Photochemical Reactor Research Articles

Gas‐phase OH oxidation kinetics of pyrazine, pyrimidine, and pyridazine

AbstractThe gas‐phase kinetics of the OH‐oxidation of three six‐membered nitrogen heterocycles C4N2H4 isomers, namely pyrazine, pyrimidine, and pyridazine, were determined in a photochemical reactor coupled to a FTIR spectrometer and a SPME‐GC/MS, at atmospheric pressure over the temperature range 298–353 K. Experiments were conducted using the relative rate method where two different references were employed for each studied compound. The obtained Arrhenius expressions are (in cm3 molecule–1 s–1) urn:x-wiley:05388066:media:kin21486:kin21486-math-0001These results were compared with available literature data for other heterocyclic compounds and discussed in terms of structure–reactivity and temperature dependency. Their tropospheric lifetimes with respect to reaction with OH radicals were then calculated and found to be of the order of 29, 34, and 37 days for pyrazine, pyrimidine, and pyridazine, respectively.

The CO2 photoconversion over reduced graphene oxide based on Ag/TiO2 photocatalyst in an advanced meso-scale continuous-flow photochemical reactor.

This study aims at examining the use of an advanced meso-scale continuous-flow photochemical reactor for the photocatalytic conversion of CO2 with water into fuel over TiO2 (P25), Ag/TiO2, and Ag/TiO2/RGO catalysts. The silver loaded photocatalysts were prepared by one-step process via hydrothermal method. The prepared photocatalysts were characterized by various characterization techniques in order to identify the morphological, chemical, physical, and optical properties. The photocatalytic activity of the as-prepared catalysts was firstly examined by the photoelectrochemical (PEC) measurements and secondly by the photocatalytic reduction of CO2 in the proposed setup. Liquid products were analyzed using gas chromatography-mass spectrometry (GC-MS) and total organic carbon (TOC) techniques. It was found that the ternary composite revealed an outstanding performance towards CO2 photocatalytic reduction, where its selectivity was directed towards methanol production. The incorporation of graphene nanosheets enhanced the photocatalytic reduction of CO2 by 3.3 and 9.4 times compared with Ag/TiO2 and bare TiO2, respectively, using the proposed photochemical reactor in a continuous mode. This study sheds the light on a novel type of a photocatalytic reactor where CO2 conversion over Ag/TiO2/RGO ternary composite was evaluated. A meso-scale continuous-flow photochemical reactor.

Mobility of insecticide residues and main intermediates in a clay-loam soil, and impact of leachate components on their photocatalytic degradation

This work assesses the behavior (adsorption, degradation and leaching) of four insecticides (chlorantraniliprole, thiametoxam, imidacloprid and pirimicarb) and their main reaction intermediates in a clay-loam textured soil (1.6% OM). Following the batch equilibrium method, the KOC (as log values) ranged from 1.2 to 3.9 (thiametoxam and pirimicarb, respectively). All the insecticides were moderately persistent (t½ = 39–100 days) in the following order: thiametoxam > imidacloprid > pirimicarb > chlorantraniliprole. Two major transformation products, desmethyl-formamido pirimicarb and desmethyl pirimicarb, were formed as consequence of dealkylation of the parent compound. Using disturbed soil columns only thiametoxam (93% of the initial amount) and imidacloprid (42% of the initial amount) were recovered from leachates. In the case of pirimicarb and chlorantraniliprole, 74% and 30%, respectively, were recovered from the soil. Thiametoxam and imidacloprid can be catalogued as mobile compounds, while pirimicarb and chlorantraniliprole are classified as immobile according to the screening indices used (GUS and ELI). Leachates containing thiametoxam and imidacloprid were subjected to photocatalytic treatment for 240 min using TiO2/Na2S2O8 with the help of a photochemical reactor equipped with LED lamp. Both compounds had a very fast degradation rate (half-lives ≤ 0.5 min) in deionized water, while their half-lives were 112 min and 178 min, respectively, in leaching water. This implies a strong effect of the water matrix composition, mainly due to organic matter dissolved (quenching). Only traces of thiametoxam urea and hydroxy imidacloprid were detected during the photocatalytic experiment.

