Iron-nickel bimetallic nanoparticles: Surfactant assisted synthesis and their catalytic activities

Journal of Molecular Liquids 282 (2019) 448–455

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Iron-nickel bimetallic nanoparticles: Surfactant assisted synthesis and their catalytic activities Sarah Saad Alruqi, Shaeel Ahmad AL-Thabaiti, Zaheer Khan ⁎ Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia

a r t i c l e

i n f o

Article history: Received 25 October 2018 Received in revised form 4 February 2019 Accepted 4 March 2019 Available online 11 March 2019 Keywords: Surfactant Bimetallic CTAB SDBS Morphology

a b s t r a c t Iron-Nickel core-shell bimetallic nanoparticles was synthesized by seed-growth co-reduction of their corresponding metal precursors (Fe(NO3)3 and Ni(NO3)2) for the first time by using chemical reduction method in absence and presence of shape-controlling cetyltrimethylammonuim bromide (CTAB) and sodium dodecylbenzenesulfonate (SDBS). UV–visible spectra revealed that the formation of core-shell NPs strongly depends on the reduction potential of Fe3+ and Ni2+ ions in an aqueous solution. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and X-ray diffraction (XRD) were used to determine the surface morphology and elemental composition of the NPs. The Fe-Ni NPs was used as a catalyst to the hydrogen generation from hydrolysis of sodium borohydride under various experimental conditions. The various activation parameters such as Ea = 75.1 kJ mol−1, ΔH# = 69.9 kJ mol−1 and ΔS# = −104.5 JK−1 mol−1 were calculated using Arrhenius and Eyring equations and discussed. Fe/-Ni was also used as an effective adsorbent for the removal of golden yellow MR from dying wastewater. Langmuir adsorption parameters were evaluated by using linear-form of the isotherm. The maximum adsorption capacity (Q0max = 181.1 mg/g) was calculated for Fe25-Ni75. © 2019 Elsevier B.V. All rights reserved.

1. Introduction The bimetallic nanoparticle synthesis with controlled shape, size, density, morphology and composition is of immense interest due to their distinctive physical and chemical properties as compared to their bulk counterparts [1–4]. These nanomaterials proved wide range of potential applications in different fields of science and technology like biomedicines, photocatalysis, magnetic recoding, and optoelectronics [5,6]. Metal nanoparticles gained lot of interest because of their high chemical stability, optical properties, excellent conductivity and enhanced antibacterial properties [7]. The nickel nanoparticles gained much attention due to their potential applications as nanocatalyst and for their technologically important conducting and magnetic properties [8]. The Ni(OH) 2 nanoparticles have been used in rechargeable battery systems and their optimum performance are greatly influenced by the structural and compositional characterizes of the synthesized nanoparticles [9]. In comparison to monometallic nanoparticles, bimetallic nanoparticles have gained much interest due to their enhanced properties biological and catalytic properties [10,11] despite of the same composition. The development of novel synthetic procedures for bimetallic nanoparticles synthesis and their enhanced application has received great attention in recent times [12,13]. ⁎ Corresponding author. E-mail address: [email protected] (Z. Khan).

https://doi.org/10.1016/j.molliq.2019.03.021 0167-7322/© 2019 Elsevier B.V. All rights reserved.

