Immobilized P-25 Tio2/Montmorillonite And P-25 Tio2/Organo-Montmorillonite Bilayer Systems For The Synergistic Photocatalytic-Adsorption Removal Of Methylene Blue And Humic Acid From Aqueous Solutions
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Date
2015-12
Authors
Ngoh, Ying Shin
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
This research revolved around the development of immobilized P-25
TiO2/montmorillonite and P-25 TiO2/organo-montmorillonite bilayer systems for the
synergistic photocatalytic-adsorption removal of methylene blue (MB) and humic
acid (HA) from aqueous solutions. The initial stage of the development of the bilayer
systems involved batch adsorption study of the sub-layer adsorbent. Immobilized
montmorillonite (MT-PVAB/GP) was prepared for the adsorption of MB whereas
immobilized organo-montmorillonite (2.0-O-MT-PVAB/GP) was fabricated for HA
adsorption process. The MT-PVAB/GP and 2.0-O-MT-PVA were characterized by
using field emission scanning electron microscopy (FE-SEM), energy dispersive xray
(EDX), attenuated total reflectance-fourier transform infrared spectroscopy
(FTIR-ATR), N2 adsorption-desorption analysis and zeta potential measurements.
The MB and HA adsorption processes were affected by adsorbent loading, solution
pH, aeration rate, initial concentration and also, contact time. The kinetic data for
adsorption of MB and HA were found to obey pseudo-second order kinetic model
and intra-particle diffusion was the major rate limiting step for the adsorption
processes. The adsorption isotherm study revealed that the MB and HA adsorption
processes were best fitted with the Langmuir isotherm model. The maximum
monolayer adsorption capacity, qm of MT-PVAB/GP towards MB was 111 mg g-1.
Meanwhile, the qm of HA adsorption at UV254 and Colour436 was determined as
31.75 and 29.59 mg g-1, respectively. The thermodynamic parameters values
indicated that the MB and HA adsorption processes were favourable at higher
temperature, endothermic and spontaneous. For the subsequent fabrication of the
bilayer systems, the optimum composition of the sub-layer adsorbent of either MTPVAB/
GP or 2.0-O-MT-PVAB/GP and the upper layer P-25 TiO2 was determined
systematically by their synergistic photocatalytic-adsorption behaviour towards MB
and HA, respectively. The optimized P-25 TiO2/MT-PVAB/GP and P-25 TiO2/2.0-
O-MT-PVAB/GP bilayer systems were characterized by cross-sectional SEM, EDX,
UV-vis diffused reflectance spectroscopy (UV-vis DRS) and photoluminescence
spectroscopy (PLS). The synergistic photocatalytic-adsorption activity of the bilayer
systems were primarily driven by their adsorption capacities which in turn were
manipulated by solution pH, aeration rate, initial concentrations; higher separation
rate of photo-generated electron-hole pairs and lower band gap energy as compared
to the monolayer P-25 TiO2/GP system. The UV irradiance intensity also affected the
photocatalytic activity of the bilayer systems. The P-25 TiO2/MT-PVAB/GP
displayed enhancement in the synergistic photocatalytic-adsorption removal rate by
3.51 folds as compared with P-25 TiO2/GP. Moreover, the P-25 TiO2/MT-PVAB/GP
bilayer system was highly reusable whereby on the average, the P-25 TiO2/MTPVAB/
GP managed to remove 99.7 ± 0.14 % of MB at the average rate of 0.123 ±
0.006 min-1 throughout the 10 cycles of reuse. On the other hand, the P-25 TiO2/2.0-
O-MT-PVAB/GP demonstrated increase in the synergistic photocatalytic-adsorption
removal rate of HA at UV254 by an average of 2.10 and 3.34 folds in comparison to
P-25 TiO2/MT-PVAB/GP and P-25 TiO2/GP, respectively. The P-25 TiO2/2.0-OMT-
PVAB/GP bilayer system also exhibited good reusability where on the average,
99.4 ± 0.16 % of HA at UV254 was eliminated with the average rate of 0.057 ± 0.004
min-1 during the 10 cycles of repeated applications. The photo-mineralization of MB
and HA were reflected by total organic carbon (TOC) analysis and reduction in pH
values. The HA intermediate products formed during the photocatalytic-adsorption
process by P-25 TiO2/2.0-O-MT-PVAB/GP were identified by liquid
chromatography – mass spectrometry (LC-MS) analysis. This research demonstrated
that the combination of photocatalyst and absorbent in an immobilized bilayer
manner is advantageous and feasible for synergistic photocatalytic-adsorption
removal of organic pollutants from aqueous solution.
Description
Keywords
immobilized P-25 TiO2/montmorillonite and P-25 TiO2/organo-montmorillonite