Electrospun nanofibers applications in caries lesions: prevention, treatment and regeneration.

Dental caries is a multifactorial disease primarily mediated by biofilm formation, resulting in a net loss of mineral content and degradation of organic matrix in dental hard tissues. Caries lesions of varying depths can result in demineralization of the superficial enamel, the formation of deep cavities extending into the dentin, and even pulp infection. Electrospun nanofibers (ESNs) exhibit an expansive specific surface area and a porous structure, closely mimicking the unique architecture of the natural extracellular matrix (ECM). This unique topography caters to the transport of small molecules and facilitates localized therapeutic drug delivery, offering great potential in regulating cell behavior, and thereby attracting interest in ESNs' applications in the treatment of caries lesions and the reconditioning of the affected dental tissues. Thus, this review aims to consolidate the recent developments in ESNs' applications for caries lesions. This review begins with an introduction to the electrospinning technique and provides a comprehensive overview of the biological properties and modification methods of ESNs, followed by an introduction outlining the basic pathological processes, classification and treatment requirements of caries lesions. Finally, the review offers a detailed examination of the research progress on the ESNs' application in caries lesions and concludes by addressing the limitations.

Fabrication and enhanced visible-light photocatalytic H2production of B-doped N-deficient g-C3N4/CdS Hybrids with robust 2D/2D hetero-interface interaction.

2D layered photocatalysts with proper electronic structure have sparked much attention in the field of visible-light photocatalysis for H2production. Herein, by simply calcining the mixture of ultrathin g-C3N4(CNN) and NaBH4, heteroatom B and N defect were simultaneously introduced into g-C3N4. The obtained modified g-C3N4(BDCNN) was further coupled with 2D flower-like CdS nanosheet. The optimal 2D/2D BDCNN/CdS-15% heterojunction behaved ideal photocatalytic activity for H2revolution by water splitting, and the highest H2revolution rate was as high as 1013.8µmol g-1h-1, which was 6.7 times, 2 times, and 5.8 times of the corresponding values of pristine CNN, BDCNN and CdS respectively. It was evidenced that the band structure of 2D/2D BDCNN/CdS-15% was well tuned for better visible-light adsorption and higher separation efficiency of photo-induced carriers for enhancing H2revolution performance. The achievement in this study provided informative principles for exploring g-C3N4based heterojunctions with higher H2-production performance.

Improved Esterification of Citric Acid and n-Butanol Using a Dense and Acid-Resistant Beta Zeolite Membrane.

In this work, a dense and acid-resistant beta zeolite membrane was applied to improve the esterification of citric acid and n-butanol, for the first time. Through the continuous removal of the by-product water via pervaporation (PV), the conversion of citric acid was significantly enhanced from 71.7% to 99.2% using p-Toluenesulfonic acid (PTSA) as catalyst. PTSA was a well-known strong acid, and the membrane kept almost no change after PV-esterification, indicating the superior acid resistance of beta zeolite membrane. Compared to the use of acid-resistant MOR zeolite membrane by PV-esterification, a consistently higher conversion of citric acid was obtained using a high-flux beta zeolite membrane. The results showed that high water permeation on the beta zeolite membrane, with good acid resistance, had a strong promoting effect on esterification, leading to an improved conversion. In addition, the citric acid conversion of 97.7% could still be achieved by PV-esterification at a low reaction temperature of 388 K.

A novel amelogenesis-inspired hydrogel composite for the remineralization of enamel non-cavitated lesions.

