photocatalysis

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Selective Photocatalysts in Organic Synthesis :

Selective Photocatalysts in Organic Synthesis 2 Shamsa Munir Ph.D Physical Chemistry

Outline:

Outline 3 Introduction Photocatalysts in Organic Synthesis Synthesis of Phenol Conclusions

Outline:

Outline 4 Introduction Photocatalysts in Organic Synthesis Synthesis of Phenol Conclusions

Photocatalysis: the process:

Photocatalysis: the process 5 Photocatalyst + hν → h + + e - h + + D→ D ● + e ─ + A → A ● ─

TiO2 based Photocatalysis:

TiO 2 based Photocatalysis 6

Photocatalytic Applications of TiO2:

Photocatalytic Applications of TiO 2 7 Worth mentioning photocatalytic potential of Titanium dioxide Water purification Environmental cleaning Sterilization of Molds, Fungi and bacteria Organic Synthesis

Water Purification and Environmental Cleaning :

Water Purification and Environmental Cleaning Organics and pollutants in waste water are completely oxidized to CO 2 Utilize ultraviolet light for the breakdown of organic molecules including oil and hydrocarbons. Finds wide applications in cleaning due to its hydrophilic nature. 8 Transparent TiO 2 Window glass

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Outline 9 Introduction Photocatalysts in Organic Synthesis Synthesis of Phenol Conclusions

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To synthesize important organic compounds by simple routes Introduce environmental friendly processes Development of cost effective synthesis procedures 10 The main goals of introducing photocatalysts in organic synthesis are:

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Outline 11 Introduction Photocatalysts in Organic Synthesis Synthesis of Phenol Conclusions Acknowledgments

Industrial Synthesis of Phenol: the Cumene Process:

Industrial Synthesis of Phenol: the Cumene Process Overview of Cumene Process Chemistry Benzene and propylene reacts according to Friedal Craft’s Mechansim The process is named after Cumene the reactive intermediate Cumene converted to phenol by a series of steps Various acid catalysts such as AlCl 3 , solid phosphoric acid and acidic zeolites 12

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Cumene Process: Production of Cumene Undesired products Safety Problems Side reactions 13

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Hydroperoxide Radical 14

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Problems associated with Cumene Process:

Problems associated with Cumene Process Many by products associated with the process Safety aspects e.g. Cumene is flammable Process economics Oxidation Cleavage Product purification units 16

Photocatalytic Synthesis of Phenol :

Photocatalytic Synthesis of Phenol Electron density at metal surface treated as plasma Fluctuations in electron density leads to plasmons capable of absorbing UV/ Visible radiation Enhanced photocatalytic activity due to: Increased charge separation Absorption spectrum shifts to visible light 17 Exploiting Plasmonic Photocatalysts

Synthesis of TiO2 plasmonic photocatalysts:

Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental Synthesis of TiO 2 plasmonic photocatalysts 18 180 ° C 2 hrs Cooled to room temperature Ti( OBu ) 4 (10 mL ) + 40 mL ethanol + 1.2 ml hydrofluoric acid White Precipitate TiO 2 Microspheres Synthesis of TiO 2 Microspheres

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 19 Noble-metal loading M@TiO 2 M= Au, Ag, Pt HAuCl 4 . 4H 2 O aqueous solution blue ethanol solution with TiO 2 suspension (Irradiated with UV light) stirring for 10 min Blue suspension changed to auburn Injection (in dark)

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 20 Noble metal deposition on titania UV irradiation ( λ > 320 nm) Photogenerated electrons trapped by Ti 4+ forming Ti 3+ ions

Characterization of M@TiO2:

Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental Characterization of M@TiO 2 21 XRD patterns of naked TiO 2 -microspheres and noble-metal@TiO 2 -microspheres.

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 22 UV/Vis diffuse-reflectance spectra of noble-metal@TiO 2- microspheres with loading of 1 wt % noble metal SPR peaks of Au (540 nm), Ag (451 nm) and Pt (<450 nm)nanoparticles

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 23 SEM images of (a–c) Ag@TiO 2 -microspheres, (d–f) Au@TiO 2 -microspheres and (g– i ) Pt@TiO 2 -microspheres with loading of 1 wt % noble metal. (j–l) EDS spectra of the corresponding composites.

