Graphene Oxide/Polyamidoamine G4 as a High Efficient and Eco-Friendly Adsorbent for Dichromate Ions.

In this study, GO/PAMAM4 was used as a biocompatible nanocomposite adsorbent to adsorb dichromate (DC) ions. In alkaline solutions, DC ions changed to chromate ions which were not adsorbed on the surface of adsorbent. Thus, experiments were carried out in acidic and neutral water solution. Under these conditions, adsorption sites of adsorbent were protonated primary and ternary amine groups of adsorbent shown as -NH3+  and -NHR2+, respectively, that adsorbed DC ions through electrostatic interaction. Adsorption isotherms of DC on GO/PAMAM4 were obtained under various ionic strengths, pHs and temperatures. Isotherms were analyzed by the ARIAN model. The highest observed adsorption capacity of this process was 246.7 mg g-1 at pH=0 and 318 K. Tests at pH=2 showed that this process was endothermic. Adsorption kinetic experiments were carried out under various initial DC concentrations, pHs, temperatures, shaking rates and ionic strengths and were analyzed by the KASRA model and intraparticle diffusion, ISO and NIPPON equations. Pb2+, Cd2+, Cr3+ and tannic acid (TA) were separated by GO/PAMAM4 from DC ions and the GO/PAMAM4 was recycled by using an alkaline solution.

Comparison of Kinetics of Adsorption of Permanganate on Co-Al-Layered Double Hydroxide and MoS2 Nanocompounds.

Permanganate  ions were adsorbed on carbonate intercalated Co-Al-layered double hydroxide (Co-Al-LDH) and MoS2 and after a while the adsorbed  ions were reduced to MnO2. Reduction of adsorbed  ion was catalyzed on the surface of carbonate intercalated Co-Al-LDH but  ions reacted with MoS2 surface. Adsorption kinetic tests were carried out at different temperatures, ionic strengths, pH, initial adsorbate concentrations and shaking rates. The adsorption kinetics was studied by the kinetics of adsorption study in the regions with constant adsorption acceleration (KASRA) model and KASRA, ideal-second-order (ISO), intraparticle diffusion, Elovich and (non-ideal process of adsorption kinetics (NIPPON) equations.In this work, a new equation called NIPPON equation was introduced. In this equation, it was assumed that during a non-ideal process, adsorbate species molecules were adsorbed simultaneously on the same type adsorption sites with different activities. Indeed, the average values of adsorption kinetic parameters were calculated by the NIPPON equation. Also, the character of boundaries of regions obtained from the KASRA model can be determined by this equation.

GO/PAMAM as a High Capacity Adsorbent for Removal of Alizarin Red S: Selective Separation of Dyes.

Adsorption of Alizarin Red S (ARS) on graphene oxide/poly(amidoamine) (GO/PAMAM) was studied at different ARS initial concentrations, temperatures, pHs, shaking rates and contact times. Adsorption sites of GO/PAMAM were phenolic -OHgroup of GO and amine groups (-NH2, -NH3+ and -NHR2+) of PAMAM dendrimer moieties of GO/PAMAM. At pH = 2 and 318 K, maximum adsorption capacity of the adsorbent was 1275.2 mg g-1 which is one of the highest capacity in the literature. Thus, GO/PAMAM in this work acted as a superadsorbent for ARS. At the incipient of adsorption, molecules were adsorbed on sites that was reaction-controlled step, (Ea = 114.5 kJ mol-1). Adsorption of on the remaining sites was diffusion-controlled. In alkaline media, two other types of ARS molecules were identified during that were adsorbed on and sites. Further increasing the pH of the solution, decreased the number these two sites and yielded a reduced adsorption capacity . Methylene blue (MB), thionine (Th), pyronin Y (PY), acridine orange (AO), methyl blue (MEB) and janus green (JG) dyes were selectively separated from their mixtures with ARS molecules using GO/PAMAM at pH of 2. The used adsorbent was recycled efficiently by using ethylenediamine very fast.

Adsorption Mechanism of Congo Red on Mg-Al-layered Double Hydroxide Nanocompound.

In this work, congo red (CR) was removed by applying carbonate intercalated Mg-Al-layered double hydroxide (Mg-Al-LDH) nanocompound as an adsorbent. Batch adsorption experiments performed under various temperatures, ionic strengths, initial CR concentrations, alkalinities and shaking rates. The maximum adsorption capacities of Mg-Al-LDH for CR were 100, 105 and 86.8 mg g-1 at 308, 318 and 328 K, respectively. Adsorption sites of Mg-Al-LDH for CR were -OH groups attached to Al atoms of adsorbent layers. Adsorption isotherms of the process were studied by the ARIAN model and analysis of obtained data showed that there were two kinds of adsorption sites on the surface of Mg-Al-LDH. Results of instrumental analysis showed that these adsorption sites were -OH groups located on the surface of mesopores and micropores of adsorbent and were named MP and 003 sites, respectively. The kinetic data were studied by the KASRA model and ISO and intraparticle diffusion (pore-diffusion) equations which showed that CR molecules were adsorbed at first on the MP sites. Also, during the adsorption of CR on MP sites the interaction of CR with adsorbent surface was rate-controlling step. Furthermore, during CR adsorption on 003 sites, adsorption kinetics was diffusion-controlled.

Study of Adsorption Mechanism of Congo Red on Graphene Oxide/PAMAM Nanocomposite.

