High surface area-activated carbon from Glycyrrhiza glabra residue by ZnCl2 activation for removal of Pb(II) and Ni(II) from water samples

A high-surface-area activated carbon was prepared by chemical activation of Glycyrrhiza glabra residue with ZnCl₂ as active agent. Then, the adsorption behavior of Pb(II) and Ni(II) ion onto produced activated carbon has been studied. The experimental data were fitted to various isotherm models. According to Langmuir model, the maximum adsorption capacity of Pb(II) and Ni(II) ions were found to be 200 and 166.7 mg g⁻¹, respectively, at room temperature. Kinetic studies showed the adsorption process followed pseudo second-order rate model. High values of intra-particle rate constants calculated shows the high tendency of activated carbon for removal of Pb(II) and Ni(II) ions.     

Removal of lead ions using phosphorylated sawdust

To increase the uptake capacity of lead ions, surface of sawdust were modified into phosphate groups. The phosphorylated sawdust prepared through chemical reaction with H₃PO₄ (85%) showed a high uptake capacity of about 1.45 mmol Pb/g-dry mass at pH 4. The component of phosphorylated sawdust was analyzed by EDX (energy dispersive X-ray) and the increase of phosphate group was confirmed. The phosphorylated sawdust had a high uptake capacity at low temperature of 10 °C and could remove lead ions of about 98% with 0.04 g of modified sawdust. Also, most of adsorption of lead ions was completed within 40 min.     

Adsorption of perchlorate onto raw and oxidized carbon nanotubes in aqueous solution

Perchlorate (ClO₄^?) is an emerging trace contaminant. The adsorption of ClO₄^? on raw and oxidized carbon nanotubes (CNTs) was investigated to elucidate the affinity mechanism of CNTs with anion pollutants. The adsorption of ClO₄^? into different CNTs increased in the order multi-walled CNTs < single-walled CNTs < double-walled CNTs (DWCNTs). Co-existing anions (SO₄^2?, NO₃^?, Cl^?) significantly weakened ClO₄^? adsorption, while the co-existence of Fe³⁺ and cetyltrimethylammonium cations increased ClO₄^? adsorption 2- to 3-fold. ClO₄^? adsorption was promoted by oxidized DWCNTs due to the introduction of more oxygen-containing functional groups, which served as additional adsorption sites. The pH values significantly affected the zeta potential of raw and oxidized DWCNTs and thus ClO₄^? adsorption. The pH-dependent curves of ClO₄^? adsorption on CNTs were distinct from those of conventional sorbents (e.g., activated carbon and resin). Maximum ClO₄^? adsorption occurred at pH = the isoelectric point (pH_IEP) + 0.85 rather than at pH < pH_IEP, which cannot be explained by electrostatic interactions alone. Hydrogen bonding is proposed to be a dominant mechanism at neutral pH for the interaction of ClO₄^? with CNTs, and variations of ClO₄^? affinity with CNTs in different pH ranges are illustrated.     

Flame atomic absorption spectrometric determination of Cd,Pb, and Cu in food samples after pre-concentration using 4-(2-thiazolylazo) resorcinol-modified activated carbon

This work aimed to develop a solid-phase extraction method using low-cost activated carbon produced from waste and modified with 4-(2-thiazolylazo) resorcinol for Cd(II), Pb(II), and Cu(II). The results showed that quantitative recovery of analytes was obtained at pH 6 with 3 M nitric acid as the eluent and a sample volume up to 1000 mL. The method was validated using certified reference material and addition-recovery tests. The limits of detection (LODs) for Pb(II), Cd(II), and Cu(II) were 2.03 μg L⁻¹, 0.15 μg L⁻¹, and 0.19 μg L⁻¹, respectively. The procedure was applied for determination of analytes in food samples.     

