Specific Rate Constants Research Articles

Ternary transition metal organic frameworks (MOFs) CuZn-MIL101 (Fe) for peroxymonosulfate activation to degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA): A non-radical pathway dominated by singlet oxygen

In this study, ternary CuZn-MIL101(Fe) MOFs were prepared by introducing Cu and Zn ions into MIL-101(Fe) to obtain catalysts with excellent peroxymonosulfate (PMS) activation properties. The comprehensive characterization analysis revealed that although the adsorption performance of CuZn-MIL101(Fe) decreased, the PMS activation performance was significantly improved and complete degradation of MCPA was reached in 20 min. Calculation of the specific rate constants (kSA) yielded that the intrinsic activity of CuZn-MIL101(Fe) for PMS was 34 and 37 times higher than that of CuZn0.25-MIL101(Fe) and Cu0.25Zn-MIL101(Fe), respectively. The quenching experiments combined with electron paramagnetic resonance (EPR) spectroscopy verified the composition of the active substances in the system, whose contributions were in the order of O21 > ·OH > SO4⋅− > O2⋅. Using PMSO as a probe, an important role of high-valent iron was found in the system. The HOMO-LUMO gap of MCPA was calculated to be 0.205 eV by density functional theory (DFT), and the difference in adsorption energy of MCPA when adsorbing different radicals was investigated. The intermediate products were obtained by GC-MS and analyzed for toxicity, and the mechanism of singlet oxygen-dominated degradation of MCPA was proposed, which laid the foundation for the subsequent in-depth study of phenoxyacetic acid-based herbicides.

Graphitic carbon nitride thin films for light-induced photocatalysis in a slit geometry microreactor

A combination of a photocatalysis and a micro-flow technology provides a highly capable tool for the design and utilisation of functional thin films. Here, they are represented by graphitic carbon nitride films, potentially used for photo-oxidations in environmental chemistry or for hydrogen evolution by water splitting. The optimised synthesis involves a study of the role of monomers, solvents, calcination temperatures, particle size, etc., in respect of the achieved photocatalytic activity. Films were prepared from the mixture of milled powder catalysts and a binder, dried, and subjected to post-processing treatments (post annealing, plasma application). The intended functionality was assessed in two types of reactions, photo-oxidation of a fluorescent dye, Rhodamine B, and photo-oxidation of a common antibiotic, Tetracycline. The performance was compared for the bulk catalyst, and for the thin film. In either case, the same part of light spectrum, concentrations, and other conditions were applied. However, for the thin films, a special experimental setup was utilised. It had the appearance of a micro-flow apparatus designed as a slit geometry photo-microreactor. Comparison of the two different reaction systems revealed the advantages of the thin film catalyst, which was immobilised directly on the photo-microreactor wall. The specific rate constant was more than 50 times higher in this arrangement for both model reactants. In addition, thin films of g-C3N4 were stable and well adherent during the microreactor tests with the repetitive reaction cycles. Plasma treatment considerably increased the hydrophilicity of the dried thin films, which resulted in their substantially higher photoactivity.

Kinetics Study of Co-Solvent effect in Alkaline Hydrolysis of Diethyl Pathalate Ester

The base catalyzed hydrolysis of diethyl pathalate has been carried out titrometically in water-ethanol binary solvent mixture covering range of 30 to 70% (v/v) of solvent composition at different Temperature (20 to 400C). The reaction followed second order rate constant which decreases with increase of solvent composition. The salvation and desolvation concept are used to explain the solvent influence on rate and mechanism is the reaction. The relation between changes in dielectric constant due to variation of reaction mixture and change in specific rate constant has been explained on the basis of electrostatic and non-electrostatic contribution of solvent mixture. Calculated value of Iso-composition activation energy is found to be increases with increase of solvent composition. The thermodynamic parameters (G*, H*&S*) has been determined with help of Wynne Jone and Eyring equation which show the great dependency on solvent composition.

