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The selective photocatalytic oxidation of organic substances is today considered one of the green techniques to synthesize important starting materials in different technological applications. This work reports an efficient, simple and cheap strategy for the synthesis of a new photocatalytic CuBi2O4-TiO2 (CBO/TiO2) heterosystem at room temperature. The prepared powders were characterized by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The photocatalytic activity was evaluated by performing a probe reaction, namely the partial oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde (4-MBAld) in aqueous solution under irradiation of simulated sunlight. The CBO/TiO2 coupled systems showed a higher photoactivity than the single photocatalysts reaching a selectivity of 45% towards 4‑methoxy-benzaldehyde with an alcohol conversion of 77% after 4 h of irradiation. Furthermore, although a high alcohol conversion was achieved, the selectivity towards 4-MBAld was significant, unlike what has been reported in the literature for many heterogeneous photocatalytic reactions whose selectivity generally decreases significantly with the increasing conversion of the starting alcohol molecule. The improved photocatalytic activity could be attributed to the partial coverage of the TiO2 surface by CBO which reduces the subsequent oxidation of the formed aldehyde.

A long-term test at a laboratory scale with a closed system (a coral reef aquarium) has been carried out to study the potentialities of photocatalytic ozonation and photocatalysis for the removal of noxious organic compounds in recirculating systems (aquaria and recirculating aquaculture systems) working with a minimum make up of new water. Attention has been focused not only on the depuration capabilities but also on possible negative phenomena, some of which could become apparent only at long times. After having tuned the system by setting appropriate operating conditions and procedures, positive results were obtained. In particular, it was observed that the alternation of photocatalytic ozonation with photocatalysis with definite cycle allowed to severely limit the presence of the organic compounds, which otherwise could accumulate in the system, and at the same time to control the formation of bromate, the ozonation side-product of main concern. In addition, the values of other parameters, which are important for water quality, remained at satisfactory values. It was also verified that the prepared photocatalytic films maintained a good photocatalytic activity even after several months of utilization in seawater. These results demonstrate that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of sustainable aquaculture.

The knowledge of the rate equation is fundamental for the assessment of the activity of the photocatalytic material and for the study, design and optimization of photocatalytic reactors. In the case of photocatalytic reactions, the local volumetric rate of photon absorption (LVRPA) affects the reaction rate and its inherently uneven distribution within a “slurry” reactor makes complex a correct kinetic analysis. In the present work it is shown which are the critical aspects of the kinetic analysis in slurry reactors and how to carry out photocatalytic experiments to minimize the misinterpretations of the experimental results. In particular, the influence of the type of illumination and of the operating conditions (recirculation flow rate, optical thickness) are studied. For instance, it is shown that the average values of the reaction rate and of the rate of photon absorption give no direct insight on the intrinsic kinetic if the reactor is not uniformly illuminated and the optical thickness is beyond a given value, which is significantly higher than the one usually suggested in literature for a “safe” kinetic analysis. Furthermore, the estimation of the average rate of photon absorption must take into account the backscattering of radiation from the reactor. In any case, the utilization of a proper mathematical model allows carrying out a sound kinetic analysis also in critical situations as those which can arise with an illumination by LEDs.

In this work anaerobic heterogeneous photocatalytic solar/UV light reforming of glycerol in aqueous media was performed with Pt-photodeposition and noble metal free modified TiO2 photocatalysts prepared through ball milling, a very simple and cheap coupled catalyst preparation method. Different amounts of Cu2O or 3% CuO were loaded on TiO2 using ball milling and during each run glycerol conversion, hydrogen and CO2 formed in the gas phase and 1,3-dihydroxyacetone (DHA) and glyceraldehyde (GA) in the liquid phase were determined. The results were compared with the aim to verify the effectiveness of Cu2O in replacing Pt. Using noble metal free photocatalysts, 33% glycerol conversion, 10.3% and 5.4% selectivity towards DHA and GA, respectively, a CO2 concentration of 0.16 mM, and a H2 concentration of 1.01 mM corresponding to 0.17 mmol h−1 g−1 were obtained. Ex situ photoelectrochemical characterization confirmed the formation of a heterostructure between TiO2 and copper oxide and the effectiveness of Cu2O towards H2 formation.

