Photodegradation Of 4-nitrophenol Research Articles

Preparation and photoactivity of samarium loaded anatase, brookite and rutile catalysts

Pure and samarium loaded anatase, brookite and rutile nanopowders were synthesized by thermohydrolysis of TiCl4. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (SSA) determination, UV–vis diffuse reflectance spectroscopy (DRS), atomic force microscopy (AFM), contact angle (CA) measurements and photoluminescence (PL) spectroscopy. The photocatalytic activity of pure and Sm-loaded TiO2 polymorphs was investigated by employing the photodegradation of 4-nitrophenol as probe reaction in a liquid-solid system. Loading with Sm resulted in an improvement of the photoreactivity of the three TiO2 polymorphs. The beneficial effect was explained by an increased separation efficiency of the photogenerated electron–hole pairs. Thin films were obtained by dip coating from water dispersions of the bare and loaded samples. The addition of samarium caused a reduction of the contact angle of the films. A nearly superhydrophilic property was exhibited by the Sm-loaded brookite film.

Preparation of Sm-loaded brookite TiO 2 photocatalysts

Pure and Sm-loaded brookite nanoparticles and thin films were prepared using TiCl 4 as precursor of TiO 2. The samples were characterized by X-ray diffraction (XRD), specific surface area (SSA) determination, diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. The photocatalytic activity of the powders was investigated by employing the photodegradation of 4-nitrophenol in a liquid–solid system whilst the photoreactivity of the films was tested by evaluating the rate of degradation of 2-propanol in a gas–solid system. Loading with Sm resulted in a significant improvement of the photoreactivity of brookite and the beneficial effect was attributed to an increased separation efficiency of the photogenerated electron–hole pairs. The content of samarium was an important factor affecting the photocatalytic activity. The optimum amount of samarium was 1% for the powders and 0.1% for the films. There is a relationship between PL spectra and photoactivity, namely, the lower the PL intensity, the higher the photocatalytic activity.

Investigation of homogeneous photosensitized oxidation activities of palladium and platinum octasubstituted phthalocyanines: Oxidation of 4-nitrophenol

Photosensitized oxidation of 4-nitrophenol was studied in organic solutions with seven octasubstituted thio and aryloxy palladium and platinum phthalocyanines acting as photosensitizers. Kinetic studies conducted also showed that the complexes have different singlet oxygen quenching constants with direct implication on the quantum yield of photodegradation of 4-nitrophenol (Φ4-NP). Palladium analogues gave better results than the platinum analogues in terms of Φ4-NP with palladium-(dodecylthio)phthalocyanine giving the highest yield of 1.8×10−3. Gas chromatography (GC) and liquid chromatography connected to a mass spectrometer (LC–MS) were used to confirm the photodegradation products which were hydroquinone and 1,4-benzoquinone.

Cardanol: from waste of the cashew agro-industry to bio-based catalysts used for the photodegradation of 4-nitrophenol in water

Cardanol: from waste of the cashew agro-industry to bio-based catalysts used for the photodegradation of 4-nitrophenol in water

Heterointegration of Pt/Si/Ag Nanowire Photodiodes and Their Photocatalytic Properties.

Photocatalyst mediated photoelectrochemical processes can make use of the photogenerated electrons and holes onsite for photocatalytic redox reactions, and enable the harness and conversion of solar energy into chemical energy, in analogy to natural photosynthesis. However, the photocatalysts available to date are limited by either poor efficiency in the visible light range or insufficient photoelectrochemical stability. We show that a Pt/Si/Ag nanowire heterostructure can be rationally synthesized to integrate a nanoscale metal-semiconductor Schottky diode encased in a protective insulating shell with two exposed metal catalysts. The synthesis of Pt/Si/Ag nanowire diodes involves a scalable process including the formation of silicon nanowire array through wet chemical etching, electrodeposition of platinum and photoreduction of silver. We further demonstrated that the Pt/Si/Ag diodes exhibited highly efficient photocatalytic activity for a wide range of applications including environmental remediation and solar fuel production in the visible range. In this article, photodegradation of indigo carmine and 4-nitrophenol were used to evaluate the photoactivity of Pt/Si/Ag diodes. The Pt/Si/Ag diodes also show high activity for photoconversion of formic acid into carbon dioxide and hydrogen.

Enhanced photoactivity of CuPp-TiO 2 photocatalysts under visible light irradiation

Three novel porphyrins, 5,10,15-tri-phenyl-20-[4-(3-phenoxy)-propoxy]phenyl porphyrin, 5,15-di-phenyl-10,20-di-[4-(3-phenoxy)-propoxy]phenyl porphyrin and 5-phenyl-10,15,20-tri- [4-(3-phenoxy)-propoxy]phenyl porphyrin, and their corresponding copper(II) complexes were synthesized and characterized spectroscopically. The photocatalytic effects of TiO 2 samples impregnated with copper(II) porphyrins was investigated by photodegradation of 4-nitrophenol (4-NP) in aqueous solution under visible light. The photocatalysts were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectra and FT-IR spectra. The results indicated that CuPps were successfully loaded and interacted with the surface of TiO 2 microsphere, which is crucial to enhance the activity of the catalytic composite under visible light.

