Nanosheet-assembled ZnFe2O4 hollow microspheres for high-sensitive acetone sensor

Unveiling the synergy: Biocompatible alginate-cellulose hydrogel loaded with silk fibroin and zinc ferrite nanoparticles for enhanced cell adhesion, and anti-biofilm activity

Combining a biocompatible hydrogel scaffold with the cell-supportive properties of silk fibroin (SF) and the unique functionalities of ZnFe2O4 nanoparticles creates a promising platform for advanced nanobiomaterials. The research is centered on synthesizing a natural hydrogel using cellulose (Cellul) and sodium alginate (SA) combined with SF and zinc ferrite nanoparticles. A range of analytical and biological assays were conducted to determine the biological and physicochemical properties of the nanobiocomposite. The hemolysis and 2,5-diphenyl-2H-tetrazolium bromide (MTT) assays indicated that the SA-Cellul hydrogel/SF/ZnFe2O4 nanobiocomposite was a biocompatible against human dermal fibroblasts (Hu02) and red blood cells (RBC). In addition, aside from demonstrating outstanding anti-biofilm activity, the nanobiocomposite also promotes the Hu02 cells adhesion, showcasing the synergistic effect of incorporating SF and ZnFe2O4 nanoparticle. These promising results show that this nanobiocomposite has potential applications in various biomedical fields.

Hollow S-Doped ZnFe2O4 Microcubes with Magnetic Separability for Photocatalytic Removal of Uranium(VI) under Different Light Intensity

Under xenon lamps, ZnFe2O4 (ZFO) has been shown to be effective in removing uranium through photocatalysis. However, its performance is still inadequate in low-light environments due to low photon utilization and high electron-hole complexation. Herein, S-doped hollow ZnFe2O4 microcubes (Sx-H-ZFO, x = 1, 3, 6, 9) were synthesized using the MOF precursor template method. The hollow morphology improves the utilization of visible light by refracting and reflecting the incident light multiple times within the confined domain. S doping narrows the band gap and shifts the conduction band position negatively, which enhances the separation, migration, and accumulation of photogenerated charges. Additionally, S doping increases the number of adsorption sites, ultimately promoting efficient surface reactions. Consequently, Sx-H-ZFO is capable of removing U(VI) in low-light environments. Under cloudy and rainy weather conditions, the photocatalytic rate of S3-H-ZFO was 100.31 μmol/(g·h), while under LED lamps (5000 Lux) it was 72.70 μmol/(g·h). More interestingly, a systematic mechanistic investigation has revealed that S doping replaces some of the oxygen atoms to enhance electron transfers and adsorption of O2. This process initiates the formation of hydrogen peroxide, which reacts directly with UO22+ to form solid studtite (UO2)O2·2H2O. Additionally, the promising magnetic separation capability of Sx-H-ZFO facilitates the recycling and reusability of the material. This work demonstrates the potential of ZnFe2O4 extraction uranium from nuclear wastewater.

Synthesis, characterization, and preliminary insights of ZnFe2O4 nanoparticles into potential applications, with a focus on gas sensing

This work presents a hydrothermal-based facile method for synthesizing ZnFe2O4, whose size can be controlled with the concentration of sodium acetate used as a fuel and its physical changes at nanoscales when exposed to two different gases. The structural, morphological, compositional, and electronic properties of the synthesized samples are also presented in this paper. The crystal structure of the synthesized samples was determined using an X-ray Diffractometer (XRD). The results revealed fluctuations in the size, lattice parameter, and strain in the nanoparticles with increasing the concentration of sodium acetate. Field-Emission Scanning Electron Microscopy (FESEM) was used to determine synthesized materials' morphology and particle size. It revealed that the particles possessed approximately spherical morphology whose size decreased significantly with the increasing amount of sodium acetate. Transmission Electron Microscopy (TEM) was utilized to determine the structure, morphology, and elemental distributions in particles at the nanoscale, and it confirmed the findings of XRD and FESEM analyses. The high-resolution TEM (HRTEM) imaging analysis of the nanoparticles in our studied samples revealed that the particles predominantly possessed (001) type facets. X-ray photoelectron spectroscopy (XPS) and core-loss electron energy loss spectroscopy (EELS) showed an increasing fraction of Fe2+ with the decreasing size of the particles in samples. The Brunauer, Emmett, and Tellers (BET) analysis of samples revealed a higher surface area as the particle size decreases. In addition, the determined surface area and pore size values are compared with the literature, and it was found that the synthesized materials are promising for gas-sensing applications. The ab initio calculations of the Density of States (DOS) and Band structure of (001) surface terminating ZnFe2O4 were carried out using Quantum Espresso software to determine the bandgap of the synthesized samples. They were compared to their corresponding experimentally determined bandgap values and showed close agreement. Finally, in-situ TEM measurement was carried out on one of the four studied samples with robust properties using Ar and CO2 as reference and target gases, respectively. It is concluded from the presented study that the size reduction of the ZnFe2O4 nanoparticles (NPs) tunes the bandgap and provides more active sites due to a higher concentration of oxygen vacancies. The in-situ TEM showed us a nanoscale observation of the change in one of the crystal structure parameters. The d spacing of ZnFe2O4 NPs showed a noticeable fluctuation, reaching more than 5% upon exposure to CO2 and Ar gases.

