The adsorption behavior of colloidal maghemite (γ‐Fe2O3) nanoparticles, passivated by oleic acid and dispersed in octane solution, onto three different substrates (Si, Si3N4, and SiO2) is investigated. The average nanoparticle size is 10 nm, with a size variation (σ) less than 5 %. The adsorption of particles is strongly dependent on both the type of substrate and the particle concentration in solution. By a single‐dipping process, we have obtained a maximum coverage of 0.45 on a Si substrate, but much less on other substrates (0.19 on Si3N4 and 0.14 on SiO2). The particle coverage was drastically increased by the multiple‐adsorption process, where the process of dipping and drying was repeated multiple times. With this process, we can obtain a maximum particle coverage of about 0.76 on a Si substrate and 0.61 on a thermally grown SiO2 substrate.

The effect of solvents of colloidal solution and substrate withdrawing speed during dip-coating on the nanoparticle-layer formation of sterically stabilized iron oxide ͑␥-Fe 2 O 3 ͒ nanoparticles on Si substrates is investigated. From the solutions with 10 13 -10 14 mL −1 particle concentrations dispersed in hexane, octane, decane, and tetradecane, the multilayer is formed from hexane while the uniform monolayer is formed from octane, decane, and tetradecane. Because the particle layer is formed by direct adsorption and convective flux of particles from solution to substrate, the multilayer formation from hexane is due to the highest interaction energy between particle and substrate and the highest convective flux to the meniscus region of the substrate caused by the highest evaporation rate. Lowering the substrate withdrawing speed increases the particle coverage from ϳ60 to ϳ80% at 0.001 mm/s as locally forming the multilayer regions, which is explained by increased convective flux at reduced speed. These results verify that the colloidal particle delivery to the substrate is determined by factors such as particle-substrate interactions, substrate withdrawing speed, and the evaporation rate of solvent.The chemically synthesized colloidal nanoparticles, having a highly controllable size and shape with excellent uniformity and having the possibility to form two-and three-dimensional ordered self-assembly upon drying solvent by the van der Waals interaction between particles, have been highlighted as one of the most promising building blocks for nanodevice applications with their unique electrical, optical, and magnetic properties. 1-6 In particular, the formation of an ordered, self-assembled layer on the solid substrate is highly required to fabricate solid-state devices such as electroluminescence devices, 7,8 sensors, 9 photodetectors, 10 photonic crystals, 11 electrical memory devices, 12-14 and magnetic storage devices. 15,16 Among the various approaches to form the ordered layer, such as the Langmuir-Blodgett method, 17-19 spin-coating, 7,20 and dipcoating, 21-27 the dip-coating process has been known to readily form either a self-limited monolayer, thanks to the stabilization of particle by surfactant, 27 or a multilayer by alternatively adsorbing glue layers and particles. 15,21 The particle-layer formation during dipcoating has been explained to be driven either by the "convective assembly" in meniscus 22-24 or by the "direct adsorption" from the solution. 21,26,27 In "convective assembly," the particles with a size from several tens of nanometers to micrometers move toward liquid meniscus driven by incoming solution flux resulting from the solvent evaporation and eventually pinned at the edge of meniscus. As the substrate is pulled out with a controlled withdrawing speed, the particles at the meniscus condense to form an ordered layer by lateral capillary force. 28,29 Because the convective assembly is kinetically controlled, the parameters such as evaporation rate of solvent, substrate withdrawing spee...

The Raw water from Deer Creek (DC) reservoir and Little Cottonwood Creek (LCC) reservoir in the Utah, USA were collected for jar test experiments. This study examined the removal of arsenic and turbidity by means of coagulation and flocculation processes using of aluminum sulfate and ferric chloride as coagulants for 13 jar tests. The jar tests were performed to determine the optimal pH range, alum concentration, ferric chloride concentration and polymer concentration for arsenic and turbidity removal. The results showed that a comparison was made between alum and ferric chloride as coagulant. Removal efficiency of arsenic and turbidity for alum (16 mg/L) of up to 79.6% and 90.3% at pH 6.5 respectively were observed. Removal efficiency of arsenic and turbidity for ferric chloride (8 mg/L) of up to 59.5% at pH 8 and 90.6% at pH 8 respectively were observed. Optimum arsenic and turbidity removal for alum dosages were achieved with a 25 mg/L and 16 mg/L respectively. Optimum arsenic and turbidity removal for ferric chloride dosages were achieved with a 20 mg/Land 8 mg/L respectively. In terms of minimizing the arsenic and turbidity levels, the optimum pH ranges were 6.5 and 8for alum and ferric chloride respectively. When a dosage of 2 mg/L of potassium permanganate and 8 mg/L of ferric chloride were employed, potassium permanganate can improve arsenic removal, but not turbidity removal.

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