Photocatalytic Reactor Research Articles

Porous fixed-bed photoreactor for boosting C–C coupling in photocatalytic CO2 reduction

Solar-driven CO2 conversion to chemical fuels in an aqueous solution is restricted not only by photocatalysts but also by mass transfer. Here, a regulatable three-phase interface on a porous fixed-bed is constructed for efficient C–C coupling in photocatalytic CO2 reduction. The photocatalytic results show that ∼90% selectivity towards C2+ products is obtained by a Cu/Cd0.5Zn0.5S photocatalyst, with a yield of 6.54 ​μmol/h (an irradiation area of 0.785 cm2), while only 0.94 ​μmol/h (an irradiation area of 19.625 cm2) is achieved with a commonly used suspension photocatalytic reactor. We find that under the same CO2 feed rate, the local CO2 concentration in this porous fixed-bed photoreactor is obviously higher than in the suspension photoreactor. The larger local CO2 coverage derived from a higher CO2 supply and aggregation enhances the C–C coupling, thereby generating more C2+. Even an observable three-phase interface on the porous fixed-bed can be regulated by adjusting the CO2 supply, for which the optimal gas inlet rate is 5–10 sccm.

Photocatalytic Reactor as a Bridge to Link the Commercialization of Photocatalyst in Water and Air Purification

The development of clean and sustainable teleology is vital to treat the critical environmental pollutants. In the last decade, the use of photocatalytic reactors has been widely reported for organic pollutants degradation. From photocatalysis’s application in environmental remediation, the primary technical issue to scientists is always the efficiency. The enhanced photocatalytic efficiency is mainly depended on the materials improvement. However, the design of photoreactors lags behind the development of photocatalysts, which strongly limit the widespread use of photocatalysis technology in environmental remediation. The nanoparticles separation, mass transfer limitation, and photonic efficiency have always been problematic and restrict the high photocatalytic efficiency of photoreactors. To overcome these bottleneck problems, the most popular or newfangled designs of photoreactors employed in air and water treatment has been reviewed. The purpose of this review is to systematize designs and synthesis of innovative TiO2-based photoreactors and provides detailed survey and discussion on the enhanced mechanism of photocatalytic performance in different TiO2-based photoreactors. The most studied photoreactors are the following: packed bed reactor, film reactor and membrane reactor, which have some limitations and advantages. A comprehensive comparison between the different photocatalytic performance of TiO2-based photoreactors is presented. This work aims to summarize the progress of TiO2-based photoreactors and provides useful information for the further research and development of photocatalysis for water and air purification.

Degradation of pollutants in solid and gas states using waterborne acrylic nanocomposite paints

In this study, TiO2/SiO2 nanoparticles were synthesized using titanium tetraisopropoxide and tetraethoxysilane in a two-step sol-gel route. FTIR, XRD, UV–Vis, and XPS techniques were used to characterize the synthesized nanoparticles. Fe-SEM was utilized to evaluate the particle size of the synthesized nanoparticles (30.35 ± 4.52 nm). Photo-degradation of rhodamine B (Rh.B) as a solid pollutant model and NO2 as a typical gaseous pollutant was assessed on the surface of the waterborne-acrylic coatings containing TiO2/SiO2 nanoparticles (TSC.La) under direct sunlight irradiation and accelerated weathering conditions and the results were compared with a P25–TiO2 nanoparticle (UT.La) embedded coating samples.To evaluate the degradation of Rh.B, color coordinates (L*a*b*) were measured, while the degradation of NO2 was determined in a batch-designed photocatalytic reactor by measuring the reduction in gas concentration. For the TSC.La-sample exposed to accelerated weathering conditions, the changes in a* parameter (Δa*) were about 60%, which was 44 times greater than the changes in this parameter for the sample exposed to sunlight. The surface morphology of the exposed samples to the accelerated weathering conditions was evaluated using AFM and BET measurements. The AFM results indicated that TiO2/SiO2 nanoparticles lead to less surface degradation of the paints compared to the commercial TiO2 nanoparticles. NO2 concentration decreased steadily in the reactor from 30 to 27 ppm, at an RH%<20 in the presence of UT.La or TSC.La-samples after 45 and 60 min of UV exposure. This reduction in gas concentration is equivalent to photocatalytic power of 6 and 8 mLm−2h−1, for the two samples, respectively.

