Theoretical Surface Area Research Articles

Selective gas adsorption and I–V response of monolayer boron phosphide introduced by dopants: A first-principle study

Abstract Two-dimensional (2D) materials have gained tremendous research interests for gas sensing applications because of their ultrahigh theoretical specific surface areas and unique electronic properties. Here, we investigate the adsorption of CO, SO2, NH3, O2, NO and NO2 gas molecules on pure and doped boron phosphide (BP) systems using first-principles calculations to exploit their potential in gas sensing. Our results predict that all six gas molecules show stronger adsorption interactions on impurities-doped BP over the pristine monolayer BP. Al-doped BP shows the highest sensitivity to all gas molecules, but N-doped BP is more suitable as a sensing material for SO2, NO and NO2 due to the feasibility of desorption. We further calculated the current–voltage (I–V) relation by mean of nonequilibrium Green’s function (NEGF) formalism. The I–V curves indicate that the electronic properties of the doping systems change significantly with gas adsorption by studying the nonparamagnetic molecules NH3 and the paramagnetic molecules NO, which can be more likely to be measured experimentally compared to graphene and phosphorene. This work explores the possibility of BP as a superior sensor through introducing the appropriate dopants.

Development and Testing of Large Format Graphene Supercapacitors

Of the many suggested applications of graphene, energy storage is one that often attracts much attention with potential improvements in energy, power and lifetime of such devices often postulated. One such energy storage device that is frequently associated with graphene application is the Supercapacitor. The electrodes found in supercapacitor devices are characterized by a high electronic conductivity and a high surface area, usually in excess of 1000 m2 g-1. Graphene as a pristine material is known to have high electrical conductivity and a theoretical surface area of around 2630 m2 g-1 but pristine graphene of such high conductivity is not available at scales needed for making such devices or at a cost that is practical. Furthermore, the actual specific surface areas of graphene powders currently available are considerably lower than the theoretical value. It is often reported in the literature that small research cells using graphene as active material offer excellent performance but the performance of cells at a larger prototype scale are rarely encountered. This is due to availability and cost of the graphene material, problems in its processing and availability of necessary equipment. The lack of information regarding larger format graphene cells presents issues when comparing performances with more established materials such as activated carbon, the mainstay of commercial supercapacitor devices. Whilst some metrics associated with small scale graphene cells can be reliably scaled to commercial devices, others cannot and rely on a number of assumptions that often do not hold true for such a material. In the current work three commercially available graphene nanoplatelets have been selected based on their availability (in multiple Kg scales), their cost and their specific surface areas (between 750 and 300 m2 g-1). The development of these materials into electrodes and their inclusion in A5 sized pouch cells of >300 F capacitance is demonstrated, with their performance compared in cells at the coin and pouch scale, and to cells of the same size and format using activated carbon as the active material. A number of issues encountered in the scale up and development of the inks and electrodes required are highlighted with their solutions, including the higher than expected ESR of electrodes and the need for conductive additives, viscosity effects and gelling not observed at the small scale but hugely problematic at the pilot scale, and “islanding” electrodes after coating and drying at scale. The production of A5 sized pouch cells from ca. 60 m of each electrode type is demonstrated and extensive testing presented including EIS, float testing for extended periods, galvanostatic, and constant power testing at currents up to 200 A. The results of the testing is discussed in light of the surface areas of starting graphenes as well as electrodes and comparisons made between the values at pouch cell and those extrapolated from coin cell level, and also to those of comparable pouch cells using activated carbons as active material.

