Research On Photodegradation Of Styphnic Acid And Photocatalysis-membrane Separation Reactor

As a kind of advanced oxidation processes, TiO₂ photocatalysis is being deeply andwidely studied recently. The key of the research focuses on the improvement ofphotoreaction activity of TiO₂ catalyst, and the separation and recycle of the catalyst. Bothare the precondition and foundation of the practical applications of TiO₂ photocatalysis.To evaluate the photocatalytic activity of samples, the photooxidation of 2, 4,6-Trinitroresorcinol (styphnic acid) was carried out in a series of experiments. To improvephotocatalytic efficiency of TiO₂ catalyst, SnO₂ acted as electron captor was coupled on thesurface of TiO₂ to heighten separation ratio of photo-generated electrons and holes.Nonmetal ion N was involved in the crystal lattice of TiO₂ which brought about thevisible-light sensitization of TiO₂. Magnetic photocatalyst (TiO₂/Fe₃O₄), which are liableto be separated and recycled, were prepared using Fe₃O₄ as support. To accomplish therecycle of catalyst membrane filtration technology was combined with Photooxidation andmake the system run continuously. The primary study was listed as following:(1) Poisonous organic pollutant 2, 4, 6-Yrinitroresorcinol (styphnic acid) could bedegraded effectively in TiO₂ photocatalytic suspension system. An optimal concentration ofTiO₂ existed under a definite irradiation degree of UV, 1g·L^-1 in the experiment. The resultsof duality linear regression indicated that the reaction time was an important variable forthe evaluation of ln(C₀/C). Reaction velocity of photocatalytic degradation decreased withthe accretion of the initial consistence of the pollutant. The fitting addition of O₂, H₂O₂,Fe³⁺, Cu²⁺ and Zn²⁺ which played the role as electron acceptor could raise the degradationrate of the reaction. And a lower pH was favorable to the degradation of styphnic acid. Theabsorption of character peek of styphnic acid was reduced with the operation of thereaction, which was consistent with the trend of TOC degradation rate. It indicated thedegradation of the organic pollutant.(2)TiO₂-SnO₂ coupled catalytic particles have been prepared with SnO₂ aggrading onTiO₂ in the method of symmetrical precipitation. The best way to obtain the catalysts shouldbe: 1.0 mol·L^-1 NH₄HCO₃ acted as precipitator dropped at the velocity of 0.2 mL·s^-1 intothe solution with the initial concentration of Sn⁴⁺ 0.02 mol·L^-1, and pulsator stirred at aspeed of 200 r·min^-1 simultaneously, the whole reaction acted at 20℃, the mass ratio ofTiO₂ and SnO₂ was 9:1. Then the deposition should be calcined at 600℃. The degradationrate of 50 mg·L^-1 2, 4, 6-Trinitroresorcinol was 93.2ï¼…in compared with 79.9ï¼…when economical TiO₂ was used as catalyst. TiO₂-SnO₂ coupled catalyst were composed withanatase TiO₂ and square crystalline SnO₂. Sn/Ti atom ratio on the samples surface washigher than which was in the inner phase and coupled SnO₂-TiO₂ was formed. Because ofthe involvement of SnO₂, the energy gap of the coupled catalyst was increased by 0.1 eV.Effectively separation of photo-generated electrons and holes was accomplished andphotocatalytic efficiency was improved because of the photo carrier transmitted in coupledcatalyst on the surface of which Sn-O-Ti bond was shaped.(3) N-doped photocatalyst was prepared by symmetrical precipitating action. N-dopingcould be carried out at a lower temperature (300℃), and NH₄HCO₃ was chosen asprecipitating agent and source of nitrogen. N-doped photocatalyst was obtained throughultrasonic separation and calcinations in N₂ atmosphere of the deposit, which was generatedin the reaction of Ti(SO₄)₂ and NH₄HCO₃. Moreover, the catalyst showed excellentphotocatalytic activity under the irradiation of UV and visible light, light absorptionshowed red-shift and absorption region has been enlarged to 468nm. Washing determine thepossibility of N-doped. The samples calcined after washing was specially yellow whichindicated N was doped, while the samples without treatment of washing showed white. TheTi-O bond changed because of the doping of nonmetal ions N. It was estimated theformation of N-Ti-O asymmetric deformation vibrations band. Doped N was dispersed intothe TiO₂ crystal lattice simultaneously, and the N-Ti-O net was shaped consequencely. Theelectron binding energy of O atom decreased. Photocatalyst existed in the formation ofdifferent crystal phase. N-doping could counteract the disadvantages of the crystal shape ofobtained catalyst calcined under lower temperatures, and the catalyst showed goodperformance of photoreaction.(4)Magnetic photocatalyst TiO₂/Fe₃O₄ (the mass ratio is 3:1) has been prepared in themethod of mechanochemistry using Fe₃O₄ as magnetic support. Ti⁴⁺ in the crystal lattice ofTi-O-Ti has been partially substituted by Fe³⁺, which brought about the structure of Ti-O-Febridging oxygen. The photocatalytic ability of obtained coupled catalyst was close to theability of purchased TiO₂. The doping of SiO₂ impurity brought in the process ofmechanical attrition, which was ascribed to the equipment by chinaware material, has notinfluenced the photocatalytic ability and magnetic separation ability of catalyst.Photocatalytic reaction was first-order reaction kinetics. The experiments have been carriedout to test the ability of magnetic separation of catalyst with magnetic reactor which weremade by ourselves. The separation rate was as high as 93ï¼…which meant the bettermagnetic separate ability of prepared catalyst. (5)TiO₂ particles of 20nm diam. in suspension liquor could be intercepted very well inphotocatalysis-membrane separation reactor, in which polypropylene hollow fibermembrane of 0.1μm～0.2μm diam. has been used. The optimum pressure in the operationwas 0.02MPa. The concentration of catalysts effects lightly to membrane flux in theaverage concentration range of photocatalytic reaction. Increasing aeration intensity couldmitigate the pollution degree on deposit layer and reduce the resistance of membrane, theeconomical aeration intensity is 0.4m³Â·h^-1 in the system. Membrane flux would increasewhen solution pH approach to the equipotential point of TiO₂, vice versa. Differentelectrolyte in the solution made influence to the property of charge on the surface ofparticles: CaCl₂ make the resistance decreased, Na₂SO₄ increased and the exist of NaCleffected slightly. Studies showed that the reversible resistance is the main reason causingmembrane fouling. Controlling suction pressure, choosing logical aeration intensity andperiodic running can greatly alleviate membrane reversible fouling. Flux of pollutedmembrane could be recovered up to 99ï¼…by means of washing by water, ultrasoniccleaning, dipping in 0.5ï¼…NaOH+0.2ï¼…NaClO liquid, and then 0.5ï¼…HCl in turn.The photocatalytic of 2, 4, 6-Trinitroresorcinol experiments was carried out inphotocatalysis-membrane separation reactor. The concentration of 20 nm diam. TiO₂ was1.5 g·L^-1, operation press 0.02 MPa, 13 minutes of suction time 2 minutes of suctionsuspended time, about 2h of waterpower average settle time. The continuous operation for30 days is described, the results showed that turbidity removal of out water was＞99.9ï¼….