Junction Effect on the Photocatalytic Activity of Mixed-Phase TiO2 Nanoparticles

Active TiO2 photocatalysts were prepared under mild experimental conditions by thermohydrolysis of TiCl4 in pure water at 100 {degree sign}C. The preparation method is very simple and does not require the use of expensive thermal or hydrothermal treatments. Depending on the TiCl4/H2O ratio, pure rutile, binary mixtures of anatase and rutile or anatase and brookite, or ternary mixtures of anatase, brookite and rutile, can be obtained. 4-nitrophenol photodegradation was used to evaluate the photoactivity of the various powders. The high photocatalytic activity of the mixed samples was explained by the presence of junctions among different polymorphic TiO2 phases that allows an improved charge separation of the photogenerated electron-hole pairs, hindering their recombination.

Photocatalytic Activity of Novel Tin Porphyrin/TiO2 Based Composites

Three dichloro Sn(IV) porphyrins, trans-dichloro[5,10,15,20-tetra-[2 or 3 or 4-(3-phenoxy)-propoxy]phenyl porphyrin]tin(IV) and the corresponding dihydroxo Sn(IV) porphyrins trans-dihydroxo[5,10,15,20-tetra-[2 or 3 or 4-(3-phenoxy)-propoxy]phenyl porphyrin]tin(IV) were synthesized and characterized spectroscopically. The dihydroxo Sn(IV) porphyrin−TiO2 composites were also prepared and characterized, and an interaction between TiO2 and tin porphyrin molecules involving the axial −OH ligand with the TiO2 surface was proposed. The photocatalytic activity was investigated by testing the photodegradation of 4-nitrophenol (4-NP) in aqueous solution under both visible and UV−vis light irradiation. It was found that the distinct space tropisms of peripheral substituents in meso sites of the porphyrin ring lead to different efficiencies in photodegrading the 4-NP.

Photocatalytic activity of TiO 2/SiO 2 systems

Silica-supported TiO 2 powders were synthesized by a wet method under mild conditions. The aim of the work was the preparation of TiO 2/SiO 2 additives for photocatalytic cements. Three types of commercial SiO 2 were used as supports: Cabot, Axim and Fly Ash. Cabot silica was ultra-pure whereas the other two silica contained different percentages of various oxides. The TiO 2/SiO 2 samples, denoted TiO 2/Cabot, TiO 2/Axim and TiO 2/Fly Ash, were prepared by boiling suspensions obtained by addition of silica to a solution of TiCl 4 in water (volume ratio 1:10). The photocatalytic activity was evaluated in a gas–solid system both in batch and in continuous reactors using 2-propanol as probe molecule. SEM-EDX analysis revealed that titanium dioxide was quantitatively deposited on silica. TiO 2/Axim and TiO 2/Fly Ash were scarcely active whereas a good photoactivity was exhibited by the TiO 2/Cabot sample both in the batch and in the continuous system. Consequently only the last sample was tested for both NO x abatement and for 4-nitrophenol photodegradation in a liquid–solid system.

The photocatalytic activity of novel, substituted porphyrin/TiO 2-based composites

Four novel porphyrins, 5-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,15-di-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15-tri-[3-(3-phenoxy)-propoxy]phenyl porphyrin, 5,10,15,20-tetra-[3-(3-phenoxy)-propoxy]phenyl porphyrin, and their corresponding Cu(II) porphyrins, were synthesized and characterized spectroscopically. The photodegradation of 4-nitrophenol in aq. suspension was used to determine the photocatalytic activity of polycrystalline TiO 2 samples which had been impregnated with the Cu(II) porphyrins, as sensitizers. The photocatalytic activity of the composite depends mainly on the amount of sensitizer on the TiO 2 surface rather than the nature of the substituted porphyrins.

Highly Active Photocatalytic TiO2 Powders Obtained by Thermohydrolysis of TiCl4 in Water

Highly active photocatalytic TiO2 samples were synthesized by thermohydrolysis of TiCl4 in water at 100 °C. Rutile, binary mixtures of anatase and rutile or anatase and brookite or ternary mixtures of anatase, brookite, and rutile were obtained depending on the TiCl4/H2O ratio. Rietveld refinements were employed to evaluate the crystalline phases and composition of the mixtures. The effect of the aging time on the phase composition was also studied. The band gap values of the samples were obtained by the diffuse reflectance spectra. The position of the flat band potentials of anatase, brookite, and rutile was determined measuring the photovoltage as a function of the suspension pH. From these data, the relative positions of the energy bands of the three semiconductors were estimated. 4-Nitrophenol photodegradation was used to evaluate the photoactivity of the various samples. Some powders were more active than Degussa P25. The most efficient samples consisted of a ternary mixture of anatase, brookite, and...

