Nitrogen Defects Research Articles

Uncovering temperature-tempted coordination of inclusions within ultra-high-strength-steel via in-situ spectro-microscopy

Despite the common challenge of investigating non-metallic inclusions within ultra-high-strength-steel (UHSS) at sub-micrometer scale via conventional methods, probing nitride inclusions at elevated temperatures is vital for guiding steel’ performance. Herein, an in-situ spectro-microscopic determination using advanced Synchrotron X-ray absorption spectroscopy (XAS) coupled with photoelectron emission microscopy (PEEM) is employed to explore the local structure and electronic properties of selective h-boron nitride (h-BN) containing inclusions (A1 and A2) embedded within steel matrix. While the variation in the relative intensity of π∗/σ∗ excitonic peaks at spatially different locations refers to the polarization and or thickness effects. Several minute features observed in the 192–195 eV energy range show oxygen (O) substituted nitrogen (N) defects (ON,2N,3N), which are more dominant in A2 inclusion. The observed dominance further explains the relatively high intense π∗ peak in A2 due to increased localization. Weak shoulder on the left side of π∗ peak in both room and high-temperature XAS spectra is ascribed to the interaction between h-BN and the local environment, such as Ca-based inclusion or steel matrix. Defects are commonly found in h-BN, and precise identification of the same is vital as they affect the overall physical, chemical, and mechanical properties. Moreover, significant changes in high-temperature B K-edge XAS spectra, such as relative intensity of π∗/σ∗ excitonic peaks at the same location and reduced intensity of defects, suggest the adjusting nature of BN inclusion, complicating their precise prediction and control towards clean steel production.

Defect-rich potassium amide: A new solid-state potassium ion electrolyte

One of the major obstacles to the application of potassium-ion batteries in large-scale energy storage is the lack of safe and effective electrolytes. KNH2, a new potassium-ion solid electrolyte has been developed in this study. Its ionic conductivity reaches 4.84 × 10−5 S cm−1 at 150 °C and can reach 3.56 × 10−4 S cm−1 after mechanochemical treatment. The result from electron paramagnetic resonance (EPR) measurement shows that the increment of ionic conductivity is dependent on the concentration of nitrogen defects in the KNH2 electrolyte. To the best of our knowledge, this is the first report that adopts inorganic amide as an electrolyte for potassium-ion battery and initiates the search for a new amide-based solid electrolyte for an all-solid-state potassium-ion battery.

Diamond-destructive mantle metasomatism: Evidence from the internal and external textures of diamonds and their nitrogen defects

Metasomatic processes modify the composition of the subcratonic lithospheric mantle and can either form or destroy diamonds. The composition of these metasomatic agents is uncertain and has been mostly deduced from chemical zonation and overprints recorded by associated mantle silicates. Diamonds experience partial dissolution (resorption) during their residence in the mantle due to mantle metasomatism and later during their ascent in kimberlite magma. Diamonds, enclosed inside mantle xenoliths during the whole duration of ascent in kimberlite magma, can preserve their pre-kimberlite surface features, which record the last diamond-destructive metasomatic event to have occurred in the mantle. The geometry of diamond dissolution features acquired during mantle storage can provide information about diamond-destructive metasomatic events in the mantle. Diamond samples recovered from inside mantle xenoliths are extremely rare and mostly limited to eclogitic lithology, which suggests that variable resistance of different mantle lithologies to disintegration in kimberlite magma may affect representativity of these sample. Here we use whole diamond populations from exploration parcels and apply our earlier developed set of criteria to distinguish between kimberlitic and pre-kimberlitic surface features on diamonds. The study used diamonds (<1 to 4.5 mm size) from eight kimberlites in three localities: Orapa cluster, Botswana (BK1, AK15, and AK1 kimberlites), Ekati Mine, Northwest Territories, Canada (Grizzly, Leslie, Koala, and Misery kimberlites), and Snap Lake kimberlite dyke, Northwest Territories, Canada. The host kimberlites cover seven different volcaniclastic and coherent kimberlite lithologies, and our previous studies demonstrated a correlation between the style of kimberlitic resorption on diamonds and the host kimberlite lithology for these samples. From the total of 3256 studied diamonds, we identified 534 diamonds with pre-kimberlite surface textures. These pre-kimberlite surface textures display six distinct types, which are present in all the studied diamond parcels regardless of their geographic locality and host kimberlite lithology. The relative proportions of these types depend on the geographic locality showing linkage to a specific mantle source. We examined the relationship between the surface features on diamonds, their growth patterns revealed in cathodoluminescence (CL) images, the content and aggregation of nitrogen defects using Fourier transform infrared spectroscopy (FTIR), and nitrogen content in specific growth zones of diamonds obtained using secondary ion mass spectrometry (SIMS) for 82 Ekati diamonds.Our data show that growth step-faces develop on diamonds with complex multi-crystal cores, whereas flat-faced octahedra with simple oscillatory-zoned growth patterns derive from single growth events. Initial stages of dissolution affecting only outer growth zones develop simple serrate laminae on diamonds, while more extensive dissolution exposes more complex growth zones developing various shapes of laminae and etch features (trigons and irregular asperities). The effect of internal growth patterns on dissolution features is more profound during pre-kimberlitic than kimberlite-related resorption likely due to the greater role of defects in diamond dissolution at mantle conditions.Comparison with the results of diamond dissolution experiments shows that metasomatism by C-O-H fluid is not destructive to diamond, while carbonate-silicate melt-driven metasomatism causes diamond dissolution. Continuous change in the silicate content of silicate‑carbonate melts and temperature variations within 200 °C can explain all pre-kimberlite dissolution features observed in this study. Similar pre-kimberlite dissolution features on diamonds from both the Zimbabwe and Slave cratons suggests that these metasomatic processes are widespread and affected the mantle below the eight studied kimberlites.

