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Nanotube-structured TiO2 electrodes on Ti plates were formed in ethylene glycol solution by the anodic oxidation method applied for different times and calcined at 500 °C. Different amounts of WO3 were decorated on the nanotube surfaces electrochemically. The electrodes were characterized, and the effects of the nanotube length on the Ti plate, decorated WO3 amount, electrolyte concentration, applied potential, and type of radiation source on the oxidation of 3-methylpyridine were investigated, together with the product distribution/selectivity. In a photoelectrocatalytic system, the vitamin B3 yield increased significantly (ca. 17 fold) under UVA by decorating nanotube-structured TiO2 with WO3, whilst low reaction rates and no products were found under Vis irradiation, as only unselective photolytic reactions occurred. This unexpected result was clarified for the first time in the literature.

The photoelectrocatalytic (PEC) oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B3 was investigated by using Pt, Au and Pd loaded (as single or bimetallic) nanotube structured TiO2 on Ti plate in water under UVA irradiation. Nanotube structured TiO2 on Ti plate samples were prepared as anode by anodic oxidation method in ethylene glycol solution in different times, and then they were calcined at 500 °C to be obtained in crystalline form. The anodes were loaded with noble metals by electrochemical reduction method and characterized by XRD, XPS, SEM, and photocurrent techniques. The TiO2 on the plates was in the anatase phase. The loaded metals were in metallic form and heterogeneously dispersed on the TiO2 surface in different sizes. The results indicate that a high amount of metal loading negatively affected the PEC activity of the metal loaded samples because UVA irradiation inside the nanotubes was inhibited by the presence of the metal. On the contrary, low amount of Pd showed high PEC activity and high product selectivity values with respect to the pristine sample. PEC experiments were also more selective than the photocatalytic ones for vitamin B3 production. Electrocatalytic (EC) and photocatalytic (PC) experiments were also conducted, however no or low activity was obtained, respectively. PEC experiments showed to be more selective than the PC ones for vitamin B3 production.

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.

This chapter reports on some characterization techniques that are commonly used for catalysts and photocatalysts. Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), UV–visible (UV–Vis), photoluminescence (PL), and electrochemical characterization techniques are presented with experimental details and actual case studies from literature are discussed. The chapter starts with adsorption phenomena on (photo)catalysis and adsorption isotherms are presented. Then BET analysis technique and its applications in (photo)catalysis are explained. Morphological properties (SEM), functional groups, and the interaction of substrate (and intermediates) with the catalyst under dark or under irradiation are discussed using the FTIR technique. The discussion moves on with estimation of band-gap energies and oxidation states of loaded or metal-doped catalysts (through UV–Vis), and to the identification of impurity/defects levels and the investigation of recombination mechanisms by PL. Finally, as electrochemical characterizations, linear sweep and cyclic voltammetry, chronoamperometry (photocurrent), electrochemical impedance spectroscopy, and Fermi level estimation are presented. Special attention is given to comparative assessment between catalysts and photocatalysts, for both powder and supported samples.

Selective photocatalytic oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B-3 by using pristine and Pt loaded home prepared (HP) rutile and commercial TiO2 photocatalysts, under UV, UV-vis and visible irradiations in water, was performed in friendly environmental conditions. The photocatalysts were characterized by XRD, SEM-EDAX, BET, DRS, XPS and TGA techniques. The influence of pH on reactivity and total selectivity to 3-pyridinemethanal and vitamin B3 was studied. Under very acidic conditions (pH = 2) no or low activity (depending on photocatalyst) was observed, whereas by increasing the pH from 4 to 12 very high total selectivity was achieved. The Pt loading was beneficial for selectivity whereas the reactivity was positively affected only for crystalline HP sample. This last sample showed good activity under visible irradiation, exhibing an about 4 times higher conversion than the other samples. The influence of the position of the benzylic group in pyridine (2-pyridinemethanol and 4-pyridinemethanol) was also studied. The results showed that to synthesize vitamin B3 in green conditions the photocatalyst should be poorly crystalline or Pt loaded. (C) 2016 Elsevier B.V. All rights reserved.

