Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

The overall goal of this protocol is to show the proof of concept of a humidity sensor based on a silver zeolite polymer composite prepared via spray coating. This video can help some problems in the material science field, such as the lack of direct responsive humidity sensors, therefore, we propose a humidity sensor based on zeolite polymer composites. The main advantage of this technique is that it's an easy and cost-effective way to produce a humidity sensor, which can be reused multiple times.

Demonstrating the procedure will be Bjorn Dieu, a technician from our group. To begin this procedure pre-treat the zeolite materials as outlined in the text protocol. Then dissolve 13.76 grams of lithium nitrate in two liters of deionized water.

Pour 0.5 liters of this lithium nitrate solution into a one liter high density polyethylene flask. Add three grams of the pre-treated sodium Linde type A zeolite. Then agitate the flask overnight at room temperature using an end-over-end shaker oven.

After agitation is complete, filter the suspension using a Buchner funnel. Wash the recovered powder three times with deionized water. Then mix the powder with 0.5 liters of fresh lithium nitrate solution in a clean one liter HDPE flask.

Agitate, filter and wash as before. Repeat this process four additional times. Next heat the recovered zeolite powder in a muffle oven overnight at 450 degrees celsius.

Use a temperature ramp up of five degrees celsius per minute with intervals of one hour at 80 degrees celsius and 110 degrees celsius. After heating is complete, use 200 milliliters of deionized water to dissolve 74.8 milligrams of silver nitrate in a 250 milliliter HDPE bottle. Add one gram of the partially exchanged lithium LTA zeolite.

Then agitate the solution overnight at room temperature in an end-over-end shaker oven. After agitation is complete, filter the suspension using a Buchner funnel. Wash the recovered zeolite powder three times with deionized water.

Then heat treat the powder in a muffle oven overnight at 450 degrees celsius. Use a temperature ramp up of five degrees celsius per minute with intervals of one hour at 80 degrees celsius and 110 degrees celsius. After heating is complete, use a desiccator containing a saturated potassium sulfate solution to cool the sample under controlled humidity conditions.

Perform spectra and thermogravimetric analysis as detailed in the text protocol. In a volumetric flask dilute one milliliter of commercial 50 weight-percent polyethylenimine solution to 100 milliliters using deionized water. Mix the PEI solution with 250 milligrams of treated zeolite material in a 125 milliliter HDPE bottle.

Shake the suspension vigorously. Then pour the suspension into a spray bottle. Clean a quartz plate by rinsing it with deionized water and acetone consecutively.

Then dry the plate in an oven for one hour at 80 degrees celsius. After drying is complete, place the quartz plate horizontally on a clean sheet of aluminum foil. Then coat one side by spraying three times for three seconds each time from a distance of 10 centimeters.

Dry the coated plate in an oven for 30 minutes at 50 degrees celsius. Repeat the spray coating and drying process another four times until the film is uniform. Make sure the layer is nicely homogeneous.

Next, place the coated quartz plate into the sample compartment of an in-house heating vacuum cell. Close the sample chamber of the cell by placing a rubber ring and a clean quartz plate on top of the coated plate. Then seal the cell using a Teflon stopper and screws.

Dehydrate the sample by applying a high vacuum overnight using a pressure of 10 to the minus three millibar. Using a UV lamp, visually monitor the emission color changes of the film. Next, open the sample chamber.

Use the UV lamp to monitor visible emission color changes upon film re-hydration. Test the reversibility of the film by repeating the dehydration re-hydration process, monitoring changes with the UV lamp each time. In this study, a luminescent humidity sensor is fabricated with partially lithium exchanged sodium Linde type A zeolites.

The luminescent properties are dependent on the water content of the system. As the emission color shifts from yellow to green to blue when removing water from the system. The representative results of thermogravimetric analysis and temperature dependent luminescence experiments are shown here.

TGA analysis correlates temperature to the hydration level of the zeolite. While temperature seems to be directly related to the emission color. Together these results confirm that the sensors luminescent properties are dependent on system water content.

After watching this video you should have a good understanding of how to produce a humidity sensor based on silver zeolite polymer composites. Don't forget that working with zeolites can be hazardous and precautions such as wearing a dust mask should always be taken while performing this procedure.