High antibacterial and photocatalytic activity of solution combustion synthesized Ni0.5Zn0.5Fe2O4 nanoparticles: Effect of fuel to oxidizer ratio and complex fuels

Ceramics International xxx (xxxx) xxx–xxx

Contents lists available at ScienceDirect

Ceramics International journal homepage: www.elsevier.com/locate/ceramint

High antibacterial and photocatalytic activity of solution combustion synthesized Ni0.5Zn0.5Fe2O4 nanoparticles: Effect of fuel to oxidizer ratio and complex fuels H. Aalia, N. Azizia, N. Javadi Baygia, F. Kermania, M. Mashreghib, A. Youssefic, S. Mollazadeha,∗, J. Vahdati Khakia, H. Nasirid a

Department of Materials Engineering, Faculty of Engineering, Ferdowsi University of Mashhad (FUM), Azadi Sq, Mashhad, Iran Department of Biology, School of Science, Ferdowsi University of Mashhad, 91775-1436, Mashhad, Iran Par-e-Tavoos Research Institute, Mashhad, Iran d Department of Materials Engineering, Birjand University of Technology, Birjand, Iran b c

ARTICLE INFO

ABSTRACT

Keywords: Solution combustion synthesis Complex fuel Photocatalytic degradation Antibacterial activity Ni0.5Zn0.5Fe2O4

High antibacterial and photocatalytic Ni0.5Zn0.5Fe2O4 nanoparticles were synthesized via solution combustion synthesis method using complex fuels i.e. glycine & urea. Employing a mixed-fuel system for synthesis of nanopowders improved the photodegradation of methylene blue as dye molecule to 85% along with 100% growth inhibition against bacteria (E. coli and S. aureus). The minimum inhibitory concentration of particles was 0.25 mg/mL and 0.125 mg/mL against the gram-negative and gram-positive bacterium, respectively. The effect of fuel type (glycine & urea), fuel to oxidizer ratio (φ = 0.8, 1, and 1.4), and complex fuels (mixing urea and glycine with different molar proportions) on the synthesis process as well as the physicochemical properties of the as-synthesized nanopowders were investigated. XRD, FTIR, EDS, and elemental mapping results implied that the formation of single-phase product relied on the φ value. Well-crystalline single-phase Ni0.5Zn0.5Fe2O4 particles with an estimated crystallite size of 8.9-22.4 nm, were synthesized at φ=0.8 and 1.4. Combusted particles using urea at φ = 1.4 displayed saturation magnetization of 67 emus/g (without further sintering process), the specific surface area of 150 m2/g, and particle size around 30 nm.

1. Introduction Among various magnetic spinel ferrites, Ni–Zn ferrites with the general formula of NixZn(1-x)Fe2O4 have unique characteristics which makes them a promising candidate for different application [1,2]. Several authors reported that Ni0.5Zn0.5Fe2O4 had significant magnetic properties in comparison to the other compositions of Ni–Zn ferrites [3]. Additionally, Zn0.5Ni0.5Fe2O4 nanoparticles are a promising compound for photocatalytic degradation of the organic pollutants under UV or solar light owing to the small band gap (2.2 eV) and magnetic properties of ferrites [4]. Qasim et al. reported that synthesized Zn0.5Ni0.5Fe2O4 powders displayed high photoactivity with photocatalytic efficiency around 60% [4]. During the past years, the bactericidal activity of other spinel ferrites such as cobalt ferrites with the general formula of M0.5Co0.5Fe2O4 was investigated. Obtained results indicated that Ni0.5Co0.5Fe2O4 and Zn0.5Co0.5Fe2O4 displayed promising antibacterial activity [5]. Jesudoss et al. stated that the

∗

antibacterial activity of Mn–Ni ferrite nanoparticles is influenced by the content of the Ni component in the phase composition of manganese ferrite. The higher amount of Ni, the higher bactericidal effect [6]. The antibacterial activity of Ni0.5Zn0.5Fe2O4 nanoparticles has not been explored yet. However, it can be anticipated that co-substitution of both Ni and Zn in the structure of ferrite could significantly enhance its bactericidal activity against the bacterium. An overview of the previous reports on the physical and chemical properties of Ni0.5Zn0.5Fe2O4 particles demonstrate that this compound can have the antibacterial, photocatalytic, and magnetic properties altogether. Synthesizing method is an essential factor which affects the properties of synthesized powders. Variety of methods such as co-precipitation [7], hydrothermal [8], sol-gel [9], sonochemical [10], reverse microemulsion [11], have been reported for the synthesis of Ni0.5Zn0.5Fe2O4 nanopowders by numerous researchers. Table 1 represents the summary of the results of previous studies on Ni0.5Zn0.5Fe2O4 nanoparticles synthesized by various methods [3,4,12–22]. Solution combustion synthesis (SCS) is a

Corresponding author. E-mail address: [email protected] (S. Mollazadeh).

https://doi.org/10.1016/j.ceramint.2019.06.159 Received 7 May 2019; Received in revised form 15 June 2019; Accepted 16 June 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Please cite this article as: H. Aali, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.06.159

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Table 1 The summary of the results of previous studies on Ni0.5Zn0.5Fe2O4 nanoparticles synthesized by various methods. Synthesis method

Magnetic properties Ms Mr Hc

Reverse micro emulsion + annealing at 600 °C Co-precipitation Sol combustion + calcination process Chemical co-precipitation Sol-gel auto-combustion method Gel combustion co-precipitation Hydrothermal Citrate-gel process Solution combustion synthesis + sintering process Solution combustion synthesis Solution combustion synthesis + calcination Solution combustion synthesis + sintering Sol-gel auto-combustion

Specific Surface area (m2/g)

Particle size/ Crystallite size

Photocatalytic activity (%)

Antibacterial performance (%)

Fuel

21.69

0.5

10.62

–

2nm /5nm

–

–

–

45.44 105.2

0.83 –

7 –

– 69.7

- /20.3nm 16nm /15nm

– –

– –

89.5 43 56 36.26 28 68 72

35.23 11.7 0.4 1.14 1.1 – –

48.07 40 37 38.4 0 9.2 –

– – – – – – 44.5

35nm /42nm 500nm /250nm 22nm /16nm - /90nm 20nm /12nm 33nm /14nm 35nm /25.3nm

– – 60 – – – –

– – – – – – –

– Absolute alcohol – – Citric acid – – Citric acid Glycine

62.4 75.7

3.7 1.41

40.4 0.72

– –

100nm /34.2nm 200nm /38nm

– –

– –

Glycine Citric acid

76.3 –

– –

60.8 –

34.8 1.11

- /35.8nm - /34.5nm

– 55

– –

Glycine Diethanolamine

combustion-based method which comprises a rapid self-sustained exothermic reaction between a metal nitrate (oxidizer) and a fuel resulting in the production of well-crystalline nanometric material [23,24]. Recently, the authors stated that SCS technique induces oxygen vacancies in the crystal structure of the combusted particles. Obtained results showed that magnetic and optical properties of the obtained products were improved as a result of structural defects such as oxygen vacancies [25,26]. In our previous work [27], it was observed that saturation magnetization of solution combustion synthesized Fe3O4 particles were enhanced up to 100 emus/g which was much higher than that of reported in the literature. Accordingly, it can be assumed that synthesizing Ni0.5Zn0.5Fe2O4 particles through SCS procedure could lead to the production of high antibacterial, high photocatalytic, and high magnetic nanopowders. During the past years, several authors have synthesized Ni0.5Zn0.5Fe2O4 powders by SCS method using a single-fuel system and the photocatalytic and magnetic properties of combusted nanopowders were studied [4,13]. It is documented that different fuels have different specifications which affect the SCS parameters, i.e. combustion mode, combustion temperature (Tc), ignition temperature (Tig), and the amount of exhausting gases, during the synthesis process [23,28–32]. These factors have a significant effect on the phase composition, oxygen vacancy, crystallinity, crystallite size, particle size, morphology, surface area, and physicochemical properties of the synthesized powders [25,27,28]. Given the benefits of using fuel mixtures in the case of many metal oxides [33–37], we believed that the use of a mixture of fuels (mixed-fuel system) instead of single fuel (single-fuel system) can enhance the magnetic, photocatalytic, and antibacterial properties of Ni0.5Zn0.5Fe2O4 particles. In the current study, Zn0.5Ni0.5Fe2O4 nanoparticles were solution combustion synthesized by varying the SCS parameters (fuel type and fuel to oxidizer ratio) to develop efficient photocatalytic and antibacterial Ni–Zn ferrite nanoparticles. Thermodynamic calculations were conducted along with the characterization of as-combusted Zn0.5Ni0.5Fe2O4 powders to gain a better understanding of the correlation between SCS parameters and their influence on the phase composition, crystallinity, saturation magnetization, and morphology of particles. Accordingly, solution combustion synthesis of Zn0.5Ni0.5Fe2O4 was carried out using glycine and urea at various fuel to oxidizer ratios i.e. φ= 0.8 (fuel lean condition), 1 (stoichiometric condition) and 1.4 (fuel rich condition). Both single-fuel and mixed-fuel (with the different molar proportion of fuels) systems were examined. Eventually, a comparative study was conducted on the obtained results. The photoactivity, bactericidal effect, and saturation magnetization of as-

prepared powders were compared with that of synthesized Zn0.5Ni0.5Fe2O4 nanopowders via SCS method and other prior techniques in the literature. 2. Experimental procedure 2.1. Preparation of Zn0.5Ni0.5Fe2O4 nanoparticles Ferric nitrate (Fe(NO3)3.9H2O, 98%), Zinc nitrate (Zn(NO3)2.6H2O, 99%), Nickel nitrate (Ni (NO3)3.6H2O, 98%), glycine (C2H5NO2, 99%) and urea (CO(NH2)2, 99.5%) were utilized as the starting materials. In order to study the effect of fuel type and fuel to oxidizer ratio on the combustion mode and combustion temperature and consequently final properties of the product, three systems were considered based on the following reaction, and combustion reactions were carried out:

