Study On Covalent Functionalization And Catalytic Mechanism Of Low-Dimensional Black Phosphorus

Recent years,as a new member of the two-dimensional material family,the monolayer or few-layer black phosphorus,have attracted great interests of many researchers due to its broad bandgap,high carrier mobility and on/off current ratio,high anisotropy and other unique characteristics.Due to the weak van der Waals bonding between the layers,monolayer or few-layer black phosphorus(also known as phosphorene)can be prepared from bulk crystals by simple mechanical exfoliation.During the vigorous development of phosphorene,another zero-dimensional black phosphorus nanostructure,namely black phosphorus quantum dots,has also been successfully synthesized through chemical methods and achieved breakthroughs.Based on the unique properties of black phosphorus and quantum dot structures,the emerging zero-dimensional black phosphorus has been explored in many fields,which include physics,chemistry,biology,medicine and other disciplines.Low-dimensional black phosphorus materials have broad prospect of applications in many fields.However the main challenge of black phosphorus is its rapid oxidative degradation in circumstances.Covalent chemical modification by organic functional groups can prevent its degradation.In this article,we discuss the effect of covalent functionalization on the electronic structure of monolayer black phosphorus.We use the Many-body perturbation based on the Green’s function to study the structural system of monolayer black phosphorus covalently functionalized by forming P-C bonds through GW approximate calculation.Our results indicate that the functional groups with low concentration are preferentially adsorbed on the intrinsic vacancies in black phosphorus,which can effectively avoid the combination of the intrinsic vacancies and the oxygen in air that can form the harmful defect complex.It can delay the oxidation of black phosphorus and improve the semiconductor performance.However,the functional groups with high concentration will adsorb on the perfect lattice site of black phosphorus and introduce a defect state which may serve as a recombination center.In addition,the adsorption of the functional groups on the perfect lattice can accelerate the oxidation process of black phosphorus and then deteriorate the performance of the materials.Throughout the progress of low-dimensional black phosphorus in various areas,photocatalytic water splitting is undoubtedly a innovative and significant topic.Ourcalculation and analysis indicate that the two-dimensional black phosphorus cannot be directly applied to the photocatalytic water splitting reaction.But for black phosphorus quantum dot,its valence band maximum is below the oxidation potential of water,and the conduction band minimum is above the reduction potential of hydrogen.From the requirement of energy level matching,it can be used directly for photocatalytic water splitting.In addition,we also calculated the exciton energy level through the BSE equation.The absorption edges shift to lower energy due to the presence of excitons.As the size increases,the binding energy of exciton tend to decrease.Theoretically,there is a suitable size in which the bound excitons can be decomposed into free carriers under the certain condition to carry out catalytic reactions.Our results provide a theoretical basis and reference for the subsequent application of black phosphorus quantum dots in the field of photocatalytic water splitting.In short,the results we have achieved,both the electronic properties of covalently functionalized two-dimensional black phosphorus and the catalytic mechanism of black phosphorus quantum dots,have great innovation and value,which can provide references and new ideas for future study in these fields.