Desorption Behavior and Mechanism of NH4+ by Biochar as

Jun 1, 2016 - College of Food Sciences, South China University of Technology, 381 ... the pyrolysis of agricultural and forestal residues in the south...
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Sorption/Desorption Behavior and Mechanism of NH4+ by Biochar as a Nitrogen Fertilizer Sustained-Release Material Yanxue Cai,† Hejinyan Qi,‡ Yujia Liu,§ and Xiaowei He*,† †

College of Food Sciences, South China University of Technology, 381 Wushan Road, Guangzhou 510640, China School of Materials Science and Engineering, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China § Department of Applied Chemistry, South China Agricultural University, 483 Wushan Road, Guangzhou 510642, China ‡

S Supporting Information *

ABSTRACT: Biochar, the pyrolysis product of biomass material with limited oxygen, has the potential to increase crop production and sustained-release fertilizer, but the understanding of the reason for improving soil fertility is insufficient, especially the behavior and mechanism of ammonium sulfate. In this study, the sorption/desorption effect of NH4+ by biochar deriving from common agricultural wastes under different preparation temperatures from 200 to 500 °C was studied and its mechanism was discussed. The results showed that biochar displayed excellent retention ability in holding NH4+ above 90% after 21 days under 200 °C preparation temperature, and it can be deduced that the oxygen functional groups, such as carboxyl and keto group, played the primary role in adsorbing NH4+ due to hydrogen bonding and electrostatic interaction. The sorption/ desorption effect and mechanism were studied for providing an optional way to dispose of agricultural residues into biochar as a nitrogen fertilizer sustained-release material under suitable preparation temperature. KEYWORDS: biochar, NH4+, sorption, desorption, interaction

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INTRODUCTION Biochar is a highly aromatic and infusible solid matter charred from biomass by pyrolysis under the condition of limited oxygen, which attracts wide attention in several research fields such as agriculture, the environment, and energy.1 The understanding of biochar arises from the fertile black soil with rich charcoal over the Amazon. Scientific investigations of biochar have found a booming trend in the past decade with several prominent benefits such as improving water and nutrient holding capacity, promoting soil microbes and activity,2 and the buildup of soil organic carbon.3 Biochar also is considered as a useful carbon sink for atmospheric CO2 sequestration and thereby contributes to the mitigation of global climate changes.4,5 Recent studies are also followed with interest in environmental remediation by absorption for pollutants including heavy-metal and organic micromolecular.6,7 In addition, studies are paying more attention to the effects of increasing crop production like maize, wheat, and beans.8−10 The biochar could apply to sustaining release and reducing loss of fertilizer, such as urea,11,12 phosphate,13 and potash fertilizer,14 due to its excellent sorption capacity.15 These functions are borne by biochar surface properties, for instance, a high surface area, high pH, and surface charges.16 However, the explanation of sorption mechanism is still a matter of debate. Some literature reports that the sorption and desorption of NO3− is significantly influenced not only by pH value but also by negative charged ions (PO43− and SO42−) in the solution.17 Furthermore, for the cations, it is suggested that biochars with high surface areas did not possess better NH4+ adsorption capacities,18 which means that surface area is not the most important factor influencing NH4+ adsorption. The improvement of NH4+ adsorption is potentially associated © XXXX American Chemical Society

with the existing acidic functional groups (phenolic OH and carboxyl CO).19 On this basis, we infer that understanding the NH4+ sorption/desorption behavior and mechanism is crucial for biochar application to soils as sustained-release material. In the present work, the process and influence of ammonium sulfate sorption were studied to understand the reason for increasing fertility. The biochar was derived from three crop residues, including corncob (Zea mays L.), pomelo peel (Citrus maxima Merr.), and banana stalk (Musa nana Lour.), which are common and high-yielding in tropical Asia. Furthermore, the relationship between physicochemical properties and sorption capacity was discussed by correlation analysis, which helps to explain the molecular interaction of NH4+ and biochar as a potential use for nitrogen fertilizer sustained-release material in agriculture.

