Kitchen Synthesis of Nanorust

J.T. Mayo, Courtney Payne, Lauren Harrison, Cafer Yavuz, Dr. Mary McHale, Professor Vicki Colvin

Objectives

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Background

Having clean drinking water is one of the most fundamental necessities of life. There are many different forms of possible contamination, but among the most well-studied and problematic inorganic contaminants is arsenic. Arsenic is one of the oldest known carcinogens. In 1999, the US National Academy of Sciences reported that arsenic can cause bladder, lung and skin cancer, and possibly cause liver and kidney cancer. The physical symptoms of arsenic poisoning include: extreme fatigue, nausea, vomiting, partial paralysis, and reproductive damage.1 Arsenic is naturally occurring in water due to its abundance in certain types of rocks, but it can have anthropogenic origins as well.

Arsenic can be found all over the world, but is currently a particular problem in Third World countries due to the costly nature of water purification. It is especially abundant in Bangladesh, but arsenic has also been found in the ground water of Argentina, Chile, India, Mexico, Taiwan and Thailand. Additionally, closer to home, most states in the western US have levels of arsenic concentrations of greater than 10 parts per billion (10 ppb). This was not a cause for concern until the Environmental Protection Agency (EPA) in 2006 lowered the maximum allowable level of arsenic from 50 ppb to 10 ppb. In 2001, approximately 13 million Americans were drinking water that had elevated levels of arsenic in the water.2

Previous methods for arsenic removal have included: manganese greensand columns that have been pretreated with dilute acid, coagulation/microfiltration, iron oxide based filtration, and activated alumina. The “Arsenic Removal Using Bottom Ash” or “ARUBA” method, invented by Ashok Gadgil of the Lawrence Berkeley National Laboratory, involves coating the surface of the contaminants with bottom ash and ferric hydroxide. Bottom ash is sterile waste material from coal-fired power plants which would make the cost of remediation about 0.5 cents per kg ARUBA of which generally 4-5 grams of ARUBA is needed for 1 liter of water, initially containing 400 ppb arsenic.

Nanomagnetite synthesis for arsenic removal has been hailed as Forbes: ‘Top 5 Nanotech Breakthroughs of 2006’ and Esquire listed it as ‘Six Ideas That Will Change the World’ in 2007. Basically, the technique entails forming iron oxide nanocrystals that possess very unique and size-dependent characteristics for environmental remediation of arsenic contaminated water.

Introduction

Both iron oxide nanocrystals: Fe₃O₄ (magnetite) and Fe₂O₃ (maghemite, as it is a cross between MAGnetite and HEMatite) are ferrimagnetic materials which means they can behave as permanent magnets. Additionally, those oxides below 10 nanometers in diameter, exhibit superparamagnetic properties and are used as MRI contrast agents.

Remember that last semester, you prepared a solution of magnetite ferrofluid by mixing iron(II) chloride and iron(III) chloride in the presence of tetramethylammonium hydroxide.

Magnetite is the most magnetic of all the naturally occurring minerals on Earth and has shown a lot of promise in environmental remediation as it efficiently removes As(III) and As(V) from water, this efficiency of the removal increases ~200 times when the magnetite particle size decreases from 300 to 12 nm. Since arsenic contaminated drinking water is a major problem around the world, using magnetite as a sorbent shows a great deal of promise.

Additionally, Fe(II) compounds have been used to oxidize organic contaminants such as trichloroethylene (TCE), while inorganic contaminants such as arsenic, lead and uranium are separated out of solution. Between 10 and 20 nanometers, the contaminants can be removed from water via handheld magnets, which is an important consideration in purifying water in the Third World, where power is not a standard commodity.

We will produce nanocrystalline and functional iron oxides following a green approach by using everyday items and equipment found in kitchens worldwide. The nanocrystalline and functional oxides are produced by thermal decomposition of the iron-precursors in order to form highly uniform, isolatable nanocrystals of tunable size. The iron precursors will decompose into iron oxides in organic solvents (thermally stable non-polar solvents, aka fatty acids such as oleic acid) at temperatures in excess of 200ºC; the presence of amphiphilic stabilizers, in this case fatty acids derived from soap, limits the growth of crystalline products which are either magnetite, maghemite, or mixtures of both phases.

The beauty of this method lies in the ability to use inexpensive iron sources, such as rust, to form iron carboxylate intermediates, that when scaled to the gram level effectively produces a relatively low cost method for removal of arsenic from contaminated water (see Table 1).

Rust is a mixture of iron hydroxides, oxides, and in some cases even zero-valent iron, but is as effective as FeOOH used in any laboratory method. The fatty acid used in conventional methods is oleic acid, an unsaturated 18 carbon fatty acid. It can be replaced by many cooking oils that can be processed to create a homemade soap through saponification, by the addition of a base such as lye. The soap is allowed to cure for a few days and then dissolved in a weak acid, such as vinegar. The organic layer of the liquid can be collected and used without further processing. The “fatty acid mixture” or FAM is an impure fatty acid whose exact composition depends on the starting edible oil. Olive oil contains the most oleic acid; coconut oils contain more lineolic acid. For this lab, the FAM is derived from vegetable oil, a standard starting reactant.

Table 1. Cost comparison of the materials needed for a FAM/rust synthesis of magnetite nanocrystals with a conventional laboratory synthesis. Most of the savings results from the reduction in cost of the iron source. *Cost of the rust is an estimate.

In the kitchen synthesis, the black product that forms can be separated from the solution by simply using a handheld magnet rather than the expensive and large centrifuges used in a conventional laboratory setting.

Experimental Procedure

Caution!! While all of the following chemicals and utensils can be found in a kitchen, this procedure is potentially dangerous (even the soap is caustic). Gloves and goggles must be worn at all times!!

Materials

Part 1: Soap making process

This step requires a week of advanced preparation and has been done for you

Part 2: Oleic acid from soap with commercial vinegar

Caution!! This must be done a hood or other well-ventilated area!!

Part 3: Magnetite nanocrystals from rust and fatty acids

Caution!! This must be done a hood or other well-ventilated area!!

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This work is licensed by Mary McHale under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource.

Last edited by Mary McHale on Mar 22, 2009 11:49 am -0500.