Supplementary Materials Photocatalytic Degradation

Supplementary materials – Photocatalytic degradation

Optimization and in-line potentiometric monitoring of enhanced photocatalytic degradation kinetics of Gemifloxacin using TiO2 nanoparticles/H2O2

FawziaIbrahima, Medhat A. Al-Ghobashyb,c,*, Mohamed K. Abd El-Rahmanb and Ibrahim F. Abo-Elmagda

aAnalytical Chemistry Department, Faculty of Pharmacy, Mansoura University, Egypt

b Analytical Chemistry Department, School of Pharmacy, New Giza University, Egypt

c Bioanalysis Research Group, Faculty of Pharmacy, Cairo University, Egypt

*Correspondence:

Dr. Medhat A. Al-Ghobashy, Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo 11562, Egypt

E-mail:

Analysis techniques

RP-HPLC using isocratic elution

HPLC separation was performed using Zorbax Eclipse XDB-C18 column, 5.0 μm, 4.6× 250.0 mm (Agilent Technologies, USA) with an isocratic elution of the mobile phase composed of 10 mM ammonium acetate (pH 3.5): acetonitrile (70:30 v/v). Analysis was employed at a flow rate of 1.0 mL/min, and detection was achieved at 270 nm.

TLC-Densitometry

All TLC plates were developed using a mobile phase as mixture of methanol: ammonia 33%: ethyl acetate : acetonitrile in the ratio of (1:1:2:1 v/v/v/v). Linear ascending plate development was performed in a suitable chromatographic chamber previously saturated for 30min with the developing mobile phase. The length of band was 6mm and the densitometric scanning was performed at 270 nm.

III. Preliminary photodegradation experiments

Various methods for removal of FQs are based on chemical oxidation including advanced oxidation processes (AOPs)(Ikehata et al. 2006), Fenton oxidation(Guinea et al. 2009), ozonation(Ikehata et al. 2006), and photocatalysis(Paul et al. 2010). One of the most commonly used technologies isthe ultraviolet (UV) radiation technology which is very attractive due to its low cost, simple operation, minimal consumption of chemicals and applicability for a wide range of environmental pollutants(Ou et al. 2016, Santoke et al. 2015).

Throughout the preliminary experiments, aliquots of 25 mL of different buffered GEM solution with 100.00 µg/mL were placed in Petri dishes. Then the reaction mixture was subjected to UV irradiation;either alone or in the presence of additives as described below while stirring at low speed.Samples were completed to volume (25 mL), stored frozen, protected from light until the analysis.

As shown at Figure S1, the photodegradation process using UV only was pH dependent and effective for GEM degradation. Results demonstrated that at pH 7.0and pH 10.0degradation was higher than that at pH 4.0. This indicated clearly that the pH is an important factor to consider during optimization of photocatalytic degradation of GEM.

Gallic acid- photocatalyzed degradation

Gallic acid (GA) is one of the mainconstituents of tea leaves and herbal roots that has pro-oxidant effects(Quici &Litter 2009, Yen et al. 2002). It has been reportedthat UV irradiation in the presence of GA can lead to the generation of reactive oxygen species(Abd‐ElSalam et al. 2016, Benitez et al. 2005, Du et al. 2014). This was previously employed by our research group to prepare GA-coated magnetic nanoparticles with photocatalytic activity (Nadim et al. 2015) for degradation of Meloxicam in industrial waste water. In this study, using GA as additive did not lead to degradation of the pharmacophore of GEM.

In this experiment, we studied the effect of enhancing the photodegradation process with GA. Aliquots of 25 mL of different buffered GEM solutions with 100.00 µg/mL concentration and 0.4 mg/mL gallic acid were placed in Petri dishes. Then the reaction mixture was subjected to UV irradiation while stirring at low speed.Samples were completed to volume (25 mL), stored frozen, protected from light until the analysis.As shown in Figure S1, the photodegradation process using UV-GA hasminimal effect on GEM pharmacophore with the highestpercentage degradation at pH 10.

Titanium dioxide - photocatalyzed degradation

Titanium dioxide (TiO2) is considered a predominant photocatalyst for treatment of water pollution and has been recently applied for the remediation of fluoroquinolones.TiO2NPwas investigated because of its novel properties; economic, non-toxic,commercially available, and chemical and biological inertness(Sturini et al. 2012).It was reported that the photocatalytic processes using TiO2has high efficiency through degradation of many organic pollutants and pharmaceuticals(Kim &Choi 2005, McCullagh et al. 2007, Nadim et al. 2015, Nakata &Fujishima 2012).

