Use of quasi-3-dimensional porous electrodes for adsorption and electrocatalytic removal of impurities from waste-waters

Improvement in Electrode Performance of Novel SWCNT Loaded Three-Dimensional Porous RVC Composite Electrodes by Electrochemical Deposition Method

The three-dimensional (3D) composite electrodes were prepared by depositing different amounts of acid-functionalized single-walled carbon nanotubes (a-SWCNTs) on porous reticulated vitreous carbon (RVC) through the electrochemical deposition method. The SWCNT was functionalized by the reflux method in nitric acid and was proven by Raman and visible spectra. The optimum time for sonication to disperse the functionalized SWCNT (a-SWCNT) in dimethyl formamide (DMF) well was determined by UV spectra. The average pore size of RVC electrodes was calculated from scanning electron microscopy (SEM) images. Moreover, the surface morphology of composite electrodes was also examined by SEM study. All 3D electrodes were evaluated for their electrochemical properties by cyclic voltammetry. The result showed that the value of specific capacitance of the electrode increases with the increase in the amount of a-SWCNT in geometric volume. However, the value of specific capacitance per gram decreases with the increase in scan rate as well as the amount of a-SWCNT. The stability of the electrodes was also tested. This revealed that all the electrodes were stable; however, lower a-SWCNT-loaded electrodes had excellent cyclic stability. These results suggest that the a-SWCNT-coated RVC electrodes have promise as an effective technology for desalination.

Construction of a Novel Three-Dimensional PEDOT/RVC Electrode Structure for Capacitive Deionization: Testing and Performance

This article discusses the deposition of different amount of microstuctured poly(3,4-ethylenedioxythiophene) (PEDOT) on reticulated vitreous carbon (RVC) by electrochemical method to prepare three-dimensional (3D) PEDOT/RVC electrodes aimed to be used in capacitive deionization (CDI) technology. A CDI unit cell has been constructed here in this study. The performance of CDI cell in the ion removal of NaCl onto the sites of PEDOT/RVC electrode has been systematically investigated in terms of flow-rate, applied electrical voltage, and increasing PEDOT loading on PEDOT/RVC electrodes. It is observed that the increase in flow-rate, electric voltage, and PEDOT loading up to a certain level improve the ion removal performance of electrode in the CDI cell. The result shows that these electrodes can be used effectively for desalination technology, as the electrosorption capacity/desalination performance of these electrodes is quite high compared to carbon materials. Moreover, the stability of the electrodes has been tested and it is reported that these electrodes are regenerative. The effect of increasing NaCl concentration on the electrosorption capacity has also been investigated for these electrodes. Finally, it has been shown that 1 m³ PEDOT-120 min/RVC electrodes from 75 mg/L NaCl feed solution produce 421, 978 L water per day of 20 mg/L NaCl final concentration.

Development of new portable miniaturize solid phase microextraction of silver-APDC complex using micropipette tip in-syringe system couple with electrothermal atomic absorption spectrometry

An innovative and simple miniaturized solid phase microextraction (M-SPME) method, was developed for preconcentration and determination of silver(I) in the fresh and waste water samples. For M-SPME, a micropipette tip packed with activated carbon cloth (ACC) as sorbent, in a syringe system. The size, morphology and elemental composition of ACC before and after adsorption of analyte have been characterized by scanning electron microscopy and energy dispersive spectroscopy. The sample solution treated with a complexing reagent, ammonium pyrrolidine dithiocarbamate (APDC), was drawn into the syringe filled with ACC and dispensed manually for 2 to 10 aspirating/dispensing cycle. Then the Ag- complex sorbed on the ACC in micropipette was quantitatively eluted by drawing and dispensing of different concentrations of acids for 2 to 5 aspirating/dispensing cycles. The extracted Ag ions with modifier were injected directly into the electrothermal atomic absorption spectrometry for analysis. The influence of different variables on the extraction efficiency, including the concentration of ligand, pH, sample volume, eluent type, concentration and volume was investigated. Validity and accuracy of the developed method was checked by the standard addition method. Reliability of the proposed methodology was checked by the relative standard deviation (%RSD), which was found to be <5%. Under the optimized experimental variables, the limits of detection (LOD) and enhancement factors (EF), were obtained to be 0.86 ng L(-1) and 120, respectively. The proposed method was successfully applied for the determination of trace levels of silver ions in fresh and waste water samples.

