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Two mesoporous ordered silica with MCM-41 pores arrangement were synthesized and surface modified by apost-synthetic treatment. The first composite has aminopropyl functionalities while the other features aminopropyl and methyl surface groups. Both composites were used as sorbents for Cr(VI) removal from aqueous mediaat pH ꞊ 2. In order to test the stability and durability of the sorbents, the samples were subjected to alkalineextreme conditions (pH ꞊ 10) at different times and after that tested again for Cr(VI) removal. The bifunctionalized MCM-41 retains its Cr(VI) elimination capacity unchanged after 16 h of alkaline treatment,while the aminopropyl-MCM-41 sample suffer a drop of about 30%. The fresh and alkaline treated samples werecharacterized by X ray diffraction at low angles, nitrogen sorption at 77 K, Fourier transform infrared, Thermalanalysis. The presence of the methyl moieties increases the hydrophobicity of the composite?s surface, whichinhibit the approaching of the water molecules avoiding the hydrolysis of Si?O?Si bonds of the MCM-41 poreswalls. Besides, this protective effect is reflected in the textural properties changes before and after alkalinetreatments: while the specific surface area of aminopropyl-MCM-41 goes from an initial value of 793 to 495 m2g 1 ( 37.6%), the aminopropyl-methyl-MCM-41 shows a change from 702 to 650 m2 g 1 ( 7.2%). From theseresults it can be concluded that a second functionalizing agent that expose methyl-residues increases the stabilityof an aminopropyl-MCM-41 based-material, increasing the potential of this type of nanostructured compositesfor aqueous media applications.1. IntroductionThe family of nanostructured mesoporous materials known as M41Sfeature interesting characteristics including regular arrays of cylindricalpores, high specific surface area, controllable pore diameters rangingbetween 2 and 10 nm, good thermal stability, a highly tailorable surfacechemistry and low cost of manufacture, which make it appealing for itsapplication in different adsorption-based technologies [1,2]. The abilityto control surface composition through the anchorage of differentchemical species and the unique structural properties of such porousmaterials, give rise to a large quantities of different kind of compositeswith several types of actives sites [3,4]. As an example, amino-modifiedMCM-41, a member of this family with hexagonal mesoporousarrangement, has proved to be a good candidate for environmental [5],biotechnological [6] and pharmaceutical [7] applications. Thisorganic-inorganic composite has the ability of generating electrostaticinteraction with diverse analytes, showing good performance andselectivity in these adsorption-based processes even when analytes areimmersed in complex aqueous matrices [8,9]. This mesoporoussilica-based framework has a surface charge which is modulated by pHdue to the presence of ?NH2 and Si?OH surface groups, which have pKavalues of �9 and � 7, respectively [10].Remediation of contaminated water sources is a priority concernworldwide where the application of silica-based composites as sorbentscan offer practical and efficient solutions. This is mainly because theremediation of contaminated water through adsorption phenomenon isa simple process, which can even be carried out in undeveloped or ruralareas without electricity. However, due to the wide range of possible* Corresponding author.E-mail address: nfellenz@unrn.edu.ar (N. Fellenz).Contents lists available at ScienceDirectSolid State Sciencesjournal homepage: http://www.elsevier.com/locate/sssciehttps://doi.org/10.1016/j.solidstatesciences.2020.106300Received 19 December 2019; Received in revised form 6 April 2020; Accepted 24 May 2020 1 ( 37.6%), the aminopropyl-methyl-MCM-41 shows a change from 702 to 650 m2 g 1 ( 7.2%). From theseresults it can be concluded that a second functionalizing agent that expose methyl-residues increases the stabilityof an aminopropyl-MCM-41 based-material, increasing the potential of this type of nanostructured compositesfor aqueous media applications.1. IntroductionThe family of nanostructured mesoporous materials known as M41Sfeature interesting characteristics including regular arrays of cylindricalpores, high specific surface area, controllable pore diameters rangingbetween 2 and 10 nm, good thermal stability, a highly tailorable surfacechemistry and low cost of manufacture, which make it appealing for itsapplication in different adsorption-based technologies [1,2]. The abilityto control surface composition through the anchorage of differentchemical species and the unique structural properties of such porousmaterials, give rise to a large quantities of different kind of compositeswith several types of actives sites [3,4]. As an example, amino-modifiedMCM-41, a member of this family with hexagonal mesoporousarrangement, has proved to be a good candidate for environmental [5],biotechnological [6] and pharmaceutical [7] applications. Thisorganic-inorganic composite has the ability of generating electrostaticinteraction with diverse analytes, showing good performance andselectivity in these adsorption-based processes even when analytes areimmersed in complex aqueous matrices [8,9]. This mesoporoussilica-based framework has a surface charge which is modulated