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1.
Loris Pietrelli 《Adsorption》2013,19(5):897-902
Poly(ethylene glycol) (PEG) is a water-soluble polymer commonly found in industrial and domestic wastewaters. In this study the adsorption onto granular activated carbon (GAC) of PEG, of different molecular weights, from aqueous solutions was examined to evaluate its applicability to wastewater treatment. Batch kinetic models have been tested to predict the rate constant of adsorption. The amount of PEG adsorbed on activated carbon depends mainly on the pH, the MW and on the solution characteristics. The adsorption at fixed temperature decrease by MW (PEG-8000 < PEG-3350 < PEG-1450) a polymer chain conformation modification can explain these effect. The large values of adsorption capacity (>350 mg/g) at low and high pH values show a great potential for GAC. The adsorption process can be described well with the Langmuir and the pseudo first order equation. The effective intraparticle diffusion coefficients of PEG molecules in the GAC adsorbent varying according to the MW values in the range 8.45 × 10?3–9.71 × 10?7.  相似文献   

2.
《Colloids and Surfaces》1987,22(1):51-76
Cationic polyacrylamides of varying molar masses but of similar charge density were tested as flocculants for kaolin suspensions. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions and the residual turbidities of the resulting supernatants. The sol concentration was kept constant at 20 g kaolin dm−3 in 10−3 mol dm−3 NaCl solution; pH was varied from 3 to 10. It was found that the subsidence rates did not reflect the trends of polymer adsorption. Polymer adsorption decreased while subsidence rates increased as the molar mass of the polymers increased. Increased adsorption of polymer with pH did not result in higher rates of subsidence. The principal effect of the quaternary cationic charge is to produce a partially extended polymer molecule at all values of the pH. The positive polymeric charge is of secondary importance to the length of the molecule in determining the efficacy of flocculation by polymer bridging and does not counteract the increasing self-repulsion of the clay particles with increasing pH which produced poor floc formation.  相似文献   

3.
The present study focuses on the proton-conducting polymer electrolytes; poly (N-vinyl pyrrolidone)–ammonium thiocyanate and poly (N-vinyl pyrrolidone)–ammonium acetate prepared by solution casting technique. The XRD analysis indicates the amorphous nature of the polymer electrolytes. The Raman spectra of the C=O vibration of pure polymer PVP at 1,663 cm?1 has been appeared as doublet in the polymer electrolytes. The introduction of this new peak in the salt-doped polymer electrolytes may be due to interaction of the cation with the polymer. The room temperature ionic conductivity σ 303κ has been found to be high, 1.7?×?10?4 S cm?1 for 80 mol% PVP–20 mol% NH4SCN and 1.5?×?10?6 S cm?1 for 75 mol% PVP–25 mol% CH3COONH4. The polymer electrolytes have been tested for their application in Zn–air battery.  相似文献   

4.
A laboratory batch study has been performed to study the effect of various physic-chemical factors such as initial metal ion concentration, solution pH, and amount of adsorbent, contact time and temperature on the adsorption characteristics of zinc (Zn2+) metal ions onto kaolin. It has been found that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn2+) on kaolin is a two steps process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intra-particle diffusion in the interior of the adsorbent which has also been confirmed by intra-particle diffusion model. The equilibrium time is found to be in the order of 60 min. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetics among pseudo-first-order and intra-particle diffusion model. The different kinetic parameters including rate constant are determined at different initial metal ion concentration, solution pH, amount of adsorbent and temperature respectively. The equilibrium adsorption results are analyzed by both Langmuir and Freundlich models to determine the mechanistic parameters associated with the adsorption process. The value of separation factor, RL from Langmuir equation also gives an indication of favorable adsorption. Finally thermodynamic parameters are determined at three different temperatures and it has been found that the adsorption process is exothermic due to negative ΔH° accompanied by decrease in entropy change and Gibbs free energy change (ΔG°).  相似文献   