The effects of the surface oxidation of activated carbon,the solution pH and the temperature on adsorption of ibuprofen

A commercial microporous–mesoporous granular activated carbon was modified by oxidation with either H₂O₂ in the presence or absence of ultrasonic irradiation, or NaOCl or by a thermal treatment under nitrogen flow. Raw and modified materials were characterized by N₂ adsorption–desorption measurements at 77 K, Boehm titrations, pH measurements and X-ray photoelectron spectroscopy. Ibuprofen adsorption kinetic and isotherm studies were carried out at pH 3 and 7 on raw and modified materials. The thermodynamic parameters of adsorption were calculated from the isotherms obtained at 298, 313 and 328 K. The pore size distribution of carbon loaded with ibuprofen brought out that adsorption occurred preferentially into the ultramicropores. The adsorption of ibuprofen on pristine activated carbon was found endothermic, spontaneous (ΔG° = −1.1 kJ mol⁻¹), and promoted at acidic pH through dispersive interactions. All explored oxidative treatments led mainly to the formation of carbonyl groups and in a less extent to lactonic and carboxylic groups. This then helped to enhance the adsorption uptake while decreasing adsorption Gibbs energy (notably −7.3 kJ mol⁻¹ after sonication in H₂O₂). The decrease of the adsorption capacity after bleaching was attributed to the presence of phenolic groups.     

Reduction of [Fe(III)EDTA]− catalyzed by activated carbon modified with KOH solution

NO and SO₂ can be eliminated simultaneously by [Fe(II)EDTA]^2? solution with a pH range of 5.6–8.0 at 25–80 °C. Activated carbon is used to catalyze the regeneration of [Fe(II)EDTA]^2?. In this paper, KOH solution has been utilized to modify the carbon to improve its catalytic capability. Experimental results show that the optimal modification factors are as follow: KOH concentration 6.0 mol l^?1, impregnation time 9 h, activation temperature 700 °C and activation time 4 h. After KOH modification, the surface area of activated carbon decreases. But its basicity is enhanced, which plays an important role in improving the catalytic characteristics of activated carbon in the reduction of [Fe(III)EDTA]^?. The experimental results demonstrate that the activated carbon modified by concentrated KOH solution can get a higher NO removal efficiency than the original activated carbon.     

Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

A novel magnetic ion imprinted polymer for selective adsorption of trace amounts of lead(II) ions in environment samples

In this work a novel ion imprinted polymer (IIP) based on 4-(vinylamino)pyridine-2,6-dicarboxylicacid (VPyDC), was coated on Fe₃O₄ nano-particles. The application of this magnetic sorbent was investigated for preconcentration and determination of trace Pb(II) ions by flame atomic absorption spectrometry. Effects of various parameters such as sample pH, adsorption/desorption time and eluent were investigated during this study. The relative standard deviation and limit of detection of the method were found to be 1.8% and 0.9 ng mL⁻¹, respectively. The accuracy of this method was confirmed using various standard reference materials, then it was used for Pb(II) determination in environmental samples.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

Continuous preparation of Fe3O4 nanoparticles combined with surface modification by L-cysteine and their application in heavy metal adsorption

L-cysteine functionalized Fe₃O₄ magnetic nanoparticles (Cys–Fe₃O₄ MNPs) were continuously fabricated by a simple high-gravity reactive precipitation method combined with surface modification through a novel impinging stream-rotating packed bed with the assistance of sonication. The obtained Cys–Fe₃O₄ MNPs was characterized by XRD, TEM, FTIR, TGA and VSM, and further used for the removal of heavy metal ions from aqueous solution. The influence of pH values, contact time and initial metal concentration on the adsorption efficiency were investigated. The results revealed that the adsorption of Pb(II) and Cd(II) were pH dependent process, and the pH 6.0 was found to be optimum condition. Moreover, the adsorption kinetic for Cys–Fe₃O₄ MNPs followed the mechanism of the pseudo-second order kinetic model, and their equilibrium data were fitted with the Langmuir isothermal model well. The maximum adsorption capacities calculated from Langmuir equation were 183.5 and 64.35 mg g⁻¹ for Pb(II) and Cd(II) at pH 6.0, respectively. Furthermore, the adsorption and regeneration experiment showed there was about 10% loss in the adsorption capacity of the as-prepared Cys–Fe₃O₄ MNPs for heavy metal ions after 5 times reuse. All the above results provided a potential method for continuously preparing recyclable adsorbent applied in removing toxic metal ions from wastewater through the technology of process intensification.     

