Hydrothermally Reduced Graphene Hydrogel Intercalated with Divalent Ions for Dye Adsorption Studies

Alvin Lim Teik Zheng,Supakorn Boonyuen,Teruhisa Ohno,Yoshito Andou

doi:10.3390/pr9010169

Abstract

Fundamental studies involving divalent ion intercalated graphene-based hydrogel are still lacking in terms of their adsorption behavior towards dye pollutants. In this study, we prepared a self-assembled Mg2+ and Ca2+ intercalated reduced graphene hydrogel (rGH) using hydrothermal treatment to evaluate the intercalation impact on the adsorption capability towards cationic dyes, methylene blue and rhodamine B. The morphological, structural, thermal, and textural properties of the divalent ion intercalated reduced graphene hydrogels were studied using Fourier transform infrared spectrometer, thermogravimetric analysis, Raman spectroscopy, scanning electron microscope-energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area analysis, and X-ray diffraction. The increased adsorption capacity of the divalent ion intercalated reduced graphene-based hydrogels towards the dye molecules resulted from the increase in the specific surface area and pore volume due to the Mg2+ and Ca2+ bridging that formed spaces between the graphene sheets framework. Adsorption kinetics and the equilibrium adsorption isotherm were fitted by a pseudo-second-order alongside intraparticle diffusion kinetic models and Langmuir isotherm respectively. In addition, the divalent ion intercalated reduced graphene hydrogel showed good generation after three cycles of simultaneous adsorption.

Highlights

Water bodies contaminated with dye-containing effluent disposed from various industries such as textile and printing often contribute to massive environmental and health problems [1,2,3,4]
The addition of MgCl2 and CaCl2 into the Graphene oxide (GO) suspension led to the intercalation between the divalent atoms and the oxygen-containing functional groups occurring between the basal plane and edges; leading to a network of continuous bridging [44,45]
In order to probe the interaction with the divalent ions, UV-visible analysis was conducted on the GO suspension which is shown in Supplementary Figure S2

Summary

Introduction

Water bodies contaminated with dye-containing effluent disposed from various industries such as textile and printing often contribute to massive environmental and health problems [1,2,3,4]. Graphene possessed a honeycomb crystal lattice composing of hexagonally sp hybridized carbon atom with a thickness of equal to one atom diameter [13] This two-dimensional (2D) material has gained prominence among researchers due to its unique properties such as possessing high surface area (2600 m2 /g), intrinsic electron mobility (200,000 cm2 /Vs), Young’s Modulus (1 TPa), and high thermal conductivity (5000 W/mK) [14,15,16]. Reduced graphene-based hydrogels can act as a templating material for the inclusion/blending with small molecules, metal/metal oxide nanoparticles, polymer complex, etc. Ample studies have been conducted using graphene-based hydrogel as promising adsorbent material for wastewater dye remediation [26,27,28,29,30,31,32]. During the hydrothermal process, superheated water acts as strong electrolyte with high diffusion and dielectric constant; readily catalyzes bond cleavage of oxygen moieties present on the basal planes of the graphene sheets [39]

Methods

Results

Conclusion