Mesoporous-Structure MOF-14-Based QCM p-Xylene Gas Sensor.

In this work, a facile synthesis method was adopted to synthesize MOF-14 with mesoporous structure. The physical properties of the samples were characterized by PXRD, FESEM, TEM and FT-IR spectrometry. By coating the mesoporous-structure MOF-14 on the surface of a quartz crystal microbalance (QCM), the fabricated gravimetric sensor exhibits high sensitivity to p-toluene vapor even at trace levels. Additionally, the limit of detection (LOD) of the sensor obtained experimentally is lower than 100 ppb, and the theoretical detection limit is 57 ppb. Furthermore, good gas selectivity and fast response (15 s) and recovery (20 s) abilities are also illustrated along with high sensitivity. These sensing data indicate the excellent performance of the fabricated mesoporous-structure MOF-14-based p-xylene QCM sensor. On the basis of temperature-varying experiments, an adsorption enthalpy of -59.88 kJ/mol was obtained, implying the existence of moderate and reversible chemisorption between MOF-14 and p-xylene molecules. This is the crucial factor that endows MOF-14 with exceptional p-xylene-sensing abilities. This work has proved that MOF materials such as MOF-14 are promising in gravimetric-type gas-sensing applications and worthy of future study.

New Application of Quartz Crystal Microbalance: A Minimalist Strategy to Extract Adsorption Enthalpy.

The capture and separation of CO2 is an important means to solve the problem of global warming. MOFs (metal-organic frameworks) are considered ideal candidates for capturing CO2, where the adsorption enthalpy is a crucial indicator for the screening of materials. For this purpose, we propose a new minimalist solution using QCM (quartz crystal microbalance) to extract the CO2 adsorption enthalpy on MOFs. Three kinds of MOFs with different properties, sizes and morphologies were employed to study the adsorption enthalpy of CO2 using a QCM platform and a commercial gas sorption analyzer. A Gaussian simulation calculation and previously data reported were used for comparison. It was found that the measuring errors were between 5.4% and 6.8%, proving the reliability and versatility of our new method. This low-cost, easy-to-use, and high-accuracy method will provide a rapid screening solution for CO2 adsorption materials, and it has potential in the evaluation of the adsorption of other gases.

Facet Engineering of Nanoceria for Enzyme-Mimetic Catalysis.

Nanomaterials with natural enzyme-mimicking characteristics have aroused extensive attention in various fields owing to their economical price, ease of large-scale production, and environmental resistance. Previous investigations have demonstrated that composition, size, shape, and surface modification play important roles in the enzymelike activity of nanomaterials; however, a fundamental understanding of the crystal facet effect, which determines surface energy or surface reactivity, has rarely been reported. Herein, fluorite cubic CeO2 nanocrystals with controllably exposed {111}, {100}, or {110} facets are fabricated as proof-of-concept candidates to study the facet effect on the peroxidase-mimetic activity. Both experiments and theoretical results show that {110}-dominated CeO2 nanorods (CeO2 NR) possess the highest peroxidase-mimetic activity due to the richest defects on their surfaces, which are beneficial to capture metal atoms to further enrich their artificial enzymatic functionality for cascade catalysis. For instance, the introduction of atomically dispersed Au on CeO2 NR surfaces not only enhances the peroxidase activity but also endows the obtained catalyst with glucose oxidase (GOx)-mimicking activity, which realizes enzyme-free cascade reactions for glucose colorimetric detection. This work not only provides an understanding for crystal facet engineering of nanomaterials to enhance the catalytic activity but also opens up a new way for the design of biomimetic nanomaterials with multiple functions.

Single Iron Site Nanozyme for Ultrasensitive Glucose Detection.

Nanomaterials with enzyme-mimicking characteristics have engaged great awareness in various fields owing to their comparative low cost, high stability, and large-scale preparation. However, the wide application of nanozymes is seriously restricted by the relatively low catalytic activity and poor specificity, primarily because of the inhomogeneous catalytic sites and unclear catalytic mechanisms. Herein, a support-sacrificed strategy is demonstrated to prepare a single iron site nanozyme (Fe SSN) dispersed on the porous N-doped carbon. With well-defined coordination structure and high density of active sites, the Fe SSN performs prominent peroxidase-like activity by efficiently activating H2 O2 into hydroxyl radical (•OH) species. Furthermore, the Fe SSN is applied in colorimetric detection of glucose through a multienzyme biocatalytic cascade platform. Moreover, a low-cost integrated agarose-based hydrogel colorimetric biosensor is designed and successfully achieves the visualization evaluation and quantitative detection of glucose. This work expands the application of single-site catalysts in the fields of nanozyme-based biosensors and personal biomedical diagnosis.