Adsorption of Gas Molecules on Graphene‐Like ZnO Nanosheets: The Roles of Gas Concentration, Layer Number, and Heterolayer

Abstract2D layered materials have gained tremendous research interests for gas sensing applications because of their ultrahigh theoretical specific surface areas and unique electronic properties, which are prone to be influenced by external factors. Here, using first principle calculations, the adsorption of several common gas molecules on graphene‐like ZnO (g‐ZnO) is systematically studied by taking the gas concentration, homolayer number, and heterolayers into considerations. The calculation results show that the adsorption energies of all the selected gas molecules are susceptible to the concentration and the homolayer number, and they incline to gradually increase with the decreasing of the gas concentration or they dramatically increase with the raising in g‐ZnO layer number combined with elevated charge transfers. Besides, choosing graphene (MoS2) as a heterolayer material to stack with g‐ZnO can enhance (weaken) the interaction with NH3 (NO2) while weakening (enhance) that of NO2 (NH3), thus facilitating the selectivity to some extent. Further, Hirshfeld charge analysis and visualization of the charge density differences between the layers reveal the different charge transfers and adsorption mechanisms before and after gas adsorption. The results indicate that g‐ZnO and its homolayer and hetero‐bilayer structures can be promising candidates as gas sensing materials and catalysis.

Influence of copper loading on mesoporous alumina for catalytic NO reduction in the presence of CO

We report our investigation of copper loading on mesoporous alumina samples as a potential catalyst for simultaneous NO (Nitric oxide) and CO (carbon monooxide) redox reaction. The synthesised catalysts were carefully examined for their chemical phase and metal distribution within the mesoporous structure. At low copper loading within the support, majority of the copper ions were incorporated within the pore structure as independent ions and without any evidence of the formation of bulk copper-oxide. This observation was further substantiated by XPS and pore structure analysis. The catalyst’s activity towards NO reduction was critically analysed and correlated to the catalyst loading, the number of active catalyst sites and theoretical catalyst surface area. The catalytic activity is described using L-H mechanistic model, with the reaction site activation and regeneration step playing a crucial role in determining the reaction kinetics.

Improving blend content uniformity via dry particle coating of micronized drug powders

Content uniformity of low dose blends with fine active pharmaceutical ingredients (API) is adversely impacted due to API agglomeration caused by high powder cohesion. Dry coating using high-intensity vibratory mixing is employed to reduce API cohesion and granular Bond number as well as agglomeration as predicted by contact models, hence improve blend content uniformity (CU). Micronized acetaminophen (mAPAP) (~10μm), a model API, was dry coated with nano-silica R972P (20nm), and mixed with Avicel 102. The amount of silica was varied from 0 to 2.74wt%, corresponding to theoretical surface area coverage (SAC) from 0 to 100% respectively. Bulk density, unconfined yield strength, and dispersive surface energy results indicated dry coating with 0.27 to 1.0wt% silica was adequate for API property enhancement; further corroborated by improved CU for 5wt% API blends. Excellent CU was achieved for 3, 5 and 10wt% API loaded blends, where 30min of mixing was found to be acceptable for all three. The CU with dry coated mAPAP was significantly lower and within the acceptable range as compared to control blends without silica, as well as those with silica added during blending. Sieving of mAPAP illustrated the reduction in mAPAP agglomeration, necessary for improved CU after dry coating, corroborating model based predictions. Compared to theoretical predictions, actual CU was higher unless API agglomerate size distribution obtained via sieving was taken into account. Overall, cohesion reduction by dry coating is shown as a promising approach for improving content uniformity of cohesive API blends.

