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The ability of charcoal, a low-cost material derived from biomass pyrolysis, to be functionalized via cation exchange in an aqueous solution, providing new interesting fillers with possible antimicrobial and flame-retardant properties, is discussed here. The adducts obtained through this sustainable procedure, show a significant uptake of close to 30% by weight of well-known quaternary phosphonium salts, tetraphenyl phosphonium bromide, and dodecyl triphenyl phosphonium bromide. The new functionalized materials were characterized by elemental analysis, wide-angle X-ray diffraction, infrared spectroscopy, and thermogravimetry. Additionally, a study of changing the ratio between the reagents for both adducts was performed to improve salt uptake and optimize the cationic exchange. Dispersibility tests showed the ability of functionalization to deeply change the polarities of the carbon materials to modify the compatibility and improve the possible interactions with different media, such as different polymer matrices. [ABSTRACT FROM AUTHOR]

• TiO 2 /biochar hybrid system was easily prepared by ball milling route. • Tannery dyes removal through simultaneous adsorption and photocatalysis. • Compared with bare TiO 2 , the removal efficiency of TiO 2 /biochar was enhanced. • TiO 2 /biochar hybrid system exhibited high stability during five reuse cycles. TiO 2 /biochar (C/TiO 2) BM hybrid photocatalytic system is prepared, for the first time, by a cost-effective method (ball-milling procedure) and used for the removal of two organic dyes, labeled as Acid Blue 7 and Red RTN, employed in the tanning industry. The physicochemical properties of the (C/TiO 2) BM system are investigated by different characterization methods, evidencing the presence of TiO 2 in anatase phase in the (C/TiO 2) BM composite. The photocatalytic performance of (C/TiO 2) BM is evaluated in the degradation of Acid Blue 7 and Red RTN in the presence of UV light irradiation. The photocatalytic results of (C/TiO 2) BM show a similar degradation efficiency (about 70 %) for both dyes under UV light at the spontaneous pH of the solution (pH = 6). On the other hand, photocatalytic tests under acidic conditions (pH = 2) indicate higher adsorptive and photocatalytic properties of (C/TiO 2) BM composite with an overall removal efficiency of Acid Blue 7 and Red RTN of 86 and 95 %, respectively. Finally, (C/TiO 2) BM is reused for up to five cycles without loss of removal performances, underlining the stability of the composite. Therefore, the (C/TiO 2) BM composite could be an effective, recyclable, and stable hybrid photocatalytic material for removing tannery dyes from aqueous solutions by adsorption/photocatalysis. [ABSTRACT FROM AUTHOR]