Enhancement of solar light photocatalytic activity of TiO2-CeO2 composite by Er3+:Y3Al5O12 in organic dye degradation

The Er³⁺:Y₃Al₅O₁₂, as an upconversion luminescence agent which is able to transform the visible part of the solar light to ultraviolet light, was prepared by nitrate-citrate sol-gel method. A novel solar light photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite was synthesized using ultrasonic treatment. The X-ray diffraction (XRD) and scanning election microscopy (SEM) were used to characterize the structural morphology of the Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite. In order to evaluate the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite, the Azo Fuchsine dye was used as a model organic pollutant. The progress of the degradation reaction was monitored by UV-Vis spectroscopy and ion chromatography. The key influences on the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ were studied, such as Ti/Ce molar ratio, heat-treatment temperature and heat-treatment time. Otherwise, the effects of initial dye concentration, Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ amount, solar light irradiation time and the nature of the dye on the solar light photocatalytic degradation process were investigated. It was found that the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite was superior to Er³⁺:Y₃Al₅O₁₂/TiO₂ and Er³⁺:Y₃Al₅O₁₂/CeO₂ powder in the similar conditions.     

Synthesis of Er3+:Y3Al5O12 and its effects on the solar light photocatalytic activity of TiO2–ZrO2 composite

The Er³⁺:Y₃Al₅O₁₂ as an upconversion luminescence agent, which can transform visible light into ultraviolet light, was synthesized by nitrate?Ccitrate acid and calcined method. Then, a novel photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂, was prepared using ultrasonic dispersion and liquid boiling method. The samples were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). In succession, the degradation process of organic dye was monitored by UV?CVis spectrum and ion chromatography for verifying the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂. The influences on its photocatalytic activity such as Ti/Zr molar ratio, heat-treated temperature, and time were studied. In addition, the influences of initial concentration, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ amount, solar light irradiation time, and organic dye category on the photocatalytic degradation efficiency were also investigated. It was found the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ was superior to Er³⁺:Y₃Al₅O₁₂/TiO₂ and Er³⁺:Y₃Al₅O₁₂/ZrO₂. Therefore, the Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ is a useful photocatalytic material for the wastewater treatment duo to efficient utilization of solar light.     

Preparation of Er3+:Y3Al5O12/TiO2 composite film and influence of layer number and layer sequence on the visible-light photocatalytic activity

In this work, the Er³⁺:Y₃Al₅O₁₂ as up-conversion luminescence agent was mixed with TiO₂ and the corresponding Er³⁺:Y₃Al₅O₁₂/TiO₂ composite films were prepared on the one-sided surface of treated sheet glass through sol-gel dip-coating method. The prepared Er³⁺:Y₃Al₅O₁₂/TiO₂ composite films were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Their photocatalytic activities were examined through the degradation of some organic dyes under visible-light irradiation. The degradation process of organic dyes was monitored by UV-Vis spectrophotometer. Furthermore, some main influence factors on the visible-light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂ composite film such as heat-treatment temperature and heat-treatment time were studied. The results indicate that three layer Er³⁺:Y₃Al₅O₁₂/TiO₂ composite films with one Er³⁺:Y₃Al₅O₁₂/TiO₂ composite film (as first layer close to sheet glass) and two pure TiO₂ film (as second and third layers) display a higher visible-light photocatalytic activity during photocatalytic degradation of Azo Fuchsine. In addition, the results showed that the visible-light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂ composite film related to the layer number and layer sequence on the sheet glass. Perhaps, the research results may offer some meaningful references for developing solar energy continuous flow wastewater treatment reactor.     

Preparation of Er3+:YAlO3/Fe-doped ZnO composite and investigation on solar light photocatalytic degradation of organic dyes

The Er³⁺:YAlO₃/Fe-doped ZnO composite, a new photocatalyst which could effectively utilize visible light, was prepared. In succession, the Er³⁺:YAlO₃/Fe-doped ZnO was characterized by XRD and SEM, respectively. Acid Red B dyes, was degraded under solar light irradiation to evaluate the photocatalytic activity of the Er³⁺:YAlO₃/Fe-doped ZnO. In addition, the effects of Er³⁺:YAlO₃ content, heat-treatment temperature and time on the photocatalytic activity of Er³⁺:YAlO₃/Fe-doped ZnO were reviewed. Otherwise, the effect of initial dye concentration, Er³⁺:YAlO₃/Fe-doped ZnO amount and solar light irradiation time on the photocatalytic degradation of Acid Red B were also investigated. It was found that the photocatalytic activity of Er³⁺:YAlO₃/Fe-doped ZnO is much higher than that of Fe-doped ZnO and pure ZnO for the similar system. Perhaps, the use of the Er³⁺:YAlO₃/Fe-doped ZnO may provide a new way to take advantage of ZnO in sewage treatment aspects using solar energy.     