Modelling Nannochloropsis gaditana Growth in Reactors with Different Geometries, Determination of Kinetic Parameters and Biochemical Analysis in Response to Light Intensity

Microalgae are unicellular and photosynthetic microorganisms which grow thanks to inorganic salts, CO2 and light, and find applications in several fields thanks to their variety. The industrial application of microalgae has not often been fully exploited because of a lack of information about how microalgae respond to inputs and to different growth environments. In the present work a model able to predict the microalgae growth in reactors with different geometries was developed. We combined a Monod-like model for the specific growth rate with the Lambert-Beer law of homogeneous light distribution in thick photobioreactors. Kinetic parameters related to the cultivation of the microalga Nannochloropsis gaditana were obtained, for the first time through batch cultivation under different photon flux densities inside a quasi-isoactinic photobioreactor, in order to obtain a practically homogeneous light distribution. The maximum specific growth rate and saturation constant resulted, respectively as µmax = 0.0256 h−1 and Ik = 15.28 µE s−1m−2. These parameters were applied to the model to obtain data on microalgae growth in different geometries. Model simulation results are presented and discussed. Furthermore, biochemical analysis was performed on the biomass obtained at the end of each batch cultivation, grown both under different light intensities and in reactors with different configurations. Results indicated that lipid content increases with increasing average photon flux density. The fatty acid and carotenoids profiles markedly shift when the average light intensity varies: the PUFA content decreases and the SFA content increases when the average light intensity rises, and an accumulation of carotenoids at lower photon flux densities is observed. In conclusion, the model resulted in a useful tool, able to predict the growth of the microalga Nannochloropsis gaditana in reactors with different configurations.

Critical insights into anaerobic co-digestion of wheat straw with food waste and cattle manure: Synergistic effects on biogas yield and kinetic modeling

In this study, four batch assays were performed to ensure the synergic effects of co-digestion and find out the best inoculums to substrate ratio (ISR), carbon to nitrogen ratio (C:N), and total solid (TS) percentage in sequence. The co-digestion of three feedstocks had a 20% higher biogas yield (416 mL/gVS added) than mono-digestion with 21% volatile solids (VS) degradation. The ISR of 2 leads to the highest biogas yield (431 mL/gVS added) and VS removal (30.3%) over other ISRs (0.5, 1.0, 2.5) studied. The lower ISR (<2) tended to have lower pH due to insufficient anaerobes inside the digester. The C:N 35 (with ISR 2) yielded 17.4% higher biogas (443.5 mL/gVS added) than mono-digestion and was the highest among the C:N ratios studied with 36.6% VS removal. The VFA, alkalinity, and pH in C:N 35 assay were more stable than in other C:N assays. In the fourth batch assay, varying TS% (5, 7.5, 10, 12.5) were used with optimized ISR (2) and C:N (35). Higher TS% (10 and 12.5) had some lag phase but later achieved higher biogas production. The 12.5% TS assay achieved 80% higher biogas yield (679 mL/gVS added) over mono-digestion, i.e., highest among the TS% studied, with 48% VS removal. In conclusion, co-digestion of mixed feedstocks with ISR 2, C:N 35, and TS 12.5% could degrade almost half of the substrate available for biodegradation. Further biodegradation may require pretreatment of the recalcitrant WS. Modified Gompertz, first-order, transference, and logistic models were used for kinetic study and curve fitting of experimental data. For the optimized batch assays, the estimated specific rate constants were 0.08, 0.12, 0.083, and 0.084. The data fits well in all the models, with the coefficient of discrimination (R2) ranging from 0.882 to 0.999.

