| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- 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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| 3. |
- Chen, Zheng, et al.
(författare)
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Increased photocurrent of CuWO4 photoanodes by modification with the oxide carbodiimide Sn2O(NCN)
- 2020
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 49:11, s. 3450-3456
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Tidskriftsartikel (refereegranskat)abstract
- Tin(ii) oxide carbodiimide is a novel prospective semiconductor material with a band gap of 2.1 eV and lies chemically between metal oxides and metal carbodiimides. We report on the photochemical properties of this oxide carbodiimide and apply the material to form a heterojunction with CuWO4 thin films for photoelectrochemical (PEC) water oxidation. Mott-Schottky experiments reveal that the title compound is an n-type semiconductor with a flat-band potential of -0.03 V and, as such, the position of the valence band edge would be suitable for photochemical water oxidation. Sn2O(NCN) increases the photocurrent of CuWO4 thin films from 32 mu A cm(-2) to 59 mu A cm(-2) at 1.23 V vs. reversible hydrogen electrode (RHE) in 0.1 M phosphate buffer (pH 7.0) under backlight AM 1.5G illumination. This upsurge in photocurrent originates in a synergistic effect between the oxide and oxide carbodiimide, because the heterojunction photoanode displays a higher current density than the sum of its individual components. Structural analysis by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveals that Sn2O(NCN) forms a core-shell structure Sn2O(NCN)@SnPOx during the PEC water oxidation in phosphate buffer. The electrochemical activation is similar to the behavior of Mn(NCN) but different from Co(NCN).
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| 4. |
- Chen, Zheng, et al.
(författare)
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Reaction pathways on N-substituted carbon catalysts during the electrochemical reduction of nitrate to ammonia
- 2022
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 12:11, s. 3582-3593
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical reduction of nitrate into ammonia is one potential strategy to valorize pollutants needed to close the nitrogen cycle. The understanding of carbonaceous materials as metal-free representatives of electrocatalysts is of high importance to ensure sufficient activity and target selectivity. We report on the role of defects in cellulose-derived nitrogen-doped carbon (NDC) materials, produced by ammonolysis at different temperatures, to obtain efficient electrocatalysts for the nitrate reduction reaction (NO3RR). Carbon catalyst ammonolysis at 800 °C (NDC-800) yields the highest electrochemical performance, exhibiting 73.1% NH4+ selectivity and nearly 100% NO3− reduction efficiency with a prolonged NO3RR time (48 h) at −1.5 V vs. Ag/AgCl in a 0.1 M Na2SO4 electrolyte. We provide support to our findings by undertaking complementary structural analyses with scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, low-temperature N2 adsorption, and theoretical studies based on multi-scale/level calculations. Atomistic molecular dynamics simulations based on a reactive force field combined with quantum chemistry (QC) calculations on representative model systems suggest possible realistic scenarios of the material structure and reaction mechanisms of the NO3− reduction routes.
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| 5. |
- Chen, Zheng, et al.
(författare)
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Tailoring the Surface Properties of Bi2O2NCN by in Situ Activation for Augmented Photoelectrochemical Water Oxidation on WO3 and CuWO4 Heterojunction Photoanodes
- 2020
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 59:18, s. 13589-13597
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth(III) oxide-carbodiimide (Bi2O2NCN) has been recently discovered as a novel mixed-anion semiconductor, which is structurally related to bismuth oxides and oxysulfides. Given the structural versatility of these layered structures, we investigated the unexplored photochemical properties of the target compound for photoelectrochemical (PEC) water oxidation. Although Bi2O2NCN does not generate a noticeable photocurrent as a single photoabsorber, the fabrication of heterojunctions with the WO3 thin film electrode shows an upsurge of current density from 0.9 to 1.1 mA cm–2 at 1.23 V vs reversible hydrogen electrode (RHE) under 1 sun (AM 1.5G) illumination in phosphate electrolyte (pH 7.0). Mechanistic analysis and structural analysis using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (STEM EDX) indicate that Bi2O2NCN transforms during operating conditions in situ to a core–shell structure Bi2O2NCN/BiPO4. When compared to WO3/BiPO4, the in situ electrolyte-activated WO3/Bi2O2NCN photoanode shows a higher photocurrent density due to superior charge separation across the oxide/oxide-carbodiimide interface layer. Changing the electrolyte from phosphate to sulfate results in a lower photocurrent and shows that the electrolyte determines the surface chemistry and mediates the PEC activity of the metal oxide-carbodiimide. A similar trend could be observed for CuWO4 thin film photoanodes. These results show the potential of metal oxide-carbodiimides as relatively novel representatives of mixed-anion compounds and shed light on the importance of the control over the surface chemistry to enable the in situ activation.
