Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

Evaluation of Au–ZnO,ZnO/Ag2CO3 and Ag–TiO2 as Photocatalyst for Wastewater Treatment

Topics in Catalysis - In this work series of photocatalysts based on ZnO modified by Au and Ag2CO3 addition and Ag–TiO2 materials were synthesized and evaluated in the treatment of...     

Synthesis and characterization of V–C60/TiO2 photocatalysts designed for degradation of methylene blue

C₆₀/TiO₂ and V–C₆₀/TiO₂ composite photocatalysts were prepared with titanium (IV) n-butoxide (TNB) by a sol–gel method. Fullerene had absorptive and semiconducting properties, and vanadium could enhance the photogenerated electron transfer. The V–C₆₀/TiO₂ composite shows a good photo-degradation activity. XRD patterns of the composites showed that the C₆₀/TiO₂ composite contained a mixture of anatase and rutile phase forms while the V–C₆₀/TiO₂ composite contained a typical single and clear anatase phase. The surface properties seen by SEM and FE-SEM present a characterization of the texture on C₆₀/TiO₂ and V–C₆₀/TiO₂ composites and showed a homogenous composition in the particles for the titanium sources used. The EDX spectra for the elemental identification showed the presence of C and Ti with strong V peaks for the V–C₆₀/TiO₂ composite. From the photocatalytic results, the excellent activity of the C₆₀/TiO₂ and V–C₆₀/TiO₂ composites for degradation of methylene blue under UV irradiation could be attributed to both the effects between photocatalysis of the supported TiO₂ and charge transfer of the fullerene, and the introduction of vanadium to enhance the photogenerated electrons transfer.     

Facile synthesis and investigation of NiO–ZnO–Ag nanocomposites as efficient photocatalysts for degradation of methylene blue dye

In the present study, NiO–ZnO–Ag photocatalytic nanocomposites were synthesized using two-stage precipitation method. The synthesized composite powders were investigated and characterized using different techniques including XRD, FESEM, FT-IR, TGA and UV–Vis. XRD results showed that by increasing the Ag content, the crystallite size of ZnO decreased. FESEM micrographs showed that addition of Ag could lead to formation of more uniform particles in the size range of 30–500 nm. Diffuse reflectance spectroscopy results confirmed that addition of Ag nanoparticles led to the increase of light absorption, which was attributed to the plasmon surface resonance of Ag. Band gap energies of NiO–ZnO, NiO–ZnO–5%Ag, NiO–ZnO–3%Ag, NiO–ZnO–1%Ag and ZnO–1%Ag were estimated to be 3.13, 3.14, 3.147, 3.19 and 3.17 eV, respectively. Investigation of degradation process showed that by adding up to 1 wt% Ag to NiO–ZnO composite led to the increase of methylene blue degradation from 67% to 94%, but further addition resulted in decrease of degradation.     

Ag/Ag3PO4/TiO2双异质结催化剂的制备及光催化性能研究

通过紫外光诱导将Ag纳米颗粒沉积在Ag_3PO_4/TiO_2上,构建了Ag/Ag_3PO_4/TiO_2双异质结催化剂,通过废水中残留非那西丁(PNT)降解实验探究其光催化性能。结果表明,在紫外光照射下,以Ag/Ag_3PO_4/TiO_2为催化剂,当Ag_3PO_4质量分数为10%、催化剂用量为0.5 g·L~(-1)、初始pH值为9.0、PNT初始浓度为20 mg·L~(-1)时,PNT的降解效果最好,降解率最高可达97%。光致发光光谱显示,Ag的沉积导致Ag_3PO_4/TiO_2的光催化性能明显增强,对光生电子的转移产生积极作用,对电子-空穴对的复合产生抑制作用。     

Enhanced performance of g-C3N4/TiO2 photocatalysts for degradation of organic pollutants under visible light☆

Photocatalytic degradation is one of the most promising remediation technologies in terms of advanced oxida-tion processes (AOPs) for water treatment. In this study, novel graphitic carbon nitride/titanium dioxide (g-C3N4/TiO2) composites were synthesized by a facile sonication method. The physicochemical properties of the photocatalyst with different mass ratios of g-C3N4 to TiO2 were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 sorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and UV–vis DRS. The photocatalytic performances were evaluated by degradation of methylene blue. It was found that g-C3N4/TiO2 with a mass ratio of 1.5:1 exhib-ited the best degradation performance. Under UV, the degradation rate of g-C3N4/TiO2 was 6.92 and 2.65 times higher than g-C3N4 and TiO2, respectively. While under visible light, the enhancement factors became 9.27 (to g-C3N4) and 7.03 (to TiO2). The improved photocatalytic activity was ascribed to the interfacial charge transfer between g-C3N4 and TiO2. This work suggests that hybridization can produce promising solar materials for envi-ronmental remediation.     

