Batch and continuous mode experiments were used to determine the influence of physic-chemicals characteristics of iron oxy-hydroxides (FeOOHs) on selenium adsorption. Batch experiments and continuous ...flow rapid small-scale column tests (RSSCTs) at pH 7 and NSF (National Sanitation Foundation) water matrix, showed that the adsorption capacity of FeOOHs for Se(IV) is strongly related to positive surface charge density (PSCD), and gradually increases when synthesis pH is lowered. The highest PSCD value of 3.25 mmol OH−/g was observed at synthesis pH 2.5 (FeOOH/2.5) and the lowest, 0.45 mmol OH−/g, was observed at synthesis pH 9 (FeOOH/9). A thermodynamic study verified the endothermic (ΔΗ° 21.4 kJ/mol) chemisorption of Se(IV) by the qualified FeOOH/2.5. EXAFS data showed that Se(IV) is involved in three types of surface complexes: bidentate mononuclear edge-sharing (1E) and two types of binuclear inner-sphere (2C) linkage between the SeO32− pyramids, and Fe(O,OH)6 octahedra. The FeOOHs were evaluated by their adsorption capacity (Q10) at residual concentrations equal to the EU drinking water regulation limit of 10 μg/L, e.g. in conditions implemented in full-scale water treatment plants. The qualified FeOOH/2.5 was found to be the most effective for Se(IV) adsorption with a Q10 value 4.3 mg Se(IV)/g. In contrast, the Q10 value for Se(VI) was almost three orders of magnitude lower (10 μg Se(VI)/g) than that for Se(IV). Finally, regeneration experiments showed that FeOOHs reuse for Se(IV) removal is economically feasible and the recovery of selenium by precipitation as elemental Se contributes to green chemistry.
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•Strong correlation between the PSCD of FeOOHs and Q10 value for Se(IV)•Three orders of magnitude greater Q10 values for Se(IV) in comparison to Se(VI)•Sulfates adsorbed on Stern layer contribute to PSCD and increase Q10 value for Se(IV).•Structural sulfates of FeOOHs hinder Se(IV) adsorption.•Se(IV) is chemisorbed involving 1E and 2C linkage between the SeO32− and FeOOH.
This study provides a realistic estimation of uptake efficiency and operational cost for Se(IV) removal by the two most promising processes: coagulation/precipitation with iron salts and adsorption ...onto iron oxy-hydroxides granules. Removal efficiency at pH 7 and temperature 20 °C, corresponding to residual Se(IV) concentrations below the drinking water regulation limit 10 μg/L, was used to estimate the coagulant cost at approximately 357 €/kg Se(IV) removed, while the corresponding FeOOH cost, applying a single step adsorption process, was estimated at 2222 €/kg Se(IV) removed; however, the later was substantially decreased, and being lower than the coagulant treatment cost, when more than 5 adsorption/regeneration/reuse cycles were performed. Furthermore, the analysis of operational cost for a medium-scale drinking water plant, treating 100 m3/h with initial concentration 100 μg Se(IV)/L indicates that coagulation/precipitation process presents an operational cost of 104 €/103 m3, which is more than twice lower than the application of a single adsorption step (being 236 €/103 m3). Contrary, the operational cost of adsorption process is competitive to coagulation/precipitation process for treating 100 m3/h because of the lower energy and labor costs. The utilization of adsorbents on the commonly applied throwaway basis can be cost effective for an initial concentration below 30 μg Se(IV)/L, while for initial concentrations 50 and 100 μg/L the cost of adsorption is lower than coagulation’s after 2 and 5 cycles of reuse, respectively. In conclusion, the scenario of adsorbent regeneration and reuse is necessary in order to narrow the cost gap between coagulation/precipitation and adsorption processes.
