The electrocatalytic oxidation of urea on nickel-graphene and nickel-graphene oxide composite electrodes

Binary ruthenium dioxide and nickel oxide ultrafine particles loaded on carbon nanotubes for high-stability oxygen evolution reaction at high current densities

RuO2 is an efficient electrocatalyst for the oxygen evolution reaction (OER). However, during the OER process, RuO2 is prone to oxidation into Rux+ (x > 4), leading to its dissolution in the electrolyte and resulting in poor stability of RuO2. Here, we report a bicomponent electrocatalyst, NiO and RuO2 co-loaded on carbon nanotubes (RuO2/NiO/CNT). The results demonstrate that the introduction of NiO suppresses the over-oxidation of RuO2 during the OER process, not only inheriting the excellent catalytic performance of RuO2, but also significantly enhancing the stability of the catalyst for OER at high current densities. In contrast to RuO2/CNT, RuO2/NiO/CNT shows no significant change in activity after 150 h of OER at a current density of 100 mA cm-2. Density functional theory (DFT) calculations indicate that NiO transfers a large number of electrons to RuO2, thereby reducing the oxidation state of Ru. In conclusion, this study provides a detailed analysis of the phenomenon where low-valent metal oxides have the ability to enhance the stability of RuO2 catalysts.

A new strategy integrating peroxymonosulfate oxidation and soil amendments in contaminated soil: Bensulfuron methyl degradation, soil quality improvement and maize growth promotion

Bensulfuron methyl (BSM) residues have caused serious yield reductions of sensitive crops. Chemical oxidation is an effective remediation technology, while it affects soil quality and subsequent agricultural activity, necessitating approriate improvement measures. So Fe2O3-Mn3O4 with excellent bimetallic synergistic effect was synthesized to activate peroxymonosulfate (PMS) for BSM degradation. The catalytic activity and influencing factors were systematically predetermined in water in view of soil remediation. Results showed Fe2O3-Mn3O4/PMS oxidized 99.3 % BSM within 60 min with the help of multi-reactive species and electron transfer. Meanwhile, Fe2O3-Mn3O4/PMS treatment exhibited technical feasibility in soil that 97.6 % BSM was degraded in 5 days under the low usages of Fe2O3-Mn3O4 (0.8 %) and PMS (0.15 %). Although Fe2O3-Mn3O4/PMS decreased BSM phytotoxicity and improved maize growth, a few gaps existed between the remediated group and uncontaminated group, including biomass, length, available potassium, organic matters, pH, redox potential (Eh) and sulfate content. The introductions of biochar and chitosan in remediated soils promoted growth, increased organic matters content, improved soil resistance to acidification and decreased Eh, alleviating the negative effects of Fe2O3-Mn3O4/PMS. Overall, the study provided new insights into the combination of Fe2O3-Mn3O4/PMS and biochar and chitosan in BSM-contaminated soil, achieving BSM degradation and improvements of soil quality and plant growth.

Ceria-Graphene Oxide Nanocomposite for Electro-oxidation of Urea: An Experimental and Theoretical Investigation

This study explores the potential of ceria-graphene oxide (CeO2-GO) nanocomposites as efficient electrocatalysts for urea electro-oxidation (UOR). This work combines experimental and theoretical investigations and characterization techniques confirm the successful formation of the CeO2 embedded on graphene oxide sheets. UOR activity was found to be dependent on both OH- and urea concentrations. The optimal UOR performance was achieved in a 0.1 M urea and 1.0 M KOH solution, as evidenced by the low Tafel slope of 60 mV/dec and high turnover frequency (TOF) of 1.690 s-1. DFT calculations revealed that the CeO2-GO nanocomposite exhibited strong urea adsorption due to its favorable bond lengths (Ce-O: 2.58 Å, O-H: 1.77 Å) and high adsorption energy (-1.05 eV). These findings revealed that the CeO2-GO nanocomposites are promising as efficient and durable electrocatalysts for urea conversion to valuable products like nitrogen and hydrogen gas, with potential applications in clean energy generation and ammonia synthesis.

