Preparation of hyperbranched hydrophobic nano-silica and its superior needling-effect in PDMS defoam agent.

Hydrophobic nano silica powder is a kind of important synergist to silicone defoaming agents. The large pore volume and branched chain conformation of silica nanoparticles present superior effects on defoaming properties. However, silica nanoparticles synthesized by liquid phase easily aggregate and pore collapse because of their high surface activity and polarity, leading to poorer dispersity and limited practicability. In this paper, a novel hydrophobic silica with a hyperbranched structure was designed through in-situ modifying method with hexamethyldisilazane (HMDS) and polydimethylsiloxane (PDMS) in the liquid phase. The trimethylsilanol generated by HMDS hydrolysis reacts quickly with the highly active hydroxyl groups on the silica, causing the surface properties of the nanoparticles to transform from polar to non-polar properties. The steric hindrance of the trimethyl silicon and the reduction of the surface polarity effectively prevent silica pores from collapsing and maintain the macropore structures to realize the hyperbranched silica. At the same time, the -Si (CH3)2- from PDMS endowed the hyperbranched silica with excellent hydrophobicity. When applied in the defoaming agent, the hydrophobicity of silica contributes to dewetting the foams, and the hyperbranched spatial structures play an enhanced needling effect. Therefore, this hydrophobic hyperbranched silica exhibited a surprising defoaming effect, which significantly reduced the defoaming time from 464.4 s to less than 2 s, superior to commercial defoaming silica (155.3 s). The defoaming efficiency reached 100 % within 2 s of the end of the shaking, and the defoamer antifoaming ability was improved to reach 27.5 min, which was 77 % higher than that of commercial defoamer.

Nano-Memristors with 4 mV Switching Voltage Based on Surface-Modified Copper Nanoparticles.

The development of memristors operating at low switching voltages <50 mV can be very useful to avoid signal amplification in many types of circuits, such as those used in bioelectronic applications to interact with neurons and nerves. Here, it is reported that 400 nm-thick films made of dalkyl-dithiophosphoric (DDP) modified copper nanoparticles (CuNPs) exhibit volatile threshold-type resistive switching (RS) at ultralow switching voltage of ≈4 mV. The RS is observed in small nanocells with a lateral size of <50 nm-2 , during hundreds of cycles, and with an ultralow variability. Atomistic calculations reveal that the switching mechanism is related to the modification of the Schottky barriers and insulator-to-metal transition when ionic movement is induced via external bias. The devices are also used to model integrate-and-fire neurons for spiking neural networks and it is concluded that circuits employing DDP-CuNPs consume around ten times less power than similar neurons implemented with a memristor that switches at 40 mV.

Acetylene hydrochlorination over tin nitrogen based catalysts: effect of nitrogen carbon-dots as nitrogen precursor.

The catalysts comprising the main active compounds of Sn-Nx were synthesized using trichlorophenylstannane ((C6H5)Cl3Sn), nitrogen carbon-dots (NCDs), and activated carbon (AC) as starting materials, and the activity and stability of catalysts was evaluated in the acetylene hydrochlorination. According to the results on the physical and chemical properties of catalysts (TEM, XRD, BET, XPS and TG), it is concluded that NCDs@AC can increase (C6H5)Cl3Sn dispersity, retard the coke deposition of (C6H5)Cl3Sn/AC and lessen the loss of (C6H5)Cl3Sn, thereby further promoting the stability of (C6H5)Cl3Sn/AC. Based on the characterization results of C2H2-TPD and HCl adsorption experiments, we proposed that the existence of Sn-Nx can effectively strengthen the reactants adsorption of catalysts. By combing the FT-IR, C2H2-TPD and Rideal-Eley mechanism, the catalytic mechanism, in which C2H2 is firstly adsorbed on (C6H5)Cl3Sn to form (C6H5)Cl3Sn-C2H2 and then reacted with HCl to produce vinyl chloride, is proposed.

In Situ Observation of Low-Power Nano-Synaptic Response in Graphene Oxide Using Conductive Atomic Force Microscopy.

Multiple studies have reported the observation of electro-synaptic response in different metal/insulator/metal devices. However, most of them analyzed large (>1 µm2 ) devices that do not meet the integration density required by industry (1010  devices/mm2 ). Some studies emploied a scanning tunneling microscope (STM) to explore nano-synaptic response in different materials, but in this setup there is a nanogap between the insulator and one of the metallic electrodes (i.e., the STM tip), not present in real devices. Here, it is demonstrated how to use conductive atomic force microscopy to explore the presence and quality of nano-synaptic response in confined areas <50 nm2 . Graphene oxide (GO) is selected due to its easy fabrication. Metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation with low write current levels <1 µA (i.e., power consumption ≈3 µW), controllable excitatory post-synaptic currents, and long-term potentiation and depression. The results provide a new method to explore nano-synaptic plasticity at the nanoscale, and point to GO as an important candidate for the fabrication of ultrasmall (<50 nm2 ) electronic synapses fulfilling the integration density requirements of neuromorphic systems.

