Nanofibrous membrane of polyacrylonitrile with efficient adsorption capacity for cadmium ions from aqueous solution: Isotherm and kinetic studies

The nanofibrous membrane of polyacrylonitrile (NMP) was successfully synthesized after NaOH and NaHCO₃ treatment aiming its functionalization using electrospinning for cadmium ion (Cd²⁺) adsorption. Field emission scanning electron microscopy (FE-SEM) revealed that small particles attached to the surface of functionalized PAN nanofibers. Equilibrium was attained after 60 min following a rapid uptake of Cd²⁺ with maximum adsorption capacity and percentage removal at an optimum solution pH of 7.0. The adsorbent dose of 0.3 g and 90 mg L⁻¹ of initial Cd²⁺ concentration yielded the maximum adsorption capacity. The pseudo-second-order kinetic model was the best fitted to the adsorption data, indicating that the chemisorption is the controlling mechanism of adsorption. The physisorption was proposed based on the calculated values of the mean free energy of adsorption from the D–R isotherm (E < 8 kJ mol⁻¹). Furthermore, three-parameter isotherm models indicated the homogeneous and heterogeneous Cd²⁺ adsorption onto NMP adsorbent.     

Adsorption and thermodynamics studies of U(VI) by composite adsorbent in a batch system

The adsorption of U(VI) from aqueous solutions onto composite adsorbent (algistar) has been studied using a batch adsorber. The parameters that affect the U(VI) sorption, such as contact time, solution pH, initial U(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of composite adsorbent, and experimental results showed this to be 43.10 mg/g. The adsorption patterns of metal ions on composite adsorbent followed the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. The Freundlich, Langmuir, and D–R models have been applied, and the data correlate well with Langmuir model, and that the sorption is physical in nature (the sorption energy E _ads = 12.90 kJ/mol). Thermodynamic parameters (∆H _ads^o = −41.08 kJ/mol, ∆S _ads^o = −68.00 J/mol K, ∆G _ads (298.15 K) = −20.81 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that the composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.     

Kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain from aqueous solutions

Spent grain, a main by-product of the brewing industry, is available in large quantities, but its main application has been limited to animal feeding. Nevertheless, in this study, spent grain modified with 1 M NaCl solution as a novel adsorbent has been used for the adsorption of Pb(II) in aqueous solutions. Isotherms, kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain were studied. The equilibrium data were well fitted with Langmuir, Freundlich and Dubinin-Radushkevick (D-R) isotherm models. The kinetics of Pb(II) adsorption followed pseudo-second-order model, using the rate constants of pseudo-second-order model, the activation energy (E_a) of Pb(II) adsorption was determined as 12.33 kJ mol⁻¹ according to the Arrhenius equation. Various thermodynamic parameters such as ΔG^ads, ΔH^ads and ΔS^ads were also calculated. Thermodynamic results indicate that Pb(II) adsorption onto modified spent grain is a spontaneous and endothermic process. Therefore, it can be concluded that modified spent grain as a new effective adsorbent has potential for Pb(II) removal from aqueous solutions.     

Thermodynamic and kinetic parameters of ciprofloxacin adsorption onto modified coal fly ash from aqueous solution

Batch adsorption experiments were carried out for the removal of ciprofloxacin from aqueous solution using modified coal fly ash as adsorbent. The effects of various parameters such as contact time, initial solution concentration and temperature on the adsorption system were investigated. The optimum contact time was found to be 100 min. The isotherm adsorption data fit well with the Langmuir model, and the kinetic data fit well with the pseudo-second order and the intra-particle diffusion model. Intra-particle diffusion analysis demonstrates that ciprofloxacin diffuses quickly among the particles at the beginning of the adsorption process, and then the diffusion slows down and stabilizes. Thermodynamic parameters such as ΔG, ΔH and ΔS were also calculated. The negative Gibbs free energy change and the positive enthalpy change indicated the spontaneous and endothermic nature of the adsorption, and the positive entropy change indicated that the adsorption process was aided by increased randomness.     