Synthesis of Acridinium Photocatalysts via Site-Selective C–H Alkylation

Acridinium dyes have been broadly used as photocatalysts, but it remains synthetically challenging to fine-tune their catalytic performance by functionalization of their structural cores. Acridiniu...

Improving removal rate and efficiency of As(V) by sulfide from strongly acidic wastewater in a modified photochemical reactor

ABSTRACT Employing ultraviolet light to enhance the removal of As(V) by sulfide (S(-II)) from strongly acidic wastewater is a potential method. However, we found the arsenic trisulfide (As2S3) and elemental sulfur (S8) particles formed in this method not only vastly hinder light transmission in the wastewater but also undergo light-induced redissolution, leading to a decrease in removal rate and efficiency of As(V). Herein, As(V) removal by sulfide from strongly acidic wastewater was performed in a modified photochemical reactor to weaken the effect of the formed particles on As(V) removal. It was found that in this study, the formed particles could be efficiently removed from the photoreactor by three operations, i.e. circulation-filtration, septum setting, and lamp sleeve cleaning. The removal of As(V) was approximately 11-fold faster than that without three operations, saving 90.9% of the reaction time and 89.4% of energy consumption. The removal efficiency of As(V) also increased through weakening the light-induced redissolution of the formed particles. This study facilitates the practical application of the UV light promoted As(V) removal technology and also provides a new method to lessen the light-blocking effect in the particle-forming photochemical reaction systems.

Microfluidic Preparation of 89Zr-Radiolabelled Proteins by Flow Photochemistry.

89Zr-radiolabelled proteins functionalised with desferrioxamine B are a cornerstone of diagnostic positron emission tomography. In the clinical setting, 89Zr-labelled proteins are produced manually. Here, we explore the potential of using a microfluidic photochemical flow reactor to prepare 89Zr-radiolabelled proteins. The light-induced functionalisation and 89Zr-radiolabelling of human serum albumin ([89Zr]ZrDFO-PEG3-Et-azepin-HSA) was achieved by flow photochemistry with a decay-corrected radiochemical yield (RCY) of 31.2 ± 1.3% (n = 3) and radiochemical purity >90%. In comparison, a manual batch photoreactor synthesis produced the same radiotracer in a decay-corrected RCY of 59.6 ± 3.6% (n = 3) with an equivalent RCP > 90%. The results indicate that photoradiolabelling in flow is a feasible platform for the automated production of protein-based 89Zr-radiotracers, but further refinement of the apparatus and optimisation of the method are required before the flow process is competitive with manual reactions.

Identification and Model Predictive Control (MPC) of Aqueous Polyvinyl Alcohol Degradation in UV/H2O2 Photochemical Reactors

The performance of two continuous UV/H2O2 photoreactors in series under unsteady-state condition is studied. An input–output dynamic model is constructed to describe the degradation of water-soluble polyvinyl alcohol (PVA) in photoreactors. Identification techniques, AutoRegressive with eXogenous input (ARX) and AutoRegressive Moving Average with eXogenous input (ARMAX), are employed to construct transfer functions. The simulation is carried out for an open-loop operation by applying step changes to the input variables (PVA and H2O2 inlet concentrations and PVA feed flow rate) using the developed model. For effluent total organic carbon (TOC) and H2O2 concentrations as responses, a model predictive control (MPC) scheme is developed to control the photoreactors to maintain desired values of process variables for setpoint and load changes. The closed-loop simulation results show that the multi-input/multi-output (MIMO) MPC produce a good performance for tracking setpoint changes in the TOC and H2O2 concentrates at the photoreactor effluent and it is also able to handle process interactions and constraints. The MPC controller successfully suppresses stochastic disturbances of the inlet PVA concentration.