0.5Ni(NO3) 2 + 0.5 Zn(NO3)2 + 2Fe(NO3)3 + x NH5 C2 O2 + y CH4 N2 O Ni 0.5Zn 0.5Fe2 O4 + (2 x+ y ) CO2 + +

9 x 4

5 x x + 2y H2 O+ 4 + y+ N2 2 2

3 y+ 10 O2 2

1. Glycine–Metal nitrates system: single-fuel system utilizing glycine as fuel, combustion reactions were conducted at φ = 0.8, 1 & 1.4. 2. Urea–Metal nitrates system: single-fuel system using urea as fuel, combustion reactions were performed at φ = 0.8, 1 & 1.4. 3. Glycine/Urea – Metal nitrates system: Complex fuels system utilizing mixture of urea and glycine with different molar proportions where molar proportion of urea to glycine were considered as follows: 1:3 (25% urea, 75% glycine), 1:1 (50% urea, 50% glycine), and 3:1 (75% urea, 25% glycine), combustion reactions were carried out at φ = 0.8, 1 & 1.4. According to reaction above, 0.5 mol zinc nitrate, 0.5 mol nickel nitrate, 0.5 mol ferric nitrate, x mol glycine, and y mol urea were dissolved in the minimum amount of distilled water (4 cc) and thoroughly homogenized by the stirrer. The x and y values were different based on the amount of fuel to oxidizer ratio as well as the system used. The obtained clear solution was transferred into a crucible and rapidly heated to 270°C as far as most of the water was evaporated, and the initial solution converted into a gel. Then, the combustion reaction ignited and propagated spontaneously throughout the precursor gel resulting in the formation of a solid product. As-combusted particles were denoted 2

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

2.4. Antimicrobial activity 2.4.1. Bacterial cell preparation Gram-negative bacterium Escherichia coli and gram-positive bacterium Staphylococcus aureus were utilized as the model organisms for exploration of antibacterial activity of synthesized Zn0.5Ni0.5Fe2O4 particles. S. aureus and E. coli were grown in nutrient broth (NB) culture medium overnight at 37 °C incubator. S2000 UV–Vis spectrophotometer was employed to measure the optical density (OD) of overnight culture at 630 nm. Subsequently, the overnight culture was diluted using NB medium to obtain an OD ranged between 0.08 and 0.1 (1.5 ×.106 CFU/ mL). 2.4.2. Assessment of cell viability Ni0.5Zn0.5Fe2O4 nanoparticles were dispersed in a solvent composed of deionized water, dimethyl sulfoxide (DMSO), and glycerol. 100 μL of obtained suspension with the desired concentrations of 250, 125, 62.5, 31.2, 15.6, 7.8, 3.9, and 1.95 ppm along with 100 μL of NB culture medium were inoculated in a microplate. The diluted overnight culture was then seeded into microplate containing nanoparticles and NB culture and incubated at 37 °C overnight. The microplates also contained control wells including culture media and bacterium. Bacterial growth was evaluated after 20 h by measuring the enhancement in absorbance at 630 nm by a Stat Fax-2100 ELIZER reader. All experiments were repeated three times for statistical study.

Fig. 1. The dependency of adiabatic and combustion temperatures on the fuel to oxidizer ratio.

as FxUyGz. The upper-case letters, i.e. F, U, and G are the abbreviation of fuel to oxidizer ratio (φ), urea and glycine, respectively, and x, y, and z are individually related to φ value and molar proportions of fuels. 2.2. Characterization

3. Results and discussion

X′ Pert PW 3040/60 X-ray diffractometer (XRD) using monochromatic Cu-Kα radiation was employed to characterize the phase evolution of synthesized powders. XRD patterns were quantitively analyzed by Rietveld method using X'Pert HighScore Plus 3.05 software. A USB4718 data acquisition module was utilized to monitor the reaction temperature-time profiles. FTIR spectra of the combusted product were explored by THERMO NICOLET AVATAR 370 Fourier transform infrared (FTIR) spectrometer in the range of 400-4000 cm−1. The microstructure and morphology of the prepared powders were studied by Mira 3-XMU field emission scanning electron microscopy (FE-SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) and CM120 Philips HOLLAND transmission electron microscopy (TEM). The particle size distribution of the synthesized particles was evaluated by Vasco3 Cordouan particle size analyzer (PSA). Magnetic properties of as-combusted nanoparticles were analyzed by MDKFT vibrating sample magnetometer (VSM) at room temperature. The Brunauer–Emmett–Teller (BET) method was used to determine the specific surface area and porous structure of composite particles by PHS-1020 surface area and pore size analyzer at 77 k when the sample was degassed at 250 °C for 5 h. UV–visible spectrophotometer (CECILL 8000 UV/VIS) was utilized to explore the electronic absorption behavior of nanoparticles. The spectrum was recorded in the wavelength ranged between 200 and 800 nm from the suspension of the samples using distilled water.

3.1. Thermodynamic aspects The standard enthalpy of reaction ΔH0f and adiabatic temperature (Tad) were calculated for the reactions at fuel lean (φ < 1), fuel rich (φ > 1), and stoichiometric (φ = 1) conditions utilizing available thermodynamic data in the literature [22]. Fig. 1 indicates the dependency of the adiabatic temperature and measured combustion temperature (Tc) on φ value. As seen from Fig. 1, the adiabatic temperature is highly affected by φ value, the molar proportion of fuels and fuel type. It can be observed that Tad is increased with the enhancement of φ value and reached its maximum at φ=1.4. Furthermore, it is noticed that regardless of the value of fuel to oxidizer ratio, increasing the molar proportion of glycine in the fuel mixture is led to the enhancement of the adiabatic temperature. From the thermodynamic point of view, glycine has more negative combustion heat (-1020.6 kJmole-1) comparing to urea (-750.9 kJmole-1) [3] which justify such Tad variation trend. However, as can be seen in Fig. 1, the variation trend of Tc is incompatible with that of Tad. Such incompatibility could be due to the incomplete oxidation of fuel at the experimental condition. Moreover, all combustion temperatures are lower than calculated adiabatic temperatures, which could be attributed to the fact that combustion reaction is not entirely adiabatic owing to the radiation and conduction losses. Note that at fuel-lean and fuel-rich conditions, the exhaust of gases with different amounts decreases Tc values. In order to perceive the effect of type and amount of fuel on the combustion synthesis mechanism, the thermal profile of synthesized particles at constant φ was studied. Fig. 2 exhibits the reaction temperature-time profiles of combusted powders at φ = 1. As can be observed in Fig. 2, initiation of the combustion reaction is postponed when urea was added to the fuel mixture. Alteration of the volume of exhausting gases, enthalpy of formation and exothermicity of the reaction due to the conversion of the single-fuel system into complex fuel system may be the leading reason for such postponement in the initiation of the combustion reaction. During the experimental procedure, reactions at fuel lean and stoichiometric conditions with the high molar proportion of urea were not ignited while reactions at fuel rich condition were combusted completely. Table 2 exhibits the ignition temperature and combustion temperature of all combustion reactions. According to Table 2,

2.3. Photocatalytic performance Methylene blue (MB) was considered as contaminant molecule to evaluate the photocatalytic activity of obtained Zn0.5Ni0.5Fe2O4 particles. The degradation process was performed under sunlight at ambient temperature. The dosage of Zn0.5Ni0.5Fe2O4 powder was set as follows: 0.001 gr of synthesized powder for 50 mL of 15 M methylene blue solution. Before irradiation, the MB solution was stirred in the dark for 30 min to prepare a well-dispersed solution and ensure the adsorptiondesorption equilibrium between catalyst surface and pollutant molecules. After irradiation at regular intervals, solution samples were analyzed by Cecil 8000 UV–vis spectrometer to determine the concentration of residual MB. 3

