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1.
This study has been undertaken to investigate the relationship between Pd oxidation states on TiO2 photocatalysts and their photocatalytic oxidation behaviors of NO. Three types of Pd-modified TiO2 with different Pd oxidation states were prepared by wet impregnation method, neutralization method and photodeposition method, respectively. And these Pd-modified photocatalysts were characterized by X-ray diffraction analysis, X-ray photoelectron spectrum analysis (XPS), UV–Vis diffuse reflectance spectra and temperature programmed desorption (TPD). It was found from XPS results that the dominant oxidation states of Pd on these Pd-modified TiO2 catalysts were Pd2+, PdO, and Pd0, respectively. NO-TPD results showed that the NO adsorption capacity was improved greatly by the modification of Pd2+ ions. The activity tests showed that Pd-modified TiO2 by a wet impregnation method increased photocatalytic activity compared to pure TiO2 (Degussa P25). It was concluded that Pd2+ ions on as-prepared TiO2 catalysts provided key contributions to the improvement of photocatalytic activity. However, Pd0 and PdO deposits on TiO2 almost had no positive effect on NO oxidation. The mechanism of photocatalytic oxidation of NO in gas phase over Pd-modified TiO2 was also proposed.  相似文献   

2.

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?Chole 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.  相似文献   

3.
采用自制木粉/壳聚糖接枝丙烯酸-丙烯酰胺吸附树脂R1、R2、R3对二元金属离子Cu2 +/pb2和Zn2+/pb2+溶液中的吸附性能进行了较系统考察.pb2+离子溶液中存在竞争离子Cu2+、Zn2+时,随竞争离子浓度增加,3种吸附树脂R1、R2、R3对pb2+的吸附量明显下降,而竞争离子吸附量显著增加.二元溶液中各金属离子浓度相同时,3种树脂对竞争离子Cu2+、Zn2+的吸附量大于对pb2+的吸附量;各溶液中分别加入NaCl及NaNO3、尿素后,对pb2+离子的吸附量下降迅速.随吸附树脂用量增加,竞争离子Cu2+、Zn2+的吸附量逐渐减小,pb2+的吸附量在吸附树脂用量0.10 g/L(Zn2 +/pb2+溶液)或0.15 g/L(Cu2+/pb2+溶液)时出现最大值.溶液pH值对树脂吸附性能有显著影响.3.0<pH<5.O时,3种树脂对竞争离子和pb2+的吸附量快速增大;5< pH <9时,树脂对竞争离子和pb2+的吸附量基本不变;9<pH<ll时,树脂对pb2+的吸附量减小,而对竞争离子的吸附量或增大或减小.  相似文献   

4.

A two-component material (Fe3O4@CaSiO3) with an Fe3O4 magnetite core and layered porous CaSiO3 shell from calcium nitrate and sodium silicate was synthesized by precipitation. The structure, morphology, magnetic properties, and composition of the Fe3O4@CaSiO3 composite were characterized in detail, and its adsorption performance, adsorption kinetics, and recyclability for Cu2+, Ni2+, and Cr3+ adsorption were studied. The Fe3O4@CaSiO3 composite has a 2D core–layer architecture with a cotton-like morphology, specific surface area of 41.56 m2/g, pore size of 16 nm, and pore volume of 0.25 cm3/g. The measured magnetization saturation values of the magnetic composite were 57.1 emu/g. Data of the adsorption of Cu2+, Ni2+, and Cr3+ by Fe3O4@CaSiO3 fitted the Redlich–Peterson and pseudo-second-order models well, and all adsorption processes reached equilibrium within 150 min. The maximum adsorption capacities of Fe3O4@CaSiO3 toward Cu2+, Ni2+, and Cr3+ were 427.10, 391.59, and 371.39 mg/g at an initial concentration of 225 mg/L and a temperature of 293 K according to the fitted curve with the Redlich–Peterson model, respectively. All adsorption were spontaneous endothermic processes featuring an entropy increase, including physisorption, chemisorption, and ion exchange; among these process, chemisorption was the primary mechanism. Fe3O4@CaSiO3 exhibited excellent adsorption, regeneration, and magnetic separation performance, thereby demonstrating its potential applicability to removing heavy metal ions.

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5.

