1. Department of Environmental Science, University of Kalyani, Kalyani, Nadia 741235, West Bengal, India, Fax: +91‐33‐2582‐8282
2. Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, West Bengal, India
3. Institute of Microtechnology, University of Neuchâtel, Rue Emile Argand 11, 2009 Neuchâtel, Switzerland