Using NH2-MIL-125(Ti) for efficient removal of Cr(VI) and RhB from aqueous solutions: Competitive and cooperative behavior in the binary system

•Oxygen-containing or ammonia-containing functional groups (such as COOH, OH, NH, NH2) of NH2-MIL-125(Ti) can chelate or complex with Cr(VI), Cr(III) and RhB.•Multiple mechanisms are responsible for simultaneously removing Cr(VI) and RhB in an aqueous solution.•The removal rate of RhB increased with rising Cr(VI) concentrations, and yet the presence of RhB reduced the adsorption capacity of Cr(VI).•The enhanced adsorption of RhB might be due to the formation of Cr(VI)-RhB and Cr(III)-RhB complexes between the adsorbate and the adsorbent