Sunlight-induced synthesis of various gold nanoparticles and their heterogeneous catalytic properties on a paper-based substrate.

This work describes the light-induced preparation of various gold nanoparticles and demonstrates their possible use as efficient photothermal heating materials and practical heterogeneous catalysts under the irradiation of a solar-based light after being loaded onto a paper-based substrate. The synthesis of gold nanoparticles was accomplished under the irradiation of daily sunlight and a solar-simulated light with an intensity that was closely adjusted to the one-sun condition. Tunable sizes of gold nanoparticles were systematically controlled by the ratio of trisodium citrate and gold chloride ions, particularly with the solar-simulated light source. The size distribution and absorption properties of the resulting nanoparticles were thoroughly characterized by scanning electron microscope, dynamic light scattering, and UV-visible spectroscopy. The broad-band solar-based light sources were found to be efficient external stimuli to induce/enhance the formation of various gold nanoparticles at room temperature. As gold nanoparticles typically exhibit efficient light-induced heating properties due to their strong absorption bands, these nanoparticles were physically embedded on a filter paper to examine their photothermal heating properties and heterogeneous catalytic activity in the reduction of 4-nitrophenol under the irradiation of the solar-simulated light. As expected, the gold-loaded filter papers exhibited a systematic increase of temperature as a function of the gold nanoparticle concentration and enhanced catalytic property under the irradiation of the light, presumably caused by the photothermally induced heating property of the loaded gold nanoparticles. Overall, solar-based light sources can offer dual functions for the synthesis and application of metal nanoparticles possessing strong absorption bands.