Langmuir-Hinshelwood Kinetic Model Research Articles

Adsorption of 4-nitrophenol onto Amberlite ® IRA-900 modified with metallophthalocyanines

The adsorption of 4-nitrophenol using commercially available Amberlite ® IRA-900 modified with metal phthalocyanines (MPc) was investigated. The metallophthalocyanines immobilised onto the surface of Amberlite ® IRA-900 include Fe (FePcS 4), Co (CoPcS 4) and Ni (NiPcS 4) tetrasulphophthalocyanines, and differently sulphonated phthalocyanine mixtures of Fe (FePcS mix), Co (CoPcS mix) and Ni (NiPcS mix). Adsorption rates were fastest for the modified adsorbents at a loading of 1 × 10 −3 g MPc/g Amberlite, at pH 9. The highest amount of 4-NP removal was obtained on FePcS mix modified Amberlite ® IRA-900 with Q t = 42.9 mmol g −1 and adsorption efficiency of 86%. The recovery efficiency of 4-NP within 150 min was 76%. Using the Langmuir–Hinshelwood kinetic model, the complexes showed an order of 4-nitrophenol adsorption to be as follows: CoPcS mix > NiPcS 4 > NiPcS mix > FePcS 4 > FePcS mix > CoPcS 4. The MPc modified Amberlite ® IRA-900 was used repeatedly, following removal of 4-NP by nitric acid, without any significant loss of activity.

Effect of LED optical characteristics on temporal behavior of o‐cresol decomposition by UV/TiO2 process

AbstractBACKGROUND: An ultraviolet light‐emitting diode (UV‐LED) was used in this investigation as the light source for the photocatalytic decomposition of o‐cresol in aqueous solution because of its efficiency, design flexibility, and durability. The UV light intensities of the corn‐shaped LED tube designed in this investigation were relatively uniform due to the correct arrangement of LEDs.RESULTS: For experiments conducted with initial o‐cresol concentrations of 9 mg L−1 and pH 3, more than 80% of o‐cresols were decomposed after 8 h of irradiation. The calculated photonic efficiency (about 1·06%) for experiments conducted with continuous illumination was much lower than those (1·69–6·27%) obtained with periodic illumination.CONCLUSION: The proposed Langmuir–Hinshelwood kinetic model with modification of UV light intensity attenuation could be adequately applied to describe the temporal behavior of the o‐cresol decomposition in aqueous solution by the UV‐LED/TiO2 process. Copyright © 2007 Society of Chemical Industry

Evidence for hole participation during the photocatalytic oxidation of the antibiotic flumequine

Photocatalytic degradation of the antibiotic flumequine (FQ) was carried out on TiO 2 aqueous suspension assisted by simulated solar light. Using multivariate analysis, it was determined that the most important variable for FQ degradation is pH, where the optimal value is around 6. Hydrogen peroxide addition does not alter oxidation efficiency. Under optimised conditions, the time required to completely eliminate FQ antibiotics was 30 min. Mineralization after 60 min irradiation was around 80%. The role of hydroxyl and superoxide anion radicals was monitored by using the radical scavengers isopropanol and benzoquinone, respectively. On the other hand, the participation of oxidative holes in the reaction mechanism was evaluated by adding iodine anions (hole scavenger) to the reaction system. Isopropanol's slight influence on degradation indicated that FQ oxidation was slightly influenced by OH radicals. The presence of the iodide anion significantly inhibited degradation, thus suggesting that holes played a major role. Experiments carried out in acetonitrile, in absence of water, confirmed the significant role of holes in FQ oxidation. The inhibition of the reaction profile in the presence of benzoquinone confirms the participation of the superoxide anion in the FQ oxidation. The analysis of the reaction products suggests that photo-Kolbe decarboxylation mechanism and hydroxylation of aromatic ring are the reaction's primary steps. The Langmuir–Hinshelwood kinetic model was fitted for FQ photodegradation.

Photocatalytic degradation of Azure and Sudan dyes using nano TiO 2

The present study investigates the dependence of photocatalytic rate on molecular structure of the substrate that is degraded. The photocatalytic degradation of Azure (A and B) and Sudan (III and IV) dyes, having similar structure, but different functional groups, were investigated with two catalysts. The photocatalytic activity of solution combustion synthesized TiO 2 (CS TiO 2) was compared with that of Degussa P-25 for degrading these dyes. The effect of solvents and mixed-solvent system on photodegradation of Sudan III was investigated. The photodegradation rate was found to be higher in solvents with higher polarity. The effect of pH and the presence of metal ions in the form of chloride and nitrate salt, on degradation rate of Azure A was also investigated. The metal ions significantly reduced the photocatalysis rates. A detailed Langmuir–Hinshelwood kinetic model has been developed to explain the effect of metal ions on degradation rate of the substrate. This model elucidates the contribution of holes and electrons towards degradation of the dye.

