Colloids and Surfaces B: Biointerfaces 92 (2012) 156–160 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces B: Biointerfaces j our na l ho me p age: www.elsevier.com/locate/colsurfb Adsorptive removal of silver nanoparticles (SNPs) from aqueous solution by Aeromonas punctata and its adsorption isotherm and kinetics S. Sudheer Khan, Amitava Mukherjee, N. Chandrasekaran ∗ Centre for Nano Biotechnology, VIT University, Vellore 632014, India a r t i c l e i n f o Article history: Received 18 May 2011 Received in revised form 15 November 2011 Accepted 16 November 2011 Available online 25 November 2011 Keywords: Aeromonas punctata Zeta potential Adsorption isotherm Kinetics Silver nanoparticles removal a b s t r a c t Silver nanoparticles (SNPs) are being increasingly used in many consumer products and industrial appli- cation. The release of SNPs to the environment is a major concern. Here we have studied the adsorptive removal of SNPs by a SNP resistant bacterial species Aeromonas punctata, isolated from the sewage envi- ronment. The influence of zeta potential on adsorption was investigated at acidic, neutral and alkaline pH and with varying salt (NaCl) concentrations. The rate of adsorption and removal of SNPs was decreases with increase in pH and salt concentration. The zeta potential study suggests that, the adsorption of SNPs on the cell surface was related to electrostatic force of attraction. The equilibrium adsorption isotherm and kinetics of adsorption were also studied. The adsorption equilibrium isotherms fitted well to the Langmuir model. The kinetics of adsorption fitted best to pseudo-first-order. A. punctata was able to remove 4.42 and 3.85 mg/L of SNPs at pH 5 and 7 respectively. The present study can be used for the effective removal of SNPs which is released into the environment and sewage treatment systems. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Silver nanoparticles (SNPs) are extensively used in consumer products industrial applications due to its antimicrobial prop- erty [1,2]. Nowadays, use of SNPs is increasing in a large number of consumer products. There are more than 1000 nano-based consumer products in market [3], of which silver nanoparticles incorporated consumer products, including clothing and cosmet- ics are about 200 [4]. Worldwide, the present production of SNP is estimated to be 500 tonnes/year [5]. Thus, the possible build- up of the nanoparticles in the environment is becoming a major concern [6]. With the increased application of these nanoparticles, possibly a large amount of nanoparticles will be discharged into environment [7]. Impellitteri et al. [8] revealed that the SNPs can easily leak into waste water during washing from SNPs impregnated clothes and the washing systems, thus potentially disrupting beneficial bacte- ria used in waste-water treatment facilities, and the endangering aquatic organisms in lakes, streams and other fresh water systems. The release of SNPs to the sewage treatment plants was estimated to be 270 tonnes/year [9]. Kaegi et al. [10] reported the release of SNPs from painted walls. In aquatic habitats, the nanoparticles could accumulate in the fish body and directly enter into food chain ∗ Corresponding author. Tel.: +91 416 2202624. E-mail addresses: nchandrasekaran@vit.ac.in, nchandra40@hotmail.com (N. Chandrasekaran). [11]. The nanoparticles have adverse effects on human health due to its smaller size and large surface area [12]. Due to these rea- sons, nanoparticles are being included as a category of emerging potential toxic contaminants and the stability of these nanopar- ticles in environment needs to be investigated. There are a few studies which reported the possible involvement of zeta potential in toxicological effect of SNPs [13]. But the role of zeta potential on adsorption and removal of SNPs by bacterial species is not reported. In absence of adequate prior reports, this study aims to investigate the removal of SNPs by environmental bacterial species Aeromonas punctata. A. punctata was previously reported as SNP resistant [14]. Consequently, the aim of this study was to investigate (i) the influ- ence of zeta potential for the adsorption of SNPs on bacterial cell (ii) the adsorption isotherms and kinetics of adsorption at different pH values and (iii) the influence of salt concentration on adsorption of SNPs. 2. Materials and methods 2.1. Materials All chemicals and media were obtained from Himedia Labora- tories Ltd., Mumbai. SNPs were obtained from Sigma Aldrich, USA. Nanoparticles were dispersed using an ultrasonic processor with a frequency of 132 kHz (Crest, USA). The microorganism used in this study was A. punctata, isolated from the sewage environment, Vellore, India. 0927-7765/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2011.11.032