Competitive interactions of NH3 and toluene with biochar modified by pre- and post-treatments of H3PO4 in dual adsorption systems

Abstract

Biochar modified by H3PO4 treatment can be used to purify malodorous gases during bio-drying of sludge, but the current understanding of multi-component adsorption of malodorous gases through biochar is limited. This study examined the adsorption mechanism of mixed malodorous gases including toluene and ammonia (NH3) on two kinds of biochar modified via H3PO4 pretreatment before and after pyrolysis. The biochar obtained by H3PO4 pretreatment of biomass before pyrolysis (C550) preferred to adsorb NH3 whether in the single or the dual system. In contrast, the biochar obtained by H3PO4 reprocessing after pyrolysis of biomass (C350-550) tended to adsorb toluene in the dual system but was more efficient in absorbing NH3 in the single system. The pseudo-second-order kinetic model indicated the synergistic adsorption between NH3 and toluene for all biochar samples. In-situ DRIFTS of C350-550 during adsorption demonstrated the formation of amino functional groups caused by NH3 chemical adsorption with -OH (or -COOH) in the dual system. These increases in basic groups on C350-550 could enhance the surface zero potential point of C350-550, thereby improving the non-polarity of C350-550 and benefit the adsorption of weak polar toluene.