Recent Progress in Spinel Ferrite (MFe2O4) Chemiresistive Based Gas Sensors

Gas-sensing technology has gained significant attention in recent years due to the increasing concern for environmental safety and human health caused by reactive gases. In particular, spinel ferrite (MFe2O4), a metal oxide semiconductor with a spinel structure, has emerged as a promising material for gas-sensing applications. This review article aims to provide an overview of the latest developments in spinel-ferrite-based gas sensors. It begins by discussing the gas-sensing mechanism of spinel ferrite sensors, which involves the interaction between the target gas molecules and the surface of the sensor material. The unique properties of spinel ferrite, such as its high surface area, tunable bandgap, and excellent stability, contribute to its gas-sensing capabilities. The article then delves into recent advancements in gas sensors based on spinel ferrite, focusing on various aspects such as microstructures, element doping, and heterostructure materials. The microstructure of spinel ferrite can be tailored to enhance the gas-sensing performance by controlling factors such as the grain size, porosity, and surface area. Element doping, such as incorporating transition metal ions, can further enhance the gas-sensing properties by modifying the electronic structure and surface chemistry of the sensor material. Additionally, the integration of spinel ferrite with other semiconductors in heterostructure configurations has shown potential for improving the selectivity and overall sensing performance. Furthermore, the article suggests that the combination of spinel ferrite and semiconductors can enhance the selectivity, stability, and sensing performance of gas sensors at room or low temperatures. This is particularly important for practical applications where real-time and accurate gas detection is crucial. In conclusion, this review highlights the potential of spinel-ferrite-based gas sensors and provides insights into the latest advancements in this field. The combination of spinel ferrite with other materials and the optimization of sensor parameters offer opportunities for the development of highly efficient and reliable gas-sensing devices for early detection and warning systems.

A humidity-resistant and room temperature carbon soot@ZIF-67 composite sensor for acetone vapour detection

Zeolitic imidazolate framework-67 (ZIF-67), carbon nanoparticles (CNPs), and the CNPs@ZIF-67 composite were prepared and used to fabricate sensors for the detection of acetone vapour. The prepared materials were characterized using transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier-transform infrared spectroscopy. The sensors were tested using an LCR meter under the resistance parameter. It was found that the ZIF-67 sensor did not respond at room temperature, the CNP sensor had a non-linear response to all analytes, and the CNPs/ZIF-67 sensor had an excellent linear response to acetone vapour and was less sensitive to 3-pentanone, 4-methyl-1-hexene, toluene and cyclohexane vapours. However, it was found that ZIF-67 improves carbon soot sensor sensitivity by 155 times, wherein the sensitivity of the carbon soot sensor and carbon soot@ZIF-67 sensor on acetone vapour was found to be 0.0004 and 0.062 respectively. In addition, the sensor was found to be insensitive to humidity and the limit of detection was 484 ppb at room temperature.

A novel insight into the microwave induced catalytic reduction mechanism in aqueous Cr(VI) removal over ZnFe2O4 catalyst

Aqueous Cr(VI) pollution is an emerging environmental issue. Herein, a sphere-like ZnFe₂O₄ catalyst with a size of ∼430 nm was prepared by a solvothermal method, by which the aqueous Cr(VI) in a 50 mL solution with concentration of 50 mg/L was completely removed after 10 min-microwave (MW) irradiation. "Surface temperature visualization" tests and COMSOL simulations showed that the surface temperature of the as-prepared ZnFe₂O₄ catalysts could be as high as > 1000 °C only after 300 s MW irradiation, and the work function calculations and scavenging experiments demonstrated that the excited electrons derived by the "hot spots" effect of the ZnFe₂O₄ catalysts reduced the Cr(VI) to Cr(III). Kinetic reaction process of the reduction of *Cr₂O₇^2- to *CrO₃H₃ over the ZnFe₂O₄ catalysts was clarified by using DFT calculation, and the results indicated that *Cr₂O₇^2- adsorbed on the Fe atoms was more easily to be reduced, and that Fe atoms played more significant roles than the Zn and O atoms in ZnFe₂O₄ catalysts. The present study not only proves that the MW induced ZnFe₂O₄ catalytic reduction was promising for ultrafast remediation of toxic Cr(VI), but also provides a new insight into the corresponding mechanism.

Rational design of direct Z-scheme magnetic ZnIn2S4/ZnFe2O4 heterojunction toward enhanced photocatalytic wastewater remediation

The rationally designed heterojunction photocatalysts with magnetic semiconductors and easy recyclability have received considerable attention due to their great advantages in practical application. In our work, a series of ZnIn2S4/ZnFe2O4 Z-scheme heterojunction photocatalysts with superior magnetic properties were synthesized by a gentle chemical bath method and utilized for the effective photodegradation and Cr(VI) reduction under irradiation. Systematic evaluation experiments revealed that the derived ZnIn2S4/ZnFe2O4 photocatalysts exhibited enhanced photocatalytic efficiency for RhB degradation and Cr(VI) reduction as compared with pristine ZnIn2S4 and ZnFe2O4, which was primarily due to the close contact interface and the formation of Z - scheme charge transfer mechanism between ZnFe2O4 rods and ZnIn2S4 nanosheets. Moreover, the as-synthesized photocatalyst could be easily recycled with a remarkable photocatalytic performance because of its magnetic separation characteristic. The present work opens up a vast prospect for the design of highly efficient and magnetically separable photocatalysts for environmental remediation.

