Photocatalytic Microreactor Research Articles

Optimization and Parameter Investigation of the Planar Photocatalytic Microreactor.

The microreactor could break the limitation of mass transfer and photon transmission in photocatalysis. Through a facile assembly method, a planar photocatalytic microreactor was constructed to fit most of the photocatalysts regardless of their strict preparation method. This microreactor exhibits a 2.41-fold efficiency compared to a bulk reactor. Parameters that affect the photocatalytic performance were discussed in detail by experiment and calculation. The diffusion rate is the main bottleneck in a planar microreactor under a laminar flow. The microreactor with lower height shows higher efficiency owing to faster mass transfer, while the length and width affect slightly. Elevating the light power density provides a diminishing benefit. Faster flow speed reduces the apparent degradation percent but increases the chemical reaction rate, in fact. The reaction rate increases to 9.31 times by reducing the height from 500 to 100 μm and grows another 1.76 times by adding the flow speed from 10 to 40 mL/h. This work illustrates the influence of parameters on planar photocatalytic microreactors and offers a promising prospect for large-volume photocatalytic water treatment.

The integrated microfluidic photocatalytic planar reactor under continuous operation

An integrated microfluidic planar reactor is essential for achieving efficient and enhanced photocatalytic water treatment. Optimization of catalysts is an area of intense study owing to the need to enhance the performances of microreactors. A high-efficiency photocatalytic microreactor is presented here by combining a planar microreactor with a high-efficiency photocatalyst. TiO2 nanoparticles doped with Y and Yb were prepared to improve the photocatalytic reaction efficiency. First, better performance is achieved with the Y, Yb/TiO2 and TiO2 microreactors than conventional bulk reactors because of good photodegradation and a high reaction rate. Then, the Y, Yb/TiO2 film microreactor exhibits not only efficient catalytic activity with UV light but also higher photocatalytic activity under visible light irradiation than that achieved by a TiO2 film microreactor. The reaction rate constant of the Y, Yb/TiO2 film microreactor is approximately 0.530 s–1, which is twice that of the TiO2 film microreactor. Moreover, the performances under continuous and intermittent reactions are compared to evaluate the stability of the microreactor, thereby building the foundation for practical application of continuous water treatment in the microreactor.The planar microreactor provides a convenient platform for studying photodegradation under various conditions, such as different temperatures, flow rates, light irradiation (UV and Vis), and reaction modes (continuous and intermittent).

Three-dimensional monolithic TiO2/ZIF-8/AgCl/Ag-based photocatalytic microreactor for efficient degradation of organic pollutants

Photocatalytic degradation of organic pollutants based on solar light is regarded as an important strategy for addressing water scarcity issue. However, efficient utilization of light in this process requires careful optimization of the photocatalytic reactor layout to maximize the interaction between light, photocatalyst and reactant molecules. Herein, a three-dimensional monolithic photocatalytic microreactor, in which in-situ grown TiO2/ZIF-8/AgCl/Ag was distributed on the surface of polydopamine (PDA)-modified melamine sponge (MS), was developed. The structural and optical properties were examined using SEM, TEM, HRTEM, XRD, XPS, FT-IR, EIS and TPR characterizations. Methylene blue (MB) was selected as the pollutant model, and the results showed that the photocatalytic microreactor had the super-fast degradation ability of MB due to high specific surface area, synergistic effects caused by TiO2/ZIF-8/AgCl/Ag hybrid structure and enhanced light-matter interaction. A MB removal rate (99.99%) was obtained within 8 min under visible light irradiation. After six times recycling, the photocatalytic microreactor still showed high photodegradation ability (90%). The radical scavenging experiments and electron spin resonance analysis showed that ·O2-, h+ and ∙OH were the reactive groups that played a role in the reaction system, and then a possible catalytic mechanism of TiO2/ZIF-8/AgCl/Ag was proposed.

