I have submitted this dissertation to the Department of Chemistry, Indian Institute of Technology, Guwahati, for the award of the degree of Doctor of Philosophy. Not for obtaining the degree of Doctor of Philosophy in Chemistry, there is an authentic record of his research work. This is the motivation of this thesis to investigate the detailed photophysical properties of Cdots and implement them for sensing applications.
Structural randomness limits the use of these modern environmentally friendly and easy-to-synthesize nanomaterials in the fields of organic electronics, photovoltaics, energy storage and conversion. By taking advantage of the enhanced photoluminescence efficiency of Cdots due to doping, a dual light-emitting nanocomposite system was fabricated for ratiometric intracellular pH sensing. Finally, the enhanced conductivity nature of the composite system was successfully used for the sensing of nitro-explosive compounds based on I-V characteristic studies.
Carbon dots 01
- Discovery of Carbon dots 01
- Synthetic Methods 02
- Composition and Structure 02
- Properties of Cdots 03
- Absorption and Photoluminescence 03
- Electroluminescence and Chemiluminescence
- Photoinduced Electron Transfer Properties 05
- Up-conversion Properties 06
- Applications of Cdots 06
- Bio-imaging and Bio-sensing 06
- Drug Delivery 06
- Chemical Sensing 07
- Light-emitting Devices (LED) and
- Phtocatalysis 08
- Electrocatalysis 09
- Solar cells 09
26 Cdots were also used as the emitting layer in LEDs by Veca et al. 27 Similarly, Yuan et al. reported monochromatic electroluminescent LEDs using Cdot bandgap emission. a) Schematic of the photoluminescence and chemiluminescence mechanisms of Cdots in the presence of oxidizing species such as KMnO4 and cerium(IV).29 (Reprinted with permission from ref. 29. Copyright 2012 Royal Society of Chemistry). Due to their smaller size, good biocompatibility, and sustained drug release, Cdots have been used as a good nanocarrier and drug release tool. So far, the outstanding optical properties of Cdots have been extensively used to design noble sensing probes.
Cdots have been used to detect several small molecules such as melamine, 63 picric acid, 64 2,4-dinitrophenol, 65 tetracyclines, 66 quercetin, 67 amoxicillin. So far, various metal-based catalysts and their composite systems have been used to improve reaction kinetics. 90 Nitrogen and sulfur co-doped Cdots were used as the surface modifier of ZnO by Wang et al.
Motivation 10
Recently, several Cdot-based composites have been reported as a photosensitizer for dye-sensitized solar cells,87 a hole transporter in perovskite solar cells, 88 a counter electrode for quantum dot-sensitized solar cells.89 Zhang et al. The incorporation of Cdots was found to reduce the surface energy of the ZnO layer, facilitating the efficient transport and collection of photogenerated carriers. Schematic representation of the device for the fabrication of inverted organic solar cells together with the structural formula of the active layer components and the synthesis procedure of Cdots.91 (Reprinted with permission from ref. 91).
As discussed in the previous sections, only the graphical characteristics and corresponding phenomena of Cdots have been widely investigated so far. Although some results have been reported on their catalytic behavior and their application in photovoltaics, the lack of structural arrangement further limits their successful implementation, resulting in lower efficiency values. Therefore, there is a clear need to introduce a simple methodology to obtain high-quality crystalline nature in this green and easy-to-synthesize carbon allotrope in order to successfully implement it in the fabrication of miniaturized devices related to energy conversion and organic photovoltaics.
Overview of the Thesis 11
One-pot hydrothermal synthesis of highly luminescent nitrogen-doped amphoteric carbon dots for bioimaging Bombyx Mori Silk – natural proteins. Hair fiber as a precursor for synthesizing sulfur and nitrogen co-doped carbon dots with tunable luminescent properties. One-step synthesis of highly photoluminescent self-doped carbon dots as multifunctional biosensors for the detection of iron ions and pH.
Nitrogen-doped carbon dots via hydrothermal synthesis: naked-eye fluorescent sensor for dopamine and used for multicolor cell imaging. Fabrication of HA/PEI-functionalized carbon dots for tumor targeting, intracellular imaging, and gene delivery. Boron-doped carbon dots, that is, B-Cdots, were synthesized from citric acid monohydrate and thiourea in the presence of boric acid.
Results and Discussion 26
The details of the synthesis procedure of the same are explained in the experimental part. Time scan of luminescence intensity of three as-synthesized carbon dots (i.e., B-Cdots, Cdots, and P-Cdots). The color rendering index (CRI) and correlated color temperature (CCT) of the same were calculated to be 82 and 6300K, respectively (Figure 2.12.b, c).
The input concentration ratios of the carbon dots were the same in the composite whose spectra are shown in Figure 2.11. No significant change in the intensity ratio of the composite was observed in the presence of the above-mentioned interfering species. The emission intensity ratios of the composite material were also monitored in the presence of biothiols (such as GSH and Cys; 5 μl of a 1 M solution) and ROS species (36% H2O2; 5 μl).
The subsequent weight loss in the range of 220 to 700 °C was due to the continuous degradation of the polymer. A digital photograph of the composite film is shown in Figure 3.7.b (inset) and the circuit setup for studying the I-V characteristics is included in Figures 3.7.c. Schematic of the conductivity of the composite film in terms of the initial concentration of Cdot in the reaction mixture (which is expressed as volume percent).
Sensor response curve of the Cdot-PPy composite film in the presence of different concentrations of picric acid. Powder XRD pattern of the carbon dots without phosphorus inside the structure (c) and with phosphorus doped inside the structure (d). This trend correlates strongly with the trend in crystallinity of the phosphorus-doped carbon dots.
