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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Separation of Light Hydrocarbons through Selective Molecular Exclusion by a Microporous Metal–Organic Framework

Abstract [Zn 2 (sdc) 2 (bpe)] (compound 1 , sdc=4,4′‐stilbenedicarboxylate, bpe=1,2‐bis(4‐pyridyl)ethane)), a doubly interpenetrated, pillared‐layer microporous metal–organic framework has been solvothermally synthesized and structurally characterized by single‐crystal X‐ray diffraction. The structure features a common Zn 2 (COO) 4 paddle‐wheel building unit. Compound 1 undergoes structural change upon solvent removal. The activated phase (compound 2 ) displays permanent porosity, excellent thermal/moisture stability, and interesting hydrocarbon adsorption properties. Gas adsorption experiments show that compound 1 selectively adsorbs saturated/unsaturated C 2 hydrocarbons but excludes C 3 and C 4 hydrocarbons at room temperature. We have collected single‐component adsorption isotherms of six light hydrocarbons and calculated adsorption selectivities of various binary hydrocarbon mixtures by ideal adsorbed solution theory (IAST). The results show that compound 1 possesses remarkably high selectivity towards C 2 over C 3 /C 4 hydrocarbons and the separation is achieved by selective molecular exclusion.

Wang, Hao↗
DOE OSTI2016

Insights into the Ring‐Opening of Biomass‐Derived Furanics over Carbon‐Supported Ruthenium

Abstract The selective ring‐opening of cellulose‐derived furanic molecules is a promising pathway for the production of industrially relevant linear oxygenates, such as 1,6‐hexanediol. 2,5‐Dimethylfuran (DMF) is employed as a model compound in a combined experimental and computational investigation to provide insights into the metal‐catalyzed ring‐opening. Ring‐opening to 2‐hexanol and 2‐hexanone and ring‐saturation to 2,5‐dimethyltetrahydrofuran (DMTHF) are identified as two main parallel pathways. DFT calculations and microkinetic modeling indicate that DMF adsorbs on Ru in an open‐ring configuration, which is potentially a common surface intermediate that leads to both ring‐opening and ring‐saturation products. Although the activation barriers for the two pathways are comparable, the formation of DMTHF is more thermodynamically favorable. In addition, steric interactions with co‐adsorbed 2‐propoxyl, derived from the solvent, and the oxophilic nature of Ru play key roles to determine the product distribution: the former favors less bulky, that is, ring‐closed, intermediates, and the latter retards O−H bond formation. Finally, we show that the hydrodeoxygenation of oxygenated furanics, such as 5‐methylfurfural and (5‐methyl‐2‐furyl)methanol, on Ru occurs preferentially at oxygen‐containing side groups to form DMF, followed by either ring‐opening or ring‐saturation.

Gilkey, Matthew J.↗
DOE OSTI2017

On the Structure-Property Relationships of Cation-Exchanged ZK-5 Zeolites for CO 2 Adsorption

The CO 2 adsorption properties of cation-exchanged Li-, Na-, K-, and Mg-ZK-5 zeolites were correlated to the molecular structures determined by Rietveld refinements of synchrotron powder X-ray diffraction patterns. Li-, K-, and Na-ZK-5 all exhibited high isosteric heats of adsorption (Qst) at low CO 2 coverage, with Na-ZK-5 having the highest Qst (ca. 49 kJ mol -1 ). Mg2+ was located at the center of the zeolite hexagonal prism with the cation inaccessible to CO 2 , leading to a much lower Qst (ca. 30 kJ mol-1) and lower overall uptake capacity. Multiple CO 2 adsorption sites were identified at a given CO 2 loading amount for all four cation-exchanged ZK-5 adsorbents. Site A at the flat eight-membered ring windows and site B/B* in the γ-cages were the primary adsorption sites in Li - and Na-ZK-5 zeolites. Relatively strong dual-cation adsorption sites contributed significantly to an enhanced electrostatic interaction for CO 2 in all ZK-5 samples. This interaction gives rise to a migration of Li + and Mg 2+ cations from their original locations at the center of the hexagonal prisms toward the α-cages, in which they interact more strongly with the adsorbed CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Probing the Kinetic Origin of Varying Oxidative Stability of Ethyl- vs. Propyl-spaced Amines for Direct Air Capture

