Production of carbon -doped titanium dioxide (C-TiO 2 ) from polytitanium-coagulated sludge as an adsorbent or photocatalyst for pollutant removals

Chemically enhanced primary sedimentation (CEPS) using titanium coagulants could produce the Ti-loaded sludge with promising material recycle and utilization options. This study investigated two approaches for the recovery and utilization of Ti-based CEPS sludge: (1) a current technology of sludge calcination in the absence of N-2 atmosphere to transform Ti to carbon-doped TiO2 (C-TiO2, with a low C content) as a photocatalyst, and (2) a prospective technology of carbonization of the sludge in the presence of N-2 atmosphere to produce C-TiO2 (high C content) as an adsorbent. Both approaches can be applied for the recycle and utilization of the materials of the Ti-based CEPS sludge. Calcination at 400-800 degrees C led to the predominant anatase-TiO2 formation (spherical granules with particle size of around 20-25 nm), while rutile crystal phase appeared at 900 degrees C. The as-obtained C-TiO2 performed effectively for the adsorption or photocatalytic degradation of rhodamine B (RB) and methyl orange (MO), as the model pollutants, in wastewater treatment. The C-TiO2 with rich activated carbon content (20.0-38.3%, functioned as adsorbents) achieved high-efficient RB and MO adsorption by up to 98% in 20 min, while the C-TiO2 with low activated carbon content (1.5-12.6%, functioned as photocatalysts) degraded 99.6% of RB and 97.0% of MO from initial 20 mg/L in 210 min by photocatalytic degradation under UV illumination.