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A Simple and Facile Approach to Create Charge Reversible Pores via Hydrophobic Anchoring of Ionic Amphiphiles Sonu Kizhakeppura, B.V.V.S. Pavan Kumar, Subi J. George, and Muthusamy Eswaramoorthy ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b16194 • Publication Date (Web): 20 Feb 2017 Downloaded from http://pubs.acs.org on February 28, 2017

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ACS Applied Materials & Interfaces

A Simple and Facile Approach to Create Charge Reversible Pores via Hydrophobic Anchoring of Ionic Amphiphiles Sonu K. P., † B. V. V. S. Pavan Kumar, † Subi J. George,*,‡ and Muthusamy Eswaramoorthy*,† †

Nanomaterials and Catalysis Lab, Chemistry and Physics of Materials Unit, and

‡

Supramolecular Chemistry Laboratory, New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560064, India.

* To whom the correspondence should be addressed Muthusamy Eswaramoorthy (Email: [email protected]) and Subi J. George (Email: [email protected])

ACS Paragon Plus Environment

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ABSTRACT

Mesoporous silica based charge reversal systems have gained significant attention in the recent years due to a variety of applications such as drug delivery, dye adsorption, catalysis, chromatography etc. Such systems often use covalent strategies to immobilize functional groups on the silica scaffold. However, lack of dynamism, modularity and post-synthetic flexibility associated with covalent routes limit their wider applicability. Alternatively, supramolecular routes are gaining increased attention owing to their ability to overcome these limitations. Here, we introduce a simple and facile non-covalent design for a highly reversible assembly of charged amphiphiles within mesopores. Hexyl pendant groups were covalently attached to the surface to provide hydrophobic anchoring for charged amphiphiles to enable facile switching of surface charge of the mesoporous silica. This charge switchable surfaces were used for fast and selective adsorption of dyes from aqueous solutions.

KEYWORDS: charge reversal, hydrophobic interaction, mesoporous materials, supramolecular chemistry, dye adsorption, recyclable scaffold


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1. INTRODUCTION Systems capable of manipulating surface charge fascinated the research community over the past few decades owing to their applications in drug/gene delivery,1-7 perm-selective ion transport,8-10 anti-bacterial coatings,11 bacterial targeting,11-12 switchable cell adhesion,13 cellular internalization,14 separation15-17 etc. Fabrication of charge-reversal systems based on mesoporous silica allows us to study and exploit the switching of surface charge by virtue of their high surface area and porosity.18-21 Typically, charge convertible systems are fabricated by employing covalent routes to immobilize responsive moieties to the mesoporous surface.22-23 However, covalent routes are often irreversible with limited post-synthetic flexibility. In this context, supramolecular noncovalent approaches towards functionalization are receiving increased attention in recent years, due to their ability to lend reversibility and flexible modularity to these rigid porous solid matrixes.24-25 Recently, we have introduced a non-covalent design strategy based on redoxresponsive charge-transfer (C-T) modules to reversibly modify the pore size and surface charge of mesoporous silica. The reversibility was achieved through oxidation and reduction of the acceptor moieties.25-26 However, continuous redox cycles to switch the pore characteristics cause acceptor moieties to degrade over time limiting its potential for recyclability over large number of cycles. Thus, there exist a need for robust non-covalent strategies to enable the fabrication of highly reversible charge-convertible systems that can withstand a considerable number of cycles. Herein, we introduce a non-covalent approach utilizing hydrophobic interactions27 and charged amphiphiles to reversibly manipulate surface charge of mesoporous silica (Figure 1). The silica surface modified with hexyl groups can non-covalently anchor the charged amphiphiles to the pore surface, by hydrophobic co-assembly, to modulate the surface charge of the mesopores.


