Preparation of MOF-derived ZnO/Co3O4 nanocages and their sensing performance toward H2S.

We report a type of micro-electro-mechanical system (MEMS) H2S gas sensors with excellent sensing performance at the ppb level (lowest detection limit is 5 ppb). The sensors were fabricated with ZnO/Co3O4 sensing materials derived from Zn/Co-MOFs by annealing at a suitable temperature of 500 °C. ZnO/Co3O4-500 exhibits the highest response when exposed to 10 ppb H2S gas at 120 °C, and the response/recovery times are 10 s/21 s. Moreover, it exhibits outstanding selectivity, long-term stability (retained 95% response after 45 days), and moisture resistance (only a minor fluctuation of 2% even at 90% RH). This can be ascribed to the fact that ZnO/Co3O4-500 has regular morphology, abundant oxygen vacancies (52.8%) and high specific surface area (96.5 m2 g-1). This work provides not only a high performance H2S MEMS gas sensor but also a systematic study of the effect of the annealing temperature on the sensing performance of ZnO/Co3O4 sensing materials derived from bimetal organic frameworks.

Si doped Fe-N/C catalyst for oxygen reduction reaction directed by ordered mesoporous silica nanospheres template strategy.

Template-assisted synthesis strategy is an effective approach to prepare high performance oxygen reduction catalyst. The Fe-N/C catalysts were prepared via high temperature pyrolysis of the composites containing Fe-loaded mesoporous silica nanospheres and polypyrrole wrapped on it (Fe/mSiO2@PPY). Fe loading ways combined with polymerization means of pyrrole greatly influence the structure and morphology of the final catalysts. By controlling the type of templates (mesoporous, microporous and nonporous templates) and synthesis conditions, Si doped Fe-N/C (Si-Fe-N/C) catalyst with hollow shell structures was obtained. The multiple heteroatom co-doping of Si, Fe and N in carbon framework are confirmed by EDS, XPS and Raman. The co-doping of Fe and N increases the oxygen reduction reaction (ORR) catalytic activities, while the doping of Si facilitates graphitization degree of carbon framework. The electrochemical performance of the Si-Fe-N/C catalyst was evaluated by the linear sweep voltammograms (LSV). It exhibits higher current density (5.4 mA cm-2) and more positive half-wave potential (0.83 V vs. RHE), which is comparable to commercial Pt/C catalyst. Stability tests show that the Si-Fe-N/C catalyst possesses excellent durability and more than 90% of its original activity can be retained after 50,000 s running at 0.68 V (vs. RHE).

The growth behavior of brain-like SnO2 microspheres under a solvothermal reaction with tetrahydrofuran as a solvent and their gas sensitivity.

In this paper, the growth behavior of brain-like SnO2 microspheres synthesized by a tetrahydrofuran (THF) solvothermal method was studied. Unlike water or ethanol as the solvent, THF is a medium polar and aprotic solvent. Compared with other common polar solvents, the THF has no strong irregular effects on the growth process of SnO2. In addition, the viscosity of THF also helps the SnO2 to form a regular microstructure. The growth behavior of the brain-like SnO2 microspheres is controlled by changing the synthesis temperature of the reaction. The SEM and TEM results reveal that the SnO2 forms particles first (125 °C/3 h), and then these nanoparticles connect to each other forming nanowires and microspheres (diameter ≈ 1-2 µm) at 135 °C for 3 h; finally the microspheres further aggregate to form double or multi-sphere structures at 180 °C for 3 h. In this paper, the brain-like SnO2 microspheres obtained at 125 °C for 3 h were selected as sensitive materials to test their gas sensing performance at different operating temperature (50 °C and 350 °C). The H2S was tested at 50 °C which is the lowest operating temperature for the sensor. The combustible gas (H2/CH4/CO) was measured at 350 °C which is the highest temperature for the sensor. They all have extremely high sensitivity, but only H2S has excellent selectivity.

Monodispersed gold nanoparticles entrapped in ordered mesoporous carbon/silica nanocomposites as xanthine oxidase mimic for electrochemical sensing of xanthine.

