Reply to Comments on ‘Chitosan functionalized with 2[-bis-(pyridylmethyl) aminomethyl]4-methyl-6-formyl-phenol: Equilibrium and kinetics of copper(II) adsorption’ by Yuh-Shan Ho: Discussion on pseudo second order kinetic expression

The present communication reports a short history on the pseudo second order kinetic models previously reported for sorption systems. This present paper presents the information citing the original presentation of pseudo second order kinetic expression.     

Arsenic adsorption using copper (II) oxide nanoparticles

Arsenic poisoning is a major problem in today's life. To reduce its concentration in drinking water, different metal based compounds were explored as arsenic adsorbents. In the present study, copper (II) oxide nanoparticles were prepared by thermal refluxing technique and used as an adsorbent for arsenic removal from water. Characterization of the adsorbent using TEM, BET, XRD and FTIR implied that the prepared adsorbent was in nano size and had excellent adsorption behavior with surface area of 52.11 m²/g. Systematic adsorption experiments were carried out with different process parameters such as contact time, adsorbent mass, pH, temperature and stirring speed and found that copper (II) oxide had very good efficiency towards arsenic adsorption. Thermodynamic parameters and adsorption kinetics were studied in detailed to know the nature and mechanism of adsorption. Results showed that the adsorption process followed pseudo second order kinetic and endothermic behavior. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. The adsorption process followed Langmuir isotherm with an adsorption capacity of 1086.2 μg/g. A regeneration study was proposed in order to reuse the adsorbent for better economy of the process. Finally, a process design calculation is reported to know the amount of adsorbent required for efficient removal of arsenic from aqueous medium.     

Synthesis of cross-linked poly(4-vinylpyridine) and its copolymer microgels using supercritical carbon dioxide: Application in the adsorption of copper(II)

Compared with conventional precipitation polymerization method, cross-linked poly(4-vinylpyridine) (P4VP) and its microgels copolymerized with α-methacrylic acid (MAA) were synthesized through a new route of stabilizer-free polymerization in supercritical fluids. The yellow, dry, fine powders were directly obtained from precipitation polymerization of 4-vinylpyridine in supercritical carbon dioxide (scCO₂) at pressures ranging from 70.0 to 230 bar, using N,N′-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. The capacity of this microgel for adsorption of copper(II) was also studied. At higher cross-linker concentrations, a high yield of the cross-linked P4VP microgel was generated in scCO₂, and its particle size was less than 300 nm. Polymerization of cross-linked P4VP in scCO₂ was extremely sensitive to the density of the continuous phase. The adsorption followed the Langmuir isotherm. The adsorption capacities of cross-linked P(4VP-co-MAA) and cross-linked P4VP were 47.2 and 26.9 mg g⁻¹, respectively.     

Bis[4-(methylthio)phenylmethyleneaminophenyl] disulfide, 2-[4-(methylthio)phenyl]-2,3-dihydro-1,3-benzothiazole,and its nickel(II) and cobalt(II) complexes: Synthesis,adsorption on gold surface and electrochemical characterization

2-[4-(Methylthio)phenyl]-2,3-dihydro-1,3-benzothiazole (1) and bis[4-(methylthio)phenylmethylene-aminophenyl] disulfide (2) were synthesized. Novel coordination compounds of Ni(II) and Co(II) with 2-[4-(methylthio)phenylmethyleneamino]thiophenol, M(1)₂ (M=Co (3); M=Ni (4)), were prepared by reacting 1 with M(OAc)₂·6H₂O or MCl₂·6H₂O in EtOH solution. The structure of 2 was proved by X-ray crystallography. Electrochemical behavior of 1–4 in CH₃CN solution and at the surface of a gold electrode was studied by cyclic voltammetry. The modification of the electrode by ligand 1 and its complexes with Ni²⁺ and Co²⁺ is described in detail. Two procedures were used to obtain a self-assembled monolayer of a metal complex on the gold surface: the adsorption of prepared coordination compound 3 or 4 on the electrode and the initial modification of the electrode with ligand 1 followed by the formation of a coordination complex between the ligand adsorbed on the electrode and a metal salt occurring in solution. On the basis of the electrochemical data, it was found that the structure of complexes formed on the surface differs from that of the complexes produced in solution.     

