Removal of Cu(II) from aqueous solutions by recycled tire rubber

A batch adsorption system was applied to study the adsorption of Cu(II) ions from aqueous solutions by crumb rubber. The effects of pH ranging from 1.5 to 7.0, contact time ranging from 6 to 96 h and initial metal concentration ranging from 1 mg L^− 1 to 50 mg L^− 1 on the removal of Cu(II) were studied. Results show that adsorption of Cu(II) is pH-dependent and the best results are obtained at pH = 6.0. Results also show that copper uptake is accompanied by displacement of zinc and therefore probably involves an ion exchange type mechanism. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. Results clearly show that crumb rubber is an effective adsorbent for the removal of Cu(II) from aqueous solutions.     

Equilibrium and kinetic modelling of the adsorption of Cd ions onto chestnut shell

A study on the removal of Cd²⁺ ions from aqueous solutions by acid formaldehyde pretreated chestnut (Castanea sativa) shell was conducted in batch conditions. The influence of different parameters: adsorption time, temperature (15, 25 and 35 °C) and initial concentration of Cd²⁺ ions (15.3, 50.5 and 87.3 mg L^− 1), on cadmium uptake was analysed. Cadmium free and cadmium loaded chestnut shell were characterized by FTIR spectroscopy, which evidenced the functional groups involved in cadmium uptake. Cadmium adsorption equilibrium could be described by the Freundlich adsorption model at all the temperatures essayed, which predicted shell heterogeneity. The Cd²⁺ adsorption process by chestnut shell followed the pseudo second order kinetic model. Cadmium sorption capacity increased with decreasing temperature at an initial concentration of 15.3 mg L^− 1 and with increasing initial cadmium concentration at a temperature of 25 °C. The second order kinetic constant, which increased with increasing temperature, was used to calculate the energy of adsorption as equal to 19.2 kJ mol^− 1.     

Impact of pH on the removal of fluoride, nitrate and boron by nanofiltration/reverse osmosis

The objective of this study was to evaluate the impact of pH on boron, fluoride, and nitrate retention by comparing modelled speciation predictions with retention using six different nanofiltration (NF) and reverse osmosis (RO) membranes (BW30, ESPA4, NF90, TFC-S, UTC-60, and UTC-80A). Retention was explained with regard to speciation, membrane properties, and ion properties such as charge, hydrated size, and Gibbs energy of hydration. Flux was independent of pH, indicating that pH did not alter pore size and hence permeability for all membranes except UTC-60. Membrane charge (zeta potential) was strongly dependent on pH, as expected. Boron and fluoride retention depended on membrane type, pH, which correlated closely to contaminant speciation, and was due both to size and charge exclusion. While retention at low and neutral pH was a challenge for boron, high boron retention was achieved (> 70% above pH 11). Fluoride retention was generally > 70% above pH 7. Nitrate retention depended on membrane, and was mostly pH independent (as was the speciation). The presence of a background electrolyte matrix (20 mM NaCl and 1 mM NaHCO₃) reduced nitrate and boron retention (at high pH) due to charge shielding, and enhanced the retention of fluoride in single feed solutions, suggesting preferential transport of Cl⁻ compared to F⁻ with Na⁺.     

Preparation and characterization of spherical activated carbons from oil agglomerated bituminous coals for removing organic impurities from water

A new and simple method of producing of spherical activated carbons (SACs) from different bituminous coals, i.e., gas coal, gas-coking coal and orthocoking coal, is presented. Coal agglomerates of spherical shape obtained by oil agglomeration using rapeseed oil and linseed oil, were subjected to carbonization and activation with steam at 850 °C. The SACs prepared from gas-coking coal (hvAb) agglomerates were characterized by the best developed porous structure with surface area S_BET of about 800 m²/g and pore volume of 0.40 cm³/g. The adsorption capacity of the produced SACs was determined in terms of substituted phenolic compounds. The adsorption of 2-chlorophenol (OCP), 4-chlorophenol (PCP) and 4-nitrophenol (PNP) from aqueous solutions was studied under a static conditions on the SAC prepared from gas-coking coal agglomerated using rapeseed oil. At high concentrations of the solute the adsorption behavior of OCP was found to be different in comparison to PCP and PNP. The adsorption of the two last phenolic compounds on the selected SAC is very well described by Langmuir adsorption model. For OCP a two-stepped adsorption isotherm was obtained. The Langmuir isotherm equation fits very well only for the first stage of the OCP adsorption.     

