Photocatalysis in water environments using artificial and solar light

Principles of Photocatalysts and Their Different Applications: A Review

Human existence and societal growth are both dependent on the availability of clean and fresh water. Photocatalysis is a type of artificial photosynthesis that uses environmentally friendly, long-lasting materials to address energy and environmental issues. There is currently a considerable demand for low-cost, high-performance wastewater treatment equipment. By changing the structure, size, and characteristics of nanomaterials, the use of nanotechnology in the field of water filtration has evolved dramatically. Semiconductor-assisted photocatalysis has recently advanced to become among the most promising techniques in the fields of sustainable energy generation and ecological cleanup. It is environmentally beneficial, cost-effective, and strictly linked to the zero waste discharge principle used in industrial effluent treatment. Owing to the reduction or removal of created unwanted byproducts, the green synthesis of photoactive nanomaterial is more beneficial than chemical synthesis approaches. Furthermore, unlike chemical synthesis methods, the green synthesis method does not require the use of expensive, dangerous, or poisonous ingredients, making it a less costly, easy, and environmental method for photocatalyst synthesis. This work focuses on distinct greener synthesis techniques utilized for the production of new photocatalysts, including metals, metal doped-metal oxides, metal oxides, and plasmonic nanostructures, including the application of artificial intelligence and machine learning to the design and selection of an innovative photocatalyst in the context of energy and environmental challenges. A brief overview of the industrial and environmental applications of photocatalysts is also presented. Finally, an overview and recommendations for future research are given to create photocatalytic systems with greatly improved stability and efficiency.

Coffee-waste templated CeOx/TiO2 nanostructured materials for selective photocatalytic oxidations

An environmentally friendly solvent-free approach was tested using spent coffee as a biomass sacrificial template for the preparation of TiO₂ modified with CeO_x. The use of coffee as a template pursues the preparation of a nanostructured heterojunction without the need for a solvent. Two variables were optimized in the synthesis process, i.e. calcination temperature and proportion of CeO_x. Firstly, bare coffee-template titania was prepared to explore the effect of the calcination temperature, within 500-650 °C. The anatase phase was obtained up to 600 °C. Higher temperatures, i.e. 650 °C, led to the appearance of rutile (10%) and efficient removal of the sacrificial agent (0.6% residue). The maximum photocatalytic activity in terms of conversion, in the oxidation of benzyl alcohol, was achieved employing the bare coffee-template TiO₂ at 650 °C, and it was found comparable to the benchmarked P25. The incorporation of ceria in the solvent-free approach considerably improved photocatalytic benzaldehyde production. No changes in the XRD pattern of TiO₂ were appreciated in the presence of ceria due to the low amount added, within 1.5-6.0%, confirmed by XPS as superficial Ce³⁺/Ce⁴⁺. The UV-visible absorption spectra were considerably redshifted in the presence of Ce, reducing the bandgap values of bare titania. An optimum amount of ceria in the structure within 3-0% was found. In this case, the selectivity towards benzaldehyde was ca. 75%, 3 times higher than the selectivity value registered for the benchmarked P25 or the bare prepared TiO₂.

Interdependence of Kinetics and Fluid Dynamics in the Design of Photocatalytic Membrane Reactors

Photocatalytic membrane reactors (PMRs) are a promising technology for wastewater reclamation. The principles of PMRs are based on photocatalytic degradation and membrane rejection, the different processes occurring simultaneously. Coupled photocatalysis and membrane filtration has made PMRs suitable for application in the removal of emerging contaminants (ECs), such as diclofenac, carbamazepine, ibuprofen, lincomycin, diphenhydramine, rhodamine, and tamoxifen, from wastewater, while reducing the likelihood of byproducts being present in the permeate stream. The viability of PMRs depends on the hypotheses used during design and the kinetic properties of the systems. The choice of design models and the assumptions made in their application can have an impact on reactor design outcomes. A design’s resilience is due to the development of a mathematical model that links material and mass balances to various sub-models, including the fluid dynamic model, the radiation emission model, the radiation absorption model, and the kinetic model. Hence, this review addresses the discrepancies with traditional kinetic models, fluid flow dynamics, and radiation emission and absorption, all of which have an impact on upscaling and reactor design. Computational and analytical descriptions of how to develop a PMR system with high throughput, performance, and energy efficiency are provided. The potential solutions are classified according to the catalyst, fluid dynamics, thickness, geometry, and light source used. Two main PMR types are comprehensively described, and a discussion of various influential factors relating to PMRs was used as a premise for developing an ideal reactor. The aim of this work was to resolve potential divergences that occur during PMRs design as most real reactors do not conform to the idealized fluid dynamics. Lastly, the application of PMRs is evaluated, not only in relation to the removal of endocrine-disrupting compounds (EDCs) from wastewater, but also in dye, oil, heavy metals, and pesticide removal.

