As nanotechnology continues to push the boundaries of materials engineering, hexagonal boron nitride (h-BN)-dubbed "white graphene"-is driving a revolution in the field of quantum dots. This paper focuses on the precise deconstruction and functional reconstruction of the h-BN material system. It overcomes the size control limitations of traditional mechanical exfoliation through an innovative liquid nitrogen ultrasonic freeze-thaw exfoliation technique; achieves dimensional transformation from nanosheets to quantum dots via solvothermal methods; and further endows quantum dots with new functional properties through a thiourea doping strategy. These preparation protocols, validated by SCI publications, provide a replicable materials engineering paradigm for cutting-edge fields such as photoelectrocatalysis and biosensing.

Ultrasonic Two-Dimensional Material Exfoliator

Preparation of Hexagonal Boron Nitride Nanosheets

Using commercial h-BN with a particle size of 1 μm as the raw material, hexagonal boron nitride nanosheets (h-BNNSs) were prepared via liquid nitrogen ultrasonic freeze-thaw exfoliation. The specific experimental steps are as follows:

 

Weigh 0.3 g of h-BN powder and disperse it in a mixed solvent of water, anhydrous ethanol, and acetone (water:ethanol:acetone = 45:3:2). Ultrasonicate for 5 minutes to ensure uniform dispersion.

Transfer the mixture to a 50 mL plastic beaker and immerse it in liquid nitrogen for rapid freezing until completely solidified.

Transfer the fully frozen h-BN solid from step (2) to a SCIENTZ ultrasonic two-dimensional material exfoliator for ultrasonication until it completely melts into a solution.

Repeat steps (2) and (3) five times. After 5 cycles of freeze-thaw exfoliation, centrifuge the mixture at 1500 rpm for 10 minutes. Collect the supernatant to obtain the h-BNNSs solution, and dry it in a blast drying oven to yield h-BNNSs powder.

Preparation of Hexagonal Boron Nitride Quantum Dots

Using h-BNNSs prepared in the previous section as the precursor, and ethanol and N,N-dimethylformamide (DMF) as reaction solvents, boron nitride quantum dots (BNQDs) were synthesized via a solvothermal method. The detailed procedures are as follows:

 

Weigh two portions of 0.1 g h-BNNSs powder, dissolve them separately in 20 mL of anhydrous ethanol and 20 mL of DMF, and ultrasonicate each mixture in an ultrasonic two-dimensional material exfoliator for 3 hours.

Transfer the ultrasonicated mixtures to 50 mL stainless steel hydrothermal reactors with polytetrafluoroethylene liners. Place the reactors in a vacuum drying oven and heat to 180°C for 12 hours.

After the reaction, allow the reactors to cool to room temperature. Transfer the solutions to 50 mL centrifuge tubes and centrifuge at 10,000 rpm for 5 minutes. Collect the supernatants.

Filter the supernatants from step (3) through a 0.22 μm microporous membrane to obtain white and pale yellow solutions, which are the ethanol/BNQDs dispersion and DMF/BNQDs dispersion, respectively.

Preparation of Thiourea-Doped Hexagonal Boron Nitride Quantum Dots

Using thiourea as the dopant, h-BNNSs (prepared in the previous section) as the precursor, and DMF as the reaction solvent, thiourea-doped hexagonal boron nitride quantum dots (S-BNQDs) were synthesized via a one-pot solvothermal method. The specific steps are as follows:

 

Weigh 0.1 g of h-BNNSs powder and 0.05 g of thiourea, dissolve them in 20 mL of DMF, and ultrasonicate the mixture in an ultrasonic two-dimensional material exfoliator for 3 hours.

Transfer the ultrasonicated mixture to a 50 mL stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. Place the reactor in a vacuum drying oven and heat to 180°C for 12 hours.

After the reaction, allow the reactor to cool to room temperature. Transfer the solution to a 50 mL centrifuge tube and centrifuge at 10,000 rpm for 5 minutes. Collect the supernatant.

Filter the supernatant from step (3) through a 0.22 μm microporous membrane to obtain a white filtrate, which is the S-BNQDs dispersion.

 

All the aforementioned methods have been validated for effectiveness and have been published in academic papers.

 

The liquid nitrogen freeze-thaw exfoliation, solvent-regulated synthesis, and thiourea doping processes established in this study enable the precise preparation of functional quantum dots from micron-sized h-BN. Through standardized parameter control, the protocol effectively addresses issues such as excessive structural defects and size inhomogeneity in traditional methods, providing a stable and reliable material foundation for the development of advanced nano-optoelectronic devices. As laboratory-developed preparation strategies meet industrial demands, the future of two-dimensional materials is steadily taking shape.