J. Nig. Soc. Phys. Sci. 5 (2023) 1438

Journal of the
Nigerian Society

of Physical
Sciences

Photocatalytic and antibacterial activities of green-mediated
Khaya senegalensis-silver nanoparticles and oxidized carbon

nanotubes

A. H. Labuloa, A. D. Ternab,∗, O. F. Oladayoa, H. Ibrahima, N. S. Tankoa, R. A. Ashonibarec, J. D.
Opeyemia, Z. Tywabi-Ngevad

aDepartment of Chemistry, Federal University of Lafia, Lafia, Nasarawa State, Nigeria
bDepartment of Chemistry, Federal University of Technology, PMB 1526, Owerri, Imo State, Nigeria

cDurable Crops Research Department, Nigerian Stored Products Research Institute, P.M.B. 1489, Ilorin, Kwara State, Nigeria
d Department of Chemistry, Faculty of Science, Centre for Rubber Science and Technology, Nelson Mandela University, Gqeberha, South Africa, 6001.

Abstract

This study investigated the photocatalytic and antibacterial activities of plant-mediated silver nanoparticles (AgNPs) from a medicinal plant extract
of Khaya senegalensis (K. senegalensis) and oxygen functionalized carbon nanotubes (oCNTs), respectively. The CNTs were functionalized using
acid treatment. The green synthesized AgNPs from K. senegalensis (KS-AgNPs) and oCNTs were characterized by UV–Visible spectroscopy,
Fourier transform infrared spectroscopy (FTIR), transmission emission microscopy (TEM), scanning electron microscopy (SEM), and X-ray
diffraction (XRD). The formation of KS-AgNPs was confirmed by the UV–Vis absorption spectra, which showed an absorption band at 427 nm
with a color change from yellow to brown. The morphology of KS-AgNPs was spherical in shape, with an average particle size of 9.30 nm. The
FTIR analyses revealed distinctive functional groups, such as, hydroxyl (O-H), amines (N-H), and carbonyl (C-O), which were directly involved
in the synthesis and stability of AgNPs. The XRD spectra was distinctive with five intense peaks at 2θ angles of 38.12°, 44.28°, 64.43°, 77.48°,
and 81.54o while oCNTs gave intense peaks at 2θ angles of 26.43o, 42.36o, 44.46o, 54.51o, 59.98o, and 77.40o. The photocatalytic property of
green synthesized KS-AgNPs was determined to be 40.7 % higher than that of oCNTs when applied for treatment of industrial waste water. The
ability of green-mediated KS-AgNPs to inhibit against gram-positive and gram-negative bacteria was observed to be that gram (-) bacteria (E.
coli) was more susceptible to KS-AgNPs than the gram (+) bacteria (S. aureus), in which case their susceptibility was least in oCNTs for both
bacteria, respectively.

DOI:10.46481/jnsps.2023.1438

Keywords: Khaya senegalensis, silver nanoparticles, carbon nanotubes, photocatalytic, antibacterial activity

Article History :
Received: 08 March 2023
Received in revised form: 01 May 2023
Accepted for publication: 05 May 2023
Published: 22 June 2023

© 2023 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license

(https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Communicated by: E. A. Emile

∗Corresponding author tel. no: +2348100049983
Email address: ternaaugustine2020@gmail.com (A. D. Terna )

1. Introduction

New research suggest to possibilities to create antibacterial
and photocatalytic compounds that are more effective and
less toxic for usage in order to tackle water pollution, which

