Degradation and adsorption of rhodamine B and phenol on TiO<Subscript>2</Subscript>/MCM-41

TiO₂/MCM-41 composites with various titania content were prepared by loading titania into the mesopores of MCM-41 molecular sieves by sol-gel method, and were used as photocatalysts to degrade Rhodamine B (RhB) and phenol. The efficiency of organic contaminants removal was increased significantly compared with pure TiO₂. Ti/Si ratio, namely, the content of TiO₂ was determined by ICP-AES method. TiO₂/MCM-41 composites were characterized by X-ray diffraction, UV-Vis absorption spectroscopy and N₂ adsorption techniques. Experimental results demonstrated that most of the RhB was adsorbed instead of being degradated by TiO₂/MCM-41 due to the large specific surface area of MCM-41, while most of phenol was degradated. It turned out that the TiO₂/MCM-41 with the highest Ti/Si ratio of 0.8220 (wt) had the highest catalytic activity.     

Electrospinning fabrication of mesoporous nano Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>@activated carbon fiber membrane for hybrid removal of phenol from waste water

A mesoporous iron–titanium mixed-oxides@activated carbon(AC) fiber membrane was fabricated by an electrospinning method and applied to the treatment of phenol waste water. The physical and chemical properties of the composite fiber membrane were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption, UV–Vis light diffuse reflectance spectroscopy (DRS), Raman spectroscopy, respectively. The results indicate that the composite nanofiber membrane is composed of α-Fe₂O₃, anatase TiO₂ and activated carbon phases with a specific surface area of 231 m² g^–1 and narrow pore size distribution of 3–6 nm. DRS reveals that the composite membrane has high photons absorption from both ultraviolet light and visible light irradiation owing to the combination of Fe₂O₃, TiO₂ and carbon. The prepared nano Fe₂O₃–TiO₂@AC fiber membrane can act as an efficient reusable photocatalyst and adsorbent for 100% remo val of phenol pollutant. This hybrid technique is hopeful to be widely used in the treatment of various organic waste waters.     

Physical properties of nano-titania hollow fibers and their photocatalytic activity in the decomposition of phenol

A series of nano-titania (TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared using tetra-n-butyl titanate (Ti(OC₄H₉)₄) as precursor and cotton fiber as the template. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption-desorption measurements were employed to characterize the morphology, crystal structure, and surface structure of the samples. The photocatalytic activities of the samples were studied by phenol photodegradation in water under UV irradiation. The effect of calcination temperature, photocatalyst dosage, initial concentration of phenol and irradiation time on the photodegradation of phenol was studied. Results showed that the TiO₂ fiber materials have hollow structures, indicating that these materials had a large specific surface area. The fiber structure material showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light, and the sample calcined at 500°C exhibited the highest phenol photodegradation efficiency. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fiber remained ca. 90% of photocatalytic activity of the fresh sample after being used four times. Moreover, TiO₂ fiber was easily recovered by centrifugal separation from water.     

Low temperature preparation of anatase TiO2-coated activated carbon

Anatase titania sols were synthesized at low temperature (i.e. 75 °C) by hydrolysis of titaniumn-butoxide in abundant acidic aqueous solution. The prepared TiO₂ nanoparticles were loaded on activated carbon in a rotatory evaporator under vacuum, and then the composite photocatalyst was employed for the removal of phenol from water. The apparent rate constant and quantum yield of the composite photocatalyst enhanced 5 and 2.5 times, respectively, compared to single phase titania. The activated carbon with strong adsorbent activity provided sites for the adsorption of phenol, and the adsorbed phenol migrated continuously onto the surface of TiO₂ particles which were located mainly at the exterior surface of the activated carbon. Some phenol remained adsorbed on the catalyst when no traces of phenol were detected in the water. This adsorbed phenol could be degraded by illuminated titania while maintaining UV-irradiation. The photocatalyst was used for six cycles with degraded rate of phenol still higher than 80%.     

