Competitive adsorption of aqueous metal ions on an oxidized nanoporous activated carbon

Spectroelectrochemical study of carbon structural and functionality characteristics on vanadium redox reactions for flow batteries

Vanadium redox flow batteries have applications for large-scale electricity storage. This paper reports the influence of carbon structural characteristics of sustainable walnut shell-derived carbons in carbon/polyvinylidene fluoride composite electrodes on vanadium redox reactions. Pyrolysis, gasification, and chemical treatment procedures were used to modify the structural characteristics of carbons. Carbon functional groups were modified by chemical treatment with HNO3, heat treatment with K2CO3, and high-temperature NH3 treatment. Carbon porous structures were characterized using gas adsorption studies. Raman spectroscopy and X-ray diffraction were used to characterize the carbon molecular structure. Functional groups were characterized using X-ray photoelectron spectroscopy, acid/base titrations, temperature-programmed desorption, and Fourier transform infrared spectroscopy. The influence of carbon structure, porosity, and surface functional groups on the redox reactions of vanadium was investigated using cyclic voltammetry and electrical impedance spectroscopy. The VO2+/VO2 + and V2+/V3+ couples had well-defined peaks in cyclic voltammetry, with the former being the most intense, but the V3+/VO2+ couple was not observed for samples carbonized under nitrogen. The results show that V2+/V3+ and VO2+/VO2 + couples observed in cyclic voltammograms were enhanced for carbonization temperatures up to 800 °C. Electrical impedance spectroscopy also showed impedance trends. The electrochemistry results are primarily related to changes in carbon structure and the catalysis of V3+ oxidation by surface functional groups in the carbon structure. The V3+/VO2+ couple was limited by slow kinetics, but it occurs on specific oxygen and nitrogen sites in the carbon structure. The oxidation of V(iii) to V(iv) only occurs on a limited number of surface sites, and the outer-sphere electron transfer to oxidize V(iii) takes place at much more positive potentials. The coulombic, voltage, and energy efficiency of the carbon electrodes were suitable for batteries.

Conversion of char from pyrolysis of plastic wastes into alternative activated carbons for heavy metal removal

The valorization of post-consumer mixed plastics in pyrolysis processes represents an abundant reservoir of carbon that can be effectively converted into useful chars. This process not only holds appeal in terms of improving plastic waste concerns but also contributes to the reduction of greenhouse gas emissions, thus aligning with the principles of a circular economy paradigm. In this study, the char produced from the pyrolysis of post-consumer mixed plastic waste has been activated with Na2CO3, KOH, NaOH, and K2CO3 to improve the textural, structural, and composition characteristics, leading to improved adsorption capability. These characteristics were studied by N2 adsorption-desorption isotherms, scanning electron microscopy, elemental and immediate analysis, and X-ray photoelectron spectroscopy. The developed surface area (SBET) was 573, 939, 704 and 592 m2 g-1 for Na2CO3, KOH, NaOH and K2CO3 activated carbons, respectively. These activated chars (ACs) were tested for the adsorption of heavy metals in both synthetic waters containing Pb, Cd, and Cu and industrial wastewater collected at an agrochemical production plant. Na2CO3-AC was the best performing material. The metal uptake in synthetic waters using a batch set-up was 40, 13 and 12 mg g-1 for Pb, Cd and Cu. Experiments in a column set-up using Na2CO3-AC resulted in a saturation time of 290, 16, and 80 min for Pb, Cd, and Cu synthetic waters, respectively, and metal uptakes of 26.8, 4.1, and 7.9 mg g-1, respectively. The agrochemical effluents, containing mainly Cr, Cu, Mn, and Zn were tested in a plug-flow column. The metal uptake notably decreased compared to synthetic water due to a competition effect for active sites.