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Further, the surface-charge of these materials can be reversibly modified by regeneration of the parent material by washing with a suitable solvent followed by the re-loading with an appropriate charged amphiphile. By virtue of the soft nature of the interactions and regenerative treatment, the system could demonstrate remarkable reversibility in switching the surface charge. Although the non-covalently adsorbed surfactant molecules are shown to influence the nature of porous materials28, they have been less explored in terms of their ability to reversibility modify the pore characteristics. 2. EXPERIMENTAL SECTION 2.1 Materials. Pluronic P123 (EO20PO70EO20, Sigma Aldrich), tetraethyl orthosilicate (TEOS, Sigma Aldrich, 99%), Trichloro(hexyl)silane (Sigma Aldrich, 97%), Congo Red (Sigma Aldrich), Methylene blue (Sigma Aldrich), Sodium dodecyl sulfate (SDS, Sigma Aldrich), Myristyltrimethylammonium bromide (MTAB, Sigma Aldrich) were used in this study as received. Solvents were procured from Spectrochem and were distilled under argon before use. 2.2 General characterization and equipments. TEM images were obtained from JEOL JEM3010 with an accelerating voltage of 300 kV. FE-SEM images were obtained by means of NovaNano SEM-600 (FEI, Netherlands). Powder XRD patterns were recorded by Bruker-D8 diffractometer using Cu Kα radiation, (λ =1.54 Å, Step size: 0.02, Current: 30 mA and Voltage: 40 kV). FT-IR spectra were recorded on a Bruker IFS 66v/S spectrometer. Thermogravimetric analysis experiments were carried out using Mettler Toledo 850 from 30 oC to 1000 oC in oxygen stream with a heating rate of 10 oC/min. The N2 adsorption-desorption analysis at 77 K were carried out on Autosorb-1C (Quantachrome corp.). The samples were outgassed at 95 oC for 12 h under high vacuum before the analysis. The specific surface areas were calculated according to the multipoint BET method using the Quantachrome software (ASiQwin). Ultrahigh purity gases


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(99.9995%) were used for all analysis. Zeta potential measurements were carried out on Malvern Zetasizer Nano ZS system. Electronic absorption spectra were recorded on a Perkin Elmer Lambda 900 UV-Vis-NIR spectrometer. 2.3 Synthesis of SBA- 15. Monodispersed SBA- 15 rods were synthesized following a previously reported procedure. In a typical synthesis procedure, a mixture containing 4.0 g of Pluronic P123, 30 g of water and 120 g of 2 M HCl aqueous solution in a Teflon-lined container was stirred at 35 °C overnight. 8.50 g of TEOS was added to this mixture under vigorous stirring. After 5 min of stirring, the mixture was kept under static conditions at 35 °C for 20 h, followed by 24 h at 100 °C. The solid product was dried and then calcined at 550 °C. 2.4 Synthesis of SBA- C6. 1 g of calcined mesoporous silica rods were degassed for 5 h under vacuum and dispersed in dry toluene (100 mL) under ultrasonication. 2 mL of trichloro(hexyl)silane (10 mmol) was added to the dispersion under N2 bed and stirred overnight at room temperature. The obtained SBA- C6 was washed with toluene (1x40 ml), and ethanol (1x40 ml) and subjected to soxhlet extraction in ethanol. The product was dried at 60 °C under vacuum. 2.5 Molecular Assemblies of surfactant inside mesoporous channel. To 50 mg of SBA- C6 taken in a small vial, 300 µL ethanol was added and the mixture was sonicated for 5 min. To this dispersion, 5 mL of aqueous solution of surfactant (10 mM, SDS or MTAB) was added. The mixture was stirred for 3 h at room temperature and centrifuged to collect the solid product. The solid was washed with water (2x10 ml) and dried at 60 °C. 2.6 Disassembly of surfactant molecules from mesopores. To 50 mg of surfactant assembled SBA- C6 (SBA-C6 -SDS or SBA-C6 -MTAB), 5 mL of methanol was added and the mixture was sonicated for 5 min. The dispersion was heated at 60 °C under vigorous stirring for 30 min. The


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dispersion was centrifuged to collect the solid product. The solid was washed with water (2x10 mL) and dried at 60 °C. 2.7 Zeta potential measurements. To 10 mg of SBA-C6 or SBA-C6-MTAB or SBA-C6-SDS taken in a vial, 0.1 mL ethanol was added and the mixture was sonicated for 2 min. To this dispersion 3 mL of water was added and sonicated for 2 min, again. The pH of the dispersion was adjusted to 5.5 using 1 mM HCl/ NaOH - solutions. The temperature was maintained at 25 o

