SnO2纳米粒子的溶剂热制备及光致发光性质

以SnCl4·5H2O为原料,乙二胺为溶剂,用溶剂热法在180℃合成了SnO2纳米粒子,用XRD和TEM对其结构和形貌进行了表征,对SnO2纳米粒子的红外谱图、漫反射谱图以及光致发光性能进行了分析,探讨了乙二胺辅助合成SnO2纳米粒子的化学原理和生长机制。结果表明,用乙二胺辅助成长法合成的SnO2纳米粒子的粒径在40nm左右,粒径分布均匀,分散性较好。SnO2纳米粒子光致发光在340、432和672nm处有3个强峰,在472和540nm处有2个弱峰,其中340nm处的峰为紫外近带边激子发射峰,432、472和540nm处的峰是由氧缺陷引起的,672nm处的峰归因于表面态的氧缺陷引起的能带中深能级跃迁。     

Rich photoluminescence emission of SnO2–SiO2 composite aerogels prepared with a co-fed precursor sol–gel process

Tin oxide–silica composite aerogels were successfully prepared with a co-fed precursor sol–gel process. The crystallinity of the tin oxide nanoparticles, embedded in the mesoporous SiO₂ network, was improved with increasing the post-reaction thermal treatment temperature. The composite aerogels exhibited a rich photoluminescence (PL) emission contributed by both SnO₂ and SiO₂. The PL peak of 346 nm was from the near band edge emission of the tin oxide nanoparticles, and the ones located at 310 and 476 nm were attributable to the oxygen deficiencies of the silica network. Three more emission peaks, 387, 432, and 522 nm, were observed, with the 387 nm peak contributed by the oxygen vacancies V_O⁺⁺, the 432 nm peak by the Sn interstitials, and the 522 nm peak by the oxygen vacancies V_O⁺, respectively, of the tin oxide nanoparticles. The intensities of these three defect level emissions were found decreased, as compared to that of the near band edge emission, with increasing the post-reaction thermal treatment temperature as the tin oxide crystallinity improved.     

Solvent Extraction of Picric Acid from Acid Aqueous Solutions into Cyclohexane with Trioctylphosphine Oxide and Trioctylamine

The solvent extraction of picric acid(Hpic) from acid aqueous chloride solutions into cyclohexane with trioctylphosphine oxide(TOPO) and trioctylamine(TOA) was examined and the UV-visible spectrum of the organic phase was studied. In the organic phase, the acid associates with one or two TOPO molecules but it associates with only one TOA molecule. The absorption peak of the 1:1 associate with TOPO appears only in the UV range and thus it is assumed to be a hydrogen-bonded molecular adduct. The 1:2 associate with TOPO and the 1:1 associate with TOA, on the other hand, has a marked absorption peak in the visible range which is quite similar to that of picrate ions and thus the extracts are assumed to be ion pairs in which an electron transfers from the hydrogen atom to the oxygen atom in the OH-group. For this reason, the spectrum of TOPO extract is dependent on the amount of free extractant but that of TOA extract is not.     

Structural,electronic paramagnetic resonance and magnetic properties of praseodymium-doped rare earth CeO2 semiconductors

In this work, praseodymium (Pr) doped cerium oxide (CeO₂) was prepared using the microwave-assisted hydrothermal method (MAH) and the properties were investigated by X-ray diffraction analysis (XRD), Raman spectroscopy, Field Emission Gun Scanning Electron Microscope (FEG-SEM), BET method, Photoluminescence spectroscopy (PL), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet–visible spectroscopy (UV–Vis), Electron paramagnetic resonance spectroscopy (EPR) and Magnetometry. The results showed that increasing the Pr-doping promotes a structural disorder due to increased oxygen vacancies. XRD confirmed a cubic structure without deleterious phases with modifications in the structure caused by alteration in the cerium oxidation state as well as changes in the crystallite size and strain obtained by Wellinson-Hall method. Raman spectroscopy shows that changing the Pr content results in samples with different defect densities at short range. FEG-SEM showed that the nanocrystals are agglomerated with small particles tend to aggregate spontaneously to decrease the surface energy. BET method showed that the Pr doping results in a gain of specific surface area. PL indicated that Pr³⁺ leads to distinct emissions; red emission associated to oxygen vacancies located near the conduction band (shallow defects), green emission associated to electron-hole recombination and orange emission associated to shallow defects and electron-hole recombination. FTIR indicated the complete process of nucleation with no other phase. UV–Vis showed the transitions between oxygen 2p, cerium 4f and praseodymium 4f states. The EPR signal shows events occurring around 344 mT. These events can be related due the presence of paramagnetic elements containing unpaired electrons, such as Ce (III), which is indicative of cerium reduction caused by Pr ions, as evidenced by Rietveld data. Regardless of the Pr concentration used in this research, the magnetic measurements show a superparamagnetic system below the blocking temperature of ~20 K and a paramagnetic system above this temperature, which indicates no significant changes in the average size of the nanoparticles. Surface area, crystallite size and the temperature are important parameters, which control the magnetic properties of such N-type semiconductors.     

