| 1. |
- Chen, Zheng, et al.
(författare)
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Graphitic nitrogen in carbon catalysts is important for the reduction of nitrite as revealed by naturally abundant N-15 NMR spectroscopy
- 2021
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :20
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Tidskriftsartikel (refereegranskat)abstract
- Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state N-15 NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in N-doped carbon at natural N-15 isotope abundance. Here we report a green chemistry approach for the synthesis of N-doped carbon using cellulose as a precursor, and a study of the catalytic properties and atomic structures of the related catalyst. N-doped carbon (NH3) was obtained by the oxidation of cellulose with HNO3 followed by ammonolysis at 800 degrees C. It had a N content of 6.5 wt% and a surface area of 557 m(2) g(-1), and N-15 ssNMR spectroscopy provided evidence for graphitic nitrogen besides regular pyrrolic and pyridinic nitrogen. This structural determination allowed probing the role of graphitic nitrogen in electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) showed higher electrocatalytic activities in the OER and HER under alkaline conditions and higher activity for nitrite reduction, as compared with a catalyst prepared by the carbonization of HNO3-treated cellulose in N-2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analyses by means of C-13 and H-1 ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N-2 adsorption were performed and provided support to the findings. The results show that directly-excited N-15 ssNMR spectroscopy at natural N-15 abundance is generally capable of providing information on N-doped carbon materials if relaxation properties are favorable. It is expected that this approach can be applied to a wide range of solids with an intermediate concentration of N atoms.
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| 2. |
- Ma, Zili, et al.
(författare)
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Structural Properties of NdTiO2+xN1-x and Its Application as Photoanode
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:2, s. 919-929
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Tidskriftsartikel (refereegranskat)abstract
- Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O2-) in a parent oxide by nitrogen (N3-), are encouraging candidates for photoelectrochemical (PEC) water splitting because of their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO2N, we investigated the paramagnetic counterpart NdTiO2+xN1-x. The electronic structure was explored both experimentally and theoretically at the density functional theory (DFT) level. A band gap (E-g) of 2.17 eV was determined by means of ultraviolet-visible (UV-vis) spectroscopy, and a relative negative flat band potential of -0.33 V vs reversible hydrogen electrode (RHE) was proposed via Mott-Schottky measurements. N-14 solid state nuclear magnetic resonance (NMR) signals from NdTiO2+xN1-x could not be detected, which indicates that NdTiO2+xN1-x is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit a noticeable photocurrent, Nb2O5 and CoOx overlayers were deposited to extract holes and activate NdTiO2+xN1-x. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride to fabricate photoanodes.
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| 3. |
- Budnyak, Tetyana, et al.
(författare)
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LignoPhot : Conversion of hydrolysis lignin into the photoactive hybrid lignin/Bi4O5Br2/BiOBr composite for simultaneous dyes oxidation and Co2+ and Ni2+ recycling
- 2021
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Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi5+ ions at the surface region, yielding thus a modified hetero-junction Bi4O5Br2/BiOBr. The material contains 18.9% of Bi4O5Br2/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/Bi4O5Br2/BiOBr decreases the dye concentration from 80 mg L-1 to 12.3 mg L-1 for RhB (85%) and from 80 mg L-1 to 4.4 mg L-1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.
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| 4. |
- Lu, Can, et al.
(författare)
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Sensibilization of p-NiO with ZnSe/CdS and CdS/ZnSe quantum dots for photoelectrochemical water reduction
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:2, s. 869-877
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Tidskriftsartikel (refereegranskat)abstract
- Core/shell quantum dots (QDs) paired with semiconductor photocathodes for water reduction have rarely been implemented so far. We demonstrate the integration of ZnSe/CdS and CdS/ZnSe QDs with porous p-type NiO photocathodes for water reduction. The QDs demonstrate appreciable enhancement in water-reduction efficiency, as compared with the bare NiO. Despite their different structure, both QDs generate comparable photocurrent enhancement, yielding a 3.8- and 3.2-fold improvement for the ZnSe/CdS@NiO and CdS/ZnSe@NiO system, respectively. Unraveling the carrier kinetics at the interface of these hybrid photocathodes is therefore critical for the development of efficient photoelectrochemical (PEC) proton reduction. In addition to examining the carrier dynamics by the Mott–Schottky technique and electrochemical impedance spectroscopy (EIS), we performed theoretical modelling for the distribution density of the carriers with respect to electron and hole wave functions. The electrons are found to be delocalized through the whole shell and can directly actuate the PEC-related process in the ZnSe/CdS QDs. The holes as the more localized carriers in the core have to tunnel through the shell before injecting into the hole transport layer (NiO). Our results emphasize the role of interfacial effects in core/shell QDs-based multi-heterojunction photocathodes.
