Aqueous Pb Research Articles

Hybrid electrocoagulation/adsorption system using aluminum electrodes and novel GO@ZIF-7 nanocomposite for the effective removal of Pb(II) from wastewater

Water pollution resulting from heavy metals including lead [Pb(II)] is a major health concern for humans, animals, and aquatic life. Pb(II) is a highly hazardous contaminant that must be effectively removed from water before reuse or discharge. In this study, a hybrid electrocoagulation/adsorption system (EC/A) using aluminum electrodes integrated with a novel adsorbent GO@ZIF-7 nanocomposite, was studied for aqueous phase Pb(II) removal. The hybrid EC/A system yielded a near complete Pb(II) removal. The system was optimized using the Response Surface Methodology (RSM) based design of experiments (DOE) technique; specifically using the central composite design (CCD) the study analyzed the impacts of four primary process variables (i.e., current density, Pb(II) initial concentration, dosage of GO@ZIF-7 nanocomposite, and conductivity) on the Pb(II) removal. Notably, the findings show the significant role of current density in the Pb(II) removal process, particularly at a current density of 1.5 mA/cm2. The above-mentioned RSM design along with the analysis of variance (ANOVA) based statistical analysis and optimization, confirmed the suitability of the proposed RSM-based equations for Pb(II) removal modeling. Collectively, the findings of this study indicate that the proposed hybrid EC/A system using aluminum electrodes integrated with a novel GO@ZIF-7 nanocomposite has a significant practical viability as suggested by the remarkably high Pb(II) removal efficiency. Furthermore, this study also presents the effectiveness of three advanced machine learning (ML) based models, i.e., artificial neural network (ANN), eXtreme Gradient Boosting (XGBoost), and Random Forest Regression, for predictingthe Pb(II) removal using the EC/A process.

Selective extraction of lead from chelator-rich effluents using a biomass-based sorbent

The efficient removal of lead (Pb) from waste streams containing chelators presents a significant challenge due to the high stability and mobility of Pb-chelator complexes. This study investigates a novel approach utilizing a biomass-based sorbent, proline-incorporated dithiocarbamate-modified cellulose with epoxy-cross-linkage (DMC-Pro-Epo6), to extract Pb from effluents with excess chelators. DMC-Pro-Epo6 exhibited exceptional Pb(II) sorption performance under controlled and various chelator-rich conditions. The sorbent maintained high sorption efficiency even with 100-fold excess chelator concentration and competing metal ions. DMC-Pro-Epo6 also outperformed commercially-available ion-selective sorbents in terms of separation efficiency. The sorption kinetics followed a pseudo-second order model, demonstrating rapid sorption with equilibrium reached within 20 min. The maximum sorption capacities of DMC-Pro-Epo6 obtained from the Langmuir isotherm model were 1267 and 659 µmol g−1 in Pb(II)-containing aqueous solution and Pb(II)-containing EDTA solution, respectively. X-ray photoelectron and absorption spectroscopy analyses, along with sorption parameters, confirmed a chemisorption mechanism for Pb(II) sorption onto DMC-Pro-Epo6. Validation of the protocol using real waste samples with complex chelator and base metal ion matrices resulted in a quantitative and selective extraction of 92 to 99 % of Pb(II). This success suggests the potential for scaling up the developed process. Compared to conventional treatment methods, the proposed technique offers a more efficient and streamlined process for separating metal ions and chelators from effluents.

Ion-selective electrode based on polyurethane-immobilized di-(2-ethyl hexyl) phosphoric acid for low-concentration aqueous Pb2+ detection and quantification

This study used a polyurethane (PU)-based ion selective electrode (ISE) immobilized with di-(2-ethyl hexyl) phosphoric acid (D2EHPA) to detect and quantify Pb2+ ions at low concentrations (10−10 to 10−1 M) in aqueous solution. PU, synthesized from castor oil (Ricinus communis L.), was utilized as the ISE membrane matrix. The ISE demonstrated a sensitivity of 26.24 ± 0.12 mV/decade, a detection limit of 1.44 × 10−7 M, and a response time of 10 s. We maintained the measurement stability for up to six days of storage.The results of Pb2+ quantification produced by ISE were compared with the results using atomic absorption spectroscopy (AAS), indicating similar Pb2+ concentrations in both artificial and real wastewater samples (calculated t-value < theoretical t-value). Therefore, this ISE is suitable for detecting trace levels of Pb2+ and quantifying them with high accuracy.