Adsorption study of dimethylaminostyryl benzazoles onto Na-montmorillonite

The adsorption of 2-(4′-dimethylaminostyryl)benzoxazole (DMASBO) and its benzothiazole analogue (DMASBT) onto Na-montmorillonite (Na⁺-MMT) was studied. The adsorption data have been fitted with Freundlich and Dubinin-Radushkevich (D-R) equation to find the characteristic parameters of each model. From D-R isotherm, it was concluded that the adsorption is of chemical nature. The equilibrium adsorption constant, K_c, was determined and has been used to calculate the enthalpy and entropy of the adsorption process. The mechanism of the adsorption has been investigated by fluorescence, IR, X-ray and ESR spectroscopic measurements. These measurements indicate oxidation of the styryl dyes by the Lewis acidic sites of the clay and formation of radical cations at Na⁺-MMT surface without intercalation into the interior.     

Application of the statistical rate theory of interfacial transport to investigate the kinetics of divalent metal ion adsorption onto the energetically heterogeneous surfaces of oxides and activated carbons

Divalent metal cation adsorption from solution onto oxides or activated carbons can be described by the Surface Complexation Model (SCM). We assumed that the adsorbent surface is strongly energetically heterogeneous and derived the adsorption isotherm using rectangular distribution of adsorption energy and condensation approximation for the local isotherm equation. Assuming additionally that the bulk concentration of divalent metal ion is low and does not change considerably during the adsorption process and next applying the Statistical Rate Theory of Interfacial Transport (SRT) we derived the Elovich equation—the experimental formula describing adsorption kinetics.     

Synthesis of graphene oxide-poly(2-hydroxyethyl methacrylate) composite by dispersion polymerization in supercritical CO2: adsorption behavior for the removal of organic dye

The use of a biocompatible and thermoresponsive polymer, poly(2-hydroxyethyl methacrylate) (PHEMA) grafted onto the surface of graphene oxide (GO) as an adsorbent for the removal of a cationic dye (methylene blue [MB]) from an aqueous solution is examined in this work. GO–PHEMA forms a hydrogel in water thus overcoming the problem faced by carbon-based adsorbent materials during post-treatment (i.e., separation of adsorbent from the aqueous phase). The GO–PHEMA composite was synthesized using a green approach through dispersion polymerization in supercritical CO₂. The successful preparation of this composite was confirmed by a series of characterization techniques. The adsorption behavior of the composite toward MB such as the effect of the adsorbent dosage, pH, contact time, dye concentration, and recyclability were observed. In addition, the adsorption isotherm, kinetics and thermodynamics were investigated. According to the experimental data, the adsorption parameters were found to fit well into the Freundlich adsorption isotherm with a correlation coefficient of 0.975 and a maximum predicted adsorption capacity of 39.41 mg g^?1 at 25 °C. The adsorption kinetics studies showed that the adsorption behavior followed a pseudo-second-order reaction. On the other hand, the thermodynamics studies showed that the adsorption of MB on GO–PHEMA composite followed spontaneous and endothermic adsorption process with an efficient adsorption temperature at 45 °C. The experimental results also showed that the GO–PHEMA composite could remove 99.8% of the dye in 45 min. Therefore, GO–PHEMA composite is a favorable green adsorbent for environmental applications.     

