the-effect-interfacial-chemical-bonding-tio2-sio2-composites-on-their

The Effect of Interfacial Chemical Bonding in TiO<sub>2</sub>-SiO<sub>2</sub> Composites on Their Photocatalytic NOx Abatement Performance

The chemical bonding of particulate photocatalysts to supporting material surfaces is of great importance in engineering more efficient and practical ...

University of Aberdeen

The photocatalytic conversion of various nitroaromatic compounds in alcohols employing four different types of TiO(2) (Sachtleben Hombikat UV100 as anatase, Crystal Global R34 as rutile, Evonik-Degussa Aeroxide P25 as an anatase-rutile mixture, and home-made mesoporous anatase) has been studied. The effect of platinization of these different types of TiO(2) on the reaction sequence has also been investigated. Upon irradiation of an ethanolic solution of m-nitrotoluene, as a model reaction, in the presence of the bare photocatalyst, different products were obtained according to the applied photocatalyst. It was found that the surface properties of the photocatalyst play an important role in the reaction pathway and thus in the selectivity of the products. In all cases, a simultaneous reduction of the nitro compound and an oxidation of the alcohol are induced by the photogenerated electrons and holes, respectively. An imine is then produced upon condensation of the generated aldehyde and amino compounds. Rutile was found to be more selective towards the primary amino compound (m-toluedine) while anatase catalysts gave a mixture of m-toluidine and its imine (N-ethylidene-3-methylaniline). A cyclization reaction of the produced imine to generate methyl quinoline was observed when Aeroxide P25 was used as a photocatalyst. Employing platinized TiO(2), the hydrogenation of the produced imine yielding N-alkylated products was found to occur in all cases. However, the selectivity towards the mono N-alkylated product was the best using platinized Hombikat UV100. This selectivity was found to be also influenced by the loaded amount of Pt, the platinization method, and the illumination time but not by the light intensity.

Factors affecting the selectivity of the photocatalytic conversion of nitroaromatic compounds over TiO2 to valuable nitrogen-containing organic compounds.

The adsorption of water and deuterium oxide on TiO2 surfaces was investigated in the dark as well as under UV(A) irradiation using in situ ATR-FTIR spectroscopy under oxygen and oxygen free conditions. Adsorption of H2O-D2O mixtures revealed an isotopic exchange reaction occurring onto the surface of TiO2 in the dark. Under UV(A) irradiation, the amount of both OH and OD groups was found to be increased by the presence of molecular oxygen. Furthermore, the photocatalytic formation of hydroperoxide under oxygenated condition has been recorded utilizing Attenuated Total Reflection Fourier Transformed Infrared (ATR-FTIR) spectroscopy which appeared as new band at 3483 cm(-1). Different possible mechanisms are discussed in terms of the source of hydroxyl groups formed and/or hydration water on the TiO2 surface for the photocatalytic reaction and photoinduced hydrophilicity.

In situ ATR-FTIR study of H2O and D2O adsorption on TiO2 under UV irradiation.

The nitrate selectivity of TiO2 has important consequences for its efficiency as a NOx depollution photocatalyst. Most emphasis is typically given to photocatalyst activity, a measure of the rate at which NOx concentrations are reduced, but a reduction in NOx concentration (mainly NO + NO2) is not necessarily a reduction in atmospheric NO2 concentration because the catalytic process itself generates NO2. With NO2 being considerably more toxic than NO, more emphasis on nitrate selectivity, a measure of the NOx conversion to nitrate, and how to maximize it, should be given in engineering photocatalytic systems for improved urban air quality. This study, on the importance of adsorbed water in the photocatalytic oxidation of NOx, has identified important correlations which differentiate the role that water plays in the oxidation of NO and NO2. This observation is significant and offers insights into controlling nitrate selectivity on TiO2 and the potential for increased effectiveness in environmental photocatalyst applications.

Article	Year
Factors affecting the selectivity of the photocatalytic conversion of nitroaromatic compounds over TiO2 to valuable nitrogen-containing organic compounds. Physical chemistry chemical physics : PCCP\| PubMed ID: 23340499	2013
In situ ATR-FTIR study of H2O and D2O adsorption on TiO2 under UV irradiation. Physical chemistry chemical physics : PCCP\| PubMed ID: 26266701	2015
Different Roles of Water in Photocatalytic DeNOx Mechanisms on TiO2: Basis for Engineering Nitrate Selectivity? ACS applied materials & interfaces\| PubMed ID: 28474882	2017

Amer Hakki

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