Embedded ZnO nanorod array/TiO2/GO coated optical fiber in a photocatalytic microreactor for Cefixime degradation: Diffused or focused light sources effect

A new high-efficiency continuous photocatalytic system composed of a microreactor and an optical fiber coated with a ZnO nanorod array/TiO2/GO with a retention time of 4–7 min was introduced. Using a new step-by-step chemical bath deposition method, a ZnO nanorod array coated with TiO2 and GO was grown on the surface of an optical fiber with different mass ratios. The coated photocatalytic layer was characterized using XRD, XPS, Raman spectra, UV-drs, TEM, and SEM. The photocatalytic degradation efficiency of Cefixime (CEF) in the microreactor was studied under irradiation from two diffusing and focusing light sources to determine the effect of light radiation type on the efficiency. ZnO nanorods/TiO2 coated optical fiber (Ti/Zn weight ratio = 0.37) and GO deposition during the growth of ZnO nanorods demonstrated the highest degradation efficiency. The operational and geometrical parameters were optimized as fiber length = 15 cm, fiber diameter = 500 µm, CEF concentration = 10 ppm, and pH = 4.8. The removal efficiency under these conditions was approximately 67 % with a diffused light source and 80.1 % with a focused light source. The coated photocatalytic composite showed high stability to the liquid flow after 1200 min of continuous operation, indicating the ZnO nanorods/TiO2/GO coating method's success.

Degradation of binary mixtures of water pollutants in a photocatalytic microreactor: Competitive kinetics with explicit radiation absorption effects

The photocatalytic degradation of 17-α-ethinylestradiol (EE2) and phenol in aqueous solutions was studied using a continuous flow, planar microreactor under simulated sunlight. A TiO2 thin film was employed as photocatalyst. The degradation rates of single compounds and binary mixtures were well described by the Langmuir-Hinshelwood equation, including competitive terms for the companion pollutant and the intermediate products, and the effect of photon absorption by the photocatalyst. The absorbed radiation in the microreactor was calculated from the optical properties of the TiO2 film and the application of the Net Radiation method. The estimation of the kinetic parameters was carried out by numerical integration of coupled mass balance equations for EE2 and phenol employing the Runge-Kutta method, and adjusting the kinetics parameters with a nonlinear least-squares solver. The objective of this routine was to minimize the sum of the squares of the differences between the simulated and experimental outlet concentrations of EE2 and phenol under different operating conditions. Using this approach, intrinsic kinetic parameters were obtained. The model was able to predict the degradation of both organic pollutants under different inlet concentrations, irradiation levels, and fluid flow rates. This methodology can be extended to assess the simultaneous degradation of multi-component systems.

Degradation of binary mixtures of dyes by step-scheme quaternary photocatalyst in continuous flow-loop ultrasound assisted micro-photoreactor

The development and design of micro-scale photocatalytic systems to achieve the degradation of organic pollutants such as dyes to improve environmental conditions is very desirable. In the current study, a microfluidic-based ultrasound-assisted photocatalytic microreactor was used for degradation of a mixture of cationic dyes including RhB and MB in binary mode by quaternary CeO2/Co3O4/Ag/Ag3PO4 step-scheme (S- scheme) photocatalyst under visible LED light. Various characterizations were performed to determine the morphology and structure of the photocatalyst. The ultrasound-assisted photocatalytic micro-photoreactor shows a much higher degradation performance than the simple micro-photoreactor for the degradation of cationic dyes. Besides, the batch process shows higher photocatalytic activity compared to the micro-photoreactor under ultrasound-assisted process. In addition, the reaction constant of CeO2/Co3O4/Ag/Ag3PO4 composite in ultrasound assisted micro-photoreactor are about 0.0087 1/s and 0.0081 1/s (RhB and MB) which are almost 2.3 and 1.7 times higher than micro-photoreactor due to free radicals, ultrasonic waves and Dean vortices. The observation of findings illustrated the photocatalytic degradation of dyes by the as-prepared composite in various processes were in the order of batch mode > ultrasound assisted micro-photoreactor > micro-photoreactor. The strategy of micro-photoreactor with ultrasonic waves using photocatalytic composite to improve dye degradation performance can lead to the development of advanced micro-photoreactor based on photocatalytic composites with high performance for wastewater treatment applications.

