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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

A set of metals modified TiO

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.

Abstract: Within the current production systems, the need for low environmental impact processes to produce chemicals, the treatment of aqueous effluents and the production of fuels is becoming an increasingly urgent challenge. In this context, photoelectrocatalysis (PEC), which couples the electrochemical method (EC) with photocatalysis (PC), can be considered a valid alternative to traditional catalytic processes. It increases the photocatalytic and the electrochemical efficiency by improving the separation of the photoproduced electrons and holes on the active electrode surface and addressing the partial oxidation products formation by selecting the applied potential values. This review is concerned with the possibility of forming PEC high-added-value chemicals, sometimes with the contemporary production of hydrogen, by using different materials for the fabrication of photoanodes and photocathodes in different solvents and system configuration, obtaining very interesting values of conversion, selectivity, and Faradaic efficiencies. In particular, the review presents results related to the production of valuable compounds by the valorisation of alcohols, biomass derivatives and some peculiar organic substrates, highlighting the influence of electrode composition, applied bias, electrolyte type, and solvent.

In this work the photocatalytic (PC) and photoelectrocatalytic (PEC) reforming of furfuryl alcohol (FA) under environmental friendly conditions was investigated. Both H2 evolution and partial oxidation to furfuraldehyde were followed. For the first time TiO2 based photocatalysts were studied and the photocatalytic activity of home prepared photocatalysts was compared with that of commercial ones under both UVA and simulated solar irradiation. PEC tests were performed by using home prepared TiO2 nanotubes (TiO2 NTs) as photoanode and Pt free Ni foam as cathode to improve the Hydrogen Evolution Reaction (HER). Both the partial FA oxidation reaction rate and H2 evolution rate were normalized for the lamp specific power to account for the different photon flux and the rates were higher for PEC process. PEC is a promising strategy for the valorization of biomasses with simultaneous H2 production in spite of the cost of the bias.

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.

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.

This study investigated the treatment of a shipboard slop containing commercial gasoline in a pilot plant scale consisting of a membrane biological reactor (MBR) and photocatalytic reactor (PCR) acting in series. The MBR contributed for approximately 70% to the overall slop purification. More precisely, the biological process was able to remove approximately 40%, on average, of the organic pollution in the slop. Nevertheless, the membrane was capable to retain a large amount of organic molecules within the system, amounting for a further 30% of the influent total organic content removal. However, this affected the membrane fouling, thus resulting in the increase of the pore blocking mechanism that accounted for approximately 20% to the total resistance to filtration (2.85∙10 13 m −1 ), even if a significant restoration of the original membrane permeability was obtained after chemical cleanings. On the other hand, the biological treatment produced a clear solution for the photocatalytic system, thereby optimizing the light penetration and generation of highly oxidizing active oxygen species that enabled the degradation of bio-recalcitrant compounds. Indeed, low total organic carbon (TOC) values (

"Properties of titanium dioxide" presents a survey of the main physicochemical properties of TiO2 upon which rely all of the applications of this material. Structures and morphologies of titanium dioxide have been taken into account, also in correlation with thermodynamic properties. Bulk and surface defectivity has been described in detail, because of its relevant consequences in terms of catalytic activity. The basic mechanisms of interaction between photons and TiO2 have been discussed on the basis of the optoelectronic features of the semiconductor. Finally, electrical, mechanical, and rheological properties of TiO2 have been presented.

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.

This review presents a survey of some heterogeneous photocatalytic processes for the synthesis of high-value added compounds carried out in photocatalytic membrane reactors (PMRs). The two technologies can be easily integrated due to the similar conditions at which they usually operate. Furthermore, significant advantages derive from the coupling and in some cases also synergistic effects can be observed. These features have been highlighted for the photocatalytic syntheses reviewed along with engineering and design aspects investigated for some industrially relevant high-value added compounds. Notably, photocatalytic syntheses carried out in PMRs are still rare mainly because interdisciplinary competences and collaborations are often required in this field. However, we hope that a survey of the recently reported examples may inspire researchers for future developments and new opportunities.

This chapter deals with water treatments by advanced oxidation processes (AOPs) based on chemical and photochemical reactions. The most used processes are described, and for each of them, the main reaction mechanisms, principles, advantages, drawbacks, performances and formation of by-products, coupled with technologies and their applications to waters and wastewater depollution, have been analysed, supporting the main results of studies published in the pertinent literature.

