David A. Ladner

Solubility of nano‐zinc oxide in environmentally and biologically important matrices

Increasing manufacture and use of engineered nanoparticles is leading to a greater probability for release of engineered nanoparticles into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles, dissolution to Zn(2+) , or some combination thereof. The goal of this study was to determine the relative solubilities of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18-7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (∼5 mg/L), but much more dissolution was observed in Dulbeccos modified Eagles medium, in which the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low Zn solubility, likely because of precipitation of a Zn carbonate solid phase. Precipitation of a Zn-containing solid phase in RPMI also appeared to limit Zn solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on Zn solubility from precipitation of less soluble solid phases.

Functionalized nanoparticle interactions with polymeric membranes

A series of experiments was performed to measure the retention of a class of functionalized nanoparticles (NPs) on porous (microfiltration and ultrafiltration) membranes. The findings impact engineered water and wastewater treatment using membrane technology, characterization and analytical schemes for NP detection, and the use of NPs in waste treatment scenarios. The NPs studied were composed of silver, titanium dioxide, and gold; had organic coatings to yield either positive or negative surface charge; and were between 2 and 10nm in diameter. NP solutions were applied to polymeric membranes composed of different materials and pore sizes (ranging from ≈ 2 nm [3 kDa molecular weight cutoff] to 0.2 μm). Greater than 99% rejection was observed of positively charged NPs by negatively charged membranes even though pore diameters were up to 20 times the NP diameter; thus, sorption caused rejection. Negatively charged NPs were less well rejected, but behavior was dependent not only on surface functionality but on NP core material (Ag, TiO(2), or Au). NP rejection depended more upon NP properties than membrane properties; all of the negatively charged polymeric membranes behaved similarly. The NP-membrane interaction behavior fell into four categories, which are defined and described here.

Comparing graphene, carbon nanotubes, and superfine powdered activated carbon as adsorptive coating materials for microfiltration membranes

Multi-walled carbon nanotubes (MWCNTs), nano-graphene platelets (NGPs), and superfine powdered activated carbon (S-PAC) were comparatively evaluated for their applicability as adsorptive coatings on microfiltration membranes. The objective was to determine which materials were capable of contaminant removal while causing minimal flux reduction. Methylene blue and atrazine were the model contaminants. When applied as membrane coatings, MWCNTs had minimal retention capabilities for the model contaminants, and S-PAC had the fastest removal. The membrane coating approach was also compared with a stirred vessel configuration, in which the adsorbent was added to a stirred flask preceding the membrane cell. Direct application of the adsorbent to the membrane constituted a greater initial reduction in permeate concentrations of the model contaminants than with the stirred flask setup. All adsorbents except S-PAC showed flux reductions less than 5% after application as thin-layer membrane coatings, and flux recovery after membrane backwashing was greater than 90% for all materials and masses tested.

Understanding dendritic polymer–hydrocarbon interactions for oil dispersion

This study examines the interactions of poly(amidoamine) dendrimers and hyperbranched poly(ethyleneimine) polymers with model linear and polyaromatic hydrocarbons. Large-scale complexations were formed for both types of dendritic polymers hosting the linear but not the polyaromatic hydrocarbon. Furthermore, both types of dendritic polymers exhibited a strong and comparable hosting/dispersion capacity for the polyaromatic hydrocarbon, while the hyperbranched polymers at concentrations below 30 μM showed a consistently higher hosting capacity than the dendrimers for the linear hydrocarbon. Such complexity in hosting capacity of the two types of dendritic polymers is attributed to the more hydrophobic interior and less steric hindrance of the hyperbranched polymers for the partitioning of the hydrocarbons.

Structure–Function Relationship of PAMAM Dendrimers as Robust Oil Dispersants

PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intramolecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, ∼30%. This unexpected change in the interior protonation state causes electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications.

Effect of bead milling on chemical and physical characteristics of activated carbons pulverized to superfine sizes