Mimicking Metalloenzyme Microenvironments in the Transition Metal-Single Atom Catalysts for Electrochemical Hydrogen Peroxide Synthesis in an Acidic Medium

Electrochemical reduction of oxygen into hydrogen peroxide in an acidic medium offers an energy-efficient and green H2 O2 synthesis as an alternative to the energy-intensive anthraquinone process. Unfortunately, high overpotential, low production rates, and fierce competition from traditional four-electron reduction limit it. In this study, a metalloenzyme-like active structure is mimicked in carbon-based single-atom electrocatalysts for oxygen reduction to H2 O2 . Using a carbonization strategy, the primary electronic structure of the metal center with nitrogen and oxygen coordination is modulated, followed by epoxy oxygen functionalities close to the metal active sites. In an acidic medium, CoNOC active structures proceed with greater than 98% H2 O2 selectivity (2e- /2H+ ) rather than CoNC active sites that are selective to H2 O (4e- /4H+ ). Among all MNOC (M = Fe, Co, Mn, and Ni) single-atom electrocatalysts, the CoNOC is the most selective (> 98%) for H2 O2 production, with a mass activity of 10 A g-1 at 0.60 V vs. RHE. X-ray absorption spectroscopy is used to identify the formation of unsymmetrical MNOC active structures. Experimental results are also compared to density functional theory calculations, which revealed that the structure-activity relationship of the epoxy-surrounded CoNOC active structure reaches optimum (ΔG*OOH ) binding energies for high selectivity.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Comparative Assessment of Different Yeast Cell Wall-Based Mycotoxin Adsorbents Using a Model- and Bioassay-Based In Vitro Approach

Frequently reported occurrences of deoxynivalenol (DON), beauvericin (BEA), and, to a lesser extent, ochratoxin A (OTA) and citrinin (CIT) in ruminant feed or feedstuff could represent a significant concern regarding feed safety, animal health, and productivity. Inclusion of yeast cell wall-based mycotoxin adsorbents in animal feeds has been a common strategy to mitigate adverse effects of mycotoxins. In the present study, an in vitro approach combining adsorption isotherm models and bioassays was designed to assess the efficacy of yeast cell wall (YCW), yeast cell wall extract (YCWE), and a postbiotic yeast cell wall-based blend (PYCW) products at the inclusion rate of 0.5% (w/v) (ratio of adsorbent mass to buffer solution volume). The Hill's adsorption isotherm model was found to best describe the adsorption processes of DON, BEA, and CIT. Calculated binding potential for YCW and YCWE using the Hill's model exhibited the same ranking for mycotoxin adsorption, indicating that BEA had the highest adsorption rate, followed by DON and CIT, which was the least adsorbed. PYCW had the highest binding potential for BEA compared with YCW and YCWE. In contrast, the Freundlich isotherm model presented a good fit for OTA adsorption by all adsorbents and CIT adsorption by PYCW. Results indicated that YCW was the most efficacious for sequestering OTA, whereas YCWE was the least efficacious. PYCW showed greater efficacy at adsorbing OTA than CIT. All adsorbents exhibited high adsorption efficacy for BEA, with an overall percentage average of bound mycotoxin exceeding 60%, whereas moderate efficacies for the other mycotoxins were observed (up to 37%). Differences in adsorbent efficacy of each adsorbent significantly varied according to experimental concentrations tested for each given mycotoxin (p < 0.05). The cell viability results from the bioassay using a bovine mammary epithelial cell line (MAC-T) indicated that all tested adsorbents could potentially mitigate mycotoxin-related damage to bovine mammary epithelium. Results from our studies suggested that all tested adsorbents had the capacity to adsorb selected mycotoxins in vitro, which could support their use to mitigate their effects in vivo.

Biochars and activated carbons as adsorbents of inorganic and organic compounds from multicomponent systems - A review

Biochars are obtained by biomass pyrolysis, whereas activated carbon is a biochar that has undergone chemical or physical activation. Owing to the large surface area and easy surface modification both solids are widely applied as adsorbents. They are low-costs materials, they could be regenerated and their disposal is not troublesome. Adsorption of heavy metals, dyes, pharmaceuticals on the surface of biochars and activated carbons, from simple systems of adsorbate containing only one compound, are described extensively in the literature. The present paper provides an overview of reports on adsorption of inorganic and organic compounds onto these two types of adsorbents from the mixed adsorbate systems. The described adsorbate systems have been divided into those consisting of: two or more inorganic ions, two or more organic compounds and both of them (inorganic and organic ones). The research of this type is carried out much less frequently due to the more complicated description of interactions in the mixed adsorbate systems.

