Sonal Singhal

Tailoring the photo-Fenton activity of spinel ferrites (MFe2O4) by incorporating different cations (M = Cu, Zn, Ni and Co) in the structure

Magnetic bimetallic nanospinels (MFe2O4; M = Cu, Zn, Ni and Co) with sizes ranging between 15–30 nm were synthesized using a facile and viable sol–gel method. Fourier transform infrared spectral analysis of all the samples demonstrated the formation of M–O bond in the spinel structure. Structural exploration of all the nano materials using powder X-ray diffraction and high resolution transmission electron microscopy revealed the formation of a single phase cubic spinel structure. All the materials exhibited a magnetic temperament with high surface areas (92–151 m2 g−1). Furthermore, the band gaps calculated from the diffuse reflectance spectra were quite narrow (1.26–2.08 eV) for all the samples, hence the ferrites could act as visible light driven photocatalysts. The prepared nanospinels are proposed to be promising heterogeneous photo-Fenton catalysts under visible light for the degradation of organic pollutants. The catalytic results revealed that the rate of reaction was significantly influenced by the cation in the spinel structure as the degradation order was observed to be CuFe2O4 (k = 0.286 min−1) > ZnFe2O4 (k = 0.267 min−1) > NiFe2O4 (k = 0.138 min−1) > CoFe2O4 (k = 0.078 min−1). The reaction conditions were optimized for all the ferrites as the photodegradation was influenced by the ferrite dosage (0.25–1.00 g L−1), pH (2–5) and the H2O2 concentration (4–27 mM). The experimental data disclosed that the ferrite activity was sensitive to sintering temperature. The materials displayed remarkable stability in the reaction as they could be magnetically separated using an external magnet and recycled for up to 4 consecutive cycles. There was no significant loss in activity of all the materials, demonstrating the excellent ability of the ferrites to remove organic pollutants from wastewater.

CoMn0.2Fe1.8O4 ferrite nanoparticles engineered by sol–gel technology: an expert and versatile catalyst for the reduction of nitroaromatic compounds

Highly stable and magnetically recoverable CoMn0.2Fe1.8O4 ferrite nanoparticles with a large surface area were successfully engineered using the sol–gel technology and proposed as a heterogeneous catalyst for the reduction of nitroarenes. The morphological and physicochemical properties of the synthesized nanocatalyst were characterized using the powder X-ray diffraction technique, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, scanning electron microscopy. The nanoparticles were found to be highly porous and spherical with an average diameter of ∼20 nm. The lattice interplanar distance of 0.25, 0.24, 0.30, 0.20 nm determined by high resolution transmission electron microscopy completely agreed with the d-spacing values corresponding to the (3 1 1), (2 2 2), (2 2 0), (4 0 0) planes, respectively, provided by the XRD data. Magnetic characterization was performed using a vibrating sample magnetometer and the value of saturation magnetization was found to be 35.89 emu per g. The specific surface area was calculated using the BET method, which was determined to be 114.22 m2 g−1. Kinetic analysis for the reduction of 2-nitroaniline was performed using UV-visible spectroscopy. The reduction reaction followed pseudo first-order kinetics with respect to the concentration of nitroarene substrate. The pseudo first-order rate constant value was 0.74 min−1 in the presence of 10 mol% of the catalyst. The extent of catalytic activity was explored for various amino, bromo, chloro and methyl derivatives of nitroarenes and almost 100% selectivity and 100% conversions (confirmed by GC-MS) were achieved for all the analogs.

Substituted Co–Cu–Zn nanoferrites: synthesis, fundamental and redox catalytic properties for the degradation of methyl orange

Co0.6Zn0.4Cu0.2MxFe1.8−xO4 (M = Zn2+, Co2+, Ni2+ and Mn3+. x = 0.2, 0.4, 0.6 and 0.8) magnetically recyclable catalysts have been synthesized via a sol–gel auto combustion method. The structural and magnetic properties of the prepared samples were investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometry (VSM). The XRD analysis of the synthesized samples confirmed the formation of a single-phase cubic spinel structure and the average crystallite sizes of the nanoparticles estimated using the Debye–Scherrers equation were found to be 40–60 nm after annealing at 1000 °C (within an error of ±2 nm). The lattice constant increases with an increase in all metal ion substitution. The hysteresis curves of the samples exhibited reduction of the saturation magnetization and coercivity with substitution of all the metal ions in Co–Cu–Zn nano ferrites. The DC electrical resistivity decreased with an increase in temperature, indicating the semiconducting nature of the ferrite samples. Manganese substituted Co–Cu–Zn nanoferrites showed the best catalytic activity among all the magnetic nanoferrites. All the magnetic nanoferrites can be easily recovered by using a magnet and no decrease in the efficiency was observed after several consecutive rounds of reaction.