A set of metals modified TiO2 photocatalysts were prepared starting from titanium tetraisopropoxyde and different metal precursors to study the influence of the addition of the various foreign agents on the physico-chemical and photocatalytic properties of the catalysts. The powders were characterized by X-ray diffraction, Raman spectroscopy, specific surface area measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence, temperature programmed desorption after CO2 adsorption. The photocatalytic activity was evaluated using as probe reactions the partial oxidation of three aromatic alcohols: benzyl alcohol (BA), 4-methoxy benzyl alcohol (4-MBA), and 4-hydroxy benzyl alcohol (4-HBA) under simulated solar light irradiation. Different oxidation and selectivity values were obtained for the three substrates depending not only on the type of metals but also on the nature and position of the substituent in the phenyl ring of benzyl alcohol. As a general behaviour, the doped samples allowed the achievement of a greater selectivity especially for 4-MBA even if sometimes with minor conversions. The presence of W or Nb was beneficial for both conversion and selectivity for all the substrates with respect to bare TiO2. Graphical abstract

This study reports the anaerobic reduction of maleic acid to succinic acid in aqueous dispersion of different TiO2 based photocatalysts. Some home prepared and commercial solids containing different polymorphic phases of TiO2 and loaded with Pt and Ru were compared at different acidic pHs. The aim of the work was to verify the feasibility of the process and to determine the best samples and the optimal experimental conditions of the reaction. The best selectivity towards succinic acid was 23.2 % at 70 % of maleic acid conversion. Fumaric acid was also formed as another high added value compound, and its quantity was related to the experimental conditions and the photocatalyst used.

Partial photocatalytic oxidation of salicyl alcohol (2-hydroxybenzyl alcohol) to salicylaldehyde in water was investigated under environmental friendly conditions in the presence of home-prepared and commercial TiO2 (Merck and Aeroxide P25) samples under UVA irradiation. The photocatalysts were characterized by using BET, XRD, SEM and/or TEM techniques. The effects of crystallinity degree, pH (3–11) and presence of a hole trap (ethanol) on the photocatalytic activity and product selectivity were investigated. 4-Hydroxybenzyl alcohol was also used to study the influence of the position of the substituent group in the aromatic ring. High alcohols conversion and product selectivity values were obtained at pH = 11 by using well crystallized TiO2 samples. The conversion values significantly decreased by increasing the hole trap concentration, whereas the selectivity values increased slightly. The selectivity towards the corresponding aldehyde after 30% of alcohol conversion was significantly higher for 4-HBA (48%) than for 2-HBA (32%), due to the role of the para position of the substituent group. In order to clarify the different selectivity of the products, various experiments have been also performed starting from the products; these results indicate that the selectivity is also strongly dependent on the stability of the formed products under the experimental conditions used. By concluding, this article reports that the conversion and selectivity values for the studied reaction depend both on the TiO2 type and on the substrate.

The present review summarizes some of the main results achieved in electrochemical, photocatalytic, and (photo)-electrocatalytic systems for the reduction of carbon dioxide. After a preliminary survey of the electrocatalytic and photocatalytic systems in terms of materials used, efficiencies, operating conditions, and product distribution, it is shown how the combination of the two approaches affords often higher efficiency than the single technologies and allows better control of the product distribution. In fact, the peculiar energetic distribution at the interface of irradiated semiconductors under opportune electrical bias enables enhancement of the spatial separation of the photogenerated charges and minimization of the external energy required in electrochemical applications. Even though the efficiency of CO2 reduction is still far away from being industrially appealing, in some cases the photoelectrocatalytic systems are promising tools to be further investigated for sustainable green chemistry based CO2 utilization. The aim of this review is to examine the strengths and the weaknesses of the different approaches considering that sometimes one of the three methods can be used more successfully than the others, depending on the desired product(s) and the materials used as photocatalysts or as the (photo)electrode.

The influence of pH on the photocatalytic partial oxidation of 4-methoxybenzyl alcohol (MBA) and vanillyl alcohol (VA) to their corresponding aldehydes in aqueous suspension under UVA irradiation was investigated by using poorly crystalline home-prepared and crystalline commercial TiO2 (BDH, Merck and Degussa P25) photocatalysts. The results clearly show as tuning pH can strongly impart selectivity and activity to photocatalytic processes which are often quite unselective in aqueous suspensions. It was found that pH effect on reaction rate and product selectivity strongly depended on TiO2 crystallinity and substrate type. In the case of MBA oxidation, photoreactivity and selectivity were very high at low pH values for all of TiO2 catalysts, and the crystalline samples showed to be more active than the poorly crystalline ones. At pH= 1 the photoactivity of Degussa P25 was the highest one, and 88% selectivity at 50% conversion was determined. At acidic pH values, selectivity and activity were higher in the presence of HCl than H2SO4 or H3PO4. For VA oxidation, high selectivity values were obtained at high pH’s for all of the samples, and the crystalline samples showed higher activity at the alkaline pH values with respect to that observed at the acidic ones. Experiments starting from the obtained products, that are p-anisaldehyde and vanillin, showed that the selectivity depends on the resistance of those compounds to be subjected to further oxidation under the experimental conditions used.

