Degradation processes of organic compounds over UV-irradiated TiO2. Effect of ozone

UV irradiation of TiO₂ promotes electrons from the valence band to the conduction band. The capabilities of the resulting redox system to degrade organic pollutants in water and the variety of products formed is illustrated here by the case of 2,3-dimethylpyrazine. Two debated questions, viz. (i) which electron-donors are implicated to fill in the electron deficiencies in the valence band? and (ii) is superoxide chemically involved in the photocatalytic degradations?, are addressed by using quinoline, the photo-Fenton reaction and superoxide dismutase. Finally, the favourable effect of ozone is exemplified by the photoctalytic removal of monochloroacetic acid.     

Determination of nitrites and nitrates in plasma-activated deionized water by microchip capillary electrophoresis

In this work, we present the application of a fast and sensitive microanalytical method, microchip capillary electrophoresis (MCE), for the determination of NO₂⁻ and NO₃⁻ ions in deionized water treated by atmospheric pressure plasma jet (APPJ). The MCE technique consisted of an online combination of isotachophoresis with zone electrophoresis, both performed on the microchip. The argon plasma has been characterized by optical emission spectroscopy (OES) and Fourier transform infrared spectroscopy (FTIR). OES confirmed the presence of argon excited species (Ar I) emission (4p → 4s) lines, N₂ emission bands (second positive system C³Π_u → B³Π_g), and OH band (A²∑⁺ → X²Π Δv = 0), as well as the presence of NO and excited NO₂. The presence of NO₂ molecules was also confirmed by FTIR absorption spectroscopy. The performance of the developed MCE method was evaluated for linearity, limit of detection, limit of quantitation, precision, and accuracy, and the concentration of NO₂⁻ and NO₃⁻ in the water as a function of the water treatment time was monitored.     

Energy Methods for Problems with Nonhomogeneous Boundary Conditions

This paper employs the weighted energy method to derive estimates for the dynamic behavior of solutions to boundary and initial boundary value problems with nonhomogeneous boundary conditions. In particular, the method is applied to the heat and Laplace equations in a bounded or unbounded region. Extensions to related equations are also studied. Similar estimates but for the spatial behavior is obtained for the heat equation and the backward in time heat equation. Results for blow-up in finite time of solutions to certain nonlinear equations are generalized to include nonhomogeneous boundary conditions, while solutions that vanish on part of the boundary are briefly discussed in the final section.     

Determination of total sulfite in wine. Zone electrophoresis-isotachophoresis quantitation of sulfate on a chip after an in-sample oxidation of total sulfite

This work deals with the determination of total sulfite in wine. The determination combines an in-sample hydrogen peroxide oxidation of total sulfite in alkalized wine to sulfate with the separation and quantitation of the latter anion by zone electrophoresis (ZE) on-line coupled with isotachophoresis (ITP) on a column-coupling chip. Sample clean up, integrated into the ITP-ZE separation, eliminated wine matrix in an extent comparable to that provided by a highly selective distillation isolation of sulfite. At the same time, conductivity detection, employed to the detection of sulfate in the ZE stage of the ITP-ZE combination, provided for sulfate the concentration limit of detection corresponding to a 90 microg/l concentration of sulfite in the loaded sample (0.9 microl). Such a detectability allowed a reproducible quantitation of total sulfite when its concentration in wine was 15 mg/l. Formaldehyde binding of free sulfite in wine, included into the pre-column sample preparation, prevented an uncontrolled oxidation of this sulfite form. This step contributed to an unbiased determination of sulfate present in the original wine sample (this determination corrected for the concentration of sulfate determined in the sample after the peroxide oxidation of sulfite to the value equivalent to the total sulfite). The 99-101% recoveries of sulfite, determined for appropriately spiked wine samples, indicate a very good accuracy of the present method. Such a statement also supports excellent agreements of the results of quantitation based on the in-sample peroxide oxidation of the total sulfite (bound sulfite released at a high pH) with those in which this analyte was isolated from wine by distillation (bound sulfite released at a very low pH).     

An integrated multiphase flow sensor for microchannels

The flow regimes of microscale multiphase flows affect the yield and selectivity of microchemical systems, and the heat transfer properties of micro heat exchangers. We describe an integrated optical sensor that uses total internal reflection to detect the structure of multiphase flows in microchannels. The non-intrusive sensor enables detection of individual slugs, bubbles, or drops, and can be used to continuously determine their number and velocity. The sensor performance is modeled using ray-tracing techniques, and tested for several channel geometries. Both gas-liquid and liquid-liquid flows are investigated in microchannels with rectangular and triangular cross-sections. Statistical properties of the flow, derived from the sensor signal, compare favorably to commonly-used dynamic pressure measurements. We demonstrate the integration of the sensor into a planar multichannel microreactor. An existing glass layer used as a waveguide allows us to monitor flows in optically inaccessible channels. This sensor configuration can be integrated into layers of vertically-stacked multichannel microreactors.

List of symbols

Roman symbols a Radius of largest sphere inscribed in channel [m] - A_ch Channel cross-sectional area [m²] - Ca Capillary number [-] - Critical capillary number [-] - d_h Hydraulic diameter [m] - d_sensor Distance prism surface-sensor origin [m] - E₀ Incident light energy [J] - E_r Emerging light energy [J] - f(t_pass) Probability density function (PDF) of slug dwell times [1/s] - f Focal length [m] - f_slug Slug frequency [Hz] - F(t_pass) Probability distribution of slug dwell times [-] - g(t) Arbitrary function of time [-] - h Liquid film thickness [m] - j_G Superficial gas velocity [m/s] - j_L Superficial liquid velocity [m/s] - l Slug length [m] - N Number of samples [-] - n Refractive index [-] - N_c Number of channel corners [-] - n_i Refractive index of incident medium [-] - n_r Number of reflections [-] - n_t Refractive index of transmitting medium [-] - n_slug Number of slugs [-] - p Gas inlet pressure [Pa] - r Reflectance [-] - R_XX(x,) Autocorrelation function [-] - R_Xp(x,) Cross correlation function [-] - r Slug radius at infinite distance from leading slug tip [m] - s Standard deviation of measured slug dwell times [s] - t Time [s] - t Measurement time interval [s] - t_pass Slug dwell time [s] - U_b Slug (bubble) velocity [m/s] - W Bin size of slug dwell time histogram [-] - x Streamwise coordinate [m] - X(x,t) Phase density function [-] - Y Surface tension of the gas-liquid interface [N/m] - Volumetric gas flow rate [m³/s] - Volumetric liquid flow rate [m³/s] - Volumetric oil flow rate [m³/s] - Volumetric water flow rate [m³/s] - z Normal coordinate [m]Greek symbols Void fraction [-] - _c Critical angle for total internal reflection [^°] - _i Incident angle [^°] - Laser wavelength [m] - µ Liquid viscosity [Pa s] - Normalization factor [-] - _h Dimensionless liquid film thickness [-] - _r Dimensionless radius [-] - _x Dimensionless streamwise position [-] - _r Dimensionless slug radius at infinite distance from leading slug end [-] - Standard deviation of the slug dwell time distribution [s] - Time shift [s] - Contact angle [^°]