2D Nanomaterials for Energy and Environmental Sustainability

The evolution of novel nanomaterials in the last decades has boomed the field of nanotechnology leading to the diversity of applications for sustainable growth. In the group of nanomaterials, the emerging two-dimensional (2D) materials are highlighted since the advent of graphene. This chapter introduces the 2D nanomaterials beyond graphene such as transition metal dichalcogenides, hexagonal boron nitride, 2D elemental nanomaterials (black phosphorus, borophene, silicene, etc.), MXenes, 2D perovskites, and metal oxides. Furthermore, this chapter systematically contributes to the synthesis approaches widely adopted for the growth of 2D nanomaterials. Discussions on the several types of bottom-up and top-down techniques, such as chemical vapour deposition, physical vapour deposition, plasma-enhanced chemical vapour deposition, wet chemical hydrothermal and chemical exfoliation methods, are addressed which have grown intense interest among the scientific as well as the industrial community. The 2D nanomaterials are considered as  thin-layered capable of providing a larger surface area for both physical and chemical interactions that enable their unique properties. Therefore, some of the attributes, such as the properties and characterizations related to the structural, optical, electronic, thermal, magnetic, and mechanical properties of different 2D nanomaterials, are discussed. Finally, as a concluding remark, the future aspects of 2D nanomaterials are covered.

The increasing global demand for energy in today’s world has led to the discovery of new generation nanomaterials to bridge the gap between energy demand and efficient energy production. Generally, the energy conversion is a continuous cycle of reform and reuse. There are several processes where the energy is received from one form (such as sunlight and heat) and can be converted to another form (mainly into electrical signals). To tinker with efficient energy conversions, the emergence of two-dimensional (2D) materials has led the grounds in improving the state-of-the-art energy conversion technologies. This chapter is therefore motivated from the astonishing signs of progress made by the new generation 2D nanomaterials which have placed a firm position for efficient energy conversion in optoelectronics, thermoelectrics, and water electrolysis for cost-effective production of pure hydrogen fuel. This chapter first focuses on the brief discussion on 2D nanomaterials (transition metal dichalcogenides, layers perovskites, and 2D metal–organic frameworks) highlighting the properties and surface modifications for performance-related systems. Special attention will be given to provide a profound understanding of the fundamental properties and reaction kinetics in energy conversion systems which is essential for the design of efficient energy devices. Secondly, the focus will be directed to the applications of 2D nanomaterials for efficient energy conversion where particularly the evolutionary progress in solar cells, electrochemical water splitting, and piezo/thermoelectric devices will be highlighted. Finally, the developmental opportunities and some strategies to address the challenges in these exciting 2D nanomaterials are summarized.

With the advent of twenty-first century, several modern technologies and devices became accessible to common people making dependence of our day-to-day activities indisputable. These devices require enormous amount of electrical energy to perform their task, while the energy supply depends on the charge/discharge behavior of the used material. Above circumstances motivated the quest for new and hybrid material for technological developments to cover the breach between demand and supply, where a variety of nanomaterials owing to their emergent properties proved themselves to be extraordinary for the purpose. Recently, 2D nanomaterials, for instance, graphene, conducting polymers (CP), transition metal compounds, etc., owing to their exceptional physio-chemical features and versatility have introduced themselves as a strong contender for energy related applications. These 2D nanomaterials attributed with modifiability, large surface area to volume ratio, durability and various unique electronic, electrochemical and optical properties due to different chemical interactions are being preferred over other nanomaterials of other dimensions. Though 2D nanomaterials have significantly made their explicit position in the energy storage device market but to comprehend their potential, more research and efforts are required, along with understanding the mechanistic involved in them. This chapter brings some valuable insight into different properties and applications of numerous 2D nanomaterials with a focus on the electrochemical properties and the involved mechanism.

The rise in industrialization and extensive agricultural practices have resulted in widespread release of toxic contaminants into surface and groundwaters. These include organic contaminants such as dyes, antibiotics, pharmaceuticals; inorganic contaminants such as heavy metal ions (HMIs) and biological contaminants. They are recognized to pose adverse effects on environment as well as humans. To solve this problem, many researchers employed photocatalysis technique as the most favorable process for environmental remediation due to its cost-effectiveness and energy-saving.. Nowadays, various 2D nanomaterial-based photocatalysts are widely applied for the degradation of water contaminants using photocatalysis method. In this chapter, some of the potential 2D nanomaterial photocatalysts based on transition metal dichalcogenides (TMDs), MXenes and Phosphorene nanostructures with high surface/volume ratio, greater degradation efficiency, abundant active sites, compatible functional groups and diverse band structures are presented. This chapter concisely describes the impact of organic contaminants on living systems, followed by the synthesis and properties of 2D nanomaterial-based photocatalysts. The photocatalytic degradation of various dyes and antibiotics using 2D nanomaterial-based photocatalysts including the mechanistic pathway is also discussed. Finally, the future outlooks and challenges associated with the application of 2D nanomaterial-based photocatalysts in degradation are mentioned.

