Controlled synthesis of gold nanorods and integrated with titanium dioxide for enhancing visible light-driven antioxidant activity

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In this work, gold nanorods (AuNRs) with well-controlled aspect ratios were prepared using a modified seedgrowth method and covered by TiO2 layers through the hydrothermal reaction to improve stability. Integrating TiO2 with plasmonic rod-like gold nanoparticles could enhance their photo activity by the local surface plasmon resonance (LSPR) effect. AuNRs aspect ratios were controlled by varying the amount of seed solution, reducing agents, surfactant (CTAB), and titanium (IV) but oxide. The optical properties of formed AuNRs can be tuned in the spectral range from 400 to 900 nm by adjusting the ratio between seed solution and reducing agent concentration.

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Nội dung Text: Controlled synthesis of gold nanorods and integrated with titanium dioxide for enhancing visible light-driven antioxidant activity

Cite this paper: Vietnam J. Chem., 2023, 61(S2), 7-13 Research Article DOI: 10.1002/vjch.202300037 Controlled synthesis of gold nanorods and integrated with titanium dioxide for enhancing visible light-driven antioxidant activity Thu Anh Nguyen1,2, Ngan Thi Kim Nguyen1,2, Sy Van Vu1,2, Linh Ngoc To1,2, Vinh Hoang Lam1,2, Tien Nu Hoang Lo3, In Park3,4, Tien Huu Ho5, Khuong Quoc Vo1,2* 1 Faculty of Chemistry, University of Science, Vietnam National University - Ho Chi Minh City, 227 Nguyen Van Cu Street, Ward 4, District 5, Ho Chi Minh City 70000, Viet Nam 2 Vietnam National University Ho Chi Minh City, Linh Trung Ward, Thu Duc City, Ho Chi Minh City 70000, Viet Nam 3 Research Institute of Clean Manufacturing System, Korea Institute of Industrial Technology (KITECH), 89 Yangdaegiro-gil, Ipjang-myeon, Cheonan 31056, South Korea 4 KITECH school, University of Science and Technology (UST), 176 Gajeong-dong, Yuseong-gu, Daejeon 34113, South Korea 5 Thu Dau Mot University, Number 6, Tran Van On Street, Phu Hoa Ward, Thu Dau Mot City, Binh Duong Province 75000, Viet Nam Submitted February 17, 2023; Revised April 8, 2023; Accepted May 5, 2023 Abstract In this work, gold nanorods (AuNRs) with well-controlled aspect ratios were prepared using a modified seed- growth method and covered by TiO2 layers through the hydrothermal reaction to improve stability. Integrating TiO 2 with plasmonic rod-like gold nanoparticles could enhance their photo activity by the local surface plasmon resonance (LSPR) effect. AuNRs aspect ratios were controlled by varying the amount of seed solution, reducing agents, surfactant (CTAB), and titanium (IV) but oxide. The optical properties of formed AuNRs can be tuned in the spectral range from 400 to 900 nm by adjusting the ratio between seed solution and reducing agent concentration. Besides, the absorption of the UV-light function of TiO2 and the antioxidant properties of gold nanoparticles were also integrated to prepare a kind of multifunctional material. The obtained AuNRs/TiO2 were then determined by ultraviolet-visible spectroscopy (UV- Vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). Microscopic images (TEM, SEM) revealed that the average particle size of the AuNRs decorated in the titanium dioxide ranged from 20 to 60 nm, depending on the experimental parameters. Furthermore, HRTEM, EDS, and SAED results provided more precise information insight into the formed gold nanocrystals. The AuNRs/TiO2 exhibited superior antioxidant activity by reducing free 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals at different concentrations. The results indicated that AuNRs/TiO2 improves antioxidant and optical absorption activities. The antioxidation effect was proved more excellent than solely used of spherical, rod-liked gold nanoparticles or TiO2 nanoparticles. This novel design of AuNRs/TiO2 may open a new avenue for facilitating multifunctional nanoparticles in cosmetic applications. Keywords. Gold nanorods, titanium dioxide, antioxidant activity, multifunctional nanomaterials. 1. INTRODUCTION Nanomaterial-based use for preparing antioxidant supporting the catalyst dispersion,[2,3] and limiting agents has attracted much attention in the last few their aggregation under turnover conditions.[4,5] years. By utilizing external light-induced, the effect However, the main issue in solely utilizing titanium of antioxidant activity is further enhanced. TiO2 dioxide is low efficiency for solar light-driven played a critical role as a photo absorber,[1] applications because of the wide band gap (about 3.2 7 Wiley Online Library © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
