The use of microwave irradiation for preparation and fast-acting regeneration of magnetic biochars

Abstract

The application of microwave irradiation for rapid synthesis of magnetic biochar from agricultural waste with the subsequent modification of carbon matrix by magnetic nanoparticles was performed. The magnetic biochar was characterized by 57Fe Mössbauer spectroscopy, X-ray diffraction, a low-temperature nitrogen adsorption method, and electron microscopy. Except of magnetic properties, modification of biochar brings surface texture increase (SBET = 21.1 m2/g for char precursor versus 139.1 m2/g for magnetic biochar), and therefore better adsorption properties. The magnetic biochar was tested as an adsorbent of As5+ oxyanion and methylene blue (MB) to study the sorption mechanism and regeneration process. Magnetic biochar is the excellent adsorbent of arsenic (Qm = 24.9 mg/g; pH = 3.8). In the regeneration procedure, fast-acting microwave irradiation (10 s) significantly increases the value of the As5+ desorption rate constant as well as the initial desorption rate. The adsorption of MB on the magnetic biochar (Qm = 55.0 mg/g; pH = 10.2) was realized to study microwave-induced thermal regeneration. After short microwave treatment (30 s), a degradation of MB was observed (no absorption in the UV/VIS spectrum), whereas six degradation products were detected (HPLC/ESI-MS) and proposed formulas were revealed. Longer irradiation (60 s) caused total degradation of MB.