In this work, NiO was prepared by calcining nickel oxalate and it was used to remove six different kinds of dye from aqueous solution. The experimental results showed that NiO exhibited selective and excellent removal adsorption capacity towards acid orange 7 (AO7), indigo disulfonate (ID) and Congo red (CR) which were anionic dyes that contain a negatively charged sulfonic group (–SO3-) but no adsorption selectivity for the binary anionic dye system. The effects of influential parameters, including contact time, initial solution pH, and temperature, on the adsorption capacities towards AO7 and ID were systematically investigated. The adsorption process is spontaneous and exothermic for AO7, but endothermic for ID. The pseudo-second-order kinetic model and the Langmuir isotherm model well described the adsorption process. The maximum adsorption capacities were 178.57 and 227.27 mg/g for AO7 and ID under ambient temperature (25 ± 1 °C), respectively. The experimental and characterization results revealed that the excellent removal capacities towards AO7 and ID by NiO may result from the electrostatic attraction between Ni2+ and –SO3-. Finally, the promising result proves that NiO also has a great adsorption potential for actual wastewater.

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