Two-step Reduction Process Research Articles

Photon-enhanced thermionic emission solar cells based on boron-doped graphene/carbon nanosphere composite aerogel photocathode material

This study employed a two-step hydrothermal reduction process and freeze-drying technique. Initially, carbon nanosphere composite aerogels (CNSs) were synthesized through the hydrothermal reduction of glucose. Subsequently, boron-doped graphene/carbon nanosphere composite aerogel (BGA/CNS) was prepared by utilizing graphene oxide (GO) and boric acid as carbon (C) and boron (B) sources, respectively, in conjunction with CNS. The photo-enhanced thermionic electron emission (PETE) performance of the samples was assessed using a custom-made device. Boron atom doping was found to modulate the bandgap of graphene aerogel and induce P-type semiconductor characteristics, while the addition of CNSs increased its specific surface area, thereby enhancing its photoelectric properties. The results indicated that BGA/CNS-8h exhibited superior PETE effects, with a short-circuit current, open-circuit voltage, and maximum power of 5.81 µA, −2.10V, and −1.57µW.

Significantly enhanced photo response of hydrazine hydrate reduced graphene oxide films modified with swift heavy ion irradiation of silver (Ag8+) ions

In this paper, a multistep reduction process of graphene oxide (GO) is discussed. It is basically a two-step reduction process. In the first step, the GO sample is reduced by hydrazine hydrate. In the second step, it is further reduced by a swift heavy ion irradiation beam of silver (Ag8+) ions of 100 MeV energies. Ion beam irradiation causes defects in the hydrazine hydrate reduced graphene oxide (rGO) samples. FTIR study confirms the removal of oxygen containing functional groups. The pore volume and pore density of the samples seem to increase with increase in the ion irradiation doses. It is also seen that the electrical conductivity and specific surface area increases with dose of ion irradiation. The prepared samples were tested for photo response measurement and among all the sample, R5 had the highest photo response of 6.25 % at 30 mW/cm2. The photodetection response seems to increase with increase in intensity of light.

Development of a reduced mechanism for methane combustion in OpenFOAM: A computational approach for efficient and accurate simulations

The primary aim of this study is to develop a more efficient reaction mechanism for accurately simulating methane combustion, with a specific focus on ignition delay, laminar flame speed, and 2-D simulated flames, while also reducing computational time. Ten reduced reaction mechanisms for methane combustion were evaluated, with only one, "SK30," meeting the required accuracy standards. However, SK30 proved to be computationally intensive when simulating a 2-D premixed flame at a microscale. To address this challenge, a two-step reduction process was implemented. Firstly, an automated algorithm utilized direct relation graphs and sensitivity analysis with ignition delays as a reference to streamline the mechanism while maintaining accuracy. Subsequently, the second step involved identifying key reactions that had a more significant impact on flame speed than ignition delay through sensitivity analysis. Any missing reactions were then added judiciously, prioritizing the retrieval of the missing but important reactions to overall accuracy while minimizing computational cost. This process resulted in a novel mechanism comprising 25 species and 132 reactions for methane-air combustion. The validity of this mechanism was confirmed through comparison with a benchmark model, demonstrating satisfactory agreement in 1-D flame speed and 2-D premixed flame modeling. Most notably, the new mechanism substantially reduced processing time, achieving a 50 % speedup compared to SK30.

Insight into the generation of near infra-red (NIR) absorbing species in electrochromic surface-anchored metal-organic frameworks.

Due to their versatility and easy processing, Surface-Anchored Metal-Organic Frameworks (SurMOFs) have gained interest in recent times as promising electrochromic thin films. Herein a step forward in their use and characterization was achieved thanks to the integration of {Zn2(PDICl4)2} SurMOFs in a multi-layer electrochromic device (ECD), based on a membrane-like electrolyte. The optical and electrochemical properties of the ECD were fully characterized, revealing a two-step reduction process localized on the organic ligand and involving subsequent near infra-red (NIR) and cyan absorbing states, leading to optical modulation of the films. The species responsible for this absorption were isolated and identified in the reduced states. In parallel to experimental characterization, quantum chemistry was successfully used to investigate the structure-property relationship of the SurMOF, revealing additional information regarding the structure and the local environment of the electrochromic ligand.

