Absence Of Polyvinylpyrrolidone Research Articles

Unveiling the Rational Development of Stimuli-Responsive Silk Fibroin-Based Ionogel Formulations.

We present an approach for the rational development of stimuli-responsive ionogels which can be formulated for precise control of multiple unique ionogel features and fill niche pharmaceutical applications. Ionogels are captivating materials, exhibiting self-healing characteristics, tunable mechanical and structural properties, high thermal stability, and electroconductivity. However, the majority of ionogels developed require complex chemistry, exhibit high viscosity, poor biocompatibility, and low biodegradability. In our work, we overcome these limitations. We employ a facile production process and strategically integrate silk fibroin, the biocompatible ionic liquids (ILs) choline acetate ([Cho][OAc]), choline dihydrogen phosphate ([Cho][DHP]), and choline chloride ([Cho][Cl]), traditional pharmaceutical excipients, and the model antiepileptic drug phenobarbital. In the absence of ILs, we failed to observe gel formation; yet in the presence of ILs, thermoresponsive ionogels formed. Systems were assessed via visual tests, transmission electron microscopy, confocal reflection microscopy, dynamic light scattering, zeta potential and rheology measurements. We formed diverse ionogels of strengths ranging between 18 and 642 Pa. Under 25 °C storage, formulations containing polyvinylpyrrolidone (PVP) showed an ionogel formation period ranging over 14 days, increasing in the order of [Cho][DHP], [Cho][OAc], and [Cho][Cl]. Formulations lacking PVP showed an ionogel formation period ranging over 32 days, increasing in the order of [Cho][OAc], [Cho][DHP] and [Cho][Cl]. By heating from 25 to 60 °C, immediately following preparation, thermoresponsive ionogels formed below 41 °C in the absence of PVP. Based on our experimental results and density functional theory calculations, we attribute ionogel formation to macromolecular crowding and confinement effects, further enhanced upon PVP inclusion. Holistically, applying our rational development strategy enables the production of ionogels of tunable physicochemical and rheological properties, enhanced drug solubility, and structural and energetic stability. We believe our rational development approach will advance the design of biomaterials and smart platforms for diverse drug delivery applications.

Polymer photosensitizing systems containing porphyrins, dinitrosyl iron complexes, and sodium alginate in the generation of singlet oxygen

The activity of photosensitizing systems based on water-soluble photoditazine (PDZ) and hydrophobic fluorinated tetraphenylporphyrin (TPPF20) solubilized polyvinylpyrrolidone (PVP) (in the case PDZ) and pluronic F127 (in the case TPPF20) was studied in a model reaction of tryptophan (Trp) photooxidation. We also studied the effect of dinitrosyl iron complex (DNIC) and sodium alginate (SA) polysaccharide on the photosensitizing activity of both PDZ in the presence of PVP and TPPF20 solubilized with pluronic F127 in a model reaction of Trp photooxidation. It was shown that TPPF20 solubilized with pluronic F127 exhibits high photocatalytic activity in the presence of both DNIC and SA. It was also shown that PVP is able to prevent the damaging effect exerted by active NO radicals produced during the photodecomposition of DNIC on PDZ molecules. Moreover, it was demonstrated that SA does not influence the photocatalytic activity of PDZ in the presence and absence of PVP. Using the dynamic light scattering method, it was found that SA macromolecules in the presence of PVP are capable of self-association, which, due to the ‘excluded volume’ effect, can cause a slight increase in the rate of photocatalytic reaction. The effectiveness of using PDZ in combination with PVP in the presence of SA and DNIC as a photosensitizer in antimicrobial photodynamic therapy was studied via in vivo experiments on a model of a full-layer planar wound in laboratory rats. Morphological studies have shown that under photodynamic action on wounds, the use of these systems (compared to photoexcitation of an aqueous solution of the initial PDZ) stimulates the transition of the inflammatory phase to the reparative (proliferative) phase. In addition, the process of cleansing wounds from microflora and devitalized tissues is accelerated, the disturbed microcirculation is restored, the proliferation of fibroblasts and blood vessels, and collagen synthesis are accelerated. It is suggested that the PDZ-PVP-SA-DNIC systems can be used in PDT procedures for the treatment of inflammatory diseases of the skin and soft tissues.

