The Role of the Double Layer for the Pseudocapacitance of the Hydrogen Adsorption on Platinum

Pseudocapacitances such as the hydrogen adsorption on platinum (HAoPt) are associated with faradaic chemical processes that appear as capacitive in their potentiodynamic response, which was reported to result from the kinetics of adsorption processes. This study discusses an alternative interpretation of the partly capacitive response of the HAoPt that is based on the proton transport of ad- or desorbed hydrogen in the double layer. Potentiodynamic perturbations of equilibrated surface states of the HAoPt lead to typical double layer responses with the characteristic resistive-capacitive relaxations that overshadow the fast adsorption kinetics. A potential-dependent double layer representation by a dynamic transmission line model incorporates the HAoPt in terms of capacitive contributions and can computationally reconstruct the charge exchanged in full range cyclic voltammetry data. The coupling of charge transfer with double layer dynamics displays a novel physicochemical theory to explain the phenomenon of pseudocapacitance and the mechanisms in thereon based supercapacitors.

Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Experimental Studies on the Removal of Aluminium Ions from Synthetic Aqueous Solution by Hydroxyapatites

In this work we have presented the results obtained in the adsorption behavior of hydroxyapatite with different treatment towards aluminium ions from synthetic wastewaters. Experiments were performed in batch technique at different pH values, temperatures, sorbent dosage, contact time and initial aluminium concentration. The thermodynamic studies on the adsorption process of aluminium onto hydroxyapatite indicated that the process is spontaneous and endothermic. The Langmuir, Freundlich, Flory-Huggins, Dubinin-Radushkevich and Temkin equilibrium models were applied to the description of experimental data. The adsorption of aluminium follows the Langmuir adsorption isotherm. The kinetics of adsorption was evaluated using the pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models. The rate of aluminium adsorption was successfully described by a pseudo-second-order kinetic model. The obtained results indicated that hydroxyapatite treated with Pluronic P123 surfactant has a higher sorption capacity toward aluminium ions (117.65 mg g−1) than hydroxyapatite treated with Pluronic F127 surfactant (109.89 mg g−1) while untreated hydroxyapatite exhibited the lowest one (104.17 mg g−1).

Simultaneously Remove and Visually Detect Ce4+ Based on Nanocomposite of UiO-66-NH2/CPA-MA

Effective strategies to deal with rare earth pollution are urgently needed due to the overexploitation of rare earths resource. In this study, a novel nanocomposite of UiO-66-NH2/CPA-MA denoted as UA was successfully synthesized, which can simultaneously remove and detect Ce4+ in water. The hybrid consists of UiO-66-NH2 and CPA-MA. Based on the high adsorption performance of UiO-66-NH2, it can remove Ce4+ with high capacity by adsorption. Moreover, it can change its color from olive drab to light cyan depending on the adsorbed Ce4+ concentration, and the chroma is linearly related to the Ce4+ concentration. So, UA can be used to qualitatively and quantitatively detect Ce4+ by its color changing. The kinetics of adsorption course was investigated in details. The anti-inference ability of the nanocomposite in coexisting systems was carefully evaluated. The results indicate that UiO-66-NH2/CPA-MA is highly potential to deal with Ce4+ pollutions due to its bifunctionality.

Kinetics of Adsorption Competition of Pb-Cu and Pb-Methylene Blue in Aqueous Solution using Silica Gels from Coal Fly Ash

The present study investigates the removal of Pb2+ using silica gel (SG) in the presence of the Cu2+ (Pb-Cu) and methylene blue (Pb-MB) ion competitor. These pollutants are toxic and harmful to the ecosystem. The presence of the multicomponent pollutants causes more complications to remove from the water system. The adsorptions were examined in a batch system under certain experimental conditions (pH solution system and contact time). Meanwhile, the FTIR spectrophotometer determines the differences adsorption interaction in silica functional groups before and after adsorption. The results showed that the silanol group of silica gel acted as an adsorption site. In the single systems, the adsorption capacity of silica gel follows the order MB > Cu2+ > Pb2+ of around 84.03; 64.81; and 56.88 mg.L−1, respectively. The kinetic adsorptions of both single and binary systems were best fitted to pseudo-second-order models. In the binary solution systems, both adsorption capacity and adsorption rate of each component decreased compared to the single system. The results indicated that the cationic competitors influenced the Pb2+ adsorption, or vice versa, depending on the amount of charge and adsorption affinity.

Capture of aqueous radioiodine species by metallated adsorbents from wastestreams of the nuclear power industry: a review

Abstract Iodine-129 poses a significant challenge in the drive towards lowering radionuclide emissions from used nuclear fuel recycling operations. Various techniques are employed for capture of gaseous iodine species, but it is also present, mainly as iodide anions, in problematic residual aqueous wastestreams, which have stimulated research interest in technologies for adsorption and retention of the radioiodine. This removal effort requires specialised adsorbents, which use soft metals to create selectivity in the challenging chemical conditions. A review of the literature, at laboratory scale, reveals a number of organic, inorganic and hybrid adsorbent matrices have been investigated for this purpose. They are functionalised principally by Ag metal, but also Bi, Cu and Pb, using numerous synthetic strategies. The iodide capacity of the adsorbents varies from 13 to 430 mg g−1, with ion-exchange resins and titanates displaying the highest maximum uptakes. Kinetics of adsorption are often slow, requiring several days to reach equilibrium, although some ligated metal ion and metal nanoparticle systems can equilibrate in < 1 h. Ag-loaded materials generally exhibit superior selectivity for iodide verses other common anions, but more consideration is required of how these materials would function successfully in industrial operation; specifically their performance in dynamic column experiments and stability of the bound radioiodine in the conversion to final wasteform and subsequent geological storage. Article highlights Metallated adsorbents for the capture and retention of radioiodine in the nuclear industry are assessed. The strengths and weaknesses of organic, inorganic and hybrid support matrices and loading mechanisms are discussed. Pathways for progression of this technology are proposed. Graphic abstract

Simultaneously Remove and Visually Detect Ce4+ Based On Nanocomposite of UiO-66-NH2/CPA-MA

Effective strategies to deal with rare earth pollution are urgently needed due to the overexploitation of rare earths resource. In this study, a novel nanocomposite of UiO-66-NH2/CPA-MA denoted as UA was successfully synthesized, which can simultaneously remove and detect Ce4+ in water. The hybrid consists of UiO-66-NH2 and CPA-MA. Based on the high adsorption performance of UiO-66-NH2, it can remove Ce4+ with high capacity by adsorption. Moreover, it can change its color from olive drab to light cyan depending on the adsorbed Ce4+ concentration, and the chroma is linearly related to the Ce4+ concentration. So UA can be used to qualitatively and quantitatively detect Ce4+ by its color changing. The kinetics of adsorption course were investigated in details. The anti-inference ability of the nanocomposite in co-existing systems were carefully evaluated. The results indicate that UiO-66-NH2/CPA-MA is highly potential to deal with Ce4+ pollutions due to its bi-functionality.