25728288, 2023, S2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300037 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Khuong Quoc Vo et al. eV),[6] which permits 4-7% of the solar light 2.2. Preparation of gold nanorods by the seed- radiation to be used.[7] For the purpose of using the mediated modification method and integrated ultraviolet and visible parts of the solar spectrum, AuNRs into the TiO2 substrate noble metal nanoparticles are integrated with TiO2 due to several factors, such as the localized surface Preparation of the seed colloid: In the typical plasmon resonance[8] and electron collecting ability. procedure, a 1.0 mL volume of 5.0 mM HAuCl4 The aspect ratios of AuNRs could be designed by aqueous solution was added to 20 mL of 0.1 M optimizing different experimental factors such as the CTAB surfactant solution. The mixture was then precursors, seed, reducing agent concentration, magnetic stirred for 30 sec at a rate of 600 rpm, surfactant, temperature, additives, pH condition, followed by dropping 120 µL of 0.1 M NaBH4 aging time, and temperature.[9] Gold nanoparticles solution. The seed colloids were then left (AuNPs) were found to be able to scavenge free undisturbed for 2 hours and the best use time is radicals and interrupt the chain reaction in the about 2-5 hours after preparing. oxidation process. Using gold nanoparticles in Seed growth process: Firstly, the growth solution designing the potential antioxidant agent based on was prepared by mixing 0.3 mL of 4.0 mM AgNO3 solution and 1.0 mL of 5.0 mM HAuCl4 into a 10 AuNPs was previously proposed.[10,11] mL volume of 0.1 M CTAB. The mixture was This research focuses on the simple approach to stirred at 600 rpm for about 1 minute for the the controlled synthesis of rod-like gold reagents to be evenly dispersed. Subsequently, 55 nanoparticles by investigating the appropriate µL of 0.1 M ascorbic acid was added dropwise to reaction parameters. The obtained AuNRs with size the above mixture, and the color of the solution and shape uniformity were selected for integration turned from yellow to pale-yellow and transparent in into the TiO2 substrate in a simple sol-gel method. one minute. A 15 µL volume of the seed solution The process’s efficiency can be achieved by was continuously added to the seed-growth mixture governing the AuNRs and titanium butoxide and stirred for 30 seconds. precursors. The main advantage of integrating The AuNRs colloids, after rinsing (see SI- AuNRs into TiO2 is combining the local surface experimental part), was added with 100 µL of 0.1 M plasmon resonance of AuNRs in the visible and HCl followed by magnetic stirring at 800 rpm for 30 near-infrared regions with the absorption ability of minutes to remove the CTAB presented on the TiO2 in the ultraviolet range to enhance the optical surface of gold nanorods. At the same time, a TiO2 properties. This combination effect could be utilized sol colloid consisting of titanium(IV) butoxide and in the antioxidate activity due to the generation of isopropanol was also prepared (the process of sol electrons by the incident solar light. Furthermore, we colloid was introduced in the Supporting also evaluated the antioxidant activity of the information part). The AuNRs colloidal solution was prepared nanomaterials through the DPPH free added with 160 µL of the TiO2 colloids while radical scavenging testing. vigorously stirring at 1200 rpm. This mixture was continuously stirred for 24 hours for the high yield 2. MATERIALS AND METHODS of decoration of AuNRs on the TiO2. 