Experimental and Numerical Analysis of A Novel Ceria Based Abrasive Slurry for Interlayer Dielectric Chemical Mechanical Planarization

In this study, a novel slurry containing ceria as the abrasive particles was analyzed in terms of its frictional, thermal and kinetic attributes for interlayer dielectric (ILD) CMP application. The novel slurry was used to polish 200-mm blanket ILD wafers on an <TEX>$IC1000_{TM}$</TEX> K-groove pad with in-situ conditioning. Polishing pressures ranged from 1 to 5 PSI and the sliding velocity ranged from 0.5 to 1.5 m/s. Shear force and pad temperature were measured in real time during the polishing process. The frictional analysis indicated that boundary lubrication was the dominant tribological mechanism. The measured average pad leading edge temperature increased from 26.4 to <TEX>$38.4\;^{\circ}C$</TEX> with the increase in polishing power. The ILD removal rate also increased with the polishing power, ranging from 400 to 4000 A/min. The ILD removal rate deviated from Prestonian behavior at the highest <TEX>$p{\times}V$</TEX> polishing condition and exhibited a strong correlation with the measured average pad leading edge temperature. A modified two-step Langmuir-Hinshelwood kinetic model was used to simulate the ILD removal rate. In this model, transient flash heating temperature is assumed to dominate the chemical reaction temperature. The model successfully captured the variable removal rate behavior at the highest <TEX>$p{\times}V$</TEX> polishing condition and indicates that the polishing process was mechanical limited in the low <TEX>$p{\times}V$</TEX> polishing region and became chemically and mechanically balanced with increasing polishing power.

Studies of Photocatalytic Degradation of Trace-Level MC-LR in Water on Thin Film of Titanium Dioxide

MCs are produced by cyanobacteria and cause concerns in potable water due to toxicity. Conventional treatments are poor at removing MCs. In the present study, the photocatalytic degradation of MC-LR was conducted using nano-TiO2 thin film, prepared by sol-gel and dip-coating method, with UV 365nm irradiation. According to analysis results from solid-phase extraction combined with HPLC method, the trace-level MC-LR is easily to be removed by photocatalytic system. The degradation efficiency of MC-LR is influenced by the pH conditions, initial concentration due to adsorption of MC-LR on TiO2 thin film. The maximum initial rate of photocatalytic degradation occurs at pH 4 and over 95% of 20μg/L MC-LR is decomposed within 120min. The kinetic equations and parameters revealed that degradation reaction of trace level MC-LR, which depicted by pseudo first order kinetics process in appearance, was in accordance with Langmuir-Hinshelwood kinetics model well, the corresponding rate constant k and Langmuir adsorption constant K were determined to be 19.72μg/l·min-1 and 6.57×10-4l/μg, respectively.

EPR and kinetic investigation of free cyanide oxidation by photocatalysis and ozonation

Oxidation of free cyanide in aqueous suspensions of three commercial TiO2 specimens, with different anatase crystal size, has been carried out in a batch photoreactor by simultaneously applying ozonation and photocatalysis. Dissolved ozone participates both in homogeneous and catalytic reactions with cyanide; the extents of these two processes are comparable to that of the photodegradation with oxygen. The reactivity results are well described by the Langmuir-Hinshelwood kinetic model, providing the values of the kinetic and equilibrium adsorption constants for the catalytic and photocatalytic reactions contributing to cyanide oxidation. The cyanide concentration decreases faster with time for catalysts with increasing anatase crystal size, being more marked under UV irradiation. EPR studies on gaseous ozone adsorption on the three samples in the dark have shown stronger ozone interactions with Ti4+ and O2− ions of the samples with largest anatase crystal size, leading to the formation of significant signals of Ti3+ and s O−−O2 radicals than with the anatase with the lowest crystal size, where ozone was mainly adsorbed on water molecular arrangements covering its surface. The hampering of the ozone and/or cyanide adsorption by the water molecular arrangements covering the surface of the catalyst with the lowest crystal size would justify the low cyanide degradation rate observed for this sample.

