AuPd bimetallic nanoparticles: Single step biofabrication, structural characterization and catalytic activity

Accepted Manuscript Title: AuPd bimetallic nanoparticles: single step biofabrication, structural characterization and catalytic activity Author: Preeti Dauthal Mausumi Mukhopadhyay PII: DOI: Reference:

S1226-086X(15)00553-5 http://dx.doi.org/doi:10.1016/j.jiec.2015.12.005 JIEC 2744

To appear in: Received date: Revised date: Accepted date:

4-8-2015 11-10-2015 1-12-2015

Please cite this article as: P. Dauthal, M. Mukhopadhyay, AuPd bimetallic nanoparticles: single step biofabrication, structural characterization and catalytic activity, Journal of Industrial and Engineering Chemistry (2015), http://dx.doi.org/10.1016/j.jiec.2015.12.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical abstract:

2

The room temperature biofabrication of AuPd-NPs using aqueous leaf extract of Delonix

3

regia was reported. The nature, morphology and size of nanoparticles were analyzed using

4

UV-Visible spectroscopy, DLS, XRD, TEM and EDX techniques. Nearly spherical

5

crystalline AuPd-NPs were synthesized within size range of 3-31 nm. Appearance of broad

6

intense reflection at 39.29° position, nearer to the mean of Pd (40.26°) and Au (38.37°)

7

reflections suggested fabrication of AuPd-NPs. Furthermore, as-formed AuPd-NPs showed

8

recyclable catalytic efficiency towards the reduction of 3-Nitroaniline and it remained at

9

about 93 % even after recycling for 5 consecutive cycles in terms of normalized activity

cr

us

an

parameter.

Ac ce p

te

d

M

10

ip t

1

11 12 13 14 15 16 1 Page 1 of 24

ip t

AuPd-NPs are biofabricated using aqueous leaf extract of Delonix regia. Characterization of AuPd-NPs is done with UV-Visible, DLS, TEM, XRD, EDX and FTIR. Nearly spherical, crystalline AuPd-NPs are fabricated within size range of 4-30 nm. AuPd-NPs shows recyclable catalytic efficiency towards the reduction of 3-NA.Catalytic efficiency of AuPd-NPs remained at about 77 % even after 5 cycles.

cr

AuPd bimetallic nanoparticles: single step biofabrication, structural characterization and catalytic activity

an

Tel.: +91 261 2201645, fax: +91 261 2227334, 2201641

us

Preeti Dauthal, Mausumi Mukhopadhyay*[email protected]; [email protected] Department of Chemical Engineering, S.V. National Institute of Technology, Surat, Gujarat, India

te

d

M

Abstract The room temperature biofabrication of AuPd-NPs using aqueous leaf extract of Delonix regia was reported. The nature, morphology and size of nanoparticles were analyzed using UV-Visible spectroscopy, DLS, XRD, TEM and EDX techniques. Nearly spherical crystalline AuPd-NPs were synthesized within size range of 3-31 nm. Appearance of broad intense reflection at 39.29° position, nearer to the mean of Pd (40.26°) and Au (38.37°) reflections suggested fabrication of AuPd-NPs. Furthermore, as-formed AuPd-NPs showed recyclable catalytic efficiency towards the reduction of 3-Nitroaniline and it remained at about 93 % even after recycling for 5 consecutive cycles in terms of normalized activity parameter.

Ac ce p

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

Keywords Bimetallic, Biofabrication, Delonix regia, AuPd-NPs, 3-Nitroaniline 1. Introduction Fabrication of bimetallic nanoparticles (NPs) is of recent research interest due to their bifunctional and synergistic properties [1,2]. As far as the technological and scientific aspect is concerned, the bimetallic NPs exhibit enhanced optical, catalytic, chemical, and biological properties compare to their monometallic counterparts [1,3,4]. Generally, bimetallic NPs are fabricated through chemical [2], electrochemical [5], thermolysis [6], sonochemical [7], and radiation-induced methods [8]. However, in spite of their extensive use, these techniques not only utilize toxic chemical reducing agents but also require expensive experimental setup. In addition, sometimes these methods face the problem of phase separation at atomic level, which leads to the formation of core-shell NPs [9]. Thus, the development of reliable ecobenign and economical methods for fabrication of alloy bimetallic NPs remains stills a challenge. Strategies to address rising environmental concerns through development of costeffective, sustainable techniques by use of eco-friendly solvents and biodegradable polymers are the need of the day. Recently, intense research is focussed towards the biofabrication of NPs by exploiting natural resources viz. plants and microorganisms. This method is suitable for fabrication of biocompatible NPs for pharmaceutical and biomedical usage. The study on 2 Page 2 of 24

biofabrication of bimetallic NPs is less reported in the literature. So far very few studies are available for biofabrication of alloy type bimetallic NPs such as AuAg [10], AgPd [11], and AuPd [3].

us

cr

ip t

In previous studies, our research group identified and fabricated monometallic NPs of different metals such as Au [12], Pd [13], Se [14], Pt [15], Ag [16], and SnO2 [17] using different biological resources in aqueous medium. Here, for the first time, biofabrication of bimetallic alloy AuPd-NPs is carried out using aqueous leaf extract of Delonix regia (D. regia). Metal reducing potential of D. regia is already proved earlier for economical and ecobenign fabrication of monometallic palladium NPs [13]. Metal reducing potential of one other plant species of same genus is also reported earlier for fabrication of silver NPs [18]. Nature of biofabricated bimetallic NPs are evaluated using various characterization techniques viz. UV-Visible spectroscopy, XRD, TEM, EDX coupled with SEM, DLS, and FTIR.

te

d

M

an

Nitro-aromatic compounds are, on average 500-times more toxic than their corresponding amino derivatives [19]. Degradation of these organic compounds is very difficult. However, the widespread use in the manufacture of drugs, rubber chemicals, explosives, insecticides and dyes leads to their continuous release into the environment. So discharge of nitroaromatic compounds in water and environment is the matter of major concern for environment pollution nowadays. Application of biofabricated bimetallic NPs for the reduction of these nitro-aromatic compounds to less toxic amino analogs can pave a way for environmental remediation. The bimetallic NPs shows catalytic ability for a variety of reactions with superior activity and durability as compare to their monometallic counterparts [1,2]. In this study authors evaluated the catalytic potential of biofabricated NPs for the reduction of toxic nitro-organic pollutant 3-Nitroaniline (3-NA). Kinetic evaluation of 3-NA reduction was carried out using different concentrations of AuPd-NPs (500-2000 µg) and at different reaction temperature (10-50 °C). Recyclability study of AuPd-NPs catalysts was also carried out in a view of industrial importance.

