A novel nano-sized MoS2 decorated Bi2O3 heterojunction with enhanced photocatalytic performance for methylene blue and tetracycline degradation

In this paper, MoS₂ was used as a band-suitable semiconductor to construct the Bi₂O₃/MoS₂ heterostructured photocatalysts for the first time via a deposition-hydrothermal method. The XRD, SEM and HRTEM analysis indicated that the surface of Bi₂O₃ was decorated with MoS₂ nanoparticles and Bi₂O₃/MoS₂ heterojunctions were formed. The performances on photocatalytic degradation of methylene blue (MB) and tetracycline (TC) were evaluated under visible light irradiation. The results demonstrated that the Bi₂O₃/MoS₂ heterojunctions displayed remarkably improved photocatalytic activity for both MB and TC degradation, compared to the base material (Bi₂O₃). Specifically, as the molar ratio of MoS₂ was 23.81%, the obtained Bi₂O₃/MoS₂-23.81 heterojunctions exhibited promising photocatalytic activities, and approximately 100% MB and 97% TC were degraded within 100 min, respectively. The superior photocatalytic activity was mainly attributed to its large surface area, high visible-light harvesting and the efficient separation of photogenerated electrons and holes caused by the unique heterojunction architecture. Notably, the Bi₂O₃/MoS₂ heterojunctions showed remarkable stability in recycling photocatatlytic experiments. The active species trapping and terephthalic acid (TA) fluorescence experiments indicated that the •OH was the major reactive oxidizing species for MB degradation. Furthermore, the intermediates were detected by UPLC-MS spectrometry and the possible degradation pathways for MB and TC were proposed. Finally, a possible reaction mechanism of Bi₂O₃/MoS₂ heterojunctions for the photodegradation MB was also proposed. This interesting interfacial architecture strategy will provide useful insights for designing and fabricating new class of binary heterojunctions with high-efficient photocatalytic activity towards practical application.     

Synthesis and photocatalytic activity of Na+ co-doped CaTiO3:Eu3+ photocatalysts for methylene blue degradation

The Na⁺ co-doped CaTiO₃:Eu³⁺ powders were produced through the solution combustion method. The phase structure and optical properties of the synthesized samples were adequately characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and scanning electron microscopy (SEM). The XRD patterns revealed that a low level of Eu³⁺ doping could not cause lattice distortion of CaTiO₃. Photoluminescence (PL) displayed the CaTiO₃:0.5% Eu³⁺ sample synthesized at 900 °C has the weakest PL emission and the low electrons and holes recombination rate. The morphology of the sample was small nanoscale spherical particles. The UV–vis diffuse reflection spectra proved that doping Na⁺ and Eu³⁺ enlarged the absorption region and reduced band energy of pure CaTiO₃. The photocatalytic properties of Na⁺ co-doped CaTiO₃:Eu³⁺ samples were investigated via degrading methylene blue (MB) under ultraviolet light irradiation. The CaTiO₃:0.5% Eu³⁺, 0.5% Na⁺ sample, by contrast, exhibited the greatest photocatalytic property and the degradation rate was as high as 96.62%, which makes it a promising multi-functional material (photocatalytic material and red phosphor) for decreasing organic pollution in water.     

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.     

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.     

Characterization and evaluation of ZnO/CuO catalyst in the degradation of methylene blue using solar radiation

Catalysts based on the combination of zinc oxide and copper oxide were synthesized at a 80:20 mass ratio by the Pechini method and calcined at 500, 600 and 700 °C for 1 h. These catalysts were characterized by XRD, SEM, FT-IR, BET, UV-Vis, TGA and XRF. They were subsequently tested for the removal of methylene blue dye by means of heterogeneous catalysis combined with solar radiation through a RCCD experimental design, analyzing the concentrations of H₂O₂ and methylene blue, as well as radiation exposure time and pH. The average crystallite size obtained was of 26.21, 28.21 and 35.91 nm for the respective calcined samples. The XRF was effective in determining the elements present in the catalyst, consisting of 75% zinc oxide and 25% copper oxide. The values of surface area were of 7.54, 7.19 and 3.92 m²/g, respectively. The experimental design showed that the catalyst calcined at 500 °C exhibited the highest removal efficiency (93%) of methylene blue with a dye concentration of 20 mg/L. Despite the need to carry out new studies to optimize the process, results suggest that the application of solar photocatalysis in the treatment of methylene blue with ZnO/CuO is a feasible alternative.     

