SOLVOTHERMAL PROCESSES: A ROUTE TO NOVEL MATERIALS, WELL DEFINED NANOPARTICLES and HYBRID NANO-SYSTEMS. Gérard DEMAZEAU Emeritus Professor, ICMCB, CNRS

SOLVOTHERMAL PROCESSES:

A ROUTE TO NOVEL MATERIALS,

WELL DEFINED NANOPARTICLES

and HYBRID NANO-SYSTEMS.

Gérard DEMAZEAUEmeritus Professor, ICMCB, CNRS

University BORDEAUX 1« Sciences and Technologies »

Vice-Président of ISHA(International Solvothermal Hydrothermal Association)

SOLVOTHERMAL PROCESSESBucarest ,october 5-7 ,2007

• Dear Colleagues

• I apologize to be absent during this important Meeting organized by my friend Prof. Radu PITICESCU.

• After strong efforts for organizing a specific Session devoted to « Solvothermal Reactions » during the international High Pressure

Conference (AIRAPT/EHPRG) in Catania (sept.15-23, 2007) • and

the participation to the XVIIIth Mendeleev Conference in Moscow (sept.22sept.28,2007) for presenting an invited lecture on « Solvothermal

Processes »I was obliged –due to health problems- to stop during one week my activity!!!

All my best wishes for the success of this Meeting .

Nevertheless ,I shall try to do the best for supporting your scientific project

A “solvothermal reaction can be defined as a chemical reaction (or a transformation) between precursor(s) in a solvent (in a close system) at a

temperature higher than the boiling temperature of this solvent and under high pressure”

autogeneous pressure or imposed pressure. Subcritical or supercritical domain. Homogeneous or heterogeneous system.

SOLVOTHERMAL REACTIONS

SOLVOTHERMAL PROCESSES: FROM NOVEL MATERIALS TO HYBRID NANO-SYSTEMS.

WHAT ARE THE MAIN FACTORS CHARACTERIZING HIGH PRESSURES

Pressure is always involved in Solvothermal Processes( autogeneous our imposed pressure) consequently

it is necessary to take into account the different factors induced by such a parameter

• The weak energy involved by pressure,

• The negative V value leading to the denser phases,(V being the volume difference between the final state and the starting state)

• The improvement of the reactivity.

• FIRST FACTOR: THE ENERGY WHAT IS THE DIFFERENCE BETWEEN PRESSURE

AND TEMPERATURE FROM AN ENERGETICAL POINT OF VIEW?

• 1)Comparison of the energy conveyed by HIGH PRESSURES and the energy of a CHEMICAL REACTION

Pressure (en bar) Medium Energy (en cal/mol)

1000 Gas 3000

1000 Solid 1

10000 Solid 5

100000 Iron 20

100000 H2O 1000

1 Chemical Reaction 20000


• 2) Comparison between Pressure and Temperature:

1 liter of water, T=20 →T=25°C, P=1bar (constant) Energy = 20kJoules

• Using a constant temperature (T=20°C) what is the pressure

value able to be reached with this energy ???

P=4000bar (400MPa)

• CONSEQUENTLY: Due to the small energy conveyed by pressure

such a parameter can be developed in Biosciences.


• Brief history- Hydrothermal reactions (using aqueous solutions) have

been developed at the end of the XIX Century →objective to prepare geomaterials.

- Development of hydrothermal crystal growth SPEZIA 1898-1909- Industrial crystal growth of -quartz and piezo-electric materials- Development of hydrothermal synthesis of new materials- 1990 Development of non-aqueous solvents

hydro = H2OSolvo = solvent

Proposition of solvothermal reactions(G. Demazeau-Bordeaux)for developing non-oxides. systems


• DEVELOPMENT OF SOLVOTHERMAL REACTIONS• Main types of chemical reactions involved in

Solvothermal processes:• - oxidation/reduction,

- hydrolysis,• - thermolysis,

- complexation,- metathesis……

• The control of such reactions associated to the formation of the target material implies :

→to improve the knowledge of the chemistry in non-aqueous solvents


• Different research fields are implied in solvothermal processes: MATERIALS CHEMISTRY and MATERIALS SCIENCE

Synthesis of novel materials Research of low-cost processes Preparation of micro- or nano-crystallites Growth of single crystal of functional materials Low-temperature sintering processes Thin film deposition

DEVELOPMENT OF RESEARCH DOMAINS AT THE INTERFACE BETWEEN DIFFERENT

DISCIPLINARIES. Hybrid Materials (inorganic chemistry/Organic

chemistry). Hybrid Systems (nano-chemistry/Biosciences)


• Main parameters involved in Solvothermal Reactions:

-The nature of the reagents• Chemical composition, size of the crystallites …

- The chemical composition of the solvent-• Such a parameter is able to open new research areas concerning the composition of the expected

materials:• Synthesis of intermetallic compounds, oxides, nitrides, phosphides, borides…..

