3D Hierarchical ZnIn2S4 Nanosheets with Rich Zn Vacancies Boosting Photocatalytic CO2 Reduction

Zinc vacancy (V_Zn) is successfully introduced into 3D hierarchical ZnIn₂S₄ (3D‐ZIS). The photo‐electrochemical experiments demonstrate that the charge separation and carrier transfer are more efficient in the 3D‐ZIS with rich V_Zn. Of note, for the first time, it is found that V_Zn can decrease the carrier transport activation energy (CTAE), from 1.14 eV for Bulk‐ZIS (Bulk ZnIn₂S₄) to 0.93 eV for 3D‐ZIS, which may provide a feasible platform for further understanding the mechanism of photocatalytic CO₂ reduction. In situ Fourier transform infrared (FT‐IR) results reveal that the presence of rich V_Zn ensures CO₂ chemical activation, promoting single‐electron reduction of CO₂ to CO₂^?. In addition, in situ FT‐IR and CO₂ temperature programmed desorption results show that V_Zn can promote the formation of surface hydroxyl. To the best of current knowledge, there are no reports on the photoreduction of CO₂ simply by virtue of 3D‐ZIS with V_Zn and few literature reports on the photocatalytic reduction of CO₂ concerned with CTAE. Additionally, this work finds that surface hydroxyl may play a crucial role in the process of CO₂ photoreduction. The work may provide some novel ways to ameliorate solar energy conversion performance and a better understanding of photoreaction mechanisms.     

Ni1−xCoxSe2?C/ZnIn2S4 Hybrid Nanocages with Strong 2D/2D Hetero-Interface Interaction Enable Efficient H2-Releasing Photocatalysis

Designing a semiconductor-based heterostructure photocatalyst for achieving the efficient separation of photogenerated electron-hole pairs is highly important for enhancing H₂ releasing photocatalysis. Here, a new class of Ni_1−xCo_xSe₂–C/ZnIn₂S₄ hierarchical nanocages with abundant and compact ZnIn₂S₄ nanosheets/Ni_1−xCo_xSe₂^ C nanosheets 2D/2D hetero–interfaces, is designed and synthesized. The constructed heterostructure photocatalyst exposes rich hetero-junctions, supplying the broad and short transfer paths for charge carriers. The close contacts of these two kinds of nanosheets induce a strong interaction between ZnIn₂S₄ and Ni_1−xCo_xSe₂ C, improving the separation and transfer of photo-generated electron-hole pairs. As a consequence, the distinctive Ni_1−xCo_xSe₂ C/ZnIn₂S₄ hierarchical nanocages without using additional noble-metal cocatalysts, display remarkable H₂-relaesing photocatalytic activity with a rate of 5.10 mmol g⁻¹ h⁻¹ under visible light irradiation, which is 6.2 and 30 times higher than those of fresh ZnIn₂S₄ nanosheets and bare Ni_1−xCo_xSe₂ C nanocages, respectively. Spectroscopic characterizations and theory calculations reveal that the strong interaction between ZnIn₂S₄ and Ni_1−xCo_xSe₂ C 2D/2D hetero-interfaces can powerfully promote the separation of photo-generated charge carriers and the electrons transfer from ZnIn₂S₄ to Ni_1−xCo_xSe₂ C.     

Nanostructured Metal Sulfides: Classification,Modification Strategy,and Solar-Driven CO2 Reduction Application

Solar-driven conversion of CO₂ into high value-added fuels is expected to be an environmental-friendly and sustainable approach for relieving the greenhouse gas effect and countering energy crisis. Metal sulfide semiconductors with wide photoresponsive range and favorable band structures are suitable photocatalysts for CO₂ photoreduction. This review summarizes the recent progress on metal sulfide semiconductors for photocatalytic CO₂ reduction. First, the fundamentals, mechanisms and some principles, like product selectivity, of photocatalytic CO₂ reduction are introduced. Then, according to the elemental composition, the metal sulfide photocatalysts applied for CO₂ reduction are classified into binary (CdS, ZnS, MoS₂, SnS₂, Bi₂S₃, In₂S₃,Cu₂S, NiS/NiS₂, and CoS₂), ternary (ZnIn₂S₄, CdIn₂S₄, CuInS₂, Cu₃SnS₄, and CuGaS₂), and quaternary (Cu₂ZnSnS₄) systems, in which their crystal structures, photochemical characteristics, and photocatalytic CO₂ reduction applications are systematically demonstrated. Especially, the diverse modification strategies for improving the activity and product selectivity of photocatalytic CO₂ reduction on these metal sulfides are summarized. Finally, the current challenges and future directions for the development of metal sulfide photocatalysts for CO₂ reduction are proposed. This review is expected to serve as a powerful reference for exploiting high-efficiency metal sulfide photocatalysts for CO₂ conversion and furthering related mechanism understanding.     

