Photocatalytic activity of polyaniline/Fe-doped TiO2 composites by in situ polymerization method

This study was focused on the photocatalytic activity of polyaniline (Pani)/iron doped titanium dioxide (Fe–TiO₂) composites for the degradation of methylene blue as a model dye. TiO₂ nanoparticles were doped with iron ions (Fe) using the wet impregnation method and the doped nanoparticles were further combined with Pani via an in situ polymerization method. For comparison purposes, Pani composites were also synthesized in the presence undoped TiO₂. The photocatalyst and the composites were characterized by standard analytical techniques such as FTIR, XRD, SEM, EDX and UV–Vis spectroscopies. Fe–TiO₂ and its composites exhibited enhanced photocatalytic activity under ultraviolet light irradiation. Improved photocatalytic activity of Fe–TiO₂ was attributed to the dopant Fe ions hindering the recombination of the photoinduced charge carriers. Pani/Fe–TiO₂ composite with 30?wt.% of TiO₂ nanoparticles achieved 28% dye removal and the discoloration rate of methylene blue for the sample was 0.0025?min^?1. FTIR, XRD, SEM, EDX and UV–Vis spectroscopies supported the idea that Fe ions integrated into TiO₂ crystal structure and Pani composites were successfully synthesized in the presence of the photocatalyst nanoparticles. The novelty of this study was to investigate the photocatalytic activity of Pani composites, containing iron doped TiO₂ and to compare their results with that of Pani/TiO₂.     

Pd–Fe/TiO2 catalysts for phenol degradation with in situ generated H2O2

This study deals with the degradation of phenol over Pd–Fe/TiO₂ catalysts at mild conditions in the presence of in situ generated H₂O₂ from oxygen and formic acid. This catalytic system demonstrated interesting ability to oxidize phenol by Fenton process in a one-pot reaction without the addition of ferrous ion. Lower Pd content catalysts, despite producing a higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the 5Pd–5Fe catalyst in phenol degradation. A close interaction between Pd and iron oxide species is necessary to obtain high active catalysts. These results highlight the advantage of in situ generation of H₂O₂, for oxidation reactions with respect to conventional Fenton process.     

Improving the Photocatalytic Activity of Modified Anatase TiO2 with Different Concentrations of Aluminum under Visible Light: Mechanistic Survey

Visible light‐driven Al‐doped TiO₂ with different aluminum contents (2, 5 and 10 mol%) were synthesized via a facile sol–gel method. Fourier transform infrared (FTIR), UV‐visible diffuse reflectance, energy dispersive X‐ray (EDX) spectroscopy as well as X‐ray diffraction (XRD), X‐ray fluorescence (XRF) and scanning electron microscopy (SEM) methods were used for the characterization of the obtained nanoparticles. The photocatalytic performance of the samples was evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. The yield of the degradation RhB was estimated to be 71%, 89%, 65% and 56%, for the bare TiO₂, 2%, 5% and 10% Al‐doped TiO₂, respectively. It was found that 2 mol% of Al‐doped TiO₂ shows the best photocatalytic performance. In low concentration of dopant, separation of photogenerated electron–hole pairs promoted, and subsequently, the degradation efficiency increased. It was proposed that the degradation of RhB by 2 mol% Al‐doped TiO₂ photocatalyst follows both N‐deethylation and chromophore cleavage mechanisms, while the N‐deethylation still predominated over cleavage of dye chromophore structure. The key role of hydroxyl radicals in RhB degradation was verified by the effects of scavengers. In addition, the photocatalyst can be reused for three runs without any significant loss of its catalytic activity.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

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.     

