Divalent Heavy Metal Research Articles

Microstructural Evaluation and Linkage to the Engineering Properties of Metal-Ion-Contaminated Clay

The rapid progress of urbanization and industrialization has led to the accumulation of large amounts of metal ions in the environment. These metal ions are adsorbed onto the negatively charged surfaces of clay particles, altering the total surface charge, double-layer thickness, and chemical bonds between the particles, which in turn affects the interactions between them. This causes changes in the microstructure, such as particle rearrangement and pore morphology adjustments, ultimately altering the mechanical behavior of the soil and reducing its stability. This study explores the effects of four common metal ions, including monovalent alkali metal ions (Na+, K+) and divalent heavy metal ions (Pb2+, Zn2+), with a focus on how ion valence and concentration impact the soil’s microstructure and mechanical properties. Microstructural tests show that metal ion incorporation reduces particle size, increases clay content, and transforms the structure from layered to honeycomb-like. Small pores decrease while large pores dominate, reducing the specific surface area and pore volume, while the average pore size increases. Although cation exchange capacity decreases, cation adsorption density per unit surface area increases. Monovalent ions primarily disperse the soil structure, while divalent ions induce coagulation. Macro-mechanical tests reveal that metal ion contamination reduces porosity under loading, with compressibility rises as the ion concentration increases. Soils contaminated with alkali metal ions shows higher compression coefficients at all loads, while heavy metal ions cause higher compression under lower loads. Shear strength, the internal friction angle, and cohesion in metal-ion-contaminated clay decrease compared to uncontaminated field-state clay, with greater declines at higher ion concentrations. The Micropore Morphology Index and hydro-pore structural parameter effectively characterize both micro- and macrostructural properties, establishing a quantitative relationship between HPSP and the engineering properties of metal-ion-contaminated clay.

The superior adsorption capacity of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3 for five divalent heavy metal cations and the adsorption mechanism of biogenic α-Mn2O3: Experimental and DFT investigations

Manganese oxides play a crucial role in the adsorption of heavy metals in the environment. However, there is currently a lack of information regarding the comparative adsorption efficiency of heavy metals between biogenic and chemogenic manganese oxides. In this work, we compared the adsorption performance of biogenic and chemogenic α-Mn2O3 towards Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II). Mineral characterization analyses revealed that biogenic α-Mn2O3 exhibited a polycrystalline nature, whereas chemogenic α-Mn2O3 displayed a monocrystalline nature with a lower impurity content compared to biogenic α-Mn2O3. Under acidic conditions, biogenic α-Mn2O3 demonstrated a significantly higher adsorption capacity, ranging from 3 to 6 times greater than its chemogenic counterpart, within an initial heavy metal concentration range of 0.2–1.0 mM. This superiority can be attributed to the presence of more abundant functional groups and a greater content of hydroxyl O species on the surface of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3. During the adsorption process of biogenic α-Mn2O3, there were observed ionic exchanges between Mn(II) and these cations. More importantly, biogenic α-Mn2O3 bound with these cations probably through the formation of -O/OH/S complexes. The adsorption selectivity of biogenic α-Mn2O3 towards the five heavy metals was experimentally determined to follow the order of Ni(II) > Pb(II) > Cu(II) > Zn(II) > Cd(II). The electronic interaction between biogenic α-Mn2O3 and these cations indicated that Ni(II), Pb(II) and Cu(II) were more likely to share electrons with O atoms on the surface of biogenic α-Mn2O3 compared to Zn(II) and Cd(II).

