Investigation of the Photocatalytic Hydrogen Production of Semiconductor Nanocrystal-Based Hydrogels

Destabilization of a ligand-stabilized semiconductor nanocrystal solution with an oxidizing agent can lead to a macroscopic highly porous self-supporting nanocrystal network entitled hydrogel, with good accessibility to the surface. The previously reported charge carrier delocalization beyond a single nanocrystal building block in such gels can extend the charge carrier mobility and make a photocatalytic reaction more probable. The synthesis of ligand-stabilized nanocrystals with specific physicochemical properties is possible, thanks to the advances in colloid chemistry made in the last decades. Combining the properties of these nanocrystals with the advantages of nanocrystal-based hydrogels will lead to novel materials with optimized photocatalytic properties. This work demonstrates that CdSe quantum dots, CdS nanorods, and CdSe/CdS dot-in-rod-shaped nanorods as nanocrystal-based hydrogels can exhibit a much higher hydrogen production rate compared to their ligand-stabilized nanocrystal solutions. The gel synthesis through controlled destabilization by ligand oxidation preserves the high surface-to-volume ratio, ensures the accessible surface area even in hole-trapping solutions and facilitates photocatalytic hydrogen production without a co-catalyst. Especially with such self-supporting networks of nanocrystals, the problem of colloidal (in)stability in photocatalysis is circumvented. X-ray photoelectron spectroscopy and photoelectrochemical measurements reveal the advantageous properties of the 3D networks for application in photocatalytic hydrogen production

Synthesis of metal-free functionalized g-C3N4 nanosheets for enhanced photocatalytic activity

A new visible-light active polymeric semiconductor was fabricated covalently functionalizing the g-C3N4 using halogenated phenyl groups. 4-bromobenzonitrile was employed to introduce organic motifs into g-C3N4 networks through a convenient one-pot thermally induced process. The functionalization of the g-C3N4 with the halogenated phenyl group extended the original π-conjugation system, leading to the enhancement of visible-light absorption, and the separation of charge carriers. Introducing the new group, the g-C3N4 pore structure was enriched, resulting in a larger specific surface area and an increase in active sites. The functionalization led to an easier exfoliation of the g-C3N4 framework into thinner layers, enhancing its dispersion ability in the water. Under visible-light irradiation, the as-prepared semiconductor exhibited increased photocatalytic activity to the pristine g-C3N4. The photocatalytic performances were investigated on a simple organic compound, methanol, a model dye, rhodamine B, and an emergent contaminant, 4-nitrophenol. This research provided new insights on metal-free modified g-C3N4 as a visible-light photocatalyst