Degradation of methyl orange by atmospheric DBD plasma: Analysis of the degradation effects and degradation path

The degradation process of methyl orange solution by dielectric barrier discharge (DBD) plasma using a board-DBD reactor was studied. The percentage destruction reached 99% after 35 min treatment. The pH value of the methyl orange solution decreased with the treatment time and it reached a constant value when discharged for 20 min. The COD value of the methyl orange solution decreased by 57.9% for 30 min treatment. The degradation path was suggested based on the analysis of the molecular structure of methyl orange, intermediate products and the molecular bond energies.     

Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19

The decoloration of reactive dye C.I. Reactive Blue 19 (RB 19) using combined ultrasound with the Fenton process has been investigated. The effect of varying the concentrations of hydrogen peroxide and iron sulfate, initial pH, ultrasonic power, initial dye concentration and dissolved gas on the decoloration and degradation efficiencies was measured. Calibration of the ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using the Fricke dosimeter and degradations were carried out with a 20 kHz probe type transducer at 2, 4, 6 and 8 W cm⁻² of acoustic intensity at 15, 25, 50 and 75 mg L⁻¹ initial dye concentrations. First order rate kinetics was observed. It was found that while the degradation rate due to ultrasound alone was slow, sonication significantly accelerated the Fenton reaction. While the results were similar to those reported for other dyes, the effects occurred at lower concentrations. The rate and extent of decoloration of RB 19 increased with rising hydrogen peroxide concentration, ultrasonic powers and iron sulfate concentration but decreased with increasing dye concentration. An optimum pH value of pH = 3.5 was found. The rate of decoloration was higher when dissolved oxygen was present as compared with nitrogen and argon confirming the solution phase mechanism of the degradation.     

Effect of electrostatic interaction on the methylene blue and methyl orange adsorption by the pristine and functionalized carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with cysteamine groups by several percentage of mass as adsorbents, then kinetics adsorption capacity was investigated for methylene blue (MB) and methyl orange (MO) as anionic and cationic dyes adsorbate molecules, respectively. The effect of temperature (from 283 to 303 K), contact time and initial concentration of the MB and MO dyes in a solution (10 to 40 ppm) was considered. The optimal contact time was found to be about 60 min. Some kinetics model such as pseudo-first-order, pseudo-second-order, intra-particle diffusion and the Elovich were tested. The adsorptions of MB dye on the pristine and functionalized MWCNT surfaces were found to be the intra-particle diffusion and the pseudo-second-order kinetic model, respectively and for adsorption of MO dye by the pristine and low functionalized MWCNTs and highly functionalized tubes, found to be the pseudo-second-order and intra-particle diffusion kinetic model, respectively, based on the chi-square statistic (X²) and also high correlation coefficient (R²) values.     

Removal of four kinds of volatile organic compounds mixture in air using silent discharge reactor driven by bipolar pulsed power

A silent discharge reactor initiated by bipolar pulsed power substituting the traditional ac power was used to remove the volatile organic compounds (VOC_s) mixture of acetone, benzene, tetrachloroethylene and m-xylene. The results indicated that the silent discharge driven by bipolar pulsed power could effectively input pulsed energy, produce strong instant discharge and energetic particles, and thus enhance the removal efficiency of the mixed VOC_s. The order of the removal efficiency of mixed VOC_s followed as acetone < benzene < tetrachloroethylene < m-xylene no matter what power supply was used. Comparing with single-compound, the removal efficiency of m-xylene only fell a little but those of the other three components fell a lot in the process of the mixed VOC_s treatment. In addition, controlling the status of electrical discharge plasma by changing the discharge parameters (such as capacitance of the pulse capacitor and pulse repetitive rate) was found to be an efficient way to enhance the removal efficiency of the mixed VOC_s. In this system, the Cp = 2 nF was the optimal capacitance for the bipolar power supply combined with the silent discharge reactor that had the best energy conversion efficiency for removal of mixed VOC_s. A higher pulse repetitive rate and longer residence time could also increase the removal efficiency of mixed VOC_s.     