WS2 Nanorod as a Remarkable Acetone Sensor for Monitoring Work/Public Places

Here, we report the synthesis of the WS₂ nanorods (NRs) using an eco-friendly and facile hydrothermal method for an acetone-sensing application. This study explores the acetone gas-sensing characteristics of the WS₂ nanorod sensor for 5, 10, and 15 ppm concentrations at 25 °C, 50 °C, 75 °C, and 100 °C. The WS₂ nanorod sensor shows the highest sensitivity of 94.5% at 100 °C for the 15 ppm acetone concentration. The WS₂ nanorod sensor also reveals the outstanding selectivity of acetone compared to other gases, such as ammonia, ethanol, acetaldehyde, methanol, and xylene at 100 °C with a 15 ppm concentration. The estimated selectivity coefficient indicates that the selectivity of the WS₂ nanorod acetone sensor is 7.1, 4.5, 3.7, 2.9, and 2.0 times higher than xylene, acetaldehyde, ammonia, methanol, and ethanol, respectively. In addition, the WS₂ nanorod sensor also divulges remarkable stability of 98.5% during the 20 days of study. Therefore, it is concluded that the WS₂ nanorod can be an excellent nanomaterial for developing acetone sensors for monitoring work/public places.

CsPbBr3-Based Nanostructures for Room-Temperature Sensing of Volatile Organic Compounds

All-inorganic halide perovskites, as a dominant member of the perovskite family, have been proven to be excellent semiconductors due to the great successes for solar cells, light-emitting diodes, photodetectors, and nanocrystal photocatalysts. Despite the remarkable advances in those fields, there are few research studies focusing on gas and humidity-sensing performances, especially for pure CsPbBr₃ and heterogeneous CsPbBr₃@MoS₂ composites. Here, we first report a valuable CsPbBr₃ sensor prepared by electrospinning, and the excellent gas sensing performances are investigated. The CsPbBr₃ sensor can quickly and effectively detect ethanolamine at room temperature. The response time is only 16 s, and the response to 100 ppm ethanolamine is as high as 29.87, besides the excellent repeatability and good stability. The theoretical detection limit is estimated to be 21 ppb. Furthermore, considering the irreplaceable role of heterostructures in regulating the electronic structure and supporting rich reaction boundaries, we also actively explored the EA sensitivity of inorganic CsPbBr₃-based heterogeneous composites CsPbBr₃@MoS₂. At the same time, the roles of the critical capping agents OA and OAm are systematically investigated. This work demonstrates the great potential of all-inorganic halide perovskites in promising volatile organic compound detection.

CuxCo1-xFe2O4 (x = 0.33, 0.67, 1) Spinel Ferrite Nanoparticles Based Thermoplastic Polyurethane Nanocomposites with Reduced Graphene Oxide for Highly Efficient Electromagnetic Interference Shielding

CuxCo1-xFe2O4 (x = 0.33, 0.67, 1)-reduced graphene oxide (rGO)-thermoplastic polyurethane (TPU) nanocomposites exhibiting highly efficient electromagnetic interference (EMI) shielding were prepared by a melt-mixing approach using a microcompounder. Spinel ferrite Cu0.33Co0.67Fe2O4 (CuCoF1), Cu0.67Co0.33Fe2O4 (CuCoF2) and CuFe2O4 (CuF3) nanoparticles were synthesized using the sonochemical method. The CuCoF1 and CuCoF2 exhibited typical ferromagnetic features, whereas CuF3 displayed superparamagnetic characteristics. The maximum value of EMI total shielding effectiveness (SET) was noticed to be 42.9 dB, 46.2 dB, and 58.8 dB for CuCoF1-rGO-TPU, CuCoF2-rGO-TPU, and CuF3-rGO-TPU nanocomposites, respectively, at a thickness of 1 mm. The highly efficient EMI shielding performance was attributed to the good impedance matching, conductive, dielectric, and magnetic loss. The demonstrated nanocomposites are promising candidates for a lightweight, flexible, and highly efficient EMI shielding material.

Temperature-Based Selective Detection of Hydrogen Sulfide and Ethanol with MoS2/WO3 Composite

A sensitive and temperature-based selective sensor toward hydrogen sulfide and ethanol using MoS₂/WO₃ composite as a sensing surface was developed in this work. The MoS₂/WO₃ nanocomposite was successfully obtained using a facile two-step method. Structural analysis revealed the successful formation of the composite. Further, the n-type semiconducting nature as revealed in the initial gas-sensing measurements was also confirmed via Mott-Schottky plots. The composite-based sensor showed preferential detection of ethanol (260 °C) and hydrogen sulfide (320 °C) by simply modulating the temperature of the sensor device. The device also displayed repeatability and long-term stability at respective operating temperatures. Improved sensitivity and selectivity are ascribed to synergistic effects arising from the formation of n-n type heterostructures. The present work indicates the potential use of composite-based heterojunctions to tune the sensing parameters and provide new possibilities to enhance the applications of MoS₂ and metal-oxide semiconductor-based composites.