C with the help of inbuilt thermostat in Zetasizer Nano ZS. 2.8 Dye adsorption studies. To 10 mg (accurately weighed) surfactant assembled SBA-C6

(SBA-C6-MTAB or SBA-C6-SDS) taken in a vial, 50 µL ethanol was added and the mixture was sonicated to get a uniform dispersion. To this dispersion 950 µL aqueous solutions containing pre-calculated amount respective dye(s) was added. The mixture was stirred at room temperature for 1 hour. The dispersion was centrifuged to collect the solid product and washed extensively with known volume of water. All the supernatants were collected and the remaining dye (s) in the supernatant was calculated using Beer- Lambert’s law. The absorbance was determined using UV-Vis spectrometer. 3. RESULTS AND DISCUSSION Mesoporous silica, SBA- 15 rods of length 1-3 µm (Figure S1 in Supporting Information) having hexagonally packed mesochannels of diameter ca. 10 nm were obtained (Figure S1c) by typical sol- gel method.29 The pores were functionalized with hexyltrichlorosilane to obtain covalently attached hexyl groups on the silica surfaces (SBA-C6) (Figure S2). Fourier transform infra-red spectra (FT-IR) of SBA-C6 showed intense C-H stretching vibrations between 2850 cm1

to 3000 cm-1 confirming hexyl functionalization (Figure 2a). The X-ray diffraction patterns of

SBA-15 and SBA-C6 showed small angle peak corresponding to (100) plane, revealing that the


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hexagonal meso-structure was retained after functionalization (Figure S3). Transmission electron micrographs (TEM) of SBA-15 and SBA-C6 also suggest retention of mesoporous periodicity upon hexyl functionalization (Figure S1c, d). The amount of hexyl groups attached to the silica surface was found to be 1.6 mmol/g (13.6 % w/w) by thermogravimetric analysis (TGA) (Figure 3). The nitrogen physisorption isotherms for SBA-15 and SBA-C6 obtained at 77 K were type IV isotherms typical of mesoporous materials with narrow pore size distribution (Figure 2b). Barrett-Joyner-Halenda (BJH) pore size distribution30 showed a shift of average pore size (~ 1.7 nm) from 10.3 nm for SBA-15 to 8.6 nm for SBA-C6 (Figure 2b inset). Further, the number of hexyl groups on SBA-C6 was calculated to be 1.9 molecules per nm2 area using TGA and nitrogen physisorption measurements (See SI text for details). The functionalization of silica with hexyl groups rendered the pore surface of SBA- C6 hydrophobic in contrast to pristine SBA-15 which is polar in nature. To enable the co-assembly, aqueous solution of charged amphiphiles/ surfactants was mixed with SBA-C6 (see Experimental Section

for

details).

For

instance,

myristyltrimethylammonium

bromide

(MTAB,

CH3(CH2)12CH2N+(CH3)3 Br-), a positively charged surfactant with 14- carbon alkyl chain (Figure S4b) was non-covalently assembled in the mesopores of SBA-C6 to form SBA-C6 MTAB by soaking SBA-C6 in MTAB solution for 3 h. The amount of MTAB assembled in to pores of SBA-C6 was found to be 0.35 mmol/g (11.8 % (w/w)) (determined by TGA, Figure 3 and SI text for calculation). The assembly of MTAB within the pores was followed through nitrogen physisorption isotherms which showed a reduction in the average pore size from 8.6 nm to 7.4 nm (Figure 4a-c). This reduction of pore size was not commensurate with the molecular length of the MTAB (~ 2.1 nm). This difference suggests that the assembled MTAB molecules are arranged in a slanted orientation within the mesopores. The pore size distributions of SBA-C6


