Transition metal titanium (Ti) doped LaFeO3 nanoparticles for enhanced optical structural and magnetic properties

A series of LaFe1−xTixO3 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles have been successfully synthesized by simple co-precipitation technique. The synthesized samples (calcined at 800° C/3hr) were characterised for structural, optical and magnetic properties. Structural phase formation of the crystal shows orthorhombic planes of these samples phases. The average crystallite size (Dc) is decreasing with a dopant and found to be varying between ∼ 9 and 25 nm. Tailored surface morphology was analyzed using scanning electron microscope (FESEM) and transmission electron microscopes (TEM) with selected area electron diffraction pattern (SAED) also confirms the evolution of orthorhombic phases. Diffuse reflectance spectra (DRS) are recorded to evaluate the variation of optical band gap (Eg) upon titanium doping into the LaFeO3 system. The obtained results attributed that Eg values are increasing with dopant altering between 2.05 and 2.61 eV. The metal oxide (M - O) stretching vibrations and few functional groups are detected from infrared spectra (IR). The weak ferromagnetic behaviour is observed from hysteresis loop behaviour. Additionally, the large hysteresis loop behaviour induces no saturation up to 15 kOe in nanoparticles coercivity (Hc) and anisotropy constants (K1) are eventually decreasing with ‘x’ values

Noncovalent and Nonspecific Molecular Interactions of Polymers with Multiwalled Carbon Nanotubes

Polymer composites containing variable amounts of multiwalled carbon nanotubes (MWNTs) have been prepared using solution dispersion and melt-shear mixing. Various polymer composites with 1 wt % MWNTs have been found to dissolve homogeneously in organic solvents. The amount of polymer coated or wrapped MWNTs dissolved in the solution was quantified using UV-vis absorbance at 500 nm and the concentration ratio of [MWNTs]solution/[MWNTs]composite was close to 1. A nonspecific polymer adsorption through multiple-weak molecular interactions of CH groups with MWNTs in the composites has been identified through FTIR spectroscopy. The composites of polybutadiene with different wt % of MWNTs showed slight changes in the CH bending vibrations, indicating the presence of intermolecular CH-π interactions. The dissolution of various polymer composites containing low concentration of MWNTs in organic solvents was attributed to polymer coating on the MWNTs via noncovalent and nonspecific CH-π interactions. The dissolution of MWNTs in organic solvents using common polymers used in this study indicates that the coating or wrapping is a general phenomenon occurring between polymers and carbon nanotubes

Enhanced Polymer Grafting from Multiwalled Carbon Nanotubes through Living Anionic Surface-Initiated Polymerization

Anionic surface-initiated polymerization of ethylene oxide and styrene has been performed using multiwalled carbon nanotubes (MWNTs) functionalized with anionic initiators. The surface of MWNTs was modified via covalent attachment of precursor anions such as 4-hydroxyethyl benzocyclobutene (BCBEO) and 1-benzocyclobutene-1′-phenylethylene (BCB-PE) through Diels-Alder cycloaddition at 235 °C. Surface-functionalized MWNTs-g-(BCB-EO) n and MWNTs-g-(BCB-PE) n with 23 and 54 wt % precursor initiators, respectively, were used for the polymerizations. Alkoxide anion on the surface of MWNTs-g-(BCB-EO) n was generated through reaction with potassium triphenylmethane for the polymerization of ethylene oxide in tetrahydrofuran and phenyl substituted alkyllithium was generated from the surface of MWNTs-g-(BCB-PE) n using sec-butyllithium for the polymerization of styrene in benzene. In both cases, the initiation was found to be very slow because of the heterogeneous reaction medium. However, the MWNTs gradually dispersed in the reaction medium during the polymerization. A pale green color was noticed in the case of ethylene oxide polymerization and the color of initiator as well as the propagating anions was not discernible visually in styrene polymerization. Polymer grafted nanocomposites, MWNTs-g-(BCB-PEO) n and MWNTs-g-(BCB-PS) n containing a very high percentage of hairy polymer with a small fraction of MWNTs (\u3c1 wt %) were obtained. The conversion of ethylene oxide and the weight percent of PEO on the surface of the MWNTs increased with increasing reaction time indicating a controlled polymerization. The polymer-grafted MWNTs were characterized using FTIR, 1H NMR, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy (TEM). Size exclusion chromatography of the polymer grafted MWNTs revealed broad molecular weight distributions (1.3 \u3c Mw/Mn \u3c 1.8) indicating the presence of different sizes of polymer nanocomposites. The TEM images showed the presence of thick layers of polymer up to 30 nm around the MWNTs. The living nature of the growing polystyryllithium was used to produce diblock copolymer grafts using sequential polymerization of isoprene on the surface of MWNTs

Well-Defined Poly(4-vinylbenzocyclobutene): Synthesis by Living Anionic Polymerization and Characterization