Novel magnetic organic-inorganic hybrids based on aromatic polyamides and ZnFe2O4 nanoparticles with biological activity

Magnetic nanoparticles were creatively selected as stable, inexpensive, biodegradable, facile recoverable, and functionalizable supports for a variety of synthetic and natural polymers. Herein, for the first time, aromatic polyamide was synthesized on the magnetic core of zinc iron oxide (ZnFe₂O₄). Terephthaloyl chloride and derivations of phenylenediamine were employed as monomers in this polymerization process. The toxicity of the synthesized hybrid at the highest concentration (1000 μg/ml) is 13.65% and on the other hand, the cell viability percentage is 86.35%. So, the prepared hybrid is biocompatible and non-toxic to Hu02 cells. Also, it has antibacterial ability against gram-positive and gram-negative bacteria. Because the results show that the minimum inhibitory concentration (MIC) of the synthesized polymer for bacteria such as Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 is in the range of 500-1000 µg/ml. Moreover, the hemolytic effect of ZnFe₂O₄ based hybrid was below 9% at the concentration of 1000 μg/ml. Therefore, it is compatible with red blood cells.

Enhanced Propanol Response Behavior of ZnFe2O4 NP-Based Active Sensing Layer Induced by Film Thickness Optimization

Development of gas sensors displaying improved sensing characteristics including sensitivity, selectivity, and stability is now possible owing to tunable surface chemistry of the sensitive layers as well as favorable transport properties. Herein, zinc ferrite (ZnFe2O4) nanoparticles (NPs) were produced using a microwave-assisted hydrothermal method. ZnFe2O4 NP sensing layer films with different thicknesses deposited on interdigitated alumina substrates were fabricated at volumes of 1.0, 1.5, 2.0, and 2.5 µL using a simple and inexpensive drop-casting technique. Successful deposition of ZnFe2O4 NP-based active sensing layer films onto alumina substrates was confirmed by X-ray diffraction and atomic force microscope analysis. Top view and cross-section observations from the scanning electron microscope revealed inter-agglomerate pores within the sensing layers. The ZnFe2O4 NP sensing layer produced at a volume of 2 μL exhibited a high response of 33 towards 40 ppm of propanol, as well as rapid response and recovery times of 11 and 59 s, respectively, at an operating temperature of 120 °C. Furthermore, all sensors demonstrated a good response towards propanol and the highest response against ethanol, methanol, carbon dioxide, carbon monoxide, and methane. The results indicate that the developed fabrication strategy is an inexpensive way to enhance sensing response without sacrificing other sensing characteristics. The produced ZnFe2O4 NP-based active sensing layers can be used for the detection of volatile organic compounds in alcoholic beverages for quality check in the food sector.

Ex-situ XPS analysis of yolk-shell Sb2O3/WO3 for ultra-fast acetone resistive sensor

The preparation of fast, highly responsive and reliable gas sensing devices for the detection of acetone gas is considered to be a key challenge for the development of accurate disease diagnosis systems through exhaled respiratory gases. In the paper, yolk shell Sb₂O₃/WO₃ is synthesized and its gas sensing performance was studied by static test system. Special, the maximum response value of 1:1 Sb₂O₃/WO₃ yolk-shell (WO₃-1 YSL) sensor to 100 ppm acetone can reach as high as 50.0 at 200 ℃. And it also exhibits excellent response/recover time (4 s/5 s), low detection limit (2 ppm) and superior selectivity towards acetone. More importantly, in mixed selective gas test, the sensor shows high selectivity towards acetone. And the mechanism is analyzed by ex-situ XPS. The excellent gas-sensing performance can be attributed to unique yolk-shell structure, which facilitates the rapid transport of charge carriers from the surface to the bulk and provides more active sites for gas adsorption and desorption; the heterojunction between of Sb₂O₃ and WO₃, which promotes oxygen pre-adsorption on the surface and increasing the interfacial potential; the increased oxygen vacancies which allowing more chemisorbed oxygen to form.

Silver Doped Zinc Stannate (Ag-ZnSnO3) for the Photocatalytic Degradation of Caffeine under UV Irradiation

Contaminants of emerging concerns (CECs) spread across a wide range of organic product compounds. As biorecalcitrants, their removal from conventional wastewater treatment systems remains a herculean task. To address this issue, heterogenous solar driven advanced oxidation process based-TiO2 and other semiconductor materials has been extensively studied for their abatement from wastewater sources. In this study, we have synthesized by hydrothermal assisted co-precipitation Ag doped ZnSnO3. Structural and morphological characterizations were performed via X-ray diffraction (XRD), Fourier transform infra-red (FTIR), N2 adsorption-desorption at 77 K by Brunauer-Emmet-Teller (BET) and Barrett, Joyner, and Halenda (BJH) methods, Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), and UV-visible absorption in Diffuse reflectance spectroscopy (UV-vis/DRS) mode. Crystallite size estimate for Ag-ZnSnO3 and undoped form was 19.4 and 29.3 nm, respectively, while respective TEM particle size estimate was 79.0 nm and 98.2 nm. BET surface area and total pore volume by BJH for Ag-ZnSnO3 were estimated with respective values of 17.2 m2/g and 0.05 cm3/g in comparison to 18.8 m2/g and 0.06 cm3/g for ZnSnO3. Derived energy band gap (Eg) values were 3.8 eV for Ag-ZnSnO3 and 4.2 eV for ZnSnO3. Photocatalytic performance of Ag-ZnSnO3 was tested towards caffeine achieving about 68% removal under (natural) unmodified pH = 6.50 and almost 100% removal at initial pH around 7.5 after 4 h irradiation. The effect of initial pH, catalyst dosage, pollutant concentration, charge scavengers, H2O2, contaminant inorganic ions (anions) as well as humic acid (HA) on the photocatalyst activity over caffeine degradation were assessed. In accordance with the probation test of the reactive species responsible for photocatalytic degradation process, a reaction mechanism was deduced.

