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.     

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.     

Effect of heat treatment on morphology and thermal decomposition kinetics of multiwalled carbon nanotubes

High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG–DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (～203 kJ mol^?1 and 280 kJ mol^?1) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 °C and 1800 °C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (E_a ≈ 178 kJ mol^?1; n = 1) even in oxidative atmosphere.     

Adsorption behavior of caffeine as a green corrosion inhibitor for copper

Electrochemical and impedance experiments were carried out to evaluate the corrosion behavior of copper in aerated 0.1 mol L^? 1 H₂SO₄ solutions in the presence of three xanthine derivatives with similar chemical structures. The corrosion rate of copper was found to increase in the presence of theophylline and theobromine and decrease in the presence of caffeine. The adsorption and inhibitory effect of caffeine on copper surfaces in aerated 0.1 mol L^? 1 H₂SO₄ solutions were then investigated in detail by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), contact angle measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and fluorescence experiments. The data obtained indicate that caffeine behaves as a cathodic-type inhibitor adsorbing onto the copper surface according to the Temkin isotherm, with the negative ?G°_ads value of ? 31.1 kJ mol^? 1 signifying a spontaneous adsorption process. The corrosion inhibition efficiency increased with caffeine concentration in the range of 1.0–10.0 mmol L^? 1. Furthermore, the EIS results obtained at the open-circuit potential and surface analysis (SEM, EDS and fluorescence) clearly demonstrated the adsorption of the organic compound onto the copper electrode. The contact angle measurements revealed the formation of a hydrophobic protective film. This film covers up to 72% of the total active surface, acts as a protective barrier and prevents interaction between the metal, water and oxygen molecules.     

Nucleation and crystallization behaviors of nano-crystalline lithium–mica glass–ceramic prepared via sol–gel method

The paper investigates the effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramics, taking the composition LiMg₃AlSi_3(1+x)O_10+6xF₂ (x = 0.5) and 8 mass% MgF₂ synthesized by sol–gel technique. Here, X-ray diffraction, thermal analysis and transmission electron microscopy were used to assess the structural evolutions of as-synthesized nano-crystalline lithium–mica glass–ceramics. It was found that MgF₂ crystals perform as nuclei centers for the mica crystallization hence; a large quantity of mica crystallites obtained following the nucleation process at 400 °C for 12 h. For both the un-nucleated and nucleated samples, the crystallization activation energy was measured as 400.2 and 229.6 kJ mol^?1, respectively. Consequently, the calculated Avrami exponents demonstrated that the growth mechanism of mica crystallites, while applying appropriate nucleation treatment, changes from needle-like to three-dimensional growth.     

Thermal behavior of some organic/inorganic composites based on epoxy resin and calcium carbonate obtained from conch shell of Rapana thomasiana

Thermal behavior of some diglycidyl ether of bisphenol A/p-aminobenzoic acid systems with calcium carbonate as a filler were studied. The kinetics parameters of the curing reactions were estimated using the variable peak exotherm method of Kissinger and Ozawa. The most probable kinetic model and the kinetic parameters of the degradation process were also estimated. The energies of crosslinking reactions are situated in the range of 46–57 kJ mol^?1 for the first exotherm and between 68 and 72 kJ mol^?1 for the second exotherm. The cured resins have a good thermal stability and the activation energies of degradation reactions are situated in the range of 178–218 kJ mol^?1.     

Crystallization kinetics of a low melting PbO-ZnO-P2O5 glass

A low-melting water-resistant 40P₂O₅-50PbO-10ZnO glass with a glass transition temperature T_g ≅ 338°C has been prepared. Differential thermal analysis (DTA), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) absorption spectroscopy techniques were applied for both qualitative and quantitative characterization and crystallization of (Pb_5/6Zn_1/6)₃P₄O₁₃ in glass. Kinetics of crystallization was analyzed based on the Johnson-Mehl-Avrami model. It was found that the surface nucleation mode, having the morphology index n ≅ 1, is dominant. The activation energy of crystallization was found to be 312 kJ mol⁻¹ by a non-isothermal DTA method, while 363 and 344 kJ mol⁻¹ by isothermal XRD and FTIR methods, respectively. These values agree with each other to a reasonable extent. Peak intensity of a specific vibrational mode in FTIR absorption spectra was found to be applicable for quantitative kinetic analysis should suitable calibration using a standard specimen be done.     

