Synthesis and characterization of fluoropolymers with intrinsic microporosity and their hydrogen adsorption studies

Microporous polymers with rigid organic architecture offer a wide range of efficient on board hydrogen storage at low temperature. The fluoropolymers with intrinsic microporosity (MP1 and MP2) were synthesized and characterized. Characterization technique such as high resolution transmission electron microscopy (HRTEM) revealed that the highly stable microporous structure of MP2 was composed of nanoporous frame work which was further supported by the computational study. The high surface area and microporosity of the polymers were estimated by measuring the N₂ gas adsorption. The MP1 and MP2 exhibit BET surface areas 666 and 1050 m²/g respectively. The micropore size distribution curves show a higher concentration of subnanometer pores. The hydrogen storage capacity of the prepared polymers are promising and the performance relative to other microporous polymers is comparable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tuning and thermal exfoliation graphene-like carbon nitride nanosheets for superior photocatalytic activity

In this work, ultrathin graphene-like carbon nitride nanosheets with rich nanoporous and excellent hydrophilic characteristics were synthesized by a simple and effective thermal exfoliation of bulk g-C₃N₄. In order to fully understand the effect of thermal exfoliation conditions on the texture, surface state, and photocatalytic activity of the resulting g-C₃N₄, a series of exfoliated g-C₃N₄ were prepared by adjusting the thermal exfoliation temperature and time. The detailed characterization and analysis distinctly suggested that increasing exfoliation temperature led to a large number of nitrogen vacancies and increased specific surface area, further prolonging exfoliation time, the thermal exfoliation degree was enhanced, more carbon vacancies and enlarged pore volume formed in the resulting products. Further, the exfoliation degree and photocatalytic ability of the resultant products were enhanced by increasing thermal exfoliation temperature and time. The optimized ultrathin graphene-like carbon nitride nanosheets exhibited a 89.6% degradation efficiency for Rh6G only in 10 min, which was much faster than other such nanosheets reported in previous literature.     

Zn-Al类水滑石磷吸附剂的制备及其吸附性能

采用共沉淀法制备了一系列Zn-Al类水滑石吸附剂,并考察了制备条件对其磷酸盐吸附性能的影响。结果表明,在制备温度为70℃、共沉淀剂为NaOH、陈化时间为6 h及焙烧温度为300℃时得到的Zn-Al类水滑石对城市污水处理厂污泥脱水液中磷酸盐的吸附效果最好,其饱和吸附容量达72.46 mg P·(g吸附剂)^-1。该吸附剂吸附水中磷的动力学拟合效果表现为假二级动力学方程>Elovich方程>假一级动力学方程。吸附等温线符合Langmuir吸附模型。     

Synthesis of surface-functionalized graphene nanosheets with high Pt-loadings and their applications to methanol electrooxidation

Surface-functionalized graphene nanosheets (GNSs) were synthesized from natural graphite via chemical oxidation and subsequent thermal exfoliation. High Pt metal loadings, up to 80 wt.%, were deposited over the synthesized GNS supports and the Pt particle size was maintained at less than 3 nm. The current densities of methanol electrooxidation with these Pt/GNS catalysts were at least twice as large as those observed with conventional Pt/C catalysts. Furthermore, these Pt/GNS catalysts maintained high Pt mass activities with increased Pt loading on the working electrode, ranging from 0.2 to 2.0 mg/cm². This improved mass activity indicates that our electrocatalysts are able to provide more efficient Pt utilization for alcohol electrooxidation compared to conventional catalysts.     

Electrochemical enhancement of adsorption capacity of activated carbon fibers and their surface physicochemical characterizations

The adsorption of activated carbon fibers (ACFs) and their surface characteristics were investigated before and after electrochemical polarization. The adsorption kinetics of m-cresol showed the dependence on polarized potential, and the adsorption rate constant increased by 77.1%, from 6.38 × 10⁻³ min⁻¹ at open-circuit (OC) to 1.13 × 10⁻² min⁻¹ at polarization of 600 mV. The adsorption isotherms at different potentials were in good agreement with Langmuir isotherm model, and the maximum adsorption capacity increased from 2.28 mmol g⁻¹ at OC to 3.67 mmol g⁻¹ at polarized potential of 600 mV. These indicated that electrochemical polarization could effectively improve the adsorption rate and capacity of ACFs. The surface characteristics of ACFs before and after electrochemical polarization were evaluated by N₂ adsorption-desorption isotherms, scanning electron microscope (SEM), zeta potential and Fourier transform infrared spectroscopy (FTIR). The results showed that the BET specific surface area and pore size increased as the potential rose. However, the surface chemical properties of ACFs hardly changed under electrochemical polarization of less than 600 mV. This study was beneficial to understand the mechanism of electrochemically enhanced adsorption.     