On the meniscus deformation when the pulsed voltage is applied

Effect of the pulsed voltage on the meniscus deformation was investigated. Results show that both the pulsed voltage and its width as well as the bias voltage affected the behaviour of spraying. There appeared three spraying modes, e.g. dripping, pulsating jet and cone-jet. Cone-jet has been created by applying a pulsed voltage of 1.5 kV to a bias voltage of 5.0 kV for 300 ms.     

ZnO nanocubes with (1 0 1) basal plane photocatalyst prepared via a low-frequency ultrasonic assisted hydrolysis process

The crystallographic plane of the ZnO nanocrystals photocatalyst is considered as a key parameter for an effective photocatalysis, photoelectrochemical reaction and photosensitivity. In this paper, we report a simple method for the synthesis of a new (1 0 1) high-energy plane bounded ZnO nanocubes photocatalyst directly on the FTO surface, using a seed-mediated ultrasonic assisted hydrolysis process. In the typical procedure, high-density nanocubes and quasi-nanocubes can be grown on the substrate surface from a solution containing equimolar (0.04 M) zinc nitrate hydrate and hexamine. ZnO nanocubes, with average edge-length of ca. 50 nm, can be obtained on the surface in as quickly as 10 min. The heterogeneous photocatalytic property of the sample has been examined in the photodegradation of methyl orange (MO) by UV light irradiation. It was found that the ZnO nanocubes exhibit excellent catalytic and photocatalytic properties and demonstrate the photodegradation efficiency as high as 5.7 percent/μg mW. This is 200 times higher than those reported results using a relatively low-powered polychromatic UV light source (4 mW). The mechanism of ZnO nanocube formation using the present approach is discussed. The new-synthesized ZnO nanocubes with a unique (1 0 1) basal plane also find potential application in photoelectrochemical devices and sensing.     

A DC corona discharge on a flat plate to induce air movement

This paper describes a DC surface corona discharge designed to modify the airflow around a flat plate. The electrode configuration consisted of two thin copper layers placed on each side of the plate's attack edge. Discharge optical measurements with a photomultiplier tube indicated that the light emitted by the plasma is pulsating at a frequency that increases with applied voltage. Moreover, with voltage higher than a threshold value, the electric discharge changes regime with brighter pulses. This discharge also induced an “ionic wind” whose velocity was measured with a pressure sensing probe (up to 1 m/s). Experiments with the particle image velocimetry system in a subsonic wind tunnel showed that this discharge can reduce the separated airflow on the flat plate for a flow of 14 m/s (Reynolds number of 187,000).     

Decoloration of azo dye by a multi-needle-to-plate high-voltage pulsed corona discharge system in water

The decoloration efficiency of azo dye (Acid Orange 7, AO7) using a multi-needle-to-plate high-voltage pulsed corona discharge system was investigated in this paper. The effect of several parameters, including peak pulse voltage and pulse frequency of the discharge system, initial pH and electrical conductivity of the dye solution, mode of needle electrode distribution and gas flow rate on the decoloration rate of the dye wastewater was reviewed. The results obtained show that the pulsed discharge system with a multi-needle-to-plate electrode could dispose azo dye wastewater efficiently. The decoloration rate increased with an increase in applied peak pulse voltage and pulse frequency. Decoloration was more efficient in the acidic solution, and the decoloration rate displayed no marked change under solutions of differing electrical conductivity. For the case in which we example the effect of gas flow rate on the decoloration efficiency of Acid Orange solution, we found that better decoloration efficiency occurred using the seven-needle-to-plate discharge system, which had more discharge anodes.     

