Thesis (M. Eng.) - Asian Institute of Technology, 2022

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Nanotechnology

Due to the prevalent global water crisis, susceptibility to heavy metal pollution has become concerning for many communities. As a potential solution, the capacitive deionization (CDI) technique was proposed for its energy and material recovery over the conventional metal removal techniques. In recent works, the adsorption capability is further enhanced with the incorporation of MnO2 into the electrodes for the CDI operation. However, this type of electrode is still limited by its complex synthesis method. In this work, a simpler alternative, cyclic voltammetry electrodeposition, was used to prepare MnO2/activated carbon cloth electrode and the effects of the synthesis conditions on the electrode{u2019}s characteristics were studied. The adsorption capabilities of the electrode in CDI operation were also investigated on various metal species {u2013} chromium, cadmium, copper, and lead {u2013} with varying operating conditions: adsorption of individual metal species with varied applied voltage and flow rate, adsorption from mixtures of multiple metal species, and adsorption under continuous multiple cycle operation. Using cyclic voltammetry for the electrodeposition, the electrode{u2019}s areal capacitance increased with higher depositing scan rate and depositing cycles, reaching 134.51 mF/cm2 at 25 mV/s scan rate and 10 cycles compared to 107.25 mF/cm2 of the raw ACC. The MnO2/ACC electrodes in CDI operation were able to achieve the adsorption capacity of 8.76, 6.48, 3.64, and 3.41 mg/g for Cr3+, Pb2+, Cu2+, and Cd2+ , respectively. The adsorption capacity would reduce with either increased flow rate or decreased applied voltage. For the adsorption from the mixtures of multiple metal species, the adsorption capacity of each species was reduced down to 2.79, 5.26, 3.52, and 1.43 mg/g for Cr3+, Pb2+, Cu2+, and Cd2+, respectively; this is attributed to the high ion activity in the solution. Lastly, for the adsorption under multiple cycles, the adsorption capacity of each species decreased with each cycle. This is believed to be from the lower desorption rate compared to the adsorption rate, reducing the available adsorption capacity in the following cycles.