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The importance of adsorption in water purification and the need to guard against erroneous conclusions often associated with the use of equilibrium adsorption model studies in adsorption systems informed this work. Water purification by adsorption of Congo red (CR) from synthetic aqueous solution to acid treated corncob charcoal (ATCC) was carried out at three different pH values (8.0, 10.5, and 12.0) and at temperatures 10–40 °C. The maximum adsorption capacity of ATCC for CR was 85.8 mg/g at pH 12. The resulting data from the batch adsorption studies were plotted at different temperatures and were fitted to linear form of three isotherm models; Freundlich, Langmuir, and Temkin. Though all three models fitted the experimental data linearly, only Langmuir model was able to account for the observed thermodynamic behavior of the adsorbent–adsorbate systems under the pH conditions. The standard enthalpy values for the adsorption of CR on ATCC at pH 8.0, 10.5, and 12.0 were −5.010 ± 0.312, −7.024 ± 0.440, and −71.426 ± 3.130 kJ mol−1, respectively. The corresponding entropies at pH 8.0, 10.5, and 12.0 were 98.7 ± 1.0, 87.8 ± 1.5, and 129.0 ± 10.5 J mol−1 K−1, respectively. The effect of pH on the thermodynamic quantities were rationalized on the basis of the type of interaction between the CR and the adsorbent. To determine the most suitable model, it was important to juxtapose the observed dependence of adsorption affinity on temperature with the thermodynamic information of the adsorption studies. [ABSTRACT FROM AUTHOR]

In this study, a modified metal hydroxides on surface of Lewatit resin (HMO @LM500, where M indicates to Al, Fe, Mn or Zn) were designed and used as efficient adsorbents for uranium (U(VI)) ions capture from aqueous solution. The prepared materials were characterized by using transform infrared spectroscopy, scanning electron microscope, energetic dispersive x-ray techniques. Batch adsorption methods were done to investigate all factors affecting adsorption process such as the effect of pH, concentration, contact time and temperature. Optimum values of each parameter were calculated as pH of 1.8, temperature of 298 K (25 °C), contact time of 60min for the removal of uranium ions. Analysis within the nonlinear isotherm models indicates that the Liu model offers the best description for the equilibrium data since it has the highest R² value and the lowest error analysis value when compared with the other models. The calculated adsorption capacity of Liu model is 217.06mg g-1, whereas analysis within the nonlinear kinetic models indicate that pseudo-second-order behavior is involved. The thermodynamic examination of the equilibrium data proved that the adsorption process of U(VI) was found to be a spontaneous and exothermic process. The ΔH0 and ΔS0 parameters were calculated as ~66.5827 kJ mol-1 and ~0.2051 kJ mol-1 K-1, respectively. Therefore, the prepared adsorbent can be applied to capture of U(VI) ions from aqueous medium. [ABSTRACT FROM AUTHOR]

Turkey tail (Trametes versicolor), cheap fungal biomass (TTFB), was used for the adsorption of CR from aqueous medium. Batch studies conducted to study the effect of pH (2.0–10.0), agitation speed (50–400 rpm), contact time (0–180 min), adsorbate concentration (300 and 500 mg/L), and temperature (303–333 K). TTFB characterized by FTIR, BET, SEM, and pHpzc. The maximum monolayer adsorption capacities of CR on TTFB were 318.1, 368.4, 394.8, and 415.7 mg/g at 303, 313, 323, and 333 K, respectively. The adsorption of CR was pH-dependent and maximum adsorption attained at pH 2.0 at all temperatures. Adsorption kinetic data evaluated by using the PFO and PSO non-linear equations. The kinetic data perfectly illustrated by the PSO model with R2 > 9935. Langmuir, Freundlich, D-R, and Temkin nonlinear isotherms applied for the experimental data, and it observed that the experimental data well fitted and found to be in good agreement with the Langmuir model (R2 > 0.9961) as compared with another three models. The values of ΔG° (–3.4159 to −6.1149 kJ/mol), ΔH° (23.2 kJ/mol), and ΔS° (0.088 kJ/mol K) revealed that the adsorption process was spontaneous, feasible and endothermic (ΔG° < 0, ΔS° > 0, and ΔH° > 0). The regeneration experiments indicated that the TTFB could successfully retain CR, even after five consecutive adsorption-desorption cycles. The binding of CR onto the TTFB surface was through electrostatic interactions. Therefore, TTFB considered as highly recyclable and efficient adsorbent material for CR as it can easily separate from the aqueous phase. [ABSTRACT FROM AUTHOR]