Application of TiO2/Er3+:Y3Al5O12 composite to photo-degrade acid red B dye under sun light irradiation

In this work, an upconversion luminescence agent, Er³⁺:Y₃Al₅O₁₂, was synthesized and its absorption and fluorescent spectra was determined. By calculation, the upconversion efficiency of the emission peak at 320 nm was estimated to be about 3.4%. And then, TiO₂/Er³⁺:Y₃Al₅O¹² composite was prepared by simple ultrasonic dispersion and liquids boil methods. The obtained composite was characterized by X-ray diffrac-tion. The effect of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite with different Er³⁺:Y₃Al₅O₁₂ doping amount, heat-treated temperature and heat-treated time on photodegradation of acid red B under sun light was investigated in detail. It was found that the photocatalytic activity of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite was much higher than that for the similar system with only TiO₂ powder. These results support the usefulness of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite in the process of photodegrading dye wastewater and using the sun light.     

Photocatalytic degradation of organic dyes by Er<Superscript>3+</Superscript>: YAlO<Subscript>3</Subscript>/Co- and Fe-doped ZnO coated composites under solar irradiation

In this work, the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites were prepared by the sol-gel method. Then, they were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). Photo-degradation of azo fuchsine (AF) as a model dye under solar light irradiation was studied to evaluate the photocatalytic activity of the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites. It was found that the photocatalytic activity of Co- and Fe-doped ZnO composites can be obviously enhanced by upconversion luminescence agent (Er³⁺: YAlO₃). Besides, the photocatalytic activity of Er³⁺: YAlO₃/Fe-doped ZnO is better than that of Er³⁺: YAlO₃/Co-doped ZnO. The influence of experiment conditions, such as the concentration of Er³⁺: YAlO₃, heat-treatment temperature and time on the photocatalytic activity of the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites was studied. In addition, the effects of solar light irradiation time, dye initial concentration, Er³⁺: YAlO₃/Co- and Fe-doped ZnO amount on the photocatalytic degradation of azo fuchsine in aqueous solution were investigated in detail. Simultaneously, some other organic dyes, such as Methyl Orange (MO), Rhodamine B (RM-B), Acid Red B (AR-B), Congo Red (CR), and Methyl Blue (MB) were also studied. The possible excitation principle of Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites under solar light irradiation and the photocatalytic degradation mechanism of organic dyes were discussed.     

The influence of Yb, B, and Ga-doped Er3+:Y3Al5O12 on solar light photocatalytic activity of TiO2 in degradation of organic dyes

Five up-conversion luminescence agents (Er³⁺:Y₃Al₅O₁₂, Er³⁺:Yb _n Y_{3 ? n} Al₅O₁₂, Er³⁺:Y₃B _a Al_{5 ? a} O₁₂, Er³⁺:Y₃Ga _b Al_{5 ? b} O₁₂, and Er³⁺:Yb _n Y_{3 ? n} B _a Ga _b Al_{5 ? a ? b} O₁₂) were synthesized using sol-gel method and then the corresponding coated composites (Er³⁺:Y₃Al₅O₁₂/TiO₂, Er³⁺:Yb _n Y_3?n Al₅O₁₂/TiO₂, Er³⁺:Y₃B _a Al_{5 ? a} O₁₂/TiO₂, Er³⁺:Y₃Ga _b Al_{5 ? b} O₁₂/TiO₂, and Er³⁺:Yb _n Y_{3 ? n} B _a Ga _b Al_{5 ? a ? b} O₁₂/TiO₂) as photocatalysts were prepared by sol-gel coating process. The XRD and SEM were used to confirm the crystalline phase and surface morphology. The UV-vis absorption and fluorescence-emission spectra were used to research the effect of doping category and amount on the up-conversion emission ability. The photocatalytic activities were detected through the degradation of Acid Red B dye in aqueous solution. Some key parameters of catalyst amount and initial concentration of organic dye on solar light photocatalytic degradation were also examined. The extensive feasibility of prepared photocatalysts in solar light degradation was detected by other organic dyes. The results suggest that the photocatalysts can be widely used in sewage treatment.     

