Catalytic reduction of nitrophenols by a novel assembled nanocatalyst based on zerovalent copper-nanopolyaniline-nanozirconium silicate

Journal Pre-proof Catalytic reduction of nitrophenols by a novel assembled nanocatalyst based on zerovalent copper-nanopolyanilinenanozirconium silicate

Mohamed E. Mahmoud, Mohamed F. Amira, Magda E. Abouelanwar, Seleim M. Seleim PII:

S0167-7322(19)35114-1

DOI:

https://doi.org/10.1016/j.molliq.2019.112192

Reference:

MOLLIQ 112192

To appear in:

Journal of Molecular Liquids

Received date:

11 September 2019

Revised date:

28 October 2019

Accepted date:

21 November 2019

Please cite this article as: M.E. Mahmoud, M.F. Amira, M.E. Abouelanwar, et al., Catalytic reduction of nitrophenols by a novel assembled nanocatalyst based on zerovalent coppernanopolyaniline-nanozirconium silicate, Journal of Molecular Liquids(2019), https://doi.org/10.1016/j.molliq.2019.112192

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© 2019 Published by Elsevier.

Journal Pre-proof Catalytic reduction of nitrophenols by a novel assembled nanocatalyst based on

zerovalent copper-nanopolyaniline-nanozirconium silicate Mohamed E. Mahmoud*, Mohamed F. Amira, Magda E. Abouelanwar and Seleim M. Seleim Faculty of Sciences, Chemistry Department, Alexandria University, P.O. Box 426, Ibrahimia 21321, Alexandria, Egypt. E.Mail:[email protected], Telephone number: 0020-1140933009, Fax number: 00203-3911794

Abstract A novel nanocatalyst (Cu0-NPANI-ZrSiO4) was fabricated via solvent free

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microwave synthesis for surface immobilization of zerovalent copper nanoparticles

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(Cu0-NPs) on modified nanopolyaniline (NPANI) with nanozirconium silicate. The assembled nanocatalyst was characterized by different techniques to confirm the

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structure, thermal stability, surface morophology and nanoscale size. Cu 0-NPANI-

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ZrSiO4 nanocatalyst was then subjected to extensive investigation and evaluation

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of its potential capability for reduction of a series of nitrophenol (NPhs) derivatives. The Langmuir-Hinshelwood mechanism was applied on the catalytic

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reduction of 2-nitrophenol (2NP), 3-nitrophenol (3NP) as well as 4-nitrophenol (4NP) and the reaction rate constants (k) were calculated through the pseudo-first-

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order kinetics due to the presence of excessive NaBH4. The results revealed a pseudo-first-rate type of reaction with high constant (k). The reduction of NPhs by

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NaBH4 as a reducing agent over Cu0-NPANI-ZrSiO4 was explored in different pH values (2-10) of NPhs and the results confirmed the strong dependency of the reduction process on the pH. In low pH, high reduction efficiency was established and confirmed from the pseudo-first-rate constant k (min-1) for 4NP, 3NP and 2NP as 0.811, 0.249 and 0.584, respectively at pH 2 and these values were then finally decreased to 0.112, 0.1 and 0.116 at pH 10, respectively. Rate constant (k) was in a good correlation with concentration of [H 3O+] ion. An extrathermodynamic study for reaction rate (k) through isokinetic relationship was mathematically expressed. The calculated thermodynamic parameters led to an extrathermodynamic analysis 1

Journal Pre-proof as a type of compensation effect to give a good linearity plot with the slope to

represent the isokinetic temperature, β that was identified as 298.82 at 298K. Keywords:

Catalytic

reduction;

Nitrophenols;

Zerovalent

Copper;

Extrathermodynamic; Langmuir-Hinshelwood mechanism. 1. Introduction Nitroaromatic compounds are classified as harmful organic compounds and the most important multilateral pioneer in artificial organic chemistry and

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intermediates in the dyes industry, agricultural chemicals and pharmaceuticals [1,

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2]. One of most common nitroaromatics are nitrophenols (NPhs) which are

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classified as extremely toxic to human beings and to all aquatic life [3]. It has been reported that exposure of NPhs may cause damages to central nervous system,

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blood system, skin sensitization, immunotoxicity,

mutagenicity and primary

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organs (lung, kidney, eye), etc [4]. In particular, NPhs have been listed as ‘‘priority pollutants’’ by the United State Environmental Protection Agency (USEPA)

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because of their higher solubility and stability in water as well as their easy

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penetration to underground water through soil [5, 6]. A very important deal was the formation of highly efficient catalyst utilized

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in the reduction of NPhs to be a source of amines [7]. In order to lower the kinetic barrier between electron donor and electron acceptor found in redox or decomposition reactions of pollutants a noble metal nanoparticles (NPs) such as Cu, Au, Pd, Pt, Ir, and Ag-based catalysts can be used [8-10] as well as other metallic species or composites [11-15]. Among the noble metal catalysts, copper nanoparticles (Cu0-NPs) hold a unique place over other metal nanoparticles like Ag, Au and Pt and their diversified application in the laboratory as well as in industry level due to its low cost and the outstanding electrical, catalytic, thermal conduction, mechanical, and optical properties [16]. Cu0-NPs are offered in nanometer scale, sharply different from bulk form and in mild reaction conditions 2

Journal Pre-proof give better yields and in contrast to other catalysts it has short reaction time [17,

18]. Several methods are generally applied to produce Cu0-NPs such as thermal decomposition, solvothermal method and reduction of metal salts, microemulsion techniques, microwave heating, laser ablation, sonochemical reduction and radiation [19]. High catalytic effect and simple preparation methods for metal nanocatalysts supported by polymer were the reason in high interest of these compounds [20,

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21]. From all conducting polymers, polyaniline (PANI) is a suitable host matrix for the dispersion of metal NPs to obtain heterogeneous catalysts [22]. Also,

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conductivity of the polymers can be increased through the action of metal NPs

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incorporated into PANI through various approaches and PANI is capable of

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preventing metal NPs from agglomeration [23, 24].