Pb(II) biosorption using DAP/EDTA-modified biopolymer (Chitosan)

Abstract

In this study, chitosan was chemically modified with only diammonium phosphate (DAP) and DAP/EDTA (ethylenediaminetetraacetic acid) mixture for the removal of Pb(II) ions from aqueous solution. Modified chitosan forms were analyzed using thermo-gravimetric analyzer (TGA), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) to investigate the thermal degradation behavior, structural modifications, and the surface texture of the cross-linked chitosan adsorbents, respectively. The adsorption results were analyzed by well-known kinetic and isotherm models. The kinetics of metal adsorption followed the pseudo-second-order model. The maximum sorption capacities obtained from the Langmuir isotherm model were 126?mg/g for diammonium phosphate-modified Chitosan (DMC) and 137?mg/g for DAP/EDTA-modified chitosan (EDMC). The thermodynamic analysis showed that the metal removal process was endothermic in nature.     

Water purification of removal aqueous copper (II) by as-grown and modified multi-walled carbon nanotubes

This study compares aqueous copper (II) adsorbed onto as-grown and modified carbon nanotubes (CNTs), using H₂SO₄ and H₂SO₄/KMnO₄ processes. H₂SO₄ and H₂SO₄/KMnO₄ modifications reduced pH_iep and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that some functional groups were formed on modified CNTs. The adsorption capacity of copper (II) onto modified CNTs was greater than that of as-grown CNTs, especially at pH 6. The results demonstrate that the modified processes increased the adsorption capacity because the functional groups were generated on the modified surfaces of the CNTs. Additionally, the adsorption capacity of copper (II) onto as-grown and modified CNTs both increased with temperature, and the results indicated that the Langmuir isotherm fitted the experimental data well. Simulation results indicated that the ΔH⁰ values of as-grown, H₂SO₄-modified CNTs and H₂SO₄/KMnO₄-modified CNTs were 4.83, 14.37 and 29.92 kJ/mol, respectively. Based on ΔH⁰, the adsorption of Cu²⁺ onto H₂SO₄/KMnO₄-modified CNTs is suggested to proceed simultaneously by physisorption and chemisorption but that onto as-grown and H₂SO₄-modified CNTs may proceed only by physisorption.     

DNA-Binding Study of Tetraaqua-bis(p-nitrobenzoato)cobalt(II) Dihydrate Complex: [Co(H2O)4(p-NO2C6H4COO)2]·2H2O

The interaction of [Co(H₂O)₄(p-NO₂C₆H₄COO)₂]^· 2H₂O with sheep genomic DNA has been investigated by spectroscopic studies and electrophoresis measurements. The interaction between cobalt(II) p-nitrobenzoate and DNA has been followed by gel electrophoresis while the concentration of the complex was increased from 0 to 14 mM. The spectroscopic study and electrophoretic experiments support the fact that the complex binds to DNA by intercalation via p-nitrobenzoate into the base pairs of DNA. The mobility of the bands decreased as the concentration of complex was increased, indicating that there was increase in interaction between the metal ion and DNA.     

Recent studies in adsorption of Pb(II), Zn(II) and Co(II) using conventional and modified materials:a review

ABSTRACT

Heavy metal contamination and its detrimental effects on human health and environment have been a worldwide concern. Over the years, various technologies have been adapted to tackle this problem. Adsorption is still considered to be one of the most feasible and cost-effective methods for treating wastewater contaminated with heavy metals. Adsorbents such as activated carbon, clay, zeolites and silica have been studied extensively in the past. Modification of these conventional adsorbents and the synthesis of nonconventional adsorbents such as nanocomposites and metal organic frameworks (MOF’s) have been the main focus of study in recent times. This review article attempts to present a detailed account of various adsorbents and their removal efficiencies for the treatment of wastewater contaminated with lead(II), zinc(II) and cobalt(II) in the current decade. Influence of various parameters, adsorption isotherms and kinetics best described for their removal have also been reviewed in detail. It is observed that most of the adsorbents followed pseudo second order kinetics suggestive of a chemisorption process. After conducting a thorough review of more than 120 recently published papers, it can be inferred that nanomaterials and nanocomposites have shown excellent adsorption capacity for removal of these heavy metals.     

Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

Ion-exchange adsorption of copper(II) ions on functionalized single-wall carbon nanotubes immobilized on a glassy carbon electrode

The cation-exchange property of oxidatively treated carbon nanotubes (CNTs) is newly reported. Single-wall carbon nanotubes (SWNTs), which were oxidatively treated, were immobilized on a glassy carbon surface and, on this CNT-modified electrode, Cu(II) ions were spontaneously adsorbed and their redox waves electrochemically measured. It is suggested that the adsorption of the cationic Cu(II) ions occurs by their electrostatic interaction with the negatively charged carboxylic anions on the CNTs after the ion-exchange with protons. The surface coverage of the adsorbed Cu(II) ions depending on the dipping time, the amount of immobilized CNTs, and the Cu(II) concentration was estimated from the electrochemical chronocoulometric measurements. The effect of the ionic strength on the adsorption of the Cu(II) ions was investigated and the adsorption strengths of various alkali metal cations and protons were compared. It is hoped that this new cation-exchange property of CNT-modified electrodes may extend their range of electrochemical applications.     

