Apparent First-order Reaction Kinetics Research Articles

Synergetic effect of titanium dioxide ultralong nanofibers and activated carbon fibers on adsorption and photodegradation of toluene

Effective adsorption and photodegradation of volatile organic compounds (VOCs) especially for the high concentrations still remained great challenges. Herein, we firstly fabricated ultralong TiO2 nanofiber/activated carbon fiber (TiNF/ACF) porous composites by deposition of TiNFs within ACF felts. The ultralong TiNFs with diameters of 30–100nm and lengths of >200μm were originated from the ordered aggregates of nanocrystals along the [101] direction. The TiNF/ACF porous composites possessed excellent adsorption property for toluene, and the adsorption performances were fit well with pseudo-second-order kinetics model. Their adsorption efficiency reached 98.9% at the toluene concentration of <4600ppm and 85.7% even at the high concentration of 13,800ppm. Moreover, the synergetic effect between the TiNFs and ACFs improved remarkably the photodegradation activity of the composites. The ACFs not only increased the quantum efficiency of TiO2 by hindering the recombination of electron-hole pairs, but also enhanced the light adsorption ability by reducing the TiO2 band gap energy (Eg) to 2.99eV. At the toluene concentrations of 115ppm or 230ppm, the photocatalytic time in which toluene degraded into CO2 and H2O was only 5h or 13h, respectively. The photodegradation kinetics of toluene matched well with the apparent first-order reaction kinetics model at high concentration of 690ppm, while that matched well with the semi-empirical power-law expression equation of CO2 desorption at low concentrations of 115ppm. Hence, the TiNF/ACF porous composites with excellent adsorption and photocatalytic activities had great application potentials for VOC removal.

Thermogravimetric and kinetic analysis of bio-crude from hydrothermal liquefaction of Enteromorpha prolifera

Bio-crude upgrading process by thermal treatment without the presence of neither catalysts nor hydrogen is a promising technique. Mechanism and kinetics of bio-crude thermal decomposition are crucial for the development of thermal upgrading process. In this paper, thermogravimetric and kinetic analysis of bio-crude from hydrothermal liquefaction of Enteromorpha prolifera was performed under non-isothermal conditions at different heating rates. A two-step reaction mechanism, a volatilization step followed by a thermal reaction step, was proposed based on the experimental results. The most probable reaction model was determined through a universal integral method, and the kinetic parameters were obtained simultaneously. At heating rate of 10K/min, the volatilization step can be described by a 1-D diffusion model and the thermal reaction step followed apparent first-order reaction kinetics. The apparent activation energy was also estimated by using several isoconversional methods. However, further analysis proved that the basis of isoconversional method was violated.

Application of the electro-Fenton process to mesotrione aqueous solutions: Kinetics, degradation pathways, mineralization and evolution of the toxicity

&lt;p&gt;The kinetics and the mechanism of degradation of the mesotrione herbicide by three electrochemical advanced oxidation processes (EAOPs) systems, namely electro-Fenton (EF) with Pt anode (EF-Pt), anodic oxidation with BDD anode (AO) and EF-boron doped diamond anode (EF-BDD), were investigated in acidic aqueous solutions. The degradation of mesotrione obeyed apparent first-order reaction kinetics, and its absolute rate constant value with hydroxyl radicals at pH 3.0, determined by the competitive kinetics method, was found to be 8.20 × 10&lt;sup&gt;8&lt;/sup&gt; L mol&lt;sup&gt;–1&lt;/sup&gt; s&lt;sup&gt;–1&lt;/sup&gt;. Fourteen different mesotrione degradation products were separated and/or identified using HPLC / MS&lt;sup&gt;n&lt;/sup&gt; analyses. A rationalized scheme was proposed for the reaction pathways of mesotrione degradation in the EF process. The mesotrione mineralization yield values ranged between about 58 and 97%&lt;strong&gt; &lt;/strong&gt;for a 6-h electrolysis time, according to the type of EAOP system and the electrolysis current intensity value. The evolution of the toxicity of mesotrione aqueous solutions with electrolysis time (&lt;em&gt;t&lt;/em&gt;) was investigated during treatment by the EF-Pt and EF-BDD systems. Toxicity was measured with the Microtox® method, based on the luminescence inhibition of marine bacteria &lt;em&gt;Vibrio fischeri&lt;/em&gt;. The curves % inhibition &lt;em&gt;vs.&lt;/em&gt; time were found to depend on the toxicity of formed mesotrione degradation products.&lt;/p&gt;

Removal of uranium(VI) from aqueous solution using sponge iron

Direct reduced iron (DRI), also called sponge iron, was used for the removal of U(VI) from aqueous solution. Batch experiments were conducted to evaluate the effect of various factors including contact time, solution pH, DRI dosage and initial uranium concentration on this removal process. The result suggested that U(VI) can be rapidly removed by DRI and this removal process followed an apparent first-order reaction kinetics. The optimum pH for uranium removal was between 2.0 and 4.0. Whether U(VI) can be fully removed was influenced by the molar ratio of DRI to U(VI) in solution. The aqueous U(VI) can be removed completely when this ratio was more than ca. 1,000. The U(VI) removal capacities of DRI decreased with increasing DRI dosages at a constant concentration of U(VI), but increased almost linearly with increasing initial U(VI) concentrations at a fixed dosage of DRI. The maximum U(VI) removal capacity was 5.71 mg/g DRI. Finally, the possible mechanism of U(VI) removal by DRI was also discussed. The XPS and XRD analysis showed that U(VI) was deposited as UO3 onto DRI surface, indicating that U(VI) can be removed without reduction.

