Solvothermal synthesis of octahedral and magnetic CoFe2O4-reduced graphene oxide hybrids and their photo-Fenton-like behavior under visible-light irradiation

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO-LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO-LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Investigation of the photocatalytic activity of magnetically recoverable g-C3N4/CoFe2O4/Bi2MoO6 particles for purifying tetracycline antibiotics: synthesis, characterization, ecotoxicity analysis, and plant toxicity test

To purify water polluted by tetracycline antibiotics, a new visible light-driven magnetically recoverable photocatalyst, g-C3N4/CoFe2O4/Bi2MoO6, was prepared in this study, and it effectively removed tetracycline antibiotics. Its rapid recycling was achieved by external magnets, which greatly increased material utilization. After four repeated uses, the degradation rate of tetracycline antibiotics by the g-C3N4/CoFe2O4/Bi2MoO6 composite photocatalyst remained at a high level, and the magnetic separation performance remained stable. Subsequently, it was further discovered that the degradation mechanism of this photocatalytic system was consistent with a double Z-type mechanism, which enabled two transport channels for photogenerated electrons, and was favorable for the separation of the photogenerated electron-hole pairs and prolonged the lifetime of the photogenerated carriers. The active substances playing an important role in the photocatalytic system were ˙O2- and h+. In addition, the possible intermediates in the photocatalytic process were detected by GC-MS analysis, and a degradation mechanism was proposed. The ecotoxicity of the degradation products and intermediates was evaluated using the Toxicity Estimation Software Tool (TEST), and the mung bean seed cultivation test was carried out to visually and efficiently illustrate that the g-C3N4/CoFe2O4/Bi2MoO6 photocatalyst can effectively degrade antibiotics, with low ecotoxicity of the degradation products. This provides a new idea for the removal of organic pollutants using light energy.

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.

Reduced Graphene Oxide-Modified Spinel Cobalt Ferrite Nanocomposite: Synthesis, Characterization, and Its Superior Adsorption Performance for Dyes and Heavy Metals

This work is dedicated to the synthesis, characterization, and adsorption performance of reduced graphene oxide-modified spinel cobalt ferrite nanoparticles. The as-synthesized reduced graphene oxide cobalt ferrite (RGCF) nanocomposite has been characterized using FTIR spectroscopy, FESEM coupled with EDXS, XRD, HRTEM, zeta potential, and vibrating sample magnetometer (VSM) measurements. FESEM proves the particle size in the range of 10 nm. FESEM, EDX, TEM, FTIR, and XPS analyses provide the proof of successful incorporation of rGO sheets with cobalt ferrite nanoparticles. The crystallinity and spinel phase of cobalt ferrite nanoparticles have been shown by XRD results. The saturation magnetization (M _s) was measured as 23.62 emu/g, proving the superparamagnetic behavior of RGCF. The adsorption abilities of the synthesized nanocomposite have been tested using cationic crystal violet (CV) and brilliant green (BG) and anionic methyl orange (MO) and Congo red (CR) dyes. The adsorption trend for MO, CR, BG, and As(V) follows RGCF > rGO > CF at neutral pH. Adsorption studies have been accomplished by optimizing parameters like pH (2-8), adsorbent dose (1-3 mg/25 mL), initial concentration (10-200 mg/L), and contact time at constant room temperature (RT). To further investigate the sorption behavior, isotherm, kinetics, and thermodynamic studies have been conducted. Langmuir isotherm and pseudo-second-order kinetic models suited better for the adsorption of dyes and heavy metals. The maximum adsorption capacities (q _m) obtained have been found as 1666.7, 1000, 416.6, and 222.2 mg/g for MO, CR, BG, and As, respectively, with operational parameters such as T = 298.15 K; RGCF dose: 1 mg for MO and 1.5 mg each for CR, BG, and As. Thus, the RGCF nanocomposite was found to be an excellent adsorbent for the removal of dyes and heavy metals.

