My thesis involves taking a layered material of manganese oxide (MnO2) and performing two experiments on it to see if the structure of the material can be changed in a way that could potentially improve its properties. My thesis focuses on whether generating these structural changes can work, so measuring the properties of the resulting structures is left to future research. The first experiment was to try to expand the inner layer of material, which is the space between the stacked sheets, without causing the sheets to separate completely.
If successful, this could increase the surface area of the material, which is very beneficial for energy storage applications. The second experiment was to try to completely separate the layers of the material to get tiny nanosheets and then stack these nanosheets again with gold nanoparticles between them. Direction a is in and out of the page, b is left and right on the page, and c is up and down the page.
Imagine the front face of the cube - which is a plane, and the atoms at the corners of that face are atoms in that plane. Something similar can be said about the right and top faces of the cube, written as (010) and (001) respectively. There are many other planes in this cube alone using combinations of directions abc.
Through the use of the Tyndall effect and XRD, the results of this experiment showed that pillaring was.
Introduction
Energy Storage
From this equation, it can be seen that there are three ways to increase the capacitance of a double-plate capacitor: increasing the area of the plates,. Reducing the distance between the plates can only work up to a point because when the plates get too close, a charge flow can occur that prevents the capacitor from storing that charge. Much research has been done to find better dielectric materials, and currently one of the best materials (in a .scientific sense, not a practical sense) is calcium copper titanate2.
They can achieve higher power density than batteries and higher energy density than ordinary capacitors3, and are therefore of. In a supercapacitor, two electrodes that have a porous material with a high surface area are placed in an electrolyte solution with a barrier separating them. When a potential is applied, ions of the electrolyte form a double layer structure at the electrode-electrolyte interfaces3.
Positive ions adsorb to the porous material on the negative electrode and negative ions on the positive electrode, creating a potential difference on the surface of each electrode with the oppositely charged ions still in the electrolyte solution. This is what stores the charge in a supercapacitor, and is similar to the positively/negatively charged plates that store the charge in a traditional one. This mechanism is very different from that of a battery, although an electrolyte solution is used.
The advantages of this supercapacitor setup is that each electrode first acts as its own capacitor, so the electrodes pair. Second, the distance between positive and negative ions in the interface double layer is very small, on the order of nanometers3, which increases the capacitance of the supercapacitor. Third, the porous electrode material can achieve much larger surface area than a metal plate for the same projected area, which also increases the capacitance.
Finally, supercapacitors retain all the advantages that traditional capacitors have over batteries, including an extremely high cycle life and the ability to release their energy very quickly. Because the number of ions that can adsorb to the porous material determines the amount of charge that can be stored, the energy density of the supercapacitor can be increased if the surface of this material can be increased4. Therefore, it is extremely important and useful for the practical application of supercapacitors to develop suitable high surface area electrode materials.
Layered Materials
Experimental Procedure
Preparation of Layered Parent Phase K x MnO 2
Preparation of Protonated Layered Phase H 0.45 MnO 2
Pillaring of H x MnO 2
Exfoliation of H x MnO 2 and Flocculation with Gold Nanoparticles
The mixture was stirred at 700 RPM for 10 minutes, and then the flocs were allowed to settle. The liquid was decanted and the remaining solid flocs were washed by adding DI water, centrifuging at 10,000 RPM for 10 min and decanting the liquid a total of 3 times, to remove any remaining TBAOH from the flocs. The flocs were dried at room temperature in air and under vacuum, and characterized using XRD and a scanning electron microscope (SEM).
Characterization and Data Analysis
Results and Discussion
Material Synthesis
The XRD data for H0.45MnO2, the ion-exchanged material, is shown in Figure 5, overlaid with the K0.45MnO2 data for comparison. From Figure 5 it can be seen that the (001) peak is significantly shifted to lower 2θ. A shift of the (001) peak to lower corner corresponds to a larger spacing between atomic planes in that direction, which in this case is the stacking direction of the MnO2.
This means that during the ion exchange, the interlayer expanded, which means that the ion exchange was successful and the correct phase was formed.
Pillaring
From Figures 6 and 7, it can be seen that no noticeable peak shift occurred after any of the column steps, using either the linear or tertiary amine. Any slight shift that is present is likely attributable to sample drift, as the peak location is very sensitive to sample drift at low angles. This suggests that the pole did not occur, because if there had been expansion of the interlayer, the tip would have shifted more.
Furthermore, after the final column step, not only did no column occur, but there is evidence that the material actually flaked. First, it can be seen from these images that the color of the liquid is brownish, which suggests that there is something in the liquid, probably exfoliated MnO2 nanosheets. A laser can be seen in a liquid, which means the laser light is being scattered by something, according to the Tyndall effect.
The Tyndall effect is the scattering of light by particles in a suspension or colloid, and will not occur in a true solution where molecules are dissolved. The fact that the light is scattered suggests that something is in suspension, very likely the MnO2 nanoplates, suggesting that the material exfoliated rather than became pillars.
Au Intercalation
Conclusions
In this investigation, the expansion of the intermediate layer (pillaring) in H0.45MnO2 using linear and tertiary amine organic molecules was unsuccessful. The XRD data showed no evidence of a change in the interlayer spacing and there is evidence to support exfoliation of the multilayer material. Therefore, the hypothesis that these organic molecules lead to interlayer expansion cannot be verified by this study.
The intercalation of Au nanoparticles into layered MnO2 using an exfoliation/flocculation method seemed successful. XRD data showed that Au was present in the flakes, and EDS analysis confirmed this. However, SEM and EDS analysis showed that the Au was not uniformly dispersed.
There is evidence that Au nanoparticles introduced prior to flocculation agglomerated into larger particles. There were also areas of multi-layered, re-stacked MnO2 sheets with no Au present, indicating a non-uniform distribution of Au particles. Therefore, the hypothesis that exfoliation and flocculation of MnO2 sheets with Au nanoparticles would cause the nanoparticles to become uniformly embedded in the interlayer cannot be verified.
Suggestions for Future Work
Due to the potentially interesting behavior of Au nanoparticles with light, it would also be interesting to perform photocatalytic and photoelectric property measurements on the Au-MnO2 layered material. These properties can be valuable for supercapacitor applications, but also for many other applications where light plays an important role, such as solar cells. The phenomenon of plasmon resonance, one of the factors that led to the selection of Au for this experiment, can only occur on metallic surfaces, so the agglomeration of nanoparticles into larger particles with significant bulk material can hinder any potentially interesting or useful light-based material. properties of this material.
Suggestions of possible changes to the method include vigorous stirring of the mixture during flocculation, the use of smaller diameter gold particles, or the use of a more stable gold nanoparticle suspension.
Geng, F.; Ma, R.; Ebina, Y.; Yamauchi, Y.; Miyamoto, N.; Sasaki, T., Giant swelling of inorganic layered materials: A bridge to two molecular thins. Watanabe, M.; Sasaki, T., Synthesis of a Li−Mn oxide with disordered layer stacking through flocculation of exfoliated MnO2 nanosheets and its electrochem.
