Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for Reduction of 4-Nitrophenol

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1 Journal of Cluster Science (2018) 29: ( ().,-volV)( ().,-volV) ORIGINAL PAPER Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for Reduction of 4-Nitrophenol Hannaneh Heidari 1 Received: 7 January 2018 / Published online: 24 February 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract In this work, silver nanoparticles (Ag NPs) prepared through in situ green and facile synthesis by using nanofibrillated cellulose (NFC) hydrogel as support, stabilizer and reducing agent by two different methods. Their catalytic abilities were examined for conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The structure of as-synthesized composites with different AgNO 3 concentrations were characterized by ultraviolet visible spectroscopy, field emission scanning electron microscopy, transmission electron microscopy; energy dispersive spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Results show that all nanocomposites demonstrated excellent catalytic activity. Among them, Ag@NFC-2 sample, with spherical and well-dispersed Ag NPs along the nanofiber, produced by the second method having 0.25 M AgNO 3 concentration presented outstanding catalytic efficiency. Keywords Silver nanoparticles Nano cellulose Catalyst Reduction of nitrophenol Introduction Among the metallic nanoparticles (NPs), silver as the most frequently used inorganic NP, has attracted much interest owing to its special properties and wide applications such as in the synthesis of advanced polymer nanocomposites [1], sensors [2], biology detection [3] and as heterogeneous catalysts in many catalytic processes [4]. However, pure nanoparticles including Ag NPs tend to agglomerate because of their high surface energies, remarkably leading to a reduction in their catalytic activity. One effective approach to overcome these problems is immobilization or encapsulation of Ag NPs on/into various matrices [5]. Three main methods of preparation Ag NPs have been reported: First, UV irradiation reduction; Second, thermal decomposition; and third, chemical reduction that is the most commonly used method. This method, requires the presence of reductants like sodium borohydride, hydrazine hydrate or stabilizing agents. But using of them are environmentally undesirable and required additional steps & Hannaneh Heidari h.heidari@alzahra.ac.ir 1 Department of Chemistry, Faculty of Physics and Chemistry, Alzahra University, Vanak, Tehran , Iran during synthesis [6]. From the above perspective, biopolymers have attracted great interest from researchers both in industry and in academia [7]. Cellulose as one of the most numerous biopolymers has attracted great attention of researchers because of unique properties such as good biocompatibility, biodegradation and environmental benefits. Furthermore, it is proper for the reduction of metal cations due to rich hydroxyl and ether groups on the surface which makes it as promising supporting biomaterial for NPs synthesis [5]. On the other hand, 4-nitrophenol (4-NP), which is a pollutant in industrial wastewaters and nonbiodegradable material, can be harmful to human health and the environment. However, the reduced form, 4-Ap, is useful, less toxic, safety and industrially important precursor compound with various applications [8]. So, it is an already challenging task to expand a simple and fast method for this conversion process. Different methods such as adsorption and biological treatment have been introduced, but a commonly-used and more suitable method is the catalytic reduction by sodium borohydride in the presence of various nanoscale materials [9]. There are numerous metal catalysts loaded onto various supporting matrices for assessing their catalytic performance such as nanoalloys [8], metal oxides [10, 11], polystyrene [12, 13], polyacrylic

