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 2024. IPS-2022-02-4780 Kušić 1 1. Experimental procedure for obtaining photocatalysts and co-catalyst materials Synthesis of SnS2-TiO2 Titanium (IV) n-butoxide (Ti(OCH 2 CH 2 CH 2 CH 3 ) 4 , Across Organics, USA), SnCl 4 .5H 2 O (98%, Sigma Aldrich, USA), Thioacetamide (C 2 H 5 NS, Sigma Aldrich, USA), glacial acetic acid (CH 3 COOH, Fluka, Germany), C 2 H 5 OH (96%, Carlo ErbaReagenti, France), pentadecafluorooctanoic acid (PFOA), milli-Q water. All the chemicals used as obtained from the company without any further purification. Synthesis of SnS 2 In order to synthesize SnS 2 , appropriate amounts of SnCl 4 .5H 2 O (0.2M) and C 2 H 5 NS (0.4M) were dissolved in a mixed solution of ethanol and glacial acetic acid (95:5) with stirring. After 15 min of stirring, sample solution was transferred into a Teflon-lined autoclave which further placed in an oven at 120°C for 12 h. hereafter, the cooled sample was centrifuged and washed several time with water and ethanol before drying it at 65°C for 16h. Synthesis of TiO 2 In a 100 mL solution of ethanol and glacial acetic acid (95:5), 5 mL aliquot of Ti(OCH 2 CH 2 CH 2 CH 3 ) 4 was added under vigorous stirring. The resulting clear solution was transferred to an autoclave and sealed tightly. The autoclave was then kept in an oven and maintained at 180°C for 12 h. The obtained white suspension was subjected to centrifugation and washed thoroughly to remove any impurities. The washed solid was then dried in an oven at 65°C. Synthesis of SnS 2 -TiO 2 To prepare SnS 2 -TiO 2 composites, the appropriate amounts of precursors used for the synthesis of SnS 2 and TiO 2 were mixed in a total volume of 100 mL of ethanol and acetic acid in a 19:1 ratio. The mixture was stirred continuously for 15 minutes to ensure homogeneity. The resulting clear solution was transferred into a tightly sealed autoclave, which was then placed in an oven maintained at 180 ° C for 12 hours. After cooling, the sample was centrifuged to separate the solid material, which was thoroughly washed to remove any impurities. The washed solid was dried in an oven at 65 ° C, and the resulting yellow material was finely ground using a mortar and pestle. IPS-2022-02-4780 Kušić 2 OTHER SEMICONDUCTING MATERIALS SYNTHETIZED Preparation of SrTiO3 and N-SrTiO3 Chemicals: Strontium hydroxide octahydrate (Sr(OH) 2 .8H 2 O, Sigma-Aldrich, USA), Sodium hydroxide (NaOH, lachner, Czech Republic), Polyethylene glycol (Sigma Aldrich, USA), Deggusa P-25 (TiO 2 ), Ethanol (EtOH), Ammonium nitrate (NH 4 NO 3 ), Milli-Q water. All the chemicals used in the study were reagent grade and used as received without additional purification. Synthesis 1: SrTiO 3 was prepared by a facile solvothermal route. For this 6.60 g of Sr(OH) 2 .H 2 O were added into water and dissolved at 100 ° C with vigorous stirring (Solution A). Meanwhile, a suspension of Deggusa P-25 in ethanol was prepared by stirring it for 20 minutes (solution B). After which, solution B was mixed with solution A followed by the subsequent addition of 20 mL NaOH (5M), 20 mL of polyethylene glycol, and 20 mL of milli-Q water with stirring. The final mixed solution was transferred in an autoclave, sealed and placed in a hot air oven for 24h at 200 C for 24 h. The resulting sample was centrifuged to collect the solid material which was washed several times with water and ethanol and kept for drying at 70 °C. Synthesis 2: For the synthesis of nitrogen doped SrTiO 3 (N-SrTiO 3 ) all the conditions were kept similar as used for the synthesis of SrTiO 3 , only, NH 4 NO 3 was used as nitrogen source. IPS-2022-02-4780 Kušić 3 Preparation of Ag3PO4/Cu2O Chemicals: Following chemicals were used for the synthesis of Ag3PO4/Cu2O nanocomposite: Copper acetate monohydrate (Cu(CH 3 COO) 2 ×H 2 O, Kemika, Zagreb, Croatia), D (+)-glucose anhydrous (C6H12O6, Gram-Mol, Zagreb, Croatia), Cetyltrimethylammonium bromide (CTAB, Vienna, Austria), anhydrous Silver nitrate (AgNO3, Lachner, Neratovice, Czech Republic), Sodium phosphate dibasic anhydrous (Na2HPO4, Fluka, Steinheim, Germany), Hydrochloric acid (HCl, VWR Chemicals, Vienna, Austria), Sodium hydroxide (NaOH, Lachner,Neratovice, Czech, Republic), Milli-Q water. Synthesis 1: To prepare Cu 2 O, Copper acetate monohydrate (Cu(CH 3 COO) 2 ×H 2 O) and Dglucose 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. 