Ac ce p

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

2. Materials and methods 2.1. Materials Gold-III-chloride-trihydrate (HAuCl4.3H2O; 99 %), palladium-II-chloride (PdCl2; 99 %), sodium borohydride (NaBH4; 98 %), and 3-NA (C6H6N2O2; 98 %) were bought from HiMedia Laboratories Pvt. Ltd. Mumbai, India. All chemicals used for the study were of analytical grade and double-distilled deionized water was used for experiment. Leaves of D. regia were collected from the campus of Sardar Vallabhbhai National Institute of Technology, Surat, Gujarat, India.

2.2. Preparation of aqueous leaf extracts of D. regia D. regia leaf extract was prepared according to the method reported earlier in literature [16]. 30 g of the fresh leaves of D. regia was heated with 120 mL of double-distilled water at 60 °C for 10 min. After that, the solution was filtered with Whatman filter paper no. 40. Filtrate was obtained as a clean light greenish-brown solution. This filtrate was used further for the biofabrication of bimetallic AuPd-NPs.

3 Page 3 of 24

cr

ip t

2.3. Biofabrication of AuPd-NPs Biofabrication of bimetallic AuPd-NPs were initiated by the addition of a well-mixed aqueous solution (900 mL) of HAuCl4.3H2O (0.5 × 10-3 M) and PdCl2 (0.5 × 10-3 M) to 100 mL of aqueous solution of D. regia leaf extract. This solution was kept in shaker at 500 rotation per minute (RPM) for 3 h at room temperature (RT) (28 ± 2 °C). Spontaneous reduction of salt solution was resulted in the fabrication of bimetallic AuPd-NPs. Monometallic NPs were also prepared for comparison purpose. Monometallic NPs were prepared by substituting the mixture of aqueous HAuCl4.3H2O/PdCl2 solution by individual salt solution of HAuCl4.3H2O and PdCl2 in two separate experiments.

us

2.4 Quantification of total phenolic acid (TPA), total flavonoids (TF) and total protein (TP) in D. regia leaf extract before and after bioreduction of salt solution (HAuCl4.3H2O:PdCl2)

d

M

an

TPA, TF and TP contents of D. regia leaf extract before and after bioreduction of salt solution (HAuCl4.3H2O:PdCl2) was measured using three different colorimetric assays (i.e. Folin-Ciocalteu’s colorimetric assay for TPA; aluminium chloride colorimetric assay for TF; Bradford protein assay for TP) following Dauthal and Mukhopadhyay, 2013 [13]. Quantification of TPA, TF and TP was done on the basis of standard curve of gallic acid, quercetin and bovine serum albumin respectively. Results expressed in g of gallic acid equivalent per 100 g fresh weight (g GAE/100 g fw), g of quercetin equivalent per 100 g fresh weight (g QE/100g fw) and g of bovine serum albumin equivalent per 100 g fresh weight (g BSAE/100g fw).

te

2.5. Catalytic reduction of 3-NA using biofabricated AuPd-NPs In a typical experiment, 3 mL of 3-NA (0.5 × 10-3 M) was mixed with aqueous solution of 0.12 mL NaBH4 (1.0 M) in glass vial. 1 mg of AuPd-NPs was then added to above reaction mixtures with constant stirring at RT. UV-Visible absorption spectra of reaction mixture were measured at every 1 min interval to observe the change in the reaction mixture. Blank reaction was also carried out for the reduction of 3-NA in the absence of catalyst. Catalyst concentration and reaction temperature dependent catalytic reduction was also carried out for kinetic evaluation of catalytic reduction. Furthermore, recyclability of biofabricated AuPdNPs was tested for 5 consecutive cycles of catalytic reduction of 3-NA. To judge the recyclability of catalyst, AuPd-NPs were recovered from the reaction mixture by centrifugation at 20,000 RPM for 10 min, followed by washing with distilled water. Centrifuged AuPd-NPs were then dried in an oven at 60 °C for 2h. Recycled catalytic used further for next catalytic run using same procedure. Catalytic potential of monometallic AuNPs and Pd-NPs were also evaluated using above mentioned procedure.

Ac ce p

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

2.6. Characterization Absorbance behaviour of AuPd-NPs was recorded by UV-Visible spectrophotometer (DR 5000, HACH, USA). Z-average and ζ potential distribution of the colloidal AuPd-NPs were determined by DLS (Zetasizer Nano ZS90, Malvern, UK). Size, morphology and selected area electron diffraction (SAED) pattern of biofabricated AuPd-NPs were analysed using TEM (CM-200, Philips, UK). The composition of biofabricated NPs were identified by EDX (INCA X-sight, Oxford Instruments, UK) coupled with SEM (JSM-6380LV, JEOL, Japan). 4 Page 4 of 24

Structure of AuPd-NPs were determined by XRD (X’Pert Pro, PANalytical, Holland) equipped with Cu-Kα radiation (45 kV, 35 mA). Identification of functional group of leaf extract responsible for metal ions reduction and stabilization of NPs was done by FTIR (Magna-550, Nicolet, USA).

M

an

us

cr

ip t

3. Results and discussion 3.1. UV-Visible analysis UV-Visible analysis was carried out to compare the absorbance behaviour of bimetallic NPs with individual monometallic NPs (Au-NPs and Pd-NPs) and also with their physical mixture (Fig. 1). UV-Visible analysis of aqueous HAuCl4.3H2O salt solution initially showed absorption peak at 287 nm indicating the existence of Au3+ ions. Similarly PdCl2 salt solution showed a strong absorption band at around 300 nm and a shoulder at 415 nm indicating the existence of Pd2+ ions in the mixture [13]. These peaks were due to charge transfer between the metal ions and corresponding ligands in aqueous solutions. Appearance of surface Plasmon resonance (SPR) peak centered at 535 nm, in contrast with HAuCl4.3H2O spectrum attributed to the metal charge transfer transition of the Au3+ ions to Au0 and confirmed the fabrication of Au-NPs. Similarly appearance of a broad continuous absorption spectrum (in contrast with PdCl2 spectrum), which gradually increases in intensity from the visible to ultraviolet region, suggested complete reduction of the initial Pd2+ ions to Pd0.

