Biobased Poly(ethylene furanoate) Polyester/TiO2 Supported Nanocomposites as Effective Photocatalysts for Anti-inflammatory/Analgesic Drugs

Article abstract of DOI:10.3390/molecules24030564

In the present study, polymer supported nanocomposites, consisting of bio-based poly(ethylene furanoate) polyester and TiO₂ nanoparticles, were prepared and evaluated as effective photocatalysts for anti-inflammatory/analgesic drug removal. Nanocomposites were prepared by the solvent eVaporation method containing 5, 10, 15, and 20 wt% TiO₂ and characterized using Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Thin films of them have been prepared by the melt press and optimization of the photocatalytic procedure was conducted for the most efficient synthesized photocatalyst. Finally, mineralization was evaluated by means of Total organic carbon (TOC) reduction and ion release, while the transformation products (TPs) generated during the photocatalytic procedure were identified by high-resolution mass spectrometry.

Full text of DOI:10.3390/molecules24030564

molecules
Article
Biobased Poly(ethylene furanoate)
Polyester/TiO2 Supported Nanocomposites
as Effective Photocatalysts
for Anti-inflammatory/Analgesic Drugs
Anastasia Koltsakidou 1, Zoi Terzopoulou 2 , George Z. Kyzas 3 , Dimitrios N. Bikiaris 2
and Dimitra A. Lambropoulou 1,
*
1
Laboratory of Environmental Pollution Control, Department of Chemistry,
Aristotle University of Thessaloniki, GR–541 24 Thessaloniki, Greece; akoltsakidou@gmail.com
Laboratory of Polymer Chemistry and Technology, Department of Chemistry,
Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Greece; terzoe@gmail.com (Z.T.),
dbic@chem.auth.gr (D.N.B.)
2
3
Hephaestus Advanced Laboratory, Eastern Macedonia and Thrace Institute of Technology,
GR-654 04 Kavala, Greece; kyzas@teiemt.gr
*
Correspondence: dlambro@chem.auth.gr; Tel.: +30-2310-997687
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editors: Dimitrios Bikiaris and Dimitrios G. Papageorgiou
Received: 16 January 2019; Accepted: 1 February 2019; Published: 4 February 2019
ꢀꢁꢂꢃꢄꢅꢆ
Abstract: In the present study, polymer supported nanocomposites, consisting of bio-based
poly(ethylene furanoate) polyester and TiO2 nanoparticles, were prepared and evaluated as effective
photocatalysts for anti-inflammatory/analgesic drug removal. Nanocomposites were prepared
by the solvent eVaporation method containing 5, 10, 15, and 20 wt% TiO2 and characterized
using Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC),
wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), and scanning electron
microscopy (SEM). Thin films of them have been prepared by the melt press and optimization
of the photocatalytic procedure was conducted for the most efficient synthesized photocatalyst.
Finally, mineralization was evaluated by means of Total organic carbon (TOC) reduction and ion
release, while the transformation products (TPs) generated during the photocatalytic procedure were
identified by high-resolution mass spectrometry.
Keywords: poly(ethylene furanoate); polyester; titanium dioxide; nanocomposites; pharmaceuticals;
photocatalysis
1. Introduction
During the last decades, photocatalysis is used for the treatment of a variety of pollutants
such as dyes, pesticides pharmaceuticals, and various endocrine disrupting compounds [1–4].
Titanium dioxide has been reported as one of the most efficient photocatalysts, mostly because of its
low cost, the high chemical, photo, and biological stability and high catalytic activity. Apart from that,
development of multifunctional TiO2-based materials for biomedical applications were extensively
reported in literature [5–8]. Titanium dioxide is commercially available in the form of powder
that shows the greatest surface area and efficiency. However, when applied to wastewater in the form
of powder, it suffers from the following drawbacks: Low light utilization efficiency of suspended
photocatalyst, due to the attenuation loss suffered by light rays [9]; requirement of post-treatment
recovery, that is both time and money consuming, and also leads to the loss of catalyst [10]; and possible
cause of un-favorable human health problems associated with the mobility of the powder form [11].
Molecules 2019, 24, 564; doi:10.3390/molecules24030564
www.mdpi.com/journal/molecules