Effect of Carbon Support and Synthesis Method on Pt NP Utilization and Activity

A key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). Higher utilization of Pt catalyst can be realized by understanding the effect of the carbon support microstructure on the distribution and formation of Pt nanoparticles (NPs) and by optimizing the synthesis method. In this work, Pt NPs were fabricated using a simple alcohol reduction method and then varying the carbon support pore structure and surface properties. The catalysts were then tested for their activity in 1 M C2H5OH + 0.5 M H2SO4 solutions. For Pt NP preparation, either ethanol or butanol were used as the solvent and reductant. The ethanolic or butanolic solution containing H2PtCl6 was then added to the carbon support dispersed in the same solvent at room temperature, and the mixture was heated at the boiling point for 2 hrs. In the case of the ethanol solvent, an aqueous alkaline solution was added to ensure the completion of Pt reduction [1]. However, this step was not used during synthesis when using butanol, due to its higher reducing power. Three types of carbon supports were investigated, Vulcan carbon (VC), Ketjenblack (KB), and colloid-imprinted carbon powders (CICs). The structure and distribution of the Pt NPs were confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Figure 1 shows the cyclic voltammograms of JM Pt/VC and Pt/CIC85 (i.e., 85 nm pore size), prepared by both the ethanol and butanol synthesis methods, in 0.5 M H2SO4. Even though the theoretical specific surface areas were 70-80 m2/gPt (particle size of 3-3.5 nm), the electrochemical active surface area (ECSA) was found to depend on the synthesis method and the carbon support. The ethanol oxidation activity of catalysts per Pt area for the three carbon supports is shown in Figure 2. A strong dependence on the carbon microstructure was observed, with Pt/CIC and Pt/KB, showing a higher activity than Pt/VC, likely due to their higher content of mesopores in the catalyst layer [2]. The correlation between catalyst activity and the carbon microstructure for each synthesis method will be discussed in detail.

General Synthetic Method for N-Doped Macroporous Graphene-Encapsulated Mesoporous Metal Oxides and Its Application As New Anode Materials for Sodium-Ion Hybrid Supercapacitors

Employing graphene as an electrode material is advantageous for energy storage devices because it is flexible, highly electrically conductive, chemically stable, and has large theoretical surface area. However, graphene generally suffers from serious agglomeration and re-stacking due to its strong pi-pi stacking and van der Waals interactions between graphene nanosheets during charge-discharge process. To fully use the potential merits of graphene and improve the kinetics of electrode materials in energy storage devices, composites of graphene and metal oxides have been tested as electrode. Metal oxides in the composites, prevent the re-stacking of graphene. Graphene layers in the composites also suppress the volume change and agglomeration of metal oxide and provide a highly conductive matrix for metal oxide. We report a general method to synthesize mesoporous metal oxide@N-doped macroporous graphene composite by heat-treatment of electrostatically co-assembled amine-functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N-doped macroporous graphene simultaneously. Four mesoporous metal oxides (WO3-x, Co3O4, Mn2O3 and Fe3O4) were encapsulated in N-doped macroporous graphene. Used as an anode material for sodium-ion hybrid supercapacitors (Na-HSCs), mesoporous reduced tungsten oxide@N-doped macroporous graphene (m-WO3-x@NM-rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m-WO3-x@NM-rGO is based on Na+ intercalation/de-intercalation. To the best of our knowledge, this is the first report on Na+ intercalation/de-intercalation properties of WO3-x and its application to Na-HSCs.

Review—Critical Considerations of High Quality Graphene Synthesized by Plasma-Enhanced Chemical Vapor Deposition for Electronic and Energy Storage Devices

Graphene is a promising electrode material not only due to its intrinsic properties like good electrical conductivity, high mechanical strength and high chemical stability, but also because of its high theoretical surface area of 2630 m2 g−1. In this report, the effect of CVD parameters to the growth of high quality graphene on metal substrates by using plasma enhanced chemical vapor deposition (PECVD) was extensively studied. Interestingly, synthesizing high quality graphene by PECVD technique is not only depending on the CVD parameters, but also depending on the catalysts and its plasma sources. It was found that Ni and Cu are the most favored metal catalysts for PECVD graphene growth. With high solubility of carbon (> 0.1 at. %), Ni effectively promote the growth of multilayer graphene by PECVD. However, large-area synthesis has made relatively inexpensive Cu as one of the most attractive substrates for monolayer graphene growth. Further details on the potential use of different transition metal catalysts in synthesizing graphene and consequently the specific usage of graphene based devices are discussed in this report.

Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals.

Amazing conductivity, perfect honeycomb sp2 arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity.

(Invited) Nanostructured Graphene Electrodes for High Performance and Stretchability

Chemically derived graphene oxide (GO) and its derivatives are promising candidates for a variety of carbon-based functional nanostructures and hybrid architectures, because of their unique characteristics that include high theoretical surface area, tunable electrical conductivity, excellent solution processability, and high mass producibility at low cost. However, the irreversible stacking due to the strong π–π interactions between graphene nanosheets during drying or reduction processes significantly decreases the solution processability as well as accessible surface area. In this talk, I firstly present a sea-urchin-shaped template approach for fabricating highly crumpled graphene balls in bulk quantities with a simple process. Simultaneous chemical etching and reduction process of graphene oxide (GO)-encapsulated iron oxide particles results in dissolution of the core template with spiky morphology and conversion of the outer GO layers into reduced GO layers with increased hydrophobicity which remain in contact with the spiky surface of the template. After completely etching, the outer graphene layers are fully compressed into the crumpled form along with decrease in total volume by etching. The crumpled balls exhibit significantly larger surface area and good water-dispersion stability than those of stacked reduced GO or other crumple approaches, even though they also show comparable electrical conductivity. Furthermore, they are easily assembled into 3D macroporous networks without any binders through typical processes such as solvent casting or compression molding. The graphene networks with less pore volume still have the crumpled morphology without sacrificing the properties regardless of the assembly processes, producing a promising active electrode material with high gravimetric and volumetric energy density for capacitive energy storage. For the second part, using a facile ice-templated self-assembly process with reduced graphene sheets and vanadium phosphate (VOPO4) nanosheets, we realize a vertically porous nanocomposite of layered VOPO4 and graphene nanosheets with high surface area and high electrical conductivity. The resulting 3D VOPO4–graphene nanocomposite has a much higher capacitance of 527.9 F g–1 at a current density of 0.5 A g–1, compared with ~247 F g–1 of simple 3D VOPO4, with solid cycling stability. The enhanced pseudocapacitive behavior mainly originates from vertically porous structures from directionally grown ice crystals and simultaneously inducing radial segregation and forming inter-stacked structures of VOPO4–graphene nanosheets. This VOPO4–graphene nanocomposite electrode exhibits high surface area, vertically porous structure to the separator, structural stability from interstacked structure and high electrical conductivity, which would provide the short diffusion paths of electrolyte ions and fast transportation of charges within the conductive frameworks. In addition, an asymmetric supercapacitor (ASC) is fabricated by using vertically porous VOPO4–graphene as the positive electrode and vertically porous 3D graphene as the negative electrode; it exhibits a wide cell voltage of 1.6 V and a largely enhanced energy density of 108 Wh kg–1. In the last part, we also used the ice-templated vertically porous graphene nanostructures as a stretchable supercapacitor electrode. Radially compressed honeycomb structures exhibited nearly-zero poission ratio structures and maintained their structure and electrical conductivity even at 50 % of starched states. The capacitive performance of these compressed honeycomb structures also shows fairly high over 130 F g-1 and these high performance still be maintained at highly stretched condition.

P-Doped Porous Carbon as Metal Free Catalysts for Selective Aerobic Oxidation with an Unexpected Mechanism.

An extremely simple and rapid (seconds) approach is reported to directly synthesize gram quantities of P-doped graphitic porous carbon materials with controlled P bond configuration. For the first time, it is demonstrated that the P-doped carbon materials can be used as a selective metal free catalyst for aerobic oxidation reactions. The work function of P-doped carbon materials, its connectivity to the P bond configuration, and the correlation with its catalytic efficiency are studied and established. In direct contrast to N-doped graphene, the P-doped carbon materials with higher work function show high activity in catalytic aerobic oxidation. The selectivity trend for the electron donating and withdrawing properties of the functional groups attached to the aromatic ring of benzyl alcohols is also different from other metal free carbon based catalysts. A unique catalytic mechanism is demonstrated, which differs from both GO and N-doped graphene obtained by high temperature nitrification. The unique and unexpected catalytic pathway endows the P-doped materials with not only good catalytic efficiency but also recyclability. This, combined with a rapid, energy saving approach that permits fabrication on a large scale, suggests that the P-doped porous materials are promising materials for "green catalysis" due to their higher theoretical surface area, sustainability, environmental friendliness, and low cost.

