Amphoteric Behavior Research Articles

Thermodynamic description of Be(II) solubility and hydrolysis in acidic to hyperalkaline NaCl and KCl solutions

The solubility of Be(II) is investigated in carbonate-free dilute to concentrated HCl–NaCl–NaOH, KCl–KOH, NaOH and KOH solutions. Undersaturation experiments were performed under Ar atmosphere at T= (22 ± 2) °C. XRD, XPS, SEM and quantitative chemical analysis confirm that α-Be(OH)2(cr) is the solid phase controlling the solubility in all evaluated systems. No transformation of α-Be(OH)2(cr) to β-Be(OH)2(cr) or ternary solid phases Na/K–Be(II)–OH(s) is observed in the investigated systems within the timeframe of this study (t ≤ 600 days). An amphoteric solubility behaviour of Be(II) is observed with a solubility minimum at pHm ≈ 9.5 (with [Be(II)] ≈ 10−6.8 M), regardless of the ionic strength. The combination of solubility data determined in acidic pHm conditions and the hydrolysis scheme reported in the literature for cationic hydrolysis species of Be(II) is used for the determination of the solubility constant of α-Be(OH)2(cr), log *K°s,0 = (6.9 ± 0.4). Slope analysis of the solubility data in alkaline to hyperalkaline conditions and 9Be NMR support the predominance of the monomeric hydrolysis species Be(OH)2(aq), Be(OH)3– and Be(OH)42− within the strongly alkaline pHm-conditions relevant in cementitious systems. The comprehensive solubility dataset collected within this study in combination with extensive solid and aqueous phase characterization allow the development of a complete chemical, thermodynamic and (SIT) activity model for the system Be2+–Na+–K+–H+–Cl––OH––H2O(l). This model provides an accurate and robust tool for the evaluation of Be(II) solubility and speciation in a diversity of geochemical conditions, including source term calculations of beryllium in the context of the nuclear waste disposal Safety Case.

Effect of Arsenic Depletion on the Silicon Doping of Vapor–Liquid–Solid GaAs Nanowires

It is well known that chemical potential driving the vapor–liquid–solid growth of nanowires oscillates in synchronization with the monolayer growth. In III–V nanowires, this occurs due to depletion of group V atoms in a catalyst droplet. The amphoteric behavior of silicon doping, which often changes from n‐type in planar GaAs layers to p‐type in nanowires, is attributed to low arsenic concentrations. Herein, we present an analytical model which quantifies the doping oscillations over the monolayer formation cycle, and its impact on the electron‐to‐hole ratio for the silicon doping of GaAs nanowires. It is shown that arsenic depletion can easily double the amphoteric effect and strongly favor the tendency for p‐type doping. On a more general ground, the nanowire doping process appears highly sensitive to the chemical potential oscillations related to a restricted amount of material in a nanoscale catalyst.

Chemically modified biochar derived from effluent treatment plant sludge of a distillery for the removal of an emerging pollutant, tetracycline, from aqueous solution

Distilleries are among the most pollution-generating industries as their ≈80% raw material converted into waste. In the present study, sustainable biochar was prepared from distillery sludge (DS) by chemical activation with KOH, ZnCl2, and H3PO4 (coded as DS-K, DS-Z, DS-H) and used for the removal of tetracycline, an emerging pollutant. Additionally, biochar was also prepared by adding the distillery sludge and oily sludge from sugar mill in the ratio of 2:1 (coded as DS-O). The raw sludge and prepared biochar were characterized by various sophisticated techniques like XRF, XRD, TGA-FTIR, BET, FE-SEM, and zeta potential analyzer. FTIR, coupled with the TGA system, gave traces of CO2 and H2O (steam) as the temperature of the sample increased. Batch adsorption study showed TC removal efficiencies of 57%, 64%, 43%, and 70% by DS-K, DS-Z, DS-H, and DS-O, respectively, at optimum conditions: Co = 20 mg L−1, time = 300 min, rpm = 160 ± 5, dose = 1 g L−1, T = 25 ±1 °C, and pH = 6. Experimental data was well-fitted in both pseudo-first-order and pseudo-second-order kinetic models. Langmuir isotherm nicely described the adsorption of TC onto biochar. pH played a significant role in the adsorption due to the amphoteric behavior of TC. Reusability studies showed a marginal decrease in removal efficiencies of ≈ 9%, ≈ 7%, ≈ 4%, and ≈ 8% after three consecutive runs with DS-O, DS-Z, DS-K, and DS-H, respectively.

