Synthesis And Application Of K₇Ti₄O₄F₇with Light Catalysis At Visible Light

With the development of society and economy, the environmentalpollution has become a focus problem need to be solved which isharmful to human health and survival. Under the condition of light,photocatalyst can stimulate the producing active free radicals, whichcan be used in the decomposition of pollutants. Since it has advantagesof high photochemical conversion efficiency, high stability, and it hasfunction to degraded many kinds of organic pollutants, so it can be usedfor the management of environmental pollution. Nano TiO₂,with thecharacteristic of small size, big specific surface area, low band gap（3.2ev） and high activity,a wide applications in environmentalprotection,which can be used to treat wastewater including organicpollutants and inorganic pollutants.But when the nano TiO₂proceed photocatalytic reaction, thereaction rate is relatively slow, the catalytic efficiency is lower, underUV irradiation, its energy consumption and cost more higher. In order toimprove the photocatalytic activity of nano TiO₂, increase the reactionrate, and reduce the cost, the following three aspects can be considered:one is control the crystal of nano TiO₂, the second one is doping thenano TiO₂using metal ions with different valence or metalloid, the thirdone is compositing nano TiO₂with other semiconductor compounds.Recent studies show that photocatalytic activity of TiO₂doped with Fimproved obviously, and the reasons are analyzed. In addition, theTi-based metal oxides have been studied as UV light-responsivephotocatalysts, such as SrTiO₃, K₂Ti₆O₁₃and Na₂Ti₆O₁₃etc. However,little has been reported about the Ti-based metal fluoride andoxyfluoride materials as photocatalysts. Although some of them havebeen prepared using solid-state method or thermal decomposition route, such as K₃TiOF₅, K2TiOF4and K₇Ti₄O₄F₇etc, but until now few studieshad been conducted to uncover the properties of these compounds. Inthe basis of previous work,the photocatalytic activity at ultraviolet andvisible light of Ti-based metal fluoride and oxyfluoridematerials—K₇Ti₄O₄F₇was studied. In order to improve thephotocatalytic activity of K₇Ti₄O₄F₇, it was complexed with the carbonnanotube.K₇Ti₄O₄F₇with single crystal structure is synthesized using theK2TiF6as raw material, and it is characterized by scanning electronmicroscope （SEM）, transmission electron microscope （TEM） and X-raypowder diffraction. Multi-walled carbon nanotubes （MWNT） andsingle-walled carbon nanotubes （SWNT） are dispersed with threedifferent dispersant （Polyacrylic acid （PAA）, polystyrene （PS） andsodium dodecyl benzene sulfonate （SDBS））. CNT film is obtained byfiltering dispersed solution at low pressure with the Al2O3film asbasement, which is characterized by TEM. And the gas selective ofK₇Ti₄O₄F₇is explored, whether it can be used for gas separation.The results of the study indicated that:1. The best condition of synthesis K₇Ti₄O₄F₇reaction system isdetermined as follows: the volume of water is12mL, the KOHconcentration is2M, the pH value is6.6, and the reaction time is8h（240mg K₂TiF₆）.2. The MWNT dispersed by PAA and PS can get free-standing film,but the film is easy to be broken under outside force. MWNT dispersedby SDBS can’t get free-standing film. PAA and PS are unable todisperse SWNT, compared with them, SWNT dispersed by SDBS canobtain free-standing film, and the film has stable structure which is noteasy to be broken under outside force.3. Methyl orange solution can be completely photocatalyticdegradated with K₇Ti₄O₄F₇in90min under UV irradiation. Undervisible light irradiation, methyl orange can be degradation16.15%after6h by K₇Ti₄O₄F₇. K₇Ti₄O₄F₇was loaded on single-wall carbonnanotubes,and film was built by filtering. Under visible light irradiation, methyl orange can be degradated19.96%after6h, the degradation ofmethyl orange increased by23.59%compared to pure K₇Ti₄O₄F₇.