**2. Materials and Methods**

PEO (MW: 900,000 g mol<sup>−</sup>1, Acros Organics) and PVA (99% hydrolysis and medium MW, USA). Glutaraldehyde (GA) (Alfa Aesar, 25 wt.% in H2O) and 4-sulphophthalic acid (SPA) (Sigma-Aldrich, 99.9 wt.% in H2O) were used as covalent and ionic crosslinkers, respectively [30]. Titanium (IV) oxide rutile (TiO2, <5 μm, ≥99.9%, Sigma-Aldrich, Darmstadt, Germany) and H3PO4 (Fisher Chemical, 85 wt.%)

### *2.1. Synthesis*

2.1.1. Synthesis of Phosphated Titanium Oxide Nanotube (PO4-TiO2)

TiO2 nanotubes were synthesised as mentioned in the previous work [19]. TiO2 nanotubes were mixed to 0.1 mol/L−<sup>1</sup> phosphoric acid in a molar ratio 1:1 and the suspension

was shaken in hot water (80 ◦C). The mixture was rinsed with H2O and dried overnight at 110 ◦C. The powder was then burned in a muffle furnace at 450 degrees Celsius.
