Lack of proper effluent disposal methods in industries has led to an exacerbation of the risk posed by heavy

metal contaminants present in industrial wastewater. Several approaches have been explored to mitigate these

harmful threats but, most of these approaches have several limitations such as, lacking selectivity, removing

essential ions along with heavy metals, high post-treatment cost and generating toxic byproducts which further

contaminates the environment. To address these difficulties, nanoparticles have recently been employed to

the nanoparticles, to enhance the adsorption affinity of the nanoparticles towards available heavy metal ions

present in the wastewater. The biosynthesized Ag-Cu-Al NPs was first confirmed by an obvious color shift from

grey to olive green after adding the aqueous leaves extract to the trimetallic salt solution of silver nitrate, copper

chloride and aluminum oxide. UV-vis spectroscopy of the nanoparticles presented a distinct peak maximum at

405 nm. The possible secondary metabolites responsible for bio-reduction, capping and homogeneity of the

nanoparticles were assessed using FTIR. The crystalline nature and particle size of the NPs were investigated

using XRD. SEM-EDS analysis revealed the surface texture and constituent elements of the NPs. Adsorption

studies demonstrated that the biosynthesized Ag-Cu-Al nanoparticles acts as a highly efficient nano-adsorbent

for the removal of lead, iron and chromium from industrial wastewater.

Keywords: Nanoparticles, Wastewater, Heavy metals, Biosynthesis, Hierochloe odorata, Adsorption.

diversity. Heavy metals accrue in aquatic habitats through mining activities, industrial discharges and natural

occurrences like weathering of rocks leading to contamination of surface water, groundwater, and sediments,

where they exert toxic effects on flora and fauna. For instance, mercury bioaccumulates in fish through food

chains, reaching concentrations that harm predatory species and human consumers [2]. Heavy metals have also

been proven to degrade soil quality when contaminated wastewater is used for irrigation. Lead and cadmium

alter microbial communities essential for nutrient cycling, reducing the soils inherent fertility and agricultural

yields [3].

Unlike other biodegradable contaminants, heavy metal’s non-biodegradable characteristics enhances their

doggedness and increased concentration in the environment. This often leads to extensive and indefinite heavy

metal pollution of the soil, water and the ecosystem [4]. When humans are exposed to heavy metals through

heavy metals, Pb, Cu, Cd, Cr, Ni and Mn. These pollutants constitute a great risk to the biota, resulting in a range

of diseases and dysfunction. For example, exposure to lead (Pb) has been linked with cardiovascular issues,

kidney damage, hyperactivity, mental retardation, and dermatitis. Conversely, susceptiveness to Chromium has

been linked with the development of acute respiratory issues, skin disorders, kidney failure, and enfeebled

immune systems [8]. The acceptable concentration of lead (II) and Chromium (VI) ion in drinking water by

World Health Organization (WHO) is 0.05 mg/L [9]. Also, the presence of these contaminants can contribute to

the development of skin exfoliation, disruption of thyroid function, development of liver cirrhosis and

gastrointestinal issues such as death of organisms, stalled growth, diarrhea and reduced reproductive rate [10,

11]. Therefore, the need to immediately implement efficient treatment methods for industrial wastewater and

prevent its release into the environment and alleviate these detrimental consequences cannot be overemphasized.

metal treatment can be very expensive and difficult to scale-up for large-scale industrial effluent treatment

applications. For instance, graphene-based materials such as activated carbon are produced consequent upon

high heat and pressure requirements, which are energy consuming and expensive [2, 12]. To address these

difficulties, nanomaterial-based routes have emerged as encouraging solutions due to their distinct properties

and diverse applications in heavy metal remediation [14].

Nanoparticles, owing to their minute size and large surface-to-volume ratio, exhibit enhanced reactivity and

adsorption capacities, making them exceptional contenders for heavy metal removal [15]. Several research have

shown that nanomaterials as well possess notable redox and catalytic properties. Their large surface area provides

several active sites for interaction with heavy metal ions, expediting efficient adsorption and modification

processes. Additionally, the tunability of nanomaterials allows for the alteration of their properties to target

and titanium dioxide have been widely recognized for their potential in environmental remediation [18, 19].

Metallic nanoparticles have garnered significant attention among the numerous types of nanoparticles due to

their exceptional stability in thermal and biological processes, photochemical effective adsorption capabilities,

low toxicity and affordability [20]. When compared to monometallic nanoparticles, multi-metallic (trimetallic)

nanoparticles, composed of various metals, provide a unified system that can display unique features. They

exhibit enhanced catalytic activity and antibacterial effect, diversified shapes, high selective detection and

sensitivity, high level of stability, and chemical transformation [21]. These enhanced characteristics are

consequent upon the synergistic effects of the three metals that makes up the trimetallic nanoparticles [22].