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 2. Temperature-time profile of combusted samples at φ=1 with different molar proportion of fuels. Table 2 Ignition temperature (Tig) and combustion temperature (Tc) of as-synthesized samples. Samples

Tig (°C)

Tc (°C)

F0.8U0G1 F0.8U1G3 F0.8U1G1 F1U0G1 F1U1G3 F1U1G1 F1U3G1 F1.4U0G1 F1.4U1G3 F1.4U1G1 F1.4U3G1 F1.4U1G0

142 150 148 162 143 162 188 148 165 175 229 325

291 476 476 1093 1190 1194 1200 478 512 610 612 864

combustion reaction at φ = 1.4 using urea is ignited at 325 °C while it is reported that decomposition of urea starts at 135 °C [38]. Accordingly, it can be inferred that part of urea eliminates from the system before the initiation of the combustion reaction. Consequently, at fuelrich condition, the excessive urea compensates the fuel deficiency and supplies the required energy for complete combustion reaction, whereas at fuel lean and stoichiometric conditions combustion reaction does not occur owing to the insufficient amount of urea. Three different combustion modes were observed during the experiments:

Fig. 3. The dependency of (a) combustion mode and (b) generation of exhausting gases on fuel to oxidizer ratio.

comparison with the smoldering and SHS–flaming modes. Fig. 3b indicates that increasing the fuel to oxidizer ratio enhanced the amount of exhausting gases which could lead to the formation of powders with small particle size [39]. 3.2. X–ray diffraction

a Flaming mode: reaction spontaneously initiated along with vigorous flame over the entire precursor media. b SHS – flaming mode: reaction initiated locally in a self-sustained manner propagating throughout the media with a weak flame. c Smoldering mode: reaction initiated along with the generation of a significant amount of gases. The flame was not detected in this mode.

Fig. 4(a-c) illustrates the phase composition of the synthesized particles at φ=0.8, 1, and 1.4, respectively. Results of the Rietveld refinement of XRD patterns including crystallite size, crystallinity percentage, estimation of phase constituents, volume, and lattice constant relating to Zn0.5Ni0.5Fe2O4 phase are reported in Table 3. According to XRD patterns as well as reported phase constituents in Table 3, combusted particles at φ=0.8 and 1.4 are composed of single-phase Zn0.5Ni0.5Fe2O4 (ICDD card No. 008-0234) while ZnO (ICDD card No. 01-0778-0191) phase is crystallized in the combusted samples at φ=1 as well as some of the synthesized samples at φ=1.4 as an impurity. Comparing XRD patterns with obtained combustion temperatures (Fig. 1 and Table 2) specifies that single-phase Zn0.5Ni0.5Fe2O4 nanoparticles is obtained at temperatures below 900 oC. Consequently, in the case of synthesized samples at φ=1, Zn0.5Ni0.5Fe2O4 phase could undergo partial decomposition due to the high combustion temperature

The dependency of the combustion mode, as well as the amount of exhausting gases on fuel to oxidizer ratio (φ), are indicated in Fig. 3a and Fig. 3b, respectively. Fig. 3a shows that regardless of the fuel type, combustion mode is strongly affected by the φ value. The mode of combustion changes from smoldering to flaming and then alter to SHS/ smoldering when φ value changes from 0.8 to 1 and 1.4, respectively. It can be noticed that combustion mode is affected by the combustion temperature as well. The flaming mode resulted in higher Tc in 4

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 4. XRD patterns of synthesized particles at (a) φ=0.8, (b) φ=1, and (c) φ=1.4.

(Tc > 1000 °C) leading to the evolution of ZnO phase. Note that in our recent work [40], it was specified that ambient oxygen interfered in the synthesis process resulting in the oxidation of the obtained product. Therefore, it can be concluded that interference of ambient oxygen during the synthesis process could be the other factor responsible for the presence of ZnO phase in combusted samples at φ=1 and φ=1.4 (F1.4U3G1 and F1.4U1G3 samples). According to Table 3, the estimated lattice parameters for synthesized Zn0.5Ni0.5Fe2O4 are a=b=c=8.39 A° demonstrating that these particles have cubic crystal structure which is in good agreement with that of reported in the ICDD card (8.399 A° ). It is essential to note that the crystallite size of combusted particles was strongly influenced by the φ value (Table 3). The crystallite size order of as-combusted Ni–Zn ferrite nanopowders is as follows: synthesized particles at φ=1 > synthesized particles at φ=1.4 > synthesized particles at φ=0.8. Several authors reported that reaction temperature plays an important role in controlling the

crystallite size; the higher temperature leads to higher crystallite size [41]. As explained earlier, Tc order of combusted powders was as follows: synthesized powders at φ=1 > synthesized powders at φ=1.4 > synthesized powders at φ=0.8 which justifies the variation trend of crystallite size of combusted nanopowders. 3.3. FTIR spectra As-synthesized Zn0.5Ni0.5Fe2O4 particles were analyzed by FTIR spectroscopy, and the observed absorption bands are summarized in Table 4. FTIR spectra of F0.8U0G1, F1U0G1, and F1.4U0G1 samples are shown in Fig. 5 to inspect the effect of fuel to oxidizer ratio on the phase composition of the prepared powder. According to Table 4, FTIR spectrum of all combusted samples displays two absorption bands in the ranges of 408 – 422 cm-1 and 549 – 573 cm-1 which are attributed to Mocta–O, and Mtetra–O bonds, respectively [42]. Furthermore, observed

Table 3 Results of the Rietveld refinement of XRD patterns. wt. % of observed phases Samples code

Crystallite size (nm)

Lattice constants (Å) a=b=c

Volume (Å3)

(Ni, Zn)0.5Fe2O4

ZnO

Amorphous Content (%)

Crystallinity (%)

F0.8U0G1 F0.8U1G3 F0.8U1G1 F1U0G1 F1U1G3 F1U1G1 F1U3G1 F1.4U0G1 F1.4U1G3 F1.4U1G1 F1.4U3G1 F1.4U1G0

10.6 9.1 8.9 31.3 36.2 58.3 37.4 12.4 20.2 22.0 22.4 19.5

8.36 8.38 8.38 8.36 8.37 8.40 8.41 8.40 8.39 8.39 8.40 8.36

585.82 589.00 588.37 585.21 586.10 593.45 595.25 594.54 591.42 591.79 591.93 586.22

61.50 60.45 51.00 51.70 59.53 67.45 58.22 41.19 61.13 53.72 52.57 74.42

– – – 9.37 7.57 9.00 4.05 – 2.0 – 3.1 –

38.50 39.55 49 38.93 32.90 23.55 37.73 58.81 36.87 46.28 44.33 25.58

61.5 60.45 51.0 61.07 67.1 76.45 62.27 41.19 63.13 53.72 55.67 74.42

5

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

to 1.4 enhanced the macro-porosity in the obtained powders using glycine (single-fuel system). However, in the complex fuel system, the macro-porosity of powder is decreased by increasing the φ amount (regardless of the molar proportion of fuels). Previous studies suggested that the amount of fuel (fuel to oxidizer ratio) has a significant effect on the amount of energy and gases generated during the combustion reaction [47]. As the φ increases, the amount of energy and exhausting gases increase as well. Based on the thermodynamic results (Table 2 and Fig. 1), Tc is raised to its maximum value by increasing the φ from 0.8 to 1 and then it is decreased by increasing the φ value to 1.4. It is worth noting that, although Tc is increased, the volume of exhausting gases is also increased. Therefore, high macro-porosity of combusted samples through the single-fuel system could be due to the generation of a large amount of gases. In the case of synthesized powders through mixed fuels system, employing urea along with glycine as well as enhancement of φ value increased the Tig in these reactions that induce loss of exhausting gases [28]. Therefore, high Tc alongside the loss of gases decreases the macro-porosity of particles. Despite the high magnification of FESEM images, the shape of the particles is difficult to discuss in detail. However, it can be observed that most of the synthesized samples contain particles with an irregular shape. Fig. 7(a-c) illustrates the EDS spectra of synthesized samples through system 1, i.e. F0.8U0G1, F1U0G1, and F1.4U0G1 sample, to explore the residual Carbon in the final product. As can be seen in Fig. 7, residual C is only presented in the combusted sample at φ=1.4 owing to incomplete oxidation of glycine resulted from insufficient oxidizer (metal nitrate). Fig. 8a and b depict the EDS spectra and elemental mapping of sample F1.4U1G0, respectively. As shown in Fig. 8a, Ni, Zn, Fe, and O ions are the only elements that present in as-prepared powder indicating the purity of the combusted sample. The elemental mapping results (Fig. 8b) demonstrate the homogenous distribution of ions throughout the as-synthesized ferrite nanoparticles. Moreover, the quantitative results imply that the composition of Zn, Ni, and Fe components that were initially dissolved in water is maintained in the final powder.

