Composites of Quasi-Colloidal Layered Double Hydroxide Nanoparticles and Agarose Hydrogels for Chromate Removal.

Min-Kyu Kim,Gyeong-Hyeon Gwak,Jae-Min Oh

doi:10.3390/nano6020025

Abstract

Composite hydrogels were prepared that consisted of quasi-colloidal layered double hydroxide (LDH) nanoparticles and agarose via the electrophoretic method, starting from three different agarose concentrations of 0.5, 1, and 2 wt/v%. The composite hydrogel was identified to have a uniform distribution of LDH nanoparticles in agarose matrix. Microscopic studies revealed that the composite hydrogel had a homogeneous quasi-colloidal state of LDHs, while the simple mixture of LDH powder and agarose hydrogels did not. It was determined that agarose concentration of the starting hydrogel did not significantly influence the amount of LDH that developed in the composite. The chromate scavenging efficiency of the composite hydrogel and corresponding agarose or mixture hydrogel was evaluated with respect to time, and chromate concentration. In general, the composite hydrogels exhibited much higher chromate removal efficacy compared with agarose or mixture hydrogels. Through estimating chromate adsorption by LDH moiety in the composite or mixture hydrogel, it was suggested that the agarose component facilitated the stability and dispersibility of the quasi-colloidal state of LDH nanoparticles in the composite resulting in high adsorption efficacy. From Freundlich isotherm adsorption fitting, composites were determined to possess beneficial cooperative adsorption behavior with a high adsorption coefficient.

Highlights

Layered double hydroxides (LDHs) are a family of two-dimensional layered structures and are known to have a high anionic removal property due to its strong positive surface charge and exchangeable interlayer anions [1]
We could conclude that LDH nanoparticles existed in a colloid-like state being entrapped by the agarose moiety
It was revealed that LDH nanoparticles inside the hydrogel were homogeneously distributed with proper inter-particle distance, while the LDH-agarose mixture exhibited agglomeration of the LDH nanoparticles

Summary

Introduction

Layered double hydroxides (LDHs) are a family of two-dimensional layered structures and are known to have a high anionic removal property due to its strong positive surface charge and exchangeable interlayer anions [1]. In these instances, delaminated LDHs suspended in water were mixed with a hot agarose solution and cooled down to obtain a monolith This composite system was reported to show high removal efficiency for several anions such as SO4 2 ́ , Iand HPO4 2 ́ , while maintaining the possibility of easy collection after water treatment. Another example of a monolith containing LDH is reported by Tokudome et al They prepared an LDH-based monolith having interconnected hierarchical channels through a sol-gel process utilizing poly (ethylene oxide) and polypropylene oxide [12]. We examined the effect of agarose concentration in the starting hydrogel on the amount of electrophoretically-generated LDH, quasi-colloidal state of LDH nanoparticles, and chromate scavenging ability of the composites

Characterization of Electrophoretically Prepared LDH-Agarose Composites

Quantification of LDH in Composites

Chemicals

Identification of LDH in Composites through Reconstruction

Characterization

Conclusions