Solvothermal synthesis of WO3/TiO2/carbon fiber composite photocatalysts for enhanced performance under sunlight illumination

Carbon fiber (CF)‐based WO₃/TiO₂ composite catalysts (WO₃/TiO₂/CF) were successfully synthesized by solvothermal method. The catalysts were characterized by XPS, SEM, BET, XRD, FTIR, Raman and UV–Vis. The analyses confirmed the WO₃/TiO₂ nanoparticles with high crystallinity deposited on the carbon structure. The photocatalytic degradation of Orange II azo dye under UV and sunlight illumination with the synthesized catalyst was explored. The composite catalyst displayed high performance (85%) for Orange II degradation while that of for WO₃/TiO₂ was found as 76%. The effects of CF amount, solution pH, initial dye concentration and catalyst dose on photocatalytic performance were studied. It was found that the degradation efficiency increased from 68% to 90% with the increasing CF amount from 3 wt% to 5 wt%, while the further increase in CF amount (7–10 wt%) decreased the photodegradation due to the blocking the active sites of WO₃/TiO₂. The enhanced photocatalytic efficiency was mainly attributed to the electrical properties of the CF and reduced bandgap.     

The influence of precursor’s composition and concentration on cadmium doped TiO<Subscript>2</Subscript> film

The purpose of this article is to emphasize that new nanomaterials offer a number of attractive alternatives for solar energy use in wastewater photocatalysis. The wastewater from the textile industry contains dyes and heavy metals. Thin films of cadmium doped TiO₂ (Cd-TiO₂) were coated by a doctor blade using TiO₂ Degussa P25 and cadmium precursor (cadmium nitrate). The photocatalytic efficiency of cadmium doped TiO₂ is strongly influenced by crystal structure, particle size, particle morphology, porosity and doping. The pore size distribution and the roughness analysis have been studied by the atomic force microscopy (AFM) of the thin films. The photocatalytic activity of the samples was tested in Methyl orange and Methylene blue photodegradation. Cadmium doped TiO₂ catalyst does not significantly decrease the efficiency of photodegradation processes, and, in some situations, improves dye photodegradation.     

超临界流体干燥法制备纳米TiO2-SnO2-SiO2复合光催化剂及其光催化性能研究

半导体多相光催化法作为一种污染治理新技术越来越受到人们的重视,在所使用的半导体光催化剂中,TiO2以无毒,催化活性高,价廉,无污染等特点,成为最具有前途的绿色环保型催化剂之一[1],但其自身具有局限性,如禁带宽度大,需在近紫外光下才能激发产生电子空穴对,对太阳光的利用率仅     

Light expanded clay aggregate (LECA) as a support for TiO<Subscript>2</Subscript>, Fe/TiO<Subscript>2</Subscript>, and Cu/TiO<Subscript>2</Subscript> nanocrystalline photocatalysts: a comparative study on the structure,morphology, and activity

In this work, TiO₂ and doped TiO₂ photocatalysts (Fe/TiO₂ and Cu/TiO₂) were synthesized by the sol–gel method. The main objective of this study was to investigate the influence of dopants on the structure, morphology, and activity of the catalysts in powder and immobilized states. XRF, XRD, and SEM methods were used to characterize the catalysts. The structure and phase distribution of the nanocrystalline powders were identified by XRD. Nanoparticles crystallite size and the degree of crystallinity were affected by doping. The anatase contents of catalysts were achieved as follows: TiO₂ (5.89 %) < Fe/TiO₂ (42.17 %) < Cu/TiO₂ (70.28 %). It was indicated that the activity of the catalysts strongly depends on the anatase content. Under the same circumstances, copper-modified TiO₂ exhibited a twofold higher photocatalytic activity compared with TiO₂. The nanostructured catalysts were immobilized on light expanded clay aggregate (LECA) granules in order to investigate the effect of a novel support on the activity of the catalysts. Morphological changes are recognizable in the SEM images. Activity tests indicated that the best catalytic performance was assigned to Cu/TiO₂/LECA. After 120 min of irradiation, 61 % degradation of phenol in synthetic wastewater was achieved. The high photocatalytic activity of Cu/TiO₂/LECA confirms that LECA is as an excellent support.     

