Insights into electrochemical nitrogen reduction reaction mechanisms:Combined effect of single transition-metal and boron atom

Developing single-atom catalysts(SACs) for electrochemical devices is a frontier in energy conversion.The comparison of stability,activity and selectivity between various single atoms is one of the main research focuses in SACs.However,the in-depth understanding of the role that the coordination atoms of single atom play in the catalytic process is lacking.Herein,we proposed a graphene-like boroncarbon-nitride(BCN) monolayer as the support of single metal atom.The electrocatalytic nitrogen reduction reaction(eNRR) performances of 3 d,4 d transition metal(TM) atoms embedded in defective BCN were systematically investigated by means of density functional theory(DFT) computations.Our study shows that the TM-to-N and B-to-N π-back bonding can contribute to the activation of N_(2).Importantly,a combined effect is revealed between single TM atom and boron atom on eNRR:TM atom enhances the nitrogen reduction process especially in facilitating the N_(2) adsorption and the NH3 desorption,while boron atom modulates the bonding strength of key intermediates by balancing the charged species.Furthermore,Nb@BN3 possesses the highest electrocata lytic activity with limiting potential of-0.49 V,and exhibits a high selectivity for nitrogen reduction reaction(NRR) to ammonia compared with hydrogen evolution reaction(HER).As such,this work can stimulate a research doorway for designing multi-active sites of the anchored single atoms and the innate atoms of substrate based on the mechanistic insights to guide future eNRR research.

Microemulsion Synthesis of Mesoporous β-tricalcium Phosphate Powder with a Novel System

The synthesis of mesoporous β-tricalcium phosphate(β-TCP)powder was performed by using the microemulsion approach,with hexadecyltrimethyl ammonium bromide(CTAB)/cyclohexane/n-octyl alcohol microemulsion system.The influences of different pH values and calcination temperatures on the phase composition of the β-TCP powder were studied.The in vitro proliferation of bone marrow mesenchymal stem cells(BMSCs)in the suspensions of β-TCP powders with meso-structure was studied.The phase composition,mesoporous structure,powder morphology,cell morphology and the optical density(OD)were characterized through X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),Fourier transform infrared(FTIR)spectroscopy,Nadsorption-desorption isotherms,inverted phase contrast microscopy and Multiskan spectrum,respectively.The mesoporous β-TCP powder with specific surface area of 12.85 m^(2)/g and the average pore size 7.11 nm was obtained through the microemulsion approach(100 g/L CTAB/250 mL/L cyclohexane/250 mL/L n-octyl alcohol)with a controlled pH of 7.0,after calcinating the powder at 800℃.It was confirmed that mesoporous β-TCP powder benefits the activity of BMSCs more than the non-mesoporous β-TCP powder.

Na_(2)O/Li_(2)O Ratio Dependency on the Thermal,Mechanical,Dielectric Properties and Chemical Stabilities of Li_(2)O-Al_(2)O_(3)-SiO_(2) Glass

Li_(2)O-Al_(2)O_(3)-SiO_(2) based glasses were investigated as potential protection glass for electronic devices due to their excellent mechanical properties,such as high hardness,toughness,and scratch resistance.In this paper,Li_(2)O-Na_(2)O-Al_(2)O_(3)-SiO_(2) glass with different Li_(2)O/Na_(2)O ratio components were prepared by meltquenching method,and the effects of Na_(2)O/Li_(2)O ratio on the glass densities,structure,thermal,mechanical properties,and chemical stabilities were studied.The experimental results indicate that the glass transition temperature increases with the increases in Na_(2)O/Li_(2)O ratios,due to larger ion radius.While the thermal expansion coefficient slightly decreases from 11.4×10^(-6) to 11.09×10^(-6)/℃.The elastic modulus increases from 57 to 72 GPa.The bending strength reaches maximum 80.90 MPa when the Na_(2)O/Li_(2)O ratio is 1.7,then decreases as the ratio further increases.In addition,the Vicker’s hardness gets to 7.37 GPa with largest Na_(2)O/Li_(2)O ratio.Moreover,the dielectric loss and dielectric constant increases as the ratio increases.The Raman structure analysis shows the Q4[Si-O-Si]decreases as Na_(2)O/Li_(2)O ratio increases,which is responsible for the characteristic properties change.Moreover,the glass shows lowest mass loss in 10vol%HF solutions when the ratio is 1.4,while 1.7 in 5wt%NaOH solution.

