As(V) removal from aqueous media using α-MnO2 nanorods-impregnated laterite composite adsorbents

We present a novel way of enhancing the utility of low cost readily available laterite by impregnating it with the α-MnO₂ nanorods, thus making a composite material suitable for the removal of As(V) from aqueous media. The composites were synthesized by two methods: (i) ball-milling of a physical blend of laterite with pre-synthesized MnO₂; and (ii) in situ formation of MnO₂ in the presence of laterite. The BET surface area of composites prepared by both methods was markedly higher compared to un-modified laterite, and the presence of MnO₂ in the composite was also confirmed by XRD analysis and TEM microscopy. The adsorption capacity for As(V) was found to be highly pH dependent and the adsorption kinetics followed a pseudo second-order kinetic model. The Langmuir adsorption isotherm was found to be the best model to describe the adsorption equilibrium of As(V) onto un-modified laterite as well both ball-milled and in situ formed composite. The adsorption capacities at room temperature and pH 7.0 were found to be 1.50 mg g^?1, 8.93 mg g^?1 and 9.70 mg g^?1, for un-modified laterite, ball-milled and in situ formed composite, respectively.     

An eco-friendly process: Predictive modelling of copper adsorption from aqueous solution on Spirulina platensis

The adsorption of copper ions on Spirulina platensis was studied as a function of contact time, initial metal ion concentration, and initial pH regimes. Characterization of this adsorbent was confirmed by FTIR spectrum. Modified Gompertz and Logistic models have not been previously applied for the adsorption of copper. Logistic was the best model to describe experimental kinetic data. This adsorption could be explained by the intra-particle diffusion, which was composed of more than one sorption processes. Langmuir, Freundlich, and Redlich–Peterson were fitted to equilibrium data models. According to values of error functions and correlation coefficient, the Langmuir and Redlich–Peterson models were more appropriate to describe the adsorption of copper ions on S. platensis. The monolayer maximum adsorption capacity of copper ions was determined as 67.93 mg g^?1. Results indicated that this adsorbent had a great potential for removing of copper as an eco-friendly process.     

Novel negatively charged hybrids. 3. Removal of Pb2+ from aqueous solution using zwitterionic hybrid polymers as adsorbent

Using zwitterionic hybrid polymers as adsorbent, the adsorption kinetics and isotherm, thermodynamic parameters of ΔG, ΔH and ΔS for the removal of Pb²⁺ from aqueous solution were investigated. It is indicated that the adsorption of Pb²⁺ ions on these zwitterionic hybrid polymers followed the Lagergren second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption process might be Langmuir monolayer adsorption. The negative values of ΔG and the positive values of ΔH evidence that Pb²⁺ adsorption on these zwitterionic hybrid polymers is spontaneous and endothermic process in nature. Moreover, the zwitterionic hybrid polymers produced reveal relatively higher desorption efficiency in 2 mol dm^?3 aqueous HNO₃ solution, indicating that they can be recycled in industrial processes. These findings suggest that these zwitterionic hybrid polymers are the promising adsorbents for Pb²⁺ removal and can be potentially applied in the separation and recovery of Pb²⁺ ions from the waste chemicals and contaminated water of lead-acid rechargeable battery.     

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe₃O₄ nanoparticle (Fe₃O₄@Al(OH)₃ NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g^?1 at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (ΔH⁰) and entropy change (ΔS⁰) was 6.836 kJ mol^?1 and 41.65 J mol^?1 K^?1, which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe₃O₄@Al(OH)₃ NPs as adsorbent could reach 0.3 mg L^?1 with an initial concentration of 20 mg L^?1, which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe₃O₄@Al(OH)₃ NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.     

Thermodynamic and kinetic studies for the adsorption of Hg(II) by nano-TiO2 from aqueous solution

Titanium dioxide nanocrystals were employed, for the first time, for the sorption of Hg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 420 min and the maximum adsorption of Hg(II) on the TiO₂ was observed to occur at pH 8.0. The adsorption data correlated with Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin isotherms. The Freundlich isotherm showed the best fit to the equilibrium data. The Pseudo-first order and pseudo-second-order kinetic models were studied to analyze the kinetic data. A second-order kinetic model fit the data with the (k₂ = 2.8126 × 10^?3 g mg^?1min^?1, 303 K). The intraparticle diffusion models were applied to ascertain the rate-controlling step. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were calculated which showed an endothermic adsorption process. The equilibrium parameter (R_L) indicated that TiO₂ nanocrystals are useful for Hg(II) removal from aqueous solutions.     