Degradation of Nitrobenzene by Mackinawite through a Sequential Two-Step Reduction and Oxidation Process.

Mackinawite (FeS) has gained increasing interest due to its potential application in contaminant removal by either reduction or oxidation processes. This study further demonstrated the efficiency of FeS in degrading nitrobenzene (ArNO2) via a sequential two-step reduction and oxidation process under neutral conditions. In the reduction stage, FeS rapidly reduced ArNO2 to aniline (ArNH2), with nitrosobenzene (ArNO) and phenylhydroxylamine (ArNHOH) serving as the intermediates. X-ray photoelectron spectroscopy (XPS) analysis indicated that both Fe(II) and S(II) in FeS contributed electrons to the reduction of ArNO2. In the subsequent oxidation stage with oxygen, by addition of 0.5 mM tripolyphosphate (TPP), ArNH2 generated in the reduction process could be effectively oxidized to aminophenols by hydroxyl radicals (•OH), which would undergo eventual mineralization via ring-cleavage reactions. TPP exerted a favorable role in enhancing •OH production for ArNH2 degradation by promoting the formation of the dissolved Fe(II)-TPP complex, thus enhancing the homogeneous Fenton reaction. Additionally, TPP adsorption inhibited the surface oxidation reactivity of FeS due to the change of Fe(II) coordination. Finally, the effective degradation of ArNO2 by FeS in actual groundwater was demonstrated by using this sequential reduction and oxidation approach. These research findings provide a theoretical basis for a new FeS-based remediation approach, offering an alternative way for comprehensive removal of ArNO2.

Deep decarburization of molybdenum and tungsten powders by wet hydrogen

The control of residual carbon content is an urgent problem to be solved for the preparations of molybdenum and tungsten powders by method of carbothermic reduction of their oxides. In this paper, finer Mo (W) powder with a low residual carbon content was prepared by a two-step reduction process consisting of carbothermal pre-reduction of MoO3 (WO3) at 1050 °C and following deep hydrogen reduction. During the deep hydrogen reduction process, with the increases of hydrogen reduction temperature and dew point, the residual carbon contents of the finally prepared Mo and W powders gradually decreased, while the particle sizes of Mo and W powders gradually increased. The lowest residual carbon and oxygen contents of Mo and W powders obtained after hydrogen reduction at 1100 °C with the hydrogen dew point of 41 °C were 0.007 wt% (carbon content) and 0.104 wt% (oxygen content), as well as 0.010 wt% and 0.086 wt%, respectively. In addition, the mean particle sizes of them were 1032 nm and 998 nm under this condition, respectively.

Electrooxidation of methanol and ethanol catalyzed by high-performance three-dimensional graphene-supported PdM (Co, Cu) binder-free electrode

PdM/RGN (M = Co, Cu) self-supporting composite electrodes were synthesized via a simple two-step spontaneous reduction process using Ni foam as the substrate and reduced graphene oxide as support layer. The composites were characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were performed to study the electrocatalytic activities of the prepared electrodes for methanol and ethanol oxidation. The performances of PdM/RGN for methanol and ethanol oxidation increased and then decreased as the atomic ratio of Pd to M (Co, Cu) increased. The Pd6Co1/RGN and Pd6Cu1/RGN electrodes exhibited markedly superior catalytic activity and long-term stability. The peak current densities of Pd6Cu1/RGN and Pd6Co1/RGN electrodes reached 0.36 and 0.29 A/cm2 for methanol electrooxidation and which reached 0.8 and 0.5 A/cm2 for the ethanol electrooxidation, respectively. This excellent performance is owing to the three-dimensional structure of nickel foam, the improving specific surface area and the synergistic effect between Pd and M.

