Modeling the effect of surface heterogeneity in equilibrium of heavy metal ion biosorption by using the ion exchange model

Effects of different substrates on the adsorption behavior of supported-adsorbents: A case study of MoS2 for Ag+ adsorption

Supported-adsorbents growing on the substrate in situ are equipped with the advantages of high adsorption capacity, excellent regeneration performance, and adaptability to complex wastewater. However, the effects of substrate on the adsorption properties of supported-adsorbent are rarely considered, which will hinder its development and scale-up applications. In this study, the influences of different substrates (Ti, Mo, W, CC) on the Ag⁺ adsorption behavior of supported-MoS₂ adsorbents were investigated. The adsorption kinetics, adsorption mechanism, and the renewability of these supported-MoS₂ were compared orderly. As a result, MoS₂ grown on a tungsten substrate (MoS₂-W) exhibits a remarkable adsorption capacity for Ag⁺ (1.98 mg cm^-2 and 598.80 mg g^-1), which is 6.38-33 times more than the other three supported-MoS₂. Moreover, the MoS₂-W also possesses an ultrahigh distribution coefficient (24.80 mL cm^-2) for Ag⁺, and the selection coefficient can reach 1984. XRD and electrochemical characterization analysis indicated that Ag⁺ adsorption performance of supported-MoS₂ is positively correlated with the degree of its amorphous structure. Substrate W with the terrific electrical properties which may facilitate the disordered growth of MoS₂, resulting in more active sites exposed, and endow MoS₂-W with outstanding Ag⁺ capture performance. Finally, the supported-MoS₂ retains a high removal efficiency of Ag⁺ after 5 cycles of adsorption and desorption. This study provides a novel perspective for promoting the practical application of supported-sorbents to recycle heavy metals.

CaFu MOF as an efficient adsorbent for simultaneous removal of imidacloprid pesticide and cadmium ions from wastewater

Heavy metal ions and pesticides are the noteworthy toxic substances which must be removed from contaminated water for safeguarding public health. The higher levels of these substances in natural water may adversely affect the human health, climate and the eco-framework. The adsorptive removal of hazardous constituents employing metal organic frameworks has drawn considerable attention of researchers during the last decade. From this point of view, single crystal of calcium fumarate [Ca(C₄H₄O₄)_1.5 (H₂O)(CH₃OH)₂] has been developed and analyzed by single crystal X-ray crystallography which confirmed the formation of 3-D metal organic frameworks (MOFs). The synthesized MOFs was employed for simultaneous adsorptive removal of imidacloprid, a high consumption pesticide, and highly toxic Cd (II) from aqua ecosystem. The effect of variation in experimental conditions such as solution pH, adsorbent dosage, contact time, initial concentration and temperature on adsorption was systematically evaluated. Both the imidacloprid and Cd(II) exhibited maximum adsorption at pH 6.5 and 7.8, respectively. The equilibrium empirical data was fitted into Langmuir, Freundlich and Temkin isotherms. The adsorption capacity of CaFu MOFs was observed to be 467.23 and 781.2 mg g^-1 for imidacloprid and cadmium ions, respectively. The adsorbed pollutants were desorbed from the adsorbent using dilute HCl, and the material was reused for five adsorption-desorption cycles without any appreciable loss of adsorption capacity. Therefore, the 3-D CaFu MOFs could be utilized as a novel material for adsorptive removal of imidacloprid pesticide as well as Cd (II) from wastewater.

Effective removal of radioactive cesium from contaminated water by synthesized composite adsorbent and its thermal treatment for enhanced storage stability

A composite adsorbent for the removal of radioactive cesium (¹³⁷Cs) was synthesized by immobilizing potassium cobalt ferrocyanide in the micro pores of the zeolite chabazite. The synthetically optimized composite adsorbent demonstrates a rapid cesium adsorption rate under both salt-free and high-salt conditions with a high distribution coefficient of cesium (≥10⁵ mL/g). Although both components have the same ion-exchange reaction between potassium and cesium, the reaction by ferrocyanide component was predominant, which derived hundred times higher distribution coefficient of the composite adsorbent than that of pure chabazite. A thermal stabilization process was studied for improving the storage and/or disposal stability of the spent adsorbent. The formation of a eutectic system within the spent adsorbent reduced the stabilization temperature to 1000 °C from 1200 °C. Accordingly, the leaching of cesium was remarkably reduced by the remineralization to the stable pollucite. The stable impregnation of ferrocyanide component in the chabazite pores derived the reduction of cesium volatility enabling the high temperature stabilization method. Our experimental results provide evidence that the composite adsorbent has clear advantages on the cesium removal from contaminated water and its stabilization via thermal-treatment.

