Wastes Treatment: Hydrothermal electrolytic oxidation of wastewater

Abstract

Electrochemical evolution of hydrogen gas, oxygen gas and chlorine at the electrodes is the usual reaction in conventional electrolysis of aqueous salt solution. However, here we demonstrate that the electrolysis governing reaction in hydrothermal solutions is different from the electrolysis performed at atmospheric pressure and temperatures up to 100°C. Experimental electrolytic reaction of aqueous salt solution carried out inside a sealed 300-mL batch autoclave showed that; accumulation of hydrogen gas, oxygen gas and chlorine is highly suppressed under hydrothermal (250°C and 7 MPa) conditions. We have also observed that, when organics are present in the aqueous salt solution being hydrothermally electrolyzed, an effective oxidation of organics is accomplished. Furthermore, for hydrothermal electrolytic oxidation (HEO) with oxygen gas added, experimentally observed TOC removal profile demonstrates apparent anodic oxidation electrical current efficiency of almost 200% for highconcentrated acetic acid solutions.     

电子束蒸发法在多孔氧化铝膜上制备银纳米点阵列

采用二步阳极氧化法在草酸溶液中制备了高度有序的多孔阳极氧化铝(Porous Anodic Alumina,PAA)薄膜。以多孔氧化铝薄膜为模板,采用真空电子束蒸发的方法在多孔氧化铝模板上制备出了高度有序的金属银纳米点阵列体系。扫描电镜(SEM)测试结果表明,所制备的金属银纳米点阵列与多孔阳极氧化铝膜的多孔阵列具有完全相同的有序结构,阵列中银纳米颗粒的形状接近球形,其直径大约为70nm,与氧化铝模板的孔径基本一致。研究了高度有序银纳米点阵列的形成过程。     

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m² g⁻¹) can be successfully obtained by reduction under optimal conditions.     

多孔氧化铝膜上自组织生长Sn纳米点阵列的研究

以多孔阳极氧化铝膜(porous anodic alumina, PAA)为基片，采用真空电子束蒸发的方法在多孔氧化铝膜上制备了高度有序度的Sn纳米点阵列.锡纳米点阵的XRD与块体锡的完全相同，扫描电镜(SEM)测试结果表明，所制备的金属Sn纳米点阵与阳极氧化铝膜的多孔阵列具有完全相同的有序结构，阵列中每个Sn纳米粒子的形状为球形的，其直径接近于PAA膜的孔直径.对Sn纳米点阵形成过程和形成机理进行了讨论.     

Plasma electrolytic saturation of titanium and its alloys with light elements

This review is devoted to analyzing the results of the thermochemical treatment of titanium-alloy surfaces under plasma action in electrolytes. Plasma electrolytic saturation (PES) with light elements is found to have advantages over alternative methods. Electrolyte compositions by means of which titanium is rapidly saturated with nitrogen, carbon, boron, and oxygen are presented. The treatment modes and characteristics of the modified layers, such as the phase and elemental composition, surface roughness and microhardness, friction coefficient, wear rate, and corrosion resistance, are discussed. Attention is paid to the thermophysical and electrochemical aspects of PES, in particular, to the specifics of titanium heating and its anodic dissolution and oxidation.     

Arrays of ordered Ag nanowires with different diameters in different areas embedded in one piece of anodic alumina membrane

Nanochannel arrays with the same nanochannel density but different nanochannel diameters in different areas in one piece of anodic alumina membrane had been created. SEM observations on one piece of this type of anodic alumina membrane show that the nanochannel diameters radially decrease from 80 nm to 60 nm and to 40 nm along the radial direction. Therefore, using this type of membrane as a template, ordered Ag nanowire arrays with the same nanowire density but with diameters decreasing radially were obtained by electrodeposition. SEM and TEM images taken of different areas of the Ag nanowire arrays show that we can control the growth of aligned Ag nanowires with different diameters in a single process at the same time. Using this type of template in combination with other fabrication techniques, nanometer-scale fibrils, rods, wires, and tubules of metal, semiconductors, carbon, and other materials with same density but different diameters in different areas can be fabricated. The simultaneous integration of ordered nanowire structures with different diameters embedded in a single anodic alumina membrane could be useful in nanodevice manufacture as well as electronics, optoelectronics and magnetics. PACS 81.05.Bx; 82.80.Fk; 85.30.Vw     

Fabrication of metal nanodot arrays using a porous alumina membrane as a template

Thin nanodotstructured metal films and heterostructured nanodot arrays (metal nanodot arrays/Si) with a high density and uniform distribution for various kinds of metals (Au, Al, Ag, Pb, Cu, Sn, and Zn) were fabricated by thermal vacuum evaporation using an anodic porous alumina membrane as a template. However, for such metals as Sn, Zn, and Pb with relatively lower melting point as compared with Al it was found that heterostructured nanodot arrays were not formed by a single stage of evaporation. For these metals, we developed a new method termed “two step evaporation method”. The size and the arrays of dots were depended on the pore structure in the anodic porous alumina template. The technique demonstrated in this report is simple and suitable for the preparation of nanodot arrays in the large area for materials which could be vacuum evaporated.     

