Seed-Mediated Hot-Injection Synthesis of Tiny Ag Nanocrystals on

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Seed-mediated hot injection synthesis of tiny Ag nanocrystals on nanoscale solid supports and reaction mechanism Ahmed Barhoum, Mohamed Fawzy Rehan, Hubert Rahier, Mikhael Bechelany, and Guy Van Assche ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10405 • Publication Date (Web): 30 Mar 2016 Downloaded from http://pubs.acs.org on March 31, 2016

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 Applied Materials & Interfaces 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 34

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 Applied Materials & Interfaces

Seed-mediated hot injection synthesis of tiny Ag nanocrystals on nanoscale solid supports and reaction mechanism Ahmed Barhoum1,2,3,*, Mohamed Rehan4,5, Hubert Rahier1, Mikhael Bechelany6, Guy Van Assche1,* 1

Physical Chemistry and Polymer Science, Department of Materials and Chemistry, Vrije

Universiteit Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium 2

Chemistry Department, Faculty of Science, Helwan University (HU), 11795 Helwan, Cairo,

Egypt 3

SIM vzw, Technologiepark 935, BE-9052 Zwijnaarde, Belgium

4

Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM),

Wiener Street 12, D-28359 Bremen, Germany 5

Textile Research Division, National Research Centre, Dokki, Cairo 12311, Egypt

6

Institut Européen des Membranes, UMR 5635 Université Montpellier CNRS ENSCM, Place

Eugene Bataillon, F-34095 Montpellier cedex 5, France *Email: [email protected], [email protected]

ABSTRACT: Controlling the size and shape of noble Ag nanocrystals (NCs) is of great interest because of their unique size- and shape-dependent properties, especially below 20 nm, and because of interesting applications in drug delivery, sensing, and catalysis. However, the high surface 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

energy and tendency of these tiny NCs to aggregate, deteriorates their unique properties and limits their applications. In order to avoid the aggregation of Ag NCs and improve their performance, we report a seed-mediated hot injection approach to synthesize highly dispersed tiny Ag NCs on a nanosized solid CaCO3 support. This simple, low cost, and effective chemical approach allows for synthesizing highly uniform Ag NCs (~10 nm) on the surface of presynthesized CaCO3single NCs (~52 nm) without any aggregation of the Ag NCs. Viscose fibers were coated with the Ag@CaCO3 composite NPs produced, as well as with ~126 nm Ag NPs for reference. The Ag@CaCO3 composite NPs show excellent UV protection and antibacterial activity against Escherichia coli. In addition, they give a satin sheen gold to a dark gold color to the viscose fibers, while the Ag NPs (~126 nm) result in a silver color. The proposed synthesis approach is highly versatile and applicable for many other noble metals, like Au or Pt. Keywords: hot injection, heterogeneous nucleation, clusters, calcium carbonate single crystals, tiny silver nanocrystals, citrate reduction mechanism, multifunctional fibers

1. INTRODUCTION Over the past decade, significant progress has been made in the control of the size and shape of nanocrystals (NCs) of noble metals.1,2 Silver exhibits good optical reflectivity, antimicrobial activity, and the highest thermal and electrical conductivity among all metals, resulting in Ag being a widely used material in many areas.3 The size, shape, and surface modification of Ag strongly influence its properties and thus its performance in applications.4 As the shape of Ag crystals is controlled and the size reduced to the nanometer range, Ag exhibits a relatively distinct optical, electrical, and catalytic behavior, accounting for the geometrical factors, and electronic and quantum size effects.5,6 For instance, Ag3 clusters and nanometer Ag particles

2 ACS Paragon Plus Environment

Page 2 of 34

Page 3 of 34

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


(~3.5 nm) on Al2O3 supports can catalyze and direct propylene epoxidation by O2 to selectively form propylene oxide with high activity at low temperatures.4 Various synthetic routes have been applied to synthesize Ag particles with dimensions from subnanometers clusters7 to several microns8, having different morphologies such as nanocubes,9 nanoprisms,10 nanodiscs,11 nanowires12 and nanoflowers.13 The simplest and commonly used synthetic route is the chemical reduction of a Ag salt solution. The reduction of silver ions (Ag++ e- → Ag0) has a relatively large positive standard reduction potential (E°= +0.799 V). Therefore several reducing agents, such as sodium citrate (E° = −0.180 V), hydrazine (E° = −0.230 V), and sodium borohydride (E° = −0.481 V),14 can successfully reduce Ag+ ions into metallic silver Ag0 in solution.15,16 The use of a strong reducing agent, such as borohydride (NaBH4), results in small particles of uniform particle distribution, however, controlling the generation of larger particles is difficult. The use of citrate, a weaker reductant, results in a slower reduction rate and the size distribution is usually far from narrow.15 Using either weak (Na-citrate) or strong (NaBH4) reducing agents Ag NPs of particle sizes between 10 nm and 50 nm with a well-defined shape and desired monodispersity cannot be achieved. The co-reduction method employing two different reductants (i.e., NaBH4 and citrate) or the use of stabilizing agents17can offer better control on nucleation and growth of Ag NPs.16,18 Strong stabilizing agents, such as polyvinylpyrrolidone (PVP), cap the Ag nuclei, keep the nuclei dispersed, and further control their growth.19 The selective adsorption of the stabilizing or capping agents on the growing nuclei/crystals changes the energy of the crystal facets and controls their growth rates, and therefore directs the growth, determining the final size and shape of the Ag NPs.6 For example, PVP and Br- ions can selectively bind to {100} facets of Ag and slowdown their growth rate, favoring the formation of nanobars and nanocubes.12 Contrariwise, citrate ions can bind more



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

strongly to {111} than {100} facets, resulting in the formation of nanoplates with a large portion of {111} facets on the crystal surface.20,21,22 Silver NPs are a typical nanomaterial with broad-spectrum antibacterial effects, on both Gramnegative and Gram-positive bacteria. Going back in time Ag was the first material utilized for sutures and abdominal surgery by ancient Greek and Romanssince well tolerated by the human body. However, these early prostheses presented lots of clinical problems.23 Recent investigations suggest that tiny Ag NPs can bind to the DNA of bacterial cells and viruses, preventing their replication.24,25,26 However, the aggregation of the Ag NPs leads to a loss of surface area and decreased in antibacterial activity.25 To avoid extensive aggregation of Ag NPs during synthesis, processing, and application, it is advantageous to synthesize NPs on an appropriate solid support. Recently, Kim et al. synthesized Ag NPs on the surface of SiO2 NPs, forming Ag@SiO2 composite NPs, having excellent antibacterial abilities.27 Jung et al.28 developed a nano plasmonic-paper, consisting of golded-coloured silver nanoislands on cellulose fibers, to serve as a chromatographic column for the separation of small molecules in aqueous solution as well as sensing substrate for highly sensitive nanoplasmonic detection. In this paper, we report on a simple, low cost, environmentally friendly method for controlling the size, morphology, dispersibility, and antimicrobial activity of Ag NCs through the synthesis of Ag NCs onto a solid nanocrystal support (CaCO3 NC). Tiny Ag NCs (~10 nm) were synthesized onto the surface of CaCO3 NCs using the hot injection method, in which the CaCO3 slurry containing trisodium citrate is gradually injected into a hot AgNO3 solution. Nanosized CaCO3 particles are an inexpensive nanoscale support, and are less aggressive and easier to prepare than other inorganic supports (e.g., TiO2, ZnO, and SiO2 NPs). Furthermore, nanosized CaCO3 particles have a lower surface charge than TiO2, ZnO, and SiO2 NPs, which make them


Page 4 of 34

Page 5 of 34

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


easier to redisperse in aqueous medium.29 The hot injection method is effective in inducing burst nucleation and results in the fabrication of tiny Ag NCs with a narrower size distribution.26 The weight ratio of Ag:CaCO3 was optimized and a possible mechanism of nucleation, growth, and crystallization of Ag NCs on a CaCO3 NP surface will be presented based on XRD and TEM analyses. We further exploited the unique characteristics of Ag@CaCO3 composite NPs by coating them onto textile fibers, imparting coloration, antibacterial, and UV-protection functions to the viscose fibers. These modified fibers can be used for producing multifunctional fabrics for fashion apparel, textiles for furnishing, as well as for sensing and biomedical applications.