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 2

is the primary cause of infectious diseases [1]. Producing
eco-friendly nanoparticles follows the principles of green
chemistry, in which naturally existing bioactive chemicals
in plants serve as reducing and capping agents while also
preserving the environment [2]. By adjusting the concen-
tration of plant extract, it is possible to create shape- and
size-dependent nanoparticles under regulated conditions [1],
[3]. The treatment of industrial wastewater, in particular
that is produced by the textile dying process, is a serious
environmental concern. The destruction of organic dyes
and bacteria by nanoparticles’ catalytic activity makes them
potentially useful for the treatment of industrial wastewater
[4]. Clean, pure drinking water is currently a major issue
due to the rise of so many startup companies and the need
to address environmental degradation [5]. Applications for
nanoparticles (NPs) in the oxidative degradation of harmful
pigments and environmental pollutants seem to be numerous
[6]. The enhanced photocatalytic and degrading effectiveness
is due to the small, crystalline, particle size, surface clustering,
significant optical absorption in the visible range, quick charge
transfer, reduced electron-hole charge recombination, and high
oxidizing ability of the nanoparticles [7]. NPs have been found
to have very sporadic antibacterial action against S. aureus and
high antibacterial activity against E. coli [1]. The combination
of surface area, electrostatic interactions between the anionic
dye and cationic surface of the nanocatalyst, and the oxidation
of polyphenolic/phenolic chemicals or flavonoids present on
the surface of the nanoparticles enhances the photocatalytic
degradation process of nanoparticles [8]. Moreover, smaller-
sized silver nanoparticles (AgNPs) have greater surface areas
and more active sites available for the degradation of organic
dyes via electron transfer [4]. Further studies have revealed that
the high surface-to-mass ratios and unique activities of silver
nanoflowers—which are brought on by the high densities of
edges, corners, and stepped atoms on their nano-petals—have
enhanced photocatalytic qualities over semi-spherical AgNPs
[9].

AgNPs made from aqueous leaf extracts have been re-
ported for water remediation [10], as it facilitates the catalytic
breakdown of dyes in the presence of visible light [5]. At
the moment, bacterial resistance to antimicrobial drugs is the
biggest obstacle to treating infectious diseases [10]. AgNPs
may infiltrate bacterial cells and injure them by interacting with
DNA and other molecules containing phosphorus and sulfur, as
silver reacts strongly with these elements. This possibility has
been highlighted [10]. The antibacterial effects of AgNPs on
bacteria may be caused by their capacity to bind to the surface
of bacterial cell membranes and impair the permeability and
respiration of the bacterium cell [10]. In wastewater, Gram
positive and negative microorganisms are frequently present
[4]. It has been demonstrated that gram-negative bacteria are
more susceptible to the antibacterial effects of green-mediated
AgNPs than gram-positive pathogens [8]. Controlled oxidation
is typically used to insert oxygen-containing groups, such as
ketone, phenol, lactone, carboxyl group, ether, acid anhydride,
etc., to the surfaces of CNTs [11]. The photocatalytic activity

of the composite photocatalyst is highly associated with the
amount of integrated MWCNTs [12]. MWCNTs have attracted
a lot of interest because of their exceptional physical char-
acteristics and adaptable morphologies [13]. As a new class
of nanovectors for therapeutic administration, functionalized
multi-walled carbon nanotubes (fMWCNTs or oMWCNTs) are
demonstrating their effectiveness in the transport and cellular
translocation of therapeutic compounds [14], [15], [16]. These
f-CNTs can distribute drugs to cells or organs and can be
made using one or more bioactive ingredients from the class
of compounds that includes peptides, proteins, nucleic acids,
and pharmaceuticals [17], [18], [19]. According to the number
of concentric layers, CNTs are divided into single-wall (with
a typical diameter of 0.4 – 2 nm) and multi-wall (with more
layers) (with a typical diameter of 10 – 100 nm) [14]. The
carbon nanotube’s surface is covered in functional groups,
which inhibit undesirable absorption and desorption processes
[20], [21], [22], [23]. In this instance, undesirable absorption
takes the form of biological medium molecule attachment and
potential carbon nanotube content distribution [21]. Since
good aqueous stability is a crucial quality for bio-medical
applications, CNTs may be more cost-effective and effective
than conventional antibiotic therapy because their surfaces can
be modified to reduce hydrophobicity and improve adhesion
through chemical attachment of proteins and polymers [14].
Gram-positive and gram-negative bacteria are both susceptible
to CNTs’ antibacterial action [24]. The physical manner of
bactericidal action and the generation of oxidative stress, which
result in cell membrane damage brought on by the CNTs, are
responsible for this activity [24], [25]. The effects of CNTs on
infections caused by multidrug-resistant bacteria have been the
subject of several in-vitro research [16], [19], [26].

This study was the first to investigate K. senegalensis for
the production of silver nanoparticles. In order to compare the
effectiveness of the photocatalytic and antibacterial activities of
green-synthesized silver nanoparticles (KS-AgNPs) and func-
tionalized carbon nanotubes (oCNTs), respectively, a compara-
tive analysis of both materials’ properties was conducted when
applied for treatment of industrial waste water.

