A facile and green strategy to synthesize N/P co-doped bio-porous carbon with high yield from fungi residue for efficient VOC adsorption

Abstract This paper reports a facile and green strategy using hydrothermal treatment coupled with (NH4)3PO4 activation of fungi residue to synthesize N/P co-doped porous carbon. (NH4)3PO4 has no corrosion effect on reactor and attains high carbon yield, ca. 64.5 wt%. Hydrothermal treatment, cross-linked action by (NH4)3PO4, and low-temperature pyrolysis contribute to high carbon yield. To evaluate the economy, another index Qfr (mg/g-fr) is proposed to express the adsorption capacity based on the dosage of original fungi residue. Comparing with H3PO4 and CO(NH2)2, (NH4)3PO4 activation exhibits the highest adsorption capacity of PhH (benzene). Accordingly, its Qfr has surpassed KOH activated carbon, ca. 84.2 > 31.4 mg/g-fr. The abundant surface functional groups of N/P (7.20 and 5.54 at.%) and mesopores-dominant hierarchical pore structure contribute to its excellent adsorption performance. DFT (density functional theory) calculations demonstrate that N/P co-doped porous carbon possesses the highest adsorption binding energy, ca. −1.07 eV. Next, four types of VOC compounds with different physicochemical properties are evaluated for adsorption, i.e., PhH (84.2 mg/g-fr), DCE (dichloroethane, 128.7 mg/g-fr), MeOH (methanol, 23.7 mg/g-fr) and MTHM (methyl mercaptan, 26.0 mg/g-fr). Multi components co-adsorption, adsorption thermodynamics, and recyclability analysis are also evaluated for industrial application. Competitive adsorption still exists but the total adsorption capacity is close to or slightly lower than sole adsorption capacity. After four cycles by low-temperature regeneration, the capacity of tri-component adsorption only decreases 28.0%. Economic analysis demonstrates that the cost of (NH4)3PO4 activation is obviously lower than KOH activation and even superior to commercial activated carbon. Above all, this paper successfully exploits new approach for renewable adsorbents synthesis with facile and green strategy.