Photocatalytic properties of incorporated NiO onto clinoptilolite nano-particles in the photodegradation process of aqueous solution of cefixime pharmaceutical capsule

Accepted Manuscript Title: Photocatalytic properties of incorporated NiO onto clinoptilolite nano-particles in the photodegradation process of aqueous solution of cefixime pharmaceutical capsule Author: Asieh Pourtaheri Alireza Nezamzadeh-Ejhieh PII: DOI: Reference:

S0263-8762(15)00405-0 http://dx.doi.org/doi:10.1016/j.cherd.2015.10.031 CHERD 2064

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

27-6-2015 16-9-2015 19-10-2015

Please cite this article as: Pourtaheri, A., Nezamzadeh-Ejhieh, A.,Photocatalytic properties of incorporated NiO onto clinoptilolite nanoparticles in the photodegradation process of aqueous solution of cefixime pharmaceutical capsule, Chemical Engineering Research and Design (2015), http://dx.doi.org/10.1016/j.cherd.2015.10.031 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.

Photocatalytic properties of incorporated NiO onto clinoptilolite nano-particles in the photodegradation process of aqueous solution of cefixime pharmaceutical capsule Asieh Pourtaheria,b, Alireza Nezamzadeh-Ejhieha,b,c* Department of Chemistry, Shahreza Branch, Islamic Azad University, P.O. Box 311-86145,

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a

Young Researchers and Elite Club, Shahreza Branch, Islamic Azad University, Shahreza, Iran Razi Chemistry Research Center (RCRC), Shahreza Branch, Islamic Azad University,

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c

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Isfahan, Iran, Tel. No. +98 31-53292500

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Corresponding Author E-mail address: [email protected]

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b

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Shahreza, Isfahan, Iran, Tel. No. +98 31-53292515, Fax No. +98 31-53291018

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Abstract The photocatalytic degradation of cefixime was studied using NiO/nano-clinoptilolite

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(NiO/NCP) as a heterogeneous photocatalyst under Hg-lamp irradiation. For this goal, nanoparticles of clinoptilolite (NCP) prepared via mechanical ball-mill method were ion exchanged,

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calcined and characterized by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy

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(DRS), transmission electron microscope (TEM) and Fourier transformation infra red (FT-IR) techniques. The degradation process was monitored during the experimental runs by UV/Vis

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absorption spectroscopy as well as COD and HPLC methods. The best degradation results were obtained at the following optimal conditions: 0.25 g L−1 of the photocatalyst containing 13.3%

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NiO, 50 times diluted cefixime solution at pH 5. The kinetics of the process was well modeled

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by the first order (Langmuir–Hinshelwood) model.

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Keywords: Clinoptilolite, NiO, Photodegradation, Cefixime, Nano-particles.

1. Introduction

Discharging of hazardous organic compounds and pharmaceuticals, especially antibiotics, to the environment causes to serious problems for human health. Hence removal of these materials has been interested by different researchers (Shariffuddin et al., 2013; Das et al., 2013; Vondrackova et al., 2015). Cefixime is active against gram positive and gram negative aerobic bacteria and is a primary candidate for switch therapy owing to its very good efficacy and safety profile. About 40-50% of the oral dose of cefixime can be adsorbed from the gastrointestinal tract (Adam et al., 2011; Zafar Iqbal et al., 2011; Jain et al., 2010; Ensafi et al., 2013).

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Among the various methods for removing pollutants from water and wastewater, advanced oxidation processes (AOPs) are the most famous methods for this goal. In heterogeneous photocatalysis, as the most famous AOP method, a semiconductor material is irradiated by a

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photon with energy higher enough than the band gap energy of the semiconductor (Khataee et al., 2014; Padilla-Robles et al., 2014; Gupta et al., 2012). This generates electron–hole pairs on

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the catalyst surface which can reduce or oxidize the organic materials present in aqueous

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solutions. The generated electrons and holes can also react with water and dissolved oxygen, respectively, and produce hydroxyl and super oxide radicals as powerful oxidizing agents that

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can attack pollutants and transform them to smaller fragments and finally to CO2 and H2O (Nezamzadeh-Ejhieh et al., 2010; Xiao-gang et al., 2009).

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Nickel oxide (with energy band gap about 3.6-4 eV) has been received considerable attention

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in photocatalytic processes (Kalam et al., 2013; Tahmasian et al., 2012; Duan et al., 2012).

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Supporting the semiconductors onto a suitable support, such as zeolites, significantly increased their photocatalytic activity. Zeolites have been investigated as potential supports for

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photocatalytic systems because of their unique advantages including: cation exchange, catalyst, molecular sieving, charge and shape and size selectivity, adsorption etc. (Doocey et al., 2004; Nezamzadeh-Ejhieh et al., 2012; Farias et al., 2010). Hence, in this work, nano-particles of natural clinoptilolite were used for increasing the photocatalytic activity of NiO in the photodegradation of an aqueous solution of pharmaceutical cefixime tablet under Hg-lamp irradiation. In general, reduction of particle size causes larger external surface areas available for interaction, shorter diffusion path lengths, reducing mass and heat transfer resistances (Charkhi et al., 2010). The effects of some key operating factors were studied to obtain the best photocatalytic degradation efficiency. To have a more applicable photocatalyst, we prompted to

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use the samples with more similarity to a real sample instead of using a common pure synthetic solution. Hence, a Cefixime pharmaceutical tablet aqueous solution was subjected in the present

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work.

