Low-loading gold in situ doped with sulfur by biomolecule-assisted approach for promoted electrochemical carbon dioxide reduction

For electrochemical carbon dioxide reduction(CO_(2)RR),CO_(2)-to-CO conversion is considered an ideal route towards carbon neutrality for practical applications.Gold(Au)is known as a promising catalyst with high selectivity for CO;however,it suffers from high cost and low mass-specific activity.In this study,we design and prepare a catalyst featuring uniform S-doped Au nanoparticles on N-doped carbon support(denoted as S-Au/NC)by an in situ synthesis strategy using biomolecules.The S-Au/NC displays high activity and selectivity for CO in CO_(2)RR with a Au loading as low as 0.4 wt.%.The Faradaic efficiency of CO(FECO)for S-Au/NC is above 95%at−0.75 V(vs.RHE);by contrast,the FECO of Au/NC(without S)is only 58%.The Tafel slope is 77.4 mV·dec−1,revealing a favorable kinetics process.Furthermore,S-Au/NC exhibits an excellent long-term stability for CO_(2)RR.Density functional theory(DFT)calculations reveal that the S dopant can boost the activity by reducing the free energy change of the potential-limiting step(formation of the*COOH intermediate).This work not only demonstrates a model catalyst featuring significantly reduced use of noble metals,but also establishes an in situ synthesis strategy for preparing high-performance catalysts.

Engineering Coordination Environment of Cobalt Center in Molecular Catalysts for Improved Photocatalytic CO_(2) Reduction

The creation of effective and inexpensive catalysts is essential for photocatalytic CO_(2) reduction.Homogeneous molecular catalysts,possessing definite crystal structures,are desirable to study the relationship between catalytic performance and coordination microenvironment around catalytic center.In this report,we elaborately developed three Co(II)-based molecular catalysts with different coordination microenvironments for CO_(2) reduction,named[CoN_(3)O]ClO_(4),[CoN_(4)]ClO_(4),and[CoN_(3)S]ClO_(4),respectively.The optimal[CoN_(3)O]ClO_(4) photocatalyst has a maximum TON of 5652 in photocatalytic reduced CO_(2) reduction,which is 1.28 and 1.65 times greater than that of[CoN_(4)]ClO_(4) and[CoN_(3)S]ClO_(4),respectively.The high electronegativity of oxygen in L1(N,N-bis(2-pyridylmethyl)-N-(2-hydroxybenzyl)amine)provides the Co(II)catalytic centers with low reduction potentials and a more stable*COOH intermediate,which facilitates the CO_(2)-to-CO conversion and accounts for the high photocatalytic activity of[CoN_(3)O]ClO_(4).This work provides researchers new insights in development of catalysts for photocatalytic CO_(2) reduction.

Single titanium-oxide species implanted in 2D g-CsN4 matrix as a highly efficient visible-light CO2 reduction photocatalyst

A visible-light-response, efficie nt and robust photo-catalyst for CO2 reduction is highly desirable. Herein, we demonstrate that single titanium-oxide species impla nted in two-dime nsion al (2D) graphitic carb on n itride (g-C3N4) matrix (2D TiO-CN) can efficie ntly photo-catalyze the reduction of CO2 to CO under the irradiation of visible light. The synergistic interaction between single titanium oxide species and g-C3N4 in 2D TiO-CN not only enhances the separation of photo-excited charges, but also results in visible light response of single titanium-oxide species, realizing high activity of CO2 photo-reduction with extremely high CO generation rate of 283.9 pmol·h^-1·g^-1, 5.7, 6.8 and 292.2 times larger than those of TQ2/CN hybrid material, CN and commercial TiO2, respectively. Time-resolved fluoresce nee and electron spin resonance spectroscopy revealed the catalytic mechanism of the fabricated 2D TiO-CN photocatalysts for CO2 reduction.