Molecules 2019, 24, 564
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In order to overcome all the aforementioned drawbacks, continuous efforts are being made to
support TiO2 on various substrates. Membranes that are commonly used to purify water and to
separate TiO2 particles from treated water are an ideal material to support TiO2. Since Anderson et al.
introduced the photocatalysis by immobilizing TiO2 in a membrane [12], many scientists have applied
it to both organic [13–15] and inorganic membranes [16]. Polymers such as polyamide, polysulfone,
polyethersulfone, polyvinylidene fluoride, polypropylene, polyacrylonitrile, and cellulose acetate have
been used as substrates for TiO2 based photocatalysts [17]. Moreover, the importance of immobilizing
TiO2 in a polymer matrix can also be noted for different important applications, as for example,
in hybrid photovoltaics [18]. Due to the ongoing progress in hybrid solar cells, the reached efficiency
values become more and more competitive with conventional photovoltaics. The morphology of
the active layer turned out to be very important for these devices. Mainly titania (TiO2) of different
morphologies is used as a major component in such hybrid solar cells. In addition to research focusing
on increasing device efficiencies, the development of alternative, more environmentally friendly hybrid
solar cell fabrication routes is interesting.
Polymer support appears to be highly suitable for TiO2 due to a series of advantages.
Firstly, polymers are innoxious materials, chemically inert and mechanically stable with high
durability [19]. They can offer pre-concentration of the organic pollutants on their surface, increasing
the efficiency of adsorption and subsequent oxidation, due to their hydrophobic nature [19].
Furthermore, they are inexpensive, readily available with thermos-softening properties, which increase
the ease of coating TiO2 on them by simple thermal treatment methods [20]. Finally, many of them
have high UV-resistance, hence they do not undergo oxidation readily [21].
Bio-based polymers that are either biodegradable or at least partly bio-based, constitute one of
the fastest growing markets [22–28], due to the great concern about the depletion of fossil resources,
as well as the growing accumulation of plastic waste in the environment. During the last years,
the production of furan derivatives from sugars has become exciting in chemistry and in catalysis
studies, because it aids one of the major routes for achieving sustainable energy supply and chemicals
production. 5-HMF, 2,5-FDCA, and 2,5-dimethylfuran (2,5-DMF) have been called the “sleeping giants”
of renewable intermediate chemicals and can be produced from biomass after its fermentation [29,30].
FDCA is considered the bio-based equivalent of terepthalic acid, therefore its polyester poly(ethylene
furanoate) (PEF) is very promising as the bio-based alternative of poly(ethylene terephthalate)
(PET) [31].
Since PEF is expected to be the bio-based polyester that will gradually replace its fossil-based
counterpart PET, studying its properties and possible uses is a fast-developing research interest area.
The furan ring provides PEF higher polarity, making it more compatible with TiO2 nanoparticles
and therefore more suitable as a support polymer for TiO2 photocatalysts.
The usual methods of supporting TiO2 on polymers are sol-gel and sputtering, however sol-gel
techniques result in photocatalysts with amorphous TiO2, instead of the preferred anatase form,
and require post-deposition thermal treatment in temperatures above 300 ◦C in order to recrystallize
it [32]. Another possible approach for the support of TiO2 on polymers is solution mixing, which is
an inexpensive technique that occurs in inert conditions and does not affect the crystal structure of
anatase. Additionally, in comparison with sputtering or hot-pressing methods, it allows the polymeric
substrate to form stronger interactions with the TiO2 nanoparticles.
In the context of development environmentally friendly materials and based on the fact
that the furan ring polarity makes the PEF a suitable substrate for the immobilization of TiO2, the aim
of this study was the synthesis of PEF/nTiO2 nanocomposites, as a first stage of membrane PEF/TiO2
synthesis investigation, containing various concentrations (wt%) of TiO2. Additionally, the main
objective of this study was to assess the application of the promising PEF/TiO2 membrane
configuration in the photocatalytic treatment of commonly detected contaminants like Non-Steroidal
Anti-Inflammatory Drugs (NSAIDs). Among all the human medicines, NSAIDs are one of the most
frequently recommended pain killer medicines. Large amounts of these painkillers are prescribed in

Molecules 2019, 24, 564
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human medical care, but more often, they are sold without prescription as so-called ‘over-the-counter’
drugs. Residues of NSAIDs are usually present in surface water and ground water or eVen in
drinking water [33–35]. Despite this, they have been detected in wastewater treatment plants, sewage
sludge, and agricultural soils due to application of manure contaminated with pharmaceuticals,
irrigation with non-reclaimed or treated wastewater [36]. Therefore, removal of NSAIDs from water
systems is necessary considering its potentially harmful impacts on the environment. In the present
study, a mixture of such extensively found contaminants in the aquatic system such as Ibuprofen
(IBU), Diclofenac (DCF) and Acetaminophen (ACM) was selected. These NSAIDs are among
the most frequently utilized drugs and the NORMAN experts have included them in the list of
the ‘emerging contaminants’.
Further emphasis was given to optimize the photocatalytic procedure using different parameters
(drug concentration, catalyst concentration and pH). To the best of our knowledge, this is the first study
regarding the synthesis of PEF/TiO2 nanocomposites, eValuation of its properties, and its application
for the photocatalytic treatment of pharmaceuticals.
2. Results and Discussion
2.1. Synthesis and Characterization of PEF/TiO2 Photocatalysts
PEF was synthesized from DMFD by the two-step melt polycondensation method with the use
of TBT catalyst (Scheme 1). The final product had a IV value of 0.45 dL g−1, which is within
the values reported for the same catalyst in previous studies [37,38] and what was found by GPC PEF
has Mn = 11200 g mol−1. Since the polyester exhibited a yellow discoloration, a purification process
took place in order to remove impurities and unreacted monomers. For this reason, PEF was dissolved
in a mixture of trifluoroacetic acid/chloroform 1/4 v/v and precipitated in cold methanol. The product
obtained after the purification was a white powder, which means that some decomposition products
formed during synthesis of PEF have been removed during this treatment [39].
Scheme 1. Synthesis of PEF with the two-step polycondensation reaction.
TiO2 was supported on the synthesized PEF by preparing PEF/TiO2 nanocomposites
with the solution mixing method firstly and after melt pressing thin films (1 mm) in final TiO2
concentrations 5, 10, 15, and 20 wt% have been prepared. The morphology and dispersion of
the nanocomposites powder was studied by SEM and EDX element mapping. SEM micrographs
and their corresponding Ti maps are presented in Figure 1. The respective mapping images reveal
satisfactory dispersion of the nanoparticles into the polymer matrix, and the density of the maps
increases while increasing TiO2 concentration. This suggests that PEF is capable of supporting TiO2
quantities up to 20 wt%.

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Figure 1. SEM micrographs and Ti mapping of (a) PEF/TiO2 5%, (b) PEF/TiO2 10%, (c) PEF/TiO2 15%,
and (d) PEF/TiO2 20%.

