Preparation of rare earth-doped ZnO hierarchical micro/nanospheres and their enhanced photocatalytic activity under visible light irradiation

Rare earth-doped ZnO hierarchical micro/nanospheres were prepared by a facile chemical precipitation method and characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, UV-visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. The results showed that the as-synthesized products were well-crystalline and accumulated by large amount of interleaving nanosheets. It was also observed that the rare earth doping increased the visible light absorption ability of the catalysts and red shift for rare earth-doped ZnO products appeared when compared to pure ZnO. The photocatalytic studies revealed that all the rare earth-doped ZnO products exhibited excellent photocatalytic degradation of phenol compared with the pure ZnO and commercial TiO₂ under visible light irradiation. Nd-doped ZnO had the highest photocatalytic activity among all of the rare earth-doped ZnO products studied. The optimal Nd content was 2.0 at% under visible light irradiation. The enhanced photocatalytic performance of rare earth-doped ZnO products can be attributed to the increase in the rate of separation of photogenerated electron–hole pairs and hydroxyl radicals generation ability as evidenced by photoluminescence spectra.     

溶剂热合成多级ZnO微球及其光催化降解苯酚

以乙二醇为溶剂,KAc为助剂,采用溶剂热法合成多级ZnO微球。通过改变反应温度来调控ZnO微球形貌,并对合成的ZnO微球进行XRD、SEM、PL和UV-Vis DRS等表征分析。结果表明,合成的ZnO为六方纤锌矿晶体结构,由短纳米棒自组装成多级微球。在紫外-可见光照射下,ZnO表现出优异的光催化降解苯酚活性,180℃合成的ZnO样品光催化活性明显优于其他温度合成的样品。用0.1 g的ZnO降解100 mL浓度为5 mg·L^(-1)的苯酚溶液,光照150 min降解率达94.5%。多级ZnO微球光催化性能的提高可推测为较窄的禁带宽度(3.08 eV)有利于吸收光子,较小的晶粒尺寸(25.38 nm)、粗糙的表面以及中空结构有利于反应液与催化剂表面的充分接触。此外,由捕获实验证实光催化降解苯酚的机理是羟基(·OH)为主要的活性自由基,在苯酚降解过程中起主要作用。     

Growth and optical properties of hierarchical flower-like ZnO nanostructures

The integration of low dimensions nanoscale building blocks into 3D architectures has attracted great scientific attention. We have obtained the novel hierarchical flower-like ZnO nanostructures self-assembled by nanorods via a facile hydrothermal method. The as-synthesized samples were characterized with various technologies. The field emission scanning electron microscope (FESEM) images indicated that hydroxide ions play a significant role on the formation of hierarchical flower-like ZnO nanostructures. The X-ray diffraction (XRD) result proved that the nanocrystals were well crystallized hexagonal wurtzite structure. A possible growth mechanism of the nanostructures was proposed based on the effects of hydroxide ions. And the TEM imagines provided some important evidence for the proposed growth mechanism. UV–vis adsorption and photoluminescence (PL) spectra results indicated that the obtained ZnO nanostructurs have a good optical-absorption and photoluminescence property. The as-synthesized ZnO nanostructures exhibited superior photocatalytic performance, which was higher than that of commercially available ZnO.     

Synthesis and photocatalytic activity of g-C3N4/ZnO composite microspheres under visible light exposure

In this paper, a novel g-C₃N₄/ZnO composite microspheres (CZCM) with enhanced photocatalytic activity under visible light exposure were successfully prepared by a self-assembly method followed by calcination in the air. A hierarchical structure in which ZnO microspheres were closely covered with g-C₃N₄ nanosheets was constructed. The microstructure and photocatalytic activities of the CZCM were characterized. The photocatalytic property of CZCM was evaluated by degrading solution Methyl Orange (MO) and Tetracycline (TC). The effects of varied contents of g-C₃N₄ on the photocatalytic capability of CZCM were systematically investigated and the results show that the optimized CZ-15% sample exhibit much higher photocatalytic degradation efficiency than that of bare g-C₃N₄ or ZnO under identical conditions. The analysis of Photoluminescence (PL) and photocurrent (PC) independently conformed that the photo-induced electron-hole (e^?-h⁺) pairs in the CZCM were effectively generated and responsible for the observed photocatalysis. The enhanced adsorption of visible-light and the effective charge separation on the surface of CZCM enabled significant improvement of photocatalytic performance. According to the experimental results and relative energy band levels of the two semiconductors, a possible photocatalysis mechanism for the reaction process is proposed.     

