Biochar Surface Oxygenation by Ozonization for Super High Cation Exchange Capacity

Abstract

Biochar cation exchange capacity (CEC) is a key property central to better retention of soil nutrients and reduction of fertilizer runoff. This paper reports a breakthrough process to improve biochar CEC value by a factor of nearly 10 through biochar surface oxygenation by ozonization. The CEC value of the untreated biochar was measured to be anywhere between 14 and 17 cmol/kg. A 90 min dry ozonization treatment resulted in an increased biochar CEC value of 109−152 cmol/kg. Simultaneously, the biochar ozonization process resulted in a reduction of biochar pH from 9.82 to as low as 3.07, indicating the formation of oxygen-functional groups including carboxylic acids on biochar surfaces. Using the technique of X-ray photoelectron spectroscopy (XPS), the formation of oxygen-functional groups including carboxylic acids on biochar surfaces have been observed at a nanometer molecular scale following the ozonization treatment. The molar O/C ratio (0.31:1) on ozonized biochar surface as analyzed by XPS was indeed significantly higher than that (0.16:1) of the control biochar surface. The molar O/C ratio from the elemental analysis data also showed an increase from the nonozonized sample (0.077:1) to the dry-ozonized sample (0.193:1). Fourier-transform infrared (FTIR) spectroscopy analysis also showed an increase in the content of oxygen-functional groups in the form of carbonyl groups on biochar surfaces upon ozonization, which can also produce certain amount of oxygenated biochar molecular fragments that may be solubilized by liquid water, potentially leading to greater effects upon application of biochar in soil.

Impacts of rice-husk biochar on soil microbial biomass and agronomic performances of tomato (Solanum lycopersicum L.)

“…The E.CEC of the soil, basic cations and micronutrient values were elevated after biochar application. This is important as biochar cation exchange capacity (CEC) is germane in helping soil to retain nutrients, reduce fertilizer runoff, and improve soil water retention 31 . The increase in CEC and other properties have to do with the level of minerals present in the biomass or feedstock 27 .…”

How biochar works, and when it doesn't: A review of mechanisms controlling soil and plant responses to biochar

“…Using methods considered suitable for biochar, CEC ranges from approximately 50 to 200 mmol kg −1 (Graber et al, 2017; Mitchell et al, 2013), and anion exchange capacity (AEC) is typically also less than 200 mmol kg −1 (Lawrinenko et al, 2017). As CEC of fresh biochar is relatively low compared with CEC of many soil components, applying biochar typically does not increase the soil CEC immediately (Kharel et al, 2019). However, the CEC and AEC of biochar increase over time as additional functional groups form on biochar surfaces (see Section 2.3), increasing its ability to sorb and retain cations and anions (Hagemann, Joseph, et al, 2017; Hagemann et al, 2017; Rechberger et al, 2017; de la Rosa et al, 2018; Wang et al, 2019).…”

Effect of Production Technique on Corncob Biochar Quality

“…CEC is an indicator of soil fertility, buffer capacity, and water holding capacity [29]. Biochar with a high CEC value is needed to improve soil quality.…”