Fabrication, Photocatalytic And Adsorption Of Immobilized Tio2/Chitosan-Montmorillonite And Tio2/Polyaniline Bilayer Systems For The Removal Of Methyl Orange Dye From Aqueous Solutions
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Date
2016-09
Authors
Bahrudin, Noor Nazihah
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Abstract
This study was an effort to develop two immobilized bilayer systems for the photocatalytic-adsorptive removal of methyl orange (MO) dye from aqueous solution. The immobilized bilayer systems involving specific adsorbents and TiO2 on the glass plates namely TiO2/chitosan-montmorillonite (TiO2/CS-MT/GP) and TiO2/polyaniline (TiO2/PANI/GP) systems had been fabricated via a dip coating technique. In this study, CS-MT and PANI, respectively functioned as the sub-layer while TiO2 photocatalyst was made as the top layer. Initially, the respective adsorbent sub-layer of both systems was optimized via a batch adsorption study and characterized by using scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FT-IR) and N2 adsorption-desorption analysis. The addition of MT powder to CS matrix decreased the swelling degree, improved the mechanical strength and surface area (SBET) of CS-MT from 3.82 to 4.38 m2 g-1 while the addition of ENR50-PVC decreased the SBET of PANI powder from 9.16 to 8.50 m2 g-1 but improved its mechanical strength. The photocatalytic activity assessment of the bilayer systems was performed under the irradiation of a 45 Watts compact fluorescent lamp. The optimum adsorbent sub-layer loading was found to be 1.27 and 0.63 mg cm-2 for TiO2/CS-MT/GP and TiO2/PANI/GP, respectively, while the optimum TiO2 loading for TiO2/CS-MT/GP and TiO2/PANI/GP was 2.54 and 1.27 mg cm-2, respectively. The TiO2/CS-MT/GP and TiO2/PANI/GP systems obeyed the
Lagergren’s pseudo first order and Ho and Mc Kay’s pseudo second order adsorption kinetic model, respectively. On the other hand, the Freundlich isotherm model could explain the adsorption mechanism at equilibrium whereas intra-particle diffusion was one of the rate limiting steps for both systems. The bilayer systems produced more •OH radicals than the single layer TiO2 due to better charge separation rate of electron-hole pairs while the band gap of TiO2 was reduced from 3.02 eV to 2.94 and 2.95 eV for TiO2/CS-MT/GP and TiO2/PANI/GP system, respectively. The optimum operating conditions for the photocatalytic-adsorption activity of the bilayer systems were at ambient pH (6.5), 40 mL min-1 of aeration flow rate and 20 mg L-1 of MO initial concentration. The TiO2/CS-MT/GP could maintain the reusability on the average removal of 97.7 ± 1.0 % and 0.088 ± 0.008 min-1 removal rate throughout the 10 cycles, while the photocatalytic activity of TiO2/PANI/GP was better at the first three cycles, but started to cease out at the 4th cycle with the removal average of 62.7 ± 10.2 % and 0.017 ± 0.003 min-1 removal rate. Nevertheless, the removal rate of the MO of the TiO2/CS-MT/GP system was 4 times better than TiO2/GP while it was 2.5 times for the TiO2/PANI/GP system. The mineralization of MO attained 82.8 % by TiO2/CS-MT/GP and 73.2 % by TiO2/PANI/GP after 10 hours of treatment. Meanwhile, the degradation pathways showed that the main intermediate species produced were 4-{(E-[4-(methylamino)phenyl] diazenyl}benzenesulfonate and 4-{(E-[4-aminophenyl] diazenyl}benzenesulfonate. Comparatively, the TiO2/CS-MT/GP system showed better photocatalytic-adsorptive removal of the MO dye than the TiO2/PANI/GP system.
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An effort to develop two immobilized bilayer systems for the photocatalytic-adsorptive removal , of methyl orange (MO) dye from aqueous solution.