Synthesis of multi-shelled ZnO hollow microspheres and their improved photocatalytic activity

Herein, we report an effective, facile, and low-cost route for preparing ZnO hollow microspheres with a controlled number of shells composed of small ZnO nanoparticles. The formation mechanism of multiple-shelled structures was investigated in detail. The number of shells is manipulated by using different diameters of carbonaceous microspheres. The products were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The as-prepared ZnO hollow microspheres and ZnO nanoparticles were then used to study the degradation of methyl orange (MO) dye under ultraviolet (UV) light irradiation, and the triple-shelled ZnO hollow microspheres exhibit the best photocatalytic activity. This work is helpful to develop ZnO-based photocatalysts with high photocatalytic performance in addressing environmental protection issues, and it is also anticipated to other multiple-shelled metal oxide hollow microsphere structures.     

Hierarchical ZnO/Ag nanocomposites for plasmon-enhanced visible-light photocatalytic performance

Surface plasmon resonance (SPR) of the noble metals improve the photocatalytic activity of semiconductor metal oxides in the visible light region. This work reports the facile preparation of SPR induced visible light active hierarchical ZnO/Ag nanocomposite photocatalysts by using environmental friendly two-step method. The prepared nanocomposites analyzed by using various techniques such as powder-XRD, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, photoluminescence spectroscopy, and photocurrent measurements. The results indicate the formation of hierarchical ZnO/Ag nanocomposites, which shows surface plasmon absorbance and enhanced photocurrent responses. Because of the SPR effect, the nanocomposites show improved visible light photocatalytic activity by enhancing the electron-hole pair separation in Rhodamine B degradation system.     

不锈钢丝网上氧化锌纳米线阵列的 可控生长及光催化性能研究

利用水热法在不锈钢丝网上制备了氧化锌纳米线阵列,借助扫描电镜（SEM）对产物的形貌进行了表征,探讨了反应物浓度和反应时间对产物形貌的影响,并以橙黄Ⅱ为目标降解物,研究了不同生长条件下氧化锌纳米线阵列的光催化降解性能。研究结果表明：硝酸锌浓度和反应时间对氧化锌纳米线阵列的密度、长度、直径和晶形有重要影响,在硝酸锌浓度为0.1 mol/L、反应时间为6 h条件下,制得的氧化锌纳米线阵列具有较佳的光催化活性,多次循环实验结果表明其稳定性较高。另外,双层叠合的氧化锌纳米线的光催化降解性能优于单层氧化锌纳米线的实验结果,其不锈钢丝网的网状结构为制备多维纳米阵列和薄膜提供了一种新的研究思路。     

Synthesis, characterization and photocatalytic recital of nest-like zinc oxide photocatalyst

3D nest-like ZnO nanostructures are synthesized via hydrothermal method operated at ambient temperature (80 °C). The as-synthesized ZnO nanostructures are assembled by numerous ultrathin nanosheets resulting into formation of many grooves which improved the photocatalytic property. The as-synthesized ZnO sample is characterized by XRD, FESEM, FT-IR, Raman spectra, BET surface area and photoluminescence spectra analysis. Moreover, the photocatalytic efficiency of as-synthesized ZnO nanostructures is evaluated for degradation of methylene blue (MB) dye degradation. A comparision with the commercial counterpart reveals that the as synthesized nest-like ZnO degrades MB dye more efficiently. The present synthetic method can provide an effective route for synthesis of other hierarchically structured metal oxides also.     