Graphene oxide/poly(amidoamine) (GO/PAMAM) nanocomposite adsorbed high quantities of congo red (CR) anionic dye in 0.1 M NaCl solution, with the maximum adsorption capacity of 198 mg·g-1. The kinetics and thermodynamics of adsorption were investigated to elucidate the effects of pH, temperature, shaking rate, ionic strength, and contact time. Kinetic data were analyzed by the KASRA model and the KASRA, ISO, and pore-diffusion equations. Adsorption adsorption isotherms were studied by the ARIAN model and the Henry, Langmuir, and Temkin equations. It was shown that adsorption sites of GO/PAMAM at experimental conditions were phenolic hydroxyl groups of GO sheets and terminal amine groups of PAMAM dendrimer. Analysis of kinetic data indicated that amine sites were located on the surface, and that hydroxyl sites were placed in the pores of adsorbent. CR molecules interacted with the adsorption sites via hydrogen bonds. The molecules were adsorbed firstly on the amine sites, and then on the internal hydroxyl sites. Adsorption kinetic parameters indicated that the interaction of CR to the -NH3⁺ sites was the rate-controlling step of adsorption of CR on this site and adsorption activation energies calculated for different parts of this step. On the other hand, kinetic parameters showed that the intraparticle diffusion was the rate-controlling step during the interaction of CR molecules to -OH sites and activation energy of this step was not calculable. Finally, the used GO/PAMAM was completely regenerated by using ethylenediamine.

Organic-Inorganic Hybrid Polymers as Adsorbents for Removal of Heavy Metal Ions from Solutions: A Review.

Over the past decades, organic-inorganic hybrid polymers have been applied in different fields, including the adsorption of pollutants from wastewater and solid-state separations. In this review, firstly, these compounds are classified. These compounds are prepared by sol-gel method, self-assembly process (mesopores), assembling of nanobuilding blocks (e.g., layered or core-shell compounds) and as interpenetrating networks and hierarchically structures. Lastly, the adsorption characteristics of heavy metals of these materials, including different kinds of functional groups, selectivity of them for heavy metals, effect of pH and synthesis conditions on adsorption capacity, are studied.

Kinetics and thermodynamics of adsorption of Fuchsin acid on nickel oxide nanoparticles.

NiO nanoparticle was used to adsorb fuchsin acid (FA) from aqueous solution. In the used concentration range of FA, its adsorption isotherms on NiO nanoparticles were three-region. NiO nanoparticle was prepared via the thermal decomposition of the tris(ethylenediamine)Ni(II) nitrate complex as a new precursor. In this work, effects of temperature, concentration, particle size, shaking rate, contact time, pH of the solution were investigated. Adsorption process was exothermic in the first and second regions and endothermic in the third region. Adsorption kinetics was studied by a number of equations including the KASRA, pseudo-first-order, pseudo-second-order, Elovich, Avrami and pore-diffusion equations. Adsorption acceleration and adsorption velocity values of this process were obtained by the KASRA equation and it was shown that with increase in FA concentration or temperature or shaking rate, initial adsorption velocity values of process increase.

Adsorptive removal of methylene blue by agar: effects of NaCl and ethanol.

Adsorption of methylene blue (MB) on agar was investigated as a function of temperature (308-328 K), different concentrations of NaCl and HCl and various weight percentages of binary mixtures of ethanol with water. It was observed that the maximum experimental adsorption capacity, qm, exp, in water is up to 50 mg g-1 and decreases with increase in weight percentage of ethanol and NaCl and HCl concentration compared to that of water. Analysis of data using ARIAN model showed that MB adsorbs as monomer and dimer on the surface of agar. Binding constants of MB to agar were calculated using the Temkin isotherm. The process is exothermic in water and other solutions. The mean adsorption energy (E) value indicated binding of MB to agar is chemical adsorption. Kinetics of this interaction obeys from the pseudo-second-order model and diffusion of the MB molecules into the agar is the main rate-controlling step.

Kinetics of Crystal Violet Fading in the Presence of TX-100, DTAB and SDS.

The rate constant of alkaline fading of crystal violet (CV+) was measured in the presence of non ionic (TX-100), cationic (DTAB) and anionic (SDS) surfactants. This reaction was studied at 283-303 K. The rate of reaction showed remarkable dependence on the electrical charge of the used surfactants. It was observed that the reaction rate constant increased in the presence of TX-100 and DTAB and decreased in the presence of SDS. Binding constants of CV+ with TX-100 and DTAB and the related thermodynamic parameters were obtained by classical (or stoichiometric) model. The results show that binding of CV+ to TX-100 is endothermic and binding of CV+ to DTAB and SDS is exothermic in the used concentration range of surfactants.

Adsorption of malachite green on silica gel: effects of NaCl, pH and 2-propanol.

Adsorption of malachite green (MG) on silica gel was studied as a function of temperature (308-328 K), pH, different concentrations of NaCl and various weight percentages of binary mixtures of 2-propanol with water. It was observed that the adsorption capacity decreases with increase in weight percentage of 2-propanol and NaCl and HCl concentration compared to that of in water. Results showed that in the presence of 2-propanol, surface aggregates of MG form on silica gel due to aggregation of MG molecules in these solutions, reverse desorption occurs. Binding constants of MG to silica gel were calculated using the Langmuir and bilayer isotherms. The process is exothermic in water and endothermic in NaCl solutions. The mean adsorption energy (E) value 9.0-14.2 kJ mol(-1) indicated chemical adsorption.