Pb Cations Research Articles

Removal, mechanistic and kinetic studies of Cr(VI), Cd(II), and Pb(II) cations using Fe3O4 functionalized Schiff base chelating ligands.

The Schiff base chelating ligands; (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol (L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2) and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3) were immobilized on Fe3O4 magnetic nanoparticles (MNPs) and utilized in the extraction of Cr(VI), Cd(II) and Pb(II) metal cations from aqueous solutions. The compounds synthesized, denoted as L1@ Fe3O4, L2@Fe3O4, and L3@Fe3O4, were characterized using FT-IR spectroscopy, TEM-SEM, VSM, and BET/BHJ techniques for analysis of functional groups, surface morphology, magnetic properties, and degree of porosity of the adsorbents, respectively. BET/BHJ technique confirmed the mesoporous nature of the compounds as their pore diameters ranged between 15 and 17nm. The initial optimization conditions of pH, adsorbent dosage, initial metal concentration, and contact time on adsorption were studied using L1@ Fe3O4. The optimum efficiencies recorded were 68% and 46% for Cr(VI) and Cd(II), respectively, obtained at pH 3, and a metal concentration of 20ppm while an efficiency of 99% was recorded for Pb(II) cations at pH 7 and a metal concentration of 100ppm. Compounds L2@Fe3O4 and L3@ Fe3O4 were also used in the extraction of metal cations from aqueous solution and gave efficiencies of 22%, 56%, and 78% for L2@ Fe3O4 and 19%, 90%, and 59% using L3@ Fe3O4 for Cr(VI), Cd(II), and Pb(II), respectively. The maximum adsorption capacities of L1@ Fe3O4 for Cr(VI), Cd(II), and Pb(II) cations were obtained from the Langmuir isotherm as 32.84, 41.77, and 450.45mg/g, respectively. The experimental data was analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. Both linear and non-linear forms of kinetic isotherms; Langmuir, Freundlich, Redlich-Peterson, and Temkin were utilized to investigate the nature of adsorption on L1@Fe3O4. The mechanistic studies deduced that the Langmuir isotherm and pseudo-second-order kinetic model better described the adsorption process both yielding high correlation coefficient values (R2 > 0.98).

Surface Cation Cross‐Locking Enables Non‐Destructive “On‐Demand” Synthesis of Anion‐Exchanged CsPbX3 Perovskite Nanocrystals

AbstractPost‐synthetic halide anion exchange is considered a “double‐edged sword” for perovskite nanocrystals (PNCs), which offer unique access to color tunability while bringing about surface defects. Herein, a novel surface cation cross‐locking (SCCL) strategy is proposed to achieve the anion‐exchanged CsPbX3 PNCs (X is Cl, Br, I) with non‐destructive emissions. This is achieved using a dendritic ligand of Pentaerythritol tetrakis (3‐mercaptopropionate) (PETMP) as a surface cross‐locker, which can form the multiple coordination to the surface Pb cation of octahedral [PbX6]4− during the fast halide anion exchange via four end‐thiolates and four side‐carboxylates. As a result, the red‐ and blue‐emitting anion‐exchanged CsPbX3 PNCs exhibit high photoluminescence quantum yield (PLQY) values of >97%, close to the parent green‐emitting CsPbBr3 PNCs. Moreover, the “on‐demand” synthesis of anion‐exchanged CsPbX3 PNCs is also performed via autonomous robotic in‐flow experimentation. This work provides a new general post‐synthetic way for the full‐color CsPbX3 PNCs with compositions that are inaccessible via direct synthetic routes.

Synergism in the electrocatalytic properties of cobalt phthalocyanine-carbon nanotube-polymeric electrospun nanofibers immobilized on a gold electrode for the detection of lead(II) ions