2. EXPRIMENTAL SECTION 2.1. Materials A pure grade of calcium oxide (CaO, 97+%, Acros Organics), silver nitrate (AgNO3, 99+%, Sigma), carbon dioxide gas (CO2, 99+%, Air Liquide), trisodium citrate dehydrate (Na3C6H5O7·2H2O, 99+%, Sigma), sodium oleate (C18H33NaO2, 99+%, Sigma), ethanol (C2H5OH, 99+ %, Sigma), and monodistilled water were used for the synthesis of single crystals. Viscose Rayon fibers (Lenzing Viscose®) were kindly supplied by Lenzing AG (Lenzing, Austria) and used without further treatment.

2.2. Preparation of Ag@CaCO3 composite NPs The CaCO3 single crystals were prepared using wet bubbling carbonation (CaO-H2O-CO2) according to the procedure described previously.30,31 Dry CaO powder, approximately 11.2 g, was first calcinated at 1000 °C for 2 h, and added at 500 °C to 400 mL distilled water containing 0.4 g sodium oleate, equivalent to 2 wt% based on the theoretical yield of CaCO3. The slurry was left to cool to room temperature in a closed polypropylene (PP) bottle, and then CO2 gas was 5 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

injected at 1 L.min-1 flow rate into the lime slurry under vigorous stirring. The pH of the reaction medium was monitored with a pH meter (Jenway 3305). When the pH value decreased from 14 to 9,32 which indicates that the CaO was completely converted to CaCO3, the CO2 injection was stopped. CaCO3 single NCs of about 50 nm were obtained and dried at 120 °C for 24 h. For comparison, unmodified and citrate-modified CaCO3 NCs were prepared under the same conditions in order to study the influence of in situ modification with sodium oleate. The tiny Ag NCs were synthesized onto the prepared CaCO3 NCs via the hot injection approach. Four Ag@CaCO3 nanocomposites (indicated as Ag-Ca 5%, Ag-Ca 10%, Ag-Ca 15% and Ag-Ca 20%) were prepared from AgNO3, trisodium citrate, and the synthesized CaCO3NCs in an alcoholic solution. For preparing the nanocomposites Ag:CaCO3 weight ratios of 5, 10, 15, and 20 wt%, respectively, were selected. The Ag:citrate molar ratio was kept constant at value of 3:1 for all syntheses. In practice, 4 g of the dry CaCO3NCs and the desired amount of trisodium citrate were dispersed in 50 mL ethanol using a high shear mixer at 1000 rpm for 30 min. The obtained slurry was then diluted with 200 mL water and sonicated under vigorous stirring at 30% power using a W-385 Sonicator for 30 min, to completely break any remaining agglomerates. An appropriate amount of AgNO3 was dissolved in 200 mL water at 90 °C. The CaCO3 dispersion was gradually injected into the hot AgNO3 solution at 90 °C using a 10 mL plastic syringe with vigorous stirring and sonication. After complete addition of the CaCO3 dispersion, the solution was kept for 1 h at 90 °C under sonication with a power of 30%. The obtained products were filtered, washed, and then dried at 120°C for 2 hr. For comparison, pure Ag NPs (4 g) were prepared using the same method without CaCO3, and were used as a reference. To study the influence of post-modification by trisodium citrate, oleate-modified CaCO3 NCs were postmodified with trisodium citrate. To an oleate-modified CaCO3 NCs dispersion (4 g CaCO3 NCs


Page 6 of 34

Page 7 of 34

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


dispersed in 450 mL of ¼ v/v ethanol in water) a total of 6.4 g trisodium citrate was added. The mixture was kept at 90 °C under sonication and continuous stirring. Next, the CaCO3 NCs were filtered and washed three times with 100 mL distilled water and dried at 120 °C for 24 h.

2.3. Characterization of Ag@CaCO3compositeNPs Phase identification and average crystallite size of the prepared pure Ag NPs, pure CaCO3 NCs, and Ag@CaCO3compositeNPs were determined using X–ray diffraction (Bruker D500) with CuKα (λ = 1.5406 Å) radiation. The particle size, morphology, and elemental composition were characterized using transmission electron microscopy (TEM, Jeol JEM-2010) and field emission scanning electron microscopy (FE-SEM, Jeol JSM-7000F). Particle size distribution analysis is based on more than 50 particles. By operating the TEM in the energy dispersive X-ray spectroscopy (EDS) scanning mode, the elemental distribution of the as-synthesized Ag@CaCO3 composite NPs was mapped and the integrated intensities of Ca, C, O and Ag were displayed as a function of the beam position. The Ag:CaCO3 weight ratio was determined by means of thermogravimetric analysis (TGA, TA Instruments Q5000). The nanocomposite powders were dried isothermally at 60 °C for 30 min before heating to 900 °C at a heating rate of 10 K·min–1 under 25 mL·min–1 air flow. The water contact angle (WCA) was measured with a Kruss DSA100 contact angle analyzer. The prepared CaCO3 powders were compressed into discs using a typical press for KBr pellets for IR analysis.33,34 The zeta potential of CaCO3 particles in suspension (pH 7) was measured at 25°C using a Zeta meter 3.0 equipped with a microprocessor unit (Malvern Instrument Zetasizer 2000).33 Bonding structures were analyzed using a Fourier transform infrared spectrometer (FTIR-460 plus, JASCO model 6100, Japan). Spectra were collected in transmission mode using KBr pellets (1:100 sample to KBr weight ratio, resolution 4



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

Page 8 of 34

cm−1, 64 scans per spectrum). All the given values are based on three measurements at least for each sample.

2.4. Application of Ag@CaCO3composite NPs on viscose Fibers The prepared Ag NPs and Ag@CaCO3 composite NPs were immobilized on viscose fibers using a wet chemistry method (dip-pad-dry-cure process). In brief, approximately 0.1 g of the synthesized powders was dispersed in 100 mL monodistilled water using an ultrasonic bath for 30 min. Afterwards the viscose fibers (~ 2 g) were dipped into the solution for 1 h under sonication. The fibers were rinsed with running monodistilled water to remove the unassembled NPs, pressed with a padder, dried at 90 °C for 5 min, and finally cured at 120 °C for 3 min. The distribution of the NCs on the viscose fibers was characterized using FE-SEM.

2.5. UV-vis absorbance, transmission, and antibacterial activity tests The UV-vis absorbance, UV transmission, and antibacterial activity tests were performed on the treated viscose fibers. All the given values are based on three measurements at least for each sample. The color coordinates (L*, a* and b*) of the treated fibers were determined for a 10°observer and D65 illumination using a beam reflectance spectrophotometer (KONICA MINOLTA).

The

color

coordinates

describe

lightness

(black

L* = 0

and

white

(L* = 100), a* represents the (+)red/(−)green axis, and b* represents the (+)yellow/(−)blue axis.29 UV-vis absorption spectra of the treated viscose fibers were measured with a UV-vis spectrophotometer (Mulgrave Victoria 3170). The UV protection factor (UPF) was determined by measuring the UV transmission through viscose fibers using a UV–vis spectrophotometer (Varian Cary 300). For the antibacterial activity tests, Gram-negative bacteria, Escherichia coli


Page 9 of 34

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


(E. coli) ATCC 11229, were used as test organisms. The antibacterial activity test was performed by recording the optical density (OD) at λ = 620 nm as a function of time for a liquid nutrient growth medium containing E. coli culture and the treated viscose fibers. The increase in optical density reflects the extent of E. coli growth in the nutrient medium.