- The mild temperature conditions-• Temperature is mainly used for improving the diffusion of chemical species,• The mild temperature conditions allow- if the reaction is kinetically controlled- to prepare metastable

materials.

- The pressure in liquid phase is limited (10 <P<500 MPa)• Pressure is developed in order-

(i) through the interactions between liquid/solid phases or between solvated chemical species (in solution) – to improve the reactivity,

(ii) through the “densification effect” to orientate the structure of the expected materials.


ROLE OF THE REAGENTS IN SOLVOTHERMAL PROCESSES

SYNTHESIS OF A NEW-CLASS OF BI-DIMENSIONNAL OXIDES ISOSTRUCTURAL TO PHYLLOSILICATES:

THE PHYLLOSILOXYDES.

(P. REIG , G. DEMAZEAU ,R. NASLAIN)

ICMCB ,LCTS, University Bordeaux 1


The thermal stability of phyllosilicates is limited by OH groups.2OH- O2-+H2O+

Anionic substitution OH-O2- in the phyllosilicates lattice.

But: correlated with cationic substitutions

SOLVOTHERMAL SYNTHESIS OF PHYLLOSILOXIDES


• The anionic sustitution OH-O2- leads to an increase of the anionic charges

• Consequently such an anionic substitution is correlated with cationic substitutions.

One possibility:

Al3+(Td) Si4+ (Td)

Mg2+(Oh) Al3+ (Oh)


sol-gel process: sol gel aerogel

Conventional Solid State Solvothermal processProcess (500 1000°C) solvent = methoxy-ethanol

precursor = aerogelMixture of 3D silicates T=500°C, 50P150MPa, t24h

single phase

-

-


I.R.Spectroscopy

K(Mg2Al) Si4 O12

K Mg3 (Si3Al)O10(OH)2

X. Ray DiffractionScanning Electron Microscopy H.R.T.M.

K Mg3 (Si3Al)O10(OH)2 K(Mg2Al) Si4 O12



• X-ray diffraction analysisThe X-ray spectrum of the resulting single phase is similar to that of the

initial « mother phase » : mica with the phlogopite structure.

Ir spectroscopy

K Mg3 (Si3Al) O10(OH)2 strong absorption band due to OH group ( 3700 – 3800 cm-1).

K (Mg2Al) Si4O12 NO absorption band corresponding to OH groups.

Electronic Microscopy.SEM: platelets (l 0.2 μm)TEM: layered structure (interlayer distance corresponding

to the phlogopite structure)

ROLE OF THE SOLVENT IN SOLVOTHERMAL PROCESSES

(A) Synthesis of metastable compounds

The solvent, can induce the formation of very stable complex ions and such complex ions can act as template for stabilizing metastable compounds.

Example: LI J., CHEN Z., WANG R.J., PROSERPIO D.M. Coordination Chem. Rev. (1999) 190-192 p. 707.

Ethylenediamine has a strong coordination ability towards the divalent transition metals (Mn2+, Fe2+, Co2+, Ni2+, Zn2+)M2+ + 3en M(en)3

2+

M(en)32+ characterized by an octahedral geometry can act as

template for building new metastable materials.



(B) Orientation to a metastable structural form

LU J., QI P., PENG Y., MENG Z., YANG Z., YU W., QIAN Y. Chem. Mater. (2001) 13 p. 2169.

precursors: MnCl2, 4H2O and SC(NH2)2

4 solvents have been evaluated:H2O or ethylenediamine able to form a stable Mn complex

-MnS rocksaltnon polar C6H6 -MnS wurtzite (Metastable)tetrahydrofuran (THF) -MnS zinc-blende (Metastable)when no stable complexes are stabilized the solvothermal reaction is kinetically controlled leading to the stabilization of two metastable forms.



(C) The oxidation-reduction properties inducing a specific composition.

PANDA S.K., GORAI S., CHAUDURI S. Mater. Sci Eng. B. (2006) 129 p. 265.have underlined the role of the oxidation-reduction process induces by the solvent during the solvothermal synthesis of SnS crystallites from Sn metal.

Such a solvothermal process can be described through three steps:(1) Sn0 + (few amounts of H2O) Sn2+ + 2e-

(2) Sn2+ + n en. Sn(en)n2+

(3) Sn(en)n2+ + S2- SnS.



