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TiO2 (rutile) embedded inulin—A versatile bio-nanocomposite for photocatalytic degradation of methylene blue
Accepted Manuscript Title: TiO2 (Rutile) embedded Inulin–A versatile Bio-nanocomposite for photocatalytic degradation of methylene blue Author: G. JayanthiKalaivani S.K. Suja PII: DOI: Reference:
S0144-8617(16)30018-2 http://dx.doi.org/doi:10.1016/j.carbpol.2016.01.054 CARP 10733
To appear in: Received date: Revised date: Accepted date:
16-8-2015 9-1-2016 25-1-2016
Please cite this article as: JayanthiKalaivani, G.,TiO2 (Rutile) embedded InulinndashA versatile Bio-nanocomposite for photocatalytic degradation of methylene blue, Carbohydrate Polymers (2016), http://dx.doi.org/10.1016/j.carbpol.2016.01.054 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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TiO2 (Rutile) embedded Inulin – A versatile Bio-nanocomposite for photocatalytic
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degradation of methylene blue
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G. JayanthiKalaivani1, S. K. Suja2
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Department of Chemistry, Lady Doak College, Madurai-625002, Tamilnadu, India
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E-mail id:1 [email protected] 2
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[email protected] ABSTRACT
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Inulin, a water soluble carbohydrate polymer, was extracted from Allium sativum L by
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hot water diffusion method. A novel bio-nanocomposite was prepared by embedding TiO2
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(Rutile) onto the inulin matrix. The extracted inulin and the prepared bio-nanocomposite were
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characterized using UV-Visible, FT-IR, XRD, SEM, TEM and TGA techniques. The
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photocatalytic activity of the bio-nanocomposite for the degradation of methylene blue was
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studied under UV illumination in batch mode experiment and was found to be twice as high as
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that of pristine TiO2. The kapp for inulin-TiO2 (0.0449 min-1) was higher than that for TiO2
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(0.0325min-1) which may be due to the synergistic action of inulin and TiO2. The stabilization of
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photo excited electron suppressed the electron-hole pair recombination thereby inducing the
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electrons and the holes to participate in the photo reduction and oxidation processes, respectively
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and enhancing the photocatalytic activity.
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______________________________________________________________________________
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Key words: Inulin; TiO2; Rutile; bio-nanocomposite; photocatalytic activity; methylene blue.
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Chemical compounds studied in this article
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Inulin (PubChem CID: 16219508); TiO2 –Rutile (PubChem CID:26042); Methylene blue
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(PubChem CID:6099)
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1. Introduction
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Over a past few years, there has been a growing concern for the degradation of organic
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dye molecules from industrial effluents. Several techniques viz., adsorption, photocatalysis,
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ozonization, bioremediation etc., have been employed for waste-water treatment and recycling.
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Among them heterogeneous photocatalysis proved to be the most common and the cheapest
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process which is based on the absorption of photons of energy greater than the band gap energy
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and is found to be the most effective as it leads to complete mineralization of the organic dye
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pollutants (Rushengyuan, Rongbo, Wenzhong & Jingtang, 2005; Susann et al, 2013; Boroski et
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al, 2009). Several inorganic semiconductor nanoparticles such as SiO2, TiO2, Fe2O3, Al2O3, ZrO2,
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ZnO, CdS, ZnS etc., have been used as photo catalysts. But the most widely used among them is
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TiO2 owing to its ability to break down organic pollutants and achieve complete degradation and
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mineralization. Although they are not activated by visible light but by UV light, still they are
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advantageous over others as they are chemically and biologically inert, photo chemically stable,
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relatively easy to produce, cheap and can be used without posing serious problems to the
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environment (Fujishima, Rao & Tryk, 2000).
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TiO2 was found to exist in different polymorphs viz., rutile, anatase, hollandite, brookite,
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fluorite, pyrite, ramsdellite, columbite, cotunnite, modified fluorite, bronze, baddeleyite and
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hexagonal Fe2P-type phases (Qi-Jun et al., 2015); the most common forms are anatase, brookite
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and rutile. Generally, anatase is more active than rutile despite its lower band gap of 3.0 eV
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compared to that of anatase TiO2 (3.2 eV). This might be because of the existence of the
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conduction band edge at a relatively less negative position, lower oxygen adsorbing capacity and
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higher recombination of the short-lived photocharges in the rutile phase compared to that of
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anatase phase. The photocatalytic activity of vanadium doped TiO2 and sulfated TiO2 in the rutile
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form for the degradation of methylene blue dye have been tried out (Mohamed & Mater M. Al-
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Esaimi, 2006). Recently Susann et al., (2013) have reported that the enhancement in the
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photocatalytic degradation rates of aqueous pollutants and gaseous pollutants respectively had
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been achieved by simple modification of nanocrystalline rutile- TiO2 photocatalysts with redox
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co-catalysts based on copper and iron oxides. The photocatalytic efficiency of Polyterthiophene
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derivatives/TiO2 (rutile) nanocomposites has been examined for the degradation of methylene
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blue under UV light and sunlight irradiation (Ruxangul, Yakupjan, Adalet, Ahmat, Zhang &
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Tursun, 2014).
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So far, several attempts have been made to improve the photocatalytic efficiency of TiO2
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in the visible region by suitable modification for the degradation of visible-light sensitive dye
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which is taken as the model pollutant. In such a case indirect photocatalysis predominates over
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direct photocatalysis. Moreover, such modified photocatalyst cannot be used for the degradation
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of dyes that are not sensitive to visible light (Susann et al., 2013). The major problem with TiO2
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which limits its commercial applications is that the ultrafine nanopowders agglomerate with each
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other forming clusters and causing adverse effects in the catalytic performance (Abdelaal &
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Mohamed, 2013) and poses problem with its recovery from the reaction medium and its reuse.
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This can be overcome by the immobilization of TiO2 onto support matrix, suitably biological
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materials which will form organic/inorganic hybrid and nanocomposites (Rushengyuan et al,
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2005). Biopolymer composites incorporating inorganic nanoparticles have been receiving
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considerable attention as it improves the performance properties of the individual materials
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(Zhou, Liu, Qi & Zhang, 2006). Immobilization of TiO2 nanoparticles onto the biopolymer
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matrix not only prevents agglomeration of the nanoparticles but also facilitates the process of
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recovery and reuse of TiO2 (Abdelaal et al, 2013). Several works have been reported on the use
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of biopolymers like chitosan (Yuvaraj & Jae-Jin, 2014; Hasmath Farzana M & Sankaran
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Meenakshi, 2014; Omkar, Avadhani & Singh, 2015), cellulose (Antoni et al, 2013),
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methylcellulose (Mohammed, Mojtaba, Nazr & Terry, 2007) etc., for the preparation of
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composite materials. Recently surface imprinted chitosan-TiO2 composite has been prepared and
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their utility for selective photocatalytic degradation of methyl orange has been studied (Xiao, Su
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& Tan, 2015).
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Inulins are polymers composed mainly of fructose units, and typically have a terminal
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glucose. The fructose units in inulins are joined by β (2→1) glycosidic bonds of various length,
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terminated generally by a single glucose unit (Robertfroid, 2007). In nature, it is the second most
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abundant storage carbohydrate after starch. Some inulin-containing plants commonly used in
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human nutrition are leek, onion, garlic, asparagus, Jerusalem artichoke, dahlia, chicory, yacon,
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etc. Allium sativum L. (Garlic) belonging to Liliaceae family contains 62-68% water, 26-30 %
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carbohydrate, 1.5-2.1 % protein, 1-1.5 % aminoacids, 1.1-3.5 % organosulphur compounds and
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1.5 % fiber (Puthanapura et al., 2011). Carbohydrates account for about 77 % of dry weight.
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Inulin being a versatile, biocompatible, biodegradable and water soluble carbohydrate polymer
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can thus serve as a matrix for the immobilization of TiO2, thereby improving its photocatalytic
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efficiency and reusability for the degradation of organic pollutants.
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The photocatalytic efficiency of TiO2 incorporated in an attractive matrix viz., cellulose
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nanofibers for the degradation of methylene blue have been studied (Alexandra, Zhenyu, Robert,
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Jean & Lia, 2013). The presence of a biopolymeric material along with inorganic nanoparticles
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will not only provide an alternative for water treatment but also prevent contamination
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(Alexandra et al, 2013). The present study has been aimed to improve the photocatalytic
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efficiency of rutile form of TiO2 by embedding them into a novel biopolymer- inulin which was
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extracted from Allium sativum L (Garlic).
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2. Materials and methods Rutile-TiO2 (Molecular weight 79.87, ultra-pure nanopowder-APS- 250 nm (99.5%
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assay), SRL Pvt. Ltd., Mumbai), commercially available Inulin (Loba Chemie Pvt. Ltd., Mmbai),
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methylene blue (Molecular formula: C16H18N3ClS and molecular weight: 319.85 g mol-1, NICE
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chemicals Pvt. Ltd., Kochi) used for the study were of analytical grade and were used as
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received. Ca(OH)2 (SRL Pvt. Ltd., Mumbai), HCl and Distilled ethanol (90%) were used. Garlic
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(Allium sativum L) bulbs were purchased from local market and used. For all solution
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preparations, millipore water obtained by a Milli-Q water purification system was used.
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2.1. Extraction of inulin from Allium sativum L.
