Novel organic dye sorbent: synthesis and adsorption properties of multi-walled carbon nanotubes modified with gallic amide units

Abstract

By reacting acyl chloride-MWCNTs with gallic amino derivative containing three long alkyl chains, novel gallic-MWCNTs 4 was prepared in good yield. Its structure was characterized by Fourier translation infrared spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The gallic derivative content of gallic-MWCNTs was 14.5 wt%. Its adsorption experiments for four cationic and anionic dyes [Orange G sodium salt (OG), Brilliant ponceau 5R (BP), Neutral red (NR), and Methylene blue (MB)] were investigated. The adsorption process attained to adsorption equilibrium in 2.5 h under the condition of 5.0 mg of sorbent in dye solutions (10 mL, 2.0 × 10−3 M) in the thermostatic shaker bath with a shaking of 200 rpm at 25°C. The saturated adsorption capabilities were 0.642 mmol/g (289 mg/g), 0.537 mmol/g (324 mg/g), 0.891 mmol/g (256 mg/g), and 0.823 mmol/g (310 mg/g), respectively. The adsorption processes were exothermic and spontaneous, and obeyed pseudo-second-order model and the Langmuir isotherm equation. The adsorption capacities for anionic dyes (OG and BP) decreased with the increase in the pH values of solution and the adsorption capacities for cationic dyes (NR and MB) showed reverse changes.