Heterogeneous Photocatalytic Process Research Articles

A review of green hydrogen production based on solar energy; techniques and methods

Abstract The study examines the methods for producing hydrogen using solar energy as a catalyst. The two commonly recognised categories of processes are direct and indirect. Due to the indirect processes low efficiency, excessive heat dissipation, and dearth of readily available heat-resistant materials, they are ranked lower than the direct procedures despite the direct procedures superior thermal performance. Electrolysis, bio photosynthesis, and thermoelectric photodegradation are a few examples of indirect approaches. It appears that indirect approaches have certain advantages. The heterogeneous photocatalytic process minimises the quantity of emissions released into the environment; thermochemical reactions stand out for having low energy requirements due to the high temperatures generated; and electrolysis is efficient while having very little pollution created. Electrolysis has the highest exergy and energy efficiency when compared to other methods of creating hydrogen, according to the evaluation.

The Challenges of Integrating the Principles of Green Chemistry and Green Engineering to Heterogeneous Photocatalysis to Treat Water and Produce Green H2

Nowadays, heterogeneous photocatalysis for water treatment and hydrogen production are topics gaining interest for scientists and developers from different areas, such as environmental technology and material science. Most of the efforts and resources are devoted to the development of new photocatalyst materials, while the modeling and development of reaction systems allowing for upscaling the process to pilot or industrial scale are scarce. In this work, we present what is known on the upscaling of heterogeneous photocatalysis to purify water and to produce green H2. The types of reactors successfully used in water treatment plants are presented as study cases. The challenges of upscaling the photocatalysis process to produce green H2 are explored from the perspectives of (a) the adaptation of photoreactors, (b) the competitiveness of the process, and (c) safety. Throughout the text, Green Chemistry and Engineering Principles are described and discussed on how they are currently being applied to the heterogeneous photocatalysis process along with the challenges that are ahead. Lastly, the role of automation and high-throughput methods in the upscaling following the Green Principles is discussed.

Degradation of PAHs using TiO2 as a semiconductor in the heterogeneous photocatalysis process: A systematic review

Polycyclic Aromatic Hydrocarbons (PAHs) are organic compounds formed by benzene rings fused in their structure, arranged in different ways, and may have different radicals and organic functions. The contamination of soil, air, and water environments has increased, and studies of alternative remediation of contaminated sites. Removal of PAHs in the medium can be done by a series of techniques such as biofiltration, biodegradation; adsorption; and phytoremediation. One method that has been widely studied is heterogeneous photocatalysis. It is an Advanced Oxidative Process (AOP) and alternative technology to those traditionally used and can degrade toxic organic compounds of environmental relevance until their complete mineralization. This article aims to present a systematic review on the action of Advanced Oxidative Processes, in particular heterogeneous photocatalysis, used by titanium dioxide (TiO2) on PAH. This systematic review presents the main information obtained from 86 research articles, taken from four databases, on advanced oxidative processes, heterogeneous photocatalysis, and the use of TiO2 in the degradation of PAHs. In addition, we present a discussion on how these reaction mechanisms, the formation of reaction sub-products, and verifying the need for experimental studies that detect the toxicity of the formed compounds and compare them with the initial reaction molecules. It should be noted that experimental studies of heterogeneous photocatalysis for PAH degradation are needed to clarify whether there was the formation of more toxic compounds, as well as in vitro and in vivo toxicity, in addition, of course, to the formation of CO2 and H2O, which are the products desired at the end of the reaction, which would not harm the aquatic biota nor cause harm to human beings.

Photocatalytic ceramic membrane: Effect of the illumination intensity and distribution

The principles and application of heterogeneous photocatalytic processes have gained wide attention, especially to the effectiveness of the process. In this work a mono and a multi-LED lamp are used to study the impact of the UV light intensity and distribution on the semiconductor surface during the degradation of organic compounds in water. A well-defined scan of the electromagnetic radiation profile on the surface of the membrane was obtained and evaluated. Comparing two lamp configurations with a total photon flux of 210 W.m−2 and using a filtration rate of 9.7 L.m−2.h−1, resulted in 20 % more degradation for the most homogeneous light distribution. Furthermore, the reaction rate relation to the photon flux was also studied, with a surface reaction model that includes possible mass transfer limitations. The surface reaction constant increased linearly with the irradiation intensity for the complete studied range [50 to 550 W.m−2] for the most homogeneous illumination distribution. A less uniform distribution resulted in a less than proportional reaction rate constant with respect to the incident photon flux between 100 and 210 W.m−2. This work adds valuable information to the photocatalysis field to improve the light efficiency in a photoreactor to enhance the degradation of pollutants.

