Journal of Colloid And Interface Science (v.372, #1)
Characterization and mechanism analysis of Mo–N-co-doped TiO2 nano-photocatalyst and its enhanced visible activity
by Xiuwen Cheng; Xiujuan Yu; Zipeng Xing (pp. 1-5).
Display Omitted► Mo–N–TiO2 was synthesized through hydrolysis-precipitation and sonication methods. ► The light absorption edge of Mo–N-codoped TiO2 was shifted to visible light region. ► The activity enhanced mechanism was discussed in detail. ► This study provides a new way to synthesize visible light photocatalyst.In this study, Mo–N-co-doped TiO2 nano-photocatalysts have been synthesized through hydrolysis-precipitation method, combined with sonication posttreatment. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). XRD showed that co-doping with Mo and N favored the formation of anatase and retarded the growth of crystallite size. XPS revealed that N was incorporated into the lattice of TiO2 through substituting oxygen atoms and coexisted in the forms of β-N and γ-N in co-doped TiO2. Meanwhile, Mo was also incorporated into the lattice of TiO2 through substituting titanium atoms and existed in the form of Mo6+. DRS indicated that the light absorbance in visible region was improved by co-doping with Mo and N, leading to a narrower band gap and higher visible light photocatalytic activity for the degradation of phenol than that of pure and N-doped TiO2. The enhanced visible light photocatalytic activity of Mo–N-co-doped TiO2 nano-photocatalyst was attributed to the small crystallite size, narrow band gap and intense light absorbance in visible region. This study provides a new method to synthesize visible light active TiO2-based photocatalyst.
Keywords: Mo–N-co-doped; TiO; 2; Photocatalysis; Sonication; Phenol
Novel compaction resistant and ductile nanocomposite nanofibrous microfiltration membranes
by Seyed Shahin Homaeigohar; Mady Elbahri (pp. 6-15).
Display Omitted► Zirconia nanoparticles were added to an electrospun nanofibrous membrane to minimize compaction. ► Tensile properties of the membrane were also enhanced without any brittleness. ► Hydrophobicity declined. ► Water permeability improved considerably owing to the achievements. ► The high permeability implies a very low energy consuming water filtration.Despite promising filtration abilities, low mechanical properties of extraordinary porous electrospun nanofibrous membranes could be a major challenge in their industrial development. In addition, such kind of membranes are usually hydrophobic and non-wettable. To reinforce an electrospun nanofibrous membrane made of polyethersulfone (PES) mechanically and chemically (to improve wettability), zirconia nanoparticles as a novel nanofiller in membrane technology were added to the nanofibers.The compressive and tensile results obtained through nanoindentation and tensile tests, respectively, implied an optimum mechanical properties after incorporation of zirconia nanoparticles. Especially compaction resistance of the electrospun nanofibrous membranes improved significantly as long as no agglomeration of the nanoparticles occurred and the electrospun nanocomposite membranes showed a higher tensile properties without any brittleness i.e. a high ductility. Noteworthy, for the first time the compaction level was quantified through a nanoindentation test. In addition to obtaining a desired mechanical performance, the hydrophobicity declined. Combination of promising properties of optimum mechanical and surface chemical properties led to a considerably high water permeability also retention efficiency of the nanocomposite PES nanofibrous membranes. Such finding implies a longer life span and lower energy consumption for a water filtration process.
Keywords: Electrospinning; Membrane; Nanocomposite nanofiber; Mechanical properties; Water filtration
Uniform metal nanoparticles produced at high yield in dense microemulsions
by Krishna Kowlgi; Ugo Lafont; Michael Rappolt; Ger Koper (pp. 16-23).
Display Omitted► Bicontinuous microemulsions as optimal nanoparticle templates. ► Size range=1.8−17nm with narrow distribution=±1nm. ► Mass yield of nanoparticles=3% of template. ► Nanoparticle uniformity and immobilization guarantee long-term stability.This article demonstrates that bicontinuous microemulsions are optimal templates for high yield production of metal nanoparticles. We have verified this for a variety of microemulsion systems having AOT (sodium bis (2-ethyhexyl) sulphosuccinate) or a fluorocarbon (perfluoro (4-methyl-3,6-dioxaoctane)sulphonate) as surfactant mixed with water and oils like n-heptane or n-dodecane. Several types of metal nanoparticles, including platinum, gold and iron, were produced in these microemulsions having a size range spanning 1.8−17nm with a very narrow size distribution of ±1nm. Remarkably high mass concentrations up to 3% were reached. Size and concentration of the nanoparticles could be varied with the stoichiometries of the reagents that constituted them. The optimization towards high yield while maintaining low size polydispersity is due to the decoupling of the time scales for the precipitation reaction and for coarsening. In actual fact, coalescence is essentially prevented by the immobilization of nanoparticles within the bicontinuous microemulsion structure.
Keywords: Nanoparticle; Microemulsion; Bicontinuous; AOT; Fluorocarbon; Platinum
Preparation of core–shell CaCO3 capsules via Pickering emulsion templates
by Xiaoli Wang; Weizheng Zhou; Jian Cao; Weichang Liu; Shiping Zhu (pp. 24-31).
Display Omitted► Large scale preparation of high quality CaCO3 core/shell capsules was achieved. ► CaCO3 particles were used as Pickering emulsion stabiliser and the nucleation sites. ► Homogeneous nucleation in the bulk was inhibited by control the addition of CaCl2. ► Without any additives, highly pure CaCO3 capsules showed prolonged flavor release.Micron size and food grade pristine CaCO3 particles were used to stabilize an oil in water Pickering emulsion. The particles also acted as nucleation sites for the subsequent crystallization of CaCO3 with the addition of CaCl2 and CO2 gas as precursors. After the controllable crystallization process, a dense CaCO3 shell with a few microns in thickness was formed. The CaCO3 shell was proven to be calcite without the presence of crystallization modifiers. The crystallization speed and the shell integrity were controlled by manipulating the addition of CaCl2 amount during the different crystallization stages; therefore, the homogeneous nucleation in the bulk was almost inhibited, and the heterogeneous nucleation at the oil–water interface on pristine CaCO3 particles was the main contribution to the growth of the shell. The encapsulated limonene flavor in CaCO3 capsules showed a prolonged release in neutral water at 85°C, while a burst release at pH 2 water as expected. The method is a simple and scalable process for creating inorganic core–shell capsules and can be used for producing food grade capsules for controlling the flavor release or masking undesirable taste in mouth.
Keywords: CaCO; 3; Capsule; Pickering emulsion; Crystallization; Encapsulation; Slow release
Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system
by Luigi Gentile; Bruno F.B. Silva; Sandor Balog; Kell Mortensen; Ulf Olsson (pp. 32-39).
