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Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand Kriti Bijalwan a, Aditi Kainthola a, Himani Sharma b, Charu Dwivedi a,⇑ a b
Department of Chemistry, Doon University, Dehradun 248001, India Department of Physics, Doon University, Dehradun 248001, India
a r t i c l e
i n f o
Article history: Received 15 September 2019 Received in revised form 26 November 2019 Accepted 5 January 2020 Available online xxxx Keywords: Alloy nanoparticles Au-Ag bimetallic nanoparticles Alkali activated sand Sand supported catalyst 4-Nitrophenol
a b s t r a c t Gold-Silver (Au-Ag) bimetallic alloy nanoparticles exhibit improved catalytic activity in comparison to the monometallic nanoparticles due to synergistic effect. In this work Au-Ag bimetallic alloy nanoparticles (BNPs) have been supported on alkali activated sand which acts as an inert support material, stabilizes the nanoparticles and prevents their agglomeration. In addition to providing high surface area for adsorption, sand is inexpensive and environmentally benign. Au-Ag alloy nanoparticles were prepared via co-reduction mechanism using polymer as a stabilising agent. Alkali activated sand was coated with the alloy nanoparticles using surface adsorption method. Efficient reduction of 4-Nitrophenol to 4Aminophenol by NaBH4 in the presence of BNPs supported on alkali activated sand was investigated. Also, the heterogenous nature of the catalyst makes it highly reusable due to its effortless separation from the reaction medium. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction Nitrophenols are anthropogenic, toxic and bio-refractory organic compounds that are used to manufacture a variety of pesticides, synthetic dyes and pharmaceuticals. Among nitrophenols, 4-Nitrophenol (4-NP) is found in the agricultural runoff as well as the textile industrial effluents [1]. This compound is toxic and can potentially damage the vital organs in humans and animals. This pollutant is highly persistent in the environment and is difficult to remove from water using conventional treatment methods [2]. Therefore, it is important to eliminate this harmful organic compound. Degradation of 4-NP using nanoparticles of Pt, Au, Cu and Ag has already been investigated extensively [3–5]. Bimetallic alloy nanoparticles synthesized using various methods tend to show better and more pronounced catalytic activity than the monometallic nanoparticles. They exhibit a combination of properties associated with the constituent metals. This leads to enhanced physical and chemical characteristics due to the synergistic effect [6–7]. Their higher catalytic activity can also be
⇑ Corresponding author. E-mail address: [email protected] (C. Dwivedi).
attributed to the high surface area and the presence of interfacial regions which have a greater electron density than the monometallic nanoparticles [8]. The metallic nanoparticles can be deposited on various support material to establish an improved overall efficiency of the catalytic process. Kuroda et al. deposited gold nanoparticles directly on the poly methylmethacrylate (PMMA) beads and the system showed the highest catalytic activity among polymer supported Au nanoparticle systems. They concluded that the activity of the metal nanoparticles, depends on the structure of the support material as well as on the interaction between the nanoparticles and the surface functional groups of the support material [9]. The support material used in this system is sand, which is granular in texture. The easy availability of this natural resource makes it an ideal material for use in various industries [10]. Sand exhibits high stability along with considerable adsorption efficiency making it an excellent support material. Its easy availability, recoverability and reusability makes it a cost-effective carrier. Sand contains a high content of silica in the form of SiO2 along with other minerals. Silica can undergo surface modifications resulting in the formation of new functional groups which can lead to better adsorbent-adsorbate interactions. The surface modification increases the surface area for adsorption and thus the adsorption
https://doi.org/10.1016/j.matpr.2020.01.089 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
2
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
potential of sand [11]. The activated sand provides a large surface area for the adsorption of high concentration of Au-Ag alloy nanoparticles. Herein, we are reporting alkali activated sand coated with Au-Ag alloy nanoparticles as an efficient and environment friendly catalytic system which can be used to reduce 4-NP to 4aminophenol (4-AP) by sodium borohydride. This reaction has been monitored using a UV–visible spectrometer by observing the decrease in the characteristic absorption peak of 4Nitrophenolate ion at 400 nm.