Recover the activity of sintered supported catalysts by nitrogen-doped carbon atomization.

The sintering of supported metal nanoparticles is a major route to the deactivation of industrial heterogeneous catalysts, which largely increase the cost and decrease the productivity. Here, we discover that supported palladium/gold/platinum nanoparticles distributed at the interface of oxide supports and nitrogen-doped carbon shells would undergo an unexpected nitrogen-doped carbon atomization process against the sintering at high temperatures, during which the nanoparticles can be transformed into more active atomic species. The in situ transmission electron microscopy images reveal the abundant nitrogen defects in carbon shells provide atomic diffusion sites for the mobile atomistic palladium species detached from the palladium nanoparticles. More important, the catalytic activity of sintered and deactivated palladium catalyst can be recovered by this unique N-doped carbon atomization process. Our findings open up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.

Ultrafine Tungsten Oxide Nanowires: Synthesis and Highly Selective Acetone Sensing and Mechanism Analysis.

By using WCl6 as a precursor and absolute ethanol as a solvent, ultrafine W18O49 nanowires (UFNWs) were synthesized by a one-pot solution-phase method and used as gas sensing materials. Their crystal structure, morphology, and specific surface area can be regulated by controlling precisely the content of the WCl6 precursor in the solution. It has been found that, when the content of the precursor is 4 mg/mL, the formed products are UFNWs with a diameter of about 0.8 nm, only one crystal plane [010] is exposed, and the specific surface area is 194.72 m2/g. After the gas sensing test, we found that they have excellent selectivity to acetone. The response of 50 ppm acetone reaches 48.6, the response and recovery times are 11 and 13 s, respectively. In order to evaluate the interaction between W18O49 surfaces and different volatile organic compound (VOC) molecules, we simulated and calculated the adsorption energy (EAds) among different W18O49 surfaces and different VOCs by DFT. The calculated results are in agreement with the experimental results, further confirming the ultrahigh selectivity of W18O49 UFNWs to acetone. The above results demonstrate that the high selectivity of W18O49 UFNWs to acetone is due to the exposure of its single crystal plane [010]. This work has practical significance for better detection of acetone.

Structural evolution induced by Au atom diffusion in Ag2S.

Atom diffusion processes govern the structure and composition of core-shell nanomaterial, which play a crucial role in determining their properties. By using aberration-corrected high-resolution transmission electron microscopy and X-ray absorption near-edge structure spectroscopy in combination with in situ X-ray diffraction, we confirm that single-atom diffusion of Au to Ag2S occurs, and that the transition from the Au@Ag2S core-shell nanostructure to AuAgS-AuAgx or Ag3AuS2-AuAgx heterostructures was observed. Moreover, the phase of the ternary sulfide induced by Au single-atom diffusion in Ag2S is determined by the ratio of Au and Ag, thus exhibiting a significant difference in the photocatalytic activity performance.

2D MOF induced accessible and exclusive Co single sites for an efficient O-silylation of alcohols with silanes.

Co single atoms anchored on ultrathin two-dimensional nitrogen-doped carbon (Co SAs/2D N-C) were in situ derived from 2D metal-organic frameworks (MOFs). These ultrathin nanosheets functionalized by the isolated Co atoms possess a high density of active sites and accessible surfaces, exhibiting an exceptional catalytic performance in the oxidation of silanes.

Thermal Emitting Strategy to Synthesize Atomically Dispersed Pt Metal Sites from Bulk Pt Metal.

