The present study describes the feasibility of a novel adsorbent cum photocatalyst, poly(pyrrole-co-aniline)-coated TiO2/nanocellulose composite (P(Py-co-An)-TiO2/NCC), to remove eosin yellow (EY) from aqueous solutions. The removal of EY was investigated by batch adsorption followed by photocatalysis. The effect of various adsorption parameters like adsorbent dose, pH, contact time, initial concentration, and ionic strength has been optimized for treating effluents from the dye industry. Adsorption of EY reached maximum at pH 4.5 and complete removal of dye was achieved using 3.5 g/L of P(Py-co-An)-TiO2/NCC. Adsorption equilibrium data were fitted with Langmuir and Fritz-Schlunder isotherm models and the kinetics of adsorption follows a second-order mechanism. The adsorption capacity of P(Py-co-An)-TiO2/NCC was found to be 3.39 × 10−5 mol/g and reached equilibrium within 90 min. The photocatalytic degradation of adsorbed dye under sunlight was possible and about 92.3% of dye was degraded within 90 min. The reusability of P(Py-co-An)-TiO2/NCC was also investigated. The results indicate that P(Py-co-An)-TiO2/NCC is the best material for the wiping out of EY from aqueous solutions.
Textile dyes are the largest group of chemicals being produced all over the world. The effluents from manufacturing and textile industries are discarded in large quantities into rivers and lakes causing water pollution and affect the ecosystem seriously [
TiO2 has been extensively used as a photocatalyst, owing to its inexpensive, nontoxic, and photoelectric properties [
Anchoring of TiO2 on various supports including carbon, glass fibers, montmorillonite, organic materials, and zeolites may increase their photochemical stability. Organic materials with UV light resistance have been widely used as supports for TiO2 photocatalyst, since they have the advantages such as low cost and easy separation from reaction solution. Cellulose, obtained from wood pulp and cotton, is such a material used for this purpose due to its low cost and easy availability. Cellulose has been explored as a substrate for composite materials because of the presence of functional groups that may be employed in various activation processes. Additionally, it was suggested that the holes’ scavenging ability increases with the increasing number and spatial distribution of the hydroxyl groups in the polyhydroxyl compounds [
Conducting polymers such as polypyrrole, polyaniline, and polythiophene have functioned as dopants which shift the border of the TiO2 particles to longer wavelengths, thereby improving the optical absorption in the visible region. These hybrid conducting polymer/TiO2 composites exhibit excellent properties unlike those of the individual materials, such as controlled conductivity and thermal or mechanical stability, and these properties have made them potentially applicable as anode materials for lithium-ion batteries [
As we know, eosin yellow (EY) is widely used for staining purposes; however, it is listed as a carcinogen. The present work is aimed at wiping out the textile dye, EY, from the environment for the well-being of the organisms. In the present work, a novel polymer composite, poly(pyrrole-co-aniline)-coated TiO2/nanocellulose composite [P(Py-co-An)-TiO2/NCC] was prepared for the adsorptive removal of EY from aqueous solutions, followed by photocatalytic degradation under sunlight. For the preparation of this polymeric hydrogel, glutaraldehyde, the agent widely used for industrial water treatment and a preservative, was selected as a crosslinker.
Sawdust of
Cellulose has been extracted from sawdust and was converted to nanocrystals following the procedure reported earlier [
NC (0.2 g), HNO3 (5 mL, 0.1 M), and absolute ethanol (100 mL) were mixed with each other and the mixture was ultrasonically dispersed for 1 h. After dispersion, 1 mL of titanium(IV) isopropoxide was added to this mixture slowly with a constant pressure funnel under magnetic stirring. The reaction temperature was kept at 40°C for 4 h. Finally, the suspension was diluted fivefold with water, centrifuged, and then washed with water repeatedly. The precipitate was dialyzed against deionized water for 2 days and then freeze-dried.
P(Py-co-An)-TiO2/NCC was synthesized by chemical oxidation of its respective monomers, Py and An, by keeping their molar ratios constant at 1 : 1. The aqueous solution of TiO2/NCC (240 mg in 100 mL) was mixed with a solution of pyrrole (3 mL), aniline (3 mL), and HCl (37%, 0.16 mL) for 30 min where after APS (0.46 g) and of FeCl3 (8.0 g) was added, respectively, in the solution for polymerization initiation, and stirred for 3 h. The obtained product with a layer of poly(pyrrole-co-aniline) was filtered, washed with ethanol, and dried at 50°C. The dried product, designated as P(Py-co-An)-TiO2/NCC, was sieved to get an average particle size of 0.096 mm and used for adsorption followed by photocatalytic experiments.
