Oxidative Decolourisation of Rosaniline Hydrochloride (RAH)

Oxidative Decolourisation of Rosaniline Hydrochloride (RAH)energizing, thermodynamic studies for oxidation of rosaniline hydrochloride dishonor by persulphate in ambient temperaturesZ. M. Abou-Gamra*AbstractThe dynamics of the oxidative decolourisation of rosaniline hydrochloride (RAH) by sodium persulphate was studied spectrophotometrically over pH govern 3.5-9.5 at 30-45 oC. The chemical reaction was second order with respect to dye and half order to persulphate. Increasing the pH of the medium increased the rate of decolourisation dramatically in alkaline medium. The Activation Parameters were make up to be 62.11 kJ mol-1, 90.33 kJ mol-1 and -98.44J K-1 mol-1 with respect to energizing energy, free energy and entropy respectively. Addition of sodium chloride and sodium sulphate had no effect on the rate of decolourisation.Key wards Kinetics, Mechanism, Degradation, Rosaniline, Persulphate.1. IntroductionTextile discolour influence is significant source of env press outmental pollution. It produces large amounts of highly colored effluents, which generally toxic resistant to destruction by biological treatment methods. galore(postnominal) physical, chemical processes such as adsorption 1, electrochemical 2, photocatalytic 3 are used to remove the dyes from waste water. Chemical oxidative processes seem to provide anopportunity for prospective use in industrial wastewater. Examples of such authorizationly effective chemical oxidants for oxidative processes include Fenton reagent 4-5, KBrO3 6-7 and KClO3 8.*corresponding author e-mail emailprotectedThe use of persulfate has recently aid as an alternative oxidant in the chemical oxidation of contaminants 9-12. Persulphate (KPS) is one of the strongest oxidants known in aqueous solution and has a higher potential (Eo = 2.01 V) than H2O2 (Eo = 1.76 V) 13 put back 1. It offers some advantages over other oxidants as a solid chemical at ambient temperature with ease of storage and transport, high stability, high aqueous solubility and relatively low cost. It has great capability for degrading numerous organic contaminants through free radicals ( SO4-. and HO.) generated in the persulphate system 12.Basic dyes, such as, crystal violet, malachite young and roseaniline hydrochloride are used cotton tannin, mordant printing and discolour in stuff. Rosaniline is triphenylmethane dyes with amino stem on each phenyl ring. Its structure is easily reducible where the chromophore group is destroyed and the compound loses its colour. Redox reaction of rosaniline hydrochloride by sulphite and nitrite ions are reported early 14-16.This work focused on the kinetic study of oxidation of rosaniline hydrochloride with persulphate at ambient temperature spectrophotometrically. The effects of pH, dye, persulphate meannesss and temperature were studied. Also machine as well as rate law equation for the reaction is proposed.2. Experimental2.1. Reagents and materialsAll chemicals were of pure form and were used without further purification. Rosaniline hydrochloride BDH (molecular weight =337.8, max = 540 nm). The chemical structure of (RAH) is given in (Fig.1). NaCl and Na2SO4 were purchased from Merck. All solutions were prepared using bidistilled water. Stock solutions of dye (1 mM), K2S2O8 (100mM) were prepared. The pH is adjusted by HCl and NaOH solutions.2.2. Kinetic experimentsAll kinetic measurements were carried out using a Cecil 292 spectrophotometer equipped with a water-jacketed cell holder. The reactants (dye and K2S2O8+NaOH) were thermostated for 15 min., then mixed thoroughly and promptly transferred to an absorption cell. The progress of the reaction was monitored at 540 nm. The pH of the reaction was adjusted using Griffin pH-meter fitted with a combined glass calomel electrode.3. Results and DiscussionKinetic study for oxidation of (RAH) by (KPS) was followed at max= 540nm. Figure 2 shows the decreasing of absorbance with cartridge clip. Figure 2 also sho ws that about 85% of rosaniline is removed in 60 minutes at temperature 25 oC.3.1 Kinetic studyIn the present study, zero-, first- and second-order reaction kinetics were used to study the decolourization kinetics of (RAH) by (KPS). The single expression were represented belowCt = Co kotlnCt = -k1t + ln Co1/Ct = 1/Co+ k2twhere Ct is the concentration of (RAH) at reaction time t.Regression analysis based on the zero-, first- and second-order reaction kinetics for the decolourization of (RAH) by (KPS) was conducted and the results were shown in (Fig. 3). Since plotting of At versus time did not give straight line zero-order kinetics is excluded. Comparing the regression coefficients (R2) obtained from (Fig. 3b) and (Fig. c), it