Sodium hydroxide (naoh)

To prepare the TiO₂–CS composites and TiO₂ hollow structures, Ti(IV) butoxide (Sigma-Aldrich, Schnelldorf, Germany; reagent grade; 97%), HCl (VWR Chemicals, Debrecen, Hungary; 37%), NaOH (Molar Chemicals, Halásztelek, Hungary; a.r.; 50%) H₂O₂ (Sigma-Aldrich, Schnelldorf, Germany; 30%), and ultrapure water (Millipore Milli-Q, Budapest, Hungary) were used. Carbon sphere templates were synthesized by using ordinary table sugar (sucrose, Magyar Cukor Zrt., Koronás^TM, Kaposvár, Hungary) as carbon source, acetone (Molar Chemicals; 99.96%), and Milli-Q water for their purification. As model pollutant phenol (Spektrum 3D; analytical grade) was used to examine the photocatalytic activities. Our own ‘Rutile-H2’ TiO₂ (a nonhollow structural, rutile TiO₂ with improved visible light excitability, published in our previous work [43 (link)]) and ‘Rutile-H2_calc’ (a TiO₂ synthesized by the calcination of Rutile-H2 the same way as the TiO₂ hollow structures were synthesized, only without the addition of CS templates) were used as references together with commercial Evonik Aeroxide P25.

2-Propanol (HiPerSolv CHROMANORM for HPLC, VWR, Radnor, PA, USA), acetonitrile (Promochem Optigrade, LGC Standards GmbH, Wesel, Germany) were gradient grade for liquid chromatography. TiCl₄ (≥98%, Fluka Chemie AG, Buchs, Switzerland), NaOH (99.9%, Molar Chemicals Ltd., Halásztelek, Hungary), Dimethyl sulfoxide, DMSO (≥99.9%, Sigma-Aldrich, St. Louis, MO, USA) were used as received. 5,5-dimethyl-1-pyrroline N-oxide, DMPO, was synthesized as previously described [36 (link)], and it was freshly distilled before use. High purity deionized water was obtained by a LaboStar 7 TWF-UV (SG Wasseraufbereitung und Regenerierstation GmbH, Barsbüttel, Germany) system.

Melatonin (powder <98% (TLC), Cas number: 73-31-4, Mw: 232.28), polyvinyl alcohol (PVA, Mowiol^® 18–88, average molecular weight Mw ~130.000 g mol⁻¹), polylactic acid, chloroform (Chl, Anhydrous, contains amylenes as stabilizer, <99%) and N,N-dimethylformamide (DMF, Anhydrous, 99.8%) were obtained from Sigma-Aldrich (Budapest, Hungary). Ethanol 96%, Polysorbatum 80 (Tween^® 80), potassium dihydrogen phosphate and sodium hydroxide were purchased from Molar Chemicals (Budapest, Hungary). Materials were used without additional purification and deionized water was of analytical grade.