CO2/O2-enhanced ethane dehydrogenation over a sol–gel synthesized Ni/ZrO2–MgO nanocatalyst: Effects of Mgo,ZrO2,and NiO on the catalytic performance

A series of catalysts synthesized via the sol–gel method to study the effect of ZrO₂ and MgO and their mixture in ethane dehydrogenation over the Ni/ZrO₂–MgO nanocatalyst in the presence of CO₂/O₂. The catalysts were characterized by XRD, FESEM, EDX, FTIR, and BET techniques. The homogenous dispersion of applied elements in the structure and on the surface of all synthesized catalysts was clear according to the XRD and EDX results, respectively. Synthesized ZrO₂ formed small crystallites while MgO as a high crystalline material depicted large crystallites on the surface. Having these two in the ZrO₂–MgO mixture controlled the observed large crystallite size of MgO and the particle size of the catalyst. The mixture of MgO and ZrO₂ having both beneficial basic and acidic properties resulted in the better catalyst compared to ZrO₂ and MgO. Finally, evaluating the effect of having NiO in the mixture of ZrO₂–MgO confirmed the significant impact of Ni-based catalysts in oxidative dehydrogenation of ethane. Of course, these phases affected all together on the observed results. This cooperation mentioned as the synergistic effect in this study. The best catalyst among the studied ones was Ni/ZrO₂–MgO that demonstrated an ethylene yield of 55.2%.     

Synthesis and characterization of heterogeneous ZnO/CuO hierarchical nanostructures for photocatalytic degradation of organic pollutant

In the current study, ZnO, CuO and ZnO/CuO mixed metal oxide nano-composites with different molar ratio of Zn/Cu (10:1, 8:1, 6:1, 4:1, 2:1) were prepared via low temperature hydrothermal synthesis technique. The consequences of different synthesis conditions such as molar ratio, pH and processing temperature on physicochemical properties of ZnO/CuO nano-composites were also studied. The surface morphology, elemental composition, crystal structure, chemical states and optical characteristics of the prepared nano-composite materials were determined using various techniques such as field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD), X-ray photo-electron spectroscopy (XPS) and UV–visible diffused reflectance spectra (UVDRS). A morphological change in bitter gourd structured ZnO as well as improved optical response of ZnO after incorporation of CuO was observed. The decreased recombination rate of charge carriers, effectual generation of photoinduced charge carriers, formation of hetero-junction system and unique morphology are the responsible factors for improved photodegradation characteristics of prepared ZnO/CuO nano-composites. Role of active species and pH of dye solution in degradation process was also studied.     

静电纺丝法制备CuO/SnO2复合材料及其气敏特性研究

为研究p型材料和n型材料复合时气敏特性的变化,采用静电纺丝法分别制备了CuO、SnO_2以及3种比例混合的CuO/SnO_2复合纳米纤维材料,并通过XRD及SEM对其形貌、微观结构等进行表征.测试了该5种材料对丙酮、甲醛、甲醇、乙醇、甲苯等VOC气体的敏感特性.研究表明,CuO/SnO_2=2∶1的复合材料对丙酮、甲苯和乙醇的的响应值有一定提高;CuO/SnO_2=1∶1的复合材料对丙酮具有很高响应的同时,对乙醇和甲苯的响应产生了一定的抑制作用,从而大大提高了材料的选择性.其机理是:半导体材料复合后,在复合材料的表面会有更多的氧吸附,导致更多的VOC气体在半导体材料表面发生反应,使材料的电阻值变化更加明显,提高了材料的响应值.     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Abstract

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ～500 nm diameter and ～0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.     

Facile and selective approach towards synthesis of a series ZSM-5/ZSM-12 catalysts for methanol to hydrocarbons reactions: Applying different synthesis driving force and conditions

The use of ultrasonic waves was developed for synthesis of zeolites at shorter crystallization time with improving their desirable properties. A series of nanostructured ZSM-5/ZSM-12 composite zeolites with different Si/Al ratios and alkalinity using organic templates were prepared by hydrothermal and sonochemical synthesis methods. The physicochemical properties of synthesized nanocatalysts such as structure, morphology, textural, and acidity were characterized via XRD, FESEM, N₂ physisorption, FTIR, TPD-NH₃, TGA-DTG techniques. The results revealed that increasing the Si/Al ratio and alkalinity in the hydrothermal samples enhanced the crystallization, formation of amorphous microcrystals, and dominant phase of MFI with decreasing MTW competitive phase. Zeolites synthesized by high-temperature and short-time sonochemical method had higher crystallinity, less dominant phase of ZSM-5, smaller crystals, greater surface areas, higher concentration of Brønsted acid sites, and stronger strength of moderate/strong acid sites. The catalytic performance of the zeolites for MTH conversion was evaluated under a reaction temperature of 450 °C at different times on stream. The results showed that the sonochemical zeolite had a higher methanol conversion (100%), higher selectivity toward olefins (28% vs. 19%) with more C₃⁼/C₂⁼ ratio (0.79 vs. 0.58), and lower alkanes selectivity (66% vs. 72%) after 240 min TOS.     

