Abstract The adsorption of [octakis(2-trimethylammoniumethylsulfanyl)-porphyrazinatocobalt]octaiodide from aqueous solution onto negatively charged sepiolite is investigated. The effects of temperature, dye and solid concentration and contact time on adsorption were evaluated. Adsorption experiments were analyzed in the light of zeta potential measurements and desorption behavior of the dye–sepiolite composite. Experimental data were analyzed using four adsorption kinetic models, of which a pseudo-second-order kinetic model was found to be superior. Experimental equilibrium data were fitted to five adsorption isotherm models, from which the free energy, enthalpy and entropy of the adsorption processes were determined. Adsorption onto sepiolite was exothermic and spontaneous. AAS and FTIR were used to elucidate the adsorption mechanism. The novel composite is considered to be useful in optical and catalytic applications.