RETRACTED: High sorption of U(VI) on graphene oxides studied by batch experimental and theoretical calculations

The graphene oxides (GOs) have been studied extensively in multidisciplinary areas owing to their excellent physicochemical properties. The high theoretical surface areas and large amounts of oxygen-containing functional groups at the basal planes and the edge sites ensure their high sorption capacity for heavy metal ions and radionuclides from large volumes of aqueous solutions. Herein, the GOs were applied as adsorbents to remove U(VI) from aqueous solutions at different experimental conditions, and the results showed that the sorption of U(VI) on GOs was strongly dependent on pH and was not affected by ionic strength obviously. The sorption capacity of U(VI) on GOs is calculated to be 1330 mg/g at pH 4.5 and T = 20 °C, which is much higher than any other today’s materials. The interaction mechanism of U(VI) on GOs was simulated by the computational DFT calculations, and the results evidenced that the variation in pH values led to significant changes in the circumstance of functional groups on GOs. As the pH value increased, the weak physical sorption/outer-sphere surface complexation between the GOs and U(VI) at low pH turned into strong chemical sorption/inner-sphere surface complexation with the negative charged –O− or –COO− groups induced by the deprotonation of the functional groups at high pH.

Nanocomposite of Iron Oxide-Reduced Graphene Oxide Applied as High-Performance Anode Materials for Lithium Ion Batteries

: Novel nanostructured iron oxide-reduced graphene oxide composites were synthesized by a facile one-step hydrothermal method in an ethylene glycol (EG)–water system. Different phases of iron oxides were detected by adjusting fabrication parameters including the EG/H2O ratio, base content and iron ions concentration. Electrochemical propertyof fabricated nanocomposites as anode material was examined in a coin–type cell. The high–rate capacity and cycling stability were found, which is attributed to the improved lithium storage capability due to the application of graphene sheet acting as conductive materials for iron oxide nanoparticles. This study provides a favorable approach for exploring the nanocomposites of metal oxide-graphene anode for lithium ion battery applications. Introduction: Currently,α–Fe2O3 has been considered as a promising candidate for lithium ion batteries due to its much higher theoretical capacity of 1350 mAhg‾1 than that of commercial graphite anode materials and its environmental friendly fabrication methods from low–cost resources [1]. In particular, the use of nanomaterials is an effective path to improve rate capabilities of solid state electrodes in batteries attributed to their relatively small diffusion lengths. Furthermore,graphene, with an excellent electronic conductivity, a high theoretical surface area of 2630 m2/g and superior mechanical properties, is a significantly promising component for high performance electrode materials [2]. In this study, an anode material of iron oxide nanoparticles (mainly α–Fe2O3)–reduced graphene oxide for lithium ion battery has been synthesized and reported. Experimental: FeCl3·6H2O (1.08 g) and NaOH (0.8 g) was dissolved in EG (30 ml) by ultrasonication for 1 hour.Then 10 ml deionized water and 15 mg graphene oxide was added to the mixture under stirring to get a homogeneous solution. The solution was transferred into a 50 ml teflon–lined stainless steel autoclave, sealed and heated at 200oC for 10 hours. The product was collected by centrifuging and washed by ethanol and deionized water alternatively for several times, which was followed by drying at 80oC. Morphologies and phases of synthesized nanocomposites were characterized by scanning electron microscopy (SEM), Raman scattering spectroscopy, X-ray diffraction (XRD), high resolution transmission electron microscopy(TEM). Results: Typical XRD pattern of the products was illustrated in Fig.1 that demonstrated the co–existence of α–Fe2O3 and Fe3O4. Diffraction peaks can be indexed to either the rhombohedral phase of α-Fe2O3 (JCPDS NO.84-0307) or the cubic phase of Fe3O4 (JCPDS NO.65-3107). The characteristic peak of graphene oxide located at 10.4° was not found, confirming the formation of graphene. Fig. 1 also showed the SEM image of fabricated iron oxide nanoparticles that were uniform with the diameter about 50 nm, indicating XRD pattern in good agreement with SEM results. Raman spectra also confirmed that the typical features of reduced graphene oxide with the presence of D band (1348 cm−1) and G band (1598 cm−1).