Developing a facile route to access active and well-defined single atom sites catalysts has been a major area of focus for single atoms catalysts (SACs). Herein, we demonstrate a simple approach to generate atomically dispersed platinum via a thermal emitting method using bulk Pt metal as a precursor, significantly simplifying synthesis routes and minimizing synthesis costs. The ammonia produced by pyrolysis of Dicyandiamide can coordinate with platinum atoms by strong coordination effect. Then, the volatile Pt(NH3) x can be anchored onto the surface of defective graphene. The as-prepared Pt SAs/DG exhibits high activity for the electrochemical hydrogen evolution reaction and selective oxidation of various organosilanes. This viable thermal emitting strategy can also be applied to other single metal atoms, for example, gold and palladium. Our findings provide an enabling and versatile platform for facile accessing SACs toward many industrial important reactions.

Unraveling the enzyme-like activity of heterogeneous single atom catalyst.

Herein, we report a heterogeneous single iron atom catalyst exhibiting excellent peroxidase, oxidase and catalase enzyme-like activities (defined as single atom enzymes, SAEs), exceeding those of Fe3O4 nanozymes by a factor of 40. Our findings open up a new family of artificial materials that mimic natural enzymes.

Highly sensitive ethanol gas sensor based on ultrathin nanosheets assembled Bi2WO6 with composite phase.

Bismuth tungstate (Bi2WO6) has many intriguing properties and has been the focus of studies in a variety of fields, especially photocatalysis. However, its application in gas-sensing has been seldom reported. Here, we successfully synthesized assembled hierarchical Bi2WO6 which consists of ultrathin nanosheets with crystalline-amorphous composite phase by a one-step hydrothermal method. X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques were employed to characterize its composition, morphology, and microstructure. By taking advantage of its unique microstructure, phase composition, and large surface area, we show that the resulting Bi2WO6 is capable of detecting ethanol gas with quick response (7 s) and recovery dynamic (14 s), extremely high sensitivity (Ra/Rg = 60.8@50 ppm ethanol) and selectivity. Additionally, it has excellent reproducibility and long-term stability (more than 50 d). The Bi2WO6 outperform the existing Bi2WO6-based and most of the other state-of-the-art sensing platforms. We not only provided one new member to the field of gas sensor, but also offered several strategies to reconstruct nanomaterials.

Pt9 Ni Wavelike Nanowires with High Activity for Oxygen Reduction Reactions.

Platinum (Pt)-based nanostructures are the most efficient catalysts for the oxygen reduction reaction (ORR) in acid media. Here, Pt9 Ni wavelike nanowires (W-NWs) have been synthesized by etching Pt3 Ni@PtNi2 core-shell nanowires with 2,5-dihydroxyterephthalic acid for 24 hours. Compared to the commercial Pt/C catalyst, the free-standing Pt9 Ni W-NWs show improvements of up to 9.3 times for mass activity and 12.6 times for specific activity, respectively.

Ultrathin Palladium Nanomesh for Electrocatalysis.

An ordered mesh of palladium with a thickness of about 3 nm was synthesized by a solution-based oxidative etching. The ultrathin palladium nanomeshes have an interconnected two-dimensional network of densely arrayed, ultrathin quasi-nanoribbons that form ordered open holes. The unique mesoporous structure and high specific surface area make these ultrathin Pd nanomeshes display superior catalytic performance for ethanol electrooxidation (mass activity of 5.40 Am g-1 and specific activity of 7.09 mA cm-2 at 0.8 V vs. RHE). Furthermore, the regular mesh structure can be applied to support other noble metals, such as platinum, which exhibits extremely high hydrogen evolution reaction (HER) activity and durability.

Atomically dispersed Au1 catalyst towards efficient electrochemical synthesis of ammonia.

Tremendous efforts have been devoted to explore energy-efficient strategies of ammonia synthesis to replace Haber-Bosch process which accounts for 1.4% of the annual energy consumption. In this study, atomically dispersed Au1 catalyst is synthesized and applied in electrochemical synthesis of ammonia under ambient conditions. A high NH4+ Faradaic efficiency of 11.1% achieved by our Au1 catalyst surpasses most of reported catalysts under comparable conditions. Benefiting from efficient atom utilization, an NH4+ yield rate of 1,305 µg h-1 mgAu-1 has been reached, which is roughly 22.5 times as high as that by supported Au nanoparticles. We also demonstrate that by employing our Au1 catalyst, NH4+ can be electrochemically produced directly from N2 and H2 with an energy utilization rate of 4.02 mmol kJ-1. Our study provides a possibility of replacing the Haber-Bosch process with environmentally benign and energy-efficient electrochemical strategies.