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Physicochemical properties of SiO2–ZrO2 oxide have attracted much spots due to incorporated thermal and chemical inertness stability, mechanical strength

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[25, 26]. Zircon (ZrSiO4) can be prepared through electric/thermal fusion of ZrO2 and SiO2. As a result of its high temperature resistance, ZrSiO4 is utilized as a filler

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material in intumescent coating formulation, an efficient fire retarding, heat

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shielding material and applicability in heterogeneous catalysis. Moreover, ZrSiO4 and their other composites were characterized to exhibit different insolubility characters in aqueous and non-aqueous solutions [27-31]. Therefore, ZrSiO4 may be regarded as excellent sorbent for removal of different pollutants from real water. Based on the above mentioned characteristic of PANI, ZrSiO4 and Cu0-NPs, we herein present an efficient and simple method to synthesize a new nanocatalyst based on using a solvent free microwave process to fabricate Cu0-NPANI-ZrSiO4 nanocatalyst for application in reduction of some selected nitrophenol (NPhs) derivatives. This work aims to explore the advantages of synthetic approach, characterization and catalytic behavior of Cu0-NPANI-ZrSiO4 nanocatalyst. 3

Journal Pre-proof

2. Experimental 2.1. Chemicals and solutions Chemical used were acquired as listed in Table 1. 2.2. Instruments Instruments used in the characterization of NPANI-ZrSiO4 and Cuo-NPANIZrSiO4 are listed in Table 2.

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2.3. Synthesis of Cu0-NPANI-ZrSiO4 nanocatalyst

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2.3.1. Synthesis of copper nanoparticles (Cu0-NPs)

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Synthesis of Cu0 nanoparticles was accomplished by the chemical reduction method as previously described [32]. Equal volumes of 0.04 mol L-1 CuSO4.5H2O

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and 0.13 mol L-1 of NaBH4 were used. Dropwise addition of NaBH4 on the solution

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of CuSO4 was done and vigorously mixed and stirred. It was noticed that a colorless gas was evolved due to the release of hydrogen gas from the chemical

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reduction of Cu2+ ions to Cu0 and brown red color nanoparticles were formed due

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to the appearance of Cu0-NPs.

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2.3.2. Microwave-assisted synthesis of NPANI- ZrSiO4 16.5 mmol of aniline and 50 mL distilled water (DW) were stirred vigorously together for 10 min. It was kept for half hour at 0–5oC. 17.5 mmol of K2S2O8 was dissolved in 200 mL DW, added as one part to aniline solution and the reaction was completed by stirring for another one hour [33]. Addition of (1.0 g) ZrSiO4 and was remained for 24 hr at 0-5oC. NPANI-ZrSiO4 nanocomposite was filtrated and washed with water as well as grinded with 10 mL water. A microwave oven was used for drying this mixture. The water mixing step was followed by microwave heating step for about five cycles. Finally drying overnight at 50–60°C to produce NPANI-ZrSiO4 nanocomposite. 4

Journal Pre-proof 2.3.3. Microwave-assisted synthesis of Cu0-NPANI-ZrSiO4 nanocatalyst

Cu0-NPANI-ZrSiO4 nanocatalyst was prepared by addition of 100 mg of Cu0NPs with 200 mg of NPANI-ZrSiO4 in a mortar and heavily grinded with 10 mL DW and exposed to microwave irradiation inside the oven for 30 seconds. This step was repeated four times till the color of Cu0-NPANI-ZrSiO4 become green and then dried in an oven at 70 oC to give dark green powder of Cu0-NPANI-ZrSiO4 nanocatalyst. The Flowchart 1 represents the different routes to synthesize the

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aimed Cu0-NPANI-ZrSiO4 nanocatalyst.

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2.4. Catalytic activity tests of NPhs

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The catalytic activity of Cu0-NPANI-ZrSiO4 was investigated by the reduction of a series of NPhs. Briefly, 2.5 mL of 4NP (0.12 mM), 3NP (0.5 mM) and 2NP

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(0.5 mM) solution was added separately into a quartz cuvette followed by 0.5 mL

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fresh solution of NaBH4 (1 mg mL-1). Finally, 300 µL of Cu0-NPANI-ZrSiO4 nanocomposite (1 mg mL-1) was added and the reaction progress was followed by

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a UV–Vis spectrophotometer at 25 oC. The UV–Vis absorption spectra were recorded every one minute. The kinetics of the reaction was investigated to

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compute the rate constant, order of the reaction and activation energy The values

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of pH 2, 4, 6, 8 and 10 of NPhs were used for kinetic studies. In addition, several temperatures such as 298 K, 303 K, 308K and 313 K were used to determine the thermodynamic parameters. During the reduction of NPhs, the solution changed to colorless thereby indicating a visual confirmation of the reduction process. 3. Results and Discussion 3.1. Morphology and chemical structure of Cu0-NPANI-ZrSiO4 Different characterization approaches were applied to confirm Cu0-NPANIZrSiO4 nanocatalyst including FT-IR spectra, HR-TEM, SEM, TGA, XRD and BET. The spectra of NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4 are clarified in 5

