Enhanced mass transfer using roughened rotating cylinder electrodes in turbulent flow

Cylindrical electrodes have been roughened by machining groove patterns, pyramidal knurling, and superimposing wires and meshes for which the degree of roughness has been calculated. By rotating the electrodes in a turbulent regime, mass transfer for cathodic copper electrodeposition has been measured and the degree of consequent enhancement (relative to an equivalent smooth cylinder) calculated. Typically, the surface area has been increased by 10–40% and the mass transfer rate by 100–300% for turbulent flow defined by 7000<Re<80 000.Nomenclature A (A _R) area of cathodic (rough) cylinder (cm²) - C exponent - C _B metal ion concentration in bulk solution (mol cm^–3) - d _s (d _R) diameter of smooth (rough) cylinders (cm) - D diffusion coefficient of metal ion (cm²s^–1) - F Faraday's constant - I _L limiting current density (mA cm^–2) - j ₀ dimensionless mass transfer factor (=ShSc ^c) - k _L mass transfer coefficient (=I _L/zFC _B) - k _s,k _R k _L values for smooth and rough cylinders - m, n exponents - P pitch, or roughness element spacing (cm) - Re Reynolds number (=Ud/v) - Ré d _R U _R/v - Re _s dU _s/v - Sc Schmidt number (=v/D) - Sh Sherwood number (=k _L d/D) - St Stanton number (=k _L/U) - U _s (U _R) peripheral velocity at smooth (rough) cylinders (cm s^–1) - U ₀ friction velocity (cm s^–1) - w width of wire mesh opening (cm) - z valency change, number of electrons - groove depth (cm) - kinematic viscosity (cm² s^–1) - groove width     

Enhanced mechanical properties of 3D printed alumina ceramics by using sintering aids

Stereolithography based 3D printing provides an efficient pathway to fabricate alumina ceramics, and the exploration on the mechanical properties of 3D printed alumina ceramics is crucial to the development of 3D printing ceramic technology. However, alumina ceramics are difficult to sinter due to their high melting point. In this work, alumina ceramics were prepared via stereolithography based 3D printing technology, and the improvement in the mechanical properties was investigated based on the content, the type and the particle size of sintering aids (TiO₂, CaCO₃, and MgO). The flexural strength of the sintered ceramics increased greatly (from 139.2 MPa to 216.7 MPa) with the increase in TiO₂ content (from 0.5 wt% to 1.5 wt%), while significant anisotropy in mechanical properties (216.7 MPa in X-Z plane and 121.0 MPa in X–Y plane) was observed for the ceramics with the addition of 1.5 wt TiO₂. The shrinkage and flexural strength of the ceramics decreased with the increase in CaCO₃ content due to the formation of elongated grains, which led to the formation of large-sized residual pores in the ceramics. The addition of MgO help decrease the anisotropic differences in shrinkage and flexural strength of the sintered ceramics due to the formation of regularly shaped grains. This work provides guidance on the adjustment in flexural strength, shrinkage, and anisotropic behavior of 3D printed alumina ceramics, and provides new methods for the fabrication of 3D printed alumina ceramics with superior mechanical properties.     

Fabrication of double-sided field-emission light source using a mixture of carbon nanotubes and phosphor sandwiched between two electrode layers

A double-sided surface light source based on field emission (FE) using an alternating current power source is demonstrated. Carbon-nanotube (CNT) emitters and ZnS phosphor are mixed and screen-printed onto two pieces of indium tin oxide glass that were assembled together with the coated surfaces facing each other to make a parallel-plate, diode-structure FE device. The device has a double-sided luminance distribution with a turn-on field of 2 V/μm, a good uniformity, and a stable luminance of 4000 cd/m². The results show that CNTs not only act as good field emitters but also as an electrically conductive network around the isolated phosphors. The network prevents electric arcing and thus extends the lifetime of the device.     

Surface modification and dispersion of ceramic particles using liquid-liquid extraction method for application in supercapacitor electrodes

Particle extraction through liquid-liquid interface (PELLI) was used for the extraction of MnO₂, Mn₃O₄, FeOOH and ZnO particles from an aqueous synthesis medium to the n-butanol phase. The benefits of PELLI were demonstrated by the fabrication of supercapacitor electrodes, which showed good electrochemical performance at high active mass loadings. Octyl gallate (OG) was found to be an efficient and versatile extractor for the ceramic particles. The phase transfer of the particles resulted in reduced agglomeration, which allowed for improved electrolyte access to the particle surface and facilitated their mixing with conductive multiwalled carbon nanotube (MWCNT) additives. It was shown that OG is a promising extractor material for the fabrication of ceramic-ceramic, ceramic-metal and ceramic-MWCNT nanocomposites. The strong adsorption of OG on the particle surface involved bridging or chelating bidentate bonding of the catechol group to the metal atoms. The capacitive properties of FeOOH-MWCNT electrodes were tested in the negative potential window. MnO₂-MWCNT and Mn₃O₄-MWCNT electrodes were investigated for charge storage in the positive potential window. The highest capacitance of 5.7 F cm⁻² for positive electrodes was achieved using MnO₂-MWCNT composites with active mass loading of 36 mg cm⁻². The Mn₃O₄-MWCNT electrodes exhibited improved capacitance retention at high charge-discharge rates.     

