Phenylamine-Functionalized rGO/TiO₂ Photocatalysts: Spatially Separated Adsorption Sites and Tunable Photocatalytic Selectivity

The preferential adsorption of targeted contaminants on a photocatalyst surface is highly required to realize its photocatalytic selective decomposition in a complex system. To realize the tunable preferential adsorption, altering the surface charge or polarity property of photocatalysts has widely been reported. However, it is quite difficult for a modified photocatalyst to realize the simultaneously preferential adsorption for both cationic and anionic dyes. In this study, to realize the selective adsorption for both cationic and anionic dyes on a photocatalyst surface, the negative reduced graphene oxide (rGO) nanosheets and positive phenylamine (PhNH₂) molecules are successfully loaded on the TiO₂ surface (PhNH₂/rGO-TiO₂) with spatially separated adsorption sites, where the negative rGO and positive PhNH₂ molecules work as the preferential adsorption sites for cationic and anionic dyes, respectively. It was interesting to find that although all the TiO₂ samples (including the naked TiO₂, PhNH₂/TiO₂, rGO-TiO₂, and PhNH₂/rGO-TiO₂) clearly showed a better adsorption performance for cationic dyes than anionic dyes, only the PhNH₂/rGO-TiO₂ with spatially separated adsorption-active sites exhibited an opposite photocatalytic selectivity, namely, the naked TiO₂, PhNH₂/TiO₂, and rGO-TiO₂ showed a preferential decomposition for cationic dyes, while the resultant PhNH₂/rGO-TiO₂ exhibited an excellently selective decomposition for anionic dyes. In addition, the resultant PhNH₂/rGO-TiO₂ photocatalyst not only realizes the tunable photocatalytic selectivity but also can completely and sequentially decompose the opposite cationic and anionic dyes.