2 476 H. Heidari acid/polyvinyl alcohol nanofibers [14], silane [15], graphene oxide [16 21], carbon [22 25], nano-silica [26, 27] and cellulose [28 35]. Based on the aforementioned properties of cellulose, in the present study, a new catalytic system including lowcost nanofibrillated cellulose-based Ag nanocomposite was prepared by a facile route. Functional groups in nanofibrillated cellulose could be used for the in situ reduction of Ag particles without adding any reducing agent or a stabilizer. The structure of the nanocomposites was characterized. The study of catalytic reduction of 4-nitrophenol indicated excellent catalytic efficiency of the as-prepared nanocomposites. 50 mm AgNO 3 solution (Ag@NFC-2, Ag@NFC-3 and Ag@NFC-4) was gently (about 5 ml/minute) added into the reaction mixture. The contents were then kept under continuous heating at 65 C for 2 h. The contents were then cooled down to room temperature and the product was separated from the mixture solution, washed several times with double-distilled water and stored in dark conditions at 4 C (Ag@NFC- 2, Ag@NFC-3, Ag@NFC-4) [36]. Experimental Materials and Instrumentation Nanofibrillated cellulose (NFC) was purchased from nanonovin polymer company, Iran. The other commercially available chemicals were purchased from Merck Company. Ultraviolet visible (UV Vis) measurements were performed using Lambda-25 UV Vis spectrometer (Perkin-Elmer, United States). IR spectra were recorded from KBr disk using Fourier transform infrared spectroscopy (FT-IR) Bruker Tensor 27 instrument. Fieldemission scanning electron microscopy (FE-SEM) with a TESCAN MIRA3. Transmission electron microscopy (TEM) images have been taken with a Ziess, model EM900. The energy dispersive spectroscopy (EDS) analysis was done using a SAMx-analyzer. The X-ray diffraction patterns (XRD) were obtained using a Phillips PW1730 X-ray diffractometer. The diffraction patterns were recorded using Cu-K a radiation at 40 kv and 30 ma. The samples were scanned in a 2h range between 10 and 70. Fig. 1 UV Vis adsorption spectra of (a) pure NFC and (b) Ag@NFC- 1 composite Preparation of Ag@NFC Nanocomposites The catalysts were prepared by two modified methods. 1. The NFC hydrogel (3.3%) (1.2 g) was immersed in AgNO 3 solution (50 ml, 250 mm) at 100 C for 24 h. Then the hydrogel was washed with deionized water to remove the untreated AgNO 3. Finally, Ag@NFC nanocomposite, was obtained by air-drying (Ag@NFC-1) [5] gr NFC hydrogel (3.3%) was soaked in 10 ml double-distilled water and its ph was adjusted to 12 by NaOH solution. The reaction mixture was then heated at constant temperature 65 C for 30 min followed by stirring. Afterwards, 50 ml of 250 mm, 150 mm and Fig. 2 FT-IR spectra of (a) NFC and (b) Ag@NFC-1 composite

3 Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for 477 Fig. 3 FE-SEM images of a NFC, b Ag@NFC-1 (0.25 M AgNO 3 ), c Ag@NFC-2 (0.25 M AgNO 3 ) and d Ag@NFC-3 (0.15 M AgNO 3 ) composites Catalytic Reduction of 4-Nitrophenol The catalytic reduction of 4-nitrophenol to 4-aminophenol was carried out using 4-nitrophenol (20 mm, 0.25 ml), sodium borohydride solution (5 M, 0.25 ml) and DI water (19.5 ml) in presence of certain amount of the composite containing AgNPs as a catalyst. As the reaction proceeded, the yellow color of initial solution started to fade and changed gradually to colorless. At each time interval, the aqueous solution was withdrawn and UV Vis absorption spectra over the scanning range from 250 to 550 nm were recorded till the peak due to the presence of nitro group at 400 nm disappeared completely [14]. Results and Discussion Catalyst Characterization UV Vis spectra of pure NFC and Ag@NFC composite are shown in Fig. 1. For pure NFC, no bands appear in the spectrum (Fig. 1a). In contrast, in composite, the maximum absorption band at 410 nm is due to the formation of silver nanoparticles (Fig. 1b). An et al. [37] has been reported that the surface plasmon resonance (SPR) band at 410 nm attributed to the presence of Ag NPs in the nanocomposite catalyst. FTIR spectra of pure NFC and Ag@NFC-1 composite are presented in Fig. 2. The vibrational bands at the range

4 478 H. Heidari Fig. 4 EDS spectra of a Ag@NFC-1, b Ag@NFC-2 (0.25 M AgNO 3 ) and c Ag@NFC-3 (0.15 M AgNO 3 ) composites Fig. 5 TEM image of Ag@NFC-2 of cm -1, and 3400 attributed to the C O and C O C, C H and OH bonds weakened in the composite due to the Ag particle coverage on the cellulose. Decreasing in the intensity for OH bond indicated the conversion of OH functional groups to C=O because of the Ag as an oxidizing agent. In the Ag@NFC-1 nanocomposite an additional weak band at cm -1 corresponding to C=O bond was observed. The signals around 1373 and 1424 cm -1 is related to CH and CH 2 bending mode, respectively (Fig. 2) [5, 38]. The morphology of the catalysts was investigated by FE-SEM (Fig. 3). Figure 3a displays the SEM image of the initial NFC consisting of nanofibrils with diameters of about nm and lengths up to several micrometers.

