A Novel UV-Shielding and Transparent Polymer Film: When Bio

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A Novel UV-Shielding and Transparent Polymer Film: When Bioinspired Dopamine-Melanin Hollow Nanoparticles Join Polymer Yang Wang, Jing Su, Ting Li, Piming Ma, Huiyu Bai, Yi Xie, Mingqing Chen, and Weifu Dong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b08763 • Publication Date (Web): 25 Sep 2017 Downloaded from http://pubs.acs.org on September 25, 2017

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ACS Applied Materials & Interfaces

A Novel UV-Shielding and Transparent Polymer Film:

When

Bio-inspired

Dopamine-Melanin

Hollow Nanoparticles Join Polymer Yang Wang, Jing Su, Ting Li, Piming Ma, Huiyu Bai, Yi Xie, Mingqing Chen*, and Weifu Dong* * Corresponding author. E-mail: [email protected]. [email protected].

Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China Keywords: dopamine-melanin, hollow nanoparticles, polymer, transparency, UV-shielding

ABSTRACT: Ultraviolet (UV) light is known to be harmful to human health and cause organic materials to undergo photodegradation. In this article, bio-inspired dopamine-melanin solid nanoparticles (Dpa-s NPs) and hollow nanoparticles (Dpa-h NPs) as UV-absorbers were introduced to enhance the UV-shielding performance of polymer. First, Dpa-s NPs were synthesized through autoxidation of dopamine in alkaline aqueous solution. Dpa-h NPs were prepared by the spontaneous oxidative polymerization of dopamine solution onto polystyrene (PS) nanospheres template, followed by removal of the template. Poly(vinyl alcohol) (PVA)/Dpa nanocomposite films were subsequently fabricated by a simple casting solvent. UV irradiation

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protocols were set up, allowing selective study of the extra-shielding effects of Dpa-s vs Dpa-h NPs. In contrast to PVA/Dpa-s films, PVA/Dpa-h films exhibit stronger UV-shielding capabilities and can almost block the complete UV region (200-400 nm). The excellent UVshielding performance of the PVA/Dpa-h films mainly arises from multiple absorption due to hollow structure and large specific area of Dpa-h NPs. Moreover, the wall thickness of Dpa-h NPs can be simply controlled from 28 to 8 nm depending on the ratio between PS and dopamine. The resulting films with Dpa-h NPs (wall thickness ~8 nm) maintained relatively high transparency to visible light because of the thinner wall thickness. The results indicate that the prepared Dpa-h NPs can be used as a novel UV absorber for next-generation transparent UVshielding materials.

INTRODUCTION The ultraviolet (UV) region of solar UV light includes wavelengths that fall in UVC (220−280 nm), UVB (280−320 nm), and UVA (320−400 nm) categories. The overexposure of UV radiation can deeply cause severe negative effects on human health.1 UV light can also activate chromophores and promote photodegradation of polymer materials.2-3 In this context, ultraviolet protective materials have gained an extent of attention, particularly for fabricating optically transparent and UV-shielding polymeric composites via the addition of organic and inorganic UV absorbers.4 Although, the majority of traditional organic UV absorbers showing a good UV-block performance, they also suffer from photodegradation, migration, and aggregation.5-6 Inorganic metal oxide nanoparticles (e.g., TiO2, ZnO, SiO2, and Al2O3) can also absorb UV radiation.4,

7-10

Whereas, owning to the inherently wide band gaps, their UV


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absorption is not complete.11 On the other hand, inorganic nanoparticles always show obvious photocatalytic effects and can degrade polymer matrices.12 Recently, Hernán Míguez et al fabricated photonic crystal multilayers based on ZrO2/SiO2 nanoparticles.13-14 The film exhibited strong UV-shielding behavior without photocatalytic effect. However, the transparency of the film is only ~60%, and the process is relatively complicated. Therefore, it is necessary to search for transparent UV-shielding materials with excellent UV-shielding performance over the whole UV region. To date, ongoing efforts are focused on using solid nanoparticles as UV-absorbers. Generally, the properties of solid nanoparticles are mainly determined by their sizes and morphologies. In contrast to solid nanoparticles, hollow nanostructures always show improved performance when used as optical material, because of their porosity, lower density, lower refractive index and high surface areas. Natural melanin nanoparticles is a special kind of biomacromolecules with many functions, such as photoprotection, photothermal conversion, and free radical scavenging property.15-21 Our previous work reported polymer-based UV-shielding materials with outstanding photostability by incorporating sepia eumelanin.22 However, the shielding property to the UVA region of this films is about only 30%. And it is a challenge to get a good balance between shielding property and transparency. Synthetic melanin nanoparticles (often termed “polydopamine”), which is usually prepared by chemical oxidation of dopamine, exhibit similar physical and chemical properties to natural melanin.23-24 Generally, dopamine-melanin oligomer self-assemble to form nanoparticles that further aggregate and form black precipitate in the solution.25 In recent years, many different structures of dopamine-melanin, such as capsule and core-shell structures are of particular interest because of their unique structural properties and potential applications as drug delivery, catalysts, and biomedical materials.26-29 Dopamine-melanin layer onto particles


