Photocatalytic Microreactor Research Articles

Development of a Photocatalytic Microreactor with Separated Oxidation/Reduction Channels

Development of a Photocatalytic Microreactor with Separated Oxidation/Reduction Channels

Synthesis of free-standing Ta3N5 nanotube membranes and flow-through visible light photocatalytic applications.

We report on free-standing Ta3N5 nanotubular membranes with open top and bottom, used as visible-light-active, flow-through photocatalytic micro-reactors. We grow first a robust anodic Ta2O5 layer, lift-off a membrane and convert to Ta3N5. Such membranes can easily, in a flow-through mode, degrade methylene blue under visible light (wavelength >400 nm) or solar illumination.

Real-time spectroscopic monitoring of photocatalytic activity promoted by graphene in a microfluidic reactor

Photocatalytic microreactors have been utilized as rapid, versatile platforms for the characterization of photocatalysts. In this work, a photocatalytic microreactor integrated with absorption spectroscopy was proposed for the real-time monitoring of photocatalytic activity using different catalysts. The validity of this method was investigated by the rapid screening on the photocatalytic performance of a titanium oxide (TiO2)-decorated graphene oxide (GO) sheet for the degradation of methylene blue under monochromatic visible irradiation. The sampling interval time could be minimized to 10 s for achieving real-time detection. The best photocatalytic activity was observed for an optimized TiO2/GO weight mixing ratio of 7:11, with a reaction rate constant up to 0.067 min−1. The addition of GO into TiO2 enhances photocatalytic activity and adsorption of MB molecules. The synthetic reaction rate constant was up to approximately 0.11 min−1, which was also the highest among the catalysts. The microreactor exhibited good sensitivity and reproducibility without weakening the performance of the photocatalysts. Consequently, the photocatalytic microreactor is promising as a simple, portable, and rapid screening tool for new photocatalysts.

Microfluidic-based photocatalytic microreactor for environmental application: a review of fabrication substrates and techniques, and operating parameters.

Photochemical technology with microfluidics is emerging as a new platform in environmental science. Microfluidic technology has various advantages, like better mixing and a shorter diffusion distance for the reactants and products; and uniform distribution of light on the photocatalyst. Depending on the material type and related applications, several fabrication techniques have been adopted by various researchers. Microreactors have been prepared by various techniques, such as lithography, etching, mechanical microcutting technology, etc. Lithography can be classified into photolithography, soft lithography and X-ray lithography techniques whereas the etching process is divided into wet etching (chemical etching) and dry etching (plasma etching) techniques. Several substrates, like polymers, such as polydimethyl-siloxane (PDMS), polymethyle-methacrylate (PMMA), hydrogel, etc.; metals, such as stainless steel, titanium foil, etc.; glass, such as silica capillary, glass slide, etc.; and ceramics have been used for microchannel fabrication. During degradation in a microreactor, the degradation efficiency is affected by few important parameters such as flow rate, initial concentration of the target compound, microreactor dimensions, light intensity, photocatalyst structure and catalyst support. The present paper discusses and critically reviews fabrication techniques and substrates used for microchannel fabrication and critical operating parameters for organics, especially dye degradation in the microreactor. The kinetics of degradation has also been discussed.

Recent Advances in Fabrication of Photocatalytic Micro-Reactor

Microfluidic technology has been increasingly applied in field of photo catalytic reactor because of the large surface to volume ratio, shorter diffusion distance of the reactant solution, higher mixing efficiency and lower cost. This article reviews the detail progress in fabrication of micro-reactor for degradation of dye in waste water. Importantly, dye degradation required uniform UV light exposure which could be resolved by carrying out degradation in a micro-reactor. This paper discussed several of potential and commercial photocatalytic micro-reactor fabrication and configurations, in particular, the polydimethyl siloxane (PDMS) photocatalytic reactors.

Performance of a Metal Ion‐Doped Titania‐Coated Planar Photocatalytic Microreactor

AbstractA novel planar photocatalytic microreactor coated with metal ion‐doped TiO2 was fabricated by chemical etching and sol‐gel techniques. The photocatalytic activity of the microreactor was evaluated by studying the degradation of methylene blue (MB) under ultraviolet light, visible light, and sunlight, and encouraging results were obtained. Analyses of the degradation products indicate that demethylation and ring‐opening reactions took place and that the mineralization of MB is a slow process. Kinetic studies of the MB degradation show that metal ion doping increases the reaction order. Comparing the applied microreactor with other conventional microchannel photocatalytic reactors, nearly the same degradation ratios and relatively higher degradation rates per unit reaction volume were obtained.

