Mingming Zou

Amine coupled ordered mesoporous (Co–N) co-doped TiO2: a green photocatalyst for the selective aerobic oxidation of thioether

Usually oxygen cannot participate in the selective oxidation reaction of thioether to sulfoxide, which is attributed to its inactive feature. Although UV-light irradiation can activate O2, this process also results in UV-induced hole (hvb+) generation. This oxidative species and O2 can be consumed for the formation of free radical intermediates that leads to uncontrolled auto-oxidation products resulting in low selectivity. Current work aims to develop an approach for the aerobic oxidation of thioether to sulfoxide by exploring the synergy between triethylamine and mesoporous Co–N–TiO2 (nitrided @ 500 °C for 2 h) microspheres (with a large surface area: 124 m2 g−1); the oxidation is carried out via visible-light photoredox catalysis. Triethylamine, due to its electron donating ability, acts as a redox mediator. With a lower band gap and level of conduction band minimum (−0.605 V vs. NHE), the Co–N–TiO2 sample has the ability to be an efficient and selective catalyst. Excellent conversion from the selective oxidation of thioanisole (76.4%) under 12 h visible light irradiation is observed. It may be noted that Co doping into TiO2 alone does not aid in obtaining a good photocatalyst; in fact this sample shows the Moss–Burstein effect. We have also shown that the reported photocatalyst is applicable for the conversion of several other thioethers to sulfoxides; generally high conversion rates and selectivities are observed. The reaction mechanisms are studied using UV-visible absorption spectra and the oxidation–extraction photometry (OEP) method. This result is likely useful for further exploration of surface complex photocatalysts for many other aerobic oxidation reactions.

Multi-Electron Surface Complexes as Photocatalyst for Selective Aerobic Oxidation in Visible Light Irradiation

Current work presumes to develop an environmentally friendly and energy-saving process to achieve aerobic oxidation of thioether reaction catalyzed by multi-electron surface complexes (i. e. triethylamine and mesoporous Mo-N-TiO2 microspheres) through visible-light photoredox catalysis. The high electron donating ability of triethylamine is employed to mediate the reaction process. The as-prepared Mo-N-TiO2 catalysts exhibit remarkable catalytic properties; band gap (2.48 eV) and level of conduction band minimum (-1.62 eV), this system plays significant roles in conversion and/or selective oxidation of thioanisole (66.35%) under visible light irradiation. The complete conversion is achieved within 12 h. This result indicates that there is rapid and continous thioanisole conversion in the reaction set-up, being effective as a result of electronic coupling effect between the catalyst and mediator. Now and then,we believe that these kinds of multi-electron surface complexes should apply to many aerobic oxidation reactions for organic synthesis.

W-N-TiO2 with positive enough level of valence band maximum and narrowing bandgap for selective aerobic oxidation in visible-light irradiation

A kind of surface complex (triethylamine and mesoporous W-N-TiO2 microspheres with large surface area: 117.5 m2g-1) catalysis was achieved via visible-light photoredox catalysis. Triethylamine behaves as a true redox mediator due to its highly favorable donating ability. With a lower bandgap (2.43 eV) and higher valence band maximum (2.905 V), W-N-TiO2 has the ability to play an active catalytic role yielding excellent conversion and selective oxidation of thioanisole (75.16%) within 12 h under visible-light irradiation. In addition, the reaction and the photocatalyst are applicable to other kinds of thioethers, generally producing high conversion rates and selectivities for the product sulfoxides. The reaction paths were elucidated to reveal that these kinds of surface complexes show characteristics that are likely to be applicable to many aerobic oxidation reactions in future.

Synthesis, characterization of Cu, N co-doped TiO2 microspheres with enhanced photocatalytic activities

The mesoporous Copper, nitrogen co-doped TiO2 microspheres was prepared via solvothermal approach, followed by nitriding treatment under an ammonia gas flow. The crystalline structures of the as-prepared catalyst and the chemical compositions of Cu,N co-doped TiO2 were determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. The photocatalytic activity of the as-prepared sample was investigated by monitoring the degradation of Rhodamine-B under visible light irradiation. Experimental results indicated that mesoporous Cu,N co-doped TiO2 microspheres showed higher photocatalytic activity than Cu-TiO2 microspheres and anatase TiO2 under visible light irradiation. The higher photocatalytic activity of the mesoporous Cu,N co-doped TiO2 microspheres sample could be attributed to the synergistic effects of large BET surface area, extended light absorption, efficient charge separation which was stabilized by the presence of oxygen vacancies. It was discovered that, valence states maintain stability after nitriding treatment. The sample synthesized from 0.1% molar quantity of Cu dopant, and nitrided at 400°C for 30 min gave the highest photocatalytic activity. Correspondence to: Minghui Yang, Ningbo Institute of Industrial Technology, Chinese Academy of Sciences, No. 1219 Zhongguan West Road, Zhenhai District, Ningbo, 315201 China, Tel/Fax: +86-411-85168242, E-mail: myang@nimte.ac.cn

Enhanced Photocatalytic Response of N Doped Niobium Titanates Prepared by Ion Exchange Process

Herein we report the homogeneous and effective substitution of O by N in the layered titanates. The resultant materials HTiNbO5-xNx (350°C, 30 min) unveiled extraordinary band-to-band excitation and increased absorption intensity (induced by oxygen vacancies). Upward shift of valence band maximum by N 2p states is confirmed by photoelectron spectroscopy and is concluded as the source of band-to-band visible light excitation. The electrons generated upon visible light excitation in the conduction band of HTiNbO5-xNx (350°C, 30 min) had strong reduction ability, reducing O2 into active O2•- radicals during photocatalysis. These findings are the clear evidence for the substantial role of doped N in achieving band-to-band visible-light photon excitation in layered titanates. The new physical insights into substitutional N in layered titanates with hydrogen bond (weak bond energy) gained here may have important implications for developing other efficient visible light photocatalysts by nonmetal doping.