Gas-assisted exfoliation of boron nitride nanosheets enhancing adsorption performance

A gas exfoliation strategy for controllable preparation of boron nitride (BN) nanosheets with few-layered structure were reported. The green exfoliation process provides the BN nanosheets remarkable increment of adsorption capacities to organic contaminants, which is ascribed to better exposure of active sites originating from the larger surface area and thinner layer. Moreover, the prepared BN also exhibits outstanding recyclability.     

Preparation of short carbon nanotubes by mechanical ball milling and their hydrogen adsorption behavior

Short multi-wall carbon nanotubes (MWNTs) with open tips were obtained by mechanical ball milling. The microstructure characteristics of MWNTs before and after ball milling were checked by transmission electron microscopy (TEM). The effect of ball milling on the hydrogen adsorption behavior of the MWNTs was studied. The hydrogen adsorption experiments were carried out at room temperature under a pressure of 8-9 MPa. The hydrogen adsorption capacity of carbon nanotubes milled for 10 h was 0.66 wt%, which was about six times that of MWNTs without milling. For the carbon nanotubes milled with MgO for 1 h, a hydrogen adsorption capacity of 0.69 wt% was obtained. The enhancement of hydrogen adsorption might result from the increase of defects and surface area of the MWNTs caused by ball milling.     

Influence of the alignment degree of CVD-grown carbon nanotubes on their functionalization and adsorption capacity

Oxygen functionalized multiwalled carbon nanotubes (CNTs) were prepared from aligned and bundle-like CVD-grown CNTs by chemical treatment with different reagents of increased oxidation degree. As the severity in the oxidation degree increases elimination of the amorphous carbon is observed. However, contrary to what was previously reported, aligned CNTs treated in less severe oxidation conditions they exhibit an increased number of oxygen containing functional groups (COH/CO groups). Meanwhile, when treated in the more severe oxidation conditions, they have the highest number of COOH groups due to the appearance of defects and shortening of the tubes. In the benzene adsorption in water, aligned CNTs display faster kinetics in all cases. The best adsorption capacity is achieved with aligned CNTs treated in very severe conditions possibly due to their enhanced solubility in water, which favors electrostatic interactions and π–π interactions between the benzene rings and the CNT walls.     

重金属离子在泥煤中的饱和吸附容量与离子结构之间的关系

以泥煤泥炭为吸附剂进行了N i2 ,Cu2 ,Cd2 ,Ce4 ,Eu3 ,Dy3 ,Lu3 的吸附实验,选用极化指数、共价指数与吸附指数来表征重金属离子结构差异。聚类分析可将7种重金属离子分为5类,较好的Langmuir等温吸附方程拟合后计算得到饱和吸附容量由大到小排列顺序为:Cu2 >N i2 >Cd2 >Lu3 >Ce4 >Dy3 >Eu3 ,吸附指数与饱和吸附容量具有很好地线性关系,建立了泥煤对重金属的饱和吸附容量与重金属吸附指数之间的模型关系。     

CuO/凹凸棒石黏土复合材料的制备及其吸附、抑菌性能研究

以凹凸棒石粘土为载体,采用共混水热法制备了纳米氧化铜/凹凸棒石黏土复合材料前驱体,450℃煅烧后得到凹凸棒石黏土负载的多孔氧化铜复合材料,考察了其吸附、抑菌性能。结果表明,复合材料中CuO的质量分数为50%时,亚甲基蓝色度的去除率达80%以上,对金黄色葡萄球菌和大肠杆菌的增长具有良好的抑制作用。     