3. RESULTS AND DISCUSSION 3.1. X-ray powder diffraction The diffraction pattern of the CaCO3 NCs prepared is indexed to calcite (JCPDS 005-0586)16 and the diffraction pattern of pure Ag NPs is indexed to a cubic crystalline structure (JCPDS 0040783)(Figure 1). The diffraction patterns of the Ag@CaCO3 nanocomposites contain two sets of peaks (Figure 1). Three strong characteristic peaks at 2θ = 38.1°, 44.2°, and 64.4° correspond to crystalline cubic silver (JCPDS 004-0783), while the other set of strong peaks corresponds to the calcite crystal structure (JCPDS 005-0586). The average crystallite size of the synthesized NCs is ~ 60±2 nm for pure CaCO3, ~50±2 nm for pure Ag, and ~12±1, 10±1, 8±1 and 20±2 nm for Ag NCs of the Ag@CaCO3 composite NPs (Ag-Ca 5%, 10%, 15% and 20%), respectively.



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

Page 10 of 34

Figure 1. XRD diffraction pattern of the prepared CaCO3 NCs, Ag NPs, and Ag@CaCO3 composite NPs

3.2. Electron microscopy FE-SEM images of the synthesized CaCO3 NPs and pure CaO particles are given in Figure 2. The in situ modification of CaCO3 during the carbonation process was performed with either 2 wt% sodium oleate or trisodium citrate. The oleate in situ modification provided nanosized particles with a rhombohedral morphology (52±5 nm) (Figure 2a).The in situ modification of CaCO3 with 2 wt% trisodium citrate during the carbonation process results in rod-like CaCO3 NPs (Figure 2b), displaying a poorer control on the shape and size distribution of the CaCO3 particles. Citrate ions can bind to the CaCO3 surface with two –COO– groups at the same time, while still having –COO– and –OH groups available for other interactions, versus only one – COO– for oleate. Although citrate is a suitable candidate to reduce Ag+ into Ag0, it is not an appropriate additive to control the size and shape of CaCO3 at the nanoscale. Figure 2d show that nanosized Ag NPs (126±12 nm) were obtained after reduction in the absence of CaCO3.


Page 11 of 34

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 2. SEM images of the prepared samples: (a) 2 wt% oleate modified CaCO3 NCs; (b) 2 wt% citrate modifiedCaCO3 particles, (c) pure CaO particles; and (d) pure Ag NPs

The TEM images, given in Figure 3, show nanosizedAg@CaCO3 composite NPs, with spherical Ag NCs sitting as darker dots on the lighter rhombohedral CaCO3 NPs (51 ± 9 nm). The composition of the tiny NCs on the CaCO3 NPs was confirmed by TEM-EDS elemental mapping (Figure 4). The mean particle size of Ag NCs on the CaCO3NPs is about 17 ± 7, 15 ± 4, 9 ± 2 and 33 ± 8 nm for Ag-Ca 5%, 10%, 15% and 20%, respectively. The Ag-Ca 15% composite NPs shows the most uniform particle size, while the Ag-Ca 20% composite NPs shows aggregation of Ag NCs and the presence of much larger Ag particles (Figure 3). In all composite samples it appears as if the Ag NCs are sitting on the crystal edges of the CaCO3 NCs, which might be due to a faster nucleation of the Ag NCs on the more energetic positions. Moreover, for all Ag@CaCO3 composite NPs studied all observed Ag NCs were attached to CaCO3 (no free Ag NCs were observed in TEM).



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. TEM images at different magnifications for the Ag@CaCO3 composite NPs

Figure 4. EFTEM elemental mapping of Ca, C, O and Ag atoms in the Ag-Ca 15% composite NCs; displaying the integrated intensity of chemical maps from Ca-K, C-K, O-K and Ag-L


Page 12 of 34

Page 13 of 34

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


3.3. Thermogravimetric analysis (TGA) TGA weight loss curves of the pure CaCO3 NCs, pure Ag NPs, and Ag@CaCO3 composite NPs upon heating to 900°C are shown in Figure 5. Pure Ag NPs show a loss of only 0.3 wt% in the temperature range 60 to 500 °C and no weight change is observed above 500 °C. The weight loss of synthesized pure CaCO3 NCs and the Ag@CaCO3 composite NPs happens in two steps: a first weight loss of 3-3.5 wt% is seen from 60 to 500 °C, and a second loss of 34-42 wt% is observed from 500 to 1000°C. The mass loss between 60 and 500 °C is attributed to the loss of physically and chemically sorbed water, as well as to the decomposition of the adsorbed oleate and citrate. The weight loss observed from 500 to 1000 °C for the CaCO3 NCs and Ag@CaCO3 composite NPs is attributed to the decarbonation of CaCO3. Comparing the decarbonation weight loss with the one for pure CaCO3 NCs, the synthesized nanocomposites have an estimated Ag content of ~ 3.8 wt% for Ca-Ag 5%, ~9.6 wt% for Ca-Ag 10%, ~ 14.2 wt% for Ca-Ag 15%, and ~ 9.8 wt% for Ca-Ag 20%. Somewhat surprisingly, the TGA results indicate that the Ca-Ag 15% nanocomposite has the highest Ag content. The lower Ag content for Ca-Ag 20% can be attributed to complexation, as explained in the formation mechanism (see next section).

Figure 5. TGA of the prepared CaCO3 NCs, Ag NPs, and Ag@CaCO3 composite NPs



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

Page 14 of 34

3.4. Mechanism of Ag@CaCO3 composite NPs formation The present study combined several strategies to control the growth of Ag NPs onCaCO3NCs. We will discuss this referring to the principles of the classical and nonclassical theories of nucleation.30-32 Our approach combines the following strategies:

(i) Synthesis of nanosolid support “CaCO3 NCs” Our previous studies,30,31 show that soaking hot CaO (500 °C) in water at room temperature leads to the fracturing of the hot CaO particles into smaller particles as a result of the thermal shock and dissolution effects. Upon soaking the hot CaO particles, the CaO particle surface becomes partially hydrated, forming a sparingly soluble layer of Ca(OH)2 covering the CaO particles. The bubbling carbonation is started by injecting CO2 gas at 1 L.min-1. The carbonation of the Ca(OH)2 layer by the CO32- ions formed upon injection of CO2 gas in the solution generates tiny amorphous CaCO3 nuclei that readily crystallize, forming calcite CaCO3 NCs.30 The reduction of the CaO particle size increases the CaO surface area and accelerates the rate of nucleation of CaCO3 upon introduction of CO2. The use of 0.5 M CaO, a surfactant concentration of 2 wt% (based on the expected theoretical CaCO3 weight), and a high CO2 flow rate (1 L·min−1) results in the precipitation of single calcite particles of 52 nm rhombohedral morphology. The high CO2 flow rate (1 L.min-1) leads to a high number of CO2 bubbles in solution, and increases the total interfacial area between CO2 bubbles and the solution, as well as the rate of CO2 conversion into CO32− ions, leading to a high nucleation rate, shortening the reaction time (growth time), and resulting in a decrease of the crystallite and particle size. Finer crystals with narrower size distribution were formed compared to using as received CaO particles or calcinated particles that were cooled down to room temperature.29


Page 15 of 34

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


(ii) In situ modification of the CaCO3 NCs The in situ modification of CaCO3 NCs with sodium oleate produces uniform CaCO3 single NCs (~52 nm). As the concentration of sodium oleate used was well above the critical micelle concentration (CMC, 0.18 mM),35oleate ions self-assemble to form micelles and adsorb on the unreacted CaO particles and on the CaCO3 clusters, nuclei, and on the CaCO3 NCs produced in the reaction medium (schematized in Figure 6-i and ii). On the monolayer of oleate ions covering the surface of the CaCO3 NCs, with the hydrophilic head group bonded to the CaCO3 surface, a second layer of oleate ions self-assembles in tail-to-tail arrangement, forming a double layer structure (Figure 6-ii).35 These oleate ions stabilize the CaCO3 NCs, and control the hydration, clustering, nucleation, and growth, as well as the surface properties of the CaCO3 NCs and their (re)dispersion. When the slurry of CaCO3 NCs is filtered and washed, the oleate concentration decreases to a value lower than the CMC for oleate, and hence the double layer structure is destroyed, removing the second layer of the surfactant, changing behavior of the particles from hydrophilic to hydrophobic (Figure 7), and resulting in precipitated aggregates of assembled oleate-modified CaCO3 NCs (Figure 6-iii).35 The presence of oleate molecules at the dry CaCO3 NCs surface enhances the diffusion of water and ethanol molecules at the CaCO3 particleparticle interface in the aggregates and results in a very easy redispersion of the dried CaCO3NCs by sonication in an alcoholic solution (Figure 6-iv).



