Carbon nanotubes function as vital inorganic nanomaterials with demonstrated potential for application in electronic devices, new energy production systems, advanced composite materials, information storage technologies and biomedical fields. CNTs experience extensive aggregation through van der Waals forces and different interactions which reduces their dispersibility and control thus limiting their practical applications. The application of dispersants enables effective distribution of CNTs in water-based solutions thereby addressing their aggregation challenge. Biomolecules represent one of the dispersant categories that researchers use most frequently. CNTs can achieve dispersion through proteins as well as DNA sequences and small biomolecules which possess aromatic structures.
The example of lysozyme reveals how its hydrophobic cavity binds to CNT surfaces effectively based on Figure 1. The interactions between lysozyme and CNTs mainly include: CNTs and lysozyme connect through π–π stacking interactions between tryptophan residues and CNTs along with hydrophobic interactions between the hydrophobic parts of lysozyme and CNTs. The binding of lysozyme to CNTs enables hydrophilic groups to interact with external water molecules which aids in the improved distribution of CNTs in liquid solutions. CNTs with dimensions spanning hundreds of nanometers to several micrometers enable multiple lysozyme molecules to attach to their surfaces which results in enhanced dispersion properties. To achieve rapid dispersion of CNTs through biomolecules requires the use of sonication assistance.
Figure 1. Lysozyme-assisted CNT dispersion: (a) Schematic diagram; (b) Electron micrograph of CNTs before dispersion; (c) Electron micrograph of CNTs after dispersion; (d) Photograph of CNT dispersion solution by lysozyme
Instruments and Reagents
- Instruments: The experiment requires an ultrasonic cleaner along with a low-speed centrifuge, balance, spectrophotometer and several glassware items including glass funnels and test tubes as well as colorimetric tubes and cuvettes.
- Reagents: CNTs (solid, diameter 10–20 nm, length 1–2 μm), lysozyme, glycine, tea leaves.
Experimental Procedures
(1) Solution Preparation
Take 10 mg of lysozyme and combine it with 10 mL of deionized water. To avoid vigorous shaking which generates bubbles and denatures lysozyme mix gently to achieve a 1.0 mg·mL-1 lysozyme solution.
Add 10 mg of glycine to 10 mL of deionized water and mix the solution until it reaches a concentration of 1.0 mg·mL-1.
Measure 1 gram of tea leaves and boil them in 50 milliliters of water for five minutes. Once the solution has cooled down filter it and then use the resulting filtrate in the next experiments.
(2) Biomolecule-Assisted Dispersion of CNTs
Measure out 1 mg of CNTs and transfer them into a glass test tube. Pour 5.0 mL of lysozyme solution into the tube and gently shake for 2 minutes. After allowing the solution to stand for 10 minutes perform centrifugation at 3000 rpm for 5 minutes. Collect the supernatant using a rubber pipette before transferring it to a cuvette. Examine the original lysozyme solution to check for any blackening of the supernatant and document any color difference. To investigate how glycine solution and tea extract impact CNT dispersion perform the identical test procedure.
(3) Ultrasonically Assisted Biomolecule Dispersion of CNTs
Take a measurement of 1 mg of CNTs to put into a glass test tube. Pour 5.0 mL of lysozyme solution into the mixture and perform a gentle shaking action for two minutes. Insert the test tube into an ultrasonic cleaner and run the sonication process for 10 minutes. Perform a centrifugation step at 3000 rpm for 5 minutes. A rubber pipette should be used to obtain the supernatant which should then be transferred into a cuvette. Use the lysozyme solution as a control to determine if the supernatant has changed to black and record any changes in color. Apply the same steps using glycine and tea extract to examine how they affect CNT dispersion.
(4) Comparison of Dispersion Efficiency
The supernatants collected from steps (2) and (3) should be organized by their color intensity levels and entered into Table 1. Document the order of biomolecules used in the experiment and note if ultrasonic assistance was utilized.
Table 1 Biomolecule-assisted dispersion of CNTs under different conditions
| Serial No. | Color of Dispersion | Biomolecule | Ultrasonicated or Not |
| 1 | |||
| 2 | |||
| 3 | |||
| 4 | |||
| 5 | |||
| 6 |
Mix a small volume of the lysozyme-based CNT solution which was prepared with ultrasonic aid with water and continue diluting until a pale brown color develops. Pour 3 mL of diluted solution into a cuvette and conduct absorbance measurements between 400 to 700 nm in 10 nm intervals with a spectrophotometer. First plot the absorption curve of CNTs in the visible spectrum before comparing it to the standard CNT absorption curve.
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