Xiangkai Kong

Metal-free catalytic reduction of 4-nitrophenol to 4-aminophenol by N-doped graphene

The metal-free catalytic reduction of 4-nitrophenol (Nip) to 4-aminophenol (Amp) mediated by N-doped graphene (NG) was reported. Nip could be reduced to Amp completely without any by-product generation. The activity of the NG is comparable with some of the previously reported metallic catalysts. Interestingly, the NG sheet catalyzed reaction follows pseudo-zero-order kinetics, while all the metallic catalysts follow pseudo-first-order kinetics. The in situ FTIR experiment demonstrated that Nip ions will combine with NG via the O atoms of their hydroxyl groups. Theoretical calculations verified this adsorption model, and confirmed that the adsorption of Nip ions is the critical step, leading to the pseudo-zero-order kinetics. Moreover, only the carbon atoms next to the doped N atoms on NG surface can be activated, serving as the active sites. As expected, all four kinds of the doped N atoms are beneficial to the adsorption and activation of Nip, contributing to the catalytic reduction reaction.

Multifunctional Fe3O4@C@Ag hybrid nanoparticles as dual modal imaging probes and near-infrared light-responsive drug delivery platform.

Multifunctional nanocarriers based on Fe(3)O(4)@C@Ag hybrid nanoparticles with a diameter of 200 nm were fabricated by a facile method. Silver (Ag) nanoparticles were deposited onto the surface of Fe(3)O(4)@C nanospheres in dimethyl formamide (DMF) solution by reducing silver nitrate (AgNO(3)) with glucose. The nanocarriers of doxorubicin (DOX) with a high loading content of 997 mg/g and near-infrared (NIR) light-responsive drug delivery based on Ag nanoparticles were realized. Strong fluorescence can be observed in cell nucleus due to the presence of DOX after irradiated by NIR, and most cells were in the state of apoptosis, which indicates NIR-regulated drug release was realized. Moreover, measurements show that the nanocarriers could also be used as magnetic resonance imaging (MRI) contrast agents and fluorescent probes. The combination of synergistic NIR controlled drug release and dual modal imaging of MRI and two-photon fluorescence (TPF) imaging could lead to a potential multifunctional system for biomedical diagnosis and therapy.

Enhanced Oxygen Reduction Reactions in Fuel Cells on H‐Decorated and B‐Substituted Graphene

In the light of recent experimental research on the oxygen reduction reaction (ORR) with carbon materials doped with foreign atoms, we study the performance of graphene with different defects on this catalytic reaction. In addition to the reported N-graphene, it is found that H-decorated and B-substituted graphene can also spontaneously promote this chemical reaction. The local high spin density plays the key role, facilitating the adsorption of oxygen and OOH, which is the start of ORR. The source of the high spin density for all of the doped graphene is attributed to unpaired single π electrons. Meanwhile, the newly formed C-H covalent bond introduces a higher barrier to the p electron flow, leading to more localized and higher spin density for H-decorated graphene. At the same time, larger structural distortion should be avoided, which could impair the induced spin density, such as for P-substituted graphene.

Probing the influence of different oxygenated groups on graphene oxide's catalytic performance

Hydrothermally treated graphene oxide was found to be a new metal-free catalyst for reduction from 4-nitrophenol to 4-aminophenol. Based on the combined experimental and theoretical investigations, hydroxyl and alkoxy radicals, as well as holes were found beneficial to the catalytic performance, while epoxy and carboxyl groups were unfavorable and should be avoided in practical applications.

The positive influence of boron-doped graphyne on surface enhanced Raman scattering with pyridine as the probe molecule and oxygen reduction reaction in fuel cells

The impacts of doped B and N atoms on graphyne have been investigated systematically. It is concluded that B substituted graphyne could be a good substrate for surface enhanced Raman scattering (SERS) with pyridine as the probe molecule and it is also beneficial to oxygen reduction reaction (ORR) in fuel cells. The doped B atom will introduce holes to the graphyne, changing the electronic structure of the planer sheet and resulting in local positive charge centers. The positive charged areas on the flat surface will not only attract pyridine to form strong chemical bonds at the interface, enhancing the chemical mechanism of SERS, but also will promote the adsorption of OOH molecule on itself, facilitating ORR in fuel cells. The source of the local high spin density is originated by the unpaired pz electrons of the carbon atoms in the hexagonal ring close to the doped B atom, which also will contribute to the ORR.