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2. Experimental

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2.1. Materials and reagents

The natural zeolite tuffs, belong to the Semnan region in the north-east of Iran, were

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purchased from Afrand Touska Company (Isfahan, Iran). Cefixime tablet (400 mg) was prepared from Tehran Shimi Company (Tehran, Iran). All other used reagents were of analytical grade and

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obtained from Merck. Hydrochloric acid and sodium hydroxide were used for pH adjustment.

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All solutions were prepared in deionized water.

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2.2. Preparation of the nano-clinoptilolite and catalysts

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Nano clinoptilolite (NCP) particles were obtained by mechanical method in a laboratory type ball-mill. To remove the water soluble and magnetic impurities, the obtained NCP was heated on a magnetic stirrer at 70 °C for 8 h (repeated 3 times). The suspension was centrifuged and the solid particles air dried. To prepare the NiO/NCP catalysts with different NiO contents, 0.5 g NCP powder was ion exchanged in 0.1, 0.2, 0.3 and 0.5 mol L−1 Ni(II) solutions (as chloride salt) and stirred at room temperature for 24 h. The suspensions were centrifuged and air dried. Finally, the obtained Ni(II)-NCP samples were calcined in a furnace at 450 °C for 12 h to obtain the NiO-NCP catalysts. 2.3. Characterization methods

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Nano-particles of clinoptilolite were prepared using a planetary ball mill (PM100). Amount of nickel was measured by atomic absorption spectrometer, PerkinElmer AAnalyst 300 (Air–C2H2, λ= 232 nm). In order to remove photocatalyst particles, the suspensions were centrifuged with

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“type-H-11n” and 5500 rpm for 5 min. The pH of point of zero charge (pHPZC) was determined

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by the reported method in our previous work (Nezamzadeh-Ejhieh et al., 2014).

The following instruments were used for characterization of samples: UV-Vis

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Spectrophotometer (JASCO, V-670 Japan, for recording UV–Vis diffuse reflectance spectra);

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FT-IR (Nicolet single beam FT-IR, Impact 400D using KBr pellet); XRD diffractometer (Bruker, D8ADVANCE equipped with Ni filtrated Cu Kα radiation at 1.5406 Ǻ); Transmission electron

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microscope (TEM, CM10, Philips); UV–Vis absorption spectrophotometer (Carry 100 Scan); High-performance liquid chromatography (HPLC, Agilent 1200 Series); Total organic carbon

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2.4. Preparation of cefixime solution

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(TOC) analyzer (Shimadzu TOC-VCSN).

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A cefixime (CF) tablet (400 mg, average weight of tablet 0.9977 ± 0.0077 g) was completely powdered in an agate mortar. 100 mg of the powder was then dissolved in 20 mL water and it was shaken for 30 min and filtered in 100 mL volumetric flask and diluted with water (stock solution). The 10, 50 and 100 times diluted solutions were prepared using serial dilution method. 2.5. Photocatalytic performance testing Photodegradation experiments were performed with a photocatalytic reactor system. A suspension of 50 times diluted cefixime solution at pH 5 containing 0.25 g L-1 of the NiO13.3%NCP catalyst in a cylindrical Pyrex-glass cell (5 cm inside diameter and 10 cm height) was irradiated with a medium pressure Hg lamp (75 W, Philips, I-line, maximum emission at 365.4 5 Page 5 of 36

nm (UV-A), located 10 cm above the reactor). To ensure the homogeneity of suspension it was magnetically stirred during the irradiation process. The blank solution had the same conditions of

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analyte without the photocatalyst. To determine the degradation extent of cefixime, the suspension was sampled out and

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centrifuged to remove solid particles. The decrease of absorbance of cleaned sample at λmax of

the following equation:

(1)

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%D = [(Ao – A)/Ao] × 100

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cefixime (286 nm) was used for the determination of degradation extent of cefixime (D%) using

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Based to the Beer–Lambert’s law Ao (absorbance of solution before irradiation process) and A (absorbance of solution at 't' time irradiation) are proportional to Co and C, which Co and C are

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respectively the concentration of cefixime before and after the irradiation process at time (t). The

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pseudo first order Langmuir–Hinshelwood kinetics was used for the calculation of rate constants

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(k) from the slopes of the straight-line segment of plots of ln(C/Co) versus t. To easy of calculations, plots of ln(A/Ao) versus 't' were used (Nezamzadeh-Ejhieh et al., 2014). 3. Results and discussion 3.1. Characterization

