Dongju Zhang

Theoretical Study of the Adsorption of Carbon Monoxide on Pristine and Silicon-Doped Boron Nitride Nanotubes

In order to explore the novel application of boron nitride nanotubes (BNNTs), we investigate reactivities of pristine and silicon-doped (Si-doped) (8,0) single-walled BNNTs towards the CO molecule by performing density functional theory calculations. Compared with weak physisorption on the pristine BNNT, the CO molecule presents strong chemical interaction with the Si-doped BNNT, as indicated by the calculated geometrical structures and electronic properties for these systems. It is suggested that doping BNNTs with silicon is expected to be a suitable strategy for adjusting the properties of BNNTs, and that Si-doped BNNTs are expected to find novel applications in nanotechnology.

Understanding the mechanism of cellulose dissolution in 1-butyl-3-methylimidazolium chloride ionic liquid via quantum chemistry calculations and molecular dynamics simulations

While N,N′-dialkylimidazolium ionic liquids (ILs) have been well-established as effective solvents for dissolution and processing of cellulose, the detailed mechanism at the molecular level still remains unclear. In this work, we present a combined quantum chemistry and molecular dynamics simulation study on how the ILs dissolve cellulose. On the basis of calculations on 1-butyl-3-methylimidazolium chloride, one of the most effective ILs dissolving cellulose, we further studied the molecular behavior of cellulose models (i.e. cellulose oligomers with degrees of polymerization nxa0=xa02, 4, and 6) in the IL, including the structural features and hydrogen bonding patterns. The collected data indicate that both chloride anions and imidazolium cations of the IL interact with the oligomer via hydrogen bonds. However, the anions occupy the first coordination shell of the oligomer, and the strength and number of hydrogen bonds and the interaction energy between anions and the oligomer are much larger than those between cations and the oligomer. It is observed that the intramolecular hydrogen bond in the oligomer is broken under the combined effect of anions and cations. The present results emphasize that the chloride anions play a critically important role and the imidazolium cations also present a remarkable contribution in the cellulose dissolution. This point of view is different from previous one that only underlines the importance of the chloride anions in the cellulose dissolution. The present results improve our understanding for the cellulose dissolution in imidazolium chloride ILs.

A theoretical study of silicon-doped boron nitride nanotubes serving as a potential chemical sensor for hydrogen cyanide

In order to search for a novel sensor to detect and control exposure to hydrogen cyanide (HCN) pollutant molecule in environments, the reactivities of pristine and silicon-doped (Si-doped) (8, 0) single-walled boron nitride nanotubes (BNNTs) towards the HCN molecule are investigated by performing density functional theory (DFT) calculations. The HCN molecule presents strong chemisorption on both the silicon-substituted boron defect site and the silicon-substituted nitrogen defect site of the BNNT, which is in sharp contrast to its weak physisorption on pristine BNNT. A remarkable charge transfer occurs between the HCN molecule and the Si-doped BNNT as proved by the electronic charge densities. The calculated data for the electronic density of states (DOSs) further indicate that the doping of the Si atom improves the electronic transport property of the BNNT, and increases its adsorption sensitivity towards the HCN molecule. Based on calculated results, the Si-doped BNNT is expected to be a potential resource for detecting the presence of toxic HCN.

Silicon-doped carbon nanotubes: a potential resource for the detection of chlorophenols/chlorophenoxy radicals

Chlorinated phenols and chlorophenoxy radicals are known as predominant precursors for forming polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF), which are highly carcinogenic and persistent organic pollutants (POPs). Density functional theory (DFT) calculations have been carried out to explore the potential possibility of carbon nanotubes (CNTs) serving as the resource for detecting and/or adsorbing these PCDD/PCDF precursors. Based on the calculated results on a pristine (8, 0) CNT and a Si-doped (8, 0) CNT with and without the presence of a 2-chlorophenol (2-CP)/2-chlorophenoxy radical (2-CPR), the typical representative of chlorophenols/chlorophenoxy radicals, we propose that pristine carbon nanotubes (CNTs) may be unsuitable for the desired applications due to their poor capability for catching chlorinated phenols/chlorophenoxy radicals, on the other hand, Si-doped CNTs are expected to be a potential resource for detecting and/or adsorbing (concentrating) these PCDD/PCDF precursors. The present results provide a guide to the relevant experimentalists, who are exploring novel applications of CNT-based materials in nanoscience and nanotechnology, and/or searching for suitable resources for detecting chlorophenols/chlorophenoxy radicals.

Density functional theory study on the geometrical and electronic structures of a new thinnest boron nanotube

Single-walled boron nanotubes (BNTs), which has been synthesized successfully recently, were imagined as duals (hexagonal pyramidal structures) of carbon nanotubes (CNTs) in the literature. In this work, we call attention to the fact that BNTs are not limited to hexagonal pyramidal structures constructed from the so-called Aufbau principle, and alternatively, we propose that the thinnest BNT may be a geometrical analog of the corresponding CNT. As shown by our density functional theory calculations, both the tubular open-end cluster models and the infinitely long tube possess high structural, dynamic, and thermal stability, which should be of interest for attempts at its synthesis. Compared to the energetically most stable isomers of the corresponding clusters, the thinnest BNT might be a metastable structure, and from an electronic view of point, it was predicted to have metallic conductivity like hexagonal pyramidal BNTs predicted previously, in contrast to semiconducting crystalline rhombohedral α- and β-boron.

Theoretical study on the mechanism of the side reaction of 1-butyl-3-methylimidazolium cation with d-glucose

To understand the non-inert nature of ionic liquids in cellulose chemistry, density functional theory calculations were carried out to investigate the reaction of 1-butyl-3-methylimidazolium cation ([bmim](+)) with model compounds α- and β-glucoses (the basic units of cellulose and its degradation products) in the absence and presence of base, triethylamine (TEA).The calculated energy barriers for the reactions of [bmim](+) with α- and β-glucoses without TEA were 67.97 and 66.19 kcal mol(-1), respectively. With the assistance of TEA, the barriers were reduced to 48.17 and 46.96 kcal mol(-1), due to the enhanced electrophilic abilities of H6 and nucleophilic abilities of C2 induced through deprotonation of the C2 atom, respectively. The present results rationalize the experimental finding well and provide a clear explanation on why imidazolium-based ionic liquids are considered as non-inert solvents in cellulose chemistry.

A New Pathway for Activation of C–C and C–H Bonds by Transition Metals in the Gas Phase

C–H and C–C bond activation of hydrocarbons at metal centres are of fundamental importance in biochemistry, organometallic chemistry, and catalysis. The present work aims to search for novel mechanisms for activation of C–C and C–H bonds by transition metals in the gas phase. Using high-level density functional calculations, we systemically studied the reactions of Ti+, V+, and Fe+ with ethane, and proposed new pathways of C–C and C–H bond activation—concerted activation of C–C and C–H bonds, and 1,2-H2 elimination. These two pathways clearly differ from the general addition–elimination mechanism.