Desulfurization of Gas Oil Using a Solar Photocatalytic Microreactor

The desulfurization of dibenzothiophene (DBT) was studied in a homemade Y-shape catalytic microreactor utilizing solar incident energy. The microchannel was coated with TiO2 nanoparticles. Performance of the microreactor was investigated using different conditions (e.g., DBT concentration, LHSV, operating temperature, and (H2O2/DBT) ratio). Our experiments show that, in the absence of UV light, no reaction takes place. The results revealed that outlet concentration of DBT decreases as the mean residence time in the microreactor increases. Also, it was noted that operating temperature has a positive impact on the degradation rate of DBT while LHSV showed a different image. The results reported an optimum (H2O2/DBT) ratio which gave maximum conversion of DBT. Kinetic study was carried out which confirmed that desulfurization of DBT followed a pseudo-first order reaction at 30 and 50oC, respectively. However deviation from linearity was observed at 60oC. Comparison between microreactor's performance and performance of batch reactors from published literature were illustrated. The Comparison confirmed the unique characteristics of the microreactor.

Desulfurization of gas oil using a solar photocatalytic microreactor

The present work is devoted to investigate the performance of a homemade Y-shape catalytic microreactor for degradation of dibenzothiophene (DBT), as a model of sulphur compounds including in gas oil, utilizing solar incident energy. The microchannel was coated with TiO2 nanoparticles which were used as a photocatalyst. Performance of the microreactor was investigated using different conditions (e.g., DBT concentration, LHSV, operating temperature, and (H2O2/DBT) ratio). Our experiments show that, in the absence of UV light, no reaction takes place. The results revealed that outlet concentration of DBT decreases as the mean residence time in the microreactor increases. Also, it was noted that operating temperature showed a positive impact on the degradation rate of DBT while LHSV showed a different image. The results reported an optimum (H2O2/DBT) ratio which gave maximum conversion of DBT which vary with initial concentration. Kinetic study was carried out which confirmed that desulfurization of DBT followed a pseudo-first order reaction at 30 and 50oC, respectively. However deviation from linearity was observed at 60oC. Comparison between microreactor´s performance and performance of batch reactors from published literature were illustrated. The Comparison confirmed the unique characteristics of the microreactor.

PROTOTYPING OF PHOTOCATALYTIC MICROREACTOR AND TESTING OF PHOTODEGRADATION OF ORGANIC DYE

A photocatalytic microreactor is defined as a microfluidic device, which is integrated with a photocatalytic coating of TiO2 deposited on the inner surface of microchannels. This device is capable of degradation of organic dye solution in water in a continuous flow under the action of ultraviolet light. The objectives of this work were to present a rapid and economically viable approach for the prototyping photocatalytic microfluidic devices and to evaluate their photodegradation capability for organic dyes by ultraviolet-visible spectrophotometry. Prototyping of polydimethylsiloxane PDMS/TiO2/glass microreactors includes several procedures such as mold preparation, microchannel confection on PDMS surface, deposition of TiO2 on these microchannels, O2 plasma treatment of PDMS/TiO2 and glass surface for sealing these two parts. The efficiency of the photocatalytic microreactors was evaluated by fluxing two organic dye solutions, rhodamine B and methylene blue, with different flow rates of between 2 and 4 mL h-1. When the flow rate at 2 mL h-1was applied, discoloration of ~ 65% was achieved for both dye solutions, while PDMS/glass microchannels, without TiO2 film, demonstrated much lower discoloration of between 24 and 42% for rhodamine B and methylene blue, respectively. This confirmed that TiO2 was successfully deposited onto PDMS microchannels.

Real time, in situ observation of the photocatalytic inactivation of Saccharomyces cerevisiae cells.

