Solanum xanthocarpum Plant as a Potential Low Cost Adsorbent for the Removal of Methylene Blue from Aqueous Solutions Muhammad Iqbal Zaman, a Siffat Uullah Khan, a Aysha Shahnaz, a Abdul Niaz, a Sadullah Khan, b Nawshad Muhammad, c Matiullah Khan, b and Khizar Hussain Shah d a Department of Chemistry, University of Science and Technology, Bannu, 28100, Pakistan b National Center of Excellence, Physical Chemistry University of Peshawar, Peshawar, 25120, Pakistan c Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore, Pakistan d Department of Chemistry, COMSATS University Islamababd, Abbottabad Campus, Abbottabad, 22060, Pakistan; khizarshah@ciit.net. pk (for correspondence) Published online 5 October 2018 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.12955 This study reports the removal of methylene blue (MB) from aqueous solution by powdered fruit of Solanum xanthocar- pum plant which is important in terms of its applicability in the decontamination of water through an environmental friendly and low cost adsorbent. The biosorbent has a BET surface area of 3.09 m 2 /g while FE-SEM and FTIR analyses show that it is a porous material having OH, C H, C O, and SO 3 - H surface groups. The sorption equilibrium experi- ments show that sorption of MB increases with increasing pH, temperature, initial concentration, and sorbent dosage. The sorption equilibrium data fits well to Langmuir adsorption iso- therm. The values of the isosteric heat of sorption (ΔH), being positive are consistent with the endothermic nature of the sorp- tion process. Sorption kinetics experiments of MB onto the bio- sorbent show that equilibrium is established in about 180 minutes at both the pH values of 6 and 5.2 and that the data give best fit to pseudo-second order kinetics model. The maximum adsorption capacity of the biosorbent for MB is about 0.05067 mmol/g. Sorption data along with the spectro- scopic analyses suggests that MB is removed from the aqueous solution by the sorbent mostly through ion exchange, adsorp- tion, diffusion, and surface precipitation. © 2018 American Insti- tute of Chemical Engineers Environ Prog, 38: S166–S175, 2019 Keywords: biosorption, methylene blue, Langmuir model, Freundlich isotherm, textile wastewaters INTRODUCTION Due to increasing industrialization and urbanization of the modern world, large quantities of industrial wastewater con- taining toxic diazo dyes and heavy metal ions are pumped into our surrounding soil and water bodies [1,2]. These highly toxic effluents coming out mostly from paper, textile, printing, cos- metics, leather, pulp, plastic, and electro-plating industries into the soil biota have posed serious threats to living organisms including human beings and the ecosystem [1–5]. Although heavy metals contamination of soil and waters is equally a seri- ous problem, yet the dyes contamination in wastewater is one of the major causes of environmental pollution today. It has been reported that processing industries use more than 10,000 types of dyes for various kinds of applications [6,7] and among them, the highest rates of toxicity are reported to associate with basic and diazo direct dyes [8,9]. Studies reveal that the presence of these dyes is not only aesthetically displeasing but also their presence in water bodies reduces the penetration of sunlight into water and thereby affects the aquatic ecosystem by affecting photosynthesis and the growth of aquatic life [8,10–13]. Methylene blue (MB), being a basic dye is reported to be toxic and causes several health risks in humans upon expo- sure such as nausea, vomiting, eye injury, and methemoglobi- nemia [8,9]. On the other hand it has enormous applications in many fields of science and technology. For example chem- ists use it as a redox indicator, biotechnologists use it to stain tissue samples and detect nucleic acids, while in medicines, it is used for treatment of a lot of diseases such, schizophrenia (manic-depressive psychosis), infection by herpes simplex virus, and chronic urolithiasis (formation of kidney and blad- der stones). It is also used for identification of bacteria, for a quick estimation of percentage of viable cells in a yeast sam- ple and as a stain for surgical medical markings [14,15]. Therefore, due to its excessive use a large quantity of this dye is released and in such a situation it become extremely important to device a careful and affective prior treatment technology before its discharge into the soil and water bod- ies [7,8,11]. In order to cope with the threat of industrial dyes stuff, sev- eral treatment technologies have been tested for their removal from wastewater, including biological treatment, membrane fil- tration, electrochemical processes, adsorption, and ion exchange [16–19]. However, most of these processes have lim- ited applications due to some serious drawbacks associated with them such as time of operations, economic viability, sludge production, and disposal problem [20,21]. Conse- quently, among all these processes adsorption has been © 2018 American Institute of Chemical Engineers S166 March 2019 Environmental Progress & Sustainable Energy (Vol.38, No.S1) DOI 10.1002/ep