Observed Reaction Rate Constants Research Articles

Microkinetic modeling of CO2 hydrolysis over Zn-(1,4,7,10-tetraazacyclododecane) catalyst based on first principles: Revelation of rate-determining step

Density functional theory (DFT) calculations were used to study the mechanism of CO2 hydrolysis by Zn-(1,4,7,10-tetraazacyclododecane), also referred to as zinc–cyclen, and evaluate the associated thermodynamic and kinetic parameters. A microkinetic model was then built based on the kinetics and thermodynamics derived from first principles. The model describes the sigmoidal dependence of the observed reaction rate constant on pH, which is similar to behavior observed for CO2 hydrolysis catalysts in nature, i.e., human carbonic anhydrase. The inflection point is identical to the pKa value of the zinc–cyclen complex, in good agreement with previous results. The overall reaction rate constant was calculated to be 3055M−1s−1, which is in excellent agreement with the range of experimental values reported (2691.5–3300M−1s−1). Importantly, though, the microkinetic model quantifies how the reaction rate and the associated overall rate constant varies as a function of time, underscoring that observed overall rate constants are a function of the species’ concentrations used to extract them, which may not be the initial conditions. The decrease in initial reaction rate over 0–12ms was ascribed to the decrease in the concentration of the catalytic form, Zn-OH−, which was primarily converted to Zn-HCO3−. Through calculating the ratio of the net rate to the forward rate of each elementary reaction, the rate-limiting step of the catalytic cycle was identified as the adsorption of CO2. To aid in the interpretation of the complex microkinetic model, an analytical rate expression was derived based on a simplified potential energy surface comprised of three major regions: the adsorption of CO2, the release of HCO3− via displacement by water, and the deprotonation of Zn-H2O. Analysis showed quantitatively how the observed reaction rate constant depends not only on how fast a CO2 molecule is captured but also on how deep the Zn-HCO3− sits.

Degradation of cylindrospermopsin by using polymorphic titanium dioxide under UV–Vis irradiation

The frequent occurrence of cyanobacterial harmful blooms due to eutrophication necessitates the development of appropriate water treatment technologies for the released cyanotoxins. In this study, nanoparticles composed of anatase–brookite–rutile polymorphic titanium dioxide (PM-TiO2) were synthesized using a modified sol–gel method with a low temperature oil bath for the photocatalytic degradation of cylindrospermopsin (CYN), an important cyanotoxin that has been only little explored with respect to water treatment technologies. The physiochemical properties of synthesized PM-TiO2 nanoparticles, such as the formation of heteronanostructure (with 66% anatase, 22% brookite and 12% rutile), high surface area (207m2/g), small particle size (∼5nm), and bandgap (Eg=3.0eV), endow PM-TiO2 to be an effective photocatalyst for CYN treatment under UV–Vis irradiation. Moreover, the impacts of certain process parameters (i.e. photocatalyst loading, pH and presence of natural organic matter (NOM)) were examined and discussed in detail. It was found that the presence of NOM decreased the observed reaction rate constants by 52% and 95% compared to clean water samples when 2 and 10mg/L NOM were applied, respectively. In particularly, when two natural water samples from East Fork Lake and Toledo Water Plant were applied as the matrices in the photocatalytic experiments, the degradation rate constants were reduced by 90% and 75%, respectively. This work demonstrates that the polymorphic TiO2 containing three phases can be effective photocatalyst for cyanotoxin treatment, however, the degradation kinetics are inhibited significantly in the presence of NOM. Therefore, pretreatment is necessary to remove NOM before the photocatalytic treatment of surface water containing CYN.

