Carbonization of Manchurian Nut Shell in the Synthesis of Microporous Carbon-based Adsorbents: An Electron Paramagnetic Resonance, Thermal Analysis and Nitrogen Adsorption Study

Abstract

Carbonization of Manchurian nut shells (MNSs) in argon medium at 400–700°C was studied by electron paramagnetic resonance (EPR) and thermal analysis. Thermal treatment of MNS leads to the formation of radicals stabilized in the solid matrix, the concentration of which decreases with an increase in temperature from 400 to 700°C. A simultaneous increase in EPR signals intensity of paramagnetic species in the structure of carbon materials is observed. Activation of carbonized MNS with CO₂ leads to the formation of microporous adsorbent. The texture of adsorbent depends on the concentration of radicals in the carbonization products: radical concentration of 4.2−4.7 × 10²⁰ spin/g leads to the formation of material with specific surface area (S_BET) of 760–800 m²/g, total pore volume (V_ads) of 0.32–0.34 cm³/g and micropore volume (V_micro) of 0.26–0.27 cm³/g; a decrease in radicals concentration to 0−4 × 10¹⁸ spin/g also reduces S_BET to 670–700 m²/g, V_ads to 0.28 cm³/g and V_micro to 0.24 cm³/g.