Graphene oxide, kaolinite clay and PVA-derived nanocomposite aerogel as a regenerative adsorbent for wastewater treatment applications

Abstract

Present work addressed the polyvinyl alcohol (PVA)-assisted gelatinisation of thoroughly dispersed graphene oxide (GO) and Kaolinite clay sheets into hydrogel, followed by lyophilisation to prepare the lightweight (0.024 g.cm−3) and remarkably porous (96.6%) clay-GO-PVA (CGP) composite aerogel by removing of frozen water (ice) through sublimation. The macroporous channels in CGP aerogel besides the mesoporosity of constituent materials facilitated the mass transfer (wastewater) and enhanced the accessibility of surface-active sites for dye adsorption. The CGP aerogel enriched with ample oxygen functionalities exhibited negative zeta potential (−25 mV), facilitating higher adsorption of cationic dyes than anionic ones. The excellent fitting of MB dye adsorption by Langmuir equilibrium isotherm suggested uniform dye adsorption on the surface of CGP aerogel with a maximum adsorption capacity of 535 mg.g−1. The spectroscopic analyses (XPS, FTIR, Raman) revealed charge-driven electrostatic attraction, hydrogen linkages (dipole-dipole and Yoshida), π-π, and n-π interactions between the surface-active sites of CGP aerogel and organic dyes as major adsorptive pathways. The MB dye adsorption increased with temperature and gradually declined with increasing ionic strength of simulated wastewater. The weak acidic to neutral pH range showed higher adsorption of MB dye by CGP aerogel. The size, charge, and hetero atoms of organic dyes, surface-active sites, charge, and porosity of aerogel, along with accessibility to adsorption sites through structural porosity, governed the adsorption process. The CGP aerogel showed excellent regenerability for subsequent batches and exhibited 98% MB dye removal efficiency even after seven adsorption-desorption cycles. Such porous nanocomposite aerogel shows immense potential for wastewater treatment applications to remove organic pollutants.