One-pot synthesis of carbon nanotube/zinc sulfide heterostructures: Characterization and effect of electrostatic interaction on the optical properties

Tuning the Optical Band Gap of Semiconductor Nanocomposites—A Case Study with ZnS/Carbon

“…These findings are highlighting the great potential that the internal effects in nanocomposites exhibit to fine tune the electronic properties of its components and can be of substantial interest in the design of new photo-or electrocatalysts. Furthermore, these theoretical considerations can be supported by our experimental findings in which ZnS nanoparticles (synthesized with a Zn/S ratio > 1, suggesting a Zn rich surface) conjugated to oxidized CNTs (covered with negatively charged carboxyl groups on its surface, confirmed by zeta potential measurements) show an increased optical band gap (about ∼0.1 eV) when compared to the pristine ZnS nanoparticles [10].…”

“…Technical graphitized carbon particles on the other hand are presenting quite rugged surfaces with local curvatures similar to MWCNTs. In Reference [10] the authors therefore did check, whether MWCNTs and a commercial carbon material (Vulcan from Cabot) did show similar effects after functionalization and combination with ZnS QDs. They did find the same optical signature in both kinds of composite.…”

“…To research what influence the actual physical binding of the carbon support to the QD in nanocomposites exerts we investigated two different cases of a functionalized CNT (10,10) binding to a cysteamine terminated QD. The oxidized CNT was constructed by destroying two C-C bonds within a hexagon of the CNT structure.…”

“…All materials (quantum dots with ligands, functionalized carbon nanotubes, heteroaggregates and composites) were synthesized by standard wet chemical methods and characterized by standard procedures, as described in detail in prior work [10,11] and references therein. Typical quantum dots are charged positively, whereas the CNTs due to oxygen-dominated surface groups are exhibiting negative charge.…”

“…A typical case of the conditions described above are nanocomposites formed from ligand-stabilized semiconductor QDs and a functionalized carbon support: depending on the specific local arrangements and environments spectral shifts in absorption (and excitonic emission) have been observed. They have been detected in emission as a Stark shift of the excitonic luminescent state in a CdSe/ZnS core shell QD conjugated to electrostatically charged carbon nanotubes (CNTs) [ 9 ] or more directly in the excitation spectra of pure ZnS nanoparticles conjugated to oxidized CNTs [ 10 ]. In the latter work an attempt was made to control the distance between quantum dots and charged support by the synthetic protocol applied: the composites were either made by electrostatically controlled heteroaggregation (leading to a more distant and loose arrangement due to the presence of ligand and solvation shells and with a morphology depending on ratios of positively and negatively charged components [ 11 ]) or by direct growth of the quantum dots on the support, leading to a more intimate connection [ 10 ].…”