Sunil P. Lonkar

Recent advances in chemical modifications of graphene

Graphene has attracted the interest of chemists, physicists, and materials scientists due to its extraordinary structural, mechanical, and electronic properties. While pristine graphene is desirable for applications that require a high electrical conductivity, many other applications require modified or functionalized forms of graphene, such as graphene oxide, reduced graphene, or other functionalized forms. Structurally modifying graphene through chemical functionalization reveals the numerous possibilities for tuning its structure; several chemical and physical functionalization methods have been explored to improve the stabilization and modification of graphene. In this review, we report recent progress towards the chemical modification of graphene, including both covalent and noncovalent methods, for use in various applications.

Self photostabilizing UV-durable MWCNT/polymer nanocomposites

A potentially active hindered amine light stabilizer (HALS) was successfully anchored onto multiwalled carbon nanotubes (MWCNTs) and used as a light-stabilizing yet reinforcing multifunctional nanofiller to obtain UV-durable polymer nanocomposites. The influence of such light stabilizing MWCNTs on the photo-oxidation behaviour and structure-properties of polypropylene (PP) was studied. The composites were prepared by solution mixing of MWCNTs followed by melt compounding with polypropylene (PP). The resulting composite exhibits excellent UV-durability showing an almost 20 fold increase in the induction period of photo-oxidation. Moreover, the hydrophobic HALS was found to be compatibilizing enough to achieve homogeneous dispersion of exfoliated nanotubes into a polymer matrix. The rheological characterizations predict the formation of a percolated network structure. The obtained nanocomposites present markedly improved mechanical properties which underline the reinforcing ability of functionalized MWCNTs. Overall combination of HALS and MWCNTs offers an attractive route to combine multifunctionality into new hybrid UV-durable polymer nanocomposites. Such materials may possess great potential for outdoors high performance applications.

Antioxidant intercalated layered double hydroxides: a new multifunctional nanofiller for polymers

An antioxidant intercalated layered double hydroxide (A.O-LDH) nanohybrid system constructed using host–guest chemistry and employed as multifunctional nanofiller to fabricate highly durable polymer composites, namely polypropylene (PP) nanocomposites. The intercalated antioxidants efficiently prolonged the degradation in PP, their high hydrophobic nature facilitated the filler dispersion and simultaneously the mineral nano sheets observed to be reinforcing the polymer matrix. The A.O-LDH/PP nanocomposites were prepared using melt intercalation technique. Both X-ray diffraction and transmission electron microscopy measurements revealed a fine dispersion of A.O-LDH nanolayers into the polymer matrices. The rheological and dynamic mechanical analysis reveals the superior toughness for such hybrid materials. Moreover, the resulting composites exhibit enhanced thermal stability and photo-oxidative durability. The crystallization behavior in PP is also found to be positively altered by the presence of A.O-LDH.

A supramolecular approach toward organo-dispersible graphene and its straightforward polymer nanocomposites

Highly dispersible graphene nanosheets were straightforwardly synthesized by in situ reduction in the presence of hydroxyl-functionalized imidazolium ionic liquids as a supramolecular template. Therefrom, a biodegradable poly(e-caprolactone) (PCL)/graphene nanocomposite was prepared via a “grafting-from” approach based on the hydroxyl functionalities available from as-modified graphene nanosheets. The work opens up a path for a wide range of strategies in the fabrication of graphene/polymer nanocomposites.

One-Pot Microwave-Assisted Synthesis of Graphene/Layered Double Hydroxide (LDH) Nanohybrids

A facile and rapid method to synthesize graphene/layered double hydroxide (LDH) nanohybrids by a microwave technique is demonstrated. The synthesis procedure involves hydrothermal crystallization of Zn–Al LDH at the same time in situ reduction of graphene oxide (GO) to graphene. The microstructure, composition, and morphology of the resulting graphene/LDH nanohybrids were characterized. The results confirmed the formation of nanohybrids and the reduction of graphene oxide. The growth mechanism of LDH and in situ reduction of GO were discussed. The LDH sheet growth was found to prevent the scrolling of graphene layers in resulting hybrids. The electrochemical properties exhibit superior performance for graphene/Zn–Al LDH hybrids over pristine graphene. The present approach may open a strategy in hybridizing graphene with multimetallic nano-oxides and hydroxides using microwave method.

In situ formed graphene/ZnO nanostructured composites for low temperature hydrogen sulfide removal from natural gas

Nanostructured composites of graphene and highly dispersed sub-20 nm sized ZnO nanoparticles (TRGZ) were prepared via a novel method combining freeze-drying and thermal annealing. A direct synthesis implies thermal reduction of graphite oxide and in situ ZnO formation which acted as mutual spacers preventing restacking of the graphene layers and eventual aggregation of the nanoparticles at moderate temperatures. A series of compositions with different weight ratios of ZnO nanoparticles were prepared and used as a reactive sorbent in low temperature hydrogen sulfide (H2S) removal from natural gas. The composite sorbent having a ZnO mass ratio of 45.1 wt% showed a significantly greater H2S adsorption capacity (3.46 mmol g−1) than that of pure ZnO (1.06 mmol g−1), indicating that hybridization of ZnO with grpahene significantly improved the H2S removal ability. Such enhancement was mainly attributed to the higher surface area, greater pore volume and unique morphology at the nanoscale in the graphene–ZnO hybrid.

Applications of Graphene in Catalysis

The extraordinary and unique physical, chemical, and mechanical properties of graphene have led to the development of graphene-based materials for a wide range of applications in different fields. Amongst, the use of graphene-based materials in the field of catalysis has attracted the interests of researchers in the last few years. Due to its extremely high surface area and adsorption capacities, graphene is expected to function as an excellent catalyst support material. Moreover, an ability to tune its structure using desired functionalities have added significant versatility for such materials in metal free catalyst systems. The interest is due to the activity and stability of graphene based catalysts through tailoring its structures/morphologies, catalytic performance, and design for synthesis, catalytic mechanisms. This editorial note summarizes the versatile applications of graphene-based catalysts in organic synthesis as a carbocatalyst, metal free catalysis, in photocatalysis, and as a catalyst support and provides an outlook on future trends and perspectives for graphene applications in sustainable catalysis.

Nanostructured Three‐Dimensional (3D) Assembly of 2D MoS2 and Graphene Directly Build From Acidic Graphite Oxide

A 3D highly interconnected macroporous network of reduced GO having finely dispersed few-layered 2D MoS2 nanosheets was constructed through direct use of acidic graphite oxide (GO) for the first time. This facile and technologically scalable process can afford efficient hydrodesulfurization electrocatalysts as potential anode materials at lower cost, and can circumvent the poor thermal stability and recyclability of the material. The strategy provided here can be the basis to design and develop practical processes to address the ultimate goal of large-scale manufacturing of hybrids composed of 2D materials for various energy and catalysis applications.