Solid–liquid partitioning and speciation of Pb(II) and Cd(II) on goethite under high pH conditions, as examined by subnanomolar heavy metal analysis, X-ray absorption spectroscopy, and surface complexation modeling

The adsorption of heavy metals on iron oxides generally increases with pH and is almost complete at neutral to slightly alkaline pH. However, almost complete adsorption on a linear scale does not imply sufficient removal of the heavy metals in terms of their toxicity. Here, we elucidated the chemical reactions that determine the solid–liquid partitioning of Pb(II) and Cd(II) on goethite at high pH. While the removal of both heavy metals was almost complete on a linear scale above pH 7 for Pb(II) and pH 9 for Cd(II), the dissolved metal concentrations decreased on a logarithmic scale with pH, reaching minima at around pH 10 for Pb(II) and pH 10–11 for Cd(II), and then they increased with pH thereafter. The XAFS spectra of Pb(II)- or Cd(II)-adsorbed goethite prepared at pH > 11 were almost the same as those at neutral pH, suggesting that removal of the heavy metals from solution was achieved by a single adsorption reaction over the entire pH range. Based on the observed macroscopic and microscopic adsorption behaviors at high pH, a robust surface complexation model was developed to predict the solid–liquid partitioning of divalent heavy metals over the entire pH range.

A novel method for MSWI fly ash resource based on calcium component regulation and CO2 mineralization

While accelerated carbonation has been widely studied for the disposal of municipal solid waste incineration (MSWI) fly ash, there has been limited consideration for high-value applications of carbonization products and environmental risks. High-performance CaCO3 ceramics and cement pastes were produced in a low-carbon and sustainable manner by combining calcium extraction, CaCO3 crystal transformation, and cold sintering to reduce the environmental risks associated with heavy metals in MSWI fly ash. The mechanisms of CaCO3 crystal transformation, dissolution-reprecipitation, stabilization of heavy metals (HMs), and hydration of acid-leached solids were explored. Experiments and density functional theory results show that calcite has a stabilizing impact on divalent HMs (Ba, Cd, Ni, Pb, and Zn) (Ei < 0). According to the principles of thermodynamics and crystallography, temperature, pH, and reaction time affected the gradual transition of Vaterite to calcite. The optimal reaction conditions were 10 % ammonia water and 10 min reaction time. Vaterite in CaCO3 ceramics demonstrated outstanding mechanical properties (compressive strength > 265 MPa) based on pressure solution creep. The potential risk of acid-leached solids in alkaline environments was low (The overall pollution toxicity index is only 15). Calcium sulfate (>50 %) in acid-leached solid reacted with aluminate to form ettringite. Strongly alkaline cement pastes with high compressive strengths (>40 MPa) generated from acid-leached cementitious materials posed a low risk of HMs leaching. Throughout the disposal process, HMs leaching concentration in leachate and reaction solution fulfilled Class III groundwater criteria (GB/T 14848–2017). This approach offers environmental benefits and demonstrates broad applicability across diverse alkaline solid waste types.

Sequestration of divalent heavy metal ions from aqueous environment by adsorption using biomass-bentonite composites as potential adsorbent: Equilibrium and kinetic studies

Hybrid clay adsorbents have been investigated in recent studies as cheap and effective adsorbents for eliminating micropollutants, such as heavy metal ions from aqueous solution. Here, we modified bentonite (BEN) with palm kernel shell and groundnut shell by calcination to obtain palm kernel shell-modified bentonite (BPKS) and groundnut shell-modified bentonite (BGS). We studied the batch equilibrium adsorption of Pb2+, Cd2+ and Ni2+ ions under the influence of dosage, solution pH, contact time and concentration. Under these conditions, we found that the modified adsorbents (BGS and BPKS) had a higher equilibrium adsorption (qe) for the metal ions than unmodified BEN. BEN exhibited Langmuir adsorption capacities (Qo) of 32.47, 14.04 and 14.16 mg/g for Pb2+, Cd2+ and Ni2+, respectively. BGS and BPKS had Qo values of 29.15, 14.27, 16.61 and 31.75, 17.67, 15.625 mg/g for Pb2+, Cd2+, Ni2+, respectively. Investigations revealed that the rate of adsorption on the three adsorbents is best described by a pseudo-second-order kinetic model, with R2 values ≥ 0.9; the intra-particle diffusion model establishes a surface interaction mechanism involving the exchange of electrons between the surfaces of the adsorbents and the adsorbate. Scanning electron microscopy results suggest porous and heterogeneous adsorbent surfaces, indicating a physio-sorption phenomenon. The modifications increased the surface area of BEN from 78.435 to 194.850 and 140.650 m2/g in BGS and BPKS, respectively, using BET surface area analysis. However, the average pore width of BEN reduces from 3.8 to 3.3 nm in both BGS and BPKS. Also, the modification enhanced the cation exchange capacity in BPKS only. The findings from this study offered invaluable insights into how biomass can enhance the physicochemical properties of BEN, as needed for practical environmental application and/or optimization, during the removal of Pb2+, Cd2+ and Ni2+ ions from aqueous media.

