Polyferric-titanium composite coagulants with hydrogen bond domain expansion effect for superior coagulation performance

This study developed novel polyferric titanium chlorides (PFTC) with varying Fe/Ti ratios and basicity (B) to achieve safe and effective surface water treatment. The formation of Fe-O-Ti was confirmed through the characterization of PFTC and its impact on physicochemical properties and coagulation performance was thoroughly investigated. Additionally, the molecular-level coagulation mechanism was elucidated. The results demonstrated that PFTC exhibited remarkable stability, with a distinct pH-stable phase during alkaline titration. PFTC showed excellent bridging adsorption capacity, achieving bovine serum albumin (BSA) removal efficiency of 78.33%. The flocculation rate increased to more than 222%, producing larger, denser flocs with superior settling performance, while posing no environmental risks to treated water. XPS and FTIR analyses revealed that hydrogen bond was the primary mechanism driving bridging adsorption. Molecular docking analysis indicated that PFTC hydrolysates formed stronger hydrogen bonds with higher binding energy at key BSA residues compared to polyferric chloride (PFC). According to XDLVO theory, the dominant hydrogen bond range between PFTC and BSA was more than 2.75 times greater than that of PFC and BSA. The hydrogen bond domain expansion effect, coupled with robust hydrogen bond, overcame distance barriers, enabling PFTC to establish strong bridging adsorption interactions with a broader range of BSA molecules, thereby enhancing coagulation efficiency. This study provides valuable insights into the interaction mechanisms between PFTC and BSA, supporting the practical application of polymeric metal composite coagulants.