Facile protocol for reduction of nitroarenes using magnetically recoverable CoM0.2Fe1.8O4 (M = Co, Ni, Cu and Zn) ferrite nanocatalysts

Transition metal doped cobalt ferrite (CoM0.2Fe1.8O4 (M = Co, Ni, Cu, Zn)) nanoparticles were fabricated using the sol–gel methodology. The obtained ferrite nanoparticles were annealed at 400 °C and characterized using Fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), vibrating sample magnetometry (VSM) and energy dispersive X-ray (EDX) and scanning transmission electron microscopy (STEM). In the FT-IR spectra two bands in the range 1000–400 cm−1 were observed corresponding to the M–O bond in the tetrahedral and octahedral sites. XRD patterns confirmed the formation of a cubic spinel structure with a Fdm space-group. HR-TEM analysis revealed a quasi-spherical shape with particle sizes in the range 20–30 nm for all the synthesized ferrite nanoparticles. The lattice inter-planar distances of 0.29, 0.25, 0.21 and 0.16 nm obtained from HR-TEM corresponding to the (2 2 0), (3 1 1), (4 0 0) and (5 1 1) lattice planes respectively were in complete agreement with the XRD data. The EDX-STEM confirmed the elemental composition as per the desired stoichiometric ratio. The catalytic efficiency of the synthesized ferrite samples was explored for the reduction of nitrophenols. Cu substituted cobalt ferrite nanoparticles (CoCu0.2Fe1.8O4) possessed excellent catalytic activity while CoM0.2Fe1.8O4 (M = Co, Ni and Zn) were inactive for the same. The substrate scope of the developed protocol was also evaluated for the reduction of various CH3-, NH2-, Br-, Cl− etc. substituted nitroaromatic compounds.

Tuning the properties of cobalt ferrite: a road towards diverse applications

Cobalt ferrite has gained great scientific interest because of its unique properties and exceptionally promising applications. A large number of synthetic methods, such as sol–gel auto-combustion method, co-precipitation method, ball milling method, microemulsion method, polyol method, etc. have been used for its synthesis. Synthetic methodologies and heat treatment given to the sample strongly influence the particle size of the synthesized ferrite, which in turn determines its properties. In addition, the properties of cobalt ferrite can be altered by different chemical modifications such as substituting one or more ions from the lattice with some other metal ion, modifying the reaction conditions, compositing with different inorganic matrices etc. The most prominent influence on the properties of ferrites is exerted by variation in cation distribution. Among all the factors the major influence on the cation distribution is laid by doping. Guest metal ions according to their site preference occupy different lattice sites, thereby, changing the structural, magnetic, electrical and the catalytic properties of cobalt ferrite. In this review, we summarize the significant developments involving modifications in synthesis and properties of cobalt ferrite. This review also highlights the advances in the applications of cobalt ferrite in the fields of catalysis, biomedicine and sensors.

Enhanced Photocatalytic Degradation of Methylene Blue Using /MWCNT Composite Synthesized by Hydrothermal Method

Multiwalled carbon nanotubes (MWCNTs) were synthesized using arc discharge method at a magnetic field of 430 G and purified using HNO3/H2O2. Transmission electron micrographs revealed that MWCNTs had inner and outer diameter of ~2 nm and ~4 nm, respectively. Raman spectroscopy confirmed formation of MWCNTs showing G-band at 1577 cm−1. ZnFe2O4 and ZnFe2O4/MWCNT were produced using one step hydrothermal method. Powder X-ray diffraction (XRD) confirmed the formation of cubic spinel ZnFe2O4 as well as incorporation of MWCNT into ZnFe2O4. Visible light photocatalytic degradation of methylene blue (MB) was studied using pure ZnFe2O4 and ZnFe2O4/MWCNT. The results showed that ZnFe2O4/MWCNT composite had higher photocatalytic activity as compared to pure ZnFe2O4. After irradiation for 5 hours in the visible light, MB was almost 84% degraded in the presence of ZnFe2O4 photocatalyst, while 99% degradation was observed in case of ZnFe2O4/MWCNT composite. This enhancement in the photocatalytic activity of composite may be attributed to the inhibition of recombination of photogenerated charge carriers.

Optical, X-Ray Diffraction, and Magnetic Properties of the Cobalt-Substituted Nickel Chromium Ferrites (CrCoNi1−FeO4, =0,0.2,0.4,0.6,0.8,1.0) Synthesized Using Sol-Gel Autocombustion Method

Cobalt-substituted nickel chromium ferrites (CrCo𝑥Ni1−𝑥FeO4, 𝑥=0,0.2,0.4,0.6,0.8,1.0) have been synthesized using sol-gel autocombustion method and annealed at 400 °C, 600 °C, 800 °C, and 1000 °C. All the ferrite samples have been characterized using UV-VIS spectrophotometery, FT-IR spectroscopy, Transmission Electron Microscopy, powder X-Ray Diffraction, and magnetic measurements. Typical FT-IR spectra of the samples annealed at 400°C, 600°C, 800°C, and 1000°C exhibit two frequency bands in the range of ~480 cm−1 and ~590 cm−1 corresponding to the formation of octahedral and tetrahedral clusters of metal oxide, respectively. TEM images reveal that crystallite size increases from ~10 nm to ~45 nm as the annealing temperature is increased from 400°C to 1000°C. The unit cell parameter “a” is found to increase on increasing the cobalt concentration due to larger ionic radius of cobalt. Also, as the cobalt concentration increases, the saturation magnetization increases from 4.32 to 19.85 emu/g. This is due to the fact that cobalt ion replaces the less magnetic nickel ions. However, the coercivity decreases with increase in cobalt concentration due to the decrease in anisotropy field. The band gap has been calculated using UV-VIS spectrophotometry and has been found to decrease with the increase of particle size.

