Analysis of the Effect of Conditions of Preparation of Nitrogen-Doped Activated Carbons Derived from Lotus Leaves by Activation with Sodium Amide on the Formation of Their Porous Structure.

Mirosław Kwiatkowski,Xin Hu

doi:10.3390/ma14061540

Abstract

This paper presents results of the analysis of the impact of activation temperature and mass ratio of activator to carbonized precursor R on the porous structure of nitrogen-doped activated carbons derived from lotus leaves by carbonization and chemical activation with sodium amide NaNH2. The analyses were carried out via the new numerical clustering-based adsorption analysis (LBET) method applied to nitrogen adsorption isotherms at −195.8 °C. On the basis of the results obtained it was shown that the amount of activator, as compared to activation temperatures, has a significantly greater influence on the formation of the porous structure of activated carbons. As shown in the study, the optimum values of the porous structure parameters are obtained for a mass ratio of R = 2. At a mass ratio of R = 3, a significant decrease in the values of the porous structure parameters was observed, indicating uncontrolled wall firing between adjacent micropores. The conducted analyses confirmed the validity of the new numerical clustering-based adsorption analysis (LBET) method, as it turned out that nitrogen-doped activated carbons prepared from lotus leaves are characterized by a high share of micropores and a significant degree of surface heterogeneity in most of the samples studied, which may, to some extent, undermine the reliability of the results obtained using classical methods of structure analysis that assume only a homogeneous pore structure.

Highlights

The rapid growth of industrialization and urbanization is resulting in an increase in the level of pollution emitted to the natural environment
The results of the earlier calculations carried out via the BET, T-plot and DR methods based on nitrogen adsorption isotherms determined at −195.8 ◦C [31], collected and presented in Table 1, demonstrate that in the case of activated carbons prepared at R = 1, as the activation process temperature values increased, the value of structure parameters increased too, i.e., the SBET specific surface area calculated by the BET method, the Smicro, T-Plot micropore surface area calculated by the T-plot method, and the micropore volume Vmicro DR, Vmicro T-Plot, Vmicro Density Functional Theory (DFT) calculated successively using the DR, T-plot and DFT methods as well as the total pore volume Vtotal DFT calculated by the DFT method
On the basis of the results obtained, it was shown that the amount of activator, as compared to activation temperatures, has a significantly greater influence on the formation of the porous structure of activated carbons

Summary

Introduction

The rapid growth of industrialization and urbanization is resulting in an increase in the level of pollution emitted to the natural environment. The surface of activated carbons is hydrophobic, which allows for adsorption processes from aqueous solutions and gaseous streams with a high degree of humidity. The large increase in interest in activated carbons in recent centuries and the increase of research to expand their manufacture processes are due both to increased needs in traditional fields of application and the development of new technologies based on the use of these materials. Adsorption processes from the liquid phase on activated carbons are used, among others, in the treatment of water intended for food, in the food industry and in the treatment of wastewater from industrial processes [4]. Adsorption processes from the gaseous phase on activated carbons are used in the treatment of gaseous streams, in the separation of gaseous mixtures, in the recovery of solvents and in natural gas and hydrogen storage processes [5]

Methods

Results

Discussion

Conclusion