1 Introduction

Nanoscience and nanotechnology are divest fields that modify bulk materials and improve their optical, electronic, magnetic, and catalytic properties [1], these properties are targeted at improving human lives. As global warming has ravaged the universe, the world scientists are trying hard to open new doors to finding novel technologies in the development of new materials with unique characteristics [2] but of low environmental hazard. The known two types of nanomaterials are the organic and inorganic nanoparticles. The former being poly-ɛ-lysine, quaternary ammonium compounds, cationic quaternary polyelectrolytes, and Chitosan. The latter being mainly oxides of silver (Ag), iron (Fe), titanium (Ti), copper (Cu), zinc (Zn) and other transition element. The stability of the inorganic particles at variable temperature gave it a wide range of industrial applications [3, 4]. Metallic nanoparticles are synthesized by different techniques; the more frequently employed methods are the chemical and physical methods. Several chemical methods had been identified, but researchers work more on chemical reduction, electrochemical techniques, and photochemical reactions in synthesizing and modifying nanomaterials [1, 3, 5]. The attrition and pyrolysis techniques took center stage under physical method, although the technique is brand as wasteful due to its high cost, high-energy consumption and low output rate [3, 6]. The consciousness of environmental deterioration has cautioned scientists to look towards greener approach which is an inexpensive nontoxic approach in synthesizing and fabricating nanomaterials [1]. Recently extracts of unicellular organisms, as well as plants have recorded tremendous success in the synthesis of nanoparticles of different shapes and sizes [7]. However, synthesis of nanomaterials using microorganisms is arduous because of the complex and complicated nature of isolating, maintaining cell cultures and multiple purification steps. Hence, it is advisable to synthesize nanoparticles using plant materials due to their availability and the procedure of biogenic synthesis is cost efficient, less tedious as compared to biosynthesis using fungal sources [8]. Several metal oxide nanoparticles had been produced with possible industrial applications. Among these, ZnO is the most exploited at nano-dimensions because of its exceptional scientific properties attributed to its band gap and large excitonic binding energy [9]. It has become a focal point of nowadays research considering its tremendous antimicrobial activity against a wide range of microorganisms. S. aureus, E. coli, Salmonella, Listeria monocytogenes, and the fungus Fusarium [10, 11]. Doping ZnO nanoparticles with Copper, Cobalt, Nickel, rare earth metals, and transition elements, as impurities modified the nanoparticles to enhance their electrical, optical and biological activities [12,13,14]. Silver and Copper doped ZnO nanoparticles have gained great interest in growing a full scope of innovative applications including field effect transistors, field emission arrays, ultraviolet lasers, light emitting diode, sensors, biosensors, catalyst, energy storage and solar cell [15, 16].

In recent times nanomaterials are synthesized with templates which are perceived easy with simplified procedures to give room for better fabrication of more sophisticated nanomaterials [17]. Templates are categorized into two groups of soft and hard. Porous solids like anodic aluminium oxide (AAO) membranes, colloid beads, ordered mesoporous inorganic materials, and zeolites are regarded as hard templates. Soft templates are organic molecules, long-chain polymers, supermolecular aggregates, structure-directing agents, surfactants, gels, micelles, and different types of biological species (biotemplates). Soft templates did not only render more sufficient synthetic processes, but also have the ability to be easily removed, these have proven their effectiveness and shown their ability in high quality encapsulation techniques [18, 19]. Dyes were believed to be substances that only impact colour to textiles, sequel to the dominance of synthetic dyes. But with the arrival of natural dyes, their benefits and values have been appreciated in all areas of life, especially in natural medicine, food and recently nanotechnology [20]. Natural dyes are usually not a single entity, but a variety of closely related chemical compounds, which enhance their therapeutic roles in natural medicine, impact colour to fabrics, reduce and cap ions in nanoscience. The complex chemical constituents in natural dyes are Anthraquinones, Naphthoquinones, Benzoquinones, Flavonoids, Carotenoids and Tannins [21]. Synthesis of nanoparticles by solvent extracted dyes from B. ferruginea is sparingly reported, implying the plant is underexploited on nanodimension. This motivated our interest in this research. Our focus is to extract dyes from B. ferruginea that belongs to the family Euphorbiaceae and found mostly in Savannah regions. It has dark grey, rough and oftentimes marked scaly bark [22]. The plant is a major actor in traditional medicine; with its extract playing a significant role in the formulation of a traditional gargle “egun efu” and water treatment [23]. A handful of reports on the bark extract has proven its high anti-typanocidal, anti-molluscidal, antimicrobial and anti-inflammatory properties [24]. The leaves also demonstrated curative effecst towards the treatment of diabetes and as a purgative. [25, 26]. The curative strength of B. ferruginea has been attributed to its high antioxidants and phytochemicals, hence it can serve as an excellent agent in the reduction of Zn(CH3COO)2, Cu (CH3COO)2 and AgNO3 to their nanoparticles and nanocomposites, as well as capped the ions to their states.