Core-shelled electrospun nanofibers (ENFs) comprising of a polyvinyl acetate (PVA) shell encapsulating a composite of polyaniline (PANI), tetra-4-(3-oxyflavonephthalocyaninato)cobalt(II) (CoPc-flav), carboxylic acid functionalized multiwalled carbon nanotubes (f-MWCNTs) and an annealed conductive top layer of Nafion (Nf) were used to fabricated a chemically modified gold electrode (Au|ENFs-1-Nf) via the adsorption method. The electrocatalytic sensing capabilities of the Au|ENFs-1-Nf electrode towards Pb(II) ions were evaluated. In comparison to the bare gold electrode and other chemically modified electrodes (CMEs), the Au|ENFs-1-Nf electrode was less prone to fouling showing more stable analyte signal and less compromised background electrolyte currents. The Au|ENFs-1-Nf electrode could detect the Pb(II) cations in a reproducible manner ranging from 8 to 125 μM where limits of detection and quantification of 0.51 and 1.55 μM were obtained, respectively. The analytical performance of the aforementioned CME rendered a comparable percentage recovery (103 %) with that of Inductively coupled plasma-optical emission spectroscopy (ICP-OES) (115 %).

Microphases deriving from Ba2ZrF8 structure type: III: Structural approach of dis-Sr17Zr9F70, Sr23Zr12F94, Pb29Hf15F118. General model of formation of M′2p-1MpF8p-2 microphases

The domain Sr1-xZrxF2+2x studied at 670 °C between the limits 0.340 ≤ x ≤ 0.353 show the presence of a new phase Sr17Zr9F70 and of modulated phases, all deriving from Ba2ZrF8 structure type. In the same domain studied below 600 °C, Sr17Zr9F70 tends to lose its long range ordering between Sr cations and Sr vacancies, tripling the b lattice parameter; moreover a new monoclinic superstructure Sr23Zr12F94 [a = 3sinβ×a (Ba2ZrF8); b = b (Ba2ZrF8); c = c (Ba2ZrF8), β = 105.31°] is also characterized. The homologous Hf phases are isostructural.With Pb, between 555 and 530 °C, another superstructure Pb29Zr15F118 [a = 5 × a (Ba2ZrF8); b = b (Ba2ZrF8); c = c (Ba2ZrF8] and its isotypic Pb29Hf15F118 are evidenced and their structure is solved in great part with a similar cationic disorder between Pb cations and Pb vacancies. Between 530 and 510 °C, a second much more complex superstructure exists but has not been characterized.Moreover, at 630 °C, single crystals of Pb2HfF8 are obtained which allows to confirm that, contrary to Ba2ZrF8, Pb2HfF8 is non-centrosymmetric (Pn21a space group). but the atomic positions deviate only slightly from centrosymmetry.A general structural model for all these M′2p-1MpF8p-2 (p = 6, 9, 12, 15) microphases is developed.

Sequestration of Pb(II) using channel-like porous spheres of carboxylated graphene oxide-incorporated cellulose acetate@iminodiacetic acid: optimization and mechanism study

The adsorption property of the costless green cellulose acetate (CA) was boosted by the dual modifications: inner modification by incorporating carboxylated graphene oxide (COOH-GO) into the CA spheres and outer modification by the surface modification of the COOH-GO@CA spheres by iminodiacetic acid (IDA) for removing Pb(II). The adsorption experiments of the Pb(II) proceeded in a batch mode to evaluate the adsorption property of the COOH-GO@CA@IDA spheres. The maximal Pb(II) adsorption capacity attained 613.30 mg/g within 90 min at pH = 5. The removal of Pb(II) reached its equilibrium within 20 min, and the removal % was almost 100% after 30 min at the low Pb(II) concentration. The Pb(II) adsorption mechanism was proposed according to the kinetics and isotherms studies; in addition, the zeta potential (ZP) measurements and X-ray Photoelectron Spectroscopy (XPS) analysis defined the adsorption pathways. By comparing the XPS spectra of the authentic and used COOH-GO@CA@IDA, it was deduced that the contributed chemical adsorption pathways are Lewis acid–base, precipitation, and complexation. The zeta potential (ZP) measurements demonstrated the electrostatic interaction participation in adsorbing the cationic Pb(II) species onto the negatively charged spheres (ZP = 14.2 mV at pH = 5). The unique channel-like pores of the COOH-GO@CA@IDA spheres suggested the pore-filling mechanism of Pb(II). The promising adsorption results and the superb recyclability character of COOH-GO@CA@IDA enable it to extend of the bench scale to the industrial scale.