Preparation and characterization of amino/thiol bifunctionalized magnetic nanoadsorbent and its application in rapid removal of Pb (II) from aqueous system

To explore the effect of coexisted amino and thiol groups on adsorption of heavy metal, a novel magnetic nanoparticle was prepared by sequentially modification with (3-Chloropropyl) trimethoxysilan, polyetherimide, epichlorohydrin and thiourea. Subsequently, it was characterized by TEM, N₂ adsorption/desorption, FTIR Spectroscopy, zeta potential, and VSM. The maximum adsorption capacity for Pb²⁺, Cd²⁺ and Cu²⁺ reached 110.13 mg·g^-1, 40.23 mg·g^-1 and 29.37 mg·g^-1, respectively. The adsorption of the magnetic nanoparticles with different surface group for heavy metals were compared, which indicated that the amino and thiol group played an important role in the adsorption of heavy metals. Especially, the adsorption capacity increased dramatically after modification with the thiol group, which was attributed to the synergistic coordination of -NH₂ and -SH. The adsorption kinetics is consistent with the quasi-second-order kinetics equation, and the adsorption thermodynamic process is consistent with the Langmuir isotherm equation. The effects of experimental conditions, such as pH, the concentration of metals, adsorption time and temperature, on adsorption of Pb²⁺ were studied in detail. In addition, over 90% of removal rate was remained after 6 cycles. The magnetic nanoadsorbents was a promising nanoadsorbent with high adsorption speed, simultaneous adsorption of various heavy metals, strong anti-interference ability and reusability.

Highly promoted removal of Hg(ii) with magnetic CoFe2O4@SiO2 core–shell nanoparticles modified by thiol groups

A simple and environmentally friendly material, CoFe₂O₄@SiO₂–SH, was prepared successfully with CoFe₂O₄ nanoparticles coated by SiO₂ which was further functionalized with thiol groups (–SH).

Novel application of nanozeolite for radioactive cesium removal from high-salt wastewater

Finding a striking peculiarity of nanomaterials and evaluating its feasibility for practical use are interesting topics of research. We investigated the application of nanozeolite's outstanding reactivity for a rapid and effective method for radioactive cesium removal in the wastewater generated from nuclear power plant accident, as a new concept. Extremely fast removal of cesium, even without stirring, was achieved by the nanozeolite at efficiencies never observed with bulk materials. The nanozeolite reached an adsorption equilibrium state within 1 min. Cesium adsorption by nanozeolite was demonstrated at reaction rates of orders of magnitude higher than that of larger zeolite phases. This observation was strongly supported by the positive correlation between the rate constant ratio (k2,bulk/k2,nano) and the initial Cs concentrations with a correlation coefficient (R(2)) of 0.99. A potential drawback of a nanoadsorbent is the difficulty of particle settling and separation because of its high dispersivity in solution. However, our results also demonstrated that the nanozeolite could be easily precipitated from the high-salt solution with ferric flocculant. The flocculation index reached a steady state within 10 min. A series of our experimental results met the goal of rapid processing in the case of emergency by applying the well-suited nanozeolite adsorption and flocculation.

Competitive adsorption of metals onto magnetic graphene oxide: comparison with other carbonaceous adsorbents

Competitive adsorption isotherms of Cu(II), Pb(II), and Cd(II) were examined on a magnetic graphene oxide (GO), multiwalled carbon nanotubes (MWCNTs), and powered activated carbon (PAC). A series of analyses confirmed the successful synthesis of the magnetic GO based on a simple ultrasonification method. Irrespective of the adsorbents, the adsorption was highly dependent on pH, and the adsorption was well described by the Langmuir isotherm model. The maximum adsorption capacities of the adsorbents were generally higher in the order of Pb(II) > Cu(II) > Cd(II), which is the same as the degree of the electronegativity and the hydrated radius of the metals, suggesting that the metal adsorption may be governed by an ion exchange between positively charged metals and negatively charged surfaces, as well as diffusion of metals into the surface layer. The adsorption of each metal was mostly lower for multi- versus single-metal systems. The antagonistic effects were influenced by solution pH as well as the type of metals, and they were higher in the order of the magnetic GO > MWCNT > PAC. Dissolved HS played a greater role than HS adsorbed onto the adsorbents, competing with the adsorption sites for metal complexation.

Binding of bivalent metal cations by α-l-guluronate: insights from the DFT-MD simulations

Theoretically calculated free energy profiles give insight into the molecular aspects of metal ion binding by uronate biopolymers.

Versatile heavy metals removal via magnetic mesoporous nanocontainers

Versatile heavy metal ions removal is performed via iron oxide core mesoporous silica shell nanocontainers functionalized with diethylene triamine pentaacetic acid.