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. Synthesis 3: 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 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. IPS-2022-02-4780 Kušić 4 Preparation of ZnSe Chemicals: Zinc nitrate hexahydrate (Zn(NO3)3×6H2O, Carlo Erba reagents, Italy, France), Sodium selenite (Na2SO3, Across Organics, Geel, Belgium), Hydrazine hydrate (N2H4.H2O, Sigma Aldrich, USA), Hydrochloric acid (HCl, VWR Chemicals, Vienna, Austria), Milli-Q water. Synthesis: In a 100 mL of 56 mM aqueous NaOH solution 0.832 g of Zn(NO 3 ) 2 ×6H 2 O and 0.521 g EDTA-(2Na + ) were dissolved followed by the addition of 0.4842 g of Na 2 SeO 3 . Then 10 mL of N 2 H 4 .H 2 O was added with stirring. The obtained sample solution was transferred in an autoclave and heated at 180°C for 6 h in an oven. The solution was cooled down and 5 mL of 1M HCl was added after that solid sample was collected through centrifugation, washed with water followed by ethanol and dried at 70°C in an oven. Preparation of CuGaS 2 Chemicals: Cupric chloride (CuCl2, Sigma Aldrich, USA), Gallium chloride anhydrous (GaCl3, TCI, Tokyo, Japan), Thiourea (N2H4CS) and Ethylenediamine (EDA) were purchased from thermos Scientific, USA, milli-Q water. Synthesis: In a typical experiment, 3.23 g of CuCl 2 was dissolved in 120 mL of water, and then excess of thiourea (5.48 g) was mixed to which 15 mL of ethylenediamine was poured and stirred. After 10 minutes of stirring 4.23 g of GaCl 3 was added and stirred vigorously for next 20 minutes. The autoclave was sealed and placed in an oven for 15 h at 150°C. The cooled sample was further centrifuged washed and dried at 70°C. Preparation of carbon quantum dots (CQDs) For the synthesis of CQDs 1 g of D-glucose was taken in 120 mL of milli-Q water and filled in an autoclave which was then placed inside an oven for 12 h at a maintained temperature 170°C. The obtained brownish-black sample solution was dialyzed for 5 days through a spectra/por membrane (MWCO: 12-14 kDa) in milli-Q water. The water of dialysis process was changed almost every day. The dialyzed sample was further concentrated by evaporating some water at 70°C for 4 h. IPS-2022-02-4780 Kušić 5 Preparation WO 3 and ZnWO 4 Synthesis: ZnWO 4 photoanodes was prepared by electrodeposition from a 25 mL of 25 mM Zn(NO 3 ) 2 xnH 2 O and 25 mM H 2 W 2 O 11 . The acidic peroxytungstate precursor was synthesized by dissolving metallic tungsten powder (0.95 g) in 10 mL of 30% hydrogen peroxide in a cold water bath. After complete dissolution, excess peroxide was decomposed using a platinum mesh catalyst. The solution was diluted to 25 mM in a 70 : 30 water:2-propanol mixture. The pH of the starting mixture was approximately 1.9, and the acidity of the final deposition solution was adjusted to pH 1.1 by adding 5% nitric acid solution. ZnWO 4 was electrodeposited onto FTO glass by chronoamperometry method at o,6 V in a stirred solution. The films were subsequently annealed in air at 500˘C for 2 h. WO 3 films were electrodeposited from the same deposition solution as the ZnWO 4 films, without Zn(NO3) precursor. IPS-2022-02-4780 Kušić 6 2. Characterization and evaluation of synthetized photocatalyst properties METHODS Optoelectronic properties determination Photoelectrochemical