Biosynthesis of NPs employing natural recourses such as plants, carbohydrates, proteins and seeds can potentially eliminate the necessity of extra capping agent by making the NPs more biocompatible [14,15]. Hexagonal, spherical, triangular nanoplates, nanorods and amorphous FeNPs have been prepared by various investigators using extracts of plants and their parts [16–18].Fe-Pd bi-metallic NPs was prepared in presence of starch and suggested that starched NPs displayed better degradation activity than those prepared without a stabilizer [19]. The Fe-Ni bi-metallic NPs was prepared by metal salt precursor reduction with NaBH4 and used to the degradation of orange G [20]. Dual properties of FeNPs such as sorbent and reductant for the removal of nickel was reported and suggested that Ni2+ ions first formed a surface complex and then reduced on the FeNPs surface [21,22]. Generally, lithium, sodium and potassium hydrides have been used for the generation of hydrogen for the fuel cell. Out of these, sodium borohydride (NaBH4) easily generates hydrogen at room temperature even without catalyst. The catalytic activity of transition metals and their nanoparticles mainly allied due to their d orbital properties. Various mono-, and bi-metallic metal catalysts such as Ni [23], Fe/Ni [24], Fe composites [25], Ni/Fe and Pd/Fe [26], Ni/Fe [27], Fe/Ni [28], Fe/Ni [29] and Pd [30] were utilized as an adsorbent and/or catalyst to the removal of toxic dyes and aromatic compounds from dying wastewater as well as for the generation of hydrogen during the hydrolysis of NaBH4 in alkaline solution. It has been established that the Fe-based bimetallic nano-materials has many advantages over the mono-metallic NPs in

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wastewater treatment technology because Fe acts as a reducing agent and second metal plays the role of catalyst [31]. The sequestration of dyes from industrial effluent had been made by biological, chemical, radiation, and photo-chemical techniques [32–34]. Golden yellow MR is a water soluble anionic azo type, human carcinogen, which yielding a colloidal solution and was used in various textile industries [35]. Herein, we report the synthesis of Fe-Ni core-shell NPs of different compositions using biomass of Pithecellobium dulce in presence of CTAB and SDBS. The present work also explores the utility of Fe-Ni to the hydrogen generation from the alkaline solution of sodium borohydride. The activation parameters (activation energy, activation enthalpy and activation entropy) for catalytic hydrolysis were also determined by using the Arrhenius and Eyring equations and discussed. The equilibrium isotherm, thermodynamic and process parameters affecting the adsorption of Golden yellow MR dye on Fe-Ni were also evaluated for the first time using Langmuir adsorption isotherm. 2. Experimental section 2.1. Chemicals Metal salt precursors (NiNO3, and Fe(NO3)3, BDH, 99%), sodium borohydride (BDH, 99%), cetyltrimethylammonium bromide (C19H42BrN, Sigma-Aldrich, 98%), sodium dodecylbenzenesulfonate (C18H29NaO3S) were used without further purification. Other chemical were of reagent grade. Deionized water was used as a solvent in the preparation of all reagent solutions. 2.2. Synthesis of Fe-Ni NPs by seedless method The legumes of Pithecellobium dulce were collected in May 2017, chopped into the small slices, removed the seeds and dried for 24 h at room temperature under shade. In a typical experiment, 10 g of mesocarp washed and finally ground Pithecellobium dulce powder in a reaction beaker with 100 cm3 deionized water and then heating the mixture of 20 min at 60 °C. The extract obtained was used as a reducing agent for the synthesis of Fe-Ni. In a typical experiment, 5.0 ml extract was added in the different reaction vessels containing Fe(NO3)3 (2.0 ml to 10.0 of 0.01 M/L), Ni(NO3)2 (2.0 ml to 10.0 ml of 0.01 M/L), CTAB (2.0 ml to 12.0 ml of 0.01 M/L), and required amount of water for dilution (total volume = 50 ml). As the reaction time increased, the formation of perfect transparent dark brown color was observed, indicating the reduction of Fe3+ and Ni2+ ions by the active phenolic and/or sugars constituents of the extract. For surfactants capped Fe-Ni NPs, the required concentrations of CTAB and SDBS were added separately into the reaction mixture (Fe3+ + Ni2+ + extract). The presence of Fe3+ ions were not detected in the reaction mixture by UV–visible spectroscopy, which suggests the complete reduction of Fe3+ into Fe0 by active chemical constituents of extract. The prefect transparent bimetallic NPs with different molar ratios of precursor metal salts (Fe3+ and Ni2+) could be prepared without any precipitation. For solid preparation, the particles were ageing in solution, filtered through a Whatman filter paper and washed extensively with deionized and CO2 free double distilled water and finally with acetone. The separated Fe-Ni were vacuum dried at 30 °C for 24 h. The dried powder was stored in an amber glass bottle and used immediately for characterization and batch adsorption experiments.