2. Experimental 2.1. Materials Gold(III)chloride hydrate was purchased from Lobachemie, India. Silver nitrate, sodium borohydride and 4-nitrophenol were purchased from Sisco Research Laboratory chemicals, India and sodium chloride 99% was purchased from Sigma Aldrich. All the chemicals were used without any further purification. All the experiments were performed in the double distilled water. The sand used as support material was obtained from Bindal river bed in Dehradun, Uttarakhand, India. It was sieved manually and cleaned thoroughly multiple times with distilled water before usage.
2.2. Synthesis Au-Ag alloy nanoparticle were synthesized by co-reduction method described elsewhere [12]. Briefly, the solution was made by NaBH4 induced co-reduction of HAuCl4 and AgNO3 in the presence of a stabilizing polymer. Instantaneous reaction occurred and a prominent color change was observed in the solution as shown in Fig. 1(a). Alkali activated sand is used as an inactive support material. It was first washed thoroughly with soap solution followed by washing with distilled water to remove the impurities. Normal sand was exfoliated and activated by sodium hydroxide solution. It was left undisturbed to facilitate complete settlement of the sand particles at the bottom of the flask. It was then washed with distilled water to lower the pH and dried in a muffle furnace [11]. The bimetallic nanoparticles coated alkali activated sand system was prepared by adding Au-Ag alloy nanoparticles to activated sand by surface adsorption method as shown in Fig. 1(b). This method ensures uniform and high-quality coating even on irregular and complex structures. It was then completely dried in a hot air oven. 2.3. Catalytic reduction of 4-nitrophenol The alkali activated sand coated with bimetallic nanoparticles was used as a catalyst in the reduction reaction of 4-NP by sodium
Fig. 1. (a) UV–Vis spectrum and image of Au-Ag bimetallic nanoparticles; (b) Schematic representation of the reduction of 4-NP to 4-AP in the presence of Au-Ag nanoparticles coated alkali activated sand used as a catalyst.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
3
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
borohydride. In this study the catalytic efficiency of the Au-Ag nanoparticles coated alkali activated sand system was observed. The concentration of 4-NP used was fixed at 30 mM and the concentration of NaBH4 and the amount of catalyst was kept constant at 10 mM and 1 mg, respectively. Freshly prepared NaBH4 solution was added to the 4-NP solution followed by the catalyst. From the absorbance at kmax = 400 nm the concentration of 4-nitrophenolate was determined.
3. Results and discussion Fig. 2(a) represents the UV–Vis spectra of the catalytic reduction of 4-NP in the presence of NaBH4 using bimetallic nanoparticles coated on alkali activated sand system. The intermediate step in the reduction reaction involves the formation of 4nitrophenolate ion under basic condition, which results in a red shift from 317 nm to 400 nm [5]. The catalytic reduction is studied by monitoring the decrease in the intensity of the characteristic peak of 4-NP at 400 nm and the simultaneous formation of a new peak at 290 nm associated with the formation of 4-AP. In the absence of the catalytic system the absorption peak at 400 nm remains unaltered indicating that NaBH4 itself is unable to initiate the reduction process. On addition of the catalyst the
colour of the solution disappears with time which is indicated by a corresponding decrease in the absorption peak at 400 nm. The two isosbestic points present at 280 nm and 314 nm indicate the complete conversion of 4-NP to 4-AP with no side product formation [13]. The time required for the conversion of 30 mM 4-NP to 4AP using the Au-Ag nanoparticles coated alkali activated sand system is observed to be 5 min, which proves that the catalytic system is not only cost-effective and environment friendly but also highly efficient. Normal or untreated sand has a relatively smooth surface and tightly packed particles [11]. Untreated sand does not bind to the Au-Ag nanoparticles efficiently like the activated sand. Au-Ag nanoparticles cannot be combined with untreated sand to form a catalytic system for the reduction of 4-NP to 4-AP. The alkali activated sand shows a significant difference in its surface morphology after treatment as compared to the untreated or normal sand. Modified sand has a rough consistency along with thin cracks and small pores on its surface. Treatment with alkali leads to the removal of surface impurities and exfoliates the sand particles [11]. Fig. 2(b) shows that the alkali activated sand on its own has no role in catalytic reduction of 4-NP and has absolutely no effect on the rate of the reaction it only improves the overall efficiency of the catalytic process. Alkali activated sand is used here as an inert support material that facilitates easy adsorption and anchors the BNPs on its surface in a manner that prevents their agglomeration. In this system the interaction between BNPs and the surface of alkali activated sand is strong enough to prevent leaching and light enough to allow the reduction of 4-NP. The major problem faced in case of using a homogeneous nanoparticles catalyst is its recovery after the completion of the reaction [14]. Using alkali activated sand as a support material for Au-Ag BNPs helps in recovering the Au-Ag BNPs and facilitates easy separation of the catalyst from the reaction medium. Table 1 Effect of BNPs loading on alkali activated sand and the variation of the time taken for the catalytic reduction of 4-NP.
