Tanapon Phenrat

Bio: Tanapon Phenrat is an academic researcher from Naresuan University. The author has contributed to research in topics: Zerovalent iron & Polyelectrolyte. The author has an hindex of 27, co-authored 72 publications receiving 6225 citations. Previous affiliations of Tanapon Phenrat include Chulalongkorn University & Carnegie Mellon University.

Nanoparticle Aggregation: Challenges to Understanding Transport and Reactivity in the Environment

Abstract: Unique forms of manufactured nanomaterials, nanoparticles, and their suspensions are rapidly being created by manipulating properties such as shape, size, structure, and chemical composition and through incorporation of surface coatings. Although these properties make nanomaterial development interesting for new applications, they also challenge the ability of colloid science to understand nanoparticle aggregation in the environment and the subsequent effects on nanomaterial transport and reactivity. This review briefly covers aggregation theory focusing on Derjaguin-Landau-Verwey-Overbeak (DLVO)-based models most commonly used to describe the thermodynamic interactions between two particles in a suspension. A discussion of the challenges to DLVO posed by the properties of nanomaterials follows, along with examples from the literature. Examples from the literature highlighting the importance of aggregation effects on transport and reactivity and risk of nanoparticles in the environment are discussed.

Aggregation and Sedimentation of Aqueous Nanoscale Zerovalent Iron Dispersions

Abstract: Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.

Ionic strength and composition affect the mobility of surface-modified Fe0 nanoparticles in water-saturated sand columns.

Abstract: The surfaces of nanoscale zerovalent iron (NZVI) used for groundwater remediation must be modified to be mobile in the subsurface for emplacement. Adsorbed polymers and surfactants can electrostatically, sterically, or electrosterically stabilize nanoparticle suspensions in water, but their efficacy will depend on groundwater ionic strength and cation type as well as physical and chemical heterogeneities of the aquifer material. Here, the effect of ionic strength and cation type on the mobility of bare, polymer-, and surfactant-modified NZVI is evaluated in water-saturated sand columns at low particle concentrations where filtration theory is applicable. NZVI surface modifiers include a high molecular weight (MW) (125 kg/mol) poly(methacrylic acid)-b-(methyl methacrylate)-b-(styrene sulfonate) triblock copolymer (PMAA-PMMA-PSS), polyaspartate which is a low MW (2−3 kg/mol) biopolymer, and the surfactant sodium dodecyl benzene sulfonate (SDBS, MW = 348.5 g/mol). Bare NZVI with an apparent ζ-potential of −3...

Stabilization of aqueous nanoscale zerovalent iron dispersions by anionic polyelectrolytes: adsorbed anionic polyelectrolyte layer properties and their effect on aggregation and sedimentation

Abstract: Nanoscale zerovalent iron (NZVI) particles are 5–40 nm sized Fe0/Fe-oxide particles that rapidly transform many environmental contaminants to benign products and are a promising in situ remediation agent. Rapid aggregation and limited mobility in water-saturated porous media limits the ability to deliver NZVI dispersions in the subsurface. This study prepares stable NZVI dispersions through physisorption of commercially available anionic polyelectrolytes, characterizes the adsorbed polymer layer, and correlates the polymer coating properties with the ability to prevent rapid aggregation and sedimentation of NZVI dispersions. Poly(styrene sulfonate) with molecular weights of 70 k and 1,000 k g/mol (PSS70K and PSS1M), carboxymethyl cellulose with molecular weights of 90 k and 700 k g/mol (CMC90K and CMC700K), and polyaspartate with molecular weights of 2.5 k and 10 k g/mol (PAP2.5K and 10K) were compared. Particle size distributions were determined by dynamic light scattering during aggregation. The order of effectiveness to prevent rapid aggregation and stabilize the dispersions was PSS70K(83%) > ≈PAP10K(82%) > PAP2.5K(72%) > CMC700K(52%), where stability is defined operationally as the volume percent of particles that do not aggregate after 1 h. CMC90K and PSS1M could not stabilize RNIP relative to bare RNIP. A similar trend was observed for their ability to prevent sedimentation, with 40, 34, 32, 20, and 5 wt%, of the PSS70K, PAP10K, PAP2.5K, CMC700K, and CMC90K modified NZVI remaining suspended after 7 h of quiescent settling, respectively. The stable fractions with respect to both aggregation and sedimentation correlate well with the adsorbed polyelectrolyte mass and thickness of the adsorbed polyelectrolyte layers as determined by Oshima’s soft particle theory. A fraction of the particles cannot be stabilized by any modifier and rapidly agglomerates to micron sized aggregates, as is also observed for unmodified NZVI. This non-dispersible fraction is attributed to strong magnetic attractions among the larger particles present in the polydisperse NZVI slurry, as the magnetic attractive forces increase as r6.

Surface Modifications Enhance Nanoiron Transport and NAPL Targeting in Saturated Porous Media

Abstract: Rapid in situ degradation of chlorinated solvents present as nonaqueous phase liquids (NAPL) can be accomplished using reactive zerovalent nanoiron particles. Prior studies have shown that nanoiron...

Mammalian caspases: structure ,a ctivation ,s ubstrates, and functions during apoptosis

Abstract: ■ Abstract Apoptosis is a genetically programmed, morphologically distinct form of cell death that can be triggered by a variety of physiological and pathological stimuli. Studies performed over the past 10 years have demonstrated that proteases play critical roles in initiation and execution of this process. The caspases, a family of cysteine-dependent aspartate-directed proteases, are prominent among the death proteases. Caspases are synthesized as relatively inactive zymogens that become activated by scaffold-mediated transactivation or by cleavage via upstream proteases in an intracellular cascade. Regulation of caspase activation and activity occurs at several different levels: ( a) Zymogen gene transcription is regulated; ( b) antiapoptotic members of the Bcl-2 family and other cellular polypeptides block proximity-induced activation of certain procaspases; and ( c) certain cellular inhibitor of apoptosis proteins (cIAPs) can bind to and inhibit active caspases. Once activated, caspases cleave a variety of intracellular polypeptides, including major structural elements of the cytoplasm and nucleus, components of the DNA repair machinery, and a number of protein kinases. Collectively, these scissions disrupt survival pathways and disassemble important architectural components of the cell, contributing to the stereotypic morphological and biochemical changes that characterize apoptotic cell death.

Present and Future of Surface-Enhanced Raman Scattering

Abstract: The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport

Abstract: Plastic litter is widely acknowledged as a global environmental threat, and poor management and disposal lead to increasing levels in the environment. Of recent concern is the degradation of plastics from macro- to micro- and even to nanosized particles smaller than 100 nm in size. At the nanoscale, plastics are difficult to detect and can be transported in air, soil, and water compartments. While the impact of plastic debris on marine and fresh waters and organisms has been studied, the loads, transformations, transport, and fate of plastics in terrestrial and subsurface environments are largely overlooked. In this Critical Review, we first present estimated loads of plastics in different environmental compartments. We also provide a critical review of the current knowledge vis-a-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and contaminant cotransport in the environment. Important factors that affect aggregation and deposition in natural subsurface environments are identified and c...