Presence Of Surface OH Groups Research Articles

Structure and oxygen evolution reaction performance of Ni-supported catalysts based on steam-exploded poplar

Using renewable steam-exploded poplar (SEP) as carbon source, nickel metal doped carbon hybrid materials were designed to synthesize catalysts (Ni/SEP) with certain oxygen evolution reaction (OER) properties and were compared with nickel catalysts supported on metal organic framework structure (ZIF67-Ni). The roles of SEP support in Ni-based catalyst were considered. Scanning electron microscope (SEM) images confirmed that the fiber could better hinder the aggregation of metal particles. Fourier transform infrared spectroscopy (FT-IR) indicated the presence of surface OH groups after the reduction process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the major form of metallic Ni in the resulting Ni catalysts. Carbon materials as carriers, the synergetic effect of Ni-doped, and carbon carrier played an important role in facilitating the kinetics of OER, which was similar to the carrier of metal-organic frame material. Notably, the Ni/SEP (11.3 mF/cm-2) and ZIF67-Ni (37.2 mF/cm-2) with better OER performance exhibited a smaller double layer capacitances (Cdl), suggesting the intrinsic OER catalytic activity of the Ni/SEP and ZIF67-Ni were much higher in comparison to the ZIF67-Ni/SEP. Moreover, the inferior performance of Ni/SEP further indicated that the synergistic effect between carbon and Ni/NiO contributes to the enhanced OER activity.

Cu-MOF nanosheets modified nickel foam: A versatile platform for highly sensitive electrochemical detection of transferrin in simulated human blood serum

Transferrin (TRF) is a type of glycoprotein present in blood plasma that plays a vital role in facilitating the absorption, storage, and movement of iron(III) ions within the circulatory system of multiple vertebrates. Herein, we report one-pot solvothermal synthesis of Copper Metal-Organic Framework nanosheets modified nickel foam (Cu-MOF/NF) for electrochemical detection of transferrin (TRF) in simulated human blood serum. The crystal structure of the Cu-MOF nanosheets was determined through X-ray diffraction (XRD), while Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) analysis were employed to investigate the vibrational modes and the presence of surface OH groups, respectively. The nanosheet morphology of the Cu-MOF was observed and characterized using scanning electron microscopy (SEM) micrographs.The as-fabricated Cu-MOF/NF exhibits a sensitivity of 1.36 mA/x (x = mg.mL−1cm−2) for a linear range of concentrations from 1 mg mL−1 – 100 mg mL−1 with a low limit of detection (LOD) of 0.81 mg mL−1. The sensor exhibited good selectivity for TRF, even in the presence of interfering ions such as bovine serum albumin, ascorbic acid, uric acid, and urea, with concentrations 100-fold higher than TRF. The porous nickel foam with high conductivity, offers numerous active sites and pathways for ion transport, as well as pathways for electron transport during electrochemical catalytic reactions. This performance of the sensor is attributed to Cu 2+/Cu+ redox couple at the octahedral sites of the Cu-MOF facilitating the electro-oxidation of TRF and charge-carrier delocalization during the catalytic reaction. The as-fabricated sensor is successful in the determination of trace level TRF concentration the human blood serum with excellent recovery percentages of 108.33% This proves Cu-MOF/NF as a promising platform for various electrochemical analytical applications.

Sonochemical Combined Synthesis of Nickel Ferrite and Cobalt Ferrite Magnetic Nanoparticles and Their Application in Glycan Analysis.

The combination of the sonochemical activation of Ni(NO3)2 and Co(NO3)2 in the presence of Fe(NO3)3 and polyethylene glycol and consecutive heat treatment of the formed metal hydroxides offers a cheap and efficient method for the preparation of nickel ferrite and cobalt ferrite magnetic nanoparticles, which can be successfully applied in the selective capture of fluorescently derivatized N-glycans from human serum. XRD measurement revealed that, besides the ferrite phase, nickel and cobalt oxides also form during heat treatment. The amount of simple metal oxides can be well controlled by the temperature of the heat treatment, since increasing temperature yielded higher spinel content. For both nickel and cobalt, the best heat treatment temperature was found to be 673 K, where the samples contained 84.1% nickel ferrite, and in the case of cobalt, almost pure (99.6%) cobalt ferrite could be prepared. FT-IR and zeta potential measurements indicated the presence of surface OH groups, which aided in the dispersion of the particles in water and, in addition, can promote the adsorption of polar compounds. The practical applicability of the magnetic nanopowders was demonstrated in the purification of fluorescently derivatized N-glycans (from human serum). Cobalt ferrite was found to be the most effective. Owing to the easy preparation and the simplicity of the magnetic separation the pure cobalt ferrite, magnetic nanoparticles could be efficient tools for the selective enrichment of serum N-glycans in HPLC measurements.