Amine-based adsorbents are promising for direct air capture of CO 2 , yet oxidative degradation remains a key unmitigated risk hindering wide-scale deployment. Borrowing wisdom from the basic auto-oxidation scheme, insights are gained into the underlying degradation mechanisms of polyamines by quantum chemical, advanced sampling simulations, adsorbent synthesis, and accelerated degradation experiments. The reaction kinetics of polyamines are contrasted with that of typical aliphatic polymers and they elucidate for the first time the critical role of aminoalkyl hydroperoxide decomposition in the oxidative degradation of amino-oligomers. The experimentally observed variation in oxidative stability of polyamines with different backbone structures is explained by the relationship between the local chemical structure and the free energy barrier of aminoalkyl hydroperoxide decomposition, suggesting that its energetics can be used as a descriptor to screen and design new polyamines with improved stability. In conclusion, the developed computational capability sheds light on radical-induced degradation chemistry of other organic functional materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

The many studies that have been conducted on water adsorption on zeolites were carried out in “adsorption” mode, from adsorption isotherms or single-point measurements, with the samples being first degassed at high temperature, and then exposed to water vapor at variable partial pressure. Here, we report Thermogravimetric Analysis (TGA) studies of HZSM-5 saturated with water at room temperature, thus studying water adsorption in “desorption” mode. In this work, TGA was used to ascertain the amount of water remaining as a function of the pretreatment temperature, and to identify the temperature at which one water molecule per framework Al atom persists. Solid-state 1H NMR spectroscopy, combined with molecular modeling, provided evidence for water molecules hydrogen bonded to Brønsted acid sites and formation of oxonium species for distinct water per framework Al atom. TGA is shown to be a simple and expeditious technique to measure the number of Brønsted acid sites in aluminosilicate zeolites, with advantages over the traditional methods of IR or TPD of dangerous adsorbed ammonia or pyridine. TGA of adsorbed water also provides information on the water clusters formed at the acid sites of HZSM-5, which are proportional to the number of acid sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Reduction of Pertechnetate by Chemical and Photochemical Approaches and Incorporation of Tc(IV) into Titanium Dioxide

Technetium-99 is a prevalent fission product from nuclear waste. The long half-life (211,000 yr) and environmental mobility of pertechnetate (TcO 4 - ) render Tc particularly challenging to isolate and stabilize. Here, in this study, we present two approaches for development of potential wasteforms using titanium dioxide, TiO 2 . Approach 1 is a low temperature chemical synthesis of TiO 2 doped with Tc(IV) from TcO 4 - intended to mimic the Tc waste stream from the UREX family of separations and removes 98.5 % of the Tc, mainly present as edge-shared Tc(IV) pairs. Approach 2 utilizes TiO 2 to photocatalytically reduce TcO 4 - to Tc(IV) stabilized on the surface of or within the TiO 2 lattice. The %Tc removed from solution and adsorbed to TiO 2 is pH dependent, with the maximum Tc(IV) adsorbed at pH 3–4 as either TcO 2 or edge-sharing Tc(IV) octahedra. The Tc(IV)-TiO 2 composites materials formed by both approaches are suitable for consolidation into a dense wasteform by Hot Isostatic Pressing (HIPing).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Protein adsorption onto nanoparticles induces conformational changes: Particle size dependency, kinetics, and mechanisms

The use of nanomaterials in bioapplications demands a detailed understanding of protein–nanoparticle interactions. Proteins can undergo conformational changes while adsorbing onto nanoparticles, but studies on the impact of particle size on conformational changes are scarce. We have shown that conformational changes happening upon adsorption of myoglobin and BSA are dependent on the size of the nanoparticle they are adsorbing to. Out of eight initially investigated model proteins, two (BSA and myoglobin) showed conformational changes, and in both cases this conformational change was dependent on the size of the nanoparticle. Nanoparticle sizes ranged from 30 to 1000 nm and, in contrast to previous studies, we attempted to use a continuous progression of sizes in the range found in live viruses, which is an interesting size of nanoparticles for the potential use as drug delivery vehicles. Conformational changes were only visible for particles of 200 nm and bigger. Using an optimized circular dichroism protocol allowed us to follow this conformational change with regard to the nanoparticle size and, thanks to the excellent temporal resolution also in time. We uncovered significant differences between the unfolding kinetics of myoglobin and BSA. In this study, we also evaluated the plausibility of commonly used explanations for the phenomenon of nanoparticle size-dependent conformational change. Currently proposed mechanisms are mostly based on studies done with relatively small particles, and fall short in explaining the behavior seen in our studies.

