Discoloration Kinetics Research Articles

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

Uniform adhesive TiO2–ZrO2 films co-sputtered on polyester (PES) under low intensity sunlight irradiation discolored methylene blue (MB) within 120min. The discoloration kinetics was seen to be accelerated by a factor four by TiO2–ZrO2–Cu containing ∼0.01% Cu, as determined by X-ray fluorescence (XRF). TiO2–ZrO2–Cu also increased also accelerated by a factor the discoloration of MB compared to TiO2/Cu(PES). MB discoloration was also monitored under visible light in the solar cavity by using a 400nm cutoff filter. Photocatalyst surfaces were characterized by spectroscopic methods showing the film optical absorption and by X-ray photoelectron spectroscopy (XPS), the surface atomic percentage concentration up to 120nm (∼600 layers). The band-gaps of TiO2–ZrO2 and TiO2–ZrO2–Cu were estimated for films co-sputtered for different times. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR), the systematic shift of the predominating νs(CH2) vibration-rotational MB bands was monitored up to complete MB discoloration under low intensity solar simulated light. Evidence is presented for the OH generation by TiO2–ZrO2–Cu participating in the self-cleaning mechanism. The photo-induced interfacial charge transfer (IFCT) on the TiO2–ZrO2–Cu is discussed in terms of the electronic band positions of the binary oxides and Cu intra-gap states. This study presents the first evidence for a Cu-promoted composed of two binary oxide semiconductors accelerating the self-cleaning performance.

Stability of Cu species and zeolite structure on ecological heterogeneous Fenton discoloration–degradation of yellow 5 dye: Efficiency on reusable Cu‐Y catalysts

The discoloration‐degradation of yellow 5 dye was achieved through the heterogeneous Fenton reaction using Cu‐Y catalysts. Cu‐Y materials were prepared by an aqueous ion exchange method from the NH4‐Y parent zeolite. The solids are characterized by X‐ray diffraction, nitrogen physisorption, EPR and, 27Al and 29Si NMR spectroscopies. Discoloration around 100% with 60% of COD removal was achieved before 90 min at 50°C using the next reaction conditions: 50 mL of colored solution containing 50 ppm of dye, 0.129 mmol of H2O2, catalyst mass/volume of solution ratio (g L−1)= 0.016 and pH = 4–5. The influence of temperature and H2O2 concentration was also studied. The discoloration kinetics were modeled using the pseudo‐first order reaction. High catalytic activity was observed even after four reaction cycles, which is credited to the good stability of the Cu species and the zeolite structure. Because the Fenton reaction was favored by the acid media provided by the Cu‐Y catalyst and temperature, the addition of any acid was not necessary, avoiding the generation of sludge, resulting in an eco‐friendly process. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 990–998, 2015

TiO2/clay as a heterogeneous catalyst in photocatalytic/photochemical oxidation of anionic reactive blue 19

A TiO2-coated Tunisian clay (TiO2–clay) was synthesized by a typical impregnation method. The physicochemical characterization points to a successful impregnation of titania on the clay surface. The activity of this structured catalyst was studied in the photocatalytic/photochemical oxidation of anionic reactive blue 19 (RB 19). The effect of UVA and solar irradiation (UV-solar) was studied at room temperature. TiO2–clay demonstrated an effective degradation of RB 19 under both types of irradiation. Moreover, in this study, the effects of various oxidants such as hydrogen peroxide (H2O2), potassium peroxodisulfate (K2S2O8) and sodium carbonate (Na2CO3) were thoroughly investigated. H2O2 was a promising oxidant for promoting RB 19 degradation under UVA. The kinetics of discoloration of RB 19 followed a pseudo-first-order rate law. We can remark that 20min of UV irradiation was enough to achieve 100% discoloration of the aqueous solution. However, under UV–Vis, HPLC and chemical oxygen demand measurements indicated, that a longer reaction time (of around 45min) was required for achieving the complete dye mineralization. The findings clearly demonstrated the applicability of this TiO2/clay catalyst for the photocatalytic oxidation of RB 19.

