Abstract
Synthesis of activated carbon from waste biomass is of current interest towards sustainability. The properties of biomass-derived activated carbon largely depend on the carbonization process. This study reports the preparation of mesoporous activated carbon with extremely high surface area from hemp bast fiber using hydrothermal processing. Hot water processing (390–500 °C) followed by activation using KOH and NaOH was investigated at different mass ratios. The described approach was found to enhance the mesoporosity (centered at 3.0 to 4.5 nm) of the hemp-derived activated carbon (HAC) from activation [confirmed by BJH (Barrett-Joyner-Halenda) pore size distribution and TEM (transmission electron microscopy) imaging]. BET (Brunauer-Emmett-Teller) results showed that the product has an extremely high surface area (2425 m2/g) while the surface functional groups (–OH, –COOH, C=C/C–C) were confirmed by FTIR (Fourier transform infrared spectroscopy) and further quantified by XPS (X-ray photoelectron spectroscopy). Increasing KOH concentration was found to enhance the surface area with a maximum biochar-to-KOH (g/g) ratio of 1:3. The crystallite domain size of HAC was determined using Raman spectroscopy of different wavelengths. The procedure described in this study is an environmentally friendly scalable route for the mass production of activated carbon using hemp fiber.
Highlights
Activated carbon is a well-known porous material with large surface area and pore volume, and is extensively used for gas separation, solvent recovery, contaminant removal from water, wastewater treatment, and as a catalyst/catalyst support for different energy storage and conversion processes [1]
Hydrothermal processing of hemp bast fiber followed by chemical activation can be an alternative approach for making carbon materials
The Brunauer–Emmett–Teller (BET) surface area, pore diameter, and pore volume of hemp-derived activated carbon (HAC) and biochar were determined from nitrogen adsorption and desorption isotherm data obtained at −196 ◦ C in a constant-volume adsorption apparatus (Tristar II 3020, Micromeritics Instrument Corporation, Norcross, GA, USA) using 99.995% pure
Summary
Activated carbon is a well-known porous material with large surface area and pore volume, and is extensively used for gas separation, solvent recovery, contaminant removal from water, wastewater treatment, and as a catalyst/catalyst support for different energy storage and conversion processes [1]. I.e., physical and chemical, are used to prepare activated carbonaceous materials from biomass [5]. Prior to either the physical or chemical activation process, the carbon precursor needs to be carbonized to produce char. KOH and NaOH are compared as activating agents while hemp bast fiber was chosen as the carbon precursor because of its unique fibrous structure to make carbonaceous materials [10]. Wang et al [11] used sulphuric acid solution in their process to prepare carbon material from hemp fiber whereas Yang et al [12] and Rosas et al [13] conducted the carbonization reaction in the presence of phosphoric acid. Hydrothermal processing of hemp bast fiber followed by chemical activation can be an alternative approach for making carbon materials. The current study synthesizes hemp-derived carbon materials and characterizes them in detail by various physicochemical techniques including BET (Brunauer-Emmett-Teller) surface area and BJH (Barrett-Joyner-Halenda) pore size distribution, XRD (X-ray powder diffraction), SEM (scanning electron microscopy), TEM (transmission electron microscopy), Raman, TG-DTA (thermogravimetric & differential thermal analysis, FTIR (Fourier transform infrared spectroscopy), and XPS (X-ray photoelectron spectroscopy) analysis
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