te

d

UV-Visible spectrum of physical mixture of monometallic NPs was represented by a low intensity SPR peak at 535 nm. It was completely dampened in absorption spectrum of AuPdNPs. This was due to the fact that, during formation of bimetallic NPs, surface Plasmon energies of group 11 metals (d10s1) was generally supressed by the group 10 metals (d8s2) [4]. The diminished SPR peak of Au-NPs (535 nm) in bimetallic NPs suggested interaction between Au and Pd metals, resulted the formation of bimetallic AuPd-NPs. This result was consistent with previous reports [20, 21], where dipolar Plasmon oscillations of Ag or Au was strongly damp out by Pt or Pd. In addition, absence of the bands of Au3+ and Pd2+ ions, in UV-Visible spectrum of AuPdNPs suggested that Au3+:Pd2+ were reduced to Au0:Pd0 and no significant variation observed in the absorption behavior of AuPd-NPs during the interaction time of 3h-12h suggested the completion of reduction reaction of salt solution (HAuCl4.3H2O:PdCl2) within 3h.Visual observation of colloidal solution of NPs also confirmed the fabrication of AuPd-NPs (blackish brown color), Au-NPs (intense ruby red), Pd-NPs (brown) and physical mixture of Au-NPs and Pd-NPs (ruby red).

Ac ce p

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

3.2. XRD analysis To verify the structure of AuPd-NPs, XRD diffractogram of AuPd-NPs was compared with monometallic NPs (Fig. 2). Biofabricated NPs exhibited a new set of Bragg reflections present at 39.29°, 45.59°, 66.48°, and 79.77° positions, which were located between facecentered cubic (fcc) Au0 (JCPDS no. 04-0784, SG.: Fm3m (225)) and Pd0 (JCPDS no. 050681, SG.: Fm3m (225)) confirmed the metal state of Au0Pd0 in AuPd-NPs. So these reflections were indicated (111), (200), (220), and (311) planes of the bimetallic alloy AuPdNPs [21]. For comparison, broad intense (111) reflection of AuPd-NPs (39.29°) was compared with (111) reflection of pure Au (38.37°) and pure Pd (40.26°) (inset in Fig. 2). The position of the (111) reflection in AuPd-NPs clearly indicated an intermediary scattering angle between those of the monometallic NPs as it was very close to the mean values of pure Au and pure Pd reflection, suggested alloying interaction of Au and Pd metals. Earlier 5 Page 5 of 24

an

us

cr

ip t

research was also reported single absorption peak in bimetallic alloy NPs, generally located between the absorption peaks of contributing NPs [22]. However, core-shell NPs generally exhibited two peaks that was related to the absorbance of two contributing metal as cores or shells [22]. The d-spacing of the (111) reflection of AuPd-NPs (2.293 Ǻ) was also observed between those of the individual Au-NPs (2.346 Ǻ) and Pd-NPs (2.240 Ǻ). This was well consistent with d-spacing data reported earlier for alloy bimetallic AuPd-NPs [21]. Due to the almost similar interplanar spacing, Au and Pd atoms were easily formed alloy structure. The intense reflection at (111) in comparison with other three reflections were indicated the preferred growth direction of the nanocrystals. Particle size calculated using half width of the dominating (111) reflection, was 25 nm, close to TEM-derived data. The particles size was also calculated for pure Au (34 nm) and pure Pd (19 nm) NPs using their (111) reflections. The decrease in the size of bimetallic AuPd-NPs, with respect to the monometallic Au, was explained by considering the velocity of growth of the individual NPs. Incorporation of Pd in the reaction mixture obstructed the particle size growth of bimetallic AuPd-NPs due to the lower ionization potential of Pd (8.33 eV) as compare to Au (9.22 eV) [23].

te

d

M

3.3. TEM and SAED analysis TEM micrograph represented well defined predominantly spherical shaped bimetallic AuPdNPs (Fig. 3a-b). Particles size histogram of 150 nanoparticles prepared from Fig. 3a-b, indicated particle size distributed in the range of 3-31 nm (Fig. 3c). The peak of the Gaussian fit of the histogram indicated the average size (µ) of the prepared NPs with standard deviation (σ) (12.16 ± 6.01 nm). Histogram obtained from TEM micrograph of AuPd-NPs suggested that, majority of the particles (70%) were resided in size range of 6.15 nm (-1σ) and 18.18 nm (+1σ). No core shell structure observed in TEM micrograph, also verified the alloy nature of bimetallic NPs, which was corroborated with the results of XRD analysis. The SAED analysis of the particle showed four spotty diffraction rings in SAED pattern corresponding to four different crystal reflection of cubic structure of AuPd-NPs with the spa ce group Fm3m [21]. Appearance of four spotty diffraction rings instead eight diffraction rings (produced by two phase-segregated (core-shell) metals) suggested fabrication of bimetallic alloy NPs (inset in Fig. 3b).

Ac ce p

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

The crystallite size of AuPd-NPs was calculated as 25 nm in XRD analysis and it was consistent with the particle size distribution in TEM analysis (3-31 nm). However, Z-average diameter of AuPd-NPs was observed quite high in DLS analysis (81.83 nm). The basic reason behind the size difference in TEM, DLS and XRD analysis attributed to the different instrument response to particle number, volume, mass, optical property and sample preparation method. In DLS analysis, size measurement is based on the phenomenon of Brownian motion which measured the hydrodynamic diameter of particles in colloidal solution. Hydrodynamic diameter of particles is generally higher than the size measured by other techniques as the various forces of interaction works in the colloidal solution like van der Waals force of attraction. DLS instrument is known to measure the shell thickness of a capping agent enveloping the NPs along with the actual size of the metallic core. However, in XRD the particle size calculation is based on the Debye-Scherrer Eq., where calculation of crystallite size is based only on the prominent XRD peak of materials. However, in TEM analysis dry forms of synthesized particles directly analysed under electron microscope [13, 15]. Therefore, TEM is the appropriate technique for the estimation of exact particle size. 6 Page 6 of 24

37 38 39 40 41 42 43 44 45 46 47 48 49 50

ip t

3.4. EDX analysis Nature and elemental composition of biofabricated NPs was again confirmed by quantitative EDX analysis (Fig. 4). EDX spectrum was obtained by plotting kilo electron volt (keV) against counts per second/electron volt (cps/eV). EDX spectrum was confirmed the coexistence of both metals, Au and Pd, in single NPs (characteristic X-ray peaks present at 2.20 keV and 2.80 keV for pure Au and Pd).

