Advanced Oxidation Processes in Triton X100 and W

Authors: Bożena Czech Wiesława ĆwikłaBundyra

Publish Date: 2012/06/29

Volume: 223, Issue: 8, Pages: 4813-4822

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Abstract

Photocatalytic methods were applied to remove the recalcitrant or toxic pollutants from the water The two models of wastewater containing either nonionic surfactant Triton X100 or commercially available washup liquid were tested in a selfconstructed band reactor during the laboratory studies The photocatalyst being typed TiO2 was supported by porous Al2O3 and modified by the addition of Cu Fe Zn Ni Mo or Co The photocatalysts were characterised by N2 adsorption–desorption XRF XRD SEMEDX Raman and UV–Vis spectroscopy All catalysts were efficient in the photocatalytic oxidation of surfactants and they enabled at least 85  COD reduction TiO2/Al2O3 photocatalysts modified by the transition metals were efficient only for more complicated compositions of surfactants The effect of H2O2 001 vol addition was also examined and compared with a type of compound and catalyst used—in this case a positive effect for Triton X100 was only observed over the photocatalyst modified by Ni When it comes to the washup liquid photoremoval all studied photocatalysts seem to be slightly influenced by H2O2 addition It was also observed that it is not economically justified to conduct such treatment for more than 2 hSurfactants because of their specific features are widely used in the households as detergents or care products and in various industries pesticides chemicals textiles or pharmaceuticals They are common pollutants in the wastewater It has been confirmed that generally nonionic surfactants at lethal concentrations depending on various tests from 00025 to 300 mg/dm3 are more toxic than others anionic 03 to 200 mg/dm3 Periods of long acclimation are required during the conventional treatment and they typically result in a quite incomplete degradation LiwarskaBizukojc et al 2005 Finally introduced into water ecosystem some of the pollutants such as alkylphenyl polyethoxylatetype nonionic surfactants eg Triton X100 TX are suspected to be the endocrine disrupters in aquatic organisms Saien et al 2011 In order for the surfactants to be removed the heterogeneous photocatalysis as a one of the advanced oxidation processes AOPs can be applied successfully ArslanAlaton and Erdinc 2006 Fabbri et al 2009 The observed progress in the field of AOPs has made them as alternatives or as a complement to conventional wastewater treatment The main advantage of AOPs is that they can be used both independently or as pretreatment technique for improving the biodegradability and efficiency of further treatments Ioannou et al 2011TiO2 is a widely tested photocatalyst in the studies concerning the photocatalytic removal of contaminants Ollis et al 1991 Friedmann et al 2010 However the recycling and recovery of typically used TiO2 powder photocatalysts in industry are quite troublesome and uneconomical which becomes the main disadvantage of using the suspended systems Therefore many efforts are being made to immobilize TiO2 and construct reactors with an immobilized active phase Chong et al 2010Nowadays photocatalytic studies are being conducted in three main areas catalyst modifications reactor construction and process modification Lin et al 2010 The catalyst modifications include metal and nonmetal doping Janus et al 2009 Yalcin et al 2010 Transition metal ion doping has been suggested to increase the response to solar spectrum over 380 nm and to develop the photocatalytic activity by introducing the defects into TiO2 lattice and reducing e−/h+ pair recombination The result of the above has been the increased rate of OH formation The photocatalytic processes and their efficiency can also be enhanced by adding the auxiliary electron acceptors such as H2O2 and O3 Friedmann et al 2010 but the results are not obvious and depend on many factors H2O2 is one of the cheapest oxidants and in the presence of UV irradiation at 254 nm its photolysis into 2 OH has been observed However the addition of too high H2O2 concentration hinders the process since the excess of H2O2 captures the radicals Daneshvar et al 2004The double aptitude of the photocatalyst to simultaneously adsorb reactants and to absorb photons efficiently is one of the primary factors affecting the photocatalysis It has been observed that due to the preadsorption of reactants on the surface of TiO2 during the photocatalytic reaction the process of electron transfer is more efficient Popa et al 2010 The supported porous catalysts with higher surface area are often being chosen since apart from easier disposal they ensure a high density of active centers for photocatalytic reactions and an enhanced light harvesting because of light reflection and scattering by the pores Herrmann 2010Since all strategies surface deposition of transition metals on photocatalyst porous materials as the support for TiO2 and H2O2 as additional source of OH can enhance photooxidation it was proposed to study the synergistic effect of both support Al2O3 H2O2 addition and dopant Cu Zn Fe Co Ni Mo on the UV photocatalytic activity of TiO2 In the present investigation we carried out a series of studies aiming for the determination of the catalytic activity of Al2O3 supported and modified TiO2 photocatalysts in the removal of the pollutants from wastewater As photocatalysts TiO2/Al2O3 modified by Cu Zn Ni Fe Co or Mo were used These dopants were chosen because of their ability to increase the solar spectrum response towards Vis or enhance the UV photoactivity The aim of the research was also to investigate the role of dopant on UV photocatalytic activity of studied catalysts The photocatalytic oxidation of TX a nonionic surfactant and a mixture of common surfactants containing both nonionic and anionic compounds available as commercial washup liquid WL were investigated The effectiveness of the removal was measured in the following configurations TiO2/UV/O2 and TiO2/UV/O2/H2O2 TX was chosen because of its main features it is a widely used nonionic surfactant and it can be considered as an endocrine disrupting compound in the aquatic environment Typically used in households washup liquid was used to examine the photoremoval of commercially available products that are not analytical gradeAll the chemicals used for the preparation of the photocatalysts were analytical grade and used without further purification The modified TiO2 catalysts supported by γ–Al2O3 INS Pulawy Poland were chosen for the studies The catalysts were prepared using the classical impregnation method CIM according to the procedure described in PasiecznaPatkowska et al 2010 For the impregnation of TiO2/Al2O3 sample TiO2 were used 5 wt aqueous solutions of nitrates zincII copperII cobaltII ironIII nickelII and molybdenum salt NH46Mo7O24•4H2O POCH Gliwice Poland resulted in samples CIMZn CIMCu CIMCo CIMFe CIMNi and CIMMo respectively The effect of doping was compared with the sample TiO2 as referenceThe experiments concerning the photocatalytic degradation of organics in the wastewater were conducted in a band reactor of our own construction described in a previous paper Czech and CwiklaBundyra 2007 applying the procedure described in the already mentioned paper PasiecznaPatkowska et al 2010 The band reactor is equipped with the UV lamp 254 nm 50 Hz with a light intensity of 15–22 mW/cm2 measured by the Radiometer VLX254 Vilber Lourmat 254 nm The employed UV lamp emitted light of more than 95  within the UV light wavelength

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