Tailoring the porosity of chemically activated hydrothermal carbons: Influence of the precursor and hydrothermal carbonization temperature

Abstract

Advanced porous materials with tailored porosity (extremely high development of microporosity together with a narrow micropore size distribution (MPSD)) are required in energy and environmental related applications. Lignocellulosic biomass derived HTC carbons are good precursors for the synthesis of activated carbons (ACs) via KOH chemical activation. However, more research is needed in order to tailor the microporosity for those specific applications. In the present work, the influence of the precursor and HTC temperature on the porous properties of the resulting ACs is analyzed, remarking that, regardless of the precursor, highly microporous ACs could be generated. The HTC temperature was found to be an extremely influential parameter affecting the porosity development and the MPSD of the ACs. Tuning of the MPSD of the ACs was achived by modification of the HTC temperature. Promising preliminary results in gas storage (i.e. CO 2 capture and high pressure CH 4 storage) were obtained with these materials, showing the effectiveness of this synthesis strategy in converting a low value lignocellulosic biomass into a functional carbon material with high performance in gas storage applications. IntroductionHydrothermal Carbonization (HTC) is now a well-established thermochemical synthesis alternative to produce functional carbon materials with a tunable chemical structure from pure carbohydrates or lignocellulosic biomass [1][2][3].During HTC, biomass-derived precursors are converted into valuable carbon materials using water as reaction medium at mild temperatures (< 200°C) under self-generated pressures [4]. Even though this methodology has been known for almost 100 years [5], its full potential, as a synthetic route for carbon materials having important applications in several fields such as catalysis, energy storage, CO 2 sequestration, water purification, soil remediation, has been revealed only recently, mainly via the work of Dr. Titirici and coworkers [6].Under hydrothermal conditions monosaccharides are dehydrated to 5-hydroxymethylfurfural (5-HMF) via the well-known Lobry de Bruyn-Alberta van Ekstein rearrangement [7]. Once 5-HMF is formed, it is in situ "polymerised" yielding the HTC carbon product [8]. While most of the research efforts focus on the exploitation of HMF for the production of chemicals, bioplastics and biofuels [9], the Titirici´s group rediscovered these processes for the production of green and valuable carbon and carbon-hybrid materials [1,4].One of the main limiting factors, hindering the effective and straightforward exploitation of HTC carbons for several end-applications (eg. catalysis, separation science, energy production and storage), is their low surface area and porosity [10]. In the case of monosaccharide derived HTC carbons, this problem has been elegantly overcome by using hard\soft-templating strategies or by addition of structural directing agents [11][12][13]. Such synthetic routes are effective because of the homogeneous nature of the pre-HTC aqueous reaction mixt...

High-Surface-Area Mesoporous Activated Carbon from Hemp Bast Fiber Using Hydrothermal Processing

“…It is generally believed that the KOH activation process of any carbon material enhances the pore structure and morphology with a substantial increase in specific surface area [14]. [18] -614 Orange peel [19] CO 2 618 Glucose [20] KOH 1197 Palm date seed [21] NaOH 1282 Desert shrub [22] ZnCl 2 1296 Rice husk [23] H 3 PO 4 1498 Hazelnut shell [24] KOH 1700 Glucose [25] KOH 1704 Sucrose [26] H 3 PO 4 2120 Glucose [26] NaOH 2129 Starch [27] KOH 2190 Rye straw [28] KOH 2200 Eucalyptus sawdust [29] KOH 2252 Corncobs [30] KOH 2300 Hemp bast fiber (this study) KOH 2425 Figure 1 provides the N 2 adsorption-desorption isotherms at −196 • C and pore size distributions of HAC, where HACs were prepared using different biochar-to-KOH ratios at a synthesis temperature of 390 • C. All the adsorption-desorption isotherms exhibit a type IV isotherm with a type IV hysteresis loop (according to IUPAC classification) in the relative pressure range from 0.4 to 1.0. Type IV isotherms are an indication of the existence of well-developed mesopores in the structure, whereas a type IV hysteresis loop indicates the formation of asymmetric, slit-shaped mesopores, attributable to rapid gas evolution and open channels [31].…”

Porous carbons from hydrothermal carbonization of corn stover for highly efficient CO2 capture

“…The surface area of AC 800-2-2 prepared by activation of hydrothermal treated corn stover was much higher than CS 800-2-2 which was prepared by direct activation of corn stover without hydrothermal treatment. The hydrothermal carbonization pretreatment of corn stover probably has a homogenizing effect, which removes undesirable mineral matter from the carbonaceous material [20]. Table 1.…”

Exceptional Adsorption of Phenol and p-Nitrophenol from Water on Carbon Materials Prepared via Hydrothermal Carbonization of Corncob Residues

“…Various biomasses have been converted to carbon materials through the HTC method (Titirici et al 2007;Fuertes 2009a, 2009b;Calucci et al 2012;Gao et al 2013;Budai et al 2014). HTC hydrochars normally need to be further upgraded to functional carbon materials via physical activation using an activating agent such as air, CO2, or water steam (Román et al 2013) or KOH chemical activation (Regmi et al 2012;Falco et al 2013a).…”