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MATERIALS AND METHODS

Materials. The experimental samples were collected from common agricultural waste, including corncob (C), pomelo peel (P), and banana stalk (B). These samples were heated-air-dried at 80 °C for 12 h to remove the free water. Then, the biomasses were pyrolyzed in a tube furnace at four different temperatures (200 °C, 300 °C, 400 °C, and 500 °C, respectively) for 5 h under a nitrogen flow of 50 mL/min to limit the oxygen. The preparation process is outlined briefly in Figure S1. The products were cooled to room temperature under the condition of nitrogen gas for the following experiments. Sorption and Desorption Experiment. Twenty-five milligram biochar samples were dispersed into 4 mL of citrate buffer solution Received: January 10, 2016 Revised: April 29, 2016 Accepted: June 1, 2016

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DOI: 10.1021/acs.jafc.6b00109 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry (pH 7.0). The citrate buffer solution was prepared by 184 g of citric acid and 147.5 g of KOH dissolved in ultrapure water, respectively, followed by mixing two kinds of solution and adjusting the pH to 7.0 by NaOH. The ammonium sulfate solution was prepared by dissolving 100 mg of ammonium sulfate into 1000 mL of ultrapure water as nitrogen stock solution at the concentration of 100 mg/L, and then it was added into the biochar solution with certain volume to 5 mL. The final ammonium sulfate−biochar mixed solutions, with the same volume and different concentrations, were sealed and shaken at 27 °C in a shaking water bath at 80 rpm for 7 days until sorption equilibrium. The adsorptivity was determined by the Freundlich sorption isotherm equation as follows:20 Q e = KFCe1/ n

Statistical analyses were performed using the one-way analysis of variance (ANOVA) procedure by SPSS 17.0 software. The level of significance was set at 0.05.

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RESULTS AND DISCUSSION The Sorption and Desorption Effect of NH4+. According to the Freundlich model, the content of NH4+ within the solid and liquid phases was calculated and fitted (showed in Figure 1). The results indicated that three biochar samples all exhibited sorption effectiveness, and the same properties were

(1)

where Qe (mg/kg) is the equilibrium solid-phase concentration and Ce (mg/L) is the equilibrium aqueous concentration. In general, the sorption balance constant (KF) and the exponential parameter (n) were considered as the evaluation criterion of sorption capacity. Desorption experiment analysis depended on the sorption experiment. After the sorption equilibrium of 7 days, 2 mL of supernatant was extracted and filtered by 0.22 μm filters after centrifuging at 4500 rpm for 20 min to determine the content of NH4+, and the same volume buffer was supplemented into the original solution. Under the same equilibrium conditions, the desorption experiment was repeated for 3 cycles, which includes 7 days per cycle for a total of 21 days. The extent of desorption was described by release ratio, which was calculated as

release ratio (%) = (Q 0 − Q t)/Q 0

(2)

where Q0 and Qt represent the initial concentration and the concentration of solid-phase concentration at sorption equilibrium after 3 cycles of desorption. The content of NH4+ was determined by the indophenol blue method.21 The mixed solutions of sorption and desorption experiments were centrifuged at 4500 rpm for 20 min. Afterward, 2 mL of supernatant was collected and filtered by 0.22 μm filters to react with 1.2 mL of phenol sodium and 0.9 mL of 0.9% sodium hypochlorite for 30 min. The reaction product was diluted to 10 mL for calculating the content of NH4+ by a UV/vis spectrophotometer (UV-2450, Shimadzu, Japan) at 625 nm, which was the characteristic sorption from the reaction product. Recorded absorbance values of samples were compared with the standard curve of ammonium sulfate (x = 22.34y + 0.01, R2 = 0.99) to calculate NH4+ content. Functional Group Analysis. Fourier transform infrared spectroscopy (FTIR) was determined to observe the functional group change of biochar obtained from different plants at four gradient temperatures. The FTIR spectra of samples were recorded from 4000 to 800 cm−1 using a FTIR spectrometer (Equinox 55 Bruker Banner Lane, Coventry, Germany). Each spectrum was obtained on average with 16 scans at a resolution of 4 cm−1. In addition, all samples were characterized for their elemental composition (Vario EL cube, Elementar, Germany), including C, H, O, N, and S, to count the relative amounts of functional groups. The Physical Properties of Biochar. The porosity parameters of the surface area (SA), pore volume (PV), and pore width (PW) were determined from nitrogen gas sorption isotherm by a surface area and porosity analyzer (Gemini VII 2390, Micrometrics, USA). The Brunauer−Emmett−Teller (BET) method was used to calculate the specific surface area of samples, which had passed through a 100-mesh sieve before measurement. Thermogravimetric analysis was performed using a simultaneous thermal gravimetric analyzer (TGA-60, Shimadzu, Japan) for studying the thermal decomposition of experimental samples at different temperatures. The tested samples, weighing between 2 and 4 mg, were placed in the aluminum crucible and warmed up from 40 to 600 °C at a heating rate of 10 °C/min under the nitrogen flow of 30 mL/min. The thermal weight loss (TG) and derivate thermal (DTG) analysis were investigated. Statistical Analysis. All data were presented as mean of three replicates with their standard deviation indicated (mean ± SD).