Comparative Evaluation of Light-Driven Catalysis: A Framework for Standardized Reporting of Data

Light-driven homogeneous and heterogeneous catalysis require a complex interplay between light absorption, charge separation, charge transfer, and catalytic turnover. Optical and irradiation parameters as well as reaction engineering aspects play major roles in controlling catalytic performance. This multitude of factors makes it difficult to objectively compare light-driven catalysts and provide an unbiased performance assessment. This Scientific Perspective highlights the importance of collecting and reporting experimental data in homogeneous and heterogeneous light-driven catalysis. A critical analysis of the benefits and limitations of the commonly used experimental indicators is provided. Data collection and reporting according to FAIR principles is discussed in the context of future automated data analysis. The authors propose a minimum dataset as a basis for unified collecting and reporting of experimental data in homogeneous and heterogeneous light-driven catalysis. The community is encouraged to support the future development of this parameter list through an open online repository.

Two-Dimensional ZnS/SnS2 Heterojunction as a Direct Z-Scheme Photocatalyst for Overall Water Splitting: A DFT Study

Direct Z-scheme photocatalysts have attracted extensive attention due to their strong redox ability and efficient separation of photogenerated electron-hole pairs. In this study, we constructed two types of ZnS/SnS₂ heterojunctions with different stacking models of ZnS and SnS₂ layers, and investigated their structures, stabilities, and electronic and optical properties. Both types of heterojunctions are stable and are direct Z-scheme photocatalysts with band gaps of 1.87 eV and 1.79 eV, respectively. Furthermore, their oxidation and reduction potentials straddle the redox potentials of water, which makes them suitable as photocatalysts for water splitting. The built-in electric field at the heterojunction interface improves the separation of photogenerated electron-hole pairs, thus enhancing their photocatalytic efficiency. In addition, ZnS/SnS₂ heterojunctions have higher carrier mobilities and light absorption intensities than ZnS and SnS₂ monolayers. Therefore, the ZnS/SnS₂ heterojunction has a broad application prospect as a direct Z-scheme visible-light-driven photocatalyst for overall water splitting.

Imposed dynamic irradiation to intensify photocatalytic reactions

Dynamic irradiation is a potent option to influence the interaction between photochemical reactions and mass transport to design high performant and efficient photochemical processes. To systematically investigate the impact of this parameter, the photocatalytic reduction of nitrobenzene was conducted as a test reaction. Dynamic irradiation was realized through provoked secondary flow patterns, multiple spatially distributed light emitting diodes (LEDs) and electrical pulsation of LEDs. A combined experimental and theoretical approach revealed significant potential to enhance photochemical processes. The reaction rate was accelerated by more than 70% and even more important the photonic efficiency was increased by more than a factor of 4. This renders imposed dynamic irradiation an innovative and powerful tool to intensify photoreactions on the avenue to large scale sustainable photochemical processes.

