Gold Nanocluster-Silver Nanoparticle-MoS2 Heterostructures as SERS-Active Catalysts With Enhanced Electron-Donating Capability.

It remains an extreme challenge to activate thermodynamically unfavorable, chemically inert methane molecules under mild conditions. Herein, we report a molecular-like nickel-thiolate hexameric clu...

Electronic states and photocatalytic performances of SnS2-based binary and ternary vdW heterostructures

Until now, the concept of metal (0) atomic quantum clusters or nanoclusters (NCs) and their increasing role in nanotechnology due to their novel and exceptional properties in important industrial fields (such as catalysis) has not been included at the education level. Here, syntheses of both metal nanoparticles (NPs) and metal nanoclusters (with sizes below ≈1–2 nm) are used for understanding the large differences between both types of nanomaterials. In this experiment we highlight the catalytic and photocatalytic properties of silver NCs, as well as the plasmon band, as the main optical difference between metal NPs and NCs. In the first step of the experiment, the synthesis of different sizes and shapes of AuNPs is carried out and changes in their plasmon band are discussed. In a second step, students conduct the anisotropic growth of AuNPs, catalyzed by silver NCs (Agn, where n is the number of atoms forming the cluster), which do not display a plasmon band. Finally, it is shown that Agn NCs can induce AuNP photocorrosion, which can be avoided by introducing molecules with more negative redox potential (called hole scavengers). Redox properties of Agn NCs are used in this laboratory experiment to discuss with the students several important physicochemical issues, such as absolute and hydrogen redox potential scales, electronic and optical properties of nanomaterials, semiconductor band gap, photogenerated electron–hole pairs (excitons), catalysis and photocatalysis, the role of hole scavengers, or spontaneous process and free energy. This very new area at the bottom of nanotechnology is ideal to make chemistry relevant and engaging for students. It allows them to learn fundamentals by using chemistry that is at the frontier of research, and they are able to do this in an accessible way.

In situ fabrication of oxygen deficient Bi2MoO6/InVO4/CeVO4 dual S-scheme ternary heterostructure for robust photocatalytic H2 and H2O2 production

Thiolate-protected metal nanoparticles containing a few to few hundred metal atoms are interesting materials exhibiting unique physicochemical properties. They encompass the bulk-to-molecule transition region, where discrete electronic states emerge and electronic band energetics yield to quantum confinement effects. Recent progresses in the synthesis and characterization of ultrasmall gold nanoparticles have opened up new avenues for the isolation of extremely monodispersed nanoparticles with atomically precision. These nanoparticles are also called nanoclusters to distinguish them from other regular metal nanoparticles with core diameter >2 nm. These nanoclusters are typically identified by their actual molecular formulas; prominent among these are Au25(SR)18, Au38(SR)24, and Au102(SR)44, where SR is organothiolate. A number of single crystal structures of these nanoclusters have been disclosed. Researchers have effectively utilized density functional theory (DFT) calculations to predict their atomic and electronic structures, as well as their physicochemical properties. The atomically precise metal nanoclusters have been the focus of recent studies owing to their novel size-specific electrochemical, optical, and catalytic properties. In this Account, we highlight recent advances in electrochemistry of atomically precise metal nanoclusters and their applications in electrocatalysis and electrochemical sensing. Compared with gold nanoclusters, much less progress has been made in the electrochemical studies of other metal nanoclusters, and thus, we mainly focus on the electrochemistry and electrochemical applications of gold-based nanoclusters. Voltammetry has been extremely powerful in investigating the electronic structure of metal nanoclusters, especially near HOMO and LUMO levels. A sizable opening of HOMO-LUMO gap observed for Au25(SR)18 gradually decreases with increasing nanocluster size, which is in line with the change in the optical gap. Heteroatom-doping has been a powerful strategy to modify the optical and electrochemical properties of metal nanoclusters at the atomic level. While the superatom theory predicts 8-electron configuration for [Au25(SR)18]- and many doped nanoclusters thereof, Pt- and Pd-doped [PtAu24(SR)18]0 and [PdAu24(SR)18]0 nanoclusters show dramatically different electronic structures, as manifested in their optical spectra and voltammograms, suggesting the occurrence of the Jahn-Teller distortion in these doped nanoclusters. Furthermore, metal-doping may alter their surface binding properties, as well as redox potentials. Metal nanoclusters offer great potential for attaining high activity and selectivity in their electrocatalytic applications. The well-defined core-shell structure of a metal nanocluster is of special advantage because the core and shell can be independently engineered to exhibit suitable binding properties and redox potentials. We discuss recent progress made in electrocatalysis based upon metal nanoclusters tailored for water splitting, CO2 conversion, and electrochemical sensing. A well-defined model nanocatalyst is absolutely necessary to reveal the detailed mechanism of electrocatalysis and thereby to lead to the development of a new efficient electrocatalyst. We envision that atomically controlled metal nanoclusters will enable us to systematically optimize the electrochemical and surface properties suitable for electrocatalysis, thus providing a powerful platform for the discovery of finely tuned nanocatalysts.