The already reported protocol for the extraction of inulin from garlic (Puthanapura et al,
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2011; Azza et al., 2011) was followed with slight modification and the detailed procedure was
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described as follows. About 100 g of Allium sativum L (Garlic) bulbs were crushed and blended
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well. The crushed garlic was extracted with 150 ml of hot millipore water and filtered through
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muslin cloth. The pH of the filtrate was increased to 8 by adding 0.1 M calcium hydroxide
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(Gaafar, Serag, Boudy & Gazar, 2010; Anan´ina, Andreeva, Mycots & Oganesyan, 2009). The
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solution was allowed to stand for an hour. The residue formed at this stage was removed and to
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the resulting filtrate 0.8 M HCl was added drop wise to decrease the pH to 7. The filtrate was
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then concentrated. The yield of the concentrate was found to be 16 %. It was then refrigerated
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and lyophilized to get the dry powder. The lyophilized inulin (yield: 14.2 %) was then stored at
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4ºC for further use.
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2.2. Preparation of inulin- TiO2 Composite Inulin-TiO2 bio-nanocomposite was prepared by solvent casting method. 1g of inulin was
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dissolved in 20 ml of millipore water and the inulin solution was then magnetically stirred (10
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min) for complete dissolution. 0.5 g of TiO2 (33 wt % with an APS of 250 nm) was added to the
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inulin solution and magnetically stirred for 15 min. Subsequently the mixture was sonicated for
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15 min by ultra-waving in a water bath to improve the dispersion of TiO2 nanoparticles in the
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polymer matrix. Equal volume of ethanol was added to the homogenous mixture and the formed
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composite was separated by using Buchner funnel. It was dried and refrigerated for future use.
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The yield of the composite was found to be 96%.
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2.3. Characterization techniques The absorption spectra of Inulin, TiO2 and Inulin-TiO2 bio-nanocomposite were recorded
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using Thermo Scientific Helious Alpha UV-Visible spectrophotometer in the wavelength range
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of 200-800 nm. Fourier transform infrared spectra were obtained using IR Affinity- I Fourier
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transform Infrared spectrophotometer, Shimadzu in % transmittance mode covering the wave
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number between 400 and 4000 cm−1. Spectroscopy grade KBr was used as the window material.
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The prepared samples were mixed with dried KBr, and pelletized. The surface morphology of the
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isolated inulin and its composite were examined by Scanning Electron Microscopy (VEGA 3
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TESCAN) with tungsten heated cathode intended for both high vacuum and low vacuum
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operations and by using Transmission Electron Microscope (FEI Technai Spirit G2) with a high
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resolution for 20-120 kV operation. The crystal structure was studied using X-ray diffractometer
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(Phlips X‘Pert-PRO) operating in the reflection mode with Cu-Kα radiation (40 kV, 30 mA).
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Thermogravimetric analysis (Perkin Elmer Diamond TG/DTA) at a heating rate of 20ºC per min
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in nitrogen atmosphere was used to study the thermal stability of the powder samples Inulin and
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it’s composite. The elemental analysis had been carried out using elementar (Vario EL III).
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HPLC (1260 infinity LC system, Agilent technologies, India) equipped with the 1290 Infinity
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Diode Array Detector that provides the data rate required for high resolution separations. A
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pressure range of up to 600 bar with a flow rate up to 5 mL/min was used. Lyophilizer (Christ
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Alpha 1-2 LD plus, Fisher Bioblock Scientific, Germany) was used to freeze dry the sample to
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get the dry powder. Photo reacting system (Photoreactor Multilamp type HML-comapct-LP-88,
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Heber Scientific, India) which has a reaction chamber with built-in highly polished imported
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anodized aluminium equipped with 12 UV lamps (254 nm) was used to perform the
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photocatalytic degradation of MB dye. The reaction temperature was maintained at 298K.
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2.4. Photocatalytic activity
The study of the photocatalytic activity of Inulin-TiO2 bio-nanocomposite for the
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degradation of methylene blue (MB) was carried out under UV irradiation. The UV-visible
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absorbance spectrum of the reaction mixture containing MB dye solution and catalyst with
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respect to the irradiation time was recorded in order to determine the concentration of MB upon
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photocatalytic degradation after separating the catalyst. A decrease in the intensity of bands at
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660 nm was observed with respect to the radiation time.
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The MB dye solutions were first saturated with the bio-nanocomposite in order to avoid
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adsorption phenomenon interfering with the photocatalytic degradation process. The MB dye
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solutions of various concentrations (10 to 50 ppm) were prepared by suitable dilution from 1000
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ppm. 50 ml of MB dye solutions of varying concentrations (50 to 10 ppm) was mixed separately
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with 0.01 g of Inulin-TiO2 bio-nanocomposite. The dye solutions were then illuminated with UV
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lamp in a photoreactor of wavelength 254 nm with an output of 17.0 µW/cm2 and a lamp current
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of 0.170 A. The suspensions were removed at every 15 min intervals and centrifuged to remove
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the photocatalyst if any. The degradation efficiency was investigated by measuring the
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absorbance of the MB solutions at 660nm using UV- visible spectrophotometer. The percentage
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degradation of the dye was calculated using the equation (1).
3. Results and discussion
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3.1. Elemental analysis
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The elemental analysis of the isolated inulin revealed the percentage composition of C (40.53 %), H (7.06 %), N (0.000%) and S (0.000%).
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3.2. Morphological studies
Biopolymers are very sensitive to imaging techniques that are used to characterize them
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as they are soft and deformable materials. The morphology of inulin and bio-nanocomposite
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were observed using Scanning Electron Micrographs (SEM). The TiO2 nanoparticles were well
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embedded on the surface of inulin matrix using the proposed method of preparing the Inulin-
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TiO2 bio-nanocomposite. Spherical shape of TiO2 was found to be retained in the composite also
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and this observation was supported by TEM analysis.
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The surface morphology and the particle diameter were obtained using TEM. TEM
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images and the EDAX data of TiO2 and the prepared nanocomposite were shown in Fig. 1. The
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agglomeration of pristine TiO2 nanoparticles was prevented due to the formation of inulin shell
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on the surface of TiO2 in the composite (Ali, Sepideh & Akbar, 2012). In the composite the TiO2
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preserves its spherical shape and its diameter got reduced from 95.6 nm to 64.6 nm thus
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indicated an increase in the surface area. EDAX data revealed the presence of Ti in the
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composite.
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(d)
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(f)
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Fig. 1. SEM images of (a) inulin, (b) TiO2, (c) inulin-TiO2, TEM images of (d) TiO2 (e) Inulin-
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TiO2 and EDAX of (f) TiO2, (g) Inulin-TiO2
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3.3. Spectral Studies The UV-Visible spectra of inulin, TiO2 and inulin-TiO2 bio-nanocomposite were shown in
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Fig.2 (a). Inulin has shown a strong absorption at 249 and 290 nm. Inulin is made up of a chain of
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fructose molecules terminated at the end with glucose unit. Though both fructose and glucose
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units crystallize in the cyclic forms, in solution, there exists a very small equilibrium between the
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cyclic and acyclic forms. The existence of the acyclic form creates a carbonyl group (Thomas et
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al., 2010). This leads to the appearance of a peak at 290 nm owing to n→π* transition of the
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terminal C=O group that is formed due to the scission of the glycosidic bond. The peak at 249nm
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may be due to π-π* transition. There are several reasons for the bathochromic shift of π-π*
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transition. It may be due to the stabilization of π* more than the π in polar solvent, the presence of
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large number of auxochromes and may be due to hydrogen bonding interactions of the –OH
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groups with water molecules (Donald et al., 2007). The coexistence of cyclic and acyclic form of
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glucose and fructose was reflected in the IR spectrum also.
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TiO2 has shown strong absorption at 296 nm. When TiO2 nanoparticles were incorporated
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into the polymer matrix, a slight shift in the absorption band of TiO2 from 296 nm to 305 nm was
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observed which indicated the formation of inulin- TiO2 composite. The red shift in the
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wavelength upon composite formation was also an indication of decrease in the band gap (Ali et
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al., 2012).
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FT-IR spectroscopy offers valuable information on the shift in the stretching frequencies
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upon composite formation. The FT-IR spectra of inulin, TiO2 and inulin-TiO2 bio-nanocomposite
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were shown in Fig. 2(b). The FT-IR spectrum of inulin shows peaks at 3426 cm-1 corresponding
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to the –OH stretching vibration. A broad band with maximum intensity at 1022 cm-1 with two
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shoulders at 1130 and 940 cm−1 corresponding to the stretching vibrations of C-O-C groups and
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ring vibrational modes in the composition of cyclic structures was observed. Broad band with low
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intensity arises at 1649 cm−1 which can’t be used as specific for inulin in biological mixture, as
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usually this region is characteristic for amides (Grube, Bekers, Upite, & Kaminska, 2002). The
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appearance of this peak may be due to the coexistence of the open-chain form of a
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monosaccharide with a closed ring form where the aldehyde or ketone carbonyl group carbon
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(C=O) and hydroxyl group (-OH) react together to form a hemiacetal with a new C-O-C bridge
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(Finar, 2009). The peaks observed at 2924 cm-1 and 2360 cm-1 may be attributed to -CH stretching
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and bending vibrations. In addition, the peaks observed in the region 1200-800 cm-1 in the
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spectrum of inulin corresponded to carbohydrate region. In the IR spectrum of TiO2 the peaks at
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3447 cm-1 is due to –OH stretching which indicated the presence of physically absorbed water
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molecule. The peak at 640 cm-1 and 534 cm-1 was ascribed to Ti-O stretching mode (Xiaofeng Lu
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et al., 2006; Anastasios et al, 2011). Slight shift in the position of Ti-O stretching peaks was
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observed for inulin-TiO2 bio-nanocomposite indicating the interaction of TiO2 with inulin. Peak at
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3426 cm-1 for inulin was shifted to 3412 cm-1 in the presence of TiO2 nanoparticles and this
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clearly indicated the interaction of Ti with –OH group of inulin. The peak observed for both TiO2
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and inulin-TiO2 bio-nanocomposite at 440 cm-1 (Ti-O bending mode) could be attributed to the
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existence of TiO2 in the rutile phase (Lan Wang et al, 2014). These observations confirm the
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incorporation of TiO2 nanoparticle into the biopolymer matrix.
