Photocatalytic Reactor Research Articles

Bismuth Vanadate Encapsulated with Reduced Graphene Oxide: A Nanocomposite for Optimized Photocatalytic Hydrogen Peroxide Generation

The photocatalytic H2O2 production is a sustainable and eco-friendly process. Bismuth vanadate (BiVO4 or BVO) is a promising photocatalyst with a low band gap energy. Reduced graphene oxide (rGO) is known for promoting the transport of charges and preventing the recombination of photogenerated electron–hole pairs. This study proposes a synthesis method based on an electrostatic self-assembly approach for functionalizing BVO with GO for photocatalytic H2O2 generation. Different amounts of GO loading on BVO have been taken to assess and optimize the quality of xrGO–BVO (where x = 0.5, 1, 2, and 4 wt %) composites for effective H2O2 generation. H2O2 shows stability under acidic conditions; hence, the effectivity of the xrGO–BVO was tested using acids with different strengths. 1rGO–BVO exhibited efficient H2O2 generation in the presence of oxalic acid, promoting two-electron O2 reduction reaction with a good cyclic stability. A photocatalytic flow reactor study has also been presented to assess the feasibility of continuous H2O2 generation.

3D-printed polyamide structures coated with TiO2 nanoparticles, towards a 360-degree rotating photocatalytic reactor

3D-printed polyamide structures coated with TiO2 nanoparticles were obtained by a simple impregnation method. This novel type of 3D reactor was evaluated for its photocatalytic activity towards the degradation of methylene blue under UV light using a 360-degree rotating stage. Rotation improved the photocatalytic activity under UV light for all the 3D structures. The best photocatalytic structure showed a 94.1 % methylene blue degradation, after 180 min under UV irradiation with 360-degree rotation.

Engineering waveguide surface by gradient etching for uniform light scattering in photocatalytic applications

In photoreactors, non-uniform light distribution leads to regions either with an overabundance of light or insufficient light irradiation. The integration of light-guiding elements such as waveguides into photocatalytic reactors has been an emerging approach to improve light delivery. However, traditional waveguides with constant surface properties experience an exponential decay in scattering light intensity under side irradiation. This reduces the light propagation length and hinders the scale-up potential. In this work, we derive the relationship between attenuation coefficients with etching time, determine the correlation between etching time and waveguide location for uniform scattering, and experimentally validate different light scattering profiles by engineering the surface roughness distribution of waveguides. We apply a dimensionless number, the coefficient of variation, to characterize the relative light distribution uniformity for gradient-etched, uniform-etched, and unmodified waveguides. Scattering light uniformity via gradient etching is more than 13 times higher than that for uniform-etching. In addition, the light distribution for gradient etching exhibits improved uniformity than other approaches, such as tip coating, physical carving, and engineered pillars. We then evaluate the effect of different light scattering profiles on photocatalytic activities in a photodegradation test for methylene blue, with non-etched, uniform-etched, and gradient-etched waveguides serving as internal light-guiding elements. Gradient-etched waveguides show ∼4 times improvement in photodegradation activity over uniform-etched designs and ∼8 times over non-etched configurations. This result underscores gradient etching for waveguides as a viable approach for precision light delivery to increase the light distribution uniformity, thus enhancing reaction rates for photocatalytic reactors.

Application of ZnO-Nd Nano-Photocatalyst for the Reactive Red 198 Dye Decolorization in the Falling-Film Photocatalytic Reactor.

A large amount of Reactive red 198 (RR198) is released yearly into the environment. RR198 is toxic for human and aquatic creatures; therefore, it should be removed from wastewater before releasing into the environment. In this study, the nano ZnO-Nd -photo-catalyst for the first time was synthesized by the combustion method. First, the physical characteristics of the generated nano photocatalyst were evaluated using FESEM, XRD, Bandgap calculation, and FTIR analysis. Then, the ZnO-Nd nano-photocatalyst was suspended into the contaminated water with RR198 dye in a falling-film photocatalytic reactor. The effects of parameters such as the amount of H2O2, catalyst dose, pH, and initial concentration of dye were investigated during the experiments. Finally, the decolorization process with the falling-film photocatalytic reactor was optimized using response surface methodology (RSM). The physical characteristics showed that the average particle size of the synthesized ZnO-Nd was 40 nm. Doping ZnO with Nd reduced the photocatalyst energy bandgap by 14%. The results indicated that the optimum amount of catalyst dose and pH level was 0.1 g/L and 5, respectively. The simultaneous usage of H2O2 and ZnO-Nd with an H2O2/dye ratio of two increased dye removal performance by 90%. The results demonstrated that the developed equations can be applied to predict the performance of the falling-film photoreactor. This study showed that using the nano ZnO-Nd photocatalyst in a falling-film photocatalytic reactor under optimum operating conditions is an appropriate way to remove RR198 from water.

