Comparative studies of chitosan and its nanoparticles for the adsorption efficiency of various dyes

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Abstract

Chitosan has been considered as a chelating agent with the potential for the adsorption of dyes, metal ions and proteins. This study was aimed to prepare and characterize different fungal chitosan nanoparticles (FCI-1 to FCI-6 NPs) by ionic gelation method and to evaluate its efficacy on the sorption of various commercial dyes. Morphological observations showed that the FCI-1 is nearly spherical in shape with particle size ranging from 2 to 30 nm, as determined by electron microscopic studies. Electron micrograph revealed that FCI-1 NPs were stable even after eighteen months of storage at 4 °C. Adsorption efficiencies of FCI-1 NPs and FCI-1 were estimated against various dyes such as RBB, MO, DR, NBB and CSB using spectrophotometry. Out of the dyes tested, FCI-1 NPs showed better adsorption efficiency for CSB whereas only RBB followed Langmuir isotherm. The adsorption of remaining dyes may probably be through random adsorption. The results indicated that FCI-1 NPs could be used as efficient sorbents in treating industrial dye effluents.

Introduction

Synthetic dyes are used widely in dyeing and printing processes; among them many dye wastes are harmful and carcinogenic [1], causing a serious hazard to aquatic living organisms. Many conventional treatment technologies such as the tricking filter, activated sludge, chemical coagulation, carbon adsorption and photo-degradation processes for the dye removal have been investigated extensively [2]. Waste waters containing dyes are difficult to remove because of their inert properties. Another difficulty arises during the removal of dyes by the presence of minimum quantity of dye molecules in wastewater. The high costs involved in removing trace amounts of impurities make the conventional methods of removing dyes unpopular to be applied at a large scale [3]. Amongst the numerous techniques of dye removal, adsorption is the procedure of choice and gives the best results as it can be used to remove different types of coloring materials [4], [5], [6], [7]. Many studies have been made on the possibility of adsorbents using activated carbon, peat, chitin, silica, fly ash, clay and others [8], [9], [10], [11], [12]. However, the adsorption capacity is not very large; to improve adsorption performance new adsorbents are still under development.

Many adsorbents have been tested, in particular mineral sorbents [13], and activated carbon [14]. Though activated carbon has received a great deal of attention because of its high efficiency and high sorption capacity, its use is limited by its non-selectivity and poor reusability. So, there is still a need for the development of alternative sorbents, especially low-cost sorbents. Biosorption processes have shown promise for the removal of organic and mineral contaminants using peat, wood and its derivatives, agriculture wastes, or fungal biomass [10], [15], [16]. However, several factors, including variability in composition, source, and low-sorption capacities, have limited their use despite their low cost.

Chitosan has been under consideration due to its high amount of amino and hydroxyl functional groups with potential for the adsorption of dyes, metal ions and proteins [17], [18], [19], [20]. In acid solutions, the amino groups of chitosan are much easier to be protonated and they adsorb the dye anions strongly by electrostatic attraction. Further, chitosan forms gel when it is subjected to pH below 6. To obtain more rigid beads, the ionic cross-linker sodium tripolyphosphate (TPP) can be used [21]. Recently, adsorption techniques using chitosan based composites have been developed to adsorb dyes as an alternative to conventional wastewater treatment processes [22], [23].

The present work deals with the preparation and characterization of fungal chitosan nanoparticles from Cunninghamella echinulata (Thaxter) Thaxter and its application on the adsorption and determination of adsorption isotherms with various dyes such as Remazol Brilliant Blue (RBB), Methyl Orange (MO), Disperse Red 13 (DR), Napthol Blue Black (NBB) and Chicago Sky Blue 6 B (CSB) dye (Fig. 1).

Section snippets

Derivation of fungal chitosan

Chitosan was derived from fungus Cunninghamella echinulata (Thaxter) Thaxter [24] by alkali insoluble method. The details of the fungal chitosan isolates are mentioned in Table 1. The derived chitosan was freeze dried (Flexi-Dry MP) and stored at −20 °C.

Preparation of chitosan nanoparticles (FCI NPs)

The chitosan NPs were prepared by ionic gelation according to the method of Hu and coworkers [25]. Two milligrams of six different FCI (FCI-1 to FCI-6) were dissolved in 1 mL of 0.5% acetic acid. The solution was made up to 37.5 mL and a quantified

Results and discussions

Azo and anthraquinone colorants are the two major classes of synthetic dyes and pigments representing about 90% of all organic colorants. It is significant to note that dye molecules have diverse and complex structures, and their adsorption behaviour is directly related to the chemical structure, the dimensions of the dye organic chains, and the number and positioning of the functional groups of the dyes; these are important factors influencing adsorption. However, adsorption is affected by the

Conclusion

Fungal chitosan nanoparticles (FCI NPs) prepared by ionic gelation method using TPP showed that FCI-1 was nearly spherical in shape with average particle size ranging from 7 − 30 nm. HRTEM observations showed that FCI-1 NPs were stable for a period of 18 months at 4 °C. FCI-1 NPs and FCI-1 were subjected for the determination of adsorption isotherms of various dyes; among them RBB followed Langmuir isotherm. It is suggested that FCI-1 NPs may be used as adsorbents to treat commercial dye

Declaration for conflict of interest

This article does not contain any studies with human participants or animals performed by any of the authors.

Acknowledgements

The authors thank the University Grants Commission (UGC), New Delhi, India for providing fellowship. The authors are grateful to National Centre for Nanoscience and Technology, University of Madras for providing electron microscopy facilities. The authors acknowledge the support by Dr P. Pandikumar for proofreading the manuscript. Thank you for your consideration of this manuscript.

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