3.1.1. Determination of loaded NiO in the catalysts The atomic absorption spectroscopy (AAS) results of nickel determination showed that NiO was successfully loaded onto clinoptilolite nano-particles in different prepared catalysts (Table 1). The theoretical cation exchange capacity (CEC) of clinoptilolite has been reported about 2.16 meq g−1 (Ahmed et al., 2010; Faghihian et al., 2010) which confirms that clinoptilolite is a good 6 Page 6 of 36

cation exchanger. According to the results, with increasing in concentration of nickel from 0.05 to 0.1 mol L−1 the entered nickel cations into the zeolite structure was increased and thereafter decreased due to decreasing in the activity if nickel cations at higher concentrations. On the other

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hand, due to equilibrium nature of ion exchange process of zeolites, both concentration of the entering cation and ionic strength of solution significantly affect the extent of entered cation in

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the zeolite framework. According to photodegradation results, the catalyst containing 13.3% NiO

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(NiO13.3%-NCP) showed the best efficiency among the prepared catalysts. Hence, this catalyst

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was used in the next experiments and will refer the "optimized catalyst".

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3.1.2. XRD patterns

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Fig. 1A shows XRD patterns of raw NCP (a), NiO13.3%-NCP (b) and bulk NiO (c). The

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characteristic lines of the used nanoparticles at 2θ degrees of 10°, 11.4°, 13.5°, 17.4°, 19.6°,

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22.3°, 25.8°, 26.6°, 28.2° and 30.2° can be indexed to clinoptilolite crystallite structure data (JCPDS No. 39-1383) (Tao et al., 2010; Soylu et al., 2010). This confirms that the prepared clinoptilolite nano particles retained its original crystallinity during ball-mill process. The weak peaks located at 2θ values of 37° and 43.5° in XRD pattern of NiO13.3%-NCP (the pattern ‘b’) can be indexed to NiO structural data [JCPDS No. 04-0835] (Kalam et al., 2013; Deraz et al., 2012; Kalam et al., 2012). Inset of Fig. 1A shows the XRD pattern of bulk NiO (Kalam et al., 2012). Comparison of the XRD patterns of NiO13.3%-NCP and raw NCP samples indicates the absence of any structural damage in NCP during ion exchange and calcination processes. Our results are in accordance with the literature (Nezamzadeh-Ejhieh et al., 2010; Amereh et al., 2010).

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By analyzing of the β, excess of width line of the diffraction peaks in radians, λ, the wavelength of X-ray and θ, the Bragg angle in degrees, the particles size (d) of NCP and

(Chen et al., 2011): d=0.9 λ/β cosθ

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(2)

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NiO13.3%-NCP samples was estimated about 30 nm by using the following Scherrer equation

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3.1.3. FT-IR studies

Fig. 1B shows FT-IR spectra of the micronized clinoptilolite (CP), NCP and NiO13.3%-NCP

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samples in the range of 2000–450 cm−1. The observed frequencies at 1648, 1075, 802, 611 and 469 cm−1 for the micronized clinoptilolite show good agreement with IR data of clinoptilolite

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reported in the literature (Nezamzadeh et al., 2013; Nezamzadeh-Ejhieh et al., 2011). Similar

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lines were observed for the NCP sample. Changes of the characteristic peaks took place between

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the NCP (the values in the parentheses) and NiO13.3%-NCP. The characteristic are seen at 479 (467) cm−1, 615 (610) cm−1 (T–O bending), 798 (801) cm−1 (symmetrical stretching), 1082 (1072) cm−1 (asymmetrical stretching), showing the shift of some bands for NiO13.3%-NCP sample. When NiO are combined with zeolite via Ni–O–Si or Ni–O–Al bonds, the torsions of Ni–O– are restricted by the solid surface bonding (Li et al., 2005). Thus, the energy of the torsion vibration of such bonds became weaker, leading to the red shift of the loaded NiO in FTIR spectrum. In addition, a new absorption band at 530 cm−1 was found in the FT-IR spectrum of NiO13.3%-NCP that indicates incorporation of NiO in the zeolite (Kalam et al., 2013). 3.1.4. DRS analysis

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The UV–Vis diffuse reflectance spectra (DRS) of CP, NiO13.3%-NCP and NCP are presented in Fig. 2A. A strong absorption peak was observed in the UV region between 248–252 nm, which may be attributed to the band gap absorption in sample. The band-gap energy of NiO has

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been reported about 3.5-4 eV (Kalam et al., 2012). Band gap energy of the loaded samples was estimated by Kubelka-Munk function using the (αhν)n = β(hν-Eg) (or λ=[(hc)/(hν)]=1240/(hν)),

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where Eg is the band gap of the proposed semiconductor (eV), h is Planck's constant (J s), c is the

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speed of light (m s-1), ν (or λ) is the frequency (or wavelength) of light (s-1 or nm), β is the absorption constant and α is the absorption coefficient defined by the Beer-Lambert’s law as α=

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([2.303×Abs]/d), where d and Abs are the sample thickness and sample absorbance, respectively. For precise determination of α, some corrections should be done to the absorption due to

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reflection; also, n is the index with different values of 1/2, 3/2, 2, and 3. The band gap can be

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determined by extrapolating of the linear portion of the (Ahν)n -hν curve. The band gap energies

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of the NiO-NCP sample was estimated about 2.9 eV which shows a red shift with respect to the bulk NiO. In general, the existence of impurities, the synthesis method, the crystalline network

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and the average crystal size of the semiconductor are main affecting factors on changing the band-gap energy (Chopra et al., 1990; Harraz et al., 2010). 3.1.5. TEM analysis

The grain size of NCP and NiO13.3%-NCP was determined by the transmission electron microscope. TEM images of samples are shown in Fig. 2B-C. As shown, the used clinoptilolite particles have nano dimensions before and after NiO loading. TEM results of particles size are in good agreement with the calculated results by the Scherrer’s equation.

