Monthly Archives: September 2023

Synthesis and Characterization of a Highly Electroactive Composite Based on Au Nanoparticles Supported on Nanoporous Activated Carbon for Electrocatalysis

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Synthesis and Characterization of a Highly Electroactive Composite Based on Au Nanoparticles Supported on Nanoporous Activated Carbon for Electrocatalysis

Electrocatalysis: Gold nanoparticles with diameter between 5 and 20 nm evenly distributed onto porous activated carbon (Norit) were obtained using a facile “one-pot” chemical synthesis technique with very high metal utilization. The AuNP/C nanocomposite was characterized using SEM, HAADF-STEM electron tomography and electrochemical techniques, revealing a very large electroactive surface area (EASA). The figure shows the HAADF-STEM image (a) and the respective EDX elemental distribution (b) for the AuNP/C composite with 9.3 % Au-loading developed in this work (Au is marked in red and C in green).


Abstract

A facile, “one-pot”, chemical approach to synthesize gold-based nanoparticles finely dispersed on porous activated carbon (Norit) was demonstrated in this work. The pH of the synthesis bath played a critical role in determining the optimal gold-carbon interaction, which enabled a successful deposition of the gold nanoparticles onto the carbon matrix with a maximized metal utilization of 93 %. The obtained AuNP/C nanocomposite was characterized using SEM, HAADF-STEM electron tomography and electrochemical techniques. It was found that the Au nanoparticles, with diameters between 5 and 20 nm, were evenly distributed over the carbon matrix, both inside and outside the pores. Electrochemical characterization indicated that the composite had a very large electroactive surface area (EASA), as high as 282.4 m2 gAu −1. By exploiting its very high EASA, the catalyst was intended to boost the productivity of glucaric acid in the electrooxidation of its precursor, gluconic acid. However, cyclic voltammetry experiments revealed a very limited reactivity towards gluconic acid oxidation, due to the spacial hindrance of gluconic acid molecule which prevented diffusion inside the catalyst nanopores. On the other hand, the as-synthesized nanocomposite promises to be effective towards the ORR, and might thus find potential application as anode catalyst for fuel cells as well as for the scalability of all those electrochemical reactions involving small molecules with high diffusivity and catalysed by noble metals (i. e. CO2, CH4, N2, etc..).

Mechanistic Insights into Formation of Residual Solid in Lignin Depolymerization

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Mechanistic Insights into Formation of Residual Solid in Lignin Depolymerization

The mechanism for residual solid (char) formation in lignin depolymerization is proposed. The results demonstrate that the lignin-char is composed of a multiplicate layer of alternate lignin and coke. During the lignin conversion, residual solid is generated from the G and S units in phenolic oligomer via the pathways of alkyl aryl ether rearrangement, α-hydroxyl coupling reaction, and aldol condensation.


Abstract

Current techniques of lignin conversion are challenged by the low carbon utilization efficiency resulting from the severe generation of residual solid (char). Therefore, a better understanding of pathway for char formation is significant and highly desired for lignin valorization. In this work, we propose a fundamental mechanistic insight into char formation in lignin depolymerization, using hydrothermal decomposition as model reaction. The results demonstrate that the char featuring a multi-layer construction of coke and oligomer contains mainly G units, primarily generated from native G-lignin and demethoxylation of S-lignin. Instead, H-lignin contributes to the formation of volatile monophenols. Furthermore, new methylene bridges form between the benzene rings in lignin, which consequently results in the formation of recalcitrant char. Based on these observations, a plausible mechanism for char formation is proposed and verified by the density functional theory calculation.

Is Ethanol Essential for the Lithium‐Mediated Nitrogen Reduction Reaction?

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Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

The crucial ethanol-formed solid-electrolyte interphase (SEI) in Li-nitrogen reduction reaction (NRR) enables ammonia synthesis, even in an ethanol-free electrolyte. The role of ethanol goes beyond acting as a proton shuttle; it facilitates a good SEI and participates in electrolyte transformations.