Photocatalytic degradation of organic compounds by Au-TiO2/sepiolite composites as the highly efficient catalysts

Photocatalytic oxidation of methyl orange (MO) and Congo red (CR) as typical model organic contaminants was investigated in aqueous solution within a cooperating Au/TiO₂/sepiolite heterostructure system under UV light irradiation. The Au/TiO₂/sepiolite composites with a single-crystalline (anatase) framework was synthesized by a facile sol-gel method using titanium tetrachloride as a TiO₂ precursor and depositing metal Au on the surface of TiO₂ nanostructures via a facile chemical reduction process. The crystal structure, surface area, light adsorption and the photoinduced charge separation rate of the photocatalyst prepared were characterized in detail. As compared with the pristine TiO₂, the Au/TiO₂/sepiolite hybrid material exhibited good photocatalytic efficiency (90%) for the UV-light photooxidation of methyl orange, which is four-fold of that of reference TiO₂. In addition, Au/TiO₂/sepiolite hybrid material also shows a good photodegradation performance toward Congo red removal. The highly efficient photocatalytic activity is associated with the strong adsorption ability of sepiolite for aromatic dye molecules, fast photogenerated charge separation due to the formation of Schottky junction between TiO₂ and metallic Au. This work suggests that the combination of the excellent adsorption properties of sepiolite and the efficient separation effect of noble metallic nanoparticles provides a versatile strategy for the synthesis of novel and highly efficient photocatalysts.     

F and Fe co-doped TiO2 with enhanced visible light photocatalytic activity

Four different sols, pure TiO₂, F doped TiO₂, Fe doped TiO₂, and F–Fe co-doped TiO₂ sols, were prepared by peroxidation at low temperature. The crystal structure, morphology, light adsorption, and photocatalytic properties of the pure and doped TiO₂ were examined by X-ray diffraction, transmission electron microscopy, and ultraviolet–visible spectrophotometry. The relationship between the average size, crystal type, range of visible light absorption, and photocatalytic activity and content and type of doped ions were investigated. The results showed that the average size of the F–Fe co-doped TiO₂ composed of both the anatase and rutile phases was the same as that of pure TiO₂. Furthermore, the visible light photocatalytic activity of the F–Fe co-doped TiO₂ was significantly improved over pure TiO₂, F-doped TiO₂, and Fe-doped TiO₂ due to the large red shift in the light adsorption edge.     

Modification of the Optical and Electronic Properties of TiO<Subscript>2</Subscript> By N Anion-Doping for Augmentation of the Visible Light Assisted Photocatalytic Performance

In this work, a nitrogen-doped anatase TiO₂ nanocrystal is prepared by a modified sol-gel preparation method using the nonionic surfactant (polyoxyethylene sorbitan monooleate) as a structural controller and a soft template. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, UVVis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy techniques. Then the photocatalytic activity of these samples is assessed by the photocatalytic oxidation of phenol under visible light irradiation. The phenol concentration is measured using a UV-Vis spectrometer. Experimental results show that N-doping leads to an excellent visible light photocatalytic activity of the TiO₂ nanocatalyst. Furthermore, the formation energy and electronic structure of pure and N-doped anatase TiO₂ are described by density functional theory (DFT) calculations. It is found that N-doping narrowed the band gap of bare TiO₂, which leads to an excellent visible light photocatalytic activity of N–TiO₂ nanocatalysts. Therefore, the prepared N–TiO₂ photocatalyst is expected to find the use in organic pollutant degradation under solar light illumination.     

Preparation and photocatalytic activity of B,Ce Co-doped TiO2 hollow fibers photocatalyst

A series of B, Ce co-doped TiO₂ (B, Ce-TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared by template method using boric acid, ammonium ceric nitrate and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500°C in an N₂ atmosphere for 2 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and UV-visible spectroscopy (UV-Vis) were employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photocatalytic performance of the samples was studied by photodegradation phenol in water under UV light irradiation. The results showed that the TiO₂ fiber materials have hollow structures, and the fiber structure materials showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light. In the experiment condition, the photocatalytic activity of B, Ce co-doped TiO₂ fibers was optimal of all the prepared samples. In addition, the possibility of cyclic usage of B, Ce co-doped TiO₂ fiber photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fibers remained above 90% of that of the fresh sample after being used four times. The material was easily removed by centrifugal separation from the medium. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Transition metal loaded TiO2 for phenol photo-degradation

Photocatalytic degradation of phenol under both UV radiation and visible light, using TiO₂ (Degussa P-25) and TiO₂ loaded with some transition metal ions (Co, Cu, Fe and Mo) was examined. From the series of metal loaded catalysts, Mo/TiO₂ was the most efficient one. In the presence of Mo, neither TiO₂ anatase/rutile fraction nor its pore size diameter has been affected. However, Mo made its surface more acidic. The percentage of phenol degradation reached under visible light was significantly lower than that under UV radiation due to the lower degree of light absorption by the catalyst surface. From the series of studied catalysts, 2 wt% Mo/TiO₂ was the most efficient one. The synergetic effect between S_BET, mean pore size diameter, catalyst agglomerate size, band gap, ZPC and the type of Mo_xO_y species on TiO₂ surface, depending on Mo loading, created its photocatalytic performance.     

