Hydrothermal Synthesis of Biomass-Derived Magnetic Carbon Composites for Adsorption and Catalysis

Abstract

The synthesis of magnetic iron–carbon composites (Fe/C) from waste avocado seeds via hydrothermal carbonization (HTC) has been demonstrated for the first time. These materials are shown to be effective in adsorption and catalytic applications, with performances comparable to or higher than materials produced through conventional processing routes. Avocado seeds have been processed in high-temperature water (230 °C) at elevated pressure (30 bar at room temperature) in the presence of iron nitrate and iron sulfate, in a process mimicking natural coalification. Characterization of the synthesized material has been carried out by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES), Fourier-transform infrared spectroscopy (FT-IR), magnetometry, and through surface area measurements. The supported iron particles are observed to be predominately magnetite, with an oxidized hematite surface region. The presence of iron catalyzes the formation of an extended, ordered polymeric structure in the avocado seed-derived carbon. The magnetic Fe/C has been demonstrated as an adsorbent for environmental wastewater treatment using methylene blue and indigo carmine. Kinetic analysis suggests that the adsorbates are chemisorbed, with the positive surface charge of Fe/C being preferential for indigo carmine adsorption (49 mg g–1). Additionally, Fe/C has been evaluated as a heterogeneous catalyst for the hydroalkoxylation of phenylacetylene with ethylene glycol to 2-benzyl-1,3-dioxolane. Product yields of 45% are obtained, with 100% regioselectivity to the formed isomer. The solid catalyst has the advantages of being prepared from a waste material and of easy removal after reaction via magnetic separation. These developments provide opportunities to produce carbon-based materials for a variety of high-value applications, potentially also including energy storage and biopharmaceuticals, from a wide range of lignocellulosic biomass feedstocks.

Methylene Blue Dye Adsorption on Iron Oxide-Hydrochar Composite Synthesized via a Facile Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels’ Waste

“…G. Davies et al used avocado seeds to prepare hydrochar and iron oxidecarbon through hydrothermal carbonization. They applied the prepared samples in MB dye adsorption and found their maximum adsorption capacity to be about 246 mg/g and 25 mg/g, respectively [17]. In this work, iron oxide-hydrochar composite and iron oxideactivated hydrochar were synthesized through microwave hydrothermal carbonization treatment.…”

“…This method sometimes results in blocking the pores, and the magnetic materials can be leached out [9,16]. In the simultaneous way, the magnetic precursor is added to the hydrochar during the synthesis [17]. In this method, the magnetic material is not only on the hydrochar surface, but it is well-dispersed through the hydrochar [18,19].…”

Facile Synthesis and X-band Microwave Absorption Performance of Activated Carbon Materials from Palm Kernel Shell Waste

“…The biowaste can be converted into the high value-porous activated carbon with large speci c surface area that is commonly used for several kinds of applications such as adsorbent [16,17], catalyst [18,19], to energy storage systems [20][21][22][23]. Compared to commercial carbon materials, activated carbon-based biowaste can be synthesized by the facile process through hydrothermal [24,25], chemical activation [26-28], or pyrolysis carbonization [29][30][31]. Recently, activated carbon-based biowaste materials by facile preparation have been studied for microwave absorber application.…”

Walnut Shell Biowaste Valorization via HTC Process for the Removal of Some Emerging Pharmaceutical Pollutants from Aqueous Solutions

“…Some studies in the literature have presented different types of biowastes that have been converted through this process in HCs and further used as adsorbents, including agricultural waste (corn stalks and straws [ 26 ], sugarcane bagasse [ 27 ], pine needles [ 28 ], palm leaves [ 17 ]), fruit and vegetable waste (orange peels [ 29 ], rotten apples and grape bagasse [ 30 , 31 ], coconut shells [ 32 ], avocado seeds [ 33 ], rice husk [ 34 ]), municipal and animal waste (sewage sludge [ 35 ], cardboard and paper sludge, horse manure [ 34 ]), and coffee husks [ 36 ]. The HCs were used in water decontamination applications for both organic pollutants such as dyes, including methylene blue (MB) [ 27 , 37 , 38 ], Congo red (CR) [ 39 , 40 ], and crystal violet (CV) [ 41 ]; pharmaceuticals, including triclosan (TCS) [ 34 ], paracetamol (PRM) [ 42 ], diclofenac (DCF), and ibuprofen (IBP) [ 43 ]; and inorganic pollutants, such as heavy metals (Pb 2+ [ 13 , 17 ], Cu 2+ [ 35 , 44 ], PO 4 3− [ 45 ]).…”