Removal of crystal violet from wastewater using synthesized graphene quantum dots as adsorbents: kinetic approach

Aromatic triarylmethane dyes residues cause serious water pollution in environment. Adsorbents, such as graphene oxide (GO), have great potential for using them for removal of dyes such as crystal violet (CV) from wastewater. The GO was prepared from graphite-flakes (G) through chemical exfoliation method. The synthesized materials were characterized by the scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), ultraviolet-visible, and Fourier transform infrared spectroscopies and then were tested their potential toward removal of the CV from aqueous solution via adsorption. Different parameters, i.e., adsorbent nature, adsorbent dose, appropriate temperature, contact time, and concentration of dye, were used to check the efficiency of adsorbents for the removal of the CV. Adsorption experimental results show that the removal capacity of dye for graphene oxide, graphite, and graphene quantum dots (GQDs) were recorded, i.e., 32.12, 33.48, and 34.46 mg/g, respectively, at T = 303 K with 0.1 g/L adsorbent dosage and 200 mg/L of adsorbate content for reaching efficient treatment time (60 min). The adsorption results show that the maximum removal efficiencies of the CV by the GO, the graphite (G), and the GQDs were recorded as: 94.86, 93.25, and 99.1%, respectively, for a 50 mg/L of dye solution. Moreover, the thermodynamic parameters show that the percent removal of dye and adsorption capacity in (mg/g) were enhanced with an incline in heating; this meant that the dye uptake for these adsorbents acted endothermic process. The Gibbs energy free (- ?G), entropy (+ ?S), and enthalpy (+ ?H) values showed that the uptake/adsorption of CV by these adsorbents is spontaneous, endothermic, and entropy-driven in nature. The kinetic experiment shows that the adsorption data of CV dye on G, GO, and GQDs obey both the pseudo-first and pseudo-second-order adsorption mechanism. The adsorption on the prepared samples follows Langmuir and Freundlich isotherm models. Among these models the most fitted model was Langmuir adsorption isotherm and that the adsorption process is mostly performed by chemisorption with single coverage layer.

Automated summary

Aromatic triarylmethane dyes residues cause serious water pollution in the environment. Adsorbents such as graphene oxide (GO) have been found to effectively remove crystal violet (CV) dye from wastewater. Different parameters and experimental results indicate that GO, graphite, and graphene quantum dots (GQDs) have high removal capacities for CV dye, with GQDs showing the highest efficiency. Thermodynamic and kinetic experiments suggest that the adsorption process is spontaneous, endothermic, and follows both pseudo-first and pseudo-second-order kinetics. The Langmuir adsorption isotherm model fits the adsorption data best, indicating chemisorption with single coverage layer.