A topotactic tailored synthesis of waxberry-like mixed-phase TiO2 hollow spheres for dye-sensitized solar cells

The waxberry-like mixed-phase Ti O₂hollow microstructures （WMTHMs） are controllably prepared via a topotactic synthetic method,involving the synthesis of monodispersed Ca Ti O₃precursors by a solvothermal method and subsequently transforming them into Ti O₂through a Na₂EDTA-assisted ion-exchange process.The ratio of anatase-rutile is adjustable,and the two phases are connected well with each other.WMTHMs are composed of radially aligned nanorods,speedi...     

球磨法制备Y3+/TiO2光催化剂及处理海水养殖废水

采用机械球磨法制备Y~(3+)修饰TiO_2光催化剂,利用紫外-可见漫反射光谱(UV-Vis DRS)、X射线光电子能谱(XPS)、X射线粉末衍射(XRD)、扫描电镜(SEM)等对其进行表征,在紫外光下,以亚甲基蓝(MB)为去除物来考察催化剂活性并优化球磨工艺。将最佳条件下制得的Y~(3+)/TiO_2光催化剂负载于不同半径的塑料浮球上,分别在紫外光和模拟太阳光照射下处理海水养虾废水,通过CODCr(chemical oxygen demand)及三维荧光观察有机物含量变化。结果表明,当Y~(3+)的物质的量分数为2%,球磨时间4 h,球料质量比4∶1,转速为500 r·min~(-1)时,MB光催化降解反应速率常数可达0.111 3 min~(-1),是纯TiO 2的4.2倍。由UV-Vis DRS、XPS、N_2吸附-脱附、XRD、SEM等表征结果显示,2%Y~(3+)/TiO_2样品的禁带宽度降低至3.05 eV,光吸收发生红移,并产生可见光响应,表面吸附氧含量明显增加,比表面积增大到104 m~2·g~(-1)。采用纯TiO_2及2%Y~(3+)/TiO_2为光催化剂处理养虾废水,在可见光和紫外光下CODCr的去除率分别为14.7%和18.8%、26.9%和37.5%。考察3种直径分别为1、2、3 cm负载Y~(3+)/TiO_2浮球的光催化效果,显示直径为2 cm浮球效果最佳,CODCr去除率可达38.5%。     

Mercury removal from aqueous solution by adsorption on?activated carbons prepared from olive stones

The textural characterization of a series of activated carbons prepared from olive stones, by carbonization at different temperatures (400, 550, 700 and 850 °C) and thermal activation with CO₂, has been investigated using N₂ adsorption at −196 °C and CO₂ adsorption at 0 °C. The effect of pre-oxidation of the carbonized precursor has also been studied, using temperature-programmed decomposition (TPD), to evaluate the effect of oxygen content of the chars in the performance of the obtained activated carbons for mercury removal. The adsorption of Hg(II) cations from aqueous solutions at room temperature by the prepared activated carbons was studied. Experimental results show that all samples exhibit a large microporosity (pore diameter below 0.56 nm). The amount of surface oxygen groups increased after pre-oxidation treatment, this enhancing the Hg(II) uptake (up to 72%). It can be concluded that these groups make the support more hydrophilic, thus providing a more efficient adsorption of Hg(II). The formation of a great amount of surface oxide groups such as carboxyl, phenol and lactone alters the surface charge properties of the carbon, this enhancing the surface-Hg(II) interaction.     

TiO2/polyaniline composites： An efficient photocatalyst for the degradation of methylene blue under natural light

Polyaniline (PAn) sensitized nanocrystalline TiO_2 composites (TiO_2/PAn) were successfully prepared and used as an efficient photocatalyst for the degradation of dye methylene blue (MB).The results showed that PAn was able to sensitize TiO_2 efficiently and the composite photocatalyst could be activated by absorbing both the ultraviolet and visible light (λ:190～800nm),whereas pure TiO_2 absorbed ultraviolet light only (λ<380nm).Under the irradiation of natural light,MB could be degraded more efficiently on the TiO_2/PAn composites than on the TiO_2.Furthermore,it could be easily separated from the solution by simple sedimentation.     

