In this work, we have successfully developed a new and consistent model to describe the growth of gold nanoparticles (Au NPs) via citrate reduction of auric acid (HAuCl4) by carefully assessing the temporal evolution of the NP sizes and surface charges by means of dynamic light scattering (DLS) and zeta-potential measurements. The new model demonstrates that the nucleation and growth of the Au NPs occur exclusively in the particles of the complexes of Au(+) ions and sodium acetone dicarboxylate (SAD) derived from the citrate/HAuCl4 redox reaction, which proceeds as described by the classic LaMer model. Concomitant with the Au NP growing therein, the Au(+)/SAD complex particles undergo reversible agglomeration with the reaction time, which may result in an abnormal color change of the reaction media but have little impact on the Au NP growth. Built on the new model, we have successfully produced monodisperse quasi-spherical Au NPs with sizes precisely regulated from 2 to 330 nm via simple citrate reduction in a one-pot manner. To date, highly uniform Au NPs with sizes spanning such a large size range could not be formed otherwise even via deliberately controlled seeded growth methods.

Monodisperse, quasi-spherical silver nanoparticles (Ag NPs) with controlled sizes have been produced directly in water via adding the aqueous solutions of the mixtures of AgNO3 and sodium citrate to boiling aqueous solutions of ascorbic acid (AA). Different compounds, including NaCl, NaBr, KI, Na2SO4, Na2CO3, Na2S, and Na3PO4, are added to the AgNO3/citrate mixture solutions to form new silver compounds with fairly low solubility in water, which are used as precursors instead of soluble Ag(+) ions to synthesize Ag NPs via AA/citrate reduction. This enables us not only to produce monodisperse, quasi-spherical Ag NPs but also to tune the sizes of the resulting NPs from 16 to 30 nm according to the potential of new silver precursors as well as the concentrations of anions.

We present a simple and effective strategy for high yield synthesis of well-dispersed, core-shell Au-Pt nanodendrites (CS Au-Pt NDs) via overgrowth of platinum on in situ 5.5 nm gold nanoparticles in water at room temperature. The sizes of the resulting CS Au-Pt NDs are 14 nm, which should be the smallest so far to the best of our knowledge. The average dimensions of the small Pt branches on the Au nanoparticle surfaces are about 2.6 nm  4.2 nm, which lead to a significantly increased electrochemically active surface area (up to 35.2 m 2 g À1 ). It is found that the morphology of CS Au-Pt NDs is dependent on the reaction conditions such as the incubation time of citrate-HAuCl 4 solution, the mixing time of citrate-HAuCl 4 -K 2 PtCl 4 solution before AA addition, and Pt-to-Au and AA-to-Pt molar ratios. In comparison with commercial Pt black (0.12 A mg Pd À1 ), the resulting Au-Pt 5 NDs show a superior catalytic activity towards methanol oxidation (0.45 A mg Pd À1 ) due to the electronic interaction between the Au cores and Pt branches in bimetallic Au-Pt NDs and the high fraction of atomic steps, kinks, and corner atoms on the surfaces of the Pt branches.

We present a simple strategy for synthesis of water-soluble, monodisperse, highly fluorescent gold nanoclusters (Au NCs) with sizes of 1.8 nm by co-reduction of glutathione and citrate for 24 h at 50 °C. The fluorescence intensity of the GS/C–Au NCs obtained is pH-dependent and can be reversibly adjusted in the pH range from 4.1 to 8.6.

The Turkevich method, involving the reduction of HAuCl4 with citrate in boiling water, allows the facile production of monodisperse, quasispherical gold nanoparticles (AuNPs). Although, it is well-known that the size of the AuNPs obtained with the same recipe vary slightly (as little as approximately 4 nm), but noticeably, from one report to another, it has rarely been studied. The present work demonstrates that this size variation can be reconciled by the small, but noticeable, effect that the latent heat in boiling water has on the size of the AuNPs obtained by using the Turkevich method. The increase in latent heat during water boiling caused an approximately 3 nm reduction in the size of the as-prepared AuNPs; this reduction in size is mainly a result of accelerated nucleation driven by the extra heat. It was further demonstrated that, the heating temperature can be utilized as an additional measure to adjust the growth rate of AuNPs during the reduction of HAuCl4 with citrate in boiling water. Therefore, the latent heat of boiling solvents may provide one way to control nucleation and growth in the synthesis of monodisperse nanoparticles.