Superparamagnetic ZnFe2O4 Nanoparticles-Reduced Graphene Oxide-Polyurethane Resin Based Nanocomposites for Electromagnetic Interference Shielding Application

Superparamagnetic ZnFe2O4 spinel ferrite nanoparticles were prepared by the sonochemical synthesis method at different ultra-sonication times of 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The structural properties of ZnFe2O4 spinel ferrite nanoparticles were controlled via sonochemical synthesis time. The average crystallite size increases from 3.0 nm to 4.0 nm with a rise of sonication time from 25 min to 100 min. The change of physical properties of ZnFe2O4 nanoparticles with the increase of sonication time was observed. The prepared ZnFe2O4 nanoparticles show superparamagnetic behavior. The prepared ZnFe2O4 nanoparticles (ZS25, ZS50, and ZS100) and reduced graphene oxide (RGO) were embedded in a polyurethane resin (PUR) matrix as a shield against electromagnetic pollution. The ultra-sonication method has been used for the preparation of nanocomposites. The total shielding effectiveness (SET) value for the prepared nanocomposites was studied at a thickness of 1 mm in the range of 8.2-12.4 GHz. The high attenuation constant (α) value of the prepared ZS100-RGO-PUR nanocomposite as compared with other samples recommended high absorption of electromagnetic waves. The existence of electric-magnetic nanofillers in the resin matrix delivered the inclusive acts of magnetic loss, dielectric loss, appropriate attenuation constant, and effective impedance matching. The synergistic effect of ZnFe2O4 and RGO in the PUR matrix led to high interfacial polarization and, consequently, significant absorption of the electromagnetic waves. The outcomes and methods also assure an inventive and competent approach to develop lightweight and flexible polyurethane resin matrix-based nanocomposites, consisting of superparamagnetic zinc ferrite nanoparticles and reduced graphene oxide as a shield against electromagnetic pollution.

Breath Acetone Sensing Based on Single-Walled Carbon Nanotube-Titanium Dioxide Hybrids Enabled by a Custom-Built Dehumidifier

Acetone is a metabolic byproduct found in the exhaled breath and can be measured to monitor the metabolic degree of ketosis. In this state, the body uses free fatty acids as its main source of fuel because there is limited access to glucose. Monitoring ketosis is important for type I diabetes patients to prevent ketoacidosis, a potentially fatal condition, and individuals adjusting to a low-carbohydrate diet. Here, we demonstrate that a chemiresistor fabricated from oxidized single-walled carbon nanotubes functionalized with titanium dioxide (SWCNT@TiO₂) can be used to detect acetone in dried breath samples. Initially, due to the high cross sensitivity of the acetone sensor to water vapor, the acetone sensor was unable to detect acetone in humid gas samples. To resolve this cross-sensitivity issue, a dehumidifier was designed and fabricated to dehydrate the breath samples. Sensor response to the acetone in dried breath samples from three volunteers was shown to be linearly correlated with the two other ketone bodies, acetoacetic acid in urine and β-hydroxybutyric acid in the blood. The breath sampling and analysis methodology had a calculated acetone detection limit of 1.6 ppm and capable of detecting up to at least 100 ppm of acetone, which is the dynamic range of breath acetone for someone with ketosis. Finally, the application of the sensor as a breath acetone detector was studied by incorporating the sensor into a handheld prototype breathalyzer.

Role of Surfaces in the Magnetic and Ozone Gas-Sensing Properties of ZnFe2O4 Nanoparticles: Theoretical and Experimental Insights

The magnetic properties and ozone (O₃) gas-sensing activity of zinc ferrite (ZnFe₂O₄) nanoparticles (NPs) were discussed by the combination of the results acquired by experimental procedures and density functional theory simulations. The ZnFe₂O₄ NPs were synthesized via the microwave-assisted hydrothermal method by varying the reaction time in order to obtain ZnFe₂O₄ NPs with different exposed surfaces and evaluate the influence on its properties. Regardless of the reaction time employed in the synthesis, the zero-field-cooled and field-cooled magnetization measurements showed superparamagnetic ZnFe₂O₄ NPs with an average blocking temperature of 12 K. The (100), (110), (111), and (311) surfaces were computationally modeled, displaying the different undercoordinated surfaces. The good sensing activity of ZnFe₂O₄ NPs was discussed in relation to the presence of the (110) surface, which exhibited low (-0.69 eV) adsorption enthalpy, promoting reversibility and preventing the saturation of the sensor surface. Finally, the O₃ gas-sensing mechanism could be explained based on the conduction changes of the ZnFe₂O₄ surface and the increase in the height of the electron-depletion layer upon exposure toward the target gas. The results obtained allowed us to propose a mechanism for understanding the relationship between the morphological changes and the magnetic and O₃ gas-sensing properties of ZnFe₂O₄ NPs.