An in situ microscopy technique was developed to observe in real time the photocatalytic inactivation process of Saccharomyces cerevisiae (S. cerevisiae) cells by palladium-modified nitrogen-doped titanium oxide (TiON/PdO) under visible light illumination. The technique was based on building a photocatalytic micro-reactor on the sample stage of a fluorescence/phase contrast microscopy capable of simultaneously providing the optical excitation to activate the photocatalyst in the micro-reactor and the illumination to acquire phase contrast images of the cells undergoing the photocatalytic inactivation process. Using TiON/PdO as an example, the technique revealed for the first time the vacuolar activities inside S. cerevisiae cells subjected to a visible light photocatalytic inactivation. The vacuoles responded to the photocatalytic attack by the first expansion of the vacuolar volume and then contraction, before the vacuole disappeared and the cell structure collapsed. Consistent with the aggregate behavior observed from the cell culture experiments, the transition in the vacuolar volume provided clear evidence that photocatalytic disinfection of S. cerevisiae cells started with an initiation period in which cells struggled to offset the photocatalytic damage and moved rapidly after the photocatalytic damage overwhelmed the defense mechanisms of the cells against oxidative attack.

Low-cost polymeric photocatalytic microreactors: Catalyst deposition and performance for phenol degradation

The feasibility of using flexible polymer microtubes as photocatalyst supports was investigated by using PFA tubes of various inner diameters (i.d.). Catalyst immobilisation was performed by loading a prepared TiO2 suspension into the tubes, which were then subjected to a quick thermal treatment at 285°C. The presence of the catalyst on the inner walls of the tubes was confirmed by SEM-EDS analysis, and the thicknesses of the resulting catalytic layers were evaluated by SEM for different catalyst precursor concentrations. The performances of the reactors were investigated by the photocatalytic degradation of phenol. The apparent reaction rates observed on these reactors were found to be one order of magnitude larger than found in a small batch vessel operating with suspended slurry. The effects of the number of catalytic coatings, the concentration of the catalyst precursor suspension, the reactor inner diameter and the initial pH of the solutions on the performance of the reactor were investigated.

Novel method of screening the oxidation and reduction abilities of photocatalytic materials

Two analytical methods for the evaluation of photocatalytic oxidation and reduction abilities were developed using a photocatalytic microreactor; one is product analysis and the other is reaction rate analysis. Two simple organic conversion reactions were selected for the oxidation and reduction. Since the reactions were one-to-one conversions from the reactant species to the product species, the product analysis was simply performed using gas chromatography, and the reactions were monitored in situ in the photocatalytic microreactor using the UV absorption spectra. The partial oxidation and reduction abilities for each functional group can be judged from the yield and selectivity, and the corresponding reaction rate, while the total oxidation ability can be judged from the conversion. We demonstrated the application of these methods for several kinds of visible light photocatalysts.

Study on photocatalytic organic reactions using photocatalytic microreactors.

Photocatalytic organic reactions were performed using automatic photocatalytic microreactor, where several open-end capillaries with photocatalytic materials coated inside were just soaked in a test tube including a reactant solution. Organic reactions of the alkyl radicals generated from carboxylic acids due to the photo-Kolbe reaction was studied, in analogy with the reactions using a photosensitizer. This methodology features the reusability of the reactor and an easy process for analysis due to easy separation of the reactant solution.

Modeling intrinsic kinetics in immobilized photocatalytic microreactors

The article presents a simple model for immobilized photocatalytic microreactors following a first order reaction rate with either light independency or light dependency described by photon absorption carrier generation semiconductor physics. Experimental data obtained for various residence times, catalyst thicknesses and photon flux densities proved that the model is capable of describing the reactor performance. The extracted reaction rate constant reveals the intrinsic kinetics as both external and internal mass transport are accounted for. The effect of light is also considered by defining a criterion for neglecting light intensity based on film thickness and absorption coefficient. For the first time k values on the order of magnitude of 101s−1 are reported. In the end, performance parameters are also derived for the light dependent model for which the internal effectiveness factor reveals both mass transfer and light limitations.

A high efficiency microfluidic-based photocatalytic microreactor using electrospun nanofibrous TiO2 as a photocatalyst

We present a novel microfluidic-based photocatalytic microreactor by using electrospun nanofibrous TiO2 as a photocatalyst for the first time. The microreactor exhibits not only a simple fabrication process, but also much higher photocatalytic activity than that achieved by a TiO2 film microreactor.

