Work placement portfolio

GEORGE CHOUSOSJULY 2015

Work placement at Demokritos

Cardiff University:◦ Course: Environmental Geoscience (sandwich year)◦ Placement year: an extension of the course, takes place between the

2nd and 3rd educational year.

Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety:◦ Energy, Safety and Environmental Technologies Division

◦ Environmental Research Lab (air quality and climate change studies, solar energy systems, alternative fuels energy carriers, human exposure assessment)

Duration of placement: 11 months (September 2014- July 2015)

Training

CHEMICAL ANALYSES:

Chemical analysis of particulate matter (PM):

◦ Organic/elemental carbon (OC/EC)◦ Ions

◦ Cations (Na+, K+, Ca+)◦ Anions (F-, SO4

2-, NO3-)

Chemical analysis of volatile organic compounds (VOCs).

Bibliography

AIR QUALITY REMEDIATION METHODS:

Heterogeneous photocatalysis.

Bibliography

Chemical analyses

What is air pollution? “The presence in or introduction into the air of a substance which has harmful or poisonous effect”

Types of substances:◦ Particulate matter (acids, organic chemicals, metals, soil or dust particles)/ heart attacks, irregular

heartbeat ,aggravated asthma, decreased lung function etc.◦ Nitrogen oxides (highly reactive gasses, emissions from cars, trucks and buses, power plants and off-road

equipment/ respiratory problems)◦ Volatile organic compounds (VOCs) [(benzene, toluene, ethylbenzene, xylenes.)/ concentration in the indoor

environment higher (up to 10 times) than outdoors/ paints, cleaning supplies, pesticides, building materials, copiers and printers etc./ eye, nose, throat irritation, headaches, nausea, damage to liver, kidney, and central nervous system.]

◦ Ozone (ground-level) [chemically created from the interaction NOx, VOCs + sunlight]/ Harmful for people with asthma]◦ Carbon monoxide [colourless, odourless gas emitted from combustion processes (mobile sources)/ reduce the oxygen

delivery to the body’s organs, death at high levels)]◦ Sulphur dioxide (highly reactive gasses, fossil fuel combustion from power plants (73%), extraction of metal ores,

burning of high sulphur containing fuels e.g. locomotives, large ships etc/ respiratory system problems) ◦ Lead (fuels in on-road motor vehicles, e.g. cars and trucks, industrial sources/ today: ore and metal processing and

piston-engine aircraft/ nervous system, kidney function, immune system, reproductive and development systems and cardiovascular system + oxygen carrying capacity in blood)

Particulate matter (PM) Complex mixture of extremely small particles and/or liquid droplets.

Acids (nitrates and sulphates), organic chemicals, metals and soil or dust particles.

Sources: tobacco smoke, combustions, resuspension of accumulated dust, cooking, use of spray.

Sizes: PM10 (coarse particles)- <10μm PM2.5 (fine particles)- <2.5μm PM1 (ultrafine particles)- <1μm

Particulate matter (PM)OC/EC

OC/EC (organic/elemental carbon) aerosol analyser.

Measurements of carbon concentration in particulate matter, specifically PM2.5 and PM10.

Theory of operation:◦ Quartz filter placed in a quartz oven.◦ Oven is purged with helium (He).◦ Temperature ramp increases the temperature in oven thermally

desorbing organic compounds pyrolysis them into a manganese dioxide (MnO2) oven.

◦ Carbon fragments flow through the MnO2 oven converted into CO2 gas swept out and mixed with hydrogen gas.

◦ The mixture flows through a heated nickel catalyst converted to methane, which is measured using a FID (flame ionization detector).

◦ Oven temperature drops and the flow stream is altered to an oxidizing He/O2 carrier gas mixture.

◦ A second temp ramp occurs and any elemental carbon is oxidized off the filter and into the oxidizing oven.

Thermal-optical transmittance/reflectance method.

Protocols followed: EUSAAR2 NIOSH870 IMPROVEA

Particulate MatterIons

Ion chromatographer system DIONEX 1100 & DIONEX 5000

Fields of application:◦ Investigation of aqueous systems, e.g. drinking water, rivers,

rain water.◦ Analysis of ions in chemical products, foods, cosmetics.◦ Ultra-trace analysis, such as the semi-conductor and power

industry.

Theory of operation:◦ Tissue quartz filters subjected to ultrasonic extraction using

6ml of nanopure water and 0.5ml isopropanol.◦ Sample is introduced via a sample loop in the injector.◦ Sample is the pumped with the eluent onto the column

sample ions are attracted to the charged stationary phase of the column.

