Synthesis and Characterization of pH-Responsive Organic–Inorganic Hybrid Material with Excellent Catalytic Activity

Poly(N-isopropylmethacrylamide-co-methacrylic acid) [p(NipAam-Mac)] microgels were synthesized and used as microreactors to fabricate silver nanoparticles. Pure and hybrid microgels were characterized using Ultraviolet–Visible (UV/Vis) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and transmission electron microscopy (TEM). Catalytic activity of hybrid microgels and mechanism of catalysis by this system was explored using different reaction conditions. At the same temperature, apparent rate constant (k_app) was found to be varied from 0.0414 to 0.7852 min^?1 by increasing the concentration of NaBH₄ from 2.49 to 22.41 mM at constant concentration of substrate and catalyst. However upon extra increase in concentration of NaBH₄ from 22.41 to 37.35 mM reduced the value of k_app to 0.2178 min^?1. Likewise, the value of k_app was found to be increased from 0.1242 to 0.5495 min^?1 with increasing the concentration of 4-nitrophenol [Para-nitrophenol (p-Np)] from 0.063 to 0.079 mM keeping other parameters constant. Further increase in concentration of p-Np caused decline in the value of k_app. Kinetic data reveals that catalytic reduction of p-Np obeys Langmuir–Hinshelwood mechanism and p-Np is converted to p-Ap on the surface of the silver nanoparticles passing through various reaction intermediates.     

ULTRASOUND-ASSISTED N-ALKYLATION OF PHTHALIMIDE UNDER PHASE-TRANSFER CATALYSIS CONDITIONS AND ITS KINETICS

In this work, N-butylation of potassium phthalimide was carried out under ultrasonic-assisted phase-transfer catalysis condition using n-bromobutane as an alkylating agent. The mechanism of the solid-liquid reaction of alkyl halide and potassium salt of phthalimide in an organic solvent was verified in this work. The kinetics of the reaction depends on the amount of catalyst, agitation speed, type of quaternary ammonium salts, volume of water, type of organic solvent, volume of organic solvents, temperature, and the frequency of the ultrasound. Five different onium salts were examined for the reaction and tetrahexylammonium bromide showed maximum catalytical activity. An improvement of the reaction outcome (yield and reaction time) was achieved through the immersion of the reactor into an ultrasound bath. The rate of the reaction is two times faster under ultrasonic condition (k_app = 10.7 × 10^?3 min^?1) than silent condition (k_app = 5.5 × 10^?3 min^?1) and is five times faster when the reaction is carried out in acetonitrile medium than in cyclohexane medium. The reaction is very fast under anhydrous condition. Based on the experimental data, a rational mechanism for the reaction is proposed.     

UV-induced Persulfate Oxidation of Organic Micropollutants in Water Matrices

ABSTRACT

The efficacies of UV photolysis, UV-activated persulfate (UV/PS), and combined UV/Fe²⁺-activated persulfate (UV/PS/Fe²⁺) systems for degrading of different organic micropollutants in ultrapure water and groundwater were examined and compared. The studied micropollutants belonging to the different classes involved an artificial sweetener acesulfame K (ACE), beta-lactam antibiotic amoxicillin (AMX), and endocrine disrupting compound 4-nonylphenol (NP). Among the studied systems, the UV/PS/Fe²⁺ process showed the highest performance both in degradation and in mineralization of ACE (UVA-induced systems; k_app = 0.126 1/min and 80.3% TOC removal) and AMX (UVC-induced systems; k_app = 1.383 1/min and 85.4% TOC removal), followed by the UV/PS process. In the case of NP trials, the application of UVC/PS systems was the most promising, and after careful adjustment of oxidant concentration, it demonstrated a considerable improvement in the target compound degradation (at a NP/PS molar ratio of 1/4 k_app = 0.024 1/min) compared with the UVC photolysis (k_app = 0.016 1/min). Irrespective of the applied UV-induced treatment process, the efficacy of target compounds degradation was lower in groundwater as compared with ultrapure water trials.     

Synthesis,characterization and catalytic study of a novel iron(III)-tridentate Schiff base complex in sulfide oxidation by UHP

An hydrazone Schiff base-iron(III) complex using salicylidene benzoyl hydrazine (L) as ligand has been synthesized and characterized by elemental analyses, IR, ¹H and ¹³C NMR and UV–Vis spectroscopy. Oxidation of sulfides to sulfoxides in one-step was conducted by this complex catalyst using urea hydrogen peroxide (UHP) in mixture of CH₂Cl₂/CH₃OH (1:1) under air at room temperature. The effect of the reaction conditions on the oxidation of methylphenylsulfide was studied by varying the amount of the catalyst, reaction temperature, reaction time and the amount of UHP. The results showed that using this system in the oxidation of sulfides, sulfoxides were obtained as the main products, together with variable amounts of sulfones (?9%), depending on the nature of the substrate.     