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3.2. Effect of variables influence on degradation efficiency 3.2.1. Effect of NiO loading To study the effect of extent of NiO loaded onto NCP on the photodegradation efficiency of

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the process, four catalysts were prepared by ion exchanging of NCP in 0.1, 0.2, 0.3 and 0.5 mol L−1 of Ni2+ aqueous solutions. As shown in Table 1, their NiO contents were 13.3, 10.8, 8.9 and

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5.8%, respectively. Increasing in the concentration of Ni(II) in ion exchange solutions led to

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decrease the extent of Ni(II) exchanged because of reducing the activity of Ni(II) cations and increasing in the counter ions interactions at higher concentrations. The photodegradation

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efficiencies of the prepared catalysts were investigated using 0.2 g L−1 suspensions of NiO/NCP catalysts and the corresponding results are collected in Fig. 3A. To evaluate the kinetic behavior

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of the photocatalytic process, ln(Ao/A) was plotted versus irradiation time (Nezamzadeh-Ejhieh

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et al., 2010) as a function of loaded extent of NiO (inset of Fig. 3A). The rate constants, k

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(min−1), were calculated from the straight-line portion of the first order plots. The k values (k × 103) of 6.7, 1.5, 1.8 and 1.0 min−1 were respectively obtained for the catalysts containing 13.3,

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10.8, 8.9 and 5.8% of NiO. Hence, the catalyst containing 13.3% NiO (NiO13.3%-NCP) was used as the optimized catalyst for next studies. Really, catalysts with low NiO content can absorb lesser photons and hence they can generate the lesser hole/electron pairs. This finally led to reducing the production of OH• and consequently the degradation rate (Nezamzadeh et al., 2013). 3.2.2. Effect of dosage of the catalyst

In preliminary experiments, the effect of direct photolysis and surface adsorption on the removal of cefixmie was studied. Based on the results, the removal extents of 8 and 4.5% were respectively obtained for direct photolysis and surface adsorption process after 2 h and then remained constant. These results confirm that UV irradiation of cefixime molecules may broke 10 Page 10 of 36

some bonds of the molecules and produce organic radicals which are lesser reactive than the hydroxyl radicals. To reach a constant adsorption/desorption process and to remove the surface adsorption effect in the removal of the pollutant, before irradiation of samples the suspensions

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were shaken 2 h at dark.

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The influence of the catalyst dosage on the photodegradation of cefixime was investigated in the range from 0.25 to 4 g L−1 of the optimized catalyst which of results are presented in Fig. 3B.

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The corresponding rate constants are summarized in Table 1. A 0.25 g L−1 of the catalyst was

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used as optimum dose, because the higher dosages of the catalyst led to decrease the photodegradation efficiency. This phenomena may be explained by aggregation of nano-particles

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of the catalyst at dosage above 0.25 g L−1 causing a decrease in the number of surface active sites and increase in opacity and light scattering of the particles, led to decrease in the passage of

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photons through the sample (Nezamzadeh-Ejhieh et al., 2012; Pino et al., 2012). In the

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aggregated particles, it would be expected that some excited or activated semiconductors will

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deactivate by collision with ground state semiconductors which cause to generate lesser electronhole pairs (Nezamzadeh-Ejhieh et al., 2014). Therefore, generation of hydroxyl radicals was decreased which led to reducing the collision of cefixime molecules with hydroxyl radicals and consequently the degradation rate.

3.2.3. Effect of the initial concentration of cefixime The effect of initial concentration of the solution on the photocatalytic degradation rate was investigated over the concentration range of 10 to 100 times diluted solutions and the corresponding results are presented in Fig. 4A. Results showed that the rate of photodegradation was decreased with increasing in the initial solution concentration of cefixime. This can be explained in terms of either saturation of the limited number of accessible active sites on the 11 Page 11 of 36

photocatalyst surface, or poisoning (deactivation) of the active sites of the catalyst. High solution concentration induce the formation of intermediates that could be adsorbed onto the catalyst surface and deactivate the active sites (Vaez et al., 2012; Chowdhury et al., 2011). Also,

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increasing in the concentration of drug led to decreasing the number of photons that arrive to the surface of the catalyst and photodegradation activity diminished (Gupta et al., 2011). At high

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diluted solution (100 times diluted), the density of cefixime molecules per unit volume of the

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solution was decreased and due to low lifetime of hydroxyl radicals (Nezamzadeh-Ejhieh et al., 2010), these radicals react with other substances present in the solution instead of cefixime

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molecules.

