Activation of poplar and spirulina with H3PO4: Marked influence of biological structures of the biomasses on evolution structure of activated carbon

Abstract

Terrestrial and aquatic biomasses can theoretically be used as feedstocks for producing activated carbon (AC). However, their differences in composition and biological structure would affect pore characteristics of resulting AC. In this work, activation of poplar and spirulina with H3PO4 at medium to high temperatures (400, 550 and 700 °C) was conducted, which was followed by detailed characterization of the produced AC. The results showed that the presence or absence of sugary structures in poplar and spirulina made marked difference in evolution of pore structures of AC. The oligomers derived from cellulose/hemicellulose in poplar crosslinked with phosphates via esterification/polycondensation and further aromatized with temperature. This turned H3PO4-derivatives into skeleton of the poplar-derived AC, which served as the base for creating the AC obtained at 400 °C with highest specific surface area (1380.9 m2g−1) and capability for adsorption of tetracycline (68.8 mg/g). In comparison, low content of carbohydrate together with thermal melting and agglomeration of proteins/lipids in spirulina produced the AC with sponge-like morphology and maximum specific surface area of only 157.1 m2g−1. H3PO4 efficiently catalyzed conversion of -OH and CO in sugary structures of poplar, forming stable CO bonds, which, however, did not work in activation of spirulina.