Modulating the immobilization process of Au nanoparticles on TiO2(110) by electrostatic interaction between the surface and ionic liquids

Abstract

We found that the adsorption states of Au nanoparticles (NPs) on TiO(2)(110) varied with the ionic liquids (ILs) that encapsulate the NPs during the entire process from synthesis of NPs to immobilization of the NPs on the surface at 323 K. Five kinds of ILs, including three 1-butyl-3-methylimidazolium ([C(4)MIm]) cation-based ILs of tetrafluoroborate ([C(4)MIm][BF(4)]), hexafluorophosphate ([C(4)MIm][PF(6)]) and bis(trifluoromethylsulfonyl)amide ([C(4)MIm][NTf(2)]), and two [BF(4)] anion-based ILs of 1-(methoxymethyl)-1-methylpyrrolidinium ([PY1,1O1][BF(4)]) and N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium ([N122,1O2][BF(4)]), were used. They provided different adsorption states of the Au NPs on the surface. We considered the determinant factor for the adsorption states of NPs on the surface from the viewpoint of electrostatic interactions between IL and IL and between IL and the surface. We deduced the influence of these interactions from the increments of NP's diameter and the amount of NPs after the immobilization, and obtained the order of anions as [BF(4)] ≈ [NTf(2)] > [PF(6)] for the three [C(4)MIm] based ILs and the order of cations as [PY1,1O1] > [C(4)MIm] > [N122,1O2] for the three [BF(4)] based ILs. Interestingly, the above orders were no match with the conventional physicochemical and chemical parameters but β of Kamlet-Taft solvent descriptors and Lewis basicity of anions in the case of anions of ILs. The results of anions indicate that the chemical natures of ILs might affect the immobilization of NPs through hydrogen bonding or coordination bonding with the surface. We suggested that such a trend in anions was 'local viscosity' of ILs in the vicinity of surface. Besides, layer formation of IL on the surface might be also an influential factor to control the size of NPs and the surface density of NPs. Our results show that the combination of a charged surface and charged molecules has the potential for controlling locations of the NPs on the surface preferentially with tuning the electrostatic interaction.

Revealing Hydrogenation Reaction Pathways on Naked Gold Nanoparticles

“…It has already been demonstrated that, depending on sputtering parameters, it is possible to obtain AuNPs of small sizes (1−10 nm) on pure IL, 53−55 pure inorganic oxides (TiO 2 ), 56 and ILs supported on inorganic oxides (ILs dispersed on TiO 2 ). 57 It is also worth noting that, in all cases, the AuNP surface is exclusively composed of metallic gold (Au(0)), as determined by XPS (Figure 1g). Furthermore, there is a positive shift in the Au binding energies (for instance, see Au 4f components in Table 1 and Figure 1 and Au valence band (VB) in Figure S6 in the Supporting Information ) of the AuNPs onto γ-Al 2 O 3 , with respect to those on the IL-hybrid γ-Al 2 O 3 (B1 and B2), suggesting that, in the latter case, the interaction of the AuNPs with the γ-Al 2 O 3 support was decreased by the presence of the IL pair layers.…”

“…Although these IL layers are thin, previous reports on hydrogenation processes described that similar thin IL layers produce the best compromise between the hydrogenation activity and the selectivity enhacement by IL substrate/product discrimination. 55,57,60 These behaviors were ascribed to the effect on the concentration of reactants available at the catalytic center by the distinct reactant solubility/ miscibility in the IL 62−64 or to the IL interaction with specific catalytically active particle sites: i.e., a proposed ligand-like interaction with different surface sites on Pt or PdNPs by the use of the IL 1-n-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (BMI•NTf 2 ). 60,62,65 The IL pair interaction with the AuNPs was further confirmed by comparing the XPS spectra of B1, B2, Au/B1, and Au/B2 (see Figure S8 in the Supporting Information).…”

Sputtering onto liquids: a critical review

“…They further dissolved the Ag nanocubes by chemical etching to create Au/Ag nanocubes and Au nanoframes [157]. The team of Torimoto also showed the adsorption of Au NPs on a TiO 2 (110) substrate with the IL encapsulating the NPs on the TiO 2 surface [180]. Through a post-treatment, they immobilized the Au NPs and removed the IL layers, resulting in self-assembled Au NP arrays on the TiO 2 (110) substrate [180].…”

Recent Progress in Nanoparticle Synthesis via Liquid Medium Sputtering and its Applications

“…Suzuki et al proposed a novel strategy for controlling the adsorption positions of NPs on solid substrates by varying the electrostatic interactions between the substrate surface and the ILs, by using a rutile TiO 2 (110) single crystal surface and Au NPs obtained from liquid medium sputtering [31]. The authors revealed that the combination of a charged surface and charged molecules had the potential to afford control of the NP location on the surface, by tuning the electrostatic interactions.…”

“…First, metal NP synthesis using ionic liquids will be discussed, which includes the synthesis of single material NPs and the effect of sputtering conditions [19][20][21][22][23][24][25][26][27], various alloying strategies [15,23,24,28], and techniques for transferring synthesized NPs [29][30][31]. Subsequently, we discuss NP synthesis using low-volatile polymers, including the use of thiol compounds and transfer techniques [32][33][34][35][36][37][38][39].…”