O1 & O2A; Laboratory reports on synthesis, preparation, immobilization and characterization of photocatalytic materials

IPS-2022-02-4780 Kušić University of Zagreb Faculty of Chemical Engineering and Technology Zagreb, Croatia & University of Ljubljana Faculty of Chemistry and Chemical Technology Ljubljana, Slovenia O1 & O2A; Laboratory reports on synthesis, preparation, immobilization and characterization of photocatalytic materials (D1.1, D1.2, D1.3, D1.4 and D2.1) Project: Solar-assisted photocatalytic degradation of perfluorinated compounds in water (SoAPperF), IPS-2002-02-4780. Project leaders: Prof. Hrvoje Kušić (PhD), Croatia, and Prof. Urška Lavrenčič Štangar (PhD), Slovenia Start: 1/11/2022 End: 31/10/2025 Zagreb, November 2025. IPS-2022-02-4780 Kušić 1 1. Experimental procedure for obtaining photocatalysts and co-catalyst materials Indium oxide (In 2 O 3 ) Pure In 2 O 3 was synthesized by dissolving 1.59 g of In(NO 3 ) 3 ×xH 2 O into a 100 mL mixed solution of water and ethanol (70:30 v/v) followed by the addition of 1.80 g of urea and 0.36 g of CTAB, respectively. The resulting sample solution was stirred on a magnetic stirrer with a stirring speed of 600 rpm for 50 min. Thereafter, the obtained clear solution was transferred in a Teflon vessel, sealed tightly and kept at 170 °C for 12 hours. Afterward, the sample was cooled to room temperature and centrifuged at 4000 rpm. The solid product was washed thoroughly with water followed by ethanol, and then dried at 65 °C. The dried white powder was further calcined in a muffle furnace for 2 hours at 500 °C resulting to which a yellowish (pale yellow) colored In 2 O 3 was obtained. Strontium titanate and iron-doped strontium titanate (SrTiO 3 , Fe-SrTiO 3 ) To prepare SrTiO 3 , 2.116 g of Sr(NO 3 ) 2 and 3.4 g of Ti(OBu) 4 were dissolved in 50 mL of water (Solution A) and ethanol (Solution B), respectively, in a 1:1 molar ratio. Solution A was then added to Solution B while stirring continuously at 700 rpm. After mixing, 20 mL aqueous solution of 5 M NaOH was added to the resulting solution and stirred for 20 minutes. The mixture was transferred to a hydrothermal reactor and placed in a hot air oven at 200 °C for 16 hours. Afterward, the sample was cooled to room temperature and centrifuged at 4000 rpm. The solid product was washed thoroughly with water followed by ethanol, and then dried at 65 °C. Fe-doped SrTiO₃ was synthesized following the SrTiO₃ hydrothermal procedure, with Fe(NO₃)₃ꞏ9H₂O used as the iron source. Sr(NO₃)₂ was dissolved in water (Solution A) to prepare a 0.2 M strontium precursor, while Ti(OBu)₄ was dissolved in ethanol (Solution B) at a concentration adjusted to achieve the desired Fe/Ti molar ratio. The required amount of Fe(NO₃)₃ꞏ9H₂O was calculated based on the targeted composition and added to Solution A. Under continuous stirring at 700 rpm, Solution A containing Sr and Fe precursors was added to Solution B. After homogenization, 20 mL of 5 M NaOH was introduced, and the mixture was stirred for an additional 20 min. The suspension was then transferred to a Teflon-lined hydrothermal reactor and heated at 200 °C for 16 h. After cooling to room temperature, the product was collected by centrifugation at 4000 rpm, washed repeatedly with water and ethanol, and dried at 65 °C. IPS-2022-02-4780 Kušić 2 Graphene oxide (GO) A modified Hummers method was used in which graphite (3 g, mesh <100) was mixed with 69 mL of cooled 97% H₂SO₄ and 1.5 g of dry NaNO₃ in an ice bath while maintaining the