2. Materials and Methods

2.1. Collection of plant materials and waste-water samples
Khaya senegalensis (African mahogany) leaves were col-

lected from Lafia, Nigeria, in February, 2022. Test bacterial
species (Escherichia coli and Staphylococcus aureus) and in-
dustrial waste water were procured and sourced from Genet-
ics and Biotechnology Department, Akwa Ibom State Univer-
sity and Eastern Obolo oil producing community, Akwa Ibom,
Nigeria, respectively. Silver nitrate (AgNO3) (99.80 %) was
purchased from Merck South Africa. Multi-walled-carbon nan-
otubes (outside diameter 8 – 15 nm, length 15 µm) were ob-
tained from Times Nano. Ltd. (Chengdu, China). All the
reagents and chemicals used in this study were of analytical
grade. Aqueous solutions were prepared using double-distilled
water.

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 3

2.2. Preparation of plant extract

Fresh leaves of K. senegalensis (1) were properly cleaned
under running tap water followed by washing with distilled wa-
ter. Dried leaves (5 g) were ground into a powder and extracted
with double-distilled water (ratio 1:10), the mixture was boiled
for 25 min in a water bath at 70 °C. The mixture was then fil-
tered with a Whatman Paper (No. 14) and kept in a dark bottle
in a refrigerator for further analysis [27].

Figure 1: Khaya senegalensis leaves

2.3. Synthesis of silver nanoparticles from plant extract

In a typical experiment, 1 mM AgNO3 was added to 4 mL
leaf extract in a 250 mL beaker and stored in a conical flask at
room temperature for the reduction of Ag+ to Ag0. A colour
change from dark green to brown visually identifying the for-
mation of AgNPs [28]. Green-mediated AgNPs were purified
after several centrifugation at 20,000 rpm for 30 mins [29]. K.
senegalensis synthesized AgNPs were labeled as KS-AgNPs
and stored in an air-tight plastic sample vial for further use 2.

Figure 2: Reaction pathway for reduction of silver ions to silver nanoparticles
using K. senegalensis leaves extract.

2.4. Preparation of oxidized carbon nanotubes (oCNTs)

The oCNTs was obtained by acid treatment (oxidizing) of
CNTs with H2SO4/HNO3 (3:1, v/v) [30]. 1 mL 0.1 M AgNO3
solution was then added into 20 mL 4 mg/mL oCNTs solutions
drop-wisely under assistance of ultra-sonication [31], [32]. The
oxidized CNTs were successively eluted with deionized water,
then by NH4OH, water, HCl and deionized water until the pH
of filtrate was stabilized.

2.5. Characterization

Green synthesized KS-AgNPs’ surface plasmon resonance
(SPR) peak was identified by observing UV-Visible spectra be-
tween 300 and 700 nm [33]. The phytochemical functional
groups, which are found in the Khaya senegalensis leaves
extract employed in the capping and bio-reduction of silver
ions were identified using PerkinElmer Spectrum and Fourier
Transform Infrared (FTIR) (PerkinElmer, Inc. Waltham, Mas-
sachusetts, USA) spectrometer in the between 400 and 4000
cm-1. XRD analysis was performed using Bruker D8 X-ray
diffractometer to determine the biosynthesized AgNPs crystal-
lite size and structure. Morphological characteristics (i.e., size
and shape) were examined using Scanning Electron Microscope
JEOL JSM-IT 300 (JEOL) Ltd., Tokyo, Japan) working at a
30 kV voltage. Transmission electron microscopy (TEM) im-
ages were acquired on Tecnai G2 F20S-TWIN TEM (FEI Ltd.,
USA). The elemental composition of the green-mediated NPs,
were observed using Energy Dispersive X-ray (EDX) analysis
(JSM-7610F).

