Adsorption Of H2O2 Research Articles

Green synthesis of a dendritic Fe3O4 @Feo composite modified with polar C-groups for Fenton-like oxidation of phenol

In this work, a hierarchical dendritic Fe3O4@Fe0 composite modified with polar C-groups was obtained by electrodeposition and post-solvothermal methods. SEM, EDS, TEM, XRD, Zeta analysis and ESR were employed to study the structure and composition of catalyst, and the catalytic capability was evaluated by phenol degradation experiments. With the increase of water ratio in thermal solution, the composition of prepared catalyst changes into Fe3O4/Fe2O3 from Fe/Fe3O4, and the dendritic structure turns into particle-like structure. The phenol degradation experiments indicate the catalyst prepared in pure-ethanol solution possesses the optimal catalytic capability, which has a Fe@Fe3O4 core-shell structure with some polar C-groups on Fe3O4 outer layer. Under the condition of 0.18 g/L of catalyst dosage, 6 mmol/L H2O2 and pH = 4.0, the composite catalyst prepared in pure ethanol could remove 98% phenol for 5 min, greatly higher than dendritic bare Feo under the same condition. The enhancement of degradation efficiency by Fenton-like reaction might be ascribed to polar groups that facilitate the adsorption of H2O2, phenol and hydroxyl radicals and promote the transformation of FeIII to FeII on the catalyst surface. This work provides a new insight into the design and application of high-efficient Fe0-based Fenton-like composite catalysts for wastewater purification.

Thermally-assisted photodegradation of lignin by TiO2/H2O2 under visible/near-infrared light irradiation

As a bio-recalcitrant organic pollutant in paper mill effluent, lignin is generally removed by an advanced oxidation process, such as a TiO2/H2O2 photocatalytic technique under irradiation with ultraviolet light, which only accounts for less than 5% of sunlight. Herein, we reported a TiO2/H2O2-based thermally-assisted photocatalytic process that allows lignin to be efficiently degraded under visible/near-infrared light at an elevated temperature. Adsorption of H2O2 on TiO2 nanoparticles and an increase of temperature facilitate the production and separation of charge carriers under near-infrared and visible light irradiation, accelerate carrier transfer at the TiO2-electrolyte interface and promote the production of hydroxyl radicals. A higher level of H2O2 addition results in an increased degradation rate of lignin, while the optimal temperature for the thermally-assisted photodegradation of lignin is 70°C. A charge carrier excitation and transfer process was proposed for the TiO2/H2O2 thermally-assisted photocatalytic process. This work describes a new method for the photodegradation of organic pollutants, such as residual lignin in paper mill effluent, using wide band gap semiconductors under visible and near-infrared light irradiation.

Fe doped CeO2 nanosheets as Fenton-like heterogeneous catalysts for degradation of salicylic acid

Fe doped CeO2 nanosheets with various Fe/Ce ratios were synthesized by solvothermal method (ST) and catalytic performances were evaluated by the degradation of salicylic acid (SA) in the presence of H2O2 (Fenton-like oxidation). The Fe-CeO2 mixed oxides were characterized by SEM, TEM, XRD, EPR, Raman, H2-TPR and XPS, which indicated that 2% Fe doped CeO2 nanosheets (2Fe-CeO2) showed the largest concentration of surface oxygen vacancies and the highest catalytic activity under the optimum reaction conditions due to the complex adsorption of SA and H2O2 on the surface Ce3+. DMPO spin trapping EPR studies and analysis of intermediate products by LC-MS indicated that superoxide species (O2−/HOO) played a crucial role in the oxidation degradation process, meanwhile, the probable pathway of SA degradation was proposed. The strong adsorption of not-fully degraded low molecular weight organic acids (LMWOAs) on the active sites decreased the reusability of 2Fe-CeO2 catalyst, however, the catalytic activities could be recovered by a simple calcination treatment in air atmosphere.