Hybrid nitrate selective resin (NSR-NanoZr) for simultaneous selective removal of nitrate and phosphate (or fluoride) from impaired water sources

Reverse osmosis (RO) has been increasingly applied in municipal wastewater reuse facilities. Nitrate (N) and phosphate (P) -laden reject streams from RO demand near-complete NP removal before inland brine disposal to avoid serious eutrophication effects. In addition, elevated nitrate and fluoride levels in groundwater is a threat to public drinking water safety. Selective removal of both nitrate and phosphate, or fluoride through a single adsorbent is promising because of its small footprints, minimum sludge production, and potential NP recovery. This study presents a new ion exchange adsorbent, NSR-NanoZr, for simultaneous selective removal of both nitrate and phosphate, or fluoride. NSR-NanoZr is fabricated by doping zirconium oxide nanoparticles (ZrO2-Nano) into a nitrate selective resin (NSR), which tributyl quaternary ammonium functional groups contribute to the nitrate selectivity and Lewis acid-base interactions between ZrO2-Nano and ligands result in the high affinity towards phosphate and fluoride. Lab-scale studies showed that NSR-NanoZr exhibited a completely reversal selectivity and removed both NP selectively from municipal secondary wastewater for multiple cycles. Synergistic application of a weak-acid cation exchanger (WAC) enhanced the phosphate capacity of NSR-NanoZr due to the amphoteric sorption behavior of the ZrO2-Nano. Field-scale studies demonstrated the potential of NSR-NanoZr in removing fluoride together with nitrate.

Morphological, chemical and electrical characterization of a family of commercial nanofiltration polyvinyl alcohol coated polypiperazineamide membranes

Three AFC membranes from PCI, of the thin film composite (TFC) nanofiltration type, have been characterized by using XPS, AFM, Contact angles, Zeta potential and permeation experiments. This plethora of complimentary methods portrays a deep and exhaustive description of these membranes that could be used to tune fabrication and modification of nanofiltration membranes to get better properties.Morphological properties, including porosity, water permeability, fractal dimension, Wenzel parameter and roughness, correlate well with pore sizes. While functional characteristics as, for example wettability correlate well with the O/N ratio. Increasing O/N ratios should be interpreted as caused by increasing PVA coverages.The charge on the membrane’s surface is ordered in a different way for different pH but are quite similar anyway. The effect of charges on retention of 1:1, 1:2 and 2:1 salts (as tested with NaCl, Na2SO4 and CaCl2) increases with increasing O/N and wettability. Consequently, the trend of salt retentions can be explained in terms of the PVA coverage and the details of the amphoteric behavior of the three AFC membranes studied.

Effect of pH on the photocatalytic degradation of remazol brilliant blue dye using zirconia catalyst

EGZrO2 catalyst was successfully synthesized using electrochemical method with an established of photocatalytic activity evaluation. An amount of 0.20 g/L of EGZrO2 catalyst was found to provide the optimum dosage for 10 mg/L remazol brilliant blue (RBB) dye resulting in a complete degradation (99.8%) within 1.5 h of contact time. The catalyst showed good performance in pH 3 (acidic medium) due to the influence of surface charge properties (amphoteric behavior). The excellence photoresponse in visible light regions gave advantage to the photoreaction which is cost effective, practicable, and more eco-friendliness.