Ultrasonic degradation of poly(methyl methacrylate-co-alkyl acrylate) copolymers

The copolymers, poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA), of different compositions were synthesized and characterized. The effect of alkyl acrylate content, alkyl group substituents and solvents on the ultrasonic degradation of these copolymers was studied. A model based on continuous distribution kinetics was used to study the kinetics of degradation. The rate coefficients were obtained by fitting the experimental data with the model. The linear dependence of the rate coefficients on the logarithm of the vapor pressure of the solvent indicated that vapor pressure is the crucial parameter that controls the degradation process. The rate of degradation increases with an increase in the alkyl acrylate content. At any particular copolymer composition, the rate of degradation follows the order: PMMAMA > PMMAEA > PMMABA. It was observed that the degradation rate coefficient varies linearly with the mole percentage of the alkyl acrylate in the copolymer.     

Optimization of biodiesel production in a hydrodynamic cavitation reactor using used frying oil

The present work demonstrates the application of a hydrodynamic cavitation reactor for the synthesis of biodiesel with used frying oil as a feedstock. The synthesis involved the transesterification of used frying oil (UFO) with methanol in the presence of potassium hydroxide as a catalyst. The effect of geometry and upstream pressure of a cavitating orifice plate on the rate of transesterification reaction has been studied. It is observed that the micro level turbulence created by hydrodynamic cavitation somewhat overcomes the mass transfer limitations for triphasic transesterification reaction. The significant effects of upstream pressure on the rate of formation of methyl esters have been seen. It has been observed that flow geometry of orifice plate plays a crucial role in process intensification. With an optimized plate geometry of 2 mm hole diameter and 25 holes, more than 95% of triglycerides have been converted to methyl esters in 10 min of reaction time with cavitational yield of 1.28 × 10^?3 (Grams of methyl esters produced per Joule of energy supplied). The potential of UFO to produce good quality methyl esters has been demonstrated.     

Terahertz pulse driven Josephson junctions

The voltage response of a Josephson junction to a pulsed terahertz current is evaluated in the limit of a negligible junction capacitance (overdamped limit). The time-dependent superconductor phase difference across the junction is calculated in the framework of the standard resistive shunted junction model by using a perturbative method. The pulsed current bias affects the time average value of the voltage across the junction and current steps are induced in the current–voltage characteristics for voltage values depending on the pulse repetition rate. The current step height is proportional to the square of the pulse time width (τ) to the period (T) ratio. A fast response detector for pulsed Terahertz radiation is proposed, with an expected responsivity of the order of 0.1 V/W and an equivalent noise power of about 3 × 10^?10 W/Hz^1/2.     

Kinetics of microplasma atmospheric ion generation correlated with discharge current

The conditions necessary for achieving a stable bipolar ion generation (in the order of 10⁶ ion/cm³) and lower ozone concentration (less than 50 ppb) using a surface discharge microplasma device (SMD) by adjusting the applied voltage and frequency were experimentally determined and investigated. Measurements of the discharge current characteristics of the SMD revealed saturation against the frequency (1.5–2.5 kHz, depending on the applied voltage). The ion and ozone concentrations both increased in step with the discharge current in the lower frequency region. The ion concentration reached equilibrium in the frequency range of 200–500 Hz, and the point of equilibrium within that range depended on the applied voltage. The ozone concentration did not reach equilibrium under our experimental conditions (ozone concentration < 100 ppb). The kinetics of the ion/ozone generation rate with a focus on the plasma reaction and recombination of bipolar ions is discussed.     

Alternate pulses of ultrasound and electricity enhanced electrochemical process for p-nitrophenol degradation

