Chitosan/chitin composite membrane reinforced with nanocellulose for the removal of cadmium ions from wastewater / Thaneissha Marimuthu

Thaneissha , Marimuthu (2022) Chitosan/chitin composite membrane reinforced with nanocellulose for the removal of cadmium ions from wastewater / Thaneissha Marimuthu. PhD thesis, Universiti Malaya.

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Abstract

Various green initiatives are being taken perpetually to upgrade the quality of environment and inculcate the society with the mind set of sustainability. In conjunction with this, a porous chitosan/chitin whiskers membrane reinforced with cellulose nanomaterial is fabricated for the removal of cadmium (II) ions in wastewater. This composite membrane consists of matrix and filler which are collectively made up of natural polymers such as chitosan, chitin and cellulose. In this study, chitosan was chosen as the main material for matrix due to the presence of prolific functional groups in its polymer chain. In respective to the first objective, porous structure was successfully induced in chitosan (CS) membrane by using polyethylene glycol (PEG) as pore forming agent where the result was proved through FESEM. Besides enhancing the porosity, PEG aids to improve the water uptake of membrane. Notably, the membrane with mass ratio of CS:PEG = 75:25 performs well, giving adequate mechanical strength and desirable pore size. Thus, this composition was maintained for the rest of this study. In line with second objective, the addition of chitin whiskers (CH) successfully enhanced mechanical performances. Particularly at 0.9% of chitin content, the tensile strength increased by 58.2% compared to CS membrane without chitin whiskers addition. This is attributed to the strong electrostatic interaction and hydrogen bonds between chitosan and chitin whiskers. Nonetheless, the water contact angle increases gradually upon increasing the loading of chitin. Therefore, CS/0.6CH membrane which offers mutual benefits between the mechanical performance and pure water flux was selected for further study. Then, the effect of incorporation of unmodified and modified cellulose nanomaterial on mechanical and physicochemical properties of composite membranes was determined respectively. In this case, cellulose nanocrystals (CNC) were synthesized from microcrystalline cellulose and further chemical modification (esterification) was performed using succinic anhydride to produce SCNC. Interestingly, the membranes incorporated with 1% CNC and 1% SCNC exhibited enhancement in mechanical properties, wettability, porosity and water flux respectively owing to nano size range that offers high surface area and versatile functional groups. Despite exhibiting lower mechanical properties, carboxyl enriched CS/0.6CH/SCNC-1 bestowed better physicochemical properties and water flux compared to CS/0.6CH/CNC-1. Thus, the final objective aimed to get a deeper understanding on the adsorption behaviour of heavy metal ions towards CS/0.6CH/SCNC-1 using Response Surface Methodology (Central Composite Design) approach. The optimum parameters suggested attaining maximum removal efficiency of cadmium (90.09%) at pH 6, 95 ppm and 110 minutes. This experimental data is best described using Langmuir isotherm and pseudo-second order kinetic model for the removal of cadmium ions from wastewater. The functional groups of membrane predominantly contributed to excellent removal efficiency of cadmium via two main interactions which are electrostatic attraction and chelation. Finally, adsorption-desorption was performed up to 3 cycles using Ethylenediaminetetraacetic acid (EDTA) without compromising the efficiency. Overall, these bio-polymer nanocomposite membranes have a great potential as advanced technology for scavenging heavy metal ions in wastewater and aids to achieve the standard of effluent discharge in accordance with Environmental Quality Act 1974 in Malaysia.

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