Rice husks as a sustainable silica source for hierarchical flower-like metal silicate architectures assembled into ultrathin nanosheets for adsorption and catalysis

Metal silicates have attracted extensive interests due to their unique structure and promising properties in adsorption and catalysis. However, their applications were hampered by the complex and expensive synthesis. In this paper, three-dimensional (3D) hierarchical flower-like metal silicate, including magnesium silicate, zinc silicate, nickel silicate and cobalt silicate, were for the first time prepared by using rice husks as a sustainable silicon source. The flower-like morphology, interconnected ultrathin nanosheets structure and high specific surface area endowed them with versatile applications. Magnesium silicate was used as an adsorbent with the maximum adsorption capacities of 557.9, 381.3, and 482.8 mg/g for Pb²⁺, tetracycline (TC), and UO₂ ²⁺, respectively. Ni nanoparticles/silica (Ni NPs/SiO₂) exhibited high catalytic activity and good stability for 4-nitrophenol (4-NP) reduction within only ∼160 s, which can be attributed to the ultra-small particle size (∼6.8 nm), good dispersion and high loading capacity of Ni NPs. Considering the abundance and renewability of rice husks, metal silicate with complex architecture can be easily produced at a large scale and become a sustainable and reliable resource for multifunctional applications.