A Review of the Dynamic Mathematical Modeling of Heavy Metal Removal with the Biosorption Process

Biosorption has great potential in removing toxic effluents from wastewater, especially heavy metal ions such as cobalt, lead, copper, mercury, cadmium, nickel and other ions. Mathematically modeling of biosorption process is essential for the economical and robust design of equipment employing the bioadsorption process. However, biosorption is a complex physicochemical process involving various transport and equilibrium processes, such as absorption, adsorption, ion exchange and surface and interfacial phenomena. The biosorption process becomes even more complex in cases of multicomponent systems and needs an extensive parametric analysis to develop a mathematical model in order to quantify metal ion recovery and the performance of the process. The biosorption process involves various process parameters, such as concentration, contact time, pH, charge, porosity, pore size, available sites, velocity and coefficients, related to activity, diffusion and dispersion. In this review paper, we describe the fundamental physical and chemical processes involved in the biosorption of heavy metals on various types of commonly employed biosorbents. The most common steady state and dynamic mathematical models to describe biosorption in batch and fixed-bed columns are summarized. Mathematical modeling of dynamic process models results in highly coupled partial differential equations. Approximate methods to study the sensitivity analysis of important parameters are suggested.

Enhanced Protein Adsorption Capacity of Macroporous Pectin Particles with High Specific Surface Area and an Interconnected Pore Network

There has been much interest in developing protein adsorbents using nanostructured particles, which can be engineered porous materials with fine control of the surface and pore structures. A significant challenge in designing porous adsorbents is the high percentage of available binding sites in the pores owing to their large surface areas and interconnected pore networks. In this study, continuing the idea of using porous materials derived from natural polymers toward the goal of sustainable development, porous pectin particles are reported. The template-assisted spray drying method using calcium carbonate (CaCO₃) as a template for pore formation was applied to prepare porous pectin particles. The specific surface area was controlled from 177.0 to 222.3 m² g^-1 by adjusting the CaCO₃ concentration. In addition, the effects of a macroporous structure, the specific surface area, and an interconnected pore network on the protein (lysozyme) adsorption capacity and adsorption mechanism were investigated. All porous pectin particles performed rapid adsorption (∼65% total capacity within 5 min) and high adsorption capacity, increasing from 1543 to the highest value of 2621 mg g^-1. The results are attributed to the high percentage of available binding sites located in the macropores owing to their large surface areas and interconnected pore networks. The macroporous particles obtained in this study showed a higher adsorption capacity (2621 mg g^-1) for lysozyme than other adsorbents. Moreover, the rapid uptake and high performance of this material show its potential as an advanced adsorbent for various macromolecules in the food and pharmaceutical fields.

Amino-assisted AHMT anchored on graphene oxide as high performance adsorbent for efficient removal of Cr(VI) and Hg(II) from aqueous solutions under wide pH range

The adsorbents with high adsorption capacity for simultaneously removing Cr(VI) and Hg(II) from aqueous solutions under broad working pH range are highly desirable but still extremely scarce. Here, a novel adsorbent with multidentate ligands was facilely fabricated by covalently bonding 4-amino-3-hydrazino-5-mercapto- 1,2,4-triazole on graphene oxide via the Schiff's base reaction. The maximum adsorption capacities of Cr(VI) and Hg(II) on the current adsorbent were 734.2 and 1091.1 mg/g, which were 14.36 and 5.61 times higher than that of the pure graphene oxide, respectively, exceeding those of most adsorbents previously reported. More interestingly, Cr(VI) and Hg(II) concentrations were decreased from 2 mg/L to 0.0001 mg/L for Hg(II) and 0.004 mg/L for Cr(VI), far below the WHO recommended threshold for drinking water. Moreover, the adsorbent shows an excellent performance for simultaneous removal of Cr(VI) and Hg(II) with more than 99.9% and 98.6% removal efficiencies in aqueous solutions. Finally, the adsorbent was successfully applied in dealing with the real industrial effluent, implying huge potential in industrial application. This work offers a new possibility for the removal of the metallic contaminants by rational designing target groups and ligands.