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir–Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm? 1 and 0.984 ppm min? 1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.  相似文献   

6.
研究了1%和10%(V/V)模拟正丙醇废水在UV/TiO2体系、UV/H2O2体系、Fe2+/H2O2体系和UV/TiO2/Fe2+/H2O2体系等4种工艺条件下的降解动力学过程,对比了降解动力学特点及工艺参数对动力学常数的影响,优化工艺参数。结果表明,UV/TiO2体系和Fe2+/H2O2体系的降解过程可分为零级反应阶段和一级反应阶段,转折点分别在反应开始后2 h和氧化剂浓度为6.7 g/L,UV/H2O2体系和UV/TiO2/Fe2+/H2O2体系分别符合零级反应和一级反应规律;相同工艺参数条件下,6 h反应后,组合工艺UV/TiO2/Fe2+/H2O2体系在处理效率达85%,比前3个体系分别高52.0%、8.3%和32.0%,与UV/TiO2体系和Fe2+/H2O2体系的处理效率之和持平,其协同效应提高了速率常数,在目标物浓度降低时依然可维持较高降解速率。而目标物浓度提高10倍后,UV能量利用率提高35.5倍,氧化剂用量是Fe2+/H2O2体系的1/7.1。  相似文献   

7.

Nitrogen-doped titanium dioxide (TiO2) and Fe–N-codoped TiO2 layers on fly ash cenospheres (FAC) as floating photocatalyst were successfully prepared through sol–gel method. Photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)–Vis diffuse reflectance spectroscopy (DRS), and nitrogen adsorption analyses for Brunauer–Emmett–Teller (BET) specific surface area. Photocatalytic efficiency of the prepared catalyst was evaluated through using the decomposition of Rhodamine B (RhB) as a model compound under visible light irradiation. Photocatalytic activity and kinetics of catalyst under visible light were detected in details from different Fe/Ti mole ratios by detecting photodegradation of RhB. Experimental results show that when the calcination temperature was 550 °C, the dosage of FAC was 3.0 g, and the mole ratio of Fe/Ti was 0.71 %; the synthesized Fe–N-TiO2/FAC photocatalyst presented as anatase phase and that N and Fe ions were doped into TiO2 lattice. The material’s specific surface area was 34.027 m2/g, and UV–Vis diffuse reflectance spectroscopy shows that the edge of the photon absorption has been red shifted up to 400–500 nm. Fe–N-codoped titanium dioxide on FAC had excellent photocatalytic activity during the process of photodegradation of RhB under visible light irradiation.

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8.
1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO2 in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO2 nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO2 under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO2 were evaluated. Results show that the N-doped TiO2 can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min?1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min?1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO2 catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO2 under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO2 under visible light was 0.03078 L mg?1, and the apparent reaction rate constant (k) was 1.3941 mg L?1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology.  相似文献   

9.

Acetaminophen (ACT) is one of the most frequently detected pharmaceuticals in aqueous environments, and treatment of ACT were generally carried out by photocatalytic degradations under high energy UV irradiation. In this study, potassium ferricyanide was utilized as a quadruple-elemental dopant in a TiO2 photocatalyst in order to enhance its visible-light activity. Two critical parameters (amounts of dopants and durations of calcination) of the synthesis of the photocatalyst by a sol–gel method were systematically evaluated. Crystal structure of the doping TiO2 was examined by X-ray diffraction while the effects of the two parameters on the photocatalytic activity were elucidated by various characterizations. Increasing the amount of dopant or the duration of calcination red-shifted the UV–vis DRS of the doped TiO2. The estimated band gap energy of the doped TiO2 decreased slightly as the amount of dopant increased, but it increased as the duration of calcination increased. The FT-IR yielded characteristic peaks that revealed the effects of the two parameters, whereas the SEM images revealed the morphological evolutions of each effect. The photocatalyst, synthesized at optimum conditions was able to remove 99.1 % acetaminophen with rate constant of 7.9 × 10−3 min−1, which was 4.88 times greater than virgin TiO2. In general, this study not only optimized synthetic conditions of the new visible-light active photocatalyst for ACT degradation but also presented characterizations conducted by SEM, XRD, UV–vis DRS, and FTIR to elucidate the relationship between modified structure and the photocatalytic activity.