Anodic TiO2 Nanotubes on 3D-Printed Titanium Meshes for Photocatalytic Applications.

In this work, large 3D Ti meshes fabricated by direct ink writing were wirelessly anodized for the first time to prepare highly photocatalytically active TiO2 nanotube (TNT) layers. The use of bipolar electrochemistry enabled the fabrication of TNT layers within the 3D Ti meshes without the establishment of an electrical contact between Ti meshes and the potentiostat, confirming its unique ability and advantage for the synthesis of anodic structures on metallic substrates with a complex geometry. TNT layers with nanotube diameters of up to 110 nm and thicknesses of up to 3.3 μm were formed. The TNT-layer-modified 3D Ti meshes showed a superior performance for the photocatalytic degradation of methylene blue in comparison to TiO2-nanoparticle-decorated and nonanodized Ti meshes (with a thermal oxide layer), resulting in multiple increases in the dye degradation rate. The results presented here open new horizons for the employment of anodized 3D Ti meshes in various flow-through (photo)catalytic reactors.

Photocatalytic Degradation of Skim-Latex-Vapor Odor Using Iron-Doped Zinc Oxide

The photocatalytic degradation of the vapor odor of skim natural rubber latex, which is composed of volatile organic compounds (VOCs-NR), was conducted using iron-doped zinc oxide (Fe-ZnO) photocatalyst nanoparticles. The research objectives were to study the photocatalyst, to develop the photocatalytic reactor used for the photodegradation of VOCs-NR, and to analyze the odor reduction of the degraded VOCs-NR. Fe-ZnO was prepared by the sol-gel method and immobilized onto fiberglass cloth as the support material, followed by annealing. The Fe-ZnO nanoparticles were dispersed on the fiberglass surface. A photocatalytic reactor was developed for the gas phase. The research findings showed that gas chromatography-mass spectroscopy detected 24 dominant chemical components in the VOC-NR stock before photocatalytic degradation. The components decreased to 11 after 30 min, only 3 components remained after 40 min of the photocatalytic process, and no component was observed after 80 min of photoirradiation. An organoleptic test was conducted to validate that the odor degraded to a very low level.

3D-printed photoreactor with robust g-C3N4 homojunction based thermoset coating as a new and sustainable approach for photocatalytic wastewater treatment

Recently, the rapid technological advancement in photocatalysis has gained popularity as a means of addressing climate change and environmental degradation issues. The rapid surge in interest for 3D-printing process has delivered solutions for a broad spectrum of needs primarily due to its flexibility, cost effectiveness and environmental friendliness. In addition, the development in synergizing photocatalysis and 3D-printing technology has provided an optimistic outlook for sustainable wastewater treatment. In present study, a 3D-printed photocatalytic reactor was successfully designed and constructed via digital light processing technique. Besides that, a visible-light sensitive photocatalyst, graphitic carbon nitride homojunction was synthesized via a facile hydrothermal approach. The as-developed photocatalyst was then prepared in a form of thermoset coating and subsequently applied onto the base of 3D-printed photoreactor. A series of characterization tests were conducted to gain an in-depth understanding of the surface morphology and topology, chemical structure, thermal stability, elemental compositions, and surface wettability of the photocatalyst system. The photocatalytic performance of the graphitic carbon nitride homojunction-based thermoset coating was evaluated via Rhodamine B (RhB) dye degradation under the irradiation of a 50 W LED light. A removal efficiency of 95.62% was achieved within 24 h with a corresponding kinetic rate constant of 2.1 × 10−3 min−1. The recyclability of the photocatalytic system was verified by assessing its photoactivity for five consecutive cycles and retained 98.5% of its initial photoactivity. Overall, this research work may intrigue more exploration between interdisciplinary researchers in the field of photocatalysis and additive manufacturing, especially for sustainable environmental remediation.

Estimation of the radiation field for CPC photocatalytic reactors using a novel six-flux model in two dimensions (SFM-2D)

In the present work, we introduced a new Six Flux Model in two dimensions (SFM-2D) for the estimation of the local volumetric rate of photon absorption (LVRPA) in polar coordinates. This novel model was applied on a compound parabolic collector (CPC) photocatalytic reactor using the Ray-Tracing Technique (RTT) and Lambert's cosine law. The volumetric rate of photon absorption per unit reactor length (VRPA/H) and overall volumetric rate of photon absorption (OVRPA), calculated with SFM-2D, were compared with SFM-1-DR (diffuse reflectance) and SFM-HG (Henyey-Greenstein).We obtained an analytical solution of the radiant transfer equation (RTE) based on a novel SFM-2D. The most relevant result was a simple algebraic expression from a detailed mathematical development. In addition, we included Lambert's cosine law and the radiation absorption by the fluid to estimate the radiant field in a compound parabolic photoreactor CPC. The numerical results, obtained with simulations, were compared satisfactorily to those reported in previous works at different operating conditions; the global performance of the new model described discrepancies less than 0.5%.

