Computational Design Of Graphyne-Supported Single-Atom Nanozymes

A single-atom catalyst is a catalyst in which single atoms are uniformly and dispersedly supported on a base material.The"single atom catalyst"was first proposed in 2011 when it was reported that single Pt atoms can be stably supported on the surface of Fe O_x and exhibit high catalytic activity for CO oxidation.So far,numbers of single-atom catalyst systems have been synthesized and reported,such as M-N₄(M=Co,Fe,Zn,etc.),Fe-N₅,Pt/Cu,Pt/Ce O₂,etc.The geometric and electronic structure of the catalytic center of M-N₄ and M-N₅ are similar to the metal-nitrogen activate sites of natural metalloproteases.The Fe-N₅ single-atom catalysts have been reported to have similar activity to natural oxidases.Compared with natural enzymes,single-atom nanozymes have higher stability,and the structure of the active center is unambiguous and controllable,which has become one of the research hotspots in the field of biomimetic catalysis.So far,single-atom catalysts have been reported to have the mimicking characteristics of simulating peroxidase,catalase,oxidase and superoxide dismutase,etc.,and can be used for the degradation of organic pollutants,antibacterial,anti-inflammatory,and therapeutic diagnosis.Investigating the geometry and electronic structures of single-atom catalysts and the molecular mechanism that mimics the activity of natural enzymes at the molecular level is the foundation for the development and application of single-atom nanozymes.The high activity of single-atom catalysts depends on their stable geometric structures and special electronic structures.The interaction between the single metal atom and the supporting substrate material is a decisive factor for its stability.When the interaction between the metal atom and the carrier is weak,the metals are easy to aggregate to form clusters.Herein,density functional theory(DFT)calculations were performed to study the electronic structure of graphyne(GY)supported Pd complex(Pd@GY)and its peroxidase mimicking activities.Besides,the effects of chemical modifications by different chemical groups(-H,-F,-Cl,-Br,-NH₂,-NO₂)on their electronic structures and enzyme-like activities were discussed.Secondly,the interactions between 30 transition metals(TM,Sc–Au)and the surface of synthesized graphodiyne(GDY)were investigated to evaluate whether GDY can disperse and fix metal atoms.The molecular mechanisms responsible for the peroxidase-mimicking activities on the stable TM@GDY were then studied.The results are summarized as following.(1)Pure GY has no peroxidase-mimicking activity while Pd@GY has.The chemical modifications by different groups(-H,-F,-Cl,-Br,-NH₂,-NO₂)can change the conduction/valence band energy values and the distribution of frontier molecular orbitals of GY and Pd@GY.They can also change the rate-limiting steps of the catalytic cycle for the Pd@GY peroxidase mimics.The rate-limiting step of Pd@GY-F has a lower energy barrier which leads to better peroxidase-mimicking activity.(2)19 transition metals,including Sc–Cu,Zr,Nb,Ru–Pd,La–Ta and Os–Pt,can be stably dispersed on the surface of GDY and not easily aggregate to form dimers,which proves that GDY is good support material for metal dispersion and fixation.The possible decomposition path of H₂O₂ was then studied on the surface of the stable TM@GDY complexes.The results indicate that the hydroxyl adsorption energy E_ads,OHhas good linear relationship with the decomposition reaction energy E_r of H₂O₂,so it has the ability to predict the selectivities and activities of TM@GDY mimicking peroxidase and catalase.Using E_ads,OH as the POD activity descriptor,we predict that Fe/Co/Ni/Cu@GDY may have higher peroxidase-mimicking activities.The above results provide theoretical insights for the regulations of the geometric structures,electronic structures and enzyme-like activities of graphyne-based single-atom nanozymes.