2.1. Materials 2.3. Characterization Hexadecytrimethylammonium bromide (CTAB, Field emission scanning electron microscopy (FE- 99.0%) was purchased from HIMEDIA (Mumbai, SEM) technique was used to determine the size and India). Sodium borohydride (NaBH4, 99.9%), silver shape of the gold nanorods (JEOL JSM-7600F, nitrate (AgNO3, 99.9%), titanium(IV) butoxide JEOL Ltd., USA). Elemental composition (Ti(OCH2CH2CH2CH3)4, reagent grade, 97.0%), characterization of AuNRs/TiO2 was done by the isopropanol ((CH3)2CHOH, anhydrous, 99.5%), L- energy dispersive spectroscopy (EDS) unit: Oxford ascorbic acid (C6H8O6, 99.0%), and DI water (>18 Instrument 50 mm2 x-max and a cathode MW, Millipore, conductivity < 4.3 µS/cm) were fluorescence detector (Gatan Mono CL4, UK). The obtained from Sigma Aldrich (Darmstadt. dynamic light scattering (DLS) technique was used Germany). Gold(III) chloride hydrate to evaluate the average size and size distribution of AuNRs, conducted on the SZ-100 particle size (HAuCl4.4H2O, 99.5%, trace metal basic) was (Horiba, Instrument Co. Ltd, Japan). Transmission obtained from Sinopharm Chemical Reagent Co., electron microscopy (TEM) images were collected Ltd. (Beijing, China). on a JEM-2100 (JEOL Ltd., Japan) at an © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 8
25728288, 2023, S2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300037 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Controlled synthesis of gold nanorods … acceleration voltage of 200 kV. The high-resolution 3.1. Preparation and characterization of gold electron microscopy (HRTEM) technique was nanorods (AuNRs) carried out on a JEOL, ARM 200F (JEOL Ltd., Japan). Controlled synthesis of gold nanoparticles’ size and morphology is one of the most critical issues for 2.4. Studied the antioxidant activity of developing nanomaterials in the cosmetic and AuNRs/TiO2 biomedical fields. The characteristics of noble nanoparticles, such as the shape, size, and surface Briefly, a 100 µL of 6.0 mM DPPH was dissolved chemistry, and surfactant agent, highly affect their entirely in 2900 µL methanol, followed by stirring at biological activities.[12-14] Firstly, the aspect ratio and the rate of 800 rpm at room temperature for 30 the shape of AuNRs were manipulated by choosing minutes to prepare the blank sample. The obtained the ultra-small-sized seed and varying the volume of solution was measured using the UV-Vis ascorbic acid. The UV-Vis spectra could provide spectroscopy method at the maximum absorbance information about the optical properties of small- wavelength of 517 nm. The samples of AuNRs and sized seed particles and AuNRs (see figure S1c), AuNRs/TiO2 with various gold nanoparticle supported by the TEM image (see figure S1a- concentrations ranging from 0.14 to 20 ppm were supporting information). The seeds synthesized with mixed with the 6.0 mM DPPH solution (dissolved in the surfactant CTAB are commonly used to prepare the methanol solvent). The testing samples were single-crystal gold nanorods and do not present any irradiated using the simulated solar light based on localized surface plasmon resonance peaks.[15,16] The Light-emitting diodes (LEDs) (TopSolar 200W). Au seed colloidal solution color was light The light intensity was 200 mW/cm2, and the brown (see left inset - figure S1a). Direct irradiation time was 12 hours. Afterward, the observation of the formed gold seed nanoparticles samples were measured three times to obtain the can be seen by TEM images (see figure S1a). average results. The below equation gives the Typically, most of the seeds formed are very small percentage of DPPH reduction by using AuNRs and in size (below 4.0 nm) based on the TEM images AuNRs/TiO2: measurement, which can be obtained by using a strong reducing agent, such as sodium borohydride, ADPPH − A(DPPH+Au) with the excess amount. Q% = × 100% Figure 1 shows the UV-Vis spectrum and SEM ADPPH images of as-prepared AuNRs with various volumes where, ADPPH + Au: absorbance intensity of testing the of the seed colloids. The main part of Figure samples. ADDPH: absorbance intensity of DPPH in 1(a) presents the variation of the longitudinal the blank samples. plasmon resonance peaks (ranging from 630 to 850 nm), functioning to the aspect ratio and the 3. RESULTS AND DISCUSSION morphologies of formed AuNRs. There is clearly a a b c d k e f g Figure 1: (a) UV-Vis spectra of AuNRs colloidal solution synthesized with different seed solution volumes (curve g-k: 15, 20, 30, 40, 50 µL). (b-f) SEM images of AuNRs samples using 50, 40, 30, 20, and 15 µL volumes of seed colloid © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 9
