An official website of the United States government
Abstract Self‐sustaining photocatalytic NO3−reduction systems could become ideal NO3−removal methods. Developing an efficient, highly active photocatalyst is the key to the photocatalytic reduction of NO3−. In this work, we present the synthesis of Ni2P‐modified Ta3N5(Ni2P/Ta3N5), TaON (Ni2P/TaON), and TiO2(Ni2P/TiO2). Starting with a 2 mM (28 g/mL NO3−−N) aqueous solution of NO3−, as made Ni2P/Ta3N5and Ni2P/TaON display as high as 79% and 61% NO3−conversion under 419 nm light within 12 h, which correspond to reaction rates per gram of 196 μmol g−1 h−1and 153 μmol g−1 h−1, respectively, and apparent quantum yields of 3–4%. Compared to 24% NO3−conversion in Ni2P/TiO2, Ni2P/Ta3N5and Ni2P/TaON exhibit higher activities due to the visible light active semiconductor (SC) substrates Ta3N5and TaON. We also discuss two possible electron migration pathways in Ni2P/semiconductor heterostructures. Our experimental results suggest one dominant electron migration pathway in these materials, namely: Photo‐generated electrons migrate from the semiconductor to co‐catalyst Ni2P, and upshift its Fermi level. The higher Fermi level provides greater driving force and allows NO3−reduction to occur on the Ni2P surface.
more »
« less
Intrinsic thermal expansion and tunability of thermal expansion coefficient in Ni-substituted Co 2 V 2 O 7
Abstract Framework oxide materials are well-known for exhibiting not only negative thermal expansion (NTE), but also demonstrating thermal expansion that can be controlled using composition as a tuning parameter. In this work, we study the intrinsic thermal expansion properties of Co2V2O7, which has shown bulk linear NTE, and attempt to understand how substituting Ni2+for Co2+will affect the thermal expansion. The isomorphic solid solution is synthesized through solid-state methods and characterized using x-ray diffraction (XRD), diffuse reflectance spectroscopy, and neutron diffraction. The size difference between Ni2+and Co2+as well as the polyhedral volume of each Co2+metal coordination environment in the crystal structure allows Ni2+to partially be directed toward one crystallographic site over the other. Variable temperature synchrotron XRD data are employed to understand intrinsic thermal expansion. Across the solid solution, no intrinsic NTE is observed at the microscopic level, yet a degree of tunability in the thermal expansion coefficient with Ni substitution is demonstrated. The disparities between the intrinsic and bulk thermal expansion properties suggest that a morphological mechanism may have resulted in NTE in the bulk.
more »
« less
- Award ID(s):
- 2137437
- PAR ID:
- 10468001
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Physics: Materials
- Volume:
- 6
- Issue:
- 4
- ISSN:
- 2515-7639
- Format(s):
- Medium: X Size: Article No. 045011
- Size(s):
- Article No. 045011
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Here we report a series of nitrogen‐rich conjugated macrocycles that mimic the structure and function of semiconducting 2D metal–organic and covalent organic frameworks while providing greater solution processability and surface tunability. Using a new tetraaminotriphenylene building block that is compatible with both coordination chemistry and dynamic covalent chemistry reactions, we have synthesized two distinct macrocyclic cores containing Ni−N and phenazine‐based linkages, respectively. The fully conjugated macrocycle cores support strong interlayer stacking and accessible nanochannels. For the metal–organic macrocycles, good out‐of‐plane charge transport is preserved, with pressed pellet conductivities of 10−3 S/cm for the nickel variants. Finally, using electrochemically mediated CO2capture as an example, we illustrate how colloidal phenazine‐based organic macrocycles improve electrical contact and active site electrochemical accessibility relative to bulk covalent organic framework powders. Together, these results highlight how simple macrocycles can enable new synthetic directions as well as new applications by combining the properties of crystalline porous frameworks, the processability of nanomaterials, and the precision of molecular synthesis.more » « less
-
Abstract AMXcompounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on theM‐site in the planarMX‐layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu1−xZn0.5xSb solid solution. The transition from a fully‐occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn0.5Sb) leads to non‐linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on theMand Sb‐sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK−1at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximumzTincreases from 0.09 to 0.7 as we go from EuCuSb to EuZn0.5Sb.more » « less
-
Abstract The incorporation of CO2into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of NiIIto NiIby either Zn or Mn, followed by CO2insertion into NiI‐alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu‐Xantphos)NiIIBr2by Zn affords NiIspecies. (tBu‐Xantphos)NiI‐Me and (tBu‐Xantphos)NiI‐Et complexes undergo fast insertion of CO2at 22 °C. The substantially faster rate, relative to that of NiIIcomplexes, serves as the long‐sought‐after experimental support for the proposed mechanisms of Ni‐catalyzed carboxylation reactions.more » « less
-
Abstract In this work, a new type of multifunctional materials (MFMs) called self‐regenerative Ni‐doped CaTiO3/CaO is introduced for the integrated CO2capture and dry reforming of methane (ICCDRM). These materials consist of a catalytically active Ni‐doped CaTiO3and a CO2sorbent, CaO. The article proposes a concept where the Ni catalyst can be regenerated in situ, which is crucial for ICCDRM. Exsolved Ni nanoparticles are evenly distributed on the surface of CaTiO3under H2or CH4, and are re‐dispersed back into the CaTiO3lattice under CO2. The Ni‐doped CaTiO3/CaO MFMs show stable CO2capture capacity and syngas productivity for 30 cycles of ICCDRM. The presence of CaTiO3between CaO grains prevents CaO/CaCO3thermal sintering during carbonation and decarbonation. Moreover, the strong interaction of CaTiO3with exsolved Ni mitigates severe accumulation of coke deposition. This concept can be useful for developing MFMs with improved properties that can advance integrated carbon capture and conversion.more » « less