Enamel non-cavitated lesions (NCLs) are subsurface enamel porosity from carious demineralization. The developed enamel cannot repair itself once NCLs occurs. The regeneration of mineral crystals in a biomimetic environment is an effective way to repair enamel subsurface defects. Previously, an amelogenin-derived peptide named QP5 was proven to repair demineralized enamel. In this work, inspired by amelogenesis, a novel biomimetic hydrogel composite containing the QP5 peptide and bioactive glass (BG) was designed, in which QP5 could promote enamel remineralization by guiding the calcium and phosphorus ions provided by BG. Also, BG could adjust the mineralization micro-environment to alkalinity, simulating the pH regulation of ameloblasts during enamel maturity. The BQ hydrogel composite showed biosafety and possessed capacity for enamel binding, ion release and pH buffering. Enamel NCLs treated with the BQ hydrogel composite showed a higher reduction in lesion depth and mineral loss both in vitro and in vivo. Moreover, compared to the hydrogels containing only BG or QP5, groups treated with the BQ hydrogel composite attained more surface microhardness recovery and color recovery, exhibiting resistance to erosion and abrasion of the remineralization layer. We envision that the BQ hydrogel composite can provide a biomimetic micro-environment to favor enamel remineralization, thus reducing the lesion depth and increasing the mineral content as a promising biomimetic material for enamel NCLs.

Hierarchical S-Scheme Heterostructure of CdIn2S4@UiO-66-NH2 toward Synchronously Boosting Photocatalytic Removal of Cr(VI) and Tetracycline.

Developing highly efficient photocatalysts toward synchronously removing heavy metals and organic pollutants is still a serious challenge. Herein, we depict hierarchical S-scheme heterostructured photocatalysts prepared via in situ anchoring UiO-66-NH2 nanoparticles onto the CdIn2S4 porous microsphere structures assembled with numerous nanosheets. In the mixed system of Cr(VI) and tetracycline (TC), the optimal photocatalyst (CIS@U66N-30) shows remarkable photocatalytic activities toward the synchronous removal of Cr(VI) (97.26%) and TC (close to 100% of) under visible-light irradiation for 60 min, being the best removal rates among those of the reported photocatalysts, and sustains the outstanding stability and reusability. Its reaction rate constants of Cr(VI) reduction and TC degradation are about 2.06 and 1.58 folds that in the single Cr(VI) and TC systems, respectively. The enhanced photocatalytic activities of CIS@U66N-30 mainly result from the following synergism: (1) its hierarchical structure offers abundant active sites, and the S-scheme migration mechanism of charge carriers in the heterostructure accelerates the separation and migration of the useful photoinduced electrons and holes with the high redox capability; (2) Cr(VI) and TC can serve as the electron scavenger for TC oxidation degradation and the hole and •OH scavenger for Cr(VI) reduction, respectively, further enhancing the separation and utilization efficiency of photoinduced electrons and holes. Besides, the possible TC degradation pathway and plausible S-scheme photocatalytic mechanism over CIS@U66N-30 for the concurrent elimination of Cr(VI) and TC are proposed.

In situself-assembly fabrication of ultrathin sheet-like CuS modified g-C3N4heterojunction and its enhanced visible-light photocatalytic performance.

Photocatalysts with heterojunction structure have been widely used for organic degradation. In this study, CuS/g-C3N4heterojunction was formed byin situself-assembly via a simply hydrothermal method. A series of characterizations were applied to analyzing the morphology, structure, optical properties and photo-induced electron transfer of the samples. The effect of CuS mass ratio in the CuS/g-C3N4composite on methyl blue (10 mg l-1) degradation under visible-light illumination was discussed. When CuS mass ratio was 60%, CuS/g-C3N4behaved the highest photocatalytic efficiency which is 17 times higher than that of pure g-C3N4, and the optimal heterojunction exhibited promising photocatalytic stability as well. The synthesized CuS/g-C3N4with intimate contact and promising photocatalytic performance provides important implications on analogous researches on g-C3N4-based heterojunctions for photocatalytic applications.

Nitrogen-rich triazine-based porous polymers for efficient removal of bisphenol micropollutants.

