J. Nig. Soc. Phys. Sci. 3 (2021) 262–266

Journal of the
Nigerian Society

of Physical
Sciences

Novel developments of ZnO/SiO2 nanocomposite: a
nanotechnological approach towards insect vector control

Ezra Abbaa,∗, Zaccheus Shehub,c, Danbature Wilson Lamayib, Kennedy Poloma Yoriyoa, Rifkatu
Kambel Dogarab, Nsor Charles Ayuka

aDepartment of Zoology, Faculty of Science, Gombe State University, Gombe, PMB 127, Gombe, Nigeria
bChemistry Department, Faculty of Science, Gombe State University, Gombe, PMB 127, Gombe, Nigeria

cDepartment of Chemistry, College of Natural Science, Makerere University, P.O. Box 7062, Kampala

Abstract

Recently, there is increasing efforts to develop newer and effective larvicides to control mosquito vectors. This study was carried out to examine
the efficacy of ZnO/SiO2 nanocomposite synthesized using Gum Arabic against Culex quinquefasciatus larvae. The elemental composition,
morphology, functional groups and surface plasmon resonance of the ZnO/SiO2 nanocomposite was analyzed by Energy dispersive X-ray analysis
(EDX), Scanning electron microscope (SEM), FTIR and UV-Visible spectroscopy respectively. In bioassay, larvae were exposed to three different
concentrations of synthesized ZnO/SiO2 nanocomposite. The mortality rates at concentrations of 10, 20 and 25 were found to be (70%, 80%,
86%), (56%, 64%, 84%) and (44%, 48%, 76%) for 1st , 2nd , and 3rd instar respectively. This study revealed that the synthesized ZnO/SiO2
nanocomposite exhibit high larvicidal activity; 1st instar (LC50=4.024, LC90= 39.273 mg/l), 2nd instar (LC50=8.767, LC90=51.069 mg/l) and 3rd

instar (LC50=13.761.LC90=81.809 mg/l)

DOI:10.46481/jnsps.2021.198

Keywords: Culex quinquefasciatus, Vector control, Nanotechnological, ZnO/SiO2 nanocomposite

Article History :
Received: 15 April 2021
Received in revised form: 05 July 2021
Accepted for publication: 24 July 2021
Published: 29 August 2021

c©2021 Journal of the Nigerian Society of Physical Sciences. All rights reserved.
Communicated by: T. O. Owolabi

1. Introduction

Application of chemical insecticides in order to kill mosquito
larvae or pupae in the water is known as larviciding. Larvicid-
ing is generally more effective and target-specific than adulti-
ciding (applying chemicals to kill adult mosquitoes). The most
common synthetic chemicals used in controlling mosquitoes’
larvae are methoprene, pyrethroids, diflubenzuron, malathion,
dichlorodiphenyltrichloroethane (DDT), organophosphate temephos

∗Corresponding author tel. no:
Email addresses: gemanamsly@gmail.com (Ezra Abba ),

ezra.abba@gmail.com (Nsor Charles Ayuk)

and as well as phytochemicals [1-3]. However, synthetic chem-
icals (insecticides) are known to cause serious environmental
problem thereby killing non-target organism and affecting hu-
man health. Moreover, continuous application of synthetic chem-
icals (insecticides) results in control failures due to develop-
ment of resistance by the mosquitoes (vectors) [4]. Hence, it
has been reported that ZnO and SiO2 nanoparticles provides a
lay down of a novel green nanotechnology to control insect pest
including mosquitoes’ larvae [5-8]. ZnO/SiO2 nanocomposites
have been synthesized using various techniques such as chem-
ical vapor deposition, sputtering, chemical etching and sol gel
process and they are used in different applications such as an-

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timicrobial, photonic crystals, photocatalysts, gas sensors, vac-
uum fluorescent display and varistors etc., [9-19]. But based
on our search, there was no report on the effect of ZnO/SiO2
nanocomposites against mosquito larvae except for the individ-
ual ZnO and SiO2 nanoparticles.