can be seen that R2 of the second-order reaction kinetics (Fig. 3c) was 0.9995, which was obviously much better than that based on the first-order (R2 = 0.9394) reaction kinetics. The results indicated that the decolorization kinetics of (RAH) followed the sec ond-order kinetics well. found on the above analysis, the second-order kinetic rate constants for the decolourization of (RAH) at different reaction conditions were shown in disconcert 2.3.2. Effect of pHA thermally activated persulphate oxidation system is known to involve SO4. and HO. radicals depending on the pH of the medium. According to literature survey, SO4. is predominant oxidant radicals at pH 7, both SO4. and HO. are present at neutral pH and HO. is predominant radical at pH 99. Keeping the concentration of (RAH), (KPS) and temperature constant and change the pH in range 3.5 to 9.5, the rate of reaction is increased by increasing the pH value, (Fig. 4). Increasing the pH in range 3.5 to 9.5 increased observed rate constant from 6.7x 10-4 to 6.8 x 10-3 mol dm3 s-1, Table 2. This is probably attributed to the effect of hydroxyl ion on (RAH) which converting it to a carbinol base with no conjugation structure. All studies have done at pH = 9 since dyeing cotton performed i n alkaline medium 17.3.3. Effect of dye concentrationThe effect of initial (RAH) concentration of aqueous solution of rosaniline on oxidation process by persulphate was investigated since pollutant concentration is important parameter in wastewater treatment. The observed rate constant decreases linearly with increasing the initial concentration of rosaniline, (Fig. 5). This is attributed to relatively let down of SO4-. and HO. results from the increasing of rosaline concentration while concentration of persulphate and hydroxyl ions remains the same. The obtained results was in good agreement earlier reported 18-19.3.4. Effect of persulphate concentrationIncreasing the persulphate concentration in rang 410-3 to 2.4x 10-2 mol dm-3 increasing the rate constant from 3.1310-3 to 9.9210-3 mol-1dm3 s-1 at pH= 9 and temperature 40oC, Table 2. Plotting of log kobs versus log K2S2O8 give straight line of tilt equals 0.63 indicating the order of reaction with respect to persulphate is half, (Fig. 6). This is similar to results obtained by T. Mushinga and S. Jonnalagadda 20. Also the fraction order ( n = 0.779) with respect to persulphate is obtained by M. Ahmadi et al19.3.5. Effect of temperatureThe variation of the temperature in range of 303-318 K increases the rate of decolourization of rosaniline, (Fig. 7). The activation energy was calculated from Arrhenius plot and Eyring equation and was found to be 62.11 kJ mol-1. The activation energy for decolourisation of RY84 was 45.84 kJ mol-119 while for decolourisation of CV by persulphate was 28.9 kJ mol-118. Chen-Ju Liang and Shun-Chin Huang present that the activation energy for MB with persulphate was 87 and 90 kJ mol-1 in acidic and alkaline medium respectively 9. The other activation parameters were determined and are found to be 90.33 kJ mol-1 and -98.44 JK-1 for free energy and entropy respectively.3.6. Effect of inorganic anionsThe potent effect of persulphate as oxidizing agent in destroying the organic conta minants is high redox potential of sulphate free radical. The front line of other species in waste water such as chloride, sulphate and phosphate could reduce its oxidation efficiency. It is reported earlier 21 that chloride can react with sulphate free radicals according to the following applianceChloride concentrations had insignificant effect in studied range 0.008- 0.08 mol dm-3. Also the presence of sulphate did not reduce the decolourisation rate. Similar results are observed earlier 21-23.4. Reaction Mechanism and Rate LawThe probable mechanism of reaction involves the hold of conjugation of roseaniline hydrochloride. Since the fraction order of persulphate is observed, It handlely that the initial reaction is thermal decomposition of persulphate,Applying equilibrium approximation and assuming an equilibrium between the reactant and product of (eq. 1)From (eqs.5 6)If the proposed mechanism and rate low are probable, so plotting of kobs versus S2O82-1/2 should yielded stra ight line passing by origin and the slope should be equals k x K1/2. victimization the data in Table 3 and the plot gave straight line passing by the origin with slope =0.065 (R2 = 0.9557) which support the proposed mechanism.ConclusionIn this study, (RAH) was successfully degraded in aqueous solutions by the persulphate and it was found that the reaction of (RAH) abjection follows the second-order kinetic model with respect to (RAH) and half order to persulphate. 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