Nguyen Thuy Van

Synthesis, characterisation, adsorption ability and activity of Cu,ZnO@UiO–66 in methanol synthesis

Metal–organic framework UiO–66 was synthesised by solvothermal method. The influence of synthesis conditions on the quality of UiO–66 was studied. The obtained material was characterised by XRD, IR, TGA, SEM, TEM, AAS and nitrogen physisorption measurements (BET). Physisorption measurement of different gases (CO2, H2, CH4 and CO2/CH4) was carried out using a high pressure volumetric analyser. Synthesised UiO–66 in the form of ball shaped crystals possessed high surface areas of up to 1041 m2.g−1, micropore volume of 0.913 cm3.g−1, pore radius of 15 and thermal stability of up to 423C. According to experimental results, at 30 bar, CO2 storage capacity of the synthesised UiO–66 is nine times higher than that of H2 and four times higher than that of CH4. The [emailxa0protected]–66 and Cu,[emailxa0protected]–66 catalysts were prepared and tested in the hydrogenation of CO and CO2. As it followed from investigation, Cu,[emailxa0protected]–66 catalyst has been shown to be the best one with the yield of methanol reaching 229.04 μmol.g−1.h−1 and 153.93 μmol.g−1.h−1in the hydrogenation of CO and CO2, respectively.

Silicon–Rich Silicon Oxide Thin Films Fabricated by Electro-Chemical Method

Porous silicon (PS) has attracted increasing research interest in basic physics as well as applications since 1990 when Canham reported on the efficient visible photoluminescence (PL) of porous silicon (Canham, 1990). Structurally, PS consists of many pores and silicon residuals and usually can be described as a homogeneous mixture of silicon, air and, even silicon dioxide. Based on porosity, PS can be classified into three types: nano, mesoand macro-pores. In the case of PS nano-pores, the size of both the silicon residuals and the air voids (pores) can be in the range of few nanometers. The exciton Bohr radius in Si is around 4.3 nm, so that quantum confinement can occur and change the electronic structure of those silicon nanocrystals. On the other hand, because the value of porosity is directly linked to the effective index of refraction of the PS layer, this layer appears as an effective medium, where the refractive index has a tunable value between the index of refraction of bulk Si and that of the air (pores). Those changes in the electronic structure and refractive index of PS when compared with bulk Si make it fascinating as both a low-dimensional material and an optical one. The considerable and controllable changes in the electronic structure and refractive index of PS fabricated by electrochemical anodization make it a promising material for photonics in comparison with bulk silicon and/ or pure silica. Using the oxidation process in O2 environment at high temperature, the PS samples become siliconrich silicon oxides (SRSO), which has high chemical instability and avoids the aging of the PS that is important condition for optical devices such as planar optical waveguides, optical interference filters, micro-cavities, etc (Bettotti et al., 2002). During the last decade, Erbium (Er)-doped silicon-rich silicon oxide has attracted much interest due to its big potential application in Si-based optoelectronic devices for telecom and optical sensors. The Er-ions implanted in SRSO materials produce light emission at around wavelength range of 1540 nm, which corresponds to minimum light absorption in silica-based glass fibers. In this regard, a lot of studies have been carried out to improve the luminescence efficiency of this material. Such studies have revealed that co-implantation of Er and O2 induce a strong enhancement in the Er-ions related emission at range of 1540 nm. In first case, samples were prepared by co-implanting Si and Er into silica thin films or co-sputtering Si, Er2O3 and SiO2 on the silicon substrate (Shin et al., 1995). In second case, samples were prepared by implanting Er-ions into SiO2 films containing Si-nanocrystals (nc-Si) and/or by Er-ion electrochemical deposition on silicon-rich oxide (SRSO) layers. The room temperature luminescence emission at the range of 1540 nm from Er-electrochemically doped porous

Porous silicon as a promising material for photonics

Electrochemical etching – a usual technique in nanotechnology – creates porous silicon with novel and useful properties. The considerable and controllable changes in the electronic structure and refractive index of porous silicon make it a promising material for photonics in comparison with bulk silicon. In this paper, we review as well as report on some interesting and unique properties of porous silicon material. In studying porous silicon as a low-dimensional material, we focus on the effect of the surface passivation of silicon nanocrystals on photoluminescence characteristics of such zero-dimensional crystals. As an optical material, we demonstrate the fabrication method and optical properties of the planar waveguide as well as the active waveguide and optical interference filters operated in infrared wavelengths. In addition, we investigated the effect of energy transfer from silicon nanocrystals to erbium ions in the erbium-doped porous silicon waveguide and also elaborate on the origins of the difference between the reflectivity spectra from fabricated filters and that of the simulation program.

