Synthesis of rGO/CoFe2O4 Composite and Its Magnetorheological Characteristics

In this study, composite particles of rGO/CoFe2O4 were synthesized using a solvothermal method to fabricate a low-density magnetorheological (MR) material with enhanced sedimentation stability. The morphology and crystallographic features of rGO/CoFe2O4 were characterized via SEM, TEM, and XRD, and its magnetic properties were tested using VSM. The MR fluid was formulated by blending rGO/CoFe2O4 particles into silicone oil. Under different magnet strengths (H), a rotational rheometer was used to test its MR properties. Typical MR properties were observed, including shear stress, viscosity, storage/loss modulus, and dynamic yield stress (τdy) following the Herschel-Bulkley model reaching 200 Pa when H is 342 kA/m. Furthermore, the yield stress of the MR fluid follows a power law relation as H increases and the index changes from 2.0 (in the low H region) to 1.5 (in the high H region). Finally, its MR efficiency was calculated to be about 104% at H of 342 kA/m.

Promising photocatalytic and antimicrobial activity of novel capsaicin coated cobalt ferrite nanocatalyst

In this study, CoFe₂O₄ nanoparticles were prepared by the co-precipitation method then surface modified with Capsaicin (Capsicum annuum ssp.). The virgin CoFe₂O₄ NPs and Capsaicin-coated CoFe₂O₄ NPs (CPCF NPs) were characterized by XRD, FTIR, SEM, and TEM. The antimicrobial potential and photocatalytic degradation efficiencies of the prepared samples via Fuchsine basic (FB) were investigated. The results revealed that CoFe₂O₄ NPs have spherical shapes and their diameter varied from 18.0 to 30.0 nm with an average particle size of 25.0 nm. Antimicrobial activity was tested on Gram-positive (S. aureusATCC 52923) and Gram-negative (E. coli ATCC 52922) by disk diffusion and broth dilution methods to determine the zone of inhibition (ZOI) and minimum inhibitory concentration (MIC), respectively. UV-assisted photocatalytic degradation of FB was examined. Various parameters affecting the photocatalytic efficiency such as pH, initial concentration of FB, and dose of nanocatalyst were studied. The in-vitro ZOI and MIC results verified that CPCF NPs were more active upon Gram-Positive S. aureus ATCC 52923 (23.0 mm ZOI and 0.625 μg/ml MIC) than Gram-Negative E. coli ATCC 52922 (17.0 mm ZOI and 1.250 μg/ml MIC). Results obtained from the photocatalytic activity indicated that the maximum FB removal achieving 94.6% in equilibrium was observed using 20.0 mg of CPCF NPS at pH 9.0. The synthesized CPCF NPs were effective in the removal of FB and also as potent antimicrobial agent against both Gram-positive and Gram-negative bacteria with potential medical and environmental applications.

Hematite: A Good Catalyst for the Thermal Decomposition of Energetic Materials and the Application in Nano-Thermite

Metal oxides (MOs) are of great importance in catalysts, sensor, capacitor and water treatment. Nano-sized MOs have attracted much more attention because of the unique properties, such as surface effect, small size effect and quantum size effect, etc. Hematite, an especially important additive as combustion catalysts, can greatly speed up the thermal decomposition process of energetic materials (EMs) and enhance the combustion performance of propellants. This review concludes the catalytic effect of hematite with different morphology on some EMs such as ammonium perchlorate (AP), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenete-tranitramine (HMX), etc. The method for enhancing the catalytic effect on EMs using hematite-based materials such as perovskite and spinel ferrite materials, making composites with different carbon materials and assembling super-thermite is concluded and their catalytic effects on EMs is also discussed. Therefore, the provided information is helpful for the design, preparation and application of catalysts for EMs.

