Effect of silica-core gold-shell nanoparticles on the kinetics of biohydrogen production and pollutant hydrogenation via organic acid photofermentation over enhanced near-infrared illumination.

A biological photoinduced fermentation process provides an alternative to traditional hydrogen productions. In this study, biohydrogen production was investigated at near IR region coupled to a near-field enhancement by silica-core gold-shell nanoparticles (NPs) over a range of acetate concentrations (5-40 mM) and light intensities (11-160 W/m2). The kinetic data were modeled using modified Monod equations containing light intensity effects. The yields of H2 and CO2 produced per acetate were determined as 2.31 mol-H2/mol-Ac and 0.83 mol-CO2/mol-Ac and increased to 4.38 mmol-H2/mmol-Ma and 2.62 mmol-CO2/mmol-Ma when malate was used. Maximum increases in H2 and CO2 productions by 115% and 113% were observed by adding NPs without affecting the bacterial growth rates (6.1-8.2 mg-DCM/L/hour) while the highest hydrogen production rate was determined as 0.81 mmol/L/hour. Model simulations showed that the energy conversion efficiency increased with NPs concentration but decreased with the intensity. Complete hydrogenation application was demonstrated with toxic 2-chlorobiphenyl using Pd catalysts.

Effects of temperature and SO3 on re-emission of mercury from activated carbon under flue gas conditions.

Mercury (Hg) is a toxic and bio-accumulating heavy metal that is predominantly released via the combustion of coal. Due to its toxicity, the Environmental Protection Agency (EPA) has introduced Mercury and Air Toxics Standards (MATS) Rule regarding allowable Hg emissions. In order to reduce emissions, power plants have widely adopted activated carbon (AC) injection. AC injection has proven to be an effective method to reduce Hg emissions, but the re-emission of previously adsorbed Hg during unit operation, likely due to changing temperature or flue gas composition, could be problematic. This study specifically examined the effects of temperature and sulfur trioxide (SO3) concentration, by ramping temperature and SO3 concentration independently and simultaneously, on AC samples that are already exposed to flue gas and saturated in presence of Hg, sulfur dioxide (SO2) and nitric oxide (NO). Of these two suspected factors to cause re-emission, temperature had the greater impact and resulted in re-emission of both elemental and oxidized Hg with a greater fraction of oxidized Hg, which can be attributed to elemental Hg being more strongly bonded to the AC surface. Surprisingly, exposing the samples to increasing concentrations of SO3 had nearly no effect under the conditions examined in this study, possibly as a result of the samples being already saturated with sulfur prior to the SO3 ramp tests to simulate transient conditions in the plant.

Rhodopseudomonas palustris-based conversion of organic acids to hydrogen using plasmonic nanoparticles and near-infrared light.

The simultaneous elimination of organic waste and the production of clean fuels will have an immense impact on both the society and the industrial manufacturing sector. The enhanced understanding of the interface between nanoparticles and photo-responsive bacteria will further advance the knowledge of their interactions with biological systems. Although literature shows the production of gases by photobacteria, herein, we demonstrated the integration of photonics, biology, and nanostructured plasmonic materials for hydrogen production with a lower greenhouse CO2 gas content at quantified light energy intensity and wavelength. Phototrophic purple non-sulfur bacteria were able to generate hydrogen as a byproduct of nitrogen fixation using the energy absorbed from visible and near-IR (NIR) light. This type of biological hydrogen production has suffered from low efficiency of converting light energy into hydrogen in part due to light sources that do not exploit the organisms' capacity for NIR absorption. We used NIR light sources and optically resonant gold-silica core-shell nanoparticles to increase the light utilization of the bacteria to convert waste organic acids such as acetic and maleic acids to hydrogen. The batch growth studies for the small cultures (40 mL) of Rhodopseudomonas palustris demonstrated >2.5-fold increase in hydrogen production when grown under an NIR source (167 ± 18 µmol H2) compared to that for a broad-band light source (60 ± 6 µmol H2) at equal light intensity (130 W m-2). The addition of the mPEG-coated optically resonant gold-silica core-shell nanoparticles in the solution further improved the hydrogen production from 167 ± 18 to 398 ± 108 µmol H2 at 130 W m-2. The average hydrogen production rate with the nanoparticles was 127 ± 35 µmol L-1 h-1 at 130 W m-2.

High Total Dissolved Solids Water Treatment by Charged Nanofiltration Membranes Relating to Power Plant Applications.

Selective desalination through nanofiltration (NF) is of great interest for many industrial applications including reuse of power plant scrubber wastewater and treatment of water containing high concentrations of TDS (total dissolved solids). This work seeks to understand the effect ion interactions at the membrane interface have on rejection and flux performance of charged NF membranes. NF membranes were also effective for low energy desalination of scrubber wastewater from Georgia Power Plant Bowen, composed primarily of Ca2+, Mg2+, Cl-, and SO4 2-. As NF membranes have the capability for selective separations, 80% water recovery was achieved experimentally while maintaining an overall rejection of over 60% for Ca2+ and Cl-. The occurrence of CaSO4 precipitation at high water recovery was observed. The effect of precipitation on osmotic pressure and the effect of Cl- counterions on increasing gypsum solubility were explored for water recovery operation. This work expands on a previous work on the topics of desalination of multi-ionic solutions by incorporating the use of large scale membrane modules (0.59 m2) with several synthetic solutions as well as actual scrubber water containing precipitating elements, Ca2+ and SO4 2-. It was observed that the spiral wound membrane modules maintained a stable water permeability over the 144 day course of tests.

