Comparison of two cationic chitosan-based flocculants prepared by photocatalysis and photoinitiation systems: Synthesis mechanism, structure and performance in water treatment

Abstract Flocculants as the traditional water treatment agents were widely applied in water treatment, sludge thickening and dewatering, oil exploitation and papermaking. The synthesis of organic polymer flocculants via high-efficient initiation system has aroused special attention in the development of flocculant. Herein, a chitosan-based flocculant (CS-g-DAC(T)) was synthesized through ultraviolet (UV) initiation of titanium dioxide (TiO2) It was compared with other chitosan-based flocculant (CS-g-DAC(V)) synthesized by a traditional photoinitiator, VA-044, in terms of initiation efficiency, initiation mechanism, flocculant characteristics, molecular structures and flocculant performances in water treatment. Holes (h+), superoxide radicals (O2•-) and hydroxyl radicals ( OH) were generated in the initiation processes of TiO2 and VA-044. TiO2 generated more O2•- and less OH compared with VA-044. CS-g-DAC(T) owned the higher ratio of C = N to C-N in molecular structure, the little higher removal efficiency in water treatment and larger floc size than CS-g-DAC(V). The effect of charge neutralization of CS-g-DAC(T) and CS-g-DAC(V) were close. TiO2 possessed the potential to substitute the traditional photoinitiator in synthesis of organic polymer flocculants and improved the molecular structure and flocculation efficiency of flocculants.