5.
A surface molecular imprinting technology was developed to adsorb Ce(III) ions that showed much higher adsorption affinity and selectivity for than for other metal ions. The batch adsorption process was studied with respect to effects of pH value, residence time, temperature, and initial concentration of Ce(III) ion. The maximum adsorption capacity is 43 mg g?1 at an initial Ce(III) concentration of 300 mg L?1 and at a sorbent dosage of 1.0 g L?1. A Langmuir isotherm fits the experimental data. The imprinted sorbent exhibits a much higher separation and selectivity for the target imprinted ion than the non-imprinted polymer. Cerium ion can be desorbed with 1M hydrochloric acid solution which is also proven by scanning electron microoscopy and X-ray diffraction experiments. The limit of detection is 37 ng mL?1. The sorbent has been applied to the determination of trace cerium in different environmental samples with satisfactory results.  相似文献   

6.
《Soft Materials》2013,11(2-3):195-212
Abstract

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from 60Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range ?10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with FVP=0.19 has been estimated to be gH2O/gPolymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10?11 m2 s?1 and 4.5×10?11 m2 s?1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol?1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.  相似文献   

7.
In this work, β-CD-based polyurethane copolymers (β-CDPU) have been prepared by reacting β-CD with hexamethylene diisocyanate as cross-linked agent in dry DMF. This polymer showed high selectivity for preconcentration of Pb(II) at trace level prior to its flame atomic absorption spectrometric determination. The effect of several parameters such as pH, flow rate of sample, eluent kind and volume was investigated. The adsorption behaviors and mechanisms of Pb(II) on the samples were also studied. The maximum adsorption amount of Pb(II) was 8 mg g?1 with the preconcentration factor of 250 for Pb(II). The Langmuir isotherm was proved to describe the adsorption data better than the Freundlich isotherm and a pseudo-first-order kinetic model fits the adsorption kinetic processes well. The calibration curve was linear in the range of (3–200 ng mL?1) with a correlation coefficient of 0.9996. The limit of detection based on three times the standard deviation of the blank was 1.15 ng mL?1. The relative standard deviations for the determination of 10 and 100 ng mL?1 of Pb(II) were 3.60 and 0.43 % (n = 10), respectively. The method was successfully applied to the determination of lead in some environmental samples such as Tehran and Bushehr drinking water, river water and dust samples.  相似文献   

8.
The objective of this work is to study the behavior of a neutral polymer, polyvinylpyrrolidone (PVP), in a mixture of water and ethanol. A comparison of the experimental results with a theoretical model of effective solvent interaction with polymer (ESIP) was made. To do so, dynamic light scattering experiments were used to measure the hydrodynamic radius of PVP (M w = 3.6 × 105 g·mol?1) as a function of the ethanol fraction, x A, in the medium at 25 °C. We show that the polymer adopts an ideal chain–globule–coil conformation transition as the ethanol molar fraction varies. This transition is attributed to the change of the solvent quality which results from water and ethanol complex formation. On the other hand, the ternary PVP/water/ethanol system was described by the ESIP model. From the polymer–effective solvent interaction, the second virial coefficient of the polymer/effective solvent and the preferential adsorption parameter were calculated. The obtained results are in agreement with the reported experiments.  相似文献   

9.
Structure and properties of the dispersions of multiwalled carbon nanotubes (MWCNTs) in N,N-dimethylacetamide (DMAc) with different dispersing polymers: polyvinylpyrrolidone (PVP), poly(ethyleneoxide), triblock copolymers poly(ethyleneoxide)-b-poly(propyleneoxide)-b-poly(ethyleneoxide) (Pluronic F127 and Pluronic F108), ethylenediamine tetrakis(ethoxylate-b-propoxylate) tetrol, and ethylenediamine tetrakis(propoxylate-b-ethoxylate) tetrol (Tetronic) of different molecular weights were studied. All studied polymers were shown to be able to disperse MWCNT in DMAc, and MWCNT dispersions appear free of aggregates by visual inspection even after 3 months of keeping at room temperature. Dispersions were characterized by UV–VIS absorption spectroscopy and dynamic light scattering measurements. PVP was found to be the best dispersing polymer for MWCNT in DMAc. It was shown that the yield of the dispersed MWCNT and the average particle size of the MWCNT in DMAc depend on the chemical nature, molecular weight of the dispersing polymer, and solvent quality. The difference in dispersive capacity of the studied polymers is attributed to different dispersion mechanisms for PVP (“polymer wrapping” model) and for other studied dispersing polymers (“loose adsorption” model), which have different efficiencies in DMAc. It was revealed that an increase of dispersing polymer (PVP) concentration at the range of 4.7–37.6 g l?1 results in an average particle size enlargement and MWCNT final concentration reduction.  相似文献   

