Polypyrrole

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Article

Facile Template Synthesis of Microfibrillated Cellulose/ Polypyrrole/ Silver Nanoparticles Hybrid Aerogels with Electrical Conductive and Pressure Responsive Properties Sukun Zhou, Meng Wang, Xiong Chen, and Feng Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b01020 • Publication Date (Web): 08 Nov 2015 Downloaded from http://pubs.acs.org on November 16, 2015

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 free 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 accessible to all readers and 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.

ACS Sustainable Chemistry & Engineering 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 27

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 Sustainable Chemistry & Engineering

Facile Template Synthesis of Microfibrillated Cellulose/ Polypyrrole/ Silver Nanoparticles Hybrid Aerogels with Electrical Conductive and Pressure Responsive Properties Sukun Zhou, Meng Wang, Xiong Chen and Feng Xu* Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, 35 Tsinghua East Rd, Beijing, 100083, China * Corresponding author, E-mail: [email protected]. Tel/Fax: +86-10-62337993.

Abstract Sustainable microfibrillated cellulose (MFC) aerogels are considered to be good templates for the growth of functional organic or inorganic nanoparticles. In this work, MFC aerogels with high porosity (99.9%) and low density (2.91mg/cm3) were produced by freeze-drying. Then the obtained MFC aerogels were used as templates for the synthesis of MFC/polypyrrole (PPy)/silver nanoparticles (Ag) hybrid aerogels by a simple dip-coating method. Our results demonstrated that the obtained hybrid aerogels maintained the attractive features of the pristine MFC aerogels, such as the high porosity, low density, high compressive stress during the preparation process. Compared with MFC aerogels and MFC/PPy hybrid aerogels, the MFC/PPy/Ag hybrid aerogels exhibited enhanced antimicrobial and electrical conductive properties due to the combination of PPy and Ag. Moreover, the electrical conductivity and compressible properties of the MFC/PPy/Ag hybrid aerogels led to their pressure responsive property. These features make the hybrid aerogels promising candidates for wound healing, energy storage and pressure sensing applications. Keywords: Microfibrillated Cellulose, Polypyrrole, Silver Nanoparticles, Dip-Coating, Antimicrobial, 1

ACS Paragon Plus Environment


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

Electrical Conductive, Pressure Responsive. Introduction Aerogels are highly porous, ultralightweight and sponge-like materials prepared from solvent-swollen gel networks.1 Currently, aerogels have aroused considerable interest due to their low density, low thermal transport, high porosity, and large surface area.2 Applications of aerogels include lightweight construction,3 temperature and acoustic insulation,4 catalyst,5 sensing and electronics.6 However, the traditional aerogels are usually produced from silica and they tend to be brittle, which limits their potential applications. In the past several decades, there has been extensive search for ductile aerogels and the flexibility has been achieved by using native cellulose nanofiber, based on microfibrillated cellulose (MFC).7 MFC is one of the most rigid nanoscale building blocks prepared from disintegration of cellulose, and it shows particular promise for use in materials due to its sustainability, biodegradability, high strength and high aspect ratio.8 The typical width of MFC is in the range of 5-20 nm and its length may reach several micrometers.9 MFC possesses high Young’s modulus (~138 GPa) and high flexibility because of its unique structure, in which there are crystalline regions as well as amorphous regions.10 The aerogels made from MFC have the advantages of high porosity (over 99%),7-8 low density (less than 5 mg/cm3),11-12 and high specific surface areas (over 300 m2/g), encouraging the development of MFC aerogels as biological templates for nanotubes,2 conductive materials13, cobalt-ferrite nanoparticles,14 and other functional materials15 to achieve ideal magnetic16 and electrical characteristics.8 Recently, hybrid materials of cellulose and conductive polymers have attracted a great deal of attention.8, 17 Polypyrrole (PPy) is one of the most attractive conductive polymer with interesting properties, such as biocompatibility, electrical conductivity and antibacterial properties.18 It can be synthesized from 2


Page 2 of 27

Page 3 of 27

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


aqueous suspension at neutral pH by chemical or electrochemical polymerization. It has been shown that PPy can be coated on MFC,19 cotton fiber,20 jute fiber21 by in situ polymerization-induced adsorption process, and the obtained composites showed antibacterial properties against Escherichia coli. Whereas the oxidant for preparation of pyrrole in the literature generally focus on iron chloride (FeCl3),22 ammonium peroxydisulfate ((NH4)2S2O8)

23

and cerium sulfate (Ce(SO4)2),24 the direct in situ polymerization of PPy

can readily be prepared by silver nitrate (AgNO3).25 During polymerization, the redox reaction between the Ag+ and the polypyrrole chains leads to the reduction of Ag+ to metallic silver nanoparticles.26 As silver also shows antibacterial and electrical conductive properties, the incorporation of silver would further improve the antibacterial and electrical conductive effect of PPy. Most of the preparation method for the nanocellulose-conducting polymer hybrid materials is mixing the solution of nanocellulose and conducting monomer, and then the mixed solution was dried to obtain the hybrid materials.13, 19, 27 In fact, mixing the nanocellulose solution and the conducting monomer may result in the aggregation of nanocellulose, thus leading to the inhomogeneous structure of the hybrid materials. Moreover, the mechanical properties of the nanocellulose may be significantly affected by the conducting monomer. To solve these problems, we attempted to find a simple way to functionalize cellulose aerogels and preserve the properties of nanocellulose aerogels. In this work, we fabricated MFC/PPy/Ag hybrid aerogels using MFC aerogels as templates by a simple dip-coating method. The attractive features of the pristine MFC aerogels were preserved during the preparation process. In addition, the incorporation of PPy and Ag made the aerogels exhibiting antimicrobial, electrical conductive and pressure sensing properties. To the best of our knowledge, the present work is the first to report on aerogels based on MFC, PPy and Ag, and this work provide a new way to multifunctionalize cellulose aerogels. 3



