Synthesis of zinc oxide and carbon nanotube composites by CVD method: photocatalytic studies

The present work describes the synthesis of multiwall carbon nanotubes (CNT), zinc oxide (ZnO) and their photocatalytic evolutions. Nickel doped fumed SiO₂ used as substrate for the synthesis of CNT by in chemical vapour deposition method. In-situ synthesis of ZnO:CNT composites was achieved in alkaline ethanolic medium with zinc chloride and CNT. The prepared composites were investigated by the Fourier Transform Infrared spectroscopy, confocal Raman spectroscopy, diffuse reflectance UV–visible spectrophotometer (DRS), X-ray diffraction, X-ray Photoelectron Spectroscopy (XPS), Brunaur–Emmett–Teller surface area and field emission scanning/transmission electron microscopy. The composites were employed in the degradation methylene blue and Reactive red-198 under visible light irradiation. The photocatalytic activity was determined by the spectrophotometric technique. The percentage of degradation was more for ZnO:CNT composites and shows higher capacitance, when compared to that of ZnO and CNTs. The recovered and reused catalysts catalytic activity was compared with that of fresh catalyst.     

Facile preparation of Bi-doped ZnO/β-Bi2O3/Carbon xerogel composites towards visible-light photocatalytic applications: Effect of calcination temperature and bismuth content

This work aimed to study the development and properties of Bi-doped ZnO/β-Bi₂O₃/Carbon xerogel composites towards visible light photocatalysis applications. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dispersive energy spectroscopy, infrared spectroscopy, nitrogen adsorption isotherms, Raman spectroscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the developed composites was evaluated through the photodegradation of the 4-chlorophenol molecule and by chronoamperometry tests. The results obtained show that the calcination temperature poses a major influence in the final structure of the materials developed. The calcination temperature of 600 °C resulted in the formation of the β-Bi₂O₃ and Bi⁰ phases, consequently enhancing the photocatalytic activity of the composites due to the increased charge mobility provided by the heterojunctions between zinc oxide, carbon xerogel, bismuth oxide and metallic bismuth. The composite with intermediate bismuth composition (XC/ZnO–Bi₂O₃ 5%) displayed the best photocatalytic response among the materials tested, which was confirmed by its increased photocurrent generation capability. The photocatalytic mechanism is highly dependent in the generation of hydroxyl radicals and the composite presents good reusability properties.     

Microwave-assisted hydrothermal synthesis of cellulose/ZnO composites and its thermal transformation to ZnO/carbon composites

Development of a simple and rapid method for the preparation of cellulose/ZnO composites is of great importance for broadening and improving their potential applications. In this work, the cellulose/ZnO composites were synthesized via the microwave-assisted hydrothermal method using cellulose, zinc nitrate hexahydrate, and ammonia in an aqueous solution. The influence of the cellulose on ZnO crystals was investigated in detail. Cell cytotoxicity of the as-obtained cellulose/ZnO composites was explored. All the cell viability values of the cellulose/ZnO composites were above 95%, indicating that cellulose/ZnO composites had essentially no cytotoxicity. ZnO/carbon (ZnO/C) composites were obtained by calcination at 600 °C in the N₂ atmosphere using cellulose/ZnO composites as precursors. The flower-shaped ZnO crystals could still maintain their morphologies via the N₂ atmosphere calcination. These ZnO/C composites exhibited good photocatalytic performances under both UV and visible light irradiation. Under the UV light irradiation, the degradation efficiency values of methylene blue and rhodamine B dyes were up to 99% and 97%, respectively. The kinetic linear model curves of the photocatalytic degradation of the two dyes could be assigned to the pseudo-first-order kinetics model. This work provided a potential strategy for the synthesis of metallic oxide/cellulose composites, which have broadened the applications of the composites.     