Divergent redistribution behavior of divalent metal cations associated with Fe(II)-mediated jarosite phase transformation

The Fe(II)/Fe(III) cycle is an important driving force for dissolution and transformation of jarosite. Divalent heavy metals usually coexist with jarosite; however, their effects on Fe(II)-induced jarosite transformation and different repartitioning behavior during mineral dissolution-recrystallization are still unclear. Here, we investigated Fe(II)-induced (1 mM Fe(II)) jarosite conversion in the presence of Cd(II), Mn(II), Co(II), Ni(II) and Pb(II) (denoted as Me(II), 1 mM), respectively, under anaerobic condition at neutral pH. The results showed that all co-existing Me(II) retarded Fe(II)-induced jarosite dissolution. In the Fe(II)-only system, jarosite first rapidly transformed to lepidocrocite (an intermediate product) and then slowly to goethite; lepidocrocite was the main product. In Fe(II)–Cd(II), -Mn(II), and -Pb(II) systems, coexisting Cd(II), Mn(II) and Pb(II) retarded the above process and lepidocrocite was still the dominant conversion product. In Fe(II)–Co(II) system, coexisting Co(II) promoted lepidocrocite transformation into goethite. In Fe(II)–Ni(II) system, jarosite appeared to be directly converted into goethite, although small amounts of lepidocrocite were detected in the final product. In all treatments, the appearance or accumulation of lepidocrocite may be also related to the re-adsorption of released sulfate. By the end of reaction, 6.0 %, 4.0 %, 76.0 % 11.3 % and 19.2 % of total Cd(II), Mn(II), Pb(II) Co(II) and Ni(II) were adsorbed on the surface of solid products. Up to 49.6 %, 44.3 %, and 21.6 % of Co(II), Ni(II), and Pb(II) incorporated into solid product, with the reaction indicating that the dynamic process of Fe(II) interaction with goethite may promote the continuous incorporation of Co(II), Ni(II), and Pb(II).

Studies on adsorption properties of magnetic composite prepared by one-pot method for Cd(II), Pb(II), Hg(II), and As(III): Mechanism and practical application in food

A one-pot synthesis afforded a magnetic, crosslinked polymer adsorbent (m-P6) with a variety of functional groups to realize simultaneous adsorption of Cd2+, Pb2+, Hg2+, and As3+. The material was characterized by TEM-EDS, XRD, FT-IR, VSM, and XPS. Kinetic and isothermal analyses suggested mainly chemisorption processes of heavy metal ions that form multiple layers on heterogeneous surfaces. Theoretical adsorption capacities calculated by a pseudo-2nd-order kinetic model and the Sips isothermal model were 282.88 mg/g for Cd2+, 326.18 mg/g for Pb2+, 117.85 mg/g for Hg2+, and 320.29 mg/g for As3+. m-P6 not only can efficiently adsorb divalent heavy metals (Cd2+, Pb2+, Hg2+), but also demonstrate a process of adsorption-driven catalytic oxidation by single-electron transfer (SET) from As3+ to As5+. In application, in addition to adsorption in water, m-P6 is capable of minimizing matrix interference, and extracting trace heavy metals in a complex environment (cereal) through easy operations for improving the detection accuracy, as well as it is potential for application in detection of trace heavy metals in foodstuffs. m-P6 can be readily regenerated and efficiently recycled for 5 cycles using eluent E12 and dilute acid.

A plasmid containing the human metallothionein-II gene selectively distinguishes trivalent lanthanum from several divalent heavy metal cations during monoclonal antibody-assisted agarose gel electrophoresis.

