Govindan Muthuraman

The combined removal of methyl mercaptan and hydrogen sulfide via an electro-reactor process using a low concentration of continuously regenerable Ag(II) active catalyst

In this study, an electrocatalytic wet scrubbing process was developed for the simultaneous removal of synthetic odorous gases namely, methyl mercaptan (CH(3)SH) and hydrogen sulfide (H(2)S). The initial process consists of the absorption of CH(3)SH and H(2)S gases by an absorbing solution, followed by their mediated electrochemical oxidation using a low concentration of active Ag(II) in 6M HNO(3). Experiments were conducted under different reaction conditions, such as CH(3)SH and H(2)S loadings, active Ag(II) concentrations and molar flow rates. The cyclic voltammetry for the oxidation of CH(3)SH corroborated the electro-reactor results, in that the silver in the 6M HNO(3) reaction solution significantly influences the oxidation of CH(3)SH. At a low active Ag(II) concentration of 0.0012 M, the CH(3)SH removal experiments demonstrated that the CH(3)SH degradation was steady, with 100% removal at a CH(3)SH loading of 5 gm(-3) h(-1). The electro-reactor and cyclic voltammetry results indicated that the removal of H(2)S (100%) follows a mediated electrocatalytic oxidation reaction. The simultaneous removal of 100% of the CH(3)SH and H(2)S was achieved, even with a very low active Ag(II) concentration (0.0012 M), as a result of the high efficiency of the Ag(II). The parallel cyclic voltammetry results demonstrated that a process of simultaneous destruction of both CH(3)SH and H(2)S follows an H(2)S influenced mediated electrocatalytic oxidation. The use of a very low concentration of the Ag(II) mediator during the electro-reactor process is promising for the complete removal of CH(3)SH and H(2)S.

Gaseous trichloroethylene removal using an electrochemically generated homogeneous low-valent ligand-free Co(I) electrocatalyst by electro-scrubbing.

The interest in heterogeneous Co(OH)2 electrocatalysts for energy applications has increased steadily. This study focused on a ligand-free homogeneous electrocatalyst for the degradation of gaseous trichloroethylene (TCE) in NaOH in a divided electrolytic cell. The initial electrolysis results revealed a change in the oxidation reduction potential (ORP) of [Co(II)(OH)4](2-) (Co(II)) from -267 mV to -800 mV on anodized Ti during electrolytic reduction identifies low-valent homogeneous [Co(I)(OH)4](3-)(Co(I)) formation in 10 M NaOH. Cyclic voltammetry analysis of Co(II) at different anodized electrodes, Ag, carbon and Ti, in a 10 M NaOH solution, showed no stripping like peak in the reverse scan only the Ti electrode, supporting the formation of low-valent Co(I). UV-vis spectral analysis of the electrolyzed solution showed an enhanced peak corresponding to metal-to-ligand transition, demonstrates Co(I) formation. Co(II) reduction reached a maximum yield of 18% at 30 mA cm(-2) on an anodized Ti cathode. For gaseous TCE removal, continuous mode electro-scrubbing was adopted and degradation was monitored using an online FTIR gas analyzer that showed 99.75% degradation of TCE in the presence of homogeneous Co(I). Three consecutive regenerations of Co(I) and degradation steps of TCE confirmed the possibility of industrial applications in a sustainable manner.

Innovative reductive remediation of carbon tetrafluoride at room temperature by using electrogenerated Co1

Among the non-CO2 greenhouse gases, carbon tetrafluoride (CF4) is the most recalcitrant and should be eliminated from the atmosphere. In the present study, a non-combustion electroscrubbing method was used in an attempt to degrade CF4 with an electrogenerated Co1+ mediator in a highly alkaline medium. The initial absorption experiments revealed 165mgL-1 CF4 gas dissolved in 10M NaOH. Different mediator precursors, [Co(II)(CN)5]3-, [Ni(II)(CN)4]2-, [Cu(II)(OH)4]2-, and [Co(II)(OH)4]2-, were used and the electroscrubbing results showed that the electrogenerated Co1+ or [Co(II)(OH)4]2- precursor effectively degraded up to 99.25% of the CF4 gas. The variations in [Co(II)(OH)4]2- reduction efficiency and cyclic voltammetry revealed CF4 degradation followed by electrogenerated Co1+ mediated reduction. The increased zeta potential (+6mV) of the electrogenerated Co1+ showed that the degradation reaction occurs preferably at the solution interface. Electroscrubbing for CF4 removal and the resulting products were controlled by the carrier gas. Air and H2 carrier gases lead to the formation of CHF3 and COF2. N2 as the carrier gas caused 99.25% degradation with ethanol as a product. An 80% CF4 degradation efficiency with CHF3 as the product was observed when a mixture of N2 and air was used as the carrier gas.

Influence of cathode on the electro-generation of peroxydisulfuric acid oxidant and its application for effective removal of SO2 by room temperature electro-scrubbing process.

Peroxydisulfuric acid oxidant (H2S2O8) was electro-generated using boron doped diamond (BDD) anode in an undivided electrolytic cell under the optimized conditions and used for the oxidative removal of gaseous SO2. The influence of the nature of cathode material on the formation yield of H2S2O8 was investigated with Ti, Pt, Zr and DSA electrodes in a flow type electrolytic cell under batch recirculation mode. Among the various cathodes employed Ti exhibited a good performance and the formation yield was nearly doubled (0.19 M) compared to the reported value of 0.07 M. The optimization of electrode area ratio between the anode and cathode brought out the fact that for nearly 8 times smaller Ti cathode (8.75:1) the achieved yield was ∼65% higher than the 1:1 ratio of anode and cathode. The highest concentration of 6.8% (0.48 M) H2S2O8 was seen for 35 cm(2) BDD anode with 4 cm(2) Ti at 20 °C with the measured redox potential value of +1200 mV. The oxidative removal of SO2 in an electro-scrubbing column attached to the online production of peroxydisulfuric acid under the optimized conditions of cell parameters shows that SO2 removal efficiency was nearly 100% for 25 and 50 ppm inlet concentrations and 96% for 100 ppm at the room temperature of 25 °C.

Enhanced stability and electrochemical performance of a BaTiO3/PbO2 electrode via a layer obtained with layer electrodeposition

Herein, the electrodeposition of BaTiO3 and PbO2 on Ti using the layer-by-layer method under different current densities (CDs) and times, was investigated. The weight difference in the deposited BaTiO3 explains the BaTiO3 weight decrease by one order with the increasing CD from 0.025 A cm to 0.125 A cm and also follows the same trend during the PbO2 deposition. The PbO2 deposition at different CDs demonstrates that the deposited PbO2 weight increases by one order with the increasing CD. Also, cyclic voltammetry results explain the low and moderate deposition CDs and the time suitably shows the PbO2 redox behavior. According to SEM and XRD, a CD of 0.05 A cm affects the formation of crystalline BaTiO3 and PbO2 more than higher or lower CDs. Finally, the BaTiO3 and PbO2 layer-by-layer electrode electrodeposited at a moderate CD showed a better stability than the electrode including only PbO2. The use of BaTiO3 is promising for the stability of the PbO2 electrode preparation.