Journal Pre-proof Figure 1. The FT-IR spectrum of NPANI-ZrSiO4 nanocomposite (Figure 1a)

denotes the distinguished bands of NPANI at 1507 and 1491cm-1 which are equivalent to the ring-stretching vibrations of the quinoid and benzenoid rings of aniline. C═N+‫ ‏‬stretching‫ ‏‬peak close to 1292 cm-1 is adjacent to the quinoid structure, while C—N stretching vibration band at 1141 cm-1 is in the alternate units of quinoi-benzenoid-quinoid rings. The strong peak at 3227 cm-1 exists as a result of the N—H stretching mode. There are peaks at 2920 and 2816 cm-1 due to asymmetric and symmetric C—H stretching vibrations [34, 35] but with more

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sharpness to allude the complete binding and surface coverage of ZrSiO 4-NPs by

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the appearance of three distinguishable peaks at 434, 603 and 871 cm-1 which are

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correlated to the metal-oxygen bonding in the form of Si—O and Zr—O [36] with NPANI to produce NPANI-ZrSiO4. Figure 1b illustrates the spectrum after loading

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of Cu0-NPs onto NPANI-ZrSiO4 nanocomposite to produce Cu-NPANI-ZrSiO4

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nanocatalyst. The peaks in Figure 1b are similar to those detected in Figure 1a except the intensity of some peaks are less than those found in Figure 1a due to

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loading of Cu0-NPs on NPANI-ZrSiO4 and appearance peaks of Cu0-NPs .The opportunities of the existence of Cu2O or CuO impurities were avoided by no

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noticeable peaks at 623 cm−1, 588, 534 and 480 cm−1. The appearance of a new

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band at 3557 cm-1 is because of broad band of O—H group of water adsorption, which manifests the interaction of Cu0-NPs with (O-H) group [37]. In addition two peaks at 1576 and 1491 cm−1 are owing to the C=C stretching bond. The surface morphology of NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4 are presented in Figure 2. Figure 2a describes the morphology of NPANI-ZrSiO4 which has different porous particles and rough shape with particle size (39.4778.49) nm that indicates the proficient coating of ZrSiO4-NPs with NPANI. Figure 2b shows the image of Cu0-NPANI-ZrSiO4 nanocatalyst after dispersion of Cu0NPs on the surface of NPANI-ZrSiO4 nanocomposite to give a completely different particles distribution in the form aggregates. The possible aggregation may be 6

Journal Pre-proof interpreted on the basis that most of the observed pores in NPANI-ZrSiO4

nanocomposite were loaded and blocked with zerovalent copper (Cu0) to produce the designed and aimed Cu0-NPANI-ZrSiO4 nanocatalyst. Furthermore, the HR-TEM was acquired for NPANI-ZrSiO4 and Cu0-NPANIZrSiO4 as denoted in Figure 3. The image of NPANI-ZrSiO4 nanocomposite (Figure 3a) displays rough surface and fine particles of ZrSiO4-NPs scattered on NPANI surface (7.22-22.09) nm. The image illustrated in Figure 3b refers to the

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surface coverage of NPANI-ZrSiO4 with Cu0-NPs to produce the target Cu0-

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NPANI-ZrSiO4 nanocatalyst with average size (30.8-57.5) nm. The thermal stability of Cu0-NPANI-ZrSiO4 nanocomposite has been studied in

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the temperature range 20–600°C to compare with the thermogram of NPANI-

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ZrSiO4 as represented in Figure 4. The NPANI-ZrSiO4 nanocomposite (Figure 4a)

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presented two thermal decay stages at 27–316°C (% loss = 12.53%) and 316600°C (% loss = 51.14%) because of the direct losses of surface adsorbed water

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and other decayed organics. The thermogram of Cu0-NPANI-ZrSiO4 (Figure 4b) exhibits two thermal decomposition steps at 26-100oC (% loss = 1.71%) and 100-

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600oC (% loss = 21.68%) due to direct losses of surface adsorbed water and other

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decayed organic constituents, respectively. The XRD patterns of NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4 are symbolized in Figure 5 and the XRD standard card of Cu0 is given in Figure 1S (Supplementary materials). The XRD of NPANI-ZrSiO4 (Figure 5a) exhibits several characteristic peaks at 2ϴ = 19.91o with interlayer distance (d) = 4.46Ao, 27.24° with d = 3.27Ao, 26.88o with d = 3.31Ao, 33.69° with d = 2.66Ao, 35.46o with d = 2.53Ao and 53.3° with d = 1.72Ao. The observed peaks at 2ϴ = 19.91o and 26.88o to NPANI could be ascribed to periodicity parallel and perpendicular to NPANI chain [38, 39]. This is due to the possible overlap of NPANI intense peak at 2Ɵ = 27.24° with that associated with ZrSiO4-NPs. Furthermore, the 7

Journal Pre-proof crystallography of ZrSiO4-NPs is specified by the appearance of characteristic

peaks at 2ϴ = 33.69o and 35.46o [40]. Figure 5b magnificates the crystallography of Cu0-NPANI-ZrSiO4 which is identical to Figure 5a but with the appearance of a new peaks attractable to Cu0-NPs. One of the peak was characterized to overlap with NPANI-ZrSiO4 at 53.3o with d = 1.72Ao. The characteristic peaks of Cu0-NPs were found at 42.196o with d = 1.29o and 42.2o with d = 2.14Ao but with low intensity due to full loading on NPANI- ZrSiO4 [41].

