Flower-like Co3O4 Research Articles

Redox behavior in hydrothermally synthesized thistle flower-like Co3O4–NiO-GO composite for advanced supercapacitor electrodes

The advancement in carbon derivatives has significantly boosted the efficacy of recently produced electrodes designed for energy storage applications. Utilizing the hydrothermal technique, conductive single and composite electrodes comprising Co3O4–NiO-GO were synthesized and utilized in supercapacitors within three-electrode systems. The Co3O4–NiO-GO composite electrode demonstrated better rate capability and excellent long-term reliability, as well as a noteworthy energy density at comparatively large power levels. The Co3O4–NiO-GO hybrid electrode had an ideal capacitance of 986.5 F/g at an applied current density of 1 A/g, according to the data. Furthermore, after 5000 cycles, this composite electrode displayed an outstanding cycling stability of 90.4 %. The results indicate that the combined electrode surpasses individual metallic oxide electrodes, with the addition of graphene oxide contributing to the improved performance. When the efficiency of the three samples was evaluated, it was clear that this Co3O4–NiO-GO electrode outperformed the GO/Co3O4 and GO/NiO electrodes. This improvement can be due to the composite electrode's synergistically impact from Co3O4, NiO, and GO.

Chemical vapor deposition-grown single-layer graphene-supported nanostructured Co3O4 composite as binder-free electrode for asymmetric supercapacitor and electrochemical detection of caffeic acid

In this study, we developed a monolayer graphene/nanostructured cobalt oxide (MLG/Co3O4) composite for asymmetric supercapacitor and electrochemical sensor applications. The MLG was grown by chemical vapor deposition process and the Co3O4 nanostructures were electrodeposited on the MLG surface. Scanning electron microscopy proved that there were flower-like nanostructured Co3O4 densely electrodeposited on the MLG surface. At a current density of 3 mA cm−2, the MLG/Co3O4 composite produced an areal capacitance of 3.73 F cm−2. After 10,000 cycles, the composite electrode still had 93.6 % of its initial capacitance at 5 mA cm−2. The asymmetric system displayed an areal capacitance of 929 mF cm−2 at 4 mA cm−2 with good cycle stability. The asymmetric electrode produced a specific energy of 51 μWh cm−2 and a specific power of 11.1 mW cm−2. Cyclic voltammetric measurements demonstrated that the composite showed redox peaks at 0.48 eV and 0.09 eV toward the determination of CA. With a sensitivity of 0.13 µA/µM/cm2 and a limit of detection of 0.009 µM, the composite showed CA concentrations, ranging from 0.5 to 480 M. The composite displayed excellent selectivity and the current produced for the interfering compounds was exceedingly low. Using the composite electrode, the spiked CA in red wine and green tea samples recovered remarkably effectively.

Morphology engineering of Co3O4 spinel for efficient oxidation of lean methane at low temperature

Nowadays, the development of high-performance non-noble metal catalysts is an important research direction for controlling methane emissions from liquefied natural gas (LNG)-powered vehicles and vessels, and Co3O4 spinel has attracted great attention. In this work, Co3O4 catalysts with different morphologies (flower, sheet, particle, and cube) were synthesized by hydrothermal method and their catalytic performance was evaluated. The results showed that the flower-like Co3O4 (Co3O4-F) catalyst exhibited the highest activity in the lean methane oxidation with the T90 (temperature at the methane conversion of 90%) of 365 °C. Compared to other catalysts, Co3O4-F contained an amount of Co3+ sites and the weakest Co3+-O bond, which facilitated the extraction of active lattice oxygen and the initial oxidation of methane to intermediate products (formate and -COO-) on the catalyst surface. Meanwhile, the abundant oxygen vacancies on the surface of the Co3O4 catalyst could efficient activate O2 to form active oxygen species, which promoted the oxidation of intermediate products to CO2 and H2O. The methane oxidation over the Co3O4-F was confirmed to conform with Mars-van Krevelen mechanism. This work provides a facile way to enhance the methane oxidation activity of Co3O4 catalysts by modulating the morphology.

