Facile Fabrication of ZnO-ZnFe2O4 Hollow Nanostructure by a One-Needle Syringe Electrospinning Method for a High-Selective H2S Gas Sensor

Herein, a facile fabrication process of ZnO-ZnFe2O4 hollow nanofibers through one-needle syringe electrospinning and the following calcination process is presented. The various compositions of the ZnO-ZnFe2O4 nanofibers are simply created by controlling the metal precursor ratios of Zn and Fe. Moreover, the different diffusion rates of the metal oxides and metal precursors generate a hollow nanostructure during calcination. The hollow structure of the ZnO-ZnFe2O4 enables an enlarged surface area and increased gas sensing sites. In addition, the interface of ZnO and ZnFe2O4 forms a p-n junction to improve gas response and to lower operation temperature. The optimized ZnO-ZnFe2O4 has shown good H2S gas sensing properties of 84.5 (S = Ra/Rg) at 10 ppm at 250 ∘C with excellent selectivity. This study shows the good potential of p-n junction ZnO-ZnFe2O4 on H2S detection and affords a promising sensor design for a high-performance gas sensor.

Exposing unsaturated Cu1-O2 sites in nanoscale Cu-MOF for efficient electrocatalytic hydrogen evolution

Conductive metal-organic framework (MOF) materials have been recently considered as effective electrocatalysts. However, they usually suffer from two major drawbacks, poor electrochemical stability and low electrocatalytic activity in bulk form. Here, we have developed a rational strategy to fabricate a promising electrocatalyst composed of a nanoscale conductive copper-based MOF (Cu-MOF) layer fully supported over synergetic iron hydr(oxy)oxide [Fe(OH)x] nanoboxes. Owing to the highly exposed active centers, enhanced charge transfer, and robust hollow nanostructure, the obtained Fe(OH)x@Cu-MOF nanoboxes exhibit superior activity and stability for the electrocatalytic hydrogen evolution reaction (HER). Specifically, it needs an overpotential of 112 mV to reach a current density of 10 mA cm−2 with a small Tafel slope of 76 mV dec−1. X-ray absorption fine structure spectroscopy combined with density functional theory calculations unravels that the highly exposed coordinatively unsaturated Cu1-O2 centers could effectively accelerate the formation of key *H intermediates toward fast HER kinetics.

Carbon Sphere Template Derived Hollow Nanostructure for Photocatalysis and Gas Sensing

As a green and preferred technology for energy crisis and environmental issues, continuous research on photocatalysis and gas sensing has come forth at an explosive rate. Thus far, promising synthetic methods have enabled various designs and preparations of semiconductor-based nanostructure which have shown superior activity. This review summarized various synthetic routines toward carbon sphere template derived hollow nanostructures and their successful attempts in synthesize doping, solid solution, heterostructure, and surface modified nanostructures for heterogeneous photocatalysis and gas sensing. Moreover, the challenges and future prospects are briefly discussed. It is eagerly anticipated that this review may broaden the view and in-depth understanding of carbon sphere template derived hollow nanostructures while expected to have further progresses in heterogeneous photocatalysis, gas sensing and other related fields which will make great contributions to their application.

A hierarchical hollow-on-hollow NiCoP electrocatalyst for efficient hydrogen evolution reaction

Superior activity and stability of a NiCoP electrocatalyst towards the hydrogen evolution reaction are achieved by constructing a unique hierarchical “hollow-on-hollow” nanostructure.

Preparation of CuCrO2 Hollow Nanotubes from an Electrospun Al2O3 Template

A hollow nanostructure is attractive and important in different fields of applications, for instance, solar cells, sensors, supercapacitors, electronics, and biomedical, due to their unique structure, large available interior space, low bulk density, and stable physicochemical properties. Hence, the need to prepare hollow nanotubes is more important. In this present study, we have prepared CuCrO2 hollow nanotubes by simple approach. The CuCrO2 hollow nanotubes were prepared by applying electrospun Al2O3 fibers as a template for the first time. Copper chromium ions were dip-coated on the surface of electrospun-derived Al2O3 fibers and annealed at 600 °C in vacuum to form Al2O3-CuCrO2 core-shell nanofibers. The CuCrO2 hollow nanotubes were obtained by removing Al2O3 cores by sulfuric acid wet etching while preserving the rest of original structures. The structures of the CuCrO2-coated Al2O3 core-shell nanofibers and CuCrO2 hollow nanotubes were identified side-by-side by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The CuCrO2 hollow nanotubes may find applications in electrochemistry, catalysis, and biomedical application. This hollow nanotube preparation method could be extended to the preparation of other hollow nanotubes, fibers, and spheres.

Assembly of Polyacrylamide-Sodium Alginate-Based Organic-Inorganic Hydrogel with Mechanical and Adsorption Properties

Hydrogels have been widely used in water purification. However, there is not much discussion and comparison about the effects of different nanofillers on the reinforcement and adsorption performances of hydrogels, which can be subjected to rapid water flow and possess strong adsorption ability. In this work, polyacrylamide (PAAM)-sodium alginate (SA) interpenetrating polymer network-structured hydrogels were prepared by in situ polymerization. PAAM formed the first flexible network and SA constructed the second rigid network. Three kinds of inorganic nanoparticles including carbon nanotubes (CNTs), nanoclays (NCs), and nanosilicas (NSs) were incorporated into a PAAM-SA matrix via hydrogen bond. The obtained hydrogels exhibited a macroporous structure with low density (≈1.4 g/cm3) and high water content (≈83%). Compared with neat PAAM-SA, the hydrogels with inorganic nanoparticles possessed excellent mechanical strengths and elasticities, and the compression strength of PAAM-SA-NS reached up to 1.3 MPa at ε = 60% by adding only 0.036 g NS in a 30 g polymer matrix. However, CNT was the best filler to improve the adsorption capacity owing to its multi-walled hollow nanostructure, and the adsorption capacity of PAAM-SA-CNT was 1.28 times higher than that of PAAM-SA. The prepared hydrogels can be potential candidates for use as absorbents to treat wastewater.