Conversion of Carbon Dioxide into Value Added Chemicals Using Electrochemical Reduction Method on Supported Bimetallic Catalysts

Currently, many studies reveal that the level of carbon dioxide in the atmosphere is rising continuously and disrupt the environment due to its cause for global warming. For this reason, advanced and emerging technologies associated with conversion of CO2 are highly essential. Among many of the methods, electrocatalytic reduction of CO2 is the most efficient and easy way to reduce CO2 into CO, alcohols, hydrocarbons and other products. Bimetallic nanoparticles of Au and Cu and the parent monometallics of each metal are synthesized and supported on functionalized multiwalled carbon nanotubes (MWCNT). The supported bimetallic nanoparticles are dispersed uniformly on fiber carbon papers (CP). To evaluate and correlate the performance of the reduction, tuning the size and structural properties of AuCu electrocatalyst are investigated by incorporating polyvinylpyrrolidone (PVP) for electrochemical reduction (ECR) of CO2. Different amounts of PVP are applicable for each bimetallic and monometallic electrocatalysts (AuCu/MWCNT/CP, Au/MWCNT/CP and Cu/MWCNT/CP). The significant role of PVP on the atomic distribution of AuCu nanoparticles (NPs) and its particle size have been studied in advance. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) are key measurements to estimate the alloying extent of Au Cu in the alloy including the coordination numbers of each metal. The electrocatalysts, which are prepared with PVP, have a better activity and selectivity compared to the bimetallic synthesized without PVP. The amount of PVP affects the structure and significantly minimizes the size of NPs that influences the activity and selectivity of products. At -0.91 V vs. RHE, the faradaic efficiency (FE%) of CO using AuCu/CNT (1.5 g PVP) was around 88%, but in the absence of PVP, the same test resulted in ~71%, indicating the effect of PVP in the product selectivity.

Influence of plant growth regulators and salicylic acid on the production of some secondary metabolites in callus and cell suspension culture of Satureja sahendica Bornm.

The impact of combinations of plant growth regulators (PGRs) on callus culture of Satureja sahendica Bornm. was investigated. In nodal explants, the response of secondary metabolite production to different concentrations of PGRs was analyzed regarding the presence and absence of polyvinylpyrrolidone (PVP). The explants were cultured on MS media in presence of auxins (2,4-dichlorophenoxyacetic acid and naphthylacetic acid) and cytokinins (thidiazuron and kinetin); which were used in equal concentrations of 0.5, 1, and 2 mg l-1. The treatment of 2 mg l-1 2,4-D + 2 mg l-1 Kin (MD3) led to the highest production of total phenolics (4.303 ± 0.449 mg GAE g-1) and flavonoids (24.903 ± 7.016 mg QE g-1). Moreover, the effect of salicylic acid (SA) on the production of secondary metabolites in cell suspension culture of Satureja sahendica was evaluated. The cell suspension culture was established by culturing the nodal-derived friable callus in the liquid medium containing different concentrations of SA (0, 100, 150, 200 µM). An inverse relationship exists between the fresh mass and secondary metabolites contents. In addition, there was a significant difference among concentrations of SA in the production of total phenolics and flavonoid compounds. SA enhances secondary metabolites production and decreases cell fresh mass.

Efficient Electrocatalytic Reduction of Carbon Dioxide Using Supported Bimetallic Catalysts By Altering the Size and Structure of Nanoparticles

Bimetallic nanoparticles of Au and Cu and the corresponding monometallics of each metal are prepared and supported on functionalized multiwalled carbon nanotubes (MWCNT). The supported bimetallic nanoparticles are dispersed uniformly on fiber carbon papers (CP). To evaluate and relate the performance of the reduction, tuning the size and structural properties of AuCu electrocatalyst are studied and investigated by incorporating polyvinylpyrrolidone (PVP) for electrochemical reduction (ECR) of CO2. Different amounts of PVP are applicable for each bimetallic and monometallic electrocatalysts (AuCu/MWCNT/CP, Au/MWCNT/CP and Cu/MWCNT/CP). The significant role of PVP on the atomic distribution of AuCu nanoparticles (NPs) and its particle size have been studied in advance. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) are key measurements to estimate the alloying extent of Au and Cu in the alloy including the coordination numbers of each metal. The electrocatalysts, which are prepared with PVP, have a better activity and selectivity compared to the bimetallic synthesized without PVP. The amount of PVP affects the structure and significantly minimizes the size of NPs that influences the activity and selectivity of products. At -0.91 V vs. RHE, the faradaic efficiency (FE%) of CO using AuCu/CNT (1.5 g PVP) was nearly 87%, but in the absence of PVP, the same test resulted in ~70%, indicating the effect of PVP in the product selectivity is shown clearly.

