Preparation Of Micro/Nano Structured MnO_x Capable Of Extremely Fast Catalytic Degradation Of Organic Pollutant

It is important to decompose organic pollutants at high efficiency.As an excellent catalyst to degrade organic dyes,MnOx with different oxidation states,morphologies and crystal phases has been synthesized under controllable conditions.Hydrothermal method is the most convenient and effective method,which can combine with mechanical stirring for expected homogeneous and monodisperse micro/nanostructured MnOx.The high ratio of low valence MnOx microhydrangeas(HRLV-MOMs)formed of radically aligned MnOx nanosheets,having the MnO,Mn2O3 and ?-MnO2 with the ratio of 49.2%,32.3%and 18.5%,respectively,are synthesized in a single one-step stirring hydrothermal procedure.Nanosheets in HRLV-MOMs do not stack,facilitating the efficient exposure and usage of more MnOx surfaces.HRLV-MOMs can very quickly catalyze H2O2 to degrade organic dyes completely.The catalytic degradation of crystal violet and ethyl violet is so fast that the dynamic process cannot be experimentally tracked.As comparison,HRLV-MOMs without any substrate catalyze H2O2 to degrade methylene blue(MB)with the high catalytic degradation efficiency of 100.0 mg·gHRLv-MOMs-1·min-1,4 times of the largest reported value of MB degradation by pure MnOx.The HRLV-MOMs exhibit good recyclability and durability,whose morphology and crystal phase are well kept after 10 cycles.The extremely fast catalytic degradation process is mainly attributed to the substantial hydroxyl(OH)radicals,predominantly catalytically induced by the high ratio of low valence MnOx(MnO,Mn2O3),different from the mostly reported pure MnO2.The superoxide anion(O2·-)radicals induced by MnO2 further speed up the decomposition of organics.The amounts of both radicals are quantitatively determined to be 74.0 mg·gHRLV-MOMs-1 and 6.6 mg·gHRLV-MOMs-1,respectively,which are important parameters however not been reported previously in catalytic degradation of organics.In this thesis,MnO2 hollow nanorod urchins(HNRUs,?4 ?m),MnO2 hollow nanospheres(HNSs,?500 nm),MnO2 nanowires(NWs)and MnO2 nanowire urchins(NWUs,?5 ?m)are obtained through controlling hydrothermal reaction conditions including composition and concentration of different reactants,reaction time and temperature.The performance of their catalytic degradation of MB with H2O2 is studied.The results show the catalytic degradation efficiency sequence as follows:MnO2 HNRUs(16.2 mg·gMnO2 HNRUs-1·min-1)>MnO2 HNSs(4.0 mg·gMnO2 HNSs-1·min-1)>MnO2 NWs(3.9 mg·gMnO2NWs-1·min-1)>MnO2 NWUs(3.4 mg·gMnO2NWUs-1·min-1).In addition,MnO2 HNRUs have better cycling stability,whose morphology and crystal phase are well kept after 2 cycles.The effective catalysis of MnO2 HNRUs is due to the crucial role of ·OH radicals by the addition of tert butanol(TBA)and p-benzoquinone(p-BQ)as radical scavengers.These results deepen the fundamental understanding for active species in catalytic degradation process of organic dyes with MnOx,especially low valence MnOx,for efficient usage of the exposed catalytic surfaces as well as immediate and practical significance for catalysis applications in water treatment for a better environment.