Engineered polymeric nanoparticles for soil remediation

Hydrophobic organic groundwater contaminants, such as polynuclear aromatic hydrocarbons (PAHs), sorb strongly to soils and are difficult to remove. We report here on the synthesis of amphiphilic polyurethane (APU) nanoparticles for use in remediation of soil contaminated with PAHs. The particles are made of polyurethane acrylate anionomer (UAA) or poly(ethylene glycol)-modified urethane acrylate (PMUA) precursor chains that can be emulsified and cross-linked in water. The resulting particles are of colloidal size (17-97 nm as measured by dynamic light scattering). APU particles have the ability to enhance PAH desorption and transport in a manner comparable to that of surfactant micelles, but unlike the surface-active components of micelles, the individual cross-linked precursor chains in APU particles are not free to sorb to the soil surface. Thus, the APU particles are stable independent of their concentration in the aqueous phase. In this paper we show that APU particles can be engineered to achieve desired properties. Our experimental results show that the APU particles can be designed to have hydrophobic interior regions that confer a high affinity for phenanthrene (PHEN) and hydrophilic surfaces that promote particle mobility in soil. The affinity of APU particles for contaminants such as PHEN can be controlled by changing the size of the hydrophobic segment used in the chain synthesis. The mobility of colloidal APU suspensions in soil is controlled by the charge density or the size of the pendent water-soluble chains that reside on the particle surface. Exemplary results are provided illustrating the influence of alternative APU particle formulations with respect to their efficacy for contaminant removal. The ability to control particle properties offers the potential to produce different nanoparticles optimized for varying contaminant types and soil conditions.     

Control of the structure,morphology and dielectric properties of bismuth titanate ceramics by praseodymium substitution using an intermediate fuel agent-assisted self-combustion synthesis

The volatilization of bismuth (Bi) species and bismuth oxide (Bi₂O₃) leads to the presence of the oxygen vacancies (V _O⁰⁰) and consequently restrains the properties of bismuth titanate (BIT; Bi₄Ti₃O₁₂). This report presents the incorporation of different atomic ratios of praseodymium ion (Pr³⁺: x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) into the BIT (Bi_4−x Pr _x Ti₃O₁₂) ceramics through an intermediate fuel agent-assisted self-combustion synthesis (IFSC). X-ray diffraction and Raman spectroscopy results revealed that some of bismuth ion (Bi³⁺) in the pseudo-perovskite layer containing Ti–O octahedra was substituted by Pr³⁺ ion. The substitution by ion with a smaller ionic radius caused the structure distortion and consequently resulted in the phase transformation from an orthorhombic symmetry to a tetragonal symmetry. Besides, it suppressed the volatilization of Bi and Bi₂O₃ and increased the stability of metal–oxygen octahedra in the BIT. These play a crucial role to control the crystal growth, as well as limit the V _O⁰⁰. Dense ceramic with a relative density up to 96.2% was obtained by incorporating Pr³⁺ with atomic ratio of 1.0. It exhibited high dielectric constant as 908.19 and low dissipation factor as 0.0011. The results address the possibility to control the structure, morphology and dielectric properties of BIT ceramic by incorporating Pr³⁺ ion through IFSC.     

Carbon-incorporated TiO2 photoelectrodes prepared via rapid-anodic oxidation for efficient visible-light hydrogen generation

Carbon-incorporated titanium dioxide (TiO₂) photoelectrodes with different structural features were prepared via rapid-anodic oxidation under different electrical potentials and exposure times. The interstitial carbon arising from the pyrogenation of ethylene glycol electrolytes induced a new C2p occupied state at the bottom of the conduction band, which lowered the band gap energy to ∼2.3 eV and consequently enabled the visible-light responsiveness. Photoelectrodes with nanotubular structures provided higher photoconversion efficiency (η) and hydrogen (H₂) evolution capability than those with irregular structures. The increased aspect ratio, wall thickness, and pore size of the nanotube arrays contributed to η through greater photon excitation and penetration. However, this contribution is limited by the high recombination of the charge carriers at ultra-high aspect ratios. Photoelectrodes with a nanotube length of ∼19.5 μm, pore size of ∼103 nm, wall thickness of ∼17 nm, and aspect ratio of ∼142.5 exhibited remarkable capability to generate H₂ at an evolution rate of up to ∼508.3 μL min⁻¹ cm⁻² and η of ∼2.3%.     

Influences of pH on the structure,morphology and dielectric properties of bismuth titanate ceramics produced by a low-temperature self-combustion synthesis without an additional fuel agent

Bismuth titanate (BIT) ceramics were prepared by incorporating low-temperature self-combustion synthesis and pH modification. The pH value of the initial precursor was adjusted to 3, 5 and 7 by the addition of ammonium hydroxide (NH₄OH) with different amount. The reaction between ammonium ions (NH₄⁺) and nitrate ions (NO₃^?) induced the formation of ammonium nitrate (NH₄NO₃), in turn to favor the combustion by enhancing the decomposition rate. Excessive hydroxyl ions (OH^?) at higher pH value dominated the chelating of the metal carboxylate and the metal ions, resulting in a strong hybridization between bismuth (Bi) and oxygen (O), and also the suppression of the independent volatility of Bi and bismuth oxide (Bi₂O₃). Such conditions contributed to the formation of pure BIT via the low-temperature self-combustion synthesis without the use of an additional fuel agent. A BIT ceramic with high relative density (91.35%) that exhibited a high dielectric constant of ～340 and a low dissipation factor ～0.028 was obtained by the synthesis method at the neutral condition. Furthermore, it offers ability for the use in high temperature applications up to 675 °C.     

Engineered polymeric nanoparticles for bioremediation of hydrophobic contaminants

Sorption of hydrophobic organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), to soil has been shown to limit their solubilization rate and mobility. In addition, sequestration of contaminants by sorption to soil and by partitioning in nonaqueous phase liquids (NAPLs) reduces their bioavailability. Polymeric nano-network particles have been demonstrated to increase the "effective" solubility of a representative hydrophobic organic contaminant, phenanthrene (PHEN) and to enhance the release of PHEN from contaminated aquifer material. In this study, we investigate the usefulness of nanoparticles made from a poly(ethylene) glycol modified urethane acrylate (PMUA) precursor chain, in enhancing the bioavailability of PHEN. PMUA nanoparticles are shown to increase the mineralization rate of PHEN crystal in water, PHEN sorbed on aquifer material, and PHEN dissolved in a model NAPL (hexadecane) in the presence of aquifer media. These results show that PMUA particles not only enhance the release of sorbed and NAPL-sequestered PHEN but also increase its mineralization rate. The accessibility of contaminants in PMUA particles to bacteria also suggests that particle application may be an effective means to enhance the in-situ biodegradation rate in remediation through natural attenuation of contaminants. In pump-and-treat or soil washing remediation schemes, bioreactors could be used to recycle extracted nanoparticles. The properties of PMUA nanoparticles are shown to be stable in the presence of a heterogeneous active bacterial population, enabling them to be reused after PHEN bound to the particles has been degraded by bacteria.