Continuous-flow Photocatalytic Reactor Research Articles

Highly efficient visible-light-driven photocatalytic disinfection of flowing bioaerosol using mono/multilayer MXene based catalyst

In this study, two kinds of 2D materials (nanoscale mono/multi-layer MXene) were prepared, and a new visible-light-driven photocatalyst MXene@In2S3 was synthesized by one-step hydrothermal preparation. Due to the better conductivity and larger specific surface area of the monolayer MXene, monolayer MXene@In2S3 exhibited greater transient response photocurrent and smaller interfacial charge transfer resistance than those of multilayer MXene@In2S3 under visible light irradiation. All these indicated that the synergistic effect of type-II heterojunction and TiO2/Ti3C2Tx interface provided a shorter and more direct channel for electron transfer between In2S3, TiO2 and MXene. When bioaerosol was sterilized by dynamic continuous flow photocatalytic reactor carrying monolayer MXene@In2S3, it can reach 1.55 lg in 9.6 s (multilayer MXene@In2S3 was 1.19 lg). Biological particles of different particle sizes were effectively removed from the bioaerosol. The excellent photocatalytic disinfection performance was due to the oxidation substances (holes, ·O2– and ·OH) produced by the photocatalyst under visible light irradiation. Microbial cell membrane permeability was disrupted, causing irreversible physical damage that will ultimately lead to sustained inactivation within 16 h. Due to the unique physical and chemical properties of the two-dimensional material MXene, it has scope for further exploration in the field of disinfection and air purification.

Continuous flow photocatalytic reactor using TiO2‐coated foams, modeling and experimental operating mode

AbstractThis article aims to build a modeling and simulating tool of the operation of a continuous flow heterogeneous photocatalysis reactor. Continuous flow is well‐known in reactor engineering for allowing advanced control of reactor and scaling‐up with great confidence, but little research has addressed it's potential for this kind of application. In developing this model, particular attention was paid to the coupling which occurs at local scale between the radiative transfer and the reaction kinetics of advanced oxidation of a target organic micro‐pollutant. The solution of the radiative transfer equation by Monte Carlo method was applied to a photocatalyst supported on a macroporous ceramic foam forming an efficient 3D support. After identification of the kinetic law of degradation, the dynamic simulation model was validated through comparison with a series of experiments performed for different but constant irradiations and for variable irradiations approaching, in term of intensity and dynamics, natural solar radiation.

Design Aspects of a Continuous Flow Photocatalytic Reactor and its Application to Degrade Methylene Blue and Textile Wastewater

AbstractA continuous flow photocatalytic reactor was developed by combining the reaction kinetics and mass balance concept. The concept of cascade aerator was also considered in designing it as a stepped reactor. The reactor was used to investigate the photocatalytic degradation of methylene blue in aqueous solution by Ag+ doped TiO2 (2 g/L) under UV irradiation by 15 W UV lamps (254 nm). Methylene blue solution (20 ppm) was found to be decolorized by >99, 97, 85 and 57 % under flow rates of 1, 1.5, 2 and 3 L/h, respectively after 120 minutes. The corresponding mineralization was >80, 78, 75 and 54 %, respectively. At higher flow rates (Re number 208.2 and 415.5) >99 % decolourization was achieved by recycling the solution 5 and 7 times with fresh doses of photocatalyst. At steady state, maintained by repeating the addition of photocatalyst at fixed time intervals, the dye solution could be decolourized continuously by >99, 97 and 76 % at flow rates of 1, 2 and 3 L/h, respectively while the mineralization was >82, 79 and 62 %, respectively. The reactor was also effectively used to mineralize textile wastewater collected from a textile mill in Kolkata. The mineralization was greater than 75, 73 and 64 % at flow rates of 1, 2 and 3 L/h, respectively after 120 minutes. The efficiency of the reactor depended upon the residence time of the contaminant in the reactor. At steady state, the design data simulated well with the corresponding experimental data.