Fabrication of nitrogen-doped reduced graphene oxide/tricobalt tetraoxide composite aerogels with high efficiency, broadband microwave absorption, and good compression recovery performance

The fabrication of advanced graphene-based microwave absorbing materials with thin thickness, wide bandwidth, strong absorption strength, and low filling ratio remains a huge challenge. In this paper, nitrogen-doped reduced graphene oxide/tricobalt tetraoxide (NRGO/Co3O4) composite aerogels were synthesized by a three-step method of solvothermal reaction, high-temperature calcination, and hydrothermal self-assembly. The results showed that the attained NRGO/Co3O4 composite aerogels had a unique three-dimensional porous network structure, extremely low bulk density, and good compression recovery. Furthermore, the effect of the addition amounts of flower-like Co3O4 on the complex dielectric constant and microwave absorption properties of NRGO/Co3O4 composite aerogels was investigated. When the addition amount of Co3O4 was equal to 15 mg, the prepared binary composite aerogel showed the strongest absorption strength of –62.78 dB and a wide absorption bandwidth of 5.5 GHz at a thin thickness of 2.13 mm and a low filling ratio of 15 wt.%. It was worth noting that the maximum absorption bandwidth could reach 6.32 GHz (11.68–18 GHz, spanning the entire Ku-band) at a thickness of 2.24 mm. In addition, the possible microwave absorption mechanism of NRGO/Co3O4 composite aerogels was also proposed. Therefore, this paper will provide a new and simple strategy for preparing RGO-based porous nanocomposites as lightweight, efficient, and broadband microwave absorbers.

Cobalt Oxide 2D Nanosheets Formed at a Polarized Liquid|Liquid Interface toward High-Performance Li-Ion and Na-Ion Battery Anodes.

Cobalt oxide (Co3O4)-based nanostructures have the potential as low-cost materials for lithium-ion (Li-ion) and sodium-ion (Na-ion) battery anodes with a theoretical capacity of 890 mAh/g. Here, we demonstrate a novel method for the production of Co3O4 nanoplatelets. This involves the growth of flower-like cobalt oxyhydroxide (CoOOH) nanostructures at a polarized liquid|liquid interface, followed by conversion to flower-like Co3O4 via calcination. Finally, sonication is used to break up the flower-like Co3O4 nanostructures into two-dimensional (2D) nanoplatelets with lateral sizes of 20-100 nm. Nanoplatelets of Co3O4 can be easily mixed with carbon nanotubes to create nanocomposite anodes, which can be used for Li-ion and Na-ion battery anodes without any additional binder or conductive additive. The resultant electrodes display impressive low-rate capacities (at 125 mA/g) of 1108 and 1083 mAh/g, for Li-ion and Na-ion anodes, respectively, and stable cycling ability over >200 cycles. Detailed quantitative rate analysis clearly shows that Li-ion-storing anodes charge roughly five times faster than Na-ion-storing anodes.

MOF-derived flower-like Fe-doped Co3O4 porous hollow structures with enhanced n-butanol sensing properties at low temperature

Metal oxide-based gas sensors are widely used in the detection of toxic and harmful gases due to their advantages of high precision, convenient use and stable performance, but their application range is limited due to the high working temperature. In this work, MOF-derived flower-like Fe-doped Co3O4 porous hollow structures are obtained using a simple solvothermal method. The obtained samples are characterized in terms of their crystalline structure, morphology, chemical composition, optical properties and specific surface area. This study systematically investigates the sensing performance of pristine and Fe-doped Co3O4 samples. The results show that the 2 at% Fe-Co3O4 sample has the best n-butanol sensing properties. This sample exhibits high response and rapid response/recovery speed at a low working temperature of 110 °C, as well as good repeatability and anti-humidity features. The enhanced sensing properties can be attributed to several factors, including the adjustment of baseline resistance, increase in oxygen vacancies, decrease in bandgap, and the formation of unique hollow and porous structures. Overall, this work provides valuable insights into the potential applications of Fe-doped Co3O4 materials in sensing technologies.