Cellulose/castor oil‐based polyurethane film composite for aqueous Cd and Pb adsorption: Evaluation using laser‐induced breakdown spectroscopy

AbstractCastor oil‐based polyurethane has been researched for its utility in heavy metal adsorption. To improve the adsorptive performance, the polymer can be incorporated with cellulose—a renewable and widely available biopolymer. The aim of this research was to synthesize a film composite prepared from castor oil‐based polyurethane and cellulose for adsorptive removal of aqueous Cd and Pb. One‐shoot synthesis method was employed by mixing cellulose filler with castor oil and toluene diisocyanate (TDI). Characterization was carried out by FT‐IR, SEM, TGA, DSC, and contact angle analyses. Batch adsorption was carried out for the Cd and Pb with variations in contact time and initial pH, before analyzed for the adsorptive performance using 1064 nm Nd:YAG laser spectroscopy. The resulted adsorbents had improved thermal stability, and lower hydrophobicity. Adsorption of Pb and Cd increased 2 and 35 times after the addition of 0.1 g cellulose, respectively. Batch adsorption test revealed that the optimum conditions are 120‐min contact time and pH of 9 and 7 (for Cd and Pb, respectively). In conclusion, incorporation of cellulose could modify the characteristics of castor oil‐based polyurethane film and improve the adsorption of Cd and Pb.

Stable sandwich-type electrochemical lead ions sensor based on bismuth-metal organic framework and Mxene

For electrochemical Pb2+ detection, high sensitivity and stability are essential owing to the mutagenicity, carcinogenicity, and teratogenicity of aqueous Pb2+ ions. Herein, a three-dimensional bismuth-containing metal-organic framework (Bi-MOF) was synthesized using a hydrothermal method, followed by post-synthetic functionalization with thiol (-SH) groups. A sandwich-type Bi-MOF-SH/Mx/Bi-MOF-SH/GCE multilayer sensitive electrochemical sensor was then constructed on the surface of the glassy carbon electrode for Pb2+ detection. Differential pulse anodic stripping voltammetry (DPASV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to evaluate the performance of the sensor. The developed multilayer sensor demonstrated an exceptionally high current response, good sensitivity (0.03–20.0 μg/L), and an ultra-low level of detection of 0.012 μg/L (S/N=3) towards Pb2+ ions. The as-prepared electrode showed high stability, repeatability, and selectivity among possible interfering ions (Na+, Ca2+, Cu2+, Zn2+, K+, Mg2+, Al3+, and Cd2+), suggesting potential for use in real-world applications.

Adsorptive removal of Pb(II) ions from aqueous effluents using O-carboxymethyl chitosan Schiff base-sugarcane bagasse microbeads

In this study, a novel and cost-effective approach was employed to prepare an effective Pb(II) adsorbent. We synthesized highly porous CMCSB-SCB microbeads with multiple active binding sites by combining carboxymethylated chitosan Schiff base (CMCSB) and sugarcane bagasse (SCB). These microbeads were structurally and morphologically characterized using various physical, analytical, and microscopic techniques. The SEM image and N2-adsorption analysis of CMCSB-SCB revealed a highly porous structure with irregularly shaped voids and interconnected pores. The CMCSB-SCB microbeads demonstrated an impressive aqueous Pb(II) adsorption capacity, reaching a maximum of 318.21 mg/g, under identified optimal conditions: pH 4.5, 15 mg microbeads dosage, 30 min contact time, and Pb(II) initial concentration (350 mg/L). The successful adsorption of Pb(II) onto CMCSB-SCB beads was validated using FTIR, EDX, and XPS techniques. Furthermore, the experimental data fitting indicated a good agreement with the Langmuir model (R2 = 0.99633), whereas the adsorption kinetics aligned well with the pseudo-second-order model (R2 = 0.99978). The study also identified the Pb(II) adsorption mechanism by CMCSB-SCB microbeads as monolayer chemisorption.