Synthesis and performance of a composite photocatalyst based on polyester-supported carbon nitride nanosheets for selective oxidation of anisyl alcohol

Heterogeneous photocatalysis represents an essential organic synthesis strategy for the sustainable development of new routes to the highly efficient production of fine chemicals. This work describes a coating method using polyester fibre (PES) to support carbon nitride nanosheets (GCN-TS). PES surface was treated with HNO3 aqueous solutions with different concentrations (0.2 – 5% v/v), which enhanced the adhesion of the GCN-TS on PES fibres. The surface of coated PES treated with 1% v/v HNO3 results in a homogeneous deposition of the photocatalyst and increased hydrophilicity. The photocatalytic synthesis of p-anisaldehyde by oxidation of anisyl alcohol in an aqueous solution assisted by 417 nm visible light-emitting diodes resulted in 95% yield operating in batch mode. The prepared material could be reused, maintaining its photocatalytic performance during five consecutive tests. Aiming at industrial processing, the synthesis of anisaldehyde was performed using the same catalyst in a continuous flow photocatalytic reactor. The performance of the process depends on the residence time of the mixture containing the reactant, as the contact with the immobilised photocatalyst determines the yield.

Photocatalytic disinfection of different airborne microorganisms by TiO2/MXene filler: Inactivation efficiency, energy consumption and self-repair phenomenon

Bacteria, fungi and viruses are airborne microorganisms, which can survive and spread in the form of aerosols, posing a serious threat to human health. A dynamic continuous flow photocatalytic reactor containing TiO2/MXene filler was developed to study the inactivation characteristics of four different microorganisms treated by ultraviolet and photocatalysis. By establishing the kinetic fitting model (−lgNpcN0=εAbΦNE1IrtPC+A), it was known that there were differences in the inactivation efficiency of airborne microorganisms with different microstructures. The introduction of catalysis greatly reduced the energy consumption of disinfection. The electrical efficiency per log order (EE/O) of UV254 inactivated E. coli was reduced from 0.012 to 0.015 kW·h·m−3 to 0.0016–0.0040 kW·h·m−3. Furthermore, the self-repair phenomenon was not obvious in a very short time (40 h) under UV irradiation, but the microbial activity continued to decline after photocatalytic treatment. Short wave ultraviolet had stronger penetration than long wave ultraviolet. High radiation intensity can provide more photons and produce more reactive oxygen species (ROS) for photocatalysis, while too high humidity (RH=95%) will inhibit it. Appropriate residence time (4.3 s) can efficiently treat airborne microorganisms with higher concentration (109 CFU·m−3). These external factors affected the photocatalytic disinfection process of different kinds of microorganisms.

Reducing the risk of exposure of airborne antibiotic resistant bacteria and antibiotic resistance genes by dynamic continuous flow photocatalytic reactor

In this study, based on the dynamic photocatalytic reactor constructed by the new photocatalyst TiO2/MXene, the purification process of different biological particles in aerosol was systematically studied. Multidrug resistant bacteria were easier to inactivate than common bacteria of the same kind, whether under UV conditions or photocatalysis. Photocatalyst was loaded on porous polyurethane sponge filler so that the combined effect of adsorption and advanced oxidation significantly improved the antibiotic resistant bacteria (ARB) disinfection effect. The inactivation efficiency of two ARBs under UV254 increased by 1.2 lg and 2.1 lg. In addition, it was found that the microorganisms treated by UV had slight self-repair phenomenon in a short time, while the microbial activity decreased continuously after photocatalysis. With the addition of photocatalyst, the particle size distribution of airborne Escherichia coli decreased and the micro morphology of cells was more seriously damaged. Antibiotic resistance genes (ARGs) carried by ARB can be dissociated into the environment after cell destruction, but it can be removed at a high level (sul2 can achieve 2.11 lg) in the continuous reactor at the same time. While avoiding secondary pollution, it also provides a powerful solution for airborne ARGs control.

Simple Fabrication of a Continuous-Flow Photocatalytic Reactor Using Dopamine-Assisted Immobilization onto a Fluoropolymer Tubing

A flow reactor has been found to be advantageous for a photocatalytic reaction due to enhanced transport phenomena and photon transfer. A fluoropolymer is a promising material for fabricating a photocatalytic flow reactor because it is transparent, commercially available, and inexpensive. However, its high hydrophobicity and chemically inert nature makes it difficult to coat photocatalysts. In this work, we successfully developed a protocol to immobilize photocatalysts (TiO2–P25) onto the wall of a perfluoroalkoxy alkane tubing. The immobilization was enabled by the initial depositions of polydopamine and polyethyleneimine (PEI) layers. Then, through an ionic interaction, P25 was immobilized onto the PEI layer. A layer-by-layer PEI–P25 assembly yielded a high photocatalyst loading, which in turn enhanced the photocatalytic activity significantly. A continuous-flow operation of the photocatalytic methylene blue decolorization was demonstrated with negligible leaching of the photocatalysts and minimal loss in activity over time. A transport phenomenon inside the tubular reactor was modeled to elucidate the effect of the process parameters on kinetic and adsorption parameters. This simply fabricated flow reactor shows a great potential for photocatalytic applications.