Nickel oxide grafted andic soil for efficient cesium removal from aqueous solution: adsorption behavior and mechanisms

An andic soil, akadama clay, was modified with nickel oxide and tested for its potential application in the removal of cesium from aqueous solution. Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and powder X-ray diffraction (XRD) results revealed the nickel oxide was successfully grafted into akadama clay. N2 adsorption-desorption isotherms indicated the surface area decreased remarkably after modification while the portion of mesopores increased greatly. Thermogravimetric-differential thermal analysis (TG-DTA) showed the modified akadama clay had better thermostability than the pristine akadama clay. Decreases in cation exchange capacity (CEC) and ζ-potential were also detected after the modification. Adsorption kinetic and isotherm studies indicated the adsorption of Cs+ on the modified akadama clay was a monolayer adsorption process. Adsorption capacity was greatly enhanced for the modified akadama clay probably due to the increase in negative surface charge caused by the modification. The adsorption of Cs+ on the modified akadama clay was dominated by an electrostatic adsorption process. Results of this work are of great significance for the application of akadama clay as a promising adsorbent material for cesium removal from aqueous solutions.

Binding of heavy metals by algal biosorbents. Theoretical models of kinetics, equilibria and thermodynamics

Biosorption is an extensively studied technology applied for the removal of heavy metal ions and other pollutants from aqueous solutions. Most biosorption research is focused on the experimentally measured sorption isotherms, kinetics and thermodynamics. The aim of this paper is to review a class of theoretical models developed for the interpretation of such experimental data related to biosorption of metal cations by alginate-containing sorbents (e.g. algal biosorbents). The focus is put on: (i) modeling the biosorption equilibrium isotherms (including the description of the pH and ionic strength effects); (ii) thermodynamics of biosorption; (iii) kinetics of biosorption; and (iv) metal ion binding modes. This review facilitates the choice of the model suitable for the given type of data and describes the most common mistakes made during the data analysis (e.g. the use of incorrect or oversimplified models).

Adsorption of cesium from aqueous solution using agricultural residue--walnut shell: equilibrium, kinetic and thermodynamic modeling studies

A novel biosorbent derived from agricultural residue - walnut shell (WS) is reported to remove cesium from aqueous solution. Nickel hexacyanoferrate (NiHCF) was incorporated into this biosorbent, serving as a high selectivity trap agent for cesium. Field emission scanning electron microscope (FE-SEM) and thermogravimetric and differential thermal analysis (TG-DTA) were utilized for the evaluation of the developed biosorbent. Determination of kinetic parameters for adsorption was carried out using pseudo first-order, pseudo second-order kinetic models and intra-particle diffusion models. Adsorption equilibrium was examined using Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. A satisfactory correlation coefficient and relatively low chi-square analysis parameter χ(2) between the experimental and predicted values of the Freundlich isotherm demonstrate that cesium adsorption by NiHCF-WS is a multilayer chemical adsorption. Thermodynamic studies were conducted under different reaction temperatures and results indicate that cesium adsorption by NiHCF-WS is an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

Sorption of lead, copper, and cadmium by calcium alginate. Metal binding stoichiometry and the pH effect

Binding of heavy metal ions by calcium alginate has been described in the literature with many different models. In the present study, two most basic models were used to systematically compare their simultaneous description of metal uptake dependence on pH and metal ion concentration in the bulk solution. The experimental datasets corresponding to the binary sorption systems containing protons and heavy metal ion (cadmium, lead, or copper) were taken from the literature. The applicability and limitations of both models are discussed. Neither of the models gave a completely satisfactory description of all data. The two-site occupancy model yielded better results compared to the one-site occupancy model when considering the coherence of the parameters (e.g., affinity constants) but the quality of the obtained fits is similar in both cases.

Effective heavy metal removal from aqueous systems by thiol functionalized magnetic mesoporous silica

A thiol-functionalized magnetic mesoporous silica material (called SH-mSi@Fe(3)O(4)), synthesized by a modified Stöber method, has been investigated as a convenient and effective adsorbent for heavy metal ions. Structural characterization by powder X-ray diffraction, N(2) adsorption-desorption isotherm, Fourier transform infrared spectroscopy and elemental analyses confirms the mesoporous structure and the organic moiety content of this adsorbent. The high saturation magnetization (38.4 emu/g) make it easier and faster to be separated from water under a moderate magnetic field. Adsorption kinetics was elucidated by pseudo-second-order kinetic equation and exhibited 3-stage intraparticle diffusion mode. Adsorption isotherms of Hg and Pb fitted well with Langmuir model, exhibiting high adsorption capacity of 260 and 91.5mg of metal/g of adsorbent, respectively. The distribution coefficients of the tested metal ions between SH-mSi@Fe(3)O(4) and different natural water sources (groundwater, lake water, tap water and river water) were above the level of 10(5)mL/g. The material was very stable in different water matrices, even in strong acid and alkaline solutions. Metal-loaded SH-mSi@Fe(3)O(4) was able to regenerate in acid solution under ultrasonication. This novel SH-mSi@Fe(3)O(4) is suitable for repeated use in heavy metal removal from different water matrices.