10.
The removal of Th4+ ions from aqueous solutions was investigated using single-layer graphene oxide (GO) as a sorbent which was prepared by the modified Hummers’ method through batch adsorption experiments at room temperature. Structural characterizations of the sorbent were also investigated. The influences of the pH value of solution, contact time, sorbent dose, ionic strength, the initial metal ion concentration and temperature on the adsorption of Th4+ were also investigated. These results indicated that the adsorption of Th4+ was dependent on the pH and independent on the ionic strength. The sorbent provided significant Th4+ removal (>98.7 %) at pH 3.0 and the adsorption equilibrium was achieved after only 10 min. The Langmuir adsorption isotherm fit the absorption profile very closely, and indicated that a maximum adsorption capacity of 1.77 mmol g?1 of GO (411 mg g?1) after 2 h. The thermodynamic parameters showed that this adsorption process was endothermic and spontaneous. Moreover, the desorption level of Th4+ from GO, by using 0.1 mol L?1 H2SO4 as a stripping agent, was 84.2 ± 1.2 %, and that of 0.5 mol L?1 HNO3 as a stripping agent, was 79.8 ± 3.0 %.  相似文献   

11.
The utilization of diatomite as potential adsorbent to remove malachite green (MG) from aqueous solution was developed. The characterization of the diatomite was evaluated by scanning electron microscope (SEM) and Brurauer Emmerr Teller (BET). The operating variables of pH, diatomite mass, initial MG concentration, and adsorption reaction time were studied. The equilibrium, kinetics, and thermodynamic parameters were investigated as well. It was found that the diatomite was composed of integral and almost circle sieve tray with lots of small pores on it, which afforded the diatomite high specific surface area of 46.09 m2 g?1. The optimum pH and reaction time were 7 and 90 minutes, respectively. The MG removal increased accordingly as the diatomite mass increased. The isotherm results showed that the equilibrium data were fitted to Langmuir model better, indicating the MG adsorption was better characterized by mono-layer. The maximum mono-layer capacity obtained from Langmuir was 23.64 mg g?1 at 25°C. The kinetic studies indicated that experiment data followed pseudo-second-order model better. It also revealed that intraparticle diffusion was not the only rate-controlling step. The thermodynamic results concluded that the adsorption process was endothermic and more favorable at high temperature. Researches confirmed the applicability of diatomite as an efficient adsorbent and low-cost process to remove hazardous materials.  相似文献   

12.
The polyaniline dispersions stabilized with poly(N-vinylpyrrolidone) (PANI/PVP) were synthesized by oxidative polymerization with different mass ratios of PANI and PVP and different molar concentrations of the components in the polymerization mixture. The composite powders prepared from colloidal PANI/PVP dispersions were characterized by thermogravimetry and differential thermal analysis. The change in the ratio of PANI and PVP as well as the starting molar concentrations of aniline hydrochloride and oxidant has influence on the resulting properties of the dispersions. Concerning the doping, the results show that PANI/PVP powders are stable up to approximately 160 °C. Degradation of polymer chains starts at temperatures above 250 °C. The PANI/PVP composite powders with lower content of PANI exhibit slightly higher thermal stability. Further, colloidal PANI/PVP dispersions were screen-printed on aluminum foil for infrared spectroscopic characterization and on poly(ethylene terephthalate) foil for electrical measurements. The sheet resistance of printed layers measured by two-point probe was of the order of tens to thousands of kΩ sq?1. The influence of both the change in the composition and the drying temperature is discussed.  相似文献   

13.
The removal of Hg(II) ions from aqueous solution by adsorption onto cross-linked polymeric beads of carboxymethyl cellulose (CMC) and sodium alginate was studied at fixed pH (6) and room temperature 28 ± 0.2°C. The cross-linked polymeric beads were characterized by FTIR spectra. Sorption capacity of the polymer for the mercury ions was investigated in aqueous media consisting different amounts of mercury ions (2.5 to 100 mg dm?3) and at different pH values (2 to 8). Adsorption behavior of Hg(II) ions could be modeled using both the Langmuir and Freundlich isotherms. The dynamic nature of adsorption was quantified in terms of several kinetic constants such as rate constants for adsorption (k1) and Lagergreen rate constant (Kad). The influence of various experimental parameters such as effect of pH, contact time, solid-to-liquid ratio, salt effect, and temperature effect etc. were investigated on the adsorption of Hg(II) ions.  相似文献   