Surface Structure Engineering of Nanosheet-Assembled NiFe2O4 Fluffy Flowers for Gas Sensing

In this work, we present a strategy to improve the gas-sensing performance of NiFe₂O₄ via a controllable annealing Ni/Fe precursor to fluffy NiFe₂O₄ nanosheet flowers. X-ray diffraction (XRD), a scanning electron microscope (SEM), nitrogen adsorption–desorption measurements and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure, morphology, specific surface area and surface structure. The gas-sensing performance was tested and the results demonstrate that the response was strongly influenced by the specific surface area and surface structure. The resultant NiFe₂O₄ nanosheet flowers with a heating rate of 8 °C min⁻¹, which have a fluffier morphology and more oxygen vacancies in the surface, exhibited enhanced response and shortened response time toward ethanol. The easy approach facilitates the mass production of gas sensors based on bimetallic ferrites with high sensing performance via controlling the morphology and surface structure.

Rational design of interface refining through Ti4+/Zr4+ diffusion/doping and TiO2/ZrO2 surface crowning of ZnFe2O4 nanocorals for photoelectrochemical water splitting

The interplay between diffusion/doping and surface passivation of TZF NCs exhibits a breakthrough photocurrent density of 0.73 mA cm⁻² (1.23 V vs. RHE) with 98% stability over 10 h in the TZF/Al₂O₃/CoO_x photoanode.

Ultrasonic-assisted preparation and characterization of magnetic ZnFe2O4/g-C3N4 nanomaterial and their applications towards electrocatalytic reduction of 4-nitrophenol

Nanoball-structured ferromagnetic zinc ferrite nanocrystals (ZnFe₂O₄ NPs) entrapped with graphitic-carbon nitride (g-C₃N₄) was produced via straightforward and facile sonochemical synthetical technique (titanium probe; 100 W/cm² and 50 KHz). The morphological (SEM), elemental (EDS), diffraction (XRD), XPS, and electrochemical studies (CV) have been carry out to verify the nanostructure and shape of the materials. The ZnFe₂O₄ NPs/g-C₃N₄ electrode (GCE) was constructed which displayed outstanding electrochemical ability towards toxic 4-nitrophenol (NTP). A sensitive, selective, reproducible, and durable electrochemical NTP sensor was developed by ZnFe₂O₄ NPs/g-C₃N₄ modified electrode. The modified sensor exhibited a high sensitivity and 4.17 nanomolars of LOD. It's greater than the LOD of previously reported NTP modified sensors. The real-time experiments of the modified electrochemical (ZnFe₂O₄ NPs/g-C₃N₄ electrode) sensor were successfully explained in various water (river and drinking) samples and its showed high standard recoveries. Therefore, sonochemical synthetical method and fabrication of modified electrode were developed this work based on environmental analysis of NTP sensor.

Size-controllable synthesis of zinc ferrite/reduced graphene oxide aerogels: efficient electrochemical sensing of p-nitrophenol

In this study, a nonaqueous method for the synthesis of size-controlled highly crystalline zinc ferrite/reduced graphene oxide (ZFO/rGO) aerogel was provided by using benzyl alcohol as the medium. In our findings, benzyl alcohol was introduced not only as the solvent, but the structure-directing agent and strong reducing agent during the nucleation and growth of ZnFe₂O₄ nanoparticles (NPs). The characterization analysis indicated that ZnFe₂O₄ NPs were immobilized on the multilayer rGO with a controllable size of 12 nm. Moreover, the 3D ZFO/rGO aerogel shows excellent electrochemical property as a facile electrochemical sensor for the detection of p-nitrophenol (p-NP). The ZFO/rGO electrochemical sensing offers the advantages of wide linear range (1-500 μmol l^-1), excellent sensitivity (23.985 mA mM^-1 cm^-2), good stability and selectivity (<8.8%). In addition, the possible reaction mechanism of 3D ZFO/rGO aerogel was explained during the detection process under acidic condition. Significantly, our results not only provided insight into the possible reaction mechanism of 3D ZFO/rGO nanocomposite, but proposed the way for the synthesis of highly crystalline materials through a benzyl alcohol-mediated method.

Electrode Materials for Supercapacitors: A Review of Recent Advances

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Facile Solvothermal Synthesis of Hollow BiOBr Submicrospheres with Enhanced Visible-Light-Responsive Photocatalytic Performance

In this work, hierarchical hollow BiOBr submicrospheres (HBSMs) were successfully prepared via a facile yet efficient solvothermal strategy. Remarkable effects of solvents upon the crystallinities, morphologies, and microstructures of the BiOBr products were systematically investigated, which revealed that the glycerol/isopropanol volumetric ratio played a significant role in the formation of hollow architecture. Accordingly, the underlying formation mechanism of the hollow submicrospheres was tentatively put forward here. Furthermore, the photocatalytic activities of the resulting HBSMs were evaluated in detail with photocatalytic degradation of the organic methyl orange under visible light irradiation. Encouragingly, the as-obtained HBSMs with striking recyclability demonstrated excellent visible-light-responsive photocatalytic performance, which benefits from their large surface area, effective visible light absorption, and unique hollow feature, highlighting their promising commercial application in waste water treatment.