Monodispersed Au nanoparticles in ordered mesoporous carbon/silica (Au/OMCS) nanocomposites were prepared by the solvent evaporation induced self-assembly. Au/OMCS nanocomposites were characterized through XRD, BET, and TEM. The obtained nanocomposites exhibit uniform mesopores with the size of 18 ± 2 nm. And ultrafine Au nanoparticles with the size of 3~7 nm are well dispersed in the cavities. An ultrasensitive nanoenzyme sensor was fabricated based on a Au/OMCS-modified electrode. The Au/OMCS-modified electrode displays high xanthine oxidase-like catalytic activity evaluated through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The DPV response currents are linearly dependent on concentrations of xanthine (Xa) in the range 0.10-20 µM, along with a high sensitivity of 6.84 µA µM-1 cm-2 and very low detection limit of 0.006 µM (S/N = 3) under the optimal working potential of 0.64 V vs. SCE. Interference experiments show that the nanoenzyme sensor has no obvious responses to most potentially interfering species at a potential of 0.64 V. The fabricated sensor has been applied to the determination of Xa in spiked urine samples with recoveries ranging from 98.26 to 101.4%. Graphical abstract.

Rational Design of Yolk-Shell CuO/Silicalite-1@mSiO2 Composites for a High-Performance Nonenzymatic Glucose Biosensor.

In this study, an interface coassembly strategy is employed to rationally synthesize a yolk-shell CuO/silicalite-1@void@mSiO2 composite consisting of silicalite-1 supported CuO nanoparticles confined in the hollow space of mesoporous silica, and the obtained composite materials were used as a novel nonenzymatic biosensor for highly sensitive and selective detecting glucose with excellent anti-interference ability. The synthesis of CuO/silicalite-1@mSiO2 includes four steps: coating silicalite-1 particles with resorcinol-formaldehyde polymer (RF), immobilization of copper species, interface deposition of a mesoporous silica layer, and final calcination in air to decompose RF and form CuO nanoparticles. The unique hierarchical porous structure with mesopores and micropores is beneficial to selectively enrich glucose for fast oxidation into gluconic acid. Besides, the mesopores in the silica shell can effectively inhibit the large interfering substances or biomacromolecules diffusing into the void as well as the loss of CuO nanoparticles. The hollow chamber inside serves as a nanoreactor for glucose oxidation catalyzed by the active CuO nanoparticles, which are spatially accessible for glucose molecules. The nonenzymatic glucose biosensors based on CuO/silicalite-1@mSiO2 materials show excellent electrocatalytic sensing performance with a wide linear range (5-500 µM), high sensitivity (5.5 µA·mM-1·cm-2), low detection limit (0.17 µM), and high selectivity against interfering species. Furthermore, the unique sensors even display a good capability in the determination of glucose in real blood serum samples.

Direct electrodeposition of cable-like CuO@Cu nanowires array for non-enzymatic sensing.

Vertically aligned cable-like CuO@Cu nanowires array was synthesized using a template-directed electrodeposition strategy. The morphology, crystal structure, and surface property of nanowires array were investigated by SEM, HRTEM, XRD, and XPS, respectively. It is found that the free standing namowires are highly dense, and possess about 20 µm in length and 200 nm in diameter. The bulk Cu nanowires are assembled by a number of single crystalline Cu nanoparticles and surface is wrapped by a thin layer of amorphous CuO with size of 2.5 nm. Electrocatalytic activity of the nanowires array towards glucose oxidation was investigated by cyclic voltammetry and amperometry in alkaline media. The nanowires array with 3×3 mm(2) was then used to fabricate a non-enzymatic glucose sensor. The sensor exhibits a wide concentration range of 1×10(-6)M-1×10(-2) M for glucose, with an ultra-high sensitivity of 1250.8 µA mM(-1) cm(-2) and excellent anti-interference ability. The good sensing performances could be attributed to the integration of the superior electrocatalysis of high density of Cu nanowires array and the outer shell of negatively charged CuO against interferences.

