Embedding Noble-Metal-Free Ni<Subscript>2</Subscript>P Cocatalyst on g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> for Enhanced Photocatalytic H<Subscript>2</Subscript> Evolution in Water Under Visible Light

Photocatalytic hydrogen evolution is considered as one of the promising pathways to settle the energy crises and environmental issues by utilizing solar energy. In this paper, noble-metal-free Ni₂P was used as cocatalyst to enhance g-C₃N₄ for photocatalytic hydrogen production under visible light irradiation (λ?>?420 nm). Characterization results indicated that Ni₂P nanoparticles were successfully loaded onto g-C₃N₄, which can significantly contribute to accelerate the separation and transfer of photogenerated electron. The hydrogen evolution rate reached ～?270 µmol h^?1 g^?1 and the apparent quantum yield (AQY) was ～?2.85% at 420 nm. Meanwhile, there is no obviously decrease of the hydrogen production rate even after 36 h under visible light illumination. In addition, the mechanism of photocatalytic hydrogen evolution was also elaborated in detail.

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Synthesis of MIL-101@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposite for enhanced adsorption capacity towards CO<Subscript>2</Subscript>

MIL-101@g-C₃N₄ nanocomposite was prepared by solvothermal synthesis and used for CO₂ adsorption. The parent materials (MIL-101 and g-C₃N₄) and the MIL-101@g-C₃N₄ were characterized by X-ray diffraction, argon adsorption/desorption, Fourier transform infrared spectroscopy, thermal analysis (TG/DTA), transmission electronic microscopy, and Energy-dispersive X-ray spectroscopy. The results confirmed the formation of well-defined MIL-101@g-C₃N₄ with interesting surface area and pore volume. Furthermore, both MIL-101 and MIL-101@g-C₃N₄ were accomplished in carbon dioxide capture at different temperatures (280, 288, 273 and 298 K) at lower pressure. The adsorption isotherms show that the nanocomposite has a good CO₂ adsorption affinity compared to MIL-101. The best adsorption capacity is about 1.6 mmol g^?1 obtained for the nanocomposite material which is two times higher than that of MIL-101, indicating strong interactions between CO₂ and MIL-101@g-C₃N₄. This difference in efficacy is mainly due to the presence of the amine groups dispersed in the nanocomposite. Finally, we have developed a simple route for the preparation of an effective and new adsorbent for the removal of CO₂, which can be used as an excellent candidate for gas storage, catalysis, and adsorption.     

Photocatalytic Activity of a TiO<Subscript>2</Subscript> Photocatalyst Doped with C<Superscript>4+</Superscript> and S<Superscript>4+</Superscript> Ions Having a Rutile Phase Under Visible Light

C⁴⁺ and S⁴⁺-codoped titanium dioxide (TiO₂) having a rutile phase was prepared. By doping C⁴⁺ and S⁴⁺ ions into a TiO₂ lattice, the absorption edge of rutile TiO₂ powder was largely shifted from 400 to 700 nm. 2-Methylpyridine and methyleneblue were photocatalytically oxidized at high efficiency on C⁴⁺ and S⁴⁺-doped TiO₂ under visible light at a wavelength longer than 5 nm.     

Effect of TiO<Subscript>2</Subscript> loading on the activity of V/TiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the catalytic oxidehydrogenation of ethylbenzene with carbon dioxide

TiO₂-Al₂O₃ mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO₂ were prepared by sol-gel method and impregnated with different amounts of VO _x . Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H₂-TPR), and ammonia temperature programmed desorption (NH₃-TPD). TiO₂ content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO₂ content was 50 wt-%.     

Porous-C<Subscript>3</Subscript>N<Subscript>4</Subscript> with High Ability for Selective Adsorption and Photodegradation of Dyes Under Visible-Light

Porous-C₃N₄ with high photocatalytic activity of anionic dyes was successfully synthesized by a SiO₂-template method. Its photocatalytic selectivity could easily be switched to cationic dye via a simple post-treatment in NaOH solution. Through careful investigation of influencing parameters (the photocatalytic performances, the structure and surface characteristics of the catalysts), the selective degradation of various dyes is closely related to the adsorption selectivity of the porous g-C₃N₄ catalysts, which originated from the different surface charge. This study provides a new insight into developing metal-free g-C₃N₄ photocatalyst with high efficiency and selectivity in environmental purification.     

Li<Subscript>2</Subscript>Cu<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> + SiO<Subscript>2</Subscript>/Ti compositions for the catalytic afterburning of diesel soot

Two methods were used to obtain a catalytically active oxide coating on the surface of titanium for the catalytic afterburning of diesel soot: plasma electrochemical formation of an oxide film on the surface of titanium and extraction pyrolytic deposition of the Li₂Cu₂(MoO₄)₃ compound. The Li₂Cu₂(MoO₄)₃/TiO₂ + SiO₂/Ti compositions synthesized by the single-step extraction pyrolytic treatment of the oxidized surface of titanium ensured a high burning rate of soot of ∼300°C. The subsequent deposition of Li₂Cu₂(MoO₄)₃ lowers the activity of the catalyst, due probably to the growth of molybdate phase crystallites and the filling of open oxide film pores. Double lithium-copper molybdate is able to reduce appreciably the concentration of CO in the oxidation products of soot. The advantages of these methods are the possibility of forming high-cohesion durable coatings on surfaces of any complexity, the simplicity of their implementation, and high productivity and low cost. The obtained results can be recommended for use in developing methods for creating composite coatings on catalytic soot filters.     

