Abstract
We demonstrate a low-temperature synthesis of hydrophilic, penicillamine-stabilized hybrid CdS-Au nanoparticles (NPs) utilizing different Au concentrations. The obtained hybrid nanomaterials exhibit photoluminescence quenching and emission lifetime reduction in comparison with their raw semiconductor CdS NPs counterparts. An increase of concentration of Au present at the surface of CdS leads to lower photoluminescence intensity and faster emission decays, suggesting more efficient charge separation when larger Au domains are present. For photocatalysis studies, we performed methylene blue (MB) absorption measurements under irradiation in the presence of CdS-Au NPs. After 1 h of light exposure, we observed the absorbance decrease to about 35% and 10% of the initial value for the CdS-5Au and CdS-7.5Au (the hybrid NPs obtained in a presence of 5.0 and 7.5 mM Au), respectively, which indicates MB reduction caused by electrons effectively separated from holes on metal surface. In further similar photocatalysis experiments, we measured bovine serum albumin (BSA) integrated photoluminescence intensity quenching in the presence of CdS-Au NPs, with a 50% decrease being obtained for CdS-2.5Au NPs and CdS-5Au NPs, with a faster response rate detected for the system prepared with a higher Au concentration. The results suggest hole-driven reactive oxygen species (ROS) production, causing BSA degeneration. Finally, we performed two-photon excited emission (TPEE) measurements for CdS-5Au NPs, obtaining their two-photon absorption (TPA) cross-section values up to 15.8 × 103 GM (Goeppert-Mayer units). We conclude that the obtained water-soluble CdS-Au NPs exhibit potential triple functionalities as photocatalysts for reduction and oxidation reactions as well as materials for two-photon absorption applications, so that they may be considered as future theranostics.
Highlights
A popular trend of novel material engineering is to design more advanced materials, especially nanomaterials, which display several functionalities at one time
On the basis of the results presented above, we conclude that we successfully synthesized hybrid CdS-Au NPs, which exhibit triple photocatalytic, photosensitizing, and nonlinear optical properties
transmission electron microscopy (TEM) images of CdS-Au nanohybrids and decrease of photoluminescence intensity, as well as lifetime shortening in comparison with as-synthesised raw CdS NPs, allow us to state that Au was effectively deposited at the surface of semiconductor NPs
Summary
A popular trend of novel material engineering is to design more advanced materials, especially nanomaterials, which display several functionalities at one time. Those materials are considered useful in such fields as, among many others, medicine, energy generation, conversion, and storage. Among various functionalities that may be engineered into materials, catalytic properties merit attention. Catalysts are often necessary and even irreplaceable to carry out certain chemical reactions. As they are not reactants, they are not consumed and processed to products during reaction. Photocatalysts gain particular interest as they enable conversion of, for example, solar into chemical energy, allowing chemical reactions to occur. A very important branch of photo-driven catalytic reactions is those using nanoparticles (NPs) as a controlling factor in processes such as wastewater treatment [3,4], CO2 reduction [5,6], or hydrogen generation [7,8]
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