Nitrogen-defect induced trap states steering electron-hole migration in graphite carbon nitride

Defect structures of semiconductors intrinsically regulate the trap states, excitons and active charge carriers for artificial photosynthesis systems. A g-C3N4 system with abundant nitrogen defects was prepared through a thermal polycondensation strategy to reveal the role of trap states and exhibited a 20-fold enhanced H2 evolution efficiency relative to bulk g-C3N4 under visible light irradiation. Subsequent femtosecond transient absorption spectroscopy study found that the N-defect induced shallow trap states can capture photogenerated electrons to inhibit deep trapping and direct recombination of photogenerated charges. The active electrons in shallow trap states can enhance the photocatalytic H2 evolution when compared with the inactive electrons in deep trap states. Mid-infrared transient absorption spectroscopy also confirmed the increased quantity of shallow-trapped electrons without interference of other signals. This work provides new insights for steering depth of trap states and photocatalytic processes through N defects to achieve high photocatalytic performance using femtosecond transient absorption spectroscopy.

Outstanding catalytic performance of metal-free peroxymonosulfate activator: Important role of chrysotile

A metal-free peroxymonosulfate catalyst based on chrysotile and graphite carbon nitride (g-C3N4) was synthesized for the first time. The abundant hydroxyl groups of chrysotile can react with amine groups of urea-derived intermediates and accelerate formation of double nitrogen defects (N-vacancy and cyano group) in g-C3N4, which can drastically improve the activation efficiency of PMS. The introdution of chrysotile can greatly increase the reaction time of hydroxyl and amine groups, and promote the generation of double nitrogen defects. This catalyst displayed superior catalytic performance for rhodamine B (RhB) degradation than bare chrysotile and g-C3N4. Moverover, this catalyst also has good cycle performance, structural stability and universal applicability, which provides an idea for the comprehensive utilization of asbestos tailings and environmental remediation.

Excited State Dynamics in Dual-Defects Modified Graphitic Carbon Nitride.

Significant efforts are focused on defect-engineering of metal-free graphitic carbon nitride (g-C3N4) to amplify its efficacy. A conceptually new multidefect-modified g-C3N4 having simultaneously two or more defects has attracted strong attention for its enhanced photocatalytic properties. We model and compare the excited state dynamics in g-C3N4 with (i) nitrogen defects (N vacancy and CN group) and (ii) dual defects (N vacancy, CN group, and O doping) and show that the nonradiative recombination of charge carriers in these systems follows the Shockley-Read-Hall mechanism. The nitrogen defects create three midgap states that trap charges and act as recombination centers. The dual-defect modified systems exhibit superior properties compared with pristine g-C3N4 because the defects facilitate rapid charge separation and extend the spectrum of absorbed light. The system doped with O shows better performance due to enhanced carrier lifetime and higher oxidation potential caused by a downshifted valence band. The study provides guidance for rational design of stable and efficient photocatalytic materials.

