Adsorption of Mercury(II), Lead(II), Cadmium(II) and Zinc(II) from Aqueous Solutions using Mercapto‐Modified Silica Particles

This article presents a novel systematic approach to the fabrication of highly functionalized, silica (SiO₂) nanoparticles used for the adsorption of heavy‐metal ions (Hg²⁺, Pb²⁺, Cd²⁺, Zn²⁺). Almost monodispersed silica (SiO₂) nanoparticles with narrow particle size distributions of around 85 ± 5 nm were formed using the Stöber process. The prepared SiO₂ nanoparticles were successfully surface‐treated during a one‐step procedure by the covalent attachment of mercaptopropyl groups onto the surfaces of the SiO₂ nanoparticles. A FTIR spectra analysis confirmed that the binding of the mercaptosilane molecules onto the surface of the silica nanoparticles mediated the Si–O–Si and –SH vibrations. TEM/EDXS micrographs indicated the almost monodispersed and spherical morphology of the prepared product with strong signals of Si and S, thus implying that the coating procedure involving the mercapto groups onto the silica surface had been successfully accomplished. The final results for the heavy‐metal (Hg²⁺, Pb²⁺, Cd²⁺, Zn²⁺) adsorption showed the strongest affinity within the following sequence Hg²⁺ (99.9%) > Pb²⁺ (55.9%) > Cd²⁺ (50.2%) > Zn²⁺ (4%). Adsorption equilibrium was achieved after 1 h for all the analyzed samples.     

Removal of lead,copper, nickel,cobalt, and zinc from water by a cancrinite-type zeolite synthesized from fly ash

As a low Si/Al ratio zeolite, cancrinite received very scant study in previous studies on the adsorption removal of heavy metals from water. In this study, a cancrinite-type zeolite (ZFA) was synthesized from Class C fly ash via the molten-salt method. Adsorption equilibriums of Pb²⁺, Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺ on ZFA were studied in aqueous solutions and were well represented by Langmuir isotherms. The increase of pH levels during the adsorption process suggests that the uptake of heavy metals on ZFA was subjected to an ion exchange mechanism. It is found that the maximum exchange level (MEL) follows the order: Pb²⁺ (2.530 mmol g^?1) > Cu²⁺ (2.081 mmol g^?1) > Zn²⁺ (1.532 mmol g^?1) > Co²⁺ (1.242 mmol g^?1) > Zn²⁺ (1.154 mmol g^?1). Comparison with previous studies shows that the MEL of ZFA is higher than the commonly used natural zeolites; and it is also comparable to (or higher than) several synthetic zeolites and ion exchange resins. The high MEL of heavy metals on ZFA is attributed to the high cation exchange capacity (CEC) and proper pore size of cancrinite. The pseudo-first-order kinetics suggests that the ion exchange processes were diffusion-controlled.     

Adsorption and equilibrium adsorption modeling of bivalent metal cations on viscose rayon succinate at different pHs

A viscose rayon succinate (VRS) was studied as a chelating fiber for the removal of metal ions from an aqueous solution. VRS was synthesized successfully from viscose rayon (VR) and succinic anhydride in the presence of dimethylsulfoxide (DMSO), and was characterized by C¹³ nuclear magnetic resonance ¹³C NMR, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) analysis. The maximum bivalent metal ion adsorption capacity of the VRS was 6.2 meq/g. Studies on the adsorption behaviour of VRS and its ability to remove bivalent trace metals such as Cu²⁺, Zn²⁺, Pb²⁺, and Ni²⁺ from an aqueous solution were performed both by FT-IR and quantitative analyses at different pHs. The results showed that the adsorption of metals on VRS increased as pH increased, and furthermore, that the adsorption capacity of metal ions could be classified as Cu²⁺ > Zn²⁺ > Ni²⁺ > Pb²⁺. The adsorption modeling for the interpretation of empirical data was carried out by assuming a probability factor, P(A), and a degree of protonation, χ. Surface potential, Ψ₀, and an effective ratio of surface equilibrium constants, K_effect, were obtained using the model.     