◦ The charged eluent elutes the retained ions go through the detector and are depicted as peaks on a chromatograph.

What do the results mean/ how can we use them

Volatiles organic compounds (VOCs)

GC (gas chromatographer) equipped with an FID (flame ionization detector), a thermal desorption unit and a cryotrapper (GERSTEL TDS3)

EN ISO 16017 method

Calibration using a 10μl syringe, spike in the glass tube 1μl of the standard solution inert helium (He) flew though the tube for 30min, rate about 100 ml/min

What do the results mean/ how can we use them

Project CEN, European Committee for Standardization, an association that unites the National Standardization

Bodies of 33 European countries.

One of the three organizations recognised by the European Free Trade Association (EFTA) developing and defining voluntary standards at European level. Its activities relate to a wide variety of fields, amongst one of them is the environment.

Project’s goal to investigate which of the protocols used had the least amount of deviation amongst the results.

Filters obtained from four different sites all over Europe Italy, Germany and (2) the Netherlands.

OC/EC instrument

Protocols used: EUSAAR2 NIOSH870 IMPROVEA

My obligations towards the campaign:◦ Chemically analysed the filters/ record the results in the logbook. ◦ The filters that I analysed were approximately 600.

Air quality remediation methodsPHOTOCATALYSIS

Photocatalytic decomposition of atmospheric gas pollutants using building materials infused with titanium dioxide

(TiO2).

Basic principles of heterogeneous photocatalysis

Photocatalysis is the acceleration of a chemical reaction, e.g. oxidation, by the use of light energy.

System requirements:◦ Photocatalyst: a semiconductor material

e.g. metal oxides (TiO2, ZnO, ZrO2,CdS etc.)

Electronic structure: electrons present in Valence Band (VB), empty Conduction Band (CB). ◦ Intermediate: gas or liquid form◦ Irradiation: hv>EBG (UV light <410nm)

Basic principles of heterogeneous photocatalysis

Mechanics of the photocatalytic activity

◦ Photons with energy larger than the EBG

◦ Electrons from VB are transferred to CB, creating pairs of free electrons (eCB

-) and positive holes (hVB+).

◦ Transfer of electrons (e-) to the surface and reaction with the adsorbed receivers and donors or recombination (heat and light production)

◦ Formation of reductive oxygen radicals (O2

-) and hydroxyl radicals (OH-) by reacting with the electrons and the holes, respectively, which in turn can oxidize organic and inorganic compounds.

Fields of application of the photocatalytic activity

Applications: ◦ Air purification.◦ Smell elimination.◦ Protection of urban environment,

such as road domain and buildings.◦ Development of super-hydrophilic

surfaces with self-cleaning and anti-fogging attributes.

◦ Limitation of the bacterial proliferation in a hospital or medical environment.

◦ Purification and cleaning of the water

Titanium dioxide (TiO2) as a photocatalyst

Titanium dioxide (TiO2) is a [1]n –type semiconductor electrical conductivity value is between that of a conductor and an insulator.

Current uses:◦ Pharmaceutical products◦ Cosmetic products◦ Grooming and toiletries◦ Paints◦ Food colouring (E171)

Mainly found in the naturally occurring mineral Ilmenite.

[1] LARGE ELECTRON CONCENTRATION THAN HOLE CONCENTRATION

Titanium dioxide (TiO2) as a photocatalyst

A) Rutile:◦ Tetragonal crystal system◦ Energy gap: 3.02 eV 413nm◦ Stable at high temperatures

B) Anatase: ◦ Tetragonal crystal system ◦ Energy gap: 3.23 eV 388nm◦ Stable at low temperatures:

◦ If subjected to temperatures over 450o C , it transforms into rutile.

◦ Higher photocatalytic action:◦ Difference in EG. Higher reduction activity since its energy gap is

higher than of rutile, thus requiring less energy to initiate redox reactions

◦ Difference in crystal structure

C) Brookite: ◦ Rare form ◦ At temperatures over 750oC it transforms into rutile

A

B

C

Photocatalytic advantages of TiO2 against other semiconductor materials

◦ High photocatalytic activity

◦ High availability.

◦ Low cost.

◦ Low to no toxicity.

◦ Biological and chemical inertness and

stability

◦ Activation at environment conditions (low

energy costs).

◦ High resistance to photo-corrosion.

