Heterogeneous Single- and Double-Atom Catalysis for Environmental Remediation and Public Health Protection
Open AccessChemical and biological contamination found in an aquatic environment continuously pose threats to human health and ecosystem. There is always an urgent need for advancing effective, robust, and sustainable water treatment methods to degrade emerging contaminants and inactivate pathogenic microorganisms. Heterogeneous single- and double-atom catalysis integrating the advantages of both homogeneous and heterogeneous catalysis has arguably become the most active new frontier in catalysis that can potentially upgrade the current catalytic advanced oxidation processes in treating contaminated water. This dissertation for the first time focuses on the development of heterogeneous single-atom catalysts (SACs) and double-atom catalysts (DACs) in environmental remediation of organic contaminants and pathogen disinfection for public health protection.First, we developed a heterogeneous single-atom Fe catalyst supported on a nitrogen-rich carbon support (Fe-CN), which mimicked the active sites of peroxidase enzymes to display the peroxidase-like activities for oxidizing a broad spectrum of contaminants of emerging concern (CECs) by activating peroxides such as peroxymonosulfate (PMS). Since the local bonding environment of single-atom metal centers is critical to the catalytic reactivity and selectivity of heterogeneous SACs, we tailored the electronic structure of Fe atoms by introducing oxygen heteroatom into catalysts for the preparation of a heterogeneous single-atom Fe catalyst supported on an oxygen-doped, nitrogen-rich carbon support (SAFe-OCN). By investigating the catalytic performance of Fe-CN-activated PMS (Fe-CN/PMS) and SAFe-OCN-activated PMS (SAFe-OCN/PMS) systems in CEC degradation, we found that SAFe-OCN, with a catalytic center of Fe coordinated with both nitrogen and oxygen, showed 5.13-times increased phenol degradation kinetics upon activating PMS compared to Fe-CN catalyst where Fe was only coordinated with nitrogen. Wet-lab experiments together with molecular simulations demonstrated that SAFe-OCN catalyst activated PMS to produce nonradical species (i.e., high-valent Fe-oxo species) which induced the oxidation treatment, and SAFe-OCN catalyst was an excellent multiple-electron donor which could potential-readily form high-valent Fe species upon oxidation compared to Fe-CN. In the SAFe-OCN/PMS system, most selected CECs (i.e., sulfamethoxazole, 4-chlorophenol, bisphenol A, diclofenac, atrazine, salicylic acid, and phenol) were amenable to degradation and SAFe-OCN showed excellent performance for contaminant degradation in complex water matrices and high stability in oxidation. Although SAC is a new frontier in heterogeneous catalysis because the well-defined and atomically dispersed metal centers on catalyst supports can maximize the metal utilization efficiency and help achieve high catalytic activity and selectivity, the catalytic performance of heterogeneous SACs might suffer from its structural simplicity. Therefore, we increased the density of Fe active sites on Fe-based SACs (Fe SACs) by introducing another Fe site to develop Fe-based DACs (Fe-Fe DACs). Fe species on Fe-Fe DACs still maintained the atomically dispersed nature, and the introduction of an adjacent Fe site increased the binding strength between metal atoms and the targeted intermediates. This time, Fe SACs and Fe-Fe DACs were developed on pristine graphitic carbon nitride (CN) and sulfur-doped graphitic carbon nitride (SCN). Regardless of whether catalysts were prepared on the support of CN or SCN, Fe-Fe DACs were 3.32–3.50 times more reactive than their counterpart of Fe SACs for phenol oxidation by activating PMS. In addition, Fe-Fe DAC developed on SCN (Fe–Fe/SCN) and Fe SAC developed on SCN (Fe/SCN) degraded phenol 10.4 and 11.0 times faster than Fe-Fe DAC developed on CN (Fe–Fe/CN) and Fe SAC developed on CN (Fe/CN), respectively. Notably, all catalysts had a similar Fe loading (0.51 ± 0.09 wt %). These results highlighted the excellent performance of catalytic oxidation by introducing the Fe–Fe dimer and the S-dopant into the catalyst, and we further demonstrated that Fe–Fe/SCN activated PMS likely through a nonradical route of catalyst-mediated electron transfer. As the best catalyst candidate in this part of our study, Fe–Fe/SCN was employed in pathogen disinfection treatment for public health protection. We decided to look at the disinfection efficacy of Fe–Fe/SCN-activated PMS system for inactivating emerging coronaviruses, and murine hepatitis virus strain A59 (MHV-A59) was used as a surrogate for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This Fe–Fe/SCN catalyst enhanced PMS disinfection kinetics for inactivating MHV-A59 by 2.17–4.60 times when compared to PMS treatment alone in diverse environmental media including simulated saliva and freshwater. The molecular-level mechanism of MHV-A59 inactivation was also elucidated. Fe–Fe double-atom catalysis promoted the damage of not only viral proteins and genomes but also internalization, a key step of virus lifecycle in host cells, for enhancing the potency of PMS disinfection. In summary, the designed heterogeneous SACs and DACs activated peroxides to produce nonradical species (i.e., high-valent Fe-oxo species) or derive nonradical-driven pathways (i.e., catalyst-mediated electron-transfer) for advancing the oxidation treatment under peroxide activation for effective degradation of contaminants of emerging concern (CECs) and pathogen inactivation in complex water matrices. The electronic structure of Fe atoms was tailored by introducing different heteroatoms (i.e., oxygen and sulfur) into catalysts, and this helped evaluate the importance of local bonding environment to the catalytic reactivity and selectivity of Fe SACs and Fe-Fe DACs, which in turn facilitated contaminant degradation and pathogen disinfection even in complex water matrices. And the synergistic effects of double-Fe atoms on Fe-Fe DACs were systematically investigated to demonstrate the superiority of heterogeneous DACs over their counterparts of heterogeneous SACs. To understand the mechanisms of contaminant degradation, both experimental and theoretical approaches were used to identify the reactive species involved in single- and double-atom catalysis treatments. The biomolecules and biofunctions of pathogens were quantitatively evaluated at the molecular level to clearly illustrate the disinfection action and potency of single- and double-atom catalysis on the microorganisms. We believe that heterogeneous single- and double-atom catalysts can optimize the oxidation treatment processes in both chemical and biological decontamination treatments and less chemical and energy input will be required.
- All rights reserved
Notice to Authors
If you are the author of this work and you have any questions about the information on this page, please use the Contact form to get in touch with us.