25728288, 2023, S2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300037 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Khuong Quoc Vo et al. a b c d e f Figure 2: SEM images of AuNRs samples were prepared with the decrease of 0.10 M ascorbic acid volume from (a) 95, (b) 75, to (c) 55 µL of while keeping the volume of 4.0 mM AgNO3 at 0.3 mL. (d-f) Morphologies evolution of AuNRs as changing the amount AgNO3 to 0.5 mL as studied the reducing agent volume from 95 to 55 µL blue shift in the longitudinal surface plasmon resonance position to a shorter wavelength (around b c 630 nm) when the seed colloid volume increases from 15 to 50 µL. The other peaks around 500 to 550 nm are assigned to the transverse surface plasmon resonance of gold nanorods.[1,17] In the case of 15 µL, the maximum absorbance wavelength was a visualized at around 850 nm (figure 1a-curve red). It was also observed the morphology changed from sphere to rod-like when the volume of seed colloids decreased from 50 to 15 µL. For the sample synthesized with 15 µL, the SEM image presented that gold nanoparticles formed with a high yield of rod-like shape and highest aspect ratios than the d others (figure 1f). Oppositely, a large number of pseudo-spherical was observed for the 50 µL seed colloid volume (figure 1b). These findings were supported by dynamic light scattering (DLS) results (see figure S4c). The AuNRs prepared with 50 µL of seed colloid have a size distribution of approximately 40-60 nm, while the particles formed with 15 µL of seed colloid mainly range from 50-82 nm (See figure S4b). Figure 3: (a) Compared UV-Vis spectra of the Another critical factor in the seed-mediated AuNRs/TiO2 (curve blue) and AuNRs (curve method is using mild reductant, such as ascorbic red). (b), (c) TEM images of the as-synthesized acid, for slowly producing gold atoms in the AuNRs and TiO2 decorated with AuNRs (scale colloidal solution. The AuNRs with a high aspect bars for all, 20 nm); (d) EDS spectrum of the ratio synthesized with 55 µL of ascorbic acid show AuNRs/TiO2 substrate the two characteristic peaks at 535 and 830 nm (see AuNRs revealed that at a low volume of reducing figure S2-curve a), corresponding to transverse and agent (see figure 2c), AuNRs formed with a large longitudinal plasmon resonance of rod-like particles. number of rod-like particles compared with a high As the volume of ascorbic acid increases from 55 to volume of ascorbic acid (figure 2a). Moreover, the 95 µL, the longitudinal plasmon peak shifts from formed particles at ascorbic acid volume of 55 µL 830 to 615 nm (see figure S2). SEM analysis of the also have relatively uniform geometric lengths and © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 10
25728288, 2023, S2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300037 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Controlled synthesis of gold nanorods … a b c d e f Figure 4: (a-c) TEM images of AuNRs decorated on the TiO2 as varying the titanium(IV) butoxide to isopropanol volume ratios 2:8, 3:7, and 4:6, (d-f) corresponding high-resolution transmission microscopy (HR-TEM) images on one rod-like particle covered by TiO2 narrow size distributions. Only a small number of in the TEM images (figure 4a), it is possible to spherical or pseudo-spherical nanoparticles were clearly distinguish the AuNRs not covered by the formed in the colloidal solution. This point strongly TiO2 or moving deep inside the substrate. If not supports the above UV-Vis observation. In addition, covered by the TiO2, the lattice fringes with a d- the effect of CTAB concentration on the formation spacing of 0.145 nm assigned to the (2 2 0) lattice of gold nanorods was investigated through UV-Vis plane of Au could be observed on the HR-TEM spectroscopy (see figure S3). At