# Presentation: 081196

## Small particle chemistry: Reasons for differences and related conceptual challenges 

- D. R. Baer and J. E. Amonette
- Pacific Northwest National Laboratory
- Richland, WA
- P. G. Tratnyek
- Oregon Health and Sciences University
- Beaverton, OR

- September 15-16, 2003
**Interagency Grantees Meeting/Workshop - Nanotechnology and the Environment: Applications and Implications**

## Topics

**Characterization and Challenges** in making, handling and characterizing nanoparticles – *nanoparticles may have an impact on the environment, but the environment also impacts the nature of the nanoparticles*.
**Different ways that small** or nano-structure **makes a chemical difference**.
**Specific Program**:  Reaction Specificity of Nanoparticles in Solution: Application of the Reaction of Nanoparticulate Iron with Chlorinated Hydrocarbons and Oxyanions

**Topics**

## Pacific Northwest National Laboratory

- Located in Richland, Washington
- Approximately 3,500 employees
- We deliver breakthrough science and technology to meet key national needs with a large environmental focus:
- Fundamental Science  	Environmental Science and Technology
- Energy Future	              National & Homeland Security

## Small Particles Impact Many PNNL and DOE Missions

*Small Particles and Nano-structures have impact in each DOE mission areas and some topic cross several areas*

## Nano-structured Reactive Materials Systems (Nano-chemistry)

- Control of the chemical and physical properties of hierarchal materials structures containing nano-sized components  to control and optimize material properties and chemical reactivity
-  Application Areas
- Catalysts for fuel cells, bioprocessing, waste reduction and the chemical industry
- Inexpensive photovoltaic and other energy conversion devices
- Highly selective sensing materials and systems
- Structure optimized for energy transport
-   Science Issues
- Tune nanomaterial physical and chemical properties
- Place structures in appropriate hierarchal environments
- Integrate structures into mesoscopic and macroscopic systems
- Develop theory and computation approaches to predict properties

- Focus Area of Nanoscience and Technology Initiative
- and Joint Institute for Nanoscience

## Small Particles Important for Contaminant 

**U(VI) Micro- and Nano-precipitates Exist within Grain Fractures of Quartz and Feldspar in BX-102 Sediment 61**

**Tank Wastes at Hanford**

**40,000,000 Gallons**

**Small Particles Important for Contaminant **
**Transport in “Natural” System**

## Control of nanostructure is a gateway

- catalysis

- pre-concentration

- detection

- H2 storage

- Transition states

- Signal transduction

- chemisorption

- sorption

- Surface
- interactions
- at the
- nanoscale

- synthesized
- nanostructures

- nanobiological
- machines

- One portion of the Nanoscience and Nanotechnology Landscape

## Harnessing Enzymes: An Application of Proteins

- Stable enzymes entrapped in nanopores may one day be routinely used to  inactivate pollutants.
- Enzymes in this environment are stable for extended periods of time.
- Sensors, catalysts and separations

**Harnessing Enzymes:**** An Application of Proteins**

***Pacific Northwest National Laboratory***

***J. Am. Chem. Soc*****. 2002, 124, 11242−3**

**Notes:**
Nanomembrane pore size is 30 nanometers. 
Membrane immobilized enzyme. Further development of these kinds of strategies could result in clean up of polluted sites. 

Using enzymes embedded in these membranes can facilitate more efficient chemical processes. 

## Environmental Molecular Sciences Laboratory National User Facility

* **Dr. William R. Wiley, Director of PNNL 1984-1994.  EMSL is located in Richland, Washington.*

**  ****Signature Characteristics**
- Integration of **theory****,** modeling, and simulation with **experiment**.
**Multidisciplinary** teams and collaborative mode of operation to solve major scientific problems of interest to DOE and the nation.
- Teams who develop extraordinary **tools and methodologies**.

