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sensing properties of Jens Martensson 15/05/2020 - 31/05/2020 Nb 2 - - PowerPoint PPT Presentation

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Influence of the size of coal ash FAU zeolites used as dopants on the 2nd Coatings and Interfaces Web Conference sensing properties of Jens Martensson 15/05/2020 - 31/05/2020 Nb 2 O 5 thin films. K. Lazarova 1 , S. Boycheva 2 , M. Vasileva 1

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SLIDE 1

Jens Martensson

1 Institute of Optical Materials and Technologies ‘‘Acad. J. Malinowski’’, Bulgarian Academy of Sciences, Sofia, Bulgaria 2,3 Technical University of Sofia, Bulgaria 2 Department of Thermal and Nuclear Power Engineering; 3 College of Energy and Electronics

Institute of Optical Materials and Technologies

2nd Coatings and Interfaces Web Conference 15/05/2020 - 31/05/2020

Influence of the size of coal ash FAU zeolites used as dopants on the sensing properties of Nb2O5 thin films.

  • K. Lazarova1, S. Boycheva2, M. Vasileva1, D. Zgureva3 and
  • T. Babeva1

1

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SLIDE 2

Jens Martensson 1.

Coal ash - pollutants and possibilities for their utilization

2.

Na-X Faujasite (FAU) zeolites - synthesis from coal ashes

3.

Wet-milling of synthesized zeolites

4.

Thin films from Nb2O5 doped with milled and not-milled zeolites

5.

Characterization of thin films -

  • ptical and sensing properties

6.

Summary

2

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SLIDE 3

Jens Martensson Coal is the largest source of energy from fossil fuels used for generating electricity in the world. The electricity produced in Bulgaria in 2018, allocated according to the primary energy resource and used production technology.

3

4% 1% 40% 36% 12% 7%

Thermal Power Plants (TPP) on gas TPP Black and Brown Coal TPP Lignite Nuclear power plant Water Electric Power Plant Solar, wind and biomass energy

  • Different opportunities for

utilization have been explored, including for the synthesis of zeolites.

  • Ash macro-component

composition is considered as an alumosilicate material.

  • 1. Releases of gaseous

emissions - sulfur, nitrogen and carbon oxides

  • 2. Generation of solid

waste - ash

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Jens Martensson

4

Greenhouse effect

Zeolites are materials with a unique porous structure, with active centers and mobile cations of alkaline and alkaline-earth metals.

For the purposes of developing CO2 capture technologies in the search for new solid phase sorbents, zeolites have also been studied. Carbon dioxide CO2 Volatile Organic Compounds (VOСs)

They have valuable features such as :

adsorbents separators catalysts ion exchangers LTA FAU Released gas emissions

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Jens Martensson

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  • 2. Na-X Faujasite (FAU) zeolites - synthesis from coal ashes

LTA and FAU zeolites have the highest carbon capture potential Zeolite from coal ash - they

Pore size 7.35 Å Free volume 27.42 %

FAU

Pore size 4.21 Å Free volume 21.43 %

LTA

highly developed specific surface

Zeolites synthesized from pure starting materials Allowing the physical adsorption of molecules of CO2 from size 3.2 Å Determine their good catalytic activity High content of iron oxides (-Fe2O3, α-Fe2O3, -Fe3O4) In combination with microcomponents such as Cu, Co, Mn, V, W The process of synthesis is carried out in three stages:

1) Dissolving aluminosilicates of the ash in the alkaline solution; 2) Precipitation of an alumosilicate hydrogel; 3) Crystallization of zeolite from the alumosilicate gel on undissolved solid particles.

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Jens Martensson

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FAU type zeolites synthesized from coal fly ash Part of the zeolites are subjected to subsequent wet milling in a ball mill for 60 s to reduce their size to submicron values.

  • 3. Wet-milling of synthesized zeolites

Not milled zeolites

10 000x 5 000x

Milled zeolites ∨ Agglomerations

  • f

indistinguishable particles are

  • bserved

before milling and

  • ctahedral shape crystallites typical of the FAU

phase. ∨ Inclusions of particles from other zeolite phases are also found, which often accompany the crystallization of FAU from coal fly ash. ∨ After the mechanical processing, a clear separation of the individual particles of about 1-1.5 μm size is observed.

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Jens Martensson

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FAU type zeolites synthesized from coal fly ash Part of the zeolites are subjected to subsequent wet milling in a ball mill for 60 s to reduce their size to submicron values.

  • 3. Wet-milling of synthesized zeolites

10 100 1000 10000 5 10 15 20 25 30

d3=111 nm d2=716 nm

Milled 60s Not milled

Intensity(a.u.) Size(nm)

d1=1472 nm

Size distribution changes from monomodal (d1) in the case of non-milled zeolites to bimodal (d2 and d3) for milled samples: d1 = 1470 nm d2 = 716 nm and d3 = 111 nm

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Jens Martensson

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Sol-gel method

Spin-coating Thin films from Nb2O5 doped with milled and not-milled zeolites Deposited on a silicon substrate, Speed - 4000 rpm, Heated for 30 min at 320°C

  • 4. Thin films from Nb2O5 doped with milled and not-milled zeolites

Milled and not-milled FAU zeolites Nb2O5 + not-milled FAU Nb2O5 + milled FAU and Deposited thin films in three volume concentrations 1% 2.5% 5%

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Jens Martensson

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  • 5. Characterization of thin films - optical and sensing properties

n, k и d - calculated by nonlinear algorithm for minimizing the difference between measured and calculated values of the reflectance R.