Surface Energy Mediated Sulfur Vacancy of ZnIn2S4 Atomic Layers for Photocatalytic H2O2 Production

Constructing rich defect active site structure for material design is still a great challenge. Herein, a simple surface engineering strategy is demonstrated to construct one-unit-cell ZnIn₂S₄ atomic layers with the modulated surface energy of S vacancy. Rich surface energy can regulate and control the rich S vacancy, which ensures rich active sites, higher charge density and effective carrier transport. As a result, the ZnIn₂S₄ atomic layers with rich surface energy affords an obvious enhancement in H₂O₂ productive rate of 1592.04 µmol g⁻¹ h⁻¹, roughly 14.58 times superior to that with poor surface energy. Moreover, the in situ infrared diffuse reflection spectrum indicates that S vacancy as the oxygen reduction reaction active site is responsible for the critical intermediate *O₂⁻ and *OOH, corresponding to two-electron oxygen reduction reaction. This study provides a valuable insight and guidance for constructing controllably defects to achieve highly efficient H₂O₂ production.     

Recent Progress in Electrocatalytic Methanation of CO2 at Ambient Conditions

Electrochemical CO₂ reduction under ambient conditions is a promising pathway for conversion of CO₂ into value-added products. In recent years, great achievements have been obtained in the understanding the mechanism and development of efficient and selective catalysts for electrochemical CO₂ reduction. However, the electrochemical CO₂ reduction is still far from practical applications. Based on the gap between current research and practical applications, the state-of-the-art of the theoretical and experiment investigations on different electrocatalysts for the electrocatalysis of CO₂ to CH₄ is systematically and constructively reviewed. First of all, strategies for enhancing the catalytic activity and selectivity of electrochemical reduction of CO₂ to CH₄ are also examined in this review. The modulated strategies mainly involve the following aspects: i) tuning the applied potentials, ii) morphology engineering, iii) crystallographic facets engineering, iv) defect engineering, v) alloying. Furthermore, the influence of the electrolyte on the activity and selectivity for electrocatalysis of CO₂ to CH₄ is also reviewed. This review will build a systematic understanding in the electrochemical CO₂ reduction to CH₄ and may help to provide new insight for designing and optimizing the catalysts and/or electrolyte.     

Rational Engineering of Multilayered Co3O4/ZnO Nanocatalysts through Chemical Transformations from Matryoshka‐Type ZIFs

Hybrid metal oxides with multilayered structures exhibit unique physical and chemical properties, particularly important to heterogeneous catalysis. However, regulations of morphology, spatial location, and shell numbers of the hybrid metal oxides still remain a challenge. Herein, binary Co₃O₄/ZnO nanocages with multilayered structures (up to eight layers) are prepared via chemical transformation from diverse Matryoshka‐type zeolitic imidazolate frameworks (ZIFs) via a straightforward and scalable calcination method. More importantly, the obtained ZIF‐derived metal oxides (ZDMOs) with versatile layer numbers exhibit remarkable catalytic activity for both gas‐phase CO oxidation and CO₂ hydrogenation reactions, which are directly related to the sophisticated shell numbers (i.e., Co₃O₄‐terminated layers or ZnO‐terminated layers). Particularly, in situ reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicate that the promotional effects of the multilayered structures indeed exist in CO₂ hydrogenation, wherein the key reaction intermediates are quite different for five‐layer and six‐layer ZDMOs. For instance, *HCOO is the predominant intermediate over the six‐layer ZDMO; on the contrary, *H₃CO is the crucial species over the five‐layer ZDMO. The ZnO/Co₃O₄ interface should be the active sites for CO₂ hydrogenation to *HCOO and *H₃CO species, which are ultimately converted to the products (CH₄ or methanol). Accordingly, the work here provides a convenient way to facilely engineer multilayered Co₃O₄/ZnO nanocomposites with precisely controlled shell numbers for heterogeneous catalysis applications.     