5 Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for 479 (Fig. 6). NFC in this study exhibited characteristic peaks related to cellulose lattice planes locating at 2h = (110) and (200) (Fig. 6a). X-ray diffractogram of Ag@NFC-1 and Ag@NFC-4 also showed the same characteristic peaks of cellulose I crystal and other newly emerged peaks at 2h = 38.08, and that corresponded to the (111), (200) and (220) crystal planes on the basis of face centered cubic (fcc) structure of Ag NPs (Fig. 6b, c) [6, 38]. These results showed that the silver ions were successfully reduced to metallic Ag in NFC network. The Evaluation of the Catalytic Performance Fig. 6 XRD patterns of (a) NFC (b) Ag@NFC-1and (c) Ag@NFC-4 Figure 3b d showed the SEM image of the Ag@NFC nanocomposites. In all nanocomposites, the large number of NPs were distributed on the surface of nanofibril indicating that the in situ formation of Ag nanoparticles. As seen, the average size of the Ag nanoparticles was about nm. The EDS spectra for Ag@NFC-1, Ag@NFC-2 and Ag@NFC-3 nanocomposites are respectively presented in Fig. 4a c. It clearly exhibits the presence of C, O and Ag elements. The peaks of C and O appear from NFC and the intense peak at around 3 kev related to the Ag signal. Furthermore, increasing the Ag content to wt% was observed, indicating the Ag had been successfully loaded on the surface of nanofibrillated cellulose. TEM images of Ag@NFC-2 nanocomposite with 0.25 M AgNO 3 solution as shown in Fig. 5. It showed that individual, spherical AgNPs with nearly uniform distribution and a size smaller than 30 nm could be formed along the fibers. Crystalline structure of NFC and the as-prepared product were determined using X-ray diffraction (XRD) As shown in Fig. 7a e the results of the catalytic reduction of 4-NP to 4-AP in the presence of excess NaBH 4 as reducing agent and Ag@NFC nanocomposites. The reaction progress was analyzed by UV Vis spectroscopy. Figure 7a showed that the reaction did not occur in the presence of NFC alone over a period of 30 min. After the addition of composite catalysts with the progress of the reaction, when its yellow color faded with time, the absorbance at 400 nm (the peak of 4-nitrophenolate ion) decreased, while the absorbance at 290 nm (due to 4-AP) increased. The Ag@NFC catalysts with different Ag content were added into mixture solutions and the results were shown in Fig. 7. The Ag@NFC-2 possessed the highest catalytic activity and the reaction had completed within 3 s. EDS spectra in Fig. 4 show that Ag@NFC-2 has highest amount of Ag, which could contribute to the highest catalytic activity of Ag@NFC-2. The Ag NPs operate as an active electron transfer intermediate between BH 4 and 4-NP molecules [6]. The catalytic reduction was completed after 3, 10 and 240 s at room temperature for Ag@NFC-2, Ag@NFC-3 and Ag@NFC-4, respectively (Fig. 7b e). The linear plot of ln (C t /C 0 ) versus reduction time for the 4-NP catalytic reduction over the Ag@NFC composites with different Ag loading (Ag@NFC-2, Ag@NFC-3 