Discrimination of 1- and 2-Propanol by Using the Transient Current Change of a Semiconducting ZnFe2 O4 Chemiresistor

A semiconducting metal oxide (SMO) chemiresistor (ZnFe₂ O₄ ) is used for discriminating two isomeric volatile organic compounds (VOCs), namely 1- and 2-propanol. The transient current of the SMO chemiresistor is correlated with the aerobic oxidation of organic vapors on its surface. The changes in transient current of the ZnFe₂ O₄ chemiresistor are measured at different temperatures (260-320 °C) for detecting equal concentrations (200 ppm) of the two structural isomers of propanol. The transient current of ZnFe₂ O₄ reflects a faster oxidation of 2-propanol than 1-propanol on the surface. First-principles calculations and kinetic studies on the interaction of 1- and 2-propanol over ZnFe₂ O₄ provide further insight in support of the experimental evidence. The calculations predict more spontaneous adsorption of 2-propanol on the (111) surface of ZnFe₂ O₄ than 1-propanol. Kinetic parameters for the oxidation of isomeric vapors are estimated by modelling the transient current of ZnFe₂ O₄ using the Langmuir-Hinshelwood reaction mechanism. The faster oxidation of 2-propanol and comparatively lower activation energy for the respective process over ZnFe₂ O₄ is justified in accordance to the chemical structures of vapors. The findings have strong implications in exploring a new technique for discriminating isomeric VOCs, which is significant for environmental monitoring and medical applications.

Low-temperature H2S gas sensor based on spherical Ag3PO4-doped SnO2

An efficient method for detecting H₂S gas at low temperatures using micrometer-sized spherical Ag₃PO₄-doped SnO₂materials synthesized by hydrothermal and chemical precipitation methods is reported.

Synthesis and acetone sensing properties of ZnFe2O4/rGO gas sensors

Hollow spheres of pure ZnFe₂O₄ and of composites of ZnFe₂O₄ and reduced graphene oxide (rGO) with different rGO content were prepared via a simple solvothermal method followed by a high-temperature annealing process in an inert atmosphere. The X-ray diffraction analysis confirmed that the introduction of rGO had no effect on the spinel structure of ZnFe₂O₄. In addition, the results of field-emission scanning electron microscopy and (high-resolution) transmission electron microscopy indicated that the synthesized samples had the structure of hollow spheres distributed uniformly onto rGO nanosheets. The diameters of the spheres were determined as about 600-1000 nm. The gas sensing test revealed that the introduction of rGO improved the performance of the sensing of acetone to low concentration, and the ZnFe₂O₄/rGO composite gas sensor containing 0.5 wt % of rGO exhibited a high sensitivity in sensing test using 0.8-100 ppm acetone at 200 °C. The response of the 0.5 wt % ZnFe₂O₄/rGO sensor to 0.8 ppm acetone was 1.50, and its response to 10 ppm acetone was 8.18, which is around 2.6 times more pronounced than the response of pure ZnFe₂O₄ (10 ppm, 3.20). Moreover, the sensor showed a wide linear range and good selectivity.

Continuously Improved Photocatalytic Performance of Zn2SnO4/SnO2/Cu2O Composites by Structural Modulation and Band Alignment Modification

Improving the photocatalytic performance of multi-component photocatalysts through structural modulation and band alignment engineering has attracted great interest in the context of solar energy utilization and conversion. In our work, Zn₂SnO₄/SnO₂ hierarchical architectures comprising nanorod building block assemblies were first achieved via a facile solvothermal synthesis route with lysine and ethylenediamine (EDA) as directing agents, and then chemically etched in NaOH solution to enlarge the surface area and augment active sites. The etched Zn₂SnO₄/SnO₂ hierarchical architectures were further decorated by Cu₂O nanoparticles though an in situ chemical deposition method based on band alignment engineering. In comparison with unetched Zn₂SnO₄/SnO₂, the specific surface area of Zn₂SnO₄/SnO₂/Cu₂O hierarchical architectures became larger, and the responsive region and absorbance intensity became wider and higher in the whole visible-light range. Zn₂SnO₄/SnO₂/Cu₂O hybrid photocatalysts presented enormously improved visible-light photocatalytic behaviour for Rhodamine B (RhB) decomposition. The enhancement of photocatalytic behaviour was dominantly attributed to the synergy effect of the larger specific surface area, higher light absorption capacity, and more effective photo-induced charge carrier separation and migration. A proposed mechanism for the enormously promoted photocatalytic behaviour is brought forth on the basis of the energy-band structure combined with experimental results.

MOFs-Derived Porous NiFe2O4 Nano-Octahedrons with Hollow Interiors for an Excellent Toluene Gas Sensor

Toluene is extensively used in many industrial products, which needs to be effectively detected by sensitive gas sensors even at low-ppm-level concentrations. Here, NiFe2O4 nano-octahedrons were calcinated from NiFe-bimetallic metal-organic framework (MOFs) octahedrons synthesized by a facile refluxing method. The co-existence of p-Phthalic acid (PTA) and 3,3-diaminobenzidine (DAB) promotes the formation of smooth NiFe-bimetallic MOFs octahedrons. After subsequent thermal treatment, a big weight loss (about 85%) transformed NiFe2O4 nanoparticles (30 nm) into NiFe2O4 porous nano-octahedrons with hollow interiors. The NiFe2O4 nano-octahedron based sensor exhibited excellent gas sensing properties for toluene with a nice stability, fast response, and recovery time (25 s/40 s to 100 ppm toluene), and a lower detection limitation (1 ppm) at 260 °C. The excellent toluene-sensing properties can not only be derived from the hollow interiors combined with porous nano-octahedrons to favor the diffusion of gas molecules, but also from the efficient catalytic activity of NiFe2O4 nanoparticles.

