Mechanistic insight into phase transfer agent assisted ultrasonic desulfurizationBhasarkar, Jaykumar B.; Singh, Mohit; Moholkar, Vijayanand S.
doi: 10.1039/c5ra12178gpmid: N/A
This paper attempts to gain physical insight into the phase transfer agent (PTA) assisted ultrasonic oxidative desulfurization process. Essentially, the synergistic links between mechanisms of PTA and ultrasound/cavitation have been identified by coupling experimental results with simulations of cavitation bubble dynamics and Arrhenius & thermodynamic analysis of reaction kinetics. It is revealed that ultrasonic oxidative desulfurization has a radical-based mechanism with a low activation energy. However, due to the high instability of radicals, the frequency factor is small leading to low dibenzothiophene (DBT) oxidation. PTA-assisted oxidative desulfurization has an ionic mechanism with a much higher activation energy. The synergistic effect of fine emulsification generated by micro-convection due to ultrasound and cavitation, and PTA-assisted interphase transport of oxidant results in almost complete oxidation of DBT. It is thus established that synergy between the mechanisms of ultrasound/cavitation and PTA is predominantly of a physical nature. Moreover, the effect of PTA is more marked for an ultrasonic system than a mechanically agitated system.
Effect of carbon dioxide on pore structure characteristics of dewatered lignite and the relevance to its moisture-adsorbing capacityWei, Fanjing; Jing, Xiaoxia; Yang, Yunlong; Liao, Junjie; Chang, Liping; Bao, Weiren
doi: 10.1039/c5ra22501apmid: N/A
Lignite with a high moisture content is needed to effectively remove water and maximally restrain the re-adsorption capacity of dewatered coal. The ambient gas during lignite drying is an important factor influencing the physical properties of dewatered samples. CO2 is the main component of exhaust gas, which has been reused in flash drying technology. The relationship between the drying characteristics of a typical Chinese lignite and the pore structure changes of dewatered coal in a CO2 atmosphere, and the effect on the behavior of re-adsorbing moisture were studied. Drying experiments of lignite samples under an Ar atmosphere were also carried out for comparison. The moisture re-adsorption experiments of dewatered coal samples were conducted at 30 °C under relative humidity of 75%. The results show that the drying efficiency of coal samples under a CO2 atmosphere is higher than that under an Ar atmosphere due to the swelling effect caused by the adsorption of CO2, but this difference between CO2 and Ar becomes gradually smaller with increase in the drying temperature. The dewatered coal sample obtained under a CO2 atmosphere shows a stronger ability to re-adsorb moisture caused by the swelling effect, which could be attributed to the changes of the structure of the coal sample in this atmosphere and the increase of the surface area where the moisture is primarily absorbed. The total moisture content in the coal sample after re-adsorbing moisture follows a linear relationship with the specific surface area of dewatered lignite.
A reference material of single-walled carbon nanotubes: quantitative chirality assessment using optical absorption spectroscopyTian, Ying; Jiang, Hua; Anoshkin, Ilya V.; Kauppinen, Lauri. J. I.; Mustonen, Kimmo; Nasibulin, Albert G.; Kauppinen, Esko I.
doi: 10.1039/c5ra23326gpmid: N/A
A reference material is essential to enable and accelerate commercialization of new materials. The National Institute of Standards and Technology (NIST) of the United States recently released the world's first reference material of a single-walled carbon nanotube (SWCNT) dispersion known as RM8281. Although the description of the material have been well documented by NIST, the chirality population, one of the most important properties, is yet unidentified for the RM8281. Here, we present for the first time a quantitative chirality assessment of the RM8281 reference material by using a method based on optical absorption spectroscopy. A universal background model has been established for SWCNT solid film samples, which proves to be the key to the successful chirality assessment. Our results show that approximately 75% of SWCNTs in RM8281 have diameters distributing in a narrow range of 0.7–0.9 nm, and about 69% of SWCNTs have chiral angles ranging from 15° to 30°. For the whole population, semi-conducting SWCNTs (∼74%) prevail significantly over metallic ones (∼26%). Importantly, ∼25% of the total RM8281 SWCNT population was found to be (6,5) nanotube. High-resolution transmission electron microscopy and electron diffraction technique were utilized to complete an adequate statistical analysis of chirality distribution in RM8281, giving a satisfactory agreement with the above absorption spectrum measurements, thus, validating absorption spectroscopy serving as a fast and standard protocol for quantifying the SWCNT chirality population.