Enhanced performance in dye-sensitized solar cells via carbon nanofibers-platinum composite counter electrodes

A composite counter electrode (CE) made of electrospun carbon nanofibers (ECNs) and platinum (Pt) nanoparticles has been demonstrated for the first time to improve the performance of dye-sensitized solar cells (DSCs). The new ECN-Pt composite CE exhibited a more efficient electro-catalytic performance with lower charge transfer resistance (R(ct)), larger surface area, and faster reaction rate than those of conventional Pt. It reduced the overall series resistance (R(se)), decreased dark saturation current density (J(0)) and increased shunt resistance (R(sh)) of the DSCs, thereby leading to a higher fill factor (FF) and larger open circuit voltage (V(oc)). The reduced electron transport resistance (R(s)) and faster charge transfer rate in the CE led to a smaller overall cell series resistance (R(se)) in the ECN-Pt composite based DSCs. The DSCs based on an ECN-Pt CE achieved a η of ～8%, which was improved over those of pure Pt or ECN based cells.     

Enhanced extraction efficiency of bioactive compounds and antioxidant activity from Hippophae rhamnoides L. by-products using a fast and efficient extraction method

In this study, a novel method named high-speed homogenization coupled with ultrasound-assisted extraction (HSH-UAE) followed by high-performance liquid chromatography (HPLC) was employed and investigated for the extraction and determination of main flavonoids rutin, quercetin-3-O-glucoside, quercetin, kaempferol and isorhamnetin from Hippophae rhamnoides L. by-products. Optimal conditions for HSH-UAE, proposed by the single factor and the Box–Behnken design (BBD) tests coupled with response surface methodology (RSM), were 68% ethanol concentration, ultrasonic power 250 W, homogenate speed 9000 rpm, liquid/solid ratio 22 mL/g and extraction time 12 min. The extraction yields of five main flavonoids were significantly improved by HSH-UAE than UAE and high-speed homogenization-assisted extraction (HSHAE). Furthermore, the antioxidant activity of HSH-UAE extracts was assessed by 1,1-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays with IC₅₀ value of 0.091 mg/mL and 2.837 mmol FeSO₄/g DW. Good linear ranges were obtained for five main flavonoids in the range of 2.5–500 μg/mL with the coefficient higher than 0.99. The recoveries of the five flavonoids were in the range of 97.87–99.26%. The limit of detection (LOD) and the limit of quantification (LOQ) for the main flavonoids were within the ranges of 0.28–0.46 and 0.89–1.74 μg/mL, respectively. The present results showed that the proposed method HSH-UAE could be developed as a fast and efficient method for extracting the active ingredients from medical edible plant materials for potential application.     

Carbon nanotube modified electrodes for enhanced brightness in organic light emitting devices

Acid oxidised multiwall carbon nanotubes (COOH-MWCNT) have been introduced as a hole injection buffer layer in an organic light emitting diodes (OLED). We show that the OLED with COOH-MWCNT as a buffer layer provides higher brightness with lower operating voltages. The addition of a COOH-MWCNT buffer layer has enabled a further increase in the brightness of our OLED devices operating in excess of 20,000 cd/m² due to enhanced hole injection by several orders of magnitude. The increase in current injection and brightness does not alter the optical emission spectrum at different operating voltages in these devices. A model is proposed to explain this increase in current injection and brightness based on the modified electron energy band alignment.     

Separation and recovery of copper from waste printed circuit boards leach solution using solvent extraction with Acorga M5640 as extractant

Waste printed circuit boards (WPCBs) have received extensive attention in recent years because of its harmfulness and resource. In this work, two-step leaching process was carried out by using steel pickling waste liquor (SPWL) as the leaching agent. The leaching solution contains a variety of metals, especially iron, which will have an effect on the recovery of copper. Acorga M5640 (M5640) extractant with a kerosene diluent was used to recover copper from WPCBs leach solution, and the separation factor is adopted to analyze the effects of these metal ions. The effect of different parameters such as pH of aqueous phase, phase ratio (O/A), M5640 concentration, contact time as well as the concentration of H₂SO₄ as stripping reagent were investigated. Over 90.0% copper was extracted with pH 1.1, phase ratio (O/A) 1/1, M5640 concentration 16%, contact time 3 min at room temperature. For the stripping process, the 60 s contact time and 2.5 mol/L H₂SO₄ concentration are suitable with 90.0% stripping percentage of copper. Copper extraction isotherm accords with Langmuir isotherm equation and the results show that iron is the most influential metal ion for copper extraction, which will reduce the theoretical saturation of the extractant. The extractant M5640 has excellent reuse performance and can be recycled more than 10 times, which demonstrated M5640 has the industrial application value in the extraction of copper from WPCBs leach solution.     

