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Transition metal-N-doped carbon has been demonstrated to mimic natural enzyme activity; in this study, cobalt–nitrogen co-doped carbon (Co-N-C) nanomaterial was developed, and it could be an oxidase mimic. Firstly, Co-N-C with oxidase-like activity boosts the chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce the oxidized TMB (oxTMB). And the aromatic primary amino group of oxTMB reacts with nitrite (NO2−) to form diazo groups. Based on this background, we developed a cascade system of a Co-N-C-catalyzed oxidation reaction and a diazotization reaction for nitrite determination. The low detection limit (0.039 μM) indicates that Co-N-C is superior compared with the vast majority of previously reported nitrite assays. This study not only provides a novel nanozyme with sufficiently dispersed active sites, but it also further applies it to the determination of nitrite, which is expected to expand the application of nanozymes in colorimetric analysis. [ABSTRACT FROM AUTHOR]

ZIF-8-induced photocatalytic CeO2/ZnO nanobelts with curled edges were synthesized by following a facile electrospinning method for low-cost photodecomposition of methylene blue (MB). Phase structure and morphological evolution of different samples can be dominantly adjusted by introducing appropriate amount of zeolitic imidazolate framework-8 (ZIF-8) into the precursor solution. CeO2/ZnO heterostructures exhibit the optimal 96.59% photodegradation of MB organic pollutant in 70 min, approximately 7.43 times than that of pure CeO2. The curled microstructure can produce tunable surface activity and a unique electron transport process, facilitating the cycling efficiency of Ce3+/Ce4+ pairs on the surface of materials. Meanwhile, the formation of CeO2-ZnO heterojunctions contributes to regulating the crystal nucleation and growth during the high-temperature reaction and reducing the recombination rate of electron/hole pairs during the photocatalytic degradation. Thus, the obtained CeO2/ZnO composites may be a promising candidate for MB degradation in industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

Porous MoO3/V0.13Mo0.87O2.935 heterostructures self-assembled with 2D nanosheets have been primarily prepared by a facile method for effectively detecting ethanol at room temperature. The V0.13Mo0.87O2.935 phase contributes to modified microspheres and improved surface/interface structures. The enhanced sensing mechanism benefits from the effects of MoO3–V0.13Mo0.87O2.935 heterojunctions and tunable microstructure. [ABSTRACT FROM AUTHOR]

Tunable In2O3 hierarchical microstructures consisting of single crystalline octahedral particles and polycrystalline fibers have been synthesized by one-step electrospinning combined with a subsequent calcination process, in which their enhanced gas-sensing mechanism is mainly ascribed to the synergistic effect of two typical structural units. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hierarchical WO 3 /ZnWO 4 nanofibers with WO 3 nanoparticles on surface are gained. • Unique morphology relies on the introducing of ZIF-8 by one-step electrospinning. • WO 3 /ZnWO 4 sensors display excellent sensing behavior to low concentration HCHO. • Sensing mechanism depends on combination of various physicochemical characteristics. • Construction strategy can be used for other WO 3 -based sensors by similar method. Abstract Hierarchical WO 3 /ZnWO 4 1D fibrous heterostructures with tunable in-situ growth of WO 3 nanoparticles on surface have been fabricated by the original one-step electrospinning technology combined with subsequent calcination process. Phase composition and morphology can be transformed from bead-like WO 3 fibers to hierarchical WO 3 /ZnWO 4 1D composites with the introduction of ZIF-8 into the precursor solution, which was mainly attributed to the combination of nucleation competition and crystal planes matching mechanisms during heat treatment. Compared with pure WO 3 and WO 3 /ZnWO 4 -10%, WO 3 /ZnWO 4 -5% displayed the highest specific surface area value evaluated to be 268.57, indicating the prominent enhanced absorption behavior for targeted organic species. It is found that WO 3 /ZnWO 4 -5% composites have a response about 44.5 for 5 ppm HCHO, which was almost 8 times higher than that of sensor based on pure WO 3 nanofibers at the optimal operating temperature. Meanwhile, the fast response/recovery time (12/14 s) and excellent stability characteristics (recycling, long-term, and humidity stability) towards HCHO can be also observed for WO 3 /ZnWO 4 -5% samples. The enhanced gas-sensing mechanism based on WO 3 /ZnWO 4 composites can be ascribed to the synergistic effect of effective heterojunctions, large specific surface area, multiple reaction sites, and unique surface/interface electron transmission. The design and construction of hierarchical WO 3 /ZnWO 4 1D materials attest to the significant potential of their use as novel gas sensors for detecting low concentration HCHO. [ABSTRACT FROM AUTHOR]

