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The interplay between high film crystallinity and n-type doping in enhancing the performance of ZnFe2O4 thin film photoanodes has been revealed. Maximum benefit was achieved for the ca. 300 nm-thick photoactive layer with superior photon harvesting.

A novel Ni-based 2,2′-bisdipyrrinato complex bearing peripheral benzoic acid groups (Ni-bisdpmCOOH) has been synthesized and characterized. Electrochemical investigations revealed a high energy LUMO level that, combined with its absorption properties extending up to the NIR region, is compatible with its use as a sensitizer in thermodynamically uphill photocatalytic reactions, such as proton and carbon dioxide photoreduction. A sensitized photo-anode was prepared by adsorbing Ni-bisdpmCOOH onto a TiO2 film, which showed an incident photon to current efficiency, measured at 0.62 V vs. RHE, extending up to the visible light region. This demonstrates that electronically excited Ni-bisdpmCOOH is effectively able to inject electrons into the conduction band of TiO2, thus opening the way for effective TiO2 sensitization or MOF implementation of the molecule itself for energetic applications.

The effect of TiO2 surface fluorination on the hydrogen peroxide evolution occurring in photocatalytic runs was investigated employing the azo dye Acid Red 1 (AR1) and two model organic molecules with acidic properties, i.e. formic acid (FA) and benzoic acid (BA), as substrates of oxidative degradation. While AR1 and BA photocatalytic degradation on fluorinated titanium dioxide (F–TiO2) was markedly faster than on unmodified TiO2, because of enhanced hydroxyl radical formation, H2O2 concentration during the photodegradation of both substrates on F–TiO2 was lower, possibly because of the reduced rate of interfacial electron transfer. By contrast, FA underwent slower photocatalytic degradation on F–TiO2, but, at the same time, hydrogen peroxide concentration was relatively high, while no H2O2 could be detected during FA photodegradation on unmodified TiO2. Photocatalytic runs in the presence of the nitrate anion, able to react with the CO2˙− species produced from FA oxidation, but not with conduction band electrons, demonstrated that CO2˙− plays a relevant role in H2O2 formation during FA degradation on F–TiO2. In fact, surface fluoride, having a shielding effect at the semiconductor–water interface, not only inhibits the photocatalytic decomposition of H2O2, but also favours CO2˙− desorption and reaction with dissolved O2, generating H2O2. By contrast, CO2˙− mainly gives electron transfer to the conduction band of naked TiO2 and surface reduction of the photocatalytically produced H2O2.

Photocatalysis and sonolysis exhibit synergistic effects in the degradation of organic molecules in aqueous suspension, when low ultrasound frequency (i.e. 20 kHz) is employed. The degradation of the azo dye Acid Orange 8 in aqueous suspensions was systematically evaluated under sonolysis, photocatalysis and sonophotocatalysis as a function of dye concentration, amount and type of photocatalyst (TiO2 or ZnO) and catalase addition, in terms of pseudo-first-order degradation rate constants. The evolution of hydrogen peroxide was also monitored. Synergistic effects of the combination of ultrasound and photocatalysis should mainly involve the aqueous phase and be due to an increased concentration of reactive radicals, consequent to the action of ultrasound on the peroxide species produced by both photocatalysis and sonolysis.

Poly(ethylene terephthalate) (PET) and cotton fibres, treated in an appositely set up RF SF6 plasma reactor under different operating conditions, were characterised by XPS, EPR, DSC, XRD, ATR analyses, water contact angle and water droplet roll-off angle measurements. The ageing of plasma-treated samples was also investigated under different post-treatment conditions. Plasma treatment led to efficient implantation of fluorine atoms on the surface of both polymers; this resulted in water repellence without altering the bulk properties of the polymers. The radical species formed in the plasma-activated polymer surface were involved in its fluorination and in the subsequent uptake of atmospheric oxygen. Surface reorganisation of polymer segments, tending to reduce the interfacial energy between the polymer and the phase in contact with it, induced the surface modifications observed under ageing and in samples plasma-treated several times. An increase in the depth of the fluorinated layer, leading to outstanding stable hydrorepellence, was achieved by repeated SF6 plasma treatments, followed by surface rearrangements favoured by swelling.

