Electronic structure study of Ce_1−<i>x</i>A_<i>x</i>O₂ (A = Zr & Hf) nanoparticles: NEXAFS and EXAFS investigations

Sharma, Aditya,Varshney, Mayora,Shin, Hyun-Joon,Park, Yong Jun,Kim, Min-Gyu,Ha, Tae-Kyun,Chae, Keun Hwa,Gautam, Sanjeev The Royal Society of Chemistry 2014 Physical Chemistry Chemical Physics Vol.16 No.37

<P>Single phase nanoparticles (NPs) of CeO<SUB>2</SUB>, Ce<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB>, Ce<SUB>0.5</SUB>Hf<SUB>0.5</SUB>O<SUB>2</SUB> and Ce<SUB>0.5</SUB>Hf<SUB>0.25</SUB>Zr<SUB>0.25</SUB>O<SUB>2</SUB> were successfully synthesized by co-precipitation method at constant pH and temperature. The X-ray diffraction results revealed that the additive atoms did not segregate to form secondary phases but led to grain size variation in the NPs. The 10 Dq values in the near edge X-ray absorption fine structure (NEXAFS) spectra at the O K-edge did not vary in the same way as the average grain size was changed for the doped CeO<SUB>2</SUB> NPs. The deconvolution of Ce M<SUB>5</SUB>-edge and detailed analysis of O K pre-edge peak have shown the higher Ce<SUP>+3</SUP>/(Ce<SUP>+3</SUP> + Ce<SUP>+4</SUP>) ratio in the Zr- and Hf-doped samples. The local atomic structure around the Ce, Zr and Hf atoms was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy at Ce K-edge, Zr K-edge and Hf L<SUB>3</SUB>-edge, respectively, and the EXAFS data were fitted with the theoretical calculations. The 4f occupancy, Ce<SUP>+3</SUP>/(Ce<SUP>+3</SUP> + Ce<SUP>+4</SUP>) ratio of Ce ions, coordination number of Ce and Ce–Ce/Ce–O bond distances were sensitive to the additive atoms but not explicitly changed according to the grain size variation in the NPs.</P> <P>Graphic Abstract</P><P>4f-occupation, Ce<SUP>+3</SUP>/Ce<SUP>+4</SUP> ratio and grain-size effects in Zr- and Hf-substituted CeO<SUB>2</SUB> nanoparticles are investigated by NEAXFS and EXAFS. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp02409e'> </P>

Mechanistic insights into the interaction between energetic oxygen ions and nanosized ZnFe₂O₄: XAS-XMCD investigations

Singh, Jitendra Pal,Kaur, Baljeet,Sharma, Aditya,Kim, So Hee,Gautam, Sanjeev,Srivastava, Ramesh Chandra,Goyal, Navdeep,Lim, Weol Cheol,Lin, H.-J.,Chen, J. M.,Asokan, K.,Kanjilal, D.,Won, Sung Ok,Lee, The Royal Society of Chemistry 2018 Physical Chemistry Chemical Physics Vol.20 No.17

<P>The interactions of energetic ions with multi-cation compounds and their consequences in terms of changes in the local electronic structure, which may facilitate intriguing hybridization between O 2p and metal d orbitals and magnetic ordering, are the subject of debate and require a deep understanding of energy transfer processes and magnetic exchange mechanisms. In this study, nanocrystals of ZnFe2O4 were exposed to O<SUP>7+</SUP> ions with an energy of 100 MeV to understand, qualitatively and quantitatively, the metal-ligand field interactions, cation migration and magnetic exchange interactions by employing X-ray absorption fine structure measurements and X-ray magnetic circular dichroism to get deeper mechanistic insights. Nanosized zinc ferrite nanoparticles (NPs) with a size of ∼16 nm synthesized in the cubic spinel phase exhibited deterioration of the crystalline phase when 100 MeV O<SUP>7+</SUP> ions passed through them. However, the size of these NPs remained almost the same. The behaviour of crystal deterioration is associated with the confinement of heat in this interaction. The energy confined inside the nanoparticles promotes cation redistribution as well as the modification of the local electronic structure. Prior to this interaction, almost 42% of Zn<SUP>2+</SUP> ions occupied AO4 tetrahedra; however, this value increased to 63% after the interaction. An inverse effect was observed for metal ion occupancies in BO6 octahedra. The L-edge spectra of Fe and Zn reveal that the spin and valence states of the metal ions were not affected by this interaction. This effect is also supported by K-edge measurements for Fe and Zn. The t2g/eg intensity ratio in the O K-edge spectra decreased after this interaction, which is associated with detachment of Zn<SUP>2+</SUP> ions from the lattice. The extent of hybridization, as estimated from the ratio of the post-edge to the pre-edge region of the O K-edge spectra, decreased after this interaction. The metal-oxygen and metal-metal bond lengths were modified as a result of this interaction, as determined from extended X-ray absorption fine structure measurements. These measurements further support the observation of cation migration from AO4 tetrahedra to AO6 octahedra and <I>vice versa</I>. The Fe L-edge magnetic circular dichroism spectra indicate that Fe<SUP>3+</SUP> ions occupying sites in AO4 tetrahedra and BO6 octahedra exhibited antiferromagnetic-like ordering prior to this interaction. The NPs that interacted with energetic O ions displayed a different kind of magnetic ordering.</P>

