating the surface temperature to thermodynamically promote endothermic CO2 chemisorption. Benefiting from this integrated Schottky-defect-photothermal coupling mechanism, the Nb2C/Nb2O5-x heterostructure delivers enhanced CO2 reduction activity compared with pristine Nb2O5-x and Nb2C, establishing a broadly applicable design paradigm for MXene-derived photocatalysts featuring cooperative charge transfer and thermally assisted molecular activation.

The rational design of heterostructured photocatalysts that simultaneously enable efficient carrier separation, photothermal synergy, and controllable reaction pathways is crucial for advancing CO2 conversion. Here, a Ni/Ti3C2Clx MXene heterojunction is synthesized via Lewis acid molten-salt etching, featuring ultrathin Ni platelets strongly anchored to the MXene substrate through interfacial TiNi3 bonding. This architecture establishes an S-scheme charge transfer pathway, as evidenced by in situ irradiated X-ray photoelectron and X-ray absorption spectroscopy, which confirm efficient carrier transfer and separation, while femtosecond transient absorption spectroscopy reveals ultrafast interfacial dynamics. Under photothermal conditions, the cooperative interplay of metallic Ni, surface NiOx, and the conductive MXene substrate couples directional charge migration with thermally assisted molecular activation and barrier lowering, thereby enabling regulated CO2 hydrogenation product distribution between CH4 and CH3OH. Density functional theory demonstrates that surface-state evolution, rather than simple oxidation degree, modulates adsorption energetics and alters the relative barriers of CH4 and CH3OH pathways, such that moderately oxidized Ni-NiOx interfacial ensembles favour methanol forming intermediates, whereas extensive oxidation suppresses CH3OH formation. Collectively, these findings demonstrate a robust strategy for exploiting MXene-based heterojunction interfaces in photothermal catalysis and underscore the pivotal role of surface state regulated reaction pathways in steering product distribution during CO2 hydrogenation.

Heterogeneous catalysis relies on advanced, tunable materials offering structurally defined active sites and large accessible surface areas. Among the various material types, two-dimensional nanomaterials with high aspect ratios feature a high fraction of exposed atoms and thus efficient atom utilization. After more than a decade since the first report of MXene synthesis, these two-dimensional transition-metal carbides and nitrides, composed of alternating one-atom-thick metal and carbide/nitride layers with surface terminations, have found applications in diverse catalytic areas. This review focuses on the use of MXenes as solid catalysts in thermal or photothermal reactions, while electro- and photocatalysis are excluded as they have been extensively reviewed elsewhere. Section 2 briefly summarizes MXene synthesis and structural features, followed by Section 3 describing the nature and characterization of catalytically active sites, including surface groups, vacancies, and metal-support interfaces that arise from the synthesis conditions. Section 4 emphasizes best practices for ensuring reproducible and stable catalytic performance, with turnover frequency as a key comparative metric. Sections 5 and 6 highlight some representative thermal and photothermal reactions, underscoring the high light-to-heat conversion efficiency of MXenes. This review concludes with current challenges and future prospects, anticipating rapid progress with MXene-based heterogeneous catalysis.

The solar-powered CO2 conversion via the photocatalysis route offers a sustainable pathway toward carbon neutrality while mitigating energy/environmental pressure. Nevertheless, the selective and efficient conversion of CO2 via photoreduction to C2 products remains a formidable challenge. Here, we engineered a dual-single-atom photocatalyst by controllably embedding Pd and Cu single atoms into a TiO2 matrix. The optimized catalyst (Cu0.5Pd0.5/TiO2) exhibits the outstanding yield (119.2 µmol/gcat) and selectivity (84.8%) for acetic acid production from CO2 photoreduction, performed in seawater and in a photothermal-aided reactor. Various in situ/ex situ characterizations were employed to investigate atomic-level structure-performance correlation and reaction mechanism in practical condition. In situ x-ray photoelectron spectroscopy, in situ atomic force microscopy-Kelvin probe force microscopy, transient-state surface photovoltage, and in situ electron paramagnetic resonance (EPR) collectively indicate that loading Pd and Cu single atoms onto TiO2 apparently accelerates charge kinetics. This modification results in increased photogenerated electrons for CO2 reduction, facilitating C─C coupling and hydrogenation reactions. Additionally, in situ infrared (IR) spectroscopy and theoretical computations affirm the pivotal function of Pd single atoms for lowering the energy barrier to form the *OCCO intermediate, apparently improving selectivity for acetic acid production. Overall, our work presents an innovative approach to tackle kinetic and thermodynamic challenges for light-induced CO2-to-C2 conversion.

