Study on the removal of heavy metal ions from industry waste by carbon nanotubes: Effect of the surface modification: a review

Abstract

Removal of noxious materials such as heavy metal ions (which are hazardous above certain ppm concentration) from wastewater is one of the biggest environmental challenges that suffers the Downloaded by [New York University] at 19:39 22 June 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 economy nowadays. On the basis of their versatility, environmental friendliness, the adsorption was proved to be a most economical and efficient technology, which is used extensively for their removal from the aqueous media. Among the various developed adsorbents used so far, carbon nanotubes (CNTs) show a unique impact on the fast adsorption and rapid removal of noxious impurities from the aqueous source. CNTs festooned on the sources like activated carbon, nanoparticles and nanocomposities enhanced the efficiency and potential of the adsorbent. Due to their unique structural, electronic, optoelectronic, semiconductor, as well as mechanical, chemical and physical properties, they have been extensively used to remove heavy metals in wastewater treatment. The adsorption mechanisms is majorly contributed by the chemical interactions between the metal ions and the functional groups present on the surface of the CNTs.Greater the surface area more will be the number of reducing groups hence more attributable to better CNT sorption performances.Graphical Abstract: schematic for interaction of carbon nanotube with heavy metal ions in aqueous solution

The role of nanomaterials as effective adsorbents and their applications in wastewater treatment

“…However, the atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms, therefore they can attract adsorbates [48][49][50][51][52]. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (an adsorbate bound to the surface by weak van der Waals forces), chemisorption (an adsorbate tethered through covalent bonding [53] or due to electrostatic attraction [26]). …”

“…Such adsorbents such as activated carbon (AC), zeolites, biomaterials, polymers, have been used extensively for wastewater treatment [22][23][24][25][26][27][28][29][30][31]. However, the adsorption efficiency of these materials is relatively low [26]. Therefore, it has become essential to find more efficient adsorbents.…”

“…For this purpose, conventional methods such as reduction, precipitation, adsorption, oxidation and ion exchange are commonly used. However, among them the adsorption process is the most suitable method because of its high efficiency and economic consideration [22][23][24][25][26]. Such adsorbents such as activated carbon (AC), zeolites, biomaterials, polymers, have been used extensively for wastewater treatment [22][23][24][25][26][27][28][29][30][31].…”

“…A variety of efficient, lowcost and eco-friendly nanomaterials with unique functionalities have been proposed for potential applications in detoxification of industrial effluents, groundwater, surface water and drinking water [34,37]. An ideal adsorbent for wastewater treatment purposes should satisfy the following criteria [26]: (1) should be environmentally benign; (2) should demonstrate a high sorption capacity and high selectivity especially to the pollutants occurring in water at low concentration; (3) the adsorbed pollutants can be easily removed from its surface, and (4) should be recyclable. In recent years, many studies have proved that the nanomaterials can satisfy most of these requirements [38][39][40].…”

Adsorption of Ammonium Ions onto Multi-Walled Carbon Nanotubes

“…CNTs can be classified into three types: single-walled (SWCNTs), multi-walled (MWCNTs), and functionalized (f-CNTs) [12][13][14][15]. Such materials have already played a key role in the effective removal of several organic contaminants from water [16].…”