Table 4 Observed absorption bands from FTIR spectra of combusted powders. Sample

F0.8U0G1 F0.8U1G3 F0.8U1G1 F1U0G1 F1U1G3 F1U1G1 F1U3G1 F1.4U0G1 F1.4U1G3 F1.4U1G1 F1.4U3G1

Absorption Band (cm-1) Metal - O

N-H

O-H

C–H

411,565 408,573 409, 571 415, 570 412, 570 415, 559 415, 561 422, 570 411, 568 414, 555 413, 549

3180,3415 3243, 3439 – – – – – 1595 1595 1592 3195, 3321

1619 3432 3436 – – – – 3332 3338 3340 –

1384 1384 1384 – – 1383 1384 1398 1389 1384 –

3.5. Magnetic properties

Fig. 5. FTIR spectra of prepared powders at different fuel to oxidizer ratio (0.8, 1, and 1.4) using glycine.

Magnetization curves at room temperature and saturation magnetization (Ms) of the as-synthesized powders through systems 1-3 are indicated in Fig. 9a and b, respectively. As shown in Fig. 9a, all combusted particles display a narrow hysteresis loop revealing the soft magnetic behavior of the as-synthesized Zn0.5Ni0.5Fe2O4 nanoparticles [14]. Fig. 9b illustrates that Ms of synthesized samples at φ=0.8 is decreased from 40.4 emus/g to 30.8 emus/g with the enhancement of the molar proportion of urea in the fuel mixture which agrees with increasing of the amorphous content in these samples (Table 3). However, Ms value of combusted samples at φ=1.4 is enhanced (from 19 emus/g to 67 emus/g) when the molar proportion of urea in the fuel mixture is raised. According to Table 3, by enhancement of the molar proportion of urea in the fuel mixture, crystallinity of as-combusted powders at φ=0.8 and φ=1.4 is decreased and increased, respectively, which is in excellent agreement with the variation of Ms value in these samples [48]. In case of combusted samples at φ=1, Ms value of F1U0G1, F1U1G3, F1U1G1 samples is lower than that of sample F1U3G1 that might be due to the presence of more amount of non-magnetic phase (ZnO) in these samples [49]. Among all synthesized particles, F1.4U1G0 sample exhibits the highest saturation magnetization of 67 emus/g. Such Ms value could arise from its high crystallinity (74.4%) comparing to that of other samples. An overview of VSM results reveals that high Ms values (64 emus/g and 67 emus/g) achieved when the molar proportion of urea was higher than glycine in the fuel mixture. It is important to note that previous authors reported magnetization of 4.9 emus/g [12], 5 emus/g [22], and 56 emus/g [4] for the as-synthesized Ni0.5Zn0.5Fe2O4 particles which is lower than that of as-combusted Ni0.5Zn0.5Fe2O4 powders in this study.

absorption bands in the range of 1000 – 4000 cm-1 are related to the residual organics, i.e. O–H, N–H, and C–H bonds [43–45]. Fig. 5 illustrates that the presence of absorption bands corresponding to the residual organics in FTIR spectra of synthesized particles relies on the amount of fuel to oxidizer ratio. As can be observed in the figure, residual organics present in the combusted nanoparticles at φ=0.8 and 1.4, whereas no residual organics can be detected in prepared powders at φ=1. Note that presence of residual organics in the synthesized samples at fuel lean (φ = 0.8) and fuel rich (φ = 1.4) conditions could be related to the decomposition of excessive metal nitrates and fuel, respectively. According to our recent study [40], although ambient oxygen interferes in the synthesis process, the amount of interfered oxygen is not enough for complete oxidation of fuel at fuel rich conditions. This results in the presence of residual fuel in the final product. At fuel lean condition, lack of fuel leads to an incomplete combustion reaction of metal nitrates resulting in the presence of residual metal nitrate. 3.4. Microstructure FESEM images of synthesized powders through systems 1-3 are represented in Fig. 6(a-l), respectively. As shown in Fig. 6, all synthesized powders are macro-porous and highly agglomerated owing to the liberation of gases and generation of high combustion temperature (Fig. 1), respectively [27,46]. Comparing the FESEM images at variable φ values determines that improvement of fuel to oxidizer ratio from 0.8 6

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 6. FESEM images of synthesized nanoparticles at various fuel to oxidizer ratio utilizing single and mixed fuels.

3.6. Evaluation of the antibacterial performance

decreasing the concentration of Ni0.5Zn0.5Fe2O4 powders from 0.25 mg/ mL to 0.125 mg/mL increased the bactericidal effect of Ni–Zn ferrite particles against S. aureus bacterium (Fig. 10b). Several authors suggested that metallic nanoparticles exhibit antibacterial activity rely on their particle size as well as the structure and chemical composition of the cell wall of the bacterium [50]. Various mechanisms for the bactericidal effect of nanomaterials are reported in the previous studies. Generation of reactive oxygenated species (ROS) i.e. O•2 , HO•, and H2O2, from the surface of nanomaterials is the most accepted mechanism for the antibacterial action of nanomaterials [51,52]. These highly reactive species penetrate the cell wall of bacteria resulting in the cell devastation [53]. The release of oxidation cations such as Ni2+, Mn2+, Zn2+, Ag+, Fe3+, etc., from metal oxide nanoparticles, is reported as the corresponding mechanism for the antimicrobial action of ceramic nanoparticles against various microorganisms [54]. Another proposition maintains that strong electrostatic interactions between nanoparticles (particles having a size larger than 10 nm) and bacterial cells contribute to the bactericidal effects of nanomaterials [55,56]. The strong electrostatic interactions result in the accumulation of nanopowders on the outer surface of the bacterium plasma membrane leading to the surface tension. Such surface tension causes membrane depolarization, membrane disruption, leakage of the intracellular components, and cell death [57,58]. For a better understanding, the schematic of the different antibacterial mechanisms is represented in Fig. 11. Based on the above-said mechanisms, the desirable bactericidal effect of the synthesized Ni0.5Zn0.5Fe2O4 could arise from one or all of these mechanisms. Referring to Table 5, the average particle size of the samples is in excellent agreement with the mechanism mentioned above. It can be inferred that the accumulation of the synthesized Ni0.5Zn0.5Fe2O4 particles on the surface of the bacterium cell could be the leading factor for such antibacterial activity. In addition, the liberation of Ni2+, Zn2+, and Fe3+ ions from synthesized nanopowders might be another mechanism for such antimicrobial performance. However, further investigation is required to determine the exact mechanism relating to the antimicrobial activity of combusted Ni0.5Zn0.5Fe2O4 nanoparticles.

To explore the antibacterial activity of as-combusted Ni0.5Zn0.5Fe2O4 nanoparticles, E. coli and S. aureus was utilized as a bacterium. For this purpose, as-prepared single-phase Ni0.5Zn0.5Fe2O4 particles with high saturation magnetization (Ms ≥ 40 emus/g) i.e. F0.8U1G3, F0.8U0G1, F1.4U1G3, F1.4U0G1, and F1.4U1G0 samples, were considered as antibacterial samples. Moreover, the particle size distribution of selected samples was evaluated. Table 5 represents the average particle size of selected samples for antibacterial analysis. As can be observed in the Table, the particle size of the samples ranged from 11 nm to 30 nm. Such particle size distribution reveals that the selected samples could perform as antibacterial material. The antibacterial performance of as-synthesized samples against gram-negative bacterium E. coli and gram-positive bacterium S. aureus are illustrated in Fig. 10a and b, respectively. According to Fig. 10a, F0.8U1G3 sample displayed the highest inhibition rate of 100% at 0.25 mg/mL against E. coli bacterium. The highest inhibition rate of 100% against S. aureus bacterium is exhibited by F1.4U1G0 sample at the concentration of 0.125 mg/mL (Fig. 10b). Comparing the above results along with literature results showed that co-substitution of Zn and Ni components in the structure of ferrite positively enhanced the antimicrobial performance of Ni–Zn ferrite nanoparticles. Note that the inhibition rate of all synthesized Ni0.5Zn0.5Fe2O4 nanoparticles is higher than that of other metal substituted ferrites that reported in the literature [50]. Sanpo et al. investigated the bactericidal effect of synthesized transition-metal substituted cobalt ferrite nanoparticles via sol-gel route against E. coli and S. aureus bacteria [5]. Obtained results indicated that the antimicrobial activity of nickel-doped cobalt ferrite exhibited higher inhibition rate against both E. coli (70%) and S. aureus (90%) bacterium in comparison with zinc-doped cobalt ferrite (50% & 70%). It is important to note that the antibacterial activity of Ni0.5Zn0.5Fe2O4 nanoparticles highly depends on the concentration of nanoparticles as well as the particle size. According to Fig. 10a and b, the inhibition rate of E. coli bacterium is decreased when the concentration of Ni0.5Zn0.5Fe2O4 nanopowders decreased from 0.25 mg/mL to 0.125 mg/mL. However, 7

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 7. The EDS spectra of synthesized samples using glycine at (a) φ=0.8, (b) φ=1, and (c) φ=1.4.