400 600 800 20 40 60

Reflectance (%) Wavelength (nm)

Concentration of zeolites 1% 2.5% 5%

Reflectance spectra of the films are measured in order to study their optical properties and to calculate the thickness.

Nb2O5 + milled FAU

Reflectance spectra of Nb2O5 films with milled zeolites Thickness (d) Refractive index (n) Extinction coefficient (k)

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SLIDE 10

Jens Martensson

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  • 5. Characterization of thin films - optical and sensing properties

1 2 3 4 5 40 50 60 70 80 90 100

d (nm)

Zeolites concentration (%)

milled not milled

Dependence of thickness d on zeolite concentration (b) of thin Nb2O5 films embedded with not-milled and milled fly ash FAU zeolites.

  • Films doped with not-milled zeolites have

thickness around 78 nm

  • 80

nm for 1% concentration and there is a slight increase in d to 84 nm at concentration of 2.5 %. There is no further increase of d with concentration.

  • Films doped with milled zeolites have clear

tendency

  • f

increasing thickness with concentration of zeolites – from 62, 73 and 77 nm for 1, 2.5 and 5 % respectively.

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Jens Martensson

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  • 5. Characterization of thin films - optical and sensing properties

Dispersion curves of refractive index of thin Nb2O5 films embedded with not-milled and milled fly ash FAU zeolites.

  • normal dispersion curves
  • lower thickness, higher density and refractive index as

compared to samples doped with not - milled zeolites.

  • more pronounced decrease in n with increasing the zeolite

concentration.

Using smaller zeolites

1. Precise control and deposition of thin films with a specific thickness. 2. Control of the refractive index of the films.

Dependence of refractive index n at wavelength of 600 nm on zeolite concentration of thin Nb2O5 films embedded with not-milled and milled fly ash FAU zeolites.

Films of Nb2O5 + milled FAU

1 2 3 4 5 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4

Refractive index

Zeolites concentration(%)

Miled 60s Not milled

400 500 600 700 800 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6

Refractive index

Wavelength(nm)

Not milled FAU zeolites 1% 2.5% 5% Milled 60s FAU zeolites 1% 2.5% 5%

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Jens Martensson

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Sensing properties toward liquid acetone

  • 5. Characterization of thin films - optical and sensing properties

Sensing properties determination method Measuring of the reflection spectra of thin films before and after exposure to liquid acetone. Calculation of the acetone induced change in the reflection ΔR. 1 2

400 450 500 550 600 650 700

10 20 30

R(%) Wavelength(nm)

Air Acetone

2.5 % milled zeolites film

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Jens Martensson

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Sensing properties toward liquid acetone

  • 5. Characterization of thin films - optical and sensing properties

5 10 15 20 25

5% 2.5% Zeolite concentration (%)

R(%)

Milled for 60s Not milled

1%

1 2

Zeolite concentration dependence of reflectance change induced by exposure to liquid acetone of FAU not-milled (blue bars) and milled (magenta bars) embedded in thin Nb2O5 films. Measurements are conducted at room temperature.

 The addition

  • f

not-milled zeolites results in a 1.6 - 2.5 % change in ΔR as increase of concentration leads to decrease

  • f reflectance change.

 In the case of films with milled zeolites - as the amount of zeolites increases, the change in the reflection coefficient ΔR increases from 7.6 to 19.4. Milled zeolites samples: ≈20 % max change Not - milled zeolites samples: 2.5 % max change

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Jens Martensson

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Selectivity for films of Nb2O5 + milled FAU

  • 5. Characterization of thin films - optical and sensing properties

1 2

Zeolite concentration dependence of reflectance change induced by exposure to liquid acetone (yellow) and ethanol (green) of milled zeolites embedded in thin Nb2O5 films. Measurements are conducted at room temperature.

 The optical response toward ethanol is almost 8 times weaker as compared to acetone.  Increase of concentration of milled zeolites leads to increase

  • f

the change in the reflection coefficient ΔR. Acetone: ≈20 % max change for highest concentration Ethanol:

  • av. 2.5 % max change

for all concentrations

5 10 15 20

5% 2.5% Zeolite concentration (%)

R(%)

Acetone Ethanol

1%

  • Similar measurements made with liquid ethanol for

films with milled zeolites .

  • Ethanol

selected as probing liquid due to its similar to acetone refractive index: 1.361(eth) and 1.359(ac).

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Jens Martensson

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 FAU zeolites of coal ash with a particle size of 1470 nm have been synthesized by alkaline atmospheric conversion.  The possibility of reducing zeolites particle size in half and simultaneously obtaining particles of about 100 nm in size by wet milling has been demonstrated.  Successfully have been deposited composite thin films comprising Nb2O5 matrix and fly ash FAU zeolites in concentrations from 1 to 5 % with good optical quality and reflectance coefficient in range 47 – 58 %.  The possibility of controlling the refractive index and sensing properties of the films through variation of concentration and size of particles has been shown. The value of n varies in a wide range from 1.6 to 2.2.  The liquid-induced changes for samples with milled zeolites are eight times higher than changes in films doped with not-milled zeolites.  The sensitivity is higher toward acetone compared to ethanol.

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Jens Martensson

Acknowledgements: The financial support

  • f

Bulgarian National Science Fund (BNSF) under the project DN 17/18 (12.12.2017) is highly

  • appreciated. Research equipment of distributed research infrastructure

INFRAMAT (part

  • f

Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science under contract D01-284/17.12.2019 was used in this

  • investigation. The assistance of Prof. Vera Marinova from IOMT-BAS in

the process of zeolite milling is highly appreciated.

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