Porous Silica Born From Rice Husks

A semicrystalline form of porous silica can be prepared from rice husks, according to the international team that developed the process (ACS Appl. Mater. Interfaces, DOI: 10.1021/am201619u). Silica is widely used commercially in applications that include sorption, gas separation, and catalysis. Porous high-surface-area forms of the material are generally made from silicon alkoxide precursors, which are prepared via multistep, energy-intensive, acid-based processes using raw materials such as sand. The new method, developed by Luyi Sun of Texas State University, San Marcos; Weixing Wang of South China University of Technology, in Guangzhou; and coworkers may lead to more economical and environmentally benign silica preparation methods. The team reports that pyrolysis of rice husks liberates the biogenic silica from the husk cell walls. The silica forms 4.2-nm-diameter particles that fuse into amorphous particles in the 25- to 30-nm range. By adjusting the temperature and exposing the larger nanoparticles to potassium cations, the team can coax the particles to melt and fuse, thereby forming aggregates with tunable pore size and morphology.