Living anionic polymerization of 4-vinylbenzocylobutene was performed in benzene at room temperature using sec-butyllithium as the initiator. Results of the kinetic studies indicated the termination- and transfer-free nature of the polymerization. Homopolymers with predictable molecular weights and narrow molecular weight distributions were produced, excluding the interference of the cyclobutene rings during initiation and propagation. Thermogravimetric analysis of poly(4-vinylbenzocyclobutene) in air showed a small weight gain at ~200 °C, a rapid decomposition at ~455 °C, and a gradual decomposition at ~566 °C. This behavior was attributed to the formation of radicals from the pendent benzocyclobutene functionality through o-quinodimethane intermediates and simultaneous decomposition/cross-linking reactions at high temperature. The living nature of the polymerization was also examined via sequential copolymerization with butadiene to form diblock copolymers

Controlled Covalent Functionalization of Multiwalled Carbon Nanotubes using [4 + 2] Cycloaddition of Benzocyclobutenes

Surface modification of carbon nanotubes (CNTs) through covalent functionalization is vital for the development of high-performance composite materials, chemosensors, nanoelectronics, photovoltaic devices, as well as for a range of biomedical applications. Several methods have been developed to functionalize CNTs. The introduction of acid groups by acid digestion disrupts the structural integrity of CNTs. Apart from shortening the tubes, oxidatively generated acid groups are inhomogenously located at the tips of broken CNTs and, hence, functionalization using acid groups as precursors does not give a statistical distribution of functional groups throughout the surface of the CNTs

Carbon Nanotubes with Covalently Linked Porphyrin Antennae: Photoinduced Electron Transfer

Functionalization of carbon nanotubes through surface modification has attracted significant interest recently. Covalent and noncovalent functionalization strategies involving reactions of organic or polymeric molecules onto carbon nanotubes have primarily focused on dispersion or dissolution properties. Incorporation of light absorbing antenna chromophores through a covalent linkage with the extended π electrons of a carbon nanotube would constitute an ideal supramolecular nanoassembly for generating singlet excited energy and its conversion to chemical energy. Porphyrins are one such class of molecules used in assemblies of donor-acceptor materials in molecular electronics and photovoltaic devices. Several fullerene-based molecular systems with covalently linked porphyrins and metalloporphyrins have been synthesized; their interesting photoinduced electron-transfer processes have been studied. Noncovalent interaction of metalloporphyrins and freebase porphyrins with single-wall carbon nanotubes (SWNTs) has been used for dispersion and also for separation of semiconducting and metallic tubes. Recently, a noncovalently interacting donoracceptor system consisting of an anionically functionalized porphyrin and a cationically functionalized pyrene stacked on SWNTs has been shown to exhibit electron-transfer properties. A donor-acceptor system with a covalent linkage between the light-harvesting antenna and the acceptor reaction center could enhance the efficiency of photoinduced electron transfer and energy transfer. Supramolecular structures consisting of covalently grafted porphyrins to carbon nanotubes have not been synthesized so far as an efficient donor-acceptor system. In this communication, we report the synthesis of meso-substituted porphyrin-grafted carbon nanotubes ((por)n-g-CNTs), including multiwalled nanotubes ((por)n-g- MWNTs) and SWNT ((por)n-g-SWNTs), and the study of their photoinduced electron-transfer properties

Inimer Mediated Synthesis of Hyperbranched Polyglycerol via Self-Condensing Ring-Opening Polymerization

A series of hyperbranched polyglycerols (HPGs) have been synthesized using glycol as an initiator in the presence of potassium counterion ([K⁺]₀/[−OH]₀ = 0.75) and employing batch monomer addition (BMA) to obtain insight into the kinetics of the polymerization. The first-order time–conversion plots show that the polymerization is fast up to ∼200 min, and the rate decreases substantially with increasing reaction time. Size exclusion chromatography of the HPGs during the polymerization indicates the presence of two living species in the reaction: a large fraction that grows into oligomers (<3000 g/mol) and becomes stabilized at higher conversion and a small fraction, growing faster and able to sustain a larger degree of polymerization (>140 000 g/mol). ¹³C NMR of the oligomer HPG shows signals corresponding to epoxy ring headgroup at 45.1 and 52.0 ppm and confirms the formation of epoxy anion, an inimer, via intermolecular proton transfer from glycidol. Self-condensing ring-opening polymerization of epoxy inimer produces ill-defined hyperbranched inimer–oligomers in high yield along with a small fraction of high molecular weight HPG that propagates without significant transfer to glycidol. The differential scanning calorimetry analysis shows the HPG exhibited two distinct <i>T</i>_gs (<−50 and >−20 °C) indicating the oligomer and high molecular weight fractions are immiscible, which is attributed to conformational constraint of two different types of branching. A mechanism of the formation of HPGs is proposed involving inimer-mediated equilibrium between oligomers and high molecular weight HPGs. The slow monomer addition (SMA) protocol was employed to reveal the existence of inimers during the reaction, supporting the proposed mechanism