Self-assembled growth of C60 nanowhiskers on anodic porous alumina membranes

Unique structured claw-like C₆₀ nanowhiskers were fabricated on an anodic porous alumina membrane. Tips of the C₆₀ nanowhiskers are shaped like cusps, which directly extend into the nanopores of the alumina membrane. It is revealed that the surface stress of the alumina membrane with a highly ordered nanopore arrangement due to thermal treatment is responsible for self-assembled growth of the observed C₆₀ nanowhiskers. The ordering of the nanopore arrangement in the anodic porous alumina membrane helps to form the C₆₀ nanowhiskers along the nanopore channels. The shape and structure of the C₆₀ nanowhiskers are promising characteristics for applications in nanodevices such as field-emission tips and nanoprobes. PACS 61.46.+w; 61.48.+c; 33.20.Fb     

双光路同向起偏测量含金属阳极氧化铝膜的消光比

用阳极氧化的方法制备了阳极氧化铝膜,向其孔中分别镀入了铜和银,利用UV-3101型分光光度计测试了其透射光谱和偏振光谱,并研究了样品的偏振特性与入射角的关系.实验结果表明,这种含金属阳极氧化铝膜在近红外波段表现出良好的消光比,且入射角的大小对其消光比有着明显的影响.     

含纳米金属阵列阳极氧化铝膜的偏振特性

利用阳极氧化铝的纳米多孔阵列结构特性，将金属Cu电镀到氧化铝的孔中，得到含有金属纳米阵列的氧化铝膜。实验发现，这种氧化铝膜确实象金属线栅偏振器一样表现出偏振特性，是一种新型微偏振器件。它在波长大于500nm时吸收很小，在波长为1．5μm时有高达67．1％的透射率和25．6dB的消光比。该氧化铝膜的偏振特性与阳极氧化和电镀条件有关。随着电流密度的增大，金属柱增多，光学损失增大，透射率降低，而偏振度增大。但是当电流密度增加到某一数值时，偏振度降低。通过优化制备条件，可得到高效率的氧化铝微偏振器。这种微偏振器制作简单，体积小，在光电通信领域有着非常广泛的应用前景。     

Self-correlation function for determination of geometrical parameters in Nanoporous Anodic Alumina Films

Self-correlation functions have been applied to top-view high-resolution scanning electron microscopy micrographs of anodic alumina nanoporous arrays in order to determine their ordering degree and geometrical parameters; as a result, self-correlation images were obtained. These images are formed in the real space and can be used to make quantitative and qualitative surface analysis. The developed method for surface analysis has been applied to three series of porous anodic alumina films grown using sulphuric acid based electrolytes with concentrations of 3, 10, and 20 wt% and applying voltages from 25 down to 5 V. Significant changes in ordering degree, interpore distances, and pore diameters have been observed. In addition, in this study, the existence of an anodization window for self-ordering regimes for each acid concentration used in the electrolytic solution is also revealed.     

Controlled synthesis of titanium nanochains using a template

Nanochains have unique properties due to their organized structures. We synthesized nanochains of titanium using crown ether as a template exploiting a simple sliding technique. The nanochains of Ti were formed with an average diameter of the sphere nodes around 80 nm separated by organic molecules with a space of 1–5 nm. The method developed here is the simplest reported to date. This process can be used for making nanostructures of different metallic materials. Trapping titanium ion particles is important to reduce the risk of the same material in the biomedical applications. The metallic nanochains are potentially applicable for making electronic and optical devices.     

Pluronic P123 assisted synthesis of hollow InSn/In2O3 hybrid nanoparticles by solution dispersion

A detailed analysis of the optimum regimes of pulsed current metal electrodeposition into pores of porous anodic alumina PAA is presented. A simple model based on cathodic and anodic current transients is developed. The model is based on a simplified equivalent circuit consisting of two capacities related to the barrier and porous parts of porous anodic alumina. Nanowires of Cd, Zn, In, Ni, Co, Ag, and Cu were embedded into PAA by pulsed electrodeposition using an asymmetric rectangular ac signal. Deposited metal nanowires were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical spectroscopy, Auger electron spectroscopy (AES), and X-ray diffractometry (XRD).     