Display Omitted► Dynamic phase diagram of the 40wt.% C16E4/D2O system. ► Rheo-SANS, rheo-SALS, and rheology elucidate the shear-induced transitions. ► Intermediate lamellar phase of larger d-spacing(Lα+) in coexistence with the initial short d-spacing (L α). ► The bending modulus (bilayer bending rigidity) as a parameter that governs the lamellar-to-MLV transition.In this study, we investigate structural transitions of tetraethylene glycol monohexadecyl ether (C16E4) in D2O as a function of shear flow and temperature. Via a combination of rheology, rheo-small-angle neutron scattering and rheo-small-angle light scattering, we probe the structural evolution of the system with respect to shear and temperature.Multi-lamellar vesicles, planar lamellae, and a sponge phase were found to compete as a function of shear rate and temperature, with the sponge phase involving the formation of a new transient lamellar phase with a larger spacing, coexisting with the preceding lamellar phase within a narrow temperature–time range.The shear flow behavior of C16E4 is also found to deviate from other nonionic surfactants with shorter alkyl chains (C10E3 and C12E4), resembling to the C16E7 case, of longer chain.
Keywords: Dynamic phase diagram; Shear-induced; Lamellar; MLV; Vesicles; Sponge; Rheology; Rheo-SANS; Rheo-SALS; Nonionic; C; 16; E; 4; Bending rigidity
Shell modulation by tailoring substituents in chitosan for LbL-assembled microcapsules
by Renjie Zhang; Wenhua Li; Helmuth Möhwald; Weiping Sui; Zhipeng Wang; Changyou Gao (pp. 40-44).
Display Omitted► By AFM we study the morphology of microcapsules through tailoring substituents. ► The thickness of HPCS-capsules is >3 times larger than that of QACS-capsules. ► A scheme is described concerning the molecular conformation and charges carried.By AFM we report the successful modulation of shell structure (morphology and shell thickness) of microcapsules through tailoring molecular substituents of chitosan. The shell thickness of hollow (HPCS/SA) n ( n=5, 7, 9) capsules is more than 3 times that of the (QACS/SA) n ( n=5, 7, 9) capsules, due to less charges carried by the neutral –NH2 substituent group and the induced coily conformation in HPCS, while more charges carried by the positively charged–N(CH3)3+ substituent and the induced extended conformation in QACS (HPCS: hydroxyl propyl chitosan; QACS: quaternary ammonium chitosan; SA: sodium alginate). The ultrathin shells of microcapsules assembled in this work by the layer-by-layer (LbL) self-assembly technique rather than the traditional method of mixing CS, SA and CaCl2 enable the thickness modulation characterization by AFM on the atomic scale. These microcapsules with tunable shell thickness provide important guidance for potential drug delivery and sustained release.
Keywords: Microcapsules; Layer-by-layer (LbL); AFM; Modulation; Polysaccharides
Investigating the evolution of the phase behavior of AOT-based w/o microemulsions in dodecane as a function of droplet volume fraction
by R. Ganguly; N. Choudhury (pp. 45-51).
Display Omitted► AOT-based w/o microemulsions in dodecane were studied by DLS and viscometry. ► Inter-micellar attraction has been found to weaken at high droplet concentration. ► This transforms the phase separation characteristics of these microemulsions. ► It also has significant influence on the droplet aggregation characteristics.AOT-based water in oil (w/o) microemulsions are one of the most extensively studied reverse micellar systems because of their rich phase behavior and their ability to form in the absence of any co-surfactant. The aggregation characteristics and interaction of the microemulsion droplets in these systems are known to be governed by AOT–oil compatibility and water to AOT molar ratio ( w). In this manuscript by using Dynamic Light Scattering (DLS) and viscometry techniques, we show that droplet volume fraction too plays an important role in shaping the phase behavior of these microemulsions in dodecane. The phase separation characteristics and the evolution of the viscosity and the hydrodynamic radius of the microemulsion droplets on approaching the cloud points have thus been found to undergo complete transformation as one goes from low to high droplet volume fraction even at a fixed ‘ w’. Modeling of the DLS data attributes this to the weakening of inter droplet attractive interaction caused by the growing dominance of the excluded volume effect with increase in droplet volume fraction. In the literature, the inter droplet attractive interaction driven phase separation in these microemulsions is explained based on gas–liquid type phase transition, conceptualized in the framework of Baxter adhesive hard sphere theory. The modeling of our viscosity data, however, does not support such proposition as the characteristic stickiness parameter ( τ−1) of the microemulsion droplets in this system remains much lower than the critical value (τc-1≈10.25) required to enforce such phase transition.
Keywords: AOT; Microemulsion; Viscosity; Hydrodynamic radius; Phase separation
Aggregation behavior of gemini pyrrolidine-based ionic liquids 1,1′-(butane-1,4-diyl)bis(1-alkylpyrrolidinium) bromide ([C npy-4-C npy][Br2]) in aqueous solution
by Shaohua Zhang; Han Yan; Mingwei Zhao; Liqiang Zheng (pp. 52-57).
Display Omitted► Gemini pyrrolidine-based ionic liquids [C npy-4-C npy][Br2] are synthesized. ► [C npy-4-C npy][Br2] have higher surface activity compared with their monomers. ► The aggregation driving force of [C npy-4-C npy][Br2] is different from their monomers.Three gemini pyrrolidine-based ionic liquids, 1,1′-(butane-1,4-diyl)bis(1-alkylpyrrolidinium) bromide ([C npy-4-C npy][Br2], n=10, 12, 14), were synthesized. Their aggregation behavior in aqueous solution was systematically investigated by surface tension, electrical conductivity, and steady-state fluorescence. Compared with their corresponding monomers, N-alkyl- N-methylpyrrolidinium bromide (C nMPB), [C npy-4-C npy][Br2], have higher surface activity. The special structure of [C npy-4-C npy][Br2] that has a spacer in their hydrophilic head groups results in a lower surface excess concentration ( Γmax) and a larger molecular cross-sectional area ( Amin). Electrical conductivity studies show a lower degree of counter-ion binding to the aggregates. A smaller aggregation number (N agg) is observed by the pyrene fluorescence quenching method. A series of thermodynamic parameters(ΔGagg0,ΔHagg0,-TΔSagg0) of aggregation derived from electrical conductivity indicate that the aggregation of [C npy-4-C npy][Br2] is enthalpy-driven, while aggregation of C nMPB is entropy-driven at low temperatures but enthalpy-driven at high temperatures.
Keywords: Gemini pyrrolidine-based ionic liquids; Aggregation behavior; Surface tension; Electrical conductivity; Steady-state fluorescence
Solution combustion synthesis of Co oxide-based catalysts for phenol degradation in aqueous solution
by Hanwen Liang; Ying Yue Ting; Hongqi Sun; Ha Ming Ang; Moses O. Tadé; Shaobin Wang (pp. 58-62).