Culex quinquefasciatus is a vector of lymphatic filariasis.
The breeding site of Culex species includes; gutters and wa-
ter retention sites having organic matter. Filariasis has been
reported to be a public health problem in Africa as well as
other part of the world [20-22]. Thus, to prevent mosquito
bornediseases and improve the quality of public health, it is
necessary to control mosquito larvae. In this study, ZnO/SiO2
nanocomposite was synthesized using Gum Arabic and was
tested against the larvae of Culex quinquefasciatus. The forma-
tion of ZnO/SiO2 nanocomposite was confirmed using ultraviolet–
visible (UV–Vis) spectrophotometry, Scanning electron microscopy
(SEM) coupled energy dispersive X-ray (EDX) spectroscopy
and Fourier transforms infrared (FTIR) spectroscopy.

2. Materials and Methods

2.1. Collection of Gum Arabic (Acacia senegalensis)
A fresh A. senegalensis extrudes were collected from Bil-

liri Local Government of Gombe State. The Gum extract were
neatly collected and allowed to dry properly under the sun. The
Gum Arabic was crushed to powder using pestle and mortar.

2.2. Synthesis of ZnO/SiO2 Nanocomposite
One gram (1 g) of Gum Arabic was poured into a beaker

containing 40 ml of distilled water which was magnetically
stirred for 10 minutes at 90◦C. Following this, 2 g of Zn(NO3)6
.6H2O and 2 g of silica gel were added and stirred for 30 min-
utes. Upon addition of Zn(NO3) 6 .6H2O and silica gel the
aqueous solution changed to milk colour. With time the so-
lution became viscous. A cloudy formation at the bottom of the
beaker indicated the formation of resin. The resin obtained was
placed in a furnace at 450 oC for two hours to obtain ZnO/SiO2
nanocomposite [23].

2.3. Characterization of the Green synthesized ZnO/SiO2 nanocom-
posite

ZnO/SiO2 Nanocomposite was characterized using Ultraviolet-
visible Spectroscopy, Fourier transformed infrared spectroscopy
(FT-IR) and Scanning Electron Microscopy (SEM) coupled with
energy dispersed x-ray techniques.

2.4. Collection of Culex quinquefasciatus larvae
Culex quinquefasciatus mosquito larvae were collected from

different areas of Gombe metropolis. Using ladle and a collec-
tion bottle, the ladle was lowered into the water (breeding site)
at an angle of about 45o until one side is just below the surface
of the water. While dipping, care was taken not to disturb the
larvae which may cause them to swim downward. The larvae
were maintained and fed in the laboratory with glucose for the
larvicidal bioassay. The collection was done based on previous
literature [23].

Figure 1. UV-Visible spectrum for ZnO/SiO2 nanocomposite.

2.5. Larvicidal Activity of ZnO/SiO2 Nanocomposite
The test was carried out according to our previous work

[24]. 0.1g of ZnO/SiO2 nanocomposite was weighed and di-
luted with distilled water in a 1000 ml volumetric flask and
shaked to obtain 100 mg/L concentration. The bioassay was
done by placing different instars (1st – 3rd ) of the larvae into
200 ml of plastic container with four replicates and a control
in each of the instars, each replicate comprised of twenty-five
larvae. 100 ml of dechlorinated water was added in each of
the replicates. Finally, 10 mg/L, 20 mg/L and 25 mg/L of the
ZnO/SiO2 Nanocomposite concentrations were inoculated into
each of the replicates. And percentage mortality was calculated
as follows:

2.6. Statistical Analysis
Percentage mortality, Probit analysis, Chi square and Cor-

relation analysis were calculated and tabulated using (SPSS,
2016).

3. Result and Discussion

3.1. Ultraviolet visible analysis
Absorption spectrum of synthesized ZnO/SiO2 nanocom-

posite at different wave lengths ranging from 260 to 380 nm
revealed the maximum absorption wavelength of 280 nm, (Fig-
ure 1). Elsewhere, maximum absorption wavelength of 300 nm
was reported for CaO/SiO2 nanocomposite [25]. This optical
property is in the same range with the one in the current.