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3.4. X-Ray Diffraction studies
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XRD patterns of inulin, TiO2 and inulin-TiO2 were shown in Fig. 2(c). The diffractogram
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of inulin had shown a single weak wide peak around 15.72° 2θ indicating that extracted inulin
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was amorphous. Strong diffraction peaks at 27°, 36°, 54° and 56° corresponding to (110), (101),
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(211) and (220) planes respectively, were observed in the diffractogram of TiO2 which indicated
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that it exists in the rutile phase [JCPDS no: 88-1175] (Lan Wang et al, 2014; Kheamrutai, Pichet
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& Boonlaer, 2008). All these diffraction peaks were also observed in Inulin-TiO2 bio-
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nanocomposite but the intensity of diffraction peaks were found to be lower compared to that of
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TiO2. This suggested that in the composite, TiO2 was still present in the rutile phase without any
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phase transformation and the amorphous inulin reduced the mass-volume percentage of TiO2 and
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sequentially weakened the diffraction peaks of TiO2. This observation confirmed that TiO2 was
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embedded onto the inulin matrix.
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The crystallite size was calculated using Sherrer’s equation (Kaifu et al, 2009), D=
0.9 β cos θ
(2 )
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Where D is the crystallite size, λ is the wavelength of the radiation, θ is the Bragg’s angle and β
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is the full width at half maximum. From the diffraction pattern, the average crystallite size for
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TiO2 and Inulin-TiO2 bio-nanocomposite was found to be 90.5 nm and 61.2 nm respectively. The
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reduction in the size of TiO2 suggested that the surface area of TiO2 increased upon composite
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formation.
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(a)
(b)
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Fig. 2. (a) UV-Visible absorption spectra, (b) IR Spectra and (c) X- Ray Diffractograms of
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Inulin, TiO2 and Inulin-TiO2
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Morphology index (M.I.) can be calculated using the equation, M .I . =
FWHM h FWHM h + FWHM p
(3)
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Where FWHM refers to full width at half maximum value and the subscripts h refers to the
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highest peak and p refers to a particular peak for which M.I to be obtained. The range of
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morphology index for TiO2 (0.5-0.73) and Inulin-TiO2 (0.5 to 0.55) indicated that the particle
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size distribution of TiO2 in the composite was uniform compared to that of pristine TiO2.
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(Theivasanthi & Alagar, 2011).
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3.5. Thermal Studies Thermogravimetric analysis was used to determine the thermal stability of the extracted
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biopolymer and it’s composite. The TG curves for the Inulin, TiO2 and Inulin-TiO2bio-
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nanocomposite were presented in Fig. 3. It was noticed that the thermal stability of the inulin was
285
lower compared to that of its composite.
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(a) (b) (c) Fig. 3. TGA – DTA curves of (a) Inulin, (b) TiO2 and (c) Inulin-TiO2 In the TG curve of inulin, four distinct weight loss regions were observed. The first
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weight loss of about 10 % corresponding to the loss of moisture absorbed from the surroundings
291
by inulin was observed between the temperature range 20 ºC and 100 ºC. The second weight loss
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around 26 % observed in the temperature range 100-160 oC may be due to the decomposition of
293
inulin. The third weight loss around 160-380 oC represents the combustion of inulin and the
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fourth weight loss around 34 % between 380 oC and 620 oC may be due to the loss of molecular
295
fragment of the inulin and degradation of the rest of the polymeric fragments into carbon (Norio
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& Hayashi, 2007).
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In the TGA curve of TiO2, there were three distinct regions observed, one and two
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corresponding to weight loss and the third corresponding to weight gain. The first one starts at
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room temperature until upto105 ºC, with a weight loss of about 0.9 %, whereas the second one
300
was observed in the range of 200-540 ºC, with a weight loss of about 1.7 %.The weight loss in
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the first stage may be attributed to the removal of absorbed water. The second weight loss may
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be due to the decomposition of TiO2. Above 540 ºC the increase in weight can be attributed to
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the oxygen gain from air. A possible rearrangement of the TiO2 structure leading to the phase
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transformation from rutile to anatase would have occurred above 540 ºC.
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The thermogram of inulin-TiO2 bio-nanocomposite had shown three distinct weight loss
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regions. The weight loss of about 8 % observed in the temperature range 40- 120 ºC may be due
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to the removal of associated water molecules. The second weight loss of about 28 % observed
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around 180-300 ºC may be due to the degradation of the polymer chain whereas the third
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continuous weight loss of about 48 % in the temperature range 300-520ºC may be due to the
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degradation of TiO2 incorporated in the inulin matrix. The comparison of the thermograms of
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inulin with TiO2 and inulin-TiO2 bio-nanocomposite indicated that the composite was thermally
312
more stable than inulin and TiO2. No significant weight loss was observed for inulin-TiO2 bio-
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nanocomposite when heated beyond 520 ºC which indicated the improvement in the thermal
314
stability of inulin upon incorporation of TiO2 nanoparticles.
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Analysis of DTA curves revealed the physical and chemical changes that occur in
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compounds. In the DTA curve of inulin, the glass transition temperature was observed at 150 oC.
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The exothermic peak appeared at 220 oC indicated the point of crystallization of the amorphous
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inulin. An endothermic peak observed at 440 oC corresponded to the melting temperature. The
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temperature corresponding to the melting of the composite got increased to 480 oC which might
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be due to the incorporation of TiO2. The appearance of intense exothermic peak at 550 oC may
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be due to the oxidation of inulin and the intensity of this peak got suppressed in case of inulin-
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TiO2 bio-nanocomposite which may be due to the suppression of oxidation of inulin by TiO2.
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The decomposition of the biopolymer inulin occurred at 660 oC.
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3.6. Photocatalytic degradation of MB
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The adsorption of MB by inulin, TiO2 and inulin-TiO2 bio-nanocomposite was studied
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and it was observed that the efficiency of dye adsorption was found to be in the order inulin-TiO2
328
> inulin > TiO2. This might be due to the increase in the availability of the number of surface
329
active sites for the adsorption of MB upon composite formation. Control experiments have also
330
been conducted by irradiating the MB dye solution without the addition of TiO2 or inulin-TiO2
331
bio-nanocomposite and it was observed that no degradation of dye occurred in the absence of the
332
photocatalyst. The adsorption and the photo degradation ability of TiO2 and inulin-TiO2 bio-
333
nanocomposite before and after UV irradiation, respectively, were compared. The results
334
indicated that the photo degradation ability of the composite was found to be greater than that of
335
TiO2.
336
The photocatalytic degradation ability of inulin-TiO2 against varying concentrations of
337
MB solution and at various time intervals was studied. The intensity of the colour of MB
Page 12 of 24
13
solutions got reduced when all or part of the auxochromic groups degraded. This is reflected by
339
the considerable shift in the spectral band from 660 nm to 650 nm during the course of the photo
340
assisted degradation (Fig.4). Such a shift was not observed without illumination of UV –light.
341
This indicated that in the presence of UV irradiation, photocatalytic degradation predominated
342
over simple adsorption process (Xiao et al., 2015). Moreover, adsorption process was favoured
343
in the absence of UV irradiation.
M
an
us
cr
ip t
338
344
(a)
(b)
346 347
Ac ce p
te
d
345
(c)
348
Fig. 4. UV-Visible absorption spectra (a) for the degradation of MB (30 ppm) using TiO2 and
349
inulin-TiO2 with and without illumination of UV light (b) for the degradation of MB (30 ppm)
350
using inulin-TiO2 at various time intervals (Inset: Calibration Curve) and (c) variation of the
351
concentration of MB upon photocatalytic degradation using inulin-TiO2 with time (Inset: %
352
degradation of MB at various time intervals)
Page 13 of 24
14
As the initial concentration of the dye increased from 10 to 50 ppm, the degradation
354
efficiency of the photocatalyst decreased. This may be due to the increase in the surface coverage
355
of the MB dye or its degradation products over a period of time. Also the high concentration of
356
dye molecules on the surface of the photocatalyst caused shielding of UV light radiation. As a
357
result, the concentration of OH· radical on the surface of photocatalyst decreased which led to
358
decrease in the degradation efficiency of the photocatalyst (Xiaorong et al, 2014). This was
359
reflected in the decrease in the apparent rate constant of photocatalytic dye degradation as the
360
initial concentration of the dye increases. The % degradation increased from 95% to 99 % when
361
it was exposed from 90 min to 120 min for 10 ppm concentration of MB dye. The same trend of
362
increased % degradation was observed for other concentrations of MB dye used.
us
cr
ip t
353
363
366 367
Photocatalytic degradation of MB dye was found to follow pseudo first order kinetics
an
365
3.8. Kinetics of Photocatalytic degradation
(Rahul, Usha, Gautam & Sumit, 2014) and the expression was given as ln
C0 = kapp t C
M
364
(4)
Where kapp – apparent rate constant; C0 – initial concentration of MB dyes (mg/L);
369
C−concentration of MB dye (mg/L) at various time intervals. The kapp values can be evaluated
370
from the slope of the straight line plot between ln
C0 C
and t which was shown in Fig. 5(a).