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followed by the removal of inner template to form robust dopamine-melanin capsules. It has attracted extensive attention due to its advantages of precise control over the size, wall thickness and functions of the obtained capsules. To the best of our knowledge, the use of dopaminemelanin hollow nanoparticles as UV absorber rarely has been reported. Taken above into account, the strategy of this study is to investigate the UV-shielding effects of hollow dopamine-melanin nanoparticles, analyze the mechanism involved, and establish a comparison with that of solid dopamine-melanin nanoparticles. To achieve those goals, solid dopamine-melanin nanoparticles (Dpa-s NPs) and hollow dopamine-melanin nanoparticles (Dpa-h NPs) with similar size and shape were prepared. PVA/Dpa nanocomposite films were prepared by a green and simple solution-cast method. To demonstrate the intricate structure-function correlation, UV−vis absorption spectra and Rhodamine B photodegradation measurement were carried out. It was found that PVA/Dpa-s films can merely shield against UV light with wave-length lower than 300 nm and are not sensitive to radiation in the 300-400 nm region. In contrast, PVA films with the addition of Dpa-h NPs almost block the whole UV light (200-400 nm). Interestingly, the transmittance of nanocomposite films can also be improved with decreasing the wall thickness of Dpa-h NPs. The results are promising for new production of a significant UV-shielding and transparent material for photosensitive substances. EXPERIMENTAL SECTION Materials. Poly(vinyl alcohol) (PVA) was purchased from Sinopec Ningxia Vinylon Works. Styrene (St, 98% Aldrich), 2,2’-azobis(2-methyl propionamidine) dihydrochloride (AIBA, 97%, Aldrich co., USA) were used without further purification. Poly (vinyl pyrrolidone) (PVP, Mw = 55,000


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g/mol) was used as a stabilizer. Dopamine hydrochloride, and RhB were all ware purchased from Aladdin Industrial. Synthesis of Dpa-s NPs with a diameter of ~150 nm Dpa-s NPs were prepared according to the literature.23 Dopamine hydrochloride and NaOH solution were added to deionized water, and magnetically stirred. Dpa-s NPs were purified repeatedly by centrifugation (15000 rpm for 30 min). Synthesis of Dpa-h NPs The monodisperse PS nanospheres were prepared according to the literature.30 In brief, PVP (4.12 g) and AIBA (0.05 g) were dissolved in deionized water (250 mL), and St (25 g) was added to above mixture. The reaction temperature was gradually increased to 70 ℃ and kept for 24 h. The products were cooled in an ice bath and filtered to remove any aggregates. The PS nanoparticles were purified by repeated centrifugation (14500 rpm for 30 min) and washed with deionized water three times. The as-prepared PS nanospheres (0.2 g) were added into Tris/HCl (pH=8.5, 90 mL) buffer with dopamine (0.1 g) to prepare core-shell NPs (PS@Dpa). The reaction proceeded for 24 h at room temperature with constant shaking. PS@Dpa NPs were centrifuged (14500 rpm for 30 min) and washed with water. The Dpa-h NPs were obtained by etching the PS cores from PS@Dpa NPs with THF. The resulting Dpa-h nanoparticles were washed with deionized water three times by centrifugation/redispersion cycles. Preparation of PVA/Dpa nanocomposites films PVA/Dpa nanocomposite films were prepared by casting method. Dpa-s NPs and Dpa-h NPs (prescribed amount) were added into aqueous PVA solution and stirred to obtain homogeneous mixture. Then nanocomposite films were prepared by solution casting and were


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dried in vacuum oven at 80 ℃ for 6 h. The resulting films were quite uniform with an average thickness of about 35 µm. UV-shielding performance of PVA and nanocomposite films The UV absorption properties of nanocomposite films were investigated by absorption spectroscopy using a UV−vis spectra. The transmittance date were used to calculate the ultraviolet protection factor (UPF) using the following equations:

UV protection factor UPF =

(1)

where E(λ) is the relative erythema action spectrum, S(λ) is the spectral irradiance (Wm-2 nm1

), T(λ) is average spectral transmittance of fabric, dλ is bandwidth, λ is wave length.