Novel Indium Vanadium Oxide Nanosheet-Supported Nickel Iron Oxide Nanoplate Heterostructure for Synergistically Enhanced Photocatalytic Degradation of Tetracycline

Semiconductor-based heterogeneous photocatalytic oxidation processes have received considerable attention for the remediation of toxic pollutants. Herein, InVO4/NiFe2O4 nanocomposites were synthesized using a facile hydrothermal technique. Furthermore, various characterization results revealed the successful loading of NiFe2O4 nanoplates over InVO4 nanosheets, thereby signifying the formation of a heterostructure. The performance of the synthesized photocatalyst was tested for tetracycline (TC) antibiotic removal. The optimized InVO4/NiFe2O4 nanocomposite exhibits maximum photodegradation of TC molecules (96.68%) in 96 min; this is approximately 6.47 and 4.93 times higher than that observed when using NiFe2O4 and InVO4, respectively. The strong interaction between the InVO4 nanosheets and NiFe2O4 nanoplates can improve the visible-light absorption and hinder the recombination of charge carriers, further enhancing the photocatalytic performance. Moreover, hydroxyl radicals play a crucial role in the photodegradation of TC antibiotics.

Manganese Dioxide Nanoparticles Prepared by Laser Ablation as Materials with Interesting Electronic, Electrochemical, and Disinfecting Properties in Both Colloidal Suspensions and Deposited on Fluorine-Doped Tin Oxide.

Nanoparticles (NPs) of α-MnO2 have high applicability in photoelectrochemical, heterogeneous photocatalysis, optical switching, and disinfection processes. To widen this panorama about MnO2 NPs, the formation of this material by laser ablation and deposition by dip-coating on fluorine-doped tin oxide (FTO), were considered in this study. The optical, spectroscopic, electrochemical characterization, and the evaluation of the antimicrobial activity, plus the photocatalytic response, were measured herein in colloidal media and deposited. For the deposition of NPs on FTO sheet, an anode is produced with a pseudocapacitive behavior, and 2.82 eV of band gap (GAP) in comparison with colloidal NPs for a value of 3.84 eV. Both colloidal suspension and deposited NPs have intrinsic antibacterial activity against two representative microorganisms (E. coli and S. aureus), and this biological activity was significantly enhanced in the presence of UVA light, indicating photocatalytic activity of the material. Thus, both the colloidal suspension and deposited NPs can act as disinfecting agents themselves or via light activation. However, an antibacterial behavior different for E. coli and S. aureus was observed, in function of the aggregation state, obtaining total E. coli disinfection at 30 min for deposited samples on FTO.

Photocatalytic removal of cefazolin in a photoreactor packed with TiO2-P25 nanoparticles supported on glass beads: an artificial neural network modeling

ABSTRACT To operationalise the heterogeneous photocatalysis process, the present study investigated the efficiency of TiO2-P25 nanoparticles immobilised on glass beads using the heat attachment method to remove cefazolin (CEF) as an antibiotic contaminant. The characteristics of the glass beads coated with TiO2-P25 nanoparticles were probed by the Scanning Electron Microscopy (SEM) technique. The immobilised TiO2-P25 nanoparticles manifested considerable efficiency in CEF removal in different operational conditions. The impact of various parameters, such as the ultraviolet light radiation time, initial concentration of CEF, light source power, inlet liquid volumetric flow rate, and pH of the solution, on the efficiency of CEF removal were examined. The results reveal that the removal percentage goes up as the irradiation time, volumetric flow rate, pH of the solution, and light source power increase while declining with a rise in the initial concentration of CEF. According to the findings, an initial CEF concentration of 20 mg L−1 is entirely removed by 40 min UV irradiation with a 16 W light source, the volumetric flow rate of 300 mL min−1, and the pH of 9.5. The reaction rate constant and adsorption coefficient of CEF on immobilised TiO2 were estimated at 0.622 mg L−1 min−1 and 0.095 mg−1 L via Langmuir- Hinshelwood kinetics. The outcomes of the mineralisation studies also display a considerable reduction of TOC and evolution of significant mineralisation products, like , , , and . The experimental results were modelled by artificial neural networks (ANN). Comparing the experimental results with the ANN-predicted data shows the acceptable efficiency of modelling with ANN. The minimum MSE, R2 value for all data (validation, training, and test), and R2 value for simulated data were obtained at 0.00027811, 0.9971, and 0.9809, respectively. The relative importance of the parameters affecting the process evaluated by the ANN weights indicates that the irradiation time is the most important factor in the photocatalytic removal of CEF.