Different synthesis methods have been investigated for the synthesis of trimetallic nanomaterials but, the

biogenic synthesis route has proven to be most affordable and environmentally friendly. This method involves

the reduction of metal ions by biological entities to form nanoparticles. Distinct plants, microbes, and

(Also known as sweet grass) is an aromatic herb native to North America. It is used ceremonially through burning

the dried and braided grass stems for an incense or smudge. Its distinctive sweet scent is associated to the

This work aimed to investigate the biogenic synthesis of Ag-Cu-Al trimetallic nanoparticles using aqueous leaves

extracts of Hierochloe odorata, characterization of the biosynthesized trimetallic nanoparticles using

spectroscopic and microscopic techniques, and to investigate its possible application in the removal of heavy

metals Lead (Pb), Iron (Fe) and Chromium (Cr) from simulated wastewater solution. The aqueous leaves extract

of the plant used serves as reductant, organic ligands, and stabilizers due to the presence of diverse secondary

metabolites present in the extract. There has been no previous report of the use of biosynthesized AgCu-Al

trimetallic nanoparticles in heavy metal removal hence, this study intends to harness the synergistic effect of the

trimetallic nanoparticles coupled with the biologically active components from Hierochloe odorata present in

Nigeria and identified by a plant taxonomist. The chemicals used were analytical grade copper (II) chloride

States of America. The chemical compounds and substances were used as received without further refinement

or alteration.

Accurately weighed 10 grammes of fresh Hierochloe odorata leaves was washed with running tap water and

rinsed with distilled water for removal of dust particles. Subsequently, the leaves were cut into pieces, weighed

and transferred into a 500 mL beaker containing 100 mL of distilled water and then placed on a hotplate for 15

minutes at 30

C after which it was allowed to cool and then filtered using Whatman filter paper No. 1.

to obtain a homogenous mixture. The prepared salt solutions were then stored for subsequent use 2.2.3

copper and aluminum salts concurrently with the aqueous leaves extract. 30 mL of the leaf extract was added to

150 mL of 0.1 M AgNO

-CuCl

continuous stirring on a magnetic stirrer. After a little while, a colour change was observed indicating the

formation of the trimetallic nanoparticles. The nanoparticles formed was centrifuged at 3000 rpm for 15 minutes,

The biosynthesized trimetallic nanoparticles was put through certain spectroscopic and microscopic

characterization methods to determine the size, morphology and composition of the biosynthesized

nanoparticles. UV-Visible spectroscopic measurements of the biosynthesized nanoparticles were analyzed using

the T70 PG Instruments’ UV- Spectrophotometer. The possible secondary metabolites present in the plant extract

Exactly 1.27 g, 2.94 g and 3.25 g of FeCl₂, K₂Cr₂O₇, and Pb(C₂H₃O₂)₂ respectively were weighed and transferred

into separate beakers containing 100 ml each of deionized water in order to prepare 0.1 M solutions of the various

metal salts. Adsorption studies were carried out by mixing 2, 4, 6, 8 and 10 mg of biosynthesized silver-copper-

aluminum trimetallic nanoparticles (Al-Ag-Cu TMNPs) with 5 ml each of 0.1 M FeCl₂, K₂Cr₂O₇ and

Pb(C₂H₃O₂)₂ Solutions (Simulated waste water). The solutions were then placed in an ultrasonic bath to ensure

that the nanoparticles dissolved properly in the test solution.

Atomic Absorption spectrophotometer (AAS) was used to analyze the concentration of the metal ion present in

the simulated waste water, with and without the biosynthesized trimetallic nanoparticles. The amount of metal

ion absorbed by the adsorbent (nanoparticles) was evaluated and percentage removal calculated as;

Cu-Al are shown on plate 1. After addition of 30 ml of aqueous leaf extract of Hierochloe odorata the colour of

the 150 mL of the 0.1 M trimetallic salt solution of Ag-Cu-Al changed from grey to olive green indicating the

formation of Ag-Cu-Al trimetallic nanoparticles. The excitation of the surface plasmon resonance action in the

highest composition thereby forming the outer shell while aluminum forms the inner core shell.

Plate 2: SEM-EDS images of Ag-Cu-Al nanoparticles

Adsorption has been proven to be one of the most widely applied techniques in wastewater treatment due to its

simplicity, cost-effectiveness, and high efficiency in removing heavy metals and other toxic contaminants from

excessive secondary pollutants, making it an environmentally sustainable approach for water purification. The

technique relies on the interaction between the adsorbate molecules or ions and the active sites available on the

surface of the adsorbent material [33]

Metallic nanoparticles such as Ag–Cu–Al trimetallic nanoparticles present a promising adsorbent candidate for