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Total ammonia nitrogen (TAN) uptake by sodium functionalized graphene oxide as an efficient adsorbent was evaluated and optimized using response surface methodology (RSM). Batch adsorption tests were carried out based on a central composite design experimental plan at 3 pH levels (6, 7, and 8) and 3 temperature levels (5, 25, and 45°C). The equilibrium condition was reached within 5 min. Quadratic models for percent TAN removal (R%) and solid phase TAN concentration (qe) as response were obtained and evaluated by statistical analysis to predict the experimental data. The models were reduced by eliminating insignificant terms. The final reduced models were significant (p <.0001) with R2 values.96 for R% and.97 for qe, respectively. The optimum pH and temperature to reach the maximum values for R% (58.23%) and qe (27.45 mg/g) were predicted by the RSM. The laboratory experiments were in very good agreement with the predicted optimized values for R% and qe by RMS as the error was 1.2 and 0.3%, respectively. [ABSTRACT FROM AUTHOR]

A sub-monolayer of atomic sodium was deposited on a LiF(001) surface at 40 K. The adsorbed sodium exists at the surface as single atoms and clusters. The surface was dosed with 1 L of HF, to form adsorbed (HF)2...Nan (n=1,2,3,...) complexes, which were then irradiated by 640 nm laser light, to induce charge-transfer reaction. The reaction-product atomic H(g) was observed leaving the surface by two-color Rydberg-atom time-of-flight (TOF) spectroscopy. The TOF spectrum of the desorbed H atoms contained two components; a “fast” component with a maximum at ≈0.85 eV, and a “slow” component with a maximum at 0.45 eV. These two components were attributed to photoreaction on adsorbed single atoms and clusters of sodium, respectively. The fast component exhibited a structure (48±17 meV spacing) near the high-energy end of spectrum. This structure was attributed to vibration of NaFHF photoproduct residing on the surface. The cross section of the harpooning event in the Na...(HF)2 adsorbed complex was determined as (9.1±2.0)×10-19 cm2. To interpret the experimental vibrational structure and the relative energies of the fast and slow components of the TOF spectrum, high-level ab initio calculations were performed for reactants Nan...(HF)m (n,m=1,2) and reaction products NanFmHm-1. The calculated NaF–HF and Na–Na(HF)2 bond dissociation energies indicated that photoexcitation of the precursor complexes led not only to ejection of H atoms, but also to dissociation of the Nan...(HF)2 (n=1,2) species through cleavage of the NaF–HF and Na–Na(HF)2 bonds. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photolysis of H[sub 2]S adsorbed on LiF(001) was studied by means of hydrogen Rydberg-atom time-of-flight spectroscopy. The H-atom translational energy distributions using 193.3 nm radiation showed three main features: a high energy channel attributed to H atoms escaping the surface without collisions (DIR); a vibrational progression from v=0 to v=5 [EL(v=0) and INEL(v>0)]; and a low energy channel attributed to multiple inelastic collisions [INEL(2)]. The vibrational progression can be attributed to two concurrent processes: the primary production of vibrationally excited SH in the dissociative event, and a secondary T→V energy transfer between the outgoing translationally hot H atom and a neighboring H[sub 2]S(ad) molecule. The coverage dependence and angular distribution of the DIR, EL, and the INEL(v>0) channels has been used to define a minimum set of required H[sub 2]S(ad) geometries. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photodissociation of chlorine adsorbed on a LiF(001) surface at 25-70 K has been investigated by means of angularly resolved resonantly enhanced multiphoton ionization spectroscopy (REMPI). The translational-energy distributions and angular distributions for forming Cl(g) photofragments were determined. Photolysis was performed employing 351 nm radiation, with laser pulse energies of 0.3-1.2 mJ/cm2. A peak in the translational energy of Cl(g) at about 0.4 eV was identified as being due to the direct photodissociation of the Cl[sub 2](ad) molecule by 3.5 eV photons. Particular interest attached to the observation of a further channel (termed "A") for photodissociation leading to Cl(g) with translational energy peaking at ∼1 eV and extending to 1.5 eV. The available photon energy renders it highly unlikely that this "high-energy" Cl(g) originates in Cl[sub 2](ad). Channel A had the same linear dependence of Cl-atom flux on laser pulse-energy as did the lower energy (0.4 eV) channel, termed "B," but differed from it in exhibiting a slow approach to steady state. It appears that channel A requires the prior build-up of Cl(ad) concentration due to the photodissociation of Cl[sub 2]. It is proposed that this leads to the formation of a steady-state concentration of Cl[sub 2]...Cl which when photolyzed yields high-energy Cl(g) via channel A. Channel A exhibits a distinctive angular distribution at low coverage and a characteristic Cl[sup *]/Cl ratio, as compared with channel B. The suggested mechanism for channel A is Cl[sub 2]...Cl+hν→Cl[sub 3][sup *]→Cl[sub 2]•Cl→Cl[sub 2]+Cl (where* is an electronically excited state and • represents repulsion in the lower electronic state to which Cl[sub 3][sup *] reverts). This mechanism is interpreted in terms of an extensive diatomics-in-molecules (DIM) model for the trichlorine radical, shown to be in agreement with high level ab initio multireference internally contracted configuration int... [ABSTRACT FROM AUTHOR]