Experimental study and mechanistic kinetic modeling for selective production of hydrogen via catalytic steam reforming of methanol

The mechanistic kinetic model using Langmuir–Hinshelwood (LH) approach has been developed for the steam reforming of methanol (SRM), accompanied by the reverse water gas shift (rWGS) reaction over a Cu/ZnO/Al 2O 3 catalyst. The major products of steam reforming of methanol were hydrogen and carbon dioxide with small amount of carbon monoxide which is formed as a secondary product. The kinetics study was performed over a wide range of reaction temperature and contact-time in an integral reactor under the conditions of no diffusion limitation. The five intrinsic LH kinetic models were proposed based on two reaction mechanisms, and subjected to the rigorous parameter estimation and model discrimination in order to obtain the appropriate kinetic model. The parameters were estimated by nonlinear least square regression for which correlation among the parameters was minimized by temperature centering of Arrhenius and van’t Hoff equations. A good agreement was obtained between the experimental and model predicated results for the LH model based on formation of formic acid from formaldehyde, and formation of adsorbed CO and surface hydroxyls from formate species as the rate-determining steps for methanol steam reforming and reverse water gas shift reactions respectively.

Kinetic analysis on photocatalytic degradation of gaseous acetaldehyde, ammonia and hydrogen sulfide on nanosized porous TiO2 films

abstractThe characteristics of the UV illumination-assisted degradation of gaseous acetaldehyde, hydrogen sulfide, and ammonia on highly active nanostructured-anatase and rutile films were investigated. It was found that the anatase film showed a higher photocatalytic activity than the counterpart did, however, the magnitude of difference in the photocatalytic activity of both films decreased in the order ammonia > acetaldehyde > hydrogen sulfide. To elucidate the reasons for the observation, the adsorption characteristics and the kinetics of photocatalytic degradation of the three reactants on both films were analyzed. The adsorption analysis examined using a simple Langmuir isotherm, showed that adsorbability on both films decreased in the order ammonia > acetaldehyde > hydrogen sulfide, which can be explained in terms of the decreasing electron-donor capacity. Acetaldehyde and ammonia adsorbed more strongly and with higher coverage on anatase film (1.2 and 5.6 molecules/nm2, respectively) than on rutile (0.6 and 4.7 molecules/nm2, respectively). Conversely, hydrogen sulfide molecules adsorbed more strongly on rutile film (0.7 molecules/nm2) than on anatase (0.4 molecules/nm2). Exposure to UV light illumination brought about the photocatalytic oxidation of the three gases in contact with both TiO2 films, and the decrease in concentration were measured, and their kinetics are analyzed in terms of the Langmuir–Hinshelwood kinetic model. From the kinetic analysis, it was found that the anatase film showed the photocatalytic activities that were factors of ∼8 and ∼5 higher than the rutile film for the degradation of gaseous ammonia and acetaldehyde, respectively. However, the activity was only a factor of ∼1.5 higher for the photodegradation of hydrogen sulfide. These observations are systematically explained by the charge separation efficiency and the adsorption characteristics of each catalyst as well as by the physical and electrochemical properties of each reactant.

Some Remarks on So-Called Heterogeneous Photocatalysis and on the Mechanical Application of the Langmuir-Hinshelwood Kinetic Model

Article Some Remarks on So-Called Heterogeneous Photocatalysis and on the Mechanical Application of the Langmuir-Hinshelwood Kinetic Model was published on January 1, 2007 in the journal Journal of Advanced Oxidation Technologies (volume 10, issue 1).

Kinetics of Ru-catalyzed sodium borohydride hydrolysis

Chemical hydrides have been identified as a potential medium for on-board hydrogen storage, one of the most challenging technical barriers to the prospective transition from gasoline to hydrogen-powered vehicles. Systematic study of the feasibility of the sodium borohydride systems, and chemical-hydride systems more generally, requires detailed kinetic studies of the reaction for use in reactor modeling and system-level experiments. This work reports an experimental study of the kinetics of sodium borohydride hydrolysis with a Ru-on-carbon catalyst and a Langmuir-Hinshelwood kinetic model developed based on experimental data. The model assumes that the reaction consists of two important steps: the equilibrated adsorption of sodium borohydride on the surface of the catalyst and the reaction of the adsorbed species. The model successfully captures both the reaction's zero-order behavior at low temperatures and the first-order behavior at higher temperatures. Reaction rate constants at different temperatures are determined from the experimental data, and the activation energy is found to be 66.9 kJ mol −1 from an Arrhenius plot.