FeOOH coupling and nitrogen vacancies functionalized g-C3N4 heterojunction for efficient degradation of antibiotics: Performance evaluation, active species evolution and mechanism insight

In this study, the highly active g-C3N4-based photocatalysts were first constructed by assembling amorphous FeOOH nanoparticles on g-C3N4 nanosheets with nitrogen defects (FeOOH NPs/Nvac-CNNS). Such photocatalysts showed 92.83% and 73.86% degradation and mineralization efficiency of the oxytetracycline hydrochloride (OTC) within 90 min, respectively. Meanwhile, Response Surface Method (RSM) predicted that under optimal conditions (electricity 18.586 A, initial pH 6.371 and dosage 0.6 g/L), OTC degradation efficiency of 94.331% can be achieved. FeOOH NPs/Nvac-CNNS exhibited the excellent reutilization and practical application potential in OTC pollution purification of high and low concentration. The synergistic effect of N vacancies and FeOOH coupling endowed CNNS with advantages, such as the carrier’s fast separation, good visible-light adsorption, H2O2 fast decomposition and excellent molecular oxygen activation. Such advantages greatly contribute to OTC efficient removal in water. Based on the liquid chromatograph-mass spectrometer (LC-MS) analysis, the five possible degradation pathways of OTC were provided. Furthermore, through the quantitative structure-activity relationship (QSAR) analysis, biological toxicity prediction results of OTC and its intermediates indicated that the FeOOH NPs/Nvac-CNNS/vis system had great potential to achieve green and harmless treatment of OTC pollution.

Precisely Tailoring Nitrogen Defects in Carbon Nitride for Efficient Photocatalytic Overall Water Splitting.

Precisely tailoring the nitrogen defects has been verified to be a promising approach for promoting the photocatalytic efficiency of C3N4. Herein, two-coordinated-N vacancies are selectively introduced into the C3N4 framework by a facile Cl- modification method, whereas its concentration can be facilely tuned by varying Cl- usage in the process of thermal polymerization. Impressively, the optimal defective C3N4 (20 mg) exhibited superior hydrogen and oxygen evolution rates of 48.2 and 21.8 μmol h-1, respectively, in photocatalytic overall water splitting and an apparent quantum efficiency of 6.9% at 420 nm, the highest of reported single-component C3N4 photocatalysts for overall water splitting. Systematic studies including XPS, DFT simulations, and NEXAFS reveal that Cl- modification preferentially facilitates the introduction of two-coordinated-N vacancies through tuning the formation energy and promotes charge carrier separation efficiency, thereby greatly enhancing the photocatalytic efficiency. This work allows for a viable approach to rationally designing defective C3N4 for efficient photocatalysis.

Tunable gyromagnetic augmentation of nuclear spins in diamond

Nuclear spins in solids exhibit long coherence times due to the small nuclear gyromagnetic ratio. This weak environmental coupling comes at the expense of slow quantum gate operations, which should be as fast as possible for many applications in quantum information processing and sensing. In this work, we use nitrogen-vacancy (NV) centers in diamond to probe the nuclear spins within dark paramagnetic nitrogen defects (P1 centers) in the diamond lattice. The gyromagnetic ratio of the P1 nuclear spin is augmented by hyperfine coupling to the electron spin, resulting in greatly enhanced coupling to radiofrequency control fields. We then demonstrate that this effect can be tuned by variation of an external magnetic field. Our work identifies regimes in which we are able to implement fast quantum control of dark nuclear spins, and lays the foundations for further inquiry into rapid control of long-lived spin qubits at room temperature.

Enhanced Conductivity and Microstructure in Highly Textured TiN1-x /c-Al2O3 Thin Films.