Enhanced removal of 8-quinolinecarboxylic acid in an activated carbon cloth by electroadsorption in aqueous solution

The effect of the electrochemical treatment (potentiostatic treatment in a filter-press electrochemical cell) on the adsorption capacity of an activated carbon cloth (ACC) was analyzed in relation with the removal of 8-quinolinecarboxylic acid pollutant from water. The adsorption capacity of an ACC is quantitatively improved in the presence of an electric field (electroadsorption process) reaching values of 96% in comparison to 55% in absence of applied potential. In addition, the cathodic treatment results in higher removal efficiencies than the anodic treatment. The enhanced adsorption capacity has been proved to be irreversible, since the removed compound remains adsorbed after switching the applied potential. The kinetics of the adsorption processes is also improved by the presence of an applied potential.

Enhanced photocatalytic-electrolytic degradation of Reactive Brilliant Red X-3B in the presence of water jet cavitation

Photocatalysis, electrolysis, water jet cavitation (WJC), alone and in combinations were applied to degrade an azo dye, Reactive Brilliant Red X-3B (X-3B). Experiments were conducted in a 4.0 L aqueous solution with different initial dye concentrations, TiO₂ dose, and solution pH. WJC substantially increased the photocatalytic, electrolytic and photocatalytic-electrolytic rates of the dye removal. The observed first-order rate of X-3B decolorization in the process of combined photocatalysis and electrolysis coupled with WJC was 1.6-2.9 times of that in the process of combined photocatalysis and electrolysis coupled with mechanical stirring. The rate enhancements may be attributed primarily to the reduced diffusion layer thickness on the electrodes and the deagglomeration of photocatalyst particles due to the chemical and physical effects of WJC. Under the conditions of 80 mg/L X-3B solution, 100 mg/L TiO₂ dose and solution pH 6.3, 97% and 71% of color and chemical oxygen demand (CODCr) were removed, respectively, within 90-min photocatalytic-electrolytic treatment coupled with WJC. During this process, azo groups and naphthalene, benzene and triazine structures of the dye can be destroyed. Industrial textile effluent was also investigated, and a positive synergistic effect between photocatalytic-electrolytic system and WJC was observed considering color removal.

Molecular Structure Effects in the Adsorption Behaviour of some Aromatic Heterocyclic Compounds at High-Area Carbon-Cloth in Relation to Waste-Water Purification

Adsorption behaviours of some structurally related aromatic heterocyclic compounds at an high-area carbon-cloth material have been investigated in relation to waste-water purification. Adsorption processes were followed by monitoring the concentration of adsorbates in a specially designed cell using an in situ UV spectrophotometric method. The rates of adsorption were compared by treating the data according to first-order kinetics. Among the seven heterocyclic compounds studied, thiophene was found to exhibit the highest adsorption rate. This was attributed to the presence of the electron-donative S heteroatom in the structure of this compound. The influences of the dipole moment, the orientation at the C-cloth surface and the size of the heterocyclic adsorbate compound, as well as the type of heteroatom in the ring and the adsorbates’ hydration parameters, on the extent of adsorption of these compounds at the C-cloth were investigated.