Municipal, industrial, and agricultural wastewaters contain high concentrations of nitrogen in the form of ammonia and ammonium ions. This nitrogen has a range of polluting effects and must be removed before discharge. Multiple methods are currently under investigation for the removal or capture of total ammonia nitrogen (TAN). TAN in aqueous media shows unique behavior making it necessary to study its interactions with potential absorbents in detail. In this study, sodium functionalized graphene oxide (GO-Na) was used for TAN removal from aqueous media by ion exchange. Batch adsorption experiments were performed to investigate the adsorption capacity of GO-Na and. The mechanism of adsorption was investigated using multiple models including Elovich and intra-particle diffusion models. The adsorption kinetics followed the pseudo-second-order model. Experimental data was well described by a Langmuir isotherm model with a maximum adsorption capacity of 32 mg/g. The adsorption energies and thermodynamic parameters indicated weak interactions were dominant with an overall exothermic and spontaneous process. The weak interactions resulted from the ion-exchange of sodium cation on the surface of graphene oxide with ammonium cations in the liquid phase, which also results in the easy regeneration of the adsorbent with NaCl which is a non-toxic, environmentally friendly and inexpensive salt in nature. [ABSTRACT FROM AUTHOR]

Studies the photolysis of HCl adsorbed on LiF(001) by Rydberg-atom time-of-flight spectroscopy. Results of the experiments performed in an ultrahigh vacuum chamber; Modification in the behavior of energy distributions; Photorecoiling of hydrogen.

Discusses the use of hydrogen Rydberg-atom time-of-flight spectroscopy to study the photolysis of HX, where X maybe chlorine, bromine or iodine, adsorbed on lithium fluoride. Adsorption characteristics; Inability of HI to wet the surface under equilibrium conditions; Corresponding translational energies of H-atoms as calculated from the bond energies.

The α-alkylation of acetophenone with benzyl alcohol through borrowing hydrogen has been studied using nickel catalysis. Ni/SiO2-Al2O3 was found to be the best catalyst for this transformation and the corresponding alkylated acetophenone was obtained with 93% isolated yield. Following the objectives of clean and sustainable chemistry, the reaction occurs under solvent-free conditions and requires only a catalytic amount of base. This protocol was next applied to a wide range of ketones and alcohols and the desired products were isolated with 18–86% yields (26 examples). The recovery and recyclability of the nickel catalyst was also investigated and it was found to be active over 5 runs without significant loss of activity. Surprisingly, the active catalyst appears to include an amorphous nickel hydroxide layer. [ABSTRACT FROM AUTHOR]

ABSTRACT Thermally induced changes in surface wettability, dewetting behavior, and proton transport of 'self-assembled' nanothin Nafion® films (4-300 nm) on SiO2 substrate is reported. Thermal annealing induces switching of the surface wettability of 55 nm and thinner films from hydrophilic to super-hydrophobic. Thickness dependence of this behavior is observed with higher annealing temperature required for lower thickness films, indicating highly restrictive mobility of Nafion® ionomer as film thickness decreases. Dewetting is only observed for 4-nm thin film. Significant suppression in proton conductivity upon thermal annealing was noted. Similarly, two other bulk properties, water uptake and swelling, were found to decrease upon annealing. This work reports a systematic examination of the thickness dependence of thermally induced changes in both surface and bulk properties of ultra-thin Nafion®. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1267-1277 [ABSTRACT FROM AUTHOR]

A specialized genetic algorithm (GA) is used to search the structural space of samarium-doped ceria (SDC) for the most energetically stable configurations which will predominate in low temperature fuel cells. A systematic investigation of all configurations of 3.2% SDC and a GA investigation of 6.6% SDC are presented for the first time at the DFT+U level of theory. It was found that Sm atoms prefer to occupy the nearest neighbor (NN) position relative to the oxygen vacancy at 3.2%, while at 6.6%, a balance exists between various Sm–vacancy interactions and the vacancies prefer to be separated by ∼6 . Also, the migration barriers for oxygen diffusion are calculated amongst the best structures in 3.2% and 6.6% SDC and are found to be comparable to the barriers in Gd-doped ceria at the DFT+U level of theory. While the migration calculations provide insight on the oxygen diffusion mechanism in this material, the favored configurations from our GA enable future research on concentrated SDC and contribute to the atomistic understanding of the influence of dopant–vacancy and vacancy–vacancy interactions on ionic conductivity. [ABSTRACT FROM AUTHOR]

Classical force field simulations and genetic algorithms are used to navigate low-energy configurations of samarium-doped ceria (SDC) at a number of concentrations, up to 20% SDC, such that the experimentally observed peak in ionic conductivity is mapped out in its entirety and fresh insight into samarium's role is reported. [ABSTRACT FROM AUTHOR]

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Nickel oxide yttria-stabilized zirconia (NiO–YSZ) anode materials were synthesized via hydrolysis of the corresponding chloride solutions with NH3, NH3+NaOH, and NaOH as precipitation agents. Powder properties such as crystallite size, morphology, and sintering behavior of the final NiO–YSZ materials were also studied. The mechanism of the formation of NiO–YSZ was established for the different co-precipitation techniques by the direct observation of Ni(NH3) n+2 complexes, Ni(OH)2 and NiO at different stages of the synthesis process. A direct relationship between the precipitation agent, the order of calcination from dry sample to final product, the final composition, the crystallite sizes and particle sizes of NiO, and the sinterability of the final products was established. A comparison of the powder and individual component properties indicate that the choice of precipitation agent greatly influences the final characteristics. Ni/YSZ materials prepared by NH3+NaOH precipitation offer higher Ni dispersion and nanocrystallinity of both the Ni and YSZ phases. The conductivity of both prepared materials compares well with mixed-oxide materials of higher Ni content. [ABSTRACT FROM AUTHOR]

Depth resolved X-ray photoelectron spectroscopy (XPS) combined with a 25 μm liquid jet is used to quantify the spatial distribution of 3 nm SnO2 nanoparticles (NPs) from the air-water interface (AWI) into the suspension bulk. Results are consistent with those of a layer several nm thick at the AWI that is completely devoid of NPs. [ABSTRACT FROM AUTHOR]