Titanium nitride thin films are used as an electrode material in superconducting (SC) applications and in oxide electronics. By controlling the defect density in the TiN thin film, the electrical properties of the film can achieve low resistivities and a high critical temperature (Tc) close to bulk values. Generally, low defect densities are achieved by stoichiometric growth and a low grain boundary density. Due to the low lattice mismatch of 0.7%, the best performing TiN layers are grown epitaxially on MgO substrates. Here, we report for the first time a Tc of 4.9 K for ultrathin (23 nm), highly textured (111), and stoichiometric TiN films grown on 8.75% lattice mismatch c-cut Al2O3 (sapphire) substrates. We demonstrate that with the increasing nitrogen deficiency, the (111) lattice constant increases, which is accompanied by a decrease in Tc. For highly N deficient TiN thin films, no superconductivity could be observed. In addition, a dissociation of grain boundaries (GBs) by the emission of stacking faults could be observed, indicating a combination of two sources for electron scattering defects in the system: (a) volume defects created by nitrogen deficiency and (b) defects created by the presence of GBs. For all samples, the average grain boundary distance is kept constant by a miscut of the c-cut sapphire substrate, which allows us to distinguish the effect of nitrogen deficiency and grain boundary density. These properties and surface roughness govern the electrical performance of the films and influence the compatibility as an electrode material in the respective application. This study aims to provide detailed and scale-bridging insights into the structural and microstructural response to nitrogen deficiency in the c-Al2O3/TiN system, as it is a promising candidate for applications in state-of-the-art systems such as oxide electronic thin film stacks or SC applications.

Effect of oxygen atoms adsorption and doping on hexagonal boron nitride

h-BN is an excellent material, which can be used as insulating coating in aerospace field. However, it was reported that oxygen is inevitably attached to surface of h-BN when it works in oxygen-rich environment. In particularly, oxygen is doped when h-BN has defects. In this study, the effect of oxygen adsorption and doping on monolayer h-BN is studied by first principles . We found that mono-oxide, meta-dioxide and meta-trioxide can destroy the symmetry to a relatively large extent than para-dioxide, which reduces the band gap. Meanwhile, oxygen can repair the lattice when h-BN has a nitrogen defect, while multiple oxygen-doped will result in lattice distortion of different degrees when there are many defects. In particularly, the band gap of single-oxygen doping based on diatomic vacancy is relatively small. This study is helpful to evaluate the properties of h-BN in atomic-oxygen-rich environment. And it has certain significance for the application of h-BN in band gap engineering. • Adsorption of oxygen atoms on h-BN with different types of defects was calculated. • Under para-dioxide, band gap of h-BN is larger than others. • Oxygen can repair the lattice when h-BN has a nitrogen defect. • Adsorption and doping can change the symmetry and thus the band gap value.

Synergistic effect of biomass-derived carbon decoration and nitrogen defects on seaweed-like tubular g-C3N4 for enhanced photocatalytic H2 evolution

This work presents biomass-derived carbon modified N-deficient seaweed-like tubular g-C3N4 by facile thermal polymerization of freeze-dried sodium alginate, KOH and urea mixture, generating efficient and low-cost photocatalyst for H2 production.

Uncovering the multifaceted roles of nitrogen defects in graphitic carbon nitride for selective photocatalytic carbon dioxide reduction: a density functional theory study.

Surface defect engineering on the nanoscale has attracted extensive research attention lately; however, its role in modulating the properties and catalytic performance of a semiconducting material has not been comprehensively covered. Here, we systematically unraveled the effect of defect engineering towards textural, electronic and optical properties of graphitic carbon nitride (g-C3N4), as well as its photocatalytic mechanism of CO2 reduction using first-principle calculations by density functional theory through the introduction of various defect sites. Among the five unique atoms in g-C3N4, the vacancy site was found to be the most feasible at the two-coordinated nitrogen, N2. By initiating N2 point defects, an asymmetric electron density distribution was engendered around the vacancy region, which resulted in an evolution of semiconducting properties. We also discovered an improved charge separation efficiency and CO2 adsorption affinity in g-C3N4, which rendered a more thermodynamically feasible pathway for CO2 reduction to CO, CH3OH and CH4 fuels. This theoretical finding is hoped to shed light on the importance of the defect engineering strategy towards photocatalytic enhancement in g-C3N4.

Nitrogen defect-containing polymeric carbon nitride for efficient photocatalytic H2 evolution and RhB degradation under visible light irradiation.