Preparation of Ag-sensitized ZnO and its photocatalytic performance under simulated solar light

ZnO was prepared rapidly by microwave heating method. The results of scanning electron microscopy show that the leaflike ZnO is composed of self-assembled ZnO particles of 30–50 nm. Ag-sensitized ZnO composite was prepared by UV-photoreduction and glycol reduction, respectively. The composite was characterized by means of scanning electron microscopy, X-ray diffraction and photoluminescence. The ZnO and Ag/ZnO prepared were applied in photocatalytic degradation of phenol and methyl orange as model of organic pollutant in water under simulated solar light. The results show that Ag doping in both methods of UV-photoreduction and glycol reduction can remarkably improve the photocatalytic activity of ZnO under simulated solar light. The utilization ratio of Ag in glycol reduction is high and the optimum content of Ag in Ag/ZnO composite is only 1.33%. Therefore, the glycol reduction is a novel and excellent method for preparing Ag-sensitized ZnO composite with high photocatalytic activity.     

CuO nanosheets/ZnO nanorods synthesized by a template-free hydrothermal approach and their optical and magnetic characteristics

Nanostructured CuO/ZnO heterojunctions were fabricated via a template-free hydrothermal reaction. The prepared CuO/ZnO nanocomposites are composed of one dimensional (1D) hexagonal ZnO nanorods and two-dimensional (2D) monoclinic CuO nanosheets. The single crystal nature of both ZnO and CuO was confirmed. Optical spectra show the widened absorption range from UV to visible light, which suggests the potential of the obtained CuO/ZnO composites for visible-light-driven photocatalyst. The point defects at the interface play the leading role in triggering ferromagnetism of CuO/ZnO composites. Fundamentally, the ferromagnetism can be understood by the charge-transfer mechanism according to Stoner theory. The findings can give a further insight into the ferromagnetic origin of nonmagnetic composites and the integration of ferromagnetic and photocatalytic properties into an identical sample.     

Structural,optical and photocatalytic properties of ZnO nanorods: Effect of aging time and number of layers

ZnO thin films were prepared by sol–gel dip coating method onto glass substrates. The effects of aging time of the starting solution (2, 10 and 30 days) and the number of coats (2, 5 and 10 coatings) on structural, morphological and optical properties were investigated. Photocatalytic efficiency was also assessed. X-ray diffraction analysis indicates that all the films exhibit a Zincite-type structure with a preferred grains orientation along the [002] direction. The preferred orientation factor (POF) increases with aging time while the crystallite size decreases. The field emission scanning electron microscopy observations reveals nanorods morphology. The length of ZnO nanorods increase with increasing number of layers whereas their length decreases as a function of aging time while adopting a random orientation. A high optical transparency is observed for all ZnO thin films, ranging from 90 up to 96%. Methylene Blue (MB) dye photocatalytic degradation was found increases with aging time, reaching almost 94% after 10 h under UV irradiation. The apparent reaction rate (K_app) obtained by Langmuir-Hinshelwood model increases with increasing aging time from, from 0.218 h⁻¹ for 2 days to reach a steady state around 0.270 h⁻¹. Nevertheless, a small variation of K_app was recorded when varying the number of coats; 0.223–0.226 h⁻¹.     

Adsorption and photocatalytic decomposition of methylene blue on mesoporous metallosilicates

Mesoporous silica and mesoporous metallosilicates with Al, Ti and Fe as foreign metal species were successfully synthesized by the rapid room temperature method. Mesoporous metallosilicates with low contents of foreign metals possessed high surface area (S_a), large mesopore volume (V_mp) and highly ordered hexagonal mesoporous structure. Increases in foreign metal contents caused disordering the mesoporous structures and lowering the S_a and V_mp values. Bleaching of aqueous methylene blue (MB) by mesoporous silica and metallosilicates was investigated. Mesoporous aluminosilicate and ferrosilicate with cation-exchangeable ability showed the excellent property for the adsorption of MB of cationic dye, while mesoporous ferrosilicate and titanosilicate which absorbed UV lights catalyzed the photocatalytic decomposition of MB under UV-illumination.     