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3.2.4. Effect of solution pH on the degradation process

The photocatalytic degradation of the cefixime was investigated by varying the solution pH in

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the range of 3–11 and the corresponding results are depicted in Fig. 4B and Table 1. Insets of

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Fig. 4B show the molecular structure of cefixime and the plotted curve for the determination of

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pHPZC of the catalyst. The photodegradation rate was increased from pH 3 to 5 and thereafter decreased. The pHpzc for the catalyst was estimated about 6.7 while this value for pure NiO has been calculated by different methods and reported between 6.5 to 7 (Liu et al., 2012). Hence, in the NiO-NCP catalyst a thin layer of NiO covered the clinoptilolite nanoparticles so it is determining the surface charge of the obtained catalyst. At pH values smaller than pHpzc the charge of the catalyst surface is positive while it is negative above it. At stronger acidic pHs (pH 3), it may some cefixime molecules be at protonated form and repulsive forces between these molecules and the positive catalyst surface prevent to reach pollutant molecules near the catalyst surface where hydroxyl radicals produced. Hence with increasing in pH to 5, this charge is enough to bring neutral pollutant molecules near the catalyst surface due to attractive forces 12 Page 12 of 36

between the relatively positive charged catalyst surface and non-bonding electrons on nitrogen and oxygen atoms of cefixmie molecules which there are as de-protonated form at this pH. In addition, at pH 3, acidification of the solution by HCl, produces more HClO•− radicals due to

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reaction of Cl− and •OH which show a much lower activity than •OH and hence the degradation efficiency was decreased (Ensafi et al., 2013). Also, dissolution of some NiO molecules from the

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catalyst surface at pH 3 can count as another reason for decreasing the activity of the proposed

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catalyst. This in turn confirms that a heterogeneous process is responsible for the degradation of

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the pollutant not homogeneous Ni(II) cations.

At pH about 7, the charge of the catalyst surface is zero and no attraction is present with

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neutral pollutant molecules and the degradation rate was decreased. At basic pHs, the repulsive force between the negatively charged surface of the NiO/NCP catalyst and the non-bonding

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electron pairs of amine and hydroxyl groups of cefixime caused to a decrease in the

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photodegradation efficiency (Nezamzadeh-Ejhieh et al., 2011). In addition, competition of

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hydroxyl anions with pollutant molecules for adsorption on the surface of the photocatalyst caused to decrease in the degradation efficiency at strong basic pHs (Sohrabnezhad., 2011). At strong basic pHs, the H2O2• and HO2• radicals were also formed due to the reaction of •OH with high present amounts of -OH. The reactivity of these radicals with organic pollutant is very lower than •OH. Also, due to the presence of high amounts of OH radicals, the radical-radical reactions takes place at higher pH values caused to reduction in the degradation extent (NezamzadehEjhieh et al., 2011; Qamar., 2010). 3.2.5. Effect of support and alcohol

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The role of NCP on the efficiency of the photodegradation process was evaluated by performing some experiments using various substrates including: raw NCP and CP, NiO13.3%NCP, NiO-CP, nano-NiO and bulk NiO. The experimental results are presented in Fig 5A. As

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shown, using the NCP as a support for NiO caused to a considerable increase in the photodegradation activity of NiO. Results confirmed that supported NiO onto nanoparticles of

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clinoptilolite (NiO13.3%-NCP) displays higher photocatalytic activity than pure NiO nano-powder.

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It is interesting that the supported NiO onto micronized clinoptilolite showed also greater photodegradation activity with respect to the both bulk and nano NiO particles. These

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observations show the importance of the zeolitic bed due to super adsorption capability of the zeolite (Charkhi et al., 2010). Based on the results, it can be concluded that the NiO13.3%-NCP is

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more active than pure NiO nano-powder due to its remarkable ability in gathering the organic

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substance near the NiO particles. However, presence of nanoparticles of both NiO and

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clinoptilolite caused to increase in the photodegradation efficiency of the process, because of their high specific surface area and therefore high surface activity (Rajic et al., 2010). As shown,

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un-supported MCP and NCP do not participate to photodegradation process. To compare the activity of the proposed photocatalyst with TiO2, same experiment was done using TiO2 as catalyst (0.25 g L-1) at the same experimental conditions. As shown in Fig. 5A, TiO2 is less active than the supported NiO onto NCP and CP. Another comparison was also done for photocatalytic activities of 0.25 g L-1 of NiO13.3%-NCP with 0.25 g L-1 and 0.033 g L-1 (correspond to NiO value in 0.25 g L-1 of NiO13.3%-NCP) of TiO2. The degradation extents of 62 ± 2, 38 ± 1.5 and 23 ± 2 (averaged based on 3 replicates) were respectively obtained for the mentioned doses of the catalysts after 3 h photodegradation process. We believe that NiO particles were only formed at ion exchange sites of clinoptilolite which cause to fix them on 14 Page 14 of 36

these sites and hence prevent from aggregation of NiO. Zeolite can also accept the conduction band electrons of NiO and disperse them in its network structure, preventing from electron-hole

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recombination as desirable phenomena in the photocatalytic processes. Based on literature, light alcohols such as iso-propanol (i-PrOH) have very weak adsorption

