Abstract
Biochar is increasingly gaining attention due to multifunctional roles in soil amelioration, pollution mitigation and carbon sequestration. It is a significant challenge to compare the reported results from world-wide labs regarding the structure and sorption of biochars derived from various precursors under different pyrolytic conditions due to a lack of a simple linkage. By combining the published works on various biochars, we established a quantitative relationship between H/C atomic ratio and pyrolytic temperature (T), aromatic structure, and sorption properties for naphthalene and phenanthrene. A reverse sigmoid shape between T and the H/C ratio was observed, which was independent of the precursors of biochars, including the ash contents. Linear correlations of Freundlich parameters (N, log Kf) and sorption amount (log Qe, log QA) with H/C ratios were found. A rectangle-like model was proposed to predict the aromatic cluster sizes of biochars from their H/C ratios, and then a good structure-sorption relationship was derived. These quantitative relationships indicate that the H/C atomic ratio is a universal linkage to predict pyrolytic temperatures, aromatic cluster sizes, and sorption characteristics. This study would guide the global study of biochars toward being comparable, and then the development of the structure-sorption relationships will benefit the structural design and environmental application of biochars.
Highlights
Relationship can offer a potential way to solve the problem of comparison
An isotherm-separation method was used to quantitatively calculate the contribution of partition and adsorption[3]. These analysis further declared a transitional sorption mechanism from partition-dominant at low pyrolysis temperature to adsorption-dominant at high pyrolysis temperature for biochar[3], which was extensively confirmed by subsequent studies
The H/C atomic ratio generally decreased with heating temperature, which was consistent with the reported increasing aromaticity because H/C was an index of aromaticity[3,22]
Summary
Relationship can offer a potential way to solve the problem of comparison. Due to its heterogeneous nature, biochar structure was distinguished between non-carbonized matter and carbonized matter, which acted as a partition phase and adsorbent, respectively[3]. To achieve these quantitative relationship and make them more convincing and representative, we collected hundreds of published data from our previous works and others regarding different pyrolytic temperatures, various feedstocks and structural characteristics of biochars, and sorption properties of naphthalene and phenanthrene as model HOCs. According to Johannes Lehmann and Stephen Joseph’s suggestions, biochar as a commercial product is defined as “the product of heating biomass in the absence of or with limited air to above 250 °C, which is intended for use as a soil application or broader for environmental management”[40]. A quantitative relationship between the charring temperature (T) and the H/C atomic ratio, between H/C and aromatic cluster size, and between sorption properties and H/C was hopefully achieved
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