Incorporating the recovered carbon black produced in an industrial-scale waste tire pyrolysis plant into a natural rubber formulation

This paper presents the experimental results obtained after incorporating the recovered Carbon Black (rCB) produced in an industrial-scale waste tire pyrolysis plant into a Natural Rubber (NR) formulation. The purpose of this study is to increase the technical knowledge on the use of rCB as a sustainable raw material in the rubber industry. The rCB and virgin Carbon Black (vCB) (ref. N550) under study were characterized using elemental and proximate analyses, X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM) were used, and different measures, including the Brunauer-Emmett-Teller (BET) surface area (S_BET), particle size distribution (PSD), specific gravity, and pH, were estimated. The effect of rCB incorporation on the rheological, thermal, structural, and mechanical properties of the NR composites was assessed and compared to those obtained with vCB alone. The NR composites were prepared using different loads of vCB (20, 30, 40, and 50 phr), which was also replaced with rCB at different proportions (0, 50, and 100%). According to the characterization results, rCB offers lower reinforcement properties than vCB, which is attributable to its higher volatile matter and ash contents, higher apparent PSD, lower presence of acidic functional groups, and lower S_BET. Despite this, interesting performances can be achieved when rCB is partially incorporated into the formulations or by increasing its load in the composites. For instance, when 50% of vCB was replaced with rCB, the values of the aforementioned properties were found to be between those obtained with the NR composites prepared with vCB and rCB. In addition, when increasing the rCB loading, some properties matched the behavior exhibited by vCB alone, thus compensating for the low reinforcement properties of rCB. These results are expected to provide an important impetus to move towards circular economy strategies having very positive impacts from the sustainable perspective.

Comparative studies on the adsorption of metal ions from aqueous solutions using various functionalized graphene oxide sheets as supported adsorbents

Graphene oxide (GO) was chemically modified by bis(2-pyridylmethyl)amino groups (BPED) through a multistep procedure. For comparison, and to justify the grafting of BPED groups onto the GO sheets, the GO-based material obtained after each step was used as a solid phase adsorbent for removing Cu(II), Ni(II) and Co(II) metal ions from aqueous solutions. The influence of metal ion concentrations, pH, contact time and temperature on their adsorption onto the GO-based adsorbents was investigated and the GO-EDA-CAC-BPED adsorbent showed the highest ability to adsorb Cu(II), Ni(II) and Co(II) with a concentration of 250 mg.L^-1 at pH = 7. Additionally, it was demonstrated that the equilibrium adsorption capacities of these metal ions followed the order of Cu(II)>Ni(II)>Co(II) whatever the GO-based adsorbent. Moreover, to examine the underlying mechanism of the adsorption process, pseudo-first order, pseudo-second order, Elovich or Roginsky-Zeldovich and intraparticle diffusion models were fitted to experimental kinetic data. It was shown that the pseudo-second-order model was the most appropriate one to describe the adsorption of heavy metal ions by the GO-based materials. Finally, it was demonstrated that their desorption/regeneration capacities were higher than 10 cycles, opening the path to the removal of metal ions from wastewater solutions.

Binding Capacity and Selectivity of Functionalized and Un-functionalized Carbon Nanotubes for Development of Copper-Detecting Printable Sensor

Carbon nanotubes (CNTs) have unique properties which can be modified through surface functionalization. The ability of several functionalized and un-functionalized CNTs to bind copper was investigated as a first step toward developing a printable CNT-based sensor to detect copper in aqueous systems. Binding capacity and specificity were shown to vary by functionalization and vendor. CNTs from two vendors were tested, and the equilibrium binding data was fitted using two isotherm models. Calculated q_max (mg/g) values indicated one vendor's carboxyl-functionalized CNTs had the greatest binding capacity (94-115 mg/g), while other carboxyl-functionalized CNTs and amine-functionalized CNTs had similar capacities to un-functionalized CNTs (15-30 mg/g). Hydroxyl-functionalized CNTs had the lowest copper binding capacity (7-8 mg/g) of the CNTs tested. Freundlich isotherms showed no obvious trends in binding affinity, but suggested that binding was primarily due to chemisorption. Variations in CNT size, functionalization percentage, and purity could explain, partially, the observed adsorption differences.