Design, preparation and evaluation of a high performance sensor for formaldehyde based on a novel hybride nonocomposite ZnWO3/rGO

The ultrasound wave assisted synthesis of a novel ZnWO₃/rGO hybrid nono composition (ZnWO₃/rGO HNC) as a high performance sensor for formaldehyde (FA) has been reported. Different techniques of analysis such as XRD, FE-SEM, TGA, XPS, HRTEM and BET were applied for morphological and spectroscopic characterization of the ZnWO₃/rGO HNC. The sensing evaluation of the constructed sensor showed high selectivity, sensitivity and a linear correlation between achieved responses and concentration of target gas (1-10 ppm) with R² = 0.993 at temperature of 95 °C. The determination of FA was validated and performed using gas chromatography-mass spectrometry combined by solid phase micro-extraction after derivatization with O-(2,3,4,5,6-pentafluoro-benzyl)-hydroxylamine hydrochloride. Validation was carried out in terms of limit of detection linearity, precision, and recovery. The mechanistic evaluation of sensing behavior of the ZnWO₃/rGO HNC was interpreted based on large specific surface area (SSA) to volume, mesoporous structure and the heterojunction between rGO and ZnWO₃ at the interface between the rGO and ZnWO₃.

NiO/NiCo2O4 Truncated Nanocages with PdO Catalyst Functionalization as Sensing Layers for Acetone Detection

Achieving a novel structural construction and adopting appropriate catalyst materials are key to overcoming inherent limitations of gas sensors in terms of designing sensing layers. This work introduces NiO/NiCo₂O₄ truncated nanocages functionalized with PdO nanoparticles, which were proved to possess the ability of effective acetone detection. The device realized an enhanced acetone-sensing sensitivity, together with excellent selectivity and long-term stability. The sensing performance is far better than sensors based on NiO/NiCo₂O₄ solid nanocubes and NiO/NiCo₂O₄ truncated nanocages without PdO decorating, which is related to cooperative effects of the high specific surface area and efficient catalytic activity. The results provide promising metal-organic frameworks (MOFs)-derived material with the optimization of catalytic performance, demonstrating the remarkable potential for acetone sensors.

Coordination polymer-derived nano-sized zinc ferrite with excellent performance in nitro-explosive detection

Herein, a mixed metal coordination polymer, {(H₂pip)[Zn_1/3Fe_2/3(pydc-2,5)₂(H₂O)]·2H₂O} 1 {where H₂pip = piperazinediium and pydc-2,5 = pyridine-2,5-dicarboxylate}, was successfully synthesized using a hydrothermal technique. To confirm the structure and phase purity of 1, single crystals of an isomorphous pure Fe compound, {(H₂pip)[Fe(pydc-2,5)₂(H₂O)]·2H₂O} 1a, were synthesized based on similar synthetic conditions. Single crystal X-ray data of 1a confirmed the one-dimensional anionic metal-organic coordination polymer hydrogen bonded with protonated piprazine (piperazinediium) and lattice water molecules. The phase purity of 1 and 1a were confirmed via powder X-ray diffraction. Compound 1 was systematically characterized using IR, TGA, SEM, and EDX elemental mapping analysis. Compound 1 was used as a single source precursor for the preparation of nano-sized ZnFe₂O₄via thermal decomposition. The as-obtained ZnFe₂O₄ was fully characterized using PXRD, SEM, TEM, and EDX elemental mapping analysis. It was found that ZnFe₂O₄ was formed in its pure form with particle size in the nano-dimension. The aqueous dispersion of nano-sized ZnFe₂O₄ exhibits a strong emission at 402 nm upon excitation at 310 nm. This emissive property was employed for luminescence-based detection of nitroaromatic explosives in an aqueous medium through luminescence quenching for the first time. Importantly, selective detections have been observed for phenolic nitroaromatics based on differential luminescence quenching behaviour along with a detection limit of 57 ppb for 2,4,6-trinitrophenol (TNP) in water.

Hollow NiFe2O4 microspindles derived from Ni/Fe bimetallic MOFs for highly sensitive acetone sensing at low operating temperatures

A gas sensor based on hollow NiFe₂O₄ microspindles delivers unprecedentedly high sensitivity towards acetone vapor as well as good selectivity and cycling stability at a low working temperature.

Improved gas sensing properties of silver-functionalized ZnSnO3 hollow nanocubes

Porous silver-functionalized ZnSnO₃ hollow nanocubes as a gas sensor with an ultra-fast response and recovery speed for acetone detection.

The Morphologies of the Semiconductor Oxides and Their Gas-Sensing Properties

Semiconductor oxide chemoresistive gas sensors are widely used for detecting deleterious gases due to low cost, simple preparation, rapid response and high sensitivity. The performance of gas sensor is greatly affected by the morphology of the semiconductor oxide. There are many semiconductor oxide morphologies, including zero-dimensional, one-dimensional, two-dimensional and three-dimensional ones. The semiconductor oxides with different morphologies significantly enhance the gas-sensing performance. Among the various morphologies, hollow nanostructures and core-shell nanostructures are always the focus of research in the field of gas sensors due to their distinctive structural characteristics and superior performance. Herein the morphologies of semiconductor oxides and their gas-sensing properties are reviewed. This review also proposes a potential strategy for the enhancement of gas-sensing performance in the future.