Enhanced Photocatalysis of Pentachlorophenol by Metal-Modified Titanium (IV) Oxide

The effects of four metals (Ag, Au, Pt, and Cu) doped on TiO₂ on the photocatalysis of pentachlorophenol (PCP) were investigated. The results of this study indicated that all four metals-doped TiO₂ catalysts were able to enhance the efficiency of PCP photocatalysis with an optimum metallic content of 0.1 wt%. For the metal-doped TiO₂ samples (Au, Pt, and Cu), the patterns of light absorption were significantly extended toward visible light spectra in the wavelengths between 400 and 800 nm. The photocatalysis of PCP was pH dependent with the maximum degradation rate achieved in the solution at pH 3. The formation of chloride ion corresponded with the concentration of PCP degraded which confirmed that dechlorination was the major pathway of PCP photocatalysis. The overall toxicities of PCP samples were reduced with the extension of light exposure using the microtox test. The results of PCP photocatalysis are also discussed based on the characteristics of metal/TiO₂ including X-ray differential (XRD) patterns, Brunquer Emmett Teller (BET) specific area analysis, and Ultra Violet (UV)-Vis absorption spectra.     

Kinetics and mechanism of TNT degradation in TiO2 photocatalysis

The photocatalytic degradation of TNT in a circular photocatalytic reactor, using a UV lamp as a light source and TiO(2) as a photocatalyst, was investigated. The effects of various parameters such as the initial TNT concentration, and the initial pH on the TNT degradation rate of TiO(2) photocatalysis were examined. In the presence of both UV light illumination and TiO(2) catalyst, TNT was more effectively degraded than with either UV or TiO(2) alone. The reaction rate was found to obey pseudo first-order kinetics represented by the Langmuir-Hinshelwood model. In the mineralization study, TNT (30 mg/l) photocatalytic degradation resulted in an approximately 80% TOC decrease after 150 min, and 10% of acetate and 57% of formate were produced as the organic intermediates, and were further degraded. NO(-)(3) NO(-)(2), and NH(+)(4) were detected as the nitrogen byproducts from photocatalysis and photolysis, and more than 50% of the total nitrogen was converted mainly to NO(-)(3)in the photocatalysis. However, NO(-)(3) did not adsorbed on the TiO(2) surface. TNT showed higher photocatalytic degradation efficiency at neutral and basic pH.     

Photocatalytic degradation of p-nitrophenol on nanometer size titanium dioxide surface modified with 5-sulfosalicylic acid

The surface of nanometer size TiO(2) was simply and fast modified by chemical adsorption in saturated solution of 5-sulfosalicylic acid. After surface modification, a stable, yellow surface complex was formed quickly, the wavelength response range of TiO(2) was expanded, it has obvious absorption in the region from 320 to 450 nm; the adsorption efficiency of p-nitrophenol (PNP) by TiO(2) was enhanced from 42% to 84%. The photocatalytic activity was tested on the degradation of PNP. The influences of catalyst and its dosage, pH value, and PNP concentration on the degradation were investigated. On optimal photodegradation conditions, including initial pH 4.0, PNP 5 mg l(-1), catalyst 100 mg, irradiation time 120 min with 160 W high-pressure mercury lamp, the degradation efficiency of PNP was increased from 40% to 88% after surface modification. Surface modification led not only to an increase in the light utilization, but also improved the surface coverage of PNP in comparison with the pure TiO(2). Both of these factors are crucial for the photocatalytic activity of heterogeneous photocatalysis, especially for photodegradation of benzenoid pollutants.     

Photocatalytic degradation of dyes on a magnetically separated photocatalyst under visible and UV irradiation

A novel kind of magnetically separable photocatalyst of TiO2/SiO2/gamma-Fe2O3 (TSF) is prepared. Scanning tunnel microscope (STM) and X-ray diffractometer (XRD) were used to characterize the structure of the photocatalyst. In the TSF photocatalyst, a TiO2 shell is for photocatalysis, a gamma-Fe2O3 core as a carrier is for separation by the magnetic field and a SiO2 membrane between the TiO2 shell and the gamma-Fe2O3 core is used to weaken the adverse influence of gamma-Fe2O3 on the photocatalysis of TiO2. Three kinds of dyes, Fluoresein, Orange II and Red acid G, were used to examine the photocatalytic activity of TSF. Due to strong UV adsorption of the gamma-Fe2O3, the photocatalytic activity of TSF was lower than that of the pure TiO2. Deducting the light absorption of the gamma-Fe2O3 particles, the photocatalytic activity of TSF was found to be higher than that of the P25 under UV irradiation. On the other hand, the photocatalytic activity of TSF under visible irradiation was much lower than that of the P25 TiO2 even deducting the visible light absorption of the gamma-Fe2O3 particles. Differences in the photocatalytic mechanisms under UV and visible irradiation lead to the differences in the photodegradation characteristics of dyes on TSF. The recycled TSF exhibited a good repeatability of photocatalytic activity.     

