Preparation of graphene-supported-metal-phthalocyanine and mechanistic understanding of its catalytic nature at molecular level

The fundamental mechanistic understanding of the working principle of metal phthalocyanine (MPc) + H2O2 system, at molecular level, is in its nascent stage. In this paper, a green strategy was employed for the immobilization of sulfonated cobalt phthalocyanine (CoPc) onto reduced graphene with assistance of bio-synthesized nanocellulose, and the resulting graphene-supported-CoPc (CoPc&G) was applied for the catalytic degradation of phenol solution with H2O2 as oxidant. More than 90% of phenol can be removed within 75 min, and the existence of graphene clearly has a positive effect on the catalytic activity. Theoretical calculations were conducted to unveil the catalytic nature of CoPc&G. H2O2 was favorably chemisorbed onto CoPc&G in the form of OOH-, hydroxyl radicals were favorably formed by homolytic cleavage of OO bonds, and ΔG value for the formation of reactive species was decreased with the existence of graphene. Density of states (DOS) analysis shows that graphene could effectively boost the electronic activity, reduce HOMO-LUMO gap, and strengthen the polarizability of the catalyst, thereby lower the free energy gap for the enhanced generation of reactive species. A detailed catalytic degradation route of phenol with CoPc&G + H2O2 system was established based on the combination of theoretical calculations and experimental results.