Trivalent lanthanide ions are known for their ability to interact with calcium-binding sites in various proteins. There is a need to assess the bioavailability of lanthanides and other heavy metals introduced into the body as components of implants or as contrast agents. This study aimed to develop a method to address bioavailability and/or presence of trivalent lanthanide ions by examining electrophoretic mobility in an agarose gel of a plasmid harboring the human metallothionein-II gene (hMT-II). Mobility of the plasmid was specifically altered by a monoclonal antibody raised against the zinc-binding transcription factor that controls the activity of the hMT-II gene. This study showed that the plasmid acquired a lanthanide-specific mobility pattern that allowed the presence of lanthanide ions to be readily determined in a 0.8% agarose gel. These findings suggest that this plasmid/monoclonal antibody combination under selected conditions may be useful in industrial, environmental, and biomedical settings to identify, separate, or capture lanthanide ions in complex mixtures that contain an array of metal ions.

First-principles study on the adsorption of divalent heavy metal ions by black phosphorus in water

With the rapid development of electronics, the application and research of two-dimensional materials have been at the forefront of the world’s scientific research. Black phosphorus (BP) has the advantages of large specific surface area, anisotropy, band tunability, high electrical conductivity and high theoretical specific capacity, which make it very promising for research in the fields of medicine, aerospace and electrochemistry. This paper calculates the electronic structure and adsorption properties of BP in water for different heavy metal ions of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text], including adsorption energy, bandgap, electron density and Mulliken population analysis, based on the first-principles approach of density generalized theory. First principles are quantum mechanical calculations based on density functional theory (DFT), which is a dominant well-developed method in the field of materials simulations, with low errors and high efficiency, especially in systems containing metallic particles. The results showed that the Pb[Formula: see text] adsorption system in water was more stable than the Hg[Formula: see text] adsorption system and the Cd[Formula: see text] adsorption system. The bandgap values of 0.617, 0.785 and 0.715[Formula: see text]eV of BP after adsorption of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text] in water are smaller compared to 0.891[Formula: see text]eV of intrinsic BP, and its properties change from direct bandgap semiconductor to indirect bandgap semiconductor. The higher the stability of a system for the adsorption of different heavy metal ions by BP, the higher the internal electron activity of the adsorption system and the amount of electron transfer. Meanwhile, it is concluded that the electrons mainly transfer from P to heavy metal ions in all the adsorption systems. The electron transfer of the BP-Pb[Formula: see text], Hg[Formula: see text], and Cd[Formula: see text] adsorption system occurs mainly in the p, s, and s/p orbitals, respectively. The above content investigated the electronic structure changes and internal electron transfer of heavy metal ions adsorbed by black phosphorus in water, expecting to provide a new reference basis for the detection of heavy metal ions in industrial wastewater using black phosphorus.

Immobilization and characteristics of potassium magnesium phosphate on copper ions

Potassium magnesium phosphate cement (MKPC) can be used in the fields of solidification of heavy metal ions in hazardous waste. Scholars have demonstrated that MKPC has a good curing effect on Cu2+. However, Cu2+ can lead to a significant decrease in the mechanical properties of solidified matrix, resulting in a decrease in compressive strength and even fragility. In view of the existing problems in the current research, a method of MgKPO4·6H2O strengthening MKPC solidifying Cu2+ is proposed to solve the problem of significant mechanical property loss of solidified matrix in the later stage, while also ensuring excellent solidifying effect. The evolution process and morphology of MKPC products after solidifying Cu2+ are studied. In addition, the long-term solidifying effect of MKPC is also tested. The results shows that MKPC with MgKPO4·6H2O has a relatively stable 180d solidifying effect on Cu2+, with a leaching concentration of 7.64 mg/L, which meet the standard requirements. The products of MKPC solidified Cu2+ include Mg.95Cu.05O and Cu3(PO4)2. The process of strengthening and solidifying Cu2+ by MKPC with MgKPO4·6H2O includes adsorption, chemical bond and physical encapsulation. MgKPO4·6H2O provides an auxiliary alkaline environment for the solidification of Cu2+ and has adsorption properties, improving the immobilization effect of Cu2+ and achieving long-term immobilization stability. This study provides a new idea for the solidification of other waste containing divalent heavy metal ions using MKPC with MgKPO4·6H2O.