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

Page 16 of 34

Figure 6. Scheme (not to scale) showing the different stages of the formation of Ag@CaCO3 composite NPs: (i-iii) synthesis and in situ modification of CaCO3 NCs with oleate; (iv) redispersion of the oleate-modified CaCO3 NCs in alcoholic solution (water:ethanol = 4:1 v/v) containing trisodium citrate in ultrasonic bath; (v) stabilization of the CaCO3 NCs by adsorption of the citrate molecules on the NCs surface; (vi) hot-injection of the CaCO3 dispersion into hot AgNO3 solution (90°C) followed by reduction of the Ag+ ions and the formation of the tiny Ag NCs on CaCO3 NCs. (a)

(b)

Figure 7. Images show the water contact angle of (a) unmodified and (b) in situ oleate modified CaCO3 prepared via the wet bubbling carbonation technique.


Page 17 of 34

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


(iii) Post surface modification of oleate-modified CaCO3 NPs with citrate Trisodium citrate is soluble in water and insoluble in ethanol. When trisodium citrate is added to the oleate-modified CaCO3 NCs dispersion, the citrate ions replace the oleate ions on the CaCO3 NCs surface. Figure 8a shows FT-IR spectra of the unmodified CaCO3; in situ-modified CaCO3 with oleate; and post-modified CaCO3 with trisodium citrate. Unmodified CaCO3 samples show characteristic absorption peaks appearing at 3445, 2515, 2355, 1420, 872, and 710 cm−1. The broad absorption peaks at 3445 cm−1 are assigned to the stretching vibration of the O−H bond attributed to the sorbed water (hydroxyl groups) on the surface of CaCO3 particles. The peaks around 2355 cm−1 are attributed to CO2 in the atmosphere. The peaks at 1420, 872, and 710 cm−1 are ascribed to atomic bonding structure of calcite.36 The peak at 2515 cm−1 is an overtone of the peaks at 1447, 877, and 712 cm−1. In situ-modified CaCO3 with oleate shows peaks at 2955, 2925, and 2885 cm−1 (CH stretching region of long alkyl chain of oleate) that prove the presence of oleate at the surface of CaCO3.31 The spectrum of CaCO3 NPs post-modified with citrate shows the same peaks as oleate-modified CaCO3 (in situ), but the broad absorption peak assigned to the stretching vibrations of O−H is shifted to 3475 cm−1. Moreover, the relative intensity of the C-H stretching peaks (3000-2800 cm-1) related to the long alkyl chain decreases. These results indicate that both citrate and oleate are adsorbed on the surface of CaCO3. The TGA mass loss curves (Figure 8b) show that the amount of adsorbed oleate and/or citrate reaches up to 1.31.5 wt% (compare to unmodified CaCO3 at 500 °C). Zeta potential measurements show that the surface charge of the unmodified CaCO3 NCs is about -11.2±0.5 mV, while that of in situ oleatemodified CaCO3 NCs is about -15.1±0.6 eV. CaCO3 NCs post modified with citrate the surface charge of the obtained CaCO3 NCs increased to -18.6 ± 0.4 mV. This indicates the successful adsorption of oleate on the CaCO3 NCs surface and the replacement of oleate ions on the CaCO3



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

Page 18 of 34

NC surface by citrate ions during post modification. Trivalent citrate forms stronger complexes with Ca2+ ions, likely due to the affinity of the citrate carboxyl and hydroxyl for the Ca2+ ions on the CaCO3 NC surface. Examples of similar complexation strength trends can be found in literature.37 For instance, magnesite and dolomite dissolution rates were promoted by organic ligands (via surface Mg2+−organic ligand complexation) with the following effectiveness: citrate > oxalate > acetate.38,39At the citrate concentrations used, a fraction of the citrate is used cover the CaCO3 NCs, while the excess is dissolved in the dispersion. (a)

(b)

Figure 8. FT-IR spectra (a) and TGA mass loss curves (b) of the prepared CaCO3 particles: unmodified CaCO3; (b) in situ-oleate modified CaCO3; and post-citrate modified CaCO3.

(iv) Ag nanocrystal deposition by hot-injection route and citrate reduction In this work, we developed a hot-injection route to grow tiny Ag NCs on the CaCO3 NC surface. The gradual injection of the citrate-modified CaCO3 NC dispersion into a hot AgNO3 solution induces the reduction of Ag+ by citrate, resulting in an acetone dicarboxylate intermediate that decomposes rapidly into acetoacetate, while formate and/or CO2 are released as byproducts.3In both steps there is an electron transfer to Ag+ ions, leading to their reduction to metallic silver


Page 19 of 34

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


Ag0,3,40 and the formation of Agxy+ clusters. The extent of the citrate reduction of the Ag+ ions is strongly influenced by the concentration of citrate ions and the reaction temperature.18 In general, citrate ions could serve as reduction, stabilizing and complexing agents. At room temperature and citrate:Ag molar ratio of 3:1 the reduction reaction takes a week and the final product shows a wide size distribution.41,42,43 In this study, the reduction was performed with good control in one hour at a reaction temperature of 90 °C and a citrate:Ag molar ratio of 3:1. The 3:1molar ratio was selected as the citrate reduction approaches completion at this higher citrate concentration, while only a small fraction of Ag+ ions gets reduced at an equimolar citrate:Ag ratio. Henglein and Giersig41 demonstrated that citrate ions do not act only as reducing agents but also as stabilizers, resulting in partly agglomerated large particles with many imperfections at a low citrate concentration (˂ 10-4). Pillai and Kamat18 showed that citrate ions influence the particle growth at the early stages by complexing with Ag2+ dimers and that they slow down the cluster growth, contributing to the formation of larger Ag NCs of varying shape and size. Later, theoretical simulations were performed by Kilin et al44 who reported that citric acid is more likely to bind to the Ag(111) surface than to the Ag(100) surface and that the citrate oxidation products could be CO2 and acetone-1, 3-dicarboxylate. Jiang et al.42state that citrate ions can bind on Ag NP surfaces but weaker than other capping agents, such as cetyltrimethylammonium bromide (CTAB) and poly vinylpyrrolidone (PVP).42The complexation effect of citrate was extensively investigated by Djokic45 and Jiang et al.42 Djokic45 showed that citrate can form a stable complex with Ag+ ions, resulting in a white substance having very limited solubility in aqueous media.46 Jiang et al.42 further confirmed the formation of Ag-citrate complexes [Ag3(C6H5O7)n+1]3n− by ESI mass spectrometry analysis and concluded that these



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

Page 20 of 34

complexes can largely influence the formation and kinetic growth of Ag NPs; the higher the amount of citric acid, the slower the Ag NPs grow. (v) Seed-mediated growth hot-injection route The seed-mediated hot-injection route is known to produce uniform tiny NCs,47,48 having a narrow size distribution compared with the cold-precursor loading method.49 The rapid formation of Agxy+ clusters in the medium upon the gradual injection of the citrate-modified CaCO3 NC dispersion into the hot AgNO3 solution induces the formation of Ag NCs. All observed Ag NCs were attached to surface of the CaCO3 NCs, no free Ag NCs were observed. Citrate ions, as well as remaining oleate ions and ethanol molecules, adsorb on the surface of Ag clusters and nuclei, protecting them from aggressive agglomeration, inhibiting the homogeneous formation of Ag NCs, and controlling the growth of the heterogeneous nuclei.18,50 Citrate ions on the CaCO3 NCs surface may act as a bridge between (clusters of) Ag+ ions and the CaCO3 NCs surface, enhancing the nucleation of Ag at the surface of the CaCO3 NCs (heterogeneous nucleation). In this view, cellulose fibers or their derivative, cellulose acetate, can be used as seed-mediated growth for synthesis of tunable colored Ag NPs. The size, shape and colors of the Ag NPs can be controlled by altering the concentration of Ag+ ions, reductant concentration in the growth medium.51