Graphene-based versus alumina supports on CO2 methanation using lanthanum-promoted nickel catalysts

The valorization of CO2 as a biofuel, transforming it through methanation as part of the power-to-gas (P2G) process, will allow the reduction of the net emissions of this gas to the atmosphere. Catalysts with 13 wt.% of nickel (Ni) loading incorporated into alumina and graphene derivatives were used, and the effect of the support on the activity was examined at temperatures between 498 and 773 K and 10 bar of pressure. Among the graphene-based catalysts (13Ni/AGO, 13Ni/BGO, 13Ni/rGO, 13Ni-Ol/GO, 13Ni/Ol-GO, and 13Ni/Ol-GO Met), the highest methane yield was found for 13Ni/rGO (78% at 810 K), being the only system comparable to the catalyst supported on alumina 13Ni/Al2O3 (89.5% at 745 K). The incorporation of 14 wt.% of lanthanum (La) into the most promising supports, rGO and alumina, led to nickel-support interactions that enhanced the catalytic activity of 13Ni/Al2O3 (89.5% at lower temperature, 727 K) but was not effective for 13Ni/rGO. The resistance against deactivation by H2S poisoning was also studied for these catalysts, and a fast deactivation was observed. In addition, activity recovery was impossible despite the regeneration treatment carried out over catalysts. The resistance against deactivation by H2S poisoning was also studied for these catalysts, observing that both suffered a rapid/immediate deactivation and which in addition/unfortunately was impossible to solve despite the regeneration treatment carried out over catalysts.

Water-Stable Fluorous Metal-Organic Frameworks with Open Metal Sites and Amine Groups for Efficient Urea Electrocatalytic Oxidation

Urea oxidation reaction (UOR) is one of the promising alternative anodic reactions to water oxidation that has attracted extensive attention in green hydrogen production. The application of specifically designed electrocatalysts capable of declining energy consumption and environmental consequences is one of the major challenges in this field. Therefore, the goal is to achieve a resistant, low-cost, and environmentally friendly electrocatalyst. Herein, a water-stable fluorinated Cu(II) metalorganic framework (MOF) {[Cu2 (L)(H2 O)2 ]·(5DMF)(4H2 O)}n (Cu-FMOF-NH2 ; H4 L = 3,5-bis(2,4-dicarboxylic acid)-4-(trifluoromethyl)aniline) is developed utilizing an angular tetracarboxylic acid ligand that incorporates both trifluoromethyl (-CF3 ) and amine (-NH2 ) groups. The tailored structure of Cu-FMOF-NH2 where linkers are connected by fluoride bridges and surrounded by dicopper nodes reveals a 4,24T1 topology. When employed as electrocatalyst, Cu-FMOF-NH2 requires only 1.31 V versus reversible hydrogen electrode (RHE) to deliver 10 mA cm-2 current density in 1.0 m KOH with 0.33 m urea electrolyte and delivered an even higher current density (50 mA cm-2 ) at 1.47 V versus RHE. This performance is superior to several reported catalysts including commercial RuO2 catalyst with overpotential of 1.52 V versus RHE. This investigation opens new opportunities to develop and utilize pristine MOFs as a potential electrocatalyst for various catalytic reactions.

Decoration of alkalization-intercalated Ti3C2 with ZIF-8@ZIF-67-derived N-doped carbon nanocage for detecting 4-nitrophenol

The highly effective alk-Ti₃C₂/bimetallic Co, Zn embedded N-doped carbon (Co-Zn-NC) composite was fabricated by a convenient self-assembled method strategy and applied to  the reduction of 4-nitrophenol(4-NP). Co-Zn-NC nanocage was synthesized by using designed core-shell ZIF-8@ZIF-67 as sacrificial template. The Co-Zn-NC was prepared by pyrolysis of ZIF-8@ZIF-67 at 900 °C with high-specific surface area and hollow structure, which facilitates the dispersion of Co species and produces abundant Co-Nx active sites. In addition, the electrochemical property and specific surface area of Ti₃C₂ were improved by alkaline treatment. As a result, compared with alk-Ti₃C₂ and Co-Zn-NC, the alk-Ti₃C₂/Co-Zn-NC sensor showed higher activity and stability in detecting 4-NP. The alk-Ti₃C₂/Co-Zn-NC sensor has a wide determination range of 2-500 μM and a low detection limit of 0.23 μM for 4-NP. In addition, the newly developed alk-Ti₃C₂/Co-Zn-NC sensor displayed satisfactory reproducibility and  good stability in detecting 4-NP in aqueous samples.