Biotechnology & Applied Microbiology↗
DOE OSTI2014

Applicability of Density Functional Theory in Reproducing Accurate Vibrational Spectra of Surface Bound Species

The structural equilibrium parameters, the adsorption energies, and the vibrational frequencies of the nitrogen molecule and the hydrogen atom adsorbed on the (111) surface of rhodium have been investigated using different generalized-gradient approximation (GGA), nonlocal correlation, meta-GGA, and hybrid functionals, namely, Perdew, Burke, and Ernzerhof (PBE), Revised-RPBE, vdW-DF, Tao, Perdew, Staroverov, and Scuseria functional (TPSS), and Heyd, Scuseria, and Ernzerhof (HSE06) functional in the plane wave formalism. Among the five tested functionals, nonlocal vdW-DF and meta-GGA TPSS functionals are most successful in describing energetics of dinitrogen physisorption to the Rh(111) surface, while the PBE functional provides the correct chemisorption energy for the hydrogen atom. It was also found that TPSS functional produces the best vibrational spectra of the nitrogen molecule and the hydrogen atom on rhodium within the harmonic formalism with the error of 22.62 and 21.1% for the NAN stretching and RhAH stretching frequency. Thus, TPSS functional was proposed as a method of choice for obtaining vibrational spectra of low weight adsorbates on metallic surfaces within the harmonic approximation. At the anharmonic level, by decoupling the RhAH and NAN stretching modes from the bulk phonons and by solving one- and two-dimensional Schr€odinger equation associated with the RhAH, RhAN, and NAN potential energy we calculated the anharmonic correction for NAN and RhAH stretching modes as 231 cm21 and 277 cm21 at PBE level. Anharmonic vibrational frequencies calculated with the use of the hybrid HSE06 function are in best agreement with available experiments.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Multiple dynamic regimes in colloid-polymer dispersions: New insight using X-ray photon correlation spectroscopy

We present an X-ray photon correlation spectros- copy (XPCS) study of dynamic transitions in an anisotropic colloid-polymer dispersion with multiple arrested states. The results provide insight into the mechanism for formation of repulsive glasses, attractive glasses, and networked gels of col- loids with weakly adsorbing polymer chains. In the presence of adsorbing polymer chains, we observe three distinct regimes: a state with slow dynamics consisting of finite particles and clusters, for which interparticle interactions are predominantly repulsive; a second dynamic regime occurring above the satu- ration concentration of added polymer, in which small clusters of nanoparticles form via a short-range depletion attraction; and a third regime above the overlap concentration in which dynamics of clusters are independent of polymer chain length. The observed complex dynamic state diagram is primarily gov- erned by the structural reorganization of a nanoparticle cluster and polymer chains at the nanoparticle-polymer surface and in the concentrated medium, which in turn controls the dynamics of the dispersion

36 MATERIALS SCIENCE↗
DOE OSTI2020

Intensive agricultural management‐induced subsurface accumulation of labile phosphorus in Midwestern agricultural soils dominated by tile lines

