Elsevier

Carbohydrate Polymers

Volume 95, Issue 1, 5 June 2013, Pages 434-440
Carbohydrate Polymers

Cellulose acetate–zirconium (IV) phosphate nano-composite with enhanced photo-catalytic activity

https://doi.org/10.1016/j.carbpol.2013.02.045Get rights and content

Abstract

Cellulose acetate–zirconium (IV) phosphate nanocomposite (CA/ZPNC) was synthesized by sol–gel technique at pH 0–1 and was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA/DSC). Ion exchange capacity, pH titration, elution concentration, elution behaviour, thermal stability and distribution coefficient were investigated to explore ion exchange behaviour of CA/ZPNC. The nanocomposite showed an ion-exchange capacity of 1.4 mequiv. g−1 for Na+ and was highly selective for Pb2+ and Zn2+ over many other metal ions. The photocatalytic activity of the CA/ZPNC was explored for degradation of a model Congo red dye from aqueous phase. 90% of dye was removed in 60 min of irradiation. Simultaneous adsorption and photocatalysis had synergetic effect on dye degradation.

Highlights

Cellulose acetate Zr (IV) phosphate nanocomposite was synthesized. ► The ion exchange capacity of CA/ZPNC was explored. ► CA/ZPNC was highly selective for lead ions. ► CA/ZPNC proved to be an efficient photocatalyst for dye degradation.

Introduction

Several industries such as textile, paper, paint, and dyestuffs consume large quantity of water and utilize chemicals and dyes to form products; as a consequence, several toxic metals and chemicals are discharged continuously into the water bodies. The discharged industrial pollutants deteriorate the water quality and may cause adverse effect on human health due to their toxic, mutagenic and carcinogenic nature (Gupta et al., 2010, Huang and Chen, 2009, Korbahti et al., 2011, Zhao et al., 2012). Congo red – an anionic dye has been known to cause an allergic reaction and is known to be metabolized to benzidine which in turn is a human carcinogen (Chatterjee, Lee, Lee, & Woo, 2009).

Wastewaters containing synthetic dyes and toxic metal ions are difficult to treat, since they are recalcitrant, resistant to biological oxidation/reduction, and are stable to oxidizing agents. The conventional methods such as coagulation, flocculation, precipitation, membrane separation, solvent extraction, adsorption and reverse osmosis are not able to treat industrial effluent effectively (Vilhera, Goncalves, & Mota, 2004). In practice, no single process provides adequate treatment and a combination of different processes is often used to improve the water quality in a greener and more economic way.

It is now well documented that low cost bio-adsorbent based adsorption processes are effective and economic methods for wastewater remediation (Gupta et al., 2007a, Gupta et al., 2007b, Gupta et al., 2011b, Gupta et al., 2009, Jain et al., 2003, Mittal et al., 2009, Mittal et al., 2010a, Mittal et al., 2008, Mittal et al., 2010b, Gupta et al., 2011a). A large variety of non-conventional bio-adsorbents have been employed to remove metal ions and dyes from aqueous phase. Much attention has been focused on fungal or bacterial biomass and biopolymers that are harmless and are ubiquitously available in nature (Constantin et al., 2013, Gupta et al., 2010, Oei et al., 2009, Yang et al., 2012). However, lack of stability, intricacies in separation from aqueous phase and low recovery after desorption are the major limitations for large scale application of bio-absorbents (Gupta et al., 2010).

In order to meet the stringent environmental regulation, the photocatalytic reactions have advantages over classical and non-conventional methods for dye degradation due to their simplicity and rapid degradation based on hydroxyl radical formation. Nowadays, hybrid organic–inorganic nanocomposites are materials of choice because of their multifunctionality due to a combination of different compounds incorporated. Recent examples can be found in the range of TiO2, BiOCl, Fe2O3, CuS and ZnO based nanocomposites (Dong et al., 2012, Liu et al., 2013, Virkutyte et al., 2012). Primarily, adsorption of pollutants on the catalyst surface is a pre-requisite for the effective photo-degradation process (Qourzal, Tamimi, Assabbane, & Ait-Ichou, 2005). However, little work has been done to develop hybrid nano-bio-composite material with high adsorption capacity and enhanced photocatalytic activity (Gupta, Ali, Saleh, Nayak, & Agarwal, 2012).

