ORIGINAL ARTICLE Green synthesis of magnetite nanoparticles using aqueous pod extract of Dolichos lablab L for an efficient adsorption of crystal violet K. Basavaiah 1 & Mebrahtu Hagos Kahsay 1,2 & Dharmasoth RamaDevi 3 Received: 16 March 2018 /Accepted: 12 June 2018 # Springer International Publishing AG, part of Springer Nature 2018 Abstract We report, an aqueous pod extract of Dolichos lablab L. mediated synthesis of magnetite nanoparticles (Fe 3 O 4 NPs) for an efficient adsorption of organic dye pollutant from contaminated water. The Fe 3 O 4 NPs were capped and stabilized with phytoconstituents of D. lablab L. The product Fe 3 O 4 NPs was characterized by range of instrumental facilities such as Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, FT-Raman spectroscopy, X-ray diffraction, Field emission scanning electron microscopy, Energy dispersive X-ray spectroscopy, Transmission electron microscopy, vibrating sample magnetometer, and thermogravimetric analysis. The synthesized 12.5 nm spherical shaped Fe 3 O 4 NPs were used as adsorbent for elimination of crystal violet (CV) from contaminated water. It is found that the dye removal efficiency of Fe 3 O 4 NPs was critically depends on pH of the reaction medium and dosage of Fe 3 O 4 NPs. Adsorption data were analyzed using Langmuir, Freundlich, and Temkin isotherms as well as pseudo- first-order and pseudo-second-order kinetic models. The overall outcome of adsorption best fitted to Langmuir and psepseudo- second-order with their corresponding correlation coefficients of (R 2 = 0.996) and (R 2 = 0.977), respectively The biomolecules capped can act as a valuable adsorbent for removal of pollutant organic dyes from industrial outflow. Keywords Adsorption . Crystal violet . Fe 3 O 4 NPs . Dolichos lablab pod . Green synthesis . Pseudo-second-order 1 Introduction During the last two decades, magnetite nanoparticles (Fe 3 O 4 NPs) have attracted considerable attention to researchers due to their unique chemical and physical properties and many tech- nological applications. Fe 3 O 4 NPs have been exclusively stud- ied owing to their special properties and potential technological applications such as magnetic storage media [1], catalyst for dye removal [2], adsorbent [3], magnetic resonance imaging [4, 5], drug delivery [6], ferrofluids [7], biosensors [8], hyperthermia treatment of cancer [9–11] and organic synthesis [12]. Fe 3 O 4 NPs have been exclusively employed for wastewater treatment due to their dynamic morphology, desired size, magnetic prop- erty and value saturation magnetization value [13]. Among all water treatment techniques, the adsorption process is one of the most widely used owing to a benefit of high adsorption efficien- cy and non toxic by products release into treated water [14]. Various synthesis methods mostly physical and chemical methods have been reported for Fe 3 O 4 NPs such as, redox- based hydrothermal method [15], solvothermal synthesis [ 16], co-precipitation [17], flame spray synthesis [ 18], sol-gel method [19], electrochemical processes [20], high energy ball milling [21], and sonochemical synthesis [22]. However, physical and chemical methods bring argument to environmental and biologi- cal risks on account of the use of toxic precursors, capping agents, solvents and toxic reducing agents especially hydrazine [23], so- dium borohydride (NaBH 4 ), carbon monoxide (CO) [24], and dimethyl formamide (DMF) [25] during synthesis of Fe 3 O 4 NPs [26]. Therefore, the researchers are profoundly motivated to green synthesis of Fe 3 O 4 NPs via nature-friendly, and inexpen- sive approach for environmental and medical applications. More recently, green chemistry drew attention to many re- searchers for synthesis of Fe 3 O 4 NPs by using various biolog- ical entities such as plants, and microbes (bacteria, fungi, yeasts, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42247-018-0005-1) contains supplementary material, which is available to authorized users. * K. Basavaiah klbasu@gmail.com 1 Department of Inorganic and Analytical Chemistry, Andhra University, Visakhapatnam 530003, India 2 Faculty of Natural and Computational Sciences, Woldia University, 400 Woldia, Ethiopia 3 A.U College of Pharmaceutical Sciences, Andhra University, Visakhapatnam 530003, India Emergent Materials https://doi.org/10.1007/s42247-018-0005-1