Figure 1. Sorption isotherms for NH4+ on different sorbents of (a) corncob, (b) pomelo peel, and (c) banana stalk at 27 °C. The X axis and Y axis are aqueous-phase and solid-phase concentrations, respectively. B

DOI: 10.1021/acs.jafc.6b00109 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry found in these samples with a relationship between adsorptivity and preparation temperatures. A better adsorptivity was exhibited under the condition of 200 °C, which had retained more functional groups, while the adsorptivity was reduced with an increased temperature. Generally, the exponential parameter (n), calculating from the Freundlich sorption isotherm equation, was considered as the evaluation criterion, for which a value of more than 2 indicated an easy sorption and less than 0.5 indicated a hard behavior.20 As shown in Table 1, the corncob Table 1. Regression Parameters of NH4+ Sorption Isotherms for Various Biochar Samples n C-200 C-300 C-400 C-500 P-200 P-300 P-400 P-500 B-200 B-300 B-400 B-500

2.004 1.149 0.896 0.653 1.785 1.350 0.879 0.727 2.017 1.340 0.815 0.728

± ± ± ± ± ± ± ± ± ± ± ±

0.013 0.055 0.099 0.036 0.020 0.059 0.082 0.052 0.021 0.041 0.053 0.028

Log KF

R2

± ± ± ± ± ± ± ± ± ± ± ±

0.985 0.987 0.976 0.990 0.988 0.998 0.985 0.989 0.984 0.992 0.983 0.981

3.323 2.567 2.039 1.399 2.810 2.572 1.885 1.488 2.902 2.507 1.727 1.241

0.105 0.026 0.077 0.089 0.122 0.022 0.017 0.039 0.102 0.118 0.085 0.072

Figure 3. FTIR spectra of biochar samples including (a) corncob, (b) pomelo peel, and (c) banana stalk.

and Log KF value, which means the amount of sorption by unit concentration in Table 1. In the process of pyrolyzation at a lower temperature, the biomass conversion retained a lot of aliphatic structures, changing to aromatic structures with increased temperature, although some research suggested that the biochar material may be provided with a better adsorptivity with a higher preparation temperature about 500 °C for the adsorbate of organic micromolecular.22,23 However, these adsorbates mainly included aromatic structure compared to ammonium with a substantial difference. Besides, some studies indicated that the biomass, prepared at a lower temperature, showed a better sorption for urea24 and ammonium,25 which were consistent

Figure 2. (a) The desorption process of C-300 sample during three cycles in total of 21 days. (b) The total release ratio of different sorbents.

(C-200) and banana stalk (B-200) samples displayed an easy sorption with n = 2.004 and 2.017, respectively. In addition, the adsorptivity of other samples showed a normal property, and it was reduced with increased temperature as shown in Figure 1 C

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Table 2. Concentrations of the Concerned Elements and Porosity Parameters by BET Method of Different Biochar Samples ultimate analysis (%) C-200 C-300 C-400 C-500 P-200 P-300 P-400 P-500 B-200 B-300 B-400 B-500

elemental ratio

porosity params

C

H

O

N

S

H/C

(O + N)/C

SA (m2/g)

PV(m3/g)

PW (nm)