In the present work, dialysis was used to recover vanillin while being produced by partial photocatalytic oxidation of ferulic acid in an aqueous solution at ambient temperature. The relatively high value of the permeate flux through a dense polyether-block amide membrane allowed continuously extracting vanillin from the reacting solution, thus avoiding its successive oxidation. The rate of vanillin formation was improved, compared to other reactor configurations, because intermediate compounds permeated from the reacting solution and did not hinder the reaction, while ferulic acid permeated in the opposite direction to partially replenish the reactor with the substrate. The photocatalytic membrane reactor obtained by the effective coupling of dialysis with the photocatalytic reaction improved the production yield. For instance, with the utilized experimental set up, the total amount of vanillin produced after 5 h in the membrane reactor was more than one-third higher than in the photocatalytic reactor without dialysis. The results obtained with a mathematical model agree with the experimentally observed behavior. The model allowed estimating vanillin diffusivity in the membrane and showed that concentration polarization might limit the process.

The present chapter reports some economical aspects of the cerium oxide market. Porter’s and PESTEL analyses have been used to evidence the strengths and weaknesses of the ceria market, along with the potentiality and opportunities within the years to come. The wide use of CeO2 nanoparticles in many applications requires to consider also issues related to their toxicity and environmental fate. In this regard, some contradictory reports in the relevant literature have been surveyed, thus highlighting the need for further and detailed investigation on these topics in order to propose effective strategies of risk assessment and environmental remediation.

The depletion of fossil fuel requires the search for alternative renewable feedstock and environmentally friendly methods for the production of high value-added compounds and fuels. In this context, the efficient use of biomass has emerged as a significant research field as it represents an alternative green and renewable carbon source. Various technologies have been explored for this purpose and heterogeneous photocatalysis represents a valid alternative to the catalytic methods since it can be carried out under mild experimental conditions without the addition of harmful oxidizing agents. Different biomass components have been used as the starting materials, and many valuable chemicals have been obtained with different selectivity depending on some experimental conditions as, for instance, type of photocatalyst, solvent, and physico-chemical features of the catalysts. Moreover, by carrying out the reaction in de-aerated systems, in addition to high added value compounds, hydrogen can be obtained in the gaseous phase. In particular, photocatalytic conversion of lignocellulose, carbohydrates, 5-hydroxymethyl-2-furfural and glycerol (considering only the partial oxidation products) is reported.

In the present work, an integrated process combining three different technologies, i.e. heterogeneous photocatalysis, homogeneous ozonation and adsorption on granular activated carbon (GAC) was used for the treatment of a synthetic solution simulating saline wastewater. The synergistic effects between the different methods enhance the oxidation rate of the organic compounds in the integrated process, so that its use may result sustainable. It has been found that a relatively low oxidation rate is sufficient to obtain the highest synergy between the three technologies and to maximize the performances. In particular, coupling ozonation and photocatalysis resulted in 20% enhancement in terms of reaction rate with respect to the sum of the rates of the single technologies. The contemporary presence of GAC and photocatalytic ozonation led to further enhancement of the whole system efficiency, obtaining a reaction rate 15% higher than the sum of the rates of the above mentioned single technologies.

Significant production of elemental bromine (Br2 ) was observed for the first time when treating bromide containing solutions at acidic pH, with TiO2 photocatalyst, ozone, or a combination thereof. Br2 selectivities up to approximately 85 % were obtained and the corresponding bromine mass balance values satisfied. The process is general and may be applied at a laboratory scale for green bromination reactions, or industrially as a cheap, safe, and environmentally sustainable alternative to the currently applied bromine production methods.