Competitive heavy metal adsorption onto new and aged polyethylene under various drinking water conditions

The study goal was to identify factors that influence copper (Cu), iron (Fe), lead (Pb), manganese (Mn), and zinc (Zn) loading on new and aged low-density polyethylene (LDPE) under various drinking water conditions. The applied aging procedure increased LDPE surface area, hydrophilicity and the number of oxygen containing functional groups. Aged LDPE adsorbed up to a 5 fold greater metals than the new LDPE: Cu > Pb, Zn > Mn. Water pH (5.5 to 10.5) significantly altered LDPE surface metal loading. The organic carbon leached from plastic pipes inhibited Cu adsorption (-43.8%), but other metals were less impacted (-5.7% to -9.1%). The addition of free chlorine and corrosion inhibitor retarded metal adsorption to suspended LDPE materials. Overall, by changing water conditions total metal loadings (i.e., Cu, Mn, Pb and Zn) were altered 20.1 to 35.4%. When Fe was present, Cu (-4.0%) and Pb (-4.5%) loadings were reduced, while lesser impacts were found for Mn and Zn. Cu²⁺, Pb²⁺ and Zn²⁺ hydroxides and oxides were identified as the major metal deposit forms on the LDPE surface by XPS. To better predict metal fate in plastic piping systems, plastic surface characteristics, dissolved organics, water pH, hydraulic conditions and microbial growth should be considered.

Adsorption behaviours and mechanisms of heavy metal ions' impact on municipal waste composts with different degree of maturity

Composting may change the adsorption characteristics and mechanisms of organic materials due to their differences in organic chemical functional groups and surface structures. The adsorption properties of heavy metals onto the municipal solid waste compost (MSW-C) and its secondary fermentation form (MSW-SC) were comparatively investigated in single, binary and multiple solutions by batch experiments. In the single-metal system, the maximum adsorption capacities of Cu, Zn, Cd and Ni onto MSW-SC were 29.2, 26.3, 38.1 and 22.0 mg g^-1, respectively, and showed higher than that of MSW-C. The adsorption fitted best with the pseudo-second-order kinetics and Langmuir isotherms. The competitive adsorption results indicated that the composts exhibited good selectivity in the adsorption of Cu over Cd, Zn and Ni; thus, for the quaternary-metal systems, the adsorption sequence was Cu > Zn > Cd > Ni. Humic acid content, cation exchange capacity and surface area were increased following the secondary composting. FTIR analysis indicated amine and aromatic compounds were main binding sites accounting for metal sorption. SEM-EDX analysis suggested that the MSW-SC had rough surfaces and stronger adsorption capacity. Decreasing percentage of exchangeable metals was found in the metal-loaded MSW-SC based on a speciation analysis. This study highlights the interactive impacts of different metals during adsorption by compost with different maturity, the secondary composting process was a multifunctional improvement of sorption characteristics and MSW-SC was developed to be a highly efficient biosorbent.

Use of polymeric sub-micron ion-exchange resins for removal of lead, copper, zinc, and nickel from natural waters

This research investigated the removal capacity of polymeric sub-micron ion-exchange resins (SMR) for removal of lead, copper, zinc, and nickel from natural waters in competition with natural organic matter (NOM). Polymeric SMR particles were created and tested to ensure that they were adequately dispersed in the solution. They removed little NOM (10% or less) from river water and wastewater, indicating that competition from NOM was not a major concern. SMR were able to remove 82%±0.2% of lead, 46%±0.6% of copper, 55%±20% of zinc, and 17%±2% of nickel from river water spiked with 500μg/L of each. Similarly, in wastewater, they were able to remove 86%±0.1% of lead, 38%±0.8% of copper, 28%±1% of zinc, and 11%±1% of nickel.

Equilibrium and Kinetic Study of Lead and Copper Ion Adsorption on Chitosan-Grafted-Polyacrylic Acid Synthesized by Surface Initiated Atomic Transfer Polymerization

In this work, we synthesized chitosan grafted-polyacrylic acid (CS-g-PA) through surface-initiated atom transfer radical polymerization (SI-ATRP). We also studied the adsorption process of copper and lead ions onto the CS-g-PA surface. Adsorption equilibrium studies indicated that pH 4.0 was the best pH for the adsorption process and the maximum adsorption capacity over CS-g-PA for Pb²⁺ ions was 98 mg·g⁻¹ and for Cu²⁺ it was 164 mg·g⁻¹, while for chitosan alone (CS), the Pb²⁺ adsorption capacity was only 14.8 mg·g⁻¹ and for Cu²⁺ it was 140 mg·g⁻¹. Furthermore, the adsorption studies indicated that Langmuir model describes all the experimental data and besides, pseudo-second-order model was suitable to describe kinetic results for the adsorption process, demonstrating a larger kinetic constant of the process was larger for Pb²⁺ than Cu²⁺. Compared to other adsorbents reported, CS-g-PA had comparable or even superior adsorbent capacity and besides, all these results suggest that the new CS-g-PA polymers had potential as an adsorbent for hazardous and toxic metal ions produced by different industries.