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| 6. |
- 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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| 7. |
- A. da Cruz, Márcia G., et al.
(författare)
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Electrochemical Depolymerization of Lignin in a Biomass-based Solvent
- 2022
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 15:15
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Tidskriftsartikel (refereegranskat)abstract
- Breaking down lignin into smaller units is the key to generate high value-added products. Nevertheless, dissolving this complex plant polyphenol in an environment-friendly way is often a challenge. Levulinic acid, which is formed during the hydrothermal processing of lignocellulosic biomass, has been shown to efficiently dissolve lignin. Herein, levulinic acid was evaluated as a medium for the reductive electrochemical depolymerization of the lignin macromolecule. Copper was chosen as the electrocatalyst due to the economic feasibility and low activity towards the hydrogen evolution reaction. After depolymerization, high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy revealed lignin-derived monomers and dimers. A predominance of aryl ether and phenolic groups was observed. Depolymerized lignin was further evaluated as an anti-corrosion coating, revealing enhancements on the electrochemical stability of the metal. Via a simple depolymerization process of biomass waste in a biomass-based solvent, a straightforward approach to produce high value-added compounds or tailored biobased materials was demonstrated.
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| 8. |
- A. da Cruz, Márcia G., et al.
(författare)
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Solvent-free synthesis of photoluminescent carbon nanoparticles from lignin-derived monomers as feedstock
- 2023
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Ingår i: Green Chemistry Letters and Reviews. - 1751-8253 .- 1751-7192. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescent carbon nanoparticles (CNPs), such as carbon dots (CDs), have attracted much attention owing to a unique set of properties, like high and tunable fluorescence. In this way, the use of carbon-rich lignin has been demonstrated to be a sustainable approach to producing a broad range of photoluminescent CNPs. However, the valorization of this complex polyphenol is limited when it comes to green and efficient ways of conversion. In addition, the existing solvothermal approaches using lignin often result in CDs with low photoluminescence, while flammable and/or toxic solvents are employed. Here, we depolymerized technical lignins, i.e. kraft and soda, through electroreductive cleavage in two different sustainable media: deep eutectic solvent and levulinic acid. After depolymerization, lignin-derived monomers were generated, with a predominance of aryl ether and phenolic groups, which were further combined with 1,2-Phenylenediamine to produce N-doped CNPs in a solvent-free approach. Photoluminescent CNPs with varied sizes were generated (5–50 nm), which presented a wide photoluminescence emission, from blue to red, depending on solvent polarity. These results demonstrate a feasible and sustainable route for the solvent-free synthesis of photoluminescent CNPs using lignin-derived monomers as carbon source, which may find applications in a wide range of fields.
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| 9. |
- Bilgic, Mehmet B., et al.
(författare)
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An unusual zig-zag 2D copper(i) coordination polymer as an outstanding catalyst for azide–alkyne “click” chemistry at room temperature
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:46, s. 17543-17546
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Tidskriftsartikel (refereegranskat)abstract
- A straightforward method for the synthesis of a two-dimensional (2D) new copper(I) coordination polymer, namely Cu(bzpdc), containing the ligand benzophenone 4,4′-dicarboxylate, and its effective use as catalyst for the azide–alkyne click chemistry at room temperature is reported. Zig-zag formation caused by cuprophilic interactions resulted in an unprecedented crystal structure with a very high copper content (45.5% by weight). The catalyst was stable up until 300 °C and tolerant to various solvents, including water. Cu(bzpdc) showed excellent catalytic activity for click reactions of several organic azides and alkynes having different functional groups at room temperature and is comparable to its homogenous analogues. The recyclability of Cu(bzpdc) was also tested and proven to be effective.
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| 10. |
- 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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