Platinum-group elements (Rh,Pt, Pd) and Au distribution in snow samples from the Kola Peninsula,NW Russia

In April 1996 snowpack samples were collected from the surroundings of the ore roasting and dressing plant at Zapoljarnij and the nickel smelters at Nikel and Monchegorsk, Kola Peninsula, NW Russia. In the laboratory, filter residues of snowpack samples (fraction>0.45 μm) from 15 localities (close to the nickel processing centres) were chemically for precious metals (Rh, Pt, Pd, Au) and Te by graphite furnace atomic absorption spectrometry (GFAAS) analysis, and for Cu and Ni by ICP-MS. Values up to 2770 ng/l Pd, 650 ng/l Pt and 186 ng/l Au were found in the filter residues. Additionally, platinum-group elements (PGE) and Au contents in ore samples from Noril’sk¹, as well as in technogenic products (“Cu–Ni-feinstein” and copper concentrate) processed at the Monchegorsk smelter complex, were analysed using flameless atomic absorption spectroscopy (FAAS) for comparison with results obtained from snow. Rh, Pt, Pd and Au distribution data show the presence of two ore components (Noril’sk and Pechenga). Concentrations of these metals decrease with distance from the industrial sources and with the prevailing wind direction (generally north–south). Microscopic investigations and electron microprobe analysis of polished sections of snow filter residues (>0.45 μm) also reveal differences between particles from the two sources.     

Photocatalytic degradation of textile dye X3B by heteropolyoxometalate acids

Reactive brilliant red X3B, one recalcitrant textile dye, was decolorized in water by (Photo)-Fenton reactions and TiO(2) photocatalysis [Chemosphere 43 (2001) 1103]. Complementary to this study, the present work has shown the effectiveness of several Keggin-type heteropolyoxomatalates (POM) as a photocatalyst for X3B degradation in water at pH 1.0 under UV light (lambda>/=320 nm) irradiation. Among four POMs, the relative activity was observed to be H(3)PW(12)O(40)z.Gt;H(4)SiW(12)O(40)>H(4)GeW(12)O(40)>H(3)PMo(12)O(40). The reaction was dependent of pH, light intensity and the catalyst loading, but not obviously of the molecular oxygen dissolved in water. Compared to the photocatalyst of TiO(2) (Degussa p25), H(3)PW(12)O(40) was less efficient for the dye bleaching and mineralization. The mechanism study reveals that hydroxyl radicals are involved in the degradation of X3B (and Rhodamine B) by POM photocatalysis.     

Photocatalytic degradation of lignin using Pt/TiO2 as the catalyst

Photocatalytic degradation of lignin was studied with the use of catalysts TiO(2) and Pt/TiO(2). The influence of several experimental parameters, i.e. pH, catalyst dosage and illumination on lignin degradation was investigated. The results showed that application of UV irradiation alone has almost no effect on the reduction of dissolved organic carbon (DOC) and American Dye Manufacture Institute value (ADMI). However, the addition of TiO(2) and Pt/TiO(2) reduced the original DOC (251 mg l(-1)) by more than 40% within 30 min of treatment and the reaction can be simulated with pseudo-first order kinetics. Rapid degradation of lignin was observed in acidic solution using either TiO(2) or Pt/TiO(2) as the catalyst compared to high pH cases. The content of Pt in the Pt/TiO(2) catalyst is 1%. In addition, too much catalyst addition has not increased the DOC and ADMI reduction proportionally. The investigation also indicated that the photocatalytic degradation rates could be enhanced 1-6 times faster after doping TiO(2) with Pt in different pH cases. A modified Nernst type model was adopted to simulate the decoloring process using TiO(2) and Pt/TiO(2) based on the profiles of oxidation reduction potential during the photocatalytic reaction. The developed equation can be used to predict the color removal efficiency of lignin wastewater by the photocatalytic process.     

Photoelectrocatalytic degradation of pentachlorophenol in aqueous solution using a TiO2 nanotube film electrode

Titanium dioxide (TiO2) nanotube film electrodes are fabricated by the anodic oxidation method. Scanning electron microscopy (SEM) showed that these tubes were well aligned and organized into high-density uniform arrays. XRD analysis showed the TiO2 nanotubes to be in the anatase crystal form. The TiO2 nanotube film electrode exhibited increased photoelectrocatalytic (PEC) capability compared to a traditional TiO2 film electrode fabricated using the anodizing method for pentachlorophenol (PCP) degradation in aqueous solution. The bias potential, pH value, and electrolyte concentration were shown to be important factors influencing the degradation of PCP by the PEC method using the TiO2 nanotube film electrode as the working electrode.     