Dual crosslinking of low-methoxyl pectin by calcium and europium for the simultaneous removal of pharmaceuticals and divalent heavy metals

The contamination of water resources by heavy metals and pharmaceuticals is a significant threat to human health and the environment. Pectin is a promising material for removing heavy metals from water. However, its removal efficacy for other types of pollutants is limited. In this study, we developed a novel approach to enhance the remediation capacity of pectin (with a low degree of methylation) by crosslinking it with different agents: calcium, europium, and their combination. We performed scanning electron microscopy, infrared spectroscopy, and X-ray diffraction experiments to understand the molecular structure of pectin after gelation with the three agents. Our results showed that calcium, europium, and their combination all induce the gelation of pectin. However, the reticulated pectin structures exhibited significant structural differences depending on the type of crosslinking agent used, which affected the adsorption capacity. Specifically, calcium cations partially formed a crystalline “egg-box” structure, whereas europium cations produced a more homogeneous network without crystalline regions. The dual-crosslinking system comprising calcium and europium cations resulted in an intermediate network with both crystalline and amorphous regions. Our findings suggest that dual-cross-linked pectin is a highly effective adsorbent for the simultaneous removal of both heavy metals and pharmaceutical products. This novel approach of crosslinking pectin with multiple agents has the potential to significantly enhance its remediation capacity, offering a promising solution for the simultaneous removal of multiple pollutants from water.

A fully π-conjugated covalent organic framework with dual binding sites for ultrasensitive detection and removal of divalent heavy metal ions

Covalent organic frameworks (COFs) have become a promising candidate for the remediation of heavy metal pollution. However, researches on COF adsorbents still have challenges on maintaining good optical properties and adsorption performance under harsh conditions. Herein, a fully π-conjugated COF with dual binding sites (Bpy-sp2c-COF) is reported for rapid fluorescence recognition and enhanced adsorption towards divalent heavy metal ions. The vinylene-linkage lattice shows strong luminescence and excellent stability in both strong acidity and basicity. Bpy-sp2c-COF demonstrates not only nanomolar-scale detection of divalent heavy metal ions, but also good adsorption capacity (Hg2+ 718.48, Ni2+ 278.64, Cu2+ 260.11, and Co2+ 126.23 mg/g). Experimental and theoretical studies reveal the intramolecular charge transfer as the fluorescence quenching mechanism. Further simulation results demonstrate the cyano and bipyridine groups on the lattice can act as dual binding sites for divalent heavy metal ions. Experimental results confirmed the adsorption capacity of Bpy-sp2c-COF superior to that of COFs with either cyano groups (Hg2+ 415.34, Ni2+ 165.60, Cu2+ 160.55, and Co2+ 73.14 mg/g), or bipyridine groups (Hg2+ 369.25, Ni2+ 133.41, Cu2+ 133.32, and Co2+ 69.23 mg/g). Besides, robust regeneration of the adsorbent could be achieved over 10 cycles. The fully π-conjugated COF with dual binding sites provides a new approach for designing next-generation sensors and adsorbents with excellent performances.