Effects of doping amounts of K3[Fe(CN)6] and calcunation duration on visible light absorbance of TiO2 photocatalysts

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10.
This study synthesized multiwall carbon nanotube (MWNT)–titania (TiO2) composites and examined their characteristics and photocatalytic performance for the cleaning of gas-phase benzene, toluene, ethyl benzene, and o-xylene (BTEX) under simulated indoor conditions. Optical and spectral surveys of the as-synthesized composite confirmed that the TiO2 nanoparticles were bound intimately to the MWNT networks. The photocatalytic performance was evaluated using an annular-type reactor inner-coated with MWNT–TiO2 or Degussa P25 TiO2. The composite revealed gas removal ability superior to that of stand-alone TiO2. This composite was also less affected by humidity during toluene decomposition compared to the previous result obtained from a stand-alone TiO2. Unlike another previous result obtained from the TiO2, the performance of the composite was not affected by changes in input concentration (IC) within a simulated indoor air quality range (0.1–1.0 ppm) but it decreased significantly when the IC was increased to 5 and 10 ppm. As the flow rate was decreased from 4.0 to 1.0 L min?1, the average efficiency for the target compounds increased to 95% or ~100%. The MWNT–TiO2 composite could be applied effectively to the decomposition for BTEX under certain simulated indoor conditions.

Implications: Unlike water applications, there are few reports of gas-phase applications of multiwall carbon nanotubes (MWCNT)–TiO2 composites. This study found that MWCNT–TiO2 composites showed performance in the removal of toxic gaseous aromatic superior to that of stand-alone TiO2. In addition, the pollutant degradation efficiency of the composite was less affected by humidity than for a stand-alone TiO2 unit within a simulated indoor relative humidity range. Moreover, unlike the TiO2 unit, the composite's performance was not affected by variations in the input concentrations within the simulated indoor air quality (IAQ) range. In addition, the decomposition efficiencies increased to 100% with decreasing flow rate.  相似文献   

11.
The removal and mechanism of Cu2+ and Cd2+ from aqueous single-metal solutions were investigated by using a novel biosorbent from waste-activated sludge. A series of adsorption experiments was designed to disclose the effects of the key factors on the adsorption capacity of the biosorbent for the metal ions. The mass ratio of the biosorbent to metal ion was optimized as 2 to balance the adsorption capacity and the removal efficiency. A right shaking speed (150 r/min) not only ensured enough contact frequency between the sorbent and the adsorbate but also reduced the mass transfer resistance. The natural pH value (about 5.5) of the metal solutions benefited a high adsorption capacity of the biosorbent and avoided the consumption of acid or base for pH adjustment. The adsorption reactions belonged to the endothermic process between 15 and 45 °C. As the scanning electron microscopy (SEM) images showed, the meshy structure with long chains and many branches was ideal for the biosorbent to quickly capture the metal ions. The energy-dispersive X-ray (EDX) spectra confirmed that the adsorbed metal ions lay in the precipitates of the adsorption reactions. According to the FTIR analyses, the functional groups responsible for Cu2+ adsorption majorly consisted of O–H, N–H, COOH, CONH2, and the groups containing sulfur and phosphorus, while those for Cd2+ adsorption contained O–H, N–H, COOH, and CONH2. The differences in the responsible functional groups explained the phenomenon that the adsorption capacity of the biosorbent for Cu2+ was higher than that for Cd2+.  相似文献   

12.

Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg0) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Sex/Activated carbon (Sex/AC) was synthesized and applied to remove Hg0 in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Sex/AC reached 17.98 mg/g Hg0 adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg0 removal above 85% at the NO and SO2 conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Sex/AC. Chemical adsorption plays a dominant role in Hg0 removal: Selenium anchored on the surface of AC would capture Hg0 in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg0 released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg0 to HgO. This work provided a novel and highly efficient carbon-based sorbent -Sex/AC to capture the mercury in coal combustion flue gas.

Selenium-modified porous activated carbon and the interface functional group promotes the synergistic effect of physical adsorption and chemical adsorption to promote the adsorption capacity of Hg0.

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13.
TiO2-supported manganese oxide catalysts formed using different calcination temperatures were prepared by using the wet-impregnation method and were investigated for their activity in the low-temperature selective catalytic reduction (SCR) of NO by NH3 with respect to the Mn valence and lattice oxygen behavior. The surface and bulk properties of these catalysts were examined using Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Catalysts prepared using lower calcination temperatures, which contained Mn4+, displayed high SCR activity at low temperatures and possessed several acid sites and active oxygen. The TPD analysis determined that the Brönsted and Lewis acid sites in the Mn/TiO2 catalysts were important for the low-temperature SCR at 80~160 and 200~350 °C, respectively. In addition, the available lattice oxygen was important for attaining high NO to NO2 oxidation at low temperatures.

