Langmuir-Hinshelwood Kinetic Model Research Articles

Phototocatalytic decolorization of 5-[4-(dimethylamino) phenylmethylene]-2-thioxo-4-thiazolidinone using nano-powder zinc oxide at various basic buffer pHs

Decolorization of 5-[4-(dimethylamino)phenylmethylene]-2-thioxo-4-thiazolidinone was photocatalyzed by nano-sized zinc oxide at various basic buffer solutions with pHs of 9–13. Various effectual physicochemical parameters such as dye concentration, dosage of photocatalyst, irradiation time, and pH of solution on photocatalytic decolorization under high-pressure mercury lamp illumination were optimized. The dye was found to be decolorized effectively at optimum conditions within 90–180 min. The kinetic studies showed a pseudo-first-order kinetic behavior regarding the Langmuir–Hinshelwood kinetic model at all basic pHs. The pseudo-first-order rate constants (kobs) of photocatalytic process were evaluated in the range of 1.80 × 10−2–4.40 × 10−2 for the studied pHs (9, 10, 12, and 13). Furthermore, kr, rate constant of decolorization at catalyst surface, and KA, adsorption constants of dye were calculated based on the Langmuir–Hinshelwood model at investigated pHs.

Adsorption–photodegradation of humic acid in water by using ZnO coupled TiO2/bamboo charcoal under visible light irradiation

ZnO coupled TiO2/bamboo charcoal (ZnO-TiO2/BC) was prepared using the sol–gel method combined with microwave irradiation. The ZnO-TiO2/BC and TiO2/BC were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption (BET), and UV–vis diffuse reflectance spectroscopy (UV–vis-DRS). The ZnO dopant promoted the transformation of anatase TiO2 to rutile phase, and a significant red shift of absorption edge was brought out due to the interfacial coupling effect between ZnO and TiO2 particles. The BET specific surface area and total pore volume decreased with ZnO doping, indicating that some micropores were blocked. SEM studies indicated that ZnO was almost uniformly deposited on the surface of the ZnO-TiO2/BC. The adsorption and photocatalytic degradation experiments showed that the photo-degrade efficiency for Zno-TiO2/BC was higher than that of TiO2/BC, and for both composites, the removal efficiency of HA increased as pH decreased from 10.0 to 2.0. The degradation of HA by ZnO-TiO2/BC and TiO2/BC fitted well with the Langmuir–Hinshelwood kinetics model, and HA degradation was achieved through a synergistic mechanism of adsorption and photocatalysis. ZnO-TiO2/BC could be used as an effective and alternative photocatalyst for the treatment of water contaminated by organic pollutants.

Investigation of Electron Behavior in Nano‐TiO2 Photocatalysis by Using In Situ Open‐Circuit Voltage and Photoconductivity Measurements

The in situ open-circuit voltages (Voc ) and the in situ photoconductivities have been measured to study electron behavior in photocatalysis and its effect on the photocatalytic oxidation of methanol. It was observed that electron injection to the conduction band (CB) of TiO2 under light illumination during photocatalysis includes two sources: from the valence band (VB) of TiO2 and from the methanol molecule. The electron injection from methanol to TiO2 is slower than that directly from the VB, which indicates that the adsorption mode of methanol on the TiO2 surface can change between dark and illuminated states. The electron injection from methanol to the CB of TiO2 leads to the upshift of the Fermi level of electrons in TiO2 , which is the thermodynamic driving force of photocatalytic oxidation. It was also found that the charge state of nano-TiO2 is continuously changing during photocatalysis as electrons are injected from methanol to TiO2 . Combined with the apparent Langmuir-Hinshelwood kinetic model, the relation between photocatalytic kinetics and electrons in the TiO2 CB was developed and verified experimentally. The photocatalytic rate constant is the variation of the Fermi level with time, based on which a new method was developed to calculate the photocatalytic kinetic rate constant by monitoring the change of Voc with time during photocatalysis.