Selective tungsten deposition into ordered nanohole arrays of anodic porous alumina by electron-beam-induced deposition

The selective deposition of a metal (tungsten) into ordered nanohole arrays of an anodic porous alumina membrane was performed using an electron-beam-induced deposition process. After deposition, the membrane was observed and analyzed using electron microscopy and energy-dispersive X-ray spectroscopy. It is shown that the deposition was preferentially conducted in the holes in the irradiated area of the electron beam. A calculation of the electron-beam intensity explains the reason for the preferential deposition in the holes. PACS 81.07.-b; 81.16.Rf; 61.46.+w     

The investigation of photoluminescence centers in porous alumina membranes

To investigate the origin of blue photoluminescence (PL) in porous alumina membrane, we have prepared an anodic aluminum oxide film with a pore diameter of 40 nm in oxalic acid solution by a two-step anodization process. Our results show that the as-prepared alumina membrane is amorphous and exhibits a broad emission band peaking at around 452 nm with two sub-peaks located at 443 nm and 470 nm. As indicated by the PL excitation spectra, there are two excitation peaks which can account for the sub-peaks observed in the PL emission band. We have proposed that the broad emission band with two sub-peaks can be attributed to two luminescence centers in porous alumina membranes, namely, oxygen defects and oxalic impurities. Furthermore, we have rationalized that the two emission centers show similar influence on the PL band in the blue region based on a simple model. PACS 81.07.-b; 81.16.Dn; 79.60.Jv     

ENHANCED PHOTOLUMINESCENCE OF Eu(III)-ANCHORED POROUS ANODIC ALUMINA FILM

We report here the enhanced luminescence of Eu(III)-anchored porous anodic alumina prepared by self-assembling Eu(III) acetylacetonate, and investigate the luminescence mechanisms. Porous anodic alumina can emit visible light due to a lot of oxygen vacancies formed in the anodic oxidation. The existence of oxygen vacancies resulted in e^?-h⁺ pairs when excited. Eu(II) exists stably by forming Eu²⁺-hole complexes. The enhanced luminescence of Eu(III)-anchored porous anodic alumina is attributed to the complex luminescence of e^?-h⁺ through luminescence center Eu²⁺.     

Preparation of thin anodic alumina membranes and their utilization for template electrodeposition

A method for the preparation of arrays of anodic aluminium-oxide porous films on a metal frame is proposed. The suggested approach makes it possible to obtain very thin porous-oxide films possessing a high mechanical strength, which are suitable for various practical applications such as templates for the formation of one-dimensional nanostructures or membranes for gas separation and liquid filtration. To demonstrate the possibility of the utilization of thin anodic alumina films as the templates for nanowire formation, cobalt nanowires with 50 nm diameter are prepared using 5 μm thick alumina membranes.     

Photoluminescence effect of Ru dye on alumina membranes with ordered pore arrays

We have investigated the quenching luminescence and the luminescence mechanisms of self-assembled Ru(II)L₂X₂ (Ru(II)(4,4’-dicarboxyl-2,2’-bipyridyl)₂(SCN)₂) dye in porous anodic alumina. Porous anodic alumina can emit visible light due to numerous oxygen vacancies formed during anodic oxidation. Energy transfer from the porous anodic alumina to the dye molecules causes the quenching and red shift of the PL peak, which gives a fundamental understanding of the PL mechanism in porous anodic alumina. Received: 29 May 2001 / Accepted: 3 August 2001 / Published online: 30 October 2001     

Investigation of the super-long alumina nanowire array synthesized with a novel method

Alumina nanowire array standing on porous anodic alumina (PAA) membrane has been directly and efficiently synthesized in oxalic acid solution by one-step electrochemical anodic oxidation with changing anodic voltages. The morphology of the nanowires on PAA was observed by scanning electron microscopy (SEM). The different patterns on the surface of the sample were synthesized due to the reaction time. The fine structure of the patterns has shown that the pattern is composed of the alumina nanowire array and the morphologies of the patterns can mainly be attributed to the differences in the length of the alumina nanowires. The method of selected area electron diffraction (SAED) for transmission electron microscopy (TEM) has shown that these nanowires are amorphous. An etching model was given to explain the formation mechanism of the amorphous alumina nanowires.     

Synthesis of highly ordered nanopores on a photoresist template for applications in nanofabrications

Template synthesis involves preparation of nanostructures of the desired material within the pores of a nanoporous membrane. In this paper we report on the fabrication of a new type of template, photoresist spin-coated on a conductive glass substrate, as an alternative to the commonly used track-etch polymeric membranes and anodic aluminium oxide. The nanopores on the photoresist are created by photolithography using a pre-designed pattern map stored in a Focused-Ion-Beam (FIB) machine. The pores created are highly ordered, of uniform and desired diameters of between 20–35 nm, and run the full length of the resist membrane. Pore dimensions are tenable in the range of 10 nm to hundreds nanometres in diameter and in the range of several micrometers in membrane thickness. We conclude that, in addition to being functionally similar to anodic alumina, the photoresist template is simpler and safer to fabricate making it a better alternative to in-house prepared anodic alumina templates and track-etch polymeric membranes.