Achieving both rapid adsorption rate and high adsorption capacity for bisphenol micropollutants from aquatic systems is critical for efficient adsorbents in water remediation. Here, we elaborately prepared three nitrogen-rich triazine-based porous polymers (NTPs) with similar geometric configurations and nitrogen contents (41.70-44.18 wt%) while tunable BET surface areas and micropore volumes in the range of 454.7-536.3 m2 g-1 and 0.20-0.84 cm3 g-1, respectively. It was systematically revealed that the synergy of hydrogen bonding, π-π electron-donor-acceptor interaction, and micropore preservation promoted the rapid (within 5 min) and high capacity adsorption of bisphenols by NTPs. Particularly, microporous-dominated NTPs-3 with the highest micro-pore volume (0.84 cm3 g-1) displays remarkable adsorption capacity towards bisphenol A as evidenced by the adsorption capacity of 182.23 mg g-1. A simple column filter constructed by NTPs-3 also expressed good dynamic adsorption and regeneration capacity. This work provided new insight into the rational design and engineering of nitrogen-rich porous polymers for the remediation of micropollutant wastewater.

Preparation of Pebax 1657/MAF-7 Mixed Matrix Membranes with Enhanced CO2/N2 Separation by Active Site of Triazole Ligand.

Fillers play a critical role in the performance of mixed matrix membranes (MMMs). Microporous metal azolate frameworks (MAFs) are a subclass material of metal-organic frameworks (MOFs). Due to the uncoordinated nitrogen of the organic ligands, MAF-7 (SOD-[Zn(mtz)2], Hmtz = 3-methyl-1,2,4-triazole, window: d = 0.34 nm) shows excellent CO2 adsorption performance. In this work, Pebax 1657/MAF-7 MMMs were prepared by a sample solution casting method with MAF-7 particles as fillers for the first time. By means of X-ray diffraction (XRD), scanning electron microscope (SEM), infrared radiation (IR), and thermogravimetry (TG), the compositional and structural properties of the mixed matrix membrane with different filler content were analyzed. The results show that the compatibility of MAF-7 and Pebax is good with a filler content of 5 wt.%. The pure gas testing showed that mixed matrix membrane has a high ideal CO2/N2 selectivity of 124.84 together with a better CO2 permeability of 76.15 Barrer with the optimized filler content of 5 wt.%. The obtained membrane showed 323.04% enhancement in selectivity of CO2/N2 and 27.74% increase in the permeability of CO2 compared to the pristine membrane at 25 °C and 3 bar. The excellent separation performance may be due to the ligands that can afford a Lewis base active site for CO2 binding with the uniform dispersion of MAF-7 particles in Pebax and the favorable interface compatibility. The obtained membrane overcomes the Robeson's upper bound in 2008 for CO2/N2 separation. This work provides a new strategy by utilizing MAFs as fillers with triazole ligand to enhance the gas separation performance of mixed matrix membranes.

Template Removal and Surface Modification of an SSZ-13 Membrane with Heated Sodium Chloride for CO2/CH4 Gas Separation.

Hydrothermal synthesis with an organic template of N,N,N trimethyl-1-adamantammonium hydroxide (TMAdaOH) is the most commonly used method to prepare an SSZ-13 zeolite membrane. In this paper, the synthesized membrane was treated in heated sodium chloride to remove TMAdaOH instead of calcination in air. The surface of the membrane was modified by the heated NaCl and resulted in an improved CO2/CH4 gas separation selectivity. TMAda+ in the channels of SSZ-13 zeolite decomposed completely, and the treatment time was shortened significantly compared with calcination in air. The recrystallization of zeolite reacting with heated NaCl was the possible reason for the improved gas separation performance of the membrane.

Enhanced H2evolution performance by carbonized SiC/g-C3N4heterojunction under visible-light illumination.

In this study, carbonized silicon carbide/graphitic carbon nitride ((SiC/C)/g-C3N4) composites were fabricated via a facile calcination method. The optimal SiC/C/g-C3N4composite shows an excellent visible-light photocatalytic activity for water splitting, with the highest hydrogen evolution amount being 200.2µmol, which is four times higher than that of pure g-C3N4when triethanolamine and platinum (1.0 wt%) are used as the sacrificial agent and cocatalyst, respectively. With an intimate interface between SiC/C and g-C3N4, the energy band structure of g-C3N4was well engineered for photocatalytic H2production. This study provides a novel method for fabricating g-C3N4-based heterojunctions for application in environmental conservation.

The pH-Responsive Property of Antimicrobial Peptide GH12 Enhances Its Anticaries Effects at Acidic pH.