449

spectra (EDX). X-ray diffraction patterns of the Fe-Ni were also measured using Rigaku X-ray diffractometer operating at 40 kV and 150 mA, and Fison (VG) ESCA 210 spectrometer equipped with an MgKα X-ray source. Samples for TEM examination were prepared by depositing a drop of resulting sol on copper grid coated with carbon film. 2.4. Adsorption of dye Adsorption activity of Fe-Ni was tested by removal of golden yellow MR. In a typical experiment, 20 mg of Fe-Ni and 10 mg/l of dye was kept in a reaction vessel, and placed on water bath. The solution was kept in dark to attain the adsorption-desorption equilibrium. The solution was then exposed to sun light. In the second set of experiments, reaction mixture was directly exposed to sun light. The amount of adsorbate uptake at equilibrium (qe, mg/g) is calculated using the following relation. qðeÞ ¼

ðΔC ÞV m

ð1Þ

where ΔC = (C0 - Ce). C0 and Ce are initial and equilibrium concentrations (mg/l) of dye red, respectively. V = volume of dye solution (liter) and m = mass of adsorbent (mg). 2.5. Catalytic activity for hydrogen generation In a typical experiment, a requisite amount of NaBH4 solution was taken in a three-necked reaction vessel and opening was associated to a gas burette. The response was started with the expansion of required measure of thermally equilibrated colloidal solution of Fe-Ni NPs. The rate of hydrogen gas evaluation was estimated by utilizing the wateruprooting strategy. Various kinetic experiments were carried out to establish the role of catalyst, NaBH4 and temperature. Eq. (2) was used to calculate the rate of hydrogen generation. r¼

V tm

ð2Þ

where r, V and m are the hydrogen rate generation (ml·min−1·g−1), generated volume (ml), time (min) and weight of the catalyst (g), respectively. The values of rate were computed form the initial straight slope of the plot of generated volume of hydrogen versus time. The Arrhenius behavior for hydrogen generation from NaBH4 in presence of Fe-Ni catalyst can be represented as follows: r ¼ krxn ¼ A0 exp

  −Ea RT

ð3Þ

where r = reaction rate (ml·min−1·g−1). A0 = pre-exponential factor, Ea = activation energy (kJ mol−1), R = universal gas constant (8.314 J mol−1 K−1), and T = temperature in Kelvin. Eq. (3) can be written as Eq. (4). logr ¼ logA0 −

Ea 2:303RT

ð4Þ

The slope of log r against 1/T therefore equals to −Ea / 2.303 R. 3. Results and discussion 3.1. UV–visible spectra of NPs

2.3. Characterization of NPs Shimadzu UV-260 spectrophotometer was used to record the spectra of as prepared NPs. The morphology and structure of resulting Fe-Ni NPs were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). Elemental analysis of nanoparticles determined from the energy dispersive X-ray

Fig. 1 shows the spectra of PDE extract and as prepared mono-, and bi-metallic Fe-Ni in absence and presence of CTAB under the same experimental conditions. It is well known that an aqueous solution of Fe3+ ions has a weak absorption peak at 325 nm, which disappeared completely in presence of extract and colorless reaction solution became dark yellow to gray with reaction time. As can be seen from

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Fe-Ni NPs [40]. Thus, we may state confidently that the Fe-Ni core-shell bi-metallic NPs are formed during the co-reduction of metal salts precursor. Effect of [Fe3+] and [Ni2+] was also determined on the formation of transparent Fe-Ni sols. Table 1 clearly shows that the metal ions ratio has significant role in the preparation of stable transparent Fe-Ni metal NPs. The equimolar concentrations of metal salt precursor (Fe and Ni) and presence of CTAB (= 0.8 mM/L) as stabilizer were found to be the optimum reaction conditions to the synthesis of prefect transparent dark brown color colloidal solution of Fe-Ni sols. 3.2. Size, morphology and composition of iron‑nickel nanoalloy