Adsorption separation of vinyl chloride and acetylene on activated carbon modified by metal ions

This work mainly involved the adsorption separation of vinyl chloride and acetylene on modified activated carbons. Six metal ions with different hardness were loaded on activated carbon respectively. The effect of metal ions on the adsorption separation performance of vinyl chloride and acetylene was investigated. The experimental results shown that the separation factor of C₂H₃Cl to C₂H₂ over modified activated carbon followed the order: Al(III)/AC > Mg(II)/AC > Fe(III)/AC > AC > Zn(II)/AC ≈ Cu(II)/AC > Ag(I)/AC. The effect of the hardness of metal ions on the adsorption capacity of C₂H₂ was more remarkable than that of C₂H₃Cl, thus the separation factor of C₂H₃Cl to C₂H₂ increased with the rising of absolute hardness of the metal ions.     

Preparation,modification and industrial application of activated carbon from almond shell

Almond shell was used to prepare activated carbon using physical activation method, consisted of carbon dioxide (CO₂) gasification. The effects of the preparation variables which were activation temperature, activation time and carbon dioxide flow rate on the adsorption capacity of iodine and methylene blue solution were investigated. The optimal activated carbon was obtained by these conditions as follows: 800 °C activation temperature, 100 cm³/min carbon dioxide flow rate and 120 min activation time. The characterization of carbon materials is performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ¹³C (CP/MAS and MAS) solid-state NMR, nitrogen adsorption (BET) and Boehm's titration method. For an industrial application, the optimal activated carbon was ammoxidated to improve its adsorption capacity toward total organic carbon from Tunisian industrial phosphoric acid. The influence of experimental parameters such as specific consumption, initial concentration, contact time, agitation speed and temperature on TOC removal was studied.     

Cooperative adsorption of bisphenol-A and chromium(III) ions from water on activated carbons prepared from olive-mill waste

The aim of this study was to investigate the simultaneous adsorption of bisphenol A (BPA) and chromium ions from aqueous solution on activated carbons (both commercial and prepared from olive-mill waste), analyzing both kinetic and equilibrium adsorption data. The effects of solution pH and ionic strength on the adsorption processes were also studied, as well as the chemical interactions between the carbon surface and the pollutants. The activated carbon prepared from olive-mill waste showed: a large surface area (up to 1641 m² g⁻¹), a highly heterogeneous micropore distribution, and a basic chemical nature. The pore volume diffusion model was used to predict the adsorption kinetics of both pollutants. The effective diffusion coefficients ranged between 1.15 × 10⁻⁶ and 9.18 × 10⁻⁷ cm² s⁻¹ for the BPA–Cr(III) system and between 1.65 × 10⁻⁶ and 2.8 × 10⁻⁶ cm² s⁻¹ for the Cr(III)–BPA system. The presence of both Cr(III) and BPA in the binary systems increases the adsorption effective diffusion coefficients and therefore the overall adsorption rate of each pollutant. The increased adsorption of each adsorbate when both pollutants are present is due to the in situ formation of complex compounds between Cr(III), acting as central metallic cation, and BPA, acting as ligand, during adsorption of both adsorbates on activated carbon.     

Metal sorption on macroporous poly(GMA-co-EGDMA) modified with ethylene diamine

Two samples of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), poly(GMA-co-EGDMA), with different porosity parameters were synthesized by suspension copolymerization and modified by ring-opening reaction of the pendant epoxy groups with ethylene diamine (EDA). The samples were characterized by mercury porosimetry, FT-IR spectroscopy and elemental analysis. The sorption rate of the modified copolymer, poly(GMA-co-EGDMA)-en for Cu(II) ions determined under non-competitive conditions was relatively rapid, i.e. the maximum capacity was reached within 30 min. Batch sorption capacities for Cu(II), Fe(II), Mn(II), Cd(II), Zn(II), Pb(II), Cr(III) and Pt(IV) ions were determined under non-competitive conditions in the pH range 1.25–5.5 at room temperature. The maximum sorption capacities of poly(GMA-co-EGDMA)-en under non-competitive conditions were 1.30 mmol/g for Pt(IV) at pH 5.5, 1.10 mmol/g for Cu(II) at pH 5.5, 1.06 mmol/g for Pb(II) at pH 1.25 and 0.67 mmol/g for Cd(II) ions at pH 5.5. The selectivity of poly(GMA-co-EGDMA)-en towards Cu(II), Co(II), Ni(II), Pb(II) and Pt(IV) ions was investigated under competitive conditions. Poly(GMA-co-EGDMA)-en showed high selectivity for Pt(IV) over Cu(II), Co(II), Ni(II) and Pb(II) ions at pH 2.1. At pH 5.5, the metal sorption capacities of poly(GMA-co-EGDMA)-en decreased in the order: Cu(II) > Co(II) > Pt(IV) ≈ Ni(II) > Pb(II). Regeneration of the Cu(II), Ni(II) and Pb(II) loaded poly(GMA-co-EGDMA)-en with 2 M H₂SO₄ showed that the polymer can be reused in several sorption/desorption cycles.     