Preparation and characterization of TiO2/acid leached serpentinite tailings composites and their photocatalytic reduction of Chromium(VI)

Composite TiO2/acid leached serpentine tailings (AST) were synthesized through the hydrolysis–deposition method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and surface area measurement (BET). The XRD analysis showed that TiO2 coated on the surface of acid leached serpentine tailings was mixed crystal phases of rutile and anatase, the grain size of which is 10–30nm. SEM, TEM, and EDS analysis exhibited that nano-TiO2 particles were deposited on the surface and internal cavities of acid leaching serpentine tailings. The XPS and FT-IR analysis demonstrated that the coating process of TiO2 on AST was a physical adsorption process. The large specific surface area, porous structure, and plentiful surface hydroxyl group of TiO2/AST composite resulted in the high adsorption capacity of Cr(VI). The experimental results demonstrated that initial concentration of Cr(VI), the amount of the catalyst, and pH greatly influenced the removal efficiency of Cr(VI). The removal kinetics of Cr(VI) at a relative low initial concentration was fitted well with Langmuir–Hinshelwood kinetics model with R2 value of about unity. The as-prepared composites exhibited strong adsorption and photocatalytic capacity for the removal of Cr(VI), and the possible photocatalytic reduction mechanism was studied. The photodecomposition of Cr(VI) was as high as 95% within 2h, and the reusability of the photocatalysis was proven.

Photo-degradation of butyl parahydroxybenzoate by using TiO2-supported catalyst

The present work evaluates the potential of the photocatalysis (PC) process for the degradation of butylparaben (BPB). Relatively high treatment efficiency was achieved by comparison to photochemical process. Prior to photocatalytic degradation, adsorption (AD) of BPB occurred on the titanium dioxide (TiO2)-supported catalyst. AD was described by Langmuir isotherm (KL = 0.085 L g(-1), qm = 4.77 mg g(-1)). The influence of angle of inclination of the reactor, pH, recirculation flow rate and initial concentration of BPB were investigated. The PC process applied under optimal operating conditions (recirculation flow rate of 0.15 L min(-1), angle of inclination of 15°, pH = 7 and 5 mg L(-1) of BPB) is able to oxidize 84.9-96.6% of BPB and to ensure around 38.7% of mineralization. The Langmuir-Hinshelwood kinetic model described well the photocatalytic oxidation of BPB (k = 7.02 mg L(-1) h(-1), K = 0.364 L mg(-1)).

Photodegradation of sulfamethazine in an aqueous solution by a bismuth molybdate photocatalyst

The objective of this study was to synthesize bismuth molybdate (Bi2MoO6) nanostructures with different morphologies for potential application in the removal of sulfamethazine (SMZ) from wastewater. Bismuth molybdate nanostructures were synthesized via a simple hydrothermal route followed by calcination. The nanosheet and microsphere morphologies of the Bi2MoO6 obtained were controlled by adjusting the pH value of the reactants. The solids were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy, N2-Brunauer–Emmett–Teller and UV–vis DRS methods. The optimal catalyst with the best photocatalytic performance was determined by batch experiments. The Langmuir–Hinshelwood kinetic model was employed to examine the heterogeneous photocatalysis reaction. The results indicated that the photocatalyst was very effective for SMZ photodegradation under solar light irradiation and that the photolysis followed pseudo-first order kinetics. The catalyst with the optimal photocatalytic performance could be obtained by controlling the precursor pH value, and the nanocrystalline morphology of the Bi2MoO6 played an important role in determining its catalytic activity. The main reactive species involved in the photocatalytic degradation of SMZ were identified, showing that superoxide radicals and holes were mainly responsible for the SMZ photodegradation by Bi2MoO6. Five reaction intermediates/products were observed and identified by gas chromatography–mass spectrometry (GC–MS) analysis, and a tentative reaction pathway was proposed. Toxicity tests further confirmed that the toxicity of the initial SMZ solution was efficiently eliminated during this photocatalytic process.

