Hierarchically Structured Calcium Silicate Hydrate-Based Nanocomposites Derived from Steel Slag for Highly Efficient Heavy Metal Removal from Wastewater

Calcium silicate hydrate (CSH) is a potential new material for effective heavy metal adsorption, but the high manufacturing costs and difficult reusability have restricted its large-scale application. Herein, we report a green and facile strategy to prepare amorphous and hierarchically structured CSH-based nanocomposites from steel slag for heavy metal removal. The obtained flowerlike CSH-based materials showed fast adsorption rates and superior adsorption capacities for all employed heavy metal ions (Cu(II), Pb(II), and Zn(II)), with maximum adsorption capacities of approximately 244, 273, and 508 mg/g, respectively. The adsorption kinetics were all well fitted to the pseudo-second-order model, and the adsorption equilibrium fitted the Langmuir model. The excellent adsorption performance could be attributed to the release of Ca2+ and OH– from the CSH nanosheets. Moreover, as a case study, the obtained CSH–Cu(II) after absorption can be converted and reused as an photocatalyst by simply heating at 300 °C, which shows an excellent degradation efficiency of ∼90% for methylene blue within 150 min under simulated sunlight irradiation. This work lays the foundation for the development of an environmentally friendly route of "solid waste → adsorbent → catalyst", which will be of great significance for solid waste utilization as well as water purification.