(vi) Controlling the citrate ion concentration and temperature Experimentally it is observed that the citrate ion concentration exerts a drastic effect on the shape and size distribution of the Ag NCs that are formed (Figure 3). Crystallite size measurements obtained from XRD and particle size measurements from TEM indicate that Ag-Ca 15% shows the smallest value of crystallite size (~ 8 nm) for an average particle size of 8±2 nm. The


Page 21 of 34

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


nanocomposite Ag-Ca 15% was prepared using 12×10-3 M Ag+ and 37×10-3 M citrate. Under these conditions, the citrate ion concentration is sufficient to form relatively stable Agxy+ clusters and protect them from aggressive aggregation. For Ag-Ca 5% and Ag-Ca 10%, Ag NCs with a crystallite size of 12±1 and 10±1 nm and a particle size distribution of 17±7 and 15±4 nm were obtained (See Figure 3), respectively. For Ag-Ca 20%, at the highest Ag+ (16×10-3 M) and citrate (49×10-3 M) concentrations, aggregation of Agxy+ clusters seems to be induced and a very broad size distribution is observed (33 ± 8 nm) with in some cases multiple crystallites (See Figure 3, Ag-Ca 20%). Also for this material, the TEM pictures did not show free Ag NPs. However, TGA showed that Ag-Ca 20% contains a lower amount of Ag compared to Ag-Ca 15% (See Section 3.3). This indicates that the increase in the Ag+ and citrate ion concentration from Ag-Ca 15% to Ag-Ca 20% resulted in a decrease of the citrate reduction efficiency, which is attributed to the formation of stable Agcitrate complexes at high citrate concentration. Also in case of the non-seed-mediated route for the reduction of Ag with citrate, reported in literature,43 a narrow citrate concentration range ((15)×10-4 M citrate for 1×10-4 M of Ag) is found in which tiny NPs are formed. The fact that in our work tiny Ag NPs are still obtained at much higher citrate concentrations, up to 37×10-3 M, is probably due to the efficient heterogeneous nucleation in the seed-mediated approach. Figure 9 summarizes the different steps in the seed-mediated formation of Ag NCs by citrate reduction on the surface of CaCO3 NC.



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

Page 22 of 34

Figure 9. Scheme (not to scale) showing the different steps in the seed-mediated formation of tiny Ag NCs on the CaCO3 NC surface covered by a monolayer of citrate ions: (i) homogenous clusters formation; the complexation and redox reaction of Ag+ and citrate ions in the solution induces the homogeneous formation of tiny clusters (Agxy+) stabilized by citrate ions; (ii) Adsorption/desorption of Agxy+ clusters on the CaCO3 NC surface; (iii) heterogeneous formation of Agxy+ clusters on the CaCO3 NCs surface, possibly facilitated by the citrate monolayer adsorbed on the CaCO3 NCs surface; further citrate electron transfer reduction of Ag+ to metallic silver Ag0 on the surface; (iv) heterogeneous nucleation; densification and formation of stable amorphous Ag0 nuclei on the CaCO3 surface; and (v) growth and crystallization of the amorphous Ag0 nuclei to form spherical Ag NCs. The further growth of the Ag NCs is controlled by the adsorption of citrate ions.


Page 23 of 34

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


3.5. Coloration, UV-protection and antibacterial functions The history of using metal-based nanoparticles as coloring materials dates back more than 4000 years, as the ancient Egyptians were using synthesized PbS nanocrystals of ~5 nm to dye their hair. The Lycurgus Cup, dating back to Roman times, is made of a dichroic glass that contains Au–Ag-Cu nanoparticulate alloys of 50 nm diameter.52 Ag NPs were also employed in luster decorations of medieval and renaissance pottery, in which the surface of nanoparticles contributes to ceramic color.53 The scientific story of preparing colored nanoparticles began much later however. The variation of optical properties of nanomaterials with decreasing particle size was discovered as early as 1908 by the German physicist Gustav Mie’s, who performed early dark-field microscopy studies on colloidal Au NPs. Somewhat later, Mie’s theory has been used to explain the optical properties of Ag NPs of complex shape.54,55 Recently, metal nanoparticles have been used as multifunctional additives for coloring a wide varies of polymeric materials, especially natural fibers and textile fabrics such as nylon, polyester and cotton. Park et al.56 have change the color of cellulose to dark-yellow and dark-brown by immersing cellulose in a solution containing Pd and Ag NPs, respectively. Kelly and Johnston used Ag NPs to color merino wool fibers and fabrics.57 Solomon et al.58 have found that the color of solution containing 12 nm Ag NPs, from yellow, dark yellow, violet to greyish, as aggregation of the Ag NPs proceeded. Therefore, the reaction conditions, including immersion time, stirring rate and quantities of reagents, must be carefully controlled to obtain stable colored particles. To evaluate the coloring capacity of our Ag@CaCO3 composite NPs for textile applications, viscose fibers were colored using Ag NPs or Ag@CaCO3 composite NPs. SEM was used to observe the blank viscose fibers and the deposition of Ag NPs and Ag@CaCO3 composite NPs on the fiber surface. As shown in Figure 10, the Ag and Ag@CaCO3 NPs (Ag-Ca 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

Page 24 of 34

immobilized evenly on the fiber surface and no bulk aggregates were observed. The surface of treated fibers is covered by a sufficient amount Ag NPs and Ag@CaCO3 composite NPs.

Figure 10. SEM images of the viscose fibers: (a) blank viscose fibers; (b) with deposited Ag NPs; and (c,d) with deposited with Ag-Ca 15% nanocomposite.

Figure 11. Photos of viscose fibers samples: (a) blank viscose fibers; (b) viscose fibers loaded with Ag NPs; and (c) viscose fibers loaded with Ag@CaCO3 15 wt% composite NPs.

The Ag@CaCO3 treated viscose fibers show a color shade from satin sheen gold to dark golden, while the Ag NP-treated fibers are silver grayish color (Figure 11). The color measurements of Ag@CaCO3 treated fibers were accurately determined after washing and drying, according to the 24 ACS Paragon Plus Environment

Page 25 of 34

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


CIE (L*, a*, b*) system59 (see Table 1). The all Ag@CaCO3 treated fibers show significant decrease of L* values along with increase of a* and b* values. The decrement in L* is a result of coloration of fibers, which becomes more deeply. The significant increase in a* and b* values is attributed to the golden colorations acquired after immobilization. Coloration of cellulosic fibers is very important in textile industry but light fading of dyes is a common phenomenon in textile research. The anisotropic Ag NPs are different from traditional dyes, in that it is not the chromophore of traditional dyes but the shape and size of nanoparticles that determine the colors. These brilliant hues of the treated fibers arise due to strong absorptions in the visible range for the prepared Ag@CaCO3 nanocomposite,57 which arise from the coherent oscillation of conduction band electrons from the resonance interaction with the electromagnetic field of visible light. This phenomena known as surface plasmon resonance (SPR) and theoretically explained by Mie theory.60

Table 1. Colorimetric data for untreated and treated viscose fibers Sample

L*

a*

b*

Blank

95.9±0.4

−0.13±0.01

4.4±0.2

Ag

79.2±0.5

1.21±0.22

11.1±0.5

Ag-Ca 5%

69.3±0.5

3.91±0.24

44.5±0.5

Ag-Ca 10%

58.1±0.7

4.10±0.37

45.4±0.4

Ag-Ca 15%

48.3±0.2

5.30±0.18

31.2±0.4

Ag-Ca 20%

49.2±0.8

5.71±0.48

32.1±0.7

Colors*

*The colours of the untreated and treated viscose fibers were determined after washing and drying using EASY RGB color convertor

The immobilization of Ag NPs and Ag@CaCO3 on fiber surfaces could be also confirmed by the observation of the characteristic Plasmon in UV-vis spectra. As shown in Figure 12a, the treated



