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The effect mechanism of Cu2+, Zn2+ and Ni2+ ions in wastewater on photocatalytic activity remained unknown. For phenol-4-sulfonic acid (PSA) photodegradation, we fabricated anatase/rutile/activated carbon fiber composites (A/R/ACFs) by the hydrothermal deposition of rutile TiO2 nanorods and anatase TiO2 nanoparticles on ACFs. A/R/ACFs exhibited better photocatalytic activity than both R/ACFs and A/ACFs because anatase/rutile heterojunctions supported electron transfer from rutile to anatase. All Cu2+, Zn2+ and Ni2+ ions in wastewater improved the chemical stability of PSA by forming PSA-Cu(II), PSA-Zn(II) and PSA-Ni(II) complex compounds, and thus inhibited the PSA photodegradation. Notably, the as-formed photoelectrons over A/R/ACFs were partly consumed due to the reduce reaction of Cu2+ ions into Cu+/Cu0, avoiding electron-hole recombination and improving PSA photodegradation efficiency. No reduce reaction of Zn2+ and Ni2+ ions occurred during the PSA photodegradation process. Hence, the A/R/ACFs are an effective photocatalyst for wastewater purification, and low Cu2+ concentrations facilitated the PSA photodegradation. [ABSTRACT FROM AUTHOR]