Self-Assembled Porphyrin Nanofiber Membrane-Decorated Alumina

Subscriber access provided by Kaohsiung Medical University

Article

Self-Assembled Porphyrin Nanofiber Membrane-Decorated Alumina Channels for Enhanced Photoelectric Response Dan Zhang, Shuqi Zhou, You Liu, Xia Fan, Mingliang Zhang, Jin Zhai, and Lei Jiang ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b05695 • Publication Date (Web): 30 Oct 2018 Downloaded from http://pubs.acs.org on October 30, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31 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

ACS Nano

Self-Assembled Porphyrin Nanofiber MembraneDecorated Alumina Channels for Enhanced Photoelectric Response Dan Zhang, †,⊥ Shuqi Zhou, †,⊥ You Liu,† Xia Fan,*,† Mingliang Zhang,*,‡,§ Jin Zhai† and Lei Jiang† †Key

Laboratory of Bio-Inspired Smart Interfacial Science and Technology of the Ministry of

Education, School of Chemistry, Beihang University, Beijing 100083, People’s Republic of China ‡Engineering

Research Center for Semiconductor Integrated Technology, Institute of

Semiconductors, Chinese Academy of Sciences, Beijing 100083, People’s Republic of China §College

of Materials Science and Opto-Electronic Technology, University of Chinese Academy

of Sciences, Beijing 101408, People’s Republic of China KEYWORDS: enhanced photoelectric response, heterogeneous nanochannels, self-assembly, tetra(4-sulfonatophenyl)porphyrin, hourglass-shaped alumina

ABSTRACT: Photoresponsive nanochannel systems whose ionic transportation properties can be controlled by the photoelectric effect, such as for green chlorophyll pigments in plants, are

ACS Paragon Plus Environment

1

ACS Nano 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

Page 2 of 31

attracting widespread attention. Herein, we prepared photoresponsive heterogeneous nanochannels by decorating self-assembled tetra(4-sulfonatophenyl)porphyrin (TPPS) nanofiber membranes on a membrane of hourglass-shaped alumina (Al2O3) nanochannels using the diffusion-limited patterning (DLP) method. The close arrangement of large-area nanofibers promoted the photoresponse sensitivity of the heterogeneous nanochannels, which showed the highest ionic transportation current. With illumination comparable to sunlight in intensity, the photoresponsive ionic current was approximately 9.7 µA, demonstrating photoswitching, which could be used to regulate the reversible transformation of ionic currents. Meanwhile, the cooperative effect of the TPPS nanofibers assembled at the entrance to the nanochannels and the TPPS molecules inside the nanochannels allowed the heterogeneous nanochannels to exhibit a good rectifying performance.

Biological nanochannels in living organisms are important for maintaining normal life processes, including energy conversion, signal transformation, information storage and molecule or ion recognition, and play critical roles in a variety of physiological activities with changing external environmental stimuli.1-5 However, protein-based lipid bilayers are fragile and, consequently, are also susceptible to deterioration in vivo, so they are not fully compatible with practical devices.6,7 Fortunately, fabricating artificial solid-state nanochannels with superior structural controllability and improved property stability is a promising avenue for overcoming these challenges.8-11 To date, various artificial nanochannels that exhibit smart responses to changes in illumination, pH, ions, molecules, voltage and temperature have been developed.12-19 In particular, photoresponsive artificial nanochannels have received widespread attention


2

Page 3 of 31 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

ACS Nano

because they are able to achieve photoregulated ionic transmembrane transportation with temporal and spatial control.20,21 In general, nanochannels are prepared by introducing photoresponsive molecules, such as spiropyran, azobenzene, hydroxypyrene, retinal molecules and photoacids/bases onto the inner wall of the channel or into electrolyte solutions to realize optical gating, optical switching and identification under alternating illumination.12,22-26 In addition, some photoresponsive nanochannel systems whose ionic transportation properties can be controlled by the photoelectric effect, such as for green chlorophyll pigments in plants, have been reported.27 For example, under ultraviolet irradiation, the photoresponsive ionic currents of TiO2 nanotube arrays are enhanced.28 This photoelectric ability reached a maximum with a responsive current of approximately 561.46 nA for N3/Al2O3 composite nanochannels.21 However, how to further improve this photoelectric effect for real-world applications, such as µA-level photoresponsive current and sustainable power generation remains a great challenge. Recently, heterogeneous nanochannels composed of two different membrane materials have attracted increasing attention because each membrane has nanoscale channels/pores and can produce effective confined effects for ionic transportation, resulting in excellent performance, such as the highest rectification ratio yet to be reported.29,30 In addition, further tedious modification procedures are not necessarily required, and these materials can exhibit various intelligent responses.13,31-35 Therefore, the use of photoresponsive molecules to directly form nanofiber membranes whose ionic transportation behavior can be controlled by nanointerstices between the assembled nanofibers and the surface properties of the membrane may further promote the overall efficiency of energy utilization and lead to innovations in photoelectric response nanochannel systems.


3

ACS Nano 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

Page 4 of 31

Porphyrin relatives participate in a series of paramount processes in photosynthesis in nature. Thus, the corresponding synthetic substitutes are often used to construct optical energy conversion devices.36,37 Certain porphyrins, such as TPPS, can further self-assemble into nanostructures, which show excellent optical and electronic properties.38,39 To promote the photoelectric effect, heterogeneous TPPS/Al2O3 nanochannels were prepared by first depositing a large-area nanofiber membrane onto one side of a membrane of hourglass-shaped Al2O3 nanochannels to allow the self-assembly of photoresponsive TPPS molecules (Scheme 1a). Here, a well-developed diffusion-limited patterning (DLP) method was exploited,40,41 in which TPPS solution diffuses from the bulk solution into one segment of the hourglass-shaped Al2O3 nanochannels (Figure S1). At pH 2.5, two SO3- groups of TPPS are protonated, and the residual peripheral SO3- groups, as well as central NH+ groups (Scheme 1b), lead to a zwitterionic neutral species (the red dotted line box).38,42 In this case, ionic interactions between the negative and positive groups of the neighboring molecules, as well as the π-π interactions between the porphyrin rings of adjacent molecules, occur much like a “spread deck of cards” (Scheme 1c).38,43 Therefore, the TPPS aggregations cannot pass through the small Al2O3 channel tip barriers due to the restricting effect of the channel geometry, which allows them to self-assemble and effectively form a nanofiber membrane on the top surface of the Al2O3 nanochannels. The closely arranged self-assembled nanofibers promote the entire photoelectric response of heterogeneous nanochannels such that the responsive currents under illumination at an intensity approximating that of sunlight reach the microampere level. Simultaneously, the heterogeneous nanochannels generate a good ionic rectification performance that is dependent on the joint effect of the TPPS nanofibers assembled on the Al2O3 nanochannel surface and the TPPS molecules grafted inside the nanochannels.


