Synthesis and Characterization of Carbon-Based Nanomaterials from Lignin
Mun, Sung Phil
Hassan, EI Barbary M.
The main objective of this research was to develop a catalytic thermal conversion process for production of carbon-based nanomaterials (CNs) from kraft lignin. Four specific objectives were to: (1) understand the structural evolution of kraft lignin during its thermal treatment process; (2) investigate effects of temperature, and iron catalyst loading and morphology on the catalytic thermal conversion of kraft lignin to CNs, understand lignin catalytic thermal conversion mechanism; (3) explore potential applications of CNs synthesized from kraft lignin as an adsorbent for lead removing from contaminated water; (4) and propose effective methods for graphene material characterization. Experimental results indicated that the crystallinity of CNs from non-catalytic thermal conversion of kraft lignin increased and amorphous potion in CNs decreased with increased temperature. Specifically, as temperature increased from 500 to 1000 °C, CNs had its lateral crystallite size (La) increased from 6.97 to 13.96 angstrom, its lattice space (d002) decreased from 3.56 to 3.49 angstrom, and its crystallite (Lc) thickness was between 8 to 9 angstrom. The process of catalytic thermal conversion of kraft lignin yielded graphene-based nanomaterials such as multilayer graphene-encapsulated iron nanoparticles (MLGEINs), multilayer graphene (MLG) sheets, and MLG nanoribbons. Producing MLGEINs required a minimum temperature of 750 °C. The minimum temperature for producing MLG sheets and MLG nanoribbons was found to be 600 °C. It was found that carbonous gases from kraft lignin decomposition acted as the carbon source for MLG sheets and MLG nanoribbons formation, and solid carbon from carbonized lignin acted as the carbon source for the formation of MLGEINs. The yield of CNs increased with increased iron loading. Solid iron nanoparticles as a catalyst favor to form MLG nanoribbons, while iron nitrate favors to form MLGEINs. MLGEINs showed a good sorption capacity for aqueous Pb2+. The adsorption mechanism was mainly dominated by ion-exchange reaction. The final lead contains MLGEINs can be rapidly separated from solution through a magnet. FTIR, Raman, and HRTEM techniques are effective tools for characterizing defects in graphene-based materials. XRD technique is useful to evaluate the average structure parameters of graphene-based materials. SEM technique can be used to characterize morphology of graphene-based materials.