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The BET-multipoint method was used to set up the N2 adsorption/desorption processes of both NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4 as represented in Figure

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6. In addition the identified surface area, pore volume and pore size values were

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characterized as 14.7 and 22.9 m2/g, 5.08x10-2 and 7.76x10-2 cm3/g as well as 13.8 and13.54 nm for NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4, respectively as listed in

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Table 3. It is evident that the surface area and pore volume of Cu0-NPANI-ZrSiO4

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were increased due to surface coverage with the small Cu0 particle size compared to those of NPANI-ZrSiO4 to confirm the surface immobilization of Cu0 onto

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NPANI-ZrSiO4 to produce the aimed catalyst. However, the detected surface area

reported

catalysts

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of NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4 are higher than other previously such

as

Ag3PO4@MWCNTs

(1.9473

m2/g)

and

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Ag3PO4@PPY@MWCNTs (1.8651 m2/g) [11] and in the same time lower than other important catalysts such as LaFeO3/SiO2 (139.6 m2/g), LaFeO3/TiO2 (69.5 m2/g), LaFeO3/Ce2O3 (72.9 m2/g) and LaFeO3/Al2O3 (105.6 m2/g) as previously reported [15]. 3.2. Catalytic reduction of NPh The catalytic performance of Cu0-NPANI-ZrSiO4 nanocomposite catalyst for the reduction of 4NP, 3NP and 2NP using NaBH4 was investigated. The reduction rate of 4NP to 4AP by NaBH4 was completed in 10 min, while the reduction rates of 3NP and 2NP to 3AP and 2NP by NaBH4 were established at 7 and 5 min, 8

Journal Pre-proof respectively. Aqueous solution of 4NP exhibited a peak at 317 nm (yellow color)

after the addition of NaBH4 and this was red shifted to the first excitation peak of 4NP at 400 nm (green-yellow color), due to the formation of 4-nitrophenolate ion in solution. This corresponds to the characteristic peak of −NO2, which is demonstrated to exhibit an isobestic point to confirm a single product formation by the given catalyzed reaction in Figure 7a [42]. A new peak at 300 nm, associated with −NH2 of 4AP, appeared and increased with the addition of Cu0-NPANIZrSiO4 catalyst to demonstrate that the toxic 4NP pollutant in water was rapidly

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and efficiently reduced to 4AP under the acceleration of Cu0-NPANI-ZrSiO4

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nanocatalyst [43]. The UV–Vis absorption spectra (Figure 7a and b) during the

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catalytic reduction of 3NP and 2NP into 3AP and 2AP shifted the absorption peaks from 272 and 277 nm to 414 and 390 nm, respectively indicating that −NO 2 group

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in 3NP and 2NP was gradually reduced to −NH2 to form 3AP and 2AP,

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respectively under the acceleration action of Cu0-NPANI-ZrSiO4 catalyst [43]. Furthermore, the reduction processes of NPhs to Aphs by NaBH4 were

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thermodynamically possible but the three nitrocompounds exhibited negligible change in the absorption spectra after adding of NaBH4 because of the existence of

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kinetic barrier. Moreover, when Cu0-NPANI-ZrSiO4 nanocatalyst had been added

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into the reaction medium, the intensity of the reaction substrates diminished gradually as the reaction proceeded along with a concomitant increase of a new peak corresponding to the formation of the aminophenol products, and there no side reaction was taken place in the reduction reaction (Figure 8a and b) [44]. The reduction reaction can be described as illustrated in Scheme 1. 3.2.1. Effect of temperature on catalytic reduction rate of NPhs The pseudo-first-order rate constant (k) of the reaction was determined using temperature range (25–40oC) at pH 7. The thermodynamic parameters such as activation energy (Ea), enthalpy of activation (∆H#), entropy of activation (∆S#), 9

Journal Pre-proof and free energy of activation (∆G#) for the heterogeneous catalytic reduction of

4NP, 3NP and 2NP by Cu0-NPANI-ZrSiO4 nanocatalyst were computed for all nitrocompounds. Firstly, the activation energy (Ea) was computed from the Arrhenius Eq. (1). (1) While entropy of activation values (∆S#) were calculated from the intercept (lnA)

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which equal 1+ ln (RT/Nh)+ ∆S#/R and Enthalpy of activation (∆H#) from Eq. (2).

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(2)

(3)

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From the obtained values of ∆H#, ∆S#and ∆G# are computed from Eq. (3).

The Langmuir-Hinshelwood model has been approved to analyze the kinetic

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manner of catalytic reduction of 4NP, 3NP as well as 2NP and the reaction rate constants (k) were evaluated by the pseudo-first-order kinetics due to the presence

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of excessive NaBH4. The k values were deduced from the plot of lnAt/Ao vs the

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reaction time (Eq. (4)) [43].

