## 3 Results and Discussion
### UV-Vis Absorption Spectrum Analysis
#### 3.3.2 Light Absorption Spectra of the MXene Based Ionanofluid  
Electronic transition (excitation of electrons to a higher energy state from the ground state) occurs when UV and visible radiation interacts with objects. The UV region falls in the wavelength range between 10 to 380 nm, and the visible region falls between 380 to 780 nm. The possible transitions are pi to pi star (n-\(\pi^{\bullet}\)), n to pi star (n-\(\pi^{\bullet}\) transition), sigma to sigma star (\(\sigma\)-\(\sigma^{\bullet}\) transition), and n to sigma star (n-\(\sigma^{\bullet}\) transition). The transition from \(\sigma\) to \(\sigma^{\bullet}\) electrons needs a wavelength of light absorption that does not fall in the UV-Vis range. Therefore, the UV-Vis region can show the only \(\pi\) to \(\pi^{\bullet}\) and n to \(\pi^{\bullet}\) transition. The visible region possesses 36 to 76 kcal/mol of photon energies, while the UV region (\(>\)200 nm wavelength) has photon energies of 143 kcal/mol, which is needed to promote electrons to higher energy orbital. In photocatalytic, photovoltaic, optoelectronic, transparent conducting electrode instruments, the visible and UV light absorption are significant. The absorbance spectral curves were plotted using the UV-Vis spectrometer measurements. Nanofluids comprising \(\pi\) electrons and n electrons (non-bonding electrons) absorb energy as UV light to stimulate these electrons into higher molecular orbitals. Figure 8 demonstrates the ionic liquids' effect on the absorbance spectra of the formulated DG/MXene nanofluid on the first day for 0.1 to 0.4 wt% mass concentration. For the first day and seventh day, a direct relationship was found between the MXene concentration and the absorbance spectra of the as-prepared DG/MXene nanofluid containing [EMIM][OSO4] ionic liquid. The effect of ionic liquid and the MXene nanoparticle concentration was detected in the range of 240 to 800 nm, which attributes to the region of UV, visible, and infrared. The absorbance of all as-prepared samples escalated intermittently with the decreasing wavelength of 240 to 800 nm. Nanofluid with lower nanoparticle concentration (0.1 wt%) showed limited absorbance spectra at the UV region, whereas high concentrated samples (0.2 to 0.4 wt%) showed more absorbance peaks in all regions. Within the visible range of 380 to 780 nm, a wide absorbance spectrum was observed that became noticeable with the MXene concentration rise, which was due to the surface plasmon resonance of MXene nanoparticles. These results confirmed that MXenes can absorb light at UV as well as visible regions when combined with aqueous solutions. From the graph, it was clear that the maximum absorption peaks for 0.1, 0.2, 0.3, and 0.4 wt% concentration were observed at the UV region of range 220 to 380 nm, which was due to the transition of \(\pi\)-\(\pi^{\bullet}\) and n-\(\pi^{\bullet}\) electrons. These transitions were mainly caused by C=C and C=O functional groups' bonding, which was very similar in carbon and graphene-based nanofluids. For 0.1 wt%, there was no sign of light being absorbed in the visible region, which meant that the only electron jumps that took place were from \(\pi\) bonding to \(\pi\) antibonding orbitals. Additionally, except for 0.1 wt% concentration, all the other samples showed absorbance peaks over a whole range of given wavelengths confirming a whole range of energy jumps. This occurred when the vibrations and transformations in the molecules shifted the orbitals' energies, constantly leading to the change of energy gap between them. As a consequence, absorption happened over several wavelengths rather than one specific wavelength. The measured absorbance spectra of the prepared ionanofluids on the seventh day after preparation is depicted in Figure 9. It was observed that the ionic liquid-based MXene nanofluids have limited optical absorbance in the UV and visible light wavelengths when compared to the first day.