Kinetic Study for Reactive Red 84 Photo Degradation Using Iron (III) Oxide Nanoparticles in annular reactor

Iron oxide nanoparticles (Fe2O3 NPs) were prepared by mixing iron(II) sulfate (FeSO4) and hydrogen peroxide (H2O2) in aqueous solution at pH 3. Fe2O3 NPs are used to degrade Reactive Red-84 (RR-84) azo dye in a glass annular photo-reactor using a white light lamp. The presence of Fe2O3 NPs was verified by HRTEM analyses. Kinetic studies were made varying the reagents concentration and the reaction rate was controlled increasing the concentration of iron ions in comparison with H2O2. Langmuir-Hinshelwood (L-H) kinetic model was performed to analyze heterogeneous catalytic reactions under illumination conditions. The elimination process of azo dye followed the pseudo first-order kinetic according to L-H model. The adsorption process of the azo dye on the catalytic surface was determinant for the dye photodecomposition. The linear expression of the Langmuir adsorption isotherm under darkness was further used to establish the maximum amount of dye adsorbed Qmax=0.80 ± 0.18 mg*mgcatalyst-1 and the adsorption constant kads=0.016 ± 0.004 L*mg-1. The Langmuir-Hinshelwood equilibrium constant for dye adsorption under illumination conditions was KL-H=0.03 ± 0.02 L*mg-1. This similarity with adsorption constants could depict an evidence which suggest that Fe2O3 NPs are presents in Fenton´s reaction (FeSO4/H2O2) interacting as catalysts in the degradation of organic substrates.

Removal of cationic Rhodamine-B dye using nano-titania with anatase crystalline structure and kinetic analysis of the photocatalytic reaction

Heterogeneous photocatalytic removal of Rhodamine-B (RhB) dye from liquid phase was done using anatase-phase nanocrystalline TiO2 synthesized via a modified sol-gel process. The anatase-phase nanocrystalline TiO2 was characterized using various analytical techniques including XRD, UV-vis DRS, PL, and FTIR to investigate its phase composition and structure, nanocrystalline size, band gap energy, photoluminescence and surface properties of the prepared systems. The photocatalytic discoloration efficiency of anatase-phase nanocrystalline titania was investigated by monitoring the decomposition of RhB dye as target compounds in an aqueous solution. The results showed that the as-prepared anatase-phase nanocrystalline TiO2 was excellent for degradation of RhB molecule, and the crystallite size, excitonic PL and surface hydroxyl content have intimate relationship with the decomposition efficiency of RhB. The reaction mechanism was proposed and the results demonstrate that the role of direct photolysis on RhB dye degradation can be neglected. Meanwhile, the Langmuir-Hinshelwood kinetic model describes the photodecay date of RhB in consistent with a first order powder law and thus photocatalytic oxidation reaction followed a pseudo-first-order kinetics.

The kinetics of decalin ring opening over a Ir/H-Beta catalyst

The selective ring opening of decalin over Pd/H-Y-30, Ir/H-Beta-300 and Ir/H-Beta-25 catalysts, measured in a stirred, batch reactor at 350°C and 3MPa H2, showed that Ir/H-Beta-25 (SiO2/Al2O3=25) had the highest activity and yield of ring-opened products. The effect of temperature (275–350°C) and pressure (3–6MPa) on the activity and product selectivity was further investigated over the Ir/H-Beta-25 catalyst. The highest ring-opened product yield (53mol%) was obtained at a decalin conversion of 90mol% at 325°C and 6MPa H2. A Langmuir–Hinshelwood kinetic model, that assumed a bifunctional catalytic process in which hydrogenation and dehydrogenation reactions occurred on metal sites and isomerization, ring-opening and cracking occurred on acid sites, was successfully applied to the data. The model included the effect of catalyst deactivation associated with the catalyst acid sites. Activation energies estimated from the model parameters showed that the ring opening of isomers had the lowest activation energy (141kJ/mol), whereas cracking had the highest (159kJ/mol).