Cationic and Anionic Surface Binding Sites on Nanocrystalline Zinc Oxide: Surface Influence on Photoluminescence and Photocatalysis

To probe the influence of the surface on the overall nature of zinc oxide nanocrystals (ZnO NCs) this paper examines the effects of surface modifiers: cobalt Co(II) and trimethylsilanolate, on the properties of ZnO NCs. A clear relationship between the surface, photocatalytic (PC), and photoluminescent (PL) character of ZnO is observed. With potassium trimethylsilanolate and cobalt(II) acetate we have determined that anionic binding sites occupied by silanolate contribute to 40% of the PL character of the defect emission (500-550 nm). Photodegradation of 4-nitrophenol was used as a probe to evaluate the effect of surface modification on the PC performance of ZnO NCs. At maximum silanolate modification the PC activity of ZnO was reduced by 50%. Modification of ZnO NCs with Co(II) resulted in the transfer of photoexcited electrons to the cobalt center where consequent nonradiative recombination, at energies lower than required for PC, was observed via a comparable decrease in both PL and PC activity. These results are critical for using ZnO NCs in sensory, photocatalytic, and electronic applications.

Tungstophosphoric acid supported on polycrystalline TiO2 for the photodegradation of 4-nitrophenol in aqueous solution and propan-2-ol in vapour phase

Abstract The present work reports the preparation of samples based on Millennium PC-500 TiO 2 loaded with different amounts of tungstophosphoric acid (up to 30% in weight) and their characterisation by means of different physicochemical techniques: powder X-ray diffraction, N 2 adsorption–desorption at −196 °C, transmission electron microscopy, UV–vis and FT-IR spectroscopies and thermogravimetric analyses. The acidity of samples was evaluated by FT-IR using pyridine as probe molecule, and the catalysts activity was tested for the photodegradation of 4-nitrophenol in aqueous solution and for the photo-oxidation of propan-2-ol in vapour phase. The results show a noticeable improvement (8 and 2.5 times faster in the photodegradation rate of 4-nitrophenol and propan-2-ol, respectively), in both regimes for these specific substrates, when tungstophosphoric acid is dispersed over the oxide up to a certain amount (20% in weight). A partial leaching of the polyoxometalate was also detected in solution for samples loaded with the largest amounts on this compound.

Preparation of N-doped TiO2: characterization and photocatalytic performance under UV and visible light

Nanocrystalline N-doped TiO(2) samples were prepared by using TiCl(4) or TiOSO(4) as precursors. The powders were characterized by X-ray diffraction, BET specific surface area measurements, scanning electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested using the photodegradation of 4-nitrophenol under UV and visible light.Some samples were more active than commercial Degussa P25. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed in the samples obtained from TiCl(4). Two absorption edges were observed in the samples derived from TiOSO(4) and calcined at 400 degrees C: the main edge due to TiO(2) and the second one due to the presence of a localised midgap band that induces the visible light activity.

Inorganic gels as precursors of TiO2 photocatalysts prepared by low temperature microwave or thermal treatment

A simple procedure for preparing active TiO2 photocatalysts is presented. The starting materials were unusual TiO2 gels formed from TiCl4. The use of microwaves for a very short time enhanced the TiO2 crystallinity preventing an increase of particle size and minimizing the decrease of specific surface area. This result makes this preparation very attractive. The formation of the gels was monitored through measurements of viscosity. All the samples were characterized by means of X-ray diffraction, diffuse reflectance spectroscopy and BET specific surface area measurements. The photoactivity of the samples was evaluated using the photodegradation of 4-nitrophenol in liquid–solid regimen and gaseous 2-propanol as probe reactions. Commercial TiO2 Degussa P25 was used for the sake of comparison.

Photocatalytic activity of nanocrystalline TiO2 (brookite, rutile and brookite-based) powders prepared by thermohydrolysis of TiCl4 in aqueous chloride solutions

Abstract Nanocrystalline TiO2 powders were synthesized by thermohydrolysis of TiCl4 in HCl or NaCl aqueous solutions. Rutile, mixtures of brookite and rutile or mixtures of anatase, brookite and rutile were obtained depending on the acidity of the medium. Crystalline phases and composition of the mixtures were identified by using XRD analysis. Pure brookite nanoparticles, separated from the mixtures of brookite and rutile by simple peptization with water, were stable against transformation to rutile up to 750 °C. The prepared TiO2 powders were characterized by thermal analysis, diffuse reflectance spectroscopy and BET surface area determinations. The band gap of bulky brookite was estimated 3.29 eV. 4-Nitrophenol photodegradation was used to evaluate the photocatalytic activity of the various samples. The highest activity corresponded to the powders consisting of more than one crystalline phase.

