Efficient DBT removal from diesel oil by CVD synthesized N-doped graphene as a nanoadsorbent: Equilibrium, kinetic and DFT study

Abstract

Adsorptive Dibenzothiophene (DBT) removal from diesel oil stream on nitrogen doped graphene (N-doped graphene) was considered. The N-doped graphene was synthesized by chemical vapor deposition (CVD) method at 1000 °C using camphor and urea. The adsorbent was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and Nitrogen adsorption/desorption technique. Adsorption parameters such as temperature, time, concentration and mass loaded were optimized by experimental design method. Experimental kinetic data was fitted to Pseudo second order model successfully. Frendulich model was recommended for experimental isotherm data. However, Tempkin model was presented because of the importance of interaction between pyridinic nitrogen and DBT aromatic structure. The results indicate that not only the pore volume and surface area but also types of surface functionalities have an important role for DBT adsorption process, especially for the adsorbates with aromatic structures. The adsorption capacity was calculated up to 73.4 mg/g which is 1.25 times higher than the adsorption capacity of pristine. Thermal regeneration stability, fast adsorption kinetics and high adsorption capacity make N-G4 a potential promising adsorbent for DBT removal. Besides, density functional theory calculations revealed that an increase in the number of doped N atoms as well as the presence of a mono or divacancy defect in N-doped graphene can enhance the adsorption energy of DBT.