Selenium Partitioning and Removal Across a Wet FGD Scrubber at a Coal-Fired Power Plant.

Selenium has unique fate and transport through a coal-fired power plant because of high vapor pressures of oxide (SeO2) in flue gas. This study was done at full-scale on a 900 MW coal-fired power plant with electrostatic precipitator (ESP) and wet flue gas desulfurization (FGD) scrubber. The first objective was to quantify the partitioning of selenium between gas and condensed phases at the scrubber inlet and outlet. The second objective was to determine the effect of scrubber operation conditions (pH, mass transfer, SO2 removal) on Se removal in both particulate and vapor phases. During part of the testing, hydrated lime (calcium hydroxide) was injected upstream of the scrubber. Gas-phase selenium and particulate-bound selenium were measured as a function of particle size at the inlet and outlet of the scrubber. The total (both phases) removal of Se across the scrubber averaged 61%, and was enhanced when hydrated lime sorbent was injected. There was evidence of gas-to-particle conversion of selenium across the scrubber, based on the dependence of selenium concentration on particle diameter downstream of the scrubber and on thermodynamic calculations.

Engineered Iron/Iron Oxide Functionalized Membranes for Selenium and Other Toxic Metal Removal from Power Plant Scrubber Water.

The remediation of toxic metals from water with high concentrations of salt has been an emerging area for membrane separation. Cost-effective nanomaterials such as iron and iron oxide nanoparticles have been widely used in reductive and oxidative degradation of toxic organics. Similar procedures can be used for redox transformations of metal species (e.g. metal oxyanions to elemental metal), and/or adsorption of species on iron oxide surface. In this study, iron-functionalized membranes were developed for reduction and adsorption of selenium from coal-fired power plant scrubber water. Iron-functionalized membranes have advantages over iron suspension as the membrane prevents particle aggregation and dissolution. Both lab-scale and full-scale membranes were prepared first by coating polyvinylidene fluoride (PVDF) membranes with polyacrylic acid (PAA), followed by ion exchange of ferrous ions and subsequent reduction to zero-valent iron nanoparticles. Water permeability of membrane decreased as the percent PAA functionalization increased, and the highest ion exchange capacity (IEC) was obtained at 20% PAA with highly pH responsive pores. Although high concentrations of sulfate and chloride in scrubber water decreased the reaction rate of selenium reduction, this was shown to be overcome by integration of nanofiltration (NF) and iron-functionalized membranes, and selenium concentration below 10 µg/L was achieved.

Iron-Based Nanoparticles for Toxic Organic Degradation: Silica Platform and Green Synthesis.

Iron and iron oxide nanoparticles (NPs) are finding wide applications for the remediation of various toxic chloro-organic compounds (such as trichloroethylene, TCE), via reductive and oxidative processes. In this study, Fe NPs (30-50 nm) are synthesized by reduction from ferric ions immobilized (by ion exchange) on a platform (two types of sulfonated silica particles), in order to prevent the NP agglomeration. Next, the Fe NPs are oxidized and their effectiveness for the oxidative dechlorination of TCE via the heterogeneous decomposition of hydrogen peroxide to OH• on the surface of the iron oxide NPs was demonstrated. For the reductive approach, the use of ascorbic acid as a "green" reducing agent in conjunction with a secondary metal (Pd) inhibits NP oxidation and agglomeration through surface adsorbed species. The Fe/Pd NPs have been successfully applied for the dechlorination of TCE (k(SA), surface-area normalized reaction rate, = 8.1 ×10(-4) L/m(2)h).

Sulfur-Functionalization of Porous Silica Particles and Application to Mercury Vapor Sorption.

Silanol (SiOH) groups on silica particle surfaces undergo silylation reactions with organosilane molecules to give functionalized particles, which are used in many applications. The determination of the extent of this reaction is important for proper design of functionalized materials, depending upon the application. Two types of porous silica particles (206 and 484 m2 g-1; 9.6 and 2.9 nm average pore diameter, respectively), and colloidal silica (Ludox) with a nonporous base particle of 22 nm diameter, were functionalized with sulfur-containing silanes, 3-mercaptopropyl trimethoxy silane (MPTMS), and bis[3-(triethoxysilyl) propyl]-tetrasulfide (S4). Maximum extent of functionalization was determined with S4 using Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), and total S analysis. For the two types of porous silica particles, FTIR indicated that 54 and 17% of the silanol groups were functionalized with S4, and TGA indicated that the functionalized particles were 12 and 11 mass % MPTMS, respectively. These results were independently confirmed with total sulfur analysis. Extents of functionalization were determined for varying the silane structure on the same silica particle. MPTMS reacted with 38% of functional groups, while S4 reacted with 17%; the mass % of silane is the same regardless of silane structure on the same silica particle. Characterization by DSC indicated a glass transition occurs in the silane layer of the S4-functionalized silica at about 85 °C, but not in the MPTMS functionalized particles. Finally, mercury sorption breakthrough curves indicate the pore characteristics of the S4 functionalized samples.