Regulating the Metallic Cu–Ga Bond by S Vacancy for Improved Photocatalytic CO2 Reduction to C2H4

Artificial photosynthesis, which converts carbon dioxide into hydrocarbon fuels, is a promising strategy to overcome both global warming and energy crisis. Herein, the geometric position of Cu and Ga on ultra-thin CuGaS₂/Ga₂S₃ is oriented via a sulfur defect engineering, and the unprecedented C₂H₄ yield selectivity is ≈93.87% and yield is ≈335.67 µmol g⁻¹ h⁻¹. A highly delocalized electron distribution intensity induced by S vacancy indicates that Cu and Ga adjacent to S vacancy form Cu–Ga metallic bond, which accelerates the photocatalytic reduction of CO₂ to C₂H₄. The stability of the crucial intermediates (*CHOHCO) is attributed to the upshift of the d-band center of ultra-thin CGS/GS. The C–C coupling barrier is intrinsically reduced by the dominant exposed Cu atoms on the 2D ultra-thin CuGaS₂/Ga₂S₃ in the process of photocatalytic CO₂ reduction, which captures *CO molecules effectively. This study proposes a new strategy to design photocatalyst through defect engineering to adjust the selectivity of photocatalytic CO₂ reduction.     

Proton Turnover Dominated Cascade Route for CO2 Photoreduction

Photoreduction carbon dioxide (CO₂) and water (H₂O) into valuable chemicals is a huge potential to mitigate immoderate CO₂ emissions and energy crisis. To date, tremendous attention is concentrated on the improvement of independent CO₂ reduction or H₂O oxidation behaviors. However, the simultaneous control of efficient electron and hole utilization is still a huge challenge due to the complex cascade redox reactions. Here, a proton turnover exists in the whole CO₂ photoreduction process is discovered, which is defined as the pivot to concatenate the hole and electron behaviors. As a demonstration of the concept, the efficient activated hydrogen (*H) production centers of copper (Cu) and rapid hydrogenation centers of nickel (Ni) are coupled by an alloying strategy, and the proton turnover behaviors could be directly determined by adjustment of the molar ratios of Cu_xNi_y. Moreover, Cu₃Ni₁–TiO₂ exhibits the highest electron selectivity of 93.7% for methane (CH₄) production with a rate of 175.9 µmol g⁻¹ h⁻¹, while Cu₁Ni₅–TiO₂ reaches up to the highest carbon monoxide (CO) electron selectivity and generation rate at 84.4% and 164.6 µmol g⁻¹ h⁻¹, respectively. Consequently, the experimental and theoretical analysis all clarify the predominate proton turnover effect during the overall CO₂ photoreduction process, which directly determines the categories and generated efficiency of C-based products by regulating variable reaction pathways. Therefore, the revelation of the proton turnover pivot could broaden the new sights by bidirectional optimization of dynamics during the overall CO₂ photoreduction system, which favors the efficient, selective, and stable photocatalytic CO₂ reduction with H₂O.     

Hydroxide‐Membrane‐Coated Pt3Ni Nanowires as Highly Efficient Catalysts for Selective Hydrogenation Reaction