Enhanced CO oxidation performance over hierarchical flower-like Co3O4 based nanosheets via optimizing oxygen activation and CO chemisorption

Enhancing low-temperature activity is a focus for carbon monoxide (CO) elimination by catalytic oxidation. In this work, the hierarchical flower-like silver (Ag) modified cobalt oxides (Co3O4) nanosheets were prepared by solvothermal method and applied into catalytic CO oxidation. The doped Ag species in the form of AgCoO2 induced the prolongated surface Co–O bond and weaker bond intensity. Consequently, the oxygen activation/migration ability and redox capacity of Ag0.02Co were enhanced with more oxygen vacancies. The chemisorbed CO was preferentially converted to CO2 but not carbonates. The inhibited carbonates accumulation could avoid the coverage of active sites. According to Density functional theory (DFT) calculations, the electron transfer from AgCoO2 to Co3O4 promote electron donation ability of Co3O4 layer, benefiting for oxygen activation. Moreover, the longer Co–C and C–O bond length suggest the weakened chemisorption strength and higher active of CO molecule. The Ag modified Co3O4 exhibited more satisfactory activity at lower temperature. Typically, it realized 100% CO conversion at 90 °C, and displayed 6.3-fold higher reaction rate than pristine Co3O4 at 40 °C. Moreover, the Ag0.02Co exhibited outstanding long-term stability and water resistance. In summary, the optimized oxygen activation, CO chemisorption and interfacial electron transfer synergistically boosted the CO oxidation activity on Ag modified Co3O4.

Interface Manipulation of Composite Solid Polymer Electrolyte with Polydopamine to Construct Durable and Fast Li+ Conduction Pathways

Taking advantage of light weight, flexibility, and flame retardancy, solid polymer electrolytes (SPEs) provide a feasible solution to these safety concerns and to the enhancement of energy density for lithium-ion batteries (LIBs). However, the development of SPEs is still restricted by low ionic conductivity. Herein, we develop a type of SPE filler built by flower-like Co3O4 microspheres as a lithiophilic backbone and polydopamine (PDA) as a multifunctional coating for the engineering of the interphase properties of the polyether-based SPEs. The hierarchical structure of Co3O4 affords large interfacial contact area with SPEs and effectively suppresses the regular crystallinity of poly(ethylene oxide) (PEO) segments. Moreover, the PDA coating layers with diverse surface functionalities serve as a versatile mediator to finely tune ionic distribution and transport behavior via multiple Lewis acid–base interactions. We uncover the interphase characterizations and their synergistic effects to enhance Li+ conductivity and mechanical/electrochemical stability. This study provides intriguing alternatives for developing composite solid polymer electrolytes (CPEs), for which we further demonstrate the potential application of Co3O4@PDA-based CPEs in all-solid-state LIBs.

Facile Synthesis of MOF-Derived Hierarchical Flower-Like Sr-Doped Co3O4 Structure for Effective TEA Sensing

Metal-organic framework (MOF)-derived metal oxide semiconductors (MOSs) have drawn great attention because of their abundant pore structures, large surface area, and good gas accessibility. Herein, hierarchical flower-like Sr-doped cobalt oxide (Co3O4) structure is obtained utilizing MOF as a self-sacrificing template. Compared with undoped Co3O4, the 2 mol% Sr-doped Co3O4 shows better triethylamine (TEA) sensing performance. It exhibits not only high response values of 52 (the response of undoped Co3O4 are about 3.3) and short response/recovery time (40/58 s) to 100 ppm TEA at a low working temperature of 160 °C, but also excellent selectivity and long-term stability, which show that the as-obtained flower-like Sr-doped Co3O4 structure is an effective material to detect TEA gas. The enhanced sensing properties are attributed to the synergistic effect of the creation of more oxygen vacancies and larger surface area of flower-like structure.

In situ construction of a flower-like Z-scheme Co3O4/CoO heterostructure with superior photoelectrocatalytic performance

Photoelectric catalytic oxidation (PEC) is a promising strategy to degrade antibiotic refractory pollutants into CO2 and H2O. A flower-like Co3O4/CoO catalyst with tight interfacial contact was constructed by the in-situ reduction of a part of CoO from the flower-like Co3O4 surface. The Co3O4/CoO heterostructure was fully characterized, and its PEC performance was investigated. The removal rate of tetracycline (TC) by Co3O4/CoO was 98.2% within 150 min, which was nearly 1.5 and 2.0 times those of Co3O4 and CoO, respectively. The significant improvement of Co3O4/CoO was attributed to the establishment of the built-in electric field on the heterojunction contact interface, which accelerated the charge transfer in the interface. Meanwhile, the significant synergistic effect between the electrocatalytic and photocatalytic processes in PEC, with a synergistic factor reaching 3.7, realized the spatial separation of charge carriers and generated more active species that participate in TC degradation. Density functional theory (DFT) calculations and electron paramagnetic resonance (ESR) results proved that the charge transfer mechanism followed the Z-scheme heterojunction structure. Furthermore, two possible degradation pathways of TC were proposed by liquid chromatography-mass spectrometry. This work provided a promising catalyst for removing antibiotic pollutants.