MICROBIAL BIOREMOVAL OF DIVALENT TOXIC METALS

The problems of polymetallic wastewater treatment from mining enterprises as well as the accumulation of organic waste are acute worldwide. The application of any existing methods of wastewater purification is ineffective and impossible due to the huge volumes and high concentrations of metals. Similarly, modern methods are ineffective for the treatment of huge amounts of organic waste. Therefore, there is a necessity to develop novel environmental biotechnologies providing the simultaneous degradation of organic waste and detoxification of toxic metals. The purpose of the work was to theoretically substantiate and experimentally confirm the possibility of toxic divalent cations removal using dissimilatory sulfate reduction via anaerobic fermentation of ecologically hazardous model organic waste. Colorimetric and potentiometric methods were used for pH and redox potential measurement; volumetric and chromatographic methods – to control volume and composition of synthesized gas; permanganate method – to determine the concentration of dissolved organic carbon (DOC); photocolorimetric method via the qualitative reaction with Nessler’s reagent was used to determine the concentration of ammonium ions. The Co2+ and Ni2+ content in medium was determined by a colorimetric method with 4-(2-pyridylazo)resorcinol (PAR). Fermentation parameters were calculated with the use of mathematical and statistical ones. Modified Postgate B medium with different sources of carbon and energy (potatoes, alanine, and meat) was used for cultivation of dissimilatory sulfate reducing bacteria. The anaerobic microbiome obtained from the sludge of methane tanks showed high efficiency to remove Co2+ and Ni2+ from the liquid medium. The highest efficiency (100% in 9 days) was observed when alanine was used as a source of carbon and energy. The slowest metal precipitation process occurred using meat (20 days). Also, the use of a protein substrate did not provide the expected alkalinization of the medium, which could significantly accelerate the process of metal precipitation. The precipitation of cobalt and nickel cations during the hydrogen fermentation of potato starch was complicated by acidification of the medium, but it was equally effective when the pH was adjusted. The proposed approach, the slow dissimilatory sulfate reduction, due to the sparingly soluble calcium sulfate as electron acceptor, can be used as a basis for the development of new biotechnologies for the treatment of wastewater contaminated with divalent heavy metals with the simultaneous treatment of ecologically hazardous compounds.

#2981 IRON DEFICIENCY AND CADMIUM LEVELS IN KIDNEY TRANSPLANT RECIPIENTS

Abstract Background and Aims A higher plasma level of cadmium, a nephrotoxic divalent heavy metal, has been associated with an increased risk of graft failure in kidney transplant recipients (KTRs). The drivers of cadmium toxicity in KTRs are incompletely understood. We hypothesize that iron deficiency (ID) increases cadmium absorption and accumulation by upregulation of divalent metal transporters. Here, we first investigated whether ID is associated with higher plasma cadmium levels. As increased cadmium levels have previously been associated with cancer, cardiovascular disease, and diabetes in other populations, we also examined whether plasma cadmium levels are associated with all-cause mortality in KTRs. Method We used data from stable KTRs ≥1 year after transplantation who participated in the TransplantLines Food and Nutrition Cohort study. Plasma cadmium and iron status parameters, i.e., ferritin, iron, and transferrin saturation (TSAT), were measured at baseline. ID was defined as TSAT&amp;lt;20% and ferritin &amp;lt;300 µg/L. Linear regression analyses were applied to study the association between iron status parameters and cadmium levels. Multivariable Cox regression analyses were used to investigate the association of plasma cadmium levels with all-cause mortality, adjusted for age, sex, BMI, smoking status, history of cardiovascular disease, glucose, HbA1c, systolic blood pressure, eGFR, cholesterol, and ID at baseline. In sensitivity analyses, we repeated these analyses using an alternative definition of ID, TSAT&amp;lt;20% and ferritin&amp;lt;100 µg/L (IDalt). Results We included 670 KTRs (age 53±13 years, 58% males, median 5.4 (IQR, 1.9-11.7) years after transplantation). KTRs with ID (30% of all KTRs, median plasma cadmium level 63 (IQR, 48-76) ng/L) had higher cadmium levels than KTRs without ID (median 56 (IQR, 42-75) ng/L, P = 0.01, Figure 1). ID was not associated with plasma cadmium after adjustment for age, sex, and smoking status. However, within the ID group, TSAT (β = -0.016, P = 0.01) and serum iron (β = -0.023, P = 0.01) were inversely associated with log-transformed cadmium levels, independently of age, sex, and smoking status. Sensitivity analysis yielded similar results: KTRs with IDalt (23% of all KTRs) had higher cadmium levels than KTRs without IDalt (median 61 (IQR, 49-76) ng/L vs median 57 (IQR, 42-75) ng/L, P = 0.03). Furthermore, in Cox regression analysis, KTRs in the highest tertile of plasma cadmium levels (70 ng/L to 330 ng/L) had an increased risk of mortality (hazard ratio 2.80, 95%CI 1.47-5.36, P = 0.01) compared to KTRs in the lowest cadmium tertile (19 ng/L to 48 ng/L) during a median follow-up of 4.9 (IQR, 3.5-5.5) years. No significant interaction by iron status was observed for the association between plasma cadmium and mortality. Conclusion KTRs with ID had higher cadmium levels than KTRs without ID, and higher plasma cadmium levels were independently associated with a higher mortality risk. The association of cadmium with mortality was not different between individuals with and without ID at baseline. Further investigations should determine whether ID correction prevents cadmium accumulation in KTRs.