The construction of hollow structures and the incorporation of metal nanoparticles have been shown to be two potential approaches to achieving high-performance microwave absorption. In this study, a hollow polyhedron material featuring an FeN/Fe-doped carbon matrix was synthesized by an acidification corrosion and pyrolysis strategy. The formation of heterojunctions, coupled with the design of hollow structures, significantly improved the dielectric loss capacity of the material. Furthermore, the incorporation of magnetic metal nanoparticles not only increased the magnetic loss but also enriched the loss mechanisms of the material, leading to an overall improvement in the magnetic loss. Under the synergistic effects of these factors, the material exhibited exceptional microwave absorption properties. In particular, at a material thickness of only 2.3 mm, the minimum reflection loss value of the FeN/Fe@HC nanocomposite reached -64.5 dB with an effective absorption bandwidth of 5.1 GHz. These results further highlight the importance of a hollow structure design and metal atom doping in improving microwave absorption performance.

Recent developments in material synthesis involve avariety of physical and chemical approaches which has substantially influenced the field of nanotechnology. These strategies play a significant role in many prospects such as synthesis of nanoparticles of variable shapes and uniform particle size distribution. Toxic chemicals in these strategies for the synthesis of metal nanoparticles create hazardous concerns for the environment. In contrary, the biological approach includes the use of bioactive components which are highly biodegradable in nature. Hence biological approach is considered as a promising method for the eco-friendly synthesis of noble metal nanoparticles. Although these noble metal nanoparticles can be synthesised in various forms such as nano-sols, nano-colloids, nano-crystallines, nanorods, nanotubes and nanowires using a variety of physical as well as chemical approaches. Besides their shape and morphology, the size of noble metal nanoparticles should be efficiently tailored to achieve the desired medical application. The increase in surface area increases the possibility of causing the aggregation of nanoparticles which limit their functionalities. The surface functionalization of noble metal nanoparticles was done using chemical dispersants such as surfactants or polyelectrolytes to avoid the aggregation. This functionalisation improves the stability of the noble metal nanoparticles but at the same time it alters the surface chemistry of the nanoparticles. It is crucial for producing the nanoparticles in such a way that they could be size controlled, inexpensive and eco-friendly. The objective of this review is, therefore, to reveal the past and present scenarios, specifically the possibilities of noble metal nanoparticles in applications. Furthermore, it also documents the detailed information about the strategies involved in the use of plant extracts as reducing agents in the synthesis of metal nanoparticles and the incorporation of metal nanoparticles into polymeric materials for environmental applications. This review paper mainly summarizes the various synthesis methods of gold and silver nanoparticles and their applications in biomedicine.

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Open AccessCCS ChemistryRESEARCH ARTICLE10 Jun 2022Bulky Thiolate-Protected Silver Nanocluster Ag213(Adm-S)44Cl33 with Excellent Electrocatalytic Performance toward Oxygen Reduction Chen-Guang Shi, Jian-Hua Jia, Yaling Jia, Guangqin Li and Ming-Liang Tong Chen-Guang Shi Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-sen University, Guangzhou, Guangdong 510006 , Jian-Hua Jia *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-sen University, Guangzhou, Guangdong 510006 , Yaling Jia Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-sen University, Guangzhou, Guangdong 510006 , Guangqin Li Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-sen University, Guangzhou, Guangdong 510006 and Ming-Liang Tong *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-sen University, Guangzhou, Guangdong 510006 https://doi.org/10.31635/ccschem.022.202201960 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Atomically precise gold and/or silver nanoclusters play a key role in crystallography and coordination chemistry. Compared with gold nanoclusters, silver nanoclusters become unstable and difficult to crystallize due to the high reactivity of metal silver. Herein, we report a silver nanocluster Ag213(Adm-S)44Cl33 ( Ag213) coprotected by bulky thiolates and chlorides. The low surface thiolate coverage (about 45%) endows Ag213 with high catalytic activity. Supported on activated carbon, Ag213 nanoclusters exhibit excellent electrocatalytic oxygen reduction performance with Eonset and E1/2 values of 0.89 and 0.72 V, respectively, close to the values of commercial Pt/C catalyst. This is the first report