Effect of core-shell reversal on the structural,magnetic and adsorptive properties of Fe2O3-GO nanocomposites

Effect of core-shell reversal on the nanocomposites of graphene oxide (GO) and ferric oxide (Fe₂O₃) was studied. Fe₂O₃@GO core-shell nanosheets were synthesized by sonication method, while the GO@Fe₂O₃ core-shell nanospheres by employing N,N′-dicyclohexylcarbodimide as the binding agent for the wrapping of GO sheets on pre-formed Fe₂O₃ nanoparticles (NPs). The phase composition, crystallinity and morphology of the nanocomposites were characterized by FT-IR, TEM, SEM-EDS, VSM, BET surface area study and XRD techniques. The saturation magnetization (M_s) was 1.25 and 0.51 emu g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO respectively owing to the dependence of magnetic properties on the reversal of core-shell. BET analysis revealed the surface area of 100.32 m² g⁻¹ and 45.69 m² g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO nanocomposites respectively. The fabricated nanocomposites were analyzed as adsorbents for the uptake of Pb (II) ions. The impact of various factors affecting adsorption process such as pH, adsorbent dose, contact time, temperature and metal ion concentration was also investigated. GO@Fe₂O₃ core-shell nanospheres showed a higher adsorption capacity for Pb (II) ions as compared to Fe₂O₃@GO core-shell nanosheet with the maximum adsorption capacities (q_m) of 303.0 and 125.0 mg g⁻¹ respectively. The equilibrium data was estimated by Freundlich, Langmuir, D-R and Temkin isotherm models. Thermodynamic analysis confirmed the spontaneous and exothermic nature of the adsorption process. The adsorption kinetics was significantly fitted to pseudo-second order model. The results confirmed that core-shell reversal can significantly alter the adsorptive properties of Fe₂O₃-GO nanocomposite     

Utilization of Crofton weed for preparation of activated carbon by microwave induced CO2 activation

Crofton weed was converted into a high-quality activated carbon (CWAC) via microwave-induced CO₂ physical activation. The operational variables including activation temperature, activation duration and CO₂ flow rate on the adsorption capability and activated carbon yield were identified. Additionally the surface characteristics of CWAC were characterized by nitrogen adsorption isotherms, FTIR and SEM. The operating variables were optimized utilizing the response surface methodology and were identified to be an activation temperature of 980 °C, an activation duration of 90 min and a CO₂ flow rate of 300 ml/min with a iodine adsorption capacity of 972 mg/g and yield of 18.03%. The key parameters that characterize quality of the porous carbon such as the BET surface area, total pore volume and average pore diameter were estimated to be 1036 m²/g, 0.71 ml/g and 2.75 nm, respectively. The findings strongly support the feasibility of microwave heating for preparation of high surface area porous carbon from Crofton weed via CO₂ activation.     

Synthesis of NIPAAm-based polymer-grafted silica beads by surface-initiated ATRP using Me4Cyclam ligands and the thermo-responsive behaviors for lanthanide(III) ions

