Ag nanoparticles anchored on NiO octahedrons (Ag/NiO composite): An efficient catalyst for reduction of nitro substituted phenols and colouring dyes

The development of an efficient sustainable catalyst for effective removal of hazardous chemicals, viz. nitrophenols and organic dyes, from wastewater is a challenging task. Herein, facile synthesis of Ag/NiO composites by anchoring Ag nanoparticles (NPs) on NiO octahedrons with different amounts of Ag NPs (AN-5% (5% Ag), AN-10% (10% Ag) and AN-15% (15% Ag)) has been demonstrated. SEM (scanning electron microscopic) and TEM (transmission electron spectroscopic) images ensured the proper anchoring of spherical Ag NPs (particle size = 16.54 +/- 1.88 nm) on octahedron particles of NiO, which was also ensured by XPS (X-ray photoelectron spectroscopy) analysis. Moreover, the resulting composites have an average surface area (49-52 m(2)g(-1)) and pore size (2.39-2.26 nm). All three synthesized Ag/NiO composites (100 mu L) catalyzed the complete reduction of para-np (4-nitrophenol: 0.1587 mM) within 2-3 mM in the presence of 0.04 M NaBH4. Among them, AN-5% has been chosen because of the lowest anchored Ag (5%) to obtain the optimized catalyst's amount (50 mu L) and concentration of para-np (0.1587 mM). AN-5% also exhibited excellent catalytic activity towards different nitro substituted phenols, viz. ortho-np (2-nitrophenol), meta-np (3-nitrophenol), para-np (4-nitrophenol) and tri-np (2,4,6-trinitrophenol). AN-5% displayed similar to 100% catalytic efficiency for reducing meta-np in 2 min with the apparent first order rate constant (k(app)) and normalized rate constant (K-nor) as 1.99 s(-1) and 398.14 s(-1) g(-1), respectively. Additionally, AN-5% (29.41 mu g mL(-1)) reduced >95% of the colouring dyes (10 ppm) such as CONG-R (congo red: 95% in 6 min), METH-O (methyl orange: 97.5% in 7 min), METH-B (methylene blue: 98.3% in 10 min) and RHOD-B (rhodamine B: 99.2% in 5 min). AN-5% not only demonstrated catalytic reduction towards individual pollutants, but also showed excellent activity for reduction of the mixtures of nitrophenols/dyes and for treatment of simulated industrial effluent samples (EFF1, EFF2) and a real industrial sample (textile dye-bath effluent). AN-5% can also be reused up to several cycles with almost same efficiency and followed the Langmuir-Hinshelwood apparent first order kinetics model.

Automated summary

This article presents the development of an efficient and sustainable Ag/NiO catalyst for the removal of hazardous chemicals from wastewater. The catalyst, composed of anchored Ag nanoparticles on NiO octahedrons, demonstrates excellent catalytic activity for the reduction of nitrophenols and organic dyes. It also shows promising performance in treating mixtures of pollutants and real industrial wastewater samples.