Enhanced Adsorption of Aqueous Pb(II) by Acidic Group-Modified Biochar Derived from Peanut Shells

Using peanut shells, a sustainable agricultural waste product, as its raw material, the acid group-modified biochar (AMBC) was prepared through phosphoric acid activation, partial carbonization, and concentrated sulfuric acid sulfonation for efficient removal of lead ion from aqueous solutions. Characterization techniques such as N2 isothermal adsorption–desorption, SEM, XRD, FT-IR, TG-DTA, and acid–base titration were utilized to fully understand the properties of the AMBC. It was found that there were high densities of acidic oxygen-containing functional groups (-SO3H, -COOH, Ph-OH) on the surface of the AMBC. The optimal adsorption performance of the AMBC for Pb(II) in water occurred when the initial concentration of Pb(II) was 100 mg/L, the pH was 5, the dosage of the adsorbent was 0.5 g/L, and the contact time was 120 min. Under the optimal conditions, the removal ratio of Pb(II) was 76.0%, with an adsorption capacity of 148.6 mg/g. This performance far surpassed that of its activated carbon precursor, which achieved a removal ratio of 39.7% and an adsorption capacity of 83.1 mg/g. The superior adsorption performance of AMBC can be caused by the high content of acidic oxygen-containing functional groups on its surface. These functional groups facilitate the strong binding between AMBC and Pb(II), enabling effective removal from water solutions.

Competitive Adsorption of Aqueous Cd(II) and Pb(II) Solutions onto Silicas Synthesized with Saponin as Template Agent

The aim of the research was to prepare silica adsorbents using an environmentally friendly pathway, a template synthesis with saponin biosurfactant as a structure-directing agent. The adsorbents prepared in this way exhibit improved adsorption properties while maintaining environmental innocuousness. For the preparation of porous silica, the biosurfactant template sol–gel method was used with tetraethoxysilane as a silica precursor. The silica adsorbents were analyzed by FTIR spectroscopy, nitrogen adsorption–desorption and SEM/EDX microscopy, TEM/HRTEM microscopy, and thermogravimetric analyses. Batch tests were carried out to remediate Pb(II)/Cd(II) ions in single/binary aqueous solutions, and the effect of the surfactant on the adsorption properties was assessed. The optimal adsorption parameters (pH, contact time, initial concentration of metal ions) have been determined. The adsorption was fitted using Langmuir and Freundlich adsorption isotherms and kinetic models. Mathematical modeling of the retention process of Pb(II) and Cd(II) ions from binary solutions indicated a competitive effect of each of the two adsorbed metal ions. The experimental results demonstrated that saponin has the effect of modifying the silica structure through the formation of pores, which are involved in the retention of metal ions from aqueous solutions and wastewater.

Na/N Co-doped Seaweed Biochar Composite for Efficient Removal of Aqueous Pb(II) and Cu(II).