2 Materials and methods

2.1 Chemicals

The following chemicals Zn(CH3COO)2, Cu (CH3COO)2, AgNO3,n-hexane and methanol were obtained from Sigma-Aldrich and used without further purification. All solutions were prepared with deionize water.

2.2 Sample collection and preparation

The bark of Bridelia ferruginea used as the source of the dye was collected from a farmland at Ido Usi, Ekiti State of Nigeria, Sun dried, ground, sieved to have uniformed particles and were stored in an airtight container for the extraction of the dye.

2.3 Extraction of dye

Soxhlet apparatus was used for the extraction of dyes. The Pulverized sample was loaded in the thimble and mounted on the round bottom flask. The sample was first defatted with n-Hexane for 6 h at a heating rate of 68 °C. The defatted samples were offloaded from the thimble, sundried to remove the trapped n-hexane and reloaded for the dyes extraction using methanol at the heating rate of 65 °C. The dyes were oven dried at 40 °C to powder.

2.4 Green synthesis of nanoparticles and nanocomposites

The nanoparticles were synthesized using green synthesis method as reported by Yedurkar et al, [27], with the exclusion of NaOH that acted as a pH stabilizing agent. 10 g of the dye was dissolved in 100 ml of methanol, filtered with Whatman filter paper to remove any undissolved particles. 50 ml of the dye’s filtrate was added 100 ml (0.5 M) of Zn(CH3COO)2 was allowed to stand for 2 h at room temperature. The initial light brown colouration of the solution became a deep brown crowded solution indicating the complete formation of the precipitate. This affirmed the reduction of zinc acetate to zinc oxide nanoparticles. The mixture was stirred for 1 h, centrifuged for 30 min and washed severally with deionized water and ethanol. The pure reduced ZnO nanoparticles were oven dried at 80 °C for 6 h and calcined at 500 °C for 1 h. The nanocomposites were synthesized by mixing 100 ml (0.5 M) of Zn(CH3COO)2 with 100 ml (0.05 M) of AgNO3 or Cu (CH3COO)2 for the synthesis of ZnO–Ag and ZnO–Cu respectively. The solution was stirred for 2 min on a magnetic stirrer and the methanolic extract of the dye was added to the mixture. The finishing protocol for ZnO was adopted for the composites. Figure 1 presents a schematic representation of the synthetic pathway for the particles (Scheme 1).

Fig. 1
figure 1

FTIR of a ZnO Nanoparticle b ZnO–Ag Nanocomposite c ZnO–Cu Nanocomposite d dye of B. ferruginea

Full size image
Scheme 1
scheme 1

Schematic representation of the synthetic pathway of ZnO nanoparticles (NP) and ZnO–Ag and ZnO–Cu nanocomposite

Full size image

2.4.1 Reaction mechanism for the synthesis of ZnO nanparticle and ZnO–Ag nanocomposite

The presence of tannins, terpenoid and flavonoids in the dye extract which behave as ligands and their special ability to chelate various metal ions enhance the reduction and subsequent stabilization of the ions to their nano form. Among the phytochemical constituents, flavonoids readily chelate metal ions and create complex compounds due to their ability to donate electrons and hydrogen atoms. Zinc acetate, Copper acetate and silver trioxonitrate (V) dissolved in water to become freely moving ions as shown in the Eqs. (1 and 2) for Zinc acetate.

$${\text{Zn}}\left( {{\text{CH}}_{3} {\text{COO}}} \right)_{2} \to {\text{H}}_{3} {\text{C}} - {\text{CO}}_{2}^{ - } {\text{Zn}}^{2 + }$$
(1)
$${\text{H}}_{3} {\text{CO}}_{2}^{ - } {\text{Zn}}^{2 + } \mathop{\longrightarrow}\limits^{{{\text{H}}_{2} {\text{O}}}}{\text{H}}_{3} {\text{C}} - {\text{CO}}_{2}^{ - } + {\text{Zn}}^{2 + }$$
(2)

The free ions attack the active sites on the phenolic compound present in the dye extract to gain stability hence, reducing it to its nano form. The large number of “OH” functional groups in phytochemical is a major factor in the reduction process. This factor favours the formation of a hydrophilic surfaces arising from the dissolved oxygen (from air) molecules, that are suitable for the growth of nanoparticles [28]. The Mechanism pathway for the synthesis of ZnO–Ag nanocomposite is the same as ZnO–Cu nanocoposite synthesis (Scheme 2).