Rational design of effective catalysts with both high activity and selectivity is highly significant and desirable for hydrogenation reaction. In this paper, for the first time an efficient approach to controllably construct 1D metal nanowires (NWs) coated with hydroxide (Ni_xM(OH)₂ (M = Mn, Fe, Co, Cu, and Al)) membranes as highly active and selective hydrogenation catalysts is reported. The optimized Ni₃₂Cu(OH)₂ membrane coated Pt₃Ni nanowires show much enhanced selectivity of 87.9% for the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde instead of hydrocinnamyl alcohol, in contrast with the pristine Pt₃Ni nanowires and Pt₃Ni nanowires on Ni(OH)₂ membranes. The enhanced selectivity of Pt₃Ni@Ni₃₂Cu(OH)₂‐2 NWs is ascribed to confinement/poisoning effects of the coated Ni₃₂Cu(OH)₂ membranes as well as the intimate interaction between the Pt₃Ni NWs and Ni₃₂Cu(OH)₂ membranes, as confirmed by X‐ray photoelectron spectroscopy. The coated structures also show good stability after five recycle runs. The present work highlights the importance of surface engineering for the design of multicomponent composites with desirable activity and selectivity toward hydrogenation reaction and beyond.     

Low‐Temperature Growth of SnO2 Nanorod Arrays and Tunable n–p–n Sensing Response of a ZnO/SnO2 Heterojunction for Exclusive Hydrogen Sensors

Uniform SnO₂ nanorod arrays have been deposited at low temperature by plasma‐enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO₂ nanorod sensor to H₂ gas. The ZnO‐modified SnO₂ nanorod sensor shows a normal n‐type response to 100 ppm CO, NH₃, and CH₄ reducing gas whereas it exhibits concentration‐dependent n–p–n transitions for its sensing response to H₂ gas. This abnormal sensing behavior can be explained by the formation of n‐ZnO/p‐Zn‐O‐Sn/n‐SnO₂ heterojunction structures. The gas sensors can be used in highly selective H₂ sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification.     

In Situ Topochemical Transformation of ZnIn2S4 for Efficient Photocatalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran

Photocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) coupled H₂ production offers a promising approach to producing valuable chemicals. Herein, an efficient in situ topological transformation tactic is developed for producing porous O-doped ZnIn₂S₄ nanosheets for HMF oxidation cooperative with H₂ evolution. Aberration-corrected high-angle annular dark-field scanning TEM images show that the hierarchical porous O-ZIS-120 possesses abundant atomic scale edge steps and lattice defects, which is beneficial for electron accumulation and molecule adsorption. The optimal catalyst (O-ZIS-120) exhibits remarkable performance with 2,5-diformylfuran (DFF) yields of 1624 µmol h⁻¹ g⁻¹ and the selectivity of >97%, simultaneously with the H₂ evolution rate of 1522 µmol h⁻¹ g⁻¹. Mechanistic investigations through theoretical calculations show that O in the O-ZIS-120 lattice can reduce the oxidation energy barrier of hydroxyl groups of HMF. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) results reveal that DFF^* (C₄H₂(CHO)₂O^*) intermediate has a weak interaction with O-ZIS-120 and desorb as the final product. This study elucidates the topotactic structural transitions of 2D materials simultaneously with electronic structure modulation for efficient photocatalytic DFF production.     

Revealing the Sudden Alternation in Pt@h-BN Nanoreactors for Nearly 100% CO2-to-CH4 Photoreduction

How to develop an efficient photocatalyst with high activity and high selectivity is the biggest challenge limiting the application of photocatalysis. A reasonable design of the nanoreactor model is an effective strategy. Herein, a series of Pt nanoparticles coated with hexagonal boron nitride (Pt@h-BN) nanoreactors highly dispersed on a photochemically inert carrier, Al₂O₃ substrate, are synthesized. The results show that as the number of h-BN coating layers increases, the selectivity of photocatalysis is altered from nearly 100% CO₂-to-CO to nearly 100% CO₂-to-CH₄, and the optimized space-time yield of CH₄ is up to 184.7 μmol g_(Pt)⁻¹ h⁻¹ with three-layer coating. The in situ characterizations reveal the cleavage of the CO on Pt to be the rate determining step and the existence of the key intermediate CO₂⁻ species on the surface of Pt@h-BN facilitates CH₄ formation. Notably, combined with detailed simulation calculations, this work reveals that the confinement effect in Pt@h-BN attributes the electrons mobility behavior and alleviate the interaction of CO Pt. What is more, the change of the reaction site is the essence for the sudden alternation. This work will bring a new insight to the selective catalysis of noble metals in the gas-solid phase.     