The photoisomerization of trans-caffeic acid to cis-caffeic acid has been studied in the presence of N2 in homogeneous aqueous solutions and in suspensions of various TiO2 catalysts. The results supported the hypothesis of an energy transfer process from TiO2 to the substrate due to the recombination of the photogenerated electron–hole pairs. The differences among the measured photostationary [cis]/[trans] ratios have been attributed to the different physico-chemical properties of the catalysts. In particular, the lowest ratio measured in the presence of Merck TiO2 was ascribed to the very low adsorption of trans-caffeic acid onto the surface of this sample. In the presence of O2 and at alkaline pHs, cis-caffeic acid cyclized to esculetin both in the absence and in the presence of irradiation.

This review deals with the parameters that influence heterogeneous photocatalysis (PC) for selective synthesis of high-value chemicals by itself or in combination with other technologies. In particular, the parameters related to the photocatalysts, such as crystallinity degree, type of polymorph, surface acid-base properties, exposure of particular crystalline facets, coupling of different semiconductors, position of the valence and conduction band edge, addition of doping agents, and those related to the reaction system, such as setup configuration and reactor geometry, type of solvent, type and amount of photocatalyst, affecting the selectivity toward specific products are described and discussed. The presented results highlight that a precise evaluation of the efficiency of the process is a challenging but necessary task to be approached in order to allow real applications of photocatalytic processes.

The photocatalytic oxidation of trans-ferulic acid to vanillin in water has been studied by using various TiO2 and WO3-loaded TiO2 samples as catalysts. Different values of selectivity were obtained depending on the physico-chemical properties of the single samples and a vanillin selectivity of 10% was reached in the presence of the commercial TiO2 Merck. Higher selectivity values were obtained by impregnation of TiO2 with H2WO4 followed by calcination. The increased production of vanillin exhibited by the obtained WO3-loaded TiO2 powders was attributed to a reduced further oxidation of the aldehyde caused by the presence of the practically inactive tungsten trioxide hydrate on the TiO2 surface. The best result (ca. 25% of selectivity) was obtained with the WO3(1%)/TiO2 sample.

There are problems in photocatalysis that researchers cannot disregard in a rigorous study of photocatalytic systems. The purpose of the present work is to show how chemical reaction engineering can answers to the previous questions, thus helping scientists to face researches on photocatalysis more successfull and consistenty

Different methods to integrate reaction and separation in a membrane reactor are studied in the present work, with the aim being to highlight the pros and cons of the different alternatives and the effects of the intervening parameters. The coupling of the two processes can take place inside a single apparatus or using separate units. If a single apparatus is utilized, the coupling is more direct, but separate units offer higher degrees of freedom for the design with more opportunities to optimize the system without constraints. However, when using separate units, the integration of the two unit operations depends largely on the parameters intervening in the coupling procedure. These parameters are the recycle ratio, R, if a recycle stream is used to backmix part of the exiting stream, or the number, N, of blocks if the volume of the reaction and the membrane area are fractionated into multiple reaction-separation blocks. The possibility of different combinations of these two basic methods is also presented. The case study to illustrate the effect of the various parameters (R, N, the Damkohler number and the Peclet number) and to find the proper operating conditions is the photocatalytic green synthesis of an aromatic aldehyde, which is recovered from the reaction solution by a pervaporation process to avoid further oxidation. The results show that process intensification is the result of appropriately choosing the reaction system and operating conditions because these factors may substantially increase the yield.

The assessment of the rate law of slurry photocatalytic reactions appears to be a hard task, mainly because in this type of reactions the average rate of reaction, which is experimentally observed in a real reactor, could be very different from the “true” (intrinsic) rate of reaction, which cannot be measured directly. In the present work, it is shown how a proper mathematical model allows the utilization of the differential and/or the integral methods of kinetic analysis. The mathematical model must take into account not only the momentum and the mass balances, but also the radiative transfer equation. However, the discrimination among different proposed kinetic laws remains difficult since these laws usually predict very similar behaviors. In the case of “photodifferential” reactors, kinetic analysis can be carried out considering just the measured average rates of reaction without utilizing the mathematical model. For instance, it is shown that, with a photodifferential reactor, the fitting of the average rate of reaction vs. the substrate concentration gives a satisfactory appraisal not only of the kinetic parameters but also of the average rate of photon absorption. A sufficiently low value of the optical thickness (less than 2.5) is the main requirement to approach the photodifferential condition. Anyway, a strategic choice of the experimentally investigated values of the independent variables (e.g. substrate concentration and irradiance to the reactor) is important for the comprehensiveness of the kinetic analysis.

