Reductant-Free Synthesis of Silver Nanoparticles-Doped Cellulose

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Reductant-Free Synthesis of Silver Nanoparticles-Doped Cellulose Microgels for Catalyzing and Product Separation Yangyang Han, Xiaodong Wu, Xinxing Zhang, Zehang Zhou, and Canhui Lu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00889 • Publication Date (Web): 28 Sep 2016 Downloaded from http://pubs.acs.org on October 4, 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 Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33

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

ACS Sustainable Chemistry & Engineering

Reductant-Free Synthesis of Silver NanoparticlesDoped Cellulose Microgels for Catalyzing and Product Separation Yangyang Han, Xiaodong Wu, Xinxing Zhang* , Zehang Zhou and Canhui Lu* State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, No. 24 South Section 1 of First Ring Road, Chengdu 610065, China Abstract A novel and straightforward synthetic strategy was developed to prepare silver nanoparticles-doped cellulose microgels (Ag NPs@CMG) nanohybrids at room temperature. Residual alkali (sodium hydroxide/urea) from cellulose dissolving system was reused and acted as a functional accelerant, which made it possible for Ag+ to be reduced to Ag0 by CMG at room temperature, yielding Ag NPs decorated on CMG. The as-prepared Ag NPs@CMG nanohybrids exhibited excellent catalytic performance in reduction of 4-nitrophenol and organic dyes. Moreover, the Ag NPs@CMG nanohybrids were capable to form a desirable porous membrane for catalyzing and simultaneous product separation. Reactants passing through the membrane could be catalytically transformed to product, which is of great significance for water treatment. As a demonstration, three kinds of organic dye solutions were successfully decolorized by using Ag NPs@CMG nanohybrids based membrane. The simplicity, sustainability, and straightforwardness of this approach to prepare high-efficient catalyst and functional membrane open up new possibilities for large-scale production and application of bioresources/noble metal nanohybrids in various fields.

Corresponding author: Xinxing Zhang and Canhui Lu *E-mail address: [email protected] & [email protected]

1 Environment ACS Paragon Plus


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

Key words: cellulose microgels, silver nanoparticles, residual alkali, catalyzing, product separation Introduction Noble metal-based nanohybrid materials play an important role in physical, chemical and biological industries due to their unique photonic1, magnetic2, electrochemical3, especially catalytic properties4-5. Tremendous efforts have been made to efficiently fabricate functional noble metal nanohybrids.6-8 However, poisonous reducing agents (such as sodium borohydride and hydrazine) are usually employed in the synthesis of these noble metal nanohybrids.9-10 On the other hand, extra capping or dispersing agents are generally necessary to obtain uniform and stable dispersion of metal nanomaterials. This is against the present trend towards sustainable as well as economical development. Therefore, synthesis of noble metal nanohybrids with lower environmental and economic cost is highly demanded in various fields. Cellulose is an inexhaustible natural resource which represents the most abundant polysaccharide material on earth.11 In recent years, several methods have been established for cost-efficient and sustainable synthesis of noble metal nanohybrids by using cellulose as green reducing agents or supporting matrices.12-17 For example, Thielemans et al. developed a one-step synthesis of palladium nanoparticles (Pd NPs) supported on cellulose nanocrystals, which acted as both reducing agent and support material.15 Liu et al. prepared gold (Au) NPs@bacterial cellulose nanohybrids at 110 °C using amidoxime-grafted bacterial cellulose as a reducing agent and carrier for the synthesis of Au NPs.16 Besides, Moores et al. reported that cellulose nanocrystals could perform as support and reductant for the synthesis of silver (Ag) NPs from bulk Ag metal.17 Despite of these pioneering works, there are still big challenges for their practical application because of drawbacks such as low volume output of cellulose nanocrystals, sophisticated surface functionalization procedure, and particularly high temperatures employed in the reactions. Hence, the development of simple, economical and large-scale compliant approach to noble metal nanohybrids by utilizing cellulose becomes a fascinating issue. Cellulose gels prepared by sol-gel method have high porosity, a large surface area, abundant available functional groups and high mechanical strength,18-19 which make it an attractive candidate as supporting


Page 2 of 33

Page 3 of 33

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


materials. The recently developed low-cost, low-toxicity and effective alkali aqueous solution system as a cellulose solvent provides a straightforward way to design and fabricate functional cellulose gels.20 Unfortunately, the massive residual alkali from the dissolving system has to be removed by time-consuming (usually several days) and water-consuming dialysis, which is economically and ecologically infeasible for practical application. Therefore, rational dispose of the waste alkali is of great significance as far as the call of the world for energy and sustainability. In this work, we propose a novel and mild approach to synthesize Ag NPs-doped cellulose microgels (Ag NPs@CMG) at room temperature by reusing residual alkali as a functional accelerant. The CMG with a unique microstructure acted as a reducing agent and supporting matrix for non-agglomerated synthesis of Ag NPs. Notably, residual alkali from the dissolving system dramatically accelerated the reduction of Ag+ by CMG at room temperature, yielding well dispersed Ag NPs supported on CMG. The resultant flexible and porous Ag NPs@CMG nanohybrids exhibited high activity in catalytic reduction of 4-nitrophenol (4-NP) and organic dyes. This excellent catalytic performance of Ag NPs@CMG nanohybrids allowed us to fabricate a porous membrane for efficient catalyzing and simultaneous product filtration. Because of the cost-efficient and sustainable characteristics, the present approach is suitable for industrial scale production and application of bio-resources/noble metal nanohybrids.

