Adsorption of metal ions by surface modified polycarbonates derived from waste optical DISCS / Saidu Akun Abdallah

Saidu Akun , Abdallah (2022) Adsorption of metal ions by surface modified polycarbonates derived from waste optical DISCS / Saidu Akun Abdallah. PhD thesis, Universiti Malaya.

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Abstract

Plastic has been widely used in various industrial sectors due to its outstanding properties and economical advantages. Since huge volumes of production and consumption are associated with increased market demand, plastic waste has brought about environmental concerns due to its non-biodegradable nature; polycarbonate from optical compact discs and digital versatile discs are one of the significant waste. Instead of being destined for landfills and incinerators, a more sustainable option is turning the waste optical discs into valuable products, considering the chemical modification opportunity granted by polycarbonate molecular structure. This study, therefore, attempts to retrieve polycarbonate from waste optical discs and alter them chemically into adsorptive materials for the removal of metal ions mainly mercury(II). In this work, the polycarbonate was recovered via extraction-precipitation strategy and subsequently modified into nitrated, aminated, thiol-modified polycarbonates. The products were characterized with various instrumental techniques before being subjected to adsorption studies. The adsorptive removal process with respect to individual adsorbent was evaluated using response surface methodology, while the adsorption isotherms, kinetics, and thermodynamic were modelled by batch experiments. The adsorption data best fit the Freundlich isotherm and followed a pseudo-second-order kinetic for all the cases (coefficient of determination > 0.9), which implied favorable chemisorption related to the surface functionalization. The thiol-modified polycarbonate prompted further investigation for copper(II) removal considering the highest adsorption capacity; the fittings again satisfied the Freundlich isotherm and the pseudo-second-order kinetic. Under the experimental settings optimized from the response surfaces, the adsorbents exhibited promising adsorptive removal efficiency (consistent with model prediction) regardless of the water matrices. Even for three adsorption-desorption cycles, the mercury(II) adsorptive removal performance of thiol modified polycarbonate remained more than 80%. These findings suggested that the waste-derived polycarbonate-based materials could be potential adsorbents for the treatment of metal contaminants in the aqueous system.

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