1. Introduction

Two-dimensional materials (2D materials) are materials with a single or few layers of atomic thickness. Since the first successful isolation of graphene, 2D materials have become a hotspot for nanomaterials research due to their unique physical and chemical properties. Graphene has triggered extensive research interest with its excellent mechanical strength and electrical conductivity, which has driven in-depth studies of other 2D materials such as transition metal dichalcogenides (TMDs), black phosphorus, and borophene. These materials exhibit tunable band gaps and strong optoelectronic interactions, showing great potential in fields such as nanoelectronics, optoelectronic devices, energy storage, and biomedicine[1].

This paper systematically reviews and analyzes the basic properties of 2D materials, their main applications, and their future directions. Through a comprehensive literature review and case studies, the potential and challenges of 2D materials in various frontier fields are revealed. The research approach includes summarizing the major advances and issues in current 2D materials research and exploring their specific applications in nanoelectronics, optoelectronic devices, energy storage, and biomedicine. The significance of the research lies in understanding and addressing the current challenges, accelerating the practical application of 2D materials, and promoting scientific and technological progress and industrial development. This paper provides an up-to-date research review for academia and an important reference for industry in the development and application of 2D materials.

2. Basic Properties of Two-Dimensional Materials

2.1. Structure and Composition

Graphene, the first isolated 2D material, exhibits remarkable electronic properties due to electric field effects in thin films at the atomic level [2]. The crystal structure of graphene consists of hexagonal honeycomb planes formed by carbon atoms in sp2 hybridized orbitals, with each carbon atom bonded to three neighboring carbon atoms via σ-bonds, while the fourth valence electron forms a π-bond. This structure gives graphene unique electronic properties, such as high carrier mobility and the quantum Hall effect.

2.2. Electronic Properties

Transition metal dichalcogenides (TMDs) are promising materials for electronic and optoelectronic applications due to their tunable band gaps and strong photomatter interactions [3]. For example, MoS2 has a direct bandgap structure with a high absorption coefficient in the visible range, making it ideal for photovoltaic conversion applications. The bandgap of TMDs can be tuned by the number of layers, strain, and doping to meet the needs of different electronic and optoelectronic devices.

2.3. Mechanical Properties

Two-dimensional materials usually have excellent mechanical properties, and graphene is especially known for its extremely high strength and toughness. With a Young's modulus as high as 1 TPa and a breaking strength of about 130 GPa, graphene is one of the strongest materials known. These excellent mechanical properties give 2D materials a wide range of potential applications in flexible electronic devices and nanocomposites.

2.4. Optical Properties

2D materials exhibit unique properties in the field of optics, such as strong light absorption and luminescence properties. Graphene has broadband light absorption properties and can effectively absorb light from the ultraviolet to infrared wavelengths, while TMDs such as MoS2 exhibit strong photoluminescence properties, especially in the monolayer state. The optical properties of these materials can be modulated by external electric fields, strain, and doping, which provide new possibilities for optoelectronic device applications.

3. Main Application Areas of 2D Materials

3.1. Nanoelectronics

Graphene has attracted much interest in 2D materials due to its excellent mechanical strength and electrical conductivity. Graphene's high carrier mobility gives it great potential for use in high-speed electronic devices such as field effect transistors (FETs) and radio frequency (RF) devices. For example, IBM has developed graphene transistors that can operate at higher frequencies, paving the way for the next generation of high-speed computers and communication devices.

Single-layer MoS2 transistors show high switching ratios and mobility, highlighting their potential for applications in nanoscale electronic circuits. MoS2's bandgap is similar to that of silicon, making it an ideal replacement for silicon-based electronics. For example, single-layer MoS2 transistors have switching ratios as high as 10^8, which makes them promising for important applications in low-power electronic devices.

3.2. Photovoltaic Devices

TMDs have important application prospects in solar cells due to their tunable bandgap and high light absorption coefficient. For example, MoS2 and WS2 have been widely studied for making high-efficiency thin-film solar cells. These materials can significantly improve photoelectric conversion efficiency, reduce cost, and be suitable for flexible and wearable devices.

The unique optical properties of TMDs allow them to excel as photodetectors. They are able to detect optical signals over a wide spectral range with high sensitivity and fast response times, making them suitable for a wide range of photovoltaic applications. For example, MoS2-based photodetectors are able to operate at low light intensities, making them ideal for use in night-vision equipment and astronomical observations.

3.3. Energy Storage

2D materials exhibit excellent performance in lithium-ion batteries due to their large specific surface area and excellent electrical conductivity. For example, graphene and TMDs are used to make high-capacity and high-magnification electrode materials. These materials can significantly increase the energy density and charge/discharge rate of batteries and extend battery life.

Graphene-based supercapacitors have high energy and power densities, excellent charge/discharge performance, and a long cycle life, making them ideal for energy storage devices. For example, the charging time of graphene supercapacitors can be reduced to a few seconds, making them suitable for fast-charging devices and energy storage systems.

3.4. Biomedicine

Graphene and its derivatives have important application prospects in drug delivery. They have a high drug loading capacity and good biocompatibility and can be used in targeted drug delivery and controlled release systems. For example, graphene oxide nanosheets can be loaded with anticancer drugs to achieve efficient killing of cancer cells.

The high specific surface area and excellent electrical properties of 2D materials allow them to excel in biosensors. For example, graphene-based sensors can efficiently detect biomolecules such as DNA, proteins, and glucose with high sensitivity and a fast response time. For example, graphene-based glucose sensors can monitor the blood glucose level of diabetic patients in real-time.