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power on surface of catalysts in aqueous media and direct oxidation of them by photogenerated holes is negligible. Thus, alcohols are usually used as diagnostic tools of •OH radicals mediated

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mechanism. Among alcohols, i-PrOH is more easily oxidized by •OH radicals with a rate

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constant of 1.9×109 M−1 S−1 via a diffusion limiting control (Khodami et. al, 2015; Chen et al, 2005). In this study, the effect of different dosages of i-PrOH on the degradation activity of the

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proposed catalyst on the degradation extent of the pollutant was studied at the optimized conditions (0.25 g L-1 of NiO13.3%-NCP, 50 times diluted cefixime solution at pH 5) at irradiation

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time of 180 min. Based on the rsults, addition of i-PrOH at 0.01 and 0.1 mol L-1 doses caused to

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significant decrease in the degradation extent of the pollutant from its initial value (62% in the

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absence of i-PrOH) to 33% and 20%, respectively.

3.2.6. Confirm the photodegradation process As mentioned, UV-Vis was used for the calculation of photodegradation extent of the pollutant. The changes in the UV–visible spectra during the photodegradation process of cefixime (50 times diluted cefixime aqueous solution) in the presence of NiO13.3%-NCP catalyst (0.25 g L−1, pH 5) are shown in Fig. 5B. After 300 min irradiation of the suspension, up to 80% of the pollutant was degraded. The decrease in the absorbance of samples at λmax=286 nm indicates the degradation of the drug in the applied conditions. The characteristic adsorption 15 Page 15 of 36

band of cefixime around 286 nm was decreased rapidly with slight hypsochromic shifts (268 nm) during UV irradiation, but there are no new absorption bands appeared even in ultraviolet range

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(λ>200 nm) which show the degradation of cefixime molecules to smaller fragments. The chemical oxygen demand test (COD), which shows the total quantity of oxygen required

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for the oxidation of organic matter to CO2 and water (Nasuhoglu et al., 2011; Li et al., 2012), was used to confirm the degradation of the pollutant. The obtained results are presented in the

to 398 mg L-1 during the irradiation process. On the other hand, with progress of the

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inset of Fig. 5B which shows the decrease in the remained COD from initial value of 1440 mg L-

photodegradation process, most of organic matter was degraded to smaller species (especially

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inorganic compounds) and hence the required chemically oxygen demand was decreased. Based on the COD results, the photodegradation efficiency was found to be 72.3%, confirming that the

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good potential of the used photocatalytic technique for degradation of cefixime.

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To confirm the complete degradation of the pollutant, photodegradation of a sample was

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studied under the optimized conditions and the reduction of total organic carbon (TOC) was followed. Decrease in TOC extent of the samples during 0 to 4 h photodegradation process is shown in Fig. 6A. A sharp TOC decrease of 73% was observed during initial 1 h of degradation and thereafter it was nearly plateau up to 240 min (92% decrease in TOC). This indicates the formation of intermediates that are resistant to further degradation. On the other hand, cefixime molecules were almost completely degraded to very small fragments and it would be expected that a major part of the molecule was converted to water and carbon dioxide. The extent of degradation or mineralization of the proposed pollutant was also followed using HPLC. The HPLC chromatograms in the inset of Fig. 6A show that the intensity of main peaks

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where located at retention times of 1.2 and 4 min was decreased during the irradiation process. During 180 min irradiation of the proposed suspension, some weak peaks were observed between 1.30-2 retention times which disappeared after 300 min irradiation of the suspension. In

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addition, the weak peak at 2.2 min was disappeared during 180 and 300 min irradiation time, while a new peak was observed after 4 min retention time during 180 min irradiation process

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which was disappeared after 300 min. Some new weak peaks were also observed between 2-3

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min retention times after 300 min irradiation time. These observations confirm that the original structure of cefixime was destroyed during the irradiation process and some smaller fragments

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produced. In our idea, the mineralization of nitrogen containing compounds in the drug may

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yield either of NO3–, NH3 or N2, whereas those of ‘C’, ‘H’, and ‘O’ may yield CO2 and H2O. 3.2.7. Reusing experiments

d

One advantage of heterogeneous catalysis is the ease of separation of catalysts from the

te

reactants or products, which results in the possibility to reuse or recycle them without additional

Ac ce p

steps. The reusing of the NiO13.3%-NCP for the photocatalytic degradation of cefixime was investigated at the optimized conditions (50 times diluted cefixime solution, pH 5, 0.25 g L−1 of the catalyst for 3 h). Between each experiment, the recovered sample was removed by centrifuge and dried at 100, 300 and 700 ◦C for 2 h. The photocatalytic activity of the reused catalysts, in terms of the obtained cefixime degradation efficiency, was steadily decreased during successive re-using, but this decrease in the efficiency was lesser with increasing the drying temperature (Fig. 6B). This decrease can be explained by the formation of by-products and their accumulation on the active surface sites of the catalyst (Nezamzadeh-Ejhieh et al., 2010). In addition, during the recycling of the photocatalyst some photocatalyst particles may be loosen and cause to change the ratio of photocatalyst/solution volume from its optimum value. The 17 Page 17 of 36

drying of the catalyst at higher temperatures cause to elimination of adsorbed by-products from the catalyst surface, which is beneficial to refresh the surface resulting in the recovery of catalytic activity. But the heat treatment will also induce the catalyst aggregation after several

ip t

recycles resulting in the decrease of surface area, finally leading to the decrease in the

cr

photocatalytic activity (Brigante et al., 2011).