CuO nanoparticles incorporated in hierarchical MFI zeolite as highly active electrocatalyst for non-enzymatic glucose sensing.

A hierarchical MFI zeolite, with typical micro/meso bimodal pore structures, was prepared by desilication method. CuO nanoparticles (NPs) were incorporated into the hierarchical MFI zeolite by impregnation method. CuO/hierarchical zeolite composites were characterized by X-ray diffraction, transmission electron microscopy and nitrogen sorption. It is shown that the CuO nanoparticles are mostly dispersed in the mesopores with remaining of the crystallinity and morphology of the host zeolite. CuO nanoparticles located in hierarchical zeolite exhibit the excellent electrocatalytic performances to oxidation of glucose in alkaline media. The electrocatalytic activity enhances with increasing the loading content of CuO from 5% to 15%. The composites were fabricated for nonenzyme glucose sensing. Under the optimal conditions, the sensor shows a wide linear range from 5×10(-7) to 1.84×10(-2) M with a low detection limit of 3.7×10(-7) M. The sensor also exhibits good repeatability, long-term stability as well as high selectivity against interfering species.

Fabrication of enrofloxacin imprinted organic-inorganic hybrid mesoporous sorbent from nanomagnetic polyhedral oligomeric silsesquioxanes for the selective extraction of fluoroquinolones in milk samples.

This paper reports a nanomagnetic polyhedral oligomeric silsesquioxanes (POSS)-directing strategy toward construction of molecularly imprinted hybrid materials for antibiotic residues determination in milk samples. The imprinted polymeric layer was facilely obtained through the copolymerization of active vinyl groups present on the nanomagnetic POSS (Fe3O4@POSS) surface and functional monomer (methacrylic acid) binding with template (enrofloxacin). Herein, the octavinyl POSS acted as not only the building blocks for hybrid rigid architectures but also the cross-linker for the formation of effective recognition sites during the imprinting process. The molecularly imprinted Fe3O4@POSS nanoparticles (Fe3O4@MI-POSS) demonstrated much higher adsorption capacity and selectivity toward enrofloxacin molecules and its analogs than the non-imprinted Fe3O4@POSS (Fe3O4@NI-POSS) materials. The imprinted particles were applied as a selective sorbent in solid-phase extraction focusing upon sample pretreatment in complex matrices prior to chromatographic analysis. The three FQs (ofloxacin, enrofloxacin, danofloxacin) could be selectively extracted from the biological matrix, while the matrix interferences were effectively eliminated simultaneously under the optimum extraction conditions. A simple, rapid and sensitive method based on the Fe3O4@MI-POSS material combined with HPLC-UV detection was then established for the simultaneous determination of three FQs from milk samples. The average recoveries of the three FQs were in the range of 75.6-108.9%. The relative standard deviations of intra- and inter-day ranging from 2.91 to 8.87% and from 3.6 to 11.5%, respectively. The limits of detections (S/N=3) were between 1.76 and 12.42 ng mL(-1). It demonstrates the effectiveness of trace analysis in complicated biological matrices utilizing magnetic separation in combination with molecularly imprinted solid-phase extraction, the rich chemistry of POSS makes it possible to be an ideal platform for generating molecular imprinted hybrid materials is also exhibited.

Highly ordered mesoporous tungsten oxides with a large pore size and crystalline framework for H2S sensing.

An ordered mesoporous WO3 material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers as a structure-directing agent through a solvent-evaporation-induced self-assembly method combined with a simple template-carbonization strategy. The obtained mesoporous WO3 materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m(2) g(-1)). The mesoporous WO3-based H2S gas sensor shows an excellent performance for H2S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H2S sensing.

Mesostructured nanomagnetic polyhedral oligomeric silsesquioxanes (POSS) incorporated with dithiol organic anchors for multiple pollutants capturing in wastewater.

