Electrical Energy Per Order Research Articles

Decolourization of an Azo Dye by Heterogeneous Photocatalysis

The decolourization of the azo dye Acid Orange 7 was investigated using a heterogeneous photocatalysis which comprised irradiating aqueous solutions of the dye with UV light at a wavelength of 254 nm in the presence of either (TiO 2 + ZnO) mixture, [ ( Ti O 2 + ZnO ) / S 2 O 8 2 − + or [(TiO 2 + ZnO)/Ag 2SO 4] at a pH of 6.1. It was observed that the dye decolourization was enhanced using UV / [ ( Ti O 2 + ZnO ) / S 2 O 8 2 − ] and UV/[(TiO 2 + ZnO)/Ag 2SO 4] catalytic systems over UV/(TiO 2 + ZnO) alone. Also, it can be seen that increasing the concentration of oxidant (Na 2S 2O 8 or Ag 2SO 4) added to (TiO 2 + ZnO) mixture led to a higher rate of dye decolourization. Electrical energy per order (EE/O) was proposed to assess the relative performance of each catalytic system used. It was found that EE/O decreases with increasing the concentration of Na 2S 2O 8 and Ag 2SO 4.

A comparative study of quantum yield and electrical energy per order ( EEo) for advanced oxidative decolourisation of reactive azo dyes by UV light

This paper evaluates the quantum yield and electrical energy per order ( E Eo) efficiency of Reactive Orange 4 (RO4) and Reactive Yellow 14 (RY14) azo dyes by three advanced oxidation processes (AOPs). Both dyes were completely decolourised by all these processes. The relative decolourisation efficiencies of these processes were in the following order: Fe 2+/H 2O 2/UV > UV/TiO 2 > UV/H 2O 2. The low efficiency of UV/H 2O 2 process is mainly due to low UV absorption by hydrogen peroxide at the 365 nm. The figure of merit E Eo values showed that UV/H 2O 2 process consumes more electrical energy than the other two processes. The electrical energy consumption is in the following order: UV/H 2O 2 > UV/TiO 2 > Fe 2+/H 2O 2/UV. At low initial dye concentration higher quantum yield was observed in UV/TiO 2 process, whereas in photo-Fenton process higher quantum yield was observed at high initial dye concentration. The structure of dye molecule also influences the quantum yield and E Eo value.

Evaluation of Electrical Energy Per Order (EEO) with Kinetic Modeling on Photooxidative Degradation of C. I. Acid Orange 7 in a Tubular Continuous-Flow Photoreactor

The photooxidative decolorization of C. I. Acid Orange 7 (AO7), a commercial monoazo textile dye, in the UV/H2O2 process has been investigated in a tubular continuous-flow photoreactor. The decolorization rate follows pseudo-first-order kinetic with respect to the AO7 concentration. The rate constant of the interaction of ·OH radicals with the AO7 molecules has been estimated through the adoption of a simplified kinetic model (6.1 × 108 M-1s-1). This model allows for predicting the concentration of AO7 in different photoreactor lengths for different flow rates and initial concentrations of H2O2 and AO7. For electrical energy cost evaluation, the figure-of-merit electrical energy per order (EEO) was estimated from experimental and calculated data. The results show EEO is very sensitive to the initial concentrations of H2O2 and AO7.

Fundamental approach to the fluence-based kinetic and electrical energy efficiency parameters in photochemical degradation reactions: polychromatic light

When the logarithm of the concentration of a photolyzed component is plotted against the fluence, one usually obtains a first-order plot, and from the slope one can obtain a "fluence-based rate constant". In this study, theoretical expressions are derived for fluence-based rate constants for both monochromatic and polychromatic radiation, and are shown to be fundamental and not dependent on experimental parameters. Therefore, such rate constants can be reproduced from one laboratory to another, as long as the polychromatic light source exhibits similar spectral characteristics. An important quantity that can be obtained from the fluence-based rate constant is the quantum yield. As an example, the quantum yield for the photolysis of atrazine is determined to be 0.033 using the monochromatic fluence-based rate constant. The analysis is extended to the polychromatic light sources, and the expression of polychromatic fluence-based rate constant is derived and validated experimentally for atrazine and NDMA. The new concepts are developed further to analyze the figure-of-merit electrical energy per order (EEO), and it is shown that the EEO depends on the same fundamental photochemical parameters. Key words: fluence-based rate constant, quantum yield, UV radiation, fluence rate, kinetics, photochemical parameters.

