Platinum Nanoparticles Immobilized on Electrospun Membranes for Catalytic Oxidation of Volatile Organic Compounds.

Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally friendly way of emission abatement. Noble metal catalysts are typically preferred due to high activity and stability. In this paper, the preparation of a thermally stable polybenzimidazole electrospun membrane, which can be used as a support for a platinum catalyst applicable in the total oxidation of volatile organic compounds, is reported for the first time. In contrast to commercial pelletized catalysts, high porosity of the membrane allowed for easy accessibility of the platinum active sites to the reactants and the catalytic bed exhibited a low pressure drop. We have shown that the preparation conditions can be tuned in order to obtain catalysts with a desired platinum particle size. In the gas-phase oxidation of ethanol, acetone, and toluene, the catalysts with Pt particle sizes 2.1 nm and 26 nm exhibited a lower catalytic activity than that with a Pt particle size of 12 nm. Catalysts with a Pt particle size of 2.1 nm and 12 nm were prepared by equilibrium adsorption, and the higher catalytic activity of the latter catalyst was ascribed to more reactive adsorbed oxygen species on larger Pt nanoparticles. On the other hand, the catalyst with a Pt particle size of 26 nm was prepared by a solvent evaporation method and contained less active polycrystalline platinum. Last but not least, the catalyst containing only 0.08 wt.% of platinum achieved high conversion (90%) of all the model volatile organic compounds at moderate temperatures (lower than 335 °C), which is important for reducing the costs of the abatement technology.

Synthesis, Characterization, and Gas Adsorption Performance of Amine-Functionalized Styrene-Based Porous Polymers.

In recent years, porous materials have been extensively studied by the scientific community owing to their excellent properties and potential use in many different areas, such as gas separation and adsorption. Hyper-crosslinked porous polymers (HCLPs) have gained attention because of their high surface area and porosity, low density, high chemical and thermal stability, and excellent adsorption capabilities in comparison to other porous materials. Herein, we report the synthesis, characterization, and gas (particularly CO2) adsorption performance of a series of novel styrene-based HCLPs. The materials were prepared in two steps. The first step involved radical copolymerization of divinylbenzene (DVB) and 4-vinylbenzyl chloride (VBC), a non-porous gel-type polymer, which was then modified by hyper-crosslinking, generating micropores with a high surface area of more than 700 m2 g-1. In the following step, the polymer was impregnated with various polyamines that reacted with residual alkyl chloride groups on the pore walls. This impregnation substantially improved the CO2/N2 and CO2/CH4 adsorption selectivity.

Glycidyl and Methyl Methacrylate UV-Grafted PDMS Membrane Modification toward Tramadol Membrane Selectivity.

Pharmaceutical wastewater pollution has reached an alarming stage, as many studies have reported. Membrane separation has shown great performance in wastewater treatment, but there are some drawbacks and undesired byproducts of this process. Selective membranes could be used for pollutant investigation sensors or even for pollutant recovery. The polydimethylsiloxane (PDMS) membrane was first tested on separated and mixed antibiotic (ATB) water solutions containing sulfamethoxazole (SM), trimethoprim (TMP), and tetracycline (TET). Then, the bare and ultra-violet grafted (UV-grafted) PDMS membranes (MMA-DMAEMA 10, GMA-DMAEMA 5, and GMA-DMAEMA 10) were tested in tramadol (TRA) separation, where the diffusion coefficient was evaluated. Finally, the membranes were tested in pertraction with a mixture of SM, TMP, TET, and TRA. The membranes were characterized using the following methods: contact angle measurement, FTIR, SEM/EDX, and surface and pore analysis. The main findings were that TET was co-eluted during mixed ATB pertraction, and GMA-DMAEMA 5 was found to selectively permeate TRA over the present ATBs.

Modified Single-Walled Carbon Nanotube Membranes for the Elimination of Antibiotics from Water.

