Chandan Borgohain

CoFe2O4–ZnS nanocomposite: a magnetically recyclable photocatalyst

A new synthesis of a CoFe2O4–ZnS magnetic nanocomposite has been achieved and used as an efficient photocatalyst in the degradation of methyl orange in water under UV irradiation. The photocatalyst is magnetically recoverable from the reaction medium and suitable for multiple uses with sustained catalytic activity.

Newly developed Fe3O4–Cr2O3 magnetic nanocomposite for photocatalytic decomposition of 4-chlorophenol in water

Chlorophenols, typically 4-chlorophenols are highly toxic and non-biodegradable organic contaminants which pose serious threat to the environment, particularly when released into aqueous medium. The removal of these pollutants by efficient method has received worldwide concern in recent past. A new Fe3O4-Cr2O3 magnetic nanocomposite was synthesized by wet chemical method under ultrasonic irradiation. Microstructure and morphology of the nanocomposite were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and a transmission electron microscope (TEM). Magnetic and optical properties were studied by a vibrating sample magnetometer (VSM) and an ultraviolet-visible (UV-Vis) spectrophotometer respectively. The magnetic nanocomposite (MNC) was used as photocatalyst for effective decomposition of 4-chlorophenol in water under ultraviolet (UV) irradiation.

CoFe2O4−Fe3O4 Magnetic Nanocomposites as Photocatalyst for the Degradation of Methyl Orange Dye

We report the investigation of temperature-dependent magnetic properties and photocatalytic activity of CoFe2O4−Fe3O4 magnetic nanocomposites (MNCs) synthesized by hydrothermal process. Room-temperature magnetic hysteresis (M-H) loops result enhanced saturation magnetization of 90 emu/g and coercivity (HC) of 530 Oe for CoFe2O4−Fe3O4 MNCs. With decreasing temperature to 20 K, HC increases from 500 Oe to 6800 Oe, and the M-H loops exhibit exchange coupling feature between CoFe2O4 and Fe3O4. Low- and high-temperature-dependent magnetization measurements confirm that the blocking temperature lies above 300 K and the presence of two magnetic phase transitions corresponding to CoFe2O4 and Fe3O4, respectively. The photocatalytic activity of the MNCs has been examined on the reduction of methyl orange (MO), a colored compound used in dyeing and printing textiles. The observed results suggest that the CoFe2O4−Fe3O4 MNCs act as an excellent photocatalyst on the degradation of organic contaminants and degrade 93% of MO in 5 hours of UV irradiation. The photocatalytic activity of MNCs is attributed to remarkably high band gap energy and small particle size. Also, the MNCs with a reproducible photocatalytic activity are well separable from water media by applying external magnetic field and acts as a promising catalyst for the remediation of textile wastewater.

Exchange bias effect in CoFe2O4-Cr2O3 nanocomposite embedded in SiO2 matrix

A nanogranular system composed of CoFe2O4-Cr2O3 core-shell nanoparticles (embedded in SiO2 matrix) having average particle size of 35 ± 5 nm was prepared by chemical synthesis. Structural characterizations by x-ray diffraction, Transmission Electron Microscope (TEM) show highly crystalline phase of these nanocomposites. High resolution TEM images show distorted and modified grain boundary region. CoFe2O4-Cr2O3 nanocomposites show excellent positive exchange bias effect after field cooling at 100 Oe of applied field. Both the exchange bias field and vertical shift in magnetization loop has been observed in this system below 300 K after field cooling. There is a positive loop shift of about 5 kOe along the field axis at 20 K in this system while the vertical shift is nearly 100% owing to the strong exchange bias effect. The exchange bias effect has been explained in terms of the different magnetic exchange interactions and modified grain boundary effect of CoFe2O4-Cr2O3 nanocomposites. The role of spin glas...

MICROSTRUCTURAL CHANGES UPON ANNEALING AND IT'S EFFECT ON MAGNETIC AND MECHANICAL PROPERTIES OF NANOSIZED COBALT–FERRITE

Nanocrystalline cobalt–ferrite particles of size 20–30 nm have been prepared by a reverse coprecipitation technique under the assistance of ultrasonic irradiation and heat-treatment at different temperatures (from 473 K to 1073 K). Both X-ray diffraction and transmission electron microscope analysis confirms the reduction of strain present in the material with annealing temperature. Enhancement of coercivity and magnetization value has been observed without increase in the particle size for whole range of annealing temperature. Temperature dependent magnetization loop shows considerable magnetic hardening at low temperature. The observed enhancement of the coercivity value has been attributed to the increase in magneto-crystalline anisotropy, surface effects and exchange anisotropy. The mechanical properties of the pure cobalt–ferrite samples and cobalt–ferrite reinforced alumina samples were also examined. The Vickers microhardness and the compressive properties obtained from the stress–strain relation showed higher value with annealing temperatures and higher nanoparticle content.

SYNTHESIS AND CHARACTERIZATION OF BIFUNCTIONAL CoFe2O4–ZnS NANOCOMPOSITE

The synthesis of composite magnetic nanomaterials has received increasing attention due to their electronic, magnetic, catalytic, and chemical or biological sensing properties. We have prepared cobalt ferrite–zinc sulfide nanocomposites by a chemical route. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and photoluminescence spectrometer (PL). The fluorescent magnetic nanoparticles (FMNPs) had a typical diameter of 30±5 nm and saturation magnetization of 5.8 emu g-1 at room temperature. So, these FMNPs may be potentially applied in different fields such as optoelectronic devices, biolabeling, imaging, drug targeting, bioseparation, magnetic fluid hyperthermia, etc.