Oxidization Of Carbon By Nitric Acid And Application

In the present work, cellulose, lignin and Fir wood were carbonized in different temperatures to prepare the chars. The oxidation was carried out using nitric acid as oxidant.Boehm titration, elemental analysis, nitrogen adsorption and laser particle size analyzer were employed to analyze its surface chemical properties, porous structure and particle size of the chars in order to investigate the influence of the oxidation on the properties of the chars. Based on the oxidation results, carbon quantum dots was prepared by nitric acid oxidation of the chars.The results show that oxidization increased significantly the concentration of acidic functional groups. The oxygen containing functional groups clogged the pores contained in the chars and thus decreased their surface area and pore volume. The char prepared at the higher carbonization temperature is more difficult to could be oxidized. The oxidation at a higher temperature led to a higher oxidation degree. The preparation method and the microstructure of the chars have an obvious effect on the oxidation degree of the char. Cyclic oxidation followed by a heat treatment after each oxidation increased significantly the surface area and pore volume of the chars. Oxidizing with nitric acid also led to a decrease in the particle size of the chars.Carbon quantum dots were prepared by oxidizing with nitric acid the char obtained at the carbonization temperature of 400 oC. The optimal oxidization conditions were as follows: 3 mol/L nitric acid solution, oxidation temperature of 100 oC for 4 h. After separating the suspension by neutralization, microfiltration, ultrafiltration and dialysis, the carbon quantum dots of 5~6 nm was obtained. Passivation improved fluorescence intensity of carbon quantum dots. Fluorescence intensity of the carbon quantum dots improved with the increase in the passivation time or passivation temperature. The optimal passivation temperature is 100 oC.