**E****nvironmental ****M****olecular**** ****S****ciences**** ****L****aboratory**** ****National User Facility**

**  ****EMSL Facilities**
- Chemistry and Physics of Complex Systems
- Environmental Spectroscopy & Biogeochemistry
- High Field Magnetic Resonance
- High Performance Mass Spectrometry
**Interfacial & Nanoscale Science**
- Molecular Science Computing

## Topics

- Challenges in making, handling and characterizing nanoparticles – *we need to learn how to characterize nano systems more completely and adequately*
*Emphasized comments made by Bob Hwang, Karen Swider-Lyons and Andrea Belcher. Highlights importance of creating and applying of new facilities including the new generation TEM*.
**Different ways that small** or nano-structure **makes a chemical difference**.
**Specific Program**:  Reaction Specificity of Nanoparticles in Solution: Application of the Reaction of Nanoparticulate Iron with Chlorinated Hydrocarbons and Oxyanions

**Topics**

## My view of the state of our understanding of nanoparticle chemistry?

- Nebula M100

- Kitt Peak
- 1.1 M

**Calibrating the state of our understanding**

## Calibrating the state of our understanding

- Nebula M100

- Kitt Peak
- 1.1 M

- Hubble
- Space
- Telescope

**Calibrating the state of our understanding**

**My view of the state of our understanding of nanoparticle chemistry?**

## ?

- Nebula M100

- Nanoparticle Images

- Kitt Peak
- 1.1 M

- Hubble
- Space
- Telescope

- TEM of
- Fe

**?**

**Calibrating the state of our understanding**

## Calibrating the state of our understanding

- Nebula M100

- Nanoparticle Images

- Kitt Peak
- 1.1 M

- Hubble
- Space
- Telescope

- TEM of
- Fe

- Molecular Dynamics ZnS

**Calibrating the state of our understanding**

- Need more and advanced **tools**; greater development and application of **theory and modeling**; expand **conceptual framework**

## Topics

**Characterization and Challenges** in making, handling and characterizing nanoparticles
**Specific Program**:  Reaction Specificity of Nanoparticles in Solution: Application of the Reaction of Nanoparticulate Iron with Chlorinated Hydrocarbons and Oxyanions
**Different ways that small** or nano-structure **makes a chemical difference**.

**Topics**

## THE REACTION SPECIFICITY OF NANOPARTICLES IN SOLUTION: Application to the Reaction of Nanoparticulate Iron and Iron-Bimetallic Compounds with Chlorinated Hydrocarbons and Oxyanions.

**Evidence that nanoparticles change the iron induced reduction of CCl****4**** from ****partial**** reduction toward ****full**** removal of the Cl:**
**From**
- CCl4  + H+ + Fe0  **CHCl****3** + Fe+2 + Cl-
**To**
- CCl4  + 4H+ + 4Fe0  **CH****4** + 4Fe+2 + 4Cl-

**THE REACTION SPECIFICITY OF NANOPARTICLES IN SOLUTION:**** ****Application to the Reaction of Nanoparticulate Iron and Iron-Bimetallic Compounds with Chlorinated Hydrocarbons and Oxyanions.**

**No fundamental understanding of the process.**

## Understanding the properties of Fe nanoparticles presents a host of challenging questions and problems

- Schematic representation of the different Fe(0) iron surface planes and the growth of compressively strained oxide lattices (adapted from Kwok et al. 2000).

-  What size range or structure is of importance?
-  How small of a nanoparticle contains a metallic core?
-  What is the structure of any metal in a nanoparticle?
-  What is the structure of the oxide on a nanoparticle and how does it change with particle size?
-  How do environmental effects alter nanoparticle structures and change reactivity?
-  Where do reduction reactions take place and how does this change with particle size or structure?