Antiphotocorrosion UV‐Bi2O3@PANI Photocatalyst Rich in Oxygen Vacancy Defects: Building Processes, Preparation Mechanisms, and Photocatalysis Performance

Low content of oxygen vacancy defects (OVs) and limited resistibility to photocorrosion are the core problems in the heterogeneous photocatalytic processes of bismuth oxide (Bi2O3). Herein, the strategy of “ultraviolet (UV) light‐inducing OVs” coupling with “polyaniline (PANI) combination inhibiting photocorrosion” is employed on the modification of Bi2O3. First, the high methylene blue (MB) degradation efficiency by UV3h‐Bi2O3@PANI0.5 wt% above 99.5% and the low Bi3+ dissolved concentration below 0.20 mg L−1 under visible light signify the high photocatalytic activity and stability. Then, the mechanisms for generation of OVs and inhibition of photocorrosion are proposed as follows. 1) Holes (h+) forming under irradiation, diffusing through the lattice, and reaching the surface of Bi2O3 can be regarded as a monatomic oxygen ion (OS−); 2) OS− combines and continues to be oxidized by h+, leading to the generation of O2 with the OVs left in the lattice; 3) UV‐Bi2O3 and PANI are excited to produce electrons/holes (e−/h+); 4) e−/h+ transfer in UV‐Bi2O3@PANI heterojunction leads to the separation of h+ from UV‐Bi2O3 and the inhibition of photocorrosion. Through the core problems being overcome, a new idea for the development and application of Bi2O3 with excellent performances in the field of water treatment is provided.

Addition of g-C3N4 to ZnO and ZnFe2O4 to improve photocatalytic degradation of emerging organic pollutants

The use of heterojunctions with different semiconductors has shown to be an important strategy to increase the efficiency of heterogeneous photocatalytic processes. In this regard, heterojunctions consisting of ZnO/g-C3N4 (x-Zn/gCN) and ZnFe2O4/g-C3N4 (x-ZF/gCN) were synthesized in different mass proportions of g-C3N4 (x = 10, 50 and 80%) through the following simple methods combination: mixture, sonication and thermal treatment. Observations from X-ray diffractometry (XRD), Fourier-transform infrared spectra (FTIR) and field emission scanning electron microscope (FESEM) analyses confirmed that the materials were successfully formed. The g-C3N4 incorporation was important in the textural and optical properties modification of the heterojunctions produced. In addition, in the photoluminescence spectroscopy (PL), it was possible to observe g-C3N4 influence in the 50-Zn/gCN emission profile changing, reducing the direct recombination rate of the photogenerated charges due to a probable Z-scheme mechanism. This catalyst demonstrated greater efficiency of photocatalytic degradation when compared to the remaining materials, both for cefazolin (CFZ) and reactive black 5 (RB5), reaching 78% and 95%, respectively, after 120 min. Moreover, it also revealed good photostability after five successive cycles. 50-Zn/gCN heterojunction presents a promising character in photocatalytic reactions mediated by solar light for contaminants degradation such as pharmaceutical products and dyes and can be used as an alternative to minimize the effects of water pollution caused during the COVID-19 pandemic.