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 this paper, the first photoelectrocatalytic (PEC) 3-pyridinemethanol oxidation to 3-pyridinemethanal and vitamin B-3 was investigated. To meet this aim, efficient nanotube structured TiO2 on a Ti plate as a photoanode was prepared by an anodic oxidation method in ethylene glycol and characterized by XRD, SEM, and photocurrent techniques. The effect of nanotube morphology, applied potential, Na2SO4 concentration, stirring speed of solution, and pH on the reaction activity and product selectivities were investigated. The TiO2 phase of all of the anodes was mainly the anatase one. The PEC activity, the intensity of the XRD peak and the photocurrent increased by increasing the nanotube length. The activity decreased by decreasing both the Na2SO4 concentration and the applied potential, whereas 3-pyridinemethanal selectivity increased. By increasing the stirring speed of the solution, both the activity and the 3-pyridinemethanal selectivity increased. A lower or no activity was observed for photocatalytic (PC) and electrocatalytic runs, respectively, which were carried out for the sake of comparison. No PC activity was obtained in the presence of N-2, but PEC reactions in the presence of N-2 were faster than those in the presence of O-2. The produced 3-pyridinemethanal in both N-2 and O-2 atmosphere was reduced at the cathode in the PEC reaction, but its oxidation appeared to be much more favourable. The PC reactions could not be carried out under acidic conditions, whilst the PEC ones could be performed in the pH range of 2-12. Moreover, the results indicate that the PEC method allows higher conversions and selectivities to vitamin B-3 to be obtained at pH 7 with respect to those reported in the literature.

Nitrate and bromide ions are generally considered indicators of anthropogenic pollution and seawater intrusion, respectively, in the groundwater of coastal territories. The analysis of these species is generally carried out with routine chromatographic analyses which generally afford partially merged or poorly resolved peaks. In the present paper a simple method for the correct evaluation of their concentration in water is reported. This method does not imply utilization of other instruments or technologies, only the mathematical elaboration of the data obtained from routine analysis of standard solutions containing the two species. Standard binary solutions of nitrate and bromide ions at different concentrations, ranging between 0.1 and 2 mM, were analyzed by means of ion chromatography. Splitting two partially merged chromatographic peaks and considering each resulting area as originating from a single species produces &ldquo, measured&rdquo, concentration values which differ from the nominal ones. Such a procedure generates errors (one per species) which can be written as a function of the above mentioned &ldquo, concentrations and which can be graphically represented by means of a surface in a three-dimensional (3D) space. In this way, &ldquo, concentrations of bromide and nitrate ions can be corrected by calculating the errors generated under the experimental conditions at which the chromatographic separation is performed. Notably, this is analogous with the two-dimensional (2D) calibration normally carried out for analytical purposes. Indeed, both methods allow estimation of the unknown concentration of species in solution by correlating the instrumental response with the concentration of standard solutions.

Kinetics aspects of heterogeneous catalysis and photocatalysis are reported together with the most used models developed for both fields. The chapter describes the main mechanisms involved in the different processes and the parameters used to determine their performances. A comparison of the behaviors and kinetics features of heterogeneous catalysis and photocatalysis is presented.

In the present chapter, the analogies between photocatalytic systems and the systems where the more common thermally activated reactions take place are highlighted. The objective is to propose a unified approach for the analysis and the design, which, however, must take into account how and why photocatalytic reactors differ from reactors with thermal reactions. The necessity of absorbing photons to activate the photocatalytic process adds complexity to the system, but some approaches are presented to simplify the problems and make easier their solution.

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.

The use of microreactors in (photo)catalytic processes offers new possibilities for studying and optimizing many mass and photon transfer limited reactions. In this study, we propose a scalable computational fluid dynamics (CFD) model for the prediction of photocatalytic degradation of a model pollutant (4-nitrophenol) using immobilized N-doped TiO2 grown over reduced graphene oxide (N-TiO2/rGO) in a photocatalytic microreactor working in continuous flow-recirculation mode. The mode of operation used in this study allows the reduction of mass transfer limitations inherent to heterogeneous photocatalytic reactions taking place on immobilized catalysts. A CFD model was developed for effective prediction of experimental results using COMSOL multi-physics. The experiment and the model results clearly showed a good agreement. The model parameters were determined through fitting the model with the experimental data, adsorption rate constants were estimated to be 1.76 × 104 m3 mol−1 h−1 and 0.0252 h−1 for monolayer (kads,m and kdes,m), 1.76 × 104 m3 mol−1 h−1 and 0.0126 h−1 for multilayer (kads,n and kdes,n); and the intrinsic rate constant (ks) was 2.02 h−1. This proposed model herein could serve as a practical tool to improve and optimize an extensive number of photocatalytic reactions for (waste)water applications in microreactors operating in recirculation mode.

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.

This chapter briefly presents the fundamentals of the processes of heterogeneous photocatalysis (PC). In particular, Langmuir–Hinshelwood and Eley–Rideal models that are often used to model the kinetics of heterogeneous photocatalytic reactions are described together with other models and equations derived. Moreover, some considerations about the dependence of the rate of PC on the light intensity, pH, and photocatalyst modification are done. Methods for photoreactor modeling are described, and the coupling of PC with other advanced oxidation processes (AOPs) using H2O2, O3, and peroxydisulfate is discussed. It is highlighted that coupling different technologies results in a real intensification of the global efficiency only for specific ratios of the rates of the single processes. The suitability of the practical application of the AOPs must be based on a precise process efficiency assessment, which, as the results show, is a challenging but necessary task.

