Synthesis Of Silver-containing Photocatalysts And Their Catalytic Properties

Photocatalytic technology,which is valuable in environmental pollution control,has been widely recognized and concerned.For instance,TiO2 photocatalytic technology can mineralize organic pollutants into non-toxic matter,but it suffers from highphoto-generated electron-hole recombination rate,low utilization of visible light,and difficult recovery of catalyst,etc..Thereby motivated,we herein aimed to modify TiO2 or to find new efficient and stable photocatalytic materials.Ag3PO4(2.36 eV)was an efficient photocatalytic material.By having strong binding ability,P-O bonds in the PO4 tetrahedron of Ag3PO4 significantly weakened Ag-O covalent bond,prevented Ag 4d and O 2p orbits from hybridization,and deviated 4d orbit from the bottom of conduction band.Therefore,the charges at the conduction band bottom and electrons interacted mildly,which facilitated the transfer of charges to particle surface to activate redox.By first-principles calculations,Zhu et al.ascribed the superior oxidation capacity and quantum efficiency of Ag3P04 to low valence band,and the much higher migration rate of electrons than that of holes owing to the ?*molecular orbits in conduction band.In addition,PO43-electrostatic induction should also be considered.Thus,the photocatalytic oxidation ability of Ag3PO4 is markedly increased after electrons and holes are effectively separated.Although pure Ag3PO4 is already photocatalytically active,fabricating stable and efficient Ag3PO4 photocatalytic materials with sustainable high activity remains a challenge.In this paper,the visible-light-photocatalyst Ag3PO4 and Ag/AgBrO3 are studied.The main contents are as follows:(1)Ni2+-doped Ag3PO4(Ni2+-Ag3PO4)photocatalysts with superhigh activity for photodegradation of organic pollutants were prepared by a simple hydrothermal method.The photocatalysts were characterized with X-ray powder diffractometry,transmission electron microscopy,scanning electron microscopy,ultraviolet-visible absorption spectroscopy,X-ray photoelectron spectroscopy,measurement of total organic carbon,and electron paramagnetic resonance spectrometry.The photocatalysts were evaluated by methyl orange(MO)photodegradation experiments under visible light irradiation(?>420 nm).Comparative analysis showed the optimal doping dosage was 0.05 mol/L Ni2+.The optimal Ni2+-Ag3PO4 has an MO photodegradation rate constant four times larger than pure Ag3PO4.The Ni2+ doping into Ag3PO4 can increase the level of band gap,and accelerate the utilization of photons and the separation of photo-generated charges.Therefore,the Ni2+ doping into Ag3P04 is responsible for the enhancement of photocatalytic ability.(2)F-doped Ag3PO4 was synthesized by an ion exchange method,and its structure and properties were characterized systematically by X-ray powder diffractometry,transmission electron microscopy,ultraviolet-visible absorption spectroscopy,X-ray photoelectron spectroscopy and electron paramagnetic resonance spectrometry.Doping F-ions into the crystal lattice of Ag3P04 changed the properties of particles,further inhibiting the recombination of photoinduced electrons and holes.The testing of methyl orange(MO)photodegradation showed that F0.05-Ag3P04 had the highest activity.-OH radicals were the main active species in the oxidation of MO over F0.05-Ag3P04.Doping F-substantially reduced ·OH defects on the surface of Ag3P04,which significantly increased the degradation efficiency of MO over Ag3PO4.(3)A high-activity AgBr/Ag3P04 heterojunction photocatalyst was synthesized based on etylmethylammonium bromide.Its microspheres were characterized with X-ray diffractometry,transmission electron microscopy,ultraviolet-visible absorption spectroscopy and photoluminescence spectroscopy.The new photocatalyst with higher photocatalytic activity exceptionally outperforms pure Ag3P04 and AgBr in methyl orange degradation.The enhancement of photocatalytic activity is attributed to the efficient separation of electron-hole pairs.-OH formed in the photocatalytic reaction may be the main reactive oxygen species that induces the visible-light-driven degradation.(4)A new Ag/AgBr03 photocatalyst was prepared by mixing aqueous solutions of AgNO3 and NaBrO3.The catalyst's structure and performance were investigated with X-ray powder diffraction,transmission electron microscopy,and X-ray photoelectron spectroscopy.The UV-vis absorption spectrum of Ag/AgBr03 exhibits a band gap of 3.97 eV.The results show that the Ag/AgBr03 semiconductor can be excited by ultraviolet light.The photodegradation of Rhodamine B displayed much higher photocatalytic activity than that of N-doped Ti02 under the same experimental conditions.Moreover,·OH and ·O2-generated in the photocatalysis played a key role in the photodegradation of Rhodamine B.