Abstract

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising method for decentralized ammonia synthesis using renewable energy. An organic electrolyte is utilized to combat the competing hydrogen evolution reaction, and lithium is plated to activate the inert N2 molecule. Ethanol is commonly used as a proton shuttle to provide hydrogen to the activated nitrogen. In this study, we investigate the role of ethanol as a proton shuttle in an electrolyte containing tetrahydrofuran and 0.2 M lithium perchlorate. Particularly designed electrochemical experiments show that ethanol is necessary for a good solid-electrolyte interphase but not for the synthesis of ammonia. In addition, electrochemical quartz crystal microbalance (EQCM) demonstrates that the SEI formation at the onset of lithium plating is of specific importance. Chemical batch synthesis of ammonia combined with real-time mass spectrometry confirms that protons can be shuttled from the anode to the cathode by other species even without ethanol. Moreover, it raises questions regarding the electrochemical nature of Li-NRR. Finally, we discuss electrolyte stability and electrochemical electrode potentials, highlighting the role of ethanol on electrolyte degradation.

Electronic properties, quantum capacitance and photocatalyst for water splitting of Sc2CO2 MXene under uniaxial strain

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Electronic properties, quantum capacitance and photocatalyst for water splitting of Sc2CO2 MXene under uniaxial strain

Uniaxial strain can effectively modulate photocatalytic capacity for overall water splitting. Sc2CO2 under strains within appropriate pH scope are potential photocatalyst for water redox reaction. Sc2CO2 under tensile strain is potential cathode materials. Wide voltage keeps the electrode type of materials under strain. Sc2C with mixed termination is further explored.


Abstract

MXenes have wide applications because of the structural flexibility and compositional diversity. Quantum capacitance, electronic and photocatalytic properties of Sc2CO2 monolayer under uniaxial strains are investigated by first-principles calculation. Sc2CO2 monolayer can withstand stress up to 13.96 N/M and about 14% tensile uniaxial strain limit. Sc2CO2 undergoes a transition from semiconductor to metal at −15% uniaxial strain. Sc2CO2 under uniaxial strains are only used for the water reduction at pH = 0. Sc2CO2 under uniaxial strains of −10%, −7%, −3%, 0%, and 4% within the appropriate pH scope are potential photocatalysts for water redox reaction. Sc2CO2 with −15% uniaxial strain is promising anode material, and Sc2CO2 with tensile uniaxial strain is more potential cathode material. Wide voltage improves the top quantum capacitance at negative bias under uniaxial strain and keeps the type of electrode materials. Quantum capacitance of Sc2C with mixed termination (Sc2CO0.59F1.19(OH)0.22) under uniaxial strain is explored. The introduction of uniaxial strain and mixed termination has little effect on the electrode type of Sc2CO2 MXene.

Development of Mixed Matrix Membranes with Penetrating Subnanochannels for Efficient Molecule/Ion Separation

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Development of Mixed Matrix Membranes with Penetrating Subnanochannels for Efficient Molecule/Ion Separation

Cell membranes with penetrating ion channels have unique pathways for efficient transportation of molecules and ions, providing an excellent model for the construction of high-performance mixed matrix membranes (MMMs). In this minireview, recent advances in the design and construction of MMMs with penetrating subnanochannels as well as their applications in gas separation and ion sieving are discussed in detail.


Abstract

Membrane-based separation technologies are becoming increasingly prominent in many important industrial separation applications. In the past decade, nanoporous materials, as promising filler components for high-performance mixed matrix membranes (MMMs), have seen a boom given the merits of remarkable chemical and structural variability. However, it remains challenging to address the trade-off effect of MMMs between molecular/ionic selectivity and permeability. Biological ion channels that penetrate through cell membranes have provided new insights for the construction of novel structures of MMMs. In recent years, MMMs with cell membrane-like structures have gained much attention and achieved significant progress in the field of separation. In this minireview, recent advances in the design and construction of MMMs with penetrating subnanochannels are summarized. After that, the applications of these MMMs with penetrating subnanochannels in gas separation and ion sieving are highlighted and discussed in detail. Finally, the future developments and challenges for the MMMs with penetrating subnanochannels are prospected.