Throughout this study, aliquots of 25 mL of buffered GEM solutions with 100.00 µg/mL concentration and 0.8mg/mL TiO2NP were placed in Petri dishes. Then the reaction mixture was subjected to UV irradiation while stirring at low speed. At the end of the incubation period, samples were filtered through 0.2 μm syringe filter.Samples were completed to volume (25 mL), stored frozen, protected from light until analysis.The results of this trial clearly indicated that TiO2 can efficiently catalyze the photodegradation of GEM in the presence UV irradiation as shown in Figure S1 especially at pH 7.0 and 10.0.However, appearance of peaks corresponding to degradation products of closely related physicochemical properties indicated that the pharmacophore has not been fully degraded in this experiment.

Titanium dioxide/Gallic acid - photocatalyzed degradation

In this experiment, TiO2NP and GAwere combined in one experiment. Throughout this study, aliquots of 25 mL of buffered GEM solutionsof100.00 µg/mL concentration, GA 0.4mg/mL and 0.8mg/mL TiO2NP were placed in Petri dishes. Then the reaction mixture was subjected to UV irradiation while stirring at low speed. At the end of the incubation period, samples were filtered through 0.2 μm syringe filter then completed to volume (25 mL), stored frozen, protected from light until the analysis.TLC results shows that samples of UV/TiO2/GAhave a lowerpercentage degradation than UV/TiO2 alone. This could be attributed to the photodegradation of GA itself and possible overlap in peak area with the target analyte(Figure S1). Figure S2 shows that degradation at pH 10.0was the highest among the studied pH values.

Titanium dioxide/H2O2 - photocatalyzed degradation

In order to develop a suitable and rapid effective method, we enhanced photodegradation process with H2O2 to generate hydroxyl radicals (OH•) that lead to nonselective oxidation of FQs with high mineralization rate.Throughout this study, aliquots of 25 mL of different buffered GEM solutions with 100.00 µg/mL concentration and 0.8mg/mL TiO2NP were placed in Petri dishes. H2O2(2 mM) was then added and the reaction mixture was subjected to UV irradiation while stirring at low speed. At the end of the incubation period, samples were filtered through 0.2 μm syringe filter, sodium sulfite was added to stop the reaction as previously described (Liu et al. 2003).The amount of sodium sulfite required to stop the reaction in these experiments were calculated to be stoichiometrically equivalent to the added H2O2 (1:1 M ratio), The stoichiometric dose needed of sodium sulfite to accurately quench 1 mg/L H2O2was 3.7 mg/L.As per our preliminary studies; amounts of 6.3, 3.9 and 1.5 mg sodium sulfite were found sufficient to quench 2, 1.25 and 0.5 mM H2O2, respectively.Then samples were completed to volume (25 mL), stored frozen, protected from light until the analysis.As shown in Figure S3 and S4, the addition of hydrogen peroxide (UV/TiO2/H2O2) resulted in the highestpercentage degradation results among the preliminary experiments. H2O2 concentration was found a critical factor in order to track the differences between different sets of experimental conditions while designing our experiments.

Figure S1: Scanned TLC plate showing the peaks obtained from photodegraded sample of GEM (100.00 μg/mL) upon irradiation with UV light for 3 h:1)with 0.4 mg/mL gallic acid in water, 2) UV onlyat pH 4.0, 3)UV only at pH 7.0, 4)UV only at pH 10.0, 5)with 0.4 mg/mL gallic acid at pH 4.0, 6)with 0.4 mg/mL gallic acid at pH 7.0, 7) with 0.4 mg/mL gallic acid at pH 10.0, 8)in the presence of 0.8 mg/mL TiO2NP at pH 4.0, 9)in the presence of 0.8 mg/mL TiO2NP at pH 7.0, 10)in the presence of 0.8 mg/mL TiO2NP at pH 10.0, 11) with 0.4 mg/mL gallic acid in the presence of 0.8 mg/mL TiO2NP at pH 4.0, 12) with 0.4 mg/mL gallic acid in the presence of 0.8 mg/mL TiO2NP at pH 7.0 and 13) with 0.4 mg/ml gallic acid in the presence of 0.8 mg/mL TiO2NP at pH 10.0.

Figure S2: HPLC chromatogram showing the result of photodegradation of GEM (100.00 μg/mL) upon exposure to UV light for 3 h in the presence of 0.8 mg/mL TiO2NP and 0.4 mg/mL Gallic acid (A) at pH 4.0 and (B) at pH 7.0 and (C) at pH 10.0.