A comprehensive dynamic kinetic model for the UVC/H2O2 process: application to zinc bacitracin degradation in wastewater as a case study.

A dynamic kinetic model is presented for the UVC/H2O2-driven process. The model comprises 103 reactions, including background species, such as HCO3-/CO32-, NO2-, NO3-, SO42-, Cl-, and H2PO4-/HPO42/PO43- anions, and effluent organic matter (EfOM) was validated based on experimental data obtained for the photooxidation of the nonribosomal peptide antibiotic zinc bacitracin (Zn-Bc, 34 μmol L-1). The set of ordinary differential equations for 38 species was combined with the molar balances describing the recirculating tubular photoreactor used. Predictions for the photolytic and UVC/H2O2 processes confirmed the good agreement with experimental data, enabling the estimation of fundamental kinetic parameters, such as the direct photolysis quantum yield (Ф254 nm, Zn-Bc = 0.0143 mol Einstein-1) and the second-order rate constants for the reactions of Zn-Bc with HO•, HO2•, and O2•- radicals (2.64 × 109, 1.63 × 103, and 1.49 × 104 L mol-1 s-1, respectively). The predicted optimum process conditions correspond to [H2O2]0 = 6.8 mmol L-1 and a specific photon emission rate of 11.1 × 10-6 Einstein L-1 s-1. Zn-Bc photooxidation was significantly impacted by wastewater constituents, particularly EfOM and HCO3-/CO32- (i.e., alkalinity), resulting in a degradation rate about 32% lower compared to that obtained in deionized water. In particular, EfOM acts as a strong radical scavenger and inner filter. In addition, simulations pointed out the continuous tubular photochemical reactor as the best configuration for treating Zn-Bc-containing wastewater. This study hence provides a comprehensive modeling approach, especially useful for predicting the effect of complex water matrices on the performance of the UVC/H2O2 treatment process.

An investigation of scale effect and applicability of compact light sources in microchannel reactors applied to pollutant abatement.

In this work, the performance of microreactors irradiated with conventional (fluorescent) and UV-LED light was evaluated. For this purpose, a microfluidic reactor with an equivalent diameter of 133.5 μm was used. In addition, the effect of scale variation on the performance of photochemical reactors was assessed using reactors with three internal diameters (600, 1200, and 2300 μm), 2 residence times (30 and 60 s), and two sources of UVA radiation (A with irradiance of 115 W m-2 and B with irradiance of 44 W m-2). Also, the relationship between the configuration of the photocatalyst film and the effect of the scale on the performance of photochemical reactors was experimentally and theoretically investigated. For both cases, methylene blue dye was used as a model pollutant and titanium dioxide (TiO2) as a photocatalyst deposited on the inner wall of the photocatalytic reactors. For the residence time of 30 s, the smaller the reactor diameter, the greater was the degradation (22, 18, and 6%, respectively, for lamp A and 17, 16, and 8 %, respectively, for lamp B). The influence of the diameter of the reactor was also observed for the residence time of 60 s, but only for the reactor with a 2300-μm internal diameter. The reactors with diameters 600 and 1200 μm only showed different results when illuminated with lamp B (33 and 28% of methylene blue conversion, respectively). Moreover, computational simulation results suggested higher efficiency as the reactor's diameter is decreased and an optimum thickness of photocatalyst film to maximize the performance of devices in which photocatalytic reactions are carried out.

Nonlinear System Identification for Aqueous PVA Degradation in a Continuous UV/H2O2 Tubular Photoreactor

In this study, the performance of three black-box identification techniques using linear autoregressive with exogenous input (ARX), nonlinear ARX (NARX), and Hammerstein–Wiener (HW) algorithm to model the dynamics of UV/H₂O₂ continuous tubular photochemical reactor for the treatment of poly(vinyl alcohol) (PVA) based on experimental data is investigated. In addition, the inherent nonlinearity of the reaction process is assessed. The reactor dynamics in the NARX model is estimated by wavelet, sigmoid, and tree partition networks along with the assessment of the performance of each model. Although a sigmoid network describes the nature of chemical processes better, the results show that tree partition network-based NARX is the most suitable estimator for the studied process as represented by its highest quality of fit (91.59% for training data set and 88.17% for validation of data set), lowest loss function (mean-squared error, MSE) (0.0004279), model realizability, open-loop stability, model whiteness, and model independence.

