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Near-IR squaraine dye-loaded gated periodic mesoporous organosilica for photo-oxidation of phenol in a continuous-flow device.

Borah P, Sreejith S, Anees P, Menon NV, Kang Y, Ajayaghosh A, Zhao Y - Sci Adv (2015)

Bottom Line: The dye-loaded and azobenzene-gated PMO (Sq-azo@PMO) exhibits excellent generation of reactive oxygen species upon excitation at 664 nm, which can be effectively used for the oxidation of phenol into benzoquinone in aqueous solution.Furthermore, Sq-azo@PMO as the catalyst was placed inside a custom-built, continuous-flow device to carry out the photo-oxidation of phenol to benzoquinone in the presence of 664-nm light.By using the device, about 23% production of benzoquinone with 100% selectivity was achieved.

View Article: PubMed Central - PubMed

Affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore, Singapore.

ABSTRACT
Periodic mesoporous organosilica (PMO) has been widely used for the fabrication of a variety of catalytically active materials. We report the preparation of novel photo-responsive PMO with azobenzene-gated pores. Upon activation, the azobenzene gate undergoes trans-cis isomerization, which allows an unsymmetrical near-infrared squaraine dye (Sq) to enter into the pores. The gate closure by cis-trans isomerization of the azobenzene unit leads to the safe loading of the monomeric dye inside the pores. The dye-loaded and azobenzene-gated PMO (Sq-azo@PMO) exhibits excellent generation of reactive oxygen species upon excitation at 664 nm, which can be effectively used for the oxidation of phenol into benzoquinone in aqueous solution. Furthermore, Sq-azo@PMO as the catalyst was placed inside a custom-built, continuous-flow device to carry out the photo-oxidation of phenol to benzoquinone in the presence of 664-nm light. By using the device, about 23% production of benzoquinone with 100% selectivity was achieved. The current research presents a prototype of transforming heterogeneous catalysts toward practical use.

No MeSH data available.


Related in: MedlinePlus

Photoisomerization of azo@PMO.(A) Schematic representation of reversible isomerization between trans-azo@PMO and cis-azo@PMO under light irradiation and heat. a.u., absorbance units. (B) UV/Vis absorption spectra of Ph-PMO-NH2, cis-azo@PMO, and trans-azo@PMO (1.5 mg ml−1 in aqueous solution). The changes in the UV/Vis absorption spectra due to the isomerization of trans-azo@PMO to cis-azo@PMO (1.5 mg ml−1) were recorded under the irradiation of 383-nm UV light for 20 min. (C) Absorbance changes of the UV/Vis spectra of azo@PMO at 383 nm as a function of cycles upon alternating UV light irradiation and heating at 55°C.
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Figure 2: Photoisomerization of azo@PMO.(A) Schematic representation of reversible isomerization between trans-azo@PMO and cis-azo@PMO under light irradiation and heat. a.u., absorbance units. (B) UV/Vis absorption spectra of Ph-PMO-NH2, cis-azo@PMO, and trans-azo@PMO (1.5 mg ml−1 in aqueous solution). The changes in the UV/Vis absorption spectra due to the isomerization of trans-azo@PMO to cis-azo@PMO (1.5 mg ml−1) were recorded under the irradiation of 383-nm UV light for 20 min. (C) Absorbance changes of the UV/Vis spectra of azo@PMO at 383 nm as a function of cycles upon alternating UV light irradiation and heating at 55°C.

Mentions: UV/Vis absorption studies (Fig. 2) were carried out to obtain an insight into the photothermal response of azo@PMO in aqueous solution. The UV/Vis absorption spectrum of Ph-PMO-NH2 exhibits broad scattering in water with a maximum of 320 nm corresponding to the phenyl unit in the PMO skeleton (Fig. 2A). Similarly, trans-azo@PMO in water presents a signature absorption peak at 380 nm corresponding to the π-π* transition of the azobenzene unit (Fig. 2A). The irradiation of trans-azo@PMO under 380-nm light for 20 min shows a decrease in the absorption intensity at 380 nm, with concomitant formation of a new band at 460 nm corresponding to the cis isomer, that is, cis-azo@PMO (Fig. 2A). Furthermore, we demonstrated the reversible process of the trans-cis isomerization between trans-azo@PMO and cis-azo@PMO up to six cycles (Fig. 2B), proving the efficient trans-cis isomerization capability of azo@PMO in aqueous solution.


