1,721,256 research outputs found
Photocatalytic production of hydrogen
No full textThe photocatalytic production of hydrogen represents a fascinating way to convert and store solar energy in the form of chemical energy, i.e. as hydrogen, the ideal fuel for the future, which can be produced either by water splitting, or, more efficiently, by photo-reforming of organics in either liquid or gas phase. Starting with a brief historical background, the fundamentals of photocatalytic hydrogen production are outlined, together with the mechanistic aspects of the process. The most recent achievements in the field are also discussed, concerning both the development of innovative materials able to exploit a larger portion of the solar spectrum compared to traditional photocatalytic materials, and the different set-ups and devices which have been developed in recent years
Synergistic effects of sonolysis combined with photocatalysis in the degradation of an azo dye
No full textPhotocatalysis 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
Effects of surface modification and doping on the photocatalytic activity of TiO2
No full textThe photocatalytic activity of titanium dioxide prepared by different synthetic routes, including flame spray pyrolysis, and modified either by noble metal nanoparticles deposition or by surface fluorination, or by doping with non metal p-block elements was tested in both down-hill and up-hill reactions, including the degradation of organic molecules in water suspension and the parallel hydrogen peroxide production by oxygen reduction and hydrogen production from water splitting or methanol steam reforming. Photoactivity results are discussed in relation to the structure and absorption properties of the photocatalytic materials, which may affect the photocatalytic electron transfer paths. Selected examples include the effect of gold nanoparticles deposition on the photocatalytic oxidation of organic substrates, the effect of fluorine doping on the absorption and action spectra of the materials, the effects of noble metal nanoparticles deposition and of the inlet alcohol/water composition on the reaction paths involved in the photo-steam reforming methanol
Photochemistry of N-benzylideneanilinium cations in concentrated sulphuric acid solutions
No full textThe photoreversible E reversible arrow Z isomerization of a series of protonated N-benzylideneanilines (X-C6H5CH=NC6H5-Y; X=H, N(CH3)(2); Y=H, NO2) was investigated in concentrated sulphuric acid solution. The UV absorption spectra of the E isomers are practically independent of substituents on benzene rings and suggest a planar conformation for protonated N-benzylideneanilines. The UV spectra of Z isomers were obtained from photostationary state conditions at two wavelengths. Also the quantum yields of E --> Z and Z --> E photoisomerization are not markedly affected by the ring substituents and are compatible with a photoreversible process occurring through a common excited state
Hydrogen production by photo-steam reforming of methanol : effect of noble metal deposition on TiO2
No full textEnhanced photocatalytic formation of hydroxyl radicals on fluorinated TiO2
No full textDirect experimental evidence of the higher concentration of hydroxyl radicals generated on fluorinated titanium dioxide (F - TiO2) under irradiation was obtained by spin-trapping EPR measurements. The faster photoinduced bleaching of the azo dye Acid Red 1 (AR1) observed in the presence of F - TiO2 was explained by the high affinity of the azo double bond towards OH radicals. Moreover, the pronounced decrease of the AR1 bleaching rate by addition of 2-propanol, as hydroxyl radicals scavenger, on F - TiO2 and not on naked TiO2 demonstrated that on fluorinated titania AR1 is mainly degraded via OH radical attack
Effects of iron species in the photocatalytic degradation of an azo dye in TiO2 aqueous suspensions
No full textThe effects of Fe(III) species on the photocatalytic degradation of azo dye Acid Red 1 (AR1) have been studied in titanium dioxide aqueous suspensions under irradiation in the 315- 400 nm range. The initial increase of the photocatalytic degradation rate observed in water suspensions containing Fe(III) aquo ions (10-5 to 10-4 M) was attributed to the increased amount of dye adsorbed on the iron(III)-modified semiconductor surface. This was confirmed by the fact that iron species not adsorbed on the semiconductor, such as ferrioxalate complexes and Fe(II) species, had no kinetic effects. The mineralization kinetic profiles obtained under simultaneous sonication further confirmed the role of AR1 adsorption. The accumulation of hydrogen peroxide during the photocatalytic degradation of the dye was completely suppressed in the presence of all iron species, mainly due to the Fenton reactions consuming H2O2 in the aqueous phase, although a decrease in the rate of H2O2 formation cannot be excluded, due to the competition between adsorbed Fe(III) species and adsorbed oxygen for photo-promoted conduction band electrons
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