Trimethoprim　(TMP),　as　a　widely　used　chemotherapeutic　antibiotic　agent,　has　caused　potential　risks　to　the　aquatic　environment.　In　this　study,　magnetic　Co-doped　Fe3O4/α-FeOOH　was　fabricated　by　a　facile　one-step　ageing　method　and　used　for　activation　of　peroxymonosulfate　(PMS)　in　TMP　degradation.　It　was　found　that　low　catalyst　(0.5　g/L)　and　PMS　addition　(0.2　mM)　led　to　the　high　degradation　efficiency　of　TMP　(97.2%,　kobs　=　0.11211　min−1)　over　a　wide　range　of　pH.　The　oxidation　of　active　radical　(SO4·−)　and　non-radical　singlet　oxygen　(1O2)　co-acted　on　TMP　degradation.　Besides,　PMS　was　activated　through　the　cycles　between　Co(II)/Co(III)　and　Fe(II)/Fe(III).　Fifteen　degradation　intermediates　of　TMP　were　identified　by　LC-MS,　and　three　possible　degradation　pathways　including　hydroxylation,　demethylation,　and　cleavage　were　proposed.　The　recovered　catalysts　exhibited　high　stability　and　reusability,　maintaining　80%　TMP　removal　efficiency　with　inappreciable　metal　leaching　(0.012　mg/L　of　Co,　0.113　mg/L　of　Fe)　after　six　cycles.　Besides,　the　Co–Fe3O4/α-FeOOH/PMS　system　was　highly　tolerant　to　inorganic　anions　and　actual　water　bodies　(river　water,　lake　water,　tap　water,　and　sewage　plant　effluent).　Overall,　this　work　provided　a　promising　way　to　the　potential　application　of　Fe-based　binary　metal　oxide　for　PMS　activation.　©　2022　Elsevier　Ltd