The development of cost-effective, efficient and stable materials helps to provide the affordable solutions to get safe and fresh water to increasing population with health guidelines of emerging contaminants. Nanomaterials (NMs)-based techniques involve the design, synthesis, manipulation, characterization and exploitation of materials for adsorption and separation of target species from the contaminated and waste water. NMs show better adsorption capacity and catalytic for number chemical species and microbes because of their small size and large surface area that favors the purification and treatment of waste or contaminated environmental water. Here, we present the chemical properties, adsorption/removal mechanism and applications of advanced NMs such as magnetic nanoparticles (MNPs), carbon nanotubes (CNTs), graphene and graphene oxide (GO), titanium oxide (TiO2), silica (SiO2), silver (Ag), gold (Au) NPs and zeolites in effective and efficient removal of toxic metal ions, organic and inorganic chemical substances and disease-causing microbes from contaminated and wastewater.
Top1. Introduction
Water is a most important resource for vitality for life on earth and sustaining human life. The major civilizations of the world originated nearby the water reservoirs or river due to the ample supply of water and fertile land. Water is a universal solvent that dissolves most of the organic and inorganic substances to meet the requirement of the life. Providing clean and safe water is a necessity and it is also challenging attempt to sustain the same level (LVovich 1979; Postel et al., 1996; World Health Organization 2013). About, millions of people die every year because of contaminated drinking water incorporated with water borne microorganism, toxic chemical substances and thousands of children die due to the water-related problems and diseases. At present, more than billions of people in the world lack to access the safe drinking water and a couple of decades the supply of safe water would suppose to be reduced one-third of the present scenario (Hutton et al., 2007; Mara 2003; Ashbolt 2004; Moore et al., 2003). The limited supply of fresh water to the increasing populations throughout the world is due to the drastic exploitation of water resources for domestic, industry and irrigation purposes in many parts of the world. The increased disposal of industrial, domestic and agricultural and mining wastages into surface and ground water bodies cause the contamination of several inorganic, organic and microbes (Ritter et al., 2002; Fawell et al., 2003). The inorganic species such as arsenic (As), mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr) and selenium (Se), etc.; organic substances such as pesticides, dyes and phenolic compounds etc.; and microbes such as bacteria and viruses could cause contamination of water (Cao et al., 2014; Yu et al., 2014; Walcarius et al., 2010). Today, the providing of safe and clean water to the fast-growing world population is on the high challenge and needs the plan to sustain the life for future generations.
There are several technologies have been developed for the removal of toxic chemical substances from environmental water samples, including chemical oxidation or reduction (Kohler et al., 2006; Theepharaksapan et al., 2011), chemical precipitation, coagulation or flocculation (Kim et al., 2002; RubI et al., 2009), UV or chlorination (Zhang et al., 2015), ozone treatment (Xiao et al., 2015), adsorption (Kojima et al., 2002), biological treatment (Rosal et al., 2010), reverse osmosis (Jian et al., 1999), membrane filtration (Amin et al., 2014) and ion exchange system (Velizarov et al., 2001). The use of conventional chemical oxidation or reduction through the activated sludge or carbon process unable to remove complex materials comprises of pharmaceuticals, surfactants, dyes various industrial additives. Activated sludge and biological trickling filters come under the biological treatment systems are also not efficient in removing the wide range of chemical substances and remain soluble in the effluent (Urase et al., 2005). Coagulation and flocculation process showed an ineffective in removing the variety of pharmaceutical drugs in different investigations (Vieno et al., 2006). The purification of water by chlorination is implemented to prevent the growth of bacteria and pathogens; however, this treatment causes the undesirable tastes and odors with different by-products (Becher, 1999). Ozone and UV treatment are used to stop the growth of microbes but these techniques are found to very expensive (Adams et al., 2002). Purification of water through the membrane filtration such as microfiltration, ultrafiltration, nano-filtration and reverse osmosis are found most effective and efficient techniques. All these filtration techniques are pressure driven process and removal of contaminants are dependent on the pore size of a semi-permeable membrane which is found specific for the removal specific particulates from water. Microfiltration, ultrafiltration, nano-filtration and reverse osmosis are cost-effective because these techniques require a more energy for the removal of contaminants (Walha et al., 2007; Saleh et al., 2016; Saleh et al., 2012).