Catalytic reduction/degradation of methyl orange by metal nanoparticle containing systems: a critical review

Abstract

Organic dyes are widely used in many industries, producing health issues after being discharged into wastewater. Methyl orange (MO) is an organic azo dye which is also released into wastewater from different industries and causes toxicity in the environment. Recently, eco-friendly approaches to remove MO from water have garnered significant interest. Among these, the application of inorganic metal nanoparticles (IMNPs) for the catalytic and photocatalytic reduction of MO is an emerging approach for effective and sustainable pollutant remediation. Various IMNPs, which are used for reduction of MO or conversion of MO into eco-friendly products recently through catalytic and photocatalytic reactions, are discussed in this review, as is the synthesis of mono- and bimetallic nanoparticles with and without capping agents which affect their stabilization as well as catalytic performance against MO. The capping agents enhance the catalytic performance of both mono- and bimetallic nanoparticles, recyclable properties, and tuning ability. Additionally, the characterization techniques employed to examine the properties of IMNPs and to monitor the catalytic reduction of MO are discussed. Future research directions should prioritize the separation and characterization of the products formed after MO catalytic treatment to assess their potential applications and improve reaction rates.

Fig. 1. pH of medium effects on the structure of methyl orange.

Scheme 1. Synthesis of methyl orange.

Fig. 2. Synthesis of silver nanoparticles with the help of plant extract.

Fig. 3. Silver nanoparticles synthesis by microwave irradiation along with capping agent.

Fig. 4. Synthesis of silver nanoparticles in microgels by in situ reduction method.

Fig. 5. Fe/Co/Ni tri-metal nanoparticles synthesis.

Fig. 6. Metal nanoparticles fabrication with (a) graphene oxide, (b) mesoporous SiO₂, (c) N-doped C dots, (d) metal–organic frameworks, (e) chitosan, and (f) microgels.

Fig. 7. Catalytic reduction mechanism of methyl orange in the presence of NaBH₄ and metallic nanocatalyst in capping agent.

Fig. 8. Photocatalytic degradation mechanism of methyl orange.

Muhammad Arif