Unzipping of Single-Walled Carbon Nanotube for the Development of Electrocatalytically Active Hybrid Catalyst of Graphitic Carbon and Pd Nanoparticles

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Tunable Hybridized Morphologies Obtained through Flash Joule Heating of Carbon Nanotubes

Hybrid carbon nanomaterials, such as those that incorporate carbon nanotubes into graphene sheets, have been found to display interesting mechanical and electrical properties because of their covalent bonding and π-π stacking domains. However, synthesis of these hybrid materials is limited by the high energetic cost of techniques like chemical vapor deposition. Here, we demonstrate the solvent- and gas-free synthesis of a 2D carbon nanotube/graphene network through flash Joule heating of pristine carbon nanotubes. The relative proportion of each morphology in the hybrid material can be tuned by varying the pulse time, as confirmed by Raman spectroscopy and microscopy. Triboindentation of epoxy composites made with the hybrid material shows increases of 162% and 64% to the hardness and Young's modulus, respectively, compared with the neat epoxy. These results demonstrate that flash Joule heating can be used to inexpensively convert carbon nanotubes into a hybrid network of nanotubes and graphene for use as an effective reinforcing additive in epoxy composites.

Reduced graphene oxide: Biofabrication and environmental applications

Green synthesis of high-quality reduced graphene oxide (rGO) from agro-industrial waste resources remains attractive owing to its outstanding environmental benefits. The remarkable properties of rGO include excellent morphology, uniform particle size, good optical properties, high conductivity, nontoxicity, and extraordinary chemical stability. Traditional methods for the synthesis of rGO nanomaterials involve several chemical reactions including oxidation, carbonization, toxic solvent, and pyrolysis which produce harmful byproducts. Green preparation of rGO is an emerging area of research in graphene technology which is cost-effective and sustainable in the procedure. Owing to the uniform particle rGO particle size, these smart nanomaterials have wide applicability, including in metal ions and pollutant sensing and adsorption, photocatalysis, optoelectrical devices, medical diagnosis, and drug delivery. Here we review the physicochemical properties of rGO, the biowaste sources and green methods of rGO synthesis, and the diverse applications of rGO, including in water purification and the biomedical fields. With this review, covering more than 200 research articles published on rGO in the last eight years ending in 2022, we aim to provide a quick guide for researchers seeking up-to-date information on the properties, production, and applicability of rGO, with special attention to rGO applications in water purification and the biomedical fields.

Hydrothermal Unzipping of Multiwalled Carbon Nanotubes and Cutting of Graphene by Potassium Superoxide

The dual use of potassium superoxide (KO₂) to unzip multiwalled carbon nanotubes (MWCNTs) and cut graphene under hydrothermal conditions is described in this work. The KO₂-assisted hydrothermal treatment was proven to be a high-yield method for forming graphene nanoribbons and dots or sub-micro-sized graphene nanosheets. Starting with functionalized MWCNTs, the method produces water-dispersible graphene nanoribbons with characteristic photoluminescence depending on their width. Using pristine graphene, the hydrothermal treatment with KO₂ produces nanosized graphene sheets and graphene quantum dots with diameters of less than 10 nm. The latter showed a bright white photoluminescence. The effective hydrothermal unzipping of MWNTs and the cutting of large graphene nanosheets is a valuable top-down approach for the preparation of graphene nanoribbons and small nanographenes. Both products with limited dimensions have interesting applications in nanoelectronics and bionanotechnology.

Emergence of carbon nanoscrolls from single walled carbon nanotubes: an oxidative route

Carbon nanoscrolls (CNS), a one dimensional (1D) helical form of carbon, have received enormous attention recently due to their unique structure, superior properties and potential applications. In this work, radial merging of HiPCO single walled nanotube (SWNT) bundles and emergence of CNS are reported following a reflux action involving wet oxidation, HCl washing and annealing at 900 °C. We observe macroscopic quantities of graphene sheets (GS) in the post-treated sample and beautiful manifestation of curling and folding of the GS into CNS. Here, a simple solution based oxidative route for successful merging and exfoliation of SWNT bundles and subsequent formation of CNS are demonstrated and discussed in view of Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies. Direct evidence of emergence of CNS from SWNTs via synthesis of GS through a simple oxidative method is reported for the first time.

Progress and Prospects on the Fabrication of Graphene-Based Nanostructures for Energy Storage, Energy Conversion and Biomedical Applications

Graphene, a two-dimensional (2D) layered material has attracted much attention from the scientific community due to its exceptional electrical, thermal, mechanical, biological and optical properties. Hence, numerous applications utilizing graphene-based materials could be conceived in next-generation electronics, chemical and biological sensing, energy conversion and storage, and beyond. The interaction between graphene surfaces with other materials plays a vital role in influencing its properties than other bulk materials. In this review, we outline the recent progress in the production of graphene and related 2D materials, and their uses in energy conversion (solar cells, fuel cells), energy storage (batteries, supercapacitors) and biomedical applications.