Pollution from harmful heavy metal ions such as Pb(II) and Cu(II) is causing serious environmental and health problems. In this study, Sodium and nitrogen co-doped porous carbon material (Na/NABc) was successfully prepared from seaweed, sodium hydroxide, and dicyandiamide. The experimental results showed that Na/NABc is an excellent adsorbent for the effective removal of Pb(II) and Cu(II) from water bodies. Specifically, 99.8% of Pb(II) and 64.6% Cu(II) (100 mg/L) were removed within 12 h using 10 mg Na/NABc(10%) at 25 °C. The adsorption of Pb(II) and Cu(II) in aqueous solution by Na/NABc(10%) was efficient and rapid in the first stage. The theoretical maximum removal capacities of Na/NABc for Pb(II) and Cu(II) were 959.6 and 299.1 mg/g, respectively. Pb(II) and Cu(II) ions were adsorbed quickly in the first 60 min, and the kinetics data were generally consistent with a pseudo-second-order model. Na/NABc(10%) had a large distribution coefficient for Pb(II) (8.38 L/mg) and Cu(II) (1.17 L/mg). The possible mechanisms were precipitation, Ion exchange, and surface complexation. The removal rate can reach about 70% after five cycles, and the release of sodium meets the standard. The results of this study demonstrate the potential applicability of Na/NABc(10%) for adsorption of heavy metals from aqueous solution.

Characterizations of a functionalized disused plastic-derived membrane and investigation of the effects of process variables on its adsorptive uptake of Pb2+ from simulated effluent using response surface methodology

This work focuses on the characterization and performance of the adsorptive membrane produced (via blending) functionalized waste polyethylene water sachets bags (PESWAB) with biopolymers. An adsorptive membrane (5.0 µm pore size) and (2.0 mm thickness) was fabricated from 9.0 g wt composite of PESWAB, chitosan, and cellulose acetate in the corresponding ratios of 1:2:1. Zeta potential, FTIR, SEM/EDX, water contact angle, and TGA/DTA were used to characterize the membrane. Response surface methodology (RSM) was used to model the effects of process variables on the adsorptive uptake of Pb2+ from simulated effluent. The zeta potential was shown to be between −26 and −68 mV at a pH between 4.6 and 9.5. This indicates a good level of stability and adsorptive potential. A hyrophilic membrane was suggested by the low average water contact angle of 79.0°. The gradual decomposition of the membrane indicated that the membrane dope solution was homogeneous. The membrane proved to be a quick and efficient adsorbent for the removal of aqueous Pb2+, as evidenced by the adsorption efficiency (92.0 %) realized at an optimum time of 65 min. The optimization result demonstrated that the RSM predicted and validated removal efficiencies were 96.78 % and 93.95 %, respectively. The regression model's applicability is supported by a low coefficient of variation (0.095 %), a P-value (<0.0001), a high model F-value of 4921.15, and a coefficient of determination (R2) value of 0.9996.

Use of sludge stabilization products for remediation of heavy metal (loid)s-contaminated mine tailings: Physicochemical, biochemical and microbial mechanisms

The sludge stabilization products (hereinafter referred to “Composts”) added in different addition ratios (30 %, 50 % and 80 %) were applied to remediate the heavy metal(loid)s-contaminated mine tailings. Physicochemical, biochemical and microbial characteristics at day 0 and 180 were systematically investigated. The Composts added in different ratios could all remediate the mine tailings in terms of significantly decreased bulk density, increased organic matters, porosity, germination index, pH and DHA activity, as well as obviously declined aqueous extractable Cu, Pb, As, Cd, Hg, Cr, Zn and Ni (p < 0.05). Taken phytotoxicity alleviation and metal (loid)s mobility inhibition into consideration, the 50 % Composts was the most recommended in this study, with the highest reduction (82.9 %∼91.4 %) in aqueous heavy metal (loid)s concentration comparted to the un-amended. The transformation of Cu, Pb, As, Cd and Hg from exchangeable to more stable forms (especially organically-bound form), due to their enhanced complexation with humus through promoted organic matters aromatization, was considered to drive the alleviation of their leaching pollution in mine tailing soil. While the declined aqueous extractable Cr, Zn and Ni were more likely ascribed to the increased pH value. Further, different from fungal communities not sensitive during remediation, the highest porosity and DHA activity by the 50 % Composts amendment benefited the improved archaeal diversity and enriched bacterial family Bacillaceae (capable of heavy metals biomineralization), further significantly (p < 0.05) contributing to the decrease in Cd mobility. Overall, this study highlights the effective role of the Composts in alleviating heavy metal(loid)s pollution in mine tailings and further clarifies the multiple mechanisms including immobilization, pH adjusting and microbial effects.