Fig. 8. a) EDS spectra and (b) elemental mapping of F1.4U1G0 sample. 8

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 9. a) Magnetization curves at room temperature and (b) saturation magnetization value of all synthesized nanoparticles.

Fig. 10. Antibacterial performance of as-synthesized nanoparticles against (a) E. coli and (b) S. aureus bacterium.

Table 5 Particle size distribution of selected samples for antibacterial analysis. Sample

F0.8U0G1

F0.8U1G3

F1.4U0G1

F1.4U1G3

F1.4U1G0

Average particle size (nm)

18

11

27

26

30

According to Table 6, the energy band gap of all samples is about 2.2 -2.4 eV. Such narrow band gap indicates that these samples can absorb visible solar energy [59]. To evaluate the photocatalytic performance of the selected samples, methylene blue (MB) was utilized as the model dye. The photocatalytic experiments were carried out under sunlight irradiation utilizing 15 M methylene blue solution. Fig. 13a indicates the degradation percentage of MB via Ni0.5Zn0.5Fe2O4 powders as a function of irradiation time. As shown in Fig. 13a, the degradation percentage of MB by F0.8U1G3, F0.8U0G1, F1.4U1G3, F1.4U0G1, and F1.4U1G0 samples after 4 h of reaction is about 82%, 83%, 86%, 84%, and 85%, respectively, which is higher than that of reported (60%) for synthesized Ni0.5Zn0.5Fe2O4 particles by previous researchers [4]. With respect to the similarity of the degradation percentages, the kinetic analysis of removal of methylene blue was conducted to provide deeper insight through the photocatalytic performance of the samples. Fig. 13b represents the kinetic linear curves of the methylene blue's photocatalytic removal via as-prepared powders. It can be observed that the photocatalytic degradation rate of MB molecule follows the first-order kinetics model based on the following equation:

3.7. Photocatalytic degradation of methylene blue The selected samples for antibacterial analysis were also considered as photocatalyst samples to evaluate the photoactivity of obtained Ni0.5Zn0.5Fe2O4 nanoparticles. During the elimination process of contamination, molecules can be eliminated through adsorption and/or photocatalytic processes. Therefore, in order to evaluate the photoactivity of the selected samples, the optical properties of these samples were explored using UV–visible absorption spectroscopy, and the results represented in Fig. 12. As shown in Fig. 12, no sharp absorption peak attributing to Ni0.5Zn0.5Fe2O4 can be observed in the wavelength range studied in this investigation. Optical band gaps of the samples were estimated using the Tauc relationship. The value of optical band gap is illustrated as an inset in Fig. 12, as well. The observed energy band gaps of the selected samples are summarized in Table 6.

Ln C/C0 = -kt 9

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 11. Schematic of various possible mechanisms for antibacterial activity of synthesized powders.

photocatalytic reactivity of powders is affected by the crystallinity of the particles [60]. Referring to Table 3, the higher photocatalytic activity of F1.4U1G0 sample could be due to its high crystallinity (74.4%). It can be inferred that F1.4U1G0 is the most active sample rely on its high degradation rate and degradation percentage in comparison with the other synthesized samples. In addition, recent studies proposed that lattice distortion significantly improves the photocatalytic activity [61]. According to Table 3, the as-prepared F1.4U1G0 sample is lattice-distorted (lattice constant equal to 8.36 Å) which justifies its desirable photocatalytic efficiency. The absorption spectrum of F1.4U1G0 sample is presented in Fig. 13c. There is considerable degradation of MB dye (32%) under the dark condition. Such degradation percentages under the dark condition imply that MB molecules were mainly degraded through adsorption process on account of the high surface area and high crystallinity of this sample. After applying the sunlight, it can be inferred that both adsorption and photocatalytic processes were responsible for MB degradation in the presence of solar light. Based on the literature reviews, the photocatalytic activity of the nanoparticles attributes to the enhancement of photoinduced carriers (electron (e-) and hole (h+)) due to increasing of the separation efficiency via electronic interaction [4]. The sensitivity of Ni0.5Zn0.5Fe2O4 particles to daylight irradiation (narrow band gap-Table 6) forms the basis for degradation of dye molecules. During daylight irradiation, an electron is exited from VB to CB leading to the formation of electron-hole pair (photoinduced carrier). The generated photoinduced carriers move to the surface of nanoparticle resulting in the degradation of dye through the reaction between the photoinduced carrier and adsorbed species. The interactions between electron-hole pair and adsorbed species are presented below (equations (1)-(6)) to gain deeper insight into the degradation mechanism of methylene blue (MB). As can be seen, the reactions between photoinduced carriers ((e-) and (h+)) between H2O, O2, and OH result in the formation of free radicals, i.e. OH• and O•2 , which are responsible for the degradation of MB [4,62].

Fig. 12. UV–visible spectra of the selected samples for photocatalytic analysis. Table 6 Energy band gap of selected samples for photocatalytic analysis. Sample

F0.8U0G1

F0.8U1G3

F1.4U0G1

F1.4U1G3

F1.4U1G0

Energy band gap (eV)

2.2

2.3

2.4

2.4

2.4

Where C0 is the initial concentration of methylene blue (mg/l), C is the concentration of the MB at different interval times (mg/l), k is the reaction rate constant (mg/(l min)), and t is the sunlight irradiation time (min). According to Fig. 13b, the slope of curve fitting lines gives the rate constant for degradation of methylene blue. Accordingly, the degradation rate order of samples is as follows: F0.8U1G3 < F1.4U0G1 < F0.8U0G1 < F1.4U1G3 < F1.4U1G0 revealing that as-synthesized Ni0.5Zn0.5Fe2O4 nanoparticles using urea at φ=1.4 possesses the highest degradation rate in comparison with the other combusted nanopowders. Based on the literature reviews,

e + O2

O•2 + H2 O h+

+ OH

HO•2 10

(1)

O•2

+ H2 O

HO•2 + OH

H2 O2 +

(2) (3)

OH•

OH•

(4)

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

Fig. 13. (a) Degradation percentage of MB in the presence of synthesized samples, (b) kinetic linear curves of MB's photocatalytic removal via as-prepared powders, (c) absorption spectra of F1.4U1G0 sample, (d) nitrogen adsorption-desorption isotherm of synthesized F1.4U1G0 sample, and (e) TEM image of sample F1.4U1G0.

H2 O2

2 OH•

OH• + MB

CO2 + H2 O

(5)

Synthesized nanopowder shows a significant specific surface area of 150 m2/g (higher than that of reported in the literature) with an average pore diameter of 2.1 nm. It is documented that liberation of a large amount of reaction gases during the synthesis process results in the fragmentation of the large particles and enhances the surface area of the prepared powder [30–32,65]. As explained before, the mode of the combustion reaction related to F1.4U1G0 sample was smoldering with the liberation of a large amount of gases which justifies its significant surface area. Furthermore, the BJH pore size distribution which is depicted as an inset in Fig. 13d indicates that the obtained powder has

(6)

In order to give a deeper elaboration of such high MB degradation percentage by F1.4U1G0 sample, BET analysis was applied to this sample. Fig. 13d exhibits the nitrogen adsorption-desorption isotherm of synthesized F1.4U1G0 sample. According to the International Union of Pure and Applied Chemistry (IUPAC), the adsorption-desorption isotherm of the as-combusted sample is classified as type IV with H3 hysteresis loop revealing the mesoporous nature of particles [63,64]. 11

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

3.8. Oxygen vacancy evaluation

Table 7 The concentration of oxygen vacancies in the structure of synthesized samples. Sample

Total pressure of released gases from SCS chamber (Pa)

Ov,max (ξ * 10-5)

F0.8U0G1 F0.8U1G3 F0.8U1G1 F1U0G1 F1U1G3 F1U1G1 F1U3G1 F1.4U0G1 F1.4U1G3 F1.4U1G1 F1.4U3G1 F1.4U1G0

43497.3 44246.47 45172.05 29070.33 29722.72 30699.5 32223.18 34162.56 35295.51 36872.06 39298.43 43038.71

2.65391 2.65472 2.65567 2.63067 2.63176 2.63336 2.63578 2.63994 2.64163 2.64389 2.6472 2.65193