Kinetic study of thermophilic anaerobic digestion of sugarcane vinasse in a single-stage continuous stirred tank reactor

Vinasse, the liquid waste from the bottom of a bioethanol distillation column, is a potential feedstock for biogas production due to its high organic content. Vinasse is discharged at a high temperature, i.e., 60–80 °C. Therefore, thermophilic anaerobic digestion is more efficient to directly treat the vinasse at a high organic loading rate (OLR). This study investigated the performance of thermophilic anaerobic digestion on sugarcane vinasse inoculated with acclimated digested cow manure (DCM). The experiment was run at varied OLRs (1,2; 1.8 and 2.4 gCOD.L−1.day−1). The process was carried out in a continuous stirred tank reactor (CSTR) with controlled pH (7 ± 0.5) and oxidation-reduction potential/ORP (−500 ± 10 mV). During the 111 days of the experiment, we monitored the volatile fatty acids (VFA), total chemical oxygen demand (tCOD), and soluble chemical oxygen demand (sCOD), as well as methane and biogas production rates, to evaluate the reactor performance. The experimental data were fitted on the Anaerobic Digestion Model 1 (ADM 1) using the AQUASIM® software. The data were categorized in three process stages observed in this study: stabilization, enrichment, and steady-state. The kinetic parameters, i.e., the coefficient of affinity (KS,ac, KS,pro) and the specific growth rate (km,ac and km, pro), were obtained from the data fitting. The good fit of ADM 1 to the data highlighted the flexibility of ADM 1 to represent a dynamic system of a thermophilic anaerobic digestion system with simultaneous changes in both process variables and microbial composition. The data fitting gave consistently low Ks values in the lower OLR of 0.2 gCOD. L−1.day−1 up to the higher OLR of 2.4 gCOD. L−1.day−1. The Ks values, which were less than 1/1000 of the specific growth rate constants (km), indicated that the combined effects of the thermophilic condition and vinasse composition increased the microbial-substrate affinity (showed by KS) more essentially than the microbial growth rate (addressed by km). In addition, inhibitory effects were not observed with all OLR values tested in this study.

Effect of Intersystem Crossings on the Kinetics of Thermal Ion-Molecule Reactions: Ti+ + O2, CO2, and N2O.

A selected-ion flow tube apparatus has been used to measure rate constants and product branching fractions of 2Ti+ reacting with O2, CO2, and N2O over the range of 200-600 K. Ti+ + O2 proceeds at near the Langevin capture rate constant of 6-7 × 10-10 cm3 s-1 at all temperatures to yield 4TiO+ + O. Reactions initiated on doublet or quartet surfaces are formally spin-allowed; however, the 50% of reactions initiated on sextet surfaces must undergo an intersystem crossing (ISC). Statistical theory is used to calculate the energy and angular momentum dependences of the specific rate constants for the competing isomerization and dissociation channels. This acts as an internal clock on the lifetime to ISC, setting an upper limit on the order of τISC < 1e-11 s. 2Ti+ + CO2 produces 4TiO+ + CO less efficiently, with a rate constant fit as 5.5 ± 1.3 × 10-11 (T/300)-1.1±0.2 cm3 s-1. The reaction is formally spin-prohibited, and statistical modeling shows that ISC, not a submerged transition state, is rate-limiting, occurring with a lifetime on the order of 10-7 s. Ti+ + N2O proceeds at near the capture rate constant. In this case, both Ti+ON2 and Ti+N2O entrance channel complexes are formed and can interconvert over a barrier. The main product is >90% TiO+ + N2, and the remainder is TiN+ + NO. Both channels need to undergo ISC to form ground-state products but TiO+ can be formed in an excited state exothermically. Therefore, kinetic information is obtained only for the TiN+ channel, where ISC occurs with a lifetime on the order of 10-9 s. Statistical modeling indicates that the dipole-preferred Ti+ON2 complex is formed in ∼80% of collisions, and this value is reproduced using a capture model based on the generic ion-dipole + quadrupole long-range potential.

Intensification of Dry Reforming of Methane on Membrane Catalyst: Confirmation and Development of the Hypothesis.