Photocatalytic conversion of methane (CH4) to liquid oxygenates under mild conditions remains challenging due to the need to simultaneously regulate C–H bond activation, oxygen activation, C–C coupling, and over-oxidation. This paper reports a Ru-modified TiO2 photocatalyst (0.5RT) that integrates isolated Ru atoms, neighbouring Ru configurations, and possible subnanometric RuOx–like clusters on TiO2. Advanced structural characterization techniques such as Aberration-corrected HAADF-STEM and X-ray absorption spectroscopy reveal that these Ru species are highly dispersed and primarily coordinated by oxygen on TiO2. In this CH4/O2/H2O system, Ru–O–Ti atomic sites promote interfacial charge transfer and CH4 polarization, while RuOx-like clusters enhance reactant adsorption and promote O2 activation. Additionally, neighbouring Ru configurations facilitate the local coexistence of methyl-related intermediates and oxygenated C1 intermediates, thereby promoting acetate formation. Therefore, 0.5RT produces liquid oxygenate production yield of 668 μmol gcat-1 acetic acid (CH3COOH) and 653 μmol gcat-1 formic acid (HCOOH) after 4 h of irradiation, with a CH3COOH/HCOOH molar yield ratio of 1.02. Mechanistic insights from in situ spectroscopies and density functional theory calculations reveal that Ru atomic sites promote C–H polarization, whereas RuOx-like clusters promote O2 adsorption and O–O bond weakening. Their close proximity favours C–C coupling toward CH3COOH formation.

Photocatalytic selective oxidation for hydrocarbon valorization generally faces selectivity challenges. This work reports a rational design of an S-scheme heterojunction comprising oxygen-deficient BiVO4-OVs and g-C3N4. Remarkably, under mild LED irradiation (10 W) at ambient temperature, the system achieved > 99% ethylbenzene conversion and acetophenone selectivity, substantially outperforming single-component counterparts. Systematic experiments combined with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations elucidated a novel dual reaction mechanism: (i) The photogenerated holes (h(+)) on heterojunction structures demonstrate appropriate oxidizing capability, that enabling direct benzylic C(sp(3))-H bond activation. (ii) The tailored oxygen vacancies simultaneously modulate reactant adsorption/desorption dynamics and the space charge separation of S-scheme heterojunctions catalyse tert-butyl hydroperoxide (TBHP) decomposition into superoxide radicals (O-2(center dot-)), which subsequently function as the real active species to form radical-adduct intermediates. This work establishes an efficient photocatalytic selective oxidation strategy through synergistic interface engineering and precision defect control.

Methane, a potent greenhouse gas and a chemically inert molecule, presents a major challenge for catalytic conversion. Existing methods are energy-intensive, while photocatalysis offers a promising solar-driven alternative; yet, its efficiency and selectivity are often hampered by uncontrolled radical reactivity and inefficient charge separation. Here we have developed a full-solar-spectrum photocatalyst by constructing a Schottky heterojunction with Pd deposited on Co3O4 derived from a metal–organic framework. The narrow bandgap and black colouration of Co3O4 enable broad solar absorption, while its tailored band structure minimizes overoxidation and undesired by-products by suppressing reactive species, including O2•−, ·OH and ·OOH. The work function difference between Pd and Co3O4 establishes an interfacial electric field that promotes directional carrier migration and reduces recombination. This design achieves efficient solar utilization, precise radical regulation and robust charge separation, delivering a C2H6 production rate from CH4 of 16.1 mmol per gram catalyst per hour with 96.2 The success of photocatalytic coupling of CH4 has been limited by the low solar absorption of wide-bandgap semiconductors and the uncontrolled oxidation caused by radical oxygen species. Here a Pd/Co3O4 heterojunction derived from a metal–organic framework demonstrates the selective conversion of CH4 to C2H6 by less reactive oxygen species under full-solar-spectrum irradiation.

Photocatalytic CO2 conversion offers a sustainable route for solar fuel production but is hindered by weak CO2 adsorption, inefficient charge separation, and inadequate stabilization of key intermediates. Covalent organic frameworks (COFs) provide a modular platform, yet the structure-function relationships that govern their photocatalytic performance remain insufficiently understood. Here, a triazine-imine COF (TPT-COF) integrated with Co(II) bipyridine complexes (Cobpy) is developed to elucidate the functional role of triazine moieties in facilitating efficient CO2-to-CO conversion. Comparative analysis with a triazine-free analog (TPB-COF) reveals that triazine incorporation enhances Lewis basicity and CO2 chemisorption, while simultaneously inducing a distinct Co & horbar;N5Cl coordination environment that promotes dual-channel charge transport and interfacial electron injection. In situ and time-resolved spectroscopic studies, together with density functional theory calculations, consistently demonstrate that the triazine framework stabilizes the *COOH intermediate by lowering the reaction barrier. As a result, Cobpy-TPT-COF achieves a CO evolution rate of approximate to 1.3 mmol g-1, exceeding its imine-based counterpart by over an order of magnitude. These findings provide mechanistic insight into COF-molecular hybrid systems and establish guiding principles for the rational design of next-generation photocatalysts for solar-driven CO2 reduction.