Biomass waste (Chinese traditional medicine residues) is one of the most promising sources of biochar. Here, the present study illustrated the activated biochar (BCA) was prepared using the herb residue (Astragalus membranaceus) via sodium carbonate (Na2CO3) activation for the removal of Cefradine (CF) in wastewater. The adsorbents were characterized by scanning electron microscopy, N2 adsorption-desorption analysis, Fourier transform infrared spectrum, X-ray diffraction, X-ray photoelectron spectroscopy and zeta potential analysis. The effects of initial pH value, BCA dosage, initial CF concentration and coexisting ion for CF removal were investigated. BCA showed much higher absorption capacity for CF (qm=64.76 mg/g) than the pristine biochar (BC). The uptake capacity of BCA and BC for CF was found to be pH-dependent. The analysis of the kinetic and isotherm studies indicated that strong chemical-sorption interactions occurred on the surface of BCA. The removal mechanisms of CF onto BCA would include π-π EDA interaction, hydrogen bonding, ion exchange and electrostatic adsorption. In addition, the fixed bed experiments demonstrated that BCA could be a promising and highly effective adsorbent to treat large volume of CF-contaminated wastewater. [ABSTRACT FROM AUTHOR]

Two novel adsorbents (AGD301 and ArgD301) were successfully prepared through ring-opening reaction. The adsorption performance and recognition selectivity of AGD301 and ArgD301 towards AuCl4− were studied by batch adsorption experiments. The results showed that adsorption time, pH, temperature and solution concentration had a significant influence on the adsorption performance. At 298 K and pH of 2, the equilibrium adsorption capacity of AGD301 and ArgD301 towards AuCl4− could reach 400.75 and 451.67 mg·g−1, respectively. In addition, AGD301 and ArgD301 possessed excellent selectivity and good reusability. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the efficiency of activated carbon prepared from agricultural waste (olive stones; OS) on diclofenac (DCF) adsorption in aqueous solutions. The prepared charcoals were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM)/Energy Dispersive X-Ray Analyser (EDX), and Brunauer-Emmett-Teller (BET) analysis techniques. The results show that DCF adsorption is favorable in acid medium and low temperature. The adsorption kinetics follows a pseudo-second-order kinetic model. The adsorption was found to be spontaneous (ΔG° < 0) for OS600°C, whereas the negative values of the enthalpy (ΔH°) suggest an exothermic adsorption for both adsorbents. [ABSTRACT FROM AUTHOR]

Functional cross-linked polymers (Poly(AA-co-DVB)) were synthesized using a one-step method. The properties of Poly(AA-co-DVB) were measured by SEM, FTIR, and TGA. The adsorption capacity of the Poly(AA-co-DVB) was investigated using methylene blue as an adsorbate. The effect of the mole compositions of acrylic acid and divinylbenzene monomers on the adsorption capacity was investigated in detail. The initial pH of solutions and contact time were also studied. The kinetics and isotherms of the adsorption process were also investigated. The result showed that the maximum equilibrium adsorption capacity was 1698.9 mg/g at room temperature and the adsorption kinetic was well fitted by a pseudo-second-order model and the adsorption isotherm agreed well with the Langmuir model. [ABSTRACT FROM PUBLISHER]

Based on the abundance of seed-watermelon pulp (SWP) in Xinjiang, China, SWP was employed to prepare low-cost adsorbent toward the removal of methylene blue (MB). The effects of contact time at different initial concentration were studied. The widely used adsorption isotherm models including Langmuir, Freundlich, and Temkin isotherms were employed to depict the adsorption process. The Langmuir isotherm was best fitted to the experimental data. Batch kinetic studies showed that an equilibrium time of 300 minutes was needed for the adsorption. The adsorption properties can be well described by pseudo-second-order kinetic model and the MB uptake was not controlled by intraparticle diffusion mechanism. [ABSTRACT FROM AUTHOR]