Retention and Inactivation of Quality Indicator Bacteria Using a Photocatalytic Membrane Reactor

The development of effective disinfection treatment processes is crucial to help the water industry cope with the inevitable challenges resulting from the increase in human population and climate change. Climate change leads to heavy rainfall, flooding and hot weather events that are associated with waterborne diseases. Developing effective treatment technologies will improve our resilience to cope with these events and our capacity to safeguard public health. A submerged hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using ultraviolet-C low-pressure mercury lamps, as well as ultraviolet-C and ultraviolet-A light-emitting diodes panels) and the combination of both treatment processes (membrane filtration and photolysis) to retain and inactivate water quality indicator bacteria. The developed photocatalytic membranes effectively retained the target microorganisms that were then successfully inactivated by photolysis and advanced oxidation processes. The new hybrid reactor could be a promising approach to treat drinking water, recreational water and wastewater produced by different industries in small-scale systems. Furthermore, the results obtained with membranes coated with titanium dioxide and copper combined with ultraviolet-A light sources show that the process may be a promising approach to guarantee water disinfection using natural sunlight.

Construction of novel metal-free graphene oxide/graphitic carbon nitride nanohybrids on carbon cloth and efficient degradation of RhB under visible light irradiation

Photocatalytic technology has a wide range of application prospects, but due to the low degradation efficiency of photocatalytic materials at the present stage, difficult to recycle and other problems, seriously restricted its development, so it is urgent to prepare the efficient photocatalytic material. This article reports a novel metal-freephotocatalyst of the construction of graphene oxide (GO)/graphite-phase carbon nitride (g-C3N4) heterojunction on carbon cloth (CC). The GO/g-C3N4 /CC photocatalyst has excellent degradation rate of Rhodamine B (RhB) in the visible light. Due to the formation of a heterojunction between g-C3N4 and GO, the light absorption of the photocatalyst was improved and the rapid recombination of photocarriers was reduced. After 5 cycles, there was no significant reduction in photocatalytic activity. We designed a new type of multi-layer membrane filter photocatalytic reactor, RhB put into the device to simulate the flow of waste water and degrade. The results show that the filter film photocatalyst shows good photocatalytic activity of RhB degradation. The introduction of carbon cloth substrate solves the problems of separation and cycle life of this photocatalyst.

Inactivation of plant pathogenic bacterium Ralstonia solanacearum in drainage solution from hydroponic system by a rotating advanced oxidation contactor equipped with TiO2/zeolite composite sheets

A rotating advanced oxidation contactor (RAOC) equipped with TiO2/zeolite composite sheets was developed to inactivate the plant pathogenic bacterium Ralstonia solanacearum in drainage solution (DS) from a hydroponic system. The inactivation efficiency of R. solanacearum in DS and pure culture solution (PS) by the RAOC was compared with that achieved by a submerged composite sheet photocatalysis reactor (SSPR). The initial number of living bacteria (N0) was adjusted to around 106–107 CFU mL−1. The inactivation efficiency of R. solanacearum by the SSPR at 4.0 × 107 CFU mL−1 of N0 significantly decreased compared with that at 1.8 × 106 CFU mL−1 of N0 owing to the attenuation of UV intensity by light absorption and scattering by solids derived from R. solanacearum, while the RAOC achieved >2-log inactivation during 24 h of treatment regardless of N0. The inactivation of R. solanacearum by the RAOC decelerated after 6 h, possibly because of competition for reactive oxygen species between R. solanacearum and products accumulated by inactivation of R. solanacearum. The ratio of rate constants for inactivation of R. solanacearum in DS to that in PS by the RAOC was 8 times that for the SSPR. This shows that the RAOC greatly mitigates the light attenuation and inhibitory effects of coexisting substances on inactivation of R. solanacearum in the DS. The RAOC is therefore a promising and upscalable photocatalytic reactor for efficient inactivation of R. solanacearum in DS.

