Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films

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Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films M. Saroja a,⇑, M. Venkatachalam a, P. Gowthaman a, M. Sathishkumar b a b

Department of Electronics, Erode Arts and Science College, Erode, Tamilnadu, India Department of Electronics, Nehru Arts and Science College, Coimbatore, Tamilnadu, India

a r t i c l e

i n f o

Article history: Received 30 September 2019 Accepted 3 December 2019 Available online xxxx Keywords: Mn doped ZnS Sol gel technique antimicrobial activity Microorganisms photo catalytic degradation

a b s t r a c t The undoped and manganese (Mn) doped zinc sulphide (ZnS) thin film has been deposited on the glass substrate by sol gel dip coating method. The influence of different Mn concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 wt%) on the structural, morphological, element composition , functional group and optical properties were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, Fourier transmission infrared spectroscopy, UV–Visible spectroscopy and photoluminescence. In addition antimicrobial activity of as-deposited ZnS thin film has been evaluated by in vitro disk diffusion method against different microorganisms. Besides the photo catalytic degradation properties of methylene blue dye (MBD) and methyl orange dye (MOD) under UV light irradiation has been evaluated. From this investigation Mn doped ZnS thin film revelled excellent antimicrobial activity and photo catalytic degradation properties compare undoped ZnS thin film. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Nanoelectronics, Nanophotonics, Nanomaterials, Nanobioscience & Nanotechnology.

1. Introduction The past two decades in the field of science and technology semiconductor nanomaterials are widely attracted researchers due to their unique physical and chemical properties. Among all semiconductors, Zinc sulphide (ZnS) is an important II–VI group nontoxic semiconductor with hexagonal wurtzite and cubic zinc blende crystal structures with band gap energy of 3.5 eV and 3.7 eV respectively, high refractive index, high transmittance and low optical absorbance in the visible, infrared spectral range [1– 4]. Therefore ZnS thin film has been used in a variety of potential applications such as solar cells, optoelectronics, and ultraviolet light emitting diodes, flat panel displays, sensors, electroluminescent, antimicrobial activities and photo catalytic [5–9]. There are several physical and chemical techniques used to prepare ZnS thin films such as chemical bath deposition, thermal evaporation, microwave irradiation, spray pyrolysis, pulsed laser deposition, electron beam evaporation, sputtering, screen printed technique and sol gel dip coating technique and so on [10–18]. Among the all preparation method, the sol gel dip coating is a very simple

⇑ Corresponding author. E-mail address: [email protected] (M. Saroja).

method for preparing ZnS thin film due to low cost, smooth surface, perfect bonding and thickness control of the film [19–20]. The variety of transition metal doped ZnS semiconductors have been reported and it was utilized one of the important semiconductors in environmental applications like dye decolourization, antimicrobial, waste water treatment, dye removal and so on. The metal doped ZnS thin film reveals high electrons and holes in photo excitation, the high negative potential reduction of the excited electron in the conduction band in aqueous solution. Recently number of transient metal doped ZnS thin film such as Cu, Al, La, Ag, Ni and Eu revels excellent photo catalytic degradation for various organic pollutants dyes under visible and sunlight irradiation has been reported, especially Mn doped ZnS were found to improve photo catalytic degradation due to the synthesis method and doped concentration. In our earliest work, pure and different plant extract capped ZnS NPs and their antimicrobial activity and photo catalytic degradation properties were improved the organic pollutants dye degradation due to large particle size and narrow band gap and excellent, antimicrobial activity [21–25]. In this present research we reported, undoped and manganese (Mn) doped zinc sulphide (ZnS) nanocrystalline thin films with different concentration of Mn from (Zn1
x Mnx S) x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1 wt% were coated on the glass substrates by using sol gel dip coating technique. Further, the influence of

