S-doping α-Fe2O3 induced efficient electron-hole separation for enhanced persulfate activation toward carbamazepine oxidation: Experimental and DFT study

Abstract

• S-doped α-Fe 2 O 3 was synthesized successfully via a three-steps method. • UV/PS/S-α-Fe 2 O 3 process presented excellent performance for CBZ removal. • S-α-Fe 2 O 3 exhibited slower electrons-holes recombination rate and narrower band gap. • ·OH, SO 4 - ·, O 2 – · and h + were responsible for CBZ degradation in UV/PS/S-α-Fe 2 O 3 process. • The hydroxylation, deamination, decarbonylation, ketonization and ring cleavage were the main degradation routes. As a typical iron-based oxide semiconductor with abundant reserves, α-Fe 2 O 3 has been widely used in the domain of photocatalysis and environmental remediation. Here, sulfur doped α-Fe 2 O 3 (S-α-Fe 2 O 3 ) has been successfully fabricated through coprecipitation, hydrothermal and calcination processes and applied to activate persulfate (PS) for carbamazepine (CBZ) degradation under UV irradiation. Systematic characterizations were conducted to analyze the morphology, structure and chemical composite of S-α-Fe 2 O 3 . UV/PS/S-α-Fe 2 O 3 process showed remarkably enhanced photocatalytic performance for CBZ degradation. The degradation rate constant (7.78 × 10 −2 min −1 ) was about 2.2 and 14.1 times as high as that of UV/PS/α-Fe 2 O 3 (3.60 × 10 −2 min −1 ) and UV/PS (5.53 × 10 −3 min −1 ) processes, respectively. With increasing PS concentration and photocatalyst dosage, the removal efficiency of CBZ both increased. UV/PS/S-α-Fe 2 O 3 process can efficiently and steadily operate in a wide pH range of 3.0–8.0. The introduction of water matrix species (i.e. chloride, bicarbonate, nitrate and humic acid) exerted different effects on CBZ degradation. S-dopant was doped via forming ≡Fe III -SO 4 2- bond on S-α-Fe 2 O 3 surface, and doped sulfur functioned as surface electrons trapping centers derived from DFT study. The band gap value of S-α-Fe 2 O 3 was reduced and the separation efficiency of photogenerated electrons and holes was improved. Hydroxyl radicals, sulfate radicals, superoxide radicals and holes all contributed to CBZ destruction. Furthermore, two major routes of CBZ degradation were proposed as hydroxylation and deamination, then followed by decarbonxylation, ketonization and ring cleavage based on the results of HPLC-MS and DFT calculation.