Superfine powdered activated carbon (S-PAC) is an adsorbent material with particle size between roughly 0.1-1 μm. This is about an order of magnitude smaller than conventional powdered activated carbon (PAC), typically 10-50 μm. S-PAC has been shown to outperform PAC for adsorption of various drinking water contaminants. However, variation in S-PAC production methods and limited material characterization in prior studies lead to questions of how S-PAC characteristics deviate from that of its parent PAC. In this study, a wet mill filled with 0.3-0.5 mm yttrium-stabilized zirconium oxide grinding beads was used to produce S-PAC from seven commercially available activated carbons of various source materials, including two coal types, coconut shell, and wood. Particle sizes were varied by changing the milling time, keeping mill power, batch volume, and recirculation rate constant. As expected, mean particle size decreased with longer milling. A lignite coal-based carbon had the smallest mean particle diameter at 169 nm, while the wood-based carbon had the largest at 440 nm. The wood and coconut-shell based carbons had the highest resistance to milling. Specific surface area and pore volume distributions were generally unchanged with increased milling time. Changes in the point of zero charge (pH(PZC)) and oxygen content of the milled carbons were found to correlate with an increasing specific external surface area. However, the isoelectric point (pH(IEP)), which measures only external surfaces, was unchanged with milling and also much lower in value than pH(PZC). It is likely that the outer surface is easily oxidized while internal surfaces remain largely unchanged, which results in a lower average pH as measured by pH(PZC).

PAMAM dendrimer for mitigating humic foulant

Poly(amidoamine) (PAMAM) dendrimers have been established as efficient ligands for the removal of humic acid (HA) foulant, based upon electrostatic and hydrophobic interactions, as well as hydrogen bonding. This proof-of-concept study indicates the broad utility of dendritic nanotechnology for water treatment and environmental applications.

Emerging role of photovoltaics for sustainably powering underdeveloped, emerging, and developed economies

With the advent of low-cost solar photovoltaic (PV) panels and our ability to generate, store, and use electrical energy locally without the need for long-range transmission, the world is about to witness transformational changes in electricity infrastructures. The use of DC electricity enhances systemwide efficiency. DC microgrids and nanogrids powered by solar PV systems and gigawatt batteries for electricity storage can sustainably power the needs of all human beings equitably and empower every individual. Ultralarge-scale manufacturing of PV systems and batteries, a vertically integrated business model, and a targeted monetary policy of quantitative easing can rapidly power all human activities.

The control of N-nitrosodimethylamine, Halonitromethane, and Trihalomethane precursors by Nanofiltration

Nanofiltration (NF) is a promising technology for removing precursors of disinfection byproducts (DBPs) from source waters prior to oxidant addition in water treatment. The aims of this study were to investigate (i) the removal efficiencies of N-nitrosodimethylamine (NDMA), halonitromethane (HNM), and trihalomethane (THM) precursors by NF membranes from different source water types (i.e. surface water, wastewater impacted surface water, and municipal and industrial wastewater treatment effluents), (ii) the impact of membrane type, and (iii) the effects of background water components (i.e., pH, ionic strength, and Ca2+) on the removal of selected DBP precursors from different source waters. The results showed the overall precursor removal efficiencies were 57-83%, 48-87%, and 72-97% for NDMA, HNM, and THM precursors, respectively. The removal of NDMA precursors decreased with the increases in average molecular weight cut off and negative surface charge of NF membranes tested, while the removal of THM precursors was slightly affected. pH changes increased the removal of NDMA precursors, but pH did not affect the removal of THM and HNM precursors in municipal WWTP effluent. On the other hand, pH changes had little or no effect on DBP removal from industrial WWTP effluent. In addition, regardless of the membrane type or background water type/characteristics, ionic strength did not show any impact on DBP precursor removals. Lastly, an increase in Ca2+ concentration enhanced the removal of NDMA precursors while a slight decrease and no effect was observed for THM and HNM precursors, respectively, in municipal WWTP effluent.

Superfine powdered activated carbon incorporated into electrospun polystyrene fibers preserve adsorption capacity

A composite material consisted of superfine powdered activated carbon (SPAC) and fibrous polystyrene (PS) was fabricated for the first time by electrospinning. SPAC is produced by pulverizing powdered activated carbon. The diameter of SPAC (100-400nm) is more than one hundred times smaller than conventional powdered activated carbon, but it maintains the internal pore structure based on organic micropollutant adsorption isotherms and specific surface area measurements. Co-spinning SPAC into PS fibers increased specific surface area from 6m2/g to 43m2/g. Unlike metal oxide nanoparticles, which are non-accessible for sorption from solution, electrospinning with SPAC created porous fibers. Composite SPAC-PS electrospun fibers, containing only 10% SPAC, had 30% greater phenanthrene sorption compared against PS fibers alone. SPAC particles embedded within the polymer were either partially or fully incorporated, and the accessibility of terminal adsorption sites were conserved. Conserving the adsorptive functionality of SPAC particles in electrospun non-woven polymeric fiber scaffolding can enable their application in environmental applications such as drinking water treatment.