V2O5 Nanosheets/Reduced Graphene Oxide Nanocomposite As a High-Performance Cathode Material for Lithium-Ion Batteries

Among the existing cathode materials, V2O5 is a promising cathode candidate because of its high energy density, abundance, easy synthesis, as well as low cost. However, due to quite low diffusion coefficient of lithium ions (10-12-10-13 cm2 s-1), irreversible phase transitions during deep discharge, and vanadium dissolution into the electrolyte, the practical use of V2O5 as a cathode material shows poor rate capability and cycling stability1,2. Incorporating the nanostructured V2O5 with high conductive materials to build a hybrid material is one of the most promising strategies to improve the electrochemical property of the V2O5 based anod3. Among these conductive materials, graphene nanosheet (GNS), with the exceptional properties of excellent electronic conductivity of 103-104 S m-1, high theoretical surface area of 2630 m2 g-1, and high mechanical flexibility is much more attractive. Extensive studies of GNS-V2O5 nanocomposites have been investigated. However, it is worth noting that most of the reported nanocomposites constitute by the GNS with the zero-dimensional (0-D) nanoparticles or one-dimensional (1-D) V2O5 nanofiber/nanorod. To the best of our knowledge, the 3-D nanocomposites combining the GNS layer with 2-D V2O5 nanosheets have not been reported so far. Herein, we demonstrate a simple solvothermal method to directly self-assemble 2-D V2O5 nanosheets on the reduced graphene oxide, forming 3-D nanocomposite (V2O5 nanosheet/RGO hierarchical nanocomposite). Briefly, vanadium oxytriisopropoxide (VO(OiPr)3) and graphene oxide (GO) were dispersed into ethyl alcohol by ultrasonicaiton to produce a V-precursor/GO dispersion. Then, the dispersion was transferred to a Teflon-lined stainless steel autoclave and heat-treated in an electric oven. The obtained composite was further annealed at 300°C in air to make V2O5 crystallized and reduce GO to RGO. The detailed preparation procedures can be found in the experimental section.When used as a cathode material, the V2O5 nanosheets/RGO nanocomposites exhibits highly reversible capacity and good rate capability over bulk material. The V2O5 nanosheets/RGO nanocomposite anode was able to charge/discharge at high current densities of 15A g-1 (50C), with the discharge capacities of approximately 176 mA h g-1. Meanwhile, a discharge capacity of 102 mA h g-1 can be delivered after 160 cycles at 2C, showing a good cycling stability. The improved performance could be attributed to the enhanced electron transport and Li+ diffusion that result from the hierarchical nanostructure of V2O5 nanosheets/RGO nanocomposite (showing in Figure 1).Reference:[1] S. Q. Wang, S. R. Li, Y. Sun, X. Y. Feng, C. H. Chen, Energy & Environmental Science 2011, 4, 2854.[2] Y. X. Tang, X. H. Rui, Y. Y. Zhang, T. M. Lim, Z. L. Dong, H. H. Hng, X. D. Chen, Q. Y. Yan, Z. Chen, Journal of Materials Chemistry A 2013, 1, 82.[3] X. H. Rui, J. X. Zhu, D. Sim, C. Xu, Y. Zeng, H. H. Hng, T. M. Lim, Q. Y. Yan, Nanoscale 2011, 3, 4752.

