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Surface structures of nanoparticles (NPs) designed at the atomic level are vital to enhance the catalytic performance and stability of NPs. In this work, we report the engineering of plate-like and platelet-like BiVO4 NPs for the formation of heterojunctions with Bi2O3. The morphology and size of NPs were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy, SAED and powder X-ray diffraction (XRD) were carried out to show the structural composition and they confirmed monoclinic phases for both BiVO4 and Bi2O3. BiVO4 NPs notoriously have low surface area and pore volume, thus HPEI was incorporated to improve these properties. Brunuer–Emmett–Teller (BET) technique was used to characterize the surface area (SBET) of the photocatalysts and SBET was increased by 88% after the addition of 0.15 mM HPEI during synthesis. Diffuse reflectance spectroscopy was used to elucidate the optical properties of NPs and a blueshift in the heterojunctions was observed due to the incorporation of Bi2O3. Tuning of {010} monoclinic BiVO4 was achieved after the addition of 0.5 M NaCl which resulted in plate-like morphologies showing improved optical and electronic properties. Uniform platelet-like BiVO4 NPs were synthesized successfully after the addition of 0.15 mM HPEI, and this also induced impaired dispersion and size reduction. The calculated band positions of BiVO4 and Bi2O3 in the heterojunctions were well positioned for carrier charge separation, which was confirmed by the flat band potentials that were 0.553, − 0.47, − 0.70 and − 0.77 V for Bi2O3, p-BiVO4, 0.15HPEI–0.5NaCl–BiVO4–Bi2O3 and 0.5NaCl–BiVO4. [ABSTRACT FROM AUTHOR]

• Large nanotubular TiO 2 photocatalytic membranes prepared by anodization. • Galvanostatic anodization improves the process over potentiostatic conditions. • Confirmed activity for photocatalytic methanol oxidation and E.coli inactivation. • Hybrid process proved synergism between filtration and photocatalysis. • Nanotubular TiO 2 do not significantly improve activity of nanoparticulate TiO 2. Hybrid photocatalysis/membrane processes constitute promising alternatives for water and wastewater treatment because they combine the efficiencies of filtration membranes technology and the oxidative effect of the photocatalytic process, increasing the lifetime of the membranes. The main challenge of these systems is the incorporation of the titanium dioxide (TiO 2) catalyst without altering the filtration properties of the membrane and the photocatalytic activity of the catalyst. One way to achieve this goal is generating the TiO 2 layer by direct anodization of titanium supports under controlled conditions to form titanium dioxide nanotubes (TiO 2 -NTs). This work reports the development of novel photocatalytic titanium membranes based on the formation of TiO 2 -NT arrays by anodization under both potentiostatic and galvanostatic conditions, and the scaling-up of the most promising systems to operational membrane photoreactors. The results demonstrated that the galvanostatic method displays more controlled tuneability to obtain NTs formation than the potentiostatic method on porous surfaces. However, despite the formation of TiO 2 -NTs structures, the observed photocatalytic activity is lower than that exhibited by TiO 2 nanoparticles deposited directly on the membrane, although in this case the transmembrane pressure is significantly higher, and therefore the operational pumping costs are greater. Synergistic effects of photocatalysis and microfiltration are clearly demonstrated in the application of the hybrid system to the removal of bacteria for water disinfection processes, showing a significant improvement in the inactivation of E. coli bacteria in water with respect to the bare membrane. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New mechanistic kinetic model proposed for NO x photocatalytic oxidation. • Intrinsic kinetic parameters for NO x removal determined in the ISO 22197-1 reactor. • Radiation homogeneity validated by numerical simulation. • Plug flow hypothesis confirmed by computational fluid dynamics simulation. • Successful model validation with prediction errors in the conversion below 13%. Abstract An air purification reactor working under the standard ISO 22197-1 is studied and used for the determination of the intrinsic kinetic parameters of the NOx photocatalytic removal. A new mechanistic kinetic model considering explicitly the radiation step is proposed. The derived reaction rate expressions for NO and NO 2 include the dependence on the concentration of NO, NO 2 and the local superficial rate of photon absorption. The air purification reactor was modelled using a numerical simulation methodology to validate homogeneity of the light distribution reaching the catalyst surface and go deep in the knowledge of fluid dynamic behaviour. Based on these results, general guidelines of the reactor behaviour working under the ISO 22197-1 standard can be stablished, being the first time that this reactor is modelled with a global predictive approach. Radiation intensity over the catalyst surface was confirmed to reach the specified value of 10 ± 0.5 W m−2. Plug flow can be applied in the studied reactor with an axial dispersion module lower than 0.001. However, the diffusion of chemical species in the reactor was also studied, as well as the impact of mass transfer phenomena on the accuracy of the calculated kinetic parameters. A comprehensive simulation model of the ISO reactor, including fluid dynamics, radiation, photochemical reaction and mass transfer was developed. The simulation results confirm that the kinetic parameters obtained without considering mass transfer limitation fail to reproduce the experimental data, whereas a global error lower than a 17% was achieved including the diffusion of the species in the reactor. The proposed methodology, experimentally validated, could be successfully applied to the prediction of the performance of different type of photocatalytic reactors or even open systems for NOx pollutants. [ABSTRACT FROM AUTHOR]

