(2013). A CO-CO2 analyzer (ZRH Infrared Gas Analyzer, CAI) connected to the set-up was used to detect the concentration of CO2 before and after the experiment. doi: 10.1016/j.ultsonch.2009.08.011, Hagemann, N., Spokas, K., Schmidt, H.-P., Kgi, R., Bhler, M., and Bucheli, T. (2018). DM: interpretation of results and revising the manuscript. doi: 10.1016/j.biortech.2010.06.088, Jahirul, M. I., Rasul, M. G., Chowdhury, A. doi: 10.1002/aic.14347, Chen, Y., Yang, H., Wang, X., Zhang, S., and Chen, H. (2012). The baselines of the graphs were revised in Origin lab (Version 2019b) to allow a correct comparison of the intensity of the peaks. A new peak at 43 appeared for samples pyrolyzed at 600 and 700C that indicated the development of atomic order in the increasingly carbonized material (Keiluweit et al., 2010). The maximum values were observed for MS, ranging from 0.78 to 0.96 for 500 to 800C, respectively, consistent with their surface area data (Table 2). Sonochem. 44, 12471253. doi: 10.1016/j.biortech.2014.11.011, Zhang, J., L, F., Luo, C., Shao, L., and He, P. (2014). Although surface areas for agro-industrial chars are lower than herbaceous ones, they follow a similar trend. Above 600C, decomposition for all the biochars completed and the curves became stable. doi: 10.1021/ef3018783, Li, H., Dong, X., Da Silva, E. B., De Oliveira, L. M., Chen, Y., and Ma, L. Q. XRD-thermal combined analyses: an approach to evaluate the potential of phytoremediation, phytomining, and biochar production. The decomposition of lignin and the quick release of H2 and CH4 contribute to a sharp increase of the surface area and pore volumes from 500 to 600C. The adsorption capacities for the sorbent materials can be explained using the adsorption isotherm plots as shown in Figures S2, S3. Additionally, as for raw chars, ultrasonicated herbaceous biochars possessed higher surface areas and pore volumes than agro-industrial chars. Effect of ultrasonic irradiation on preparation and properties of ionogels. 62, 345352. Photochemical and acoustic interactions of biochar with CO2 and H2O: applications in power generation and CO2 capture. The X-ray diffraction plots of raw and aminated samples are shown in Figures 8A,B. Biomass Bioenergy 37, 97105. In addition to that, the isotherms also characterize the adsorbent materials in terms of their porosity. doi: 10.1016/j.biortech.2012.05.042, PubMed Abstract | CrossRef Full Text | Google Scholar, Al-Wabel, M. I., Al-Omran, A., El-Naggar, A. H., Nadeem, M., and Usman, A. R. (2013). Food Chem. In brief, adsorption experiments were conducted in a temperature-controlled tubular reactor (alumina oxide, Al2O3). 118, 158162. Appl. Bioresour. doi: 10.1016/j.jclepro.2017.04.115, Lee, S., Filburn, T. P., Gray, M., Park, J.-W., and Song, H.-J. Sust. Notably, higher pyrolysis temperatures gave rise to the peak at 23 consistent to the literature (Kim et al., 2012). The raw samples show overall similarity in their surface morphology, having rough and non-porous structure. All raw biochars exhibited a gradual increase in adsorption capacity in the range of 6788% while increasing the temperature from 500 to 600C. All the raw samples demonstrated a slight increase (413%) in CO2 capture capacity at 700C compared with 600C, which can be substantiated as per the elemental analysis data (C and N contents) (Table 3). Int. MS, Miscatanthus; SG, Switchgrass; CS, Corn stover; SB, Sugarcane bagasse; R, Raw; US, Ultrasound Activated. doi: 10.3390/en7020548, Sajjadi, B., Chen, W.-Y., Adeniyi, A., Mattern, D. L., Mobley, J., Huang, C.-P., et al. J. Anal. Carbon 43, 5366. doi: 10.1016/j.chemosphere.2017.03.072, Li, M., Liu, Q., Guo, L., Zhang, Y., Lou, Z., Wang, Y., et al. 141, 8388. The more the adsorbed volume, the higher will be the adsorption capacity. A., and Ashwath, N. (2012). This further indicates the decrease of aliphatic hydrocarbon and development of aromatic structure of biochar with increasing pyrolysis temperature (Major et al., 2018) as found from elemental analysis results that showed increased %C content at elevated temperature (Table 3 and Table S1). For instance, elemental analysis results (Table 3) expressed intense %N contents for aminated biochars at 600C. Res. (2016). Graphitization of miscanthus grass biocarbon enhanced by in situ generated FeCo nanoparticles. For instance, CS follows an increasing trend of %C content up to 700C with a gradual rise of ash content and reduction of H/C and O/C ratios and %N contents. The ratio of the disorder-induced band (D band) to the Raman-allowed band (G band) is termed the intensity ratio (ID/IG). This result is likely due to the degradation and depolymerization of lignocellulosic structure. As observed from the figures the effect of sonication is more observable for agro-industrial (CS, SB) chars than herbaceous biochars (MS, SG). Similar structural features are also observed for CS (Figure 3A) and SB (Figure 4A), which exhibit rough, irregular and bundle like shapes. 