temperature at 0 °C under constant stirring in a round-bottom flask. KMnO₄ (9 g) was then added slowly, ensuring the temperature remained below 20 °C, and the mixture was stirred while keeping the temperature at or below 35 °C for 30 min. After 1 h of total stirring, 138 mL of DI water was added slowly, ensuring the temperature did not exceed 98 °C. The mixture was cooled to room temperature and diluted with 1 L of DI water without stirring. Subsequently, 30% H₂O₂ was added gradually until effervescence ceased. The obtained dispersion was washed with 5% HCl to remove MnO₂, followed by repeated water washing in a centrifuge until the supernatant reached near-neutral pH. The product was then sonicated for 1 h in an ultrasonic cleaner to exfoliate the material, dialyzed for 3 weeks using a Spectrum-Pore membrane to remove remaining impurities, and finally vacuum-dried at 35 °C for 4 weeks. Carbon quantum dots from lignin (CQD) Lignin (0.300 ± 0.005 g) was dispersed in 30 mL of Milli-Q water in a round-bottom flask and sonicated for 20 min, ensuring that the ultrasonic bath did not overheat; the bath water was replaced if necessary to maintain a stable temperature. Hydrochloric acid was then added (either 20 µL or 1 mL, depending on the experimental condition), and the suspension was stirred for 30 min once the temperature reached 60 °C, with the flask connected to a condenser. After this period, the condenser was removed and 0.3 g of 3-aminoboronic acid was added as the dopant. The mixture was stirred continuously and heated to 90 °C; after reaching this temperature, stirring was maintained for 1 h. The reaction mixture was subsequently allowed to cool to room temperature while stirring for approximately 15 min. The suspension was then filtered through a 0.45 µm nylon membrane and transferred into a Teflon-lined hydrothermal reactor, where it was heated at 200 °C for 10 h. The following day, the product was filtered twice through a 0.22 µm nylon membrane. Dialysis tubing was rinsed with distilled water and filled with the filtered sample, followed by dialysis for a minimum of 48 h with periodic replacement of the external water. The final concentration of the obtained solution was determined gravimetrically. At the end of the procedure, the CQDs were lyophilized. IPS-2022-02-4780 Kušić 3 Graphitic carbon nitride (g-C 3 N 4 ) Melamine (13 g) was placed in an alumina crucible and calcined in a muffle furnace at 550 °C for 4 h to obtain bulk g-C₃N₄, which was then ground thoroughly in a mortar. To prepare exfoliated g-C₃N₄ nanosheets, 5 g of the bulk material was dispersed in 30% H₂SO₄ and stirred for 22 h. The resulting suspension was sonicated for 1 h, followed by centrifugation and thorough washing with water and ethanol. The washed product was dried at 65 °C under vacuum for 24 h to obtain g-C₃N₄ nanosheets. Copper (I) oxide (Cu 2 O) To prepare Cu 2 O, Copper acetate monohydrate (Cu(CH 3 COO) 2 ×H 2 O) and D-glucose was mixed in 120 mL of water in 1:1 molar ratio. After that 1.093 g of CTAB was added in the mixed solution as a stabilizer. The resulting solution was taken in a Teflon lined stainless steel vessel, sealed tightly and was kept inside an oven for 12 h at 100 °C. The sample was cooled at room temperature and centrifuged at 4000 rpm, the collected solid sample was washed with water and ethanol to remove any unwanted impurities. Then it was dried under the vacuum at 60 °C for 24 h. Silver phosphate (Ag 3 PO 4 ) Synthesis 2: 2.718 g of anhydrous AgNO 3 was