Study On Preparation And Photocatalytic Activity Of Metal Lons Doped Titanium Dioxide/Zeolite Composites

It has been deeply studied on the treatment of organic pollutants inwastewater by semiconductor photocatalytic degradation. Thepollutants can be entirely broken down to non-poisonous matters byphotocatalytic degradation which can be finished at normal temperatureand pressure in short time, so photocatalysis method has become oneof the most effective methods to degrade vary kinds of pollutants.Titanium dioxide has became an important and developingphotocatalyst for its higher stability and activity, cheapness,non-poisonous difficulty to dissolve in the acid and alkali conditions.However, usual suspension photocatalysis oxidation had somedisadvantages, such as inclination to inactivate and agglomerate,difficulty to reuse and easiness to cause the second pollution. Theseshortcomings seriously limited the application of titanium dioxide. Soresearchers focused the emphases on the syntheses of the immobilizedphotocatalyst that could enhance its photocatalytic activity. It waspossible to introduce defect or change location crystallization degreeson the semiconductor surface by mixing metal ions, which prolong thetime of the compound of the electron and hole, and availably increasethe optical catalytic activity of TiO₂. The titanium dioxide sol wassynthesized by acid-catalyzed sol-gel method and then the metal ionsdoped TiO₂/zeolite photocatalyst supported on natural zeolite wasobtained. The chemical combination was achieved between titaniumdioxide and the mineral that has a bigger specific surface area. Theexperimental results showed:Firstly, Preparation and Photocatalytic Activity of Rare Earth MetalIons doped TiO₂/ natural zeolite composites were discussed. Diameterof Natural zeolite and Photocatalytic Activity of Rare Earth Metal Ionsdoped TiO₂/zeolite composites had a direct relationship. PhotocatalyticActivity of titanium dioxide was better when the tiameter of Naturalzeolite was scrappier. And the concentration of Rare Earth Metal Ionsinfluenced Photocatalytic Activity of titanium dioxide. The experimentalresults showed that making use of Rare Earth Metal Ions doped andnatural zeolite supported titanium dioxide treated at 200 ℃ had the bestphotocatalytic activity. Structure test showed it was anatase that had thebest crystallization and the biggest content at 200℃ . The synthesizedtitanium dioxide transformed from anatase to rutile gradually when thecalcinated temperature increased. But at the same time theconfiguration of the natural zeolite had little change. The producing ofelectron and hole were easier for anatase than that of rutile, so thefomer had a higher photocatalytic activity. The photocatalyticdegradation rate of organphosphorous pesticides can reach to91.62% when the conditions were as follow: UV lamp, high pressuremercury vapor lamp, λ=365nm, the diameter of zeolite was 0.15mm,only La3+ was doped, TiO2:La3+=100:3.0, no acid and oxidant wereadded , illuminating time was 120min. When Nd3+ and Yb3+ were dopedrespectively with the same conditions, the Photodegradation rate were78.06% and 58.72%. The cation exchange capacity of zeolite withdifferent diameter and photocatalyst self-made reduced since that theywere doped. It was probable that the TiO2 doped with Rare Earth MetalIons affect the tunnel of zeolite or the titanium on the zeolite were builtup, so the result were reduced since that they were doped with RareEarth Metal Ions.Secondly, Preparation and Photocatalytic Activity of Metal IonsDoped TiO2/ natural zeolite composites were dealt with. When diameterof natural zeolite was 0.20mm, and natural zeolite was treated 2h at200℃ and doped concentration of Metal Ions was TiO2:Xn+=100:3.0(Xn+ :Metal Ions), preparation Metal Ions doped TiO2/ natural zeolitecomposites. The influence factors—the initial pH, the addition ofhydrogen peroxide, the content of titanium dioxide ,the initialconcentration of methyl -orange and the reaction time onphotocatalysis degradation— were studied further with methyl -orangeas aim contaminants. The results showed that Metal Ions doped TiO2/natural zeolite composites methyl -orange could be easily decomposed.The problem in using titanium dioxide as a photocatalyst wasrecombination of electron and hole. One strategy for inhibiting theirsrecombination was to add other electron accepters to the reaction. Itcould reduce the electron/hole recombination and then producemore ·OH on the surface of titanium dioxide, which increased thedegradation rate of the methyl -orange. The methyl -orange couldincrease the oxidation rate with increasing Hydrogen peroxideconcentration. Above the optimal concentration, hydrogen peroxidecaused a significant inhibition of the degradation rate of the methyl -orange. So the degradation rate also connected with the concentrationof the methyl-orange. The initiative acidity of methyl – orange affectedphotocatalyst, the methyl – orange could be easily decomposed atstrong alkaline conditions pH=9.0 and could be broken down at pH=4.0.The dosage of photocatalyst and The initiative concentration of methyl –orange affect the degradation rate like the Hydrogen peroxide, whichexisted the optimal dosage—0.4000g/100mL and 10.0mg/L. Thephotocatalyst without washing and the torrefaction repeatedly utilized 6times, the catalytic Activity was scarcely influenced. It could beconcluded that the photocatalyst could be reused when itsphotocatalytic activity became stability.In a word, the experiment made TiO2 activator adopting impureload and machine-made load. The TiO2/zeolite having higherphotocatalytic activity was made with natural zeolite, metal Ions andusing the acid-catalyzed sol-gel method. It was concluded that thepreparation of TiO2/zeolite having higher photocatalytic activityoptimized the application of TiO2 and enlarged the utilization of naturalzeolite with special structure and performances in synthesizingadvanced functional materials.