Display Omitted► One-step solution combustion was firstly employed to prepare supported Co oxide catalysts. ► Co/SiO2 exhibited high and stable performance in phenol degradation. ► Metal oxide dispersion and support surface basicity are important factors influencing catalytic performance.Solution combustion using urea as a fuel was employed to synthesise Co oxide and Al2O3-, SiO2- and TiO2-supported Co oxide catalysts. The catalysts were characterised using several techniques such as N2 adsorption/desorption, XRD, FTIR, UV–vis diffuse reflectance and SEM–EDX, and their catalytic activity was evaluated in phenol degradation in aqueous solution with sulphate radicals. Solution combustion is a simple and effective method in preparation of supported Co catalysts. Co3O4 was the major Co crystal phase in the samples prepared via the combustion synthesis. Bulk Co3O4 particles were not effective in reaction, but supported Co oxides showed higher activity than unsupported Co oxide. The supports influenced Co dispersion and catalytic activity. Co/TiO2 exhibited the highest activity, but it deactivated much faster than other two supported catalysts. Co/SiO2 showed a comparable activity to Co/Al2O3 and the best stability among the three Al2O3-, SiO2- and TiO2-supported Co catalysts.
Keywords: Solution synthesis; Urea fuel; Co oxide; Phenol degradation; Water treatment
Investigation of the physicochemical properties of CuO–CoO binary metal oxides supported on γ-Al2O3 and their activity for NO removal by CO
by Yuanyuan Lv; Hongliang Zhang; Yuan Cao; Lihui Dong; Lingling Zhang; Kaian Yao; Fei Gao; Lin Dong; Yi Chen (pp. 63-72).
Display Omitted► Both CuO and CoO species were highly dispersed on γ-Al2O3 support at lower loadings. ► Surface dispersed Cu–O–Co species was considered to exist in CuO–CoO/γ-Al2O3 catalysts. ► The reduced Cu–O–Co (Cu-□-Co species) was presumed to be the active species. ► Surface synergetic oxygen vacancy (SSOV) played an important role in NO–CO reaction.The dispersion and physicochemical behaviors of CuO–CoO binary metal oxides supported on γ-Al2O3 were characterized by XRD, LRS, XPS, H2-TPR, and in situ FT-IR techniques. Their activities were evaluated by NO–CO model reaction. The results indicated that (a) for lower loadings, CuO and CoO were able to be highly dispersed on the surface of γ-Al2O3 support; (b) the interaction between dispersed CuO and CoO upon γ-Al2O3 was discussed in the view of incorporation model. According to this model and obtained results, the surface dispersed Cu–O–Co species were considered to exist on the surface of γ-Al2O3; (c) CO or/and NO adsorption FT-IR results evidenced that the surface dispersed copper species could be reduced to lower valence by CO and the NO adsorption species converted with the increase in the temperature; (d) the surface dispersed Cu–O–Co species could be reduced to active Cu-□-Co species by CO among the mixture atmosphere. The formation of the surface synergetic oxygen vacancy (SSOV) was a crucial factor in the process of the NO–CO reaction. And a possible reaction pathway was tentatively proposed to discuss the NO–CO reaction based on all of these results.
Keywords: CuO–CoO/γ-Al; 2; O; 3; Cu–O–Co species; NO–CO reaction; Incorporation model; Surface synergetic oxygen vacancy
Photovoltaic properties of dye-sensitized solar cells associated with amphiphilic structure of ruthenium complex dyes
by Ken-Yen Liu; Chiao-Ling Hsu; Jen-Shyang Ni; Kuo-Chuan Ho; King-Fu Lin (pp. 73-79).
Display Omitted► The ruthenium dyes tend to aggregate into vesicles in their acetonitrile/tert-butanol solutions. ► The ruthenium dye with aliphatic side chains is easy to create voids after adsorption to TiO2. ► The created voids will increase the charge recombination and hence decrease Voc.Photovoltaic properties of Ru(2,2′-bipyridine-4,4′-bicarboxylic acid)(4,4′-bis(11-dodecenyl)-2,2′-bipyridine)(NCS)2 (denoted as Ru-C) related to its adsorption behavior onto the mesoporous titanium oxide (TiO2) were investigated in association with its amphiphilic structure compared with those of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 (commonly known as N3 dye). Both dyes tended to aggregate and form vesicles in their acetonitrile/tert-butanol solutions. As the vesicles were adsorbed to TiO2, the dyes which did not participate in bonding to TiO2 would re-dissolve into the solution and create the voids on the surface of TiO2. The voids for N3 dyes would be filled in time, whereas a great deal of voids for Ru-C dye remained, presumably due to its aliphatic side chains retarding further adsorption. The dye sensitized solar cell (DSSC) using Ru-C dye has lower power conversion efficiency compared with N3 dye, which is partly due to the remaining voids that increase the charge recombination. Besides, the N3 dye that is capable of injecting the excited electrons from both ligands to TiO2 also enhances the photocurrent. Therefore, although using amphiphilic dye for DSSC may have a merit of long term stability, its tendency of void formation on TiO2 mesoporous layer needs to be concerned.
Keywords: DSSC; Ruthenium dye; Amphiphilic; Adsorption; TiO; 2; Photovoltaic
Photocatalytic decolourisation of Reactive Red 4 dye by an immobilised TiO2/chitosan layer by layer system
by M.A. Nawi; S. Sabar; Sheilatina (pp. 80-87).
.Display Omitted► Immobilised TiO2/chitosan layer by layer system was examined as photocatalyst. ► TiO2/chitosan layer by layer system was 32 times better than a single layer of TiO2. ► Thin layer of TiO2 and acidic condition were favourable. ► The mechanisms were adsorption, photocatalytic degradation and charge transfer. ► The photocatalyst was highly efficient, sustainable and reusable.The synergistic photocatalysis–adsorption processes by the immobilized TiO2/chitosan layer by layer system on a glass support (TiO2/CS/glass) were investigated for the decolourisation of Reactive Red 4 (RR4) dye solution. Effects of different reaction parameters such as TiO2 loading, initial pH of the solution, visible light, dissolved oxygen and radical quenchers were studied. The decolourisation rate of RR4 by TiO2/CS/glass was more than 32 times faster than a single layer of TiO2 but was highly dependent on the TiO2 loading and the initial pH of the solution. A thin layer of TiO2 and acidic conditions favoured the adsorption of RR4 at the TiO2/CS interface. The h+/OH species that diffused from the TiO2 layer into the TiO2/CS interface oxidised the chemisorbed RR4 anions at the interface, and the generated electrons were then transferred to the conduction band of TiO2. Excess electrons in the conduction band of TiO2 increased the number of superoxide ions produced and thus improved the photocatalytic decolourisation of RR4. Therefore, apart from the synergistic photocatalysis–adsorption processes, a charge transfer process was also found to be responsible for maintaining the efficiency, sustainability and reusability of the TiO2/CS/glass layer by layer system.
Keywords: Photocatalysis; Adsorption; Charge transfer; Titanium dioxide; Chitosan; Layer by layer
Microwave assisted solvent free green preparation and physicochemical characterization of surfactant-anchored cellulose and its relevance toward the effective adsorption of chromium
by S. Kalidhasan; Priyanka Amba Gupta; Vinusha Reddy Cholleti; A. Santhana Krishna Kumar; Vidya Rajesh; N. Rajesh (pp. 88-98).
