Sustainable engineering of rice husk-derived mesoporous silica for optimal dispersion and reinforcement in A380 aluminum composites

Valorization of agricultural biomass for the production of functional nanomaterials is a key paradigm within the circular economy strategy, thereby mitigating waste management challenges and securing sustainable precursors. In this work, rice husk ash (RHA) was utilized as a biogenic silica precursor for the synthesis of mesoporous silica nanoparticles (RH–SiO 2 ) via an alkaline extraction followed by surfactant-assisted precipitation, with cetyltrimethylammonium bromide (CTAB) acting as a soft template for pore formation. The synthesis process demonstrated promising green metrics, including a yield of 91.5%, along with theoretical atom economy and E-factor values of 30.8% and 2.25, respectively. Physicochemical characterization revealed that controlled calcination of the raw biomass at 700 °C substantially removed the organic matrix, thereby increasing the silica content from 24.7 wt% in the raw biomass to 90.3 wt% in the RHA, while preserving a reactive, amorphous, and polymorph-free structure. The synthesized nanoparticles exhibited a hierarchical mesoporous structure, comprising primary spheres with a uniform dimension of approximately 19 nm and a prominent specific surface area of 193 m 2 g -1 , compared to 58 m 2 g -1 for the control sample synthesized without CTAB. Fourier Transform Infrared (FTIR) spectroscopy confirmed the successful development of a pure siloxane (Si–O–Si) network and the substantial removal of the surfactant following a final calcination step at 600 °C. Furthermore, to evaluate their reinforcing efficiency, the prepared RH–SiO 2 nanoparticles were incorporated into a gas-atomized A380 aluminum matrix via mechanical alloying and subsequent vacuum hot pressing at 510 °C. Structural and microhardness evaluations demonstrated that the low-energy milling window facilitated excellent nanoparticle de-agglomeration, rendering these biogenic mesoporous nanostructures highly efficient reinforcement phases for advanced metal matrix surface nanocomposites, significantly enhancing the microhardness to 75 HV.