4

Page 5 of 31 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

ACS Nano

RESULTS AND DISCUSSION The typical morphological evolution of the self-assembled surface and the cross-section of the TPPS/Al2O3 heterogeneous nanochannels with variations in TPPS molecule aggregation were characterized by scanning electron microscopy (SEM) (Figure 1). The diameter of the asprepared naked alumina nanochannels was 40-50 nm at both the top and bottom surfaces (Figure 1a1-1a3), while the tip region of the nanochannels had a small diameter of approximately 10 nm (Figure S4a). The thickness of the membrane of Al2O3 nanochannels was approximately 100 μm (Figure S4b). Thus, the samples appear semitransparent in the optical images. When the TPPS molecules were allowed to deposit onto the Al2O3 nanochannels for longer times, the heterogeneous membrane whose area approximately is 0.28 cm2 changed from yellow-green to dark-green (Figure S5). At an assembly time of 30 min, the TPPS aggregation occurred around the edge of the hexagonal pores of the alumina nanochannels (Figure 1b1-1b3). The length and thickness of the nanofibers was approximately 200 nm and 40 nm, respectively. The pores of the Al2O3 could still be clearly observed after 30 min of TPPS deposition. As shown in Figure 1c11c3, the nanofibers began to take more shape when the time was extended to 60 min. At an assembly time of 75 min (Figure 1d1-1d2), the number and the length of the nanofibers significantly increased such that the vast majority of pores became shielded. One to two nanofiber layers with a thickness of approximately 110 nm were observed in the corresponding cross-sectional SEM image (Figure 1d3). At this time, new absorption bands at approximately 493 and 702 nm were distinctly observed for the heterogeneous nanochannels compared to the naked Al2O3 nanochannels, as shown in the UV-Vis absorption spectra (Figure S6), and these were considered to be the characteristic peaks of the TPPS aggregations.39,43 When the assembly time was 120 min, the length of the nanofibers increased to a few micrometers, and most of the


5

ACS Nano 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

Page 6 of 31

entrances to the nanochannels were masked (Figure 1e1-1e2). The thickness of the TPPS nanofiber membrane reached 200 nm (Figure 1e3). The microscopic morphology of the TPPS nanofibers fabricated with these assembly times was further investigated by transmission electron microscopy (TEM, Figure S7). With increasing assembly time, the formed TPPS fibers become longer and increased in number. Some fibers even joined together and tended to form an ordered membrane. Moreover, this type of morphological evolution of the TPPS fibers was further confirmed by SEM observations of the heterogeneous nanochannels after other specific assembly durations (Figure S8). Notably, no TPPS nanofibers were observed on the bottom surface of the nanochannels or inside the nanochannels (Figure S9). However, cross-sectional fluorescence images of the heterogeneous nanochannels indicate that the molecular grafting of TPPS takes place in the inner wall of one segment of the hourglass-shaped Al2O3 nanochannels (Figure S10). Here, strong contrast between the TPPS-modified and the unmodified nanochannel segments was achieved in the fluorescence images due to the different scattering and/or absorbing effects of Al2O3 and TPPS. In the fluorescence spectra, we observed two emission peaks at approximately 653 and 717 nm, which were generated by the transition of the first excitation singlet state S1 to S0 in a TPPS molecule (Figure S11). However, as the TPPS deposition time increased, the fluorescence intensity became weaker, which was ascribed to the aggregation of TPPS fibers, resulting in quenching of the fluorescence of TPPS with a high quantity and density.44 DLP enables the patterning of labile molecular species in solution onto surfaces, and its influencing factors include channel geometry, diffusion time, and reactant concentration.40,41 Therefore, we propose the following possible mechanism of self-assembled membrane formation on the top surface of the Al2O3 membrane. When the TPPS solution is added to one side of the


6

Page 7 of 31 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

ACS Nano

electrochemical cell, the TPPS solution will diffuse and modify the inner wall of the hourglassshaped Al2O3 nanochannels. However, when TPPS aggregates reach the Al2O3 tip region, they cannot pass the barrier and thus fold back, giving rise to an increased local concentration of TPPS on the top surface of the Al2O3 and further allowing the TPPS molecules to self-assemble, effectively forming a nanofiber membrane on the top surface of the Al2O3 nanochannels,45,46 as shown in Figure S12a. When the hourglass-shaped nanochannels are changed into cylindrical ones, most of the TPPS molecules pass directly through the channels (Figure S12b), and few are deposited onto the inner walls. SEM investigation of the top and bottom surface and the crosssection of the cylindrical nanochannels before and after modification showed no TPPS aggregates in this case (Figure S13). Therefore, the tip region is critical to the confined transportation of ions or molecules that eventually results in the formation of a TPPS nanofiber membrane. Changes in the ionic transportation properties of the TPPS/Al2O3 heterogeneous nanochannels with deposition time were investigated by measuring the transmembrane ionic current using a 10 mM KCl electrolyte at pH 6.5. Unmodified Al2O3 nanochannels exhibited linear I-V curves due to their symmetrical geometry and their surface charges, while ionic rectification behavior in the form of nonlinear I-V curves was observed for the heterogeneous nanochannels. The ionic transportation currents of the heterogeneous nanochannels at negative voltages were higher than those at positive voltages, and the ionic rectification ratio was defined as the absolute value of ionic transportation current |I - | at -1.6 V divided by that |I + | at +1.6 V. As shown in Figure 2a, when the time increased from 30 to 75 min, the ionic current at 1.6 V gradually decreased, while the magnitude of the ionic flux at -1.6 V changed slightly, meaning that the rectifying behavior increased. However, as shown in Figure 2b, as the time increased from 75 to 150 min, the