模拟室内环境下掺杂TiO_2纳米晶体的光催化性能

采用环境测试舱模拟可见光下的室内环境,以甲醛气体的光催化降解为探针反应,评价了通过溶胶-凝胶法分别制备的8种（银Ag、铜Cu、铁Fe、钨W、铈Ce、镧La、硫S和氯C l）掺杂TiO2纳米晶体的光催化活性及对甲醛气体的去除效果。用X射线衍射、激光粒度分析和紫外-可见分光光谱表征了掺杂钠米TiO2的微晶尺寸、晶体结构与光学性能。结果表明,Cu掺杂可以提高TiO2对氧的吸附能力,减少纳米粒子表面光生电子与光生空穴的复合,使TiO2的光吸收带边发生红移且有利于对可见光的吸收,从而使Cu掺杂TiO2在模拟室内环境下光催化甲醛气体的能力得到明显提高。     

Simultaneous oxidation of EDTA and reduction of metal ions in mixed Cu(II)/Fe(III)-EDTA system by TiO2 photocatalysis

Both the photooxidation of EDTA and the photoreduction of metal ions in metal-EDTA systems were investigated. EDTA oxidation by TiO(2) photocatalysis occurred sequentially as Cu(II)-EDTA>Cu(II)/Fe(III)-EDTA>Fe(III)-EDTA. For Cu(II)-EDTA, EDTA was completely decomposed after only 60min of irradiation. The rate of EDTA decomposition was directly correlated with the initial Cu(II) concentration in the case of a mixed Cu(II)/Fe(III)-EDTA system. The metal ions in a single metal-EDTA complex were removed following significant decomposition of EDTA. For a mixed Cu(II)/Fe(III)-EDTA system, however, no copper was removed whereas almost all of the iron was removed. The iron and copper species deposited on the TiO(2) surface were identified via EPR and XPS as mixed FeO/Fe(3)O(4) and Cu(0)/Cu(2)O, respectively.     

Photocatalytic degradation of pentachlorophenol on TiO2 sol-gel catalysts

The photocatalytic degradation of pentachlorophenol (PCP) in aqueous solution was investigated using TiO2 catalysts. The samples were prepared by the sol-gel method using different gelation pH and different calcination temperatures. The solids were characterized by specific surface area, X-ray diffraction, UV-Vis absorbance, FTIR and pentachlorophenol adsorption. The catalytic activity of the solids was evaluated in a conventional photoreactor at 298 K using 30 ppm of pentachlorophenol. It was found that the reaction follows a first-order reaction and the kinetic constant values change slightly with the pH of gelation and more significantly with the calcination temperature.     

溴掺杂TiO2光催化剂的制备与性能研究

以KBr和Ti（SO4）2为原料,通过水热法制备了高催化活性的溴掺杂纳米TiO2（Br-TiO2）光催化剂,利用XRD、XPS、TEM、BET和UV-Vis DRS等测试手段对其进行了表征。通过苯酚降解实验评价了Br-TiO2的光催化活性。结果表明,700℃焙烧、溴与钛的摩尔比为0.35∶1时,Br-TiO2具有最佳光催化活性。该催化剂为晶体发育完整的锐钛矿相TiO2,粒径平均大小为50 nm,比表面积为16.81 m2/g,在紫外区的吸收得到加强,光催化能力优于Degussa P-25。确定了降解苯酚的最佳条件：催化剂投加量为0.5 g/L,苯酚初始浓度为10 mg/L,pH值为6.0。     

壳聚糖双冠醚的合成及其对金属离子的吸附性能研究

将二苯并16－冠－5氯代乙酸酯冠醚分别接枝到西佛碱型壳聚糖冠醚CT－15C和CT－18C上,制备了1,4－壳聚糖双冠醚CT－15CAC和CT－18CAC,经元素分析、FT－IR红外光谱分析和X－射线粉末衍射分析表征了结构。研究了CT－15CAC和CT－18CAC对Pd^2 、Ag^ 、Pt^4 、Au^3 、Cu^2 、Hg^2 的静态吸附性能,并与CT－15C和CT－18C进行了比较。结果表明,这4种吸附剂对贵金属离子如Au^3 、Ag^ 、Pt^4 、Pd^2 都具有较好的吸附性能,并能在Cu^2 和Hg^2 共存的条件下选择吸附Pd^2 ,而且壳聚糖双冠醚CT－15CAC和CT－18CAC比壳聚糖单冠醚CT－15C和CT－18C具有更好的选择性。     

The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples.     

