Degradation Kinetics and Mechanism of Polychloromethanes Reduction at Co-MoS2/Graphite Felt Electrode

Mohammed Dauda,Chanbasha Basheer,Muhammad H Al-Malack,Almaz Jalilov,Mohammad Nahid Siddiqui

doi:10.3390/catal11080929

Abstract

In this study, the electrochemical dechlorination of different polychloromethanes (CCl4, CHCl3, and CH2Cl2) on a Co-MoS2 graphite felt cathode was investigated. The Co-MoS2 electrocatalyst was prepared hydrothermally on a graphite felt support. The prepared catalyst’s characterization revealed the formation of hybridized CoSx and MoS2 nanosheets deposited on the pore structures of graphite. The influencing factor for the electro-dechlorination parameters such as applied current density, pH, and sample concentration on the dechlorination rate was optimized. A significant capacitive reduction current density peak of approximately 1 mA/cm2 was noted for CCl4 at a potential of −0.3 V (vs. AgCl). The dechlorination mechanism was attributed to the stepwise hydrogenolysis mechanism that involves the organochlorides bond cleavage by H* insertion. It was noted that the Co-MoS2 graphite felt electrode exhibited excellent catalytic activity toward the reduction of each of the chlorinated compounds with high selectivity toward the higher-order organochloride. Moreover, the dechlorination rates for each of the compounds were suited to the first-order kinetic model, and the estimated apparent rate constants showed the dechlorination in the following sequence CH2Cl2 (k3 = 9.1 × 10−5 s−1) < CHCl3 (k2 = 1.5 × 10−3 s−1) < CCl4 (k1 = 2.8 × 10−3 s−1).

Highlights

Polychloromethanes that include carbon tetrachloride and chloroform are among the most ubiquitous classes of volatile halogenated contaminants commonly found in surface water, groundwater, and soil [1]
The bare graphite felt (GF) used as a support for the Co doping of MoS2 (Co-MoS2) catalyst deposited has a porous 3-D
The appearance of orderly spaced lattice fringes with an inter-planar distance of 0.35 nm in the HRTEM result further confirms the crystalline phase of Co-MoS2 [24]

Summary

Introduction

Polychloromethanes that include carbon tetrachloride and chloroform are among the most ubiquitous classes of volatile halogenated contaminants commonly found in surface water, groundwater, and soil [1] These compounds have been discharged into the environment because of their extensive use as organic solvents by several industrial processes [2]. Electrocatalytic hydrodechlorination employs a catalyst electrode and an externally applied electron (applied current) that serve as the reactant to initiate the reduction process through catalytic generation of reductive species (H*- atomic hydrogen) that effectively detoxify the organochloride contaminants [1] In this approach, the reductive species are continuously generated in situ via water dissociation and does not require the addition of a hydrogen donor. Compared to the hydrodechlorination reaction, the cathodic polarization of the catalyst electrode during electrocatalytic hydrodechlorination processes serves to protect the electrode against deactivation, which in turn, allows for its long-time usage

Methods

Results

Conclusion