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.     

Immobilization of Bacillus sp. in mesoporous activated carbon for degradation of sulphonated phenolic compound in wastewater

Xenobiotic compounds are used in considerable quantities in leather industries besides natural organic and inorganic compounds. These compounds resist biological degradation and thus they remain in the treated wastewater in the unaltered molecular configurations. Immobilization of organisms in carrier matrices protects them from shock load application and from the toxicity of chemicals in bulk liquid phase. Mesoporous activated carbon (MAC) has been considered in the present study as the carrier matrix for the immobilization of Bacillus sp. isolated from Effluent Treatment Plant (ETP) employed for the treatment of wastewater containing sulphonated phenolic (SP) compounds. Temperature, pH, concentration, particle size and mass of MAC were observed to influence the immobilization behavior of Bacillus sp. The percentage immobilization of Bacillus sp. was the maximum at pH 7.0, temperature 20 °C and at particle size 300 μm. Enthalpy, free energy and entropy of immobilization were ? 46.9 kJ mol^? 1, ? 1.19 kJ mol^? 1 and ? 161.36 J K^? 1 mol^? 1 respectively at pH 7.0, temperature 20 °C and particle size 300 μm. Higher values of ΔH⁰ indicate the firm bonding of the Bacillus sp. in MAC. Degradation of aqueous sulphonated phenolic compound by Bacillus sp. immobilized in MAC followed pseudo first order rate kinetics with rate constant 1.12 × 10^? 2 min^? 1.     

Corrosion inhibition of aluminum in hydrochloric acid solution by alkylimidazolium ionic liquids

The effects of newly synthesized three alkylimidazolium ionic liquids—1-butyl-3-methylimidazolium chlorides (BMIC), 1-hexyl-3-methylimidazolium chlorides (HMIC) and 1-octyl-3-methylimidazolium chlorides (OMIC)—on the corrosion of aluminum in 1.0 M HCl were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss methods. All measurements showed that the inhibition efficiency increased with increase in the concentration of inhibitor and the effectiveness of these inhibitors was in the order of OMIC > HMIC > BMIC. Polarization curves revealed that the studied inhibitors were mixed type inhibitors. The adsorption of the inhibitors on the aluminum surface obeyed Langmuir adsorption isotherm and had a physical mechanism. The effect of temperature on the corrosion behavior in the presence of 5 × 10^?3 M of inhibitors was studied in the temperature range of 303–333 K. The associated activation energy of corrosion and other thermodynamic parameters such as enthalpy of activation (ΔH), entropy of activation (ΔS), adsorption equilibrium constant (K_ads) and free energy of adsorption (ΔG_ads) were calculated to elaborate the mechanism of corrosion inhibition.     

Preparation,characterization and thermolysis of nitrate and perchlorate salts of 2,4,6-trimethylaniline

Nitrate and perchlorate salts of 2,4,6-trimethylaniline have been prepared and characterized by X-ray crystallography and gravimetric analyses. Their thermal decomposition has been studied by TG, TG–DSC and ignition/explosion delays. It has been observed that proton transfer from substituted anilinium ion to nitrate and perchlorate ion regenerate amine, HNO₃ and HClO₄ in condensed phase at higher temperature, where oxidation–reduction between amine and acids leads to ignition and explosion. The kinetics of thermal decomposition was evaluated by applying model fitting as well as isoconversional methods. The values of calculated activation energy of nitrate and perchlorate salts are 77.9 and 118.2 kJ mol^?1 respectively. The possible pathways of thermolysis of these salts have also been proposed.     

Thermodynamic functions of the grain-like ZnO nanostructures

Grain-like ZnO nanostructures were prepared by a simple microemulsion-mediated hydrothermal route, and were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). In order to associate thermodynamic functions of nano ZnO with bulk ZnO, a novel thermochemical cycle was designed. Combined with in situ microcalorimetry, the standard molar enthalpy of formation, standard molar Gibbs free energy of formation and standard molar entropy of the obtained products at 298.15 K were successfully acquired as (? 322.36 ± 0.42) kJ mol^? 1, (? 318.74 ± 0.03) kJ mol^? 1 and (44.61 ± 1.02) J mol^? 1 K^? 1, respectively.     