dissolved in 80 mL of water to prepare solution A. Solution B was prepared by dissolving 1.136 g of Na 2 HPO 4 in 40 mL of water. Hereafter, solution B was added drop wise into solution A with stirring, yellow colour precipitate was obtained. The stirring was continued for 10 minutes. The pH of precipitated solution was adjusted at 6 by adding HCl or NaOH. After that, the sample was filled in an autoclave and placed in an oven at 120 °C for 6 h. The resulting sample was allowed to cool, centrifuged, washed well with water. The solid yellow slurry was dried at 70°C in an oven. Composite Cu 2 O/Ag 3 PO 4 119.8 mg of as prepared Ag 3 PO 4 was dispersed ultrasonically in 120 mL of water for 25 minutes. In the dispersed solution, Cu(CH 3 COO) 2 ×H 2 O and D-glucose were added in equimolar ratio (1:1) followed by the addition of CTAB (0.025 M). The sample was continuously stirred for 20 minutes then transferred into a teflon lined autoclave. The tightly sealed autoclave was kept in oven at 100 °C for 12 h. The resulting sample solution was IPS-2022-02-4780 Kušić 4 centrifuged and washed with water and ethanol to remove any kind of impurity if present. The collected solid sample was dried in a vacuum oven at 60 °C for 24 h. Composite C 3 N 4 /Fe-SrTiO 3 200 mg of g-C 3 N 4 (exf.) was dispersed in 50 mL of water and sonicated for 30 minutes in an ultrasonic cleaner, in the resulting colloidal solution 2.116 g of Sr(NO 3 ) 2 was dissolved (solution A). Another solution was prepared by the subsequent addition of 3.30 g and 0.122 g of Ti(OBu)4 and FeN 3 O 9 ×9H 2 O in 50 mL of ethanol (solution B). Thereafter, solution A was added to solution B followed by the addition of 5 M of 20 mL NaOH with continuous stirring. After 20 minutes of stirring, the mixed sample was poured into a Teflon lined autoclave and heated at 200 °C for 16 hours. The autoclave was cooled down and the obtained sample was centrifuged and washed four times with water and two times ethanol. The resulting slurry was dried under the vacuum at 65 °C. Composite CQD-In 2 O 3 For the preparation of the composites, In₂O₃ was used along with CQDs employed in their liquid form. The concentration of the CQD dispersions had been previously determined gravimetrically (Type 1: 20 µL HCl CQD: 0.175 mg/mL, total volume 16 mL; Type 2: 1000 µL HCl CQD: 0.125 mg/mL, total volume 20 mL). For the preparation of the 0.03 CQD– In₂O₃ composite, In 2 O 3 and CQD dispersions were used as follows: (i) 16 mL CQDs (20 µL HCl route) were combined with 90.53 mg In₂O₃; or (ii) 20 mL CQDs (1000 µL HCl route) were combined with 80.83 mg In₂O₃. In₂O₃ powder was dispersed in a glass flask in 20 mL of ethanol. The suspension was sonicated for 15 min, while CQDs were separately sonicated for 15 min in glass vials. Subsequently, the In₂O₃ suspension was heated to 40 °C and stirred at 200 rpm (avoiding vortex formation), with the flask wrapped in aluminum foil. CQDs were added dropwise over 30 min (one drop every ~4 s). After the complete addition of CQDs, the temperature was increased to 90 °C and the mixture was stirred at 200 rpm until nearly all solvent had evaporated. The resulting material was then calcined at 300 °C for 3 h. In the end, the composites were washed twice with water, twice with ethanol, and dried 65 °C for 3 h. IPS-2022-02-4780 Kušić 5 Composite rGO-In 2 O 3 The rGO-In₂O 3 composites were synthesized as follows. In₂O₃ nanoparticles (200 mg) were dispersed in 10 mL of water and sonicated for 10 min to obtain a uniform