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Oxygen vacancy and dopant concentration dependent magnetic properties of Mn doped TiO2 nanoparticle
Biswajit Choudhury,Amarjyoti Choudhury 한국물리학회 2013 Current Applied Physics Vol.13 No.6
Mn doped TiO2 nanoparticles are synthesized by solegel method. Incorporation of Mn shifts the diffraction peak of TiO2 to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO2 show peaks at g ¼ 1.99 and 4.39, characteristic of Mn2þ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO2, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn3O4. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn2þ ions via oxygen vacancy (Fþ center). Increase in Mn concentration increases the fraction of Mn3O4 phase and thereby increases the paramagnetic ordering.
Biswajit Choudhury,Amarjyoti Choudhury 한국물리학회 2013 Current Applied Physics Vol.13 No.1
Doping of Nd distorts the lattice structure of CeO2, increases the lattice strain and expands the lattice. Oxygen vacancies and other ceria related defects contribute to the lattice strain. Shifting and broadening of the F2g Raman peak of doped sample, compared to pure CeO2, is indicative of local structure distortion on doping. Dopant induced enhancement of oxygen vacancies, in the CeO2 lattice, is further confirmed by the generation of a new Raman peak at 543 cm1 that is otherwise absent in the pure one. UVevis spectroscopy gives an understanding of the different types of fef electronic transition of Nd in the crystalline environment of CeO2. Effective band gap of CeO2 reduces upto Nd concentration of 2.5%. The band gap, however, increases at 4% of Nd due to BursteineMoss shift. Photoluminescence intensity of pure CeO2 decreases with Nd concentration owing to the increase in the number of non radiative oxygen vacancies. These vacancies act as luminescence quencher and reduce the emission intensity. Photoluminescence excitation spectra confirm the presence of these oxygen vacancies in the CeO2 nanocrystallites.
Choudhury, Sk Mohiuddin,Bhuiyan, Mohammad Musharraf Uddin,Rahman, Mohammad Moshiur,Rahman, Md. Masudur,Sharif, Md. Newaz,Bhattacharjee, Jayonta,Bari, Farida Yeasmin,Juyena, Nasrin Sultana The Korean Society of Embryo Transfer 2017 한국동물생명공학회지 Vol.32 No.4
Cryopreservation of oocytes by vitrification technique may contribute a lot in the field of reproductive biotechnology. The objectives of the present study were to evaluate the effectiveness of two cryo-devices for vitrification of immature oocytes of indigenous zebu cows. Slaughter house derived immature cumulus-oocyte-complexes (COCs) of cows were vitrified using 15% dimethyl sulphoxide (DMSO) as cryoprotective agent (CPA) with 0.5 mol sucrose in TCM 199 supplemented with 20% FBS. Vitrification of COCs was completed after immediate plunging of COCs loaded cryotop or French mini straw into the liquid nitrogen ($LN_2$). Then the COCs containing cryotop or French mini straws were warmed in 0.25 mol sucrose and 20% FBS supplemented TCM 199 followed by in vitro culture in $50{\mu}l$ droplets of bicarbonate buffered TCM 199 supplemented with 10% FBS, pyruvate, FSH and oestradiol for 24 hrs at $39^{\circ}C$ with 5% CO2 in humidified air. After maturation culture, oocytes were denuded and examined under inverted microscope for presence of polar body as the indication of maturation. Denuded oocytes were also stained by whole mount technique using 1% orcein to examine the maturation by presence of MII chromosomes. The in vitro maturation rate was significantly (p<0.05) higher in oocytes vitrified and warmed using crytop ($47.1{\pm}6.9%$) than that of French mini straw ($15.9{\pm}12.5%$). Moreover, in vitro maturation rate was significantly (p<0.05) highe r in control oocytes (not vitrified) ($84.5{\pm}14.2%$) than that of vitrified oocytes. In conclusion, cryotop is better than French mini straw as cryo-device for vitrification of bovine immature oocytes.
Choudhury, Abhik,Ali, Shahzad,Khan, Abu T. Korean Chemical Society 2015 대한화학회지 Vol.59 No.4
Hydrated ferric sulfate can be used as an efficient and reusable catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine-trione derivatives via one-pot three-component condensation reaction of phthalhydrazide, aromatic aldehydes and cyclic-1,3-diketones in ethanol under reflux conditions.
Choudhury, Arup,Bonso, Jeliza S.,Wunch, Melissa,Yang, Kap Seung,Ferraris, John P.,Yang, Duck J. Elsevier 2015 Journal of Power Sources Vol.287 No.-
<P><B>Abstract</B></P> <P>A novel nanohybrid material composed of vanadium pentoxide nanofibres (VNFs) and exfoliated graphene were prepared by <I>in-situ</I> growth of VNFs onto graphene nanosheets, and explicated as electrode material for supercapacitor applications. The existence of non-covalent interactions between VNFs and graphene surfaces was confirmed by Raman and Fourier transform infrared (FTIR) spectroscopes. Morphological analysis of the nanohybrid revealed that the VNF layer uniformly grown on the graphene surfaces, producing high specific surface area and good electronic or ionic conducing path. High crystalline structure with small d-spacing of the VNFs on graphene was observed in X-ray diffraction (XRD) analysis. Compared to pristine VNF, the VNF/graphene nanohybrid exhibited higher specific capacitance of 218 F g<SUP>−1</SUP> at current density of 1 A g<SUP>−1</SUP>, higher energy density of 22 Wh kg<SUP>−1</SUP> and power density of 3594 W kg<SUP>−1</SUP>. Asymmetric supercapacitor devices were prepared using the Spectracarb 2225 activated carbon cloth and VNF/graphene nanohybrid as positive and negative electrode, respectively. The asymmetric device exhibited capacitance of 279 F g<SUP>−1</SUP> at 1 A g<SUP>−1</SUP>, energy density of 37.2 Wh kg<SUP>−1</SUP> and power density of 3743 W kg<SUP>−1</SUP>, which are comparable and or superior to reported asymmetric devices consisting of carbon material and metal oxide as electrode components.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Preparation of novel nanohybrid by <I>in-situ</I> growth of V<SUB>2</SUB>O<SUB>5</SUB> nanofibres on graphene. </LI> <LI> Electrochemical characterizations of the nanohybrid for supercapacitor application. </LI> <LI> Maximum capacitance observed for asymmetric devices. </LI> <LI> Energy density of asymmetric devices was 69% higher than that of symmetric device. </LI> </UL> </P>