The percentage blocking for UV-A (320-400 nm) was calculated by Eq. (2):

UV − A blocking% = 100 −

&

&

%

(2)

The percentage blocking for UV-B (280-320 nm) was calculated by Eq. (3): &

UV − B blocking% = 100 −

&

%

(3)

The UPF value is used to estimate how much the material reduces UV exposure. UV-shielding performance of PVA and nanocomposite films The degradation behavior of RhB solution in the presence of photocatalyst (TiO2) under high-pressure mercury lamp (150 W) was conducted to evaluate the UV-shielding performance of films. Briefly, 25 mg TiO2 and 50 mL of RhB solution (1×10-5 M) were mixed for complete dispersion. Prior to irradiation, the suspension was stirred in the dark for 30 min at ambient temperature to reach adsorption/desorption equilibrium. PVA or nanocomposite films was used to cover the mouth of the beaker before UV irradiation. The distance between of the lamp and the film was about 10 cm. The photocatalytic degradation of RhB solution was carried out under


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constant stirring. At given intervals (t), 4 mL of the suspension were collected and centrifuged to remove the photocatalyst. The absorbance of RhB at 552 nm was measured by a TU-1901 UV−vis spectrophotometer. The UV-shielding performance was calculated as I =At/A0×100%, where A0 is the initial absorbance of RhB solution without UV radiation, At is the absorbance of the remaining RhB solution protected with film under UV radiation. Characterizations The morphologies of synthesized Dpa-s NPs and Dpa-h NPs were observed using scanning electron microscopy (SEM, HITACHI S4800) and transmission electron microscopy (TEM, Philips TECNAI 20).The Brunauer–Emmet–Teller (BET) surface area was determined by using a Micromeritics ASAP 2020 MP instrument with nitrogen adsorption at 77 K. FT−IR spectra of samples were recorded on a Nicolet 6700 FT-IR spectrometer. A total of 50 scans in wavenumber range 4000-400 cm-1 were taken, with resolution of 4cm-1. The optical properties of samples were investigated using a TU-1901 UV-vis spectrophotometer. The cross-sectional surfaces of the pure PVA and PVA/Dpa nanocomposites were carried out on SEM. The samples were fractured in liquid nitrogen. Results and discussion Dpa-s NPs were synthesized by oxidation of dopamine similar to previous reports.23 Dopamine was dissolved in deionized water under mild stirring. NaOH solution were injected into the above mixture solution. The reaction was allowed to proceed for 5 h. Dpa-s NPs were obtained by centrifugation and washed with deionized water for three times. TEM and SEM images show the size and shape of generated Dpa-s NPs (ca. 150 nm size spheres, Figure 1).


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Figure 1. SEM images of Dpa-s NPs. Dpa-h NPs were prepared according to Scheme1. First, monodisperse PS spheres were synthesized as template materials and coated with oxidation and self-polymerization of dopamine. SEM image of PS and PS@Dpa core-shell NPs are shown in Figure 2. All NPs are spherical in shape and can be well dispersed in water. PS spheres show a smooth spherical morphology with an average diameter of 120 nm. PS@Dpa NPs have a clearly distinguish from PS spheres. The size of obtained PS@Dpa NPs is around 150 nm, and the surfaces of PS@Dpa NPs are much rougher than those of PS spheres. Then Dpa-h NPs were formed after selective etching PS core by THF.


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Scheme 1. Procedure for the fabrication of Dpa-s and Dpa-h NPs.

Figure 2. SEM images of synthesized PS spheres (a, b) and PS@Dpa core-shell spheres (c, d) respectively.


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The TEM images of Dpa-s and Dpa-h NPs are shown in Figure 3a-c. The hollow structure of Dpa-h NPs can be clearly viewed, and the wall thickness of Dpa-h NPs is about 15 nm (Figure 3c). The hollow characteristics of Dpa-h NPs are also disclosed by the presence of several broken nanoparticles (inset in Figure 3b), Figure 3d shows nitrogen adsorption-desorption isotherms of as-obtained Dpa-s and Dpa-h NPs. The surface area of Dpas NPs is only 10.5 m2g-1. Dpa-h NPs show large surface area as 55.3 m2g-1.

