Novel in situ synthesis of copper nanoparticles supported on reduced graphene oxide and its application as a new catalyst for the decomposition of composite solid propellants

Can graphene improve the thermal conductivity of copper nanofluids?

Copper (Cu) nanofluids (NFs) have attracted attention due to their high thermal conductivity, which has conferred a wide variety of applications. However, their high reactivity favors oxidation, corrosion and aggregation, leading them to lose their properties of interest. Copper capped by graphene (Cu@G) core@shell nanoparticles (NPs) have also attracted interest from the medical and industrial sectors because graphene can shield the Cu NPs from undesired phenomena. Additionally, they share some properties that expand the range of applications of Cu NFs. In this work, new Morse potentials are reported to reproduce the behavior of Cu@G NPs through molecular dynamics. Coordination-dependent Morse parameters were fitted for C, H, and Cu based on density functional theory calculations. Then, these parameters were implemented to evaluate the thermal conductivity of Cu@G NFs employing the Green-Kubo formalism, with NPs from 1.5 to 6.1 nm at 100 to 800 K, varying the size, the number of layers and the orientation of the graphene flakes. It was found that Cu@G NFs are stable and have an improved thermal conductivity compared to the Cu NFs, being 3.7 to 18.2 times higher at 300 K with only one graphene layer and above 26.2 times higher for the graphene-trilayered NPs. These values can be higher for temperatures below 300 K. Oppositely, the size, homogeneity and orientations of the graphene flakes did not affect the thermal conductivity of the Cu@G NFs.

Dense, Three-Dimensional, Highly Absorbent, Graphene Oxide Aerogel Coating on ZnCo2O4/ZnO Particles Exerts a Synergistic Catalytic Effect for Ammonium Perchlorate Thermal Decomposition

As a new type of carbon material, graphene oxide aerogel (GA) is widely used in catalysis due to its porous structure, high-efficiency adsorption, and superb conductivity. In this study, GA was prepared into a dense coating layer surrounding ZnCo₂O₄/ZnO particles to form a composite GA-ZnCo₂O₄/ZnO by means of a hydrothermal, blast drying, and vacuum-freeze-drying approach applied to catalyze the thermal decomposition of ammonium perchlorate (AP). The physicochemical properties of the obtained GA-ZnCo₂O₄/ZnO were characterized by different analytical methods. Scanning electron microscopy (SEM) analysis exhibited that GA is coated on the surface of ZnCo₂O₄/ZnO, forming a dense layer. Brunner Emmet Teller (BET) measurement results show that GA-ZnCo₂O₄/ZnO has a smooth macropore distribution curve and a larger specific surface area. Moreover, The catalytic effect investigation on AP with GA-ZnCo₂O₄/ZnO: the high temperature decomposition (HTD) peak temperature of AP in the presence of 5 wt % GA-ZnCo₂O₄/ZnO was reduced from 441 to 294 °C, and the exotherm of AP was expanded from 205 to 1275 J/g at a heating rate of 15 °C/min. Through the calculation, GA-ZnCo₂O₄/ZnO makes the activation energy and Gibbs free energy of the AP pyrolysis lower so that the reaction is easier to occur. Thermogravimetric-mass (TG-MS) spectrometry revealed that during thermal decomposition of AP, GA-ZnCo₂O₄/ZnO leveraged the synergistic catalysis of ZnCo₂O₄/ZnO and GA that boosted the flow of electrons from ClO₄^- to O₂ and increased the absorption of the gas product to accelerate the AP pyrolysis. These results provided a facile strategy to prepare GA-based composite catalysts with extraordinary application prospects in the domain of solid propellants.

Sonochemical synthesis of a copper reduced graphene oxide nanocomposite using honey and evaluation of its antibacterial and cytotoxic activities

The combination of graphene-based materials and inorganic nanoparticles for the enhancement of the nanomaterial properties is extensively explored nowadays. In the present work, we used a sonochemical method to synthesize a copper/reduced graphene oxide (Cu/RGO) nanocomposite using Australian honey and vitamin C as capping and reducing agents, respectively. The honey-mediated copper/reduced graphene oxide (H/Cu/RGO) nanocomposite was then characterized through UV-visible, XRD, HRTEM, and FTIR analysis. The copper nanoparticles (Cu-NPs) in the nanocomposite formed uniform spherical shapes with a size of 2.20 ± 0.70 nm, which attached to the reduced graphene oxide (RGO) layers. The nanocomposite could suppress bacterial growth in both types of bacteria strains. However, in this study, the nanocomposite exhibited good bactericidal activity toward the Gram-positive bacteria than the Gram-negative bacteria. It also showed a cytotoxic effect on the cancer colorectal cell line HCT11, even in low concentrations. These results suggested that the H/Cu/RGO nanocomposite can be a suitable component for biomedical applications.

Mechanistic Insights into the Thermal Decomposition of Ammonium Perchlorate: The Role of Amino-Functionalized Magnetic Nanoparticles

This work reports the characterization and application of two promising nanocatalysts for the thermal decomposition of ammonium perchlorate (AP). To obtain these composite materials, magnetite nanoparticles (Fe₃O₄ NP_s) were functionalized with two different amine derivative groups, tertiary amine (Fe₃O₄ NP_s-A1) and quaternary amine. X-ray photoelectron spectroscopy and differential scanning calorimetry provided mechanistic insights into the thermal decomposition of AP. Furthermore, tertiary and quaternary amine groups play a critical role, where the presence of an extra proton could favor an electron-proton transfer as the rate-determining step. Moreover, Fe₃O₄ NP_s-A1 causes a diminution of the high-temperature decomposition of AP positively to 335 °C, increasing the energy release by 278 J g^-1 and consequently affording the lowest activation energy (102 kJ mol^-1), indicating a low degree of thermal stability, and accelerating the thermal decomposition of AP.