AlO(OH)纳米片和纳米棒的水热法制备及其对牛血清白蛋白的吸附作用

以EDTA-2Na为螯合剂,铝盐为铝源,尿素为沉淀剂,采用水热法并使反应物以气液界面接触反应合成勃姆石型[AlO(OH)]纳米片及纳米棒;以透射电子显微镜(TEM)、X射线衍射仪(XRD)、傅里叶红外光谱仪(FTIR)等仪器对样品的尺寸、相位、形貌等进行了表征。结果表明,反应温度、时间等对样品的形貌、结晶度等起决定作用,合成的AlO(OH)对牛血清白蛋白(BSA)有较高的吸附能力,且在Al与BSA的质量比为1∶2时,吸附效果最佳。     

The effect of oxidation on the surface chemistry of sulfur-containing carbons and their arsine adsorption capacity

Two carbons with different sulfur contents were prepared and oxidized either by heating in air or by chemical treatment. The samples were then tested as adsorbents of arsine in dynamic conditions at room temperature, both in dry conditions and in the presence of moisture. Chemical and structural features of the initial and arsine-exposed materials were analyzed by energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analyses, sorption of nitrogen and sorption of water. It was found that oxygen- and sulfur-containing groups participate in arsine oxidation to arsenic tri- and pentoxide and/or in the formation of arsenic sulfides. This occurred either via activation of oxygen or a direct involvement of these groups in reactions with arsine. A very hydrophilic surface of sulfur-containing carbons, which causes the presence of adsorbed water, even in dry conditions, enhances arsine removal. On the other hand, in moist conditions water totally occupies the pore system blocking the catalytic action of the surface toward oxidation, which leads to a very limited or zero AsH₃ adsorption capacity.     

Synthesis and characterisation of hydrophilic and organophilic graphene nanosheets

Hydrophilic graphene nanosheets were rapidly synthesized by reacting graphene oxide nanosheets with poly(sodium 4-styrene sulfonate) and simultaneously reducing by hydrazine hydrate under hydrothermal conditions. Organophilic graphene nanosheets were prepared by reacting with octadecylamine and reduction by hydroquinone through a reflux process. Ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy measurements confirmed the attachment of organic molecules to the graphene nanosheets to achieve hydrophilic and organophilic affinity. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analysis indicated that the crystal structure of the graphene nanosheets was maintained intact after chemical functionalisation.     

Synthesis of hollow carbon nano-onions and their use for electrochemical hydrogen storage

In this study, we report an efficient method for synthesis of well-graphitized hollow carbon nano-onions (CNOs). CNOs were firstly fabricated by chemical vapor deposition (CVD) method at 850 °C using an Fe–Ni alloy catalyst with diameters of 10–15 nm. Then hollow CNOs were obtained by annealing as-prepared CNOs at 1100 °C for 3 h. It is found that during the CVD growth, the presence of nickel retards the deactivation of Fe–Ni–C austenite, providing the possibility for the growth of up to two hollow CNOs from each alloy particle. The subsequent high-temperature annealing led to the escaping of the Fe–Ni alloy from the graphitic layers, and the re-catalysis of precipitation and graphitization of the carbon atoms previously dissolved in the alloy particle (Fe_0.64Ni_0.36) to form hollow CNOs. The hollow CNOs exhibit good performance as materials for electrochemical hydrogen storage, with a discharge capacity of 481.6 mAh/g under a current density of 500 mA/g, corresponding to a hydrogen storage capacity of 1.76 wt.%. Our results demonstrate that the hollow CNOs are promising materials as a storage medium for hydrogen as a fuel source.     

Synthesis of dendritic silver nanostructures and their application in hydrogen peroxide electroreduction

Well-defined silver (Ag) dendritic nanostructures were successfully synthesized by electrodeposition without the use of any template or surfactant. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the as-prepared Ag nanomaterials. These dendrites are aggregates of Ag nanoparticles, which are highly crystalline in nature. The concentration of AgNO₃ affects the shape of the nanoparticles. In addition, the electrochemical properties of the Ag dendrite-modified glassy carbon electrode (Ag/GC) were characterized by cyclic voltammetry and chronoamperometry. Results indicated that the as-obtained Ag dendrites exhibited favorable electroreduction activity towards oxygen (O₂) and hydrogen peroxide (H₂O₂). When used as a sensor, the Ag/GC electrode exhibited a wide linear range of 0.005–12 mM H₂O₂, with a remarkable sensitivity of 7.39 μA/mM, a detection limit of 0.5 μM, estimated at a signal-to-noise ratio of 3, and a rapid response time (within 5 s). Moreover, the electrode showed good reproducibility, anti-interferant ability and long-term stability.     

