Enhanced Antibacterial Activity at Ag-Cu Nanojunctions: Unveiling the Mechanism with Simple Surfaces of CuNPs-on-Ag Films.

Deposition of CuNPs on silver film gives rise to the formation of active Ag-Cu interfaces leading to dramatic enhancements in antibacterial activity against Escherichia coli. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDAX) analyses reveal that CuNPs are covered in a thin Cu2O shell, while X-ray photoelectron spectroscopy measurements (XPS) reveal that the Ag film samples contain significant amounts of Ag2O. XPS analyses show that the deposition of CuNPs on Ag films leads to the formation of a photoactive Ag2O-Cu2O heterostructure. Following a Z-scheme mechanism, electrons from the conduction band of Ag2O recombine with photogenerated holes from the valence band of Cu2O. Consequently, electrons at Cu2O's conduction band render Cu reduced and cause reductive activation of surface oxygen species on Cu forming reactive oxygen species (ROS). Interaction between metallic Cu and ROS species leads to the formation of a Cu(OH)2 phase. Both ROS and Cu(OH)2 species have previously been reported to lead to enhanced antibacterial properties. Holes on Ag2O produce a highly oxidized AgO phase, a phase reported to exhibit excellent antibacterial properties. Quantitative analysis of Cu and Ag high-resolution X-ray photoelectron spectroscopy (HR-XPS) spectra directly reveals several-fold increases in these active phases in full agreement with the observed increase in antibacterial activities. This study provides insight and surface design parameters by elucidating the important roles of Ag and Cu's bifunctionality as active antibacterial materials.

Nanocrystalline BEA-CNT Composites with High Metal Dispersion Obtained via Inter-Zeolite Transformation for Antibacterial Application.

The rational design of interface materials containing carbon nanotubes (CNTs) and zeolites (zeolite-CNTs) is a promising perspective in chemical and biochemical communities because they exhibit several outstanding properties such as tunable hydrophobicity-hydrophilicity at interfaces. In this contribution, we report the fabrication of Ag-incorporated nanocrystalline BEA-carbon nanotube (CNT) composites via the one-pot inter-zeolite transformation of the micron-sized FAU-CNT composite in the presence of a Ag precursor. By varying the crystallization time, the inter-zeolite transformation mechanism was explored. Indeed, this process involves an amorphous intermediate of aluminosilicate species with a significant change of the crystal morphology in the presence of CNTs in the synthesis gel. Interestingly, the redispersion of metal particles was observed after the inter-zeolite transformation process, resulting in the high dispersion of metal nanoparticles over BEA nanocrystals. Notably, it was revealed that the Ag sites were also stabilized in the presence of CNT interfaces, leading to the availability of highly active Ag+ ions. To illustrate the beneficial aspect of designer materials, the synthesized Ag-incorporated BEA-CNT composites exhibited high antibacterial activity againstEscherichia coli due to the synergistic effect of the active Ag+ species and appropriate hydrophobic and hydrophilic properties of the hybrid material interfaces. This first example opens up perspectives of the rational design of zeolite-CNT interfaces with high metal dispersion via the inter-zeolite transformation approach for biomedical applications.

Nanoscale carbon dot-embedded metal-organic framework for turn-on fluorescence detection of water in organic solvents.

An easy-to-use, highly selective, and real-time organic solvent quality assessment is desirable to detect water contamination in organic solvents. Herein, a one-step procedure using ultrasound irradiation was used for encapsulating nanoscale carbon dots (CDs) into metal-organic framework-199 (HKUST-1) to form CDs@HKUST-1 composite. The CDs@HKUST-1 exhibited very weak fluorescence due to photo-induced electron transfer (PET) from the CDs to the Cu2+ centers, acting as a fluorescent sensor in its off-state. The designed material can detect and discriminate water from other organic solvents, driven by turn-on fluorescence. This highly sensitive sensing platform could be applied for the detection of water in ethanol, acetonitrile, and acetone with wide linear detection ranges of 0-70% v/v, 2-12% v/v, and 10-50% v/v and limits of detection of 0.70% v/v, 0.59% v/v, and 1.08% v/v, respectively. The detection mechanism is attributed to the interruption of the PET process due to the release of fluorescent CDs after treatment with water. A smartphone-based quantitative test was successfully developed to monitor the water content in organic solvents utilizing CDs@HKUST-1 and a phone color processing application, thus making it possible to develop an on-site, real time and easy-to-use sensor for water detection.