Dental caries is closely related to the acidification of the biofilms on the tooth surface, in which cariogenic bacteria bring about a dramatic pH decrease and disrupt remineralisation equilibrium upon the fermentation of dietary sugars. Thus, approaches targeting the acidified niches with enhanced anticaries activities at acidic pH are highly desirable. In our previous study, a cationic amphipathic α-helical antimicrobial peptide GH12 (Gly-Leu-Leu-Trp-His-Leu-Leu-His-His-Leu-Leu-His-NH2) was designed with good stability, low cytotoxicity, and excellent antibacterial effects. Considering its potent antibacterial activity against the acidogenic bacteria and its histidine-rich sequence, it was speculated that GH12 might show enhanced antimicrobial effects at an acidic pH. In this study, the pH-responsive property of GH12 was determined to evaluate its potential as a smart acid-activated anticaries agent. GH12 possessed much lower minimal inhibitory concentrations and minimal bactericidal concentrations against various kinds of bacteria at pH 5.5 than at pH 7.2. Employing Streptococcus mutans, the principal caries pathogen, as the model system, it was found that GH12 showed much stronger bactericidal effects on both planktonic S. mutans and S. mutans embedded in the biofilm at pH 5.5. In addition, short-term treatment with GH12 showed much more effective inhibitory effects on water-insoluble exopolysaccharides synthesis and lactic acid production of the preformed S. mutans biofilm at pH 5.5. As for the mechanism exploration, it was found that the net positive charge of GH12 increased and the tryptophan fluorescence intensity heightened with the peak shifting towards the short wavelength at pH 5.5, which demonstrated that GH12 could be more easily attracted to the anionic microbial cell membranes and that GH12 showed stronger interactions with the lipid membranes. In conclusion, acidic pH enhanced the antibacterial and antibiofilm activities of GH12, and GH12 is a potential smart anticaries agent targeting the cariogenic acidic microenvironment.

Different Hydrogen Bond Changes Driven by Surface Segregation Behavior of Imidazolium-Based Ionic Liquid Mixture at the Liquid-Vacuum Interface.

In this work, molecular dynamics (MD) simulations were carried out to study the behaviors of a binary ionic liquid (IL) mixture consisting of equimolar [C2C1Im][BF4] and [C4C1Im][BF4], as well as two corresponding pure ILs, at the liquid-vacuum interface. Our simulation results show that the competition of nonpolar interactions between different alkyl chains of two cations results in an obvious surface segregation behavior of the IL mixture at the interface, indicating an enhanced aggregation of the [C4C1Im]+ cations but a weakened aggregation of the [C2C1Im]+ cations at the outermost surface. More interestingly, different hydrogen bond (HB) changes between two imidazolium cations at the interface can be driven by such surface segregation behavior, where the [C2C1Im]+ cations rather than the [C4C1Im]+ ones have more and stronger HBs with the [BF4]- anions by comparison with the corresponding pure ILs at the interface. Meanwhile, it is interesting to find that such a stronger HB would lower the rotations of the imidazolium rings of interfacial [C2C1Im]+ cations. By contrast, the [C4C1Im]+ cations at the outermost surface rotate faster owing to their weaker HB. In addition, the orientation analysis uncovers that there is a major decrease for the orderliness of interfacial [C2C1Im]+ cations, but a minor decrease for that of interfacial [C4C1Im]+ cations, from the pure IL to the IL mixture. Such distinct results are closely related to the surface segregation between the [C2C1Im]+ and [C4C1Im]+ cations in the IL mixture and their interfacial HB properties. Thus, our simulation results afford a deep insight into the surface segregation effect on the HB behavior of the imidazolium-based IL mixture at liquid-vacuum interface.

Molecular-level insights into the structures, dynamics, and hydrogen bonds of ethylammonium nitrate protic ionic liquid at the liquid-vacuum interface.

