Two-stage ignition exists in the low-temperature combustion process of n-heptane and the first-stage ignition also shows a negative temperature coefficient(NTC) phenomenon. To study key reactions and understand chemical principles affecting the first-stage ignition of n-heptane, a lumped skeletal mechanism with 62 species is obtained based on the detailed NUIGMech1.0 mechanism using the directed relation graph method assisted by sensitivity analysis and isomer lumping. The lumped mechanism shows good performance on ignition delay time under wide conditions. The study revealed that the temperature after the first-stage ignition is higher and a larger amount of fuel is consumed at lower initial temperatures. The temperature at the first-stage ignition is relatively insensitive to the initial temperature. Further sensitivity analysis and reaction path analysis carried out based on the lumped mechanism show that the decomposition of RO2 to produce alkene and HO2is the most important reaction to inhibit the first-stage ignitions. The chain branching explosion closely related to the first-stage ignition will be terminated when the rate constant for the RO2 decomposition is larger than that of the isomerization of RO2 to produce QOOH. The NTC behavior as well as other characteristics of the first-stage ignition can be rationalized from the competition between these two reactions. 相似文献
The two-dimensional (2D) C3N has emerged as a material with promising applications in high performance device owing to its intrinsic bandgap and tunable electronic properties. Although there are several reports about the bandgap tuning of C3N via stacking or forming nanoribbon, bandgap modulation of bilayer C3N nanoribbons (C3NNRs) with various edge structures is still far from well understood. Here, based on extensive first-principles calculations, we demonstrated the effective bandgap engineering of C3N by cutting it into hydrogen passivated C3NNRs and stacking them into bilayer heterostructures. It was found that armchair (AC) C3NNRs with three types of edge structures are all semiconductors, while only zigzag (ZZ) C3NNRs with edges composed of both C and N atoms (ZZCN/ CN) are semiconductors. The bandgaps of all semiconducting C3NNRs are larger than that of C3N nanosheet. More interestingly, AC-C3NNRs with CN/CN edges (AC-CN/CN) possess direct bandgap while ZZ-CN/CN have indirect bandgap. Compared with the monolayer C3NNR, the bandgaps of bilayer C3NNRs can be greatly modulated via different stacking orders and edge structures, varying from 0.43 eV for ZZ-CN/CN with AB′-stacking to 0.04 eV for AC-CN/CN with AA-stacking. Particularly, transition from direct to indirect bandgap was observed in the bilayer AC-CN/CN heterostructure with AA′-stacking, and the indirect-to-direct transition was found in the bilayer ZZ-CN/CN with ABstacking. This work provides insights into the effective bandgap engineering of C3N and offers a new opportunity for its applications in nano-electronics and optoelectronic devices. 相似文献
In this study, Pd based on 2-Aminopyrimidine and 1H-benzo[d]imidazol-2-amine functionalized Fe3O4 magnetic nanoparticles [(Pd-APM-PSi-Fe3O4) and (Pd-BIA-PSi-Fe3O4)] was designed and used for the synthesis of di aryl ether by Ulmann cross-coupling reactions. Ulmann reaction performed with mixing of the arylhalides and phenol derivatives in DMF solvent. The prepared catalysts were characterized with various analytical techniques such as FT-IR, XRD, TGA, SEM, TEM, EDX, ICP and VSM. Pd-APM-PSi-Fe3O4 and Pd-BIA-PSi-Fe3O4 catalysts demonstrated good to excellent yields catalytic efficiency for Ulmann reactions in comparison with to commercial palladium catalysts. The catalyst is easily recycled and reused without loss of the catalytic activity. The combined merits of reusable catalyst conditions make the condensation with safe operation, no leaching of pd into environment, low pollution, rapid access to products and simple workup. Also, these novel magnetic nanocatalysts are superior to the industry standard Pd in every relevant aspect. They feature a way higher initial activity, a much more convenient separation, better recycling, and less contamination of the products. Last but not least, they can be very easily prepared from commercially available Fe3O4 nanoparticles using standard laboratory equipment. 相似文献