Scheme 2
scheme 2

Schematic mechanism for the synthesis of a ZnO Nanoparticles and b ZnO–Ag nanocomposite (Idea from work of Ahmad et al. [29] and Mohammed et al. [28])

Full size image

2.5 Phytochemical analysis of the dye

Phytochemical screening was performed on the dye to ascertain the presence of reducing and capping agent present in the dye extracts. The assays to investigate are; tannins, steroids, phlobatannins, saponins, flavornoids, phenols, anthocyanins and terpenoids and using established methods [31,30,32, 33].

2.5.1 Test for tannin

10 ml of bromine water was added to the 0.5 g aqueous extract. Decoloration of bromine water comfirmed the presence of tannins

2.5.2 Test for steroids

2 ml of chloroform and concentrated H2SO4 were added with the 5 ml aqueous plant crude extract. In the lower chloroform layer red color appeared that indicated the presence of steroids

2.5.3 Test for phlobatainin

1% aqueous HCl acid was added to 5 ml of the extract, it was then boiled with the help of Hot plate stirrer. The absence of a red precipitate was evidence for the absent of phlobatannins in this sample.

2.5.4 Test for saponins

5.0 ml of distilled water was vigorously mixed with aqueous crude plant extract in a test tube. Few drops of olive oil was added to the mixture upon froth appearance and vigorously mixed. The appearance of foam confirmed the presence of saponins.

2.5.5 Test for flavonoids

Alkaline Reagent Test were used to confirm the presence of flavonoids in bark of B. ferruginea. 2 ml of 2.0% NaOH mixture was mixed with crude aqueous extract of the plant; concentrated yellow color was produced, which became colorless when 2 drops of diluted acid was added to the mixture. This result showed the presence of flavonoids.

2.5.6 Test for phenol

5 ml of the methanolic plant extract was mixed with 2 ml of 2% FeCl3 solution. A blue-green or black coloration indicated the presence of phenols

2.5.7 Test for cyanogenic glycoside

Sodium picrate test or Guignard reaction was used to confirm the presence of anthocyanins. A soaked filter paper strips was first in 10% picric acid and then in 10% sodium carbonate and dried. The extracts were taken in small bottles and the strips were suspended from the mouth of the container and the lids were tightly closed with portion of the s trip stuck in the lid. The strips did not turn brick red nor maroon indicating the absence of cyanogenic glycosides (anthocyanins)

2.5.8 Test for terpenoids

Chloroform (2 ml) was added to aqueous plant extract (5 ml) and evaporated on a water bath and then boiled with 3 ml of concentrated H2SO4. A grey coloration attests to the presence of terpenoids.

2.6 Characterization of biosynthesized ZnO nanoparticles and ZnO nanocomposite of Silver or Copper

The FTIR (Shimadzu Co. Ltd., Kyoto, Japan) was used with KBr pellets in the wavelength range 4000–500 cm−1 for identification of the functional groups involved in the reduction of the precursors to nanoparticles and nanocomposites. The phase formation, purity and crystallinity of the nanoparticles were recorded using XRD (GBC eMMA). The visual properties of ZnO nanoparticles and nanocomposites were investigated, based on UV–Vis absorption spectra in the wavelength range of 200–800 nm. The morphologies, elemental composition and particle size were investigated using SEM equipped with an EDX (Quanta 200—FEI coupled to EDS probe) and TEM (TECNAI G2 SPIRIT-FEI).

3 Results and discussion

3.1 Phytochemical analysis

The methanolic dye extract was screened for major phytochemicals as shown in Table 1. Aside the biological and the therapeutic properties, the metabolites are reported to have excellent reducing and stabilizing ability towards the reduction of bulk metals to the nano forms [34]. High extract yields of phenols and terpenoids were recorded in the dye. This is ascribed to the high polarity of methanol solvent to a variety of plant constituents [31]. The presence of these molecules gives the dyes the expected self-assemblage and ability to cap the metal nanoparticles formed, thereby inducing controlled morphology [35].