Abstract In addition to surface runoff, subsurface P loss through tile lines in agricultural lands has received attention over the last decade. It is not clearly understood how this strong ligand, phosphate, is distributed in subsoils (≤180 cm), contributing to subsurface P loss. We hypothesized that subsurface accumulation of labile P as a result of long‐term intensive agricultural management contributes to subsurface P loss. The depth sequence distribution of P and its speciation and reactivity were investigated in tile‐line‐dominated Midwestern agricultural fields via chemical extraction and digestion, batch desorption experiments, and X‐ray absorption near‐edge structure spectroscopy. The results suggest that labile P in subsoils exceeds the eutrophication‐inducing level (>0.01 mg L –1 ). Because of intensive agricultural management, total P was ∼400 mg kg –1 in surface soils and ∼200‐300 mg kg –1 in subsoils. The depth sequence distribution of P indicated the translocation of P to subsoils. Although phosphate and phytic acid adsorbed by Al or Fe (oxyhydro)oxides and calcite were found in surface soils, phosphate adsorbed to calcite, hydroxyapatite, or both were the dominant P species in subsoils. Phosphate was highest in surface soils and decreased sharply with increasing depth. Slightly alkaline soil in subsoils suppressed the release of P but the process was continuous after 30 d. Subsurface P loss was influenced by the dissolution and desorption process of inorganic P phases and preferentially transported P from surface soils. Subsurface P loss should be considered in strategies to reduce agricultural P loss in the Gulf of Mexico.

Xu, Suwei↗
DOE OSTI2023

Hierarchically Templated Synthesis of 3D‐Printed Crosslinked Cyclodextrins for Lycopene Harvesting

Abstract Plants produce a wide range of bioactive phytochemicals, such as antioxidants and vitamins, which play crucial roles in aging prevention, inflammation reduction, and reducing the risk of cancer. Selectively harvesting these phytochemicals, such as lycopene, from tomatoes through the adsorption method is cost‐effective and energy efficient. In this work, a templated synthesis of 3D‐printed crosslinked cyclodextrin polymers featuring nanotubular structures for highly selective lycopene harvesting is reported. Polypseudorotaxanes formed by triethoxysilane‐based telechelic polyethylene glycols and α‐cyclodextrins (α‐CDs) are designed as the template to (1) synthetically access urethane‐based nanotubular structures at the molecular level, and (2) construct 3D‐printed architectures with designed macroscale voids. The polypseudorotaxane hydrogels showed good rheological properties for direct ink writing, and the 3D‐printed hydrogels were converted to the desired α‐CD polymer network through a three‐step postprinting transformation. The obtained urethane‐crosslinked α‐CD monoliths possess nanotubular structures and 3D‐printed voids. They selectively adsorb lycopene from raw tomato juice, protecting lycopene from photo‐ or thermo‐degradations. This work highlights the hierarchically templated synthesis approach in developing functional 3D‐printing materials by connecting the bottom‐up molecular assembly and synthesis with the top‐down 3D architecture control and fabrication.

Chemistry↗
DOE OSTI2025

Microstructure‐Dependent Sodium Storage Mechanisms in Hard Carbon Anodes

Sustainable energy storage is essential to support the transition to renewables and meet the increasing demand for energy. Sodium‐ion batteries (NIBs) are attractive for grid‐scale energy storage due to the abundance and low cost of sodium, sustainability of other battery components, and electrochemical performance. Hard carbon (HC) is a leading anode material for NIBs, but its complex microstructure complicates the understanding of sodium storage mechanisms. Using X‐ray total scattering and density functional theory calculations, this study clarifies how HC's microstructural variations influence sodium storage across the slope (high potential) and plateau (low potential) regions of the potential capacity curve. In the slope region, sodium initially adsorbs at high‐binding energy defect sites and subsequently intercalates between graphene layers, adsorbing at low‐binding energy defect sites, correlating with different slopes observed during initial sodiation. Initial irreversibility arises from sodium trapping at surface defects and solid electrolyte interface formation. In the plateau region, sodium simultaneously intercalates and fills pores, influenced by pore size, interlayer spacing, and defect concentration. HCs with larger pore sizes form larger sodium clusters. In conclusion, the proposed mechanism underscores the role of microstructure engineering in enhancing HC performance and advancing NIBs for grid‐scale energy storage.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Removal of phosphorus using biochar derived from Fenton sludge: Mechanism and performance insights

