The Preparation Of Series TiO₂/PTh Photocatalysts By Low-temperature Hydrothermal Method And Their Photocatalytic Properties

TiO₂photocatalyst has caused wide attention of scholars at home and abroad because ofmany advantages of excellent photocatalytic performance. However, there are many problems.TiO₂of suspended phase exist some shortcomings, such as easy agglomerate, difficult recycle,no continuous operation. TiO₂was loaded on the surface of bulk materials exist the decreaseof catalytic efficiency because of transfer efficiency and catalyst amount. TiO₂was loaded onthe surface of Fe₃O₄and has close contact,on the one hand, TiO₂molecules may migrate tomagnetic core Fe₃O₄and lead to weaken of magnetism and decrease of recovery rate, on theother hand, Fe₃O₄might permeate to TiO₂and lead to recombination of photogeneratedelectrons and light and decrease of catalytic efficiency because the forbidden band of Fe₃O₄band is narrow.The prepared composite material caused strong magnetic shielding effect by addinginorganic inert isolation layer（SiO₂,Al₂O₃） between the magnetic core and TiO₂and decreasethe rate of recovery.In order to obtain efficient catalyst, the method of high temperaturecrystallization is usually adopted, therefore, there are many problems. First of all, Fe₃O₄isoxidized and lead to magnetism lose and decrease of magnetic recovery rate. Secondly,high-temperature calcination of TiO₂lead to compaction and agglomeration, not only thespecific surface area decrease, but hydroxyl on the surface of TiO₂also is difficult to surviveunder high temperature,which greatly reduce the catalytic efficiency of photocatalyst.At thesame time, the TiO₂has wide band gap （3.2eV） and can only absorb UV wavelengths below387nm, but the abundant solar energy only contains about5%ultraviolet light and more isvisible light,which greatly reduces the utilization rate of the solar energy. These disadvantageslimit the practical application of TiO₂photocatalyst.In allusion to the problems of the above. This paper has done the following work:1、9kind of magnetic photocatalysts TPTF of shell/shell/core structure was prepared bythe hydrothermal reaction method at low temperature （170℃,pH=7±0.2） through designingorthogonal test,using polythiophene magnetic beads （PF） as the carrier and using Fe₃O₄asmagnetic core, using polythiophene （PTh） which has the advantages of good rigidity, acidresistance-alkali resistance, high temperature resistance and good environmental stability asorganic inert isolation layer.The following instruments are used for catalyst characterization:using transmission electron microscopy （TEM） observe morphology of catalyst;using X raydiffraction （XRD） measure phase composition of catalyst; using fourier infraredspectrophotometer （FT-IR） analyse surface properties of samples; using vibrating samplemagnetometer （VSM） characterize magnetic intensity of photo-catalyst, using particle sizedistribution measure the size distribution of catalyst;using experiments results of degradationof phenol catalyst and reduction of Cr（VI） study the photo-catalytic activity of catalyst;usingthe magnetic recovery rate inspect recovery performance of photo-catalysts; using repeated photocatalytic experiments evaluate the service life of catalysts.2、TiO₂/PTh（TP） catalyst which has response under visible light was prepared by thehydrothermal reaction method at low temperature （170℃,pH=7±0.2）. Using transmissionelectron microscopy （TEM） observe morphology of catalyst; using fourier infraredspectrophotometer （FT-IR） analyse surface properties of samples; using UV-vis diffusereflectance spectroscopy characterize the response wavelength of catalyst; photocatalyticreaction are conducted in the combined light and visible light by using Phenol, Cr（VI） andrhodamine B as model pollutant to photocatalytic activity of the prepared photocatalyst undervisible light. Through the research and the experimental results,we obtain the followingconclusions:（1） The TiO₂which has mixed crystal structure （anatase and rutile type accounted for93.6%, accounting for6.4%） was prepared by the hydrothermal reaction method at lowtemperature （170℃,pH=7±0.2）, the grain size of TiO₂is between4-6nm, it has excellentcatalytic activity and is comparative with P25.（2） The level of nTi⁴⁺is90,75and60, n thiophene monomer is8,5and2.5,nFe₃O₄is1.TPTF1^TPTF9that was prepared through designing orthogonal test are has goodphotocatalytic activity and followed the first order reaction kinetics equation in degradation ofphenol and the reduction of Cr（VI） experiments.（3） The best degradation of phenol is TPTF6(nTi⁴⁺:n thiophene monomer: nFe₃O₄=75:2.5:1) in TPTF1^TPTF9; The best reduction of Cr（VI） is TPTF5(nTi⁴⁺:nthiophenemonomer:nFe₃O₄=75:5:1).（4） The reaction rate constant （K） which is comparative with pure TiO₂of photo-catalytic degradation of phenol is0.0253by TPTF6. The reaction rate constant decreased onlydecrease0.0048after the5cycle. The rate constant of photocatalytic reduction of Cr（VI） is0.0123by TPTF5after5repeated use, comparing with0.0229of the former,decreasing0.0106.（5） TPTF6and TPTF5have stronger magnetic induction intensity and good magneticrecovery performance. After5repeated use, the magnetic recovery rate of TPTF6decreasefrom94.7%to89.3%, the magnetic recovery rate of TPTF5decrease from89.2%to81.9%.Polythiophene not only provides a connection point for TiO₂and Fe₃O₄and link them closetogether, which form a complete system, but also polythiophene effectively prevente themagnetic core and TiO₂direct contact and diffusion, avoiding recombination of photo-generated electron-hole and dissolution of magnetic nuclear, enhancing the catalytic activityand magnetic recovery performance of photocatalyst. After recycled use5times, TPTF6’sreaction rate constant（K）, saturation magnetization and magnetic recovery rate are0.0205,1.59and89.3%emu/g, which slightly lower than the first0.0253,1.85and94.7%, whichillustrate that TPTF photocatalyst which use polythiophene as inert isolation layer hasexcellent photocatalytic activity and magnetic recovery performance and has a good application prospect.（6） The TiO₂/PTh(nTi⁴⁺:n thiophene monomer=100:1,100:0.5and100:0.25)photocatalyst was prepared at low-temperature hydrothermal method successfully and itsphysical characterization was characterized. TiO₂/PTh photocatalyst followed first-orderreaction kinetics equation in degradation of phenol, Cr（VI） and rhodamine B. The photo-catalytic reaction rate constant（K） of photocatalyst in composite light is significantly higherthan visible light in the process of degradation of phenol, Cr（VI） and rhodamine B. Thephotocatalytic reaction rate constant（K） of TP1^TP3were higher than those of P25and pureTiO₂in the degradation of phenol, Cr（VI） and rhodamine B at visible light,which show thatpolythiophene in a certain extent enhanced response of TiO₂in visible light. At the same time,TP1^TP3, catalytic effect of TP2is best, its molar ratio is nTi⁴⁺:n thiophene monomer=100:0.5. The degradation efficiency of phenol by TP1^TP3in the composite light werelower than those of P25and pure TiO₂, its causes and mechanism need to be further studied.（7）In this test, the proportion of the orthogonal experiment design is unperfect. The bestdegradation effect of phenol by TPTF6is best, its molar ratio is nTi⁴⁺:n thiophene monomers:nFe₃O₄=75:2.5:1, namely, thiophene monomer level will be reduced in the later experiment inorder to study the optimal level.（8）The original shell/shell/core structure is built as "egg structure". The abstract theory isimaged, which provides the basis for the analysis of the problems which are encounteredduring the experiment and laid a foundation for further research.