Dr. Magdalena Morozova

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Modification of functional nanomaterial for photocatalysis

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Hosted by: Modification of functional nanomaterial for photocatalysis Morozova Magdalena, Dytrych P., Dzik P., Kluson P., Krysa J., Solcova O. Institute of Chemical Process Fundamentals of the ASCR, v. v. i ., Czech Republic.

Modification of functional nanomaterial for photocatalysis:

Modification of functional nanomaterial for photocatalysis Morozova M agdalena , Dytrych P., Dzik P., Kluson P., Krysa J., Solcova O . Institute of Chemical Process Fundamentals of the ASCR, v. v. i. Rozvojova 2/135, Prague 6, Czech Republic http://www.icpf.cas.cz/ morozova @icpf.cas.cz

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Aim of the work Preparation of thin TiO 2 sol-gel layers Sol-gel method with molecular template Influence of - surfactant (length of hydrophilic chain) - doping ions (Fe, Ce, Zr) - calcination temperature (450 – 750 °C, boro-aluminosilicate glass) - deposition techniques ( dip-coating, spray-coating, inkjet printing ) Characterization of structural and photo-induced properties of the layers by physical and electrochemical methods 1

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Template sol-gel method t-Octylphenoxypoly(ethoxyethanol) The sol-gel method: - utilization of reverse micelles - non-polar solvent – cyclohexane, xylene - surfactant - TritonX 102 ( N =12 ) - polar solvent - water H 2 O + Ti IV + dopant Hydrophilic part (oxyethylene chain) Lipophilic part H 2 O + Ti IV alkoxide *P. Kluson, S. Kment, M. Morozova, P. Dytrych, J. Krysa; Ultrathin functional films of titanium(IV) oxide , Chem. papers 66 (2012) 446-460. Reverse micelles system 2 Calcination at 450 °C for 4h.

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Deposition techniques: - dip-coating - spray-coating - inkjet printing Thin layers preparation Length of hydrophilic chain: Triton X15, X45, X114, X100, X102 Doping: - metallic compounds (Fe, Ce, V,….) - non-metallic compounds (C, S, N) Calcination temperature: - 450 °C (anatase) - 550 °C (anatase/rutile) - 750 °C (rutile/anatase) Anatase 3 Rutile

Layers characterization:

Layers characterization Structural properties: - crystallographic form and particle size ( XRD, Raman spectroscopy ) - layer morphology ( optical microscopy, SEM, AFM ) - layer thickness ( XRR, NanoCalc, elipsometrie, SEM ) - optical properties ( UV-Vis sepctrophotometry ) - mechanical stability Photo-induced properties: - photocatalytic decomposition of azo dye ( Acid Orange 7 ) - photo-e lectrochemical methods ( cyclic and linear voltammetry, amperometry, OCP ) 4

Photo-induced properties characterization:

- Azo dye acid orange 7 (AO7) as model compound, concentration 2 . 5·10 -6  mol dm -3 , abs. max 485 nm - Light intensity 20 W m -2 (320-400 nm) Hydrazo form Azo form Photocatalytical setup 1) Magnetic stirrer, 2) UV lamp, 3) TiO 2 layer, 4) cuvette with reaction solution, 5) cooling Optoelectrochemical setup Incident-Photon-Current Conversion Efficiency 1) UV Hg lamp (500 W) , 2 ) Liquid filter , 3 ) Monochromatic filter 365 nm , 4 ) Automatic shutter , 5 ) Electrochemical cell IPCE factor Electrolyte Na 2 SO 4 (0.1 mol dm - 3 ) Electrochemical cell Photo-induced properties characterization Intensity of the incident light (365 nm) = 10 W m -2 a) Working Electrode - sample b) Auxiliary Electrode - Pt sheet c) Reference Electrode - AgCl 5

