Nanoporous Carbon Magnetic Hybrid Derived from Waterlock Polymers and Its Application for Hexavalent Chromium Removal from Aqueous Solution

Georgios Asimakopoulos,Apostolos Avgeropoulos,Dimitrios Moschovas,Michael A Karakassides,Angeliki Karakassides,Christina Gioti,Maria Baikousi,Athanasios B Bourlinos,Constantinos E Salmas,Alexios P Douvalis

doi:10.3390/c7040069

Abstract

Sodium polyacrylate is the superabsorbent waterlock polymer used in disposable diapers, which are the third largest single consumer item in landfills. As diapers are difficult to recycle, their use produces an incredible amount of environmental waste. In the present article, we present a reliable and facile approach to transform sodium polyacrylate, the main constitute in the used diapers, in a carbon-based magnetic sorbent material, capable for use in environmental applications. A nanoporous carbon magnetic hybrid material was prepared by reacting NaPA with iron acetate species under chemical activation conditions. Analysis of the characterization results revealed, the creation of a nanoporous structure, with high specific surface area value (SgBET = 611 m2/g), along with the formation of nanosized zero valent iron nanoparticles and iron carbide (Fe3C), inside the carbon pore system. 57Fe Mössbauer spectroscopy verified also the existence of these two main iron-bearing phases, as well as additional minor magnetic phases, such as Fe3O4 and γ-Fe2O3. Vibrating sample magnetometry (VSM) measurements of the obtained hybrid confirmed its ferromagnetic/ferrimagnetic behavior. The hybrid material demonstrated a rapid sorption of Cr(VI) ions (adsorption capacity: 90 mg/g, 24 h, pH = 3). The results showed highly pH-dependent sorption efficiency of the hybrids, whereas a pseudo-second-order kinetic model described their kinetics.

Highlights

A porous carbon magnetic hybrid (NaPA@MAC) comprised of magnetic iron species such as Fe0, Fe3 C, magnetite and/or maghemite nanoparticles immobilized onto a porous carbon has been prepared, characterized, and tested for Cr(VI) treatment
The porous carbon phase was derived from the pyrolysis of sodium polyacrylate, a superabsorbent polymer used in disposable diapers
The development of nanoparticles was based on the affinity of acetic acid vapors to react with the dispersed iron cations in the supporting phase to first form iron acetate precursor species which further produce the magnetic nanoparticles upon pyrolysis

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Superabsorbents (SAs) are defined as the materials which can absorb and hold large quantities of liquids, in comparison with their dry weight [1,2,3]. The most well-known material among them, is the sodium polyacrylate (NaPA), a super absorbent polymer (SAP), which structure is composed of very long carbon chains bonded with sodium atoms in repeating units, with the chemical formula of –CH2 –CH(COONa). When sodium polyacrylate is exposed to water, the higher concentration water molecules outside the polymer, attract the polar water molecules inside the polymer chains, via osmosis [4].

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Results

Conclusion