Development and characterization of an enzymatic time-temperature indicator (TTI) based on Aspergillus niger lipase

Time-temperature indicator (TTI) has been widely applied in the food industry. A lipase type TTI prototype was developed in this study based on the reaction between Aspergillus niger lipase and glycerol tributyrate. Four lipase type TTIs contain substrates with different concentrations, and the discoloration kinetics of the four lipase type TTIs were investigated. The mathematical model for TTI has been simulated, which expressed the relationship of the changes of TTI's color with time and temperature. The activation energies of four lipase type TTIs were 42.12 kJ/mol, 36.84 kJ/mol, 31.60 kJ/mol and 34.42 kJ/mol, respectively. The A. niger lipase based TTI prototype has potential to become an enzymatic TTI product.

Time‐temperature superposition principle application to the hygrothermal discoloration of colored high‐density polypropylene/wood composites

Discoloration kinetics of wood plastic composites (WPCs) made of recycled high density polyethylene (HDPE) during accelerated hygrothermal aging test at 45–65°C was conducted by means of time‐temperature superposition principle (TTSP). Color parameters measured with a spectrophotometer by CIELAB color system showed that L* and ΔE* increased while a* and b* decreased with aging time and temperature. A single horizontal shift was adequate for the superposition of color parameter master curves, indicating temperature can be used as accelerating factor to the discoloration of the studied WPCs. The regression line for Arrhenius plot showed a linearity for color parameters (R2 = 0.9996), suggesting TTSP concept can be used to analyze and predict the discoloration kinetics of WPCs at low aging temperature. The prediction of color parameters at ambient aging temperature (21°C) can be extended to 7.2 years. The activation energy calculated from color parameters using TTSP method was 85.5 kJ/mol and similar to the reported values of HDPE thermal relaxation reactions calculated from other methods in the open literature. POLYM. COMPOS. 37:1016–1020, 2016. © 2014 Society of Plastics Engineers

Influence of Operational Parameters in the Heterogeneous Photo-Fenton Discoloration of Wastewaters in the Presence of an Iron-Pillared Clay

An iron-pillared Tunisian clay (Fe-PILC) was prepared and used as the catalyst in the heterogeneous photo-Fenton oxidation of Red Congo and Malachite Green in aqueous solution. The catalyst Fe-PILC was characterized by XRF, XRD, BET, and FTIR methods. This physicochemical characterization pointed to successful iron pillaring of the clay. The influence of several operational parameters such as the pH, H2O2 concentration, catalyst dosage, and initial dye concentration was evaluated. A solution pH in the range 2.5–3, the addition of 8 mL of 200 mg/L H2O2, and a catalyst dosage of 0.3 g/L appeared as the most favorable reaction conditions for achieving complete discoloration, either for Red Congo or Malachite Green, although oxidation was found to be slower and more complicated in the former case. The kinetics of discoloration of both dyes followed a pseudo-first-order rate law. In general, 20 min of UV irradiation was enough to achieve 100% discoloration of the aqueous solution. UV–vis and chemical oxygen demand measurements indicated, however, that longer reaction times of around 1 h were required for achieving dye mineralization. Leaching tests confirmed a very low amount of dissolved iron and good stability of the catalyst, with almost unaltered discoloration efficiency upon three cycles. Hence, taking into account the favorable photocatalytic properties and low leaching of iron ions, such iron-pillared clay can be considered a promising catalyst for dye wastewater treatment.

Effects of PMMA/anisole hybrid coatings on discoloration performance of nano zerovalent iron toward organic dyes

To elucidate the effects of poly(methylmethacrylate) (PMMA)/anisole coatings on discoloration performance of nano zerovalent iron (NZVI), PMMA/anisole co-modified NZVI (PNZVI) was fabricated. PMMA/anisole-assisted fabrication of NZVI, to form PNZVI, has enhanced the oxidation resistance of NZVI and reduced its agglomeration. However, such coatings on NZVI surface gave an inhibition to discoloration reactivity of NZVI toward the selected dyes (i.e. acid fuchsine, sunset yellow and methyl orange). Further exploration showed that increasing initial concentration of acid fuchsine demonstrated an enhanced inhibition of the hybrid coatings to its discoloration efficiency by NZVI, whereas increasing NZVI dosage and solution temperature demonstrated a decreased inhibition to its discoloration efficiency. Additionally, the increased pH value reduced the discoloration reactivity of NZVI toward acid fuchsine but weakened the inhibition of the hybrid coatings. Such inhibitory effects might be ascribed to the inhibited mass transfer, blocked reactive sites, restrained electron transfer and reactive species caused by the hybrid coatings. Interestingly, the chloride ions are favorable for the enhancement of PNZVI reactivity whereas unfavorable for bare NZVI, and the discoloration kinetics by PNZVI and bare NZVI can both be well-described by empirical rate equation. This study suggests that polymer coatings play a crucial role between particle stability and reactivity of NZVI.