Effects of wood vinegar on properties and mechanism of heavy metal competitive adsorption on secondary fermentation based composts

In this study, secondary municipal solid waste composts (SC) and wood vinegar treated secondary compost (WV-SC) was prepared to investigate the capability for single-heavy metals and multi-metal systems adsorption. The adsorption sequence of WV-SC for the maximum single metals sorption capacities was Cd (42.7mgg^-1) > Cu (38.6mgg^-1) > Zn (34.9mgg^-1) > Ni (28.7mgg^-1) and showed higher than that of SC adsorption isotherm. In binary/quaternary-metal systems, Ni adsorption showed a stronger inhibitory effect compared with Zn, Cd and Cu on both SC and WV-SC. According to Freundlich and Langmuir adsorption isotherm models, as well as desorption behaviors and speciation analysis of heavy metals, competitive adsorption behaviors were differed from single-metal adsorption. Especially, the three-dimensional simulation of competitive adsorption indicated that the Ni was easily exchanged and desorbed. The amount of exchangeable heavy metal fraction were in the lowest level for the metal-loaded adsorbents, composting treated by wood vinegar improved the adsorbed metals converted to the residue fraction. This was an essential start in estimating the multiple heavy metal adsorption behaviors of secondary composts, the results proved that wood vinegar was an effective additive to improve the composts quality and decrease the metal toxicity.

Surface sodium lignosulphonate-immobilized sawdust particle as an efficient adsorbent for capturing Hg2+ from aqueous solution

In this work, the soluble sodium lignosulphonate (LS_Na) molecules were successfully grafted onto the surface of pine sawdust (PSD) particles to obtain an efficient adsorbent (PSD-LS) for removing Hg²⁺ from wastewater. In advance, the surface of sawdust particles were carboxymethylated by chloroacetic acid, the LS_Na would be anchored on the surface by a heterogeneous esterification reaction occurred between the hydroxyl of LS_Na and carboxyl on PSD surface. The resultant product (PSD-LS) exhibited a good adsorption performance for Hg²⁺ with adsorption capacity up to 164.77 mg/g and it was characterized by scanning electron microscope (SEM), energy dispersive X-ray diffraction (EDX), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The effects of pH, contact time, adsorption temperature and initial concentration on the adsorption of Hg²⁺ were investigated. Results showed that the pseudo-second-order kinetics and Langmuir isotherm model could describe the adsorption process better. In addition, the composite adsorbent has outstanding reusability with high and stable desorption rates under several continuous cycle. These findings suggested that PSD-LS was a potential adsorbent to remove hazardous metal ions from wastewater.

Competitive sorption of Pb(II), Cu(II) and Ni(II) on carbonaceous nanofibers: A spectroscopic and modeling approach

The competitive sorption of Pb(II), Cu(II) and Ni(II) on the uniform carbonaceous nanofibers (CNFs) was investigated in binary/ternary-metal systems. The pH-dependent sorption of Pb(II), Cu(II) and Ni(II) on CNFs was independent of ionic strength, indicating that inner-sphere surface complexation dominated sorption Pb(II), Cu(II) and Ni(II) on CNFs. The maximum sorption capacities of Pb(II), Cu(II) and Ni(II) on CNFs in single-metal systems at a pH 5.5±0.2 and 25±1°C were 3.84 (795.65mg/g), 3.21 (204.00mg/g) and 2.67 (156.70mg/g)mmol/g, respectively. In equimolar binary/ternary-metal systems, Pb(II) exhibited greater inhibition of the sorption of Cu(II) and Ni(II), demonstrating the stronger affinity of CNFs for Pb(II). The competitive sorption of heavy metals in ternary-metal systems was predicted quite well by surface complexation modeling derived from single-metal data. According to FTIR, XPS and EXAFS analyses, Pb(II), Cu(II) and Ni(II) were specifically adsorbed on CNFs via covalent bonding. These observations should provide an essential start in simultaneous removal of multiple heavy metals from aquatic environments by CNFs, and open the doorways for the application of CNFs.

