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The present paper attempts as how the pigments comprising of nano-sized hematite particles deposited on mica surfaces in optimum conditions offer an excellent pearlescent properties. To record the influencing parameters on the synthesis process, response surface methodology (RSM) technique was used where temperature of reaction, synthesis time and concentration of urea were selected as variable parameters. Taking into account colorimetric parameters, the whole process was then analyzed by "Design Expert" software that finally gave following optimum factors: reaction temperature=82.02°C, synthesis time=11.98 h, urea concentration=37.5 g/l. Once the above optimum parameters selected, seemingly, the spherical hematite particles of about 60 nm in diameter are deposited uniformly on mica surfaces.

Although biomass-derived metal-free electrocatalysts for oxygen reduction reaction (ORR) have garnered increasing attention, their ORR performance is lower than that of commercial 20% Pt/C. To improve their ORR performance, a series of porous carbons with high $N$ contents are prepared by pyrolyzing a mixture of spinach leaf powder and urea at different mass ratios (1:0, 1:5, 1:10, and 1:15) at a high temperature; the resultant materials are labeled as S-850, S-850-5, S-850-10, and S-850-15, respectively. The results indicate that the $N$ contents in the as-synthesized S-850, S-850-5, S-850-10, and S-850-15 products are 5.43, 5.74, 5.93, and 5.93 at%, respectively, which gradually increase with increasing urea contents, while the $P$ and $S$ contents (0.7 and 0.3 at%, respectively) show no change. Among all the as-synthesized products, the sample obtained by the addition of 10 wt.% urea (S-850-10) exhibits the best ORR catalytic performance in an O₂-saturated 0.1 M KOH solution with a half-potential of 0.748 V and a diffusion-limited current density of −4.76 mA cm${}^{-2}$ at 0.4 V. The half-potential and diffusion-limited current density of S-850-10 are improved by 0.53% and 8.61% compared to those of S-850 (0.744 V and −4.35 mA cm${}^{-2}$ at 0.4 V, respectively). These findings indicate that urea can be used as an $N$ resource to increase the $N$ content of biomass-derived metal-free porous carbon, enhancing its ORR performance.

In the International Space Station, urine is considered something to be treated. However, urine is mainly composed of water and urea, while they have been demonstrated as an excellent hydrogen carrier for sustainable energy supply. Through the simple chemical coprecipitation and hydrothermal reaction, the needle-like NiMoO₄ crystals were synthesized with the average width around 500nm and length up to 4$\mu$m. The resulted products were thoroughly characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy and ultraviolet–visible spectrum. The needle-like NiMoO₄ crystals exhibited excellent electrocatalytic oxidation toward urea at anode in alkali solution, leading to the increased performance of hydrogen evolution reaction at cathode with the lower electrochemical potential and energy consumption required to drive the reaction. The high electrocatalysis of the needle-like NiMoO₄ crystals toward urea oxidation reveals their great potential for future application to clean the urine/urea-rich wastewater and to produce hydrogen in space station and environmental wastewater.

The amorphous nickel/carbon microspheres (Ni/C-MSs) were synthesized through dehydration and carbonization of glucose at high temperature and high pressure. The obtained Ni/C-MSs and the Ni/C-800-MSs (calcined at 800${}^{\circ }$C) were thoroughly characterized on morphology, composition and catalytic performance. It is found that the Ni/C-MSs showed good catalytic performance for hydrogen generation from aqueous H₃NBH₃ at room temperature. Urea was oxidized electrocatalytically by Ni/C-800-MSs in alkaline medium, indicating a viable method for wastewater remediation and simultaneous production of valuable hydrogen.

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin (H₄TPPS) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl, diacid TPPS (H₄TPPS) exists as a monomer up to 75 μM H₄TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H₄TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 10⁵M^-1.cm^-1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H₄TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D₂O at pH 2, no aggregation is observed. These spectral observations suggest that the H₄TPPS aggregation involves intermolecular hydrogen bonding.

In this work, highly active graphitic carbon nitride composite photocatalysts with an isotype heterojunction semiconductor structure have been prepared through the molecular composite precursors consisting of urea and melamine. These photocatalysts were characterized by XRD, SEM, TEM, UV-Vis, BET and transient photocurrent responses. The photodegradation of dyes in aqueous solution under visible-light irradiation has been investigated over carbon nitride photocatalysts consisting of different urea/melamine mass ratios. Further studies by photocurrent indicate that the photosynergistic effect of isotype heterojunction can remarkably enhance the photoinduced interfacial charge transfer, thereby increasing the charge separation during the photocatalytic reaction.

Replacing the high theoretical potential of anodic water decomposition (oxygen evolution reaction) with the low theoretical potential of urea oxidation reaction (UOR) is an urgent need for hydrogen energy storage and conversion. Cobalt nitride nanoflakes, high-performance bifunctional catalysts supported on nickel foam (Co${}_{5.47}$N NF/NF), were synthesized by hydrothermal and calcination method. The morphology and composition of the catalyst were studied by XRD, XPS, SEM, TEM, HRTEM and elemental analysis. In order to conduct electrochemical performance and stability, a two-electrode electrolyzer composed of Co${}_{5.47}$N NF/NF as both anode and cathode materials is constructed (Co${}_{5.47}$N NF/$\mathrm{\text{NF}}||{\mathrm{\text{Co}}}_{5.47}$N NF/NF). Only a voltage of 1.687V is needed to complete 100$\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$. It is much lower than the voltage of Pt/$\mathrm{\text{C}}||{\mathrm{\text{IrO}}}_2$ (1.816V), because of which it is believed that this work provides a valuable route for the design of inexpensive and efficient urea electrolysis-assisted hydrogen generation.

For the treatment of dye wastewater, it is of great significance to develop new adsorbents with high adsorption capacity and good separation effect. In this study, the Fe-Co magnetic activated carbon material (CN-Fe-Co-AC) was first prepared by high-temperature calcination. CN-Fe-Co-AC is physically characterized by various methods. CN-Fe-Co-AC can efficiently and quickly remove the organic dyes methylene blue (MB) and acid blue 80 (AB80). The adsorption of MB and acid blue based on CN-Fe-Co-AC adsorbent is mainly through the specific surface area and the functional groups on the surface. During this recovery process, the adsorption activity of CN-Fe-Co-AC for MB and AB80 decreased slightly. Kinetic data can be described using a Pseudo-second-order model and the data for adsorption equilibrium can be described using the Langmuir isotherm. The theoretical adsorption capacities of MB and AB80 are 104.82mg/g and 26.94mg/g, respectively. After repeated use of five times, the removal rate of MB exceeded 96%, and the removal rate of AB80 exceeded 75%. The excellent adsorption performance and recyclability of CN-Fe-Co-AC indicate that this material has certain potential application value.