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WAXD was employed in order to clarify the crystalline structure of PEF and TiO2 in
the nanocomposites. The resulting diffraction patterns are shown in Figure 2. Neat PEF has some
weak diffraction peaks at 15.8, 20.2, 25.2, and 27.2◦, which reveal that it is crystallized in the
β-crystal
form [40]. Its crystal structure is sustained in the nanocomposites with 5 and 10% wt % TiO2, but is
significantly reduced in concentrations of 15 and mainly 20 wt%, as evidenced by the very weak
diffraction peaks. TiO2 powder exhibits an intense diffraction peak at 25.1◦, which corresponds to
the form of anatase. This peak is also present in the nanocomposites, indicating that the anatase
structure remains the main form of TiO2 in the catalysts, which is the desired one since it is able to
degrade compounds via photocatalysis [41]. Especially in the nanocomposites with 15 and 20 wt%
TiO2, the nanofiller is well crystallized, with strong diffraction peaks, suggesting that it will retain its
photocatalytic activity [32].
Figure 2. X-ray diffraction patterns of PEF and its nanocomposites with TiO2.
FTIR spectra of the polyesters were recorded to confirm their structure and possible interactions
between polymer matrix and TiO2 (Figure 3). The spectrum of PEF exhibits absorption bands
at 3645 cm−1 due to the RCH2OH hydroxyl group vibration, at 3563 cm−1 due to the O-H bending
of the carboxylic hydroxyls, at 3435 cm−1 due to the O-H bending of the hydroxyl end groups of
the polyester, at 3123 cm−1 and 3004 cm−1, due to the C-H bending of the furan ring, at 2976 cm−1
of the C-H bending vibrations, at 1737 cm−1 of the carbonyl group’s bending, at 1575 cm−1 due to
the bending vibrations of the =C-H of the furan ring, at 1271 cm−1 and 1225 cm−1 due to the Csp2-O
and Csp3-O bonds of the furan ring, and at 1136 cm−1 due to the C-O bending vibration of the ester
group. The spectra of the nanocomposites do not exhibit noticeable differences compared with neat PEF,
therefore the presence of TiO2 did not affect the chemical structure of the polymer. A small peak in
the region 450–500 cm−1 that increases in area with increasing the nanofiller content is also observed
and can be attributed to the Ti-O stretching vibration. Additionally, since the main peaks of PEF are
recorded at the same positions in nanocomposites, it can be said that there are no covalent interactions
or hydrogen bonding between PEF matrix and TiO2 nanoparticles.

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Figure 3. FTIR spectra of PEF and its nanocomposites with TiO2.
Thermal characterization of PEF and its nanocomposites was performed with DSC and TGA
(Figure 4). The characteristic temperatures Tm and Tg, as well as the crystallinity are presented in Table 1.
The melting point of PEF appears at 213.8 ◦C, as a broad endothermic peak. After the incorporation
of nTiO2, melting point values are not significantly affected in low filler content 5 wt%, but start to
decrease slightly in the presence of 10–20 wt% nTiO2. This shift could be attributed to the lower degree
of crystallinity that these nanocomposites have or due to the formations of imperfect crystals. As can be
seen from enthalpy of fusion the degree of crystallinity reduces gradually by increasing TiO2 content.
This is clear eVidence that the nanoparticles, due to the higher amount added, restrict the ability of
macromolecular chains to fold and form crystal structures. For this reason, the degree of crystallinity
(Xc) was reduced significantly in nanocomposites with 15 and 20 wt% TiO2, which is in good agreement
with WAXD findings. In contrast, Tg is increased in the nanocomposites, indicating their hindering effect
towards the movement of the macromolecular chains.
Figure 4. (a) DSC thermograms and (b) TGA thermograms of PEF and its nanocomposites with TiO2.

Molecules 2019, 24, 564
Table 1. DSC data (
7 of 22
∆
H0m = 137 J/g [42]), Ti (initiation of degradation temperature), Tmax (temperature where
degradation occurs on the fastest rate) and solid residue of PEF and its nanocomposites with TiO2.
◦
Sample
Tm (oC)
Tg (oC)
∆Hm (J/g)
Xc (%)
Ti (oC)
Tmax (oC)
Residue at 550 C (%)
PEF
213.8
213.8
211.4
211.3
211.5
88.0
88.3
88.4
89.1
90.2
46.17
45.91
44.98
38.63
30.21
33.70
33.51
32.83
28.20
22.05
390.3
385.0
384.7
397.0
406.2
416.2
424.8
426.7
426.0
433.3
7.0
PEF/TiO2 5%
PEF/TiO2 10%
PEF/TiO2 15%
PEF/TiO2 20%
14.6
17.8
28.5
31.2
The effect of TiO2 on the thermal stability of PEF was studied by TGA. The characteristic
degradation temperatures and solid residue are also presented in Table 1. It can be seen that PEF
is a thermally stable polyester, since it starts to degrade after 390 ◦C. Thermal stability is increased
for all the nanocomposites, with increasing filler content, as evidenced by the Tmax. The amounts of
solid residue at 550 ◦C are increasing, while increasing TiO2 content, as was expected, due to the high
added TiO2 amounts. Furthermore, from these residues it is clear that the whole amount of added
TiO2 was incorporated inside the polymer matrix.
2.2. Photocatalytic Degradation Process
2.2.1. Effect of TiO2 Amount on Drug Removal
Due to the increased concern for the usage of immobilized TiO2 catalysts, all the synthetized
catalysts (600 mg L−1 of each) with the concentration of TiO2 ranging from 5 to 20 wt%, were eValuated
−1
for the degradation of anti-inflammatory drugs mixture (5 mg L of each compound), at inherent pH.
The selected drugs are found very often in wastewaters as well as in surface waters. For example,
IBU is a non-steroidal, antipyretic drug that is recognized with a huge global consumption rate [42
]
and has been detected in effluents of municipal WWTPs and in surface waters at concentrations levels
−1
between ng L−1 and
for the relief of fever, headaches, and some minor pains, which has been commonly detected in surface
waters, ground waters, wastewaters, and even drinking waters, along with its toxic metabolites [44 45].
DCF is frequently detected in secondary effluent, surface water, and drinking water at concentrations
range of from 1.2 to 4.7
g L−1, respectively [46]. DCF is also one of the monitored pollutants by
µg L
[43]. ACM is a mild analgesic that is commonly used in combinatory drugs
,
µ
European Commission (EC), since itself and its transformation by-products pose a serious threat to
public health and ecosystems according to the persistence and ecotoxicity in the water [47].
Mixture’s degradation by all studied catalysts, under SSL, follows first-order kinetics according
to the high values of correlation coefficient, R2 = 0.99 (lnCo/C vs. time), for all the compounds.
The kinetic profiles are depicted in Figure 5a–c, while the kinetic rate constants are in Figure 5d.
All four catalysts exhibit photocatalytic activity, while, as expected, the immobilized catalyst
with the 20 wt% of TiO2 is the most efficient for the removal of the drug mixture, since the kinetics
obtained are faster for all studied compounds. The elimination of all compounds by PEF/TiO2 20 wt%
catalyst was almost complete during the first 90 min of the procedure. Therefore, further experiments
were only conducted for PEF/TiO2 20 wt% catalyst. Preliminary adsorption experiments were
also carried out using 5 mg L−1 of each compound as the initial concentration. Under dark
conditions, negligible adsorption of the target compounds on the catalyst’s surface (600 mg L−1
of PEF/TiO2 20 wt%) was observed.