In-situ construction of Zr-based metal-organic framework core-shell heterostructure for photocatalytic degradation of organic pollutants

Photocatalysis is an eco-friendly promising approach to the degradation of textile dyes. The majority of reported studies involved remediation of dyes with an initial concentration ≤50 mg/L, which was away from the existing values in textile wastewater. Herein, a simple solvothermal route was utilized to synthesize CoFe₂O₄@UiO-66 core-shell heterojunction photocatalyst for the first time. The photocatalytic performance of the as-synthesized catalysts was assessed through the photodegradation of methylene blue (MB) and methyl orange (MO) dyes at an initial concentration (100 mg/L). Under simulated solar irradiation, improved photocatalytic performance was accomplished by as-obtained CoFe₂O₄@UiO-66 heterojunction compared to bare UiO-66 and CoFe₂O₄. The overall removal efficiency of dyes (100 mg/L) over CoFe₂O₄@UiO-66 (50 mg/L) reached >60% within 180 min. The optical and photoelectrochemical measurements showed an enhanced visible light absorption capacity as well as effective interfacial charge separation and transfer over CoFe₂O₄@UiO-66, emphasizing the successful construction of heterojunction. The degradation mechanism was further explored, which revealed the contribution of holes (h⁺), superoxide (•O₂ ^-), and hydroxyl (•OH) radicals in the degradation process, however, h⁺ were the predominant reactive species. This work might open up new insights for designing MOF-based core-shell heterostructured photocatalysts for the remediation of industrial organic pollutants.

Facile preparation of CoFe-based oxide nanosheets derived from CoFe-layered double hydroxide for the thermal catalytic decomposition of ammonium perchlorate

In this work, CoFe-based oxide nanosheets were prepared by a facile method and its catalysis effects on the thermal decomposition of ammonium perchlorate (AP) were studied. CoFe-based oxide nanosheets were obtained from hydrothermal process and high-temperature treatment of CoFe-layered double hydroxide. The samples were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The thermal catalytic decomposition of AP with CoFe-based oxide nanosheets as catalysts was investigated by differential scanning calorimetry and coupling Fourier transform infrared spectrometer. The results showed that the CoFe-based oxide samples with the width size of 200–300 nm and the thickness size of ∼10 nm show the inherent catalytic ability. With 10 wt% of CoFe-based oxide nanosheets added, the decomposition temperature of AP was reduced by 127.5 °C from 431.0 °C to 303.5 °C. The apparent activation energy was decreased by 61.1 kJ/mol from 177.3 kJ/mol of raw AP to 116.2 kJ/mol of AP with 10 wt% of CoFe-based oxide nanosheets added. The thermal catalysis decomposition mechanism of AP with CoFe-based oxide nanosheet material promoting was proposed. This work offered a novel idea toward preparation and application of functional material layered double hydroxide in the field of energetic materials.

Comparative Study on Thermal Response Mechanism of Two Binders during Slow Cook-Off

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the changes of colors and the intensity of infrared characteristic peaks were designed to characterize the differences in the thermal response mechanisms of the HTPB and HTPE binder systems. As a solid phase filler to accidental ignition, the weight loss and microscopic morphology of AP (30~230 °C) were observed by TG and SEM. The defects of the propellant caused by the cook-off were quantitatively analyzed by the box counting method. Above 120 °C, the HTPE propellant began to melt and disperse in the holes, filling the cracks, which generated during the decomposition of AP at a low temperature. Melting products were called the “high-temperature self-repair body”. A series of analyses proved that the different thermal responses of the two binders were the main cause of the slow cook-off results, which were likewise verified in the propellant mechanical properties and gel fraction test. From the microscopic point of view, the mechanism of HTPE’s slow cook-off performance superior to HTPB was revealed in this article.