Photocatalysis for arsenic removal from water: considerations for solar photocatalytic reactors.

The following work provides a perspective on the potential application of solar heterogeneous photocatalysis, which is a nonselective advanced oxidation process considered as a sustainable technology, to assist in arsenic removal from water, which is a global threat to human health. Heterogeneous photocatalysis can oxidize trivalent arsenic to pentavalent arsenic, decreasing its toxicity and easing its removal with other technologies, such as chemical precipitation and adsorption. Several lab-scale arsenic photocatalytic oxidation and diverse solar heterogeneous photocatalytic operations carried out in different reactor designs are analyzed. It was found out that this technology has not been translated to operational pilot plant scale prototypes. General research on reactors is scarce, comprising a small percentage of the photocatalysis related scientific literature. It was possible to elucidate some operational parameters that a reactor must comply to operate efficiently. Reports on small-scale application shed light that in areas where other water purification technologies are economically and/or technically not suitable, and the solar energy is available, shed light on the fact that solar heterogeneous photocatalysis is highly promissory within a water purification process for removal of arsenic from water.

Efficient Hydrogen Production by an rGO/TiO2 Composite Material from Ammonia Borane Hydrolysis in a Photocatalytic Reactor

Efficient Hydrogen Production by an rGO/TiO₂ Composite Material from Ammonia Borane Hydrolysis in a Photocatalytic Reactor

Absorbed radiation and kinetic model in photocatalysis by TiO2

Abstract The current work studies a novel and affordable methodology to estimate and quantify the photon flux absorbed and the amount of light that leaves from an illuminated photocatalytic system with TiO2 suspended in water. To achieve it, a new parameter B F S λ w a t $BF{S}_{\lambda }^{wat}$ is defined and presented. It indicates, for every wavelength, the fraction of the incoming radiation which is not absorbed by the system. B F S λ w a t $BF{S}_{\lambda }^{wat}$ was estimated by means of actinometric experiments in a jacketed reactor and a model based on Beer–Lambert law. For wavelengths below 388 nm and TiO2 concentrations between 0.05 and 2 g L−1, experimental values of B F S λ w a t $BF{S}_{\lambda }^{wat}$ were between 0.77 and 0.27. In the second part of the work, a simple kinetic model, which breaks down the effect of incident radiation and kinetic constant, is developed. For this, the photon flux absorbed by TiO2, previously determined, was included in the model. This new model was tested in the photocatalytic degradation of 2,4-dichlorophenol under different TiO2 concentrations. The kinetic model fits satisfactorily the experimental values and a new kinetic constant kʹ ap [mol·L−1 Einstein−1] was obtained, which is independent of the amount of catalyst loaded to the system. This achievement may be very useful for an easy initial comparison, design or scaling up of different photocatalytic reactors with similar geometry.

Feasibility of Solar Updraft Towers as Photocatalytic Reactors for Removal of Atmospheric Methane-The Role of Catalysts and Rate Limiting Steps.

Due to the alarming speed of global warming, greenhouse gas removal from atmosphere will be absolutely necessary in the coming decades. Methane is the second most harmful greenhouse gas in the atmosphere. There is an emerging technology proposed to incorporating photocatalysis with solar updraft Towers (SUT) to remove methane from the air at a planetary scale. In this study, we present a deep analysis by calculating the potential of methane removal in relation to the dimensions and configuration of SUT using different photocatalysts. The analysis shows that the methane removal rate increases with the SUT dimensions and can be enhanced by changing the configuration design. More importantly, the low methane removal rate on conventional TiO2 photocatalyst can be significantly improved to, for example, 42.5% on a more effective Ag-doped ZnO photocatalyst in a 200 MW SUT while the photocatalytic reaction is the rate limiting step. The factors that may further affect the removal of methane, such as more efficient photocatalysts, night operation and reaction zone are discussed as possible solutions to further improve the system.