Electrosorption-enhanced solid-phase microextraction using activated carbon fiber for determination of aniline in water

Electrosorption-enhanced solid-phase microextraction (EE-SPME) based on activated carbon fiber (ACF) was developed for determination of aniline in aqueous solution. A porous ACF, served as working electrode in electrosorption procedure, was prepared and attached to a commercial manual SPME device. Parameters affecting the adsorption efficiency were investigated. Under optimized condition, which was 400 mV electrosorption potential, 0.01 M Na(2)SO(4) electrolyte, pH 7, and electrosorption at 40 degrees C for 10 min, the method exhibited wide linear range (0.1-100 microg L(-1), R(2)=0.9980), good repeatability of adsorption (RSD 6.15%, n=6), and low detection limit (0.02 microg L(-1)). The feasibility of the method was evaluated by analyzing lake water spiked with aniline. Comparison was made with direct immersion (DI) ACF-SPME without electrosorption enhancement. The proposed procedure was demonstrated to be a simple, fast, sensitive sample preparation method for determination of aniline in water samples.

Electrochemically enhanced adsorption of phenol on activated carbon fibers in basic aqueous solution

Electrosorption isotherms and thermodynamics of phenol on activated carbon fibers (ACFs) in basic solution, as well as the factors (bias potential, initial concentration, and electrolyte) affecting adsorption/electrosorption kinetics, were investigated. The kinetics, which followed the Lagergren adsorption rate law, exhibited a variety of responses depending on bias potential, initial concentration, and electrolyte. The electrosorption isotherms were in agreement with the classical models of Langmuir and Freundlich, but the former gave more satisfactory correlation coefficients. With electrosorption at a bias potential of 700 mV from the basic solution, a nearly 10-fold enhancement of maximum adsorption capacity was achievable. The electrosorption free energy (DeltaG(ads)), enthalpy (DeltaH(ads)), and entropy (DeltaS(ads)) of phenol on the ACFs were calculated from adsorption isotherms at different temperatures. The results indicated that electrosorption of phenol in basic solution was spontaneous and exothermic. Furthermore, it was assessed that electrosorption occurred by dipole-dipole interaction with DeltaH(ads) of -20.14 kJ mol(-1) besides suppositional electrostatic interaction.

Adsorption kinetics and isotherms of pesticides onto activated carbon-cloth

Adsorption of pesticides ametryn, aldicarb, dinoseb and diuron from aqueous solution onto high specific area activated carbon-cloth was studied. Kinetics of adsorption was followed by in situ UV-spectroscopy and the data were treated according to various rate models. The extent of adsorption was determined at the end of 125 min adsorption period. Rate constants and the extent of adsorption for the four pesticides were found to follow the order: dinoseb > ametryn > diuron > aldicarb. Adsorption isotherms were derived at 25 degrees C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined. The types of interactions between the surface and pesticide molecules were discussed.

Adsorption of phthalic acid and its esters onto high-area activated carbon-cloth studied by in situ UV-spectroscopy

The adsorption behavior of phthalic acid and its three esters dimethyl phthalate, diethyl phthalate and diallyl phthalate onto high-area activated carbon-cloth was studied by in situ UV-spectroscopic technique. The effect of ionization of phthalic acid on its adsorption was examined by carrying out the adsorption process in three media; water, 1 M H(2)SO(4) and 0.005 M NaOH. Maximum adsorption was observed in 1 M H(2)SO(4) and almost no adsorption in 0.005 M NaOH. These results were discussed in terms of electrostatic and dispersion interactions between the adsorbate species and the carbon-cloth surface taking the point of zero charge (pH(pzc)) of the carbon-cloth into account. The adsorption process for the phthalate species studied was found to follow the first-order rate law, and the rate constants were determined. The isotherm data for the adsorption of phthalic acid and its esters were derived experimentally and fitted to Langmuir and Freundlich isotherm equations. Both equations were found to represent the experimental isotherm data almost equally well.