Multi-component adsorption of copper, nickel and zinc from aqueous solutions onto activated carbon prepared from date stones

The removal of Cu(2+), Ni(2+), and Zn(2+) ions from their multi-component aqueous mixture by sorption on activated carbon prepared from date stones was investigated. In the batch tests, experimental parameters were studied, including solution pH, contact time, initial metal ions concentration, and temperature. Adsorption efficiency of the heavy metals was pH-dependent and the maximum adsorption was found to occur at around 5.5 for Cu, Zn, and Ni. The maximum sorption capacities calculated by applying the Langmuir isotherm were 18.68 mg/g for Cu, 16.12 mg/g for Ni, and 12.19 mg/g for Zn. The competitive adsorption studies showed that the adsorption affinity order of the three heavy metals was Cu(2+) > Ni(2+) > Zn(2+). The test results using real wastewater indicated that the prepared activated carbon could be used as a cheap adsorbent for the removal of heavy metals in aqueous solutions.

Reducing hazardous heavy metal ions using mangium bark waste

The objective of this study was to evaluate the characteristics of mangium bark and its biosorbent ability to reduce heavy metal ions in standard solutions and wastewater and to assess changes in bark characteristics after heavy metal absorption. The experiments were conducted to determine heavy metal absorption from solutions of heavy metals alone and in mixtures as well as from wastewater. The results show that mangium bark can absorb heavy metals. Absorption percentages and capacities from single heavy metal solutions showed that Cu(2+) > Ni(2+) > Pb(2+) > Hg(2+), while those from mixture solutions showed that Hg(2+) > Cu(2+) > Pb(2+) > Ni(2+). Wastewater from gold mining only contained Cu, with an absorption percentage and capacity of 42.87 % and 0.75 mg/g, respectively. The highest absorption percentage and capacity of 92.77 % and 5.18 mg/g, respectively, were found for Hg(2+) in a mixture solution and Cu(2+) in single-metal solution. The Cu(2+) absorption process in a single-metal solution changed the biosorbent characteristics of the mangium bark, yielding a decreased crystalline fraction; changed transmittance on hydroxyl, carboxyl, and carbonyl groups; and increased the presence of Cu. In conclusion, mangium bark biosorbent can reduce hazardous heavy metal ions in both standard solutions and wastewater.

Competitive Fixed-Bed Adsorption of Pb(II), Cu(II), and Ni(II) from Aqueous Solution Using Chitosan-Coated Bentonite

Fixed-bed adsorption studies using chitosan-coated bentonite (CCB) as adsorbent media were investigated for the simultaneous adsorption of Pb(II), Cu(II), and Ni(II) from a multimetal system. The effects of operational parameters such as bed height, flow rate, and initial concentration on the length of mass transfer zone, breakthrough time, exhaustion time, and adsorption capacity at breakthrough were evaluated. With increasing bed height and decreasing flow rate and initial concentration, the breakthrough and exhaustion time were observed to favorably increase. Moreover, the adsorption capacity at breakthrough was observed to increase with decreasing initial concentration and flow rate and increasing bed height. The maximum adsorption capacity at breakthrough of 13.49 mg/g for Pb(II), 12.14 mg/g for Cu(II), and 10.29 mg/g for Ni(II) was attained at an initial influent concentration of 200 mg/L, bed height of 2.0 cm, and flow rate of 0.4 mL/min. Adsorption data were fitted with Adams-Bohart, Thomas, and Yoon-Nelson models. Experimental breakthrough curves were observed to be in good agreement (R2>0.85andE%<50%) with the predicted curves generated by the kinetic models. This study demonstrates the effectiveness of CCB in the removal of Pb(II), Cu(II), and Ni(II) from a ternary metal solution.

Highly efficient performance of activated carbon impregnated with Ag, ZnO and Ag/ZnO nanoparticles as antimicrobial materials

Materials for biological contacts.