Ac ce p
te
d
368
371 372 373 374
(a) Fig. 5. Plot between (a) ln
(b)
C0 C
and time and (b) 1/ kapp and C0
Half-life (t1/2) of MB dye degradation was given by the expression
Page 14 of 24
15
t1 =
375
2
0.6931 kapp
(5)
It was assumed that photocatalytic degradation of MB dye mainly takes place on the
377
surface of the photocatalyst, the Langmuir- Hinshelwood equation for the reaction rate could be
378
written as (Jiamei, Can, Hong & Jianhao, 2013).
379
r=
− dC = k ×θ B × θ HO˙ dt
(6)
ip t
376
Where k − the surface reaction rate constant; θB − fractional surface site coverage by MB ;
381
θHO˙ − fractional surface site coverage by HO˙ which is assumed to degrade MB.
383
(Jiamei, et al., 2013).
384
Hence the equation can be rearranged as
an
r = k1θ B
385
(7)
where k1 – new rate constant which is equal to kθHO˙ nads K B C0 = n0 1 + K B C0
387
θB =
388
1 1 = + nads n0
1 n0 K B
1 C0
(8) (9)
d
386
us
The amount of HO˙ radicals is considered as constant during the degradation process
M
382
cr
380
where KB is the adsorption equilibrium constant of MB and C0 is the initial concentration of MB,
390
nads is the number of dye molecules adsorbed and no refers to the initial number of dye
391
molecules.
392
Substituting the expression for θB from equation (8) into the expression for rate in equation (7),
394
395
Ac ce p
393
te
389
r=
1 1 + K B C0 1 = = r k1 K B C kapp C
1
kapp 396
k1 K B C =k C (1+ K BC0 ) app
1 kapp
(10) (11)
=
1 + K B C0 k1 K B
(12)
=
C 1 + 0 k1 K B k1
(13)
397
A plot between 1/kapp and C0 (Fig. 5(b)) for the same amount of inulin-TiO2 content
398
indicated that as the concentration of dye increases 1/kapp also increases. The k1 and KB values as
Page 15 of 24
16 399
determined from the slope and the intercept were found to be 3.1738 ppm min-1 and 0.0165 min
400
ppm-1, respectively. The values of θB for various concentrations of MB dye can then be evaluated
401
by using equation (8) and presented in Table 1.
402
Table 1. Langmuir- Hinshelwood kinetic parameters for the degradation of dye kapp
(ppm)
(min-1)
10
0.0449
0.9969
15.43
0.14
20
0.0393
0.9947
17.64
30
0.0350
0.9983
19.80
cr
r2
C0
40
0.0317
0.9944
50
0.0286
0.9897
us
t1/2 (min)
0.25 0.33
21.86
0.40
24.23
0.45
an
404
θB
ip t
403
The kapp value obtained when TiO2 was used for the photocatalytic degradation of MB
406
dye was found to be less compared to that obtained when inulin-TiO2 was used. The kapp values
407
for the photo degradation of 10 ppm MB dye solution using TiO2 and inulin-TiO2 were found to
408
be 0.0325 min-1 and 0.0449 min-1, respectively. The t1/2 value obtained for inulin-TiO2 (15.43
409
min) was found to be lesser than that for TiO2 (21.32 min). The prevention of agglomeration of
410
TiO2 in the composite due to the presence of inulin provides larger surface area causing
411
improved photocatalytic activity (Ali, Sepideh & Ali Akbar, 2012). The decrease in the
412
degradation efficiency of the photocatalyst with increase in the concentration of the dye was
413
reflected in the kapp and θB values. The kapp values (Table 1.) were found to decrease with increase
414
in the concentration of dye due to increase in the surface coverage (θB) of the MB dye which
415
may also block the penetration of UV light, thereby decreasing the amount of photo generated
416
electrons.
418 419
d
te
Ac ce p
417
M
405
3.9. Mechanism of photocatalytic degradation of MB using Inulin-TiO2 composite The mechanism of generation of reactive oxygen species that is responsible for the
420
degradation of MB dye upon illumination of UV radiation on inulin-TiO2 bio-nanocomposite
421
(Vinod, Shilpi, Deepak, Kothiyal, Gavrav, 2013).
422 423
hν Inu-TiO2 → Inu-TiO2 (e− CB + h+ VB)
(i)
424
Inu-TiO2 (e− CB) + O2→ Inu-TiO2 + O2−˙
(ii)
425
Inu-TiO2 (h+ VB) + H2O → Inu-TiO2 + H+ + ˙OH
(iii)
Page 16 of 24
17
O2−˙+ H2O → HO2˙ + OH−
(iv)
427
MB + h+ → [O] products
(v)
428
MB + ˙OH → Mineral end products
(vi)
429
MB + e− CB → [H] products
(vii)
an
us
cr
ip t
426
430
Fig. 6. Schematic representation for the mechanism of photocatalytic degradation of MB using
432
inulin-TiO2 bio-nanocomposite
M
431
Upon UV irradiation on the surface of the bio-nanocomposite, electron (e−) and hole (h+)
434
pairs was generated (Fig. 6.). The photo induced electrons that were transferred to the surface of
435
inulin were responsible for the reduction of dissolved oxygen to produce highly reactive
436
superoxide anion radical (O2−˙) which formed other oxidative radicals (˙OH2) in presence of
437
water. The photo generated holes will then be reacted with water to form hydroxyl radicals
438
(˙OH).The holes and ˙OH both were extremely reactive as they were chemically unstable when
439
in contact with organic compounds. Hence they oxidized the MB dye molecules to form
440
oxidation products. The oxidation of MB dye to the mineral end products was mainly due to the
441
combined effect of ˙OH and O2˙radicals.
te
Ac ce p
442
d
433
The problem with the recombination of electron-hole pairs formed after excitation of
443
TiO2photocatalystwas found to be overcome by the presence of inulin. Inulin which is enriched
444
with–OH functionalities helped in the stabilization of the photo excited electron which has got
445
transferred from the conduction band to the surface of inulin. This prevented its recombination
446
with the holes present in the valence band of TiO2 thereby increasing the lifetime of photo
447
excited electrons. Hence the expected enhancement in the photocatalytic degradation efficiency
448
of inulin-TiO2 bio-nanocomposite was achieved.
449 450
3.10. Comparative data of degradation efficiency of various photocatalysts
Page 17 of 24
18 451 452
The literature data shown in Table 2 suggested that the proposed nanocomposite was found to be efficient in the photocatalytic degradation of methylene blue.
453 454
TiO2/cotton fibers
95.35
120
Amount of catalyst (g) 2.5
TiO2-Cellulose nanofiber
60
60
0.01
polyaniline / Bi2SnTiO7
100
220
Chitosan-TiO2
90
TiO2-Fe3O4bentonite
90
456 457 458
92
Volume and Concentration of MB dye 50 ml of 50 ppm
an
25ml
0.3
300 mL of 0.025 mM
-
5 ppm
90
0.03
100ml of 30 ppm
120
0.01
50 ml of 50 ppm
d
Ac ce p
Inulin-TiO2 bio-nanocomposite
-
ip t
Time (min)
Reference
cr
Degradation (%)
us
Photocatalyst
M
Table 2. Degradation of methylene blue dye using various photocatalyst
te
455
Shi Zhong Liang et al., 2010 Alexandra et al., 2013
Yunjun Yang & Jingfei Luan, 2012 Yuvaraj, Haldorai & Jae-Jin Shim, 2014 Wei, Hongyao, Hang, Tonggang & Yanmei, 2015 Present work
4. Conclusion
Inulin was extracted from Allium sativum L and the TiO2 nanoparticles were then
459
successfully incorporated onto the inulin-matrix. The prepared composite was tested for its
460
photocatalytic activity against the degradation of MB and it was proved to exhibit very good
461
activity compared to that of pristine TiO2. The enhancement in the photocatalytic activity as
462
reflected in the apparent rate constant (0.0325 min-1 for TiO2; 0.0449 min-1 for inulin-TiO2 (ratio
463
2:1)) may be due to synergistic reinforcement of the properties of both inulin and TiO2.The
464
prevention of agglomeration of TiO2 in the composite due to the presence of inulin provides
465
larger surface area causing improved photocatalytic activity. Moreover, the stabilization of photo
466
generated electrons, the prevention of the recombination of electron- hole pairs and the recovery
467
of the catalyst could be achieved using the novel bio-nanocomposite used. The newly
Page 18 of 24
19 468
synthesized bio-nanocomposite will therefore act as an effective photocatalyst and will be
469
utilized for the degradation of many more organic pollutants viz., crystal violet, methyl red,
470
methyl orange etc., in future.