Cu/ZnO Catalysts Derived from Bimetallic Metal–Organic Framework for Dimethyl Ether Synthesis from Syngas with Enhanced Selectivity and Stability

Direct conversion of syngas to dimethyl ether (DME) through the intermediate of methanol allows more efficient DME production in a simpler reactor design relative to the conventional indirect route. Although Cu/ZnO‐based multicomponent catalysts are highly active for methanol synthesis in this process, the sintering issue of Cu during the prolonged reaction generally deteriorates their performance. In this work, Cu/ZnO catalysts in a novel octahedron structure are prepared by a two‐step pyrolysis of Zn‐doped Cu‐BTC metal–organic framework (MOF) in N₂ and air. The catalyst CZ‐350/A, hybrid of MOF‐derived Cu/ZnO sample CZ‐350 and γ‐Al₂O₃ for methanol dehydration, displays the best activity for DME formation (7.74% CO conversion and 70.05% DME selectivity) with the lowest deterioration rate over 40 h continuous reaction. Such performance is superior to its counterpart CZ‐CP/A made via the conventional coprecipitation method. This is mainly due to the confinement of Cu nanoparticles within the octahedron matrix hindering their migration and aggregation. Besides, partial reduction of ZnO in the activated CZ‐350 prompts the formation of Cu⁺‐O‐Zn, further facilitating the DME production with the highest selectivity compared to literature results. The results clearly indicate that Cu and ZnO distribution in the catalyst architecture plays an important role in DME formation.     

Effect of CuO addition to Nd(Zn1/2Ti1/2)O3 ceramics on sintering behavior and microwave dielectric properties

The microwave dielectric properties and microstructures of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ ceramics prepared by the conventional solid-state route were investigated. The prepared Nd(Zn_1/2Ti_1/2)O₃ exhibits a mixture of Zn and Ti showing 1:1 order in the B-site. As an appropriate sintering aid, not only did CuO lower the sintering temperature, it could effectively hold back the evaporation of Zn in the Nd(Zn_1/2Ti_1/2)O₃. Moreover, CuO only resided in boundaries, which was confirmed by EDX analysis. The measured lattice parameters of CuO-doped Nd(Zn_1/2Ti_1/2)O₃ (a = 5.4652 ± 0.0005 ?, b = 5.6399 ± 0.0007 ?, c = 7.7797 ± 0.0008 ? and β = 90.01 ± 0.01°) retained identical to that of the pure Nd(Zn_1/2Ti_1/2)O₃ in all cases. In comparison with the pure Nd(Zn_1/2Ti_1/2)O₃ ceramics, specimen with 1 wt.% CuO addition possesses a compatible combination of dielectric properties with a ε_r of 30.68, a Q × f of 158,000 GHz (at 8 GHz) and a τ_f of − 45 ppm/°C at 1270 °C. It also indicated a 60 °C lowering in the sintering temperature. The proposed dielectrics can be a very promising candidate material for microwave or millimeter wave applications requiring extremely low dielectric loss.     

Preparation and characterization of NiO, Fe2O3, Ni0.04Zn0.96O and Fe0.03Zn0.97O nanoparticles

Nickel oxide (NiO), iron (III) oxide (Fe₂O₃), and mixed oxide (Ni_0.04Zn_0.96O and Fe_0.03Zn_0.97O) nanoparticles were synthesized by modified sol–gel method. The nanoparticle structural and morphological properties were investigated by infrared spectroscopy (FTIR), X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), and Mössbauer spectroscopy. The mixed oxides were characterized by energy-dispersive X-ray spectroscopy (EDX). The oxide precursor powders were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The average sizes of the obtained NiO and Ni_0.04Zn_0.96O nanocrystallites were evaluated by X-ray line broadening using Scherrer's equation and were found to be 36 and 23 nm, respectively. Fe₂O₃ and Fe_0.03Zn_0.97O nanoparticles presented similar sizes, around 19 nm. EDX spectroscopy indicated that the calculated compositions of the mixed oxides were nearly consistent with their estimated molar ratios.     

