Preparation And Optical Response Of Gold-platinum And Copper-platinum Nanoparticles In Quantum Size Regime

Noble metal nanoparticles(NPs)have attracted extensive research attention due to their unique properties and applications in catalysis,photonics,electronics,and biotechnology.Significantly,the properties of noble-metal nanostructures can be tailored to improve their performance in a variety of applications by controlling their size,shape,composition,and porosity.Noble metal(such as Au,Ag,Cu,etc.)is closely linked with plasmonics.The surface plasmon resonances have distinctive behavior,which lead to practical and potential applications in quantum optics,nanocatalysis,sensors,information storage and biology.For the applications in photocatalysis,great efforts have been dovoted to improve photocatalytic efficiency of the metal nanoparticles via the enhanments of localized surface plasmon resonances and the synergistic effect of bimetals.Plasmonic metal NPs themselves could be utilized as photocatalysts and the surface plasmon resonance possess the unique capacity to enhance the photocatalytic activity.The photocatalysis efficiency is positively related to the surface area/volume ratio and the SPR strength.As the size decreases,the surface area/volume ratio increases but the SPR strength dramatically decreases for the ultrasmall nanopaticles.Therefore,the optimization of catalysis efficiency in the quantum size regime has been attracted increasing interest recent years.Usually,the metals with strong SPR(such as Ag,Au,and Cu)have poor intrisinc catalytic activity,and the metals with excellent catalytic efficiency(such as Pt and Pd)have weak SPR.The combination of gold and copper,which have strong surface plasmon resonance,and platinum,which have high catalytic efficiency,can significantly improve the photocatalytic efficiency through the synergistic effect of bimetal.The synergistic effect of bimetals significantly improve the photocatalytic efficiency.The more prominent feature of above mentioned bimetallic NPs is the SPR,which has a high-efficient light harvesting ability and a largely enhanced local field.Subsequently,the plasmon decay and the formation of energetic electron could transfer towards the high chemically active material to promote the catalytic reaction.In this paper,we focus on the local surface plasmon characteristics of quantum-sized gold-platinum and copper-platinum core-shell nanoparticles.We prepared quantum-sized gold-platinum and copper-platinum core-shell nanoparticles,and studied their local surface plasmon optical properties and their applications in photocatalytic reactions.First,we synthesized quantum-sized Pt@Au core-shell nanoparticles.Compared to the quantum-sized Au core nanoparticles with a diameter d _Au=3.6±0.4 nm,the SPR wavelength of Pt@Au with a 0.7 nm Pt shell monotonically shifted by 7.9 nm as the size increased(the thickness of the Pt shell increased).In contrast,the SPR wavelength of Pt@Au with a 7 nm shell was red-shifted by 29.5 nm as the size increased(Pt shell thickness increased)compared to the 35 nm Au core nanoparticles in the classical size scheme.The photocatalytic reaction rate of quantum-sized Pt@Au to 4-NP:Na BH₄ is twice that of the classical size Pt@Au,indicating that the enhanced photocatalytic activity is attributed to strong plasmon resonance and quantum size Pt@gold nanoparticles.Specific surface area.For Pt@Au nanoparticles in SPR-enhanced(MB:H₂O₂)photocatalysis,the quantum-catalyzed nanoparticle has a photocatalytic efficiency greater than that of a classically sized nanoparticle,and it is almost independent of the amount of Pt on Au.Therefore,we can conclude that quantum plasmon resonance plays a major role in the enhanced photocatalysis of Pt@Au nanoparticles.These observations reveal the importance of quantum plasmon resonance for enhanced photocatalytic activity.Second,we synthesized quantum-sized Pt@Cu core-shell nanoparticles and studied their surface plasmon resonance and plasmon-enhanced photocatalytic activity in the quantum size range.Compared with quantum-sized Cu core nanoparticles(d Cu=3.7±0.5 nm),as the size increases(the thickness of the Pt shell increases),as the Pt/Cu ratio increases from 0%to 4%,Pt@Cu core-shell nanoparticle The SPR wavelength of the particles shifted from 574 nm to 566.8 nm.When the Pt/Cu ratio was further increased to 14%,the SPR was red shifted from 566.8 nm to 573.7 nm.We studied the photocatalytic activity of quantum-sized Pt@Cu nanoparticles.It was observed that the photocatalytic activity of the quantum size Pt@Cu increased as the thickness of the Pt shell increased.These findings reveal the importance of quantum plasmon resonance for enhancing photocatalytic activity.First,we synthesize Pt@Au and Pt@Cu core-shell NPs with optimized quantum SPR,comparatively investigate their catalytic activites via two model reactions with and without SPR enhancement,and demonstrate that the quantum SPR of gold plays a dominant contribution for the photocatalytic activity of Pt@Au NPs.In the extinction spectra,the SPR wavelength of Pt@Au core-shell NPs in quantum size regime monotonously blue-shifts as the thickness of Pt shell increases.On the contrary,the SPR wavelength of Pt@Au core-shell NPs in classical size regime red-shifts as the thickness of Pt shell increases.The different results indicate the classical size effect and the strong quantum size effect,respectively.Interestingly,as the Pt shell thickness increases,the SPR wavelength of Pt@Cu core-shell NPs in quantum size regime firstly blue-shifts and then red-shifts.The photocatalytic activities of the core-shell NPs with different Pt shell thickness are compared by using the two model reactions of the photoreduction of 4-nitrophenol(4-NP)and the photodegradation of methylene blue(MB).The photocatalytic rate for 4-NP:Na BH₄ is enhanced by the strong plasmon resonance and the large surface area/volume ratio of quantum-sized core-shell NPs.These findings reveal the significance of the quantum plasmon resonance on the enhancement of photocatalytic activity.Finally,we tried to synthesis Cu-Pt alloy and gold nano-cup,and explored the influencing factors affecting its morphology.