Preparation And Adsorption Properties Of Low-Sulfur Expanded Graphite(EG)

Expanded graphite is a novel carbon material, it appears porous structure and a large surface area. So it has a strong adsorption capacity to the macromolecular compound, and has been widely used in various fields. In recent years, expanded graphite plays more and more important role in dealing with industrial wastewater and adsorption of oil spills.In this paper the optimum preparation conditious of low-sulfur expanded graphite has been studied. Same means such as FE-SEM, XRD, FT-IR and TG-DTA has been used to characterize the physical properties of expanded graphite. Meantime, the volume influence of the amount of expanded graphite, initial dye concentration, temperature, pH and stirring speed in adsorption processes of rhodamine B and methyl orange have been examined. The effects of oil viscosity in the adsorption process of various oil has been also studied; Moreover, adsorption kinetics and adsorption thermodynamic for EG adsorbing two kinds of dyes have been studied. The obtained results are as follows:Expanded graphite has porous wormlike morphology and three stage pore structure.The optimum conditions for preparing the low sulfur expandable graphite are as follows:natural flake graphite(g): perchloric acid(mL): glacial acetic acid(mL): potassium permanganate(g) = 8: 20: 14: 1, intercalation temperature is 20 ℃, intercalation time is60 min, microwave puffing power is 420 W, puffing time is 15 s.The influence order of the factors is as follows: CH3 COOH volume > HClO4 volume > intercalation temperature > intercalation time>puffing power.During the adsorption processes of rhodamine B and methyl orange by increasing the amount of expanded graphite, initial concentration of the dye solution, temperature and stirring speed, the adsorption quantity of EG can be improved. Moreover, the adsorbability of expanded graphite can be increased with increasing viscosity of oil;Based on the research of exfoliated graphite dosage, the initial concentration of the dye solution, adsorption temperature, stirring speed and pH value, we have found that the adsorption process follows the pseudo-second-order model, the liquid film diffusion internal diffusion within the particles and surface adsorption processes are included in the adsorption two dyes.The results showed that Langmuir adsorption models could be used to describe the adsorption processes of rhodamine B and methyl orange, indicating that it is a monolayer adsorption based on physical adsorption. In the two adsorption processes, reaction enthalpy change △H>0 indicating endothermic reaction, and elevated temperatures are conducive to the reaction; The adsorption entropy change ΔS > 0, show that the adsorption is a process of entropy increment; the adsorption free energy change ΔG<0,indicating that the adsorption is a spontaneous process. The value of the reaction active energy is in the range of 8 kJ·mol-1 to 30 kJ·mol-1.