Tuning of Metal loading:

Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental Tuning of Metal loading 24 UV irradiation of TiO 2 microspheres for variable time Ag@TiO 2 –microspheres formed by AgNO 3 injection

Photocatalytic oxidation of benzene under visible light:

Visible-light-induced catalytic oxidation of benzene in water with Au@TiO 2 –microspheres (with 1 wt % loading of noble metal) in the presence of aqueous phenol 25 Photocatalytic oxidation of benzene under visible light Phenol Benzene

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Visible-light-induced catalytic oxidation of benzene in water with Pt@TiO 2 –microspheres (with 1 wt % loading of noble metal) in the presence of aqueous phenol 26 Phenol Benzene

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Visible-light-induced catalytic oxidation of benzene in water with Ag@TiO 2 -microspheres (with 1 wt % loading of noble metal) in the presence of aqueous phenol 27 Phenol Benzene

Variation in the yield and selectivity of phenol formation over different photocatalysts.:

Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental Variation in the yield and selectivity of phenol formation over different photocatalysts. 28

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 29 (a) Visible-light-induced catalytic oxidation of benzene with Au@TiO 2 -microsphere composites with 1–3 wt % of Au. (b) UV/Vis diffuse- reflectance spectra of Au@TiO 2 -microsphere composites

Mechanism of Photocatalytic Oxidation:

Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental Mechanism of Photocatalytic Oxidation 30

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Zheng , Z., Huang, B., Qin, X., Zhang, X., Dai, Y., & Whangbo , M-H. (2011) Applied Catalysis B:Environmental 31 Strong absorption with maximum at 570 nm Electron transfer from the Au NPs to theTiO 2 resulting in diminished absorption Recovered SPR absorption with the addition of phenol

Manipulating TiO2 with Siliceous Mesocellular Foams :

Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental Manipulating TiO 2 with Siliceous Mesocellular Foams TiO 2 nanoparticles entrapped into MCF prepared by modified one pot co-condensation method Organo -grafting of TiO 2 @MCF to obtain the methylsilylated sample (TiO 2 @MCF/CH 3 ) 32 Triethoxymethylsilane

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental Post UV-irradiation treatment: selective removal of methylsilyl groups 33 TiO 2 /MCF/CH 3 /UV Half gram of TiO 2 /MCF/CH 3 powder + 30 ml water 24 hr irradiation with 300 W - Xe arc lamp

Characterization of Titania Entrapped in Hydrophobically Modified Foam:

Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental Characterization of Titania Entrapped in Hydrophobically Modified Foam 34 XRD patterns of control TiO 2 and TiO 2 @MCF samples. The anatase peaks are indicated by * mark. Anatse structure TiO 2 @MCF size of crystallites = 9 nm Size of pure TiO 2 crystallites = 16 nm

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental 35 Diffuse reflectance UV–visible spectra (DRUVS) of TiO 2 and TiO 2 @MCF. Absorption onset edge shifted to shorter wavelengths Smaller size of TiO 2 in MCF Consistent with XRD results

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental 36 FT-IR spectra of the prepared catalyst samples. Si–O–Si stretching vibration 1070 / cm and 800 / cm Si–OH vibration 960 / cm CH 3 symmetric deformation of Si–CH 3 1276 / cm

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental 37 Water contact angle images of the prepared catalyst pellet samples Water contact angle measurements TiO 2 @MCF/CH 3 shows the largest contact angle Smallest contact angle due to hydrophilic nature

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental 38 Thermo-gravimetric analysis of the catalyst samples presaturated with water vapor adsorption Thermo gravimetric analysis of the catalysts Nearly 50% weight loss due to more water vapors saturation Less loss (around 40%) by most hydrophobic TiO 2 @MCF/CH 3 .

Photocatalytic activity: Oxidation of Benzene:

Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental Photocatalytic activity: Oxidation of Benzene 39

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Zhang, G., Yi, J., Shim, J., Leea , J., & Choi , W. (2011) Applied Catalysis B: Environmental 40 Selectivity and Yields of Phenol with Different Forms of Photocatalysts

Outline:

Outline 41 Introduction Photocatalysts in Organic Synthesis Synthesis of Phenol Conclusions

Conclusions:

Conclusions Photocatalysts provide alternate synthetic routes for industrially important compounds that are more efficient and environmentally benign. Photocatalysts like TiO 2 can be manipulated to form plasmonic photocatalysts through noble metal loading. Increased efficiency of plasmonic photocatalysts attributed to increased charge separation and red shift of the absorption spectrum. Among the three photocatalysts M@TiO 2 (M=Au, Pt, Ag), Au@TiO 2 exhibits a high yield (63%) and selectivity (91%) for the oxidation of benzene to phenol in aqueous phenol. 42

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The selective photocatalytic conversion of benzene to phenol can be achieved by carefully controlling the local environment of the catalysts. The enhanced yield and selectivity of TiO 2 @MCF/CH 3 /UV is attributed to increased adsorption of more hydrophobic benzene and desorption of hydrophilic phenol. 43

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XRD pattern of Rutile(left) and anatase(right) TiO2:

XRD pattern of Rutile(left) and anatase(right) TiO 2 45

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