Enhanced osteogenic potential of unzipped carbon nanotubes for tissue engineering

Carbon nanotubes (CNTs) have attracted significant interest for various applications owing to their superior physicochemical properties. The unzipping of multi-walled carbon nanotubes was accomplished by strong acid treatment. The solution of unzipped carbon nanotubes (u-CNTs) was homogeneous and stable. The u-CNTs were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The dimensions and morphologies of the synthesized u-CNTs were examined by transmission electron microscopy and scanning electron microscopy. The u-CNTs exhibited increased zeta potential and diameter compared with pure CNTs. A decrease in the thermal stability was observed in the u-CNTs compared with pure CNTs. The u-CNTs exhibited better biocompatibility than pure CNTs in the presence of bone marrow-derived mesenchymal stem cells, showing improved biocompatibility. The u-CNT-treated media generated lower amounts of reactive oxygen species than pure CNTs. Enhanced mineralization was observed in the u-CNT-treated groups compared with the pure CNTs and the control, indicating its better osteogenic potential. The upregulation of osteogenic-associated gene markers in u-CNT groups compared with pure CNTs confirms their superior osteogenic potential. Thus, u-CNTs are potential candidates for tissue engineering applications, especially bone tissue.

Electrochemical Dealloying-Assisted Surface-Engineered Pd-Based Bifunctional Electrocatalyst for Formic Acid Oxidation and Oxygen Reduction

Synthesis of non-Pt bifunctional electrocatalyst for the anodic oxidation of liquid fuel and cathodic reduction of oxygen is of great interest in the development of energy conversion devices. We demonstrate a facile room-temperature synthesis of surface-engineered trimetallic alloy nanoelectrocatalyst based on Co, Cu, and Pd by thermodynamically favorable transmetallation reaction and electrochemical dealloying. The quasi-spherical Co _xCu _yPd _z trimetallic catalysts were synthesized by the thermodynamically favorable reaction of K₂PdCl₄ with sheetlike Co _mCu _n bimetallic alloy nanostructure. The surface engineering of Co _xCu _yPd _z was achieved by electrochemical dealloying. The surface-engineered alloy electrocatalyst exhibits excellent bifunctional activity toward formic acid oxidation reaction (FAOR) and oxygen reduction reaction (ORR) at same pH. The elemental composition and lattice strain control the electrocatalytic performance. The elemental composition-dependent compressive strain weakens the adsorption of oxygen-containing species and favors the facile electron transfer for FAOR and ORR. The engineered alloy electrocatalyst of Co_0.02Cu_13.8Pd_86.18 composition is highly durable and delivers high mass-specific activity for ORR and FAOR. It delivers mass-specific activities of 1.50 and 0.202 A/mg_Pd for FAOR and ORR, respectively, in acidic pH. The overall performance is superior to that of as-synthesized Pd and dealloyed bimetallic Co_2.7Pd_97.3 and Cu_5.61Pd_94.39 nanoelectrocatalysts.

Electrocatalytic Activities towards the Electrochemical Oxidation of Formic Acid and Oxygen Reduction Reactions over Bimetallic, Trimetallic and Core–Shell-Structured Pd-Based Materials

The structural design of nanosized electrocatalysts is extremely important for cathodic oxygen reduction reactions (ORR) and anodic oxidation reactions in small organic compounds in direct fuel cells. While Pt is still the most commonly used electrode material for ORR, the Pd electrocatalyst is a promising alternative to Pt, because it exhibits much higher electrocatalytic activity towards formic acid electrooxidation, and the electrocatalytic activity of ORR on the Pd electrode is the higher than that of all other precious metals, except for Pt. In addition, the mass activity of Pt in a core–shell structure for ORR can be improved significantly by using Pd and Pd-based materials as core materials. Herein, we review various nanoscale Pd-based bimetallic, trimetallic and core–shell electrocatalysts for formic acid oxidation and ORR of polymer electrolyte fuel cells (PEFCs). This review paper is separated into two major topics: the electrocatalytic activity towards formic acid oxidation over various Pd-based electrocatalysts, and the activity of ORR on Pd-based materials and Pd core–Pt shell structures.

Chemical Design of Palladium-Based Nanoarchitectures for Catalytic Applications

Palladium (Pd) plays an important role in numerous catalytic reactions, such as methanol and ethanol oxidation, oxygen reduction, hydrogenation, coupling reactions, and carbon monoxide oxidation. Creating Pd-based nanoarchitectures with increased active surface sites, higher density of low-coordinated atoms, and maximized surface coverage for the reactants is important. To address the limitations of pure Pd, various Pd-based nanoarchitectures, including alloys, intermetallics, and supported Pd nanomaterials, have been fabricated by combining Pd with other elements with similar or higher catalytic activity for many catalytic reactions. Herein, recent advances in the preparation of Pd-based nanoarchitectures through solution-phase chemical reduction and electrochemical deposition methods are summarized. Finally, the trend and future outlook in the development of Pd nanocatalysts toward practical catalytic applications are discussed.