Environmental Photocatalytic Degradation of Antidepressants with Solar Radiation: Kinetics, Mineralization, and Toxicity

This work is focused on the kinetics, mineralization, and toxicological assessments of the antidepressant drug amitriptyline hydrochloride (AMI) in UV or solar illuminated aqueous suspensions of ZnO, TiO₂ Degussa P25, and TiO₂ Hombikat. ZnO was proven to be the most effective photocatalyst, and it was used for all further experiments under solar irradiation. The highest reaction rate was observed at 1.0 mg/mL of catalyst loading. In the investigated initial concentration range (0.0075–0.3000 mmol/L), the degradation rate of AMI increased with the increase of initial concentration in the investigated range. The effects of H₂O₂, (NH₄)₂S₂O₈, and KBrO₃, acting as electron acceptors, along with molecular oxygen were also studied. By studying the effects of ethanol and NaI as a hydroxyl radical and hole scavenger, respectively, it was shown that the heterogeneous catalysis takes place mainly via free hydroxyl radicals. In the mineralization study, AMI photocatalytic degradation resulted in ~30% of total organic carbon (TOC) decrease after 240 min of irradiation; acetate and formate were produced as the organic intermediates; NH₄⁺, NO₃⁻, NO₂⁻ ions were detected as nitrogen byproducts. Toxicity assessment using different mammalian cell lines, showed that H-4-II-E was the most sensitive one.

Critical review of photocatalytic disinfection of bacteria: from noble metals- and carbon nanomaterials-TiO2 composites to challenges of water characteristics and strategic solutions

This critical review covers ways to improve TiO₂-based photocatalysts, how water characteristics may affect photocatalytic disinfection, and strategies to tackle the challenges arising from water characteristics. Photocatalysis has shown much promise in the disinfection of water/wastewater, because photocatalysis does not produce toxic by-products, and is driven by green solar energy. There are however several drawbacks that are curbing the prevalence of photocatalytic disinfection applications: one, the efficiency of photocatalysts may limit popular utilization; two, the water characteristics may present some challenges to the process. TiO₂-based photocatalysts may be readily improved if composited with noble metals or carbon nanomaterials. Noble metals give TiO₂-based composites a higher affinity for dissolved oxygen, and induce plasmonic and Schottky effects in the TiO₂; carbon nanomaterials with a tunable structure, on the other hand, give the composites an improved charge carrier separation performance. Other than photocatalyst materials, the characteristics of water/wastewater is another crucial factor in the photocatalysis process. Also examined in this review are the crucial impacts that water characteristics have on photocatalysts and their interaction with bacteria. Accordingly, strategies to address the challenge of water characteristics on photocatalytic disinfection are explored: one, to modify the semiconductor conduction band to generate long-lifetime reactive species; two, to improve the interaction between bacteria and photocatalysts.

Isomerization and Degradation of Levoglucosan via the Photo-Fenton Process: Insights from Aqueous-Phase Experiments and Atmospheric Particulate Matter

So far, studies on the conversion of stereochemistry under photo-Fenton conditions and their atmospheric implication are still rare. Here, we found that the biomass burning marker, the chiral compound levoglucosan (L), undergoes oxidative degradation under photo-Fenton conditions and can be isomerized into mannosan (M) and galactosan (G) simultaneously. Among the formic acid, acetic acid, and oxalic acid in the degradation products of levoglucosan, it was found that the yield of formation of formic acid in the photo-Fenton pathway can be as high as 86%. It is worth noting that both levoglucosan and its isomers are present in the atmosphere and their concentrations are strongly correlated. At the same time, the range of their concentration ratios, L/(G + M), measured in the photo-Fenton experiments in the laboratory was found to agree well with that measured in atmospheric PM_2.5 samples. However, the sources of L, G, and M in the atmosphere are complex, and the photo-Fenton reaction may be an essential pathway for the distribution of L, G, and M in the atmosphere.

Effects of Thiophene and Benzene Ring Accumulation on the Photocatalytic Performance of Polymers

Six polymers were prepared with 4,4',4″-(1,3,5-triazine-2,4,6-triyl)triphenylamine as the amine unit, and six different aldehyde units as substrates. The effects of the number of thiophene and benzene rings on the degradation of tetracycline (TC) in water were studied using polymer photocatalysts, and the reaction mechanism was discussed. The results indicate that ThTA-3 containing three thiophene group monomers and BATA-1 with one benzene ring unit monomer have higher absorption and utilization of visible light. In addition, ThTA-3 and BATA-1 have stronger charge separation and transfer capabilities and better morphology and thermal stability.