Preparation and photocatalytic performance of Zn2SnO4/ZIF-8 nanocomposite

Zn₂SnO₄(ZTO)/ZIF-8 nanocomposite photocatalysts were prepared by solution method and hydrothermal method. The structures and properties of ZTO/ZIF-8 nanocomposites were studied. Results indicate that ZTO is adsorbed on the surface of ZIF-8 after recombination. The addition of ZIF-8 can inhibit the recombination of photoelectron-hole pairs, which significantly improve the photocatalytic activity of ZTO. After the addition of ZIF-8, the adsorption performance of the composite is slightly improved, which is attributed to the high specific surface area of ZIF-8. In the removal efficiency of 20 mg/L MB dye solution, the photocatalytic activity of ZTO/0.4 wt%ZIF-8 nanocomposite is 75% after 120 min. In addition, the structural stability and cyclic properties of ZTO/ZIF-8 are investigated, and the degradation efficiency is still 71% after four cycles.     

Intensifying the photocatalytic degradation of methylene blue by the formation of BiFeO3/Fe3O4 nanointerfaces

A novel highly efficient photocatalyst composite BiFeO₃/Fe₃O₄ has been synthesized by mechanosynthesis and applied to the degradation of Methylene Blue under visible light. Structural, optical and photocatalytic properties of the proposed photocatalyst composites are carefully investigated. The nanointerfaces, associated to ferrous Fe²⁺ ions of the Fe₃O₄ nanoparticles, improve the photocatalytic efficiency when compared with pure BiFeO₃ or Fe₃O₄. The time required to the complete degradation of Methylene Blue solution is 40 min for the sample with 20% of Fe₃O₄ which is more than 7 times faster than the time required using BiFeO₃ alone. Moreover, with the addition of H₂O₂ a complete degradation is achieved just after 10 min, which is faster than any other photocatalytic reaction reported for BiFeO₃-based materials. This enhancement is assumed to be related to an electron drain process due to the difference between energy levels of the conduction bands of BiFeO₃ and Fe₃O₄ combined with the direct Fenton-like process associated with the Fe²⁺ ions of the composites.     

ZnO溶胶的制备及其抑菌性和光催化性能研究

以二水合醋酸锌和KOH为原料,聚乙烯吡咯烷酮(PVP)为表面修饰剂,制备了稳定透明的ZnO溶胶。利用X射线衍射仪、扫描电子显微镜、紫外可见分光光度计、荧光光谱仪和高效液相色谱仪对其进行了表征和测试。考察了二水合醋酸锌、KOH和PVP的用量对ZnO粒径及溶胶稳定性的影响;以金黄色葡萄球菌、大肠杆菌、绿脓杆菌、洋葱假单胞菌、白色念珠菌和黑曲霉为测试对象,采用琼脂稀释法测定ZnO溶胶的最小抑菌浓度(MIC);并对亚甲基蓝、乐果和乙酰甲胺磷溶液进行光催化性能研究。实验结果表明:在添加10 mmol二水合醋酸锌、15 mmol KOH和1.6 g PVP的较佳条件下合成的ZnO溶胶最为稳定,ZnO粒径分布均匀;ZnO溶胶有效地抑制了菌种的生长,其对金黄色葡萄球菌和洋葱假单胞菌的抑菌效果最好;同时高效地降解了亚甲基蓝、乐果和乙酰甲胺磷溶液,表现出较好的光催化活性。     

Structural,optical and magnetic behavior of (Pr,Fe) co-doped ZnO based dilute magnetic semiconducting nanocrystals

The development of ZnO-based dilute magnetic semiconductor nanostructures co-doped with rare-earth and transition metals has attracted substantial attention for spintronics application. In this work, Pr (1%) and Fe (1%, 3%, and 5%) co-doped ZnO nanoparticles (NPs) were synthesized via co-precipitation method, and their structural, morphological, optical, photoluminescence, and magnetic properties were investigated. The single-phase wurtzite hexagonal crystal structure of all samples was detected via X-ray diffraction. Morphological analysis revealed spherical shape of the NPs with an average size in 20–50 nm range. The ultraviolet (UV)–visible measurements showed a redshift in the UV band and a slight change in the bandgap of the co-doped NPs. Fourier transform infrared analysis proved the existence of different functional groups in all synthesized NPs. X-ray photoelectron spectroscopy confirmed that Pr and Fe ions incorporated in the host ZnO lattice exhibit Pr³⁺ and Fe³⁺ oxidation states, respectively. Photoluminescence analysis showed that incorporated ions induce characteristic emission bands and structural defects in the synthesized NPs. Magnetic characterization indicated that the ZnO NPs exhibit a diamagnetic nature. However, the (Pr, Fe) co-doped NPs exhibit ferromagnetism at room temperature because of the interactions between Pr³⁺ and Fe³⁺ ions and trapped electrons mediated by bound magnetic polarons. Excellent optical and magnetic properties of synthesized samples may render them promising candidates for spintronics applications.     