Removal of metal ions from wastewater using EB irradiation in combination with HA/TiO₂/UV treatment

The electron beam (EB) irradiation technology was applied for removal of Cu(2+), Sr(2+), and Co(2+) ions from wastewater. The aim of this study is to achieve an efficient treatment process of wastewater using EB and introducing a combination of humic acid (HA) as a natural organic polymer and ultraviolet irradiation of a TiO2 (TiO2/UV), as a suspended catalyst in the treatment of wastewater solutions (TiO2/UV+HA). The experimental results showed that the percentage removal of Cu(2+), Sr(2+), and Co(2+)ions was 41%, 87% and 75% respectively, at 125 kGy. In the presence of TiO2 photocatalyst and exposure of the investigated wastewater to ultraviolet rays before irradiation by the EB the percentage removal of Cu(2+) ions became 51%, while the percentage removal of both Sr(2+) and Co(2+) ions was slightly improved; was 87% and 75%, respectively at the same EB dose. On the other hand, by introducing the combination of TiO2/UV+HA, only an irradiation dose of about 50kGy led to removal of Cu(2+), Sr(2+), and Co(2+) completely from the wastewater. Mechanisms of interactions between HA and Cu(2+), Co(2+) and Sr(2+) metal ions were suggested and discussed.

Competitive adsorption of Pb(II), Cu(II) and Zn(II) onto xanthate-modified magnetic chitosan

The competitive adsorption of Pb(II), Cu(II) and Zn(II) onto a novel xanthate-modified magnetic chitosan (XMCS) was systematically investigated in single and ternary metal systems. In single system, equilibrium studies showed that the adsorption of Pb(II), Cu(II) and Zn(II) followed the Langmuir model and the maximum adsorption capacities were found to be 76.9, 34.5 and 20.8mg/g, respectively. In ternary system, the combined action of the metals was found to be antagonistic and the metal sorption followed the order of Pb(II)>Cu(II)>Zn(II); the Langmuir isotherm fitted the data of Pb(II) and Cu(II) well while the isotherm data of Zn(II) correlated well with the Freundlich model. The Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS) studies showed that the thiol and amino group participated in the adsorption of Pb(II), Cu(II) and Zn(II).

Heavy metal ion adsorption behavior in nitrogen-doped magnetic carbon nanoparticles: isotherms and kinetic study

To clarify the heavy metal adsorption mechanism of nitrogen-doped magnetic carbon nanoparticles (N-MCNPs), adsorption capacity was investigated from the adsorption isotherms, kinetics and thermodynamics points of view. The obtained results showed that the equilibrium adsorption behavior of Cr(3+) ion onto the N-MCNPs can be applied to the Langmuir model and pseudo-second-order kinetics. It indicated that the fabricated N-MCNPs had the homogenous surface for adsorption and all adsorption sites had equal adsorption energies. Furthermore, the adsorption onto N-MCNPs taken place through a chemical process involving the valence forces. According to the thermodynamics, the adsorption process is spontaneous and endothermic in nature which means that the adsorption capacity increases with increasing temperature due to the enhanced mobility of adsorbate molecules. The effects of the solution pH and the species of heavy metal ion on the adsorption uptake were also studied. The synthesized N-MCNPs exhibited an enhanced adsorption capacity for the heavy metal ions due to the high surface area and large amount of nitrogen contents.

Displacement mechanism of binary competitive adsorption for aqueous divalent metal ions onto a novel IDA-chelating resin: isotherm and kinetic modeling

Adsorptive properties for Cu (II), Pb (II) and Cd (II) onto an iminodiacetic acid (IDA) chelating resin were systematically investigated at the optimal pH-value in both single and binary solutions using batch experiments. The Langmuir isotherm model and the pseudo second-order rate equation could explain respectively the isotherm and kinetic experimental data for sole-component system with much satisfaction. The maximum adsorption capacity in single system for Cu (II), Pb (II) and Cd (II) was calculated to be 2.27 mmol/g, 1.27 mmol/g and 0.65 mmol/g individually. The initial adsorption rate followed the order as Cu (II)>Pb (II)>Cd (II) at the fixed initial concentration, and for each metal the initial sorption rate increased as the initial concentration increased. In addition, the modified Langmuir model could describe the binary competitive adsorption behavior successfully, with which the interaction coefficient was obtained to follow the order as Cu (II)<Pb (II)<Cd (II). Furthermore, in every case of the investigated three binary systems, the reduction in both the uptake amounts and distribution coefficients testified the antagonistic competitive phenomena. Obviously, this novel IDA-chelating resin possessed of a good selectivity toward Cu (II) over Pb (II) and Cd (II) for the obtained highest separation factor values were up to 21.30 and 133.91 in the range of tested. This interaction mechanism between the favorable component and other metal ions could mainly contribute to the direct displacement impact which be herewith illustrated schematically.