Effect Of Nanoparticle Aggregation Research Articles

Doping of polyethersulfone nanofiltration membranes: antifouling effect observed at ultralow concentrations of TiO2 nanoparticles

Doping of nanofiltration membranes with TiO2 nanoparticles was studied in the ultralow concentration range, in the absence of photocatalysis. Blended polyethersulfone/TiO2 flat-sheet membranes were manufactured and investigated in terms of pure water flux, permeability, fouling resistance and solute rejection. The membranes were synthesized at four different polymer concentrations by the phase inversion method, using 1-methyl-2-pyrrolidone (NMP) and deionized water as solvent and coagulant, respectively. The influence of TiO2 addition was investigated in an unusually low concentration interval (0.035–0.375 wt%). The membrane morphology was studied by determining particle size distributions of TiO2 to explore the effect of nanoparticle aggregation. Furthermore, membranes were characterized by hydrophilicity (contact angle), morphology (SEM), porosity, mechanical strength (bursting pressure) and thermal analysis (TGA). Membrane fouling was studied with humic acids as model organic foulants. Overall, a remarkable improvement in the permeability was observed with the addition of ultralow amounts of nanoparticles to the polymer. The optimum permeability was found to be as low as 0.085 wt%, using a constant rejection of dyes as the boundary condition. It was shown that rejection of solutes is not negatively influenced by the increase in permeability. In addition, the resistance against membrane fouling was found to be above 12% for the TiO2 blended membranes.

Influence of aggregation on thermal conductivity in stable and unstable nanofluids

We study the effect of nanoparticle aggregation on thermal conductivity (k), viscosity (η) and size distribution of a stable and unstable nanofluid of iron oxide (Fe3O4) and copper oxide (CuO), respectively. The k, η, and size are found to be time independent in Fe3O4 while they are time dependant in CuO nanofluid. The microscopic study shows a progressive increase in the size of aggregate from nano to micron in CuO nanofluid. Our results show the prominent role of agglomeration on thermal properties and the importance of surface functionalization for improved stability and performance of nanofluids.

Magnet-Induced Temporary Superhydrophobic Coatings from One-Pot Synthesized Hydrophobic Magnetic Nanoparticles

In this paper, we report on the production of superhydrophobic coatings on various substrates (e.g., glass slide, silicon wafer, aluminum foil, plastic film, nanofiber mat, textile fabrics) using hydrophobic magnetic nanoparticles and a magnet-assembly technique. Fe(3)O(4) magnetic nanoparticles functionalized with a thin layer of fluoroalkyl silica on the surface were synthesized by one-step coprecipitation of Fe(2+)/Fe(3+) under an alkaline condition in the presence of a fluorinated alkyl silane. Under a magnetic field, the magnetic nanoparticles can be easily deposited on any solid substrate to form a thin superhydrophobic coating with water contact angle as high as 172 degrees , and the surface superhydrophobicity showed very little dependence on the substrate type. The particulate coating showed reasonable durability because of strong aggregation effect of nanoparticles, but the coating layer can be removed (e.g., by ultrasonication) to restore the original surface feature of the substrates. By comparison, the thin particle layer deposited under no magnetic field showed much lower hydrophobicity. The main reason for magnet-induced superhydrophobic surfaces is the formation of nano- and microstructured surface features. Such a magnet-induced temporary superhydrophobic coating may have wide applications in electronic, biomedical, and defense-related areas.

Diffusion, aggregation, and the thermal conductivity of nanofluids

The effects of nanoparticle aggregation and diffusion are difficult to separate using most nanofluid thermal conductivity data, for which the temperature dependence is collected sequentially. The present work captures the instantaneous temperature-dependent thermal conductivity using cross-sectional infrared microscopy and tracks the effects of aggregation and diffusion over time. The resulting data are strongly influenced by spatial and temperature variations in particle size and concentration and are interpreted using a Monte Carlo simulation and rate equations for particle and heat transport. These experiments improve our understanding of nanofluid behavior in practical systems including microscale heat exchangers.

Visible-light responsive cerium ion modified titania sol and nanocrystallites for X-3B dye photodegradation

The cerium ion (Ce4+) modified titania sol and nanocrystallites were prepared by chemical coprecipitation–peptization and hydrothermal synthesis methods, respectively. XRD patterns show that Ce4+-TiO2 sol particles had anatase semicrystalline structure. And the calcined Ce4+-TiO2 powder was composed of predominant anatase titania and crystalline cerium titanate (11.18wt.% CexTi(1−x)O2). AFM micrograph shows that ultrafine particles were well dispersed in sol system and average particle size was about 10nm. Ce4+-TiO2 nanocrystallites have grown into 70nm in mean size. The difference in calculated particle size (2.41nm for sol particle and 4.53nm for crystallite) by XRD Scherrer’s formula was mainly due to aggregation effect of nanoparticles. The experimental results exhibit that Ce4+-TiO2 sol and nanocrystallites can effectively photodegrade reactive brilliant red dye (X-3B) with the dye/Ce4+-TiO2/visible-light reaction system. Moreover, photocatalytic reaction also can carry out in hydrosol reaction system as well as in suspension reaction system. And Ce4+-TiO2 sol has shown higher efficiency than nanocrystallites in respect of photocatalytic activity. Meanwhile, dye photodegradation mechanisms involving photolysis, photocatalysis, photosensitized photocatalysis and interband photocatalysis were proposed regarding different photocatalytic reaction system.