Simultaneous determination of hydroquinone and catechol by a reduced graphene oxide-polydopamine-carboxylated multi-walled carbon nanotube nanocomposite

A reduced graphene oxide–polydopamine–carboxylated multi-walled carbon nanotube (RGO–PDA–cMWCNT) nanocomposite was fabricated via a facile, one-pot procedure and was characterized by a variety of techniques. A novel electrochemical sensor based on RGO–PDA–cMWCNT was constructed to determine hydroquinone (HQ) and catechol (CT) simultaneously. This newly prepared nanocomposite shows excellent electrocatalytic efficacy in the electrode reaction of the two isomers. Specifically, the peak-to-peak potential difference between the two dihydroxybenzenes is 115 mV for oxidation, which is obviously larger than similar electrochemical sensors. The established method displays a wide linear range from 0.5 to 5000 μM with a detection limit (S/N = 3) of 0.066 μM for HQ and 0.073 μM for CT. In addition, this electrochemical approach has been tested to measure the two dihydroxybenzenes in real samples and satisfactory results were recorded.

A novel reduced graphene oxide–polydopamine–carboxylated multi-walled carbon nanotube nanocomposite (RGO–PDA–cMWCNT) was fabricated for the sensitive and simultaneous determination of hydroquinone (HQ) and catechol (CT).

Heterobimetallic Catalysts for the Thermal Decomposition of Ammonium Perchlorate: Efficient Burning Rate Catalysts for Solid Rocket Motors and Missiles

We show the synthesis and characterization of four heterobimetallic compounds derived from s-indacene of general formula [{(CO)₃Mn}-s-Ic-{MCp*}]^q with M = Fe, Co, Ni, and Ru; q = 0, 1+. The complexes reported here were characterized by ¹H and ¹³C NMR, elemental analysis and FT-IR. Additionally, the X-ray crystal structure of [(CO)₃Mn-s-Ic-FeCp*] (1) and Mössbauer spectra are reported. The heterobimetallic compounds exhibit higher quasireversible redox potentials compared with ferrocene and catocene under the same reaction conditions. The complexes were tested as catalysts on the thermal decomposition of ammonium perchlorate examined by a differential scanning calorimetry technique to study their catalytic behavior. Compound (1) causes a decrease of ammonium perchlorate's decomposition temperature to 315 °C, consequently increasing the heat release by 138 J·g^-1. Conversely, [{(CO)₃Mn}-s-Ic'-{CoCp*}] (2) presents a higher heat release (2462 J·g^-1), comparable to catocene.

Size-Controlled Transformation of Cu2O into Zero Valent Copper within the Matrix of Anion Exchangers via Green Chemical Reduction

Composite materials containing zero valent copper (ZVC) dispersed in the matrix of two commercially available strongly basic anion exchangers with a macroreticular (Amberlite IRA 900Cl) and gel-like (Amberlite IRA 402OH) structure were obtained. Cu0 particles appeared in the resin phase as the product of the reduction of the precursor, i.e., copper oxide(I) particles previously deposited in the two supporting materials. As a result of a one-step transformation of preformed Cu2O particles as templates conducted using green reductant ascorbic acid and under mild conditions, macroporous and gel-type hybrid products containing ZVC were obtained with a total copper content of 7.7 and 5.3 wt%, respectively. X-ray diffraction and FTIR spectroscopy confirmed the successful transformation of the starting oxide particles into a metallic deposit. A scanning electron microscopy study showed that the morphology of the deposit is mainly influenced by the type of matrix exchanger. In turn, the drying steps were crucial to its porosity and mechanical resistance. Because both the shape and size of copper particles and the internal structure of the supporting solid materials can have a decisive impact on the potential applications of the obtained materials, the results presented here reveal a great possibility for the design and synthesis of functional nanocrystalline solids.

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.

Controllable synthesis of multi-shelled NiCo2O4 hollow spheres catalytically for the thermal decomposition of ammonium perchlorate

The compatible catalytic structure of NiCo₂O₄ was modified into multi-shelled hollow spheres by one-pot synthesis, followed by heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmet–Teller (BET) and N₂ adsorption–desorption approaches were used for the characterizations of nanoparticles and multi-shelled hollow porous structures and the morphologies and crystal structures of these hollow spheres, respectively. Differential scanning calorimetry (DSC) was adopted for comparing the thermal decomposition performances of ammonium perchlorate (AP) catalyzed by adding different contents of multi-shelled NiCo₂O₄ hollow spheres. Impressively, the experimental results showed that the NiCo₂O₄ hollow spheres exhibited more excellent catalytic activity than NiCo₂O₄ nanoparticles as a result of their large specific surface areas, good adsorption capacity and many active reduction sites. The decomposition temperature of AP with multi-shelled NiCo₂O₄ hollow spheres could be reduced up to 322.3 °C from 416.3 °C. Furthermore, a catalytic mechanism was proposed for the thermal decomposition of AP over multi-shelled NiCo₂O₄ hollow spheres based on electron transfer processes.

Double-shelled NiCo₂O₄ hollow spheres synthesized by a facile hydro-thermal method showed excellent catalytic properties for the thermal decomposition of AP.