A series of Fe-silicalites with MFI structure, employed as catalysts in the title reaction, was investigated by FTIR analysis, using pyridine as the probe molecule for acidity determination. The oxidation reaction was also monitored by FTIR spectroscopy on the best-performing catalyst. An optimal content and distribution of extra-framework iron assures high selectivity, while high acidity increases benzene conversion, but lowers the phenol yield. Benzene conversion to phenol occurs on N2O-pretreated Fe-silicalite catalysts only and N2O does not adsorb as such on the catalyst, even at low temperature, but undergoes decomposition: this confirms the activating role of N2O in the reaction mechanism. Under the experimental conditions adopted in reaction monitoring, the yield of adsorbed phenol is maximal around 550 K and the reaction is paralleled by the complete oxidation of benzene to CO2 .

Propagation radicals generated during the photopolymerization and photo-cross-linking of a trimethacrylate and a vinylmethacrylate monomer have been characterized by EPR and ENDOR spectroscopy at different temperatures. Also, radical decay has been investigated at 363–423 K. The EPR spectral shape reflects a fast exchange process between two radical conformations and is sensitive to the mobility of the polymeric structure surrounding radicals. ENDOR spectra show 1H-matrix lines and a band around 45 MHz, which has been attributed to the interaction of the unpaired electron with the hydrogen nuclei of a freely rotating methyl group. Radical decay and dynamic phenomena involving radicals have been interpreted in the light of a dispersive kinetic model, which allows the evaluation of useful parameters for polymer characterization.

The photocatalytic behaviour of a series of ammonium fluoride (NH(4)F)-doped titania (TiO(2)) photocatalysts was investigated in the decomposition of acetic acid in aqueous suspensions and in the gas phase mineralization of acetaldehyde. Very similar photocatalytic activity trends, usually increasing with increasing the calcination temperature for a given nominal dopant amount, were obtained for the two test reactions. Moderately doped TiO(2) calcined at 700 °C, consisting of pure anatase, was the best performing photocatalyst in both reactions. The photocatalytic oxidation of acetic acid was investigated systematically as a function of irradiation wavelength, by collecting so-called action spectra. By comparing the shapes of the action spectra with those of the absorption spectra of the investigated photocatalysts a model is proposed, based on spectral features deconvolution, which allows a clear distinction between inactive light absorption and effective photoactivity in acetic acid decomposition.

Pyridine and ammonia have been used as probe molecules for the quantitative analysis of surface acidity of some solid catalysts by FTIR spectroscopy. For pyridine, a scale of acidity and an evaluation of the relative acid strength at different temperatures (373–773 K) were obtained for both Bronsted- and Lewis-acid sites. Correlation was verified between the concentration of Bronsted sites and the catalytic activity of the catalysts examined for the dehydration of 2-(2-hydroxyethyl)pyridine to 2-vinylpyridine. In contrast, ammonia was a much less reliable probe, mainly due to the overlapping of the resulting IR absorption bands. Moreover, it decomposed even at rather low temperatures, when adsorbed onto the catalysts.

The formation of trapped radicals under UV irradiation of ethylene glycol dimethacrylate in the presence of different amounts of photoinitiator, as well as radical decay at different temperatures (90–150 °C) after the end of irradiation, have been studied by electron paramagnetic resonance (EPR) spectroscopy. A fitting procedure of the EPR signals revealed that the nine-line EPR spectrum can be attributed to the propagating radical, undergoing a fast exchange process between two conformations. This radical also gives an ENDOR spectrum even at room temperature, thus suggesting that the polymer structure is essentially solid. At least one different radical species is present in highly photo-cross-linked samples. At temperatures above 100 °C, the hyperfine structure of the nine-line EPR spectrum is partly washed out, owing to a spin–spin exchange phenomenon between radicals. This becomes more evident with increasing degree of polymerization and cross-linking during radical decay kinetic runs and also affects the rate of exchange between the two radical conformations.

