ORIGINAL PAPER Catalytic Degradation of Methyl Orange and Selective Sensing of Mercury Ion in Aqueous Solutions Using Green Synthesized Silver Nanoparticles from the Seeds of Derris trifoliata Neethu Cyril 1,2 • James Baben George 3 • Laigi Joseph 1,4 • V. P. Sylas 1 Received: 20 November 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract In the present study, bio-augmented silver nanoparticles with Derris trifoliata seed extract (AgNP-DT) have been developed. Formation of AgNP-DT has been confirmed with X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FTIR). Even though introduced for the first time as a catalyst owing to high surface area, the as-prepared nanoparticles showed one of the best catalytic activity in the reduction of a water soluble azo dye–methyl orange. An incredible pseudo-first order rate constant (0.3208 min -1 ) and activity parameter (1086 s -1 g -1 ) were obtained for the catalytic reduction of methyl orange with 4.9 lg AgNP-DT. Furthermore, AgNP-DT exhibits a good selectivity and sensitivity towards mercury(II) ions over other metals in aqueous solution. Absorbance of AgNP-DT exhibits a good linear relationship against concentration of Hg 2? with a limit of detection (LOD) of 1.55 lM. The mechanism of sensing activity of AgNP-DT was elucidated by measuring the variation in the zeta potential of the system with increasing concentration of Hg 2? . Moreover the proposed method could be practicably applied for the detection of Hg 2? in real water samples with a percentage recovery in range of 91.41–108.07%. & V. P. Sylas sylas@mgu.ac.in; mgubioenergy@gmail.com 1 School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala 686 560, India 2 Department of Chemistry, Assumption College, Changanasserry, Kottayam, Kerala 686 101, India 3 Department of Chemistry, St. Berchman’s College, Changanasserry, Kottayam, Kerala 686 101, India 4 Department of Chemistry, Government College, Nattakom, Kottayam, Kerala 686 013, India 123 Journal of Cluster Science https://doi.org/10.1007/s10876-019-01508-9