Optimization of reaction systems plays a key role in preventing the backward reaction of water splitting. 'Nanoreactors' are formed with nanoporous photocatalyst in a facile H(2) production system, hexane-water biphase system. The rate of H(2) evolution could reach 63.37 mmol h(-1) g(-1) in the biphase system (40% higher than that in the single phase system).