• Hierarchical C-N/Co/Ti composite derived from MOF/TBOT precursor is obtained. • Structure consists of dodecahedron-like particles covered with twisted nanotubes. • Ti and Co are effectively separated in the upper and lower ends of nanotubes. • C-N/Co/Ti eletrocatalyst exhibits superior ORR properties than that of Pt/C. • Novel mechanism is ascribed from the phase composition and microstructure. C-N/Co/Ti composites derived from ZIF-67@TiO 2 precursors have been fabricated by a facile thermal treatment process. The morphology and composition are highly dependent on the available parameters inferring of exact hydrolysis of tetrabutyl titanate and sintering temperature. The obtained hierarchical microstructure is composed of numerous dodecahedron-like hollow boxes decorated with in-situ growth of size-tunable and twisting nanotubes on surfaces. The effective elemental separation of Ti and Co on the upper and lower ends of nanotubes can be realized by regulating the ionic migration and crystalline phase formation process at a high temperature. The as-prepared C-N/Co/Ti composites exhibit the enhanced electrocatalytic activities to oxygen reduction reaction (ORR) via a favorable four-electron pathway and the desired reaction kinetics with the low Tafel slope (67.8 mV dec−1), as well as the excellent methanol tolerance in comparison with the Pt/C electrocatalysts. The superior ORR electrocatalytic performance would be mainly contributed to the combination of the designed multi-phase composition, the enhanced surface adsorption/desorption, the modified surface/interface electron transfer mechanism, and the constructed Co/Ti double-active sites on different locations of microstructure. The present work presents a new insight for the synthesis of C-N-based inorganic composite with outstanding electrocatalytic behavior for ORR process. [ABSTRACT FROM AUTHOR]

• Tunable C-N/SnO 2 /Co 3 O 4 microspheres were prepared via an electrospinning route. • The introduction of ZIF-67 affects the composition and gas-sensing property. • C-N/SnO 2 /Co 3 O 4 microspheres show excellent gas-sensing performance to TEA. • The threshold limit of response can be observed as the exposure to 5 ppm TEA. • Synergistic combination of p-n heterojunction and C-N components was discussed. Composition-tunable C-N/SnO 2 /Co 3 O 4 microspheres with available gas-sensing behavior were successfully fabricated via a facile electrospinning technology, mainly achieved by different adding amounts of ZIF-67. It is found that both the introduction of C-N components and the formation of p-n heterojunction can effectively accelerate electron transmission and enhance the gas sensitivity properties of the material toward trimethylamine (TEA). The highest response of C-N/SnO 2 /Co 3 O 4 microspheres can reach up to approximately 154.3, calculated to be 9 times for 50 ppm triethylamine molecules at a temperature of 360 °C than that of C-N/SnO 2 microspheres. Moreover, the threshold limit value of gas response can be observed as the exposure to even a concentration of merely 5 ppm TEA, indicating their potential application on detecting TEA released during the decay process of prawn in the low concentration region. [ABSTRACT FROM AUTHOR]