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Figure 5. Effect of TiO2 amount immobilization at the efficiency of the anti-inflammatory drug
mixture degradation under SSL, ( ) ACM; ( ) IBU; ( ) DCF; ( ) variation of degradation kinetic
a
b
c
d
rate (k) versus TiO2 % content, (Co(drug) = 5 mg L−1); and (C(catalyst) = 600 mg L−1).
2.2.2. Effect of Drug Concentration
Additionally, experiments were conducted in order to investigate the effect of the initial
concentration of the mixture (2.5–10 mg L−1 of each compound), keeping the rest of the parameters
constant. According to the results (Figure 6a), an increase in the concentration of the mixture
leads to a decrease in the photocatalytic rate constants that could be attributed to the lower ratio
of active oxidative species to the substrate molecules, which has also been reported elsewhere [48–50].
The concentration of 5 mg L−1 for each drug was selected for further experiments and the effect of
several parameters to pollutants removal was evaluated, since this concentration enables the proper
monitoring of the degradation kinetics. The degradation curves obtained for each drug are given in
detail in the Supplementary Materials (Figure S1).
2.2.3. Effect of Catalyst Loading
Different concentrations of PEF/TiO2 20% catalyst, ranging from 400 to 1000 mg L−1
were employed, in order to study the effect of catalyst’s concentration on the degradation of
the mixture (Figure 6b). The detailed degradation curves are given in the Supplementary Materials
(Figure S2). Generally, when increasing the concentration of the catalyst, the surface of the particles
also increases, making available a higher number of active sites for adsorption and generation of
the oxidant species, until an optimum catalyst mass corresponding to the maximum absorption
,

Molecules 2019, 24, 564
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of photons reaching the catalytic bed. Figure 6b represents the results of the above study.
Obviously, until 800 mg L−1, as the concentration rises, there is an increase at the rate constant of
each compound. Above the concentration until 800 mg L−1, the rate constant either reaches a plateau
(for ACM) or decreases (for IBU and DCF).
2.2.4. Effect of pH
During the heterogeneous photocatalytic treatment, the pH of the semiconductor’s solution
can be a determining factor for the efficiency of the whole procedure. The pH value affects the charge
of the catalyst’s surface, as well as the reactant’s charge and cause either electrostatic repulsion or
attraction between them [51
,52]. In our case, TiO2 is amphoteric and consequently and its point of
zero charge (pzc) is widely reported at pH
∼
6.7. Therefore the TiO2 surface is positively charged in
acidic media (pH < 6.7), whereas it is negatively charged under alkaline conditions (pH > 6.7) [53].
Additionally, the PEF polymeric immobilization of TiO2 may be charged as either negative or positive,
since its furanic ring or carboxyl groups are pH dependent. For example, the carboxylic acid groups are
feasibly ionized to release the protons under basic condition and the carboxylate anion and the proton
tend to combine under acidic condition [54].
Figure 6. The effect of operational parameters on degradation kinetic rate (k) of anti-inflammatory
drug mixture, (
catalyst loading (Co(drug) = 5 mg L−1); and (
(Co(drug) = 5 mg L−1, C((PEF/TiO2 20wt %) = 600 mg L−1).
a
) effect of mixture concentration (C(PEF/TiO2 20 wt% = 600 mg L−1); (
b
) effect of
c) effect of pH, during photocatalytic treatment

