User:Melissa Novy/Notebook/CHEM-572/2013/02/06

Objectives

• Make 50 mL 5 M KNO₃ solution for ionic strength adjustments with silver ion-selective electrode.
• Make agar solution and plate E. coli cells.
• Analyze cells with UV-vis spectrophotometry.
• Make PLA2002D + 5wt% Laponite (PLA + 5LMT) using dichloromethane.
• Analyze XRD data obtained on 2013/02/05.

XRD on 95AgLMT

• Laponite

• The XRD spectrum for Laponite established that the d-spacing between layers of clay is about 2.55 nm, as shown by the 2θ peak at around 35°. The 2θ peak at around 20° represents the d-spacing between two clay layers, as the d-spacing value is roughly twice that of 2.55 nm. In addition, the sample of Laponite was not very crystalline, as expected, due to the low intensity values of the peaks.

• 95AgLMT stirred for 24 h and made on 2013/01/30.

• The XRD spectrum for 95AgLMT displayed 2θ peaks at around 20°, 35°, 48°, and 44°. The first two peaks are due to the structure of Laponite, while the last two peaks, with d-spacing values of 2.359 nm and 2.044 nm, respectively, are due to the presence of silver. Literature indicates that these peaks represent either crystalline silver or silver nanoparticles. However, as the structure of Laponite remained unchanged, it must be concluded that little to no silver ions were exchanged into the clay galleries. Instead, the silver became boudn to the outside of Laponite.

Agar Solution and Agar Plates

• The plates made on 2013/01/30 were unusuable, so the plates were remade using the same protocol as before.
• However, modifications to the recipe were as follows:
  • 12.5 g Teknova LB medium
  • 7.5 g ??? agar

Calculations for 5 M KNO₃

  MW KNO3: 101.10 g/mol
  0.050 L × 5 M KNO3 = 0.25 mol KNO3
  0.25 mol KNO3 × (101.10 g/1 mol KNO3) = 25.275 g KNO3

• Actual mass KNO₃: 25.2756 g
• Actual molarity KNO₃: 5.00 M
• KNO₃ was placed in a glass screw-top bottle and 50 mL of pure H₂O was added. The solution was stirred and heated at 70°C for 3 hours to dissolve the KNO₃.

PLA2002D + 5wt% Laponite Film

• 1 g of PLA was dissolved in 10 mL of dichloromethane in a fume hood.
• 0.05 g Laponite was dispersed in 5 mL of dichloromethane, and then added to the PLA solution.
• The solution was stirred for 1 h and then cast into a Teflon dish.
• The dish was left under the fume hood to encourage evaporation of the dichloromethane.

UV-Vis on E. coli Cells

• Absorbance was measured at 650 nm with a Shimadzu UV-1800 spectrophotometer using plastic cuvettes. 2 mL of each sample was pipetted into a clean plastic cuvette.
• The absorbance of DH5α was 1.800.
• The absorbance of DH10B was 1.82.