Effect of Fe_(2)O_(3)on the Structure,Physical Properties and Crystallization of CaO-Al_(2)O_(3)-SiO_(2)Glass

The calcium aluminosilicate-based glasses(CaO-Al_(2)O_(3)-SiO_(2),CAS)with different Fe_(2)O_(3)content(0.10wt%,0.50wt%,0.90wt%,and 1.30wt%)were prepared by traditional melt-quenching method.The glass network structure,thermal and mechanical properties,and crystallization behavior changes were investigated by nuclear magnetic resonance spectrometer,Fourier-transform infrared spectro-photometer,X-ray diffractometer,differential scanning calorimetry and field emission scanning electron microscope measurements.The change of Q^(n)in glass structures reveals the glass network connectivity decreases due to the increasing content of Fe_(2)O_(3)addition,resulting in the increasing of non-bridging number in glass structure.The glass densities slightly rise from 2.644 to 2.681 g/cm^(3),while Vickers’s hardness increases at first,from 6.469 to 6.901 GPa,then slightly drops to 6.745 GPa,with Fe_(2)O_(3)content increase.There is almost no thermal expansion coefficient change from different Fe_(2)O_(3)content.The glass transmittance in visible range gradually decreases with higher Fe_(2)O_(3)content,resulting from the strong absorption of Fe^(2+)and Fe^(3+)ions.The calculated activation energy from thermal analysis results first decreases from 282.70 to 231.18 kJ/mol,and then increases to 244.02 kJ/mol,with the Fe_(2)O_(3)content increasing from 0.10wt%to 1.30wt%.Meanwhile,the maximum Avrami constant of 2.33 means the CAS glasses exhibit two-dimensional crystallization.All of the CAS glass-ceramics samples contain main crystal phase of anorthite,the microstructure appears lamellar and columnar crystals.

Evaluation of activated sludge properties’changes in industrial-wastewater pre-treatment:role of residual aluminum hydrolyzed species with different polymerization degree

With the widespread introduction of pre-coagulation prior to the biological unit in various industrial wastewater treatments,it is noteworthy that long-term accumulation of residual coagulants has certains effect on both micro and macro characteristics of activated sludge(AS).In this study,the morphology distributions of residual aluminum salts(RAS)and their effects on the removal efficiency of AS were investigated under different PAC concentrations.The results showed that the dominance of medium polymeric RAS,formed under an appropriate PAC dose of 20 mg/L enhanced the hydrophobicity,flocculation,and sedimentation performances of AS,as well as the enzymatic activity in cells in the sludge system,improving the main pollutants removal efficiency of the treatment system.Comparatively the species composition with monomer and dimer/high polymer RAS as the overwhelming parts under an over-dosed PAC concentration of 55 mg/L resulted in excessive secretion of EPS with loose flocs structure and conspicuous inhibition of cellular activity,leading to the deterioration of physico-chemical and biological properties of AS.Based on these findings,this study can shed light on the role of the RAS hydrolyzed species distributions,closely relevant to Al dosage,in affecting the comprehensive properties of AS and provide a theoretical reference for coagulants dosage precise control in the pretreatment of industrial wastewater.

Computational screening study of double transition metal carbonitrides M′_(2)M″CNO_(2)-MXene as catalysts for hydrogen evolution reaction

Two-dimensional(2D)transition metal carbonitrides(MXene)have attracted growing interest in electrocatalytic hydrogen production due to its structural and electronic properties.In this work,the hydrogen evolution reaction(HER)activity of all 64 Oterminated ordered double transition metal carbonitrides in the form of M′_(2)M″CNO_(2)(M′=Ti,V,Cr,Zr,Nb,Mo,Hf,Ta;M″=Ti,V,Cr,Zr,Nb,Mo,Hf,Ta)has been investigated by well-defined density functional theory(DFT)calculations.The results indicate that there are 11M′_(2)M″CNO_(2)-MXene candidates whose HER performance is superior to that of Pt.Moreover,according to the stability screening,it is proved that Ti_(2)NbCNO_(2),Mo_(2)TiCNO_(2),and Ti_(2)VCNO_(2) are more stable than other candidates.Especially,Ti_(2)NbCNO_(2) have the potential to be perfect HER catalyst with the small Gibbs free energies of hydrogen adsorption(ΔGH)value of 0.02 eV,abundant catalytic sites on the C-side,and better stability.This work paves the way on designing excellent HER catalyst candidates based on M′_(2)M″CNO_(2)-MXenes.

Effects of groove-textured surfaces filled with Sn-Ag-Cu and MXene-Ti_(3)C_(2) composite lubricants on tribological properties of CSS-42L bearing steel

To improve the tribological performance of CSS-42L bearing steel,smooth surfaces(SSs),groovetextured surfaces(GSs),GSs with Sn-Ag-Cu(GSs-SAC),and GSs with Sn-Ag-Cu-Ti_(3)C_(2)(GSs-SACT)were prepared on CSS-42L.In addition,experimental studies were conducted on tribological properties.The obtained results indicated that GSs-SACT exhibited the best anti-friction and noise reduction performances.These remarkable tribological performances were attributed to the synergistic effects of grooves,Sn-Ag-Cu,and MXene-Ti_(3)C_(2).The inconsistent rules of frictional forces were improved by the grooves and SACT,which inhibit the friction-induced noise.The micro-nano size-effects of MXene-Ti_(3)C_(2) enhanced the repairing effect and anti-friction property of composite lubricants,which improved the profile characteristics of GSs-SACT.

