Oxide Hydrosols Research Articles

Noncovalent Stabilization of Water-Soluble Zinc Phthalocyaninate in Graphene Oxide Hydrosol

Noncovalent Stabilization of Water-Soluble Zinc Phthalocyaninate in Graphene Oxide Hydrosol

Noncovalent Stabilization of Water-Soluble Zinc Phthalocyaninate in Graphene Oxide Hydrosol

The possibility of stabilization of zinc(II) 2,3,9,10,16,17,23,24-octa[(3,5-sodium biscarboxylate)phenoxy] phthalocyaninate (ZnPc16) by its hybridization with the surface of graphene oxide (GO) sheets via van der Waals or coordination bonds with functional groups of the carbon matrix in the GO hydrosols has been investigated. A combination of physicochemical analysis methods (scanning electron microscopy, fluorescence microscopy, powder X-ray diffraction, and Raman spectroscopy) has been employed to confirm the integration of ZnPc16 with GO nanosheets and to study the morphology and structure of the obtained hybrid materials. Using electronic absorption spectroscopy, it has been found that, regardless of the hybridization method, the binding of the macrocycles to the inorganic particles increases the stability of ZnPc16 in an aqueous medium being irradiated with visible light. The analysis of spectral kinetic data has shown that, in contrast to the system obtained by direct integration of ZnPc16 and GO, the hybrid material formed by coordination bonding of the components via zinc acetate (Zn(OAc)2) as a binding metal cluster is able to exhibit photocatalytic properties in oxidative photodegradation of some model organic pollutant substrates (rhodamine 6G, 1,5-dihydroxynaphthalene, and 1,4-nitrophenol). The proposed colloid-chemical approach to the stabilization of photoactive water-soluble phthalocyaninates makes it possible to increase their resistance to photoinduced self-oxidation and can be adapted for various derivatives of tetrapyrrole compounds possessing photosensitizing properties.

Influence of the sign of the zeta potential of nanodiamond particles on the morphology of graphene-detonation nanodiamond composites in the form of suspensions and aerogels

A new method of using the detonation nanodiamond with positive and negative zeta potential as a spacer for aerogels based on graphene oxide is presented. It is shown that the dosed addition of detonation nanodiamonds' particles to the suspension of graphene oxide hydrosol made it possible to triple the specific surface area of the resulting aerogel compared to graphene oxide aerogel, and this effect is more significant when nanodiamonds with a positive zeta potential are used. It was also shown that aerogels derived from graphene oxide and detonation nanodiamond with a positive zeta potential have a specific morphology with graphene oxide platelets being twisted. This effect is discussed in terms of the change in the average zeta potential of the initial mixtures. Keywords: two-component systems, carbon materials, colloid chemistry.

Preparation of graphene oxide/chitosan complex and its adsorption properties for heavy metal ions

AbstractGraphene oxide hydrosol was added dropwise to the surface of chitosan (CS) to successfully obtain graphene oxide/chitosan composite (GC). The composite material was characterized by scanning electron microscopy and X-ray diffraction. The prepared adsorbent was used to simulate the static adsorption of copper, lead, and cadmium ions from 100 mL of 50 mg/L simulated wastewater samples. When the pH of the simulated wastewater is 6, initial dosage is 70 mg, adsorption time is 90 min, and temperature is 20°C; the adsorption capacities for copper, lead, and cadmium are 60.7, 48.7, and 32.3 mg/g, respectively. The adsorption and desorption cycle experiments show that the adsorption capacity of GC for copper ions can reach 86% of the initial adsorption capacity after ten cycles. The adsorption of lead ions on the composite conforms to the Freundlich adsorption isotherm model.

Smaller-lateral-size graphene oxide hydrosols sealed in dialysis bags for enhanced trace Pb(II) removal from water without re-pollution

In this work, presented is a novel and facile strategy to enhance Pb(II) adsorption capacity of graphene oxide (GO) hydrosols via the modified Hummers’ method, using the smaller-sized natural flake graphite as starting materials. The as-prepared micron GO (MGO) and submicron GO (SMGO) hydrosols were sealed in dialysis bags for adsorptive separation of Pb(II) from water to avoid secondary pollution. The effects of pH and contact duration on Pb(II) adsorption on MGO and SMGO as well as their thermodynamics and kinetics were investigated comparatively. Their performances for recycling and regeneration were also evaluated. The results indicated that SMGO exhibited an enhanced maximum sorption capacity for Pb(II) up to 1162.60 mg·g−1 higher than MGO by 25.75% and achieved adsorption equilibrium faster, which can be attributed to the fact that SMGO has more oxygen-containing functional groups on the sheet basal planes and especially at the sheet edges than SMGO. The adsorption of Pb(II) on MGO and SMGO was a spontaneous and endothermic process and well fitted the pseudo-second-order kinetics and the Langmuir sorption model. Significantly, MGO and SMGO nanosheets still kept the high sorption capacities of 514.26 mg·g−1 and 700.35 mg·g−1 after the 5 cycles, respectively, promising of enormous potential applications.

