Subramanyan Vasudevan

Electrochemistry: as cause and cure in water pollution—an overview

This article reviews both the pollution by the electrochemical industry and the use of electrochemistry to clean water. Main pollutants include Pd, Cd, Ni, Hg and other metals and cyanide as well as organic pollutants. The cause for water pollution by electrochemistry is due to the effluents from different electrochemical industries such as mercury from chlor-alkali industry; lead, cadmium and mercury from battery industry; heavy metals and organic contaminants from electroplating wastes; contaminants from corrosion processes; and persistent organic pollutants from the synthesis and use of pesticides, dyes and pharmaceuticals. Most pollutants can be successfully eliminated or converted to non-toxic materials by methods based on the electrochemical principles. Electrochemical depolluting methods are mainly electrodialysis, electrocoagulation, electroflotation, anodic processes, cathodic processes and electrochemical advanced oxidation processes.

Remediation of phosphate-contaminated water by electrocoagulation with aluminium, aluminium alloy and mild steel anodes.

The present study provides an electrocoagulation process for the remediation of phosphate-contaminated water using aluminium, aluminium alloy and mild steel as the anodes and stainless steel as the cathode. The various parameters like effect of anode materials, effect of pH, concentration of phosphate, current density, temperature and co-existing ions, and so forth, and the adsorption capacity was evaluated using both Freundlich and Langmuir isotherm models. The adsorption of phosphate preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. The results showed that the maximum removal efficiency of 99% was achieved with aluminium alloy anode at a current density of 0.2 A dm(-2), at a pH of 7.0. The adsorption process follows second-order kinetics.

The adsorption of phosphate by graphene from aqueous solution

Graphene was prepared by a facile liquid phase exfoliation and characterized by Raman spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy and zeta potential measurements. A systematic study of the adsorption process was performed by varying pH, ionic strength and temperature. The experimental results showed that graphene is an excellent phosphate adsorbent with an adsorption capacity of up to 89.37 mg g−1 at an initial phosphate concentration of 100 mg L−1 and temperature of 303 K. The adsorption kinetics was modeled by first and second order rate, Elovich and Weber and Morris intraparticle diffusion models. The rate constants for all of these kinetic models were calculated and the results indicate that the second order kinetics model was well-suited to model the kinetic adsorption of phosphate. The Langmuir, Freundlich and D–R isotherm models were applied to describe the equilibrium isotherms and the isotherm constants were determined. Equilibrium data were well-described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was a spontaneous and endothermic process.

Effects of alternating and direct current in electrocoagulation process on the removal of cadmium from water

In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of cadmium from water using aluminum alloy as anode and cathode. The results showed that the removal efficiency of 97.5 and 96.2% with the energy consumption of 0.454 and 1.002 kWh kl(-1) was achieved at a current density of 0.2A/dm(2) and pH of 7.0 using aluminum alloy as electrodes using AC and DC, respectively. For both AC and DC, the adsorption of cadmium was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature.

Nitrate reduction in water: Influence of the addition of a second metal on the performances of the Pd/CeO2 catalyst

An attempt is made to improve the catalytic nitrate reduction on Pd/CeO(2) catalysts by the addition of a second metal. The influence of the second metal such as Sn, In and Ag on the Pd/CeO(2) for nitrate reduction is explored. The second metal is introduced over monometallic Pd/CeO(2) by a redox reaction. Pd/CeO(2) is more active than the bimetallic catalysts under pure hydrogen flow. Whereas in presence of CO(2) the monometallic Pd/CeO(2) is inactive for nitrate reduction, bimetallic catalysts are found to be more active than under pure hydrogen flow and also than the monometallic catalyst with a low selectivity towards ammonium ions, undesired product of the reaction. The Pd-Sn/CeO(2) catalyst is comparatively the most suited for nitrate reduction.

Studies Relating to Removal of Arsenate by Electrochemical Coagulation: Optimization, Kinetics, Coagulant Characterization

The present investigation aims to remove arsenate [As(V)] by electrochemical coagulation using mild steel as anode and cathode. The results showed that the optimum removal efficiency of 98.6% was achieved at a current density of 0.2 A dm−2, at a pH of 7.0. The effect of current density, solution pH, temperature, co-existing ions, adsorption isotherm, and kinetics has been studied. Kinetics reveals that the removal of arsenate by electrochemical coagulation is very rapid in the first 15 min and remains almost constant with the progress of reaction. The adsorption kinetics obeys the second-order rate expression. An equilibrium isotherm was measured experimentally and the results were analyzed by Langmuir, Freundlich, Dubinin- Redushkevich, and Frumkin using the linearized correlation co-efficient. The characteristics parameters for each isotherm were determined. The Langmuir adsorption isotherm was found to fit the equilibrium data for arsenate adsorption. Temperature studies showed that the adsorption was endothermic and spontaneous in nature.