Implications: Recently, various Mn catalysts have been evaluated as SCR catalysts. However, there have been no studies on the relationship of adsorption and desorption properties and behavior of lattice oxygen according to the valence state for manganese oxides (MnOx). Therefore, in this study, the catalysts were prepared by the wet-impregnation method at different calcination temperatures in order to show the difference of manganese oxidation state. These catalysts were then characterized using various physicochemical techniques, including BET, XRD, TPR, and TPD, to understand the structure, oxidation state, redox properties, and adsorption and desorption properties of the Mn/TiO2 catalysts.  相似文献   

14.
TiO2-supported activated carbon felts (TiO2–ACFTs) were prepared by dip coating of felts composed of activated carbon fibers (ACFs) with either polyester fibers (PS-A20) and/or a polyethylene pulp (PE-W15) in a TiO2 aqueous suspension followed by calcination at 250 °C for 1 h. The as-prepared TiO2–ACFTs with 29–35 wt.% TiO2 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption. The TiO2–ACFT(PS-A20) samples with 0 and 29 wt.% TiO2 were microporous with specific surface areas (S BET) of 996 and 738 m2/g, respectively, whereas the TiO2–ACFT(PE-W15) samples with 0 and 35 wt.% TiO2 were mesoporous with S BET of 826 and 586 m2/g, respectively. Adsorption and photocatalytic activity of the as-prepared samples were evaluated by measuring adsorption in the dark and photodegradation of gaseous acetaldehyde (AcH) and methylene blue (MB) in aqueous solution under UV light. The TiO2 loading caused a considerable decrease in the S BET and MB adsorption capacity along with an increase in MB photodegradation and AcH mineralization. Lemna minor was chosen as a representative aquatic plant for ecotoxicity tests measuring detoxification of water obtained from the MB photodegradation reaction with the TiO2–ACFT samples under UV light.  相似文献   

15.
Cu/La共掺杂TiO2光催化氧化水中的氨氮   总被引:1,自引:0,他引:1  
采用水解-沉淀法制备了Cu/La共掺杂纳米TiO2催化剂,利用XRD、XPS和BET技术对其进行表征,并考察了在紫外灯下,共掺杂TiO2对氨氮的光催化氧化工艺条件。物相结构和比表面积测试结果表明,共掺杂催化剂具有较好的锐钛矿晶型,孔径分布为4~8 nm,Cu/La共掺杂TiO2La以La3+,Cu是以Cu2+、Cu+的形式掺杂进入TiO2的晶格。光催化实验表明:所得改性光催化剂对氨氮的去除及焦化废水的处理均具有较高的催化活性。  相似文献   

16.
The present work involves the photocatalytic mineralization of glyphosate on a plug flow reactor by UV/TiO2. The effect of catalyst loading shows an optimal value (0.4 g L?1) which is necessary to mineralize glyphosate. The kinetic rate of glyphosate mineralization decreases with the increasing initial concentration of glyphosate, and the data can be described using the first-order model. An alkaline environment is conducive to glyphosate mineralization. The mineralization efficiency increases with elevated flow rate to 114 mL min?1, which is followed by a decrease with a further increase in flow rate due to the reduction of the residence time. The presence of external oxidants (K2S2O8, H2O2 and KBrO3) and photosencitizer (humic acid) can significantly enhance glyphosate mineralization. Photocatalysis oxidation ability of the three studied oxidants decrease in the order of: S2O8 2? > BrO3 ? > H2O2. Finally, the Langmuir–Hinshelwood (L-H) model was used to rationalize the mechanisms of reactions occurring on TiO2 surfaces and L-H model constants were also determined.  相似文献   

17.
We investigated the adsorption and decomposition of sulfamethazine (SMT), which is used as a synthetic antibacterial agent and discharged into environmental water, using high-silica Y-type zeolite (HSZ-385), titanium dioxide (TiO2), and TiO2–zeolite composites. By using ultrapure water and secondary effluent as solvents, we prepared SMT solutions (10 μg/L and 10 mg/L) and used them for adsorption and photocatalytic decomposition experiments. When HSZ-385 was used as an adsorbent, rapid adsorption of SMT in the secondary effluent was confirmed, and the adsorption reached equilibrium within 10 min. The photocatalytic decomposition rate using TiO2 in the secondary effluent was lower than that in ultrapure water, and we clarified the inhibitory effect of ions and organic matter contained in the secondary effluent on the reaction. We synthesized TiO2–zeolite composites and applied them to the removal of SMT. During the treatment of 10 μg/L SMT in the secondary effluent using the composites, 76 % and more than 99 % of the SMT were decomposed within 2 and 4 h by photocatalysis. The SMT was selectively adsorbed onto high-silica Y-type zeolite in the composites. Resultantly, the inhibitory effect of the coexisting materials was reduced, and the composites could remove SMT more effectively compared with TiO2 alone in the secondary effluent.  相似文献   

18.