Semiconductor Energy gap (eV)

Wavelength (nm)

ZnO 3.2 390WO3 2.8 443

TiO2 3.0 380

CdS 2.5 497CdSe 1.7 730

Factors affecting the photocatalytic performance Material

◦ Particle size (1-100 nm)

◦ Surface features (method of preparation)

◦ Chemical modification of crystal lattice ◦ Insertion of metal or non-metal ions (doping)◦ Combing TiO2 with other semiconductor compounds◦ Deposition of noble metals

Increase the active surface of the catalyst stronger photon absorption better surface coverage from pollutant higher reaction rates

Increase of complexity, geometric roughness and surface porosity increase active surface area higher absorption percentages

• Improving photo-activity of semiconductor under UV radiation, while extending the activity to larger wavelengths (visible light)

• Easier separation of the photo-induced charge carriers (e-, h+)

• Hindrance of recombination

Factors affecting the photocatalytic performance External factors

◦ Type/Intensity of radiation

◦ Initial concentration

◦ Temperature

◦ Humidity

◦ Oxygen

◦ Chemical compounds mixture

Low wavelengths photons energy higher activityIncrease in intensity photon flux higher photocatalytic performance

Directly related to the present conditions and the type of compound

Photocatalytic activity at ambient temperature scale (20o-40oC)Small variations have no particular influence

Water molecules assist to the formation and regeneration of OH.

humidity rates suspension of photocatalytic oxidation emergence of competitive adsorption phenomena between the water and pollutant molecules

the concentration the photocatalytic activity An excess of oxygen full oxidation and to limitation of by-product formation

Acceleration or deceleration

Factors affecting the photocatalytic performance Deactivation

◦ Photocatalyst deactivation

◦ Recovery methods

Formation of by-products that remain adsorbed on the surface of the catalyst, taking away active sites and blocking the adsorption of new water molecules, preventing the formation of OH.

• Exposure of catalyst in dry or humidified air stream

• Irradiation with UV light• Heat treatment at high temperatures• Surface treatment with the usage of

humidified stream of hydrogen peroxide

Humidity (%RH)

1) TCE, Acetone, Methanol:◦ The increase of water molecules (water

vapour concentration) works antagonistically with the gas molecules at occupying active sites on the surface lower reaction rates

2) Toluene:

Water molecules suspend the accumulation of carbon on the surface of the semiconductor accelerating the photocatalytic activity.

Initial concentration

The photocatalytic reaction rate increases as the initial concentration increases, for all the pollutants, but at a particular concentration and above it remains stable.

The kinetics can be expressed by:r = (k*K*C)/ (1+ K*C)

r: reaction ratek: reaction rate constant K: adsorption equilibrium constant

The photocatalytic degradation rate relates to k and K; therefore, a higher adsorption constant does not always result in a higher reaction rate.

Intensity of UV radiation

◦ For illumination levels below 1000-2000 μW cm-2, the photocatalytic degradation rate increases linearly with photon flux, but for levels above 1000-2000 μW cm-2 the rate increases with the square root of photon flux.

◦ Wavelength of UV light:◦ Germicidal lamp (200-300 nm, max at 254

nm)◦ Black light (315-400 nm, max at 352nm)Both lamps have sufficient energy to promote photocatalytic reaction, but germicidal lamp’s photo flux was higher higher degradation rate.

Chemical compound mixture

◦ Presence of NO:◦ The conversion of BTEX is higher than BTEX

solely. ◦ This enhancement is due to the formation

of hydroxyl radicals (OH.) according to this reaction:

NO + HO2. NO2 + OH.

The degree of influence for each of the organic compounds depends on the reaction rate of each with the hydroxyl radicals (OH.).

◦ Presence of BTEX: ◦ NO conversion decreased and generated a

lower secondary pollutant, NO2.

