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SiO2-engineered nanoparticles (SiO2-ENPs) are one of the most commonly employed nanomaterials. There was a lack of research on the comprehensive effects of environmental factors on the stability of SiO2-ENPs. In the present work, the aggregation size, surface charge, and percentage of nanoparticles have been studied under the presence of monovalent/divalent cations combined with natural organic matter (NOM), in an effort to provide a comprehensive investigation of the stability of SiO2-ENPs in complex environmental conditions. Results show that NOM adsorbed to the particles and made their zeta potential more negative, hence stabilizing them by electrostatic repulsion, and the stability of nano-SiO2 in NOM solutions follows the order of pH 9 > pH 7 > pH 5. In addition, SiO2-ENPs size in solutions with humic acid (HA) was larger than that with fulvic acid (FA). The aggregation of SiO2-ENPs enhanced with the increase of cation concentrations, and divalent cations (Ca2+) show stronger influence on SiO2-ENPs aggregate than monovalent cations. Divalent cations partially neutralized the adsorbed organic matter, and aggregation was enhanced with Ca2+, suggesting the presence of specific Ca2+-NOM bridges. The aggregation of SiO2-ENPs in electrolyte (CaCl2 or NaCl) and CaCl2 + NOM solutions follows in the order of pH 5~pH 9 > pH 7, showing that weakly acidic or alkaline conditions are not favorable for the stability of SiO2-ENPs in complex environmental systems. [ABSTRACT FROM AUTHOR]

In this study, we showcase the use of silicon dioxide (SiO2) nanoparticles and hexamethyldisilazane (HMDS) treatment to regulate the thin film morphology and manipulate charge transport of solution-processed, small-molecular, organic semiconductors. 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was blended with SiO2 nanoparticles as an exemplary organic semiconductor. A higher concentration of SiO2 nanoparticles were observed near the edge of TIPS pentacene crystals and enlarged the width of crystal edges. This greatly reduced the dendritic crystal growth pattern of TIPS pentacene and contributed to its enhanced orientation uniformity. In addition, the HMDS treatment effectively passivated the silanol groups on the hydrophilic gate dielectrics. As a result, bottom-gate, top-contact TIPS pentacene/SiO2 nanoparticle-based organic thin-film transistors boosted a performance consistency enhancement (defined by the ratio of average mobility to the standard deviation of mobility). The combinational approach to employ SiO2 nanoparticles and HMDS treatment as demonstrated in this work sheds light on important applications in high-performance organic electronics devices on flexible substrate. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a crucial reaction for various energy conversion and storage devices, but the sluggish kinetics and the usage of noble metals greatly restrict its practical device applications. In this work, a well-designed high-performance catalyst for ORR was synthesized via a facile one-step Co-MOF carbonization method, in which Co-MOF was prepared using the cobalt acetate tetrahydrate and 2,2′-bipyridyl-5,5′-dicarboxylic acid (H2bpydc) as the only raw materials and H2bpydc as the favorable carbon and nitrogen source for in situ nitrogen doping and metallic cobalt reduction. The resultant 3D mesoporous carbon foam catalyst with embedded Co nanoparticles (CoN-CF) is enriched with nitrogen, which exhibits high specific surface area and abundant N-doping active sites for catalytic ORR. In particular, the optimized CoN-CF-700 sample displays the best catalytic performances including onset potential of 0.94 V, half-wave potential of 0.85 V, long-term durability and superior resistance to methanol poisoning. The demonstrated synthetic strategy provides a new insight into easy-synthesis and high-economy routes for metal-N-C catalysts and a deeper understanding of the effects of microstructures on catalytic mechanisms. [ABSTRACT FROM AUTHOR]

Memristor crossbar arrays have great potential in brain inspired computing and the next generation high-density memories. The sneak current issue, however, seriously degrades their performance with increasing array size. Selectors with volatile threshold switching (TS) behavior have become important components of the arrays to suppress this issue. Ag/Ta2O5/Pt diffusive devices have promising TS characteristics as selectors, including high ON/OFF ratio and low OFF current. However, their unidirectional TS excludes their application in arrays consisting of bipolar memristors. Bipolar memristors require voltage biases of different polarities to enable the device programming, thus selectors with bidirectional TS are essential for them. In this study, we realize reproducible bidirectional TS behavior on Ag/Ta2O5/Pt diffusive devices. The ON/OFF ratio and the OFF current of the device are ∼107 A and ∼ 10−12 A, respectively. The switching voltage is ∼ 0.35 V and the hold voltage is ∼ 0.125 V. The TS behavior can be also optimized by choosing suitable compliance current during a voltage sweep. Simulations of nanoparticles diffusion are also carried out to study the mechanism of this bidirectional TS process. The simulations show that this behavior can be attributed to the outer diffusion of Ag nanoparticles from an Ag electrode and their accumulation near the Pt electrode under the voltage sweep, which can serve as an additional counter active electrode. This work illustrates that Ag/Ta2O5/Pt diffusive devices are promising candidates for selector applications in bipolar memristor crossbar arrays. [ABSTRACT FROM AUTHOR]