Determining the Best Absorbent for a Model PAH, Procion Red Dye, Using Porous Materials
Toby Coggins* Sarah Cirildo Chemistry 112-510
Abstract
The results of three different porous materials’ ability to isolate procion red dye were compared. The spectrophotometric data of each, (charcoal, magnetic zeolite, and zeolite) taken after mixing were compared, and the major finding was that the charcoal was best at isolating the dye. By comparing the absorbance, and moles of dye removed by the solid material it was possible to determine the best remediation agent.
Introduction
Polycyclic aromatic hydrocarbons (PAH) are potentially cancer causing matter that can be detected in many different places like the soil we cultivate, the water we drink, and even the air we breathe.1It is becoming increasingly important to remove these pollutants from the environment and while methods of destructive oxidation have been used, porous solids have proven to be effective.2 To test the ability for solid porous materials to effectively rid an environment of PAH the three materials were put to the test. In this case procion red dye was used to model a PAH.
Materials and Methods
To begin, the two types of zeolite were created. For the non-magnetized zeolite 50mL of 3.0 M NaOH in a 250 mL beaker and placed on a hot plate with a magnetic stir bar. 3.75 grams of sodium aluminate was stirred and dissolved. While the sodium aluminate solution was being heated and dissolved another hotplate was obtained and 50 mL of distilled water was placed in a 150 mL beaker. When the water came to a boil 2.65 grams of sodium silicate was added and dissolved. When both solutions were at slow boils the sodium silicate solution was added to the sodium aluminate solution. With a thermometer in the solution the temperature was maintained at 90°C for one hour and stirred to prevent lumps. The solution was cooled for five minutes and equal amounts were placed in centrifuge tubes and spun for ten minutes at 5000 RPM. When completed the supernatant was removed and distilled water was added and respun. The remaining solid was placed in a contained and dried in an oven.
Magnetized zeolite was then synthesized by adding 50mL NaOH in a 250 mL beaker, placed on a hotplate with stir bar and heated. 3.75 grams of sodium aluminate was added and dissolved. 50mL distilled water was being heated in a 150mL beaker and when it began to boil 2.65 grams of sodium silicate was added and dissolved. When both solutions reached a slow boil the silicate solution was poured into the aluminate solution. The solution was then kept at 90°C for one hour. The mixture was stirred so no lumps would form, and then the .78 grams of FeCl3 and .39 grams of FeSO4*7H2O and stirred until dissolved. Heat was removed and the solution cooled for 5 minutes before continuing. Equal amounts of the solution were put in centrifuge tubes and spun down for 10 minutes at 5000 RPM. The supernatant was decanted and distilled water added to the 10mL mark and respun for 10 minutes at 5000 RPM. The supernatant was again discarded and the solid removed with a spatula into a container to be oven dried.
To begin testing the ability of the porous solids so remediate the solution, the spectrophotometer was calibrated and allowed to warm up. Distilled water served as the “blank” cuvette. Absorption spectra for the undiluted dye was taken (absorption vs wavelength) and exported. A standard or calibration curve was taken by taking the serial dilutions and measuring their absorbance and concentrations. The wavelength parameter was set to 495-570 and each of the dilutions (100%, 50%, 25%, 12.5%) were placed and their respective concentrations entered when the dialog box appeared. To create the dilutions 10mL undiluted dye was obtained and used to create the remaining three concentrations. 5mL of undiluted stock was mixed with 5mL DI water to create .025M (50%) solution, 5mL of the 50% solution was mixed with 5mL of DI water to create .00125M (25%) solution, and finally 5mL of the 25% solution was mixed with 5mL of DI water to create a .00625M (12.5%) solution. Absorbance and wavelength was then taken from the subsequent isolation of the model PAH. Equal amounts of the porous solids, no more than .100 grams total were ground up using a mortar and pestle and added to the centrifuge tubes with the respective dilution and was spun at 5000 RPM for 10 minutes. This process was repeated for each of the materials. The supernatant left over was then extracted using a serological pipet and placed in a cuvette. At this point the spectrophotometer is set to absorbance vs wavelength with the range from 495-570. Each cuvette was placed in the slot and the “collect” button pushed until all data for that specific material was complete, then “stop” was pushed. It was important that the cuvette was aligned correctly before being inserted into the spectrophotometer.
Results and discussion
Figure 1: Figure 2:
In figure 1 the calibration curve is depicted, which helps with the calculation of the concentration of the remediated solution. To determine what porous solid isolated the most procion red dye the Beers law equation given by was used to find the concentration of the solution and ultimately get the grams of the dye removed. The absorbance can be taken Figure 2 simply displays the of the procion red dye, which allowed for all sample data to be collected at that point (530.5 nM).
FIGURE 3:
Charcoal
Zeolite
Magnetized Zeolite
Mass (g)
.0267
.0289
.0258
Absorbance
.03645
.25519
.25417
Concentration (mM) ()
Initial Amount of Dye (moles)
.05mM.00005M
.05mM.00005M
.05mM.00005M
Final Amount of Dye (moles)
.002695mM.000002695M
.01887 mM.00001887M
.01887mM.00001887M
Dye Removed (moles)
Displayed above in figure three is the calculation of moles of dye removed for the three materials. Since the value of “b” is 1cm it was not included in the formula, and the molar absorptivity “ was the slope of the calibration curve which could be used to determine concentration. The concentration needed to be converted to “M” and was multiplied by the liters of the solution to cancel out and end up with moles. It was determined that the charcoal removed more moles of procion red dye than the magnetic zeolite or zeolite. The two zeolites were very similar in their PAH removal ability. The absorbance recorded for each also tell a story. Less light was being absorbed in the charcoal than the two zeolites.
Three different parameters for determining feasibility of these porous materials could include: absorptive ability, price, and abundance of material. When choosing a material to complete a job the one that soaks up the best would be the top choice; in this case charcoal. Price is a very important aspect because it is necessary for it to be easily manufactured and readily available when needed. If it becomes too expensive to produce or source problems can arise.
Conclusions
This lab was conducted to determine the best solid porous material for removing a model PAH from a mixture.