Facile synthesis of MgCo2O4 nanosheets and its catalysis effect on the decomposition of ammonium perchlorate

The catalysis effects of MgCo2O4 nanosheets on the thermal decomposition of ammonium perchlorate (AP) were investigated. The MgCo2O4 nanosheets were synthesized with a facile free-template hydrothermal method. The chemical structure and micro morphology of MgCo2O4 nanosheets were characterized. Moreover, the catalysis thermal decomposition properties of AP using composite metal oxides MgCo2O4 nanosheets with different contents (1wt%, 3wt%, and 5wt%) as catalysts were investigated. The results showed that the reducing decomposition temperature of AP was 155.9 °C from 431 °C to 275.1 °C with 5wt% MgCo2O4 added. The heat release of AP was increased of 907 J/g at least. In addition, the catalysis thermal decomposition mechanism of AP with the existence of MgCo2O4 nanosheets was explained. With the increasing temperature, the accumulated electrons (e-) and holes (h+) excited was activated at the surface of MgCo2O4 nanosheets, which accelerated H transfer from H atom of NH4+ to O atom of ClO4- and boosted AP decomposition.

An efficient and magnetically recoverable g-C3N4/ZnS/CoFe2O4 nanocomposite for sustainable photodegradation of organic dye under UV-visible light illumination

Effective improvement of an easily recoverable photocatalyst is equally vital to its photocatalytic performance from a practical application view. The magnetically recoverable process is one of the easiest ways, provided the photocatalyst is magnetically strong enough to respond to an external magnetic field. Herein, we prepared graphitic carbon nitride nanosheet (g-C₃N₄), and ZnS quantum dots (QDs) supported ferromagnetic CoFe₂O₄ nanoparticles (NPs) as the gC₃N₄/ZnS/CoFe₂O₄ nanohybrid photocatalyst by a wet-impregnation method. The loading of CoFe₂O₄ NPs in the g-C₃N₄/ZnS nanohybrid resulted in extended visible light absorption. The ferromagnetic g-C₃N₄/ZnS/CoFe₂O₄ nanohybrid exhibited better visible-light-active photocatalytic performance (97.11%) against methylene blue (MB) dye, and it was easily separable from the aqueous solution by an external bar magnet. The g-C₃N₄/ZnS/CoFe₂O₄ nanohybrid displayed excellent photostability and reusability after five consecutive cycles. The favourable band alignment and availability of a large number of active sites affected the better charge separation and enhanced photocatalytic response. The role of active species involved in the degradation of MB dye during photocatalyst by g-C₃N₄/ZnS/CoFe₂O₄ nanohybrid was also investigated. Overall, this study provides a facile method for design eco-friendly and promising g-C₃N₄/ZnS/CoFe₂O₄ nanohybrid photocatalyst as applicable in the eco-friendly dye degradation process.

Effect of Graphene Concentration on the Electrochemical Properties of Cobalt Ferrite Nanocomposite Materials

A two-step process was applied to synthesize the cobalt ferrite-graphene composite materials in a one-pot hydrothermal reaction process. Graphene Oxide (GO) was synthesized by a modified Hummer's method. The synthesized composite materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). The XRD and FTIR results were in good agreement with the TGA/DTG observations. SEM and TEM disclosed the spherical shape of the nanoparticles in 4-10 nm. The optimized CoFe2O4-G (1-5 wt.%) composite materials samples were tried for their conductivity, supercapacity, and corrosion properties. The CV results demonstrated a distinctive behavior of the supercapacitor, while the modified CoFe2O4-G (5 wt.%) electrode demonstrated a strong reduction in the Rct value (~94 Ω). The highest corrosion current density valves and corrosion rates were attained in the CoFe2O4-G (5 wt.%) composite materials as 5.53 and 0.20, respectively. The high conductivity of graphene that initiated the poor corrosion rate of the CoFe2O4-graphene composite materials could be accredited to the high conductivity and reactivity.

Improving safety and thermal decomposition performance by the in situ synthesis of core–shell structured ammonium perchlorate/cobalt acetate hydroxide composites

The AP/Co₃(CH₃COO)₅(OH) composites of the core–shell structure were prepared, the safety and thermal decomposition properties of AP were improved simultaneously, and the possible catalytic mechanism was analyzed.