Preparation of biomorphic porous calcium titanate and its application for preconcentration of nickel in water and food samples

Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol–gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol–gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4–8, but the adsorbed nickel ion could be completely eluted using 2 mol L^? 1 HNO₃. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g^? 1 and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol^? 1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (E_a) was 25.291 kJ mol^? 1 for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.     

Removal of Pb(II) ions from aqueous solution by adsorption using bael leaves (Aegle marmelos)

Biosorption of Pb(II) on bael leaves (Aegle marmelos) was investigated for the removal of Pb(II) from aqueous solution using different doses of adsorbent, initial pH, and contact time. The maximum Pb loading capacity of the bael leaves was 104 mg g^?1 at 50 mg L^?1 initial Pb(II) concentration at pH 5.1. SEM and FT-IR studies indicated that the adsorption of Pb(II) occurs inside the wall of the hollow tubes present in the bael leaves and carboxylic acid, thioester and sulphonamide groups are involved in the process. The sorption process was best described by pseudo second order kinetics. Among Freundlich and Langmuir isotherms, the latter had a better fit with the experimental data. The activation energy E_a confirmed that the nature of adsorption was physisorption. Bael leaves can selectively remove Pb(II) in the presence of other metal ions. This was demonstrated by removing Pb from the effluent of exhausted batteries.     

Determination of ultratrace levels of lead (II) in water samples using a modified carbon paste electrode based on a new podand

A new podand of 1,1′-thiobis(naphthalene-2,1-diyl)bis(2-aminobenzoate) (TNBA) was synthesized and used as a suitable carrier for construction of Pb²⁺ modified carbon paste electrode (CPE). The effects of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dioctyl pththalate (DOP), dibutyl phthalate (DBP) and paraffin oil were studied. The best performance was obtained with a matrix composition of CPE with a DOP/graphite powder/TNBA weight percent ratio of 35/60.5/4.5. The sensor exhibits significantly enhanced selectivity toward Pb²⁺ ion over the concentration range 8.0 × 10^? 8 to 1.0 × 10^? 2 mol L^? 1 with a lower detection limit of 5.0 × 10^? 8 mol L^? 1 and a Nernstian slope of 29.0 ± 0.2 mV decade^? 1 of lead activity. It has a fast response time of 8 s with a working pH range from 3.5 to 7. The interaction between TNBA and Pb²⁺ was studied spectrophotometrically and it exhibits that the stoichiometry of the complex is 1:1 in acetonitrile solution. Finally, the electrode was satisfactorily used as an indicator electrode in complexometric titration of Pb²⁺ with EDTA and in direct determination of lead in various water samples.     

Removal of nickel from electroplating rinse waters using electrostatic shielding electrodialysis/electrodeionization

Electrostatic shielding zones made of electrode graphite powder were used as a new type of ionic and electronic current sinks. Because of the local elimination of the applied electric field, voltage and current within the zones, ions are led inside them and accumulate there. The current sinks were implemented in electrostatic shielding electrodialysis of a simulated nickel plating rinse water containing 100 mg L^?1 nickel and electrodeionization of a 0.001 M NiSO₄ solution with simultaneous electrochemical regeneration of the ion exchange resin beds. Pure water was obtained with a Ni²⁺ ion concentration of less than 0.1 mg L^?1 at a flow rate of 2.02 × 10^?4 dm³ s^?1 diluate stream and a current density of 30 A m^?2.     