Analysis of structural,optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals

In this paper, the structural, optical and magnetic properties of pure ZnO and Fe/Co co-doped ZnO nanoparticles are presented. Rietveld refinement of XRD pattern revealed the single phase wurtzite structure for prepared samples. FTIR study confirmed the formation of tetrahedral coordination between zinc and oxygen ions. SEM and TEM techniques were used to examine the morphology of samples. The absorption spectra showed the decrease in optical energy band gap with Fe/Co co-doping in ZnO. PL spectra demonstrated five peaks correspond to the ultraviolet region, violet, violet-blue, blue-green and green in the visible region. Emission peak in the UV region is attributed to near band-edge excitonic emission. Other four emission peaks in PL spectra are related to different defect states. M-H curve showed room temperature ferromagnetic (RTFM) behaviour of doped ZnO sample. This paper enhances the understanding of structural, optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals for application in spintronics, solar cells, and ceramics.     

pH dependent morphology and texture evolution of ZnO nanoparticles fabricated by microwave-assisted chemical synthesis and their photocatalytic dye degradation activities

ZnO nanostructures are well-known photocatalysts for the degradation of toxic organic dyes and their morphology, size, and other physicochemical properties play important roles in their photocatalytic performance. To study the effect of size, morphology, and synthesis conditions in photocatalytic performance, we synthesized ZnO nanoparticles of different morphologies through a simple microwave-assisted chemical process at different pH values of the reaction mixture. Different pH values of the reaction mixture produced ZnO nanoparticles of different morphologies and sizes. The nature of the pH controlling agent and final pH of the reaction mixture were seen to have considerable effects on the lattice parameters and microstrain of the ZnO nanocrystals, along with their photocatalytic performance. We observed that while the ZnO nanostructures synthesized at very high pH values of the reaction mixture have a high specific surface area, their photocatalytic activity is higher when they are synthesized at acidic pH or pH near the isoelectric point of ZnO. The results demonstrate that the photocatalytic activity of ZnO nanostructures not only depends on their size or specific surface area but also strongly depends on the concentration of catalytic sites at their surface.     

ZnO,Al/ZnO and W/Ag/ZnO nanocomposite and their comparative photocatalytic and adsorptive removal for Turquoise Blue Dye

In the present investigation, ZnO, Al/ZnO, and W/Ag/ZnO nanocomposites were prepared and employed as an adsorbent and photocatalyst for the removal of Turquoise Blue Dye (TBD) as a function of various process variables. The dye removal (maximum) was observed at pH range 2–3, adsorbent dose of 0.05–0.1 g, contact time 60 min, 170–200 mg/L initial TBD dye concentration at 30 ⁰C. The adsorption of dye on to nanocomposite followed pseudo second order kinetics and Langmuir equilibrium model. The thermodynamics study revealed the spontaneous and exothermic dye adoption nature on to nanocomposites. On the other hand, the TBD dye photocatalytic removal was efficient in pH range 2–3, catalyst dose 0.05 g, 5 mg/L dye initial concentration within 60 min of visible light exposure. The TBD dye degradation followed first-order kinetics model. The SEM and FTIR analysis were also performed of dye loaded and unloaded ZnO, Al/ZnO, and W/Ag/ZnO along with desorption study of using NaOH as eluting agent. The W/Ag/ZnO showed higher efficiency (adsorption and photocatalysis) versus ZnO and Al/ZnO and results revealed that the nanocomposites are efficient, which could be applied for the adsorptive and photocatalytic remediation of dyes from industrial effluents.     