The applicability of atom transfer radical polymerization (ATRP) to the copolymerization of N-isopropylacrylamide (NIPAAm) with N-vinyl-2-pyrrolidone (NVP) was examined in CuCl/CuCl₂-catalyst system using tris[2-(dimethylamino)ethyl]amine (Me₆TREN) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me₄Cyclam) as ligands. In the Me₆TREN system, less reactive NVP not only does not quantitatively copolymerize but also interferes with homopolymerization of NIPAAm units. In contrast, the Me₄Cyclam system under heating was more active, although the controllability for polymer homogeneity is lower than Me₆TREN system. The application of active Me₄Cyclam system to surface-initiated ATRP has successfully prepared silica beads surface-modified with NIPAAm copolymers of NVP and 4-vinylpyridine (VPy). The thermo-responsive behavior of surface-grafted NIPAAm-based polymers was investigated for lanthanide trivalent ions (Ln(III)) in different pH solutions. In the weak acidic solutions of pH = 5.4–5.6, all the surface-grafted polymers including poly(NIPAAm) exhibited only adsorption behavior with regular selectivity (Eu³⁺ > Sm³⁺ > Nd³⁺ > Ce³⁺ > La³⁺) below the phase-transition temperatures. In the more acidic solution of pH = 2.9, the surface-grafted poly(NIPAAm) and NVP copolymers exhibited adsorption and desorption behaviors below and above the phase-transition temperatures, while VPy copolymers exhibited only adsorption independent of temperature change. Furthermore, the adsorption capacity of all the surface-grafted polymers was deteriorated by the lowering of pH. The observed desorption and the deterioration of adsorption capacity suggest the weakening of adsorption strength for Ln(III) in low pH solutions. In this study, a possible adsorption/desorption mechanism of Ln(III) on surface-grafted NIPAAm-based polymers is discussed.     

Synthesis and characterization of magnetic polyHIPEs with humic acid surface modified magnetic iron oxide nanoparticles

Magnetic macroporous polymer monoliths have been prepared using styrene/divinylbenzene (S/DVB) high internal phase emulsions (HIPEs) as templates. Humic acid surface modified iron oxide magnetic nanoparticles (Fe₃O₄@HA) have been used to prepare magnetic emulsion templates. The effect of magnetic particle concentration has been investigated by changing the ratio of Fe₃O₄@HA nanoparticles in the continuous phase. Highly macroporous polymers with magnetic response were obtained by the removal of the internal phase after the curing of emulsions at 80 °C. Fe₃O₄@HA particles were characterized by XRD and FTIR. The porosity, pore morphology and magnetic properties of the macroporous polymers were characterized as a function of the Fe₃O₄@HA concentration by scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET) molecular adsorption method and vibrating sample magnetometry (VSM), respectively. BET and VSM measurements demonstrated that the specific surface area and the saturation magnetization of the polymer monoliths were changed according to the Fe₃O₄@HA concentration between 8.77–35.08 m² g^?1 and 0.63–11.79 emu g^?1, respectively. Resulting magnetic monoliths were tested on the adsorption of Hg(II) and atomic absorption spectroscopy (AAS) was used to calculate the adsorption capacities. The maximum adsorption capacity of the magnetic monoliths was calculated to be 20.44 mmol g^?1 at pH 4.     

Enhanced CO2/N2 selectivity in amidoxime-modified porous carbon

In this work, we examine the use of the amidoxime functional group grafted onto a hierarchical porous carbon framework for the selective capture and removal of carbon dioxide from combustion streams. Measured CO₂/N₂ ideal selectivity values for the amidoxime-grafted carbon were significantly higher than the pristine porous carbon with improvements of 65%. Though the overall CO₂ capacity decreased slightly for the activated carbon from 4.97 mmol g⁻¹ to 4.24 mmol g⁻¹ after surface modification due to a reduction in the total surface area, the isosteric heats of adsorption increased after amidoxime incorporation indicating an increased interaction of CO₂ with the sorbent. Total capacity was reproducible and stable after multiple adsorption/desorption cycles with no loss of capacity suggesting that modification with the amidoxime group is a potential method to enhance carbon capture.     

Preparation of microporous activated carbon and its modification for arsenic removal from water

Arsenic removal from water was investigated using activated carbon. The chemical activated carbon (CAC) prepared using H₃PO₄ from jute stick largely featured micropore structure with surface functional groups, while meso- and macropore structures were mainly developed in physical activated carbon (PAC). The CAC and PAC reduced arsenic concentration to 45 and 55 μg L⁻¹, respectively, from 100 μg L⁻¹ while iron-loaded CAC reduced to 3 μg L⁻¹, which is lower than the upper permissible limit (10 μg L⁻¹). The micropore structure of CAC along with complexation affinity of iron species towards arsenic species attributed to enhanced separation of arsenic.