7

ACS Nano 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

Page 8 of 31

magnitude of the ionic flux at -1.6 V began to decrease gradually, whereas that at 1.6 V changed only slightly due to the decrease in pore size caused by the deposited TPPS nanofibers. Therefore, the rectification ratio of the heterogeneous TPPS/Al2O3 nanochannels dramatically increased with increasing deposition time, reaching about approximately 12 at 75 min, and then decreased (Figure 2c). Moreover, the rectifying ratio at 60 min was slightly higher than that at 90 min. The ionic concentration is considered one of the most important factors influencing the ionic transportation behavior of nanochannels.30,47-50 Therefore, we used different concentrations of KCl electrolytes to further examine the influence of the heterogeneous nanochannels fabricated with an assembly time of 75 min on ionic transportation behavior at -1.6 V (Figure 2d) and 1.6 V (Figure 2e). The ionic conductance of the heterogeneous nanochannels with an electrolyte concentration of 0.1-10 mM grew slowly and remained very low. However, when the electrolyte concentration was approximately 80 mM, the ionic conductance quickly increased linearly.51-53 Hence, the ionic rectification of the heterogeneous nanochannels was affected by not only the surface charge54-56 but also the permeability of the TPPS nanofiber membrane. As shown in Figure 2f, the rectification ratio exhibited a “parabolic” trend with increasing KCl concentration, reaching a maximum value at 10 mM. In addition, the concentration-dependent ionic transportation behavior of the heterogeneous nanochannels fabricated with an assembly time of 60 min (Figure S14a), 75 min (Figure S14b), and 90 min (Figures S14c and S14d) showed similar trends. Therefore, 10 mM KCl (pH 6.5) was used as an electrolyte solution, unless otherwise specified. Heterogeneous nanochannels composed of amphoteric membrane materials may bring about an asymmetrical surface charge distribution or geometry between two openings and affect ionic transportation.35,57,58 In this work, the ionic transportation properties of the TPPS/Al2O3


8

Page 9 of 31 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

ACS Nano

heterogeneous nanochannels were influenced by not only the TPPS molecules inside the nanochannels but also the TPPS nanofibers assembled over the entrance to the nanochannels (Figure 3). As shown in Figure 3, in pH 6.5 KCl solution, the alumina surface was positively charged with terminal -OH2+ groups because the isoelectric point (pI) of alumina is approximately 8.5,59 while on the other side of the channel, the side modified with TPPS, the surface is negatively charged overall because of terminal negatively charged -SO3- groups and neutral -NH groups, which have a pKa of approximately 2.5 and 5, respectively.39,42,60 Accordingly, the surface charge distribution of the heterogeneous nanochannel was functionalized as a positive-negative charge junction. Under a negative bias, cations (K+) in the self-assembled TPPS side are preferentially attracted to the tip region. Meanwhile, anions (Cl-) preferentially migrate from the Al2O3 side to the tip region. Therefore, an ion-enriched region forms inside the nanochannels, and the switch is turned “on”. Under a positive bias, ionic transportation proceeds in the opposite direction, causing a region of ion depletion inside the nanochannels and turning the switch “off”.61-63 When the assembly time was controlled at 30 min, few, sparsely deposited TPPS fibers were observed on the surface of the Al2O3 nanochannels, and the nanofiber membranes did not form effectively. As the tip region of the heterogeneous nanochannels plays a major role in governing selective ionic transportation, slight rectification was observed under these conditions (Figure 3a). At an assembly time of 75 min, the TPPS nanofiber networks constituted a membrane at the entrance to the Al2O3 nanochannels and caused a decrease in the pore size and an increase in the number of -SO3- groups in the heterogeneous nanochannels. Thus, the thickness of the electric double layer of the heterogeneous nanochannels increased. The assembled TPPS fibers contributed greatly to the ionic rectification compared to the TPPS molecules modifying the inside of the nanochannels,


9

ACS Nano 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

Page 10 of 31

which were used to construct a heterogeneous junction for forming regions of ion enrichment and depletion (Figure 3b). As a result, more K+ ions transported across the heterogeneous nanochannel membrane, leading to an optimal ionic rectification ratio of 12. However, when an assembly time of 120 min was used, the TPPS network became thicker and tighter, blocking some of the heterogeneous nanochannels and decreasing the membrane permeability. The electrolyte ions could then hardly penetrate the nanochannels, which in turn reduces the rectification ratio (Figure 3c).64 Therefore, the ionic rectification of the TPPS/Al2O3 heterogeneous nanochannels strictly depends on the cooperation of the assembled TPPS nanofibers at the entrance to the nanochannels and the tip junction formed by the grafted TPPS molecules inside the nanochannels and the positively charged Al2O3 surface. Constructing artificial nanochannel systems with outstanding photoelectric responses is quite important for real-world applications. Under UV-Vis radiation, electronic transition from ground-state π orbitals (HOMO) to excited-state π* orbitals (LUMO) occurs in the TPPS molecules.60,65,66 This leads to an increase in the density of the electron cloud of the nanofiber surface, resulting in an increase in the interactions between the electrolyte ions and the surface charges, which ultimately leads to an increase in the ionic current. As shown in Figure 4a, the ionic current of the heterogeneous nanochannels with an assembly time of 75 min at -1.6 V is 76.6 µA. Thus, a current density of 2.74 A m-2 is obtained. Upon exposure to illumination approximately as intense as sunlight, the ionic transportation currents of the heterogeneous nanochannels are obviously higher than those of nanochannels in the dark. The insets of this figure illustrate the region corresponding to the dotted line box. The responsive current was defined as |I on| - |I off|, i.e., the absolute value of the current with illumination minus that without illumination at +1.6 V or -1.6 V. The responsive current of the heterogeneous nanochannels