suspension. Separately, 1 mg (for 0.5% rGO-In₂O 3 ) or 3 mg (for 1.5% rGO-In₂O 3 ) of graphene oxide (GO) was dispersed in 10 mL of water by sonication for 10 min to form a homogeneous GO dispersion. The In₂O₃ suspension was then combined with the GO dispersion, stirred for 5 min, and subsequently sonicated for 4 h. The resulting mixture was heated to 95 °C under vigorous stirring. Hydrazine solution (40%, 9 µL) and ammonia solution (25%, 70 µL) were then added to the mixture. After 1 h of stirring, the suspension was filtered, washed with water and ethanol, and dried at 100 °C for 12 h. WO3 and WO 3 modified by Zn and Ga Electrochemical synthesis of WO3 photocatalysts, peroxotungstic acid (H₂W₂O₁₁) was carried out by dissolving tungsten powder (0.95 g) in 10 mL of 30% hydrogen peroxide, H 2 O 2 , according to the reaction: 2 W(s) + 10 H 2 O 2 (aq) → H 2 W 2 O 11 (aq) + 9 H 2 O(l) The dissolution of tungsten powder lasted about 60 min. After complete dissolution, the excess peroxide was decomposed using a platinum mesh catalyst, which was left overnight (Figure 1). The solution was quantitatively transferred and diluted to 25 mM in a mixture of water and 2-propanol in a ratio of 70:30. The pH of the initial mixture was approximately 1.9, and the acidity of the final precipitation solution was adjusted to pH 1.1 by adding 2 – 3 mL of 5% nitric acid. (a) (b) Figure 1. a) dissolving tungsten powder in hydrogen peroxide and b) the reaction of the remaining hydrogen peroxide at Pt mesh IPS-2022-02-4780 Kušić 6 A three-electrode system (working electrode-FTO glass, Pt counter electrode and reference electrode-SCE) was used for the electrodeposition of WO 3 on FTO slides. WO 3 films were electrochemically deposited on FTO slides, which were previously cleaned with ethanol, acetone and redistilled water in an ultrasonic bath for 10 minutes. The area 2 cm 2 was immersed in a peroxotungstic acid solution, and the electrodeposition process was carried out at E = -0.645 V without stirring for 10 and 20 min (Figure 2). Figure 2. Three-electrode system for electrodeposition of WO 3 and modified WO 3 After film deposition, the WO 3 electrode was annealed at 500 °C for 2 hours in an oven and left to cool overnight. The electrodes of modified WO3 were prepared in the same way, with the addition of Zn(NO 3 ) 2 x6H 2 O of different masses, which are m 1 = 0.0925 (sample 3) g and m 2 = 0.2770 g (sample 4). Sample 5 was prepared from the solution in which the electrochemical synthesis of modified WO 3 was carried out, the oxide was precipitated by the sol-gel process. Sample 6 was synthesized electrochemically, similar as sample 2 and in addition 100 L of the synthesis solution containing Wand Znsalts was drop casted over sample 2. Table 1. Name of samples Electrode Composition Sample 1 WO 3 – synthesis 10 min Sample 2 WO 3 – synthesis 20 min Sample k 3 modified WO 3 (0.0925 g Zn(NO 3 ) 2 x6H 2 O) Sample 4 modifiedWO 3 IPS-2022-02-4780 Kušić 7 (0.277 g Zn(NO 3 ) 2 x6H 2 O) Sample 5 modifiedWO 3 sol-gel Sample 6 modified WO 3 + drop casting WO 3 electrodes modified with gallium were prepared by adding a certain mass of GaCl 3 to the solution before electrodeposition onto FTO slides, after which the solutions were left on a stirrer for 30 minutes. The mass of GaCl 3 was 0.220 g,. The electrodeposition of these electrodes was carried out in the same way as the electrode of pure WO3. The obtained electrodes are shown in Figure 3. Figure 3. Electrodes obtained by the chronoamperometry method The second