Biomass chars have attracted interest as soil amendments in agriculture and environmental remediation and are formed by natural and anthropogenic fires. Air present during or after pyrolysis can have major effects on the physical-chemical properties of chars. Three air-oxidation (AO) processes were carried out on chars made from maple wood: concurrent-with-pyrolysis air oxidation (CPAO); post-pyrolysis hot air oxidation (PPAO); and accelerated ambient air oxidation (AAAO) either in warm water under an oxygen atmosphere or in dilute hydrogen peroxide solution, both meant to simulate long-term aging in the environment. Zeta potential measurements reveal that AO-treated chars generally are more negatively charged than the corresponding untreated char due to creation of acidic functionality. Naphthalene adsorption increased in proportion to PPAO temperature and O2 concentration by up to 15-fold. Naphthalene adsorption also increased dramatically by CPAO treatment in proportion to O2 concentration. Interestingly, AAAO treatments significantly decreased adsorption of naphthalene. Adsorption of paraquat, a dicationic herbicide, was enhanced by CPAO and especially by PPAO, but was only slightly enhanced by AAAO treatments. We hypothesize that PPAO and CPAO ream (enlarge) pores and while all AO treatments create oxygen functional groups on surfaces. The former appears to be most important for enhancing adsorption, even for cationic compounds. This research provides insights into the environmental effects of air oxidation and the design of biochars with greater adsorption affinity.

Effects of air-oxidation induced changes in biomass chars on their adsorption of contaminants

2019 Fall National Meeting

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