Habitat complexity reduces prey vulnerability: An experimental analysis using aquatic insect predators and immature dipteran prey

Nabaneeta Saha,Goutam K. Saha,Gautam Aditya 한국응용곤충학회 2009 Journal of Asia-Pacific Entomology Vol.12 No.4

The effects of alternative prey and structural complexity of habitat on the selection of mosquito larvae by aquatic insect predators were evaluated in the laboratory. The water bugs Anisops bouvieri, Diplonychus (=Sphaerodema) rusticus, and D. annulatus, and the odonate nymphs, Ceriagrion coromandelianum and Brachydiplax chalybea chalybea, selected mosquito larvae based on their abundance relative to chironomid larvae and on the levels of habitat complexity. The effect of one prey species on the other was asymmetrical, as indicated through prey selectivity values. Compared to open habitat, the presence of macrophytes reduced the vulnerability of mosquito larvae while the effect was reverse in the presence of sediments. When both sediment and macrophytes were present in habitats, all the predators except D. annulatus consumed more mosquito larvae than chironomid larvae. The clearance rate, an indicator of predatory efficiency, varied among the predator species and habitat types. The results suggest that the outcome of the interactions between insect predators and mosquito immatures was context-dependent and that it was mediated by the presence of alternative controphic species and the habitat complexity. The effects of alternative prey and structural complexity of habitat on the selection of mosquito larvae by aquatic insect predators were evaluated in the laboratory. The water bugs Anisops bouvieri, Diplonychus (=Sphaerodema) rusticus, and D. annulatus, and the odonate nymphs, Ceriagrion coromandelianum and Brachydiplax chalybea chalybea, selected mosquito larvae based on their abundance relative to chironomid larvae and on the levels of habitat complexity. The effect of one prey species on the other was asymmetrical, as indicated through prey selectivity values. Compared to open habitat, the presence of macrophytes reduced the vulnerability of mosquito larvae while the effect was reverse in the presence of sediments. When both sediment and macrophytes were present in habitats, all the predators except D. annulatus consumed more mosquito larvae than chironomid larvae. The clearance rate, an indicator of predatory efficiency, varied among the predator species and habitat types. The results suggest that the outcome of the interactions between insect predators and mosquito immatures was context-dependent and that it was mediated by the presence of alternative controphic species and the habitat complexity.

Butterfly diversity in Kolkata, India: An appraisal for conservation management

Swarnali Mukherjee,Soumyajit Banerjee,Goutam K. Saha,Parthiba Basu,Gautam Aditya 국립중앙과학관 2015 Journal of Asia-Pacific Biodiversity Vol.8 No.3

An appraisal of butterfly species diversity was made using Kolkata, India as a model geographical area. Random sampling of rural, suburban, and urban sites in and around Kolkata metropolis revealed the presence of 96 butterfly species, dominated by Lycaenidae (31.25%) over Nymphalidae (28.13%), Hesperiidae (18.75%), Pieridae (12.50%), and Papilionidae (9.38%). Suburban sites accounted for 96 species, followed by rural (81 species) and urban (53 species) over the study period. The relative abundance of the butterflies varied with the site, month, and family significantly. It is apparent that the urban areas of Kolkata can sustain diverse butterfly species which includes species of requiring conservation effort. Considering the landscape of Kolkata, steps to enhance urban greening should be adopted to maintain butterfly diversity and sustain the ecosystem services derived from them.