an appropriate images of a single AuNR (figure 4d). The lattice CTAB concentration of 100 mM, two plasmonic fringes of AuNRs would not be revealed in the appeared at 525 and 840 nm, strongly suggesting the HRTEM micrograph of particles in case of moving formation of AuNRs in the colloidal solution. inside the TiO2 substrate (figure 4f). The d-spacing of TiO2 lattice fringes was measured at 0.356 nm, 3.2. Synthesis of AuNRs/TiO2 indexed to the (1 0 1) plane of TiO2 rutile (figure 4e and f). The selected area electron diffraction The optical properties of AuNRs/TiO2 were technique was further used to analyze the crystalline evaluated through UV-Vis spectroscopy. Figure structure of AuNRs. The bright concentric points are 3 illustrates the absorbance spectrum of AuNRs and observed in the pattern of the AuNRs particle (see AuNRs decorated in the TiO2 with two prominent figure S5). These spots are symmetry about the peaks. Both spectra show strong light absorbance with a wavelength longer than 800 nm compared to the absorption of TiO2. Besides, no absorbance peak observed for the TiO2 spectrum proved that the presence of AuNRs could enhance the optical properties of AuNRs/TiO2. The morphology of the AuNRs and AuNRs decorated on TiO2 were studied by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) (figure 4). Based on the contrast degree in the obtained micrograph because of the differential electron densities of Au and TiO2, the darker regions were the AuNRs while lighter areas represented to TiO2 substrate. The AuNRs could be seen clearly to move Figure 5: Antioxidation activity of AuNRs/TiO2, into the TiO2 substrate, producing an eccentric individual AuNRs, AuNPs, TiO2 and Trolox matrix with separated rod-like particles. As observed studied by DPPH free radical scavenging method © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 11
25728288, 2023, S2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300037 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Khuong Quoc Vo et al. pattern's center, interpreted as the formation of ratio. The nanoparticles might be able to donate the AuNR particles that exist as a single crystalline electron to neutralize the unstable free radicals, thus structure.[18] interrupting the oxidation chain process. The elemental characterization of the AuNRs/TiO2 sample was further conducted by 4. CONCLUSION energy dispersive X-ray spectroscopy (EDS) (see figure 3d). Several low-intensity peaks assigned to The gold nanorods with controlled size, about 30 nm silver (Ag), and carbon (C) also appear in the EDS for length and 3.0 for aspect ratios, have been spectrum. These signals are related to the emission successfully prepared through the seed-mediated from the excess precursor, additive, or by-product on method by adjusting the various reaction factors, the surface of AuNRs/TiO2. The strong intensity such as the amount of seed, ascorbic acid, and silver peaks corresponding to gold (Au), titanium (Ti), and ion. Subsequently, the AuNRs have been integrated oxygen (O) are observed in the spectrum, indicating into the TiO2 substrate through a modified sol-gel a high atomic percentage of these elements on the method to enhance the solar light absorbance ability. surface of nanomaterials. The antioxidant activity of AuNRs/TiO2 was To the possibility of further application in the investigated via the DPPH free radical scavenging preparation of cosmetic products, the stability of the assay, which showed that AuNRs/TiO2 could reduce AuNRs dispersion system is one of the critical the free radical at very low concentrations (0.14 to factors directly related. The stability of AuNRs/TiO2 2.25 ppm) compared to the previous reports. Our was studied by UV-Vis spectroscopy (see figure S6- study can open up much potential in cosmetic and supporting information). The results based on the personal care product applications. intensity of the plasmon peak showed that the AuNRs/TiO2 stayed stable after five days of storage Conflicts of interest. There are no conflicts to and under the salt ions media. declare. 3.3. Antioxidation activity Acknowledgements. 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