Abstract: A three‐dimensional numerical model was solved for a turbulent incompressible steady flow and the discrepancies and similarities between the software OpenFOAM® and ANSYS® Fluent on the flow modeling were analyzed. The evaluation was performed for the meshing, setup, and simulation step of the modeling process. Outcomes were contrasted with experimental data to validate the fluid flow obtained with both softwares. With this aim, an experimental pulse‐response technique was applied to obtain the residence time distribution (RTD) curve to be compared with the RTD curves achieved from the modeling. Additionally, images of the tracer transport in the experimental reactor were taken, showing good agreement with the computational fluid dynamics (CFD) predictions. [ABSTRACT FROM AUTHOR]

This work describes the procedure for the simulation of the operation of a photocatalytic reactor by using a multiphysics computational fluid dynamics (CFD) model based on the determination of the intrinsic kinetics parameters in an optically differential photoreactor. The model includes the rigorous description of the hydrodynamics, radiation transfer, mass transport and chemical reaction rate based on a mechanistic kinetic model. Possible existence of dead and recirculation zones has been identified from the flow field, showing a non-uniform flow through the reactor domain. The theoretical laminar profile is not reached due to the short length of the annular core and the departure from the ideal models has been quantified. The predicted velocity field has been experimentally validated with good agreement by injecting a tracer. The radiation field was simulated for slurry TiO 2 suspensions with concentrations between 0.005 and 5 g·L −1 , showing an optimum catalyst loading around 0.1–0.2 g·L −1 . Above this value, the increase in the absorption of radiation is negligible, whereas a more non-uniform radiation profile develops, keeping the most external regions of the reactor in the dark. The results of photocatalytic activity, using methanol oxidation as test reaction, showed good agreement between model predictions and experimental data, with errors between 2% and 10% depending on the catalyst concentration. The successful validation confirms not only the scientific background of the model, but also supports its applicability for engineering purposes in the design and optimization of large scale photocatalytic reactor to overcome some of limitations hindering the industrial development of this technology. [ABSTRACT FROM AUTHOR]

A novel method for preparing hybrid polymer-titania nanotube (TNT) arrays with promising optical, catalytic and filtration applications is reported. The procedure is based on a one-step rapid galvanostatic anodization followed by the transfer of the TNT arrays to a polymer support by applying heat and pressure. The fraction of open-ended tubes can be controlled by changing the intensity of the current at the end of the anodization step. For example, completely open-ended or close-ended TNT arrays can be obtained by applying high or low current intensity, respectively at the end of the anodization process. The reported procedure allows the one-step simple and rapid preparation of flexible hybrid polymer-TNT materials which have great potential for photonic flow-through membranes. [ABSTRACT FROM AUTHOR]

This work focused on the computational fluid dynamics (CFD) modeling of H2/N2 separation in a membrane permeator module containing a supported dense Pd-based membrane that was prepared using electroless pore-plating (ELP-PP). An easy-to-implement model was developed based on a source–sink pair formulation of the species transport and continuity equations. The model also included the Darcy–Forcheimer formulation for modeling the porous stainless steel (PSS) membrane support and Sieverts' law for computing the H2 permeation flow through the dense palladium film. Two different reactor configurations were studied, which involved varying the hydrogen flow permeation direction (in–out or out–in). A wide range of experimental data was simulated by considering the impact of the operating conditions on the H2 separation, such as the feed pressure and the H2 concentration in the inlet stream. Simulations of the membrane permeator device showed an excellent agreement between the predicted and experimental data (measured as permeate and retentate flows and H2 separation). Molar fraction profiles inside the permeator device for both configurations showed that concentration polarization near the membrane surface was not a limit for the hydrogen permeation but could be useful information for membrane reactor design, as it showed the optimal length of the reactor. [ABSTRACT FROM AUTHOR]

• Heterojunction BiVO 4 -Bi 2 O 3 proved to be viable for degradation of atrazine in water. • The heterojunction formation improved photodegradation of atrazine. • Atrazine was degraded to a less toxic compound, cyanuric acid. • Holes, hydroxyl, and superoxide radicals were responsible for the degradation. Conventional methods have been reported to fail to completely remove contaminants of emerging concern (CECs) during wastewater treatment. Thus, new methods are required to improve wastewater treatment to completely remove the CECs from water. In this paper, we present the degradation of atrazine in aqueous solution using heterojunctions of BiVO 4 and Bi 2 O 3 that were synthesized from different morphologies of BiVO 4 (truncated octahedron, plate-like, and platelet-like). The nanoparticles (NPs) were characterized using a scanning electron microscope, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. It was observed that the heterojunctions were successfully synthesized and the observed morphologies for the BiVO 4 were truncated octahedron, plate-like and platelet-like. The most effective heterojunction in the removal of atrazine was 0.5NaCl-BiVO 4 -Bi 2 O 3. The 0.15HPEI-0.5NaCl-BiVO 4 -Bi 2 O 3 had a reduced reaction rate compared to 0.5NaCl-BiVO 4 -Bi 2 O 3 , even though characterization showed that it was expected to be the most effective of all the NPs. The degradation of atrazine proceeded through dehalogenation, followed by the dealkylation and further deamination into cyanuric acid, a stable and less toxic compound. Data from LCMS/MS showed the formation of hydroxyatrazine, desethylhydroxyatrazine, and ammeline as intermediates. The degradation of several concentrations of atrazine revealed that the heterojunction efficiently removed >90 % of atrazine. [ABSTRACT FROM AUTHOR]