Decontamination of Heavy Metals from Wastewater Effluent Using Polypyrrole/Polyvinylpyrrolidone Nanoparticles

Polypyrrole nanoparticles prepared in the presence and absence of polyvinylpyrrolidone (PPy/PVP) fine black powders have been synthesized as adsorbents for the removal of copper Cu (Ⅱ) and iron Fe (Ⅲ) ions from aqueous solution. PPy and PPy/PVP were chemically prepared by using ferric chloride as an oxidant, and distillate water as a solvent with and without polyvinylpyrrolidone as a surfactant. The prepared PPy and PPy/PVP adsorbents were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area, and Fourier Transform Infrared spectroscopy (FTIR). The results display BET surface area equals 7.88 and 21.93 for PPy and PPy/PVP, respectively. The data also shows that PPy/PVP acts as flawless adsorbent for the removal of copper and iron ions from aqueous solution with sequestration percentage of 90% and 83% in 2 hours respectively.

Determination of total antioxidant capacity of Cynara Scolymus L. (globe artichoke) by using novel nanoparticle-based ferricyanide/Prussian blue assay

A novel ferricyanide/Prussian blue (PB) assay for total antioxidant capacity (TAC) determination was developed exploiting the formation of PB nanoparticles in the presence of polyvinylpyrrolidone (PVP) as stabilizer. This improved method, named as “nanoparticle-based ferricyanide/Prussian blue assay (PBNP)”, was applied to the TAC measurement of Cynara Scolymus L. (globe artichoke). The calibration results of the novel (PBNP) method were compared with those of a similar nanoparticle PB method performed in the absence of PVP, and of a sodium dodecyl sulfate-modified and acid-optimized ferricyanide reference assay. Compared to similar common Fe(III)-based TAC assays, much higher molar absorptivities, pointing out higher response to different kinds of antioxidants, were obtained with PBNP for all tested antioxidants, and lower LOD and LOQ values were achieved for thiols. As an additional advantage, methionine, not responding to other electron-transfer based TAC reagents, could be measured. PBNP could detect various antioxidants with one-two orders-of-magnitude lower LOD values than those of widely used TAC assays like CUPRAC and Folin-Ciocalteau well correlating with the proposed assay.

Mild Homogeneous Synthesis of Gold Nanoparticles through the Epoxide Route: Kinetics, Mechanisms, and Related One-Pot Composites.

A new one-pot homogeneous methodology at room temperature to obtain Au nanoparticles (AuNP) on the basis of the epoxide route is presented. The proposed method takes advantage of the homogenous generation of OH- moieties driven by epoxide ring-opening, mediated by chloride nucleophilic attack. Once reached alkaline conditions, the reducing medium allows the quantitative formation of AuNP under well-defined kinetic control. A stabilizing agent, such as polyvinylpyrrolidone (PVP) or cetyltrimethylammonium chloride (CTAC), is required to maintain the AuNP stable. Meanwhile their presence dramatically affects the reduction kinetics and pathway, as demonstrated by the evolution of the UV/Vis spectra, small-angle X-ray scattering (SAXS) patterns, and pH value along the reaction. In the presence of PVP nanogold spheroids are obtained following a similar reduction mechanism as that observed for control experiments in the absence of PVP. However, if CTAC is employed a stable complex with AuIII is formed, leading to a different reaction pathway and resulting in ellipsoidal-like shaped AuNP. Moreover, the proposed methodology allows stabilize the growing AuNP, by coupling their formation with nonalkoxidic sol-gel reactions, leading to nanocomposite gels with embedded metallic nanoparticles. The epoxide route thus offers a versatile scenario for the one-pot preparation of new metal nanoparticles-inorganic/hybrid matrices nanocomposites with valuable optical properties.

Templated Solid-State Fabrication of Quadrangled Mn–Co Mesoporous Oxides for Degradation of Methylene Blue in Water

Abstract By using soft reactive grinding route, mesoporous Mn–Co oxides were fabricated in the presence or absence of polyvinylpyrrolidone (PVP), respectively. Physicochemical properties of samples...