Table 1 Phytochemical constituents of Bridelia ferruginea
Full size table

Among the metabolites, terpenoids and phenols isolated from plants are implicated in successfully catalyzing the reduction of bulk material to nano ions [30, 34]. The ability of phenol to act as capping agent lies in the presence of hydroxyl and carboxylic group which makes it a good chelator [36], impacting it with ability to stabilize metal ions [37]. The presence of the two metabolites gave the dye the expected strength to reduce bulk materials and stabilize the metal ions. The absence of anthocyanine confirmed report in literatures that, it can only exist in storage tissues of the plants [38].

3.2 FTIR spectroscopy of the synthesized nanoparticles and nanocomposites

FTIR (Fig. 1) was used to identify the possible functional groups that are actively involved in the reduction of Zn(CH3COO)2, AgNO3 and Cu(CH3COO)2 to various nanoparticles and nanocomposite. A broad peak at 3394.83 cm−1 for B. ferruginea dyes is assigned hydrogen O–H band stretching, but shifted to 3618.58 cm−1 on the spectra of ZnO nanoparticles, ZnO–Ag and ZnO–Cu nanocomposites [39]. The dyes have a crest at 1635.69 cm−1 which is characteristic of aldehydes C=O stretches, but slightly moved to higher frequencies on the spectra of ZnO nanoparticles, ZnO–Ag and ZnO–Cu nanocomposite. A H-C˗H asymmetric and symmetric stretch peak was found at 2931 cm−1 on the dye’s spectrum, but at 2924.18 cm−1 for ZnO–Cu and 2808.92 cm−1 for ZnO–Ag nanocomposites. The peak at 1527 cm−1 on the dye spectra is for N–H bends. This however appears as N–H stretching at 3286 cm−1 for ZnO–Ag. The spectral bands at 1419.66 cm−1, 1427.37 cm−1 and 1450.52 cm−1 confirmed the presence of C-H bending, while 1103.32 cm−1, 1072.46 cm−1, 1095.60 cm−1 correspond to C-O stretching for ZnO, ZnO–Ag, ZnO–Cu respectively. The crest at 1411.94 cm−1 on the FTIR spectra of the dyes is typical of S=O stretching, but this appeared on a lowered frequency of 1404.22 cm−1 on ZnO–Ag nanocomposite. The functional groups between 686.68 and 879.57 cm−1 correlates to metal oxide bands [5].

The absence of S=O, N–H bends, H-C-H asymmetric and symmetric bands on the spectra of ZnO nanoparticles and ZnO–Cu nanocomposite spectra confirmed that the functional groups were used up in the reduction of the zinc acetate and Copper acetate [40]. All the band and functional groups identified are peculiar to the phytoconstituents identified in the phytochemical screening [41].

3.3 UV–visible spectroscopy

Figure 2 presents the UV–Vis absorption spectra of ZnO nanoparticles, ZnO–Ag and ZnO–Cu nanocomposites and the dye. There is an excitonic peak between 206 nm for the dyes and 251 nm for the ZnO–Ag, these peaks are characteristic of the polyphenolic compounds which acted actively during the synthetic and reduction processes between the phyto-compounds of B. ferruginea, and metal precursors [42]. These peaks also pointed to presence of ZnO nanoparticles, which lies much below the bandgap wavelength [41]. Peaks between 300 and 400 nm are characteristic of ZnO nanoparticles which may be due to the electron transition from the valence band to the conduction band. The appearance of distinctive peaks of low absorption intensity on the spectra of ZnO nanoparticles, ZnO–Ag and ZnO–Cu nanocomposite between 320 and 360 nm confirmed the formation of ZnO nanoparticles [43]. The reduction in the peak intensity in the spectra of the ZnO–Ag and ZnO–Cu indicated the inclusion of Ag2+ and Cu2+ in the matrix of the nanocomposites and suggested some level of agglomeration with irregular shapes [44]. The region of absorption of the spectrum suggested the suitability of the nanomaterials for both UV and visible region [45].