Abstract A phosphorus removal biochar adsorbent was prepared from Fenton sludge. The adsorption process was optimized, and its phosphorus adsorption mechanism was discussed. It was found that the phosphorus adsorption performance of biochar prepared from single Fenton sludge (FBC‐400) was better than that of co‐pyrolysis of Fenton sludge and bamboo powder. The optimum condition was that Fenton sludge pyrolyzed at 400°C (FBC‐400). FBC‐400 had a larger specific surface area than that prepared by co‐pyrolysis with bamboo powder. And the high content of iron element could provide a higher surface charge of the biochar, thereby increasing the electrostatic adsorption of phosphorus onto FBC‐400. The phosphorus adsorption was highly pH dependent by FBC‐400, which can enhance electrostatic adsorption and increase adsorption capacity in acidic conditions. The effect of coexisting anion on adsorption performance was mainly affected by CO 3 2− , reducing the adsorption capacity by at least 49%, whereas other anions had no obvious interference. The adsorption process of FBC‐400 accorded with the pseudo‐second‐order kinetic model and the Langmuir model, which indicated that the adsorption process was monolayer adsorption and mainly chemical adsorption, and the maximum saturated phosphorus adsorption capacity was 8.77 mg g −1 . The mechanisms for phosphorus adsorption were electrostatic adsorption and inner‐sphere complexing. 1 M NaOH was used for desorption, and the adsorption capacity remained at 81% in the fifth cycle. Practitioner Points The Fenton sludge biochar usage as an adsorbent could be a win‐win strategy to convert waste biomass to valuable ‐ product. The adsorption process accorded with the Langmuir model, the maximum phosphorus adsorption capacity was 8.77 mg/g at 25°C. The adsorption mechanisms were electrostatic adsorption and inner‐sphere complexing. 1M NaOH was used for desorption, and the adsorption capacity remained at 81% in the fifth cycle.

Liu, Yanfang↗
DOE OSTI2019

Batch Adsorption and Column Transport Studies of 2,4,6-Trinitrotoluene in Chinese Loess

In present study, batch and column tests were conducted to investigate the kinetic and thermodynamic characteristics of the adsorption and transport of 2,4,6-trinitrotoluene (TNT) in Chinese loess with specific focus on the role of inherent colloid particles. Batch tests showed that a lot of TNT was absorbed in suspended colloid particles, and its adsorption reached equilibrium after about 10 h, the adsorption process can be best-fit by the pseudo-second order kinetic and Freundlich model. The adsorption was spontaneous, endothermic process, implying the adsorbed TNT is likely to release from soil matrix. These portend that the adsorbed TNT has a potential to co-transport with inherent colloid particles in loess. The column tests identified the potential, and showed TNT transport had obvious retardation effect, which may be ascribed to the release and transport of inherent colloidal particles as a key carrier. These findings are helpful to evaluate the loess interception and antifouling performance.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

NMR relaxometry characterization of water adsorption in corn stover anatomical fractions

Nuclear magnetic resonance (NMR) relaxometry is applied to provide direct measurement of water adsorption in anatomical fractions of corn stover. NMR transverse T 2 relaxation time distribution measurements indicate multiple water populations, which vary with anatomical fraction and water adsorption. Measured T 2 data are used to calculate thermodynamic properties of Brunauer-Emmet-Teller adsorption theory using a model to estimate mono and bilayer relaxation. T 2 data are used directly to determine rotational diffusion correlation times indicating adsorption interaction strength. T 1 -T 2 longitudinal-transverse relaxation time correlation measurements quantify differences in the molecular level structural order of the adsorbate surface water as a function of water activity, i.e. relative humidity or water vapor partial pressure. The T 1 /T 2 ratio provides a measure of the surface energy related to the adsorption strength and surface diffusive mobility of the water adsorbate and differentiates the anatomical fractions. Furthermore, the results indicate that direct measurement of NMR relaxation times can be used to characterize corn stover biomass water adsorption, data relevant to processing and handling considerations.

09 BIOMASS FUELS↗
DOE OSTI2014

Optimization of electrode characteristics for the Br-2/H-2 redox flow cell

The Br-2/H-2 redox flow cell shows promise as a high-power, low-cost energy storage device. The effect of various aspects of material selection, processing, and assembly of electrodes on the operation, performance, and efficiency of the system is determined. In particular, (+) electrode thickness, cell compression, hydrogen pressure, and (-) electrode architecture are investigated. Increasing hydrogen pressure and depositing the (-) catalyst layer on the membrane instead of on the carbon paper backing layers have a large positive impact on performance, enabling a limiting current density above 2 A cm(-2) and a peak power density of 1.4 W cm(-2). Maximum energy efficiency of 79 % is achieved. In addition, the root cause of limiting-current behavior in this system is elucidated, where it is found that Br- reversibly adsorbs at the Pt (-) electrode for potentials exceeding a critical value, and the extent of Br- coverage is potential-dependent. This phenomenon limits maximum cell current density and must be addressed in system modeling and design. These findings are expected to lower system cost and enable higher efficiency.

