Abstract
This study focused on a comparison of the adsorption properties of graphene oxide (GO) and its composites that were prepared via cross-linking with chitosan (CTS) or Al3+ species, respectively. Comparative material characterization was achieved by several complementary methods: SEM, NMR spectroscopy, zeta-potential, dye-based adsorption, and gas adsorption at equilibrium and dynamic conditions. SEM, solids NMR, and zeta-potential results provided supporting evidence for cross-linking between GO and the respective cross-linker units. The zeta-potential of GO composites decreased upon cross-linking due to electrostatic interactions and charge neutralization. Equilibrium and kinetic adsorption profiles of the GO composites with methylene blue (MB) in aqueous media revealed superior uptake over pristine GO. The monolayer adsorption capacity (mg g−1) of MB are listed in descending order for each material: GO–CTS (408.6) > GO–Al (351.4) > GO (267.1). The gas adsorption results showed parallel trends, where the surface area and pore structure of the composites exceeded that for GO due to pillaring effects upon cross-linking. The green strategy reported herein for the preparation of tunable GO-based composites revealed versatile adsorption properties for diverse heterogeneous adsorption processes.
Highlights
Graphene oxide (GO) prepared from graphite is a promising material for large industrial scale fabrication of graphene [1,2,3]
Graphene oxide (GO) materials were prepared by cross-linking graphene oxide (GO) with CTS and Al3+ ions, respectively
The GO sorbent materials were characterized by several complementary methods, such as solid-state 13C and 27Al NMR spectroscopy and zeta potential results
Summary
Graphene oxide (GO) prepared from graphite is a promising material for large industrial scale fabrication of graphene [1,2,3]. The adsorption performance of modified GO sheets is promising, the uptake properties of GO sheets is not sufficient for large-scale practical applications because of the relatively low surface area (SA), porosity, and stability in aqueous media [14,15]. This can be attributed to the rearrangement of the graphitic structure of GO sheets after chemical modification via reduction and exfoliation treatments through chemical and thermal methods [14]. The limited interlayer sheet distance and low structural stability of layered GO limits its effective uptake properties toward target adsorbates in gas and aqueous media. The shrinkage of framework materials caused by inadequate support of the structure was estimated to render 50% of the accessible pore volume for adsorption-based applications [16]
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