Influence of oxidation process on the adsorption capacity of activated carbons from lignocellulosic precursors

A set of activated carbon materials non-oxidised and oxidised, were successfully prepared from two different lignocellulosic precursors, almond shell and vine shoot, by physical activation with carbon dioxide and posterior oxidation with nitric acid. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, namely nitrogen adsorption at 77 K, elemental analysis (C, H, N, O and S), point of zero charge (PZC) and FTIR. A judicious choice was made to obtain carbon materials with similar structural properties (apparent BET surface area ∼ 850-950 m²g⁻¹, micropore volume ∼ 0.4 cm³g⁻¹, mean pore width ∼ 1.2 nm and external surface area ∼ 14-26 m²g⁻¹). After their characterisation, these microporous activated carbons were also tested for the adsorption of phenolic compounds (p-nitrophenol and phenol) in the liquid phase at room temperature. The performance in liquid phase was correlated with their structural and chemical properties. The oxidation had a major impact at a chemical level but only a moderate modification of the porous structure of the samples. The Langmuir and Freundlich equations were applied to the experimental adsorption isotherms of phenolic compounds with good agreement for the different estimated parameters.     

Adsorption of bovine serum albumin and fibrinogen on hydrophilicity-controllable surfaces of polypyrrole doped with dodecyl benzene sulfonate—A combined piezoelectric quartz crystal impedance and electrochemical impedance study

Combined measurements of piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance (EI) were utilized to monitor in situ adsorption of two proteins (bovine serum albumin and fibrinogen) onto the hydrophilicity-controllable surfaces of polypyrrole (PPY) doped with dodecyl benzene sulfonate (DBS). Three of these polymer films, PPY/DBS-I, PPY/DBS-II and PPY/DBS-III, were obtained by galvanostatic electropolymerization of pyrrole in aqueous solutions containing 0.6, 1.2 and 2.0 mmol L⁻¹ sodium dodecyl benzene sulfonate (SDBS), respectively. The PPY/DBS-II obtained from electropolymerization of pyrrole in the presence of 1.2 mmol L⁻¹ SDBS (the critical micelle concentration of SDBS in aqueous solution, CMC) exhibited the greatest hydrophobicity, as suggested by contact angle measurement. And the saturation-adsorption amounts for both proteins were found to be greatest on the surface. The kinetics and adsorption mechanisms of both proteins adsorbed on these three surfaces were discussed. Langmuir and Freundlich models were used for explaining the adsorption behavior of proteins, giving that Langmuir model is better for bovine serum albumin (BSA) and both model are not so available for fibrinogen.     

Acid treatment of south Tunisian palygorskite: Removal of Cd(II) from aqueous and phosphoric acid solutions

The object of this work is to study the modifications of Tunisian palygorskite upon HCl treatment and to investigate the ability of natural and acid treated palygorskite to adsorb heavy metal ions. Chemical analysis, X ray diffraction, infrared spectra, MAS-NMR methods, BET surface and surface charge of HCl treated palygorskite have been reported. It was established that acid leaching at reflux temperature resulted in an increase in the amount of Mg, Fe and Al extracted and in surface area from 59.7 to 437 m² g^− 1 for 2 M HCl samples and from 59.7 to 360 m² g^− 1 for 4 M HCl samples, due to a dissolution of the octahedral sheet and the creation of mesoporosity. ²⁹Si-MAS-NMR studies yield information on changes occurring in the structure of the mineral. During acid treatment the clay structure is progressively transformed into amorphous silica (essentially for samples treated by HCl 4 M for 10 h and HCl 2 M for 35 h).Natural palygorskite and the activated samples were applied as adsorbents for the removal of Cd(II) from aqueous solutions. The effects of various experimental parameters were investigated. The adsorption isotherms of activated palygorskites for Cd(II) could be described by the Freundlich model. The acid activated sample showed a higher adsorption capacity for Cd(II) than the natural palygorskite. The retention of Cd(II) ions by palygorskite occurs dominantly by specific adsorption. A different behaviour was observed in the phosphoric acid medium. Despite increases in the surface areas upon acid activation, improvements in the adsorption were not observed, as a result of the decreasing number of negative surface sites, as main centers for specific adsorption.     