Magnetic moment and Mössbauer spectral studies of spin-crossover in tris(N,N′-dialkyldithiocarbamato)iron(III) complexes and their thermal decomposition

Room temperature Mössbauer spectra of tris(N,N′-dialkyldithiocarbamato)iron(III) complexes [(R2NCS2)3Fe] (R = Me, Et, n-Pr, i-Pr, n-Bu and i-Bu) exhibit an asymmetric doublet which can be resolved into two doublets, each corresponding to high and low spin states in equilibrium. The quadrupole splitting (ΔEQ), in general, increases with the molecular weight of the alkyl group in both the cases. Plots of magnetic moment (μeff) versus temperature show that dimethyl-, diethyl-, di-n-propyl- and di-n-butyl-substituted dithiocarbamato complexes are equilibrium mixtures of high and low spin states at room temperature, but increasingly adopt low spin at the liquid nitrogen temperature. However, the di-i-propyl- and di-i-butyl-substituted dithiocarbamato complexes exhibit primarily low spin state in the 77–350 K range, with a small contribution (<15%) of high spin state. Fe—S stretching vibrations in far i.r. region also show spin equilibrium states. Thermogravimetric studies show fast decomposition in the 200–300 °C range, yielding Fe(SCN)3 as an intermediate product followed by slow decomposition, leading finally to constant weight corresponding to Fe2O3 at ca. 650 °C. Mössbauer spectra of the final products of all the complexes exhibit a six line spectrum with Heff = 517 ± 3 kOe corresponding to that of α-Fe2O3 without any possibility of Fe2S3 as proposed in literature.

Designing different morphologies of NiFe2O4 for tuning of structural, optical and magnetic properties for catalytic advancements

In order to understand the potential of nanostructured materials in the field of catalysis, grave efforts are required towards the synthesis of structurally well-defined systems in the context of shape and morphology. So, in the present investigation efforts have been made towards the synthesis of different morphologies of NiFe2O4via a hydrothermal route. The effects of using different reaction conditions on the morphological, structural, magnetic, surface and catalytic properties have been evaluated. The formation of different morphologies via adopting different synthetic methodologies has been confirmed from FE-SEM and HR-TEM techniques. The development of six different morphologies viz. nanoflowers, nanooctahedrons, nanoparticles, nanorods, nanospheres and nanocorns has been achieved. The variations in structural parameters have been studied using XRD. The band gap of all the synthesized morphologies has been found to be in the visible range (1.36–1.56 eV). The surface areas of the synthesized morphologies have also been found to vary greatly with the morphology and nanocorns found to possess a maximum surface area of 904.7 m2 g−1. The catalytic activity of the synthesized samples was studied for the removal of organic pollutants via oxidation and reduction techniques. The catalytic activity has been found to depend upon the morphology, with nanocorns exhibiting the highest catalytic activity both for the oxidation and reduction reactions. All the synthesized morphologies exhibited an inherent magnetic character with an excellent catalytic activity and thus can be effectively used as catalysts for the cleaning of the environment.

Encrustation of cobalt doped copper ferrite nanoparticles on solid scaffold CNTs and their comparison with corresponding ferrite nanoparticles: a study of structural, optical, magnetic and photo catalytic properties

Cobalt doped copper ferrite nanoparticles and their nanocomposites with carbon nanotubes (CNTs) were synthesized by microemulsion method where sodium dodecyl sulphate was used as soft templating agent to control the particle size and shape. Powder X-ray diffraction technique confirmed the formation of cobalt doped copper ferrite nanoparticles and their corresponding nanocomposites. A significant decrease in the lattice parameter was observed using Le-bail refinement method which confirmed the doping of cobalt ion in to the copper ferrite lattice. Appearance of peak at around 25.9° indicated that CNTs remain unaffected during synthesis procedure. High Resolution Transmission Electron Microscopy (HR-TEM) was used to estimate the particle size, shape and uniformity of all the synthesized samples. Particle size was observed to be around 4–5 nm. A fine layer of ferrite nanoparticles on the surface of CNTs was also confirmed. Optical studies of the entire samples showed wide coverage of visible light spectrum from 675–1050 nm. Magnetic studies of the all samples were carried out using vibrating sample magnetometer and a significant increase in the saturation magnetization and coercivity values with cobalt ion doping was observed. This increase could be attributed to the higher magnetic moment of Co2+ ions (3 μB) as compared to Cu2+ ion (1 μB) at B-sub lattice. Comparative photocatalytic activity was also elevated and it was found that ferrite–CNTs nanocomposites show higher catalytic activities for the degradation of Rhodamine B dye in comparison with the ferrite nanoparticles.