Solar photocatalytic degradation of mono azo methyl orange and diazo reactive green 19 in single and binary dye solutions: adsorbability vs photodegradation rate

The objective of this study was to examine the effects of adsorbability and number of sulfonate group on solar photocatalytic degradation of mono azo methyl orange (MO) and diazo Reactive Green 19 (RG19) in single and binary dye solutions. The adsorption capacity of MO and RG19 onto the TiO₂ was 16.9 and 26.8 mg/g, respectively, in single dye solution, and reduced to 5.0 and 23.1 mg/g, respectively, in the binary dye solution. The data obtained for photocatalytic degradation of MO and RG19 in single and binary dye solution were well fitted with the Langmuir-Hinshelwood kinetic model. The pseudo-first-order rate constants of diazo RG19 were significant higher than the mono azo MO either in single or binary dye solutions. The higher number of sulfonate group in RG19 contributed to better adsorption capacity onto the surface of TiO₂ than MO indicating greater photocatalytic degradation rate.

Modelling and design of microchannel reactor for photocatalysis

Chemical reactions in a microreactor can offer new possibilities for many chemical engineering application fields and have been employed in photocatalysis studies. The purpose of this work is to investigate the photocatalytic degradation of salicylic acid (SA) as a pollutant model, in a continuous flow microchannel reactor in order to evaluate the influence of radial concentration profile on the photocatalytic efficiency. The study has been developed on both experimental and theoretical aspects. Microreactors have been manufactured by stereolithography in epoxy resin (Accura® SI 30) and are composed of a channel with a rectangular cross-section of about 1 mm2 with different aspect ratios defined as width/depth. Photocatalytic experiments have been performed at different flow rates. Results can be predicted by the Langmuir-Hinshelwood (LH) kinetic model coupled with surface diffusion. Computational fluid dynamics (CFD-Comsol Multiphysics) can model phenomena and confirmed the reliability of our experimental results with diffusion limitation at low flow rate.

Comparative Study on Photocatalytic Degradation of Mono Azo Dye Acid Orange 7 and Methyl Orange under Solar Light Irradiation

The objective of this study was to investigate and compare the kinetic photocatalytic degradation of mono azo dyes Acid Orange 7 (AO7) and Methyl Orange (MO) under solar light irradiation with titanium dioxide (TiO2) as a photocatalyst. Several operational parameters affecting the photocatalytic degradation of dye were evaluated such as different azo dyes, initial dye concentration, TiO2 dosage, with and without aeration and sunlight irradiation. The data obtained was well fitted with the Langmuir–Hinshelwood kinetic model. It was observed that the pseudo-first-order rate constants for AO7 were higher than MO in all cases, indicating that the photocatalytic degradation of AO7 was easier and more rapid than MO. The analysis of chemical oxygen demand and UV–Vis spectra shows the AO7 and MO not only being decolorized due to the breakdown of azo bond but also being mineralized if the azo dye solutions were continually exposed to solar light irradiation after the decolorization process.

Lack of enhanced photocatalytic formation of iodine on particulate semiconductor mixtures

Under UV-A light illumination, formation of iodine from iodide ion on the surfaces of anatase TiO2, ZnO, Fe2O3, CeO2, MoO3, Bi2O3, and Nb2O5 increases with the concentration of iodide ion, airflow rate and light intensity and conform to the Langmuir-Hinshelwood kinetic model. Measurement of the particle size of the semiconductor oxides by light scattering method and deduction of the same from the determined specific surface area show that the oxide particles agglomerate in suspension. However, mixtures of any two listed particulate semiconductors do not show enhanced photocatalytic formation of iodine indicating absence of interparticle charge transfer. The results are rationalized.

