Preparation And Photocatalytic Degradation Of Methyl Orange Imprinted Membrane Using TiO₂ As Matrix

In recent years,with the rapid development of Chinese dyestuff industry,China has become the No.1 dye manufacturer in the world.Meanwhile,it has also brought serious pollution problems of dye wastewater.Semiconductor photocatalytic oxidation is believed to be a promising and environmentally-friendly wastewater treatment technology,which can achieve clean decontamination and avoid a second pollution in the process by using sunlight to degrade the dye wastewater.Due to the high chemical stability of TiO₂ photo catalyst,it has the advantages of deep valence band,resistance to corrosion,non-toxicities and so on;therefore,there are many researches on the application of TiO₂ photocatalyst both at home and abroad.In the initial development stage of the photocatalysis,TiO₂ suspension system is used for the photocatalytic degradation of organic compounds.But in the suspension system,the powder of TiO₂ semiconductor catalyst is minimal,and it is easy to agglomerate in aqueous solution.Therefore,in order to achieve an ideal photocatalytic degradation effect,it must be kept stirring to prevent condensation.At the same time,the powder of TiO₂ photocatalyst is difficult to be separated and recovered.The depth of light radiation is blocked by suspended catalyst particles,and the catalytic ability is weakened,which makes the suspension system difficult to become a practical application technology.Therefore,researchers began to study the TiO₂ on the substrate to make the membrane or particles on the carrier of the immobilized catalyst.Although,the catalytic activity of TiO₂ on the membrane or the carrier is decreased,it is possible to obtain higher catalytic efficiency when using advanced load technology and photochemical reactor.On the other hand,the catalytic degradation lacks selectivity.There is often a high concentration of non-toxic substances and low concentrations of toxic substances in the wastewater.In practical applications,the low concentrations of toxic substances need to be removed.However,the non-specific combination makes the catalyst preferentially degrade the high concentration of non-toxic substances,and the substances with low concentrations of highly toxic are left.Therefore,in order to improve the target of the catalyst in the process of wastewater treatment,there is important scientific significance to prepare for the target recognition and separation dye molecules with high selectivity.Molecularly imprinted polymer is a kind of compound that has specific selectivity to specify the target molecules.Firstly,the dye molecules are used as template molecules;then,the carrier and the functional monomers are polymerized to obtain the cross-linked polymer;finally,the molecular imprinted polymer with specific recognition can be obtained by the template molecule elution.Using molecular imprinting technique can improve the special recognition and selectivity of TiO₂ photocatalytic degradation.This research has great application prospect,which has great significance to realize the industrialization of organic substance in the wastewater treatment.The main contents of this thesis are listed as follows:（1）Preparation of TiO₂/calcium alginate composite membrane and photocatalytic degradation of dyes.The alginate has the characters of good stability,film-forming property,and biocompatibility.In the research,the sodium alginate was used as membrane substrate,and Nano TiO₂ as photocatalyst,the Nano TiO₂ and sodium alginate were mixed to form casting solution.After calcium ion was cross-linked,TiO₂/calcium alginate composite membranes of controllable thickness were prepared and wiped film on the glass plate.Through the experiment,a new method for the convenient,fast and environmental protection of TiO₂ nanoparticles was proposed,and the repeated use of T/CA composite membrane was studied.The catalyst was characterized by scanning electron microscope（SEM）,transmission electron microscopy（TEM）,Fu Liye（FT-IR）,X ray diffraction（XRD）and Thermo Gravimetric Analysis（TGA）.The photocatalytic degradation of dyes was studied.The results showed that the mechanical properties and degradation rate of T/CA composite membrane were almost unchanged after 5 times of repeated use.（2）Preparation of TiO₂/CNT/CA film and its photocatalytic degradationThe CNT,TiO₂ and sodium alginate were fully mixed to form the casting solution,then scrape the film on the glass plate.After calcium ion crosslinking,the TiO₂/CNT/CA composite membrane was preparated.The means of SEM,TEM,FT-IR,XRD and TGA were used to characterize the film.Through experiments,this paper studied the photocatalytic degradation,swelling ratio,mechanical properties and repeated use performance of the TiO₂/CNT/CA composite film with dry and wet state.SEM showed that the surface of TiO₂/CNT/CA film was very rough,and there were obvious folds,large specific surface area.Experiments showed that the wet TiO₂/CNT/CA membrane of had good degradation ability to MO,and its ability to degrade increased and enhanced with increasing TiO₂ content.The TiO₂/CNT/CA film also showed a good performance of repeated degradation.Furthermore,the swelling properties and mechanical properties of TiO₂/CNT/CA composite membrane were also significantly enhanced by the addition of CNT.（3）Preparation of molecularly imprinted polysiloxane using TiO₂ as matrix and photocatalytic degradation propertiesThe molecularly imprinted polysiloxane powder was prepared,with TiO₂ as matrix,MO dye as a template,TPS、KH-570 and KH-550 as functional monomer.Using SEM,TEM,FT-IR,XRD and TGA analysis means of characterization testing,we study the polysiloxane adsorption and photocatalytic degradation properties of the imprinted and the non-imprinted,and further explore the optimum ratio between the silane and its coupling agent combination,thus achieve the best performance of the light absorption and photocatalytic degradation.The results showed that:the best silane coupling agent was KH550+TPS and KH550+KH570;Compared with that of the non-imprinted polysiloxane,molecularly imprinted polysiloxane using TiO₂ as matrix had higher adsorption capacity and catalytic degradation rate for methyl orange dye.（4）Preparation of methyl imprinted polysiloxane/calcium alginate membrane using TiO₂ as matrix and photocatalytic degradation propertiesThe first step was the preparation of molecularly imprinted polysiloxane methyl orange powder by using TiO₂ as matrix;and then it was mixed in sodium alginate aqueous solution to get casting solution.After calcium ion cross-linking,methyl imprinted polysiloxane/calcium alginate composite membrane with TiO₂ as matrix was prepared,and film was wiped on the glass plate.Then,it was characterized by SEM,TEM,FT-IR,XRD and TGA and other analysis methods.The mechanical,adsorption properties of dyes and photocatalytic degradation properties of the composite membranes with different components were tested.The results showed that the thermal properties of composite membrane,which was obtained by adding molecular imprinting polysiloxane methyl orange powder with TiO₂ as matrix,have improved than that of pure calcium alginate.Its strength also increased while the toughness was basically unchanged;After UV irradiation,the calcium ion of the cross-linking agent in the composite was not degraded,although the alginate macromolecules were degraded,there was little difference in the strength of the hydrogels compared with the results before the degradation.As the content of the methyl orange imprinted polysiloxane with the TiO₂ as matrix was increased,the adsorption amount of MO on the composite membrane increased gradually.When the proportion of TiO₂ and sodium alginate was 30%（weight）,the imprinting efficiency reached the maximum.With the increase of the content and degradation time of methyl orange imprinted polysiloxane by using TiO₂ as matrix,the degradation rate increased gradually.