Photocatalytic degradation of ketamine using a reusable TiO2/SiO2@Fe3O4 magnetic photocatalyst under simulated solar light

TiO2 heterogeneous photocatalytic processes can carry out efficient abatement of various organic pollutants; however, the difficult recyclability of catalysts largely hinders their application. This study aims to develop a TiO2/SiO2@Fe3O4 core-shell structure magnetic photocatalyst for the degradation of ketamine, a recalcitrant pharmaceutical pollutant commonly found in aquatic environments. The structure and morphology of the TiO2/SiO2@Fe3O4 photocatalyst were comprehensively characterized. Compared with commercial P25 TiO2, the fabricated TiO2/SiO2@Fe3O4 photocatalyst exhibited a higher ketamine degradation efficiency under simulated solar irradiation, with a pseudo-first-order rate constant of 0.1768 min–1 (conditions: [ketamine]0 = 0.3 μM, [TiO2/SiO2@Fe3O4] = 100 mg/L and pH = 7). Additionally, the magnetic TiO2/SiO2@Fe3O4 was easily recovered and showed stable performance, with the ketamine degradation rate only slightly decreasing from 100% to 91% within six cycles of use. The mechanistic investigation demonstrated the participation of •OH, h+ and •O2– in ketamine photocatalytic degradation, with •O2– playing the dominant role. During the photocatalytic pathways of ring opening, oxygen addition, N-demethylation and hydroxylation, ketamine was decomposed into byproducts and further achieved efficient mineralization and detoxification (performed by the Microtox® acute toxicity test), showing the promising potential of TiO2/SiO2@Fe3O4 for use in water purification.

Synthesis and Application of Innovative and Environmentally Friendly Photocatalysts: A Review

Modern society faces two major challenges: removing pollutants from water and producing energy from renewable sources. To do this, science proposes innovative, low-cost, and environmentally friendly methods. The heterogeneous photocatalysis process fits perfectly in this scenario. In fact, with photocatalysis, it is possible both to mineralize contaminants that are not easily biodegradable and to produce hydrogen from the water splitting reaction or from the conversion of organic substances present in water. However, the main challenge in the field of heterogeneous photocatalysis is to produce low-cost and efficient photocatalysts active under visible light or sunlight. The objective of this review is to compare the new proposals for the synthesis of innovative photocatalysts that reflect the requirements of green chemistry, applied both in the removal of organic contaminants and in hydrogen production. From this comparison, we want to bring out the strengths and weaknesses of the proposals in the literature, but above all, new ideas to improve the efficiency of heterogeneous photocatalysis guaranteeing the principles of environmental and economic sustainability.

Arsenite to Arsenate Oxidation and Water Disinfection via Solar Heterogeneous Photocatalysis: A Kinetic and Statistical Approach

Arsenic (As) poses a threat to human health. In 2014, more than 200 million people faced arsenic exposure through drinking water, as estimated by the World Health Organization. Additionally, it is estimated that drinking water with proper microbiological quality is unavailable for more than 1 billion people. The present work analyzed a solar heterogeneous photocatalytic (HP) process for arsenite (AsIII) oxidation and coliform disinfection from a real groundwater matrix employing two reactors, a flat plate reactor (FPR) and a compound parabolic collector (CPC), with and without added hydrogen peroxide (H2O2). The pseudo first-order reaction model fitted well to the As oxidation data. The treatments FPR–HP + H2O2 and CPC–HP + H2O2 yielded the best oxidation rates, which were over 90%. These treatments also exhibited the highest reaction rate constants, 6.7 × 10−3 min−1 and 6.8 × 10−3 min−1, respectively. The arsenic removal rates via chemical precipitation reached 98.6% and 98.7% for these treatments. Additionally, no coliforms were detected at the end of the process. The collector area per order (ACO) for HP treatments was on average 75% more efficient than photooxidation (PO) treatments. The effects of the process independent variables, H2O2 addition, and light irradiation were statistically significant for the AsIII oxidation reaction rate (p < 0.05).

Unraveling photocatalytic electron transfer mechanism in polyoxometalate-encapsulated metal-organic frameworks for high-efficient CO2 reduction reaction

Unraveling the fundamental electron transfer mechanism is vital to deeply understand the heterogeneous photocatalysis process so as to develop new efficient photocatalysts. Herein, we present a deep investigation on the electron-transfer mechanism in heterogeneous photocatalytic CO2 reduction reaction by adopting a new type of structurally clear polyoxometalate-encapsulated metal-organic frameworks {Hn[Cd6L6Cl7]4[POM]8} (L=1,4-di(4H-1,2,4-triazol-4-yl)benzene, POM={SiW12}, {PW12} and {PMo12}, abbr.POM@CdMOF) as model photocatalysts. Transient photovoltage measurements indicate that various POM guests in photoactive CdMOF hosts show different electron transfer behaviors and charge separation pathways, inducing different photocatalytic activities. Thereinto, SiW12@CdMOF and PW12@CdMOF exhibit high photocatalytic CO2 reduction activities with CO yields of 4.35 mmolCO·molCd−1·h−1 and 3.60 mmolCO·molCd−1·h−1 comparably to most reported photocatalysts, whereas the performance of PMo12@CdMOF is poor. The in-situ transient photovoltage and DFT calculations revealed the key regulation role of different POM units on the interfacial electron transfer and the adsorption behavior of the important intermediates, thus describing a feasible route to efficiently perform the photocatalytic CO2 reduction. This work may provide a new and significant guideline for exploring high-performance photocatalysts.