In this paper, chitosan hydrogel beads were modified with gemini surfactant C12-4-C12 · 2Br and then used for the adsorption and removal of Congo red dye. The effects of pH, inorganic salt, temperature, shaking rate, and surfactant concentration were investigated in detail. The gemini surfactant concentration was the main factor, and the maximum adsorption amount was observed at 0.5% C12-4-C12 · 2Br. The Sips isotherm model fit well with the equilibrium experimental data, and the values of the heterogeneity factor (n) indicated heterogeneous adsorption. The adsorption kinetics was found to follow the pseudo-second-order rate model better than the pseudo-first-order rate model. [ABSTRACT FROM AUTHOR]

We studied the adsorption of Brilliant Yellow (BY) from aqueous solutions onto sepiolite and determined the adsorption equilibrium isotherms. We applied pseudo-first-order and pseudo-second-order kinetic models; the adsorption of BY onto sepiolite was best described by the pseudo-second-order kinetic model. The experimental data obtained at different temperatures were analyzed using various isotherm models; the Koble-Corrigan isotherm model provided the best fits for the BY adsorption data at all temperatures. The thermodynamic parameters of the BY adsorption onto sepiolite indicated that the adsorption process is spontaneous and exothermic in nature. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) and powder-activated carbon (PAC) were used as adsorbents for adsorption of nitrofurazone, a veterinary medicine, from aqueous solutions. The adsorbents were characterized using FTIR transform infrared spectroscopy, N2adsorption/desorption isotherms, and scanning electron microscopy. The effects of initial pH, contact time, and temperature on adsorption capacity of the adsorbents were investigated. For MWCNT and PAC, the result showed that when the pH value was ranged from 2.0 to 10.0, the dosage of adsorbent was 0.02 g, and adsorptive time is 4 hours, the removal efficiencies for nitrofurazone were 96.8% and 94.7%, and the corresponding maximum capacities at 283 K were close to 50.8 mgg−1and 59.9 mgg−1, respectively. For nitrofurazone, the pseudo-second-order kinetic model provided the best fit to the experimental data. The Boyd model indicated the mechanism for adsorption processes was mainly external mass transfer, while the effect of particle internal diffusion was relatively weak. Liu model could best fit to the experimental data of isothermal adsorption. The data of adsorption thermodynamics showed that the adsorption process was spontaneous. [ABSTRACT FROM PUBLISHER]

In the present study, adsorption capacity of mercury(II) on β-zeolite, zeolite Y, and mordenite is investigated. It has been observed that removal rate of Hg(II) is better with zeolite Y than β-zeolite and mordenite, whereas, adsorption capacity of β-zeolite is found to be more than that of zeolite Y and mordenite. Five equilibrium isotherms have been tested to fit the adsorption data. The kinetic data are analyzed using the pseudo-first order, pseudo-second order, and diffusion models. The Freundlich isotherm model shows better fit for β-zeolite and zeolite Y, whereas, in the case of mordenite, Temkin isotherm fits the data well. The kinetic data of adsorption of Hg(II) on β-zeolite, zeolite Y, and mordenite fit well with pseudo-second order. Diffusion studies show that the adsorption of mercury on β-zeolite and zeolite Y are intraparticle diffusion controlled, and mordenite is film-diffusion controlled. [ABSTRACT FROM AUTHOR]

The removal of some of pollutants including catechol, 3-methylcatechol, 3-methoxycatechol, and 2,3-dihydroxybenzoic acid by adsorption onto activated carbon cloth (ACC) at 35.0 ± 0.1°C was investigated. The equilibrium experimental data were fitted to Langmuir, Freundlich, Temkin, Langmuir-Freundlich, and Redlich-Peterson isotherms. Also the kinetic experimental data were fitted to the pseudo-first-order and pseudo-second-order kinetic models. It was found that the pseudo-second-order model describes the kinetic of adsorption better than the other one. By comparing the obtained results with the previously reported data, it can be concluded that ACC is a high efficient adsorbent for removal of phenolic compounds from aqueous solutions. [ABSTRACT FROM AUTHOR]

