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Rapid industrialization with the increase in the population leads to the water crisis. The number of industries using heavy metals such as copper, chromium, nickel, zinc, etc. in their process is also leaving behind the effluent containing a large amount of heavy metals which discharged directly to the water bodies. There are constraints set by the regulatory bodies of government on the industries to maintain an upper level discharge limit for each of the metal ion. There are various methods available for the removal of metal ions which are selected according to the requirement. Adsorption is one of the optimal solutions for the removal of metal ions from industrial effluent streams. It is helpful in reducing the operational cost and size of equipment along with the increase recovery of metal ions. Adsorption is a surface phenomenon so the foremost property required for a perfect adsorbent is the higher surface area. Nanoparticles are now being preferred to be used as an adsorbent due to their large surface area which is a very important characteristic for a desired adsorbent. Development of nanoparticles has been the subject of enormous interest since the past decade. They have incredible adsorption properties due to the presence of high-energy adsorption sites and they also have excellent binding energies or interaction potentials for physisorption than traditional adsorbents. This study summarized the use of nanomaterial for the removal of metal ions from wastewater streams. It also highlights the various types of nanomaterials, their fabrication method and characteristics. The mechanism of metal adsorption onto various nanomaterials is also described in this study.

In the present study, an alumina nanoparticle adsorbent is developed using solution combustion synthesis method and is further utilized for the removal of zinc (Zn(II)) and color black G (CBG) from wastewater. The developed adsorbent is characterized using SEM-EDS technique. The effect of various parameters such as the initial concentration, the contact time, the mass of adsorbent and the solution pH are studied for the removal of Zn(II) and CBG. The equilibrium time for both, Zn(II) and CBG is obtained to be approximately 4.5 h. The maximum adsorption of Zn(II) is found at pH value of 7 while the maximum removal of CBG is obtained at pH value of 2. The Langmuir isotherm model is found suitable for explaining the adsorption behavior of Zn(II) (R 2 = 0.976) and CBG (R 2 = 0.974) onto alumina nanoparticles, which supports the monolayer formation of Zn(II) and CBG during the adsorption process. The maximum adsorbent capacity of alumina nanoparticles for the removal of Zn(II) and CBG are obtained as 1,047.83 and 263.16 mg g -1 , respectively. The kinetic data obtained during the experiments are better fitted with the pseudo-first-order model for both, Zn(II) (R 2 = 0.989) and CBG (R 2 = 0.971). A statistical analysis is also carried out to develop the mathematical equation which relates the different independent parameters (initial metal concentration, pH, time and mass of adsorbent) with the dependent parameter (adsorption capacity). The optimum values of independent parameters are estimated using Microsoft Solver.

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