https://doi.org/10.1016/j.matpr.2019.12.009 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Nanoelectronics, Nanophotonics, Nanomaterials, Nanobioscience & Nanotechnology.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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Mn concentration on the crystalline structure, surface morphology, elemental compositions, optical properties, functional group, antimicrobial activity and photo catalytic degradation of asdeposited ZnS thin films has been investigated. 2. Experimental details 2.1. Preparation of undoped and Mn doped ZnS thin film Undoped and Mn doped ZnS thin films were prepared by using zinc sulphate (ZnSO47H2O), thiourea (NH2CSNH2), manganese sulphate (MnSO4H2O), ammonia (NH3), commercial glass substrate and deionized water. The entire materials are utilized as good analytic grade (Sigma Aldrich) without further purification. In a typical preparation of undoped ZnS thin film by mixing 1:1 M ratio of zinc sulphate (ZnSO47H2O) and thiourea (NH2CSNH2). 0.1 M of ZnSO47H2O was dissolved in 100 mL of deionized water and the solution treated 30 min continuous stirring (200 rpm) on magnetic stirrer at room temperature. At the same time 0.1 m of NH2CSNH2 dissolved in 100 mL of deionized water and the solution treated 90 min continuous stirring the NH2CSNH2 solution was added drop by drop and the final solution pH level were adjusted (pH = 10) by adding 21 mL of NH3 and the solution kept 60 min continuous stirring (200 rpm), the resultant homogeneous transparent solution was formed and it was subjected to slow evaporation at room temperature for 60 min. In as-doped ZnS thin film, the different concentrations (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) of MnSO4H2O was dissolved in 10 mL of deionised water and the solution treated 30 min continuous stirring (200 rpm). In the ZnSO47H2O solution prepared by the same experimental process presented above but before adding NH2CSNH2 solution and

NH3 solution different concentration (Zn1-x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1 wt%) of Mn solution was added drop by drop and the solution kept 90 min continuous stirring (200 rpm). Before the dip coating, the glass substrates (1.5  1.5 cm2) was cleaned by conventional method using chromium try oxide, acetone, and ethanol followed by isopropyl alcohol and deionized water in an ultrasonic baths and slides is dried 100 °C for 30 min. The pre cleaned substrates immersed vertically in a final ZnS solution for 5 min dip durations and dried 5 min at 90 °C, the above dip and dry process were repeated 10 times to improve the film thickness by using automatic dip coating unit with infrared dryer (Holmarc: HO-TH-02B) and the as-deposited thin films were annealed at 400 °C for 5 h to improve ZnS thin film crystalline. For comparative study the as-deposited ZnS thin film abbreviated as the following namely Mn doped (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 wt%) is ZnS, ZnS:Mn 2 wt%, ZnS:Mn 4 wt%, ZnS:Mn 6 wt%, ZnS:Mn 8 wt% and ZnS:Mn 10 wt%. Fig. 1 show the chemical abstract for preparation and application of undoped and Mn doped ZnS nanocrystalline thin film. 2.2. Characterization techniques The as-deposited ZnS thin films were successfully characterized by the following techniques. The crystal structure has been determined by X-ray diffraction techniques by (X’per PRO model) using Cu–Ka radiation (k = 1.54056 Å), at 40 keV in the 2h range of 10°– 80° with 0.1° step size, The as-deposited ZnS thin film formation, morphology and chemical composition of ZnS thin film were investigated by using JEOL JSM 840 SEM with 40 kV acceleration voltages. The Perkin Elmer UV/VIS/NIR (k = 19) spectrophotometer and Perkin Elmer LS 55 spectrometer use to analyse the optical

