Sustainable Thermochemical Single-Step Process To Obtain Magnetic Activated Carbons from Chestnut Industrial Wastes

Abstract

A novel thermochemical process based on a single step was optimized to obtain magnetic activated carbons from an industrial biomass waste. Anhydrous iron chloride was used as an activating agent and mixed directly with the chestnut shell waste. The effect of the activation temperature (220–800 °C) on the chemical, morphological, textural, and magnetic properties of the materials was studied. The results demonstrated the presence of different iron compounds depending on the activation temperature set as well as their influence on morphological and textural development of the magnetic activated carbons (BET specific surface area, S BET, up to 568 m2 g–1, total pore volume, V TOT, up to 0.294 cm3 g–1 vs 1 m2 g–1 and 0.007 cm3 g–1, respectively, for the raw biomass waste). The techniques employed, especially Mössbauer spectroscopy, showed relative contributions of the different iron compounds (magnetite, maghemite, metallic iron, and so on) in the materials. The higher activation temperature (800 °C) favored the formation of metal Fe and iron carbide. Additionally, the magnetic properties measured by vibrating sample magnetometry confirmed the coexistence of different ferromagnetic phases with the remanent magnetization, M R, (up to 3.88 emu/g) and coercivity, H c, (up to 140 Oe), being larger as the activation temperature increases. A higher activation temperature favored the development and evolution toward other iron compounds, while at low temperature, 220 °C, the presence of these compounds were null, and their behavior resembled the results obtained for the original biomass waste.

Review on Activated Carbons by Chemical Activation with FeCl3

“…The increase of the activation temperature produced activated carbons with more developed porosity. In this sense, Rodríguez-Sánchez et al [69] observed an increase of the total surface area with activation temperatures in the range of 220 to 800 • C when activating chestnut industrial wastes. However, the use of very high activation temperatures resulted in a lower porosity, as indicated by the lower amount of N 2 adsorbed (mainly in the micropore range, P/P o < 0.4) when increasing the activation temperature from 800 up to 1000 • C ( Figure 4B).…”

“…Fu et al [65] prepared an activated carbon from biomass after washing with a 0.1-M solution of HCl and with a pH PZC of 5.70. The activation of chestnut waste with FeCl 3 at different activation temperatures yielded carbons with surface pH values between 2.3 and 5.2 after washing with distilled water [69]. Our research group synthesized an activated carbon from lignin by FeCl 3 activation using microwave irradiation and a washing step with a 0.1-M aqueous solution of HCl with a pH PZC of 5.0 (results not published).…”

“…Some studies have analyzed the iron species by Mössbauer spectroscopy more deeply. Figure 9 represents the room-temperature Mössbauer spectra of activated carbons obtained by chemical activation with FeCl 3 of chestnut industrial waste at different activation temperatures [69]. At the lowest activation temperature, 220 • C, very low absorption is observed because of the low iron concentration.…”

“…Room-temperature Mössbauer spectra of activated carbons at different activation temperatures (a) 220, (b) 400, (c) 500, (d) 600, (e) 700, and (f) 800 • C (reprinted from[69] with the permission of the ACS, 2019).…”

Facile One-Step Pyrolysis of ZnO/Biochar Nanocomposite for Highly Efficient Removal of Methylene Blue Dye from Aqueous Solution

“…This finding could be explained by the formation of small ZnO nanoparticles on the biochar surface and within the porous structure of the ZBCs. These particles could block the pores and decrease the amount of nitrogen adsorbed, BET surface area, and porosity …”