Application of modified graphene oxide-chitosan composite for the removal of 2-methylpyridine using fixed bed adsorption and subsequent regeneration of the adsorbent by UV photolysis

Abstract

This article focuses on the development of a photolytically regenerable and practically applicable graphene oxide nanomaterial (GON) based composite adsorbent for the fixed-bed column treatment of 2-methylpyridine (2Mp). The transformation of nano-sized GON into a macro-sized adsorbent was achieved by crosslinking it with a biocompatible crosslinker, chitosan, and then coating it onto sand (abbreviated as GCS). FTIR revealed the nature of the crosslinking as amide bonding. GCS was found to interact with 2Mp via hydrogen-bonded ionic pair mechanism. Column studies of GCS with 2Mp followed Thomas kinetics at variable flow rates, bed depths and initial 2Mp concentrations. The adsorption capacity of GCS was 7.8 mg/g. The hydraulic character of flow was determined as laminar (Re < 1). Doehlert Design of experiment was used in modeling/optimization of experimental data. The polynomial model predicted an optimal column breakthrough time of 645.9 ± 10.63 min, with a regression coefficient of 0.99. Linear terms of bed depth and flow rate had the most impact on prediction. Thereafter, the regeneration of exhausted GCS was performed using direct UV photolysis, based on the SALDI mechanism. No photocatalysts/chemicals were necessary. Regeneration efficiency of 96.5 % was obtained using irradiation time of 30 min and power input of 0.96 W/cm2. GCS was reusable in 10 cycles of adsorption-regeneration, without losing significant adsorption capacity. The spent liquor obtained afterwards was remediated using batch photolysis prior to its discharge into the eco-system. Therein, the mechanism for photo-degradation of 2Mp was found, where succinic acid was detected as the eco-friendly end product. This study overcomes the practical difficulty in application of photolysis to large influent volumes by first isolating 2Mp on the GCS surface and then subjecting it to photolytic treatment in a 95.56 % smaller solution volume.