Heterocyclic modification of chitosan for the adsorption of Cu (II) and Cr (VI) ions

A heterocyclic modification of chitosan has been attempted for development of an effective adsorbent material for removal of metal ions. The modified polymer was characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) techniques. The adsorption capacity exhibited for Cu (II) and Cr (VI) were 83.75 and 85.0 mgg^?1, respectively, which is a significant improvement over chitosan. The adsorption on the modified polymer was a second-order kinetic process and followed Langmuir isotherm model. The thermodynamic analysis indicated exothermic and spontaneous nature of adsorption. About 80% of the adsorbed metal ions were desorbed in appropriate stripping solutions indicating reusability.     

Removal of Copper (II) and Nickel (II) Ions from Aqueous Solutions by a Composite Chitosan Biosorbent

Abstract

A composite chitosan biosorbent (CCB) was prepared by coating chitosan on to ceramic alumina. The adsorption characteristics of the sorbent for copper and nickel ions were studied under batch equilibrium and dynamic flow conditions at pH 4.0. The equilibrium adsorption data were correlated with Langmuir, Freundlich, and Redlich‐Peterson models. The ultimate monolayer capacities, obtained from Langmuir isotherm, were 86.2 and 78.1 mg/g of chitosan for Cu(II) and Ni(II), respectively. In addition, dynamic column adsorption studies were conducted to obtain breakthrough curves. After the column was saturated with metal ions, it was regenerated with 0.1 M sodium hydroxide. The regenerated column was used for a second adsorption cycle.     

Regeneration of spent bleaching earth and its adsorption of copper (II) ions from aqueous solutions

This study was designed to provide a comprehensive investigation into heat and acid reactivation of spent bleaching earth (SBE) and adsorption of Cu(II) ions from aqueous solutions. Heat treatment was the master variable in SBE regeneration. Dilute acid treatment did not constitute an effective SBE reactivation protocol for this purpose. Solvent extraction of residual oil using excess methylethyl ketone followed by heating at 370 °C was, therefore, the most effective reactivation procedure. Highly adsorptive materials with > 98% removal of Cu(II) ions from solution were obtained. Thus, > 80% Cu adsorption was reversible at SBE silicate sites because of their higher proportion in the adsorbent.     

Cationic conjugated polyelectrolyte-based fluorometric detection of copper(II) ions in aqueous solution

A series of water-soluble cationic polyfluorene copolymer containing 2,2′-bipyridine moieties (PFP-P_1-3) in the backbone were designed and synthesized as the fluorescent probes for Cu²⁺ ions. In the absence of the Cu²⁺ ion, the PFP-P₂ exhibits strong fluorescence emission in aqueous solution. Upon adding the Cu²⁺ ion, the PFP-P₂ coordinates to Cu²⁺ ions through weak N?Cu interactions, and its fluorescence is efficiently quenched by the Cu²⁺ ion with a Stern-Volmer constant (K_sv) of 1.44 × 10⁷ M⁻¹. The new method has high sensitivity with a detection limit of 20 nM. The minor interference from other heavy metal ions clearly shows that the PFP-P₂ can be used as the Cu²⁺ ion probe with good selectivity.     

Kinetics and thermodynamics of Cu(II) adsorption on oil shale wastes

The oil shale waste material, retorted shale, was utilized as an adsorbent for Cu(II) removal from aqueous solution. The kinetics and thermodynamic adsorption was investigated during a series of batch adsorption experiments. The removal efficiency was controlled by solution pH, temperature, initial ion concentration and contact time. Two simple kinetic models, pseudo-first-and second-order, were used to investigate the adsorption mechanisms. The pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. Langmuir and Freundlich models were used to fit the equilibrium data, which showed that Langmuir best-fitted these data. Thermodynamic parameters such as free energy, enthalpy and entropy were calculated to predict the nature of the adsorption process.     