The present study has been undertaken in order to test the real potential of photocatalytic ozonation in a bench-scale recirculating aquaculture system working on a 180 L reef coral aquarium. Notably, this choice may be considered representative. In fact, (i) the system is virtually closed so that fresh water turnover is practically negligible, (ii) the presence of living organisms is highly diversified (corals, fishes, molluscs, echinoderms and crustaceans) and some of them are particularly sensitive to water quality, (iii) high salinity strongly puts a strain on the purification system. The hereby presented purification method has been named REWAQUA, which stands for REcycling Water for AQUAculture and AQUAria. REWAQUA allows purification rates higher than the sum of the rates of the single technologies (photocatalysis and ozonation) operating in series. Furthermore the production of bromate ions, which are carcinogenic by-products of ozonation, is efficiently controlled. Two years observation of the reef coral aquarium reveals that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of a sustainable aquaculture.

Dimethyl carbonate (DMC) is here proposed – for the first time – as a green organic solvent for photocatalytic synthesis. In this work, the photocatalytic partial oxidation of phenanthrene in dimethyl carbonate (DMC) by using anatase TiO2 as the photocatalyst is described as paradigmatic example of a green synthetic process starting from polycyclic aromatic hydrocarbons (PAHs). For comparison, the same reaction carried out also in ethanol, 1-propanol or 2-propanol is reported. The use of DMC as the solvent allowed us to achieve 19% and 23% selectivity towards 9-fluorenone and 6H-benzo[c]chromen- 6-one, respectively. The proposed approach may represent both a new green synthetic process and an environmentally friendly route to degradation of PAHs.

A batch cylindrical photocatalytic reactor, externally irradiated by 1–6 UV fluorescent lamps and containing a stirred slurry of polycrystalline TiO2, was modeled by coupling a modified Langmuir–Hinshelwood kinetics together with a two-dimensional light intensity field. The radiation field has been determined on the main assumptions of diffuse radiation, isotropic scattering and negligible backward reflected photon flow. The model has been applied to the photocatalytic oxidation of organic substrates which do not undergo homogeneous photochemical degradation. The model is characterized by the following four parameters: the kinetic constants of substrate adsorption, desorption and degradation and the exponent of the power law expressing the kinetics dependence on the light intensity. The model constants may be determined by applying a simple least-squares best fitting procedure.

A process for the preparation of molecular bromine, by means of advanced oxidation processes or their combination is disclosed

Demographic growth and management of water and food resources are probably the most challenging issues of the coming years. In this scenario, intensive aquacultura will be increasingly important in the near future

The photoproduction of vanillin is studied in aqueous medium starting from trans-ferulic acid, isoeugenol, eugenol or vanillyl alcohol by using both commercial and home prepared TiO2 samples as photocatalysts and batch Pyrex photoreactors. The photo-oxidation at room temperature of these compounds produces vanillin with a selectivity ranging from 1.4 to 21 mol% with respect to the converted substrate. An investigation on the intermediates was performed in the case of trans-ferulic acid; for this substrate the most important intermediates were homovanillic acid, vanillyl mandelic acid, trans-caffeic acid, formic acid, acetic acid, and oxalic acid. The carbon mass balance, including CO2 derived from the mineralization, was made for all of the substrates at irradiation times corresponding to the highest selectivity to vanillin. High closure of the carbon balance was obtained with vanillyl alcohol (ca. 90%) and trans-ferulic acid (ca. 80%).

WOS: 000266963000002, A method for determining the amount of substrate adsorbed onto the catalyst surface in liquid-solid photocatalytic system under reaction conditions (photoadsorption) is proposed. The method has been applied to the photocatalytic oxidation of benzyl alcohol carried Out in aqueous suspensions of a home prepared TiO2 catalyst. The influence of alcohol concentration, catalyst amount and irradiation power on photoadsorption was investigated. The photoadsorption per unit mass of catalyst increased by increasing concentration of benzyl alcohol and irradiation power but it decreased, increasing the catalyst amount. By taking into account the photoadsorption phenomena, the kinetic modeling of the photooxidation process has been carried Out and the parameters of the model have been determined. The results indicate that all these parameters are favorably affected by an increase of the photon How absorbed per unit mass of catalyst