Photo and Chemical Reduction of Copper onto Anatase‐Type TiO2 Nanoparticles with Enhanced Surface Hydroxyl Groups as Efficient Visible Light Photocatalysts

In this study, the photocatalytic efficiency of anatase‐type TiO₂ nanoparticles synthesized using the sol–gel low‐temperature method, were enhanced by a combined process of copper reduction and surface hydroxyl groups enhancement. UV–light‐assisted photo and NaBH₄‐assisted chemical reduction methods were used for deposition of copper onto TiO₂. The surface hydroxyl groups of TiO₂ were enhanced with the assistance of NaOH modification. The prepared catalysts were immobilized on glass plates and used as the fixed‐bed systems for the removal of phenazopyridine as a model drug contaminant under visible light irradiation. NaOH‐modified Cu/TiO₂ nanoparticles demonstrated higher photocatalytic efficiency than that of pure TiO₂ due to the extending of the charge carriers lifetime and enhancement of the adsorption capacity of TiO₂ toward phenazopyridine. The relationship of structure and performance of prepared nanoparticles has been established by using various techniques, such as XRD, XPS, TEM, EDX, XRF, TGA, DRS and PL. The effects of preparation variables, including copper content, reducing agents rate (NaBH₄ concentration and UV light intensity) and NaOH concentration were investigated on the photocatalytic efficiency of NaOH‐modified Cu/TiO₂ nanoparticles.     

Preparation of a visible light-driven Bi2O3–TiO2 composite photocatalyst by an ethylene glycol-assisted sol–gel method,and its photocatalytic properties

A visible light-driven Bi₂O₃–TiO₂ composite photocatalyst was prepared by an ethylene glycol-assisted sol–gel method in which ethylene glycol acted as a polycondensation agent to capture metal ions by reacting with bismuth and titanium sources via a complex polycondensation pathway. The photocatalyst was characterized by X-ray photoelectron spectroscopy, X-ray diffraction, acquisition of N₂ adsorption–desorption isotherms, transmission electron microscopy, and UV–visible diffuse reflectance spectroscopy. The results revealed that the Bi₂O₃–TiO₂ composite was of smaller particle size, greater specific surface area, and had stronger absorbance in the visible light region than pure TiO₂. The photocatalytic activity of the as-prepared catalyst was evaluated by degradation of rhodamine B under visible light irradiation (λ > 400 nm); the as-prepared Bi₂O₃–TiO₂ composite was substantially more active than pure TiO₂. This was ascribed to the high surface area and the heterojunction structure.     

超声波制备介孔结构的氮掺杂TiO2纳米晶及其可见光催化性能

采用超声波辐射法制备了具有介孔结构的高浓度氮掺杂TiO₂纳米晶(N/TiO₂).采用N₂物理吸附、X射线粉末衍射、X射线光电子能谱、透射电镜、光致发光谱和紫外-可见漫反射光谱等手段对N/TiO₂进行了表征.以波长为400~660nm的可见光为光源,以水体污染物邻苯二甲酸二甲酯为降解对象,考察了不同制备方法对N/TiO₂光催化性能的影响.结果表明,超声波辐射使氮掺杂浓度提高了2.2倍,该法制备的N/TiO₂同时具有较好的介孔结构,表现了更高的光催化降解邻苯二甲酸二甲酯的活性.其活性提高的主要原因是N/TiO₂含有更高浓度的氮和对可见光具有更强的吸收能力.     

Microwave‐Hydrothermal Preparation and Visible‐Light Photoactivity of Plasmonic Photocatalyst Ag‐TiO2 Nanocomposite Hollow Spheres

Visible‐light‐driven plasmonic photocatalyst Ag‐TiO₂ nanocomposite hollow spheres are prepared by a template‐free chemically‐induced self‐transformation strategy under microwave‐hydrothermal conditions, followed by a photochemical reduction process under xenon lamp irradiation. The prepared samples are characterized by using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N₂ adsorption‐desorption isotherms, X‐ray photoelectron spectroscopy, UV/Vis and Raman spectroscopy. Production of ?OH radicals on the surface of visible‐light illuminated TiO₂ was detected by using a photoluminescence method with terephthalic acid as the probe molecule. The photocatalytic activity of as‐prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under visible‐light irradiation. The results show that the surface plasmon absorption band of the silver nanoparticles supported on the TiO₂ hollow spheres was red shifted, and a strong surface enhanced Raman scattering effect for the Ag‐TiO₂ nanocomposite sample was observed. The prepared nanocomposite hollow spheres exhibits a highly visible‐light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of pure TiO₂ and commercial Degussa P25 (P25) powders. Especially, the as‐prepared Ag‐TiO₂ nanocomposite hollow spheres at the nominal atomic ratio of silver to titanium ( R ) of 2 showed the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2.     