Preparation of Gd-Doped TiO2 Nanotube Arrays by Anodization Method and Its Photocatalytic Activity for Methyl Orange Degradation

Gd-doped TiO2 nanotube arrays with 3D ordered and high specific surface (176 m2/g) area are successfully prepared on a Ti foil surface via an anodizing method. The characterizations of Gd-doped TiO2 nanotube arrays are carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectrometer (EDX), optical contact angle measurer, and ultraviolet (UV) fluorescence spectrophotometer, respectively. The results reveal that the Gd-doped TiO2 nanotube arrays form on the Ti foil surface with a length of about 50.5 μm and 100 nm in diameter, and the growth direction grown along the (101) direction of anatase crystal. Under the optimized reaction conditions (60 V, 10 h, 0.01mol/L Gd3+), the crystal phase of Gd-doped TiO2 show an excellent nanotube structure, possess a beneficial photocatalytic performance for methyl orange (MO) (Degradation rate was 95.8%) and an excellent hydrophilic property (The optical contact angle was 4.9°). After doping with Gd, the hydrophilic and photocatalytic properties of the TiO2 nanotubes are further improved.

Process analytical technology (PAT) as a versatile tool for real-time monitoring and kinetic evaluation of photocatalytic reactions

Combining in situ Raman spectroscopy with multivariate data analysis enables the real-time monitoring and kinetic evaluation of photocatalytic reactions. The applicability is demonstrated on the photooxidation of 4-methoxythiophenol.

Nanomaterials for Environmental Purification and Energy Conversion

Nanomaterials, engineered structures of which a single unit is sized (in at least one dimension) between 1 to 100 nm, are probably the fastest growing market in the world [...]

A fluidized-bed reactor for the photocatalytic mineralization of phenol on TiO2-coated silica gel

TiO₂ photocatalysis represents a promising class of oxidation techniques that are intended to be both supplementary and complementary to the conventional approaches for the removal of refractory and trace organic contaminants in water and air. Powdered TiO₂ dispersion systems employed in most studies require an additional separation step to recover the catalyst from the effluent water, which represents a major drawback for large scale applications. The optimization of photocatalytic treatment systems involves merging the benefits of catalyst immobilization on a retainable support, thus eliminating the need for downstream catalyst separation, maximization of photon-exposed catalyst area, and continuous operation.

Aiming to integrate such conditions into a single system, a bench-scale annular photo-reactor with concentric UV-C lamp was built to study the photocatalytic mineralization of phenol on fluidized silica gel beads coated with sol-gel-synthetized TiO₂. Reactor efficiency was investigated for different silica particle diameters (224, 357 and 461 μm), fluidized-bed concentrations in the bulk liquid (5, 10, 20 and 30 g L⁻¹), initial phenol concentrations in the aqueous solution (0.25 mmol L⁻¹ to 4.0 mmol L⁻¹), and single and multiple sol-gel depositions. Then, the resulting optimum reactor configuration was compared to that of the same process on suspended Degussa P25 TiO₂ nanoparticles under similar experimental conditions. The latter is expected to be more efficient, but post-treatment catalyst recovery, being an energy intensive process, represents a major limitation for large scale applications. Process efficiency was measured as a function of the accumulated energy necessary for the mineralization of 50% of the initial dissolved chemical oxygen demand (COD), or, Q_0.5. Results showed that for any given mass of fluidized bed material, photo-oxidation efficiency increases with decreasing particle size (even for bed concentrations with similar equivalent surface area), decreasing initial phenol concentrations, and increasing number of sol-gel coatings. It was found that, for any given particle size and contaminant mass, there is an optimum bed concentration of 20 g L⁻¹ for which Q_0.5 reaches a minimum. Finally, under the optimum configuration, the fluidized-bed reactor efficiency is only 30% lower than that of photocatalysis on suspended TiO₂ nanopowder, thus making the proposed fluidized system a viable alternative to slurry-TiO₂ reactors.