10

Page 11 of 31 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

ACS Nano

fabricated with a deposition time of 75 min was 9.9 and 3.2 µA at -1.6 V and +1.6 V, respectively. The corresponding photoresponsive current density at -1.6 V was approximately 0.354 A m-2. Therefore, heterogeneous nanochannels maintained a better ionic rectification ratio before and after illumination. To further verify the optical properties of the system, the ionic transportation properties of naked Al2O3 and heterogeneous nanochannels with assembly times of 60 and 90 min were also investigated. The ionic currents of naked Al2O3 exhibited linear I-V curves, and the magnitude of the ionic current observed with illumination remained constant compared with that of observed without illumination (Figure S15a). The responsive current of heterogeneous nanochannels with an assembly time of 60 (Figure S15b) and 90 min (Figure S15c) reached the µA level. Comparing the data for the membranes allowed to self-assemble for 60, 75, and 90 min shows that the longer the TPPS assembly time is, the higher the photoresponsive currents of the resulting heterogeneous nanochannels will be, with photoresponsive currents first increasing significantly and then increasing slightly. Therefore, the photoresponsive ionic currents of heterogeneous nanochannels directly composed of closepacked nanofiber membranes can effectively elevate the photoelectric effect such that the responsive currents reach nearly 10 µA under the intensity of sunlight. In photoinduced nanochannel systems, it is desirable to realize the photoswitching property to efficiently regulate the reversible transformation between the “on” and “off” states by controlling the illumination.23,26 With alternating illumination, the ionic currents of the heterogeneous nanochannels with an assembly time of 75 min increased and subsequently decreased, which represents the “on” and “off” states, respectively. Furthermore, there was no significant loss of current in the heterogeneous nanochannels during the switching cycle, regardless of the use of 1.6 V (Figure 4c) or 1.6 V (Figure 4d), which indicates good stability and reversibility of the


11

ACS Nano 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

Page 12 of 31

system. Simultaneously, these results are supported well by the I-t curves of the heterogeneous nanochannels (Figure S16). In detail, upon illumination at an intensity roughly amounting to that of sunlight, the responsive current of the heterogeneous nanochannels with an assembly time of 90 min at -1.6 V reached 9.7 µA (Figure S16c, top). Even if the illumination intensity was reduced to 11 mW cm-2, the responsive current of the heterogeneous nanochannels still reached approximately 640 nA, which is 14% higher than that of N3/Al2O3 composite nanochannels.21 CONCLUSION In summary, we developed a facile approach, based on the self-assembly of TPPS molecules by noncovalent interactions, for fabricating photoresponsive heterogeneous TPPS/Al2O3 nanochannels by modifying Al2O3 membranes of hourglass-shaped channels with TPPS nanofibers. The heterogeneous nanochannels showed photoresponsive currents reaching the microampere level under illumination comparable to sunlight because the close arrangement of large-area nanofibers promotes the photoelectric effect. Additionally, the heterogeneous nanochannels exhibited a reversible photoswitching property. Actuated by the cooperative effect of the deposited TPPS nanofiber membrane and the tip region, as well as the surface charges of the membrane, the ionic rectifying ratio of the heterogeneous nanochannels reached nearly 12. Therefore, we anticipate that these heterogeneous TPPS/Al2O3 nanochannels have potential for various applications, such as nanofluidic diodes, photoelectric response and sustainable power generation. EXPERIMENTAL SECTION Fabrication of hourglass-shaped Al2O3 nanochannels. The hourglass-shaped Al2O3 nanochannels were prepared using a double-side anodization method combined with an in situ


12

Page 13 of 31 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

ACS Nano

pore-opening process. A clean Al foil (purity = 99.999%) was first electropolished in a solution mixture of HClO4 and ethanol (1:4 volume ratio) at 5°C under a voltage of 17 V for 3 min, in which the Al foil was used as the anode with a graphite plate as the cathode. Then, the first anodization was carried out in a 0.3 M H2C2O4 solution at 5°C. The resulting porous oxide layer was removed in a mixed acid solution containing 6 wt% phosphoric acid and 3.5 wt% chromic acid at 90°C for 2 h. In the second anodization step, the corresponding Al substrate was anodized under the same electrolyte conditions as those in the first anodization until the anodized current decreased to nearly zero. Finally, in situ pore opening was carried out in the original electrolyte oxalic acid for 30 min to penetrate the two oxide barrier layers. The detailed microstructure of the hourglass-shaped Al2O3 nanochannels was characterized by SEM (Hitachi, S4300). Fabrication of heterogeneous TPPS/Al2O3 nanochannels. The as-prepared Al2O3 nanochannels were mounted between the two halves of the homemade electrochemical cell. According to the DLP method, one half-cell was filled with 2 mM TPPS aqueous solution as a self-assembly reagent diffusing through one entrance to the hourglass-shaped alumina nanochannels, while the other half-cell was filled with 0.5 M sodium chloride solution (Figure S1).40,41 Therefore, TPPS self-assembled on only one segment of the hourglass-shaped Al2O3. To investigate the effect of TPPS assembly time on the dynamic variations in the surface topography of the heterogeneous TPPS/Al2O3 nanochannels, a series of heterogeneous nanochannels were obtained with TPPS assembly times of 30, 45, 60, 75, 90, 105, 120, and 150 min. A scheme of the heterogeneous nanochannel formation process as the assembly time increased is shown in Figure S2. The naked Al2O3 nanochannels and heterogeneous nanochannels were then characterized by fluorescence microscopy (Vision Engineering Co., UK), fluorescence spectroscopy (Shimadzc, RF-5301pc), SEM (Hitachi, S4300), and TEM (Hitachi, HT7700).


13

ACS Nano 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

Page 14 of 31

Measurements of ionic transportation. The ionic transportation properties of the heterogeneous nanochannels under conditions of different ionic concentrations and illumination were evaluated by measuring the ionic current across the channel with a Keithley 6487 picoammeter (Keithley Instruments, Cleveland, OH) in a custom-designed electrochemical cell with a quartz window, as shown in Figure S3. The heterogeneous nanochannels were mounted within the two halves of the cell, which was filled with aqueous KCl at a pH of 6.5 adjusted with 0.1 M HCl or KOH solution. Ag/AgCl electrodes were used to apply a transmembrane voltage from -1.6 to 1.6 V across the nanochannels. The current-voltage (I-V) measurements were performed by varying the KCl electrolyte concentration from 0.1 mM to 100 mM or alternating the illumination state at 10 mM KCl. A solar light simulator (CMH-250, Aodite Photoelectronic Technology, Ltd., Beijing) was used as the light source, with an intensity of approximately 116.4 mW cm-2, the equivalent of sunlight. During the ionic current measurements of the heterogeneous nanochannels, the anode always faced the side of the naked Al2O3 nanochannels, and the cathode faced the side of the self-assembled TPPS aggregates. All measurements were carried out at room temperature. ASSOCIATED CONTENT The authors declare no competing financial interests. Supporting Information The following Supporting Information is available free of charge on the ACS Publications website SEM image of hourglass-shaped Al2O3 nanochannels; Schematic illustration of preparation device, measurement device, the formation process, and possible mechanism of formation of