## Three (of several) Senses of Small

-   **Size** **and surface area effects**
- 1 nm – 100 nm **Fundamental materials properties remain** the same but size, shape and surface area alter some behaviors  work function, solubility, chemical potential, contaminate sorption
-   **Critical Size and Characteristic Length Scale **Interesting or unusual properties because the **size of the system approaches some critical length** (includes quantum effects). **Many characteristics** of material may have normal or nearly **normal** behavior
-   **New**** (Non-extensive) Properties** Systems not large enough to have extensive properties. Particles become effectively polymorphs of “bulk” materials and statistical homogeneity may not be valid.

**size ******** ******** ********  d**
**= correlation length**
**d = range of intermolecular forces**

-  Kelvin equation for solubility
-  Gibbs-Thompson relation for 	chemical potential

- What do we we mean by small particle and why does their chemistry change?

## Gibbs-Thompson relation as an estimate of dependence of particle energy on size

- (r) - () = 2/r
- = surface free energy,  = molecular volume
- r = particle radius
- This effect becomes significant at for metals at 2-3 nm
- Assumes that surface free energy is independent of size!

- Significant effects are predicted for nanosized particles when materials properties are well defined and constant

**Nanoparticle Energy 1**

## Often the materials properties are not constant. 

- Calorimetric measurements show that the energy dependence of supported Pb particles vary much more quickly than predicted by the Gibbs-Thompson relationship.
- “This shows that the surface energy increases substantially as the radius decreases below 3 nm.”
- C.T Campbell et. al. Science 298 (2002) 811-814

**Nanoparticle Energy 2**

- Often the materials properties are not constant.

## The materials properties may not be uniquely defined They may depend on the environment. 

**Nanoparticle Energy 3**

- The Molecular Theory of Small Systems
- Faraday Lecture, 1983
- R. S. Rowlinson, Chemical Society Reviews, Vol 12, (1983) 251-265

**The materials properties may not be uniquely defined They may depend on the environment**.

- For small systems, some of the thermodynamic functions of importance,  **pressure** and **energy density** are not uniquely defined.
- Small systems can be defined when the system **size ******** ******** ********  d ******** l  ****(often ******** nm)**
- = correlation length;  d =  range of intermolecular forces; l = thickness of an interface
- For systems smaller than ** ****thermodynamics and statistical mechanics lose their meaning. **

**A Different Approach to Nanothermodynamics**
- Terrell L. Hill, Nano Letters Vol 1 (2001) 273-275

- “In contrast to macrothermodynamics, the **thermodynamics of a small system will usually be ****different in different environments**.”

## Water-driven structure transformation in nanoparticles at room temperature 

***Nature***** 424, 1025 - 1029 (28 August 2003); **
**Water-driven structure transformation**** in nanoparticles at room temperature**** **
**HENGZHONG ZHANG*, BENJAMIN GILBERT*, FENG HUANG & JILLIAN F. BANFIELD**** **

- Vacuum

- With H20 on surface

- Should an environmental influence on nano-particle structure be a surprise?
- No - Consistent with theory and even experiments on “bulk” surfaces.

## Most reactions on this surface take place at defect sites

**Most reactions on this surface take place at defect sites**

## Surface Structure Influenced by Both Bulk Defects and Environment

**(1x1) and (1x2) surface structures on TiO****2**** (110) **S. Gan, Y. Liang, D.R. Baer and A. W Grant Surface Sci 475 (2001) 159-170

- Surface Science 540 (2003) 157-171

## Nanoparticles are often polymorphs of bulk material with different physical and chemical properties

**Nanoparticles are often polymorphs of bulk material with different physical and chemical properties**

**Lattice Constant for Pt as a function of cluster size**
- Klimenkow et al, Surf. Sci. 391 (1997) 27-36

**Stable structures of TiO****2**** as a function of cluster size**
- Ranade et al Proc. Nat. Acad. Sci. 99 (2002) 6476

- Lattice Constant [Å]

- Particle Size [Å]

- Interrelationships among “bulk” structure and defects, surface structures, the environment and reactivity mean the nanoparticle properties depend on size, environment and history.