Photocatalytic hydrogen generation in the presence of ethanolamines over Pt/ZnIn2S4 under visible light irradiation

Using ethanolamine (EA), diethanolamine (di-EA) and triethanolamine (tri-EA) as electron donors, the photocatalytic hydrogen evolution and decomposition of the electron donors (pollutants) over Pt/ZnIn2S4 have been investigated. The Pt was deposited on ZnIn2S4 by in situ photoreduction. The three ethanolamines improve notably photocatalytic hydrogen generation with their simultaneous degradation, and their activity order for hydrogen evolution is tri-EA≫di-EA>EA. The adsorption of these donors on ZnIn2S4 was monitored by in situ attenuated total reflection infrared spectroscopy (ATRIR). The order of their adsorption intensity is EA>di-EA≫tri-EA. The activity order depends on their molecular structure and adsorption performance. The effect of concentration of the pollutants on the hydrogen generation rate is consistent with a Langmuir–Hinshelwood kinetic model. The weak basic condition is favorable for the photocatalytic hydrogen generation. A possible reaction mechanism was discussed.

Photocatalytical removal of bentazon using commercial and sol–gel synthesized nanocrystalline TiO2: Operational parameters optimization and toxicity studies

In this work we compared the photocatalytic activity of sol–gel synthesized nanocrystalline TiO2 material (ECT-1023t) and a commercial TiO2 (Degussa P25) in the elimination, mineralization and detoxification of waters contaminated by the herbicide bentazon and its toxic intermediates under UV light. Adsorption and kinetics studies were undertaken and the effect of adding two different co-oxidants (H2O2 and S2O82-) was analyzed for both photocatalysts. The optimal basic operating parameters (pH, photocatalyst load, initial concentration of bentazon) to eliminate the herbicide and its toxic intermediates were established for both photocatalysts. The most efficient TiO2 for removal of bentazon and its toxic intermediates was ECT-1023t at pH=7. The apparent initial rate constant of bentazon degradation was two times higher for ECT-1023t than for P25. A Langmuir–Hinshelwood kinetic model showed satisfactory bentazon degradation of up to 0.25mM for P25 and up to 0.05mM for ECT-1023t. From FTIR studies, it seems that the interaction of bentazon with both photocatalysts occurred through the SO2 group. The most efficient photocatalyst for detoxification of treated solution was ECT-1023t, using the marine bacteria Vibrio fischeri as the test organism. When using an initial bentazon concentration of 0.265mM, the evolution of toxicity saw a 72% reduction in bioluminescence inhibition for ECT-1023t and only a 33% reduction for P25 after 2h of irradiation. No inhibitory growth effect of the herbicide bentazon and its photoproducts was observed for either photocatalyst in any of the irradiated samples collected at predetermined times when Lemna minor was used as the test organism. In parallel, the three photoproducts formed in the earlier steps of bentazon degradation were identified by LC–MS and a comparison on the evolution of these compounds by using both photocatalysts was performed. The results showed that the intermediates formed by hydroxylation of aromatic ring are in highest concentration when ECT-1023t is used. On the contrary, the hydroxylation of isopropyl group in bentazon is the main pathway of bentazon photodegradation when P25 is used as catalyst.

Kinetics of Nitrate Hydrogenation in Water on Alumina and Niobia Supported Palladium-Copper Catalysts

Abstract The kinetics of nitrate hydrogenation in water over niobia- and alumina-supported Pd-Cu catalysts were examined. A Langmuir-Hinshelwood kinetic model fitted concentration data, providing consistent kinetic and thermodynamic parameters. The kinetic model assumed a bimolecular surface reaction as the rate-determining step, with two types of sites. Pd-Cu/gamma-Al2O3 was active and selective under the reaction conditions. However, Pd-Cu/Nb2O5 deactivated during time on stream, and a deactivation function was added to the kinetic model to best fit the experimental data.

Photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene in the gas-phase over TiO2-based catalysts