A Holistic Approach to Model the Kinetics of Photocatalytic Reactions

Understanding and modeling kinetics is an essential part of the optimization and implementation of chemical reactions. In the case of photocatalytic reactions this is mostly done one-dimensionally, i.e., only considering the effect of one parameter at the same time. However, as discussed in this study, many of the relevant reaction parameters have mutual interdependencies that call for a holistic multi-dimensional approach to accurately model and understand their influence. Such an approach is described herein, and all the relevant equations given so that researchers can readily implement it to analyze and model their reactions.

Effect of dissolved silica on photocatalytic water purification with a TiO2 ceramic catalyst

If photocatalytic water purification technologies will find practical applications, the impact of total dissolved solids in the source water on the activity of the photocatalyst must be evaluated. In this study, we evaluated the effects of SiO₃^2- in water on a TiO₂ ceramic photocatalyst; specifically, we determined the effects of SiO₃^2- on the rate of photocatalytic degradation of formic acid (as a model contaminant) and on the rate of photocatalytic inactivation of Escherichia coli in an aqueous solution. Both the rate of formic acid degradation and the sterilization rate decreased with increasing SiO₃^2- concentration. On the other hand, at a given SiO₃^2- concentration, the activity of the photocatalyst did not decrease over the course of 120 h, and the surface structure of the photocatalyst did not change (i.e., no precipitate formed on the surface). The decreases in photocatalytic activity due to the presence of SiO₃^2- could be recovered by flushing the experimental apparatus with distilled water. These results show that the reason for the lower photocatalytic activity in the presence of SiO₃^2- than in its absence was due to adsorption of SiO₃^2- onto the surface of the TiO₂ photocatalyst and that SiO₃^2- adsorption was an equilibrium process in water.

Towards visible-light photocatalysis for environmental applications: band-gap engineering versus photons absorption-a review

A range of different studies has been performed in order to design and develop photocatalysts that work efficiently under visible (and near-infrared) irradiation as well as to improve photons absorption with improved reactor design. While there is consensus on the importance of photocatalysis for environmental applications and the necessity to utilized solar irradiation (or visible-light) as driving force for these processes, it is not yet clear how to get there. Discussion on the future steps towards visible-light photocatalysis for environmental application is of great interest to scientific and industrial communities and the present paper reviews and discusses the two main approaches, band-gap engineering for efficient solar-activated catalysts and reactor designs for improved photons absorption. Common misconceptions and drawbacks of each technology are also examined together with insights for future progress.

Solar Concentration for Wastewaters Remediation: A Review of Materials and Technologies

As the effectiveness of conventional wastewater treatment processes is increasingly challenged by the growth of industrial activities, a demand for low-cost and low-impact treatments is emerging. A possible solution is represented by systems coupling solar concentration technology with advanced oxidation processes (AOP). In this paper, a review of solar concentration technologies for wastewater remediation is presented, with a focus on photocatalyst materials used in this specific research context. Recent results, though mostly on model systems, open promising perspectives for the use of concentrated sunlight as the energy source powering AOPs. We identify (i) the development of photocatalyst materials capable of efficiently working with sunlight, and (ii) the transition to real wastewater investigation as the most critical issues to be addressed by research in the field.

Response Surface Methodology Optimization for Photodegradation of Methylene Blue in a ZnO Coated Flat Plate Continuous Photoreactor

In this paper, a continuous flat plate photoreactor with ZnO coating was studied in the photodegradation of methylene blue. The structural properties of catalyst were characterized by means of X-ray diffraction, Field emission scanning electron microscopy (FESEM), and energy dispersive X-ray (EDX). The XRD results indicate that high crystalline ZnO particles with average size of 13.5 nm were coated on the glass plate. The thickness of ZnO layer was 39.67 μm and the coating was uniform and crack free. The EDX showed clear border between glass and ZnO layer which confirmed no material transfer between glass and ZnO layer during thermal treatment. The influence of reactor parameters such as the slope of the glass plate, number of UV lamps, distance between lamp and ZnO coated glass plate and flow rate of wastewater was investigated using optimal custom design which is a subset of response surface methodology (RSM). The results indicated that the maximum photodegradation of methylene blue was achieved under the following conditions: plate slope of 9, 3 UVA lamps, 12 ml/s wastewater flow rate and 10 cm distance between lamp and glass plate. The response of surface methodology at optimum conditions was 65.05% while experimental value was 64.66%, showing good agreement between the experimental values and those predicted by the models, with relatively small errors which were only 0.64. The kinetic study was also performed for methylene blue photodegradation at optimum conditions.