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| 5. |
- Ma, Zili, et al.
(författare)
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CeTiO2N oxynitride perovskite : paramagnetic N-14 MAS NMR without paramagnetic shifts
- 2021
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Ingår i: Zeitschrift für Naturforschung. B, A journal of chemical sciences. - : Walter de Gruyter GmbH. - 0932-0776 .- 1865-7117. ; 76:5, s. 275-280
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Tidskriftsartikel (refereegranskat)abstract
- N-14 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of diamagnetic LaTiO2N perovskite oxynitride and its paramagnetic counterpart CeTiO2N are presented. The latter, to the best of our knowledge, constitutes the first high-resolution N-14 MAS NMR spectrum collected from a paramagnetic solid material. The unpaired 4f-electrons in CeTiO2N do not induce a paramagnetic N-14 NMR shift. This is remarkable given the direct Ce-N contacts in the structure for which ab initio calculations predict substantial Ce -> N-14 contact shift interaction. The same effect is revealed with N-14 MAS NMR for SrWO2N (unpaired 5d-electrons).
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| 6. |
- Rokicińska, Anna, et al.
(författare)
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Impact of Mn addition on catalytic performance of Cu/SiBEA materials in total oxidation of aromatic volatile organic compounds
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 546
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Tidskriftsartikel (refereegranskat)abstract
- Dealuminated BEA zeolite (SiBEA) was chosen as a support of metal oxide(s) phase for catalytic combustion of volatile organic compounds (VOCs). Copper and/or manganese oxide(s) were deposited at various Cu/Mn molar ratios. Factors influencing the catalytic activity were found by chosen physicochemical methods, including XRD, XRF, low-temperature N-2 adsorption, FT-IR, UV-Vis-DRS, STEM-EDX, XPS and H-2-TPR. Depending on the chemical composition, CuO, (CuxMn3-x)(1-delta)O-4, Cu-doped Mn3O4 or Mn2O3 was formed as the dominant phase. The active phase particles were located mainly in the interparticle voids of the zeolite support. SiBEA gained Lewis acid sites after the introduction of the metal oxide phase, especially in the case of CuO deposition. The presence of copper in the catalytic system resulted in enhanced reducibility of the active phase, and in a consequence in high catalytic activity in the total oxidation of aromatic VOCs, which proceeds according to the Mars-van Krevelen mechanism. After the introduction of Mn, the co-existence of different valence forms was found due to the redox equilibrium: Cu2+ + Mn3+ = Cu+ + Mn4+. Definitely, the addition of Mn to Cu/SiBEA increased the number of available surface vacancies and had a beneficial effect on the catalytic performance.
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| 7. |
- Zhang, Tong, et al.
(författare)
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Atomic-Level Understanding for the Enhanced Generation of Hydrogen Peroxide by the Introduction of an Aryl Amino Group in Polymeric Carbon Nitrides
- 2021
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435 .- 2155-5435. ; 11:22, s. 14087-14101
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous catalysts are often “black boxes” due to the insufficient understanding of the detailed mechanisms at the catalytic sites. An atomic-level elucidation of the processes taking place in those regions is, thus, mandatory to produce robust and selective heterogeneous catalysts. We have improved the description of the whole reactive scenario for polymeric carbon nitrides (PCN) by combining atomic-level characterizations with magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy, classical reactive molecular dynamics (RMD) simulations, and quantum chemistry (QC) calculations. We disclose the structure–property relationships of an ad hoc modified PCN by inserting an aryl amino group that turned out to be very efficient for the production of H2O2. The main advancement of this work is the development of a difluoromethylene-substituted aryl amino PCN to generate H2O2 at a rate of 2.0 mM·h–1 under the irradiation of household blue LEDs and the identification of possible active catalytic sites with the aid of 15N and 19F MAS solid-state NMR without using any expensive labeling reagent. RMD simulations and QC calculations confirm and further extend the experimental descriptions by revealing the role and locations of the identified functionalities, namely, NH linkers, −NH2 terminal groups, and difluoromethylene units, reactants, and products.
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