Promoting the circular economy: Valorization of a residue from industrial char to activated carbon with potential environmental applications as adsorbents

Pyrolysis of residues enriched with carbon, such as in agroforestry or industrial activities, has been postulated as an emerging technology to promote the production of biofuels, contributing to the circular economy and minimizing waste. However, during the pyrolysis processes a solid fraction residue is generated. This work aims to study the viability of these chars to develop porous carbonaceous materials that can be used for environmental applications. Diverse chars discharged by an industrial pyrolysis factory have been activated with KOH. Concretely, the char residues came from the pyrolysis of olive stone, pine, and acacia splinters, spent residues fuel, and cellulose artificial casings. The changes in the textural, structural, and composition characteristics after the activation process were studied by N2 adsorption-desorption isotherms, scanning electron microscopy, FTIR, elemental analysis, and XPS. A great porosity was developed, SBET within 776–1186 m2 g−1 and pore volume of 0.37–0.59 cm3 g−1 with 70–90% of micropores contribution. The activated chars were used for the adsorption of CO2, leading to CO2 maximum uptakes of 90–130 mg g−1. There was a good correlation between the CO2 uptake with microporosity and oxygenated surface groups of the activated chars. Moreover, their ability to adsorption of contaminants in aqueous solution was also evaluated. Concretely, there was studied the adsorption of aqueous heavy metals, i.e., Cd, Cu, Ni, Pb, and Zn, and organic pollutants of emerging concern such as caffeine, diclofenac, and acetaminophen.

PbO2 reductive dissolution by dissolved Mn(III) in the presence of low molecular weight organic acids and humic acid.

Although Mn(III) complexes with organic ligands have been previously identified, the information about their stability and reactivity is scarce. In the present study, we analyzed the formation and stability of three different complexes: Mn(III)-citrate, Mn(III)-tartrate, and Mn(III)-humic acid (HA), as well as their reactivity toward an element of high environmental concern, lead (Pb).Our results indicate that the stability of studied complexes is highly dependent on pH. The Mn(III) complexes with citrate and tartrate degrade below pH 8, due to the electron transfer reaction between Mn(III) and the ligand, while the Mn(III)-HA complex's degradation is slower and less sensitive to pH. At pH 4, less than 40% of the initial Mn(III)-HA was found to be stable.The reactivity of the complexes was different depending on the ligand and its concentration. The Mn(III)-citrate and Mn(III)-tartrate complexes effectively reduced PbO2 and releases aqueous Pb2+, although significant differences were found with increasing ligand concentration. There was no evidence of the reduction of PbO2 by Mn(III) when it forms a complex with HA. This is likely due to the large size of HA moieties that prevent the Mn(III) component of the complex from getting close enough to the PbO2 surface to initiate electron transfer and lead to the reduction of Pb(IV) by HA itself.

Efficient removal of aqueous Pb(II) ions by magnetic alginate composite microcapsules containing canola straw‐derived biochar as the reinforcing fillers

AbstractWith the rapid development of industry, water pollution caused by lead has caused great harm to human health. In this study, alginate is used as a base and blended with biochar to form calcium alginate hydrogel beads with high mechanical properties through ionic cross‐linking. Besides, the material (BC/MCAC) is prepared by the material (C‐γ‐Fe2O3) as a magnetizing agent and to remove lead. Then, a series of batch experiments and material characterizations are performed to evaluate the adsorption process of the material. The results show that the maximum adsorption capacity of BC/MCAC to Pb(II) is 211.6 mg g−1 at pH = 7. The adsorption process is well described by the Langmuir adsorption isotherm and pseudo‐second‐order kinetic model. This indicates that the lead adsorbed by BC/MCAC is a monolayer chemisorption that occurs on a uniform surface. After three regeneration cycles, BC/MCAC is found to retain 82.37% of the lead adsorption capacity and has good regeneration ability. Lead is removed by BC/MCAC mainly through the complexation of oxygen‐containing functional groups, electrostatic interaction, and ion exchange. BC/MCAC allows for more sustainable use of the wastes and is expected to be a new type of lead adsorbent for industrial wastewater.