Chromium Adsorption Reveals a Persistent Hydroxylation of Vacuum-Annealed α-Al2O3(0001)

We address herein the question of the termination of the Al-terminated α-Al 2 O 3 (0001) surface. Over decades, various analyses made by different groups repeatedly suggested the presence of a residual coverage of surface OH groups on Al 2 O 3 crystals and powders after annealing in vacuum. However, other authors came to contrary conclusions, thus maintaining a persistent blur on the issue. The present work examines the Cr/alumina interface via Cr K absorption edge analysis (Extended X-Ray Absorption Fine Structure and X-ray Absorption Near Edge Structure) and photoemission with the support of density functional (DFT) calculations. Experiments support the presence of surface OH groups to account for the observed environment as well as the oxidation state of Cr adatoms (Cr 3+). Following a comprehensive DFT-based analysis of Cr z+-O n H m configurations (z=0 to 6, n and m=0 to 3), the Cr 3+-O 2 H alumina-supported surface moieties are found to successfully fit the XAS edge calculations. Most importantly, the combination of experiment and theory that is developed unambiguously demonstrates the presence of surface OH groups on α-Al 2 O 3 (0001) after annealing in vacuum.

Influence of surface hydroxylation on the Ru atom diffusion on the ZrO2(101) surface: A DFT study

The adsorption and diffusion of ruthenium adatoms on the (101) surface of tetragonal zirconia was studied by means of periodic Density Functional Theory (PBE+U) calculations. The surface termination has a decisive role in determining the diffusion capability of the adsorbed Ru atoms. On the defect-free and fully dehydroxylated surface, Ru adatoms have several stable adsorption sites with adsorption energies as large as 2.5–2.9eV However, the kinetic diffusion barriers between adjacent adsorption sites are around 0.5–0.6eV, indicating a rather fast diffusion process. Surface oxygen vacancies, if present, strongly bind ruthenium adatoms and act as nucleation sites. On hydroxylated surfaces, the adsorption energy of Ru atoms is comparable to the dehydroxylated case, but the kinetic barriers for diffusion are remarkably higher, thus indicating that adsorbed species are less mobile in presence of surface OH groups. The effect is more pronounced for high concentrations of OH groups, since this results in hydrogen bonded hydroxyl units that further limit the diffusion process. These results indicate a possible way to increase the life-time of RuZrO2 heterogeneous catalysts by tuning the level of surface hydroxylation, in order to slow down sintering of metal particles via Ostwald ripening process.

Ambient pressure XPS and IRRAS investigation of ethanol steam reforming on Ni-CeO2(111) catalysts: an in situ study of C-C and O-H bond scission.

Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Infrared Reflection Absorption Spectroscopy (AP-IRRAS) have been used to elucidate the active sites and mechanistic steps associated with the ethanol steam reforming reaction (ESR) over Ni-CeO2(111) model catalysts. Our results reveal that surface layers of the ceria substrate are both highly reduced and hydroxylated under reaction conditions while the small supported Ni nanoparticles are present as Ni(0)/NixC. A multifunctional, synergistic role is highlighted in which Ni, CeOx and the interface provide an ensemble effect in the active chemistry that leads to H2. Ni(0) is the active phase leading to both C-C and C-H bond cleavage in ethanol and it is also responsible for carbon accumulation. On the other hand, CeOx is important for the deprotonation of ethanol/water to ethoxy and OH intermediates. The active state of CeOx is a Ce(3+)(OH)x compound that results from extensive reduction by ethanol and the efficient dissociation of water. Additionally, we gain an important insight into the stability and selectivity of the catalyst by its effective water dissociation, where the accumulation of surface carbon can be mitigated by the increased presence of surface OH groups. The co-existence and cooperative interplay of Ni(0) and Ce(3+)(OH)x through a metal-support interaction facilitate oxygen transfer, activation of ethanol/water as well as the removal of coke.

