Nitrate and nitrite electrocatalytic reduction on Rh-modified pyrolytic graphite electrodes

The electrochemical reduction of nitrate and nitrite anions was investigated on Rh-modified pyrolytic graphite electrodes prepared by potentiostatic electrodeposition with the use of a double-pulse technique. Several important parameters (pH, temperature and composition of electrolytic medium, electrolysis potential) were varied. Only ammonia and nitrite ions were detected among NO₃⁻ reduction products, while NO₂⁻ ions are straightforwardly reduced to ammonia. The experimental data (CV measurements and the results of electrolyses) clearly show that Rh/graphite electrodes are much more efficient for NO₂⁻ reduction than for that of NO₃⁻ at room temperature which was confirmed by the determination of rate constants of corresponding reactions and the activation energy of NO₂⁻ reduction. The influence of carboxylate anions and tetraalkylammonium cations on the electrocatalytic activity of Rh/graphite electrodes was investigated and the inhibiting effect of HCOO⁻ anions on hydrogen evolution reaction and nitrate reduction was demonstrated.     

Eutectoid scaffold as a potential tissue engineer guide

Biphasic scaffolds were prepared according to the eutectoid composition from subsystem silicocarnotite-tricalcium phosphate by the polymeric replica method. Two polyurethane templates were used to explore the possibility of fabricating the scaffold on demand. The obtained scaffolds were characterized mineralogically by X-Ray Diffraction (XRD), the chemical groups analyzed by Attenuated Total Reflectance-Fourier Transformed Infrared Spectroscopy (ATR-FTIR), microstructurally by Scanning Electron Microscopy (SEM) fitted with Energy Dispersive X-Ray Spectroscopy (EDS), and additionally by field emission SEM (FESEM) for the topography study. Finally, the mercury porosimetry analysis was performed for the microporosity study. The obtained results confirmed the possibility of controlling macro- and microporosity on the scaffold, which allowed their synthesis for specific needs.     

Nitrate and nitrite reduction of a sulphide-rich environment

A sulphide-rich anaerobic sludge acclimated with a molasses wastewater was used to carry out studies on nitrate and nitrite reductions in continuously stirred batch reactors. It was shown that a COD/N-NO_x ratio as high as 65·6 mg mg⁻¹ did not promote dissimilatory reduction of nitrogen oxides to ammonia. Denitrification was characterized by a probable accumulation of gaseous intermediates, nitric oxide (NO) and nitrous oxide (N₂O), by sulphide consumption with concomitant elemental sulphur production and by an increase of the redox potential. In addition, sulphate reducers were completely inhibited by nitrogenous oxides. Cultures performed without any carbon source proved that denitrifiers were able to use sulphides as electron donors. Furthermore, while a lag phase preceded nitrate denitrification, nitrite was consumed immediately. Chemical reduction of nitrite by ferrous iron (Fe²⁺) was considered to be responsible for this difference. Evidence of such a chemodenitrification has been presented by using a sterilized sludge which kept its ability to reduce nitrite while it lost its capacity to use nitrate. Moreover, this chemical activity was favoured by Fe²⁺ addition. Finally, it has been suggested that during the cultures performed with non-sterilized sludge, a biological reduction of the ferric ions (Fe³⁺) would be coupled to nitrite chemodenitrification and would allow a regeneration of Fe²⁺. © 1998 SCI     

Exhaustive oxidation/reduction of nitrite, nitrate and hydrazine using a square wave potential regime

Exhaustive oxidation–reduction of nitrite, nitrate and hydrazine was achieved by application of a square wave potential regime to a platinum electrode. The parameters of the square wave were chosen after investigation of the adsorption behaviour of the three compounds. The three compounds were found to adsorb and desorb at a platinum electrode in the potential window from –0.2 V to 1.3 V and hence the lower potential of the square wave was –0.2 V while the upper potential was 1.3 V. The square wave was applied to a solution containing the test compound for 10 h. The results of analysis indicated a decrease in the concentration of the tested compounds with respect to the control sample. The optimal frequencies for the conversion were 10, 50 and 10 for nitrite, nitrate and hydrazine, respectively. Analysis of solutions for possible products of the exhaustive oxidation gave negative tests for NO^–₂, NO^–₃, and NH₃ leaving the possibility of conversion to nitrogen as the end product.     