Selected area electron diffraction (SAED) examination (Figure 5.2) of the assembled system revealed their polycrystalline nature. Addition of zinc acetate dihydrate in the Cdot medium causes selective binding of the free PO43-.
Conclusion 47
Conducting Carbon Dot-Polypyrrole Nanocomposite for Sensitive
- Results and Discussion 55
- Conclusion 65
Experimental Section 70
After the reaction, the final product was cooled to room temperature and dissolved in 10 ml of water. The dark brown solution thus obtained was then centrifuged (15,000 rpm, 25 min, refrigerated centrifuge, SIGMA 3-30K), followed by dialysis (1 kDa dialysis membrane) of the collected supernatant for up to 12 h for further purification. After synthesis, the final product was centrifuged (15,000 rpm, 25 min), followed by dialysis of the supernatant (1 kDa dialysis membrane, up to 12 h) for further purification.
Here, QS= quantum yield of the sample; QR = reference quantum yield; IS = area under the PL curve of the sample; IR = area under the PL reference curve; AR = reference absorbance; AS = sample absorbance; ηS = refractive index of the sample solution; ηR = reference refractive index. The sample cuvette was then irradiated with a laser source (high-power 2W 808 nm focusable IR laser; MOD808-2W, laser type: diode) for 8 min with stirring, for homogeneous heat distribution through aqueous dispersions. For the control experiment, only water (without any Cdots) was irradiated with the laser source as well, maintaining all the aforementioned experimental conditions.
After stabilizing the condenser temperature, different concentrations (4.5 mg/mL, 10 mg/mL, 20 mg/mL, 30 mg/mL, 40 mg/mL, 80 mg/mL) of P-Cdot solutions were found and homogeneously distributed Cdots. were taken in a 1 liter evaporating flask and irradiated with simulated solar illumination (1 W/cm2) for 15 min. We found that the presence of P-Cdots and Cdots in water can significantly increase the rate of water evaporation due to their extensive photothermal heat generation efficiency compared to normal water evaporation. To calculate the evaporation efficiency η, we performed separate sets of experiments where the pressure inside the evaporation flask was the standard atmospheric pressure of 1.01 bar.
𝑬 equation 4.2 Here he is the specific enthalpy of water vapor, m is the mass of water evaporated per. We use the standard value of 2260 J/g as the heat of vaporization of water at a pressure of 1.01 bar.1 The energy input E for the experimental setup is the incident simulated solar energy of 5 J/s and m corresponds to the mass of water evaporates in 15 minutes, i.e. for P-Cdot and Cdot assisted (concentration - 80 mg/ml) photothermal evaporation of seawater, the above experimental procedure was followed in the presence of simulated solar radiation (1 W/, cm2).
Salinity and pH of the water samples were carefully measured using a salinity measuring probe (model: HI98194).
Results and Discussion 74
On the other hand, TEM analysis of Cdots (with a relatively larger size of 6.5 ± 1.5 nm, Figure 4.7.a and b) revealed their mostly amorphous, quasigraphite nature. In the case of Cdots, we found a broad diffraction peak with low intensity, asymmetrically centered at a 2θ value of 20o (Figure 4.8.a). After irradiation with the laser source, although we found that both carbon dots caused an increase in the scattering temperature, P-Cdots were found to be more efficient than Cdots.
The initially measured salinity and pH of the water samples (collected from the Bay of Bengal, Persian Gulf water and the average seawater salinity sample) are listed in Table 4.5. Based on detailed experimental analyzes followed by computational refinement, we propose the formation of the orthorhombic crystalline pattern of the unit cell in the carbon point structure. Importantly, these constituent particles of the assembly had diameters very similar to those of the precursor P-Cdots (3.0 ± 1.0 nm, Figure 5.1.c, d)).
A careful investigation of the TEM images for Zn,P-Cdots revealed the presence of distinct polycrystalline domains in the assembled nanostructure. Sharp peaks due to the aforementioned d-spacing values were also identified in the powder XRD pattern of the same at 49.9o and 37.0o, respectively. 3 However, as we reported earlier, 1 microwave treatment of the precursors in the presence of phosphoric acid results in the formation of crystalline Cdots (P-Cdots) with characteristic X-ray diffraction (XRD) patterns (Figure 5.6.a, b. ).
Powder XRD pattern of (a) Cdots without phosphorus in the structure showing the amorphous nature of the same and (b) P-Cdots synthesized from citric acid monohydrate (210 mg), thiourea (210 mg) and phosphoric acid (11.1 % w/ w, input concentration) (c) X-ray powder diffraction pattern of Zn crystalline assembly, P-Cdot. 11 The dispersion of the obtained white precipitate of Zn, P-Cdots also showed absorption at ~278 nm and ~342 nm thus indicating the integration of Cdots within the structure (Figure 5.11.b). 12 Zn,P-Cdots showed excitation-dependent tuning due to Cdots as well, along with the shift of the excitation maximum to 370 nm (the corresponding peak was found to be at 460 nm, Figure 5.11.d).
For this, P-Cdots and the assembled crystalline system of the same (Zn, P-Cdots) were firstly adsorbed separately inside the activated carbon material followed by deposition on the nickel (Ni) substrate in order to provide EDL capacitor electrodes. Electrochemical impedance spectroscopy (EIS) measurements were further performed to study the electrochemical performance of the electrodes. Electrochemical performance of electrodes prepared with different concentrations of Zn, P-Cdots added to activated carbon.
Conclusion 94
Zinc Ion Induced Assembly of Crystalline Carbon Dots with Excellent
- Results and Discussion 102
- Conclusion 125
Summary and Future Prospects 129
