Ananas Comosus Peel Extract Mediated Synthesis of Cobalt Oxide Nanoparticles for Hexavalent Chromium Removal and Antibacterial Activity

Abstract

Hexavalent chromium ion from different sources is the most series water pollutant, which causes carcinogenic and related problem to humans and animals. In addition, the development of antibiotic -resistant bacteria is one of the most series problems in health centers, and so required new drugs development to mitigate the problem. The focus of this research was biosynthesis of Co3O4 NPs to address the problems as an adsorbent and a nano-drug. Co3O4 NPs were synthesized via a biological method using Ananas comosus peel extract as a template in the presence of 0.5M of cobalt nitrate hexahydrate in different volume ratios such as 1:1(50 mL of precursor salt to 50 mL of extract), 1:2 (33.3 mL of precursor salt to 66.7 mL of extract), and 2:1(66.7 mL of precursor salt to 33.3 mL of extract). The synthesized Co3O4 NPs were characterized using TGA-DTA, XRD, SEM EDS, UV-Vis DRS, BET, and FTIR. TGA-DTA analysis showed that the biosynthesized Co3O4 was stable above 500 and SEM analysis result showed spherical shaped Co3O4 NPs. From the XRD result, the average crystallite size was found to be 12.58, 13.40, and 22.05 nm for 1:1, 1:2, and 2:1 ratios, respectively. The chemical composition and morphology of Co3O4 NPs was studied by SEM EDS analysis. The energy band gap and specific surface area of Co3O4 NPs of 1:1, 1:2, and 2:1 volume ratios were estimated to be 3.33, 2.95, 2.70 eV with UV-Vis DRS, and 24.7, 23.7, and 22.5 m 2 /g with BET analysis respectively. FTIR analysis confirmed the presence of bioactive compounds in peel extract and indicated the formation of Co-O bond stretching. The 1:1 volume ratio showed enhanced adsorption efficiency due to small average crystal size and high surface area to volume ratio and, selected for adsorption of Cr (VI) ions in aqueous solution. After optimization of each parameter the maximum adsorption efficiency of Cr (VI) was achieved to be 95% using 1g adsorbent, at 2pH, 20 mg/L initial concentration and 120 min contact time at room temperature. The adsorption isotherm model was found to be best fitted to Freundlich's isothermal model (R2 = 0.999) and the adsorption kinetics was found to fit pseudo 2ndorder kinetic model with R2=0.994 in presence of Co3O4 (1:1) NPs. In addition the antibacterial activity of Co3O4 nano-drug synthesized using 1:1, 1:2, and 2:1 ratios was investigated and was found in the range of 8-11, 9-13, and 7-10 mm inhibition zone, respectively against E.coli, S.aureus, P.aeruginosa, and S. pyogen, which was done using disc diffusion method.