Adsorption of Lead from Water Using MnO2-Modified Red Mud: Performance, Mechanism, and Environmental Risk

A manganese dioxide-modified red mud (Mn-RM) was developed as an adsorbent for the effective removal of lead ions (Pb2+) from wastewater. Various methods were used to characterize the prepared Mn-RM, analyze its adsorption performance, and evaluate the associated environmental risks post-adsorption. The results revealed that Mn-RM has a large surface area (38.91 m2/g) and a developed porous structure (0.02 cm3/g). The adsorption process exhibited good agreement with the Langmuir isotherm and pseudo-second-order kinetic models, showcasing a theoretical maximum saturation adsorption capacity of 721.35 mg/g. The adsorption mechanism primarily involves electrostatic attraction, ion exchange, and chemical precipitation. The optimal treatment conditions were determined by utilizing a response surface model, resulting in a maximum Pb2+ removal efficiency of 87.45% at pH 5.21, a dosage of 0.83 g/L, and an initial concentration of 301.04 mg/L. The risk assessment code (RAC) for each heavy metal in Mn-RM was less than 1%, indicating low environmental risk. Furthermore, the synthetic toxicity index (STI) values showed a significant decrease post-treatment. This study introduces the concept of “controlling waste with waste”, offering a cost-effective approach to both utilizing red mud and removing aqueous Pb2+ while ensuring environmental safety and minimal ecological impact.

Recognizing adsorption of aqueous Cr(VI), As(III), Cd(II), and Pb(II) ions by amino groups hollow polymer adsorbent

The mechanism from the molecular level and the selectivity for the removal of metal ions from aqueous has become a hotspot in current water treatment. In this study, a sulphydryl-modified hollow polymer adsorbent was designed with intrinsic amine and grafted sulphydryl groups for efficient uptake of Cr(VI), As(III), Cd(II), and Pb(II) by taking advantage of their properties of abundant functional groups, discrete hollow chambers, and high porosity. Interestingly, the benzenoid amine/quinoid imine functional groups have a stronger affinity for Cr(VI) than Cd(II) or As(III) and Pb(II). The formation of approximately 65.7% Cr(III) indicates the redox reaction from Cr(VI) to Cr(III). The electron-donating comes from benzenoid amine and oxidized to quinoid imine or protonated oxidized nitrogen units (-N = +) with Cr(VI) reduced to Cr(III) for the increase of more than double of quinoid imine and a new functional group of -N = +. Ion exchange between –COO- groups and As(III)/Cd(II), the chelation of –SH groups for Pb(II)/As(III) are plausible mechanisms.

Comparative Screening Study on the Adsorption of Aqueous Pb(II) Using Different Metabolically Inhibited Bacterial Cultures from Industry

The global concern about the water pollution caused by heavy metals necessitates effective water treatment methods. Adsorption, with its substantial advantages, stands out as a promising approach. This study delves into the efficiency of Pb(II) removal using metabolically inhibited microbial cultures. These cultures encompass waste-activated sewage sludge (SS), industrially sourced bioremediation microbes (commercial 1—C1 and commercial 2—C2), an industrially acquired Pb(II) remediating consortium (Cons), and refined strains (derived from Cons) of Paraclostridium bifermentans (PB) and Klebsiella pneumoniae (KP). Our findings reveal maximum Pb(II) adsorption capacities of 141.2 mg/g (SS), 208.5 mg/g (C1), 193.8 mg/g (C2), 220.4 mg/g (Cons), 153.2 mg/g (PB), and 217.7 mg/g (KP). The adsorption kinetics adhere to a two-phase pseudo-first-order model, indicative of distinct fast and slow adsorption rates. Equilibrium isotherms align well with the two-surface Langmuir model, implying varied adsorption sites with differing energies. The Crank mass transfer model highlights external mass transfer as the primary mechanism for Pb(II) removal. Surface interactions between sulfur (S) and lead (Pb) point to the formation of robust surface complexes. FTIR analysis detects diverse functional groups on the adsorbents’ surfaces, while BET analyses reveal non-porous agglomerates with a minimal internal surface area. The Pb(II) recovery rates are notable, with values of 72.4% (SS), 68.6% (C1), 69.7% (C2), 69.6% (Cons), 61.0% (PB), and 72.4% (KP), underscoring the potential of these cost-effective adsorbents for treating Pb(II)-contaminated aqueous streams and contributing to enhanced pollution control measures. Nevertheless, optimization studies are imperative to evaluate the optimal operational conditions and extend the application to adsorb diverse environmental contaminants.

