Relationship between biochars' porosity and adsorption of three neutral herbicides from water.

The porous biochars have exhibited good adsorption to many organic pollutants, but the relationship between biochars' porosity and their adsorption capacity is not clear at the moment. In this work, six biochars were produced from different feedstocks and under different pyrolysis conditions, and used for adsorption of three neutral herbicides from water. The results demonstrated that the adsorption capacity was dominated by the mesopore (1.7-50 nm) area of biochars, instead of their total surface area, according to the analysis of surface area-normalized adsorption data with both Langmuir model and a mixed adsorption and partition model. The results implied the inaccessibility of most micropores in biochars to the organic molecules with nano-scale molecular dimension, and alkalis in feedstock and an oxygen-containing atmosphere in heat treatment for producing biochars would favor the development of mesopores.