The change of coordination environments induced by vacancy defects in hematite leads to a contrasting difference between cation Pb(II) and oxyanion As(V) immobilization

Hematite is an iron oxide commonly found in terrestrial environments and plays an essential role in controlling the migration of heavy metal(loid)s in groundwater and sediments. Although defects were shown to exist both in naturally occurring and laboratory-synthesized hematite, their influences on the immobilization of heavy metal(loid)s remain poorly understood. In this study, hematite samples with tunable vacancy defect concentrations were synthesized to evaluate their adsorption capacities for the cation Pb(II) and for the oxyanion As(V). The defects in hematite were characterized using XRD, TEM-EDS mapping, position annihilation lifetime spectroscopy, and XAS. The surface charge characteristics in defective hematite were investigated using zeta potential measurements. We found that Fe vacancies were the primary defect type in the hematite structure. Batch experiments confirmed that Fe vacancies in hematite promoted As(V) adsorption, while they decreased Pb(II) adsorption. The reason for the opposite effects of Fe vacancies on Pb(II) and As(V) immobilization was investigated using DFT calculations and EXAFS analysis. The results revealed that Fe vacancies altered As–Fe coordination from a monodentate to a bidentate complex and increased the length of the Pb–Fe bond on the hematite surface, thereby leading to an increase in As(V) bonding strength, while decreasing Pb(II) adsorption affinity. In addition, the zeta potential analysis demonstrated that the presence of Fe vacancies led to an increase in the isoelectric point (IEP) of hematite samples, which therefore decreased the attraction for the cation Pb(II) and increased the attraction for the oxyanion As(V). The combination of these two effects caused by defects contributed to the contrasting difference between cation Pb(II) and oxyanion As(V) immobilization by defective hematite. Our study therefore provides new insights into the migration and fate of toxic heavy metal(loid)s controlled by iron minerals.

Promising agent for the efficient extraction of Co(II) ions from aqueous medium and its metal complexes: Synthesis, theoretical calculations and solvent extraction

A novel ligand 2,2′-((ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(4-((3-(4-methyl-1H-imidazol-1-yl)-5-(trifluoromethyl)phenyl)diazenyl)phenol) and its Co(II), Ni(II) and Cu(II), complexes were synthesized. These compounds were identified using elemental analysis, ICP-OES, FT-IR, thermal analysis, magnetic susceptibility, and molar conductivity techniques. 1H-, 13C-, and 19F-NMR spectra were used to describe the ligand further. 2,2′-((ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(4-((3-(4-methyl-1H-imidazol-1-yl)-5-(trifluoromethyl)phenyl)diazenyl)phenol) behaved as a bidentate, and the metal:ligand ratio of the complexes was 1:1, according to elemental analysis, stoichiometric analysis, and spectroscopic data on the synthesized molecules. Using DFT/B3LYP method and the 6-311G(d,p) basis set, the optimized molecular geometries, chemical shifts, vibrational frequencies, HOMO(SOMO)-LUMO energies, and molecular electrostatic potential diagrams of the synthesized compounds in the ground state were determined. In the calculations, the LANL2DZ basis set, which is the effective core potentials for Co(II), Ni(II) and Cu(II) ions, was used. When all of the theoretical data produced by quantum chemical calculations were compared to the experimental data, it was found that there was a good agreement between the two. Additionally, utilizing several transition metal picrates, including Mn(II), Pb(II), Cd(II), Zn(II), Ni(II), Co(II), Cu(II), Hg(II) and Fe(II) cations, the extraction capacity of the ligand was examined. The ligand demonstrated a significant rate of Co(II) cation removal from the aqueous medium in solvent extraction investigations, which also showed a great affinity for Co(II) ions.

Optimization of an experimental study of cationic Pb metal adsorption by resin polymer

