Fractal characteristics of biochars derived from Penicillin v potassium residue pyrolysis

Abstract

Biochar is widely used as adsorbent and catalyst carrier. Penicillin V Potassium residue (PVPR) as a hazardous waste with high organic content has the great potential to produce biochar. The adsorption performance and loading capacity of biochar largely depend on the pore structure, surface area and other physical properties. In this paper, PVPR and its pyrolysis biochar were characterized by Scanning electron microscopy (SEM), Atomic Force Microscope (AFM) and Brunauer–Emmett–Teller (BET) analysis methods. Then the changes of their 2D surface morphology, 3D roughness and pore structure with the pyrolysis temperature were analyzed using the box fractal dimension (DB), power spectral density fractal dimension (DP), and Frenkel-Halsey-Hill fractal dimension (DF), respectively. Based on the above analysis, grey relational analysis was introduced to evaluate the factors affecting the surface fractal dimensions of biochars. Results indicated that the raw sample had smooth surfaces and lower fractal dimension. The release of volatiles during pyrolysis resulted in a large number of slit-shaped microporous structures on the surface of biochar. DB and DF of the biochar obtained at 400-500℃ were in the range of 1.8–1.9 and 2.8–2.9, respectively, indicating that the biochar had a more complex 2D surface morphology and pore structure. Besides, DP of the biochar obtained at 500℃ reached the maximum value, showed that the biochar had roughest surface. As the pyrolysis temperature increased to 600-700℃, the pores were transformed to the ink bottle-shaped mesopores due to the organic matter reduced greatly. Meanwhile, the K-salts on the char surface transferred from organic phase to inorganic phase. The grey correlation between DP and average roughness (Ra) reached 0.8687. Besides, the grey correlation between internal surface area of the pore and DF (high) reached 0.9362, respectively. The findings will provide guidance for further studies on the adsorption and catalytic characteristics of biochar from PVPR pyrolysis.