Introducing defects in polymeric carbon nitride (CN) in a predetermined way is a great challenge to explicate the effect of defects on the photocatalytic activity. Herein, we provide a pathway to synthesize g-C3N4 with nitrogen defects by simply calcining melamine and trithiocyanuric acid at elevated temperature. Nitrogen defects at the N-bridging sites lead to an intermediate energy gap between the valence band and the conduction band, which greatly increases the photon absorption in the visible light range. Electron paramagnetic resonance (EPR) and photoluminescence (PL) verify that the significantly improved light utilization efficiency and rapid charge transfer correlate with nitrogen defects. The hydrogen evolution rate of 2SCN reached 41.4 μmol h−1, about 20.7 times that of pure g-C3N4, and its degradation rate for rhodamine B (RhB) is about 2.5 times that of CN. The experimental results proved that the photoinduced electron–hole pairs react with adsorbed O2 to form ˙O2−, facilitating the photodegradation of organic pollutants.

Formation of flaky carbon nitride and beta-Indium sulfide heterojunction with efficient separation of charge carriers for enhanced photocatalytic carbon dioxide reduction

The flaky carbon nitride containing nitrogen defects (NDCN) could effectively perform the photocatalytic reduction of carbon dioxide (CO2) due to its abundant active sites. Reducing the recombination of electrons and holes was also a method of semiconductor photocatalyst design. A nanosphere ball-flower Indium sulfide (In2S3) was synthesized via a simple hydrothermal approach, and then calcined to obtain the β-In2S3/NDCN heterojunction photocatalyst and applied for CO2 photocatalytic reduction. The best total yield (carbon monoxide, CO: 20.32 μmol·g−1·h−1; methane, CH4: 2.12 μmol·g−1·h−1) could be obtained at the optimized 20% β-In2S3/NDCN under near room temperature and pressure and without using any sacrificial agents or promoters, almost 1.7 times higher compared with NDCN. The composite catalyst still exhibited excellent stability after four cycles. The improvement of excellent performance was due to not only the enhancement of fine CO2 adsorption/activation and the light absorption ability, but also attributed to the formation of heterojunction, which accelerated the effective separation of electrons and holes. This work might provide a novel approach to design carbon nitride heterojunction photocatalysts with nitrogen defects for CO2 utilization.

Investigation on thermal conductivity of graphene/Si heterostructure based on molecular dynamics simulation

The effect of doping and defects on thermal conductivity of Graphene/Si interface structure based on molecular dynamics simulation is investigated. With the nitrogen and boron doping defect ration increasing, the thermal conductivity of heterostructure shows decline trend. But the boron doping effect to thermal conductivity of heterostructure is higher than that of nitrogen doping. It is analyzed that due to the mass of nitrogen and boron is different, the harmonic effect of lattice vibration happens to some extent. The interfacial thermal conductivity decreases monotonously with hydrogenation rate. Hydrogenated graphene has a greater influence on the thermal conductivity in Zigzag direction. When the hydrogenation rate reaches 5%, the thermal conductivity decreases to 77.8 W/mK. Intrinsic defects of graphene will greatly reduce the thermal conductivity of single-layer graphene/Si interface, and single vacancy defects have the greatest influence on thermal conductivity. It builds a basis for future work on progress investigation of thermal property of graphene film heterostructure.

Nanostructuring Nickel–Zinc–Boron/Graphitic Carbon Nitride as the Positive Electrode and BiVO4-Immobilized Nitrogen-Doped Defective Carbon as the Negative Electrode for Asymmetric Capacitors

Rationally designed compounds with exceptional surface functionalities are greatly necessary for efficient energy-storage technologies. Herein an aqueous battery-type hybrid supercapacitor device is fabricated based on amorphous nickel–zinc–boron/graphitic carbon nitride (Ni–Zn–B/g-C3N4) nanosheet network structures as the cathode and a bismuth vanadate-anchored carbon nanotube matrix with nitrogen dopants and defect sites (BiVO4/NC) as the anode. Interconnected nanosheet-assembled Ni–Zn–B/g-C3N4 porous networks are developed via a scalable liquid-phase reduction method, while the BiVO4/NC nanocomposite frameworks are prepared by a simple chemical precipitation route and annealing treatment. Because of the unique compositional and structural features as well as enhanced electrochemical properties, the as-assembled Ni–Zn–B/g-C3N4//BiVO4/NC aqueous alkaline device with a large working potential of 1.6 V exhibits a remarkable energy-storage capability with a high energy density of 78.4 Wh kg–1 and a power density of 907.7 W kg–1 together with a good cyclic performance (85.3% retention after 8000 cycles). Considering the intriguing results and reasonable design of the cathode and anode materials, this work provides a significant prospect for designing a high-performance energy-storage system. The intrinsically enhanced electrochemical performances of heterostructured Ni–Zn–B/g-C3N4 and BiVO4/NC demonstrate their potential utilization in energy-storage systems.