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

Materials and Methods Materials A softwood kraft pulp was provided by Northwood Pulp and Timber Limited (Canada). TEMPO, sodium phosphate, sodium chlorite, sodium hypochlorite, pyrrole, AgNO3, FeNO3 and other chemicals were purchased from Lan Yi (China) and used without further purification. Preparation of MFC aerogels MFC suspensions were prepared from softwood kraft pulp according to a previously published method.28 Briefly, the pulp was oxidized by TEMPO and then the TEMPO-oxidized cellulose suspension was fibrillated by a high pressure homogenizer (APV-2000, 100 MPa) for 20 min. Thereafter the as-prepared MFC suspensions (0.2 wt%) were frozen at two temperatures: -196 °C (liquid nitrogen), -18 °C (refrigerator). After complete freezing, the frozen samples were subjected to freeze-drying using a freeze-dryer (Scientz-10N, China) and the pristine MFC aerogels were obtained. During freeze-drying, the cold trap temperature was below -55 °C and the vacuum was below 0.08 mbar. The obtained MFC aerogels frozen at -196 °C and -18 °C were named as M1 and M2. Preparation of MFC/PPy/Ag hybrid aerogels The obtained MFC aerogels with a thickness of 2 cm and a diameter of 4 cm were dipped into pyrrole aqueous solutions (2.0 mmol/L, 50 ml) for one hour to ensure penetration equilibrium of pyrrole into the aerogel network. Then the pyrrole adsorbed MFC aerogels were removed from the solution and dipped into 50 ml oxidants solutions at an ice-water bath for 1 h to complete the polymerization. Finally, the aerogels were rinsed thoroughly with water to remove the unreacted pyrrole, followed by the freeze-drying. Thus, the hybrid aerogels were obtained. The mixtures of AgNO3 and Fe (NO3)3 solutions were used as the 4


Page 4 of 27

Page 5 of 27

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


oxidants and the oxidant-to-pyrrole mole ratio was 2.5. The concentrations of the mixed AgNO3 and Fe (NO3)3 solutions used in the polymerization were given in Table 1. Table 1. Concentrations of AgNO3 and Fe (NO3)3 used for the oxidation of pyrrole. Sample

AgNO3 (mmol/L)

Fe (NO3)3 (mmol/L)

Percentage of AgNO3 (%)

MFC/PPy (MP)

0

2.5

0

MFC/PPy/Ag-1(MPA1)

1.0

1.5

40

MFC/PPy/Ag-2(MPA2)

1.5

1.0

60

MFC/PPy/Ag-3(MPA3)

2.0

0.5

80

MFC/PPy/Ag-4(MPA4)

2.5

0

100

Characterization Fourier transform infrared spectroscopy (FTIR) was performed on an infrared spectrophotometer (Nicolet iN10-MX, ThermoScientific) and X-ray Diffraction (XRD) patterns of the aerogels were recorded on a D8-Advance X-ray Diffraction Analyzer. Thermogravimetric Analysis (TGA) was performed on a Shimadzu DTG-60 thermal analyser from 20 to 800 °C with a heating rate of 20 °C min-1 under nitrogen atmosphere at a flow rate of 50 mL min-1. The morphology of the MFC suspension and aerogels were observed by transmission electron microscopy (TEM, JEOL, JEM-1010, Japan) and scanning electron microscope (SEM, Hitachi, S-3400 N II, Japan) equipped with energy dispersive X-ray spectroscopy (EDS). The specific surface areas of the aerogels were determined by a Gemin V (Micromeritics, Norcross, GA) at the temperature of liquid nitrogen. Densities (ρgel) of the aerogels were calculated by weighing the aerogels and measuring their volumes. The weight of the aerogels was measured by an analytical balance 5



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

(readability 0.0001 g) and the dimensions of the aerogels were measured by a digital caliper at five different positions. The porosities of the aerogels (P) were calculated by the density of the aerogels (ρgel) and the density of the solid (ρsolid) using eq (1), P (%) = 100 × (1 − ⁄ ) (1) Mechanical Property and Shape Recovery Ability Compression tests were performed with a Zwick Testing System equipped with a 50 N loading cell. Each aerogel was cut into a cylinder shape with a diameter of 10 mm and a height of 20 mm. The sample was placed between the testing plates and compressed with a speed of 2 mm/min to 60% of its original thickness. Five replicates were measured for each sample. After the sample had been unloaded, the shape recovery was calculated according to the eq (2). S (%) = 100 - ε (2) where ε is the strain at the final position when the force detected reached 0 N. Antimicrobial Properties and Cytotoxicity Evaluation The antimicrobial properties of the hybrid aerogels were investigated by checking the growth inhibition zones around the aerogels. The antimicrobial test was done against Escherichia coli (E. coli) as the model of Gram-negative bacteria and Staphylococcus aureus (S. aureus) as the model of Gram-positive bacteria. The aerogels were compressed into films and then the films were cut into a disc shape with 1.5 cm diameter and were placed on the cultured agar plates, which were then incubated at 37 °C for 24 h. Cytotoxicity of the aerogels were tested with the Mouse embryo fibroblast (L929 cells) using the MTT assay method according to the literature.29 Electrical Conductivity Measurements 6