Fire-resistant and highly electrically conductive silk fabrics fabricated with reduced graphene oxide via dry-coating

Large-scale and functional silk fabrics were prepared by depositing synthetic graphene oxide (GO) hydrosol onto fabrics via an environmentally friendly “dry-coating” method and subsequently reduced in l-ascorbic acid solution. Through this modification method, the reduced GO (rGO) sheets deposited uniformly on the silk fabric surface were firmly combined with fibres. Up to 19.5wt% rGO could be deposited relative to the fabric weight. The morphology and structure of prepared rGO-coated silk fabric were characterised by scanning electron microscopy, X-ray diffraction, and Raman spectrometry. In comparison with pristine silk fabric, the modified silk fabric exhibited improved fire resistance and smoke suppression properties. The sheet resistance of rGO-coated silk fabric decreased to 0.13kΩ/sq. Washing test indicated that the rGO-coated silk fabrics prepared had good durability for common use. The functional silk fabric deposited with 19.5wt% rGO was designed into a fire-resistant conductor that kept conducting even after 60s of combustion and can be applied in the fire-fighting field. The silk fabric deposited with 3.9wt% rGO was successfully assembled into a human motion signal sensor; this easily fabricated, highly sensitive, and flexible sensor has potential for use as wearable devices.

Effect of Microwave Fields on the Properties of Silicates with an Aluminum-Sodium-Chloride Modifier

The results of microwave treatment of silicates (bentonite clay and diatomite), the impact of microwaves on the structure and technological characteristics of water suspensions of silicates, and the physical and mechanical properties of the ceramic material obtained on their basis are examined. The effect of additives (aluminum oxide hydrosol, stabilized with hydrochloric acid, and sodium chloride) on the processes accompanying heating of water suspensions of silicates and the physical-mechanical properties of the ceramic material based on them is investigated.

Synthesis of hydrated tungsten(VI) oxide sols by peptization

A method has been developed for the synthesis of hydrated tungsten oxide hydrosols, with this method being based on potassium tungstate hydrolysis followed by peptization of the formed precipitate. The influence of the conditions of precipitation, aging, and washing of the precipitate on the particle phase composition and shape and the degree of precipitate peptization has been studied. Hydrosol-particle sizes have been determined by different methods. It has been found that the dispersed phase of the hydrosols consists mainly of platelike particles of hydrated tungsten oxide WO3 · 2H2O with a number-average size of 52 nm. The sols are stable to aggregation in a pH range of 3.0–4.5. The zeta potential of the particles ranges from–33 to–38 mV.

Flame retardancy and ultraviolet resistance of silk fabric coated by graphene oxide

Silk fabrics were coated by graphene oxide hydrosol in order to improve its flame retardancy and ultraviolet resistance. In addition, montmorillonoid was doped into the graphene oxide hydrosol to further improve the flame retardancy of silk fabrics. The flame retardancy and ultraviolet resistance were mainly characterized by limiting oxygen index, vertical flame test, smoke density test, and ultraviolet protection factor. The synergistic effect of graphene oxide and montmorillonoid on the thermal stabilization property of the treated silk fabrics was also investigated. The results show that the treated silk fabrics have excellent flame retardancy, thermal stability, smoke suppression, and ultraviolet resistance simultaneously.

Organic solvents-enabled hydrothermal preparation of graphene hydrogels

The graphene hydrogels (GHGs) could be prepared via hydrothermal process using graphene oxide (GO) hydrosol. However, the formation of GHGs is unavailable when the GO concentration is low. In this work, we successfully address this problem with the aid of some organic solvents such as tetrahydrofuran, acetone and ethanol. The as-obtained GHGs have different mesopore structure and interior microstructure depending on the organic solvents used. Ethanol-enabled GHGs (eGHGs) show a cross-linked three-dimensional (3D) network structure composed of random dispersed graphene, and greatly enhance the cycling stability of Si nanoparticles as an anode material for lithium ion batteries. This work extends the possibility of synthesizing network graphene macroform.

A simple and feasible in-situ reduction route for preparation of graphene lubricant films applied to a variety of substrates

In this work, we present a simple and feasible method with broad applicability for the in-situ reduction and assembly of graphene lubricant films on various substrates. We adopt graphene oxide hydrosol as the precursor solution and creatively introduce an adherent coating of polydopamine that can be firmly bonded onto a wide range of substrates and acts as an active transition layer and in-situ reducing agent, aiming at obtaining the reduced graphene oxide (rGO) films thereon without addition of exogenous reducing agent. Experimental results prove that rGO nanosheets have been successfully assembled onto the substrates and the in-situ synthesized rGO film presents excellent morphology, outstanding friction reduction and wear resistance properties.

Stability of tungsten(VI) oxide dispersions in electrolyte solutions

The aggregation stability of tungsten oxide hydrosols is studied by the photometric and electrooptical methods. Coagulation thresholds determined in solutions of 1 : 1, 2 : 1, and 3 : 1 electrolytes obey the Schulze-Hardy rule. The coagulation is shown to occur by the barrier mechanism predominantly through adhering of small particles to large ones without considerable changes in the sizes of the latter.

