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The modified carbon nitride nanozyme could realize biomimetic catalysis application for evaluation of total antioxidant capacity via self-cascade photocatalytic H 2 O 2 production. [Display omitted] The peroxidase mimics usually requires the addition of exogenous hydrogen peroxide (H 2 O 2), which greatly hinder their practical applications. Herein, through rational co-modification of multiple elements (potassium (K), chlorine (Cl) and iodine (I)), the modified carbon nitride nanomaterials (KCl/KI-CN) could serve as efficient bifunctional catalysts. The multiple elements doping and the incorporation of cyano groups (C N) are deemed to enhance their photocatalytic and peroxidase-like activity, respectively. Based on the photocatalytic function, H 2 O 2 can be produced continuously and steadily via two-electron oxygen reduction over modified carbon nitride under visible light irradiation. Subsequently, the KCl/KI-CN could catalyze the chromogenic substrate by the in-situ produced H 2 O 2. Taking advantage of the bifunctional properties of modified carbon nitride, we for the first time demonstrate a self-cascade catalytic process and apply successfully for the ascorbic acid (AA) detection and versatile total antioxidant capacity (TAC) evaluation. This paper not only prepares an efficiently bifunctional catalyst but also provides a new self-cascade photocatalytic H 2 O 2 production strategy for the peroxidase-like application. [ABSTRACT FROM AUTHOR]

High levels of uric acid (UA) in humans can cause a range of diseases, and traditional assays that rely on uric acid enzymes to break down uric acid are limited by the inherent deficiencies of natural enzymes. Fortunately, the rapid development of nanozymes in recent years is expected to solve the above-mentioned problems. Hence, we used a host–guest strategy to synthesize a platinum nanoparticle confined in a metal–organic framework (Pt NPs@ZIF) that can sensitively detect UA levels in human serum. Unlike previously reported free radical-catalyzed oxidation systems, its unique electron transfer mechanism confers excellent peroxidase-like activity to Pt NPs@ZIF. In addition, UA can selectively inhibit the chromogenic reaction of TMB, thus reducing the absorbance of the system. Therefore, using the peroxidase-like activity of Pt NPs@ZIF and using TMB as a chromogenic substrate, UA can be detected directly without relying on natural enzymes. The results showed a relatively wide detection range (10–1000 μM) and a low detection limit (0.2 μM). Satisfactory results were also obtained for UA in human serum. This study with simple operation and rapid detection offers a promising method for efficiently detecting UA in serum. [ABSTRACT FROM AUTHOR]

One-dimensional MoO3/ZnMoO4/CoMoO4 hierarchical structures with sequential layered and granulated constitutional units on surfaces have been successfully designed and fabricated, mainly derived through the introducing of bi-component MOF and the effective element migration mechanism. Based on the different adding ratios of Co and Zn sources, the obtained hierarchical structure can be composed of the central MoO3 nanobelts, the outer uniform ZnMoO4 shell, and the outermost tunable CoMoO4 nanoparticles. The well-organized ZnMoO4 shell and CoMoO4 nanoparticles grown on MoO3 surface provide favorable opportunities for improving the surface absorption and chemical reaction, electron transport paths, and electron transfer efficiency. Compared with MoO3 nanobelts and MoO3/ZnMoO4 composites, the optimal MoO3/ZnMoO4/CoMoO4 sensors exhibit superior gas-sensing response value of 505.67 for 10 ppm triethylamine (TEA) at 270 °C as well as excellent gas selectivity and long-term stability. The superior gas-sensing performance is mainly attributed to the combination of the designed multi-level effective heterojunctions, large specific surface area, the enhanced surface adsorption/reaction, and the particular surface/interface electron transport process. More importantly, the current work presents a new insight of original gas-sensing MoO3/ZnMoO4/CoMoO4 hierarchical structures for detecting the variation of freshness in shrimp storage, indicating the practical applications in chemical detector and biosensor fields. [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]

Graphical abstract Highlights • SnS 2 /ZIF-8 derived porous flower-like SnO 2 /ZnO heterostructures were obtained. • New self-assembled SnS 2 flower-like microstructures were used as templates. • SnO 2 /ZnO composites exhibit high sensitivity and selectivity to TEA at 200 °C. • Tunable morphology and n–n heterojunctions play a key role for gas sensing property. • The method can be used for obtaining other heterostructures with novel shapes. Abstract SnO 2 -based flower-like sensitive materials derived from the self-assembled SnS 2 microstructures with more active areas and less agglomeration represent an alternative option for new generation of gas sensors. Meanwhile, the introduction of ZIF-8 for semiconductor surface functionalization is expected to get multi-functional hybrid materials with synergistic effects of individual components. In the present work, SnS 2 /ZIF-8 derived porous flower-like SnO 2 /ZnO heterostructures have been synthesized by a facile template method and the subsequent heat-treatment process. Beside the uniform morphology with tunable composition and size distribution, the attractive findings are focused on the enhanced triethylamine (TEA) gas-sensing properties of the obtained composites. SnO 2 /ZnO heterostructures show an obvious improvement in TEA gas sensing performance at the operating temperature of 200 °C, giving a response of about 17.7–50 ppm TEA, which was about 2.2 times higher than that of the sensors based on pure SnO 2. [ABSTRACT FROM AUTHOR]