Figure S3: Scanned TLC plate showing the peaks obtained from standard sample of GEM (100.00 μg/mL) 1)at pH 4.0, 2)at pH 7.0, 3)at pH 10.0 and obtained from photodegraded sample of GEM (100.00 μg/mL) upon exposure to UV light for 3 h 4)with 0.4mg/mL gallic acid, 5) with 2mM H2O2 in the presence of 0.8 mg/mL TiO2NP at pH 4.0, 6) with 2mM H2O2 in the presence of0.8 mg/mL TiO2NP at pH 7.0 and 7) with 2mM H2O2 in the presence of 0.8 mg/mL TiO2NP at pH 10.0.

Figure S4: HPLC chromatogram showing the result of photodegradation of GEM (100.00 μg/mL) upon exposure to UV light for 3 h in the presence of 0.8 mg/mL TiO2NP and 2mM H2O2 (A) at pH 4.0 and (B) at pH 7.0 and (C) at pH 10.0.

References

Abd‐ElSalam HAH, Al‐Ghobashy MA, Al‐Shorbagy M, Nassar N, Zaazaa HE, Ibrahim MA (2016): Correlation of in vivo and in vitro assay results for assessment of free radical scavenging activity of green tea nutraceuticals. Journal of food science 81, C1707-C1715

Benitez FJ, Real FJ, Acero JL, Leal AI, Garcia C (2005): Gallic acid degradation in aqueous solutions by UV/H 2 O 2 treatment, Fenton's reagent and the photo-Fenton system. Journal of hazardous materials 126, 31-39

Du Y, Chen H, Zhang Y, Chang Y (2014): Photodegradation of gallic acid under UV irradiation: Insights regarding the pH effect on direct photolysis and the ROS oxidation-sensitized process of DOM. Chemosphere 99, 254-260

Guinea E, Brillas E, Centellas F, Cañizares P, Rodrigo MA, Sáez C (2009): Oxidation of enrofloxacin with conductive-diamond electrochemical oxidation, ozonation and Fenton oxidation. A comparison. Water research 43, 2131-2138

Ikehata K, Jodeiri Naghashkar N, Gamal El-Din M (2006): Degradation of aqueous pharmaceuticals by ozonation and advanced oxidation processes: a review. Ozone: Science and Engineering 28, 353-414

Kim S, Choi W (2005): Visible-light-induced photocatalytic degradation of 4-chlorophenol and phenolic compounds in aqueous suspension of pure titania: demonstrating the existence of a surface-complex-mediated path. The Journal of Physical Chemistry B 109, 5143-5149

Liu W, Andrews SA, Stefan MI, Bolton JR (2003): Optimal methods for quenching H 2 O 2 residuals prior to UFC testing. Water Research 37, 3697-3703

McCullagh C, Robertson JM, Bahnemann DW, Robertson PK (2007): The application of TiO 2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review. Research on Chemical Intermediates 33, 359-375

Nadim AH, Al-Ghobashy MA, Nebsen M, Shehata MA (2015): Gallic acid magnetic nanoparticles for photocatalytic degradation of meloxicam: synthesis, characterization and application to pharmaceutical wastewater treatment. RSC Advances 5, 104981-104990

Nakata K, Fujishima A (2012): TiO 2 photocatalysis: design and applications. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 13, 169-189

Ou H-s, Ye J-s, Ma S, Wei C-h, Gao N-y, He J-z (2016): Degradation of ciprofloxacin by UV and UV/H 2 O 2 via multiple-wavelength ultraviolet light-emitting diodes: Effectiveness, intermediates and antibacterial activity. Chemical Engineering Journal 289, 391-401

Paul T, Dodd MC, Strathmann TJ (2010): Photolytic and photocatalytic decomposition of aqueous ciprofloxacin: transformation products and residual antibacterial activity. Water Research 44, 3121-3132

Quici N, Litter MI (2009): Heterogeneous photocatalytic degradation of gallic acid under different experimental conditions. Photochemical & Photobiological Sciences 8, 975-984

Santoke H, Tong AY, Mezyk SP, Johnston KM, Braund R, Cooper WJ, Peake BM (2015): UV Photodegradation of Enoxacin in Water: Kinetics and Degradation Pathways. Journal of Environmental Engineering 141, 04015027

Sturini M, Speltini A, Maraschi F, Profumo A, Pretali L, Irastorza EA, Fasani E, Albini A (2012): Photolytic and photocatalytic degradation of fluoroquinolones in untreated river water under natural sunlight. Applied Catalysis B: Environmental 119, 32-39

Yen G-C, Duh P-D, Tsai H-L (2002): Antioxidant and pro-oxidant properties of ascorbic acid and gallic acid. Food Chemistry 79, 307-313

1