Synergistic adsorption of Cd(II) with sulfate/phosphate on ferrihydrite: An in situ ATR-FTIR/2D-COS study

Elucidation of the co-adsorption characteristics of heavy metal cations and oxyanions on (oxyhydr)oxides can help to better understand their distribution and transformation in many geological settings. In this work, batch adsorption experiments in combination with in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were applied to explore the interaction mechanisms of Cd(II) with sulfate or phosphate at the ferrihydrite (Fh)–water interface, and the two-dimensional correlation spectroscopic analysis (2D–COS) was used to enhance the resolution of ATR-FTIR bands and the accuracy of analysis. The batch adsorption experiments showed enhanced adsorption of both sulfate (S) and phosphate (P) on Fh when co-adsorbed with Cd(II); additionally, the desorbed percentages of Cd(II) were much lower in the P + Cd adsorption systems than those in the S + Cd adsorption systems. The spectroscopic results suggested that in the single adsorption systems, sulfate primarily adsorbed as outer-sphere complexes with a small amount of bidentate inner-sphere complexes, while the dominant adsorbed species of phosphate were largely the bidentate nonprotonated inner-sphere complexes, although there was significant pH-dependence. In the co-adsorption systems, the synergistic adsorption of Cd(II) and sulfate was dominantly attributed to the electrostatic interaction, as well as the formation of Fe–Cd–S (i.e., Cd-bridged) ternary complexes. In contrast, Fe–P–Cd (i.e., phosphate-bridged) ternary complexes were found in all of the co-adsorption systems of phosphate and Cd(II); furthermore, electrostatic interaction should also contribute to the co-adsorption process. Our results show that in situ ATR-FTIR in combination with 2D–COS can be an efficient tool in analyzing the co-adsorption mechanisms of anions and heavy metal cations on iron (oxyhydr)oxides in ternary adsorption systems. The co-existence of Cd(II) with sulfate or phosphate can be beneficial for their accumulations on Fh, and phosphate is more efficient than sulfate for the long-term immobilization of Cd(II)

Efficient degradation of cefotaxime by a UV plus ferrihydrite/TiO2+H2O2 process: the important role of ferrihydrite in transferring photo-generated electrons from TiO2 to H2O2

Background Developing effective removal processes for antibiotics has attracted increasing interest recently. In this work, a novel strategy involving the combination of photocatalysis with Fenton reaction using ferrihydrite/TiO2 (Fh/TiO2) nanohybrids was developed to efficiently degrade the antibiotic cefotaxime. Fh/TiO2 nanohybrids were synthesized by simply growing Fh on the surface of commercially available TiO2. We expected that Fh of Fh/TiO2 could capture photo-generated electrons from TiO2, inhibiting the recombination of electron-hole pairs; also, by virtue of Fe(III)/Fe(II) cycle on Fh/TiO2, photo-generated electrons could be continually transferred to H2O2 to produce center dot OH. Accordingly, high degradation efficiency of cefotaxime could be achieved. Results With UV light and H2O2, Fh/TiO2 with a Fe/Ti molar radio of 7% showed high catalytic activity indeed, and its degradation rate for cefotaxime was nearly three times higher than that of TiO2. The decomposition of H2O2 and production of center dot OH in the UV+7%Fh/TiO2+H2O2 system were also increased markedly. The large amount of Fe(II) on 7%Fh/TiO2 determined in this system supported our hypothesis that Fh of 7%Fh/TiO2 could capture photo-generated electrons from TiO2. Although dissolved iron was observed, the contribution of Fenton reaction by dissolved iron was rather limited. After four consecutive cycles, 7%Fh/TiO2 still retained good stability. Conclusions The UV+7%Fh/TiO2+H2O2 system provides a potential alternative in degradation of cefotaxime for further practical application, and it has the following advantages: high catalytic activity, simple preparation method, good stability and low cost, as well as continued catalytic activity after total consumption of H2O2. (c) 2019 Society of Chemical Industr

Temperature-Dependent Structure and Dynamics of Water Intercalated in Layered Double Hydroxides with Different Hydration States

Properties of water confined in layered double hydroxides (LDH) are relevant with hydration, dehydration, and protonic conduction in interlayer galleries. Evolutions of structure and dynamics of water in LDHs (Mg2Al(OH)(6)Cl center dot mH(2)O) with temperature are disclosed through molecular dynamics simulations performed in the range from 300 to 430 K. LDHs with m = 0.78 and 1.44 which characterize two different hydration states are investigated. Water in the lower hydration state is characterized with higher ordered structure. Irrespective of water content, water becomes less hydrogen bonded and more disordered as temperature increases. This leads to a large decrement in dehydration enthalpy, which facilitates dehydration energetically. Irrespective of temperature or water content, water exhibits the preference for being fixed in hydroxyl sites and it diffuses through jumping between neighbor sites. Jump diffusion approximately exhibits an Arrhenius dependence on temperature. A jump is a collective process consisting of water translation and hydroxyl group reorientation, which is reflected in the high activation energy and low attempt frequency. Hydronium ions may be transported through jumping between neighbor sites, making a contribution to proton transfer in interlayer galleries

Special Issue Advances in Applied Clay Science Intercalated nanomaterials: From functional clays to advanced hybrid lamellar compounds Preface

International audienceno abstrac

Strategies for Enhancing the Heterogeneous Fenton Catalytic Reactivity: A review

Heterogeneous Fenton reactions have gained widespread attention in removing recalcitrant organic contaminants as the reaction between solid Fenton catalysts and H2O2 can generate highly reactive hydroxyl radicals (HO[rad]). However, several drawbacks, such as the low-speed generation of Fe(II), high consumption of H2O2, and acidic reaction conditions (generally at ˜ pH 3), are always the core issues that hamper the large-scale application of heterogeneous Fenton reactions in environmental remediation. Thus, a large number of studies have been devoted to tackling these drawbacks, and this paper intends to comprehensively review the developed strategies for enhancing heterogeneous Fenton reactivity, mainly over the last decade. Based on a comprehensive survey of previous studies, we categorize these strategies according to their reaction mechanisms. For example, introducing additional electrons (e.g., from external electric fields, electron-rich materials, semiconductors, plasmonic materials, or doped metals) to heterogeneous Fenton catalysts can accelerate the generation of Fe(II); the in situ generation of H2O2 can be achieved by combining ultrasound, electricity, semiconductors, and iron-based catalysts in the system; and controlling the specific morphologies and exposed facets of heterogeneous Fenton catalysts can greatly promote the decomposition of H2O2. In addition, we briefly introduce some recent novel heterogeneous Fenton-like reactions that are of particular interest, including constructing dual reaction centers (i.e., the electron-poor center and the electron-rich center) and synthesizing single-atom catalysis-based heterogeneous Fenton-like catalysts. Moreover, this review article analyzes and compares the merits of each strategy for enhancing heterogeneous Fenton/Fenton-like reactions. We believe this review can motivate the construction of novel and efficient heterogeneous Fenton/Fenton-like systems and help readers choose proper Fenton/Fenton-like reaction systems for industrial applications.</p