Preparation Of K₂Ta₂O₆/Ag/g-C₃N₄ Z Photocatalyst And The Application In Simulated Dye Wastewater Treatment

Printing and dyeing wastewater has the characteristics of large volume,large color,high stability,toxic and harmful,and difficult to degrade,which seriously threatens the safety of water environment and human production and life.As a new discipline,photocatalytic technology brings hope to the treatment of printing and dyeing wastewater.In this paper,a series of pyrochlore type K2Ta2O6were prepared by hydrothermal method by controlling hydrothermal temperature,hydrothermal time and KOH concentration.In order to find the best preparation conditions,the degradation rate of methylene blue(MB)simulated dye wastewater was taken as the reference index,and its photocatalytic performance,morphology and phase were investigated by X-ray diffraction(XRD),field emission scanning electron microscope(FE-SEM)and UV visible spectrophotometer(UV-VIS).When the hydrothermal temperature reaches 180℃or above,the raw materials can basically react completely.With the increase of hydrothermal temperature,the particle size of samples increases significantly;With the increase of hydrothermal time,more K2Ta2O6 photocatalysts can be formed.The results showed that the optimal reaction conditions were as follows:hydrothermal temperature 180℃,hydrothermal time 24 hours,KOH concentration 2.5 mol/L.K2Ta2O6 prepared under the above conditions has a regular octahedral structure with a band gap of about 4.5 eV.Under 3 × 8 W UV irradiation,86.695%of MB can be degraded in 3 hours.On this basis,the graphite phase g-C3N4 was successfully prepared by hydrothermal method and secondary calcination method.The prepared samples have lamellar structure,the thickness of which is about 117-234nm,and the length of which is about 24nm μm.The band gap is about 2.5eV.It can degrade 5%MB in 3 hours under the irradiation of 35W xenon lamp.K2Ta2O6/g-C3N4 composite photocatalysts with different mass ratios were prepared by ultrasonic dispersion method.When the mass ratio of K2Ta2O6 to g-C3N4 was 1:2,the photocatalyst had the highest photocatalytic activity,and the catalytic mechanism was proposed.Although the suitable band gap structure can make K2Ta2O6 and g-c3n4 form type Ⅱ heterojunction,due to the limitation of type Ⅱ heterojunction itself,the improvement of photocatalytic performance is not obvious.K2Ta2O6/Ag/g-C3N4 composite photocatalysts with different mass fraction of Ag were prepared by photoreduction method.The photocatalytic performance of K2Ta2O6/Ag/g-C3N4 composite photocatalysts was investigated with the degradation rate of MB as the reference index.The crystal structure,phase,morphology and light absorption characteristics of K2Ta2O6/Ag/g-C3N4 composite photocatalysts were characterized by XRD,SEM,UV-Vis and EDS.K2Ta2O6 and g-c3n4 are closely adsorbed on each other,and the surface of K2Ta2O6 has irregular protrusion,which is the surface loaded Ag.The EDS spectrum also shows this point well.With the increase of Ag content,the absorption of K2Ta2O6/Ag/g-C3N4 composite photocatalyst in the visible light range is gradually enhanced,the composite photocatalyst has the best photocatalytic performance.On this basis,the effects of MB concentration,dosage of photocatalyst and pH value on the photocatalytic performance of K2Ta2O6/Ag/g-C3N4 were also investigated.PH value has a great influence on the photocatalytic activity.High pH value can improve the photocatalytic activity,otherwise it can inhibit the photocatalytic activity.When pH was 12.5,97.58%of MB could be degraded.