Polydiacetylene stabilized gold nanoparticles – extraordinary high stability and integration into a nanoelectrode deviceLiffmann, R.; Homberger, M.; Mennicken, M.; Karthäuser, S.; Simon, U.
doi: 10.1039/c5ra17545cpmid: N/A
A new diacetylene containing photopolymerizable ligand molecule was developed, and tailored for applications in nanoelectronic devices based on gold nanoparticles. This ligand molecule consists of a thiol group, a diacetylene unit and a terminal carboxylic group. The thiol group guarantees preferred binding to the gold nanoparticles surface whereas at the same time the carboxylic group enables electrostatic stabilization. Applying this ligand molecule, gold nanoparticles in the size range of 12–13 nm were prepared. The diacetylene unit was polymerized upon UV irradiation leading to a polymeric ligand shell. Investigations including colloidal stability towards NaCl, DTT displacement reactions, and temperature were performed and indicate an extraordinary high degree of steric and electrostatic stabilization. Individual or at least a few of these particles were immobilized in between nanoelectrodes, thus forming nanoelectronic devices, which were characterized by transport measurements.
A low-cost and one-step synthesis of a novel hierarchically porous Fe3O4/C composite with exceptional porosity and superior Li+ storage performanceYang, Luyu; Liu, Wei; Wang, Huanlei; Liu, Shuang; Wang, Jifei; Chen, Jiaxin
doi: 10.1039/c5ra24166apmid: N/A
A hierarchical pore structure is believed to be an excellent architecture for metal oxide anode materials of lithium-ion batteries (LIBs). However, the difficulty and complication in synthesis limit their further application. In this work, a novel Fe3O4/C composite with a hierarchical pore carbon (HPC) network has been synthesized simply by one-step pyrolysis synthesis using ferrous gluconate as the precursor. This hierarchical porous framework derived from a loose assembly of the intersecting porous carbon rods presents a wide range of pore sizes and a rather large surface area (>226 cm2 g−1). Embedded with well-crystalline Fe3O4 particles, the resulting Fe3O4@HPC composite exhibits a high capacity of 1112 mA h g−1 at the end of the 100th cycle and an enhanced rate performance of above 600 mA h g−1 at a high current density of 2000 mA g−1. This might derive from the unique hierarchical pore system with a high overall porosity, which can not only facilitate the electrolyte diffusion but also alleviate severe volume variation efficiently in lithium ion insertion/extraction. More importantly, this provides us with a successful example to fabricate advanced anode materials simply by one-step pyrolysis of cheap organic–inorganic hybrids at low-cost.
Preparation of anti-corrosion superhydrophobic coatings by an Fe-based micro/nano composite electro-brush plating and blackening processWei, Yan; Hongtao, Liu; Wei, Zhu
doi: 10.1039/c5ra15640hpmid: N/A
Superhydrophobic coatings with high strength and corrosion resistance on hard metal surfaces have been attracting significant attention in recent years. In this paper, a quick and easy method using Fe-based micro/nano composite electro-brush plating and subsequent modification with stearic acid was established for fabricating superhydrophobic surfaces on A3 steel plates. The processing parameters including the working voltage, the brushing speed and the micro-TiO2 particle concentration were studied to determine their influences on the wettability. A blackening process was conducted to further improve the corrosion resistance of the Fe-based plating layer with high water repellency. The surface morphology and chemical composition were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Corrosion resistance ability was measured using an electrochemical workstation. The results suggested that: the rough structure of the superhydrophobic coatings can be successfully fabricated by electro-brush plating technology with appropriate parameters; after post-treatment by stearic acid, the contact angle of the composite coating was up to 156° and the sliding angle was even as low as 1° under the optimal process. Meanwhile blackening treated superhydrophobic coatings still maintained excellent superhydrophobicity and the self-corrosion potential improved by 0.116 V compared to the untreated brush plating layer and the prepared superhydrophobic coatings achieved an excellent long term anti-corrosion performance.
Photo-synergistic promoted in situ generation of Bi0–BiSbO4 nanostructures as an efficient catalyst for nitrobenzene reductionLiu, Mengqing; Lv, Li; Du, Xiaomeng; Lang, Junyu; Su, Yiguo; Zhao, Yanxia; Wang, Xiaojing
doi: 10.1039/c5ra20004kpmid: N/A
This work reports on the synthesis of BiSbO4 micro-flowers by a facile hydrothermal method. All as-prepared samples were carefully characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. TEM and XPS results indicated that partial Bi3+ ions in BiSbO4 nanoparticles were in situ converted into metallic bismuth to form Bi0–BiSbO4 nanostructures in the presence of NaBH4 during the reduction of 4-nitrophenol. The as-prepared Bi0–BiSbO4 was found to be an efficient, renewable and green noble metal free catalyst toward catalytic reduction of nitrobenzenes. Moreover, UV light can promote the reduction of Bi3+ to metallic bismuth, which can robustly and photo-synergistically accelerate the apparent reaction rate for catalytic reduction of nitrobenzenes into aminobenzenes. The in situ generation of Bi0–BiSbO4 nanostructures may provide new possibilities for the development of novel bismuth-based systems for catalytic applications.