Figure 3. TEM images of (a) Dpa-s NPs and (b,c) Dpa-h NPs at different magnifications (Inset b shows SEM image of Dpa-h NPs). (d) Nitrogen adsorption–desorption isotherms of samples.


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The FT-IR spectra of Dpa-s and Dpa-h NPs were collected, as shown in Figure 4a. The two FT-IR spectra are almost equivalent to each other. The peaks from 3700 to 3300 cm-1 is attributed to ν(N−H) and ν(O−H) stretching modes. The absorption peaks at 1615 cm-1 is attributed to stretching of C=C bond of aromatic rings, and the peak at 1520 cm-1 is assigned to of C−N in indolequinone.31 The UV−vis absorption spectra of Dpa-s NPs and Dpa-h NPs are illustrated in Figure 4b. Dpa-s NPs exhibits a broad band monotonic absorbance, which is consistent with the well-known optical characteristics of natural melanin related to photoprotection.32 In contrast, Dpa-h NPs have a stronger absorption over the wavelength range of 200-350 nm due to larger surface and pore volume.

a

b

Dpa-s Dpa-h

1.0

Dpa-s Dpa-h 0.8

1615

Absorbance

1

Transmittance (%)

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


1520

0.6

3500

3000

2500

2000

1500

-1

1000

2

0.4

0.2

4000

2

0.0 200

1

300

400

Wavenumber (cm )

500

600

700

800

Wavelength (nm)

Figure 4. FT-IR spectra (a) and UV−vis absorption spectra (b) of Dpa-s and Dpa-h NPs (The inset shows photograph of Dpa NPs dispersed in water). UV-shielding performance of PVA/Dpa nanocomposite Films Figure 5 presents the UV−vis transmittance spectra of pure PVA film and PVA/Dpa nanocomposite films. PVA/Dpa-s films can almost block the whole UV light below 300 nm even with a low content of Dpa-s NPs (0.5 vol %). When Dpa-s NPs increases to 1 vol %,


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about 88 % of UVB light and 67% of UVA light are shielded, whereas the transparency deceases. More interestingly, PVA/Dpa-h nanocomposite films have relatively wider UVshielding bands and high UV-shielding efficiency. For instance, PVA/Dpa-h (0.5 vol %) film completely block UV light below 320 nm containing the whole UVB light. When 1 vol % of Dpa-h NPs are used, about 84% of the UVA is efficiently filtered out. Besides the UVshielding property, PVA/Dpa-h film is more transparent in the visible range than that of PVA/Dpa-s film. Table 1 shows the percentage UV-A and UV-B radiation blocking and UPF of pure PVA and PVA nanocomposite films. The UPF values of PVA film is very low (about 1). With increasing Dpa-s NPs loading to 2 vol %, the UPF of film is about 20.01. Furthermore, the UPF values of PVA/Dpa-h (2 vol %) film is as high as 84.51.

a

100

b

UVC UVB UVA 80

60

40 PVA 0.5 vol% 1 vol% 2 vol% 5 vol%

20

0 200

100 UVC UVB UVA 80

300

400

500

600

700

800

Transmittance (%)

Transmittance (%)

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

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60

40 PVA 0.5 vol% 1 vol% 2 vol% 5 vol%

20

0 200

300

400

500

600

700

800

Wavelength (nm)

Wavelength (nm)

Figure 5. UV−vis light transmittance spectra of (a) PVA/Dpa-s films and (b) PVA/Dpa-h films. Table 1. Percentage of blocking from UV-A and UV-B and UPF values of samples. Sample