M

an

us

cr

Table 1 represented the elemental composition and weight (%) of Au to Pd in bimetallic NPs. Approximate content of Au/Pd was in the ratio of 4:1. The ratio of Pd content was relatively less compared to that of Au in spite of reduction carried out with 1:1 molar ratios of Au:Pd. This was due to the difference in standard reduction potential of Au(III) (AuCl4-/Au, +1.002 V vs NHE) than the one of Pd(II) (Pd2+/Pd, 0.951 V vs NHE) [24, 25]. This thermodynamic property favored the formation of Pd shell over Au core and suggested that maximum of the primary formed nucleus of bimetallic NPs were of Au atoms. In reality, however, the formation of Pd-NPs is much slower than the formation of Au-NPs. The different reaction rates of Au-NPs and Pd-NPs formation are then supposed to lead to bimetallic AuPd-NPs with an inhomogeneous alloy structure, being Au-rich in the core and Pd rich at the surface. This present ratio of Au/Pd in AuPd-NPs was consistent with the results of Shubin et al. 2012, which stated approximate molar ratio of 4:1 for Au/Pd in bimetallic NPs [6].

te

d

Considering the slightly more positive standard reduction Au3+/Au0 a galvanic replacement reaction (GRR) between Au(III) and Pd(II) (Eq. 1) is not expected to be favorable. One probable reason for the observed favorable GRR-like Pd deposition associated with Au etching [25]. In contrast to the thermodynamic expectation from the reduction potentials, it could possible through the adsorption of chloride (from PdCl2) on the Au-NPs surface, induced the local chloride concentration at the Au-NPs surface, and therefore facilitate Au0 oxidation to Au3+. This leads to the gradual consumption of Au atoms and at the same time, the production of Pd0. The reduced dimensions of the Pd0 and the large number of vacancy defects generated by the replacement reaction allowed the inter-diffusion of the Pd0 and Au0 and formation of inhomogeneous alloy NPs, being Au-rich in the core and Pd rich at the surface [26].

Ac ce p

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

The presence of weak signals of C, O and Cl in EDX spectrum suggested the presence of residual organic moieties of leaf extract as surface capping ligands for NPs. In the EDX spectrum, K(α) and K(β) signals of Cl present at 2.621 and 2.815 keV overlaps with L(α) and L(β) signals of Pd at 2.838 and 2.990 keV. The reason contributed to this spectral interference is poor energy resolution of the EDX for characteristic X-ray peaks from different families related to different elements [25]. However, significantly low weight % of Cl (0.44 %) as compare to the Pd (15.32 %) (Table 1) attributed to the appearance of very small peak (*) around the spectral line of Cl at 2.621 keV. Therefore, high weight % of Pd suggested intense peak present around the spectral line of 2.838 and 2.990 keV predominantly belongs to Pd. However, L(γ) signal (*) of Pd present at significant distance from L(α) and L(β) spectral line of Pd.

7 Page 7 of 24

d

M

an

us

cr

ip t

3.5. DLS and ζ potential analysis Particle size of colloidal AuPd-NPs was measured using dynamic light scattering, indicated Z-average diameter of 81.83 nm (Fig. 5a). ζ potential of biofabricated colloidal AuPd-NPs was also evaluated in aqueous medium. The ζ potential was found to be -21.1 mV (Fig. 5b). The negative value of ζ potential suggested existence of repulsive forces among synthesized NPs and thereby increases in the stability. There was not much agglomeration of the AuPdNPs observed means the stability of these nanoscaled particles. Fig. 5. 3.6. Explanation of a plausible mechanistic pathway of bioreduction FTIR analysis was conducted to determine the plausible mechanistic path for bioreduction and stabilization of the metal precursors. FTIR spectrum of leaf extract indicated the plentiful of metal reducing polar polyphenolic [28] compounds in D. regia leaf extract [13]. However, slight shift observed in the positions of stretching vibration in the FTIR spectrum of leaf extract after bioreduction suggested the role of hydroxyl group of polar polyphenolic compounds in bioreduction reaction [28] (Fig. 6a-b). Significant reduction in the concentration of TPA and TF of D. regia leaf extract after bioreduction of salt solution (HAuCl4.3H2O:PdCl2) also suggested the role of these bioorganic compounds in biofabrication of AuPd-NPs (Table 2). Significant variation observed in the spectral features of FTIR stretching before and after bioreduction of salt solution also asserted the same. However, it was found that the TP content estimated in D. regia leaf extract was relatively low as compare to the TPA and TF and no significant variation observed in the concentration of TP after bioreduction. As a consequence, in the redox reaction water soluble TPA and TF would serve as the key electron donor and played significant role in biosynthesis of AuPd-NPs.

te

D. regia leaf represents a complex storehouse of many antioxidant polyphenolic compounds like phenolic acid, flavonoids, flavanols, tannins and flavonoid glycosides [27-31]. It is well known that -OH and C=O groups of these polyphenolic compounds have strong ability to bind metal ions and antioxidant potential of these compounds resides mainly in their ability to donate electron/hydrogen atom [32]. Recently, electron/hydrogen atom donation ability various polyphenolic compounds such as quercetin, gallic acid, catechin and tannic acid as chemical agents are also reported for the synthesis various metallic NPs such as Ag-Se, Pd, Ag and Au-NPs [33-37]. Therefore, it is very much likely that reactive hydrogen of polar polyphenolic compounds of leaf extract may be responsible for the biofabrication of AuPdNPs and number of polyphenolic compounds acts synergistically in bioreduction reaction and got oxidized. After considering all the facts, the plausible general mechanism of bioreduction reaction involved the mixture of polyphenolic compounds, according to the redox reaction, illustrated in Scheme 1, where hydroxyl group of polyphenols were oxidized to an α,βunsaturated carbonyl group (quinone form) [32]. The Au3+/Pd2+ ion were simultaneously reduced to zero valent form in the presence of nascent hydrogen or free electron generated during the oxidation of polyphenolic compounds. These adjoining (Au0/Pd0) atoms were further collided with each other to form AuPd-NPs.

