CO Oxidation over Anatase TiO2 Supported Au: Effect of Nitrogen Doping

Nitrogen doped yellowish anatase phase of titania support (TiO_2?x N _x ) was prepared by hydrolysis of titanium (IV) butoxide with 15% NH₄OH followed by filtration, drying and calcination at 450 °C for 3 h. For comparison, TiO₂ was prepared by hydrolysing titanium (IV) butylate with distilled water. Deposition precipitation method was used for Au loading on TiO_2?x N _x and TiO₂. These were characterised by XRD, Laser Raman spectroscopy, transmission electron microscopy, BET surface area analyser, and UV–visible spectrophotometry. UV–visible (diffused reflectance) spectrum of TiO_2?x N _x support shows a distinct absorption band around 450 nm wavelength indicating for N doping. Whereas, TiO₂ does not show any absorption band in the visible region. The activity of gold loaded on these supports was tested for CO oxidation reaction. Effect of different pre-treatment conditions and effect of moisture on these catalysts were studied, and the results obtained were interpreted on the basis of nitrogen doping, optoelectronic properties, ability of oxygen uptake of the support and particle size of gold.     

Diagnosis of Prostate Cancer and Prostatitis Using near Infra-Red Fluorescent AgInSe/ZnS Quantum Dots

The link between the microbiome and cancer has led researchers to search for a potential probe for intracellular targeting of bacteria and cancer. Herein, we developed near infrared-emitting ternary AgInSe/ZnS quantum dots (QDs) for dual bacterial and cancer imaging. Briefly, water-soluble AgInSe/ZnS QDs were synthesized in a commercial kitchen pressure cooker. The as-synthesized QDs exhibited a spherical shape with a particle diameter of 4.5 ± 0.5 nm, and they were brightly fluorescent with a photoluminescence maximum at 705 nm. The QDs showed low toxicity against mouse mammary carcinoma (FM3A-Luc), mouse colon carcinoma (C26), malignant fibrous histiocytoma-like (KM-Luc/GFP) and prostate cancer cells, a greater number of accumulations in Staphylococcus aureus, and good cellular uptake in prostate cancer cells. This work is an excellent step towards using ternary QDs for diagnostic and guided therapy for prostate cancer.     

CO oxidation over titanate nanotube supported Au: Deactivation due to bicarbonate

New experimental findings, which offer further information concerning the deactivation mechanism of CO oxidation over titania nanotube (TN) supported gold, are reported. Contrary to earlier reports by others, we have observed that the formation of bicarbonate species during CO oxidation on the Au/TN catalyst is a competing reaction that leads to catalyst deactivation. We regard the formation of bicarbonate species not as an intermediate step but rather a product of the CO₂ produced during CO oxidation. The bicarbonate species detected at 1290 cm^?1 was very stable and only desorbed at relatively high temperatures. In the presence of water the bicarbonate species (1290 cm^?1) did not form under reaction conditions. CO₂-TPD results implied that water possibly reacted with and removed the already formed bicarbonate species and prevented its further formation and in the process promoted the reaction and prevented deactivation. The possible reactions of how water (OH) might remove the gold associated bicarbonate and hence reactivate and promote the oxidation of CO are discussed. The mechanisms for the formation of the observed bicarbonate may account for the deactivation of the Au/TN catalyst during CO oxidation; this reaction would consume the OH groups on Au which have been reported as essential in the mechanism of CO oxidation. The above hypothesis of CO₂ being able to chemisorb on gold nanoparticles is not unique. Based on IR studies [N.M. Schubert, A. Venugopal, M.J. Kalich, V. Plazk, R.J. Behm, J. Catal. 222 (2004) 32; B. Schumacher, Y. Denkwitz, V. Plzak, M. Kinne, R.J. Behm, J. Catal. 224 (2004) 449], evidence was provided which pointed to the fact that CO and CO₂ competed for adsorption on the same site on Au surfaces. To the best of our knowledge, this is the first time that DRIFTS and CO₂-TPD have been combined to show that CO₂ is adsorbed on the gold-nanoparticles in the form of bicarbonate to the detriment of the oxidation of CO.     

CO oxidation: Deactivation of Au/TiO2 catalysts during storage

In a study of the phenomenon of catalyst deactivation during storage, Au/TiO₂ catalyst was stored under various conditions, viz. vacuum, nitrogen, air, refrigeration, dark, and light, and tested for CO oxidation activity at regular intervals. The data shows that the catalyst deactivates under all the storage conditions over 12 months and that storage in vacuum significantly enhances the rate and extent of deactivation. Storage in light accelerates the deactivation. The catalyst appears to deactivate through a combination of Au(III) reduction, Au nanoparticle agglomeration, loss of surface hydroxyl groups, loss of surface moisture, and accumulation of surface carbonates and formates. The rate and extent of catalyst deactivation can be limited by storing the catalyst in the dark at sub ambient temperature (refrigerator) and under inert atmosphere.     

Potassium Titanate: An Alternative Support for Gold Catalyzed Carbon Monoxide Oxidation?

It has been found that gold supported on potassium titanate, KTiO₂(OH) can, under some circumstances, exhibit a superior performance for the oxidation of carbon monoxide, relative to that obtained with titania as a support. It appears that the dispersions of gold on the two types of support are sufficiently similar that other factors are responsible for the improved activity noted. It may be that the higher basic character and/or detailed structural features of the titanate surface plays a role.     

EPDM rubber reinforced with titania generated by nonhydrolytic sol‐gel process

EPDM rubber was reinforced with titania in situ generated by using a nonhydrolytic sol‐gel (NHSG) process starting from TiCl₄ as titania precursor and tert‐butanol as oxygen donor. Titania particles in anatase form and with average diameter of 6 nm were synthesized via NHSG route and then the same procedure was adopted in presence of EPDM rubber to obtain composites containing up to 30 wt% of filler. Extraction and equilibrium swelling tests suggested an interfering effect of the NHSG reaction on the vulcanization process of the rubber resulting to a crosslink density which decreased in the presence of titania. Quasi‐static and dynamic‐mechanical characterizations indicated that the presence of titania as rigid filler in both the unvulcanized and vulcanized EPDM matrix led to a significant increase in stiffness and stress at break. The experimental values of modulus were systematically higher than the values predicted by classical equations suggesting an additional stiffening contribution deriving from the molecular interaction between the rubber and the filler. POLYM. ENG. SCI., 54:2544–2552, 2014. © 2013 Society of Plastics Engineers