CHEM 201 Lecture Notes - Lecture 4: Azo Compound, Nanofluid, Magnetic Separation

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Published on 2 Nov 2019
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Chemistry 211 Fall 2019 10
Experiment 2: Magnetic Nanoparticles Synthesis and Application
What lab skills will you practice in Expt 2?
Measuring both mass and volumes
Performing a temperature-controlled synthesis
Performing a pH-controlled synthesis
Magnetic separation
What learning objectives are being studied?
Determine ground state electron configurations using
Aufbau, Pauli and Hund’s principles.
Identify paramagnetic and diamagnetic species.
Convert between magnitudes of measurement units
in the metric system: kilo, deci, milli, micro, nano.
Learn about the principles of colorimetry,
nanoparticles and surface chemistry (adsorption).
What report writing skills will you use?
Recording and summarizing observations
Evaluating observations
Interpreting results in discussion section
REMINDER:
Before coming to the laboratory, complete the pre-
lab exercises. You will not be allowed to perform
the experiment until you have presented your pre-
lab results to your TA.
Background:
Nanoscience studies materials that have at least one dimension smaller than 100 nm and which exhibit properties that
are different from the bulk material properties. Although nanotechnology is an area of science that has gained a lot of
attention in the past few years, nanoparticles have been used for centuries. Circa the fourth century AD, the Roman
Empire was using gold and silver nanoparticles to colour glass, as is seen in many stained glass windows.1 Particles of
gold and silver which are a few nanometers in diameter can exhibit a variety of colours, from red to green to blue
depending on their exact size and shape; these colors differ quite a lot from the colour of gold or silver bulk samples of
you may have seen before. Nanotechnology has since become much more diverse, as nanoparticles are now being used
in nanofluids for cooling systems2, as platforms for drug delivery3, and also as sorbents for different chemical species4.
In the latter example, nanoparticles can be used to remove pollutant compounds (such as heavy metals and textile dyes)
from wastewater.
The production of fabrics and textiles is a large industry, particularly in Asia. It involves
many aqueous steps, including staining and de-staining of fabrics, where large amounts of
dye are discarded into the wastewater. Most of the dyes used in the textile industry are large
organic molecules such as the brightly coloured azo dyes (Figure 1). These dyes can be
partially broken down through bioremediation (bacterial digestion), however many of these
breakdown products are often equally as toxic as the dyes themselves and still need to be
removed from wastewater.5 As well, methods like this require optimal water conditions to
see an appreciable change in contaminant concentration and these can be difficult to
maintain.5 Other methods of waste management have been tested as well, however the use of
nanoparticles is quickly gaining attention in this area. In general, dye molecules are able to
adsorb onto the surface of different metals and metal oxides. Metal and metal oxide
nanoparticles are especially effective as sorbent as their surface area to volume ratio is very
large which means that only a small quantity of material is required.
One noteworthy sorbent is magnetite (Fe3O4), a naturally occurring mineral in the earth’s
crust that has been of great interest for many years. One of the most interesting properties of
1 Freestone, I; Meeks, N; Sax, M; Higgitt, C., Gold Bull. 2007, 40/4, 270-277.
2 Nguyen, C.T.; Roy, G; Gauthier, C; Galanis, N., Appl. Therm. Eng. 2007, 8-9, 1501-1506.
3 Tang, W; Xu, H; Kopelman, R; Philbert, M.A., Photochem. Photobiol. 2005, 81, 242-249.
4 Petrova, T.M.; Fachikov, L;Hristov, J. Int. Rev. Chem. Eng. 2011, 3(2), 134-152.
5 Sarnaik, S; Kanekar, P., J. Appl. Bacteriol. 1995, 79, 459-469.
N
N
OH
S
O-
OO
Na+
Figure 1.
Orange II, an azo dye.
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Chemistry 211 Fall 2019 11
magnetite is its magnetic behaviour due to the presence of iron(II) and iron(III) ions within its structure. Both of these
ions possess unpaired electrons which is a requirement to generate a magnetic material.
As you learned in class, an electron’s spin is either ‘spin up’ (ms = +½) or ‘spin down’ (ms = -½). A good way to think
of these two directions is to view spin as a vector, with a magnitude (same for both up and down) and a direction (up or
down). When pairing electrons within an orbital of an atom, Pauli’s exclusion principle states that no two electrons of
the same spin can be paired in the same orbital. In the case of pairing two electrons of opposing spin in an orbital of an
atom, the spins will “cancel” each other out (again, think of two vectors with equal magnitude, but opposite directions
one step forward, one step back, and your net motion is zero). This does not mean that the spins of the electrons are
destroyed, but instead that the electrons become more attracted to one another than to an external magnetic field. This is
the cause of diamagnetic behavior. Diamagnetic materials tend to be very slightly repelled by a magnetic field.
Conversely, paramagnetic compounds possess isolated unpaired electrons. The spin of each unpaired electron in a
paramagnetic compound is free to align itself with an external magnetic field. Although the electron spins will respond
to an external magnetic field, bulk paramagnetic samples (on the macroscopic scale) will only be very slightly attracted
to a magnet (magnetic forces pulling on the paramagnetic sample are much weaker than the force required to overcome
the sample’s inertia, and hence will not move).
Finally, in materials that behave as magnets, like magnetite Fe3O4, not only are there unpaired electrons within the
material, but there is a permanent internal alignment of the spin of these unpaired electrons. The chemical structure and
bonding pattern within these materials are responsible for the internal alignment of the spins. The net magnetization of a
sample is the sum of all the vectors due to the electron spins if they all align in the same and fixed direction, a large net
magnetization arises, which is what we refer to as a ferromagnet, or more simply, a magnet.
In this lab, you will use a coprecipitation method in basic solution to produce your nanoparticles:
Fe2+ (aq) + 2 Fe3+ (aq) + 8 OH (aq) Fe3O4 (s) + 4 H2O (l) [1]
Critical thinking will be essential when performing this synthesis. You will also have to think about how to most
effectively use your nanoparticles to extract Orange II, a common textile dye, from water (Figure 1). To do this, you
must exploit both the innate sorbent and magnetic properties of magnetite.
OVERALL SCORE FOR EXPERIMENT 2: 20 MARKS WORTH 20 PERCENT OF LABORATORY GRADE
1. Pre-Laboratory Assignment & Notebook Preparation (4 marks)
2. Laboratory Report (16 marks)
Procedure:
The following is to be done in pairs. Partners should record their own observations in their self-duplicating notebook.
Your TA must initial and then collect your duplicate copy as you leave the lab.
CAUTION MUST BE USED WHEN HANDLING MATERIALS:
Ammonium hydroxide (NH4OH) is both corrosive and toxic.
Magnetite nanoparticles (once synthesized) may cause respiratory irritation upon inhalation.
To prevent inhalation, ensure dry product is stored in a closed container.
ALL WASTE MUST BE DISPOSED OF IN THE WASTE CONTAINER
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