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

Page 26 of 34

fibers exhibited strong absorption in the 350-500 nm range which is attributed to a surface plasmon absorption band of Ag NCs of Ag@CaCO3. Amongst all the treated fibers, the Ag-Ca 15%-treated fibers show the highest UV-Vis absorption. The Ag@CaCO3 treated fibers also show high UV protection properties, with a UV transmittance of less than 10% between 350 and 400 nm for Ag-Ca 15% (Figure 12b). All Ag@CaCO3 treated fibers have a lower UV transmittance than the Ag NPs (~126 nm) treated fibers. Compared to the treated fibers, the blank viscose fibers have the highest transmittance for UV light (above 80%). In general, the UV-protection offered by textile fibers is considered perfect when the UV transmittance is less than 5%. The excellent UV-protection of the treated viscose fibers is a combined result of strong absorption and strong scattering properties of the Ag@CaCO3 composite NPs in the UV range. The Ag-Ca 15%-treated fibers also show marked antibacterial activity, as can be seen from the lack of increase in optical density over time (Figure 12). Ag NPs (~126 nm) and the other Ag@CaCO3 NPs show a limited bacterial growth (a limited increase in optical density), while the E. coli bacteria control culture nor blank viscose fibers show any inhibition effect on the bacterial density (Figure 12c). Interestingly, Lvasket al.61 reported that the antimicrobials activity of Ag NPs is size dependent. The activity of a series of Ag NPs (1–80 nm) against different types of organisms showed that Ag NPs having a diameter of ~ 10 nm most strongly interact with bacteria. According to a recent review,61 the marked antibacterial activity of tiny Ag NCs (~10 nm) against E. coli bacteria may be caused by several mechanisms: (i) tiny Ag NCs bind to the surface of the cell membrane and drastically disturb its proper functions, such as permeability and respiration. Sondiet al.62 found that tiny Ag NCs attach to the cell membrane surfaces and cause leaching of lipopolysaccharides and a subsequent loss of structural integrity and impermeability; (ii) tiny Ag NCs penetrate inside the bacteria cells and cause further damage by


Page 27 of 34

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


interacting with S- or P-containing compounds, like DNA63; (iii) tiny Ag NCs efficiently catalyze the formation of free radicals inside the bacterial cells, which causes oxidative stress and cell death64; and (iv) tiny Ag NCs serve as a source of Ag+ ions. The tiny Ag NCs can either bind to or penetrate the bacterial cells, and then dissolve in the close vicinity of the outer cell surface or inside the cells, providing Ag+ ions that are more bio-available than free Ag+ ions in the bulk medium that contains the bacterial cells.65

Figure 12. Properties of viscose fibers, and viscose fibers treated with Ag NPs or Ag@CaCO3 composite NCs: (a) UV-vis absorbance; (b) UV transmittance; and (c) antibacterial activity. The pristine viscose fibers and an E. coli bacteria control culture are given for reference. 27 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

Page 28 of 34

CONCLUSION In this work, we developed a novel hot injection route to produce for the first time tiny Ag NCs (~10 nm) with narrow size distribution and good dispersivity onto a nanoscale CaCO3 support. This synthesis route involves the combination of (i) In situ modification of the CaCO3 NCs “seeds” with anionic surfactant (sodium oleate), (ii) Controlling the reaction environment by dispersing CaCO3 NCs into an alcoholic solution containing sodium citrate, (iii)Citrate reduction and seed-mediated growth of the Ag NCs by injecting the CaCO3 NC dispersion into a hot AgNO3 solution, and (iv) Adjusting the citrate:Ag mole ratio and the Ag:CaCO3 ratio to control the composition and structure of the final Ag@CaCO3 composite NCs. This highly versatile approach proved to be effective for the formation of tiny Ag NCs with a smaller size and a narrower size distribution. When Ag@CaCO3 NCs are deposited onto viscose fibers, a (golden) coloration of the viscose fibers is achieved due to the surface plasmon resonance effect of Ag NCs. In addition to bright colors, the Ag@CaCO3 treated viscose fibers exhibit good UV protection properties (a low UV transmittance) and excellent antibacterial activity against Escherichia coli, resulting in promising multifunctional materials for (bio)medical applications. The seed-mediated hot injection approach developed in this work is highly versatile and is applicable for the deposition of tiny nanocrystals other noble metals, such as Au, Pt, or Pd, on various kinds of nanosized substrates, like metal, metal oxides, ceramics, or polymers nanoparticles.

AUTHOR CONTRIBUTIONS


Page 29 of 34

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 authors of this article and their contribution to this work are as follows: Ahmed Barhoum, 60%; Guy Van Assche 20%; Mohamed Rehan, Hubert Rahier, and Mikhael Bechelany are equally participating by 20%.

ACKNOWLEDGMENT

Ahmed Barhoum would like to thank FWO - Research Foundation Flanders (grant no V450315N) and the Strategic Initiative Materials in Flanders (SBO- project no. 130529 INSITU) for financial support. A.B. thanks Prof. Detlef W. Bahnemann (Institute of Technical Chemistry, Leibniz Universität Hannover, Germany), Prof. Said Elsheikh (Central Metallurgical Research and Development Institute, Egypt), Prof. Samya El-Sherbiny and Prof. Fatma Morsy (Printing and Packaging Lab., Helwan University, Egypt), and Prof. Alain Dufresne (The International School of Paper, Print Media and Biomaterials, France) for their help and valuable discussions. Part of this work was performed, by Ahmed Barhoum in the lab of Prof. Detlef W. Bahnemann, during Ahmed Barhoum visit to Institute of Technical Chemistry, Leibniz Universität Hannover, Germany. Notes: The authors declare no competing financial interest.

REFERENCES (1) (2)

(3)

(4)

Chang, S.; Chen, K.; Hua, Q.; Ma, Y.; Huang, W. Evidence for the Growth Mechanisms of Silver Nanocubes and Nanowires. J. Phys. Chem. C 2011, 115 (16), 7979–7986. Niu, W.; Zheng, S.; Wang, D.; Liu, X.; Li, H.; Han, S.; Chen, J.; Tang, Z.; Xu, G. Selective Synthesis of Single-Crystalline Rhombic Dodecahedral, Octahedral, and Cubic Gold Nanocrystals. J. Am. Chem. Soc. 2009, 131 (2), 697–703. Rycenga, M.; Cobley, C. M.; Zeng, J.; Li, W.; Moran, C. H.; Zhang, Q.; Qin, D.; Xia, Y. Controlling the Synthesis and Assembly of Silver Nanostructures for Plasmonic Applications. Chem. Rev. 2011, 111 (6), 3669–3712. Lei, Y.; Mehmood, F.; Lee, S.; Greeley, J.; Lee, B.; Seifert, S.; Winans, R. E.; Elam, J. W.; Meyer, R. J.; Redfern, P. C.; Teschner, D.; Schlögl, R.; Pellin, M. J.; Curtiss, L. A.; Vajda, S. Increased Silver Activity for Direct Propylene Epoxidation via Subnanometer 29 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

(5) (6) (7) (8) (9) (10)

(11)

(12)

(13) (14)

(15)

(16)

(17)

(18)

(19)

(20)

(21) (22)