Display Omitted► The molecular interaction between cellulose, surfactant and Cr+6 is discussed. ► Microwave irradiation under solvent free conditions is used for the synthesis. ► The sorbent offers an adsorption capacity of 16.67mgg−1. ► Mechanism involves balanced electrostatic force and H-bonding. ► Regeneration of the sorbent is done using NaOH effectively.The molecular interaction between tetrabutylammonium iodide (TBAI) and cellulose and its potential application for the adsorption of chromium is discussed in this paper. The biosorbent was prepared under solvent free conditions using microwave irradiation. A subtle balance between electrostatic and the hydrophobic effects governs the interaction of biopolymer with the surfactant. The interaction between the biosorbent and chromium was comprehensively studied using spectroscopic, thermal and surface analysis techniques. The various analytical parameters that influence the adsorption were optimized, and the maximum adsorption capacity of Cr(VI) obtained from the Langmuir isotherm model was found to be 16.67mgg−1. The sorption thermodynamics indicated the spontaneity and exothermic nature of adsorption. The biosorbent could be effectively regenerated using NaOH, which imparts greener aspect to the overall process.
Keywords: Chromium(VI); Microwave heating; Cellulose; Surfactant; Adsorption
Adsorption of aromatic compounds on porous covalent triazine-based framework
by Jingliang Liu; Enmin Zong; Heyun Fu; Shourong Zheng; Zhaoyi Xu; Dongqiang Zhu (pp. 99-107).
Display Omitted► Covalent triazine-based framework (CTF) is a good adsorbent for aromatic compounds. ► Adsorption of polar aromatic compounds on CTF is stronger than the nonpolar ones. ► Specific, non-hydrophobic mechanisms responsible for this adsorption enhancement. ► Higher adsorption capacity for polar and/or ionic compounds than Amberlite XAD-4. ► CTF shows fast adsorption/desorption kinetics and high adsorption reversibility.Covalent triazine-based frameworks (CTFs) are an emerging class of polymers whose adsorption properties of organic chemicals are not well understood. The main objective of this work was to evaluate combined effects of the functional groups of aromatic solutes and the triazine structure of a synthesized CTF on adsorption in aqueous solutions. Adsorption of the hydroxyl-, amino-, nitro-, and sulfonate-substituted monocyclic and bicyclic aromatic compounds was generally stronger than their non-substituted, nonpolar counterparts (benzene and naphthalene). When compared with Amberlite XAD-4 resin, one of the most common and widely used polymeric adsorbents, the CTF showed much stronger adsorption toward the polar and/or ionic compounds. To explain the adsorption enhancement of CTF, several specific, non-hydrophobic mechanisms were proposed, including hydrogen bonding (hydroxyl- and amino-substituted compounds), electrostatic attraction (anionized compounds), and π–π electron-donor–acceptor (EDA) interaction (nitroaromatic compounds) with the triazine structure of CTF. The hypothesized mechanisms were further supported by the observed pH dependence of adsorption. Resulting from size exclusion, adsorption of large-size dissolved humic acids on the homogeneous, nanopored (1.2nm in size) CTF was negligible and did not affect adsorption of aromatic solutes. Additional advantages of fast adsorption/desorption kinetics and complete adsorption reversibility made CTF a superior adsorbent for aromatic compounds.
Keywords: Covalent triazine-based framework; Adsorbent; Adsorption; Aromatic compounds removal; Water treatment
Bisphenol-A modified hyper-cross-linked polystyrene resin for salicylic acid removal from aqueous solution: Adsorption equilibrium, kinetics and breakthrough studies
by Huanxiao Hu; Xiaomei Wang; Shengyong Li; Jianhan Huang; Shuguang Deng (pp. 108-112).
Display Omitted► Bisphenol-A modified hyper-cross-linked resin adsorbents. ► Shift of pore structures from mesopores to micropores. ► Improved efficiency for removing salicylic acid by adsorption. ► Report of micropore diffusion time constants. ► Adsorption and desorption column dynamics.In this study, a series of bisphenol-A modified hyper-cross-linked polystyrene resins labeled as HJ-L00, HJ-L02, HJ-L04, HJ-L06 and HJ-L08 were synthesized, characterized and evaluated for adsorptive removal of salicylic acid from aqueous solutions. The structural characterization results indicated that the resins possessed predominant micropores/mesopores, moderate specific surface area and a few bisphenol-A groups on the surface. All the bisphenol-A modified hyper-cross-linked resins were effective for removing salicylic acid from aqueous solutions, and sample HJ-L02 had the largest adsorption capacity. The adsorption equilibrium data were correlated by the Freundlich isotherm model, and a positive adsorption enthalpy was obtained. The kinetic data were analyzed with two diffusion models and indicated that the intra-particle diffusion was the sole rate-controlling step in the first stage. The dynamic experimental results showed that the breakthrough point of the HJ-L02 adsorbent was at 90.2BV (bed volume, 1BV=10mL) for a feed concentration of 500.0mg/L of salicylic acid, and 14.0BV of 1% of sodium hydroxide could completely regenerate the HJ-L02 adsorbent column.
Keywords: Hyper-cross-linked resin; Polystyrene; Adsorption; Salicylic acid
Degradation of carbofuran derivatives in restricted water environments: Basic hydrolysis in AOT-based microemulsions
by Jorge Morales; José A. Manso; Antonio Cid; Carlos Lodeiro; Juan Carlos Mejuto (pp. 113-120).
Display Omitted► Basic hydrolysis of carbofuran derivatives in AOT/ iC8/water microemulsions. ► Catalytic effects for 3-hydroxy-carbofuran and carbofuran were observed. ► Inhibitory effects for 3-keto-carbofuran were observed. ► New insights into hydrolysis mechanisms of carbofurans in restricted water media were found.The effect of sodium bis(2-ethylhexyl)sulfosuccinate/isooctane/water microemulsions on the stability of 2,2-dimethyl-2,3-dihydro-1-benzofuran-7-yl methylcarbamate (carbofuran, CF), 3-hydroxy-2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate (3-hydroxycarbofuran, HCF) and 3-keto-2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate (3-ketocarbofuran, KCF) in basic media has been studied. The presence of these microheterogeneous media implies a large basic hydrolysis of CF and HCF on increasing surfactant concentration and, also, on increasing water content in the microemulsion. The hydrolysis rate constants are approximately 2- and 10-fold higher than those in pure water for HCF and CF, respectively. In contrast, a steep descent in the rate of decomposition for KCF was observed. These behaviours can be ascribed to the presence of CF derivatives both in the hydrophilic phase and in the lipophilic phase, while the hydroxyl ions are only restricted to the water pool of the microemulsion (hydrophilic phase). The kinetic rate constants for the basic hydrolysis in AOT-based microemulsions have been obtained on the basis of a pseudophase model. Taking into account that an important part of soils are colloids, the possibility of the presence of restricted water environments implies that soil composition and its structure will play an important role in the stability of these carbamates. In fact, we observed that the presence of these restricted aqueous media in the environment, in particular in watersheds and in wastewaters, could reduce significantly the half-life of these pesticides (33% and 91% for HCF and CF, respectively).