Fig. 1. Chemical abstract for preparation and characterization of undoped and Mn doped ZnS thin films.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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absorbance of the ZnS thin film recorded with a wavelength range 200–900 nm at room temperature and Photoluminescence spectra of the samples were recorded with a 40 W Xenon lamps. The bimolecular bonding and functional group were analysed by JASCO FT/ IR-6600 instrument with 400–4000 cm
1 spectral range. 2.3. Antimicrobial susceptibility test preparations In vitro disc diffusion method has been used to determine antimicrobial activity of prepared ZnS thin film against different microorganisms such as Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), Staphylococcus aureus (S. aureus) and two fungus culture Aspergillus niger (A. niger), Candida albicans (C. albicans), all the microorganisms was obtained from microbial type culture collection (MTCC) institute of microbial technology, India and the Mueller Hinton agar plates (MHA) obtained from Hi media Mumbai. All the stock culture maintained 4 °C on slopes of nutrient agar, Before transfer stock culture in to MHA plate treated different purification process such as 15 mL of molten media poured in to sterile plates and allow 5 min to solidify and optical density of plates corresponding to 2.0  106 colony forming units (CFU/ml) for bacteria and plate were incubated without agitation for 24 h at 37 °C. The 0.1% of stock cultures was swapped to surface pf MHA plate and allowed 5 min to dry, Than 60 mg/disc is placed in to plate surface and each disc have 6 mm width. The as-deposited ZnS thin film solution (thin film with active area dissolved (1.2  1.5 cm2) in 5 mL of deionized water for comparison evaluation) were loaded all disc surface with different concentration and allow 5 min to diffuse, then the diffused MHA plates were kept Incubation at 37 °C for 24 h during the incubator zone of inhibition (Zol) was formed around the disc, transparent millimetre ruler use to determine Zol [26]. 2.4. Photo catalytic experimental setup The photo catalytic activity of as-deposited ZnS thin film was evaluated by the MBD and MOD degradation under UV light supplied by the 120 W high-pressure mercury lamp irradiation, the lamp was kept 10 cm distance between the liquid surfaces [25]. Then the as-deposited thin film with active area (1.5  1.5 cm2) of photo catalyst was added in 100 mL (1  10
5 M) of MBD and MOD aqueous solution for comparative and mixture was stirred in the dark for 30 min to attain equilibrium condition on the catalyst solution and it was kept continuous stirring (300 min)

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(120 rpm) throughout process of experiment, at regular time intervals (30 min), 3 mL of aqueous suspensions (MBD and MOD) was taken from the mixture and analyse concentration of degradation by using a Perkin Elmer UV/VIS/ NIR (k = 19) spectrophotometer at wavelength of 622 nm for MBD and 460 nm for MOD respectively. The degradation efficiency (%) = (C0
C) / C0  100%. Here the suspensions concentration is C of dye at each irradiated time interval. C0 is the initial concentration of dye. 3. Result and discussion 3.1. Crystalline structures Fig. 2(A) and (B) shows the XRD pattern of undoped and Mn doped ZnS thin film with different doping concentration, it can be seen that all as-deposited sample exhibit three major diffraction peaks at 2h equal to 28.56°, 47.96° and 55.66° are corresponding to (1 1 1), (2 2 0) and (3 1 1) reflection plane, it shows that there is no other impurity peaks can be observed by different doping of Mn concentration and all the samples were exhibit cubic structures and it is matched with ICDD powder diffraction file 80-0020. The analysis of Mn doped (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 wt%) ZnS thin film, the major peak corresponding to the (1 1 1) plane was slightly increased with dopants concentrations. The results shows that the diffraction peak in the range of 28.56° were studied and the samples indicates that the peak of undoped ZnS and ZnS:Mn wt% were no changes, but in the ZnS: Mn 4 wt% to ZnS:Mn 10 wt% peaks were slightly shifted towards the lower angles with increasing Mn doping concentrations it is indicate that interplanner spacing is increased, to compare with undoped ZnS and the Mn doped Zinc lattice parameter was decreased a = b = 4.391 (Å) to 4.345 (Å) which indicate Mn ionic (0.53 Å) are added in the host lattice of zinc (0.74 Å) because the smaller ionic radius of Mn. Moreover to compare all as-deposited thin films, the crystallite size increases with increase Mn concentrations up to ZnS:Mn wt% and further Mn concentrations is increase, crystallite size were decrease at ZnS:Mn 8 wt% and ZnS: Mn 10 wt%. Specially ZnS:Mn 6 wt% nanocrystals exhibits large lattice plane to compare all other samples due to Mn ions have sufficient energy to absorb zinc ions to form a good crystallite size during the annealing process. The average crystallite from Debye–Scherrer’s equation and is given in Table 1.

