Abstract:
Congo red dye is one of many dangerous dye substances known to man. Its presence even in trace amounts poses great risk to living organisms. In this work, graphene nanoparticles were prepared from coal using both chemical and thermal methods and were used to remove Congo red dye from aqueous solution. The prepared adsorbents were analysed using scanning electron microscopy, Energy dispersive X-ray, Fourier transmission infrared spectroscopy and X-ray diffraction. The various adsorption parameters of pH, contact time, concentration and temperature were investigated using batch procdure. The Langmuir, Freundlich and Temkin Isotherm models as well as Kinetic parameters were used to analyse and determine adsorption mechanism. Optimal pH for the removal of Congo red was pH 5 for raw coal and SCG-2 and pH 3 for SCG-1. The Langmuir Isotherm gave the best fit for both raw coal and SCG-1 while SCG-2 best fits into the Temkin isotherm. Maximum amounts absorbed per gram of adsorbent were 36 mg/g for raw coal, 163 mg/g for SCG-1 and 99 mg/g for SCG-2 at 25 oC. The pseudo-second order model appropriately described the kinetic data and intra-particle diffusion revealed that other mechanisms beyond diffusion such as complexation or Hydrogen bond formation was involved. The adsorption thermodynamics revealedthat the process was endothermic for raw coal and SCG-2 while that of SCG-1 was exothermic and spontaneous with ΔG values at 12.71 kJ/mol, -0.9 kJ/mol and 8.00 kJ/mol for raw coal, SCG-1 and SCG-2 respectively.. The study showed that all investigated adsorbents can effectively be used to remove Congo red dye from industrial wastewater effluents. However, the chemically treated graphene gave the best percentage removal at 99% with raw coal and SCG-2 averaging 90% removal rate