on the electrocatalytic oxygen reduction reaction of nanoclusters with more than 100 silver atoms. Ag213 with the diameter of 2.75 nm comprises a core–shell structure Ag7@Ag32@Ag77@Ag97. The strong plasmonic absorption band at 454 nm reveals the metallic nature of Ag213. Interestingly, halide is of importance. Chloride facilitates the formation of Ag213 and Ag56(Adm-S)33Cl16 ( Ag56 Cl) while bromide can promote the formation of Ag56(Adm-S)33Br16 ( Ag56 Br). This work provides an example for the study of large-sized metal nanoclusters and nanocluster-based electrocatalysts. Download figure Download PowerPoint Introduction Atomically precise gold and/or silver (hereinafter referred to as Au/Ag) nanoclusters protected by organic ligands have been widely studied in the last few decades because of their unique atomic arrangement, reactivity, and various applications.1–11 With the help of single-crystal X-ray diffraction (SCXRD) and crystallography, the total structures of many metal nanoclusters and/or clusters with hundreds of Au/Ag atoms have been determined12–21 in order to deeply understand their structure as well as their optical, electronic, magnetic, and catalytic properties.22–30 These nanoclusters are usually composed of metal cores with defined geometries and metal–organic protective layers. Much work focuses on Au/Ag nanoclusters protected by thiolate,31–33 phosphine,34,35 alkynyl,36–38 amide,39,40 selenolate,41,42N-heterocyclic carbene,43,44 and the mixed ligands.45–49 Large-sized metal nanoclusters play a key role in crystallography and coordination chemistry. The strong quantum-size effects are manifested in their physicochemical properties. So far, a few of the atomically precise metal nanoclusters with more than 200 Au/Ag atoms have been reported, such as Ag206, Ag210-211, Au246, (AuAg)267, Au279, Ag307, and Ag374.50–56 However, the synthesis and separation of large-sized (>2 nm) monodisperse metal nanoclusters is still a challenge. Compared with gold nanoclusters, silver nanoclusters become unstable and difficult to crystallize due to the high reactivity of metal silver.57–59 To further improve the stability of silver nanoclusters, it is desirable to introduce the second protective group. For example, Yu and Zhu et al. obtained a nanocluster Ag100 featured with a face-centered cube using thiolate/phosphine mixed ligands.60 Per the analyses of silver nanoclusters with more than 100 metal atoms, including Ag112,61 Ag136,56 Ag141,62 Ag146,63 Ag206,50 and Ag210-211,51 it has been found that halide has an important influence on the synthesis of these nanoclusters due to the strong binding between halide and silver.64 The two largest known silver nanoclusters, Ag307 and Ag374,55,56 for instance, are both coprotected by the 4-tert-butylbenzenethiolate/halide mixed ligands. The difference is that the former has 60 chlorides in the intermediate layer while the latter has all halides in the surface shell, which facilitates the formation of a larger metal core Ag207 as well as the unique surface ligand distribution. Inspired by the bulky thiolates employed in nanocluster Ag141 and its low surface thiolate coverage (∼57%),62 we chose 1-adamantanethiolate (Adm-S) to achieve low surface coverage of thiolates and chose halide as the coprotective group to enhance the stability of silver nanoclusters. Fortunately, we were able to isolate a giant nanocluster, Ag213(Adm-S)44Cl33 ( Ag213), by using Adm-S and chloride. Ag213 with the diameter of 2.75 nm comprises a core–shell structure of Ag7@Ag32@Ag77@Ag97. As far as we know, it is one of the three largest silver nanoclusters. The surface thiolate coverage of Ag213 is only about 45%, suggesting the possibility of high surface reactivity. There have been a number of reports on the electrocatalytic oxygen reduction reaction (ORR) involving Pd and/or Au nanoclusters,65 but few report on the electrocatalyst based on Ag nanoclusters.66 Supported on activated carbon, Ag213 nanoclusters exhibit excellent performance in electrocatalytic ORR. This is the first report on the electrocatalytic ORR of nanoclusters with more than 100 silver atoms. Experimental Methods Materials Silver trifluoromethanesulfonate (AgOTf) was purchased from Adamas Reagent Co., Ltd. (Shanghai, China). Adm-SH was purchased from Beijing HWRK Chemical Co., Ltd. (Beijing, China). Sodium borohydride (NaBH4) was purchased from Beijing Innochem Science & Technology Co., Ltd. (Beijing, China). All the chemical reagents were used as received without further purification. Synthesis of Ag213(Adm-S)44Cl33·4CH2Cl2 (Ag213·4CH2Cl2) In a 20 mL glass bottle, AgOTf (0.25 mmol, 64.2 mg) and Adm-SH (0.12 mmol, 20 mg) were dissolved in a mixture of methanol/dichloromethane (MeOH/DCM, 4 mL, v/v = 1:1), then added to 6 mL DCM. To the mixture after stirring for 30 min, Ph4PCl (0.1 mmol, 37.4 mg) and Et3N (100 μL) were successively added within a few minutes. After another 15 min, the freshly prepared NaBH4 aqueous solution (2 mL, 30 mg/mL) was added under