Evidencing the synergistic effects of carbonization temperature, surface composition and structural properties on the catalytic activity of biochar/ bimetallic composite

The effect of pyrolysis temperature on biochar properties is more exacerbated when combined with the presence of metallic dopants on the surface of the lignocellulosic material. Herein, we investigate the relationship between the surface composition (SC), the graphitization degree (GD), the particle size (PS) and the catalytic activity of mandarin peel biochar decorated with copper and nickel alloy. All biochar samples were prepared by a wet impregnation of the metal ions followed by slow pyrolysis of the Cu2+/Ni2+-loaded biomass at temperatures ranging from 300 degrees to 700 degrees C, for 15 min and under N2 atmosphere. Interestingly, the biochar with the highest GD was obtained at 300 degrees C; its surface contained CuNi alloy and NiO, whereas it contained only the bimetallic alloy for all samples fabricated at 500 and 700 degrees C. The 300 degrees C and 500 degrees C samples have mean PSs in the nanoscale regime, 71 & PLUSMN; 12 nm and 54 & PLUSMN; 12 nm, respectively. On contrast, the 700 degrees C biochar composites have very broad PS distributions in the 30-400 nm size range. They were also found to be the least graphitized samples. Prac-tically, the 300 degrees C nanocomposite was the most active catalyst for the oxidative degradation of Methylene Blue, chosen as a model reaction for the catalytic performance testing. The degradation was total under H2O2 con-ditions, and the kinetic experimental data fitted the pseudo-first-order with degradation apparent constant 0.071 min-1. Despite its lowest mean particle size and graphitization degree, higher than the graphitization degrees of the 700 degrees C nanocomposites, the sample elaborated at 500 degrees C was the least active catalyst. Its highest K to C atomic ratio suggests that potassium emerging from the biochar surface had a poisoning effect which deactivated the CuNi alloy. Conclusively, these findings permitted to gain more insights into the synergistic effects of surface composition, particle size and graphitization degree on the catalytic activity of Biochar-supported CuNi alloy elaborated at different pyrolysis temperatures.