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Surfactant No. of groups Form * rms factor ** [nm] Triton X 15 N = 1-2 amorphous 0.2 Triton X 45 N = 4-5 amorphous 0.4 Triton X 114 N = 7-8 crystalline 0.5 Triton X 100 N = 9-10 crystalline 0.9 Triton X 102 N = 12 crystalline 0.7 Effect of the hydrophilic chain length * Calcination at 450 °C , ** 4 TiO 2 layers Length of hydrophilic chain in surfactant TX 15 TX 102 Anatase * M. Morozova, P. Kluson, J. Krysa, M. Zlamal, O. Solcova; Role of the template molecular structure on the photoelectrochemical functionality of the sol–gel titania thin films , J Sol-Gel Sci Technol. 52 (2009) 398-407. XRD analysis

Photo-induced properties:

Layers No. Rate constant [s -1 ] Conversion [%] Quantum yield [%] Degradation rate [ mol /s W] 3 Lrs 3 . 9 ·10 -5 49 2 . 0 ·10 -7 9 . 5 ·10 -11 4 Lrs 5 . 9 ·10 -5 60 3 . 3 ·10 -7 1 . 1 ·10 -10 5 Lrs 1 . 6 ·10 -4 93 1 . 2 ·10 -6 1 . 4 ·10 -10 6 Lrs 3 . 1 ·10 -4 99 2 . 5 ·10 -6 1 . 5 ·10 -10 Photo-induced properties AO7 concentration 2 . 5·10 -6   mol dm -3 - Light intensity 20 W m -2 (320-400 nm) - abs. max 485 nm Photocatalytic parametrs Effect of used Triton X Effect of number of deposited layers TX 45 TX 100 TX 114 TX 102 TX 15 Amperometry Photocatalysis 7

Deposition techniques:

Deposition techniques Dip-coating Inkjet printing Spray-coating Layers r ms factor [ nm ] Thickness SEM** [ nm ] M [ nm ] ±1nm Dip-coating 0.4 330 7.5 Inkjet printing 1.4 340 8.2 Spray-coating 2.2 310 10.4 * * f or 3 layers and 6 sprayed cycles - XRD analysis, Raman spectroscopy => pure anatase phase for all samples - Absorption edge (355 ± 5 nm ) - Smooth layer surface * M. Morozova, P. Kluson, P. Dzik, M. Vesely, M. Baudys, J. Krysa, O. Solcova; The influence of various deposition techniques on the photoelectrochemical properties of the titanium dioxide thin film , J Sol-Gel Sci Technol. 65 (2013) 452-458. 8

Mechanical stability test:

Mechanical stability test Layer before Layer after Dip-coating – after 4060 cycles cca 40-50 % of layer was removed Inkjet printing – the major part of the layer was already removed from the substrate after 10 cycles with 0.25 kg load Spray-coating - after 4060 cycles cca 20-30 % of layer was removed - testing device ELCOMETER 1720 Washability tester (Technical University in Liberec) - friction element – felt disc with density 0.56 g cm -3 - 1160 cycles with load of 0.25 kg and 2900 cycles with load of 0.5 kg Dip-coating Inkjet printing Spray-coating 9

Photo-induced properties:

Deposition technique Rate constant [s -1 ] Dip-coating 1 . 96·10 -5 Inkjet printing 1 . 83·10 -5 Spray-coating 2 . 07·10 -5 - Difference in IPCE values is caused by the various surface/bulk defects ratio and their concentration in the layers. - The higher photocurrent, the lowe r ratio of bulk to surface defects. - constant potential 600 mV Photo-induced properties Quantum yield [%] Photocatalytic activity is low and almost similar. The higher photocatalytic activity can be supposed for layers with higher surface roughness. Amperometry 10

Calcination temperature:

Calcination temperature Temperature [ ° C] Confidence Interval (± 5 %) Anatase Rutile 450 100-98 0-2 550 90-85 10-15 650 45-35 55-65 750 25-20 75-80 The calculated ratio of anatase/rutile structure distribution in thin layers A natase/rutile structure Anatase structure The ratio of the crystallographic structure distribution was calculated by deconvolution integration method from the peak area at 541–491 cm -1 (anatase) and at 483–431 cm -1 (rutile). vibration lines for anatase phase (642, 519, 399 and 148 cm -1 ) vibration lines of rutile phase (612, 447, 240 cm -1 ) The anatase layer thickness is 330 nm, clusters about 20 nm. (450 °C) The mixed anatase/rutile layer thickness is 370 nm, clusters about 80 nm. (750 °C) Raman spectroscopy