Coupled Diffusion and Abiotic Reaction of Trichlorethene in Minimally Disturbed Rock Matrices

Laboratory experiments were performed using minimally disturbed sedimentary rocks to measure the coupled diffusion and abiotic reaction of trichloroethene (TCE) through rock core samples. Results showed that, for all rock types studied, TCE dechlorination occurred, as evidenced by generation of acetylene, ethene, and/or ethane daughter products. First-order bulk reaction rate constants for TCE degradation ranged from 8.3 × 10(-10) to 4.2 × 10(-8) s(-1). Observed reaction rate constants showed a general correlation to the available ferrous iron content of the rock, which was determined by evaluating the spatial distribution of ferrous iron relative to that of the rock porosity. For some rock types, exposure to TCE resulted in a decrease in the effective diffusivity. Scanning electron microscopy (SEM) indicated that the decrease in the effective diffusivity was due to a decrease in the porosity that occurred after exposure to TCE. Overall, these coupled diffusion and reaction results suggest that diffusion of TCE into rock matrices as well as the rate and extent of back-diffusion may be substantially mitigated in rocks that contain ferrous iron or other naturally occurring reactive metals, thereby lessening the impacts of matrix diffusion on sustaining dissolved contaminant plumes in bedrock aquifers.

Study of Malachite Green Fading in Water–Ethanol–Ethylene Glycol Ternary Mixtures

The rate constant of malachite green (MG+) alkaline fading was measured in water–ethanol–ethylene glycol ternary mixtures. This reaction was studied under pseudo-first-order conditions at 283–303 K. In each series of experiments, the concentration of ethanol was kept constant and the concentration of ethylene glycol was changed. It was shown that due to hydrogen bonding and hydrophobic interaction between MG+ and alcohol molecules the observed reaction rate constant, $$ k_{\text{obs}} $$ , increased in the water–ethanol–ethylene glycol ternary mixtures. The fundamental rate constants of MG+ fading in these solutions ( $$ k_{1} $$ , $$ k_{ - 1} $$ and $$ k_{2} $$ ) were obtained by the SESMORTAC model. Analysis of $$ k_{1} $$ and $$ k_{2} $$ values in solutions containing constant ethanol concentrations show that in low concentrations of ethylene glycol, hydrogen bonding formed between ethanol and ethylene glycol molecules and in high concentrations of ethylene glycol, ethanol as a solvent for ethylene glycol affected the reaction rate.

Catalytic ozonation of 2,4-Dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger

Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (kobs ) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the kobs value increased from 19.3 to 26 M−1 s−1 and 67 M−1 s−1 when varying the alumina dose from 1 to 2 and 4 g L−1, respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L−1, the kobs values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M−1 s−1, respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M−1 s−1 were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.

Sorption of Arsenic from Aqueous Solution by Nanoscale Zinc

In this study, nanoscale zinc particles were used for arsenic removal under batch experiments. The aims of the study were to investigate the suitability of nanoscale zinc particles for arsenite [As(Ш)] adsorption and an analysis of factors affecting As(Ш) adsorption efficiency. These nanoscale zinc particles can effectively remove As(Ш) from aqueous solution. Over 98% As(Ш) was removed within 90 min in a concentration of 0.56 mg·L−1, with a 1.25 g·L−1 dose of nanoscale zinc particles. The kinetics of As(Ш) adsorption followed the pseudo-first-order model with observed reaction rate constants (k obs) of 0.0292 min−1. Besides, the results demonstrated that the arsenic removal percentage was affected apparently by pH, the amount of nanoscale zinc, the initial concentration and arsenic species. Based on the result, nanoscale zinc particles can be used for remediating As-affected groundwater usually containing substantial As(III) without preoxidation of As(III) to As(V).

Degradation of decabromodiphenyl ether by nano zero-valent iron immobilized in mesoporous silica microspheres

The agglomeration of nanoparticles reduces the surface area and reactivity of nano zero-valent iron (NZVI). In this paper, highly dispersive and reactive NZVI immobilized in mesoporous silica microspheres covered with FeOOH was synthesized to form reactive mesoporous silica microspheres (SiO 2@FeOOH@Fe). The characteristics of SiO 2@FeOOH@Fe were analyzed by transmission electron microscopy, Fourier transform infrared spectroscopy simultaneous thermal analysis, X-ray photoelectron spectroscopy, and Brunnaer–Emmett–Teller surface area analysis. The mean particle size of the reactive mesoporous silica microspheres was 450 nm, and its specific surface area was 383.477 m 2 g −1. The degradation of dcabromodiphenyl ether (BDE209) was followed pseudo-first-order kinetics, and the observed reaction rate constant could be improved by increasing the SiO 2@FeOOH@Fe dosage and by decreasing the initial BDE209 concentration. The stability and longevity of the immobilized Fe nanoparticles were evaluated by repeatedly renewing the BDE209 solution in the reactor. The stable degradation of BDE209 by SiO 2@FeOOH@Fe was observed within 10 cycles. Agglomeration-resistance and magnetic separation of SiO 2@FeOOH@Fe were also performed. The improved dispersion of SiO 2@FeOOH@Fe in solution after one-month storage and its good performance in magnetic separation indicated that SiO 2@FeOOH@Fe has the potential to be efficiently applied to environmental remediation.