Fig. 2. (a) Time dependent absorption spectra for the catalytic reduction of 4-NP by NaBH4 in presence of bimetallic nanoparticles coated on alkali activated sand; (b) No change in the absorbance value of 4-NP in presence of alkali activated sand.
Ratio of amount of BNPs to alkali activated sand
Time (min)
1:1 3:1 5:1
18.0 5.0 Leads to the leaching of excess BNPs from the sand surface
Fig. 3. Reusability graph of the Au-Ag BNPs loaded on alkali activated sand for 4-NP reduction.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
4
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 A comparative study for the catalytic activity of the different catalysts for 4-NP reduction to 4-AP. Catalyst Amount Au/Ag BNPs supported on Montmorillonite Au NPs over PMMA Homogeneous Au-Ag BNPs Au-Ag BNPs supported on alkali activated sand
1.0 mg 3.5 mg 50 mL 1.0 mg
3.1. Effect of BNPs loading The completion of the reaction in the case of the reduction of 4NP to 4-AP is self-indicated by a colour change from yellow to colourless. Therefore, it is better to express catalytic activity in terms of the time taken for the completion of the reaction. In this system the ratio of the amount of the BNPs to that of the amount of the alkali activated sand was varied in order to study the effect of loading of BNPs on the catalytic system. The time taken for the reduction of 4-NP at different BNPs to activated sand ratios was observed. Table 1 shows that as the amount of the BNPs onto the alkali activated sand increases, the time taken for the catalytic reduction decreases. After this the further loading resulted in leaching of the BNPs in the reaction medium. It was observed that the best catalytic activity is shown by the system with BNP:Activated sand ratio 3:1, therefore all the studies were carried out with this optimal loading condition. The leaching of excess nanoparticles as a result of using higher volume of BNPs could be detected with the help of UV–Visible spectroscopy where on leaching, a peak corresponding to the Au-Ag BNPs was observed near 450 nm.
Conc. of 4-NP (M) 10 10 10 10
6 6 5 5
Reaction Time (min)
Reference
10.0 10.0 3.0 5.0
[14] [9] [12] Present work
reduction of 4-NP to 4-AP was investigated. The catalytic activity proves the catalyst to be extremely efficient. The reduction of 4NP to 4-AP took place completely without any side product formation. This catalytic system has several benefits over the others used for the reduction of 4-NP as sand particles are heavy and therefore settle down at the bottom of the reaction container. This facilitates an effortless separation of the catalyst from 4-AP formed. As investigated, the Au-Ag BNPs coated on alkali activated sand were stable, eco-friendly and highly recyclable thus having a potential for industrial applications. Declaration of Competing Interest There is no conflict of interest. Acknowledgements The authors acknowledge University Grants Commission, India (Project No. F.30-371/2017 BSR) and Doon University, Uttarakhand, India for their support to carry out this work.
3.2. Reusability
References
Using an inert support material makes the BNPs catalyst heterogenous in nature which allows removal of the catalyst from the reaction medium after the completion of the reaction and the catalyst can then be reused. This is especially favourable for the industrial applications where reusability and recyclability are important for a catalyst. In the present system an investigation has been made on the reusability of the catalyst and its efficiency. After the completion of the reaction, the catalyst was used in the next cycle after separation from the reaction medium by simple decantation followed by washing with distilled water and drying. As shown in the Fig. 3. the catalyst was used in the reduction of 4-NP, 8 times and the reduction reactions were monitored for 1 h. It was observed that even after 8 cycles the catalytic efficiency decreases by only 16%. The Table 2. presents a comparison of the catalytic efficiency of the investigated work with the other similar published works. It presents that the Au-Ag bimetallic alloy nanoparticles coated on alkali activated sand reduces 4-NP in lesser time when compared with Au/Ag nanoparticles supported on other inert materials. The reason behind this is the electronic interaction between the Au and Ag in the Au-Ag BNPs. The Au-Ag BNPs without support exhibit better catalytic activity but are not reusable, also it is difficult to recover them after the completion of the reaction. Using alkali activated sand as an inert support helps in recovery of BNPs and improves the overall catalytic efficiency of the system. Therefore, Au-Ag BNPs supported on alkali activated sand can be used as alternative catalyst in the reduction of 4-NP at room temperature.