and Ag@NFC-4) were shown in Fig. 7f. Reaction rates are determined by measuring the absorbance values at 400 nm as a function of time [39]. Due to much higher concentration of NaBH 4 compared to 4-NP in the reaction, the reduction rate can be independent of NaBH 4 concentration. Generally, the reduction of 4-NP to 4-AP can be assumed as a pseudo-first-order kinetics with respect to the concentration of 4-NP. Pseudo-first order rate constant could be calculated by Langmuir Hinshelwood equation [10]. lnðc t =C 0 Þ ¼ lnða t =A 0 Þ ¼ kt where, k is the rate constant. C 0 and C t represents the initial concentration of 4-NP and the concentration at time t,

6 480 H. Heidari Fig. 7 UV Vis spectra of 4-NP aqueous solution catalyzed with a NFC, b Ag@NFC-2, c Ag@NFC-3 (0.02 gr), d Ag@NFC-3 (0.01 gr), e Ag@NFC-4 composites at different reaction time. f The plot of LnA t /A 0 versus time for the reduction of 4-NP using Ag@NFC-2 (0.25 M AgNO 3 ), Ag@NFC-3 (0.15 M AgNO 3 ) and Ag@NFC-4 (0.05 M AgNO 3 ) Table 1 Comparison of rate constants (k) and activity parameter (k 0 ) for the reduction of 4-nitrophenol with different Ag composites as catalysts Entry Catalyst k (s -1 ) k 0 (s -1 g -1 ) References 1 Ag/cotton [6] 2 Co-doped CuO NP [10] 3 Ag-NP/C [24] 4 AgNPs@NH 2 -CP [34] 5 Fe 3 O 4 /Ag@NFC [35] 6 Ag/NFC This work respectively. A 0 is the initial absorbance and A t is the absorbance at any time t. The rate constant of the best catalyst (Ag@NFC-2) was estimated to be s -1 by the slope. To compare catalytic activity with the reported catalysts used for 4-NP reduction, the ratio of rate constant k to the total mass of the catalyst (m), k 0 (k 0 = k/m) was introduced as a normalized activity parameter [6]. The catalytic activity of

7 Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for 481 was 2.33 s -1 g -1, it was higher than the other listed catalysts in Table 1. Conclusions In this work, the Ag NPs were synthesized successfully by in situ reduction using nanofibrillated cellulose. Then, the catalytic efficiency of pure NFC and Ag@NFC nanocomposites in 4-NP conversion to 4-Ap were evaluated. Ag@NFC-2 exhibited the best catalytic achievement for the reduction compared with other Ag nanocomposites. This improvement in activity is related to both the preparation method and concentration of AgNO 3. Choosing an appropriate method for preparation of nanocomposites, using a green and cost effective biopolymer, also introducing a more effective catalyst lead to shorter reduction periods are the main advantages of this work. Acknowledgements The author gratefully acknowledge from the Research Council of Alzahra University for financial support. References 1. A. Maleki and M. Kamalzare (2014). Catal. Commun. 53, K.-S. Lee and M. A. EI-Sayed (2006). J Phys Chem B 110, P. Alivisatos (2004). Nat. Biotechnol. 22, X. Y. Dong, Z. W. Gao, K. F. Yang, W. Q. Zhang, and L. W. Xu (2015). Catal. Sci. Technol. 5, V. Sadanand, N. Rajini, B. Satyanarayana, and A. V. Rajulu (2016). Int. J. Polym. Anal. Charact. 