Abstract In the present work, the photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) in the gas phase over various UV-irradiated TiO 2 -based catalysts was studied. Specifically, five catalysts were tested: four based on P25 from Degussa adding 0.25% (w/w) Pt, Fe or Ce (P25, P25/Pt, P25/Fe, P25/Ce) and one prepared according to the isopropoxide method. Inlet BTEX concentrations ranged in 0.5–21 ppmv, whereas oxygen concentration was fixed (21%, v/v) at all experiments and the residence time was adjusted to 11.5 s. Ce addition to P25 catalyst led to the highest photocatalytic oxidation rates for benzene and ethylbenzene, whereas P25 proved to be the most active catalyst on toluene photo-oxidation. Regarding m-xylene, the choice of the most effective catalyst depended on m-xylene reactor concentration. Taking all experimental results into account, P25/Ce was the most effective catalyst due to its superiority in the case of benzene and ethylbenzene and its comparable performance to the base catalyst for toluene and m-xylene photocatalytic oxidation. In general, all P25 based catalysts were more active than the isopropoxide catalyst. All conversions showed great dependence on the inlet concentration of the target compound. Water addition to the reactor during ethylbenzene photo-oxidation enhanced the rates achieved for all catalysts tested. It has to be noted that the differences in the reaction rates achieved from catalyst to catalyst decreased with water vapours addition to the reactor. Finally, a Langmuir–Hinshelwood kinetic model has been applied to the experimental data obtained. The kinetic data obtained confirmed the strong beneficial effect of Ce addition to P25 catalyst on benzene and ethylbenzene photocatalytic oxidation.

Shape and Size-Tailored Pd Nanocrystals to Study the Structure Sensitivity of 2-Methyl-3-butyn-2-ol Hydrogenation: Effect of the Stabilizing Agent

Uniform Pd nanocrystals of cubic, octahedral and cube-octahedral shapes were synthesized via a solution-phase method using two stabilizers: poly (vinyl pyrrolidone) (PVP) and di-2-ethylhexylsulfoccinate (AOT) and tested in the hydrogenation of 2-methyl-3-butyn-2-ol. The AOT-stabilized Pd nanocrystals were found to be an order of magnitude more active, but less selective than those stabilized by PVP. This could be attributed to a stronger interaction of PVP with surface Pd by adsorbed N-containing groups. The results obtained were rationalized applying a two-site Langmuir–Hinshelwood kinetic model that allowed predicting 3–4 nm cubic or octahedral nanocrystals stabilized by AOT as the optimum active phase ensuring the highest production rate of target MBE.

Evaluation of the adsorption and rate constants of a photocatalytic degradation by means of HS-MCR-ALS. Study of process variables using experimental design

The effect of the catalyst type, the catalyst concentration and the pH on the global rate of the photocatalytic degradation of C.I. Acid Yellow 9 was studied. Adsorption and rate constants related to the physical adsorption on the catalyst surface and the degradation of the dye upon illumination were calculated by applying hybrid hard- and soft-multivariate curve resolution alternating least squares (HS-MCR-ALS), including the Langmuir–Hinshelwood kinetic model as hard restriction, to the UV–visible spectra recorded during the photocatalytic degradation process. The influence of the variables on the degradation rate was assessed using the experimental results obtained from a full factorial 23 experimental design. Physical adsorption was more relevant when TiO2 was employed as a catalyst. The global rate of the photocatalytic degradation of the dye was found to be closely related to the catalyst type, its concentration level and the interaction between both factors. pH was only found to be relevant when TiO2 was used. The photodegradation of C.I. Acid Yellow 9 was optimal when using high concentrations of ZnO as catalyst.

Effect of Rb<sup>+</sup> -Doping on the Crystallization, Phase Transition and Photocatalytic Activity of Nanosized TiO<sub>2</sub> Catalyst

In order to study the ion effect on titania phase structure, crystallite size, and photocatalytic activity, Rb+-doped TiO2 nanoparticles were prepared via a modified sol-gel method and characterized by means of X-ray diffraction, Energy Dispersive X-rays spectroscopy and transmission electron microscopy. The photocatalytic activity of the elaborated powders was studied following the degradation of methyl orange. The results indicate that doping Rb+ increases the BET surface area of TiO2 crystals, decreases the crystal size, reduces the diminishing rates of surface area with increasing calcinations temperature, raises the temperature at which anatase changes into rutile phase, and so significantly increases the photocatalytic activity of TiO2. The kinetics of the methyl orange degradation fits Langmuir-Hinshelwood kinetics model well.