A temperature stable (Ba1–xCex)(Ti1–x/2Mgx/2)O3 lead-free ceramic for X4D capacitors

A novel dielectric ceramic {(Ba1–xCex)(Ti1–x/2Mgx/2)O3, x = 0.06, BCTM6} with excellent temperature stability (−55 to 65 °C, TCC ≤ ±3.3%, ε′RT ∼ 2242, tan δ < 0.023) was developed for X4D capacitors. Phase structure was found to transfer from tetragonal to cubic phase with increasing x and the solubility limitation of Ce/Mg was determined to be 0.10 by X-ray diffraction (XRD) for (Ba1–xCex)(Ti1–x/2Mgx/2)O3. The formation of 2CeBa•−MgTi’’ dipoles was believed to be responsible for the elimination of oxygen vacancies, leading to the low dielectric loss of BCTM6. An electron paramagnetic resonance (EPR) signal at g ∼ 1.98 suggested the ionization of Ba vacancies in (Ba1–xMgx)(Ti1–yCey)O3 (BMTC), indicative of the amphoteric behavior of Mg2+.

Derivation of a pH Dependent Solid-Liquid Interfacial Tension and Theoretical Interpretation of the Physicochemistry of Dewetting in the CO2-Brine-Silica System

The solid-liquid interfacial tension is a fundamental parameter in areas of wettability pertaining to adhesive bonds and petroleum engineering practice. In wettability issues related to surface functionalized polymeric materials design to achieve specific adhesive properties, the solid-liquid interfacial tension can be pH dependent due to amphoteric behavior. In this paper, we have used the theory of pH dependent surface charging and the 2-pk model as well as the site binding model of the electric double layer theory to derive a pH dependent solid-liquid interfacial tension equation. &#x0D; &#x0D; Following the fundamental relationship between solid-liquid interfacial tension and contact angle in light of Young&amp;rsquo;s equation, we have extended the theoretical basis of the derivation. Consequently, we have also derived a pH dependent cosine of the thermodynamic contact angle. Both equations give satisfactory explanations for observed experimental data available in the literature.

ProDOT-Assisted Isomerically Pure Indophenines.

Reactions between 3,4-propylenedioxythiophenes (ProDOTs) and N-alkyl isatins under ambient conditions result in isomerically pure indophenine materials as confirmed by TLC and 1H NMR analysis. The resulting low band gap materials exhibit favorable inter- and intramolecular interactions, high thermal stabilities, low energy electronic transitions, and amphoteric redox behavior.

Amphotericity-spectroscopy correlations in Eu doped sodium bismuth titanate (Na0.5Bi0.5TiO3)

Optical characteristics of a doped material depend on the site wherein the dopant resides. In mixed A-site perovskites, the dopant has several possibilities. This, in turn, correlates with the emission spectrum of the doped material. Here we choose Eu3+ as the dopant since it is a well-known and efficient red-luminophore. Sodium bismuth titanate (NBT-Na0.5Bi0.5TiO3) is selected as a host due to its ability to accommodate Eu over large concentration windows while maintaining optical activity. For compositions x ≥ 0.04, we show that Eux:NBT has amphoteric behavior (i.e., simultaneous dopant substitution in two competing sites). Eu3+ occupancy in Bi and Ti-sites are quantitatively estimated using Rietveld refinement. Also, the appearance of A1g breathing vibrational mode (830–860 cm−1) in Raman spectra shows the presence of Eu3+ on the Ti-site. Photoluminescence (PL) emission shows sharp and intense bands at ∼592 nm, ∼615 nm, and ∼687 nm, and one weak band at ∼652 nm, corresponding to f–f transitions of Eu3+. To evaluate the optical characteristics with varying site-substitution of Eu3+; Judd–Ofelt parameters and radiative properties are calculated for the first time in this mixed A-site titanate system. From the values of asymmetric ratios; Eu3+ ion is shown to occupy the non-centrosymmetrical sites (Bi-sites) of NBT. However, at x = 0.04, Ω2 < Ω4, which indicates long-range effects and hence Eu occupancy in centrosymmetric sites (Ti-sites). This study opens up avenues for further exploration of correlations between dopant-concentration, amphotericity, and spectrochemical response in other systems. The amphoteric behavior of dopants can tune emission intensities and produce multi-emission colors using a single-dopant. This would have implications for luminescence-based applications.

