Hierarchical Porous Chitosan Sponges as Robust and Recyclable Adsorbents for Anionic Dye Adsorption

Mei Wang,Jonghwan Suhr,Yifei Ma,Xuyuan Chen,Stephanie K Lee,Bumyong Yoon,Jae-Do Nam,Lijie Ci,Yan Sun,Sung Yong Hong,Long Chen

doi:10.1038/s41598-017-18302-0

Abstract

Biomass waste treatment and detrimental dye adsorption are two of the crucial environmental issues nowadays. In this study, we investigate to simultaneously resolve the aforementioned issues by synthesizing chitosan sponges as adsorbents toward rose bengal (RB) dye adsorption. Through a temperature-controlled freeze-casting process, robust and recyclable chitosan sponges are fabricated with hierarchical porosities resulted from the control of concentrations of chitosan solutions. Tested as the adsorbents for RB, to the best of our knowledge, the as-prepared chitosan sponge in this work reports the highest adsorption capacity of RB (601.5 mg/g) ever. The adsorption mechanism, isotherm, kinetics, and thermodynamics are comprehensively studied by employing statistical analysis. Importantly and desirably, the sponge type of chitosan adsorbents exceedingly facilitates the retrieving and elution of chitosan sponges for recyclable uses. Therefore, the chitosan sponge adsorbent is demonstrated to possess dramatically squeezable capability with durability for 10,000 cycles and recyclable adsorption for at least 10 cycles, which provides an efficient and economical way for both biomass treatment and water purification.

Highlights

With the desirable features of non-toxicity, biodegradability and a high concentration of amino groups, chitosan can offer advantages in adsorbing anionic dyes from the polluted water due to the cationic nature of chitosan derived from the -NH2 groups
Chitosan adsorbent has been fabricated into the powder-type to enlarge the specific surface area and enhance the adsorption capacity, while the powder-type chitosan adsorbent suffers from the retrieving difficulties[14]
The chitosan sponges are obtained after washing the residual acetic acid by a 1 M NaOH solution from the chitosan foams developed in the previous step

Summary

Introduction

With the desirable features of non-toxicity, biodegradability and a high concentration of amino groups, chitosan can offer advantages in adsorbing anionic dyes from the polluted water due to the cationic nature of chitosan derived from the -NH2 groups. Elution of dyes and reuse of the retrieved adsorbents still remain significant challenges for the use of the powder-type adsorbents. In this sense, a monolith type adsorbent is preferable in the dye adsorption, which is generally in a hydrogel, foam or membrane type[18,19], facilitating the retrievability of the adsorbent. Given that the issues and essential requirements for dye adsorbents, in this study, hierarchical porous chitosan sponges as adsorbents for adsorption of rose bengal (RB), a toxic anionic dye, are fabricated by a precisely controlled freeze-casting technique. Durable recyclability of the robust chitosan sponge adsorbents is confirmed

Methods

Results

Conclusion