A novel alternated ultrasonic and electric pulse enhanced electrochemical process was developed and used for investigating its effectiveness on the degradation of p-nitrophenol (PNP) in an aqueous solution. The impacts of pulse mode, pH, cell voltage, supporting electrolyte concentration, ultrasonic power and the initial concentration of PNP on the performance of PNP degradation were evaluated. Possible pathway of PNP degradation in this system was proposed based on the intermediates identified by GC–MS. Experimental results showed that 94.1% of PNP could be removed at 2 h in the dual-pulse ultrasound enhanced electrochemical (dual-pulse US-EC) process at mild operating conditions (i.e., pulse mode of electrochemical pulse time (T_EC) = 50 ms and ultrasonic pulse time (T_US) = 100 ms, initial pH of 3.0, cell voltage of 10 V, Na₂SO₄ concentration of 0.05 M, ultrasonic powder of 48.8 W and initial concentration of PNP of 100 mg/L), compared with 89.0%, 58.9%, 2.4% in simultaneous ultrasound enhanced electrochemical (US-EC) process, pulsed electrochemical (EC) process and pulsed ultrasound (US), respectively. Moreover, energy used in the dual-pulse US-EC process was reduced by 50.4% as compared to the US-EC process. The degradation of PNP in the pulsed EC process, US-EC process and dual-pulse process followed pseudo-first-order kinetics. Therefore, the dual-pulse US-EC process was found to be a more effective technique for the degradation of PNP and would have a promising application in wastewater treatment.     

Properties of droplet formation made by cone jet using a novel capillary with an external electrode

A capillary with an external electrode for cone-jet mode of electrospray has been developed to spot a droplet accurately on a substrate surface. The external electrode is made by gold deposition around tip of a glass capillary. The electrospray was made by applying a positive pulsed dc voltage to the solution in the capillary. Using a positive bias voltage to the external electrode, the meniscus of the solution at the tip deformed to be more sharp, and center of the meniscus was prolonged. This deformation stabilized the trajectory of the jet from the Taylor cone at the tip. From the experimental result, accuracy of positioning of the droplet having 0.3 pL volume was improved with the standard deviation of 1.1 μm, from that of 2.5 μm for conventional capillary without the external electrode.     

Carbon fiber formation in electrical discharges in hydrocarbons

The process of synthesis of carbon fiber from hydrocarbon vapours in low-current electrical-discharge plasma was investigated in the paper. The carbon fibers were effectively synthesised in discharge of positive polarity generated between a stainless steel needle and a plate made of nickel alloy, for the discharge current ranged from 1 mA up to 3 mA. The experiments were carried out at normal pressure in cyclohexane vapours with argon as carrier gas. The diameter of produced fibers varied from about 20 to 70 μm. The growth rate of the fiber was about 0.25 mm/s.     

Optimal ablation of fluorine-doped tin oxide (FTO) thin film layers adopting a simple pulsed Nd:YAG laser with TEM00 mode

In material processing, a laser system with optimal laser parameters has been considered to be significant. Especially, the laser ablation technology is thought to be very important for fabricating a dye-sensitized solar cell (DSSC) module with good quality. Moreover, the TEM₀₀ mode laser beam is the most dominant factor to decide the incident photon to current conversion efficiency (IPCE) characteristics. In order to get the TEM₀₀ mode, a pin-hole is inserted within a simple pulsed Nd:YAG laser resonator. And the spatial field distribution is measured by using three pin-hole diameters of 1.6, 2.0 and 4.0 mm, respectively. At that moment, each case has the same laser beam energy by adjusting the discharge voltage and pulse per second (pps). From those results, it is known that the pin-hole size of 1.6 mm has the perfect TEM₀₀ mode. In addition, at the charging voltage of 1000 V, 10 pps, the feeding speed of 6.08 mm/s and the overlapping rate (OL) of 62%, the scanning electron microscope (SEM) photograph of fluorine-doped tin oxide (FTO) thin film layers shows the best ablation trace.     

Synthesis of LiFePO4 nanoparticles and their electrochemical properties

LiFePO₄ nanoparticles were synthesized via polyol process. The temperature of the solution was rapidly increased up to 320 °C to obtain larger particles and the temperature was maintained for 16 h in a round-bottomed flask attached to a refluxing condenser. The X-ray diffractrion (XRD), pattern was indexed on the basis of orthorhombic olivine structure. The LiFePO₄ compound prepared through polyol process exhibited a high crystallinity. The particles show the various shapes with size ranging from 100 to 300 nm. The initial discharge curve of LiFePO₄ capacity shows 168 mA h/g at the 0.1C rate in the voltage range of 2.5–4 V with well-formed plateau.     