并流沉淀法合成Fe掺杂ZnO及其光催化脱氮性能

以Zn（NO₃）₂·6H₂O与NH₃·H₂O为原料,采用并流沉淀法合成了Fe掺杂ZnO,通过X射线衍射（XRD）、场发射扫描电镜（FE-SEM）、透射电子显微镜（TEM）、紫外可见漫反射（UV-vis DRS）及比表面积（BET）等测试方法对产物的结构与形貌进行了表征;并以吡啶（Py）石油醚溶液为模拟污染物,考察了其光催化脱氮性能。结果表明,当Fe掺杂量不高于1.0%时,所有复合物均拥有单一的六方晶系纤锌矿结构,尚未出现其他物相。Fe掺杂可有效抑制ZnO晶粒的生长,增大产品的比表面积,并拓宽其光响应范围,显著提高催化剂的光催化活性。处理初始浓度为10 μg·g^-1的Py石油醚溶液,0.50% Fe光催化剂投加量为0.6 g·L^-1,光照距离10 cm,经150 W高压汞灯照射50 min,Py的降解率达到65.3%。     

EDTA-assisted template-free synthesis and improved photocatalytic activity of homogeneous ZnSe hollow microspheres

Homogeneous ZnSe hollow microspheres were synthesized on a large scale through an EDTA-assisted mixed solvothermal strategy without any surfactants and templates. The as-synthesized ZnSe microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis absorption spectroscopy. The results of photodegradation of methylene blue (MB) indicate that the hollow microspheres exhibit a visible-light-responsive photocatalytic behavior. As compared with the bulk ZnSe, the photocatalytic efficiency for the hollow microspheres was enhanced remarkably, which might be related with the hollow aggregates of ZnSe nanocrystallites.     

Enhanced photocatalytic performance of ZnO/multi-walled carbon nanotube nanocomposites for dye degradation

The ZnO nanowire/multi-walled carbon nanotube (MWNT) nanocomposites have been successfully synthesized by one-step hydrothermal method using zinc chloride as Zn source. Their photocatalytic degradation performances on methylene blue and Rhodamine 6G have been investigated under UV irradiation. Experimental results show that the photocatalytic efficiency of the as-synthesized ZnO/MWNT nanocomposites is 3 times higher than that of pure ZnO nanowires. The enhanced photocatalytic activity is attributed to the fast transfer of photo-generated electrons from ZnO to MWNTs, leading to low recombination rate of photo-induced electron–hole pairs.     

Synthesis of hierarchical porous ZnO microspheres and its photocatalytic deNOx activity

Hierarchical porous metal oxide nanostructures have currently attracted much interest because their unique structures with large surface area, high porosity and low density are greatly valuable for functional applications in catalysis, biological engineering and photoelectronics device. Herein, hierarchical porous ZnO microspheres were fabricated by a facile hydrothermal method with subsequent calcination. The sample morphology has been characterized by scanning electron microscopy and transmission electron microscopy. The powder X-ray diffraction has also been used to determine the crystalline structure of the synthesized materials. The effect of calcination temperature on the crystalline structure of synthesized nanostructures has been systematically investigated. The photocatalytic activities of the obtained samples have been evaluated by means of photocatalytic decomposition of nitrogen monoxide (NO).     

Synthesis and Characterization of Hierarchical Biomorphic Mesoporous TiO2 Nanosheets Using Caltrop-Stem as Biotemplate

Biomorphic TiO₂ nanosheets with hierarchical mesoporous structures were synthesized through facile infiltration and thermal decomposition using caltrop stems as biotemplates. Thermo-gravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscope, atomic force microscopy, N₂ adsorption–desorption equipment and UV–visible diffuse reflectance spectra were applied to characterize the microstructures of the samples. Results indicate that the as-synthesized TiO₂ nanosheets with thickness of about 5 nm are composed of anatase phase. The surfaces of TiO₂ nanosheets were constructed by a large number of mesopores, which pore diameter is in the range of 3.5–9 nm. Compared to TiO₂ powders (P25), the as-synthesized TiO₂ nanosheets exhibit a clear red shift (20 nm) showing an enhanced visible photocatalytic activity. The photocatalytic activity of the TiO₂ nanosheets for the decolorization of methylene blue under sunlight irradiation is superior to P25 powders.     