Screening and optimization of highly effective ultrasound-assisted simultaneous adsorption of cationic dyes onto Mn-doped Fe3O4-nanoparticle-loaded activated carbon

The ultrasound-assisted simultaneous adsorption of brilliant green (BG) and malachite green (MG) onto Mn-doped Fe₃O₄ nanoparticle-loaded activated carbon (Mn-Fe₃O₄-NP-AC) as a novel adsorbent was investigated and analyzed using first derivative spectrophotometry. The adsorbent was characterized using FT-IR, FE-SEM, EDX and XRD. Plackett–Burman design was applied to reduce the total number of experiments and to optimize the ultrasound-assisted simultaneous adsorption procedure, where pH, adsorbent mass and sonication time (among six tested variables) were identified as the most significant factors. The effects of significant variables were further evaluated by a central composite design under response surface methodology. The significance of independent variables and their interactions was investigated by means of the analysis of variance (ANOVA) within 95% confidence level together with Pareto chart. Using this statistical tool, the optimized ultrasound-assisted simultaneous removal of basic dyes was obtained at 7.0, 0.02 g, 3 min for pH, adsorbent mass, and ultrasonication time, respectively. The maximum values of BG and MG uptake under these experimental conditions were found to be 99.50 and 99.00%, respectively. The adsorption process was found to be followed by the Langmuir isotherm and pseudo-second order model using equilibrium and kinetic studies, respectively. According to Langmuir isotherm model, the maximum adsorption capacities of the adsorbent were obtained to be 101.215 and 87.566 mg g⁻¹ for MG and BG, respectively. The value of apparent energy of adsorption obtained from non-linear Dubinin–Radushkevich model (4.348 and 4.337 kJ mol⁻¹ for MG and BG, respectively) suggested the physical adsorption of the dyes. The studies on the well regenerability of the adsorbent in addition to its high adsorption capacity make it promising for such adsorption applications.     

Ultrasonic-assisted synthesis of graphene oxide – fungal hyphae: An efficient and reclaimable adsorbent for chromium(VI) removal from aqueous solution

In this study, a hybrid film bio-nanocomposite material was developed based on the graphene oxide/fungal hyphae (GO-FH) interaction. The developed GO-FH bio-nanocomposite material was used for the removal of hexavalent chromium from aqueous solution. The GO-FH bio-nanocomposite material was prepared by ultrasonic irradiation technique. The synthesized GO-FH bio-nanocomposite material was characterized by XRD, FT-IR, SEM, TEM and TGA. The adsorption experiments were carried out in batch mode to optimize parameters such as pH, adsorbent dosage, initial Cr(VI) ion concentration, contact time and shaking speed. The results indicated that the adsorption of Cr(VI) onto GO-FH bio-nanocomposite material was pH dependant, with the maximum adsorption capacity of 212.76 mg/g occurred at pH 2.0. The adsorption studies followed, Langmuir isotherm and pseudo second order kinetic model. Findings demonstrates that GO-FH bio-nanocomposite material exhibited excellent regeneration performance.     

Cr(VI) adsorption mechanism on rice husk ash burned at low temperature by method of IR spectra

Boehm titration method was used to analyze functional groups on cell surface of rice husk ash burned at low temperature in the present paper. Effects of initial pH value and temperature on Cr(VI) adsorption were studied, adsorption capacity was tested with the help of kinetic models and adsorption isotherms, instruments of Fourier transform infrared spectroscopy(FTIR) and scanning electron microscope (SEM) were used to check characteristics and adsorption mechanism of Cr(VI). The results indicated that optimal removing rate was achieved at initial pH value 5, and pH values of aqueous solution changed little be fore and after adsorption process. The adsorbent of rice husk ash could remove Cr(VI) effectively, and the maximum removing rate could be 95% with Cr(VI) concentration 20 mg x L(-1) and achieve 1-2 level of state standard(GB8978-1996). The adsorption process fits pseudo-second-order kinetic model and Langmuir isotherm better, the maximum adsorption capacity of Cr(VI) was 3.2776 mg x g(-1). Results of FTIR showed that amide II band, Si--O--Si, O--Si--O were important for Cr(VI) removal. SEM micrographs revealed that series of needle-shaped precipitation appeared on cell surface, and inorganic precipitation mechanism and redox mechanism might work in the test. As a kind of low cost adsorbent, rice husk ash can be applied to remove heavy metals in environment with great potential.     