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(4)

Figures 9a, b and c show first order plots of the catalytic reduction of 4NP, 3NP and 2NP, respectively over Cu0-NPANI-ZrSiO4 nanocatalyst at 25oC, 30oC, 35oC and 40oC. Hereby, the estimated values of k were found 0.293, 0.348, 0.834 and 1.365 min-1 for 4NP, respectively. While for 3NP, k values were 0.221, 0.280, 0.365 and 0.443 min-1, respectively and finally, the values of k for 2NP were 0.33, 0.378, 0.542 and 0.691 min-1, respectively. The apparent activation energy (Ea) values of the three nitroderivatives were obtained from the slope (−Ea/R, R is ideal gas constant) of the Arrhenius equation (Eq. (1)) as represented in Figure 10. Knowing that the rate constants at different temperatures are expressed in sec-1, 10

Journal Pre-proof hence, the good linearity of the plots indicate that heat capacity of activation (∆C p#)

have zero value. The thermodynamic parameters could be also determined from Erying Eq. (5). ( )

(

)

(5)

As shown in Figure 11, the ∆S# can be identified from the intercept and ∆H# and calculated from the slope, while Ea and ∆G# computed from Eqs. (2) and (3),

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respectively. The positive enthalpy of activation (∆H#) values indicates that the reaction is endothermic and therefore energetically not favoured. While the

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negative values of ∆S# refer to more stabilized activated complex [45]. As listed in

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Tables 4a and b, the ∆H# and Ea values are different among the three NPhs

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substrates, while the corresponding values of ∆G# are more or less constant. This behavior is true and can be discussed according to the known fact which states that

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the free energy of activation (∆G#) and not energy of activation (Ea), (or ∆H#) determine the reaction rate. Accordingly, ∆S# value plays an important role as seen

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given in Table 4a and b.

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from the dramatic changes within the three substrates (4NP, 3NP and 2NP) as

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3.2.1.1. Isokinetic relationship An extrathermodynamic analysis of reaction rate (k) in the form of isokinetic relationship is mathematically described by Eq. (6). (6) Where β is the isokinetic temperature and computed from the slope of isokinetic plot (∆H# vs -∆S#). The parallel changes in ∆H# and ∆S# lead to small changes in ∆G# and for such a closely related series, a common reaction mechanism is supported. Figures 12a and b represent the isokinetic plot among 4NP, 3NP and 2NP series. A good linearity plot gives a slope to represent the isokinetic 11

Journal Pre-proof temperature that equal 298.82 and 298.23 at 298 and 303K, respectively. It is clear

that the values are nearer to the corresponding experimental temperature leading to the compensation effect type. This means that these reactions are shared the same mechanism. Moreover, the large negative ∆S# values as shown in Tables 4a and b give a good indication that these reactions proceed with the retention of intermediate configuration. The accurate explanation of compensation effect undergoes in terms of solvent-solute interaction. Any effect that guides to a stronger binding between a solute and solvent molecules will lower the ∆H#. It will

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also lower the ∆S# by restricting the vibrational and rotational degrees of freedom

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of the solvent molecules leading to a fairly exact compensation between ∆H # and

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T∆S# (β ≈ T) and therefore to a very small effect on ∆G # (as given in Tables 4a and

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2b ).

3.2.2. Effect of pH on the catalytic reduction of 4NP, 3NP and 2NP

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The dependency of catalytic reduction of 4NP, 3NP and 2NP by Cu0-NPANI-

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ZrSiO4 nanocatalyst was studied in different pH of nitro solutions. The reduction of 4NP, 3NP and 2NP Cu0-NPANI-ZrSiO4 nanocatalyst was found strongly

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dependent on the pH value (2-10); low pH was found highly productive in the reduction efficiency. As shown in the Figure 13a, b and c and listed out in Table 5,

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the k values for 4NP, 3NP and 2NP reduction were 0.811, 0.249 and 0.584 min-1 at pH 2 and then decreased to 0.112, 0.1 and 0.116 min-1 at pH 10, respectively. Furthermore, k for 4NP, 3NP and 2NP reduction decreases upon increasing the pH values (Figure 14). The high reactivity of Cu0-NPANI-ZrSiO4 nanocatalyst at low pH value is mainly resulted from surface charge of Cu0-NPANI-ZrSiO4 and pKa of 4NP (7.15), 3NP (8.36) and 2NP (7.23) which means that the surface is positively charged at pH < 4. Since the reduction of 4NP, 3NP and 2NP over Cu0-NPANIZrSiO4 nanocatalyst in the presence of NaBH4 follows the Langmuir-Hinshelwood kinetics and adsorption is the first step for the reduction reaction, the negatively 12

charged BH4

-1

Journal Pre-proof can be easily adsorbed onto the positively charged Cu0-NPANI-

ZrSiO4 surface at low pH values, resulting in an enhanced reduction efficiency in the rates of 4NP, 3NP and 2NP under acidic condition [46]. 3.2.2.1. Empirical correlation between rate constant (k) and [H +] Rate constant (k) was found in a good correlation with concentration of [H3O+] ion, this can be extracted from the plotting of logk against log [H+] at 27oC for NPhs series as shown in Figure 15. The best fitted linear least square lines

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follow the empirical Eq. (7) in the form.

(7)

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where a and b are empirical constants. The last equation can takes another form as

(8)

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given by Eq.(8).

where a and b are characterized for each reaction system. This empirical equation

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represents a new finding relation in this study field. The a and b values for 4NP, 3NP and 2NP are (1.43 and 0.099) for R2 0.930, (0.32 and 0.049) for R2 0.992 and

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(0.75 and 0.079) for R2 0.973, respectively.

