Evolution of nickel sulfide hollow spheres through topotactic transformation

In this study, a topotactic transformation route was proposed to synthesize single-crystalline beta-NiS hollow spheres with uniform phase and morphology evolving from polycrystalline alpha-NiS hollow spheres. Uniform polycrystalline alpha-NiS hollow spheres were firstly prepared with thiourea and glutathione as sulfur sources under hydrothermal conditions through the Kirkendall effect. By increasing the reaction temperature the polycrystalline alpha-NiS hollow spheres were transformed to uniform beta-NiS hollow spheres. The beta-NiS crystals obtained through the topotactic transformation route not only have unchanged morphology of hollow spheres but are also single-crystalline in nature. The as-prepared NiS hollow spheres display a good ability to remove the organic pollutant Congo red from water, which makes them have application potential in water treatment.