Solvothermal synthesis of transition metal (iron/copper) and nitrogen co−doped carbon nanomaterials: comparing their peroxidase−like properties

In this work, iron- and nitrogen-doped carbon nanomaterials (Fe–N-CNMs) and copper- and nitrogen-doped CNMs (Cu–N-CNMs) were synthesized through a facile one-pot solvothermal approach. Their peroxidase-like properties were studied and compared. The Michaelis-constant K_m of Fe–N-CNMs with H₂O₂ or TMB as the primary substrate is 19 µM and 78 µM at optimal conditions, respectively, while K_m of Cu–N-CNMs with H₂O₂ or TMB as the primary substrate is 2.4 mM and 0.44 mM at optimal conditions, respectively. The K_m values of both types of materials are lower than or comparable to those of horseradish peroxidase (HRP). Moreover, under the same mass concentration, Fe–N-CNMs is superior to Cu–N-CNMs in achieving higher values of the maximum reaction rate V_max (e.g., 5.67 × 10^–8 M/s for Fe–N-CNMs compared to 4.68 × 10^–8 M/s for Cu–N-CNMs with H₂O₂ as the primary substrate). However, it was also found that under high concentrations of substrates (3,3,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂)), the reaction rates of Fe–N-CNMs are saturated, but the reaction rates of Cu–N-CNMs are increasing versus the concentrations of substrates and are higher than those of Fe–N-CNMs. Experimental results showed that synergistic efforts of both the catalytic mechanism and the product-microaggregation process could be involved in the Cu–N-CNM-based reaction to enhance the measured reaction rates. Potential applications were discussed on the basis of the reaction characteristics of these two peroxidase-like materials.