Photocatalytic Degradation of the Herbicide Erioglaucine in the Presence of Nanosized Titanium Dioxide: Comparison and Modeling of Reaction Kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir–Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm− 1 and 0.984 ppm min− 1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.

Contribution of Metal Species to the Heterogeneous Photocatalytic Degradation of Natural Organic Matter

The role of organic matters which are high molecular weight macromolecules in natural water supplies and their subsequent removal by advanced oxidation technologies has gained importance because they posses a substantial capacity to complex dissolved metal species. The present study was conducted to evaluate the impact of aqueous Cr(VI) and Mn(II) species on the photocatalytic oxidation of humic acids as a major component of natural organic matter in aquatic systems. The photocatalytic decolorization rate of humic acid was followed by pseudo-first-order and Langmuir Hinshelwood kinetic models. The presence of aqueous Cr(VI) and Mn(II) species did not significantly alter the degradation efficiency (≤20%) in terms of first-order kinetic model. Although the impact of manganese species could be considered as insignificant, a substantial adsorption effect could be assessed as reflected by respective Langmuir-Hinshelwood kinetic model parameters.

Kinetics of photocatalytic VOCs abatement in a standardized reactor

A standardized micro-pilot scale continuous flow apparatus has been built up, using two types of differential photoreactors, and equipped with a refined control of the working conditions in order to study the photocatalytic degradation as a way to abate VOCs in air. Kinetic measurements have been carried out on trichloroethylene (TCE), methanol and benzene as model pollutants. The absence of diffusional limitation and of reaction product effect on the kinetics have both been demonstrated under our working conditions. The influences of concentration, light flux and temperature on the initial degradation rate have been studied. A simple Langmuir–Hinshelwood kinetic model has been verified for TCE and methanol, whereas benzene degradation was more complex and did not follow this simple mechanism. The determined experimental data aim at being useful in the scaling-up of photocatalytic reactors.

Photocatalytic degradation of trace-level of Microcystin-LR by nano-film of titanium dioxide

Microcystins, a group of hepatotoxin produced by cyanobacteria in eutrophic freshwater, have proven unreliable to be removed by conventional treatments. In this study, the photocatalytic degradation experiments of Microcystin-LR were conducted using nano-TiO2 thin film, prepared by solgel and dip-coating method, with low UVA intensity irradiation. Analysis results from SPE (solid-phase extraction) combined with HPLC method showed that Microcystin-LR whose initial concentration (μg/L) around that occurs naturally was easily to be removed by photocatalytic system. The degradation efficiency of toxin was influenced by the pH conditions, initial concentration and UV intensity. The maximum initial rate of photocatalytic degradation occurred at pH 4 and over 95% of 20 μg/L Microcystin-LR was decomposed within 120 min under 400 μW/cm2 UV illumination. The kinetic equations and parameters revealed that degradation reaction of trace level MC-LR, which was depicted by Langmuir-Hinshelwood kinetics model, was in accordance with pseudo first order kinetics process in appearance well. Under the condition of pH=6.7, irradiation intensity=400 μW/cm2 and initial concentration=20 μg/L, the corresponding pseudo-first-order rate constant k and half-life were determined to be 0.0157 min−1 and 44 min, respectively. During the range of 200–1000 μW/cm2, the degradation rate increases with incident intensity to the 0.82 power and the corresponding apparent quantum yield (Φapp) was found to be 5.19×10−8 g/J approximately.

Kinetics of TiO2-Catalyzed Ultrasonic Degradation of Rhodamine Dyes

The ultrasonic degradation of two dyes, Rhodamine B $(C_2_8H_3_1ClN_2O_3)$ and Rhodamine Blue $(C_2_8H_3_2N_2O_3)$, were studied in the absence of catalyst and in the presence of two catalysts (combustion-synthesized anatase $TiO_2$ and commercial Degussa P-25 $TiO_2$. The rate of degradation of catalyzed reaction was higher than that obtained with in the absence of the catalysts. Among the catalysts, combustion-synthesized anatase $TiO_2$ degraded the dyes faster when compared to the degradation with commercial Degussa P-25 catalyst. A Langmuir-Hinshelwood kinetic model was developed and the kinetic rate parameters were determined. The effect of other operating parameters, such as initial concentration, pH, temperature, and power intensity, was also investigated. The degradation rate increased with decreasing pH, increasing temperature, and higher intensity.