Materials and Methods Materials Filter paper was purchased from commercial sources and subjected to cutting and shredding processes. Silver nitrate (AgNO3), 4-nitrophenol (4-NP), sodium borohydride (NaBH4), sodium hydroxide (NaOH), urea, carboxymethylcellulose sodium, methylene blue (MB), and methyl orange (MO) were purchased from Chengdu Kelong Chemical Plant (China). Rhodamine 6G (R6G) was purchased from Aladdin Company. All reagents were used without further purification.

Fabrication of Ag NPs@CMG nanohybrids Filter paper cellulose was dried at 80 °C for 12 h to remove the moisture. The aqueous dissolving system that contained 7 wt% NaOH and 12 wt% urea was pre-cooled to -12 oC in a refrigerator. Then a desired



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

amount of cellulose (2 wt%, according to the weight of aqueous solution) was added to the pre-cooled dissolving system and stirred vigorously for 5 min to obtain a transparent solution. Subsequently, 10 g of the viscous cellulose solution was dropwise added into 100 mL deionized water with magnetic stirring, forming CMG suspension. Without removing the residual NaOH and urea, a desired amount of AgNO3 solution was added to the CMG suspensions (the final concentrations of Ag+ in CMG suspension were 0.2, 0.5 and 1.0 mM, respectively), and stirred for 24 h at room temperature (about 25 oC). The resultant product (Ag NPs@CMG) was filtered and washed with deionized water to remove the residual chemical reagents. The Ag NPs@CMG nanohybrids were dispersed in deionized water (100 g) and sonicated for 10 min to obtain Ag NPs@CMG nanohybrids suspension.

Catalytic performance test In order to evaluate the catalytic activity of the synthesized Ag NPs@CMG nanohybrids, the reduction of 4NP by NaBH4 catalyzed with Ag NPs@CMG nanohybrids was employed as the model reaction. In a typical experiment, NaBH4 aqueous solution (45 mL, 40 mM) was mixed with 4-NP solution (5 mL, 1.2 mM). As a result, the concentration of 4-NP and NaBH4 in the reaction solution was 0.12 and 36 mM, respectively. Then the Ag NPs@CMG nanohybrids were added into the mixture solution at room temperature (containing 0.014 mg Ag). Subsequently, a certain amount of the mixtures was taken in a sealed quartz cuvette with an optical path of 1 cm and analyzed via UV-vis spectroscopy at intervals of 2 min. For catalyzing and simultaneous product filtration, Ag NPs@CMG (25 mL, 0.5 mM, containing 1.35 mg Ag) was deposited on a filter paper in a glass sand funnel equipped with filter conical flask. 50 mL mixture solution (0.12 mM 4-NP and 36 mM NaBH4) was added to the vacuum filtration funnel coated with a layer of Ag NPs@CMG membrane. The collected solution in conical flask was analyzed by UV-vis spectroscopy. In order to testify the reusability of the Ag NPs@CMG catalyst, the membrane washed with deionized water, and reused in the next cycle.

Catalytic reduction of dyes In a typical experiment for catalytic reduction of organic dyes, MB aqueous solution (40 mL, 10 mg/L) was mixed with fresh NaBH4 aqueous solution (40 mL, 50 mM). The Ag NPs@CMG nanohybrids (1 mL, 0.5 mM, containing 0.054 mg Ag) as the catalyst were added into the mixture solution at room temperature. In addition,


Page 4 of 33

Page 5 of 33

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 catalytic reduction of MO and R6G by NaBH4 in the presence of Ag NPs@CMG nanohybrids was also explored respectively. NaBH4 aqueous solution (10 mL, 50 mM) was added into MO aqueous solution (40 mL, 10 mg/L) and subsequently Ag NPs@CMG nanohybrids (0.2 mL, 0.5 mM, containing 0.011 mg Ag) were added into the mixed solution. R6G aqueous solution (40 mL, 10 mg/L) was mixed with NaBH4 aqueous solution (10 mL, 50 mM) and then Ag NPs@CMG nanohybrids (0.5 mL, 0.5 mM, containing 0.027 mg Ag) were used to catalyze the reduction of the R6G. The catalytic reduction of organic dyes was recorded by monitoring the maximum absorbance (λmax) of the dyes with UV-vis spectrophotometer.

Characterization The morphology of the Ag NPs@CMG sample was observed by scanning electron microscope (SEM, JEOL JSM-5600, Japan) and transmission electron microscope (JEOL JEM-100CX, Japan) equipped with high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The particle sizes of Ag NPs@CMG on SEM image and Ag NPs on TEM image were measured using Image-J software. At least 100 particles were analyzed. The UV-vis spectra were recorded on a Shimadzu UVmini1240 spectrophotometer (Japan) by using a quartz cuvette with an optical path of 1 cm at room temperature. Carboxymethylcellulose sodium was used as a stabilizer for samples in the process of UV-vis measurement, which has no characteristic UV-vis absorption peak as shown in Figure S1. Fourier transform infrared spectroscopy (FTIR) studies were conducted on a Nicolet 6700 spectrophotometer (USA) and the spectra were recorded from 4000 to 500 cm-1 at a resolution of 2 cm-1. X-ray diffraction (XRD) patterns were recorded on a Philips Analytical X'Pert X-diffractometer (Philips Co., Netherlands) with Cu Ka radiation (λ=0.1540 nm) at an accelerating voltage of 40 kV and a current of 35 mA in the range of 5-80o with a step interval of 0.03o at room temperature. Samples for XRD and FTIR characterizations were prepared by freeze-drying the CMG and Ag NPs@CMG nanohybrids followed by oven-drying. The morphology of the Ag NPs@CMG membrane after filtration was observed by scanning electron microscopy (SEM, JEOL JSM-5900LV, Japan). The sample of Ag NPs@CMG membrane was prepared by freeze-drying.