Designing dual-defective photocatalyst of Z-scheme H-BiVO4/D-NG composite with hollow structures for efficient visible-light photocatalysis of organic pollutants

Photocatalytic degradation using sunlight is attractive due to its high efficiency, low cost and environmental friendliness. This study successfully synthesized a dual-defective H-BiVO4/D-NG hollow structure photocatalyst was discretely decorating hollow BiVO4 (H-BiVO4) on dual defect graphene (D-NG) by hydrothermal method. The characterization of the structure, morphology, optical and electrochemical properties was carried out. The effects of different catalysts, annealing temperature, catalyst dosage and different reaction temperature on the photocatalytic degradation of BPA were investigated to explore the property of photocatalytic reactor. Especially, the H-BiVO4/D-NG composite showed the highest photocatalytic activity, which could degrade 98% of BPA in 30 min and remove 81% of total organic carbon (TOC) in 120 min. In addition, the cycling experiments and XRD patterns before and after the photocatalytic reaction showed that the catalyst exhibited outstanding stability, which is conducive to practical applications in the field of photocatalysis. Furthermore, electron spin resonance (ESR) and active radical trapping experiment indicated that the prepared nanocomposites followed a direct Z-scheme mechanism. The results showed that a combined strategy of introducing defect engineering and morphology control in photocatalyst design can effectively improve photocatalytic activity. It's expected to provide new ideas for the preparation of high-performance photocatalysts.

Photocatalytic reactors and their scale up: literature review

Photocatalysis reactions have been extensively studied for the degradation of recalcitrant substances. It is known that the activation of the photocatalyst occurs with the absorption of photons of energy greater than or equal to the band gap, causing electrons from the valence band to be transferred to the conduction band, resulting in a gap in the valence band. On a laboratory scale, many works have already been developed. The most used configuration is the cylindrical reactor, where the light source is placed in the center, immersed in the reaction medium, protected by a quartz cell. Xenon, LED and mercury lamps are the most used due to the wavelength at which they emit electromagnetic radiation. Heterogeneous catalysts are also used to improve the efficiency of the process, but when used dispersed in the medium, there is a difficulty in separating them after the operation, and when used immobilized, there are barriers related to their fixation in the system. For the scale up, a change in the lighting source to sunlight, replacement of quartz by glass, and different ways of reusing the catalysts for greater economy were observed.

Transport and surface reaction model of a photocatalytic membrane during the radical filtration of methylene blue

• A photocatalytic membrane was fabricated for water purification and it was tested and described. • Synergy between photocatalytic degradation and membrane filtration is explored. • Simple 1D mass transport model describes the dead-end photocatalytic membrane process. • A methylene blue discoloration of 68–23% was reached with the lowest to the highest filtration rate. This study explores the synergy between photocatalytic oxidation and membrane filtration using a photocatalytic membrane. Titanium dioxide coated alumina membranes were fabricated and tested in a customized Photocatalytic Membrane Reactor (PMR) module. The discoloration of methylene blue (MB), 3.2 mg·L −1 in an aqueous solution, was evaluated in dead-end filtration mode. A simple 1D analytic transport and surface reaction model was used based on advection and diffusion, containing intrinsic retention by the membrane and reaction kinetics to predict the permeate concentration. The discoloration of MB by the photocatalytic membrane could be well described by a single retention and reaction rate constant (second Damköhler number) for fluxes from 1.6 to 16.2 L·m −2 ·h −1 . The model furthermore indicates the potential synergy between membrane retention, which leads to increased concentration, and accompanying photocatalytic conversion, at the membrane surface.

Heteropoly acid nanocomposite for disinfection and dye removal of licorice wastewater: fabrication of a novel fixed-bed photocatalytic reactor

Heteropoly acid nanocomposite for disinfection and dye removal of licorice wastewater: fabrication of a novel fixed-bed photocatalytic reactor

Photocatalytic degradation of pesticide monocrotophos in water using W-TiO2 in slurry and fixed bed recirculating reactor

Slurry and fixed bed Recirculating type photocatalytic reactor (RTPR) was fabricated to study the degradation of monocrotophos pesticides in water using W-doped TiO2. Different parameters such as light conditions, dopant concentration, calcination temperature, catalyst loading, and initial concentration of MCP at pH = 5 were optimized in the slurry reactor and about 99% of MCP degradation in 200 min was observed. The catalyst was also immobilized on the Clay beads. The photoactive efficiency of W-TiO2 coated clay beads was tested using RTPR for the degradation of MCP (2L, 25 mg L−1) at its natural pH under solar irradiation conditions (600 W m−2 avg.) at an optimized flow rate of 400 ml min−1 and controlled temperature of 25 ± 1 °C and 100% degradation of MCP was observed in 360 min of reaction time. Furthermore, 91.57% and 87.89% reduction in COD of MCP was observed while analyzing the mineralization studies of suspended and fixed bed reactors, respectively.