Efficient Degradation of Oxytetracycline in a Novel Plug-In Three-Dimensional Photocatalytic Microreactor

The combination of a photocatalytic reaction and microfluidic technology is an increasingly popular method utilized to continuously degrade wastewater. In this work, a novel photocatalytic microreactor with TiO2 loaded on the channel center insert was designed and the photocatalytic degradation process of oxytetracycline (OTC) was investigated. Parameters such as TiO2 loading, OTC initial concentration, light intensity, and ion (NO3– and SO42–) concentrations were systematically investigated. The results show that the degradation efficiency of OTC was 56% under the optimal experimental conditions. Compared with the conventional miniaturized photocatalytic reactors, the reaction rate constant and space–time degradation efficiency of the plug-in three-dimensional photocatalytic microreactor proposed in this work were 1–2 orders of magnitude higher. In addition, dimensionless correlation was obtained to predict the degradation efficiency. This work provides a promising microfluidic technology for the process intensification of photocatalytic reaction and wastewater treatment.

Efficient and stable monolithic microreactor with Ag/AgCl photocatalysts coated on polydopamine modified melamine sponge for photocatalytic water purification

The advantages of photocatalytic microreactors, including large specific surface area, rapid mass transfer, continuous flow operation capability and low safety hazards promote the application in the field of water purification., We propose a monolithic microreactor for depositing Ag/AgCl photocatalysts on the surface of the polydopamine(PDA) -modified melamine sponge(MS) backbone. The experimental results revealed that the monolithic microreactor enables to completely degrade methylene blue(MB) under visible light irradiation within 10 min and can photodegrade 250 L m−2 of MB per hour. Moreover, we confirmed that the lifetime of MS/PDA/Ag/AgCl can be extended by a simple in situ chemical recovery method, thus making the monolithic microreactor reusable for a long time. In conclusion, the prepared monolithic microreactor has high efficiency of photodegradation, high throughput and reusability, and displays broad application prospects in the field of photocatalytic water purification.

Hierarchical optofluidic microreactor for water purification using an array of TiO2 nanostructures

Clean water for human consumption is, in many places, a scarce resource, and efficient schemes to purify water are in great demand. Here, we describe a method to dramatically increase the efficiency of a photocatalytic water purification microreactor. Our hierarchical optofluidic microreactor combines the advantages of a nanostructured photocatalyst with light harvesting by base substrates, together with a herringbone micromixer for the enhanced transport of reactants. The herringbone micromixer further improves the reaction efficiency of the nanostructured photocatalyst by generating counter-rotating vortices along the flow direction. In addition, the use of metal-based substrates underneath the nanostructured catalyst increases the purification capacity by improving the light-harvesting efficiency. The photocatalyst is grown from TiO2 as a nanohelix film, which exhibits a large surface-to-volume ratio and a reactive microstructure. We show that the hierarchical structuring with micro- to nanoscale features results in a device with markedly increased photocatalytic activity as compared with a solid unstructured catalyst surface. This is evidenced by the successful degradation of persistent aqueous contaminants, sulfamethoxazole, and polystyrene microplastics. The design can potentially be implemented with solar photocatalysts in flow-through water purification systems.

Palladium-modified TiO2 films in a photocatalytic microreactor: evaluation of radiation absorption properties and pollutant degradation efficiency.

Pure (TiO2) and 0.1 nominal atomic percent of palladium-modified TiO2 (Pd-TiO2) films were synthesized via a sol-gel method and compared through their physicochemical properties and photocatalytic activity in the degradation of an emerging contaminant, 17-α-ethinylestradiol (EE2). The activity of the films was studied using a continuous flow, planar microreactor under simulated sunlight. Catalysts characterization included X-ray diffraction, UV-Visible diffuse reflectance and transmittance spectroscopy, atomic force microscopy, transmission electron microscopy, Raman spectroscopy, N2 physisorption analysis, and X-ray photoelectron spectroscopy. The modification of TiO2 with palladium confined the size of anatase phase crystallites, increased the specific surface area and improved radiation absorption. PdO domains on TiO2 were observed. In all the tested conditions, higher conversion of EE2 was achieved with the Pd-TiO2 film compared with the TiO2 film, presenting an 80% increase in the reaction rate. The performance of the catalytic films was also assessed by the calculation of two efficiency parameters: radiation absorption efficiency and quantum efficiency of reaction. The Pd-TiO2 film showed a notable enhancement of the absorption of the incident radiation and a more efficient utilization of the absorbed photons to degrade the target pollutant.