模拟可见光下掺杂TiO_2对甲醛溶液光催化降解

模拟自然条件下的可见光,以甲醛的光催化降解为探针反应,评价了通过溶胶-凝胶法分别制备的8种（银Ag、铜Cu、铁Fe、钨W、铈Ce、镧La、硫S、氯Cl）掺杂TiO2纳米晶体的光催化活性及对甲醛水溶液的去除效果。用X射线衍射、激光粒度分析和紫外-可见分光光谱表征了掺杂纳米TiO2的微晶尺寸、晶体结构与光学性能。结果表明：Ce离子尽管有较大的半径但是主要还是掺杂到晶格中,Ce掺杂可以促进TiO2由非正分锐钛矿相向锐钛矿相和金红石相的转变,抑制载流子复合,使TiO2的光吸收带边发生红移且有利于对可见光的吸收,从而使Ce掺杂TiO2在模拟可见光下光催化甲醛水溶液的能力得到明显提高。     

The effect of background irradiation on photocatalytic efficiencies of TiO2 thin films

TiO(2) thin films were prepared on quartz pipe substrates. Effects of the thickness of the films, the wavelength of the UV light and La doping on efficiencies of background irradiated photocatalysis were investigated, and simultaneously was compared with those of foreground irradiated photocatalysis. The results showed that there was an optimal thickness of the film corresponding with each wavelength of the light source limited in the range from 300 nm to 388 nm in the case of background irradiated photocatalysis, which was quite different from that of foreground irradiated one. But in both cases, the film's photocatalytic activities were enhanced by La non-uniformly doping. The results are useful for the design of high-efficiency photocatalytic reactors.     

TiO2光催化处理络合铜废水的实验研究

研究了以悬浮态TiO2为催化剂,在紫外光的作用下对络合铜废水进行光催化反应,分别考察了常温下TiO2投加量、反应时间、废水初始pH值、反应气氛等因素对处理效果的影响,并探讨了反应机理。结果表明：TiO2投加量为2 g/L,废水pH=4,300 W高压汞灯照射下,载入60 mL/min的空气反应40 min,120 mg/L EDTA络合铜废水的Cu（II）与COD的去除率达到最高,分别为96.56%和57.67%。     

TiO2光催化处理络合铜废水的实验研究

研究了以悬浮态TiO2为催化剂,在紫外光的作用下对络合铜废水进行光催化反应,分别考察了常温下TiO2投加量、反应时间、废水初始pH值、反应气氛等因素对处理效果的影响,并探讨了反应机理。结果表明:TiO2投加量为2 g/L,废水pH=4,300 W高压汞灯照射下,载入60 mL/min的空气反应40 min,120 mg/L EDTA络合铜废水的Cu(II)与COD的去除率达到最高,分别为96.56%和57.67%。     

Removal of Cr(VI) and humic acid by using TiO2 photocatalysis

The removal efficiencies of Cr(VI) and HA, using a TiO(2)-mediated photocatalytic process, were investigated with variations in the pH, TiO(2) dosage and Cr(VI)/HA ratio. During the photocatalytic reaction, the total removal of Cr(VI) occurred through adsorption onto TiO(2), as well as its reduction to Cr(III). However, oxidation and adsorption were identified as important removal processes for the treatment of HA. Due to the anionic type adsorption onto TiO(2) and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while that of HA increased with increasing pH. The TiO(2) dosage was also an important parameter for the removal of Cr(VI). As the TiO(2) dosage was increased to 2.5 g l(-1), the removal of Cr(VI) was continuously enhanced, but decreased at dosages above 3 g l(-1) due to the increased blockage of the incident UV light used for the photocatalytic reaction. The removal of Cr(VI) was greatly enhanced when the system contained both HA and Cr(VI) compared to Cr(VI) alone. Also, the removal of HA was greatly enhanced when the system contained both HA and Cr(VI) compared to HA alone. The removal of Cr(VI) was continuously enhanced as the HA concentration gradually increased; however, no further increase was observed above 20 mg l(-1) HA due to the increased absorption of the UV light. This result supports that the photocatalytic reaction, with illuminated TiO(2), could be applied to more effectively treat wastewater containing both Cr(VI) and HA than that containing a single species only.     

Superior photodecomposition of pyrene by metal ion-loaded TiO₂ catalyst under UV light irradiation

BACKGROUND: The photocatalytic degradation of pyrene under UV (125 W Hg-Arc, 10.4 mW/cm2) irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc. As the reduction potential of these metals lies below the conduction band (CB) position (?0.1 eV) of TiO2, the photoexcited electron transfer occurs more readily and reduces electron–hole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO2 because of rapid Fermi energy equilibrium between the CB of TiO2 and its surface adsorbed metal ions. RESULTS AND DISCUSSION: The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni2+ having more negative reduction potential (?0.25 eV) than the CB of TiO2 imparts negligible co-catalytic activity to TiO2 photoreaction. It also revealed that loading of Au3+ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe+3 and Au3+ ions gradually increases from 0.1 to 2 wt.%, the pyrene photodecomposition rate also become faster.