D ¼ 0:9k=ðbcoshÞ

ð1Þ

Fig. 2. (A) XRD patterns of undoped and Mn doped ZnS thin films.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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Table 1 Calculated average crystallite size and lattice parameters of ZnS thin films with different Mn concentrations. ZnS concentration with Mn (wt%)

2h (hkl)

0 2 4 6 8 10

28.56(1 1 1) 28.56(1 1 1) 28.45(1 1 1) 28.45(1 1 1) 28.45(1 1 1) 28.45(1 1 1)

D spacing

3.3871 3.3869 3.3870 3.3866 3.3865 3.3868

FWHM (Radian)

0.2053 0.1984 0.1784 0.1574 0.1683 0.1694

Lattice constants Lattice a (Å)

Parameter b (Å)

4.8758 4.8829 6.0381 6.3067 6.0732 5.9989

3.2453 3.2496 2.9853 2.4784 2.0916 1.9743

Average crystallite size (nm)

41.75 43.12 47.96 54.36 50.82 50.51

Fig. 3. SEM image of undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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where D is the mean of crystallite size, 0.9 is the constant shape factor, k = 1.54056 Å is represents the wavelength of incident beam Cu–Ka, b is a full width at half maximum and h is the diffraction angle in radian.

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gradually by increasing doping Mn concentration due to substitution of Mn into Zn lattice. Table 1 shows the different atomic ratio of ZnS thin films with different Mn concentration. 3.3. Function group analysis

3.2. Surface morphology and composition analysis Surface morphology of as-deposited ZnS thin film has been studied by SEM. The different doping concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) of Mn induced observable changes in surface morphology it was shown in Fig. 3(a)–(f). The results show the as-deposited ZnS thin film consists of fine homogeneous, smooth and dense, grain size, high film coverage and no cracks on the substrate. The random distributed angular shaped grains were formed in undoped ZnS surface and Mn concentration is increased the grain sizes of the film also increase due to agglomeration effect. The grain size of ZnS thin films was increase up to ZnS:Mn 6 wt% it shown in Fig. 3(a)–(d) further, when increasing Mn concentration 8% and 10% grain sizes were decreased due to grains dissolve and porosity in film surface and it was covered spherical shaped structure. Generally the grain size was varied due to growth of grain boundaries by the different factors like nature of the precursor, type, concentration of the solvent, doping concentration and annealed temperature. The chemical composition of as-deposited ZnS thin film samples was analysed by using energy dispersive X-ray (EDX). Fig. 4 (a)–(f) shows the EDX spectra of undoped and Mn doped ZnS thin film with different concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1)respectively, the undoped ZnS thin film contain well defined EDX spectra corresponding to Zn and S composition without presence of any other impurity. Fig. 4(b)–(f) shows the different concentration of Mn doped ZnS thin film it showed well defined fine peaks corresponding to Zn, Mn and S concentration, Beside the Mn doping concentration increase the intensity of the EDX peaks also increased. However, the ratio of Zn/S decreased

The different functional group analysis of as-deposited ZnS thin film was investigated by using Fourier transforms infrared spectroscopy is shown in Fig. 5. All the as-deposited ZnS thin film the several peaks observed at 510, 612, 903, 1086, 1425, 1524, 2219 and 3040 cm
1. The peaks appearing at 510 and 612 cm
1 stretching vibration of Zn–S bond, the peak at 903 and 1086 cm
1 observed corresponding to the stretching of (C–C) due to alkenes and (C–O) with epoxy, amino acids. In undoped ZnS thin film the peak at 1425 cm
1 corresponding to bending vibration of (O–H) but all the Mn doped ZnS thin film O–H bending slightly shifted to 1524 cm
1 due to the presence of hydroxyl. The peak at 2219 cm
1 corresponding to bending vibration of CO2 stretching and broad absorbance peaks at 3040 cm
1 corresponds to (O–H) bonding. From this result, all the Mn doped ZnS thin film presence the same absorbance peaks which is presented in undoped ZnS but the peak intensity was increased with increase Mn concentration, from the result ZnS:Mn 6 wt% thin film having strong bonding with all functional group [27]. 3.4. Optical properties Optical properties of undoped and Mn doped ZnS thin film coated on the glass substrate was investigated from the absorbance wavelength range of 200–900 nm. Fig. 6(a) shows the optical absorbance of as-deposited ZnS thin film with different concentration Mn (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) concentration at 473 °C its absorbed strong peaks wavelength from 300 to 400 nm and low absorption peaks appeared at wavelength above 400 nm. The strong absorption peaks of as-deposited thin films