Results and discussion Synthesis of Ag NPs@CMG nanohybrids



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

In order to better understand the facile approach to Ag NPs@CMG nanohybrids, the entire synthesis process is schematically illustrated in Figure 1a. Firstly, cellulose was dissolved in a NaOH/urea system and formed a homogeneous and transparent solution. CMG was formed via sol-gel transition by dropwise adding cellulose solution into water under vigorous magnetic stirring. Then, AgNO3 solution was directly added to the alkali CMG suspension without removing the residual alkali. In this strong alkali condition, CMG was capable of reducing Ag+ to Ag0 at room temperature, simultaneously yielding Ag NPs anchored on the CMG supporting matrix. The reducing process of Ag+ by CMG in strong alkali condition at room temperature can be revealed by the concomitant change in the color of the reaction mixture. As given in Figure 1b, the color of the reaction mixture was light yellow at the beginning and gradually changed to dark brown as a function of time. Notably, the entire process just proceeded at room temperature without any heating and employing any other reducing, capping or dispersing agents. The economic and ecological benefits of this process, including reuse of residual alkali and avoiding energy consumption, make it promising for industrial application.

Figure 1. Schematic illustration for the facile synthesis of Ag NPs@CMG nanohybrids (a) and digital camera photos showing the color changes of CMG-Ag+ (0.5 mM) mixture as a function of time (b). 6 Environment ACS Paragon Plus

Page 6 of 33

Page 7 of 33

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


Characterization of Ag NPs@CMG nanohybrids UV-vis spectra show that a surface plasmon resonance (SPR) band around 400 nm can be observed for Ag NPs@CMG nanohybrids as shown in Figure 2a, confirming the presence of Ag NPs.21 With increasing concentration of Ag+, the SPR band of Ag NPs@CMG nanohybrids becomes higher and broader. Besides, the characteristic band of Ag NPs@CMG nanohybrids shifts from 390 nm to 426 nm. These results indicate that higher concentration of Ag+ leads to larger Ag NPs with higher dispersity. In addition, the colors of Ag NPs@CMG suspensions differ from each other with increasing the concentration of Ag+, from yellow (0.2 mM Ag+) to dark brown (1.0 mM Ag+) as shown in Figure 2a (inset photos), indicating more Ag NPs formed with higher Ag+ concentration.22 In order to investigate the roles of CMG and alkali in synthesis of Ag NPs, contrast experiments were conducted. When Ag+ was added into the alkali solution (same concentration) in the absence of CMG, no Ag NPs could be obtained as revealed from the UV-vis spectra (Figure 2b). Similarly, characteristic absorption band of Ag NPs was not observed in Figure 2b when the residual alkali was removed from CMG suspension. These results suggest that both CMG and residual alkali play indispensable roles in the synthesis of Ag NPs@CMG nanohybrids at room temperature.

Figure 2. UV-vis spectra and digital camera photos (inset) of Ag NPs@CMG nanohybrids with different concentrations: 0.2, 0.5, and 1.0 mM (a). UV-vis spectra of Ag NPs prepared under different variables (b).



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

XRD patterns (Figure S2a) reveal the crystal structure of CMG and Ag NPs@CMG nanohybrids. For CMG, the diffraction peaks at 2θ = 12o, 20o and 22o, corresponding to the (11-0), (110), and (200) crystal planes, are characteristic peaks of cellulose II crystal.23 In the spectrum of Ag NPs@CMG nanohybrids (0.5 mM), peaks at 2θ= 38 o, 64 o and 77 o, assigned to the (111), (220) and (311) lattice planes, can be indexed to the face centre cubic crystal structure of Ag in accordance with the values in standard card (JCPDS Card No. 4-783),22 indicating that metal Ag was successfully synthesized in Ag NPs@CMG nanohybrids. In order to further investigate the role of CMG played in the reduction of Ag+, the change in the chemical structure of CMG was investigated by FTIR. As shown in Figure S2b, original CMG exhibits typical characteristics of cellulose around 3200-3500 cm−1 (νOH), 2850-3000 cm−1 (νCH), and 1059-1162 cm−1 (νC-O and νC-O-C).24 After the reducing reaction, a new peak at 1655 cm−1 can be observed, which can be assigned to the C=O stretching.25 This revealed that the abundant hydroxyl groups of CMG were oxidized during the reduction of Ag+, which is in accordance with our previous works.24-25

Morphology observation of Ag NPs@CMG nanohybrids The morphology of Ag NPs@CMG nanohybrids was characterized by SEM and shown in Figure 3. The Ag NPs@CMG nanohybrids display random shapes (Figure 3a) and are highly dispersed with an average size of 2.8 µm according to the distribution histogram (Figure 3b). It is worth noting that the individual Ag NPs@CMG nanohybrid exhibits a three dimensional porous structure at high magnification as shown in Figure 3c-d. The 3D porous structure of CMG played as a good scaffold/template for the growth of Ag NPs and could obstruct the agglomeration of Ag NPs during synthesis. Compared with cellulose bulk gel, the micro-size and the porous microstructure of CMG are expected to endow the resultant Ag NPs@CMG nanohybrids with higher catalytic activity.