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As presented at Figure 6c, the effect of pH on the photocatalytic degradation of
the anti-inflammatory drug mixture was studied for pH values ranging from two to 10. The effect
of pH for each drug is also given at Supplementary Materials (Figure S3), expressed as degradation
curves. For very acidic conditions (pH 2) the degradation kinetics are obviously slow for all the studied
compounds. This is probably attributed to the combined effect of the protonation process and the H+
excess in the solution, which does not favor the generation of hydroxyl radicals [55]. For ACM
the degradation kinetic increases by the increase of pH until pH 8. For very basic pH, there is a small
decrease. The pKa of ACM is 9.71 [56], which means that it is presented in cationic form for pH < 9.71,
therefore, when the catalyst is negatively charged (pH > 6.7), there is the maximum adsorption of
ACM to the catalyst’s surface, which is pH 8 in our study. In the case of IBU, the higher reaction
rate was observed for acidic pH (pH = 4), which is consistent with findings that acidic conditions
favor IBU degradation [57]. IBU is a weakly acidic compound with pKa = 4.8 [58], so at pH values
that exceeded its pKa, the molecule was present in its an-ionic form, which decreases the efficiency of
the photocatalytic treatment.
Finally, for DCF, there were no significant differences as far as the degradation kinetic is concerned
for pH, 4.8 and 10. The pKa of DCF is approximately 4.50 [59], so at pH 6, which is close to pzc of
TiO2, it is probably negatively charged that does not favor the adsorption on the catalyst’s surface.
The increase at pH 8 and 10, compared to pH 6, for IBU and DCF can be explained by the increase in
generation of hydroxyl radicals, which is favoured at basic conditions [55]. For further experiments,
the inherited pH (approximately pH = 4) was selected.
2.2.5. Mineralization Process
In order to assess the efficiency of PEF/TiO2 20% for the degradation of the anti-inflammatory
drug mixture, mineralization studies were conducted. The concentration of each drug was 5 mg L−1
,
while the concentration of the catalyst was 600 mg L−1. The mineralization was studied for 360 min
of irradiation (Figure 7). Although, all compounds degrade quite fast (during the first 90 min of
treatment), TOC removal follows a slow rate reaching approximately 50% decrease after 360 min,
demonstrating that the photocatalytic treatment needs prolonged irradiation times for leading to
complete mineralization. This is probably due to the transformation products formed from the degradation
of parent compounds. The chloride ions released from the degradation of DCF, reaches almost 100%
from the first 120 min of treatment, probably indicating that the transformation products released are
chloride-free or that the transformation products of DCF also degrade quickly. Nitrite ions were also
released during the photocatalytic treatment, from the degradation of DCF and ACM. Their release
reached approximately 70% at the 240 min of irradiation, while no nitrate ions are observed.

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Figure 7. The effect of operational parameters on degradation kinetic rate (k) of anti-inflammatory
drug mixture, ( ) effect of
) effect of mixture concentration (C(PEF/TiO2 20 wt% = 600 mg L−1); (
catalyst loading (Co(drug) = 5 mg L−1); and (
) effect of pH, during photocatalytic treatment
a
b
c
(Co(drug) = 5 mg L−1, C((PEF/TiO2 20 wt%) = 600 mg L−1).
2.2.6. By-Product eValuation
An attempt to identify the TPs generated by the heterogeneous photocatalytic degradation
of the anti-inflammatory drug mixture by PEF/TiO2 20 wt% under SSL was also conducted.
The data obtained by high-resolution mass spectra, are given by Table 2. In this study, five TPs
generated during IBU photodegradation were identified (Figure 8).
Table 2. High resolution mass spectra data for IBU, DCF, and ACM and their identified TPs derived
from mass spectrometric analysis.
tR
(min)
Pseudo-Molecular
Ion Formula
Theoretical
m/z [m − H]
Experimental
m/z [m − H]
∆
Code Name
RDBE
−
−
(ppm)
14.41
12.56
12.50
12.02
9.45
IBU
C13 H17 O2
C13 H17 O3
C12 H15 O2
205.1229
221.1178
191.1072
175.1123
133.0653
149.0603
205.1233
221.1183
191.1078
175.1129
133.0660
149.0610
5.5
5.5
5.5
5.5
5.5
5.5
4.844
4.880
5.985
6.615
9.082
8.681
I-TP1
I-TP2
I-TP3
I-TP4
I-TP5
C12 H15
O
C9 H9 O
C9 H9 O2
8.87
tR
(min)
Pseudo-Molecular
Ion Formula
Theoretical
Experimental
∆
Code Name
RDBE
m/z [m + H]+
m/z [m + H]+
(ppm)
14.26
12.38
12.96
8.81
16.84
6.15
15.96
11.98
14.02
12.70
5.18
DCF
D-TP1a
D-TP1b
D-TP2
D-TP3
D-TP4
D-TP5
D-TP6
D-TP7
D-TP8
ACM
C14H12Cl2NO2
C14 H12 O3 N Cl2
C14 H12 O3 N Cl2
C6 H6 O N Cl2
C14H10O3NCl2
C14H12O4 NCl2
C14H10O2NCl2
C13H10ONCl2
C13H10O2NCl2
C13H8Cl2NO2
C8 H10 O2 N
296.0245
311.0116
311.0116
177.9825
310.0038
328.0138
294.0089
266.0167
282.0062
280.0013
152.0712
296.0233
312.0180
312.0180
177.9812
310.0026
328.0132
294.0072
266.0123
282.0074
280.0055
152.0696
8.5
8.5
8.5
3.5
9.5
8.5
9.5
8.5
8.5
9
−2.231
−2.805
−2.805
−5.033
−2.016
−1.798
−3.777
−4.120
−3.229
0.941
4.5
−6.609