Porous structures in stacked, crumpled and pillared graphene-based 3D materials

Graphene, an atomically thin material with the theoretical surface area of 2600m2g−1, has great potential in the fields of catalysis, separation, and gas storage if properly assembled into functional 3D materials at large scale. In ideal non-interacting ensembles of non-porous multilayer graphene plates, the surface area can be adequately estimated using the simple geometric law ∼2600 m2g−1/N, where N is the number of graphene sheets per plate. Some processing operations, however, lead to secondary plate–plate stacking, folding, crumpling or pillaring, which give rise to more complex structures. Here we show that bulk samples of multilayer graphene plates stack in an irregular fashion that preserves the 2600/N surface area and creates regular slot-like pores with sizes that are multiples of the unit plate thickness. In contrast, graphene oxide deposits into films with massive area loss (2600–40m2g−1) due to nearly perfect alignment and stacking during the drying process. Pillaring graphene oxide sheets by co-deposition of colloidal-phase particle-based spacers has the potential to partially restore the large monolayer surface. Surface areas as high as 1000m2g−1 are demonstrated here through colloidal-phase deposition of graphene oxide with water-dispersible aryl-sulfonated ultrafine carbon black as a pillaring agent.

XRD analysis of nanocrystalline anatase powders prepared by various chemical routes: correlations between micro-structure and crystal structure parameters

Nanocrystalline anatase powders synthesised by various chemical processes as super/subcritical fluid extraction, sol-gel technique and hydrolysis of titanium alkoxides in hydrogen peroxide were studied by X-ray diffraction (XRD) whole profile modelling method (WPPM) in order to reveal correlations between structural and micro-structural parameters as well as sample treatment conditions. Anisotropy of the diffraction line broadening due to truncated bipyramidal shape of anatase crystals was discussed. The hkl-anisotropy can be very strong but also almost negligible in dependence on relative ratio of the crystallite dimensions. The latter was the case for the studied samples. The size of synthesised anatase nanoparticles was within the range 3–25 nm. The theoretical total surface area of crystallites calculated from XRD was in a good correlation with the surface area measured by the nitrogen physisorption up to the temperature 400–450 °C, when the particles started to agglomerate. At atomic scale a unit cell volume contraction with decreasing crystallite size and a significant deficiency in the Ti-site occupancy was observed. Both effects were attributed to the presence of Ti-vacancies and a linear coefficient between the relative cell volume contraction and the fraction of Ti-vacancies was estimated to (–0.017 ± 0.003).

PREPARATION OF POROUS POLYACRYLONITRILE ULTRATHIN FIBERS BY ELECTROSPINNING WITH NONSOLVENT INDUCED PHASE SEPARATION

Porous polyacrylonitrile(PAN) ultrathin fibers with nanopore structures were prepared by electrospinning a ternary system of PAN/dimethyl sulphoxide(DMSO)/N,N′-dimethylformamide(DMF) using a water bath at 3℃.We investigated the effects of proportion of DMSO to DMF,collection medium,PAN concentration,applied voltage and needle to collector distance on the diameter and surface porosity of PAN ultrathin fibers.The optimum electrospinning parameters are given as PAN concentration of 15 wt%,DMSO/DMF proportion of 1∶1(W/W),applied voltage of 16 kV,needle to collector distance of 5 cm,solution flow rate of 0.7 mL/h,relative humidity of 40%~70% and room temperature of 25℃.The diameter,morphology and porosity of porous PAN ultrathin fibers were characterized by scanning electron microscope,showing the fibers,which were obtained under the optimum conditions,were porous throughout with a diameter ranging from 420 nm to 490 nm,an average diameter of 468 nm and surface porosity of 3.4%.The BET specific surface area was measured by nitrogen adsorption and desorption isotherms.It can reach 43.86 m2/g,which is 5 times higher than the theoretical surface area of smooth and nonporous 468 nm PAN fibers.Moreover,nonsolvent induced phase separation has been proposed to be the main mechanism for the formation of porous PAN fibers,which is confirmed by the ternary phase diagram of PAN/(DMSO+DMF)/H2O.

