Schottky Junction Enhanced Photosynthesis of Hydrogen Peroxide by Ultrathin Porous Carbon Nitride Supported Ni Nanoparticles.

Artificial photosynthesis for high-value hydrogen peroxide (H2O2) through a two-electron reduction reaction is a green and sustainable strategy. However, the development of highly active H2O2 photocatalysts is impeded by severe carrier recombination, ineffective active sites, and low surface reaction efficiency. We developed a dual optimization strategy to load dense Ni nanoparticles onto ultrathin porous graphitic carbon nitride (Ni-UPGCN). In the absence and presence of sacrificial agents, Ni-UPGCN achieved H2O2 production rates of 169 and 4116 µmol g-1 h-1 with AQY (apparent quantum efficiency) at 420 nm of 3.14% and 17.71%. Forming a Schottky junction, the surface-modified Ni nanoparticles broaden the light absorption boundary and facilitate charge separation, which act as active sites, promoting O2 adsorption and reducing the formation energy of *OOH (reaction intermediate). This results in a substantial improvement in both H2O2 generation activity and selectivity. The Schottky junction of dual modulation strategy provides novel insights into the advancement of highly effective photocatalytic agents for the photosynthesis of H2O2.

Screening of Transition Metal Supported on Black Phosphorus as Electrocatalysts for CO2 Reduction.

The electrocatalytic CO2 reduction (CO2RR) is an effective and economical strategy to eliminate CO2 through conversion into value-added chemicals and fuels. However, exploring and screening suitable 2D material-based single-atom catalysts (SACs) for CO2 reduction are still a great challenge. In this study, 27 (3d, 4d, and 5d, except Tc and Hg) transition metal (TM) atom-doped black phosphorus (TM@BP) electrocatalysts were systematically investigated for CO2RR by density functional theory calculations. According to the stability of SACs and their effectiveness in activating the CO2 molecule, three promising catalysts, Zr@BP, Nb@BP, and Ru@BP, were successfully screened out, exhibiting outstanding catalytic activity for the production of carbon monoxide (CO), methyl alcohol (CH3OH), and methane (CH4) with limiting potentials of -0.79, -0.49, and -0.60 V, respectively. A catalytic relationship between the d-band centers of SACs and the limiting potential of CO2RR was used to estimate the catalytic activity of catalysts. Furthermore, Nb@BP has high selectivity for CO2RR to CH3OH compared to H2 formation, while the hydrogen evolution reaction significantly impacts the synthesis of CO and CH4 on Zr@BP and Ru@BP. Nitrogen atom doping in BP is beneficial for enhancing the selectivity of CO2RR, but it is detrimental to the activity of CO2RR. This study offers theoretical guidance for synthesizing highly efficient CO2RR electrocatalysts and further enhances structural modulation methods for layered 2D materials.

Niobium Modification of CeO2 Tuning Electron Density of Nickel-Ceria Interfacial Sites for Enhanced CO2 Methanation.

CO2 methanation has attracted considerable attention as a promising strategy for recycling CO2 and generating valuable methane. This study presents a niobium-doped CeO2-supported Ni catalyst (Ni/NbCe), which demonstrates remarkable performance in terms of CO2 conversion and CH4 selectivity, even when operating at a low temperature of 250 °C. Structural analysis reveals the incorporation of Nb species into the CeO2 lattice, resulting in the formation of a Nb-Ce-O solid solution. Compared with the Ni/CeO2 catalyst, this solid solution demonstrates an improved spatial distribution. To comprehend the impact of the Nb-Ce-O solid solution on refining the electronic properties of the Ni-Ce interfacial sites, facilitating H2 activation, and accelerating the hydrogenation of CO2* into HCOO*, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations were conducted. These investigations shed light on the mechanism through which the activity of CO2 methanation is enhanced, which differs from the commonly observed CO* pathway triggered by oxygen vacancies (OV). Consequently, this study provides a comprehensive understanding of the intricate interplay between the electronic properties of the catalyst's active sites and the reaction pathway in CO2 methanation over Ni-based catalysts.

