Abstract
Plant fibers represent a rich and inexpensive source of easily renewable carbon fibers with various potential applications. In this study, nitrogen-doped carbon flakes (NCFs) and nitrogen-doped hollow carbon fibers (NHCFs) were prepared from Calotropis procera fibers (CPFs) by controlling the conditions of the carbonization process. The pre-oxidation of CPFs plays a vital role in maintaining their morphology after carbonization at high temperature. Scanning electron microscopy (SEM) images confirmed that the carbonized CPFs at 400 οC without pre-oxidation produced NCFs-4, but after carbonization at 500 and 600 οC via the pre-oxidation process, the hollow-fibers retained their morphology and produced NHCFs-5 and NHCFs-6, respectively. Structural characterization of the NCFs and NHCFs was conducted by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), Raman spectroscopy and X-ray diffraction (XRD) and BET analysis. All samples showed a mixture micro/mesoporous structure with a BET surface area of 474.66, 469.29 and 987.80 m2/g for NCFs-4, NHCFs-5 and NHCFs-6, respectively. The prepared NCFs and NHCFs were applied as effective adsorbents for the removal of cationic crystal violet dye (CV) from polluted water. The obtained results showed that the NHCFs-6 sample exhibited a maximum adsorption capacity of 160.18 mg/g. The prepared samples follow the order NHCFs-6 > NCFs-4 > NHCFs-5. The nonlinear Redlich-Peterson model successfully simulated the adsorption isotherm of CV dye removal. The kinetics study demonstrated that the pseudo-first-order (PFO) model is the best model for simulating adsorption kinetics on the NHCFs-6 surface, while the pseudo-second-order model was the best model on the surface of NCFs-4 and NHCFs-5.
[Display omitted]
•Carbon fibers and flakes were prepared from Calotropis procera fruit.•The morphology of fibers and flakes are controlled by carbonization conditions.•Prepared carbon fibers and flakes used as powerful adsorbent for dyes removal.•Adsorption isotherm and kinetic were studied by different nonlinear models.•The adsorption mechanism was concluded as endothermic and spontaneous process.