51.16 62.18 74.68 83.52 52.62 61.75 75.13 82.01 52.52 63.18 76.88 85.21

5.74 4.26 3.67 2.83 5.13 4.60 3.55 2.61 4.48 3.20 2.27 1.91

42.35 29.86 19.80 12.00 40.84 31.54 18.12 12.57 41.02 30.73 18.47 10.98

0.62 0.69 0.67 0.67 1.15 1.97 2.06 2.12 1.80 1.50 1.25 1.25

0.08 0.07 0.00 0.06 0.08 0.05 0.08 0.03 0.06 0.06 0.02 0.05

1.35 0.82 0.59 0.41 1.17 0.89 0.57 0.38 1.02 0.61 0.35 0.27

0.63 0.37 0.21 0.11 0.60 0.41 0.20 0.14 0.62 0.39 0.19 0.11

4.38 4.59 4.77 4.94 3.22 3.49 3.89 4.19 3.86 4.16 4.72 4.88

0.009 0.011 0.012 0.012 0.01 0.009 0.013 0.014 0.007 0.010 0.012 0.013

4.22 5.86 6.57 6.63 6.05 6.54 7.23 7.25 6.88 6.94 7.49 7.75

decrease and disappearance of carboxyl group. For the corncob and banana stalk samples, above 400 °C, a characteristic peak in the range of 1400 to 1440 cm−1 appeared due to −C−CH3 stretching, indicating that a methylation process of biochar materials under a high temperature. Moreover, peaks at 840 and 870 cm−1 were assigned to the characteristic peak of tetrasubstituted benzene, and the peaks at 1314 or 1319 cm−1, attributed to the characteristic peak of oxalate, were decreased with the temperature increment. In brief, the content of oxygen functional groups, including −COOH, CO, and −COC−, showed a reducing trend with the increased preparation temperature. The results were consistent with previous research;29 the increased pyrolysis temperature could lower functional group activity. Surface functional groups of biochar were changed by thermal cracking, causing changes of microstructure and properties simultaneously. Finally, it generated numerous differences in the sorption behavior and mechanism. Element analysis was an important method to study the biochar, for which elemental composition could be determined for the support of physicochemical properties. The elemental composition, including C, H, O, N, and S, are shown in Table 2. The relative amount of C element increased from about 50% to 85% obviously with increased preparation temperature while other elements declined, results similar to those reported.30 In the pyrolysis process, the polymer undergoes dehydration, dehydrogenation, and decarboxylation reactions, leading to the increase of C with the decrease of H and O relatively. Meanwhile, single bonds were changed to double bonds between carbon atoms, and the saturated aliphatic hydrocarbons transformed to unsaturated or aromatic hydrocarbon structures. The value of (N + O)/C represents the polarity as a positive relation, and the H/C value expresses the aromaticity of biochar, a lower value meaning a higher aromaticity. As outlined in Table 1, above 400 °C, the H/C values were all lower than 0.7, considering that the major part of biochar was aromatic structure.31 Along with increased preparation temperature, the biochar’s aromaticity increased when polarity was reduced, and hence it was provided with sorption for some micromolecules with benzene ring due to a firm π−π conjugated system.32 Nevertheless, this theory did not apply in the sorption mechanism of NH4+. The Physical Properties of Biochar. The vesicular structure of biochar could not only improve the efficiency of the sorption with an excellent specific surface area but also affect the activity and diversity of microorganisms in the environmental soil.33 As shown in Table 2, the SA, PV, and PW

with the results of this study. The adsorptivity may relate to the structure of the adsorbent target and the structural changes of carbon itself. Desorption experiments were divided into 3 periods in total 21 days following sorption experiments. The C-300 sample was selected to understand the desorption process with similar results of other samples (Figure 2a). In the 3 desorption periods, the release ratio was increased continuously from the first to the third desorption. After 3 desorption periods, under the condition of different preparation temperatures, the release ratio displayed a significant difference as shown in Figure 2b. The release ratio did not reach 10% at the preparation temperatures of 200 and 300 °C of three biochar samples, indicating that the adsorptivity of NH4+ was strong at these temperatures, leading to a difficult desorption. At a pyrolysis temperature of 400 °C, the release ratio was around 30%, and a higher release ratio was found in the 500 °C samples. The NH4+ capture ability of biochar was weakened with the rising temperature, which was similar to sorption experiment results. Moreover, the release ratio of corncob samples was higher than the others at every preparation temperature due to the different composition from various plant sources.26 Biochar has the potential to add environmental and economic value as a nitrogen fertilizer sustained-release material for NH4+ enrichment. The Functional Group Analysis. Biochar is a kind of carbon polymer containing various functional groups on the surface due to different preparation conditions. FTIR analysis showed that the surface of biochar was rich in −COOH, CO, −OH, and other functional groups presenting various physical and chemical properties. Figure 3 shows the FTIR spectra of three biochars with different preparation temperatures. A broad sorption band around 3400 cm−1 was generally regarded as the results of −OH and −NH2 stretching vibration in all spectra. Besides, the peaks of 2924 and 2856 cm−1 (−CH2− or −CH3 stretching), present in the aliphatic and alicyclic compounds,27 were also found in all samples. A characteristic peak at around 1610 cm−1 was observed owing to the stretching vibration of −CC− and the antisymmetric stretching vibration of −COC− from aromatic hydrocarbons; and this peak appeared a blue shift with the increased preparation temperature because more quantities of aromatic structures were produced, resulting in a stronger conjugate effect,28 especially for pomelo peel sample. In addition, for the P-200 and P-300 samples, a CO stretching peak of −COOH was found at 1718 cm−1, which disappeared at the increased preparation temperature. Similar results were found in corncob samples probably because oxygen functional groups were split by high temperature leading to the D