Ac ce p

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

Further, AuPd-NPs formed in the presence of D. regia leaf extract were separated, washed properly with distilled water, dried and analyzed by FTIR spectroscopy (Fig. 6c). Significant peaks observed at 3434 and 2922 cm-1 in FTIR spectrum of AuPd-NPs represented (O-H) and (C-H) stretching of polyols. Stretching vibration present at 1638 and 1559 cm-1 were associated with (C=C) and (C-C) stretching vibration of aromatic rings. The absorption band 8 Page 8 of 24

located at around 1457, 1403 and 1230 cm-1 were related with (C-O-C), (O-H) and (C-OH) vibrations of polyols. Further, a strong stretching vibration located at 1019 and 1736 cm-1 in FTIR spectra of AuPd-NPs represented C-N stretching of amines and C=O stretching of oxidized polyphenol (quinones). These observations suggested the adsorption of different water soluble polyphenolics at the surface of NPs as capping and stabilizing agents. 3.7. Catalytic activity of biofabricated AuPd-NPs for 3-NA reduction NPs with dominating (111) planes with sharp edges and corners were expected decent catalytic activity [40]. XRD pattern of AuPd-NPs (Fig. 2) suggested predominant orientation of (111) plane, and thus catalytic activity. Hence, for evaluation of catalytic activity of biofabricated AuPd-NPs, 3-NA reduction was selected as model reaction. The progression of reduction reaction was monitored using UV-Visible spectroscopy analysis. Significant reduction observed in absorption peak of 360 and 280 nm (characteristic UV-Visible peak of 3-NA) (Fig. 7a) in the presence of AuPd-NPs catalyst, confirmed the formation of 3phenylenediamine (3-PDA) within 5 min [41]. Absorbance changes of 3-NA at 360 nm in consecutive UV-Visible absorption spectra were recorded to monitor the kinetic of the reaction. As the initial concentration of NaBH4 greatly exceeded that of 3-NA, so it was assumed that the concentration of NaBH4 remained constant during the reduction reaction. Hence, rate of catalytic reduction was assumed to be dependent only on the concentration of 3-NA. Therefore, reduction reaction was assumed to follow pseudo-first-order-kinetics. Apparent rate constant (kapp) was calculated through Eq.2, where At and A0: absorbance of 3-NA at time t and 0. The kapp of this catalytic reduction was calculated to be 18.62 × 10-2 min-1 from the plot ln (3-NAt/3-NA0) versus time t at 360 nm (Fig. 7b). This reaction proceeded under mild conditions, at RT and in an aqueous medium. Thus use of AuPd-NPs in the treatment of industrial toxic wastewater containing nitro-organic effluents was possible. Toxic effect of NaBH4 was also reduced during the reaction because the reaction mechanism involves production of less toxic sodium metaborate (NaBO2) in form of Na+BO2−.

29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

The effect of the concentration of biofabricated AuPd-NPs on the reduction of 3-NA was studied at RT, keeping other parameters constant. From Table 2, it is evident that the kapp for reduction reactions of 3-NA increases proportional to the AuPd-NPs concentration. This observation justified the fact that the catalytic reaction usually takes place at the surface of NPs [42]. Therefore, increase in the kapp value was due to the accessibility of more interaction sites of NPs, which ultimately increased the kapp of reduction reactions. Earlier research also supported this observation that the rate of the reaction generally increases linearly with the concentration of the catalysts [43]. Reduction of 3-NA was also studied at 10 to 50 °C temperature range. It was observed that the rate of reduction of 3-NA increases with increase in temperature (Table 3). The temperature coefficient (Q10) for the catalytic reduction of 3-NA was calculated using Eq.3, where kapp2 and kapp1: apparent rate constant at reaction temperature T2 and T1. Q10 calculated for reduction of 3-NA was increased by a factor of 1.3-1.7 for every 10 °C rise in temperature.

44 45 46 47

Further, analysis was carried out to derive relationship between kapp and Ea associated with different nano-catalyst system. For that Arrhenius plots was prepared between ln (kapp)

Ac ce p

te

d

M

an

us

cr

ip t

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

9 Page 9 of 24

M

an

us

cr

ip t

Fig. 8. Mechanism of catalytic reduction of 3-NA in presence of NaBH4 using AuPd-NPs as catalyst was explained in Fig. 9. Role of NaBH4 in the catalytic reduction of 3-NA can be explained on the basis of Langmuir-Hinshelwood model. In the present catalytic reduction, NaBH4 ionizes initially in water to offer BH4−. BH4− provides surface hydrogen, which helped in proper mixing of AuPd-NPs in the reaction medium and offered a favourable environment for the reaction. The diffusion and adsorption of 3-NA on AuPd-NPs surface and followed by hydrogen transfer mediated by AuPd-NPs surface from BH4− to 3-NA produced 3-PDA. In this catalytic reaction, BH4− acted as the electron donor, while 3-NA acted as the electron acceptor. AuPd-NPs served as catalyst to provide active sites to promote catalytic reduction. This catalytic reduction was facilitated by the high driving force created by NPs mediated hydrogen transfer arise by the shift in the energy level in the presence of highly electroninjecting BH4− ions [44]. BH4− finally oxidized into BO2− and the resultant of the reaction in the form of BO2− and 3-PDA. Thus, AuPd-NPs played the role of catalyst by lowering the activation energy of the reactions. However, no reaction was observed in the absence of AuPd-NPs.

d

3.8. Catalytic recyclability of biofabricated AuPd-NPs for 3-NA reduction Leaching of metal during successive usage was led to loss of the catalytic activity of heterogeneous catalysts. In order to evaluate the recyclability of bimetallic AuPd-NPs, recycle tests were conducted for the reduction of 3-NA. AuPd-NPs were recovered by centrifugation followed by washing and drying. To establish easy recovery of AuPd-NPs from the reaction, volume of reaction mixture was increased by 10 times. Recycled catalyst was reused for 5 consecutive cycles of 3-NA reduction using same procedure. In order to evaluate the catalytic activity of AuPd-NPs catalyst during each cycle of 3-NA reduction, normalized activity parameter (K) was used. K is the ratio of kapp to the total mass (m) of the recycled catalyst used during each cycle (Table 5). It was observed that the catalytic ability remained at about 93 % even after recycling for 5 consecutive cycles, in terms of K, indicated the remarkable stability of the AuPd-NPs catalysts during reactions. This was due to the protective covering of bio-organic compounds around NPs. Protective covering of bio-organic prohibited the loss of the NPs, thereby provided excellent durability to the AuPd-NPs during reduction reactions. However, gradual decline in K was due to the loss of catalyst during recycling process. Electron transfer efficiency of catalyst was decreased as the number of cycle increased. Surface poisoning of catalyst by the product was another reason attributed to gradual decline in K. Thus, cyclic stability and slight reduction in catalytic activity of the bimetallic AuPd-NPs during recycling was of high significance in terms of its use as a potential catalyst for industrial applications.

te

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

against 1/T for different nanocatalyst system (Fig. 8). The Ea calculated from the slope (Ea/R) of the linear regression of In (kapp) against 1/T using Arrhenius equation (Eq. 4), where A: frequency factor; Ea: activation energy; R: universal constant; T: absolute temperature. From the Arrhenius equation, Ea was calculated to be 33.17 kJ mole-1 for reduction of 3-NA.