A Facile Method for Preparation of Polymer Particles Having a “Cylindrical” Shape

AbstractA facile and novel approach to prepare monodisperse polystyrene (PS) particles having a “cylindrical” shape was discovered. Spherical PS particles prepared by dispersion polymerization were stirred in a polyvinylpyrrolidone (PVP) aqueous solution for several hours using a magnetic stirrer at room temperature. In the presence of PVP, the spherical PS particles deformed into cylindrical shapes following stirring; however, the particles did not deform in the absence of PVP. The deformation rate of the particles was affected by the molecular weight of the dissolved PVP. This stirring method is not only highly efficient and high yielding, but also applicable to other materials such as polymethyl methacrylate. Moreover, the cylindrical particles were successfully applied as particulate surfactants in a Pickering emulsion system, which exhibited excellent stability in comparison to a system using spherical particles as a surfactant. In the first case, the emulsion was left standing for more than 4 months.

A Facile Method for Preparation of Polymer Particles Having a "Cylindrical" Shape.

A facile and novel approach to prepare monodisperse polystyrene (PS) particles having a "cylindrical" shape was discovered. Spherical PS particles prepared by dispersion polymerization were stirred in a polyvinylpyrrolidone (PVP) aqueous solution for several hours using a magnetic stirrer at room temperature. In the presence of PVP, the spherical PS particles deformed into cylindrical shapes following stirring; however, the particles did not deform in the absence of PVP. The deformation rate of the particles was affected by the molecular weight of the dissolved PVP. This stirring method is not only highly efficient and high yielding, but also applicable to other materials such as polymethyl methacrylate. Moreover, the cylindrical particles were successfully applied as particulate surfactants in a Pickering emulsion system, which exhibited excellent stability in comparison to a system using spherical particles as a surfactant. In the first case, the emulsion was left standing for more than 4 months.

One pot synthesis of Sb2S3 nanocrystalline films through a PVP-assisted hydrothermal process

In this paper, nanocrystalline antimony sulfide (Sb2S3) thin films were prepared on a tin-doped indium oxide (ITO) substrate via a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal method. The crystal structure, morphology and optical properties of the Sb2S3 films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV–vis spectroscopy. Well-crystallized Sb2S3 films possessed a honeycomb-like morphology with a whole thickness of approximately 360 nm on the ITO substrate and had a band gap of 2.0 eV. The reaction parameters that influenced the formation of Sb2S3 films, such as reaction time, temperature and quantity of PVP were investigated. PVP was found to play an important role in the formation of the honeycomb-like Sb2S3 films. In the absence of PVP, only large aggregates formed on the ITO substrate. A possible growth mechanism of the Sb2S3 films has been proposed. Furthermore, the as-synthesized Sb2S3 film exhibited a photocurrent density of −0.025 mA cm−2 at 0 V (vs. RHE) in a neutral solution, close to that of the heated Sb2S3 film. A stability test demonstrated that the as-synthesized Sb2S3 film was stable in both neutral and acidic solutions. This investigation might provide a feasible method for preparing high-quality Sb2S3 films to be used in solar energy conversion.

A Novel Spherulitic Self-Assembly Strategy for Organic Explosives: Modifying the Hydrogen Bonds by Polymeric Additives in Emulsion Crystallization

A novel strategy to prepare spherical crystals of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) has been developed by introducing polymeric additives into the antisolvent emulsion crystallization. The spherical crystals are induced by modifying the intermolecular hydrogen bonds network of LLM-105. The results show that the concentration of polyvinylpyrrolidone (PVP), which acts as a polymeric additive, is a crucial factor to get quite different morphologies of LLM-105 crystal products. X-like shaped crystals have been produced in the absence of PVP. In contrast, spherical crystals have been obtained in the presence of PVP. Importantly, LLM-105 spherulites with a mean particle size of 78.0 μm can be obtained by adding a proper amount of PVP, which has a narrow size distribution (CV = 31.2). In addition, time-resolved morphological evolution processes of X-like shaped and spherical crystals have been performed. Meanwhile, 1H NMR experiments also have been conducted to understand the intermolecular hydrogen bonds between LLM-105 molecules and the polymer. Inspired by the result of the above experiments, an LLM-105 spherulitic formation mechanism has been proposed. Furthermore, LLM-105 spherulites exhibit more excellent mechanical and safety properties. It is suggested that these spherulites have a great potentiality in the military application. Therefore, this polymer-induced spherical crystallization method is significantly important for the design and fabrication of organic small molecules with spherical shapes.