Keywords: Pesticides; Colloids; Microemulsions; Basic hydrolysis; Surfactants
A comparative kinetic study on ultra-deep hydrodesulfurization of pre-treated gas oil over nanosized MoS2, CoMo-sulfide, and commercial CoMo/Al2O3 catalysts
by Hamdy Farag; Isao Mochida (pp. 121-129).
Display Omitted► Synthesis of nanosized MoS2 and Co-promoted MoS2 catalysts. ► Kinetics of gas oil hydrodesulfurization. ► Nanosized catalysts show higher hydrodesulfurization activity than the commercial CoMo/Al2O3 catalyst. ► HDS results of sulfur-containing compounds do not necessarily be typical to that for real feedstock.Unsupported nanosized MoS2 and CoMo-sulfide catalysts were synthesized, and their catalytic performances for the deep hydrodesulfurization (HDS) of treated gas oil were investigated as compared with that of a CoMo/Al2O3 catalyst. The HDS reactions were carried out in a batch autoclave reactor at 340°C and 3MPa H2. The CoMo-sulfide catalyst shows the highest activity and can reduce the sulfur content to less than 10ppm. The decrease in total sulfur content as a function of reaction time was found to follow pseudo-second order kinetics (empirical form). The change in the concentration of some individual representative sulfur-containing species in gas oil as a function of time was found to follow pseudo-first-order kinetics. However, the change in combined concentration of these species in the gas oil during HDS with the reaction time was found to corroborate pseudo-second-order kinetics. A kinetic model approach was proposed from which an estimation of the intrinsic kinetic data can be achieved. The model fitted the obtained data reasonably well, suggesting its potential for better assessment of the catalytic activity in the HDS of real feedstock. The study reveals that ranking of catalyst activities using model refractory sulfur-containing compounds does not necessarily imply a typical rank in case of investigating the real feedstocks.
Keywords: Hydrodesulfurization; Gas oil; MoS; 2; Catalyst
The effect of various treatment conditions on natural zeolites: Ion exchange, acidic, thermal and steam treatments
by Ayten Ates; Christopher Hardacre (pp. 130-140).
Display Omitted► The extraction of the embedded iron in natural zeolites into the extra-framework. ► The homogenisation of zeolites via ion exchange, acid and steam treatments. ► Determination of a relationship between the composition and stability of the zeolites. ► Improvement of characteristics of natural zeolites by a range of chemical and temperature treatments.Two different natural zeolites having different phase compositions were obtained from different regions of Turkey and modified by ion-exchange (0.5M NH4NO3) and acid leaching using 1M HCl. The natural and modified samples were treated at low temperature (LT), high temperature (HT) and steam (ST) conditions and characterised by XRF, XRD, BET, FTIR, DR–UV–Vis, NH3-TPD and TGA. Ion-exchange withNH4+ of natural zeolites results in the exchange of the Na+ and Ca2+ cations and the partial exchange of the Fe3+ and Mg2+ cations. However, steam and acidic treatments cause significant dealumination and decationisation, as well as loss of crystalline, sintering of phases and the formation of amorphous material. The presence of mordenite and quartz phases in the natural zeolites increases the stability towards acid treatment, whereas the structure of clinoptilolite-rich zeolites is mostly maintained after high temperature and steam treatments. The natural and modified zeolites treated at high temperature and in steam were found to be less stable compared with synthetic zeolites, resulting in a loss of crystallinity, a decrease in the surface area and pore volume, a decrease in the surface acidity as well as dealumination, and decationisation.
Keywords: Natural zeolite; Dealumination; Decationisation; Treatment; Steaming
Enrofloxacin sorption on smectite clays: Effects of pH, cations, and humic acid
by Wei Yan; Shan Hu; Chuanyong Jing (pp. 141-147).
Display Omitted► Multiple sorption mechanisms are responsible for the high ENR sorption capacity. ► pH, ionic strength, and clay conformation affect surface and interlayer sorption. ► Cation selectivity and hydrophobic sites on clay surface control ENR sorption.Enrofloxacin (ENR) occurs widely in natural waters because of its extensive use as a veterinary chemotherapeutic agent. To improve our understanding of the interaction of this emerging contaminant with soils and sediments, sorption of ENR on homoionic smectites and kaolinite was studied as a function of pH, ionic strength, exchangeable cations, and humic acid concentration. Batch experiments and in situ ATR–FTIR analysis suggested multiple sorption mechanisms. Cation exchange was a major contributor to the sorption of cationic ENR species on smectite. The decreased ENR sorption with increasing ionic strength indicated the formation of outer-sphere complexes. Exchangeable cations significantly influenced the sorption capacity, and the observed order was Cs− stretch, coupled CO stretch and OH deformation, and the result of irreversible desorption FTIR spectra indicated that OH of the carboxyl group was involved in the formation of inner-sphere surface complexes. The XRD analysis confirmed that interlayer intercalation is an important contributor to ENR sorption, while humic acid had a negligible contribution to the interlayer intercalation. The results of this study provide new insight into the molecular mechanisms of ENR sorption on clay minerals.
Keywords: Enrofloxacin (ENR); Sorption; Clay mineral; ATR–FTIR
Surface integration approach: A new technique for evaluating geometry dependent forces between objects of various geometry and a plate
by Daniel Dantchev; Galin Valchev (pp. 148-163).
Display Omitted► We developed a new approach, which we called surface integration approach. ► Using it we derived exact results in the case of an ellipsoid-plate interaction. ► The toroidal shape was generalized and analytical results were obtained. ► Result for the van der Waals force between red blood cell and a plate were obtained.We present a new approach, which can be considered as a generalization of the Derjaguin approximation, that provides exact means to determine the force acting between a three-dimensional body of any shape and a half-space mutually interacting via pairwise potentials. Using it, in the cases of the Lennard-Jones, standard and the retarded (Casimir) van der Waals interactions we derive exact expressions for the forces between a half-space or a slab of finite thickness and an ellipsoid in a general orientation, which in the simplest case reduces to a sphere, a tilted fully elliptic torus, and a body obtained via rotation of a single loop generalized Cassini oval, a particular example of which mimics the shape of a red blood cell. The results are obtained for the case when the object is separated from the plane via a non-polar continuous medium that can be gas, liquid or vacuum. Specific examples of biological objects of various shapes interacting with a plate like substrates are also considered.
Keywords: Van der Waals force; Lennard-Jones force; Sphere; Ellipsoid; Tilted fully elliptic torus; Red blood cell; Cassini oval
Mass transport characteristics of alkyl amines in a water/ n-decane system
by Marion Winkelmann; Lena Schneider; Wolfgang Gerlinger; Bernd Sachweh; Reinhard Miller; Heike Petra Schuchmann (pp. 164-169).