Photoelectrocatalytic (PEC) synthesis of 2,5-furandicarbaldehyde (FDC) from 5-(hydroxymethyl)-2-furaldehyde (HMF) has been performed in water by using TiO2 films on Ti layer prepared by thermal annealing of Ti (Ti/TiO2) and TiO2 nanotube on Ti (Ti/TiO2NT) prepared by anodic oxidation as photoanodes. The latter ones showed better activity. In order to improve both activity and selectivity, Ti/TiO2NT was loaded with Pt by photoreduction method. 5-Formyl-2-furoic acid (FFA) was also produced by using Pt loaded Ti/TiO2NT photoanodes. The photoanodes were characterised by using XRD, SEM and XPS techniques. Allotropic phase of TiO2 photoanodes was mainly rutile, whereas trace amounts of anatase phase were found in some samples of TiO2 nanotube photoanodes. The distribution of TiO2 nanotubes on Ti are well organised. In addition, primary particle sizes of TiO2 were increased by increasing thermal treatment temperature; however primary particle sizes of TiO2 in Ti/TiO2NT are higher than that of other samples. The photoanode preparation temperature, bias and medium pH were optimised by following PEC HMF oxidation reaction. Photocatalytic and electrocatalytic HMF oxidations were also performed for comparison and negligible activities were observed. Finally efficient Pt loaded Ti/TiO2NT photoanodes were investigated for PEC selective and active FDC (selectivity up to 40%) and FFA (selectivity up to 18%) syntheses in environmental friendly conditions. (C) 2016 Elsevier B.V. All rights reserved.

It has been recently reported by Palmisano et al. (2015) [1] that the oxidation of 2-methoxybenzyl alcohol (2-MBA) to 2-methoxybenzaldehyde (2-MBAD) proceeds in water under near-UV light with an unexpected catalytic effect of 2-MBAD. In order to investigate the catalytic role of aldehyde in photolytic oxidation of ortho-substituted benzyl alcohols (OSBAs), reactivity runs were carried out with 2-methylbenzyl alcohol (2-MeBA), 2-nitrobenzyl alcohol (2-NBA), 2-hydroxybenzyl alcohol (2-HBA) and 2-chlorobenzyl alcohol (2-CIBA) in the absence and in the presence of their corresponding aldehyde. None of those alcohols showed a measurable oxidation rate even in the presence of their aldehydes but 2-NBA was oxidised very fast, although no corresponding carbonyl product was obtained. The possible catalytic role of 2-MBAD was investigated for the photolytic oxidation of 4-methoxybenzyl alcohol (4-MBA), 4-nitrobenzyl alcohol (4-NBA), 2-CIBA, 2-HBA, 2-MeBA and ferulic acid (FA). The results showed that 2-MBAD acts as a catalyst only for 4-MBA, 2-HBA and FA. The photocatalytic oxidation of OSBAs in the presence of powdered TiO2 has been also carried out in order to investigate the mutual influences, if any, between homogeneous and heterogeneous processes. The reactivity runs were carried out with TiO2 photocatalyst in water and under near-UV irradiation; a home-prepared (HP) TiO2 sample was used along with Degussa P25. HP catalyst showed the best performance: the 2-MBA half-life time was 5 times smaller and the selectivity to aldehyde 13 times higher than in the presence of Degussa P25. (C) 2016 Elsevier B.V. All rights reserved.

The photoelectrocatalytic partial oxidation of 4-methoxybenzyl alcohol in aqueous solution irradiated by near-UV light was carried out in a three-electrode batch reactor. TiO2 films were either deposited by dip-coating of a TiO2 sol onto a Ti foil and subsequent calcination or generated on Ti plates by thermal oxidation in air at 400-700 degrees C. The effects of the anode preparation method and bias potential values on conversion and selectivity to the corresponding aldehyde were investigated. The photoelectrocatalytic results were compared with the photocatalytic and electrocatalytic ones. The results indicated that no reaction occurred during the electrocatalytic experiments, whereas the photocatalytic reactivity was positively influenced by the application of a small bias (0.75 V vs. saturated calomel electrode). By applying the previous bias the highest initial degradation rates, r(0), and selectivities to 4-methoxybenzaldehyde, S, were obtained in photoelectrocatalytic experiments by using Ti plate calcined at 500 degrees C (r(0) = 0.1507 mM h(-1), S=85%) or TiO2 film prepared by dip-coating and calcined at 700 degrees C (r(0) = 0.1339 mM h(-1), S=90%). In order to investigate the influence of the substituent groups on reactivity and selectivity, photoelectrocatalytic runs with benzyl alcohol, 2-methoxybenzyl alcohol, 3-methoxybenzyl alcohol, 2,4-dimethoxybenzyl alcohol, 2,3,4-trimethoxybenzyl alcohol, 4-nitrobenzyl alcohol and 4-hydroxybenzyl alcohol have been performed. The selectivity and reactivity values increased by increasing the electron-donor properties of the substituent groups. This positive effect, however, was obtained only if the electron-donor group is in para or ortho position with respect to the alcoholic group. (C) 2012 Elsevier B.V. All rights reserved.