Solution-Phase Synthesis Of Nanostructured In₂O₃ And In₂S₃ And Their Properties Research

This paper is focused on the controlled synthesis of indium oxide(In₂O₃) and indium sulfide(In₂S₃) nanostructures,n-type semiconducting oxide ofâ…¢-â…¥compounds,through solution-phase chemistry routes.Investigations are based on three aspects:controlled synthesis,formation mechanisms,and properties and applications.The contents mainly include metastable corundum-type In₂O₃ nanoplates' preparation,the effects of precursors on the products,formation mechanism and photocatalytic properties;the cubic In₂O₃ nanocubes' preparation, size-controlling,the film of the nanocuboids fabricated onto various substrates via layer by layer self-assembly technique and their optical properties;fabrication of Indium oxide with flowerlike hierarchical structure;synthesis of ultra thin tetragonalβ-in₂S₃ nanotubes,formation mechanism,optical and photocatalytic properties; synthesis and characterization of In₂O₃ nanoparticles and nanobelts via hydro/solvothermal routes.Through In₂O₃ and In₂S₃ nanocrystals' preparation, size-controlling,formation mechanisms and optical and photocatalytic properties,we intend to study the intrinsic controlling mechanism of the nanocrystal formation and look for more effective ways to synthesis of nanostructural materials.1.Direct solution synthesis of corundum-type In₂O₃:effects of precursors on productsNanostructured metastable corundum-type In₂O₃ was directly synthesized by a low temperature solvothermal method.The as-prepared products were characterized by X-ray diffractions(XRD),Scan Electron Microscopy(SEM),Transmission Electron Microscopy(TEM) and Fourier Transform Infrared(FT-IR) spectrum in detail. H-In₂O₃ nanoparticles exhibit as hexagonal nanoplates with a side length of 100-200 nm and a thickness of ca.30 nm.The effects of precursors on the products were investigated.It is proposed that the existence of-OCH₃ in the H-In₂O₃ precursor leads to a hydrolysis process rather than thermal decomposition to form the H-In₂O₃. Gas-Chromatography(GC) and Nuclear Magnetic Resonance Spectrum(NMR) of reaction solutions also reveal that the formation of the C-In₂O₃ only goes through the simple thermal decomposition of Ln(acac)₃,while the hydrolysis is the main process during the formation of H-In₂O₃.The present direct solution preparation provides a low-temperature route to H-In₂O₃ and there is no crystalline intermediate during the formation of H-In₂O₃.Moreover,the H-In₂O₃ exhibited higher photocatalytic activity for the degradation of phenol than C-In₂O₃ nanocubes and commercial Degussa P25.2.Synthesis of In₂O₃ nanocuboids and the corresponding self-assembled filmsIn₂O₃ nanocuboids have been solvothermally synthesized using indium acetylacetonate as precursor.The size of the nanocuboids could be tunable by adjusting the solvent.The particle sizes of the products obtained from ethanol, n-buthanol,n-octanol and benzene are respectively 21,12,8,6 nm.The PL(all the samples excited at 330 nm,room temperature) emission behaviors of the In₂O₃ nanocrystals with different sizes are nearly identical with strong PL peaks centered at 451 nm(blue),548 nm,568 nm(yellow),and 616 nm(orange),which indicating varied oxygen vacancies in the structure and induce the formation of new energy levels in the band gap.Furthermore,the film of the nanocuboids has been fabricated onto various substrates via layer by layer self-assembly technique.The thickness of homogeneous monolayer of In₂O₃ is 6.39-15.15 nm.UV-vis absorption spectroscopy provided evidence for subsequent growth of multilayer film,exhibiting progressive enhancement of optical absorption.PL spectrums of multilayer films were also detected.3.Fabrication,characterization and photoluminescence properties of In₂O₃ NanoflowersA simple solvothermal route based on indium complex as precursor was developed to synthesize 3-dimensional(3D) hierarchical flowerlike nanostructure. Indium oxide with the same flowerlike hierarchical structure was directly obtained in one-step.The In₂O₃ nanoflowers are well dispersed,have a uniform diameter of ca. 30-50 nm nm,and are composed of nanoparticles of ca.3-5 nm size. Because the decomposition of In(acac)₃was too slow in toluene,the grown speed of In₂O₃ nanocrystals was also too slow.So the random aggregation of produced In₂O₃ nanocrystals was happened to decrease the surface energy rather than grown larger.When increasing reaction time to 24 h,the perfect nanoflowers can be obtained.The photoluminescence(PL) spectra were used to characterize the products.It is observed that the PL spectrum of In₂O₃ naoflowers at room temperature exhibit peaks centered at 438 nm(blue),546 nm,569 nm(yellow),618 nm(orange) in the range of visible light.4.Synthesis and photocatalytic property of ultrathinβ-In₂S₃ nanotubesUltra thin tetragonalβ-In₂S₃ nanotubes have been successfully synthesized for the first time via a simple solvothermal route.The tubular structure is end-closed,with od ca.10-20 nm,thicknessof tubes wall about 2 nm and lengths more than 1μm.The reaction process was followed the track by XRD,SEM,TEM,FT-IR,HR-TEM,TGA and EA at different times in detail.Furthermore,the effects of reaction parameters on the formation of nanostructures were also discussed,and the formation mechanism was proposed.Lauryl mercaptan decomposed under the solvothermal conditions to release S^2-,and S^2- further reacted with the dissolved In³⁺ in the system to form In₂S₃ species.In₂S₃ nanocrystals were aggragated to form nanosheets.After a rolling process of nanosheets under high temperature or thermal stress,the nanotubes formed.The optical properties of obtainedβ-In₂S₃ nanotubes were also studied.UV-vis spectrum indicates the strong quantum confinement of the excitonic transition expected forβ-In₂S₃ nanotubes.Furthermore,β-In₂S₃ nanotubes' better photocatalytic property for the degradation of RhB than commercial Degussa P25.5.Synthesis and characterization of In₂O₃ nanocrystals via hydro/solvothermal routes.In this chapter,we introduced a kind of convenience route to prepare In₂O₃ nanoparticles and nanobelts.In the hydrothermal/solvothermal system,we use In(NO₃)₃·4H₂O as the indium source,adjusting the hydrolysis reaction of indium salt via control the water content of the system in order to control morphologies of the products.In ethanol solvothermal reaction system,the generated In(OH)₃ from hydrolysis of indium salt further dehydrated to form In₂O₃ nancrystals.The conversion of In(OH)₃ into In₂O₃ can be proposed as a "dissolution-recrystallization" mechanism,and the driving force is the lower solubility of the In₂O₃ compared to the In(OH)₃ in the system.In the hydrothermal system,the indium ions completely hydrolyzed.Due to the alkali of sodium oleate in water can provide plenty of OH^- to promote the growth of nanocrystals,the In(OH)₃ belt-like structure obtained.After heat-treatment at 300℃,In₂O₃ single crystals nanobelts produced.The as-synthesized In₂O₃ nanocrystals reveal UV absorption around 273,323 nm repectively,exhibiting a distinct blue-shifted to the bulk In₂O₃.Such blue-shift could be contributed to the existence of weak quantum confinement effect.The room temperature PL spectra of as-prepared In₂O₃ nanoparticles and nanobelts are clearly different,which is due to existence of different oxide-deficiency states from the different synthesis routes.