14

Page 15 of 31 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

ACS Nano

heterogeneous TPPS/Al2O3 nanochannels; Characterization analysis of photographs, SEM, TEM, fluorescence and UV-Vis absorption of heterogeneous TPPS/Al2O3 nanochannels; SEM images, photographs and fluorescence images of cylindrical Al2O3 nanochannels; Effect of electrolyte concentrations on ionic transportation properties; I-V curves and I-t curves of heterogeneous TPPS/Al2O3 nanochannels under alternating illumination. AUTHOR INFORMATION Corresponding Author *Email: [email protected]. *Email: [email protected]. ORCID Xia Fan: 0000-0002-0555-2010 Author Contributions ⊥D.

Zhang and S. Zhou contributed equally to the study.

ACKNOWLEDGMENTS This work was supported by the National Key Research and Development Program of China (2017YFA0206902, 2017YFA0206900), the National Natural Science Foundation (21471012, 21771016), and the Fundamental Research Funds for the Central Universities. We are grateful to Prof. Yanming Sun for prividing fluorescence spectroscopy (Shimadzc, RF-5301pc). REFERENCES


15

ACS Nano 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

Page 16 of 31

(1) Ying, Y.-L.; Zhang, J.; Gao, R.; Long, Y.-T. Nanopore-Based Sequencing and Detection of Nucleic Acids. Angew. Chem. Int. Ed. 2013, 52, 13154—13161. (2) Xu, J.; Lavan, D. A. Designing Artificial Cells to Harness the Biological Ion Concentration Gradient. Nat. Nanotechnol. 2008, 3, 666—670. (3) Taruno, A.; Vingtdeux, V.; Ohmoto, M.; Ma, Z.; Dvoryanchikov, G.; Li, A.; Adrien, L.; Zhao, H.; Leung, S.; Abernethy, M.; Koppel, J.; Davies, P.; Civan, M. M.; Chaudhari, N.; Matsumoto, I.; Hellekant, G.; Tordoff, M. G.; Marambaud, P.; Foskett, J. K. CALHM1 Ion Channel Mediates Purinergic Neurotransmission of Sweet, Bitter and Umami Tastes. Nature 2013, 495, 223—226. (4) Gouaux, E.; MacKinnon, R. Principles of Selective Ion Transport in Channels and Pumps. Science 2005, 310, 1461—1465. (5) García-Giménez, E.; Alcaraz, A.; Aguilella, V. M.; Ramírez, P. Directional Ion Selectivity in A Biological Nanopore with Bipolar Structure. J. Membr. Sci. 2009, 331, 137—142. (6) Xia, F.; Guo, W.; Mao, Y; Hou, X.; Xue, J.; Xia, H.; Wang, L.; Song, Y.; Ji, H.; Ouyang, Q.; Wang, Y.; Jiang, L. Gating of Single Synthetic Nanopores by Proton-Driven DNA Molecular Motors. J. Am. Chem. Soc. 2008, 130, 8345—8350. (7) Martin, C. R.; Siwy, Z. S. Learning Nature’s Way: Biosensing with Synthetic Nanopores. Science 2007, 317, 331—332. (8) Han, C.; Hou, X.; Zhang, H.; Guo, W.; Li, H.; Jiang, L. Enantioselective Recognition in Biomimetic Single Artificial Nanochannels. J. Am. Chem. Soc. 2011, 133, 7644—7647. (9) Kudr, J.; Skalickova, S.; Nejdl, L.; Moulick, A.; Ruttkay-Nedecky, B.; Adam, V.; Kizek, R. Fabrication of Solid-State Nanopores and Its Perspectives. Electrophoresis 2015, 36, 2367— 2379.


16

Page 17 of 31 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

ACS Nano

(10) Pérez-Mitta, G.; Tuninetti, J. S.; Knoll, W.; Trautmann, C.; Toimil-Molares, M. E.; Azzaroni, O. Polydopamine Meets Solid-State Nanopores: A Bioinspired Integrative Surface Chemistry Approach to Tailor the Functional Properties of Nanofluidic Diodes. J. Am. Chem. Soc. 2015, 137, 6011—6017. (11) Zhang, H.; Tian, Y.; Jiang, L. Fundamental Studies and Practical Applications of BioInspired Smart Solid-State Nanopores and Nanochannels. Nano Today 2016, 11, 61—81. (12) Sun, Y.; Ma, J.; Zhang, F.; Zhu, F.; Mei, Y.; Liu, L.; Tian, D.; Li, H. A Light-Regulated Host-Guest-Based Nanochannel System Inspired by Channelrhodopsins Protein. Nat. Commun. 2017, 8, 260. (13) Zhang, Z.; Xie, G.; Xiao, K.; Kong, X.-Y.; Li, P.; Tian, Y.; Wen, L.; Jiang, L. Asymmetric Multifunctional Heterogeneous Membranes for pH- and Temperature-Cooperative Smart Ion Transport Modulation. Adv. Mater. 2016, 28, 9613—9619. (14) Fang, R.; Zhang, H.; Yang, L.; Wang, H.; Tian, Y.; Zhang, X.; Jiang, L. Supramolecular Self-Assembly Induced Adjustable Multiple Gating States of Nanofluidic Diodes. J. Am. Chem. Soc. 2016, 138, 16372—16379. (15) Siwy, Z. S.; Howorka, S. Engineered Voltage-Responsive Nanopores. Chem. Soc. Rev. 2010, 39, 1115—1132. (16) Pérez-Mitta, G.; Marmisolle, W. A.; Trautmann, C.; Toimil-Molares, M. E.; Azzaroni, O. An All-Plastic Field-Effect Nanofluidic Diode Gated by a Conducting Polymer Layer. Adv. Mater. 2017, 29, 1700972. (17) Ali, M.; Yameen, B.; Neumann, R.; Ensinger, W.; Knoll, W.; Azzaroni, O. Biosensing and Supramolecular Bioconjugation in Single Conical Polymer Nanochannels. Facile Incorporation