Corrosion inhibition of carbon steel and antibacterial properties of aminotris-(methylenephosphonic) acid

In this work, the corrosion inhibition property and the antibacterial activity of the aminotris-(methylenephosphonic) acid (ATMP) have been studied. ATMP has been evaluated as a corrosion inhibitor for carbon steel in 1 M HCl solution using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. According to the experimental results, the inhibition efficiency increased with increasing inhibitor concentration. Tafel polarization study showed that the ATMP acts as a mixed inhibitor. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. Adsorption of ATMP on the carbon steel surface obeyed the Langmuir adsorption isotherm. The calculated ΔG_ads value showed that the corrosion inhibition of the carbon steel in 1 M HCl is mainly controlled by a physisorption process. In addition, the effect of immersion time on the corrosion of carbon steel was also studied in this work using ac impedance technique. The corrosion inhibition mechanism of ATMP was discussed. This inhibitor can be also used as biocide in aqueous environments. Our results showed that ATMP have an antibacterial effect against both Gram positive and Gram negative bacteria. The lowest MIC (0.2 mg l^?1) was measured for Pseudomonas fluorescens while the highest MIC was measured for Escherichia coli (3.1 mg l^?1). In addition, the results showed that the MIC of ATMP against Listeria innocua in a buffered medium (pH 6.5) was of ca. 4-fold higher than MIC measured in unbuffered medium. Thus, our findings showed that the antibacterial activity of ATMP is a result of a combined effect of the pH solution and the chemical nature of the used phosphonate molecule.     

Removal of Congo Red from aqueous solution by cattail root

In this study, cattail root was used to remove Congo Red (CR) from aqueous solution. The effects of operation variables, such as cattail root dosage, contact time, initial pH, ionic strength and temperature on the removal of CR were investigated using batch adsorption technique. Removal efficiency increased with increase of cattail root dosage and ionic strength, but decreased with increase of temperature. The equilibrium data fitted well to the Langmuir model (R² > 0.98) and the adsorption kinetic followed the pseudo-second-order equation (R² > 0.99). Thermodynamics parameters such as standard free energy change (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were analyzed. The values of ΔG° were between ?7.871 and ?4.702 kJ mol^?1, of ΔH° was ?54.116 kJ mol^?1, and of ΔS° was ?0.157 kJ mol^?1 K^?1, revealing that the removal of CR from aqueous solution by cattail root was a spontaneous and exothermic adsorption process. The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61 mg g^?1 at 20, 30 and 40 °C, respectively. These results suggest that cattail root is a potential low-cost adsorbent for the dye removal from industrial wastewater.     

Poly(hydroxyethyl methacrylate) nanobeads containing imidazole groups for removal of Cu(II) ions

Poly(hydroxyethyl methacrylate) (PHEMA) nanobeads with an average size of 300 nm in diameter and with a polydispersity index of 1.156 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanobeads was found to be 996 m²/g. Imidazole containing 3-(2-imidazoline-1-yl)propyl(triethoxysilane) (IMEO) was used as a metal-chelating ligand. IMEO was covalently attached to the nanobeads. PHEMA-IMEO nanobeads were used for the removal of copper(II) ions from aqueous solutions. To evaluate the degree of IMEO loading, the PHEMA nanobeads were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 973 µmol IMEO/g of polymer. The PHEMA nanobeads were characterized by transmission electron microscopy and fourier transform infrared spectroscopy. Adsorption equilibrium was achieved in about 8 min. The adsorption of Cu²⁺ ions onto the PHEMA nanobeads was negligible (0.2 mg/g). The IMEO attachment into the PHEMA nanobeads significantly increased the Cu²⁺ adsorption capacity (58 mg/g). Adsorption capacity of the PHEMA-IMEO nanobeads increased significantly with increasing concentration. The adsorption of Cu²⁺ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cu⁺, Cd²⁺, Pb²⁺ and Hg²⁺ was also investigated. The adsorption capacities are 61.4 mg/g (966.9 µmol/g) for Cu²⁺; 180.5 mg/g (899.8 µmol/g) for Hg²⁺; 34.9 mg/g (310.5 µmol/g) for Cd²⁺ and 14.3 mg/g (69 µmol/g) for Pb²⁺. The affinity order in molar basis is observed as Cu²⁺ > Hg²⁺ > Cd²⁺ > Pb²⁺. These results may be considered as an indication of higher specificity of the PHEMA-IMEO nanobeads for the Cu²⁺ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for PHEMA-IMEO nanobeads.     