[1] K.V.K. Palanivelu, Degradation of nitrophenols by Fenton and photo-Fenton processes, J. Photochem. Photobiol. 170 (2005) 83–95. [2] H. Zhang, C. Fei, D. Zhang, F. Tang, Degradation of 4-nitrophenol in aqueous medium by electro-Fenton method, J. Hazard. Mater. 145 (2007) 227–232. [3] P. Liu, M. Zhao, Silver nanoparticle supported on halloysite nanotubes catalysed reduction of 4-nitrophenol (4-NP), Appl. Surf. Sci. 255 (2009) 3989–3993. [4] S. Saha, A. Pal, S. Kundu, S. Basu, T. Pal, Photochemical green synthesis of calcium-alginate-stabilized Ag and Au nanoparticles and their catalytic application to 4-nitrophenol reduction, Langmuir 26 (2010) 2885–2893. [5] A. Ganguly, P. Ramakrishna, M. Ramakrishna, L. Karanam, C. Janardhana, A.M. Rao, Catalytic reduction of 4-nitrophenol using biogenic gold and silver nanoparticles derived from Breynia rhamnoides, Langmuir 27 (2011) 15268– 15274. [6] N. Berahim, W.J. Basirun, B.F. Leo, M.R. Johan, Synthesis of bimetallic goldsilver (Au-Ag) nanoparticles for the catalytic reduction of 4-nitrophenol to 4aminophenol, Catalysts 8 (2018) 412. [7] A.K. Singh, Q. Xu, Synergistic catalysis over bimetallic alloy nanoparticles, ChemCatChem 5 (2013) 652–676. [8] M.S. Holden, K.E. Nick, M. Hall, J.R. Milligan, Q. Chen, C.C. Perry, Synthesis and catalytic activity of pluronic stabilized silver-gold bimetallic nanoparticles, RSC Adv. 4 (2014) 52279–52288. [9] K. Kuroda, T. Ishida, M. Haruta, Reduction of 4-nitrophenol to 4-aminophenol over Au nanoparticles deposited on PMMA, J. Mol. Catal. A: Chem. 298 (2009) 7–11. [10] M. Gavrilita, Environmental impacts of sand exploitation. Analysis of sand market, Sustainability 9 (2017) 1118. [11] A. Sharma, Z. Syed, U. Brighu, A.B. Gupta, C. Ram, Adsorption of textile wastewater on alkali-activated sand, J. Cleaner Prod. 220 (2019) 23–32. [12] C. Dwivedi, A. Chaudhary, S. Srinivasan, C.K. Nandi, Polymer stabilized bimetallic alloy nanoparticles: synthesis and catalytic application, Colloid Interface Sci. Commun. 24 (2018) 62–67. [13] S. Wunder, F. Polzer, Y. Lu, Y. Mei, M. Ballauff, Kinetic analysis of catalytic reduction of 4-nitrophenol by metallic nanoparticles immobilized in spherical polyelectrolyte brushes, J. Phys. Chem. 114 (2010) 8814–8820. [14] B. Bagchi, P. Thakur, A. Kool, S. Das, P. Nandy, In situ synthesis of environmentally benign montmorillonite supported composites of Au/Ag nanoparticles and their catalytic activity in the reduction of p-nitrophenol, RSC Adv. 4 (2014) 61114–61123.