To eliminate lead (Pb) ions from metallic solutions, the cationic resin in solid form was utilized. The characterization of the adsorbent was performed using GTA/GTD, SEM spectroscopy, and EDX analysis. The results of these analyses provided insights into the structure and composition of the resin. The removal of Pb (II) ions was found to be highly dependent on various parameters. Firstly, the pH of the metal solution played a crucial role, as the adsorption capacity increased with the pH of the solution, at a maximum equal to (R = 84.78%), at a pH = 8.0. Additionally, the concentration of Pb (II) ions present in the solution influenced the adsorption technique’s capacity, with higher concentrations leading to increased adsorption, analysis overhead of high concentration present (100 mg L−1) of the metal lead (II) study, a saturation corresponding a plateau to the resin polymeric saturation is 93.18 mg g−1. To determine the optimal mass of the resin adsorbent, a study was conducted to maximize the removal of Pb (II) ions, at the mass 1.0 g showed that the proportion of inorganic pollutants removed from Pb (II) is entirely qualitative (100%). Furthermore, the effect of temperature on the adsorption process was investigated. It was observed that the rate of the Pb (II) adsorption process decreased as the temperature increased. Kinetic studies were performed to gain further insights into the adsorption process. Pseudo-first-order and pseudo-second-order models, along with the intra-particle diffusion model, were utilized for this purpose. The results indicated that the adsorption process was fast, as evidenced by the findings from the pseudo-second-order study. The saturation technical process was studied, employing several different isothermal models, including Langmuir, Freundlich, and Temkin. Among these models, the Langmuir model was found to best describe the phenomenon of lead metal adsorption by the resin polymeric, is equal to 11.23 mg g−1, with the experimental value precisely (R2 = 0.999). Finally, various thermodynamic techniques were applied to analyze the adsorption process. The thermodynamic parameters such as ΔG° (− 9.78 to − 9.27 kJ mol−1), ΔH° (14.85 kJ mol−1), and ΔS° (0.017 kJ mol−1) were determined. These values indicated that the adsorption process was endothermic and spontaneous, further emphasizing its impetuous nature. The results of the molecular dynamics calculations demonstrated that amino groups are very important in defining the characteristics of cation adsorption. We conclude that this new adsorbent has the potential to significantly improve the process of regularly removing heavy metal ions from wastewater.

Highly efficient removal of trace heavy metals by high surface area ordered dithiocarbamate-functionalized magnetic mesoporous silica.

The study describes synthesizing and characterizing a novel dithiocarbamate-functionalized magnetic nanocomposite. This nanocomposite exhibits several desirable properties, including a large pore diameter of 2.55 nm, a high surface area of 1149 m2/g, and excellent capturing capabilities. The synthesis process involves the preparation of highly porous magnetic nanocomposites, followed by functionalization with dithiocarbamate functional groups through a reaction with carbon disulfide and amine. The synthesized nanocomposite was thoroughly characterized using various techniques, including X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The performance of the mesoporous nanocomposite as an adsorbent for removing Pb(II), Cd(II), and Cu(II) cations from contaminated water was evaluated. The study finds that the maximum removal efficiency for Pb(II), Cd(II), and Cu(II) cations is achieved at pH values above 4. The optimal contact time for achieving 100% removal efficiency of the mentioned cations ranged between 60 and 120 min. Within this time range, the adsorbent exhibited efficient capture of the heavy metal cations from contaminated water. Additionally, the appropriate amount of adsorbent required for complete elimination of the heavy metal cations is determined. For Cd(II), the optimal dosage was found to be 50 mg of the adsorbent. For Cu(II), the optimal dosage was determined to be 40 mg. Finally, for Pb(II), the optimal dosage was 30 mg. The adsorbent's regeneration capability was demonstrated, showing that it could be reused for five consecutive runs.

Stereochemically Active Lone-Pair Containing Metal Substitution in Polar Axis toward a Giant Phase-Matchable Optical Nonlinear Silicate Crystal Li3(OH)PbSiO4.

Atoms in special lattice sites can play a crucial role in realizing materials properties, which is long pursued but difficult to control. Herein, by adopting a stereochemically active lone-pair-containing metal substitution strategy, a nonlinear-optical (NLO) silicate crystal Li3(OH)PbSiO4 was successfully synthesized, featuring [PbSiO4]∞ layers with the perfect orientation of the stereochemically active lone-pair Pb(II) cation in the polar-axis lattice. Li3(OH)PbSiO4 overcomes the long-standing problem of silicates, that is, poor nonlinear properties because it exhibits both the largest birefringence of 0.082 and the largest phase-matchable second-harmonic-generation (SHG) efficiency of 21 × KDP among the known silicates. The successful polar-axis lattice substitution could offer a new direction for realizing the rational control of materials structures and properties.