At present, the world is facing the most challenging environmental issues including air and water pollution due to rapid industrialization, indiscriminate increase in population and energy demands. To address these issues, adsorption techniques that are simple, efficient, cheap with less environmental impact are employed for capturing toxic gases and water pollutants. Two-dimensional (2D) nanomaterials are emerging as a new class of adsorbents in contrast to the traditional adsorbents. This could be attributed to their high surface area-to-volume ratio, atomic-level thickness, excellent mechanical strength and entirely accessible active sites. Recently, many scientists have vested their research interests in atomically thin 2D nanomaterial composites for a variety of applications such as removal of toxic gases and water treatment, to name a few. This chapter mainly focuses on the state-of-the-art development of novel 2D nanomaterials, namely metal nitrides (MXenes), phosphorene and transition metal dichalcogenides (TMDCs) as potential adsorbents for the adsorptive removal of toxic gases from the air, and organic dyes, and heavy metal ions (HMIs) removal from aqueous media. At first, the synthesis and properties of various types of 2D nanomaterial composites used for the adsorptive removal of water pollutants and toxic gases are reviewed and outlined in brief. Then, the removal of HMIs, organic dyes, and toxic gases using different 2D nanomaterials composites are discussed in detail. The chapter finally concludes with current challenges and future research needed to further advance the development of novel 2D nanomaterial composites for environmental remediation.

In this century, water scarcity is one of the most crucial issues to be resolved. A practical substitute for resolving this problem is seawater desalination. Membrane-based technologies (e.g., membrane distillation, reverse osmosis, and pervaporation) are compelling and sufficiently proposed for water desalination purposes. However, polymers face some issues like degradation and low penetrability of water and increase energy consumption and overall water desalination costs. 2D nanoporous materials such as graphene oxide, MXenes, metal organic frameworks (MOFs), transition metal dichalcogenides (TMDCs), boron nitrides nanosheets, zeolite, MoS₂, etc., with large surface area, mechanical strength, and having atomically thin structure are regarded to be the ideal substitution for water purification and desalination. 2D nanomaterials-based membranes have been used to increase the membrane's overall performance in desalination and water purification. Nevertheless, these nanomaterials’ exceptional properties can lower the energy consumption and increase the efficiency for desalination, which led to the immense attempt in fabrication and commercialization. Here, we have discussed the synthesis, properties, and water purification/desalination performance of 2D nanomaterials-based membranes.

Environmental protection from ever-increasing pollution represents the most formidable challenge in this era of technological expansion. With the aim of efficient monitoring and detection of hazardous pollutants, various rapid and effective sensory devices have been designed. The newly emerged 2D nanomaterials, beyond graphene, such as transition metal compounds (TMDs, TMOs, etc.), MXenes, metal–organic frameworks (MOFs), phosphorene are some good candidates to serve as efficient sensing platforms as they possess superior physicochemical characteristics which are necessary for sensing applications. Additionally, they provide flexibility toward the modern fabrication technology required to fulfill the demand for next-generation high-performance electrochemical sensors. The mass and electron transport kinetics of 2D nanocomposite electrodes and their interaction mechanism with analytes is mainly governed by electrical conductivity, electrochemical activity, surface chemistries, and active sites. In this chapter, the recent advancements in 2D nanomaterials-based electrochemical sensors for the monitoring of air and water quality have been overviewed. The underlying working principles of different electrochemical sensing techniques followed by the key factors responsible for selectivity and sensitivity are outlined. Then, the performance of different 2D nanocomposite-based electrochemical sensors, in particular, for the detection of various hazardous gases, heavy metal ions, and other inorganic/organic contaminants, etc., have been highlighted.

Biological contaminants have always been posing a threat to human health and environment. The contaminants like bacteria, viruses, protozoa, fungi, and parasites have evolved to adapt and multiply in different environments leading to inevitable consequences. There is a paramount need to detect and isolate these biological contaminants from air, water, and food with good selectivity and sensitivity. The developed systems that are based on the process of adsorption of contaminants mostly use conventional chemical treatments. However, these systems are not efficient due to the associated disadvantages of low sensitivity, low adsorption capacity, receptive to biofouling, to mention a few. Recently, various 2D nanomaterials have emerged as the material of choice to overcome these issues. Graphene-based nanomaterials are well known for their capability to detect biological contaminants in the environment. These 2D nanomaterials are reported to have high specificity, great adsorption capacity, and antimicrobial activity due to their characteristic structural features. Other 2D nanomaterials like transition metal dichalcogenides (TMDs), Mxenes, silicene, germanene, and phosphorene provide promising alternatives. This chapter discusses the role of different 2D nanomaterials and their composites as new alternatives for the detection and removal of biological contaminants.