The photocatalytic selective oxidation of alcohols to aldehydes has garnered significant interest; however, developing photocatalysts with high conversion efficiency and selectivity under mild conditions remains challenging. In this research, we presented a straightforward solvothermal approach for synthesizing Bi2MoO6 through precise modulation of the ethanol-to-ethylene glycol (EG) combination. Notably, this strategy enables controlled generation of surface oxygen vacancies (OVs) while effectively maintaining the material's welldefined spherical superstructures composed of uniform nanosheets. The OVs modified the electronic structure of Bi2MoO6, enhancing light absorption and enabling simultaneous utilization of photogenerated electrons and holes to produce reactive oxygen species (center dot O2- and center dot OOH), thereby driving efficient benzyl alcohol conversion. A gradient in OVs concentration was further confirmed through systematic characterization. Theoretical calculations demonstrate that OVs enhance adsorption and activation of reactants and lower the work function and the free energy. Thus, BMO-2 delivers exceptional catalytic performance under blue LED irradiation and air atmosphere, attaining 99.8 % benzyl alcohol conversion and 99.9 % benzaldehyde selectivity after 12 h, demonstrated the protocol as a mild, green, highly efficient, highly selective, and precisely controllable photocatalytic transformation. This work presents a promising strategy to design photocatalysts through concurrent control of morphology and surface defects, while providing a mild alternative for the oxidation of benzyl alcohols.

The rapid increase in atmospheric CO2 levels due to industrialization underscores the urgent need for innovative carbon valorization strategies. Photocatalytic CO2 reduction presents a sustainable solution; however, conventional systems suffer from inefficient charge separation and limited product applicability. Herein, a green and scalable tandem strategy is developed by integrating S-scheme photocatalysis with palladium-catalyzed carbonylation. A rationally designed CeO2/Bi2S3 heterojunction leverages its hierarchical structure, broad visible-light absorption, oxygen-vacancy-mediated charge dynamics, and the S-scheme charge transfer mechanism to achieve highly efficient photocatalytic CO2-to-CO conversion (14.05 mmol g-1, 98% selectivity). The generated CO is directly utilized in a subsequent carbonylation reaction under mild conditions, yielding high-value amides with near-quantitative CO utilization. This integrated approach eliminates the risks of CO handling and enhances economic viability, providing a direct and effective route for converting CO2 into fine chemicals. By bridging photocatalysis with industrial catalysis, this work advances sustainable carbon recycling technologies and opens avenues for the development of efficient CO2 conversion systems.

Covalent organic frameworks (COFs) have garnered significant interest as advanced platforms for carbon capture, utilization, and storage, owing to their high surface area, tunable porosity, and excellent chemical stability. However, their practical deployment for carbon dioxide (CO2) capture, particularly under the low-concentration conditions characteristic of industrial flue gas, remains a major challenge. Herein, an amine-functionalized COF, designated TaTp-COF, is synthesized via spontaneous enol-to-ketoamine tautomerization, introducing a high density of uniformly distributed secondary amine groups that enhance CO2 binding affinity. TaTp-COF delivers an impressive CO2 uptake of 5.0 mmol g1 at 0 degrees C and 1 bar, alongside outstanding thermal stability and cycling durability. Importantly, it maintains high adsorption efficiency at low CO2 partial pressures, demonstrating strong potential for flue gas treatment. The material also achieves exceptional CO2/N2 selectivity (233, V:V = 15:85), surpassing most reported porous adsorbents. Spectroscopic analyses, complemented by theoretical calculations, confirm the formation of carbamic acid species upon CO2 adsorption, indicative of strong host-guest interactions and efficient amine site utilization. The uniform dispersion of active centers contributes to enhanced binding strength, suppressed desorption at elevated temperatures, and reduced secondary emissions. This work positions TaTp-COF as a promising next-generation adsorbent for scalable and energy-efficient CO2 capture and flue gas purification, while offering valuable design insights for functionalized COFs in sustainable gas separation technologies.