Tunable microwave absorption and shielding effectiveness in the nanocomposite of 3D hierarchical flower-like Co3O4 and rod-like polyindole

• 3D hierarchical composites of Co 3 O 4 /polyindole/paraffin were successfully prepared. • Electromagnetic properties of composites improved as the Co 3 O 4 /PIn ratio increased. • A 25 wt% Co 3 O 4 /PIn paraffined composite achieve RL = −21.5 dB and EAB = 3.5 GHz. • Total shielding effectiveness ( SE T ) was increased by the increase of Co 3 O 4 /PIn. • SE T of 25 wt% Co 3 O 4 /PIn paraffined composite was four times higher than 5 wt% one. Due to the rapid development of wireless electronic devices, achieving an excellent microwave absorber is crucial in modern life. The composite of flower-like Co 3 O 4 and rod-like polyindole (PIn) was embedded in the paraffin matrix for tunable microwave absorption performance and shielding effectiveness. Investigation of microwave absorption features of Co 3 O 4 /PIn paraffined composites in the X band frequency range revealed a good performance for 25 wt% Co 3 O 4 /PIn paraffined composite with reflection loss and an effective absorption bandwidth of −21.5 dB and 3.5 GHz (covered ∼ 83% X band). The pretty good microwave absorption performance of this composite originated from magnetic loss (by Co 3 O 4 ), dielectric loss (by PIn), and heat transfer capability (by paraffin). Shielding effectiveness was also increased with the increase of Co 3 O 4 /PIn loading percentage, with a total shielding effectiveness of 28.1 dB with the most contribution from shielding effectiveness for absorption. This work provides an easy and low-cost approach for tunable microwave absorption and shielding effectiveness for practical applications.

The Flower-like Co3O4 Hierarchical Microspheres for Methane Catalytic Oxidation

The development of non-noble Co3O4 catalysts exposing highly active crystal planes to low-temperature methane oxidation is still a challenge. Hence, a facile solvothermal method was adapted to construe flower-like Co3O4 hierarchical microspheres (Co3O4-FL), which are composed of nanosheets with dominantly exposed {112} crystal planes. The flower-like hierarchical structure not only promotes the desorption of high levels of active surface oxygen and enhances reducibility, but also facilitates an increase in lattice oxygen as the active species. As a result, Co3O4-FL catalysts offer improved methane oxidation, with a half methane conversion temperature (T50) of 380 °C (21,000 mL g−1 h−1), which is much lower than that of commercial Co3O4 catalysts (Co3O4-C). This study will provide guidance for non-noble metal catalyst design and preparation for methane oxidation and other oxidative reactions.

Robust and selective electrochemical sensing of hazardous photographic developing agents using a MOF-derived 3D porous flower-like Co3O4@C/graphene nanoplate composite

Here we present a facile, rapid and reliable electrochemical sensor for quantitative analysis of hazardous photographic developing agents, including metol (MT), hydroquinone (HQ) and catechol (CC). They have been identified as usual contaminants in environment and water samples. This sensor is based on a nanocomposite of three-dimensional (3D) porous flower-like Co3O4@C hybrid and graphene nanoplates (Co3O4@C/GNP). The Co3O4@C/GNP compoiste is prepared by a two-steps procedure, consisting of the composite synthesis of a Co-MOF precursor and GNPs in the first step and subsequently direct calcination process in the N2 atmosphere. The morphology, composition, and electrochemical behavior of the Co3O4@C/GNP composite is characterized by using microscopic methods and electrochemical techniques, revealing its 3D porous structure, abundant pores, a large electrode active area, a high conductivity, outstanding electrocatalytic and sensing performance toward MT, HQ, and CC. Taking advantages of a huge electroactive surface area and a fast electron transfer rate of GNPs and strong electrical catalytic ability of the Co3O4@C hybrid, the fabricated Co3O4@C/GNP sensor displays high sensitivity for quantitative analysis of MT, HQ and CC. Their detection limits are as low as 5.1, 14.7 and 169 nM (S/N = 3), respectively. Beyond that, the proposed Co3O4@C/GNP electrochemical sensor shows strong reproducibility, good stability and selectivity in the voltammetric quantitation of these analytes. It has been also successfully applied in measuring these photographic developing agents in water environment. Consequently, the fabricated Co3O4@C/GNP composite is expected to be an excellent electrode material in the applications of electrochemical sensing.