A simplified method for synthesis of Fe3O4@PAA nanoparticles and its application for the removal of basic dyes

A simplified method for synthesis of polyacrylic acid-bound iron oxide magnetic nanoparticles (Fe₃O₄@PAA NPs) was reported. The as-prepared nanoparticles were characterized by TEM, FT-IR, VSM and XRD. Characterization results indicated that PAA was successfully introduced onto the surface of Fe₃O₄ and did not cause any changes in magnetic property. The Fe₃O₄@PAA NPs were used to adsorb rhodamine 6G (R6G) as a model basic dye pollutant from aqueous solution. Kinetics data and adsorption isotherms were better fitted by pseudo-second-order kinetic model and Langmuir isotherm, respectively. The adsorption equilibrium could be reached at about 20 min, showing that the as-prepared adsorbent exhibited extremely rapid adsorption rate. The aqueous solution of the Yellow River was chosen as the test sample, and the results showed that the magnetic adsorbent was efficient for the removal of the basic dye in the real sample.     

Adsorption of Cr(VI) from Aqueous Solutions Onto Raw and Acid-Activated Reşadiye and Hançılı Clays

ABSTRACT

The adsorption of Cr(VI) from aqueous solutions onto raw and acid-activated clays—namely, Re?adiye region clay (R, raw Re?adiye region clay; R-H₂SO₄, acid-activated with H₂SO₄ Re?adiye region clay; R-HCl, acid-activated with HCl Re?adiye region clay) and Hanç?l? region clay (H, raw Hanç?l? region clay; H-H₂SO₄, acid-activated with H₂SO₄ Hanç?l? region clay; H-HCl, acid-activated with HCl Hanç?l? region clay)—was studied in a batch system. For optimization of the Cr(VI) adsorption on raw clays and acid-activated clays, the effect of pH, temperature, initial Cr(VI) concentration, time, and adsorbent dosage were investigated. X-ray diffraction analyses of raw and acid-activated clays were used to determine the effects of acid-activating on the layer structure of the clays. The surface characterizations of clays and modified clays were performed by using FT-IR spectroscopy. The Langmuir and Freundlich adsorption models were employed to describe the equilibrium isotherms, and thus the isotherm constants were determined. The data obtained from our investigations were well described by the Langmuir model. The adsorption capacity of the adsorbents Re?adiye and Hanç?l? clays were found to be 0.0269, 0.0144, and 0.0170 mmol/g for H, H-HCl, and H-H₂SO₄ and 0.0356, 0.0276, and 0.0422 mmol/g for R, R-HCl, and R-H₂SO₄, respectively. The results show that the adsorption was strongly dependent on pH of the medium, initial Cr(VI) concentration and temperature. The removal of Cr(VI) reached saturation in about 120 min, and the adsorption process of Cr(VI) was observed as exothermic. A maximum removal of 73% was noted at 1.0 × 10^?4 M concentration of Cr(VI) in solution for H-HCl. Furthermore the enhancement of removal of Cr(VI) was observed from pH 3 to 4. The results are discussed to highlight the influence of acid activation on Cr(VI) adsorption characteristics of the clays.     

Chemical and electrochemical investigations of high carbon steel corrosion inhibition in 10 % HCl medium by quinoline chalcones