Size Effects. Science 2010, 328 (5975), 224–228. Sun, Y. Controlled Synthesis of Colloidal Silver Nanoparticles in Organic Solutions: Empirical Rules for Nucleation Engineering. Chem. Soc. Rev. 2013, 42 (7), 2497–2511. Wu, Y.; Wang, D.; Li, Y. Nanocrystals from Solutions: Catalysts. Chem. Soc. Rev. 2014, 43 (7), 2112–2124. Ng, K. H.; Liu, H.; Penner, R. M. Subnanometer Silver Clusters Exhibiting Unexpected Electrochemical Metastability on Graphite. Langmuir 2000, 16 (8), 4016–4023. Zhang, W.; Qiao, X.; Chen, J. Synthesis of Silver nanoparticles—Effects of Concerned Parameters in Water/oil Microemulsion. Mater. Sci. Eng. B 2007, 142 (1), 1–15. Yu, D.; Yam, V. W.-W. Controlled Synthesis of Monodisperse Silver Nanocubes in Water. J. Am. Chem. Soc. 2004, 126 (41), 13200–13201. Cathcart, N.; Kitaev, V. Monodisperse Hexagonal Silver Nanoprisms: Synthesis via Thiolate-Protected Cluster Precursors and Chiral, Ligand-Imprinted Self-Assembly. ACS Nano 2011, 5 (9), 7411–7425. Yu, P.; Huang, J.; Yuan, C.-T.; Tang, J. Synthesis of Silver Nanoprisms and Nanodiscs an Applications in Fluorescence Blinking Suppression. J. Chinese Chem. Soc. 2010, 57 (3B), 528–533. Sun, Y.; Mayers, B.; Herricks, T.; Xia, Y. Polyol Synthesis of Uniform Silver Nanowires: A Plausible Growth Mechanism and the Supporting Evidence. Nano Lett. 2003, 3 (7), 955–960. Hong, L.; Li, Q.; Lin, H.; Li, Y. Synthesis of Flower-like Silver Nanoarchitectures at Room Temperature. Mater. Res. Bull. 2009, 44 (6), 1201–1204. Natalia L. Pacioni , Claudio D. Borsarelli , Valentina Rey, A. V. V. Silver Nanoparticle Applications; Alarcon, E. I., Griffith, M., Udekwu, K. I., Eds.; Engineering Materials; Springer International Publishing: Cham, 2015. Dong, X.; Ji, X.; Jing, J.; Li, M.; Li, J.; Yang, W. Synthesis of Triangular Silver Nanoprisms by Stepwise Reduction of Sodium Borohydride and Trisodium Citrate. J. Phys. Chem. C 2010, 114 (5), 2070–2074. Oliveira, M. M.; Ugarte, D.; Zanchet, D.; Zarbin, A. J. G. Influence of Synthetic Parameters on the Size, Structure, and Stability of Dodecanethiol-Stabilized Silver Nanoparticles. J. Colloid Interface Sci. 2005, 292 (2), 429–435. Rehan, M.; Mashaly, H. M.; Mowafi, S.; Abou El-Kheir, A.; Emam, H. E. MultiFunctional Textile Design Using in-Situ Ag NPs Incorporation into Natural Fabric Matrix. Dyes Pigm. 2015, 118, 9–17. Pillai, Z. S.; Kamat, P. V. What Factors Control the Size and Shape of Silver Nanoparticles in the Citrate Ion Reduction Method? J. Phys. Chem. B 2004, 108 (3), 945– 951. Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem. Int. Ed. Engl. 2009, 48 (1), 60–103. Wiley, B. J.; Chen, Y.; McLellan, J. M.; Xiong, Y.; Li, Z.-Y.; Ginger, D.; Xia, Y. Synthesis and Optical Properties of Silver Nanobars and Nanorice. Nano Lett. 2007, 7 (4), 1032–1036. Jin, R.; Cao, Y.; Mirkin, C. A.; Kelly, K. L.; Schatz, G. C.; Zheng, J. G. Photoinduced Conversion of Silver Nanospheres to Nanoprisms. Science 2001, 294 (5548), 1901–1903. Jin, R.; Cao, Y. C.; Hao, E.; Métraux, G. S.; Schatz, G. C.; Mirkin, C. A. Controlling 30 ACS Paragon Plus Environment

Page 30 of 34

Page 31 of 34

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


Anisotropic Nanoparticle Growth through Plasmon Excitation. Nature 2003, 425 (6957), 487–490. (23) Sanders, D. L.; Kingsnorth, A. N. From Ancient to Contemporary Times: A Concise History of Incisional Hernia Repair. Hernia 2012, 16 (1), 1–7. (24) Lu, L.; Sun, R. W.-Y.; Chen, R.; Hui, C.-K.; Ho, C.-M.; Luk, J. M.; Lau, G. K. K.; Che, C.-M. Silver Nanoparticles Inhibit Hepatitis B Virus Replication. Antiviral Ther. 2008, 13 (2), 253–262. (25) Deng, Z.; Zhu, H.; Peng, B.; Chen, H.; Sun, Y.; Gang, X.; Jin, P.; Wang, J. Synthesis of PS/Ag Nanocomposite Spheres with Catalytic and Antibacterial Activities. ACS Appl. Mater. Interfaces 2012, 4 (10), 5625–5632. (26) Tran, Q. H.; Nguyen, V. Q.; Le, A.-T. Silver Nanoparticles: Synthesis, Properties, Toxicology, Applications and Perspectives. Adv. Nat. Sci. Nanosci. Nanotechnol. 2013, 4 (3), 033001. (27) Kim, Y. H.; Lee, D. K.; Cha, H. G.; Kim, C. W.; Kang, Y. S. Synthesis and Characterization of Antibacterial Ag−SiO 2 Nanocomposite. J. Phys. Chem. C 2007, 111 (9), 3629–3635. (28) Jung, H.; Park, M.; Kang, M.; Jeong, K.-H. Silver Nanoislands on Cellulose Fibers for Chromatographic Separation and Ultrasensitive Detection of Small Molecules. Light Sci. Appl. 2016, 5 (1), e16009. (29) Morsy, F. A.; El-Sheikh, S. M.; Barhoum, A. Nano-Silica and SiO2/CaCO3 Nanocomposite Prepared from Semi-Burned Rice Straw Ash as Modified Papermaking Fillers. Arab. J. Chem. 2014. (30) Barhoum, A.; Van Assche, G.; Makhlouf, A. S. H.; Terryn, H.; Baert, K.; Delplancke, M.P.; El-Sheikh, S. M.; Rahier, H. A Green, Simple Chemical Route for the Synthesis of Pure Nanocalcite Crystals. Cryst. Growth Des. 2015, 15 (2), 573–580. (31) Barhoum, A.; Rahier, H.; Abou-Zaied, R. E.; Rehan, M.; Dufour, T.; Hill, G.; Dufresne, A. Effect of Cationic and Anionic Surfactants on the Application of Calcium Carbonate Nanoparticles in Paper Coating. ACS Appl. Mater. Interfaces 2014, 6 (4), 2734–2744. (32) El-Sheikh, S. M.; El-Sherbiny, S.; Barhoum, A.; Deng, Y. Effects of Cationic Surfactant during the Precipitation of Calcium Carbonate Nano-Particles on Their Size, Morphology, and Other Characteristics. Colloids Surf., A.. 2013, 422, 44–49. (33) El-Sheikh, S. M.; Barhoum, A.; El-Sherbiny, S.; Morsy, F.; El-Midany, A. A.-H.; Rahier, H. Preparation of Superhydrophobic Nanocalcite Crystals Using Box–Behnken Design. Arab. J. Chem. 2014. (34) Barhoum, A.; Ibrahim, H. M.; Hassanein, T. F.; Hill, G.; Reniers, F.; Dufour, T.; Delplancke, M. P.; Van Assche, G.; Rahier, H. Preparation and Characterization of UltraHydrophobic Calcium Carbonate Nanoparticles. IOP Conf. Ser. Mater. Sci. Eng. 2014, 64 (1), 012037. (35) Barhoum, A.; Van Lokeren, L.; Rahier, H.; Dufresne, A.; Van Assche, G. Roles of in Situ Surface Modification in Controlling the Growth and Crystallization of CaCO3 Nanoparticles, and Their Dispersion in Polymeric Materials. J. Mater. Sci. 2015, 50 (24), 7908–7918. (36) El-Sherbiny, S.; El-Sheikh, S. M.; Barhoum, A. Preparation and Modification of Nano Calcium Carbonate Filler from Waste Marble Dust and Commercial Limestone for Papermaking Wet End Application. Powder Technol. 2015, 279, 290–300. (37) Miller, Q. R. S.; Kaszuba, J. P.; Schaef, H. T.; Bowden, M. E.; McGrail, B. P. Impacts of 31 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

(38) (39)

(40)

(41)

(42)

(43) (44)

