pH-Responsive Nanoporous Membranes From Self-Assembly/Sintering of SiO2@Au Core-Shell Nanospheres

We prepared nanoporous membranes by self-assembly of gold-coated silica nanospheres, followed by sintering at 1000 °C. We modified the nanopore surface with ionizable functional groups, by forming a monolayer of L-cysteine or by surface-initiated polymerization of methacrylic acid. Diffusion experiments for the cationic dye Rhodamine B through L-cysteine-modified membranes showed a decrease in flux upon addition of an acid due to the nanopore surface becoming positively charged. Diffusion experiments for the neutral dye, ferrocene carboxaldehyde, through the PMAA-modified membranes showed a 13-fold increase in flux upon addition of an acid resulting from the protonated polymer collapsing onto the nanopore surface leading to larger pore size.