Tunable terahertz group slowing effect with plasmon-induced transparency metamaterial.

We present a tunable plasmon-induced transparency (PIT) metamaterial for manipulating the group velocity of terahertz (THz) waves. The metamaterial is composed of metal split rings and photoconductive silicon strips. The strong PIT effect with slowing down THz waves is generated by the bright-bright mode coupling between the high-order plasmon mode and the lattice surface mode via electromagnetic destructive interference. By varying the conductivity of silicon strips, the group slowing performance is dynamically tunable. The group delay can achieve beyond 20 ps with the group index as high as 592, showing the promising application for THz signal manipulation.

Speciation of Mercury in Selected Areas of the Petroleum Value Chain.

Petroleum, natural gas, and natural gas condensate can contain low levels of mercury (Hg). The speciation of Hg can affect its behavior during processing, transport, and storage so efficient and safe management of Hg requires an understanding of its chemical form in oil, gas and byproducts. Here, X-ray absorption spectroscopy was used to determine the Hg speciation in samples of solid residues collected throughout the petroleum value chain including stabilized crude oil residues, sediments from separation tanks and condensate glycol dehydrators, distillation column pipe scale, and biosludge from wastewater treatment. In all samples except glycol dehydrators, metacinnabar (ß-HgS) was the primary form of Hg. Electron microscopy on particles from a crude sediment showed nanosized (<100 nm) particles forming larger aggregates, and confirmed the colocalization of Hg and sulfur. In sediments from glycol dehydrators, organic Hg(SR)2 accounted for ∼60% of the Hg, with ∼20% present as ß-HgS and/or Hg(SR)4 species. ß-HgS was the predominant Hg species in refinery biosludge and pipe scale samples. However, the balance of Hg species present in these samples depended on the nature of the crude oil being processed, i.e. sweet (low sulfur crudes) vs sour (higher sulfur crudes). This information on Hg speciation in the petroleum value chain will inform development of better engineering controls and management practices for Hg.

Mobility of Four Common Mercury Species in Model and Natural Unsaturated Soils.

Mercury (Hg) occurs as a myriad of species in environmental media, each with different physicochemical properties. The influence of Hg speciation on its transport in unsaturated soils is not well studied. Transport of four Hg species (dissolved inorganic Hg (II) species, a prepared Hg(II) and dissolved organic matter (DOM) complex, Hg(0), and HgS nanoparticles) was measured in sand and soil packed columns with partial water saturation under simulated rainfall (low ionic strength solution without DOM) and landfill leachate (high DOM content and high ionic strength) influent conditions. The Hg(II)-DOM species had the highest mobility among the four Hg species evaluated, and HgS particles (∼230 nm hydrodynamic diameter) had the poorest mobility, for all soil and influent conditions tested. The addition of 2 wt % clay particles to sand greatly retarded the transport of all Hg species, especially under simulated rainfall. DOM in the column influent facilitated the transport of all four Hg species in model and natural soils. For simulated rainfall, the transport trends observed in model sands were consistent with those measured in a sandy soil, except that the mobility of dissolved inorganic Hg(II) species was significantly lower in natural soils. For simulated rainfall, Hg transport was negligible in a high organic content (∼3.72 wt %) soil for all species except Hg-DOM. This work suggests that the Hg-DOM species presents the greatest potential for vertical migration to groundwater, especially with DOM in the influent solution.

Rational Design of High-Performance Cationic Organic Network Adsorbents.

Development of high-performance ionic organic network (ION) adsorbents is of great importance for water remediation. However, the research on IONs is still nascent, especially, the design philosophy regarding contaminant adsorption has rarely been explored. In this contribution, we optimized the adsorption efficiency of IONs by increasing the density of charged sites and improving their accessibility. We first produced a new cationic organic network (CON), CON-LDU4, with a high density of positive sites via synthesis from tetra(4-pyridyl)ethene. Compared to the analogue CON-LDU2 that synthesized from tetra(4-(4-pyridyl)phenyl)ethene, CON-LDU4 exhibited higher efficiency in adsorption of methyl blue, indicating that the higher ionic density results in the higher adsorption efficiency. To further improve the accessibility of the active sites, another new CON material (CON-LDU5) was synthesized by employing a hard template. CON-LDU5 exhibited a larger specific surface area than CON-LDU4, with clearly enhanced adsorption efficiency. Finally, CON-LDU5 was used to capture CrO42- ions in water with fast adsorption kinetics (k2 = 0.0328 g mg-1 min-1) and high adsorption capacity (369 mg g-1).

Effect of dispersion on adsorption of atrazine by aqueous suspensions of fullerenes.

With the widespread application of fullerenes, it is critical to assess their environmental behaviors and their impacts on the transport and bioavailability of organic contaminants. The effects of fullerene particle size, chemistry of the solution, and natural organic matter on the adsorption of atrazine by aqueous dispersions of fullerenes (C(60)) were investigated in this work. The results showed that the Polanyi-Manes model could fit the adsorption isotherms well. Smaller sizes of fullerene particles led to increased available sites and, consequently, enhanced the adsorption of atrazine on C(60). However, intensely dispersed C(60) systems might not possess suitably high adsorptive capacities due to surface chemistry change. Adsorption of atrazine by aqueous dispersions of C(60) increased with a decrease in the pH of the solution. Introduction of humic acid significantly reduced the size of the C(60) particles, and resulted in the increase of the adsorption amount. Fullerene materials, once released into the aquatic environment, are inclined to form aqueous suspensions with different degrees of dispersion, which would greatly affect the transport and fate of organic contaminants.

Impact of mercury speciation on its removal from water by activated carbon and organoclay.

Mercury (Hg) speciation can affect its removal efficiency by adsorbents. This study assessed the removal of dissolved inorganic Hg(II) species (Hg(II)*), ß-HgS nanoparticles (HgS NP), and Hg complexed with dissolved organic matter (Hg-DOM) by three sorbents: activated carbon (AC), sulfur-impregnated activated carbon (SAC), and organoclay (OC). The effect of ionic composition, solution ionic strength, and natural organic matter (NOM) concentration on the removal of each Hg species was also evaluated. The three adsorbents were all effective in removing Hg(II)*, Hg-DOM, and HgS NPs. Increasing ionic strength decreased the removal of Hg(II)* species due to the formation of ionic Hg species with lower affinity for the sorbents. Added NOM decreased the removal of Hg(II)* and HgS NPs by all sorbents with the OC sorbent being most susceptible to NOM fouling. On a surface area-normalized basis, the OC removed all types of Hg species better than the AC and SAC samples. Moreover, adsorbed Hg-DOM transformed to a ß-HgS phase on the OC, but not for AC and SAC. These studies indicate that both Hg speciation and the water quality parameters need to be considered when designing sorbent-based emission controls to meet Hg removal targets.

Plasma-induced degradation of diphenylamine in aqueous solution.

The liquid-phase degradation induced by a gaseous plasma was investigated. The plasma was generated between an electrolytic solution and an anode tip by means of contact glow discharge electrolysis (CGDE). Aqueous diphenylamine was smoothly oxidized and eventually degradad to inorganic carbon. Results indicated that the degradation rate can be considerably raised by prolonging the discharge time and the optimum pH value was 6.0 for diphenylamine degradation. Fe2+ shows an evident accelerated effect on the diphenylamine elimination, meanwhile the presence of H2O2 benefited the degradation but the presence of n-butanol inhibited the degradation, demonstrating that the hydroxyl radicals were the most responsible oxidants in the diphenylamine degradation. The major intermediate products resulted from the degradation were identified by an HPLC analysis and a degradation path way was proposed.