Research On Synthesis,characterization And Photocatalytic Degradation Of Direct Orange S By BiMSnO₅?M=Er,Sm,Yb,Y?

China is a country producing dye a great quantity,discharging a large amount of dye wastewater every year,which has caused serious environmental pollution.Photocatalytic technology is an emerging technology in the field of solar energy utilization.Because of its advantages of green,energy saving,high efficiency and no secondary pollution,it has attracted increasing attention and become a hot point in the treatment of dye wastewater.In this paper,eight novel photocatalysts were successfully prepared by the high temperature solid state sintering method in the first time,BiErSnOs,BiSmSnO₅,BiYbSnO₅,BiYSnO₅,Er2SnO₅,Sm2SnO₅,Yb2SnO₅ and Y₂SnO₅.The obtained samples were characterized by X-ray diffraction?XRD?,Ultraviolet-visible spectroscopy?UV-vis?,Scanning electron microscope-energy dispersive spectroscopy?SEM-EDS?,Transmission electron microscope-selected area electron diffraction?TEM-SAED?,X-ray photoelectron spectroscopy?XPS?and Specific surface and pore size distribution measuring instrument?BET?.The test results showed that:eight samples were pyrochlore structure and cubic crystal system,with space group of Fd-3m?227?.Through the Material Studio software structure refinement,the unit cell parameter a of BiErSnOs,BiSmSnO₅,BiYbSnO₅,BiYSnO₅,Er2SnO₅,Sm2SnO₅,Yb2SnO₅ and Y₂SnO₅ were 10.3827 A,10.5139 A,10.3360 A,10.4192 A,10.3412 A,10.4573 A,10.2544 A and 10.3705 A respectively.All the samples were irregular granular,with uneven particle size distribution and smaller specific surface area,and the particle sizes of BiErSnOs,BiSmSnO₅,BiYbSnO₅ and BiYbSnO₅ were significantly smaller than that of Er2SnO₅,Sm2SnO₅,YbSnO₅ and Y₂SnO₅,and the crystallinity of the first four samples were significantly better than that of the latter four.In addition,the band gap or the maximum absorption wavelength of BiErSnOs,BiSmSnO₅,BiYbSnO₅,BiYSnO₅,Er2SnO₅,Sm2SnO₅,Yb2SnO₅ and Y₂SnO₅ were 1.86 eV or 667 nm,2.59 eV or 479 nm,2.24 eV or 554 nm,2.32 eV or 534 nm,3.05 eV or 406 nm,2.93 eV or 423 nm,3.59 eV or 345 nm and 3.73 eV or 331 nm,and BiErSnO₅ had the narrow band gap,possessing the highest absorption performance to visible light.In the visible light photocatalytic degradation experiments,Direct Orange S as the target pollutant,the dosage of the eight photocatalysts and the dye initial concentration were determined to be 1.0g/L and 0.025mmol/L.And the photocatalytic activity of the eight samples and nitrogen doped titanium dioxide?N-TiO2?was compared under the same experimental conditions.The effects of light intensity,pH and inorganic salt on the photocatalytic activity of BiErSnOs were also investigated in detail.The experimental results show that:After 20 minutes,the removal rates of Direct Orange S by BiErSnO₅,BiSmSnO₅,BiYbSnO₅,BiYSnO₅,Er2SnO₅,Sm2SnO₅,Yb2SnO₅,Y₂SnO₅ and N-TiO2 were 98.32%,84.44%,96.09%,94.64%,68.08%,79.12%,60.16%,55.80%and 80.64%respectively,and the removal rate of TOC were 94.64%,81.48%,92.09%,89.49%,62.18%,73.18%,56.03%,49.98%and 76.65%without adjusted pH under 500W xenon lamp irradiation.BiErSnO₅ had the highest photocatalytic activity,of which dye removal rate and TOC removal rate were increased by 21.9%and 23.5%respectively with respect to N-TiO2.The enhancement of the light intensity was beneficial to the photocatalytic reaction.The acidic or strong alkaline conditions were favorable for the photocatalytic reaction,but neutral or alkalescent conditions had opposite effect.Moreover,NaCl played a role in promoting photocatalytic reaction,and Na2SO4 played a negative role.In addition,the photocatalytic degradation mechanism of Direct Orange S was studied with BiErSnO₅ as photocatalyst through adding different scavengers which can eliminate relevant active groups.Also,the performance stability of BiErSnOs was tested.The results showed that dissolved oxygen was the most important factor of photocatalytic degradation of Direct Orange S by BiErSnOs,followed by the superoxide anion and the hole,and the hydroxyl radical was the weakest.After four times recycling experiment,BiErSnOs could maintain a high photocatalytic activity.