AC Particles Research Articles

Bioturbation Delays Attenuation of DDT by Clean Sediment Cap but Promotes Sequestration by Thin-Layered Activated Carbon

The effects of bioturbation on the performance of attenuation by sediment deposition and activated carbon to reduce risks from DDT-contaminated sediment were assessed for DDT sediment-water flux, biouptake, and passive sampler (PE) uptake in microcosm experiments with a freshwater worm, Lumbriculus variegatus. A thin-layer of clean sediment (0.5 cm) did not reduce the DDT flux when bioturbation was present, while a thin (0.3 cm) AC cap was still capable of reducing the DDT flux by 94%. Bioturbation promoted AC sequestration by reducing the 28-day DDT biouptake (66%) and DDT uptake into PE (>99%) compared to controls. Bioturbation further promoted AC-sediment contact by mixing AC particles into underlying sediment layers, reducing PE uptake (55%) in sediment compared to the AC cap without bioturbation. To account for the observed effects from bioturbation, a mass transfer model together with a biodynamic model were developed to simulate DDT flux and biouptake, respectively, and models confirmed experimental results. Both experimental measurements and modeling predictions imply that thin-layer activated carbon placement on sediment is effective in reducing the risks from contaminated sediments in the presence of bioturbation, while natural attenuation process by clean sediment deposition may be delayed by bioturbation.

Capacitive properties of polypyrrole/activated carbon composite

Electrochemical synthesis of polypyrrole (PPy) and polypyrrole / activated carbon (PPy / AC) - composite films, with a thickness between 0.5 and 15 ?m were performed in a three electrode cell containing 0.1 mol dm-3 Py, 0.5 mol dm-3 NaClO4 dissolved in ACN, and dispersed particles of AC (30 g dm-3). Electrochemical characterization of PPy and PPy / AC composites was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The linear dependences of the capacitance (qC), redox capacitance (qred), and limiting capacitance (CL) of PPy and PPy / AC - composite films on their thickness (L), obtained by electrochemical and impedance analysis, indicate a nearly homogeneous distribution of the incorporated AC particles in the composite films (correlation coefficient between 0.991 and 0.998). The significant enhancement of qC, qred, and CL, was observed for composite films (for ?40 ? 5%) in respect to that of the ?pure? PPy. The decreased values of a volume resistivity in the reduced state of the composite film, ? = 1.3 ? 106 ? cm (for L = 7.5 ?m), for two orders of magnitude, compared to that of PPy - film with the same thickness, ? ? 108 ? cm, was also noticed.

Degradation and mineralization of furfural in aqueous solutions using heterogeneous catalytic ozonation

The main aim of this experiment was to study the degradation of furfural in wastewater using catalytic ozonation process with granular activated carbon as a catalyst. Influences of the following parameters were investigated on furfural degradation; initial furfural concentration, solution pH, GAC dosage, and reaction time. In order to gain an understanding of the mechanism, involved these experiments were done in the presence of some radical scavengers. A significant synergistic effect between ozone and activated carbon was obtained in the oxidation and mineralization of furfural compared to single ozonation and adsorption on GAC processes, thus verifying the positive effect of coupling ozonation and GAC to degrade toxic compounds such as furfural. Furthermore, this study demonstrated that the efficiency of furfural removal increased with a decreasing size of AC particles due to an increased surface area. Measurements of COD in SOP and COP showed that more degradation and mineralization of furfural occurred in COP (80.2%) compared to single ozonation process (42.4%). Desorption studies were performed and they showed that percentages for recovery of furfural from GAC used in COP and single adsorption processes were 3.5 and 85.4, respectively.

