The Study Of Synthesis And Photocatalytic Activities Of Molybdenum Trioxide Microcrystalline

Due to the unique structure and excellent optical properties,MoO3was considered a promising material for various industrialapplications such as gas sensors, photochromic and electrochromicdevice, display materials, battery systems and catalysts for treatingwastewater and air purification. MoO3has three commonpolymorphs: thermodynamically stable α-MoO3, metastable β-MoO3and hexagonal metastable h-MoO3. Among these phases, withmultiform nano-structures and excellent stabilities, the stable α-MoO3phase has been generally researched, whereas the hexagonalmetastable h-MoO3is much less known. Because of the higherchemical activity and narrower band gap, h-MoO3was consideredhas great research value and broad application prospects in field ofphotocatalytic. So this paper focused on the research preparations,crystal growth law and photocatalytic performance of h-MoO3.MoO3powders were successfully synthesized by facilehydrothermal method using (NH4)6Mo7O24·4H2O and concentratedHNO3as the raw materials. The influence of four basic technologicalfactors on structure, morphology and photocatalytic performance ofh-MoO3: pH value of precursor solution, Mo(Ⅵ) concentration inprecursor solution, thermal temperature, thermal time were studiedrespectively. The results showed that: α-MoO3will transform into h-MoO3when changing pH value of precursor solution. When pHvalues range from0.5to2.0, pure h-MoO3microcrystallites will beobtained. And the mixture phase of h-MoO3and α-MoO3has the best photocatalytic performance. Pure h-MoO3crystallites will be alsoobtained with the Mo(Ⅵ) concentration is0.04~0.6mol/L, thermaltemperature is60~200℃and thermal time is2~36h. The rodstructure with the uniform size and arranged orderly will be obtainedwhen the Mo(Ⅵ) concentration is0.07mol/L, and greatphotocatalytic performance is displayed. When temperature is120℃and thermal time is24h the products both have poor crystallinities,but they have excellent photocatalytic performance.In order to improve the photocatalytic performance of the h-MoO3, we control the morphology of the products by adding NaNO3,CH3COONa, CTAB and PEG-4000as template agents on the basis ofthe optimal process parameters. Results show that the products areh-MoO3microrod array structure when the template agents areNaNO3and CH3COONa; the morphology of the product is compositeof many micro-sized and a small amount of nano-sized particleswhen template agent is PEG-4000. When the template agent is CTABthe product will have strong orientation growth trend along (100)and (200) crystal plane, eventually form nanoflowers structureassembled by h-MoO3nanosheets. And the product obtained with thetemplate agent is CTAB has the fastest and best photocatalyticdegradation rate, which the photocatalytic efficiency reached97%within60minutes, the reason may be related to the loose structureof nanoflowers assembled by h-MoO3nanosheets.At last of this paper we studied several synthesis methods of h-MoO3microcrystallites in low temperature. Such as water bathmethod, micro-wave method, microwave-ultrasonic method,microwave-uvtravilet method and microwave-ultrasonic-uvtraviletmethod. The results showed that: water bath temperature has greatinfluence on the size of product, and the higher temperature thegreater in size. The different methods combinations of microwave,ultrasonic and uvtravilet can get different h-MoO3microcrystallitesin morphologies and crystallinities. On the basis of microwave, thejoining of uvtravilet can make h-MoO3crytcal grow along orientation of (100) crystal plane, and the joining of ultrasonic isgood for the phase structure of product develop into cross structure.