The corrosion inhibitive effect of 3-(3-oxo-3-phenyl-propenyl)-1H-quinolin-2-one (PPQ) and 3-(3-oxo-3-phenyl-propenyl)-1H-benzoquinolin-2-one (PPBQ) on high carbon steel (HCS) in 10 % HCl media was evaluated by chemical (weight loss) and electrochemical (electrochemical impedance spectroscopy and potentiodynamic polarization technique) measurements. The inhibition efficiencies obtained from weight loss and electrochemical measurements were in good agreement. The inhibition efficiency was found to increase with the increase in inhibitor concentration but decreased with rise in temperature. Potentiodynamic polarization studies revealed the mixed mode inhibition of inhibitors. The adsorption behavior of these inhibitors on the HCS surface was found to obey the Langmuir adsorption isotherm. The thermodynamic parameter values of free energy of adsorption (?G _ads) and enthalpy of adsorption (?H _ads) revealed that the inhibitor was adsorbed on the HCS surface via both chemisorption and physisorption mechanisms. The adsorption mechanism of inhibition was supported by spectroscopic techniques (UV–visible, FT-IR, and wide-angle X-ray diffraction), surface analysis (SEM–EDS), and adsorption isotherms.     

Removal of lead(II) by adsorption onto Viscumalbum L.: Effect of temperature and equilibrium isotherm analyses

The removal efficiency of Viscumalbum L. from lead containing aqueous solutions was investigated. The effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature was investigated using a batch adsorption technique. The optimum pH for Pb(II) adsorption was found as 3.0 for Viscumalbum L. Results were analyzed by the Langmuir, Freundlich, Temkin and Harkins-Jura, equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. The Langmuir model agrees very well with experimental data than the other models. According to Langmuir isoterm, the monolayer saturation capacity (Q_o) is 769.23 mg/g at 25 °C. Models and the isotherm constant were evaluated depending on temperature. Thermodynamic parameters such as ΔH^o, ΔS^o and ΔG^o were calculated. The adsorption process was found to be endothermic and spontaneous. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data.     

Adsorption and solid phase extraction of 8-hydroxyquinoline from aqueous solutions by using natural bentonite

The nitrogen-heterocyclic compound 8-hydroxyquinoline (8HQ) is one of the components of coal tar and has a wide variety of uses in industry. Because of its toxicity for aquatic organisms and harmful effects for human health, the removal of 8HQ from aqueous solutions by adsorption onto natural bentonite was investigated in the present work. The experimental results show that the optimum pH value of 2.5 is favourable for the 8HQ adsorption. The experimental data were fitted well with the pseudo-second-order kinetic and Langmuir adsorption isotherm models at all studied temperatures. The maximum adsorption capacity obtained from the Langmuir isotherm model at 20 °C was 120.6 mg g⁻¹. The calculated thermodynamic results such as ΔG° (−24.3 kJ mol⁻¹) and ΔH° (−9.56 kJ mol⁻¹) indicate that the adsorption process is spontaneous and exothermic in nature. Solid phase extraction of 8HQ was also performed. The X-ray diffractometry (XRD), Fourier Transform Infrared (FTIR) and thermogravimetric (TG) analyses were carried out in order to confirm the 8HQ adsorption onto bentonite. According to the obtained results, natural bentonite can be a reusable and effective adsorbent for the removal of 8HQ.     

Interaction of C2N2 with clean and oxygen dosed Cu(111) surface studied by AES,ELS and TDS measurements

The adsorption and surface reaction of cyanogen on clean and oxygen covered Cu(111) have been investigated. From electron energy loss measurements, thermal desorption spectroscopy and electron beam effects in Auger spectroscopy, it is proposed that cyanogen adsorbs dissociatively on Cu(111) at 300 K. The activation energy for the desorption was calculated to be 180 kJ/mol. Cyanogen adsorption onto oxygen predosed Cu(111) is inferred to produce the NCO surface species. This interpretation was aided by data of electron energy loss measurements and from HNCO adsorption onto Cu(111) at 300 K. A reaction began in the co-adsorbed layer above 400 K, yielding CO₂ and N₂.     