Theoretical study of transition metal-doped ß12 borophene as a new single-atom catalyst for carbon dioxide electroreduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a viable and cost-effective approach for the elimination of CO2 by transforming it into valuable products. Nevertheless, this process is impeded by the absence of exceptionally active and stable catalysts. Herein, a new type of electrocatalyst of transition metal (TM)-doped ß12-borophene (TM@ß12-BM) is investigated via density functional theory (DFT) calculations. Through comprehensive screening, two promising single-atom catalysts (SACs), Sc@ß12-BM and Y@ß12-BM, are successfully identified, exhibiting high stability, catalytic activity and selectivity for the CO2RR. The C1 products methane (CH4) and methanol (CH3OH) are synthesized with limiting potentials (UL) of -0.78 V and -0.56 V on Sc@ß12-BM and Y@ß12-BM, respectively. Meanwhile, CO2 is more favourable for reduction into the C2 product ethanol (CH3CH2OH) compared to ethylene (C2H4) via C-C coupling on these two SACs. More importantly, the dynamic barriers of the key C-C coupling step are 0.53 eV and 0.73 eV for the "slow-growth" sampling approach in the explicit water molecule model. Furthermore, Sc@ß12-BM and Y@ß12-BM exhibit higher selectivity for producing C1 compounds (CH4 and CH3OH) than C2 (CH3CH2OH) in the CO2RR. Compared with Sc@ß12-BM, Y@ß12-BM demonstrates superior inhibition of the competitive hydrogen evolution reaction (HER) in the liquid phase. These results not only demonstrate the great potential of SACs for direct reduction of CO2 to C1 and C2, but also help in rationally designing high-performance SACs.

Regulation of the Coordination Structures of Transition Metals on Nitrogen-Doped Carbon Nanotubes for Electrochemical CO2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO2RR) has been extensively studied due to its potential to reduce the globally accelerating CO2 emission and produce value-added chemicals and fuels. Despite great efforts to optimize the catalyst activity and selectivity, the development of robust design criteria for screening the catalysts and understanding the role of water and potassium for CO2 activation poses a significant challenge. Herein, a rapid method for screening single-atom catalysts (SACs) possessing different coordination structures toward the CO2RR process to form CO, namely, a metal atom supported on nitrogen-doped carbon nanotubes (M@CNT, M@1N_CNT, M@2N_CNT, and M@3N_CNT), was established using large-scale density functional theory computations. Adopting the free energy of *CO2 and *OH as screening descriptors, Fe@CNT, Cu@1N_CNT, Pd@2N_CNT, and Ni@3N_CNT were found to exhibit high activity for CO in the gas phase with the overpotential values of 0.22, 0.11, 0.13, and 0.05 V, respectively. Water and potassium present on the surface of the active sites can accelerate the activation of CO2 relative to the gas phase. Ni@3N_CNT shows the highest activity and selectivity in the environment having four water and one potassium. Particularly, the least absolute shrinkage and selection operator regression study revealed that the CO2 adsorption is intrinsically governed by the number of electrons lost by the metal atom in the three N-doped systems, which can be correlated to the distance of the metal atom from the plane of the coordination atom in the M@CNT system. Besides, the study proposes equations for the calculation of the free energy of CO2 adsorption. The current work not only advances the exploration of highly active SACs for the heterogeneous electrocatalytic systems for CO2RR but also highlights the significance of water and potassium in the aqueous solution.

Microporous 3D Covalent Organic Frameworks for Liquid Chromatographic Separation of Xylene Isomers and Ethylbenzene.

Microporous covalent organic frameworks (COFs) hold great potential for small molecule separation but are yet challenging to design and synthesize. Here we report a framework interpenetration strategy to make microporous COFs for efficient separations of C8 alkyl-aromatic isomers. Two pairs of microporous three-dimensional (3D) salen- and Zn(salen)-based COFs are prepared by Schiff-base condensation of ethanediamine with tetrahedral tetra(salicylaldehyde)-silane or -methane derivatives in the presence or absence of metal ions. The four 3D COFs are isostructural and have a 7-fold interpenetrated diamondoid open framework with less than 8.0 Å wide tubular channels. They exhibit permanent porosity, high thermal stability, and good chemical resistance. The two COFs functionalized with uncoordinated salen groups can serve as stationary phases for high-performance liquid chromatography to provide baseline separation of xylene isomers and ethylbenzene with excellent column efficiency and precision, whereas the COFs with Zn(salen) motifs cannot achieve high-resolution separation. The salen-COFs showed high affinity to the o-xylene, allowing fast and selective separation of the o-isomer from the other isomers within 7 min. This is the first report utilizing COFs to separate the practically important aromatic isomers. This work highlights new opportunities in designing microporous COFs and paves the way to expand the potential applications of COF materials.