Molecules 2019, 24, 564
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Table 2. Cont.
4.48
4.70
3.30
3.80
3.98
4.65
A-TP1a
C8 H10 O3 N
C8 H10 O3 N
C8 H10 O4 N
C8 H10 O4 N
C8 H10 O4 N
C8 H10 O4 N
168.0661
168.0661
184.0610
184.0610
184.0610
184.0610
168.0647
168.0647
184.0598
184.0598
184.0598
184.0598
4.5
4.5
4.5
4.5
4.5
4.5
−4.877
A-TP1b
A-TP2a
A-TP2b
A-TP2c
A-TP2d
−4.877
−3.446
−3.446
−3.446
−3.446
Figure 8. TPs products generated from IBU by PEF/TiO2 20 wt% under SSL.
According to the generated TPs, IBU mostly goes under degradation by hydroxylation,
demethylation, decarboxylation, cleavage of isobutyl moiety, and oxidation of hydroxyl groups.
The TPs generated from the degradation of IBU are in accordance to those obtained in previous studies
by the oxidation techniques [60–65].
Initially, HO
TP, induced decarboxylation and formation of I-TP3, which was further transformed to I-TP4.
Additionally, a methyl group of IBP molecule was attacked by HO to form a demethylated
•
attack IBP molecule to form mono-hydroxylated species (I-TP1). The above
•
intermediate (I-TP2). In another third pathway, detachment of isobutyl group occurs, which leads to
the formation of 2-phenylpropanoic acid (I-TP5). The evolution profiles of the above TPs are given in
Figure 9. TPs emerged within the first 15 min of irradiation and remained abundant in the solution
for 120 min of the applied.
In the case of DCF, nine TPs were identified (Figure 10). DCF transformation under oxidizing
experimental conditions appears to proceed mainly by oxidation and hydroxylation reactions
between chloroaniline and phenylacetic acid. The reaction of HO with the aromatic ring forms
•
a resonance-stabilized carbon-centered radical with the subsequent elimination of hydrogen radical,
leading to the formation of the mono hydroxylated species (D-TP1,a,b). These mono hydroxylated
TPs were further oxidized, resulting in the production of D-TP4 and D-TP5, while D-TP6 and their
decarboxylated derivatives were formed by the loss of their carboxylic moiety. TP6 was probably
further transformed to D-TP7 and D-TP8. Furthermore, the presence of D-TP3 suggests that one
(of the four) monohydroxylated derivatives is further oxidized into the correspondent keto-derivative.
Additionally, the formation of D-TP2 indicates the cleavage of the C–N bond of DCF as a preferential
route, which originated from a series of C–N cleavage products. D-TP1,a,b and D-TP2 were
mainly detected, at higher relative intensities compared to the other TPs, so only their eVolution
profiles were obtained, depicted in Figure 11. All are detected by the first 10 min of the process.
D-TP2 has a maximum at 120 min. D-TP1,a,b decrease after the first 10 min, reaching undetectable

Molecules 2019, 24, 564
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levels at 180 min. The proposed degradation pathway has also been indicated by several studies
regarding DCF oxidation [66,67].
Figure 9. Evolution profiles of TPs generated from IBU by PEF/TiO2 20 wt% under SSL,
−1
C0(drug) = 5 mg L−1, and C(PEF/TiO2 20 wt%) = 600 mg L
.
Figure 10. TPs products generated from DCF by PEF/TiO2 20 wt% under SSL.

Molecules 2019, 24, 564
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Figure 11. Evolution profiles of TPs generated from DCF by PEF/TiO2 20 wt% under SSL,
−1
C0(drug) = 5 mg L−1, and C(PEF/TiO2 20 wt%) = 600 mg L
.
In this study, hydroxylation can be considered as the main pathway of ACM
transformation, since both the mono and di-hydroxylated derivatives of ACM have been identified
(A-TP1,a,d and A-TP2,a,b,c,d) (Figure 12). The oxidation and subsequent degradation of ACM
via hydroxylation is also proposed by several studies over ACM degradation [68,69].
Figure 12. TPs products generated from ACM by PEF/TiO2 20 wt% under SSL.
The generated TPs present a peak at 120 min and are eliminated completely at 240 min of
the photocatalytic procedure, as indicated in Figure 13.
All in all, the generated HO from PEF/TiO2 20% TiO2 under SSL, appear to be the main reactive
•
specie to the photocatalytic degradation of all the three studied compounds in the anti-inflammatory
drug mixture.

Molecules 2019, 24, 564
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Figure 13. Evolution profiles of TPs generated from ACM by PEF/TiO2 20 wt% under SSL.
2.2.7. Reusability Studies
From practical point of view, the stability of photocatalysts is an essential qualification feature.
For this reason, the reusability of PEF/TiO2 20% wt% was studied in three utilization cycles under
simulated solar irradiation. The experimental procedure was similar to that described in Section 3.5,
but in this case, after each reaction, the material was rinsed with water and dried in an oven at 50 ◦C
for 8 h before being reused in two additional consecutive photocatalytic experiments. It can be
found that there is no significant change in the rate constants of the three target drugs in the three
consecutive experiments. According to the results a reduction in the rate constant between 12% and 18%
was observed in the third run with respect to the second run for all the studied compounds, indicating
the good stability of these materials under the applied reaction conditions, which is attributed to
the enhanced binding nature of PEF towards TiO2.
3. Materials and Methods
3.1. Materials
2,5-furan dicarboxylic acid (purum 97%), ethylene glycol anhydrous 99.8% (EG), tetrabutyltitanate
(TBT) catalyst of analytical grade, Ibuprofen (IBU), acetaminophen (ACM) and diclofenac (DCF)
sodium were obtained from Sigma-Aldrich (Steinheim, Germany). Titanium dioxide P25 from Evonik
(Marl, Germany) (particle size 20–30 nm; crystal structure: ~80% anatase and 20% rutile; surface area:
56 m2/g, zero point of charge ~6.3–6.8) was used as photocatalyst. LC-MS-grade methanol was supplied
by Merck (Athens, Greece). Ultrapure water for the experiments was obtained from a Millipore Waters
Milli-Q water purification system (Merck SA Hellas, Athens, Greece).
3.2. Polyester Synthesis
PEF was synthesized through the two-stage melt polycondensation (esterification
and polycondensation) in a glass batch reactor, as described in our previous work [70].
2,5-dimethylfuran-dicarboxylate (DMFD) was prepared using 2,5-FDCA, anhydrous methanol
and concentrated sulfuric acid, as described previously [70]. DMFD and ethylene glycol in
a molar ratio of diester/diol = 1/2.2 were charged into the reaction tube of the polyesterification
apparatus with 400 ppm of TBT. The reaction mixture was heated at 150 ◦C under argon flow for 2 h
◦
◦
and stirring speed 350 rpm, at 160 C for an additional 2 h and finally at 170 C for 1 h. This first
step (transesterification) is considered complete after the collection of almost all the theoretical