us

4. Conclusion

The results of this work confirmed that supporting of NiO onto clinoptilolite nanoparticles

an

significantly increased its photodegradation activity, so NiO supported onto clinoptilolite nanoparticles (NCP) can degrade more cefixime molecules with respect to both bulk NiO and

M

NiO nanoparticles. Also, supported NiO onto NCP showed better degradation activity than TiO2.

d

Amount of supported NiO significantly depends on concentration of Ni(II) in ion exchange

te

solution because ionic strength of this solution affect the ion exchange extent. Amount of NiO entered into the zeolitic bed significantly affects the degradation extent of the pollutant, so the

Ac ce p

catalyst containing 13.3% NiO showed the best degradation activity for the 50 times diluted cefixime

solution

at

pH

5.

18 Page 18 of 36

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Brigante, M., Schulz, P.C., 2011. Remotion of the antibiotic tetracycline by titania and titania–

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magnetic nanoparticles, a new catalyst for voltammetric determination of cefixime. Colloids and Surfaces, B: Biointerfaces 102, 687– 693. Faghihian, H., Kabiri-Tadi, M., 2010. Removal of zirconium from aqueous solution by modified clinoptilolite. Journal of Hazardous Materials 178, 66–73. Farias, T., Menorval, L.Ch., Zajac, J., Rivera, A., 2010. Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants. Colloids and Surfaces, B: Biointerfaces 76, 421–426.

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cr

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Simultaneous

M

determination of cefdinir and cefixime in human plasma by RP-HPLC/UV detection method:

d

Method development, optimization, validation, and its application to a pharmacokinetic study.

Ac ce p

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Journal of Chromatography, A 879, 2423– 2429.

25 Page 25 of 36

Figure Captions:

ip t

Fig. 1. A) XRD patterns of NCP (a) and NiO13.3%-NCP (b) (inset: XRD pattern of reference NiO (c); B) FT-IR spectra of CP, NCP and NiO13.3%-NCP.

cr

Fig. 2. A) UV-Vis DRS spectra of CP, NiO13.3%-NCP and NCP; B) and (C): TEM images of

us

NCP and NiO13.3%-NCP, respectively.

Fig. 3. A) Effect of the dose of semiconductor on the photodegradation efficiency (amount

an

catal.= 0.2 g L-1, 50 times diluted cefixime solution, pH 4.3); B) Effect of the amount of

4.3); Insets: ln(A/A0) versus time.

M

NiO13.3%-NCP on the photodegradation efficiency (50 times diluted cefixime solution, pH

d

Fig. 4. A) Effect of cefixime concentration on the photodegradation efficiency (amount of

te

NiO13.3%-NCP =0.25 g L-1); B) Effect of pH on the photodegradation efficiency (amount of

Ac ce p

NiO13.3%-NCP =0.25 g L-1, 50 times diluted cefixime solution), (First inset: cefixime structure, Second inset: pHPZC determination of the catalyst). Fig. 5. A) Role of support on the photodegradation efficiency of cefixime, B) Decrease in UVVis absorbance during irradiation process, inset: changing in COD of solution during irradiation process, (Conditions: 0.25 g L-1 of NiO13.3%-NCP, 50 times diluted cefixime solution at pH 5). Fig. 6. A) Remaining TOC during the photodegradation experiments; Inset: Decrease in HPLC during irradiation process in the photodegradation of cefixime; B) Reusability of the NiO-

26 Page 26 of 36

NCP photocatalyst in the photodegradation of cefixime after 300 min irradiation time,

Ac ce p

te

d

M

an

us

cr

ip t

(Conditions: 0.25 g L-1 of NiO13.3%-NCP, 50 times diluted cefixime solution at pH 5)

27 Page 27 of 36

Tables:

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Table 1: Definition of catalysts, their NiO content and reaction rate constants for

Dosage of the optimized catalyst (g L-1)

Ccefixime (times of dilution)

Solution pH

NiO%

2.4% 6.3% 13.3% 10.8% 8.9% 5.8%

us

Ac ce p

te

d

Parameter

NiO% in catalysts

Rate constant values Values 2.4 6.3 13.3 10.8 8.9 5.8 0.25 0.5 1 4 Stock solution 10 50 100 3 5 7 9 11

M

NiO2.4%-NCP NiO6.8%-NCP NiO13.3%-NCP NiO10.8%-NCP NiO8.9%-NCP NiO5.8%-NCP

an

Catalysts

The properties of the catalysts CNi in ion exchange solution (M) 0.025 0.05 0.1 0.2 0.3 0.5

cr

the degradation of cefixime as a function of experimental parameters

k × 103 0.04 1.1 6.7 1.5 1.8 1.0 7.9 2.3 1.8 1.7 1.9 2.6 6.5 3.2 3.3 7.9 3.2 3.0 0.1

28 Page 28 of 36

615 547

798

479

te

1715 1638

NiO-NCP

1648

CP

40

469 1221

B

0 1800

517

1214

NCP

1082

80

802 730 611

1651

Ac ce p

Transmittance (a.u.)