Role of Different Fuels and Sintering Temperatures in the Structural, Optical, Magnetic, and Photocatalytic Properties of Chromium-Containing Nickel Ferrite: Kinetic Study of Photocatalytic Degradation of Rhodamine B Dye

In the present paper, nanocrystalline samples of NiCrFeO₄ were synthesized by the combustion method using different fuels such as glycine, urea, and poly(vinyl alcohol) and subjected to heat treatment at different temperatures of 600, 700, 800, and 1000 °C for 6 h. The formation of phases with highly crystalline structures was confirmed by XRD and Rietveld refinement analysis. The optical band gap of NiCrFeO₄ ferrites lies in the visible range, making them suitable photocatalysts. BET analysis reveals that the surface area of the phase synthesized using PVA is much higher than that synthesized using other fuels at each sintering temperature. In addition, there is a significant decrease in the surface area with sintering temperature for the catalysts prepared using the fuels PVA and urea, while it almost remains constant in the case of glycine. Magnetic studies demonstrate the dependence of saturation magnetization on the nature of the fuel and on the sintering temperature; moreover, the coercivity and squareness ratio confirm the single domain nature of all the synthesized phases. We have also performed photocatalytic degradation of the highly toxic Rhodamine B (RhB) dye by employing all the prepared phases as photocatalysts using the mild oxidant H₂O₂. It is observed that the photocatalyst prepared using PVA as the fuel exhibited the best photocatalytic activity at all sintering temperatures. All the three photocatalysts prepared using different fuels showed a decrease in the photocatalytic activity with increasing sintering temperature. From the chemical kinetic point of view, the degradation of RhB by all the photocatalysts was found to follow pseudo-first-order kinetics.

CoFe2O4 Hollow Spheres-Decorated Three-Dimensional rGO Sponge for Highly Efficient Electrochemical Charge Storage Devices

The energy demand, the crisis of fossil fuels, and the increasing popularity of portable and wearable electronics in the global market have triggered the demand to develop high-performance flexible all-solid-state supercapacitors that are capable of delivering high energy at high power density as well as being safely entrenched in those electronics. Herein, we have designed a nanocomposite, 80CF_hs-20rGO_sp, which exhibits a high specific capacitance (C _S) value of 1032 F g^-1 at 3 A g^-1. Utilizing this nanocomposite as the cathode and reduced graphene oxide sponge (rGO_sp) as the anode, a flexible all-solid-state asymmetric device has been fabricated. In this device, poly(vinyl alcohol) (PVA) gel embedded with a mixture of 3 M KOH and 0.1 M K₄[Fe(CN)₆] was used as an electrolyte cum separator. The fabricated device showed the capability to deliver an energy density of 65.8 W h kg^-1 at a power density of 1500 W kg^-1 and retained its capability even after various physical deformations. The device also exhibited a long cycle life and retained ∼96% of its C _S value after 5000 cycles. Moreover, the fabricated flexible all-solid-state device successfully illuminated light-emitting diodes, which proved its potential use in real-life supercapacitor applications. The obtained results revealed the excellent electrochemical performances of the fabricated device and rendered it a promising candidate in the energy sector.

A controllable one-pot hydrothermal synthesis of spherical cobalt ferrite nanoparticles: synthesis, characterization, and optical properties

We herein report the controllable synthesis of spherical cobalt ferrite nanoparticles with average crystallite size in the range of 3.6–12.9 nm using a facile, eco-friendly, hydrothermal method. The hydrothermal treatment was carried out by utilizing cobalt nitrate, ferric nitrate, and ammonium hydroxide in the presence and absence of Arabic gum as a surfactant agent. The purity and crystallinity of the products were tuned by varying reaction conditions such as reaction time (0.5–8 h), reaction temperature (120–180 °C), percentage of ethylene glycol (0–100% (v/v)), pH (8–9.6), and amount of Arabic gum (0–2 g). We characterized the prepared products using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy analysis (EDS), selected area electron diffraction (SAED) patterns, and UV-visible diffuse reflectance spectra (DRS). The optimal hydrothermal treatment was performed at 180 °C and pH 9.6 for 4 h in aqueous media. The results also revealed that the as-prepared spinel cobalt ferrite nanoparticles have an estimated optical band gap energy in the range of ca. 1.6–1.9 eV, indicating the semiconducting characteristics of the products.

A controllable synthesis of spherical cobalt ferrite nanoparticles with average crystallite size in the range of 3.6–12.9 nm using a facile, eco-friendly, hydrothermal method.

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.