Constructing mesoporous phosphated titanium oxide for efficient Cr(III) removal.

Heavy metal removal by environmental-friendly nanostructured TiO2 adsorbent is a promising strategy to facilitate wastewater treatment. Here, a boiling water synthetic approach is explored to prepare mesoporous phosphated TiO2 (PTO) used for Cr(III) adsorption in polluted water. We obtain mesoporous 8-PTO (synthesized with 8% molar ratio of H3PO4) with a high specific surface area (278 m2/g), narrow size distribution (<5 nm), low pHzpc (pH of zero point of charge) value (∼1.0), and abundant surface hydroxyl group, which is attributed to the introduction of H3PO4 during the hydrolysis process of TiCl4 in boiling water. Importantly, the obtained 8-PTO shows better thermal stability than pure TiO2 and retains mesoporous structure after thermal treatment owning to [PO4] tetrahedral incorporated into the network of [TiO6] octahedral. The optimized 8-PTO exhibits superior Cr(III) adsorption up to 92 mg/g in sewage, which makes it one of the best materials among TiO2 adsorbent known for Cr(III) Removal (10-83 mg/g). Additionally, the as-prepared mesoporous 8-PTO adsorbent possesses an excellent reusability without significant degradation and can largely avoid the generation of secondary contaminants. A linear relationship (R2  = 0.9985) between adsorption capacity and hydroxyl content percentage of different PTO samples is revealed, indicating that the surface hydroxyl groups play a decisive role in the adsorption process. This study provides a facile approach to synthesize high specific surface area mesoporous phosphated TiO2 with rich surface functional groups for efficient Cr(III) removal in sewage.