A simple and efficient electrochemical sensor for folic acid determination in human blood plasma based on gold nanoparticles–modified carbon paste electrode

Folic acid (FA) is a water soluble vitamin that exists in many natural species. The lack of FA causes some deficiencies in human body, so finding a simple and sensitive method for determining the FA is important. A new chemically modified electrode was fabricated for determination of FA in human blood plasma using gold nanoparticles (AuNPs) and carbon paste electrode (CPE). Gold nanoparticles–modified carbon paste electrode (AuNPs/CPE) was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experimental parameters such as pH, scan rate (ν) and amount of modifier were studied by cyclic voltammetry and the optimized values were chosen. The electrochemical parameters such as diffusion coefficient of FA (D_FA), electrode surface area (A) and electron transfer coefficient (α) were calculated. Square wave voltammetry as an accurate technique was used for quantitative calculations. A good linear relation was observed between anodic peak current (i_pa) and FA concentration (C_FA) in the range of 6 × 10^? 8 to 8 × 10^? 5 mol L^? 1, and the detection limit (LOD) achieved 2.7 × 10^? 8 mol L^? 1, that is comparable with recently studies. This paper demonstrated a novel, simple, selective and rapid sensor for determining the FA in the biological samples.     

A comparative study on fabrication of Mn2 + selective polymeric membrane electrode and coated graphite electrode

Poly(vinyl chloride)-based membranes of two ligands 2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₁) and N2,N4-di(cyanoethyl)-2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₂) were fabricated and explored as Mn^2 + ion selective electrodes. The performance of the polymeric membranes electrodes of ionophores with different plasticizers (dibutylphthalate, benzoic acid, o-nitrophenyloctyl ether, 1-chloronapthalene and tri-n-butylphosphate) and anion excluders (sodium tetraphenylborate and potassium tetrakis p-(chloro phenyl)borate) was looked in to and the better results were obtained with the membrane having composition L₂: NaTPB: DBP: PVC as 6: 3: 56: 35 (w/w; mg). The coated graphite electrode (CGE) with same composition was also fabricated and investigated as Mn^2 + selective electrode. It was found that CGE showed better response characteristics than PME. The potentiometric response of CGE was independent of pH in the range 3.0–9.0 exhibiting the Nernstian slope 29.5 ± 0.3 mV decade^? 1 of activity and working concentration range 4.1 × 10^? 7–1.0 × 10^? 1 mol L^? 1 with a limit of detection 6.7 × 10^? 8 mol L^? 1. The electrode showed a fast response time of 12 s with a shelf life of 105 days. The proposed CGE could be successfully used for the determination of Mn^2 + ions in different water, soil, vegetables and medicinal plants also used as an indicator electrode in potentiometric titration with EDTA.     

A Ho(III) potentiometric polymeric membrane sensor based on a new four dentate neutral ion carrier

In this research, we report a new Ho^3 +-PVC membrane electrode based on N-(4,5-dimethyl-2-(picolinamido)phenyl)picolinamide (H₂Me₂bpb) as a suitable ion carrier. Poly vinylchloride (PVC)-based membrane composed of H₂Me₂bpb with oleic acid (OA) as anionic additives, and o-nitrophenyloctyl ether (NPOE) as plasticized solvent mediator. The sensor exhibits a Nernstian slope of 20.1 ± 0.2 mV decade^? 1 over the concentration range of 1.0 × 10^? 6 to 1.0 × 1^? 2 mol L^? 1, and a detection limit of 5.0 × 10^? 7 mol L^? 1 of Ho^3 + ions. The potentiometric response of the sensor is independent of the solution pH in the range of 3.5–9.4. It has a very short response time, in the whole concentration range (< 10 s), and can be used for at least eight weeks. The proposed electrode shows a good selectivity towards Ho^3 + ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. To assess its analytical applicability the proposed Ho^3 + sensor was successfully applied as an indicator electrode in the titration of Ho^3 + ion solutions in certified reference materials, alloy samples and for the determination of the fluoride ion in two mouthwash preparations.     