Synthesis and characterization of Gd-doped SnO2 nanostructures and their enhanced gas sensing properties

In the present work, we report the influence of Gd-doping on structural, optical and gas sensing properties of SnO₂ nanoparticles. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed formation of tetragonal rutile type structure of both undoped and Gd-doped SnO₂ nanoparticles. The crystallite size has been found to decrease with increase in dopant concentration which was confirmed from XRD and TEM techniques. It has been observed that Raman surface modes are directly related to the surface area of nanoparticles. Photoluminescence (PL) spectroscopy confirmed large number of oxygen vacancies in 3% Gd-doped SnO₂ nanoparticles. It has been observed that 3% doped sensor displayed exceptionally large sensor response towards ethanol which is about 27 times larger than that of undoped sensor. The optimum operating temperature of doped sensors has reduced as compared to undoped sensor. The enhanced sensor response of Gd-doped nanoparticles has been attributed to small crystallite size, large number of oxygen vacancies, high surface basicity and increased contribution of Raman surface modes. Moreover, it has been observed that 3% Gd doped SnO₂ nanoparticle sensor is highly selective towards ethanol.     

Sol-gel–mediated synthesis of TiO2 nanocrystals: Structural,optical, and electrochemical properties

Nanoparticles of titanium dioxide were prepared using the sol-gel method without any impurity. Rietveld refinement of XRD data confirmed the anatase phase of synthesized nanoparticles with space group I4_1/amd (141). XRD pattern revealed the crystalline nature of synthesized nanopowder. The average crystallite size of synthesized nanoparticles was calculated 7.5 nm. The electrochemical performance of synthesized TiO₂ nanopowder was investigated as working electrode. The electrochemical reaction was found diffusion-controlled as observed from cyclic voltammetry (CV) studies at different scan rates. The diffusion-controlled charge storage mechanism also confirmed by charge transfer resistance and Warburg impedance, as calculated from the EIS analysis. SEM micrograph showed the plate-like structure grown in cluster cloud of particles of synthesized TiO₂ nanocrystals. Absorbance and optical bandgap were obtained using UV-Vis spectra. De-convoluted PL spectra provided the emission pattern from the ultra-violet region to green region due to the presence of interstitial oxygen vacancies. The tune bandgap with EIS measurements of synthesized TiO₂ nanoparticles offers its potential application in energy storage devices and photovoltaic applications.     

Bismuth-catalyzed synthesis of ZnO nanowires and their photoluminescence properties

By means of heating a mixture of Zn and Bi powders, we have successfully prepared ZnO nanowires. Since the produced nanowires correspond to the pure hexagonal ZnO phase with no catalytic nanoparticles being observed at the tips, the growth is dominated by the base-growth mechanism, in which Bi species at the bottom of the nanowires played a catalytic role. Photoluminescence (PL) analysis of indicated that the integrated intensity ratio of the 2.5 eV-band to the UV band increased with increased growth temperature. An increase of the Bi₂O₃ phase itself, Bi₂O₃ phase-induced oxygen vacancies, and an increase of oxygen vacancies in ZnO with increasing growth temperature were responsible for the intensification and the appearance of the 2.5 eV-band.     

Bright green emission and temperature dependent localized bound exciton transitions from undoped ZnO films

Bright green luminescence is achieved from undoped ZnO films prepared by the reaction of oxygen and zinc powder. The green emission band is considered to be mainly due to the singly ionized oxygen vacancies. Temperature dependence of exciton transitions in the undoped ZnO films has been investigated in the range from 10 to 270 K. The PL spectrum at 10 K is dominated by neutral donor-bound exciton (D°X) emissions. The dominant emission centered at about 3.303 eV at above 45 K can be attributed to the localized bound exciton (LBX) transitions related to basal plane stacking faults. LBX transitions can survive up to near room temperature due to the LBX binding energy of 68 meV.     