This article presents an analysis of kinetic studies of dry methane reforming (DRM) in a reactor with a membrane catalyst (RMC) in the modes of a contactor with “diffusion” and “forced” mass transfer. Comparison of the specific rate constants of the methane dissociation reaction in membrane and traditional reactors confirmed the phenomenon of intensification of dry methane reforming in a membrane catalyst (MC). It has been experimentally established that during DRM, a temperature gradient arises in the channels of the pore structure of the membrane catalyst, characterized by a decrease in temperature towards the inner volume of the MC, and initiates the phenomenon of thermal slip. The features of this phenomenon are highlighted and must be considered in the analysis of kinetic data. The main provisions of the hypothesis explaining the effect of intensification by the occurrence of thermal slip in the channels of the pore structure of the MC are formulated. The proposed hypothesis, based on thermal slip, explains the difference in rate constants of traditional and membrane catalysts, and substantiates the phenomenological scheme of DRM stages in a reactor with a membrane catalyst.

Electro-sensing base for hazardous pesticide 2, 4-DCP and its quantification in real samples at ZnO@Cu core-shell nanoparticles in the presence of cationic surfactant

We developed a novel sensor using carbon paste electrode (CPE) modified with cationic surfactant cetyltrimethylammonium bromide (CTAB) and the core-shell nanoparticles (NPs) of zinc oxide at copper (ZnO@Cu) to study an electrochemical behavior of 2, 4 - dichlorophenol (2, 4 - DCP), a harmful molecule. The core-shell ZnO@Cu NPs/CTAB/CPE is proved to be sensitive because of its sensing features for 2, 4-DCP. The sensor showed excellent electro-catalytic behavior and elevation in peak current in the presence of phosphate buffer solution (PBS) of 0.2 M strength. Advanced techniques like transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS), and scanning electron microscope (SEM) were employed to ZnO@Cu core-shell NPs characterization. The cyclic voltammetry (CV), as well as square wave voltammetry (SWV) techniques, were applied to study electro-kinetic parameters, including specific heterogeneous rate constant, charge transfer coefficient, accumulation time, scan rate, the effect of temperature, pH, the energy of activation, enthalpy, entropy, Gibb's free energy, and the number of electrons transferred in the 2, 4 - DCP electro-oxidation. By SWV technique, the 2, 4 - DCP molecule was analyzed in vegetables, fruits, water, and soil samples.

Dynamic Optimization Approach to Estimate Kinetic Parameters of Monod-Based Microalgae Growth Models.

The biomass concentration of microalgae growth in photobioreactor was predicted using the Monod-based growth models. Kinetic parameters such as maximum specific growth rate and saturation constant of light intensity were evaluated by nonlinear least squares methods that focused on minimizing the sum of squares error (SSE). The importance of good initial guess for the nonlinear least squares method was also discussed. The optimal control problem of the microalgae growth model was determined based on parameter sensitivity. Therefore, a dynamic optimization approach was used where an optimal input design method was formulated to obtain a control function of a problem. The dynamic state equations, additional state equations, cost function, and Hamiltonian function were used to establish a control function of microalgae growth in a photobioreactor. Hence, the biomass production of microalgae can be predicted using numerical methods such as the Taylor series method.

Kinetics Solvent Effect and Mechanism of Hydrolysis of Ethyl Caprylate Ester in Aqueous Organic Solvent Media

The specific rate constant of ethyl caprylate in alkali catalised hydrolysis in water-acetone mixture covering range of 30 to 70% (v/v) of acetone has been determined at temperature 20 to 400c. The rate of reaction decreases with increase in percentage of Acetone from 30 to 70% (v/v). The observed Activation energy decreases progressively with increase in acetone content of the medium. The effect of molar concentration of water and Dielectric constant on the reaction kinetic has also been studied. The thermodynamic parameters (DG*, DH* and DS*) has been determined which showed strong dependency on solvent composition.