Structural and ionization effects on the adsorption behaviors of some anilinic compounds from aqueous solution onto high-area carbon-cloth

The adsorption of anilinic compounds; aniline, p-toluidine, 1-napthylamine and sodium salt of diphenylamine-4-sulfonic acid from solutions in H2O, in 1 M H2SO4 or in 0.1 M NaOH onto activated carbon-cloth was studied by in situ UV spectroscopy. A specially designed adsorption cell was used for this purpose. The adsorption processes were found to follow first-order kinetics and the rate constants were determined. The pH at the point of zero charge of the carbon-cloth surface was measured as 7.4. The highest rates and extents of adsorption were observed from H2O solutions for aniline, p-toluidine and 1-napthylamine and from solution in 1 M H2SO4 for the sodium salt of diphenylamine-4-sulfonic acid. The adsorption behaviors of these four anilinic compounds in the three solutions (in H2O, in 0.1 M NaOH and in 1 M H2SO4) were explained in terms of electrostatic and dispersion interactions between carbon-cloth surface and the anilinic species. The adsorption isotherm data for the anilinic compounds were derived at 30 degrees C and treated according to Langmuir and Freundlich models. The Freundlich model was found to represent the experimental isotherm data better than Langmuir model.

Adsorption of benzoic acid onto high specific area activated carbon cloth

The adsorption of benzoic acid from aqueous solution onto high area carbon cloth at different pH values has been studied. Over a period of 125 min the adsorption process was found to follow a first-order kinetics and the rate constants were determined for the adsorption of benzoic acid at pH 2.0, 3.7, 5.3, 9.1, and 11.0. The extents of adsorption and the percentage coverage of carbon cloth surfaces were calculated at 125 min of adsorption. Adsorption isotherms at pH values of 2.0, 3.7, and 11.0 were derived at 25 degrees C. Isotherm data were treated according to Langmuir and Freundlich equations and the parameters of these equations were evaluated by regression analysis. The fit of experimental isotherm data to both equations was good. It was found that both the adsorption rate and the extent of adsorption at 125 min were the highest at pH 3.7 and decreased at higher or lower pH values. The types of interactions governing in the adsorption processes are discussed considering the surface charge and the dissociation of benzoic acid at different pH values.

Adsorption of bentazon and propanil from aqueous solutions at the high area activated carbon-cloth

Removal of the pesticides bentazon and propanil from single and bisolute solutions by adsorption at the high area activated carbon-cloth was investigated. Kinetics of adsorption was followed and adsorption isotherms of the two pesticides were determined. A special V-shaped cell with an UV cuvette attached to it was used for adsorption studies. With this cell it was possible to follow the concentration of pesticide molecule by in situ UV spectroscopy as it is adsorbed at the carbon-cloth. It was found that concentration of pesticides decreased from the same initial concentration of 4.5 x 10(-5) to 1.1 x 10(-5) for bentazon and to 9.5 x 10(-6) for propanil in about 2 h. The fits of experimental adsorption isotherm data to Langmuir and Freundlich isotherm equations were almost equally successful. Monolayer capacities determined from Langmuir isotherms of pesticides showed that bentazon has greater monolayer capacity than propanil. This conclusion was also confirmed through the 1/n parameter of Freundlich equation.

Studies on removal of metribuzin, bromacil, 2,4-D and atrazine from water by adsorption on high area carbon cloth

The removal of pesticides such as metribuzin, bromacil, 2,4-d and atrazine from aqueous solutions was studied by adsorption on high area carbon cloth. The adsorption process was followed by in situ UV-spectrophotometric technique in a specially designed adsorption cell. Spectroscopic data of the pesticides were determined in separate experiments. The extent of adsorption was quantified by calculating the amount of adsorbate adsorbed per unit area of the carbon cloth and the percentage coverage at the carbon-cloth surface. The order of extent of adsorption of the pesticides studied was found as metribuzin < 2,4-D < bromacil < atrazine. The adsorption process was found to follow a first-order kinetics and the rate constants were determined. The competitive adsorption of pesticides was also examined by carrying out the adsorption process from a solution of equimolar mixture of bromacil and metribuzin.