Integrating the g-C3N4 Nanosheet with B-H Bonding Decorated Metal-Organic Framework for CO2 Activation and Photoreduction

BIF-20, a zeolite-like porous boron imidazolate framework with high density of exposed B-H bonding, is combined with graphitic carbon nitride (g-C₃N₄) nanosheets via a facile electrostatic self-assembly approach under room temperature, forming an elegant composite BIF-20@g-C₃N₄ nanosheet. The as-constructed composite preferably captures CO₂ and further photoreduces CO₂ in high efficiency. The photogenerated excitations from the carbon nitride nanosheet can directionally migrate to B-H bonding, which effectively suppresses electron-hole pair recombination and thus greatly improves the photocatalytic ability. Compared to the g-C₃N₄ nanosheet, the BIF-20@g-C₃N₄ nanosheet composite displayed a much-enhanced photocatalytic CO₂ reduction activity, which is equal to 9.7-fold enhancements in the CH₄ evolution rate (15.524 μmol g^-1 h^-1) and 9.85-fold improvements in CO generation rate (53.869 μmol g^-1 h^-1). Density functional theory simulations further prove that the presence of B-H bonding in the composite is favorable for CO₂ adhesion and activation in the reaction process. Thus, we believe that the implantation of functional active sites into the porous matrix provides important insights for preparation of a highly efficient photocatalyst.

Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light

Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an L-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS₂ (SnS₂-C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO₂ to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS₂ lattice, resulting in different photophysical properties as compared with undoped SnS₂. This SnS₂-C photocatalyst significantly enhances the CO₂ reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS₂-C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO₂ reduction under visible light, where the in situ carbon-doped SnS₂ nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.

Construction of CuO/In2S3/ZnO heterostructure arrays for enhanced photocatalytic efficiency

Novel one-dimensional (1D) heterostructure arrays composed of CuO nanowire cores, intermediate In₂S₃ nanostructures, and ZnO nanorod sheaths (i.e. CuO/In₂S₃/ZnO heterostructure arrays) have been successfully synthesized by a multi-step process. First, single-crystalline CuO nanowires were directly grown on flexible Cu mesh substrates using a one-step annealing process under ambient conditions. Second, In₂S₃ nanostructures and ZnO nanorods were sequentially grown on the CuO nanowires by a two-step hydrothermal method at low reaction temperature. The morphology, crystal structures, and optical properties of the CuO/In₂S₃/ZnO heterostructure arrays were studied by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive spectroscopy, and photoluminescence spectroscopy. The resultant ternary CuO/In₂S₃/ZnO heterostructure arrays exhibit excellent photocatalytic activity in the photodegradation of rhodamine 6G (R6G) under 10 W UV light irradiation, which is much higher than that of single-component (CuO nanowire arrays) or two-component systems (CuO/In₂S₃ heterostructure arrays). Furthermore, the reusability test demonstrates that the CuO/In₂S₃/ZnO heterostructure arrays on the Cu mesh still maintain high photocatalytic activity in the degradation of three kinds of organic pollutants even after five cycles, without any significant decline. These findings provide an insight into the design and synthesis of new CuO-based composites to effectively improve their photocatalytic performance.

Ferrioxalate-assisted solar photo-Fenton degradation of a herbicide at pH conditions close to neutrality

The solar photo-Fenton degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution at a natural pH (pH = 5) using ferrioxalate as iron source was investigated. The kinetic model proposed and validated in a previous contribution was used to predict the reactants concentrations during the oxidation process in a non-concentrating pilot-plant solar reactor. The effects of hydrogen peroxide to 2,4-D initial concentration ratios (R), temperature, and radiation levels were studied. Furthermore, the spectral UV/visible and broadband solar radiation fluxes incident on the reactor window were evaluated by the Simple Model for the Atmospheric Radiative Transfer of Sunshine (SMARTS2) code. The complete destruction of 2,4-D and its main intermediate 2,4-dichlorophenol (2,4-DCP) was achieved in all the experimental runs in only 90 and 120 min of reaction, respectively. In agreement with these results, a reduction of toxicity in the system (expressed as % of inhibition of Vibrio fischeri) for longer times to 90 min of reaction was attained. It is important to emphasize the good agreement between kinetic model results and experimental data obtained.