Review on optofluidic microreactors for photocatalysis

Abstract Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its fullest, a well-designed photoreactor is vital. Photocatalytic optofluidic microreactors, a promising technology that brings the merits of microfluidics to photocatalysis, offer the advantages of a large surface-to-volume ratio, a short molecular diffusion length and high reaction efficiency, providing a potential method for mitigating the aforementioned crises in the future. Although various photocatalytic optofluidic microreactors have been reported, a comprehensive review of microreactors applied to these four fields is still lacking. In this paper, we review the typical design and development of photocatalytic microreactors in the fields of water purification, water splitting, CO2 fixation and coenzyme regeneration in the past few years. As the most promising tool for solar energy utilization, we believe that the increasing innovation of photocatalytic optofluidic microreactors will drive rapid development of related fields in the future.

Multiwell photocatalytic microreactor device integrating drug biotransformation modeling and sample preparation on a MALDI target

Metabolic conversion of drugs to chemically reactive products, known as bioactivation, is considered to underlie the adverse drug reactions such as idiosyncratic hepatotoxicity. As bioactivation of most drugs involves phase I oxidation, UV-induced TiO2 photocatalytic oxidation (UV/TiO2-PCO) can be used as a fast, simple and inexpensive non-enzymatic method of oxidative metabolism simulation allowing for rapid preliminary screening of candidate drugs for reactive metabolite formation. We developed and evaluated a novel prototype 96-well on-target UV/TiO2-photocatalytic microreactor setup (PCμR96) that integrates drug metabolism simulation and sample preparation directly on a MALDI target. PCμR96 allows to sequentially perform UV/TiO2-PCO of xenobiotics, GSH or protein adduct formation, protein digestion and sample concentration, followed by surface- or matrix-assisted laser desorption ionization (SALDI/MALDI) mass spectrometry (MS). Amodiaquine (AQ), a well-studied antimalarial drug that is known to undergo oxidative biotransformation, was selected as a model compound. Oxidation products of AQ and their protein adducts were obtained using PCμR96 and identified by SALDI and MALDI MS/MS analysis. The achieved AQ oxidation products were in good agreement with the known AQ metabolites produced in biological systems. Two of the products were proved to be reactive towards cysteyl thiols of human globin.

Design of a Microfluidic Photocatalytic Reactor for Removal of Volatile Organic Components: Process Simulation and Techno-Economic Assessment.

This study reports on a gas-phase photocatalytic microreactor (MR) employed for the degradation of 2-propanol in indoor air. A process flow diagram was developed and simulated in Aspen Hysys V10, and a techno-economic assessment was carried out based on the simulated results. An economic evaluation was carried out using a fixed and demand-dependent variable cost model. Decreasing the mass flow rate or the initial concentration of the 2-propanol in indoor air and increasing the diameter or length of the MR resulted in a better air remediation efficacy. Sensitivity analysis for the economics of the manufactured MR showed that the optimal plant production volume is 10,000 units per year. At this volume, the total manufacturing cost was 2.8 M$/y with a production cost of $ 127 per unit and a levelized cost of a MR (LCOM) of about $ 280 per unit. These findings herein can help bolster research into both technical and economic aspects of MR production for the photocatalytic remediation of air. The resulting design could be applied in air conditioner units and other home ventilation units for the removal of harmful volatile organic compounds in the air.