Reaction Kinetics of CO2 in Aqueous Methyl- and Dimethylmonoethanolamine Solutions

In the present work, kinetics of the carbon dioxide (CO2) reactions with N-methylmonoethanolamine (MMEA) and N,N-dimethylmonoethanolamine (DMMEA) is investigated by using a stirred-cell reactor. The reaction with the linear secondary amine, MMEA, is described by both the zwitterion and termolecular mechanisms, whereas the reaction with the tertiary amine, DMMEA, is described by the base-catalyzed hydration of CO2. Densities and viscosities of both amines in aqueous solutions are measured at 298, 303, and 308 K over a wide range of amine concentrations. The investigated reactions are of the first order with respect to both CO2 and amine. On the basis of the temperature dependence of the second-order rate constants, the activation energy is evaluated. It is found that the increase in temperature and amine concentration causes the expected increase in the values of the observed reaction rate constants.

Kinetics of malachite green fading in water-ethanol-2-propanol ternary mixtures

The rate constant of malachite green (MG+) alkaline fading was measured in water–ethanol–2-propanol ternary mixtures. This reaction was studied under pseudo-first-order conditions at 283–303 K. It was observed that the observed reaction rate constants, kobs, were increased in the presence of different weight percentages of ethanol and 2-propanol. The fundamental rate constants of MG+ fading in these solutions were obtained by using the SESMORTAC model. In each series of experiments, the concentration of one alcohol was kept constant and the concentration of the second one was changed. It was observed that at the constant concentration of one alcohol and variable concentrations of the second one, with an increase in temperature, k2 values decrease according to the trend of hydroxide ion nucleophilic parameter values and k1 values increase. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 441–453, 2011

Denitrification of simulated nitrate-rich wastewater using sulfamic acid and zinc scrap

AbstractAn enhanced chemical denitrification process was studied as an alternative treatment of nitrate-rich wastewater which cannot be easily treated using conventional biological methods. To accelerate denitrification and to reduce the conversion to ammonia, nitrite reductants were added. In a batch test with the initial nitrate concentration of 500 mg NO3− -N per L, sulfamic acid and zinc were found to be the best nitrite and metal reductants, respectively. In a column test with the initial nitrate concentration of 500 mg NO3−-N per L, optimum results were experimentally obtained over a zinc scrap column with a 1.0 molar ratio of [NH2SO3H]/[NO3−-N] and the recirculating flow rate of 6 L min−1 at pH 2.5. Approximately 98.8 % of nitrate anions were removed, and the observed reaction rate constant (k) was 0.135 min−1. Zinc consumption was reduced to 46.6 % compared to the procedure without sulfamic acid, and sulfamic acid consumption was reduced to 40 % compared to the results of our previous study. Based on these experimental results, it was concluded that chemical nitrate denitrification using sulfamic acid and zinc scrap is an effective alternative treatment protocol for nitrate-rich wastewater.

Determination of Treatability Constant and Reaction-rate Constant for an Attached-Growth Upflow Fixed-Film Reactor on Pulp and PaperWastewater Treatment

Pulp and paper industry generates large volumes of highly heterogeneous wastewaters containing compounds from wood or other raw material, process chemicals as well as compounds formed during processing. This study has designed a fixed film reactor which uses the concept of biological attached growth treatment to treat the pulp and paper wastewater. The laboratory-scale fixed film reactor is designed with a circular column of 120 cm height, 15 cm inner diameter and a total volume of 23000 cm 3 . The column which constructed in PVC was packed with PVC plastic pipes which were cut into the size of 4.5 cm length and 3 cm diameter and had a specific surface area of 42 cm 2 . An amount of 150 PVC plastic pipes were placed in the digester. The system was found could remove about 53% of BOD5 and 89% COD. The treatability constant corresponding to the depth of the reactor, k in this study is found to be 0.038 gal/min 0.5 ft and the observed reaction rate constant, K is 0.04 ft/d at 25°C. This fixed-film reactor could be operated as a trickling filter.