The present study explores the adsorption potential of Mentha piperita (an agricultural solid waste) to remove Cu2+ from aqueous solution. Different operational parameters such as the effect of pH, surfactant, equilibrium time, temperature, and initial metal ion concentrations were studied. Maximum adsorption of Cu2+ took place at pH range 5.0. Nearly 180 minutes are required to gain sorption equilibrium. The maximum adsorption capacity of mentha was 72.0 mg g−1 for Cu2+. FTIR analysis pointed out the involvement of amine (–NH2) and carboxylic (–COOH) groups in the adsorption process. Simple Langmuir and Freundlich isotherm models were used to explain the sorption phenomenon. The adsorption dependence of Cu2+ on temperature was investigated and the thermodynamic parameters ΔS0, ΔH0, and ΔG0 were calculated. The activation energy of the Cu2+ adsorption was calculated using the Arrhenius equation. The desorption of the adsorbent was found to be more than 90% by 0.1 M NaCl. [ABSTRACT FROM AUTHOR]

The objective of this study is the preparation of various types of functionalized silica particles for the capture of Cu(II) ions. Amino-functionalized silica and hybrid chitosan/silica particles have been prepared by grafting silica with amino groups and/or adsorption of chitosan on the surface of silica to develop efficient adsorbents for heavy metals ions in water. The adsorption of Cu(II) on these materials was carried out at pH 5 at 298 K. The kinetics were evaluated utilizing pseudo-first-order and pseudo-second-order models. The best interpretation for equilibrium data was given by both Langmuir and Freundlich isotherm models. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for all systems studied. This study demonstrates that the adsorption capacities for Cu(II) ions are more efficient for the bio-hybrid material compared to amino-functionalized silica. [ABSTRACT FROM AUTHOR]

In this study, the adsorption behavior of natural bentonite with respect to Fe(III) and Ni(II) has been studied in order to consider its application to purity metal finishing wastewaters. During the adsorption process, batch technique is used, and the effects of pH, bentoite amount, temperature, heavy metal concentration, bentonite treatment (calcinations of natural bentonite at 700°C, washing by deionized water to remove the excess salt from bentonite surface), and agitation time on adsorption efficiency are studied. The washed and calcined bentonite samples were labeled by WB and CB, respectively. The pH-dependence of Fe(III) and Ni(II) sorption on the bentonite is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. It was determined that adsorption of Fe(III) and Ni(II) is well fitted by the second order reaction kinetic. Furthermore, the sorption rate of Fe(III) was higher than the sorption rate of Ni(II). Adsorption of Fe(III) and Ni(II) on NB appeared to follow Langmuir isotherm. In addition, calculated and experimental adsorbed amounts of Fe(III) by the unit NB mass are very higher than Ni(II). The paper also discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Also the adsorption capacity of bentonite for Fe(III) Ni(II) and increases with increased bentonite dose. According to the equilibrium studies, the selectivity sequence can be given as Fe(III) > Ni(II). The adsorbed amount of Fe(III) and Ni(II) on washed bentonite (WB) were very higher compared to NB and CB. Our results show that bentonite could especially WB be considered as a potential adsorbent for Fe(III) and Ni(II) removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

The protection power of the cationic surfactant decylammonium acetate (DAA) in seawater has been studied to define the perfect conditions have to be found for using it as a corrosion inhibitor for copper surface. The adsorption isotherm of this surfactant on copper surface has been determined at different interval times at 30°C. The given isotherms have, in general, similar shapes exhibiting a Languimirian L-shape. The corrosion measurement has been determined according to weight loss method. The study declines that cationic DAA, in seawater, protects well the copper surface against corrosion when added with low concentrations, while high concentrations show bad inhibition efficiency. ICP spectroscopic analysis assures this result where high Cu% has been obtained in the presence of high DAA concentration. [ABSTRACT FROM AUTHOR]

