| FTIR |
Before dye adsorption: broad peak within 3400–3200 cm⁻¹, specifically 3291 cm⁻¹ (abundant –OH groups from PVA); small peak at 2925 cm⁻¹ (asymmetric stretching of aliphatic C–H in the sp³-hybridized methylene groups of the PVA backbone); sharpest peak at 1710 cm⁻¹ (C=O ester bonds and carboxyl C=O groups, indicating successful crosslinking between PVA and citric acid); broad envelope between 1150 and 1300 cm⁻¹ with maximum at 1208 cm⁻¹ (C–O stretching of the ester linkage formed between the citric acid carboxyl groups and the PVA hydroxyls), consistent with the strong carbonyl band at 1710 cm⁻¹; no distinct Ti–O peak was observed, and the FTIR could not clearly distinguish between cellulose and PVA due to overlapping functional groups. After dye adsorption: new absorption at 1642 cm⁻¹ appears only after dye treatment and is attributed to the azo (−N=N−) chromophore of the adsorbed dye; change at 1380 cm⁻¹ assigned to S=O stretching of the Avitera Light Red SE sulfonate groups (–SO₃⁻), whose appearance after treatment indicates that the sulfonate groups are present on the film; persistent C=O ester peak at 1710 cm⁻¹ confirms permanent esterification crosslinking between citric acid and PVA |
| FTIR acquisition |
PerkinElmer Spectrum-4600 (Model: Spectrum 2) at the Dyes and Chemical Engineering (DCE) Lab, BUTEX; 4000–400 cm⁻¹, covering the mid-infrared range |
| XRD |
22–23° suggested the presence of the highly crystalline (200) lattice plane of cellulose within the biofilm matrix; 19–20° (PVA lattice parameter, partially overlapping cellulose peaks and demonstrating successful composite development); the relatively reduced biofilm intensity might be associated with incorporation of microcrystalline cellulose; 27.4° and 54.3° ((110) and (211) planes of rutile TiO₂, confirming incorporation of the oxide and its polymorph); no reflection at 25.3°, the principal (101) anatase peak, indicating that the nanoparticles used here are predominantly rutile |
| XRD acquisition |
Malvern Panalytical Empyrean X-ray diffractometer; Cu Kα radiation, λ = 1.5406 Å; accelerating voltage 45 kV; tube current 40 mA; 2θ = 10–80°; step size 0.01°; continuous scanning mode |
| FE-SEM morphology |
Before dye adsorption, the biofilm had smooth and uniform surfaces with minimal irregularities, suggesting a low degree of roughness; minor irregularities from uneven MCC distribution were detected; MCC structures were clearly observed on the biofilm surface, which was nonporous and dense. After dye adsorption, the surface became non-uniform, with irregular adhesion of dye particles clearly visible; TiO₂ was largely obscured in FESEM analysis due to the low amount of TiO₂ nanoparticles used |
| FE-SEM acquisition |
ZEISS Field Emission Scanning Electron Microscope (Germany); scanned at 3 kV accelerating voltage under different magnifications |
| EDX |
0.45 keV (Ti); 0.52 keV (O); elemental mapping of C, O, and Ti strongly confirmed successful incorporation and dispersion of TiO₂ within the biofilm |
| EDX acquisition |
An integrated EDX detector measured elemental composition to confirm TiO₂ presence on the biofilm surface |
| Mechanical properties |
Tensile strength = 4.6 MPa; elongation at break = 232.73 % |
| Mechanical-test acquisition |
Universal Testing Machine, Model 1410 Titans, with a 5000 N load cell (U.K.); ASTM D882 with slight modification; sample dimensions 100 × 78 mm; grip separation 50 mm; test speed 50 mm/min; maximum stress at break was recorded |
| DSC |
Glass transition appeared broadened and slightly shifted toward higher temperatures ranging from 100 to 140 °C, suggesting restricted polymer chain mobility; T(g) = 122 °C; broadening of the T(g) peak indicated possible ester crosslinking between PVA and citric acid, further influenced by TiO₂ nanoparticles; the composite had an endothermic peak at T(m) = 221.79 °C; T(d) = 318–321 °C |
| DSC acquisition |
PerkinElmer DSC 4000 single-furnace instrument, periodically calibrated with indium and zinc using a two-point calibration at 10 °C/min; approximately 9 mg of sample heated from 20 to 350 °C at 19.8 °C/min under N₂ atmosphere against an empty reference pan; glass-transition, melting, and decomposition temperatures were recorded |
| Swelling |
The WCF biofilm reached 83 % water uptake; uptake rose steadily over the first 5 and 15 min, then slowed unevenly as the film approached equilibrium |
| Swelling acquisition |
Biofilm samples were dipped in 50 mL distilled water and weighed at 10 min intervals starting from 5 min until constant weight was obtained; excess water was blotted before each weighing; swelling percentage = (W − W₀)/W₀ × 100 %, where W and W₀ represent the swelled and dry weights of the biofilm, respectively |
| Color analysis before and after dye adsorption |
The initial biofilm was nearly white, with L* in the range of 78–80, a* around 0.14, and b* around 8.16, indicating a slight yellow tint. Table 11 prints L* = 80.38, a* = 0.14, b* = 8.16, c* = 8.16, and h* = 89.03 for the WCF Biofilm. After dye adsorption, L* dropped to 47.17; a* and b* values were 35.68 and 5.58; the hue angle h* was 8.89. The prose reports c* = 36.11, while Table 11 prints c* = 36.1. The initial pale film turned strongly red after dye adsorption |
| Color-analysis acquisition |
Film appearance was measured using an X-Rite ci7530 spectrophotometer at the DCE Lab, BUTEX. CIE L*a*b* and CIE L*c*h* values were determined to characterize color attributes before and after dye treatment |