Electrochemical removal of mercury from aqueous solution using task-specific ionic liquid immobilised on palm shell activated carbon / Hawaiah Imam Maarof

Hawaiah Imam , Maarof (2022) Electrochemical removal of mercury from aqueous solution using task-specific ionic liquid immobilised on palm shell activated carbon / Hawaiah Imam Maarof. PhD thesis, Universiti Malaya.

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Abstract

Electrode design is one of the most important criteria in providing a satisfactory performance of an electrochemical process. The conventional two-dimensional (2D) electrode provides low current efficiency despite high percentage removal and recovery of metal ions from dilute concentrations. Meanwhile, emerging advanced materials, such as task-specific ionic liquids (TSIL), have presented prominently to electrode modifications' technological advancement. In this present work, two types of threedimensional (3D) electrodes were developed. The precursor is an activated carbon derived from solid waste, namely palm shell. The performance of palm shell activated carbon (PSAC) and trioctylmethylammonium thiosalicylate immobilised on PSAC (PSAC-TOMATS) electrodes were evaluated. The prepared electrodes were electrochemically characterized by voltammetric techniques and potentio electrochemical impedance spectroscopy (PEIS). Next, the prepared electrodes were employed as the cathode in a batch-mode electrochemical process system to remove Hg from synthetic wastewater. In the preparation steps and electrochemical characterization of the PSAC electrode, 20% carbon black (CB) was found to give low electron charge resistance and the maximum current peak for the redox reaction of ferrocyanide/ferricyanide. Meanwhile, by increasing the amount of binder from 10% to 20%, the electrochemical active surface area was decreased by 42%. The most suitable supporting electrolyte for the electro characterisation of the prepared electrode was NaCl because it provides the lowest double-layer capacitance effect compared to HCl and NaOH. Cyclic voltammetry data suggest that the PSAC electrode is undergoing a quasi-reversible process for which the equivalent effect, both that of the electron transfer rate and mass transfer rate, has been taking place. The presence of interfacial interaction, such as adsorption, was also observed from the chronocoulometry analysis. The removal of Hg in a batch-mode electrochemical system was very rapid using the PSAC-TOMATS electrode. However, the modified electrode required an adequate amount of TOMATS to grant a higher percentage of Hg removal. By immobilising 0.2 g TOMATS on the PSAC, a removal of 97.1% of Hg (from an initial Hg concentration of 100 ppm) was achieved within 1.5 hours of electrochemical treatment time, while the PSAC electrode required a longer treatment time (6 hours). Additionally, the PSAC-TOMATS electrode provides higher current efficiency, higher percentage removal and lower energy consumption than the PSAC electrode. Under the electrode reusability studies, the PSAC-TOMATS electrode's efficiency was found to undergo a 15% reduction after the second cycle. However, only a slight reduction (2%) was observed for the third cycle. In conclusion, an electrochemical process using the PSAC-TOMATS electrode offers a promising approach to facilitate an effective removal of Hg from an aqueous solution.

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