Ni-doped CoFe2O4 Hollow Nanospheres as Efficient Bi-functional Catalysts

Photocatalytic reduction of chromium(VI) using multiwall carbon nanotubes/bismuth oxide nanocomposite under solar irradiation

Semiconductor photocatalysis is the most efficient advanced oxidation processes for wastewater treatment. A new carbon-based photocatalyst bismuth oxide/multi-walled carbon nanotube (Bi2O3/MWCNT) nanocomposite has a considerable impact on improving photocatalytic performance. Bi2O3/MWCNTs (BMC) nanocomposite was prepared through the hydrothermal processing with 2.5, 5, 7.5 and 10 wt% of MWCNTs. The prepared photocatalysts have been thoroughly examined by various techniques. The X-ray diffraction confirmed the prepared photocatalyst as α-Bi2O3 with high crystallinity. The band gap of Bi2O3 and BMC 7.5 nanocomposite was found to be 2.41 and 1.94 eV. The prepared photocatalyst revealed smooth and porous merged flower-like structure with respect to the addition of MWCNTs. The model pollutant chromium(VI) (Cr(VI)) has been used to check the reduction efficiency of the prepared photocatalyst under solar irradiation. It was found that BMC 7.5 nanocomposite showed enhanced photocatalytic metal ion reduction (87.48%) compared to pristine Bi2O3 (69.29%). The preliminary photocatalytic Cr(VI) ion reduction experiments were carried to determine the photoreduction efficiency of pristine bismuth oxide and bismuth MWCNT nanocomposite. The kinetic study on Cr(VI) ion reduction obeyed pseudo-first-order rate kinetics for both the prepared photocatalysts. The efficiency of the photocatalysts was further analysed by reusing the same up to 3 cycles without loss of the efficacy.

Natural coal gangue as a stable catalyst to activate persulfate: tetracycline hydrochloride degradation and its explored mechanism

The surface-bonded hydroxyl groups on CG play the dominant role in PS activation and TC removal.

Spinel ferrites (MFe2O4): Synthesis, improvement and catalytic application in environment and energy field

To develop efficient catalysts is one of the major ways to solve the energy and environmental problems. Spinel ferrites, with the general chemical formula of MFe₂O₄ (where M = Mg²⁺, Co²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Mn²⁺, etc.), have attracted considerable attention in catalytic research. The flexible position and valence variability of metal cations endow spinel ferrites with diverse physicochemical properties, such as abundant surface active sites, high catalytic activity and easy to be modified. Meanwhile, their unique advantages in regenerating and recycling on account of the magnetic performances facilitate their practical application potential. Herein, the conventional as well as green chemistry synthesis of spinel ferrites is reviewed. Most importantly, the critical pathways to improve the catalytic performance are discussed in detail, mainly covering selective doping, site substitution, structure reversal, defect introduction and coupled composites. Furthermore, the catalytic applications of spinel ferrites and their derivative composites are exclusively reviewed, including Fenton-type catalysis, photocatalysis, electrocatalysis and photoelectro-chemical catalysis. In addition, some vital remarks, including toxicity, recovery and reuse, are also covered. Future applications of spinel ferrites are envisioned focusing on environmental and energy issues, which will be pushed by the development of precise synthesis, skilled modification and advanced characterization along with emerging theoretical calculation.

A facile synthesis of nanostructured CoFe2O4 for the electrochemical sensing of bisphenol A

This work reports a novel, highly sensitive and cost-effective electrochemical sensor for the detection of bisphenol A in environmental water samples. Attractive non-noble transition metal oxide CoFe₂O₄ nanoparticles were successfully synthesized using a sol–gel combustion method and further characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Under optimal conditions, the CoFe₂O₄ nanoparticle modified glassy carbon electrode exhibits high electrochemical activity and good catalytic performance for the detection of bisphenol A. The linear calibration curves are obtained within a wide concentration range from 0.05 μmol L⁻¹ to 10 μmol L⁻¹, and the limit of detection is 3.6 nmol L⁻¹ for bisphenol A. Moreover, this sensor also demonstrates excellent reproducibility, stability, and good anti-interference ability. The sensor was successfully applied to determine bisphenol A in practical samples, and the satisfactory recovery rate was between 95.5% and 102.0%. Based on the great electrochemical properties and practical application results, this electrochemical sensor has broad application prospects in the sensing of bisphenol A.

