Construction Of Defective Structure In Bi-based Confined Layered Semiconductors And Their Application In Photocatalytic Selective Oxidation

Solar-driven photocatalytic organic synthesis can significantly reduce energy consumption and environmental pollution to achieve sustainable solar-chemical conversion,in which selective oxidation is an effective strategy for high value-added organic chemicals synthesis.In the selective oxidation reaction,organic molecules are combined with reactive oxygen species to achieve selective insert of carbon-oxygen bonds.The key is to activate oxygen molecules to forming corresponding reactive oxygen species for selective oxidation reactions.Singlet oxygen,a electrically neutral and long-lived reactive oxygen species,holds great promise in producing high value-added chemicals through selective oxidation reactions.However,the generation processes of singlet oxygen,including direct exciton energy transfer mechanism and two-step charge transfer mechanism,are more rigour than other reactive oxygen species.Many catalysts suffer from weak excitonic effects,difficult bulk exciton transfer,and mismatched redox potentials,resulting in low efficiency for singlet oxygen generation.Based on the previous research,we propose that Bi-based semiconductors with unique electronic structures are promising catalysts for singlet oxygen generation.The confined layered structure in Bi-based semiconductors could lead to strong excitonic effects,and hence activate ground state oxygen to singlet oxygen.Moreover,the hybridized Bi 6s and O 2p orbitals can also contribute to the directional transport of electron holes,leading to spatially separation and transfer of photo-generated charge carriers.Therefore,we focus on Bi-based confined layered semiconductors and further improve the generation capacity of singlet oxygen through defect construction,so as to realize the photocatalytic selective oxidation reaction with high selectivity and high efficiency.Here,by taking the confined layered Bi-based semiconductor as a platform,this paper focus on enhancing the efficiency of singlet oxygen generation in photocatalytic selective oxidation reaction via construction of defective structure,including constructing Bi-Br vacancy clusters to suppress the exciton non-radiative energy loss in BiOBr;surface modification of iodine atoms to extract bulk excitons of Bi2O2CO3 to the surface;doping of iodine atoms to realized the spatial separation of the energy bands in Bi2O2SiO3.In this paper,the fine structure of samples is studied by high-angle annular dark-field scanning transmission electron microscopy and X-ray photoelectron spectroscopy.At the same time,combined with density functional theory calculations,the processes of the exciton-phonon coupling process,surface exciton state energy,and electron/hole spatial separation ability were revealed.Benefiting from the improved singlet oxygen generation efficiency,the catalyst exhibits excellent reactivity for secondary amine oxidation,benzylamine coupling,and thioether oxidation under visible light.According to deep research of structure-property relationship,this paper provides new understandings for the design and regulation of Bi-based semiconductor photocatalysts.The details of this paper are summarized as follows:1.Due to its unique structure,confined layered semiconductors,have the potential to form strong excitonic effects.So,the conversion of solar energy into chemical energy through direct exciton energy transfer is expected to be realized in this class of materials.However,robust nonradiative decays governed by exciton-phonon interactions usually lead to rapid exciton depopulation in these systems,which sets limitations to exciton accumulation and hence to energy-transfer-initiated photocatalysis.In this regard,we propose that modulating exciton-phonon interactions for suppressing nonradiative energy loss in these systems would be a preliminary to gaining high-efficiency energy-transfer-initiated photocatalysis.By taking confined layered bismuth oxybromide(BiOBr)as a prototype,we highlighted that phonon engineering for suppressing nonradiative energy loss could be effectively implemented by introducing large-size defective structures(i.e.,Bi-Br vacancy clusters).By means of non-adiabatic molecular dynamics simulations and spectroscopic investigations,we identified that Bi-Br vacancy clusters could promote exciton-low-frequency optical phonon coupling while reduce exciton-high-frequency optical phonon coupling,which suppressed nonradiative decay of excitons in the system.As a consequence,the defective sample exhibit prolonged exciton lifetime and promoted exciton accumulation compared with the pristine counterpart.Benefitting from the optimizations,the defective sample possesses excellent performance in energy-transfer-initiated photocatalytic activation of small molecules.This work not only provides a comprehensive understanding of excitonic regulation in semiconductors,but also paves the way for designing advanced photocatalysts via phonon engineering.2.Since most photocatalytic reactions are carried out on the surface of the catalyst,extracting the photobiological species from the interior to the surface is an effective way to improve the performance of the catalytic reaction.Therefore,for exciton-mediated photocatalytic reactions,how to transfer excitons from bulk to surface is crucial.However,compared to charged photogenerated carriers,neutral excitons exhibits negligible response to electric field that is crucial to the directional transfer of charge carrier.Therefore,searching effective strategies to boost bulk exciton extraction is meaningful to gaining high-efficiency exciton-mediated photocatalysis.Herein,by taking confined layered bismuth oxycarbonate(Bi2O2CO3)as an example,we propose that the extraction of bulk exciton could be effectively implemented by constructing energy gradient via surface modification.On the basis of theoretical simulations and spectroscopic characterizations,we highlight that the incorporation of iodine atoms on the surface could modify the micro-region electronic structure and hence lead to reduced energy of surface excitonic states.The energy gradient between bulk and surface excitonic states endows iodine-modified Bi2O2CO3 with effective bulk exciton extraction.Benefiting from this feature,the iodine-modified Bi2O2CO3 sample exhibits promoted performance in triggering 1O2-mediated selective oxidation reaction.This work presents a prototype for regulating excitonic processes of semiconductor-based photocatalysts via surface modification.3.In addition to the activation of oxygen molecules to singlet oxygen via the exciton energy transfer mechanism,it can also be obtained through a two-step charge transfer mechanism.In this process,superoxide radicals are used as intermediates,and oxygen molecules interact with photogenerated electrons and holes alternately.However,the photocatalytic singlet oxygen generation still suffers from low efficiency due to mismatch redox capacities and low concentration of photo-generated carriers in charge transfer process.Herein,by taking bismuth oxysilicate(Bi2O2SiO3)with alternating heterogeneous layered structure as a model system,we show that iodine doping can facilitate the spatial redistribution of band on alternated[Bi2O2]and[SiO3]layers,thus promoting the separation and transfer of photo-generated charge carriers.Meanwhile,the band positions of Bi2O2SiO3 was optimized to match the redox potential of singlet oxygen generation.Benefiting from these features,iodine doped Bi2SiO3 exhibits efficient singlet oxygen generation with respect to its pristine counterpart,leading to promoted performance in selective sulfide oxidation reaction under visible light.This study offers a new strategy for optimizing charge transfer-mediated singlet oxygen generation.