Display Omitted► A photometrical method is applied to determine effective diffusion coefficients. ► We investigated alkyl amines at the water/ n-decane interface. ► The effective diffusion coefficient depends on the adsorption behaviour of the amines. ► Additional surface active compounds influence the effective diffusion coefficient.Water-in-decane emulsions can be applied as reaction system for the precipitation of nanoparticles. Herein the precipitation reaction is induced once an oil as well as water soluble compound (here: alkyl amines) diffuses from the continuous oil phase into a water based droplet, loaded with the reaction partner. Thus, the mass transfer and adsorption characteristics of the alkyl amine at the interface are key parameters to understand particle formation in emulsion droplets. For this reason, the effective diffusion coefficients and the interfacial tension of different alkyl amines in a water/ n-decane system were estimated. Furthermore, emulsifiers necessary for the stability of the emulsion might represent a diffusion barrier. In order to determine its influence, diffusion experiments were also conducted in the presence of emulsifier. The effective diffusion coefficients were measured using an adapted photometric method.To identify relevant adsorption characteristics of the water/ n-decane/alkyl amine systems, the interfacial tension was studied with the pendant drop technique.According to the results, we can draw three conclusions: First, the effective diffusion coefficient depends on the molecular structure of the amines. Second, regarding our materials, the surface activity and surface coverage proved to be a governing parameter to describe differences in the transport mechanism. And third, the presence of additional surface active compounds leads to a decrease of the effective diffusion coefficient.
Keywords: Effective diffusion coefficient; Interfacial tension; Alkyl amines; Two phase system
Effects of humidity and temperature on laser-assisted dip-pen nanolithography array using molecular dynamics simulations
by Cheng-Da Wu; Te-Hua Fang; Tsung-Tse Wu (pp. 170-175).
Display Omitted► The number of molecules transferred increases significantly with increasing humidity. ► The number of transferred ink molecules and their diffusion ability are highest at the dwell stage. ► The transfer efficiency of the DPN process improves as the system humidity increases to saturation. ► Vapor water molecules limit meniscus growth for temperatures above 300K.Two-dimensional dip-pen nanolithography (DPN) combined with laser-assisted heating is studied using molecular dynamics (MDs) simulations. The effects of humidity, deposition temperature, heating rate (laser-assisted patterning), and cooling rate on ink molecules are evaluated in terms of molecular transference, alkanethiol meniscus characteristics, surface binding energy, number of transferred chains, pattern characteristics, and the diffusion coefficient of ink molecules. The simulation results clearly show that the number of molecules transferred significantly increases with increasing humidity, which leads to increases in meniscus size and pattern size. The surface binding energy decreases and the diffusion coefficient of ink molecules increases with increasing humidity and deposition temperature. The dwell stage has the largest number of molecules transferred and the largest diffusion distance of ink molecules. The number of vaporous water molecules increases when the temperature is above 300K, which limits meniscus growth and leads to unstable deposition. The DPN transfer efficiency can be significantly enhanced by increasing the laser pulse energy/heating rate. The transfer efficiency improves as the system humidity increases to saturation (374 water molecules).
Keywords: Dip-pen nanolithography; Array; Humidity; Molecular dynamics; Temperature
Temperature sensitivity of capillary-driven flow: Application to age monitoring devices
by J.A. Thomas; M.P. Boyle; L.W. Hunter; J.E. Tiffany (pp. 176-182).
Display Omitted► We develop a model for predicting fluid movement through a capillary. ► We quantify the effects of temperature and orientation on the velocity of the fluid. ► The movement of the fluid can be linked to the Arrhenius relationship. ► It is easy to design a device for recording the long-term local temperature history.The effects of time-dependent temperature fluctuations on surface-tension driven fluid flow inside a capillary are modeled using classical hydrodynamics. To begin, Newton’s second law is evoked to derive a nondimensional equation of motion that describes the time-evolution of the fluid front position and velocity as a function of system geometry, fluid properties, and fluid temperature. This model is used to examine how temperature excursions affect the instantaneous and long-term position and velocity of the fluid front inside the capillary. Next, the effects of orientation on the movement of high viscosity fluids through a capillary are examined. From these findings, a procedure is developed for designing non-powered time–temperature integration devices for recording the cumulative temperature exposure history of an environment.
Keywords: Capillary rise; Wetting; Temperature exposure; Dimensionless variables; Viscosity; Microfluidics
Using bulk convection in a microtensiometer to approach kinetic-limited surfactant dynamics at fluid–fluid interfaces
by Nicolas J. Alvarez; Douglas R. Vogus; Lynn M. Walker; Shelley L. Anna (pp. 183-191).
Display Omitted► Convection reduces diffusion boundary layer thickness for surfactant transport. ► Increasing the rate of diffusion separates timescales for transport. ► Lower bounds on the adsorption rate constant were determined for two surfactants.The impact of transport of surfactants to fluid–fluid interfaces is complex to assess and model, as many processes are in the regime where kinetics, diffusion and convection are comparable. Using the principle that the timescale for diffusion decreases with increasing curvature, we previously developed a microtensiometer to accurately measure fundamental transport coefficients via dynamic surface tension at spherical microscale liquid–fluid interfaces. In the present study, we use a low Reynolds number flow in the bulk solution to further increase the rate of diffusion. Dynamic surface tension is measured as a function of Peclet number and the results are compared with a simplified convection–diffusion model. Although a transition from diffusion to kinetic-limited transport is not observed experimentally for the surfactants considered, lower bounds on the adsorption and desorption rate constants are determined that are much larger than previously reported rate constants. The results show that the details of the flow field do not need to be controlled as long as the local Reynolds number is low. Aside from other pragmatic advantages, this experimental tool and analysis allows the governing mechanisms of surfactant transport at liquid–fluid interfaces to be quantified using flow near the interface to decrease the length scale for diffusion, separating the relevant timescales.
Keywords: Surfactant transport; Dynamic surface tension; Diffusion; Adsorption kinetic barriers; Convection
Formation of 2D spherulites in Langmuir films of amphiphilic T-shaped liquid crystals
by Sascha Reuter; Elkin Amado; Karsten Busse; Martin Kraska; Bernd Stühn; Carsten Tschierske; Jörg Kressler (pp. 192-201).