Modeling PVA degradation in a continuous photochemical reactor using experimental step testing and process identification

In advanced oxidation processes (AOPs) operating in continuous mode, the flow rate and the concentration of oxidants such as H2O2 at the mixing point of the influent must be controlled so that the oxidant residuals in the effluent are minimized while the organic degradation is maximized. Designing a controller to regulate the oxidant flow rate and therefore, its concentration at the mixing point of the photoreactor influent, needs the determination of a reliable process dynamic model. In this study, a step testing technique is employed to construct a dynamic model for the degradation of polyvinyl alcohol (PVA) in a UV/H2O2 continuous annular photoreactor. The experimental design consists of preparing three initial PVA concentrations of 60, 280, and 500 mg PVA/L and conducting eight experimental tests for different inlet mass flow rates of H2O2 ranging from 0.336 to 125 mg H2O2/min. The process responses of pH solution and total organic carbon (TOC) are measured versus time for different step changes of H2O2 inlet flow rates. Process dynamic models represented by transfer functions of the continuous UV/H2O2 photoreactor are determined from the collected input-output data using graphical method, identification algorithm, and ARX (AutoRegressive with eXogenous) in Matlab environment. The dynamic models predict the data trend quite well. Variations of the steady state gain demonstrate that the PVA degradation in UV/H2O2 continuous photoreactor is a nonlinear process. Besides, the ARX algorithm generates reliable dynamic discrete models that could be used to develop digital controllers for computer control of the UV/H2O2 photochemical reactor.

A CFD study of an annular pilot plant reactor for Paracetamol photo-Fenton degradation

This work studies in detail the photo-Fenton degradation process of Paracetamol (PCT) on an annular pilot-plant reactor using Computational Fluid Dynamics (CFD). A cylindrical lamp emission model was originally implemented over the structure of the OpenFOAM(R) platform and a multicomponent reaction mixture model was used to compute the temporal evolution of the different species at each point of the reactor. Once the proposed model was experimentally validated, the influence of different operating conditions (i.e. different strategies for hydrogen peroxide (H2O2) dosage, use of low recirculation flow rates (Qr), and a completely uncovered lamp setup) was studied. The results of the analysis showed that a double addition of H2O2 (50% before the tank and 50% before the reactor) significantly reduces the reaction times of the process. Moreover, the overall PCT degradation rate does not change when Qr is increased, thus allowing the system to be operated with a recirculation flow three times lower than that the one used in the experiments. Thereby, the developed model allows identifying the reaction conditions that maximize the overall PCT conversion, making efficient use of H2O2 (main chemical reagent) and reducing the electrical energy consumption (recirculation flow) by operating the system under conditions present in large-scale photochemical reactors.

Characteristics of textile waste water of Bhilwara (Rajasthan) and its photocatalytic bleaching with SnO2 catalyst

During the last decade, Bhilwara has developed into a leading place in the textile industry in India. The water used in textile industry is almost entirely discharged as waste. The effluents are very complex, containing salt, surfactants, ionic metals and their metal complexes, toxic organic chemicals, biocides, and toxic anions, which are harmful to both flora and fauna existing on our planet. Degradation of these non-biodegradable organic compounds is not possible by conventional treatment processes. The analysis of waste water with different quality parameters and photocatalytic bleaching was examined by using UV light in photochemical reactor with SnO2 catalyst.