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles.

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic nanoparticles is developed. Guidelines for the replication of the reactor and its operation are provided in detail. Three different composite systems (Pt/graphene, Pt/TiO2, and Au/TiO2) with monodisperse and uniformly distributed particles are produced by this reactor, and the photodeposition mechanism, as well as the synthesis optimization strategy, are discussed. The synthesis methods and their technical aspects are described comprehensively. The role of the ultraviolet (UV) dose (in each excitation pulse) on the photodeposition process is investigated and the optimum values for each composite system are provided.

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles

Continuous-Flow Photocatalytic Degradation of Organics Using Modified TiO2 Nanocomposites

In this study, TiO2 nanotubes (TNTs) were fabricated on a Ti sheet following the anodic oxidation method and were decorated with reduced graphene oxide (RGO), graphene oxide (GO), and bismuth (Bi) via electrodeposition. The surface morphologies, crystal structures, and compositions of the catalyst were characterized by field emission scanning electron microscopy, Auger electron spectroscopy, X-ray diffraction, photoluminance spectra, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. The TNTs loaded with RGO, GO, and Bi were used in a continuous-flow system as photocatalysts for the degradation of methylene blue (MB) dye. It was found that the TNTs are efficient photocatalysts for the removal of color from water; upon UV irradiation on TNTs, the MB removal ratio was ~89%. Moreover, the photocatalytic activities of the decorated TNTs were higher than that of pristine TNTs in visible light. In comparison with TNTs, the rate of MB removal in visible light was increased by a factor of 3.4, 3.2, and 2.9 using RGO-TNTs, Bi-TNTs, and GO-TNTs, respectively. The reusability of the catalysts were investigated, and their quantum efficiencies were also calculated. The cylindrical anodized TNTs were excellent photocatalysts for the degradation of organic pollutants. Thus, it was concluded that the continuous-flow photocatalytic reactor comprising TNTs and modified TNTs is suitable for treating wastewater in textile industries.

Preparation of pumice-loaded CeO2/Bi2WO6 photocatalysts and treatment of tetracycline wastewater with a continuous flow photocatalytic reactor

Pumice-loaded CeO2/Bi2WO6 photocatalysts were prepared with a typical solvothermal method by using pumice as the macroporous carrier. The photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and element mapping. The preparation conditions were optimized and the photoactivity was evaluated via photocatalytic tetracycline degradation under visible light radiation. Moreover, the photocatalysts were applied to a continuous flow reactor and the optimal conditions were studied. It was found the CeO2/Bi2WO6 catalysts were successfully loaded on the surfaces and pores of pumice. The optimal catalyst/pumice loading ratio was 1:4 mmol/g, and the average load rate of the photocatalysts was 37.24%. Under visible-light irradiation, the pumice-loaded CeO2/Bi2WO6 catalysts could well photocatalytically degrade tetracycline, with a degradation rate within 90 min up to 91.72%, and were stable photocatalytically. Experiments with the continuous flow reactor showed the optimal catalyst quantity, light source intensity, pollutant concentration and hydraulic retention time were 10 g/L, 140,000 lx, 50 mg/L and 6 h, respectively, when the tetracycline degradation rate was stably improved to 90.00%.

Synthesis of sponge-loaded Bi2WO6/ZnFe2O4 magnetic photocatalyst and application in continuous flow photocatalytic reactor

The magnetic photocatalyst Bi2WO6/ZnFe2O4 was loaded on the surface of polyurethane sponge with polyvinyl butyral (PVB) as an immobilizing agent. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and element mapping. The best operating conditions of the reactor were determined to be 0.10 wt% PVB, mass ratio of sponge to catalyst = 1:1.25, volume ratio of sponge to mixture = 8 g/L and load temperature at 80 °C. The average load rate of the photocatalyst was 56.18%. The photodegradation ratio of tetracycline hydrochloride (TCH, 50 mg/L) was above 98.35% with the load of 5 g/L photocatalyst within 90 min under visible-light irradiation. The best conditions were photocatalyst quantity = 6 g/L, light source intensity = 140000 lux and pollutant concentration = 50 mg/L. The TCH photodegradation ratio reached 91.59%. The addition of PVB increased the fall-off of the photocatalyst and the magnetism of photocatalyst facilitated the recovery. The photocatalyst fall-off rate was 2.53%, and the fall-off part of the powder photocatalyst was adsorbed by magnet, and the recovery rate was 95.13%.

Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis

ABSTRACTCarbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO2) catalyst was investigated. The effects of feed flow rate, TiO2 concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO2 concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO2 concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R2 ∼ 0.964). The addition of 1 mL min−1 hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L−1, TiO2 ∼5 mg L−1 and feed flow rate ∼82.5 mL min−1. Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO2 catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.

Continuous flow photocatalytic reactor using ZnO–bentonite nanocomposite for degradation of phenol

Removal of phenol employing ZnO–bentonite nanocomposite as photocatalyst with UV irradiations is evaluated under Continuous Stirred Tank Reactor (CSTR). XRD patterns of nanocomposites indicated modifications in the lattice structure of bentonite due to intercalation of ZnO nanospheres in the matrix with particles size of 20–30 nm as revealed from TEM. Thin film of composites coated on SS plate surface exhibited ∼70% removal of phenol from the simulated effluent under at lower flow rate (10 ml min −1) and higher pH (12) at a fixed nanocomposite loading. The effluent obtained after CSTR treatment is analyzed by LC–MS which suggested that photocatalytic degradation of phenol results in the formation of adipic acid and 2,4,6-triphenoxy phenol through radical mechanism.

Transferring concepts from classical catalysis to the new field of photocatalysis

The aim of the study was to characterize the regime of operation of a newly constructed POLITEF flat-plate gas-phase continuous flow photocatalytic reactor in view of improving its construction and selecting the optimum set of operational conditions. The nanosized photocatalytic powder material (TiO2 Degussa P25, consisting of 75% anatase and 25% rutile with average anatase particle size 25 nm) was deposited as a thin film coating on a TLC aluminum sheet, pre-coated with silica gel (Merck, 0.2 μm SiO2 film), achieving loadings of 0.6 –2.0 mg TiO2/cm2. The reactor is operated either with UV light or visible light, penetrating through a quartz glass flat-plate illumination window (56 cm2 illuminated surface area). The time interval needed to reach steady-state operation conditions was established to be 5 min, applying the criterion of Wald–Wolfowitz. The model air pollutant was ethylene with a feed concentration of 1000 ppm. All the experimental runs were carried out at an optimal relative humidity of 30%, which was established in a previous work. Varying the operational parameters—ethylene contact time, ethylene/oxygen feed ratio, the kind of light and intensity of illumination—the optimum operating conditions were established, under which maximum ethylene conversion was observed. Corrigan’s criterion for the presence or absence of diffusion limitations was applied, proving that the reactor was operating in the kinetic region at low TiO2 loadings, but at high loadings, a diffusion retardation effect was observed. It was established that the flow through the reactor is laminar based on the values of the Reynolds number.

Photocatalytic decomposition of mobile-source related pollutants using a continuous-flow reactor

This study evaluated the application of a continuous-flow photocatalytic reactor for the control of two mobile-derived pollutants, methyl-tertiary butyl ether (MTBE) and naphthalene, present at in-vehicle levels. Variables tested for this study included the hydraulic diameter (HD), stream flow rate (SFR), relative humidity (RH), and feeding type (FT). The fixed parameters included contaminant concentration, ultraviolet light source, and the weight of TiO 2. In all experimental conditions the adsorption process reached equilibrium within 30 to 180 min for the target compounds, and the outlet concentrations of the photocatalytic oxidation (PCO) reactor while operating reached a steady state within 60 to 180 min. The degradation of the target compounds was dependent on RH, HD, FT, or SFR. The PCO system exhibited high degradation (up to nearly 100% for certain conditions) and mineralization efficiencies of target compounds, suggesting that this system can effectively be employed to improve indoor air quality. Moreover, it was confirmed that trichloroethylene at urban-ambient level also could enhance the degradation efficiency of naphthalene when applying the PCO technology inside vehicles.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets¶

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.