• Zr-SnS 2 /PANI nanocomposites were synthesized and optimized for photocatalysis. • Higher activity than SnS 2 , Zr-SnS 2 , SnS 2 /PANI, and many other photocatalysts. • Zr 4+ doping and PANI coupling synergistically enhanced the photocatalysis of SnS 2 . • Factors affecting the photocatalytic reduction of Cr (VI) were investigated. • Zr-SnS 2 /PANI can effectively treat the Cr (VI)-containing electroplating solution. The synergistic Zr 4+ doping and PANI coupling were used to improve the photocatalytic activity of SnS 2 nanoflakes for the treatment of aqueous Cr (VI). The Zr-SnS 2 /PANI photocatalyst was prepared by a facile two-step method. The optimal Zr-SnS 2 /PANI-6% (with the Zr/Sn molar ratio of 1:8 and the PANI content of 6 wt%) exhibited dramatically higher photocatalytic activity toward Cr (VI) reduction than SnS 2 , Zr-SnS 2 , SnS 2 /PANI, and many previously reported SnS 2 -based and PANI-containing visible-light photocatalysts. Moreover, Zr-SnS 2 /PANI-6% showed outstanding performance in the photocatalytic treatment of Cr (VI)-containing electroplating solution. Based on the measured photo-electrochemical properties of the samples, the increased photocatalytic efficiency of Zr-SnS 2 /PANI-6% was mainly due to the synergistic effect induced by the smaller bandgap, higher charge transfer efficiency, and lower electron-hole recombination rate. Furthermore, the effects of coexisting cations and anions, photocatalyst amount, initial pH, Cr (VI) concentration, environmental atmosphere, and co-presence of 1,4-benzoquinone or K 2 S 2 O 8 on photocatalytic Cr (VI) reduction over Zr-SnS 2 /PANI-6% were investigated.