Photocatalytic activity of Au/TiO<Subscript>2</Subscript> nanocomposite for azo-dyes degradation

The structural properties of Au/TiO₂ catalyst were studied by X-ray diffraction, UV-visible diffuse reflectance, photoluminescene, scanning transmission and electron microscope, and temperature programmed reduction. The photocatalytic activity of the catalysts was evaluated for the degradation of various azo-dyes such as methylene blue, methyl orange, reactive blue-4, and eosin-B under solar irradiation. It was found that TiO₂ catalyst modified with gold exhibits higher percentage of degradation compared to starting TiO₂. For example, TiO₂ showed 35% of methyl orange degradation whereas gold modified TiO₂ possessed 82%. Effect of different parameters such as pH and dye concentration has been evaluated and the photocatalytic activity was correlated with physico-chemical properties. The dye degradation rate followed first order kinetics.     

Bifunctional activated carbon with dual photocatalysis and adsorption capabilities for efficient phenol removal

Bifunctional activated carbons (AC) with the abilities of both photocatalysis and adsorption were fabricated via the sol?Cgel route combined with hydrothermal treatment and N₂ reactivation method. TiO₂ was located mainly at the entrance of the surface macropores of AC. Under UV light irradiation, efficient removal of phenol was realized by combination of adsorption and photocatalytic degradation for the obtained bifunctional materials. In insufficient light or dark, phenol removal occurred mainly through adsorption. The prepared bifunctional carbon with a mass ratio of 50 TiO₂ per AC ratio exhibited high efficiency for phenol removal. The total phenol removal capacity of 50TiO₂/AC was almost 5 times of that of pure AC and 6 times of that pure TiO₂ after 10 cycles. The prepared bifunctional carbons possess the advantages of high pollutant removal capability and good recyclability, making them promising for the efficient treatment of lightly polluted aqueous solutions.     

Fabrication of electrospun polyethersulfone/titanium dioxide (PES/TiO2) composite nanofibers membrane and its application for photocatalytic degradation of phenol in aqueous solution

The main objective of this research is to use the photocatalytic properties of PES/TiO₂ nanofibers membranes to remove the phenol as a toxic pollutant in various effluents. The uniform fibers in terms of minimum bead formation and fibers diameter were fabricated. Therefore, more TiO₂ catalysts are on the surface of the fibers which increase the active surface area of nanoparticles and consequently improve the phenol degradation efficiency. The effects of TiO₂ concentration on hydrophilicity, mechanical properties, porosity, mean pore size, and water flux of membranes were studied. The PES/TiO₂ nanofibers were evaluated for phenol degradation under UVA irradiation through a transparent membrane module. The amount of removable phenol was analyzed with high‐performance liquid chromatography. Central composite design was used as a statistical experimental design. Finally, the effect of TiO₂ content in nanofibers and initial phenol concentrations were investigated as well as pH values in synthetic wastewater, on phenol degradation. The results from analysis of variance (ANOVA) analysis indicated that TiO₂ content in nanofibers was the most important and effective parameter on phenol degradation. It was also presented that there is no significant interaction between parameters so that the effect of each parameter was investigated separately. Maximum phenol degradation was 43.0 ± 0.3% and found under conditions of TiO₂ content, initial phenol concentration, and pH value of 8%, 120 ppm, and 7, respectively.     

Characterization of Titanium Dioxide Doped with Nitrogen and Sulfur and its Photocatalytic Appraisal for Degradation of Phenol and Methylene Blue

The degradation of organic dyes in the presence of modified TiO₂ is still under intensive investigation. We report here an evaluation of the photocatalytic activity of nitrogen‐ (N‐) and sulfur‐ (S‐) doped TiO₂ for the degradation of phenol and methylene blue (MB). N‐doped TiO₂ (N–TiO₂), S‐doped TiO₂ (S–TiO₂), and N–S‐doped TiO₂ (N–S–TiO₂) were prepared using the sol–gel method. The photocatalytic activity was evaluated in a batch reactor using phenol and MB as models of pollutants. In addition, this investigation was performed using a household lamp as the visible light source. Properties of the synthesized materials in terms of Brunauer–Emmett–Teller (BET) surface analysis, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and photocatalytic ability were examined. Our study shows that N–S–TiO₂ exhibits better photocatalytic degradation ability for all the considered dyes compared to the other doped TiO₂ materials. In conclusion, we have successfully prepared and evaluated the photocatalytic activity of N‐ and S‐doped TiO₂ for the degradation of phenol and MB using an ordinary household lamp.     