Gold nanoparticle/single-walled carbon nanotube film on the surface of glassy carbon electrode and its application

A sensor based on gold nanoparticle/single-walled carbon nanotube film on the surface of glassy carbon electrode is prepared. Electrochemical behavior of adrenaline hydrochloride (AH) on the surface of gold nanoparticle/single-walled carbon nanotube modified glassy carbon electrode is investigated. A simple, sensitive, and inexpensive method for determination of AH is proposed. The oxidation peak currents is proportional to adrenaline hydrochloride concentrations in the range of 0.20 mg L^? 1 to 1.80 mg L^? 1 in 0.1 M phosphate buffer solution of pH 7.3, the detection limit for AH is 0.06 mg L^? 1, and the recoveries are in the range from 100.0 to 110.0% with RSD of 1.2–1.9% (n = 6).     

Electroanalytical properties and application of anthraquinone derivative-functionalized multiwalled carbon nanotubes nanowires modified glassy carbon electrode in the determination of dissolved oxygen

We herein report a simple, low cost and green preparation of nanowires of (anthraquinone-2-carboxylic acid/amino functionalized) multiwalled carbon nanotubes (HOOC-2-AQ/AMWCNTs) which has been further employed for the development of highly sensitive oxygen sensor. The prepared composite has been characterized by TEM and electrochemical studies. The glassy carbon electrode modified with composite shows an irreversible and good electrocatalytic activity for the reduction of oxygen. The reduction potential of the oxygen was shifted 460 mV towards the positive potential with this modified electrode as compared to bare glassy carbon electrode. The prepared material was stable with no leaching observed of the mediator. A linear response range of 0.2–6.8 mg L^?1, with a sensitivity of 5.0 μA L mg^?1 and a detection limit of 0.02 mg L^?1 were obtained with this sensor.     

Synthesis and environmental applications of cellulose/ZrO2 nanohybrid as a selective adsorbent for nickel ion

Cellulose/ZrO₂ nanohybrid has been synthesized by simple growth of ZrO₂ on cellulose matrix and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Interestingly, FESEM showed nanoparticles with an average size of 50 nm. The analytical potential of the newly prepared nanohybrid was studied for a selective extraction of nickel prior to its determination by inductively coupled plasma-optical emission spectrometry. The selectivity of nanohybrid was investigated toward eight metal ions, including Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Ni²⁺, Zn²⁺ and Zr⁴⁺. Data obtained from the selectivity study showed that nanohybrid was the most selective toward Ni²⁺. The uptake capacity for Ni²⁺ was experimentally calculated and found to be 79 mg g⁻¹. Moreover, adsorption isotherm data of Ni²⁺ on nanohybrid was well fit with the Langmuir adsorption isotherm, strongly supporting that the adsorption process was mainly monolayer on homogeneous adsorbent surfaces. Finally, data of Ni²⁺ adsorption on nanohybrid as a function of contact time displayed that equilibrium kinetics are very fast.     

Photodegradation of bisphenol-A in a batch TiO2 suspension reactor

In this work, the photocatalytic behaviors of bisphenol-A (BPA), which has been listed as one of endocrine disrupting chemicals, were carried out in a batch TiO₂ suspension reactor. The photodegradation efficiency has been investigated under the controlled process parameters including initial BPA concentration (i.e., 1–50 mg L^?1), TiO₂ dosage (i.e., 5–600 mg/200 cm³), initial pH (i.e., 3–11), and temperature (i.e., 10–70 °C). It was found that the optimal conditions in the photoreaction process could be coped with at initial BPA concentration = 20 mg L^?1, TiO₂ dosage = 0.5 g L^?1 (100 mg/200 cm³), initial pH = 7.0, and temperature = 25 °C. According to the Langmuir–Hinshelwood model, the results showed that the photodegradation kinetics for the destruction of BPA in water also followed the first-order model well. The apparent first-order reaction constants (k_obs), thus obtained from the fittings of the model, were in line with the destruction-removal efficiencies of BPA in all the photocatalytic experiments. Based on the intermediate products identified in the study, the possible mechanisms for the photodegradation of BPA in water were also proposed in the present study.     

