This method can help answer key questions in the water treatment and sustainable remediation field such as efficient removal of radioactive iodine from aqueous media by using hybrid nanocomposite materials. The main or the better thing of this technique is that radioactive elements in a mixed salt and organic substances can rapidly be removed by a simple filtration process in a highly efficient matter. Video demonstration of this matter is critical as the handling and the treatment of radioactive liquid waste requires special care including personal and environmental protection against the spread of radioactive contamination.
Demonstrating the procedures will be Ha Eun Shim, a grad student from my lab. Add 120 milliliters of chloroauric acid solution to a washed two-neck round-bottom flask and heat it to reflux under constant stirring. Quickly add 12 milliliters of sodium citrate tribasic solution to the two-neck round-bottom flask.
Reflux the resulting mixture for another 20 minutes for the complete reduction of the gold salt. Allow the colloidal suspension of nanoparticles to cool down to room temperature. Measure the concentration of the gold nanoparticles with UV-Vis spectroscopy at a wavelength of 520 nanometers using a quartz cuvette.
Now, add a single drop of gold nanoparticle suspension onto a 400-mesh carbon coated copper grid. Dry the grid at room temperature before measuring the size of gold nanoparticles with transmission electron microscopy. Keep the colloidal gold nanoparticle suspension at four degrees Celsius.
To prepare the gold nanoparticle-embedded membrane filter using a syringe unit, first wash a cellulose acetate membrane supported by a filter unit with deionized water three times. Withdraw 10 milliliters of citrate-stabilized gold nanoparticles with a sterile syringe and add it slowly into the pre-washed cellulose acetate membrane filter. Wash the filter unit with 10 milliliters of deionized water three times to remove non-immobilized gold nanoparticles.
Alternatively, to prepare the gold nanoparticle membrane filter by vacuum pump, place the cellulose acetate membrane between a filter holder fritted glass support and a graduated funnel. Connect a combined unit of the fritted glass support and graduated funnel to a recover flask and a vacuum pump. Add 10 milliliters of citrate-stabilized gold nanoparticles into the graduated funnel.
Then apply a vacuum until all gold nanoparticles are passed through the cellulose acetate membrane. Repeat the same procedure on the other side of the membrane to immobilize gold nanoparticles on both sides of the membrane. Analyze the surface of the gold nanoparticle-embedded cellulose acetate membrane or gold CAM using scanning electron microscopy under high-performance conditions with the accelerating voltages up to 15 kilovolts.
Dilute radioactive iodine in three milliliters of pure water, one molar sodium chloride, or 10 nanomolar sodium iodide, and add each solution into a Petri dish. Standard radiation safety guidelines should be observed when working with radioactive iodine. Place the gold CAM that was prepared by using a vacuum filter into the radioactive iodine solutions.
Shake them gently at room temperature. Withdraw 10 microliters of the radioactive iodine solution from the Petri dish at given time points. Then, measure the radioactivity of the aliquot using an automatic gamma counter.
Rinse the gold CAM with purified water after 120 minutes. Finally, measure the amount of radioactivity captured on the membrane using the automatic gamma counter. To remove radioactive iodine anions using a gold CAM filter, dissolve the radioactive iodine in 50 milliliters of several aqueous solutions.
Withdraw 50 milliliters of each solution with a sterile syringe and pass it through the gold CAM filter unit at an in-flow rate of about 1.5 milliliters per second using a syringe unit. Transfer five milliliters of the filtrate into a plastic vial for quantifying the radioactivity in the solution. Measure the amount of residual radioactivity in the filtrate solution using the automatic gamma counter.
Finally, perform the reusability test on the gold CAM filter as described in the text protocol. After a 30-minute incubation, the gold CAM filter captured most of the radioactive iodine in pure water and in one molar of sodium chloride. On the other hand, the adsorption of radioactivity was inhibited completely in the presence of nonradioactive sodium iodide because the surface of the gold nanoparticles was occupied by iodide anions.
The radioactive iodine solutions were passed through a filter unit containing gold CAM. The amount of the residual radioactivity in the filtrate was then measured. Excellent efficiency was obtained through the filtration step, decreasing the concentration of radioactive iodine significantly.
In particular, the desalination performance of gold CAM was not suppressed by high concentration of inorganic salts such as sodium, cesium, and strontium. Furthermore, gold CAM could be reusable for repetitive desalination of radioactive iodine in synthetic urine and seawater. Though this method can provide insight into the remediation of radioactive waste from various aqueous media, it can also be applied to other radioisotopes and toxic heavy metals by introducing metal chelators and inorganic composite on the surface of gold nanoparticles.
Following this procedure, the automatic contaminated water treatment system could be explored and designed for practical implementation of this study at large industrial scale. Don't forget that working with radioactive materials can be extremely hazardous, and precautions such as well-ventilated fume hoods, personal protections, and minimum exposure to hazardous material should always be taken while performing this procedure.