Simultaneous removal of Co, Cu, and Cr from water by electrocoagulation

This study provides an electrocoagulation process for the removal of metals such as cobalt, copper, and chromium from water using magnesium as anode and galvanized iron as cathode. The various parameters like pH, current density, temperature, and inter electrode distance on the removal efficiency of metals were studied. The results showed that maximum removal efficiency was achieved for cobalt, copper, and chromium with magnesium as anode and galvanized iron as cathode at a current density of 0.025 A dm−2 at pH 7.0. First- and second-order rate equations were applied to study adsorption kinetics. The adsorption process follows second-order kinetics model with good correlation. The Langmuir and Freundlich adsorption isotherm models were studied using the experimental data. The Langmuir adsorption isotherm favors monolayer coverage of adsorbed molecules for the adsorption of cobalt, copper, and chromium. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

Novel cross-linked anion exchange membrane based on hexaminium functionalized poly(vinylbenzyl chloride)

Hydroxide anion exchange membranes (HAEMs) are of recent research interest, since these membranes can potentially replace the noble metal catalysts used in electrochemical energy conversion systems such as fuel cells and electrolysers. The conductivity and stability of state-of-the-art anion exchange membranes are far below those required for real applications. Herein, we report a novel anion exchange membrane based on aminated and cross-linked poly(vinylbenzyl chloride) prepared by an easy, viable synthetic route. β-Hydrogen free, multi-nitrogen containing ‘hexamethylenetetramine’ was used and explored as an amination/cross-linking agent for the first time in this study. FT-IR and 1H-NMR analysis results confirmed the successful quaternization of poly(vinylbenzyl chloride) with hexamine. TGA results showed the degradation temperature of the quaternized polymer is as high as 160 °C. AFM analysis revealed that the membrane possesses phase separated morphology with hydrophobic and hydrophilic domains. The ionic conductivity of the membranes increased when the amine to polymer ratio was increased from 0.2 to 0.33, and the highest ionic conductivity achieved was 6.8 × 10−3 S cm−1. The membrane has good chemical and alkaline stability which strongly suggests that the membrane would be a promising material for electrochemical energy conversion systems.

Facile one-pot electrosynthesis of Al(OH)3 – kinetics and equilibrium modeling for adsorption of 2,4,5-trichlorophenoxyacetic acid from aqueous solution

This study presents a Al(OH)3 synthesis in a facile one-pot process by an electrodissolution method. This process is a novel process, where the adsorbents are generated in an in situ, efficient and cost-effective way for removing organic pollutants. The adsorption performance of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) onto Al(OH)3 was systematically investigated and the experimental results indicated that Al(OH)3 showed an excellent adsorption capacity toward 2,4,5-T. To optimize the removal efficiency of 2,4,5-T, different experimental parameters like the effect of current density, pH, temperature, different anodes and inter-electrode distance were carried out. The results showed that the maximum removal efficiency of 86.0% was achieved at a current density of 0.10 A dm−2 and a pH value of 7.0. The adsorption kinetics could be well described by the pseudo-second-order model and the Langmuir isotherm model showed a better fit with experimental data than the Freundlich and D–R model. Moreover, thermodynamic parameters indicate that the adsorption of 2,4,5-T on aluminum hydroxides was feasible, spontaneous and endothermic. The adsorbed Al(OH)3 was characterized by different techniques, such as SEM, EDAX, XRD and FTIR measurements.

Studies on the removal of arsenate from water through electrocoagulation using direct and alternating current

Abstract Using alternating current in an electrocoagulation process offers an alternative to conventional electrocoagulation processes, where the direct current is used. The main objective of the present investigation is to study the effects of alternating current (AC) and direct current (DC) on the removal efficiency of arsenate by electrocoagulation using magnesium as anode and cathode. The effect of current density, solution pH, temperature, co-existing ions, adsorption isotherm and kinetics has been studied. The optimum removal efficiency of 98.3% and 97.9% was achieved with the energy consumption of 0.724 and 1.035 kWh/m3 at a current density of 0.2 A/dm2, at pH of 7.0 for AC and DC, respectively. The adsorption of arsenate preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules for both AC and DC. The adsorption process follows second-order kinetics model with good correlation coefficient. Temperature studies showed that adsorption was endothermic and sp...