Synthesis of unsaturated polyphosphoester as a potential injectable tissue engineering scaffold materials

Polyphosphoester is a kind of biodegradable polymer with excellent biocompatibility and have been used in drug delivery, tissue engineering, and other bioapplications. A novel unsaturated polyphosphoester (UPPE) based on bis(1,2‐propylene glycol) fumarate (BPGF) and ethyl dichlorophosphate was synthesized by polycondensation reaction, and crosslinkable double bonds was introduced into the resulting polymer through the fumarate groups. NMR results indicate that there are three possible bonding models in polyphosphoester because of three isomers of BPGF. The GPC results express that increase in polymerization time leads to high molecular weight of polyphosphester and narrow distribution of molecular weight. After 18 h of polymerization reaction, the molecular weight reached to 5956 g mol^?1 and the polydispersity index was 1.12. The UPPE was soluble in N‐vinyl pyrrolidone and easily crosslinked by free‐radical polymerization. At the constant temperature (37°C), the maximum temperature due to heat release during crosslinking reaction varied from 41.1°C to 82.30°C and the setting time was between 1.95 and 10.28 min, according to different formulas. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3095–3101, 2006     

Chemoenzymatic synthesis of branched oligo- and polysaccharides as potential substrates for starch active enzymes

Oligo- and polysaccharides embodying the alpha-maltotriosyl-6(II)-maltotetraosyl structure were readily synthesized by transglycosylation of maltosyl fluoride onto panose and pullulan catalysed by the bacterial transglycosylase cyclodextrin glycosyltransferase (CGTase). The two products obtained proved useful for increasing the knowledge of substrate binding and processing at the active site of barley limit dextrinase that is involved in the metabolism of amylopectin by acting upon its branch points.     

Preparation of novel Pt-based nanoparticles by double potential step electrolysis and their electrocatalytic activity for oxygen reduction reaction

We have developed a novel preparation method for Pt-based nanoparticles by means of double potential step electrolysis (DPSE), in which Pt-Ni alloy deposited at the first step and Ni dissolved at the following step. A cycle of the DPSE in a nickel plating bath containing PtCl₆²⁻ led to the formation of the Pt-Ni nanoparticles with size of about 5.4 ± 1.5 nm, which gradually grew up with repeating the DPSE process, and surface Ni content of the particles by XPS was controllable by changing some parameters of the DPSE. The Pt-Ni nanoparticles deposited by the DPSE were covered with a Pt skin layer, which influence the improvement of both catalytic activity for oxygen reduction reaction (ORR) and corrosion resistance. The Pt-Ni nanoparticles by the DPSE exhibit ca. two times higher electrocatalytic activity for ORR than Pt nanoparticles, and further, of which catalytic activity was maintained high even with more than 1000 cycles of potential cycling test in H₂SO₄ solution, showing good corrosion resistance.     

Electrocatalytic hydrogenation processes controlled potential—1. The electrocatalytic reduction of nitric acid

Methods are described to control the catalyst potential during the electrocatalytic hydrogenation of nitric acid in a slurry electrode cell. The influence of traces of GeO₂ on the hydrogenation reaction is studied with a platinum electrode. Deposition of Ge on the platinum surface limits the amount of adsorbed hydrogen and enhances the nitric acid reduction. This changes the mixed potential of the hydrogen-nitric acid system on the platinum (catalyst) surface. A similar potential change occurs, when the partial hydrogen pressure in the system is altered.     

Size-dependent electrocatalytic reduction of nitrite at nanostructured films of hollow polyaniline spheres and polyaniline–polystyrene core–shells

Nanostructured films of the conducting polymer polyaniline (PANI) were prepared by its potentiostatic polymerization in the presence of thin polystyrene (PS) nanoparticle templates. Two sizes of PS nanoparticles were used (50 and 100 nm) and electron microscopic analysis showed that core–shell composite films of PANI (PANI–PS₅₀ and PANI–PS₁₀₀) and, following removal of the PS, hollow structures (PANI₅₀ and PANI₁₀₀) were formed due to the growth mechanism of PANI around the PS templates. The electrochemical behaviour of the PANI-modified electrodes was studied by cyclic voltammetry, chronocoulometry and amperometry in the presence of nitrite and it was found that nitrite reduction was enhanced by the nanostructuring of the films. The electrocatalysis was dependent on the size of the template, being more pronounced at 50 nm than at 100 nm. The hollow PANI₅₀ film was also a better catalyst than PANI–PS₅₀, whereas for structures based on 100 nm templates, the composite film was better. Such behaviour could be explained in terms of larger surface area and surface concentration of PANI₅₀ and PANI–PS₅₀ films on the electrodes and by higher differential capacitance of those films.     

