Basab Chaudhuri

Chemical oxidation of methylene blue using a Fenton-like reaction.

Oxidation by Fenton-like reactions is proven and economically feasible process for destruction of a variety of hazardous pollutants in wastewater. We report herein the oxidation of methylene blue, a basic dye of thiazine series using a Fenton-like reaction at normal laboratory temperature and at atmospheric pressure. The effects of different parameters like the initial concentrations of dye, Fe2+, and H2O2, pH of the solution, reaction temperature, and added electrolytes on the oxidation of the dye present in dilute aqueous solution in the concentration range (3.13-9.39)x10(-5)mol dm(-3) (10-30 mg l(-1)) have been assessed. The results indicate that the dye can be most effectively oxidized in aqueous solution at dye:Fe(2+):H2O2 molar ratio of 1:1.15:14.1. More than 98% removal of the dye could be achieved in 1h in the pH range 2.2-2.6 at 299 K which corresponds to about 81% reduction of the initial COD. The results will be useful for designing the treatment systems of various dye-containing wastewaters.

Estimation of ⋅OH radical reaction rate constants for phenol and chlorinated phenols using UV/H2O2 photo-oxidation

A detailed investigation on UV/H2O2 photooxidation has been carried out in order to determine the kinetics of the oxidative degradation of phenol and 2- and 4-chlorophenols in dilute aqueous solutions. Effects of different process parameters, such as initial substrate and H2O2 concentrations, substrate to H2O2 ratio on the degradation kinetics of the phenolic substrates, have been studied. Degradation rates of phenol and chlorophenols are insignificantly small with ultraviolet radiation only and also with hydrogen peroxide (in the absence of UV radiation), but the synergistic effect of UV/H2O2 results in a marked enhancement of the rates of degradation. A mechanistic model for UV/H2O2 photooxidation has been developed. Room temperature (27 degrees C) rate constants for the reaction of .OH radical (formed by absorption of photons) with the substrates have been estimated by using the model equation. The calculated rate constants are of the same order of magnitude as reported for other similar aromatic compounds.

Chemical oxidation of C. I. Reactive Red 2 using Fenton-like reactions

A detailed investigation on the kinetics of the oxidative degradation of a reactive dye, C. I. Reactive Red 2 by hydroxyl radicals generated by H202 and Fe2+ has been carried out in aqueous acidic media. Effects of different parameters like initial concentration of dye, H2O2, Fe2+, pH of the solution, reaction temperature and added electrolytes on the oxidation process have been studied. The results indicate that 1.63 x 10(-4) mol dm(-3) dye can be most effectively degraded at a dye: Fe2+: H2O2 molar ratio of 1:0.22: 8.13 at pH approximately 2.7 and at 299 K. The addition of excess 2-propanol or t-butyl alcohol, well known scavengers of hydroxyl radicals, almost stopped the degradation of the dye indicating the absence of any possible reductive pathways in the degradation. The results may be useful for designing the treatment systems of wastewater containing various reactive dyes.

A kinetic study of the oxidation of phenol, o‐chlorophenol and catechol by hydrogen peroxide between 298 K and 333 K: the effect of pH, temperature and ratio of oxidant to substrate

Kinetic studies on the oxidative degradation of phenol, o-chlorophenol and catechol present in dilute aqueous solutions in the concentration range between 50 ppm and 1000 ppm by hydrogen peroxide were conducted in a batch reactor. The temperature was varied between 298 K and 333 K. Initial rates of conversion for phenolic compounds were extremely high compared with the later part of the reaction. The pH of the reaction medium also decreased substantially during the reaction and reached a plateau in the range of 6.4 for phenol and 4.5 for catechol and chlorophenol. Conversions of phenolic substrates were found to increase with an increase in initial substrate concentration and hydrogen peroxide/substrate ratio. For a fixed initial concentration and hydrogen peroxide/substrate ratio, the conversion was found to be in the order catechol>chlorophenol>phenol. The temperature of the reaction medium was found to have a minimal effect on the degradation kinetics, probably due to simultaneous thermal decomposition of hydrogen peroxide at elevated temperature. A probable mechanistic explanation of the experimental data based on reactivity of the phenolic compounds and their stable oxygenated intermediates is discussed. © 1999 Society of Chemical Industry.

Oxidative degradation of malachite green by Fenton generated hydroxyl radicals in aqueous acidic media.

Abstract Fenton-generated hydroxyl radicals removes the color of the malachite green, a basic dye with triphenylmethane group, almost (˜98%) completely in weakly acidic aqueous media possibly through oxidative degradation pathways as evidenced from a remarkable lowering in the COD value of the product mixture in comparison to the title dye under identical conditions and almost full quenching of the reaction in presence of hydroxyl radical scavengers. The dye can most effectively be degraded at dye:Fe2+:H2O2 molar ratio of 1:3.3:81.7 for 1.08 × 10−5 mol dm−3 dye at pH 2.5–2.8 and at 299K. The rate law of the dye degradation process appears to be: −d[dye]/dt = k[dye] [Fe2+]0.79 [H2O2]0.12, where k = (33 ± 5) (dm3 mol−1)0.91 s−1 at 299K. Salts like NaCl or NaBr retard the degradation rate markedly whereas are rather innocent. In presence of Cl−, the radical reaction: may account for the gross lowering of degradation rate. The results may be helpful for designing the treatment plants of wastewater containing dyes with triphenylmethane group.

Utilisation of eggshell membrane as an adsorbent for carbon dioxide

Carbon dioxide (CO2) is a major greenhouse gas responsible for global warming. This work aims to explore a cheap and easy way for CO2 adsorption from the atmosphere, by using an eggshell membrane. Eggshell membrane could be used up to four times with intermediate regeneration with acetic acid solution. Atomic absorption spectrophotometer (AAS) analysed the amount of CO2 adsorbed as equivalent calcium (Ca) present in calcium carbonate (CaCO3). An average of 6824 mg COCO2 could be adsorbed per g of eggshell membrane. Scanning electron micrograph (SEM) was used to analyse the surface morphology of the fresh and regenerated eggshell membrane.

Adsorption of model textile dyes from aqueous solutions using agricultural wastes as adsorbents: equilibrium, kinetics and fixed bed column study

Gram husk and groundnut shell are cheap and abundantly available agricultural waste materials in India. A systematic study on the adsorption of some model dyes from aqueous solution on these low-cost adsorbents has been attempted. Model dyes used were Methylene Blue, Rhodamine B, Congo Red, Eosine Y and Metanil Yellow. Equilibrium, kinetics and column experiments were performed. Effects of different process variables have been studied. Equilibrium data fitted well in Langmuir and Freundlich isotherm equations. A model using Freundlich equation has been developed for interpretation of kinetic data. Other models such as Lagergren equation and pseudo second order equation were also used. Of these models, pseudo second order equation was found to be the most satisfactory. Column experiments were carried out with gram-husk and Rhodamine B. The data could be correlated well with BDST model.

KINETICS OF ALKALINE HYDROLYSIS OF ISOAMYLACETATE

ABSTRACT The theory of mass transfer accompanied by chemical reaction has been used to determine the kinetics of alkaline hydrolysis of isoamylacetate. The rate constant for the alkaline hydrolysis is around 9.52 cm3/(mole)(sec). This is much lower than the rate constant for alkaline hydrolysis of n-amyl acetate, which is about 85 cm3/(mole)(sec). The presence of an electrolyte like sodium chloride in the aqueous phase reduced the rate of extraction to some extent. The rates of extraction with sodium chloride in the aqueous phase and the corresponding rate constant values have been reported.