Impact of Ag on Electrochemical Recovery of UO2 in Molten LiCl-KCl Salt

To investigate the effect of fission element Ag on the electrochemical recovery of UO2, the electroreduction mechanisms of Ag+ and kinetic property of Ag+/Ag couple were first studied on W electrode by different electrochemical techniques. The electrode reactions of Ag+ and were found to be one-step and two-step reduction processes, respectively. The exchange current density of Ag+/Ag couple was estimated to be 0.0431∼0.0727 A cm−2 in the temperature range of 723∼798 K by LP technique, and its activation energy was evaluated to be 33.91 kJ mol−1. The deposition products obtained by constant potential electrolysis (CPE) were characterized by XRD and SEM-EDS, which showed the formed Ag and UO2 having pine-branch and micron-scale polyhedral structure, respectively. The influence of Ag+ on the electrochemical behavior of and morphology of UO2 were studied. The deposition potential of Ag+ was close to that of to UO2. The changes of Ag+ concentration and scan rate had no effect on the electroreduction mechanism of CPE was conducted, and the result indicated that UO2 and Ag could be co-deposited. The deposited Ag could change the morphology of recovered UO2.

G-C3N4 sheet nanoarchitectonics with island-like crystalline/amorphous homojunctions towards efficient H2 and H2O2 evolution

Photocatalystic evolution of H2O2 from water and oxygen has attracted significant attention because of environmentally friendly. The absorption in visible and hydrophilic feature of graphitic carbon nitride (g-C3N4) make it a good candidate. In this paper, a rapid post-treatment at high temperature was developed to obtain g-C3N4 nanosheets with abundant crystalline/amorphous interfaces to form homojunctions, which optimized uniplanar carrier mobility dynamics. The conversion from bulk to two-dimensional g-C3N4 resulted from the breakage of interplanar hydrogen bonds and interlayer Van der Waals force. The unique morphology not only rendered photocatalyst with larger specific surface area but also inhibited the robust volume recombination of charge carriers. The accelerated charge carriers flow at the interface, interplane and interlayer together ameliorated the separation and transfer of electrons and holes. A new-emerged n→π* transition ameliorated the poor light utilization efficiency. Beyond the increased photocatalytic H2 evolution property (779.2 μmol g−1 h−1), optimized sample displayed a H2O2 evolution activity as high as 4877.1 μM g−1 h−1 under visible light illumination, which was ∼5.8 times of that of bulk g-C3N4. Detailed photocatalytic mechanism investigation manifested that the two-step single-electron oxygen reduction process occupied the dominant status in H2O2 evolution. This work proposed a novel strategy for obtaining g-C3N4 homojunctions as a promising bi-functional metal-free catalyst to be applied in clean energy production field.

Cyano-Regulated Organic Polymers for Highly Efficient Photocatalytic H2 O2 Production in Various Actual Water Bodies.

Photocatalytic production of H2 O2 has drawn significant attention in recent years, but the yield rate of current photocatalytic systems is still unsatisfactory. Moreover, the presence of various components in actual water bodies will consume the photogenerated charges and deactivate the catalyst, severely limiting the real applications of photocatalytic H2 O2 production. Herein, a cyano-modified polymer photocatalyst is synthesized by Knoevenagel condensation with subsequent thermal polymerization. The introduction of cyano group and sulfer (S), oxygen (O) elements modulates the microstructure and energy band of the polymer catalyst, and the cyano group sites can effectively adsorb and activate O2 , realizing the generation of H2 O2 in the two-step single-electron oxygen reduction process. The reported system achieves high H2 O2 generation rate up to 1119.2µmol g-1 h-1 in various water bodies including tap water, river water, seawater, and secondary effluent. This simple and readily available catalyst demonstrates good anti-interference performance and pH adaptability in photocatalytic H2 O2 production in actual water bodies, and its photodegradation and sterilization applications are also demonstrated. This study offers new insights in developing polymer catalysts for efficient photocatalytic production of H2 O2 in various water bodies for practical application.