Page 8 of 33

Page 9 of 33

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. SEM image (a, scale bar=100 µm) and particle size distribution (b) of Ag NPs@CMG nanohybrids. SEM images with high magnifications (c, scale bar=5 µm) (d, scale bar=1 µm) of Ag NPs@CMG nanohybrids. To further investigate the microstructure of Ag NPs@CMG nanohybrids, TEM observations combined with HRTEM and SAED were carried out. As shown in Figure 4a, virtually spherical Ag NPs with desirable dispersion are anchored on the surface of interconnected network of CMG, and no aggregation of Ag NPs is observed. The corresponding statistical histogram (Figure 4b) shows that the sizes of the formed Ag NPs are almost in the range 2.0-16.0 nm, with a mean diameter of 8 nm. These results confirm that aggregation of Ag NPs was prevented via in situ synthesis of them on the hydrophilic networks of CMG. This may be attributed



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 33

to that the oxygen-containing groups (C-O-H, C=O) on CMG can act as anchor points to immobilize Ag NPs through the complexing or electrostatic interaction26, which played an important role in uniform growth and distribution of Ag NPs. In addition, few large Ag NPs can also be observed. Figure 4c and e show a HRTEM image of two individual Ag NPs, respectively. Lattice fringes are random arranged in Figure 4c and codirectionally arranged in Figure 4e, suggesting that both polycrystalline and single crystalline Ag NPs are existed in Ag NPs@CMG nanohybrids. The lattice fringe spacing in Figure 4e is measured to be 0.235 nm, corresponding to the (111) plane of the face-centered cubic (fcc) structure of AgNPs.27 Moreover, SAED pattern recorded from the Ag NPs exhibits spotty diffraction rings in Figure 4d and diffraction spots in Figure 4f, respectively, confirming the coexistence of polycrystalline and single crystalline nature. These results clearly demonstrate that well dispersed Ag NPs can be synthesized and deposited on CMG using this green and facile approach.


Page 11 of 33

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


Figure 4. TEM image of the Ag NPs@CMG nanohybrids (0.5 mM) (scale bar, 100 nm) (a) and particle size distribution of the Ag NPs (b). The HRTEM images (c and e) (scale bar, 5 nm) and the SAED patterns (d and f) of individual Ag NPs. Proposed formation mechanism of Ag NPs@CMG using residual alkali as an accelerant



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

Page 12 of 33

Based on the aforementioned results, a possible formation mechanism of Ag NPs@CMG nanohybrids using residual alkali as an accelerant is proposed in Figure 5. Cellulose is a natural polysaccharide which consists of β-(1, 4)-linked D-glucose units and contains three hydroxyl groups per anhydroglucose unit. These abundant hydroxyl groups could form intra- and intermolecular hydrogen bonding, which traps the hydroxyl groups in a low-reactivity state and weaken their reactivity. Zhang et al. demonstrated that aqueous NaOH/urea system could dramatically weaken the hydrogen bonding of cellulose and thus dissolve cellulose.28 In this study, the residual alkali during regeneration of dissolving cellulose to form CMG was intentionally reserved, aiming at weakening the hydrogen bonding of cellulose and activating the hydroxyl groups on CMG as illustrated in Figure 5. Thus, more activated hydroxyl groups could be liberated from the hydrogen bonding in cellulose, which provide great advantage for the reduction of Ag+. On the other hand, Ag+ ions are unstable in alkaline conditions and tend to form insoluble Ag2O particles. When AgNO3 was added into the CMG suspension containing massive residual alkali, Ag2O particles were formed rapidly and anchored on the interconnected network of CMG, forming Ag2O@CMG nanohybrids. Importantly, the reduction of Ag2O, which is of a different type from Ag+ species, to Ag metal is much easier than the reduction of Ag+ to Ag metal, as widely reported in literature.29-31 Consequently, another role of residual alkali in the reaction was the production of Ag2O@CMG, which created another reaction pathway for formation of the Ag NPs@CMG in an easier manner. Hence, according to the discussion above, the residual alkali accelerant not only liberated and activated more hydroxyl groups on CMG, but also promoted the formation of Ag2O, which is easier to be reduced by the activated hydroxyl groups on CMG. As a synergistic effect of the two aspects mentioned above, mild and straightforward synthesis of Ag NPs@CMG nanohybrid at room temperature without employing any other reducing, capping or dispersing agents was realized.


Page 13 of 33

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 5. Reaction scheme for the Ag NP@CMG formation. Catalytic performance of Ag NPs@CMG nanohybrids As a model catalytic reaction, the reducing reaction of 4-NP by NaBH4 was employed to evaluate the catalytic activity of the as-prepared Ag NPs@CMG nanohybrids. The process of the catalytic reaction was monitored by recording the change in characteristic absorption band of 4-NP at 400 nm with the evolution of reaction time. As shown in Figure 6a, the absorption band of 4-NP at 400 nm gradually decreases, accompanied with the appearance of a new band around 300 nm, corresponding to 4-aminophenol (4-AP). These indicate the conversion of 4-NP to 4-AP.32 The conversion rate of 4-NP was depicted by At/A0 at λ=400 nm versus reaction time, where At is the absorbance at reaction time t and A0 is the initial absorbance. In Figure 6a (inset), it is noticed that this catalytic reaction proceeded quickly at first, and slowed down as the time went on. Figure 6b shows the plot of ln(At/A0) versus reaction time. The results indicate that ln(At/A0) decreases linearly with reaction time, which is consistent with the pseudo-first-order kinetics behavior. The pseudo-first-order rate constant k at room temperature calculated from the slope is 3.4 × 10-3 s-1. The catalytic



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 33

reactions of 0.2 and 1.0 mM Ag NPs@CMG nanohybrids were shown in Figure S3. Turnover frequency (TOF, in mol 4-NP mol-1 Ag min-1) was calculated to evaluate the catalytic activity. The TOF value of 0.5 mM Ag NPs@CMG nanohybrids is 230.4 h-1 which suggesting that Ag NPs@CMG nanohybrids has an eminent catalytic activity comparing with other materials as shown in Table S1. For catalytic reduction of 4-NP, electron transferred from BH4− to 4-NP through adsorption of the reactant molecules onto the Ag catalyst surface (Figure 6c). Ag NPs with small sizes and better dispersity result more contact opportunity with reactants, thus exhibiting high catalytic activity.