Recently, cellulose based nanocomposites have drawn considerable attention because of their low cost, high-volume application, easy processability, renewable nature and possibility of recycling (Ali, 2012). There are several research efforts reporting the cellulose composite with carbon nanotubes, lignin and lumiscent CdS (Nevarez et al., 2011, Park and Kadla, 2012, Yang et al., 2012). Fitz-Binder and Bechtold (2012) investigated the adsorption of Ca2+ ions on regenerated cellulose fibres such as lyocell, viscous and model fibres. Zirconium phosphate is an inorganic ion exchanger of the class of tetravalent metal acid (TMA) salts. It has been recently demonstrated as an excellent sorbent for heavy metals due to its high selectivity, high thermal stability and absolute insolubility in water. Thakkar and Chudasama (2009) studied the exchange properties of zirconium titanium phosphate (ZTP) for the separation of Cu2+, Ni2+, Zn2+, Co2+, Cd2+, Hg2+, Pb2+, Bi2+, La3+, Ce2+, Th4+, and UO22+. Kubli et al. (2012) synthesized zirconium phosphate based microporous ion exchanger that can discriminate between CO2 and CH4. Mishima, Matsuda, and Miyake (2007) studied the photocatalytic efficacy of Zr2ON2 yielding H2 and O2 by water reduction. However major disadvantage of synthetic inorganic ion exchangers is the difficulty in preparing granulated materials with sufficient strength and suitable mechanical properties for column operations.

Until now, as far as, we could ascertain, no data is available concerning the preparation of cellulose acetate–zirconium (IV) phosphate nanocomposite as a visible light active photocatalyst. The objective of the present work is to prepare cellulose acetate–zirconium (IV) phosphate nanocomposite (CA/ZPNC) by sol–gel transformations. The ion exchange behaviour of CA/ZPNC will be explored for the adsorption of different metal ions. The photocatalytic activity of CA/ZPNC was also utilized for the degradation of Congo red (CR) dye. It was characterized by scanning electron transmission (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), thermo gravimetric and differential temperature analysis, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) and ultraviolet–visible (UV–Vis) spectroscopy and subjected to ion-exchanger photocatalytic activity study.

Section snippets

Chemicals and materials

The main reagents used were zirconium oxychloride, orthophosphoric acid, cellulose acetate and were purchased from Sigma–Aldrich, India. All reagents were used without further purification. The Congo red dye was obtained from S.D. Fine India. All other chemicals and reagents used were of analytical reagent grade. All the solutions were prepared in double distilled water.

Preparation of cellulose acetate Zirconium (IV) phosphate (CA/ZPNC)

In the present work, cellulose acetate based nanocomposite was synthesized using simple and ambient sol gel method (Fig. 1).

Characterization of CA/ZPNC

Scanning electron microscopy (SEM) images of CA/ZPNC at different magnifications are shown in Fig. 2(a and b) which exhibits rough surface with different sized particles to form microsphere. As seen in Fig. 2(c and d), TEM images signify homogeneous distribution of CA and ZP particles in nanocomposite. The darker portion represents CA wrapped in ZP while the grey part corresponds to CA in polymeric backbone. These images clearly indicate CA/ZPNC formation in the range of 50 nm.

Fig. 3(a)

Conclusion

In the present study, an ambient reaction condition method was developed to prepare cellulose acetate–zirconium (IV) phosphate nanocomposite. Spectral analysis confirmed the high level of CA and zirconium (IV) phosphate nanocomposite formation. CA/ZPNC was stable at high temperature exhibiting promising ion exchange capacity and photocatalytic activity. The ion exchange capacity decreased with increase in temperature. CA/ZPNC behaved as strong cation exchanger, showing high selectivity to Pb2+.

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