Additive Manufacturing of Functional Microarchitected Reactors for Energy, Environmental, and Biological Applications

The use of microreactors in the continuous fluidic system has been rapidly expanded over the past three decades. Developments in materials science and engineering have accelerated the advancement of the microreactor technology, enabling it to play a critical role in chemical, biological, and energy applications. The emerging paradigm of digital additive manufacturing broadens the range of the material flexibility, innovative structural design, and new functionality of the conventional microreactor system. The control of spatial arrangements with functional printable materials determines the mass transport and energy transfer within architected microreactors, which are significant for many emerging applications, including use in catalytic, biological, battery, or photochemical reactors. However, challenges such as lack of design based on multiphysics modeling and material validation are currently preventing the broader applications and impacts of functional microreactors conjugated with digital manufacturing beyond the laboratory scale. This review covers a state-of-the-art of research in the development of some of the most advanced digital manufactured functional microreactors. We then the outline major challenges in the field and provide our perspectives on future research and development directions.

Enhancement of Cr(VI) removal efficiency via adsorption/photocatalysis synergy using electrospun chitosan/g-C3N4/TiO2 nanofibers

Chitosan/g-C3N4/TiO2 (CS/CNT) nanofibers were fabricated by electrospinning technique for Cr(VI) removal through the adsorption and photocatalytic processes. The effects of crucial factors in the adsorption process including contact time (0–1440 min), pH (1–7), initial concentration of Cr(VI) (20–800 mg/L) were investigated. The photocatalytic experiment was executed in a photochemical reactor with an 800 W xenon lamp to simulate visible light. In adsorption process, at pH = 2, the adsorption capacities of chitosan (CS) nanofibers, CS/CNT10:1 (CS : g-C3N4/TiO2 = 10:1) nanofibers and CS/CNT5:1 nanofibers were 20.8, 165.3 and 68.9 mg/g, respectively, suggesting the addition of g-C3N4/TiO2 (CNT) could notably enhance the acid resistance of CS and widen its practical application. Under visible-light irradiation, the removal efficiency of Cr(VI) using CS/CNT nanofibers was appreciably improved, which was about 50 % higher than that of pure adsorption, indicating that the CS/CNT nanofibers exhibited the effective synergistic effect of adsorption and photocatalysis.

TiO2 nanofluid for oxygen mass transfer intensification in pulsed plate column

Oxygen mass transfer coefficient (kLa) is a key parameter in biochemical, photochemical, or other reactors. Pulsed plate column (PPC) has a potential application as a gas-liquid contactor. In the present work, TiO2 nanofluid mediated oxygen mass transfer intensification in PPC is studied. The pulsing velocity (A × f) and nanoparticle loading in volume percent (Φ) have an interacting effect on kLa. The effect of Φ on kLa, showed a dual regime of an increase in kLa with an increase in Φ up to a critical loading (Φ CL ) and decrease in kLa on further increase in Φ. The effect of (A × f) on kLa showed three regimes. Φ CL & kLa were found to decrease as the nanoparticle's size increased. Dimensionless correlations based on multiple regression analysis and ANN models were developed to predict the kLa values in PPC with TiO2 nanofluids.

Evaluation of the Photosonolysis Process Efficacy for the Removal of Anionic Surfactant Linear Alkyl Benzene Sulfonate from Aqueous Solutions

In this study, the experiments on the sulfonate linear alkylbenzene (LAS) solution were performed using the methylene blue active substances (MBAS) method. The effectiveness of the sonochemical and photochemical reactors for LAS degradation was evaluated with an emphasis on the effect of the contact time, pH values, type of process and initial concentrations. The experiments were carried out at the initial concentrations of 0.5 mg/L, 14.00 mg/L and 21.00 mg/L, the contact time of 8, 16, and 24 minutes, pH of 3, 7, and 11, the ultrasonic frequency of 42 kHz, the acoustic power value of 160 W, an ultraviolet lamp with 150W power and the wavelength of 254 nm. This study showed that the LAS degradation was increased along with the contact time. In addition, at alkaline pH, the removal efficiency increased as well. Overall, the results obtained from this research demonstrated that by themselves, both the sonochemical and photochemical reactors may not be useful for completely reducing the complex wastewaters with high surfactant loads, but the succession of the UV/US process has a significant effect on the removal of anionic detergents. These findings demonstrated the removal efficiency under alkaline conditions and the contact time of 24 minutes was equal to 96.97 percent.