Porous SnO 2 /NiO hollow nanofibers with effective surface transmission behavior have been prepared through a facile modified electrospinning method. The introduction of Ni component into the precursor solution can not only regulate the morphological evolution together with the nucleation and crystallization of oxide heterostructures at the elevated temperature action, but also significantly contribute to the enhancement of the gas-sensing performance for testing n-butanol gas. SnO 2 /NiO composites can present the highest response of 199 at the optimum operating temperature of 280 °C toward 100 ppm n-butanol gas, which is 4.5 times than that of pure SnO 2 nanofibers. Meanwhile, the response/recovery times of the sensors can be immensely decreased from 57/16 s of pure sample to 36/10 s as the adding amount of Ni component increasing to 5%, along with the superior selectivity and long-term stability toward n-butanol. The excellent gas-sensing properties of the sensors can be mainly attributed to the flourishing porous one-dimensional (1D) microstructure containing the closely connected p-n heterojunctions of SnO 2 and NiO, which can provide large specific surface areas with a mass of active sites to promote the reaction between n-butanol molecule and Oδ− on the surface. [Display omitted] • Porous SnO 2 /NiO hollow nanofibers were gained by a facile electrospinning method. • The introduction of Ni component regulates the morphological evolution of samples. • SnO 2 /NiO nanofibers show the excellent gas-sensing performance to n-butanol. • High response, rapid response/recovery times, and good stability can be obtained. • The mechanism is due to the p-n heterojunction and tunable porous microstructure. [ABSTRACT FROM AUTHOR]

One-step single-spinneret electrospinning synthesis of 1D fibrous hierarchical structure can not only prevent the agglomeration or restacking of fibers or particles and enlarge surface active area but also promote the directional migration of electrons in materials and achieve effective regulation of resistances. Herein, tunable SnO 2 and SnO 2 /ZnO fibrous hierarchical structures with in situ growth of monodisperse spherical-like particles on surface provide a new sight for adjusting component distribution, surface absorption and chemical reaction, electronic transmission path, and electron transfer efficiency. Compared with SnO 2 porous fibers and SnO 2 hierarchical structures, the optimal SnO 2 /ZnO sensors exhibit superior gas-sensing response value of 366-100 ppm ethanol at 260 °C as well as excellent gas selectivity and long-term stability, in which the enhanced gas-sensing mechanism is primarily derived from multilevel effective heterojunctions with unique interface electronic effects. Especially, these SnO 2 -based sensors can achieve favorable linear relationship of the response and gas concentration for sensitive trace detection in cosmetics for the first time, providing a new strategy to design composite materials for quantitative analysis of volatiles in the cosmetics evaluation process.

Morphology-tunable C-N/SnO 2 -based hierarchical microspheres with good gas sensitivity for triethylamine (TEA) have been fabricated via facile electrospinning and a subsequent calcination process. The reaction temperature and modifying calcining technology played a dominant role for the morphological evolution from precursor fibers to microspherical shapes and the formation of C-N-decorated SnO 2 phase composition. C-N/SnO 2 /ZnO composites with tunable crystallinity, microstructure, and gas-sensing performance were strictly dependent on the added amount of Zn element. Fascinatingly, the constructed C-N/SnO 2 /ZnO/Au composites can not only precisely regulate the crystal size, dispersion status, loading position, and content of Au nanoparticles but also display excellent gas-sensing properties with ultrasensitivity and high selectivity under various temperature detections. The response of C-N/SnO 2 /ZnO/Au composites can reach up to approximately 1970, calculated to be 121.6 and 23.6 times for 50 ppm TEA molecules at optimal conditions compared with C-N/SnO 2 and C-N/SnO 2 /ZnO microspheres, respectively, actually representing the highest response value at high temperatures reported to date. The superior long-aging stability of sensing behaviors and phase structures can be also observed after 1 month. More importantly, novel C-N/SnO 2 /ZnO/Au sensors were employed for availably detecting low-concentration volatiles released from the storage procedure of fishes at 80 °C, indicating the practical application in chemical detectors and biosensors at low temperature. The novel gas-sensing mechanisms derived primarily from the combination of phase compositions, morphologies, and unique surface/interface transfer processes of C-N/SnO 2 /ZnO/Au composites are presented and investigated in detail, which will contribute to the design and development of other semiconductor-based composite sensors.