Comparative Study of Zn2+, Cd2+, and Pb2+ Removal From Water Solution Using Natural Clinoptilolitic Zeolite and Commercial Granulated Activated Carbon. Equilibrium of Adsorption

Abstract

The aim of this work is to study the effectiveness of regional, low-cost natural clinoptilolitic zeolite tuff in heavy metal ions removal from aqueous solution, through comparative study with commercial granulated activated carbon. The equilibrium of adsorption of Cd²⁺, Pb²⁺, and Zn²⁺ on both adsorbents have been determined at 25, 35, and 45°C in batch mode. The granulated activated carbon has shown around three times higher adsorption capacity for Cd²⁺ and Zn²⁺ than natural zeolite, and almost the same adsorption capacity for Pb²⁺ as the natural zeolite. The metal ion selectivity series Pb²⁺ > Cd²⁺ > Zn²⁺, on a mass basis, has been obtained on both adsorbents. The Langmuir and Freundlich model have been used to describe the adsorption equilibrium. The thermodynamic parameters were calculated from the adsorption isotherm data obtained at different temperatures. The study of the influence of the acidity of the metal ion aqueous solution has shown an increase of metal ion uptake with increase of the pH. The sorption mechanism of Cd²⁺, Pb²⁺, and Zn²⁺ on natural zeolite changes from ion-exchange to ion-exchange and adsorption of metal-hydroxide with increase of the pH from 2 to 6 (and 7 for Zn²⁺). The preliminary cost calculation, based on adsorbents maximum adsorption capacity and their price, have revealed the potential of natural zeolite as an economic alternative to the granulated activated carbon in the treatment of heavy metal polluted wastewater.     

Characterization of (Fe,Al)FER synthesized in presence of ethylene glycol and ethylene diamine

(Fe,Al)Ferrierite type zeolite was hydrothermally crystallized in a gel system of sodium aluminosilicate with ethylene glycol a nitrogen-free organic compound, as well as, ethylene diamine. The zeolite crystals obtained were characterized by X-ray diffractometry (XRD), thermal analysis (TGA–DTA), electron scanning microscopy (SEM), chemical analysis, N₂ adsorption/desorption at 77 K and ²⁹Si–, ²⁷Al–, ¹³C–, and ¹H NMR spectroscopy. Fe atoms essentially occupy framework positions and rather high amounts of SiOH defect groups are present in the as-made samples.     

Theoretical Study of NO2 Adsorption on a Transition-Metal Zeolite Model

Calculations for the study of NO₂ adsorption on a transition-metal-exchanged zeolite (M=Zn, Cu, Ni, Co, Fe) were carried out using an ab initio density functional theory and pseudopotential approaches. A tritetrahedral model (T3) was used to represent the structure of the zeolite. The density functional calculations predict that the bonding energy follows the order Zn>Ni>Cu>Fe>Co. Analysis of the electronic properties shows that only in the case of Cu and Ni ions does the d¹⁰-s¹d⁹ promotion favor interaction between the NO₂ molecule and the metallic center. The optimization results show that there is a charge transfer from the metallic ion to the NO₂ molecule, which produces a weakening of the N–O bond.     

Poly(itaconic acid)-assisted ultrafiltration of heavy metal ions’ removal from wastewater

The complexation–ultrafiltration technique has been introduced as a capable system to remove heavy metals ions from wastewater. This method needs a water-soluble polymer; therefore, in this paper we synthesized super water-soluble poly(itaconic acid) (PITA) and employed it in polymer-assisted ultrafiltration process to remove Pb(II) ions from synthetic wastewater solutions. The itaconic acid can be produced from different agricultural products and is a green and eco-friendly material. Factors influencing the removal of the metals ions including poly(itaconic acid) concentration, pH and permeate flux were investigated. The results showed that the maximum percentage of metal ion removal was obtained in the basic pH (pH > 7). The flux test was performed by 200 mg/L of poly(itaconic acid) and after 60 min, the flux of membrane was 33.4 L/m²h. The simultaneously selective removal ability of the poly(itaconic acid) for adsorption of different metal ions (Pb²⁺, Sn²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) was also studied. The trend of rejection was Pb²⁺ > Cu²⁺ > Sn²⁺ > Zn²⁺ > Cd²⁺. The highest rejection of Pb(II) ions was achieved as 86%. Generally, the results of this research demonstrated that poly(itaconic acid) (with two carboxyl groups on its repeating unit) is more effective in removing heavy metals ions from wastewater in comparison with customary polymers.