To intuitively show the excellent catalytic performance, Ag NPs@CMG nanohybrids were deposited on glass sand funnel to form an Ag NPs@CMG based catalytic membrane. When the reactants (4-NP and BH4-) passed through the catalytic membrane under vacuum condition, the highly active Ag NPs@CMG catalyst could catalyze this reaction (Figure 6f). The change in color from yellow to colorless directly demonstrates the fast catalytic reaction (Figure 6d). According to the UV-vis spectra in Figure 6g, the conversion rate of 4-NP was 98% after passing through the membrane. Moreover, the high conversion rate is nearly invariable through ten cycles (Figure 6h), which exhibits the eminent reusability of this Ag NPs@CMG nanohybrids as a catalyst. SEM was used to elucidate the microscopic structure of this Ag NPs@CMG catalytic membrane. As given in Figure 6e, this catalytic membrane consisting of the Ag NP@CMG nanohybrid possesses a porous nanostructure. This unique porous nanostructure could extend the pathways of the reactants passing through the membrane, which increased the contact opportunity of reactants and catalyst and contributed to a high conversion rate. Additionally, CMG acts as a good template which can anchor the Ag NPs firmly, avoiding their exfoliation during the cyclic catalytic process. This sustainable catalytic membrane with outstanding catalytic performance might have a great potential for industrial applications.


Page 15 of 33

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


Figure 6. Time dependent UV-vis spectra for reduction of 4-NP catalyzed with 0.5 mM Ag NPs@CMG nanohybrids (containing 0.125 µmol Ag): plot of At/Ao against time (inset) (a), plot of ln(At/Ao) against time (b). Schematic diagram for the catalytic reaction (c). Digital photograph (d) and schematic illustration (f) showing the fast reduction of 4-NP catalyzed by Ag NPs@CMG catalytic membrane. SEM micrograph of Ag NPs@CMG catalytic membrane after filtration (e). UV-vis spectra for 4-NP solution before and after passing through the catalytic membrane (g). The conversion rate of 4-NP during cyclic test (h). Catalytic performance of Ag NPs@CMG in dye reductive decolorization



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 33

Organic dyes have wide applications in industries such as printing, textile, paper, paints, and plastics.33 The hazardous effects of organic dyes in waste water have become a serious environmental issue and received significant attention.34-36 In this study, we demonstrated the capabilities of Ag NPs@CMG nanohybrids in catalytic reduction of organic pollutant dyes (including MB, MO, and R6G). After the addition of Ag NPs@CMG nanohybrids into the system, the color of the mixture gradually vanished and finally bleached, revealing the catalytic reduction of the dyes. Figure 7a shows the time-dependent UV-vis absorption of MB during the reduction process. The characteristic absorption band of MB declines gradually and nearly disappears eventually after 8 min, indicating that the reduction of MB proceed completely. MO and R6G also experienced similar bleaching processes (Figure 7b-c). While, the decolorization completed at 7 and 11 min for MO and R6G respectively. These suggest that Ag NPs@CMG nanohybrids have prominent catalytic ability for dye reductive decolorization. The fast reductive decolorization of dyes could be attributed to the high catalytic activity of Ag NPs anchored on micro-sized and porous cellulose gels, which own good dispersity and large specific surface area. Aforementioned Ag NPs@CMG based catalytic membrane is also suitable for catalyzing the reduction of organic dyes. As shown in Video 1, the decolorization of R6G was achieved during reactants passing through the membrane. The solution in conical flask was analyzed by UV-vis spectroscopy (Figure 7d). The characteristic absorption band of R6G nearly vanished after passing through the membrane, indicating the complete decolorization of R6G. For comparison, bulk cellulose gel supported Ag NPs (Ag NPs@bulk gel) was prepared (see Supporting Information for method) and the catalytic performance was also evaluated. Ag NPs@bulk gel was used as a platform for the catalytic reduction of R6G and the process was recorded in Video 2. The red color of original solution faded after passing through the gel, while light red color could still be seen. As shown in Figure 7d, the characteristic band of R6G catalyzed by Ag NPs@bulk gel still remained partly, which suggests that the reduction of R6G was incomplete. The section of Ag NPs@bulk gel was observed by optical microscope (Figure S4). Ag NPs mostly concentrated in the surface layer of the gel. Although both CMG and bulk gel


Page 17 of 33

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


have porous structure, the nonuniform dispersion of Ag NPs in surface layer of Ag NPs@bulk gel hinders its application as a membrane for fast catalyzing and product separation. As another contrast experiment, we prepared cellulose nanocrystals-supported Ag NPs nanohybrid to form a similar catalytic membrane. Unfortunately, the glass sand funnel was blocked off by the nano-sized cellulose nanocrystals-supported Ag NPs nanohybrid. This indicates that Ag NPs@CMG nanohybrid is a specialized material capable of forming porous membrane on traditional glass sand funnel and exhibiting high catalytic activity. The well dispersed Ag NPs doped CMG could have potential application in membrane catalyzing and product separation.