On adsorption and electro-oxidation of some compounds on tungsten carbide; their effect on hydrogen electro-oxidation

Adsorption and electro-oxidation of carbon monoxide, ethylene, acetylene, and hydrogen sulphide on tungsten carbide, in solutions of these compounds in 1 N H₂SO₄, have been investigated. It was found that CO, C₂H₄, and C₂H₂ do not undergo adsorption and oxidation and do not affect adsorption and electro-oxidation of hydrogen. H₂S does not oxidise as well, and it does not displace adsorbed hydrogen in any measurable amounts, though it does inhibit electro-oxidation of molecular hydrogen. Methanol is inert on tungsten carbide like carbon monoxide and hydrocarbons. Electro-oxidation of formaldehyde and formic acid proceeds without apparent WC-surface coverage by the adsorbed compound.     

Synthesis and antifungal activity of reduced graphene oxide nanosheets

Reduced graphene oxide (rGO) nanosheets were produced using a modified Hummers method. Antifungal activity of rGO nanosheets was tested against three fungi i.e., Aspergillus niger (A. niger), Aspergillus oryzae (A. oryzae) and Fusarium oxysporum (F. oxysporum). The rGO inhibits the mycelial growth of the fungi and it is believed that this is due to its sharp edges. The half maximal inhibitory concentration (IC₅₀), a measure of the effectiveness of the rGO in inhibiting the fungi, was investigated. IC₅₀ values of the rGO against F. oxysporum, A. niger, and A. oryzae are 50, 100, and 100 μg ml^?1, respectively.     

Residual adsorption capacity of carbon beds

The retention time of a small (0.3 cm³) ethane pulse, to which various dry weights (1–3 g) of activated carbon were exposed, was studied as a nondestructive method of determining the residual adsorption capacity of the bed. Carbon beds, partially saturated with CCl₄ or water, adsorbed the ethane from and then desorbed the ethane into the nitrogen carrier gas stream. At a fixed flowrate and fractional carbon saturation the retention time in the bed varied linearly with carbon weight. A critical bed weight existed, below which the retention time of ethane in the bed was zero. The logarithm of a dimensionless time parameter, normalized with respect to the effective bed weight (total weight minus critical weight), was a linear function of the percentage carbon saturation (or the percentage residual adsorption capacity) of the bed. This approach constitutes a nondestructive, in situ method for determining the residual adsorption capacity of an activated carbon bed that is independent of bed weight.     

Synthesis and characterization of exfoliated polystyrene grafted hexagonal boron nitride nanosheets and their potential application in heat transfer nanofluids

Three different methods were used to develop surface-modified hexagonal boron nitride (h-BN) nanosheets, and polystyrene grafting was performed by an indirect covalent bond formation between modified h-BN nanosheets and styrene molecules through surface initiated atom transfer radical polymerization (SI-ATRP) approach. In all methods, an alkyl bromide as the ATRP-initiating site was first introduced on h-BN nanosheets and an SI-ATRP reaction of styrene from the initiator immobilized h-BN surface was achieved. The structure of synthesized PS grafted h-BN nanosheets (PS-g-h-BN) was identified and characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy methods. The functionalization promoted the exfoliation of h-BN layered structure into few layer sheets where the thickness of the sheets was dependent on the modification technique and the content of polymer grafted on nanosheets. The highest grafting content of PS-g-h-BN nanosheets was obtained around 20% which could enhance thermal conductivity of mineral oil-based nanofluids with the minimum concentration of the nanofiller (0.01 wt%). The electrical and physical properties of the nanofluid were also investigated. According to the results, the dielectric loss reduced by increase in nanofiller concentration was an indication of the enhanced dielectric nature of nanofluid. In addition, exfoliated PS-g-h-BN nanosheets dispersions were shown to be stable in mineral oil up to 2 months and this stability was linked to the presence of polymer chains followed by the formation of van der Walls interactions between the grafted polymer and the fluid.