Eco-Friendly NiO/Polydopamine Nanocomposite for Efficient Removal of Dyes from Wastewater.

The rapid development of industries discharges huge amounts of wastewater that contain surface water. For this reason, we used NiO/polydopamine (NiO/PDA) nanocomposite as an efficient material for the removal of Methyl violet 2B from water. It was synthesized and then characterized by Fourier Transform Infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, Transmission Electron Microscopy (TEM), and Brunauer-Emmett-Teller (BET). The EDX analysis confirmed the presence of O, Ni, N, and C. The composite has an average particle size of 18 nm. Its surface area is 110.591 m 2 /g. It was found that the efficiency of dye removal by adsorption on NiO/PDA exceeded that of bare NiO. The adsorption capacity of NiO and NiO/PDA are 126 and 284 mg/g, respectively. The effects of adsorbent dose, dye concentration, and pH on the removal efficiency were examined. The efficiency increased with increasing the adsorbent dose and pH, but dropped from 85 to 73% within 30 min as the initial dye concentration was increased from 0.984 to 4.92 mg/L. Such a drop in the removal efficiency is due to the blocking of the surface-active sites of NiO/PDA, with the high population of dye molecules derived from the continuous increase in dye concentration. The adsorption results of the dye fitted well with the pseudo-second-order kinetics and Langmuir isotherm. The reusability data showed that NiO/PDA was stable across three adsorption-regeneration cycles, thus it can be considered a good recyclable and efficient adsorbent. Because of these results, it can be considered that this method can be applied for the treatment of wastewater.