Fabrication of Ag/WO3 nanobars for Baeyer–Villiger oxidation using hydrogen peroxide

We report the preparation of Ag/WO₃ nanobars, mediated by cationic surfactant CTAB through hydrothermal route. XRD revealed the formation of metallic Ag supported on monoclinic WO₃ phase and TEM diagram showed the formation of bar-like structure, where supported Ag nanoparticles are in the range between 2 and 7 nm. The catalyst exhibited high activity for selective oxidation of cyclohexanone to caprolactone with H₂O₂. A cyclohexanone conversion of 97% with 99% caprolactone selectivity was achieved over this catalyst at 80 °C temperature. Moreover, the catalyst did not show any significant activity loss even after 5 reuses and proved its efficiency in the oxidation of other cycloalkanones also.     

Ag/Ag2S–TiO2 composite film formed using dual phase Ag/Ag2O layer as a sulfurized layer for enhanced photocatalytic activity

The Ag/Ag₂S–TiO₂ composite films were synthesized through vulcanizing sputtering Ag/Ag₂O dural-phase template capping layer on the TiO₂ film. After hydrothermal vulcanization using thiourea as a sulfur precursor, the initially decorated Ag₂O layer transformed into the Ag₂S. The surface morphology of the continuous block structure of the Ag/Ag₂S composite layer gradually shrinks to form irregular island grains dispersed on the surface of the composite film, with vulcanization reaction duration increased from one to 3 h. The light absorption ability of the Ag/Ag₂S–TiO₂ composite film was enhanced substantially compared to the TiO₂ film because of the surface plasmon resonance effect from the Ag particles and the narrow energy band of the Ag₂S. Among various surface morphologies of the Ag/Ag₂S–TiO₂ composite films, the irregular island Ag/Ag₂S grains-decorated TiO₂ composite film presents superior photoelectrochemical and photocatalytic degradation performances than the composite films consisting of continuous block and spider-web structure of the Ag/Ag₂S decorated layers. The synergistic effects of surface plasmon resonance, Ag pathway between the semiconductors, and Z-scheme charge transfer mechanism explain the high-efficiency photocatalytic activity of the Ag/Ag₂S–TiO₂ composite films.     

Some features of the surface modification of MgO–Al2O3–TiO2–SiO2 glass and glass ceramics by Ag diffusion

Diffusion of Ag species into the surface layers of the MgO–Al₂O₃–TiO₂–SiO₂ glass stimulates the crystallization processes therein during subsequent thermal treatment. It was found that the silver doping significantly increases the microhardness of glass and glass ceramics. The effect of the Ag diffusion and the subsequent high-temperature treatment (T > T_g) on the structure and luminescence properties of the MgO–Al₂O₃–TiO₂–SiO₂ glass was studied. The thermal evolution, structure and properties of the glass and glass ceramics were investigated by the DSC method, XRD analysis and luminescence spectroscopy. It was found that the Ag diffusion into the surface layers leads to the formation of numerous different luminescent molecular Ag_n clusters. The MgO–Al₂O₃–TiO₂–SiO₂ glass and glass ceramics subjected to the Ag diffusion can operate as effective down-converters of the radiation demonstrating the effective transformation of UV and blue light into the radiation of red and NIR spectral range.     

Performance of Pd–Ag/Al2O3 catalysts prepared by the selective deposition of Ag onto Pd in acetylene hydrogenation

The performance of Ag-promoted Pd/Al₂O₃ catalysts, which were prepared by the selective deposition of Ag onto Pd using a surface redox (SR) method, during acetylene hydrogenation was compared with that of catalysts prepared by impregnation. The Pd surface was more effectively modified with Ag added by SR, even when small amounts of Ag were added. The catalyst prepared by SR showed a higher ethylene selectivity than the one prepared by impregnation, because SR allowed both the preferential deposition of Ag on the low-coordination sites of Pd and a greater electronic modification of Pd by Ag.     

The construction of nitrogen-doped graphitized carbon–TiO2 composite to improve the electrocatalyst for methanol oxidation

The exploration of advanced catalyst supports is a promising route to obtain electrocatalysts with high activity and durability. Herein, the nitrogen-doped graphitized carbon/TiO₂ composite was fabricated and explored as support for the Pt catalyst. The composite support was constructed by carbonization of polypyrrole/TiO₂ using cobalt nitrate and nickel nitrate as graphitizing catalysts. The resulting catalyst shows enhanced electrocatalytic performance for methanol electrooxidation compared with the commercial Pt/C catalyst. The enhancement can be ascribed to combinatory effect of N-doped graphitized carbon and TiO₂, in which the tolerance to CO-poisoning and the intrinsic kinetics of methanol oxidation reaction were simultaneously improved by the bifunctional effect and the modification of the electronic structure. As a result, the as-developed nitrogen-doped graphitized carbon/TiO₂ composite present attractive advantages for the application in fuel cell electrocatalyst.     