Catalytic ozonation mechanisms of Norfloxacin using Cu-CuFe2O4

As an easily recoverable, environmentally friendly and cost-effective catalyst, CuFe₂O₄ is a promising candidate for the catalytic ozonation of antibiotics in wastewater. However, its catalytic activity is restricted due to its limited active sites and low electron transfer efficiency. In this study, cetyl trimethyl ammonium bromide (CTAB) and Cu⁰ were doped with CuFe₂O₄ to introduce more O_V, providing more active sites and improving electron transfer efficiency. Experimental results show that the optimum removal efficiency of the catalytic ozonation of Norfloxacin (NOR, a widely used antibiotic) using CTAB doped with Cu-CuFe₂O₄ as the catalyst is 81.58% with a first-order reaction kinetics constant of 0.03967 min^-1. The associated O₃ and catalyst dosages are 2.72 mg·L^-1 and 0.1 g·L^-1, respectively, which are 1.63 times and 2.22 times higher than those in an equivalent O₃ system. O_V can provide generation sites for surface hydroxyl groups and trigger ·O₂^- and ¹O₂ as the main active oxygen species. The synergistic redox cycles of Fe²⁺/Fe³⁺ and Cu⁰/Cu²⁺ accelerate electron transfer efficiency. The possible degradation pathways of NOR are identified as defluorination, naphthyridine ring-opening and piperazine ring-opening. In summary, this work proposes a new strategy for the modification of CuFe₂O₄ catalysts and provides new insights into the catalytic ozonation mechanisms for NOR removal.

PEO-PPO-PEO induced holey NiFe-LDH nanosheets on Ni foam for efficient overall water-splitting and urea electrolysis

Exploring the transition-metal-based bifunctional electrocatalysts with high performance for efficient water-splitting and urea electrolysis is significant but challenging. This work presents the in situ preparation of holey NiFe-LDH nanosheets on Ni foam (H-NiFe-LDH/NF) via a one-step hydrothermal method in the presence of PEO-PPO-PEO as the soft template. The holey NiFe-LDH nanosheets provide a high electrochemical surface area, more edge catalytic sites, and abundant oxygen vacancies. Consequently, H-NiFe-LDH/NF exhibits excellent catalytic activity to oxygen evolution, urea oxidation, and hydrogen evolution reactions (OER, UOR, and HER) with good stability in alkaline electrolytes. This electrode requires an overpotential of 261 mV for the OER, a potential of 1.480 V for the UOR to achieve a current density of 100 mA cm^-2 in alkaline solutions. By employing the self-supported electrode as both the anode and cathode, this electrolysis cell (H-NiFe-LDH/NF||H-NiFe-LDH/NF) gains current densities of 10 and 100 mA cm^-2 at low cell voltages of 1.575 and 1.933 V in the 1.0 M KOH solution. After adding 0.33 M urea, the voltages to deliver 10 and 100 mA cm^-2 respectively decrease to 1.418 and 1.691 V. The H-NiFe-LDH/NF electrode also shows excellent stability for water-splitting and urea electrolysis. This work not only contributes to developing a low-cost, high-efficiency, bifunctional electrocatalyst but also provides a practically feasible approach for urea-rich wastewater electrolysis.

Bimetallic nickel/manganese phosphate–carbon nanofiber electrocatalyst for the oxidation of formaldehyde in alkaline medium

The development of earth-abundant transition metal-based catalysts, supported by a conductive carbonaceous matrix, has received great attention in the field of conversion of formaldehyde derivatives into toxic-free species. Herein, we report a comprehensive investigation of bimetallic electrocatalyst activity towards the electrooxidation of formaldehyde. The bimetallic phosphate catalyst is prepared by co-precipitation of Ni and Mn phosphate precursors using a simple reflux approach. Then the bimetallic catalyst is produced by mixing the Ni/Mn with carbon fibres (CNFs). The structural properties and crystallinity of the catalyst were investigated by using several techniques, such as scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Brunauer Emmett−Teller theory. The system performance was studied under potentiostatic conditions. Some theoretical thermodynamic and kinetic models were applied to assess the system performance. Accordingly, key electrochemical parameters, including surface coverage (Γ) of active species, charge transfer rate (k_s), diffusion coefficient of the formaldehyde (D), and catalytic rate constant (k_cat) were calculated at Γ = 1.690 × 10⁻⁴ mmol cm⁻², k_s = 1.0800 s⁻¹, D = 1.185 × 10⁻³ cm² s⁻¹ and k_cat = 1.08 × 10⁵ cm³ mol⁻¹ s⁻¹. These findings demonstrate the intrinsic electrocatalytic activity of formaldehyde electrooxidation on nickel/manganese phosphate- CNFs in alkaline medium.

The catalytic performance of bimetallic Ni/Mn phosphate–carbon nanofiber composite catalyst is better than mono metallic catalysts toward electrooxidation of formaldehyde.