Removal of Remazol Brilliant Blue R dye from aqueous solutions by adsorption onto immobilized Scenedesmus quadricauda: Equilibrium and kinetic modeling studies

The green algae Scenedesmus quadricauda was immobilized in alginate gel beads. The immobilized active (IASq) and heat inactivated S.quadricauda (IHISq) were used for the removal of Remazol Brilliant Blue R (CI 61200, Reactive Blue 19, RBBR) from aqueous solutions in the concentration range 25-200 mg L^− 1. At 150 mg L^− 1 initial dye concentration the IASq and IHISq exhibited the highest dye uptake capacity at 30 °C, at the initial pH value of 2.0. At the same initial dye concentration in the batch system the adsorption capacity was determined for IASq as 44.2; 44.9 and 45.7 mg g^− 1 in 30, 60 and 300 min, respectively. After 300 min the adsorption capacity hardly changed during the adsorption time. The IHISq of adsorption capacity was observed as 47.6; 47.8 and 48.3 mg g^− 1 in 30, 60 and 300 min, respectively. After 300 min the adsorption capacity was not changed for 24 h. The Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Flory-Huggins isotherm models were used to fit the equilibrium biosorption data. The Langmuir, Freundlich and Dubinin-Radushkevich equations have better coefficients than Temkin and Flory-Huggins equation describing the RBBR dye adsorption onto IASq and IHISq. The monomolecular biosorption capacity of the biomass was found to be 68 and 95.2 mg g^− 1 for IASq and IHISq, respectively. From the Dubinin-Radushkevich model, the mean free energy was calculated as 6.42-7.15 kJ mol^− 1 for IASq and IHISq, indicating that the biosorption of dye was taken place in physical adsorption reactions. The experimental data were also tested in terms of kinetic characteristics and it was determined that the biosorption process of dye was well explained with pseudo-second-order kinetics.     

Electrochemical enhancement of adsorption capacity of activated carbon fibers and their surface physicochemical characterizations

The adsorption of activated carbon fibers (ACFs) and their surface characteristics were investigated before and after electrochemical polarization. The adsorption kinetics of m-cresol showed the dependence on polarized potential, and the adsorption rate constant increased by 77.1%, from 6.38 × 10⁻³ min⁻¹ at open-circuit (OC) to 1.13 × 10⁻² min⁻¹ at polarization of 600 mV. The adsorption isotherms at different potentials were in good agreement with Langmuir isotherm model, and the maximum adsorption capacity increased from 2.28 mmol g⁻¹ at OC to 3.67 mmol g⁻¹ at polarized potential of 600 mV. These indicated that electrochemical polarization could effectively improve the adsorption rate and capacity of ACFs. The surface characteristics of ACFs before and after electrochemical polarization were evaluated by N₂ adsorption-desorption isotherms, scanning electron microscope (SEM), zeta potential and Fourier transform infrared spectroscopy (FTIR). The results showed that the BET specific surface area and pore size increased as the potential rose. However, the surface chemical properties of ACFs hardly changed under electrochemical polarization of less than 600 mV. This study was beneficial to understand the mechanism of electrochemically enhanced adsorption.     