Single and double boron atoms doped nanoporous C2N-h2D electrocatalysts for highly efficient N2 reduction reaction: a density functional theory study.

The electrocatalytical process is the most efficient way to produce ammonia (NH3) under ambient conditions, but developing a highly efficient and low-cost metal-free electrocatalysts remains a major scientific challenge. Hence, single atom and double boron (B) atoms doped 2D graphene-like carbon nitride (C2N-h2D) electrocatalysts have been designed (B@C2N and B2@C2N), and the efficiency of N2 reduction reaction (NRR) is examined by density functional theory calculation. The results show that the single and double B atoms can both be strongly embedded in natural nanoporous C2N with superior catalytic activity for N2 activation. The reaction mechanisms of NRR on the B@C2N and B2@C2N are both following an enzymatic pathway, and B2@C2N is a more efficient electrocatalyst with extremely low overpotential of 0.19 eV comparing to B@C2N (0.29 eV). In the low energy region, the hydrogenation of N2 is thermodynamically more favorable than the hydrogen production, thereby improving the selectivity for NRR. Based on these results, a new double-atom strategy may help guiding the experimental synthesis of highly efficient NRR electrocatalysts.

Atomically dispersed Pd catalysts in graphyne nanopore: formation and reactivity.

The formation of single-atom noble metal catalysts on carbon materials remains a challenge due to the weak interaction between metals and pristine carbon. By means of density functional theory (DFT) calculations, it is found that the atomically dispersed Pd in graphyne nanopore is much more stable than that of relative Pd clusters. The large diffusion barrier of Pd from the most stable hollow site to the bridge site confirms the kinetic stability of such structures. While CO adsorption causes the pulling of Pd from graphyne nanopore due to the low diffusion barrier, based on DFT calculations, which can be further confirmed by ab initio molecular dynamic simulations. Finally, CO oxidation on the reconstruction of Pd@graphyne exhibits an energy barrier of 0.62 eV in the rate-limiting step through the Langmuir-Hinshelwood mechanism. After the reaction, the catalyst can be restored to the original atomically dispersed state again. This study shows graphyne is an excellent support for an atomically dispersed or single-metal catalyst.

Kinetic Research on Catalytic Degradation of Rhodamine B with Cobalt Phthalocyanine Supported Mg-Al Hydrotalcite.

Rhodamine B dye wastewater was degraded using cobalt phthalocyanine supported Mg-Al hydrotal- cite and H2O2. The effects of H2O2, temperature and concentration of Rhodamine B on the reaction kinetics were studied. The results indicate that the degradation process conforms to the equation of first order kinetics. The fastest rate constant k observed was 66.2 x 10⁻4/min⁻¹ at 62.5 °C, and the correlation coefficient R2 was 0.99733.

Revealing the elevation of Zn2+ in the brain of depressed mice by a ratiometric fluorescent probe with dual near-infrared emissions.

A mitochondria-targeted ratiometric fluorescent probe (Mito-Zn) was first designed and synthesized with dual emissions both located in the near-infrared region, for Zn2+ detection with high sensitivity and selectivity. By using the developed Mito-Zn, a high level of Zn2+ in the depressed mouse brain was discovered for the first time.

Interfacial Electronic Interactions Between Ultrathin NiFe-MOF Nanosheets and Ir Nanoparticles Heterojunctions Leading to Efficient Overall Water Splitting.