Selective removal and simultaneous immobilization of Pb cations from solutions

ABSTRACT The aim of this study was to develop a layered ammonium tin phosphate as a potential sorbent for removal of Pb2+ ions by exchange/sorption or other mechanism from contaminated solutions. A layered ammonium tin phosphate (NH4-SnP), δ-SnP – NH4 was synthesized using the hydrothermal process. XRD pattern of the NH4-SnP revealed that the final product obtained was δ-tin (IV) phosphate with the d(001)-spacing of about 14.8 Å containing ammonium ions and water molecules in the interlayers. In order to investigate the removal efficiency of Pb2+ cations by the NH4-SnP, batch-type of sorption experiments were carried out with 2 days of equilibration time at room temperature. Also, the kinetics of reaction was performed at room temperature to determine equilibrium time. The sorption isotherms for Pb2+ cations indicated that NH4-SnP showed high affinity for these ions with all the concentrations used. In addition, kinetic data showed preference for Pb2+ cations between NH4 + cation on the exchanger and Pb2+metal cation in solution. Based on these results, NH4-SnP can be proposed as an excellent sorbent for not only removal but also immobilization of Pb2+ ions from water and wastewater. Pb2+ ions were found to be immobilized as insoluble pyromorphite, Pb5(PO4)Cl after high uptakes.

A comparison of adsorption capacity of several synthesis methods of cellulose-based absorbent towards Pb(II) removal: Optimization with response surface methodology

The effects of various synthesis methods of a novel biodegradable magnetically recyclable cellulose-based adsorbent (a magnetized modified silica aerogel) on Pb(II) removal efficiency were studied. QSM (quince seed mucilage) was modified via hydrothermal and ultrasonic modes. Oven-drying and freeze-drying procedures were then used to obtain the final adsorbents. The adsorbents were named A1 to A4 and B1 to B4, depending on the synthesis and drying techniques. XRD, FTIR, BET, and SEM are characterization techniques for identifying the adsorbents. Average crystallite sizes of 15.5, 8.3, 10.9, and 2.7 nm were obtained for A1, A2, A3, and A4 samples (Scherrer formula). SEM image confirmed a Sticky bullets-like morphology. The pHpzc values of 3.4, 6.0, and 4.1 were also determined for Fe-silica aerogel, Fe-QSM, and Fe-silica aerogel-QSM samples. The highest adsorption efficiency of the A2 adsorbent towards Pb(II) cations was followed via the experimental design by the RSM (response surface methodology) approach. ANOVA results showed model F value 185 (>F0.05, 14, 15 = 2.42) and LOF F-value of 0.3831 (<F0.05, 10, 5 = 4.74) at a 95 % confidence interval. The center point run conditions were catalyst dose: 7 g/L, pH: 3.2; CPb: 11 mg/L, and contact time: 55 min, while the optimal run conditions were adsorbent dose: 1.0 g/L; pH: 2.6; CPb: 7 mg/L; and contact time: 80 min with about 94 % Pb(II) removal efficiency. The adsorption mechanism was studied, and correlation coefficient (R2) values of Langmuir (0.9814), Freundlich (0.9328), Temkin (0.8898), and Redlich-Peterson (0.9977). They have recommended that the adsorption process fit best with the Langmuir and Redlich-Peterson models. A kinetic study revealed that adsorption was well described by pseudo-second-order kinetics. The thermodynamic studies showed a spontaneous and endothermic adsorption process.

Simultaneous detection of trace Pb(II) and Cd(II) cations in ore samples by anodic stripping analysis using pMO/erGO‐modified glassy carbon electrodes

AbstractEnvironmental safety is of paramount importance for human well‐being, imposing significant demands for affordable, rapid, portable, and robust analytical tools for real‐time and on‐site water monitoring. In this context, we have developed an analytical method to efficiently detect heavy metal ions, particularly Pb2+ ions, in water samples. This method employs a stepwise‐prepared electrode comprised of a thin film of poly(methyl orange) (pMO) electrochemically deposited onto reduced graphene oxide (erGO), which is in turn coated on a glassy carbon electrode (GCE). The resulting pMO/erGO/GCE electrode was characterized using Raman spectroscopy, scanning electron microscopy (SEM), and electrochemical techniques. Square wave anodic stripping voltammetry (SWASV) was subsequently employed to detect the target ions. Importantly, the pMO/erGO/GCE electrode exhibits excellent analytical performance, featuring a broad linear concentration range spanning from 14 to 595 parts per billion (ppb), a sensitivity of 5.60 μA ppb−1 cm−2, and a theoretical calculated value of the detection limit of 0.82 ppb. The effectiveness of this sensor was validated through successful testing of aqueous samples from dissolved ores containing both lead(II) and cadmium(II) cations, as determined by atomic absorption spectroscopy.