The adsorption of two disperse dyes, disperse blue 56 and disperse red from aqueous solution onto sawdust (SD) and benzyldimethyltetradecyl ammonium (BDTDA) treated sawdust has been studied. The effect of initial concentration of dyes, pH, and contact time has been studied. The pH had a considerable influence on adsorption and optimum pH for adsorption of disperse dyes is found to be in the range of 2-3. The experimental data were analyzed using Langmuir and Freundlich adsorption isotherm equations. The experimental data were fitted well to pseudo first order kinetic model with R2>0.99. The results indicate that sawdust modified with surfactant can be employed as a low cost alternative to commercial activated carbon for the removal of disperse dyes. [ABSTRACT FROM AUTHOR]

The interaction of fluorescein‐5‐isothiocyanate (F5ITC) with gold surfaces—either uncoated or pre‐coated with passivating layers of either sodium citrate (citrate), bis(p‐sulfonatophenyl)phenylphosphine dihydrate dipotassium (BSPP), Pluronic P123 (EO 20 PO 70 EO 20 ), or Pluronic F127 (EO 100 PO 70 EO 100 )—was studied using quartz crystal microbalance (QCM) measurements in order to determine the surface coverage of F5ITC in each case. Adsorption isotherms of the polymers (P123 and F127) binding to a gold surface were also obtained. Binding of F5ITC to the gold surfaces was found to be highly dependent on the passivating layer. The surface coverage Γ F5ITC of F5ITC on gold surfaces can be listed in decreasing order as Γ F5ITC, Au >Γ F5ITC, citrate >Γ F5ITC, P123 >Γ F5ITC, BSPP >Γ F5ITC, F127 . Mechanisms for binding of F5ITC to the gold surfaces are also discussed. [ABSTRACT FROM AUTHOR]

The adsorption of two alkyl-phenyl-polyethoxy phosphate (APPEP) with ethoxy chains containing 6 and 10 units was investigated in relation with the dispersion and rheological properties of suspensions of CaCO 3 and TiO 2 particles. Data were compared to these properties of related compounds alkyl-phenyl-polyethoxy (APPE) and polyethoxy-diphosphonate (PE2P). As with APPE, APPEP gave high affinity isotherms, which are attributed to the ligand effect of the phosphate head group. The adsorption plateaus of APPEP and APPE were significantly higher than for PE2P due to the cooperative effect of the alkyl chains. The adsorption on TiO 2 decreased at higher pH up to pH 13 and decreased by addition of phosphate ions; it increased with the addition of calcium ions. Investigations showed that the dispersion with APPEP molecules was not only linked to the surface charge, but also to the formation of a thick surfactant layer. This article aims to illustrate the respective role in adsorption and dispersion of the different parts of the amphiphilic molecules: ionic head, hydrophobic tail, and ethoxy chain. [ABSTRACT FROM AUTHOR]

Carbon black dispersions are prepared using anionic, cationic, and nonionic surfactants as dispersants in aqueous medium and adsorption behavior of these surfactants is .studied along with wettability and stability. Adsorption isotherms for all the surfactants are shown to be of Langmuir type except for lauryl dimethybenzyl ammonium chloride (BKC) where the amount adsorbed increases with increase in the concentration of BKC. Out of the two anionic surfactants used [sodium dodecyl sulphate (SDS) and sodium dodecyl benzene sulphonate (SDBS)], SDBS showed higher adsorption, wettabitity and stability. Among cationic surfactants viz. cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium chloride (CPC), BKC and Stertile, stertile showed better adsorption. In the case of nonionic surfactants viz. nonylphenol ethoxylates (NP 20 and NP 40) and Triton X-100, the maximum amount of surfactant adsorbed decreased in the order NP 40 < NP20 < Triton X-100, Stability of the dispersion improved in the same order. Addition of salt resulted in increase in both effectiveness and efficiency of the ionic surfactant adsorbing on the carbon black surface while the stability decreased. Pretreatment of carbon black surface with triethanolamine had negligible effect on the adsorption behavior of non ionic surfactants hut the wettability and stability improved. [ABSTRACT FROM AUTHOR]