Surface oxygenation of biochar through ozonization for dramatically enhancing cation exchange capacity

Abstract

Background: Biochar cation exchange capacity (CEC) is a key property that is central to biochar environmental applications including the retention of soil nutrients in soil amendment and removal of certain pollutants in water-filtration applications.Results: This study reports an innovative biochar-ozonization process that dramatically increases the CEC value of biochars by a factor of 2. The ozonized biochars also show great improvement on adsorption of methylene blue by as much as a factor of about 5. In this study, biochar samples treated with and without ozone were analyzed by means of pH and CEC assays, water field capacity measurement, elemental analysis, methylene blue adsorption, and Raman spectroscopy. Gaseous products' analyses were carried out using an online universal gas analyzer over the duration of ozone treatments, and temperature changes were monitored using a thermal imaging camera. The results demonstrate a doubling of CEC with a concomitantly large drop in pH of the ozonized biochar compared with the untreated sample, brought about by the creation of acidic oxygen-functional groups on biochar surface, which may represent a significant progress toward the viability of employing biochar as a soil amendment for sustainability on Earth. Conclusions:This biochar-ozonization process technology has the potential to effectively convert conventional biochars into surface-oxygenated products with dramatically higher CEC values.

Post-processing of biochars to enhance plant growth responses: a review and meta-analysis

“…An early paper by Xue et al (2012) found that H 2 O 2 treatment of hydrochar enhanced heavy metal sorption associated with O-containing functional groups; similar results have been obtained in other studies focused on toxic metals sorption by biochars (Zuo et al 2016;Wang and Liu 2018;Xia et al 2019). Beyond increases in surface oxidation, H 2 O 2 treatment can reduce biochar pH and increase specific surface area and CEC (Lee et al 2013;Huff and Lee 2016;Huff et al 2018), though decreases in CEC have also been reported in some cases (Vaughn et al 2017), as have reductions in BET surface area (Vaughn et al 2017). H 2 O 2 treatment also generally removes inorganic mineral components from the biochar matrix (Sizmur et al 2017), which is unlikely to be beneficial to plant growth.…”

Biochar Surface Oxygenation by Ozonization for Super High Cation Exchange Capacity

“…Ozone treatment resulted in a low pH within its slurry as reported in Table 1. We think that the process of ozonization results in the breakage of C=C double bonds on the biochar material (Huff et al 2018). 23 Following that breakage, there should be organic carbon fragments of biochar with carboxylic groups "Biochar− COOH" (Huff et al 2018).…”

“…We think that the process of ozonization results in the breakage of C=C double bonds on the biochar material (Huff et al 2018). 23 Following that breakage, there should be organic carbon fragments of biochar with carboxylic groups "Biochar− COOH" (Huff et al 2018). 23 In order to further test the efficiency of ozone treatment on our biochar and to verify the formation of those "Biochar-COOH" fragments, the filtrate of the wash of the biochar was collected before and after ozonization for dissolved organic carbon concentration measurement.…”

“…22 The expected half-lives drop precipitously to <100 years for an O/C ratio of ≥0.6. An ideally designed biochar for use as both a soil amendment and carbon sequestering agent would need to enhance the O/C ratio only on the surface of biochar, 23 giving a higher CEC, while still maintaining the poly aromaticity (preferably lower O/C ratio) of the biochar core to ensure long-term stability.…”

Influence of H₂O₂ Modification on the Adsorptive Properties of Birch-Derived Biochar

“…Respectively, B30%r-P biochar had the highest CEC (30.11 cmol/kg). For comparison, unmodified hydrochar [15] [33]. Results on CEC exceeded some other adsorbents, e.g., bio-resin from arecanut husk with CEC 4.64 cmol/kg [34], sulphurised AC with 5.02 cmol/kg [35], wheat straw BC and AC with 7.42 and 4.27, respectively [36].…”