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 33

Figure 7. Time dependent UV-vis spectra and digital camera photos (inset) for reduction of MB (a), MO (b) and R6G (c) catalyzed by Ag NPs@CMG nanohybrids and plot of At/Ao against time (inset). UV-vis spectra for reduction R6G (d) and digital photographs (inset) showing the reduction of R6G catalyzed by Ag NPs@bulk gel (left) and Ag NPs@CMG (right). Apart from the desirable features in catalysis field, Ag NPs@CMG nanohybrids possess the versatility to form aerogel and film. As shown in Figure S5a, a porous and low-density (0.062 g/cm3) Ag NPs@CMG aerogel can be obtained by freeze drying, which is attributed to the distinctive porous structure of CMG. Under air-drying, Ag NPs@CMG nanohybrids formed flexile solid film (Figure S5b). Due to unique properties of Ag NPs (such as antibacterial activity, surface plasmon resonance and electrical conductivity) as well as the sustainability and environmental friendliness of CMG, the facile and mild approach to Ag NPs@CMG might provide an optional method to manufacture functional aerogels and films.


Page 19 of 33

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


Conclusions In this work, novel Ag NPs@CMG nanohybrids with high catalytic activity and product separation functionality were successfully prepared at room temperature by reusing residual alkali as a functional accelerant. Specifically, Ag NPs with mean size of 8 nm were synthesized by using regenerated CMG as a reducer as well as a supporting matrix. Meanwhile, residual alkali from the dissolving system acted as a functional accelerant, and signally promoted the reduction of Ag+ by CMG. This synthesized Ag NPs@CMG nanohybrids exhibited eminent activity in catalyzing the reduction of 4-NP and organic dyes. Moreover, a catalytic membrane based on Ag NPs@CMG was fabricated, which could continuously catalyze these reductive reactions and separate the product. This mild and straightforward synthetic approach to Ag NPs@CMG by reusing residual alkali as functional accelerant provided a new economical and sustainable strategy to design and synthesize various noble metal based nanohybrid materials.

Author information Corresponding author: Xinxing Zhang and Canhui Lu *E-mail address: [email protected] & [email protected] Tel: +86-28-85460607 Fax: +86-28-85402465

Acknowledgements The authors thank the National Natural Science Foundation of China (51673121 and 51433006) and Outstanding Young Scholars Fund of Sichuan University (2016SCU04A16) for financial support.

Supporting Information UV-vis spectrum of carboxymethylcellulose sodium. XRD patterns and FTIR spectra of CMG and Ag NPs@CMG nanohybrids. UV-visible spectra of the reduction of 4-NP catalyzed with 0.2 and 1.0 mM Ag NPs@CMG nanohybrids. Table of comparison of various catalysts for reduction of 4-NP. Optical microscope photographs of the section of Ag NPs@bulk gel. Digital photographs of Ag NPs@CMG aerogel and film.



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 33

Video 1: the reduction of R6G catalyzed by Ag NPs@CMG. Video 2: the reduction of R6G catalyzed by Ag NPs@bulk gel. These materials are available free of charge via the Internet at http://pubs.acs.org.

Reference (1). Jeong, S. H.; Choi, H.; Kim, J. Y.; Lee, T. W. Silver-based nanoparticles for surface plasmon resonance in organic optoelectronics. Part. Part. Syst. Charact. 2015, 32, 164-175. (2). Kowlgi, K. N. K.; Koper, G. J. M.; Picken, S. J.; Lafont, U.; Zhang, L.; Norder, B. Synthesis of magnetic noble metal (nano) particles. Langmuir 2011, 27, 7783-7787. (3). Zhang, T.; Wang, W.; Zhang, D.; Zhang, X.; Ma, Y.; Zhou, Y.; Qi, L. Biotemplated synthesis of gold nanoparticle-bacteria cellulose nanofiber nanocomposites and their application in biosensing. Adv. Funct. Mater. 2010, 20, 1152-1160. (4). Wang, S.; Yin, K.; Zhang, Y.; Liu, H. Glycerol hydrogenolysis to propylene glycol and ethylene glycol on zirconia supported noble metal catalysts. ACS Catal. 2013, 3, 2112-2121. (5). Mallampati, R.; Valiyaveettil, S. Eggshell membrane-supported recyclable catalytic noble metal nanoparticles for organic reactions. ACS Sustainable Chem. Eng. 2014, 2, 855-859. (6). Felix, E. M.; Antoni, M.; Pause, I.; Schaefer, S.; Kunz, U.; Weidler, N.; Muench, F.; Ensinger, W. Template-based synthesis of metallic Pd nanotubes by electroless deposition and their use as catalysts in the 4-nitrophenol model reaction. Green Chem. 2016, 18, 558564. (7). Cirtiu, C. M.; Dunlop-Brière, A. F.; Moores, A. Cellulose nanocrystallites as an efficient support for nanoparticles of palladium: application for catalytic hydrogenation and Heck coupling under mild conditions. Green Chem. 2011, 13, 288-291. (8). Liang, M.; Su, R.; Huang, R.; Qi, W.; Yu, Y.; Wang, L.; He, Z. Facile in situ synthesis of


Page 21 of 33

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


silver nanoparticles on procyanidin-grafted eggshell membrane and their catalytic properties. ACS Appl. Mater. Interfaces 2014, 6, 4638-4649. (9). Zhang, H.; Duan, T.; Zhu, W.; Yao, W. T. Natural chrysotile-based nanowires decorated with monodispersed Ag nanoparticles as a highly active and reusable hydrogenation catalyst. J. Phys. Chem. C 2015, 119, 21465-21472. (10).