Chemical synthesis of a dual branched malto-decaose: a potential substrate for alpha-amylases

A convergent block strategy for general use in efficient synthesis of complex alpha-(1-->4)- and alpha-(1-->6)-malto-oligosaccharides is demonstrated with the first chemical synthesis of a malto-oligosaccharide, the decasaccharide 6,6'-bis(alpha-maltosyl)-maltohexaose, with two branch points. Using this chemically defined branched oligosaccharide as a substrate, the cleavage pattern of seven different alpha-amylases were investigated. Alpha-amylases from human saliva, porcine pancreas, barley alpha-amylase 2 and recombinant barley alpha-amylase 1 all hydrolysed the decasaccharide selectively. This resulted in a branched hexasaccharide and a branched tetrasaccharide. Alpha-amylases from Asperagillus oryzae, Bacillus licheniformis and Bacillus sp. cleaved the decasaccharide at two distinct sites, either producing two branched pentasaccharides, or a branched hexasaccharide and a branched tetrasaccharide. In addition, the enzymes were tested on the single-branched octasaccharide 6-alpha-maltosyl-maltohexaose, which was prepared from 6,6'-bis(alpha-maltosyl)-maltohexaose by treatment with malt limit dextrinase. A similar cleavage pattern to that found for the corresponding linear malto-oligosaccharide substrate was observed.     

电催化固氮的研究进展与挑战

氨是一种重要的化工原料,主要通过传统Haber-Bosch工艺制备,该工艺有一定局限性,如耗能高,污染大,对环境造成较大影响。以氮气为原料,在常温、常压下合成氨气是目前化学领域的研究热点之一。分析几种产氨方法,其中电催化还原氮气产氨具有良好的应用前景。介绍电还原产氨原理及目前较为常用的电催化剂贵金属催化剂、非贵金属-金属催化剂和非金属催化剂,并对目前该领域遇到的挑战进行总结。     

One-step chemical reduction of graphene oxide with oligothiophene for improved electrocatalytic oxygen reduction reactions

Oligothiophene (nTP, n = 1, 2, 3) has been used as the reductant for the first time in the preparation of graphene by the reduction of graphene oxide (GO). A simple single-step chemical approach has been developed to reduce and/or functionalize GO with nTP. The reaction takes place at room temperature under stirring of a suspension of GO and nTP in MeCN. The nTP has been grafted onto the surface of GO by reacting epoxy groups together with the reduced graphene oxide (rGO). It was observed that increasing the thiophene ring (hereafter, thiophene is referred to as TP; 2,2′ bithiophene as 2TP; and 2,2′:5′,2″ terthiophene as 3TP) can enhance the reduction reaction. All instrumental experiments have confirmed that nTP not only covalently bonded to the GO but also partly restored the conjugate structure of GO, as a reducing agent. The resultant rGO with 3TP (rGO3TP) has been demonstrated to show remarkable electrocatalytic activity toward oxygen reduction reaction (ORR) compared to typical rGO. The observed ORR electrocatalytic activity induced by the intermolecular charge-transfer provides a general approach to various carbon-based metal-free ORR catalysts.     

Electrospun microporous gelatin–polycaprolactone blend tubular scaffold as a potential vascular biomaterial

The work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry     

Hollow Fe2O3 polyhedrons: One-pot synthesis and their use as electrochemical material for nitrite sensing

In this paper, hollow hematite nano-polyhedrons (Fe-HNPs) were synthesized via a facile solution route. The abundance of high indexed facets was demonstrated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. A new electrochemical biosensor for nitrite determination was then proposed by using the hematite hollow nanopolyhedron as the sensing layer. Electrochemical tests showed that the Fe-HNPs could act as efficient enzyme-like electron mediators for nitrite oxidation. As a result, the Fe₂O₃ modified biosensor exhibited excellent performance for the determination of nitrite with a response time of <10 s, linear range between 0.009 and 3 mM, and sensitivity as 19.83 μA mM^?1. A high selectivity and long-term stability toward nitrite oxidation in the presence of glucose and l-ascorbic (AA) was also observed at their maximum physiological concentrations, which made this novel Fe₂O₃ nanomaterial bounded with high indexed facets promising for sensing applications in medicine, biotechnology and environmental chemistry.     