2.6. Photocatalytic activity

KS-AgNPs and oCNTs were used as catalysts in the degra-
dation of industrial waste-water analyzed under sunlight for a
period of three days. First, the waste-water was twice diluted
with double distilled water and scanned with a UV-Vis between
300 - 700 nm wavelength [34], and the maximum wavelength
obtained (590 nm) was recorded. 10 mg of KS-AgNPs and oC-
NTs were mixed separately with 100 mL diluted waste-water
and magnetically stirred for 30 mins in order to attain equilib-
rium as working solution. First reading was noted after stir-
ring. The dispersion was then exposed to sunlight irradiation
and monitored between the hours of 9 am (GMT+1) and 4 pm
(GMT+1). 2 mL aliquot of the suspension was taken after one
hour interval, filtered and used for photocatalytic degradation
evaluation. Absorbance value measurement at 580 nm was used
to calculate the percentage dye degradation process according
to the equation below:

Decolourization(%) =
A0 − At

A0
× 100 (1)

where: A0 = absorbance of the untreated and At = absorbance
of the treated industrial waste water.

To ascertain the efficiency of both KS-AgNPs and oCNTs as
a biosynthesized catalyst, selected physicochemical properties
(i.e., pH, Total Dissolved Solid (TDS), Total hardness, Calcium,
Magnesium, Chloride, Biological Oxygen Demand (BOD) and
Total alkalinity) of the industrial waste water were assessed us-
ing standard analytical methods described by American Society
for Testing and Materials (ASTM) [35].

2.7. Antibacterial activity

The antibacterial activity of the synthesized KS-AgNPs and
oCNTs was investigated against Gram-positive (Staphylococ-
cus aureus) and Gram-negative (Escherichia coli) bacteria by
the Bauer-Kirby disk diffusion method [36]. Nutrient agar

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 4

medium was prepared according to manufacturer’s instructions
by autoclaving at 121 oC for 15 mins. After sterilization, the
agar was allowed to cool to about 45 oC, after which the molten
agar was poured into petri dishes and allowed to solidify. The
pathogens to be used as indicator organisms for antibacterial ac-
tivity were inoculated on the solidified plates by using standard
spread plate technique. A cork borer of about 2 mm in diame-
ter was used to bore holes in the plates. Both the AgNPs and
oCNTs to be tested for antibacterial activity were inoculated in
the bored holes using a pipette. For the control, antibiotic disks
were placed 2 cm away from the wall of the culture plate. The
plates were incubated at 37 °C for 24 hrs, and the zone of inhibi-
tion of bacterial growth was used as a measure of susceptibility.

3. Results and Discussion

3.1. UV-Visible spectroscopy

The green-mediated reduction of the silver metal ions to
KS-AgNPs was accompanied by a color change yellow to
brown confirms the reduction of Ag+ ions to Ago. This was
monitored using UV-Vis spectrophotometer. Figure 3 shows the
Surface Plasmon Resonance (SPR) with high band intensities
and peaks under the visible spectrum. The KS-AgNPs showed
absorbance bands within the range of 427 nm which correlate
with the results reported in other literatures on the green synthe-
sis of AgNPs [3], [37], [38], [39], [40]. The ability of the plant
extracts to act as a stabilizing and capping agent can be con-
nected to the flavonoids and protein present in K. senegalensis
aqueous extract [41].

Figure 3: UV–visible spectra of green synthesized KS-AgNPs

3.2. FTIR analysis

Figure 4 shows the spectra of the aqueous extract of K.
senegalensis, KS-AgNPs, and oCNTs. The aqueous extract of
K. senegalensis showed characteristic peaks at 3300, and 1630
cm-1 which could be attributed to hydroxyl group O–H stretch-
ing [42], and C–O stretching in the carbonyl group [43] and the
N–H group of amines [44], respectively. The broadband peak

at 3263 cm-1 observed in the KS-AgNPs spectra could be at-
tributed to the overlapping stretching mode of N–H and O–H
functional groups [44]. The C–O band at 1030 cm-1 may be
assigned to the polyols (i.e., flavones, terpenoids, and carbohy-
drates) present in the plant extract. The different assignments
are in line with those for similar compounds that have been pub-
lished in other literatures [39], [45], [46]. A broadband peak at
1549 cm-1 most probably corresponds to aromatic and unsat-
urated structure of C=C bonds was observed for oCNTs [47].
However, the acid treatment of CNTs led to the incorporation
of –COOH group at 1720 cm-1.