Molybdenum disulfide for ultra-low detection of free radicals: electrochemical response and molecular modeling

Two-dimensional (2D) molybdenum disulfide (MoS2) offers attractive properties due to its band gap modulation and has led to significant research-oriented applications (i.e. DNA and protein detection, cell imaging (fluorescent label) etc.). In biology, detection of free radicals (i.e. reactive oxygen species and reactive nitrogen (NO*) species are very important for early discovery and treatment of diseases. Herein, for the first time, we demonstrate the ultra-low (pico-molar) detection of pharmaceutically relevant free radicals using MoS2 for electrochemical sensing. We present pico- to nano- molar level sensitivity in smaller MoS2 with S-deficiency as revealed by x-ray photoelectron spectroscopy. Furthermore, the detection mechanism and size-dependent sensitivity have been investigated by density functional theory (DFT) showing the change in electronic density of states of Mo atoms at edges which lead to the preferred adsorption of H2O2 on Mo edges. The DFT analysis signifies the role of size and S-deficiency in the higher catalytic activity of smaller MoS2 particles and, thus, ultra-low detection.

Global reactivity and site selectivity of (TiO2)n nanoclusters (n = 5–10) toward hydrogen peroxide

Titanium dioxide (TiO2) is one of the most important materials with many applications in both fundamental science and technology. Among various forms of TiO2 nanostructures, clusters are the most widely used due to high surface to volume ratio. In this context, we present first principles calculations to study the size-dependent evolution of the chemical reactivity and site selectivity of (TiO2)n nanoclusters with n = 5–10. In the framework of the density functional theory, we employ the global parameters to quantitatively describe the chemical reactivity of different sizes of (TiO2)n clusters. Then, on the basis of the symmetry for each size of TiO2 cluster, susceptibility of Ti and O atoms pertinent to nucleophilic and electrophilic attacks is anticipated using local reactivity descriptors. Further, we validate the obtained reactivity pattern for considered (TiO2)n clusters by explicit adsorption of H2O2. It is found that upon the adsorption, H2O2 decomposes to two OH radicals that are stabilized by the interaction with Ti and O atoms on the cluster surface. The characterization of Ti⋯ O and O⋯ H interactions has also been performed by analyzing the parameters derived from the quantum theory of atoms in molecules.

A density functional theory study of ethylene epoxidation catalyzed by niobium-doped silica

A mechanistic study of ethylene epoxidation by hydrogen peroxide catalyzed by niobium doped in a silica mesopore is reported. Density functional theory calculations at the M06-L/aug-cc-pVDZ level were used to investigate the catalytic pathway. A five-step cycle is proposed. The initial steps are the adsorption of H2O2 to the Nb center followed by coordination of ethylene to the hydrogen peroxide. The rate-limiting step is the subsequent epoxidation of ethylene via transfer of an oxygen atom, which has a calculated enthalpic barrier of 11.6kcal/mol relative to the preceding intermediate. This is followed by desorption of the ethylene oxide product and dehydration to regenerate the catalyst. The reaction barrier is lower than reported for other catalysts in the literature, consistent with recent experimental reports of the efficacy of Nb-doped mesoporous silica catalysts [Catal. Sci. Technol.,2014, 4, 4433–4439]. The mechanistic details elucidated in the present calculations may aid in the rational design of new epoxidation catalysts and thus the factors influencing the reaction, e.g., geometry and charge changes, are discussed.

Hydrogen peroxide and photocatalysis

The formation, the adsorption and the degradation of H2O2 on different commercial TiO2 samples (anatase, rutile) and on ZnO have been investigated to better understand its participation in the photocatalytic reactions.The Langmuir and Langmuir–Hinshelwood models have been used for determining the adsorption constants and the rate constants of H2O2 disappearance on these different photocatalysts both in the dark and under UV-A irradiation.Interaction between H2O2 and TiO2 has been investigated by UV–vis spectroscopy.The adsorption of H2O2 on TiO2 samples is discussed in term of surface area and nature of TiO2 including the number of OH groups present on the photocatalysts. The nature of the yellow complex formed between H2O2 and TiO2 is discussed taking into account its stability, and the coverage rate of OH groups.The kinetic of H2O2 disappearance on the different photocatalysts is related to the adsorption but also the energy of conduction band of anatase and rutile photocatalysts.The results of the formation and decomposition of H2O2 under UV-A irradiation in the presence of ZnO photocatalyst are explained in light of its adsorption.