A flow-circulation reactor for simultaneous photocatalytic degradation of ammonia and phenol using N-doped ZnO beads

In this study, a novel continuous flow-circulation photocatalytic reactor was acquired for treatment of synthetic wastewater containing a binary mixture of ammonia and phenol. Performance of the photo-reactor was examined using synthesized N-Doped ZnO Beads (N-ZnB) within the existence of Hydrogen peroxide (H2O2) and UV irradiation. The Beads of catalyst were synthesized using modified sol–gel method. A protocol was followed for the characterization of N-ZnB catalyst by performing some common analytical methods such as SEM, EDS, Raman and DRS. N-Doping narrows in band gap energy as calculated from DRS the band gab energy reduced from 3.2 eV to 3.16 eV and reduces electron – hole pair recombination and accordingly improves the efficiency of ammonia and phenol photo-degradation. The optimum photo-degradation conditions were detected by examining the effect of operational parameters as the flow rate, pH, catalyst dosage, H2O2 concentration and initial concentration for both ammonia and phenol. At optimum conditions, N-ZnB catalyst achieved 98.3% and 95.8% degradation for both ammonia and phenol, respectively, after 2 hr of UV irradiation. Also, the reusing ability and strength of N-ZnB was investigated. The developed beads could be used as an effective catalyst for the degradation of binary mixture of ammonia and phenol from wastewater.

Theoretical study on flow and radiation in tubular solar photocatalytic reactor

Theoretical study on flow and radiation in tubular solar photocatalytic reactor

Solar chimney power plant integrated with a photocatalytic reactor to remove atmospheric methane: A numerical analysis

Methane (CH4) is the second largest contributor to global warming among all greenhouses gases. A solar chimney power plant integrated with a photocatalytic reactor (SCPP-PCR) is a promising large-scale method for removing CH4 from the atmosphere. This study used computational fluid dynamics (CFD) to investigate the performance and factors influencing photocatalytic oxidation of methane by the SCPP-PCR system. The geometry of a SCPP is the same as the prototype of the SCPP built in Manzanares (Spain). The PCR is designed based on a honeycomb monolith photoreactor. The numerical results revealed that the SCPP-PCR system can degraded 21,312 g methane per day with the actual solar radiation data when the channel diameter of the honeycomb PCR was 4 mm and channel length was 8 m. Although increasing the length or decreasing the channel diameter of the PCR would improve photocatalytic efficiency, the rate of airflow of the system would be reduced. The maximum methane purification rate of the SCPP-PCR system was determined.

Integrated process approach for degradation of p-cresol pollutant under photocatalytic reactor using activated carbon/TiO2 nanocomposite: application in wastewater treatment.

Over the years, biodegradation has been an effective technique for waste water treatment; however, it has its own limitations. In order to achieve a higher degradation efficacy, integrated processes are being focus in this area. Therefore, the present study is targeted towards the coupling of biodegradation and photocatalytic degradation of p-cresol. The biodegradation of p-cresol was performed via lab isolate Serratia marcescens ABHI001. The obtained results confirmed that ~85% degradation of p-cresol was accomplished using Serratia marcescens ABHI001 strain in 18 h. Consequently, degradation of remaining residue (remaining p-cresol concentration initially used) was also examined in a batch reactor using activated carbon-TiO2 nanocomposite (AC/TiO2-NC) as a catalyst under the exposure of UV radiation. The AC/TiO2-NC was processed via sol-gel technique and characterized by various techniques, namely Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transformed infrared spectroscopy (FT-IR). The investigation allowed p-cresol degradation further augment up to ~96% with the help of spectrophotometer trailed by high performance liquid chromatography (HPLC). This study demonstrates that integrated process (biodegradation-photodegradation) is the cost-effective bioremediation process to overcome such kinds of pollutant issues.

Modelling and simulation of a photocatalytic reactor at high TiO2 concentrations

AbstractThis work presents a model of an annular batch slurry photocatalytic reactor using titanium dioxide at high concentrations and pH close to 7. The model considers the effects of the agglomeration of catalyst particles that take place when the reactor operates close to neutral pH. It also includes the adsorption/desorption equilibrium of the contaminant on the catalyst during 1 h in darkness, followed by the photochemical reaction under UV irradiation. The reactor was modelled by a system of differential equations solved using the Micro‐Cap 12 program. This powerful software package numerically solves the differential equations as an equivalent network, providing a convenient graphical interface for model programming and plotting of results. The model was validated with measurements at several catalyst concentrations from 1–2.5 g/L. Aeroxide P25, supplied by Evonik, was used as catalyst, with UV irradiation at a wavelength of 254 nm. Orange II, a widely used azo dye, was chosen as the model contaminant. The model results were in satisfactory agreement with the experimental data. Simulations were carried out with different initial conditions, to analyze the influence of the system variables on the performance of the reactor. In this way, the optimal design criteria at high catalyst concentrations were found. The mathematical model is simple and robust and can be applied in a straightforward way to the design and scaling of photocatalytic reactors. It is also particularly attractive for educational purposes.