Sono-photo-degradation of carbamazepine in a thin falling film reactor: Operation costs in pilot plant

The photo-Fenton degradation of carbamazepine (CBZ) assisted with ultrasound radiation (US/UV/H₂O₂/Fe) was tested in a lab thin film reactor allowing high TOC removals (89% in 35min). The synergism between the UV process and the sonolytic one was quantified as 55.2%. To test the applicability of this reactor for industrial purposes, the sono-photo-degradation of CBZ was also tested in a thin film pilot plant reactor and compared with a 28L UV-C conventional pilot plant and with a solar Collector Parabolic Compound (CPC). At a pilot plant scale, a US/UV/H₂O₂/Fe process reaching 60% of mineralization would cost 2.1 and 3.8€/m³ for the conventional and thin film plant respectively. The use of ultrasound (US) produces an extra generation of hydroxyl radicals, thus increasing the mineralization rate. In the solar process, electric consumption accounts for a maximum of 33% of total costs. Thus, for a TOC removal of 80%, the cost of this treatment is about 1.36€/m³. However, the efficiency of the solar installation decreases in cloudy days and cannot be used during night, so that a limited flow rate can be treated.

Completely integrated wirelessly-powered photocatalyst-coated spheres as a novel means to perform heterogeneous photocatalytic reactions

Photocatalytic reactions can be efficiently driven by completely integrated photocatalyst–light emitter units which are wirelessly powered using resonant inductive coupling.

Two unusual 3D honeycomb networks based on Wells–Dawson arsenomolybdates with d10 transition-metal-pyrazole connectors

Two unusual 3D honeycomb networks based on Wells–Dawson arsenomolybdates were first reported, which have highly efficient catalytic ability for the degradation of organic dyes under UV irradiation and obvious electrocatalytic activities for the reduction of H₂O₂.

Order of magnitude increase in photocatalytic rate for hierarchically porous anatase thin films synthesized from zinc titanate coatings

Zinc titanate films are converted into porous anatase showing a 12-fold increase in rate compared to non-porous titania films.

Surface CuO, Bi2O3, and CeO2 Species Supported in TiO2-Anatase: Study of Interface Effects in Toluene Photodegradation Quantum Efficiency

The enhancement of active triggered by surface deposition of Cu, Bi, and Ce containing oxidic species onto a high surface area anatase is analyzed through the calculation of the quantum efficiency for toluene photodegradation under UV and Sunlight-type illumination. To this end, series of Cu, Bi, and Ce containing oxides supported on anatase were synthesized having a growing content of the Cu, Bi, and Ce surface species and characterized with X-ray diffraction and photoelectron, UV-visible, and photoluminescence spectroscopies as well as transmission electron microscopy. Utilizing the surface concentration of Cu, Bi, and Ce species as a tool, we analyzed the influence of the system physicochemical properties affecting quantum efficiency in anatase-based materials. First, employing small surface concentrations of the Cu, Bi, and Ce species deposited onto (the unperturbed) anatase, we provided evidence that all steps of the photocatalytic event, including light absorption, charge recombination, as well as surface interaction with the pollutant and chemical output as to activity and selectivity have significance in the quantitative assessment of the enhancement of the efficiency parameter. Second, we analyzed samples rendering maximum quantum efficiency within all these series of materials. The study indicates that maximum enhancement over anatase displays a magnitude strongly dependent on the efficiency level of calculation and would thus require the use of the most accurate one, and that it occurs through a balance between optoelectronic and chemical properties of the composite materials. The (Cu, Bi, Ce) oxide-anatase interface plays a major role modulating the optoelectronic properties of the solids and thus the efficiency observable.