     

Conversion of coal fly ash into zeolite and heavy metal removal characteristics of the products

Fly ash obtained from a power generation plant was used for synthesizing zeolite. Zeolites could be readily synthesized from the glassy combustion residues and showed potential for the removal of heavy metal ions. By the use of different temperatures and NaOH concentration, five different zeolites were obtained: Na-P1, faujasite, hydroxy sodalite, analcime, and cancrinite. The synthesized zeolites had greater adsorption capabilities for heavy metals than the original fly ash and natural zeolites. Na-P1 exhibited the highest adsorption capacity with a maximum value of about 1.29 mmole Pb g^-1 and had a strong affinity for Pb²⁺ ion. The metal ion selectivity of Na-P1 was determined as: Pb²⁺> Cu²⁺> Cd²⁺> Zn²⁺, consistent with the decreasing order of the radius of hydrated metal ion. The adsorption isotherm for lead by Na-P1 fitted the Freundlich rather than the Langmuir isotherm.     

Adsorption of Cd and Cr ions from industrial wastewater using Ca doped Ni–Zn nanoferrites: Synthesis,characterization and isotherm analysis

Removal of heavy metals (Cd and Cr) from industrial wastewater by adsorption onto a series of Ca substituted nickel zinc nanoferrites (Ca_xNi_0.4Zn_0.6-xFe₂O₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6)) (CNZNFs) was studied in detail. The effect of calcium doping and contact time over adsorption of cadmium and chromium ions was investigated and maximum uptake of Cd (98.25%) and Cr (51%) ions were marked by prepared nanoadsorbents. Structural studies confirmed the formation of spinel structured nanoparticles with crystallite size ranging from 24 to 38 nm while porosity was observed to vary from 52% to 58% with calcium concentration. Pseudo second order (PSO) kinetic model for adsorption of both heavy metals (cadmium and chromium) was observed to be better fitted with adsorption data. Maximum adsorption efficiencies for Cd (128.20 mg/g) and Cr (23.54 mg/g) were found by the data fit of Langmuir isotherm model. Additionally, the adsorption data was found to obey Langmuir isotherm model for both heavy metals due to higher values of correlation coefficients (R² = 0.94131 for cadmium and 0.91091 for chromium) than Freundlich isotherm model (R² = 0.5865 for cadmium and 0.4599 for chromium).     

Theoretical study of the enhanced Brønsted acidity of Zn2+‐exchanged zeolites

The effect of Zn²⁺ exchange on the Brønsted acidity of a protonic zeolite has been studied by the ab initio DFT (density functional theory) approach using the BLYP generalized gradient approximation. Three different zeolite cluster models have been compared: two 6“T” models (two 4“T” rings with an oxygen atom bridge) with Si/Al=1 and Si/Al=2 and a 4“T” model (ring form) with Si/Al=1. The Brønsted acidity has been probed by computation of the acetonitrile adsorption and the cluster deprotonation energy. The presence of Zn²⁺ does not affect the cluster Brønsted acidity but it creates a very strong Lewis site (Zn²⁺) in all models studied. On the other hand, the presence of ZnOH⁺ enhanced the Brønsted site acidity in the case of the 6T model with Si/Al=1. This enhancement is due to a change in cluster geometry and position of OH group in ZnOH⁺ upon acetonitrile adsorption.     