17

ACS Nano 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

Page 18 of 31

of Biorecognition Elements into Nanoconfined Geometries. J. Am. Chem. Soc. 2008, 130, 16351—16357. (18) Cao, J.; Zhao, X.-P.; Younis, M. R.; Li, Z.-Q.; Xia, X.-H.; Wang, C. Ultrasensitive Capture, Detection, and Release of Circulating Tumor Cells Using a Nanochannel-Ion Channel Hybrid Coupled with Electrochemical Detection Technique. Anal. Chem. 2017, 89, 10957—10964. (19) Zhao, X.-P.; Wang, S.-S.; Younis, M. R.; Xia, X.-H.; Wang, C. Asymmetric NanochannelIonchannel Hybrid for Ultrasensitive and Label-Free Detection of Copper Ions in Blood. Anal. Chem. 2018, 90, 896—902. (20) Hervás, M.; Navarro, J. A.; De La Rosa, M. A. Electron Transfer between Membrane Complexes and Soluble Proteins in Photosynthesis. Acc. Chem. Res. 2003, 36, 798—805. (21) Liu, Y.; Kong, Y.; Fan, X.; Zhai, J.; Jiang, L. N3/Al2O3 Composite Nanochannels: Photoelectric and Photoelectric-and-pH Cooperatively Controlled Ion Gating. J. Mater. Chem. A 2017, 5, 19220—19226. (22) Li, P.; Xie, G.; Kong, X.-Y.; Zhang, Z.; Xiao, K.; Wen, L.; Jiang, L. Light-Controlled Ion Transport through Biomimetic DNA-Based Channels. Angew. Chem. Int. Ed. 2016, 55, 15637— 15641. (23) Wang, H.; Liu, Q.; Li, W.; Wen, L.; Zheng, D.; Bo, Z.; Jiang, L. Colloidal Synthesis of Lettuce-like Copper Sulfide for Light-Gating Heterogeneous Nanochannels. ACS Nano 2016, 10, 3606—3613. (24) Xiao, K.; Xie, G.; Li, P.; Liu, Q.; Hou, G.; Zhang, Z.; Ma, J.; Tian, Y.; Wen, L.; Jiang, L. A Bomimetic

Multi-Stimuli-Response

Ionic

Gate

Using

a

Hydroxypyrene

Derivation-

Functionalized Asymmetric Single Nanochannel. Adv. Mater. 2014, 26, 6560—6565.


18

Page 19 of 31 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

ACS Nano

(25) Lu, S.; Guo, Z.; Xiang, Y.; Jiang, L. Photoelectric Frequency Response in a Bioinspired Bacteriorhodopsin/Alumina Nanochannel Hybrid Nanosystem. Adv. Mater. 2016, 28, 9851— 9856. (26) Wen, L.; Liu, Q.; Ma, J.; Tian, Y.; Li, C.; Bo, Z.; Jiang, L. Malachite Green DerivativeFunctionalized Single Nanochannel: Light-and-pH Dual-Driven Ionic Gating. Adv. Mater. 2012, 24, 6193—6198. (27) Rochaix, J. D. Fine-Tuning Photosynthesis. Science 2013, 342, 50—51. (28) Zhang, Q.; Liu, Z.; Hou, X.; Fan, X.; Zhai, J.; Jiang, L. Light-Regulated Ion Transport through Artificial Ion Channels Based on TiO2 Nanotubular Arrays. Chem. Commun. 2012, 48, 5901—5903. (29) Gao, J.; Guo, W.; Feng, D.; Wang, H.; Zhao, D.; Jiang, L. High-Performance Ionic Diode Membrane for Salinity Gradient Power Generation. J. Am. Chem. Soc. 2014, 136, 12265—12272. (30) Zhang, Z.; Kong, X.-Y.; Xiao, K.; Liu, Q.; Xie, G.; Li, P.; Ma, J.; Tian, Y.; Wen, L.; Jiang, L. Engineered Asymmetric Heterogeneous Membrane: A Concentration-Gradient-Driven Energy Harvesting Device. J. Am. Chem. Soc. 2015, 137, 14765—14772. (31) Guo, T.; Han, K.; Heng, L.; Cao, M.; Jiang, L. Ordered Porous Structure Hybrid Films Generated by Breath Figures for Directional Water Penetration. RSC Adv. 2015, 5, 88471— 88476. (32) Han, K.; Heng, L.; Jiang, L. Multiphase Media Antiadhesive Coatings: Hierarchical SelfAssembled Porous Materials Generated Using Breath Figure Patterns. ACS Nano 2016, 10, 11087—11095.


19

ACS Nano 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

Page 20 of 31

(33) Wen, L.; Xiao, K.; Sesha Sainath, A. V.; Komura, M.; Kong, X.-Y.; Xie, G.; Zhang, Z.; Tian, Y.; Iyoda, T.; Jiang, L. Engineered Asymmetric Composite Membranes with Rectifying Properties. Adv. Mater. 2016, 28, 757—763. (34) Han, K.; Heng, L.; Wen, L.; Jiang, L. Biomimetic Heterogeneous Multiple Ion Channels: A Honeycomb Structure Composite Film Generated by Breath Figures. Nanoscale 2016, 8, 12318—12323. (35) Zhang, Z.; Kong, X.-Y.; Xiao, K.; Xie, G.; Liu, Q.; Tian, Y.; Zhang, H.; Ma, J.; Wen, L.; Jiang, L. A Bioinspired Multifunctional Heterogeneous Membrane with Ultrahigh Ionic Rectification and Highly Efficient Selective Ionic Gating. Adv. Mater. 2016, 28, 144—150. (36) Adachi, S. I.; Nagano, S.; Ishimori, K.; Watanabe, Y.; Morishima, I. Roles of Proximal Ligand in Heme Proteins: Replacement of Proximal Histidine of Human Myoglobin with Cysteine and Tyrosine by Site-Directed Mutagenesis as Models for P-450, Chloroperoxidase, and Catalase. Biochemistry 1993, 32, 241—252. (37)

D'Souza,

F.;

Ito,

O.

