Study On Preparation And Adsorption Performance Of Hydrothermal Activated Carbon From Walnut Shell

Walnut shell is a kind of widely existed waste biomass, as well as a renewable, biodegradable and environmentally friendly natural resource. Walnut shell, an important raw material for preparing carbon material, which can be used in dealing with environmental pollutants as a new environmentally friendly carbon material. Hydrothermal carbonization has been a hot topic for carbon materials research in recent years. In this study, based on the hydrothermal carbonization, hydrothermal carbon material walnut shell was chosen as the activated precursor. The method for preparing the hydrothermal carbon material and its adsorption ability were characterized. The relative results we have got as following:Firstly, temperature is essential to the hydrothermal carbonization process within a closed container. Scanning electron microscopy, infrared spectroscopy and elemental analysis were used to characterized the products with the temperature range from 180 to 250?. The results showed that, the carbon content increased up to 70.31% at 240?, and the calorific value was also increased when compared to other temperature. The activated precursor, which was prepared with simple process and mild conditions of hydrothermal method, can be provided as basic structure for the subsequent activation. It could reduce the entire cost of the process of activated carbon preparation.Secondly, the hydrothermal carbon material which has the highest carbon content was used for the chemical activation. Different conditions on the performance of the activated carbon samples were studied, which included the activation temperature (500 ?,600?,700?, 800? and 900?), the activation time (30 min,60 min,90 min,120 min and 150 min) and the mass ratio of KOH to hydrothermal carbon (1:1,2:1,3:1,4:1 and 5:1). The optimum carbon material was prepared by univariate statistical analysis and orthogonal optimization test. The hydrothermal activated carbon properties were assessed by relative surface area, the pore volume, average pore diameter and the adsorption of methylene blue (MB). The results showed that the walnut shell hydrothermal carbon with 240 ? as a precursor, temperature 800?, mass ratio 3:1, activation time 120 min were the best optimation conditions for the hydrothermal carbonization. Based on this conditions, the absorption for MB was 498.52 mg/g, the relative surface area, total pore volume and micropore volume for the prepared activated carbon material were 2892.70 m2/g,1.281 cm3/g and 0.416, respectively. The micropore structure played important role for the prepared activated carbon material. The prepared activated carbon material has a better adsorption capacity compared to traditional activated carbon.In addition, this study have researched the effects of walnut shell hydrothermal activated carbon dosage, initial concentration, pH and residence time on adsorption capacity for MB. The corresponding sorption constants and kinetic constants were obtained by kinetic analysis and adsorption isotherm fitting. The results showed that Langmuir model can be used to characterize the absorption kinetic process. R square value of the pseudo second model was up to 0.9996 for the absorption process.