## THE REACTION SPECIFICITY OF NANOPARTICLES IN SOLUTION: 

**Program Components:**
-  Synthesis and characterization of Fe and Fe-Oxide nanoparticles, XPS, XAS, Mossbauer, TEM
-  Measurements solution and gas reactivity with Fe nanoparticles
-  Vacuum based studies of supported Fe nanoparticles
-  Models of particle structure and effects of structure on reactivity

##  Small particle and nanostructured materials chemistry is relevant to many DOE missions, including environmental topics

-  There are **many different types of small particle** and nano-materials **effects** as well as many delightful opportunities and scientific challenges
-  **More and better tools** and their use are essential to characterize the properties and environmental effects of/on nanoparticles . (Bob Hwang’s multi-dimensional analysis coordinates:   Space, time, energy, composition, environment)
-  **Theory and modeling** are essential to successful work in this area

- Summary and Concluding Thoughts

## Slide 28

## Example of Size and Surface Area Effect in Atmospheric Chemistry

- A. Laskin, D. J. Gaspar, W. Wang, S. W. Hunt, J. P Cowin, S. D. Colson, B. J. Finlayson-Pitts
*Buffering Mechanism for Sea Salt Particles – Impact for Uptake of SO**2*
- Submitted to Science 2003

## Schematic of Proposed Surface Reactions

**Schematic of Proposed Surface Reactions**

- Knipping et al., *Science* _288_ 301 (2000)

- Interface Reactions Can Raise Particle pH.
- Total change depends on size of particle and time of exposure altering the environmental reactivity of small particles versus large particles

- A. Laskin, D. J. Gaspar, W. Wang, S. W. Hunt, J. P Cowin, S. D. Colson, B. J. Finlayson-Pitts
*Buffering Mechanism for Sea Salt Particles – Impact for Uptake of SO**2*
- Submitted to Science 2003

- Small volume to surface area

## Zhang Sample

- Two general types of material:  flakey stuff and rounded particles that appear to have a skin of alteration

## Comparison of Film and Particle Ion Beam Damage

- 700

- 705

- 710

- 715

- 720

- 725

- 730

- 735

- 740

- 745

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- 0.7

- 0.8

- 0.9

- 1

- Binding Energy (eV)

- Normalized Intensity

- sputtered

- Very little selective sputtering and oxide reduction

- 700

- 705

- 710

- 715

- 720

- 725

- 730

- 735

- 740

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- 0.7

- 0.8

- 0.9

- 1

- Binding Energy (eV)

- Normalized Intensity

- Fe2O3 (?) 20 nm particles collected on Au coated Si substrate as received and after 2 kV Ar+ ion sputter (2 nm for SiO2)

- Significant reduction of particles

- As deposited

- Sputtered

- Fe 2p photoelectron peaks

## Characteristic Sizes for Physical and Chemical NANO Effects

**Critical or Characteristic Particle Sizes [nm]**

- 1

- 10

- 100

**Lattice**** **

**Constants**

**For metals Pt, Pd, Fe and Ta**

**Oxide Layers on Fe**

- Air exposed bulk metal

- Oxygen exposed nanoparticles

***Characteristic Sizes for Physical and Chemical NANO Effects***

- Anatase

- Brookite

- Rutile

**Oxide Phase Stability**

- Hematite

- Goethite

**Break down of Hall Petch Grain-Size Hardening Metal Layer Structures**

- CuO

- Lattice Parameter and Neel Temperature

## Effects of Vacuum and Sulfur Sorption of Ni Surface

**Effects of Vacuum and Sulfur Sorption of Ni Surface**

- Bulk Ni

- Ni in Vacuum

- Ni in Vacuum with S

- 5 to 10 % decrease

- Buckled 2nd layer
- 11% increase

- Even for large surfaces, vacuum and sorbates change alter structure

- Danielson and Baer  Corrosion Science 29 (1989) 1265-1274.