14.
PVA functionalized with vinylphosphonic acid was prepared as a new adsorbent for uranyl (VI) adsorption from aqueous solutions. The vinylphosphonic acid was cografted onto PVA fibers by preirradiation grafting technique. The adsorbent were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The adsorbent was observed to possess a fibrous structure and was bonded with phosphonic acid groups successfully. The adsorbent was used for the adsorption of low levels uranyl (VI) ions from aqueous solutions. The influence of analytical parameters including pH, adsorption time, amount of adsorbent, metal ion concentration, and temperature were investigated on the recovery of uranyl (VI) ion in aqueous solution. The maximum adsorption capacity (32.1 mg g?1) and fast equilibrium time (30 min) were achieved at pH of 4.5 at room temperature. Thermodynamic parameters (ΔH° = 2.695 kJ mol?1; ΔS° = 31.15 J mol?1 K?1; ΔG° = ?6.748 kJ mol?1) show the adsorption of an exothermic process and spontaneous nature, respectively. The possible coordination mechanism was illustrated. Adsorption and desorption coexist in aqueous solutions and then the system becomes equilibrium.  相似文献   

15.
The aerobic biodegradability of an extensively used synthetic polymer was monitored the first time on a laboratory-scale fixed-bed bioreactor (FBBR) applying matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Polymeric poly(vinylpyrrolidone) (PVP) was spiked at concentrations of 10 mg l(-1) onto the FBBR run with river water and the biodegradation monitored after lyophilization of aliquots of the test liquor applying MALDI-TOF-MS. The latter proved to be a powerful tool for qualitative screening purposes of PVP in a molecular mass range <20 kDa in particularly yielding a high sensitivity and shot-to-shot reproducibility. The sample-to-sample reproducibility was enhanced applying the anchor target device. Post-source decay-MALDI-TOF-MS fragmentation investigations determined the unknown end groups of PVP unambiguously. Poor biodegradability of PVP can be assumed, since even after 30 days, no oxidation of the terminal groups and no difference in the repeating units was observed. A decrease in the molecular mass distribution can be drawn back rather to adsorption of PVP in the FBBR other than to biodegradation. This was further investigated performing an adsorption experiment with sewage sludge as solid matrix and analyses of the aqueous phase and sludge samples. Extrapolating these results to the situation in wastewater treatment plants, it is highly likely that PVP is eliminated from the dissolved phase by adsorption onto sludge particles.  相似文献   

16.
Present study describes the adsorption of carbofuran (CF) from aqueous solutions using p-tetranitrocalix[4]arene based modified silica through batch and column methods. Various parameters were optimized including initial pesticide concentrations (5 mg L?1), pH (2–10), contact time (60 min) and adsorbent dosage (30 mg). Modified silica was characterized by FT-IR and scanning electron microscope. The adsorption was further explained by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models. Moreover, adsorption kinetics and adsorption thermodynamics were also investigated. Adsorption in dynamic mode was evaluated by breakthrough volumes and the Thomas model, applying batch conditions using 30 mg of modified silica at pH 5. It has been noticed that CF removal efficiency of modified silica was 98 % as compared to bare silica (48 %). Adsorption of CF on modified silica was found to be multilayer and physical in nature. Consequently, adsorption obeys pseudo-second-order kinetic equation following external mass transfer diffusion process as the rate-limiting step. Thermodynamic parameter (ΔG, ΔS, ΔH) values suggest that the adsorption of CF is spontaneous and exothermic in nature. Thomas model rate constant k TH (cm3 mg?1 min?1) and maximum solid phase concentration (q o mg g?1) was found to be 0.52 and 12.3, respectively, in dynamic mode.  相似文献   