A functionalizable organosiliceous hybrid magnetic material was facilely constructed by surface polymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) on the Fe3O4 nanoparticles. The resultant Fe3O4@POSS was identified as a mesoporous architecture with an average particle diameter of 20 nm and high specific surface area up to 653.59 m(2) g(-1). After it was tethered with an organic chain containing dithiol via thiol-ene addition reaction, the ultimate material (Fe3O4@POSS-SH) still have moderate specific area (224.20 m(2) g(-1)) with almost identical porous morphology. It turns out to be a convenient, efficient single adsorbent for simultaneous elimination of inorganic heavy metal ions and organic dyes in simulate multicomponent wastewater at ambient temperature. The Fe3O4@POSS-SH nanoparticles can be readily withdrawn from aqueous solutions within a few seconds under moderate magnetic field and exhibit good stability in strong acid and alkaline aqueous matrices. Contaminants-loaded Fe3O4@POSS-SH can be easily regenerated with either methanol-acetic acid (for organic dyes) or hydrochloric acid (for heavy metal ions) under ultrasonication. The renewed one keeps appreciable adsorption capability toward both heavy metal ions and organic dyes, the removal rate for any of the pollutants exceeds 92% to simulate wastewater with multiple pollutants after repeated use for 5 cycles. Beyond the environmental remediation function, thanks to the pendant vinyl groups, the Fe3O4@POSS derived materials rationally integrating distinct or versatile functions could be envisaged and consequently a wide variety of applications may emerge.

A resol-assisted co-assembly approach to crystalline mesoporous niobia spheres for electrochemical biosensing.

Templated pores: A resol-assisted solvent-evaporation-induced self-assembly (RA-EISA) gives unique ordered mesoporous niobia spheres by using the amphiphilic diblock copolymer PEO-b-PS as a template. The mesoporous Nb2O5 spheres have ordered hexagonal structures, large pore size and high surface area, and a nanocrystalline framework. They show excellent electrochemical sensing of hydrogen peroxide.

Sonochemical fabrication of Fe3O4 nanoparticles on reduced graphene oxide for biosensors.

This study synthesized Fe(3)O(4) nanoparticles of 30-40nm by a sonochemical method, and these particles were uniformly dispersed on the reduced graphene oxide sheets (Fe(3)O(4)/RGO). The superparamagnetic property of Fe(3)O(4)/RGO was evidenced from a saturated magnetization of 30emu/g tested by a sample-vibrating magnetometer. Based on the testing results, we proposed a mechanism of ultrasonic waves to explain the formation and dispersion of Fe(3)O(4) nanoparticles on RGO. A biosensor was fabricated by modifying a glassy carbon electrode with the combination of Fe(3)O(4)/RGO and hemoglobin. The biosensor showed an excellent electrocatalytic reduction toward H(2)O(2) at a wide, linear range from 4×10(-6) to 1×10(-3)M (R(2)=0.994) as examined by amperometry, and with a detection limit of 2×10(-6)M. The high performance of H(2)O(2) detection is attributed to the synergistic effect of the combination of Fe(3)O(4) nanoparticles and RGO, promoting the electron transfer between the peroxide and electrode surface.

A highly selective and sensitive dopamine and uric acid biosensor fabricated with functionalized ordered mesoporous carbon and hydrophobic ionic liquid.

An ordered mesoporous carbon material functionalized with carboxylic acid groups was synthesized. It was characterized by powder X-ray diffraction, transmission electron microscopy, Fourier transform IR spectroscopy and N(2) adsorption/desorption. Furthermore, this material was used to modify an electrode surface combined with a hydrophobic ionic liquid. The functionalized ordered mesoporous carbon/ionic liquid gel modified electrode shows excellent electrocatalytic performances for the oxidation of dopamine, uric acid and ascorbic acid. The presence of the ionic liquid promotes the electron transfer. Linear responses for dopamine and uric acid were obtained in the ranges of 0.1 to 500 µM and from 0.1 to 100 µM with detection limits of 4.1 and 2.5 nM (signal-to-noise ratio of 3), respectively, under optimum conditions. A quick and sensitive biosensor based on functionalized ordered mesoporous carbon and an ionic liquid has been developed for the first time for the detection of dopamine and uric acid in the presence of a large amount of ascorbic acid.