Strong Electronic Interaction between Amorphous MnO2 Nanosheets and Ultrafine Pd Nanoparticles toward Enhanced Oxygen Reduction and Ethylene Glycol Oxidation Reactions

Strengthening the interface interaction between metal and support is an efficient strategy to improve the intrinsic activity and reduce the amount of noble metal. Amorphization of support is an effective approach for enhancing the metal-support interaction due to the numerous surface defects in amorphous structure. In this work, a Pd/a-MnO₂ electrocatalyst containing ultrafine and well-dispersive Pd nanoparticles and amorphous MnO₂ nanosheets is successfully synthesized via a simple and rapid wet chemical method. Differing from the crystal counterpart (Pd/c-MnO₂), the flexible structure of amorphous support can be more favorable to electron transfer and further enhance the metal-support interaction. The synergism between Pd and amorphous MnO₂ results in the downshift of the d-band center, which is beneficial for the desorption of critical intermediates both in oxygen reduction reaction (ORR) and in ethylene glycol oxidation (EGOR). Due to the lower *^.OH desorption energy of Pd/a-MnO₂ surface, the rapid dissociation of *OH from Pd facilitates the formation of H₂O in ORR, thus demonstrating superior ORR performance comparable to Pt/C. For EGOR, the presence of amorphous MnO₂ promotes the formation of adsorbed OH species, which accelerates the desorption of intermediate CO from Pd sites, and thus exhibits excellent EGOR activity and stability.     

Engineering of Amorphous PtOx Interface on Pt/WO3 Nanosheets for Ethanol Oxidation Electrocatalysis

Direct and complete electro-oxidation of ethanol to CO₂ is highly desirable for the commercialization of the direct ethanol fuel cells but is challenging. Current electrocatalysts (mainly Pt, Pd) for ethanol oxidation reaction (EOR), unfortunately, still suffer from low CO₂ selectivity and rapid performance deterioration. In this study, a new Pt/α-PtO_x/WO₃ electrocatalyst containing amorphous PtO_x structures is successfully synthesized via a facile hydrothermal reaction following Ar atmosphere annealing. The migration of lattice oxygens in the WO₃ during the annealing process is confirmed as the mechanism for the formation and manipulation of amorphous interfaces containing PtO_x species in the Pt/α-PtO_x/WO₃ electrocatalyst. The obtained Pt/α-PtO_x/WO₃ with tunable amorphous PtO_x interfaces favors the desorption of poisoning EOR intermediates (such as CO) and high CO₂ selectivity. Therefore, the state-of-art of the Pt/α-PtO_x/WO₃ exhibits excellent EOR activity (2.76 A mg^–1), stability (47.99% of the initial activity preserved after 3600 s), and particularly high CO₂ selectivity (reached 21.9%, higher than most reported values for Pt or other noble metals based EOR catalysts). This study may provide a new strategy to improve the EOR performance of metal-based catalysts and to rationally design and prepare other high-performing electrocatalysts via engineering the amorphous interfaces.     

Highly CO2 Selective Metal–Organic Framework Membranes with Favorable Coulombic Effect

The topology and chemical functionality of metal–organic frameworks (MOFs) make them promising candidates for membrane gas separation; however, few meet the criteria for industrial applications, that is, selectivity of >30 for CO₂/CH₄ and CO₂/N₂. This paper reports on a dense CAU-10-H MOF membrane that is exceptionally CO₂-selective (ideal selectivity of 42 for CO₂/N₂ and 95 for CO₂/CH₄). The proposed membrane also achieves the highest CO₂ permeability (approximately 500 Barrer) among existing pure MOF membranes with CO₂/CH₄ selectivity exceeding 30. State-of-the-art atomistic simulations provide valuable insights into the outstanding separation performance of CAU-10-H at the molecular level. Adsorbent–adsorbate Coulombic interactions are identified as a crucial factor in the design of CO₂-selective MOF membranes.     

Fabrication and properties of photosensitive structures based on ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Photosensitive structures based on single crystals of the ZnIn₂S₄ ternary compound were fabricated and studied for the first time. The optoelectronic properties of this compound and corresponding structures were analyzed using the results of measurements of the optical-absorption spectra of ZnIn₂S₄ crystals, steady-state current-voltage characteristics, and photosensitivity of the structures at T=300 K. It is concluded that surface-barrier structures and heterojunctions based on ZnIn₂S₄ can be used as wide-band photodetectors of natural optical radiation.     