Fig. 1. UV–visible spectra of extract, monometallic (Fe and Ni) NPs, and bimetallic (Fe-Ni) NPs under different experimental conditions. Reaction conditions: [Extract] = 5.0 cm3, [Fe3+] = 1.0 × 10−3 mol dm−3, [Ni2+] = 1.0 × 10−3 mol dm−3, [CTAB] = 10.0 × 10−4 mol dm−3.

Fig. 1, the absorption below 300 nm strongly increased, decreased or featureless at longer wavelengths for mono- metallic Fe0 and Ni0 and bimetallic Fe-Ni NPs. Our UV–visible spectra are in accordance to the observations of other researchers for the featureless spectrum of Fe and Ni in the whole visible region. In order to determine the effect of CTAB and SDBS on the morphology of Fe-Ni, various experiments were performed for surfactant concentration (Table 1). The required Ni2+and Fe3+ concentrations (1:1 ratio) were mixed in a reaction vessel containing the CTAB and extract. The reaction mixture became brownish-gray, which might be due to the reduction of Fe3+ and Ni2+ with active constituent of extract in presence of CTAB. As a result, CTAB capped Fe-Ni NPs are formed (Fig. 1, blue and light blue lines). In the third set of experiments, SDBS (from 1.0 mM to 8.0 mM) was used instead of CTAB. The reaction mixture became turbid due to the formation of insoluble complex between SO3− of SDBS and Fe3+ ions (Table 1). Therefore, SDBS cannot be used as a capping agent to the preparation of iron based advanced NPs. The reduction potential of Fe3+ (Fe3+ / Fe0 = −0.04 V) is higher than Ni2+ ions (Ni2+ / Ni0 = −0.25 V) in acidic medium. Therefore, Fe3+ ions were first reduced to Fe0. Consequently, Ni2+ ions adsorbed onto Fe NPs and reduced under potential deposition. It is well known that UV–visible spectra of both mono-metallic NPs (Fe0 and Ni0) are featureless [36–39]. Absence of peak in Fe-Ni spectrum (Fig. 1; red line) indicates the formation of

Table 1 Effects of stabilizer, and reactant concentrations on the stability of Fe-Ni NPs. [CTAB] (mM) 0.0 0.2 0.4 0.6 0.8 1.2 0.0 0.0 0.0 0.8 0.8 0.8 0.8 0.8 0.8

[SDBS] (mM)

[Fe3+] (mM)

0.0 0.0 0.0 0.0 0.0 0.0 2.0 4.0 6.0 0.0 0.0 0.0 0.0 0.0 0.0

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 3.0 6.0 8.0

[Ni2+] (mM) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 3.0 6.0 8.0 1.0 1.0 1.0

Observations

pH

Pale yellow; turbid Gray turbid Gray transparent; unstable Dark gray; unstable Dark gray; stable; no SRP Dark gray; turbid; no SRP Yellow precipitate Yellow precipitate Yellow precipitate Dark gray; stable; no SRP Dark gray; stable; no SRP Pale green-turbid Dark gray; stable; no SRP Dark gray; unstable; no SRP Pale yellow-turbid

