Designing Co₃O₄/silica catalysts and intensified ultrafiltration membrane-catalysis process for wastewater treatment

An integrated cobalt oxide catalyst supported on silica (Co₃O₄/SiO₂) packed in the lumen of tubular alumina (Al₂O₃) membrane was designed to realize a Fenton-like oxidation coupling with ultrafiltration water treatment technology to remove persistent and hazardous pollutants. We employed a selection of SiO₂ support materials with a range micro/mesostructures to immobilize the Co₃O₄ catalyst. These were evaluated and screened to achieve the highest pollutant decolorization rate and maximum decolorization efficiency. Then, an integrated catalyst-membrane was developed as proof-of-concept for advanced water treatment. Batch degradation results showed acid orange 7 dye (AO7) was effectively removed using Co₃O₄ deposited on MCM-41 silica, with 97% decolorization efficiency achieved in 15 mins owing to the large surface area and high porosity of the MCM-41 support. In contrast, humic acid (HA) was relatively difficult to degrade using this catalyst, and was however found to inhibit AO7 degradation. The integrated catalyst-membrane successfully removed both AO7 and HA with only a 10% water flux reduction from 25.0 to 22.5 kg m⁻² h⁻¹ bar⁻¹ with excellent co-pollutant removal rate of 99% over 40 h. Furthermore, the integrated catalyst-membrane also removed a range of organic pollutants (neutral red, tetracycline hydrochloride, oxytetracycline) achieving > 90% rejection and 30 kg m⁻² h⁻¹ bar⁻¹. These results show that the integrated catalyst-membrane can effectively purify a binary pollutant mixture containing both hazardous dye and natural organic matter and other pharmaceutical chemicals whilst producing process water for recycling and reuse.