Accurate ab initio potential energy surface, rovibrational energy levels and resonance interactions of triplet (X~$$ \overset{\sim }{X} $$3B1) methylene

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Accurate ab initio potential energy surface, rovibrational energy levels and resonance interactions of triplet (X~$$ \overset{\sim }{X} $$3B1) methylene

Overtones of the bending mode of triplet methylene predicted from the developed ab initio PES


Abstract

In this work, we report rovibrational energy levels for four isotopologues of methylene (CH2, CHD, CD2, and 13CH2) in their ground triplet electronic state (X~$$ \overset{\sim }{X} $$3 B 1) from variational calculation up to ~10,000 cm−1 and using a new accurate ab initio potential energy surface (PES). Triplet methylene exhibits a large-amplitude bending vibration and can reach a quasilinear configuration due to its low barrier (~2000 cm−1). To construct the ab initio PES, the Dunning's augmented correlation-consistent core-valence orbital basis sets were employed up to the sextuple-ζ quality [aug-cc-pCVXZ, X = T, Q, 5, and 6] combined with the single- and double-excitation unrestricted coupled cluster approach with a perturbative treatment of triple excitations [RHF-UCCSD(T)]. We have shown that the accuracy of the ab initio energies is further improved by including the corrections due to the scalar relativistic effects, DBOC and high-order electronic correlations. For the first time, all the available experimental rovibrational transitions were reproduced with errors less than 0.12 cm−1, without any empirical corrections. Unlike more “traditional” nonlinear triatomic molecules, we have shown that even the energies of the ground vibrational state (000) with rather small rotational quantum numbers are strongly affected by the very pronounced rovibrational resonance interactions. Accordingly, the polyad structure of the vibrational levels of CH2 and CD2 was analyzed and discussed. The comparison between the energy levels obtained from the effective Watson A-reduced Hamiltonian, from the generating-function approach and from a variational calculation was given.

Efficient One‐pot Zeolite Synthesis Protocol from the Metastable *BEA to MTW Topology and Its Impact on the Methanol‐to‐Hydrocarbons Process

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Efficient One-pot Zeolite Synthesis Protocol from the Metastable *BEA to MTW Topology and Its Impact on the Methanol-to-Hydrocarbons Process

The “one-pot” inter-zeolite conversion process has been probed during the transformation from *BEA to MTW topology, which was subjected to methanol-to-hydrocarbons reactions and advanced characterization (including operando conditions) to derive structure-reactivity relationships.


Abstract

The inter-zeolite conversion is a method to convert one meta-stable zeolite to a thermodynamically stable zeolite. Despite the enormous interest, this method is yet to be popularized or standardized in the zeolite community. Intending to provide more insights into hydrothermal conversions from one zeolite to another, this work developed a novel one-pot and flexible synthetic protocol to efficiently obtain the meta-stable *BEA topology and its derived MTW topology by varying the hydrothermal crystallization time. This inter-zeolite conversion process led to changes in the zeolite framework and modified physicochemical properties during the process. Such a transformation was feasible by forming hierarchical zeolite phases sharing a similar “mtw”-based common building units, possibly driving such conversion. The structure-reactivity relationship of four different zeolite materials, synthesized from this one-pot inter-zeolite conversion method, was established concerning their performance in the methanol-to-hydrocarbon (MTH) process, which has been well supported by operando UV-vis diffuse reflectance spectroscopic study coupled with online mass spectrometry and solid-state NMR spectroscopy. As a result, the pathway to synthesize various target zeolites from an identical initial synthesis gel with desired physicochemical properties has been scrutinized.

Vanadium(IV)‐oxo Corrole Catalyzed Selective Oxidative Cleavage of Alkenes to Aldehydes

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Vanadium(IV)-oxo Corrole Catalyzed Selective Oxidative Cleavage of Alkenes to Aldehydes

An oxo[5,10,15-tris(4-nitrophenyl)corrolato]vanadium (IV) complex (cat.), has been successfully synthesized and the existence of two tautomeric forms of this complex in solution has been established. Oxo[5,10,15-tris(4 nitrophenyl)corrolato]vanadium (IV) (cat.) in the presence of H2O2 cleaves olefinic bonds to yield the corresponding aldehyde compounds. A mechanism was also proposed for these catalysis reactions.