471 472
5. Acknowledgement The authors duly acknowledge all the personnel who helped us in collecting the various
474
data presented. The authors greatly acknowledge the Management and the Department for
475
providing the necessary facilities to carry out the present work. Dr. A. Arlin Jose Amali, DST-
476
INSPIRE Faculty, Madurai Kamaraj University, is acknowledged for her kind support.
cr
ip t
473
us
477
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HIGHLIGHTS
605 606
Eco-toxicity minimization using TiO2 embedded carbohydrate nanocomposite
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Page 24 of 24
S0144-8617(16)30018-2 http://dx.doi.org/doi:10.1016/j.carbpol.2016.01.054 CARP 10733
To appear in: Received date: Revised date: Accepted date:
16-8-2015 9-1-2016 25-1-2016
Please cite this article as: JayanthiKalaivani, G.,TiO2 (Rutile) embedded InulinndashA versatile Bio-nanocomposite for photocatalytic degradation of methylene blue, Carbohydrate Polymers (2016), http://dx.doi.org/10.1016/j.carbpol.2016.01.054 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
TiO2 (Rutile) embedded Inulin – A versatile Bio-nanocomposite for photocatalytic
2
degradation of methylene blue
3
G. JayanthiKalaivani1, S. K. Suja2
4
Department of Chemistry, Lady Doak College, Madurai-625002, Tamilnadu, India
5
E-mail id:1 [email protected] 2
6
[email protected] ABSTRACT
7
cr
8
ip t
1
Inulin, a water soluble carbohydrate polymer, was extracted from Allium sativum L by
10
hot water diffusion method. A novel bio-nanocomposite was prepared by embedding TiO2
11
(Rutile) onto the inulin matrix. The extracted inulin and the prepared bio-nanocomposite were
12
characterized using UV-Visible, FT-IR, XRD, SEM, TEM and TGA techniques. The
13
photocatalytic activity of the bio-nanocomposite for the degradation of methylene blue was
14
studied under UV illumination in batch mode experiment and was found to be twice as high as
15
that of pristine TiO2. The kapp for inulin-TiO2 (0.0449 min-1) was higher than that for TiO2
16
(0.0325min-1) which may be due to the synergistic action of inulin and TiO2. The stabilization of
17
photo excited electron suppressed the electron-hole pair recombination thereby inducing the
18
electrons and the holes to participate in the photo reduction and oxidation processes, respectively
19
and enhancing the photocatalytic activity.
20
______________________________________________________________________________
21
Key words: Inulin; TiO2; Rutile; bio-nanocomposite; photocatalytic activity; methylene blue.
an
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9
23
Chemical compounds studied in this article
24
Inulin (PubChem CID: 16219508); TiO2 –Rutile (PubChem CID:26042); Methylene blue
25
(PubChem CID:6099)
26 27
1. Introduction
28
Over a past few years, there has been a growing concern for the degradation of organic
29
dye molecules from industrial effluents. Several techniques viz., adsorption, photocatalysis,
30
ozonization, bioremediation etc., have been employed for waste-water treatment and recycling.
31
Among them heterogeneous photocatalysis proved to be the most common and the cheapest
32
process which is based on the absorption of photons of energy greater than the band gap energy
Page 1 of 24
2 33
and is found to be the most effective as it leads to complete mineralization of the organic dye
34
pollutants (Rushengyuan, Rongbo, Wenzhong & Jingtang, 2005; Susann et al, 2013; Boroski et
35
al, 2009). Several inorganic semiconductor nanoparticles such as SiO2, TiO2, Fe2O3, Al2O3, ZrO2,
37
ZnO, CdS, ZnS etc., have been used as photo catalysts. But the most widely used among them is
38
TiO2 owing to its ability to break down organic pollutants and achieve complete degradation and
39
mineralization. Although they are not activated by visible light but by UV light, still they are
40
advantageous over others as they are chemically and biologically inert, photo chemically stable,
41
relatively easy to produce, cheap and can be used without posing serious problems to the
42
environment (Fujishima, Rao & Tryk, 2000).
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TiO2 was found to exist in different polymorphs viz., rutile, anatase, hollandite, brookite,
44
fluorite, pyrite, ramsdellite, columbite, cotunnite, modified fluorite, bronze, baddeleyite and
45
hexagonal Fe2P-type phases (Qi-Jun et al., 2015); the most common forms are anatase, brookite
46
and rutile. Generally, anatase is more active than rutile despite its lower band gap of 3.0 eV
47
compared to that of anatase TiO2 (3.2 eV). This might be because of the existence of the
48
conduction band edge at a relatively less negative position, lower oxygen adsorbing capacity and
49
higher recombination of the short-lived photocharges in the rutile phase compared to that of
50
anatase phase. The photocatalytic activity of vanadium doped TiO2 and sulfated TiO2 in the rutile
51
form for the degradation of methylene blue dye have been tried out (Mohamed & Mater M. Al-
52
Esaimi, 2006). Recently Susann et al., (2013) have reported that the enhancement in the
53
photocatalytic degradation rates of aqueous pollutants and gaseous pollutants respectively had
54
been achieved by simple modification of nanocrystalline rutile- TiO2 photocatalysts with redox
55
co-catalysts based on copper and iron oxides. The photocatalytic efficiency of Polyterthiophene
56
derivatives/TiO2 (rutile) nanocomposites has been examined for the degradation of methylene
57
blue under UV light and sunlight irradiation (Ruxangul, Yakupjan, Adalet, Ahmat, Zhang &
58
Tursun, 2014).
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an
43
So far, several attempts have been made to improve the photocatalytic efficiency of TiO2
60
in the visible region by suitable modification for the degradation of visible-light sensitive dye
61
which is taken as the model pollutant. In such a case indirect photocatalysis predominates over
62
direct photocatalysis. Moreover, such modified photocatalyst cannot be used for the degradation
63
of dyes that are not sensitive to visible light (Susann et al., 2013). The major problem with TiO2
64
which limits its commercial applications is that the ultrafine nanopowders agglomerate with each
65
other forming clusters and causing adverse effects in the catalytic performance (Abdelaal &
Page 2 of 24
3 66
Mohamed, 2013) and poses problem with its recovery from the reaction medium and its reuse.
67
This can be overcome by the immobilization of TiO2 onto support matrix, suitably biological
68
materials which will form organic/inorganic hybrid and nanocomposites (Rushengyuan et al,
69
2005). Biopolymer composites incorporating inorganic nanoparticles have been receiving
71
considerable attention as it improves the performance properties of the individual materials
72
(Zhou, Liu, Qi & Zhang, 2006). Immobilization of TiO2 nanoparticles onto the biopolymer
73
matrix not only prevents agglomeration of the nanoparticles but also facilitates the process of
74
recovery and reuse of TiO2 (Abdelaal et al, 2013). Several works have been reported on the use
75
of biopolymers like chitosan (Yuvaraj & Jae-Jin, 2014; Hasmath Farzana M & Sankaran
76
Meenakshi, 2014; Omkar, Avadhani & Singh, 2015), cellulose (Antoni et al, 2013),
77
methylcellulose (Mohammed, Mojtaba, Nazr & Terry, 2007) etc., for the preparation of
78
composite materials. Recently surface imprinted chitosan-TiO2 composite has been prepared and
79
their utility for selective photocatalytic degradation of methyl orange has been studied (Xiao, Su
80
& Tan, 2015).
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Inulins are polymers composed mainly of fructose units, and typically have a terminal
82
glucose. The fructose units in inulins are joined by β (2→1) glycosidic bonds of various length,
83
terminated generally by a single glucose unit (Robertfroid, 2007). In nature, it is the second most
84
abundant storage carbohydrate after starch. Some inulin-containing plants commonly used in
85
human nutrition are leek, onion, garlic, asparagus, Jerusalem artichoke, dahlia, chicory, yacon,
86
etc. Allium sativum L. (Garlic) belonging to Liliaceae family contains 62-68% water, 26-30 %
87
carbohydrate, 1.5-2.1 % protein, 1-1.5 % aminoacids, 1.1-3.5 % organosulphur compounds and
88
1.5 % fiber (Puthanapura et al., 2011). Carbohydrates account for about 77 % of dry weight.
89
Inulin being a versatile, biocompatible, biodegradable and water soluble carbohydrate polymer
90
can thus serve as a matrix for the immobilization of TiO2, thereby improving its photocatalytic
91
efficiency and reusability for the degradation of organic pollutants.
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d
81
The photocatalytic efficiency of TiO2 incorporated in an attractive matrix viz., cellulose
93
nanofibers for the degradation of methylene blue have been studied (Alexandra, Zhenyu, Robert,
94
Jean & Lia, 2013). The presence of a biopolymeric material along with inorganic nanoparticles
95
will not only provide an alternative for water treatment but also prevent contamination
96
(Alexandra et al, 2013). The present study has been aimed to improve the photocatalytic
97
efficiency of rutile form of TiO2 by embedding them into a novel biopolymer- inulin which was
98
extracted from Allium sativum L (Garlic).
Page 3 of 24
4 99 100
2. Materials and methods Rutile-TiO2 (Molecular weight 79.87, ultra-pure nanopowder-APS- 250 nm (99.5%
102
assay), SRL Pvt. Ltd., Mumbai), commercially available Inulin (Loba Chemie Pvt. Ltd., Mmbai),
103
methylene blue (Molecular formula: C16H18N3ClS and molecular weight: 319.85 g mol-1, NICE
104
chemicals Pvt. Ltd., Kochi) used for the study were of analytical grade and were used as
105
received. Ca(OH)2 (SRL Pvt. Ltd., Mumbai), HCl and Distilled ethanol (90%) were used. Garlic
106
(Allium sativum L) bulbs were purchased from local market and used. For all solution
107
preparations, millipore water obtained by a Milli-Q water purification system was used.
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109
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2.1. Extraction of inulin from Allium sativum L.
The already reported protocol for the extraction of inulin from garlic (Puthanapura et al,
111
2011; Azza et al., 2011) was followed with slight modification and the detailed procedure was
112
described as follows. About 100 g of Allium sativum L (Garlic) bulbs were crushed and blended
113
well. The crushed garlic was extracted with 150 ml of hot millipore water and filtered through
114
muslin cloth. The pH of the filtrate was increased to 8 by adding 0.1 M calcium hydroxide
115
(Gaafar, Serag, Boudy & Gazar, 2010; Anan´ina, Andreeva, Mycots & Oganesyan, 2009). The
116
solution was allowed to stand for an hour. The residue formed at this stage was removed and to
117
the resulting filtrate 0.8 M HCl was added drop wise to decrease the pH to 7. The filtrate was
118
then concentrated. The yield of the concentrate was found to be 16 %. It was then refrigerated
119
and lyophilized to get the dry powder. The lyophilized inulin (yield: 14.2 %) was then stored at
120
4ºC for further use.
