Polymerization of thiourea modified poly(acrylonitrile- Co-acrylic acid) for cationic dyes adsorption from single and binary solution

• Main Author: Adekanmi, Adeyi Abel
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Dyes and dyeing - Chemistry; Thiourea - Toxicology
• Online Access: http://psasir.upm.edu.my/id/eprint/84188/1/FK%202019%2076%20-%20ir.pdf; http://psasir.upm.edu.my/id/eprint/84188/
• Institution: Universiti Putra Malaysia

Synthetic organic dyes, especially cationic dyes are used extensively as colouring agents in many industries. The discharge of dye-bearing industrial effluents into hydrosphere, generate accumulation of unwanted colours in water, reducing photosynthesis of aqueous flora and causes biological attack towards aquatics. Besides, dye degradation products is also toxic, carcinogenic or mutagenic due to complex dye molecule structure. Hence, proper treatment of dye-containing industrial wastewater is a major environmental pollution issue for consideration. This study investigated the innovation of functional polymer-based adsorbent viz., thiourea modified poly(acrylonitrile-co-acrylic acid) that was used to sequestrate selected cationic dyes (malachite green (MG) and methylene blue (MB)) from model effluent by adsorption method. The poly(acrylonitrile-co-acrylic acid) copolymer was synthesized by redox polymerization of acrylonitrile (AN) and acrylic acid (AA) monomer, and further modified chemically with thiourea (TU) to produce TU modified poly(AN-co-AA) adsorbent. Then, single batch and fixed-bed adsorption experiments for each cationic dye, MG and MB were performed at varied operating conditions. Also, batch and packed-bed mode of adsorption for binary cationic dye solution onto TU modified poly(AN-co-AA) was studied. The adsorption process was found to be pH dependent and the initial dye concentration. The maximum single cationic dye uptake (%) for MG and MB were 92% and 96%, respectively at pH 9. The uptake of both MG and MB was an exothermic process with negative values of ΔH ᵒ and ΔGᵒ . Equilibrium data were well fitted with Langmuir, Freundlich and Temkin isotherms. The maximum Langmuir adsorption capacity of 605.58 mg/g and 440.81 mg/g was estimated respectively for MG and MB dye. Extended Langmuir model and extended Freundlich model provide a suitable description of the experimental binary data. The comparison of the single and binary isotherms elucidates an antagonistic interaction between the MG and MB ions. In addition, pseudo-second-order model was found suitable for the description of adsorption kinetic for both dyes onto TU modified poly(AN-co-AA), signifying chemisorption between adsorbent and dye molecules. The single and binary fixed-bed column performance was significantly influenced by pH, concentration of dyes, bed depth and influent flow rate; lower solution pH and higher influent flow rate leads to early breakthrough and exhaustion time, with less adsorption of MG and MB. Conversely, increase in bed-depth resulted in extended breakthrough and saturation time with improved column performance. It was found that Thomas and Yoon-Nelson models perfectly stimulated the adsorption rate and behaviour of cationic dyes entrapment than Bohart-Adams model. Based on experimental findings, TU modified poly(AN-co-AA) polymer is a promising functional regenerable adsorbent with high capacity to remove cationic dye (for individual and simultaneous) from liquid environment.