Dibakar Das

Effect of Er doping on the structural and magnetic properties of cobalt-ferrite

Nanocrystalline particulates of Er doped cobalt-ferrites CoFe(2−x)ErxO4 (0 ≤ x ≤ 0.04), were synthesized, using sol-gel assisted autocombustion method. Co-, Fe-, and Er- nitrates were the oxidizers, and malic acid served as a fuel and chelating agent. Calcination (400–600 °C for 4 h) of the precursor powders was followed by sintering (1000 °C for 4 h) and structural and magnetic characterization. X-ray diffraction confirmed the formation of single phase of spinel for the compositions x = 0, 0.01, and 0.02; and for higher compositions an additional orthoferrite phase formed along with the spinel phase. Lattice parameter of the doped cobalt-ferrites was higher than that of pure cobalt-ferrite. The observed red shift in the doped cobalt-ferrites indicates the presence of induced strain in the cobalt-ferrite matrix due to large size of the Er+3 compared to Fe+3. Greater than two-fold increase in coercivity (∼66 kA/m for x = 0.02) was observed in doped cobalt-ferrites compared to CoFe2O4 (∼29 kA/m).

Structural and ambient/sub-ambient temperature magnetic properties of Er-substituted cobalt-ferrites synthesized by sol-gel assisted auto-combustion method

Er-substituted cobalt-ferrites CoFe2−xErxO4 (0 ≤ x ≤ 0.04) were synthesized by sol-gel assisted auto-combustion method. The precursor powders were calcined at 673–873 K for 4 h, subsequently pressed into pellets and sintered at 1273 K for 4 h. X-ray diffraction (XRD) confirmed the presence of the spinel phase for all the compositions and, additional orthoferrite phase for higher compositions (x = 0.03 and 0.04). The XRD spectra and the Transmission Electron Microscopy micrographs indicate that the nanocrystalline particulates of the Er-substituted cobalt ferrites have crystallite size of ∼120–200 nm. The magnetization curves show an increase in saturation magnetization (MS) and coercivity (HC) for Er-substituted cobalt-ferrites at sub-ambient temperatures. MS for CoFe2O4, CoFe0.99Er0.01O4, CoFe0.98Er0.02O4, and CoFe0.97Er0.03O4 peak at 89.7 Am2/kg, 89.3 Am2/kg, 88.8 Am2/kg, and 87.1 Am2/kg, respectively, at a sub-ambient temperature of ∼150 K. HC substantially increases with decrease in temperature for al...

Magnetically recyclable Ni0.5Zn0.5Fe2O4/Zn0.95Ni0.05O nano-photocatalyst: Structural, optical, magnetic and photocatalytic properties

A novel visible light active and magnetically separable nanophotocatalyst, Ni0.5Zn0.5Fe2O4/Zn0.95Ni0.05O (denoted as NZF@Z), with varying amount of Ni0.5Zn0.5Fe2O4, has been synthesized by egg albumen assisted sol gel technique. The structural, optical, magnetic, and photocatalytic properties have been studied by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), fourier transform infrared spectroscopy (FTIR), UV-visible (UV-Vis) spectroscopy, and vibrating sample magnetometry (VSM) techniques. Powder XRD, TEM, FTIR and energy dispersive spectroscopic (EDS) analyses confirm coexistence of Ni0.5Zn0.5Fe2O4 and Zn0.95Ni0.05O phases in the catalyst. Crystallite sizes of Ni0.5Zn0.5Fe2O4 and Zn0.95Ni0.05O in pure phases and nanocomposites, estimated from Debye-Scherrer equation, are found to be around 15-25 nm. The estimated particle sizes from TEM and FESEM data are ∼(22±6) nm. The calculated energy band gaps, obtained by Tauc relation from UV-Vis absorption spectra, of Zn0.95Ni0.05O, 15%NZF@Z, 40%NZF@Z and 60%NZF@Z are 2.95, 2.72, 2.64, and 2.54 eV respectively. Magnetic measurements (field (H) dependent magnetization (M)) show all samples to be super-paramagnetic in nature and saturation magnetizations (Ms) decrease with decreasing ferrite content in the nanocomposites. These novel nanocomposites show excellent photocatalytic activities on Rhodamin Dye.