Page 6 of 27

Page 7 of 27

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


The electrical conductivity of the aerogels were measured with a RTS-8 4-point probe measurements (Shenzhen Four Probes Tech Co. Ltd., China) at 25 °C. A suitable current was applied over the aerogels and the corresponding voltage was measured until a repeatable value was obtained. The conductivity was computed by the eq (3): σ = 1/ρ (3) where ρ is the electrical resistivity of the aerogels. To investigate the relationship between the electrical conductivity and the compressive strain of the hybrid aerogel, the aerogel was clamped between two Pt-coated glass plates and compressed to different strain, then the conductivity was measured at each strain. Results and Discussion Preparation of the Aerogels The preparation procedure of MFC/PPy/Ag hybrid aerogels is schematically shown in Figure 1. TEM analysis (Figure 1a) of the resulting MFC suspension revealed that the MFC were well disintegrated and exhibited an average diameter in the nanometer range. The water in the MFC suspension was progressively removed by freeze-drying and sponge-like aerogels were produced without significant collapse. Figure1c, d demonstrated that the obtained MFC aerogels achieved good macroscopic integrity and could be bent without cracking. During the dip-coating process no noticeable disintegration or swelling of the MFC aerogels was observed and the MFC aerogel turned from white to black when it was dipping into the AgNO3 solution, indicating that the MFC aerogel was fully filled with PPy.

7



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

Figure 1. Preparation of MFC aerogels and MFC/PPy/Ag hybrid aerogels. (a) TEM image of MFC, (b) photograph of MFC suspension, (c-e) photographs of as-prepared MFC aerogels, (f) the MFC aerogel was dipping into the pyrrole solution, (g) the pyrrole-coated MFC aerogel was dipping into oxidant solution, (h) the obtained MFC/PPy/Ag hybrid aerogels. (i) oxidation of pyrrole with AgNO3. Chemical Structure of the Aerogels The FTIR spectra (Figure 2a) confirm the presence of PPy in the MFC/PPy and MFC/PPy/Ag hybrid aerogels. The bands at 3340 cm-1 and 3338 cm-1 are related to hydroxyl groups in MFC and -N-H groups in PPy, respectively. The addition of PPy shifted these bands to lower wavenumbers and made the bands broader in the MFC/PPy and MFC/PPy/Ag hybrid aerogels. This is ascribed to the formation of hydrogen bonding between the hydroxyl groups in MFC and -N-H groups in PPy. The band at 1574 cm-1 is assigned to the C-C asymmetric inter-ring, C=C intra-ring, and C=N stretching vibrations in PPy.30-31 These bands shifted to 1565 cm-1 and 1563 cm-1 in the MFC/PPy and MFC/PPy/Ag hybrid aerogels spectra because of 8


Page 8 of 27

Page 9 of 27

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


the hydrogen bonding between the oxygen atoms of the hydroxyl groups on the cellulose surface and the – N-H groups in the PPy.18 The bands in the wavenumber range 1050-1130 cm-1 are attributed to the C-O35 and C-O-C32-33 stretching vibrations in MFC and these vibrational bands decreased in intensity in the MFC/PPy and MFC/PPy/Ag hybrid aerogels spectra due to the addition of PPy. The XRD patterns of PPy powder, pristine MFC aerogel, MFC/PPy and MFC/PPy/Ag hybrid aerogels are shown in Figure 2b. In the pattern of the pristine MFC aerogel, the diffraction peaks at 2θ = 14.6°, 16.5° and 22.6° for (1-10), (110) and (200) planes are crystal characteristic of cellulose I, indicating that the native crystal structure of cellulose was preserved during the MFC preparation process. The pure PPy powder showed a broad diffraction peak at 26.6°, representing an amorphous phase.34 The MFC/PPy/Ag hybrid aerogels exhibited most of the characteristic peaks for pure MFC and PPy, while the intensity of the peaks for the MFC were significantly weakened and some of the characteristic peaks for MFC were disappeared, signifying the coating of PPy on the surface of MFC. In addition, the peaks located at 38.14° and 44.33°, corresponding to the (111) and (200) diffraction planes, demonstrated the successful synthesis of silver nanoparticles (JCPDS file number 04-0783).25

Figure 2. FTIR spectra (a) and XRD pattern (b) of MFC aerogels (M1), PPy, MFC/PPy and 9



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

MFC/PPy/Ag (MPA3) hybrid aerogels. Thermal Stability TGA measurements were conducted to evaluate the thermal stability of the aerogels and silver content in the hybrid aerogels. The thermal degradation of the MFC aerogel started at approximately 225 °C and the MFC/PPy aerogel exhibited a lower thermal degradation temperature of 200 °C. A possible explanation is that the adsorption of PPy on the surface of MFC leads to the reduced number of effective hydrogen bonds between cellulose nanofibers, thus leading to the lower degradation temperature.35 The MFC/PPy/Ag hybrid aerogel showed an enhancement of the degradation temperature (275 °C), which could be attributed to the shield effect induced by the incorporation of Ag nanoparticles.36 Furthermore, the amount of silver nanoparticles in MFC/PPy/Ag aerogel was determined by TGA. At 800 °C, the residues were 29.2, 45.9 and 67.0 wt% for MFC, MFC/PPy and MPA3 aerogels, respectively. Thus, the content of silver in MPA3 was calculated to be 39.4 wt% based on the following equations: At 20 °C:

CAg + CMFC+PPy = 1

At 800 °C:

CAg + 0.459 CMFC+PPy = 0.670

where CAg is the silver weight content in the MFC/PPy/Ag hybrid aerogel at 20 °C and 800 °C; CMFC+PPy is the total weight content of MFC and PPy in the hybrid aerogel at 20 °C. The silver contents in other MFC/PPy/Ag hybrid aerogels were also calculated based on the equations and the results were shown in Figure 3b. The silver contents in the hybrid aerogels increased with the increase of AgNO3 loading. The aerogel dipping in oxidant solution with high AgNO3 percentage would contain more silver nanoparticles.

10


Page 10 of 27

Page 11 of 27

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


Figure 3. (a) TGA curves of MFC aerogels (M1), PPy, MFC/PPy and MFC/PPy/Ag (MPA3) hybrid aerogels, (b) silver content in the MFC/PPy/Ag hybrid aerogels with different pyrrole loadings. Morphology Figure 4 shows the morphology of the MFC aerogel, MFC/PPy and MFC/PPy/Ag hybrid aerogel. Figure 4a showed a three-dimensional (3D) porous network structure in M1, indicating that the MFC self-assembled into a porous structure via hydrogen bonding during the freeze-drying process. However, a two-dimensional (2D) sheet-like structure was observed in M2 and the sheets were mutually connected to form a network skeleton (Figure 4b). This microstructure difference demonstrates that the morphology can be tuned by the freezing temperature. It has been reported that the aerogel structure is directly related to the size and distribution of the ice crystals in the frozen step.2 When the MFC suspension was dipped into liquid nitrogen, the water in the MFC suspension was frozen immediately. Because of the extremely low temperature, the ice crystallized quickly and the crystal size was small, leading to the homogenous 3D structure of the aerogel.37 Since M1 showed a homogenous architecture and high porosity, we chose M1 as the templates for the preparation of MFC/PPy and MFC/PPy/Ag hybrid aerogels and -196 °C was used as the freezing temperature in the following experiment. A 2D sheet-like structure was observed in the MFC/PPy aerogels and this indicated that the 11



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

incorporation of PPy turned the 3D porous structure to a 2D sheet-like structure. A possible explanation is that the adsorption of pyrrole made the MFC close to each other and the space for dispersion of MFC was not enough. Therefore, the MFC were tightly cross-linked with each other and eventually formed 2D sheet-like structures during freeze-drying.

10

PPy particles were observed in MP demonstrating the

successful polymerization of pyrrole. The morphology of MPA3 is presented in Figure 4d. Besides the 2D sheet-like structure and the PPy particles (in the white ring), the silver nanoparticles (in the yellow ring) were visible in the MFC/PPy/Ag hybrid aerogel and they were uniformly dispersed over the surface of MFC without aggregation. In addition, EDS spectra (Figure S1) showed that the main elements in MPA3 were C, O and Ag,25 which was consistent with the XRD result. TEM image (Figure 5) demonstrated the relatively uniform deposition of Ag nanoparticles and most of the Ag nanoparticles had a diameter of 10~30 nm. According to the aforementioned results, the MFC/PPy/Ag hybrid aerogel could be fabricated via the facile dip-coating synthesis method.

12


Page 12 of 27

Page 13 of 27

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


Figure 4. SEM images of aerogels: (a) M1, (b) M2, (c) MP, (d) MFC/PPy/Ag aerogel (MPA3, The Ag nanoparticles were labelled in the yellow ring and the PPy was labelled in the white ring).

Figure 5. (a) TEM image of the Ag nanoparticles on the MFC, (b) the diameter distribution of Ag nanoparticles. Density, Porosity and Specific Area Table 2 summarizes the density, porosity and specific area of the MFC aerogels, MFC/PPy and

13



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

MFC/PPy/Ag hybrid aerogels. The measured data of the MFC aerogels is in agreement with previously reported values (2.9 mg/cm3, 99.6%, 270 m2/g) for other MFC aerogels with the same MFC concentration.10 Compared with M1, M2 showed higher density, slightly lower porosity and specific area due to formation of 2D sheet-like structure. The incorporation of PPy to the MFC aerogels resulted in slightly decrease of porosity due to the denser structure compared with the pristine MFC aerogel. Interestingly, the specific area of MFC/PPy hybrid aerogels was higher than that for the M2, which showed a 2D sheet-like structure as well. A possible explanation is that the addition of PPy roughed the surface of MFC. Compared with the MFC/PPy hybrid aerogels, the incorporation of Ag significantly increased the density of the MFC/PPy/Ag hybrid aerogel due to the high density of Ag. The density of the MFC/PPy/Ag hybrid aerogels increased with the increase of silver contents. While the porosity and specific area of the MFC/PPy/Ag hybrid aerogel were not affected by the incorporation of Ag and they were similar with that for the MFC/PPy hybrid aerogel. In summary, the incorporation of Ag increased the density and specific area of the aerogels, but the high porosity (> 99%) was maintained during the MFC/PPy/Ag hybrid aerogels preparation process.