(45) (46)

(47)

(48) (49)

(50) (51)

(52) (53)

Organic Ligands on Forsterite Reactivity in Supercritical CO2 Fluids. Environ. Sci. Technol. 2015, 49 (7), 4724–4734. Pokrovsky, O. S. Kinetics and Mechanisms of Dolomite Dissolution in Neutral to Alkaline Solutions Revisited. Am. J. Sci. 2001, 301 (7), 597–626. Jordan, G.; Pokrovsky, O. S.; Guichet, X.; Schmahl, W. W. Organic and Inorganic Ligand Effects on Magnesite Dissolution at 100 °C and pH=5 to 10. Chem. Geol. 2007, 242 (3-4), 484–496. Xia, H.; Bai, S.; Hartmann, J.; Wang, D. Synthesis of Monodisperse Quasi-Spherical Gold Nanoparticles in Water via silver(I)-Assisted Citrate Reduction. Langmuir 2010, 26 (5), 3585–3589. Ershov, B. G.; Janata, E.; Henglein, A. Growth of Silver Particles in Aqueous Solution: Long-Lived “magic” clusters and Ionic Strength Effects. J. Phys. Chem. 1993, 97 (2), 339–343. Jiang, X. C.; Chen, C. Y.; Chen, W. M.; Yu, A. B. Role of Citric Acid in the Formation of Silver Nanoplates through a Synergistic Reduction Approach. Langmuir 2010, 26 (6), 4400–4408. Henglein, A.; Giersig, M. Formation of Colloidal Silver Nanoparticles: Capping Action of Citrate. J. Phys. Chem. B 1999, 103 (44), 9533–9539. Kilin, D. S.; Prezhdo, O. V.; Xia, Y. Shape-Controlled Synthesis of Silver Nanoparticles: Ab Initio Study of Preferential Surface Coordination with Citric Acid. Chem. Phys. Lett. 2008, 458 (1-3), 113–116. Djokić, S. Synthesis and Antimicrobial Activity of Silver Citrate Complexes. Bioinorg. Chem. Appl. 2008, 2008, 1–7. Patra, S.; Pandey, A. K.; Sen, D.; Ramagiri, S. V; Bellare, J. R.; Mazumder, S.; Goswami, A. Redox Decomposition of Silver Citrate Complex in Nanoscale Confinement: An Unusual Mechanism of Formation and Growth of Silver Nanoparticles. Langmuir 2014, 30 (9), 2460–2469. Wang, Y.; Wan, D.; Xie, S.; Xia, X.; Huang, C. Z.; Xia, Y. Synthesis of Silver Octahedra with Controlled Sizes and Optical Properties via Seed-Mediated Growth. ACS Nano 2013, 7 (5), 4586–4594. Kwon, S. G.; Hyeon, T. Formation Mechanisms of Uniform Nanocrystals via HotInjection and Heat-up Methods. Small 2011, 7 (19), 2685–2702. Williams, J. V.; Kotov, N. A.; Savage, P. E. A Rapid Hot-Injection Method for the Improved Hydrothermal Synthesis of CdSe Nanoparticles. Ind. Eng. Chem. Res. 2009, 48 (9), 4316–4321. Peng, S.; Sun, Y. Synthesis of Silver Nanocubes in a Hydrophobic Binary Organic Solvent. Chem. Mater. 2010, 22 (23), 6272–6279. Sarkar, P.; Bhui, D. K.; Bar, H.; Sahoo, G. P.; Samanta, S.; Pyne, S.; Misra, A. AqueousPhase Synthesis of Silver Nanodiscs and Nanorods in Methyl Cellulose Matrix: Photophysical Study and Simulation of UV-Vis Extinction Spectra Using DDA Method. Nanoscale Res. Lett. 2010, 5 (10), 1611–1618. Freestone, I.; Meeks, N.; Sax, M.; Higgitt, C. The Lycurgus Cup — A Roman Nanotechnology. Gold Bull. 2007, 40 (4), 270–277. Pérez-Arantegui, J.; Molera, J.; Larrea, A.; Pradell, T.; Vendrell-Saz, M.; Borgia, I.; Brunetti, B. G.; Cariati, F.; Fermo, P.; Mellini, M.; Sgamellotti, A.; Viti, C. Luster Pottery from the Thirteenth Century to the Sixteenth Century: A Nanostructured Thin Metallic 32 ACS Paragon Plus Environment

Page 32 of 34

Page 33 of 34

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


(54)

(55) (56)

(57) (58)

(59) (60)

(61)

(62)

(63)

(64)

(65)

Film. J. Am. Ceram. Soc. 2004, 84 (2), 442–446. Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C. The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment. J. Phys. Chem. B 2003, 107 (3), 668–677. Smiechowicz, E.; Kulpinski, P.; Niekraszewicz, B.; Bemska, J.; Morgiel, J. Effect of Silver on Cellulose Fibre Colour. Color. Technol. 2014, 130 (6), 424–431. Park, S. Y.; Chung, J. W.; Priestley, R. D.; Kwak, S.-Y. Covalent Assembly of Metal Nanoparticles on Cellulose Fabric and Its Antimicrobial Activity. Cellulose 2012, 19 (6), 2141–2151. Kelly, F. M.; Johnston, J. H. Colored and Functional Silver Nanoparticle-Wool Fiber Composites. ACS Appl. Mater. Interfaces 2011, 3 (4), 1083–1092. Agnihotri, S.; Mukherji, S.; Mukherji, S. Size-Controlled Silver Nanoparticles Synthesized over the Range 5–100 Nm Using the Same Protocol and Their Antibacterial Efficacy. RSC Adv. 2014, 4 (8), 3974–3983. Xu, B.; Huang, Y.; Watson, M. D. Cotton Color Distributions in the CIE L*a*b* System. Text. Res. J. 2001, 71 (11), 1010–1015. Vanden Bout, D. A. Metal Nanoparticles: Synthesis, Characterization, and Applications Edited by Daniel L. Feldheim (North Carolina State University) and Colby A. Foss, Jr. (Georgetown University). J. Am. Chem. Soc. 2002, 124 (26), 7874–7875. Ivask, A.; Kurvet, I.; Kasemets, K.; Blinova, I.; Aruoja, V.; Suppi, S.; Vija, H.; Käkinen, A.; Titma, T.; Heinlaan, M.; Visnapuu, M.; Koller, D.; Kisand, V.; Kahru, A. SizeDependent Toxicity of Silver Nanoparticles to Bacteria, Yeast, Algae, Crustaceans and Mammalian Cells in Vitro. PLoS One 2014, 9 (7), e102108. Sondi, I.; Salopek-Sondi, B. Silver Nanoparticles as Antimicrobial Agent: A Case Study on E. Coli as a Model for Gram-Negative Bacteria. J. Colloid Interface Sci. 2004, 275 (1), 177–182. Morones, J. R.; Elechiguerra, J. L.; Camacho, A.; Holt, K.; Kouri, J. B.; Ramírez, J. T.; Yacaman, M. J. The Bactericidal Effect of Silver Nanoparticles. Nanotechnology 2005, 16 (10), 2346–2353. Kim, J. S.; Kuk, E.; Yu, K. N.; Kim, J.-H.; Park, S. J.; Lee, H. J.; Kim, S. H.; Park, Y. K.; Park, Y. H.; Hwang, C.-Y.; Kim, Y.-K.; Lee, Y.-S.; Jeong, D. H.; Cho, M.-H. Antimicrobial Effects of Silver Nanoparticles. Nanomedicine 2007, 3 (1), 95–101. Li, W.-R.; Xie, X.-B.; Shi, Q.-S.; Zeng, H.-Y.; Ou-Yang, Y.-S.; Chen, Y.-B. Antibacterial Activity and Mechanism of Silver Nanoparticles on Escherichia Coli. Appl. Microbiol. Biotechnol. 2010, 85 (4), 1115–1122.



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

GRAPHICAL ABSTRACT


Page 34 of 34

Seed-Mediated Hot-Injection Synthesis of Tiny Ag Nanocrystals on

Recommend Documents