Leaching of elements from cement activated fly ash and slag amended soils

Very few studies have investigated the leaching characteristics of cement activated fly ash and slag treated soils, although the inclusion of cement significantly enhances the material pH and may alter the leachability of elements. In this study the leaching behavior and mechanisms of chromium (Cr), copper (Cu), iron (Fe) and sulfur (S) from cement activated fly ash and slag stabilized soils were evaluated. An array of synthetic precipitation leaching procedure (SPLP), batch water leach test (WLT), toxicity characteristic leaching procedure (TCLP) and pH-Static leach tests were conducted. A geochemical equilibrium model Visual MINTEQ was implemented to identify the leaching controlling mechanisms of the metals. Results indicated that, the leached concentrations of Cr, Cu, Fe and S in SPLP, WLT and TCLP effluents were in the range of 0.016–0.74 mg/L, 0.013–0.17 mg/L, 0.019–0.27 mg/L and 1.78–234 mg/L, respectively. Quantitative comparisons between the standard test procedures suggested the necessity of multiple test methods for a comprehensive leaching assessment. Cr and Cu showed amphoteric leaching behaviors, whereas Fe and S followed cationic leaching patterns. According to the geochemical analyses, amorphous Cr(OH)3; tenorite and Cu(OH)2; ferrihydrite and goethite; gypsum and anhydrite; could control the leaching of Cr, Cu, Fe and S, respectively. The effluent Cr concentrations frequently exceeding the U.S. EPA specified maximum contaminant level of 0.1 mg/L. Yet, the use of cement activated fly ash and slag mixed soils could be beneficial, since less toxic trivalent Cr (III) was identified through geochemical modeling.

Si Doping of Vapor-Liquid-Solid GaAs Nanowires: n-Type or p-Type?

The incorporation of Si into vapor-liquid-solid GaAs nanowires often leads to p-type doping, whereas it is routinely used as an n-dopant of planar layers. This property limits the applications of GaAs nanowires in electronic and optoelectronic devices. The strong amphoteric behavior of Si in nanowires is not yet fully understood. Here, we present the first attempt to quantify this behavior as a function of the droplet composition and temperature. It is shown that the doping type critically depends on the As/Ga ratio in the droplet. In sharp contrast to vapor-solid growth, the droplet contains very few As atoms, which enhance their reverse transfer from solid to liquid. As a result, Si atoms preferentially replace As in GaAs, leading to p-type doping in nanowires. Hydride vapor phase epitaxy provides the highest As concentrations in the catalyst droplets during their vapor-liquid-solid growth, resulting in n-type dopant behavior of Si. We present experimental data on n-doped Si-doped GaAs nanowires grown by this method and explain the doping within our model. These results give a clear route for obtaining n-type or p-type Si doping in GaAs nanowires and may be extended to other III-V nanowires.

Electron Paramagnetic Resonance Study on Oxygen Vacancies and Site Occupations in Mg-Doped BaTiO3 Ceramics.

Nominal (Ba1−xMgx)TiO3 (x = 0.015) (BM1T) and (Ba1−xMgx)TiO3 (x = 0.03–0.20) (BMT) ceramics were prepared by the mixed-oxide route at sintering temperatures (Ts) of 1200−1400 °C and 1200 °C, respectively. The solubility limit of Mg2+ in BMT was determined by XRD to be x = 0.05, and evidence was found for occupation of the A site by Mg2+. Electron paramagnetic resonance (EPR) was employed as a key technique to investigate the effect of Ts on oxygen vacancies in BM1T. The structure of BM1T changed from pseudocubic at Ts = 1200 °C to tetragonal at 1300 °C to mixed phases of hexagonal and tetragonal at 1400 °C. When Ts ≥ 1300 °C, a g = 1.956 EPR signal was observed at T = −188 °C and assigned as ionized oxygen vacancies. Mg2+ exhibited amphoteric behavior of substituting for the double cation sites. When Ts = 1400 °C, B-site Mg2+ and oxygen vacancies mainly existed in the hexagonal phase and A-site Mg2+ was dominant in the tetragonal phase. The higher tan δ was attributed to the higher concentrations of oxygen vacancies and Ti3+ in the hexagonal phase.

Dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene: A Bowl-Shaped Fragment of Fullerene C70 with Global Antiaromaticity.

Solution-phase synthesis of buckybowls remains a big challenge, and there are limited reports on the fragments of C70. Herein, we report a new basic subunit of C70 with C2v symmetry, the dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene (2CP-Per). Its aryl-substituted derivative 2CP-Per-Ar was synthesized and shows a bowl-shaped geometry according to X-ray crystallographic analysis. A fast bowl-to-bowl inversion process was observed above 183 K by variable temperature nuclear magnetic resonance (NMR), with a small inversion energy barrier. 2CP-Per-Ar displays amphoteric redox behavior with a small electrochemical energy gap (1.29 eV). Different from many other aromatic buckybowls, 2CP-Per exhibits global antiaromaticity with a strong paratropic ring current associated with the 16π-electrons rim, as revealed by NMR measurements and theoretic calculations. Its dianion is aromatic, similar to its isoelectronic structure coronene. Its dication is predicted to be aromatic, with a [6]annulene-within-[14]annulene structure.

Theoretical investigation of the anchoring and activity of a gold cluster on two-dimensional substrates

Gold nanoparticles can be used as catalysts in several chemical reactions. However, when mobile on a substrate gold nanoparticles coalesce, increasing their diameter, and reducing their catalytic properties. In this work, we performed density functional theory calculations to study the interaction of a 34 atoms gold cluster with different two-dimensional materials: pristine graphene, defective graphene (single vacancy), hexagonal boron nitride, tungsten diselenide and thiophenol functionalized graphene. An analysis of the bond strength between the gold cluster and the two-dimensional substrates shows a diverse scenario, from non-bonding or slight repulsive interactions to strong bonded cases. The examination of the band edge levels of the interacting systems (gold cluster + two-dimensional substrates) indicates that the catalytic activity of the gold cluster depends on the particular two-dimensional substrate on which it is deposited. We find that a clean non-functionalized two-dimensional substrate, the tungsten diselenide, can firmly anchor the gold cluster, and that in this situation the cluster will present an amphoteric behavior.

Bowl-Shaped Carbon Nanobelts Showing Size-Dependent Properties and Selective Encapsulation of C70.

The synthesis of carbon nanobelts (CNBs) with well-defined size and structure remains a challenging topic in nanocarbon chemistry and materials science. Herein, we report the synthesis, physical characterization, and supramolecular properties of two fully conjugated bowl-shaped CNBs (CNB1/CNB2), in which six/eight cyclopenta-rings are fused onto a macrocycle containing three/four alternately linked 2,7-pyrenyl and 2,7-phenanthryl units. The existence of five-membered rings results in a bowl-shaped geometry, as revealed by X-ray crystallographic analysis and density functional theory calculations. Both molecules contain an alternate aromatic phenanthrene- co-quinoidal pyrene structure to satisfy Clar's aromatic sextet rule. The smaller size CNB1 has a deeper bowl depth ( d = 4.997 Å) than CNB2 ( d = 3.682 Å) and cannot undergo bowl-to-bowl (BTB) inversion below 373 K in toluene. However, the larger size CNB2 shows a smaller BTB inversion barrier (∼12 kcal/mol) at the coalescent temperature (248 K), which was estimated by variable-temperature NMR measurements. Both compounds exhibit a small energy gap and amphoteric redox behavior with multiple redox waves. The dications of CBN1 and CBN2, and the tetracation of CBN2, are experimentally accessible by chemical oxidation with NO·SbF6, all displaying unusual open-shell singlet diradical character with a small singlet-triplet energy gap (Δ ES-T = -2.71 kcal/mol for CBN12+, -2.50 kcal/mol for CBN22+, and -2.00 kcal/mol for CBN24+). The dications are globally aromatic while the tetracations are globally antiaromatic according to NMR measurements and theoretical calculations (anisotropy of the induced current density, nucleus independent chemical shift, and 2D isochemical shielding surface). The small bowl-shaped CNB1 demonstrates selective encapsulation of fullerene C70 over C60, with a large association constant ( Ka = 8.066 × 105 M-1 in toluene). However, the larger size CNB2 does not exhibit any encapsulation with both C60 and C70.