set of electrodes was prepared by electrodeposition using the chronocoulometry (CC) method at a potential of E = -0.645 V and a charge of Q = 7020 mC, in order to deposit films of equal thickness depending on the charge. Two masses of GaCl3 were added, i.e. for 10% GaCl 3 the mass was 0.073 g, and for 5% GaCl 3 the mass was 0.037 g. The resulting electrodes are shown in Figure 4. IPS-2022-02-4780 Kušić 8 Figure 4. Electrodes obtained by chronocoulometry method Table 1. List of samples Electrode composition Sample 1 WO 3 (CA) Sample 2 modified WO 3 – 32% (0.220 g GaCl 3 ) Sample 3 modified WO 3 – 40% (0.277 g Zn(NO 3 ) 2 x6H 2 O) Sample 4 WO 3 (CC) Sample 5 modified WO 3 – 10% (0.073 g GaCl 3 ) Sample 6 modified WO 3 – 5% (0.037 g GaCl 3 ) TiO2 modified by Pt We prepared platinum-modified titanium dioxide (TiO2) as a phtotocatalyst for the degradation of PFOA. Titanium dioxide without platinum modification was prepared by a particulate solgel synthesis from titanium tetrachloride (TiCl4) precursor. 3.68 mL of TiCl4 were dissolved in a solution, containing 60 mL of distilled water and 4.95 mL of 12 M H2SO4. After one day IPS-2022-02-4780 Kušić 15 CasaXPS 2.3.26 software, with a Shirley type background and 75 – 25 % Gaussian−Lorentzian peak shapes. Raman Spectroscopy was performed with Bravo Handheld Raman Spectrometer, Bruker Optic. Fourier-Transform Infrared Spectroscopy (FTIR) was usedto record infrared spectra between 4000 cm−1 and 400 cm−1 using a Bruker Alpha-II (FT-IR spectrophotometer with ATR module) IPS-2022-02-4780 Kušić 16 RESULTS Optoelectronic properties Figure 1. PEC results of pure SrTiO 3 and Fe doped SrTiO 3 (a) transient photocurrent response, (b) Nyquist plot, (c) linear sweep voltammograms, and (d) Mott–Schottky Figure 2. EIS-light vs dark for pure SrTiO 3 and Fe doped SrTiO 3 IPS-2022-02-4780 Kušić 17 Figure 3. Tauc plots: (a) indirect band gap of BiVO 4 (b) indirect band gap of g-C 3 N 4 (c) direct band gap of In 2 O 3 Table 1. Band gaps of photocatalysts determined from Tauc plots Material BiVO 4 g-C 3 N 4 In 2 O 3 Band gap (eV) 2.34 2.65 3.52 IPS-2022-02-4780 Kušić 18 Figure 4. (a) UV-Visible absorbance spectra, (b) Tauc plot, and (c) Photoluminescence (PL) spectra of pure SrTiO 3 and Fe doped SrTiO 3 samples IPS-2022-02-4780 Kušić 19 Surface, structural and morphology properties Figure 5. XRD patterns of (a) BiVO 4 (b) GO (c) g-C 3 N 4 (d) In 2 O 3 Figure 6. XRD pattern of In 2 O 3 and the standard ICSD card no. 01-89-4595 (a) (c) (d) (b) IPS-2022-02-4780 Kušić 20 Figure 7. XRD pattern of Cu 2 O and GO/Cu 2 O Figure 8. XRD pattern of Ag 3 PO 4 , Cu 2 O and Ag 3 PO 4 /Cu 2 O samples IPS-2022-02-4780 Kušić 21 Figure 9. XRD pattern of In 2 O 3 (uncalcined) and In 2 O 3 (Calcined) Figure 10. XRD Pattern of (a) SrTiO 3 and Fe doped SrTiO 3 (b) Zoomed view of the most intense (110) peak IPS-2022-02-4780 Kušić 22 Figure 11. (a,b) SEM images of SK and FeSK-0.03, and (c,d) corresponding EDS spectra Figure 12. (a) SEM images of FeSK-0.05 and (b) corresponding EDS spectra Figure 13. (a) SEM images of FeSK-0.07 and (b) corresponding EDS spectra (a) (b) (a) (b) IPS-2022-02-4780 Kušić 23 Figure 14. (a) SEM images of g-C 3 N 4 and (b) corresponding EDS spectra Figure 15. SEM–EDS elemental mapping SK (Sr, Ti, O) (a) (b) IPS-2022-02-4780 Kušić 24 Figure 16. SEM–EDS elemental mapping of FeSK-0.03 (Sr, Ti, O, Na) IPS-2022-02-4780 Kušić 31 Figure 26. FTIR spectra of graphene oxide Figure 27. Raman spectra of graphene oxide IPS-2022-02-4780 Kušić 32 Characterization