This research explores the potential of using exfoliated graphite nanoplatelets, xGnP, (graphene sheets ∼10
nm thickness, ∼1
μm diameter), as reinforcement in polypropylene, PP. xGnP–PP ...nanocomposites were fabricated by melt mixing and injection molding. The feasibility of using xGnP–PP nanocomposites was investigated by evaluating the flexural strength, modulus and impact strength and studying the morphology of this system as a function of xGnP loading and aspect ratio and by comparing the xGnP–PP with composites made with commercial available reinforcements such as carbon fibers, carbon black and clays. It is concluded that the smaller aspect ratio xGnP has the strongest impact on the mechanical properties of PP, at loadings up to 5
vol.%, compared to the other reinforcements used, which reflects the compatibility between the exfoliated graphite nanoplatelets and the PP matrix and the exceptional mechanical properties of xGnP, similar to crystalline graphite.
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber ...spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region.
The major issue of raw materials’ depletion, and more specifically, of phosphorous (an important fertilizer) has currently become an emergent aspect due to expected depletion problems needing ...immediate handling. This was the reason for the implementation of the PhoReSe project that aimed to remove and recover phosphorus from the secondary (biologically treated) effluent of a municipal wastewater (biological) treatment plant (WWTP “AINEIA”, located near Thessaloniki, N. Greece), treating the wastewaters of the nearby touristic area. Regarding the phosphorous supplementary removal and recovery treatment options, two methods were examined, initially at the laboratory scale (batch experiments), i.e., (1) the adsorption of phosphorous, and (2) the chemical precipitation of phosphorus. Both methods were further applied at the pilot scale by initially performing the adsorption of phosphorous onto the AquAsZero commercial sorbent, which is a mixed manganese iron oxy-hydroxide, followed by the chemical precipitation of phosphorous implemented after the desorption process of the previously saturated adsorbent. The final precipitate of this procedure was examined as an alternative/supplementary fertilizer, this way returning phosphorus into the natural cycle. These experiments, as applied successfully in at the pilot scale, set the basis for larger-scale relevant applications for similar WWTP facilities.
Iron oxyhydroxides (FeOOHs) appear to be the optimal group of materials among inorganic adsorbents for the removal of phosphates from water, providing significant adsorption capacities. This research ...work presents a thermodynamic study of phosphate adsorption by examining five different FeOOHs sorbent nanomaterials. The otablebtained results indicated that the adsorption process in these cases was spontaneous. When the experiments were performed using distilled water, akageneite (GEH), schwertmannite, and tetravalent manganese feroxyhyte (AquAsZero), displaying ΔH° values of 31.2, 34.7, and 7.3 kJ/mole, respectively, presented an endothermic adsorption process, whereas for goethite (Bayoxide) and lepidocrocite, with ΔH° values of −11.4 and −7.7 kJ/mole, respectively, the adsorption process proved to be exothermic. However, when an artificial (according to NSF) water matrix was used, GEH, schwertmannite, lepidocrocite, and AquAsZero presented ΔH° values of 13.2, 3.3, 7.7, and 3.3 kJ/mole, respectively, indicative of an endothermic process, while only for Bayoxide, with ΔH° of −17 kJ/mole, the adsorption remained exothermic. The adsorption enthalpy values generally decreased with the NSF water matrix, probably due to the competition for the same adsorption sites by other co-existing anions as well to the possible formation of soluble phosphate complexes with calcium; however, an overall positive effect on the uptake of phosphates was observed.
Automotive and aerospace industries require new lightweight materials that enhance payload and improve efficiency via vehicle weight reduction. Employing composites, such as fiber-reinforced ...polymers, is a common approach to reducing vehicle component weight. In this work, we examine the use of atomic layer deposition (ALD) to alter the interfacial chemistry in cellulose-reinforced epoxy composites. As produced, most cellulosics are hydrophilic and immiscible in industrially relevant hydrophobic polymers. In this study, a variety of ALD-derived surface modification schemes are explored to improve resin permeation within a fibrous, cellulose-based paper preform and to increase interfacial adhesion between the epoxy and the cellulose preform. Specifically, we consider surface modification of the cellulose paper with the ALD precursors trimethylaluminum (TMA) and titanium tetrachloride (TiCl
4
) with a water oxidant to form aluminum oxide and titanium oxide-based surface chemistries. Few cycle ALD treatments (2-cycles) combined with an additional post-deposition heating step are found to make the cellulose preforms more hydrophobic. X-ray photoelectron spectroscopy verifies the presence of the metal oxide surface treatments and points towards high concentration of adsorbed adventitious carbon as the source for surface hydrophobicity. Tensile testing of laminated epoxy composites made from these cellulosic preforms indicates two mechanical property regimes depending on surface treatment: (1) high toughness and high strain for preforms that underwent only an ALD coating and (2) high modulus and high strength for preforms ALD coated and then heated at 120 °C in air. ALD treatments resulted in an 80% increase in toughness and a 47% increase in strain at break. ALD treatments with post-deposition heating resulted in a 16% increase in the elastic modulus and a 27% increase in the ultimate tensile strength. Here we propose a combination of cellulose/epoxy mechanical interlocking and interfacial adhesion as mechanisms to explain the difference in mechanical properties of the explored composites.