Chemometric study of thermal treatment effect on the P25 photoactivity for degradation of tartrazine yellow dye

In the present work, a chemometric study was carried out using a central composite rotatable design (CCRD) to evaluate the effect of thermal treatment on the P25 photoactivity for degradation of tartrazine dye. The factors investigated for thermal treatment were: temperature, heating rate and heating time, and the experimental design response was the photodegradation constant (k_app). The response surface methodology (RSM) was employed to obtain the material with higher k_app value for tartrazine photodegradation, under UV radiation, and investigate the interactions between factors of thermal treatment. The P25 used as precursor, as well as the obtained material from the optimized conditions (TTP_op), and the material with worst photocatalytic activity (TTP-17) were characterized from the N₂ physiosorption, FT-IR, SEM, XRD, DSC/TGA and PAS. The TTP_op was obtained under conditions of temperature of 298?°C, heating rate of 10?°C?min^?1 and heating time of 177?min. TTP_op showed k_app value of 25.7, while P25 and TTP-17 presented k_app values of 20.2 and 10.0, respectively.     

Electrocatalytic activities of gold-5-amino-2-mercaptobenzimidazole-M self-assembled monolayer complexes (M: Ag, Cu) for hydroquinone oxidation investigated by CV and EIS

Electrocatalytic activity of a new catalyst toward the oxidation reaction of hydroquinone as a model compound is described. The catalyst was formed by immobilizing metal cations on the topside of a gold-5-amino-2-mercaptobenzimidazole, self-assembled monolayer (Au-5A2MBI-Mⁿ⁺ SAM, Mⁿ⁺: Cu²⁺, Ag⁺) electrode. Preparation steps and the electrocatalytic activity of the catalyst were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS data were approximated by appropriate electronic equivalent circuit models from which kinetic parameters, such as charge transfer resistance, double layer capacitance, and apparent rate constant (k_app), were estimated. Excellent activity was observed for Au-5A2MBI-Ag⁺ SAM with the following order: Au-5A2MBI-Ag⁺ > Au-5A2MBI-Cu²⁺ > Au-5A2MBI, after testing many modified electrodes. The increased activity originates from a modification of the Au-5A2MBI structure by mediating the effect of Ag⁺. This behavior was understood from significant increases in the k_app without significant changes in the double layer capacitance.     

Synthesis and studies on cellulose acetate—phenol formaldehyde cationic resin

Samples of a cationic sulphonated resin have been prepared by sulphonation of a mixture of phenol with cellulose acetate in the presence of paraformaldehyde as a crosslinking agent. The samples having average swelling percentage of 123, and a cation exchange capacity of 2.6 meq g^?1 resin, are being introduced as a new catalyst in the hydrolysis of ethyl acetate ester. The synthesized cation exchanger shows a good thermal and chemical stability. Hydrolysis rate constants (k_r values) for the catalysed reaction have been determined. The calculated values of the Arrhenius activation parameters show the overall slowness of the hydrolysis reaction accompanying the formation of the rigid activated complex.     

Study of the curing process giving the rigid polyurethane foam by dynamic viscoelastic method

Dynamic viscoelastic properties of the rigid polyurethane foam, which is used in Japan as a thermal insulator for refrigerators were studied during the curing process using the RDS-7700 Dynamic Spectrometer. The curing process, in which large volume expansion and heat evolution occurred, was easily analyzed by this method. The apparent storage modulus (G′_app), the apparent loss modulus (G″_app), and the apparent loss tangent (tan δ_app) were measured as a function of cure time. The effects of the curing temperature and the amine catalyst on the curing process were investigated. It was found that the curing process proceeded through three stages: logarithm of G″_app (log G″_app) increased with increasing cure time in the first stage, log G″_app increased with increasing logarithm of cure time in the second, and the change of G″_app cannot be expressed simply in the final. Curing behavior can be estimated from changes of rheological parameters during the curing. The fluidity of reaction mixture can be also predicted from the peak time of tan δ_app.     