Ac ce p

1 2 3 4

In order to compare the catalytic activity of the bimetallic AuPd-NPs, with their monometallic counterparts, catalytic reduction of 3-NA was also carried out with D. regia mediated monometallic Au-NPs and Pd-NPs. It was observed that bimetallic AuPd-NPs showed prominently better catalytic activity; specifically kapp of the catalytic reduction of 3NA was calculated to be 18.62 × 10-2, 13.18 × 10-2 and 9.33× 10-2 min-1 for AuPd-NPs, Pd10 Page 10 of 24

te

d

M

an

us

cr

ip t

NPs and Au-NPs respectively during first cycle of catalytic reduction (Table S1 and S2 of Supplementary information). Higher catalytic activity of bimetallic NPs as compare to monometallic counterparts was attributed to synergistic electronic effects produced in the bimetallic NPs. Synergistic electronic effect induce transfer of electrons between contributing metal NPs, which ultimately lead to an increase in the electron density at the interface of the AuPd-NPs and finally improved the catalytic performance of bimetallic NPs [26,45,46]. The chemical and physical stability of the AuPd-NPs catalyst is quite important owing to its practical application in various industries. Catalytic performance exhibited a slight decrease when reused for 5 times. XRD pattern of the recycled particles is shown in Fig. 10a, which indicated that AuPd-NPs were well crystallized even after being recycled for 5 times. The XRD pattern showed that the metal state of Au and Pd was kept same (Au0Pd0) even after the 5 catalytic runs. There was no significant change observed in the morphology of AuPd-NPs (Fig. 10b). However, slight aggregation of particles attributed to increase in particles size distribution in TEM (12-18 nm) and crystallite size in XRD analysis (38 nm). Therefore, it can be elucidated that slight increase in particles size and loss of catalyst (Table 5) during recycling process may be responsible for the reduction of K (93 %) after 5 cycles of catalytic runs. Therefore, biofabricated AuPd-NPs can be considered as efficient and stable catalyst for NaBH4 mediated reduction of 3-NA as only 7 % reduction observed in the catalytic efficiency. The present study reported first time the biofabricated NPs use as the catalyst for the reduction of 3-NA. There was no data available for direct comparison. However, kapp calculated in the present study was indicated that the biofabricated AuPd-NPs possess comparable catalytic efficiency for reduction of 3-NA, when compared with other nanocatalyst systems for reduction of different nitro-organic compounds (Table 4). However, various process parameters such as reaction conditions, size of NPs, temperature, concentration of nanocatalyst used, reaction time, method of preparation of nanocatalyst and nature of supporting matrix were crucial for determining reaction rate. A comparative study of the efficiency of different NPs for the reduction of various nitro-organic pollutants was reported as in Table 6.

Ac ce p

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

4. Conclusions Room temperature biofabrication method is developed for synthesis of bimetallic AuPdNPs by simultaneous reduction of aqueous HAuCl4.3H2O/PdCl2 solution with D. regia leaf extract. With an interaction time of 3 h, crystalline, nearly spherical AuPd-NPs are fabricated in the range of 3-31 nm. EDX, SAED, UV-Visible and XRD spectrum are confirmed the fabrication of bimetallic alloy NPs. This method is proved facile and ecofriendly for fabrication of stable, potential recyclable AuPd-NPs catalyst for reduction of toxic nitro-organic pollutants. Acknowledgments Author would like to express sincere gratitude to the Sophisticated Analytical Instrument Facility (SAIF) and Department of Metallurgical Engineering & Material Science (MEMS), Indian Institute of Technology (IIT) (Bombay) for providing the research facility for sample characterizations. Author also gratefully acknowledges Electrical Research and Development Association (ERDA), Vadodara for providing necessary research facilities. References H. Liu, Q. Yang, J. Mater. Chem. 21 (2011) 11961–11967.