Multifunctional fluorescent Eu-MOF probe for tetracycline antibiotics and dihydrogen phosphate sensing and visualizing latent fingerprints.

The contamination of tetracycline antibiotics and dihydrogen phosphate (H2PO4 -) in food and the environment is one of the major concerns for human health. Herein, a water-stable carboxyl-functionalized europium metal-organic framework (Eu-MOF) was prepared and demonstrated, for the first time, as a dual-responsive fluorescent sensor of tetracycline antibiotics (oxytetracycline (OTC), tetracycline (TC), and doxycycline (DOX)) and H2PO4 - via fluorescent turn-on and turn-off, respectively. Eu-MOF presents a sensitive and selective detection of OTC with a rapid response time (1 min) and good anti-interference ability. The limits of detection (LODs) of 78 nm, 225 nm, and 201 nM were achieved for OTC, TC, and DOX, respectively. Coordination and hydrogen bonding led to energy and electron transfer from the TC to the MOF, contributing to the fluorescent enhancement mechanism. Moreover, Eu-MOF can effectively detect H2PO4 - via fluorescence turn-off with a LOD of 0.70 µM. The interactions between H2PO4 - and MOF interrupt the energy transfer from ligand to MOF, leading to fluorescence quenching. In addition, Eu-MOF was successfully applied to determine OTC and H2PO4 - in real samples, obtaining satisfactory recoveries and RSDs. More fascinating, Eu-MOF could be utilized to develop latent fingerprints on various surfaces, providing well-defined fluorescent fingerprint details in which the sweat pores can be seen with the naked eye.

Heterogeneous Enantioselective Catalysis with Chiral Encoded Mesoporous Pt-Ir Films Supported on Ni Foam.

The development of heterogeneous catalysts for asymmetric synthesis is one of the most challenging topics in chemistry, as it allows obtaining enantiomerically pure compounds. Recently, metal layers incorporating molecular chiral cavities, obtained by electroreduction of a metal source in the simultaneous presence of a non-ionic surfactant and asymmetric molecules, have been proposed for a wide range of applications, including enantioselective electroanalysis and electrosynthesis, as well as chiral separation. In contrast to this previous work, solely based on electrochemical phenomena, herein we designed and employed nanostructured chiral encoded Pt-Ir alloys, supported on high surface area nickel foams, as heterogeneous catalysts for the asymmetric hydrogenation of aromatic ketones. Fine-tuning the experimental conditions allows achieving very high enantioselectivity (>80%), combined with improved catalyst stability.

Nanoengineered chiral Pt-Ir alloys for high-performance enantioselective electrosynthesis.

The design of efficient chiral catalysts is of crucial importance since it allows generating enantiomerically pure compounds. Tremendous efforts have been made over the past decades regarding the development of materials with enantioselective properties for various potential applications ranging from sensing to catalysis and separation. Recently, chiral features have been generated in mesoporous metals. Although these monometallic matrices show interesting enantioselectivity, they suffer from rather low stability, constituting an important roadblock for applications. Here, a straightforward strategy to circumvent this limitation by using nanostructured platinum-iridium alloys is presented. These materials can be successfully encoded with chiral information by co-electrodeposition from Pt and Ir salts in the simultaneous presence of a chiral compound and a lyotropic liquid crystal as asymmetric template and mesoporogen, respectively. The alloys enable a remarkable discrimination between chiral compounds and greatly improved enantioselectivity when used for asymmetric electrosynthesis (>95 %ee), combined with high electrochemical stability.