A series of molecular dynamics simulations have been used to systematically explore the structures, dynamics and hydrogen bonds (HBs) of ethylammonium nitrate (EAN) protic ionic liquid (IL) and their mutual relationship at the liquid-vacuum interface. The simulation results clearly demonstrate that there exists a sandwich structure at the interface, with the double-layer of the EA+ cations on both sides and one intercalated layer of the NO3- anions in the middle. Wherein, the outermost cation layer prefers the orientation with the CH3 groups pointing to the vacuum phase due to the hydrophobic interactions, while the CH3 groups in the second layer direct to the bulk liquid phase owing to the HB formation between their NH3+ groups and the intercalated NO3- anions in the middle layer. On the other hand, the continuous HB strength of the cations in the outermost layer (denoted as Cation-1) is found to be almost identical with the counterpart of the cations in the second layer (denoted as Cation-2), whereas the intermittent HB strength of Cation-1 is much larger than that of Cation-2 at all temperatures. Furthermore, the rotational motion of Cation-1 with the normal vector of the C-C-N plane in the cation is faster than that of Cation-2 with the same vector, resulting from more free space in the outermost layer. On the contrary, the rotational motion of Cation-1 with the vector from the mass center of the cation to its N atom is much slower than that of Cation-2 with the same vector, which can be attributed to the combined effects of the stronger intermittent HBs of Cation-1 and the hydrophobic interactions of its CH3 group in the outermost layer.

Antimicrobial Peptide GH12 Prevents Dental Caries by Regulating Dental Plaque Microbiota.

Due to the complex microecology and microenvironment of dental plaque, novel caries prevention strategies require modulating the microbial communities ecologically and reducing the cariogenic properties effectively. Antimicrobial peptide GH12 reduced the lactic acid production and exopolysaccharide (EPS) synthesis of a Streptococcus mutans biofilm and a three-species biofilm in vitro in previous studies. However, the anticaries effects and microecological effects of GH12 remained to be investigated in a complex biofilm model in vitro and an animal caries model in vivo In the present study, GH12 at 64 mg/liter showed the most effective inhibition of lactic acid production, EPS synthesis, pH decline, and biofilm integrity of human dental plaque-derived multispecies biofilms in vitro, and GH12 at 64 mg/liter was therefore chosen for use in subsequent in vitro and in vivo assays. When treated with 64-mg/liter GH12, the dental plaque-derived multispecies biofilms sampled from healthy volunteers maintained its microbial diversity and showed a microbial community structure similar to that of the control group. In the rat caries model with a caries-promoting diet, 64-mg/liter GH12 regulated the microbiota of dental plaque, in which the abundance of caries-associated bacteria was decreased and the abundance of commensal bacteria was increased. In addition, 64-mg/liter GH12 significantly reduced the caries scores of sulcal and smooth surface caries in all locations. In conclusion, GH12 inhibited the cariogenic properties of dental plaque without perturbing the dental plaque microbiota of healthy individuals and GH12 regulated the dysbiotic microbial ecology and arrested caries development under cariogenic conditions.IMPORTANCE The anticaries effects and microecological regulation effects of the antimicrobial peptide GH12 were evaluated systematically in vitro and in vivo GH12 inhibited the cariogenic virulence of dental plaque without overintervening in the microbial ecology of healthy individuals in vitro GH12 regulated the microbial ecology of dental plaque to a certain extent in vivo under cariogenic conditions, increased the proportion of commensal bacteria, and decreased the abundance of caries-associated bacteria. GH12 significantly suppressed the incidence and severity of dental caries in vivo This study thus describes an alternative antimicrobial therapy for dental caries.

Separation Selectivity of CH4/CO2 Gas Mixtures in the ZIF-8 Membrane Explored by Dynamic Monte Carlo Simulations.

