Contribution of pyrolytic gas medium to the fabrication of co-impregnated biochar

Abstract

Co-impregnated biochars were fabricated by pyrolysis of spent coffee grounds (SCG) or glucose as carbon (C) sources under N-2 and CO2. The formed biochar samples were characterized with FE-SEM, TEM/EDS, XRD, TGA, Raman, XPS, and BET, and further used as catalytic medium for the reduction of p-nitrophenol in the presence of NaBH4. The physicochemical characteristics of biochar significantly changed with the types of C precursor and flow gas stream. The biochar from pyrolysis of SCG under N-2 gas stream showed good dispersion of Co nanoparticles (10-20 nm) in carbon matrix as compared to that produced under CO2 stream, but BET surface area was very small (4.5 m(2) g(-1)) due to pore blockage by thermal degradation products. SCG-derived biochar formed in the presence of CO2 possessed highly porous structure due to CO2-assisted C volatilization. In contrast, for glucose-derived biochar, significant reduction in porosity of biochar occurred with excess devolatilization of C under CO2 conditions, while the pyrolysis under N-2 flow produced porous biochar. These contrasting results demonstrated the significance of structure crystallinity and thermal degradability of C precursors. The catalytic performance of biochar was better correlated with the external surface area rather than microporosity.