Dye Degradation by Heterogeneous and Homogeneous Photocatalysis Processes. A Scaled-up Approach for a CPC Solar Reactor

Dye Degradation by Heterogeneous and Homogeneous Photocatalysis Processes. A Scaled-up Approach for a CPC Solar Reactor

Removal of chemical and microbial water pollutants by cold plasma combined with Ag/TiO2-rGO nanoparticles

This study aimed to investigate the synergistic effect of the cold atmospheric plasma (CAP) and heterogeneous photocatalytic processes in an aqueous solution to enhance water purification efficacy and reduce the energy cost required by CAP. 0.1% Ag/TiO2-reduced graphene oxide (rGO) nanoparticles (NPs) photo-composite were prepared and fully characterized. Data showed that Ag nanoparticles and the rGO play an important role in increasing the efficiency of the whole treatment process and the photo-composite (0.1% Ag/TiO2-1% rGO at 400 °C) revealed the highest phenol removal rate with excellent reusability. Also, complete inactivation (~ 5log10 reduction) of both E. coli and S. aureus by NPs was observed without CAP exposure, whereas a minimal effect (0.1–0.5 log10) on viruses (Adenovirus (AdV), rotavirus, and ɸX174) was observed after 10 min incubation. Interestingly, the photocatalytic virus inactivation test was promising, as it resulted in > 4.7log10 reduction of AdV at 2 min treatment, whereas < 1log10 could be reduced using only CAP at the same treatment time. Accordingly, we believe that this work could provide new insights into how the synergy between CAP and 0.1% Ag/TiO2-1% rGO photo-composite in aqueous media imposes a great potential for environmental applications, such as water purification and microbial inactivation.

Brookite vs. rutile vs. anatase: What`s behind their various photocatalytic activities?

The results of investigating the morphological, optical and electronic properties of three synthesized TiO2 polymorphs (anatase (A and A2), brookite (B and B2) and rutile (R)) show that the origin of their different catalytic efficiency in the heterogeneous photocatalytic process lies in the depths of the charge carrier traps. The presence of shallow electron traps in brookite extends the number and “lifetime” of generated holes, so brookite is a good choice as a photocatalyst in such heterogeneous photocatalytic systems where these two variables are the reaction limiting factors. Low generation and high recombination rate of charge carriers in rutile are the consequence of too deep electron traps, therefore the generated electrons are not able to participate in reactive oxygen species generation reactions on the catalyst surface. The longer “lifetime” of charge carriers generated in anatase is due to the fact that anatase belongs to the indirect band gap semiconductors. It was further revealed that the increase of the anatase crystallite size (from 10 to 20 nm) can compensate the negative effect of decreasing specific surface area (from 129.5 to 65.0 m2/g) on the photocatalytic activity of anatase. The negative effect of decreasing specific surface area was very well expressed in the case of brookite, where the photocatalytic activity dropped with decreasing specific surface area (from 17.2 to 3.0 m2/g) while keeping constant brookite crystallite size (≈ 80 nm). Heterogeneous photocatalytic experiments with the model pollutant bisphenol A show that the deposition of bisphenol A degradation products on the catalyst surface can have a detrimental effect on photocatalytic activity of low specific surface area TiO2 polymorphs. The specifics (electronic properties, geometry of particles and photocatalytic activity of each TiO2 polymorph) of the investigated heterogeneous photocatalytic system for reactive oxygen species generation are the reason that the “synergistic effect” between the anatase and rutile phase when used as a physical mixture, regardless of the ratio between them, was not expressed. The anatase phase was shadowed by small and abundant rutile nanoparticles with low photocatalytic activity, which acted also as a harvester of UV-light due to a wider UV-light absorption range. We can conclude that the less studied TiO2 polymorph brookite is worthy of investigation, as the results of the present study show that the photocatalytic activity of brookite with the adequate specific surface area is comparable to the photocatalytic activity of the widely investigated anatase TiO2. In addition, it can be concluded that in the physical mixtures of different TiO2 polymorphs, the use of TiO2 particles of close diameters is of crucial importance to achieve a “synergistic” photocatalytic effect triggered by particle collisions.