Er3+ and Yb3+ doped BaTiO3 powders and films prepared by sol-gel method

In this work, BaTiO3:Er3+ (0.5 and 5 mol%) and BaTiO3:Yb3+ (0.05 and 6 mol%) powders and films were prepared by the sol-gel method. The powders and films were characterized by means of FT-IR, XRD, Raman, SEM, and UV analyses. The evolution from xerogel to a BaTiO3 crystalline structure was monitored by FT-IR and XRD analyses. At 700 °C, the BaTiO3:Er3+ and BaTiO3:Yb3+ powders and films, synthesized by the sol-gel method in the presence or absence of PVP, crystallized in the cubic phase. The formation process of BaTiO3 under different synthesis conditions is discussed, based on the XRD, FT-IR, and Raman results. BaTiO3:Er3+ and BaTiO3:Yb3+ films were elaborated using the dip-coating technique. The thin films presented a good homogeneity. An optimal concentration of polyvinylpyrrolidone (PVP) allows to yield the BaTiO3 films with high thickness. PVP, which was used during the deposition to prepare BaTiO3 films, changes the rheological properties of “sol” PVP which significantly reduced the deposition steps and avoided film cracking. The powder’s morphology is characterized by particle agglomeration, with a faceted and irregular shape.

The effects of polyvinylpyrrolidone and thermal annealing on red shifts for absorption spectra of the nanoparticle Au/TiO2 thin film with different Au ratios

Plasmonic solar cell efficiency strongly depends on parameters of Au/TiO2 nanoparticles (NPs) embedded system including Au sizes, distribution, aggregation, and dielectric environment—polymer encapsulated around Au/TiO2 NPs. This paper briefly outlines the technological developments for preparation of the nanoparticles Au/TiO2 solutions with different Au ratios, in presence of 200, 500 mg PVP and in absence of polyvinylpyrrolidone (PVP). After that from the obtained solutions, the Au/TiO2 thin films are prepared by spin coating method aiming to get different Au nanoparticles (Au NPs) sizes with uniform dispersion. The next step, the Au/TiO2 thin films samples have been annealed at different temperatures, the absorption spectra of the different Au/TiO2 NPs thin films are investigated using the UV–Vis spectroscopy techniques. The obtained experiment results show that the absorption spectra in the case of not thermal annealing is blue shift meanwhile in the case of thermal annealing, the absorption spectra are red shifted, enhanced depending on the annealing temperatures, Au sizes, ratios and PVP amounts. The enhancement and red shifts of absorption spectra for each case of Au/TiO2 NPs thin films have been discussed and explained by interaction between PVP and Au NPs features at different annealing temperatures.

Hydrophilic bismuth sulfur nanoflower superstructures with an improved photothermal efficiency for ablation of cancer cells

Nanomaterials with intense near-infrared (NIR) absorption exhibit effective photon-to-thermal energy transfer capabilities and can generate heat to ablate cancer cells, thus playing a pivotal role in photothermal cancer therapeutics. Herein, hydrophilic flower-like bismuth sulfur (Bi2S3) superstructures with uniform size and improved NIR absorption were controllably synthesized via a facile solvothermal procedure assisted by polyvinylpyrrolidone (PVP), which could adjust the product morphology. Induced by an 808-nm laser, the as-prepared Bi2S3 nanoflowers exhibited much higher photothermal conversion efficiency (64.3%) than that of Bi2S3 nanobelts (36.5%) prepared in the absence of PVP. This can be attributed not only to the Bi2S3 nanoflower superstructures assembled by 3-dimensional crumpled-paper-like nanosheets serving as many laser-cavity mirrors with improved reflectivity and absorption of NIR light but also to the amorphous structures with a lower band gap. Thus, to achieve the same temperature increase, the concentration or laser power density could be greatly reduced when using Bi2S3 nanoflowers compared to when using Bi2S3 nanobelts, which makes them more favorable for use in therapy due to decreased toxicity. Furthermore, these Bi2S3 nanoflowers effectively achieved photothermal ablation of cancer cells in vitro and in vivo. These results not only supported the Bi2S3 nanoflowers as a promising photothermal agent for cancer therapy but also paved an approach to exploit new agents with improved photothermal efficiency.

The Role of Polyvinylpyrrolidone in Hydrothermally Synthesized Ag/ZnO Nanocomposites and Their Photocatalytic Activities.