4. Conclusion Au-Ag nanoparticles coated on alkali activated sand system was synthesized by a simple method and its catalytic activity in the
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand Kriti Bijalwan a, Aditi Kainthola a, Himani Sharma b, Charu Dwivedi a,⇑ a b
Department of Chemistry, Doon University, Dehradun 248001, India Department of Physics, Doon University, Dehradun 248001, India
a r t i c l e
i n f o
Article history: Received 15 September 2019 Received in revised form 26 November 2019 Accepted 5 January 2020 Available online xxxx Keywords: Alloy nanoparticles Au-Ag bimetallic nanoparticles Alkali activated sand Sand supported catalyst 4-Nitrophenol
a b s t r a c t Gold-Silver (Au-Ag) bimetallic alloy nanoparticles exhibit improved catalytic activity in comparison to the monometallic nanoparticles due to synergistic effect. In this work Au-Ag bimetallic alloy nanoparticles (BNPs) have been supported on alkali activated sand which acts as an inert support material, stabilizes the nanoparticles and prevents their agglomeration. In addition to providing high surface area for adsorption, sand is inexpensive and environmentally benign. Au-Ag alloy nanoparticles were prepared via co-reduction mechanism using polymer as a stabilising agent. Alkali activated sand was coated with the alloy nanoparticles using surface adsorption method. Efficient reduction of 4-Nitrophenol to 4Aminophenol by NaBH4 in the presence of BNPs supported on alkali activated sand was investigated. Also, the heterogenous nature of the catalyst makes it highly reusable due to its effortless separation from the reaction medium. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction Nitrophenols are anthropogenic, toxic and bio-refractory organic compounds that are used to manufacture a variety of pesticides, synthetic dyes and pharmaceuticals. Among nitrophenols, 4-Nitrophenol (4-NP) is found in the agricultural runoff as well as the textile industrial effluents [1]. This compound is toxic and can potentially damage the vital organs in humans and animals. This pollutant is highly persistent in the environment and is difficult to remove from water using conventional treatment methods [2]. Therefore, it is important to eliminate this harmful organic compound. Degradation of 4-NP using nanoparticles of Pt, Au, Cu and Ag has already been investigated extensively [3–5]. Bimetallic alloy nanoparticles synthesized using various methods tend to show better and more pronounced catalytic activity than the monometallic nanoparticles. They exhibit a combination of properties associated with the constituent metals. This leads to enhanced physical and chemical characteristics due to the synergistic effect [6–7]. Their higher catalytic activity can also be
⇑ Corresponding author. E-mail address: [email protected] (C. Dwivedi).
attributed to the high surface area and the presence of interfacial regions which have a greater electron density than the monometallic nanoparticles [8]. The metallic nanoparticles can be deposited on various support material to establish an improved overall efficiency of the catalytic process. Kuroda et al. deposited gold nanoparticles directly on the poly methylmethacrylate (PMMA) beads and the system showed the highest catalytic activity among polymer supported Au nanoparticle systems. They concluded that the activity of the metal nanoparticles, depends on the structure of the support material as well as on the interaction between the nanoparticles and the surface functional groups of the support material [9]. The support material used in this system is sand, which is granular in texture. The easy availability of this natural resource makes it an ideal material for use in various industries [10]. Sand exhibits high stability along with considerable adsorption efficiency making it an excellent support material. Its easy availability, recoverability and reusability makes it a cost-effective carrier. Sand contains a high content of silica in the form of SiO2 along with other minerals. Silica can undergo surface modifications resulting in the formation of new functional groups which can lead to better adsorbent-adsorbate interactions. The surface modification increases the surface area for adsorption and thus the adsorption
https://doi.org/10.1016/j.matpr.2020.01.089 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
2
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
potential of sand [11]. The activated sand provides a large surface area for the adsorption of high concentration of Au-Ag alloy nanoparticles. Herein, we are reporting alkali activated sand coated with Au-Ag alloy nanoparticles as an efficient and environment friendly catalytic system which can be used to reduce 4-NP to 4aminophenol (4-AP) by sodium borohydride. This reaction has been monitored using a UV–visible spectrometer by observing the decrease in the characteristic absorption peak of 4Nitrophenolate ion at 400 nm.
2. Experimental 2.1. Materials Gold(III)chloride hydrate was purchased from Lobachemie, India. Silver nitrate, sodium borohydride and 4-nitrophenol were purchased from Sisco Research Laboratory chemicals, India and sodium chloride 99% was purchased from Sigma Aldrich. All the chemicals were used without any further purification. All the experiments were performed in the double distilled water. The sand used as support material was obtained from Bindal river bed in Dehradun, Uttarakhand, India. It was sieved manually and cleaned thoroughly multiple times with distilled water before usage.