14


Page 14 of 27

Page 15 of 27

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


Table 2 Density, porosity and specific area of the aerogels. Sample

Density (mg/cm3)

Porosity (%)

Specific area (m2/g)

M1

2.91 ± 0.27

99.8 ± 0.02

278 ± 4.6

M2

4.36 ± 0.30

99.6 ± 0.03

203 ± 5.8

MP

4.38 ± 0.25

99.6 ± 0.02

228 ± 5.4

MPA1

5.27 ± 0.25

99.6 ± 0.03

232 ± 4.8

MPA2

5.58 ± 0.25

99.6 ± 0.03

238 ± 4.9

MPA3

5.83 ± 0.24

99.6 ± 0.03

242 ± 4.3

MPA4

6.32 ± 0.28

99.5 ± 0.04

263 ± 5.8

Mechanical Properties and Shape Recovery Ability The compressive stress-strain curves of the aerogels up to 60% strain are presented in Figure 6a. As the compressive strain gradually increased from 0 to 60%, the aerogels were conformably densified and the stresses increased with the compression owing to the continuous reduction of the pore volume.8 At 60% strain, the compressive stress of M1 and M2 were 12.89 kPa and 10.39 kPa, respectively. The reason for the slightly higher compressive stress of M1 was that the individual cellulose nanofibers in M1 would touch each other to increase the compressive resistance during the compression process. higher than that in previous reports, such as 8.5 kPa for MFC aerogels

11

38

These values were

and 8.9 kPa for CNC aerogels.1

The compressive stress of MP was 9.99 kPa at 60% strain, which was slightly lower than that for the pristine MFC aerogel due to the decrease in the degree of hydrogen bonding within the MFC network after 15



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

the incorporation of PPy. Compared with MP, the incorporation of Ag increased the compressive stress of MPA1and MPA3 to 11.65 kPa and 12.81 kPa at 60% strain, which was comparable to that for the pristine MFC aerogels. These results revealed that the incorporation of PPy and Ag using the dip-coating method induced no significant changes to the mechanical properties of the pristine MFC aerogels. The shape recovery of the aerogels was evaluated by unloading the compressed aerogels and recording the residual strain. Figure 6b presents the shape recovery of the aerogels, which was expressed as the percentage of the original thickness of the aerogels. The shape recovery of M1was about 51%, which was higher than the 47% for M2. The improved shape recovery could be attributed to the 3D porous network structure. Surprisingly, the highest shape recovery was obtained with the MP, which could recover up to 72% of its original thickness. This result can be ascribed to the steric hindrance existing between the penta cyclic of PPy and similar phenomenon has been reported for silica aerogels39 and MFC aerogels.40 Compared with MP, MPA1 and MPA3 exhibited slightly lower shape recovery because the hard Ag would destruct the elasticity of the cellulose nanofibers,41 but they still higher than that for the pristine MFC aerogels. In general, the incorporation of PPy and Ag improved the shape recovery ability of the pristine MFC aerogel.

16


Page 16 of 27

Page 17 of 27

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


Figure 6. Compressive stress-strain curves of aerogels compressed to 60% strain (a) and shape recovery of the aerogels upon unloading from 60% compression strain (b). Antimicrobial Properties and Cytotoxicity Evaluation The antimicrobial properties of the aerogels were tested on a Gram-negative bacteria (E. coli) and a Gram-positive bacteria (S. aureus). As shown in Figure 7, the pristine MFC aerogel did not show any inhibition against the tested bacteria. Whereas the MFC/PPy aerogels exhibited antimicrobial activity against E. coli due to the antimicrobial property of PPy, the inhibition effect against S. aureus could be ignored. The incorporation of Ag to the MFC/PPy aerogel resulted in significant antimicrobial activity against the Gram-positive bacteria S. aureus, which was a common cutaneous bacterium and pathogen. It has also been reported that PPy/Ag nanocomposites on cotton fabrics and on the cellulose fibers showed antimicrobial activity against S. aureus.

25-26

The cytotoxicity evaluation of the obtained aerogels were 17



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

performed using the Mouse embryo fibroblast (L929) cells. As shown in Figure 7e, the MFC aerogel showed almost no toxicity to L929 cells after 24 h and 48 h incubation. Although the introduction of PPy and Ag nanoparticles led to a slight decrease of cytocompatibility, 92% cell viability was still maintained. Considering the antimicrobial properties and the good cytocompatibility of MFC/PPy/Ag hybrid aerogel, the hybrid aerogel is a promising candidate for drug delivery and wound healing materials.