Solid-state thermal dewetted silver nanoparticles onto electrochemically grown self-standing vertically aligned ZnO nanorods for three-dimensional plasmonic nanostructures

Three dimensional (3D) plasmonic nanostructures composed of silver nanoparticles decorated ZnO NRs arrays, have been fabricated by a process combining the electrochemical growth of ZnO NRs and further formation of Ag nanoparticles by the solid-state thermal dewetting (SSD) process. The effect of SSD parameters on the morphological, structural and optical properties of the Ag NPs decorated ZnO NRs arrays has been investigated. It is possible to tune the bandgap of the Ag NPs@ZnO nanorods array 3D plasmonic nanostructure by tailoring the Ag nanoparticle sizes, allowing light manipulation at the nanoscale. The silver nanoparticles attached to the ZnO NRs arrays experienced surface plasmonic coupling effect, causing enhancement in the room temperature photoluminescence (PL) UV emission and quenching the corresponding visible light one. An enhancement in the near band edge emission PL intensity of ZnO to the deep level emission PL intensity ratio after Ag NPs decoration of the ZnO nanostructures corresponding to ca. 11 folds has been observed, indicating that the defect emission is obviously suppressed.     

Ca系永磁铁氧体工艺与磁性研究

用陶瓷工艺制备了Ca系永磁铁氧体,用X射线衍射仪分析样品的物相,用振动样品磁强计、永磁铁氧体测量仪、浮力法等对产品相关磁特性进行了检测,用扫描电子显微镜(SEM)观察样品的断面形貌。实验表明,微量Ba的掺杂促进了Ca系铁氧体片状晶粒的均匀生长,磁性能得到明显改善,矩形比(Hk/HCJ)从89%提高到96%,M*值提高2.6%,达到6 200以上,对Ca_(0.98-x)La_xBa_(0.02)Fe_(10.6-x)Co_xO_(19)(x=0.3),1 300℃保温1 h的预烧料粉碎时添加0.2%的H_3BO_3、0.4%的Si O_2,研磨之后成型,成型坯适当低温长时间的烧结更有利于Ca系永磁铁氧体磁参数的改善,如将其烧结温度控制为1 195℃并保温2 h,可获得B_r为452 m T,H_(CJ)为402 k A/m的Ca永磁铁氧体。     

ZnO nanorods surface-decorated by WO3 nanoparticles for photocatalytic degradation of endocrine disruptors under a compact fluorescent lamp

Nanoscaled tungsten oxide (WO₃) particles coated on ZnO nanorods (ZNRs) were newly synthesized by combining a hydrothermal technique with a chemical solution process. The structure, morphologies and compositions of the as-prepared WO₃–ZNR nanocomposites were characterized through XRD, FESEM, TEM and Raman measurements. The results revealed that pure monoclinic WO₃ nanoparticles with an average size range of 18–26 nm were distributed on the surfaces of ZNRs and attached strongly. Particularly, the optical properties as well as photocatalytic characteristics of pure ZNRs and WO₃–ZNR nanocomposites with different loadings of WO₃ were also examined. The absorption of WO₃–ZNR nanocomposites was redshifted due to effective immobilization of WO₃ on ZNRs. Under irradiation of a 55 W compact fluorescence lamp, the photocatalytic activities of the WO₃–ZNR nanocomposites were superior to those of pure ZNRs and P25 in the degradation of resorcinol (ReOH). Furthermore, WO₃–ZNR nanocomposites showed very favorable recycle use potential and high sedimentation rate. Other endocrine disrupting chemicals (EDCs) such as phenol, bisphenol A (BPA) and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the WO₃–ZNR nanocomposites in indoor environmental remediation.     

纳米WO_3的制备及光催化降解亚甲基蓝的研究

以钨酸钠和盐酸为原料,采用水热法制备纳米WO_3,并利用X射线衍射分析(XRD)、X光电子能谱分析(XPS)、扫描电镜(SEM)和热重分析(TG-DSC)等手段进行表征。结果表明,焙烧温度对WO_3的晶型会产生影响,焙烧温度控制在600℃可获得单斜相的WO_3。另外,考察了纳米WO_3在紫外光照射下光催化降解亚甲基蓝溶液的催化性能,结果表明,溶液初始溶度6 mg/L,初始pH=11,WO_3用量为0.2 g/100 m L,在300 W汞灯光照条件下反应2 h时,亚甲基蓝降解率为93.7%。