2.2. Synthesis Au-Ag alloy nanoparticle were synthesized by co-reduction method described elsewhere [12]. Briefly, the solution was made by NaBH4 induced co-reduction of HAuCl4 and AgNO3 in the presence of a stabilizing polymer. Instantaneous reaction occurred and a prominent color change was observed in the solution as shown in Fig. 1(a). Alkali activated sand is used as an inactive support material. It was first washed thoroughly with soap solution followed by washing with distilled water to remove the impurities. Normal sand was exfoliated and activated by sodium hydroxide solution. It was left undisturbed to facilitate complete settlement of the sand particles at the bottom of the flask. It was then washed with distilled water to lower the pH and dried in a muffle furnace [11]. The bimetallic nanoparticles coated alkali activated sand system was prepared by adding Au-Ag alloy nanoparticles to activated sand by surface adsorption method as shown in Fig. 1(b). This method ensures uniform and high-quality coating even on irregular and complex structures. It was then completely dried in a hot air oven. 2.3. Catalytic reduction of 4-nitrophenol The alkali activated sand coated with bimetallic nanoparticles was used as a catalyst in the reduction reaction of 4-NP by sodium
Fig. 1. (a) UV–Vis spectrum and image of Au-Ag bimetallic nanoparticles; (b) Schematic representation of the reduction of 4-NP to 4-AP in the presence of Au-Ag nanoparticles coated alkali activated sand used as a catalyst.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
3
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
borohydride. In this study the catalytic efficiency of the Au-Ag nanoparticles coated alkali activated sand system was observed. The concentration of 4-NP used was fixed at 30 mM and the concentration of NaBH4 and the amount of catalyst was kept constant at 10 mM and 1 mg, respectively. Freshly prepared NaBH4 solution was added to the 4-NP solution followed by the catalyst. From the absorbance at kmax = 400 nm the concentration of 4-nitrophenolate was determined.
3. Results and discussion Fig. 2(a) represents the UV–Vis spectra of the catalytic reduction of 4-NP in the presence of NaBH4 using bimetallic nanoparticles coated on alkali activated sand system. The intermediate step in the reduction reaction involves the formation of 4nitrophenolate ion under basic condition, which results in a red shift from 317 nm to 400 nm [5]. The catalytic reduction is studied by monitoring the decrease in the intensity of the characteristic peak of 4-NP at 400 nm and the simultaneous formation of a new peak at 290 nm associated with the formation of 4-AP. In the absence of the catalytic system the absorption peak at 400 nm remains unaltered indicating that NaBH4 itself is unable to initiate the reduction process. On addition of the catalyst the
colour of the solution disappears with time which is indicated by a corresponding decrease in the absorption peak at 400 nm. The two isosbestic points present at 280 nm and 314 nm indicate the complete conversion of 4-NP to 4-AP with no side product formation [13]. The time required for the conversion of 30 mM 4-NP to 4AP using the Au-Ag nanoparticles coated alkali activated sand system is observed to be 5 min, which proves that the catalytic system is not only cost-effective and environment friendly but also highly efficient. Normal or untreated sand has a relatively smooth surface and tightly packed particles [11]. Untreated sand does not bind to the Au-Ag nanoparticles efficiently like the activated sand. Au-Ag nanoparticles cannot be combined with untreated sand to form a catalytic system for the reduction of 4-NP to 4-AP. The alkali activated sand shows a significant difference in its surface morphology after treatment as compared to the untreated or normal sand. Modified sand has a rough consistency along with thin cracks and small pores on its surface. Treatment with alkali leads to the removal of surface impurities and exfoliates the sand particles [11]. Fig. 2(b) shows that the alkali activated sand on its own has no role in catalytic reduction of 4-NP and has absolutely no effect on the rate of the reaction it only improves the overall efficiency of the catalytic process. Alkali activated sand is used here as an inert support material that facilitates easy adsorption and anchors the BNPs on its surface in a manner that prevents their agglomeration. In this system the interaction between BNPs and the surface of alkali activated sand is strong enough to prevent leaching and light enough to allow the reduction of 4-NP. The major problem faced in case of using a homogeneous nanoparticles catalyst is its recovery after the completion of the reaction [14]. Using alkali activated sand as a support material for Au-Ag BNPs helps in recovering the Au-Ag BNPs and facilitates easy separation of the catalyst from the reaction medium. Table 1 Effect of BNPs loading on alkali activated sand and the variation of the time taken for the catalytic reduction of 4-NP.
Fig. 2. (a) Time dependent absorption spectra for the catalytic reduction of 4-NP by NaBH4 in presence of bimetallic nanoparticles coated on alkali activated sand; (b) No change in the absorbance value of 4-NP in presence of alkali activated sand.