Here we report a series of nonequilibrium dynamic Monte Carlo simulations combined with dual control volume (DCV-DMC) to explore the separation selectivity of CH4/CO2 gas mixtures in the ZIF-8 membrane with a thickness of up to about 20 nm. Meanwhile, an improved DCV-DMC approach coupled with the corresponding potential map (PM-DCV-DMC) is further developed to speed up the computational efficiency of conventional DCV-DMC simulations. Our simulation results provide the molecular-level density and selectivity profiles along the permeation direction of both CH4 and CO2 molecules in the ZIF-8 membrane, indicating that the parts near membrane surfaces at both ends play a key role in determining the separation selectivity. All densities initially show a sharp increase in the individual maximum within the first outermost unit cell at the feed side and follow a long fluctuating decrease process. Accordingly, the corresponding selectivity profiles initially display a long fluctuating increase in the individual maximum and follow a sharp decrease near the membrane surface at the permeation side. Furthermore, the effects of feed composition, temperature, and pressure on the relevant separation selectivity are also discussed in detail, where the temperature has a greater influence on the separation selectivity than the feed composition and pressure. More importantly, the predicted separation selectivities from our PM-DCV-DMC simulations are well consistent with previous experimental results.

Effects of Seed Crystals on the Growth and Catalytic Performance of TS-1 Zeolite Membranes.

Dense and good catalytic performance TS-1 zeolite membranes were rapidly prepared on porous mullite support by secondary hydrothermal synthesis. The properties of seed crystals were very important for the preparation of high-catalytic performance TS-1 zeolite membranes. Influences of seed crystals (Ti/Si ratios, size, morphology, and zeolites concentration of the seed suspension) on the growth and catalytic property of TS-1 zeolite membranes were investigated in details. High Ti/Si ratio, medium-size, and morphology of the seed crystals were critical for preparing the high-performance TS-1 zeolite membrane. Compared with the bi-layer TS-1 zeolite membrane (inner and outer of the mullite tube), the mono-layer TS-1 zeolite membrane had a better catalytic performance for Isopropanol IPA oxidation with H2O2. When the Ti/Si ratio, size, and morphology of the TS-1 zeolites were 0.030, 300 nm, ellipsoid, and the zeolites concentration of the seed suspension was 5%, the IPA conversion, and flux through the TS-1 zeolite membrane were 98.23% and 2.58 kg·m-2·h-1, respectively.

Enhanced Visible-Light Photocatalytic Performance of SAPO-5-Based g-C3N4 Composite for Rhodamine B (RhB) Degradation.

Novel visible-light responded aluminosilicophosphate-5 (SAPO-5)/g-C3N4 composite has been easily constructed by thermal polymerization for the mixture of SAPO-5, NH4Cl, and dicyandiamide. The photocatalytic activity of SAPO-5/g-C3N4 is evaluated by degrading RhB (30 mg/L) under visible light illumination (λ > 420 nm). The effects of SAPO-5 incorporation proportion and initial RhB concentration on the photocatalytic performance have been discussed in detail. The optimized SAPO-5/g-C3N4 composite shows promising degradation efficiency which is 40.6% higher than that of pure g-C3N4. The degradation rate improves from 0.007 min-1 to 0.022 min-1, which is a comparable photocatalytic performance compared with other g-C3N4-based heterojunctions for dye degradation. The migration of photo-induced electrons from g-C3N4 to the Al site of SAPO-5 should promote the photo-induced electron-hole pairs separation rate of g-C3N4 efficiently. Furthermore, the redox reactions for RhB degradation occur on the photo-induced holes in the g-C3N4 and Al sites in SAPO-5, respectively. This achievement not only improves the photocatalytic activity of g-C3N4 efficiently, but also broadens the application of SAPOs in the photocatalytic field.

Transcatheter arterial embolization for postoperative arterial complications after pelvic or hip surgery.

