The Role of Graphene in Improving Photocatalytic Properties of Immobilized AgCl Photocatalysts and Biomimetic High Valent Iron-oxo Catalysts: Preparation, Characterisation and Evaluation towards Contaminants Degradation

Abstract

Advanced oxidation processes have been employed to address environmental contamination issues related to the presence of synthetic industrial organic chemicals, pesticides, pharmaceutical and personal care products (PPCPs). Both photocatalysis and biomimetic catalysis have attracted great interest in this area due to their green catalyst credentials of sustainability, reusability and recyclability. Plasmonic photocatalysts consisting of silver nanoparticles anchored to silver halides (Ag@'AgX) have been increasingly investigated as potentially highly efficient visible-light photocatalysts. Enhanced performance of Ag@AgX has been observed when supported on graphene-based materials as graphene has zero banggap, is oxidatively robust, has high electron conductivity and high specific surface area. However, the relationship between catalytic performance and structure change during use for the three components AgNPs, AgCI and partially reduced graphene oxide (rGO) in the assemblages has not been previously elucidated. Strategies to control the identified problem of photo-corrosion have been explored, including wavelength adjustment, graphene oxide (GO) loading, GO reduction methods, photo-reduction period, ferric iron doping and cocatalyst modification using iron oxide (FeOx). The influence of various reaction conditions including oxygen concentration, pH, ionic strength and substrate concentration were also examined in order to understand their role in the process. The integration of photoactive and/or redox active building blocks onto carbon materials to yield multifunctional electron donor/acceptor conjugates has also recently attracted extensive interest. A fundamental understanding of how factors such as coupling with or without a linker and how the incorporation of various transition metal complexes affect the electron transfer in these systems is essential to the optimal design of "smart" molecular interfaces on the "green" catalyst. This work focused on the preparation, characterisation and evaluation of both covalently and non-covalently anchored redox active non-heme iron complexes on graphene-based nanomaterials, with the phenolate-hinged ligand 2,6- bis{[bis(2-pyridylmethyl)amino]methyl}-phenolato(1-) (denoted as bpbp in this work) and the tetraamido macrocyclic ligand (TAML) considered using various immobilization strategies (such as a microwave­assisted in situ diazonium grafting method and a normal heating-assisted diazonium grafting method). This work has progressed the development of novel sustainable catalysts for the remediation, transformation and mineralization of contaminants in the environment.