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3.2.3. Brønsted linear free energy like relationship The Brønsted equation takes the following from (Eq. (9)). (9) where catalytic rate constant given by ka and Ka represent the acid dissociation constant (pKa values of 2NP, 3NP and 4NP are 7.17, 8.28 and 7.15, respectively). In the present work a series of catalytic reduction of nitrophenols derivatives were performed at 25oC where their reactivity can be expressed in terms of Brønsted LFER. β is defined as the Brønsted constant which always being less than unity. Finally, Figure 16 shows the linear Brønsted plots for 2NP, 3NP and 4NP 13

Journal Pre-proof derivatives, respectively. The value of the slope is nearly equal to 0.13 in

accordance with the normal Brønsted constant value. Conclusion The designed and assembled Cu0-NPANI-ZrSiO4 nanocatalyst was found highly efficient in the catalytic reduction of NPhs (2NP, 3NP and 4NP). The kinetic study was accomplished for catalyzed reactions under different controlling factors such as temperature and initial pH solution. At low pH value, Cu0-NPANI-

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ZrSiO4 nanocatalyst was characterized with a high reactivity due to the positively

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charged Cu0-NPANI-ZrSiO4 at pH < 4. Thus low pH values were confirmed as highly productive to support excellent catalytic reduction reactions from which the

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k values for 4NP, 3NP and 2NP were 0.811, 0.249 and 0.584 min-1 at pH 2. The

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calculated thermodynamic parameters led to an extrathermodynamic analysis as a type of compensation effect to give a good linearity plot with the slope to represent

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the isokinetic temperature, β that was identified as 298.82 at 298K. A new

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empirical correlation between log k vs log [H+] and Brønsted free energy like

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relationship correlation was established.

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B. Xu, X. Li, Z. Chen, T. Zhang, C. Li, Pd@MIL-100(Fe) composite nanoparticles as efficient catalyst for reduction of 2/3/4-nitrophenol: Synergistic effect between Pd and MIL-100(Fe), Microporous Mesoporous Mater. 255 (2018) 1-6.

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B.M. Mogudi, P. Ncube, R. Meijboom, Catalytic activity of mesoporous cobalt oxides with controlled porosity and crystallite sizes: Evaluation using the reduction of 4-nitrophenol, Appl. Catal. B. 198 (2016) 74-82.

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T.B. Nguyen, C.P. Huang, R-a. Doong, Enhanced catalytic reduction of nitrophenols by sodium borohydride over highly recyclable Au@graphitic carbon nitride nanocomposites. Appl. Catal. B. 240 (2019) 337-347.

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Flowchart 1. Synthesis of Cu0-NPANI-ZrSiO4 nanocatalyst

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Figure 1. FTIR of (a) NPANI-ZrSiO4 and (b) Cu0-NPANI-ZrSiO4

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Figure 2a. SEM image of NPANI-ZrSiO4

Figure 2b. SEM image of Cu0-NPANI-ZrSiO4

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Figure 3a. TEM image of NPANI-ZrSiO4

Figure 3b. TEM image of Cu0-NPANI-ZrSiO4

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Figure 4. TGA Thermograms of (a) NPANI-ZrSiO4 and (b) Cu0-NPANI-ZrSiO4

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Figure 5. XRD patterns of (a) NPANI-ZrSiO4 and (b) Cu0-NPANI-ZrSiO4

Figure 6. N2 adsorption/desorption of (a) NPANI-ZrSiO4 and (b) Cu0-NPANI-ZrSiO4

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Journal Pre-proof 2 0 min 1 min 2 min 3 min 4 min 5 min 6 min 7 min 8 min 9 min 10 min

Absorbance (a.u.)

(a) 4NP

1

0 200

250

300

350

400

450

500

550

600

(b) 3NP

0 min

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1 min 2 min 3 min 4 min

-p

5 min 6 min 7 min

0 250

350

400

450

500

Wavelength (nm)

(c) 2NP

0 min

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1.4

300

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1

na

Absorbance (a.u.)

2

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Wavelength (nm)

1 min 2 min

1.2

Absorbance (a.u.)

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3 min 4 min

1.0

5 min

0.8 0.6 0.4 0.2

300

350

400

450

500

550

Wavelength (nm) 0

Figure 7. UV–Vis absorption spectrum for reduction reactions by Cu -NPANI-ZrSiO4 nanocatalyst (a) 4NP, (b) 3NP, (c) Reduction of 2NP.

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(a)

2.0

4NP 3NP 2NP

1.8

Absorbance (a.u.)

1.6 1.4 1.2 1.0 0.8 0.6

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0.4 0.2 2

4

6

8

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0

10

12

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Time (min)

(b)

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At/Ao

0.8

0.6

4NP 3NP 2NP

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1.0

0.2

0.0

0

2

4

6

8

10

Time (min) Figure 8. (a) Plots of absorbance vs time and (b) Plots of At/Ao vs time for catalytic reduction rate of 4NP, 3NP and 2NP at 25oC.

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(a) 4NP

0.0

25oC 30oC 35oC 40oC

ln(At/Ao)

-0.5

-1.0

-1.5

-2.0 0

1

2

3

4

5

6

of

Time (min)

(b) 3NP

-0.2

-0.4

-p

ln(At/Ao)

25oC 30oC 35oC 40oC

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0.0

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-0.6

-1.0 -0.5

0.0

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-0.8

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.2 0.0

(c) 2NP

25oC 30oC 35oC 40oC

ur

-0.2

na

Time (min)

-0.6

Jo

ln(At/Ao)

-0.4

-0.8 -1.0 -1.2 -1.4 -1.6 -1.8

0

1

2

3

4

5

Time (min)

Figure 9. Plot of ln (At/Ao) versus reaction time for the catalytic reduction of (a) 4NP, (b) 3NP and (c) 2NP in the presence of Cu0-NPANI-ZrSiO4 nanocatalyst at 298, 303, 308 and 313 K. Reaction parameters: [4NP], [3NP] and [2NP] = 0.12, 0.5 and 0.5 mM, respectively, [NaBH 4] =0.026 M, the amount of catalysts was o maintained constant at 300 µL at 25 C.

