Adsorption Of Reactive Dyes By Hexadecylamine And 3-Aminopropyl Triethoxysilane Modified Chitosan Beads
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Date
2016
Authors
Nasrollah Vakili, Mohammadtaghi Vakili
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Textile industry has experienced exponential growth in recent years. In these industries, many different types of dye are being used for coloring purposes. As a result, the effluent of these industries contains large amount of color and toxic compounds. These colors and toxic compounds would be detrimental to the environment if they are left untreated. As such, the textile effluent has a dye need to be treated with an efficient method before being released into water bodies. Among all treatments, adsorption process is found to be an effective method for industrial effluents treatment. Chitosan (CS) is one of abundantly available natural polymers and is an effective adsorbent due to its specific adsorption properties such as biodegradability, cationicity and low price. However, the raw CS suffers from some draw backs such as low surface area and low adsorption capacity which limit its adsorption performance. Therefore, it is necessary for CS to be modified prior to its use as an adsorbent. In the present study CS, was modified physically and chemically and then applied for adsorption of reactive dyes (reactive blue 4 (RB4) and reactive black 5(RB5)) and real textile wastewater. For physical modification, the CS powder was successfully converted to CS beads. Afterwards, the CS beads were chemically modified using hexadecylamine (HDA) and 3-aminopropyl triethoxysilane (APTES). The physicochemical properties of all prepared modified and unmodified CS beads were characterized by means of Fourier transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), nitrogen adsorption-desorption measurement, energy dispersive X-ray spectroscopy (EDX) and Zeta potential measurement. The BET surface areas of the prepared beads were in the range of 0.29 - 1.32 m2/g. Effects of pH (2-10), temperature (30-50 °C), contact time (5 to 480 min), initial dye concentration (50-500 mg/L) and adsorbent dosage (0.25-1.5 g/L) on adsorption performance of adsorbents were investigated. The maximum adsorption capacity of CS beads after modification using HDA and APTES increased from 317.1 mg/g to 433.8 mg/g, 454.7 mg/g and 468.8 mg/g at pH 4 and 30 °C for CS/APTES, CS/HDA and CS/HDA/APTES beads, respectively. This could be attributed to the presence of more cationic functional groups on the surface of modified adsorbents which resulted in an increase in the surface charge and enhance dye adsorption performance of adsorbents. The obtained adsorption data were assessed based on equilibrium adsorption isotherms, kinetics adsorption models and thermodynamic studies. For all adsorbents, the isotherm data were significantly described by Freundlich model. The kinetic study revealed that the pseudo-second-order rate model was in better agreement with the experimental data. The negative values of the thermodynamic parameters, including ΔG0 (−2.28, −4.70, −2.12 and −6.64 kJ/mol at 30 ±2 °C), ΔH0 (−172.18, −43.82, −101.62 and −74.32 kJ/mol) and ΔS0 (−560.71, −129.08, −314.58 and −223.35 J/molK) for CS beads and APTES, HDA and HDA/APTES modified beads, respectively, showed that RB4 adsorption is a spontaneous and exothermic process. Obtained results from regeneration studies showed that all prepared adsorbents were able to be used 13 times in the adsorption and desorption cycles. The CS beads modified with both HDA and APTES (CS/HDA/APTES beads) were selected to be evaluated for RB5 removal and textile wastewater treatment as well. Results showed that CS/HDA/APTES beads were able to remove 92.1% of RB5 and 93.2% of dye in textile wastewater.
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Keywords
Chitosan beads