8 Articles, This article is part of the Research Topic, https://www.frontiersin.org/articles/10.3389/fenrg.2020.00085/full#supplementary-material, Creative Commons Attribution License (CC BY). Although %N content was maximum at 500C, maximum %C content was achieved at 700C. 176, 288291. Ultrasound cavitation results in the exfoliation of the graphitic clusters of the biochar structure, removal of mineral matter, and opening of the pores, thereby increasing microporous surface area. doi: 10.1016/j.fuel.2018.08.112, Antonakou, E., Lappas, A., Nilsen, M. H., Bouzga, A., and Stcker, M. (2006). Accordingly, the microsurface area and pore volumes for MS and SG ranged between 115325 m2/g and 0.060.16 cc/g over the temperature of 500800C. Graphene-based composite materials. PLoS ONE 11:e0156894. Figure 8. Table S1 (organic analysis) depicts gradual increment in %C contents of aminated MS samples with temperature, which is consistent to what was obtained for raw chars. Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties. Higher pyrolysis temperature caused higher devolatilization, resulting in more pore volume in the samples and, in turn, a greater surface area up to 700C (Zanzi et al., 2002; Onay, 2007). Bioresour. doi: 10.1016/j.chemosphere.2015.05.084, Jiang, Z.-H., Yang, Z., So, C.-L., and Hse, C.-Y. Influence of pyrolysis temperature and holding time on properties of biochar derived from medicinal herb (radix isatidis) residue and its effect on soil CO2 emission. Pyrolysis 110, 277284. (2013). Sajjadi, B., Chen, W.-Y., and Egiebor Nosa, O. No use, distribution or reproduction is permitted which does not comply with these terms. Effect of feedstock and pyrolysis temperature on properties of biochar governing end use efficacy. doi: 10.1016/j.jaap.2014.09.016, Zambon, I., Colosimo, F., Monarca, D., Cecchini, M., Gallucci, F., Proto, A., et al. 240, 574578. Brewer, C. E. (2012). Characterization of bio-oil, syn-gas and bio-char from switchgrass pyrolysis at various temperatures. Environ. 32, 559578. For instance, as per the Figure S2A, the adsorbed volume increases for both raw and ultrasound aminated samples as temperature is increased from 500 to 700C and then reduces for 800C. Then, the reactor was cooled to 333 K and the helium gas was switched to a simulated flue gas consisting of 10 vol. For example, US-MS 700 sample (Figure 1B) shows the least alteration to their structure. Characterization of biochar from switchgrass carbonization. (2005). CO2 adsorption capacities of both raw and sono-chemically activated biochar samples synthesized at different pyrolysis temperatures. J. Taiwan Inst. The figures also indicated that the volume adsorbed is higher for biochar samples synthesized at high temperature. Comparing corn stover and switchgrass biochar: characterization and sorption properties. Biochar characterization and engineering theses and dissertations. Pyrolysis temperature has a prominent role in promoting the ultrasound effect. Sci. Technol. doi: 10.1016/j.cej.2013.10.081, Tag, A. T., Duman, G., Ucar, S., and Yanik, J. Carbon (C), nitrogen (N) and hydrogen (H), oxygen (O), sulfur (S), and the ash content of raw and activated biochars synthesized under different temperatures are summarized in Table 3 and the corresponding organic analysis on a dry ash-free basis are reported in Table S1. The fibrous surface is formed by parallel stripes and is partially covered with residual material, and pith is a more fragile and fragmented structure which is primarily cracks that connect neighboring cells on the surface of the walls. This is due to largely exposed facets of the crystal lattice that show a few peaks with high relative intensity (Zhang et al., 2020). (2017). Bioresource Technology 101, 88688872. doi: 10.3390/en5124952, Jeong, C. Y., Dodla, S. K., and Wang, J. J. Sci. 122, 2132. Adsorptive removal of Pb (II) by magnetic activated carbon incorporated with amino groups from aqueous solutions. The surface crystallinity of the biochar samples were determined from the XRD analysis in a Rigaku powder diffractometer (Rigaku, Japan) with Cu K radiation ( = 0.15406 nm). Mechanisms of metal sorption by biochars: biochar characteristics and modifications. However, the same increment was observed by 30 s of ultrasound activation at ambient conditions. J. Anal. It can be concluded from the table that the ultrasono-amine functionalized adsorbents which were prepared from miscanthus, switchgrass, cornstover and sugarcane bagasse under 700C have comparatively higher adsorption capacities (2.222.89 mmol/g) than most of the reported data. These gasses emanate throughout the structure, promoting disorder until >1,000C. Consistent with this, almost all activated biochars (except A-SG-600/700 and A-SB-700/800) demonstrated a significant increase in the ID/IG ratio compared with their pristine condition (Table S2). The enhancement of surface area and pore volumes was caused by the degradation of the organic materials (hemicelluloses, cellulose, and lignin) and the formation of vascular bundles or channel structures during pyrolysis (Kim W. K. et al., 2013; Li et al., 2013). Hence, based on the surface area analysis results it can be emphasized that miscanthus biomass pyrolyzed at 700C and sonicated had the highest possible microporous surface area that would provide more active sites for amine activation to improve the CO2 adsorption capacity. Fuel 85, 22022212. Chemosphere 178, 466478.