Study On The Controllable Preparation Of InOOH And In₂O₃ With Highly Active Crystal Planes And Their Photocatalytic And Gas-sensitive Properties

Cubic In(OH)3 hollow microcubes,orthohombic InOOH hexagram nanostructures with exposed {020} facets and hexagonal bipyramid mesostrucures with exposed high-index facets were synthesized via a facile non-surfactant hydrothermal route.Cubic In2O3 porous hollow microcubes and hexagonal In2O3 hexagrams nanostructures with exposed high-index {667} facets were prepared by calcining cubic In(OH)3 hollow microcubes and orthohombic InOOH hexagram nanostructures with exposed{020} facets at high temperature in air.Morphologies and structures of these products were characterized by means of scanning electron microscopy,transmission electron microscopy,X-ray diffraction,IR spectrum,mercury intrusion porosimetry and N2 absorption-desorption porosimetry.The growth and formation processes of InOOH and In2O3 micro/nanostructures with various geometrical morphologies and exposed facets were studied,and the possible growth mechanisms of InOOH and In2O3 micro/nanostructures were proposed.The photocatalytic behaviors and gas-sensing properties of as-obtained InOOH and In2O3 micro/nanostructures with various morphologies and exposed facets were studied,and the relations between morphology,size,exposed facets and properties were investigated.These research results would provide a base for further research on syntheses of InOOH and In2O3 micro/nanostructures,the physical and chemical properties of InOOH and In2O3 micro/nanostructures and their applications in photonic and electronic devices,lithium ion storage,gas sensor,solar cell and photocatalysis.(1)Cubic In(OH)3 hollow microcubes with different sizes were prepared via a direct reaction of InCl3 aqueous solution with NaF,NaOH and ethylene glycol(EG)at 140?,180? and 220? for 12 h.The hollow interior size and wall thickness of In(OH)3 hollow microcubes are about in the range of 2-3 ?m and 600-650 ?m,respectively.Polycrystalline cubic In2O3 porous hollow microcubes were obtained by calcining the single-crystalline cubic In(OH)3 hollow microcubes in air at 400 ? for 2 h.The influence of solvent EG molecules and NaF on the geometric shapes and hollow interiors were investigated and possible growth mechanism were proposed.The phtocatalytic activity of polycrystalline cubic In2O3 porous hollow microcubes was studied at room temperature.The result indicates that polycrystalline cubic In2O3 porous hollow microcubes were effective photocatalyst for the degradation of Methyl Orange(MO)and Rhodamine B(RhB).The photodegradation of MO and RhB catalyzed by the cubic In2O3 porous hollow microcubes is a pseudo first-order reaction.(2)InOOH hexagram structures with exposed {020} facets and different sizes were synthesized via a simple hydrothermal reaction of InCl3 aqueous solution with NaAc and EG at 180 ?,200 ? and 220 ? for 12 h.The InOOH hexagram structures are composed of radiately stretched conelike substructures.The mean diagonal diameters of the InOOH hexagram structures with exposed {020} facets obtained at 180?,200?and 220? were 1.6,1.1 and 0.7 ?m.The average size,BET specific surface area and the texture coefficient of(020)facets controlled synthesis of the InOOH hexagram nanostructures can be achieved by changing the reaction temperature.The selective adsorption of EG molecules on orthorhombic InOOH {020} facets was studied and regarded as the main reason for the existence of exposed {020} facets.A possible growth mechanism of InOOH hexagram nanostructures was proposed.The phtocatalytic activity of InOOH hexagram nanostructures with exposed {020} facets was studied at room temperature.The result indicate that the {020}facets of InOOH exhibit enhanced photocatalytic property and the InOOH hexagram nanostructures prepared at 220? for 12 h exhibit superior intrinsic potocatalytic activities to commercial TiO2 photocatalysts(P25),which can be attributed to its fairly high surface area and highest texture coefficient of InOOH {020} facets.(3)Single-crystalline hexagonal In2O3 hexagram nanostructures with exposed{6 67} high-index facets were synthesized by calcining single-crystalline orthorhombic InOOH hexagram nanostructures with exposed {020} facets at 450 ? for 2 h.The atomic arrangement of hexagonal In2O3 high-index {667} facets was studied and the results indicate that {6 67} high-index facet is composed of five(111)plane steps and one(112)plane terrace.The corresponding crystal facets transformation process from single-crystalline orthorhombic InOOH hexagram nanostructures to single-crystalline hexagonal In2O3 hexagram nanostructures was investigated in detail.A possible transformation mechanism was also proposed.The gas sensing properties of single-crystalline hexagonal In2O3 hexagram nanostructure sensors toward ethanol vapor and hydrogen gas with different concentration were tested.The sensor response of single-crystalline hexagonal In2O3 hexagram nanostructure toward 100 ppm ethanol vapor and 500 ppm hydrogen gas at the bestworking temperature are 43 and 8.2,respectively?The detection limits to ethanol vapor and hydrogen gas reaches to 100 ppb and 500 ppb respectively.The response performance of the sensors based on the single-crystalline hexagonal In2O3 hexagram nanostructures with exposed {667}high-index facets toward ethanol vapor and hydrogen gas is better than that of commercial In2O3 powder and hexagonal In2O3 irregular nanoparticles.(4)The InOOH hexagonal bipyramid mesostuctures were synthesized through a simple hydrothermal reaction of InCl3 aqueous solution with NaAc,NaF and EG at 200? for 24 h.The apex-to-apex diameter and the mean middle cross facet edge of the as-prepared InOOH hexagonal bipyramid mesostuctures are about in the range of 1.3-2.0?m and 0.9?m,respectively.The role of NaF and EG in the formation of InOOH hexagonal bipyramid mesostuctures was investigated,and a possible mechanism was also proposed.The InOOH hexagonal bipyramid mesostuctures are enclosed by±(220),±(220),±(121),±(121),±(121)and ±(121)planes of orthorhombic InOOH.The phtocatalytic activity of InOOH hexagram nanostructures with exposed {020} facets was studied at room temperature.The results indicate that the{220} and {121} facets of InOOH exhibit enhanced photocatalytic property and the InOOH hexagonal bipyramid mesostuctures exhibit much higher intrinsic potocatalytic activities than commercial TiO2 photocatalysts(P25)and InOOH hexagram nanostructures with {020} facets,which can be attributed to the higher chemical reaction activity of the exposed high-index facets.