Bimetallic nanocrystals are often advantageous over singlecomponent systems for a range of fundamental studies and applications because the associated variations in compositions and spatial distributions provide additional handles for experimentally maneuvering both the structures and properties. [1][2][3] For example, a bimetallic system may exhibit either localized surface plasmon resonance (LSPR) or catalytic properties different from each one of the constituent metals depending on the electronic coupling between the two metals. [4][5][6][7][8][9] Up till now, a number of noble metals, such as Au, Ag, Pd, Pt, and Rh have been combined to generate bimetallic nanocrystals with tunable and enhanced properties. [1][2][3][4][5][6][7][8][10][11][12][13] With regard to the spatial distributions of elements in a bimetallic system, three patterns have been observed and exploited: 1) homogeneously distributed as in an alloy or intermetallic compound; [5,6] 2) separated into two concentric layers as in a core-shell structure; [2,7,[10][11][12] and 3) separated into two side-by-side regions as in a dimeric structure. [3,8,12] Seed-mediated growth is probably the most powerful route to bimetallic nanocrystals, where pre-formed seeds of one metal serve as the sites of nucleation and then growth for another metal. It has been observed that the nucleation and growth mode of the second metal are governed by a number of physical parameters, including the (mis)match of lattice structures and constants, the correlation of surface and interface energies, and difference in electronegativity between the two metals. [5,11] For two given metals, these parameters would direct the heterogeneous nucleation and growth on a seed to follow a conformal or site-selective mode, generating a core-shell or hybrid structure. Although a recent study from our group demonstrates that these two types of bimetallic structures can both be produced with good yields in the Pd-Au system by judicially choosing a reducing agent, [12] it remains a grand challenge to spatially control the sites involved in nucleation, especially for nanocrystal seeds enclosed by a set of equivalent faces.We suspect that the nucleation and growth of a nanocrystal seed is highly sensitive to the rate at which the atoms to be deposited are generated from a precursor. This rate can be manipulated using at least three different strategies: 1) variation of the reductant and/or precursor; 2) tuning of the reaction temperature; and 3) control of precursor concentration. The last approach should be most attractive in terms of simplicity and versatility. To this end, we recently demonstrated the use of a syringe pump as an effective means to manipulate the precursor concentration and thus selectively enhance the overgrowth of Rh along the corners and edges rather than side faces of a cubic seed.[13] Herein, we further extend the capability of this approach to achieve nucleation and growth of Ag on one, three, and six of the equivalent {100} faces on a Pd seed. By simply manipulating th...

A theoretical model for electro-mechanical properties of intrinsically conductive knitted fabrics made from stainless steel multi-filament yarns under large uniaxial deformation is presented. The investigations are focused on the relationship between the load and electrical resistance of the fabric under uniaxial extension. A circuit network is proposed based on the loops configuration and fabric structure. The equivalent resistance of the fabric is obtained by solving the circuit equations of the network. In order to simplify the calculation of the contacting forces on the overlapped yarns, a two-dimensional hexagon model is used to represent the loop configurations. An image-capturing system is employed to record the images of the loop configurations during the extension process and the relationship between the configurations of the loops and the load imposed on the fabric is obtained. From the theoretical analysis and experimental investigations, it is found that the contacting resistance of the overlapped yarns in the fabric is the key factor that governs the sensitivity of the fabric sensor. In addition, the fabric structure that determines the structure of the circuit network is also an important factor affecting the characteristics of the fabric sensor.Knitted fabrics are used widely in clothing but being used as sensors for measuring strain and temperature based on their loop configurations are quite novel applications of conductive knitted fabrics [3]. The elastic and extendable substrates of the fabrics make it feasible for these sensors to be used for measuring large tensile strain.The applications of these conductive fabric sensors are based on the changes of the electrical resistance responding to stimuli such as deformation, temperature, humidity, as well as some chemicals. Hence, the resistancestimulus responses are the bases that provide the sensitivity of the fabric sensors. To date, many conductive materials and special fabric sensors have been produced accordingly [1,2,4,8,16]. Several papers have described experimental investigations of the relationships between the load/elongation and electrical resistance of the conductive fabrics [5,9,12]. However, few studies have reported on the mechanism of the conductive fabrics and the key factors of the sensitivity in detail. A theoretical model of electro-mechanical behavior of plain woven fabric made from intrinsically conductive yarn has been proposed, and relationships between the electrical resistance and fabric density, as well as uniaxial tension have been developed [10,18]. In our paper, the electro-mechanical properties of knitted fabrics made from stainless steel multi-filament yarns are investigated both theoretically and experimentally. Theoretical BASIC ASSUMPTIONSThe conductive knitted fabric is treated as a conducting body as the metallic yarn is intrinsically conductive, and the unit length resistance of the yarn is considered

Transformation of nanomaterials in aqueous environment has significant impact on their behavior in engineered application and natural system. In this paper, UV irradiation induced transformation of TiO 2 nanoparticles in aqueous solutions was demonstrated, and its effect on the aggregation and photocatalytic reactivity of TiO 2 was investigated. UV irradiation of a TiO 2 nanoparticle suspension accelerated nanoparticle aggregation that was dependent on the irradiation duration. The aggregation rate increased from <0.001 nm/s before irradiation to 0.027 nm/s after 50 h irradiation, resulting in aggregates with a hydrodynamic diameter of 623 nm. The isoelectric point of the suspension was lowered from 7.0 to 6.4 after irradiation, indicating less positive charges on the surface. ATR-FTIR spectra displayed successive growth of surface hydroxyl groups with UV irradiation which might be responsible for the change of surface charge and aggregation rate. UV irradiation also changed the photocatalytic degradation rate of Rhodamine B by TiO 2 , which initially increased with irradiation time, then decreased. Based on the photoluminescence decay and photocurrent collection data, the change was attributed to the variation in interparticle charge transfer kinetics. These results highlight the importance of light irradiation on the transformation and reactivity of TiO 2 nanomaterials. ■ INTRODUCTIONSemiconductor nanomaterials have attracted intensive interest due to their ability to drive photochemical reactions under solar light irradiation. 1−4 In particular, TiO 2 nanoparticles are widely used in photocatalytic devices to achieve environmental remediation and water splitting because of their low-cost, low toxicity and robust performance. 5,6 Modeling studies predicted the annual production of nano-TiO 2 would exceed 2.5 million tons by 2025. 7 With the high reactivity and the rising demand of nano-TiO 2 , it is essential to elucidate both their stability in the practical devices during the life cycle of these products and their transformation process after discharge into the natural environment.Typical transformation processes of nanomaterials include aggregation, dissolution, redox reaction, photochemical reaction, and biocatalyzed degradation. 8−10 A nanomaterial may participate in one or more processes, depending not only on its inherent properties but also on the surrounding environmental factors. Indeed, once introduced to the practical applications, nano-TiO 2 encounters the environmental factors (e.g., natural organic matter, ionic species and sunlight) and then nano-TiO 2 will inevitably undergo physical and chemical transformations due to their high surface reactivity and large specific surface area. These transformation pathways will in turn govern their photoreactivity and environmental fate. Because of its high chemical stability, studies on the nano-TiO 2 behavior are mainly related to aggregation process. 11−13 Typically, The hydroxyl groups covered on nano-TiO 2 surface would interact with differe...