Reaction kinetics of dye decomposition processes monitored inside a photocatalytic microreactor

The photocatalytic decomposition processes of several kinds of dyes were monitored in real-time, in a TiO(2)-immobilized microcapillary. Their fluorescence spectra were measured directly from the UV-irradiated area. The photocatalytic reactions proceeded two orders of magnitude faster in the microcapillary than in a bulk reaction, and intermediate species were easily observed, due to their high concentrations compared with those of the reactants. Even for molecules that were not originally fluorescent, fluorescence was detected for the reactants or intermediate species of all the molecules studied. Photocatalytic reactions are typically analyzed in terms of pseudo-first-order or Langmuir-Hinshelwood reaction mechanisms, but it was ascertained that all of the dyes investigated in this study decomposed via a multi-step reaction such as a simple multi-step reaction, a self-catalytic reaction, and further, a more complicated reaction, depending on the molecular structure. These reactions were simulated using models based on the reaction kinetics, and reaction mechanisms were assigned to each type of dye. The fact that intermediate species (which are difficult to observe using conventional analytical methods) were successfully detected meant that mechanisms for different dyes could be further clarified.

A novel photocatalytic microreactor bundle that does not require an electric power source

A new type of photocatalytic reactor was developed. Capillaries coated on the inside with photocatalytic materials induced an effective photocatalytic reaction by pulling up a solution under the action of capillary forces; no electric pump was required for the replacement of the chemicals, due to the concentration gradient generated in the capillaries.

Porous Photocatalytic Membrane Microreactor (P2M2): A new reactor concept for photochemistry

In this study, a new membrane microreactor concept for multiphase photocatalytic reactions is demonstrated. Microfabrication, photocatalyst immobilization and surface modification steps were performed to develop a Porous Photocatalytic Membrane Microreactor (P2M2). This concept benefits from a stable gas–liquid–solid (G–L–S) interface allowing a continuous supply of gaseous reactants and a reduced light path. A surface modification technique was devised to alter the wetting conditions of the reactor wall. Through a complete hydrophobization and a selective hydrophilization step by use of UV-light, we obtained a hydrophobic porous membrane support with hydrophilic photocatalytic microchannels. The photocatalytic degradations of methylene blue and phenol were used as model reactions to test the device, demonstrating promising degradation performance. We further demonstrated the effect of additional oxygen supply to the performance of the reactor for both reaction systems.

Capillary microchannel-based microreactors with highly durable ZnO/TiO2 nanorod arrays for rapid, high efficiency and continuous-flow photocatalysis

A novel, highly durable capillary-based photocatalytic microreactor containing TiO2 nanoparticle-coated ZnO nanorod arrays grown on the inner wall of the capillaries (IWC) was successfully constructed simply by pumping a TiO2 sol into capillaries containing preformed ZnO nanorod arrays. Methylene blue was used as a model organic compound to evaluate the photocatalytic performance of the capillary microreactors (CMs). The CMs containing ZnO/TiO2 nanorod arrays showed higher photocatalytic performance than a CM containing only ZnO nanorods at the same residence time. The effect of the number of TiO2 sol coatings and the recyclable properties of the CM were investigated. These CMs showed rapid and highly efficient photocatalytic activities and the ZnO/TiO2 nanorod arrays displayed high durability during continuous recycling. The superior photocatalytic activity of the ZnO/TiO2 nanorod-modified CMs was attributed to the topographical morphology induced by the nanorod arrays, and the combination of two semiconductors decreasing the recombination rate of photoinduced electrons and holes. These CMs show the promising application of the photodegradation of organic pollutants.

Photocatalytic reactions in microreactors

Abstract A photocatalytic microreactor with immobilized TiO 2 layer was developed and the processes of degradation and reduction of organic compounds, and amine N -alkylation in microspace were examined. These model reactions proceeded very rapidly with considerably large photonic efficiencies. In contrast to the result in a batch reactor, we successfully observed N -alkylation reaction of benzylamine by using the microreactor with immobilized Pt-free TiO 2 as well as TiO 2 /Pt. These results suggest the feasibility of a catalytic microreaction system on organic photoreactions.