Solar photocatalytic mineralization of isoproturon over TiO2/HY composite systems

https://doi.org/10.1016/j.solmat.2007.09.011Get rights and content

Abstract

The present investigation covers immobilization of titanium dioxide over HY support for the treatment of isoproturon pesticide. Catalysts are characterized by XRD, SEM–EDAX, TEM, BET surface area and UV–vis DRS. A detailed photocatalytic degradation study under solar light in aqueous suspensions with parameters like loading of TiO2 over HY, amount of the catalyst, concentration of substrate, pH effect, durability of the catalyst and comparison between suspended TiO2 and supported systems are reported. Mineralization of isoproturon is monitored by total organic carbon, chemical oxygen demand and a plausible mechanism is proposed for photocatalytic degradation based on degradation products.

Introduction

Herbicides are mainly used in agricultural applications. Phenylurea herbicides are broadly applied worldwide on agricultural soils for weed control and isoproturon (Fig. 1) is one among the widely used. It is a systemic herbicide [3-(4-isopropylphenyl)-1,1-dimethylurea] for the control of annual grasses and broad-leaved weeds in agricultural fields. Their application in modern agricultural practices is a cause for concern due to their relatively high solubility in water and low chemical and biological degradation rates. The contamination of ground and surface water [1], [2] is because of mal-agricultural practices, careless disposal of empty containers and washing of equipment. As a consequence, different strategies have been devised for the removal of these pollutants from water. Traditionally, pollutants in water are removed using activated carbon [3], nanofiltration [4], ozonation [5] and isolation of specific bacterial cultures [6]. These processes have inherent limitations in applicability, effectiveness and costs. In recent years, advanced oxidation processes (AOPs) have been proposed [7] as an attractive alternative for the treatment of contaminated ground, surface, and wastewater containing pesticides or non-biodegradable organic pollutants [8], [9], [10]. These methods are generally based on the generation of OH radicals which interact with organic pollutants leading to progressive degradation and subsequently complete mineralization. Among the AOPs, titanium dioxide mediated semiconductor photocatalysis is gaining more importance due to its high production of hydroxyl radicals, inexpensive, non-toxic, abundantly available and especially stable under irradiation. In fact, the main drawback of this approach is the need for complex filtration procedure and also decrease of radiation flux due to the turbidity of the catalyst suspension, called as shadowing effect. These problems have motivated the development of immobilization of TiO2 on different support materials like glass [11], pumice stone [12], Cuddapah stone [13], activated carbon [14] and zeolites [15], etc. In this context, zeolites have attracted greater attention due to their adsorption capacity that helps in pooling the pollutants to the vicinity of the TiO2 surface and leads to faster degradation [9], [15], [16]. Zeolites are microporous crystalline aluminosilicates with structural features that make them attractive hosts for photochemical applications, i.e. ability of photoinduced electron donor and acceptor reactions and strongly influence with extra framework cations in the photochemical reactions [17]. Furthermore, zeolites delocalize bandgap excited electrons of TiO2 and there by minimize electron–hole recombination. These interesting properties attract zeolites as catalyst support in the treatment of pesticide contaminated water. TiO2 supported on zeolites, with their large surface area and light transparent nature increases the adsorption capacity and uniform diffusion of pesticide pollutants leads to efficient degradation. The objective of present investigation is the development of an efficient HY supported TiO2 photocatalyst for complete mineralization of isoproturon in aqueous solution. Different parameters are optimized for photocatalytic degradation of isoproturon. Mineralization of isoproturon is monitored by total organic carbon (TOC) and chemical oxygen demand (COD) and an attempt is made to identify intermediates and a plausible mechanism is proposed for the isoproturon photocatalytic degradation.

Section snippets

Materials and methods

All chemicals used in the present work were of analytical grade and used as such without further purification. Isoproturon (>99% pure, Technical grade) obtained from Rhône-Poulenc Agrochimie, France and titanium dioxide P-25 (Anatase 80%, rutile 20%, surface area 50 m2 g−1 and particle size 27 nm) is from Degussa Corporation, Germany. Zeolite NH4Y (Si/Al=2.7), HCl, H2SO4, NaOH and acetonitrile are obtained from Ranbaxy Limited, India. AgSO4, K2Cr2O7, and ferrous ammonium sulfate are obtained from

XRD

The characteristic standard planes of HY (111, 220, 311, 331, 511, 440, 533, 642, and 555) are well exhibited in XRD (JCPDS card no. 81-2467) [19] with 14.0, 8.64, 7.3, 5.6, 4.7, 4.32, 3.73, 3.25, and 2.83 ‘d’ values. The incorporation of TiO2 on HY by SSD results in a decrease in the intensity of characteristic peaks of HY whereas an increasing trend in characteristic peaks of TiO2 (d=3.5, 1.89, 1.69, 1.66, and 1.48). It can be seen from Fig. 2, the gradual increase in the intensity of TiO2

Conclusion

The preparation, characterization and evaluation of TiO2/HY in the present study illustrate the adsorption and electron separation properties of zeolite framework are enhancing the photocatalytic activity of TiO2 in degradation of isoproturon. The preparation and use of TiO2/HY zeolite is an easy, simple and efficient system for the degradation of isoproturon. The characterization of TiO2 supported HY zeolite are made using XRD, SA, SEM–EDAX, TEM and UV–vis DRS techniques which revealed the

Acknowledgments

M.V.P.S. thanks CSIR, New Delhi, for providing SRF grant. The authors also thank Dr. KVR Chary for his help in surface area measurements.

References (26)

  • N.H. Spliid et al.

    Chemosphere

    (1998)
  • L. Nitschke et al.

    Chemosphere

    (1998)
  • E. Wittmann et al.

    Desalination

    (1998)
  • P.R. Gogate et al.

    Adv. Environ. Res.

    (2004)
  • K. Tanaka et al.

    J. Photochem. Photobiol. A: Chem.

    (1989)
  • M. Noorjahan et al.

    J. Photochem. Photobiol. A: Chem.

    (2003)
  • T. Torimoto et al.

    J. Photochem. Photobiol. A: Chem.

    (1997)
  • V. Durga Kumari et al.

    Appl. Catal. A: Gen.

    (2002)
  • M. Noorjahan et al.

    Appl. Catal. B: Environ.

    (2004)
  • P.K. Dutta et al.

    Curr. Opin. Solid State Mater. Sci.

    (2003)
  • C. Richard et al.

    Chemosphere

    (1996)
  • S. Parra et al.

    Appl. Catal. B: Environ.

    (2002)
  • P. Maletzky et al.

    Chemosphere

    (1998)
  • Cited by (0)

    IICT Communication no.: 070301.

    View full text