A Two-Step Reaction Mechanism of Oxygen Release from Pd/CeO2: Mathematical Modelling Based on Step Gas Concentration Experiments

A mathematical model has been developed to study the transient release of oxygen from a 1wt% Pd/CeO₂ catalyst in the 450–550 °C range based on alternate step concentration switches between CO and O₂. A two-step reaction mechanism that involves the reaction of gaseous CO with the oxygen species of PdO and of the back-spillover of oxygen from ceria to the oxygen vacant sites of surface PdO has been proven to better describe the CO and CO₂ transient response curves. The proposed mathematical model allows the estimation of the transient rates of the CO oxidation reaction and of the back-spillover of oxygen process. It also allows the calculation of the intrinsic rate constant k ₁ (s^–1) of the Eley–Rideal step for the reaction of gaseous CO with surface oxygen species of PdO to form CO₂. An activation energy of 10.1 kJ/mol was estimated for this elementary reaction step. In addition, an apparent rate constant k ₂ ^app (s^–1) was estimated for the process of back-spillover of oxygen.     

Rheo‐kinetic evaluation on the formation of urethane networks based on hydroxyl‐terminated polybutadiene

Rheo‐kinetic studies on bulk polymerization reaction between hydroxyl‐terminated polybutadiene (HTPB) and di‐isocyanates such as toluene‐di‐isocyanate (TDI), hexamethylene‐di‐isocyanate (HMDI), and isophorone‐di‐isocyanate (IPDI) were undertaken by following the buildup of viscosity of the reaction mixture during the cure reaction. Rheo‐kinetic plots were obtained by plotting ln (viscosity) vs. time. The cure reaction was found to proceed in two stages with TDI and IPDI, and in a single stage with HMDI. The rate constants for the two stages k₁ and k₂ were determined from the rheo‐kinetic plots. The rate constants in both the stages were found to increase with catalyst concentration and decrease with NCO/OH equivalent ratio (r‐value). The ratio between the rate constants, k₁/k₂ also increased with catalyst concentration and r‐value. The extent of cure reaction at the point of stage separation (x_i) increased with catalyst concentration and r‐value. Increase in temperature caused merger of stages. Arrhenus parameters for the uncatalyzed HTPB‐isocyanate reactions were evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1869–1876, 2001     

Preparation of Polymers Containing Metal–Metal Bonds along the Backbone Using Click Chemistry

The [(η⁵-C₅H₄(CH₂)₃OC(O)(CH₂)₂C≡CH)Mo(CO)₃]₂ complex (1) was synthesized and used to explore the feasibility of using the Huisgen cycloaddition reaction (a click reaction) to incorporate molecules with metal–metal bonds into polymer backbones. In a model reaction, coupling of 1 with benzyl azide was observed in 24 h using Cp*Ru(PPh₃)₂Cl as a catalyst. In contrast, the reaction of 1 with benzyl azide using a CuBr/ligand catalyst (where the ligand is either PMDETA or bipyridine), resulted in disproportionation of the Mo–Mo unit in 1. Complex 1 was also coupled with telechelic azide-terminated polystyrene oligomers. With either the CuBr/PMDETA or CuBr/bipyridine catalyst, disproportionation of the Mo–Mo bonded unit occurred before complete coupling was observed. The reaction was also slow when the Cp*Ru(PPh₃)₂Cl catalyst was used; however, no disproportionation products were observed and a high molecular weight polymer (M _n = 120,000 g/mol) was produced. The Cp*Ru(PPh₃)₂Cl catalyst was also used to couple 1 with azide-terminated poly(ethylene glycol). After 15 h, this reaction produced a polymer with M _n = 73,000 g mol⁻¹. It is concluded that, although somewhat slow, click chemistry using the Cp*Ru(PPh₃)₂Cl catalyst is an excellent method for synthesizing high molecular weight polymers with metal–metal bonds along the backbone.     

OXIDATION OF GLUCOSE ON SUSPENDED PT/C: REACTION KINETICS AND ABSORPTION STUDIES

In search of a suitable model reaction system for studying hydrodynamic properties of slurry reactors under reactive conditions, the oxidation of glucose on a suspended Pt/C catalyst was investigated. In addition to homogeneous kinetic measurements, gas absorption experiments in a stirred cell with a plane interface were also carried out at 25 to 45^°C using finely powdered catalyst particles. It was found that the oxygen consumption rale followed first order kinetics only at the very beginning of the reaction. If the total amount of reacted oxygen was considerably more than that of the initial saturation value (i.e. kinetic runs repeated after some time of aeration under vigorous stirring or lengthy gas absorption experiments), the order with respect to oxygen was ½ Furthermore, the half order rate constant dropped to about ½ to ¼ of its initial value and was constant only after an amount of about 1.5 x 10^?2mol O₂/g catalyst was reacted. A new plot is also proposed which permits the simultaneous determination of the volumetric mass transfer coefficients and the rate constants for a half order reaction from gas absorption experiments at various catalyst concentrations. The rate constants and the k_La values which were obtained from completely different methods were in reasonable agreement.     