Fig. 2
figure 2

UV-Vis Absorption spectroscopy of ZnO nanoparticles, ZnO–Ag nanocomposite, ZnO–Cu nanoparticles and dyes

Full size image

The optical band gap (Fig. 3), was estimated using Tauc’s plot for direct transition semiconductor, by extrapolating the straight line of (αhν)2 versus hν graph. High band gap energy of 4.73 eV is recorded for the dye, but was reduced to 3.24 eV in ZnO nanoparticles. The introduction of Ag and Cu impurities in the nanocomposite narrowed the band gap to 3.18 eV and 3.12 eV for ZnO–Cu and ZnO–Ag respectively.

Fig. 3
figure 3

Tauc’s plot for optical band gap of a ZnO nanoparticles, b dyes, c ZnO–Cu nanocomposite and d ZnO–Ag nanocomposite

Full size image

This narrowing of band gap became prominent as Zn2+ is gradually substituted by Cu2+ and Ag2+ in the matrix of the materials and systematically increased the number of oxygen vacancies due to their ion radii and electronegativity [46]. More so, the impurities created a special defect, which simulates the Fermi level to rise towards the conduction [41, 45, 47, 48]

Figure 4 is the XRD diffractogram of ZnO nanoparticle, ZnO–Ag and ZnO–Cu nanocomposites. The peaks at 2θ of 31.62°, 34.30°, 36.11°, 47.41°, 56.47°, 62.75°, 67.83° and 68.95° for ZnO nanoparticles diffractogram lie in the crystallographic planes of (100), (001), (101), (102), (110), (103), (112) and (201). These agree with standard JCPDS card No. 89-0510, and correspond to the Hexagonal wurtzite [42, 50,49,51]. The crystallography of ZnO–Ag showed peaks that correspond to 2θ values 26.84°, 29.46°, 31.95°, 44.96°, 47.42°, 50.89°, 53.33°, 56.28°, 63.45° and 68.82° and within the crystallographic planes of (111), (111), (200), (220), (220), (311), (222), (311), (400) and (331). These are concordant with JCPDS No. 89-4937. The peaks at 26.84°, 29.46° and 31.95° are due to the presence of bio-organic phases on the surface of the particles [44], these would have been contributed by the polyphenolic compounds. Characteristic peaks of Ag+ signal appeared at 2θ 4.96° and 63.45°. This attest to the presence of Ag+ in the ZnO–Ag nanocomposite. A similar diffractogram was reported by Dinesha et al.,when he dope ZnO with Ag [52]. However, there is an overlap of Ag+ signals with the wurtzite plane at (311), (400) and (331). The influence of doped Ag onto ZnO significantly altered the peak orientation, due to replacement of Ag+ into host ZnO crystal lattice [53]. All the other peaks confirmed in the XRD graph of ZnO–Ag nanocomposite are assigned to ZnO nanoparticles. The diffractograms of ZnO–Cu nanoparticles show peaks in the crystallographic plan of (002) and (101) which are typical of ZnO nanoparticles. The crystallographic peaks of 2θ at 35.55°, 38.65°, 47.47°, 48.66° lies in the plane of (−1 1 1), (1 1 1), (−2 0 2). These are in consonance with the XRD pattern, with the presence of copper doped on the ZnO [3]. There is an overlapping of the Cu and Zn signals, especially at a 2θ value of 62.81°, 66.02° and 67.95°. The extra peaks are plant phytoconstituents which probably escaped the washing of ZnO–Ag during the synthesis.

Fig. 4
figure 4

The X-ray Diffraction of a ZnO nanoparticle b ZnO–Ag and c ZnO–Cu nanocomposite

Full size image

The Highly absorbed diffraction peaks confirmed the significant crystallinity of ZnO, ZnO–Ag and ZnO–Cu nanomaterials. The unavailability of other diffracted peaks on the diffractogram of ZnO and ZnO–Ag authenticates the high purity of the synthesized ZnO nanoparticles [7, 41]. The decrease in peak’s intensity on the ZnO–Ag and ZnO–Cu diffractograms, is a behavioural pattern peculiar to decreased crystallite sizes in the presence of the dopant. There is a slight shift on the ZnO peaks accounting for the present AgO and CuO fussed in the ZnO wurtzite lattice. The secondary phase of AgO and CuO diffraction peaks indicated the formation of AgO- ZnO and CuO–ZnO nanocomposite. The change in the crystallite size and a shift on ZnO on the diffractogram is the confirmation of the presence of Ag and Cu incorporated into the Zn site [3, 17, 54].