Highly Active Porous Carbon-Supported CoNi Bimetallic Catalysts for Four-Electron Reduction of Oxygen

Great interest has been taken in oxygen reduction reaction (ORR), as a common cathode reaction in new energy sources such as fuel cells and metal–air batteries, to improve the current energy structure and develop new green energy sources. Noble metal Pt is still considered the best catalyst for this reaction. However, its disadvantages such as high cost, low selectivity, poor stability, and susceptibility to impurity poisoning severely limit its further industrial applications. Therefore, development of efficient and low-cost ORR reduction catalysts is particularly critical. M-Nx-C materials have been extensively studied to achieve a high ORR activity close to that of Pt catalysts. In this study, CoNi bimetallic alloy carbon-based oxygen reduction catalysts named CoNi-950 (Zn) were successfully synthesized, using a metal–organic framework (MOF) as a carbon precursor and a nitrogen source. The experimental results show that CoNi-950 (Zn) exhibits good ORR catalytic performance with an ultimate current density of 6.27 mA cm–2, which even exceeds that of some Pt/C catalysts with a mass loading of 20 wt % (5.92 mA cm–2). In addition, the active site of the catalyst was also identified by acid leaching and SCN– poisoning experiments, showing two sites in the form of CoNi-Nx and the CoNi alloy or its oxides in the material. Further experiments demonstrate that these two active sites have distinct ORR catalytic mechanisms, generating positive synergism in ORR. A mechanism in which O2 was catalytically reduced by CoNi-950 (Zn) in a four-electron transfer, i.e., a continuous two-step dual-electron transfer reduction process in alkaline electrolytes, is proposed.

Photochemical synthesis of group 10 metal nanoclusters for electrocatalysis.

Four group 10 metal nanoclusters, Ni10(4-MePhS)20, Ni11(PhS)22, Pd9(PhS)18 and Pd10(PhS)20 were synthesized from disulfides based on a photochemical reduction-oxidation cascade process, which proceeds via a different mechanism to that of the conventional two-step reduction process. The as-obtained nanoclusters possess oxidative resistance and structural robustness under different conditions. Their atomically precise structures are determined to be nickel or palladium rings in which the metal atoms are bridged by Ar-S groups. Their catalytic performance in oxygen reduction reaction was compared, and the ring size-dependent catalytic activity of the group 10 metal nanoclusters was revealed. This work provides an efficient route to atomically precise and structurally stable group 10 metal nanoclusters, and sheds light on their further applications in electrocatalysis.

Electrochemical recovery of UO2 from LiCl-KCl-UO2F2 molten salt

To recover UO2 from LiCl-KCl-UO2F2 molten salt, the electrochemical behavior of UO22 + and nucleation mechanism of UO2 were studied by a series of electrochemical techniques. The results of cyclic voltammetry and square wave voltammetry showed that UO2 was formed through two-step reduction process of UO22 + involving one electron transfer. The disproportionation reaction of UO2+ was investigated by calculating electric charge, demonstrating the disproportionation reaction occurred as 2UO2+=UO2+UO22 +. The exchange current densities of UO2+/UO2 couple were determined at various temperatures by Tafel technique, and their values increased with the increasing temperature, which was in accordance with the Arrhenius equation, therefore, the activation energy of the reaction was estimated to be 32.31 kJ mol−1. Meanwhile, the nucleation mechanism of UO2 was investigated to follow the progressive nucleation by chronoamperometry. Furthermore, potentiosatic electrolysis was performed at various applied potentials, and the results indicated that UO2 had a regular octahedral microstructure, and the applied potential affected the size of UO2 crystal. In addition, UO2 was prepared by pulse electrolysis at 2.02 V in duty ratios of 75 % and 60 %, the results of SEM showed that pulse electrolysis could avoid the formation of dendrite.

