Sains Malaysiana 51(2)(2022): 533-546 http://doi.org/10.17576/jsm-2022-5102-17 Green Synthesis of Nickle Oxide Nanoparticles for Adsorption of Dyes (Sintesis Hijau Nanozarah Nikel Oksida untuk Penjerapan Pewarna) ISRAA MUZAHEM RASHID*, SAMI DAWOD SALMAN, ALAA KAREEM MOHAMMED & YASMIN SALIH MAHDI ABSTRACT The green synthesis of nickel oxide nanoparticles (NiO-NP) was investigated using Ni(NO 3 ) 2 as a precursor, olive tree leaves as a reducing agent, and D-sorbitol as a capping agent. The structural, optical, and morphology of the synthesized NiO-NP have been characterized using ultraviolet–visible spectroscopy (UV-Vis), X-ray crystallography (XRD) pattern, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis. The SEM analysis showed that the nanoparticles have a spherical shape and highly crystalline as well as highly agglomerated and appear as cluster of nanoparticles with a size range of (30 to 65 nm). The Scherrer relation has been used to estimate the crystallite size of NiO-NP which has been found about 42 nm. The NiO-NPs have subsequently used as adsorbents for adsorption of two types of dyes; methylene blue (MB) as cation dye and methyl orange (MO) as anion dye. The removal efciency of dyes from contaminated water was investigated during various key parameters at room temperature; initial dye concentration (Co), pH, contact time (t), agitation speed, and adsorbent dosage. The maximum removal of MB dye was found to be 96% (Co=25 mg/l, pH=10, contact time=100 min, agitation speed=300 rpm and adsorbent dosage=6 g/l), while for MO the maximum removal reached 88% at (Co=20 mg/L, pH=2, t =160 min, agitation speed=300 rpm and adsorbent dosage=6 g/L). The experimental adsorption data were found to well obey Freundlich isotherm. The kinetic investigation showed that the adsorption process for both dyes followed a pseudo-second-order model with rate constants 0.0109 and 0.0079 (mg/g min) for MB and MO, respectively. Keywords: Adsorption; isotherm; kinetics; methyl orange; methylene blue; NiO nanoparticles; olive leaves ABSTRAK Sintesis hijau nanozarah nikel oksida (NiO-NP) telah dikaji menggunakan Ni(NO 3 ) 2 sebagai prakursor, daun pokok zaitun sebagai agen penurun dan D-sorbitol sebagai agen penutup. Struktur, optik dan morfologi NiO-NP yang disintesis telah dicirikan menggunakan analisis spektrofotometer ultralembayung-cahaya nampak (UV-Vis), pola pembelauan sinar-X (XRD), spektroskopi transformasi Fourier inframerah (FT-IR) dan mikroskop elektron imbasan (SEM). Analisis SEM menunjukkan bahawa nanozarah ini mempunyai bentuk sfera dan darjah hablur yang tinggi serta sangat beraglomerat dan ia hadir dalam gugusan dengan julat saiz daripada (30 hingga 65 nm). Hubungan Scherrer telah digunakan untuk anggaran saiz hablur NiO-NP yang telah dijumpai pada 42 nm. NiO-NP telah digunakan beberapa kali sebagai bahan penjerap untuk penjerapan dua jenis pewarna; metilena biru (MB) sebagai pewarna kation dan metil jingga (MO) sebagai pewarna anion. Kecekapan penyingkiran pewarna daripada air tercemar telah dikaji menggunakan beberapa parameter pada suhu bilik; permulaan kepekatan (Co) pewarna, pH, masa bertembung (t), kelajuan agitasi dan dos bahan penjerap. Penyingkiran pewarna MB maksimum yang telah dijumpai adalah 96% pada (Co=25 mg/l, pH=10, masa bertembung=100 min, kelajuan agitasi=300 rpm dan dos penjerap=6 g/l), manakala untuk MO nilai maksimum penyingkiran mencapai 88% pada (Co=20 mg/L, pH=2, masa bertembung=160 min, kelajuan agitasi=300 rpm and dos penjerap=6 g/L). Data uji kaji penjerap mendapati mengikuti model Freundlich. Kajian kinetik menunjukkan bahawa proses penjerapan untuk kedua-dua pewarna mengikuti model urutan kedua pseudo dengan kadar tetap 0.0109 dan 0.0079 (mg/g min) untuk masing-masing, iaitu MB dan MO. Kata kunci: Daun zaitun; isoterma; kinetik; metilena biru; metil jingga; nanozarah NiO; penjerapan INTRODUCTION Nickel oxide nanoparticles have greatly attracted increasing attention because of their unique characteristics such as electrical, chemical and optical properties (Pelgrift & Friedman 2013; Sun et al. 2017). NiO-NPs have several applications in diferent felds. It is widely used as an electrochromic flm, a magnetic material,