Fig. 4. EDX pattern of undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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Fig. 5. FTIR spectra of undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

Fig. 6. (A) UV absorption and (B) band gab energy of undoped and Mn doped ZnS thin films.

were 329, 336, 339, 324, 341, 346 nm for the undoped , ZnS:Mn 2 wt%, ZnS:Mn 4 wt%, ZnS:Mn 6 wt%, ZnS:Mn 8 wt%, and ZnS:Mn 10 wt% respectively, The result shows absorption edge shifted (red shifted) towards higher wavelength depending on the doping concentration of Mn. However at the ZnS:Mn 6 wt%, The absorption edge was shifted (blue shifted) towards lower wavelength to compare all other as-deposited ZnS thin film due to surface roughness of the film, electron excitation from valance band to conduction band and nature band gap value of Mn. The band gap energy of as-deposited ZnS thin films was estimated by using Tauc’s plots its relation between absorption coefficient and photon energy [28].

aht ¼ Aðht
EgÞn

ð2Þ

Where ‘a’ is an absorption coefficient, ‘ht’ is the photon energy, ‘A’ is a constant for mass reduced charge carriers and refractive index of the materials, ‘h’ is Plank’s constant, Eg is the band gap energy between the valance band and conduction band, ‘n’ is a parameter associated with direct and indirect electron band transition which equal to the value of ½ or 1/3. The estimated band gap value of undoped ZnS thin film was calculated 3.76 eV it is slightly higher than bulk ZnS in cubic structure (3.6 eV) Fig. 6(b), when increasing doping concentration of Mn up to 4% the band gap energy was decreased 3.76–3.65 eV due to decreasing absorbance peaks slightly shifted at high absorption wavelength, but in the ZnS:Mn 6 wt% thin film band gap was increased 3.82 eV it is higher than to compare all the as-deposited ZnS thin film due to large

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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variation in crystalline size and decreased absorption wavelength. In addition when Mn concentration is increased at 8% and 10% the band gap of the film decreased from 3.63 to 3.58 eV due to reduced crystalline size and estimated band gap energy of as-deposited ZnS thin film as shown in Table 2. 3.5. Photoluminescence properties Fig. 7 shows the photoluminescence (PL) properties od undoped and Mn doped ZnS thin film undoped and Mn doped ZnS thin film with an excitation wavelength of 330 nm, generally crystalline size, shape, surface of the crystal has an important role in photoluminescence emission properties. The undoped ZnS thin film exhibited broad symmetrical emission peak at 413 nm it is well known due to the recombination of holes and electron from the surface of Zn and S vacancy in the ZnS lattice related to the donor of the valance band. The PL spectra shows, different concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) of Mn doped ZnS thin films exhibits two strong emissions peaks at 424 and 578 nm which conform the formation of ZnS and Mn ions on the zinc lattice.

All the Mn doped ZnS thin film samples exhibits blue emission of broad peaks approximately at 418–423 nm which indicates the same luminescence characterization properties of undoped ZnS thin film and the second strong emission peak exhibits at 578 due to Mn ions distribution in the zinc lattice [29]. From the PL spectra increasing the Mn concentration, the intensity peaks are decreased at 418–423 nm, on the other hand, peaks which exhibit at 578 nm also increased. When Mn doping concentration is increased the distribution of Mn ions in the ZnS host lattice is increased. High PL emission was observed in ZnS:Mn 6 wt% due to high surface area, large particle size, good formation of cubic structure and nature luminescence properties of Mn. Further increasing Mn concentration at 8% and 10% the peak intensity was decreased due to high concentration of Mn ions may isolate on the zinc lattice. 3.6. Antimicrobial activities The antimicrobial activity of undoped and Mn doped ZnS thin films were evaluated by measuring the zone of inhibition with various concentrations (40, 50 and 60 lg/mL) against all the tested