Synthesis and characterization of SnO2-HMD-Fe materials with improved electric properties and affinity towards hydrogen

Tin oxide (SnO₂) was functionalized by hexamethylenediamine (HMD) grafting and incorporation of iron nanoparticles (Fe-NPs) and, then, fully characterized by X-ray diffractometry, transmission electron microscopy, diffuse reflectance spectrometry, FTIR spectrophotometery, photoluminescence spectroscopy and complexes impedance spectroscopy measurements. The covalent surface-grafting of HMD within mesopores was confirmed by the results from Fourier-transformed infrared spectroscopy. XRD and TEM study showed a dominant tetragonal structure. Fe-NPs were finely dispersed inside mesopores, producing a slight structure compaction. The crystallite size decreased in the presence of HMD and Fe-NPs. Photoluminescence (PL) insights revealed the presence of oxygen vacancies and the PL intensity was found to strongly depend on HMD grafting and Fe-NPs insertion. The incorporation of both Fe-NPs and HMD grafting appear to be responsible for electrical properties improvement. This material displayed an unprecedented surface affinity factor towards hydrogen of 8.5 μmol m⁻² at ambient temperature and pressure. This was attributed to the contribution of both physical and chemical hydrogen adsorption, and to the presence of fine Fe-NPs. These properties open promising prospects for green energy storage.     

Synthesis, characterization, and magnetic properties of monodisperse CeO2 nanospheres prepared by PVP-assisted hydrothermal method

ABSTRACT: Ferromagnetism was observed at room-temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3.6H2O using polyvinylpyrrolidone (PVP) as a surfactant. The structure and morphology of the products were characterized by; X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using ultraviolet and visible spectroscopy (UV-Vis) and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy (XANES). The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of ~ 9-19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of ~ 100-250 nm. The samples also showed a strong UV absorption and room temperature photoluminescence. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied by Vibrating Sample Magnetometer (VSM). The samples exhibited room temperature ferromagnetism (RT-FM) with a small magnetization of ~ 0.0026-0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange and the possible mechanism of formation was discussed based on the experimental results.     

Controlled synthesis of defects-containing ZnO by the French process modified with pulsed injection and its luminescence properties

Zinc oxide (ZnO) nanoparticles containing oxygen vacancies were synthesized by the French process modified with pulsed injection of nitrogen. Zinc vapor was generated by evaporation of zinc foil and carried by a carrier gas to react with co-currently supplied air. During the reaction, nitrogen gas was injected in pulse, perpendicular to the flow direction of both zinc vapor and air. Low partial pressure of oxygen and turbulence caused by pulsed injection yielded uniform ZnO nanotetrapods that contained oxygen vacancies. The content of oxygen vacancies depended upon the characteristics of the pulse, i.e. flowing and non-flowing period of the gas, pulsing cycle time, and the supplied pressure of the injected gas. Strong correlation between the presence of oxygen vacancies and the intensity of green emission in the photoluminescence spectra of ZnO was also observed.     

Shape effect of microstructured CeO2 with various morphologies on CO catalytic oxidation

Novel 3D-like CeO₂ microflowers and microspheres were synthesized by facile precipitation methods and tested for CO oxidation. Characterization by UV-Vis, PL, XPS and H₂-TPR revealed that 3D-like ceria show great superiority for favoring formation of oxygen vacancies, which in turn leads to higher oxygen mobility and reducibility. A direct relationship between the band gap of ceria and its catalytic activity towards CO oxidation was established. The activity and thermal stability of 3D-like ceria were much better than that of CeO₂ nanoparticles. The results indicated that the highly active ceria could be obtained by turning their shapes with a high concentration of oxygen vacancies.     

Preparation of cerium oxide nanoparticles in Salvia Macrosiphon Boiss seeds extract and investigation of their photo-catalytic activities

Cerium oxide nanoparticles (CNPs) with desired particle size and spherical morphology were prepared from cerium nitrate in bio media of Salvia macrosiphon Boiss seeds extract, as a green synthesis route. Then they were characterized by XRD, UV–Vis and FTIR spectroscopies, FESEM and TGA. Band gap energy of the prepared powders was also determined which was found in the range of 2.5–3.5?eV. Determination of DLS and zeta potential were showed that CNPs had the small size and unique colloidal stability, respectively. Then the photo-catalytic activity of them was investigated by degradation of Rhodamine B (RhB) dye as a model of waste water pollutants, under UV-irradiation and optimum conditions were evaluated. Results showed that decreasing the particle size increased the rate of photo-catalytic reaction remarkably but ascending the band gap energy, in contrast. The photo-catalytic mechanism was also studied by using different scavengers.     