A new electrochemical sensor for bisphenol A is reported. CoFe₂O₄ nanoparticles were synthesized by a sol–gel combustion method. A nanoparticle-modified glassy carbon electrode exhibited outstanding electrochemical performance for the detection of bisphenol A.

Controllable synthesis of CoFe2O4 electrospun nanofibers

Controllable synthesis of CoFe₂O₄ nanofibers has been realized by controlling the electrospinning process parameters.

Ultrasonochemically-induced MnCo2O4 nanospheres synergized with graphene sheet as a non-precious bi-functional cathode catalyst for rechargeable zinc-air battery

Rechargeable zinc-air batteries are considered to be more sustainable and efficient candidates for safe, low-cost energy storage because of their higher energy density and the abundance of zinc resources. Recently Zn-air batteries have aroused significant research attention, however, because an unresolved impediment due to the notorious instability of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics of the cathode catalyst limit their practical application. Herein, we report the synthesis of non-precious MnCo₂O₄ nanospheres synergized with a graphene sheet as a bi-functional cathode catalyst for rechargeable Zn-air battery application using a one-pot probe sonochemical method. Structural characterization confirms that the MnCo₂O₄ nanospheres successfully anchored on graphene sheet. X-ray photoelectron spectroscopy revealed that the Mn and Co in the MnCo₂O₄ are in mixed valence states on the graphene sheet surface and the MnCo₂O₄-graphene sheet (MCO-GS) hybrid catalyst exhibits excellent OER and ORR activity compared with their individual counterparts. A rechargeable Zn-air battery using an MCO-GS catalyst reveals unique small charge-discharge overpotential, cycling stability and higher rate capability than a bare MnCo₂O₄ (MCO) catalyst. This superiority in electrocatalytic activity combined with simplicity of material synthesis, turn the MCO-GS hybrid into a promising catalyst for a rechargeable Zn-air battery.

The synthesis of CoxNi1−xFe2O4/multi-walled carbon nanotube nanocomposites and their photocatalytic performance

A series of Co_xNi_1−xFe₂O₄/multi-walled carbon nanotube (Co_xNi_1−xFe₂O₄/MWCNTs) nanocomposites as photocatalysts were successfully synthesized, where Co_xNi_1−xFe₂O₄ was synthesized via a one-step hydrothermal approach. Simultaneously, methylene blue (MB) was used as the research object to investigate the catalytic effect of the catalyst in the presence of hydrogen peroxide (H₂O₂). The results showed that all the photocatalysts exhibited enhanced catalytic activity compared to pure ferrite. In addition, compared with the other photocatalysts, the reaction time was greatly shortened a significantly higher removal rate was achieved using 3-CNF/MWCNTs. There was no significant decrease in photodegradation efficiency after three catalytic cycles, suggesting that Co_xNi_1−xFe₂O₄/MWCNTs are recyclable photocatalysts for wastewater treatment. Our results indicate that the Co_xNi_1−xFe₂O₄/MWCNT composite can be effectively applied for the removal of organic pollutants as a novel photocatalyst.

A series of Co_xNi_1−xFe₂O₄/multi-walled carbon nanotube (Co_xNi_1−xFe₂O₄/MWCNTs) nanocomposites as photocatalysts were successfully synthesized. The results implied that this composites can be effectively applied for the removal of organic pollutant as novel photocatalysts.