measurements (PEC) OCP measurements were carried out to assess the light response of the photocatalyst and to quantify the photopotential which reflects the charge accumulation and relaxation dynamics of a photoelectrode coated with photocatalytic material. Several different photoelectrochemical measurements (PEC) were conducted; Open Circuit Potential (OCP), Impedance Spectroscopy (EIS) in fixed mode (Mott-Schottky analysis) and scan mode (Nyquist analysis) frequency, as well as Chromoaperometry (CA) and Linear Sweep Voltametry (LSV). All PEC measurements were done using a potentiostat/galvanostat (SP-150, Biologic, France) and a LED light source, corresponding absorption spectra can be find in our previous study. All PEC measurements were performed in 0.5 M solution of sodium sulphate in a three-electrode system, consisting of a platinum counter electrode, calomel reference electrode and working electrode in the form of a fluorinedoped tin oxide (FTO) glass (1 cm 2 ) coated with the photocatalytic material. The immobilization of the photocatalytic materials on FTO glass in the form of three thin layers was done using spin coating method (KW-4 A spin coater, Chemat Technology, USA) and titania/silica binder which procedure was published in previous paper. LSV measurements were carried out with a scan rate of 20 mV/s under the light illumination and in the dark coonditions. EIS measurements were carried out in the dark conditions (Mott Schottky) where frequency was fixed at 3000 Hz and under the illumination (Nyquist) where the frequency range was scanned from 100 kHz to 100 mHz at OCP and dc potential of 0 V with amplitude of ±5 mV. CA measurement was done for 300 seconds under continuous UV illumination and constant potential of 0.5 V to evaluate the photocatalytic current response over time. UV-Visible Diffuse Reflectance Spectroscopy (UV-VIS DRS) The diffuse reflectance measurements were taken on powdered samples using a UV-Vis spectrometer 2600i (Shimadzu, Japan), equipped with an ISR-2600Plus integrating sphere. Photoluminescence (PL) spectra PL analysis was conducted at room temperature using Varian Cary Eclipse fluorescence spectrophotometer (Agilent, USA) with excitation wavelengths between 395 and 430 nm. IPS-2022-02-4780 Kušić 7 Surface, structural and morphology properties determination The crystal structures of the samples were analyzed by X-ray diffractograms (XRD) acquired by using a RigakuMiniflex 600 (Tokyo, Japan) instrument with a Cu Kα target at 40 kV and 10 mA. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) was used to determine the morphology, and elemental composition of the material.The specific surface area and pore size distributions were measured on a Brunauer-Emmett-Teller (BET) analyzer. The surface charge properties of the prepared samples and mean particle size were analyzed by a Zetasizer (Malvern, UK) instrument. IPS-2022-02-4780 Kušić 8 Figure 1.Diffuse reflectance spectra of semiconducting materials: pristine BiVO4, Ag-BiVO4, and Ag-Fe-BiVO4 (A), corresponding plots of transformed Kubelka–Munk function vs. the energy of the light (B), and PL spectra (C) 0 10 20 30 40 50 60 70 80 90 250 350 450 550 650 750 Reflectance (a.u.) wavelenght, nm pristine BiVO4 Ag-BiVO4 Ag-Fe-BiVO4 0 1 2 3 4 5 6 7 8 1.5 2 2.5 3 3.5 4 4.5 5 5.5 (F(R)hν)1/2 (eV cm-1)1/2 Eg(eV) pristine BiVO4 Ag-BiVO4 Ag-Fe-BiVO4 0 50 100 150 200 250 300 350 400 450 470 490 510 530 550 570 590 intensity (a.u.) wavelenght, nm pristine BiVo4 Ag-BiVO4 Ag-Fe-BiVO4 A B C IPS-2022-02-4780 Kušić 15 The specific surface areas (SSAs) of the samples were determined using nitrogen (N 2 ) adsorption-desorption measurements. Figure X presents the N 2 adsorption-desorption isotherms for the SnS 2 -TiO 2 composite. The calculated SSA for the composite is 46 m²/g, which is higher than that of either the