A comparative study of magnetic,photocatalytic and dielectric properties of NiO nanoparticles synthesized by sol-gel and composite hydroxide mediated method

In this study, Nickel oxide (NiO) nanoparticles were synthesized by conventional sol-gel (SG) route using citric acid as an end-capping agent and composite-hydroxide-mediated (CHM) approach. XRD and FTIR confirmed the formation of NiO nanoparticles and the average crystallite size was found to be 68 and 34 nm for SG and CHM method, respectively. Raman spectroscopy revealed higher intensity of one-phonon longitudinal optical (1LO) mode in CHM nanoparticles which is attributed to the presence of defects such as Ni or oxygen vacancies. The two-magnon (2 M) band at 1472 cm⁻¹ confirmed antiferromagnetic (AFM) nature of SG nanoparticles whereas its suppression in CHM nanoparticles indicate superparamagnetic (SPM) nature of the nanoparticles due to decrease in average crystallite size. The magnetic measurements also confirmed the AFM and SPM state of SG and CHM nanoparticles, respectively in accordance with Raman spectroscopy. A sharp and low blocking temperature peak in ZFC/FC also indicates smaller and uniform sized NiO nanoparticles synthesized by CHM method. Optical studies revealed a large value of energy band gap for CHM nanoparticles due to their small average crystallite size and is attributed to quantum confinement effect. A higher photocatalytic performance was observed for CHM nanoparticles due to their large surface area and higher concentration of oxygen vacancies in accordance with Raman spectra. A higher dielectric constant was also observed for CHM nanoparticles due to increased number of grains per unit volume in smaller crystallites. In summary, CHM is one of the most simple synthesis approach that provides fine single-phase NiO nanoparticles at low calcined temperature with improved magnetic, photocatalytic and dielectric properties as compared to SG method.     

Analysis of structural,optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals

In this paper, the structural, optical and magnetic properties of pure ZnO and Fe/Co co-doped ZnO nanoparticles are presented. Rietveld refinement of XRD pattern revealed the single phase wurtzite structure for prepared samples. FTIR study confirmed the formation of tetrahedral coordination between zinc and oxygen ions. SEM and TEM techniques were used to examine the morphology of samples. The absorption spectra showed the decrease in optical energy band gap with Fe/Co co-doping in ZnO. PL spectra demonstrated five peaks correspond to the ultraviolet region, violet, violet-blue, blue-green and green in the visible region. Emission peak in the UV region is attributed to near band-edge excitonic emission. Other four emission peaks in PL spectra are related to different defect states. M-H curve showed room temperature ferromagnetic (RTFM) behaviour of doped ZnO sample. This paper enhances the understanding of structural, optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals for application in spintronics, solar cells, and ceramics.     

Strong Near‐Infrared Photoluminescence Emission of (003)‐Oriented MgTiO3 Thin Films

In this study, ilmenite‐MgTiO₃ films were sputtered on p‐type Si(111) substrates and the extrinsic effects, such as grain size, crystallinity, and orientation of photoluminescence (PL) properties of the films are discussed. To reduce the effect of oxygen vacancies (act as shallow defects) on PL emissions in the films, oxygen (O₂) was introduced as the sputtering gas and the excitation light source (λ = 532 nm) which has a corresponding energy (hν = 2.33 eV) below the shallow defect states was used. In this study, intense near‐infrared (NIR) PL emission centered at 810.1 nm at room temperature can be observed when the MgTiO₃ thin films exhibit the preferred (003)‐orientation and accompanied by the presence of hexagon‐shaped grains. In this study, the experiment results reveal that the NIR emission intensity of MgTiO₃ films highly depend on crystal orientation and/or grain morphology.     