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and SBA-C6-MTAB exhibited more or less equal full width half maximum (FWHM) suggesting uniform assembly of MTAB within the mesochannels. The number of molecules of MTAB assembled on SBA-C6 was calculated to be 0.421 molecules /nm2 area that corresponds to 22 % coverage with respect to hexyl groups which is significant enough to influence the pore characteristics. Regeneration to parent material was achieved by washing SBA-C6-MTAB with hot methanol which weakened the hydrophobic interactions between the hexyl groups and MTAB (Figure 4a-c). As the assembly of surfactant is based on the hydrophobic interactions, one would expect its organization inside the pores would be favored with all types of surfactants irrespective of their charge in the head groups. Indeed, a negatively charged surfactant- sodium dodecyl sulfate (SDS, CH3(CH2)10CH2SO4- Na+, Figure S4a) within SBA-C6 pores (SBA-C6SDS) also resulted in a concomitant reduction of pore size by 0.7 nm as shown by the PSDs calculated from the nitrogen sorption isotherms (Figure 4d). Similar to MTAB assembly, SDS assembly also caused a reduction in pore size that is not commensurate with the molecular length of SDS (~ 1.9 nm) which suggest that SDS molecules are also arranged in a slanted orientation inside the mesopores. The amount of SDS assembled into the pores was found to be 0.168 mmol/g (4.9 % (w/w)) nearly two times lower than that of the MTAB. This value corresponds to 0.202 molecules of SDS per nm2 (11 % quantitative coverage with respect to hexyl groups). The switchable assembly of charged amphiphiles into SBA-C6 was further confirmed through zeta potential measurements. SBA-C6 dispersed in water/ ethanol mixture was negatively charged ca. -15.0 ± 4 mV at pH 5.5 due to ionized silanol groups (Figure S5a). Upon addition of MTAB to SBA-C6 the zeta potential increased to +26 ± 0.5 mV, owing to the binding of MTAB to SBA-C6 surfaces (Figure S6). Washing with hot methanol removed MTAB from SBA-C6 surface and consequently zeta potential dropped to -3.7± 2 mV (nearly neutral). It is worth


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noting that the surface charge is not turning to negative (as that of SBA-C6) probably due to the neutralization of silica surface by remaining electrostatically bound MTAB molecules. In order to check the recyclability of this non-covalent approach, MTAB was re-attached to SBA-C6 by soaking it again in MTAB solution and the zeta potential was increased to + 27.7 ± 2 mV and this can be repeated more than 4 cycles. However, when MTAB was mixed with unfunctionalized SBA-15 the surface charge varied from negative to near zero value due to the charge neutralization, suggesting the importance of hexyl pendant groups to show charge reversal inside nanopores by the self-assembly of MTAB surfactant (Figure S5b). The positive surface of SBA-C6 bound with MTAB (SBA-C6-MTAB) showed a charge reversal to ca. -28.2 ± 0.5 mV on addition of SDS after the removal of MTAB (Figure 5a). This charge conversion was highly reversible as demonstrated up to 4 cycles showing the modularity of the strategy. It is worth noting that the charge reversal can happen even without having an intermediate washing step. For example, positively charged SBA-C6-MTAB (zeta potential + 31 ± 2 mV) becomes negative (zeta potential= - 30 ± 2 mV) upon soaking with SDS solution of higher concentration suggesting the replacement of MTAB with SDS. Similar competitive binding (replacement of SDS with MTAB) was observed in the case of SBA-C6-SDS upon soaking with MTAB solution (Figure 5b). In order to further understand the charge reversal achieved in our system/ strategy, adsorption studies were conducted with charged chromophores to evaluate the extent of the surface charge reversal as the adsorption proceeds by charge neutralization primarily. Methylene blue (MB; cationic dye) and Congo red (CR; anionic dye) were used as model dyes in this study (Figure S4c-d). When ethanol wet SBA-C6-MTAB and SBA-C6-SDS were mixed with aqueous solution of CR and MB respectively, complete uptake of dye from solution was observed (Figure 6a).


