Description:FIELD OF THE INVENTION
This invention relates to wet chemical method for an Advanced Room-Temperature Synthesis of Bandgap-Tuned SnO2 Quantum Dots for High-Efficiency Energy Conversion and Storage.

BACKGROUND OF THE INVENTION
The synthesis of SnO2 quantum dots with tunable bandgaps remains a challenge for energy applications such as photocatalysis, solar energy conversion, and optoelectronics. Traditional synthesis methods, including hydrothermal, solvothermal, and sol-gel processes, often require high temperatures, specialized equipment, and complex reaction conditions, making them costly and less scalable. Additionally, controlling the bandgap of SnO2 quantum dots for visible-light applications is difficult, as conventional methods typically produce particles with wide bandgaps (≥3.6 eV), limiting their efficiency in energy conversion and storage applications. A need exists for a simple, cost-effective, and scalable method to synthesize SnO2 quantum dots with optimized bandgap properties at room temperature. Several methods exist for synthesizing SnO2 quantum dots, but each has limitations:
• Hydrothermal Synthesis: Requires high-temperature and high-pressure conditions, making scalability difficult.
• Sol-Gel Method: Produces SnO2 nanoparticles but lacks precise control over quantum dot size and bandgap.
• Microwave-Assisted Synthesis: Reduces reaction time but necessitates specialized equipment and controlled heating.
• Sulfur-Doped SnO2 via Hydrothermal Methods: Previous studies have used L-cysteine as a sulfur source, but bandgap tuning is inconsistent and requires prolonged reaction times.
April 2019Journal of Materials Chemistry A 7(17):10636-1064 DOI:10.1039/c8ta12561a disclosed The electron transport layer (ETL) is a critical component in planar single junction or tandem perovskite solar cells (PSCs), dominating the separation and electron extraction of charge carriers. Herein, we introduce a facile route to synthesize a SnO 2 quantum dot (QD) colloidal solution at room temperature using an alcohol-based solvent with the additive of deionized-water. A superior homogeneous ETL is obtained by spin coating of the QD colloidal solution with post-deposition annealing. Compared to the ETL prepared with the SnCl 2 ·2H 2 O anhydrous alcohol solution, the champion power conversion efficiency of PSCs deposited on the SnO 2 QD based ETL is raised to 20.1% from 16.5%. The better performance is attributed to the excellent optical and electronic properties of the SnO 2 QD based ETL. Experimental analyses reveal that the SnO 2 QD based ETL enhances electron extraction and suppresses charge recombination, leading to improvement of solar cell performance. The appropriate concentration of the SnO 2 QD based solution is explored and the appropriate ratio of anhydrous alcohol to deionized water of the SnO 2 colloidal solution is obtained. Our results show the great potential of low temperature synthesized SnO 2 QD films for application as ETLs or interconnecting buffer layers for future highly efficient and reproducible low-temperature processed tandem PSCs.
https://www.sciencedirect.com/science/article/abs/pii/S0167577X18304713 disclosed to the influence of annealing temperature on ultra-small SnO2 quantum dots (SQDs) prepared by a simple chemical reduction process. The structural and optical properties of annealed SQDs were systematically studied by different techniques. Our results show that the crystallinity and average crystallite size of annealed SQDs increased gradually with annealing temperature. The average crystallite size was maintained below 10 nm even for high annealing temperatures. XPS peak fitting analysis yielded information on the presence of mixed ionic states of Sn2+ and Sn4+ in SQDs and further revealed that the number of Sn2+ ions decreased at high temperature. Band-edge shifts were estimated from XPS data. It was possible to shift the bandgap of annealed SQDs from UV to the visible wavelength region, which is likely to have a beneficial impact on many applications of optoelectronic devices.
