Abstract
Emerging organic pollutants (EOPs) are referred as compounds that are progressively
manufactured but are not commonly regulated nor monitored in the environment. They can
find their way into the environment through various mechanisms, and their ubiquity in various
environmental matrices has resulted in serious adverse effects in both aquatic and terrestrial
organisms. In underdeveloped and developing countries, monitoring systems for these
pollutants are lacking while more advanced pollutants control programmes are documented in
developed countries. In addition, developed countries have more sophisticated analytical
techniques for proper monitoring of EOPs. Various mechanisms through which these pollutants
enter the environment include; discharges from manufacturing facilities, agricultural practices,
direct disposal, human and animal excreta, ect. These EOPs include pharmaceuticals, personal
care products (PCPs), insecticides, UV-filters and others. Among these, pharmaceuticals have
shown to be the most consumed medicinal compounds worldwide. Therefore, their fate in the
environment is inevitable and have raised quite numerous societal concerns.
In developed countries, there is well-represented data about the occurrence of
pharmaceuticals in the environment. However, underdeveloped and developing countries lack
proper resources for monitoring of these compounds in environmental waters. Therefore, the
unmonitored concentrations of these compounds has resulted in inevitable adverse effects and
serious societal concerns. One of the main objectives of this work was to document the baseline
data about the occurrence of pharmaceuticals in underdeveloped and developing countries
which are mostly found in Africa and Asia. The occurrence was further devoted to the sources
and distribution mechanisms, which enormously contribute to their fate in the environment.
According to literature, pharmaceuticals manufacturing companies, direct disposal and human
excretion are the main sources of pharmaceuticals in the environment. Adverse effects and
future prospects were also covered. Baseline occurrence data collected indicated that
antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) are the most detected and
reported drugs in African and Asian inland wastewaters.
However, NSAIDs were detected at lower concentrations in Asian countries. β-blockers are
among the pharmaceutical classes that are highly consumed in African and Asian countries.
However, the environmental monitoring and subsequent removal of these compounds is still a
problem due to limited resources. In addition, their lowest environmental concentrations and
constant release has resulted in serious health issues and ecological imbalance. Therefore,
removal of these recalcitrant compounds from the environment is indispensable. Nonetheless,
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these pollutants become extremely diluted when they enter the environment and their direct
quantification is almost impossible. Therefore, sample preparation step is a need. After
completing the sample preparation step, the removal step is also needed to eliminate these
pollutants from the environment. This work employed adsorption as one of the best removal
technologies which has been considerably applied in the elimination of various pollutants form
the environment. However, this technology suffers from major drawback which involves the
migration of pollutants between solid and liquid phases, which does not completely solve the
problem in question. Therefore, photodegradation was also applied to mineralize the pollutants
into harmless inorganics.
To achieve the aforementioned objectives, two magnetic nanocomposites were synthesized
and these include magnetic MIL-101(Cr) (Fe3O4@MIL-101 (Cr)) and magnetic amine doped
MIL-101(Cr) (Fe3O4@NH2-MIL-101(Cr)). These materials were characterized using x-ray
powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer–
Emmett–Teller (BET), transmission electron microscopy (TEM) and vibrating sample
magnetometer (VSM). For adsorption and preconcentration, multivariate optimization
approach was used which involved simultaneous screening and optimizing factors deemed to
be affecting the processes. The chemometric designs employed included fractional factorial
design (FFD), central composite design (CCD) and response surface methodology (RSM). On
the other hand, univariate optimization was used in photodegradation optimization. Magnetic
amine doped MIL-101(Cr) was applied in magnetic solid-phase microextraction (MSPE) and
the method exhibited low limits of detection (LODs) of 0.057 and 0.065 μg L-1, and
quantification (LOQs) of 0.192 and 0.219 μg L-1 for acebutolol (ACE) and metoprolo (MET),
respectively.
In addition, the linearity as wide as from 0.2 to 1200 μg L-1 was attained. The MSPE was
applied in real samples and high extraction fficiencies (%ER) were obtained regardless of the
matrix intereferences. Magnetic MIL-101(Cr) was used as an adsorbent for the adsorption of
the selected β-blockers (ACE) and (MET) from the environment. Prior application to real
samples factors deemed to be affecting the adsorption process including pH and mass of
adsorbent (MA) were optimized using central composite design (CCD) based on response
surface methodology (RSM). The Fe3O4@MIL-101 (Cr) exhibited relatively high adsorption
capacities for both ACE and MET which were 30.9 mg/g and 28.3 mg/g, respectively. The
adsorption isotherms, kinetics and thermodynamics revealed that chemisorption was the
dominating type of interaction mechanism between the β-blockers and Fe3O4@MIL-101 (Cr)
with mean free energies exceeding 8 kJ mol-1 for both ACE and MET. Adsorption process was
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applied in the real samples and maximum removal efficiencies were still attained, indicating
that matrix complexity had insignificant effect on the adsorption process.
In the photodegradation process, ACE was used as a model analyte to evaluate the
photocatalytic efficiency of the Fe3O4@NH2-MIL-101(Cr). The phtotcatalyst exhibited low
degradation efficiency in the dark in the absence and presence of H2O2. However, the
photodegradation efficiency was greatly enhanced in the light with concentrations of ACE
approximating zero. The scavenging experiments indicated that superoxide radicals (·O2
-)
were the main reactive species dominating the mineralization of ACE. The regenerability and
reusability results suggested that the photocatalyst could be used more than three times
maintaining over 60% degradation efficiency. To attain optical and photoelectrochemical
properties of the photocatalyst, various electrochemical techniques were used and these include
Ultraviolet-visible spectroscopy diffuse reflectance spectroscopy (UV-Vis DRS),
photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). Nyquist plot
obtained from EIS revealed that the incorporation of Fe3O4 nanoparticles reduced the charge
transfer resistance (Rct), which ultimately enhanced degradation efficiency. The results from
UV-Vis DRS, scavenging experiments, EIS and Mott-Schottky analysis suggested that the
obtained heterojunction followed Z-scheme mechanism.