129Xe NMR studies of morphology and accessibility in porous biochar from almond shells

Authors: FARINA, MATTEO - University Of Milan; MAURI, MICHELE - University Of Milan; PATRIARCA, GIORGIO - University Of Milan; SIMONUTTI, ROBERTO - University Of Milan; Klasson, K Thomas; Cheng, Huai

Submitted to: RSC Advances
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2016
Publication Date: 10/25/2016
Publication URL: https://handle.nal.usda.gov/10113/5695379
Citation: Farina, M., Mauri, M., Patriarca, G., Simonutti, R., Klasson, K.T., Cheng, H.N. 2016. 129Xe NMR studies of morphology and accessibility in porous biochar from almond shells. RSC Advances. 6(105):103803-103810.

Interpretive Summary: Biochar is formed by heating an agri-based material at a high temperature under inert or semi-inert conditions. A lot of research has been done on biochar and a number of promising applications has been found. For example, the biochar from almond shells is being considered for use in removal of impurities and toxic organic compounds from water and industrial streams and removal of mercury in flue gas. In view of the complexity of the biochar carbonization and pore formation process, a better understanding of void structure and formation is useful. In this work, we used 129Xe NMR to study almond shell-based biochar samples and compared the results with the data obtained from nitrogen BET and ESEM. The 129Xe NMR spectrum consisted of two signals, corresponding to the non-adsorbed xenon and xenon adsorbed and permeated in micropores. The pressure dependence of 129Xe chemical shifts permitted an estimate to be obtained of the average pore size. The 2D EXSY and T1 measurements provided information on the accessibility of the pore system. This information gave us useful information on the pore structures in almond shell biochar and additional insight on biochar-substrate interactions in filtration or adsorption applications.

Technical Abstract: Micro and mesoporous materials are often used in catalysis, purification, composite filler, and other applications. Almond shell is an important agricultural byproduct that can be transformed to microporous and mesoporous carbon. In this work, we produced biochar from almond shell using a thermal treatment procedure in an inert atmosphere and characterized the pores with nitrogen adsorption, environmental SEM, and 129Xe NMR. The latter technique differentiates adsorbed and nonadsorbed xenon and permits the correlation of different processing conditions with xenon adsorption and diffusivity. The relevance of removing the ash produced during the charring process has been included in the study. Moreover, the xenon exchange between meso- and micro-pores has been directly observed by 129Xe NMR, demonstrating that after ash removal by water the materials have high accessibility of the pores by external fluids, thus increasing the usefulness as filtration or adsorption material.