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Photographs show the stock solution of respective dyes and the clear supernatant after complete uptake (Figure S9). Charge selective adsorption/ separation of charged chromophores from a mixture using MTAB or SDS bound SBA-C6 was also studied. SBA-C6-MTAB, when mixed with an aqueous solution containing an equimolar mixture of dyes, CR (negatively charged) was selectively absorbed leaving MB in the supernatant. Similarly, when SBA-C6-SDS used, MB was selectively absorbed leaving CR in the supernatant (Figure 6b). The kinetics of this uptake was found to be very fast (complete uptake within ~ 2 minutes for both dyes) (Figure S11). The binding titration curves of MTAB/SDS assembled SBA-C6 with respective dye were constructed to study the adsorption in greater detail (Figure 7a). The adsorption of MB to the SBA-C6-SDS showed a saturated uptake of around 0.4 mmol/g whereas the same for CR onto SBA-C6-MTAB was around 0.2 mmol/g, nearly half of that of the MB. The intercepts of MB and CR in linear Langmuir adsorption isotherm showed that the monolayer capacity of CR is about half that of MB (Figure S12). However, Langmuir binding constants for both the dyes were same (~ 1.3 × 105 M-1) suggesting a similar interaction strength operational in both the cases. CR is having two negative charges which can form neutralizing monolayer on the surface with half the number of molecules when compared with MB (which is having one positive charge) (see the inset schematics in Figure 7a). This suggest that both anionic and cationic surfactant assembly give rise to a similar magnitude of charge inside the mesopores. In order to deconvolute the extent of silanol participation in the adsorption of MB on to SBA-C6SDS, a control study was carried out in which the saturation uptake of MB on to SBA-C6 was found to be 0.15 mmol/g (Figure S10a) lower than that for SBA-C6-SDS. It clearly suggests that the SDS assembly provide additional charge on SBA-C6 surface to achieve higher uptake of positive chromophores.


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To evaluate the effects of salt concentration on the dye adsorption process, we carried out adsorption of dyes at higher ionic strength (Figure S13). In principle, one would expect relatively low adsorption of dye at higher ionic strength due to electrostatic screening of charges. However, the adsorption of MB on SBA-C6-SDS (and CR on SBA-C6-MTAB as well) at higher ionic strength was found to be similar to that of in water. In the case of CR on SBA-C6-SDS (MB on SBA-C6-MTAB as well) the effect of electrostatic repulsion was clearly observed in water as there was negligible adsorption. However, once the electrostatic interactions are screened at higher ionic strength the adsorption was enhanced. The enhanced adsorption under high ionic strength was previously observed and was attributed to the reduced repulsion between the adsorbing dyes facilitating multi-layer adsorption.31 These results clearly indicate that the electrostatic interactions are dominated over hydrophobic interactions in our system. However, once the electrostatic interactions are screened the hydrophobic interactions become pronounced in governing adsorption process. The recyclability of these materials for dye adsorption was demonstrated by washing the dye loaded MTAB/SDS assembly. The same binding titration curve was observed when an existing assembly was removed and subsequently fresh surfactant was assembled (Figure 7a). Furthermore, dye adsorption behavior of surfactant bound SBA-C6 could be completely reversed by simply changing the surfactant clearly demonstrating the modularity of these materials. SBAC6 was first bound with MTAB which showed maximum adsorption for CR, which when washed off and subjected to SDS assembly resulted in a maximum adsorption for MB (Figure 7b). Same scaffold was washed off and further put through MTAB assembly to obtain the maximum sorption to CR.


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4. CONCLUSIONS In conclusion, we have demonstrated highly reversible and modular approach to fabricate mesoporous silica based charge convertible surfaces. The strategy is based on hydrophobic interactions between hexyl pendant groups and surfactant molecules of the desired charge. The reversible nature of the assembly was confirmed by N2 sorption, zeta potential measurements and dye sorption experiments. The modularity of this approach was utilized for engineering highly recyclable materials for charge based adsorption and selective separation of dye molecules.

Figure 1. Fabrication of charge reversal surface: Charged amphiphiles are non-covalently assembled within hydrophobic mesoporous channels. Reversible manipulation of surface charges is achieved by breaking the assembly in appropriate solvent which allow the pore a new assembly. Conversion from one charge state to other is also possible through competitive amphiphile replacement.


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Figure –2: (a) FT-IR spectra of SBA-15 and SBA-C6. (b) Nitrogen sorption isotherms of SBA15 and SBA-C6 at 77 K. Inset showing corresponding normalized BJH pore size distribution.


