catalysts
Article
Fenton Degradation of Ofloxacin Using a
Montmorillonite–Fe
3
O
4
Composite
Alamri Rahmah Dhahawi Ahmad, Saifullahi Shehu Imam, Wen Da Oh and Rohana Adnan *
Citation: Ahmad, A.R.D.; Imam, S.S.;
Oh, W.D.; Adnan, R. Fenton
Degradation of Ofloxacin Using a
Montmorillonite–Fe
3
O
4
Composite.
Catalysts 2021, 11, 177. https://
doi.org/10.3390/catal11020177
Academic Editor: Vincenzo Vaiano
Received: 13 December 2020
Accepted: 25 January 2021
Published: 28 January 2021
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4.0/).
School of Chemical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia;
rahalamri@student.usm.my (A.R.D.A.); ssimam.chm@buk.edu.ng (S.S.I.); ohwenda@usm.my (W.D.O.)
* Correspondence: r_adnan@usm.my
Abstract: In this work, FeM composites consisting of montmorillonite and variable amounts of Fe
3
O
4
were successfully synthesized via a facile co-precipitation process. They were characterized using X-
ray photoelectron spectroscopy (XPS), a field emission scanning electron microscope (FESEM), energy-
dispersive X-ray spectroscopy (EDX), a transmission electron microscope (TEM), N
2
adsorption–
desorption, and Fourier transform infrared spectroscopy (FTIR) techniques to explain the effect of
Fe
3
O
4
content on the physicochemical properties of the Fe
3
O
4
–montmorillonite (FeM) composites.
The FeM composites were subsequently used as heterogeneous Fenton catalysts to activate green
oxidant (H
2
O
2
) for the subsequent degradation of ofloxacin (OFL) antibiotic. The efficiency of the
FeM composites was studied by varying various parameters of Fe
3
O
4
loading on montmorillonite,
catalyst dosage, initial solution pH, initial OFL concentration, different oxidants, H
2
O
2
dosage,
reaction temperature, inorganic salts, and solar irradiation. Under the conditions of 0.75 g/L FeM-10,
5 mL/L H
2
O
2
, and natural pH, almost 81% of 50 mg/L of OFL was degraded within 120 min in
the dark, while total organic carbon (TOC) reduction was about 56%. Although FeM composites
could be a promising heterogeneous catalyst for the activation of H
2
O
2
to degrade organic pollutants,
including OFL antibiotic, the FeM-10 composite shows a significant drop in efficiency after five cycles,
which indicates that more studies to improve this weakness should be conducted.
Keywords: Fenton degradation; ofloxacin; Fe
3
O
4
; montmorillonite; wastewater
1. Introduction
For the past few years, the high consumption of antibiotics has resulted in their
continuous detection in surface, ground, drinking, and wastewater around the world [1].
Their presence is a threat to the ecological environment due to their chemical stability and
slow biodegradation since antibiotics are harmful to microorganisms [2,3]. Among the
antibiotics, ofloxacin (OFL) is an extensively used 2nd-generation fluoroquinolone due
to its good antibacterial activity [4,5]. It is commonly used to treat bronchitis, infectious
diarrhea, pneumonia, pelvic inflammatory disease, eye infections, ear infections, gonorrhea,
respiratory tract infections, urinary tract infections, gastrointestinal infections, and skin
infections [6–8]. However, approximately 90% is excreted via urination in its original form
48 h after administration [7]. The presence of OFL in water results in unpleasant odors and
may also present a significant risk to aquatic species due to its toxicity [9,10]. Unfortunately,
OFL is still being detected in wastewater even after conventional treatment [11]. Thus, the
development of an effective method for the removal of OFL from wastewater becomes
imperative.
The Fenton reaction is an effective process that has gained widespread acceptance
due to its efficiency in degrading and even mineralizing persistent organic contaminants
with the highly reactive hydroxyl radicals (
•
OH) generated from H
2
O
2
using Fe
2+
from a
Fenton reagent [12]. However, to overcome the shortcomings of the homogeneous Fenton
process, various heterogeneous Fenton catalysts, including Fe
3
O
4
nanoparticles [13], Fe-Mn
Catalysts 2021, 11, 177. https://doi.org/10.3390/catal11020177 https://www.mdpi.com/journal/catalysts