Direct imaging and determination of the crystal structure of six-layered graphdiyne

Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the crystal structure of a six-layered graphdiyne nanosheet was directly observed by low-voltage transmission electron microscopy （TEM） using low current density. The combined use of high-resolution TEM （HRTEM） simulation, electron energy-loss spectroscopy, and electron diffraction revealed that the as-synthesized nanosheet was crystalline graphdiyne with a thickness of 2.19 nm （corresponding to a thickness of six layers） and showed ABC stacking. Thus, this work provides direct evidence for the existence and crystal structure of few-layer graphdiyne, which is a new type of two-dimensional carbon material complementary to graphene.

Enhancing photocatalytic performance of metal-organic frameworks for CO_(2) reduction by a bimetallic strategy

Metal-organic frameworks(MOFs) as a type of crystalline heterogeneous catalysts have shown potential application in photocatalytic CO_(2)reduction.However,MOF catalysts with high efficiency and selectivity are still in pursuit.Herein,by a bimetallic strategy,the catalytic performance of a Co-MOF for photocatalytic CO_(2)reduction was enhanced.Specifically,the Co-MOF based on 4,5-dicarboxylic acid(H;IDC) and4,4’-bipydine(4,4’-bpy) can catalyze CO;reduction to CO,with high efficiency but relatively low selectivity.After replacement of 2/3 Co(Ⅱ) with Ni(Ⅱ) within Co-MOF,the resulted isostructural Co_(1)Ni_(2)-MOF not only retains high efficiency for photocatalytic CO_(2)reduction,but also shows enhanced CO selectivity.The CO evolution rate reaches 1160 μmol g^(-1)h^(-1)and the CO selectivity reaches as high as 94.6%.The enhanced photocatalytic CO_(2)reduction performance is supported by theoretical calculation results.This case demonstrates that bimetallic strategy is an effective mean to optimize the catalytic performance of MOF catalysts for photochemical CO_(2)reduction.

Acetate-assistant efficient cation-exchange of halide perovskite nanocrystals to boost the photocatalytic CO_(2) reduction

The judicious implantation of active metal cations into the surface of semiconductor nanocrystal(NC)through cation-exchange is one of the facile and viable strategies to enhance the activity of catalysts for photocatalytic CO_(2)reduction,by shortening the transfer pathway of photogenerated carriers and increasing the active sites simultaneously.However,cation-exchange is hard to achieve for halide perovskite NCs owing to the stable octahedron of[PbX6]4−with strong interaction between halogen and lead.Herein,we report a facile method to overcome this obstacle by replacing partial Br−with acetate(Ac−)to generate CsPbBr_(3) NC(coded as CsPbBr_(3−x)Ac_(x)).A small amount of Ac−instead of Br−does not change the crystal structure of halide perovskite.Owing to the weaker interaction between acetate and lead in comparison with bromide,the corresponding octahedron structure containing acetate in CsPbBr_(3−x)Ac_(x) can be easily opened to realize efficient cation-exchange with Ni^(2+) ions.The resulting high loading amount of Ni^(2+) as active site endows CsPbBr_(3−x)Ac_(x) with an improved performance for photocatalytic CO_(2)reduction under visible light irradiation,exhibiting a significantly increased CO yield of 44.09μmol·g^(−1)·h^(−1),which is over 8 and 3 times higher than those of traditional pristine CsPbBr_(3) and nickel doped CsPbBr_(3) NC,respectively.This work provides a critical solution for the efficient metal doping of low-cost halide perovskite NCs to enhance their photocatalytic activity,promoting their practical applications in the field of photocatalysis.

Co-POM@MOF-derivatives with trace cobalt content for highly efficient oxygen reduction