Figure 4: FTIR spectra of green synthesized KS-AgNPs, K. senegalensis leaf
extract and oCNTs

3.3. XRD Studies

Data obtained from the silver nanoparticles were used to
obtain the plot shown in Figure 5. The diffraction patterns were
also used to obtained the peak positioning, however, a total
of five distinct peaks at 2θ with Braggs’ reflection values of
38.12o, 44.28o, 64.43o, 77.48o, and 81.54o, which corresponds
to (111), (200), (220), (311), and (222) plane of faced centered
cubic (fcc) lattice of silver, and compared with the standards
powder diffraction card of Joint Committee on Powder Diffrac-
tion Standards (JCPDS) silver file N0. 04-0783. The most sig-
nificant peak from the XRD graph is centered at 2θ = 38.117.
This may be the reason why the faced-centered cubic struc-
ture of the KS-AgNPs has grown favorably [1]. In the diffrac-
tion patterns obtained in the oCNTs XRD spectra, six distinct
peaks were observed with reflection values of 26.43o, 42.36o,
44.46o, 54.51o, 59.98o, and 77.40o, corresponding to (002),
(100), (101), (004), (103), and (110), plane of lattice respec-
tively. Similar result have been reported by [48]. The average
particle size was estimated using the Debye-Scherrer formula
as follows:

D =
kλ

β cos θ
, (2)

where D is the crystallite size of the AgNPs, λ is the wave-
length of the X-ray source (1.54056 A), β is full width at half

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 5

maximum (FWHM) of the diffraction peak in radian, k is the
Scherrer constant that varies from 0.9 to 1, and θ is the Bragg
angle in radian [49]. The average size was found to be 9.30 nm.
One of the structural changes that causes the distortions of crys-
tallographic materials is d-spacing (inter-planar spacing) [50].
The XRD method relies on the broadening of diffracted peaks to
quantify dislocation density that happens when atoms in crystal
unit cells move away from their ideal positions as a result of
numerous lattice defects (strain widening) [51].

Figure 5: XRD spectra of oCNTs and KS-AgNPs

3.4. SEM and TEM analysis

SEM images (Figure 6) shows the morphological char-
acter of the silver nanoparticle synthesized by the extract of
Khaya senegalensis (African mahogany) leaves . The SEM
image revealed a flake-like morphology for KS-AgNPs. Fig-
ure 7 shows the TEM images of a mono-dispersed spherical-
shaped green-mediated KS-AgNPs. The interaction between
the biomolecules contained in the extract suggests that the KS-
AgNPs, which are uniformly distributed and mono-dispersed
and have a spherical shape, have an active surface [7]. TEM
analysis consequently revealed that the average size of the syn-
thesized KS-AgNPs is 9.30 nm.

3.5. Photocatalytic activity of KS-AgNPs and oCNTs activity
on industrial waste water

AgNPs and CNTs have been used as catalysts to remove
halogenated organics from water, including pesticides, heavy
metals, and microbes [52]. Nanoparticles are particularly ef-
fective in water treatment and disinfection to inhibit pathogenic
bacteria and viruses due to their demonstrated antibacterial ef-
fectiveness [53].

In this study, photocatalytic activity of the bio-synthesized
KS-AgNPs and oCNTs was assessed through decolourization
of industrial wastewater under solar light after different time
intervals (54 hours). The change in color was used to iden-
tify rate of pigment degradation. After 55 hours (three days)
of exposure, increased decolorization was evident as color of

Figure 6: KS-AgNPs SEM images

Figure 7: TEM images of green synthesized KS-AgNPs at (a) 50 nm and (b)
200 nm

treated industrial wastewater changed from deep orange to light
orange color. A continuous decrease in the absorbance of the
treated wastewater obtained using UV spectrophotometer were
recorded at time interval. Steady absorbance readings obtained
at the 55th hour suggested that total degradation was attained
(Figure 8). The percentage degradation efficiency of the treated
wastewater was highest in KS-AgNPs (86.21 %) while oCNTs
had (82.14 %). Yasmin et al. (2020)[54] recorded close range
of value for AgNPs in earlier studies. In relative comparison,
KS-AgNPs, has proven to have more photocatalytic effect as
shown in Figure 8, in the degradation of wastewater than oC-
NTs, after 55 hours of exposure. The increased absorption
rate of the nano-sized silver particle distribution in KS-AgNPs
compared to oCNTs may be the cause of their higher degrad-
ing efficiency [55]. More specifically, silver metal nanoparti-
cles’ highly effective catalytic activities are a result of their dis-
tinctive properties, such as their extremely small dimensions,
high surface-to-volume ratio, high dispersivity, and capacity for
electron transfer between the donor and acceptor electron relay
systems [56], and because catalysis happens on metal surfaces
during degradation, there will be a considerable increase in sur-
face area available, which will increase the catalyst’s effective-
ness [57], in this case, KS-AgNPs.

