Revealing the evolution of local structures in the formation process of alkaline earth metal cation-containing zeolites from glasses.

Alkaline earth metal cations are ubiquitously present in natural zeolites but less exploited in synthetic zeolites due to their low solubility in water, and hence it remains elusive how they contribute to zeolite formation. Herein, harmotome, a PHI-type zeolite with Ba2+, is readily synthesized from a Ba-containing aluminosilicate glass. This glass-to-zeolite transformation process, in particular the structure-regulating role of Ba2+, is investigated by anomalous X-ray scattering and high-energy X-ray total scattering techniques. The results demonstrate that the steady Ba2+-aluminosilicate interactions not only help prevent the precipitation of barium species under alkaline synthetic conditions, but also dictate the local structures with distinct interatomic distances between the Ba2+ and the surrounding aluminosilicate species throughout the transformation process, which lead to the successful formation of harmotome without detectable impurities. This study highlights the usefulness of the comprehensive X-ray scattering techniques in revealing the formation scheme of the zeolites containing specific metal species. In addition, a promising alternative approach to design and synthesize zeolites with unique compositions and topologies by using well-crafted glasses with suitable metal cation dopants is demonstrated.

Tracking Sub-Nano-Scale Structural Evolution in Zeolite Synthesis by In Situ High-Energy X-ray Total Scattering Measurement with Pair Distribution Function Analysis.

The crystallization mechanism of zeolites remains unclarified to date because of lack of effective techniques in characterizing the local structures of amorphous precursors under synthetic conditions. Herein, in situ high-energy X-ray total scattering measurement with pair distribution function analysis is performed throughout the hydrothermal synthesis of SSZ-13 zeolite to investigate the amorphous-to-crystalline transformation at the sub-nano level in real time. Ordered four-membered rings (4Rs) are dominantly formed during the induction period, prior to the significant increase in the number of symmetric six- and eight-membered rings (6Rs and 8Rs) in the crystal growth stage. These preformed ordered 4Rs contribute to the formation of d6r and cha composite building units containing 6Rs and 8Rs with the assistance of the organic structure-directing agent, leading to the construction of embryonic zeolite crystallites, which facilitate the crystal growth through a particle attachment pathway. This work enriches the toolbox for better understanding the crystallization pathway of zeolites.

Comparison of gastrojejunostomy to endoscopic stenting for gastric outlet obstruction: An updated Systematic Review and Meta-analysis.

BACKGROUND: This study aimed to determine the optimal intervention modality for malignant GOO by comparing clinical outcomes after Gastrojejunostomy and endoscopic stenting. METHODS: Two authors independently searched Web of Science, PubMed, Embase, and the Cochrane Library for articles before February 2021 to compare the clinical outcomes of GOO patients undergoing GJ or ES. RESULTS: This meta-analysis included 31 articles with 2444 GOO patients. Although the GJ group outperformed the ES group in technical success (OR,3.79; P = 0.003), clinical success was not significantly different between the two groups (OR,1.25; P = 0.50). The GJ group had a longer hospitalization, lower re-obstruction and lower reintervention. Moreover, GJ had a better survival than ES in the gastric cancer group (HR, 0.33; P = 0.009). However, no significant statistical difference was observed in the pancreatic cancer group (HR, 0.55; P = 0.159). CONCLUSIONS: Both GJ and ES are safe and effective intervention modalities for malignant GOO. GJ had significantly improved survival in gastric cancer patients with GOO, while no significant difference was observed between the two groups in pancreatic cancer patients with GOO.

Reaction Kinetics Regulated Formation of Short-Range Order in an Amorphous Matrix during Zeolite Crystallization.

The crystallization of zeolites, a disorder-to-order transformation of aluminosilicates, has not been thoroughly understood because the nucleation events in the amorphous matrix are difficult to recognize from the diverse structural changes, especially for the dense hydrogel systems. Therefore, relationships between the synthesis conditions, the generated amorphous species, and the crystallization behavior of zeolites remain unclear. Herein, by comparatively investigating the structural evolution of the aluminosilicate matrix in a dense hydrogel system when different Si reactants (fumed silica and silicate solution) are employed, we demonstrate that the reactivity of the reactants and the kinetics of the condensation reaction is critical to the formation of short-range order in an amorphous matrix, which greatly influences the nucleation frequency of zeolites. It was revealed that an amorphous solid containing plentiful Al-rich four-membered rings and Si-rich six-membered rings could be produced when fumed silica gradually reacted with sodium aluminate solution at 80 °C. It is considered that the interaction between these rings promotes the construction of the essential building units of zeolite X (FAU). In contrast, a complex aluminosilicate matrix was formed immediately when sodium silicate solution was mixed with sodium aluminate solution due to the intense condensation reaction. Furthermore, this complex matrix became more stable when the reactant mixture was hydrothermally treated at 80 °C, which significantly impedes the crystallization process. Aging the reactant mixture at ambient temperature before heating, instead, facilitated the formation of short-range order in the amorphous matrix, which increases the nucleation frequency of zeolites.

FRET based integrated pyrene-AgNPs system for detection of Hg (II) and pyrene dimer: Applications to environmental analysis.