Preparation of flower-like Co3O4 QDs/Bi2WO6 p-n heterojunction photocatalyst and its degradation mechanism of efficient visible-light-driven photocatalytic tetracycline antibiotics

A novel flower-like Co3O4 QDs/Bi2WO6 p-n heterostructure photocatalyst was prepared by hydrothermal and ultrasonic synthesis strategies with uniformly dispersing zero-dimensional (0D) Co3O4 QDs on the three-dimensional (3D) flower-like Bi2WO6 nanosheets. The structural morphology and optical properties analysis confirmed the successful combination of the Co3O4 QDs/Bi2WO6 composite photocatalyst. Photodegradation experiments results proved that 10%-Co3O4 QDs/Bi2WO6 showed the optimum rate constant (0.017 min−1) for the degradation of TC, which was about 3.40 and 1.55 times higher than Co3O4 QDs (0.005 min−1) and Bi2WO6 (0.011 min−1), respectively. The significant improvement in the photocatalytic performance of Co3O4 QDs/Bi2WO6 was mainly attributed to the enhancement of visible light absorption capacity and the formation of p-n heterojunction, which effectively inhibited the recombination of electron/holes (e-/h+) pairs. Radical trapping experiments and electron spin resonance (ESR) spectrum demonstrated that O2– radicals were the leading active species in photocatalytic degradation. Furthermore, three-dimensional excitation-emission matrix fluorescence spectra (3D EEMs) and Liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOF MS) techniques results revealed the degradation pathway and mechanism of efficient visible-light-driven photocatalytic tetracycline antibiotics. The outstanding photocatalytic performance makes the 0D/3D Co3O4 QDs/Bi2WO6 p-n heterojunction photocatalyst a promising photocatalyst for the degradation of tetracycline antibiotics.

Metal-organic framework-derived hierarchical flower-like Mo-doped Co3O4 for enhanced triethylamine sensing properties

Metal-organic frameworks (MOFs) derived oxide semiconductors have drawn more and more attention in many fields due to their unique structural merits. Herein, hierarchical flower-like Mo-doped Co3O4 derived Co-MOF has been synthesized through a solvothermal method and following annealing process. The gas sensing measurements show that the sensing properties of Mo-doped Co3O4 sample are far superior than that of pure Co3O4. In particular, 1 at% Mo-doped Co3O4 sample exhibits high response values of 92–50 ppm TEA at 180 °C, which are about 46 times than that of pure Co3O4 sample. In addition, it shows short recovery time (33 s), excellent gas selectivity, good repeatability and long-term stability. The improved gas sensing performance can be ascribed to Mo doping and hierarchical flower-like microstructure.

Fabrication of novel flower-like Co3O4/g-C3N4 heterojunction for tetracycline degradation under visible light irradiation

In this paper, the flower-like Co3O4/g-C3N4 heterojunction was successfully synthesized via a facile hydrothermal method, and characterized by XRD, SEM, TEM, UV–Vis DRS, PL and BET technologies. In Co3O4/g-C3N4 heterojunction, the g-C3N4 presents a graphene-like nanosheet structure, and lts surfaces were deposited with flower-like Co3O4. DRS evidences that the light absorption of the Co3O4/g-C3N4 heterojunction shifted to red. PL shows that the effective separation of charge carriers was significantly enhanced, which is due to the construction of P-N heterojunction. Moreover, using TC as a simulated pollutant, the asprepared Co3O4/g-C3N4-3% shows a excellent photocatalytic performance that the degradation rate of TC could reach to 85.32% after 120 min of visible light irradiation. This paper provides a new exemplification of constructing heterojunction microstructures for high-efficiency photocatalytic removing tetracycline pollutants.