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Journal Pre-proof -3.6 4NP 3NP 2NP Arrhenius plot

-3.8 -4.0 -4.2

ln k

-4.4 -4.6 -4.8 -5.0 -5.2

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03

34

0. 0

03

32

0. 0

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-p

1/T (K-1)

03

30 03

28 0. 0

03

26 0. 0

03

24 0. 0

03

22 0. 0

03

20 0. 0

03 0. 0

0. 0

03

18

-5.6

of

-5.4

re

Figure 10. Arrhenius plot of lnk vs 1/T for 4NP, 3NP and 2NP.

-9.6

na

-9.8 -10.0 -10.2

ur

-10.4 -10.6

Jo

ln (k/T)

4NP 3NP 2NP Erying plot

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-9.4

-10.8 -11.0 -11.2

6 00 33

4 0.

00 33 0.

2 00 33

0.

0 00 33

0.

8 00 32

0.

6 00 32

0.

4 00 32

0.

2 00 32

0.

0 00 32

0.

0.

00 31

8

-11.4

1/T (K-1) Figure 11. Erying plot of lnk/T vs 1/T for 4NP, 3NP and 2NP.

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Figure 12. Isokinetic plot of 4NP, 3NP and 2NP at (a) 25 C and (b) 30 C.

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(a) 4NP

0.0

pH=2 pH=4 pH=6 pH=8 pH=10

ln(At/Ao)

-0.5

-1.0

-1.5

-2.0

-2.5 0

5

10

15

20

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Time (min)

0.2

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(b) 3NP

0.0

-p

-0.2

-0.6

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ln(At/Ao)

-0.4

-0.8

lP

-1.0 -1.2

na

-1.4 0

2

4

6

8

10

(c) 2NP

0.0

pH=2 pH=4 pH=6 pH=8 pH=10

Jo

-0.2 -0.4

ln(At/Ao)

12

Time (min)

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0.2

pH=2 pH=4 pH=6 pH=8 pH=10

-0.6 -0.8 -1.0 -1.2 -1.4 -1.6

0

2

4

6

8

10

12

Time (min)

Figure 13. Plot of lnAt/Ao vs time for (a) 4NP, (b) 3NPand (c) 2NP at different pHs.

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Journal Pre-proof 0.9

4NP 3NP 2NP

0.8 0.7

k (min-1)

0.6 0.5 0.4 0.3 0.2

4

6

8

pH

10

ro

2

of

0.1

-p

Figure 14. Relation between k (min-1) for 4NP, 3NP and 2NP at different values pHs. 0.0

lP

-0.2

na

ur

logk

-0.4

-0.6

re

4NP 3NP 2NP

Jo

-0.8

-1.0

-10

-8

-6

-4

-2

log [H+] Figure 15. Correlation between log k vs log [H+] for 4NP, 3NP and 2NP.

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Journal Pre-proof 2.0 correlation between k and Ka linear fit of 4NP, 3NP and 2NP

1.9

4+logk

1.8 1.7 1.6 1.5

1.3 0.8

1.0

1.2

1.4

1.6

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0.6

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1.4

1.8

2.0

9+logKa

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Figure 16. Brӧnsted linear free energy like relationship of 4NP, 3NP and 2NP.

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Scheme 1. Schematic digram for the reduction of NPhs derivatives by Cu0-NPANI-ZrSiO4 nanocatalyst.

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Journal Pre-proof Table 1. Chemicals and their specifications Chemical Formula

FW

assay

Zirconium silicate nanopowder

ZrSiO4-NPs, <100 nm

183.31

98.5%

Aniline Potassium persulphate 4-Nitrophenol (4NP) 3-nitrophenol (3NP) 2-nitrophenol (2NP) 4-nitroaniline (4NA) 3-nitroaniline (3NA) 2-nitroaniline (2NA) Sodium hydroxide

C6H5.NH2

93.13

99%

Company Sigma–Aldrich Chemical Company, St Louis Lobachemie, india

K2S2O8

270.31

98%

Oxford, India

C6H7NO3

139.11

99.0%

138.12

NaOH

40.0

96.0%

36.46

37%

Copper (II) sulfate pentahydrate

CuSO4.5H2O

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NaBH4

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Sodium boronhydride

99.0%

37.83

> 95%

249.69

> 98%

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HCl

-p

C6H6N2O2

hydrochloric acid

33

VWR international Ltd Poole, BH15 1 TD, England

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Reagent Name

Sigma-Aldrich Chemical Company, USA Sd. fine-chem limited (SDFCL), Mumbai, India Sigma–Aldrich Chemical Company, St Louis, USA

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Table 2. Characterization techniques and their specifications Instrument

Conditions

FT-IR

BRUKER VERTEX 70 Fourier Transform infrared spectrophotometer

in the scope 400–4500 cm−1

HR-TEM

high resolution transmission electron microscopy model JEOL JEM-2100F, Japan

acquiring the images at 80 to 200 kV

SEM

Scanning electron microscopic JSM-6360LA, JEOL Ltd.