5.2 5.9 5.8 5.9 6.0 6.0 4.7 4.7 4.5 4.4 4.4 4.4 5.4 5.3 5.2

The size, morphology, composition of Fe-Ni NPs were investigated by recording FESEM, SEM-elemental mapping, SEM-EDX, TEM, and XRD. The elemental mapping indicated the presence of iron and nickel in the as-prepared bimetallic NPs. The EDX spectrum shows the characteristic peak of Fe and Ni only (Fig. 2), which clearly suggests the formation of Fe-Ni bimetallic nanoparticles. As can be seen in Fig. 2, the mass % of Fe and Ni in the synthesized Fe/Ni are 55.7 and 44.3% (weight %) and 56.63 and 43.07% (atomic %), respectively, indicating the formation of Fe-Ni having ca. 50:50 (1:1) molar ratio. It could be seen from the EDX (Fig. 2) and SEM image (Fig. 3A) that both of the two elements of Fe and Ni were detected on the surface of the as-prepared Fe-Ni. There was no oxide formation to be detected by EDX. Fig. 3B and C shows the TEM, and XRD of as prepared Fe-Ni. Nanosphere with some irregular shaped nanoparticles with average size ca. 90 nm to 600 nm are formed under our experimental conditions (Fig. 3B). Thus, we may state confidently that the Ni2+ would be reduced on the surface of Fe0 through potential deposition. The reduction of Ni2+ ions is shown in the following Eqs.

ð5Þ

ð6Þ

In order to confirm the bimetallic nature of the as-prepared Fe-Ni NPs, XRD spectra of Fe, Ni and Fe-Ni NPs were measured and are summarized in Fig. 3C. For Fe and Ni NPs, three diffraction peaks (2θ = 35.3 0, 45.2 0 , and 65.3 0) and (2θ = 45.1 0, 55.2 0 , and 75.3 0) were observed, respectively. On the other hand, XRD of Fe-Ni shows the three peaks at 2θ = 45.50, 55.30, and 76.3.40. The presence of sharp well-defined bands patterns at 2θ = 45.50 (111), 55.30 (200), and 76.4 (220) corresponding to Fe and Ni in the Fe-Ni NPs are indicative of the formation of bimetallic Fe-Ni NPs. 3.3. Calculation of mole fraction of Fe and Ni in Fe-Ni To insure the complete reduction of Fe3+ and Ni2+ ions into Fe0 and Ni , qualitative microanalysis test were performed. In a typical experiment, NH4Cl and NH4OH were added into an aqueous solution of reaction mixture containing yellow color silver‑nickel sols. No brown precipitate was formed for Fe(OH)3. After this H2S was pass 0

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Element Fe K Ni K Totals

Weight% 55.70 44.30 100.00

451

Atomic% 56.93 43.07

Fig. 2. The FESEM image, Fe and Ni mapping, and EDX of the Fe-Ni NPs.

through the solution. NiS black precipitate was not formed. Thus, we may state confidently that that 100% metal ions were reduced into the corresponding metal. Number of moles of Fe (nFe) and Ni (nNi) = 2.14 × 10−4 and 4.98 × 10−5 M, respectively. The total n(Fe-Ni) is 2.63 × 10−4 M. Therefore, total mass of Fe-Ni, m(Fe-Ni), would de 4.11 × 10−3 g. Molecular weight of Fe-Ni (M) was calculated by using m(Fe-Ni)/n(Fe-Ni) relation and found to be 5.77 g/M. From molecular mass and density, volume of Fe-Ni could be calculated. Volume of Fe ¼ mass of Fe=density of Fe ¼ 1:19  10−2 g=7:87  10−21 g=nm3 ¼ 1:15  1018 nm3 −3

Volume of Ni ¼ 2:92  10

g=8:9  10

−21

g=nm3 ¼ 3:28  10

N¼

17

π ρ D3 NA 6M

ð8Þ

where ρ, M and D are the density, molecular weight, and diameter of as prepared iron-nickel, respectively and NA is the Avogadro number. Substituting values of these parameters in Eq. (4), the N = 1,035,612 are estimated. The [Fe-Ni] was determined with Eq. (9). C¼

NTotal NVNA

ð9Þ

nm3 where V = reaction volume, i.e., 0.05 M/L. The NTotal (Fe-Ni) = 1.58 × 10 20 atom, N = 1,035,612, V = 0.05 M/L, and NA was substituted in Eq. (9). The molar concentration of Fe-Ni is found to be 5.09 × 10−9 M/L in an aqueous solution.