Aflatoxin in raw peanut kernels marketed in Malaysia

The occurrence of aflatoxin in eighty-four samples of raw peanut kernels which are randomly collected from Malaysian supermarkets was examined. Analysis for aflatoxin was performed by solvent extraction and immunoaffinity clean-up followed by the determination using high performance liquid chromatography equipped with post-column photochemical reactor for enhanced detection and fluorescence detector. A detection limit of 0.01-0.09 ng/mL and a quantification limit of 0.04-0.30 ng/mL were obtained. The aflatoxin concentrations ranged from not detected to 97.28 ng/g in all samples investigated. About 78.57% of the samples were contaminated with aflatoxin, of which 10.71% exceeded the maximum tolerable limit of 15 ng/g set by the Codex. Average recoveries of the aflatoxin analysis were acceptable which were in the range of 74.85 ± 8.83% for AFG2 at the concentration of 0.15 ng/mL and 103.91 ± 6.45% for AFB2 at the concentration of 0.15 ng/mL. The average daily intake estimated for total aflatoxins was 10.69 ng/kg body weight. There was a significant difference (P < 0.05) in aflatoxin content between brands and locations.

Photo-generation of mercury cold vapor mediated by graphene quantum dots/TiO2 nanocomposite: On line time-resolved speciation at ultra-trace levels

Mercury speciation was achieved using a nanocomposite, consisting of graphene quantum dots (GQDs) and TiO2 nanoparticles, to mediate photo-degradation of mercurial species into the Hg cold vapor detected by atomic spectrometry. Sample solution (containing Hg2+, CH3CH2Hg, and CH3Hg at hundreds of ng L−1) was placed in quartz tube containing formic acid solution (2% v/v) and microliter aliquot of GQDs/TiO2 nanocomposite dispersion (0.6 mg of nanocomposite). The tube was placed inside a photochemical reactor then, adapted to the mercury-dedicated spectrometer. Quantitative speciation was achieved taking advantage of the differences in UV photodegradation kinetics: Hg2+ (5 min), CH3CH2Hg (9 min) and CH3Hg (13 min). Gas-chromatography cold vapor atomic fluorescence spectrometry was used to confirm the evolution of the reactions over time during photo-reaction. The limits of detection were 10 ng L−1 for CH3CH2Hg and 7 ng L−1 for Hg2+ and CH3Hg.

Facile Synthesis of N‐Doped SnO2 Nanoparticles: A Cocatalyst‐Free Promising Photocatalyst for Hydrogen Generation

AbstractA facile solution‐based one‐step synthetic approach has been employed for an easy introduction of Nitrogen (N) into SnO2 lattice under the mild condition for a cocatalyst free hydrogen generation by photocatalytic water splitting. The crystal structure and morphology of synthesized N doped SnO2 nanoparticles were confirmed by powder X‐ray diffraction and electron microscopic techniques. Analysis by X‐ray Photoelectron Spectroscopy confirms that 4.6 % N was present in SnO2 lattice, while broadband observed in the Raman spectrum reveals the presence of oxygen vacancies and disordered structure due to N‐doping. The nanoparticles exhibit high surface area (139.7 m2/g) and bandgap close to 3.45 eV as deduced from Brunauer‐Emmett‐Teller (BET) measurement and Diffuse reflectance spectroscopic technique, respectively. The photocatalytic performance of the nanoparticles was evaluated by water splitting reaction for hydrogen generation using a photochemical reactor consisting of a Xenon lamp and was performed using different scavengers. It was found that out of various scavengers, maximum hydrogen yield, i. e., 169 μmol/g was achieved by N doped SnO2 nanoparticles with methanol and the order of scavengers for hydrogen generation using N doped SnO2 nanoparticles is Methanol&gt;EDTA&gt;TEOA.