A recent study in 2019 by Kermani et al. indicated that SCS procedure results in the formation of oxygen vacancies in the synthesized powders which improves the physical and chemical properties [25]. This study also suggested that the amount of generated oxygen vacancies can be theoretically calculated through a thermodynamic model. In order to anticipate the magnetic, photocatalytic, and antibacterial properties of combusted Ni0.5Zn0.5Fe2O4 powders, the amount of generated oxygen vacancies in all synthesized particles were calculated using Kermani's model. The obtained results are presented in Table 7. As shown in the Table, at constant φ value, the higher amount of oxygen vacancies is generated in the combusted particles using a high molar proportion of urea (these samples are marked by star sign in the Table). Referring to Fig. 1, for each set of φ, the high molar proportion of urea generated the highest combustion temperature and subsequently resulted in the formation of high oxygen vacancy in the marked samples comparing to the other samples [27]. A brief comparison of the calculated oxygen vacancies with magnetic, photocatalytic, and antibacterial results is as follows:

Sample with maximum oxygen vacancy

*

*

*

pore size distribution ranged between 5 nm and 13 nm. Fig. 13e displays the TEM image of F1.4U1G0 sample. As shown in the figure, synthesized powders were agglomerated with irregular shape and average particle size of 30 nm. According to the literature reviews, small particle size, high surface area, and large pore diameter improve the photocatalytic performance, where large pore diameter of particles facilitate the surface diffusion of MB molecules (1.5 nm) and subsequently enhanced the degradation of dye molecule [13,60]. It can be inferred that substantial surface area (150 m2/g), small particle size (30 nm), high crystallinity, and desirable average pore diameter (2.1 nm) of F1.4U1G0 sample are the main factors responsible for its significant photocatalytic performance.

1. Theoretical calculations (Table 7) demonstrate that synthesized samples at φ < 1 should exhibit better magnetic behavior due to the presence of the higher amount of oxygen vacancies comparing to combusted samples at φ=1 and φ > 1. However, magnetic results indicated that synthesized samples at φ=1 and φ > 1 using the fuel mixture with the high molar proportion of urea displayed higher Ms value. Based on Kermani's model, although synthesized samples at φ < 1 have theoretically higher oxygen vacancies, decrement of reaction intensity at φ < 1 (smoldering mode-Fig. 3a) led to the

Fig. 14. Contour plots indicating the correlation between crystallinity percentage and particle size of synthesized nanopowders and a) degradation percentage of MB, b) photodegradation rate, and c) bactericidal efficiency. 12

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al.

formation of the lower amount of oxygen vacancies in these samples. 2. Among synthesized samples at φ=1 and φ > 1, F1.4U1G0 sample exhibited the highest Ms value which is in excellent agreement with the calculated oxygen vacancy generated in this sample. 3. Referring to antibacterial results, the sample with the highest oxygen vacancy (F1.4U1G0 sample) displayed a significant bactericidal effect against both E. coli and S. aureus bacterium in comparison with other samples. 4. According to the photocatalytic results, F1.4U1G0 sample displayed better photocatalytic activity comparing to the other samples. Such photocatalytic performance is in accordance with the amount of generated oxygen vacancies in this sample.

References [1] P. Priyadharsini, A. Pradeep, G. Chandrasekaran, Novel combustion route of synthesis and characterization of nanocrystalline mixed ferrites of Ni-Zn, J. Magn. Magn. Mater. 321 (2009) 1898–1903, https://doi.org/10.1016/j.jmmm.2008.12. 005. [2] M.K. Anupama, B. Rudraswamy, N. Dhananjaya, Investigation on impedance response and dielectric relaxation of Ni-Zn ferrites prepared by self-combustion technique, J. Alloy. Comp. 706 (2017) 554–561, https://doi.org/10.1016/j.jallcom. 2017.02.241. [3] A.V. Anupama, V. Kumaran, B. Sahoo, Steady-shear magnetorheological response of fluids containing solution-combustion-synthesized Ni-Zn ferrite powder, Adv. Powder Technol. 29 (2018) 2188–2193, https://doi.org/10.1016/j.apt.2018.06. 002. [4] M. Qasim, K. Asghar, B.R. Singh, S. Prathapani, W. Khan, A.H. Naqvi, D. Das, Magnetically recyclable Ni0.5Zn0.5Fe2O4/Zn0.95Ni0.05O nano-photocatalyst: structural, optical, magnetic and photocatalytic properties, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 137 (2015) 1348–1356, https://doi.org/10.1016/j.saa. 2014.09.039. [5] N. Sanpo, C.C. Berndt, C. Wen, J. Wang, Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications, Acta Biomater. 9 (2013) 5830–5837, https://doi.org/10.1016/j.actbio.2012.10.037. [6] S.K. Jesudoss, J.J. Vijaya, L.J. Kennedy, P.I. Rajan, H.A. Al-Lohedan, R.J. Ramalingam, K. Kaviyarasu, M. Bououdina, Studies on the efficient dual performance of Mn1–xNixFe2O4 spinel nanoparticles in photodegradation and antibacterial activity, J. Photochem. Photobiol. B Biol. 165 (2016) 121–132, https:// doi.org/10.1016/j.jphotobiol.2016.10.004. [7] M.U. Islam, T. Abbas, S.B. Niazi, Z. Ahmad, S. Sabeen, M.A. Chaudhry, Electrical behaviour of fine particle, co-precipitation prepared Ni-Zn ferrites, Solid State Commun. 130 (2004) 353–356, https://doi.org/10.1016/j.ssc.2004.02.019. [8] H.W. Wang, S.C. Kung, Crystallization of nanosized Ni-Zn ferrite powders prepared by hydrothermal method, J. Magn. Magn. Mater. 270 (2004) 230–236, https://doi. org/10.1016/j.jmmm.2003.09.019. [9] A.T. Raghavender, N. Biliškov, Ž. Skoko, XRD and IR analysis of nanocrystalline NiZn ferrite synthesized by the sol-gel method, Mater. Lett. 65 (2011) 677–680, https://doi.org/10.1016/j.matlet.2010.11.071. [10] M. Abbas, B.P. Rao, C. Kim, Shape and size-controlled synthesis of Ni Zn ferrite nanoparticles by two different routes, Mater. Chem. Phys. (2014) 1–9, https://doi. org/10.1016/j.matchemphys.2014.05.013. [11] S. Kumar, P. Kumar, V. Singh, U. Kumar Mandal, R. Kumar Kotnala, Synthesis, characterization and magnetic properties of monodisperse Ni, Zn-ferrite nanocrystals, J. Magn. Magn. Mater. 379 (2015) 50–57, https://doi.org/10.1016/j.jmmm. 2014.12.006. [12] C.C. Hwang, J.S. Tsai, T.H. Huang, Combustion synthesis of Ni-Zn ferrite by using glycine and metal nitrates - investigations of precursor homogeneity, product reproducibility, and reaction mechanism, Mater. Chem. Phys. 93 (2005) 330–336, https://doi.org/10.1016/j.matchemphys.2005.03.056. [13] T. Tangcharoen, A. Ruangphanit, W. Klysubun, W. Pecharapa, Characterization and enhanced photocatalytic performance of nanocrystalline Ni-substituted Zn ferrites synthesized by DEA-assisted sol-gel auto-combustion method, J. Sol. Gel Sci. Technol. 66 (2013) 387–398, https://doi.org/10.1007/s10971-013-3021-x. [14] A.S. Džunuzović, N.I. Ilić, M.M. Vijatović Petrović, J.D. Bobić, B. Stojadinović, Z. Dohčević-Mitrović, B.D. Stojanović, Structure and properties of Ni-Zn ferrite obtained by auto-combustion method, J. Magn. Magn. Mater. 374 (2015) 245–251, https://doi.org/10.1016/j.jmmm.2014.08.047. [15] R. Liu, H. Fu, H. Yin, P. Wang, L. Lu, Y. Tao, A facile sol combustion and calcination process for the preparation of magnetic Ni0.5Zn0.5Fe2O4 nanopowders and their adsorption behaviors of Congo red, Powder Technol. 274 (2015) 418–425, https:// doi.org/10.1016/j.powtec.2015.01.045. [16] S. Kumar, V. Singh, S. Aggarwal, U.K. Mandal, R.K. Kotnala, Synthesis of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite and study of its magnetic behavior at different temperatures, Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 166 (2010) 76–82, https://doi.org/10.1016/j.mseb.2009.10.009. [17] A. Bajorek, C. Berger, M. Dulski, P. Łopadczak, M. Zubko, K. Prusik, M. Wojtyniak, A. Chrobak, F. Grasset, N. Randrianantoandro, Microstructural and magnetic characterization of Ni0.5Zn0.5Fe2O4 ferrite nanoparticles, J. Phys. Chem. Solids 129 (2019) 1–21, https://doi.org/10.1016/j.jpcs.2018.12.045. [18] A. Thakur, P. Kumar, P. Thakur, K. Rana, A. Chevalier, J.L. Mattei, P. Queffélec, Enhancement of magnetic properties of Ni0.5Zn0.5Fe2O4 nanoparticles prepared by the co-precipitation method, Ceram. Int. 42 (2016) 10664–10670, https://doi.org/ 10.1016/j.ceramint.2016.03.173. [19] M.M. Rashad, D.A. Rayan, A.O. Turky, M.M. Hessien, Effect of Co2+ and Y3+ ions insertion on the microstructure development and magnetic properties of Ni0.5Zn0.5Fe2O4 powders synthesized using Co-precipitation method, J. Magn. Magn. Mater. 374 (2015) 359–366, https://doi.org/10.1016/jjmmm.2014.08.031. [20] K.H. Wu, T.H. Ting, C.I. Liu, C.C. Yang, J.S. Hsu, Electromagnetic and microwave absorbing properties of Ni0.5Zn0.5Fe2O4/bamboo charcoal core-shell nanocomposites, Compos. Sci. Technol. 68 (2008) 132–139, https://doi.org/10.1016/j. compscitech.2007.05.028. [21] C. Jiang, R. Liu, X. Shen, L. Zhu, F. Song, Ni0.5Zn0.5Fe2O4 nanoparticles and their magnetic properties and adsorption of bovine serum albumin, Powder Technol. 211 (2011) 90–94, https://doi.org/10.1016/j.powtec.2011.03.039. [22] C.C. Hwang, J.S. Tsai, T.H. Huang, C.H. Peng, S.Y. Chen, Combustion synthesis of Ni-Zn ferrite powder - influence of oxygen balance value, J. Solid State Chem. 178 (2005) 382–389, https://doi.org/10.1016/j.jssc.2004.10.045.

