State-of-the-art Flame Synthesis of Nanoparticles

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1 Verbrennung und chemisch reaktive Prozesse in der Energie- und Materialtechnik State-of-the-art Flame Synthesis of Nanoparticles Dr. Frank Ernst 200 nm Particle Technology Laboratory, Department of Mechanical and Process Engineering ETH Zurich,

2 Nanoparticles nm (at least into two dimensions) The thickness (diameter) of a human hair is 50, ,000 nm! 2

3 3

4 Melting Point, K The Melting Point Decreases with Decreasing Nanoparticle Size Au Particle diameter, Å Buffat and Borel, Phys. Rev. A 13, 2287 (1976) 4

5 Applications of Nanoparticles Large surface area per gram (adsorbents, membranes) Stepped surface at the atomic level (catalysts) Easily mix in gases and liquids (reinforcers) Superfine particle chains (recording media) Easily carried in an organism (new medicines) Cosmetics that last way into the night mm 10 nm SSA = 200 m 2 /g Some people believe that nanoparticles are a new state of matter! SSA = 0.2 m 2 /g 5

6 How are they made? Many processes & synthesis conditions Plasma-arc Laser ablation Chemical Vapor Deposition Wet-phase chemistry etc. Need synthesis technique that is: Rapid, continuous & scaleable Flame synthesis carbon black TiO 2 SiO t/year Scale-up limitations C 60 /C t/year 6

7 Particle formation & growth flames Aggregation HCl TiO 2 TiO 2 TiO 2 H 2 O TiO 2 H 2 O H 2 O HCl Coagulation T (K) O 2 TiCl 4 H 2 TiCl 4 TiCl 4 O 2 H 2 H 2 O 2 Nucleation Chemical reaction 7

8 Vapor flames Can make many interesting materials: Fillers for composites, catalysts etc. However, limited compositions H C, TiO 2, SiO 2, Al 2 O 3 He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fw Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 8

9 Vapor flames Aggregation HCl TiO 2 TiO 2 TiO 2 H 2 O TiO 2 H 2 O H 2 O HCl Coagulation T (K) O 2 TiCl 4 H 2 TiCl 4 TiCl 4 O 2 H 2 H 2 O 2 Nucleation Chemical reaction Reactants in vapor phase 9

10 Spray flames Keep aerosol processes Dispersed Product- Molecules & Cluster Droplets contain: - Organic solvent (comb. energy) - Reactant precursor compound Reactants in LIQUID phase 10

11 Spray flames 11

12 30 mm Flame synthesis 300 nm 200 nm Dispersed Product- Molecules & Cluster Vapor Flame Spray Flame Mädler, L., Kammler, H.K., Mueller, R., and Pratsinis, S.E., J. Aerosol Sci. 33 (2) (2002). 12

13 Spray flames Spray Flame Pyrolysis (FSP) Liquid enables composition flexibility Opens up many possibilities H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fw Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 13

14 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 14

15 Tailor-made particle structures (size, morphology, crystallinity etc.) with a large variety chemical compositions 15

16 Flame Spray Pyrolysis 16

17 In-situ deposition of noble metals 15 nm For applications in catalysts sensors optical devices, etc. Au on TiO 2 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 17

18 Concentration vs. crystallite size Doubling gold concentration 20 Au / TiO 2 (~ 100 m 2 /g) doubles Au crystallite size leaves support unchanged Average crystal size, nm Au wt% 4.0 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 18

19 Concentration vs. crystallite size Doubling gold concentration doubles Au crystallite size leaves support unchanged Gold particle size is independent of ceramic supporting surface area Average crystal size, nm Au / TiO 2 (~ 100 m 2 /g) Au / SiO 2 (~ 320 m 2 /g) Au wt% 4.0 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 19

20 Flame Spray Pyrolysis 20

21 Glucose sensor Proton Exchange Membrane Fuel Cell detection of hydrogen peroxide biomolecules (glucose, choline,...) Ernst et al., J. Mat.Chem., 20 (6), (2008). hydrogenation oxidation reforming electrodes for fuel cells 21

22 Hydrogenation of cyclohexene Cyclohexene conversion (%) supported (12 wt% Pt) reference (5 wt% Pt) supported (10 wt% Pt) embedded (2.6 wt-%) time (min) Ernst et al., J. Mat.Chem., 20 (6), (2008). 22

23 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 23

24 Direct deposition on sensor substrate Filter housing Water out Spray flame Support flame Shield gas Exhaust vent Water in Deposition substrate 120 C Precursor liquid Syringe pump PI MFCs Oxygen Methane Oxygen Oxygen 500 C sensing area: 7 x 3.5 mm 2 Mädler et al., European patent, Dec. 9th

25 Layer morphology top view SnO mm Deposition time: 180 s 25

26 Layer morphology top view SnO 2 5 mm 500 mm Deposition time: 180 s 26

27 Layer morphology cross section SnO 2 Al 2 O 3 5 mm Deposition time: 180 s 27

28 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 28

29 Mädler, et al., J. Appl. Phys (2002). Stark, W. J. et al., A., Chem. Commun. (2003). Strobel, R. et al., J. Catal. (2003). Examples for FSP materials Metal oxides SiO 2, TiO 2, Al 2 O 3, Bi 2 O 3, CeO 2, ZnO Mixed metal oxides SiO 2 /TiO 2,V 2 O 5 /TiO 2, ZnO/SiO 2, Zn 2 SiO 4, BaTiO 3, Ce x Zr (1-x) O y Noble metals on oxides Au, Pt, Pd on TiO 2, SiO 2, Al 2 O 3 TiO 2 Ce x Zr (1-x) O y Pt on Al 2 O 2 Bi 2 O 3 hollow ZnO/SiO 2 50 nm 5 nm 200 nm Versatile Process

30 Scale-up 40 cm Mueller et al., Chem. Eng. Sci., 58 (10), (2003). HMDSO/EtOH spray flame producing 300 g/h of silica. 30

31 BET-equivalent diameter, nm Scale-up Oxygen 12.5 l/min 50 l/min 1.26 M 3.0 M 4.7 M Vapor Flames* 40 cm SiO 2 - Production rate, g/h 1200 Mueller et al., Chem. Eng. Sci., 58 (10), (2003). HMDSO/EtOH spray flame producing 300 g/h of silica. 31

32 Lecture summary Nanoparticles for Materials Flame Spray Pyrolysis & metal-oxide materials Vapor Spray flame: extend range of accessible compositions Flame Spry Pyrolysis (FSP) Metal-oxide nanomaterials for many applications Metal on metal-oxides Sensors and emerging areas Nanoparticle Technology is a frontier for scientific advances and business opportunities 32