Degradation of metronidazole by nanoscale zero-valent metal prepared from steel pickling waste liquor

In this study, steel pickling waste liquor was employed to obtain reactive nanoscale zero-valent metal (nZVM) with the purpose of engineering application. The degradation of metronidazole reacted with as-prepared nZVM in water was investigated to explore the feasibility of using the nZVM to treat antibiotics in wastewater. The synthesized nZVM was characterized by Brunauer–Emmett–Teller (BET) surface analyzer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectrometer (EDS). The results showed that the nZVM (20–40nm) with crystalline structure had a BET surface area of 35m2/g. XPS and EDS only detected Fe, C and O on the surface, suggesting Ni and Zn distributed inside the core of nanoscale alloy. Degradation of metronidazole followed the pseudo-first-order kinetics, and the observed reaction rate constant (kobs) could be improved with increasing nZVM dosage, as well as with diminishing initial metronidazole concentration and pH. A high reaction rate was observed at reduction potential, indicating that electrons and hydrogen species produced by nZVM were driving forces of reaction. The surface area-normalized rate coefficient (kSA) for nZVM (0.254Lmin−1m−2) was 375.2 times larger than that for commercial iron powder (6.67×10−4Lmin−1m−2). Several possible pathways of degradation of metronidazole were proposed according to the results of UV–vis spectra and HPLC chromatograms.

Excited state intramolecular charge transfer reaction of 4-(morpholenyl) benzonitrile in solution: Effects of hetero atom in the donor moiety

An intramolecular charge transfer (ICT) molecule with an extra hetero atom in its donor moiety has been synthesized in order to investigate how ICT reaction is affected by hetero atom replacement. Photo-physical and photo-dynamical properties of this molecule, 4-(morpholenyl)benzonitrile (M6C), have been studied in 20 different solvents. The correlation between the reaction driving force (−ΔG r ) and activation barrier (ΔG #) has been explored in order to understand the solvent effects (static and dynamic) on the photo-excited ICT reaction in this molecule. A Kramer’s model analysis of the experimentally observed reaction rate constants indicates a solvent-averaged activation barrier of ∼4 k B T in the absence of solvent dynamical control. The reaction in M6C is therefore not a barrier-less reaction but close to the limit where conventional kinetics might break down.

Kinetics of nitrate reductive denitrification by nanoscale zero-valent iron

Nanoscale zero-valent iron (Fe 0) was synthesized for nitrate denitrification. The reduction efficiency of nitrate decreased quickly with increasing initial pH value, increased considerably with the increasing dosage of nanoscale Fe 0, and did not vary much with initial nitrate concentrations changing from 20 to 50 mg l −1 when the excessive amount of nanoscale Fe 0 was utilized. With reductive denitrification of nitrate by nanoscale Fe 0, the removal rate of nitrate reached 96.4% in 30 min with nanoscale Fe 0 dosage of 1.0 g l −1 and pH in 6.7, and more than 85% of the nitrate was transformed into ammonia. Kinetics analysis in batch studies demonstrates that the denitrification of nitrate by nanoscale Fe 0 involves reaction on the metal surface, which fits well the pseudo-first order reaction with respect to nitrate concentration. The observed reaction rate constant of reductive denitrification of nitrate was determined to be 0.086 min −1 with a nanoscale Fe 0 dosage of 1.0 g l −1 and pH in 6.7. Fast and highly effective denitrification can be achieved by nanoscale Fe 0 compared with commercial Fe 0 powder, this is due to the extremely high surface area and high reactivity for nanoscale Fe 0, which can enhance the denitrification efficiencies remarkably.