Switching Lead for Tin in PbHfO3: Noncubic Structure of SnHfO3**

AbstractThe removal of lead from commercialized perovskite‐oxide‐based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)‐perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO3 in space group Pbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)‐for‐Pb(II) substitution, i.e. SnHfO3. During this topotactic transformation, a high purity and crystallinity is conserved with Pbam symmetry, as confirmed by X‐ray and electron diffraction, elemental analysis, and 119Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO3 also possesses reversible phase transformations and is potentially polar between ≈130–200 °C. This so‐called ‘de‐leadification’ is thus shown to represent a highly useful strategy to fully remove lead from perovskite‐oxide‐based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)‐oxide materials.

Switching Lead for Tin in PbHfO3 : Noncubic Structure of SnHfO3.

The removal of lead from commercialized perovskite-oxide-based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)-perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO3 in space group Pbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)-for-Pb(II) substitution, i.e. SnHfO3 . During this topotactic transformation, a high purity and crystallinity is conserved with Pbam symmetry, as confirmed by X-ray and electron diffraction, elemental analysis, and 119 Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO3 also possesses reversible phase transformations and is potentially polar between ≈130-200 °C. This so-called 'de-leadification' is thus shown to represent a highly useful strategy to fully remove lead from perovskite-oxide-based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)-oxide materials.

Fluorinated 2-Phenylethylammonium Spacer Cations for Improved Stability of Ruddlesden–Popper Pb/Sn Halide Perovskites: Insight from First-Principles Calculations

Improving the stability of hybrid halide perovskite solar cells is essential for their commercialization in emerging cutting-edge technology. Here, we report the results of state-of-the-art first-principles calculations to achieve and understand enhancement in the stability of Ruddlesden–Popper (RP) lead/tin halide perovskites with fluorinated 2-phenylethylammonium (PEA) spacer cations. It is found that the substitution of up to five F atoms in the phenyl ring makes C slightly positively charged due to ∼0.5e charge transfer to electronegative F. This leads to the formation of electric dipoles in the spacer cation region and polarization of the charge density. This improves the formation energy and enhances the stability of the layers. The charge transfer makes some of the C 2p orbitals partly empty so that they hybridize with F 2p orbitals near the conduction band minimum. This is interesting for the charge transport perpendicular to the layers. Our study further shows that changing the metal cations Pb with Sn does not affect the orientation of the cation molecules in the pure as well as chemically tuned RP layers whereas changing the halide ions I with Br has an impact on the orientation of the organic molecules. The calculated structures of the layers agree well with the available experimental results and suggest structures of some unexplored layers that would be interesting to fabricate. The calculated electronic structure and optical properties show that the absorption coefficient is high (∼105 cm–1) for the layers having heavily fluorinated spacer cations. Furthermore, we find higher stability and a desirable lower direct band gap for Sn-based green perovskite layers compared to the Pb counterparts. Our results provide computational insight into the surface engineering of RP perovskites for further developments in this fast-growing area.

Direction of changes in porous structure and adsorption capacity during topochemical oxidation of coal activated by alkali