Percentage blocking

UPF value


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UV-A

UV-B

PVA

11.65

14.95

1.15

Dpa-s 0.5 vol %

44.01

74.88

2.20

Dpa-s 1 vol %

70.88

89.00

4.33

Dpa-s 2 vol %

93.47

98.10

20.01

Dpa-s 5 vol %

99.48

99.99

286.05

Dpa-h 0.5 vol %

48.53

99.93

2.92

Dpa-h 1 vol %

84.40

99.95

9.60

Dpa-h 2 vol %

98.22

99.99

84.51

Dpa-h 5 vol %

99.80

99.99

645.16

The UV-shielding performance of PVA and PVA nanocomposite films was further evaluated by photocatalytic degradation of RhB solution in the presence of TiO2 nanoparticles. As shown in Figure 6, PVA-protected RhB is completely degraded after irradiation for 60 min, whereas the RhB protected by PVA/Dpa-s (0.5 vol %) shows a decrease of 40%. With increasing Dpa-s NPs concentration to 2 vol %, the degraded content of RhB is about 16%. In contrast, about 25% of RhB is degraded for the sample protected by PVA/Dpa-h (0.5 vol %) film after UV radiation. As the amount of Dpa-h NPs increases, the degradation rate rapidly reduces. When the PVA/Dpa-h (2 vol %) is used as the protecting film, only 3% of RhB is degraded, indicating the excellent UV-shielding efficiency of PVA/Dpa-h nanocomposites. The reason for this UV-shielding properties is that dopaminemelanin NPs can rapidly convert the photon energy of UV light into heat. Moreover, PVA/Dpa-h nanocomposites have higher efficiency for UV-shielding performance. Generally, when UV light radiates on nanoparticle, it reflects on surface as normal particle morphology. On the other hand, the nanoparticles can inevitably lead to light scattering.


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However, the holes of Dpa-h NPs allow the UV light to shines in the inside of hollow nanoparticles, and make it difficult for the UV light to go out. After many times of reflection and absorption inside of hollow nanoparticles, the UV light will be completely captured and absorbed by Dpa-h NPs finally. Correspondingly, the UV-shielding mechanisms are shown in Scheme 2.

a

100

b

At/A0 (%)

60

40

PVA 0.5 vol% 1 vol% 2 vol% 5 vol%

20

0

100

80

80

At/A0 (%)

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

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0

10

60

40

PVA 0.5 vol% 1 vol% 2 vol% 5 vol%

20

20

30

40

50

60

0

0

10

20

Time (min)

30

40

50

60

Time (min)

Figure 6. Photodegradation curves of RhB solutions protected by (a) PVA/Dpa-s and (b) PVA/Dpa-h nanocomposite films, respectively. (The inserted photographs: the original RhB solution, the solution protected with PVA and nanocomposite films)


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Scheme 2. Schematic illustration of the UV-shielding mechanisms of PVA/Dpa-s and PVA/Dpa-h nanocomposites, respectively. Effect of Dpa-s and Dpa-h NPs on optical constants of PVA films The absorbance spectra recorded in the UV−vis region (200-800 nm) is shown in Figure 7a. As can be noticed, PVA reveals low absorbance. The appearance of new peak at 250-300 nm with nanoinclusions and the relative broadening support the possible interaction between the PVA matrix and Dpa NPs owing to the absorption edge of polymer and Dpa NPs. The optical energy gap can be deduced according to Tauc’s expression.33-35 ()* = +)* − ,- .

(1)

where α, ν, h, Eg, and A are absorption coefficient, light frequency, Planck’s constant, band gap, and a constant, respectively. The Eg can be obtained by plotting (αhν)1/2 vs hν. As shown in Figure 7b, the Eg for pure PVA was ~5.0 eV, indicating that PVA is an insulator. Incorporation of Dpa-s NPs (2 vol %) results in a decrease in band gap energies from 5.0 eV


15


to 3.9 eV. The observed variation in optical energy gap reveals a change in the optical band structure of PVA films upon nanofiller intercalations due to formation of charge-transfer complexes (CTCs) between nanofillers and PVA. Furthermore, PVA/Dpa-h nanocomposite has an Eg of 3.6 eV, which is less than that of PVA/Dpa-s nanocomposite. It is a noteworthy phenomenon that narrow band gap will enhance UV light harvesting efficiency and hence improve the UV-shielding performance. This trend is in accordance with the UV−vis absorption and RhB photodegradation results.

a

6

PVA PVA/Dpa-s 2 vol% PVA/Dpa-h 2 vol%

b

PVA PVA/Dpa-s 2 vol% PVA/Dpa-h 2 vol%

40

-1

(cm eV)

4

60 50

1/2

5

30

1/2

3

(αhν)

Absorbance

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

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2 1

20 10

0 200

300

400

500

600

700

0 1.5

2.0

2.5

Wavelength (nm)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Photon energy (eV)

Figure 7. (a) UV−vis absorption spectra of PVA and PVA nanocomposite films. (b) The inherent Tauc plot of films. The cross-sectional surfaces of the pure PVA and PVA/Dpa nanocomposites with 2 vol % Dpa NPs loading have been carried out on SEM measurement and the results are shown in Figure 8. The pure PVA is homogeneous and uniform. For nanocomposites with 2 vol % Dpa NPs, some dots are well-distributed in PVA matrix, which are considered to be Dpa NPs; no noticeable agglomerations or cluster are found across the entire fracture surfaces.


