Highly enhanced photocatalytic activity of Au nanorod–CdS nanorod heterocomposites

• Au–CdS interfaces composing different shapes of the respective nanoparticles are made.
• Photoactivity of Au nanorod–CdS nanorod > Au nanosphere–CdS nanorod interface.
• Photoexcited e−–h+ pairs of Au–CdS nanorod composite exhibited highest relaxation lifetime.
• Au nanorod–CdS nanorod interface improves the current–voltage (I–V) characteristics.
• Photoproduction of aminophenol (53%) by Au(R)–CdS(R) > 9.3% of Au(S)–CdS(R) arrays.

This paper signifies the importance of different shapes of Au and CdS-nanoparticles for fabricating Au–CdS heterocomposites {prepared by mixing or impregnation of Au-nanosphere (9.1 nm), Au-nanorod (20 nm × 8.6 nm; L × W), CdS-nanosphere (10–12 nm) and CdS-nanorod (126 nm × 5.5 nm)} onto the photoluminescence and photocatalytic study. Second derivative absorption spectra's exhibit precise onset at 441 nm (CdS-nanosphere) and 469.5 nm (CdS-nanorod) that are significantly red-shifted to 509 nm (Au-nanosphere–CdS-nanosphere), 485 nm (Au-nanosphere–CdS-nanorod), 520 nm (Au-nanorod–CdS-nanosphere) and 485.5 nm (Au-nanorod–CdS-nanorod) depending upon interfacial contact-area. XRD patterns reveal the hexagonal phase of pure and Au–CdS nanocomposites. Photoluminescence of CdS nanorods has been effectively inhibited by modifying its surface with Au-nanoparticles (0.002–0.04 wt%). Relaxation lifetime of photoexcited charge-carriers found to be improved ca. 12.5 μs for Au-nanosphere–CdS-nanorod and 34 μs for Au-nanorod–CdS-nanorod due to effective charge transfer kinetics at the interface, in contrast to prompt charge-recombination (2.7 μs) in CdS. Under UV light (10.4 mW/cm2) irradiation, Au-nanorod–CdS-nanorod exhibits the best photocatalytic activity for the oxidation of salicylic acid (86%, k = 9 × 10−3 min−1) and reduction of p-nitrophenol to p-aminophenol (53%) as a function of improved stability and better current–voltage (I–V) characteristics suitable for rapid charge transfer process during photoreaction.

Au nanorod (20 nm × 8.6 nm)–CdS nanorod (126 nm × 5.5 nm) interface exhibits longer relaxation time (34 μs) of photoexcited charge carriers relative to 12.5 μs of the Au nanosphere (9.1 nm)–CdS nanorod array that led to a superior charge separation process which significantly quenches the photoluminescence (80%), improves the salicylic acid photooxidation (86%) and photoreduction of p-nitrophenol to p-aminophenol formation (53%) by Au nanorod–CdS nanorod composite as compared to 73%, 76% and 9.3%, respectively, by Au nanosphere–CdS nanorod heterojunction.Figure optionsDownload high-quality image (87 K)Download as PowerPoint slide