Phenol degradation of waste and stormwater on a flat plate photocatalytic reactor with TiO2 on glass slide: An experimental and modelling investigation

Heterogeneous photocatalytic oxidation process using TiO2 (titanium dioxide) and UV light is a promising method to degrade a wide variety of recalcitrant organic substances such as phenol, pesticides, herbicides, etc. from waste and stormwater. Due to lack of suitable computational fluid dynamics (CFD) model, the industrial-scale application of this technique poses a few challenges indicating the need to clearly understand the hydrodynamic behaviour of the photocatalytic system and investigate the ways of improving their performance. Inadequate mixing and turbulence in a fixed photocatalytic reactor limit the performance of the reactor in terms of pollutant mass transport to the catalyst surface and pollutant degradation. In this study, a 3D flat plate photocatalytic reactor was designed and developed, and numerically analysed using CFD code FLUENT to investigate the performance of the reactor. The CFD modelling results were validated against the experimental data at various flow conditions. The CFD results including velocity and phenol concentration was found in strong agreement with the experimental results with R2 value of 0.998. The experimental results shows that the phenol degradation was 85.5% when the irradiation was 70.6 Wm−2 and initial concentration of phenol was 20 PPM The experimental results also show that the phenol degradation increases with the increase of irradiation but decreases with the increase of initial concentration. The results show that phenol degradation of the reactor decreases with the increase in flow rate as expected. The CFD model can accurately predict the velocity and the concentration of phenol at different flow rates.

Synthesis of BiOI/Mordenite Composites for Photocatalytic Treatment of Organic Pollutants Present in Agro-Industrial Wastewater.

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 °C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.

An Overview of Polymer-Supported Catalysts for Wastewater Treatment through Light-Driven Processes

In recent years, alarm has been raised due to the presence of chemical contaminants of emerging concern (CECs) in water. This concern is due to the risks associated with their exposure, even in small amounts. These complex compounds cannot be removed or degraded by existing technologies in wastewater treatment plants. Therefore, advanced oxidation processes have been studied, with the objective of developing a technology capable of complementing the conventional water treatment plants. Heterogenous photocatalysis stands out for being a cost-effective and environmentally friendly process. However, its most common form (with suspended catalytic particles) requires time-consuming and costly downstream processes. Therefore, the heterogeneous photocatalysis process with a supported catalyst is preferable. Among the available supports, polymeric ones stand out due to their favorable characteristics, such as their transparency, flexibility and stability. This is a relatively novel process; therefore, there are still some gaps in the scientific knowledge. Thus, this review article aims to gather the existing information about this process and verify which questions are still to be answered.

Solar Heterogenous Photocatalytic Degradation of Methylthionine Chloride on a Flat Plate Reactor: Effect of pH and H2O2 Addition

Methylthionine chloride (MTC) is a compound with several applications both in the clinical and medical industries. Nevertheless, such compounds can become an environmental problem, as they are not properly treated by wastewater treatment plants. This objective of this work was to study MTC degradation in a flat plate reactor through solar photolysis and heterogeneous photocatalysis processes with TiO2 as a catalyst. In addition to the processes, three pH (3.5, 6.5, and 9) and the effect of H2O2 addition (no dose, 0.5, and 1 mM/L) were tested. The results show that acidic pH is the most appropriate for MTC degradation, which ranged between 56% and 68.7% for photolysis and between 76% and 86.7% in photocatalysis. The H2O2 addition resulted in lower degradation in all cases, leading the authors to conclude that the presence of peroxide actually hinders degradation in solar photolysis and photocatalysis processes. Statistical analysis showed that the constant rate reactions calculated for every process, under the same conditions of pH and H2O2 addition, are significantly different from one another, and the three factors considered for experimental design (process, pH, and H2O2) have a statistically significant effect on MTC degradation. The collector area per order confirmed higher efficiency for photocatalysis when compared to photolysis processes.