vigorous stirring. The color of the suspension mixture immediately turned light yellow, then brown, and finally black. The reaction was continued for 3 h at room temperature and then aged in the dark for 2 days. The dark precipitate was obtained by adding 10 mL MeOH and washed with MeOH and water. The separated precipitate was again dissolved in 10 mL DCM and filtered. Black block-like crystals were obtained by diffusion of n-hexane into DCM solution after 1 month with a yield of ∼13.8% (based on Ag). Synthesis of Ag56(Adm-S)33Cl16 (Ag56Cl) The synthesis process for Ag56Cl is similar to that for Ag213. To a solution of AgOTf (0.125 mmol, 32.1 mg) and Adm-SH (0.06 mmol, 10 mg), Ph4PCl (0.025 mmol, 9.36 mg) in 6 mL DCM was added. After stirring for 10 min, Et3N (50 μL) and freshly prepared NaBH4 aqueous solution (2 mL, 15 mg/mL) were added successively. The mixture was stirred for 10 h and then washed with water. The organic phase was aged in the dark for 2 days. The dark red filtrate was collected and diffused with the mixture of ether and n-hexane (v/v = 1:1). Red plate crystals ( Ag56 Cl) and black block-like crystals ( Ag213) were obtained after several days. Synthesis of Ag56(Adm-S)33Br16 (Ag56Br) To a solution of AgOTf (0.125 mmol, 32.1 mg) and Adm-SH (0.06 mmol, 10 mg), Ph4PBr (0.025 mmol, 10.5 mg) in 10 mL DCM was added. After stirring for 30 min, Et3N (50 μL) and freshly prepared NaBH4 aqueous solution (2 mL, 15 mg/mL) were added successively. The mixture was stirred for 10 h and then washed with water. The organic phase was aged in the dark for 2 days. The red filtrate was collected and diffused with n-hexane. Red rhombic crystals were separated after several days in a yield of 37.0% (based on Ag). Electrochemistry Crystalline Ag 213 (4 mg) and activated carbon (1 mg) were mixed with naflon (40 μL) and 60% aqueous ethanol (960 μL), giving the Ag213/C ink after 30 min in an ultrasonic bath. Ag213/C ink (10 μL) was added dropwise on a glassy carbon rotating disk electrode (RDE) as the working electrode. Similarly, commercial Pt/C (5 mg) was mixed with naflon (40 μL) and 60% aqueous ethanol (960 μL), giving the Pt/C ink after 30 min in ultrasonic bath. Pt/C ink (10 μL) was added dropwise on glassy carbon RDE as the working electrode. After drying overnight in air, working electrodes were both prepared. A Ag/AgCl electrode and carbon rod were used as reference and counter electrodes, respectively. The electrolyte was 0.1 M KOH (pH 13) solution saturated with pure O2. Scan rates of 10 mV were conducted in all experiments. Results and Discussion Synthesis, characterization, and crystallography The preparation of the Ag213 nanoclusters involved the reaction of silver salt and Adm-S in a MeOH/DCM solvent mixture with the stoichiometric ratio of about 2:1. After the addition of Ph4PCl and Et3N, the mixture was reduced with fresh NaBH4 aqueous solution to form silver nanoclusters. The precipitate was obtained by adding MeOH and then was extracted with DCM. Black crystals were separated by vapor diffusion of n-hexane into the DCM solution. The composition of Ag213 was clarified by the data analyses of SCXRD (see Supporting Information Table S1), electrospray ionization mass spectrometry (ESI-MS), and energy-dispersive X-ray spectrometer (EDS). SCXRD analyses revealed that Ag213 comprised a huge silver kernel peripherally protected by Adm-S groups and chlorides (Figures 1a and 1b). The average diameter of the whole molecule was 2.75 nm and 1.80 nm excluding the organic shell. Ag213 contained a Ag116 core and a surface shell of Ag97(Adm-S)44Cl33, which was different from two much larger silver nanoclusters, Ag307 and Ag374 respectively with the core/shell of Ag167/Cl60/Ag140(RS)110Cl2 or Ag207/Ag167(RS)113Cl2Br2 (RS refers to thiolates).55,56 The Ag116 core showed pseudo-fivefold symmetry (see Supporting Information Figures S1 and S2), the same as the cores of Ag206 and Ag210-211.50,51 However, their peripheral ligand layers were completely different. The Ag116 core was surrounded by a shell consisting of 97 Ag, 44 Adm-S, and 21 Cl. 116 Ag were arranged as a three-shell Russian nesting doll architecture as Ag7@Ag32@Ag77 (Figures 1c–1e). The center was an almost ideal Ag7 decahedron, differing from Ag307 and Ag374 both with a centerd Ag13 core. The Ag–Ag bond lengths ranged from 2.797 to 2.878 Å with an average value of 2.834 Å. The second shell Ag32 was a slightly distorted Ino decadedron. The Ag–Ag bond lengths in this shell range from 2.779 to 2.907 Å with an average of 2.844 Å, which was slightly shorter than the Ag–Ag bond length of bulk silver (ca. 2.889 Å), indicating the characteristics of metallic bonds. The third shell Ag77 was also an Ino decadedron. It is worth noting that each vertex of Ag77 Ino decadedron constructs a decahedron with the corresponding vertex of Ag32 (see Supporting Information Figure S3), which is different from the reported Ag206∼211 clusters.50,51 Due to the coordination of chlorides, it was found that silver