Exploring new catalytic strategies for achieving efficient CO2 hydrogenation under mild conditions is of great significance for environmental remediation. Herein, a composite photocatalyst Zr-based MOF encapsulated plasmonic AuPt alloy nanoparticles (AuPt@UiO-66-NH2) was successfully constructed for the efficient photothermal catalysis of CO2 hydrogenation. Under light irradiation at 150 °C, AuPt@UiO-66-NH2 achieved a CO production rate of 1451 μmol gmetal−1 h−1 with 91 % selectivity, which far exceeded those obtained by Au@Pt@UiO-66-NH2 with Pt shell on Au (599 μmol gmetal−1 h−1) and Au@UiO-66-NH2 (218 μmol gmetal−1 h−1). The outstanding performances of AuPt@UiO-66-NH2 were attributed to the synergetic effect originating from the plasmonic metal Au, doped active metal Pt, and encapsulation structure of UiO-66-NH2 shell. This work provides a new way for photothermal catalysis of CO2 and a reference for the design of high-performance plasmonic catalysts. 相似文献
In this paper, we study semi-stable Higgs sheaves over compact Kähler manifolds. We prove that there is an admissible approximate Hermitian-Einstein structure on a semi-stable reflexive Higgs sheaf and consequently, the Bogomolov type inequality holds on a semi-stable reflexive Higgs sheaf. 相似文献
Indoleamine 2,3-dioxygenase (IDO), an immune checkpoint protein, can cause the depletion of tryptophan (Trp) and accumulation of its metabolite of kynurenine (Kyn) in cancer cells, and generates the immunosuppressive microenvironment that supports tumor cell growth. A novel immunoregulatory prodrug micelle based on polyethylene glycol-derivatized an IDO-selective inhibitor of 1-methyltryptophan (1-MT), PEG-Fmoc-1-MT, was developed for inhibiting the IDO activity of the conversion of Trp to Kyn in tumor microenvironments. To investigate the 1-MT distribution and Trp/Kyn ratios in mice tumors with PEG-Fmoc-1-MT prodrug micelles treatment, a HPLC–MS/MS method for simultaneous determination of 1-MT and IDO biomakers of Trp and Kyn in mouse tumors was developed and validated. Triple-quadrupole mass spectrometry with positive electrospray ionization as source ionization in multiple reaction monitoring at m/z 219.0?→?160.1, 205.0?→?118.2, 209.0?→?146.1 and 249.3?→?148.3 was used for determination of 1-MT, Trp, Kyn and matrine (internal standard). The method demonstrated good linearity at the concentrations ranging from 10 to 10,000 ng/mL and lower limits of quantitation of 1 ng/mL for 1-MT, Trp and Kyn, respectively. The validated method was successfully applied to 1-MT tumor biodistribution and Trp/Kyn ratio studies in 4T1 tumor bearing mice i.v. with PEG-Fmoc-1-MT prodrug micelles. The mice tumors with PEG-Fmoc-1-MT prodrug micelles treatment exhibited higher 1-MT accumulation and lower Trp/Kyn ratio, in comparison with those of mice with 1-MT solution treatment. The developed PEG-Fmoc-1-MT prodrug micelles could be a promising IDO immunoregulatory prodrug micelles for cancer immunotherapy.
The emergence of atomically precise metal nanoclusters with unique electronic structures provides access to currently inaccessible catalytic challenges at the single-electron level. We investigate the catalytic behavior of gold Au25(SR)18 nanoclusters by monitoring an incoming and outgoing free valence electron of Au 6s1. Distinct performances are revealed: Au25(SR)18− is generated upon donation of an electron to neutral Au25(SR)180 and this is associated with a loss in reactivity, whereas Au25(SR)18+ is generated from dislodgment of an electron from neutral Au25(SR)180 with a loss in stability. The reactivity diversity of the three Au25(SR)18 clusters stems from different affinities with reactants and the extent of intramolecular charge migration during the reactions, which are closely associated with the valence occupancies of the clusters varied by one electron. The stability difference in the three clusters is attributed to their different equilibria, which are established between the AuSR dissociation and polymerization influenced by one electron. 相似文献