Preparation of powdered carbon nitride C<Subscript>3</Subscript>N<Subscript>4</Subscript>

The basic principles of the preparation of powdered carbon nitride C₃N₄ in bulk amounts are developed. Synthetic carbon nitride C₃N₄ was identified using X-ray powder diffraction, infrared absorption, and reduction melting in a carrier gas (helium) flow with subsequent chromatographic separation.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Mohammad Arif, Blinov, Lappalainen, Filippov.     

Heat treatment of silica-fiber-reinforced BN-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> matrix composite

A new wave-transparent composite reinforced by silica fibers with a hybrid matrix comprising BN and Si₃N₄ was prepared by precursor infiltration and pyrolysis, and it was heat-treated at elevated temperatures. The variations of the composite during heat treatments were characterized and investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-received composite exhibits good mechanical properties, and it is almost amorphous. When treated at 1600°C, it turned brittle, and silica fibers in it were fused; the composite showed a good crystalline form. When treated at 2100°C, the composite broke into pieces, and the composition showed only BN. Si₃N₄ was decomposed, and silica fibers were volatilized. The presence of BN probably affected the phase transitions of silica fibers. __________ Translated from Novye Ogneupory, No. 8, pp. 49–52, August 2007.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.     

Preparation of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–ZrO<Subscript>2</Subscript> ceramic composites by self-propagating high-temperature synthesis

Results are provided for a study of Si₃N₄–ZrO₂ composite ceramic material preparation by self-propagating high-temperature synthesis from ferrosilicon and zirconium concentrate. It is noted that as a result of high-temperature dissociation of ZrSiO₄ silicon dioxide is nitrided with formation of silicon oxynitride and it is condensed in surface layers of a specimen in the form of filamentary crystals.     

Polyaniline/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> composites as novel media for anticorrosion coatings

In this paper, graphitic carbon nitride (g-C₃N₄) was first proposed for the pioneer application of anticorrosion coatings. Original g-C₃N₄ was facilely treated using HNO₃ and the exfoliated g-C₃N₄ sheets (E-g-C₃N₄) were fabricated, and then, polyaniline/E-g-C₃N₄ composites (PANI/E-g-C₃N₄) as novel anticorrosive media were synthesized by chemical oxidative polymerization and devoted to the corrosion protection of coatings. The E-g-C₃N₄ sheets and PANI/E-g-C₃N₄ composites were characterized by X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, and transmission electron microscopy. The anticorrosion properties of the samples prepared were investigated by electrochemical measurements including Tafel plots, electrochemical impedance spectra, and open-circuit potential. Accelerated corrosion tests of iron panels coated by PANI/E-g-C₃N₄ were performed in 3.5 wt% NaCl solution. Anticorrosive mechanism of PANI/E-g-C₃N₄ was discussed in detail. PANI/E-g-C₃N₄-3 fillers possessed superior corrosion inhibition than individual components on iron coatings, which was due to the synergetic effect of anticorrosion between E-g-C₃N₄ and PANI.     

Combustion of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al thermit mixtures in steel tubes

Explored was the combustion of Fe₂O₃/TiO₂/Al thermit mixtures in steel tubes upon variation in green composition and with special emphasis on the dependence of combustion temperature T _c and burning velocity U on reaction heat Q. Special attention was given to incompleteness of combustion for compositions with low Q.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Uniform color coating of multilayered TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films by atomic layer deposition

Thin film optics, based on light interference characteristics, are attracting increasing interest because of their ability to enable a functional color coating for various applications in optical, electronic, and solar industries. Here, we report on the dependence of coloring characteristics on single-layer TiO₂ thicknesses and alternating TiO₂/Al₂O₃ multilayer structures prepared by atomic layer deposition (ALD) at a low growth temperature. The ALD TiO₂ and Al₂O₃ thin films were studied at a low growth temperature of 80°C. Then, the coloring features in the single-layer TiO₂ and alternating TiO₂/Al₂O₃ multilayers using both the ALD processes were experimentally examined on a TiN/cut stainless steel sheet. The Essential Macleod software was used to estimate and compare the color coating results. The simulation results revealed that five different colors of the single TiO₂ layers were shown experimentally, depending on the film thickness. For the purpose of highly uniform pink color coating, the film structures of TiO₂/Al₂O₃ multilayers were designed in advance. It was experimentally demonstrated that the evaluated colors corresponded well with the simulated color spectrum results, exhibiting a uniform pink color with wide incident angles ranging from 0° to 75°. This article advances practical applications requiring highly uniform color coatings of surfaces in a variety of optical coating areas with complex topographical structures.