G. Bishwa Bidita Varadwaj

Layered double hydroxide- and graphene-based hierarchical nanocomposites: Synthetic strategies and promising applications in energy conversion and conservation

The persistent need for a sustainable energy economy has led researchers to focus on novel energy conversion and storage technologies, inspiring the discovery of smart material designs such as hierarchical nanocomposites. These nanocomposites have proven effective in the advancement of energy-based technologies. The synergistic properties of hierarchical nanocomposites composed of two types of two-dimensional layered materials, layered double hydroxides and graphene, have resulted in improved electrochemical as well as photocatalytic performance. Synthetic strategies and their effect on the electrochemical and photocatalytic performance of these nanocomposites as high-performance supercapacitors and water oxidation catalysts are discussed in detail in this review.

Montmorillonite supported metal nanoparticles: an update on syntheses and applications

Montmorillonite is one of the most intensively explored supporting materials in materials chemistry. In addition to its low cost and eco-friendliness, interest mainly exists in its unique properties like cation exchange and swelling ability, thereby accommodating various guest species in its interlayers. While recognizing the tremendous interest in nanoparticles because of their fundamentally novel properties and functions, researchers have noticed that the performance of these nanoparticles can be greatly enhanced by their immobilization on various supports. The interlayer space of montmorillonite at the nanometre scale provides a very good platform to accommodate these nanoparticulates. This review provides an overview of the past developments in the field of montmorillonite supported nanometals. Thus, this review aims to cover numerous aspects of material syntheses, and various fields of applications in which these materials show their significant efficacies.

A stable amine functionalized montmorillonite supported Cu, Ni catalyst showing synergistic and co-operative effectiveness towards C–S coupling reactions

The objective of this work is to prepare a cheap and highly stable heterogeneous catalyst. This was done by a simple two step approach. The first step involved the preparation of an organic–inorganic hybrid material by covalent grafting of amines on K10 montmorillonite. In the second step the N atoms of the amine groups were co-ordinated to Cu and Ni ions. Both the covalent and co-ordination forces are strong enough to make the catalyst fairly stable during the catalytic runs. The amine functionalization was confirmed by 29Si CP MAS NMR spectroscopy, FTIR spectroscopy and XPS analysis. The XPS analysis revealed Cu and Ni were present in their +2 oxidation states. This bimetallic system was discovered somewhat by curiosity when Ni was added to a previously well-established Cu catalyzed C–S coupling reaction in an attempt to enhance the catalytic activity. When this catalyst was employed in the C–S coupling reaction, it showed wonderful activity with 99% product yield, due to the synergistic effect of the metal duo.

Facile fabrication of mesoporous iron modified Al2O3 nanoparticles pillared montmorillonite nanocomposite: a smart photo-Fenton catalyst for quick removal of organic dyes

A mesoporous iron modified Al2O3 nanoparticle pillared montmorillonite nanocomposite (mesoporous Fe/APM nanocomposite) was synthesized by using sodium exchanged montmorillonite by cation-exchange, gallery-templated synthesis and impregnation method. Formation of Al2O3 nanoparticles (Al2O3 NPs) having average particle size 5.20-6.50 nm within montmorillonite, formation of mesoporous Al2O3 NPs pillared montmorillonite (mesoporous APM) from montmorillonite and formation of a mesoporous Fe/APM nanocomposite signifies the present investigation. The roles of ammonia, CTAB, octyl amine and calcination temperature for fabrication of mesoporous Fe/APM nanocomposite were highly significant. Ammonia was used for post-synthesis treatment, which helped in the formation of micellar assemblies in the interlayer space. The materials were characterized by different techniques such as N2 adsorption-desorption study, which demonstrated the mesoporosity of the material. A transmission electron microscopy (TEM) image proves the morphology and size of the Al2O3 NPs and mesoporous Fe/APM nanocomposites. X-ray diffraction technique (XRD) describes the formation of the pillaring of the Al2O3 NPs within montmorillonite (APM). It has been noted that pure montmorillonite is a micro/mesoporous material. But after pillaring of Al2O3 NPs within the montmorillonite, mesoporosity developed, which is the vital aspect of present investigation. It was observed that the mesoporous Fe/APM nanocomposite has high photo-Fenton activity towards degradation of organic dyes such as acid blue (AB) and reactive blue (RB). Nearly 100% degradation took place within 30 minutes with high concentration of dye (500 mg L(-1)) by mesoporous 5 Fe/APM nanocomposite under ambient conditions. Small particle sizes of nanocomposite, quick reduction of Fe(III) and mesoporosity are the key points for proficient degradation of AB and RB.