Reduction of nitrate by resin-supported nanoscale zero-valent iron

For environmental remediation of a contaminated groundwater, the use of nanosized zero-valent iron (nZVI) represents one of the latest innovative technologies. However, nZVI gets easily agglomerated due to its colloidal characteristics and has limited applications. To overcome this drawback, nZVI was immobilized on a supporting material. In this study, nZVI was formed and bound to ion-exchange resin spheres at the same time through the borohydride reduction of an iron salt. The pore structures and physical characteristics of the supported nZVI were investigated and its reactivity was measured using nitrate. The degradation of nitrate appeared to be a pseudo first-order reaction with the observed reaction rate constant of 0.425 h(-1) without pH control. The reduction process continued but at a much lower rate with a rate constant of 0.044 h(-1). When the simulated groundwater was used to assess the effects of coexisting ions, the rate constant was 0.078 h(-1) and it also reduced to 0.0021 h(-1) in later phase. The major limitation of ZVI use for nitrate reduction is ammonium production. By using a support material with ion-exchange capacity, this problem can be solved. The ammonium was not detected in our batch tests.

THEORETICAL STUDY ON THE KINETICS AND MECHANISM OF THE REACTION OF CYCLOHEXYL ISOCYANIDE AND 1,1,1,5,5,5-HEXAFLUROPENTANE-2,4-DIONE USING DFT METHOD

Kinetics and mechanism of the reaction between cyclohexyl isocyanide and 1,1,1,5,5,5-hexafluropentane-2,4-dione has been investigated by utilizing transition state theory and using B3LYP/6-31G* method. Based on previous experimental studies, two paths namely direct attack and conjugate addition have been proposed. Energy changes vs intrinsic reaction coordinate (IRC) along these paths have been studied both in the gas phase and considering nonspecific solvent effect under Onsager's model while all intermediate and possible transition states' geometries obtained and optimized. Small differences have been observed between gas phase and solution phase results. Taking advantage of the thermodynamic and kinetic calculated parameters, observed reaction rate constants and activation energies have been acquired. Computational results suggest that the conjugate addition path is totally unacceptable, while a new path has been proposed, which is both energetically and kinetically preferred to direct attack path. This new path undergoes the Michael addition along with a Cope–Claisen-type rearrangement. In this path, a new intermediate has been encountered for the first time, which contains a five-membered ring of four carbon atoms and one oxygen atom. NBO analysis has revealed that in such intermediate, oxygen lone pair has resonance with C – C π bond inside and C – N π bond outside of the ring leading to this species special stability. Molecular orbital calculations satisfy NBO findings.

Iron-mediated reduction rates and pathways of halogenated methanes with nanoscale Pd/Fe: Analysis of linear free energy relationship

The influence of halogen substitution in chlorinated methanes and brominated methanes on their abiotic reductive dehalogenation with nanoscale Pd/Fe bimetallic particles was investigated in this study. The 0.2% and 1.0% Pd/Fe particles, with particle sizes of less than 100nm, were synthesized in the laboratory. Reduction of the halogenated methanes with the Pd/Fe particles followed pseudo-first-order kinetics. The Pd/Fe bimetallic particles demonstrated at least an order of magnitude higher in reactivity compared to the unpalladized Fe particles of similar particle size. Comparing the 0.2% Pd/Fe and the 1.0% Pd/Fe particles, the latter exhibited higher reduction rates of various halogenated methanes. On the other hand, the reduction rates of chlorinated methanes were consistently lower than those of their brominated counterparts. The compounds with higher number of halogen substitutions were more readily reduced than the lightly halogenated ones. Coupled hydrogenolysis-elimination processes were the important mechanism for complete dehalogenation of the chlorinated and brominated methanes. From the kinetic examination of their transformation rates and mechanistic insight into the associated pathways, an attempt to analyze linear free energy relationship between the observed kinetics and the associated thermodynamic constants was performed. The observed reaction rate constants were analyzed for their correlations with one-electron potential (E(1)), two-electron potential (E(2)), bond dissociation energy (BDE) and the lowest unoccupied molecular orbital (LUMO) energy (E(LUMO)). LUMO energy appeared to be the best descriptor for the kinetic prediction, while E(1) and E(2) might be more suitable for mechanistic analysis.

