Regulation of the Volume Flow Rate of Aqueous Methyl Blue Solution and the Wettability of CuO/ZnO Nanorods to Improve the Photodegradation Performance of Related Microfluidic Reactors.

Six CuO/ZnO nanorod (CuO/ZnONR)-based microfluidic reactors were constructed for different UV irradiation durations, with which an aqueous methylene blue (MB) solution was photodegraded at varied volume flow rate Q. Via numerical and experimental routes, the effects of the Q on the kinetic adsorption rate constant Ka and the initial rate constant KA of the CuO/ZnONR-based microfluidic reactors were discussed. Moreover, a reverse contacting angle (CA) trend of CuO/ZnONRs to the reaction constant K curve of corresponding CuO/ZnONR-based microfluidic reactor suggested that the CA of CuO/ZnONRs was another key influencing factor that affected greatly the photodegradation performance of the microfluidic reactors. The Q of the aqueous MB solution and the UV irradiation duration for the photodeposition of CuO/ZnONRs were optimized to be 125 µL/min and 1.0 h, the K of the CuO/ZnONR-based microfluidic reactors reached 4.84 min-1, and the related ΔKA/K was less than 6%. Similarly, these methods and results can be employed not only to enhance the mass transport and adsorption of specific species within other nanostructured matrix material-coated microchannels but also to enlarge the actual contacting surface areas between these microchannels and the related solution, which further improve the performance of other nanostructured catalyst-based microfluidic reactors, rGO microfluidic voltage generation, and a GOx/AuNW enzymatic glucose microfluidic sensor.

Modulation of Stainless-Steel Wire Sieve-Supported ZnO Nanorods for Optimal De-Ionized Water/Diesel Oil Separation.

ZnO nanorods (ZnONRs) were hydrothermally synthesized on stainless-steel wire (SSW) sieves of various mesh sizes at different Zn2+ concentrations of the growth solution, and then treated with stearic acid (SA) for a specific duration. Using these SSW sieve-supported ZnONRs, a mixture of de-ionized (DI) water and diesel oil was separated. It was found that the SA treatment dramatically diminished the quantity of surface hydroxyl groups attached to the top and upper portions of the ZnONRs, and thus significantly enhanced the hydrophobicity of the ZnONR-coated SSW sieves. The synthesis parameters remarkably affected the surface morphology and wettability of the ZnONRs on the SSWs, which in combination with the mesh size of the SSW sieve, influenced the contact angles (CA) of the ZnONR-coated SSW sieves and the separation efficiency for DI water and diesel oil. In each batch, the ZnONR-coated SSW sieves with mesh sizes of 300, 200, and 100 produced at Zn2+ concentrations of 125, 100, and 25 mM of the growth solution had the most desirable surface morphology, and were the most hydrophobic and oleophilic; further, they gave the optimal separation efficiencies of 93%, 95%, and 90% respectively. Thus, the ZnONR-coated SSW sieve with a mesh size of 200 prepared at Zn2+ concentration of 100 mM of the growth solution can be employed as an effective separator of water and diesel oil.

ZnS and Reduced Graphene Oxide Nanocomposite-Based Non-Enzymatic Biosensor for the Photoelectrochemical Detection of Uric Acid.

In this work, we report a study of a zinc sulfide (ZnS) nanocrystal and reduced graphene oxide (RGO) nanocomposite-based non-enzymatic uric acid biosensor. ZnS nanocrystals with different morphologies were synthesized through a hydrothermal method, and both pure nanocrystals and related ZnS/RGO were characterized with SEM, XRD and an absorption spectrum and resistance test. It was found that compared to ZnS nanoparticles, the ZnS nanoflakes had stronger UV light absorption ability at the wavelength of 280 nm of UV light. The RGO significantly enhanced the electron transfer efficiency of the ZnS nanoflakes, which further led to a better photoelectrochemical property of the ZnS/RGO nanocomposites. The ZnS nanoflake/RGO nanocomposite-based biosensor showed an excellent uric acid detecting sensitivity of 534.5 µA·cm-2·mM-1 in the linear range of 0.01 to 2 mM and a detection limit of 0.048 µM. These results will help to improve non-enzymatic biosensor properties for the rapid and accurate clinical detection of uric acid.

Regulating the Polypyrrole Ion-Selective Membrane and Au Solid Contact Layer to Improve the Performance of Nitrate All-Solid Ion-Selective Electrodes.

With polymerization duration and Au3+ concentration of the electrolyte regulated, a desirable nitrate-doped polypyrrole ion-selective membrane (PPy(NO3-)-ISM) and Au solid contact layer of anticipate surface morphology were obtained, and the performance of nitrate all-solid ion-selective electrodes (NS ISEs) was improved. It was found that the roughest PPy(NO3-)-ISM remarkably increases the actual contact surface area of the PPy(NO3-)-ISMs with nitrate solution, which leads to better adsorption of NO3- ions upon the PPy(NO3-)-ISMs, and produces a larger number of electrons. The most hydrophobic Au solid contact layer avoids the formation of the aqueous layer at the interface between the PPy(NO3-)-ISM and Au solid contact layer, and ensures unimpeded transporting of the produced electrons. The PPy-Au-NS ISE for polymerization duration 1800 s and at Au3+ concentration 2.5 mM of the electrolyte displays an optimal nitrate potential response, including a Nernstian slope of 54.0 mV/dec, LOD of 1.1 × 10-4 M, rapid average response time less than 1.9 s, and long-term stability of more than 5 weeks. This indicates that the PPy-Au-NS ISE is an effective working electrode for the electrochemical determination of NO3- concentration.

High-Sensitivity Enzymatic Glucose Sensor Based on ZnO Urchin-like Nanostructure Modified with Fe3O4 Magnetic Particles.

A novel and efficient enzymatic glucose sensor was fabricated based on Fe3O4 magnetic nanoparticles (Fe3O4MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe3O4MNPs were deposited on the surface of the ZnONFs by the drop-coating process. The results showed that the urchin-like ZnONFs provided strong support for enzyme adsorption. For Fe3O4MNPs, it significantly promoted the redox electron transfer from the active center of GOx to the ZnO nanoflowers beneath. More importantly, it promoted the hydrolysis of H2O2, the intermediate product of glucose catalytic reaction, and thus improved the electron yield. The sensitivity of the Nafion/GOx/Fe3O4MNPs/ZnONFs/Au/PET sensor was up to 4.52 µA·mM-1·cm-2, which was improved by 7.93 times more than the Nafion/GOx/ZnONFs/Au/PET sensors (0.57 µA·mM-1·cm-2). The detection limit and linear range were also improved. Additionally, the as-fabricated glucose sensors show strong anti-interference performance in the test environment containing organic compounds (such as urea, uric acid, and ascorbic acid) and inorganic salt (for instance, NaCl and KCl). The glucose sensor's service life was evaluated, and it can still maintain about 80% detection performance when it was reused about 20 times. Compared with other existing sensors, the as-fabricated glucose sensor exhibits an ultrahigh sensitivity and wide detection range. In addition, the introduction of Fe3O4MNPs optimized the catalytic efficiency from the perspective of the reaction mechanism and provided potential ideas for improving the performance of other enzymatic biosensors.