Comparative anodic oxidation on boron-doped diamond electrode of two different dyes: separately and mixed

ABSTRACTTwo models of azoic and anthraquinone dyes, Acid Orange 8 (AO8) and Alizarin Blue Black B, were chosen to study their electrochemical oxidation on boron-doped diamond electrode separately and in mixture on different proportion. The influence of the initial pH (2 and 8), current density (20, 40, and 80 mA cm-²) and their mixture were investigated on discoloration and oxidation kinetics. The results obtained show that the structure of the dyes has an effect on the performance and efficiency of the electrochemical process. Alkaline pH increases anthraquinone dye oxidation rate, while the AO8 azo dye shows a maximum degradation in acidic medium. Moreover, an increase in the current density enhances the rate of degradation of two dyes solution. Study of dyes mixture attests the dependence of the color removal on the nature of predominant dye. Results also show the presence of two kinetic steps, with the first one, which lasts for 30 min, being faster than the second one.

Preliminary study on time–temperature indicator (TTI) system based on urease

Time–temperature indicator (TTI) is a small commercial device used widely in food field. A TTI system on the basis of the chemical reaction between urease and carbamide was developed. The discoloration kinetics of urease-based TTI was explored. The mathematics formula that revealed the relationships of the change of TTI color with time and temperature has been established. The activation energy of urease-based TTI was 23.05 ± 1.15 kJ/mol (±95% confidence interval). This type of TTI system has the potential to apply to some time–temperature dependence foods with similar Ea values.

TiO<sub>2</sub> PC500 Coated on Non Woven Paper with SiO<sub>2</sub> as a Binder-Assisted Photocatalytic Degradation of Reactive Black 5 in Aqueous Solution

Photocatalytic discoloration kinetics of Reactive Black 5 (RB5), a vinylsulfone dye, has been studied spectrophotometrically by following the decrease in dye concentration with time at ambient conditions using a flow loop reactor. UV lump, Black Light Blue (BLB) emitting at maximum wavelength of 365 nm and Ahlstrom Research Service paper consistent of TiO2 P500 coated on non woven paper was used respectively as source of UV light and photocatalyst. At natural pH, the result shows that photolysis of RB5 and its adsorption in the presence of photocatalyst was negligible while the photocatalytic oxidation (PCO) permits 30.8% of RB5 degradation. The degradation of dye was studied under a variety of conditions such as volumetric flow rate, initial pH, photocatalyst reuse, and in the presence of electron acceptor such as sodium persulphate ((Na)2S2O8). The degradation rates were found to be strongly influenced by all the above parameters. The circulation flow rate of 108 L/h was the best. The rate constant calculated when the initial pH was varied shows that pH 3 was more favorable for RB5 removal. Peroxydisulphate ions have the strong effect on RB5 discoloration even in dark without and with photocatalyst. When UV light was used in the presence of photocatalyst, 50 min was enough for quasi-total removal of RB5 with (0.2 M).

In situ photoelectrochemical/photocatalytic study of a dye discoloration in a microreactor system using TiO2 thin films