Transforming inorganic layered montmorillonite into inorganic–organic hybrid materials for various applications: a brief overview

The covalent grafting of organic components over the surface of montmorillonite clay forming inorganic–organic hybrid materials is reviewed. The synthesis strategies based on the reaction of silanol groups on the clay surface with organosilane reagents and the roles of various reaction parameters in the formulation of these inorganic–organic hybrid materials have been discussed in detail. The multiple potential applications of these hybrid materials in technological applications, such as adsorption of environmental pollutants, nanocomposite synthesis, health care and catalysis, are overviewed briefly in this review.

Solvent‐Switchable Regioselective Synthesis of Aurones and Flavones Using Palladium‐Supported Amine‐Functionalized Montmorillonite as a Heterogeneous Catalyst

We report the use of Pd0APTES@K10 (APTES=(3‐aminopropyl)triethoxysilane) as a heterogeneous catalyst for the regioselective synthesis of aurones and flavones from the carbonylative cyclization of 2‐iodophenol with terminal alkynes. This work emphasizes the role of the solvent on the mode of cyclization, that is, 5‐exo or 6‐endo. The 5‐exo products (aurones) were predominant over the 6‐endo products (flavones) in 1,2‐dimethoxyethane (DME), and a reversal of regioselectivity was observed in DMF to favor the 6‐endo product. This protocol provides a simple one‐pot access to a wide variety of aurone and flavone derivatives under mild reaction conditions. The heterogeneous Pd0APTES@K10 catalyst was characterized using several techniques. Furthermore, the catalyst could be reused in up to four consecutive cycles without a significant loss in catalytic activity.

A critical review of the occurrence of perfluoroalkyl acids in aqueous environments and their removal by adsorption onto carbon nanotubes

The presence of perfluoroalkyl acids (PFAAs) in aquatic environments is a cause of concern, due to their toxicity, possible ecological impact and adverse effects in man. The release of these pollutants into receiving water bodies occurs primarily through the discharge of untreated wastewater and industrial effluents. Consequently, there is a need to remediate wastewater containing these compounds before its discharge. In this review, the occurrence of PFAAs in water streams is reviewed, with the aim of providing in-depth information on the harmful effects arising through exposure to these pollutants by both man and the environment. One viable strategy for the removal of PFAAs from wastewaters is adsorption. This technique is discussed in relation to a number of conventional adsorbents and they are compared with the behaviour of a more effective adsorbent, namely, carbon nanotubes (CNTs). In particular, various functionalization strategies can increase the efficiency of CNTs for the removal of PFAAs. Sorption of PFAAs onto CNTs demonstrates good removal efficiencies and equilibrium is attained faster than with conventional adsorbents. This is attributed to the inherent properties of CNTs, such as large surface area/porosity, and the ease with which new functional groups are introduced onto the walls of the tubes. The adsorption mechanism of PFAAs is primarily enhanced through electrostatic interactions; however, other intermolecular forces, such as hydrogen bonding, hydrophobic interactions and ion-exchange, also play a role. This review aims at providing information on the occurrence and fate of PFAAs and the interactions involved in their removal from aqueous solutions by CNTs.