High adsorption of Cd (II) by modification of synthetic zeolites Y,A and mordenite with thiourea

Zeolites Y, A and mordenite (ZY, ZA and ZM) were obtained from diatomite in a template-free system, and the products were modified by thiourea (TU). Characterization studies results indicated that the TU molecules were loaded onto the exterior surfaces of the synthetic zeolites as well as the channels. Elemental analysis and energy-dispersive X-ray spectrometer proved that the TU molecules loaded on to ZA were more than ZY and ZM. Removal of Cd(II) was investigated, and it was found that the modified zeolites have higher removal capacity, modified ZA is especially noticeable. In the adsorption experiments, the effects of various parameters such as sorbent content, contact time, concentration of cadmium solution, pH, selectivity and regeneration were discussed. At the best removal efficiency by modified zeolites, the maximum adsorption capacity is 94.3 mg·g⁻¹, 103.2 mg·g⁻¹ and 89.7 mg·g⁻¹ at 25 °C, respectively. The sorbents show good efficiency for the removal of Cd(II) in the presence of different multivalent cations and have good regeneration effect. For the modified samples, removal experiments take place via ion exchange and complexation processes.     

Intercalation of halloysite from Djebel Debagh (Algeria) and adsorption of copper ions

Halloysite available in Djebel Debagh, Guelma (eastern region of Algeria) was characterised by XRF, SEM, XRD, FTIR and by CEC, specific surface area and electrokinetic measurements. The crude halloysite was modified with Mⁿ⁺(CH₃COO)_n (M = Na⁺, NH₄⁺ or Pb²⁺), and intercalation of NaCH₃COO was monitored with time. XRD showed that the intercalation rate exceeded 90% for NaCH₃COO at long reaction time. X-ray diffraction also showed an expansion of the interlamellar space of 5.5 and 6.3 Å due to the intercalation of Pb(CH₃COO)₂ and NH₄CH₃COO. FTIR proved that Mⁿ⁺(CH₃COO)_n reacted with the inner surface hydroxyl groups of halloysite, on the basis of disappearance of the frequence bands at 3676 and 3652 cm^− 1 and the appearance of new bands around 3699 and 3457 cm^− 1. Intercalation of Pb(CH₃COO)₂ and NH₄CH₃COO shifted the band at 1650 towards 1663 and 1671 cm^− 1, respectively. The untreated and intercalated halloysite samples were used for removing copper(II) ions from aqueous solutions. The adsorption isotherms were of L-type according to the classification of Giles et al. (Giles, C.H., Mac Ewan, T.H., Makhwa, S.N., Smith, D., 1960. Studies in adsorption. Part XI. A system of classification of solution adsorption isotherms and its use in diagnosis of adsorption mechanisms and in measurement of specific surface areas of solids. J. Colloid Interface Sci. 3, 3973–3993.). The adsorption of copper ions was explained by electrostatic interaction between the copper(II) ions and negatively charged binding sites on halloysite surface and ion-exchange of the cations associated with acetate within the interlayer space.     

配合物[Cu（L）2]ECu’（L）2]·CH3OH·3H2O的合成和结构表征

以邻氯蜷苯磺酸与吡啶-2-甲醛进行缩合得到席夫碱配体（KL）,然后与Cu（AeO）2．H20进行配位反应,得到了席夫碱配合物[Cu（L）2][Cu’（L】2】’CH3OH·3H2O,用面素分析、FT—IR和X-射线单晶衍射进行r表征。结果表明t配合物属]i单斜晶系,P21／c空间群。配合物的一一个独立单元由置个品格水分子、一个晶格甲醇分子和两个不同的单核铜单元构成。有趣的是,这两个荤核铜单元的组成完全相同但配位模式不同,它们均由一个铜离子和两个脱质子的席夫碱配体组成,其中一个瞥核铜单元中的两个磺酸基均参与了配位,另一个则只有一个磺酸基配位。     

配合物[Cd(IA)_2(H_2O)_4]的合成及晶体结构

以硝酸镉与吡啶-4-甲酸(HIA)为原料在水热条件下合成了配合物[Cd(IA)2(H2O)4],并用红外光谱、元素分析和X射线单晶衍射进行了表征。该配合物属三斜晶系,P-1空间群,晶胞参数为:a=6.4400(5)nm,b=6.9489(6)nm,c=9.4051(8)nm,α=95.2600(10)°,β=104.580(2)°,γ=111.570(2)°,V=0.037079(5)nm3。配合物中Cd(Ⅱ)位于变形八面体环境中,与分属于两个吡啶-4-甲酸根的2个N原子以及来自于四个配位水分子的O原子配位。