Using an ion sputtering coating device (JEOLJFC-1100E)

TGA

Thermal gravimetric analysis using TGA-50-Schimadzu, Japan

XRD

The X-ray diffraction by XRD Shimadzu lab X6100, Japan

A temperature heating range 27-600oC, a heating o -1 -1 rate 10 C min and a flow rate 20 mL min pure nitrogen atmosphere The XRD generator worked at 40 kV, 30 mA, and λ = 1 Å utilizing target Cu-Kα with secondary monochromatic. 2-Theta was started at 10° and ended at 80°. The diffraction data was recorded with step of 0.02° and a time of 0.6 s at room temperature The BET surface areas by nitrogen adsorption– desorption isotherms were determined for 24 h

ro

-p

re

lP

na

pH-measurement

Wavelength range 190 - 1100 nm Calibrated by standard buffers with pH 4.01, 7.00 and 10.00

Adwa pH-meter

ur

UV/ViS

Brunauer–Emmett–Teller by BELSORP-mini II, BEL Japan V-530 JASCO UV/ViS spectrophotometer

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BET

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Technique

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Journal Pre-proof Table 3. Surface area of NPANI-ZrSiO4 and Cu0-NPANI-ZrSiO4.

Nanomaterial NPANI-ZrSiO4 0 Cu -NPANI-ZrSiO4

a BET (m2/g) 14.7 22.9

Pore volume (cm3/g) -2 5.08x10 -2 7.76x10

Pore size (nm) 13.8 13.54

Table 4a. Activation parameters for reduction of 4NP, 3NP and 2NP by Cu0-NPANI-ZrSiO4 at pH 7 from Arrhenius plot. Temperature (K)

k (min-1)

R2

298

0.293

303

0.348

308

0.834

313

1.365

298

0.221

3NP

36.87

-12.42

86.28

0.945

of 82.58 82.54

-15.59

86.35

0.984

82.50

-12.75

86.42

0.996

82.46

-12.84

86.47

0.984

34.40

-175.26

86.62

0.28

0.997

34.36

-175.45

87.52

308

0.365

0.994

34.31

-175.59

88.40

0.443

0.997

34.27

-175.68

89.26

0.33

0.997

37.39

-162.29

85.75

0.378 0.542 0.691

0.995 0.998 0.998

37.35 37.30 37.26

-162.48 -162.62 -162.71

86.58 87.39 88.19

298 39.86

0.958

303 313

ur

na

303 308 313

Jo

2NP

Gibbs free energy of # activation (∆G ) (kJ/mol)

ro

4NP

Entropy of activation # (∆S ) (J/mol.K)

-p

85.06

Enthalpy of activation # (∆H ) (kJ/mol)

re

Activation energy (KJ/mol)

lP

Nitroderivative

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Table 4b. Activation parameters for reduction of 4NP, 3NP and 2NP by Cu0-NPANI-ZrSiO4 at pH 7 from Erying plot.

298

84.99

0.293

0.958 0.945 0.984 0.996 0.984 0.997 0.994 0.997 0.997 0.995 0.998 0.998

36

82.52

-13.47

36.81

-176.34

39.80

-163.29

ro

0.348 0.834 1.365 0.221 0.28 0.365 0.443 0.33 0.378 0.542 0.691

Entropy of activation # (∆S ) (J/mol.K)

Gibbs free energy of # activation (∆G ) (kJ/mol) 86.53

-p

85.04 85.08 85.12 36.81 36.85 36.90 36.94 39.80 39.84 39.89 39.93

re

303 308 313 298 303 308 313 298 303 308 313

Enthalpy of activation # (∆H ) (kJ/mol)

of

R2

lP

2NP

k (min-1)

na

3NP

Activation energy (kJ/mol)

ur

4NP

Temperature (K)

Jo

Nitroderivative

86.60 86.67 86.73 86.88 87.77 88.65 89.53 85.99 86.80 87.62 88.44

Journal Pre-proof

Table 5. Rate constants k (min-1) calculated from the catalytic reduction of 4NP, 3NP and 2NP at different pHs by Cu0-NPANI-ZrSiO4 nanocatalyst at 27oC.

2

R 0.998 0.996 0.992 0.998 0.998

2NP -1 k (min ) 0.584 0.312 0.273 0.185 0.116

of

3NP -1 k (min ) 0.249 0.204 0.171 0.131 0.1

ro

2

R 0.995 0.985 0.980 0.984 0.992

re lP na ur Jo

2 4 6 8 10

4NP -1 k (min ) 0.811 0.538 0.435 0.283 0.112

-p

pH

37

2

R 0.995 0.997 0.997 0.994 0.985

Jo

ur

na

lP

re

-p

ro

of

Journal Pre-proof Graphical Abstract

Schematic digram for the reduction of NPhs derivatives by Cu0-NPANI-ZrSiO4 nanocatalyst.

38

Journal Pre-proof Highlights A novel nanocatalyst (Cu0-NPANI-ZrSiO4) was assembled and characterized.



Catalytic reduction of 2-nitrophenol, 3-nitrophenol and 4-nitrophenol.



Strong dependency of the reduction process on the pH.



An extrathermodynamic study for reaction rate (k) by isokinetic relationship.



An extrathermodynamic analysis as compensation effect for linearity.

Jo

ur

na

lP

re

-p

ro

of



39