120

1370

d

A

408

M

an

us

cr

ip t

Figures:

1500

1200

1075

900

600

Wavenumber (cm-1) Fig. 1. A) XRD patterns of NCP (a) and NiO13.3%-NCP (b) (inset: XRD pattern of reference NiO (c); B) FT-IR spectra of CP, NCP and NiO13.3%-NCP. 29 Page 29 of 36

213 24 8 25 2 20 3

ip t

0.6

0.4

NiO-NCP

A CP

300

400 500 600 Wavelength (nm)

700

800

Ac ce p

te

d

M

an

200

us

NCP

0.2

cr

Abs.

0.8

213 249

1.0

Fig. 2. A) UV-Vis DRS spectra of CP, NiO13.3%-NCP and NCP; B) and (C): TEM images of NCP and NiO13.3%-NCP, respectively.

30 Page 30 of 36

-0.2

A

ln (A/Ao)

-0.3 -0.4 -0.5 -0.6 -0.7

50

100

150

200

250

ip t

50

Irradiation time (min)

cr

40 30 20

NiO 13.3%-NCP NiO 10.8%-NCP NiO 8.9%-NCP NiO 5.8%-NCP

us

Degradation efficiency (%)

60

10

0

50

100

an

0

150

200

250

300

350

M

Irradiation time (min)

-0.4

te

60

50

100

150

200

250

Irradiation time (min)

Ac ce p

Degradation efficiency (%)

-0.6

B

d

ln (A/Ao)

-0.2

40

0.25 g/L 0.5 g/L 1 g/L 4 g/L

20

0

0

50

100

150

200

250

300

350

Irradiation time (min)

Fig. 3. A) Effect of the dose of semiconductor on the photodegradation efficiency (Catal. amount= 0.2 g L-1, 50 times diluted cefixime solution, pH 4.3); B) Effect of the amount of NiO13.3%-NCP on the photodegradation efficiency (50 times diluted cefixime solution, pH 4.3); Insets: ln(A/A0) versus time. 31 Page 31 of 36

60

A

ip t

45 30 15

cr

Degradation efficiency (%)

Stock Solution 10 folds diluted 50 folds diluted 100 folds diluted

0

50

us

0 100

150

200

250

an

Irradiation time (min) B

Final pH

12

M

8

pHF

4

pHI 0 4

8

60

pH 5 pH 3 pH 7 pH 9 pH 11

12

te

d

Initial pH

Ac ce p

Degradation efficiency (%)

0

80

40

20

0

0

50

100

150

200

250

Irradiation time (min)

Fig. 4. A) Effect of cefixime concentration on the photodegradation efficiency (amount of

NiO13.3%-NCP =0.25 g L-1); B) Effect of pH on the photodegradation efficiency (amount of NiO13.3%-NCP =0.25 g L-1, 50 times diluted cefixime solution), (First inset: cefixime structure, Second inset: pHPZC determination of the catalyst).

32 Page 32 of 36

40

ip t

60

cr

20

0 50

100

150

200

Irradiation time (min)

250

Ac ce p

te

d

M

an

0

us

Degradation Efficiency (%)

A

NiO-NCP NiO-CP Nano-NiO Bulk NiO NCP CP TiO2

B

Fig. 5. A) Role of support on the photodegradation efficiency of cefixime, B) Decrease in UV-

Vis absorbance during irradiation process, inset: changing in COD of solution during irradiation process, (Conditions: 0.25 g L-1 of NiO13.3%-NCP, 50 times diluted cefixime solution at pH 5).

33 Page 33 of 36

ip t cr us an

60

B

M

50

100 300 700

40

20 10

Ac ce p

0

d

30

te

Degradation efficiency (%)

A

1

2

3

Reusing Runs

Fig. 6. A) Remaining TOC during the photodegradation experiments; Inset: Decrease in HPLC

during irradiation process in the photodegradation of cefixime; B) Reusability of the NiONCP photocatalyst in the photodegradation of cefixime after 300 min irradiation time, (Conditions: 0.25 g L-1 of NiO13.3%-NCP, 50 times diluted cefixime solution at pH 5)

34 Page 34 of 36

ip t an

40

us

60

cr

NiO-NCP NiO-CP Nano-NiO Bulk NiO NCP CP TiO2

M

20

0 0

50

100

d

Degradation Efficiency (%)

Graphical Abstract:

150

200

250

Ac ce p

te

Irradiation time (min)

Highlights

► NiO supported on clinoptilolite acts as an active center for degrading Cefixime. ► Extent of NiO loaded significantly affects on the efficiency of process. ► Results of TOD and HPLC confirm the results of degradation by UV-Vis.

35 Page 35 of 36

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d

te

Ac ce p us

an

M

cr

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