Use of Chènevotte, a Valuable Co-Product of Industrial Hemp Fiber, as Adsorbent for Pollutant Removal. Part I: Chemical, Microscopic, Spectroscopic and Thermogravimetric Characterization of Raw and Modified Samples

Abstract

FINEAU (2021–2024) is a trans-disciplinary research project involving French, Serbian, Italian, Portuguese and Romanian colleagues, a French agricultural cooperative and two surface-treatment industries, intending to propose chènevotte, a co-product of the hemp industry, as an adsorbent for the removal of pollutants from polycontaminated wastewater. The first objective of FINEAU was to prepare and characterize chènevotte-based materials. In this study, the impact of water washing and treatments (KOH, Na2CO3 and H3PO4) on the composition and structure of chènevotte (also called hemp shives) was evaluated using chemical analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray computed nanotomography (nano-CT), attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, solid state NMR spectroscopy and thermogravimetric analysis. The results showed that all these techniques are complementary and useful to characterize the structure and morphology of the samples. Before any chemical treatment, the presence of impurities with a compact unfibrillated structure on the surfaces of chènevotte samples was found. Data indicated an increase in the crystallinity index and significant changes in the chemical composition of each sample after treatment as well as in surface morphology and roughness. The most significant changes were observed in alkaline-treated samples, especially those treated with KOH.

Copper Recovery from Aqueous Solutions by Hemp Shives: Adsorption Studies and Modeling

“…The b values found for SHI-C and SHI-W (Table 3) indicate a physisorption mechanism for copper removal onto the two materials, confirming our experimental data. This is in agreement with previous studies on the adsorption kinetics of copper on the same materials and their characterisation by spectroscopic and microscopic methods after adsorption [38,59]. Other researchers working on the adsorption of Zn and Cd by lignocellulosic materials have reported similar conclusions [61,62].…”

“…The first one represents the highest metal ion uptake per unit mass of adsorbent: for hemp shives, q max increased from 6.1 mg/g for washed shives (SHI-W) to 10.2 mg/g for activated shives (SHI-C). This increase is due to the structural and chemical modifications of the adsorbent caused by the alkaline agent Na 2 CO 3 , which promotes both ion exchange properties and diffusion in the material, as recently reported [59]. The R L constant gives information about the linear (R L = 1), irreversible (R L = 0), unfavourable (R L > 1), or favourable (0 < R L < 1) adsorption nature of the process [44,56].…”

“…For SHI-W, R L values were found in the range 0.0488-0.6060, meanwhile for SHI-C, the range was 0.0008-0.0223. These results suggested copper adsorption onto hemp shives was a favourable process, especially after carbonate treatment [38,44,56,59].…”

Holistic Valorization of Hemp through Reductive Catalytic Fractionation

“…A honeycomb-like cell wall structure was observed. The average cell wall thickness was measured to be 1.95 μm (standard deviation 0.17), which is slightly thinner than that of other herbaceous crops (∼2.00–3.00 μm). − This might explain the observed high yield of monophenolic compounds. This is rationalized by an enhancement of the intrinsic kinetics of the solvent-based fractionation, where a thinner cell wall promotes mass transfer through diffusion during solvolytic lignin extraction .…”