Tucker, MC↗
DOE OSTI2017

Thorium(IV) Recovery from Water and Sea Water Using Surface Modified Nanocellulose/Nanobentonite Composite: Process Design

Thorium(Th) contamination in the ground water an emerging environmental issue and Th recovery from sea water and nuclear wastewater is of high significance, as it is a major player in the energy sector. For the adsorption and recovery of Th, polymer grafted bio materials are reported as most efficient materials. P(IA/MAA)-g-NC/NB was prepared and all the steps in the synthetic routes were monitored using FTIR, SEM–EDS, and XRD, TG. Efficiency in removal of Th(IV) by P(IA/MAA)-g-NC/NB was tested by batch adsorption technique. The pH dependent Th(IV) adsorption process, was optimized at 4.5 and adsorption equilibrium was achieved within 120 min. Experimental kinetic data correlates well with pseudo-second-order equation, indicates adsorption was chemical process via ion exchange followed by complexation reaction, also could explain the film diffusion process of adsorption. Sips isotherm proved to best fit for the adsorption of Th(IV) onto P(IA/MAA)-g-NC/NB with maximum adsorption capacity of 95.19 mg/g. Thermodynamic studies revealed the endothermic nature, feasibility and spontaneity of the adsorption process. ΔHx and ΔSx were decreased to a small extent from −5.567 to −3.439 kJ/mol and increased from 11.18 to 18.39 J/mol, respectively, with increase in surface loading from 50 to 70 mg/g, indicating that the surface of the onto P(IA/MAA)-g-NC/NB is having energetically heterogeneous surface and there may be some lateral interactions between the adsorbed Th(IV) ions Repeated adsorption–desorption study over six cycles, adsorption percentage decreases from 99.0 to 94.6 %, proved the efficiency of P(IA/MAA)-g-NC/NB as an effective adsorbent for the removal and recovery of Th(IV) from aqueous solutions. Complete removal of Th(IV) ions from seawater containing 10 mg/L with a dose of 0.25 g/L P(IA/MAA)-g-NC/NB achieved. Batch adsorption system as double stage reactor designed from the adsorption isotherm data of Th(IV) by constructing operational lines. From these could be concluded that P(IA/MAA)-g-NC/NB is a promising candidate for the effective removal and removal of Th(IV) from industrial effluents phase and sea water. The maximum adsorption capacity Qs for Ceralite IRC-50 calculated which was found to be 179.67 mg/g which are considerably lower than those for P(IA/MAA)-g-NC/NB.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Development of Nanofibers Composed of Chitosan/Nylon 6 and Tannin/Nylon 6 for Effective Adsorption of Cr(VI)

In this study, novel nanofiber materials composed of chitosan/nylon 6 and tannin/nylon 6 were synthesized by the Forcespinning® method and were used as adsorbents for effective removal of chromium(VI) from aqueous solutions. The nanofibers showed similar production rates of 3.5 g h{sup −1}. The diameters of the nanofibers ranged from 100 to 800 nm. Under the experimental conditions tested, chromium(VI) adsorption was favored at pH 3 (chitosan/nylon 6 nanofibers) and pH 2 (tannin/nylon 6 nanofibers), at a temperature of 328 K. The most suitable models for description of the kinetic data were the pseudo-second order model (chitosan/nylon 6 nanofibers) and the Elovich model (tannin/nylon 6 nanofibers). For both nanofibers, the equilibrium isotherms could be fitted by the Langmuir model. The maximum adsorption capacities were 23.9 and 62.7 mg g{sup −1} for the chitosan/nylon 6 and tannin/nylon 6 nanofibers, respectively. The thermodynamic parameters showed that the adsorption was spontaneous, favorable, and endothermic. The findings indicated that these nanofibers produced using a centrifugal technique offer excellent potential as adsorbents, with high adsorption capacities for chromium(VI).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