Efficiency and Mechanism of Ciprofloxacin Hydrochloride Degradation in Wastewater by Fe3o4/Na2S2O8

ABSTRACT

The nanosized Fe₃O₄ catalyst was synthesized via a modified reverse coprecipitation method and characterized by means of a scanning electron microscope (SEM) and an X-ray diffraction (XRD) analysis instrument. The degradation efficiency and reaction rate of Fe₃O₄ in activating sodium persulfate used to degrade ciprofloxacin were determined from the catalyst dosage, oxidant concentration, and initial pH. The results showed that under the optimum conditions of a catalyst dosage of 2.0 g·L^?1, a sodium persulfate concentration of 1.0 g·L^?1, and an initial pH of 7, the degradation rate of ciprofloxacin was 93.73%, the removal rate of total organic carbon was 78%, and the first-order reaction constant was 0.06907 min^?1 within 40 min. It was also demonstrated that the reactive oxygen species in the Fe₃O₄/sodium persulfate catalytic system were mainly composed of SO₄^– and supplemented by OH· and HO₂· using probe compounds such as ethanol, tertiary butanol, and benzoquinone.     

Enantioselective hydrogenation of ethyl pyruvate over cinchonidine-Pt/Al2O3 catalyst. A reaction kinetic approach

A new reaction kinetic approach was used to describe the enantioselective hydrogenation of ethyl pyruvate over cinchona-Pt catalyst. The above reaction was considered as the sum of two parallel reactions: (i) racemic hydrogenation resulting in R- and S-product in equal amount and (ii) enantioselective hydrogenation leading to the exclusive formation of one of the two optically isomers. New terms such as acc_diff and k _e/k _r (where k _e and k _r are the rate constants of the enantioselective and racemic hydrogenation, respectively) were introduced to characterize the relationship between the enantioselective and the racemic hydrogenation reactions. Results obtained show that the formation of R-product is rate accelerated, while the formation of S-product is decelerated. The results indicate also that the overall rate increase is a kinetic phenomenon and cannot be attributed to the suppression of the poisoning effect of CO or oligomers formed from ethyl pyruvate. The strong rate acceleration effect of achiral tertiary amines (ATAs) added to the reaction mixture was attributed to the decrease of the loss of modifier during the hydrogenation experiments.     

Kinetic study of radical polymerization. VII. Investigation into the solution copolymerization of acrylonitrile and itaconic acid by real‐time 1H NMR spectroscopy

Free radical solution copolymerization of acrylonitrile (AN) and itaconic acid (IA) was performed with DMSO‐d₆ as the solvent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. Weight ratio of the monomers to solvent and molar ratio of initiator to monomers were constant in all experiments. The initial comonomer composition was the only variable in this study. On‐line ¹H NMR spectroscopy was applied to follow individual monomer conversion. Mole fraction of AN and IA in the reaction mixture (f) and in the copolymer chain (F) were measured with progress of the copolymerization reaction. Overall monomer conversion versus time and also compositions of monomer mixture and copolymer as a function of overall monomer conversion were calculated from the data of individual monomer conversion versus time. Total rate constant for the copolymerization reaction was calculated by using the overall monomer conversion versus time data and then k_p/k_t^0.5 was estimated. The dependency of k_p/k_t^0.5 on IA concentration was studied and it was found that this ratio decreases by increasing the mole fraction of IA in the initial feed. The variation of comonomer and copolymer compositions as a function of overall monomer conversion was calculated theoretically by the terminal model equations and compared with the experimental data. Instantaneous copolymer composition curve showed the formation of alternating copolymer chain during copolymerization reaction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3253–3260, 2007     

Synthesis of new silica xerogels based on bi-functional 1,3,4-thiadiazole and 1,2,4-triazole adducts

New transparent Silica-based hybrid materials were synthesized by reaction of polymethylhydrosiloxane (PMHS) and organic compounds: 1,3,4-thiadiazole-2,5-diamine (1), 1,3,4-thiadiazole-2,5-dithiol (2) and 1H-1,2,4-triazole-3-thiol (3), in tetrahydrofuran as solvant using hexachloroplatinic acid (H₂PtCl₆.6H₂O) as a catalyst. PMHS was used as a principal network forming agent, it has been cross-linked via hydrosilylation reaction with bi-functional heterocyclic compounds, leading to the formation of colored gels. These later dried (xerogels) were characterized by numerous techniques, including spectroscopy of (FT–IR) and ¹³C and ²⁹Si CP MAS NMR. The xerogels morphology and texture were studied by scanning electron microscopy and Brunauer–Emmet–Teller method. According to N₂-physisorption results, isotherms are classified as type IV with H₂ type hysteresis loop; then, the xerogels are mesoporous materials. The optic and magnetic properties of the obtained materials were studied by UV–VIS and EPR spectroscopies, respectively. This study showed that all materials are paramagnetic semiconductors.     

