Sorption of Pure N₂O to Biochars and Other Organic and Inorganic Materials under Anhydrous Conditions

Abstract

Suppression of nitrous oxide (N2O) emissions from soil is commonly observed after amendment with biochar. The mechanisms accounting for this suppression are not yet understood. One possible contributing mechanism is N2O sorption to biochar. The sorption of N2O and carbon dioxide (CO2) to four biochars was measured in an anhydrous system with pure N2O. The biochar data were compared to those for two activated carbons and other components potentially present in soils-uncharred pine wood and peat-and five inorganic metal oxides with variable surface areas. Langmuir maximum sorption capacities (Qmax) for N2O on the pine wood biochars (generated between 250 and 500 °C) and activated carbons were 17-73 cm(3) g(-1) at 20 °C (median 51 cm(3) g(-1)), with Langmuir affinities (b) of 2-5 atm(-1) (median 3.4 atm(-1)). Both Qmax and b of the charred materials were substantially higher than those for peat, uncharred wood, and metal oxides [Qmax 1-34 cm(3) g(-1) (median 7 cm(3) g(-1)); b 0.4-1.7 atm(-1) (median 0.7 atm(-1))]. This indicates that biochar can bind N2O more strongly than both mineral and organic soil materials. Qmax and b for CO2 were comparable to those for N2O. Modeled sorption coefficients obtained with an independent polyparameter-linear free-energy relationship matched measured data within a factor 2 for mineral surfaces but underestimated by a factor of 5-24 for biochar and carbonaceous surfaces. Isosteric enthalpies of sorption of N2O were mostly between -20 and -30 kJ mol(-1), slightly more exothermic than enthalpies of condensation (-16.1 kJ mol(-1)). Qmax of N2O on biochar (50000-130000 μg g(-1) biochar at 20 °C) exceeded the N2O emission suppressions observed in the literature (range 0.5-960 μg g(-1) biochar; median 16 μg g(-1)) by several orders of magnitude. Thus, the hypothesis could not be falsified that sorption of N2O to biochar is a mechanism of N2O emission suppression.

Microwave pyrolysis of rice straw to produce biochar as an adsorbent for CO2 capture

“…The CO 2 adsorption capacity of the biochar presented in this study was very close to that reported in the literature [59]. However, it should be noted that the biochar in the literature was prepared by a two-stage slow pyrolysis process (1e5 min exposure to 700 C followed by a 10e60 min exposure to 200À500 C) [59], and the biochar in this study was prepared at approximately 300 C for 20 min only.…”

“…However, it should be noted that the biochar in the literature was prepared by a two-stage slow pyrolysis process (1e5 min exposure to 700 C followed by a 10e60 min exposure to 200À500 C) [59], and the biochar in this study was prepared at approximately 300 C for 20 min only. Besides, there was another biochar whose CO 2 adsorption capacity was lower than that of present study, and it was produced by carbonization at 600 C [60].…”

Biochar Impacts Soil Microbial Community Composition and Nitrogen Cycling in an Acidic Soil Planted with Rape

“…Although the ways to decrease nitrification N 2 O have not been well characterized, it has been shown that the decreases of soil N 2 O emissions were often accompanied by lower nitrification rates. 16 Several hypotheses have been proposed for N 2 O decreases by biochar, including: (i) biochar reduces levels of denitrification via improving soil aeration; 17 (ii) biochar increases the adsorption of NO 3 − , thus decreasing substrate availability for denitrification; 18 (iii) biochar increases soil pH therefore driving denitrification thorough to N 2 ; 18 (iv) biochar sorbs N 2 O; 19 and (v) biochar contains ethylene which could inhibit nitrification and thus the formation of NO 3 − and N 2 O. 20 More studies are needed to clarify the effect of biochar, especially when it is used as a soil amendment in agricultural production.…”

Gas entrapment and microbial N2O reduction reduce N2O emissions from a biochar-amended sandy clay loam soil

“…by a pH increase) leading to a decreased N 2 O/(N 2 O + N 2 ) emission ratio11151640, or (iii) the contribution of abiotic processes such as sorption of N 2 O onto biochar particles and abiotic reduction of N 2 O to N 2 by redox active compounds4142. However, systematic studies focusing on the underlying geochemical and microbial processes causing N 2 O emission mitigation are rare and the contributing mechanisms are not fully understood yet.…”