Adsorption of mercury from single and multicomponent metal systems on activated carbon developed from cherry stones

The adsorption of mercury from a single/multi-solute aqueous solution by activated carbon (AC) prepared from cherry stones (CS) by chemical activation with H₃PO₄, ZnCl₂ or KOH is studied. Three series of AC (i.e., P, H₃PO₄; Z, ZnCl₂; K, KOH) were prepared by controlling the impregnation ratio and carbonization temperature. The textural characterization of AC was carried out by gas adsorption, mercury porosimetry and density measurements. The surface chemistry was analyzed by the pH of the point of zero charge (pH_zpc), FT-IR spectroscopy and Boehm’s method. Experiments of mercury adsorption were conducted by the batch method, using aqueous solutions of mercury and of mercury, cadmium and zinc without pH adjustment. The ACs possess a wide range of pore volumes and sizes. Their microporosity is usually well developed. The meso- and macropore volumes are higher for the P carbons and K carbons, respectively. BET surface areas as a rule range between 1000 and 2000 m²?g^?1. The pH_zpc is much lower for the P carbons. The content of acidic oxygen surface groups is lower for the K carbons, whereas the content of basic groups is higher for these carbons. The kinetics of the adsorption process of mercury is faster for ACs with high volumes of large size pores. However, the surface groups have a marked unfavorable influence on the kinetics. The pseudo-second order rate constant (k₂×10^?3, g/mol?h) is higher by the order Z-4-800 (67.69)>K-3-800 (43.45)>P-3.44-400 (36.98). The incorporation of zinc and cadmium to the mercury solution usually decelerates the adsorption process for the P carbons and Z carbons and accelerates it for the K carbons. The amount adsorbed of mercury is much larger for the K carbons than for the other ACs. For the Z carbons, competition effects of zinc and cadmium on the adsorption of mercury are negligible, which indicates that mercury adsorbs specifically on surface active sites of these adsorbents.     

Dye-effect in TiO2 catalyzed contaminant photo-degradation: Sensitization vs. charge-transfer formalism

Anatase TiO₂ surfaces have been treated with 2,4,6-triphenylpyrilium hydrogen sulfate (TPPHS) dye to yield the modified TiO₂/TPPHS surface. The modified TiO₂/TPPHS surface was then supported onto activated carbon (AC) surfaces to yield a new class of catalytic system AC/TiO₂/TPPHS. The catalytic activities of naked TiO₂, TPPHS solution, TiO₂/TPPHS and AC/TiO₂/TPPHS systems were examined in photo-degradation of phenol and benzoic acid in water, using both UV and visible regions. All studied systems showed low catalytic activity when used in the visible region. In UV, the AC/TiO₂/TPPHS showed highest activity, whereas the naked TiO₂ and TPPHS solutions were the least active systems. The dye role, in enhancing activity of modified surfaces in UV degradation of contaminants, is understandable by a charge-transfer catalytic effect rather than a sensitizing effect. AC role is explainable by its ability to adsorb contaminant molecules and bringing them closer to catalytic sites.     

Preparation,Characterization and Photocatalytic Activity of Lanthanum Doped Mesoporous Titanium Dioxide

Lanthanum doped mesoporous titanium dioxide photocatalysts with different La content were synthesized by template method using tetrabutyltitanate (Ti(OC₄H₉)₄) as precursor and Pluronic P123 as template. The catalysts were characterized by thermogravimetric dif-ferential thermal analysis, N₂ adsorption-desorption measurements, X-ray diffraction, and UV-Vis adsorption spectroscopy. The effect of La³⁺ doping concentration from 0.1% to 1% on the photocatalytic activity of mesoporous TiO₂ was investigated. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of about 10 nm with high surface area of 165 m²/g. X-ray photoelectron spectroscopy measurements in-dicated the presence of C in the doped samples in addition to La. Compared with pure mesoporous TiO₂, the La-doped samples extended the photoabsorption edge into the visible light region. The results of phenol photodecomposition showed that La-doped mesoporous TiO₂ exhibited higher photocatalytic activities than pure mesoporous TiO₂ under UV and visible light irradiation.