Er~(3+)∶V_(0.01)Y_(2.99)Al_5N_(0.01)F_(0.01)O_(11.98)/BiPO_4/Pt光催化剂的制备及其在降解废水中亚甲基蓝的应用

通过溶胶-凝胶法合成了上转换发光材料Er~(3+)∶V_(0.01)Y_(2.99)Al_5N_(0.01)F_(0.01)O_(11.98)(Er∶YAG),然后利用水热法合成了BiPO_4,再利用高温煅烧法合成了Er∶YAG/BiPO_4/Pt复合物光催化剂.通过使用X-射线粉末衍射仪(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),光致发光光谱(PL)和上转换发射光谱对样品的组成、形貌及光学特征进行了表征.此外,还研究了不同甘油添加量、 Er∶YAG和BiPO_4的摩尔比例和复合温度及光催化剂的循环使用次数对Er∶YAG/BiPO_4/Pt复合物光催化剂活性的影响.实验结果显示Er∶YAG/BiPO_4/Pt复合物光催化剂具有高的光催化活性和较好的稳定性,它可以作为一种高效的光催化剂用于污水中有机污染物的处理.     

Synthesis,properties and mechanism of photodegradation of core–shell structured upconversion luminescent NaYF4:Yb3+,Er3+@BiOCl

Microspherical bismuth oxychloride (BiOCl) can only utilize ultraviolet (UV) light to promote photocatalytic reactions. To overcome this limitation, a uniform and thin BiOCl nanosheet was synthesized with a particle size of about 200 nm. As results of UV–visible diffuse reflectance spectroscopy showed, the band gap of this nanostructure was reduced to 2.78 eV, indicating that the BiOCl nanosheet could absorb and utilize visible light. Furthermore, the upconversion material NaYF₄ doped with rare earth ions Yb³⁺ and Er³⁺ emitted visible light at 410 nm following excitation with near‐infrared (NIR) light (980 nm), which could be utilized by BiOCl to produce a photocatalytic reaction. To produce a high‐efficiency photocatalyst (NaYF₄:Yb³⁺,Er³⁺@BiOCl), BiOCl‐loaded NaYF₄:Yb³⁺,Er³⁺ was successfully synthesized via a simple two‐step hydrothermal method. The as‐synthesized material was confirmed using X‐ray diffraction, scanning electron microscopy, X‐ray photoelectron spectroscopy as well as other characterizations. The removal ratio of methylene blue by NaYF₄:Yb³⁺,Er³⁺@BiOCl was much higher than that of BiOCl alone. Recycling experiments verified the stability of NaYF₄:Yb³⁺,Er³⁺@BiOCl, which demonstrated excellent adsorption, strong visible‐light absorption and high electron–hole separation efficiency. Such properties are expected to be useful in practical applications, and a further understanding of the NIR‐light‐responsive photocatalytic mechanism of this new catalytic material would be conducive to improving its structural design and function.     

Enhancing the Photocatalytic Activity of Sr4Al14O25: Eu2+, Dy3+ Persistent Phosphors by Codoping with Bi3+ Ions

The photocatalytic activity of Bismuth‐codoped Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a postannealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺, Bi³⁺ phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micrograins with sizes in the range of 0.5–20 μm. The samples present an intense greenish‐blue fluorescence and persistent emissions at 495 nm, attributed to the 5d–4f allowed transitions of Eu²⁺. The fluorescence decreases as Bi concentration increases; that suggest bismuth‐induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation, whereas only 62.49% MB degradation is achieved under UV irradiation. Our results suggest that codoping the persistent phosphors with Bi³⁺ can be an alternative to enhance their photocatalytic activity.     

Investigation of the homogeneity of the distribution of doped elements in oxide single crystals

Summary The homogeneity of the distributions of doped V and Ti in Al₂O₃:V³⁺, Y₃Al₅O₁₂:V³⁺, Al₂O₃:Ti³⁺, Y₃Al₅O₁₂:Ti³⁺ single crystals was studied by means of laser emission microanalysis. The applied statistical methods include one-way variance analysis, two-way variance analysis, regression models and the gradient method.     