Kinetics of the production of alkyl esters by transesterification of soybean oil

AbstractBiodiesel was produced by transesterification from soybean oil using methanol (methanolysis) and ethanol (ethanolysis) under conditions including NaOH/alcohol 0.50% wt, molar ratio alcohol:oil = 6:1, 600 rpm, 333 K. The evolution of biodiesel and glycerol esters concentrations were obtained by gas chromatography and liquid chromatography, respectively, as a basis for the evaluation of the kinetics of the process. A mathematical model was developed to represent the batch transesterification operations, referring to a mechanism including reactive acylglycerols and intermediates, esters, and glycerol. Considering the importance of the composition of fatty esters in biodiesel, their evolution during processing was quantified. The specific reaction rates for methanolysis and ethanolysis were 0.245 and 0.275 min−1, respectively. The concentration evolution of each fatty ester of the biodiesel was predicted by the solutions of the model equations, based on specific reaction rate constants quantified in the orders of magnitude k = 0.225–0.245 min−1 for methanolysis, and k = 0.225–0.275 min−1 for ethanolysis. Selectivity and yield values of the fatty esters were calculated: it was found Si = 23.5%–25.6% and Ri = 66.3%–89.1% for methanolysis and Si = 21.8%–26.7% and Ri = 74.1%–90.6% for ethanolysis. Based on the model, predictions of the kinetic behavior of acylglycerols reactants (triacylglycerois) and intermediates (monacylglycerois, diacylglycerois) were established.

Biodegradation of acid red 3BN dye in sequential batch reactor: parameters and kinetics studies

Abstract Textile and dye industries generate wastewater which is considered as highly polluted and carcinogenic. Due to this, treatment of wastewater is required earlier to discharge or recycle. In the present studies, treatment of dye bearing water (DBW) has been explored. The treatment was performed using activated sludge (mixed culture) for aerobic process in sequential batch reactor (SBR). The fill volume (V F) and fill time (t F) variation in the treatment of DBW was taken place. The initial value of dye concentration, chemical oxygen demand (COD), sludge, and hydraulic retention time (HRT) were found to play important role in the treatment. At optimum condition (HRT = 2.5 d), the 86.84% COD reduction of 190 mg/L COD, and 92.33% dye reduction of 339 mg/L dye were achieved. These values are equal to overall 94.85% dye reduction of 500 mg/L, and 93.15% COD reduction of 380 mg/L. As a result, 500 mg/L dye was reduced to 26 mg/L, and 380 mg/L COD was reduced to 25 mg/L. The biodegradation fitted to Monod kinetics, for which kinetics parameter values of specific growth rate constant of biomass µ = 0.0047 h−1, yield coefficient (Y) = 1.059, and substrate utilization rate (q) = 0.0044 h−1 were evaluated at HRT = 2.5 d. The results show, this process can be applied to treat Acid Red 3BN Dye Water (AR3BNDW).

Features of Hydrogen Reduction of Fe(CN)63- Ions in Aqueous Solutions: Effect of Hydrogen Dissolved in Palladium Nanoparticles.

Preliminary saturation of 2.6 nm palladium nanoparticles with hydrogen accelerates the reduction of Fe(CN)63− ions in aqueous solution three to four-fold. An analytical equation was derived describing the hydrogen saturation of palladium nanoparticles and the dependence of their catalytic activity on the hydrogen content in the metal. The specific rate constants of reduction do not depend on the content of palladium nanoparticles in the solution. A change in the temperature and pH or stirring of the solution do not affect the rate of catalytic reaction. Approaches to optimization of palladium-catalyzed reactions involving hydrogen are substantiated.