Two-dimensional (2D) material is currently a major focus in materials science research with significant efforts made on synthesis, property characterization, and technological application. These materials come in wide varieties of chemical compositions and forms which enable its suitability for application in the areas of electronics, sensors, coatings, barriers, energy storage and conversion, and biomedicine. Application of synthetic 2D nanosheets for biomedical applications including human health has been envisaged by studying the biological and environmental interactions. 2D materials exhibit wide range of behaviors, reflecting the diversity in their chemical compositions, and undergo reactive dissolution processes which are critical for understanding their behaviors and interpreting the biological response data. This review attempts to cover up-to-date account on the contemporary literature in biological responses with reference to 2D materials. This also focuses on the mesoporous silica nanoparticles in order to provide insight into its essential chemical behavior and application. The review attempts to construct a framework for detailed investigation on biological evaluation of nanomaterials. It describes a series of methodology for high-priority research in the areas like the interface of cancer chemotherapy which could generate opportunities for safe and successful development of technologies related to 2D nanomaterials.

Agriculture is one of the major concerns that are associated with sustainability and human health. The change in climatic conditions and an increasing global hunger has imposed a profound challenge on the agricultural practices. There are many reports where nanomaterials driven advancement in various agriculture practices seem to be an answer to these problems. Nanomaterials (NMs) offer amazing prospects for crop improvement leading to an increased agricultural productivity. Development of nanotechnology-based novel agro-products, viz., nanosensors, nanofertilizers, nanopesticides and nanoformulations of biocontrol agents, is currently a subject of intensive investigation. Two-dimensional (2D) nanomaterials, in particular, offer significant capabilities that stem from their intrinsic properties of high surface area enabling a high loading capacity, on-target delivery, bioavailability and protection from enzymatic degradations. 2D NMs such as graphene, TMDs and MXenes are administered as nanoformulations into plants that reduces the use of agrochemicals and nutrient losses and increases the yield through optimized water and nutrients management. Sensors designed from 2D NMs can help to monitor the quality of soil, nutrient level and presence of toxic chemicals in agricultural fields. There is no doubt that the sustainable growth of agriculture completely depends on the new and innovative techniques offered by 2D NMs. This chapter discusses the different types of 2D NMs and their role in providing sustainable agriculture practices by exploring research that shows the application of nanotechnology in agriculture.

Two-dimensional (2D) nanomaterials are considered to have a great potential for applications in various fields such as electronics, energy, sensors and biotechnology. Many consumer products using 2D nanomaterials are already in the market. Therefore, it is of utmost importance to understand the toxicity of these nanomaterials for human and environmental safety. Toxicity level of nanomaterials varies depending upon their shape, size, composition as well as their tendency to conjugate with other biological systems. Therefore, each nanomaterial should be studied in detail by considering all the aspects and parameters to determine their toxicity. However, this process is time consuming, and hence, very few literatures are available on toxicity of nanomaterials except the most common ones. Most of the 2D nanomaterials are observed to produce oxidative stress to generate cytotoxicity. Level of toxicity is also different with varying cell lines. They are also observed to impact on germination of seeds of various plant species as well as reproduction of aquatic organisms. This chapter summarizes the exposure, mechanism and level of toxicity of some popular 2D nanomaterials in the environment and human body. It further discusses different physicochemical properties that govern the toxicity of 2D nanomaterials.

The emergence of atomically thin-layered 2D-nanomaterials such as transition metal compounds (TMDs, TMOs, TMHs), MXenes (transition metal carbides/carbonitrides/nitrides), elemental 2D analogs (silicene, germanene, phosphorene, etc.), 2D organic frameworks (MOF, COF), in succession to pioneer graphene promises a significant step forward in shaping the energy and environment sustainability. Their intriguing features such as a large surface area, chemical stability, strong mechanical strength, hydrophilic nature, biocompatibility, and ease of structural tunability offer fabrication of novel advanced functional composites and devices to combat energy and environmental challenges. 2D nanomaterials are reported as excellent electrode materials to design high-performance supercapacitors, batteries, and solar cells. They also hold enormous potential for catalytic degradation, adsorption, and sensing of varied pollutants, for instance, organic dyes, heavy metals, pesticides, antibiotics, and even toxic gases. In addition, they have been realized as efficient functional membranes in desalination. Furthermore, they are extensively exploited in drug delivery and other healthcare applications. Recently, they are also being explored as smart tools in the agriculture sector for nutrient delivery, disease detection, pest control, etc. Nevertheless, there are many unresolved issues that need to be addressed in their various fields of application. Therefore, this chapter brings an insightful overview on the technological challenges as associated with 2D nanomaterials and future research perspectives to encourage further evolution in the field of energy and environment. In addition, it summarizes some of the latest patented research/products/devices that have been developed in recent times to realize the use of 2D nanomaterials at commercial scale.