Molecules 2019, 24, 564
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amount of CH3OH, which was removed from the reaction mixture by distillation and collected
in a graduate cylinder. In the second step of polycondensation, vacuum (5.0 Pa) was applied
slowly over a time of about 30 min to remove the excess of diol, to avoid excessive foaming
and to minimize oligomer sublimation, which is a potential problem during the melt polycondensation.
◦
The temperature was gradually increased (1 h) to 220 C, while stirring speed was also increased
to 720 rpm. The reaction continued at ◦this temperature for 2 h. Subsequently, the temperature
◦
was increased to 230 C for 2 h and to 240 C for an additional 1 h. After the polycondensation reaction
was completed, the polyesters were removed from the reactor, milled, and washed with dissolution in
TFA/chloroform 1/4 v/v and precipitation in cold methanol.
3.3. Photocatalyst Preparation
PEF nanocomposites with TiO2 were prepared by the solution mixing method, with a mixture of
dicloromethane/chloroform/trifluoroacetic acid as a mutual solvent. The desired amount of nanofiller
was first added into the solvent at a concentration of 1 mg/mL, and the mixture was subjected
to sonication for 1 h to obtain a uniform dispersion. At the same time, PEF was completely
dissolved in the solvent mixture at a concentration of 20 mg/mL. The PEF solution was then mixed
with the nanofiller suspension followed by stirring and sonication for 30 min. The solvent was allowed
to eVaporate in air for three days with slight stirring for the first day and then at 50 ◦C for two days
under a vacuum. After complete solvent removal, the nanocomposites were obtained in the form
◦
of powder. Powder was melt pressed in a hot press at 220 C for 10 min in order to obtain films
with 1 mm thickness. According to this procedure PEF/nTiO2 nanocomposite films containing 5, 10,
15, and 20 wt% TiO2 were obtained.
3.4. Photocatalyst Characterization
Number-average molecular weight (Mn) of PEF was measured by Gel permeation
chromatography (GPC) using a Waters 150 ◦C apparatus (Milford, MA, USA) equipped with
differential refractometer as a detector and three ultrastyragel (103, 104, 105 Å) columns ◦in
series. Hexafluoroisopropanol was used as mobile phase at a flow rate 0.5 mL/min at 40 C.
Calibration was performed using polystyrene standards with a narrow molecular weight distribution.
Fourier transform infrared spectroscopy (FTIR) spectra of all the samples were obtained using
a Perkin-Elmer FTIR spectrometer (Dresden, Germany), model Spectrum One, with the use of KBr
discs. The IR spectra were obtained in absorbance mode and in the spectral region of 400–4000 cm−1
using a resolution of 4 cm−1 and 64 co-added scans.
Wide-Angle X-ray Diffraction (WAXD) patterns of the samples were recorded using a MiniFlex
II XRD system from Rigaku Co (Chalgrove, Oxford, UK), with CuKα radiation (λ = 0.154 nm) in
the angle 2θ range from 5 to 60 degrees.
For thermal analysis measurements a Perkin-Elmer (Dresden, Germany), Pyris Diamond
differential scanning calorimetry (DSC), coupled with an Intracooler 2P cooling accessory, was used.
Samples of 10
±
0.1 mg sealed in aluminium pans were used to test the thermal behavior of
◦
◦
the polyesters. The samples were heated from 30 C to 300 C in a 20 mL/min flow of N2 with heating
◦
rate 20 C/min in order to observe the melting temperature of the as received polyesters. The samples
first were held at that temperature for 2 min, then quenched and rescanned again until 300 ◦C.
Thermogravimetric analysis (TGA) measurements were carried out by a STA 449C
(Netzsch-Gerätebau, GmbH, Selb, Germany) thermal analyzer from room temperature up to 600 ◦C
with 20 ◦C/min heating rate and 30 mL/min flow of N2 (99.9%).
Scanning electron microscopy (SEM) was carried out using a JEOL JMS-840A scanning microscope
(Tubney WoodsAbingdon, Oxfordshire, UK) was equipped with an energy-dispersive X-ray (EDX)
Oxford ISIS 300 micro-analytical system.