Performances of pretreated ceria-zirconia nanomaterials/H<SUB align="right">2O<SUB align="right">2 system for the degradation of Orange II dye

In this work, the parameters affecting the reactivity of non-sulfated and sulfated commercial ceria-zirconia (CexZr1−xO2) nanomaterials with varying Ce content (x = 1, 0.80, 0.50, 0.21, 0) towards the degradation of Orange II dye have been evaluated. Characterisation of the catalysts was performed using nitrogen adsorption, XRD, Raman, TGA thermogravimetry and DR-UV-Vis spectroscopy. Briefly, it can be deduced that the sulfation treatment mostly affects the Ce rich catalysts by increasing the crystallite size and lowering the specific surface area. It is shown that the H2O2 dissociates on Ce (III) surface sites to yield peroxide-like species. Such species played a key role in enhancing the discoloration of the dye under dark and UV-Vis conditions. By contrast, the sulfation treatment is unfavorable for the adsorption of H2O2. Sulfates interfere in the formation and the chemical stability of the surface peroxide species via pre-chelating the cerium surface centers, resulting in reducing the catalytic activity of catalysts, especially for CeO2.

A kinetic study of vapor-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1

A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was performed. The production of cyclohexene oxide was very stable with high selectivity. Based on the kinetic analysis, the gas-phase mechanism is proposed to be similar to that of the liquid-phase reaction: an Eley–Rideal type mechanism, in which the reaction between a Ti–OOH intermediate and the physisorbed alkene is the rate-determining step. When the partial pressure of water or H2O2 was varied, a compensation effect was observed. Based on the kinetic model, the compensation effect is attributed to variations in the surface coverage of intermediates, specifically the competitive adsorption of water and H2O2 at the Ti active sites. A meaningful activation energy can only be obtained at high surface coverages of H2O2 and was determined to be 40±2kJ/mol.

One-pot oxydehydration of glycerol to value-added compounds over metal-doped SiW/HZSM-5 catalysts: Effect of metal type and loading

A one-pot oxydehydration of glycerol to value-added compounds was carried out over metal-doped SiW/HZSM-5 catalyst at low temperature (90°C) and ambient pressure. Effects of metal types (Co, Ce, Ni and V) and loadings (0–8wt.%) on catalyst properties and catalytic activity were explored. Doping different types of metal and loading on the surface of SiW/HZSM-5 catalyst affected surface chemistry and textural chemistry as well as the catalytic activity for glycerol conversion and product yield distribution. The V at 6% loading most effectively enhanced the activity of SiW/HZSM-5 for a one-pot oxydehydration of glycerol to value-added compounds. The presence of V6-SiW/HZSM-5 catalyst can enhance the glycerol conversion up to 99.67% with the yields of glycolic acid, formic acid, acetic acid, acrolein, acrylic acid, and propionic acid of 19.45%, 12.03%, 23.62%, 0.25%, 36.23% and 7.06%, respectively with less than 1.5% of glycerol converting to some undesired products. The kinetic studies of a one-pot oxydehydration of glycerol over this catalyst (V6-SiW/HZSM-5) showed the rate of glycerol conversion depended upon the glycerol concentration according to the pseudo-first order kinetic rate and about the zero order with respect to the H2O2 concentration. The Eley–Rideal model, assuming the reaction between a non-dissociative adsorption of H2O2 and glycerol molecule provided the best fit with the experimental results.