122 123
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an
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2.2. Preparation of inulin- TiO2 Composite Inulin-TiO2 bio-nanocomposite was prepared by solvent casting method. 1g of inulin was
124
dissolved in 20 ml of millipore water and the inulin solution was then magnetically stirred (10
125
min) for complete dissolution. 0.5 g of TiO2 (33 wt % with an APS of 250 nm) was added to the
126
inulin solution and magnetically stirred for 15 min. Subsequently the mixture was sonicated for
127
15 min by ultra-waving in a water bath to improve the dispersion of TiO2 nanoparticles in the
128
polymer matrix. Equal volume of ethanol was added to the homogenous mixture and the formed
129
composite was separated by using Buchner funnel. It was dried and refrigerated for future use.
130
The yield of the composite was found to be 96%.
131
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5 132
2.3. Characterization techniques The absorption spectra of Inulin, TiO2 and Inulin-TiO2 bio-nanocomposite were recorded
134
using Thermo Scientific Helious Alpha UV-Visible spectrophotometer in the wavelength range
135
of 200-800 nm. Fourier transform infrared spectra were obtained using IR Affinity- I Fourier
136
transform Infrared spectrophotometer, Shimadzu in % transmittance mode covering the wave
137
number between 400 and 4000 cm−1. Spectroscopy grade KBr was used as the window material.
138
The prepared samples were mixed with dried KBr, and pelletized. The surface morphology of the
139
isolated inulin and its composite were examined by Scanning Electron Microscopy (VEGA 3
140
TESCAN) with tungsten heated cathode intended for both high vacuum and low vacuum
141
operations and by using Transmission Electron Microscope (FEI Technai Spirit G2) with a high
142
resolution for 20-120 kV operation. The crystal structure was studied using X-ray diffractometer
143
(Phlips X‘Pert-PRO) operating in the reflection mode with Cu-Kα radiation (40 kV, 30 mA).
144
Thermogravimetric analysis (Perkin Elmer Diamond TG/DTA) at a heating rate of 20ºC per min
145
in nitrogen atmosphere was used to study the thermal stability of the powder samples Inulin and
146
it’s composite. The elemental analysis had been carried out using elementar (Vario EL III).
147
HPLC (1260 infinity LC system, Agilent technologies, India) equipped with the 1290 Infinity
148
Diode Array Detector that provides the data rate required for high resolution separations. A
149
pressure range of up to 600 bar with a flow rate up to 5 mL/min was used. Lyophilizer (Christ
150
Alpha 1-2 LD plus, Fisher Bioblock Scientific, Germany) was used to freeze dry the sample to
151
get the dry powder. Photo reacting system (Photoreactor Multilamp type HML-comapct-LP-88,
152
Heber Scientific, India) which has a reaction chamber with built-in highly polished imported
153
anodized aluminium equipped with 12 UV lamps (254 nm) was used to perform the
154
photocatalytic degradation of MB dye. The reaction temperature was maintained at 298K.
156 157
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2.4. Photocatalytic activity
The study of the photocatalytic activity of Inulin-TiO2 bio-nanocomposite for the
158
degradation of methylene blue (MB) was carried out under UV irradiation. The UV-visible
159
absorbance spectrum of the reaction mixture containing MB dye solution and catalyst with
160
respect to the irradiation time was recorded in order to determine the concentration of MB upon
161
photocatalytic degradation after separating the catalyst. A decrease in the intensity of bands at
162
660 nm was observed with respect to the radiation time.
163
The MB dye solutions were first saturated with the bio-nanocomposite in order to avoid
164
adsorption phenomenon interfering with the photocatalytic degradation process. The MB dye
Page 5 of 24
6
solutions of various concentrations (10 to 50 ppm) were prepared by suitable dilution from 1000
166
ppm. 50 ml of MB dye solutions of varying concentrations (50 to 10 ppm) was mixed separately
167
with 0.01 g of Inulin-TiO2 bio-nanocomposite. The dye solutions were then illuminated with UV
168
lamp in a photoreactor of wavelength 254 nm with an output of 17.0 µW/cm2 and a lamp current
169
of 0.170 A. The suspensions were removed at every 15 min intervals and centrifuged to remove
170
the photocatalyst if any. The degradation efficiency was investigated by measuring the
171
absorbance of the MB solutions at 660nm using UV- visible spectrophotometer. The percentage
172
degradation of the dye was calculated using the equation (1).
3. Results and discussion
176
3.1. Elemental analysis
178
The elemental analysis of the isolated inulin revealed the percentage composition of C (40.53 %), H (7.06 %), N (0.000%) and S (0.000%).
M
177
179 180
(1)
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174 175
cr
C0 − Ct ×100 C0
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3.2. Morphological studies
Biopolymers are very sensitive to imaging techniques that are used to characterize them
182
as they are soft and deformable materials. The morphology of inulin and bio-nanocomposite
183
were observed using Scanning Electron Micrographs (SEM). The TiO2 nanoparticles were well
184
embedded on the surface of inulin matrix using the proposed method of preparing the Inulin-
185
TiO2 bio-nanocomposite. Spherical shape of TiO2 was found to be retained in the composite also
186
and this observation was supported by TEM analysis.
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The surface morphology and the particle diameter were obtained using TEM. TEM
188
images and the EDAX data of TiO2 and the prepared nanocomposite were shown in Fig. 1. The
189
agglomeration of pristine TiO2 nanoparticles was prevented due to the formation of inulin shell
190
on the surface of TiO2 in the composite (Ali, Sepideh & Akbar, 2012). In the composite the TiO2
191
preserves its spherical shape and its diameter got reduced from 95.6 nm to 64.6 nm thus
192
indicated an increase in the surface area. EDAX data revealed the presence of Ti in the
193
composite.
194
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(d)
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(e)
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200 201
(f)
(g)
202
Fig. 1. SEM images of (a) inulin, (b) TiO2, (c) inulin-TiO2, TEM images of (d) TiO2 (e) Inulin-
203
TiO2 and EDAX of (f) TiO2, (g) Inulin-TiO2
204 205
Page 7 of 24
8 206
3.3. Spectral Studies The UV-Visible spectra of inulin, TiO2 and inulin-TiO2 bio-nanocomposite were shown in
208
Fig.2 (a). Inulin has shown a strong absorption at 249 and 290 nm. Inulin is made up of a chain of
209
fructose molecules terminated at the end with glucose unit. Though both fructose and glucose
210
units crystallize in the cyclic forms, in solution, there exists a very small equilibrium between the
211
cyclic and acyclic forms. The existence of the acyclic form creates a carbonyl group (Thomas et
212
al., 2010). This leads to the appearance of a peak at 290 nm owing to n→π* transition of the
213
terminal C=O group that is formed due to the scission of the glycosidic bond. The peak at 249nm
214
may be due to π-π* transition. There are several reasons for the bathochromic shift of π-π*
215
transition. It may be due to the stabilization of π* more than the π in polar solvent, the presence of
216
large number of auxochromes and may be due to hydrogen bonding interactions of the –OH
217
groups with water molecules (Donald et al., 2007). The coexistence of cyclic and acyclic form of
218
glucose and fructose was reflected in the IR spectrum also.
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TiO2 has shown strong absorption at 296 nm. When TiO2 nanoparticles were incorporated
220
into the polymer matrix, a slight shift in the absorption band of TiO2 from 296 nm to 305 nm was
221
observed which indicated the formation of inulin- TiO2 composite. The red shift in the
222
wavelength upon composite formation was also an indication of decrease in the band gap (Ali et
223
al., 2012).
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FT-IR spectroscopy offers valuable information on the shift in the stretching frequencies
225
upon composite formation. The FT-IR spectra of inulin, TiO2 and inulin-TiO2 bio-nanocomposite
226
were shown in Fig. 2(b). The FT-IR spectrum of inulin shows peaks at 3426 cm-1 corresponding
227
to the –OH stretching vibration. A broad band with maximum intensity at 1022 cm-1 with two
228
shoulders at 1130 and 940 cm−1 corresponding to the stretching vibrations of C-O-C groups and
229
ring vibrational modes in the composition of cyclic structures was observed. Broad band with low
230
intensity arises at 1649 cm−1 which can’t be used as specific for inulin in biological mixture, as
231
usually this region is characteristic for amides (Grube, Bekers, Upite, & Kaminska, 2002). The
232
appearance of this peak may be due to the coexistence of the open-chain form of a
233
monosaccharide with a closed ring form where the aldehyde or ketone carbonyl group carbon
234
(C=O) and hydroxyl group (-OH) react together to form a hemiacetal with a new C-O-C bridge
235
(Finar, 2009). The peaks observed at 2924 cm-1 and 2360 cm-1 may be attributed to -CH stretching
236
and bending vibrations. In addition, the peaks observed in the region 1200-800 cm-1 in the
237
spectrum of inulin corresponded to carbohydrate region. In the IR spectrum of TiO2 the peaks at
238
3447 cm-1 is due to –OH stretching which indicated the presence of physically absorbed water
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Page 8 of 24
9
molecule. The peak at 640 cm-1 and 534 cm-1 was ascribed to Ti-O stretching mode (Xiaofeng Lu
240
et al., 2006; Anastasios et al, 2011). Slight shift in the position of Ti-O stretching peaks was
241
observed for inulin-TiO2 bio-nanocomposite indicating the interaction of TiO2 with inulin. Peak at
242
3426 cm-1 for inulin was shifted to 3412 cm-1 in the presence of TiO2 nanoparticles and this
243
clearly indicated the interaction of Ti with –OH group of inulin. The peak observed for both TiO2
244
and inulin-TiO2 bio-nanocomposite at 440 cm-1 (Ti-O bending mode) could be attributed to the
245
existence of TiO2 in the rutile phase (Lan Wang et al, 2014). These observations confirm the
246
incorporation of TiO2 nanoparticle into the biopolymer matrix.