of WO3 un-modified and modified samples Figure 28. Graphical representation of electrodeposition of WO3 and modified WO3 by chronoamperometry in a three-electrode system Figure 29. Graphical representation of linear polarization of illuminated and unilluminated electrodes in 0.5 M Na2SO4 IPS-2022-02-4780 Kušić 33 Figure 30. Graphical representation of electrochemical impedance spectroscopy response of illuminated and unilluminated electrodes in 0.5 M Na2SO4 Figure 31. Graphic representation of chronoamperometry response of electrodes in 0.5 M Na2SO4 at 0.5 V IPS-2022-02-4780 Kušić 34 Figure 32. Graphical representation of the dependence of the open circuit potential on time with periodic exposure of the electrodes to light and darkness Figure 33. Mott – Schottky analysis IPS-2022-02-4780 Kušić 35 Slika 34. UV/Vis spectroscopy Figure 35. XRD of sample 1 i 2 IPS-2022-02-4780 Kušić 36 Figure 36. XRD of sample 5 Table X. Flat band potentials Electrode E fb / V vs SCE E fb / V vs SHE Sample 2 -0.316 0.039 Sample 3 -0.147 0.456 Sample 4 -0.078 0.525 Sample 5 -0.250 0.105 IPS-2022-02-4780 Kušić 37 a) sample 2 b) sample 4 c) sample 5 d) sample 6 Figure 37. Tauc representation obtained by Kubelka-Munk transformation of diffuse reflectance spectra Table 3. Band gap energy (E g ) Electrode E bg / eV Sample 2 2.43 Sample 4 2.89 Sample 5 2.78 Sample 6 2.77 1.52.02.53.03.54.04.55.05.5 0.0 0.1 0.2 0.3 0.4 0.5 0.6 h  / eV   h  ) 2 / (eV cm -1 ) 2 1234567 0 5 10 15 20 25 h  / eV   h  ) 2 / (eV cm -1 ) 2 1234567 -2 0 2 4 6 8 10 12 14 16 18 20 h  / eV   h  ) 2 / (eV cm -1 ) 2 1234567 0 1 2 3 4 5 6 7 8 h  / eV   h  ) 2 / (eV cm -1 ) 2 IPS-2022-02-4780 Kušić 38 Figure 38. Energy band diagram for WO 3 (sample 2) i modified WO3 (sample 4) a) b) Figure 39. a) and b) Graphical representations of electrodeposition of WO 3 and modified WO 3 by chronoamperometry in a three-electrode system IPS-2022-02-4780 Kušić 39 a) b) Figure 40. a) and b) Graphical representations of linear polarization of illuminated and unilluminated electrodes in 0.5 M Na 2 SO 4 a) b) Figure 41. a) and b) Graphical representations of the Nyquist diagram for illuminated and unilluminated electrodes in 0.5 M Na2SO4 IPS-2022-02-4780 Kušić 40 a) b) Figure 42. a) and b) Graphical representations of chronoamperometry of electrodes in 0.5 M Na2SO4 at 0.5 V a) b) Figure 43. a) and b) Graphical representations of the dependence of the open-circuit potential on time IPS-2022-02-4780 Kušić 47 Figure 51. High-resolution F1s spectra of a) Pt−TiO 2 , b) Pt−TiO 2 used, c) Pt−TiO 2 NaF, d) Pt−TiO 2 used−H 2 O, e) Pt−TiO 2 used−NaCl and f) Pt−TiO 2 used-calcined. Table 2: Quantitative XPS analysis of fluorine in samples. Sample name F (at %) Pt−TiO 2 / Pt−TiO 2 used 4.70 Pt−TiO 2 NaF 2.20 Pt−TiO 2 used−H 2 O 0.90 Pt−TiO 2 used−NaCl 0.60 Pt−TiO 2 used-calcined / IPS-2022-02-4780 Kušić 48 Figure 52. TG–DSC–MS analysis of the used photocatalyst. IPS-2022-02-4780 Kušić 49 4000 3500 3000 2500 2000 1500 1000 500 0.0 0.5 1.0 1.5 2.0 Intensity (a.u.) Wavenumber (cm -1 ) glass glass+PR3 glass+PR3_used_5_pharm_210min 4000 3500 3000 2500 2000 1500 1000 500 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Intensity (a.u.) Wavenumber (cm -1 ) glass+PR3 glass+PR3_used_5_pharm_210min 4000 3500 3000 2500 2000 1500 1000 500 0.0 0.1 0.2 0.3 0.4 0.5 Intensity (a.u.) Wavenumber (cm -1 ) PET PET+PR2 PET+PR2_used_5_pharm_210min PET+PR2_used_PFOA_50h Figure 53: FT-IR spectra of S3N2 films on glass (up) and PET plastic (down) IPS-2022-02-4780 Kušić 50