A novel strategy was adopted to fabricate pH-universal Ru-based electrocatalysts. Due to the synergistic effect of the ultra-small size of Ru nanoclusters and defective CNTs with oxygen-containing groups, the Ru nanoclusters directly grown on defective carbon (O-Ru NCs/CNTs) catalysts exhibited superior hydrogen evolution activity in the whole pH window. An overpotential of only 37, 13, and 50 mV was needed to reach 10 mA cm−2 in 0.5 M H 2 SO 4 , 1.0 M KOH and 1.0 M PBS, respectively. Moreover, this catalyst has shown higher stability. This work is important for the potential application of Ru-based electrocatalysts for hydrogen production. [Display omitted] • Surfactant-free Ru nanoclusters are directly grown on CNTs via thermal reduction. • H 2 O 2 treatment can create oxygen-containing groups on the surface of CNTs. • Ru nanoclusters/defective CNTs can serve as pH-universal catalysts toward HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D flower-like In 2 O 3 /ZnO composite derived from In 2 O 3 precursor/ZIF-8 is gained. • Composite has flower-like In 2 O 3 /ZnO structure composed of needle-like nanorods. • Sensors show an excellent gas-sensing response of 188.01 to 100 ppm TEA at 120 °C. • Mechanism is mainly due to the accelerated multi-orientation electron transport. • In 2 O 3 -based sensors can be used for actual detecting area of seafood storage. Flower-like In 2 O 3 /ZnO heterostructures consisting of the assembled needle-like nanorods derived from In 2 O 3 precursor/ZIF-8 have been prepared by a two-step approach. Flower-like In 2 O 3 /ZnO structures can be achieved by adjusting the nucleation competition and crystal surface matching of In 2 O 3 and ZnO, leading to the enhancement of gas adsorption on the surface, chemical reaction kinetics, and the electron transport efficiency. In/Zn-2 sensors exhibit excellent gas-sensing response value of 188.01 to 100 ppm triethylamine at 120 °C as well as good gas selectivity, long-term stability, and linear relationship compared with pure In 2 O 3 , mainly attributed to the accelerated multi-orientation electron transport mechanism within flower-like In 2 O 3 /ZnO heterostructures. In addition, In/Zn-2 samples can be utilized to detect the practical triethylamine gas released during the storage of marine organism (fishes). [ABSTRACT FROM AUTHOR]

[Display omitted] • Cubic-like In 2 O 3 /α-Fe 2 O 3 composites assembled with porous nanoplates are obtained. • The introduction of Fe3+ component plays a vital role for morphological evolution. • In 2 O 3 /α-Fe 2 O 3 composites display superior TEA gas-sensing behavior at 170 °C. • In/Fe-2 shows the highest response and excellent cycling and long-term stability. • Sensing mechanism mainly depends on the unique microstructure and heterojunction. Cubic-like In 2 O 3 /α-Fe 2 O 3 heterostructures assembled with 2D porous nanoplates have been prepared by solvothermal method and subsequent calcination process. The introduction of Fe3+ component plays an important role for the morphological evolution of In 2 O 3 -based samples with unique crystal nucleation and growth mechanism. Compared with flower-like In 2 O 3 self-assemblies composed of tower-like structural units, In 2 O 3 /α-Fe 2 O 3 composites can display superior trimethylamine (TEA) gas-sensing behavior. For example, the optimal working temperature is reduced from 250 to 170 °C, and the response value of In/Fe-2 materials is 375.43, which is about 6.23 times than that of In 2 O 3 sensors. The enhanced gas-sensing properties are mainly attributed to large specific surface area (234.4 m2/g), the effective In 2 O 3 -α-Fe 2 O 3 heterojunctions, unique surface/interface effects, and tunable electron transmission mechanism. [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]

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]

A strategy for detection of NSE was developed based on edge-hosted single-atom Co nanozymes with dense active sites. [Display omitted] • Dense active Co-N 4 moieties in the edge sites performed higher catalytic activity. • The density of Co atoms directly affects charge redistribution. • The activation capacity of oxygen increases with the increase of the density of Co atoms. • A sensitive colorimetric immunosensor was constructed for Neuron Specific Enolas detection. Regulating the geometric and electronic structures of single-atom catalysts could promote the potential to improve their enzyme-like catalytic performance. Herein, we demonstrate that concave single-atom Co catalysts with edge-hosted and dense active Co-N 4 sites incorporated in nitrogen-doped hierarchical porous carbon (H-Co SACs) can act as highly efficient oxidase mimics. In particular, the engineered H-Co SACs with dense active Co-N 4 moieties in the edge sites were found to display 3.1 times higher catalytic activity than that of traditional intact Co single-atom catalysts (L-Co SACs). Combined experimental and theoretical simulations reveal that the geometric structure and the interactions between adjacent edge-hosted CoN 4 sites synergistically affect the electronic structure of the Co single-atom nanozymes, resulting in strong oxygen adsorption/activation and low energy barrier of the rate-determining step (RDS) in the reaction process, which are demonstrated be more beneficial for the oxidase-like catalytic performance. As a proof-of-concept application, the H-Co SACs were applied to the colorimetric enzyme-linked immunosorbent assay (ELISA) of neuron specific enolase (NSE) with a detection limit of 5.19 pg/ mL, outperforming both the intact Co single-atom catalysts and standard commercial ELISA kits. The present study could not only highlight the significance of geometric structure and active sites density effect on their enzyme-like catalytic efficiency, but also broaden their practical clinical application range of nanozymes at the atomic level. [ABSTRACT FROM AUTHOR]

