Study On The Structure Design And Catalytic Mechanism Of Two Heterojunction Photocatalysts Based On Polyhedron-like WO₃

Nowadays,environmental pollution had become a worldwide problem.For instance,a large amount of organic dye contained in untreated industrial wastewater became a hidden danger threatening the ecological environment after it was discharged into rivers and mountains.Up to now,there were many methods to degrade such organic pollutants,including photocatalytic degradation,adsorption degradation and biological treatment,etc.While,considering the cost and efficiency,the most effective way to degrade pollutants was photocatalytic degradation.However,most traditional Ti O₂ could only be stimulated by UV region light?consists of only 4%solar spectrum?,which resulted in low utilization of Solar energy.As was known,WO₃,an indirect band gap photocatalyst,due to its smaller band gap energy?Eg?,owned the good absorbing ability towards the light from the UV to the Visible light region,the stable properties and controllable morphology,now having attracted the large number of researchers.However,the practical application and popularization were severely limited,owing to its narrow sunlight utilization and fast recombination rate of photo-induced charge carriers.To solve these defects and limitations above,we firstly selected hydrothermal method to synthesize the polyhedron-like WO₃ nanoparticles,and secondly combined them with Ag₂CO₃ nanoparticles,constructing the heterojunction system at the interface of two semiconductors to accelerate the separation of photo-excited electrons and holes,resulting in that the process of charge recombination was effectively inhibited.In this work,Rhodamine B?RhB?or 2-Chlorophenol?2-CP?were selected to be targeted degraded molecule in the visible light irradiating system,a proper enhancement mechanism was presented and photocatalytic enhanced reason was studied.The main research contents were as follows:?1?Polyhedron-like WO₃ nanoparticles were also synthesized via a hydrothermal process and high temperature calcination.Series of characterization methods such as XRD,XPS,TEM,HR-TEM,SEM,EDS,BET,DRS and PL were used to analyze the prepared nanomaterials.XRD results showed that the polyhedron-like WO₃nanoparticles had a very good correspondence with the monoclinic phase WO₃?JCPDS No.43-1035?.Combined with the tested measurement of SEM and TEM,the average axial length and radial length of each polyhedron-like WO₃ was about 300 nm and 500nm.It could be seen that numerous polyhedron-like WO₃ nanoparticles were stacked together to form hierarchical WO₃ nanoflowers.The tested results of UV-vis diffuse reflectance spectra?DRS?showed that the band gap of pure polyhedron-like WO₃sample was 2.66 e V,which was only able to absorb irradiation light with a wavelength shorter than about 470 nm.To investigate the specific surface area and distribution about every pore size towards the polyhedron-like WO₃,the nitrogen and desorption isotherms were isotherms were implemented.The pore-size distribution of it was in the range 2-50 nm and the average S_BET of the polyhedron-like WO₃ was calculated to be2.6141 m²g^-1.?2?WO₃/Ag₂CO₃ and WO₃/Ag₂Mo O₄ binary heterojunction nano-catalyst was prepared by a simple impregnation-deposition method and the photocatalysts were also characterized by XRD,SEM,BET,XPS,DRS,SEM-EDS,TEM,HR-TEM,HPLC and PL,etc.By the SEM tested data,we could see numerous polyhedron-like WO₃nanoparticles were stacked together to form hierarchical WO₃ nanoflowers,Ag₂CO₃nanoparticles exhibited rod shape with a radial length of 400 nm and axial size of 1.75to 2?m,pure Ag₂Mo O₄ nanoparticles showed nanosheets with four wings?the average size of which is 1 mm?,which was comprised by numerous tiny Ag₂Mo O₄nanoparticles.After combination,it could be seen that there were numerous tiny polyhedron-like WO₃ nanoparticles anchored on the surface of Ag₂CO₃ nanorod.Furthermore,by comparing with the test results of XRD and XPS,all the diffraction peaks could be indexed very well with pure phase of Ag₂CO₃ and WO₃,suggesting the two type materials?Ag₂CO₃ and WO₃?successfully combined with each other.In addition,by using the UV-vis diffuse reflectance spectra,we could find the adsorption range of composite catalyst had a certain degree of red shift,suggesting the adsorption ability of composite catalyst could be strengthened to some extent.?3?Rhodamine B?RhB?and o-chlorophenol?2-CP?were selected as target degradants to evaluate the photocatalytic activity of prepared samples under full spectrum light irradiation.The test results suggested when the typical amount of WO₃ nanoparticles were located at 20 wt%,the composite catalyst?WO₃/Ag₂CO₃ and WO₃/Ag₂Mo O₄?showed the best photocatalytic ability,which was approximately 177 times/149 times higher than pure polyhedron-like WO₃,125 times higher than pure Ag₂CO₃,146 times higher than pure Ag₂Mo O₄ and even 17 times higher than commercial powder?P25?under same conditions.By using photoluminescence emission spectra,typical transient photocurrent responses test,and scavengers'experiments,the enhanced photocatalytic ability might be attributed to form the Z-scheme mode carriers separation system between pristine WO₃ and Ag₂CO₃/Ag₂Mo O₄,which made for more effective carriers'separation rate,which further promoted a continuous and efficient reaction.