炭吸附纳米氧化锌的制备及其光催化性能研究

以粗氧化锌和冰乙酸为原料,采用炭吸附水热法制备纳米氧化锌粉体。通过热重/差热仪（TG-DTA）、X射线衍射仪（XRD）、透射电镜（TEM）和紫外可见光谱仪（UV-Vis）等对所得催化剂的焙烧温度、物相、微粒尺寸及光吸收性能进行表征。结果表明：炭黑的吸附有效阻止了纳米氧化锌在制备、干燥以及焙烧过程的团聚和烧结,600 ℃焙烧制备的催化剂颗粒均匀,分散性好,团聚较少,平均晶粒尺寸为20 nm,比表面积约为85.25 m2/g。纳米氧化锌作光催化剂对甲基橙进行光催化降解,在60 min内降解率为97%。     

单壁碳纳米管显著增强的ZnO可见光催化活性

利用醋酸锌为原料,采用溶胶-凝胶法制备了单壁碳纳米管（SWMTs）和氧化锌的纳米复合物（ZnO/SWNTs）。用X射线衍射光谱（XRD）、拉曼光谱、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、热重分析（TGA）、傅里叶变换红外光谱（FT-IR）以及紫外-可见吸收光谱（UV-Vis）对复合物进行了表征。结果显示,粒径为10～20 nm的ZnO粒子均匀地负载在SWNTs表面,且在可见光区具有很好的光吸收性能。研究了ZnO/SWNTs光催化剂在太阳光照射下对甲基橙和亚甲基蓝的光催化降解情况。结果表明,复合物的催化活性明显高于ZnO。对于甲基橙,光照200 min后,降解率为99.8%,是纯ZnO（4.8%）的20倍;对于亚甲基蓝,仅光照20 min,降解率就达到了98.4%,是纯ZnO（4.0%）的25倍。     

Multi-walled carbon nanotubes modified Bi2S3 microspheres for enhanced photocatalytic decomposition efficiency

A series of multi-walled carbon nanotubes (MWCNTs)-loaded Bi₂S₃ nanomaterials composites (MWCNTs/Bi₂S₃) were prepared by hydrothermal method. The crystallization, morphology and other properties of the obtained MWCNTs/Bi₂S₃ composites were completely characterized by powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FT-IR), Thermal gravimetric analysis and differential thermal analysis (DTA-TG), N₂ adsorption-desorption isotherm, and UV–vis diffuse reflectance spectroscopy (DRS). In this work, the photocatalytic activity of the as-prepared materials was evaluated for methylene blue (MB) degradation under visible light irradiation. Comparing with others work, the composites showed excellent photocatalytic performance and maintained a good stability during the constant cycling experiment. Finally, a possible photocatalytic reaction mechanism on the MWCNTs/Bi₂S₃ composites was proposed.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Synthesis and characterization of polythiophene/titanium dioxide composites

Polythiophene/titanium dioxide (PT/TiO₂) composites were prepared by the in situ chemical oxidative polymerization method. The resulting PT/TiO₂ composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and field emission scanning electron microscopy (SEM). UV–Vis diffuse reflectance spectra measurements show that the PT/TiO₂ composites can adsorb light of wavelengths ranging from 200 nm to 800 nm. The PT/TiO₂ composites showed good adsorption properties and were more efficient in removing dye from solution than pure PT and pure TiO₂. The PT/TiO₂ composites exhibited photocatalytic activities to some extent under UV light illumination.     

Nanocolumnar titania thin films uniquely incorporated with carbon for visible light photocatalysis

Carbon-doped or carbon-covered titania can enhance photocatalytic performance under visible light. Here we report the first instance of synergistic effect of the carbon incorporation in anatase titania (TiO_2−xC_x:C) films with both substitutional doping and surface covered characteristics, by reactively co-sputtering Ti metal and graphite targets. The nature of incorporated carbon is characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The absorption edge of the carbon incorporated titania thin films shifted from ultraviolet to visible region and directly depended on the carbon content. The photocatalytic performance, e.g., photodegradation of methylene blue (MB), photo-reduction of silver-ions and super hydrophilicity, was greatly enhanced with increasing carbon content. The best photocatalytic activity is obtained in the TiO_2−xC_x:C film of the most carbon concentration about 9.3 at.% with a degradation rate-constant of 0.108 h⁻¹ for MB under visible-light illumination.     