Creating specific noble metal/metal-organic framework (MOF) heterojunction nanostructures represents an effective strategy to promote water electrolysis but remains rather challenging. Herein, a heterojunction electrocatalyst is developed by growing Ir nanoparticles on ultrathin NiFe-MOF nanosheets supported by nickel foam (NF) via a readily accessible solvothermal approach and subsequent redox strategy. Because of the electronic interactions between Ir nanoparticles and NiFe-MOF nanosheets, the optimized Ir@NiFe-MOF/NF catalyst exhibits exceptional bifunctional performance for the hydrogen evolution reaction (HER) (η10 = 15 mV, η denotes the overpotential) and oxygen evolution reaction (OER) (η10 = 213 mV) in 1.0 m KOH solution, superior to commercial and recently reported electrocatalysts. Density functional theory calculations are used to further investigate the electronic interactions between Ir nanoparticles and NiFe-MOF nanosheets, shedding light on the mechanisms behind the enhanced HER and OER performance. This work details a promising approach for the design and development of efficient electrocatalysts for overall water splitting.

Single and double transition metal atoms doped graphdiyne for highly efficient electrocatalytic reduction of nitric oxide to ammonia.

The electrocatalytic conversion of nitric oxide (NORR) to ammonia (NH3) represents a pivotal approach for sustainable energy transformation and efficient waste utilization. Designing highly effective catalysts to facilitate the conversion of NO into NH3 remains a formidable challenge. In this work, the density functional theory (DFT) is used to design NORR catalysts based on single and double transition metal (TM:Fe, Co, Ni and Cu) atoms supported by graphdiyne (TM@GDY). Among eight catalysts, the Cu2@GDY is selected as a the most stable NORR catalyst with high NH3 activity and selectivity. A pivotal discovery underscores that the NORR mechanism is thermodynamically constrained on single atom catalysts (SACs), while being governed by electrochemical processes on double atom catalysts (DACs), a distinction arising from the different d-band centers of these catalysts. Therefore, this work not only introduces an efficient NORR catalyst but also provides crucial insights into the fundamental parameters influencing NORR performance.

Thermal evaporation-driven fabrication of Ru/RuO2 nanoparticles onto nickel foam for efficient overall water splitting.

Developing high-performance bifunctional electrocatalysts towards the hydrogen evolution reaction/oxygen evolution reaction (HER/OER) holds great significance for efficient water splitting. This work presents a two-stage metal-organic thermal evaporation strategy for the fabrication of Ru-based catalysts (Ru/NF) through growing ruthenium (Ru)/ruthenium dioxide (RuO2) nanoparticles (NPs) on nickel foam (NF). The optimal Ru/NF shows remarkable performance in both the HER (26.1 mV) and the OER (235.4 mV) at 10 mA cm-2 in an alkaline medium. The superior OER performance can be attributed to the synergistic interaction between Ru and RuO2, facilitating fast alkaline water splitting. Density functional theory studies reveal that the resulting Ru/RuO2 with the (110) crystal surface reinforces the adsorption of oxygen on RuO2, while metallic Ru improves water dissociation in alkaline electrolytes. Besides, Ru/NF requires only 1.50 V at 10 mA cm-2 for overall water splitting, surpassing 20 wt% Pt/C/NF||RuO2/NF. This work demonstrates the promising potential of a thermal evaporation approach for designing stable Ru-based nanomaterials loaded onto conductive substrates for high performance overall water splitting.

Titanium carbide sealed cadmium sulfide quantum dots on carbon, oxygen-doped boron nitride for enhanced and durable photochemical carbon dioxide reduction.

Despite great efforts that have been made, photocatalytic carbon dioxide (CO2) reduction still faces enormous challenges due to the sluggish kinetics or disadvantageous thermodynamics. Herein, cadmium sulfide quantum dots (CdS QDs) were loaded onto carbon, oxygen-doped boron nitride (BN) and encapsulated by titanium carbide (Ti3C2, MXene) layers to construct a ternary composite. The uniform distribution of CdS QDs and the tight interfacial interaction among the three components could be achieved by adjusting the loading amounts of CdS QDs and MXene. The ternary 100MX/CQ/BN sample gave a productive rate of 2.45 and 0.44 µmol g-1 h-1 for carbon monoxide (CO) and methane (CH4), respectively. This CO yield is 1.93 and 6.13 times higher than that of CdS QDs/BN and BN counterparts. The photocatalytic durability of the ternary composite is significantly improved compared with CdS QDs/BN because MXene can protect CdS from photocorrosion. The characterization results demonstrate that the excellent CO2 adsorption and activation capabilities of BN, the visible light absorption of CdS QDs, the good conductivity of MXene and the well-matched energy band alignment jointly promote the photocatalytic performance of the ternary catalyst.