Enhanced light scattering in coatings templated with interfacially stabilized colloids

Controlling inter-pore distances enables tuning the color or whiteness of microvoid coatings. While pore spacings have been modified in limited area inverse opal films, little work has occurred studying the feasibility of controlling pore spacings and thus the appearance of scalable, spray-on, microvoid inorganic coatings. In this work we investigated using interfacially stabilized colloidal templates to increase pore spacing and thus enhance Mie scattering in porous silica films. Coatings were fabricated by forming monodisperse colloids with or without a polyvinylpyrrolidone (PVP) interfacial stabilizing layer, dispersing them in a silica precursor solution, and spraying this suspension on a substrate. The films were cured and the colloids subsequently solution extracted at mild temperatures to create porous surfaces. Coatings made with PVP coated colloids had thicker pore walls and scattered light approximately 3× more efficiently than coatings made with bare colloids. Furthermore, a viewing angle dependent color shift was observed in the PVP colloid templated coatings. Side illumination of the samples with white light causes an orange appearance under angles of specular reflection, while a light blue appearance is observed out of these angles because of strong Mie scattering of short-wavelength radiation in both situations. Lastly, modeling based on Mie scattering confirms that it is the dominant optical effect in these coatings and explains the appearance of these coatings. The approach of using interfacially stabilized colloids to improve pore separation applies to many porous films and should be considered when increased light scattering is desired.     

Derivatization of SWCNTs with cobalt phthalocyanine residues and applications in screen printed electrodes for electrochemical detection of thiocholine

Single-walled carbon nanotubes (SWCNTs) derivatized with cobalt phthalocyanine (CoPh) were applied onto screen-printed graphite electrodes (SPEs) to be used for the low-potential electrochemical oxidation of thiocholine (TCh). Covalent attachment of CoPh to SWCNTs via stable sulfonamide bonds was confirmed by Raman/FT-IR spectroscopy and thermogravimetric analysis (TGA) coupled with FT-IR detection. The resulting modified SPE surfaces (CoPh-SWCNT-SPEs) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) with the redox probe [F₃(CN)₆]^3−/4−. Detection of TCh was accomplished using cyclic voltammetry and amperometry; a lower overpotential (100 mV vs. Ag/AgCl pseudoreference electrode) was obtained using CoPh-SWCNT-SPEs as compared to unmodified SPEs and SPEs modified with non-functionalized SWCNTs (SWCNT-SPEs). The linear range for TCh detection was 0.077–0.45 mM, with a sensitivity of 5.11 × 10⁻¹ μA mM⁻¹ and a limit of detection of 0.038 mM according to the 3 s/m definition.     

Efficient degradation of aqueous methyl orange over TiO2 and CdS electrodes using photoelectrocatalysis under UV and visible light irradiation

A highly efficient photoelectrocatalytic course was realized by combining TiO₂ and CdS films. The TiO₂ films were prepared using dc reactive magnetron sputtering method, and the CdS films were deposited by chemical bath deposition (CBD) method. The X-ray diffraction (XRD), Raman, field-emission scanning electron microscope (FESEM) were used to characterize the film structure and surface morphologies. The experiment results showed that the photoelectrocatalysis by using the TiO₂ and CdS films under double-beam irradiation of UV and visible lights had higher photocatalytic activity than the sum of photoelectrocatalysis solely using TiO₂ and CdS films.     

Enhanced electrodetection of ascorbic acid in Adansonia digitata fruit by use of surface modified electrodes

Surface modified electrodes have been used to study the seed of A. digitata. The results show the ascorbic acid redox peak is greatly enhanced and the oxidation/reduction peaks coincide with those of the corresponding chemical standard. It is also shown that ascorbic acid adsorbs onto the clay-modified electrode.     

Enhanced luminescence of manganese in singly doped white light zinc phosphate glass

On the basis of a kind of zinc phosphate oxynitride glass matrix with a broadband blue light, a series of manganese single-doped glasses were obtained. A broader red emission with the higher intensity belonging to the Mn²⁺ ion was observed in this glass matrix. The mechanism of the emission from Mn²⁺ ions was clarified through Mn³⁺ as an “energy acquisition probe” to replace complex dynamic luminescence discussion, which was a fit explanation for the differences in luminescence behavior of Mn ions in prepared glasses at different degrees of redox. The research results indicated that the prepared manganese-doped glass was a potential candidate as phosphor-converted white-light-emitting diodes. An encapsulated white-light-emitting diode device based on this glass with 276 nm ultraviolet chip was achieved. It showed the CIE values of (0.33, 0.35), high CRI (Ra = 86), and low color temperature (5228 K).     

