Effect of FeSuperscript3+/Superscript ions pre

Authors: Piotr Natkański Piotr Kuśtrowski Anna Białas Janusz Surman

Publish Date: 2013/05/21

Volume: 113, Issue: 1, Pages: 335-342

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Abstract

Polyacrylic acid/montmorillonite MMT composites with various polymer contents were synthesized by in situ polymerization technique The structure of obtained materials was characterized by powder Xray diffraction and infrared spectroscopy FTIR It was found that only a limited amount of hydrogel could be introduced between the clay layers The remaining part of polymer was deposited on the external surface of clay particles The introduction of the polymer modifier significantly increased the adsorption capacity of MMT in the elimination of Fe3+ ions from aqueous solution The thermal behavior of the samples before and after the Fe3+ adsorption was examined by thermogravimetry and differential thermal analysis Moreover the composition of gaseous products evolved during decomposition was determined by FTIR The materials after Fe3+ adsorption exhibited different thermal stability in oxidizing atmosphere than the fresh samples Fe3+ cations forming FeOx species during thermal treatment appeared to be effective catalysts of polymer oxidationModification of clay structure has attracted great attention due to the possibility of obtaining promising materials to new applications Various materials based on clay minerals are extensively used in many fields of life and industry as nanocomposite fillers thickeners in paints oilbase drilling mud adsorbents of heavy metals and organic pollutants as well as catalysts eg for Fischer–Tropsch synthesis catalytic cracking Friedel–Crafts reaction combustion of volatile organic compounds oxidation of H2S 1 2 3 4 5 6 7 8 9 10One of the most often investigated and abundant layered aluminosilicate is montmorillonite MMT belonging to the smectite group In the MMT structure the sheet containing Al3+ in octahedral coordination with O2− and OH− ions is sandwiched between two sheets with Si4+ in tetrahedral coordination with O2− ions The layers are interconnected by sharing O2− at polyhedral corners and edges 11 The partial substitution of Al3+ cations by lower valency ions mainly Mg2+ leads to the generation of negative charge on the clay layers which is neutralized by hydrated exchangeable cations eg Ca2+ Mg2+ Na+ K+ located in the interlayer spaces Such a structure causes that the interlamellar space of the natural clay can be functionalized through the replacement of interlayer ions by other species for instance transition metal cations or clusters cationic surfactants or monomers 12 13 14 15MMT can be used as a component of polymer–clay nanocomposites which exhibit interesting functional and structural properties 16 Superabsorbent composites are one group of such materials in which the polymer matrix consists of hydrophilic polymers mainly of polyacrylic acid PAA 17 and its salts 18 polyacrylamide 19 20 2methylpropane sulfonic acid AMPS and their copolymers 21 22 These hybrid materials due to their functional groups are efficient adsorbents of heavy metals cations eg Pb2+ Cd2+ Cu2+ or dyes 22 23 24 often tested in water purificationThe aim of this article was the synthesis and characterization of PAA/MMT composites designed as metal adsorbents The influence of hydrogel content in a composite on the Fe3+ adsorption capacity as well as the effect of the presence of iron species on the thermal stability of the synthesized materials were investigated Since clays modified with Fe turned out to be active catalysts of various processes eg selective reduction of NO with ammonia 25 oxidation of phenol 26 alkylation of arenes 27 and dehydrogenation of alkanes 28 the hydrogel/clay composites with adsorbed Fe3+ are expected to be a novel type of catalyst precursors for the mentioned reactions Therefore investigation into their thermal behavior is crucial to optimize the conditions of calcination which could result in obtaining Fedoped aluminosilicate materials with highly dispersed transition metal oxide phaseWyoming MMT with cation exchange capacity CEC of 90 meq/100 g and the chemical composition as follows 478  O 323  Si 136  Al 25  Fe 19  Mg 09  Na 07  Ca 02  K was used to the synthesis Acrylic acid AA was purchased from Arkema France Ammonium persulfate APS and NN′methylenebisacrylamide MBA were supplied by SigmaAldrich IronIII nitrate nonahydrate and potassium thiocyanate used in adsorption studies were purchased from POCh PolandThe series of PAA/MMT composites was prepared by in situ polymerization The AA monomer was dissolved in deionized water to obtain 10 mass solution In the prepared solution various amounts of clay were dispersed MMT was introduced at MMT/AA mass ratios of 10 15 23 and 40 Subsequently the MBA crosslinking agent was added at a MBA/monomer molar ratio of 001 The mixture was stirred at 400 rpm at room temperature to obtain homogenous suspension The slurry was purged with argon for 10 min to remove oxygen and then the APS initiator at a APS/monomer molar ratio of 001 was added The mixture was heated to 338 K and kept at this temperature for 3 h until the complete polymerization of monomers Such obtained material was cut to small pieces dried at 333 K and ground to fine powder The composites were denoted as MMTPAA20 MMTPAA30 MMTPAA40 and MMTPAA50 where the number indicates the polymer content in compositeXray diffraction XRD analysis was performed by means of a Bruker D2 Phaser Xray powder diffractometer 30 kV 10 mA with Cu anode λ = 015406 nm at room temperature The patterns were collected in the 2θ range of 2–50° with step size of 002° and scan rate of 1 s

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