Photocatalytic CO2 reduction into solar fuels presents a promising strategy for carbon mitigation and sustainable energy conversion. However, single-component photocatalysts suffer from inefficient charge separation, while binary heterojunctions-even with cocatalysts assistance-often undergo rapid Coulombic recombination due to timescale mismatches between ultrafast charge transfer and slower surface reaction kinetics. To overcome these limitations, a spatially engineered Nb2C/Nb2O5/ZnO ternary heterostructure is developed by anchoring ZnO quantum dots (QDs) onto Nb2O5 nanorods grown in situ from Nb2C MXene. This architecture integrates an Nb2O5/ZnO S-scheme heterojunction and an Nb2C/Nb2O5 Schottky junction, sharing Nb2O5 as a central mediator, thereby establishing bidirectional interfacial electric fields (IEFs) that direct photogenerated electrons toward ZnO and holes toward Nb2C. In situ irradiated X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), and femtosecond transient absorption spectroscopy (fs-TAS) reveal interface-specific electronic interactions and time-resolved carrier dynamics, confirming efficient and spatially resolved charge migration across the decoupled interfaces. This spatial charge separation effectively suppresses Coulombic recombination and prolongs carrier lifetimes. Additionally, the photothermal effect of Nb2C MXene enhances CO2 chemisorption and activation at defective ZnO QDs. These synergistic effects collectively enable high-efficiency CO2 photoreduction without molecular cocatalysts or sacrificial agents, providing a mechanistically distinct and scalable approach for artificial photosynthesis.

Harnessing sunlight for photocatalytic overall water splitting offers a sustainable approach to renewable hydrogen (H2) production, addressing global energy and environmental challenges. However, the development of efficient and durable photocatalysts remains a significant obstacle. This study introduces the design and performance of a 2D/2D Schottky heterojunction composed of Cu2[CuTCPP] MOF of nanometric size and exfoliated Ti3C2 MXene for visible-light-driven overall water splitting. By leveraging the extensive interfacial contact between the two components, an interfacial electric field is generated, promoting efficient charge migration and prolonging carrier lifetimes, as confirmed through systematic density functional theory simulations, in situ irradiation X-ray photoelectron spectroscopy, femtosecond transient absorption spectroscopy, and X-ray absorption spectroscopy. Ti3C2 MXene, acting as a cocatalyst for photohole transport and accumulation, reduces oxidative degradation and slows catalyst deactivation. The synergistically enhanced light absorption properties of the Cu2[CuTCPP]/Ti3C2 heterojunction result in an impressive H2 evolution rate exceeding 5000 µmol gcat⁻1, underscoring its potential for next-generation photocatalytic systems in renewable energy applications.

The conversion of CO2 into valuable solar fuels via photocatalysis is a promising strategy for addressing energy shortages and environmental crises. Here, novel In2 O3 @Co2 VO4 hierarchical heterostructures are fabricated by in situ growing Co2 VO4 nanorods onto In2 O3 nanofibers. First-principle calculations and X-ray photoelectron spectroscopy (XPS) measurements reveal the electron transfer between In2 O3 and Co2 VO4 driven by the difference in work functions, thus creating an interfacial electric field and bending the bands at the interfaces. In this case, the photogenerated electrons in In2 O3 transport to Co2 VO4 and recombine with its holes, indicating the formation of In2 O3 @Co2 VO4 S-scheme heterojunctions and resulting in effective separation of charge carriers, as confirmed by in situ irradiation XPS. The unique S-scheme mechanism, along with the enhanced optical absorption and the lower Gibbs free energy change for the production of * CHO, significantly contributes to the efficient CO2 photoreduction into CO and CH4 in the absence of any molecule cocatalyst or scavenger. Density functional theory simulation and in situ diffuse reflectance infrared Fourier transform spectroscopy are employed to elucidate the reaction mechanism in detail.

Solar fuel synthesis is intriguing because solar energy is abundant and this method compensates for its intermittency. However, most photocatalysts can only absorb UV-to-visible light, while near-infrared (NIR) light remains unexploited. Surprisingly, the charge transfer between ZnO and CuInS2 quantum dots (QDs) can transform a NIR-inactive ZnO into a NIR-active composite. This strong response is attributed to the increased concentration of free charge carriers in the p-type semiconductor at the interface after the charge migration between ZnO and CuInS2, enhancing the localized surface plasmon resonance (LSPR) effect and the NIR response of CuInS2. As a paradigm, this ZnO/CuInS2 heterojunction is used for H2O2 production coupled with glycerin oxidation and demonstrates supreme performance, corroborating the importance of NIR response and efficient charge transfer. Mechanistic studies through contact potential difference (CPD), Hall effect test, and finite element method (FEM) calculation allow for the direct correlation between the NIR response and charge transfer. This approach bypasses the general light response issues, thereby stepping forward to the ambitious goal of harnessing the entire solar spectrum.