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3.5. Photocatalytic Degradation Experiments
Photocatalytic experiments under UV-Vis irradiation were carried out in a solar simulator
Atlas Suntest CPS+ (Linsengericht, Germany). Illumination was provided with a xenon lamp
(1.5 kW) at an irradiance of 700 W m−2. Irradiation experiments were performed using a Pyrex glass
reactor containing 100 mL of aqueous solutions, at various amounts of catalyst (400–1000 mg L−1),
while the pH ranged from two to 10. The effect of pH was studied by adjusting the solutions
with HCl 0.01 M and NaOH 0.01 M. Higher initial concentration of drugs (5 mg L−1 of each)
than the typical values found in environmental samples has been selected in the experiments in order to
obtain slower kinetics and to facilitate the follow-up of the mineralization. The suspensions were kept
in the dark for 30 min, prior to illumination, to reach adsorption equilibrium onto the semiconductor
surface. Samples were taken at different time intervals, they were filtered on syringe nylon membrane
filters (0.22 µm pore-size) and they were analyzed by LC-MS, as described in the following sections.
3.6. Analytical Procedures
3.6.1. Kinetic Studies
Drug concentrations were quantified by a HPLC system consisted of a SIL 20A autosampler
and a LC-20AB pump both from Shimadzu (Kyoto, Japan). The analytical column used
was a C18, 150
×
4.6 mm with 3.5 µm particle size (Pathfinder, Shimadzu Scientific Instruments,
Columbia, SC, USA) thermostated at 40 ◦C. The detector used was SPD 20A DAD coupled in a series
with the LC-MS 2010EV mass selective detector, equipped with an atmospheric pressure electrospray
ionization source (ESI) in a negative ionization (NI) and positive ionization (PI) mode. A mixture
of LC-MS grade water
−
0.1% formic acid and methanol with a flow rate of 0.4 mL min−1 was used
as eluent. The time program of the binary mobile phase was: initially 40% methanol, after 5 min
changed to 95% methanol and kept stable for 5 min, finally returned to 40% methanol at 12 min.
The injection volume was 20◦ µL and the total run analysis lasted 15 min. The drying gas was operated
at flow 10 L min−1 at 200 C. The nebulizing pressure was 100 psi, the capillary voltage
−
3500 V
for negative ionization and 4500 V for positive ionization, while the fragmentation voltage was set
at 1.65 V. DCF and ACM were detected at PI mode, with retention time 10.23 and 3.97 min
and 296 and 151 m/z precursor molecular ions, respectively. IBU was detected at NI mode at 11.43 min
retention time and 205 m/z precursor molecular ion, respectively.
3.6.2. By-Product eValuation
The intermediates formed during the drug mixture photodegradation were characterized by
an LTQ Orbitrap Discovery MS high-resolution system operating in the positive and negative ionization
mode. The chromatographic analysis was run on an Acquality UPLC HSS T3 column (100 × 2.1 mm,
1.8 µ
m, Waters, Milford, MA, USA) maintained at a constant temperature of 40 ◦C. Water (phase A)
and methanol (phase B) was used as mobile phases at a flow rate of 500 L min−1. A linear gradient
progressed from 90% A (initial conditions) to 0% A in 14 min, followed by a linear gradient to 90% A
in 20 min. The ESI-source parameters were as follows: Sheath and auxiliary gas flow rate 40 and eight
(nitrogen, arbitrary units), respectively; source voltage at 3.60 kV; capillary temperature was maintained
◦
at 320 C. For the fragmentation study, the voltage of the HCD collision cell was set at 40 eV. A resolving
power of 30,000 was applied and the Orbitrap mass analyzer was externally calibrated (mass accuracy
within
±
5 ppm). Chemical compositions and accurate masses of the protonated molecules and their
fragments were calculated by Xcalibur software (ThermoFisher Scientific, Waltham, MA, USA).
3.6.3. Mineralization Studies
In order to eValuate the efficiency of the photocatalytic procedure, total organic carbon
(TOC) on filtered suspensions (0.22
µm), was evaluated by a Shimadzu TOC V-csh Analyzer
equipped with a non-dispersive infrared detector. Ion chromatography (Metrohm) was also used,

Molecules 2019, 24, 564
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equipped with an automatic sampler was used for the determination of NO2−, NO3−, and Cl−
ions. The analytical column used was a Metrosep A Supp 4 (250
×
4.0 mm) with 9 µm particle size.
The eluent used was Na2CO3 1.8 mM-NaHCO3 1.7 mM with a flow rate of 1 mL min−1. The total run
analysis lasted 20 min, while the injection volume was 20 µL.
4. Conclusions
Effective photocatalysts have been prepared using biobased poly(ethylene furanoate)
polymer and high concentrations of TiO2 nanoparticles. As was found from SEM-EDX analysis,
the dispersion of nanoparticles was fine inside the polymer matrix and its thermal stability
was substantially enhanced. The crystal structure of PEF was not affected from TiO2 addition
due to the lack of interactions between inorganic nanoparticles and organic polymer matrix.
Photodegradation experiments were also conducted for a mixture commonly found in wastewaters,
anti-inflammatory/analgesic drug mixture. The parameters affecting the photodegradation procedure
were optimized for the most efficient synthesized photocatalyst (20% PEF/TiO2) and mineralization
study was conducted. TOC removal reaches 50% decrease after 360 min of photocatalytic procedure,
demonstrating that the photocatalytic treatment needs prolonged irradiation times for leading
to complete mineralization. Finally, the TPs generated during the procedure were identified by
high-resolution mass spectrometry and their eVolution profiles were given. Reutilization experiments
proved that the 20% PEF/TiO2 have good stability and reusability. The present study provides some
important new insights for the use of PEF/TiO2 materials as promising alternatives to powder TiO2
catalysts for the degradation of organic contaminants.
Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/24/3/564/s1,
Figure S1: Effect of drug concentration (C(PEF/TiO2 20 wt% = 600 mg L-1); (a) ACM; (b) IBU; (c) DCF.; Figure S2:
The effect PEF/TiO2 20 wt% loading (C0(drug)=5 mg L-1); (a) ACM; (b) IBU; (c) DCF; Figure S3: Effect of pH,
during photocatalytic treatment (Co(drug) = 5 mg L-1, C((PEF/TiO2 20 wt%) = 600 mg L-1); (a) ACM; (b) IBU;
(c) DCF.
Author Contributions: Methodology, A.K.; Validation, A.K., Z.T.; Investigation, A.K., Z.T., G.Z.K.;
Writing-Original Draft Preparation, A.K., G.Z.K, D.N.B., D.A.L.; Writing-Review & Editing, A.K., G.Z.K, D.N.B.,
D.A.L.; Supervision, D.A.L.; Project Administration, D.A.L.
Funding: This research has been co-financed -via a programme of State Scholarships Foundation (IKY)-
by the European Union (European Social Fund-ESF) and Greek national funds through the action entitled
”Strengthening Human Resources Research Potential via Doctorate Research” in the framework of the Operational
Programme ”Human Resources Development Program, Education and Lifelong Learning” of the National
Strategic Reference Framework (NSRF) 2014–2020.
Conflicts of Interest: The authors declare no conflict of interest.
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