Nitrogen defects/boron dopants engineered tubular carbon nitride for efficient tetracycline hydrochloride photodegradation and hydrogen evolution

Polymeric carbon nitride (g-C3N4) exhibits only mediocre catalytic activity in photocatalytic environmental remediation and energy conversion because of its limited light absorption and sluggish charge transfer. Herein, we assembled novel, tubular carbon nitride (D-TCN450) with nitrogen defects/boron dopants via a self-supramolecular reaction and NaBH4 thermal reduction approach. Advanced characterization results suggested that introducing the nitrogen defects/boron dopants can effectively promote light trapping, charge separation, and valance-band downshift. Density functional theory and electron spin resonance results further proved that the fusion of cyano groups (nitrogen defects) into the framework of D-TCN450 can facilitate oxygen adsorption to form superoxide radicals. As a result, D-TCN450 exhibited dramatically improved photocatalytic hydrogen evolution and photodegradation of tetracycline hydrochloride at a 4- and 9-fold enhancement compared to pristine g-C3N4, respectively. This integrated engineering strategy might provide a unique paradigm for the rational design of novel photocatalysts for sustainable remediation and energy innovation.

Influence of integrated nitrogen functionalities in nitrogen doped graphene modified WO3 functional visible photocatalyst

Nitrogen doped graphene modified WO3 nanocomposites were synthesized through an effective methodology. The prepared photocatalysts were employed as active candidates for degradation of highly toxic organics i.e., 2, 4 dichloro phenol (2, 4-DCP) and methyl orange (MO). XRD profile of N-graphene showed complete reduction of GO into N-graphene. All diffraction peaks of WO3 along with N-graphene indicated monoclinic phase of WO3. SEM and TEM images of 3.0% N-graphene/WO3 have demonstrated the mixed morphology of irregular massive rod like blocks and round shaped particles of WO3 distributed on cracked sheets of N-graphene. Nitrogen defects in graphene altered zero band gap semi-metallic graphene to semiconducting material and increased the absorption edge of N-graphene/WO3 nanocomposites towards visible region as studied in DRS analysis. FTIR and Raman studies showed the strong connection between N-graphene and WO3 by making W−O−C surface linkage. The noticeable reduction in PL emission peaks of 3.0% N-graphene/WO3 indicated obvious separation of photo induced charge carriers. The study of radical scavengers suggested that holes (h+) and •OH are the main elements for the decontamination of both MO and 2, 4-DCP. XPS analysis shows all possible C−N bonding configurations in 3.0% N-graphene/WO3. 3.0% N-graphene/WO3 composite showed the maximum photo degradation of MO (~94.0%) and 2, 4-DCP (~81.0%). The synergism between N-graphene and WO3 results into more sporty sites on catalyst and restoring of sp2 structural defects in N-graphene lattice improve the transportation of charge carriers during photocatalysis. This work provides innovative strategies for designing the N-graphene/semiconductor nanosystems with enhanced photocatalytic phenomena in the environmental cleanup remedies.

Selective oxidation of glucose to gluconic acid and glucaric acid with chlorin e6 modified carbon nitride as metal-free photocatalyst

Photocatalysis has exhibited huge potential in many reactions, but the design of metal-free photocatalytic material for selective upgrading of biomass is rarely achieved. Here, we report that the metal-free photocatalyst consisted of nitrogen-deficient carbon nitride (BNCN) and chlorin e6 (Ce6) can efficiently and selectively oxidize glucose into gluconic acid and glucaric acid. Introducing nitrogen defects could significantly enhance the optical absorption and modulate the band structure. In addition, the combination of Ce6 with BNCN further improve the optical absorption property and promote effective separation of photon-generated carriers. As expected, the resultant Ce6@BNCN catalyst gave a total selectivity of gluconic acid, glucaric acid and arabinose as high as 70.9% at glucose conversion up to 62.3%, as is superior to previously reported photocatalytic systems. The mechanism for the enhancement of catalytic performance and the reaction pathway were revealed by experimental studies combined with DFT calculations.