Enhancement of Photocatalytic Efficiency of TiO2 by Supporting on Clinoptilolite in the Decolorization of Azo Dye Direct Yellow 12 Aqueous Solutions

Structure and physico‐chemical properties of a photocatalyst, especially surface area and absorption ability, were correlated to catalytic activities in photodegradation of dye pollutants in water. In this investigation photocatalytic degradation of azo dye Direct yellow 12 (Chrysophenine G) in water was studied. Titanium(IV) oxide was supported on Clinoptilolite (CP) (Iranian Natural Zeolite) using solid‐state dispersion (SSD) method. The results show that the TiO₂/Clinoptilolite (SSD) is an active photocatalyst. The maximum effect of photo degradation was observed at 10 wt.% TiO₂, 90 wt.% Clinoptilolite. A first order reaction with k = 0.0108 min^?1 was observed. The effects of some parameters such as pH, amount of photocatalyst, initial concentration of dye were examined.     

Photo Catalytic Degradation of Azo Dyes over Mn2+ Doped TiO2 Catalyst under UV/Solar Light:An Insight to the Route of Electron Transfer in the Mixed Phase of Anatase and Rutile

Mn²⁺ ion was doped into the TiO₂ matrix and its photocatalytic activity was evaluated for the degradation of a mono azo dye methyl orange (MO) and a di‐azo dye brilliant yellow (BY) under UV/solar light. X‐ray diffraction results revealed the phase transformation from anatase to rutile due to the inclusion of Mn²⁺ ion into the TiO₂ matrix. All the doped catalysts showed a red shift in the band gap to the visible region. The degradation reaction of the dyes was found to be dependent on its structure. It was found that mono azo dye degrades faster than di azo dye under UV/solar light. The rate constant under identical conditions calculated for the degradation of MO is 2.4 times (under UV light) and 4.5 times (under solar light) higher compared to BY. Among the photocatalysts studied, Mn²⁺(0.06 at.%)‐TiO₂ showed higher activity under both UV and solar light illumination. The synergestic effect in the bicrystalline framework of anatase and rutile effectively suppresses the charge carrier recombination and enhances the photocatalytic activity. The degradation reaction was followed by UV‐visible spectroscopy and the photoproducts formed were analyzed by GC‐MS techniques.     

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.     

过硫酸盐激活协同可见光催化降解四环素的机理和降解路径

为了提升微污染水体中抗生素的降解效率,利用过硫酸钠(PDS)激活协同手性介孔TiO₂可见光催化(PDS/vis-TiO₂)对四环素(TC)进行降解。详细对比研究了以手性TiO₂作为催化剂的PDS激活(PDS/TiO₂)、可见光催化(vis-TiO₂)和PDS/vis-TiO₂三种体系中,降解污染物的活性物种和污染物降解路径等的差异。结果表明,不对称的螺旋堆积结构在手性介孔TiO₂中引入了丰富的Ti³⁺,不仅提升了其可见光响应,同时能够激活PDS生成自由基。PDS/vis-TiO₂体系中光生空穴h⁺和·OH等多种自由基可以同时参与TC的降解,5 h内其对TC去除率可达到95%以上,远超PDS/TiO₂体系(TC去除率为48.9%)和vis-TiO₂体系(TC去除率为71.1%)。PDS加入到光催化体系中,会受到光生电子的激活而产生自由基,从而消耗光生电子,提升光生空穴和电子的分离率,达到协同增强污染物的降解能力。另外PDS激活后产生自由基也会大大增加体系对TC的降解性能。密度泛函理论计算和中间产物分析结果表明,TC在PDS/vis-TiO₂体系中的降解路径包含了光生空穴h⁺攻击TC的降解路径,同时也包括自由基攻击TC的降解路径。     