Heterogeneous photocatalysis and photoelectrocatalysis have been considered as oxidation technologies to abate unselectively noxious species. This article focuses instead on the utilization of these methods for selective syntheses of organic molecules. Some promising reactions have been reported in the presence of various TiO2 samples and the important role played by the amorphous phase has been discussed. The low solubility of most of the organic compounds in water limits the utilization of photocatalysis. Dimethyl carbonate has been proposed as an alternative green organic solvent. The recovery of the products by coupling photocatalysis with pervaporation membrane technology seems to be a solution for future industrial applications. As far as photoelectrocatalysis is concerned, a decrease in recombination of the photogenerated pairs occurs, enhancing the rate of the oxidation reactions and the quantum yield. Another benefit is to avoid reaction(s) between the intermediates and the substrate, as anodic and cathodic reactions take place in different places., S. Yurdakal thanks to TÜ BITAK (Project no: 111T489) for economic support

An integrated approach to develop a composite hybrid material made of titanium dioxide functionalized with an organic conjugated phenol (DIOL) and silver NPs suitable for the selective oxidation of water soluble aromatic alcohols to aldehydes in water under UV irradiation and very mild conditions was used. The 86% selectivity observed for the Rutile/DIOL/Ag composite is, to the best of our knowledge, the highest thus far reported for partial oxidation of aromatic alcohols to aldehydes in water suspensions of titanium dioxide. The method is general as it relies on the concomitant easier adsorption of the aromatic alcohol and more facile release of the aldehyde, coupled to fast interfacial electron transfer due to the conjugated DIOL acting as a molecular electron bridge covalently bound to both silver NPs and titanium dioxide. Modification of the shuttle molecule as well as utilization of other metal NPs could potentially open the route to optimization of the selective conversion for several other photocatalytic redox reactions mediated by similar advanced titanium dioxide- based composites.

This contribution gives an account of TiO2-based selective photocatalysis as a green synthetic tool for the production of organics. Some case studies of the most common transformations carried out by means of photocatalytic reactions are illustrated.

An unusual autocatalytic photooxidation of 2-methoxybenzyl alcohol has been observed under UV irradiation in aqueous medium. The homogeneous oxidation is catalyzed by the corresponding aldehyde that is also the main oxidation product. The trend of alcohol disappearance rate matches the typical shape of an autocatalytic process, where a crucial and ambivalent role is played by the presence of molecular oxygen. Low oxygen concentrations give rise to a zero-order reaction since the beginning of irradiation, while higher amounts of oxygen reduce the alcohol oxidation rate until the aldehyde reaches a concentration high enough to speed up the alcohol's conversion. Experiments performed by varying alcohol, aldehyde and oxygen concentrations in both aqueous and organic media suggest that the alcohol oxidation is initially favored by the presence of oxygen. Once the formed aldehyde competes for photon absorption, the oxidation is driven by aldehydes alpha cleavage leading to reactive oxygenated species in aqueous medium. An excess of oxygen quenches the latter processes thus inhibiting/slowing down the reaction. (C) 2015 Elsevier B.V. All rights reserved. tAn unusual autocatalytic photooxidation of 2-methoxybenzyl alcohol has been observed under UV irradi-ation in aqueous medium. The homogeneous oxidation is catalyzed by the corresponding aldehyde that isalso the main oxidation product. The trend of alcohol disappearance rate matches the typical shape of anautocatalytic process, where a crucial and ambivalent role is played by the presence of molecular oxygen.Low oxygen concentrations give rise to a zero-order reaction since the beginning of irradiation, whilehigher amounts of oxygen reduce the alcohol oxidation rate until the aldehyde reaches a concentrationhigh enough to speed up the alcohol’s conversion. Experiments performed by varying alcohol, aldehydeand oxygen concentrations in both aqueous and organic media suggest that the alcohol oxidation is ini-tially favored by the presence of oxygen. Once the formed aldehyde competes for photon absorption,the oxidation is driven by aldehydes alpha cleavage leading to reactive oxygenated species in aqueousmedium. An excess of oxygen quenches the latter processes thus inhibiting/slowing down the reaction.

This contribution deals with a short review of some application of TiO2 to green organic synthesis. In particular to selective oxidation of aromatic alcohols under mild conditions.

