Metal ion adsorption and organic material degradation for waste water treatment using nanostructured graphitic carbon nitride

Abstract

Contamination of water can cause lots of environmental problems, therefore to purify waste water contaminants such as heavy metal ions and organic materials, adsorption and photocatalysis process were studied in here. We developed various nanostructured carbon nitride $(g-C_3N_4)$ which is consisted of tri-s-triazine nitrogen structure stacking in graphitic manner, i.e. non-structure (Bulk), MCA, HS, and 3-d cubic $g-C_3N_4$ to get large surface area and expose its functionalities such as -N=/-NH-/-NH2. The functionalities can be considered as ac-tive sites for adsorption of metal ions due to the lone pair electrons on nitrogen atom. Additionally sp2 hybridization of carbon and nitrogen atoms of $g-C_3N_4$ shows elec-trical and optical properties similarly with semiconductors which are used as photo-catalyst such as $TiO_2$. Correspondingly the semiconductor properties of $g-C_3N_4$ can utilize to remove organic materials in waste water. The metal ion adsorption isotherm studied with respect to initial concentration, pH, temperature, time, and existence of light exposure. Furthermore, organic materials were degraded using metal ion supported $g-C_3N_4$ by adsorption to enhance its photo-catalytic activity. Among various structures and metal ions, the silver ions can be remove ca. 417 mg/g onto 3-d $g-C_3N_4$ due to its large surface area and pore volume. From kinetics study, the mechanism of silver ion adsorption was investigated that chemical sorp-tion is dominant and redox sorption portion is raised with increasing sorption time. Moreover, heat of adsorption which was calculated at 298.15 and 318.15 K using Van’t Hoff and Sips isotherm equation is indicated the heterogeneity and non ideality of real process. To remove organic materials in waste water, Rhodamine B was degraded using commercial $TiO_2$ nanoaprticle, nanostructured $g-C_3N_4$, and silver ion assisted $g-C_3N_4$ by adsorption. The photocatalytic ability can be enhanced using 100 mM silver ion do...