The mechanism of the catalytic photo degradation of the
wastewater was proposed for better understanding as shown in
Figure 9.

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 6

Figure 8: Effect of exposure time on the photocatalytic degradation of industrial
wastewater after (a) first day (b) second day and (c) third day

Figure 9: Mechanism of photocatalytic activity of KS-AgNPs and oCNTs

The result of photocatalytic degradation of both KS-AgNPs
and oCNTs were compared with some results obtained from
other literatures as shown in Table 1, with a high degradation
rate observed in KS-AgNPs, confirming its excellent photocat-
alytic activity.

Sequel to the photocatalytic degradation of the waste water
analyzed, selected physicochemical parameters were also sub-
jected to evaluation before and after treatment with KS-AgNPs
and oCNTs separately as shown in Figure 10. Comparison was
also made with standard permissible limits recommended by
World Health Organization (WHO). In general, the evaluation
showed that both KS-AgNPs and oCNTs (in same quantity) sig-
nificantly reduced the parameters analyzed. However, green-
mediated KS-AgNPs greatly reduced in all parameters.

Decrease in color change of the treated industrial waste
water observed can be attributed to organic pollutants adsorp-
tion. Industrial waste water pH before (10.55) and after treat-
ment with both KS-AgNPs and oCNTs showed that KS-AgNPs
had greater reduction efficiency (7.04) in comparison to oCNTs

Figure 10: Plot of physicochemical assessment after treatment with KS-AgNPs
and oCNTs: TDS – Total Dissolved Solids, TH – Total Hardness, Ca – Calcium,
Mg – Magnesium, Cl – Chlorine, BOD – Biochemical Oxygen Demand, TA –
Total Alkalinity

(9.21). The pH decrease recorded for KS-AgNPs may be due
to waste water anionic species removal. Observation from KS-
AgNPs was however, within WHO pH permissible limit of 6.5 –
8.5. The TDS of industrial wastewater was 350.05 mg/L, treat-
ment with KS-AgNPs reduced the TDS concentration to 286.09
mg/L while oCNTs recorded a decrease of 299.19 mg/L. Sat-
isfactorily, both KS-AgNPs and oCNTs reduction were lower
than WHO recommended limit of 1000 mg/L for TDS in do-
mestic water. Higher efficiency of silver nanoparticles obtained
from K. senegalensis (KS-AgNPs) results from the reduced size
of the bio-synthesized silver ion in the water.

3.6. Antibacterial Assay
Antimicrobial activity of green synthesized KS-AgNPs,

oCNTs, and control antibiotics (Gentamicin and Ciprofloxacin)
were tested against two selected bacteria, Escherichia Coli
(Gram negative bacteria) Staphylococcus aureus (Gram posi-
tive bacteria) and investigated.

Figure 11: Inoculated plates with bore holes containing KS-AgNPs, oCNTs
and known antibiotics (Gentamicin and Ciprofloxacin) before incubation for
both (a) Gram (+) and (b) Gram (-) bacteria

The antibacterial activity ranged from 0 – 4 mm as observed
from the results in Tables 2 and 3. oCNTs produced the lowest
susceptibility to both gram-positive and gram-negative bacteria
compared to KS-AgNPs, which had higher susceptibility. KS-
AgNPs had susceptibility between 0.5 - 3.5 mm while oCNTs
had susceptibility between 0 – 0.5 mm. The known antibiotic,

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 7

Table 1: Different catalysts and their rate of decolourization of pollutants

S/N Catalyst Pollutants Effects Reference
1. H3PW12O40/GO Methyl orange, crystal violet,

and Congo red
85.62 % methyl orange, 89.78
% crystal violet, and 82.62 %
Congo red decolourization re-
spectively

[58]

2. Rambutan peel extract-
ZnO nanoparticles

Methyl orange 83.99 % decolourization [59]

