Display omitted ► Pyrite FeS2 crystallites were prepared by using K4Fe(CN)6·3H2O as Fe source. ► The as-prepared pyrite FeS2 could high-efficiently degrade organic dyes. ► The adsorption ability of the FeS2 crystallites is much higher than their photocatalytic degradation capacity. FeS2 crystallites were synthesized successfully via a solvothermal method, using potassium ferrocyanide K4Fe(CN)6·3H2O as Fe source, sulfur powder as S source in the presence of polyvinyl pyrrolidone (PVP) as dispersant. And potassium carbonate provided an alkaline environment. The phase and morphology of the products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). It was found that the temperature and solvent ratio (VEtOH:VH2O) play a crucial role in the formation of FeS2 with a cubic phase structure (pyrite). Then based on a series of experiments, the possible formation mechanism of pyrite FeS2 crystallites was proposed. In addition, research also showed that the as-prepared pyrite FeS2 crystallites could high-efficiently absorb or photocatalytically degrade some organic dyes such as Methylene blue (MB), Safranine T, Methyl orange (MO), Rhodamine B (Rh B) and Pyronine B. Furthermore, the adsorption and photocatalytic degradation abilities of FeS2 for organic dyes were also compared.