Characterization and comparison of walnut shells-based activated carbons and their adsorptive properties

Abstract

The production of low-cost biologically activated carbons (BACs) is urgent need of environmental protection and ecological sustainability. Hence, walnut shells were treated by traditional pyrolysis, direct KOH impregnation and combined activation composed of hydrothermal carbonization and two-step H3PO4- and pyrolysis-activation process to obtain porous carbon with high adsorption capacity. It was found that the best adsorption capacity for iodine and organic dye methylene blue (MB) can be obtained using the KOH impregnation at impregnation ratio of 1:1 or combined activation comprising of 2 h H3PO4 activation and 1 h pyrolysis activation at 1000°C. The produced KOH, H3PO4/pyrolysis activated BACs at the optimum conditions are superior to that of commercial ACs, 9.4 and 1.3 times for MB removal, 4 and 4.5 times for iodine number respectively. Characterization results demonstrated their porous structure with very good textural properties such as high BET surface area (1689.1 m2/g, 1545.3 m2/g) and high total pore volume (0.94 cm3/g, 0.96 cm3/g). The N2 adsorption-desorption isotherm of H3PO4/pyrolysis activated hydrochar suggested the co-existence of micro and meso-pores. Moreover, they are more effective for the removal of Fe(III) and Cr(VI) from aqueous solution than the commercial AC, suggesting a promising application in the field of water treatment.

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“…The rough surface is seen with a number of random cavities. This is due to the pores nature of the walnut shell surface [15,21,22]]. These features demonstrate the high porosity of walnut shell surface, which confirms its surface's capability to adsorb MB in its cavities.…”

“…The SEM images are shown in Figure 2a and b to observe the morphology of the walnut shell surface. Due to SEM analysis, the surface texture of raw walnut shell is mainly represented by surface folds and pore existence [21,22]. As clearly seen in SEM images, the rode-like appearance can be attributed to a cellulosic structure where lignin, cellulose, and hemicellulose are the main components [21,22]].…”

“…Due to SEM analysis, the surface texture of raw walnut shell is mainly represented by surface folds and pore existence [21,22]. As clearly seen in SEM images, the rode-like appearance can be attributed to a cellulosic structure where lignin, cellulose, and hemicellulose are the main components [21,22]]. The rough surface is seen with a number of random cavities.…”

Characterization of Ziziphus lotus’ Activated Carbon and Evaluation of Its Adsorption Potential

“…Since the introduction of this process, activated carbon has been one of the most frequently used products due to its highly developed adsorption capacity. The main characteristics of activated carbon are its porous structure, linked to the accessible specific surface area into which molecules can penetrate, the pore size distribution, and their average geometric shape [ 18 ]. The adsorption properties of activated carbon depend on the functional groups, resulting mainly from the activation process, precursors, and thermal purification [ 19 ].…”

Characterization of Activated Carbon Prepared From the Nucleus of Ziziphus Lotus (NBEG): Isothermal Study and Kinetics of Adsorption of Methylene Blue

“…Since the introduction of this process, activated carbon has been one of the most frequently used products due to its highly developed adsorption capacity. The main characteristics of activated carbon are its porous structure, in relation linked to the accessible specific surface area into which molecules can penetrate, the pore size distribution and their average geometric shape (Li et al, 2020). The adsorption properties of activated carbon depend on the functional groups, resulting mainly from the activation process, on the precursors, and thermal purification (Yousefi et al 2019).…”