PURPOSE: We aimed to study the technical and clinical outcome of urgent transcatheter arterial embolization (TAE) for postoperative arterial complications after pelvic or hip surgery, and to accumulate additional experience about the role of embolization for these injuries. METHODS: Patients who received TAE procedure for arterial complications after pelvic or hip surgery between September 1st, 2002 and December 1st, 2014 were screened on medical records and included in the analysis. Angiographic findings included active contrast agent extravasation, pseudoaneurysm formation, arteriovenous fistula, and other suspicious signs such as sighting of coarse margin or distortion of vessels. Embolic agents consisted of coils, gelatin sponge, and polyvinyl alcohol. Technical success was defined as complete occlusion of targeted artery through angiography, and clinical success as sustained resolution of symptoms. RESULTS: A total of 22 patients (15 males, 19-76 years old) were enrolled. Prior to TAE, 12 patients developed hemorrhagic shock and the remaining 10 patients had hemorrhage-related pain, hematoma, or anemia. Contrast agent extravasation occurred in 12 cases, pseudoaneurysm formation in 5 cases, and other suspicious signs in 5 cases. Injury occurred in the internal iliac artery stem in 6 cases, inferior gluteal artery in 6 cases and superior gluteal artery in 6 cases. Multiple vascular lesions appeared in 5 cases. After TAE, technical success occurred in 22 patients and clinical success in 21 patients (95.5%). A 36-year-old woman died of irreversible multiple organ failure; no other severe procedure-related complications were recorded. CONCLUSION: TAE is safe and effective for postoperative arterial complications after pelvic or hip surgery.

Single Gas Permeance Performance of High Silica SSZ-13 Zeolite Membranes.

Continuous and high silica SSZ-13 zeolite membranes were prepared on porous mullite supports from high SiO2/Al2O3 ratio or aluminum-free precursor synthesis gel. Single gas permeance (CO2 and CH4) of the high silica SSZ-13 zeolite membrane was decreased with the SiO2/Al2O3 ratio in the precursor synthesis gel, while the ideal CO2/CH4 selectivity of the membrane was gradually increased. Moreover, effects of synthesis conditions (such as H2O/SiO2 and RNOH/SiO2 ratios of precursor synthesis gel, crystallization time) on the single gas permeance performance of high silica SSZ-13 zeolite membranes were studied in detail. Medium H2O/SiO2 and RNOH/SiO2 ratios in the initial synthesis gel were crucial to prepare the good CO2 perm-selective SSZ-13 zeolite membrane. When the molar composition of precursor synthesis gel, crystallization temperature and time were 1.0 SiO2: 0.1 Na2O: 0.1 TMAdaOH: 80 H2O, 160 °C and 48 h, CO2 permeance and ideal CO2/CH4 selectivity of the SSZ-13 zeolite membrane were 0.98 × 10-7 mol/(m²·s·Pa) and 47 at 25 °C and 0.4 MPa. In addition, the SiO2/Al2O3 ratio of the corresponding SSZ-13 zeolite was 410 by X-ray fluorescence spectroscopy.

Unique orientations and rotational dynamics of a 1-butyl-3-methyl-imidazolium hexafluorophosphate ionic liquid at the gas-liquid interface: the effects of the hydrogen bond and hydrophobic interactions.

Here we report a series of molecular dynamics simulations for the orientations and rotational dynamics of the 1-butyl-3-methyl-imidazoliumhexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) at the gas-liquid interface. Compared to the bulk phase, the [BMIM]+ cations at the interface prefer to orientate themselves with their imidazolium rings perpendicular to the gas-IL interface plane and their butyl chains pointing toward the vacuum phase. Such a preferential orientation can be attributed to the combined effect of the hydrophobic interactions and the optimum loss of hydrogen bonds (HBs). More interestingly, our simulation results demonstrate that the butyl chains of cations exhibit a two-stage rotational behavior at the interface, where the butyl chains are always in the vacuum phase at the first stage and the second stage corresponds to the butyl chains migrating from the vacuum phase into the liquid phase. A further detailed analysis reveals that their rotational motions at the first stage are mainly determined by the weakened HB strength at the interface while those at the second stage are dominated by their hydrophobic interactions. Such a unique rotational behavior of the butyl chains is significantly different from those of the anions and the imidazolium rings of cations at the interface due to the lack of existence of hydrophobic interaction in the cases of the latter two. In addition, a new and simple time correlation function (TCF) was constructed here for the first time to quantitatively identify the relevant hydrophobic interaction of alkyl chains. Therefore, our simulation results provide a molecular-level understanding of the effects of HB and hydrophobic interactions on the unique properties of imidazolium-based ILs at the gas-liquid interface.