Silver nanoparticles embedded mesoporous SiO2 nanosphere: an effective anticandidal agent against Candida albicans 077

Candida albicans is a diploid fungus that causes common infections such as denture stomatitis, thrush, urinary tract infections, etc. Immunocompromised patients can become severely infected by this fungus. Development of an effective anticandidal agent against this pathogenic fungus, therefore, will be very useful for practical application. In this work, Ag-embedded mesoporous silica nanoparticles (mSiO2@AgNPs) have successfully been synthesized and their anticandidal activities against C. albicans have been studied. The mSiO2@AgNPs nanoparticles (d ∼ 400 nm) were designed using pre-synthesized Ag nanoparticles and tetraethyl orthosilicate (TEOS) as a precursor for SiO2 in the presence of cetyltrimethyl ammonium bromide (CTAB) as an easily removable soft template. A simple, cost-effective, and environmentally friendly approach has been adopted to synthesize silver (Ag) nanoparticles using silver nitrate and leaf extract of Azadirachta indica. The mesopores, with size-equivalent diameter of the micelles (d = 4-6 nm), were generated on the SiO2 surface by calcination after removal of the CTAB template. The morphology and surface structure of mSiO2@AgNPs were characterized through x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), particle size analysis (PSA), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) and high-resolution transmission electron microscopy (HRTEM). The HRTEM micrograph reveals the well-ordered mesoporous structure of the SiO2 sphere. The antifungal activities of mSiO2@AgNPs on the C. albicans cell have been studied through microscopy and are seen to increase with increasing dose of mSiO2@AgNPs, suggesting mSiO2@AgNPs to be a potential antifungal agent for C. albicans 077.

Mineral-Oxide-Doped Aluminum Titanate Ceramics with Improved Thermomechanical Properties

Investigations were carried out, on the effect of addition of kaolinite (2Al2O3·3SiO2·2H2O) and talc (Mg3Si4O10(OH)2) in terms of bulk density, XRD phases, microstructure, as well as thermal and mechanical properties of the aluminium titanate (AT) ceramics. AT ceramics with additives have shown enhanced sinterability at 1550°C, achieving close to 99% of TD (theoretical density) in comparison to 87% TD, exhibited with pure AT samples sintered at 1600°C, and found to be in agreement with the microstructural observations. XRD phase analysis of samples with maximum densities resulted in pure AT phase with a shift in unit cell parameters suggesting the formation of solid solutions. TG-DSC study indicated a clear shift in AT formation temperature with talc addition. Sintered specimens exhibited significant reduction in linear thermal expansion values by 63% (0.4210−6/C, (30–1000°C)) with talc addition. Thermal hysteresis of talc-doped AT specimens showed a substantial increase in hysteresis area corresponding to enhanced microcrack densities which in turn was responsible to maintain the low expansion values. Microstructural evaluation revealed a sizable decrease in crack lengths and 200% increase in flexural strength with talc addition. Results are encouraging providing a stable formulation with substantially enhanced thermomechanical properties.

Large magnetocaloric effect in hexagonal Yb1−xHoxMnO3

Magnetocaloric properties of polycrystalline hexagonal Yb1−xHoxMnO3 (x = 0.1, 0.2, and 0.3) compounds are studied through magnetization measurements. Temperature dependence of Zero Field Cooled magnetic moment measurements shows Neel temperature (TN1) of ∼83 K, corresponding to the Mn3+ antiferromagnetic ordering. At low temperatures (TN2 ∼ 5 K), all compounds show ferromagnetic ordering due to alignment of the Yb moments and the field induced magnetic transition is observed in the isothermal magnetization measurements. The maximum entropy change |ΔSMmax| and the relative cooling power (RCP) of Yb1−xHoxMnO3 are 3.75 ± 0.78 J/(mol K) and 90.0 ± 27 J/mol for x = 0.3 at ΔH = 100 kOe. Values of both |ΔSMmax| and RCP found to increase with increasing Ho content.

Studies on the magnetoelastic and magnetocaloric properties of Yb1−xMgxMnO3 using neutron diffraction and magnetization measurements

We report the magnetic ordering and magnetoelastic coupling of polycrystalline hexagonal Yb1−xMgxMnO3 (x = 0.00 and 0.05) compounds by using neutron diffraction measurements. The magnetocaloric properties of these Yb1−xMgxMnO3 compounds are also studied using magnetization measurements. The temperature dependence of the lattice parameters (a and c/a ratio) and unit cell volume V show anomalous behavior near TN1 ∼ 85 K (the Mn ordering temperature) due to the magnetoelastic effect. Also all the Mn–O bond distances display considerable variation at TN1. Isothermal magnetization curves measured near the Yb long range ordering temperatures indicate a field induced magnetic transition with applied field. The isothermal magnetic entropy change (−ΔSM) is calculated from the magnetization curves measured for different temperatures. Values of maximum entropy change (−ΔSmaxM), the adiabatic temperature change (ΔTad) and the relative cooling power (RCP) for these compounds are found to be 3.02 ± 0.37 J mol−1 K−1, 8.6 ± 0.95 K and 41 ± 9 J mol−1 for x = 0.00, and 2.63 ± 0.36 J mol−1 K−1, 9.06 ± 0.96 K and 40.0 ± 10 J mol−1 for x = 0.05, respectively, for ΔH = 100 kOe. Rescaling of the −ΔSM vs. T curves for various fields fit into a single curve, implying the second-order phase transition.

