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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Commodity Utilization Research » Research » Publications at this Location » Publication #352147
Title: In situ and ex situ 2D infrared/fluorescence correlation monitoring of surface functionality and electron density of biochars

Author
item Uchimiya, Sophie
item NODA, ISAO - University Of Delaware
item ORLOV, ALEXANDER - State University Of New York- College Of Environmental Science And Forestry
item RAMAKRISHNAN, GIRISH - State University Of New York- College Of Environmental Science And Forestry

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2018
Publication Date: 5/14/2018
Citation: Uchimiya,M., Noda, I., Orlov, A., Ramakrishnan, G. 2018. In situ and ex situ 2D infrared/fluorescence correlation monitoring of surface functionality and electron density of biochars. ACS Sustainable Chemistry & Engineering. 6(6):8055-8062.

Interpretive Summary: Many researchers claim biochar to be an excellent remediation reagent for both positively and negatively charged metal contaminants. Infrared spectra (FTIR) is often presented as the evidence for biochar's ability to removal heavy metals. However, the majority of functional groups are known to partition into liquid (tar/bio-oil), and not solid (biochar) phase during pyrolysis. To clarify this confusion in the biochar field, this study employed two-dimensional correlation analysis to describe the formation and removal of surface functionality during pyrolysis. Results illustrates the importance of electron density of functional groups in their fate during pyrolysis.

Technical Abstract: Carboxyl, hydroxyl, and other oxygen-containing functional groups play key roles in the interfacial reactions of soil surfaces including biochar (solid-phase slow pyrolysis product) soil amendment. Intensity and directionality in both real (synchronous) and imaginary (asynchronous) coordinates of 2D infrared correlation spectra were confirmed by the timecourses of pyrolysis reaction (temperature × wavenumber × absorbance; 10 °C min-1, 1 h residence time at 500 °C) utilizing high-density (74 total spectra) in situ DRIFTs monitoring. Similar primary trends were observed for four different lignocellulosic biomass feedstocks: cottonseed hulls, cotton ginning waste, flax shive, and pecan shell. In the OH stretch region (3100-3750 cm-1), free OH was most sensitive to pyrolysis temperature, and reacted before H-bonded OH indicating the evaporation of water, followed by the cleavage of inter-chain H-bonds. Aromatic CH (R=CHn) was the primary CH functionality (within 2700-3100 cm-1) impacted by the pyrolysis temperature perturbation, and formed as the aliphatic CHx was removed. Of C=O/C=C groups, electron-deficient C=O (1740 cm-1) was most sensitive to pyrolysis, reacted synchronously (in the same direction) with the aromatic C=C (1510 cm-1), and was formed after the most electron-rich C=O (1620 cm-1). This electron density trend in the C=O/C=C (1400-1800 cm-1) region of infrared coincided the formation of aromatic extractable carbon before aliphatic structures in 2D fluorescence emission-emission correlation spectra using 340 nm excitation wavelength. Observed temperature dependence could be used to manipulate the surface functionality and electron density of biochar soil amendment.