Probing interfacial water structure induced by charge reversal and hydrophobicity of silica surface in the presence of divalent heavy metal ions using sum frequency generation spectroscopy

HypothesisAdsorption of divalent heavy metal ions (DHMIs) at the mineral–water interfaces changes interfacial chemical species and charges, interfacial water structure, Stern (SL), and diffuse (DL) layers. These molecular changes can be detected by probing changing orientation and hydrogen-bond network of interfacial water molecules in response to changing local charges and hydrophobicity. ExperimentsSum-frequency generation (SFG) spectroscopy was used to probe changes in vibrational resonances of interfacial OH vs. DHMI concentration and pH. SFG spectra were deconvoluted using the measured surface potential and maximum entropy method in conjunction with the electrical double-layer theory for the SL and DL structures and correlated by hydrophobicity. FindingsThree surface charge reversals (CRs) were detected at low (CR1), medium (CR2), and high (CR3) pHs. Unlike CR1, SFG signals were minimized at CR2 and CR3 for DHMIs-silica systems highlighting considerable alterations in the structure of interfacial waters due to the inner-sphere sorption of metal hydroxo complexes. SFG results showed “hydrophobic-like” stretching modes at > 3600 cm−1 for Pb-, Cu-, and Zn-treated silica. However, contact angle measurements revealed the hydrophobization of silica only in the presence of Pb(II), as confirmed by an in-depth SFG analysis of the hydrogen-bond network of the interfacial water molecules in the SL.

Selective removal of copper from heavy-metals-containing acidic solution by a mechanochemical reduction with zero-valent silicon

It is always a challenge to deal with industrial wastewater containing heavy metals. Selective removal and recovery of valuable metals such as copper particularly from acidic solutions are very important from both stances of resource supplying and environmental purification. Among all the divalent heavy metals, copper has the potential of being reduced to monovalent state. A new approach was proposed to ball mill zero-valent silicon (ZVS) in CuSO4 solution and the solutions containing multi-metal ions to serve the purpose. In this study, both quantitative and qualitative data were reported on the induced mechanochemical reduction reaction to convert Cu2+ into Cu2O by ball milling with ZVS. Experimental parameters such as milling time and Si to Cu ratio were found to play important role in stimulating the reaction, and as a result, 97.32% Cu2+ was removed from the solution under Si/Cu molar ratio of 100. Even at a high concentration of sulfuric acid up to 4.6 mol/L, the copper removal percentage maintained a high value of 82.57%. Furthermore, in the sulfate solutions containing several other heavy metals of Zn, Mn, Ni, Cd, Co, Fe etc., the reduction reaction by zero-valent silicon occurred only on Cu2+ with other heavy metal ions remaining in the solutions. The feasibility of this technology has been verified by treating a leaching solution of NiS mineral, from which copper has been removed selectively from nickel, iron etc. This research may serve another purpose for applying waste silicon from the solar energy devices after lifetime in the future.

The material potential and application of activated carbon from nut shells: Mini review

This study was given an overview of nutshell-activated carbon. Nutshell was examined as potential adsorbents for several pollutants such as MB, CR, RB-19, RR 198 by researchers. In addition, activated carbon was used to remove other divalent heavy metals in wastewater. The characteristic functional groups of the material were included OH, C = O, CO, CH, CC, C = C groups. The crystal structure of the material was shown at 2θ = 20°-30°, and 40°-50° to represent the semi-crystalline structure of activated carbon. The adsorption capacity was recorded: organic dyes (30–500 mg/g, heavy metals (10–400 mg/g), phenol (5–35 mg/g) and resistance birth (100–350 mg/g). The PSO, Langmuir, and Freundlich models describe the adsorption process.

