Nanoscale self-assembly: concepts, applications and challenges

Self-assembly offers unique possibilities for fabricating nanostructures, with different morphologies and properties, typically from vapour or liquid phase precursors. Molecular units, nanoparticles, biological molecules and other discrete elements can spontaneously organise or form via interactions at the nanoscale. Currently, nanoscale self-assembly finds applications in a wide variety of areas including carbon nanomaterials and semiconductor nanowires, semiconductor heterojunctions and superlattices, the deposition of quantum dots, drug delivery, such as mRNA-based vaccines, and modern integrated circuits and nanoelectronics, to name a few. Recent advancements in drug delivery, silicon nanoelectronics, lasers and nanotechnology in general, owing to nanoscale self-assembly, coupled with its versatility, simplicity and scalability, have highlighted its importance and potential for fabricating more complex nanostructures with advanced functionalities in the future. This review aims to provide readers with concise information about the basic concepts of nanoscale self-assembly, its applications to date, and future outlook. First, an overview of various self-assembly techniques such as vapour deposition, colloidal growth, molecular self-assembly and directed self-assembly/hybrid approaches are discussed. Applications in diverse fields involving specific examples of nanoscale self-assembly then highlight the state of the art and finally, the future outlook for nanoscale self-assembly and potential for more complex nanomaterial assemblies in the future as technological functionality increases.

Electrochemical degradation of diclofenac using three-dimensional electrode reactor with multi-walled carbon nanotubes

The electro-oxidation treatment of aqueous solution containing diclofenac (DCF) on a Ti/RuO₂-TiO₂ electrode in the presence of multi-walled carbon nanotubes (MWCNTs) was studied in a three-dimensional electrochemical (3DE) reactor. The response surface methodology (RSM) based on central composite design (CCD) was utilized to determine the influence of different factors. The results revealed that the obtained polynomial experimental model had a high coefficient of determination (R² = 0.9762) based on analysis of variance. The optimum condition for the removal of DCF by the 3DE process was obtained with the initial pH of 3.8, the initial DCF concentration of 4 mg/L, the current density of 20 mA/cm², the particle electrode concentration of 70 mg/L, and the electrolysis time of 85 min. The quadratic model developed for DCF removal and subsequently the analysis of the F value illustrated that the initial pH was the most important factor in the removal of DCF. The comparative experiments between electrochemical processes showed the high electrocatalytic activity and removal efficiency of the 3DE reactor with the MWCNT particle electrode. The results also showed that the Ti/RuO₂-TiO₂ electrode, in addition to its high stability, had a very good electrocatalytic activity in the 3D reactor. The stability and reusability test proved that MWCNTs, as a particle electrode, had a potential to improve the long-term electrocatalytic degradation of DCF in the aqueous solutions. Based on the identified intermediate compounds along with the results of other studies, a possible pathway for the electrochemical oxidation of DCF by the 3DE process catalyzed with MWCNTs was proposed.

Oxidative cross-coupling reaction of catechols with active methylene compounds in an aqueous medium using an AlPO4-supported Ru catalyst

A green oxidative coupling reaction of catechols with active methylene compounds was achieved using an AlPO₄-supported Ru catalyst, where O₂ and H₂O were used as the ideal oxidant and solvent, respectively.

Multi-Stimuli-Responsive Polymeric Materials

Stimuli-responsive materials are of immense importance because of their ability to undergo alteration of their properties in response to their environment. The properties of such materials can be tuned by subtle adjustments in temperature, pH, light, and so forth. Among such smart materials, multi-stimuli-responsive polymeric materials are of pronounced significance as they offer a wide range of applications and their properties can be tuned through several mechanisms. Here, we aim to highlight some recent studies showcasing the multi-stimuli-responsive character of these polymers, which are still relatively little known compared to their single-stimuli-responsive counterpart.

Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

Controlling mesopore size and processability of transparent enzyme-loaded silica films for biosensing applications

Silica-based nanoporous thin films including large mesopores are relevant as enzyme supports for applications in biosensing. The diffusion and immobilization of large biomolecules such as enzymes in such porous films require the presence of large mesopores. Creating such morphologies based on a bottom-up synthesis using colloidal templates is a challenge in view of the combination of desired material properties and the robustness of the casting process for the fabrication of thin films. Here a strategy to reproducibly synthesize transparent porous silica thin films with submicrometer thickness and homogeneously distributed porosity is presented. For this purpose, polystyrene-poly-2-vinylpyridine (PS-P2VP) amphiphilic block copolymers are used as porogenic templates. Low-chain alcohols are employed as both selective solvents for the P2VP blocks and reaction media for silica synthesis. Rheology measurements reveal a strong influence of the block copolymer length on the behavior of PS-P2VP micelles in suspension. The pore distribution and accessibility into the film are controlled by adjusting the silica to block copolymer weight ratio. The solvent choice is shown to control not only the micelle size and the generated pore morphology but also the structural homogeneity of the films. Finally, the suitability of the synthesized films as supports for enzymes is tested using a model enzyme, horseradish peroxidase EC 1.11.1.7. Our approach is innovative, robust, and reproducible and provides a convenient alternative to synthesize large mesopores up to small macropores (20-100 nm) in nanostructured thin films with applications in biosensing and functional coatings.

Nanoarchitectured graphene-based supercapacitors for next-generation energy-storage applications

Tremendous development in the field of portable electronics and hybrid electric vehicles has led to urgent and increasing demand in the field of high-energy storage devices. In recent years, many research efforts have been made for the development of more efficient energy-storage devices such as supercapacitors, batteries, and fuel cells. In particular, supercapacitors have great potential to meet the demands of both high energy density and power density in many advanced technologies. For the last half decade, graphene has attracted intense research interest for electrical double-layer capacitor (EDLC) applications. The unique electronic, thermal, mechanical, and chemical characteristics of graphene, along with the intrinsic benefits of a carbon material, make it a promising candidate for supercapacitor applications. This Review focuses on recent research developments in graphene-based supercapacitors, including doped graphene, activated graphene, graphene/metal oxide composites, graphene/polymer composites, and graphene-based asymmetric supercapacitors. The challenges and prospects of graphene-based supercapacitors are also discussed.