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Two simple routes for the synthesis of a paper-TiO2 composite were tuned up and the efficiency of the resulting paper-TiO2 photocatalyst was investigated in the 2-propanol oxidation in gas phase. The first route involved the in-situ generation over the sheet of paper of a TiO2 layer starting from a solution of Ti (OBu)4 in tert-butanoliacetic acid, followed by hydrothermal treatment at 120 degrees C for 3 h. The sample was labelled as paper-TiO2 (H). The second approach was based on the adsorption on the paper of a ready-made suspension of titania nanoparticles (TiO2 sol), generated in autoclave at 140 degrees C and stable in acid medium at pH

Catalytic and photocatalytic 2-propanol dehydration to propene at atmospheric pressure and a temperature range of 60–120 °C were carried out in gas-solid regime by using bare and supported Keggin H 3 PW 12 O 40 (PW 12 ) and Wells-Dawson H 6 P 2 W 18 O 62 (P 2 W 18 ) heteropolyacids (HPAs). Binary materials were prepared by impregnation of the HPAs on commercial SiO 2 and TiO 2 . The Wells-Dawson was in any case more active than the Keggin heteropolyacid and the differences were enhanced when the supported samples were used. In particular, Wells-Dawson HPA supported on TiO 2 and under irradiation showed the highest activity. The HPA species played the key role both in the catalytic and photo-assisted reactions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction. The estimated apparent activation energy resulted always lower for the photocatalytic process than for the catalytic one.

In this study, various C3N4 samples were prepared and characterized. CO2 photoreduction was carried out by using C3N4 as powder and coated on glass support in a batch reactor or embedded in a Nafion membrane in a continuous reactor

Magnetic hybrid nanomaterials for the photodegradation of microcontaminats in aqueous environment

CO2 Reduction in Photocatalytic Membrane Reactor: Products Selectivity Study

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.

A series of tungsten and nitrogen doped Pt-TiO2 samples were prepared with the aim to extend the TiO2 absorption to the visible light region and to enhance the separation efficiency of the photogenerated electron/hole pairs. The physicochemical features of the powders were characterized by Xray diffraction (XRD), UV/Vis reflectance spectra, specific surface area (SSA) determinations, and transmission electron microscopy (TEM) analyses. The influence of the presence of different doping agents was evaluated, under anaerobic conditions, in the aqueous photo-reforming of glucose to form H2 at ambient pressure and temperature under a halogen lamp or natural solar light irradiation. Arabinose, erythrose, and formic acid were the main glucose partial oxidation products observed in the liquid phase, whilst H2 and CO2 were measured in the gaseous phase. The highest H2 production was observed in the presence of the Pt-TiO2-W0.25 sample.

Bare ZrO2, Ce doped ZrO2 and Er doped ZrO2 samples have been prepared by a hydrothermal process and have been used as photocatalysts for 2-propanol oxidation reaction in gas solid regime. Moreover, some preliminary tests have been carried out for CO2 reduction. The samples were physico-chemically characterized and both bare and doped ZrO2 based materials resulted active for oxidation and reduction reactions by using UV and solar irradiation. The reactivity results have been correlated with the compositional, structural and morphological features of the photocatalysts.

Polymeric C3N4 and O-doped C3N4: Photoelectrochemical and EPR Features for Selective Photocatalytic Oxidation of Alcohols to Aldehydes

EPR spectrometry servea as a unique tool by characterization of polymeric carbon nitride photocatalysts and evaluation of its photocatalytic performance in suspension.

Polymeric carbon nitride (C3N4) is a semiconductor material which is a very promising green photocatalyst with good physico-chemical properties and stability. It is a metal-free carbon based non-toxic material which can be easily obtained from earth-abundant components. The robustness and versatility of C3N4 as a photo-redox catalyst allows its use for selective oxidations by heterogeneous photocatalysis. This paper reviews the state of art in the application of C3N4 as heterogeneous photocatalyst for selective oxidation of alcohols to the corresponding aldehydes.