Nanohybrids of reduced graphene oxide and cobalt hydroxide (Co(OH)2|rGO) for the thermal decomposition of ammonium perchlorate

The catalytic activity of nanoparticles of cobalt hydroxide supported on reduced graphene oxide, Co(OH)₂|rGO, was studied for the decomposition of ammonium perchlorate (AP), the principal ingredient of composite solid propellants. Co(OH)₂|rGO was synthesized by an in situ reduction method, which avoided the application of extremely high temperatures and harsh processes. rGO stabilized the nanoparticles effectively and prevented their agglomeration. The performance of Co(OH)₂|rGO as a catalyst was measured by differential scanning calorimetry. Co(OH)₂|rGO affected the high-temperature decomposition (HTD) of AP positively, decreasing the decomposition temperature of AP to 292 °C, and increasing the energy release to 290 J g^-1. The diminution of the HTD of AP by Co(OH)₂|rGO is in between the best values reported to date, suggesting its potential application as a catalyst for AP decomposition.

Cellulose derived carbon nanofiber: A promising biochar support to enhance the catalytic performance of CoFe2O4 in activating peroxymonosulfate for recycled dimethyl phthalate degradation

We prepared carbon nanofiber (CCNF) using cellulose as the carbon source in this study and utilized for the first time as the support to enhance the catalytic performance of the cobalt ferrite (CoFe₂O₄) for peroxymonosulfate (PMS) activation. The catalytic capability of the CoFe₂O₄/CCNF nanocomposites activated PMS was investigated through degrading dimethyl phthalate (DMP), a classical organic pesticide pollutant, in water media. The influence factors like CCNF content, nanocomposite and PMS dosage, DMP content, and pH value on the degradation speed were systematically investigated and analyzed. Since CoFe₂O₄ is a spinel structured molecule which is magnetically separable, the reusability of the prepared CoFe₂O₄/CCNF nanocomposites under multiple cycles was also tested. Besides, the degradation intermediates during the catalytic process were also analyzed and identified by liquid chromatography-mass spectrometry (LC-MS) with a possible degradation mechanism. The results indicated that the prepared nanocomposite had promising catalytic capability in degrading DMP, in which the SO₄^- radicals played the main role as the active oxidation agent. Furthermore, the CoFe₂O₄/CCNF nanocomposites exhibited very good stability and reusability. The present study provides a clean biochar supported catalyst which could readily enhance the PMS activation efficiency for recycled decontamination of refractory organic pollutants in water media.

Facile green synthetic graphene-based Co-Fe Prussian blue analogues as an activator of peroxymonosulfate for the degradation of levofloxacin hydrochloride

A kind of Co-Fe Prussian blue analogues (Co-Fe PBAs), cobalt hexacyanoferrate Co₃[Fe(CN)₆]₂, and graphene oxide (GO) were combined to synthesize magnetically separable Co-Fe PBAs@rGO nanocomposites through a simple two-step hydrothermal method. The crystalline structure, morphology and textural properties of the Co-Fe PBAs@rGO nanocomposites were characterized. The catalytic performance of the nanocomposites was evaluated by PMS activation, with Levofloxacin Hydrochloride (LVF) as the target contaminant. Synergistic interactions between the Co-Fe PBAs and rGO prevented the aggregation of the Co-Fe PBAs nanoparticles, which resulted in enhanced degradation efficiencies. The influence of several critical parameters was investigated, including the reaction temperature, PMS and Co-Fe PBAs@rGO catalyst concentrations, solution pH and salt content. LVF degradation was favored at higher catalyst and PMS concentrations, high temperatures, and in neutral or weak acidic solutions. Sulphate radicals were the dominant active species in the Co-Fe PBAs@rGO/PMS system. In addition, the Co-Fe PBAs@rGO exhibited no significant decrease in LVF degradation efficiency following five catalytic cycles. Thus, the as-prepared Co-Fe PBAs@rGO nanocomposite catalyst might be applied to the removal of hard-to-degrade organics owing to its high catalytic ability to activate PMS, as well as its good reusability and recyclability.

Intuitionistic study on the critical decomposition energy of ammonium perchlorate by SEM

Critical decomposition energy of ammonium perchlorate based on SEM images.