(D) Preparation of nano-crystallites with a specific morphology.

Solvothermal preparation of nanocrystallites with a specific morphology has attracted a strong interest during these last

years.

Different compositions of nanocrystallites have been developed… but recently intermetallic nanocrystallites have been investigated.

The preparation of nanoparticles of intermetallic FePt nanowires has been selected as example.


(D) ROLE OF THE SOLVENT IN THE PREPARATIONOF INTERMETALLIC FePt NANOWIRES

- Interest of such FePt nanoparticlesIntensive Research due to its potential applications in high density storage and high performance permanent magnets.

WELLER D., DOERWER M.F. Annu. Rev. Mater. Sci. (2000) 30 p. 611. SUN S., MURRAY C.B., WELLER D., FOLKS L., MOJER A. Science (2000) 287

p. 1989.

Conventionally FePt particles were synthesized via thermal decomposition of Fe(CO)5, reduction of Platinum

acetylacetonate Pt(acac)2 and co-reduction of iron salt and Pt(acac)2.

difficulty to control the morphology of FePt nanoparticles.


(D)ROLE OF THE SOLVENT IN THE SOLVOTHERMAL PREPARATION OF INTERMETALLIC FePt NANOWIRES

In order to control the size and the morphology of PtFe nanoparticles

Development of a solvothermal process.

Precursors: Pt(acac)2 + Fe(CO)5 + (en) as solvent

(160 < T < 200°C , autogeneous pressure)

Pt(en)22+ inducing self organization leads to

the formation of FePt Nanowires.

MAO C.B., SOLIS D.J., REISS B.D., KOTTMANN S.T., SWEENEY R.Y., HAYHUST A., GEORGIOU G., IVERSON B., BELCHER A.M.

Science (2004) 303 p. 213.


Potentialities of solvothermal processes

for developing hybrid systems

Low temperature solvothermal processes allow to stabilize original hybride materials (inorganic/ organic components)

as an example:

Solvothermal synthesis of Zincophosphite (C6H16N2)Zn3(HPO4)3

FU et al. Solid State Sciences 6, 225 (2004)


At the interface between BIOSCIENCES and NANO-SCIENCES

• PEPTİDE ENGİNEERİNG FOR BİO-İNSPİRED MATERİALS(M.UMETSU et al. Tohoku University)

J. Materials Science (in press)

Peptides have affinity for non-biological materials and could mineralized inorganic materials.

ZnO semi-conductor with a direct band gap ....fabricatıon of ZnO nano-structures.

Peptide can bind the ZnO particles (but no ZnS) and further the ZnO-binding peptide selectively catalyses the synthesis of a highly anisotropic ZnO particles from a Zn(OH)2 solutıon at room temperature and medium pressure condıtıons


SOLVOTHERMAL PROCESSES: FROM NOVEL

MATERIALS TO HYBRID NANO-SYSTEMS.MAIN CHALLENGES FOR THE FUTURE ???Why and How to reduce Temperature

WHY? → FOR PRESERVING SPECIFIC COMPONENTS(in order in particular to prepare hybrid inorganic/organic or

inorganic/biological systems) → FOR INDUCING METASTABLE PHASES (but it is necessary to improve the kinetical effects) → FOR SAVING ENERGY

(sustainable development)

HOW ? TO IMPROVE THE CHEMICAL REACTIVITY TROUGH THE OPTIMIZATION

-PRECURSORS

-SOLVENT, -PRESSURE.

MAIN OBJECTIVES OF SOLVOTHERMAL PROCESSES

To open a route through new « soft chemical processes»

Kinetically controlled for stabilizing metastable systems,

To help the synthesis of specific structures using templates,

To control the nucleation/ crystal growth processes for the preparation of nanocrystallites well defined in size and morphology,

To facilitate ,through the improvement of the chemical reactivity and the development of mild temperature conditions, the synthesis of hybrid nano-systems.

CONCLUSIONS

All the objectives of SOLVOTHERMAL PROCESSES

require to optimize :

(i) The physico-chemical properties of the precursors,

(ii) The physico-chemical properties of the solvent,

(iii) The thermodynamical parameters P, T.

Solvothermal processes appear to be important in the near future, not only for developing Basic Science

But also

for developing new industrial processes in mild P,T conditions.

THANK YOU FOR YOUR ATTENTION.

Documents

SOLVOTHERMAL PROCESSES: A ROUTE TO NOVEL MATERIALS, WELL DEFINED NANOPARTICLES and HYBRID NANO-SYSTEMS. Gérard DEMAZEAU Emeritus Professor, ICMCB, CNRS