The hydrophilic and hydrophobic single-walled carbon nanotube membranes were prepared and progressively applied in sorption, filtration, and pertraction experiments with the aim of eliminating three antibiotics-tetracycline, sulfamethoxazole, and trimethoprim-as a single pollutant or as a mixture. The addition of SiO2 to the single-walled carbon nanotubes allowed a transparent study of the influence of porosity on the separation processes. The mild oxidation, increasing hydrophilicity, and reactivity of the single-walled carbon nanotube membranes with the pollutants were suitable for the filtration and sorption process, while non-oxidized materials with a hydrophobic layer were more appropriate for pertraction. The total pore volume increased with an increasing amount of SiO2 (from 743 to 1218 mm3/g) in the hydrophilic membranes. The hydrophobic layer completely covered the carbon nanotubes and SiO2 nanoparticles and provided significantly different membrane surface interactions with the antibiotics. Single-walled carbon nanotubes adsorbed the initial amount of antibiotics in less than 5 h. A time of 2.3 s was sufficient for the filtration of 98.8% of sulfamethoxazole, 95.5% of trimethoprim, and 87.0% of tetracycline. The thicker membranes demonstrate a higher adsorption capacity. However, the pertraction was slower than filtration, leading to total elimination of antibiotics (e.g., 3 days for tetracycline). The diffusion coefficient of the antibiotics varies between 0.7-2.7 × 10-10, depending on the addition of SiO2 in perfect agreement with the findings of the textural analysis and scanning electron microscopy observations. Similar to filtration, tetracycline is retained by the membranes more than sulfamethoxazole and trimethoprim.

In situ sorption phenomena can mitigate potential negative environmental effects of underground coal gasification (UCG) - an experimental study of phenol removal on UCG-derived residues in the aspect of contaminant retardation.

The aim of the study was to investigate the sorption interactions between phenol and materials obtained from four different underground coal gasification (UCG) ex-situ simulations. These interactions are significant in terms of the impact of the UCG on the groundwater environment. Sorption parameters were determined for two sample types: raw coal mined from the coal-bed and then subjected to the gasification process; and char residue acquired from the cavity formed as a result of the UCG processes. Laboratory-scale tests were carried out using deionized water and aqueous solutions with increasing concentrations of phenol (from 50 mg/dm3 to 2000 mg/dm3) at 298 K. On the assumption of physical interactions (non-specific physisorption) and due to a nonlinear mass distribution of adsorbed substances as a function of equilibrium concentration, the Freundlich isotherm model was applied to describe adsorption phenomena. The isotherms have good fitting (R2 from 0.5716 to 0.9811). Relatively high percentage phenol removal efficiency was observed for all tested chars (from 17.0% to 99.8% for the 1.0-2.5 mm fraction and from 6.9% to 99.6% for the 10.0-12.5 mm fraction). Additionally, the sorption characteristics was used to evaluate the retardation coefficients. The largest delay in the organic pollutant migration in the environment around a UCG reactor occurs for phenol transport in the layer of the post-process char from 'Wesola' after 40 bar pressure experiment.

Remediation of brownfields contaminated by organic compounds and heavy metals: a bench-scale test of a sulfur/vermiculite sorbent for mercury vapor removal.

In this study, we report for the first time a novel type of sorbent that can be used for mercury adsorption from the air-based off-gasses-vermiculite impregnated with alkali polysulfides and thiosulfates. In contrast to other sorbents, vermiculite exhibits superior thermal stability in air and low adsorption capacity for organic vapors. This allows for a more favorable design of the soil remediation unit-direct coupling of thermal desorber with catalytic oxidizer using air as a carrier gas. In the bench-scale test at 180 °C, the sulfur/vermiculite sorbent exhibited significantly higher efficiency for the adsorption of mercury vapor from the off-gasses than the commercial sulfur/activated carbon sorbent at its highest operating temperature (120 °C). The average mercury concentration in the adsorber off-gas decreased from 1.634 mg/m3 for the sulfur/activated carbon to 0.008 mg/m3 achieved with impregnated vermiculite. The total concentration of organic compounds in the soil after thermal desorption was below the detection limit of the employed analytical method.