Glass coated-nanostructure semiconductor TiO2/RGO/MoS2 for dye removal and disinfection of wastewater: Design and construction of a novel fixed-bed photocatalytic reactor

In the field of applied semiconductor, TiO2/RGO/MoS2 nanocomposite as a high performance photocatalyst has been synthesized. Prepared semiconductor has been coated on borosilicate glass rods with a facile one pot process and imbedded in the photoreactor chamber. Fabrication and presentation of an appropriate photoreactor for effective wastewater treatment has been developed. In this photoreactor continuous air by producing bubbles provides an effective mixing of the target solution. The performance of the designated system has been examined by investing the photocatalytic degradation of rhodamine B (RhB) and was more than 95% dye removal. Electrochemical investigation (Mott-Schottky, Nyquist and Bode plots) showed that long electron lifetime of TiO2/RGO/MoS2 is the main reason for high photoactivity of this nanocomposite. Optimization of the different parameters such as influence of bubbling and light intensity of the photoreactor, the initial pH and the initial concentration of RhB on the photocatalytic performance have been also studied. TOC of the reaction were conducted which showed good mineralization. The photocatalyst powder was characterized by BET, BJH, SEM, EDX, FT-IR, XRD, EIS, and ICP-OES. Low leaching has been confirmed by ICP investigation. Photocatalytic treatment of liquorice factory wastewater in several concentrations has been also studied. Disinfection capability of TiO2/RGO/MoS2, in designated system for liquorice factory wastewater has been investigated. This system is so effective to eliminate harmful microorganisms. Total coliform for liquorice factory wastewater with a 21000 MPN/100 before treatment reached to zero MPN/100 after treatment in optimum reaction conditions.

3D printed, plastic photocatalytic flow reactors for water purification

3D printing is known as a fast, inexpensive, reproducible method for producing prototypes but is also fast becoming recognised as a scalable, advanced manufacture process. Two types of lab-scale, 3D printed plastic, fixed-film, flow-through photocatalytic reactors are described, both of which are sinusoidal in shape, and only differ in that one has no baffles, reactor A, whereas the other has, reactor B. Both reactors are lined with a P25 TiO2/polylactic acid (PLA) coating, which, after UVA pre-conditioning, is used to photocatalyse the bleaching of circulating aqueous solutions of either methylene blue, MB, or phenol, PhOH, repeatably, without any obvious loss of activity. The rate of the photocatalysed bleaching of MB exhibited by reactor B shows a much lower dependence upon flow rate than reactor A, due to the greater lateral mixing of the laminar flow streams produced by the baffles. The photonic efficiencies of reactor A for the photocatalysed bleaching of MB and PhOH were determined to be 0.025% and 0.052%, respectively, and the photocatalytic space-time yields (PSTY) to be 0.98 × 10−4 and 1.49 × 10−4 m3 of reaction solution.m−3 reactor volume.day−1.kW−1, respectively. This is the first example of an all plastic, 3D printed photocatalytic reactor and demonstrates the advantages of 3D printing for prototyping. Given the 3D printing is a scalable process, possible potential areas of application are discussed briefly.Graphical abstract

Effective green ammonia synthesis from gaseous nitrogen and CO2 saturated-water vapour utilizing a novel photocatalytic reactor

The ammonia synthesis from nitrogen and hydrogen derived from water vapor in the photocatalytic process performed under mild conditions is presented. A new solution of a gas-phase photocatalytic reactor with the bed in the form of a UV transparent glass fiber cloth coated with AEROXIDE® P25 TiO2 was applied. The bed in the reactor is located just above the water surface. The gases circulate from above towards the water surface, where the produced ammonia is easily absorbed and continuously separated from the gas phase, shifting the ammonia synthesis equilibrium towards the product. The highest amount of ammonia (about 1.3 mmol NH4+/g TiO2 after 6 h) was obtained at 20 °C, and with the use of the gaseous mixture containing CO2 (15%), N2 (85%), and water vapour derived from water located at the bottom of the reactor. Carbon dioxide in the reaction environment is simultaneously reduced to carbon monoxide and methane.