atoms have a special arrangement between icosahedron and decahedron (Figure 1f and Supporting Information Figures S4–S6). It formed some short and strong Ag–Ag bonds between the second and third shells. The average value (2.834 Å) is shorter than that between Ag32 and Ag77 Ino decadedrons observed in Ag206 and Ag211 with the average values of 2.879 and 2.848 Å, respectively. The 12 rest of the 33 Cl were respectively located at the poles of pseudodecahedrons or pseudooctahedrons (Figure 1g), connecting the core Ag116 and the shell Ag97(Adm-S)44Cl21. For the outermost shell, the Ag–Ag distances are between 2.786 and 3.821 Å. Due to the coordination of the organic layer, the average value was relatively larger, reaching 3.160 Å. The bond distance details of shell-by-shell in Ag213 are shown in Supporting Information Figure S7, as well as the summary information listed in Supporting Information Table S2. Figure 1 | Structure anatomy of Ag213. (a) Top view and (b) side view of overall structure with H atoms omitted for clarity. (c) Inner core Ag7 decahedron and (d) two-shell Ag7@Ag32. (e) The three-shell Ag7@Ag32@Ag77 Ino decadedrons and (f) the third shell Ag77. (g) 12 Cl located on the pentagonal surface. (h) The organic layer containing 44 S and 33 Cl. Color code: Ag, blue, pink, orange, dark green, or red; S, yellow; Cl, green; C, gray. Download figure Download PowerPoint 44 Adm-S and 33 Cl on the surface of Ag213 were located in different coordination environments (Figure 1h). The S of Adm-S had two coordination modes, namely μ3 and μ4. In addition to 8 μ3-SAg3 on the equatorial plane, there were 36 μ4-SAg4 distributed on the surface (Figure 2a and Supporting Information Figures S8 and S9). The average distances of Ag–S are 2.481 and 2.611 Å, respectively. Cl was coordinated with Ag in μ2 or μ3 mode (Figure 2b and Supporting Information Figure S10), and the average Ag–Cl distance was 2.653 Å. In addition, it was found that ClAg5 and ClAg6 formed the pseudooctahedron and pseudodecahedron, respectively (Figure 2c and Supporting Information Figure S11). The vertical bond lengths of these polyhedrons ranged from 2.508 to 2.589 Å while the distances of other weak interactions were between 2.731 and 3.858 Å, which are much longer than the normal Ag–Cl bond lengths. (The summary of Ag-S and Ag-Cl distances is listed in Supporting Information Tables S3 and S4.) Figure 2 | The types of S/Cl-Ag motifs of Ag213, (a) μ3 and μ4 coordination modes of Adm-S group, (b) μ2 and μ3 coordination modes of Cl atom, (c) ClAg5 pseudooctahedron and ClAg6 pseudodecahedron. Color code: Ag, blue; S, yellow; Cl, green. (d) ESI-MS of Ag213 in DCM, and (e) the enlarged illustrations with experimental (black line) and simulated (red line) isotopic patterns for [Ag213(Adm-S)43Cl34+5CH2Cl2+3H]3+ (m/z = 10,600.88, calcd 10,600.77), [Ag213+5CH2Cl2+3H]3+ (m/z = 10,644.81, calcd 10,644.80), [Ag213(Adm-S)45Cl32+5CH2Cl2+3H]3+ (m/z = 10,688.45, calcd 10,688.50) and corresponding Na+-adducts [Ag213(Adm-S)43Cl34+5CH2Cl2+2H+Na]3+ (m/z = 10,607.15, calcd 10,607.10), [Ag213+5CH2Cl2+2H+Na]3+ (m/z = 10,651.15, calcd 10,651.14), [Ag213(Adm-S)45Cl32+5CH2Cl2+2H+Na]3+ (m/z = 10,695.13, calcd 10,695.18). Download figure Download PowerPoint The composition of Ag213 nanoclusters was further confirmed by ESI-MS measurements using DCM as the solvent (Figure 2d). Two mass peaks were observed at m/z = 7983.86 (calcd 7983.86) and 10644.81 and attributed to [ Ag213+5CH2Cl2+nH]n+ (n = 3, 4). The isotopic distribution was fully consistent with the simulation results (Figure 2e and Supporting Information Figure S12). There were two sets of mass peaks at m/z = 10,600.88 and 10,688.45 on either side of 10,644.81. Interestingly, the difference values between them were almost equal, that is about 43.95 ( Supporting Information Figure S13). This means that the ligand exchange between thiolate and chloride occurred.50,61 Moreover, each of the three peak groups in Figure 2e had a set of overlapping peaks, which were assigned to the corresponding Na+-adducts [ Ag213+5CH2Cl2+2H+Na]3+ (Figure 2e and Supporting Information Figure S13). The other two sets of mass peaks at m/z = 5346.83 (calcd 5346.84) and 6186.42 (calcd 6186.46) are respectively attributed to the fragments [Ag50(Adm-S)30Cl8]2+ and [Ag58(Adm-S)33Cl17+H]2+ of Ag213, which are unstable under electron spray ionization, possibly due to the weak coordination ability of chlorides. EDS analyses further confirmed the ratio of Ag/S/Cl atoms in Ag213 crystals, which was consistent with the results of SCXRD (see Supporting Information Figure S14). Unexpectedly, besides the black crystals of Ag213, a few red crystals were obtained in one pot. The composition was determined as Ag56(Adm-S)33Cl16 ( Ag56 Cl) by SCXRD (see Supporting Information Table S5) and ESI-MS. Ag56 Cl had a core–shell structure with a Ag13Cl4 core encapsulated by Ag43(Adm-S)33Cl12 shell (Figure 3a and Supporting Information Figure S15). Connecting the core to the shell were 15 Cl. This was