Seo, E.; Kim, J.; Hong, Y.; Kim, Y. S.; Lee, D.; Kim, B. S. Double hydrophilic block

copolymer templated Au nanoparticles with enhanced catalytic activity toward nitroarene reduction. J. Phys. Chem. C 2013, 117, 11686-11693. (11).

Zhang, K.; Geissler, A.; Standhardt, M.; Mehlhase, S.; Gallei, M.; Chen, L.; Thiele, C. M.

Moisture-responsive films of cellulose stearoyl esters showing reversible shape transitions. SCI. Rep. 2015, 11011. (12).

Gopiraman, M.; Bang, H.; Yuan, G.; Yin, C.; Song, K. H.; Lee, J. S.; Chung, I. M.;

Karvembu, R.; Kim, I. S. Noble metal/functionalized cellulose nanofiber composites for catalytic applications. Carbohydr. Polym. 2015, 132, 554-564. (13).

Wu, J.; Zhao, N.; Zhang, X.; Xu, J. Cellulose/silver nanoparticles composite

microspheres:eco-friendly synthesis and catalytic application. Cellulose 2012, 19, 12391249. (14).

Kaushik, M.; Basu, K.; Benoit, C.; Cirtiu, C. M.; Vali, H.; Moores, A. Cellulose

nanocrystals as chiral inducers: enantioselective catalysis and transmission electron microscopy 3D characterization. J. Am. Chem. Soc. 2015, 137, 6124-6127.



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

(15).

Page 22 of 33

Rezayat, M.; Blundell, R. K.; Camp, J. E.; Walsh, D. A.; Thielemans, W. Green one-step

synthesis of catalytically active palladium nanoparticles supported on cellulose nanocrystals. ACS Sustainable Chem. Eng. 2014, 2, 1241-1250. (16).

Chen, M.; Kang, H.; Gong, Y.; Guo, J.; Zhang, H.; Liu, R. Bacterial cellulose supported

gold nanoparticles with excellent catalytic properties. ACS Appl. Mater. Interfaces 2015, 7, 21717-21726. (17).

Kaushik, M.; Li, A. Y.; Hudson, R.; Masnadi, M.; Li, C. J.; Moores, A. Reversing

aggregation: direct synthesis of nanocatalysts from bulk metal. Cellulose nanocrystals as active support to access efficient hydrogenation silver nanocatalysts. Green Chem. 2016, 18, 129-133. (18).

Xiong, R.; Lu, C.; Wang, Y.; Zhou, Z.; Zhang, X. Nanofibrillated cellulose as the support

and reductant for the facile synthesis of Fe3O4/Ag nanocomposites with catalytic and antibacterial activity. J. Mater. Chem. A 2013, 1, 14910-14918. (19).

Han, Y.; Zhang, X.; Wu, X.; Lu, C. Flame retardant, heat insulating cellulose aerogels

from waste cotton fabrics by in situ formation of magnesium hydroxide nanoparticles in cellulose gel nanostructures. ACS Sustainable Chem. Eng. 2015, 3, 1853-1859. (20).

Li, R.; Zhang, L.; Xu, M. Novel regenerated cellulose films prepared by coagulating with

water: structure and properties. Carbohydr. Polym. 2012, 87, 95-100. (21).

Xiong, R.; Lu, C.; Zhang, W.; Zhou, Z.; Zhang, X. Facile synthesis of tunable silver

nanostructures for antibacterial application using cellulose nanocrystals. Carbohydr. Polym. 2013, 95, 214-219. (22).

Zhang, H.; Duan, T.; Zhu, W.; Yao, W. Natural chrysotile-based nanowires decorated


Page 23 of 33

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


with monodispersed Ag nanoparticles as a highly active and reusable hydrogenation catalyst. J. Phys. Chem. C 2015, 119, 21465-21472. (23).

Qi, H.; Cai, J.; Zhang, L.; Kuga, S. Properties of films composed of cellulose

nanowhiskers

and

a

cellulose

matrix

regenerated

from

alkali/urea

solution.

Biomacromolecules 2009, 10, 1597-1602. (24).

Wu, X.; Lu, C.; Zhou, Z.; Yuan, G.; Xiong, R.; Zhang, X. Green synthesis and formation

mechanism of cellulose nanocrystal-supported gold nanoparticles with enhanced catalytic performance. Environ. Sci.: Nano 2014, 1, 71-79. (25).

Wu, X.; Lu, C.; Zhang, W.; Yuan, G.; Xiong, R.; Zhang, X. A novel reagentless approach

for synthesizing cellulose nanocrystal-supported palladium nanoparticles with enhanced catalytic performance. J. Mater. Chem. A 2013, 1, 8645-8652. (26).

Dong H.; Hinestroza, J. P. Metal nanoparticles on natural cellulose fibers: electrostatic

assembly and in situ synthesis. ACS Appl. Mater. Interfaces 2009, 1, 797-803. (27).

Mondal, S.; Rana, U.; Malik, S. Facile decoration of polyaniline fiber with Ag

nanoparticles for recyclable SERS substrate. ACS Appl. Mater. Interfaces 2015, 7, 1045710465. (28).

Zhang, L.; Ruan, D.; Zhou, J. Structure and properties of regenerated cellulose films

prepared from cotton Linters in NaOH/Urea aqueous solution. Ind. Eng. Chem. Res. 2001, 40, 5923-5928. (29).