A simple and effective method for constructing highly efficient oxygen reduction catalysts with trace amount of isolated cobalt was firstly developed by the pyrolysis of Co-centered polyoxometalate@metalorganic framework (Co-POM@MOF).The Co-centered polyoxometalate ([Co W_(12)O_(40)]^(6-)) was confined in the well-defined void space of ZIF-8 to achieve homogeneous dispersion of polyoxoanions,where the isolated Co centers were well surrounded by the W-O shell and ZIF-8 framework.The Co-POM@MOF-derived N-doping porous carbon (Co-W-NC) with trace cobalt content was facilely prepared by the pyrolysis of the Co-POM@MOF under Ar atmosphere.The single dispersion of polyoxoanions in the metal-organic framework with complete separation of Co center surrounding by W-O shell and ZIF-8 framework ensures the uniform dispersion of Co atoms,confirmed by the Fourier transform extended X-ray absorption fine structure measurement.The Co-W-NC composite catalysts exhibit high performance for oxygen reduction reactions with a half-wave potential of 0.835 V in 0.1 mol/L KOH solution with excellent durability,which is much superior to that of the control samples derived from the[PW_(12)O_(40)]@ZIF-8,and the commercial Pt/C.This work highlights a new insight for constructing highly efficient catalysts via the introduction of metal-centered polyoxometalate into metal-organic framework following the high temperature treatment process.

Iron sites on defective BiOBr nanosheets:Tailoring the molecular oxygen activation for enhanced photocatalytic organic synthesis

Sunlight-driven activation of molecular oxygen(O_(2))for organic oxidation reactions offers an appealing strategy to cut down the reliance on fossil fuels in chemical industry,yet it remains a great challenge to simultaneously tailor the charge kinetics and promote reactant chemisorption on semiconductor catalysts for enhanced photocatalytic performance.Herein,we report iron sites immobilized on defective BiOBr nanosheets as an efficient and selective photocatalyst for activation of O_(2) to singlet oxygen(^(1)O_(2)).These Fe^(3+) species anchored by oxygen vacancies can not only facilitate the separation and migration of photogenerated charge carrier,but also serve as active sites for effective adsorption of 02.Moreover,low-temperature phosphorescence spectra combined with X-ray photoelectron spectroscopy(XPS)and electronic paramagnetic resonance(EPR)spectra under illumination reveal that the Fe species can boost the quantum yield of excited triplet state and accelerate the energy transfer from excited triplet state to adsorbed O2 via a chemical loop of Fe^(3+)/Fe^(2+),thereby achieving highly efficient and selective generation of ^(1)O_(2).As a result,the versatile iron sites on defective BiOBr nanosheets contributes to near-unity conversion rate and selectivity in both aerobic oxidative coupling of amines to imines and sulfoxidation of organic sulfides.This work highlights the significant role of metal sites anchored on semiconductors in regulating the charge/energy transfer during the heterogeneous photocatalytic process,and provides a new angle for designing high-performance photocatalysts.

New Crystalline Forms of Mebendazole with n-Alkyl Carboxylic Acids Neutral and Ionic Status

Structural information on the crystalline forms of mebendazole, an anti-parasitic drug, is limited, although three polymorphic forms of this drug have been reported. The present work investigates the structures and properties of different crystalline forms of mebendazole with a series of n-alkyl carboxylic acids, including trifluroacetic acid （1）, formic acid （2）, acetic acid （3）, propanoic acid （4）, butanoic acid （5）, valeric acid （6） and hexanoic acid （7）. These compounds were characterized by thermogravimetric analysis, IR spectra, as well as powder and single-crystal X-ray diffraction analysis. The R22（8） structural motif was detected in all the seven products, which was formed by a pair of N--H…O/O--H…N hydrogen bonds between mebendazole and carboxylic acid. Forms 3--7 were found to be neutral solvate, while in forms 1 and 2, proton transfer was observed from carboxylic acid to mebendazole.

Homogeneous Electrocatalytic Water Oxidation by a Rigid Macrocyclic Copper（Ⅱ） Complex

A copper（Ⅱ） complex with a rigid macrocyclic ligand has been synthesized and utilized as a homogeneous electrocatalyst for water oxidation in sodium phosphate buffer at pH 12,0.By using a glassy carbon electrode in a 3 h electrolysis,a high current density of 1.3-1.4 mA/cm2 and a turn-over number of 4 can be obtained with 1.0 mmol·L-1 of the copper catalyst at an overpotential of 750 mV.Kinetic studies revealed that the electrocatalysis with this complex is a single-site catalysis with proton-coupled electron transfers.Finally,its possible catalytic mechanism was tentatively proposed.