اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدElectrochemical removal of amphoteric ions
170
0
0.0
(
0
)
تأليف
Amit N. Shocron
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Several harmful or valuable ionic species present in sea, brackish and wastewaters are amphoteric, and thus their properties depend on the local water pH. Effective removal of these species can be challenging by conventional membrane technologies, necessitating chemical dosing of the feedwater to adjust its pH. Capacitive deionization (CDI) is an emerging membraneless technique for water treatment and desalination, based on electrosorption of salt ions into charging microporous electrodes. CDI cells show strong internally-generated pH variations during operation, and thus CDI can potentially remove amphoteric species without chemical dosing. However, development of this technique is inhibited by the complexities inherent to coupling of pH dynamics and amphoteric ion properties in a charging CDI cell. Here, we present a novel theoretical framework predicting the electrosorption of amphoteric species in flow-through electrode CDI cells. We demonstrate that such a model enables deep insight into factors affecting amphoteric species electrosorption, and conclude that important design rules for such systems are highly counter-intuitive. For example, we show both theoretically and experimentally that for boron removal the anode should be placed upstream, which runs counter to accepted wisdom in the CDI field. Overall, we show that to achieve target separations relying on coupled, complex phenomena, such as in the removal of amphoteric species, a theoretical CDI model is essential.
قيم البحث
اقرأ أيضاً
An immobile charged species provides a charged medium for transport of charge carriers that is exploited in many applications, such as permselective membranes, doped semiconductors, biological ion channels, as well as porous media and microchannels w
ith surface charges. In this paper, we theoretically study the electrochemical impedance of electrodiffusion in a charged medium by employing the Nernst-Planck equation and the electroneutrality condition with a background charge density. The impedance response is obtained under different dc bias conditions, extending above the diffusion-limiting bias. We find a transition in the impedance behavior around the diffusion-limiting bias, and present an analytical approximation for a weakly charged medium under an overlimiting bias.
We study a method for mass-selective removal of ions from a Paul trap by parametric excitation. This can be achieved by applying an oscillating electric quadrupole field at twice the secular frequency $omega_{text{sec}}$ using pairs of opposing elect
rodes. While excitation near the resonance with the frequency $omega_{text{sec}}$ only leads to a linear increase of the amplitude with excitation duration, parametric excitation near $2, omega_{text{sec}}$ results in an exponential increase of the amplitude. This enables efficient removal of ions from the trap with modest excitation voltages and narrow bandwidth, therefore substantially reducing the disturbance of ions with other charge-to-mass ratios. We numerically study and compare the mass selectivity of the two methods. In addition, we experimentally show that the barium isotopes with 136 and 137 nucleons can be removed from small ion crystals and ejected out of the trap while keeping $^{138}text{Ba}^{+}$ ions Doppler cooled, corresponding to a mass selectivity of better than $Delta m / m = 1/138$. This method can be widely applied to ion trapping experiments without major modifications, since it only requires modulating the potential of the ion trap.
Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally-efficient continuum solvation methodologies. We develop a model for the double lay
er of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the Potential of Zero Charge (PZC), and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the Nonlinear Electrochemical Soft-Sphere solvation model (NESS) which both captures the capacitance features observed experimentally, and serves as a general-purpose continuum solvation model.
The percentage removal of phenol from aqueous solution by emulsion liquid membrane and emulsion leakage was investigated experimentally for various parameters such as membrane:internal phase ratio, membrane:external phase ratio, emulsification speed,
emulsification time, carrier concentration, surfactant concentration and internal agent concentration. These parameters strongly influence the percentage removal of phenol and emulsion leakage. Under optimum membrane properties, the percentage removal of phenol was as high as 98.33%, with emulsion leakage of 1.25%. It was also found that the necessity of carrier for enhancing phenol removal was strongly dependent on the internal agent concentration.
Accurate description of the excess charge in water cluster anions is challenging for standard semi-local and (global) hybrid density functional approximations (DFAs). Using the recent unitary invariant implementation of the Perdew-Zunger self-interac
tion correction (SIC) method using Fermi-Lowdin orbitals, we assess the effect of self-interaction error on the vertical detachment energies of water clusters anions with the local spin density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation, and the strongly constrained and appropriately normed (SCAN) meta-GGA functionals. Our results show that for the relative energies of isomers with respect to reference CCSD(T) values, the uncorrected SCAN functional has the smallest deviation of 21 meV, better than that for the MP2 method. The performance of SIC-SCAN is comparable to that of MP2 and is better than SIC-LSDA and SIC-PBE, but it reverses the ordering of the two lowest isomers for water hexamer anions. Removing self interaction error (SIE) corrects the tendency of LSDA, PBE, and SCAN to over-bind the extra electron. The vertical detachment energies (VDEs) of water cluster anions, obtained from the total energy differences of corresponding anion and neutral clusters, are significantly improved by removing self-interaction and are better than the hybrid B3LYP functional, but fall short of MP2 accuracy. Removing SIE results in substantial improvement in the position of the eigenvalue of the extra electron. The negative of the highest occupied eigenvalue after SIC provides an excellent approximation to the VDE, especially for SIC-PBE where the mean absolute error with respect to CCSD(T) is only 17 meV, the best among all approximations compared in this work.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