Synthesis of adsorbent with zeolite structure from red mud and rice husk ash and its properties

There are many researches in the modification of red mud as adsorbent for treatment of wastewater or waste gases. Yet, most of them have to face up with a thorny problem caused by remaining alkali in red mud. In this study, the material with zeolite structure was synthesized by fusion method using red mud with the remaining alkali and rice husk ash as raw materials. It comprised alkaline fusion followed by hydrothermal treatment with step – change of synthesis temperature. The synthesized materials were characterized by powder X–ray diffraction (XRD), scanning electron microscopy (SEM), BET and CO2 adsorption capacity. The influences on the quality of these materialswere investigated under various calcination temperatures, calcination times and the ratios of raw materials (based on SiO2/Al2O3 ratio). The optimum reaction parameters were determined. The results depicted that the sample treated at 600 °C for 2 hours with the ratio of SiO2/Al2O3 of 1.8 had the best adsorption capacity and total specific surface area compared with the others.There are many researches in the modification of red mud as adsorbent for treatment of wastewater or waste gases. Yet, most of them have to face up with a thorny problem caused by remaining alkali in red mud. In this study, the material with zeolite structure was synthesized by fusion method using red mud with the remaining alkali and rice husk ash as raw materials. It comprised alkaline fusion followed by hydrothermal treatment with step – change of synthesis temperature. The synthesized materials were characterized by powder X–ray diffraction (XRD), scanning electron microscopy (SEM), BET and CO2 adsorption capacity. The influences on the quality of these materialswere investigated under various calcination temperatures, calcination times and the ratios of raw materials (based on SiO2/Al2O3 ratio). The optimum reaction parameters were determined. The results depicted that the sample treated at 600 °C for 2 hours with the ratio of SiO2/Al2O3 of 1.8 had the best adsorption capacity and total specific surf...

Wavelength Shift Measurement Method Without Use of Spectrometer: The New Way for Environment Photonic Sensors

The photonic sensors have shown very effectively for measuring the toxic contents in the liquid and air environments. In principle, the photonic sensors based on measurement of wavelength shift between reference condition and testing environments that we need use the spectrometer with high cost. In this paper, we present new configurations of photonic devices for measuring wavelength shift without use of spectrometer, which has a large potential for application in sensing technique with low cost. There are two configurations of photonic sensors are presented: i) first of them is based on fiber Bragg grating (FBG) combined with DFB laser diode with controlling wavelength emission by laser temperature and ii) second one is usedxa0 the fiber ring laser from Erbium-doped fiber and two FBG operated asxa0 reference and sensing probe. The etched-fiber Bragg grating (e-FBG) as sensing probe is suitable for bio- and/ or chemical sensors. A novel photonic sensor can increase sensitivity and measuring accuracy of device by the narrow line-width of reflection spectra from laser and the sensor can determine a refractive index variation of 2x10 - 4 , which is similarly for high resolution spectrometer. The experimental results show that this sensing method could determine different mixing ratios of organic solvents in liquid environment with good repeatability, high accuracy and rapid response. Keywords :

Photodegradation of Cinnamic Acid Solution in the Presence of Various Oxidizing Agents on TiO2 and Fe-TiO2 Catalysts

In this paper, TiO2 and Fe-doped TiO2 had been prepared by the sol-gel method. Physico-chemical characteristics of the catalysts were determined by the methods of BET Adsorption, XRD, FT-IR, and UV-Vis spectroscopies. Experimental results showed that the The modification of TiO2 catalyst with Fe led to reducing the crystallite size and PZC, and extending the spectrum of photon absorption to the visible region. The activity of obtained catalysts for photodegradation of cinnamic acid (CA) solution in the presence of various oxidizing agents (O2, O3 and H2O2) was investigated and the optimum reaction conditions were identified. It follows that the addition of Fe additive is able to reduce the optimal catalyst concentration 3-5 times and increase the catalytic activity. It was found that O3 and H2O2 agents showed the higher efficiency for cinnamic acid photodecomposition than usual O2. In optimum conditions, after 90 minutes reaction, the conversion of cinnamic acid in the solution achieved 58.5, 77.7 and 83.1% on TiO2 and 85.7, 82.8 and 89.4% on Fe-TiO2 in the presence of O2, O3 and H2O2 respectively.

Investigation of 1d Photonic Crystal Based on Nano-porous Silicon Multilayer for Optical Filtering

We present the fabrication, simulation, and measurements of 1D photonic crystal based on nano-porous silicon multilayer designed as an optical interference filter. Using electro-chemical etching with timely repeat steps of applied current densities, we fabricated a multilayer structure composed of alternating high- and low-index layer which achieved 90% power reflectivity at wavelength range of 1400-3000 nm. The simulation is relying on the Transfer Matrix Method (TMM) to design and predict the optical properties of nano-porous silicon multilayer as well as the relation between anodization parameters with reflection spectra. The measured reflection and transmission spectra of the nano-porous silicon multilayer show good agreement with simulation. This technique could provide a convenient and economical method to produce filters, cavities, and graded-index dielectric waveguides in the future.