Catalytic degradation of gaseous benzene by using TiO2/goethite immobilized on palygorskite: Preparation,characterization and mechanism

The nano-TiO₂/goethite/palygorskite catalysts were prepared by sol–gel method. The morphology and structure of the catalysts were analyzed by X-ray diffraction (XRD), UV–Vis reflection spectrometer, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and N₂ adsorption-desorption measurement. The results indicated that the self-made catalysts had excellent catalytic performance on gaseous benzene degradation. In the case of benzene concentration at 30 mg/m³, the degradation efficiency, over TiO₂/goethite/palygorskite composite with mass ratio of 10:5:5, reached 70.4% after 180 min 254 nm UV irradiation. The reaction mechanism and kinetics study showed that palygorskite/goethite/TiO₂ composites photocatalytic degradation benzene was mainly caused by oxidizing property of electron–holes and oxygen synergy effect.     

Multifunctional Zn0.3Al0.4O4.5 crystals: An efficient photocatalyst for formaldehyde degradation and EBT adsorption

The Zn_0.3Al_0.4O_4.5 nanoparticles (ZnAlONPs) with size of 70–90 nm are used as an efficient photocatalyst for formaldehyde (HCHO) degradation and effective adsorbent for the removal of eriochrome black-T (EBT) dye from synthetic aqueous solution. Degradation of HCHO reactions were studied using TiO₂ (homemade), TiO₂ (P-25) and ZnAlONPs by irradiating under 18 W daylight lamp source for photocatalytic degradation. The HCHO degradation rate is about 67, 76 and 89% for TiO₂ (homemade), TiO₂ (P25) and ZnAlONPs during 2 h reaction, respectively at initial formaldehyde gas concentration of 20 ppm. Maximum adsorption capacity was optimized by changing the parameters such as pH, EBT concentration and adsorbent dosage. A  200 mg of ZnAlONPs are useable for quick removal of EBT (>95%). Langmuir isotherm model showed a maximum adsorption capacity of 90.90 mgg⁻¹. The ZnAlONPs could be successfully reused upto 5^th adsorption/desorption cycle for EBT dye removal from water samples.     

Facile Biosynthesis of Calcium Hydroxide Nanoparticles Using <Emphasis Type="Italic">Andrographis echioides</Emphasis> Leaf Extract and Its Photocatalytic Activity Under Different Light Source

Effective removal of organic pollutants from wastewater becomes notable research because of its ecological and environmental importance. In the present study Andrographis echioides leaf extract was used for the synthesis of calcium hydroxide nanoparticles (Ca(OH)₂-NPs) from calcium oxide as the calcium source. The secondary metabolites present in the plant source act as a capping agent for the formation Ca(OH)₂-NPs. Further NPs were applied for photocatalytic degradation. The intention of the approach is to be low-cost preparation and easy degradation (degradation of dye without any effect) to the environment. The synthesized Ca(OH)₂-NPs was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultra violet diffuse reflectance spectroscopy, energy dispersive X-ray spectroscopy, zeta potential and high-resolution transmission electron microscopy. The photocatalytic degradation of methylene blue (dye pollutant) studied under three different light sources such as UV, visible and sun light using Ca(OH)₂-NPs. Degradation efficiency of Methylene blue dye examined under UV–Vis spectroscopy. Degradation percentage of Ca(OH)₂-NPs under UV, visible and sunlight are (98.96, 97.52 and 96.38%) respectively. The overall study suggests that Ca(OH)₂-NPs exhibit excellent photocatalytic property against UV, visible and sunlight.