Reduction of nitrates in a photocatalytic membrane reactor in the presence of organic acids

The present study explores the capability of the Photocatalytic Membrane Reactor (PMR) technology to remove nitrates from drinking water sources in the presence of organic electron donors. A systematic investigation was performed in a laboratory-pilot PMR, employing a hybrid TiO2/UV-A catalysis–ultrafiltration process, using formic acid as the most favorable hole scavenger for nitrate reduction. The naturally occurring humic acid as well as the cheaper and harmless acetic acid were also tested as sacrificial electron donors. The performance of the PMR system was evaluated in respect of nitrate and Total Organic Carbon (TOC) percentage removal. The results demonstrate the superiority of formic acid regarding nitrate reduction, followed by acetic acid and humic acid, as well as the negligible effect of nitrates on organic mineralization. Formic acid was further used to assess the effects of molar organic/nitrate ratio, catalyst dosage and power of irradiation per unit volume (PR) on nitrate reduction. With the present laboratory-pilot, the near optimum nitrate removal was ~60 % and the TOC reduction ~85 %; selectivity to dinitrogen was in the range 65–90 %. Key issues for improving this synergistic process and related R&D directions are discussed.

TiO2/SiO2 Coated 310S Stainless Steel for Hydrogen Peroxide Generation via Photocatalytic Reaction

The photocatalytic reactor was designed by assembling the parts of a photocatalyst, an ultraviolet light source and an air distribution. This prototype reactor was used to generate H2O2 via photocatalytic reaction. TiO2 and TiO2/SiO2 prepared from sol-gel method were coated on 310S stainless steel substrate using dip-coating technique. Rice husk ash was used as the source of SiO2. The major phase of all the pure TiO2 and SiO2 particles was anatase and amorphous, respectively. The surface analysis showed the coated TiO2 and TiO2/SiO2 with an average roughness of 365.391 and 1322.001 nm, respectively, compared with the average thickness of coated TiO2 which was measured to be 2.7325 μm and for TiO2/SiO2, which was 4.7856 m. The results also showed the coating of TiO2/SiO2 was highly porous at the surface compared with pure TiO2. The TiO2/SiO2 show good photocatalytic reaction activity because SiO2 doping on TiO2 increased the adsorption of O2 and H2O molecules towards the photoactive center of TiO2. Thus, the incorporation of SiO2 onto the photocatalyst helped to increase photocatalytic activity. The generation of H2O2 increased with increasing ambient humidity up to 60% RH, but then decreased. This behavior was explained by the effect of water vapor adsorption on the SiO2 surface. The air flowrate enhanced the generation of H2O2, higher air flow rate produced a higher amount of H2O2. H2O2 was generated at the highest concentration of 64 ppmv from the TiO2/SiO2 photocatalyst at ambient humidity of 60% RH and air flowrate 8.20 m/s.

Experimental and modelling studies on the photocatalytic generation of hydrogen during water-splitting over a commercial TiO2 photocatalyst P25

Hydrogen, generally perceived as an environmentally friendly fuel, possesses the potential to lower society's dependency on fossil energy sources whose utilization leads inherently to global warming problems. Its photocatalytic generation from aqueous solutions is a promising green technology competitive to traditionally employed methods such as steam reforming or water electrolysis. However, the limiting yet achievable efficiencies of this process remain unclear. To address the question of process efficiencies, we formulate a phenomenological model predicting the behavior of an experimental photocatalytic reactor. The model considers the polynomial light intensity distribution, the concentration of photocatalysts, and the finite rate of the mass transfer between liquid and gas phases. We validate the model against experimental data obtained from a study with a commercially available TiO2 P25 photocatalyst used as a gold standard in photocatalysis. The theoretical analysis shows that the mass transfer of hydrogen from the liquid to gas phase significantly affects the photoreactor dynamics. Initial accumulation of hydrogen in the liquid phase and its delayed transport to the gas phase result in a nonlinear time-dependence of the hydrogen concentration in the gas phase. The theoretical average reaction rate reaches a maximum for a photocatalyst concentration of 0.23 g/L, which is in good agreement with an experimentally obtained value of 0.25 g/L. The photonic efficiency, defined as a ratio of the average reaction rate to the average light intensity, also reaches a maximum at the same catalyst concentration and interestingly remains constant for any higher TiO2 loads. Finding the optimal photocatalyst concentration and identifying the critical role of mass transfer shall aid further research in developing and optimizing photocatalytic reactors for hydrogen production in the future.