Gomes, J. F.; Garcia, A. C.; Ferreira, E. B.; Pires, C.; Oliveira, V. L.; Tremiliosi-Filho,

G.; Gasparotto, L. H. S. New insights into the formation mechanism of Ag, Au and AgAu nanoparticles in aqueous alkaline media: alkoxides from alcohols, aldehydes and ketones as universal reducing agents. Phys. Chem. Chem. Phys. 2015, 17, 21683-21693.



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

(30).

Page 24 of 33

Nishimura, S.; Mott, D.; Takagaki, A.; Maenosono, S.; Ebitani, K. Role of base in the

formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent. Phys. Chem. Chem. Phys. 2011, 13, 9335-9343. (31).

Cai, Y.; Tan, F.; Qiao, X.; Wang, W.; Chen, J.; Qiu, X. Room-temperature synthesis of

silica supported silver nanoparticles in basic ethanol solution and their antibacterial activity. RSC Adv. 2016, 6, 18407-18412. (32).

Bogireddy, N. K. R.; Kumar, H. A. K.; Mandal, B. K. Biofabricated silver nanoparticles

as green catalyst in the degradation of different textile dyes. J. Environ. Chem. Eng. 2016, 4, 56-64. (33).

Xie, Y.; Yan, B.; Xu, H.; Chen, J.; Liu, Q.; Deng, Y.; Zeng, H. Highly regenerable

mussel-inspired Fe3O4@polydopamine-Ag core-shell microspheres as catalyst and adsorbent for methylene blue removal. ACS Appl. Mater. Interfaces 2014, 6, 8845-8852. (34).

Patra, S.; Roy, E.; Madhuri, R.; Sharma, P. K. Agar based bimetallic nanoparticles as

high-performance renewable adsorbent for removal and degradation of cationic organic dyes. J. Ind. Eng. Chem. 2016, 33, 226-238. (35).

Luo, J.; Zhang, N.; Lai, J.; Liu, R.; Liu, X. Tannic acid functionalized graphene hydrogel

for entrapping gold nanoparticles with high catalytic performance toward dye reduction. J. Hazard. Mater. 2015, 300, 615-623. (36).

Amir, M.; Kurtan, U.; Baykal. A. Rapid color degradation of organic dyes by

Fe3O4@His@Ag recyclable magnetic nanocatalyst. J. Environ. Chem. Eng. 2015, 27, 347353.


Page 25 of 33

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


For Table of Contents Only

Reductant-Free Synthesis of Silver NanoparticlesDoped Cellulose Microgels for Catalyzing and Product Separation Yangyang Han, Xiaodong Wu, Xinxing Zhang*, Zehang Zhou and Canhui Lu*

Ag nanoparticles supported by cellulose microgels under vacuum filtration for the rapid catalyzing in reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride



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

Schematic illustration for the facile synthesis of Ag NPs@CMG nanohybrids (a) and digital camera photos showing the color changes of CMG-Ag+ (0.5 mM) mixture as a function of time (b). Figure 1 152x96mm (300 x 300 DPI)

ACS Paragon Plus Environment

Page 26 of 33

Page 27 of 33

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


UV-vis spectra and digital camera photos (inset) of Ag NPs@CMG nanohybrids with different concentrations: 0.2, 0.5, and 1.0 mM (a). UV-vis spectra of Ag NPs prepared under different variables (b). Figure 2 67x29mm (300 x 300 DPI)



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

SEM image (a, scale bar=100 µm) and particle size distribution (b) of Ag NPs@CMG nanohybrids. SEM images with high magnifications (c, scale bar=5 µm) (d, scale bar=1 µm) of Ag NPs@CMG nanohybrids. Figure 3 140x129mm (300 x 300 DPI)


Page 28 of 33

Page 29 of 33

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


TEM image of the Ag NPs@CMG nanohybrids (0.5 mM) (scale bar, 100 nm) (a) and particle size distribution of the Ag NPs (b). The HRTEM images (c and e) (scale bar, 5 nm) and the SAED patterns (d and f) of individual Ag NPs. Figure 4 127x170mm (300 x 300 DPI)



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

Reaction scheme for the Ag NP@CMG formation. Figure 5 98x63mm (300 x 300 DPI)


Page 30 of 33

Page 31 of 33

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


Time dependent UV-vis spectra for reduction of 4-NP catalyzed with 0.5 mM Ag NPs@CMG nanohybrids (containing 0.125 µmol Ag): plot of At/Ao against time (inset) (a), plot of ln(At/Ao) against time (b). Schematic diagram for the catalytic reaction (c). Digital photograph (d) and schematic illustration (f) showing the fast reduction of 4-NP catalyzed by Ag NPs@CMG catalytic membrane. SEM micrograph of Ag NPs@CMG catalytic membrane after filtration (e). UV-vis spectra for 4-NP solution before and after passing through the catalytic membrane (g). The conversion rate of 4-NP during cyclic test (h). Figure 6 131x110mm (300 x 300 DPI)



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

Time dependent UV-vis spectra and digital camera photos (inset) for reduction of MB (a), MO (b) and R6G (c) catalyzed by Ag NPs@CMG nanohybrids and plot of At/Ao against time (inset). UV-vis spectra for reduction R6G (d) and digital photographs (inset) showing the reduction of R6G catalyzed by Ag NPs@bulk gel (left) and Ag NPs@CMG (right). Figure 7 118x91mm (300 x 300 DPI)


Page 32 of 33

Page 33 of 33

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


Ag nanoparticles supported by cellulose microgels under vacuum filtration for the rapid catalyzing in reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride For Table of Contents Only 84x62mm (300 x 300 DPI)


Reductant-Free Synthesis of Silver Nanoparticles-Doped Cellulose

Recommend Documents