High flow rate microreactors integratingin situgrown ZnO nanowires for photocatalytic degradation

A high flow rate, low-pressure microfluidic photocatalytic microreactor was created and demonstrated here.

Janus Emulsion Solar Concentrators as Photocatalytic Droplet Microreactors

AbstractEfficiently harvesting and conveying photons to photocatalytic reaction centers is one of the great obstacles in photocatalysis. To address this challenge, a new approach is reported that is based on employing biphasic complex emulsions as droplet‐based solar concentrators. Specifically, substrates and photocatalysts are compartmentalized into the confined space of Janus emulsion droplets comprised of a hydrocarbon partially encapsulated inside fluorocarbon oil with a large refractive index contrast. Optical confinement of the incident light due to total internal reflection at the concave internal interface of the biphasic emulsion droplets leads to a strong increase of the light intensity inside the reaction medium. In addition, the high gas solubility within the outer fluorocarbon phase promotes oxygen delivery in photocatalytic oxidation reactions. Both effects mutually contribute to a strong performance increase of a series of homogeneous and heterogeneous photocatalytic reactions even under diffuse sunlight conditions.

Research on Micro-Analysis System of Dye in Water Sample Based on Magnetic Nano-TiO2

Magnetic Nano-Photocatalytic Material (NMPC) helps separate and recover nano photocatalyst in water treatment. However, it is rarely reported that a photocatalyst can be separated online in photocatalytic microreactors. In this paper, a typical dye methylene blue was photocatalytically degraded in glass microfluidic chip by using Fe3O4@ SiO2@ TiO2 (FST) as the magnetic nanocatalyst, the UV-LED as the ultraviolet light source, and ultraviolet-visible spectrophotometer as the detector. The FST was easily separated by an external magnetic field, thereby realizing rapid online detection of methylene blue. During the preparation of FST, the hydrothermal method was used to treat the obtained FST nanoparticles in 100°C boiling water bath, and the titanium-iron ratio was optimized, so as to obtain FST nano-photocatalyst with high photocatalytic performance and good dispersibility. With 1.0 g/L FST/8%H2O2 being the catalytic oxidation system, the sample flow rate being 300 μL/h, the reaction temperature being 45 °C, the degradation rate of methylene blue has reached 100%. It only took 25 min to complete one measurement. The FST consumed per measurement was only 125 μg. The RSD of the photodegradation rate was 2.5% (n=9).

An aerogel-based photocatalytic microreactor driven by light guiding for degradation of toxic pollutants

Efficient utilization of light in photocatalytic chemical processes requires careful optimization of the photocatalytic reactor layout to maximize the interaction between the incident light, photocatalyst and reactant molecules. Herein, we report a new type of photocatalytic flow microreactor with an integrated light guide, formed by a channel fabricated inside a hydrophobic composite aerogel monolith made of silica and titania (TiO2). The liquid-filled channel simultaneously acts as a reaction vessel and as a liquid-core optofluidic waveguide, distributing the incident light over the whole reaction volume. Anatase TiO2 nanoparticles embedded in the channel walls then serve as a photocatalyst that can efficiently interact with both the guided light and the reactant solution along the channel length. Composite aerogels were synthesized with TiO2 content between 1 and 50 wt %, retaining their interconnected mesoporous network, low refractive index, and waveguide propagation losses below −3.9 dB/cm over this range of compositions. Using photocatalytic degradation of phenol – an organic compound with harmful environmental effects – as a model chemical reaction, the performance of the microreactor was systematically investigated. Reactant conversion was observed to increase with increasing incident light power, decreasing reactant flow rate and increasing mass fraction of TiO2 in the composite. An analytical model of the reactor/light guide system was developed that predicted successfully the scaling of the reactant conversion with the incident light power and reactant flow rate. The presented concept of aerogel-based optofluidic photocatalytic microreactors is readily scalable and possesses great potential for carrying out other photocatalytic reactions in both polar and non-polar solvents.