3.9. Contour plot presentation An alternative approach to present the correlation between powders characteristics and photocatalytic-antibacterial activity is to generate a contour plot. Fig. 14(a-c) illustrates the correlation between crystallinity percentage and particle size of powders with the degradation percentage, degradation rate of MB molecule as well as the bactericidal effect of synthesized Ni0.5Zn0.5Fe2O4 nanoparticles, respectively. As indicated in Fig. 14a, degradation percentage is influenced by both crystallinity percentage and particle size. The highest degradation is observed when the crystallinity and particle size are approximately ranged between 25 and 30 nm and 60%–70%, respectively. Fig. 14b shows that the degradation rate is more likely affected by crystallinity percentage rather than particle size in that higher crystallinity is led to higher degradation rate. Note that the optimum conditions given in Fig. 14b for the highest degradation rate is crystallinity percentage of ≥ 70% and 20-30 nm particle size. Fig. 14c implies that particle size is the leading factor that affects the bactericidal effect of synthesized nanopowders comparing to crystallinity percentage. The optimum conditions for high antibacterial activity are as follows: particle size < 18 nm and crystallinity percentage < 65%. 4. Conclusion Ni0.5Zn0.5Fe2O4 nanoparticles with high photocatalytic and antibacterial performance were synthesized by solution combustion synthesis (SCS) procedure using urea and glycine at various fuel to oxidizer ratio (φ = 0.8, 1, and 1.4). Experiments were carried out through single-fuel and complex fuel systems. Varying the SCS parameters, i.e. fuel type, φ value, and mixed fuels, determines the effect of SCS factors on physicochemical properties, bactericidal effect, and photocatalytic performance of obtained nanopowders. Obtained results indicated that the physical and chemical features of synthesized powders are influenced by SCS parameters (combustion temperature, combustion mode, and generation of gaseous products). These three factors were strongly affected by fuel to oxidizer ratio, fuel type, and fuel amount which subsequently overshadowed the final properties of prepared powders. Results of XRD, FTIR, EDS, and elemental mapping analysis implied that the formation of single-phase product relied on the φ value wherein the single-phase Ni0.5Zn0.5Fe2O4 obtained at φ=0.8 and some of the synthesized samples at φ=1.4. As-combusted Ni0.5Zn0.5Fe2O4 nanopowders exhibited promising saturation magnetization of 67 emus/g (without further sintering procedure) which was higher than that of synthesized Ni0.5Zn0.5Fe2O4 particle via SCS method by prior researchers. Photocatalytic evaluation of obtained nanoparticles exposed their remarkable photodegradation of methylene blue (85%). Antibacterial evaluation of particles indicated 100% growth inhibition with the minimum inhibitory concentration of 0.25 mg/mL and 0.125 mg/mL against E. coli and S. aureus bacterium, respectively. High specific surface area (150 m2/g), high crystallinity, and latticedistorted structure of synthesized particles are the leading factors for such photoactivity and antibacterial performance. 13

Ceramics International xxx (xxxx) xxx–xxx

H. Aali, et al. [23] H. qing Jiang, H. Endo, H. Natori, M. Nagai, K. Kobayashi, Fabrication and photoactivities of spherical-shaped BiVO4 photocatalysts through solution combustion synthesis method, J. Eur. Ceram. Soc. 28 (2008) 2955–2962, https://doi.org/10. 1016/j.jeurceramsoc.2008.05.002. [24] S. Mestre, M.D. Palacios, P. Agut, Solution combustion synthesis of (Co,Fe)Cr2O4 pigments, J. Eur. Ceram. Soc. 32 (2012) 1995–1999, https://doi.org/10.1016/j. jeurceramsoc.2011.11.044. [25] F. Kermani, S. Mollazadeh, J. Vahdati Khaki, A simple thermodynamics model for estimation and comparison the concentration of oxygen vacancies generated in oxide powders synthesized via the solution combustion method, Ceram. Int. 45 (2019) 904–909, https://doi.org/10.1016/j.ceramint.2019.04.053. [26] R. Ianoş, R. Lazəu, R.C. Boruntea, Solution combustion synthesis of bluish-green BaAl2O4: Eu2+, Dy3+ phosphors, Ceram. Int. 41 (2015) 3186–3190, https://doi. org/10.1016/j.ceramint.2014.10.171. [27] H. Aali, S. Mollazadeh, J.V. Khaki, Single-phase magnetite with high saturation magnetization synthesized via modified solution combustion synthesis procedure, Ceram. Int. 44 (2018) 20267–20274, https://doi.org/10.1016/j.ceramint.2018.08. 012. [28] K. Deshpande, A. Mukasyan, A. Varma, Direct synthesis of iron oxide nanopowders by the combustion Approach : reaction mechanism and properties, Chem. Mater. 16 (2004) 4896–4904, https://doi.org/10.1021/cm040061m. [29] P. Erri, P. Pranda, A. Varma, Oxidizer - fuel interactions in aqueous combustion synthesis . 1 . Iron ( III ) nitrate - model fuels, Indian Engi. (2004) 3092–3096. [30] R. Ianoş, M. Bosca, R. Lazǎu, Fine tuning of CoFe2O4 properties prepared by solution combustion synthesis, Ceram. Int. 40 (2014) 10223–10229, https://doi.org/10. 1016/j.ceramint.2014.02.110. [31] R. Ianoş, S. Borcǎnescu, R. Lazǎu, Large surface area ZnAl2O4 powders prepared by a modified combustion technique, Chem. Eng. J. 240 (2014) 260–263, https://doi. org/10.1016/j.cej.2013.11.082. [32] R. Ianoş, R. Bǎbuţǎ, R. Lazǎu, Characteristics of Y2O3 powders prepared by solution combustion synthesis in the light of a new thermodynamic approach, Ceram. Int. 40 (2014) 12207–12211, https://doi.org/10.1016/j.ceramint.2014.04.062. [33] R. Ianoş, Key-role of the recipe formulation in the solution combustion synthesis of monocalcium aluminate, CaAl2O4, Ceram. Int. 44 (2018) 21908–21913, https:// doi.org/10.1016/j.ceramint.2018.08.302. [34] R. Ianoş, R. Istratie, C. Pəcurariu, R. Lazəu, Solution combustion synthesis of strontium aluminate, SrAl2O4, powders: single-fuel versus fuel-mixture approach, Phys. Chem. Chem. Phys. 18 (2015) 1150–1157, https://doi.org/10.1039/ c5cp06240c. [35] R. Ianoş, I. Lazǎu, C. Pǎcurariu, P. Barvinschi, Solution combustion synthesis of MgAl2O4 using fuel mixtures, Mater. Res. Bull. 43 (2008) 3408–3415, https://doi. org/10.1016/j.materresbull.2008.02.003. [36] R. Ianoş, R. Lazău, S. Borcănescu, R. Băbuţă, Single-step combustion synthesis of YAlO3 powders, J. Mater. Sci. 50 (2015) 6382–6387, https://doi.org/10.1007/ s10853-015-9190-y. [37] R. Ianoş, An efficient solution for the single-step synthesis of 4CaO-Al2O3-Fe2O3 powders, J. Mater. Res. 24 (2009) 245–252, https://doi.org/10.1557/jmr.2009. 0019. [38] L. Stradella, M. Argentero, A study of the thermal decomposition of urea, of related compounds and thiourea using DSC and TG-EGA, Thermochim. Acta 219 (1993) 315–323, https://doi.org/10.1016/0040-6031(93)80508-8. [39] G. Chen, G. Song, W. Zhao, D. Gao, Y. Wei, C. Li, Carbon sphere-assisted solution combustion synthesis of porous/hollow structured CeO2-MnOx catalysts, Chem. Eng. J. 352 (2018) 64–70, https://doi.org/10.1016/j.cej.2018.07.003. [40] H. Aali, S. Mollazadeh, J.V. Khaki, Quantitative evaluation of ambient O2 interference during solution combustion synthesis process:considering iron nitrate – fuel system, Ceram. Int. (2019) 0–1, https://doi.org/10.1016/j.ceramint.2019.05.348. [41] M. Mozaffari, S. Manouchehri, M.H. Yousefi, J. Amighian, The effect of solution temperature on crystallite size and magnetic properties of Zn substituted Co ferrite nanoparticles, J. Magn. Magn. Mater. 322 (2010) 383–388, https://doi.org/10. 1016/j.jmmm.2009.09.051. [42] M. Sertkol, Y. Köseoǧlu, A. Baykal, H. Kavas, M.S. Toprak, Synthesis and magnetic characterization of Zn0.7Ni0.3Fe2O4 nanoparticles via microwave-assisted combustion route, J. Magn. Magn. Mater. 322 (2010) 866–871, https://doi.org/10.1016/j. jmmm.2009.11.018. [43] H. Aali, S. Mollazadeh, J.V. Khaki, Single-phase magnetite with high saturation magnetization synthesized via modified solution combustion synthesis procedure, Ceram. Int. (2018), https://doi.org/10.1016/j.ceramint.2018.08.012. [44] J. Zhao, J. Zhao, Y. Qian, X. Zhang, F. Zhou, H. Zhang, H. Lu, J. Chen, X. Wang, W. Yu, Solution combustion synthesis of calcium phosphate particles for controlled release of bovine serum albumin, Mater. Sci. Eng. C 50 (2015) 194–200, https:// doi.org/10.1016/j.msec.2015.02.006.