The oxidation of alcohols to carbonyl compounds in a clean fashion (i.e., with water as a solvent or under solvent‐free conditions, and using O2 or H2O2 as the primary oxidant) is the subject of considerable research efforts. A new approach for the selective oxidation of soluble aromatic alcohols in water under mild conditions via a novel composite photocatalyst has been developed. The catalyst is synthesized by grafting 4‐(4‐(4‐hydroxyphenylimino)cyclohexa‐2,5dienylideneamino)phenol and silver nanoparticles onto the surface of moderately crystalline titanium dioxide. The titanium dioxide‐based composite was first extensively characterized and then employed in the catalytic oxidation of 4‐methoxybenzyl alcohol to 4‐methoxybenzaldehyde under UV irradiation in water at room temperature. The corresponding aldehyde was obtained with unprecedented high selectivity (up to 86 %). The method is general and opens the route to fabrication of photocatalytic composites based on titanium dioxide functionalized with shuttle organic molecules and metal nanoparticles for a variety of oxidative conversions.

The oxidation of alcohols to carbonyl compounds in a clean fashion (i.e., with water as a solvent or under solvent-free conditions, and using O2 or H2O2 as the primary oxidant) is the subject of considerable research efforts. A new approach for the selective oxidation of soluble aromatic alcohols in water under mild conditions via a novel composite photocatalyst has been developed. The catalyst is synthesized by grafting 4-(4-(4- hydroxyphenylimino)cyclohexa-2,5dienylideneamino)phenol and silver nanoparticles onto the surface of moderately crystalline titanium dioxide. The titanium dioxide-based composite was first extensively characterized and then employed in the catalytic oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde under UV irradiation in water at room temperature. The corresponding aldehyde was obtained with unprecedented high selectivity (up to 86 %). The method is general and opens the route to fabrication of photocatalytic composites based on titanium dioxide functionalized with shuttle organic molecules and metal nanoparticles for a variety of oxidative conversions.

In the so-called photocatalytic ozonation (PO) synergistic effects between photocatalysis and ozonation enhance the rate of oxidation of organic compounds, therefore this integrated process is very promising for use in water treatment. In the present work, it is demonstrated that the improvement that can be obtained by the integrated process in comparison with the uncoupled processes depends on the relative weight between photocatalysis and ozonation. In this respect, it has been found that a relatively low rate of photocatalysis (0.3 times the rate of ozonation) is sufficient to get the highest synergy and to maximize the performances in the oxidation of formate, the adopted model organic compound. The benefits of the coupling of photocatalysis to ozonation are not limited to the increase of the oxidation rate, but include also the control of the ozonation by-product of main concern (bromate). The effect of the pH, of the presence of oxidizable organic compounds, of the presence of nitrogen on the formation or on the reduction of bromate are experimentally studied and discussed. The obtained results have relevance for the practical applications of PO, since on these bases it is possible to identify proper operating conditions

This special issue of Catalysis Today Journal, is dedicated to the career of Prof. Vincenzo Augugliaro, University of Palermo, Italy, in the occasion of his retirement in 2015. Prof. Vincenzo Augugliaro was Full Professor of Transport Phenomena at the University of Palermo (Italy) since 1994. He contributed to the fol- lowing research fields: chemical absorption kinetics, biochemical reactor modelling, diffusional kinetics in metallizing alloys and heterogeneous photocatalysis; in this last field he investigated on chemical kinetics of heterogeneous photocatalytic systems, modelling of heterogeneous photoreactors, radiation field in absorbing-reacting media and application of heterogeneous pho- tocatalysis to syntheses processes. He published more than 150 papers in prestigious journals and many chapters in books and is co-author of 4 patents. Prof. Augugliaro was appreciated not only for his important achievements in the field of heterogeneous photocatalysis, but also for his great effort as mentor of many master and PhD chemical engineering students. This special issue contains twenty-four original papers by researchers involved in various aspects of heterogeneous photocatalysis.

In theso-calledphotocatalyticozonation(PO)synergisticeffectsbetweenphotocatalysisandozonation enhance therateofoxidationoforganiccompounds,thereforethisintegratedprocessisverypromising for useinwatertreatment.Inthepresentwork,itisdemonstratedthattheimprovementthatcanbe obtained bytheintegratedprocessincomparisonwiththeuncoupledprocessesdependsontherelative weight between photocatalysis and ozonation. In this respect, it has been found that a relatively low rate of photocatalysis (0.3 times the rate of ozonation)issufficienttogetthehighestsynergyandtomaximize the performancesintheoxidationofformate,theadoptedmodelorganiccompound.Thebenefitsof the couplingofphotocatalysistoozonationarenotlimitedtotheincreaseoftheoxidationrate,but include alsothecontroloftheozonationby-productofmainconcern(bromate).TheeffectofthepH,of the presenceofoxidizableorganiccompounds,ofthepresenceofnitrogenontheformationoronthe reduction ofbromateareexperimentallystudiedanddiscussed.Theobtainedresultshaverelevancefor the practicalapplicationsofPO,sinceonthesebasesitispossibletoidentifyproperoperatingconditions.