Table 2 The element compositional of ZnS thin films with different Mn doping concentrations. ZnS concentration with Mn (wt%)

Zn Content %

Mn Content %

S Content %

Total %

Film thickness (nm)

Band gab energy (eV)

0 2 4 6 8 10

50.38 48.92 47.96 46.56 45.42 44.97

0.00 1.72 2.97 4.71 6.16 6.89

49.62 49.36 49.07 48.73 48.42 48.14

100 100 100 100 100 100

328 367 393 424 408 412

3.76 3.69 3.65 3.82 3.63 3.58

Fig. 7. PL spectra of undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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formed high zone oh inhibition against A. niger (12 ± 0:1mm), C. albicans (11  0:2mm), E. coli (11  0:1mm), B. subtilis (10  0:1mm), S. aureus (10  0:2mm) followed by and P. aeruginosa (06  0:1mm) from the starting concentration C. albicans has lead zone of inhibition to compare other microorganisms. At 6% Mn doped ZnS thin film zone of inhibition was formed against C. albicans (14  0:2mmÞ, E. coli (13  0:1mm), S. aureus (13  0:2mm), A. niger (13  0:1mm) followed by B. subtilis (12  0:1mm), and P. aeruginosa (10  0:1mm) at concentration of 60(lg/mL) from the starting concentration C. albicans has lowest zone of inhibition compare to other microorganisms but in the final concentration it is lead the zone of inhibition due to large crystal size. At 8% and 10% of Mn doped ZnS thin films zone of inhibition was formed against S. aureus (16  0:2mm), A. niger (15  0:1mm), C. albicans (15  0:2mm), E. coli (14  0:1mm), B. subtilis (13  0:1mm), and P. aeruginosa (13  0:1mm) and C. albicans (18  0:2mm), S. aureus (17  0:2mm), A. niger (16  0:1mm), E. coli (16  0:1m), B. subtilis (15  0:1mm), P. aeruginosa (15  0:1mm) at concentration of 60 lg/mL respectively, from the starting concentration C. albicans and S. aureus has high zone of

microorganisms by in vitro disc diffusion method using MHA plates. The antimicrobial activity of as-deposited ZnS thin film were compared with two gram negative and two gram positive bacterial cultures such as Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli), aueeus fungus culture such as Aspergillus niger (A. niger) and Candida albicans (C. albicans) with a different concentration it was clearly shown in Table 3 and Fig. 8 The undoped ZnS thin film were observed high zone of inhibition against C. albicans (09 ± 0.1 mm), S. aureus (08 ± 0.1 mm) and B. subtilis (07 ± 0.3 mm), E. coli (07 ± 0.2 mm) followed by A. niger (06 ± 0.1 mm) and P. aeruginosa (05 ± 0.1 mm) at concentration of 60 lg/mL from this result the concentration of undoped ZnS is increased and the zone of inhibition also increased. At 2% Mn doped ZnS thin film highest zone of inhibition was formed against C. albicans (10 ± 0.2 mm), S. aureus (09 ± 0.2 mm0, E. coli (09 ± 0.1 mm) followed by B. subtilis (08 ± 0.1 mm), A. niger (08 ± 0.1 mm) and P. aeruginosa (07 ± 0.1 mm0 at concentration of 60 lg/mL, from the starting concentration C. albicans has lead highest zone of inhibition to compare other microorganisms. At the concentration of (60 lg/mL) and 4% Mn doped ZnS thin film Table 3 Shows the inhibition zone of ZnS thin films with different Mn doping concentrations. Samples/Concentrations (mg/mL)