different from that distributed on the surface of Ag213 because these chlorides lead to the disorder of the Ag13 core (see Supporting Information Figures S16 and S17). A set of mass peaks at m/z = 6065.08 observed in ESI-MS spectra were assigned to [ Ag56 Cl+2H]2+ (Figures 3b and 3c and Supporting Information Figure S18), consistent with the results of SCXRD analyses. By increasing the reaction time of silver salt and Adm-S and controlling the amount of Ph4PCl, the pure product Ag213 can be obtained. Figure 3 | (a) Crystal structure of Ag56 Cl with the shell of 50% transparent and C/H atoms omitted for clarity. Color code: Ag, purple or blue; S, yellow; Cl, green. (b) ESI-MS of Ag56 Cl in DCM, with (c) the experimental (black line) and simulated (red line) isotopic patterns for [Ag56 Cl+2H]2+ (peak a, m/z = 6065.08, calcd 6065.07), [Ag56(Adm-S)33Cl17+2H]2+ (peak b, m/z = 6083.05, calcd 6083.05), [Ag57(Adm-S)33Cl16+2H]2+ (peak c, m/z = 6119.02, calcd 6119.02), [Ag57(Adm-S)33Cl17+2H]2+ (peak d, m/z = 6137.00, calcd 6137.00). Download figure Download PowerPoint Electrocatalysis It was calculated that the reported surface coverage of thiolates on Ag136 and Ag211 was ∼78% and ∼80%, respectively.51,56 Compared with those protected by small-sized thiolates, nanoclusters with bulky Adm-S are apt to provide lower surface thiolate coverage, for example Ag141 was ∼57%.62 The value of Ag213 was smaller, only about 45%, suggesting some remaining surface sites can be accessible by smaller-sized ligands such as chlorides. The particular surface structure would make Ag213 the high surface reactivity. Ag213 nanoclusters show excellent electrocatalytic performance for ORR under an alkaline environment. Ag213 crystals were mixed with activated carbon in an ultrasonic bath to form a catalyst Ag213/C loaded with 20% C. Commercial Pt/C (20 wt %) was conducted to compare with Ag213/C of the same weight. Potential values of the reversible hydrogen electrode (RHE) scale were calibrated according to the following equation: E RHE = E ( Ag / AgCl ) + 0.197 + 0.059 * pH The ORR catalytic performance was recorded by linear sweep voltammetry (LSV) measurements (Figure 4a). The onset potential (Eonset) of Ag213/C catalyst was 0.89 V, and the half-wave potential (E1/2) was 0.72 V while the values of commercial Pt/C catalyst were 1.09 and 0.90 V, respectively. The E1/2 of Ag213/C catalyst was higher than that of Ag22 (0.63 V) and AuAg21 (0.66 V) reported by Zhu et al.66 but lower than that of carbon-supported monoclinic Pd5Bi2 nanocrystals (0.93 V).67 In addition, the gold nanomolecule composites Au279/SWNT (SWNT = single-walled carbon nanotube) also showed catalytic activity with a comparable Eonset value of 0.89 V.68 The observed excellent catalytic performance of Ag213/C mentioned above can be attributed to the high surface reactivity and the unique electronic structure of Ag213.50 Figure 4 | LSV curves and UV–vis absorption spectra. (a) LSV curves of Ag213/C and Pt/C with scan rates of 10 mV/s. ORR tests were performed with RDE (geometric area = 0.196 cm2, 1600 rpm). Ag/AgCl electrode and carbon rod were used as reference and counter electrodes, respectively. The electrolyte is 0.1 M KOH (pH 13) solution saturated with pure O2. UV–vis absorption spectra of (b) Ag213 (blue line), Ag56 Cl (orange line), Ag56 Br (red line), and (c) Ag213 respectively mixed with PPh4Cl (blue line) and PPh4Br (cyan line) in DCM. Download figure Download PowerPoint UV–vis absorption The DCM solution of Ag213 showed a dominant absorption band centered at 454 nm (Figure 4b), which was similar to the surface plasmon resonance absorption band of metallic silver nanoparticles. Compared with Ag141 (460 nm), Ag210-211 (464 nm), Ag374 (465 nm), and Ag307 (473 nm),51,55,56,62 however, the absorption wavelength of Ag213 in solution was shorter. The Ag213 solution was stable at room temperature for at least 2 weeks whether or not exposed to light (see Supporting Information Figures S19 and S20). Distinct from Ag213, the Ag56 Cl had a molecule-like multiband absorption in solution, including a prominent peak at 425 nm and three shoulders at 336, 396, and 513 nm (Figure 4b). The low-energy absorption peak (513 nm) can be attributed to charge transfer within the metal core, while the high-energy absorption shoulders (336, 396, and 425 nm) mainly came from the mixing of metal-to-metal and/or metal-to-ligand charge transfer processes (MMCT and/or MLCT).61 The number of free electrons for Ag213 was calculated to be 136e (213-44-33), which is very close to, but not yet achieving, the magic shell electron count of 138e.69 The role of halide To study the role of halide in the reaction, Ph4PBr was used instead of Ph4PCl in parallel experiments. Instead of Ag213 homologue, the Ag56 Cl homologue was obtained with a formula of Ag56(Adm-S)33Br16 ( Ag56 Br) determined by SCXRD (see Supporting Information Table It is to Cl a with Adm-S to the formation of Ag213. Ph4PBr to Ag213 solution, the recorded UV–vis was similar