New CH3OH laser lines pumped with a fine-tuned high-power CO2-TEA laser

Joule-level pulses from an etalon tuned CO₂-TEA laser with an ～ 4GHz intraline tuning range have been used to pump a large number of new CH₃OH FIR laser lines. FIR wavelength measurements, pump laser offsets which produced FIR laser lines and pump laser offsets at which CH₃OH absorption lines were observed are reported. Identifications are proposed for most of the absorption lines, and an attempt to identify the FIR laser lines is described.     

FAR infrared lasing frequencies of CH2DOD

We obtained laser action from the CH₂DOD molecule optically pumped by CO₂ laser radiation. Eight lasing transitions were identified as originating from CH₂DOD; an additional 21 transitions also lased, but were assigned to the CH₂DOH molecule, and 2 to CH₃OH, even though the isotopic purity of the sample was given as 98%. The relative intensity, relative polarization and frequency of all the lines were measured. The eight lines are distributed between 145.8 μm and 479.2 μm.     

Hybrid Catalyst Coupling Zn Single Atoms and CuNx Clusters for Synergetic Catalytic Reduction of CO2

Reverse water-gas shift (RWGS) reaction is the initial and necessary step of CO₂ hydrogenation to high value-added products, and regulating the selectivity of CO is still a fundamental challenge. In the present study, an efficient catalyst (CuZnN_x@C-N) composed by Zn single atoms and Cu clusters stabilized by nitrogen sites is reported. It contains saturated four-coordinate Zn-N₄ sites and low valence CuN_x clusters. Monodisperse Zn induces the aggregation of pyridinic N to form Zn-N₄ and N₄ structures, which show strong Lewis basicity and has strong adsorption for *CO₂ and *COOH intermediates, but weak adsorption for *CO, thus greatly improves the CO₂ conversion and CO selectivity. The catalyst calcined at 700 °C exhibits the highest CO₂ conversion of 43.6% under atmospheric pressure, which is 18.33 times of Cu-ZnO and close to the thermodynamic equilibrium conversion rate (49.9%) of CO₂. In the catalytic process, CuN_x not only adsorbs and activates H₂, but also cooperates with the adjacent Zn-N₄ and N₄ structures to jointly activate CO₂ molecules and further promotes the hydrogenation of CO₂. This synergistic mechanism will provide new insights for developing efficient hydrogenation catalysts.     

2D/2D Heterojunction of Ultrathin MXene/Bi2WO6 Nanosheets for Improved Photocatalytic CO2 Reduction

Exploring cheap and efficient cocatalysts for enhancing the performance of photocatalysts is a challenge in the energy conversion field. Herein, 2D ultrathin Ti₃C₂ nanosheets, a kind of MXenes, are prepared by etching Ti₃AlC₂ with subsequent ultrasonic exfoliation. A novel 2D/2D heterojunction of ultrathin Ti₃C₂/Bi₂WO₆ nanosheets is then successfully prepared by in situ growth of Bi₂WO₆ ultrathin nanosheets on the surface of these Ti₃C₂ ultrathin nanosheets. The resultant Ti₃C₂/Bi₂WO₆ hybrids exhibit a short charge transport distance and a large interface contact area, assuring excellent bulk‐to‐surface and interfacial charge transfer abilities. Meanwhile, the improved specific surface area and pore structure endow Ti₃C₂/Bi₂WO₆ hybrids with an enhanced CO₂ adsorption capability. As a result, the 2D/2D heterojunction of ultrathin Ti₃C₂/Bi₂WO₆ nanosheets shows significant improvement on the performance of photocatalytic CO₂ reduction under simulated solar irradiation. The total yield of CH₄ and CH₃OH obtained on the optimized Ti₃C₂/Bi₂WO₆ hybrid is 4.6 times that obtained on pristine Bi₂WO₆ ultrathin nanosheets. This work provides a new protocol for constructing 2D/2D photocatalytic systems and demonstrates Ti₃C₂ as a promising and cheap cocatalyst.