Structure-activity relationship of Cu-based catalysts for the highly efficient CO2 electrochemical reduction reaction.

Electrocatalytic carbon dioxide reduction (CO2RR) is a relatively feasible method to reduce the atmospheric concentration of CO2. Although a series of metal-based catalysts have gained interest for CO2RR, understanding the structure-activity relationship for Cu-based catalysts remains a great challenge. Herein, three Cu-based catalysts with different sizes and compositions (Cu@CNTs, Cu4@CNTs, and CuNi3@CNTs) were designed to explore this relationship by density functional theory (DFT). The calculation results show a higher degree of CO2 molecule activation on CuNi3@CNTs compared to that on Cu@CNTs and Cu4@CNTs. The methane (CH4) molecule is produced on both Cu@CNTs and CuNi3@CNTs, while carbon monoxide (CO) is synthesized on Cu4@CNTs. The Cu@CNTs showed higher activity for CH4 production with a low overpotential value of 0.36 V compared to CuNi3@CNTs (0.60 V), with *CHO formation considered the potential-determining step (PDS). The overpotential value was only 0.02 V for *CO formation on the Cu4@CNTs, and *COOH formation was the PDS. The limiting potential difference analysis with the hydrogen evolution reaction (HER) indicated that the Cu@CNTs exhibited the highest selectivity of CH4 among the three catalysts. Therefore, the sizes and compositions of Cu-based catalysts greatly influence CO2RR activity and selectivity. This study provides an innovative insight into the theoretical explanation of the origin of the size and composition effects to inform the design of highly efficient electrocatalysts.

Recent advances in the theoretical studies on the electrocatalytic CO2 reduction based on single and double atoms.

Excess of carbon dioxide (CO2) in the atmosphere poses a significant threat to the global climate. Therefore, the electrocatalytic carbon dioxide reduction reaction (CO2RR) is important to reduce the burden on the environment and provide possibilities for developing new energy sources. However, highly active and selective catalysts are needed to effectively catalyze product synthesis with high adhesion value. Single-atom catalysts (SACs) and double-atom catalysts (DACs) have attracted much attention in the field of electrocatalysis due to their high activity, strong selectivity, and high atomic utilization. This review summarized the research progress of electrocatalytic CO2RR related to different types of SACs and DACs. The emphasis was laid on the catalytic reaction mechanism of SACs and DACs using the theoretical calculation method. Furthermore, the influences of solvation and electrode potential were studied to simulate the real electrochemical environment to bridge the gap between experiments and computations. Finally, the current challenges and future development prospects were summarized and prospected for CO2RR to lay the foundation for the theoretical research of SACs and DACs in other aspects.

Radical-Based cis-Selective Annulations of N,N'-Cyclic Azomethine Imines with N-Sulfonyl Cyclopropylamines.

Azomethine imines, broadly known as 1,3-dipoles, efficiently produce synthetically and biologically significant dinitrogen-fused heterocycles via predominantly concerted or ionic pathways. Herein, we describe a radical-based annulation of azomethine imines utilizing visible-light photoredox catalysis for the first time. This strategy enables the synthesis of dinitrogen-fused saturated six-membered cyclic products that have traditionally been difficult to access. Notably, our process exhibits exceptional cis diastereoselectivity, controlled by the anomeric effect. Initial mechanistic investigations reveal a tandem process comprising intermolecular radical addition and intramolecular 6-exo-trig cyclization. This work illustrates potential within the realm of visible-light-driven radical cyclization reactions involving azomethine imines.

The construction of lattice-matched CdS-Ag2S heterojunction photocatalysts: High-intensity built-in electric field effectively boosts bulk-charge separation efficiency.

