Exfoliation mechanisms of 2D materials and their applications

Due to the strong in-plane but weak out-of-plane bonding, it is relatively easy to separate nanosheets of two-dimensional (2D) materials from their respective bulk crystals. This exfoliation of 2D materials can yield large 2D nanosheets, hundreds of micrometers wide, that can be as thin as one or a few atomic layers thick. However, the underlying physical mechanisms unique to each exfoliation technique can produce a wide distribution of defects, yields, functionalization, lateral sizes, and thicknesses, which can be appropriate for specific end applications. The five most commonly used exfoliation techniques include micromechanical cleavage, ultrasonication, shear exfoliation, ball milling, and electrochemical exfoliation. In this review, we present an overview of the field of 2D material exfoliation and the underlying physical mechanisms with emphasis on progress over the last decade. The beneficial characteristics and shortcomings of each exfoliation process are discussed in the context of their functional properties to guide the selection of the best technique for a given application. Furthermore, an analysis of standard applications of exfoliated 2D nanosheets is presented including their use in energy storage, electronics, lubrication, composite, and structural applications. By providing detailed insight into the underlying exfoliation mechanisms along with the advantages and disadvantages of each technique, this review intends to guide the reader toward the appropriate batch-scale exfoliation techniques for a wide variety of industrial applications

Switchable Intrinsic Defect Chemistry of Titania for Catalytic Applications

The energy crisis is one of the most serious issue that we confront today. Among different strategies to gain access to reliable fuel, the production of hydrogen fuel through the water-splitting reaction has emerged as the most viable alternative. Specifically, the studies on defect-rich TiO2 materials have been proved that it can perform as an efficient catalyst for electrocatalytic and photocatalytic water-splitting reactions. In this invited review, we have included a general and critical discussion on the background of titanium sub-oxides structure, defect chemistries and the consequent disorder arising in defect-rich Titania and their applications towards water-splitting reactions. We have particularly emphasized the origin of the catalytic activity in Titania-based material and its effects on the structural, optical and electronic behavior. This review article also summarizes studies on challenging issues on defect-rich Titania and new possible directions for the development of an efficient catalyst with improved catalytic performance

Metal Nanoparticles as Green Catalysts

Nanoparticles play a significant role in various fields ranging from electronics to composite materials development. Among them, metal nanoparticles have attracted much attention in recent decades due to their high surface area, selectivity, tunable morphologies, and remarkable catalytic activity. In this review, we discuss various possibilities for the synthesis of different metal nanoparticles; specifically, we address some of the green synthesis approaches. In the second part of the paper, we review the catalytic performance of the most commonly used metal nanoparticles and we explore a few roadblocks to the commercialization of the developed metal nanoparticles as efficient catalysts

Immunogenicity of Externally Activated Nanoparticles for Cancer Therapy

Nanoparticles activated by external beams, such as ionizing radiation, laser light, or magnetic fields, have attracted significant research interest as a possible modality for treating solid tumors. From producing hyperthermic conditions to generating reactive oxygen species, a wide range of externally activated mechanisms have been explored for producing cytotoxicity within tumors with high spatiotemporal control. To further improve tumoricidal effects, recent trends in the literature have focused on stimulating the immune system through externally activated treatment strategies that result in immunogenic cell death. By releasing inflammatory compounds known to initiate an immune response, treatment methods can take advantage of immune system pathways for a durable and robust systemic anti-tumor response. In this review, we discuss recent advancements in radiosensitizing and hyperthermic nanoparticles that have been tuned for promoting immunogenic cell death. Our review covers both preclinical and clinical results, as well as an overview of possible future work

Transforming collagen wastes into doped nanocarbons for sustainable energy applications

Leather industry produces huge quantities of bio-waste that can be used as raw material for the bulk synthesis of carbonaceous materials. Here we report the synthesis of multifunctional carbon nanostructures from pristine collagen wastes by a simple high temperature treatment. Our studies reveal that the nanocarbons derived from the bio-waste have a partially graphitized structure with onion-like morphology and are naturally doped with nitrogen and oxygen, resulting in multifunctional properties. This synthetic route from bio-waste raw material provides a cost-effective alternative to existing chemical vapor deposition methods for the synthesis of functional nanocarbon materials and presents a sustainable approach to tailor nanocarbons for applications such as battery electrodes

Structure, Properties and Applications of Two-Dimensional Hexagonal Boron Nitride

Hexagonal boron nitride (h-BN) has emerged as a strong candidate for two-dimensional (2D) material owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. Super-thin h-BN layers have gained significant attention from the scientific community for many applications, including nanoelectronics, photonics, biomedical, anti-corrosion, and catalysis, among others. This review provides a systematic elaboration of the structural, electrical, mechanical, optical, and thermal properties of h-BN followed by a comprehensive account of state-of-the-art synthesis strategies for 2D h-BN, including chemical exfoliation, chemical, and physical vapor deposition, and other methods that have been successfully developed in recent years. It further elaborates a wide variety of processing routes developed for doping, substitution, functionalization, and combination with other materials to form heterostructures. Based on the extraordinary properties and thermal-mechanical-chemical stability of 2D h-BN, various potential applications of these structures are described

Pseudobrookite based heterostructures for efficient electrocatalytic hydrogen evolution

Synthesis of ultrathin heterostructures has received much attention in the recent past due to their unique physical and chemical properties. In this work, we report the synthesis of Fe2TiO5–TiO2 heterostructures using a simple hydrothermal technique employing natural ilmenite as the source. Hierarchically arranged nanostructures with interconnected nano-petals of thickness around 50 ​nm are obtained. The electrocatalytic properties of the synthesized Fe2TiO5–TiO2 heterostructures are enhanced following the cathodization technique. The observed enhancement in the synthesized materials’ electrocatalytic property can be attributed to the defect-rich Fe2-xTiO5-x-TiO2-x heterostructures. The current approach and technique discussed in this work offer a simple method to synthesize a nanostructured heterostructure material and create defects for enhancing electrocatalytic activity

Luminescent hybrid biocomposite films derived from animal skin waste

The leather industry generates approximately ten million tons of solid bio-wastes that can be used to synthesize various multifunctional materials with exciting properties. One such approach involves developing advanced hybrid materials, which is considered one of the key areas but the underdeveloped materials science discipline. This work explored methods to use collagen derived from leather industry bio-wastes to form hybrid films via two different ways: to produce luminescent carbon dots (Cdots) and develop hybrid films. The polymeric collagen was mixed with Cdots and reduced graphene oxide (rGO) to create flexible composite films that exhibit improved thermal, mechanical, electrical, and luminescent properties. The Cdot films displayed enhanced luminescence. The Kubelka-Munk transformation of the diffuse reflectance reveals a massive increase in absorbance in the visible light region with the addition of rGO. Besides, the developed films displayed electrical conductivity and weak ferromagnetic characteristics and showed enhanced biocompatibility. These findings highlight new avenues for converting industrial bio-wastes into useful multifunctional materials in scalable and inexpensive ways, thereby diminishing environmental pollution and enhancing environmental sustainability