Low-Cost Activated Grape Seed-Derived Hydrochar through Hydrothermal Carbonization and Chemical Activation for Sulfamethoxazole Adsorption

Abstract

Activated carbons were prepared by chemical activation with KOH, FeCl3 and H3PO4 of the chars obtained via hydrothermal carbonization of grape seeds. The hydrochars prepared at temperatures higher than 200 °C yielded quite similar proximate and ultimate analyses. However, heating value (24.5–31.4 MJ·kg−1) and energy density (1.04–1.33) significantly increased with carbonization temperatures between 180 and 300 °C. All the hydrochars showed negligible BET surface areas, while values between 100 and 845 m2·g−1 were measured by CO2 adsorption at 273 K. Activation of the hydrochars with KOH (activating agent to hydrochar ratio of 3:1 and 750 °C) led to highly porous carbons with around 2200 m2·g−1 BET surface area. Significantly lower values were obtained with FeCl3 (321–417 m2·g−1) and H3PO4 (590–654 m2·g−1), showing these last activated carbons important contributors to mesopores. The resulting materials were tested in the adsorption of sulfamethoxazole from aqueous solution. The adsorption capacity was determined by the porous texture rather than by the surface composition, and analyzed by FTIR and TPD. The adsorption equilibrium data (20 °C) fitted the Langmuir equation well. The KOH-activated carbons yielded fairly high saturation capacity reaching up to 650 mg·g−1.

Characterization of Chemically and Physically Activated Carbons from Lignocellulosic Ethanol Lignin-Rich Stream via Hydrothermal Carbonization and Slow Pyrolysis Pretreatment

“…The most relevant peaks of the spectra of chemically activated hydrochars are those related to: asymmetric C≡C stretching (2110 cm −1 ), C=C vibrations (1560 cm −1 ) and C-O-C stretching (broad band at around 1140 cm −1 ). These again corroborate the aromaticity increase that hydrochars undergo during activation, in agreement with literature [8,33]. Table 5 reports the results of the elemental analysis of the chars (hydrochars and pyrochar).…”

“…The FTIR spectra from physically and chemically activated hydrochars show a drastic decrement of functional groups compared to hydrochars without activation, however, some peaks are still observable [8,33]. The only visible peak of the spectra of physically activated hydrochars appears in black spectrum at around 2290 cm −1 and is associated to asymmetric C≡C stretching.…”

Review on Activated Carbons by Chemical Activation with FeCl3

“…An antipyrine saturation capacity of 275 mg•g −1 was obtained, a value comparable to or higher than those reported for other emerging contaminants on different activated carbons [119,120]. Diaz et al [68] analyzed the adsorption of sulfamethoxazole antibiotic on an activated carbon obtained through chemical activation of grape seed hydrochars with different chemical activating agents (KOH, FeCl 3 , and ZnCl 2 ). Although the FeCl 3 -derived activated carbon did not achieve the highest adsorption capacity, a significant saturation capacity close to 150 mg•g −1 was reported.…”

“…Besides, higher amounts of FeCl 3 can result in larger particles of iron oxides, which can act as a template for the formation of mesopores and/or precipitate in the carbon matrix, altering porous development [83,84]. Similarly, Diaz et al [68] obtained the maximum surface area at an impregnation ratio equal to 2.0 (in a 1.0-3.0 range) when activating grape seed hydrochars.…”

Sewage Sludge Hydrochar: An Option for Removal of Methylene Blue from Wastewater

“…Moreover, to enhance the adsorption capability of hydrochar, modification turned out to be an effective method [14]. By "modification" we mean a treatment in which the feedstock (hydrochar in this case) is treated with a chemical agent (e.g., KOH) via impregnation, which is not followed by a heat treatment at 500-850 • C in nitrogen typical of chemical activation [11,[15][16][17]. For instance, Regmi et al [18] tested the sorption capacities of KOH-modified hydrochar from switchgrass for removing copper and cadmium from aqueous solutions: they found a removal of about 100% within 24 h of contact time while the raw hydrochar only removed 16% of copper and 5.6% of cadmium.…”