3. Terminalia chebula fruits
extract-ZnO nanoparticles

Rhodamine B 70 % decolourization [60]

4. Tinospora cordifolia-CuO
nanoparticles

Methylene blue 80 % decolourization [61]

5. *o-Carbon nanotubes Industrial waste water (crude oil
polluted water)

82.14 % decolourization Present study

6. *KS-AgNPs Industrial waste water (crude oil
polluted water)

86.21 % decolourization Present study

Gentamicin had the highest susceptibility (4 mm), followed by
the green-mediated KS-AgNPs (3.5 mm), while oCNTs had the
least. The gram-negative bacteria (E. coli) were more suscep-
tible to KS-AgNPs than the gram-positive bacteria (S. aureus),
this is due to the thickness of the cell wall and cell composition.
Gram (-) bacteria has thinner peptidoglycan walls compare to
Gram (+) bacteria which has thicker peptidoglycan wall. How-
ever, given that small nanoparticles can easily pass through the
cell membrane, susceptibility of KS-AgNPs is thought to rely
on their size and shape [44]. AgNPs either adhere to the bacte-
rial membrane or impair membrane permeability, which has an
antibacterial impact, and they penetrate the cytoplasm and kill
bacteria by disrupting their metabolism [62], [63]. Addition-
ally, the destruction of bacterial pathogens may also be caused
by production of free radicals by the silver nanoparticles [64].

Figure 12: Antibacterial activity of (a) green-mediated KS-AgNPs and oCNTs
compared with (b) antibiotics

A study by Blasco et al. [65] demonstrated the efficiency
of AgNPs produced through green synthesis against multiple
antibiotic-resistant bacterial strains, including Staphylococcus
aureus, Staphylococcus epidermidis, Streptococcus pyogenes,
Klebsiella pneumoniae, and Salmonella typhi, which further
confirms the results obtained in this study. Moreover, AgNPs
can produce pits and gaps that reduce the permeability of bac-
terial cell membranes, resulting in the death of the bacteria [66],
[67], [68].

Table 2: Results of the antibacterial activity of the green-mediated KS-AgNPs
and oCNTs

Inhibition Zone of
E. coli bacteria
against

Inhibition
zone (mm)

Condition (sensi-
tive/resistance)

Ciprofloxacin an-
tibiotics

0 Resistance to an-
tibiotics

KS-AgNPs 3.5 Sensitive to
nanoparticle

oCNTs 0.5 Slightly sensitive

Table 3: Results of the antibacterial activity of the green-mediated KS-AgNPs
and oCNTs

Inhibition Zone of
S. aureus bacteria
against

Inhibition
zone (mm)

Condition (sensi-
tive/resistance)

Gentamicin
antibiotics

4 Sensitive to an-
tibiotics

KS-AgNPs 1.5 Sensitive to
nanoparticle

oCNTs 0.5 Slightly sensitive

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Labulo et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1438 8

The versatility of carbon-based nanomaterials, particularly
oCNTs and graphene, has shown considerable promise in bio-
logical applications such as tissue engineering, drug delivery,
and bio-imaging [69], [70]. Therefore, AgNPs are highly effec-
tive due to their clearly defined structures and substantial sur-
face areas. By attaching AgNPs to the surface of graphene ox-
ide or oxidized CNTs, certain potent antibacterial agents have
been produced [70,71].

4. Conclusions

This study describes the quick and efficient green-mediated
synthesis of KS-AgNPs employing an aqueous K. senegalensis
extract as the capping and reducing agent. The color change and
UV–vis adsorption confirm the reduction of Ag+ to Ag0. The
TEM showed spherical shape with average particle size of 9.30
nm. The FTIR results confirmed the biomolecules capping and
stability of the KS-AgNPs. The KS-AgNPs are stable and have
excellent photocatalytic and antibacterial activities in compar-
ison with oCNTs. The green produced KS-AgNPs method is
suitable for large-scale manufacturing, quick, affordable, non-
toxic, and ecologically beneficial silver nanoparticles. Over-
all, this work presents an effective method for creating smaller
silver nanoparticles, which can be employed as antibacterial
agents and to treat industrial waste water.

Acknowledgement

The authors acknowledge the Federal University of Lafia
for providing the research environment for this work. Authors
are also grateful to Mrs. Rasheedah Labulo for proofreading
this work.

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