LaFeO 3 powders doped with Sr (20 mol%) and Cu (0-10-20 mol%) were prepared by citrate auto-combustion synthesis and investigated in terms of crystal structure, morphology, surface area and optical properties. All powders showed photocurrent response in the form of a pasted and annealed electrode and as slurry electrode; the highest value was obtained for undoped orthoferrite calcined at 600 °C. Their physical–chemical properties were related to photoelectrochemical behaviour. The position of the quasi-Fermi level of electrons for all the photocatalysts calcined in the range 600–980 °C is about the same within experimental error (between −0.62 and −0.67 V with respect to Ag/AgCl reference electrode, at pH 7). Doping with 20 mol% of strontium did not influence the flat band potential of the powders, while doping with copper caused an important and reproducible change in the titration curve, indicating the presence of intermediate energy states in the samples calcined at 600 °C, but not in those calcined at 980 °C.

The configurations and performance of photocatalytic membrane reactors (PMRs) assembled with membranes (also photocatalytic type) and/or suspended photocatalyst are described. Examples of the application of PMRs in water/wastewater treatment as well as in photocatalytic synthesis are shown. An outline of the modeling of PMRs is presented with a brief economic analysis; future trends in PMRs are also discussed.

This chapter reports the properties of semiconductor materials used in heterogeneous photocatalysis together with a comparison of heterogeneous photocatalytic systems and a brief description of the types of membranes that can be used. Some aspects of membrane operations, such as fouling, separation of a photocatalyst and effectiveness of photodegradation on permeate quality are discussed.

Oxidation of ferulic acid (C10H10O4) in aqueous medium occurs by using both commercial and home prepared TiO2 samples under visible light irradiation. Among the oxidation products vanillin was found with a selectivity ranging from 1 to 2% with respect to the converted substrate. By considering that TiO2 is unable to absorb visible light and ferulic acid does not react in the absence of TiO2, the observed photoactivity may be explained by the formation of a charge-transfer complex between ferulic acid and TiO2, being the complex able to absorb visible light. Among all the tested semiconductor oxides, only Merck anatase TiO2 does not perform the oxidation of ferulic acid under visible light irradiation while it is active under near-UV irradiation. Diffuse reflectance spectra of Merck samples impregnated with ferulic acid do not show any evidence of complex formation.

The hydroxylation of phenol (a substrate containing an electron donor group) and of benzoic acid (a substrate containing an electron withdrawing group) has been carried out by the photocatalytic method in aqueous suspensions containing commercial or home prepared TiO2 samples. The aim of the work was to study the distribution of hydroxylation products when different photocatalysts were used and to correlate the selectivity to some physico-chemical features of the powders. The samples were characterized by X-ray diffraction, thermogravimetry, determination of crystalline phase percentage, specific surface area and zero charge point. The photoreactivity results indicate that the products of the primary oxidation of phenol are the ortho- and para-mono-hydroxy derivatives while those of benzoic acid are all the mono-hydroxy derivatives independently of the catalyst. The selectivity toward mono-hydroxy derivatives shows a strong dependence on catalyst hydroxylation and crystallinity degrees: the highest selectivity values were obtained by using the commercial samples that resulted the least hydroxylated and the most crystalline ones. A kinetic model, taking into account the mineralization and the partial oxidation reaction routes, is proposed by using the Langmuir–Hinshelwood model.

The integration of photocatalysis with a membrane separation process, in particular pervaporation, permits the recovery of valuable intermediate compounds (aromatic aldehydes) while they are produced avoiding their further degradation in the reactive ambient. In this way the yield and the conversion are enhanced. The coupling of the two processes is straightforward and the integration is complete even maintaining pervaporation and photocatalysis in two separate apparatuses provided that the process stream is continuously recycled at a sufficiently high flow rate. Additional advantages are: higher degree of purification of the aldehyde in the powder-free product stream, semicontinuous production and possibility of operating in a continuous mode with high values of the yield. (C) 2010 Elsevier B.V. All rights reserved.