Free‐Standing Holey Ni(OH)2 Nanosheets with Enhanced Activity for Water Oxidation

Electrochemical water oxidation is the key technology in water-splitting reactions and rechargeable metal-air batteries, which is very attractive for renewable energy conversion and storage. Replacement of precious catalysts with cost-effective and highly active alternatives is still a great challenge. Herein, based on theoretical predictions, holey structures are designed and fabricated on the free-standing conventional 2D OER catalyst. By well-controlled defects engineering, uniform tiny holes are created on the free-standing Ni(OH)2 nanosheets via a sol-gel method, with the embedded Zn components as the template for holes production. The whole preparation process is feasible and effective to make full use of the basal plane of 2D nanomaterials, which can provide higher surface area, richer defects, more grain boundaries, and edge sites, as well as greater distorted surfaces. Meanwhile, these holes developed inside the sheet structure can supply tremendous permeable channels for ions adsorption and transportation, enable a fast interfacial charge transfer and accelerate the reaction process. The as-prepared 2D holey Ni(OH)2 nanostructures exhibit excellent catalytic performance toward electrochemical water oxidation, with lower onset overpotentials and higher current densities compared with the pristine Ni(OH)2 catalyst, suggesting the holey defects engineering is a promising strategy for efficient water-splitting devices and rechargeable metal-air batteries.

The positive influence of boron-doped graphene with pyridine as a probe molecule on SERS: a density functional theory study

The influence of defects (such as vacancy and substitution atom) on SERS of graphene has been investigated systematically. It is found that B-substituted graphene has a positive effect on SERS with an enhancement factor of 103 to 104 and a frequency shift of approximately 30 cm−1, resulting from the electronic attraction between the positive charged substrate and the negative charged probe molecule, which forms a chemisorption interaction at the interface. The doped B atom could introduce some new excited states to the complex for charge transfer, and this is confirmed by the UV-Visible absorption spectra and charge difference densities.

A Generic Wet Impregnation Method for Preparing Substrate-Supported Platinum Group Metal and Alloy Nanoparticles with Controlled Particle Morphology

Mass production of shape-controlled platinum group metal (PGM) and alloy nanoparticles is of high importance for their many fascinating properties in catalysis, electronics, and photonics. Despite of successful demonstrations at milligram scale using wet chemistry syntheses in many fundamental studies, there is still a big gap between the current methods and their real applications due to the complex synthetic procedures, scale-up difficulty, and surface contamination problem of the made particles. Here we report a generic wet impregnation method for facile, surfactant-free, and scalable preparation of nanoparticles of PGMs and their alloys on different substrate materials with controlled particle morphology and clean surface, which bridges the outstanding properties of these nanoparticles to practical important applications. The underlying particle growth and shape formation mechanisms were investigated using a combination of ex situ and in situ characterizations and were attributed to their different interactions with the applied gas molecules.

Effect of temperature change on power generation of microbial fuel cell

Microbial fuel cell (MFC), which can directly generate electricity from biodegradable materials, has been receiving increasing attention. Effects of temperature change on power density, electrode potential, columbic efficiency, chemical oxygen demand removal and internal resistance in two chambers MFCs were examined in this paper. The maximum power density of 7.89 W/m3 was achieved at 37 °C, with 199% higher at 10 °C (2.64 W/m3), 24% higher at 30 °C (6.34 W/m3) and 21% higher at 43 °C, no steady power generation was observed at 55 °C. Low temperature to 10 °C might have a huge effect on anode potential, especially at higher current, but increasing the temperature to 43 °C had a main effect on the cathode performance when the MFCs have been established at 37 °C. The internal resistance of MFC was about 29 Ω at 37 °C, and increased 62% and 303% when MFC switched to 30 °C and 10 °C. Similarly, internal resistance increased 48% at 43 °C. The effect of temperature on MFC performance was expressed by internal resistance, the higher the internal resistance of MFC, the lesser the power density obtained. The Columbic efficiencies were 8.65% at 30 °C, 8.53% at 37 °C, and 13.24% at 43 °C. These results demonstrate that MFCs can effectively be operated over a wide range of temperatures.

The positive influence of boron-doped graphene for its supported Au clusters: enhancement of SERS and oxygen molecule adsorption

The interactions between Au clusters and graphene sheets with and without doping have been studied systematically. It is found that B-doped graphene is a good support for Au clusters, not only because of the charge transfer from the graphene sheet to its supported Au clusters, but also due to its stronger interaction at the interface resulting from the doped B atom, which will facilitate more electrons being transferred to the upper surface of the Au cluster. This is good for surface-enhanced Raman scattering (SERS) and molecule oxygen adsorption, beneficial to the material preparation and apparatus design for high active SERS substrates and nano-catalysts.