In this work, we report in situ studies of UV photoelectrocatalytic discoloration of a dye (indigo carmine) by a TiO(2) thin film in a microreactor to demonstrate the driving force of the applied electrode potential and the dye flow rate toward dye discoloration kinetics. TiO(2) 65-nm-thick thin films were deposited by PVD magnetron sputtering technique on a conducting glass substrate of fluorinated tin oxide. A microreactor to measure the discoloration rate, the electrode potential, and the photocurrent in situ, was developed. The dye solutions, before and after measurements in the microreactor, were analyzed by Raman spectroscopy. The annealed TiO(2) thin films had anatase structure with preferential orientation (101). The discoloration rate of the dye increased with the applied potential to TiO(2) electrode. Further, acceleration of the photocatalytic reaction was achieved by utilizing dye flow recirculation to the microreactor. In both cases the photoelectrochemical/photocatalytic discoloration kinetics of the dye follows the Langmuir-Hinshelwood model, with first-order kinetics. The feasibility of dye discoloration on TiO(2) thin film electrodes, prepared by magnetron sputtering using a flow microreactor system, has been clearly demonstrated. The discoloration rate is enhanced by applying a positive potential (E (AP)) and/or increasing the flow rate. The fastest discoloration and shortest irradiation time (50min) produced 80% discoloration with an external anodic potential of 0.931V and a flow rate of 12.2mLmin(-1).

New enzymatic time–temperature integrator (TTI) that uses laccase

A new enzyme based TTI prototype was developed using an advantageous enzyme, laccase, which has simple discoloration kinetics and is widely available. The possibility for the laccase TTI to be a qualified TTI product was investigated and the color response variable, kinetics and Arrhenius parameters of the TTI were identified. The hue value was found to be highly correlated with the concentration of laccase reaction product and determined as the color response variable. The significance of kinetics and Arrhenius relationships were sufficient for the TTI prototype to meet the general requirements of TTI products. The activation energy of laccase TTI ranged from 43.9 to 46.9kJ/mol. The results indicated that the laccase based TTI prototype could be useful as a new type of enzymatic TTI product.

Detection of the parasitic plant, Orobanche cumana on sunflower (Helianthus annuus L.) in Tunisia

This study aimed to select fungi with the potential to decolorize effluent and optimize culture conditions using the methodology of experimental design. Twenty fungi were inoculated into flasks containing the liquid synthetic medium every 24 h; aliquots were over 10 days. The culture conditions and stationary stirring of 130 rpm were evaluated. After selecting, the best fungi were subjected to an experimental design and evaluation of the production of the ligninolytics enzymes. Fungi Phanerochaete chrysosporum CCT 1999 , Lentinula edodes CCT 4519 and Curvularia lunata UFPEDA 885 reduced 100% the color of the effluent during growth under agitation while the fungus Aspergillus sp. F 75 reduced 98% the color of the effluent under the same condition. Statistical analysis confirmed a significant difference between the culture conditions evaluated, with greater efficiency of decolorization of textile effluent under agitation for most fungi evaluated. The experiment 19 was noted for facilitating discoloration in 99% of the effluent. The kinetics of discoloration shows that the fungus P. chrysosporum CCT 1999 and C. lunata UFPEDA 885 stand out for discoloration among the fungi studied. The four selected fungi proved to be good producers of the enzyme laccase.

Discoloration Kinetics of Clarified Apple Juice Treated with Lewatit® S 4528 Adsorbent Resin During Processing

The present work studies the adsorption of colored compounds in apple juice with a Lewatit® resin S 4528. The sorption equilibrium through the adsorption isotherms for 20, 35, and 50 °C was studied. The absorbance at 420 nm was used to measure the concentration of colored compounds, which permits correlating the residual concentration with the adsorbed concentration, proving that the data matched reasonably well according to the Langmuir and Freundlich models. Also, the efficiency of the adsorption process was studied for different resin/juice mass ratios at different temperatures, from which it was observed that there was an improvement in efficiency as the resin content increased, while the increase in temperature was not so important in the process. The adsorption kinetics at 35 °C for different resin/juice mass ratios was also studied. The kinetic model developed by Ibarz was used, concluding that the data matched this model reasonably well. The adsorption kinetic constant was always higher than the desorption kinetic constant, which indicates that the adsorption stage predominates the desorption stage. The adsorption kinetic constant shows a decreasing tendency with the raise in the resin/juice ratio, and the desorption kinetic constant shows an increasing tendency. The variation of the CIELab color parameters (L*, a*, and b*) with the adsorption time was studied, obtaining results that match the kinetic adsorption model proposed.