Mesoporous Ce[sbnd]Pr[sbnd]O solid solution with efficient photocatalytic activity under weak daylight irradiation

In this study, the application of mesoporous CeO2 and Pr doped CeO2 (CePrO) as photocatalysts for the degradation of Rhodamine B (RhB) from aqueous solution was investigated. Mesoporous CeO2 and CePrO were prepared using SBA-15 as template. The resultant samples were characterized by XRD, N2 adsorption–desorption, Raman, UV–vis, TEM, FT-IR, and XPS techniques. The characterization results show that the synthesized CePrO has a 2D hexagonal structure, similar to that of the template, and possesses numerous oxygen vacancies. It is worth mentioning that the visible light adsorption intensity of CePrO is much higher than that of mesoporous ceria and bulk ceria, due to simultaneous formation of doping level and mesopores. The photodegradation of RhB illustrates that the synthesized mesoporous CePrO, especially 45% CePrO, performs excellent decolorization under weak daylight irradiation. Furthermore, a novel photodegradation mechanism was proposed based on the adsorption of H2O2 over the oxygen vacancy.

Ultrasound (US), Ultraviolet light (UV) and combination (US + UV) assisted semiconductor catalysed degradation of organic pollutants in water: Oscillation in the concentration of hydrogen peroxide formed in situ

Application of Advanced Oxidation Processes (AOP) such as sono, photo and sonophoto catalysis in the purification of polluted water under ambient conditions involve the formation and participation of Reactive Oxygen Species (ROS) like OH, HO2, O2−, H2O2 etc. Among these, H2O2 is the most stable and is also a precursor for the reactive free radicals. Current investigations on the ZnO mediated sono, photo and sonophoto catalytic degradation of phenol pollutant in water reveal that H2O2 formed in situ cannot be quantitatively correlated with the degradation of the pollutant. The concentration of H2O2 formed does not increase corresponding to phenol degradation and reaches a plateau or varies in a wave-like fashion (oscillation) with well defined crests and troughs, indicating concurrent formation and decomposition. The concentration at which decomposition overtakes formation or formation overtakes decomposition is sensitive to the reaction conditions. Direct photolysis of H2O2 in the absence of catalyst or the presence of pre-equilibrated (with the adsorption of H2O2) catalyst in the absence of light does not lead to the oscillation. The phenomenon is more pronounced in sonocatalysis, the intensity of oscillation being in the order sonocatalysis>photocatalysis⩾sonophotocatalysis while the degradation of phenol follows the order sonophotocatalysis>photocatalysis>sonocatalysis>sonolysis>photolysis. In the case of sonocatalysis, the oscillation continues for some more time after discontinuing the US irradiation indicating that the reactive free radicals as well as the trapped electrons and holes which interact with H2O2 have longer life time (memory effect).

Adsorption of H2O2 at the surface of Ih ice, as seen from grand canonical Monte Carlo simulations

Adsorption of H2O2 at the (0001) surface of Ih ice is investigated by GCMC simulations under tropospheric conditions. The results are in qualitative agreement with experimental data and reveal that the main driving force of the adsorption is the formation of new H2O2–H2O2 rather than H2O2–water H-bonds. The isotherm belongs to class III and not even its low pressure part can be described by the Langmuir formalism. At low coverages H2O2 prefers perpendicular alignment to the surface, in which they can form three H-bonds with surface waters. At higher coverages parallel alignment, stabilized by H-bonds between neighbouring H2O2 molecules, becomes increasingly preferred.

The effect of transition metal substitution on the catalytic activity of magnetite in heterogeneous Fenton reaction: In interfacial view

