TiO2/activated-biochar hybrid materials: Weight ratio effects on formaldehyde adsorption and photodegradation

• Biochar selection by comparing with the preparation method and compared to a commercial material as a reference. • Hybridised between TiO2 P25 (Evonik) and biochar by varying its weight ratio to evaluate its effectiveness on the adsorption and photodegradation of formaldehyde. • APH materials provide a complete mineralisation compared to bare TiO2 P25 (Evonik) • Activated biochars in APH hybrid materials indicated more stability on photodegradation The performance of Adsorbent-Photocatalyst Hybrids (APHs) based on TiO 2 P25 (Evonik) and activated-biochar was investigated for formaldehyde (HCHO) adsorption and photodegradation in the gas phase. Two commercial biochars (birch and Norway spruce) were characterised to identify the most effective adsorbent based on surface area. A microporous wood-based activated charcoal (1374 m 2 g -1 ) served as a reference, with micropore and mesopore volumes of 0.53 and 0.74 cm 3 g -1 and pore sizes below 7 nm, for adsorption comparison with the biochars. Subsequently, the selected biochar was activated via wet and dry impregnation methods and then incorporated with TiO 2 P25 (Evonik) to form hybrid materials with various weight ratios. The hybrid materials were characterised using BET (surface area), XRF (elemental composition), total carbon analysis, TGA (thermal stability), XRD, and SEM. To evaluate the adsorption and photodegradation performance, a total flow rate of 900 mL min -1 and a HCHO concentration of 15 ppm under UV-A light were applied to the hybrid materials. The results indicated that birch-derived activated biochar with a particle size ≤0.5 mm exhibited the highest adsorption performance. When synergised with TiO 2 P25 (Evonik) at a 75:25 weight ratio, the hybrid material demonstrated the optimal photodegradation rate and complete mineralisation. The enhanced performance confirms that activated biochar improves photocatalytic efficiency by increasing HCHO availability on the TiO 2 P25 (Evonik) surface compared to pure TiO 2 P25 (Evonik). These findings provide the optimisation of TiO 2 -biochar hybrids under high-flow gas-phase conditions and highlight their potential for passive indoor HCHO removal.