Adsorption of 4-chlorophenol by inexpensive sewage sludge-based adsorbents

Sewage sludge was used as precursor to develop a potential inexpensive adsorbent by both simple drying and pyrolysis. The resulting materials were evaluated as adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solution. The dried biosolids showed a BET surface area lower than 3 m²/g, which yield a maximum adsorption capacity of 0.73 mmol 4-CP/g at pH 5.0 and 15 °C. The carbonization of biosolids under relatively mild conditions allowed obtaining materials with BET surface area up to 45 m²/g, which led to a significant increase of the maximum adsorption capacity (1.36 mmol 4-CP/g). The high ash content of the starting material (23%, d.b.) limits the development of porosity on a total dry-weight basis. Adsorption data were well fitted to the Redlich–Peterson isotherm equation whereas the most commonly used Langmuir and Freundlich equations were less satisfactory probably because of the occurrence of summative adsorption phenomenon. A thermodynamic study of the adsorption showed the spontaneous and exothermic nature of the process. Thus, simple drying and carbonization provide two ways of valorization of sewage sludge through its conversion into inexpensive low-rank adsorbents potentially useful for the removal of some hazardous water pollutants, like chlorophenols and related compounds.     

In situ stress measurements during the electrochemical adsorption/desorption of self-assembled monolayers

This paper examines the surface stress associated with the electrochemical desorption of 4-mercaptobenzoic acid (4-MBA) from (1 1 1) textured Au in aqueous 0.1 mol L⁻¹ KOH. Self-assembled monolayers of varying coverage were adsorbed onto the Au electrode surface from a 0.1 mol L⁻¹ aqueous KOH solution containing 1 mmol L⁻¹ 4-MBA. Adsorption follows Langmuir kinetics and fully formed monolayers, corresponding to 0.29 coverage with respect to the Au surface, are formed in about 120 min. XP spectra confirm the formation of the Au-S bond while FTIR spectra indicate that the 4-MBA is orientated with the carboxylate pointed away from the surface. The one-electron reductive desorption of 4-MBA occurs at a potential of −0.9 to −1.0 V vs. SSE, depending on coverage, and causes a surface stress change in the tensile direction, indicating that 4-MBA adsorption induces a compressive surface stress to the Au. At short immersion times and low monolayer coverage, the surface stress increases with coverage as the stress response is primarily governed by the Au-S bond density. SAM desorption following longer immersion times produces large stress changes with little corresponding change in SAM coverage. We attribute the additional compressive stress to stabilization of the Au-S bonding regions and the coulombic repulsion between neighboring molecules, both associated with ordering of the 4-MBA on the Au surface.     

Selective separation of contaminants from paper mill effluent using nanofiltration

Biologically treated newsprint mill effluent containing 57 mg L⁻¹ DOC and 1430 TDS was used in a screening study of nine commercial NF membranes for use as pretreatment for reverse osmosis in an end of pipe water recycling application. A salt-organic-separation (SOS) efficiency factor was developed to help rank the performance of the membranes. The SOS measures the ratio of the sum of the percentage rejection of organics and divalent cations over the percentage rejection of monvalents. It can be used to discriminate between NF membranes that are not too permeable to divalent cations or organics in which case the NF permeate will have a high chlorine demand due to the carryover of organics, or too retentive in which case all the material in the effluent will be retained and fouling problems are likely to occur. The optimum SOS efficiently for this study appeared to range from 3.5 to 5.6 for six membranes, DK, HPA-150, ESNA1-LF2, DL, TFC-SR2 and NF-270, which were categorised as membranes with an intermediate rejection. Out of these membranes ESNA1-LF2, TFC-SR2 and NF-270 were capable of operating up to 90% recovery with high permeabilities ranging from 17.7 to 22.3 L m⁻² h⁻¹ bar⁻¹.     