• ZIF-67-induced double-tubular 1D CeO 2 /Co 3 O 4 heterostructures were obtained. • The variation from nanobelt to double-tubular shape relies on the amount of ZIF-67. • Samples show high specific surface area and superior photocatalytic property of MB. • Unique morphology and heterojunction cause electron transfer synergetic mechanism. • Double-tubular CeO 2 /Co 3 O 4 composite can be a promising photocatalyst for MB. ZIF-67-induced double-tubular 1D CeO 2 /Co 3 O 4 heterostructures have been prepared by an electrospinning method with tunable morphological evolution mechanism. As the adding amount of ZIF-67 increasing, the morphologies of CeO 2 -based nanomaterials are changed from porous granular nanobelt to smooth curly shape, and finally formed a double-tubular structure. The optimal CeO 2 /Co 3 O 4 products consisting of well-dispersed double-tubular nanostructure with the external diameter of about 200 nm display high specific surface area of 196.05 m2g−1 and superior photocatalytic performance of methylene blue (MB). The rapid degradation rate of 97% within 40 min and high cycling stability without significant decrease of photocatalytic activity could be attributed to the unique electron transfer synergetic mechanism based on the combination of double-tubular microstructure and CeO 2 /Co 3 O 4 heterojunctions. [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]

Uniform flower-like α-Fe 2 O 3 architectures with self-assembled core-shell nanorods are constructed and successfully prepared via the facile process. The concentration of Fe salt plays a great significance for morphological evolution from nanorods to self-assembled microflowers. Flower-like α-Fe 2 O 3 /ZnFe 2 O 4 consisting of α-Fe 2 O 3 core and ZnFe 2 O 4 shell nanorods are derived from FeOOH/ZIF-8 precursors. The detailed studies reveal that the tunable growth of ZIF-8 nanoparticles on three-dimensional FeOOH microflowers at room temperature and the availble calcination regulation are responsible for the formation of core-shell Fe 2 O 3 /ZnFe 2 O 4 composites. The highest response value of flower-like α-Fe 2 O 3 /ZnFe 2 O 4 architectures to 100 ppm triethylamine (TEA) has been improved to 141 at 280 °C, which is calculated to be 6.2 times compared with flower-like α-Fe 2 O 3 architectures (22.7). The enhanced gas-sensing mechanism of α-Fe 2 O 3 /ZnFe 2 O 4 composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe 2 O 3 core and ZnFe 2 O 4 shell, and the improved electron transfer process. Image 1 • α-Fe 2 O 3 /ZnFe 2 O 4 composites are derived from FeOOH/ZIF-8 precursors. • Flower-like α-Fe 2 O 3 /ZnFe 2 O 4 composites consists of core-shell nanorods. • α-Fe 2 O 3 /ZnFe 2 O 4 composites have superior sensing responses for TEA. • Novel sensing mechanisms of α-Fe 2 O 3 /ZnFe 2 O 4 composites are proposed. • Core-shell heterojunctions adjust electron transfer and potential barriers. [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]

Abstract In this paper, we focused on the hydrothermal synthesis of ZnO structures with varied morphologies by finely adjusting the ratio of water to glycol, indicating the polarity of the solution affects the growth habit of the crystal. It showed that the precise control in growth rates of different ZnO crystal faces in mixed solution is the key factor to control the morphologies of ZnO samples. Compared to pure ZnO, the response value of the hemispherical ZnO/Au to 100 ppm triethylamine (TEA) has been improved to 104.8 at the operating temperature of 260 °C, and the response and recovery time are 5 and 2 s, respectively. The enhancing mechanism of as-prepared ZnO/Au hemispheres can be ascribed to the combination of the tuning of surface electron transfer, microstructures, and the electronic and chemical sensitization of Au nanoparticles, along with the formation of Schottky junction between Au nanoparticles and ZnO hemispheres. The excellent sensing performance of ZnO/Au composite hemispheres enables them to function as promising materials for actual application in the monitoring and detecting of TEA. Graphical abstract The morphological evolution with tunable growth habits of ZnO sensor substrates and gas sensing properties and mechanism of ZnO/Au composites were presented. Image Highlights • The ratio of water to glycol plays the key role for ZnO morphological evolution. • ZnO microstructures are tunable and responsible for gas sensing properties. • Hemispherical ZnO/Au composites exhibit excellent gas performance to TEA. • The mechanisms were discussed in details for hemispherical ZnO/Au sensors. • These sensors can be used for actual monitoring and detecting application of TEA. [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]