Combination mechanism of the ternary composite based on Fe3O4-chitosan-graphene oxide prepared by solvothermal method

Magnetic nanohybrid combining chitosan and graphene have demonstrated promising application in environmental remediation. Herein, ternary composite MCG based on Fe3O4, chitosan (CS) and graphene oxide (GO) was facilely prepared via solvothermal method. The as prepared composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman, Brunauer/Emmett/Teller-Barret/Joyner/Halenda (BET-BJH) and thermo gravimetric-differential thermal analysis (TG-DTA). The combination mechanism of MCG was unveiled via employing the hard-soft acid-base (HSAB) theory and spectroscopic investigations including X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible (UV–Vis) and fluorescent emission spectra. Particularly, combination mechanism of MCG was elucidated by the probable site to site interaction of the couplet components in MCG, as follows. (1) CS-Fe3O4. The primary interaction is N(NH2)-Fe(III), electron donates from N to Fe, transforming one half of the amino groups of chitosan into positive N+. (2) GO-CS. Amidation reaction is the primary interaction form, converting the other half of the amino groups of chitosan into –C(O)NH–. (3) GO-Fe3O4. Dominant interactions are those of epoxy, hydroxyl and aromatic ring with Fe(III). Moreover, MCG exhibits fair adsorption performance on divalent heavy metals in six consecutive cycles. These explorations may shed light on the design of efficient adsorbent based on Fe3O4-chitosan-graphene architecture.

Interface catalytic regulation via electron rearrangement and hydroxyl radicals triggered by oxygen vacancies and heavy metal ions.

Although the enhanced intrinsic activities of some nano-metal oxides are obtained by manufacturing oxygen vacancies (OVs), the effect of multiple roles of OVs is ambiguous. Herein, an interface catalytic regulation via electron rearrangement and hydroxyl radicals (˙OH) was proposed with the designed ZrO2 hollow sphere rich in OVs (Vo-rich ZrO2). Surprisingly, it was shown that the catalytic ability of Vo-rich ZrO2 was 9.9 times higher than that of ZrO2 with little OVs in electrochemical catalytic reduction of Pb(ii). It was found that the generation of Zr2+ and Zr3+ caused by OVs results in the rearrangement of abundant free electrons to facilitate the catalytic reaction rates. The longer bond length between Vo-rich ZrO2 and reactants, and the lower adsorption energy are beneficial for reactants to desorb, improving the conversion rates. Besides, the produced ˙OH were captured which were induced by OVs and trace divalent heavy metal ions in in situ electron paramagnetic resonance (EPR) experiments, contributing to lowering the energy barriers. This study not only revealed the enhanced interface catalytic effect of electron rearrangement and generated ˙OH triggered by OVs, but also provided unique insights into interface catalytic regulation on nano-metal oxides simulated by OVs.

Preparation and Performance of PU/Cpsf Blend Ultrafiltration Membranes for Removal of Heavy Metal Ion Rejection Studies

The performance of membranes for a specific application can be determined with the help of structural properties such as molecular weight cut-off (MWCO), morphology, and pore statistics. Heavy metal ions from aqueous streams can be separated with the help of ultrafiltration membranes. In the presence and absence of the various components of the additive poly (ethylene glycol) 600, MWCOs and pore statistics of polyurethane (PU) and carboxylated polysulfone (CPSf) blend ultrafiltration (Total Polymer Concentration = 17.5 wt %) were studied with the help of dextran of different molecular weights ranging from 19 kDa to 150 kDa. The derived pore size, porosity, and the number of pores have a remarkable relationship with the MWCO, morphology, and the flux performance of the membranes. The blend membranes rejected certain toxic divalent heavy metal ions such as copper, cadmium, nickel, and zinc by complexing them into a polymeric ligand, poly(ethyleneimine) (PEI). The effect of polymer blend compositions and additive concentrations on metal ions' rejection and permeate flux are discussed