Fabrication and photocatalytic property of ZnO nanorod arrays on Cu2O thin film

ZnO nanorod arrays were fabricated on Cu₂O thin film by a simple low-temperature liquid-phase-deposition method. The samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The UV-Vis spectroscopy showed that the obtained sample was able to absorb a large part of visible light (up to 650 nm). Their photocatalytic activities were investigated by degradation of dye methylene blue (MB) under UV-Vis and visible light irradiation. It was found that the photocatalytic activity of the ZnO/Cu₂O NRs was higher than the ZnO/ZnO NRs under UV-Vis light. In a word, Cu₂O played an important role in enhancing the photocatalytic activity of the ZnO/Cu₂O NRs.     

Mesoporous Ce<Subscript>0.8</Subscript>Zr<Subscript>0.2</Subscript>O<Subscript>2</Subscript> solid solutions-supported CuO nanocatalysts for CO oxidation: a comparative study of preparation methods

Ce_0.8Zr_0.2O₂ solid solutions were prepared by three different methods, namely, surfactant-assisted, co-precipitation, and sol–gel methods, and were used as supports of CuO nanocatalysts by the deposition-precipitation (DP) method. The prepared supports and catalysts were characterized by using XRD, N₂ adsorption, TEM, and H₂-TPR techniques. The influence of preparation methods on the low-temperature carbon monoxide oxidation activity of these CuO/Ce_0.8Zr_0.2O₂ catalysts was investigated comparatively by using a microreactor-GC system. The catalyst prepared by surfactant-assisted method is more active for low-temperature CO oxidation than the ones prepared by the co-precipitation and sol–gel methods. The support and catalysts prepared by surfactant-assisted method possess mesoporous framework, nanoscale particle size, and high surface area, improving the synergistic effect between CuO species and support, which is beneficial for enhancing the catalytic performance of low-temperature CO oxidation.     

Fabrication of KTa0.65Nb0.35O3 film by pulsed laser deposition on glass substrate with various buffer layers

KTa_0.65Nb_0.35O₃ (KTN) thin films were deposited on amorphous glass substrates using a range of single buffer layers such as indium tin oxide (ITO), zinc oxide (ZnO), 3 at% Al-doped ZnO (AZO), and 3 at% Ga-doped ZnO (GZO), as well as a variety of multi-buffer layers such as SrTiO₃ (STO)/ITO, STO/ZnO, STO/AZO, and STO/GZO using a pulsed laser deposition system. All films showed a polycrystalline perovskite phase with the exception of all single buffer layers and STO/ITO multi-buffer layers. The STO buffer layer is important for crystallizing KTN films due to the similar lattice constant and same crystal structure. The optical transmittance of all films exhibited a transmittance ?90% in the wavelength range.     

The etching characteristics of Al2O3 thin films in an inductively coupled plasma

In this study, the etching characteristics of ALD deposited Al₂O₃ thin film in a BCl₃/N₂ plasma were investigated. The experiments were performed by comparing the etch rates and the selectivity of Al₂O₃ over SiO₂ as functions of the input plasma parameters, such as the gas mixing ratio, the DC-bias voltage, the RF power, and the process pressure. The maximum etch rate was obtained at 155.8 nm/min under a 15 mTorr process pressure, 700 W of RF power, and a BCl₃ (6 sccm)/N₂ (14 sccm) plasma. The highest etch selectivity was 1.9. We used X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface. Auger electron spectroscopy (AES) was used for the elemental analysis of the etched surfaces.     

Synthesis of single crystal Bi2Te3 nanoplates via an inorganic-surfactant-assisted solvothermal route

Single crystal Bi₂Te₃ nanoplates have been successfully obtained by a solvothermal method adopting a lamellar structure as the precursor. Various techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) have been used to characterize the obtained products. The results show that the as-synthesized samples are rhombohedral-structured Bi₂Te₃ single-crystal nanoplates, whose growth direction is perpendicular to c-axis. In addition, some important experiment parameters such as the water/ethanol volume ratio and pH value have been discussed.     

Superhydrophobic CuO@Cu2S nanoplate vertical arrays on copper surfaces

The present work reports a simple method to produce hierarchical CuO architectures on copper substrate through self-generation. Subsequently, CuO@Cu₂S composites have been successfully synthesized from the hierarchical CuO precursors via a facile solution-immersion process. These products were characterized by field-emission scanning electron microscopy, x-ray powder diffraction and x-ray photoelectron spectrum. The wettability of the products was also investigated. It was found that the wettability of the CuO@Cu₂S composite film could be easily changed from hydrophilic to superhydrophobic with simple fluorination modification. Compared with other methods, the method herein is mild, economical and easy to create large area superhydrophobic materials on copper substrate.     