Dependence of sonochemical parameters on the platinization of rutile titania – An observation of a pronounced increase in photocatalytic efficiencies

Using a standing wave sonochemical reactor (SWSR), the influences of parameters of ultrasonic power input, sonication time, sonication temperature and the amount of propanol (which generates the reducing radicals) were systemically investigated to ascertain and optimize the best conditions for the sonochemical reduction of Pt from its precursor hexachloroplatinic acid and then its deposition on rutile TiO₂ (platinization of rutile titania) catalysts. Catalytic activity of the prepared platinized catalysts was tested in the reaction of methyl orange degradation. The results of photocatalytic activity study in the degradation of methyl orange further demonstrate that sonochemically as-prepared Pt/TiO₂ catalysts show a pronounced increase (～2 times) in photodegradation, even with a deposition of small amounts of platinum (1.4 wt.%), as compared to the unsupported or naked rutile titania. Although there are various parameters that influence the sonochemical platinization of rutile titania, the present optimization results clearly indicate that the best photocatalytic degradation of methyl orange can be obtained when the experimental conditions of the preparation were with an input power of 50 W, an initial hexachloroplatinic acid volume of 70 ml (which results into 1.4 wt.% Pt on TiO₂), sonication time of 90 min, 0.18 g of propanol and a temperature of 10 °C were adopted. The method of ultrasound application to prepare metal supported semiconductors has many advantages such as convenience, safety and high efficiency. Furthermore, it is hopeful that this optimization study can also be extended to the generation of similar metal supported semiconductors.     

Nitrogen fixed into HNO3 by pulsed high voltage discharge

By applying pulsed high voltage discharge to a needle-mesh reactor that using seven acupuncture needles as discharge electrode and stainless steel wire mesh as ground electrode, nitrogen from bubbling gas could be fixed into NO₂^? and NO₃^? with equivalent mol H⁺ produced in the liquid phase and a small amount of NO and NO₂ yielded in the gas phase. The HNO₂ was originally formed and then converted into HNO₃. The ·OH and H₂O₂ stimulated the conversion reaction from HNO₂ to HNO₃, which caused HNO₂ concentration increased in the first 12 min and then decreased until lower than its detection limit. The concentration of HNO₃ still increased with discharge time. After 36 min, HNO₃ was the only and ultimate product in the liquid. The total yield of HNO₂ and HNO₃ could be affected by processing parameters such as electric factors of peak voltage and frequency, mesh size of ground electrode and content of nitrogen in N₂/O₂ bubbling. Increasing peak voltage or frequency, the total yield of HNO₂ and HNO₃ increased. Gas composition had a heavy impact on the fixation efficiency that obtained its maximum value at an oxygen content of 66.7% with bubbling O₂/N₂ gas. At the end of the 36 min discharge, the HNO₃ concentration with bubbling air was 2.215 mmol L^?1 at an applied voltage of 25 kV, pulse repetition frequency of 140 Hz and ground electrode mesh of 20 × 20. The energy yield was about 1.22 g (HNO₃)/kWh.     

Ultrasound stimulus inducing change in hydrogen bonded crosslinking of aqueous polyvinyl alcohols

The effect of ultrasound (US) stimulation on the shear viscosity of aqueous polyvinyl alcohol (PVA) solution was studied when the solution was exposed to US at 23, 43, 96, and 141 kHz. The US stimulus showed a marked decrease of the shear viscosity of the solution in the order of 43 > 96 > 23 > 141 kHz, respectively, under US power dissipation of 8.5, 8.9, 8.9, and 8.8 W. Subsequently, when US exposure was stopped, the shear viscosity of PVA reverted to its original value. The US stimulation was analyzed with the US power transmitted through the PVA aqueous media. Furthermore, FT-IR spectra measured at different durations of US exposure, suggest that hydrogen bonds in the PVA segments were broken by the US exposure. We conclude that structural changes of the hydrogen bonded crosslinks of PVA were induced to include water molecules for the re-forming of crosslinks of aqueous PVA.