## 1 Background
Graphene has a variety of real-time applications because of its extraordinary excellent thermal, mechanical and electrical properties [145]. Graphene is considered a promising material for the comprehensive adsorption of wide variety of pollutants from aqueous systems owing to its theoretically large specific surface area to volume ratio (\(\approx\)2675m\({}^{2}\)/g), high Young's Modulus (\(1.06\times 10^{3}\) Gegapascals) and high thermal conductivity (\(3\times 10^{3}\) Watt per meter kelvin) [113; 146]. The wet chemical redox process is one of the most effective method for the production of graphene from graphite, where GO is an intermediate with a high density of negatively-charged reactive functional groups, viz. hydroxyl, carboxylic, and epoxy groups [147; 148; 149]. The presence of several functional groups makes GO soluble in polar and non-polar solvents as the oxygen functionality makes GO hydrophilic and the graphene domain makes GO hydrophobic. All the functional groups present on the edges and on the basal plane of GO play an important role in the heavy metal ions removal process [150]. Therefore, GO could be the best potential scavenger for the effective removal of cationic pollutants through electrostatic interactions between the positively-charged pollutants and negatively-charged functional groups of GO [27; 151]. The relative high surface area, surface functionality, and better conductivity of graphene sheets play a key role in the better adsorption of several heavy metal ions through the preconcentration of aqueous medium [67; 144]. [PERSON] et al. reported that a few layered thick GO sheet membrane can completely block the passage of pollutants in the form of liquids and gases in a dry state while facilitating the permeation of water vapors [152]. On the other hand, aggregation, which is a major disadvantage of graphene layers, could be prevented partially through its composite formation [41; 153]. In addition, composite formation may impart enhanced efficiency for the removal of heavy metal ions from wastewater due to the synergistic effects of the materials used. Electrosorption, a simple, novel, \begin{table}
\begin{tabular}{c c c c c} \hline
**Techniques** & **Materials used** & **Advantages** & **Disadvantages** & **Ref.** \\ \hline \multirow{3}{*}{Reverse Osmosis} & \multirow{3}{*}{Semi-permeable membranes} & \multirow{3}{*}{Able to remove most of the pollutants} & \multicolumn{2}{c}{Complex, nonselective,} \\  & & & & continuous energy input, plug \\  & & & politants & fouling, Low efficiency, Slow \\  & & & removal rate. & \\ \hline \multirow{3}{*}{Electro-chemical} & \multirow{3}{*}{Specific electrode materials, hybrid electrodes, coated electrode etc.} & Highly specific, able to remove suspended solids, dissolved metals. & High cost electrode required, & \\  & & & remove suspended solids, & need continuous energy input, & \\ \cline{1-1}  & & & higher cost, highly sensitive to & \\ \cline{1-1}  & & & & pH changes. & \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. ecofriendly and recently attractive heavy metal ions adsorption technique which does not requires toxic or non-toxic chemicals and involves ideal nanostructured materials with a high surface area (such as activated carbon, carbon nanotubes, and carbon aerogels) onto which an external electric field is applied to remove metal ions from aqueous solutions [93; 154; 155; 156; 157]. Hence, this review includes various surface modification approaches and post synthesis, assembly steps, which will enable the exploitation of GO as a novel adsorbent material for cost effective water purification and the removal of heavy metals through graphene and its composites, which may be helpful in the purification of potable and safe drinking water as well as the removal of heavy metal ions from wastewaters and to clean up the environmental problems.