In the present chapter it is shown how photocatalytic membrane reactors utilizing membrane processes, which are not pressure driven, can exploit various mechanisms to obtain a substantial improvement of the process. The fundamentals of this particular type of membrane reactors are reviewed including the effects of the most important parameters and the methods and rules of coupling photocatalysis and membrane separation. The survey of the studies on photocatalytic membrane reactors (PMRs) utilizing pervaporation, dialysis, membrane contactors and membrane distillation offers the opportunity of discussing the advantages with respect to PMRs adopting pressure driven membrane processes. Indeed, the strengths of the investigated processes are the high retention of the photocatalytic powders with minor fouling problems, the simpler and cheaper apparatuses and the possibility of selectively removing or recovering the products. Finally, the reasons, which currently limit the application of these membrane reactors, are illustrated together with the very interesting future perspectives.

N-doped anatase/rutile photocatalysts were prepared by a sol-gel method, using TiCl4 as TiO2 precursor and urea as N-dopant source. The catalysts required a thermal treatment at temperature higher than 300 degrees C to achieve actual nitrogen doping; this treatment also allowed obtaining crystalline and hydrophobic samples. Moreover, nitrogen doping modified the surface of samples by increasing the anatase to rutile phase ratio and hydrophilicity. The catalysts were characterized by BET specific surface area, XRD, ESEM, TGA, FT-IR, DRS and XPS measurements, with particular attention to the assessment of the N-doping effect. It was found that XPS analysis should be used together with DRS and FT-IR to discriminate whether N had been incorporated in TiO2 lattice or N species had just adsorbed on the TiO2 surface. Moreover, XPS analysis could be also used for determining the crystallinity of TiO2. The photocatalytic activity of the samples was tested for the partial oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde in water under near-UV, visible, UV-visible and simulated solar light, respectively. Commercial (Degussa P25) and undoped home-prepared TiO2 anatase-rutile catalysts were also used for comparison. The results show that N-doping improves absorption of visible light by the catalysts, but the reaction rate does not increase accordingly. Selectivity was higher in the presence of poorly crystallized catalysts, whereas doping seemed to have a slightly improving effect.

Two commercial (Merck and Sigma-Aldrich) and two home prepared (HP05 and HP05C) powdered TiO2 photocatalysts were investigated by fast field cycling nuclear magnetic resonance experiments in order to explore the nature of the interactions between water and the solid surfaces. The results were related to the activation energies determined at temperatures ranging from 303 to 353 K for the photocatalytic oxidation in water of three model molecules presenting different interactions with the solid surface (catechol, phenol, and metylbenzoate). The photoactivity results at different temperatures were comparable to each other because the runs were carried out while keeping constant the concentration of O2 in the suspensions. The study highlights the influence of the adsorbed water on the activation energy of a photocatalytic reaction. In particular, we showed that competition between water and substrate adsorption is a determining factor in the activation energy of a photocatalytic oxidation reaction.

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.

Visible-light responsive bare and metal loaded (Pt, Ag, Rh, Pd) TiO 2 photocatalysts were prepared by using a simple ultrasound treatment. This method induced bulk oxygen deficiency resulting in a narrowing bandgap (from 3.18 to 3.04 eV) and in visible light absorption. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area (SSA) and pore size distribution (PSD), UV–vis diffuse reflectance spectroscopy (DRS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was evaluated by using the 4-nitrophenol oxidation reaction and the photocatalytic oxidation of glucose with H 2 production. In the presence of the sonicated samples the 4-nitrophenol degradation and the glucose conversion increased of ca. 40% and 11%, respectively. A good H 2 evolution was, moreover, observed in the latter case. The Pt-loaded samples showed the highest photoactivity for H 2 production and it can be explained by taking into account the highest value of its working function. The obtained results open new perspectives for the synthesis of novel nano-TiO 2 -based photocatalysts capable to degrade water or airborne pollutants under visible light irradiation.

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.

The treatment by advanced oxidation processes (AOPs) of waters contaminated by organic pollutants and containing also innocuous bromide ions may generate bromate ions as a co-product. In the present work heterogeneous photocatalysis and ozonation have individually been applied and in combination (integrated process) to degrade the organic compounds in water containing also bromide anions. The results show that: i) the sole photocatalysis does not produce bromate ions and in the case of its presence, it is able to reduce bromate to innocuous bromide ions; ii) the integration of photocatalysis and ozonation synergistically enhances the oxidation capabilities; and iii) in the integrated process bromate ions are not produced as long as some oxidizable organics are present. © 2013 Elsevier Ltd.