The integrated system of pyrene and cetyltrimethyl ammonium bromide (CTAB) capped silver nanoparticles (AgNPs) with a distance (r) of 2.78nm has been developed for the detection of Hg (II) and pyrene dimer. The interaction between pyrene and AgNPs results in the fluorescence quenching of pyrene due to the energy transfer, whose mechanism can be attributed to the Forster Resonance Energy Transfer (FRET) supported by experimental observation and theoretical calculations. The developed probe shows a highly selective and sensitive response towards Hg (II) probably due to the amalgam formation, which results in the fluorescence recovery (90%) of pyrene and color change of solution from yellowish brown to colorless. The addition of Hg (II) may increase the distance between pyrene and AgNPs undergoes the 'FRET OFF' process. This system gives a selective response towards Hg (II) over other competing metal ions. Under the optimal condition, the system offers good linearity between 0.1 and 0.6µgmL-1 with a detection limit of 62ngmL-1. In addition, the system also provides an effective platform for detection of pyrene in its dimer form even at very low concentrations (10ngmL-1) on the surface of AgNPs. Therefore, it could be used as effective alternatives for the detection of Hg (II) as well as pyrene simultaneously.

Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation.

Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol-1). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

Monolithic cobalt-doped carbon aerogel for efficient catalytic activation of peroxymonosulfate in water.

As an emerging carbonaceous material, carbon aerogels (CAs) display a great potential in environmental cleanup. In this study, a macroscopic three-dimensional monolithic cobalt-doped carbon aerogel was developed by co-condensation of graphene oxide sheets and resorcinol-formaldehyde resin in the presence of cobalt ions, followed by lyophilization, carbonization and thermal treatment in air. Cobalt ions were introduced as a polymerization catalyst to bridge the organogel framework, and finally cobalt species were retained as both metallic cobalt and Co3O4, wrapped by graphitized carbon layers. The material obtained after a thermal treatment in air (CoCA-A) possesses larger BET specific surface area and pore volume, better hydrophilicity and lower leaching of cobalt ions than that without the post-treatment (CoCA). Despite of a lower loading of cobalt content and a larger mass transfer resistance than traditional powder catalysts, CoCA-A can efficiently eliminate organic contaminants by activation of peroxymonosulfate with a low activation energy. CoCA-A can float beneath the surface of aqueous solution and can be taken out completely without any changes in morphology. The monolith is promising to be developed into an alternative water purification technology due to the easily separable feature.

Turn-on fluorometric and colorimetric probe for hydrogen peroxide based on the in-situ formation of silver ions from a composite made from N-doped carbon quantum dots and silver nanoparticles.

The authors describe a fluorometric and colorimetric nanoprobe for H2O2. The detection scheme is based on the in-situ formation of silver(I) ions from a composite consisting of nitrogen-doped carbon quantum dots (N-CQDs) and silver nanoparticles (AgNPs). A drastic change occurs both in fluorescence and color of the solution of the N-CQD/AgNPs composite. The fluorescence of composite (with excitation/emission peaking at 320/384 nm) is enhanced on increasing the concentration of H2O2 due to the oxidation of silver metal in the N-CQD/AgNPs to form Ag(I) ions. The latter undergo strong coordination with the nitrogen atoms of the N-CQDs. In-situ formation of Ag(I) ions further results in a change in color of the solution from pale yellow (with a peak at 408 nm) to colorless. Under optimized conditions, the probe gives a fluorometric and colorimetric response in the 10 to 50 µM H2O2 concentration range with a 4.7 µM limit of detection. The probe is highly selective over several potentially interfering ions and agents. It was successfully applied to the determination of H2O2 in spiked samples without prior treatment. Graphical abstract Graphical presentation for specific detection of H2O2 based on the in-situ formation of Ag(I) ions from a composite consisting of silver nanoparticles and nitrogen-doped carbon quantum dots.

Magnetically separable core-shell structural γ-Fe2O3@Cu/Al-MCM-41 nanocomposite and its performance in heterogeneous Fenton catalysis.

To target the low catalytic activity and the inconvenient separation of copper loading nanocatalysts in heterogeneous Fenton-like reaction, a core-shell structural magnetically separable catalyst, with γ-Fe2O3 nanoparticles as the core layer and the copper and aluminum containing MCM-41 as the shell layer, has been fabricated. The role of aluminum has been discussed by comparing the copper containing mesoporous silica with various Cu contents. Their physiochemical properties have been characterized by XRD, UV-vis, FT-IR, TEM, nitrogen physisorption and magnetite susceptibility measurements. Double content Cu incorporation results in an improved catalytic activity for phenol degradation at the given condition (40°C, initial pH=4), but leads to a declined BET surface area and less ordered mesophase structure. Aluminum incorporation helps to retain the high BET surface area (785.2m(2)/g) and the regular hexagonal mesoporous structure of MCM-41, which make the catalyst possess a lower copper content and even a higher catalytic activity than that with the double copper content in the absence of aluminum. The catalysts can be facilely separated by an external magnetic field for recycle usage.