Enhanced adsorption performance of hierarchical S-doped Ni(OH)₂ hollow nanocomposites for the removal of Congo red

In this work, nonmetallic S was doped into hierarchical Ni(OH)₂ hollow microspheres by ethanol solvothermal method using thiourea as sulfur source. Although the morphology of precursor Ni(OH)₂ is maintained, the surface states and pore properties had greatly changed after S doping. Using the as-prepared S-doped Ni(OH)₂ as adsorbents for the removal of Congo red (CR), the S-doped Ni(OH)₂ exhibited much better adsorption capacity compared with undoped Ni(OH)₂. The adsorption behavior of both Ni(OH)₂ and S-doped Ni(OH)₂ followed the pseudo-second-order kinetic model and intraparticle diffusion model. The equilibrium data of Ni(OH)₂ could be better fitted by Langmuir model, while Freundlich model could be better used to describe the S-doped Ni(OH)₂ with a much larger adsorption capacity toward CR. The tuned microstructure and changed surface states of adsorbent after S doping may be responsible for the enhanced adsorption performance. Therefore, the doping of S species into hierarchical Ni(OH)₂ paves a new way to tune the microstructure and surface states of Ni-based materials.