Reaction of NO₂ with Zn and ZnO:  Photoemission, XANES, and Density Functional Studies on the Formation of NO₃

Abstract

Synchrotron-based high-resolution photoemission and X-ray absorption near-edge spectroscopy (XANES) have been used to study the interaction of NO2 with polycrystalline surfaces of metallic zinc and zinc oxide. NO2 exhibits a complex chemistry on metallic zinc. After adsorbing nitrogen dioxide, N, O, NO, NO2, and NO3 are present on the surface of the metal. At room temperature the NO2 molecule mainly dissociates into O adatoms and gaseous NO, whereas at low temperatures (<250 K) chemisorbed NO2 and NO3 dominate on the surface. NO2 is a very good oxidizing agent for preparing ZnO from metallic zinc. Zn reacts more vigorously with NO2 than metals, such as Rh, Pd, or Pt which are typical catalysts for the removal of NO x molecules (DeNO x process). At 300 K, the main product of the reaction of NO2 with polycrystalline ZnO is adsorbed NO3 with little NO2 or NO present on the surface of the oxide. No evidence was found for the full decomposition of the NO2 molecule (i.e., no NO2 → N + 2O). The results of density functional (DF-GGA) calculations for the adsorption of NO2 on a six-layer slab of ZnO, or INDO/S calculations for NO2 on a Zn37O37 cluster, show stronger chemisorption bonds on (0001) Zn-terminated terraces than on (0001̄) O-terminated terraces. The Zn ↔ NO2 interactions on ZnO are strong and the Zn sites probably get oxidized and nitrated as a result of them. It appears that NO2 is very efficient for fully oxidizing metal centers that are missing O neighbors in oxide surfaces. On zinc oxide, the nitrate species are stable up to temperatures near 700 K. ZnO can be useful as a sorbent in DeNO x operations.

Realizing chemical codoping in TiO2

“…The N 1s binding energies in both 6 samples are lower than that of N-O adsorption (400-406 eV) [29,30], and consistent with reported values in earlier work on N substitutional doping [31]. This clearly shows that N substitutionally dopes the O sites for both N-TiO 2 and NP-TiO 2 samples.…”

Synthesis, Characterization and Effect of pH Variation on Zinc Oxide Nanostructures

“…Such features support nanostructured synthesis and use of this exciting material for such novel unexplored applications. [2][3][4][5][6][7][8] Several deposition technique have been employed for the synthesis of zinc oxide nanostructures (nanowires, nanobelts, nanobridges, nanonails, nanoribbons, nanorods, nanotubes, and whiskers) such as physical evaporation, hydrothermal, chemical vapor deposition, cyclic feeding chemical vapor deposition, thermal evaporation, metal organic chemical vapour deposition (MOCVD), spray pyrolysis, ion beam assisted deposition, laser-ablation, sputter deposition, template assisted growth and solution method etc. [9][10][11][12][13][14][15][16][17][18][19] In addition to these techniques, precipitation/solution method is a prominent and most effective process because it offers many advantages with excellent and control over stoichiometry, compositional modification, microstructure control using capping molecules, controlled doping, with inexpensive equipments.…”

“…24) In all the results reported above, the nanostructures were grown either at higher temperature or they need, sophisticated instruments, expensive chemicals and complex reaction procedure for the growth of zinc oxide nanostructures. In this paper we report a systematic study on the morphological variation of ZnO nanostructures by controlling the pH (6)(7)(8)(9)(10)(11)(12), of the solution of zinc nitrate hexa-hydrate (Zn(NO 3 ) 2 Á 6H 2 O), hydroxylamine hydrochloride (NH 2 OHÁHCl) and sodium hydroxide (NaOH) at a very low temperature (60 C) and in a very short refluxing (20 min) time. To the best of our knowledge the use of hydroxylamine hydrochloride for the synthesis of disk to micro flower formation by the calibration of pH is presented first time and such type of report is not available in the literature.…”

Enhanced UV-Light Emission in ZnO/ZnS Quantum Dot Nanocrystals

“…It is a very useful material that can be used as a transparent electrode in solar cells, chemical sensors, and catalysts as well. 8,9) So far, however, most of researches on ZnO have been concentrated on thin film and nanowire structures, while the research on colloidal ZnO nanocrystals is relatively rare. 10) This is most likely due to the lack of reliable synthetic methods to produce ZnO particles in quantum confinement regime.…”