-:Vijay Singh(09CEB023)

Transcription

1 Heterogeneous Semiconductor Photocatalyst -:Vijay Singh(09CEB023) Guided by Azrina Abd Aziz Under Dr. Saravanan Pichiah

2 Preparation of TiO 2 Nanoparticle TiO 2 was prepared by hydrolysis and poly-condensation (solgel) of tetrabutyl titanate, Ti(OC 4 H 9 ) 4 with H 2 O. Ti(OC 4 H 9 ) 4 ) and H 2 O have been taken in molar ratio of 1:2 [50 ml Ti(OC 4 H 9 ) 4 and 100 ml H 2 O]. We mix some amount of isopropyl alcohol as a solvent to obtain a solution. The mixture was stirred vigorously under Daihan Specific Hotplate Magnetic Stirrer (250 rpm) occupied with the stirring bar for an hour simultaneously adding HNO 3 (catalyst) until it s colour becomes yellowish. The mixture was then oscillated by ultrasonic wave at K until the solution becomes more viscous. The viscous solution was then kept in the freezer at K for 2 h and dried at K for a day. Finally, dried yellowish powder was then calcined at K for 2 h in a muffle furnace to obtain the white crystal of TiO 2.

3 Characterization of Technique 1. FESEM (Field Emission Scanning Electron Microscopy) Under vacuum, electrons generated by a field emission source are accelerated in a field gradient. The beam passes through electromagnetic Lenses, focussing onto the specimen. As result of this bombardment different types of electrons are emitted from the specimen. A detector catches the secondary electrons and an image of the sample surface is constructed by comparing the intensity of these secondary electrons to the scanning primary electron beam. Finally the image is displayed on a monitor.

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5 2. EDX or EDS (Energy Dispersive X-Ray Spectroscopy) It is an analytical technique used for the elemental analysis or chemical characterization. When the sample is bombarded by the SEM's (scanning electron microscopy) electron beam, electrons are ejected from the atoms. The resulting electron vacancies are filled by electrons from a higher state, and an x-ray is emitted to balance the energy difference between the two electrons' states. The x-ray energy is characteristic of the element from which it was emitted.

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7 3. XPS X-ray Photoelectron Spectroscopy XPS measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top 1 to 10 nm of the material being analysed. XPS requires ultra-high vacuum (UHV) conditions.

8 Intensity (cps) XPS Spectra of TiO O 1s Ti 2p C 1s Binding Energy (ev)

9 4. UV-Vis Ultraviolet Visible Spectroscopy It refers to absorption spectroscopy in the visible and adjacent (UV and infrared ) ranges. It is routinely used in analytical chemistry for the quantitative determination.

10 Absorbance UV-Vis Absorption Spectra for TiO Wavelength (nm)

11 Drawbacks of TiO 2 1. Large Band gap (3.2 ev) 2. Can be activated only under UV light

12 How to do Modification Doping:- 1.Transition Metal ions(iron, chromium, copper) 2.Non-metal ions(nitrogen, carbon, and iodine )

13 Preparation of TiO 2 - x N x Nanoparticles Simple Wet Process An aqueous TiO 2 (SO 4 ) 3 solution was prepared by 20 wt.% of TiO 2 (SO 4 ) 3 and 80 wt.% of H 2 O. The prepared solution was hydrolyzed under Daihan Specific Hotplate Magnetic Stirrer (P: 650 W; f: 50/60 Hz) occupied with the stirring bar by the addition of 30% NH 3 aqueous solution until the ph reached 7. Titration was conducted slowly to prevent the ph value from exceeding 7. The hydrolysis product which is in the form of white suspended semi solid was rinsed with distilled water until the concentration of the sulphate, SO 4 2- in the rinsing water reached 0.5 ppm.

14 Determination of [SO 4 2- ] Initially the standard sulphate solution with a concentration of 0.5 ppm was prepared. The standard sulphate solution turbidity level was used as a comparison to the rinsing water using spectrometer to determine the absorbance level under the wavelength of 525 nm. Formation of barium sulphate, BaSO 4 turbidity: Measured 0.1 L of sample L buffer solution was added and mixed in stirring apparatus. While stirring, a spoonful of BaCl 2 crystals were added upon the beginning of the timing. Stir for 60 ± 2 s at constant speed.

15 Measurement of barium sulphate, turbidity: After the completion of the stirring, the solution prepared was poured into the absorption cell of spectrometer and turbidity was measured at 5 ± 0.5 min. This is the crucial step in producing visible light responsive N-doped TiO 2 due to the high concentration of SO 4 2- which will retard the reaction between the N and the TiO 2. Moreover, the low specific surface area yield from the high concentration of SO 4 2- is responsible.

16 The hydrolysis product denoted as TiO 2 - x N x was then dried in an oven at the temperature of K and calcined at K for an hour. The obtained yellow-coloured photocatalyst was grinded into smaller size in order to obtain the large specific surface area of particles.

17 Activated Carbon Activated carbon is referred to porous carbon that undergoes through a process called activation. Activation process involves high temperature treating of already pyrolyzed using so called activating agents such as carbon dioxide, char, steam, potassium hydroxide, etc. Activated carbon has great adsorption capabilities for which it is used in liquid or vapor phase filtration media. Activated carbon has surface area greater than 1,000 m 2 /g.

18 Preparation of Activated Carbon Garcinia Mangostana shell:h 3 PO 4 = 1:1 (weight ratio). An additional 5 ml of H 3 PO 4 was added to ensure all the powder is soaked in acid for complete chemical activation. The combination was then stirred till a moist pastelike texture was obtained. The impregnated powder was carbonized in the furnace at 400 C for 1 h.

19 After cooling, the now charred powder was washed repeated with Milli-Q water and soaked overnight 1% sodium hydrogen carbonate (NaHCO 3 ) solution to remove the excess or residual acid. This step was repeated until the ph of the supernatant was < 7. Finally, it was dried in the oven overnight at 100 C. The powder was again sieved to obtain particles < 1 mm in diameter as the particles agglomerate during chemical activation. The particles that were bigger than the required size were crushed and sieved again.

20 Preparation of N-TiO 2 /AC Take 1:1 = N-TiO 2 :AC (wt. % ratio) Mix with 1 L of water using magnetic stirrup for 24 h at 60 Hz Using Centrifuge(2500 rpm for 30 min), we will get a galley paste Put galley paste in oven for evaporation of water and we will get powder form Now put this powder into furnace at 400 C for 1 h.

21 Characterization FESEM The figure shows the agglomeration of TiO2 nanoparticle on the surface of the activated carbon. Moreover, the pores of the AC have been filled with the TiO2 particle. TiO 2 /CAC

22 Absorbance UV-Vis Absorption Spectra for TiO wavelength(nm)

23 Working Principle of TiO 2 The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly.

24 Application of TiO 2 as a Photocatalyst Detoxification or remediation of wastewater Energy Production Paints

25 TiO 2 offers great potential as an industrial technology for detoxification or remediation of wastewater due to several factors: Uses natural oxygen and sunlight Photocatalyst is inexpensive, readily available, non-toxic, chemically The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided. Oxidation of the substrates to CO 2 is complete.

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