https://pubs.rsc.org/en/content/articlelanding/2019/ta/c8ta12561a disclosed the electron transport layer (ETL) is a critical component in planar single junction or tandem perovskite solar cells (PSCs), dominating the separation and electron extraction of charge carriers. Herein, we introduce a facile route to synthesize a SnO2 quantum dot (QD) colloidal solution at room temperature using an alcohol-based solvent with the additive of deionized-water. A superior homogeneous ETL is obtained by spin coating of the QD colloidal solution with post-deposition annealing. Compared to the ETL prepared with the SnCl2·2H2O anhydrous alcohol solution, the champion power conversion efficiency of PSCs deposited on the SnO2 QD based ETL is raised to 20.1% from 16.5%. The better performance is attributed to the excellent optical and electronic properties of the SnO2 QD based ETL. Experimental analyses reveal that the SnO2 QD based ETL enhances electron extraction and suppresses charge recombination, leading to improvement of solar cell performance. The appropriate concentration of the SnO2 QD based solution is explored and the appropriate ratio of anhydrous alcohol to deionized water of the SnO2 colloidal solution is obtained. Our results show the great potential of low temperature synthesized SnO2 QD films for application as ETLs or interconnecting buffer layers for future highly efficient and reproducible low-temperature processed tandem PSCs.
https://pubs.acs.org/doi/10.1021/acsomega.8b02122 disclosed Because of its electrically conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting material for applications in low-emission window coatings and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidation reactions. Here, we describe a novel nonaqueous sol–gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the nonhydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temperatures in the 160–260 °C range, compatible with coating processes on flexible plastic supports. The NP size distribution, shape, and dislocation density were studied by powder X-ray powder diffraction analyzed using the method of whole powder pattern modeling, as well as high-resolution transmission electron microscopy. The SnO2 NPs were determined to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liquid-state 13C and 1H nuclear magnetic resonance (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of 13C, 1H, and 119Sn solid-state NMR as well as Fourier transform infrared (FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR, and Raman data showed the presence of organic species derived from the 1-hexanol reactant remaining within the samples. The optical absorption, studied using UV–visible spectroscopy, indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mechanical strains present within the smallest NPs perhaps associated with the organic ligands decorating the NP surface. As the size increased, we observed a correlation with an increased density of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2 NPs in the absence of chemical dopants.
Research gap
Industrial Applicability: This invention is applicable in multiple energy-related fields, including:
Photocatalysis: Efficient degradation of organic pollutants under visible light.
Solar Cells: Enhanced absorption properties for energy harvesting.
Energy Storage: Integration into nanocomposites for supercapacitors and batteries.
Hydrogen Production: Potential use in water-splitting applications.
Novel Synthesis Approach: Unlike existing methods, this wet-chemical approach operates entirely at room temperature, reducing energy consumption and equipment costs.
None of the prior art indicate above either alone or in combination with one another disclose what the present invention has disclosed. This invention relates to a wet chemical method for Advanced Room-Temperature Synthesis of Bandgap-Tuned SnO2 Quantum Dots for High-Efficiency Energy Conversion and Storage
SUMMARY OF INVENTION
Present invention describes a novel, simple, and cost-effective wet-chemical method for synthesizing bandgap-tuned tin dioxide (SnO2) quantum dots at room temperature. The process involves dissolving tin chloride dihydrate and thiourea in deionized water and stirring the solution for varying durations. The key finding is that stirring for 72 hours yields SnO2 quantum dots with a significantly reduced bandgap of approximately 2.8 eV, likely due to sulfur doping from the thiourea. This room-temperature synthesis avoids the high energy consumption and specialized equipment required by traditional methods like hydrothermal, sol-gel, and microwave-assisted synthesis. The resulting bandgap-tuned quantum dots show promise for high-efficiency energy conversion and storage applications, including photocatalysis, solar cells, supercapacitors, batteries, and hydrogen production. The novelty lies in the room-temperature synthesis approach, the optimized bandgap tuning achieved with thiourea and controlled stirring, and the potential sulfur doping mechanism.