Preparation and characterization of charcoals that contain dispersed aluminum oxide as adsorbents for removal of fluoride from drinking water

Charcoals adsorbents that contain dispersed aluminum and iron oxides have been synthesized by impregnating wood with salt solutions followed by carbonization at 500 °C, 650 °C or 900 °C. The adsorbents were characterized and their performance for fluoride removal from aqueous solution was evaluated. Aluminum and iron oxides were well dispersed into the porous charcoals. The carbons were amorphous and highly porous. XRD of the adsorbents showed crystalline iron oxide but did not show any form of crystalline aluminum oxides. All the adsorbents showed acidic surface properties. The efficiency of defluoridation was found to depend on the carbonization temperature, the pH of point of zero charge (pHPZC), and the co-existing ions. Substrates prepared at 650 °C with aluminum and iron oxides exhibited the best efficiency with a fluoride sorption capacity of 13.64 mg g⁻¹. More than 92% removal of fluoride was achieved within 24 h from a 10 mg L⁻¹ solution at neutral pH. Fluoride adsorption kinetic was well fitted by a pseudo-second order model. The amounts of residual Al and Fe in treated solution were pH dependant. At neutral pH, the amounts of dissolved Al and Fe were found to be 0.67 and 1.8 mg L⁻¹, respectively.     

Thermodynamics,kinetics, and isotherms studies for gold(III) adsorption using silica functionalized by diethylenetriaminemethylenephosphonic acid

A novel hybrid material silica gel chemically modified by diethylenetriaminemethylenephosphonic acid GH-D-P has been developed and characterized. The results of the adsorption thermodynamics and kinetics of the as-synthesized GH-D-P for Au(III) showed that this high efficient inorganic–organic hybrid adsorbent had good adsorption capacity for Au(III), and the best interpretation for the experimental data was given by the Langmuir isotherm equation, the maximum adsorption capacity for Au(III) is 357.14 mg/g at 35 °C. Moreover, the study indicated the adsorption kinetics of GH-D-P could be modeled by the pseudo-second-order rate equation wonderfully, and the adsorption thermodynamic parameters ΔG, ΔH and ΔS were −20.43 kJ mol⁻¹, 9.17 kJ mol⁻¹, and 96.24 J K⁻¹ mol⁻¹, respectively. Therefore, the high adsorption capacity make this hybrid material have significant potential for Au(III) uptake from aqueous solutions using adsorption method.     

Designed multifunctionalized magnetic mesoporous microsphere for sequential sorption of organic and inorganic pollutants

A novel magnetic microsphere with thiol-functionalized mesoporous shell was fabricated by using a colloidal chemical method and cationic surfactants (CTAB) as structure-directing agents. As a high performance adsorbent, these microspheres were examined for environmental protection applications to adsorb and remove toxic phenolic compounds and heavy metal ions, sequentially, in aqueous solution. The prepared nanocomposite microspheres were mesoporous and magnetizable, with a diameter of 350-400 nm, a high surface area of 913.14 m²/g, a pore size of 2.48 nm, and a saturation magnetization of 33.9 emu/g. These multifunctional microspheres showed excellent adsorptive capability towards toxic phenolic compounds and heavy metal ions (Hg²⁺, Pb²⁺). The cation micelle made of CTAB in the mesopores has great attractive power to phenolic compounds and the adsorption capacity was as high as 144.78 mg/g for 4-methyl-2,6-dinitrophenol. The thiol-functionalized magnetic mesoporous microsphere (TMMM) which had adsorbed phenolic compounds can further adsorb metal ions after removing CTAB. The adsorption capacity was 185.19 mg/g for Hg²⁺ and 114.7 mg/g for Pb²⁺. The TMMM can be easily removed from solution by an external magnetic field. These results suggest that this kind of nanocomposites is potentially useful materials for effectively adsorbing and removing different dangerous pollutants in aqueous solution.     