DOI: 10.1021/acs.jafc.6b00109 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry values extend with increasing preparation temperature, however, the changes were not significant in one kind of sample (p < 0.05). The surface porosity was associated with the preparation temperature, and it was also related to the plant source. During the pyrolysis process, the porosity was increased evidently from rich lignin biomass, but the increase was not discernible from the biomass containing excellent cellulose or hemicellulose.34 The contents of cellulose and hemicellulose in corncob (85.28%),35 pomelo peel (73.80%),36 and banana stalk (53.89%)35 were more than 50%, which may be the reason for a slight difference that occurred in the preparation process of these biochar samples. Figure 4 shows the weight loss (TG) and first derivate (DTG) curves for the thermogravimetric analysis, which was regarded

as the effective method for studying the pyrolysis of biomass polymers.37 Three significant weight loss stages were found in the TG and DTG curves. The initial weight loss before 100 °C was caused by moisture vaporization. Thereafter, the second weight loss began from 180 °C with a high mass-loss rate, which was similar to a previoius report.38 Besides, the pyrolysis process became different among the three samples, including the maximum loss rate at around 300 °C from corncob and banana stalk, and a lesser weight loss at 420 °C of banana stalk. Nevertheless, the maximum loss rate of pomelo peel was found at 210 °C due to its abundant pectin, which decomposed around 230 °C.39 This stage of weight loss was probably because of the dissociation from the functional group containing oxygen, which scattered by N2 via CO2 and water.40 At the third stage, a flat weight loss appeared from around 500 °C owing to the pyrolysis of heterocyclic structure forming into a more compact aromatic structure. The result of thermogravimetric analysis was consistent with the FTIR and element analysis suggesting that the biochar showed the decrease of oxygen groups and the increase of aromaticity with the rising preparation temperature. The Correlation Analysis between Sorption Capacity and Physicochemical Property. The relationship between physicochemical property and adsorptivity of biochar was analyzed depending on the Freundlich model, for which an exponential parameter (n) more than 2 indicated an easy sorption and less than 0.5 indicated a hard behavior. As shown in Figure 5a, it exhibited a negative correlation between surface

Figure 4. TG and DTG curves of biochar samples including (a) corncob, (b) pomelo peel, and (c) banana stalk.

Figure 5. Correlation analysis between sorption capacity and physicochemical property of (a) porosity parameters and (b) elemental ratio. E

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Figure 6. Sorption schematic diagram between NH4+ and biochar.

Notes

porosity parameters and sorption capacity, which decreased with the increased of SA, PV, and PW values. This result was different from former understanding, by which a larger specific surface area could cause more physical and chemical reactions leading to the enhancement of adsorption capacity; but this opinion depended on the chemical structure of certain material without significant changes, although some research indicated that the adsorption capacity was improved with increasing porosity, and the aromaticity was increased simultaneously. Besides, their adsorption targets were generally micromolecules with benzene ring.41,42 It was not clearly appropriate to explain the adsorption behavior of NH4+, which cannot form a conjugate to aromatic structures on the biochar surface. The relationship between atomic ratio and adsorptivity is shown in Figure 5b. The H/C ratio was less than 0.5, indicating stable aromatic structure with a poor sorption of NH4+. However, an excellent positive correlation (R2 = 0.98) was found between adsorptivity and (O + N)/C ratio. Under pyrolysis temperature in the range of 200 to 400 °C, the organic biomass was carbonized incompletely, numerous oxygen functional groups remaining, which could provide abundant negative potential points for the adsorption of NH4+ owing to hydrogen bonding and electrostatic interaction. With the increase of thermal decomposition temperature, the number of oxygen atoms and oxygen functional groups declined and hence the adsorption capacity of NH4+ weakened gradually (Figure 6). In conclusion, biochar is a potential and efficient way to dispose of agricultural residues with many benefits like reducing loss of fertilizer and carbon sequestration. This study suggests that the NH4+ adsorptive effect of biochar was probably because of oxygen functional groups such as −COOH, CO, and −COC− due to forming hydrogen bonding and electrostatic interaction between biochar and NH4+. The sorption capacities of NH4+ were different depending on pyrolysis temperature, which could be selected as an important parameter to produce nitrogen fertilizer sustained-release material according to diverse requirements in agricultural production.