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Figure 8. Cross-sectional SEM images of (a) pure PVA, (b) PVA/Dpa-s (2 vol %), and PVA/Dpa-h (2 vol %) nanocomposite. To investigate the effect of wall thickness of Dpa-h NPs on the transparency of PVA films, Dpa-h NPs with wall thickness control have been prepared through simply varying the amount of PS and dopamine. As shown in Figure 9a-e, the wall thickness of Dpa-h NPs can be controlled from 28 to 8 nm depending on the ratio between PS and dopamine. As the ratio increases, the wall thickness of resulting Dpa-h NPs becomes thinner. However, if the ratio reaches 4, the hollow structure is not observed because the wall is too thin to stabilize the hollow structure (Figure 9d). Figure 9f shows UV-vis spectra of PVA films with different thickness of Dpa-h NPs. The transmittance at 550 nm of PVA/Dpa-h (28 nm) film is only about 55%. Interestingly, the transmittance increases with decreasing the thickness of Dpa-h NPs. For example, PVA/Dpa-h (8 nm) film demonstrates better optical transparency as high as about 80%. Notably, PVA/Dpa-h composites exhibit a good balance between high transparency and excellent UV-shielding, outperforming other UV-shielding materials. The pink arrow in Figure 10 illustrates the trend in integrated high performance. Many processes to designing UV-shielding materials often improved in just one type of optical properties. For example, S-GO/PVA films possess a high UV-shielding of 95%, whereas the transparency is


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relatively low, only 25%.10 EP-ZnO/CdS shows high transparency and UV-shielding, however, ZnO nanoparticles always show photocatalytic effects and can degrade polymer matrices.49

Figure 9. TEM of the controlled synthesis Dpa-h NPs with the varying ratio of PS/dopamine (a) 1:1, (b) 2:1, (c) 3:1, and (d) 4:1. (e) Wall thickness with different ratio values between PS and dopamine (DA) determined using TEM. (f) UV-vis spectra of PVA/Dpa-h (2 vol %) films with different wall thickness of Dpa-h NPs.


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100 S-GO/PVA[10]

UV shielding at 400 nm (%)

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


PAA-LDH[41]

This work

PMMA/ZrO2[45]

80

MLA[13]

CF+Lignin[37]

EP-ZnO/CdS[49]

PDMS/TiO2[50]

60 Micro-TCC[40]

PSI/Mg/Al+Fe[7]

PVA/Ca0.2Zn0.8O[48] PS/ZnO[47] UV-24[43]

40

ZST[14]

Bi/Ti-MSN[38]

CAGO[39] PMMA/TiO2[46]

20

ZnO QD@SiO2[36]

PVA/TiO2[42] PI/TiO2[44]

0

0

20

40

60

80

100

Transmittance at 550 nm (%)

Figure 10. A comparison of the UV-shielding and transparency of PVA/Dpa-h composite films with other UV-shielding materials.7, 10, 13-14, 36-50 Conclusions In conclusion, we designed and prepared bio-inspired Dpa-s and Dpa-h NPs as UV absorber to enhance the UV-shielding performance of PVA. The Dpa-s NPs was synthesized through autoxidation of dopamine monomer. Dpa-h NPs were fabricated by self-assembly of dopamine monomer using PS spheres as template, following the removal of template. Compared with Dpa-s NPs, Dpa-h NPs allows multiple reflections of UV light within the interior cavity, leading to more efficient absorption of UV light and therefore offering an improved UV-shielding activity. UV−vis absorption spectra and RhB photodegradation


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measurements were carried out to investigate their UV-shielding efficiency. The result showed that PVA/Dpa-h nanocomposite films can completely block the whole UV region (200400 nm) and maintain its high transparency in the visible spectrum, which is promising to a significant UV-shielding and transparent material for photosensitive substances. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by National Natural Science Foundation of China (51373070), the Fundamental Research Funds for the Central Universities (JUSRP51624A), MOE & SAFEA, 111 Project (B13025), and the Innovation Project for College Graduates of Jiangsu Province (KYLX16_0784). AUTHOR INFORMATION Corresponding Author *[email protected]. *[email protected]. References 1.

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For Table of Contents Use Only


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A Novel UV-Shielding and Transparent Polymer Film: When Bio

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