M. Muneer

Photocatalytic degradation of a widely used insecticide Thiamethoxam in aqueous suspension of TiO2: Adsorption, kinetics, product analysis and toxicity assessment

This paper deals with the study of photocatalyzed degradation of an insecticide, Thiamethoxam in aqueous suspension of TiO2. The adsorption of Thiamethoxam on TiO2 surface under dark conditions was also investigated in order to find out equilibrium adsorption constant. The degradation kinetics was studied using spectrophotometric method under various conditions such as substrate concentration, type of catalyst, catalyst dosage, pH, and in the presence of electron acceptors such as hydrogen peroxide, potassium bromate, and ammonium persulphate under continuous purging of atmospheric oxygen, and the degradation rates were found to be strongly influenced by these parameters. The results manifested that the photocatalysis of Thiamethoxam follows pseudo-first-order kinetics. The toxicity assessments of the irradiated samples were carried out using human erythrocytes as a model system under in vitro conditions. GC-MS study showed the formation of several intermediate products which were characterised based on their molecular mass and mass fragmentation pattern. A probable mechanism for the formation of various products formed during the photocatalytic process of Thiamethoxam was also proposed.

Photodegradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid in aqueous suspensions of titanium dioxide

The photocatalytic degradation of a herbicide derivative, 2,4-dichlorophenoxy acetic acid (2,4-D, 1), has been investigated in aqueous suspensions of titanium dioxide. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time in the presence of UV light source. The degradation kinetics was investigated under a variety of conditions, such as different types of TiO2, pH, catalyst and substrate concentrations. Higher photonic efficiencies were observed with Degussa P25 as compared with other photocatalysts. The degradation products were analysed by GC-MS and probable pathways for the formation of different products were proposed.

Photocatalytic degradation of herbicide Bentazone in aqueous suspension of TiO2: mineralization, identification of intermediates and reaction pathways

Semiconductor-mediated hydrogen peroxide-assisted photocatalytic degradation of a selected herbicide, Bentazone (1) has been investigated in aqueous suspensions of TiO2 under a variety of conditions. The degradation was studied by monitoring the depletion in total organic carbon content as a function of irradiation time. The degradation kinetics was investigated under different conditions such as type of TiO2 (Anatase/Anatase-Rutile mixture), reaction pH, catalyst dosage and hydrogen peroxide (H2O2) concentration. The degradation rates were found to be strongly influenced by all the above parameters. Titanium dioxide Degussa P25 was found to be more efficient as compared with other two commercially available TiO2 powders like Hombikat UV100 and PC500 from Millennium Inorganic Chemicals. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of the irradiated mixture of Bentazone (1) indicates the formation of several intermediate products which have been characterized on the basis of molecular ion/mass fragmentation pattern and also on comparison with the National Institute of Standards and Technology (NIST) library. Plausible mechanism for the formation of different products during photocatalytic treatment of Bentazone in the presence of TiO2 has been proposed. The use of H2O2 substantially increased the efficiency of TiO2 photocatalytic degradation.

Synthesis of iron and copper cluster-grafted zinc oxide nanorod with enhanced visible-light-induced photocatalytic activity

Design of visible-light-responsive photocatalyst employing simple and cost-effective method is of great importance from commercial point of view. Herein, we report the synthesis of visible-light-sensitive ubiquitous nanoclusters of Fe3+/Cu2+-grafted ZnO nanorod using impregnation technique, which showed excellent photocatalytic activity towards the decomposition of Rhodamine B (RhB), 4-nitrophenol (4-NP) and paracetamol in aqueous suspension under atmospheric oxygen. Fe-grafted ZnO nanorod exhibited pronounced effect for the degradation of the above-mentioned pollutants compared to pure ZnO and Cu-grafted ZnO nanorod. The better activity could be due to the more positive redox potential of surface grafted Fe3+ species resulting in the generation of more hydroxyl radicals thereby, leading to higher photodegradation rate.

Photoassisted Degradation of a Herbicide Derivative, Dinoseb, in Aqueous Suspension of Titania

The titanium dioxide (TiO2) photoassisted degradation of herbicide dinoseb has been examined in aqueous suspensions under UV light irradiation. The degradation kinetics were studied under various conditions such as substrate concentration, type of catalyst, catalyst dosage, pH, and light intensity as well as in presence of electron acceptors such as hydrogen peroxide, potassium bromate, and potassium persulphate under continuous air purging, and the degradation rates were found to be strongly influenced by these parameters. The Degussa P25 was found to be more efficient photocatalyst as compared to other photocatalysts tested. Dinoseb was found to degrade efficiently in acidic pH and all the electron acceptors studied enhanced the degradation rate. The results manifested that the photocatalysis of dinoseb followed pseudo-first-order kinetics. A qualitative study of the degradation products generated during the process was performed by GC-MS, and a degradation mechanism was proposed.

Photocatalysed decolourization of two textile dye derivatives, Martius Yellow and Acid Blue 129, in UV-irradiated aqueous suspensions of Titania

Abstract Photocatalysed decolourization of two textile dye derivatives, Martius Yellow and Acid Blue 129, has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The decolourization was studied by monitoring the decrease in dye concentration as a function of irradiation time employing the UV spectroscopic analysis technique. The decolourization kinetics was investigated under different conditions such as types of TiO2 (Anatase [Hombikat UV-100 and PC500]/Anatase–Rutile mixture [Degussa P25]), initial reaction pH, catalyst dosage, dye concentration and in the presence of electron acceptors such as potassium bromate, hydrogen peroxide and ammonium persulphate. The decolourization of both dyes was also investigated under sunlight. The decolourization rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient for the decolourization of dye derivative Martius Yellow, while UV100 was better for the ...