17.
Thermal characteristics of several novel self-dyed wholly aromatic polyamide–hydrazides covalently bonded with azo groups in their main chains and containing o-hydroxy group as a substituent group in the aryl ring of the aminohydrazide part of the polymers have been investigated in nitrogen and in air atmospheres using differential scanning calorimetry, thermogravimetric analyses, infrared spectroscopy, and elemental analyses. The effect of introducing different predetermined proportions of para- and meta-phenylene moieties into the backbone chain of the polymers on their thermal characteristics has been evaluated. Azopolymers having different molecular masses of all para-oriented phenylene type units were also thermally characterized. These polymers were prepared by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide containing 3 % m v?1 LiCl as a solvent at ?10 °C. All the polymers have the same structural formula except the mode of linking phenylene units in the polymer chain. The content of para- and meta-phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0–100 mol%. The results reveal that these polymers are characterized by high thermal stability and could be cyclodehydrated into linear aromatic polymers with alternating 1,3,4-oxadiazole and benzoxazole structural units within the same polymer approximately in the region of 200–480 °C, either in nitrogen or in air atmospheres by losing water from the hydrazide and o-hydroxybenzamide groups, respectively. Along with the cyclodehydration, the polymer may lose molecular nitrogen from the azo groups. This is not a true degradation, but rather a thermo-chemical transformation reaction of the evaluated polymers into the corresponding poly(1,3,4-oxadiazolyl-benzoxazoles). The resulting poly(1,3,4-oxadiazolyl-benzoxazoles) start to decompose in the temperature range above 330–560 °C, either in nitrogen or in air atmospheres without mass loss at a lower temperature. The thermal and thermo-oxidative stabilities of the polymers are affected by the nature and amount of arylene groups incorporated into their chains, being higher for polymers with greater content of para-oriented phenylene rings, which permits more interchain hydrogen bonds as a result of greater chain symmetry, packing efficiency, and rod-like structure. Increasing the content of para-oriented phenylene rings leads to a strong improvement in both the initial decomposition temperature as well as in the residual mass at a particular temperature. The stability of the polymers was found to be independent of their molecular masses. This confirms that high thermal stability is not a polymer property which would depends upon the length of its macromolecular chains, but rather upon its chemical structure in which all and every atomic group contributes by its own thermal stability to the macroscopic properties of the whole polymer.  相似文献   

18.
Mastery over the microscopic shape and size of a nanoparticle enables accurate control of its properties for some strict application. The mechanism of shape-controlled synthesis was discussed by investigating the formation of silver nanospheres prepared by chemical reduction method using Ag(NH3)2+ as metal source, ascorbic acid as reducing agent and polyvinylpyrrolidone (K-30) as dispersant. The effects of temperature, PVP/AgNO3 mass ratio, pH value and the interaction between PVP and silver on the shape and particle size were studied by XRD and SEM. The results show that the morphology of silver particles could transform from branched to spherical and the particle size gradually decrease with the increase of PVP/AgNO3 mass ratio. The particles size can also be significantly influenced by pH value and temperature. The key point for preparing high dispersity spherical silver powder is that the growth rate of each plane of the particle must be uniform and synchronous. Silver powders with spherical particles with mean size of 0.2 μm were synthesized under the optimum conditions (PVP/AgNO3 mass ratio 0.6, pH 7, reaction temperature of 40°C).  相似文献   

19.
Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 104 – 106) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.  相似文献   

20.
We present static adsorption studies of anionic surfactants on crushed Berea sandstone. The maximum adsorption density was 0.9604 mg/g. The kinetics of adsorption process was modeled using pseudo-first-order and pseudo-second-order rate equations at 25°C and 70°C. The equilibrium adsorption process was validated using Langmuir and Freundlich adsorption models. In addition, the effects of different parameters that govern the effectiveness of these surfactants such as pH and temperature were also investigated. The kinetic study results show that the surfactant adsorption is a time dependent process. The apparent rate constant of adsorption process determined by the first-order kinetic model at 25°C and 70°C were 0.11768 and ?0.04513, respectively. The rate constant for pseudo-second-order kinetic model was 0.0086 at 25°C and 0.0101 at 70°C. The adsorption of anionic surfactant followed pseudo-second-order kinetic model. The Freundlich and Langmuir model constant were 1.6509 × 10?4 and ?9.775 × 10?5, respectively. The equilibrium results showed that the adsorption of anionic surfactant onto Berea sandstone was well described by Langmuir adsorption model. It was concluded that anionic surfactants performed better at higher pH and temperature.   相似文献   

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