to Ag56 Br (Figure indicating that Ag213 can be into Ag56 which also that bromide can promote the formation of Ag56 The core–shell structure of Ag56 Br core and (see Supporting Information Figures and was the same as Ag56 Cl. The average of Ag56 Cl and Ag56 Br were both reported clusters with similar nm), nm), and of the three largest silver nanoclusters, Ag213, coprotected by bulky thiolates and chlorides, was separated the core–shell structure with a Ag77 shell. This is the first report on electrocatalytic oxygen reduction activity of nanoclusters with more than 100 silver atoms. Supported on activated carbon Ag213 nanoclusters exhibit excellent electrocatalytic oxygen reduction due to the low surface coverage of thiolates on nanoclusters. The Eonset and E1/2 of the Ag213/C catalyst are 0.89 and 0.72 V, respectively, close to the values and 0.90 V) of commercial Pt/C catalyst. In addition, it is worth that halide is important in Chloride facilitates the formation of Ag213 and Ag56 Cl, while bromide can promote the formation of Ag56 The Ag213 solution the surface plasmon resonance absorption band of metallic silver and (see Supporting Information Figure as well while the Ag56 Cl solution has absorption This work provides a example for the study of large-sized metal nanoclusters and nanocluster-based electrocatalysts. Supporting Information Supporting Information is and SCXRD details of synthesis and ESI-MS and UV–vis and and The data were in the with of ( ( Ag56 and ( Ag56 Br). This data can be obtained free of charge of The of Information This work was by the Science of and The to Zhu in the & of Sun Yat-sen for the help with ESI-MS measurements and analyses. and and of the and Atomically with of of between and at Au Li Li Li the Chemistry of for Thiolate-Protected of and a in with and at the Chemistry of Atomically to and and of of Chemistry of Zhu C. the Crystal Structure of a and C. of a at Å Silver Nanocluster with an A Silver and with Sun of and in with and Sun with 6 Silver and and

Integration of other functional materials onto the surfaces or into the matrixes of metal–organic frameworks (MOFs) is a new strategy to acquire multifunctionality for MOFs. Herein, we report a novel means that can integrate ultrafine metal (Au or Ag) nanoparticles onto designated crystallographic planes of zeolitic imidazolate framework (i.e., ZIF-8). The key challenge herein is to determine appropriate surfactants that can help to generate the interaction between the incorporated metal nanoparticles and ZIF-8 phase. In our current work, single-layered metal nanoparticles have been added onto exterior surfaces and/or into interior bulk matrixes of ZIF-8 by forming coordination bonds. Such bonding is actually attained through the coordinative interaction between the surfactants of metal nanoparticles and partially coordinated Zn2+ions on the exterior surface of ZIF-8 crystals. Additional epitaxial growth of ZIF-8 can also be carried out, which turns the surface metal nanoparticles into ZIF-8 bulk phase. A...

We present experimental results on the multicolor (blue and green) photoluminescence from glycine-coated silver nanoclusters and small nanoparticles which can be used as novel probes for bio-imaging. Glycine-coated silver nanoclusters and nanoparticles were synthesized using thermal reduction of silver nitrate in a glycine matrix, according to a modified procedure described in literature. The size characterization with mass spectrometry, scanning electron microscopy and dynamic light scattering showed that the diameters of luminescent silver nanoclusters and small nanoparticles vary from 0.5 nm to 17 nm. Extinction spectroscopy revealed that the absorption band of the luminescent nanoclusters and nanoparticles was blue-shifted as compared to the nonluminescent larger silver nanoparticles. This effect indicated the well-known size dependence of the surface plasmon resonance in silver. The most pronounced photoluminescence peak was observed around 410 nm (characteristic SPR wavelength for silver) which strongly suggests the enhancement of the photoluminescence from silver nanoparticles by the SPR. The relative quantum yield of the photoluminescence of silver nanoclusters and nanoparticles was evaluated to be 0.09. In terms of their small size, brightness and photostability, noble metal nanoclusters and nanoparticles hold the most promise as candidates for biological cell imaging, competing with commonly used semiconductor quantum dots, fluorescent proteins and organic dyes. When applied to the problem of intracellular imaging, metal nanoclusters and small nanoparticles offer advantages over their much larger sized semiconductor counterparts in terms of ease of biological delivery. In addition, noble metal nanoparticles and nanoclusters are photostable. The high quantum yield (QY) of the photoluminescence emission signal enables the isolation of their photoluminescence from the cellular autofluorescence in cell imaging, improving the image contrast.

