Competitive adsorption of Pb(II), Cd(II) and Cu(II) onto chitosan-pyromellitic dianhydride modified biochar

Quantitative mechanisms of cadmium adsorption on rice straw- and swine manure-derived biochars

We quantified and investigated mechanisms for Cd²⁺ adsorption on biochars produced from plant residual and animal waste at various temperatures. Ten biochars were produced by pyrolysis of rice straw (RB) and swine manure (SB) at 300-700 °C and characterized. The Cd²⁺ adsorption isotherms, adsorption kinetics, and desorption characteristics were studied via a series of batch experiments, and Cd²⁺-loaded biochars were analyzed by SEM-EDS and XRD. The total Cd²⁺ adsorption capacity (Q_c) increased with pyrolysis temperature for both biochars, however, rice straw-derived biochars had greater Q_c than swine manure-derived biochars; hence, the biochar derived from rice straw at 700 °C (RB700) had the largest Q_c, 64.4 mg g^-1, of all studied biochars. Cadmium adsorption mechanisms in this study involved precipitation with minerals (Q_cp), cation exchange (Q_ci), complexation with surface functional groups (Q_co), and Cd-π interactions (Q_cπ). Both the pyrolysis temperature and feedstock affected the quantitative contributions of the various adsorption mechanisms. The relative percent contributions to Q_c for Cd²⁺ adsorption by RB and SB were 32.9-72.9% and 35.0-72.5% for Q_cp, 21.7-50.9% and 20.4-43.3% for Q_ci, 2.2-14.8% and 1.4-18.8% for Q_co, and 1.4-3.1% and 3.0-5.8% for Q_cπ, respectively. For biochars produced at higher pyrolysis temperatures, the contributions of Q_cp and Q_cπ to adsorption increased, while the contributions of Q_ci and Q_co decreased. Generally, Q_cp dominated Cd²⁺ adsorption by high-temperature biochars (700 °C) (accounting for approximately 73% of Q_c), and Q_ci was the most prominent mechanism for low-temperature biochars (400 °C) (accounting for 43.3-50.9% of Q_c). Results suggested that biochar derived from rice straw is a promising adsorbent for the Cd²⁺ removal from wastewater and that the low-temperature biochars may outperform the high-temperature biochars for Cd²⁺ immobilization in acidic water or soils.

Removal of Cd(II) and Fe(III) from DMSO by silica gel supported PAMAM dendrimers: Equilibrium, thermodynamics, kinetics and mechanism

A series of silica gel supported amino-terminated PAMAM dendrimers (SG-G1.0 - SG-G3.0) were used for the removal of Cd(II) and Fe(III) from dimethylsulfoxide (DMSO). Various parameters that influence adsorption behaviors including temperature, contact time, and initial metal ion concentration were studied. The adsorption mechanism was revealed by combining the results of experiment and density functional theory (DFT) calculation. It indicates that the adsorption capacities for Cd(II) and Fe(III) are largest among the metal ions tested. The adsorption capacity of SG-G1.0 - SG-3.0 for Cd(II) and Fe(III) follows the order of SG-G2.0 > SG-3.0 > SG-G1.0. The adsorption isotherm shows the adsorption capacities for both metal ions increases with raising the temperature and initial metal ion concentration. The adsorption isotherm is consistent with Langmuir model and the adsorption process is dominated by chemical adsorption mechanism. Thermodynamic parameters indicates that the adsorption for both Cd(II) and Fe(III) is spontaneous and endothermic. Kinetic adsorption indicates that the adsorption equilibrium times for Cd(II) and Fe(III) is about 200 and 350 min, respectively, which can be described by a pseudo-second-order model and controlled by film diffusion process. FTIR analysis and theoretical calculation revealed that the carbonyl O atoms, secondary amine N atoms, and primary amine N atoms are the primary factor responsible for PAMAM adsorption by forming tetra- and penta-coordinated chelates with metal ions.

Activated magnetic biochar by one-step synthesis: Enhanced adsorption and coadsorption for 17β-estradiol and copper

In this study, activated magnetic biochars (AMBCs) were successfully synthesized via one-step synthetic method with different temperature (300, 500 and 700 °C). Characterization experiments indicated that AMBCs had larger surface area, higher pore volume and more contained‑oxygen functional groups compared to the pristine biochar. In addition, AMBCs showed better adsorption performance for 17β-estradiol (E2) and copper (Cu(II)) in single/binary-solute systems than unmodified pristine biochar. AMBC-700 exhibited the highest capacity (153.2 mg/g) for E2, while the AMBC-300 showed the best adsorption capacity (85.93 mg/g) for Cu(II) in single-solute system. Adsorption of Cu(II) and E2 both followed by pseudo-second-order and Langmuir isothermal model. The initial pH of the solution had an effect on the adsorption of E2 and Cu(II) in single-solute system. Coadsorption experiments indicated that there existed site competition and enhancement of E2 and Cu(II) on the sorption in binary-solute system. Results from this study indicated that the E2 was adsorbed by hydrogen bonds, π-π EDA interactions. Cu(II) was mainly adsorbed via chemical complexation between contained‑oxygen functional groups and Cu(II) ions. Therefore, the AMBCs via one-step synthesis could be converted into value-added biochar as effective sorbent for simultaneous removal of E2 and Cu(II) from water.