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Authors would like to thank Miss Raslin for sample collection and constructive suggestion. (1) Antal, M. J.; Gronli, M. The art, science, and technology of charcoal production. Ind. Eng. Chem. Res. 2003, 42, 1619−1640. (2) Steinbeiss, S.; Gleixner, G.; Antonietti, M. Effect of biochar amendment on soil carbon balance and soil microbial activity. Soil Biol. Biochem. 2009, 41, 1301−1310. (3) Kimetu, J. M.; Lehmann, J. Stability and stabilisation of biochar and green manure in soil with different organic carbon contents. Aust. J. Soil Res. 2010, 48, 577−585. (4) Gaunt, J. L.; Lehmann, J. Energy balance and emissions associated with biochar sequestration and pyrolysis bioenergy production. Environ. Sci. Technol. 2008, 42, 4152−4158. (5) Cimò, G.; Kucerik, J.; Berns, A. E.; Schaumann, G. E.; Alonzo, G.; Conte, P. Effect of heating time and temperature on the chemical characteristics of biochar from poultry manure. J. Agric. Food Chem. 2014, 62, 1912−1918. (6) Zhang, X.; Wang, H.; He, L.; Lu, K.; Sarmah, A.; Li, J.; Bolan, N. S.; Pei, J.; Huang, H. Using biochar for remediation of soils contaminated with heavy metals and organic pollutants. Environ. Sci. Pollut. Res. 2013, 20, 8472−8483. (7) Li, J.; Li, S.; Dong, H.; Yang, S.; Li, Y.; Zhong, J. Role of Alumina and Montmorillonite in Changing the Sorption of Herbicides to Biochars. J. Agric. Food Chem. 2015, 63, 5740−5746. (8) Vaccari, F. P.; Baronti, S.; Lugato, E.; Genesio, L.; Castaldi, S.; Fornasier, F.; Miglietta, F. Biochar as a strategy to sequester carbon and increase yield in durum wheat. Eur. J. Agron. 2011, 34, 231−238. (9) Major, J.; Rondon, M.; Molina, D.; Riha, S. J.; Lehmann, J. Maize yield and nutrition during 4 years after biochar application to a Colombian savanna oxisol. Plant Soil 2010, 333, 117−128. (10) Rondon, M. A.; Lehmann, J.; Ramirez, J.; Hurtado, M. Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biol. Fertil. Soils 2007, 43, 699−708. (11) Manikandan, A.; Subramanian, K. S. Urea Intercalated Biochar-a Slow Release Fertilizer Production and Characterisation. Indian J. Chem. Technol. 2013, 6, 5579−5584. (12) Taghizadeh-Toosi, A.; Clough, T. J.; Sherlock, R. R.; Condron, L. M. Biochar adsorbed ammonia is bioavailable. Plant Soil 2012, 350, 57−69. (13) Hale, S. E.; Alling, V.; Martinsen, V.; Mulder, J.; Breedveld, G. D.; Cornelissen, G. The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars. Chemosphere 2013, 91, 1612−1619. (14) Nielsen, S.; Minchin, T.; Kimber, S.; van Zwieten, L.; Gilbert, J.; Munroe, P.; Joseph, S.; Thomas, T. Comparative analysis of the

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.6b00109. Schematic diagram of the pyrolysis process (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86-020-32296086. F

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DOI: 10.1021/acs.jafc.6b00109 J. Agric. Food Chem. XXXX, XXX, XXX−XXX