漂浮型氮化碳光催化剂CNx@mEP的制备及性能

针对氮化碳粉末光催化剂在应用过程中存在难以回收、光催化效率不高的问题,本研究采用“浸渍-煅烧”方法,以膨胀珍珠岩为载体,制备了一种方便回收、可多次利用的漂浮型氮化碳光催化剂CNx@mEP。采用扫描电镜（SEM）、X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）、全自动比表面及孔径分析仪（BET）、傅里叶红外光谱仪（FTIR）以及紫外可见近红外漫反射测试（UV-vis）对CNx@mEP进行了分析。分别通过染料降解实验和有害藻类去除实验考察了催化剂的光催化性能。当双氰胺使用量与膨胀珍珠岩载体的质量比为2∶1时得到的CN2@mEP材料光催化性能最好,当催化剂使用量为4g/L时,在可见光下4h降解67.2%的罗丹明B、86.8%的刚果红、31.2%的甲基橙染料和35%的铜绿微囊藻。漂浮型氮化碳光催化剂经过3次重复利用后,仍保持较为稳定的去除效率。     

Preparation, Characterization of Sulfur-Doped Nanosized TiO2 and Photocatalytic Degradation of Methylene Blue Under Visible Light

Sulfur-doped TiO₂ catalysts were prepared by a mechanochemical method. The prepared catalysts exhibited photocatalytic activity in methylene blue degradation under visible light. The catalyst structure has been characterized using UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry analysis (TGA) as well as Fourier transform infrared spectroscopy (FT-IR). UV–visible spectroscopy revealed that the absorption edge of the doped TiO₂ was red-shifted compared with bare TiO₂. XRD patterns suggested that the brookite phase became more prevalent with increasing ball milling duration. In addition, surface sulfate species were detected by FT-IR, XPS and TGA. We deduce the rise of catalytic activity is due to the synergetic effect between the brookite phase and the anatase phase that would probably retard the electron–hole recombination. On the other hand, methylene blue was found to be N-demethylated during the irradiation thus giving rise to blue-shifting of peak at 664 nm in UV–visible spectroscopy.     

Enhanced visible light-induced photoelectrocatalytic degradation of phenol by carbon nanotube-doped TiO2 electrodes

We used a modified sol-gel method to prepare titanium dioxide and multi-walled carbon nanotube (CNT) composites that we subsequently deposited onto indium tin oxide (ITO) conductive glass plates. We characterized these CNT-doped TiO₂ (CNT-TiO₂) films using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV-vis spectroscopy. The photoelectrocatalytic (PEC) activity of the composites was evaluated through their ability to mediate the degradation of phenol. XRD measurements indicated that the TiO₂ component existed solely in the anatase phase and that the crystallinity of the CNTs was low. XPS indicated that carbon atoms could substitute for both oxygen and titanium atoms in the TiO₂ lattice to form Ti-C and Ti-O-C structures, which were responsible for the extra photoabsorption and PEC activity under illumination with visible light, in addition to those provided by the CNTs and carbonaceous and Ti³⁺ species. An interphase interaction between TiO₂ and the CNTs elevated the photoabsorbance of the composites in the visible light region. A sample of TiO₂ doped with 10% CNTs and calcined at 400 °C exhibited the highest photocurrent and PEC efficiency. We systematically investigated the effects of several parameters of the PEC process, including the applied potential and pH, on the phenol conversion.     

Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst

In this paper, a stable and highly efficient plasmonic photocatalyst, Ag@AgCl, with cube-like morphology, has been successfully prepared via a simple hydrothermal method. Using methylene dichloride as chlorine source in the synthesis can efficiently control the morphology of Ag@AgCl, due to the low release rate of chloride ions. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra were used to characterize the obtained product. The photocatalytic activity of the obtained product was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation, and it was found, interestingly, that Ag@AgCl exhibits high visible light photocatalytic activity and good stability.     

Photocatalytic degradation of methyl orange using polythiophene/titanium dioxide composites

Polythiophene/titanium dioxide (PT/TiO₂) composites were prepared via in situ chemical oxidative polymerization, and the obtained composites were characterized by X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS) and transmission electron microscopy (TEM). Using methyl orange (MeO) as a target pollutant, the adsorption capacities and the photocatalytic activities of the resulting composites were investigated. The results indicate that PT/TiO₂ composites have good adsorption capacities due to the electrostatic attraction between the positively charged composite particles’ surfaces and MeO; the incorporation of PT into the composites enhances the photocatalytic degradation activity for MeO under both UV and visible light.     

Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity

Ag-doped ZnO nanoparticles with high and stable photocatalytic activity were prepared by polymer-assisted freeze-drying method with simple process and without organic solvents used. The structural morphology and optical properties of Ag-doped ZnO nanoparticles were characterized by X-ray Diffraction (XRD), Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive X-ray spectroscopy, Ultraviolet-visible Diffuse Reflectance Spectroscopy (UV–vis DRS), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transmission Infrared Spectroscopy (FTIR). Moreover, the thermoanalytical measurements (TGA–DTG) analysis is carried out for proper calcination temperature. XRD results show that Ag nanoparticles were successfully doped into ZnO lattice, and UV–vis DRS results indicate that the doped Ag nanoparticles result in ZnO exhibiting enhanced light trapping capability in the 400?nm and 600?nm range. The photocatalytic activity of Ag-doped ZnO was examined by analyzing the degradation of methyl orange (MO) and methylene blue (MB) dyes under UV light and solar light irradiation, and the results show that all Ag-doped ZnO nanoparticles exhibit better photocatalytic activity than those of pure ZnO nanoparticles at the same degradation conditions; especially the synthesized Ag-ZnO nanoparticles are easy to be recycled and have high photocatalytic stability. Based on the experimental results, the photocatalytic electron transfer path and the photocatalytic mechanism of Ag-ZnO nanoparticles under UV and solar irradiation conditions are explained and clarified.     

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.     

N-doped TiO2 nanoparticles obtained by a facile coprecipitation method at low temperature

N-doped TiO₂ nanoparticles (NPs) were synthesized using a facile synthesis route by coprecipitation method. The effect of the HNO₃ volume and calcination temperature on the structural, morphological, optical and surface properties of the N-doped TiO₂ NPs was studied. X-ray diffraction analysis showed particles of nanometric size (< 16 nm), which are consistent with HR-TEM micrographs. A slight shift of the absorption edge to higher wavelengths is observed as the HNO₃ volume and calcination temperature increases. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) show the presence and stability of nitrogen in the N-doped TiO₂ structure. The photocatalytic activity of the N-doped TiO₂ NPs was assessed by testing the degradation of rhodamine B (RhB) under ultraviolet (UV) and visible light.     

Preparation and visible light photocatalytic activity of carbon quantum dots/TiO2 nanosheet composites

Carbon quantum dots (C QDs)/TiO₂ nanosheet (TNS) composites were prepared by a simple low temperature process in which TNS were dispersed in C QDs solution, and dried at 60 °C. The C QDs/TNS composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results indicated that C QDs were well combined with TNS through surface carbon–oxygen groups. The photocatalytic activity was investigated by degradation of rhodamine B under visible light irradiation. The photocatalytic activity of C QDs/TNS composites was significantly enhanced compared with that of C QDs/P25 composites and pure TNS, which indicated that the unique up-converted photoluminescence behavior of C QDs and highly reactive {0 0 1} facets of TNS both played important roles in the enhancement of photocatalytic activity of C QDs/TNS composites.     

Co负载TiO2/氧化石墨烯纳米复合材料的水热法合成及光催化性能

首先采用改进的Hummers法制得氧化石墨烯(GO)，再利用氧化石墨烯为基体，硫酸钛和氯化钴为前驱体，并通过修饰石墨烯的聚乙烯亚胺(PEI)为交联剂，采用一步水热法成功合成了三维柱状自组装的钴负载TiO2/氧化石墨烯纳米复合材料(Co@/TiO2/PEI/RGO)。通过紫外-可见吸收光谱法、X射线衍射、透射电子显微镜和X射线光电子能谱对复合材料的结构和光电性能进行了表征。在紫外和可见光照条件下，研究了复合材料的光催化降解亚甲基蓝(MB)的性能。结果表明钴负载TiO2/RGO纳米复合材料具有较高的光催化活性，在60min内降解率为99%，可循环至少10次。     

Effect of Thermal Treatment on the Photocatalytic Activity in Visible Light of TiO<Subscript>2</Subscript>-W Flame Spray Synthesised Nanopowders

Effect of W doping as well as a thermal treatment on the structural and photocatalytic properties of TiO₂ produced by flame spray synthesis (FSS) were the subject of investigation. Structural properties were studied by means of X-ray diffraction (XRD), BET adsorption isotherm and transmission electron microscopy (TEM). The surface condition was investigated by X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) and differential thermal and thermogravimetric analysis (DTA-TGA). The photocatalytic properties were studied by optical measurements and photodecomposition of methylene blue under visible irradiation. It was found that the photoactivity in the visible region was enhanced significantly by the W-doping as well as by additional thermal treatment of those nanopowders. The obtained TiO₂-W nanopowders exhibited higher performance under visible light than P25.