Supramolecular

Donor-Acceptor

Hybrids

of

Porphyrins/Phthalocyanines with Fullerenes/Carbon Nanotubes: Electron Transfer, Sensing, Switching, and Catalytic Applications. Chem. Commun. 2009, 33, 4913—4928. (38) Friesen, B. A.; Wiggins, B.; McHale, J. L.; Mazur, U.; Hipps, K. W. A Self-Assembled Two-Dimensional Zwitterionic Structure: H6TSPP Studied on Graphite. J. Phys. Chem. C 2011, 115, 3990—3999. (39) Friesen, B. A.; Nishida, K. R. A.; McHale, J. L.; Mazur, U. New Nanoscale Insights into the Internal Structure of Tetrakis(4-sulfonatophenyl) Porphyrin Nanorods. J. Phys. Chem. C 2009, 113, 1709—1718.


20

Page 21 of 31 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

ACS Nano

(40) Karnik, R.; Castelino, K.; Duan, C.; Majumdar, A. Diffusion-Limited Patterning of Molecules in Nanofluidic Channels. Nano Lett. 2006, 6, 1735—1740. (41) Li, C.-Y.; Ma, F.-X.; Wu, Z.-Q.; Gao, H.-L.; Shao, W.-T.; Wang, K.; Xia, X.-H. SolutionpH-Modulated Rectification of Ionic Current in Highly Ordered Nanochannel Arrays Patterned with Chemical Functional Groups at Designed Positions. Adv. Funct. Mater. 2013, 23, 3836— 3844. (42) Vlaming, S. M.; Augulis, R.; Stuart, M. C. A.; Knoester, J.; van Loosdrecht, P. H. M. Exciton Spectra and the Microscopic Structure of Self-Assembled Porphyrin Nanotubes. J. Phys. Chem. B 2009, 113, 2273—2283. (43) Rotomskis, R.; Augulis, R.; Snitka, V. Hierarchical Structure of TPPS4 J-Aggregates on Substrate Revealed by Atomic Force. J. Phys. Chem. B 2004, 108, 2833—2838. (44) Chen, Y.; Zheng, M.; Xiao, Y.; Dong, H.; Zhang, H.; Zhuang, J.; Hu, H.; Lei, B.; Liu, Y. A Self-Quenching-Resistant Carbon-Dot Powder with Tunable Solid-State Fluorescence and Construction of Dual-Fluorescence Morphologies for White Light-Emission. Adv. Mater. 2016, 28, 312—318. (45) He, M.; Ding, Y.; Chen, J.; Song, Y. Spontaneous Uphill Movement and Self-Removal of Condensates on Hierarchical Tower-like Arrays. ACS Nano 2016, 10, 9456—9462. (46) Li, Z.; Wang, J.; Zhang, Y.; Wang, J.; Jiang, L.; Song, Y. Closed-Air Induced Composite Wetting on Hydrophilic Ordered Nanoporous Anodic Alumina. Appl. Phys. Lett. 2010, 97, 233107. (47) Zhang, Q.; Hu, Z.; Liu, Z.; Zhai, J.; Jiang, L. Light-Gating Titania/Alumina Heterogeneous Nanochannels with Regulatable Ion Rectification Characteristic. Adv. Funct. Mater. 2014, 24, 424—431.


21

ACS Nano 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

Page 22 of 31

(48) Fan, R.; Huh, S.; Yan, R.; Arnold, J.; Yang, P. Gated Proton Transport in Aligned Mesoporous Silica Films. Nat. Mater. 2008, 7, 303—307. (49) Apel, P. Y.; Blonskaya, I. V.; Levkovich, N. V.; Orelovich, O. L. Asymmetric Track Membranes: Relationship between Nanopore Geometry and Ionic Conductivity. Petrol. Chem. 2011, 51, 555—567. (50) Daiguji, H.; Oka, Y.; Shirono, K. Nanofluidic Diode and Bipolar Transistor. Nano Lett. 2005, 5, 2274—2280. (51) Raidongia, K.; Huang, J. Nanofluidic Ion Transport through Reconstructed Layered Materials. J. Am. Chem. Soc. 2012, 134, 16528—16531. (52) Shao, J.-J.; Raidongia, K.; Koltonow, A. R.; Huang, J. Self-Assembled Two-Dimensional Nanofluidic Proton Channels with High Thermal Stability. Nat. Commun. 2015, 6, 7602. (53) Bao, B.; Hao, J.; Bian, X.; Zhu, X.; Xiao, K.; Liao, J.; Zhou, J.; Zhou, Y.; Jiang, L. 3D Porous Hydrogel/Conducting Polymer Heterogeneous Membranes with Electro-/pH-Modulated Ionic Rectification. Adv. Mater. 2017, 29, 1702926. (54) Stein, D.; Kruithof, M.; Dekker, C. Surface-Charge-Governed Ion Transport in Nanofluidic Channels. Phys. Rev. Lett. 2004, 93, 035901. (55) 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. (56) He, Y.; Gillespie, D.; Boda, D.; Vlassiouk, I.; Eisenberg, R. S.; Siwy, Z. S. Tuning Transport Properties of Nanofluidic Devices with Local Charge Inversion. J. Am. Chem. Soc. 2009, 131, 5194—5202.