Catalytic conversion of CO,NO and SO2 on the supported sulfide catalyst: I. Catalytic reduction of SO2 by CO

Catalytic reduction of SO₂ to elemental sulfur by CO has been systematically investigated over γ-Al₂O₃-supported sulfide catalysts of transition metals including Co, Mo, Fe, CoMo and FeMo with different loadings of the metals. The sulfided CoMo/Al₂O₃ exhibited outstanding activity: a complete conversion of SO₂ was achieved at a temperature of 300°C. The reaction proceeds catalytically and consistently over time and most efficiently at a molar feed ratio CO/SO₂ = 2. A precursor CoMo/Al₂O₃ oxide which experienced sulfurization through the CO–SO₂ reaction yielded a working sulfide catalyst having a yet lower activity than the CoMo catalyst sulfided before reaction (pre-sulfiding). The catalytic activity of various metal sulfides decreased in order of 4% Co 16% Mo > 4% Fe15% Mo > 16% Mo ≥ 25% Mo > 14% Co ≥ 4% Co > 4% Fe. A DRIFT study showed that CO adsorbs exclusively on CoMo phase and that SO₂ predominantly on γ-Al₂O₃. It is suggested that the Co–Mo–S structure is more adequate than the other metal-sulfur structures for the formation of a carbonyl sulfide (COS) intermediate because of the proper strength of metal–sulfur bond, and catalytically works with γ-Al₂O₃ for the COS–SO₂ reaction.     

Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe₃O₄@SiO₂-(-NH₂/-COOH) nanoparticles were synthesized for the removal of Cd²⁺, Pb²⁺ and Zn²⁺ ions from wastewater. The results of characterization showed that Fe₃O₄@SiO₂-(-NH₂/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m²/g. The capacity of Fe₃O₄@SiO₂-(-NH₂/-COOH) to adsorb the three heavy metals was in the order Pb²⁺ > Cd²⁺ > Zn²⁺, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb²⁺, Cd²⁺ and Zn²⁺ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb²⁺, Cd²⁺ and Zn²⁺ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.     

NO SCR with propane and propene on Co-based alumina catalysts prepared by co-precipitation

Homogeneous dispersions and small size of deposited high-content cobalt on alumina were achieved by the co-precipitation method and were well maintained on the cobalt-based binary alumina catalysts with Zn, Ag, Fe, Cu or Ni as modifiers. The component and concentration of deposited cobalt species were characterized by UV–vis, EDX and XPS spectra and found to be greatly related to the Co loading, calcination temperatures and the type of additive metals. The optimal Co loading of 8 wt% and calcination temperatures of 800 °C were demonstrated. With respect to the single cobalt-based alumina catalyst, the surface concentration of Co²⁺ on the binary catalysts with addition of Fe, Cu, Ag or Ni was all reduced and accompanying with part conversion of Co²⁺ to Co₃O₄ on the Fe and Ni-modified catalysts. A slight enhanced surface Co²⁺ concentration was only achieved on the Zn-promoted catalyst. It was also demonstrated that for the case of Cu and Fe the additive metals themselves participated in the activation of propene. The octahedral and tetrahedral Co²⁺ ions were suggested as the common active sites. A maximum deNOx activity of 96% was observed on the 8Co4ZnA800 catalyst at the reaction temperatures of 450 °C, and the catalytic performance on the cobalt-based binary alumina catalysts can be described as fellows: CoZn > CoAg, CoNi > Co Cu > CoFe. Based on the in situ DRIFT spectra, different reaction intermediates R–ONO and –NCO besides –NO₂ were formed on the 8Co4ZnA800 and 8Co4FeA800 samples, respectively, demonstrating their dissimilar reaction mechanisms.     