Direct growth of F-doped TiO 2 particulate thin films with high photocatalytic activity for environmental applications

Here we report on a novel and facile approach to directly grow F-doped TiO 2 particulate thin films with superb visible light photoelectrical response and high photocatalytic efficiency by oxidizing titanium plates in the presence of H 2O vapor assisted with NaF at relatively low temperatures. The effects of the oxidation temperature and the amount of the NaF coated on the titanium plates on the morphology and the photocatalytic properties of the formed F-doped TiO 2 particulate thin films have been investigated. The formed F-doped TiO 2 particulate thin films show a significant increase in the photocurrent of photoinduced splitting of water into hydrogen and oxygen compared with that of commercial P-25 TiO 2, under irradiation of either UV or visible light. In addition, the photocatalytic activity of the formed F-doped TiO 2 particulate thin films out perform the commercial P-25 TiO 2 for the photodegradation of 4-nitrophenol under UV and visible light irradiation. The approach described in this study can be easily commercialized to fabricate F-doped TiO 2 particulate thin films on a large-scale for very promising environmental applications in the photodegradation of organic pollutants and photoinduced splitting of water into hydrogen, a green energy source.

Photocatalytic behaviour of metal-loaded TiO 2 aqueous dispersions and films

Titanium dioxide nanoparticles loaded with Ce, Co, Eu, Sm, W and Yb species were prepared by coprecipitation in mild conditions using TiCl 4 as precursor with the aim to enhance the photocatalytic activity, especially under visible light irradiation. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (SSA) determination and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of the powders of pure and loaded TiO 2 was investigated by employing the photodegradation of 4-nitrophenol as probe reaction in a liquid–solid system. Loading with suitable amounts of W, Co and Sm resulted in a significant improvement of the photoreactivity of TiO 2. This beneficial effect was attributed to an increased separation of the photogenerated electron–hole pairs. Some samples were more photoactive than commercial powders employed in the same experimental conditions. Films of TiO 2 loaded with the metals that yielded the best photocatalytic responses were prepared by the dip-coating technique. The photoactivity of the films was tested by evaluating the rate of degradation of 2-propanol in a gas–solid system. An enhancement of the photocatalytic efficiency was obtained in the presence of W and Sm.

Efficient degradation of 4-nitrophenol by using functionalized porphyrin-TiO2 photocatalysts under visible irradiation

The novel porphyrins 5,10,15,20-tetra-[4-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(a) and 5,10,15,20-tetra-[2-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(b) and their corresponding copper(II) complexes CuPp(a), CuPp(b) were synthesized and characterized by using various spectroscopic techniques. The photocatalytic activity of polycrystalline TiO2 samples impregnated with H2Pp(a), H2Pp(b), CuPp(a) and CuPp(b) as sensitizers have been investigated by carrying out the photo-degradation of 4-nitrophenol (4-NP) as a probe reaction in aqueous suspension and under visible light. The maximum photocatalytic activity was obtained using TiO2 loaded with a monolayer of the copper porphyrin CuPp(b) in the amount of 18μmol per gram of TiO2.The photocatalytic efficiency decreased in the following order: TiO2-CuPp(b), TiO2-CuPp(a), TiO2-H2Pp(b), TiO2-H2Pp(a). A possible mechanism of the photocatalytic degradation is also proposed.

Photoactivity of nanostructured TiO2 catalysts in aqueous system and their surface acid-base, bulk and textural properties

This work reports on the characterisation and determintion of the photocatalytic activity of some TiO2 catalysts prepared using TiCl4 as precursor. The samples, consisting of suspensions, dispersions or powders of nanonstructured anatase or rutile phases, were obtained in very mild conditions, i.e., by boiling the solution obtained after hydrolysis of TiCl4 at atmospheric pressure: it is worth noting that no calcination was necessary to obtain photoactive phases. The samples were characterised by X-ray diffraction (XRD), determination of the BET specific surface area (SSA), scanning electron microscopy (SEM) observations and diffuse reflectance spectroscopy (DRS). FT-IR spectroscopy was used to study the surface acidity of the solids. Photodegradation of 4-nitrophenol and gemfibrozil (5-(2,5-dimethylphenoxy)-2,2-dimethyl-pentanoic acid) was used as probe reactions to evaluate the photoactivity and the obtained results showed that the home prepared samples are effective to degrade both substrates. The photoreactivity results were compared to those obtained using commercial photocatalysts.