es7b00647_si_001.pdf (1.02 MB)
Aging Induced Changes in Biochar’s Functionality and Adsorption Behavior for Phosphate and Ammonium
journal contribution
posted on 2017-06-20, 00:00 authored by Shamim Mia, Feike A. Dijkstra, Balwant SinghBiochar, a form of pyrogenic carbon,
can contribute to agricultural
and environmental sustainability by increasing soil reactivity. In
soils, biochar could change its role over time through alterations
in its surface chemistry. However, a mechanistic understanding of
the aging process and its role in ionic nutrient adsorption and supply
remain unclear. Here, we aged a wood biochar (550 °C) by chemical
oxidation with 5–15% H2O2 and investigated
the changes in surface chemistry and the adsorption behavior of ammonium
and phosphate. Oxidation changed the functionality of biochar with
the introduction of carboxylic and phenolic groups, a reduction of
oxonium groups and the transformation of pyridine to pyridone. After
oxidation, the adsorption of ammonium increased while phosphate adsorption
decreased. Ammonium adsorption capacity was nonlinearly related to
the biochar’s surface charge density (r2 = 0.94) while electrostatic repulsion and loss of positive
charge due to destruction of oxonium and pyridine, possibly caused
the reduced phosphate adsorption. However, the oxidized biochar substantially
adsorbed both ammonium and phosphate when biochar derived organic
matter (BDOM) was included. Our results suggest that aging of biochar
could reverse its capacity for the adsorption of cationic and anionic
species but the inclusion of BDOM could increase ionic nutrient and
contaminant retention.