Removal of 17β-Estradiol by Electro-Fenton Process

The Electrochemical advanced oxidation method “Electro-Fenton” has been applied to remove 17β-estradiol (17β)- estra-1,3,5(10)-triéne-3,17-diol) in aqueous-acetonitrile mixture. This endocrine disrupting is a steroid hormone, releases from humans, animals and residual pharmaceuticals into the environmental water and usually causes suspected undesirable effects in aquatic organisms. The degradation of this organic compound by Electro-Fenton process was showed using a carbon felt cathode and platinum anode. The evolution of the concentration during treatment was followed up by high performance liquid chromatography (HPLC). The influence of operating conditions on the degradation of 17β-estradiol by Electro-Fenton step, such as initial concentration and catalyst concentration, has been investi- gated and discussed. We showed that the degradation reaction obeyed apparent first-order reaction kinetics, with absolute rate constant determined as 5.12 × 109 M–1 s–1 by competitive kinetics method taking Benzoic Acid as reference compound. The results confirm the efficiency of the Electro-Fenton process to degrade organic pollutant in aqueous-acetonitrile mixture.

Degradation and mineralization of sulcotrione and mesotrione in aqueous medium by the electro-Fenton process: a kinetic study

The degradation and mineralization of two triketone (TRK) herbicides, including sulcotrione and mesotrione, by the electro-Fenton process (electro-Fenton using Pt anode (EF-Pt), electro-Fenton with BDD anode (EF-BDD) and anodic oxidation with BDD anode) were investigated in acidic aqueous medium. The reactivity of both herbicides toward hydroxyl radicals was found to depend on the electron-withdrawing effect of the aromatic chlorine or nitro substituents. The degradation of sulcotrione and mesotrione obeyed apparent first-order reaction kinetics, and their absolute rate constants with hydroxyl radicals at pH 3.0 were determined by the competitive kinetics method. The hydroxylation absolute rate constant (k(abs)) values of both TRK herbicides ranged from 8.20 × 10(8) (sulcotrione) to 1.01 × 10(9) (mesotrione) L mol(-1) s(-1), whereas those of the TRK main cyclic or aromatic by-products, namely cyclohexane 1,3-dione, (2-chloro-4-methylsulphonyl) benzoic acid and 4-(methylsulphonyl)-2-nitrobenzoic acid, comprised between 5.90 × 10(8) and 3.29 × 10(9) L mol(-1) s(-1). The efficiency of mineralization of aqueous solutions of both TRK herbicides was evaluated in terms of total organic carbon removal. Mineralization yields of about 97-98% were reached in optimal conditions for a 6-h electro-Fenton treatment time. The mineralization process steps involved the oxidative opening of the aromatic or cyclic TRK by-products, leading to the formation of short-chain carboxylic acids, and, then, of carbon dioxide and inorganic ions.

Metomyl Degradation by Electro-Fenton and Electro-Fenton-Like Processes: A Kinetics Study of the Effect of the Nature and Concentration of Some Transition Metal Ions As Catalyst

The oxidative degradation of insecticide metomyl as active ingredient and of its commercial formulation Lanate 20 L by an electro-Fenton process using a carbon felt cathode and iron ions as catalyst was compared with different transition metal ions such as, cobalt, silver, and copper as catalyst to produce hydroxyl radicals. The effect of catalyst nature and concentration on the degradation kinetics and COD removal was investigated and optimized. For all metal ions under study as catalyst, there is an optimal concentration value for degradation kinetics and solution COD removal efficiency. Fe(III) was confirmed to be the most efficient catalyst among the metals ions tested. The metomyl oxidative degradation was found to obey apparent first-order reaction kinetics, and the absolute rate constant of the oxidation between metomyl and hydroxyl radicals at pH 3.0 was obtained by competitive kinetics method, being 5.42 × 10(9) L mol(-1) s(-1).

Kinetics of starch gelatinization during extrusion of tarhana, a traditional turkish wheat flour-yogurt mixture

Tarhana, a traditional Turkish cereal food, was extruded at different extrusion conditions (product temperature: 60–120°C; screw speed: 100–300 rpm; feed rate: 10–20 kg/h). The mean residence time and corresponding degree of starch gelatinization data were used to estimate the order of reaction, gelatinization rate constants and activation energy for starch gelatinization. Results indicate that starch gelatinization exhibited an apparent first-order reaction kinetics with a reaction order of approximately 0.8. Activation energy for gelatinization was calculated as 3325 kJ/kg mol using the Arrhenius equation.