Comparative Efficiencies for Phenol Degradation on Solar Heterogeneous Photocatalytic Reactors: Flat Plate and Compound Parabolic Collector

Phenol is a recalcitrant anthropogenic compound whose presence has been reported in both wastewater and drinking water; human exposure to phenolic substances can lead to health problems. The degradation of phenol (measured as COD decrease) through solar heterogeneous photocatalysis with immobilized TiO2 was performed in two different reactors: a flat-plate reactor (FPR) and a compound parabolic collector (CPC). A 23 full factorial experimental design was followed. The variables were the presence of TiO2, H2O2 addition, and the type of reactor. Data were fitted to the pseudo-first-order reaction-rate-kinetics model. The rate constant for photocatalytic phenol degradation with 1 mM of H2O2 was 6.6 × 10−3 min−1 for the FPR and 5.9 × 10−3 min−1 in the CPC. The calculated figures of merit were analyzed with a MANCOVA, with UV fluence as a covariate. An ANCOVA showed that the type of reactor, H2O2 addition, or fluence had no statistically significant effect on the results, but there was for the presence of TiO2. According to the MANCOVA, fluence and TiO2 presence were significant (p &lt; 0.05). The CPC was on average 17.4% more efficient than the FPR when it came to collector area per order (ACO) by heterogeneous photocatalysis and 1 mM H2O2 addition.

Integrating Photocatalysis and Microfiltration for Methylene Blue Degradation: Kinetics and Cost Estimation

AbstractMethylene blue degradation by the UV/TiO2 and UV/TiO2/H2O2 photocatalysis in a suspended photocatalytic reactor coupled with a microfiltration (MF) module is described. The kinetics of methylene blue degradation, cake layer formation on the membrane surface, and the energy consumption of the system are evaluated and discussed. In addition, cost estimation of the treatment of methylene blue by different processes is implemented. The investment and operating costs of the photocatalytic membrane reactors are calculated and compared with the UV systems and UV/TiO2‐MF.

Comparative study of energy consumption, kinetic, and performance between conventional and baffled photocatalytic reactor (BPCR) to ofloxacin photo-degradation.

Regarding the cost-effective photo-degradation of ofloxacin (OFL), present study investigates UV/sulfite /ZnO (USZ) in reactor conventional (without baffles) and baffled photocatalytic reactor (BPCR). The optimal condition was 0.77:2:50 sulfite/ZnO/OFL molar ratio, pH 7, and 30 min reaction time for 100% degradation of 200 mg L-1 concentration of OFL. As information obtained, the UZI process reduces the BOD and COD level about 66% to 86.29% within 80 min reaction, respectively. Also, BOD/COD ratio initial from 0.26 reaches 0.6 after 30 min of reaction time. Kinetic investigation increasing OFL concentration, kobs and robs increase, and, secondly, in the conventional and BPCR reactor, kobs increase is about 17% and 50% with increasing OFL concentration from 50 to 200 mgL-1. Also, figure-of-merit EEo varies from 12.66 to 17.41 and 7.26 to 10.15 kWhm3 for conventional reactor and 8.66-13.61 to 5.24-8.12 kWhm3, respectively. Also, kinetic model EEo declines from 15.23 to 8.61 and from 13.31 to 5.37 kWh m-3 in conventional and BPCR, respectively. Total cost of the system (TCS) decreases from 7.31 to 2.16 $ in conventional reactor and 4.57 to 0.55 $ in PCBR reactor. Total cost of the system (TCS) was investigated at different concentrations.