Preparation of high‐activity AgBr/Ag3PO4 photocatalyst based on hexadecyltrimethylammonium bromide and mechanism of photocatalytic enhancement

A high‐activity AgBr/Ag₃PO₄ heterojunction photocatalyst was synthesized based on hexadecyltrimethylammonium bromide. Its microspheres were characterized using X‐ray diffractometry, transmission electron microscopy and ultraviolet–visible diffuse reflectance spectroscopy. The new photocatalyst with high photocatalytic activity exceptionally outperforms pure Ag₃PO₄ and AgBr in methyl orange degradation. The enhancement of photocatalytic activity is attributed to the efficient separation of electron–hole pairs. In this photocatalytic reaction, h⁺ and ^?O^2? are the main reactive species that induce visible‐light‐driven degradation.     

Preparation,characterization and activity evaluation of p–n junction photocatalyst p-NiO/n-ZnO

In this paper, p–n junction photocatalyst NiO/ZnO was prepared by the sol–gel method using Ni (NO₃)₂ and zinc acetate as the raw materials. The structural and optical properties of the p–n junction photocatalyst NiO/ZnO were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, UV–Vis diffuse reflection spectrum (DRS) and the fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr₂O₇ ²⁻ and photocatalytic oxidation of methyl orange (MO). The results showed that the photocatalytic activity of the p–n junction photocatalyst NiO/ZnO is much higher than that of ZnO on the photocatalytic reduction of Cr₂O₇ ²⁻. However, the photocatalytic activity of the photocatalyst is much lower than that of ZnO on the photocatalytic oxidation of methyl orange. Namely, the p–n junction photocatalyst NiO/ZnO has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. The heat treatment condition also influences the photocatalytic activity strongly, and the best preparation condition is about 400 °C for 2 h. Effect of the heat treatment condition on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were discussed by the p–n junction principle.     

Straightforward Synthesis of Mn3O4/ZnO/Eu2O3-Based Ternary Heterostructure Nano-Photocatalyst and Its Application for the Photodegradation of Methyl Orange and Methylene Blue Dyes

Zinc oxide-ternary heterostructure Mn₃O₄/ZnO/Eu₂O₃ nanocomposites were successfully prepared via waste curd as fuel by a facile one-pot combustion procedure. The fabricated heterostructures were characterized utilizing XRD, UV–Visible, FT-IR, FE-SEM, HRTEM and EDX analysis. The photocatalytic degradation efficacy of the synthesized ternary nanocomposite was evaluated utilizing model organic pollutants of methylene blue (MB) and methyl orange (MO) in water as examples of cationic dyes and anionic dyes, respectively, under natural solar irradiation. The effect of various experimental factors, viz. the effect of a light source, catalyst dosage, irradiation time, pH of dye solution and dye concentration on the photodegradation activity, was systematically studied. The ternary Mn₃O₄/ZnO/Eu₂O₃ photocatalyst exhibited excellent MB and MO degradation activity of 98% and 96%, respectively, at 150 min under natural sunlight irradiation. Experiments further conclude that the fabricated nanocomposite exhibits pH-dependent photocatalytic efficacy, and for best results, concentrations of dye and catalysts have to be maintained in a specific range. The prepared photocatalysts are exemplary and could be employed for wastewater handling and several ecological applications.     

Bi3.25Sm0.75Ti3O12纳米线的水热合成及可见光催化性能

用一步水热法制备了直径约为40 nm的Bi3.25Sm0.75Ti3O12(BSmT)纳米线。BSmT纳米线为层状钙钛矿结构。紫外可见漫反射光谱表明,制备出的BSmT材料的带隙能约为2.67 eV。催化反应结果表明,BSmT的光催化活性比掺氮TiO2(N-TiO2)和纯相钛酸铋(Bi4Ti3O12,BIT)高得多,经可见光照射360 min,浓度为0.01 mmol.L-1甲基橙溶液的降解率可达到92.0%。BSmT光催化剂具有更高催化活性的原因是Sm3+离子掺杂拓展了BIT对可见光的吸收范围,同时抑制了BIT的光生电子-空穴的复合。并且BSmT光催化剂经循环使用4次后,其光催化活性并没有明显降低,表明BSmT是一种稳定有效的可见光催化剂。     

ZnO–Al2O3–CeO2–Ce2O3 mixed metal oxides as a promising photocatalyst for methyl orange photocatalytic degradation