Fe−Ni volume ¼ 1:78  1018 nm3 Fe−Ni density ¼ 2:30  10−21 g=nm3 Mole fractions of nFe (XFe) and nNi (XNi) were calculated with Eq. (7). number of moles of one component mole fractionðxÞ ¼ Total number of moles in solution

The Fe-Ni average number, N, was estimated with Eq. (8) [41].

ð7Þ

The XFe = 0.81 and XNi = 0.18 were calculated (XFe + XNi = 0.81 + 0.18 = 0.99).

3.4. Dye adsorption In order to determine the adsorption activity of Fe-Ni adsorbent, a series of adsorption experiments were carried out by varying [adsorbent] at a fixed [dye], and temperature. Fig. 4 shows the adsorption potentials of Fe-Ni with dye. In presence of Fe-Ni 70% adsorption of Golden yellow MR was observed in 2 h of reaction time (Scheme 1).

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A

B Fig. 4. Adsorption of golden yellow MR onto the surface of Fe-Ni at room temperature. Reaction conditions: [catalyst] = 0.5 g/l, [dye] = 10 mg/l, and pH = 6.7.

Hanes-Woolf linearization, the linear from of Langmuir model, was used for the calculation of Q0max and KL (Eq. (11)). Ce Ce 1 ¼ þ qe Q 0max K L Q 0max

ð11Þ

where Q0max = maximum adsorption capacity (mg/g) of an adsorbent, KL = Langmuir constant (L/mg), Ce = concentration of adsorbent at equilibrium (mg/l). Values of qe, C0, Ce for the adsorption of congo red onto the surface of Fe-Ni are calculated for different set of experiments. The Langmuir constant, Q0max and KL were estimated from the slope and intercept of the plot of Ce/qe versus Ce (Fig. 5). These values are given in Table 2 along with correlation coefficient, R2. Eq. (12) was also used for the calculation of separation factor, RL, dimensionless equilibrium parameter.

C

RL ¼

1 ð1 þ K L C 0 Þ

ð12Þ

The Q0max for golden yellow dye is = 181.1 mg/g for Fe25/Ni75. Table 2 clearly shows that the adsorption capacity of Fe-Ni nanoparticles is increase with the % composition of Ni metal. The KL = 0.011 L/mg and RL = 0.930 were estimated, which indicates that the adsorption nature was favorable. The value of RL represents the nature of the isotherm to be linear (RL = 1), irreversible (RL = 0), unfavorable (RL N 1), and favorable (0 b RL b 1). The correlation coefficient, R2, for the Langmuir isotherm model is 0.991, which revealed that the adsorption data fitted well to Langmuir equation. 3.5. Catalytic activity of Fe-Ni NaBH4 was used as a source of hydrogen in various applications. Its aqueous solution was unstable and liberate hydrogen [42]. The aqueous

Fig. 3. (A) SEM, (B) TEM, and (C) XRD of Fe-Ni NPs.

Langmuir adsorption isotherm was used to calculate the maximum adsorption capacity of the Fe-Ni. Langmuir adsorption isotherm is for monolayer adsorption. Eq. (10) gives the Langmuir adsorption isotherm.

qðeÞ

Q 0 KLCe ¼ max ð1 þ K L C e Þ

ð10Þ

Cl NO 2

N

N

N

CH2CH2CN CH2CH2CN

Scheme 1. Structure of Golden yellow MR azo dye.

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453

Fig. 6. Effects of catalysts on the hydrolysis of NaBH4. Reaction conditions: [catalyst] = 50 mg, [NaBH4] = 5.0 × 10−3 mol dm−3 and [NaOH] = 5.0 × 10−4 mol dm−3.

Fig. 5. Langmuir adsorption isotherm plot for the adsorption of Fe-Ni.