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Hybridization of photofunctional organic molecules like porphyrins with inorganic nanomaterials provides interesting photophysical properties like photo-induced electron transfer, energy transfer, or photoemission from charge transfer states. For fine tuning of these photo-functionalities, precise control over organic-inorganic interfaces, including spatial distances and orientations of organic molecules against inorganic nanomaterial, should be crucial. However, control and evaluation of the interfaces are quite difficult, mainly due to heterogeneous and unclear environments on the surface of inorganic nanomaterials like metal nanoparticles and metal nanosheet, which basically have size and/or composition distributions.Among the inorganic nanomaterials, atomically-precise metal nanoclusters (MNCs) are one of the homogeneous materials with uniform composition and distinct surface structure at an atomic level. Thus, MNCs can be an appropriate model to evaluate the effects of organic-inorganic interfaces on photophysical properties of the hybridized materials. Nevertheless, even in one of the most common and simplest MNCs like thiolate-protected Au25 cluster ([Au25(SR)18]–, SR = thiolate), two kinds of inequivalent ligands (S1, S2 in Figure 1) are present on surface. Thus, control over the regioselectivity should be required to archive precise substitution of photo-functional molecules, which has yet to be reported. In this work, we have controlled regioselectivity in the modification of [Au25(SC2Ph)18]– (SC2Ph = phenylethanethiolate) with porphyrinthiol ligands (Por) through ligand-exchange reactions. An advantage of Por as a photofunctional ligand for Au25 cluster is more bulkiness than that of original ligands (SC2Ph), which aids the isolation of mono-porphyrin-coordinated Au25 cluster ([Au25(SC2Ph)17(Por)1]–, Au25-Por1 ). Moreover, synthetic flexibility of porphyrins enabled us to control the regioselectivity in Au25-Por1 systematically.We sythesized a series of Por with a thiol moiety at different positions to evaluate the steric effect on the regioselectivity in ligand-exchange reactions (Figure 1). Porphyrin thiol with different substituents at meso-phenyl groups were also synthesized to evaluate the electronic effect. Substitution of porphyrins onto Au25 clusters was conducted by ligand-exchange reactions of [Au25(SC2Ph)18]– with 1 equivalent of Por in tetrahydrofuran. After the careful purification of the reaction mixture through size-exclusion column chromatography, we have successfully isolated Au25-Por1 in ca. 20% yield. The characterizations of Au25-Por1 were performed by MALDI-TOF-MS and 1H NMR spectroscopy, which confirmed the high purities of a series of Au25-Por1 .The regioselectivity in Au25-Por1 was evaluated through 1H NMR measurements. When using para-substituted porphyrin (PorSH) as an incoming ligand, 1H NMR spectrum of Au25-SPor1 in acetone-d 6 indicated the presence two kinds of regioisomers with the ratio of 2.5:1. Interestingly, the regioselectivity increased up to 80% (4:1) in Au25 cluster with more steric meta-substituted porphyrin (Au25-S m Por1 ), whereas the ratio reached to almost 1:1 in the case of Au25 cluster with less steric phenyl-spacer introduced porphyrin (Au25-SPhPor1 ). Because S2 position in the Au25 clusters was less steric than S1 position, we concluded that more steric ligands like m PorSH tend to be introduced at S2 position favorably. On the other hand, we hardly observed the electronic effect of Por on the regioselectivity in Au25-Por1 , indicating the importance of steric factor of an incoming ligand for precise control over the exchanged position (Figure 1). This is the first report to control over ligand-exchange position of MNCs, which could be achieved through ligand design.Finally, we briefly evaluated the photophysical properties of Au25-Por1 in toluene solution. When the Soret band of coordinated-porphyrins was photoexcited, the fluorescence quenching was clearly observed in each Au25-Por1 . Judging from the energy diagram of Au25-Por1 , electron transfer from Au25 to singlet excited state of porphyrin ligand would occur to form charge separated state. It should be noted that the quenching efficiency depended on not only the distance between electron donor and acceptor, but also the position of the coordinated chromophore. These results suggest the importance of precise modification of organic-inorganic interfaces to tune photodynamics of chromophore-nanocluster systems.In conclusion, we have successfully controlled the regioselectivity in the ligand-exchange reactions of thiolate-protected gold nanoclusters with porphyrinthiol derivatives through the steric effect. The essential roles of the ligand-introduced position on altering photodynamics of porphyrin-coordinated MNCs were also clarified, which provides an interesting insight into fine-tuning of photofunctional materials.Figure 1.Reaction scheme of ligand-exchange reaction of [Au25(SC2Ph)18]– with Por. The R groups of SR ligands were omitted for clarity. Figure 1

BackgroundThis systematic review with meta-analysis aimed to evaluate if the incorporation of metallic nanoparticles (NPs) in dental materials present antimicrobial effects without prejudice to physical and mechanical properties.Material and methodsAfter PROSPERO registration (CRD42022297684), Medline via Pubmed, Scopus, Web of Science, EBSCO, LILACS, LIVIO, Embase and grey literature such as Google Scholar, ProQuest and OpenGrey, were searched until June 26th, 2024. Meta-analysis of materials incorporated with metallic nanoparticles was performed for antimicrobial action (standardized mean differences) and mechanical properties (mean differences) through inverse variance and randomized effects (Revman, p < 0.05).ResultsFor risk of bias, studies were evaluated according to the Joanna Briggs Institute's critical assessment. Forty-four out of the 3818 articles initially identified were eligible for the review, and 30 were included in the meta-analysis. Meta-analysis pointed out that the incorporation of silver and copper presented antimicrobial activity, reducing colony forming units (CFU) when incorporated in primer and glass ionomer cement (GIC). Silver increased inhibition zones and reduced cell viability through live dead cell viability assay in primer, GIC and adhesives. Silver incorporation reduced microhardness and shear strength of adhesives and increased compressive strength of GIC and shear strength of primer.ConclusionsThe incorporation of metallic nanoparticles, especially silver copper and titanium presented benefits to antimicrobial properties compared with the original unmodified materials. However, some mechanical properties of restorative dental materials were damaged. In contrast to some studies in the literature that evaluated metallic nanoparticles, our findings indicate negative effects on properties.

21 - Metal nanoclusters for catalytic applications: synthesis and characterization