A polymer of intrinsic microporosity as the active binder to enhance adsorption/separation properties of composite hollow fibres

Sorbent hollow fibres, generally prepared by fully encapsulating an adsorbent within a polymer binder such as polyethersulfone (PES), provide a low pressure drop alternative to conventional packed beds. These fibres have a high external surface area to volume ratio, enabling smaller bed sizes, and a highly porous structure resulting in low mass transfer resistance while maximising sorption efficiency. However, adsorbent hollow fibres prepared with PES suffer from loss of some adsorption capacity due to the polymer binder. This paper describes a novel formulation of composite hollow fibres containing activated carbon and PIM-1, a polymer of intrinsic microporosity, as an active binder designed to enhance the total adsorption capacity. Octane has been selected as a model hydrocarbon, and nitrogen and octane isotherms are reported for both PES and PIM-1 based hollow fibres, each containing the same activated carbon. Theoretical BET surface areas were calculated for each type of fibre based on a weighted average of the surface areas of its individual components (i.e. polymer and carbon). The measured surface area of the PIM-1 fibres was remarkably consistent with the theoretical value, while the measured surface area and octane uptake for PES fibres were ∼10% lower than the theoretical values, indicating some blockage of the adsorbent by the polymer matrix. PIM-1 adsorbent fibres were found to fully utilise the capacity of the supported carbon, as well as providing additional sites for adsorption on the polymer, resulting in a maximum octane uptake of 50%w/w – approximately twice that of the PES-based fibres.

Electrochemical Double Layer Capacitance of Metallic and Semiconducting SWCNTs and Single Layer Graphene

The specific double layer capacitance that has been achieved with single wall carbon nanotubes (SWCNTs) is below that which is predicted from calculations based on the theoretical surface area of the CNTs and the intrinsic capacitance of the electrolyte. This paper investigates the specific capacitance of metallic (M-) and semiconducting (SC-) CNTs in order to determine if density of states (DOS)/quantum capacitance is a limiting factor in the capacitances achieved. In addition, a model system composed of a large-area single-layer graphene electrode on a nonconducting substrate has been used in order to put a lower bound on the ultimate double layer capacitance that should be achievable with CNT and graphene electrodes. We find that at the specific capacitances achieved here, the quantum capacitance of SWCNTs is not the limiting factor. In addition, the single-sided single-layer graphene electrode indicates that capacitances in excess of 550 F/g should be achievable.

Hydrophobic Derivatization of N-linked Glycans for Increased Ion Abundance in Electrospray Ionization Mass Spectrometry

A library of neutral, hydrophobic reagents was synthesized for use as derivatizing agents in order to increase the ion abundance of N-linked glycans in electrospray ionization mass spectrometry (ESI MS). The glycans are derivatized via hydrazone formation and are shown to increase the ion abundance of a glycan standard more than 4-fold. Additionally, the data show that the systematic addition of hydrophobic surface area to the reagent increases the glycan ion abundance, a property that can be further exploited in the analysis of glycans. The results of this study will direct the future synthesis of hydrophobic reagents for glycan analysis using the correlation between hydrophobicity and theoretical non-polar surface area calculation to facilitate the development of an optimum tag for glycan derivatization. The compatibility and advantages of this method are demonstrated by cleaving and derivatizing N-linked glycans from human plasma proteins. The ESI-MS signal for the tagged glycans are shown to be significantly more abundant, and the detection of negatively charged sialylated glycans is enhanced.