22

Page 23 of 31 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

ACS Nano

(57) Sui, X.; Zhang, Z.; Zhang, Z.; Wang, Z.; Li, C.; Yuan, H.; Gao, L.; Wen, L.; Fan, X.; Yang, L.; Zhang, X.; Jiang, L. Biomimetic Nanofluidic Diode Composed of Dual Amphoteric Channels Maintains Rectification Direction over a Wide pH Range. Angew. Chem. Int. Ed. 2016, 55, 13056—13060. (58) Zhang, W.; Meng, Z.; Zhai, J.; Heng, L. Ion Current Behaviors of Mesoporous ZeolitePolymer Composite Nanochannels Prepared by Water-Assisted Self-Assembly. Chem. Commun. 2014, 50, 3552—3555. (59) Kong, Y.; Fan, X.; Zhang, M.; Hou, X.; Liu, Z.; Zhai, J.; Jiang, L. Nanofluidic Diode Based on Branched Alumina Nanochannels with Tunable Ionic Rectification. ACS Appl. Mater. Interfaces 2013, 5, 7931—7936. (60) Schwab, A. D.; Smith, D. E.; Rich, C. S.; Young, E. R.; Smith, W. F.; de Paula, J. C. Porphyrin Nanorods. J. Phys. Chem. B 2003, 107, 11339—11345. (61) Karnik, R.; Duan, C.; Castelino, K.; Daiguji, H.; Majumdar, A. Rectification of Ionic Current in a Nanofluidic Diode. Nano Lett. 2007, 7, 547—551. (62) Daiguji, H.; Oka, Y.; Shirono, K. Nanofluidic Diode and Bipolar Transistor. Nano Lett. 2005, 5, 2274—2280. (63) Kalman, E. B.; Vlassiouk, I.; Siwy, Z. S. Nanofluidic Bipolar Transistors. Adv. Mater. 2008, 20, 293—297. (64) Peng, L.; Fang, Z.; Zhu, Y.; Yan, C.; Yu, G. Holey 2D Nanomaterials for Electrochemical Energy Storage. Adv. Energy Mater. 2018, 8, 1702179. (65) Ceulemans, A.; Oldenhof, W.; Gorller-Walrand, C.; Vanquickenborne, L. G. Gouterman’s “Four-Orbital” Model and the MCD Spectra of High-Symmetry Metalloporphyrins. J. Am. Chem. Soc. 1986, 108, 1155—1163.


23

ACS Nano 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

Page 24 of 31

(66) Schwab, A. D.; Smith, D. E.; Bond-Watts, B.; Johnston, D. E.; Hone, J.; Johnson, A. T.; de Paula, J. C.; Smith, W. F. Photoconductivity of Self-Assembled Porphyrin Nanorods. Nano Lett. 2004, 4, 1261—1265.


24

Page 25 of 31 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

ACS Nano

Scheme 1. (a) Schematic illustration of TPPS self-assembly on the top surface of hourglassshaped Al2O3 nanochannels during the formation of heterogeneous TPPS/Al2O3 nanochannels by diffusion-limited patterning (DLP) at pH 2.5. (b) At pH 2.5, two SO3groups of TPPS are protonated, and the residual peripheral SO3- groups, as well as central NH+ groups, lead to a zwitterionic neutral species (the red dotted line box). (c) The formation of TPPS nanofibers mainly depended on ionic interactions between the negative groups of TPPS and the positive groups of neighboring molecules, as well as the π-π interactions between the porphyrin rings of adjacent molecules, which formed a “spread deck of cards” conformation.


25

ACS Nano 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

Page 26 of 31

Figure 1. SEM images of the top surface flat and after tilting 30 degrees and the side view of TPPS/Al2O3 heterogeneous nanochannels with assembly times of (a1-a3) 0, (b1-b3) 30, (c1c3) 60, (d1-d3) 75, and (e1-e3) 120 min. The number and the length of the TPPS nanofibers deposited on the top surface of the alumina membrane increased gradually as the assembly time increased. Scale bars: 300 nm.


26

Page 27 of 31 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

ACS Nano

Figure 2. (a, b) I-V properties of heterogeneous TPPS/Al2O3 nanochannels obtained with assembly times from 30-75 and 75-150 min. (c) The rectification ratio of heterogeneous nanochannels versus assembly time first increased and then decreased, reaching the optimal value at 75 min, which was approximately 12. (d, e) Influence of electrolyte concentration on ionic conductance of the heterogeneous nanochannels with an assembly time of 75 min at -1.6 V and 1.6 V, respectively. There was a surface charge-dominant zone with lower electrolyte concentrations. (f) The rectification ratio of heterogeneous nanochannels with an assembly time of 75 min showed a “parabolic” trend with increasing salt concentration, reaching a maximum value at 10 mM.


27

ACS Nano 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

Page 28 of 31

Figure 3. Schematic illustration of the rectifying effect of heterogeneous TPPS/Al2O3 nanochannels with assembly times of (a) 30, (b) 75, and (c) 120 min in pH 6.5 KCl solution. An “on” state occurred inside the nanochannels under a negative voltage. Al2O3 carries a positive charge, while TPPS carries a negative charge. When the assembly time was 30 min, the TPPS nanofiber membrane did not form effectively, and as the tip region in the nanochannels plays a major role in governing selective ionic transportation, the rectification ratio was slight. When the assembly time was 75 min, the network formed by the TPPS nanofibers constituted a membrane, which contributed greatly to ionic rectification compared with the TPPS molecules modifying the inside of the nanochannels. More K+ ions are transported across the nanochannels, and an optimal ionic rectification ratio of 12 was achieved. However, when the assembly time was 120 min, the TPPS network became thicker and tighter, and the electrolyte ions could hardly penetrate the nanochannels, resulting in a significantly decreased rectification ratio.


28

Page 29 of 31 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

ACS Nano

Figure 4. (a) I-V properties of heterogeneous TPPS/Al2O3 nanochannels with an assembly time of 75 min under alternating illumination. The insets illustrate the region corresponding to the dotted line box. The ionic transportation currents of the heterogeneous nanochannels are greater with than without illumination. (b) The responsive current of heterogeneous nanochannels with an assembly time of 75 min at -1.6 V and 1.6 V was 9.9 and 3.2 µA, respectively. Thus, the heterogeneous nanochannels maintained a good ionic rectification ratio before and after illumination. The current-cycle curves of heterogeneous TPPS/Al2O3 nanochannels with an assembly time of 75 min at (c) -1.6 V and (d) 1.6 V with illumination (red sphere), showing high currents, and without illumination (black square), showing low currents, which represents the “on” and “off” states, respectively. The cycles with alternating


29

ACS Nano 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

Page 30 of 31

illumination indicate that the heterogeneous nanochannels showed good stability, reversibility and photoswitching.


30

Page 31 of 31 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

ACS Nano

BRIEFS We prepared a photoresponsive heterogeneous nanochannel system by decorating a membrane of hourglass-shaped Al2O3 nanochannels with self-assembled TPPS nanofibers. The system demonstrated a photoswitching capability, with photoresponsive ionic currents of up to approximately 9.7 µA. SYNOPSIS


31

Self-Assembled Porphyrin Nanofiber Membrane-Decorated Alumina

Recommend Documents