Photocatalytic experiments:Instrumentation and experimental conditions

Chamber characteristics:

◦ Chamber volume : 0.125m3

◦ 10 UV lamps, 20cm distance from

the material

◦ 2 fans for the prevention of heat

fluctuations that might affect the

photocatalytic process

◦ Cubic cell: 0.001 m3

Photocatalytic experiments:Instrumentation and experimental conditionsFLOW METRE CHEMILUMINESCENT NITROGEN

OXIDES ANALYSER

Photocatalytic experiments:Instrumentation and experimental conditions

Materials:◦ Photocatalytic cement in cube form

◦ Photocatalytic cement in powder form

Experimental conditions: ◦ Flow rate:

◦ 2.3 L/min (synthetic air)

◦ 0.8 L/min (nitrogen oxides)

◦ Duration of radiation: 4-5 hours

Photocatalytic experiments:Experimental calculation procedure

In the chamber there are 4 pollutant removal mechanisms:◦ Absorption from the chamber walls◦ Photo-degradation from the radiation ◦ Adsorption to the surface of the material◦ Photocatalytic oxidation from TiO2

Photocatalytic activity expression parameters:◦ Ph% decomposition =

◦ Destruction Rate (μg/m2s)=

◦ Destruction Velocity (m/s)=

100]/)[(x

CCCC

initial

initialfinalinitial

AsaxFCC finalinitial ])[(

finalCnRateDestructio

Photocatalytic experiments:Results

SAMPLE (cubes) BRB3 B3 BRA3

Concentration (ppb) 370-380 360-370 340-350

Ph % 17.6145 13.0808 11.5318

Destruction Rate (μg/m2s) 0.21230 0.15454 0.12662

Destruction Velocity (m/s) 0.00068 0.00048 0.00041

13.5014.0414.1814.3214.4615.0015.1415.2815.4215.5616.1016.2416.3816.520.0

50.0100.0150.0200.0250.0300.0350.0400.0450.0

BRB3

NO NOxTime

12.0012.2312.4613.0913.3213.5514.1814.4115.0415.2715.5016.1316.360.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

450.0

B3

NO NOxTime

UV lamps

UV lamps

10.5011.1611.4212.0812.3413.0013.2613.5214.1814.4415.1015.3616.020.0

50.0100.0150.0200.0250.0300.0350.0400.0

B2 (100% grey)

NO NOx

UV lamps

Photocatalytic experiments:Results

Sample (powder)

W1 (100% white)

B2 (100% grey)

R1 (100% ref)

WRAs (50% ref- 50% white)

BRC2 (90% ref- 10% grey)

Concentration (ppb)

330-340 300-310 340-350 330-340 310-320

Ph % 19.1950 41.9706 11.1456 15.6579 3.5148

Destruction Rate (μg/m2s)

0.24593 0.56604 0.15668 0.20627 0.04482

Destruction Velocity (m/s)

0.00094 0.00287 0.00050 0.00074 0.00014

10.47 11.14 11.41 12.08 12.35 13.02 13.29 13.56 14.23 14.50 15.17 15.440.0

50.0100.0150.0200.0250.0300.0350.0400.0

W1 (100% white)

NO NOx

UV lamps

10.4611.1511.4412.1312.4213.1113.4014.0914.3815.0715.3616.0516.340.0

50.0100.0150.0200.0250.0300.0350.0400.0

R1 (100% reference)

NO NOx

UV lamps

Photocatalytic experiments:Results

11.0011.2711.5412.2112.4813.1513.4214.0914.3615.0315.3015.5716.240.0

50.0100.0150.0200.0250.0300.0350.0400.0

WRAs (50% ref- 50% white)

NO NOx

UV lamps

10.1510.2310.3110.3910.4710.5511.0311.1111.1911.2711.3511.4311.5111.5912.0712.1512.2312.3112.3912.4712.5513.0313.1113.1913.2713.3513.430.0

50.0100.0150.0200.0250.0300.0350.0400.0

BRC2 (90% ref- 10% grey)

NO NOx

UV lamps

Placement learning outcomes

◦ Enhanced my skills on teamwork, communication and co-operation.◦ Development of my critical thinking on issues regarding decisions in the laboratory.◦ Broadening the horizons and expanding my knowledge on subjects concerning air pollution and

methods of remediation.◦ Contribution to tasks I was assigned by my supervisors, e.g. participating in lab’s chemical analyses.◦ Got acquainted with the usage and functionality of instruments specialised for recording and

measuring air pollution.◦ Enhanced my skills on researching for appropriate and beneficial bibliography and creating a

thematic library.◦ Practised and developed my scientific speech by giving short lectures to students, discussing

photocatalysis as a concept while presenting them the instruments that are being used.◦ Improved my abilities on utilizing Microsoft Word & Excel through assignments given to me by my

supervisors.◦ Participated as co-author in one scientific paper, that is to be submitted in a scientific journal, and in

2 abstracts submitted to the 3rd international conference for photocatalytic and advanced oxidation technologies in Gdansk, Poland and EAC, the European Aerosol Conference in Milan, Italy.