Recently, growing interest has been evoked in the application of transition metal substituted magnetite as heterogeneous Fenton catalyst in the degradation of organic pollutants. In the present study, the effect of substitution on the heterogeneous Fenton catalytic activity of magnetite was investigated in interfacial view. The substitution of transition metals improved the degradation of organic pollutants by accelerating the OH free radical generation and enhancing the adsorption of pollutant and H2O2. As the octahedral sites were exclusively exposed at magnetite surface, V3+ and Cr3+ occupying the octahedral sites not only participated in H2O2 decomposition to produce OH, but also quickened the electron transfer in the inverse spinel structure to reduce Fe3+ to Fe2+ with higher Fenton activity. Ti4+ , V3+ and Cr3+ increased the specific surface area and surface hydroxyl amount of magnetite, resulting in larger adsorption of methylene blue (MB) and H2O2 and accordingly faster degradation. In Ti-V co-doped magnetite, though Ti4+ was thermodynamically unfavorable for OH generation, Ti4+ showed a more prominent effect than V3+ on improving catalytic activity of magnetite, ascribed to its more significant effect on the increase of specific surface area and surface hydroxyl amount of magnetite. The catalytic efficiency was closely related to not only the nature of substituting metals, but also the pollutant characters. Due to the different adsorption behaviors, the degradation MB and acid orange II followed different degradation mechanism and was also described by different kinetics. The above results will be benefit for the application of transition metal substituted magnetite in environmental engineering.

Microscopic effects of the bonding configuration of nitrogen-doped graphene on its reactivity toward hydrogen peroxide reduction reaction

We report a density functional theory (DFT) study of microscopic detailed effects of the bonding configuration of nitrogen-doped graphene (N-graphene) within the carbon lattice (including pyridinic, pyrrolic, and graphitic N) on the reactivity and mechanistic processes of H2O2 reduction reaction. We simulated the adsorption process of H2O2, analyzed the mechanistic processes, and calculated the reversible potential of each reaction step of the H2O2 reduction reaction on N-graphene. The results indicate that the adsorption of H2O2 on the pristine and N-doped graphene surfaces occurs via physisorption without the formation of a chemical bond. When H(+) is introduced into the system, a series of reactions can occur, including the breakage of the O-O bond, the formation of an O-C chemical bond between oxygen and graphene, and the creation of water molecules. The results also indicate a decrease in the energy of the system and a positive reversible potential for each reaction step. The calculations of the relative energy of each reaction step and the value of the onset potential for H2O2 reduction reaction suggest that the reactivity of pristine and N-doped graphene has the following order: pyridinic N-graphene > pyrrolic N-graphene > graphitic N-graphene > pristine graphene. We also proposed an explanation based on electrostatic potential calculations for this dependence of the reactivity order on the bond configuration of the doping in N-graphene. The results of this study should help in the atomic-scale understanding of the dependence of the reactivity of N-graphene on its microstructure, inspire the study of various types of heteroatom-doped graphenes to improve their catalytic efficiency, and provide a theoretical framework to analyze their reactivities.

The impact of spectator species on the interaction of H2O2 with platinum – implications for the oxygen reduction reaction pathways

The impact of electrolyte constituents on the interaction of hydrogen peroxide with polycrystalline platinum is decisive for the understanding of the selectivity of the oxygen reduction reaction (ORR). Hydrodynamic voltammetry measurements show that while the hydrogen peroxide reduction (PRR) is diffusion-limited in perchlorate- or fluoride-containing solutions, kinetic limitations are introduced by the addition of more strongly adsorbing anions. The strength of the inhibition of the PRR increases in the order ClO4(-)≈ F(-) < HSO4(-) < Cl(-) < Br(-) < I(-) as well as with the increase of the concentration of the strongly adsorbing anions. Electronic structure calculations indicate that the dissociation of H2O2 on Pt(111) is always possible, regardless of the coverage of spectator species. However, the adsorption of H2O2 becomes strongly endothermic at high coverage with adsorbing anions. A comparison of our observations on the inhibition of the PRR by spectators with previous studies on the selectivity of the ORR shows that oxygen is reduced to H2O2 only under conditions at which the PRR kinetics is significantly limited, while the ORR proceeds with a complete four-electron reduction only when the PRR is sufficiently fast. Therefore, only a H2O2-mediated pathway that includes a competition between the dissociation and the spectator coverage-dependent desorption of the H2O2 intermediate is enough to explain and unify all the observations that have been made so far on the selectivity of the ORR.