Display Omitted► Facial T-shaped p-terphenyl derivatives amphiphilic liquid crystals studied at air–water interface. ► Different behavior of liquid crystals depends on their n-alkyl chain lengths. ► Liquid crystals with short n-alkyl chains form fluid multilayers at air–water interface. ► Liquid crystals with long n-alkyl chains crystallize in spherulitic structures. ► Spherulitic surface crystallization process reported for the first time for a Langmuir film of a liquid crystal.Langmuir films of facial T-shaped amphiphilic liquid crystals were studied at the air–water interface. The liquid crystals were composed of three incompatible segments: a central rigid rodlike p-terphenyl (TP) group, two flexible hydrophobic n-alkyl terminal chains of identical length linked through ether bonds, and one hydrophilic lateral chain of three ethylene oxide units with a carboxyl end group. In order to determine the influence of the alkyl chain length on the characteristics of condensed films three TPs having n-alkyl chains with eight (TP8/3), ten (TP10/3) or 16 (TP16/3) carbon atoms were investigated. Surface pressure – mean molecular area isotherms revealed clear differences. TP8/3 and TP10/3 exhibit an extended plateau region where a phase transition from monolayer to multilayer takes place. On the other hand, the TP16/3 isotherm showed a distinct maximum (‘spike’) corresponding to a surprising surface crystallization process which is reported for the first time for a Langmuir film of a liquid crystal. Brewster angle microscopy clearly confirmed these differences: TP8/3 and TP10/3 formed circular domains with liquid crystalline order, while TP16/3 formed well-defined two-dimensional polycrystalline spherulites which are fractured after further compression. The film thickness determined by X-ray reflectivity measurements correlated with a multilayer formation for TP10/3. The morphology of Langmuir–Blodgett (LB) films transferred onto silicon wafers and studied by atomic force microscopy also confirmed the striking different behavior (multilayer formation vs. 2D crystallization) of the TPs under investigation.
Keywords: p; -Terphenyl liquid crystal; Langmuir film; Brewster angle microscopy; Langmuir–Blodgett film; Multilayer formation; Surface spherulites
Characterisation of alkyl amines at the water/air surface with the drop and bubble profile analysis tensiometry
by Marion Winkelmann; Aliyar Javadi; Reinhard Miller; Heike Petra Schuchmann (pp. 202-206).
Display Omitted► With time, an increase in the surface tension of alkyl amines can be observed. ► The increase in surface tension can be ascribed to the evaporation of alkyl amines. ► Limiting the evaporation of alkyl amines, the equilibrium surface can be obtained.Pendant drop and buoyant bubble methods have been used to study the surface characteristics of alkyl amines at the water/air surface. The investigated alkyl amines, triethylamine and octylamine, showed unusual changes in the surface tension as a function of time: an initially steep drop and a subsequent steady increase in the surface tension until a value close to the one of the pure water/air system was observed. This phenomenon is explained by the evaporation of the alkyl amines, for which several sets of experiments have been conducted with the pendant drop and buoyant bubble methods. Using an appropriate experimental protocol, the equilibrium adsorption behaviour of the two amines can be quantitatively measured.
Keywords: Surface tension; Alkyl amine; Evaporation; Pendant drop profile tensiometry; Buoyant bubble profile tensiometry
Electroosmotic flow in a water column surrounded by an immiscible liquid
by Saeid Movahed; Sina Khani; John Z. Wen; Dongqing Li (pp. 207-211).
Display Omitted► Electroosmotic flow of aqueous solution surrounded by immiscible liquid is studied. ► Velocity in both phases increases with ς-potential at interface of the two fluids. ► Higher values of ς-potential increase slip velocity at interface of the two fluids. ► The more viscous immiscible fluid, the slower the system moves. ► Viscosity of immiscible fluid affects flatness of velocity field in aqueous solution.In this paper, we conducted numerical simulation of the electroosmotic flow in a column of an aqueous solution surrounded by an immiscible liquid. While governing equations in this case are the same as that in the electroosmotic flow through a microchannel with solid walls, the main difference is the types of interfacial boundary conditions. The effects of electric double layer (EDL) and surface charge (SC) are considered to apply the most realistic model for the velocity boundary condition at the interface of the two fluids. Effects on the flow field of ς-potential and viscosity ratio of the two fluids were investigated. Similar to the electroosmotic flow in microchannels, an approximately flat velocity profile exists in the aqueous solution. In the immiscible fluid phase, the velocity decreases to zero from the interface toward the immiscible fluid phase. The velocity in both phases increases with ς-potential at the interface of the two fluids. The higher values of ς-potential also increase the slip velocity at the interface of the two fluids. For the same applied electric field and the same ς-potential at the interface of the two fluids, the more viscous immiscible fluid, the slower the system moves. The viscosity of the immiscible fluid phase also affects the flatness of the velocity profile in the aqueous solution.
Keywords: Electroosmotic flow; Two phase flow; Immiscible liquid
Stability of binary model membranes—Prediction of the liposome stability by the Langmuir monolayer study
by A. Szcześ; M. Jurak; E. Chibowski (pp. 212-216).
Display Omitted► Stable DPPC/Chol complexes of 3:1 stoichiometry exist at the air/water interface. ► The most stable liposomes contain the smallest amount of Chol (x Chol=0.25). ► Usefulness of the Langmuir monolayer study to predict stability of liposomes.In this paper, usefulness of the Langmuir monolayer study is demonstrated for predictions of the stability of liposomes composed of dipalmitoyl phosphatidylcholine (DPPC) and cholesterol (Chol). Thermodynamic analysis of the surface pressure ( π)–area ( A) isotherms of the DPPC/Chol systems was performed, which allowed for concluding on miscibility of the components, their molecular packing, and the interactions between molecules. It was found that the most stable system, in which the strongest interactions between molecules occured, was DPPC/Chol atx Chol=0.25. The stability of liposomes of the same composition as that in the Langmuir monolayers was analyzed by determining the size distribution of vesicles and the polydispersity as a function of time. The changes of these parameters confirmed that the system of the greatest stability is that with low Chol content.
Keywords: Langmuir monolayer; Thermodynamic analysis; Liposomes; Stability
Multistep mineral fouling growth on a cation-exchange membrane ruled by gradual sieving effects of magnesium and carbonate ions and its delay by pulsed modes of electrodialysis
by Nicolás Cifuentes-Araya; Gérald Pourcelly; Laurent Bazinet (pp. 217-230).
Display Omitted► dc current leads to severe membrane fouling by calcium and magnesium salts. ► Pulsed electric field (PEF) modes of electrodialysis delay mineral fouling growth. ► Primary fouling growth depends on the diluate pH evolutions and ion migration rates. ► Sieving effects rule subsequent fouling growth and are triggered by fouling layers. ► Inverted migration rates result in marked multistep fouling crystallizations.The aim of this study was to reveal the mechanisms ruling a fouling growth on both sides of a CMX-SB cation-exchange membrane (CEM), run after run during three consecutive electrodialysis (ED) treatments. A model solution containing a high magnesium/calcium ratio (2/5) was demineralized under two different pulsed electric field (PEF) on-duty ratios and dc current. The results showed a series of mechanisms ruling a multilayer mineral fouling growth and its delay by PEFs. The nature of the fouling layer, during a first run, depended on the diluate pH-value evolutions and the ion migration rates through the membrane. A subsequent multilayer fouling growth during consecutive treatments was ruled by the already formed mineral layers, where gradual sieving effects inverted the migration rates and led to a multistep crystal growth. Calcium carbonate grew on the diluate side of CEM, starting from its amorphous phase to then crystallize in a coexisting presence of aragonite and calcite. Amorphous magnesium hydroxide appeared on CEM apparently through fouling dehydration ruled by the mineral layers themselves and by overlimiting current regimes. A delayed fouling growth was observed for PEF ratio 0.3. A long pause lapse during pulse modes was demonstrated as an important parameter for fouling mitigation.