Abstract

A practical and efficient protocol for oxidative cleavage of olefinic bonds especially in arylated olefins has been demonstrated. Herein, an oxo[5,10,15-tris(4-nitrophenyl)corrolato]vanadium (IV) complex (cat.), has been successfully synthesized and the existence of two tautomeric forms of this complex in solution has been established. Oxo[5,10,15-tris(4-nitrophenyl)corrolato]vanadium (IV) (cat.) in the presence of H2O2 cleaves olefinic bonds to yield the corresponding aldehyde compounds. In general, a high valent, oxo-(porphyrinoid)-metal complex catalyzes the epoxide formation reactions, however, in the present case, we have observed the exclusive formation of aldehydes. The reaction offered aryl aldehydes with good yields and excellent selectivity. A mechanism was also proposed for these catalysis reactions.

Iron‐Based Nanoparticles Oxygen Scavenger for Suppressing Heat‐Stable Salts Formation in Amine

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Iron-Based Nanoparticles Oxygen Scavenger for Suppressing Heat-Stable Salts Formation in Amine

The correlation of physicochemical properties of iron-based nanoparticles with their activity in oxygen-scavenging was developed. The addition of a 20 %Fe/HZSM5 oxygen scavenger to methyl diethanolamine (MDEA) did not jeopardize the CO2 absorption performance but inhibited the MDEA degradation. The absence of the degraded products prevented the formation of heat-stable salts that cause foaming issues.


Abstract

Heat-stable salts (HSS), which trigger excessing foaming in absorber, are formed when protonated methyl diethanolamine (MDEA) reacts with the more acidic degraded products in the presence of dissolved oxygen (DO). The aim is to suppress the HSS formation in MDEA solution inaugurally employing a hybrid iron-based nanoparticles (HINP) oxygen scavenger. It was discovered that the oxygen-scavenging performance of a more cost-effective 20 %Fe/HZSM5 was one-fold higher than the 20 %Fe/MCM-41. The former was verified for its superior structural properties. The Fe2+ on its surface first reacted with DO, preventing DO from oxidizing the MDEA. Consequently, the absence of hydroxyl radicals eliminated the potential of formic acid formation, hence suppressing the MDEA-acid HSS formation.

Comprehensive Phytochemical Content by LC/MS/MS and Anticholinergic, Antiglaucoma, Antiepilepsy, and Antioxidant Activity of Apilarnil (Drone Larvae)

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Comprehensive Phytochemical Content by LC/MS/MS and Anticholinergic, Antiglaucoma, Antiepilepsy, and Antioxidant Activity of Apilarnil (Drone Larvae)


Abstract

Apilarnil is 3–7 days old drone larvae. It is an organic bee product known to be rich in protein. In this study, the biological activities of Apilarnil were determined by its antioxidant and enzyme inhibition effects. Antioxidant activities were determined by Fe3+, Cu2+, Fe3+-TPTZ ((2,4,6-tris(2-pyridyl)-s-triazine), reducing ability and 1,1-diphenyl-2-picrylhydrazyl (DPPH⋅) scavenging assays. Also, its enzyme inhibition effects were tested against carbonic anhydrase I and II isoenzymes (hCA I, hCA II), acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Antioxidant activity of Apilarnil was generally lower than the standard molecules in the applied methods. In DPPH⋅ radical scavenging assay, Apilarnil exhibited higher radical scavenging than some standards. Enzyme inhibition results towards hCA I (IC50: 14.2 μg/mL), hCA II: (IC50: 11.5 μg/mL), AChE (IC50: 22.1 μg/mL), BChE (IC50: 16.1 μg/mL) were calculated. In addition, the quantity of 53 different phytochemical compounds of Apilarnil was determined by a validated method by LC/MS/MS. Compounds with the highest concentrations (mg analyte/g dry extract) were determined as quinic acid (1091.045), fumaric acid (48.714), aconitic acid (47.218), kaempferol (39.946), and quercetin (27.508). As a result, it was determined that Apilarnil had effective antioxidant profile when compared to standard antioxidants.