A solar-driven CPC photoreactor for decomposition of emerging contaminants in wastewater: Modeling and optimization

In the present work, a new component parabolic collector (CPC) was introduced as a solar photocatalytic reactor and applied in pilot-scale for degradation of Phenazopyridine (PhP) via a Solar/H2O2/S2O82-/TiO2 process. The TiO2 nanoparticles were immobilized on the outer surface of CPC receivers’ tubes by physicochemical processes. Field emission scanning electron microscopy (FESEM) was demonstrated a favorable attachment of nanoparticles on the glass tubes. Low Ti leaching during repeated experiments was approved by inductively coupled plasma (ICP) analysis. The final degrading by-products of PhP were identified and analyzed by gas chromatography-mass spectroscopy (GC-MS) analysis. Moreover, the impact of the effective parameters on the degradation of PhP during dual oxidation process in a solar-driven photocatalytic reactor such as flow rate, oxidant, PhP concentration, and pH was investigated and simulated with Artificial Neural Network (ANN) analysis and optimized with Genetic Algorithm (GA) and Ant Colony Algorithm (ACA). Consequently, the toxicity of effluent was tested with plants in optimal conditions when the oxidation step proceeded. This report summarized the current status of solar photocatalysis favorable photocatalytic activity under solar light irradiation enhanced with CPC photoreactor which was successfully prepared. Guided by studies to explore the determination of optimal conditions for disinfection of real municipal wastewater, the biological treatment was investigated. In addition, the antibacterial assessment was considered to determine the presence of bacteria after solar disinfection.

On-site reduction of nitrogen oxides at an emission hotspot using actively vented photocatalytic reactors in a highway tunnel

This study presents our solution of an active nitric oxides (NOx) control method for large traffic tunnels. A titanium dioxide (TiO2) coated carrier material is assessed using lab-based photocatalysis experiments, leading to a coating with high photocatalytic activity (deposition speed of 1.4 cm/s for nitrogen monoxide, NO). The coating is tested on several carrier materials to maximize the interaction between the reactive surface and the pollution molecules in the air. Several reactor prototype geometries and carrier materials are simulated and tested on a pilot plant scale. A coated PU-foam with 3 cm thickness and porosity of five pores per inch proved to be the most effective carrier material, while a reactor design with vertically flowed stacks of the foam carrier is capable of optimally exploiting the potential of the photocatalytic coating for high volume flows. With data from on-site measurements of the atmospheric conditions and pollution in the highway tunnel ‘Rudower Höhe’ in Berlin, Germany, we could build a simulated tunnel setup of our reactors within the tunnel. An estimate based on these simulations assumes a reduction potential of 25% of the NOx mass generated in the tunnel. In conclusion, actively vented TiO2 surfaces are controversial yet could achieve high removal rates while simple to clean or exchange.

Kinetic modeling of binary mixture of butyraldehyde and acetone with generated by-products in photocatalytic oxidation reactor

This research reports the development of a kinetic model to predict binary mixture degradation and by-product generation in a continuous flow Photocatalytic Oxidation (PCO) reactor. Butyraldehyde and acetone were chosen as a binary VOC mixture to validate the model using experiments conducted with a photocatalyst (TiO2 coated on silica fibers) under various concentration levels (0.1–1 ppm), concentration ratios of target compounds in the mixture (0.5–2), relative humidity levels (17–70%), irradiations (7–23.5 W/m2), and airflow rate (10–30 L/min). Formaldehyde, acetaldehyde, propionaldehyde, butyric acid, propionic acid, and acetic acid were detected as by-products, in which aldehydes had a higher quantity. Carbon balance analysis showed that butyraldehyde and binary mixtures mineralized into carbon dioxide at rates of 19% and 12.8%, respectively. Also, 24% of butyraldehyde and 10% of binary mixture were converted to by-products. Among three proposed scenarios for PCO reaction rate of butyraldehyde, the one including conversion of butyraldehyde directly towards propionaldehyde, acetaldehyde, and formaldehyde, provided the most accurate rate model (R2 = 0.98). Due to its faster reaction rate, butyraldehyde demonstrated a higher degradation efficiency than acetone in the binary mixture. At a constant butyraldehyde concentration, lowering the ratio of butyraldehyde/acetone to 0.5 resulted in the reduction of removal efficiency of butyraldehyde and an increase in concentration of acetaldehyde in air than other by-products. Conversely, enhancing this ratio to 2, led to improved removal efficiency of both butyraldehyde and acetone in the mixture and higher concentration of formaldehyde. Increases in air relative humidity level and velocity resulted in an increase in the outlet concentration of challenge compounds but reduced the formation of all by-products. However, raising the irradiation increased the degradation efficiency of butyraldehyde and binary mixture and, consequently, elevated the formation of by-products. The developed model was capable of properly predicting the concentration of the challenge compounds and their by-products in a binary mixture at different operating conditions.