Antibacterial and photocatalytic behaviour of green synthesis of Zn0.95Ag0.05O nanoparticles using herbal medicine extract

The present work aimed to synthesize Zn_0.95Ag_0.05O (ZnAgO) nanoparticles using rosemary leaf extracts as a green chemistry method. The characterization of Ag-doped ZnO nanoparticles was performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet–visible spectrophotometry (UV–visible). The XRD, FTIR, and UV–visible spectra confirmed the formation of the presence of hexagonal ZnAgO nanoparticles. FESEM micrograph shows that the nanoparticles have been distributed homogeneously and uniformly. The morphology of ZnAgO nanoparticles is quasi-spherical configuration. Also, the mean particle size is in the range of 22–40 nm. The photocatalytic degradation of methylene blue in the presence of Ag-doped ZnO nanoparticles is nearly 98.5% after exposing 100 min. The ultraviolet lamp was used as the light source for photocatalyst degradation. The disc diffusion method was chosen to study the antibacterial activity of as-synthesized ZnAgO nanoparticles. Antibacterial activity of Zn_0.95Ag_0.05O nanoparticles against Staphylococcus aureus and Escherichia coli revealed that the as-synthesized ZnAgO nanoparticles were efficient in inhibition of bacterial growth.     

Fabrication of novel p-CuO/n-ZnO heterojunction nanofibers by electrospinning for enhanced photocatalytic performance in the denitrification of fuel oil

CuO/ZnO p-n heterojunction nanofibers were fabricated by coupling p-type CuO with n-type ZnO nanofibers for efficacious elimination of pyridine in fuel oil. The structural and photoelectric characteristics of the as-synthesized nanofibers were systematically studied. The photodegradation system was appropriate for the oxidation of pyridine from fuel oil utilizing the ambient air without mixing with other oxidants. Under visible light illumination, more than 90% of the pyridine (100 mL, 100 μg/g) could be degraded within 60 min by 17.5 mg of MCuZn-0.5 (the photocatalyst with a Cu/Zn molar ratio of 0.5 at%). The visible-light-induced photocatalytic denitrification efficiency of the MCuZn-0.5 nanofibers was nearly 1.5 times as high as that of ZnO alone. The superior denitrification activity of p-CuO/n-ZnO heterojunction nanofibers could be attributed to the enhanced optical absorption capacity and efficacious separation of photoexcited charge pairs. In addition, five-cycle experiments confirmed that MCuZn-0.5 nanofibers also displayed satisfactory photocatalytic denitrification properties. Mechanistic investigations proposed that the photoexcited holes played a dominant role in the formation of reactant intermediates, while superoxide radicals promoted the ultimate mineralization process of pyridine.     

P123 assisted morphology-engineered and hierarchical TiO<Subscript>2</Subscript> microspheres for enhanced photocatalytic activity

In this study, hierarchical titanium dioxide (TiO₂) microspheres with controlled morphology derived from calcination treatment of hierarchical titanate microspheres were fabricated. The obtained hierarchical TiO₂ microspheres with diameters of 1 to 2 µm were composed of polycrystalline anatase nanosheets with thickness of 10 nm. The morphology was manipulated by simply adjusting the molar ratio of tetrabutyl titanate/P123. At a low molar ratio of 17.04, TiO₂ microspheres composed of a large number of nanosheets closely packed together were obtained. At a high molar ratio of 34.08, TiO₂ hybrid architectures with polycrystalline anatase hierarchical microspheres and single-crystal anatase mesoporous (approximately 5 nm) nanospheres were obtained. Investigations on evolution formation revealed that P123 played a key role in the formation of a well-defined hierarchical structure. The photocatalytic performances of the obtained samples were investigated by the degradation of methylene blue and papermaking wastewater. When compared with commercial P25, the obtained hierarchical TiO₂ microspheres exhibit superior photocatalytic activity, high degradation efficiency, and good reproducibility. The product with hybrid architectures exhibited the highest photocatalytic activity. The chemical oxygen demand and the chroma removal rate of papermaking wastewater achieved 85.5 and 100%, respectively, after 12 h of photodegradation.     