A confined micro-reactor with a movable Fe3O4 core and a mesoporous TiO2 shell for a photocatalytic Fenton-like degradation of bisphenol A

Photocatalysis and Fenton process are two primary and promising advanced oxidation processes to degrade organic pollutants. However, the practical applications of single photocatalysis and Fenton process are still limited. Introducing one of them into another to form a combined photocatalytic Fenton-like system has shown great potential but still faces challenges in designing a well-tailored catalyst. Herein, a confined photocatalytic Fenton-like micro-reactor catalyst with a movable Fe3O4 core and a mesoporous TiO2 shell has been constructed via a successive Stöber coating strategy, followed by an ultrasound assisted etching method. The resulting micro-reactor possesses well-defined yolk-shell structures with uniform mesopores (∼4 nm), a large Brunauer-Emmett-Teller (BET) surface area (∼166.7 m2/g), a high pore volume (∼0.56 cm3/g) and a strong magnetization (∼51 emu/g), as well as tunable reactor sizes (20−90 nm). When evaluated for degrading bisphenol A under solar light in the presence of peroxymonosulfate, the micro-reactor exhibits a superior catalytic degradation performance with a high magnetic separation efficiency and an excellent recycle ability. The outstanding performance can be attributed to its unique textual structure, which leads to a great synergistic effect from the photocatalytic and Fenton-like process. This study gives an important insight into the design and synthesis of an advanced micro-reactor for a combined advanced oxidation processes (AOPs).

TiO2 MOCVD coating for photocatalytic degradation of ciprofloxacin using 365 nm UV LEDs - kinetics and mechanisms

This work presents a solution for the photocatalytic degradation of the antibiotic ciprofloxacin (CIP) in water, without using P25 TiO2 powder and thus getting rid of expensive separation steps. It consists in using a TiO2 coating that is directly deposited on the optical window of a photocatalytic micro-reactor and 365 nm UV LEDs as radiation source. P25 TiO2 powder was also studied as reference. HPLC-MS was used to determine the transformation products and the pathways reactions. CIP was slowly degraded by the photolysis reaction at 365 nm: (75 % removal after 8 h of UV irradiation). However, no significant decrease of the total organic carbon (TOC) was noticed, thus showing the presence of transformation products not degraded by the action of UV-light alone. For a low catalyst amount (i.e 0.12 g of TiO2, whatever the form, powder or coating, per liter of contaminated water,), excellent CIP degradation by photocatalysis was observed. Complete CIP degradation after 1 h of irradiation was required using P25 and 8 h using TiO2 coating. Different preferential reaction pathways were identified for both TiO2 catalysts. The Langmuir-Hinshelwood model showed a very good representation of the kinetics, unlike its simplified pseudo-first order model. Photocatalysis experiments did not show a complete mineralization (60–70 % of TOC removal), but most of the aromatic transformation products were degraded. The last transformation products were identified as small aliphatic acids. There is therefore a real interest in using MOCVD coating of TiO2 for sustainable wastewater treatment to avoid expensive catalyst separation. A study with a spiked real effluent from a wastewater treatment plant was performed and a satisfactory degradation was obtained. Slower kinetics were found due to the presence of additional organic products and scavenger compounds such as HCO3−.

Elemental Sulfur-Stabilized Liquid Marbles: Properties and Applications.

Sulfur-stabilized liquid marbles were readily prepared by rolling water droplets on a sulfur (S8) powder bed. Because of the construction of a gel layer on the surface of liquid marbles, the resulting liquid marbles have shape-designable characteristics. The effects of rolling time and volume of droplets on the deformability of sulfur-stabilized liquid marbles were investigated along with their mechanical stability and lifetime. The capability of sulfur-stabilized liquid marbles to be deformed at different pH values enables these liquid marbles to act as microreservoirs with desired shapes for aqueous solutions. Immersing the sulfur-stabilized liquid marbles into organic liquids leads to an increase in the liquid marbles' lifetime, and thereby they can survive at the interface of aqueous-organic two-phased systems for a long time. Finally, the applications of sulfur-stabilized liquid marbles as photocatalytic microreactors, electrochemical microcells, and monodisperse Pickering-like emulsions were demonstrated.