Calcination temperature:

Calcination temperature * M. Morozova, P. Dytrych, L. Spacilova, O. Solcova; The influence of rutile particles on photo-induced activity of the sol–gel TiO2/ITO photo-anode , Res Chem Intermed. (2015), DOI 10.1007/s11164-015-2006-5. The influence of calcined temperature on the IPCE values for layers with various thicknesses Amperometry of the pure anatase and anatase/rutile layers R utile particles in the thin anatase layer : positively influences the electron-transfer rate decreases the recombination improves the photo-induced properties The layers with rutile particles reached much higher values of the generated photocurrent - better electron transport between the particles in the anatase/rutile layer. - light intensity 1 mW cm -2 12

TiO2 layer doped by metallic ions :

TiO 2 layer doped by metallic ions Sample TiO 2 Fe - TiO 2 Ce - TiO 2 Zr - TiO 2 S BET [m² g -1 ] Abs.edge [nm] Thickness [nm] 30.42 355 340 32.00 356 320 76.84 359 430 108.60 344 720 Textural properties, absorption edges and thicknesses of pure and doped TiO 2 samples TiO 2 Zr-TiO 2 Ce-TiO 2 Fe-TiO 2 pure TiO 2 sol from titanium alkoxide (TTIP) used as Ti (IV) precursor dopant sources - 15 % water solution of iron (III) nitrate and cerium (IV) nitrate; - zirconium propoxide in the ratio 1:9 glass substrate, dip-coating method, calcinated at 450 °C for 4 h The BET isotherm experiment were performed on the powders calcined at 450 °C and t he adsorption–desorption isotherms were measured by nitrogen at 77 K . The specific surface area ( S BET ) was calculated according to the classical Brunauer–Emmett–Teller (BET) theory for the p/p0 range = 0.05–0.25. 13

TiO2 layer doped by metallic ions :

Linear voltammetry TiO 2 layer doped by metallic ions p hoto-electrochemical properties measured in the three-compartment electrochemical cell ( electrolyte 0.1M Na 2 SO 4 ) TiO 2 /ITO electrode = working electrode the wavelength of the incident light focused by an interference filter on 365 nm (10 W m - 2 ) - Photocatalytic activity was measured by decomposition of water solution with low concentration of the dye (2.5  10 -6 mol L -1 ). - UV-A light intensity was 60 W m - 2 . Photocatalytic activity 14

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Conclusions Possibility of the simple modification of thin photo-active films generated by the template sol-gel method was demonstrated. A clear connection between the length of the oxyethylene group of the non-ionic surfactant, thickness of the deposited layer and its efficiency in generation of the photo-active species was confirmed. It was found that the used deposition techniques influenced the type of created defects similarly as their amount and ratio of the surface/bulk defects in the prepared thin films. Pure anatase or mixed anatase/rutile phases were obtained during the calcination step as the result of the selected temperature. It was verified that the presence of rutile particles in the thin layers positively influences the photo-induced properties. Doping process showed that the reverse micelles system is not suitable for preparation of the doped layers by metal lic ions – very low concentration of ions and low influence. Nevertheless, the presence of Ce ions in TiO 2 layer revealed positive effect on photocatalytic activity. 15

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Acknowledgement Colleagues - Institute of Chemical Process Fundamentals of the ASCR, v. v. i . - University of Chemistry and Technology, Prague - Brno University of Technology The financial support of the NATO project SPS (NUKR. SFPP) 984398 is gratefully acknowledged . FACULTY OF CHEMISTRY BRNO UNIVERSITY OF TEHCNOLOGY

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Thank you for attention