Figure 7. Antimicrobial activities of the MFC, MFC/PPy and MFC/PPy/Ag (MPA3) aerogels: (a, b) Escherichia coli and (c, d) Staphylococcus aureus, (e) viability of L929 cells cultured on different aerogels. Electrical Conductivity and Pressure Responsiveness The electrical conductivity of the aerogels is shown in Table S2. The pure MFC aerogels were electrically nonconductive and the introduction of electrically conducting PPy significantly increased the conductivity of the hybrid aerogels. One can note that the MFC/PPy aerogel showed a conductivity of 0.52 S m-1, which was comparable to other PPy-cellulose composites (10-1-10-2 S m-1).20, 33 Theoretically, the incorporation of Ag would improve the electrical conductivity of the MFC/PPy/Ag hybrid aerogel. However, all of the hybrid aerogels exhibited similar electrical conductivity, indicating that the Ag did not improve the electrical conductivity of the hybrid aerogel. A possible explanation is that the interface contact 18


Page 18 of 27

Page 19 of 27

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


points of Ag on the surface of MFC was not enough to form a continuous silver network, which could increase the conductivity of the MFC/PPy/Ag hybrid aerogel. The combined electrical conductive and compressible properties of the hybrid aerogels result in their pressure responsive property. The relationship between the electrical conductivity and the compressive strain of the MFC/PPy aerogel and MFC/PPy/Ag aerogel (MPA3 as a representative sample) are shown in Figure 8. Generally, when MP and MPA3 were gradually compressed from 0% to 90% strain, the electrical conductivity of the aerogels increased, because the interface contact points of the conductive PPy and Ag nanoparticles in the hybrid aerogel increased with the increase of the compressive strain, thus leading to the raise of electrical conductivity. In the region of 0% to 30% compressive strain, MPA3 exhibited a conductivity from 0.53 S m-1 to 2.50 S m-1, which was roughly the same with that for MP (from 0.52 S m-1 to 2.16 S m-1), because that the interface contact points of Ag on the surface of MFC was not enough to form a continuous silver network, which could increase the conductivity of the MFC/PPy/Ag hybrid aerogel. When the compressive strain increased from 30% to 70%, the increase of electrical conductivity for MPA3 became fast (from 2.50 S m-1 to 15.47 S m-1) compared to the MP (from 2.16 S m-1 to 3.85 S m-1). In this region, the interface contact points of silver nanoparticles increased and formed a continuous silver network, thus leading to the rapid increase of conductivity for MPA3. In the region from 70% to 90% strain, the increase of the electrical conductivity for MP and MPA3 became slowly, because the aerogels had become densified, and only few new interface contact points were formed during the compression process. At 90% strain, MPA3 showed a conductivity of 18.03 S m-1, which was about 4.3 times that for MP at the same strain, indicating that the incorporation of Ag significantly improved the conductivity of the hybrid aerogels at compressed state (>30% 19



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

strain). The hybrid aerogel has the potential to be used as electrical and pressure-sensitive materials due to the electrical conductive property and the relationship between the conductivity and compressive strain.

Figure 8. The correlation between compressive strain and electrical conductivity of the hybrid aerogels.

Conclusions In conclusion, we prepared MFC aerogels with high porosity, high specific area and low density by freeze-drying. The obtained MFC aerogels showed 3D porous structure or 2D sheet-like structure and the morphology of the aerogels could be tuned by the freezing temperature. Furthermore, we synthesized MFC/PPy/Ag hybrid aerogels using the obtained MFC aerogels as templates by a simple dip-coating method. The as-prepared hybrid aerogels exhibited enhanced antimicrobial, electrical conductive, pressure responsive properties and they could be used as drug delivery, wound healing, energy storage and pressure sensing materials. Moreover, this is a low-cost、efficient and environmentally friendly process to realize fine dispersion of nanoparticles in cellulose aerogel and the attractive properties of the pristine aerogels can be preserved during the preparation process. We foresee that the facile and intriguing preparation strategy may provide some new insights into the synthesis of multifunctional aerogels. 20


Page 20 of 27

Page 21 of 27

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


Supporting Information Description of cytotoxicity evaluation procedure; photographs of MFC aerogel dipping in the pyrrole solution and AgNO3 solution; EDS spectra of MFC/PPy/Ag hybrid aerogels; nitrogen adsorption-desorption isotherms of the aerogels; shape recovery of the aerogels upon unloading from 50% and 40% compression strain; the antimicrobial effects of the hybrid aerogels; the electrical conductivity of the aerogels. This material is available free of charge via the Internet at http:// pubs.acs.org. Corresponding Author E-mail: [email protected]. Notes The authors declare no competing financial interest. Acknowledgements The authors gratefully acknowledge the financial support from Chinese Ministry of Education (113014A), National Science Foundation for Distinguished Young Scholars of China (31225005) and the Excellent Beijing Doctorial Dissertations Project for Adviser (20131002201). References 1.

Yang, X.; Cranston, E. D. Chemically cross-linked cellulose nanocrystal aerogels with shape recovery

and superabsorbent properties. Chem. Mater. 2014, 26 (20), 6016-6025. 2.

Wang, M.; Anoshkin, I. V.; Nasibulin, A. G.; Korhonen, J. T.; Seitsonen, J.; Pere, J.; Kauppinen, E. I.;

Ras, R. H. A.; Ikkala, O. Modifying native nanocellulose aerogels with carbon nanotubes for mechanoresponsive conductivity and pressure sensing. Adv. Mater. 2013, 25 (17), 2428-2432. 3.

Fu, R.; Zheng, B.; Liu, J.; Dresselhaus, M. S.; Dresselhaus, G.; Satcher, J. H.; Baumann, T. F. The 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

fabrication and characterization of carbon aerogels by gelation and supercritical drying in isopropanol. Adv. Funct. Mater. 2003, 13 (7), 558-562. 4.

Tan, C.; Fung, B. M.; Newman, J. K.; Vu, C. Organic aerogels with very high impact strength. Adv.

Mater. 2001, 13 (9), 644-646. 5.