NaBH4 solution also contains certain amount of NaOH due to the hydrolysis of NaBH4 (Eq. (13)). NaBH 4ðaqÞ þ 2H 2 OðlÞ →NaBO2ðaqÞ þ 4H 2ðgÞ

ð13Þ

Visual observations suggested that the evolution of hydrogen gas in the form of bubbles from the water solution of NaBH4. The use of metal NPs as a catalyst with large surface area provides a potential route to increase the rate of hydrogen production [43]. NaBH4 hydrolysis is irreversible, heterogeneous, and exothermic (ΔH = − 210 kJ mol−1). Fig. 6 shows the amount of H2 generated as a function of time with self-hydrolysis of NaBH4 and in presence of monometallic (Fe and Ni NPs) and bimetallic Fe-Ni NPs. The effect of core-shell Fe-Ni on hydrogen generation was significantly higher than that of mono metallic Fe and Ni NPs. Fig. 6 (black line) also reveals that the hydrogen generation from alkaline NaBH4 solution was neglected. In order to determine the activation energy, the effect of temperature on hydrogen generation rates were investigated in the range of 25 °C to 45 °C at fixed NaBH4, NaOH and Fe-Ni catalyst. It was observed that the NaBH4 hydrolysis followed a zero-order reaction kinetics [44]. From the Arrhenius plot (Fig. 7A), the value of activation energy was calculated and found to be 75.1 kJ mol−1. The Eyring equation (Eq. (14)) was used for the calculation of activation enthalpy (ΔH#) and activation entropy (ΔS#).

ln

k ΔH# kB ΔS# ¼− þ ln þ T R h RT

ð14Þ

where k = rate constant, kB = Boltzmann constant, and h = Planck's constant. The values of ΔH# (69.9 = kJ mol−1) and ΔS# (= −104.5 J/K/mol) were calculated from the slope and intercept of the Eyring plot (ln (r/T) against 1/T (Fig. 7B), respectively. The negative value of ΔS# indicates

Table 2 Isotherm constants and hydrogen evaluation parameters for Fe-Ni NPs. Parameters

Fe25-Ni75

Fe25-Ni25

Q0max (mg/g) KL (L/mg) RL R2 Adsorption (%) H2 rate Ea (kJ mol−1)

181.1 0.011 0.93 0.991 70.0 160 ml min−1(g catalyst)−1 75.1

160.2 0.014 0.95 0.990 50 120 ml min−1(g catalyst)−1 85.2

Fig. 7. (A) Arrhenius and (B) Eyring plots for the evaluation of activation energy, enthalpy of activation and entropy for the hydrolysis of NaBH4 using Fe-Ni.