Arsenic(V) Removal from Groundwater Using Nano Scale Zero-Valent Iron as a Colloidal Reactive Barrier Material

The removal of As(V), one of the most poisonous groundwater pollutants, by synthetic nanoscale zero-valent iron (NZVI) was studied. Batch experiments were performed to investigate the influence of pH, adsorption kinetics, sorption mechanism, and anionic effects. Field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mossbauer spectroscopy were used to characterize the particle size, surface morphology, and corrosion layer formation on pristine NZVI and As(V)-treated NZVI. The HR-TEM study of pristine NZVI showed a core-shell-like structure, where more than 90% of the nanoparticles were under 30 nm in diameter. Mössbauer spectroscopy further confirmed its structure in which 19% were in zero-valent state with a coat of 81% iron oxides. The XRD results showed that As(V)-treated NZVI was gradually converted into magnetite/maghemite corrosion products over 90 days. The XPS study confirmed that 25% As(V) was reduced to As(III) by NZVI after 90 days. As(V) adsorption kinetics were rapid and occurred within minutes following a pseudo-first-order rate expression with observed reaction rate constants (Kobs) of 0.02-0.71 min(-1) at various NZVI concentrations. Laser light scattering analysis confirmed that NZVI-As(V) forms an inner-sphere surface complexation. The effects of competing anions revealed that HCO3-, H4SiO4(0), and H2PO4(2-) are potential interfering agents in the As(V) adsorption reaction. Our results suggest that NZVI is a suitable candidate for As(V) remediation.

Trichloroethene Hydrodechlorination in Water by Highly Disordered Monometallic Nanoiron

The small size and high surface-to-volume ratio makes nanoiron attractive for in situ remediation of groundwater contaminants that are susceptible to reductive transformation, e.g. trichloroethylene (TCE). Nanoiron synthesized from borohydride reduction of dissolved iron is the most widely studied. Its reactivity with chlorinated organics such as trichloroethylene (TCE) is unique compared to other nanoiron and to iron filings that are typically used for in situ groundwater remediation, e.g. (1) higher surface-area normalized TCE dechlorination reaction rate constants, (2) the formation of saturated reaction products, and (3) higher reaction rates in the presence of H2. The objectives of this study were to confirm the ability of monometallic Fe(B) to activate and use H2 for TCE hydrodechlorination and to determine how the nanoiron chemical composition and the degree of crystallinity influence nanoiron reactivity with TCE. Fresh (Fe(B)), partially oxidized (Fe(B)ox), and annealed (Fe(B)cr) nanoiron samples made from borohydride reduction of dissolved Fe(II) in a water/methanol solution were characterized by HRTEM, XRD, XPS, and N2-BET. The TCE dechlorination rate and products and the dissolved iron and boron released during reaction with TCE were measured. Fe(B) and Fe(B)ox were poorly ordered and could activate and use H2 to reduce TCE to ethane. Fe(B)cr was crystalline and could not activate and use H2 and reduced TCE to acetylene. The poorly ordered structure rather than the presence of boron (up to 5 wt %) provided the ability of Fe(B) and Fe(B)ox to activate and use H2 for TCE dechlorination. Fe(B) and Fe(B)ox underwent oxidative dissolution during TCE dechlorination, and the Fe0 in the particles was fully accessible. Particle dissolution suggests that normalizing the observed reaction rate constants with the measured specific surface area for comparison with other types of Fe0 may be inappropriate.

Development of a rate expression for predicting decolorization of C.I. Acid Black 1 in a UV/H 2O 2 process

A kinetic rate expression was developed by the experimental results of photochemical reactions that decolorize model azo dye, C.I. Acid Black 1. The decolorization was efficient by UV irradiation with hydrogen peroxide addition. The observed reaction rate constants were determined and correlated as a function of volumetric UV dosage and initial hydrogen peroxide concentration. The decolorization rate follows pseudo-first order kinetic with respect to dye concentration. The rate increases linearly by volumetric UV dosage, yet nonlinearly by hydrogen peroxide concentration. The proposed rate expression model, which considers both the kinetic mechanism and operation parameters, can predict the experimental results well. The prediction and experimental data are in a very good agreement. Besides, this model also integrates the correlation of pH and initial dye concentration in order to enlarge more versatile applications while various dye concentrations and pH range in the real case.