Preparation and characterization of hexadecyl functionalized magnetic silica nanoparticles and its application in Rhodamine 6G removal

In this paper, a new adsorbent, hexadecyl functionalized magnetic silica nanoparticles (C₁₆/SiO₂-Fe₃O₄ NPs), was prepared by a facile method. The final product was characterized by X-ray diffractometer, transmission electron microscope, Fourier transform infrared spectrometer and vibration sample magnetometer. The preparation and adsorption conditions of the adsorbent were optimized. The adsorbent prepared maintaining volume ratio of tetraethylorthosilicate to hexadecyltrimethoxysilane at 1:0.5 and their total volume at 1100 μL exhibited high adsorption capacity. The optimum pH value for the adsorption experiments was 11.00. The adsorption behavior of Rhodamine 6G onto C₁₆/SiO₂-Fe₃O₄ NPs obeyed pseudo-second-order kinetic model and Langmuir isotherm. Thermodynamic data indicated that the adsorption process was spontaneous and exothermic. The adsorption capacity of the adsorbent could reach to 35.6 mg g⁻¹, owing to the hydrophobic attraction and the enhanced electrostatic attraction. The saturation magnetization of the magnetic adsorbent was 35 emu g⁻¹, which ensured the magnetic separation after adsorption.     

Adsorption of interacting monomers on spanning clusters of polyatomic species

The adsorption-desorption process occurring on heterogeneous surfaces is studied by considering a special case where a fractal is used as adsorbent. The fractal surface is the spanning cluster corresponding to the random deposition of objects that occupy more than one site (k-mers) on a square lattice. Such a surface is characterized according to the deposited k-mer. Then, the adsorption of repulsively interacting particles adsorbed on the fractal surface is studied by using Monte Carlo simulations. Different thermodynamic quantities (adsorption isotherms, coverage susceptibility, etc.) are calculated and explained in terms of the characteristics of the substrate. A scheme to characterize the structure of the substrate by just considering the adsorption isotherm is presented and discussed.     

Adsorption on heterogeneous surfaces: The exponential equation for the overall adsorption isotherm

The adsorption isotherm for heterogeneous surfaces can be very well approximated by the exponential higher degree polynomial of variable In (p/p₀). This equation is obtainable by statistical thermodynamics methods. On some simplifying assumptions one can obtain the Dubinin-Radushkevich and Freundlich adsorption isotherms from the exponential isotherm. The energy distribution function corresponding to the exponential adsorption isotherm can be calculated in the way analogous to that for DR isoterm.     

外加阴离子吸附剂对复合污染黄土淋洗过程养分淋失的减缓机制(Ⅱ)

化学淋洗法是常用的污染场地修复方法,其经济性、简便性、安全性等指标较其他方法有较大优势。化学淋洗法存在的弊端之一是淋洗过程土壤伴存养分的同步淋失,若能在此瓶颈问题上有所突破,将会大大促进淋洗法场地修复的应用进程。本文研究的目标在于揭示合成秸秆基阴离子吸附剂对养分淋失的减缓机制,采用吸附平衡模式(等温线和动力学)与光谱分析技术(SEM和FT-IR)相结合,力图从微观层面验证宏观研究结果。Langmuir和准二级动力学方程能更好地描述硝酸根和磷酸根的吸附行为,由Langmuir方程计算得出q_m分别为7.507 5和4.194 6 mg·g-1,吸附反应为单层吸附和优惠吸附过程,主要控速步骤为化学吸附。阴离子吸附剂对硝酸根和磷酸根的吸附活化能(298 K)E_a分别为42.25和39.38 kJ·mol-1,吸附反应自发、吸热。纯净水和KOH能够实现阴离子吸附剂的再生,超声辅助和延长解吸时间对于解吸效果略有促进作用。吸附后阴离子吸附剂表面被点状分布的细微颗粒物覆盖,解吸后仅有少量枝状物零星分布。吸附前后FTIR图谱的主要波峰红移或蓝移,证实阴离子吸附剂表面及内部官能团通过静电作用与硝酸根和磷酸根结合。阴离子吸附剂对硝酸根和磷酸根的吸持固定是物理吸附和化学吸附共同作用的结果。