Structural Regulation And Photocatalytic Properties Of Phosphate Materials

Phosphate is a common inorganic material,which contains PO43-that has strong inductive effect because of the large negative charge and great dipole moment.During the photocatalytic reaction,the inductive effect of PO43-tends to attract photogenerated holes so that it can inhibit the recombination of electron-hole pairs and improve the photocatalytic activity.Thus,it has great importance in preparation of novel phosphate photocatalysts and improving the photocatalytic performance in view of microstructure control.In this thesis,we have explored some phosphate photocatalysts such as Ag₃PO₄?Cd₅H₂?PO₄?₄·4H2O?Cd₅?PO4?3OH and studied their microstructures as well as the photocatalytic performance.The main research contents are as follow:?1?Ag₃PO₄/SiO₂ composite photocatalysts have been prepared by a simple precipitation method at room temperature.The support effect of SiO₂ made the dispersion of Ag₃PO₄ increasing obviously,changing the surface structure of Ag₃PO₄ and reducing the content of Ag₃PO₄.Ag₃PO₄/SiO₂ composite photocatalysts showed excellent photocatalytic activity under the visible light irradiation.The 20 wt% Ag₃PO₄/Si O₂ composite showed the highest degradation efficiency,which was approximately twice that of pure Ag₃PO₄.The improved activity of composites was mainly attributed to the fast separation efficiency of photogenerated charge carriers and the large amount of effectively reactive species like h+ and ·O₂-.In this paper,we present a method to reduce the cost of photocatalyst by modifying with cheap oxide supports.?2?The hierarchical flowerlike Cd₅H₂?PO₄?₄·4H2O microspheres have been successfully synthesized by addition of phosphates to immobilize Cd²⁺.The influence of experimental parameters such as the initial reagents?cadmium ions and phosphate ions?and pH value on the crystal structure and morphology of the products was studied.Hierarchical Cd₅?PO₄?₂P₂O₇microspheres were readily obtained by condensation and dehydration of Cd₅H₂?PO₄?₄·4H2O precursor.Owing to the unique hierarchical structure and the strong oxidation/reduction ability,Cd₅?PO₄?₂P₂O₇ microspheres exhibited excellent photocatalytic performance,durability and structural stability for the degradation of RhB under UV light irradiation.The activity of Cd₅?PO₄?₂P₂O₇ was much higher than that of Ca?PO4?6?OH?2 and Ti2O?PO4?2?H2O?2 and comparable to that of BiPO4.The main reactive species and photocatalytic mechanism of hierarchical Cd₅?PO₄?₂P₂O₇ towards RhB degradation were also discussed.?3?Cadmium hydroxyapatite?Cd-Hap?hierarchical structures with novel supermorphologieslike quasi peanut-like,bunch-like and flower-like have been obtained by a simple template/surfactant-free and mild hydrothermal route.By properly monitoring the pH value of the reaction solutions,the morphology and structure of Cd-Hap crystals could be tuned.On the basis of a series of contrast experiments over temperature and time,the probable growth mechanism of products were proposed.The Ag₃PO₄/Cd-Hap composites showed pronounced photocatalytic property upon the degradation of MO under visible light irradiation,the 15 wt%Ag₃PO₄/Cd-Hap composite had the highest degradation efficiency CdS QDs@Cd-Hap composites also showed excellent photocatalytic H2 production activity.Surprisingly,CdS QDs-sensitized Cd-Hap with S/P ratio 7.5 showed the highest activity,the H2-production rate of which was as high as 1100 ?mol·h-1·g-1,and exceeded that of CdS by more than 5.5 times.