A Ladder-like Dopant-free Hole-Transporting Polymer for Hysteresis-less High-Efficiency Perovskite Solar Cells with High Ambient Stability.

Perovskite solar cells (PSCs) have received high attention in the past few years due to their terrific photovoltaic performance and potentially low production cost. However, the use of hole transport materials (HTMs) with hygroscopic dopants, which cause the inevitable instability of device performance, has hampered commercialization. Herein, a dopant-free polymeric HTM with functional aromatic rings was used to optimize the HTM/perovskite interface and employed in a planar n-i-p configuration. Poly(1,4-(2,5-bis((2-butyloctyloxy)phenylene)-2,7-(5,5,10,10-tetrakis(4-hexylphenyl)-5,10-dihydro-s-indaceno[2,1-b:6,5-b']dithiophene)) (IDTB) co-polymer constructed with indaceno[1,2-b:5,6-b']dithiophene and bis(alkyloxy)benzene units adopts an S⋅⋅⋅O intramolecular bond linked ladder-like planar conjugated polymer backbone. Without any dopant, the hole mobility of IDTB is in the same order of magnitude as a doped 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Also, the hydrophobic nature of IDTB facilitated the long-term stability of the perovskite underneath. The unencapsulated PSC devices made of IDTB-based HTM achieved a power conversion efficiency of 19.38 % with a high moisture stability, retaining above 80 % of initial power conversion efficiency at 65 % relative humidity for more than 10 days. The superior passivation effect to perovskite surface made a hysteresis of 0.44 % was almost the least reported for regular planar undoped polymer HTM PSCs.

Tailoring hierarchical zeolite composites with two distinct frameworks for fine-tuning the product distribution in benzene alkylation with ethanol.

A hierarchical zeolite composite, MOR@ZSM-5, with two distinct frameworks has been successfully fabricated via the repeated crystallization of ZSM-5 nanocrystals on mordenite surfaces. To avoid their phase separation, the surface of mordenite was pretreated with tetra(n-butyl)ammonium hydroxide (TBAOH) to induce the formation of the ZSM-5 nuclei, and it was subsequently modified by the continuous growth of nanocrystalline ZSM-5 on the entire area of the mordenite surfaces. Interestingly, the fully overgrown MOR@ZSM-5 composite exhibits a remarkable improvement in the ethylbenzene selectivity (>60%) obtained from the alkylation of benzene with ethanol with respect to isolated zeolites and their physical mixture due to the enhanced external surface area and hierarchical porosity as well as the reasonable acidity provided by the fully dispersed ZSM-5 nanocrystals on the mordenite surfaces. Moreover, coke species deposited on the designed composites are likely located at the external surfaces and do not considerably deteriorate the catalytic performance, whereas they are deposited predominantly in the micropores over the incompletely overgrown MOR@ZSM-5 composite. The present study illustrates the advantages of the overgrown zeolite composites of two incompatible frameworks in tailoring the hierarchical porosity, adjusting the acidic properties, and eventually controlling the product selectivity in acid-catalyzed reactions such as the alkylation of benzene with ethanol.

Regulating Payload Release from Hybrid Nanocapsules with Dual Silica/Polycaprolactone Shells.

We describe a facile strategy to synthesize hybrid nanocapsules with an oil core for hindering interactions between payloads and silica shell. Polycaprolactone/silica nanocapsules are synthesized by an interfacial sol-gel process occurring simultaneously with internal phase separation of the polymer produced by a miniemulsion-solvent evaporation technique. The localization of the polycaprolactone in the nanocapsules is depending on the ratio between polymer and silica. Formation of hybrid nanocapsules is found to significantly hinder interactions of drugs such as ibuprofen and carbamazepine with the silica surface.

Highly selective circular dichroism sensor based on d-penicillamine/cysteamine­cadmium sulfide quantum dots for copper (II) ion detection.