3.2. FT-IR Analysis
Figure 2 depict the FT-IR spectrum of ZnO/SiO2 nanocom-

posite analyzed from 450-4000 cm−1 which exhibited promi-
nent peaks at 3457.75, 1654.65, 1067.44, 701.43, and 455.97
cm−1. The band at 1067.44 cm−1 corresponds to asymmetric
stretching vibration of Si-O-Si bond. The peaks at 701.43 cm−1

corresponds to Si-OH bond [9-19,26-28]. The band at 3457.75
cm−1 indicates HO-H stretching mode for silanol group and
adsorbed water. And band at 1654.65 cm−1 indicates bending
mode of adsorbed water. The Zn-O and Si-O bond is indicated
by the peak at 455.97 cm−1 [919, 25-27]. Thus, this information
confirmed the formation of ZnO/SiO2 nanocomposite.

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Figure 2. FT-IR spectrum of ZnO/SiO2 Nanocomposite.

Table 1. Larvicidal activity of synthesized ZnO/SiO2 nanocomposite on Culex quinquefasciatus larvae. LC50 ; lethal concentration that kills 50% of larvae, LC90 ;
lethal concentration that kills 90% of larvae, r: correlation coefficient; χ2 ; chi square

Instars Conc
(mg/l)

Mortality %
Mortality

LC50
(mg/l)

LC90 (mg/l) χ2 r

1st Instar 10 17.5 70 4.024 39.273 0.076 0.999
20 20 80
25 21.5 86

2nd Instar 10 14 56 8.767 51.069 1.543 0.908
20 16 64
25 19 84

3rd Instar 10 11 44 13.761 81.809 2.75 0.826
20 12 48
25 19 76

3.3. SEM/EDX Analysis
Figure, 3A depict SEM image, 3B depict elemental data

and 3C depict EDX spectrum of ZnO/SiO2 nanocomposite. The
SEM image showed large and dispersed particles of silica coated
ZnO nanoparticles. The EDX spectrum showed different ele-
ment apart from the expected Zn, Si and O. The presence of
other element is due to Gum Arabic used in the synthesis be-
cause Gum Arabic has been reported to contained; Al, Ba, Ca,
Fe, K, Mg, Mn, P, S and Sr [28]. From Figure 3B, percent-
age composition of Si, Zn and O were 38.02, 37.42 and 7.21 %
respectively.

3.4. Larvicidal test result:
The exposure of Culex quinquefasciatus larvae to different

concentrations of the synthesized ZnO/SiO2 nanocomposite for
24hrs demonstrates their larvicidal efficacy. Table 1 show that
larval mortality significantly increased with the increase in con-
centrations of ZnO/SiO2 nanocomposite. The mortality rates of

concentrations; 10, 20 and 25 mg/l for 1st instar were 70%,
80%, 86%, 2nd instar were 56%, 64%, 84%, and 3rd instar
were 44%, 48% and 76% respectively. This study revealed that
the synthesized ZnO/SiO2 nanocomposite larvicidal activity de-
creases from 1st instar to 3rd instar. Thus, lethal concentrations
of the nanocomposite on the larvae of Culex quinquefascia-
tus were found to be (LC50=4.024 mg/l, LC90= 39.273 mgl/1),
(LC50=8.767 mg/l, LC90=51.069 mg/l) and (LC50=13.761 mg/l,
LC90=81.809 mg/l) for 1st, 2nd , and 3rd instar respectively. In
our previous studies, Ag-Co and Cu/Ni bimetallic nanoparticles
were synthesized through green pathway and it larvicidal activ-
ities were tested against Culex quinquefasciatus larvae. The
LC50 for 1st, 2nd , and 3rd instars were 5.237, 9.310 and 13.626
mg/l respectively [29]. And the LC50 for 1st, 2nd , and 3rd instars
were 14.75, 18.25 and 18.50 mg/l respectively [30]. Hence,
ZnO/SiO2 nanocomposite proved to be more effective against
Culex quinquefasciatus larvae than Ag-Co and Cu/Ni bimetal-
lic nanoparticles as reported by [29-30].

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Figure 3. (A) SEM image (B) elemental result and (C) EDX spectrum of the synthesized ZnO/SiO2 nanocomposite

4. Conclusion

In this research, ZnO/SiO2 was synthesized using Gum Ara-
bic and characterized by UV-Visible, FTIR, SEM and EDX
techniques. The larvicidal activity of ZnO/SiO2 nanocomposite
was tested against Culex quinquefasciatus larvae using desired

concentrations which showed significant results. This study
showed that, the application of ZnO/SiO2 nanocomposite can
serve as a replacement of insecticide in mosquito vector con-
trol.

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