Here we present a simple hydrothermal route for the preparation of photoactive ZnO and Ag/ZnO nanoparticles (NPs) synthesized in the presence and absence of polyvinylpyrrolidone (PVP). The low temperature synthesis is carried out in ethylene glycol (EG) medium at 180 degrees C, where EG is used as a reducing agent for the Ag+ ions. PVP is exploited as a size confining matrix for the Ag NPs. The present synthetic protocol allows the preparation of ZnO nanorods (NRs) with typical lengths of -200 nm and Ag/ZnO NPs with typical sizes of -100 nm. The photocatalytic activity of the as-prepared nanomaterials was tested for degradation of model pollutant methyl orange (MO) dye and terephthalic acid (TPA). We found that the Ag/ZnO NPs synthesized in PVP showed higher photoactivity than the commercial TiO2 (P25) powder or ZnO and Ag/ZnO NPs synthesized without PVP.

Electrodeposition of morphology- and size-tuned PbO2 nanostructures in the presence of PVP and their electrochemical studies

Micro- and nano-structured lead dioxide (PbO2) have been synthesized by electrodeposition at constant current on Ti substrate. The size and morphology of the PbO2 particles have been tuned by altering the concentration of polyvinylpyrrolidone (PVP) as the surfactant. The prepared samples (PbO2-PVPx, x refers to the percentage of PVP) were characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. Based on the compositional characterizations, the samples were found to be composed of α- and β-PbO2 with ionic and organic additives incorporated into their structure. Morphological studies revealed that the particle size and morphology of PbO2 can be controlled by altering PVP concentration. Electrochemical behavior of the prepared samples were investigated in H2SO4solution by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques. EIS results revealed that the charge transfer resistance significantly decreased in the presence of PVP (48% for the PbO2-PVP3 sample). Based on the obtained results, the presence of PVP during the synthesis greatly influences the electrochemical behavior of the resulting PbO2 film and improves reaction kinetics. The prepared electrodes have been evaluated as cathode materials in H2SO4 electrolyte. Discharge capacity of the optimized sample (in the presence of 3% PVP) was 10 times of that synthesized in the absence of PVP.

Microwave-assisted polyol synthesis of PtCu/carbon nanotube catalysts for electrocatalytic oxygen reduction

PtCu/CNT alloy electrocatalysts were prepared by microwave assisted polyol synthesis. The influence of preparation pH and the presence of polyvinylpyrrolidone (PVP) as stabilizer on catalysts nanostructure and activity towards electrocatalytic oxygen reduction was evaluated. The catalysts were alloyed at 400–600 °C for 6 h in reductive atmosphere, and characterized by TEM and XRD. The XRD patterns display a positive shift in 2θ of the Pt 111 peak, which is a good evidence for Pt–Cu alloy formation. Alloy nanoparticles already form at temperatures as low as 400 °C. Highly agglomerated PtCu nanoparticles were obtained in the absence of PVP while PVP addition resulted in dispersed and uniform nanoparticles with a mean particle size of 3.7 nm. Such small particles are a result of the considerably low temperature used during the heat treatment/alloying step. However, while Pt is nearly completely deposited on the CNTs, only smaller fractions of Cu are found in the final catalyst. A high extent of agglomeration was also noticed when the pH during polyol synthesis was increased, which is attributed to Cu-hydroxides precipitation. Pt–Cu core shell catalysts were obtained after voltammetric dealloying. Catalyst prepared at higher pH in the presence of PVP display the highest electrocatalytic activity.

Controllable synthesis and growth mechanism of α-Co(OH) 2 nanorods and nanoplates by a facile solution-phase route

A facile chemical precipitation route has been developed to control synthesis of α-cobalt hydroxide nanostructures with rod-like and plate-like morphologies. The α-Co(OH) 2 nanorods were achieved in large quantity when the experiments were carried out in the presence of a suitable shape-controlling reagent polyvinyl pyrrolidone (PVP), while the α-Co(OH) 2 nanoplates were obtained when the experiments were conducted in the absence of PVP, whilst keeping other experimental conditions constant. The chemical composition and morphologies of the as-prepared α-Co(OH) 2 nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of polymer PVP on the morphologies of α-Co(OH) 2 nanoparticles were discussed in detail. The results indicated that PVP played a key role for the formation of α-Co(OH) 2 nanorods. The growth mechanism of the as-synthesized nanorods and nanoplates were discussed in detail based on the experimental results. A possible growth mechanism has been proposed to illustrate the growth of α-Co(OH) 2 nanorods.