Highly efficient extraction of lead ions from smelting wastewater, slag and contaminated soil by two-dimensional montmorillonite-based surface ion imprinted polymer absorbent

The rapid, efficient and selective extraction of heavy metal ions is significant for wastewater pretreatment and metal ion recycle. Using montmorillonite as the template substrate and Pb²⁺ as template ions, a novel two-dimensional montmorillonite-based surface ion imprinted polymer (IIP-MMT) adsorbent is successfully synthesized via activators generated by electron transfer for atom transfer radical polymerization (AGET-ATRP). Batch adsorption experiments are performed to assess the properties of the imprinted polymer sorbent, along with its selectivity and reusability in practical extraction of Pb²⁺. It is interesting that the crosslinking density of the imprinted polymer has impact on the sorption property, where suitable density is coupled with the highest adsorption capacity and the best selectivity. Benefiting from the surface-imprinting technique and AGET-ATRP, IIP2-MMT is proved to own a highly effective Pb²⁺ adsorption capacity to reach 158.68 mg/g within 30 min, where the corresponding maximum adsorption capacity is 201.84 mg/g. Moreover, this material exhibits satisfactory stability and reusability that the high adsorptive capability of IIP-MMT retains more than 95% after six cycles. Thus, it is expected to reduce the wastewater disposal expenses. Besides, owing to the characteristics of PHEMA brushes and SHA chelating ligand, IIP-MMT has strong anti-interference and anti-blockage abilities to extract Pb²⁺ from smelting wastewater, slag and contaminated soil. Considering the low cost, excellent stability, high extraction efficiency, environmental friendliness, it is expected that the proposed material is very promising for treatment of heavy metals-contaminated wastewaters and soil, or ion recycle.

Facile one-pot hydrothermal synthesis of cubic spinel-type manganese ferrite/biochar composites for environmental remediation of heavy metals from aqueous solutions

This study reports the facile synthesis of cubic spinel-type manganese ferrite (MnFe₂O₄)/biochar (MF/BC) composites via a one-pot hydrothermal technique. Multiple characterizations demonstrated that the MnFe₂O₄ spinel nanoparticles were successfully grown on the biochar, which provides magnetic separability with superparamagnetic behavior and effective adsorption performance for heavy metals (Pb(II), Cu(II), and Cd(II)). The adsorption kinetics and isotherms can be well described with a pseudo-second-order and Sips isotherm models, respectively. Comparative adsorption in multi-heavy metal systems (binary and ternary) indicated that the adsorption affinity of MF/BC composites toward heavy metals followed the sequence of Pb(II) > Cu(II) > Cd(II), which followed the order of their covalent indexes. Thermodynamic analysis revealed that the adsorption process was endothermic and primarily governed by physisorption. This study provides a feasible and simple approach for the preparation of high-performance materials for the remediation of heavy metal-contaminated wastewater in a cost-effective manner.

A novel approach to developing a reusable marine macro-algae adsorbent with chitosan and ferric oxide for simultaneous efficient heavy metal removal and easy magnetic separation

Chitosan modified magnetic kelp biochar (Chi-KB_m) was successfully synthesized for efficient removal of heavy metals (Cu²⁺) from wastewater. Interestingly, the characterization results indicated that Chi-KB_m showed 6 times higher surface area (6.17 m²/g) than the pristine magnetic kelp biochar KB_m (0.97 m²/g). In addition, new functional groups, such as NH and CN group, have been created on the surface of biochar as a result of chitosan modification process, which in turns led to improve the Cu²⁺ adsorption capacity. The effect of pH and chitosan loading on heavy metal adsorption, and competition reaction of different metal ions adsorption were also investigated. Chi-KB_m exhibited a separation efficiency of more than 99.8%, which allows to recovery and reusability of the adsorbent material and heavy metals simultaneously. Overall, this study highlighted the Chi-KB_m is a promise adsorbent for heavy metal removal without sacrificing of the separation ability using magnetism.