Sorption characteristics of heavy metal ions by a natural zeolite

Zeolites have been shown to be effective adsorbents for the removal of heavy metals from aqueous solutions. A natural material from Cuba, containing zeolite, has been used for the removal of several metal ions, namely Cu²⁺, Zn²⁺, and Ni²⁺, to evaluate its potential use as a low‐cost adsorbent. Batch experiments have been conducted to evaluate the process kinetics and the removal equilibrium at different pH values, metal and zeolite concentrations. Pseudo‐second order kinetics and Freundlich equilibrium parameters have been obtained. Results suggested that this natural zeolite has a high potential for heavy metal retention. The selectivity of the studied metals was determined as Cu²⁺ ? Zn²⁺ > Ni²⁺, related to the first hydrolysis equilibrium constant. The metal removal efficacy was strongly dependent on pH, and to a lesser extent on metal/zeolite ratio. Copyright © 2005 Society of Chemical Industry     

Dehydrogenation of propane over ZnMOR. Static and dynamic reaction energy diagram

The dehydrogenation of propane over Zn²⁺-exchanged mordenite has been studied theoretically using ab initio density-functional calculations at different levels of theory. We compare (i) total-energy calculations based on semilocal exchange-correlation functionals with those adding semi-empirical corrections for dispersion forces, (ii) calculations based on a large periodic model of the zeolite with calculations based on small and large finite cluster models, and (iii) calculations of the free energies of activation and of the reaction rates based on harmonic transition state theory (hTST) with those based on thermodynamic integration over free-energy gradients determined by constrained ab initio molecular dynamics. Dehydrogenation proceeds in four steps: (i) adsorption of propane on the Zn²⁺ cation, (ii) dissociation of a hydrogen atom leading to the formation of a Zn-propyl complex and a Brønsted acid site, (iii) reaction of the acid proton and a β–H atom of propyl, resulting in the elimination of a hydrogen molecule, and (iv) desorption of propene from the Zn²⁺ cation.The periodic calculations demonstrate that the dispersion corrections increase the adsorption/desorption energies from 70 to 107 kJ/mol for propane and from 177 to 233 kJ/mol for propene and decrease the activation energy for H-dissociation from 73 to 61 kJ/mol, while the activation energy for the heterolytic dehydrogenation is almost unaffected with 132 kJ/mol. Hence, dispersion corrections are of foremost importance for lowering the activation energy for H-dissociation below the desorption energy of propane. While according to the periodic calculations the highest activation energies are predicted for the heterolytic dehydrogenation and the desorption of propene, cluster calculations predict a higher activation energy for H-dissociation than for H₂ elimination. Both hTST and thermodynamic integrations show that both activation processes lead to a loss of entropy because the transition state configurations admit for a lower degree of disorder than the initial and intermediate states. hTST consistently underestimates the loss of entropy, the anharmonic corrections are most important for the H-dissociation step.     

Nature of the sites of dissociative adsorption of dihydrogen and light paraffins in ZnHZSM-5 zeolite prepared by incipient wetness impregnation

A DRIFT study of ZnHZSM-5 zeolites with Si/Al ratios of 15 or 41 and a Zn loading of 0.8 wt% revealed a high thermal stability of bridging OH groups that was practically the same as in the pure hydrogen forms. It was concluded that the incipient wetness impregnation of NH₄ZSM-5 zeolite with zinc nitrate and the subsequent high-temperature treatment results only in a minor amount of ion exchange. A considerable part of the modifying zinc forms nanometric ZnO clusters inside the channels of the zeolite. The use of the low-temperature adsorption of dihydrogen as a probe indicated the appearance, after high-temperature vacuum pretreatment, of three different Lewis acid sites connected with coordinatively-unsaturated Zn²⁺ ions. The strongest Lewis sites, with an H–H stretching frequency of adsorbed molecular hydrogen of 3940 cm⁻¹, dissociatively adsorbed hydrogen, methane and propane at both room and elevated temperatures. These sites are represented either by Zn²⁺ ions on the walls of the main channels of the zeolite (α sites according to Mole et al.) or by Lewis-base pairs on the surface of nanometric clusters of zinc oxide. This revised version was published online in July 2006 with corrections to the Cover Date.     