Electrochemical etching using surface carboxylated graphite electrodes in ultrapure water

Electrochemical etching enables processing with an atomic-level accuracy, without deteriorating the physical properties of the workpiece; however, contamination of its surface with electrolytes is unavoidable. If it is possible to carry out electrochemical etching without using electrolytes, such a process will be applicable to electronic device manufacturing and precision nanoscale processing of semiconductor materials. In addition, this process does not require the use of chemicals, cleaning after processing or disposal of waste fluid, which results in a low-cost and environmentally friendly process. To develop an electrochemical etching process that does not require the use of electrolytes, we proposed a method in which a functional-group-modified electrode is used as the cathode. A carboxylated graphite electrode was prepared by treating a graphite electrode with sulfuric acid. Electrolysis of ultrapure water was carried out using the obtained electrode as a cathode. The results indicate that the electrolysis current obtained using the modified electrode is approximately six-fold that obtained using an unmodified electrode. Furthermore, we can etch a Cu surface conically in ultrapure water. The current efficiency increases by 70% at maximum, and the minimum current required for electrochemical etching decreases compared with that in the case of using an unmodified electrode.     

Improved light extraction of InGaN/GaN blue LEDs by GaOOH NRAs using a thin ATO seed layer

ABSTRACT: We investigated the effect of gallium oxide hydroxide (GaOOH) nanorod arrays (NRAs) on the light extraction of InGaN/GaN MQW blue light-emitting diodes (LEDs). The GaOOH NRAs were prepared on the indium tin oxide electrode (ITO) layer of LEDs by the electrochemical deposition method. The GaOOH NRAs with preferred orientations were grown on the ITO surface by sputtering a thin antimony-doped tin oxide (ATO) seed layer, which enhances heterogeneous reactions. The surface density and coverage were also efficiently controlled by the different growth voltages. For the LEDs with GaOOH NRAs grown at -2 V, the light output power was increased by 22% without suffering from any serious electrical degradation and wavelength shift, compared to the conventional LEDs.     

Selective emitter using a screen printed etch barrier in crystalline silicon solar cell

ABSTRACT: Low level doping of a selective emitter by etch back is an easy and low cost process to obtain a better blue response from a solar cell. This work suggests that the contact resistance of the selective emitter can be controlled by wet etching with the commercial acid barrier paste that is commonly applied in screen printing. Wet etching conditions such as acid barrier curing time, etchant concentration, and etching time have been optimized for the process, which is controllable as well as fast. Acid barrier formed by screen printing was etched with HF and HNO3 (1:200) solution for 15 seconds, resulting in high sheet contact resistance of 90 Ohm/sq. Doping concentrations of the electrode contact portion were 2x1021 cm-3 in the low Rs region and 7x1019 cm-3 in the high Rs region. Solar cells of 12.5 cm x 12.5 cm in dimensions with a wet etch back selective emitter of Jsc of 37 mA-cm-2 and efficiency of 18.13%, were fabricated. The result showed highly improved solar cell characteristics compared to those of the reference solar cell fabricated with the RIE etch back selective emitter, with Jsc of 36.90 mA-cm-2 and efficiency of 17.60%.     

轻烧粉在氯化铵体系中的萃取实验研究

开展轻烧粉(MgO)在氯化铵体系中的萃取实验研究。主要考察了Mg⁽²⁺⁾初始浓度、n(MgO)∶n(NH(2+)初始浓度、n(MgO)∶n(NH⁺_4)、温度、时间对MgO萃取率的影响,并用扫描电镜及X射线衍射光谱对过程中固相组分的组成及微观形貌进行了表征,对机理进行了分析。结果表明,Mg+_4)、温度、时间对MgO萃取率的影响,并用扫描电镜及X射线衍射光谱对过程中固相组分的组成及微观形貌进行了表征,对机理进行了分析。结果表明,Mg⁽²⁺⁾初始浓度为1 mol/L,n(MgO)∶n(NH(2+)初始浓度为1 mol/L,n(MgO)∶n(NH⁺_4)为1∶2.4,温度为110℃,反应时间2 h时,MgO萃取率大于98%。MgO-NH_4Cl-H_2O体系中,MgO先快速水化成Mg(OH)_2,而后Mg(OH)_2溶解转变为Mg+_4)为1∶2.4,温度为110℃,反应时间2 h时,MgO萃取率大于98%。MgO-NH_4Cl-H_2O体系中,MgO先快速水化成Mg(OH)_2,而后Mg(OH)_2溶解转变为Mg⁽²⁺⁾,其过程符合溶解-沉淀-溶解机理。