Remediation of cadmium contaminated water and soil using vinegar residue biochar

This study investigated a new biochar produced from vinegar residue that could be used to remediate cadmium (Cd)-contaminated water and soil. Aqueous solution adsorption and soil incubation experiments were performed to investigate whether a biochar prepared at 700 °C from vinegar residue could efficiently adsorb and/or stabilize Cd in water and soil. In the aqueous solution adsorption experiment, the Cd adsorption process was best fitted by the pseudo-second-order kinetic and Freundlich isotherm models. If the optimum parameters were used, i.e., pH 5 or higher, a biochar dosage of 12 g L^-1, a 10 mg L^-1 Cd initial concentration, and 15-min equilibrium time, at 25 °C, then Cd removal could reach about 100%. The soil incubation experiment evaluated the biochar effects at four different application rates (1, 2, 5, and 10% w/w) and three Cd contamination rates (0.5, 1, and 2.5 mg kg^-1) on soil properties and Cd fractionation. Soil pH and organic matter increased after adding biochar, especially at the 10% application rate. At Cd pollution levels of 1.0 or 2.5 mg kg^-1, a 10% biochar application rate was most effective. At 0.5 mg Cd kg^-1 soil, a 5% biochar application rate was most efficient at transforming the acid extractable and easily reducible Cd fractions to oxidizable and residual Cd. The results from this study demonstrated that biochar made from vinegar residue could be a new and promising alternative biomass-derived material for Cd remediation in water and soil.

Removal of cadmium(II) cations from an aqueous solution with aminothiourea chitosan strengthened magnetic biochar

An aminothiourea chitosan modified magnetic biochar composite (TMBC) was prepared for the efficient removal of Cd(II) from wastewater. The synthesized materials were characterized, and the detailed adsorption mechanisms and thermodynamics were studied. The adsorption experiments revealed that TMBC had a higher affinity for Cd(II) than the magnetic biochar composite, raw biochar, and other carbon‐based adsorbents did. The Cd(II) adsorption process fit the pseudo‐second‐order kinetic model, and the maximum adsorption capacities on the basis of the Langmuir model were 93.72, 121.9, and 137.3 mg/g at 298, 308, and 318 K, respectively. The practical efficacy of the adsorbent was also tested with a real mine water. The metal‐ion‐loaded TMBC could be conveniently collected by a magnet and could be easily regenerated with adsorption efficiencies up to 84% after five adsorption–desorption cycles. The as‐prepared TMBC might be a promising adsorbent for the treatment of heavy‐metal‐ion‐contaminated water or highly mineralized mine water. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46239.

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe2O3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m²/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe₂O₃ with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg₄Fe₈O₁₆C₅₆H₄₀ were also formed.

Facilitative capture of As(V), Pb(II) and methylene blue from aqueous solutions with MgO hybrid sponge-like carbonaceous composite derived from sugarcane leafy trash

Enhancing the contaminant adsorption capacity is a key factor affecting utilization of carbon-based adsorbents in wastewater treatment and encouraging development of biomass thermo-disposal. In this study, a novel MgO hybrid sponge-like carbonaceous composite (HSC) derived from sugarcane leafy trash was prepared through an integrated adsorption-pyrolysis method. The resulted HSC composite was characterized and employed as adsorbent for the removal of negatively charged arsenate (As(V)), positively charged Pb(II), and the organic pollutant methylene blue (MB) from aqueous solutions in batch experiments. The effects of solution pH, contact time, initial concentration, temperature, and ionic strength on As(V), Pb(II) and MB adsorption were investigated. HSC was composed of nano-size MgO flakes and nanotube-like carbon sponge. Hybridization significantly improved As(V), Pb(II) and methylene blue (MB) adsorption when compared with the material without hybridization. The maximum As(V), Pb(II) and MB adsorption capacities obtained from Langmuir model were 157 mg/g, 103 mg/g and 297 mg/g, respectively. As(V) adsorption onto HSC was best fit by the pseudo-second-order model, and Pb(II) and MB with the intraparticle diffusion model. Increased temperature and ionic strength decreased Pb(II) and MB adsorption onto HSC more than As(V). Further FT-IR, XRD and XPS analysis demonstrated that the removal of As(V) by HSC was mainly dominated by surface deposition of MgHAsO4 and Mg(H2AsO4)2 crystals on the HSC composite, while carbon π-π* transition and carbon π-electron played key roles in Pb(II) and MB adsorption. The interaction of Pb(II) with carbon matrix carboxylate was also evident. Overall, MgO hybridization improves the preparation of the nanotube-like carbon sponge composite and provides a potential agricultual residue-based adsorbent for As(V), Pb(II) and MB removal.