Synthesis of Ag promoted porous Fe3O4 microspheres with tunable pore size as catalysts for Fischer–Tropsch production of lower olefins

Ag promoted porous Fe₃O₄ microspheres with tunable pore size were synthesized via one-pot solvothermal method and employed as catalysts for Fischer–Tropsch synthesis. The introduction of Ag played an important role in regulating the pore size of catalysts and the dispersion of Fe. Comparable to unmodified catalyst in this system, Ag promoted Fe-based catalysts displayed excellent selectivity to lower olefins, particularly for Fe–0.9Ag with smaller pore size of 1.33 nm and Fe dispersion of 10.1%. The maximum selectivity to C₂ through C₄ olefins was 43.0 wt.%, and the selectivity to CH₄ was low to 14.8 wt.%.     

Surface Acidic and Redox Properties of V–Ag–O/TiO2 Catalysts for the Selective Oxidation of Toluene to Benzaldehyde

Previous work showed that the V–Ag–O complex oxides exhibited quite good catalytic behavior for the selective oxidation of toluene to benzaldehyde. In this work, TiO₂ was added into V–Ag–O by co-precipitation with a sol–gel method. Structural characterizations using X-ray diffraction and Fourier transform infrared spectroscopy indicated the phases of Ag₂V₄O₁₁, Ag_1.2V₃O₈ and TiO₂ in the V–Ag–O/TiO₂ before the reaction. No complex oxide phases involving titanium were observed. Thus, the addition of TiO₂ seemed to generate the interfaces between TiO₂ and the silver vanadates. The Ag₂V₄O₁₁ and part of Ag_1.2V₃O₈ were converted into Ag_0.68V₂O₅ and metallic Ag during the reaction. The results of temperature programmed reduction, microcalorimetric adsorption of NH₃ and isopropanol probe reaction in air revealed that the addition of TiO₂ might increase both the surface acidity and redox ability of the catalysts. The increased redox ability seemed to improve the activity for the oxidation of toluene, but the increased surface acidity might lead to the decrease of selectivity to benzaldehyde. The V–Ag–O/TiO₂ with 20% TiO₂ exhibited significantly improved catalytic behavior for the selective oxidation of toluene to benzaldehyde, as compared to the un-promoted V–Ag–O catalyst. The conversion of toluene reached 7.3% over the V–Ag–O/20%TiO₂ at 613 K with 95% selectivity to benzaldehyde.     

Microstructure and oxidation resistance of C-AlPO4–mullite coating prepared by hydrothermal electrophoretic deposition for SiC-C/C composites

Oxidation resistant C-AlPO₄–mullite coating for SiC pre-coated carbon/carbon composites (SiC-C/C) was prepared by a novel hydrothermal electrophoretic deposition process. The phase composition, surface and cross-section microstructure of the as-prepared multi-layer coatings were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The influence of deposition voltage on phase composition, microstructure and oxidation resistance of the as-prepared coatings was particularly investigated. Results show that the outer layer coating mainly composed of C-AlPO₄ and mullite phase can be achieved after the hydrothermal electrophoretic deposition. The thickness, density and anti-oxidation property of the C-AlPO₄–mullite coating was improved with the increase of deposition voltage from 160 V to 200 V. The multi-layer coating prepared at a voltage of 200 V exhibit excellent anti-oxidation property, which can effectively protect C/C composites from oxidation in air at 1773 K for 324 h with a weight loss of 1.01%. The failure of the multi-layer coatings is due to the generation of cross-holes in the coating, which cannot be self-cured by the metaphosphate and silicate glass layer after long time oxidation at 1773 K.     