ATP-Hydrolyzing Excitation State of the Reconstituted α3β3 Complex of ATP Synthase from the Thermophilic Bacterium PS3: Structural Characteristics Shown by Time-Resolved Small-Angle X-Ray Scattering with Synchrotron Radiation1

The ATP-hydrolyzing excitation state of the alpha 3 beta 3 complex of the ATP synthase from the thermophilic bacterium PS3 was investigated using time-resolved small-angle X-ray scattering with synchrotron radiation. The results showed the presence of the alpha 3 beta 3 complex at a steady state during ATP hydrolysis when the alpha 3 beta 3 hexamer reacted with Mg-ATP. The radius of gyration of the complex in the steady state was significantly larger than that of the Mg-AMP-PNP-hexamer complex, indicating a conformational change to an expanded structure during catalysis. This alpha 3 beta 3 complex dissociated into alpha 1 beta 1 heterodimers with apparent first-order reaction kinetics after all the ATPs were converted to ADPs. In contrast, when the alpha 3 beta 3 complex reacted with Mg-ADP, the complex dissociated into dimers with apparent first-order reaction kinetics without showing the steady state of the complex. The dimers, however, re-associated into the hexamer when Mg-ATP was added. The results were well-explained by a computer simulation based on non-linear chemical dynamics, in which a reaction mechanism that incorporates the dynamic structure of the hexamer in the steady state was considered.

Characterisation of alpha-amylase and polygalacturonase from Lygus spp. (Heteroptera: Miridae)

Polygalacturonase and α-amylase from the salivary glands of Lygus lineolaris and of L. hesperus (Heteroptera: Miridae) were optimally active at acid pH and at 40°C, and were activated by chloride ions. The rates of thermal inactivation of both enzymes followed apparent first-order reaction kinetics, from which apparent thermodynamic variables ( E a, ΔH ‡ , ΔG ‡ and ΔS ‡ ) were calculated. For both enzymes, after exposure to 60–100°C, a biphasic system was demonstrated for their thermal inactivation. Both α-amylases were more active towards gelatinised legume starches than towards soluble starch. The effect of substrate concentration upon the enzyme activities demonstrated higher maximum reaction velocities for the two enzymes from L. lineolaris, and K m V max ratios of 0·31-0·33 for α-amylase and 0·04-0·05 for polygalacturonase. The results from this study indicated the potential abilities of the two enzymes to attack pectic substances and starch in food crops and hence to have a possible potential application in polymer modification in food technology.

Trinitrobenzoylated poly( d-lysine) as a stimulator of interactions between plasminogen, plasmin, and tissue-type plasminogen activator

Trinitrobenzyl alkylation of poly( d-lysine) provides a novel powerful stimulator of tissue-type plasminogen activator. Its stimulatory effect on plasminogen activation is far greater than that of the original poly( d-lysine), and even surpasses that of fibrin. Its effect on plasmin-catalysed modification of both tissue-type plasminogen activator (t-PA) and native (Glu-1-) plasminogen are also investigated. Cleavage of one-chain t-PA to its two-chain form is monitored by measuring the increase in amidolytic activity which accompanies this transformation. Presupposing apparent first-order reaction kinetics, a theory is developed by which the rate constant, k cat/ K m = 1.0·10 6 M −1·s −1 of plasmin cleavage of one-chain t-PA can be calculated. Plasmin- catalysed transformation of 125I-labelled Glu-1- to Lys-77-plasminogen is quantified following separation by polyacrylamide gel electrophoresis at pH 3.2. A rate constant, k cat/ K m = 4.4·10 3 M −1·s −1 is obtained for the reaction between plasmin and Glu-1-plasminogen in the presence of 1 mM trans-4- (aminomethyl)cyclohexane-1-carboxylic acid. Both of the above plasmin-catalysed reactions are strongly enhanced by trinitrobenzoylated poly( d-lysine). The mechanism of action of this stimulator is elucidated by studying its binding to both activator and plasmin(ogen), and by direct comparison of the results with measurements of plasminogen activation kinetics in the presence of the stimulator. Binding studies are performed exploiting the observation that an insoluble yellow complex is formed between plasminogen and modified poly( d-lysine). Protein-polymer interactions are also studied with solubilised components in an aqueous two-phase partition system containing dextran and poly(ethylene glycol). The rate enhancement of plasminogen activation is found to be closely correlated to the association of plasminogen to the stimulator. It is proposed that the stimulator effects of this simple polymer on the enzymatic activities of both plasminogen activator and plasmin are brought about by association of the proteinase and its substrate to a common matrix. Similarities between the action of the artificial and the natural stimulator (fibrin) are stressed. These properties of trinitrobenzoylated poly( d-lysine) makes it useful as a model for the study of the regulatory mechanism of the fibrinolytic process at the molecular level.