Main Source of Microwave Loss in Transition‐Metal‐Doped Ba(Zn1/3Ta2/3)O3 and Ba(Zn1/3Nb2/3)O3 at Cryogenic Temperatures

Microwave resonator measurements were performed on high‐performance microwave ceramics Ba(Zn_1/3Ta_2/3)O₃ (BZT) and Ba(Zn_1/3Nb_2/3)O₃ (BZN) containing additives commonly used by commercial manufacturers (i.e., Co, Mn, and Ni). We find that the loss tangent, even in ambient magnetic fields, is dominated by electron paramagnetic resonance (EPR) absorption by exchange‐coupled 3d electrons in transition metal clusters at cryogenic temperatures. The large orbital angular momentum in Co²⁺ and Ni²⁺ ions of L = 3 causes strong anisotropic‐broadened dipolar interactions that extend EPR losses to zero applied field. This effect is greatest in BZN with Co concentrations greater than 0.5 mol%, dominating the losses at liquid nitrogen temperatures (77 K) and below. In samples containing Mn²⁺ ions with L = 0, the dipolar interactions and associated EPR losses in ambient fields are smaller. We show the magnetic‐field‐dependent changes in the EPR losses (i.e., tan δ) and magnetic reactive response (i.e., μ_r) are from the same mechanism, as they follow the Kramers–Kronig relation. Finally, we note that these materials can make ultra‐high Q passive microwave devices with externally controlled transfer functions, as the quality factor (Q) of the composition Ba(Co_1/15Zn_4/15Nb_2/3)O₃ at 77 K can be tuned from 1 100 to 12 000 at 10 GHz by applying practical magnetic fields.     

Understanding the adsorption behavior of oxygen on the 3C–SiC(1 1 0) surface: A first-principles study

The adsorption behavior of atomic oxygen and molecular O₂ on the 3C–SiC(1 1 0) surface is investigated by first-principles calculations. The atomic O prefers to be adsorbed at the C top site (C–O) with adsorption energy of −1.95 eV after zero-point energy correction, followed by the C–O–Si bridge site, Si–O–Si bridge site, and the Si top site (Si–O) with adsorption energies of −1.46, −1.36, and −1.13 eV, respectively. The molecular O₂ separately trapped by the second nearest neighboring C and Si atoms (C–O–O–Si, M4 type) is the most stable configuration with the adsorption energy of −2.46 eV, which is followed by the Si–O–O–Si (M5 type), C–O–O–Si (M3 type), O–Si–O (M2 type), and Si–O=O (M1 type) configurations with the adsorption energies of −2.24, −1.87, −1.07, and −0.75 eV, respectively. All these molecular O₂ adsorption configurations exhibit high tendency to dissociate with the dissociation barriers range of 0.09–0.19 eV. The adsorbed atomic O seems to be easily trapped at the C–O site due to the extremely low diffusion barrier. In addition, the infrared spectra of all the atomic O and molecular O₂ adsorption configurations are predicted and compared with available experimental observations.     

Manipulation of the ratio of Li+/Zn2+ on the structure and persistent luminescence property of Li2Zn0.9992Ge3O8:0.08%Cr3+

Long persistent luminescence (LPL) materials have been widely applied and investigated in the fields of night-safe, bio-fluorescent labeling, and optical anti-counterfeiting because of their unique properties of delayed luminescence. In this work, the focus of this research is to significantly improve the LPL properties of Li₂Zn_0.9992Ge₃O₈:0.08%Cr³⁺ by adjusting the ratio of Li⁺/Zn²⁺. On the one hand, when Li⁺:Zn²⁺ < 2:1 (Li_1.97Zn_1.0292Ge₃O₈:0.08%Cr³⁺), a deep-red LPL is produced in the 650–900 nm band for more than 50 h, which is 2.5 times longer than that without regulation. From another perspective, when Li⁺:Zn²⁺ > 2:1 (Li_2.01Zn_0.9892Ge₃O₈:0.08%Cr³⁺), the intensity of LPL is enhanced about four times compared to unregulated. The relationship between traps and LPL was comprehensively investigated by analyzing thermoluminescence spectra. Biological tissue penetration experiments were performed and a set of anti-counterfeit labels was designed. This research will provide guidance for the design of a novel persistent phosphor for the desired trap depth.