Core-shell structured Si@Cu3Si-Cu nanoparticles coated by N-doped carbon as an enhanced capacity and high-rate anode for lithium-ion batteries

• Both Cu 3 Si and NC of Si@Cu 3 Si-Cu@NC are formed during the carbonization of dopamine. • Core-double shell structured Si@Cu3Si-Cu@NC nanoparticles can effectively enhance the stability of Si-based anode. • Si@Cu3Si-Cu@NC nanoparticles shows a high performance (1105.5 mAh g -1 ) under 5A g -1 as LIB anode. Silicon based anode material is regarded as a promising candidate for Lithium ionic batteries (LIBs) due to its high theoretical specific capacity. Nevertheless, the capacity degradation triggered by high volume expansion has seriously hindered its application in LIBs. Herein, a novel structure of core-shell structured Si@Cu 3 Si-Cu nanoparticles coated by N-doped carbon (Si@Cu 3 Si-Cu@NC) is designed and synthesized via a two-step thermal reduction process. In this design, the copper shell and N-doped carbon can significantly limit and accommodate the volume change of Si during cycling. The in-situ formation of Cu 3 Si at the interface further improves the structural stability. The doping of N in carbon is conducive to the rapid transmission of electrons and ions as well as optimizes the electrochemical performance of the material. Therefore, the optimized Si@Cu 3 Si-Cu@NC nanocomposite anode shows prominent rate performance and delivers a reversible capacity of 1105.5 mAh g -1 after 100 cycles at a high current density of 5 A g -1 , which exhibits the great potential of the nanocomposite as high-performance LIBs anode material.

Ester decorated 1,2,4,5-tetraphenylbenzene electrochromic materials with AEE activity, high optical contrast, fast response, and good cycling stability

Multifunctional electrochromic materials are ideal candidates for applications in various commercial fields. In this work, a series of dual-functional materials, 1,2,4,5-tetrakis (4-carboxyphenyl)benzene esters (TCPBEs), were synthesized by decorating 1,2,4,5-tetraphenylbenzene with tetra-esters. TCPBEs exhibited aggregation-induced emission and distinct phenomenon of aggregation-enhanced emission in water/N-methyl pyrrolidone due to their polyphenyl substituted structures and electrochromic properties due to surrounding esters. TCPBEs underwent a two-step one-electron reduction process in the electrochemical behavior. The electrochromic devices based on TCPBEs showed good long-term cycling stability (i.e., Hex-TCPBE remained 90% of the initial optical contrast after 2350 cycles), high optical contrast (i.e., Et-TCPBE up to 64.5%) and coloration efficiency (i.e., Hex-TCPBE up to 261 cm2/C), rapid response (<3 s), and dual colored state. Significant changes in color from colorless bleached state to orange and brown colored states were observed. Each TCPBE demonstrated distinct electrochromic properties because of the electronic effects of different R-substituted ester groups. In general, Et-TCPBE, Hex-TCPBE, and CH3Ph-TCPBE performed better than Bn-TCPBE and CF3Ph-TCPBE. In summary, this study provides a strategy for the design of novel dual-functional electrochromic materials, which have broad application prospects in the field of multifunctional devices.

Chemical Characterization and Molecular Dynamics Simulations of Bufotenine by Surface-Enhanced Raman Scattering (SERS) and Density Functional Theory (DFT).

Bufotenine (5-hydroxy-N,N-dimethyltryptamine) is a natural tryptamine derivative with hallucinogenic activity. In this paper, we present novel chemical and molecular conformational analyses of bufotenine based on an experimental and theoretical approach integrating surface-enhanced Raman scattering (SERS) and density functional theory (DFT). For the first time, low concentrations of bufotenine in acetonitrile solutions were analyzed by SERS using two types of silver nanoparticle substrates synthesized via one- or two-step reduction processes. The vibrational characteristics of this molecule were verified by molecular dynamics simulations of Raman bands based on DFT. Here we demonstrate the potential of this integrated approach for the identification of bufotenine, a prominent hallucinogenic agent, establishing an innovative rapid and accurate sensing and characterization method of the identification of controlled substances at trace amounts.

