Indu M. Sasidharan Pillai

Photocatalytic degradation of methylene blue dye from aqueous solution using silver ion-doped TiO2 and its application to the degradation of real textile wastewater

Methylene blue dye (MB) was degraded photocatalytically in aqueous solution using Ag+ doped TiO2 under UV irradiation. The degradations of the dye using untreated TiO2 and Ag+ doped TiO2 were compared. Ag+ doped TiO2 was found to be more efficient. Using Ag+ doped TiO2 the filtration process was eliminated, as the particles became more settleable. The effect of various parameters such as catalyst loading, initial dye concentration, depth of solution, degree of adsorption, pH and O2 on dye degradation was studied. The extent of mineralization was studied by observing the COD removal at different time intervals. The effects of various interfering ions such as Cl−, NO3 −, CO3 2−, SO4 2−, Ca2+ and Fe3+ and electron acceptors such as H2O2, KBrO3 and (NH4)2S2O8 on the dye degradation was also studied. The degradation kinetics fitted well to Langmuir-Hinshelwood pseudo first order rate law. An aqueous solution of MB (20ppm) degraded by more than 99% after UV irradiation for 180 min with Ag+ doped TiO2 (2 g/L) and by more than 95% with untreated TiO2 (2 g/L). The COD removal was more than 91% with Ag+doped TiO2 and more than 86% with untreated TiO2 after 240 min. The degradation and COD removal of 5 times diluted textile wastewater was more than 98% and 79% respectively with 1 g/L Ag+ doped TiO2 after UV irradiation for 420 min.

Heterogeneous photocatalysis of real textile wastewater: evaluation of reaction kinetics and characterization.

Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag+ doped TiO2 under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag+ doped TiO2 (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis.

Multivariate optimization for electrochemical oxidation of methyl orange: Pathway identification and toxicity analysis

Electrochemical oxidation of methyl orange (Sodium 4-[(4-dimethylamino) phenyldiazenyl] benzenesulfonate) with lead dioxide coated on mild steel was modelled using response surface methodology (RSM) to analyze the influence of pH, NaCl dose and current on color and chemical oxygen demand (COD) removal. Higher current, acidic pH and 0.8–1.2 g L−1 NaCl dose had an enhancing effect on the removal efficiencies. Interaction effect of the variables highlights the action of •OH and HOCl in the oxidation of methyl orange, where HOCl has effect at lower current range. More than 90% COD removal efficiency and ∼100% color removal efficiency was obtained in 5 h at optimum conditions for an initial concentration of 50 mg L−1. High performance liquid chromatography–mass spectroscopy (HPLC-MS) analysis carried out to identify degradation intermediates revealed the absence of chlorinated intermediates, which was further verified with Fourier transform infrared spectroscopy (FTIR) analysis. The postulated pathway of degradation indicated breakdown through dealkylation, deamination, desulfonation and cleavage of an azo bond and benzene ring. The degradation of methyl orange to smaller compounds was also confirmed by Ion Chromatography (IC). Cytotoxicity analysis on HaCaT cells revealed the intermediates to be more cytotoxic than the dye, possibly due to the aromatic amines and diazines formed during the degradation process.

Electrochemical degradation of malachite green: Multivariate optimization, pathway identification and toxicity analysis

ABSTRACT Application of a newly developed electrode material, PbO2 coated on mild steel plate (MS-PbO2), for the degradation of malachite green (MG) by photocatalytic oxidation (PCO), electrochemical oxidation (ECO) and photoelectrochemical oxidation (PEC) was explored. PEC performed marginally better at lower current density. However, the performances of PEC and ECO were equally good at higher current densities. One variable at a time optimization was carried out to identify the major parameters influencing ECO. Multivariate optimization was carried out with NaCl concentration, current density and pH as the variables and chemical oxygen demand (COD) removal efficiency and current efficiency (CE) as the responses. Increasing the current density aided the COD removal efficiency, but decreased the CE. Low NaCl concentration and acidic pH were beneficial for both. The optimum condition for maximizing the COD removal efficiency and CE of MG (50 mg L−1) was obtained as NaCl concentration of 1.56 g L−1, a current density of 1.91 mA cm−2 and pH 5. The maximum predicted and experimental COD removal efficiencies were 89.41% and 90.8%, and CEs were 21.52% and 21.1%, respectively. Degradation intermediates were identified and a possible pathway of degradation was proposed. Disc inhibition study showed that the degraded samples are non-toxic. The efficacy of the method was tested for treating wastewater collected from dyebath having a COD of about 2000 mg L−1. COD removal efficiency of greater than 90% was achieved within 12 h at a current density of 7.2 mA cm−2.

Investigation onto feasibility of an adsorbent for chromium abatement with its extended application for real mine drainage water

The feasibilities of the adsorbents ferrous modified calcined bauxite (FEMCB) and ferric modified calcined bauxite (FRMCB) in the abatement of Cr(VI) was investigated in the present study. The adsorbents were characterized by scanning electron micrographs (SEM), electro diffraction spectra (EDS), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectra. Parameter optimization of both adsorbents was done and performance efficiencies in the removal of Cr(VI) were compared. Although pH and temperature seemed to have no significant role in the removal efficiency of FEMCB, sorption by FRMCB was found to be depending on both. The optimum pH and temperature was found to be 5 ± 0.2, and 30°C, respectively. At optimum conditions, both adsorbents demonstrated removal efficiencies of >99% for a concentration of 5 mg L−1. Sorption of Cr(VI) by FEMCB followed Freundlich isotherm model, while that of FRMCB fitted well with Langmuir isotherm model. The isotherm parameters were optimized by minimizing the error functions. The kinetics of sorption by FEMCB followed a pseudo-second-order model confirming chemisorptive mechanism, while FRMCB followed pseudo-first-order. Thermodynamic study revealed that sorption process was spontaneous and that the rate limiting step was governed by film diffusion. Both the adsorbents showed removal efficiencies of >99% in removing Cr(VI) from real sample of mine drainage water of concentration 1.86 mg L−1 at optimum conditions.

ELECTROCHEMICAL OXIDATION OF CRYSTAL VIOLET DYE (BASIC VIOLET 3) USING LEAD OXIDE ELECTRODES

Removal of crystal violet dye from aqueous solution by electrochemical oxidation method using Pb/PbO2 anode and mild steel cathode was studied. The effect of various parameters like concentration of supporting electrolyte, current density, area of electrode, initial dye concentration and pH on the degradation of the dye was studied. The operating condition found was 0.01 M supporting electrolyte concentration, 1.2 mA/cm 2 current density and pH 8. Under optimum conditions the colour removal was more than 99% and the COD removal was more than 80%.