Synthesis and characterization of bi-functionalized graphene and expanded graphite using n-butyl lithium and their use for efficient water soluble dye adsorption

Abstract

Two effects of an organolithium reagent (n-butyl lithium) on graphene and expanded graphite are reported. Its ability to simultaneously scavenge protons and act as a nucleophile leads to a bi-functionalized graphitic system. Subsequent treatment with carbon dioxide gas generates carboxylic functionality at the proton abstraction sites. This technique promises a greener method for single pot carboxylation for graphitic materials. The nucleophilicity of n-butyl lithium leads to efficient grafting of butyl groups. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis are used to prove the success of the reaction. Raman spectroscopy reveals more defect sites for expanded graphite compared to graphene, which leads to a higher degree of functionalization. Atomic force microscopy shows that the functional groups generated are nano-spike-shaped pendant structures attached to the graphene. These functionalized materials are used as adsorbers for efficient and fast removal of water-soluble dyes by non-covalent interaction between the dye and the carboxylic groups of the graphitic system. Spectrometric as well as kinetic studies are reported for crystal violet lactone dye adsorption. Both the modified materials show twice the adsorption capacity of the pristine materials. Superior dye adsorption properties were observed for the modified materials compared to graphene oxide.