Zero-valent iron (Fe0) has been widely used for Cr(VI) removal; however, the removal mechanisms of Cr(VI) from aqueous solution under complex hydrogeochemical conditions were poorly understood. In this research, the mixed materials containing cast iron and activated carbon were packed in columns for the treatment of aqueous Cr(VI)-Cr(III) in groundwater with high concentration of Ca2+, Mg2+, HCO3 , NO3 , and SO4 2−. We investigate the influences of those ions on Cr(VI) removal, especially emphasizing on the reaction mechanisms and associated precipitations which may lead to porosity loss by using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. The results show that the precipitations accumulated on the material surface were (Fe/Cr) (oxy)hydroxide, mixed Fe(III)-Cr(III) (oxy)hydroxides, Fe2O3, CaCO3, and MgCO3. During these reactions, the Cr(VI) was reduced to Cr(III) coupled with the oxidated Fe0 to Fe(II) through the galvanic corrosion formed by the Fe0-C and/or the direct electron transfer between Fe0 and Cr(VI). In addition, Cr(VI) could be reduced by aqueous Fe(II), which dominated the whole removal efficiency. The primary aqueous Cr(III) was completely removed together with Cr(III) reduced from Cr(VI) even when Cr(VI) was detected in the effluent, which meant that the aqueous Cr(III) could occupy the adsorption sites. In general, the combined system was useful for the Cr(VI)-Cr(III) treatment based on galvanic corrosion, and the hardness ions had a negative effect on Cr(VI) removal by forming the carbonates which might promote the passivation of materials and decrease the removal capacity of the system.

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19.
Song C  Chen P  Wang C  Zhu L 《Chemosphere》2012,86(8):853-859
Degradation of perfluorooctanoic acid (PFOA) is of great importance due to its global distribution, persistence and toxicity to bioorganisms. In present study, a composite TiO2 with multiple wall carbon nano-tubes (MWCNTs) was synthesized using sol-gel method and it was used as photocatalyst to degrade PFOA in water. The prepared composite catalyst displayed significant absorption in UV to visible light region. The loading content of TiO2 on MWCNTs could be adjusted by changing the ratio of precursor to MWCNTs. Due to the combined effect of the adsorption ability and e transport capacity of MWCNT, the composites displayed much higher photocatalytic ability to PFOA as compared to pure TiO2 under UV irradiation. The photocatalyst prepared with 10:1 of tetrabutyl titanate/MWCNT was the most effective. With the optimal dosage at 1.6 g L−1, almost 100% of PFOA was degraded in acid medium after irradiation for 8 h. It was proposed that PFOA were mainly degraded by stepwise losing a moiety of CF2.  相似文献   

20.
Metal cations and organic pollutants mostly co-exist in the natural environment. However, their interactions in adsorption processes have yet to be adequately addressed. In the current study, the effect of inorganic cations with different charges (Ag+, Zn2+, and Al3+) on the adsorption and desorption of 2,4,6-trichlorophenol (TCP) onto and from processed ash derived from wheat (Triticum aestivum L.) straw was investigated. The adsorption and desorption of TCP were both nonlinear; the isotherm and kinetics curves fitted well using the Freundlich equation and a pseudo-second-order model, respectively. The presence of Ag+ promoted TCP adsorption, while Zn2+ and Al3+ reduced TCP adsorption onto ash. The desorption of TCP from ash showed obvious hysteresis, and the presence of Ag+, Zn2+, and Al3+ caused the desorption to be less hysteretic. The suppression of TCP adsorption by Zn2+ and Al3+ was ascribed to the partial overlapping of adsorption groups between TCP and metal ions. Al3+ had a stronger inhibition effect than that of Zn2+ due to its higher binding capacity and larger hydrated ionic radius than those of Zn2+. Enhanced adsorption of TCP onto ash by Ag+ was ascribed to its ability to reduce the competitive adsorption of water molecules on ash surface by replacing the original ions, such as Na+ and Ca2+, and compressing the hydrated ionic radius of these metal ions. In addition, Ag+ was able to bind with the aromatic organic compounds containing π-electrons, which resulted in a further increase of TCP adsorption by ash.  相似文献   

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