Surface morphology of the adsorbents was investigated by SEM micrographs recorded with a JEOL JSM 6390 LA scanning electron microscope. The Brunauer-Emmett-Teller (BET) surface area was determined using a model Q7/S surface area analyzer (Quantasorb, USA). The XRD patterns were recorded using X’Pert Pro X-ray diffractometer. Patterns were recorded in the
Adsorption experiments were conducted to evaluate adsorption capacities of P(Py-co-An)-TiO2/NCC. A stock solution of EY (10−2 M) was prepared in 1 L of double distilled water. The desired concentrations of the dye solution were obtained by proper dilution of the stock solution. 0.1 g of P(Py-co-An)-TiO2/NCC was added into a stoppered bottle containing 50 mL of EY solution (10−5 M). pH of the solution was adjusted to the desired value with dilute HCl or NaOH. The mixture was shaken at 30°C for 90 min for adsorption, and then the mixture was filtered. The concentration of the dye solution before and after adsorption was estimated using UV-visible spectroscopic method. The adsorption (%) and the amount adsorbed (mol/g) were calculated as follows:
Photocatalytic degradation of the dye was studied using P(Py-co-An)-TiO2/NCC after adsorption experiment. The dye loaded swollen hydrogels were exposed to sunlight (at noon) and withdrawn at different time intervals from 5 to 120 min. Each sample is then analyzed spectrophotometrically at a wavelength of 515 nm. Degradation rate was calculated from the amount of the dye in the swollen gels as follows:
The samples obtained after photocatalytic degradation were washed thoroughly and adsorption-photocatalytic degradation experiments were repeated for four cycles in order to perform their regeneration capacity.
The photocatalyst, P(Py-co-An)-TiO2/NCC, was prepared from TiO2/NCC via chemical oxidation polymerization technique. Firstly, Cellulose was extracted from the value added product, sawdust, by acid-alkali treatment followed by bleaching with H2O2. The cellulose was made into nanocrystals via acid hydrolysis which improves its crystallinity and hydrophilicity. TiO2/NCC was prepared from NC and the precursor Ti(OiPr)4 using chemical precipitation method. PPy and PAn were coated onto TiO2/NCC by chemical oxidation polymerization of pyrrole and aniline with FeCl3. APS will generate
The surface morphology of the samples is clearly displayed in Figure
SEM photographs of (a) cellulose, (b) NC, (c) TiO2/NCC, and (d) P(Py-co-An)-TiO2/NCC.
Figure
XRD patterns of cellulose, NC, TiO2/NCC, and P(Py-co-An)-TiO2/NCC.
The FTIR patterns of cellulose, NC, TiO2/NCC, and P(Py-co-An)-TiO2/NCC are presented in Figure
FTIR spectra of cellulose, NC, TiO2/NCC, and P(Py-co-An)-TiO2/NCC.
The amount of the spent adsorbent determines the economic value of the adsorption process. The performances of the adsorbent P(Py-co-An)-TiO2/NCC and the precursor material cellulose were evaluated by varying their amounts from 0.5 to 5.0 g/L. As seen in Figure
Effect of adsorbent dose on EY adsorption onto P(Py-co-An)-TiO2/NCC.
pH value of the solution is an important controlling parameter in the adsorption process, since it affects the surface charge of the adsorbent and the degree of speciation of adsorbate. As depicted in Figure
Effect of solution pH on EY adsorption onto P(Py-co-An)-TiO2/NCC.
Possible interactions between EY and P(Py-co-An)-TiO2/NCC.
Figure
Kinetic modeling for the EY adsorption onto P(Py-co-An)-TiO2/NCC.
Additionally, the initial adsorption rate
Kinetic parameters for different concentrations were calculated by a nonlinear curve fitting method using ORIGIN program (version 7.5) and are listed in Table
Kinetic parameters for the adsorption of EY onto P(Py-co-An)-TiO2/NCC (±standard deviation;
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1 | 0.458 | 0.270 | 0.447 | 0.974 | 0.0003 | 1.234 | 0.461 | 0.262 | 0.995 | 7 × 10−5 |
5 | 2.202 | 0.279 | 2.157 | 0.977 | 0.007 | 0.003 | 2.218 | 0.015 | 0.996 | 0.0014 |
Adsorption isotherm measures the adsorption efficiency of a polymer over a range of analyte concentrations. It describes the interactive behavior between adsorbate and adsorbent and is important for predicting the adsorption capacity of adsorbent, which is the main parameter required for design of an adsorption system. The increase in concentration of dye solution caused an increase in adsorption capacity (Figure
Isotherm modeling for the EY adsorption onto P(Py-co-An)-TiO2/NCC.