Keywords: Electrodialysis; Cationic membrane; Pulsed electric field; Fouling mechanisms; Sieving effect
Fabrication and characterization of hierarchical nanostructured smart adhesion surfaces
by Hyungoo Lee; Bharat Bhushan (pp. 231-238).
Display Omitted► Nanostructured surface may show low or high adhesion depending on fibrillar density. ► Current research uses a patterning technique to fabricate smart adhesion surfaces. ► Oriented fibers of 100 and 600nm diameter exhibited gecko effect due to high density. ► Oriented fibers of 5 and 14μm diameter exhibited Lotus effect due to smaller density. ► The bending and buckling behaviors of the fibers were observed.The mechanics of fibrillar adhesive surfaces of biological systems such as a Lotus leaf and a gecko are widely studied due to their unique surface properties. The Lotus leaf is a model for superhydrophobic surfaces, self-cleaning properties, and low adhesion. Gecko feet have high adhesion due to the high micro/nanofibrillar hierarchical structures. A nanostructured surface may exhibit low adhesion or high adhesion depending upon fibrillar density, and it presents the possibility of realizing eco-friendly surface structures with desirable adhesion. The current research, for the first time uses a patterning technique to fabricate smart adhesion surfaces: single- and two-level hierarchical synthetic adhesive structure surfaces with various fibrillar densities and diameters that allows the observation of either the Lotus or gecko adhesion effects. Contact angles of the fabricated structured samples were measured to characterize their wettability, and contamination experiments were performed to study for self-cleaning ability. A conventional and a glass ball attached to an atomic force microscope (AFM) tip were used to obtain the adhesive forces via force-distance curves to study scale effect. A further increase of the adhesive forces on the samples was achieved by applying an adhesive to the surfaces.
Keywords: Adhesion; Superhydrophobic; Lotus; Gecko; Polypropylene; Hierarchical structure
Gold nanoclusters as contrast agents for fluorescent and X-ray dual-modality imaging
by Aili Zhang; Yu Tu; Songbing Qin; Yan Li; Juying Zhou; Na Chen; Qiang Lu; Bingbo Zhang (pp. 239-244).
Display Omitted► Gold nanoclusters (Au NCs) are synthesized via ambient biomineralization approach. ► The synthesized Au NCs exhibit highly fluorescent and strong X-ray absorption coefficient. ► Au NCs as dual-modality imaging contrast agents (CAs) for fluorescent and X-ray dual-modality imaging.Multimodal imaging technique is an alternative approach to improve sensitivity of early cancer diagnosis. In this study, highly fluorescent and strong X-ray absorption coefficient gold nanoclusters (Au NCs) are synthesized as dual-modality imaging contrast agents (CAs) for fluorescent and X-ray dual-modality imaging. The experimental results show that the as-prepared Au NCs are well constructed with ultrasmall sizes, reliable fluorescent emission, high computed tomography (CT) value and fine biocompatibility. In vivo imaging results indicate that the obtained Au NCs are capable of fluorescent and X-ray enhanced imaging.
Keywords: Dual-modality imaging; Gold nanoclusters; Fluorescent; X-ray imaging; Contrast agents
Preparation and characterization of a novel stimuli-responsive nanocomposite hydrogel with improved mechanical properties
by Yang Wang; Dajun Chen (pp. 245-251).
Display Omitted► Novel stimuli-responsive NC hydrogels were prepared. ► The resulting NC hydrogels exhibited high mechanical properties. ► According to the Arrhenius equation, the physical cross-link density was evaluated. ► The swelling and deswelling behaviors of NC hydrogels depend on the content of AT.A novel stimuli-responsive organic/inorganic nanocomposite hydrogel (NC hydrogel) with excellent mechanical properties was synthesized by in situ polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA), oligo (ethylene glycol) methacrylate (OEGMA) and acrylic acid (AAc), as the polymeric matrix (PMOA), and fibrillar attpulgite (AT), as the reinforcer and cross-linker. The effect of the AT content on the mechanical properties for the swollen and dried NC hydrogels was determined by tensile testing and dynamic mechanical analysis (DMA), respectively. The tensile testing results showed that the incorporation of AT nanoparticles significantly enhanced the mechanical properties of NC hydrogels. As the content of AT increased, the tensile strength, tensile modulus and effective cross-linked chain density increased. The DMA results showed that the storage modulus of AT/PMOA NC hydrogels was increased and the glass transition temperatures shifted to higher temperature compared to the pure PMOA hydrogel, which further indicated that the enhancement of mechanical property depended upon the presence and content of AT. In addition, the faster swelling rates of the NC hydrogels were observed in comparison with the corresponding physically cross-linked PMOA hydrogel, except for 1% AT/PMOA sample. However, the deswelling kinetics of NC hydrogels was obviously retarded.
Keywords: Hydrogel; Nanocomposite; P (MEO; 2; MA-co-OEGMA-co-AAc); Attapulgite
Characterizing zeta potential of functional nanofibers in a microfluidic device
by Daehwan Cho; SangGap Lee; Margaret W. Frey (pp. 252-260).
Display Omitted► A microfluidic device measures zeta potential through a pressure-driven flow. ► Operation at low flow rate produces reliable streaming currents. ► This system characterizes charge potentials of polymeric nanofibers.The measurement of surface charge on nanofibers was achieved by characterizing zeta potential of the nanofibers via a newly developed device for streaming current measurement. Low flow rates were sufficient to generate detectable streaming currents in the absence of an externally applied voltage without damaging nanofiber samples. Zeta potential was calculated by using the Helmholtz–Smoluchowski equation and the measured streaming currents. Two acrylic plates were machined and assembled to form a microfluidic channel that is 150μm high, 2.0mm wide, and 30mm long. Two electrodes for the measurement of streaming currents were housed in the top plate. Two nanofibers of pure polyacrylonitrile (PAN) fibers and charged (TiO2 incorporated) PAN fibers were prepared and characterized in the device. Monobasic sodium phosphate and dibasic sodium phosphate were used to prepare four different pH buffer solutions ranging from pH 5 to pH 8 in order to characterize the zeta potentials. The pure PAN nanofibers had negatively-charged surfaces regardless of pH. However, the zeta potentials of PAN/TiO2 nanofibers changed from positive to negative at pH 6.5. The zeta potential measurements made on the nanofibers in this new microfluidic device matched with those of the powdered raw materials using a commercial Zetasizer.
Keywords: Zeta potential; Functional nanofibers; Streaming current; Microfluidic device