Nitrogen/phosphorus enriched biochar with enhanced porosity activated by guanidine phosphate for efficient passivation of Pb(II), Cu(II) and Cd(II)

Nitrogen/phosphorus enriched biochars with enhanced porosity were prepared through a one-step pyrolysis of bamboo sawdust activated by guanidine phosphate (GP). The thermal decomposition of GP released alkaline gas and hydrogen proton to create more micropores in biochar matrix which were extended to be mesopores further. Nitrogenous/phosphorous moieties of GP were introduced into biochars efficiently via cross-linking with the carbon skeleton. GP-activated biochar pyrolyzed at 450 °C exhibited enriched surface functional groups (11.3 at.% for N, 4.1 at.% for P), resulting in high sorption capacities for aquatic Pb(II) (166.2 mg/g), Cu(II) (81.7 mg/g), and Cd(II) (60.3 mg/g). Pb(II) was passivated fast with the formation of minerals including Pb 5 (PO 4 ) 3 OH and Pb 5 (PO 4 ) 3 Cl. Cu(II) was strongly coordinated with the N-containing species especially pyridinic N. Cd(II) was also captured efficiently due to the chemical complexation, cation exchange and cation-π bonds. GP-activated biochars could be well-recycling used to capture these heavy metals. Regarding these, the activation of biomass residuals could be an efficient approach to functionalize the surface of biochars with enhanced porosity, which is great benefiting for the immobilization of heavy metals from contaminated water.