A Review on the Synergetic Effect of Plant Extracts on Nanomaterials for the Removal of Metals in Industrial Effluents

Aim: The review paper aims to explore the effect of plant extracts on nanomaterial adsorbent for the removal of toxic metals present in industrial effluents. Background: Water plays a major role in the sustainability of human life and its existence. Rapid industrialization and urbanization lead to an increase in the pollution and accumulation of hazardous substances which causes the degradation of the aquatic ecosystem. Heavy metals are considered to be a major threat to the environment. Among various metals, the International Union of Pure applied chemistry (IUPAC) has characterized heavy metals based on their intensity of toxicity and hazardous effects. Nanoparticles, due to their unique properties of particle size, exist in the range between 1- 100nm, which represents the possibility to introduce modified chemical groups on their surface functioning as capping agents. Nanoparticles with the increased surface area have specified functional groups which induce the capability of the catalytic reduction reaction and their optical characteristics impact the industrial, agricultural and environmental sectors. Objective: Magnetic nanoparticles incorporated with the enzymes and metallic sites have been widely used in both the synthesis of bio valuable products as well as in the degradation of many hazardous substances like dyes, phenolic compounds, etc. Also, they are used in the removal of metal ions present in wastewater. Methods: Superparamagnetic support nanomaterials (SPIONs) are prepared using the compounds of Fe, Cu, Ni, Mn and Mg for the distinct and unique characteristics of reusability. These metallic nanomaterials are coated with distinct materials like mesoporous and amorphous silica, polyvinyl alcohol and pyrrolidine, polyethylene glycol, polystyrene, chitosan, dextran, starch, gelatin, polystyrene, polyacrylic acid, and polymethyl methacrylate to enhance the stability of the nanomaterials. Results: In comparison to the different nanomaterials, metal oxide NPs possess increased stability, magnetic inertness, optical and electrical properties. Nanomaterials that are used in the medical applications are also used as the adsorbents to remove heavy metals from the industrial wastewater. The presence of polyphenolic compounds and flavonoids makes the plant extracts effective antimicrobial agents that impact pathogens. Moreover, these plant extracts, coupled with other nanomaterials, play a significant role in the removal of toxic pollutants from the environment. Conclusion: Polyphenolic compounds present in plant extract function as natural reducing agents; hence, integrating plant extract with metal/metal oxide nanoparticles proves to be efficient in comparison with the catalysts synthesized by using other chemical methods. These surface modified nanocatalysts tend to possess enhanced stability and specific reactivity in the system and are used in the elimination of organic and inorganic pollutants in the industrial wastewater.