Porous carbons prepared by using metal-organic framework as the precursor for supercapacitors

Several kinds of porous carbons were easily prepared by using metal-organic framework as both template and carbon precursor. Nanocasting is chosen to adjust the textures and structures with phenolic resin or carbon tetrachloride and ethylenediamine as the additional carbon sources. The carbon materials were further activated by potassium hydroxide (KOH). The electrochemical capacitance behaviors of these carbon materials were investigated in both aqueous and organic electrolytes. Energy densities of 9.4 W h kg⁻¹ in 6 M KOH and 31.2 W h kg⁻¹ in 1.5 M tetraethylammonium tetrafluoroborate acetonitrile solution can be obtained for one of the prepared porous carbon materials (MAC-A) with the surface area of 2222 m² g⁻¹ and the total pore volume of 1.14 cm³ g⁻¹. Due to its high packing density of 0.93 g cm⁻³, the related volumetric specific energy densities of 8.8 and 29.0 W h L⁻¹ can be got.     

Corrosion control of Cu-Ni alloys in neutral chloride solutions by amino acids

The corrosion inhibition of Cu-Ni alloys was investigated in aqueous chloride solutions using amino acids as environmentally safe materials. The corrosion rate was calculated in absence and presence of the corrosion inhibitor using polarization and impedance techniques. The inhibition efficiency of the different amino acids was also calculated.The experimental results have shown that a simple amino acid like glycine can be used as efficient corrosion inhibitor for the Cu-Ni alloys in neutral chloride solutions. An inhibition efficiency of about 85% could be achieved at very low concentrations of the amino acid (0.1 mM). For low Ni content alloy (Cu-5Ni), 2.0 mM cysteine shows a remarkable high (∼96%) corrosion inhibition efficiency. The experimental impedance data were fitted to theoretical data according to a proposed equivalent circuit model for the electrode/electrolyte interface, and the mechanism of the corrosion inhibition process was suggested. Different adsorption isotherms were tested and the corrosion inhibition process was found to depend on the adsorption of the amino acid molecules and/or the deposition of corrosion products on the alloy surface. The adsorption free energy of cysteine on Cu-5Ni (−37.81 kJ mol⁻¹) reveals a strong physical adsorption of the inhibitor on the alloy surface.     

Adsorption behaviour of Cu and Cd onto natural bentonite

The adsorption behaviour of Cu²⁺ and Cd²⁺ onto bentonite was studied as a function of temperature under optimized conditions of amount of adsorbent, particle size, pH, concentration of metals, and shaking time. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich and Dubinin-Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 298-333 K by batch experiments. The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK_o vs. 1 / T plots. The adsorptions were endothermic reactions. The results suggested that natural bentonite was suitable as sorbent material for the recovery and adsorption of metal ions from aqueous solutions.     

HRP biosensor based on sugar-lectin biospecific interactions for the determination of phenolic compounds

A layer-by-layer self-assembly of concanavalin A (Con A) and glycoprotein horseradish peroxidase (HRP) afforded multilayer thin films on the surface of a thiol-modifed gold electrode, through biospecific complexation of Con A and sugar residues in the glycoenzymes. The performance of the HRP biosensor is reported for the amperometric detection of phenolic compounds. The concentration of hydrogen peroxide and assembly conditions of the precursor film, such as pH, the ionic strength of the polyelectrolyte solutions and the number of assembled bilayers were investigated using catechol. With optimized conditions, the biosensor presented a linear response for catechol from 6.0 to 48.0 μmol l⁻¹, with a high sensitivity of 160 μmol⁻¹ l nA and a detection limit of 0.6 μmol l⁻¹. The response time of the biosensor for phenolic compounds was very short, reaching 95% of its maximum response in about 2 s. The differences in sensitivity observed for a series of phenolic substrates were discussed in terms of the stability of the oxidized phenolic compounds and the properties of substituents.     

Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons

Physical properties of activated carbons prepared from pinewood at different activation times (0.5, 1.5, 2.7, and 4.0 h) in steam at 900 °C were studied. The adsorption equilibria and kinetics of three dyes and three phenols (phenol, 3-chlorophenol, and o-cresol) from aqueous solutions on such carbons were then examined at 30 °C. The adsorption isotherms of phenols could be well fitted by the Freundlich equation, and those of dyes were adequately described by the Langmuir-Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of all six adsorbates could be best described by the Elovich equation. The kinetic parameters of this best-fit model were calculated and discussed.