Phase transformations of a spray-dried iron catalyst for slurry Fischer–Tropsch synthesis during activation and reaction

The consecutive phase transformations of a precipitated spray-dried iron-based catalyst for slurry Fischer–Tropsch synthesis (FTS) during activation and reaction process were investigated using Mössbauer effect spectroscopy (MES). It was found that the fresh iron catalyst activation in situ using syngas resulted in the formation of a mixture of iron carbides and superparamagnetic (spm) phases. The relatively small size of fresh iron crystallites was an important factor in the formation of ε′-Fe_2.2C. During the reduction process, Fe³⁺ (spm) phase was easier to be reduced than α-Fe₂O₃ phase. Fe₃O₄ was not an active phase for FTS. The transformation of α-Fe₂O₃ into Fe₃O₄ before carbides formation was necessary to obtain FTS activity of the iron catalyst. There was a correlation between the content of CH₄ in tail gas and the amount of iron carbides during activation. It was found that carbonization was the dominating phase transformation when the FTS reaction temperature increased from 250 °C to 270 °C. However, the oxidization was more remarkably at higher FTS reaction temperature. χ-Fe₅C₂ was the main iron phase at lower reaction temperature. The changes in the bulk compositions resulted in the variation in catalyst activity during FTS. The results of this study showed that the active phase for FTS was a mixture of carbides and corresponding amounts of superparamagnetic phase.     

Solid-liquid contacting effectiveness in trickle bed reactors

Internal and external effective wetting of a porous catalyst in a trickle bed reactor was considered. Experimental tests were carried out based on the analysis of the response curves of the reactor to a step decrease of the tracer inlet concentration.The pore filling of the catalyst pellets was practically total even at very low liquid flow rates, probably due to capillarity.The external effective wetting was interpreted in terms of an apparent internal diffusivity (D_i)_app, determined on the basis of a model which assumes a total external wetting of the catalyst. The values of (D_i)_app increased with the liquid flow rate, tending to the actual internal diffusivity D_i determined in a full reactor. The found values of (D_i)_app/D_i were used to interpret the ratio of the apparent kinetic rate constant determined in a trickle reactor k_app and that for a totally wetted catalyst k_v.The calculated values agree substantially with those proposed by Satterfield[3] from kinetic tests.     

A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D₂O at 50 °C. Online ¹H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855?±?1.3963, 0.1216?±?0.0301 and 6.9458?±?2.0113, 0.1201?±?0.0437 respectively. “Lumped” kinetic parameter (k _p k _t ^??0.5 ) was estimated from experimental data. Results showed that k _p k _t ^??0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.     

DSC curing study of catalytically synthesized maleic‐acid‐based unsaturated polyesters

Unsaturated polyesters were synthesized based on ethylene glycol and maleic acid as unsaturated dicarboxylic acid, using a variety of saturated acids in the initial acid mixture, without or with different catalysts. The curing of the polyesters produced with styrene was studied using differential scanning calorimetry (DSC) under dynamic‐ and isothermal‐heating conditions. The FTIR spectra of the initial polyesters and cured polyesters were also determined. Curing is not complete at the end of DSC scan and the unreacted bonds were quantitatively determined from the FTIR spectra and by estimation based on literature data. The value of the mean degree of conversion (α) of all double bonds (styrene unit and maleate unit) was approximately α = 0.40. Using an appropriate kinetic model for the curing exotherm of polyesters, the activation energy (E_a), the reaction order (x) and the frequency factor (k_o) were determined. Because the kinetic parameters (ie E_a, k, x) affect the kinetics in various different ways, the curves of degree of conversion versus time at various isothermal conditions are more useful to compare and characterize the curing of polyesters. The kinetic parameters are mainly influenced by the proportion of maleic acid in the polyesterification reaction mixture and secondarily by the residual polyesterification catalyst. The degree of conversion of already crosslinked polyesters is greatly increased by post‐curing them at elevated temperature and for a prolonged time. © 2002 Society of Chemical Industry