Gram negative bacteriaInhibition zone (mm) P. aeruginosa

Undoped ZnS 2 wt% 4 wt% 6 wt% 8 wt% 10 wt%

E. coli

Gram positive bacteriaInhibition zone (mm) B. subtilis

S. aureus

FungiInhibition zone (mm) A. niger

C. albicans

40

50

60

40

50

60

40

50

60

40

50

60

40

50

60

40

50

60

02 04 06 08 09 09

03 05 08 08 11 12

05 07 09 10 13 15

04 05 06 08 10 10

06 07 09 09 12 13

07 09 11 13 14 16

04 06 06 07 08 08

05 07 08 11 11 12

07 08 10 12 13 15

04 05 07 08 12 12

06 07 08 11 13 14

08 09 10 13 16 17

02 04 07 08 11 13

04 06 09 11 12 15

06 08 12 13 15 16

04 06 07 07 12 13

05 07 09 13 14 15

09 10 11 14 15 18

Fig. 8. The bar diagram for undoped and Mn doped ZnS thin films against different microorganisms.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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inhibition to compare other microorganisms. From this investigation, al the Mn doped ZnS thin film has excellent one of inhibition against gram negative, gram positive bacteria and fungus culture in various concentration to compare undoped ZnS thin film. The maximum zone of inhibition was formed against all microorganisms due to cell structure because the cell structure of both bacteria is different. The gram positive bacteria has a single thick cell wall made by peptide glycan of 20–80 nm. The gram negative bacteria have two thin layered cell walls made by lippolysaccharide layer and peptide glycan layer about 20–80 nm. Peptide glycan layer is very thin to compare gram positive layer and also it consists of repeated unit of amino acids and carbohydrate. Her the as-deposited ZnS thin films were discharged Zn and Mn ions and react with amide phosphate, carboxyl in the protein of cell membrane and continuously disrupting the cell process of the bacteria and family broke the cell wall and stop the cell growth and formed inhibition zone around cell wall. The inhibition zone of C. albicans and A. niger fungus culture also investigated from the result C. albicans has formed maximum inhibition to compare A. niger because all as-deposited ZnS thin films were easily affected and penetrate the fungus cell membrane, The Mn doped ZnS thin films have high antimicrobial activity to compare undoped ZnS thin film due to small particle size and large surface area. When the Mn doping concentration is increased due to the large surface area and crystalline size of the film and it is exhibits high Mn and Zn ions discharge. 3.7. Photo catalytic activities Photo catalytic degradation properties of undoped and Mn doped ZnS thin film with different concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) are coated on the glass substrate with annealing temperature at 473 °C were evaluated by measuring degradation of methylene blue dye, methyl orange

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dye under UV light irradiation for 300 Min and pH of aqueous solution (MBD and MOD) was maintained at 7. To evaluate the efficiency of MBD under UV light irradiation without adding any photo catalyst, the results show that both dyes degrade 2% after 300 min irradiation. Fig. 9 shows the degradation efficiency of MBD for undoped and Mn doped ZnS thin film (active area 1.5  1.5 cm2) with different concentration at each 30 min time interval for 300 min visible light irradiation. The photo degradation efficiency of undoped ZnS, ZnS:Mn 2 wt% , ZnS:Mn 4 wt%, ZnS:Mn 6 wt%, ZnS:Mn 8 wt%, ZnS:Mn 10 wt% is 81, 83, 85, 91, 87, and 89% Respectively after the 300 min of visible light irradiation. From the result efficiency of the degradation was increased approximately 10% at each 30 min time interval it can be seen that the degradation efficiency was increased with increasing irradiation time. In this result, the degradation efficiency of MBD is increased with increasing Mn concentration up to 6% (ZnS:Mn 6 wt%) beyond 6% the degradation efficiency was decreased with increasing Mn concentration at 8% and 10% due to the over concentration of Mn can cause agglomeration of photo catalyst which can reduce the active surface area for light absorption. Over all as-deposited ZnS thin film, the ZnS:Mn 6 wt% have excellent degradation efficiency to compare all as-deposited ZnS thin film due to high surface area, large particle size [30]. Fig. 10 shows MOD degradation of as-deposited ZnS thin film (active area 1.5  1.5 cm2) for 300 min visible light irradiation. The degradation efficiency of undoped ZnS, ZnS:Mn 2 wt% , ZnS: Mn 4 wt% , ZnS:Mn 6 wt%, ZnS:Mn 8 wt%, and ZnS:Mn 10 wt% is 87, 90, 91, 96, 93 and 90% after 300 min visible light irradiation respectively. The result shows efficiency of the degradation is increased approximately 10% up to 240 min with 30 min time interval. It can be observed that degradation efficiency of MOD is increased with increasing Mn concentration up to 6% (ZnS:Mn 6 wt%) due to generation of photon on the surface, large particle size, beyond 6% the degradation efficiency was decreased with