11 Page 11 of 24

te

d

M

an

us

cr

ip t

J. Pritchard, L. Kesavan, M. Piccinini, Q. He, R. Tiruvalam, N. Dimitratos, J.A. LopezSanchez, A.F. Carley, J.K. Edwards, C.J. Kiely, G.J. Hutchings, Langmuir 26 (2010) 16568– 16577. G. Zhan, J. Huang, M. Du, I. Abdul-Rauf, Y. Ma, Q. Li, Mater. Lett. 65 (2011) 2989–2991. N. Toshima, T. Yonezawa, New J. Chem. 22 (1998) 1179−1201. F. Yang, K. Cheng, T. Wu, Y. Zhang, J. Yin, G. Wang, D. Cao, J. Power Sources 233 (2013) 252–258. Y. Shubin, P. Plyusnin, M. Sharafutdinov, Nanotechnology 23 (2012) 405302. Y. Mizukoshi, K. Sato, T.J. Konno, N. Masahashi, Appl. Catal. B 94 (2010) 248–253. M. Treguer, C.D. Cointet, H. Remita, J. Khatouri, M. Mostafavi, J. Amblard, J. Belloni, J. Phys. Chem. B 102 (1998) 4310−4321. A.V. Singh, B.M. Bandgar, M. Kasture, B.L.V. Prasad, M. Sastry, J. Mater. Chem. 15 (2005) 5115−5121. G. Zhang, M. Du, Q. Li, X. Li, J. Huang, X. Jiang, D. Sun, RSC Adv. 3 (2013) 1878–1884. F. Lu, D. Sun, J. Huang, M. Du, F. Yang, H. Chen, Y. Hong, Q. Li, ACS Sustainable Chem. Eng. 2 (2014) 1212−1218. P. Dauthal, M. Mukhopadhyay, Ind. Eng. Chem. Res. 51 (2012) 13014–13020. P. Dauthal, M. Mukhopadhyay, Ind. Eng. Chem. Res. 52 (2013) 18131−18139. N. Srivastava, M. Mukhopadhyay, Powder Technol. 244 (2013) 26–29. P. Dauthal, M. Mukhopadhyay, J. Ind. Eng. Chem. 22 (2015) 185–191 P. Dauthal, M. Mukhopadhyay, J. Nanopart. Res. 15 (2013) 1366–1376. N. Srivastava, M. Mukhopadhyay, Ind. Eng. Chem. Res. 53 (2014) 13971–13979. C.K. Sathiya, S. Akilandeswari, Spectrochim. Acta A 128 (2014) 337–341. B.A. Donlon, E. Razo-Flores, G. Lettinga, J.A. Field, Biotech. Bioeng. 51 (1996) 439–449. Z.Q. Tian, B. Ren, J.F. Li, Z.L. Yang, Chem. Commun. 34 (2007) 3514–3534. L. Shi, A. Wang, T. Zhang, B. Zhang, D. Su, H. Li, Y. Song, J. Phys. Chem. C 117 (2013) 12526–12536. H.K. Chiu, I.C. Chiang, D.H. Chen, J. Nanopart. Res.11 (2009) 1137–1144. J.F. Sanchez-Ramirez, U. Pal, Superficies Vac.13 (2001) 114−116. K. Kim, K.L. Kim, K.S. Shin, J. Phys. Chem. C 115 (2011) 14844–14851. J.H. Shim, J. Kim, C. Lee, Y. Lee, Chem. Mater. 23 (2011) 4694–4700. B. Xia, F. He, L. Li, Langmuir 29 (2013) 4901−4907. A. Kirkland., S. Haigh, Nanocharacterisation, second ed., Royal Society of Chemistry, USA, 2014. K. Yoosaf, B.I. Ipe, C.H. Suresh, J. Phys. Chem. C 111 (2007) 12839–12847. F.A. Adjé, Y.F. Lozano, C.L. Gernevé, P.R. Lozano, E. Meudec, A.A. Adima, E.M. Gaydou, Ind. Crops Prod. 37 (2012) 303−310. S.S. Azab, M. Abdel-Daim, O.A. Eldahshan, Med. Chem. Res. 22 (2013) 4269−4277. G. Shabir, F. Anwar, B. Sultana, Z.M. Khalid, M. Afzal, Q.M. Khan, M. Ashrafuzzaman, Molecules 16 (2011) 7302−7319. W.M. Chai, Y. Shi, H.L. Feng, L. Qiu, H.C. Zhou, Z.W. Deng, C.L. Yan, Q.X. Chen, J. Agric. Food Chem. 60 (2012) 5013–5022. A.M. El-Sayed, S.M. Ezzat, M.M. Salama, A.A. Sleem, Phcog. J. 3 (2011) 49–56. J.F. Moran, R.V. Klucas, R.J. Grayer, J. Abian, M. Becana, Free Radic. Biol. Med. 22 (1997) 861–870. A.K. Mittal, S. Kumar, U.C. Banerjee, J. Colloid Interf. Sci. 431 (2014)194–199. M.N. Nadagouda, R.S. Varma, Green Chem. 10 (2008) 859–862. W. Wang, Q. Chen, C. Jiang, D. Yang, X. Liu, S. Xu, Colloids Surf. A 301 (2007) 73–79. M.M. Kumari, S.A. Aromal, D. Philip, Spectrochim. Acta A 103 (2013) 130–133. N. Basavegowda, K. Mishra, Y.R. Lee, New J. Chem. 39 (2015) 972–977.

Ac ce p

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

12 Page 12 of 24

an

us

cr

ip t

R. Narayanan, M.A. El-Sayed, J. Phys. Chem. B 109 (2005) 12663–12676. A. Leelavathi, T.U.B. Rao, T. Pradeep, Nanoscale Res. Lett. 6 (2011) 123. A. Murugadoss, A. Chattopadhyay, J. Phys. Chem. C 112 (2008) 11265–11271. B. Narayanan, N. Sakthivel, Bioresour. Technol. 102 (2011) 10737–10740. K. Kamata, Y. Lu, Y.N. Xia, J. Am. Chem. Soc. 125 (2003) 2384–2385. X. Peng, Q. Pan, G.L. Rempel, Chem. Soc. Rev. 37 (2008) 1619−1628. S. Tokonami, N. Morita, K. Takasaki, N. Toshima, J. Phys. Chem. C 114 (2010) 10336−10341. M.R. Regan, I.A. Banerjee, Scripta Mater. 54 (2006) 909–914. N.H. Sarker, S.N. Barnaby, A.P. Dowdell, N. Nakatsuka, I.A. Banerjee, Soft Matter 11 (2013) 403–413. V. Reddy, R.S. Torati, S. Oh, C. Kim, Ind. Eng. Chem. Res. 52 (2013) 556−564. H. Jia, X. Gao, Z. Chen, G. Liu, X. Zhang, H. Yan, H. Zhou, L. Zheng, CrystEngComm 14 (2012) 7600–7606. A. Gangula, R. Podila, M. Ramakrishna, L. Karanam, C. Janardhana, A.M. Rao, Langmuir 27 (2011) 15268–15274. Z. Gao, R. Su, R. Huang, W. Qi, Z. He, Nanoscale Res. Lett. 9 (2014) 404. S.K. Srivastava, R. Yamada, C. Ogino, A. Kondo, Nanoscale Res. Lett. 8 (2013) 70. H. Li, L. Han, J. Cooper-White, Green Chem. 14 (2012) 586–591.

te

d

M

Scheme 1 Tentative mechanism of biofabrication (bioreduction of Au3+:Pd2+) of AuPd-NPs with simultaneous oxidation of mixture of bio-organic compounds present in D. regia extract. Fig. 1 UV-Visible spectra of HAuCl4.3H2O, PdCl2, pure Au-NPs, pure Pd-NPs, physical mixture of monometallic NPs and bimetallic AuPd-NPs at 3, 6 and 12 h of reaction time. Fig. 2 XRD spectra of pure Au-NPs, pure Pd-NPs and bimetallic AuPd-NPs (inset represented dominating (111) diffraction peak of Au-NPs, AuPd-NPs, and Pd-NPs). Fig. 3 Biofabricated bimetallic AuPd-NPs (a-b) TEM micrograph (c) size distribution histogram (inset represented SAED pattern). Fig. 4 EDX spectrum of bimetallic AuPd-NPs. Fig. 5 DLS analysis of AuPd-NPs (a) hydrodynamic size distribution (b) ζ potential distribution of colloidal AuPd-NPs. Fig. 6 FTIR spectra of (a) leaf extract before bioreduction (b) after bioreduction (c) AuPdNPs. Fig. 7 UV-Visible absorption spectra for the reduction of (a) 3-NA by NaBH4 using AuPdNPs as catalyst (b) linear plot of ln (3NAt/3-NA0) versus time t for reduction of 3-NA. Fig. 8 Arrhenius plot for the reduction of 3-NA over AuPd-NPs catalyst. Fig. 9 Scheme for catalytic reduction of 3-NA. Fig. 10 Recycled AuPd-NPs (a) XRD pattern (b) TEM micrograph.