Kinetics of Photocatalytic Degradation of Chlorophenol, Nitrophenol, and Their Mixtures

The kinetics of photocatalytic degradation of binary mixtures of chlorophenol and nitrophenol was investigated using solution combustion synthesized nano-TiO2. The degradation rates of both organics decreased in the binary mixture compared to the individual degradation rates of the organics. This was attributed to interaction between the mother compounds, interaction between the intermediates, and competition for the active reaction site on the catalyst. A modified Langmuir-Hinshelwood kinetic model was developed, and the kinetic parameters were determined from initial rate analysis for the degradation of chlorophenol and nitrophenol. The evolution of intermediates was also investigated, and a possible pathway for degradation of chlorophenol and nitrophenol was proposed.

Photocatalytic hydrogen generation in the presence of chloroacetic acids over Pt/TiO 2

In the presence of chloroacetic acids, the photocatalytic hydrogen evolution and decomposition of the pollutants over Pt/TiO 2 have been investigated. The Pt/TiO 2 was prepared by photodeposition. Monochloroacetic acid and dichloroacetic acid enhance photocatalytic hydrogen generation, whereas trichloroacetic acid does not. The photocatalytic oxidation of monochloroacetic acid and dichloroacetic acid mainly produces CO 2, HCl and formaldehyde, whereas the photocatalytic oxidation of trichloroacetic acid mainly produces CO 2 and HCl. The effect of the concentration of monochloroacetic acid and dichloroacetic acid on the hydrogen generation rate is consistent with a Langmuir–Hinshelwood kinetic model. A possible reaction mechanism was discussed.

Dogmas and Misconceptions in Heterogeneous Photocatalysis. Some Enlightened Reflections

In a recent article, Ollis analyzed heretofore reported photocatalyst kinetics of surface photochemical reactions that take place in heterogeneous systems and that rely heavily on the Langmuir-Hinshelwood (LH) kinetic model to interpret the experimental observations. This model assumes a fast adsorption/desorption equilibrium step and a subsequent slow surface step. His interesting analysis of the experimental results reported in 2000 by Emeline and co-workers, Xu and Langford, and Martyanov and Savinov prompted our reexamination of the LH kinetic model along with several other dogmas that continue to propagate in the heterogeneous photocatalytic landscape. This short article discusses some of these issues and reexamines certain misinterpretations. Specifically, we reexamine (1) the a priori assumed validity of the LH kinetic model in heterogeneous photocatalysis, (2) the recombination of photogenerated free charge carriers on the solid (metal oxide) photocatalyst by the band-to-band recombination pathway, and (3) the mistaken assertion that the kinetics of a heterogeneous photoreaction are either only first-order dependent or half-order dependent on photon flow (i.e., light irradiance).

Photocatalytic oxidation of acetonitrile in gas–solid and liquid–solid regimes

Photocatalytic degradation of acetonitrile was carried out in both gas–solid and liquid–solid regimes using two commercial TiO 2 catalysts (Merck and Degussa P25). For the gas–solid regime, a continuous annular photoreactor was used. The influence on photodegradation kinetics of the gas flow rate and concentrations of acetonitrile, oxygen, and water was investigated. Acetonitrile degradation products detected in the gas phase included carbon dioxide and hydrogen cyanide. The same photoactivity was exhibited in the presence and in the absence of water vapour. The liquid–solid regime used a batch photoreactor with an immersed lamp (the same as for the gas–solid regime). The oxidation products detected in the solution were cyanide, cyanate, nitrite, nitrate, methanoate, and carbonate ions. The Langmuir–Hinshelwood kinetic model fit the photoreactivity data obtained in both regimes and allowed us to determine the rate constant and equilibrium adsorption constant values. The adsorption constant and kinetic constant value were lower in the liquid–solid regime than in the gas–solid regime. The Merck catalyst had higher values of these parameters for both regimes than the Degussa P25 catalyst. An evaluation of the possible competition between acetonitrile and water molecules for the surface sites of the photocatalyst (Ti 4+ ions and hydroxyl groups) revealed that for high H 2O/CH 3CN ratios, as is typical for the photo-oxidation process carried out in a liquid/solid regime, acetonitrile molecules were not able to provide a specific interaction with the surface sites of TiO 2, remaining dissolved in the interface water molecular layers. In contrast, for low H 2O/CH 3CN ratios, as is typical for the photo-oxidation process carried out in a gas–solid regime, acetonitrile could win the competition with water for surface hydroxyls.