Near-IR squaraine dye-loaded gated periodic mesoporous organosilica for photo-oxidation of phenol in a continuous-flow device.

Borah P, Sreejith S, Anees P, Menon NV, Kang Y, Ajayaghosh A, Zhao Y - Sci Adv (2015)

Photoisomerization of azo@PMO.(A) Schematic representation of reversible isomerization between trans-azo@PMO and cis-azo@PMO under light irradiation and heat. a.u., absorbance units. (B) UV/Vis absorption spectra of Ph-PMO-NH2, cis-azo@PMO, and trans-azo@PMO (1.5 mg ml−1 in aqueous solution). The changes in the UV/Vis absorption spectra due to the isomerization of trans-azo@PMO to cis-azo@PMO (1.5 mg ml−1) were recorded under the irradiation of 383-nm UV light for 20 min. (C) Absorbance changes of the UV/Vis spectra of azo@PMO at 383 nm as a function of cycles upon alternating UV light irradiation and heating at 55°C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643787&req=5

Figure 2: Photoisomerization of azo@PMO.(A) Schematic representation of reversible isomerization between trans-azo@PMO and cis-azo@PMO under light irradiation and heat. a.u., absorbance units. (B) UV/Vis absorption spectra of Ph-PMO-NH2, cis-azo@PMO, and trans-azo@PMO (1.5 mg ml−1 in aqueous solution). The changes in the UV/Vis absorption spectra due to the isomerization of trans-azo@PMO to cis-azo@PMO (1.5 mg ml−1) were recorded under the irradiation of 383-nm UV light for 20 min. (C) Absorbance changes of the UV/Vis spectra of azo@PMO at 383 nm as a function of cycles upon alternating UV light irradiation and heating at 55°C.
Mentions: UV/Vis absorption studies (Fig. 2) were carried out to obtain an insight into the photothermal response of azo@PMO in aqueous solution. The UV/Vis absorption spectrum of Ph-PMO-NH2 exhibits broad scattering in water with a maximum of 320 nm corresponding to the phenyl unit in the PMO skeleton (Fig. 2A). Similarly, trans-azo@PMO in water presents a signature absorption peak at 380 nm corresponding to the π-π* transition of the azobenzene unit (Fig. 2A). The irradiation of trans-azo@PMO under 380-nm light for 20 min shows a decrease in the absorption intensity at 380 nm, with concomitant formation of a new band at 460 nm corresponding to the cis isomer, that is, cis-azo@PMO (Fig. 2A). Furthermore, we demonstrated the reversible process of the trans-cis isomerization between trans-azo@PMO and cis-azo@PMO up to six cycles (Fig. 2B), proving the efficient trans-cis isomerization capability of azo@PMO in aqueous solution.

Bottom Line: The dye-loaded and azobenzene-gated PMO (Sq-azo@PMO) exhibits excellent generation of reactive oxygen species upon excitation at 664 nm, which can be effectively used for the oxidation of phenol into benzoquinone in aqueous solution.Furthermore, Sq-azo@PMO as the catalyst was placed inside a custom-built, continuous-flow device to carry out the photo-oxidation of phenol to benzoquinone in the presence of 664-nm light.By using the device, about 23% production of benzoquinone with 100% selectivity was achieved.

View Article: PubMed Central - PubMed

Affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore, Singapore.

ABSTRACT
Periodic mesoporous organosilica (PMO) has been widely used for the fabrication of a variety of catalytically active materials. We report the preparation of novel photo-responsive PMO with azobenzene-gated pores. Upon activation, the azobenzene gate undergoes trans-cis isomerization, which allows an unsymmetrical near-infrared squaraine dye (Sq) to enter into the pores. The gate closure by cis-trans isomerization of the azobenzene unit leads to the safe loading of the monomeric dye inside the pores. The dye-loaded and azobenzene-gated PMO (Sq-azo@PMO) exhibits excellent generation of reactive oxygen species upon excitation at 664 nm, which can be effectively used for the oxidation of phenol into benzoquinone in aqueous solution. Furthermore, Sq-azo@PMO as the catalyst was placed inside a custom-built, continuous-flow device to carry out the photo-oxidation of phenol to benzoquinone in the presence of 664-nm light. By using the device, about 23% production of benzoquinone with 100% selectivity was achieved. The current research presents a prototype of transforming heterogeneous catalysts toward practical use.

No MeSH data available.


Related in: MedlinePlus