Control of microwave-generated hot spots. Part V. Mechanisms of hot-spot generation and aggregation of catalyst in a microwave-assisted reaction in toluene catalyzed by Pd-loaded AC particulates

Hot spots are generated when carrying out the heterogeneous Suzuki–Miyaura cross coupling reaction for the synthesis of 4-methylbiphenyl in toluene solvent in the presence of Pd/AC catalyst (AC: activated carbon; see for example parts I–IV11For part I, see Ref. [8]; for part II, see Ref. [9]; for part III, see Ref. [2]; and for part IV, see Ref. [10].). Controlling these hot spots could render the microwave-assisted catalyzed reaction more effective. Accordingly, the present article examines the mechanism by which the hot spots are generated through particle aggregation observed by means of a high-speed camera; the influence of particle size was also examined. Moreover, the formation of hot spots within the spatial gap between two AC particles was simulated by an electromagnetic field analysis and subsequently evidenced experimentally. The heterogeneous Suzuki–Miyaura coupling reaction for the synthesis of 4-methylbiphenyl in toluene solvent in the presence of activated carbon (AC; no Pd) under microwave irradiation has been re-visited to ascertain what the effect of the reagents might be as to whether or not hot spots are formed. The presence of the reagents used in the synthesis of 4-methylbiphenyl did cause a firm connectivity between the activated carbon particles, which changed with the directions of the electric field and the magnetic field. The relationship between the generation of by-products and the formation of hot spots has also been considered in the synthesis of 4-methylbiphenyl in toluene solvent catalyzed by Pd/AC.

Composites with Macroporous Poly(vinyl alcohol) Cryogels with Attached Activated Carbon Microparticles with Controlled Accessibility of a Surface

A set of glutaraldehyde (GA) cross-linked poly(vinyl alcohol)/activated carbon (PVA/GA/AC) composites prepared in the form of monolithic rods using a cryogelation technique and studied using adsorption, mercury porosimetry, scanning electron microscopy (SEM), and quantum chemistry methods display porosity similar to that of PVA/GA cryogel at a high GA content (content ratio GA/AC = 1 and GA/PVA = 0.2). GA cross-linked PVA multilayer coverage is an effective barrier for adsorption on AC particles. Variations in surface chemistry (AC initial and oxidized in air at 300 °C for 12 h) and content (14-62.5%w/w) of ACs in PVA/GA/AC composites relatively weakly affect their textural characteristics at a high GA content (specific surface area S(BET) < 120 m²/g, pore volume V(p) < 0.35 cm³/g). However, PVA/GA/AC composite rods formed with a lower concentration of GA (content ratio GA/AC = 1/6 and GA/PVA = 1/10) have significantly greater S(BET) (∼500 m²/g) and V(p) (>0.55 cm³/g) values because of improved accessibility of the AC surface. This provides better adsorption of methylene blue as a probe compound.

Highly hydrated Nafion/activated carbon hybrids

The incorporation of highly porous activated carbon (aC) to Nafion membranes confers unprecedented levels of water uptake (4 times higher for 10 wt% aC compared to neat Nafion) at a minimal dimensional swelling and results in dramatic enhancements in ionic conductivity at low relative humidity. This behavior reveals the development of a robust network of water nanochannels formed by the carbon pores and the polymeric ionic domains which are structurally stabilized by the rigid Nafion backbone and the non-deformable aC particles.

Textural and electronic characteristics of mechanochemically activated composites with nanosilica and activated carbon

Nanosilicas (A-50, A-300, A-500)/activated carbon (AC, SBET=1520m2/g) composites were prepared using short-term (5min) mechanochemical activation (MCA) of powder mixtures in a microbreaker. Smaller silica nanoparticles of A-500 (average diameter dav=5.5nm) can more easily penetrate into broad mesopores and macropores of AC microparticles than larger nanoparticles of A-50 (dav=52.4nm) or A-300 (dav=8.1nm). After MCA of silica/AC, nanopores of non-broken AC nanoparticles remained accessible for adsorbed N2 molecules. According to ultra-soft X-ray emission spectra (USXES), MCA of silica/AC caused formation of chemical bonds Si–O–C; however, Si–C and Si–Si bonds were practically not formed. A decrease in intensity of OKα band in respect to CKα band of silica/AC composites with diminishing sizes of silica nanoparticles is due to both changes in the surface structure of particles and penetration of a greater number of silica nanoparticles into broad pores of AC microparticles and restriction of penetration depth of exciting electron beam into the AC particles.