Single-step hydrothermal synthesis of biochar from waste industrial hemp stalk core for Pb2+ sorption: Characterization and mechanism studies

Industrial hemp stalk core (IHSC)-driven hydrothermal biochars were synthesized by single-step hydrothermal with different H2SO4 concentrations as hydrothermal media for the first time. The characterization results indicated that the concentration of H2SO4 had a significant effect on the carbonization degree and affected the physicochemical properties of biochar, which in turn influenced the Pb2+ sorption ability. Among these biochars, the 50% H2SO4-activated hydrothermal biochar (HBS50) not only achieved a significant yield (49.2%), but also obtained the largest specific surface area (359.11 m2/g) and pore volume (0.357 cm3/g). Besides, the abundant functional groups were found to be exposed on the surface of HBS50. In particular, HBS50 showed excellent sorption capacity for Pb2+, reaching a maximum sorption capacity of 195.9 mg/g in a short period of time (2 h). Sorption performance of HBS50 conformed well to the Langmuir isotherm model and pseudo-second order model. Based on the sorption performance and characterization analysis, the sorption mechanisms were proposed: -OH and -COOH groups on surface of biochar took deprotonation firstly to form negatively groups and then attracted Pb2+ cations. Subsequently, most of these attracted Pb2+ cations were further fixed by surface -OH and -COOH through complex reaction. In addition, the contribution of π-π coordination with unsaturated groups (such as CC and COOR) and the electrostatic interaction for the further attachment of Pb2+ cations could not be excluded. However, ion exchange and precipitation reaction had little assistance to the sorption of Pb2+. The work offers an effective and economic method for removing aqueous Pb2+.

Effect of mineralogical characteristics evolution of vermiculite upon thermal and chemical expansions on its adsorption behavior for aqueous Pb(II) removal

Vermiculite undergoes significant changes in mineralogical characteristics upon chemical (with H2O2) and thermal (roasting) expansions, resulting in a marked impact on its adsorption behavior toward Pb(II) removal. Both chemical and thermal expansions exfoliated the tightly-stacked bulk structure of raw vermiculite into ultra-thin sheets and built abundantly nanoporous channels in the lamellar region, offering sufficient adsorption sites. Meanwhile, the surface properties of hydrophilicity and negative charge in raw vermiculite remain unaltered during expansions, thus enabling an enhanced adsorption capacity through electrostatic attraction. However, severe loss of cation exchange capacity and structural hydroxyl groups due to thermal expansion damaged mixed crystal phases in vermiculite and hydrophlogopite, leading to the poorer Pb(II) removal capability. The results demonstrate that the favorable influence of chemical expansion in raw vermiculite for Pb(II) removal is attributed to enhanced cation exchange within the interlayer, functional groups of structural hydroxyl and siloxane, and negative surface charge on hydrophilic surface.

Highly efficient ZnO nanoflowers for the removal of highly toxic aqueous Pb(II) and Cr(VI)

Highly efficient ZnO nanoflowers for the removal of highly toxic aqueous Pb(II) and Cr(VI)