Nanoporous alumina membranes are filled with multiwalled carbon nanotubes (MWCNTs) and then poly(3-hexylthiophene-2,5-diyl) (P3HT) melt, resulting in nanofibers with nanoconfinement induced ...coalignment of both MWCNT and polymer chains. The simple sonication process proposed here can achieve vertically aligned arrays of P3HT/MWCNT composite nanofibers with 3 wt % to 55 wt % MWCNT content, measured using thermogravimetric methods. Electrical and thermal transport in the composite nanofibers improves drastically with increasing carbon nanotube content where nanofiber thermal conductivity peaks at 4.7 ± 1.1 Wm–1K–1 for 24 wt % MWCNT and electrical percolation occurs once 20 wt % MWCNT content is surpassed. This is the first report of the thermal conductivity of template fabricated composite nanofibers and the first proposed processing technique to enable template fabrication of composite nanofibers with high filler content and long aspect ratio fillers, where enhanced properties can also be realized on the macroscale due to vertical alignment of the nanofibers. These materials are interesting for thermal management applications due to their high thermal conductivity and temperature stability.
Functionalized cellulose particles were studied as a potential reinforcement for an unsaturated polyester resin (UPR) system, a common material for automotive applications of fiber reinforced ...plastics. A preliminary process for incorporating freeze-dried cellulose nanocrystal (CNC) powder into UPR was developed. Three surface chemistries were explored including sulfonated, methyl(triphenyl) phosphonium (PhCNC), and maleic acid (MCNC). By optical microscopy the filler was seen to be agglomerated within the matrix. Fractography showed that these agglomerates acted as stress concentration points resulting in decreased tensile and flexural strength. With the addition of 1 wt% CNCs, the flexural and tensile modulus increased by up to 53% and 22%, respectively. Dynamic mechanical analysis indicated that the PhCNC- and MCNC-UPR samples had a 61% and 66% higher glassy modulus than neat UPR, respectively. Despite the lack of nano-scale dispersion of CNC in UPR, these results reflect potential in the use of functionalized CNC agglomerates as an additive in UPR systems to produce composites with high moduli and good thermo-mechanical stability.
The current work investigates the thermal conductivity and mechanical properties of Boron Nitride (BN)-Acrylonitrile Butadiene Styrene (ABS) composites prepared using both 3D printing and injection ...molding. The thermally conductive, yet electrically insulating composite material provides a unique combination of properties that make it desirable for heat dissipation and packaging applications in electronics. Materials were fabricated via melt mixing on a twin-screw compounder, then injection molded or extruded into filament for fused deposition modeling (FDM) 3D printing. Compositions of up to 35 wt.% BN in ABS were prepared, and the infill orientation of the 3D printed composites was varied to investigate the effect on properties. Injection molding produced a maximum in-plane conductivity of 1.45 W/m-K at 35 wt.% BN, whereas 3D printed samples of 35 wt.% BN showed a value of 0.93 W/m-K, over 5 times the conductivity of pure ABS. The resulting thermal conductivity is anisotropic; with the through-plane thermal conductivity lower by a factor of ~3 for injection molding and ~4 for 3D printing. Adding BN flakes caused a modest increase in the flexural modulus, but resulted in a large decrease in the flexural strength and impact toughness. It is shown that although injection molding produces parts with superior thermal and mechanical properties, BN shows much potential as a filler material for rapid prototyping of thermally conductive composites.
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