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CARBONLETT, vol. 26, no. 1, pp.31-42, 2018

DOI: DOI: http://dx.doi.org/10.5714/CL.2018.26.031

One-step microwave synthesis of magnetic biochars with sorption properties

Anton Zubrik1,♠ , Marek Matik1, Michal Lovás1, Katarína Štefušová1, Zuzana Danková1, Slavomír Hredzák1, Miroslava Václavíková1, František Bendek1, Jaroslav Briančin1, Libor Machala2, and Jiři Pechoušek2

Affiliation: 1Institute of Geotechnics, Slovak Academy of Sciences, Kosice 04001, Slovakia
2Department of Experimental Physics, Faculty of Science, Palacký University, Olomouc 771 46, Czech Republic

Abstract: Adsorption is one of the best methods for wastewater purification. The fact that water quality is continuously decreasing requires the development of novel, effective and cost available adsorbents. Herein, a simple procedure for the preparation of a magnetic adsorbent from agricultural waste biomass and ferrofluid has been introduced. Specifically, ferrofluid mixed with wheat straw was directly pyrolyzed either by microwave irradiation (900 W, 30 min) or by conventional heating (550°C, 90 min). Magnetic biochars were characterized by X-ray powder diffraction, Mossbauer spectroscopy, textural analysis and tested as adsorbents of As(V) oxyanion and cationic methylene blue, respectively. Results showed that microwave pyrolysis produced char with high adsorption capacity of As(V) (Qm= 25.6 mg g-1 at pH 4), whereas conventional pyrolysis was not so effective. In comparison to conventional pyrolysis, one-step microwave pyrolysis produced a material with expressive microporosity, having a nine times higher value of specific surface area as well as total pore volume. We assumed that sorption properties are also caused by several iron-bearing composites identified by Mossbauer spectroscopy ([super] paramagnetic Fe2O3, α-Fe, non-stoichiometric Fe3C, γ-Fe2O3, γ-Fe) transformed from nano-maghemite presented in the ferrofluid. Methylene blue was also more easily removed by magnetic biochar prepared by microwaves (Qm=144.9 mg g-1 at pH 10.9) compared to using conventional techniques.

Keyword: magnetic biochar, microwave pyrolysis, ferrofluid, adsorption, arsenic