Aqueous phase adsorption of organic compounds on activated carbon in fluidized bed

In this study, the adsorption of an organic compound in aqueous phase on granular activated carbon (GAC) in a liquid fluidized bed has been studied. For this purpose first a mathematical model was proposed for simulation of this process. Based on the proposed model, the adsorption kinetic and dynamic simulation of organic compounds on activated carbon were investigated. In order to check the accuracy of the proposed model, an experimental set-up was constructed. This set-up was consisted of a feed tank, a pump, a flow meter and a liquid fluidized bed absorber column. In this set up, some experiments were conducted for adsorption of methyl-orange solution on AC particles. The results obtained by the proposed model were com pared with the experimental results and once the validity of the model was verified, it was used for studying the effect of different operating parameters on the rate of adsorption in such beds.

A mechanism of photocatalytic and adsorptive treatment of 2,4-dinitrophenol on a porous thin film of TiO 2 covering granular activated carbon particles

The present work investigates the mechanism of the photocatalytic and adsorptive treatment of an aqueous DNP (2,4-dinitrophenol) solution in an annular-flow reactor installed with a TiO 2/AC-PET film (a polyethylene terephthalate film adhesively fixing activated carbon particles covered with a thin and porous film of titanium dioxide). Unfortunately, the experimental result indicates that it is impossible to correctly measure the time courses of product ion concentrations because they are adsorbed onto or desorbed from AC particles. Therefore, a computer simulation methodology using mathematical models is introduced in order to elucidate the treatment mechanism. Treatments of aqueous DNP solutions using the TiO 2-PET film reveal that the diffusion of DNP from a bulk solution to a TiO 2 film is based on the gradient of DNP concentration, generated by a rapid adsorption of DNP onto AC and photocatalytic reaction, in the very neighborhood of TiO 2 film, and this diffusion increases the DNP concentration at the surface of TiO 2 film, thereby enhancing the rate of photocatalytic decomposition. Moreover, it is found that the TiO 2/AC-PET film can lower the burden of the adsorption of DNP onto AC compared with the AC-PET film because a part of DNP molecules are photocatalytically decomposed and the percentage of this decomposition is increased at a lower linear velocity. In conclusion, the mathematical model taking into consideration a film-diffusional effect can successfully explain the complicated mechanism of the treatment of an aqueous DNP solution using the TiO 2/AC-PET film.

Granulated Carbon Nanotubes as the Catalyst Support for Pt for the Hydrogenation of Nitrobenzene

Granulated Pt/carbon nanotubes (CNTs) were found to have a much better catalytic activity in the liquid phase hydrogenation of nitrobenzene than Pt/activated carbon (AC). The granulated CNTs had much larger pores than the AC particles, which gave a faster mass transfer rate of H2 that helped produce aniline with high selectivity.

Synthesis and characterization of polyaniline/activated carbon composites and preparation of conductive films

Abstract Polyaniline was synthesized via polyaniline/activated carbon (PANI/AC) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/AC composite films were prepared by drop-by-drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/AC composite films were measured according to the standard four-point-probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/AC composites were investigated by spectroscopic methods including UV–vis, FTIR and photoluminescence. UV–vis and FTIR studies showed that AC particles affect the quinoid units along the polymer backbone and indicate strong interactions between AC particles and quinoidal sites of PANI. The photoluminescence properties of PANI and PANI/AC composites were studied and the photoluminescence intensity of PANI/AC composites was higher than that of neat PANI. The increase of conductivity of PANI/AC composites may be partially due to the doping or impurity effect of AC, where the AC competes with chloride ions. The amount of weight loss and the thermostability of PANI and PANI/AC composites were determined from thermogravimetric analysis. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the AC particles were well dispersed and isolated in composite films.

Continuous reduction of toluene vapours from the contaminated gas stream in a fluidised bed photoreactor

Continuous reduction of toluene vapours in a gas fluidised bed photoreactor was studied using TiO 2-coated activated carbon (AC/TiO 2) particles as the fluidising media. The toluene vapour concentration before treatment was in the range between 200 and 1000 ppm and was relatively high compared to previous similar research works. The experimental results showed that the effective toluene reduction duration (according to the Standards of Permissible Exposure Limits of Toluene in Taiwan) was improved for approximately 130–137% using AC/TiO 2 particles as the fluidising media compared to that using AC particles as the fluidising media in the fluidised bed photoreactor with the gas flow rate between 3 and 15 L/min. When the gas stream with the toluene vapour concentration 200 ppm, the relative humidity 30% and the flow rate 3 L/min was deducted in the fluidised bed photoreactor using AC/TiO 2 particles as the fluidising media, the conditioned gas could pass the toluene permissible exposure limit in Taiwan for more than 11 h.