Cerium oxide for the destruction of chemical warfare agents: A comparison of synthetic routes

Four different synthetic routes were used to prepare active forms of cerium oxide that are capable of destroying toxic organophosphates: a sol–gel process (via a citrate precursor), homogeneous hydrolysis and a precipitation/calcination procedure (via carbonate and oxalate precursors). The samples prepared via homogeneous hydrolysis with urea and the samples prepared via precipitation with ammonium bicarbonate (with subsequent calcination at 500°C in both cases) exhibited the highest degradation efficiencies towards the extremely dangerous nerve agents soman (O-pinacolyl methylphosphonofluoridate) and VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate) and the organophosphate pesticide parathion methyl. These samples were able to destroy more than 90% of the toxic compounds in less than 10min. The high degradation efficiency of cerium oxide is related to its complex surface chemistry (presence of surface OH groups and surface non-stoichiometry) and to its nanocrystalline nature, which promotes the formation of crystal defects on which the decomposition of organophosphates proceeds through a nucleophilic substitution mechanism that is not dissimilar to the mechanism of enzymatic hydrolysis of organic phosphates by phosphotriesterase.

Photocatalytic activity of nanostructured ZnO–ZrO2 binary oxide using fluorometric method

Evaluation of the photocatalytic activity of ZnO–ZrO2 nanomaterials using fluorescence based technique has rarely been reported. In the present work, ZnO–ZrO2 mixed oxides coupled with various ZnO dosages (0, 10, 30, 50, 70wt%) were prepared by impregnation method. These nanomaterials were characterized by studying their structural, surface and optical properties. The photocatalytic activity in term of quantitative determination of the active oxidative species (OH) produced on the surface of binary oxide was evaluated using fluorescent probe method. The interaction between ZnO and ZrO2 was affected on the photocatalytic efficiency of mixture. The results show that, the addition of ZnO to ZrO2 decreased the electron–hole recombination and increased the rate of OH radicals formation. 50wt% ZnO–ZrO2 photocatalyst exhibited much higher photocatalytic activity. The profound effect of binary oxide catalyst was generally considered due to the high surface area, small particle size, high monoclinic phase of ZrO2 content, low band gap and the presence of surface OH groups.

A comparative study of CO adsorption and oxidation on Au/Fe2O3 catalysts by FT-IR and in situ DRIFTS spectroscopies

Influences of different iron oxides, used as gold supports, on CO oxidation were tested by FT-IR spectroscopy during adsorption of CO in a vacuum and by DRIFTS spectroscopy in the reaction conditions. The two techniques yielded different results but their recombination led to very valuable and interesting conclusions. The investigation showed that the adsorption and oxidation are independent of chemical composition and structure of the supports, but that they depend only on presence of surface OH groups. Also, no correlation was observed between the catalysts with OH groups, which showed almost equal high activity, and the gold particles less than 5nm. Namely, the particles with 1.5nm did not adsorb CO at all, while particles with 4 nm showed three suitable sites for CO adsorption (2172, 2115 and 2071cm−1). The catalyst without OH groups had significantly less activity despite the fact that it is almost identical in chemical composition and structure to one of the active catalyst.

Photocatalytic oxidation of gaseous toluene on anatase TiO 2 catalyst: mechanistic aspects and FT-IR investigation

Photo-oxidation of toluene has been carried out in gas–solid regime by using polycrystalline anatase TiO 2 as the catalyst. The reacting gaseous mixture was toluene, air and water in various molar ratios. A pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing the photoreactivity experiments. The main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected. The molar conversion to benzaldehyde with respect to the initial amount of toluene was ca. 20% in the best experimental conditions. Benzene was produced only as a transient product during the first 3–4 h of irradiation. The dependence of feed composition and flow rate on the toluene fractional conversion was investigated. Selected experiments were performed by using N 2 or CO 2 instead of air. The presence of oxygen was essential for the occurrence of the photoreaction while water played an important role in order to maintain the catalyst activity. Moreover, a Fourier-transform infrared spectroscopy (FT-IR) investigation was carried out simulating the experimental conditions used during the photoreactivity experiments. The results indicated that toluene is weakly stabilised on the hydrated TiO 2 particles by hydrogen-bonding with surface hydroxyl groups, and that it is photo-oxidised to benzaldehyde only in the presence of surface OH groups.

The role of hydroxylated semiconducting surfaces in the reaction of 1,1-diphenyl-2-picrylhydrazyl with adsorbed water

Abstract The role of hydroxylated semiconducting surfaces in the intermolecular oxidation and reduction reaction of 1,1-diphenyl-2-picrylhydrazyl with adsorbed water has been explored. Major products were isolated on various catalysts, characterized and their yields determined. The reaction is the same whether a solvent is present or not. It appears that a simultaneous presence of surface OH groups and ‘F-centers’ is necessary on the surface of a catalyst for the reaction to occur. Considering the mode of catalysis a mechanism for the reaction is proposed on stoichiometric basis.