Photocatalytic membrane reactor for CO2 conversion

Study of the photocatalytic activity of Keggin and Wells Dawson heteropolyacids: role of the acidity and of the pseudo-liquid phase regime

Heteropolyacids (HPAs) are a class of molecular metal oxides called polyoxometalates, with a heteroatom in the cluster structure forming an oxo-metallic cluster with the addenda metal atoms. Due to the tunable acid-base and redox properties, HPAs have been used as catalysts both for homogeneous and heterogeneous reactions. Many efforts have been devoted to HPAs heterogeneization because, being soluble in polar solvents, their separation and recovery in liquid-solid regime reactors is a relevant practical application problem. Moreover, due to the low specific surface areas (1÷10 m2 g-1) their dispersion on supports with high surface area can increase the accessibility of the reacting species to their acidic sites and consequently their catalytic activity as Brönsted acid and oxidant catalysts. HPAs have been used in many acidic catalysed reactions, among them, the esterification of glycerol into acetins constitutes an important example due to the versatile industrial application of the products. Monoacetin (MAG) and diacetin (DAG) could be used as solvents, plasticizer, softening agent and solvent for dyes, whereas triacetin (TAG) is an antiknock additive for gasoline. The supported Keggin heteropolyacid PW12 has been prepared successfully avoiding leaching phenomena in liquid-solid regime. The composites resulted active as heterogeneous catalysts for glycerol acetylation. The hydrothermal conditions gave rise to a material where the PW12 structure and acidity was preserved giving rise to a glycerol conversion of ca. 75-80% to form mainly MAG and in less amount DAG.

CO2 conversion in continuous photocatalytic membrane reactor

Binary materials composed of the oxides SiO2, TiO2 and N-doped TiO2 and the Keggin heteropolyacid (PW12) were prepared and physicochemically characterized. They were used as catalysts and photocatalysts for the hydration of propene to 2-propanol. The characterization of the samples, particularly the electron paramagnetic resonance (EPR) spectroscopy results and the acidity properties, were useful to explain the key role played by the PW12 in the composite materials in the thermal and photoassisted catalytic processes. The simultaneous pres-ence of heat and UV light improved the activity of PW12 in the thermal process, and the binary materials showed better (photo)catalytic activities than that of the bare PW12 in almost all cases. For the first time, this work evidenced through EPR spectroscopy that the increase of reactivity under irradiation could be attributed to the ability of photoexcited PW12 to trap electrons, particularly if the PW12 is supported. Moreover, the effect of water on the reactivity was also studied.

ZrO2 based materials: preparation, characterization and photocatalytic activity for 2-propanol oxidation and CO2 reduction

Heterogeneous photocatalysis by polycrystalline semiconductor oxides is an unconventional technology that has been mainly applied for the degradation of organic and inorganic pollutants in both the vapor and liquid phase. The application of photocatalysis in synthetic routes has also been researched in recent years, demonstrating its viability as an alternative route in organic chemistry. This work illustrates the main findings in the application of heterogeneous photocatalysis to the oxidation of organic compounds dissolved in water, free of any organic co-solvent. Two main aspects of the oxidative process have been studied: the first one is the partial oxidation of various mono-substituted aromatic compounds, investigated to better understand the influence of the substituent group on the reactivity of these species and on the distribution of oxidized products. The second aspect investigated is the possibility of using heterogeneous photocatalysis for the selective oxidation of alcohols to aldehydes and ketones. The partial oxidation of alcohols to produce carbonyl compounds is of great industrial importance; generally, it is performed in environmentally harmful organic solvents at high temperatures and pressures by using stoichiometric oxygen donors that not only are expensive and toxic, but also produce large amounts of dangerous waste

The present work reports the preparation of samples based on Millennium PC-500 TiO 2 loaded with different amounts of tungstophosphoric acid (up to 30% in weight) and their characterisation by means of different physicochemical techniques: powder X-ray diffraction, N 2 adsorption–desorption at −196 °C, transmission electron microscopy, UV–vis and FT-IR spectroscopies and thermogravimetric analyses. The acidity of samples was evaluated by FT-IR using pyridine as probe molecule, and the catalysts activity was tested for the photodegradation of 4-nitrophenol in aqueous solution and for the photo-oxidation of propan-2-ol in vapour phase. The results show a noticeable improvement (8 and 2.5 times faster in the photodegradation rate of 4-nitrophenol and propan-2-ol, respectively), in both regimes for these specific substrates, when tungstophosphoric acid is dispersed over the oxide up to a certain amount (20% in weight). A partial leaching of the polyoxometalate was also detected in solution for samples loaded with the largest amounts on this compound.