Low-temperature Controllable Preparation And Optical Properties Of Bi₂O₃ Nanomaterials

Bismuth oxides?Bi₂O₃?nanomaterials,especially nanostructures with tuned size,morphology and dimensionality,have a range of applications due to their intrinsic size dependent properties and outstanding physical–chemical properties,such as particular electrical,optical and fast-ion conducting characteristics.Hence,the controllable synthesis of Bi₂O₃ nanomaterials has been a subject of intense research.This paper is dedicated to prepare bismuth oxides nanomaterials with different dimensions and crystal phases,such as?-Bi₂O₃ nanoparticles,one dimension?1D??-Bi₂O₃ nanorods and nanowires,three dimension?3D?hierarchical flower-like?-Bi₂O₃ and metastable phase?-Bi₂O₃superconstructure,metastable phase?-Bi₂O₃ tetrahedral and cubic single crystal and so on,via a simple,mild,green and cost-effective solution synthesis route,such as low temperature solution precipitation process and reverse microemulsion route.And the possible formation mechanisms of the microstructures were discussed based on experimental results.The optical absorption and photoluminescence?PL?characteristics of the as-prepared sample were investigated.?1?Bi₂O₃ nanomaterials with a diversity of morphologies?dimensions?,such as nanoparticles,nanorods,nanoplates,especially one dimension?1D?quadrangular prism nanorods,were controllably synthesized successfully by a reverse microemulsion route.The influential factors,such as water content,reaction time,reactant concentration,surfactant concentration and calcination time were considered.It was found that the size and morphology of bismuth oxide were affected mainly by water content.Calcination temperature determines the crystal form of the Bi₂O₃.And Ostwald ripening and the oriented attachment play important roles in the formation of different microstructures.According to the UV–visible diffuse reflectance spectrum,the metastable phase?-Bi₂O₃sample presents photoabsorption property from UV light region to visible light range?absorption band edge is 550 nm,longer than?-Bi₂O₃ of 460 nm?.The band gap of the?-Bi₂O₃ is estimated to be 2.30 eV,which is lower than?-Bi₂O₃ of 2.74 eV.The PL spectrum of one dimension?1D?quadrangular prism?-Bi₂O₃ nanorods shows broad emission?400-600 nm?.?2?At room temperature and ambient atmospheric pressure,one dimension?-Bi₂O₃nanowires were synthesized successfully by solution precipitation method,an efficient and convenient route,in the acetone-water mixed solvent system with the assistance of oleic acid?capping agent?and n-heptane?oil phase?.It was found that oleic acid as capping agent plays an important role in the growth control of nanowires.According to the UV–visible diffuse reflectance spectrum,the as-prepared?-Bi₂O₃ nanowires sample presents photoabsorption property from UV light region to visible light range?shorter than 455 nm?.The PL spectrum shows broad emission?400-600 nm?.?3?Several kinds of three-dimensional?3D?hierarchical constructed flower-like?-Bi₂O₃ microspheres were prepared successfully via a simple solution precipitation synthesis at low temperature?95??and ambient atmospheric pressure in 1 h.The synthesis process was operated in ethanol-water system as solvent with the assistance of glycerin or oleic acid as capping agent.By adjusting the concentration of the capping agent,various flower-like?-Bi₂O₃ microspheres were obtained,such as flower-like spherical structure formed by 3D self-assembly nanocubes,flower-like?-Bi₂O₃ superstructures built from a mass of one-dimensional nanorods,3D hierarchical constructed?-Bi₂O₃microspheres formed by the 3D self-assembly of massive imperfect nanocubes,ginkgo leaf-like?-Bi₂O₃ microstructures formed by 3D self-assembly of a bunch of nanorods.Also,by choosing other addition reagents?ethylene glycol,PEG-4000?,various Bi₂O₃ with diffrtent morphologies are obtained.The formation of the flower-like superstructures was attributed to the modification of nucleation and growth kinetics,and the guidance of self-assembly approach by capping agents.A cooperation effect of Ostwald ripening and self-assembly process led to the formation of these novel flower-like hierarchical superstructures.According to the UV–visible diffuse reflectance spectrum,these four typical samples all presents photoabsorption property from UV light region to visible light range?all shorter than 480 nm?.The absorption band edges of these three-dimensional hierarchical flower-like?-Bi₂O₃ with different morphologies are slightly different.Morphology and crystal structure?such as the existence of impurities?will affect the fluorescence emission spectrum waveform and intensity.?4?Metastable?-Bi₂O₃ were successfully prepared via a controllable,facile and mild one-step solution precipitation synthesis in ethylene glycol-water mixed solvent systems,at low temperature?80??and ambient atmospheric pressure in 40 min.By adjusting ethylene glycol?EG?volume fraction,metastable?-Bi₂O₃ submicro hexahedrons,tetrahedrons,polyhedrons and three-dimensional self-assembled hierarchical flower-like architectures were obtained respectively.The flower-like metastable?-Bi₂O₃ architectures were 3D self-assembled from tetrahedrons step by step.And the influences of assistant agent?surfactant,oleic acid,alcohol?,Bi³⁺concentration and ethylene glycol?EG?volume fraction on morphology,size,purity and optical property were also investigated in detail.According to the UV–visible diffuse reflectance spectrum,compared with the?-Bi₂O₃ and?-Bi₂O₃,the metastable?-Bi₂O₃ sample presents better photoabsorption property from UV light region to entire visible light range?230-800 nm?.On the basis of the morphology and composition evolution of as-prepared metastable flower-like?-Bi₂O₃ microstructures at different reaction stages,the formation of?-Bi₂O₃ microflowers was attributed to a synergistic effect of crystal's growth habit,Ostwald ripening and self-assembly process.The aforementioned four research systems are not mutually independent,and it is a gradual process that investigated the low-temperature controllable synthesis,characterization,formation mechanism and optical property of Bi₂O₃ with special microstructures and specific crystal phases.The results will help for better understanding of the formation of hierarchical microstructures and will also contribute some valuable information to the facile,mild,cost-effective,efficient and controllable preparation of novel microstructures of Bi₂O₃ or other metal oxides nanomaterials.