Detailed description of invention
The proposed invention presents a simple, wet-chemical synthesis of colloidal SnO2 quantum dots at room temperature. This method involves dissolving tin chloride dihydrate (SnCl2·2H2O) and thiourea (NH2CSNH2) in deionized water, followed by stirring at 500 rpm for various durations (24, 48, 72, and 96 hours). Absorption spectroscopy confirms that a stirring time of 72 hours results in the lowest bandgap (~2.8 eV), potentially due to sulfur doping from thiourea. The synthesized quantum dots are characterized using XRD, TEM, SEM, XPS, and UV-Vis spectroscopy, ensuring structural and optical consistency.
Flowchart Representation of the Synthesis Process:
1. Preparation of Precursors:
o Weigh appropriate amounts of tin chloride dihydrate (SnCl2·2H2O) and thiourea (NH2CSNH2).
o Dissolve in deionized water to form a homogeneous solution.
2. Stirring Process:
o Stir the solution at 500 rpm at room temperature.
o Vary stirring duration (24, 48, 72, 96 hours).
3. Characterization:
o Perform UV-Vis absorption spectroscopy to determine bandgap.
o Conduct XRD, SEM, TEM, and XPS analysis to confirm structure and composition.
4. Optimization & Application:
o Identify optimal stirring time (72 hours) for the lowest bandgap (~2.8 eV).
o Utilize quantum dots in energy applications such as photocatalysis and solar cells.
Explanation for Optimized Low Bandgap: The reduction in bandgap observed at the optimized 72-hour stirring duration can be attributed to two key factors:
Quantum Confinement Effect: At nanometer-scale dimensions, the quantum confinement effect typically leads to an increase in bandgap. However, prolonged stirring facilitates controlled aggregation and growth of SnO2 quantum dots, allowing them to reach an optimal size range where quantum confinement is reduced, leading to a lower bandgap.
Sulfur Doping Mechanism: The incorporation of sulfur from thiourea into the SnO2 lattice introduces localized impurity states within the band structure. Sulfur doping effectively narrows the bandgap by forming mid-gap states, enhancing visible-light absorption. XPS analysis confirms the presence of sulfur, indicating that thiourea plays a critical role in tuning the electronic structure of SnO2 quantum dots.
A. COMPARISON:
Aspect Proposed Method Hydrothermal Sol-Gel Microwave-Assisted
Temperature RT (25°C) >100°C 50-100°C 100-200°C
Bandgap (eV) 2.8 3.6-4.0 3.6-4.2 3.6-4.0
Reaction Time 72 hours 12-24 hours 24-48 hours 1-2 hours
Scalability High Low Moderate Moderate
Energy Efficiency High Low Moderate Moderate

ADVANTAGES OF INVENTION
Novel Synthesis Approach: Unlike existing methods, this wet-chemical approach operates entirely at room temperature, reducing energy consumption and equipment costs.
Optimized Bandgap Tuning: The specific use of thiourea and controlled stirring duration (72 hours) results in a significantly lower bandgap (~2.8 eV), making the material suitable for visible-light applications.
Potential Sulfur Doping: The use of thiourea, previously unexplored for SnO2 quantum dots in this context, likely introduces sulfur doping, which has been confirmed in prior literature to reduce bandgap energy.
Use of application
Industrial Applicability: This invention is applicable in multiple energy-related fields, including:
Photocatalysis: Efficient degradation of organic pollutants under visible light.
Solar Cells: Enhanced absorption properties for energy harvesting.
Energy Storage: Integration into nanocomposites for supercapacitors and batteries
Hydrogen Production: Potential use in water-splitting applications. 
, Claims:1. A Wet chemical method for synthesizing bandgap-tuned tin dioxide (SnO2) quantum dots at room temperature for High-Efficiency Energy Conversion and Storage comprising:
a) dissolving tin chloride dihydrate (SnCl2·2H2O) and thiourea (NH2CSNH2) in deionized water to form a homogeneous solution;
b) stirring the solution at approximately 500 rpm at room temperature (20°C to 30°C) for a duration of 72 hours to obtain SnO2 quantum dots.
2. The method as claimed in claim 1, wherein said Bandgap-tuned tin dioxide (SnO2) quantum dots comprising sulfur doping within the SnO2 lattice, resulting in a bandgap of approximately 2.8 eV