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Copy of thesis presentation


Sina Moradi

on 1 April 2013

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Transcript of Copy of thesis presentation

Titanium Dioxide (TiO2) Photocatalysis of Methyl Orange Under Varying Conditions of Polymorph Mixtures, Structure, Photocatalytic Light Parameters and Ultraviolet Light Pre-exposure Photocatalysis Mechanism The Use of Semiconductors as Photocatalysts: The Significance of Titania o Cheap o Suitable flat band potential o Non-toxic o High photocatalytic activity o High chemical inertia The Crystalline Phases of Titania o Anatase o Rutile o Brookite Titania Nanotubes o High photocatalytic ability o High ion-changeable ability o High surface area The Degussa P-25 Titania o Composed of about 70-80% anatase and 20-30% rutile o Mixed-phase titania trap photogenerated holes keep photogenerated electrons and control charge migration and recombination process Titania Phase Transformations o Anatase = metastable
o Rutile = Thermally stable
o Calcination temperature of 400°C = anatase
o Calcination temperature of 1000°C = rutile Light Intensity and Light Source Increasing the light intensity increases the amount of reactive oxygen species Photons with energy higher than the titania band gap is necessary for excitation The electrons of titania can only be excited by ultraviolet radiation with wavelength below 380 nm What is Photocatalysis? Light Sufficient Energy Excited electrons Redox Reactions Catalyst What is Titanium Dioxide (TiO2) aka Titania? Widely used as a photocatalyst What is Degussa P-25? A powder form of TiO2 that is a mixture of anatase and rutile
Widely used in nanotube fabrication due to its high effectiveness on degradation The Problem The growing popularity of photocatalysis as an efficient and cost-effective wastewater and air treatment calls for a lot of studies on it. The Problem (Degussa P-25) HIGH COST!!!! Objectives of the Study Vary parameters for both photocatalyst and photocatalysis method for optimum photocatalytic performance Objectives of the Study Light Conditions Light Source

visible/white light
ultraviolet (UV) light
metal halide light Significance of the Study Cost effective decomposition of organic wastes (dissolved in water)

Mineralization of organic wastes through solar energy

Determination of the correct parameters for photocatalysis rendering it more cost-effective and more efficient

Determination of answers to long term problems on titania photocatalysis limitations

Provide increase awareness and interest on titania photocatalysts in market Research Scope and Limitations Titania were fabricated at ph range 7-8
Photocatalysis carried out under room temperature
Anatase powder was used as the raw material for fabrication of the rutile phase and of the anatase nanotubes
Methyl orange (MO) was utilized as the model pollutant

Any fluctuations of the room temperature were not taken into account
Degradation of any other pollutant is not in the scope of this experiment
The study is limited to utilizing five (5) 6-watt white light fluorescent lamps as photon source for simulation of solar energy
Light intensity was measured as a function of the number of lamps utilized
The photocatalytic effectivity of doped titania is not in the scope of the study. This experiment has only dealt with undoped titania Methodology Fabrication of nanotube (hydrothermal method) Anatase titania powder + 10 M NaOH in Teflon beaker
3.75 g 30 mL

Oven heater (100°C) for 24 hours.

Washed with deionized water/0.1M HNO3 until pH of 7-8

Solids dried in an oven (100°C) for 1 hr
Solids ground using mortar and pestle and then kept in a dessicator Methodology Calcination of titania nanotube anatase: fabricated titania nanotube was heated in an oven with temp. of 400°C for 3 hours
rutile: fabricated anatase nanotube was heated in an oven with temp. of 1000°C for 4 hours Methodology Photocatalytic activity of titania Methyl Orange was used as the degrading medium
Activity lasted for 4 hours
Different parameters were varied: kind of light used, amount of light, composition of anatase-rutile mixture, pre-exposure of powder
Activity was done in an enclosed chamber
The solution for degradation composed of:

100 mL 20ppm Methyl orange
0.2 g of TiO2 powder Methodology Different kinds of set-up were done: Light sources were varied: UV light, white light, metal halide light
Amount of light energy (in watts) for UV and white light: 6W, 18W, 30W Methodology Transfer MO to black-covered sample vials
Centrifuge at 5000 rpm for 15 minutes
The solvent was slowly separated with the remaining solutes (powder).
Absorbance of methyl orange was measured using UV-Vis Spectrophotometer at 457 nm
Concentration of methyl orange samples and percent degradation were calculated, graphed Light Intensity and Light Source Sources of Errors:

room temperature
stray light
humidity and moisture content
uneven stirring
pH difference Pre-exposure and Structure Nanotubes = difference of surface area
= transport of electron from both its tips which are open
providing access of methyl orange to inner cavities


Nanotubes = low resistance to mechanical vibration
= stirring = mechanical vibration Variation of Titania Polymorph Semiconductors Titania has a large band gap (3.2 eV for anatase) enabling the utilization of only ultraviolet radiation as its photon source Possible electron-hole recombination Parameters for photocatalysis method:

Light Intensity
Light Source
UV light pre-exposure Parameters for photocatalyst:

Composition Light Intensity

six (6) watts
eighteen (18) watts
thirty (30) watts Pre-exposure

UV light pre-exposure (24 hours)
non pre-exposure (24 hours) Objectives of the Study photocatalyst parameters structure

raw powder
nanotubes composition*

90:10 anatase-rutile ratio
80:20 anatase-rutile ratio
0:100 anatase-rutile ratio *in attempt to simulate Degussa P-25 misture Condition of powder/nanotubes: 24 hrs prior to testing: Pre-exposed, kept in the dark
Titania structue: powder, nanotubes 1 2
Composition of the anatase-rutile mixture (% wt.): 80:20, 90:10, 0:100 3 Results and Discussion UV light: 3eV to 10 e12 eV
white light: 2eV to 3eV metal halide: multi-radiations in the UV and white light spectrum Pre-exposure and Structure Pre-exposure and Structure Results and Discussion anatase = higher efficiency
90:10 higher efficiency sources of errors:

rutile = hard, clump up
= difficulty for even stirring Degussa P-25 = higher efficiency than simulated mixtures Conclusion Evident manifestations of change from methyl orange color intensity and concentration in the very least, different light sources and intensities affect photocatalysis In the very least, different light sources and intensities affect photocatalysis Titania nanotubes vulnerable to mechanical damage. Application must be taken into account when selecting structure Pre-exposure gave increased degradation (even at a minimal level) Degussa P-25 = higher photocatalytic efficiency 90:10 anatase-rutile mixture > 80:20 anatase-rutile mixture > 0:100 anatase-rutile mixture END
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