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100

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90 80 SBA-15 SBA-C6

70

SBA-C6-SDS SBA-C6-MTAB

60 0

200

400

600

800 Temperature (oC)

1000

Figure 3. Thermogravimetric analysis curves of SBA-15, SBA-C6, SBA-C6 -MTAB and SBA-C6 –SDS.


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Figure 4. (a) Nitrogen adsorption isotherms of SBA-C6, SBA-C6 -MTAB and SBA-C6 after washing off the MTAB assembly showing the reversibility of the assembly. (b) BJH pore size distributions (normalized) of SBA-C6 and SBA-C6 -MTAB showing the decrease in pore size upon MTAB attachment. The recovery of pore size upon removal of MTAB is indicated by the dotted arrow. The schematic illustrates the reversibility of pore size on addition or removal of MTAB. (c) The variation of pore size (monitored through nitrogen sorption isotherms) on addition and removal of MTAB to SBA-C6 (with initial pore diameter of 8.6 nm). (d) Nitrogen sorption isotherms of SBA-C6, SBA-C6 –SDS at 77 K (inset showing corresponding BJH pore size distribution).


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Figure 5: (a) Charge conversion of SBA-C6 up on MTAB and SDS assembly. MTAB assembly on SBA-C6 showed a positive charge which changed to negative when MTAB was removed followed by SDS assembly. (b) Dynamism of Assembly: Zeta potential of (i) SBA-C6-MTAB, (ii) upon soaking in SDS solution, (iii) SBA-C6-SDS, (iv) upon soaking in MTAB solution.


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Figure 6: (a) Complete uptake of dye from the individual solution by respective surfactant bound SBA-C6. UV-Vis spectra of individual dye solutions before and after the dye uptake. (b) UV- Vis spectrum of equimolar mixture of MB and CR (1). (2) and (3) represent UV-Vis spectra of MB and CR recovered from the mixture using SBA-C6-MTAB and SBA-C6-SDS respectively. (inset shows corresponding photographs)

Figure 7: (a) Charged dye adsorption to the surface: Binding curves for MB (blue) and CR (red) on to SBA-C6-SDS and SBA-C6-MTAB respectively. (b) Reversal of dye adsorption: SBA-C6-


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MTAB showed a high loading of CR which reversed to MB up on washing followed by SDS assembly. Further, when same scaffold subjected to MTAB assembly, a high loading of CR was restored.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publication website. Experimental procedures for the synthesis of SBA-15 and SBA-C6, Instrumentation details, Details of Sample preparation for Zeta potential measurements and N2 sorption–desorption studies, TEM and FE-SEM images of SBA-15 and SBA-C6, N2 sorption–desorption isotherms, Chemical structures of surfactants and dye molecules used in the study, Other supporting figures and tables of textural parameters of SBA-15 and its derivatives. (PDF) AUTHOR INFORMATION Corresponding Author [email protected]; [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT The authors thank A. Achari and A.V. Raaghesh for helpful discussions.


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REFERENCES 1.

Feng, T.; Ai, X.; An, G.; Yang, P.; Zhao, Y., Charge-Convertible Carbon Dots for

Imaging-Guided Drug Delivery with Enhanced in Vivo Cancer Therapeutic Efficiency. ACS Nano 2016, 10, 4410-4420. 2.

Zhou, Z.; Shen, Y.; Tang, J.; Fan, M.; Van Kirk, E. A.; Murdoch, W. J.; Radosz, M.,

Charge-Reversal Drug Conjugate for Targeted Cancer Cell Nuclear Drug Delivery. Adv. Funct. Mater. 2009, 19, 3580-3589. 3.

Lee, C.-H.; Lo, L.-W.; Mou, C.-Y.; Yang, C.-S., Synthesis and Characterization of

Positive-Charge Functionalized Mesoporous Silica Nanoparticles for Oral Drug Delivery of an Anti-Inflammatory Drug. Adv. Funct. Mater. 2008, 18, 3283-3292. 4.