For evaluating the maximum adsorption capacity and adsorption mechanism, the experimental isotherm data were interpreted using the equilibrium isotherm models, such as Langmuir, Freundlich, and Fritz-Schlunder isotherm equations, as follows:
The Langmuir isotherm [
Freundlich isotherm equation can be applied to nonideal sorption on heterogeneous surfaces as well as to multilayer sorption. The value of Freundlich exponent
Isotherm parameters for the adsorption of EY onto P(Py-co-An)-TiO2/NCC at 30°C (±standard deviation;
Langmuir | Freundlich | Fritz-Schlunder | ||||||||||
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3.397 | 2.480 | 0.996 | 0.005 | 2.160 | 0.326 | 0.949 | 0.062 | 2.504 | 3.385 | 0.997 | 0.996 | 0.005 |
As suggested by Figure
The photocatalytic activities of P(Py-co-An)-TiO2/NCC were evaluated by the degradation of EY in an aqueous solution under sunlight irradiation. No degradation of EY was observed in the absence of a photocatalyst under visible light illumination. It was observed that photocatalytic degradation of EY increases with increase in irradiation time and 92.3% of the dye was degraded within 90 min. Photocatalytic degradation was found to follow first-order rate equation, for lower concentrations, as follows:
Kinetic data for the photodegradation of EY onto P(Py-co-An)-TiO2/NCC.
TiO2 particles can absorb UV light from the sunlight to create electrons (e−) in the conduction band and holes (h+) in the valence band, respectively. If the electrons and holes cannot be captured in time, they will recombine with each other within a few nanoseconds, which will reduce the photocatalytic efficiency of TiO2. However, due to the existence of the interface between polymer and TiO2, separated electrons and holes have little possibility to recombine again in the case of composites. This ensures higher charge separation efficiency and better photooxidation capacity for the nanocomposite. In addition, the conjugated polymer can absorb the visible light and produces an electron (e−) that transfers to the conduction band of TiO2 [
Thus, the heterogeneous photocatalytic degradation of an azo compound can be summarized by the following reactions [
Several authors make use of these types of conjugated polymers in the photodegradation of dye under visible light. The conjugated polymers (CPs) with extended p-conjugated electron systems showed the relatively high photoelectric conversion efficiency and charge transfer due to their high absorption coefficients in the visible part of the spectrum, high mobility of charge carriers, and good stability [
To examine the photocatalytic stability, adsorption of EY onto P(Py-co-An)-TiO2/NCC hydrogel was carried out at optimum conditions and the adsorbed dye material was exposed to sunlight for degradation. This process was repeated for four cycles and the results obtained were depicted in Figure
Adsorption-photocatalytic degradation cycle of EY on P(Py-co-An)-TiO2/NCC.
Eosin yellow (EY) is a carcinogenic dye and its exposure may cause adverse effects. Here we prepared a conductive conjugated polymer/semiconductor system, poly(pyrrole-co-aniline)-coated TiO2/nanocellulose composite (P(Py-co-An)-TiO2/NCC), for the removal of EY from aqueous solutions. The samples under preparation stage were characterized by SEM, XRD, and FTIR analyses. The systematic adsorption cum photocatalytic studies were carried out to explore the optimum conditions for the dye removal. Adsorption of dye was highly dependent on pH and 91.7% of the dye was adsorbed at pH of 4.5 within 90 min. An adsorbent dose of 3.5 g/L was needed for the complete adsorption of EY from aqueous solutions. Adsorption follows both Langmuir and Fritz-Schlunder isotherm models and pseudo-second-order kinetics, suggesting that chemisorption may be the mechanism behind the adsorption process. Photocatalytic degradation of EY under sunlight produced reliable results. P(Py-co-An)-TiO2/NCC shows excellent photocatalytic stability and recyclability. Thus, the present investigation shows that the photocatalyst, P(Py-co-An)-TiO2/NCC, is a valuable material for the adsorption and photocatalytic degradation of EY dye from aqueous solutions and can be developed as a support for the removal of EY dye from industrial effluents.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to thank the University Grants Commission, Government of India, New Delhi, for financially supporting this research under Major Research Project (MRP) F. no. 37-425/2009 (S. R. Rejeena).