Francesco Parrino

Semiconductor‐Photocatalyzed Sulfoxidation of Alkanes

In the case of the linear C16–20 alkanes the resulting alkanesulfonic acids are used as biodegradable surfactants. The primary reaction steps of this rare alkane functionalization consist of UV excitation of SO2 [3] followed by hydrogen abstraction from the alkane to produce an alkyl radical (Scheme 1). Subsequent addition reactions with SO2 and O2 generate an alkylpersulfonyl radical, which in turn produces another alkyl starter radical and the persulfonic acid. Fragmentation and hydrogen abstraction [Eqs. (2) and (3)] afford the alkanesulfonic acid.

Combination of ozonation and photocatalysis for purification of aqueous effluents containing formic acid as probe pollutant and bromide ion.

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.

Photocatalysis in dimethyl carbonate green solvent: degradation and partial oxidation of phenanthrene on supported TiO2

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.

Alcohol‐Selective Oxidation in Water under Mild Conditions via a Novel Approach to Hybrid Composite Photocatalysts

Abstract 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.

Improvement of membrane performances to enhance the yield of vanillin in a pervaporation reactor.

In membrane reactors, the interaction of reaction and membrane separation can be exploited to achieve a “process intensification”, a key objective of sustainable development. In the present work, the properties that the membrane must have to obtain this result in a pervaporation reactor are analyzed and discussed. Then, the methods to enhance these properties are investigated for the photocatalytic synthesis of vanillin, which represents a case where the recovery from the reactor of vanillin by means of pervaporation while it is produced allows a substantial improvement of the yield, since its further oxidation is thus prevented. To this end, the phenomena that control the permeation of both vanillin and the reactant (ferulic acid) are analyzed, since they ultimately affect the performances of the membrane reactor. The results show that diffusion of the aromatic compounds takes place in the presence of low concentration gradients, so that the process is controlled by other phenomena, in particular by the equilibrium with the vapor at the membrane-permeate interface. On this basis, it is demonstrated that the performances are enhanced by increasing the membrane thickness and/or the temperature, whereas the pH begins to limit the process only at values higher than 6.5.

Elemental Bromine Production by TiO2 Photocatalysis and/or Ozonation

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.

Polymers of Limonene Oxide and Carbon Dioxide: Polycarbonates of the Solar Economy

Limonene epoxide (1,2-limonene oxide) readily reacts with carbon dioxide inserted in a ring-opening copolymerization reaction and forms polycarbonates of exceptional chemical and physical properties. Both poly(limonene carbonate) and poly(limonene dicarbonate) can be synthesized using low-cost Zn or Al homogeneous catalysts. This study addresses selected relevant questions concerning the technical and economic feasibility of limonene and carbon dioxide polymers en route to the bioeconomy.

Electron transfer in ZnO–Fe2O3 aqueous slurry systems and its effects on visible light photocatalytic activity

ZnFex (x = 0.025, 0.05, and 0.1) nanocomposites and pure ZnO and Fe2O3 photocatalysts were synthesized by a simple sol–gel route and characterized by means of specific surface area (SSA) analysis, X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDS). Their photocatalytic activity was investigated under visible light by using methylene blue (MB) and benzoic acid (BA) as model compounds. Coupling ZnO and Fe2O3 results in higher photocatalytic activity with respect to the pure materials. Photoelectrochemical characterization performed in slurry systems allowed the elucidation of the electronic structure of the nanocomposites under conditions strongly mimicking the photocatalytic reaction medium. Intense electronic interactions between ZnO and Fe2O3 induce a shift of the bandgap absorption to longer wavelengths. Furthermore a shift of the photogenerated electron potential towards less negative values could be evidenced for the first time by means of these measurements. The electronic configuration obtained after coupling the two semiconductors reduces recombination through efficient electron transfer from Fe2O3 to ZnO, thus justifying the observed photoactivity results.

Heterogeneous Photocatalysis: A Promising Advanced Oxidation Process

Abstract 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.

PMRs Utilizing Non–Pressure-Driven Membrane Techniques

Abstract In this chapter, it is shown how photocatalytic membrane reactors (PMRs) 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 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 that currently limit the application of these membrane reactors are illustrated together with the very interesting future perspectives.