Photocatalytic Methane Conversion: Insight into the Mechanism of C(sp 3 )–H Bond Activation

Photocatalytic Methane Conversion: Insight into the Mechanism of C(sp ³ )–H Bond Activation

In-situ electrochemical reconstruction of tungsten carbide using Na2CO3-containing molten salt

This paper reports a novel method for rapid atomic-level reconstruction of tungsten carbide (WC) using Na2CO3-containing molten salt. Herein, WC was used as consumable anode and Na2CO3 was active species on WC anode and carbon donor. Thermodynamic calculations were used to verify the feasibility of this electrolytic method for reconstructing WC. Experimental results showed that the addition of Na2CO3 significantly enhanced dissolution efficiency of WC. Therefore, more tungsten (W) source was supplied. Electrochemical analysis demonstrated that Na2CO3 also supplied carbon by two-step reduction process, which led to the formation of WC. These experiments confirmed that cathode product was converted from W to WC by the introduction of Na2CO3 additive into molten salt. WC phase started to form at cell voltages above 2.2 V. In initial stage of reaction, carbonate was preferentially reduced in cathode region to form amorphous C. As the reaction proceeded, W ions migrated from anode and began to participate in reduction process, forming W. Finally, W was transformed to WC by carbonization process.

Preparation and properties of Al2O3 dispersed fine-grained W-Cu alloy

In this study, high-performance fine-grained W-Cu sintered blocks with the addition of dispersed Al2O3 particles were successfully produced by low temperature liquid-phase sintering, using the raw material of ultrafine W-Cu alloy powder. The ultrafine W-Cu alloy powder was obtained by a two-step reduction process composed of stages of carbothermal reaction and hydrogen deep deoxidation. The fine Al2O3 grains with uniform distribution in W-Cu alloy were introduced by spray method, leading to the decrease of W grain size and W-W connectivity. The relative densities of all sintered blocks were>97%, and a higher degree of densification ensures that the alloy has excellent comprehensive properties. With the increase of Al2O3 content, W grain size and W-W connectivity of sintered W-Cu samples decrease from 664 nm to 472 nm and 0.2 to 0.14, respectively. The W-Cu alloy with the ultimate tensile strength of 415 MPa and the highest elongation of 7.22% was obtained when the addition amount of Al2O3 was 0.5 wt%. At the same time, it also possessed the maximum bending strength of 1028 MPa and microhardness of 312 HV, respectively. In addition, due to the good network structure of Cu and uniform three-phase distribution, the sintered samples had excellent conductivity and compressive strength.

Electrochemical Behavior of Sm(III) and Electrodeposition of Samarium from 1-Butyl-1-Methylpyrrolidinium Dicyanamide Ionic Liquid

Electrodeposition of rare-earth metals using ionic liquid is considered as a potential alternative to conventional high-temperature molten salt electrolysis. Herein, the electrochemical reduction of samarium(III) at near ambient conditions is investigated using different samarium precursors, namely, triflate (Sm(OTf)3), nitrate (Sm(NO3)3.6H2O) and chloride (SmCl3), in 1-butyl-1-methylpyrrolidinium dicyanamide ([BMP][DCA]) ionic liquid. FT-infrared and Raman spectroscopy analyses of Sm3+/[BMP][DCA] solutions confirm the coordination of Sm3+ species with ion through nitrogen atom. Cyclic voltammetry of Sm3+ at glassy carbon electrode provides evidence of a two-step reduction process in all the systems via Sm3+ to Sm2+ and Sm2+ to Sm0 with peaks observed at similar reduction potentials owing to indifference in samarium(III) chemistries in each medium which is supported by a plausible mechanism. The diffusion coefficient of Sm3+ in [BMP][DCA] was determined to be 3.00 × 10−7, 3.64 × 10−8 and 1.90 × 10−7 cm2.s−1 for Sm(OTf)3, Sm(NO3)3.6H2O and SmCl3 systems, respectively. The electrodeposition of samarium was achieved on nickel and glassy carbon substrates under two different potentials and temperatures. X-ray photoelectron spectroscopy confirms that the samarium electrodeposits are a mixture of metallic and oxide forms.