PH-Mediated fine-tuning of optical properties of graphene oxide membranes

We demonstrate a pH-mediated fine-tuning method for the transmittance and optical properties of graphene oxide membranes (GOMs) which are assembled at liquid/air interface starting from graphene oxide (GO) hydrosols. The transmittance of GOM continuously decreases with the increase of the pH value of the parent hydrosol. The size and surface chemistry of GO nanosheets are discussed to how to influence the transmittance of GO hydrosol and the optical properties of the resulting membrane since a size classification occurs in acidic condition and a deoxygenate reaction is initiated by basic environment. This study indicates an easy strategy for precisely adjusting the optical properties of graphene-based membrane, which is very important for developing novel optical devices.

Synthesis of copper(II) oxide hydrosols

A procedure is developed for the synthesis of copper(II) oxide hydrosols. It is shown that the main parameters that govern the reproducibility of the synthesis results and the aggregation stability of synthesized hydrosols are the temperature of copper(II) nitrate hydrolysis and the concentration of a peptizing agent. Dispersed phase particles are shown to have a cylindrical shape with a prevailing length-to-diameter ratio of approximately 2.7.

Effect of nanodisperse particles of silicon and aluminum oxide hydrosols on structure formation of clay minerals in aqueous medium

The effect of nanodisperse particles of Al and Si oxide hydrosols on structure formation of minerals in aqueous suspensions of bentonite and refractory clays was examined. The following were determined during formation of the structure of the ceramic material: pH and structure of clay suspensions, slip fluidity, shrinkage and compressive strength of samples poured from slips made of dried and thermally activated (350°C) clays.

Biologically templated photocatalytic nanostructures for sustained light-driven water oxidation

Over several billion years, cyanobacteria and plants have evolved highly organized photosynthetic systems to shuttle both electronic and chemical species for the efficient oxidation of water. In a similar manner to reaction centres in natural photosystems, molecular and metal oxide catalysts have been used to photochemically oxidize water. However, the various approaches involving the molecular design of ligands, surface modification and immobilization still have limitations in terms of catalytic efficiency and sustainability. Here, we demonstrate a biologically templated nanostructure for visible light-driven water oxidation that uses a genetically engineered M13 virus scaffold to mediate the co-assembly of zinc porphyrins (photosensitizer) and iridium oxide hydrosol clusters (catalyst). Porous polymer microgels are used as an immobilization matrix to improve the structural durability of the assembled nanostructures and to allow the materials to be recycled. Our results suggest that the biotemplated nanoscale assembly of functional components is a promising route to significantly improved photocatalytic water-splitting systems.

Interaction of poly-N-vinylpyrrolidone with hydrated metal oxides

On the basis of data of IR spectroscopy and powder diffraction analysis, an aqueous solution of poly-N-vinylpyrrolidone was shown to interact with hydrated alumina and zirconia synthesized from corresponding metal chlorides by means of sol-gel technology. A change was shown in the nature of polymer interaction with individual components and their binary mixture at different annealing temperatures. Different mechanisms of formation of intermediate substances in the synthesis of alumina and zirconia from hydrosols in the presence of a water-soluble polymer were assumed with respect to the nature of synthesized sols. The phase composition of oxides in the course of crystallization is affected by poly-N-vinylpyrrolidone and its hydrolysis products formed by electrochemical synthesis of metal oxide hydrosols.

Synthesis and Use of Highly Dispersed Zinc Oxide

Methods for synthesis of zinc oxide hydrosols by peptization and condensation were developed. The basic colloid-chemical properties of the sols were determined: electrokinetic properties, size and phase composition of particles, and stability of hydrosols against introduction of electrolytes. The possibility of obtaining antibacterial and UV-protecting cosmetic preparations from the hydrosols obtained was demonstrated.

High rate lithium intercalation properties of V2O5/carbon/ceramic-filler composites

Abstract Composite electrodes of amorphous vanadium pentoxide/carbon/ceramic filler were prepared by mixing vanadium oxide hydrosol, acetone, carbon and ceramic fillers, and by extension on aluminum foil. High rate charge/discharge property of the composite electrode was examined, and the effect of fillers was discussed. The composite electrode had a porous structure, in which pores were 0.5–3 μm in diameter and penetrated through the composite. The composite electrode showed a large capacity of 98 mA h/g-electrode at a high current density of 17.2 mA/cm 2 (270 A/g-electrode). The relation between discharge capacity and current density was calculated by solving the simplified diffusion equation. The apparent diffusion coefficient of lithium ion in the composite electrode was found to be 10 times larger than that of electrode without fillers.

A close look at silver oxide colloid for surface-enhanced Raman scattering

A silver oxide hydrosol has been prepared by reacting silver nitrate with sodium hydroxide in an aqueous solution. The colloidal particle composition and particle size have been characterized by X-ray diffractometry and transmittance electron microscopy. We have demonstrated that the sol is surface-enhanced Raman scattering active. One major advantage of this sol is the absence of the spectral interference arising from reaction products of the sol formation process. The mechanism of surface-enhanced Raman scattering activity is essentially contributed by the silver particles generated from the photochemical process during the laser excitation.