05/00069 Russia's energy in the first half of the 21st century: forecasts, trends, problems: Saneev, B. G. et al. International Journal of Global Energy Issues, 2003, 20, (4), 382–392

The photocatalytic degradation of organophosphorus pesticides like methyl parathion (MP) and parathion (PA), under UV irradiation is studied using synthesized Zinc oxide (ZnO) nanocatalyst. Two cases were considered for removal of organophosphorus (OP) pesticides such as only UV (i.e. direct photolysis) and UV–ZnO nanocrystal. The Langmuir–Hinshelwood (L–H) relationship between the initial rate and the initial concentration indicates that the reaction occurs with the adsorbed substrate. Factors affecting the kinetics of the process such as quantum yield, electrical energy per order (EEO), dosage of nanophotocatalyst and L–H model have been discussed. The optimal conditions for degradation were obtained using 85 mg l−1 ZnO, 40% O2 (v/v) with rate constants L–H adsorption equilibrium constant (Kp = 0.127 for MP and 0.122 for PA) and rate constant of surface reaction (Kc = 0.212 for MP and 0.204 for PA). The kinetics of disappearance of OP pesticides (i.e. MP and PA) in water suspension using ZnO nanophotocatalyst illuminated at λ = 253.7 nm and examined. The quantum yield values for photodegradation of pesticides by photolysis and UV–ZnO process under the illumination of UV at 253.7 nm is calculated as 0.00072, 0.012 for MP; 0.00068 and 0.01 for PA. The EEO values for degradation of pesticide by photolysis for UV–ZnO was found to be 20,006, 1392.4 kWh m−3 for MP; 19,089 and 1387.2 kWh m−3 for PA.

The evaluation of electrical energy per order ( EEo) for photooxidative decolorization of four textile dye solutions by the kinetic model

Photooxidative decolorization of four textile dyestuffs, C.I. Acid Orange 7 (AO7), C.I. Acid Orange 8 (AO8), C.I. Acid Orange 52 (AO52) and C.I. Acid Blue 74 (AB74), by UV/H 2O 2 was investigated in a laboratory scale photoreactor equipped with a 15 W low pressure mercury vapour lamp. The decolorization of the dyes was found to follow pseudo-first-order kinetics, and hence the figure-of-merit electrical energy per order ( E Eo) is appropriate for estimating the electrical energy efficiency. The E Eo values were found to depend on the concentration of H 2O 2, concentration and basic structure of the dye. This study shows that these textile dyes can be treated easily and effectively with the UV/H 2O 2 process with E Eo values between 0.4 and 5 kW h m −3 order −1, depending on the initial concentrations of dyes and H 2O 2. The kinetic model, based on the initial rates of degradation, provided good prediction of the E Eo values for a variety of conditions.

UV Direct Photolysis of N-Nitrosodimethylamine (NDMA): Kinetic and Product Study

The ultraviolet (UV) direct photolysis of N-nitrosodimethylamine (NDMA) in aqueous solutions at pH 3 and 7 leads to dimethylamine, and nitrite and nitrate ions as the major degradation products. In addition, small amounts of formaldehyde, formic acid, and methylamine are formed. When the initial concentration of NDMA was 1 mM, only a 13% decrease in the total organic carbon (TOC) was measured at pH 7, whereas no significant change in the TOC was observed at pH 3. In the concentration range 0.01–1 mM NDMA, zero-order kinetics is obeyed, whereas first-order kinetics is followed at concentrations below 0.01 mM. The photolysis occurs much faster at pH 3 than at pH 7, which is explained by the difference in the quantum yields of the process at these two pH values. UV Direct photolysis is an efficient process for the removal of NDMA from contaminated waters, and electrical energy per order (EEO) values as low as 0.3–0.5 kWh/order/m3 were calculated for treatment of low concentrations of NDMA (0.001 mM).

Fundamental photochemical approach to the concepts of fluence (UV dose) and electrical energy efficiency in photochemical degradation reactions

For photochemical reactions in a quasi collimated beam, derivations are presented that introduce 'rate constants' based on the fluence (UV dose) received within the irradiated solution. These fluence-based 'rate constants' are shown to be fundamental and depend only on the quantum yield and the molar absorption coefficient at the irradiation wavelength. An experimental example is given, where the quantum yield for the photolysis of atrazine is determined to be 0.033. The new concepts are developed further to analyze the Figure-of-Merit Electrical Energy per Order (EEO), and it is shown that the EEO depends on the same fundamental photochemical parameters. An example of the photolysis of N-nitrosodimethylamine (NDMA) is presented, and it is shown that the EEO should decrease (increased electrical energy efficiency) as the radius of the UV reactor increases (increased path length), and should increase as the percent transmittance of the water decreases.