Tuning the photocatalytic activity of CdS nanocrystals through intermolecular interactions in ionic-liquid solvent systems

摘要

Synthetic solvent systems for the fine-tuned preparation of CdS nanocrystallites, active in visible-light photocatalytic hydrogen production, were studied. To control crystallite size and spectral properties, the CdS crystals were synthesised by using different solvent systems, containing a series of tetrabutylammonium amino carboxylate ionic liquids as the crystal-growth control agents. Six samples of CdS, all with similar physical and spectral properties, exhibited greatly varying photocatalytic activity, with the most active sample outperforming the least active one by almost 60 %. To rationalise this effect, the intermolecular interactions of the synthesis solvent system with the growing CdS nanocrystallites were characterised by using the Reichart betaine dye and the ${E{{{m N}hfill top {m T}hfill}}}$ polarity scale. A correlation was observed between the ${E{{{m N}hfill top {m T}hfill}}}$ values of the solvent system and the photocatalytic activity of the CdS nanocrystallite, suggesting that the hydrogen-bond-donating ability and/or dipolarity/polarisability interactions of the solvent system led to the preferential formation of active surfaces/surface sites on the CdS crystals. Bipolar behaviour: The rate of hydrogen production photocatalysed by CdS was found to be dependent on the solvent system employed for the synthesis of the CdS nanocrystallites (see scheme). By using a solvatochromic approach, a correlation was found between the polarity of the synthesis solvent system and the photocatalytic activity of the CdS.