4. Challenges and Solution Strategies for 2D Materials Research

4.1. Material Preparation

Mechanical exfoliation is one of the most important methods to prepare high-quality single or few-layer graphene and TMDs. This method is simple and efficient but difficult to produce on a large scale, so improvements are needed to increase productivity. For example, researchers are developing automated mechanical exfoliation equipment for large-scale production.

The chemical vapor deposition (CVD) method is a two-dimensional material preparation technique that is controllable and suitable for large-area production. By optimizing the reaction conditions, thin films of graphene and TMDs can be obtained with high quality and uniformity. For example, the CVD method has successfully prepared centimeter-scale single-crystal graphene for practical applications[4].

4.2. Performance Modulation

Doping and functionalization are effective means to modulate the properties of 2D materials. For example, the electronic and chemical properties of graphene can be modulated by doping nitrogen, boron, and other elements, thus improving its performance in the application of electronic devices and sensors. For example, nitrogen-doped graphene shows excellent catalytic activity in the oxygen reduction reaction and can be used in fuel cells and metal-air batteries[5].

Composites of 2D materials with other materials can significantly improve their performance. For example, composites of graphene with polymers show excellent performance in flexible electronics and energy storage devices. For example, graphene-polymer composites can be used to make high-strength lightweight aerospace devices[6].

4.3. Environmental and Health Safety

The environmental and biosafety of 2D materials are growing concerns. Studies have shown that certain 2D materials may be toxic under specific conditions, requiring in-depth toxicity assessments and safety studies. For example, graphene oxide is toxic to cells at high concentrations but shows good biocompatibility at low concentrations[7].

Two-dimensional materials may cause environmental impacts during their preparation and application. Green preparation techniques and environmentally friendly application strategies need to be developed to minimize negative environmental impacts. For example, researchers are developing aqueous phase stripping methods to replace organic solvents and reduce environmental pollution[8].

4.4. Toxicity Assessment

As the application of 2D materials expands, understanding their potential toxicity and long-term impacts on human health and the environment becomes crucial. Comprehensive toxicity studies are essential to evaluating the safety of 2D materials throughout their lifecycle. This includes assessing their impact on various biological systems, from cellular to organismal levels, and understanding their behavior in different environmental contexts.

Several approaches can be employed for toxicity assessment:

In vitro studies: These involve testing 2D materials on cell cultures to observe cytotoxicity, genotoxicity, and other cellular responses. For instance, studies on graphene oxide have shown varied cytotoxic effects depending on concentration and functionalization.

In vivo studies: Animal models are used to evaluate the biological impact of 2D materials, including potential inflammatory and immune responses. Long-term exposure studies help understand chronic effects and bioaccumulation.

Environmental impact assessments: These studies investigate the release, distribution, and degradation of 2D materials in natural environments. Understanding their interaction with soil, water, and air is crucial for developing mitigation strategies.

Addressing these challenges requires multidisciplinary collaboration and the development of standardized protocols for toxicity testing and environmental safety assessments. This will ensure that the benefits of 2D materials can be harnessed without compromising health and environmental integrity.

5. Future Development of Two-Dimensional Materials

Phosphorene, with high hole mobility, represents an exciting new direction in 2D semiconductor research. In the future, the discovery of more novel 2D materials will bring new opportunities and challenges to materials science. For example, new 2D materials such as silicene, germanene, and stannene show great potential in electronic and optoelectronic devices. The multifunctional properties of 2D materials give them great potential for integrated applications. For example, graphene-based composites can be used to fabricate high-performance flexible electronic devices and wearable devices. Graphene-based flexible sensors can be used to monitor human physiological signals in real-time for personalized medicine.

The commercialization of 2D materials is also promising with advances in preparation technology and cost reductions. For example, graphene has been used to make high-performance conductive inks and transparent conductive films. In addition, the applications of 2D materials in the fields of energy, environment, electronics, and biomedicine will continue to expand, bringing new opportunities for economic and social development.

6. Discussion

6.1. Conductive Inks and Transparent Films

Graphene-based conductive inks are being developed for applications in printed electronics, including flexible circuits, sensors, and touchscreens. These inks offer high conductivity, flexibility, and environmental stability, making them ideal for next-generation electronic devices. Transparent conductive films made from graphene can replace traditional indium tin oxide (ITO) films in displays and solar cells, providing a cost-effective and flexible alternative.

6.2. Energy Harvesting and Storage Solutions

2D materials are being integrated into energy harvesting devices, such as piezoelectric and thermoelectric generators, to improve efficiency and performance. In energy storage, advancements in 2D material-based batteries and supercapacitors are driving the development of high-performance, durable energy storage systems for electric vehicles, portable electronics, and grid storage.

7. Conclusion

In recent years, two-dimensional (2D) materials have attracted much attention in nanomaterials research due to their unique physical and chemical properties. This paper systematically reviews and analyzes the basic properties of 2D materials, their main application areas, and their future development directions. Through a comprehensive literature review and case studies, the potential and challenges of 2D materials in the frontier fields of nanoelectronics, optoelectronic devices, energy storage, and biomedicine are revealed. The findings show that although 2D materials such as graphene and transition metal disulfides (TMDs) excel in electronic, optical, and mechanical properties, they still face significant challenges in material preparation, property modulation, and environmental safety. This paper presents potential solutions and predicts future applications of 2D materials in emerging technologies. It is concluded that 2D materials will play a key role in science and industry as novel 2D materials continue to be discovered and technology advances. Overall, this study provides an up-to-date research review for academia and an important reference for industry in the development and application of 2D materials. Future research should aim to discover more novel 2D materials, develop multifunctional and integrated applications, and explore commercialization prospects. By addressing current challenges, the practical applications of 2D materials will be accelerated, advancing science and industry.