Preparation of Macroporous Chitosan Using NaCl as Porogen and Its Application onto Methyl Orange Adsorption

By : Baiq Octaviana D.A.

Introduction 

Dye agent is chemical which is used in industrial sectors, such as printing, textile, plastic, and synthetic dye. Environmental pollution caused by dye agent waste disposal is able to hamper photosythesis process, disturb organism growth or water ecosystems, and poison human [1]. Among several dye agents for textile industry, methyl orange which is anionic orange powder dye has molecule size 1,58 x 0,65 x 0,26 nm [2]. Methyl orange that contains azo group (N = N) is not poisonous but it is supposed to cause an allergy and hypersensitivity, so that it must be eradicated from environment [3].

Adsorption method is generally used as waste treatment, and it is still being developed. Adsorption method is simple and cheap. The adsoption process requires substance which can bond some molecules to the surface, if it has macropore form it will be more effective [4]. Macropore is solid form substance which has pore size more than 50 nm. Its applications are as catalytic substance, catalytic support, and adsorbent [5].     

Subtances which can be used as porous material generally has a large molecular mass and characteristics as inorganic or organic material, such as polypropylene, poly(vinyl alcohol), zeolit, activated carbon, and chitosan [6]. Chitosan that is cationic biopolimer is derivative compound of deacetylation reaction. Chitosan can be used as macropore material and biomedical. It has good physical and chemical characteristics : non poisonous, antibacterial, biodegradable, and safe for environment. It can be process for membrane, nanoparticle, micro-particle, gel, and nanofiber [7]. Chitosan as a nature polycationic with huge number of molecular weight exerted great amount of hydroxyl and amine groups in that long chain structure, and it have great adsorption prosperity toward macromolecules [8].

Macropore chitosan can be made by adding porogen which have functions to control the pore size of the membrane based on their particle size [9]. Some of materials as a porogen have inert properties, organic solvent, and salt compound. Those materials are silica, polyethylene glycol, glucose, CaCO₃, and NaCl [10]. The porogen infirmity in the application of macroporous materials are low in selectivity and resistance. Cross-linking agent is used  to increase chemical stability from the macroporous base material such as genipin, epichlorohydrin, and etilene glycol diglycidil ether (EGDE) [7].

In this study, NaCl (cooking salt) particles were used as porogen, and epichlorohydrin was used as cross-linker to prepare macroporous chitosan membrane compared with pure chitosan as control. The prepared chitosan membranes were used to remove methyl orange dye. The sorption efficiency was also investigated. 

Result and Discussion

In this study, the prepared MC membran using acidic solvent due to ability of membran whereas water-insoluble but soluble in organic solvent such as acetic acid. Those affected chitosan stability. Therefore, the cross-linking agent necessary for increasing chemical stability of dissolved chitosan from acidic medium. Crosslinking agent were used in ratio of chitosan and epichlorohydrin (1:20). Then, adding inorganic porogen NaCl (5, 10,and 15 g) to form chitosan membrane pores were used to determine % methyl orange adsorbed and amount of methyl orange adsorption (mg/g). The water evaporated with dried of macroporous chitosan at 70 ^oC. The membrane was washed several time with deionized water to remove NaCl to form template (Cl^- free). The result of the MC membrane shows in Fig.1.

The scanning electron micrograph (Fig.2.) show that the surface area of membrane was  little less uniformly according to the adding dosage of  NaCl. The different characteristic of MC show higher pores size than CT. Adding NaCl as porogen caused MC pores size increased in spite of the pores was not homogeneous.

Fig.1. Macroporous chitosan membrane. (a) MC/5 NaCl; (b) MC/10 NaCl; (c) MC/15 NaCl; (d) CT 

Fig.2.  Scanning Electron Microscopy (SEM) analysis. (a) MC/15 NaCl; (b) CT

The optimum pH in this study was pH 3 due to the great amount of  hydrogen atom  H⁺ in the solution  under acidic conditions. MC adsorption mechanism toward MO was shown [38]:

R – SO₃Na + H₂O → R-SO₃^- + Na⁺ .......       (1)

R-NH₃⁺ + R-SO₃^- → RNH₃⁺ O₃SR .........      (2)

In aqueous solution, the reactive dye was dissolved and the sulfonate group (R – SO₃Na) of the reactive dye was dissociated and converted to ionic dye ions. The adsorption process then proceeded due to the electrostatic interaction between these two counter-ions. Therefore, the effect of pH may be an important factor on the dye-binding capacity of MC. The effect of optimum contact time in adsorption capacity of MC obtained 92.6% at 180 min, and possessed a loading half-time (t_1/2) with adsorption amount capacity 4.53 mg/g at 14 min.

Conclusion

 

In this study, the chitosan membranes prepared by using NaCl particles as porogen exhibited excellent sorption capacity. The optimum pH, and contact time influenced the methyl orange sorption by macroporous chitosan. Methyl orange adsorption exerted pH 3 and 18 min for optimum contact time with adsorption rate constant 0.0531 min^-1. The amount of porogen are not significantly affected toward macroporous chitosan adsorption ability in methyl orange.The amount of adsorption macroporous chitosan with porogen composition 5; 10; 15 g were continued by 9,36; 9,29; and 9,40.

 

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