by pHdue to the presence of ?NH2 and Si?OH surface groups, which have pKavalues of �9 and � 7, respectively [10].Remediation of contaminated water sources is a priority concernworldwide where the application of silica-based composites as sorbentscan offer practical and efficient solutions. This is mainly because theremediation of contaminated water through adsorption phenomenon isa simple process, which can even be carried out in undeveloped or ruralareas without electricity. However, due to the wide range of possible* Corresponding author.E-mail address: nfellenz@unrn.edu.ar (N. Fellenz).Contents lists available at ScienceDirectSolid State Sciencesjournal homepage: http://www.elsevier.com/locate/sssciehttps://doi.org/10.1016/j.solidstatesciences.2020.106300Received 19 December 2019; Received in revised form 6 April 2020; Accepted 24 May 2020 37.6%), the aminopropyl-methyl-MCM-41 shows a change from 702 to 650 m2 g 1 ( 7.2%). From theseresults it can be concluded that a second functionalizing agent that expose methyl-residues increases the stabilityof an aminopropyl-MCM-41 based-material, increasing the potential of this type of nanostructured compositesfor aqueous media applications.1. IntroductionThe family of nanostructured mesoporous materials known as M41Sfeature interesting characteristics including regular arrays of cylindricalpores, high specific surface area, controllable pore diameters rangingbetween 2 and 10 nm, good thermal stability, a highly tailorable surfacechemistry and low cost of manufacture, which make it appealing for itsapplication in different adsorption-based technologies [1,2]. The abilityto control surface composition through the anchorage of differentchemical species and the unique structural properties of such porousmaterials, give rise to a large quantities of different kind of compositeswith several types of actives sites [3,4]. As an example, amino-modifiedMCM-41, a member of this family with hexagonal mesoporousarrangement, has proved to be a good candidate for environmental [5],biotechnological [6] and pharmaceutical [7] applications. Thisorganic-inorganic composite has the ability of generating electrostaticinteraction with diverse analytes, showing good performance andselectivity in these adsorption-based processes even when analytes areimmersed in complex aqueous matrices [8,9]. This mesoporoussilica-based framework has a surface charge which is modulated by pHdue to the presence of ?NH2 and Si?OH surface groups, which have pKavalues of �9 and � 7, respectively [10].Remediation of contaminated water sources is a priority concernworldwide where the application of silica-based composites as sorbentscan offer practical and efficient solutions. This is mainly because theremediation of contaminated water through adsorption phenomenon isa simple process, which can even be carried out in undeveloped or ruralareas without electricity. However, due to the wide range of possible* Corresponding author.E-mail address: nfellenz@unrn.edu.ar (N. Fellenz).Contents lists available at ScienceDirectSolid State Sciencesjournal homepage: http://www.elsevier.com/locate/sssciehttps://doi.org/10.1016/j.solidstatesciences.2020.106300Received 19 December 2019; Received in revised form 6 April 2020; Accepted 24 May 2020 1 ( 7.2%). From theseresults it can be concluded that a second functionalizing agent that expose methyl-residues increases the stabilityof an aminopropyl-MCM-41 based-material, increasing the potential of this type of nanostructured compositesfor aqueous media applications.1. IntroductionThe family of nanostructured mesoporous materials known as M41Sfeature interesting characteristics including regular arrays of cylindricalpores, high specific surface area, controllable pore diameters rangingbetween 2 and 10 nm, good thermal stability, a highly tailorable surfacechemistry and low cost of manufacture, which make it appealing for itsapplication in different adsorption-based technologies [1,2]. The abilityto control surface composition through the anchorage of differentchemical species and the unique structural properties of such porousmaterials, give rise to a large quantities of different kind of compositeswith several types of actives sites [3,4]. As an example, amino-modifiedMCM-41, a member of this family with hexagonal mesoporousarrangement, has proved to be a good candidate for environmental [5],biotechnological [6] and pharmaceutical [7] applications. Thisorganic-inorganic composite has the ability of generating electrostaticinteraction with diverse analytes, showing good performance andselectivity in these adsorption-based processes even when analytes areimmersed in complex aqueous matrices [8,9]. This mesoporoussilica-based framework has a surface charge which is modulated by pHdue to the presence of ?NH2 and Si?OH surface groups, which have pKavalues of �9 and � 7, respectively [10].Remediation of contaminated water sources is a priority concernworldwide where the application of silica-based composites as sorbentscan offer practical and efficient solutions. This is mainly because theremediation of contaminated water through adsorption phenomenon isa simple process, which can even be carried out in undeveloped or ruralareas without electricity. However, due to the wide range of possible

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