Guo, S.; Huang, Y.; Jiang, Q.; Sun, Y.; Deng, L.; Liang, Z.; Du, Q.; Xing, J.; Zhao, Y.;

Wang, P. C.; Dong, A.; Liang, X.-J., Enhanced Gene Delivery and siRNA Silencing by Gold Nanoparticles Coated with Charge-Reversal Polyelectrolyte. ACS Nano 2010, 4, 5505-5511. 5.

Han, G.; You, C.-C.; Kim, B.-j.; Turingan, R. S.; Forbes, N. S.; Martin, C. T.; Rotello, V.

M., Light-Regulated Release of DNA and Its Delivery to Nuclei by Means of Photolabile Gold Nanoparticles. Angew. Chem. Int. Ed. 2006, 45, 3165-3169. 6.

Mahkam, M.; Pakravan, A., Synthesis and Characterization of pH-Sensitive Positive-

charge Silica Nanoparticles for Oral Anionic Drug Delivery. J. Chin. Chem. Soc. 2013, 60, 293296. 7.

Zhang, H.; Kong, X.; Tang, Y.; Lin, W., Hydrogen Sulfide Triggered Charge-Reversal

Micelles for Cancer-Targeted Drug Delivery and Imaging. ACS Appl. Mater. Interfaces 2016, 8, 16227-16239.


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8.

Page 20 of 23

Brunsen, A.; Cui, J.; Ceolin, M.; Campo, A. d.; Soler-Illia, G. J. A. A.; Azzaroni, O.,

Light-Activated Gating and Permselectivity in Interfacial Architectures Combining "Caged" Polymer Brushes and Mesoporous Thin Films. Chem. Commun. 2012, 48, 1422-1424. 9.

Yameen, B.; Ali, M.; Neumann, R.; Ensinger, W.; Knoll, W.; Azzaroni, O., Single

Conical Nanopores Displaying pH-Tunable Rectifying Characteristics. Manipulating Ionic Transport With Zwitterionic Polymer Brushes. J. Am. Chem. Soc. 2009, 131, 2070-2071. 10.

Tagliazucchi, M.; Azzaroni, O.; Szleifer, I., Responsive Polymers End-Tethered in Solid-

State Nanochannels: When Nanoconfinement Really Matters. J. Am. Chem. Soc. 2010, 132, 12404-12411. 11.

Radovic-Moreno, A. F.; Lu, T. K.; Puscasu, V. A.; Yoon, C. J.; Langer, R.; Farokhzad,

O. C., Surface Charge-Switching Polymeric Nanoparticles for Bacterial Cell Wall-Targeted Delivery of Antibiotics. ACS Nano 2012, 6, 4279-4287. 12.

Pranzetti, A.; Mieszkin, S.; Iqbal, P.; Rawson, F. J.; Callow, M. E.; Callow, J. A.;

Koelsch, P.; Preece, J. A.; Mendes, P. M., An Electrically Reversible Switchable Surface to Control and Study Early Bacterial Adhesion Dynamics in Real-Time. Adv. Mater. 2013, 25, 2181-2185. 13.

Ng, C. C. A.; Magenau, A.; Ngalim, S. H.; Ciampi, S.; Chockalingham, M.; Harper, J. B.;

Gaus, K.; Gooding, J. J., Using an Electrical Potential to Reversibly Switch Surfaces between Two States for Dynamically Controlling Cell Adhesion. Angew. Chem. Int. Ed. 2012, 51, 77067710. 14.

Du, J.-Z.; Du, X.-J.; Mao, C.-Q.; Wang, J., Tailor-Made Dual pH-Sensitive Polymer–

Doxorubicin Nanoparticles for Efficient Anticancer Drug Delivery. J. Am. Chem. Soc. 2011, 133, 17560-17563.


20

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15.

Li, N.; Thia, L.; Wang, X., A CO2-responsive Surface with an Amidine-Terminated Self-

Assembled Monolayer for Stimuli-Induced Selective Adsorption. Chem. Commun. 2014, 50, 4003-4006. 16.

Ho, K. Y.; McKay, G.; Yeung, K. L., Selective Adsorbents from Ordered Mesoporous

Silica. Langmuir 2003, 19, 3019-3024. 17.