In this research article, ZnO–Al₂O₃–CeO₂–Ce₂O₃ mixed metal oxides phases were prepared by calcination of Zn–Al/Ce–CO₃ layered double hydroxides (LDH) precursors, and evaluated for the photocatalytic degradation of methyl orange (MO) as a model textile dye from aqueous solution under UV irradiation. First, Zn–Al–CO₃ and a series of Zn–Al/Ce–CO₃ with different Ce content (5, 10, 15, 20%) were synthesized through co-precipitation method at Zn/(Al+Ce) molar ratio (r) of 3, then subjected to calcination at 500 °C for 6 h. Samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis and pH point of zero charge. The experimental results of the photodegradation reveal that the photocatalyst developed from Zn–Al–Ce10%-CO₃ LDH exhibits the highest photocatalytic activity, with a degradation efficiency of 99.8% after 300 min of irradiation. This performance was mainly ascribed to the presence of difference state of Ce, leading a highest separation efficiency of electrons and holes. The recycling tests suggests a much high photostability and reusability of the photocatalyst.     

Effects of nano-YAG (Y3Al5O12) crystallization on the structure and photoluminescence properties of Nd3+-doped K2O–SiO2–Y2O3–Al2O3 glasses

Nd³⁺-doped precursor glass in the K₂O–SiO₂–Y₂O₃–Al₂O₃ (KSYA) system was prepared by the melt-quench technique. The transparent Y₃Al₅O₁₂ (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd³⁺ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd³⁺ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Photodegradation of Rhodamine B on Sulfur Doped ZnO/TiO2 Nanocomposite Photocatalyst under Visible-light Irradiation

Sulfur doped ZnO/TiO₂ nanocomposite photocatalysts were synthesized by a facile sol‐gel method. The structure and properties of catalysts were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), UV‐vis diffusive reflectance spectroscopy (DRS) and N₂ desorption‐adsorption isotherm. The XRD study showed that TiO₂ was anatase phase and there was no obvious difference in crystal composition of various S‐ZnO/TiO₂. The XPS study showed that the Zn element exists as ZnO and S atoms form SO^2?₄. The prepared samples had mesoporosity revealed by N₂ desorption‐adsorption isotherm result. The degradation of Rhodamine B dye under visible light irradiation was chosen as probe reaction to evaluate the photocatalytic activity of the ZnO/TiO₂ nanocomposite. The commercial TiO₂ photocatalyst (Degussa P25) was taken as standard photocatalyst to contrast the prepared different photocatalyst in current work. The improvement of the photocatalytic activity of S‐ZnO/TiO₂ composite photocatalyst can be attributed to the suitable energetic positions between ZnO and TiO₂, the acidity site caused by sulfur doping and the enlargement of the specific area. S‐3.0ZnO/TiO₂ exhibited the highest photocatalytic activity under visible light irradiation after Zn amount was optimized, which was 2.6 times higher than P25.     

Two color up-conversion emissions of Er<Superscript>3+</Superscript>-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders prepared by non-aqueous sol-gel method

Er³⁺-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method using the aluminum isopropoxide as precursor, acetylacetone as a chelating agent, nitric acid as a catalyzer, and hydrated erbium nitrate as a dopant under isopropanol environment. The different phase structure, including three crystalline types of (Al, Er)₂O₃ phases, α, γ, θ, and an Er–Al–O stoichiometric compound phase, Al₁₀Er₆O₂₄, was observed for the 0.01–0.5 mol% Er³⁺-doped Al₂O₃ nanopowders at the sintering temperature of 1,000 °C. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978 nm semiconductor laser diodes excitation. With increasing Er³⁺ doping concentration from 0.01 to 0.1 mol%, the intensity of the green and red emissions increased with a decrease of the intensity ratio of the green to red emission. When the Er³⁺ doping concentration rose to 5 mol%, the intensity of the green and red emissions decreased with an increase of their intensity ratio. The maximum intensity of both the green and red emissions with the minimum of intensity ratio was obtained, respectively, for the 0.1 mol% Er³⁺-doped Al₂O₃ nanopowders composed of a single α-(Al,Er)₂O₃ phase. The intensity ratio of the green emission at 523 and 545 nm increased monotonously for all Er³⁺ doping concentrations. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er³⁺-doped Al₂O₃ nanopowders.