Ac ce p

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

Table 1 Elemental composition of AuPd-NPs (%). Element Weight (%) C 17.15 O 2.79 Cl 0.44 Pd 15.32 Au 64.30 Total 100

43 13 Page 13 of 24

Table 3 kapp for reduction of 3-NA using different concentration of AuPd-NPs as catalyst at RT (Reaction condition: 3 mL of 0.5 × 10-3 M 3-NA, 0.12 mL of 1 M NaBH4). AuPd-NPs (mg) kapp × 10-2 min-1 0.5 7.12 ± 0.94 0.75 12.36 ± 0.72 1 18.62 ± 0.63 1.5 27.96 ± 1.01 2 36.39 ± 0.87

an

Table 4 kapp for reduction of 3-NA at different temperature using AuPd-NPs as catalyst (Reaction condition: 3 mL of 0.5 × 10-3 M 3-NA, 0.12 mL of 1 M NaBH4, 1 mg of NPs). -2 -1 T (°C) kapp × 10 min 10 6.3 ± 0.47 20 10.6 ± 0.58 30 18.67 ± 0.55 40 25.56 ± 1.02 50 35.67 ± 1.2

12 13 14 15

te

Table 5 K of each cycle of catalytic reduction of 3-NA (Reaction condition: 30 mL of 0.5 × 10-3 M 3-NA, 1.2 mL of 1 M NaBH4, initial mass of AuPd-NPs catalyst 10 mg). kapp (min-1 ) of catalytic Total mass (m) of K (kapp /m) (min-1g-1) Normalized reduction during each recycled AuPd-NPs used (%) data cycle during each cycle (mg) 18.57 × 10-2 ± 0.27 10 18.57 100 17.19 × 10-2 ± 0.12 9.6 17.90 96.44 16.41 × 10-2 ± 0.12 9.2 17.83 96.05 15.63 × 10-2 ± 0.28 8.9 17.56 94.57 -2 14.41 × 10 ± 0.13 8.3 17.36 93.49

Ac ce p

9 10 11

d

M

6 7 8

us

cr

3 4 5

Table 2 Quantification of TPA, TF and TP contents on the basis of standard curves of gallic acid, quercetin and bovine serum albumin respectively (Fig. S1. Supplementary information). After bioreduction of Quantification of different bioBefore bioreduction of HAuCl4.3H2O: PdCl2 organics of D. regia leaf extract HAuCl4.3H2O: PdCl2 TPA g of GAE/(100 g fw) 1.28 ± 0.07 0.62 ± 0.05 TF g of QE/(100 g fw) 0.83 ± 0.05 0.38 ± 0.03 TP g of BSAE/(100 g fw) 0.12 ± 0.02 0.09 ± 0.02

ip t

1 2

Table 6 Recent studies on reduction of different nitro-organic pollutants using NPs as catalyst. Nanoparticles NitroTemperature Size Time kapp × References composition organic (nm) (min) 10-2 pollutants (min-1) D. regia 3-NA 301 K 4-30 5 18.62 Present mediated study AuPd-NPs 2-NP RT 3-110 24 [1] Dextran mediated AuPd-NPs 14 Page 14 of 24

2-NP

RT

3.8> 37.7-8.1 [21] 20 20-50 40 and30 and 20-80

4-NA

RT

7-10

4-NP

RT

20-30 and 10-30

4-NA

RT

9

4-NA

RT

4-NP

RT

4-NP

298 K

1 2 3 4 5

25

15.2

[50]

6.5

53.04

[51]

d

12-31 8.6

36.1

[52]

RT

50

10

1.24

[53]

4-NP

288 K

2.0

12

21.65

[54]

4-NP

301 K

4-38

9

11.4

[12]

2-NP and 2NA

301 K

2-4

10 and 14

11.7 and 10.08

[13]

an

[49]

M

24.3

27

te

4-NP

60

[48]

cr

8.28 and 2.44

[47]

ip t

-

us

40

4.5

Ac ce p

Ascorbic acid mediated AuPd-NPs, Au-NPs and Pd-NPs Hydrazine hydrate mediated AuPd-NPs Gallic acidamide mediated AuPd-NPs and Pd-NPs Sapindus mukorossi mediated AuNPs Ethoxylated sterols mediated AuNPs Breynia rhamnoides mediated AuNPs Konjac glucomannan mediated AuNPs Escherichia coli mediated Au-NPs Sodium borohydride mediated PdNPs Prunus domestica mediated AuNPs D. regia mediated PdNPs

Scheme

15 Page 15 of 24

ip t cr

Figure

4 5 6 7 8

Ac ce p

te

d

M

an

us

1 2 3

Fig. 1.

9 10 11 12 13 16 Page 16 of 24

1 2 3

7 8 9 10 11 12

Fig. 2.

te

6

Ac ce p

5

d

M

an

us

cr

ip t

4

13 14 15 16

17 Page 17 of 24

ip t cr us an M d te Ac ce p 1 2

Fig. 3.

18 Page 18 of 24

ip t cr us an

1

Fig. 4.

M

2 3

7 8 9 10 11 12

te

6

Ac ce p

5

d

4

13 14

19 Page 19 of 24

ip t cr us an M 3 4 5 6

te

d 2

Ac ce p

1

Fig. 5.

7 8 9

20 Page 20 of 24

ip t cr us an M d te 2

Ac ce p

1

Fig. 6.

3

21 Page 21 of 24

ip t cr us an M te

d 2

Ac ce p

1

Fig. 7.

3

22 Page 22 of 24

1

Fig. 8.

2 3

ip t

4 5

cr

6

us

7 8

an

9

12 13 14 15 16

Ac ce p

11

te

d

M

10

Fig. 9.

17 18 19 20

23 Page 23 of 24

1 2 3

ip t

4 5

cr

6

us

7 8

Ac ce p

te

d

M

an

9

10 11

Fig. 10.

12 13 14

24 Page 24 of 24