Formation of gold and gold sulfide nanoparticles and mesoscale intermediate structures in the reactions of aqueous HAuCl4 with sulfide and citrate ions

Abstract

The effects of the molar ratio of sodium sulfide to chloroauric acid in the range of 0.5 to 5 and the time factor on the formation of the nanoparticles (NPs) of metallic Au, Au(2)S or their mixtures have been studied applying in situ and ex situ techniques (UV-Vis absorption spectroscopy, potentiometry, TEM, SPM, SERS, XPS). The products and intermediates have been compared with those for the reduction of chloroaurate with citrate ions and combinations of citrate and sulfide ions. An increase in the concentration of sulfide ions accelerates the reduction of Au(iii) complexes but hinders the nucleation and growth of Au NPs, resulting in a prolonged period before the appearance of plasmon peaks. The electrochemical potential is not directly associated with the plasmon intensities, although the potential sharply decreases simultaneously with a blue shift of the near-IR peak emerging with the Na(2)S/HAuCl(4) ratios of 0.5 to 1.5. It was concluded that the peak is due to longitudinal plasmon resonance of gold nanoplates. Au(2)S NPs, the nucleation of which is effectively inhibited, and probably some structures and fragments visible in TEM and AFM, including 2-5 nm Au NPs, crystallize in part outside the solutions. The evidence of partially liquid mesoscale structures comprising intermediate gold species as precursors of nanoparticles is presented, and their origin, ex situ transformation and role in the reaction mechanisms are discussed.

Au2Sx/CdS Nanorods by Cation Exchange: Mechanistic Insights into the Competition Between Cation‐Exchange and Metal Ion Reduction

“…Au4f spectra (Figure 1 d) show the presence of Au 1+ [ 28 ] and Au 3+ in addition to Au 0 . The absence of a signifi cant peak in the survey around 200 eV due to Cl2p eliminates any possibility of chloride of Au.…”

Transition‐Metal‐Ions‐Induced Coalescence: Stitching Au Nanoclusters into Tubular Au‐Based Nanocomposites

“…[ 9d ] After being treated with the transition metal ions, the major binding energy peaks of Au 4 f 7/2 for all of the four cases shift to 83.8-84.2 eV (Figure 2 d and Figure S7, Supporting Information), which are higher than those of the metallic Au(0) species but similar to the oxidation state of Au(I) in Au 2 S. [ 10 ] In addition, the binding energies of the added transition metal ions in each case are lower than those of their corresponding metal precursors. More specifi cally, two binding energy peaks at 934.5 and 932.4 eV are observed for Cu 2 p 3/2 (Figure 2 a), with the lower one assigned to Cu(I) species, one peak at 367.…”

A Transformation of Intermediates of Sulfide Reduction of Gold(III) on the Pyrolytic Graphite

“…реагентов [Na 2 S] 0 /[HAuCl 4 ] 0 ) могут образовываться либо металлические частицы с управляе-мыми свойствами [5][6][7][8][9][10][11][12][13], либо осадок аморфного сульфида золота (I), кристаллизации которо-го предшествует стадия относительно длительного (в течение часов и суток) существования пересыщенного раствора, содержащего, как нами было показано в серии работ [14][15][16][17][18][19], жидкие промежуточные структуры коллоидных размеров, природа которых остается малоизученной.…”

“…Также продукты сульфидного восстановления обладают повышенной, по сравнению, например, с частицами цитратного гидрозоля золота, адгезией к поверхности высокоориентированного пирографита (ВОПГ) [14,15], образуя на последнем плотную пленку, распадающуюся на воздухе на отдельные наночастицы размерами 2-5 нм.…”

“…Разложение промежуточных структур наблюдали также под действием электронного пучка в условиях ПЭМ-эксперимента [15]. В нашей недавней работе [19] показано, что появление в растворе и укрупнение жидких промежуточных структур частично за счет роста, частично за счет коалесценции, являются необходимыми условиями нуклеации.…”