Semiconductor Mediated Photocatalysed Reaction of Two Selected Organic Compounds in Aqueous Suspensions of Titanium Dioxide

Abstract Semiconductor mediated hydrogen peroxide-assisted photocatalytic degradation of two selected pesticide compounds, chloramben (1) and cyanazine (2) has been investigated in aqueous suspensions under a variety of conditions. The degradation was studied by monitoring the depletion in total organic carbon (TOC) content and decrease in substrate concentration as a function of irradiation time. The degradation kinetics of pesticide compounds 1 and 2 were investigated under different conditions such as type of TiO2 (Anatase/Anatase-Rutile mixture), reaction pH, catalyst dosage and hydrogen peroxide (H2O2) concentration. The degradation rates were found to be strongly influenced by all the above parameters. Titanium dioxide Degussa P25 was found to be more efficient as compared with other two commercially available TiO2 powders like Hombikat UV100 and PC500 from Millennium Inorganic Chemicals. GC-MS analysis of the irradiated mixture of pesticide compounds 1 and 2 indicate the formation of several intermediate products which have been characterized on the basis of molecular ion/mass fragmentation pattern and also on comparison with the NIST library. Plausible mechanism for the formation of different products involving the reaction of hydroxyl and super oxide radical anions with 1 and 2 has been proposed.

Titanium Dioxide-mediated Photocatalysed Mineralization of Two Selected Organic Pollutants in Aqueous Suspensions

Abstract Titanium dioxide-mediated photocatalytic mineralization of two selected organic pollutants such as Metalaxyl (ML) and Tinidazole (TN) has been investigated in aqueous suspensions in the presence of atmospheric oxygen under a variety of conditions. The mineralization was studied by monitoring the depletion in total organic carbon (TOC) content as a function of irradiation time. In addition HPLC analysis technique was also used to monitor the degradation of model compounds under investigations. The mineralization kinetics of both compounds were investigated under different conditions such as type of TiO2 (Anatase/Anatase-Rutile mixture), reaction pH, substrate concentration, catalyst dosage and hydrogen peroxide (H2O2) concentration. The mineralization rates were found to be strongly influenced by all the above parameters. The mineralization of both the compounds was also investigated under sunlight and the degradation efficiency was compared with that of artificial light source. An attempt was also made to identify the intermediate products formed during the photooxidation of ML and TN using GC-MS analysis technique. Both compounds showed the formation of several byproducts. A probable pathway for the formation of different products has been proposed.

Comparative photocatalytic activity of sol–gel derived rare earth metal (La, Nd, Sm and Dy)-doped ZnO photocatalysts for degradation of dyes

Rare earth metal doping into semiconductor oxides is considered to be an effective approach to enhance photocatalytic activity due to its ability to retard the electron–hole pair recombination upon excitation. Herein, we report the synthesis of different rare earth metal (La, Nd, Sm and Dy)-doped ZnO nanoparticles using a facile sol–gel route followed by evaluation of their photocatalytic activity by studying the degradation of methylene blue (MB) and Rhodamine B (RhB) under UV-light irradiation. Different standard analytical techniques were employed to investigate the microscopic structure and physiochemical properties of the prepared samples. The formation of the hexagonal wurtzite structure of ZnO was established by XRD and TEM analyses. In addition, the incorporation of rare earth metal into ZnO is confirmed by the shift of XRD planes towards lower theta values. All metal doped ZnO showed improved photocatalytic activity toward the degradation of MB, of which, Nd-doped ZnO showed the best activity with 98% degradation efficiency. In addition, mineralization of the dye was also observed, indicating 68% TOC removal in 180 min with Nd-doped ZnO nanoparticles. The influence of different operational parameters on the photodegradation of MB was also investigated and discussed in detail. Additionally, a possible photocatalytic mechanism for degradation of MB over Nd-doped ZnO nanoparticles has been proposed and involvement of hydroxyl radicals as reactive species is elucidated by radical trapping experiments.

Preparation, Characterization and Application of Polyaniline/silk Fibroin Composite

We report the electrical properties and photocatalytic activity of polyaniline (Pani) and polyaniline/silk fibroin (Pani/SF) composite. The Pani/SF composite has been synthesized first time by chemical oxidative in-situ polymerization method by using potassium persulphate (K2S2O8) in an acidic medium. Thus prepared Pani and Pani/SF composite were characterized by using Fourier-transform infrared spectroscopy, x-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The stability in terms of the DC electrical conductivity of Pani/SF composite and Pani was investigated under isothermal and cyclic aging conditions. Results indicated that the electrical properties of the composite were significantly influenced by the loading of SF to Pani and observed to be more thermally stable than those of Pani. As-prepared Pani and Pani/SF composites were studied for the degradation of methylene blue (MB) and Rhodamine B (RhB) under UV-light irradiations. The results showed that 91.4% & 85.4% degradation of RhB and MB takes place respectively after 90 min over Pani/SF composite. The decomposition rate of composite was 1.8-2.2 times greater than that of Pani. The improvement of photocatalytic activity of composite may be attributed to the electron-sink function of silk fibroin which increases the optical absorption property and separation of photogenerated charge carriers than Pani alone.