Methylene blue removal by using pectin-based hydrogels extracted from dragon fruit peel waste using gamma and microwave radiation polymerization techniques

Abstract

This research aims to compare the ability of smart hydrogel in removing the methylene blue prepared by using two different radiation methods. The extracted pectin from the dragon fruit peel (Hylocereus polyrhizus) was used with acrylic acid (AA) to produce a polymerized hydrogel through gamma and microwave radiation. The optimum hydrogel swelling capacity was obtained by varying the dose of radiation, pectin to AA ratio and pH used. From the array of samples, the ideal hydrogel was obtained at pH 8 with a ratio of 2:3 (pectin: AA) using 10 kGy and 400 W radiated gamma and microwave respectively. The performance of both hydrogels namely as Pc/AA(G) (gamma) and Pc/AA(Mw) (microwave) were investigated using methylene blue (MB) adsorption studies. In this study, three variables were manipulated, pH and MB concentration and hydrogel mass in order to find the optimum condition for the adsorption. Results showed that 20 mg of Pc/AA(G) performed the highest MB removal which was about 45% of 20 mg/L MB at pH 8. While 30 mg of Pc/AA(Mw) able to remove up to 35% of 20 mg/L MB at the same pH condition. To describe the adsorption mechanism, both kinetic models pseudo-first-order, pseudo-second-order were employed. The results from kinetic data showed that it fitted the pseudo-first-order as compared to pseudo-second-order model equation. This study provides alternative of green, facile and affective biomaterial for dye absorbents that readily available.

Keywords:

• Pectin
• hydrogel
• gamma radiation
• microwave radiation
• methylene blue

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported, in part, by research grants DLP-2014-019, FRGS/1/2014/ST01/UKM/03/1, GUP-2014-079, and DIP-2014-016 given by Universiti Kebangsaan Malaysia and the Ministry of Education.