cr
247
3.4. X-Ray Diffraction studies
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XRD patterns of inulin, TiO2 and inulin-TiO2 were shown in Fig. 2(c). The diffractogram
250
of inulin had shown a single weak wide peak around 15.72° 2θ indicating that extracted inulin
251
was amorphous. Strong diffraction peaks at 27°, 36°, 54° and 56° corresponding to (110), (101),
252
(211) and (220) planes respectively, were observed in the diffractogram of TiO2 which indicated
253
that it exists in the rutile phase [JCPDS no: 88-1175] (Lan Wang et al, 2014; Kheamrutai, Pichet
254
& Boonlaer, 2008). All these diffraction peaks were also observed in Inulin-TiO2 bio-
255
nanocomposite but the intensity of diffraction peaks were found to be lower compared to that of
256
TiO2. This suggested that in the composite, TiO2 was still present in the rutile phase without any
257
phase transformation and the amorphous inulin reduced the mass-volume percentage of TiO2 and
258
sequentially weakened the diffraction peaks of TiO2. This observation confirmed that TiO2 was
259
embedded onto the inulin matrix.
261
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The crystallite size was calculated using Sherrer’s equation (Kaifu et al, 2009), D=
0.9 β cos θ
(2 )
262
Where D is the crystallite size, λ is the wavelength of the radiation, θ is the Bragg’s angle and β
263
is the full width at half maximum. From the diffraction pattern, the average crystallite size for
264
TiO2 and Inulin-TiO2 bio-nanocomposite was found to be 90.5 nm and 61.2 nm respectively. The
265
reduction in the size of TiO2 suggested that the surface area of TiO2 increased upon composite
266
formation.
Page 9 of 24
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267
(a)
(b)
269 270
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(c)
271
Fig. 2. (a) UV-Visible absorption spectra, (b) IR Spectra and (c) X- Ray Diffractograms of
272
Inulin, TiO2 and Inulin-TiO2
273 274 275
Morphology index (M.I.) can be calculated using the equation, M .I . =
FWHM h FWHM h + FWHM p
(3)
276
Where FWHM refers to full width at half maximum value and the subscripts h refers to the
277
highest peak and p refers to a particular peak for which M.I to be obtained. The range of
278
morphology index for TiO2 (0.5-0.73) and Inulin-TiO2 (0.5 to 0.55) indicated that the particle
Page 10 of 24
11 279
size distribution of TiO2 in the composite was uniform compared to that of pristine TiO2.
280
(Theivasanthi & Alagar, 2011).
281
3.5. Thermal Studies Thermogravimetric analysis was used to determine the thermal stability of the extracted
283
biopolymer and it’s composite. The TG curves for the Inulin, TiO2 and Inulin-TiO2bio-
284
nanocomposite were presented in Fig. 3. It was noticed that the thermal stability of the inulin was
285
lower compared to that of its composite.
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(a) (b) (c) Fig. 3. TGA – DTA curves of (a) Inulin, (b) TiO2 and (c) Inulin-TiO2 In the TG curve of inulin, four distinct weight loss regions were observed. The first
290
weight loss of about 10 % corresponding to the loss of moisture absorbed from the surroundings
291
by inulin was observed between the temperature range 20 ºC and 100 ºC. The second weight loss
292
around 26 % observed in the temperature range 100-160 oC may be due to the decomposition of
293
inulin. The third weight loss around 160-380 oC represents the combustion of inulin and the
294
fourth weight loss around 34 % between 380 oC and 620 oC may be due to the loss of molecular
295
fragment of the inulin and degradation of the rest of the polymeric fragments into carbon (Norio
296
& Hayashi, 2007).
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286 287 288 289
In the TGA curve of TiO2, there were three distinct regions observed, one and two
298
corresponding to weight loss and the third corresponding to weight gain. The first one starts at
299
room temperature until upto105 ºC, with a weight loss of about 0.9 %, whereas the second one
300
was observed in the range of 200-540 ºC, with a weight loss of about 1.7 %.The weight loss in
301
the first stage may be attributed to the removal of absorbed water. The second weight loss may
302
be due to the decomposition of TiO2. Above 540 ºC the increase in weight can be attributed to
303
the oxygen gain from air. A possible rearrangement of the TiO2 structure leading to the phase
304
transformation from rutile to anatase would have occurred above 540 ºC.
Page 11 of 24
12
The thermogram of inulin-TiO2 bio-nanocomposite had shown three distinct weight loss
306
regions. The weight loss of about 8 % observed in the temperature range 40- 120 ºC may be due
307
to the removal of associated water molecules. The second weight loss of about 28 % observed
308
around 180-300 ºC may be due to the degradation of the polymer chain whereas the third
309
continuous weight loss of about 48 % in the temperature range 300-520ºC may be due to the
310
degradation of TiO2 incorporated in the inulin matrix. The comparison of the thermograms of
311
inulin with TiO2 and inulin-TiO2 bio-nanocomposite indicated that the composite was thermally
312
more stable than inulin and TiO2. No significant weight loss was observed for inulin-TiO2 bio-
313
nanocomposite when heated beyond 520 ºC which indicated the improvement in the thermal
314
stability of inulin upon incorporation of TiO2 nanoparticles.
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Analysis of DTA curves revealed the physical and chemical changes that occur in
316
compounds. In the DTA curve of inulin, the glass transition temperature was observed at 150 oC.
317
The exothermic peak appeared at 220 oC indicated the point of crystallization of the amorphous
318
inulin. An endothermic peak observed at 440 oC corresponded to the melting temperature. The
319
temperature corresponding to the melting of the composite got increased to 480 oC which might
320
be due to the incorporation of TiO2. The appearance of intense exothermic peak at 550 oC may
321
be due to the oxidation of inulin and the intensity of this peak got suppressed in case of inulin-
322
TiO2 bio-nanocomposite which may be due to the suppression of oxidation of inulin by TiO2.
323
The decomposition of the biopolymer inulin occurred at 660 oC.
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324
3.6. Photocatalytic degradation of MB
Ac ce p
325
The adsorption of MB by inulin, TiO2 and inulin-TiO2 bio-nanocomposite was studied
326 327
and it was observed that the efficiency of dye adsorption was found to be in the order inulin-TiO2
328
> inulin > TiO2. This might be due to the increase in the availability of the number of surface
329
active sites for the adsorption of MB upon composite formation. Control experiments have also
330
been conducted by irradiating the MB dye solution without the addition of TiO2 or inulin-TiO2
331
bio-nanocomposite and it was observed that no degradation of dye occurred in the absence of the
332
photocatalyst. The adsorption and the photo degradation ability of TiO2 and inulin-TiO2 bio-
333
nanocomposite before and after UV irradiation, respectively, were compared. The results
334
indicated that the photo degradation ability of the composite was found to be greater than that of
335
TiO2.
336
The photocatalytic degradation ability of inulin-TiO2 against varying concentrations of
337
MB solution and at various time intervals was studied. The intensity of the colour of MB
Page 12 of 24
13
solutions got reduced when all or part of the auxochromic groups degraded. This is reflected by
339
the considerable shift in the spectral band from 660 nm to 650 nm during the course of the photo
340
assisted degradation (Fig.4). Such a shift was not observed without illumination of UV –light.
341
This indicated that in the presence of UV irradiation, photocatalytic degradation predominated
342
over simple adsorption process (Xiao et al., 2015). Moreover, adsorption process was favoured
343
in the absence of UV irradiation.
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344
(a)
(b)
346 347
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(c)
348
Fig. 4. UV-Visible absorption spectra (a) for the degradation of MB (30 ppm) using TiO2 and
349
inulin-TiO2 with and without illumination of UV light (b) for the degradation of MB (30 ppm)
350
using inulin-TiO2 at various time intervals (Inset: Calibration Curve) and (c) variation of the
351
concentration of MB upon photocatalytic degradation using inulin-TiO2 with time (Inset: %
352
degradation of MB at various time intervals)
Page 13 of 24
14
As the initial concentration of the dye increased from 10 to 50 ppm, the degradation
354
efficiency of the photocatalyst decreased. This may be due to the increase in the surface coverage
355
of the MB dye or its degradation products over a period of time. Also the high concentration of
356
dye molecules on the surface of the photocatalyst caused shielding of UV light radiation. As a
357
result, the concentration of OH· radical on the surface of photocatalyst decreased which led to
358
decrease in the degradation efficiency of the photocatalyst (Xiaorong et al, 2014). This was
359
reflected in the decrease in the apparent rate constant of photocatalytic dye degradation as the
360
initial concentration of the dye increases. The % degradation increased from 95% to 99 % when
361
it was exposed from 90 min to 120 min for 10 ppm concentration of MB dye. The same trend of
362
increased % degradation was observed for other concentrations of MB dye used.