Stable polymer electrolytes based on polyether-grafted ZnO nanoparticles for all-solid-state lithium batteries

Solid polymer nanocomposite electrolytes composed of polyethylene oxide (PEO) macromolecules, LiN(CF3SO2)2 (LiTFSI) and polyether-grafted nano-ZnO (designated ZnO(PEGME)), are prepared and characterized in comparison with the prototypical PEO–LiTFSI film and that doped with conventional acetate group modified ZnO nanoparticles (designated ZnO(Ac)). High resolution transmission electron microscopic (HRTEM) results show that ZnO nanoparticles are dispersed homogeneously in the present PEO–LiTFSI–ZnO(PEGME) films, while those particles in PEO–LiTFSI–ZnO(Ac) aggregate badly. Atomic force microscopic (AFM) analyses prove that after storage at room temperature for a month, PEO–LiTFSI forms large dendrites while only a small amount of tiny crystals can be observed in the PEO–LiTFSI–ZnO(PEGME) film. In contrast, ZnO(Ac) particles agglomerate around the PEO–LiTFSI dendrites and separate from the original phase. This is the first direct observation on the micromorphology of the SPE films after long-term storage, which elucidates why the PEO–LiTFSI–ZnO(PEGME) electrolyte is much more stable than its counterparts. Conductivity evolutions, Li+ transport number measurements and cycle performances of the above-mentioned three typical films in all-solid-state lithium batteries also suggest that the structural merits of the polyether-grafted nanoparticles render this type of SPEs attractive in the future applications.

Comments on "Analysis of Survival of C-18 Cells after Irradiation in Suspension with Chelated and Ionic Bismuth-212 Using Microdosimetry" by Stinchcomb and Roeske (Radiat. Res. 140, 48-54, 1994)

We read with interest the recent paper by Stinchcomb and Roeske (1) on the microdosimetric analysis of C-18 cells irradiated by ac particles. The data used in their analysis were from Argonne National Laboratory experiments. These data have also been used in several intercomparison studies (2-4) of different oa-particle irradiation sources at the Pacific Northwest Laboratory (PNL), Case Western Reserve University and Argonne National Laboratory. We would like to make the following comments on the Stinchcomb and Roeske publication: 1. While we agree with the authors that the microdosimetry approach may provide more information than an average-dose approach (an accepted fact at our laboratory and others for a number of years), the purpose of the above-mentioned intercomparison was to determine the physical factors that affect dosimetry to compare biological data. These factors include: (a) different qualities and energies of radiation; (b) a-particle radioactivity from both parent and daughter radionuclides; (c) source-target geometry, which includes considerations of irradiation from radon and its progeny in the medium as well as intracellular localization of attached progeny; (d) cell and nucleus dimensions; (e) dose rates; and (f) length of exposure. These basic factors need to be resolved as the first step in any dosimetric approach. 2. An intercomparison study requires readily measurable parameters. The use of the cited parameter (Zo), defined as the specific energy deposited in the nucleus for which an individual cell has an average survival probability of l/e, is a more sophisticated concept, but it is obtained by derivation and is not directly measurable. The average dose concept (Do), which produces a 37% survival, is readily reproducible and easy to use as a point of comparison. To measure and verify the Zo concept, a method is required to deliver an exact dose (specific energy) to each nucleus of a large number of cells, and then follow them for survival analysis. We know of only a few institutions (including the microbeam facility at PNL) that have this capability. Initial experimentation with limited numbers of cells has begun with these facilities. 3. We have used the stochastic dosimetry approach at PNL to calculate probability distributions of specific energy and hit probability (5). More importantly, we have supported our hit-probability calculations with a biological measure of DNA strand breakage using single-cell gel lectrop oresis (6). In conclusion, we believe, as do the authors, that the microdosimetry approach brings additional understanding of radiobiological data, and we continue to use this approach in the analysis of data from our ongoing and collabora ive radiobiology studies.