Radicals trapped during the photopolymerization and photo-cross-linking of 2-ethyl-2-hydroxymethylpropane-1,3-diol triacrylic ester have been studied by EPR spectroscopy at different temperatures (25–180 °C) and their thermal decay has been followed at 120 °C and 150 °C. Performing a fitting procedure on the EPR signals showed that they are composed of two kinds of patterns, which superimpose with the same g value. One of them is a single-line spectrum, while the other is hyperfine-structured. An exchange between two radical conformations is revealed by the latter, with the rate depending both on temperature and on the molar fraction of radicals giving the single-line spectrum. This suggests that both species are involved in the exchange mechanism. Termination occurs preferentially between radicals giving the same EPR pattern. Second-order termination rate constants depend on the photoinitiator concentration in the irradiated photoreactive mixture and give information about the microstructure of the polymer.

The formation of trapped radicals under UV irradiation during the photopolymerization of butane-1,4-diyl diacrylate in the presence of different amounts of photoinitiator, as well as the radical decay after the end of irradiation, have been studied by EPR spectroscopy. Direct evidence that higher photoinitiator radical concentrations greatly favour radical–radical encounters is obtained. The formation of the same radical species in two different polymeric phases, one essentially rigid and the other more fluid, is at the origin of the two observed superimposed EPR patterns. The ratio R between them decreases with increasing photoinitiator concentration, owing to the formation of shorter and consequently more mobile polymer chains. In contrast, the more rigid phase seems to dominate in photopolymerized diallyl 3-oxapentane-1,5-dicarbonate. ENDOR measurements further support the correlation proposed by us between EPR spectral shape and the rigidity of the polymeric phase.

Direct evidence of the presence of extremely long-lived radicals produced in the photopolymerization of 1,6-hexanediol diacrylate and tetraethyleneglycol diacrylate has been obtained by EPR spectroscopy. As radical decay in thermal after-treatment is accompanied by additional polymerization and cross-linking, kinetic studies were carried out at different temperatures (40-120 °C) both by EPR spectroscopy and by analysis of the parallel disappearance of double bonds. Apart from EPR data at 120 °C, all experimental results show that both radical decay and double-bond conversion are first-order reactions, and kinetic constants evaluated for the two processes are practically coincident at the same temperature. Activation parameters for thermal after-treatment of the two diacrylates are almost the same, owing to the similarity in their chain length and mobility. The behaviour of the system at 120 °C, accounted for by a multiple relaxation model, is interpreted as being due to prevailing cross-linking reactions in the vitrified network of trapped radicals.

The ΔC°p values for proton addition to some aminoalcohols, aminoethers and diamines in aqueous solution have been determined at 25 and 40°C, using partial molal heat capacity data for the neutral molecules and their hydrochlorides. A comparison is made between ΔC°p, ΔS° and ΔV° values and the corresponding values for monofunctional amines, and the following features emerge for proton addition to the nitrogen atom of saturated amines in water: (1) Either in mono- or in bifunctional amines the thermodynamic reaction parameters, ΔC°p and ΔS°, change systematically in going from primary, to secondary, to tertiary amines; the same is observed for ΔV°, but only in the case of monofunctional amines. (2) The ΔC°p and ΔS° values of protonation of bifunctional amines are higher than those of monofunctional amines of the same type.Interpretation of this behaviour is made in terms of two concurrent solvation effects: (i) the charged nitrogen–water interaction which is strongly dependent on the number of N-bonded hydrogens; (ii) the hydration of alkyl residues which is less extensive when they are bound to a charged nitrogen than when the nitrogen is neutral.