A highly selective circular dichroism sensor based on cysteamine-capped cadmium sulfide quantum dots (Cys-CdS QDs) was successfully developed for the determination of Cu2+. Basically, the Cys-CdS QDs are not active in circular dichroism spectroscopy. However, the circular dichroism probe (DPA@Cys-CdS QDs) can be simply generated in situ by mixing achiral Cys-CdS QDs with D-penicillamine. The detection principle was based on measuring the circular dichroism signal change upon the addition of Cu2+. The strong CD signal of the DPA@Cys-CdS QDs dramatically decreased in the presence of Cu2+, while other cations did not result in any spectral changes. In addition, the degree of the CD signal decrease was linearly proportional to the concentration of Cu2+ in the range of 0.50-2.25 µM (r2 = 0.9919) with a detection limit of 0.34 µM. Furthermore, the proposed sensor was applied to detect Cu2+ in drinking water samples with %recovery values of 102-114% and %RSD less than 6%.

Hierarchical FAU/ZIF-8 Hybrid Materials as Highly Efficient Acid-Base Catalysts for Aldol Condensation.

The composite of hierarchical faujasite nanosheets and zeolitic imidazolate framework-8 (Hie-FAU-ZIF-8) has been successfully prepared via a stepwise deposition of ZIF-8 on modified zeolite surfaces. Compared to the direct deposition of metal organic frameworks (MOFs) on zeolite surfaces, ZIF-8 nanospheres were selectively attached to the external surfaces of the MOF ligand-grafted FAU crystals because of the enhancing interaction between the zeolite and MOF in the composite. In addition, the degree of surface functionalization can be greatly enhanced because of the presence of hierarchical structures. This behavior leads to an increase in the deposited MOF content, improving the hydrophobic properties of the zeolite surfaces. Interestingly, the designed hierarchical composite exhibits outstanding catalytic properties as an acid-base catalyst for the aldol condensation of 5-hydroxymethylfurfural with acetone. Compared to the isolated FAU and ZIF-8, a high yield of the product, 4-[5-(hydroxymethyl)furan-2-yl]but-3-en-2-one (67%), can be observed in the composite because of the synergistic effect between the Na+-stabilized zeolite framework and the imidazolate linkers bearing basic nitrogen functions. This opens up interesting perspectives for the development of new organic and inorganic hybrid materials as heterogeneous acid-base catalysts.

Charge storage mechanisms of manganese oxide nanosheets and N-doped reduced graphene oxide aerogel for high-performance asymmetric supercapacitors.

Although manganese oxide- and graphene-based supercapacitors have been widely studied, their charge storage mechanisms are not yet fully investigated. In this work, we have studied the charge storage mechanisms of K-birnassite MnO2 nanosheets and N-doped reduced graphene oxide aerogel (N-rGOae) using an in situ X-ray absorption spectroscopy (XAS) and an electrochemical quart crystal microbalance (EQCM). The oxidation number of Mn at the MnO2 electrode is +3.01 at 0 V vs. SCE for the charging process and gets oxidized to +3.12 at +0.8 V vs. SCE and then reduced back to +3.01 at 0 V vs. SCE for the discharging process. The mass change of solvated ions, inserted to the layers of MnO2 during the charging process is 7.4 µg cm-2. Whilst, the mass change of the solvated ions at the N-rGOae electrode is 8.4 µg cm-2. An asymmetric supercapacitor of MnO2//N-rGOae (CR2016) provides a maximum specific capacitance of ca. 467 F g-1 at 1 A g-1, a maximum specific power of 39 kW kg-1 and a specific energy of 40 Wh kg-1 with a wide working potential of 1.6 V and 93.2% capacity retention after 7,500 cycles. The MnO2//N-rGOae supercapacitor may be practically used in high power and energy applications.

Template synthesis of water-dispersible and magnetically responsive carbon nano test tubes.

Water-dispersible and magneto-responsive carbon nano test tubes with a controlled length (1.3 microm) and diameter (35 nm) were synthesized by using the nanochannels of anodic aluminium oxide as a template.