In-situ developed carbon spheres function as promising support for enhanced activity of cobalt oxide in oxygen evolution reaction

Highly active, stable electrocatalyst for oxygen evolution reaction (OER) is sincerely required for the practical application of water splitting to get rid from the sluggish reaction kinetics and the stability issue. Here, Co₃O₄ is studied as OER catalyst and to improve the electrocatalytic activity, carbon is chosen as the conducting support. A simple and cost-effective synthetic route is developed for the synthesis of Co₃O₄ on carbon support following hydrothermal route using various hydrolyzing agents. The heterostructure 'Co₃O₄/C' perform well in OER as a non-precious metal catalyst. The best Co₃O₄/C electrocatalyst can generate 10 and 30 mA/cm² current densities upon application of 1.623 V and 1.678 V vs. RHE whereas, bare Co₃O₄ can generate current density of 10 and 30 mA/cm² upon application of 1.677 and 1.754 V vs. RHE. Carbon in the heterostructure helps to improve the conductivity and at the same time enhances the charge transfer ability which further leads to increase current density and stability to the catalyst. Co₃O₄/C can generate unaltered current density up to 1000 cycles.

Noble Metal-Free Nanocatalysts with Vacancies for Electrochemical Water Splitting

The fast development of nanoscience and nanotechnology has significantly advanced the fabrication of nanocatalysts and the in-depth study of the structural-activity characteristics of materials at the atomic level. Vacancies, as typical atomic defects or imperfections that widely exist in solid materials, are demonstrated to effectively modulate the physicochemical, electronic, and catalytic properties of nanomaterials, which is a key concept and hot research topic in nanochemistry and nanocatalysis. The recent experimental and theoretical progresses achieved in the preparation and application of vacancy-rich nanocatalysts for electrochemical water splitting are explored. Engineering of vacancies has shown to open up a new avenue beyond the traditional morphology, size, and composition modifications for the development of nonprecious electrocatalysts toward efficient energy conversion. First, an introduction followed by discussions of different types of vacancies, the approaches to create vacancies, and the advanced techniques widely used to characterize these vacancies are presented. Importantly, the correlations between the vacancies and activities of the vacancy-rich electrocatalysts via tuning the electronic states, active sites, and kinetic energy barriers are reviewed. Finally, perspectives on the existing challenges along with some opportunities for the further development of vacancy-rich noble metal-free electrocatalysts with high performance are discussed.

Simple preparation of carbon–bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts

Carbon–bimetal oxide nanospinels synthesized by a single step of autocombustion show high activity for oxygen evolution and reduction.

Highly efficient oxygen evolution electrocatalysts prepared by using reduction-engraved ferrites on graphene oxide

A simple and efficient method was explored for synthesizing efficient ferrite-based OER electrocatalysts by using reduction-engraved ultrafine ferrite nanoparticles on a conductive GO support.

An efficient and cost-effective tri-functional electrocatalyst based on cobalt ferrite embedded nitrogen doped carbon

The development of efficient, cost-effective and long-lived electro-catalyst is necessary for the realization of practically viable water-splitting systems. A trifunctional electrocatalyst for water splitting (hydrogen evolution, oxygen reduction and oxygen evolution reaction, HER/ORR/OER) was designed via eco-friendly and facial way. CoFe₂O₄ nanoparticles embedded in nitrogen doped mesoporous carbon were prepared using chicken egg white/albumin after pyrolysis at different temperatures, 700, 800, 900 and 1000 °C. The specific surface area, pore size and the interaction between CoFe₂O₄ nanoparticles and carbon matrix were tuned via pyrolysis temperature. The catalyst prepared at 900 °C, (N/CF-EC-900) exhibit superior catalytic activity as well as the superior stability than that other nanocomposites prepared and other commercial catalyst (Pt/C, RuO₂) for water splitting. Our findings emphasize the importance of CoFe₂O₄ nanoparticles embedded in the carbon and suggest the catalytic activities with low onset potential, high current densities, small Tafel slope in basic medium.