Mercapto propyltrimethoxysilane- and ferrous sulfate-modified nano-silica for immobilization of lead and cadmium as well as arsenic in heavy metal-contaminated soil.

Nano-silica as an important part of soil is an ideal carrier of passivator material. In this paper, nano-silica was modified by silane coupling agent containing mercapto group and iron (II) salt to afford an organic-inorganic hybrid containing -S-Fe-S functional group (coded as RNS-SFe) on the surface of nano-silica. Results demonstrate that the RNS-SFe nanoparticle has network-like spheroidal shape and a primary particle size is about 18.0 nm. The RNS-SFe hybrid as a potential immobilization agent for heavy metal in soil shows excellent performance for the remediation of the contaminated soil. Specifically, with a dosage of 3.0% (mass ratio) in the soil, it can immobilize bioavailable Pb, Cd, and As by 97.1%, 85.0%, and 80.1%, respectively. Namely, the RNS-SFe hybrid can transform the bioavailable Pb, Cd, and As into insoluble mercapto metal compounds (-S-Pb-S- and -S-Cd-S-) and less soluble iron arsenate (Fe3(AsO4)2, FeAsO4) precipitate on the surface of nano-silica particle, thereby reducing the toxicity and mobility of the toxic contaminant fractions. In the meantime, the immobilized products of the Pb, Cd and As fractions have good resistance against acid leaching. These results are contributive to the application of RNS-SFe for the remediation of multi-heavy metal-contaminated soils in field.

Functional Janus-SiO2 Nanoparticles Prepared by a Novel "Cut the Gordian Knot" Method and Their Potential Application for Enhanced Oil Recovery.

Currently available methods (e.g., interfacial protection and phase separation) for preparing Janus nanoparticles are often complex and expensive. Furthermore, the preparation of Janus nanoparticles with a particle size below 10 nm is challenging. In this work, we combine an in situ surface-modification route with a chemical etching route to establish a novel "cut the Gordian knot" method for the preparation of functional Janus-SiO2 nanoparticles. Hydrophobic SiO2 nanoparticles with a three-dimensional network structure prepared via an in situ surface-modification route were dispersed in NaOH solution containing surfactant or ethanol to enable corrosion close to the modifier-nanoparticle interface with a relatively low content of surface modifiers. Thus, amphipathic Janus-SiO2 nanoparticles with a hydrophilic surface containing Si-OH species and a hydrophobic surface containing -CH3 fragments were generated. The as-prepared Janus-SiO2 nanoparticles with a size of 4-9 nm and a specific surface area of up to 612.9 m2/g can be easily dispersed in water, and they also can transfer from the water phase to the oil phase by tuning the surface polarity. Moreover, they can be tuned to achieve bidirectional regulation of surface wettability plus a reduction of the oil/water interface tension. Hence, a significant reduction (by 33∼50%) of water injection pressure and an enhanced oil recovery (EOR) (by 21.1% ∼ 26.6%) can be achieved. Apart from that, Janus-SiO2 nanoparticles are able to increase the viscosity of partially hydrolyzed polyacrylamide by 282.9% and significantly decrease its viscosity loss ratio in brine, causing an EOR of about 36.6%. With simple, low-cost, and scalable procedures, the following approach could be well applicable to fabricating Janus-SiO2 nanoparticles with a high potential for augmented water injection as well as EOR of low-permeability reservoirs.

Hydrophobic Silica with Potential for Water-Injection Augmentation of a Low-Permeability Reservoir: Drag Reduction and Self-Cleaning Ability in Relation to Interfacial Interactions.

An aqueous nanofluid containing superhydrophobic silica nanoparticles with a high surface activity and an average size of 7 nm was used to enhance the water injection of a low-permeability well. The mechanism for the aqueous nanofluid to enhance water injection was discussed. Findings indicate that the silica aqueous nanofluid can greatly increase the effective water permeability even after injecting water for 2100 pore volumes. This is because the hydrophobic silica nanoparticles can be well adsorbed onto the surface of the porous channels to cause hydrophilic to hydrophobic transformation. Both the hydrophobic capillary force and adhesion work contribute to increasing water injection; and in particular, there is a critical point in the pressure-permeability curves for the rock cores with different wettabilities. Only above the critical point, the hydrophobic rock core exhibits a higher effective water permeability than that of the hydrophilic one, which is imperative for drag reduction. Moreover, the hydrophobic rock core surface has a remarkable self-cleaning ability and can reduce the expansion ratio of clay and inhibit the formation of scale in association with the increase of effective porosity via decreasing the hydration film amount. This approach, highlighting the important role of wettability alteration in increasing water injection, could potentially promote the application of a silica aqueous nanofluid in enhanced oil recovery.