Dissertation > Excellent graduate degree dissertation topics show

Study on the synthesis and properties of adsorption and photocatalytic materials

Author: CaoYanFeng
Tutor: ZhuJian
School: Shanghai Normal University
Course: Physical and chemical
Keywords: ZSM-5-TiO2composites MCM-41@TiO2nanocomposites F modifiedMCM-41@TiO2nanocomposites adsorption photocatalysis
CLC: TB33
Type: Master's thesis
Year: 2013
Downloads: 122
Quote: 0
Read: Download Dissertation

Abstract

As we all know, titanium dioxide （TiO₂） semiconductors have been recognized asa most promising photocatalyst for the photodecomposition of contaminated waterand air, owing to suitable band gap energy for redox reactions, mechanical andchemical stability, non-toxicity to the human body and environment, low cost andconvenience of preparation. However, due to the small particle size of its powder andsolubility in aqueous medium, practical engineering applications of TiO₂photocatalysts require the particles to be fixed on a bulky support or to be blendedwith binder materials, so that the recovery from the treated water can be simplified.Furthermore, the concentration of the organic compounds once discharged into waterbodies such as rivers and sea areas is extremely lowered, making it difficult for themto be recondensed and oxidized. Beside that, TiO₂itself does not have an affinity forhydrophobic organic molecules due to its surface polarity, so that preconcentration oforganic substrates onto the catalyst surface is desirable for oxidation kinetics. As arevolutionary approach to exploit the TiO₂photocatalytic potential, an application ofhybrid materials, combined with adsorbents and TiO₂photocatalysts, has been studiedextensively for the efficient adsorption and removal of contaminants diluted in waterand air. For the above reasons, this graduation thesis mainly includes the followingthree parts.（1） Adsorption-photocatalytic synergistic removal of toluene vapor in air onZSM-5-TiO₂compositesIn this section, we mainly focused on designing TiO₂-sorbent hybridphotocatalytic materials, especially those supported on ZSM-5zeolites, with theobjective of fabricating efficient photodegradation systems toward organiccompounds diluted in air. ZSM-5-TiO₂composites were fabricated by animpregnation method. First, the TiO₂nanocrystals with diameter about5nm wereprepared by solvothermal process. Next, these TiO₂nanocrystals were loaded on theZSM-5zeolites through impregnating at a relatively low temperature about150oC.The obtained samples were characterized by SEM, TEM, XRD and XPS techniques.The fundamental adsorption-photocatalytic behaviors were investigated in theremoval of toluene vapor diluted in air. In the case of hybrid photocatalysts, the initialtoluene concentration in gas phase was significantly reduced because of adsorption into the ZSM-5. After photo-irradiation started, toluene was continuously decomposed.The results found that TiO₂nanocrystals were uniformly distributed on the surface ofZSM-5zeolites by using of impregnation method. Simultaneously the synergisticeffects between adsorption properties and photocatalysis were discussed in thissection, as well as the structure-activity relationship. The weight ratio of TiO₂andSiO₂/Al2O3ratio of the ZSM-5-TiO₂composites will significantly affecthydrophobicity index （HI）, adsorption and photocatalytic efficiency. The effect of theamount of the adsorbent on the photocatalytic activity was investigated and provideda novel physicochemical insight into adsorption-photocatalytic synergistic removal oforganic pollutants. The present study affords a fundamental understanding of hybridmaterials of TiO₂and ZSM-5zeolite, highlighting an enhancement of photocatalyticactivity of supported TiO₂on such adsorbed materials.（2） Preparation of MCM-41@TiO₂nanocomposites and the study of itsadsorption-photocatalytic performanceIn this part, we used an in situ loading method to combine TiO₂nanoparticles andMCM-41in uniform nanospheres with straight and ordered mesoporous channels, theadsorption properties and photocatalytic reactivities of MCM-41@TiO₂nanocomposites for the degradation of an aqueous p-chlorophenol and a gaseoustoluene into CO₂and H2O have been studied. The obtained samples werecharacterized by scanning electron microscopy （SEM）, transmission electronmicroscope （TEM）, X-ray diffraction （XRD） and X-ray photoelectron spectroscopy（XPS） techniques. The effect of the amount of the adsorbent on the photocatalyticactivity was investigated and provided a novel physicochemical insight intoadsorption-photocatalytic synergistic removal of organic pollutants. The calcinatingtemperature played an important role in the crystallinity of TiO₂nanoparticles and thebonding force between MCM-41and TiO₂. The present study affords a fundamentalunderstanding of hybrid materials of TiO₂and MCM-41, highlighting an enhancementof photocatalytic activity of supported TiO₂on such adsorbed materials.（3） Preparation of fluorine-containing silylation hydrophobic modificationMCM-41@TiO₂nanocomposites and the study of its adsorption-photocatalyticperformanceIn this part, MCM-41was hydrophobically modified via a simple silylationprocess using a fluorine-containing silylation agent, triethoxyfluorosilane [TEFS or SiF（OEt）3]. Structural analyses performed by XRD and N2adsorption-desorptionsuggested that the mesoporous structure and large surface area of the MCM-41wereretained even after the modification. Surface chemical information obtained from XPSindicated that the TEFS reagent was covalently anchored to the surface hydroxyl sitesand fluorine atoms existed in a≡Si-F bonding state. From the H2O adsorptionisotherm on the modified MCM-41, it was clearly shown that the modified MCM-41was more hydrophobic compared with the unmodified MCM-41. Moreover, thehydrophobically modified MCM-41was used as support for the TiO₂photocatalyst.From TEM, as well as UV-vis spectroscopy and XRD, it was confirmed that thehighly crystallized TiO₂nanoparticles were formed on the hydrophobic MCM-41surface, similar to the titanium species on the original MCM-41. With the aim ofevaluating its availability as an efficient support, photocatalytic degradation of toluenediluted in air was performed. Both the adsorption property and the TiO₂photocatalyticactivity toward these organic compounds were dramatically improved by increasingthe content of the TEFS reagent because the hydrophobically modified MCM-41worked as an efficient adsorbent to condense organic molecules instead of H2Omolecules.

Related Dissertations

CLC: > Industrial Technology > General industrial technology > Materials science and engineering > Composite materials
© 2012 www.DissertationTopic.Net Mobile