Studies on Kinetics, Isotherms, Thermodynamics and Adsorption Mechanism of Methylene Blue by N and S Co-Doped Porous Carbon Spheres

Abstract

Heteroatom-doped carbon is widely used in the fields of adsorbents, electrode materials and catalysts due to its excellent physicochemical properties. N and S co-doped porous carbon spheres (N,S-PCSs) were synthesized using glucose and L-cysteine as carbon and heteroatom sources using a combined hydrothermal and KOH activation process. The physicochemical structures and single-factor methylene blue (MB) adsorption properties of the N,S-PCSs were then studied. The optimized N,S-PCSs-1 possessed a perfect spherical morphology with a 2–8-μm diameter and a large specific area of 1769.41 m2 g−1, in which the N and S contents were 2.97 at% and 0.88 at%, respectively. In the single-factor adsorption experiment for MB, the MB adsorption rate increased with an increase in carbon dosage and MB initial concentration, and the adsorption reached equilibrium within 2–3 h. The pseudo-second-order kinetic model could excellently fit the experimental data with a high R2 (0.9999). The Langmuir isothermal adsorption equation fitted well with the experimental results with an R2 value of 0.9618, and the MB maximum adsorption quantity was 909.10 mg g−1. The adsorption of MB by N,S-PCSs-1 was a spontaneous, endothermic, and random process based on the thermodynamics analyses. The adsorption mechanism mainly involved Van der Waals force adsorption, π-π stacking, hydrogen bonds and Lewis acid–base interactions.

Natural Halloysite-Templated Synthesis of Highly Graphitic Boron-Doped Hollow Carbon Nanocapsule Webs

“…Compared with Hal@HCNCWs and HCNCWs, the C content (98.58 at%) increased while the O content (0.65 at%) decreased for B-HCNCWs, again demonstrating its highly graphitized structure. [17]. The content of non-oxygenated C-C/C=C groups was as high as 66.43%, suggesting a high graphitization degree of B-HCNCWs, which was in accordance with the outcomes of the XRD and Raman analyses.…”

“…The content of non-oxygenated C-C/C=C groups was as high as 66.43%, suggesting a high graphitization degree of B-HCNCWs, which was in accordance with the outcomes of the XRD and Raman analyses. The high-resolution O 1s spectrum could be fitted to three peaks located at 531.5, [17]. The content of non-oxygenated C-C/C=C groups was as high as 66.43%, suggesting a high graphitization degree of B-HCNCWs, which was in accordance with the outcomes of the XRD and Raman analyses.…”

“…The content of non-oxygenated C–C/C=C groups was as high as 66.43%, suggesting a high graphitization degree of B-HCNCWs, which was in accordance with the outcomes of the XRD and Raman analyses. The high-resolution O 1s spectrum could be fitted to three peaks located at 531.5, 532.5, and 534.0 eV, belonging to O=C, C–OH, and C–O–C, respectively ( Figure 4 c) [ 17 ]. The residual oxygen-containing functional groups could introduce some radicals on the surfaces of B-HCNCWs, which would greatly improve their physicochemical properties.…”

The Use of High Surface Area Mesoporous-Activated Carbon from Longan Seed Biomass for Increasing Capacity and Kinetics of Methylene Blue Adsorption from Aqueous Solution

“…It is likely that the increase of temperature would increase the diffusion rate of methylene blue molecules to the adsorption sites that would increase the likelihood of an adsorbent-adsorbate interaction, hence the increasing amount of methylene blue adsorbed. A similar temperature effect on the amount of MB adsorbed was also observed by a number of investigators working on different adsorbents, for example, tannin [76], rejected tea [77], magnetic graphene-CNTs [78], and N and S co-doped porous carbon spheres [79]. In order to gain a fuller understanding of the dye adsorption process, the various thermodynamic parameters including the values of enthalpy change (ΔH°), Gibbs free energy change (ΔG°), and entropy change (ΔS°) were estimated from the isotherm data at various temperatures by using the following equations [80]:…”

“…It is likely that the increase of temperature would increase the diffusion rate of methylene blue molecules to the adsorption sites that would increase the likelihood of an adsorbent-adsorbate interaction, hence the increasing amount of methylene blue adsorbed. A similar temperature effect on the amount of MB adsorbed was also observed by a number of investigators working on different adsorbents, for example, tannin [76], rejected tea [77], magnetic graphene-CNTs [78], and N and S co-doped porous carbon spheres [79].…”