Chaudhuri, H.; Dash, S.; Sarkar, A., SBA-15 Functionalised with High Loading of

Amino or Carboxylate Groups as Selective Adsorbent for Enhanced Removal of Toxic Dyes from Aqueous Solution. New J. Chem. 2016, 40, 3622-3634. 18.

Wang, Y.; Sun, Y.; Wang, J.; Yang, Y.; Li, Y.; Yuan, Y.; Liu, C., Charge-Reversal

APTES-Modified Mesoporous Silica Nanoparticles with High Drug Loading and Release Controllability. ACS Appl. Mater. Interfaces 2016, 8, 17166-17175. 19.

Liu, W.; Liu, J.; Yang, X.; Wang, K.; Wang, Q.; Yang, M.; Li, L.; Song, C., Phosphate

Modulated Permeability of Mesoporous Silica Spheres: A Biomimetic Ion Channel Decorated Compartment Model. J. Mater. Chem. B 2015, 3, 323-329. 20.

Liu, W.; Yang, X.; He, D.; He, L.; Li, L.; Liu, Y.; Liu, J.; Wang, K., Dopamine

Modulated Ionic Permeability in Mesoporous Silica Sphere Based Biomimetic Compartment. Colloids Surf., B 2016, 142, 266-271. 21.

Eisuke, Y.; Kazuyuki, K., Colloidal Mesoporous Silica Nanoparticles. Bull. Chem. Soc.

Jpn. 2016, 89, 501-539. 22.

Kumar, B. V. V. S. P.; Salikolimi, K.; Eswaramoorthy, M., Glucose-and pH-responsive

Charge-Reversal Surfaces. Langmuir 2014, 30, 4540-4544. 23.

Matthews, J. R.; Tuncel, D.; Jacobs, R. M.; Bain, C. D.; Anderson, H. L., Surfaces

Designed for Charge Reversal. J. Am. Chem. Soc. 2003, 125, 6428-6433.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

24.

Page 22 of 23

Carter, T. G.; Yantasee, W.; Sangvanich, T.; Fryxell, G. E.; Johnson, D. W.; Addleman,

R. S., New Functional Materials for Heavy Metal Sorption: "Supramolecular" Attachment of Thiols to Mesoporous Silica Substrates. Chem. Commun. 2008, (43), 5583-5585. 25.

Kumar, B. V. V. S. P.; Rao, K. V.; Soumya, T.; George, S. J.; Eswaramoorthy, M.,

Adaptive Pores: Charge Transfer Modules as Supramolecular Handles for Reversible Pore Engineering of Mesoporous Silica. J. Am. Chem. Soc. 2013, 135, 10902-10905. 26.

Kumar, B. V. V. S. P.; Rao, K. V.; Sampath, S.; George, S. J.; Eswaramoorthy, M.,

Supramolecular Gating of Ion Transport in Nanochannels. Angew. Chem. 2014, 126, 1328913293. 27.

Chandler, D., Interfaces and the Driving Force of Hydrophobic Assembly. Nature 2005,

437, 640-647. 28.

Ji, Q.; Yoon, S. B.; Hill, J. P.; Vinu, A.; Yu, J.-S.; Ariga, K., Layer-by-Layer Films of

Dual-Pore Carbon Capsules with Designable Selectivity of Gas Adsorption. J. Am. Chem. Soc. 2009, 131, 4220-4221 29.

Sayari, A.; Han, B.-H.; Yang, Y., Simple Synthesis Route to Monodispersed SBA-15

Silica Rods. J. Am. Chem. Soc. 2004, 126, 14348-14349. 30.

Barrett, E. P.; Joyner, L. G.; Halenda, P. P., The Determination of Pore Volume and Area

Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. J. Am. Chem. Soc. 1951, 73, 373-380. 31.

Gómez, J. M.; Galán, J.; Rodríguez, A.; Walker, G. M., Dye Adsorption onto

Mesoporous Materials: pH influence, Kinetics and Equilibrium in Buffered and Saline Media. Environ. Manage. 2014, 146, 355-361.


22

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