Nickel phosphide on Ni foam as anode and peroxymonosulfate as the chemical oxidizer for effective direct urea fuel cell

The direct urea fuel cell (DUFC) is a low cost and competitive approach for contemporaneous urine or urea-contaminated wastewater treatment and electricity generation. However, the lack of efficient urea oxidation reaction (UOR) electrocatalysts and suitable electron acceptors remains a challenge for practical applications. Here, we developed a DUFC system using Ni₂P@Ni foam as the anode and peroxymonosulfate (PMS) as the chemical oxidizers. The Ni₂P@Ni foam anode showed a high oxidation activity for UOR with an onset potential of 0.30 V vs. Ag/AgCl and Tafel slope of 34.4 mV/dec. PMS with high theoretical potential improved the cell voltage to 1.43 V. A power density of DUFC up to 4.91 mW/cm² was achieved using PMS at room temperature, which was approximately twice as high as using H₂O₂ (2.38 mW/cm²). Ni^II/Ni^III was the redox active species on the Ni₂P anode in the DUFC process, and Ni^II was electrochemically oxidized to Ni^III, which reverted to Ni^II by urea reduction. When real human urine was used as the fuel, a power density of 4.46 mW/cm² can be achieved at room temperature. This DUFC with high cell performance showed potential application in urea wastewater treatment.

Surface Decoration of Cetyltrimethyl Ammonium Bromide on SiC Particles and Its Effects on the Co-Deposition Process

Cetyltrimethyl ammonium bromide (CTAB) is used to decorate the SiC particle surface. The mechanism of the decoration process has been studied by simulation and experimental approaches. Molecular dynamics (MD) simulation finds a bilayer adsorbed structure of CTAB on the SiC particles, which is then verified by Fourier-transform infrared and thermal gravimetric analysis measurements. The MD simulation also finds that the decorative effects of CTAB on the SiC particle surface are related to the surface charge condition of the SiC particles and the concentration of CTAB. The measured zeta potential of the SiC particles shows dependence on the pH condition and the concentration of CTAB. The decorated SiC particles are used to produce composition by the co-deposition technology. With the help of CTAB, SiC particles are successfully incorporated in the deposited layer, where the content of SiC particles is dependent on the concentration of CTAB and the pH of the bath.

A highly sensitive electrochemical biosensor for protein based on a tetrahedral DNA probe, N- and P-co-doped graphene, and rolling circle amplification

A tetrahedral DNA probe can effectively overcome the steric effects of a single-stranded probe to obtain well-controlled density and minimize nonspecific adsorption. Herein, a highly sensitive electrochemical biosensor is fabricated for determination of protein using a tetrahedral DNA probe and rolling circle amplification (RCA). N- and P-co-doped graphene (NP-rGO) is prepared, and AuNPs are then electrodeposited on it for DNA probe immobilization. Benefitting from the synergistic effects of the excellent electrical conductivity of NP-rGO, the stability of the tetrahedral DNA probe and the signal amplification of RCA, the biosensor achieves a low limit of 3.53 × 10^-14 M for thrombin and a wide linear range from 1 × 10^-13 to 1 × 10^-7 M. This study provides a sensitive and effective method for the detection of protein in peripheral biofluids, and paves the way for future clinical diagnostics and treatment of disease. Graphical abstract.

Controllable synthesis of a mesoporous NiO/Ni nanorod as an excellent catalyst for urea electro-oxidation

Mesoporous rod-like structured composites of NiO/Ni have been successfully prepared via a low temperature heat treatment of the precursor NiC₂O₄·2H₂O in N₂.

Modification of graphene based on a Ba2Cu8Ni2Se12 catalyst with CoS nanospheres for a counter electrode for dye-sensitized solar cells

A novel graphene-Ba₂Cu₈Ni₂Se₁₂ catalyst with CoS nanospheres (GBC) was synthesized via a facile hydrothermal method for use as a counter electrode (CE) in dye-sensitized solar cells (DSSCs).

An Overview of the Recent Developments in Metal Matrix Nanocomposites Reinforced by Graphene

Two-dimensional graphene plateletes with unique mechanical, electrical and thermo-physical properties could attract more attention for their employed as reinforcements in the production of new metal matrix nanocomposites (MMNCs), due to superior characteristics, such as being lightweight, high strength and high performance. Over the last years, due to the rapid advances of nanotechnology, increasing demand for the development of advanced MMNCs for various applications, such as structural engineering and functional device applications, has been generated. The purpose of this work is to review recent research into the development in the powder-based production, property characterization and application of magnesium, aluminum, copper, nickel, titanium and iron matrix nanocomposites reinforced with graphene. These include a comparison between the properties of graphene and another well-known carbonaceous reinforcement (carbon nanotube), following by powder-based processing strategies of MMNCs above, their mechanical and tribological properties and their electrical and thermal conductivities. The effects of graphene distribution in the metal matrices and the types of interfacial bonding are also discussed. Fundamentals and the structure–property relationship of such novel nanocomposites have also been discussed and reported.