Fabrication of Core-Shell-Structured Organic-Inorganic Hybrid Nanocatalyst for the Expedient Synthesis of Polysubstituted Oxazoles via Tandem Oxidative Cyclization Pathway

Recyclable magnetically retrievable nanocatalysts for C–heteroatom bond formation reactions

During recent years, magnetic separation has proven to be a highly indispensable and sustainable tool for facile separation of catalysts from the reaction medium with the aid of only an external magnetic force that precludes the requirement of energy intensive, solvent based centrifugation or filtration techniques. Extensive research in the area of catalysis has clearly divulged that while designing any catalyst, the foremost features that need to be paid due attention to include high activity, ready recoverability and good reusability. Fortunately, the magnetic nanocatalysts involving a superparamagnetic core material that could comprise of iron oxides such as magnetite, maghemite or hematite or mixed ferrites (CoFe2O4, CuFe2O4) have offered bright prospects of designing the ideal catalysts by proving their efficacy as strong support material that could be further engineered with various tools of nanotechnology and efficiently catalyze various C–heterobond formation reactions. This chapter provides succinct overview of all the approaches utilized for fabricating different types of magnetic nanoparticles and strategies adopted for imparting them durability. The prime forte however remains to exclusively showcase the applications of the various types of magnetic nanocatalysts in C–O, C–N, C–S and miscellaneous (C–Se, C–Te) bond formation reactions which are anticipated to benefit the synthetic community on a broad spectrum by helping them rationalize and analyze the key features that need to be taken into account, while developing these magical nanostructured catalytic systems for boosting the green bond formation reactions/transformations.

A sustainable gateway to access 1,8-dioxo-octahydroxanthene scaffolds via a surface-engineered halloysite-based magnetically responsive catalyst

A covalently modified, surface-engineered Cu(ii)@DCH@CPTMS@MHNT nanocatalyst is synthesized, which showed incredible catalytic activity in accessing a library of xanthene scaffolds.

A Promising Platform of Magnetic Nanofluid and Ultrasonic Treatment for Cancer Hyperthermia Therapy: In Vitro and in Vivo Study

Localized hyperthermia is a very promising cancer therapy approach especially when stimulated by the exceptional properties of iron oxide magnetic nanoparticles (MNPs). This approach is a highly site-specific method for localized heating of bodily tissue without any harmful side effects that could revolutionize the practice of cancer therapy. The main objective of this study was to evaluate the cancer cell-destroying capability of MNPs in combination with ultrasound treatment as an innovative sonomagnetic cancer therapy. Magnetic nanofluids (MNFs) were synthesized by co-precipitation/sonochemical techniques in an aqueous medium without any surfactant and/or capping agent. The physicochemical characteristics of the prepared MNFs were investigated with scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared and vibrating sample magnetometry. The MNFs was used as a mediator and sonosensitizer to destroy tumor tissue when irradiated by ultrasound waves. The antitumor efficiency of MNFs in combination with pulsed ultrasound (1.5 W/cm², 1 MHz) was evaluated in vitro and in vivo. In vitro efficacy was estimated by determining the cell viability of Ehrlich ascites carcinoma cells. For in vivo experiments, female mice were inoculated subcutaneously with Ehrlich carcinoma cells to establish solid Ehrlich carcinoma. The cytotoxic concentration of MNFs (400 µg/mL) was injected intratumorally and exposed to pulsed ultrasound (1.5 W/cm², 1 MHz). The cytotoxic effect was determined in terms of tumor growth rate, apoptosis and necrosis. Our results revealed that MNFs in the presence of pulsed ultrasound cause a significant increase in the cytotoxicity effect on tumor cells. This study illustrates the high efficiency of cancer therapy as assisted by both ultrasound and magnetic nanofluid.

Temporal control of RAFT polymerization via magnetic catalysis

Magnetic core–shell structured Fe₃O₄@Fe(ii)–MOF nanoparticles have enabled the temporal control of RAFT polymerization via an “on–off” process.

An FBG magnetic sensor for oil flow monitoring in sandstone core

Monitoring the oil movement using a non-contact optical fiber probe during enhanced oil recovery is a novel technique to increase the efficiency of the process by distinguishing the oil position in the reservoir. A partially unclad fiber Bragg grating (FBG) coated with Fe₃O₄ nanoparticles as a magnetic field sensor is experimentally demonstrated. A series of six FBGs reflecting different wavelengths are fixed on the surface of sandstone. Nanofluids containing magnetite nanoparticles and alkaline-surfactant-polymer are injected continuously in two separate steps into the sandstone, which is saturated with 20% oil and 80% brine. The chamber is equipped with a solenoid that acts as a magnetic field generator. The changes in the magnetic field strength depended on the FBG-solenoid distance and the density of localized injected nanoparticles near the FBGs leads to a shift of the reflected wavelength of each single FBG accordingly. The shift is caused by the interference of different propagating modes reflected from the core-cladding and cladding-magnetite layer interfaces. The intensity of the FBG spectra decreases by injecting the nanofluid and vice versa for surfactant injection. The sensor response time of ∼21 s confirms the high reliability and repeatability of the sensing scheme. Movement of oil along the sandstone alters the wavelength shift in the FBG spectra.

Monitoring the oil movement using a non-contact optical fiber probe during enhanced oil recovery is a novel technique to increase the efficiency of the process by distinguishing the oil position in the reservoir.

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.

Design and Exploration of Catalytic Activity of Two-Dimensional Surface-Engineered Graphene Oxide Nanosheets in the Transannulation of N-Heterocyclic Aldehydes or Ketones with Alkylamines

In this work, pharmaceutically and biologically important compounds containing imidazo[1,5-a]pyridine nuclei have been synthesized via transannulation of N-heteroaryl aldehydes or ketones with alkylamines using a graphene oxide-supported copper catalyst. The nanocatalyst was fabricated by the covalent immobilization of 4-aminoantipyrine onto an amine-functionalized graphene oxide nanosupport followed by its metallation with copper acetate. Structural analysis by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction demonstrates that the two-dimensional sheet-like structure of graphene oxide is maintained even after the chemical modifications, whereas XPS revealed crucial information related to elemental composition and surface electronic states of the metal present in the catalyst. Apart from this, Fourier transform infrared spectroscopy helped in identifying the degree of oxidation and the presence of oxygenated groups in graphene oxide nanocomposites. As a heterogeneous catalyst, this graphene oxide-supported copper complex showed moderate to good catalytic activity in the C(sp3)-H bond activation/amination of a variety of substrates. This superior catalytic performance originated from the unique 2-dimensional structure of graphene oxide-based material which provided space between graphitic overlayers due to appropriate positioning of metal on their basal planes, decreasing the diffusion resistances of reactant surfaces, thus making it function as a nanoreactor. More importantly, this nanomaterial could be recovered easily and reused repeatedly by simple washing without chemical treatment with no appreciable loss in its catalytic activity, showing good potential for increasing the overall turnover number of this synthetically useful catalyst.