Effect of zinc doping on magnetic and magnetoelastic properties of cobalt ferrite synthesized by autocombustion process

Zn-doped cobalt-ferrite, with nominal compositions Co1-xZnxFe2O4(0≤x≤0.3), were synthesized by a novel auto combustion technique. The structural properties of the Zn substituted ferrites have been characterized using x-ray diffraction (XRD). The as-synthesized powders were calcined at 800°C for 3 hrs and the powders were pressed into cylindrical pellets. Solid-state sintering at 1300°C for 12 hrs of the green pellets resulted in a single phase cubic-spinel structure, as observed and analyzed from the XRD spectra. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ± 15 kOe. Magnetoelastic properties were measured using strain gauge method in a pulsed field magnetometer. Effect of zinc doping on its magnetic and magnetoelastic properties of cobalt ferrite is discussed in this paper.

Structural, magnetic and magnetocaloric properties of hexagonal multiferroic Yb1−xScxMnO3 (x = 0.1 and 0.2)

We have studied the effect of Sc doping on the structural, magnetic and magnetocaloric properties of multiferroic Yb1−xScxMnO3 (x = 0.1 and 0.2). X-ray powder diffraction shows that both samples crystallize in the hexagonal phase with P63cm space group. The structural analysis shows a decrease in the lattice parameter a, a decrease in the cell volume of the hexagonal unit cell and a decrease in the average bond length between Mn–O, with Sc substitution. Magnetic measurements show that the Neel temperature (TN) increases from 90 K for x = 0.1 to 94 K for x = 0.2 samples. Isothermal magnetic curves show that the field variation in magnetization generates a metamagnetic transition. The maximum entropy change −ΔSmaxM and the relative cooling power (RCP) of Yb1−xScxMnO3 are found to be 2.46 ± 0.40 J mol−1 K−1 and 38.5 ± 9 J mol−1 for x = 0.1 and 1.87 ± 0.31 J mol−1 K−1 and, 30.1 ± 8 J mol−1 for x = 0.2 with ΔH = 10 T. The rescaled magnetic entropy change curves for different applied fields collapse onto a single curve for materials with second-order phase transitions.

Investigation on a smart nanocarrier with a mesoporous magnetic core and thermo-responsive shell for co-delivery of doxorubicin and curcumin: a new approach towards combination therapy of cancer

In this work, we report on the synthesis and characterization of a novel and smart nanocarrier with a mesoporous magnetic core and thermo-responsive shell for co-delivery of hydrophilic doxorubicin (Dox) and hydrophobic curcumin (Cur) as a combinational therapy for cancer treatment. The P(NIPAM-MAm) coated mesoporous Fe3O4 (MIO-P(NIPAM-MAm)) nanocomposite was prepared by in situ cross linked polymerization of NIPAM and MAm on the surface of pre-synthesized mesoporous Fe3O4 nanoparticles (MIO NPs) in the presence of an oxidizer and cross linker. MIO NPs were synthesised by co-precipitation method using CTAB as the sacrificial soft template. Different characterization techniques have been used to study the physicochemical properties of MIO NPs and the MIO-P(NIPAM-MAm) nanocomposite. Particle sizes of the MIO-P(NIPAM-MAm) nanocomposite estimated by TEM were found to be in between 200–500 nm. VSM results show MIO and MIO-P(NIPAM-MAm) nanocomposites to be superparamagnetic in nature. MIO-P(NIPAM-MAm) nanocomposites exhibited a lower critical solution temperature (LCST) of 41 °C, which is suitable for controlled drug delivery applications unlike pure PNIPAM based nanocarriers. The encapsulation efficiency of Dox and Cur were found to be 96% and 90% respectively. Temperature dependent release studies from MIO-P(NIPAM-MAm)-Cur-Dox indicated a slower release of drugs (both Dox and Cur) below LCST and a sustained release above LCST. Different mathematical models (such as zero order, first order, Higuchi and Korsmeyer–Peppas) were used to fit the experimental release profiles of both drugs. MTT assays on normal and HeLa cells demonstrated the non-toxic nature of the MIO-P(NIPAM-MAm) nanocomposite. The co-loaded MIO-P(NIPAM-MAm)-Cur-Dox nanocomposite exhibited higher in vitro anti-cancer activity compared to free Dox, free Cur, and a free Dox + free Cur mixture. Such a co-loaded smart delivery system could have potential for controlled and targeted drug delivery in cancer diagnosis.