Insight into the impact of the calcination on the catalytic performance of synthetic hematite nano-rods during the photo-Fenton's oxidation of 4-chlorophenol toxic residuals

Abstract

Two distinct forms of modified hematite nanorods were synthesized from natural laterite using a simple alkaline hydrothermal process (80 °C, 55 h), followed by thermal treatment at 500 °C for 5 h to produce the calcined form (C.HM55). The as-prepared (HM55) and calcined (C.HM55) forms were evaluated in a comparative study as cost-effective and efficient nanocatalysts for the photo-Fenton oxidation of 4-chlorophenol (4-CL), a hazardous pollutant. The calcined form (C.HM55) displayed significantly better activity than HM55, reflecting the impact of the thermal on the crystallinity, morphology, reactivity, and exposed face of hematite crystals. The investigated content of 4-CL (5 mg/L) was completely oxidized after 40 min using C. HM55 at a dosage of 0.4 g/L, which can be recognized after 120 min using HM55. Also, complete mineralization was detected after 120 min (C.HM55) instead of about 240 min in the existence of HM55. The detection of the hydroxyl radicals as the essential oxidizing radicals in addition to the identified intermediate compounds suggested the main pathway of the oxidation reactions, which ended by the formation of carboxylic acids (maleic acid, formic acid, and acetic acid) and further free Cl^- in addition to CO₂ and H₂O. The toxicity properties of the treated solutions against Vibrio fischeri were assessed during the different oxidation intervals. The solutions demonstrated safety properties only after treatment intervals of 180 min, corresponding to the complete mineralization intervals and the full decomposition of the intermediate compounds. The study highlights the novelty of utilizing thermally treated hematite nanorods derived from natural laterite for advanced oxidation processes, offering a sustainable and scalable solution for water treatment applications.