146 1. IntroductIon Rapid expansion of industry and human population outburst are mainly responsible for water pollution. This creates scarcity of fresh water reservoir for drinking as well as irrigation purposes 1,3 . Dumping of untreated industrial and domestic waste containing inorganic compounds particularly heavy metal ions in water bodies causes water- borne diseases 2 . The heavy metals are highly toxic and exert adverse efects on the environment as they cannot be degraded by microorganisms 1,4,5 . Consumption of food contaminated with heavy metals depletes essential nutrients in human body causing several health disorders including cancer 6 . Among the ten heavy metals (led, arsenic, cadmium, chromium, cobalt, copper, mercury, manganese, zinc, and nickel which are of major public health concern) Ni 2+ is one of the most hazardous metals 7 . It is the 5 th most abundant element by weight of earth crust and released into water from minerals/ other sources 8 . Nickel and nickel compounds are widely used in metallurgical, chemical and food processing industries, especially as catalysts and pigments 9-12 . Nickel is also very important element for the synthesis of vitamin B 12 in biological system but presence of its excess amount causes lungs cancer, bones problems and it may develop nausea, headache as well as dry cough 13-14 . The permissible limit of NI(II) is 0.02 mgL-1 (WHO/BIS) and 2.0 mgL −1 for potable water and industrial wastewater respectively 12 . However, industrial wastewater of various industries contain nickel more than its present limit. Hence, treating waste water for removal of contaminants is essential to reduce their mobility within the terrestrial ecosystem 15 . Among the available removal techniques, adsorption is regarded as one of the most extensively used method because of simple design, low cost and no sludge formation 16,19-21 . Nanoscale metal oxides fnd applications as a cost efcient adsorbent in water treatment and remediation technology due to their small size and adsorption efciency as compared to natural sized oxide 22 . CuO nanoparticle attracts great attention as an adsorbent to remove heavy metals from polluted water because of its high efciency and low cost 18 . Ni(II) is most toxic than other valent state of same 23 . Consumption of nickel(II) contaminated water for drinking and other purposes leads to the various pathological problems 24 . Hence, Ni(II) is taken for whole experiment to be performed. To the best of our knowledge, only few reports are available on the removal of Ni 2+ using CuO nanoparticles18, but they have not tested the efciency for real life contaminated water. The aim of our present work is to synthesise copper(II) oxide NPs through an easy, economic and environment friendly process and to explore its efcacy as a low-cost adsorbent for Ni 2+ removal from contaminated water. The present study deals with synthesis and application of CuO nanoparticles to remove Ni(II) from contaminated water. 2. ExpErImEntal 2.1 materials Involved AR Grade chemicals e.g. Cupric Chloride (Merck), Hydrochloric acid (Merck), Sodium Hydroxide (Merck), capping agent polyethylene glycol (SRL), nickel chloride (Merck), acetone (Sigma Aldrich) and ethanol (Bengal chemicals) were used in the experiment. All experiments were performed using double distilled water. 2.2 Synthesis of copper oxide nps We have synthesised copper (II) oxide NPs by modifying our previously reported methods to get uniform desired particles 25 . A solution of 6.8 g CuCl 2 , 3.2 g NaOH and 4 g of polyethylene glycol (Mol wt.~ 10000) capping agent mixture Received : 09 September 2020, Revised : 16 January 2021 Accepted : 12 March 2021, Online published : 03 June 2021 Nanoscale Copper(II) Oxide: An Efcient and Reusable Adsorbent for removal of nickel (II) from contaminated Water Prasanta K. Raul * , Bodhaditya Das, Rashmi R. Devi and Sanjai K. Dwivedi DRDO-Defence Research Laboratory (DRL), Tezpur- 784 001, India. * E-mail: prasanta.drdo@gmail.com abStract The present work describes the synthesis of copper(II) oxide nanoparticles (NPs) with high surface area (52.11 m 2 /g) and its Ni(II) adsorption efciency from contaminated water at room temperature. Copper (II) oxide NPs are able to remove Ni(II) as 93.6 per cent and 93.7 per cent using 500 ppb & 1000 ppb initial concentration of nickel at near-neutral pH respectively. CuO NPs is very much efective to remove more than 75 per cent nickel over a wide range of pH even in presence of other competing ions like Cd 2+ , Pb 2+ , Cr 6+ , SO 4 2- . Prepared CuO NPs can be used to remove Ni(II) from aqueous solution in real feld application. Keywords: Nickel(II); Copper(II) oxide NPs; Contaminated water; Removal; Adsorption Defence Life Science Journal, Vol. 6, No. 2, April 2021, pp. 146-154, DOI : 10.14429/dlsj.6.16289  2021, DESIDOC