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353
363
366 367
Photocatalytic degradation of MB dye was found to follow pseudo first order kinetics
an
365
3.8. Kinetics of Photocatalytic degradation
(Rahul, Usha, Gautam & Sumit, 2014) and the expression was given as ln
C0 = kapp t C
M
364
(4)
Where kapp – apparent rate constant; C0 – initial concentration of MB dyes (mg/L);
369
C−concentration of MB dye (mg/L) at various time intervals. The kapp values can be evaluated
370
from the slope of the straight line plot between ln
C0 C
and t which was shown in Fig. 5(a).
Ac ce p
te
d
368
371 372 373 374
(a) Fig. 5. Plot between (a) ln
(b)
C0 C
and time and (b) 1/ kapp and C0
Half-life (t1/2) of MB dye degradation was given by the expression
Page 14 of 24
15
t1 =
375
2
0.6931 kapp
(5)
It was assumed that photocatalytic degradation of MB dye mainly takes place on the
377
surface of the photocatalyst, the Langmuir- Hinshelwood equation for the reaction rate could be
378
written as (Jiamei, Can, Hong & Jianhao, 2013).
379
r=
− dC = k ×θ B × θ HO˙ dt
(6)
ip t
376
Where k − the surface reaction rate constant; θB − fractional surface site coverage by MB ;
381
θHO˙ − fractional surface site coverage by HO˙ which is assumed to degrade MB.
383
(Jiamei, et al., 2013).
384
Hence the equation can be rearranged as
an
r = k1θ B
385
(7)
where k1 – new rate constant which is equal to kθHO˙ nads K B C0 = n0 1 + K B C0
387
θB =
388
1 1 = + nads n0
1 n0 K B
1 C0
(8) (9)
d
386
us
The amount of HO˙ radicals is considered as constant during the degradation process
M
382
cr
380
where KB is the adsorption equilibrium constant of MB and C0 is the initial concentration of MB,
390
nads is the number of dye molecules adsorbed and no refers to the initial number of dye
391
molecules.
392
Substituting the expression for θB from equation (8) into the expression for rate in equation (7),
394
395
Ac ce p
393
te
389
r=
1 1 + K B C0 1 = = r k1 K B C kapp C
1
kapp 396
k1 K B C =k C (1+ K BC0 ) app
1 kapp
(10) (11)
=
1 + K B C0 k1 K B
(12)
=
C 1 + 0 k1 K B k1
(13)
397
A plot between 1/kapp and C0 (Fig. 5(b)) for the same amount of inulin-TiO2 content
398
indicated that as the concentration of dye increases 1/kapp also increases. The k1 and KB values as
Page 15 of 24
16 399
determined from the slope and the intercept were found to be 3.1738 ppm min-1 and 0.0165 min
400
ppm-1, respectively. The values of θB for various concentrations of MB dye can then be evaluated
401
by using equation (8) and presented in Table 1.
402
Table 1. Langmuir- Hinshelwood kinetic parameters for the degradation of dye kapp
(ppm)
(min-1)
10
0.0449
0.9969
15.43
0.14
20
0.0393
0.9947
17.64
30
0.0350
0.9983
19.80
cr
r2
C0
40
0.0317
0.9944
50
0.0286
0.9897
us
t1/2 (min)
0.25 0.33
21.86
0.40
24.23
0.45
an
404
θB
ip t
403
The kapp value obtained when TiO2 was used for the photocatalytic degradation of MB
406
dye was found to be less compared to that obtained when inulin-TiO2 was used. The kapp values
407
for the photo degradation of 10 ppm MB dye solution using TiO2 and inulin-TiO2 were found to
408
be 0.0325 min-1 and 0.0449 min-1, respectively. The t1/2 value obtained for inulin-TiO2 (15.43
409
min) was found to be lesser than that for TiO2 (21.32 min). The prevention of agglomeration of
410
TiO2 in the composite due to the presence of inulin provides larger surface area causing
411
improved photocatalytic activity (Ali, Sepideh & Ali Akbar, 2012). The decrease in the
412
degradation efficiency of the photocatalyst with increase in the concentration of the dye was
413
reflected in the kapp and θB values. The kapp values (Table 1.) were found to decrease with increase
414
in the concentration of dye due to increase in the surface coverage (θB) of the MB dye which
415
may also block the penetration of UV light, thereby decreasing the amount of photo generated
416
electrons.
418 419
d
te
Ac ce p
417
M
405
3.9. Mechanism of photocatalytic degradation of MB using Inulin-TiO2 composite The mechanism of generation of reactive oxygen species that is responsible for the
420
degradation of MB dye upon illumination of UV radiation on inulin-TiO2 bio-nanocomposite
421
(Vinod, Shilpi, Deepak, Kothiyal, Gavrav, 2013).
422 423
hν Inu-TiO2 → Inu-TiO2 (e− CB + h+ VB)
(i)
424
Inu-TiO2 (e− CB) + O2→ Inu-TiO2 + O2−˙
(ii)
425
Inu-TiO2 (h+ VB) + H2O → Inu-TiO2 + H+ + ˙OH
(iii)
Page 16 of 24
17
O2−˙+ H2O → HO2˙ + OH−
(iv)
427
MB + h+ → [O] products
(v)
428
MB + ˙OH → Mineral end products
(vi)
429
MB + e− CB → [H] products
(vii)
an
us
cr
ip t
426
430
Fig. 6. Schematic representation for the mechanism of photocatalytic degradation of MB using
432
inulin-TiO2 bio-nanocomposite
M
431
Upon UV irradiation on the surface of the bio-nanocomposite, electron (e−) and hole (h+)
434
pairs was generated (Fig. 6.). The photo induced electrons that were transferred to the surface of
435
inulin were responsible for the reduction of dissolved oxygen to produce highly reactive
436
superoxide anion radical (O2−˙) which formed other oxidative radicals (˙OH2) in presence of
437
water. The photo generated holes will then be reacted with water to form hydroxyl radicals
438
(˙OH).The holes and ˙OH both were extremely reactive as they were chemically unstable when
439
in contact with organic compounds. Hence they oxidized the MB dye molecules to form
440
oxidation products. The oxidation of MB dye to the mineral end products was mainly due to the
441
combined effect of ˙OH and O2˙radicals.
te
Ac ce p
442
d
433
The problem with the recombination of electron-hole pairs formed after excitation of
443
TiO2photocatalystwas found to be overcome by the presence of inulin. Inulin which is enriched
444
with–OH functionalities helped in the stabilization of the photo excited electron which has got
445
transferred from the conduction band to the surface of inulin. This prevented its recombination
446
with the holes present in the valence band of TiO2 thereby increasing the lifetime of photo
447
excited electrons. Hence the expected enhancement in the photocatalytic degradation efficiency
448
of inulin-TiO2 bio-nanocomposite was achieved.
449 450
3.10. Comparative data of degradation efficiency of various photocatalysts
Page 17 of 24
18 451 452
The literature data shown in Table 2 suggested that the proposed nanocomposite was found to be efficient in the photocatalytic degradation of methylene blue.
453 454
TiO2/cotton fibers
95.35
120
Amount of catalyst (g) 2.5
TiO2-Cellulose nanofiber
60
60
0.01
polyaniline / Bi2SnTiO7
100
220
Chitosan-TiO2
90
TiO2-Fe3O4bentonite
90
456 457 458
92
Volume and Concentration of MB dye 50 ml of 50 ppm
an
25ml
0.3
300 mL of 0.025 mM
-
5 ppm
90
0.03
100ml of 30 ppm
120
0.01
50 ml of 50 ppm
d
Ac ce p
Inulin-TiO2 bio-nanocomposite
-
ip t
Time (min)
Reference
cr
Degradation (%)
us
Photocatalyst
M
Table 2. Degradation of methylene blue dye using various photocatalyst
te
455
Shi Zhong Liang et al., 2010 Alexandra et al., 2013
Yunjun Yang & Jingfei Luan, 2012 Yuvaraj, Haldorai & Jae-Jin Shim, 2014 Wei, Hongyao, Hang, Tonggang & Yanmei, 2015 Present work
4. Conclusion
Inulin was extracted from Allium sativum L and the TiO2 nanoparticles were then
459
successfully incorporated onto the inulin-matrix. The prepared composite was tested for its
460
photocatalytic activity against the degradation of MB and it was proved to exhibit very good
461
activity compared to that of pristine TiO2. The enhancement in the photocatalytic activity as
462
reflected in the apparent rate constant (0.0325 min-1 for TiO2; 0.0449 min-1 for inulin-TiO2 (ratio
463
2:1)) may be due to synergistic reinforcement of the properties of both inulin and TiO2.The
464
prevention of agglomeration of TiO2 in the composite due to the presence of inulin provides
465
larger surface area causing improved photocatalytic activity. Moreover, the stabilization of photo
466
generated electrons, the prevention of the recombination of electron- hole pairs and the recovery
467
of the catalyst could be achieved using the novel bio-nanocomposite used. The newly
Page 18 of 24
19 468
synthesized bio-nanocomposite will therefore act as an effective photocatalyst and will be
469
utilized for the degradation of many more organic pollutants viz., crystal violet, methyl red,
470
methyl orange etc., in future.
471 472
5. Acknowledgement The authors duly acknowledge all the personnel who helped us in collecting the various
474
data presented. The authors greatly acknowledge the Management and the Department for
475
providing the necessary facilities to carry out the present work. Dr. A. Arlin Jose Amali, DST-
476
INSPIRE Faculty, Madurai Kamaraj University, is acknowledged for her kind support.
cr
ip t
473
us
477
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Page 23 of 24
24
HIGHLIGHTS
605 606
Eco-toxicity minimization using TiO2 embedded carbohydrate nanocomposite
Ac ce p
te
d
M
an
us
cr
ip t
607
Page 24 of 24