Constructing　a　p–n　heterojunction　is　a　feasible　strategy　to　manipulate　the　dynamic　behaviors　of　photogenerated　carriers　through　an　internal　electric　field.　Herein,　a　novel　highly　efficient　indium　oxide/bismuth　oxyiodide　(In2O3/BiOI)　p–n　junction　photocatalyst　was　fabricated　using　a　facile　ionic　liquid-assisted　precipitation　method　for　the　first　time.　The　morphologies　were　modified　by　adding　different　amounts　of　acetic　acid　solution.　Their　hierarchical　architecture　was　beneficial　for　adsorbing　contaminants　in　wastewater,　while　the　in-situ　formed　p-n　heterojunction　between　BiOI　and　In2O3　facilitated　interfacial　charge　transfer　and　improved　the　quantum　efficiency.　Their　visible　light-responsive　photocatalytic　activities　were　systematically　investigated　by　photocatalytic　o-phenylphenol　(OPP)　and　4-tert-butylphenol　(PTBP)　oxidation.　The　degradation　rate　of　OPP　over　In2O3/BiOI-2　was　up　to　5.67　times　higher　than　that　for　BiOI.　The　excellent　activity　of　In2O3/BiOI　should　be　attributed　to　the　rapid　interfacial　charge　transfer,　depressed　carrier　recombination,　and　proper　band　potentials.　Trapping　experiments　and　electron　paramagnetic　resonance　characterizations　confirmed　the　generation　of　hydroxyl　radicals　(•OH)　and　superoxide　radicals　(•O2–),　which　have　played　a　key　role　in　decomposing　pollutants.　The　intermediate　products　generated　during　the　photocatalytic　degradation　of　OPP　were　detected　and　identified　by　liquid　chromatography-mass　spectrometry.　Meanwhile,　their　possible　molecular　structures　and　degradation　pathways　have　also　been　inferred.　©　2021　Elsevier　Inc.