Effect of Mg doping on photoluminescence of ZnO/MCM-41 nanocomposite

In this paper, photoluminescence (PL) behavior of Mg_xZn_1?xO/MCM-41 nanocomposite (where x = 0.05, 0.15, 0.25 and 0.30) is reported. Samples were characterized with small angle X-ray diffraction (SAXRD), wide angle XRD, BET (Brunauer–Emmet–Teller) surface area and pore size analyzer, field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HR-TEM) and PL spectrometer. The structure of MCM-41 was confirmed from both SAXRD and BET results. A broad PL band positioned at around 393 nm has been exhibited by ZnO/MCM-41 nanocomposite. With Mg doping, intensity of this PL band decreased for x = 0.05 and 0.15 and above this there was gradual enhancement in intensity. It was found that the intensity of the PL band, strongly depends on the particle size of ZnO. The increase in particle size along with MgO phase separation for x = 0.30 was proved by HR-TEM analysis. Interestingly, the differences in particle sizes at different concentrations of Mg did not account for shift in the PL band. A twofold enhancement in the intensity of PL band when x = 0.30 compared to bare ZnO/MCM-41 nanocomposite was observed. It is attributed for the increase in particle size which preserves the energy saved by passivation of ZnO nanoparticles and the other one is formation of heterojunction structures between ZnO and MgO. It was also evident from these results that there is increase in oxygen vacancies of ZnO crystallites with increase in particle size.     

Synthesis and photoluminescence characteristics of blue‐green luminescent aluminum oxynitride

Aluminum oxynitride (AlON), which can be regarded a nitrogen‐stabilized cubic γ‐Al₂O₃, has attracted attention in terms of its good mechanical, chemical, and optical stability. Because of its optical inertness, however, photoluminescence (PL) emission from nominally pure AlON has not been carefully investigated and evaluated. In this work, we prepared visibly luminescent AlON by nitridation of γ‐Al₂O₃ under N₂ atmosphere without adding aluminum nitride (AlN) using a high‐frequency induction heating unit. The resulting AlON exhibits a broad PL emission in the blue/green spectral region under excitation with light of ~260 nm. In the luminescent AlON sample, the excitation and emission events will occur at different sites; the electron transfer from the excitation site to the emission site is preceded by the radiative recombination process. It has also been found that the PL peak wavelength shows an anomalous blue shift by ~50 nm with increasing temperature from 78 to 500 K. The observed temperature dependent PL characteristics are governed by thermalization among multiple emitting levels. Aluminum vacancies and oxygen vacancies, both of which are introduced into the crystalline lattice during nitridation without the presence of AlN, are very likely candidates for the excitation and emission centers, respectively. Hence, the present direct nitridation method provides a simple and effective way to add an additional optical functionality to otherwise optically inactive AlON.     

Photoluminescence behavior on Sr2+ modified CaCu3Ti4O12 based ceramics

Sr²⁺ modified CaSr_xCu_3-xTi₄O₁₂ceramic powders with x?=?ranging from 0.00 to 3.00 were prepared by solid-state reaction. The effects of Sr²⁺ CCTO powders were evaluated by X-ray diffraction (XRD) with Rietveld refinement revealing a mixture of multiple phases. The Raman spectroscopy analysis pointed out that Sr²⁺ addition produces an emission in the blue region, associated to TiO₆ clusters. Optical properties by means of PL analysis showed emission near to blue region for the samples with x?=?0.00, x?=?0.15, x?=?0.30, corresponding to oxygen vacancies. The emission in the violet region is associated to deep defects while emission in the other samples is linked to shallow defects typical of disordered crystalline structures. Less prominent emission in the green region with the increase of Sr²⁺ corresponds to less self-trapped charges, less interaction between electron and hole, and donor–acceptor recombination.     

Size‐controlled preparation of nanosoy for potential biomedical applications

Soy protein isolate nanoparticles (nanosoy) have significant applications in drug delivery, wound care systems and tissue engineering. We report an optimum technique named nanoprecipitation which enabled one‐step formation of near‐monodisperse nanosoy based on solvent displacement. Excellent control over protein aggregation was achieved, producing nanoparticles in the size range of 5–15 nm. The effect of various process parameters such as temperature, solvent/non‐solvent ratio, crosslinker content and type of surfactant on the particle size was investigated. The structural and morphological features were analysed using dynamic light scattering, X‐ray diffraction and high‐resolution transmission electron microscopy. The morphological examination indicated that the particles formed were spherical in shape and further reduction in the average particle diameter was achieved by reducing the temperature and solvent/non‐solvent ratio of the reaction medium. Surface charge and stability of nanosoy dispersions were analysed using zeta potential measurements. Further, ciprofloxacin release was monitored using nanosoy as a drug carrier. This technique provides an effective and straightforward approach offering considerable advantages in terms of economic, technical and environmental performance. © 2016 Society of Chemical Industry