Photocatalytic degradation of a mixture of two anionic dyes: Procion Red MX-5B and Remazol Black 5 (RB5)

Abstract The photocatalytic degradation of a mixture of two anionic dyes, Remazol Black (RB5) and Red Procion MX-5B in presence of TiO 2 Degussa P-25 was investigated using wavelength higher than 290 nm. UV–vis spectroscopy was employed to monitor the amount of each dye in the mixture and to compare the degradation of both dyes individually and mixed. The adsorption equilibrium of each dye, the influence of pH and the initial concentration of dyes on the kinetics of discoloration and mineralization were performed and compared to their kinetics when they are individually degraded. Although no complex was put in evidence between these two coloring agents using spectroscopy UV–vis, an important modification of the RB5 adsorption is noted in the mixture. However, the presence of RB5 has no effect on the MX-5B adsorption. This difference of behaviour can be explained by considering the modification of pH by increasing the initial concentration of MX-5B in the mixture. Above 15 μmol/L, both anionic dyes are in competition for the same site. Even if the adsorption of RB5 is modified, the disappearance rate of both dyes individually or mixed are similar at low concentration of dyes. At high concentration their disappearance rates in the mixture decrease in agreement with the number of available site. Besides the study of the discoloration, we studied the evolution of Total Organic Carbon (TOC), the formation of NH 4 + , NO 3 − , SO 4 2− of both dyes during their individual or mixed photocatalytic degradation are compared. The results suggest that the mechanisms of degradation are modified in the mixture.

The use of D-optimal design to model the effects of process parameters on mineralization and discoloration kinetics of Fenton-type oxidation

The aim of this experimental investigation was to study kinetics of Fenton and modified Fenton oxidation applied to miscellaneous dye solutions. Several bench scale laboratory tests for the treatment of colored wastewaters containing model pollutant compounds, reactive azo dyes C.I. Reactive Violet 2 (RV2) and C.I. Reactive Yellow 3 (RY3) were performed. In order to examine the effects of initial Fe 2+ concentration, oxidant/catalyst molar ratio and oxidant type on TOC reduction and color removal, the following reactants were used: classic Fenton's reagent (Fe 2+/H 2O 2) and modified Fenton's reagent, where potassium peroxodisulfate, alone and in combination with hydrogen peroxide, was selected as oxidant. Response surface methodology (RSM), particularly D-optimal design, was used for the purpose. This research contributed in several ways: (i) evaluation of more effective Fenton oxidant on pollutant content reduction, in terms of TOC and color removal, (ii) assessment of the optimal reactant doses, (iii) describing the RV2 kinetic behavior in applied systems and (iv) determining the apparent rate constants. Mineralization was described by pseudo-first-order kinetics with observed rate constant k m = 0.0133 min −1. A kinetic model describing discoloration was composed of two first-order in-series reactions with discoloration rates; k 1 = 0.9447 min −1 and k 2 = 0.0236 min −1, at optimal operating conditions and with the highest initial organic load.

Modeling the mineralization and discoloration in colored systems by (US)Fe 2+/H 2O 2/S 2O 82− processes: A proposed degradation pathway

The scope of this experimental research was to study the kinetics of dye mineralization and discoloration in miscellaneous dye systems by advanced Fenton degradation, Fe 2+/H 2O 2/S 2O 8 2−, with and without ultrasound (US) employment. Reactive azo dye C.I. Reactive Violet 2 (RV2) and C.I. Reactive Yellow 3 (RY3) as well as mordant azo dye C.I. Mordant Yellow 10 (MY10) were used as model pollutants for composition of 7 different types of model dye wastewater, i.e. MY10, RV2, RY3, MY10 + RV2, MY10 + RY3, RV2 + RY3 and MY10 + RV2 + RY3 in the concentration of 50 mg L −1. The molar ratio of Fe 2+, H 2O 2 and K 2S 2O 8 (equimolar) of 1:5 was used, since it was shown as optimal. Mineralization of studied systems was enhanced by simultaneous application of Fenton and US. Mineralization extents obtained after 60 min of treatment varied from minimal 49% for RV2 + RY3 system up to maximal 73% for MY10 + RV2 + RY3 system. Almost 100% of discoloration was achieved in all studied systems within few minutes of applied process. A degradation pathway of studied azo dyes was proposed and 14 variations of mathematical model describing each system and particular process have been developed.