Fig. 9. Photo catalytic degradation efficiency of MBD using undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009

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M. Saroja et al. / Materials Today: Proceedings xxx (xxxx) xxx

Fig. 10. Photo catalytic degradation efficiency of MOD using undoped and Mn doped ZnS thin films with different concentration (a) Undoped (b) 2% (c) 4% (d) 6% (e) 8% (f) 10%.

increasing Mn concentration at 8% and 10% due to reduction of active surface area for photo catalyst. Generally, in the photo catalytic activity, the degradation process depends on the number of electron and holes pair on the photo catalyst surface during the irradiations the electron from the valance band (VB) will excite to the conduction band to increase (CB), electron hole pairs, a good photo catalyst act the adequate separation of electron and holes pair during the photo generation, the holes of the valance band react with surface of the MBD and MOD bounded, react with water (H2O) or Hydroxyl groups (OH–) and generate hydroxyl radical (OH) electrons reduced the MBD and MOD molecular oxygen to superoxide molecule to exert the degradation [31–32]. In this investigation of ZnS:Mn 6 wt% exhibits excellent degradation efficiency to compare all other as-deposited ZnS thin film due to large and specific surface area, crystallite structure, band gap and high luminescence properties. 4. Conclusion Undoped and Manganese (Mn) doped ZnS thin film were successfully coated on the glass substrates with different concentration (Zn1
x Mnx S) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) by using sol gel dip coating technique and all the samples annealing temperature at 473 °C for 5 h. All the as-deposited ZnS thin film reveals that formation of cubic crystalline structure and average crystalline size was calculated (41.75–50.51 nm), surface morphology of the film was formed smooth nano crystalline surface with different size and chemical composition were conform the elements of Zn, S and Mn without any other impurities, the different functional group were conformed from all the as-deposited ZnS thin films it is significantly increased with increasing Mn doping concentration. The optical band gap energy of as-deposited ZnS thin films were

calculated and it was decreased 3.76 to 3.58 eV and high photoluminescence emission were absorbed from all the samples, but in the ZnS:Mn 6 wt% band gap energy was increased at 3.82 eV and high PL emission intensity peak was absorbed at 423 and 578 nm due to large particle size and high absorption to compare other ZnS thin film. Antimicrobial activity of as-deposited ZnS thin film was evaluated by using in vitro disk diffusion method against different microorganisms. From this result the excellent zone of inhibition was formed against all the tested microorganisms moreover Mn doping concentration is increased. The photo catalytic degradation of MBD and MOD also investigated, from this result ZnS:Mn 6 wt% (active area 1.5  1.5 cm2) exhibits excellent degradation efficiency of MBD-91% and Mod-96% under 300 min visible light irradiation due to large and specific surface area, crystallite structure, band gap and high luminescence properties, photo catalytic degradation efficiency was increased on the percentage of photo catalyst and irradiation time. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] S. Wageh, Z.S. Ling, X. Xu-Rong, Growth and optical properties of colloidal ZnS nanoparticles, J. Cryst. Growth 255 (2003) 332–337. [2] H. Abdullah, N. Saadah, S. Shaari, Effect of deposition time on ZnS thin films properties by chemical bath deposition (CBD) techinique, World Appl. Sci. J. 19 (8) (2012) 1087–1091. [3] X. Wang, J. Shi, Z. Feng, M. Li, C. Li, Visible emission characteristics from different defects of ZnS nanocrystals, Phys. Chem. Chem. Phys. 13 (2011) 4715–4723.

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Please cite this article as: M. Saroja, M. Venkatachalam, P. Gowthaman et al., Investigation of Mn doping concentration on the structural, optical, antimicrobial and dye degradation properties of ZnS thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.009