Bioactive citrate-based polyurethane tissue adhesive for fast sealing and promoted wound healing

As a superior alternative to sutures,tissue adhesives have been developed significantly in recent years.However,existing tissue adhesives struggle to form fast and stable adhesion between tissue interfaces,bond weakly in wet environments and lack bioactivity.In this study,a degradable and bioactive citrate-based polyurethane adhesive is constructed to achieve rapid and strong tissue adhesion.The hydrophobic layer was created with polycaprolactone to overcome the bonding failure between tissue and adhesion layer in wet environments,which can effectively improve the wet bonding strength.This citrate-based polyurethane adhesive provides rapid,non-invasive,liquid-tight and seamless closure of skin incisions,overcoming the limitations of sutures and commercial tissue adhesives.In addition,it exhibits biocompatibility,biodegradability and hemostatic properties.The degradation product citrate could promote the process of angiogenesis and accelerate wound healing.This study provides a novel approach to the development of a fast-adhering wet tissue adhesive and provides a valuable contribution to the development of polyurethane-based tissue adhesives.

富氧空位修饰的铋氧硫晶体用于光催化二氧化碳还原转化为甲烷

制备高效光催化剂将二氧化碳还原转化为有价值的化学品,是缓解能源危机和环境污染的有效措施.本论文通过高温焙烧法,制备了富氧空位修饰的Bi_(2)O_(2)S光催化剂,并将其用于可见光驱动的CO_(2)光还原,确定了富氧空位修饰的Bi_(2)O_(2)S光催化剂的最佳制备条件.通过一系列实验及表征,证实了BiOS-OV中丰富氧空位的存在;结合理论计算深入分析了引入的丰富氧空位对Bi_(2)O_(2)S光催化剂的内部电子结构及光化学性能等的影响.深入研究了整个体系中光催化CO_(2)还原反应的具体步骤,旨在揭示丰富氧空位的存在引起CO_(2)光还原性能提高的根本原因.

Iron oxide nanoparticles with photothermal performance and enhanced nanozyme activity for bacteria-infected wound therapy

Metal-based nanomaterials usually have broad-spectrum antibacterial properties,low biological toxicity and no drug resistance due to their intrinsic enzyme-like catalytic properties and external field(magnetic,thermal,acoustic,optical and electrical)responsiveness.Herein,iron oxide(Fe_(3)O_(4))nanoparticles(IONPs)synthesized by us have good biosafety,excellent photothermal conversion ability and peroxidase-like catalytic activity,which can be used to construct a photothermal-enzymes combined antibacterial treatment platform.IONPs with peroxide-like catalytic activity can induce H_(2)O_(2)to catalyze the production of·OH in a slightly acidic environment,thus achieving certain bactericidal effects and increasing the sensitivity of bacteria to heat.When stimulated by near-infrared light,the photothermal effect could destroy bacterial cell membranes,resulting in cleavage and inactivation of bacterial protein,DNA or RNA.Meanwhile,it can also improve the catalytic activity of peroxidase-like and promote IONPs to catalyze the production of more·OH for killing bacteria.After IONPs synergistic treatment,the antibacterial rate of Escherichia coli and Staphylococcus aureus reached nearly 100%.It also has an obvious killing effect on bacteria in infected wounds of mice and can effectively promote the healing of S.aureusinfected wounds,which has great application potential in clinical anti-infection treatment.

Uncovering the Mechanism for Urea Electrochemical Synthesis by Coupling N2 and CO_(2) on Mo2C-MXene

In this work, the catalytic activities of MoC-MXene for the co-synthesis of urea from Nand COare reported by well-defined density functional theory(DFT) method. The calculated results show that the presence of surface functional groups is not conducive to the CO/N(C/N) coupling process in urea synthesis reaction. The exposed MoC on the surface can realize urea synthesis at the limit point of 0.69 eV, but the large transition state energy barrier(1.50 eV)indicates that bare MoC is not a promising urea catalyst. Loading single atoms can improve the urea synthesis performance of bare MoC. The energy barrier of urea synthesis reaction and the transition state energy barrier of C/N coupling reaction have dropped significantly by the atomic loading of Fe and Ti on bare MoC. Moreover, Ti doped MoC exhibits better catalytic selectivity toward urea production, making it an excellent catalyst for urea synthesis. We hope this work can pave the way for the electrochemical synthesis of urea.