(Figure Presented) Particle-larly good! Thermal annealing and etching of physical composite butyl-capped Si gels and SiO 2 nanoparticles at 900°C under an Ar atmosphere is a versatile method for the formation of 3D porous bulk Si particles (see picture). Complete etching of the SiO 2 from the SiO 2/carbon-coated Si (c-Si) composite results in the retention of the remaining c-Si as a highly porous but interconnected structure, which preserves the starting morphology.