Enhancing methane production from the invasive macroalga Rugulopteryx okamurae through anaerobic co-digestion with olive mill solid waste: process performance and kinetic analysis

The biomass valorisation of the invasive brown alga Rugulopteryx okamurae (Dictyotales, Phaeophyceae) is key to curbing the expansion of this invasive macroalga which is generating tonnes of biomass on southern Spain beaches. As a feasible alternative for the biomass management, anaerobic co-digestion is proposed in this study. Although the anaerobic digestion of macroalgae barely produced 177 mL of CH4 g−1 VS, the co-digestion with a C-rich substrate, such as the olive mill solid waste (OMSW, the main waste derived from the two-phase olive oil manufacturing process), improved the anaerobic digestion process. The mixture improved not only the methane yield, but also its biodegradability. The highest biodegradability was found in the mixture 1 R. okamurae—1 OMSW, which improved the biodegradability of the macroalgae by 12.9% and 38.1% for the OMSW. The highest methane yield was observed for the mixture 1 R. okamurae—3 OMSW, improving the methane production of macroalgae alone by 157% and the OMSW methane production by 8.6%. Two mathematical models were used to fit the experimental data of methane production time with the aim of assessing the processes and obtaining the kinetic constants of the anaerobic co-digestion of different combination of R. okamurae and OMSW and both substrates independently. First-order kinetic and the transference function models allowed for appropriately fitting the experimental results of methane production with digestion time. The specific rate constant, k (first-order model) for the mixture 1 R. okamurae- 1.5 OMSW, was 5.1 and 1.3 times higher than that obtained for the mono-digestion of single OMSW and the macroalga, respectively. In the same way, the transference function model revealed that the maximum methane production rate (Rmax) was also found for the mixture 1 R. okamurae—1.5 OMSW (30.4 mL CH4 g−1 VS day−1), which was 1.6 and 2.2 times higher than the corresponding to the mono-digestions of the single OMSW and sole R. okamurae (18.9 and 13.6 mL CH4 g−1 VS day−1), respectively.

An experimental and statistical modeling study of the reactivity of Co+(CH3Br)n (n = 0,1) with methyl bromide

The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are measured from 300 to 600 K and from 0.2 to 0.5 Torr. Results are interpreted using density functional calculations and modeled with statistical theory. In the n = 0 case, the associative product Co+(CH3Br) dominates with a rate constant between 5 and 30% of the collisional value, while a minor channel yields CoBr+ + CH3 with a rate constant increasing with temperature. 0K bond dissociation energies (BDE) are determined for Co+-Br (2.8 ± 0.1 eV) and Co+-CH3Br (2.4 ± 0.25 eV). Ligation of Co+ (i.e. n = 1) significantly increases the bimolecular reaction rate constant. CoBr+(CH3Br) + CH3 is formed and the reaction has a positive temperature dependence. Interestingly, this rate constant decreases with increasing pressure due to competition of the association channel. Ligation increases the (CH3Br)Co+-Br BDE (3.0 ± 0.1 eV) relative to Co+-Br, but decreases the (CH3Br)Co+-CH3Br BDE (1.95 ± 0.25) relative to Co+-CH3Br. Both bimolecular reactions proceed by a metal-insertion mechanism with a significantly submerged transition state that does not affect the kinetics. Instead, the endothermicity of the reaction is rate-limiting. Discussion about how energy, impact parameter, and angular momentum affect specific rate constants for dissociation to reactants, reaction to products, and association are presented.

Transport Reagents through the Pore Structure of a Membrane Catalyst under Isothermal and Non-Isothermal Conditions.

The article presents the results of an experimental comparison of methane transport in the pore structure of a membrane catalyst under isothermal and non-isothermal Knudsen diffusion conditions. It is shown that under the conditions of non-isothermal Knudsen diffusion in the pore structure of the membrane catalyst, there is a coupling of dry reforming of the methane (DRM) and gas transport, which leads to the intensification of this process. The reasons for the intensification are changes in the mechanism of gas transport, an increase in the rate of mass transfer, and changes in the mechanism of some stages of the DRM. The specific rate constant of the methane dissociation reaction on a membrane catalyst turned out to be an order of magnitude (40 times) higher than this value on a traditional (powder) catalyst.