Preparation of (ZnO)1−x(GaN)x:Mn powder and its photoluminescence properties

(ZnO)_1−x(GaN)_x:Mn²⁺ powder was prepared by a conventional solid-state reaction under an NH₃ gas flow. The sample preparation conditions including the mixing ratio of the raw materials, the annealing temperature, and the annealing time were varied. The crystallinity and the photoluminescence (PL) intensity of this fluorescent material were improved by increasing the amount of ZnO and by increasing the annealing time, and no changes was observed in the PL wavelength. The crystallinity of the samples was enhanced and the PL intensity increased markedly at annealing temperatures of 700 °C and 800 °C, respectively. Moreover, it was clarified that the sample could be synthesized at annealing temperatures of above about 650 °C.     

ZnO复合石墨相氮化碳纳米片的制备及其光催化性能研究

为了提高石墨相氮化碳光催化性能,本文以尿素、硫脲、醋酸锌为前驱体,通过氧化热剥离与共混煅烧法分别制备g-C₃N₄纳米片和ZnO/g-C₃N₄异质结复合材料,并采用TEM、FTIR、XRD、UV-Vis DRS、BET等表征手段对制备的催化剂进行结构表征。以罗丹明、大肠杆菌为探针,考察了催化剂的光催化降解性能和抑菌活性。结果表明：以尿素和硫脲为前驱体,经过氧化热剥离处理后能得到的g-C₃N₄ 2D纳米片,其比表面积更大、光催化性能更加优异,且其对罗丹明的降解率较未剥离的g-C₃N₄提高了21.2%。在40 min氙灯照射下,纯g-C₃N₄并未表现出良好的抑菌性能,而通过ZnO复合制备的ZnO/g-C₃N₄异质结复合材料,在光催化降解率和抑菌活性方面均有很大提高,其中复合20%ZnO制得的ZnO异质结复合材料表现出最佳的光催化性能...     

Phase developments in the Pb(Zn1/2W1/2)O3-Pb(Zn1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 pseudo-ternary system

The phase stability ranges in the B-site precursor (Zn_1/2W_1/2)O₂-(Zn_1/3Ta_2/3)O₂-(Zn_1/3Nb_2/3)O₂ were determined by X-ray diffraction (XRD), where wolframite, tri-αPbO₂, and columbite phases were identified. Next attempts were carried out (with the addition of PbO) for the system Pb(Zn_1/2W_1/2)O₃-Pb(Zn_1/3Ta_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃, where the perovskite phase did not develop in the entire compositions investigated. Instead, only the Pb₂WO₅ and pyrochlore phases (along with ZnO) resulted.     

Liquidus Diagram of the Ba-Y-Cu-O System in the Vicinity of the Ba2YCu3O6+x Phase Field

This paper describes the melting equilibria in the vicinity of the high T_c phase Ba₂YCu₃O_6+x, including evidence for two Ba-Y-Cu-O immiscible liquids. Melting equilibria have been investigated in purified air using a combination of differential thermal analysis (DTA), thermogravimetric analysis (TGA), powder x-ray diffraction (XRD), MgO wick entrapment of liquid for analysis, scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDS), and hydrogen reduction for determination of copper oxidation state. For relatively barium-rich compositions, it was necessary to prepare the starting materials under controlled atmosphere conditions using BaO. A liquidus diagram was derived from quantitative data for the melts involved in various melting reactions. In general the 1/2(Y₂O₃) contents of the melts participating in these equilibria were low (mole fraction <4 %). The primary phase field of Ba₂YCu₃O_6+x occurs at a mole fraction of <2.0 % 1/2Y₂O₃ and lies very close along the BaO-CuO_x edge, extending from a mole fraction of ≈43 % CuO to a mole fraction of ≈76 % CuO. It is divided by a liquid miscibility gap and extends on either side about this gap. The topological sequence of melting reactions associated with the liquidus is presented as a function of temperature. Implications for the growth of Ba₂YCu₃O_6+x crystals are discussed.     

高可见光活性磁性催化剂ZnO/ZnFe_2O_4/石墨烯的制备与表征

以硝酸锌和硫酸亚铁为原料,采用水热法一步合成了ZnO/ZnFe_2O_4纳米颗粒,再通过水合肼还原氧化石墨烯合成了ZnO/ZnFe_2O_4/石墨烯磁性催化剂。采用X射线衍射(XRD),场发射扫描电子显微镜(FESEM),透射电子显微镜(TEM),傅立叶变换红外光谱仪(FT-IR)等仪器对催化剂的结构进行了表征。以亚甲基蓝作为目标降解物,考察了不同石墨烯掺量的磁性催化剂在可见光照射下的光催化性能。结果表明,当石墨烯掺量为3%时,磁性催化剂的活性最优,可见光照射60min后亚甲基蓝溶液的降解率高达98%。磁性催化剂稳定性良好,且由于ZnFe_2O_4的存在,磁性催化剂可通过外部磁场进行回收。