Using Surface Chemistry to Explore Environmental, Catalytic, and Biomedical Applications of Porous Nanomaterials

Instruments

Varian ICP-OES 720-ES

This instrument is primarily used for quantitative elemental analysis both by our group and outside users in the chemistry and other departments on campus. With the use of the SPS3 autosampler users can run a large number of samples with minimal user intervention and setup. Sub ppm detection of transition metals is commonly achieved in our research. Bulk composition information or trace impurities can be measured in a sample due to the large available linear range. The Larsen lab uses the ICP for measurements of zeolite composition as well as transition metal absorption onto zeolites and mesoporous silica. Other groups have used the instrument to measure iron oxide nanoparticle impurities, denture impurities, solid catalyst composition and for inorganic crystal product elemental analysis.

All samples for the ICP need to be completely dissolved in aqueous solution. Colloidal or other visible particles will cause problems in the sample induction system. Acids are frequently used in our research for digestion of insoluble samples. Our group dissolves zeolites in an HF/HCl mixture, and other groups have had success with utilizing various other acids to digest their samples.  Approximatly 2 mL of the sample is required for a good run, smaller samples can be diluted to this volume if necessary. A minimum of three standard solutions for calibration, for all elements of interest, must to be used. These standards should create a standard curve containing the suspected concentration for your sample. Commercial standards are available for most elements. If you would like to use the ICP-OES in your research or would like to know more about the capabilities of the instrument feel free to contact Majid Nada at majidhameednada-nada (at) uiowa.edu.

Product information on the 720-ES can be found at the Agilent website.


Zetasizer Nano ZS (Malvern Instruments)

 

The Zetasizer Nano ZS provides the ability to measure three characteristics of particles or molecules in a liquid medium:

    -Particle size (0.6 nm to 6 μm)
    -Zeta potential (for particle size ranging from 5nm to 10μm)
    -Molecular weight (1000 to 2x107 Daltons)

The instrument is equipped with the 633nm laser and utilizes 173° detection optics for back-scatter detection.

The particle size measured by the instrument is the diameter of the sphere that diffuses at the same speed as the particle being measured. The instrument determines the size by measuring the Brownian motion of the particles in a sample using Dynamic Light Scattering (DLS) and then interpreting a size from this using established theories. The data can be presented as intensity, volume or number distribution vs. the particle size.

Zeta potential is measured using a combination of measurement techniques: Electrophoresis and Laser Doppler Velocimetry. This combination of methods allows the measurment of the particle velocity in a liquid when an electrical field is applied. By knowing the velocity of particles under applied electric field as well as the viscosity and dielectric constant of the medium the zeta potential can be calculated.

Molecular weight can be determined by use of Static Light Scattering (SLS) measurement techniques.

In the Larsen research group the instrument is primarily used for particle size and zeta potential measurements of zeolite nanoparticles. The DLS technique provides a fast and easy way to obtain the size distribution of colloidal zeolite particles during the hydrothermal synthesis, so that reaction conditions can be quickly adjusted in order to obtain the desired particle size. Zeta potential measurements are also conducted to monitor the effects of surface functionalization on the stability of zeolite particles. Zeta potential is typically measured as a function of pH and strongly depends on the type and concentration of ionic species in the medium. Other research groups in the department primarily use the DLS functionality to measure particle size distributions of synthesized nanoparticles.

If you would like to use the Zetasizer in your research or would like to know more about the capabilities of the instrument contact Sanjaya Jayalath at sanjaya-jayalath (at) uiowa.edu.

Product information can be found at the Malvern Instruments website.

 


Bruker EMX-61 EPR

The Larsen laboratory owns a Bruker Electron Paramagnetic Resonance (EPR) spectrometer used for magnetic resonance characterization of samples. EPR is a sensitive technique that provides a wealth of knowledge about the coordination environment of paramagnetic transition metal complexes of interest in our lab. The EPR instrument is capable of magnetic fields of up to 5100 G and is setup with a standard universal X-band resonator. Variable temperature control is also available within the range of 150 - 500 K. Liquid nitrogen temperatures (77 K) are also available with a liquid nitrogen Finger Dewar. Irradiation of samples by UV light is possible and additionally a gas flow system can be set up for adsorption/desorption studies. EPR samples can be either solid powders or in a liquid state. Aqueous liquid samples must be mixed with a glassing agent, such as ethylene glycol to ensure the formation of a good glass. Solid samples must be powdered prior to insertion into an EPR tube. Currently the Larsen lab works mostly with dry, solid samples at around 150 K.

The Larsen group uses EPR spectroscopy to investigate the coordination environments of transition metal - aluminosilicate systems. These include transition metal exchange, absorption and encapsulation with aluminosilicates, such as zeolites. Users from other groups in the chemistry department have used the EPR for characterizing the paramagnetic species in inorganic compounds and catalytic substrates containing transition metals. Samples containing: V, Cr, Mn, Fe, Cu, Mo and Ir have been investigated both by the Larsen group and outside users.

If you would like to use EPR spectroscopy in your research or would like to know more about the capabilities of the instrument feel free to contact Dr. Sarah Larsen.

Information about current Bruker products can be found at the Bruker Biospin website.


Mercury Beowulf Cluster

Mercury is a Class I Beowulf style cluster consisting of four nodes each with an Intel Core2 Quad CPU, 4 Gigs of RAM and a local hard drive for use as swap and scratch space. The first node (head node) serves as a PBS Torque batch scheduler, DCHP server, NTP server, PXE boot server as well as NFS centralized storage using a popular variant of the Debian Linux OS. The other three nodes are booted into Linux using Intel's PXE protocol and contain local scratch and swap hard drive partitions for calculations. The PXE approach allows for both easy administration and simple expansion of the cluster.

The cluster is used for quantum mechanical calculations that are of interest to our group. Both QM and QM/MM techniques are available on mercury through the use of the Amsterdam Density Functional (ADF) program suite. Chemical properties of interest in our group include EPR and NMR parameters for various nuclei, which can be calculated using modern DFT methods. The program packages ADF and ORCA are used in our research on mercury to calculate these magnetic resonance parameters. External users access mercury to calculate a variety of properties and systems. Current external work includes investigation of toxic compound adsorption onto aluminosilicate frameworks.

If you wish to have access to mercury or want to ask questions not covered by the documentation fell free to contact Dr. Sarah Lasren.

Information on the computational programs ADF and ORCA can be found on their respective websites. Beowulf clustering and general clustering information can be found at beowulf.org.


Quantachrome Nova 1200 Surface Area Analyzer

Our surface area analyzer is workhorse of the laboratory used to characterize materials synthesized and utilized in our laboratory. We commonly
employ nitrogen adsorption-desorption isotherms to elucidate surface area, pore volume and pore diameter of porous materials. This is used as a complementary technique to other physical methods such as TEM and p-XRD.

Nitrogen is the most commonly used adsorbate but other gases such as CO, Ar and He can be used as well is isothermal runs. The instrument is set up and run under isothermal conditions in a liquid nitrogen bath (77 K).

Examining isotherms can be particularly telling in terms of porosity and structure. For the materials we use, we often have mesoporous material (2-50 nm pores) which results in a Type IV Isotherm. This isotherm has a notable hysteresis loop at the overchange from adsorption to desorption.

If you are interesting in using or learning to use the BET instrument please contact Majid Nada at majidhameednada-nada (at) uiowa.edu.