Stability and electrocatalytic activity for oxygen reduction in WC + Ta catalyst

Tantalum (Ta)-added tungsten carbide (WC) (WC+Ta) was examined in order to obtain surperior characteristics in stability and electrocatalytic activity for the oxygen reduction reaction (ORR) in acid electrolyte. The stability and the electrocatalytic activity of the WC+Ta catalyst were electrochemically investigated and compared to the pure WC. It was proved that the stability of the tungsten carbide was significantly increased by the addition of tantalum compared to the pure WC. The enhanced stability might be due to the formation of the W-Ta alloy in the WC+Ta catalyst. The reduction current of the WC+Ta catalyst for the ORR was observed at a potential of 0.8 V (versus dynamin hydrogen eletrode (DHE)) or less noble potential. This value was about 0.35 V higher than that of the pure WC. The enhanced electrocatalytic activity for the ORR might be caused by the presence of tungsten carbide, which exists on the surface and/or sub-surface.     

Kinetics and electrocatalytic activity of nanostructured Ir-V/C for oxygen reduction reaction

Active, carbon-supported Ir-V nanoparticle catalysts have been synthesized by an ethylene glycol reduction method under controlled conditions at pH 10-13 and 120 °C, then further reduced at elevated temperature from 150 to 500 °C using IrCl₃ and NH₄VO₃ as the Ir and V precursors. The nanostructured catalysts have been characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM). Ir nanoparticles, after modification with V, show a narrow particle size distribution in the range 0.5-4.5 nm, centered at 1.8 nm, and are uniformly dispersed on Vulcan XC-72. No particle agglomeration was observed, not even at high V loadings (V:Ir = 4:1 in atomic ratio). Investigation of the catalytic activity of the Ir-V/C by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE) has revealed that the presence of V may suppress the electrochemical oxidation of Ir and stabilize the Ir active centers. About six times higher kinetic current density was obtained for Ir-V/C compared to that of the pure Ir/C catalyst at 0.8 V versus RHE for the oxygen reduction reaction (ORR). The ORR in acid solution proceeds by an approximately four-electron pathway, through which molecular oxygen is directly reduced to water. The performance of a membrane electrode assembly (MEA) prepared with the most active 40% Ir-10% V/C as the cathode catalyst in a single proton-exchange membrane fuel cell (PEMFC) generated a maximum power density of 517 mW cm⁻² at 0.431 V and 70 °C, and 100 h of stable cell operation due to no loss of catalyst sites on the cathode.     

超薄二维材料光/电催化CO2还原的最新进展

能源短缺和环境污染是全人类面临的巨大挑战,对化石燃料的过度依赖使CO₂的排放量急剧增加,如何将过量的温室气体通过清洁的方式转变为燃料或其他高值化学品,已成为全球范围内的研究热点和难点。在过去几十年的研究中,通过太阳能和电化学方法来还原CO₂被证明是十分清洁有效的方法,可以有效降低全球碳足迹,实现化石资源的高效利用。近几年来,超薄二维材料（诸如水滑石、氧化物、钙钛矿等）在催化领域的卓越性能引起了人们的广泛关注,其电子结构存在更多的调变可能,并且可以通过修饰其表面,使其在更多催化反应中发挥作用。本文总结了近几年来超薄二维材料在光催化和电催化还原CO₂的前沿进展,并总结其调变规律,为设计高效光、电催化剂提供参考。     

电催化还原水中NO_3~-的研究进展

主要综述了目前国内外电催化还原脱除NO_3~-技术的研究进展,阐述了NO_3~-电催化还原的主要反应路径及相应的中间产物,并着重介绍了几种一元/二元金属阴极催化剂,及相应的催化效率优化手段和调控原理。综述可为高效催化剂的设计和合成提供思路和参考,推动电催化还原脱除NO_3~-技术在环境污染修复等领域的应用和推广。