Ratio of amount of BNPs to alkali activated sand
Time (min)
1:1 3:1 5:1
18.0 5.0 Leads to the leaching of excess BNPs from the sand surface
Fig. 3. Reusability graph of the Au-Ag BNPs loaded on alkali activated sand for 4-NP reduction.
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089
4
K. Bijalwan et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 A comparative study for the catalytic activity of the different catalysts for 4-NP reduction to 4-AP. Catalyst Amount Au/Ag BNPs supported on Montmorillonite Au NPs over PMMA Homogeneous Au-Ag BNPs Au-Ag BNPs supported on alkali activated sand
1.0 mg 3.5 mg 50 mL 1.0 mg
3.1. Effect of BNPs loading The completion of the reaction in the case of the reduction of 4NP to 4-AP is self-indicated by a colour change from yellow to colourless. Therefore, it is better to express catalytic activity in terms of the time taken for the completion of the reaction. In this system the ratio of the amount of the BNPs to that of the amount of the alkali activated sand was varied in order to study the effect of loading of BNPs on the catalytic system. The time taken for the reduction of 4-NP at different BNPs to activated sand ratios was observed. Table 1 shows that as the amount of the BNPs onto the alkali activated sand increases, the time taken for the catalytic reduction decreases. After this the further loading resulted in leaching of the BNPs in the reaction medium. It was observed that the best catalytic activity is shown by the system with BNP:Activated sand ratio 3:1, therefore all the studies were carried out with this optimal loading condition. The leaching of excess nanoparticles as a result of using higher volume of BNPs could be detected with the help of UV–Visible spectroscopy where on leaching, a peak corresponding to the Au-Ag BNPs was observed near 450 nm.
Conc. of 4-NP (M) 10 10 10 10
6 6 5 5
Reaction Time (min)
Reference
10.0 10.0 3.0 5.0
[14] [9] [12] Present work
reduction of 4-NP to 4-AP was investigated. The catalytic activity proves the catalyst to be extremely efficient. The reduction of 4NP to 4-AP took place completely without any side product formation. This catalytic system has several benefits over the others used for the reduction of 4-NP as sand particles are heavy and therefore settle down at the bottom of the reaction container. This facilitates an effortless separation of the catalyst from 4-AP formed. As investigated, the Au-Ag BNPs coated on alkali activated sand were stable, eco-friendly and highly recyclable thus having a potential for industrial applications. Declaration of Competing Interest There is no conflict of interest. Acknowledgements The authors acknowledge University Grants Commission, India (Project No. F.30-371/2017 BSR) and Doon University, Uttarakhand, India for their support to carry out this work.
3.2. Reusability
References
Using an inert support material makes the BNPs catalyst heterogenous in nature which allows removal of the catalyst from the reaction medium after the completion of the reaction and the catalyst can then be reused. This is especially favourable for the industrial applications where reusability and recyclability are important for a catalyst. In the present system an investigation has been made on the reusability of the catalyst and its efficiency. After the completion of the reaction, the catalyst was used in the next cycle after separation from the reaction medium by simple decantation followed by washing with distilled water and drying. As shown in the Fig. 3. the catalyst was used in the reduction of 4-NP, 8 times and the reduction reactions were monitored for 1 h. It was observed that even after 8 cycles the catalytic efficiency decreases by only 16%. The Table 2. presents a comparison of the catalytic efficiency of the investigated work with the other similar published works. It presents that the Au-Ag bimetallic alloy nanoparticles coated on alkali activated sand reduces 4-NP in lesser time when compared with Au/Ag nanoparticles supported on other inert materials. The reason behind this is the electronic interaction between the Au and Ag in the Au-Ag BNPs. The Au-Ag BNPs without support exhibit better catalytic activity but are not reusable, also it is difficult to recover them after the completion of the reaction. Using alkali activated sand as an inert support helps in recovery of BNPs and improves the overall catalytic efficiency of the system. Therefore, Au-Ag BNPs supported on alkali activated sand can be used as alternative catalyst in the reduction of 4-NP at room temperature.
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4. Conclusion Au-Ag nanoparticles coated on alkali activated sand system was synthesized by a simple method and its catalytic activity in the
Please cite this article as: K. Bijalwan, A. Kainthola, H. Sharma et al., Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.089