Controlled Synthesis and Property Study of Bismuth Based Visible-light Photocatalytic Nano-/micro-materials

Author:Li Ya Zuo

Supervisor:zhao jing zhe


Degree Year:2018





Photocatalysis is one of promising techniques concerningenvironmental treatment.The development of photocatalytic materials with high efficiency,high stability,low energy consumption,wide application scope and deep oxidation capacity is the focus of environmental technology research.Metallic bismuth and bismuth-based semiconductor materials have attracted much attention because of theirunique electronic structure,excellent visible light absorption capability,efficient and stable catalytic degradation performance under visible light irradiation,and they are becoming one of the hotspots of new photocatalytic materials.On the basis of the research background,a series of bismuth based micro-/nanomaterials with excellent photocatalytic activity and good stability were obtained through mild synthetic technology in solution.The morphologies of the products were regulated and controlled through the optimization of synthetic methods,the adjustment of nucleation and growth process,the control of the grain size,morphology,crystallinity and so on.Based on the systematic study on the synthetic method,the main factors affecting the growth and morphology of the products were analyzed,and the rational growth mechanism was deduced.Visible-light photocatalytic properties of different products were examined by degrading organic pollutants,the active species in the degradation process were detected,and the reasonable degradation mechanism were proposed.The specific works are as followed:First,bismuth nanoparticles with high activity were prepared by the bottom-up chemical reduction method in aqueous solutions.The Bi@SiO2 composite nanostructures with good storage stability were successfully obtained by in-situ growth of the SiO2 protective layer.The thickness of SiO2 shell can be regulated in the range of 3-10 nm by changing the amount of TEOS and the hydrolysis time.The catalytic activity and mechanism of Bi@SiO2 nanoparticles in the thermal decomposition of ammonium perchlorate,photocatalytic degradation of RhB and colorless bisphenol A(BPA),halogenated phenols(4-fluorophenol,4-chlorophenol,2-chloro-6-fluorophenol)were studied.The correlation between thickness of SiO2 layer and catalytic activity and cycling stability was discussed,as well as the degradation mechanism.Second,bismuth nanowires(Bi NWs)with 5-10 nm in diameter and several micrometers in length were synthesized under the guidance of PVP molecules through an aqueous reduction method.The reactions were performed first in acid for rapid nucleation and then under neutral circumstances for slow growth.The key for successful preparation of the Bi NWs is the regulation of the reduction speed by control of the pH value of different reduction stages.HRTEM results show that the Bi nanowire is a polycrystalline nanostructure formed by the orientation of single crystal nanoparticles.A solution-solid-solid(SSS)mechanism was proposed for the nucleation and growth of Bi NWs in our strategy.The as-prepared Bi NWs exhibit excellent visible-light photocatalytic activities and stable recyclability for the degradation of RhB and BPA.Under visible-light excitation,the degradation rate of RhB reached 93.2%and 99.5%after illumination for 10 min and 90 min respectively.After 39 cycles,the degradation efficiency can still reach about 90%.Third,two-dimensional bismuth nanoflakes with 2-5 nm in thickness were synthesized under the reduction of sodium hypophosphite and the guidance of PVP molecules through a low temperature aqueous reduction method.The influence of nucleation and growth time,the chain length and amount of PVP molecules were investigated on the morphology and crystal structure of bismuth nanostructures,thus the optimal synthetic conditions were determined.In the photocatalytic degradation process with combined dyes of RhB and MO,the desorption and capture experiments were undergoing to examine active species.RhB dye sensitized mechanism was deduced as a result.These provide experimental and theoretical basis for the application of Bi nanostructures in visible-light catalysis.Fourth,a series of Bi/BiOCl composite photocatalysts were successfully synthesized via an aqueous reduction process.The in-situ formed BiOCl microflowers acted as the precursor of Bi/BiOCl composite architectures.The regulation of reduction temperature and time,as well as other synthetic conditions,were discussed.During the in-situ reduction process,the Bi nanodots embedded in the(001)plane of BiOCl to form Bi/BiOCl composite structures.The Bi polyhedron/BiOCl composites with superlattice structures were formed when the reductive reaction continued along the[001]direction of BiOCl crystal.We selected Bi/BiOCl samples with different Bi microstructures to study their photocatalytic performance on the degradation of organic pollutants under visible-light irradiation.The BPA degradation efficiency can reach 91%in 20 min under visible-light irradiation over Bi/BiOCl photocatalyst with superlattice structure(little amount of RhB involved for dye sensitization).Through the capturing results of active species and the electron spin resonance characterization,the degradation mechanism over Bi/BiOCl composite photocatalysts were also proposed.Fifth,we focused on the visible-light photocatalytic properties towards colorless BPA molecules of yolk-shell Bi/BiOCl micro-/nanomateials.During the synthetic process,the reaction parameters were examined including the chain length and dosage of PVP molecule,type of the additives,concentration of glucosamine hydrochloride,reaction time and temperature,chlorine sources,etc.The growth mechanism was proposed on the basis of experimental results.The abtained yolk-shell Bi/BiOCl micro-/nanostructures through the photo-reduction process showed superior photocatalytic activity towards the degradation of BPA.The capture experiments showed that h+and·O2-are effective photocatalytic active species.In summary,this paper covers the aqueous synthesis and visible-light photocatalyticstudyofbismuth-basedmicro-/nanomaterials,especially one-dimensional and two-dimensional Bi nanomaterials.The synthetic methods are simple and feasible,the morphology and size of samples are controllable and adjustable.The as-prepared Bi-based materials exhibited superior photocatalytic performance on the degradation of organic pollutants under visible-light.