Micro/Nano Structure Regulation of Bismuth Vanadate-Based Photocatalytic Materials and Their Research on Photocatalytic Properties

Author:Hu Jian Qiang

Supervisor:li chao sheng zhou yong


Degree Year:2019





Photocatalytic technology by using semiconductor photocatalysis(such as,photocatalytic water splitting into H2 and O2,photocatalytic selective organic transformations,photocatalytic removal of pollutants under solar irradiation,and so on)has been considered as one of the most promising pathways for solving the urgent global energy shortage and environmental pollution issues.There are mainly scientific problems for photocatalytic technology,at present,including:low sunlight utilization,poor apparent quantum yield(AQY),serious photon-generated carrier recombination and unsatisfactory catalytic conversion.Monoclinic bismuth vanadate(BiVO4)is a promising visible-light-active photocatalyst for water oxidation with low cost,nontoxicity,good chemical stability,and appropriate valence band edge located at ca.2.4 eV,which has become one of the hotspots in the study of the field of photocatalytic technology.However,nowdays the AQY for BiVO4 used as photocatalysts still is poor,which can not reach to the applied standards in industrialization.It is as the starting point of this thesis to regulate micro/nano structure of bismuth vanadate-based photocatalysts,from this viewpoint.Their morphologies and exposed crystal facets were tailored so that we can achieve the target of improving their photocatalytic activity.Obtaining the specific innovative research results are as follows:(1)Highly symmetrical,24-faceted,concave BiVO4 polyhedron was fabricated,bounded by multiple high-index {012},{210},{115},and {511} facets.These novel-structured BiVO4 microcrystal exhibits impressive photocatalytic performance for water oxidation in the absence of any cocatalysts.The O2 evolution rate was detected 178.8 μmol h-1,which is more than two orders of magnitude higher than that of bulk materials(1.3 μmol h-1).The corresponding apparent quantum yield(AQY)of O2 evolution was measured as high as 30.7%under 420 nm light irradiation,a new record AQY for BiVO4 to our best knowledge,and roughly 60%enhancement compared with our recent 30-facted BiVO4 microcrystal enclosed by {132},{321},and {121} {Adv.Mater.2018.30,1703119),and vigorous bubbles of O2 can be clearly observed in the solution even after continuous irradiation for 1 h.Two distinct surface properties of the high-index facets contribute to the excellent photocatatyic performance of the 24-facted BiVO4 microcrystal.Firstly,the {012},{210},{115},and {511} facets expose both unsaturated Bi and V sites,and only unsaturated Bi sites on(010)and(110).V sites are energetically favorable for water dissociation.Thus,surfaces water dissociation on the high-index facets are more vigorously beneficial to than on the low-index surfaces.Secondly,in comparison with low-index surfaces(010)and(110),high-index surfaces(012)and(511)exhibit an obvious reduction in the overpotential for the oxygen evolution reaction(OER).(2)Oxygen defect-rich,and largely exposing active {010} facet-monoclinic BiVO4 nanotube was successfully fabricated.A self-curling process of nascently generating ultrathin lamellar sheet was observed responsible for the formation of the nanotube driven by built-in strain gradients persisting in non-centrosymmetry architecture.The nanotube exhibits obviously improved photocatalytic performance for both water oxidation and selective N=N coupling reaction of 5-amino-1H-tetrazole into sodium 5,5’-azotetrazolate,more than an order magnitude enhancement relative to bulk materials.The giant enhanced photocatalytic activity can be attributed to following synergism:(1)Largely exposed {010} planes on the nanotube surface is effective for adsorption and activation of the water molecules;(2)Surface structure distortion of the curling nanosheet may lead to the escape of partial surface oxygen atoms to generate abundant oxygen vacancies,which acts as electron capture centers to promote the photogenerated electrons and holes separation;(3)The ultrathin thickness of the lamellar layer greatly shortens the migration distance of the photogenerated charge carriers from the material interior to the surface,which efficiently suppresses the recombination of photogenerated charge carriers;(4)The hollow structure may also function as a photon trap well to allow the internal multi-scattering/reflection of incidence light for the enhancement of light absorption.(3)Based on the monoclinic BiV04 nanotubes above,three-dimensional BiVO4 nanotube anchored Bi2S3 nanoribbon heterostructures have been fabricated by employing bismuth(Ⅲ)dimethyldithiocarbamate(Bi(dedc)3)as both bismuth and sulfur source of Bi2S3 nanoribbon.Benefiting from the particular heterostructured(?)RiVO4/Bi2S3 heterostructures present the obviously enhanced photocatalytic activity for reduction of CrⅥ,due to they not only effectively improve the light harvesting ability,but also sharply prevent the recombination of photo-generated electron-hole pairs of the BiVO4 photocatalysts.