The average grain size of the sample, was calculated using the Debye Scherer’s equation

$$D = \frac{0.9\lambda }{\beta \cos \theta }$$
(3)

where D is Crystal size (nm), is the wavelength of the XRD used, is FWHM, and is Bragg’s angle [40, 45, 55]. X-ray diffractogram was analyzed to obtain information about various crystalline aspects of ZnO nanoparticle, ZnO–Ag and ZnO–Cu nanocomposite materials. The average crystallite size of ZnO, ZnO–Ag and ZnO–Cu is about 19.02 nm, 18.98 and 18.90 nm respectively.

3.4 SEM and EDX analysis of ZnO nanoparticles, ZnO–Ag and ZnO–Cu nanocomposites

The morphological feature and the elemental composition of the nanomaterials synthesised were investigated using SEM equipped with an EDX as shown in Fig. 5. The SEM picture of ZnO nanoparticles confirmed the formation of nanoparticles with approximate nodular like shape. There was no significant change in the morphology upon the addition of Ag dopant but with the addition of Cu impurities, the nodular like shape aggregated into larger particles with pores but no well-defined morphology. This aggregation may be due to the presence of secondary metabolites in the leaf extracts [39] as confirmed by the XRD. The presence of Zn, O, Ag and Cu were confirmed by EDX Fig. 5(a1–c1).

Fig. 5
figure 5

SEM images of a ZnO nanoparticles, b ZnO–Ag nanocomposite, c ZnO–Cu nanoparticles and the EDX of (a1) ZnO nanoparticles (b1) ZnO–Ag nanocomposite (c1) ZnO–Cu nanocomposites

Full size image

A strong peak for O appeared at about 0.5 keV with Zn2+ ion on 1.08 keV, 8.59 keV and 9.82 keV. Ag2+ is at 3.09 keV and Cu2+ peak appeared on binding energy 8.1 keV. A strong signal of O on the EDXs of the synthesized nanomaterials, is partly contributed by X-ray emission from the phytochemicals of the dye.

3.5 TEM and SAED pattern of the materials

The TEM images in Fig. 6 give detailed structural analysis of the synthesized materials. The image (Fig. 6a shows the presence of nanorods coexisting with nanoflakes in ZnO nanoparticles. Image of ZnO–Ag in Fig. 6b revealed a polyhedral shape of ZnO with Ag dots on the surface of the metrics. The introduction of Cu impurities to form ZnO–Cu nanopcomposite, changed the nanorods and the flakes in ZnO to a spherical shape as shown in Fig. 6c. The close link between Ag and ZnO makes a strong electronic interaction that will improve the charge separation [55], this accounts for its low energy band gap when compared with ZnO–Cu nanocomposite. The average particle sizes of ZnO, ZnO–Ag and ZnO–Cu which are < 50 nm are in consonance with XRD results. The selected area SAED pattern in Fig. 6(a2–c2) show distinct bright centric ring with further ring in Fig. 6(a2) being partially illuminated confirming the irregular orientation of its nanocrystals unlike in Fig. 6(b2, c2) which indicated a regular orientation of nanocrystals [41].

Fig. 6
figure 6

TEM Image of a ZnO, b ZnO–Ag and c ZnO–Cu and SEAD Image of (2a) ZnO nanoparticles, (2b) ZnO–Ag nanocomposite, (2c) ZnO–Cu nanocomposite

Full size image

4 Conclusion

Nanoparticles and nanocomposites were effectively synthesized by a green method using Soxhlet extracted dye of B. ferruginea as a reducing and capping agent. O–H, C=O, N–H, C–O and S=O were ascertained to be the functional groups that, were involved in the reduction and stabilizing of the nano ions. The optical studies revealed a narrowing of band gap from 3.24 to 3.13 eV as Ag2+ and Cu2+ gradually substituted the Zn2+ ions in the ZnO matrix. High level of crystallinity and the average crystallite size of 19.02, 18.98 and18.90 nm was recorded for ZnO, ZnO–Ag and ZnO–Cu respectively. SEM and TEM analysis clearly indicated the formation of flakes with nanorods for ZnO, polyhedral shape with Ag dots and spherical shape upon doping of ZnO with Ag or Cu. The elemental analysis confirmed peaks for Zn, Ag, Cu and O. The bright centric ring and other non-luminous ring of the SAED revealed an irregular orientation. These findings inferred the viability of the dye extracted from B. ferruginea as a reducing and capping agent capable of synthesizing nanoparticles and nanocomposites that are eco-friendly with potentials in photovoltaic, electronics and photocatalytic applications.