Han, W.; Ren, L.; Gong, L.; Qi, X.; Liu, Y.; Yang, L.; Wei, X.; Zhong, J. Self-assembled

three-dimensional graphene-based aerogel with embedded multifarious functional nanoparticles and its excellent photoelectrochemical activities. ACS Sustainable Chem. Eng. 2014, 2 (4), 741-748. 6.

Hamedi, M.; Karabulut, E.; Marais, A.; Herland, A.; Nyström, G.; Wågberg, L. Nanocellulose

aerogels functionalized by rapid layer-by-layer assembly for high charge storage and beyond. Angew. Chem. Int. Edit. 2013, 52 (46), 12038-12042. 7.

Chen, W.; Yu, H.; Li, Q.; Liu, Y.; Li, J. Ultralight and highly flexible aerogels with long cellulose I

nanofibers. Soft Matter 2011, 7 (21), 10360-10368. 8.

Paakko, M.; Vapaavuori, J.; Silvennoinen, R.; Kosonen, H.; Ankerfors, M.; Lindstrom, T.; Berglund, L.

A.; Ikkala, O. Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalities. Soft Matter 2008, 4 (12), 2492-2499. 9.

Okita, Y.; Fujisawa, S.; Saito, T.; Isogai, A. TEMPO-oxidized cellulose nanofibrils dispersed in

organic solvents. Biomacromolecules 2010, 12 (2), 518-522. 10. Chen, W.; Li, Q.; Wang, Y.; Yi, X.; Zeng, J.; Yu, H.; Liu, Y.; Li, J. Comparative study of aerogels obtained from differently prepared nanocellulose fibers. ChemSusChem 2014, 7 (1), 154-161. 11. Jiang, F.; Hsieh, Y.-L. Amphiphilic superabsorbent cellulose nanofibril aerogels. J. Mater. Chem. A 2014, 2 (18), 6337-6342. 22


Page 22 of 27

Page 23 of 27

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


12. Jiang, F.; Hsieh, Y.-L. Super water absorbing and shape memory nanocellulose aerogels from TEMPO-oxidized cellulose nanofibrils via cyclic freezing-thawing. J. Mater. Chem. A 2014, 2 (2), 350-359. 13. Wang, Z.; Tammela, P.; Zhang, P.; Huo, J.; Ericson, F.; Stromme, M.; Nyholm, L. Freestanding nanocellulose-composite fibre reinforced 3d polypyrrole electrodes for energy storage applications. Nanoscale 2014, 6 (21), 13068-13075. 14. Korhonen, J. T.; Hiekkataipale, P.; Malm, J.; Karppinen, M.; Ikkala, O.; Ras, R. H. A. Inorganic hollow nanotube aerogels by atomic layer deposition onto native nanocellulose templates. ACS Nano 2011, 5 (3), 1967-1974. 15. Han, Y.; Zhang, X.; Wu, X.; Lu, C. Flame retardant, heat insulating cellulose aerogels from waste cotton fabrics by in situ formation of magnesium hydroxide nanoparticles in cellulose gel nanostructures. ACS Sustainable Chem. Eng. 2015, 3 (8), 1853-1859. 16. Olsson, R. T.; Azizi Samir, M. A. S.; Salazar Alvarez, G.; BelovaL; StromV; Berglund, L. A.; IkkalaO; NoguesJ; Gedde, U. W. Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates. Nat. Nanotechnol. 2010, 5 (8), 584-588. 17. Zhou, Z.; Zhang, X.; Lu, C.; Lan, L.; Yuan, G. Polyaniline-decorated cellulose aerogel nanocomposite with strong interfacial adhesion and enhanced photocatalytic activity. RSC Adv. 2014, 4 (18), 8966-8972. 18. Bober, P.; Liu, J.; Mikkonen, K. S.; Ihalainen, P.; Pesonen, M.; Plumed-Ferrer, C.; von Wright, A.; Lindfors, T.; Xu, C.; Latonen, R.-M. Biocomposites of nanofibrillated cellulose, polypyrrole, and silver nanoparticles with electroconductive and antimicrobial properties. Biomacromolecules 2014, 15 (10), 3655-3663. 19. Mihranyan, A.; Nyholm, L.; Bennett, A. E. G.; Strømme, M. A novel high specific surface area 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

conducting paper material composed of polypyrrole and cladophora cellulose. J. Phys. Chem. B 2008, 112 (39), 12249-12255. 20. Varesano, A.; Vineis, C.; Aluigi, A.; Rombaldoni, F.; Tonetti, C.; Mazzuchetti, G. Antibacterial efficacy of polypyrrole in textile applications. Fiber Polym. 2013, 14 (1), 36-42. 21. Huang, J.; Ichinose, I.; Kunitake, T. Nanocoating of natural cellulose fibers with conjugated polymer: Hierarchical polypyrrole composite materials. Chem. Comm. 2005,

(13), 1717-1719.