Apparent Pyrolysis Kinetics and Index-Based Assessment of Pretreated Peach Seeds

To better understand pyrolysis for upscaling purposes, a kinetic characterization of the process is necessary for every feedstock. Laboratory experiments allow identification of apparent kinetic models. This paper aims at the apparent kinetic investigation of peach seeds’ slow pyrolysis. Peach seeds from Greek peach fruits pyrolyzed under inert atmospheric conditions at different temperatures (475–785 °C), heating rates (100–250 °C/min) and N2 flow rates (25–200 cc/min). Prior to pyrolysis, they submitted to hexane extraction for the recovery of 36.8% wt. of the contained oils. Determination of the specific rate constant (k) and activation energy (Ea) for each considered reaction was made by using the Coats–Redfern integral non-isothermal fitting model that requires an assumption of the reaction order (n). Results revealed that a 3rd order reaction model best fits the process, the increasing of the pyrolysis temperature leads to a decrease of the activation energy (E) and pre-exponential factor (A), while nitrogen flow rate and heating rate had an opposite impact. E and A values ranged from 23 to 56 kJ/mol and 1.82 × 106 to 1.13 × 106 min−1, respectively, at different pyrolysis conditions. Furthermore, estimation of combustion and pyrolysis indexes were made to assess the suitability of peach seeds as a fuel, using isothermal thermogravimetric analyses (TGA). Results revealed that peach seeds are a suitable feedstock for pyrolysis, while prior submission of peach seeds to oils extraction, in a cascade biorefinery approach, can increase the energy and material recovery efficiency and potentially the environmental and economic benefit of the agri-food industrial sector.

Kinetics, pathways and toxicity of hexabromocyclododecane biodegradation: Isolation of the novel bacterium Citrobacter sp. Y3

This research investigated the biodegradation kinetics, pathways and ecological risk of hexabromocyclododecane (HBCD) by a novel bacterium Citrobacter sp. Y3. Results showed the biodegradation followed a first-order model. The specific degradation rate constant of HBCD were obviously higher in batch experiments with combined carbon sources (k: 0.156–0.290 d−1) than those using HBCD as the sole carbon source (k: 0.055 d−1). Correspondingly, the degradation half-life became much shorter (T1/2: 2.39–4.44 d vs T1/2: 13.7 d). HBCD could be degraded through dehydrobromination and dehalohydroxylation, of which six possible degradation products were detected. To evaluate the ecological risk of HBCD biodegradation products, acute toxicity tests were assessed for the first time. The acute toxicity decreased slowly during treatment for 3–5 d and then decreased sharply. In general, treatment by Strain Y3 is not only a biodegradation process but also a detoxification process, thus it shows potential for bioremediation of HBCD contaminated sites.

Bimetallic catalyzed decomposition of hydrogen peroxide – Kinetics, effect of support and reaction medium

Hydrogen peroxide is a versatile oxidant and has myriad industrial applications. The manuscript deals with the kinetic study for hydrogen peroxide decomposition using mono and bimetallic catalyst with different support and reaction mediums. Decomposition reaction has a major influence on three areas: (1) organic oxidations, where it is used as an oxidant to get intermediates and at times forming within the reaction as well; (2) polymer electrolyte fuel cells, where it acts as a degrading factor to cell stacks and (3) direct synthesis of peroxide through the gas-phase reaction of H2 and O2 to get H2O2. To enhance the hydrogen peroxide utility in the various processes, the decomposition activities of Au-Pd based bimetallic catalysts were tested. Bimetallic and monometallic supported catalysts were synthesized and evaluated to get the rate of decomposition. The catalysts were characterized using XRD, FTIR, TEM, and BET analysis. Hydrogen peroxide decomposition was studied in different mediums, namely, aqueous, acidic, and alkaline with/without halide to cater to the effect of change in the medium employed in different organic oxidations. First-order rate kinetics was assumed and the rate of decomposition was evaluated. Specific rate constants were evaluated and compared for all the catalysts for all the different mediums. The performance of the reaction in view of metal-support interaction and the effect of the reaction medium were studied.