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the spontaneity of the NaBH4 hydrolysis. Various investigators were used different catalyst such as Co, Ni, Raney Ni, Ag-Ni, Ru, Ni-Ru and Ni-Co-B to the generation of hydrogen from hydrolysis of NaBH4 and evaluated their activation parameters. Our value of activation energy was found to be in good agreement with the values of activation energy reported in the literature (75 kJ/mol, 71 kJ/mol, 63 kJ/mol, 57.62 kJ/mol, 47 kJ mol−1, 52.7 kJ/mol, 62 kJ/mol, respectively, for Co [45], Ni [46], Raney Ni [47], Ag-Ni, Ni-Ru [47] and Ni-Co-B [48]. Thus, we may state confidently that the as-prepared Fe-Ni is an excellent catalyst for the generation of hydrogen from alkaline hydrolysis of NaBH4. 4. Conclusions In this research work, a seed-growth method was used for the synthesis of Fe-Ni bimetallic NPs in presence of anionic and cationic surfactants. Elemental mapping and EDX results indicated that the asprepared NPs have equimolar ratio of Fe and Ni in Fe-Ni nanocomposites. Catalytic activity of bimetallic Fe-Ni was found to be higher in comparison to the corresponding monometallic NPs of Fe and Ni. The activation energy for hydrogen generation of the alkaline NaBH4 solution catalyzed by Fe-Ni was calculated to be 75.1 kJ mol−1. The Fe-Ni was also used as an adsorbent for the removal of golden yellow MR azo dye from the dying water. The heterogeneous morphology of Fe-Ni bimetallic NPs were responsible to the higher Langmuir adsorption capacity (Q 0 max = 181.1 mg/g) for the adsorption of golden yellow MR onto Fe-Ni. The resulting Fe-Ni would be used as an effective adsorbent for the removal of toxic non-biodegradable water pollutants. Acknowledgment I would like to thank King Abdulaziz City for Science and Technology for its financial support to the grant number (1-17-01-009-0052). (Also, thanks to the King Fahad Medical Research Center (KFMRC) for providing me appropriate labs for doing the practical work). References [1] A. Zaleska-Medynska, M. Marchelek, M. Diak, E. Grabowska, Noble metal-based bimetallic nanoparticles: the effect of the structure on the optical, catalytic and photocatalytic properties, Ads Colloid Interface Sci. 229 (2016) 80–107. [2] H. Zhang, M. Haba, M. Okumura, T. Akita, S. Hashimoto, N. Toshima, Novel formation of Ag/Au bimetallic nanoparticles by physical mixture of monometallic nanoparticles in dispersions and their application to catalysts for aerobic glucose oxidation, Langmuir 29 (2013) 10330–10339. [3] S.A. Alzahrani, S.A. Al-Thabaiti, W.S. Al-Arjan, M.A. Malik, Z. Khan, Preparation of ultra long a-MnO2 and Ag@MnO2 nanoparticles by seedless approach and their photocatalytic performance, J. Molecular Structure 1137 (2017) 495–505. [4] S.C. Lin, S.Y. Chen, Y.T. Chen, S.Y. Cheng, Electrochemical fabrication and magnetic properties of highly ordered silver-nickel core-shell nanowires, J. Alloys Compd. 449 (2008) 232–236. [5] A. Mahal, L. Tandon, P. Khullar, G.K. Ahluwalia, M.S. Bakshi, pH responsive bioactive lead sulfide nanomaterials: protein induced morphology control, bioapplicability, and bioextraction of nanomaterials, ACS Sustain. Chem. Eng. 5 (2017) 119–132. [6] S. Senapati, S.K. Srivastava, S.B. Singh, H.N. Mishra, Magnetic Ni/Ag core-shell nanostructure from prickly Ni nanowire precursor and its catalytic and antibacterial activity, J. Mater. Chem. 22 (2012) 6899–6906. [7] A. Panacek, L. Kvitek, R. Prucek, M. Kolar, R. Vecerova, N. Pizurova, V.K. Sharma, T. Nevecna, R.J. Zboril, Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity, J. Phy. Chem. B 110 (2006) 16248–16253. [8] H. Wang, X. Kou, J. Zhang, J. Li, Large scale synthesis and characterization of Ni nanoparticles by solution reduction method, Bull. Mater. Sci. 31 (2008) 97–100. [9] X.H. Liu, W. Liu, X.K. Lv, F. Yang, X. Wei, Z.D. Zhang, D.J. Sellmyer, Magnetic properties of nickel hydroxide nanoparticles, J. Appl. Phys. 107 (2010), 083919. [10] C.-C. Lee, Y.-Y. Cheng, H.Y. Chang, D.-H. Chen, Synthesis and electromagnetic wave absorption property of Ni–Ag alloy nanoparticles, J. Alloys Compd. 480 (2009) 674–680. [11] Q. Xiao, Z. Yao, J. Liu, R. Hai, H.Y. Oderji, H. Ding, Synthesis and characterization of Ag-Ni bimetallic nanoparticles by laser-induced plasma, Thin Solid Films 519 (2011) 7116–7119. [12] M. Tsuji, N. Miyamae, S. Lim, K. Kimura, X. Zhang, S. Hikino, M. Nishio, Crystal structures and growth mechanisms of Au@Ag Core-shell nanoparticles prepared by the microwave-polyol method, Cryst. Growth Des. (6) (2006) 1801–1807.

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