22. Proń, A.; Kucharski, Z.; Budrowski, C.; Zagórska, M.; Krichene, S.; Suwalski, J.; Dehe, G.; Lefrant, S. Mössbauer spectroscopy studies of selected conducting polypyrroles. J. Chem. Phys. 1985, 83 (11), 5923-5927. 23. Blinova, N. V.; Stejskal, J.; Trchová, M.; Prokeš, J.; Omastová, M. Polyaniline and polypyrrole: A comparative study of the preparation. Eur. Polym. J. 2007, 43 (6), 2331-2341. 24. Omastová, M.; Mosnáčková, K.; Trchová, M.; Konyushenko, E. N.; Stejskal, J.; Fedorko, P.; Prokeš, J. Polypyrrole and polyaniline prepared with cerium(IV) sulfate oxidant. Synth. Met. 2010, 160 (7–8), 701-707. 25. Omastová, M.; Mosnáčková, K.; Fedorko, P.; Trchová, M.; Stejskal, J. Polypyrrole/silver composites prepared by single-step synthesis. Synth. Met. 2013, 166 (0), 57-62. 26. Firoz Babu, K.; Dhandapani, P.; Maruthamuthu, S.; Anbu Kulandainathan, M. One pot synthesis of polypyrrole silver nanocomposite on cotton fabrics for multifunctional property. Carbohyd. Polym. 2012, 90 (4), 1557-1563. 27. Nyström, G.; Mihranyan, A.; Razaq, A.; Lindström, T.; Nyholm, L.; Strømme, M. A nanocellulose polypyrrole composite based on microfibrillated cellulose from wood. J. Phys. Chem. B 2010, 114 (12), 24


Page 24 of 27

Page 25 of 27

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


4178-4182. 28. Saito, T.; Hirota, M.; Tamura, N.; Kimura, S.; Fukuzumi, H.; Heux, L.; Isogai, A. Individualization of nano-sized plant cellulose fibrils by direct surface carboxylation using TEMPO catalyst under neutral conditions. Biomacromolecules 2009, 10 (7), 1992-1996. 29. Song, J.; Zhang, P.; Cheng, L.; Liao, Y.; Xu, B.; Bao, R.; Wang, W.; Liu, W. Nano-silver in situ hybridized collagen scaffolds for regeneration of infected full-thickness burn skin. J. Mater. Chem. B 2015. 30. Kato, H.; Nishikawa, O.; Matsui, T.; Honma, S.; Kokado, H. Fourier transform infrared spectroscopy study of conducting polymer polypyrrole: Higher order structure of electrochemically-synthesized film. J. Phys. Chem. 1991, 95 (15), 6014-6016. 31. Omastová, M.; Trchová, M.; Pionteck, J.; Prokeš, J.; Stejskal, J. Effect of polymerization conditions on the properties of polypyrrole prepared in the presence of sodium bis(2-ethylhexyl) sulfosuccinate. Synth. Met. 2004, 143 (2), 153-161. 32. Luong, N. D.; Korhonen, J. T.; Soininen, A. J.; Ruokolainen, J.; Johansson, L.-S.; Seppälä, J. Processable polyaniline suspensions through in situ polymerization onto nanocellulose. Eur. Polym. J. 2013, 49 (2), 335-344. 33. Müller, D.; Rambo, C. R.; D.O.S.Recouvreux; Porto, L. M.; Barra, G. M. O. Chemical in situ polymerization of polypyrrole on bacterial cellulose nanofibers. Synth. Met. 2011, 161 (1–2), 106-111. 34. Wang, H.; Bian, L.; Zhou, P.; Tang, J.; Tang, W. Core-sheath structured bacterial cellulose/polypyrrole nanocomposites with excellent conductivity as supercapacitors. J. Mater. Chem. A 2013, 1 (3), 578-584. 35. Lee, K.-Y.; Quero, F.; Blaker, J.; Hill, C. S.; Eichhorn, S.; Bismarck, A. Surface only modification of bacterial cellulose nanofibres with organic acids. Cellulose 2011, 18 (3), 595-605. 25



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

36. Lin, N.; Dufresne, A. Physical and/or chemical compatibilization of extruded cellulose nanocrystal reinforced polystyrene nanocomposites. Macromolecules 2013, 46 (14), 5570-5583. 37. Zhang, W.; Zhang, Y.; Lu, C.; Deng, Y. Aerogels from crosslinked cellulose nano/micro-fibrils and their fast shape recovery property in water. J. Mater. Chem. 2012, 22 (23), 11642-11650. 38. Sai, H.; Fu, R.; Xing, L.; Xiang, J.; Li, Z.; Li, F.; Zhang, T. Surface modification of bacterial cellulose aerogels’ web-like skeleton for oil/water separation. ACS Appl. Mater. Interfaces 2015, 7 (13), 7373-7381. 39. Kanamori, K.; Aizawa, M.; Nakanishi, K.; Hanada, T. New transparent methylsilsesquioxane aerogels and xerogels with improved mechanical properties. Adv. Mater. 2007, 19 (12), 1589-1593. 40. Zhang, Z.; Sèbe, G.; Rentsch, D.; Zimmermann, T.; Tingaut, P. Ultralightweight and flexible silylated nanocellulose sponges for the selective removal of oil from water. Chem. Mater. 2014, 26 (8), 2659-2668. 41. Ishikawa, M.; Oaki, Y.; Tanaka, Y.; Kakisawa, H.; Salazar-Alvarez, G.; Imai, H. Fabrication of nanocellulose-hydroxyapatite composites and their application as water-resistant transparent coatings. J. Mater. Chem. B 2015, 3 (28), 5858-5863. Table of Contents Graphic

Synopsis: Electrical conductive, pressure responsive and antimicrobial MFC/PPy/Ag hybrid aerogel was 26


Page 26 of 27

Page 27 of 27

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


prepared from sustainable MFC aerogel by using a simple dip-coating method.

27


Polypyrrole

Recommend Documents