低温固相反应合成Bi2WO6粉体及其可见光光催化性能

以Bi(NO3)3?5H2O和Na2WO4?2H2O为原料,采用固相法直接合成Bi2WO6粉体,研究了反应温度和保温时间对产物物相、形貌及可见光光催化性能的影响. 结果表明,350℃下保温2 h所得粉体含少量Bi2O3和Na2W4O13杂质,但光催化性能最好,可见光照射90 min对0.01 mmol/L RhB溶液的降解率达95%,且经5次循环后光催化活性和化学稳定性良好.     

Synthesis of 3D CQDs/urchin-like and yolk-shell TiO2 hierarchical structure with enhanced photocatalytic properties

A novel CQDs/TiO₂ hierarchical structure with enhanced photocatalytic properties was achieved by uniformly decorating urchin-like and yolk-shell TiO₂ microspheres (UYTMs) with carbon quantum dots (CQDs) through an environmentally friendly hydrothermal process. The CQDs were firstly synthesized by the electrochemical method, and the TEM, Raman and PL characterizations strongly indicated that the as-prepared CQDs exhibited good dispersion, high crystallinity and unique up-conversion properties. The UYTMs synthesized by a NaOH-assisted hydrothermal process showed stable 3D hierarchical structure and large surface area, which was beneficial for light absorption and contacting with contamination. The good combination of CQDs and UYTMs was further successfully achieved during the hydrothermal process, and demonstrated by a series of tests. The photocatalytic experiments suggested that the CQDs/UYTMs exhibited better photocatalytic activities than the pure UYTMs and P25 under both visible and UV light irradiation. The CQDs/UYTMs combining with 6?wt% of CQDs showed the best photocatalytic efficiency, while excessive CQDs tended to inhibit the photocatalytic activity. According to the results and discussions, a possible mechanism in improving the photocatalytic efficiency of the CQDs/UYTMs is significantly proposed. The up-conversion property of CQDs can broaden the absorption spectrum of CQDs/UYTMs to the visible light. Moreover, the CQDs, as the electron reservoirs, are efficient to separate the electrons and holes, leading to an improved photocatalytic activity of CQDs/UYTMs.     

Ag/AgBr/BiOBr hollow hierarchical microspheres with enhanced activity and stability for RhB degradation under visible light irradiation

Ag/AgBr/BiOBr hollow hierarchical microspheres were synthesized through a one-pot solvothermal process. The phase structure, morphology and optical property of the samples were characterized by XRD, SEM, XPS and DRS. Ag/AgBr/BiOBr hollow microspheres exhibited higher photocatalytic activity and improved stability than AgBr/BiOBr nanoplates for rhodamine B degradation under visible light irradiation. The enhanced activities of Ag/AgBr/BiOBr could be attributed to the hollow structure and Ag deposition, which is favorable for adsorption of reactants, enhancement of photoadsorption and transfer of photogenerated carriers. Ag deposition also prevented the decomposition of AgBr under light illumination and contributed to an improved stability.     

Attachment of ZnO nanoparticles onto layered double hydroxides microspheres for high performance photocatalysis

In this study, ZnO nanoparticles were successfully deposited on the surface of ZnMgAl–CO₃–LDHs microspheres to form ZnO/ZnMgAl–CO₃–LDHs heterojunction photocatalysts by coprecipitation process. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. The results show that ZnO nanoparticles with diameters about 10–80 nm are tightly grown on the nanosheets of the ZnMgAl–CO₃–LDHs microspheres. Compared with the pristine ZnMgAl–CO₃–LDHs microspheres and pure ZnO, the photocatalytic activity of the heterojunction ZnO/ZnMgAl–CO₃–LDHs photocatalyst is significantly enhanced towards the degradation of phenol under UV light irradiation. The enhancement of the photocatalytic activity of the heterojunction catalysts can be ascribed to their improved light absorption property and the lower recombination rate of the photoexcited electrons and holes during the photocatalytic reaction. The optimal molar ratio of ZnO/ZnMgAl–CO₃–LDHs for the photocatalysis is 3. The heterojunction photocatalyst ZnO/ZnMgAl–CO₃–LDHs may be a promising photocatalyst for future application in water treatment due to its excellent performance in degradation of phenol.