Acetylacetone promoted high-efficiency coagulation toward arsenite through a synchronous photooxidation process

Abstract

Titanium xerogel coagulant (TXC) is a novel Ti-based coagulants developed in recent years. TXC possess the dual functions of “photooxidation” and “coagulation”, where the former is attributed to the photoactivity of the acetylacetone (AA) constituent embedded in its skeleton. In this study, we proposed a synchronous photooxidation-coagulation strategy to improve the coagulation efficiency of TXC toward the removal of arsenite (As(III)), especially under acidic conditions. By introducing UV-254 nm irradiation, 5.0 mg Ti/L TXC removed 72.1% of As(III) at pH 5.0 (initial As(III) concentration was 1.0 mg L⁻¹), which was greatly higher than that from only coagulation (31.4%). Furthermore, the function mechanism and dose effect of AA were further investigated by constructing a UV/AA-enhanced coagulation system, in which titanium sulfate (TS) was selected as the coagulant. The results showed that the photooxidation of AA in a wide pH range (4.0–9.0) improved the removal efficiency of As(III). In the case of a high As(III) content, prolonging the reaction time and increasing the AA dose were alternative methods to achieve a satisfactory removal efficiency. In the synchronous photooxidation–coagulation system, As(III) was firstly oxidized to As(V) in solution, and then the resultant As(V) was quickly immobilized by the coagulated flocs. The turbidity and organic matter exhibited significant inhibitory effects in the removal of arsenic, whereas Fe²⁺ ions promoted the coagulation efficiency. The results from this study provide a new strategy to improve the coagulation efficiency of TXC and shed light on the application potential of gelation modification for other inorganic coagulants.