Reactivity of metal oxide clusters with hydrogen peroxide and water – a DFT study evaluating the performance of different exchange–correlation functionals

We have performed a density functional theory (DFT) investigation of the interactions of H2O2, H2O and HO radicals with clusters of ZrO2, TiO2 and Y2O3. Different modes of H2O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H2O has undergone dissociative adsorption, the adsorption of H2O2 and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO2, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H2O2 and the adsorption of H2O. Additionally, we investigated clusters of the type (ZrO2)2, (TiO2)2 and (Y2O3) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H2O2, H2O and HO˙ adsorption and the energy barrier for decomposition of H2O2. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H2O2, the functional used must include Hartree-Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H2O2 decomposition was obtained with the M06 and PBE0 functionals - the average absolute deviations from experiments are 6 kJ mol(-1) and 5 kJ mol(-1) respectively. With the M06 functional and a larger monoclinic (ZrO2)8 cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.

Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces

We performed an experimental and density functional theory (DFT) investigation of the reactions of H2O2 with ZrO2, TiO2, and Y2O3. In the experimental study we determined the reaction rate constants, the Arrhenius activation energies, and the activation enthalpies for the processes of adsorption and decomposition of H2O2 on the surfaces of nano- and micrometer-sized particles of the oxides. The experimentally obtained enthalpies of activation for the decomposition of H2O2 catalyzed by these materials are 30 ± 1 kJ·mol–1 for ZrO2, 34 ± 1 kJ·mol–1 for TiO2, and 44 ± 5 kJ·mol–1 for Y2O3. In the DFT study, cluster models of the metal oxides were used to investigate the mechanisms involved in the surface process governing the decomposition of H2O2. We compared the performance of the B3LYP and M06 functionals for describing the adsorption energies of H2O2 and HO• onto the oxide surfaces as well as the energy barriers for the decomposition of H2O2. The DFT models implemented can describe the experimental reactio...

Photocatalytic H2O2 Production from Ethanol/O2 System Using TiO2 Loaded with Au–Ag Bimetallic Alloy Nanoparticles

TiO2 loaded with Au–Ag bimetallic alloy particles efficiently produces H2O2 from an O2-saturated ethanol/water mixture under UV irradiation. This is achieved via the double effects created by the alloy particles. One is the efficient photocatalytic reduction of O2 on the Au atoms promoting enhanced H2O2 formation, due to the efficient separation of photoformed electron–hole pairs at the alloy/TiO2 heterojunction. Second is the suppressed photocatalytic decomposition of formed H2O2 due to the decreased adsorption of H2O2 onto the Au atoms.

Adsorption and dissociation of hydrogen peroxide on small Pd x M3−x (M = Pt, Cu; x = 1−3) clusters: a hybrid density functional study

The adsorption and dissociation of H2O2 on small Pd x M3−x (M=Pt, Cu; x = 1–3) clusters is investigated using the B3PW91 hybrid density functional method. Natural bond orbitals are analysed to obtain partial charges on atoms, dipole moments, bond orders, and hybrid orbitals of the Pd x M3−x –H2O2 systems. The calculated adsorption energies are in the range of −0.32 to −2.12 eV. Generally, H2O2 adsorbs on top positions through one of its oxygen atoms and only in a few cases reacts with the cluster through both oxygen and hydrogen sides. In the latter case the cluster sites which are negatively charged interact with the hydrogen atoms. Interestingly, on the triplet Pd2Pt cluster, H2O2 dissociates spontaneously to two OH that adsorb strongly on the Pd sites. In this chemical bond the oxygen p orbitals interact with the Pd d orbitals. Surprisingly, this mode of adsorption never occurs on the singlet Pd2Pt cluster and neither on other clusters with similar charge distributions. We believe that not only the electric field of the positively charged Pd atoms but also the Pd unpaired d electrons in the triplet Pd2Pt cluster make H2O2 dissociative adsorption to be thermodynamically and kinetically favoured.