Chemical-physical analysis and exfoliation of biochar-carbon matter: from agriculture soil improver to starting material for advanced nanotechnologies

Abstract

Biochar (BC) is a carbonaceous product obtained by pyrolysis, using lignocellulosic biomass. Feedstock and pyrolysis temperature affects the physical-chemical characteristics of the BC, and therefore its use and purpose. The main application of biochar is in the agricultural domain, however, it is considered as an effective strategy for the climate change mitigation, caused by the fact that carbon is not easily returned to the atmosphere during BC lifetime. Due to the presence of several carbon molecules, arranged from the thermochemical process of pyrolysis, biochar is a heterogeneous compound. Previous studies revealed a wide presence of interesting carbon molecules, therefore the biochar can be proposed as a useful material tank containing carbon structures used for different aims. Our study was focused on physical and chemical characterization of carbonaceous structures of a kind of biochar as a function of pyrolysis temperature. Biochar samples were produced by muffle furnace with the temperature range of 300 °C ÷650 °C. X-ray Diffraction (XRD) spectra were collected to determine crystal structures present in BC. Two broad peaks (002) and (100) were found corresponding to the turbostratic carbon crystallites. Raman Spectroscopy measurements were performed to examine different carbon-based molecules in the turbostratic-carbon phase of BC. Raman spectra showed an overlap between two peaks, corresponding to G band associated with graphite, and D band, displaying the aromatic rings arranged on layers, similar to graphene sheets. To separate and exfoliate carbonaceous structures, BC samples were exposed to ultrasonic bath. Atomic Force Microscopy (AFM) was used to characterize the nanostructures extracted. The presence of about 1 nm topographic height islands on mica substrate was found, consistent with a typical height of Few Layer Graphene (FLG) reported in the literature. From these results obtained, Biochar could be considered as a reservoir of materials for nanotechnology, such as graphene sheets.