Bimetallic metal–organic frameworks derived hierarchical flower-like Zn-doped Co3O4 for enhanced acetone sensing properties

Metal-organic frameworks (MOFs) derived metal oxides, as a promising gas-sensing material, have received extensive attention because of its unique advantages of abundant pore structures, high surface areas and diverse compositions. In this work, hierarchical flower-like Zn-doped Co3O4 derived from Zn/Co-MOF is prepared through a process of solvothermal synthesis and annealing. 3 mol% Zn-doped Co3O4 exhibits the highest response of 52.3 toward 100 ppm acetone at 200 °C, which is nearly 20 times higher than that of pure Co3O4. Additionally, 3 mol% Zn-doped Co3O4 based sensor displays a ppb-level detection limit for acetone, outstanding selectivity, excellent long-term stability and good independence to humidity. The probable reasons for the improved sensing properties are attributed to the changes of carrier concentration, specific surface area and chemisorbed oxygen amount due to Zn doping.

Catalytic combustion of volatile organic compounds (VOCs) over structured Co3O4 nano-flowers on silicalite-1/SiC foam catalysts

This work presents a simple method for the preparation of structured Co3O4 supported on silicalite-1/SiC foam catalyst (i.e., [email protected]/SiC), and its application to catalytic combustion of volatile organic compounds (VOCs, isopropanol as the model compound). The growth mechanism of Co3O4 on silicalite-1/SiC catalysts were systematically studied as a function of synthesis time based on comprehensive characterization using N2 adsorption-desorption analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), H2 temperature programmed reduction (H2-TPR) and X-ray photoelectron spectra (XPS). It was found that Co2SiO4 nano-sheets were formed within/on silicalite-1 coating at the initial stage of synthesis, which was further transformed into flower-like Co3O4 nano crystals on the surface of silicalite-1/SiC. The developed structured catalyst, especially the one prepared by the 40 h synthesis, i.e., [email protected]/SiC-40 h, combined high oxygen mobility, Co3+/Co2+ redox couple and improved adsorbed oxygen species, and exhibited excellent performance in complete thermocatalytic combustion of isopropanol.

Degradation of an imidazolium-based ionic liquid in water using monopersulfate catalyzed by Dahlia flower-like cobalt oxide

As the imidazolium-based ionic liquid (IL), 1-Butyl-3-methylimidazolium chloride (BMIMCl), is increasingly employed in various applications, release of BMIM cation into the environment has posed serious threats on aquatic ecology. Thus, it is imperative to eliminate BMIM from water, and, among various techniques for eliminating BMIM, chemical oxidation is the most effective technique. Nevertheless, studies of using SO4−-based chemical oxidation methods for degrading BMIM are still very limited; thus this study aims to develop an effective SO4−-based chemical oxidation process for degrading BMIM. As monopersulfate (MPS) is employed as a source of SO4−, a special cobalt (Co)-based catalyst is proposed and developed here by fabricating Co3O4 into a unique Dahlia flower-like morphology. Such a Dahlia flower-like Co3O4 (DFCoO) not only can exhibit the flower configuration, but also its floral petal components can consist of many filament-like Co3O4 nanostructures, making this DFCoO possess several advantageous properties over the conventional Co3O4 nanoparticle (NP), including higher redox activity, more reactive surface, higher surface area and larger pore volume. Thus, DFCoO shows a much higher catalytic activity than Co3O4 NP to activate MPS for degrading BMIM. A higher MPS dosage and reaction temperature also enhance BMIM degradation by DFCoO + MPS. DFCoO is reusable for activating MPS to degrade BMIM over multiple cycles. BMIM degradation mechanism and pathway by this DFCoO + MPS is also elucidated by identifying radical species and degradation intermediates. The findings of this study offer an useful approach for developing an advantageous catalyst for sulfate-based degradation of BMIMCl.

Flower-like Co3O4 sensor with rich oxygen vacancy defects for enhancing room temperature NOx sensing performances

Flower-like Co3O4 microspheres (Co3O4-f) composed of thin nanosheets with a thickness about 5 nm were successfully synthesized with a simple solvothermal method and a subsequent calcination method. The sample microstructures and morphologies were characterized by XRD, FT-IR, TEM and EPR. The gas sensitivity test results showed that Co3O4-f exhibited a higher response (72.3%) to 100 ppm NOx and a lower detection limit (less than 70 ppb), which was about twice that of Co3O4 nanoparticles (Co3O4-p). Such outstanding gas sensing performance inherent in Co3O4-f may be attributed to its flower-like structure assembled from thin nanosheets, a large amount of chemisorption oxygen, and oxygen vacancies on the Co3O4-f surface. The mechanism for enhanced gas response and its wide range of applications are discussed in detail in this paper.