SnS 2 or TiO 2 components individually. This enhancement in surface area is likely attributed to the synergistic interaction between SnS 2 and TiO 2 , leading to a more porous structure and increased surface exposure for the composite material. Hysteresis loop indicates it’s a type IV isotherm, which suggests the mesoporous structure of SnS 2 -TiO 2 . Pore size diameter of the composite is in between 2-20 nm as can be seen from the Barrett-JoynerHalenda (BJH) plot (inserts of figure X). Figure 9. N 2 adsorption-desorption isotherm and BJH plot (inserts) of SnS 2 -TiO 2 IPS-2022-02-4780 Kušić 16 The zeta potential is a key characteristic of particles, influencing both their stability and overall properties. A more pronounced zeta potential, whether positive or negative, typically enhances the stability of particle suspensions due to the electrostatic repulsion between particles carrying the same charge, which prevents aggregation. In the current study, the zeta potential was measured at -45.19 mV. The negative zeta potential value of the SnS 2 -TiO 2 composite suggests effective dispersion and stability of the particles in suspension. The average particle size of the composite measured by dynamic light scattering (DLS) techniques is 100 nm (Figure 3b). Figure 10. Zeta potentials of SnS2-TiO2 IPS-2022-02-4780 Kušić 17 Results on WO3 and its combinations a) WO3 - 10 min WO3 - 20 min Intensity / CPS  °CuK  WO 3 ICDD PDF #032-1395 BiVO 4 monoclinic ICDD PDF #075-1866 WO 2 ICDD PDF #032-1393 15 20 25 30 35 40 45 50 55 60 b) Figure 11. a) XRD patterns and b) UV/Vis reflectance spectra of WO 3 and WO 3 /BiVO 4 thin films on FTO substrate. 300 400 500 600 700 10 15 20 25 30 35 Reflectance / % Wavelength / nm WO3 - 20 min WO3 - 10 min IPS-2022-02-4780 Kušić 18 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 0 5 10 15 20 25 (F(R)hv) 2 /cm-2 eV2 hv / eV wo3 - 10 min; E = 2,3193 eV 1,52,02,53,03,54,04,55,05,5 0 5 10 15 20 25 30 35 40 hv / eV (F(R)hv) 2 /cm -2 eV 2 wo3 - 20 min, E= 2,5355 eV Figure 12.Tauc plots for the band gap determination of WO 3. IPS-2022-02-4780 Kušić 19 Table 1. Flat band potential of WO 3 calculated using the Mott-Schottky analysis, band gap energy calculated from UV/Vis reflectance spectra and crystallite size calculated from XRD using Debye-Scherrer equation. WO 3 10 min. WO 3 20 min Crystalite size / nm 26.996 33.7634 FBP / V vs. SHE 0,265 0,339 Band gap / eV 2.319 2.535 Electrochemical deposittion of WO 3 Electrode 1: WO 3 synthesised during 6 minutes Electode 2: WO 3 synthesised during 10 minutes Electrode3: WO 3 synthesised during 20 minutes Electrode 4: WO 3 synthesised during 30 minutes 0 400 800 1200 1600 2000 -12 -10 -8 -6 -4 -2 0 Elektroda 1 Elektroda 2 Elektroda 3 Elektroda 4 t (s) I (mA) Figure 13. Electrochemical deposition of WO 3 at 0,6 V IPS-2022-02-4780 Kušić 20 WO 3 electrode characterisation Figure 13. Linear polarisation for WO 3 electrode under a) dark and b) light in 0,5 mol dm -3 Na 2 SO 4 , 20 mV s -1 . 0 50 100 150 200 250 -1 0 1 2 3 4 5 6 7 8 9 Elektroda 1 Elektroda 2 Elektroda 3 Elektroda 4 t (s) I (mA) Figure 15. Chronoamperometry response for WO 3 electrode under a) dark and b) light in 0,5 mol dm -3 Na 2 SO 4 . a) b) IPS-2022-02-4780 Kušić 21 Open circuit potential monitoring 0 5000 10000 15000 20000 -0,3 -0,2 -0,1 0,0 0,1 0,2 Elektroda 2 Na2SO4 Elektroda 3 Na2SO4 t (s) E (V) Figure 16. Open circuit potential monitoring for WO 3 IPS-2022-02-4780 Kušić 22 Electrochemical impedance spectroscopy Figure 17. Nyquist diagram for WO 3 electrode 2 and 3 in 0.5 mol/dm 3 otopini Na 2 SO 4 IPS-2022-02-4780 Kušić 23 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0,0000 0,0005 0,0010 0,0015 0,0020 0,0025 0,0030 1/ C 2 (1/  F)2 E / V vs. SCE WO3 - 10 min WO3 - 20 min Figure 18. Mott-Schottky plots of WO 3 thin films on FTO substrate in 0.5 M Na 2 SO 4