Regioselective Bromination and Functionalization of Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene with Zigzag Edges.

Dibenzo[hi,st]ovalene (DBOV) is a nanographene with a combination of zigzag and armchair edges, consisting of 38 sp2 carbons. Excellent optical properties with strong red emission have been demonstrated. Here we report the regioselective bromination of DBOV bearing two mesityl groups (DBOV-Mes) by treatment with N-bromosuccinimide (NBS) under mild conditions. The dibrominated DBOV was further subjected to transition-metal-catalyzed cross-coupling reactions, that is, Suzuki and Sonogashira coupling, demonstrating the edge-decoration of DBOV with different functional groups. Notably, DBOVs arylated at the bay regions showed intense red emission and enhanced fluorescence quantum yields of up to 0.97. Amphoteric reduction and oxidation behavior were observed by cyclic voltammetry (CV) measurements. Chemical oxidation to stable radical cation species was also demonstrated, followed by reduction back to their neutral species.

Detailed analysis and performance limiting mechanism of Si delta-doped GaAs tunnel diode grown by MBE

High-performance GaAs tunnel diodes (TDs) are fabricated by using Si delta-doping technique. The GaAs TDs exhibited a high peak tunnel-current density of 2,735 A/cm2 and low specific resistivity of 1.46 × 10−4 Ω·cm2. However, the performance of the GaAs TDs deteriorated once the amount of Si delta doping exceeded a certain limit, which has been rarely reported elsewhere. Detailed analyses and numerical simulations of GaAs TDs with various amounts of Si delta doping prove that Si amphoteric behavior governs the performance limit. GaAs TDs with precisely controlled Si delta doping are suitable for cutting-edge tandem solar cell applications.

Intra- and Interpolyelectrolyte Complexes of Polyampholytes.

At present, a large amount of research from experimental and theoretical points of view has been done on interpolyelectrolyte complexes formed by electrostatic attractive forces and/or interpolymer complexes stabilized by hydrogen bonds. By contrast, relatively less attention has been given to polymer–polymer complex formation with synthetic polyampholytes (PA). In this review the complexation of polyampholytes with polyelectrolytes (PE) is considered from theoretical and application points of view. Formation of intra- and interpolyelectrolyte complexes of random, regular, block, dendritic polyampholytes are outlined. A separate subsection is devoted to amphoteric behavior of interpolyelectrolyte complexes. The realization of the so-called “isoelectric effect” for interpolyelectrolyte complexes of water-soluble polyampholytes, amphoteric hydrogels and cryogels with respect to surfactants, dye molecules, polyelectrolytes and proteins is demonstrated.

Local reactivity through fukui function on endohedral mono-metallofullerenes

Analysis of local reactivity through f−, f° and f+ Fukui functions was performed for (La, Ce, Y, Sc, Gd, Nd, Eu, Tm and Yb)@C82 − C2v(9) mono-endohedral fullerenes. A clear difference was observed for trivalent and divalent compounds. For trivalent systems an amphoteric behavior was observed, which confirms the similarity found in previous studies about chemical reactivity in (La, Ce, Y, Sc, Gd)@C82 − C2v(9) compounds. However, in spite of Nd@C82 − C2v(9) is a trivalent compound, this system does not present an amphoteric behavior. In addition, divalent systems have not an amphoteric behavior either. Interestingly, in scientific literature there are several studies on functionalization of (La, Ce, Y, Sc, Gd)@C82 − C2v(9) endohedral fullerenes, which are trivalent systems and are the ones who present the amphoteric behavior, however, there is nothing of literature about functionalization of divalent systems, one of the reasons could be that divalent systems have a low yield in comparison with trivalent systems, however, Nd@C82 − C2v(9) is a trivalent system and has a high yield, nonetheless, this system has not been functionalized either and one of the answers could be in the amphoteric or non amphoteric behavior of the compounds. Additionally, it is worth to mention that this study is the first local reactivity analysis through Fukui functions on these compounds.