Creep behavior of nanostructured Mg alloy at ambient and low temperature

Tensile creep test at temperature <0.35 T_m was carried out to investigate the creep behavior in nanostructured Mg alloy with an average grain size of 45 nm consolidated from mechanically alloyed powders using power creep law. The stress exponent is found to be larger than one and with a threshold stress. The activation energy for the creep is measured to be 76 kJ mol⁻¹ smaller than that for grain boundary diffusion in Mg. It is deduced that creep behavior is affected by the presence of impurities and nanovoids inherited from the processing history.     

Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (k_s), diffusion coefficient (D) and the surface adsorption amount (Γ^?) of ACOP on GR–CS/GCE were determined to be 0.25 s^? 1, 3.61 × 10^? 5 cm² s^? 1 and 1.09 × 10^? 9 mol cm^? 2, respectively. Additionally, a 2e^?/2H⁺ electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0 × 10^? 6 to 1.0 × 10^? 4 M with a low detection limit of 3.0 × 10^? 7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations.     

Effect of functional monomers and porogens on morphology,structure and recognition properties of 2-(4-methoxyphenyl)ethylamine imprinted polymers

2-(4-Methoxyphenyl)ethylamine imprinted polymers were obtained from seven functional monomers in four porogens, and their properties were tested. Binding experiments revealed the highest selectivity towards a template for the polymer prepared from methacrylic acid in toluene (MIP1). The binding capacities and the imprinting factors were different for the stationary and the dynamic evaluation procedures. For MIP1, the binding capacities were 6.991 ± 0.081 or 18.247 ± 0.005 μmol g^? 1, and the imprinting factors were 1.97 or 3.84, for stationary and dynamic procedures, respectively. The Scatchard analysis of MIP1 showed two classes of binding sites with values of the dissociation constants K_d equal to 16.2 and 192 μmol L^? 1. Composition of polymers was supported by ¹³C CP/MAS NMR, FTIR and SEM-EDS analyses. The binding abilities of MIP1 towards the structurally related compounds showed that the ethylamine group together with steric effects governed the recognition mechanism. Finally, the high affinity of MIP1 towards dopamine or serotonin, but low towards norepinephrine and epinephrine was demonstrated.     

Solid-phase crystallization of spray-dried glucose powders: A perspective and comparison with lactose and sucrose

The solid-phase crystallization growth kinetics of spray-dried sugar powders, including glucose, lactose and sucrose, have been studied from water-induced crystallization experiments at a relative humidity of 75% and temperatures from 15 to 40 °C on amorphous powders of these sugars produced in a laboratory-scale spray dryer (Buchi B290). All results have shown that the enthalpies and Gibbs Free Energies of activation of the sugars studied here increase during the crystallization process, suggesting that the binding energy needed for the formation of an activated complex increases as the moisture content decreases. The enthalpies of activation for glucose, lactose and sucrose crystallization have been compared by the Activated Rate equation and found to be 58 ± 8 kJ mol⁻¹, 39 ± 2 kJ mol⁻¹ and 68 ± 4 kJ mol⁻¹, for glucose, lactose and sucrose, respectively, Similarly, the entropies of activation have been calculated as −92 ± 27 J mol⁻¹ K⁻¹, −156 ± 6 J mol⁻¹ K⁻¹ and −60 ± 5 J mol⁻¹ K⁻¹ for glucose, lactose and sucrose, respectively. These different numerical values may be expected from the different structures of the sugars.     

Resonance light-scattering method for the determination of labetalol using uranyl acetate and aniline blue

A sensitive and convenient method for determining labetalol has been developed based on resonance light-scattering using ternary complex of aniline blue (AB), uranyl ion (UO₂²⁺) and labetalol. At pH 6.0–7.0, labetalol reacted with AB and UO₂²⁺ to form an ion-association complex that resulted in considerable resonance light-scattering (RLS) characterized with a peak at 356 nm. The RLS was successfully applied to the determination of labetalol. The intensity of RLS (I_RLS) at 356 nm linearly depended on the concentration of labetalol ranging from 4.0 × 10^? 7 to 2.4 × 10^? 4 mol L^? 1. The lower detection limit was 2.1 × 10^? 7 mol L^? 1. The present method is highly selective to labetalol and can successfully be applied to the determination of labetalol in human urine.