[45] J.H. Lopes, O. Mao, V. Machuca, I.O. Mazali, C.A. Bertran, Investigation of citric acid-assisted sol-gel synthesis coupled to the self-propagating combustion method for preparing bioactive glass with high structural homogeneity, Mater. Sci. Eng. C 97 (2018) 669–678, https://doi.org/10.1016/j.msec.2018.12.022. [46] H. Parnianfar, S.M. Masoudpanah, S. Alamolhoda, H. Fathi, Mixture of fuels for solution combustion synthesis of porous Fe3O4 powders, J. Magn. Magn. Mater. 432 (2017) 24–29, https://doi.org/10.1016/j.jmmm.2017.01.084. [47] Z. Cao, M. Qin, B. Jia, Y. Gu, P. Chen, A.A. Volinsky, X. Qu, One pot solution combustion synthesis of highly mesoporous hematite for photocatalysis, Ceram. Int. 41 (2015) 2806–2812, https://doi.org/10.1016/j.ceramint.2014.10.100. [48] M. Radpour, S.M. Masoudpanah, S. Alamolhoda, Microwave-assisted solution combustion synthesis of Fe3O4 powders, Ceram. Int. 43 (2017) 14756–14762, https://doi.org/10.1016/j.ceramint.2017.07.216. [49] M. Sertkol, Y. Köseoǧlu, A. Baykal, H. Kavas, A. Bozkurt, M.S. Toprak, Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles, J. Alloy. Comp. 486 (2009) 325–329, https://doi.org/10.1016/j.jallcom.2009.06.128. [50] R. Kumar, A. Umar, G. Kumar, H.S. Nalwa, Antimicrobial properties of ZnO nanomaterials: a review, Ceram. Int. 43 (2017) 3940–3961, https://doi.org/10.1016/ j.ceramint.2016.12.062. [51] H. Chen, C. Liu, D. Chen, K. Madrid, S. Peng, X. Dong, M. Zhang, Y. Gu, Bacteriatargeting conjugates based on antimicrobial peptide for bacteria diagnosis and therapy, Mol. Pharm. 12 (2015) 2505–2516, https://doi.org/10.1021/acs. molpharmaceut.5b00053. [52] H. Teymourinia, M. Salavati-niasari, O. Amiri, F. Yazdian, Application of green synthesized TiO2/Sb2S3/GQDs nanocomposite as high efficient antibacterial agent against E. coli and Staphylococcus aureus, Mater. Sci. Eng. C 99 (2019) 296–303, https://doi.org/10.1016/j.msec.2019.01.094. [53] H.J. Forman, M. Torres, Reactive oxygen species and cell signaling: respiratory burst in macrophage signaling, Am. J. Respir. Crit. Care Med. 166 (2002), https:// doi.org/10.1164/rccm.2206007. [54] W. Song, J. Zhang, J. Guo, J. Zhang, F. Ding, L. Li, Z. Sun, Role of the dissolved zinc ion and reactive oxygen species in cytotoxicity of ZnO nanoparticles, Toxicol. Lett. 199 (2010) 389–397, https://doi.org/10.1016/j.toxlet.2010.10.003. [55] G. Kasi, J. Seo, Influence of Mg doping on the structural, morphological, optical, thermal, and visible-light responsive antibacterial properties of ZnO nanoparticles synthesized via co-precipitation, Mater. Sci. Eng. C 98 (2019) 717–725, https://doi. org/10.1016/j.msec.2019.01.035. [56] L.L. Zhang, H. Bai, L. Liu, D.D. Sun, Dimension induced intrinsic physio-electrical effects of nanostructured TiO2 on its antibacterial properties, Chem. Eng. J. 334 (2018) 1309–1315, https://doi.org/10.1016/j.cej.2017.11.075. [57] V.K. Sharma, R.A. Yngard, Y. Lin, Silver nanoparticles: green synthesis and their antimicrobial activities, Adv. Colloid Interface Sci. 145 (2009) 83–96, https://doi. org/10.1016/j.cis.2008.09.002. [58] M. Arakha, M. Saleem, B.C. Mallick, S. Jha, The effects of interfacial potential on antimicrobial propensity of ZnO nanoparticle, Sci. Rep. 5 (2015) 1–10, https://doi. org/10.1038/srep09578. [59] R. Dom, R. Subasri, K. Radha, P.H. Borse, Synthesis of solar active nanocrystalline ferrite , MFe2O4 (M: Ca, Zn, Mg) photocatalyst by microwave irradiation, Solid State Commun. 151 (2011) 470–473, https://doi.org/10.1016/j.ssc.2010.12.034. [60] M.A. Ahmed, Synthesis and structural features of mesoporous NiO/TiO2 nanocomposites prepared by sol-gel method for photodegradation of methylene blue dye, J. Photochem. Photobiol. A Chem. 238 (2012) 63–70, https://doi.org/10. 1016/j.jphotochem.2012.04.010. [61] M. Nishikawa, S. Yuto, T. Nakajima, T. Tsuchiya, N. Saito, Effect of lattice distortion on photocatalytic performance of TiO2, Catal. Lett. 147 (2017) 292–300, https:// doi.org/10.1007/s10562-016-1928-x. [62] R. Tanwar, U.K. Mandal, Photocatalytic activity of Ni0.5Zn0.5Fe2O4 @polyaniline decorated BiOCl for azo dye degradation under visible light – integrated role and degradation kinetics interpretation, RSC Adv. 9 (2019) 8977–8993, https://doi. org/10.1039/C9RA00548J. [63] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report), Pure Appl. Chem. 87 (2015) 1051–1069, https://doi.org/10.1515/pac-2014-1117. [64] F. Kermani, S. Kargozar, Z. Tayarani-Najaran, A. Yousefi, S.M. Beidokhti, M.H. Moayed, Synthesis of nano HA/βTCP mesoporous particles using a simple modification in granulation method, Mater. Sci. Eng. C 96 (2019) 859–871, https:// doi.org/10.1016/j.msec.2018.11.045. [65] B. Pourgolmohammad, S.M. Masoudpanah, M.R. Aboutalebi, Effect of starting solution acidity on the characteristics of CoFe2O4 powders prepared by solution combustion synthesis, J. Magn. Magn. Mater. 424 (2017) 352–358, https://doi.org/ 10.1016/j.jmmm.2016.10.073.

14