Self-cleaning modified TiO2–cotton pretreated by UVC-light (185 nm) and RF-plasma in vacuum and also under atmospheric pressure

Two new innovative findings presented in this study are: (a) TiO2–cotton fabrics obtained by pretreatment with UVC-light (185nm) at atmospheric pressure introduced functionalities into the cotton surface enabling the chelation/binding of TiO2. This was possible since the molar absorption coefficient of O2 and N2 is very low at 185nm and (b) the radiofrequency (RF-plasma) pretreatment of cotton surface lead to the formation active binding sites on the cotton at atmospheric pressure. This unexpected RF effect was due to the drastic localized heating of the cotton leading to intermolecular H-bond breaking between the cellulose surface-OH groups of adjacent molecules with the formation of functionalized groups in the cellulose fibers. The discoloration kinetics of the wine stain on the TiO2–cotton pretreated by RF at atmospheric pressure for 10min was the most favorable. The red wine stains discoloration under Suntest simulated light was monitored by diffuse reflectance spectroscopy (DRS) and by the CO2 evolution during the stain mineralization. By X-ray photoelectron spectroscopy (XPS) it was possible to monitor the decrease of the C, N, S-species on the textile topmost layers during the discoloration process. The XPS Ti 2p3/2 peak shifts indicating Ti4+/Ti3+ oxido-reduction taking place during the photocatalysis. X-ray diffraction showed the formation of the anatase phase on the cotton. By X-ray fluorescence the loading of TiO2 before and after the discoloration process was found to be ∼0.8%. High-resolution electron microscopy (HRTEM) shows transparent TiO2 anatase 8–18nm coating the cotton with layers ∼31nm (±10%). These 3–4 TiO2 layers on the cotton did not affect the touch or handling properties of the cotton enabling the potential commercial use of the TiO2–cotton fabrics.

Characterizing the discoloration of methylene blue in Fe 0/H 2O systems

Methylene blue (MB) was used as a model molecule to characterize the aqueous reactivity of metallic iron in Fe 0/H 2O systems. Likely discoloration mechanisms under used experimental conditions are: (i) adsorption onto Fe 0 and Fe 0 corrosion products (CP), (ii) co-precipitation with in situ generated iron CP, (iii) reduction to colorless leukomethylene blue (LMB). MB mineralization (oxidation to CO 2) is not expected. The kinetics of MB discoloration by Fe 0, Fe 2O 3, Fe 3O 4, MnO 2, and granular activated carbon were investigated in assay tubes under mechanically non-disturbed conditions. The evolution of MB discoloration was monitored spectrophotometrically. The effect of availability of CP, Fe 0 source, shaking rate, initial pH value, and chemical properties of the solution were studied. The results present evidence supporting co-precipitation of MB with in situ generated iron CP as main discoloration mechanism. Under high shaking intensities (>150 min −1), increased CP generation yields a brownish solution which disturbed MB determination, showing that a too high shear stress induced the suspension of in situ generated corrosion products. The present study clearly demonstrates that comparing results from various sources is difficult even when the results are achieved under seemingly similar conditions. The appeal for an unified experimental procedure for the investigation of processes in Fe 0/H 2O systems is reiterated.

Kinetics of Disappearance and Discoloration of L-Ascorbic Acid 2-Glucoside Powders with Different Water Contents

The disappearance and discoloration of L- ascorbic acid 2- glucoside powders with water contents of 2 to 12% (w/w) during storage at a temperature from 70 to 90℃ were investigated. The disappearance of L-ascorbic acid 2-glucoside with the higher water content proceeded faster at the higher temperature. The disappearance process was expressed by the Weibull equation. The change in the L-ascorbic acid was analyzed by assuming that both the hydrolysis and decomposition of L-ascorbic acid were expressed by first-order kinetics. A kinetic comparison of the overall disappearance by the hydrolysis indicated that the hydrolysis was not the sole route for the disappearance. The discoloration kinetics was also analyzed on the basis of the modified Weibull equation. It was shown that the enthalpy-entropy compensation held for all the processes involved in the overall disappearance of L-ascorbic acid 2-glucoside, its hydrolysis, the decomposition of L-ascorbic acid and the discoloration of L-ascorbic acid 2-glucoside. It was also demonstrated that the discoloration was suppressed by the glucosylation of L-ascorbic acid, but that L-ascorbic acid 2-glucoside was more easily discolored than L-ascorbyl 6-palmitate.