21, Z. Li, Z. Jia, T. Ni, and S. Li (2017). Appl. Surf. Sci. 426, S. Menchaca-Nal, C. L. Londoño-Calderón, P. Cerrutti, M. L. Foresti, L. Pampillo, V. Bilovol, R. Candal, and R. Martínez- García (2016). Carbohydr. Polym 137, N. Ghanbari, S. J. Hoseini, and M. Bahrami (2017). Ultrason. Sonochem. 39, N. Jadbabaei, R. J. Slobodjian, D. Shuai, and H. Zhang (2017). Appl. Catal. A. Gen. 543, A. Sharma, R. K. Dutta, A. Roychowdhury, D. Das, A. Goyal, and A. Kapoor (2017). Appl. Catal. A. Gen. 543, A. Leelavathi, T. U. B. Rao, and T. Pradeep (2011). Nanoscale. Res. Lett. 6,. 12. S. Jana, S. K. Ghosh, S. Nath, S. Pande, S. Praharaj, S. Panigrahi, S. Basu, T. Endo, and T. Pal (2006). Appl. Catal. A. Gen. 313, Z. Deng, H. Zhu, B. Peng, H. Chen, Y. Sun, X. Gang, P. Jin, and J. Wang (2012). Appl. Mater. Interfaces 4, S. Xiao, W. Xu, H. Ma, and X. Fang (2012). RSC Advances. 2, K. S. Shin, Y. K. Cho, J. Y. Choi, and K. Kim (2012). Appl. Catal. A. Gen , M. Maham, M. Nasrollahzadeh, S. M. Sajadi, and M. Nekoei (2017). J. Colloid. Interface Sci. 497, T. Wu, L. Zhang, J. Gao, Y. Liu, C. Gaob, and J. Yan (2013). J. Mater. Chem. A. 1, L. Liu, R. Chen, W. Liu, J. Wu, and D. Gao (2016). J. Hazard. Mater. 320, A. A. Nafiey, A. Addad, B. Sieber, G. Chastanet, A. Barras, S. Szunerits, and R. Boukherrou (2017). Chem. Eng. J. 322, R. H. Fath, S. J. Hoseini, and H. G. Khozestan (2017). J. Organomet. Chem. 842, C. Wang, R. Ciganda, L. Yate, S. Moya, L. Salmon, J. Ruiz, and D. Astruc (2017). J. Mater. Sci. 52, J. Liu, Z. Wang, X. Yan, and P. Jian (2017). J. Colloid. Interface. Sci. 505, X. Duan, M. Xiao, S. Liang, Z. Zhanga, Y. Zeng, J. Xi, and S. Wang (2017). Carbon 119, S. Tang, S. Vongehr, and X. Meng (2010). J. Phys. Chem. C 114, X. Cui, W. Zuo, M. Tian, Z. Dong, and J. Ma (2016). J Mol Catal A Chem 423, Z. Dong, X. Le, C. Dong, W. Zhang, X. Li, and J. Ma (2015). Appl. Catal. B. Environ. 162, Z. Dong, X. Le, X. Li, W. Zhang, C. Dong, and J. Ma (2014). Appl. Catal. B. Environ. 158, J. Wu, N. Zhao, X. Zhang, and J. Xu (2012). Cellulose 19, F. U. A. Khan, S. B. Khan, T. Kamal, A. M. Asiri, I. U. Khan, and K. Akhtar (2017). Int. J. Biol. Macromolec. 102, W. Xu, W. Jin, L. Lin, C. Zhang, Z. Li, Y. Li, R. Song, and B. Li (2014). Carbohydr. Polym. 101, S. K. Das, M. M. R. Khan, A. K. Guha, and N. Naskar (2013). Green Chem. 15, H. Liu, H. Liu, S. Yang, and C. Nie (2013). Mater. Lett. 100, K. Jiang, H.-X. Zhang, Y.-Y. Yang, R. Mothes, H. Lang, and W.- B. Cai (2011). Chem. Commun. 47, M. Liang, G. Zhang, Y. Feng, R. Li, P. Hou, J. Zhang, and J. Wang (2018). J. Mater. Sci. 53, R. Xiong, C. Lu, Y. Wang, Z. Zhou, and X. Zhang (2013). J. Mater. Chem. A. 1, E. M. Narváez, H. Golmohammadi, T. Naghdi, H. Yousefi, U. Kostiv, D. Horak, N. Pourreza, and A. Merkoçi (2015). ACS Nano 9, (7), X. An, Y. Long, and Y. Ni (2017). Carbohydr. Polym. 156, J. Wu, Y. Zheng, W. Song, J. Luan, X. Wen, Z. Wu, X. Chen, Q. Wang, and S. Guo (2014). Carbohydr. Polym. 102, Y. Lu, Y. Mei, M. Schrinner, M. Ballauff, M. W. Moller, and J. Breu (2007). J. Phys. Chem. C. 111, 7676.