The purpose of the work is to evaluate the influence of topochemical oxidation (H2O2, HNO3) of carbon prepared by alkali activation of coal on porosity and ability to adsorb 4-chlorophenol (CPh), Pb(II) cations and iodine. Carbons were oxidized at the reactant/carbon ratio of 1:1 (mol/mol, 250С, 24 h). Based on nitrogen adsorption-desorption isotherms, the volumes and specific surfaces of ultramicro- (Sumi), supermicro- (Ssmi) and other pores were evaluated. Kinetics and adsorption isotherms (250С) of CPh and Pb(II) were characterized; adsorption capacities of CPh, Pb(II) and I2 were determined. The H2O2-assisted modification was found to significantly increase Sumi (from 615 to 829 m2/g), but decrease Ssmi (from 515 to 494 m2/g). The HNO3-assisted modification slightly increases Sumi (from 615 to 651 m2/g), does not change Ssmi, but forms mesopores. The CPh adsorption is best approximated by the second-order kinetics, and isotherms are well fitted with the use of the Langmuir model. The H2O2 treatment increases the CPh capacity from 314 to 389 mg/g; and the НNO3 modification significantly decreases the CPh capacity (to 189 mg/g). Modifications reduce the iodine capacity by 1.11 times (H2O2) and 2.33 times (HNO3). The Pb(II) absorption was established to describe by the second-order kinetics equation; the adsorption isotherms obey Langmuir (R20.986) and Freundlich (R20.984) models. The Pb(II) capacity slightly increases after H2O2-assisted modification (from 87 to 95 mg/g), but increases sharply (from 87 to 298 mg/g) after HNO3-assisted treatment because of significant increasing OH-acidic groups concentration.

The Production of Oxalate by Aspergillus niger under Different Lead Concentrations

In this study, using a typical acid-producing fungi, Aspergillus niger (A. niger, CGMCC 23272), we investigated the capacity of organic acid production under different lead (Pb) concentrations. A. niger has a high Pb tolerance, which can maintain the growth of hypha at 1500 mg/L Pb concentration. Oxalic acid is the primary organic acid produced by A. niger. A. niger was shown to maintain the ability to produce oxalic acid under different Pb concentrations, which ranged from 522.8 to 1130.5 mg/L. The formed lead oxalate also confirmed the production of oxalic acid by A. niger. Meanwhile, the formation of lead oxalate minerals dominated the resistance of Pb toxicity by A. niger. More than 95% of Pb cations were removed by A. niger under different Pb concentrations. The high Pb toxicity (1500 mg/L) could stimulate pyruvate dehydrogenase enzyme activities, which increased from 0.05 to 0.13 nmol/min/g after three days of incubation. The low Pb toxicity (500 and 1000 mg/L) could improve the production of oxalic acid by A. niger. This indicates that the metabolism of organic acid by A. niger can be improved by a high Pb concentration via the tricarboxylic acid cycle.

Highly Sensitive Detection of Heavy Metal Elements Using Laser-Induced Breakdown Spectroscopy Coupled with Chelating Resin Enrichment

In this study, we demonstrate a unique method for the detection of heavy metals such as chromium (Cr), copper (Cu), lead (Pb), and nickel (Ni) at trace levels in aqueous solutions via laser-induced breakdown spectroscopy (LIBS) enriched using chelating resin. Reduction in sample time preparation was shortened by tailoring the sample processing time with the aid of an enrichment method. The calibration curves and LODs of CH-90 chelating resin for enriching Cr, Cu, Pb, and Ni cations were established under the optimal conditions. The linear correlation coefficients were all above 0.98, and the detection limits were 0.148 mg/L, 0.150 mg/L, 0.149 mg/L, and 0.240 mg/L, corresponding to Cr, Cu, Pb, and Ni, respectively. The quantitative evaluation of the obtained results signifies that the proposed method is highly sensitive for detecting trace elements and offers a good correspondence of the acquired linear correlation with its calibration model. Results comparison with past studies suggests that the proposed method is able to achieve lower LODs for elements under investigation.

Lead remediation is promoted by phosphate-solubilizing fungi and apatite via the enhanced production of organic acid.

Lead (Pb) is one of the most common heavy metal pollutants in the environment, which can indirectly or directly threaten human health. Lead immobilization by apatite can reduce the effectiveness of Pb cations via the formation of pyromorphite (Pyro). However, the formation of Pyro is always depending on the release of phosphorus (P) from apatite. Phosphate-solubilizing fungi (PSF) can secrete large amounts of organic acid to promote the release of P from apatite. Although the combination of PSF and apatite has shown a huge potential in Pb remediation, this pathway needs to be more attention, especially for organic acid secretion by PSF. This research mainly reviews the possible pathway to strengthen Pb immobilization by PSF and apatite. Meanwhile, the limitation of this approach is also reviewed, with the aim of a better stabilizing effect of Pb in the environment and promoting the development of these remediation technologies.