Adsorption of aqueous Hg(II) by a polyaniline/attapulgite composite

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

“…To study Sections 3.1–3.5, the characteristics of different kinds of organic-inorganic hybrid polymers were as follows: (1) Some functional groups of these adsorbents are –SH, –COOH, amines and –S–S–, –OH, –SO 3 − and ion exchange sites of hybrid polymer; (2) adsorption processes mostly obey the Langmuir isotherm that shows the adsorption is monolayer and there is a uniform distribution of sites on the surface of adsorbents; (3) the adsorption capacity of each certain organic functional group changes depending on its content [181,214], the used organic compound, inorganic support [166,195], crosslinking agent [212], aggregation of nanoparticles [253] and the used synthesis method [182,189]; (4) in some cases, organic compounds are used only for increasing thermal and mechanical stability of adsorbents and without adsorbing heavy metal ions [224]; (5) mesoprous compounds, due to their porous structures have a rather higher adsorption capacities compared to those of organically-functionalized layered, core-shell compounds and products of sol-gel method; (6) heavy metals as cations and oxyanions are adsorbed via electrostatic interactions and the increase in the hydrophobicity of functional groups of adsorbent (e.g., –N(C 2 H 5 ) 2 [156] or from –NH 2 to –NH(propyl) to –N(propyl) 2 [178]) decreases their adsorption capacity for metal cations and increases their q max values (e.g., from trimethylammonium to tri- n -butylammonium functional groups) for the adsorption of some hydrophobic oxyanions [183]; (7) In the most cases, for example [141–147,216,221,225,241,243,249,252], the used adsorbents are recovered by acid treatment and in the cases that acid dissolves the adsorbent [199], they have used another washing solutions; (8) some ions may react with metallic ions, e.g., Cl − with Hg 2+ [226], and inhibit their adsorption; (9) some ions, e.g., Cl − [183], SO 4 2− [196] or metallic cations [252], may react with functional groups of hybrid adsorbents and decrease their adsorption capacity for heavy metal ions; (10) steric hindrance on functional group decreases its adsorption capacity [151]; (11) in most cases, adsorption capacities of organic-inorganic hybrid polymers are bigger than those of their organic or inorganic constituents; (12) most of heavy metals were adsorbed in the pH range 4–7. With the increase in alkalinity of solution, heavy metal ions convert to metal hydroxides and this decreases their affinity for interaction with binding sites of adsorbents […”

Congo red removal by PANi/Bi2WO6 nanocomposites: Kinetic, equilibrium and thermodynamic studies

“…The emeraldine base form may be transformed to emeraldine salt form by protonation/doping of amine groups in acidic medium. However, The PANi emeraldine salt based composites such as PANi/silica [10], PANi/Fe3O4 [11], PANi/montmorillonite [12], PANi/attapulgite [13] and PANi/CoFe2O4 [14] were successfully used as alternative adsorbents for wastewater treatment.…”

Kinetics and thermodynamics of Eu(III) and U(VI) adsorption onto palygorskite

“…Palygorskite as a common clay mineral is a kind of 2:1 layered hydrated magnesium aluminum silicate minerals with two bands of silica tetrahedra linked by magnesium ions in octahedral coordination [22]. Recently, the adsorption of heavy metals on palygorskite has been widely investigated such as Cu(II) [23,24], Pb(II) [25][26][27][28], Cd(II) [29][30][31] and Hg(II) [32]. However, few studies on the adsorption of radionuclides on palygorskite are available [33][34][35].…”