Synthesis and electrochemical performance of LiVOPO4–Li3V2(PO4)3 cathode materials for lithium ion batteries

Lithium-ion batteries (LIBs) present the advantages of long cycle life, high voltage, and energy density and are widely made in the field of energy storage. LiVOPO₄ (LVOP), a cathode material used in LIBs, has a high conceptual capacity of 159 mAh g⁻¹ and high operating voltage of 3.9 V. However, its low electrical conductivity and cycle performance limit its commercial applications. According to the X-ray diffraction results, orthogonal crystal LVOP and monoclinic crystal Li₃V₂(PO₄)₃ (LVP) coexisted in the synthesised composite material. The transmission electron microscopy results also indicated that the LVOP and LVP phases coexist, which were coated by carbon layer of about 2.5 nm. The discharge of LVOP–LVP composite material initially was 143.2 mAh g⁻¹, and that after 120 cycles was 132.2 mAh g⁻¹ (at 0.1 C and 3–4.5 V). Thus, the electronic conductivity and first discharge specific capacity of the material enhanced due to the introduction of fast ion conductor LVP into LVOP. Electrochemical performance improved because the introduction of LVP led to an increase in Li⁺ pervasion channels in the original material and the acceleration of the Li⁺ transmission speed.     

Novel visible light-induced g-C3N4–Sb2S3/Sb4O5Cl2 composite photocatalysts for efficient degradation of methyl orange

A series of g-C₃N₄–Sb₂S₃/Sb₄O₅Cl₂ (SCL-CX) composite photocatalysts were successfully prepared via a hydrothermal method. The as-prepared materials were characterized by TM3000, powder X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and UV–vis diffuse reflectance spectra (UV–vis DRS). The obtained photocatalyst showed higher photocatalytic activity than pure g-C₃N₄, Sb₄O₅Cl₂ and Sb₂S₃/Sb₄O₅Cl₂ (SCL). The optimum photocatalytic of the composite with the mass of 170 mg g-C₃N₄ and a degradation efficiency up to 95% for methyl orange (MO) under visible light was achieved within 60 min. The enhanced photocatalytic performance could be attributed to the stronger absorption in the visible region and the more efficient electron–hole separation.     

Structure and physical properties of Ba(PO3)2–AlF3–BaSO4 fluoro-sulfo-phosphate glasses

Alkali-earth-metaphosphate-based fluoro-sulfo-phosphate M(PO₃)₂–AlF₃–MSO₄ (MPFS, M = Ca, Sr, Ba) glasses have been developed via simultaneously incorporating fluoride and sulfate into metaphosphate glass. Their glass-forming regions were efficiently determined under the guidance of thermodynamic calculation method. The physical and structural properties of BaPFS glass were investigated in detail. Furthermore, near-infrared spectroscopic properties of Er³⁺-doped BaPFS (Er–BaPFS) glass were studied. Physical parameters, such as Abbe's number ν_d (55-75) and nonlinear refractive index n₂ (1.17-1.86 × 10⁻¹³ esu), of BaPFS glass are strongly depended on P/F/S ratio. The structure of BaPFS glass gradually depolymerizes and tends to become multianionic when Ba(PO₃)₂ is substituted by AlF₃ and BaSO₄. Anion-substitution strategy effectively modulates the property and structure of glass, providing a scheme to derive glass materials. In addition, enhanced emission at ~1.5 μm has been observed from Er–BaPFS glass along with large emission cross section (5.0-5.5 × 10⁻²¹ cm²) and long lifetime (6.7-7.3 ms), resulting in large figure of merit (3.46-3.84 × 10⁻²³ cm²·s), which is a promising candidate for solid-state laser.     

Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

Cu was loaded on the S-doped TiO₂ by electroless plating method. The prepared Cu/S–TiO₂ exhibited high photocatalytic activity for hydrogen generation, and the yield is up to 7.5 mmol h^− 1 g^− 1cat in methanol solution. Their physical structure and chemical properties were characterized by UV–Vis, XRD, XPS and EXAFS. The copper species were CuO and Cu₂O, and the sample showed excellent visible light absorption ability. Comparing with the sample prepared by chemical reducing method, the electroless plated copper on S–TiO₂ was highly dispersed, which could facilitate photo-generated charges capture, transfer and separation.     

Structural and dielectrical properties of Mg3–Ca3(PO4)2 bioceramics obtained from hydroxyapatite by sol–gel method

Mg₃–Ca₃(PO₄)₂ bioceramics were prepared from hydroxyapatite (HAp) with high Mg contents using sol–gel method. The influence of magnesium on the phase composition, crystal structure, electrical properties, chemical structure and morphological characteristics of powder bioceramics was analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Dielectrical properties of the bioceramics were investigated by a dielectric impedance spectroscopy method. It was observed that the crystallization degree for all the samples dramatically was decreased with the increasing Mg content. The average crystallite size of the samples was found to vary from 32 to 42 nm. The morphology, density and dielectric properties of the bioceramics were changed with the addition of the amount of Mg. The obtained results indicate that the Mg₃–Ca₃(PO₄)₂ bioceramics can be prepared by means of hydroxyapatite bioceramic.