Selective Adsorption of Pb(II) from Aqueous Solution by Triethylenetetramine-Grafted Polyacrylamide/Vermiculite

Amine groups play significant roles in polymeric composites for heavy metals removal. However, generating a composite with a large number of functional and stable amine groups based on clay is still a challenge. In this work, a new amine-functionalized adsorbent based on acid-activated vermiculite (a-Verm) was prepared by organic modification of silane coupling agent as bridge, followed by in situ polymerization of acrylamide (AM) and further grafting of triethylene tetramine (TETA). The obtained polymeric composite g-PAM/OVerm was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR), thermal analysis (TG/DTG), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analyses, confirming that amine groups were successfully grafted onto the surface of Verm. The efficacy g-PAM/OVerm for removing Pb(II) was tested. The adsorption equilibrium data on g-PAM/OVerm was in good accordance with the Langmuir adsorption isotherms, and the adsorption maximal value of Pb(II) was 219.4 mg·g⁻¹. The adsorption kinetic data fit the pseudo-second-order kinetic model well. Additionally, g-PAM/OVerm has better selectivity for Pb(II) ion in comparison with Zn(II), Cd(II) and Cu(II) ions. The present work shows that g-PAM/OVerm holds great potential for removing Pb(II) from wastewater, and provides a new and efficient method for the removal of heavy metal ions from industrial wastewater.

Biosorption of Cadmium by Non-Toxic Extracellular Polymeric Substances (EPS) Synthesized by Bacteria from Marine Intertidal Biofilms

Cadmium is a major heavy metal found in polluted aquatic environments, mainly derived from industrial production processes. We evaluated the biosorption of solubilized Cd²⁺ using the extracellular polymeric substances (EPS) produced by Bacillus sp. MC3B-22 and Microbacterium sp. MC3B-10 (Microbactan); these bacteria were originally isolated from intertidal biofilms off the coast of Campeche, Mexico. EPS were incubated with different concentrations of cadmium in ultrapure water. Residual Cd²⁺ concentrations were determined by Inductive Coupled Plasma-Optic Emission Spectrometry and the maximum sorption capacity (Qmax) was calculated according to the Langmuir model. EPS were characterized by X-ray photoelectron spectroscopy (XPS) before and after sorption. The Qmax of Cd²⁺ was 97 mg g⁻¹ for Microbactan and 141 mg g⁻¹ for MC3B-22 EPS, these adsorption levels being significantly higher than previously reported for other microbial EPS. In addition, XPS analysis revealed changes in structure of EPS after biosorption and showed that amino functional groups contributed to the binding of Cd²⁺, unlike other studies that show the carbohydrate fraction is responsible for this activity. This work expands the current view of bacterial species capable of synthesizing EPS with biosorbent potential for cadmium and provides evidence that different chemical moieties, other than carbohydrates, participate in this process.

Lead (Pb2+) sorptive removal using chitosan-modified biochar: batch and fixed-bed studies

Chitosan-Modified fast pyrolysis BioChar (CMBC) was used to remove Pb²⁺ from water. CMBC was made by mixing pine wood biochar with a 2% aqueous acetic acid chitosan (85% deacylated chitin) solution followed by treatment with NaOH. The characterizations of both CMBC and Non-Modified BioChar (NMBC) were done using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM), surface area measurements (S_BET), elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ζ-potential measurements. Elemental analysis indicated that chitosan accounts for about 25% weight of the CMBC. The Langmuir maximum adsorption capacity of CMBC at pH 5 was 134 mg g⁻¹versus 48.2 mg g⁻¹ for NMBC at 318 K. CMBC column adsorption studies resulted in a capacity of 5.8 mg g⁻¹ (Pb²⁺ conc. 150 mg L⁻¹; pH 5; column dia 1.0 cm; column length 20 cm; bed height 5.0 cm; flow rate 2.5 mL min⁻¹). CMBC removed more Pb²⁺ than NMBC suggesting that modification with chitosan generates amine groups on the biochar surface which enhance Pb²⁺ adsorption. The modes of Pb²⁺ adsorption on CMBC were studied by comparing DRIFTS and X-ray photoelectron spectroscopy spectra before and after Pb²⁺ adsorption.

Batch and fixed-bed column studies for the removal of lead (Pb²⁺) from aqueous solution by chitosan-modified pinewood biochar.

Characterization and adsorption properties of cross-linked yeast/β-cyclodextrin polymers for Pb(ii) and Cd(ii) adsorption

A cross-linked yeast/β-cyclodextrin polymer (Y–β-CDP) was synthesized to remove Pb(ii) and Cd(ii) from aqueous solution.

Activated biochar derived from pomelo peel as a high-capacity sorbent for removal of carbamazepine from aqueous solution

In recent years, the application of biochar to remove contaminants from aqueous solutions has become interesting due to favorable physical/chemical properties and abundant feedstocks.