Shrinkage and strength of alkaline activated ground steel slag/ultrafine palm oil fuel ash pastes and mortars

This study evaluated the contributions of steel slag and activators ratio to the shrinkage of the alkali-activated ground steel slag (G)/ultrafine palm oil fuel ash (U) or AAGU pastes and mortars. The base materials were combined such that G/U+G varied from 0 to 0.8 (pastes) and 0–0.6 (mortars) with the use of 10M-NaOH_aq and Na₂SiO_3aq (Ms = SiO₂/Na₂O of 3.3) as activators whose ratios (Na₂SiO_3aq/10M NaOH_aq) were varied as 1.0/1.0 and 2.5/1.0. The findings revealed that steel slag reduced the AAGU shrinkage through pore-refinement, elimination of microcracks, and improvement in the microstructural density and strength. The changing of Na₂SiO₃/10NaOH ratio in the synthesis of AAGU products from 2.5 to 1.0 slightly reduced the shrinkage through the modification of amorphousity and nature of the products (C-A-S-H/C-S-H). The maximum 90-day slag-free AAGU paste and mortar shrinkages were 60.80 × 10³ με and 11.82 × 10³ με but reduced to 25.88 × 10³ and 2.71 × 10³ με, respectively as G/(U+G) = 0.4 in AAGU_0.4.     

Kinetics of thermal gradient chemical vapor infiltration of large-size carbon/carbon composites with vaporized kerosene

Large-size samples of carbon/carbon composites were prepared using thermal gradient chemical vapor infiltration with kerosene precursor at 950, 1020, 1100, 1180 and 1250 °C. The temperature gradient, kinetics and density distribution of these samples were studied and the microstructure of pyrolytic carbon was examined by polarized light microscopy. The results show that the initial infiltration rate increased from 5.81 to 21.32 g min^?1 by increasing deposition temperature from 950 to 1250 °C. The densification kinetics relied on deposition temperature and competition between reaction and diffusion, and the diffusion mechanism transformed from bulk to Knudsen diffusion regime. The calculated apparent activation energy is about 68.2 kJ mol^?1. The temperature range 1020–1100 °C is appropriate for fabricating composites with high final bulk density due to high degree of pore filling and the density of sample S3 infiltrated at 1100 °C is the highest among all investigated samples.     

Determination of sulfamethoxazole in foods based on CeO2/chitosan nanocomposite-modified electrodes

An electrochemical immunosensor based on nanocomposite-modified glass carbon (GC) electrode has been developed. The biospecific surface was a CeO₂-chitosan (CHIT)-modified nanocomposite to which anti-sulfamethoxazole (SMX) polyclonal antibody (Ab) was immobilized. The assay was based on competition of SMX and horseradish peroxidase (HRP)–SMX to the antibody immobilized. Electrochemical voltammetry and impedance spectroscopy studies revealed that the presence of CeO₂-CHIT nanocomposite significantly enhanced conductivity of the electrode. The large electro-active surface area of nanoCeO₂-CHIT/GC electrode resulted in the high loading of anti-SMX polyclonal antibody. The electrochemical signals of the immunosensor mainly resulted from the HRP catalyzed hydrogen peroxide reduction in the presence of thionine. The immunosensor showed high sensitivity for the detection of SMX. The electrochemical response signals of the immunosensor were found to be linearly proportional to SMX concentration in the range from 5 × 10^? 7 to 5 × 10^? 4 mg mL^? 1 with a regression coefficient of 0.9935 and a detection limit of 3.25 × 10^? 7 mg mL^? 1. No cross-reactivity of antibodies with other antibiotics of sulfonamide family was found. Under optimal conditions, the immunosensor was successfully applied to the electrochemical determination of SMX in milk, honey and egg samples, showing excellent stability and anti-interference ability.     

Electrochemical hydrogen evolution of multi-walled carbon nanotube/micro-hybrid composite decorated with Ni nanoparticles as catalyst through electroless deposition process

Hydrogen evolution of multi-walled nanotube (MWCNT)/micro-hybrid polymer composite, decorated with Ni nanoparticles through electroless deposition process is studied by the electrochemical method. Cyclic voltammetry (CV) is utilized to clearly study the electrochemical hydrogen storage/evolution behavior of the composite through a potential window ranging from ? 1.60 to + 0.60 V (vs. Ag/AgCl). Hydrogen adsorption/desorption peaks are positioned at ? 1.52 and ? 0.05 V, respectively. Chronoamperometry is also applied to estimate active surface area (0.145 m² g^? 1) of the composite as well as the diffusion coefficient (3.4 × 10^? 11 m² s^? 1) of adsorbed hydrogen process. According to the chrono-charge/discharge technique, the capacity of fabricated Ni-MWCNT/micro-hybrid composite is estimated to be 2.98 wt.% during charging for a certain time (40 min).