Preparation and Application of Single-Atom Cobalt Catalysts in Organic Synthesis and Environmental Remediation

From Single Atoms to Clusters: Unraveling the Structural Evolution of Pt/CeO2 for Enhanced CO Oxidation

The structural evolution of catalysts and the identification of active sites are critical yet challenging aspects of heterogeneous reactions. In this work, we investigate the structural evolution of Pt/CeO2 catalysts during CO oxidation by using theoretical calculations, focusing on the influence of initial catalyst states on the resulting active sites and reactivity. Our findings reveal that under the reaction conditions, single Pt atoms gradually aggregate into Pt clusters. When single Pt atoms are substituted for surface Ce atoms (Ptin), the resulting small clusters (Ptn) are exclusively formed based on Ptin. However, when both Ptin and surface-adsorbed Pt atoms (Ptad) coexist, additional small surface-adsorbed clusters (Ptnad) are generated. An increase in the Ptad/Ptin ratio leads to a higher proportion of clusters at the active sites, which correlates with enhanced CO oxidation activity as the number of clusters increases. This study underscores the importance of understanding catalyst evolution and active site dynamics under the reaction conditions, providing theoretical insights for the rational design of more efficient catalysts.

Biochar Meets Single-Atom: A Catalyst for Efficient Utilization in Environmental Protection Applications and Energy Conversion

Single-atom catalysts (SACs), combining the advantages of multiphase and homogeneous catalysis, have been increasingly investigated in various catalytic applications. Carbon-based SACs have attracted much attention due to their large specific surface area, high porosity, particular electronic structure, and excellent stability. As a cheap and readily available carbon material, biochar has begun to be used as an alternative to carbon nanotubes, graphene, and other such expensive carbon matrices to prepare SACs. However, a review of biochar-based SACs for environmental pollutant removal and energy conversion and storage is lacking. This review focuses on strategies for synthesizing biochar-based SACs, such as pre-treatment of organisms with metal salts, insertion of metal elements into biochar, or pyrolysis of metal-rich biomass, which are more simplistic ways of synthesizing SACs. Meanwhile, this paper attempts to 1) demonstrate their applications in environmental remediation based on advanced oxidation technology and energy conversion and storage based on electrocatalysis; 2) reveal the catalytic oxidation mechanism in different catalytic systems; 3) discuss the stability of biochar-based SACs; and 4) present the future developments and challenges regarding biochar-based SACs.

Antioxidant activities of metal single-atom nanozymes in biomedicine

Nanozymes are a class of nanomaterials with enzyme-like activity that can mimic the catalytic properties of natural enzymes. The small size, high catalytic activity, and strong stability of nanozymes compared to those of natural enzymes allow them to not only exist in a wide temperature and pH range but also maintain stability in complex environments. Recently developed single-atom nanozymes have metal active sites composed of a single metal atom fixed to a carrier. These metal atoms can act as independent catalytically active centers. Metal single-atom nanozymes have a homogeneous single-atom structure and a suitable coordination environment for stronger catalytic activity and specificity than traditional nanozymes. The antioxidant metal single-atom nanozymes with the ability of removing reactive oxygen species (ROS) can simulate superoxidase dismutase, catalase, and glutathione peroxidase to show different effects in vivo. Furthermore, due to the similar structure of antioxidant enzymes, a metal single-atom nanozyme often has multiple antioxidant activities, and this synergistic effect can more efficiently remove ROS related to oxidative stress. The versatility of single-atom nanozymes encompasses a broad spectrum of biomedical applications such as anti-oxidation, anti-infection, immunomodulatory, biosensing, bioimaging, and tumor therapy applications. Herein, the nervous, circulatory, digestive, motor, immune, and sensory systems are considered in order to demonstrate the role of metal single-atom nanozymes in biomedical antioxidants.

Mediated Peroxymonosulfate Activation at the Single Atom Fe-N3O1 Sites: Synergistic Degradation of Antibiotics by Two Non-Radical Pathways

The activation of persulfates to degrade refractory organic pollutants is a hot issue in advanced oxidation right now. Here, it is reported that single-atom Fe-incorporated carbon nitride (Fe-CN-650) can effectively activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) removal. Through some characterization techniques and DFT calculation, it is proved that Fe single atoms in Fe-CN-650 exist mainly in the form of Fe-N3O1 coordination, and Fe-N3O1 exhibited better affinity for PMS than the traditional Fe-N4 structure. The degradation rate constant of SMX in the Fe-CN-650/PMS system reached 0.472 min-1, and 90.80% of SMX can still be effectively degraded within 10 min after five consecutive recovery cycles. The radical quenching experiment and electrochemical analysis confirm that the pollutants are mainly degraded by two non-radical pathways through 1O2 and Fe(IV)═O induced at the Fe-N3O1 sites. In addition, the intermediate products of SMX degradation in the Fe-CN-650/PMS system show toxicity attenuation or non-toxicity. This study offers valuable insights into the design of carbon-based single-atom catalysts and provides a potential remediation technology for the optimum activation of PMS to disintegrate organic pollutants.