The built-in electric field of heterojunction can effectively promote carrier separation and transfer. While, its interface orientation is often random, leading to lattice mismatch and high resistance, thus limiting the efficiency of interfacial charge transfer. Herein, the lattice-matched heterojunction (CdS-Ag2S) was constructed by ion-exchange epitaxial growth. The results of surface photovoltage spectroscopy (SPV), transient photovoltage spectroscopy (TPV), and time-resolved photoluminescence (TRPL) show that the lattice-matched heterojunction has higher charge separation efficiency and longer photogenerated carrier lifetime than that of lattice-mismatched one. The lattice-matched CdS-Ag2S has a high built-in electric field (BIEF) value of 103.42 and a bulk-charge separation (BCS) efficiency of 68.71%, which is about three times higher than that of the lattice-mismatched heterojunction (CdS-Ag2S-M). In addition, the photodegradation efficiency of CdS-Ag2S towards norfloxacin (NOR) was also 3.4 times higher than that of CdS-Ag2S-M. The above results and density functional theory (DFT) calculations indicate that improving the lattice matching at the heterojunction is beneficial for establishing a high-intensity built-in electric field and effectively promoting bulk-charge separation efficiency, thus achieving excellent photocatalytic performance. This work provides an essential reference for the research of high-performance heterojunction photocatalysts.

Phase-Engineered Robust Cocatalyst of NiFe Bicarbonate with Pt Dopant for Enhanced Photocatalytic Water Splitting.

Exploring efficient cocatalysts capable of accelerating surface catalytic reaction is of great significance for the development of solar-driven hydrogen production. Herein, on the basis of NiFe hydroxide, we developed a series of Pt doped NiFe-based cocatalysts to promote the photocatalytic hydrogen production of graphitic carbon nitride (g-C3 N4 ). We find that the Pt doping can trigger phase reconstruction of NiFe hydroxide and lead to the formation of NiFe bicarbonate, which displays higher catalytic activity toward hydrogen evolution reaction (HER). The Pt doped NiFe bicarbonate modified g-C3 N4 shows excellent photocatalytic activity with H2 evolution rate up to 100 µmol/h, which is more than 300 times that of pristine g-C3 N4 . The experimental and calculation results demonstrate that the greatly improved photocatalytic HER activity of g-C3 N4 is not only due to the efficient carrier separation, but also attributed to the accelerated HER kinetics. Our work may provide guidance for designing novel and superior photocatalysts.

Construction adsorption and photocatalytic interfaces between C, O co-doped BN and Pd-Cu alloy nanocrystals for effective conversion of CO2 to CO.

Photocatalytic reduction of carbon dioxide (CO2) into fuels is an auspicious route to alleviate the energy and environmental crisis brought by the continuous depletion of fossil fuels. The CO2 adsorption state on the surface of photocatalytic materials plays a significant role in its efficient conversion. The limited CO2 adsorption capacity of conventional semiconductor materials inhibit their photocatalytic performances. In this work, a bifunctional material for CO2 capture and photocatalytic reduction was fabricated by introducing palladium (Pd)-copper (Cu) alloy nanocrystals onto the surface of carbon, oxygen co-doped boron nitride (BN). The elemental doped BN with abundant ultra-micropores had high CO2 capture ability, and CO2 was adsorbed in the form of bicarbonate on its surface with the presence of water vapor. The Pd/Cu molar ratio had great impact on the grain size of Pd-Cu alloy and their distribution on BN. The CO2 molecules tended to be converted to carbon monoxide (CO) at interfaces of BN and Pd-Cu alloys due to their bidirectional interactions to the adsorbed intermediate species while methane (CH4) evolution might occur on the surface of Pd-Cu alloys. Owing to the uniform distribution of smaller Pd-Cu nanocrystals on BN, more effective interfaces were created in the Pd5Cu1/BN sample and it gave a CO production rate of 7.74 µmolg-1h-1 under simulated solar light irradiation, higher than the other PdCu/BN composites. This work can pave a new way for constructing effective bifunctional photo-catalysts with high selectivity to convert CO2 to CO.