Fabrication of novel oxochalcogens halides of manganese and tin nanocomposites as highly efficient photocatalysts for dye degradation and excellent antimicrobial activity

The dark brown and white crystals of manganese and tin (Mn2Se3Cl2O7 and SnSe3O4Cl) have been synthesized by solid-state reaction at 450 C. The morphology and the elemental analysis of newly synthesized compounds were studied by SEM and EDX Analysis. SEM analysis reveals that the particle size for Mn2Se3Cl2O7 was found to be 0.2–2.5 μm and for SnSe3O4Cl 2.0–6.0 μm. The EDX studies showed the presence of Mn, Se, O, Cl, and Sn elements. Powdered XRD confirmed the presence of a new phase present in these compounds. Under UV-vis irradiation, the kinetics of methylene blue (MB) degradation catalyzed by produced nanoparticles were monitored. The dye degradation efficiency was estimated, and results reveals that after 150 min of irradiation, almost 75% of the dye was degraded in the presence of Mn compound while 71% degradation was shown by Sn compound. Both composites display antimicrobial activity against Staphylococcus aureus and Escherichia coli with a maximum value of 34.5 mm. The maximum antimicrobial activity shown by Mn-incorporated nanocomposites estimated at 32.5 mm was against Gram-positive bacteria and 26.4 mm against Gram-negative bacteria. Similarly, the maximum antifungal activity shown by Sn incorporated estimated at 33.9 mm was compared to Gram-positive bacteria and 27.8 mm against Gram-negative bacteria.


Introduction
Industrial wastes, especially waste liquids of synthetic dyes used in the paper, food, agriculture, leather, textile and pharmaceutical industries (Farahmandjou and Abaeiyan, 2017;Altaf et al., 2020a) are highly toxic and biodegradable organic wastes that are critical to the survival of organisms, becoming the biggest problem (Sivagowri and Shivatharsiny, 2018). .Water is the most important element for life on Earth. Due to rapid population growth, the demand for water is increasing day by day (Shanmugaratnam, Rasalingam;Lv et al., 2020). Many scientists have focused and worked on efficient techniques for removing these non-biodegradable industrial pollutants from wastewater before they enter the environment (Peng et al., 2020). Several techniques such as adsorption, chlorination, filtration, and air stripping, coagulation, and membrane processes are traditional methods of treating water that are costly, time-consuming, and sometimes hazardous (Ranson et al., 2015;von Gunten, 2018;Bethi et al., 2016).
The treatment of drinking water has given rise to the advanced oxidation process (AOPs). Numerous AOPs are accessible, including moist air oxidation, electrochemical oxidation, hydrogen peroxide, heterogeneous photocatalysts, and supercritical water oxidation . The semiconductors with lower bandgaps that can produce electrons to interact with water molecules are in a distinct phase from the reaction system in heterogeneous photocatalytic AOPs. The semiconductors utilized as a catalyst for AOPs need to be affordable, easily accessible, stable, and chemically inert. They also need to demonstrate strong photocatalytic activity and low toxicity. In order to degrade organic molecules by photocatalysis, a variety of materials and agents are accessible, including simple metal oxides, transition metal oxides, nitrides, and complex oxides (O'Shea and Dionysiou, 2012).
A catalytic reaction in which light is absorbed by a substrate is referred to as photocatalysis by the International Union of Pure and Applied Chemistry (IUPAC) (Schneider et al., 2016). When a semiconductor photocatalyst is exposed to light with photon energies above the bandgap energy, electrons in the valence band (VB) are stimulated to the conduction band (CB), leaving holes in VB. Due to the fact that photocatalytic reactions take place on the surface of the photocatalyst, the photoinduced free charge carriers must first diffuse to the active sites on the photocatalytic surface in order to cause the reaction (Mills and Le Hunte, 1997;Castellote et al., 2011;Photocatalysis, 2016). The distance between the substrate's redox potential and the semiconductor photocatalyst's band edge, however, determines whether a chemical reaction can take place on the semiconductor photocatalyst on that substrate (Thermodynamic, 2012;Liu et al., 2014;Ohtani, 2014).
Researchers have been captivated by selenide compounds of different transition metal oxides due to their significant potential for use in industrial applications such as semiconductors, IR detection, energy storage devices, laser diodes, catalysis, photovoltaic electronics, and photo-detective devices. The creation of inorganic semiconductor nanocomposites has caught the interest of scientists because of their novel characteristics, including reactivity, low melting point, electrical properties, optical properties, and magnetic properties. Compared to their bulk counterparts, nanomaterials have a high surface area-tovolume ratio (Ou et al., 2017). Under solar radiation, a process known as photocatalytic breakdown, the high reactivity of nanocomposites is crucial for the removal of organic contaminants from polluted water (Jabeen et al., 2017;Ye et al., 2018). For inorganic semiconducting nanocomposites, bandgap engineering and particle size control are considered essential tools to tailor their properties for different applications across multiple industries (Zhang et al., 2004). Nanocomposites have gained a lot of attention from researchers due to their wide range of applications. Nanocomposites are those materials that contain nanoscale particles within a matrix of conventional materials. The applications of nanocomposites are in the field of biomedicine, storage devices, food and environmental sciences, electronic industry, and automotive fields. The characteristic properties of nanocomposite materials are that they are easy to synthesize, exhibit high mechanical properties, and are thermally very stable.
In the present work, a simple, cost-effective solid-state method was used to synthesize the metal selenium Oxo-halides of Mn and Sn. The characterization technique like XRD and SEM-EDX were used to analyze the new phase, structure, and composition of the compound. Moreover, the optical and antimicrobial activity was also studied. The main purpose of this study was to form the novel transition metal selenium Oxo-halides with more effective optical and antibacterial activity.

Experimental section Chemicals
MnCl 2 .H 2 O and SeO 2 and SnCl 2 and Se used as starting material for the synthesis of Mn 2 Se 3 Cl 2 O 7 and SnSe 3 O 4 Cl were purchased directly from Sigma Aldrich with 99% purity and used directly without further purification. Double distilled water was used to obtain a high-purity product. The Methylene blue dye used was of analytical grade.

Fabrication of Mn 2 Se 3 Cl 2 O 7 and SnSe 3 O 4 Cl
For the synthesis of Mn 2 Se 3 Cl 2 O 7 , MnCl 2 .H 2 O and SeO 2 were taken as a starting material in a stoichiometric ratio of 1:2 (0.323 g and 0.443 g). Whereas for the synthesis of SnSe 3 O 4 Cl, solid SnCl 2 was reacted with elemental selenium in the stoichiometric ratio of 1:8 (0.947 g and 3.115 g) respectively. After introducing the mixture into the crucibles, these were placed in a preheated muffle furnace at 450 C for 48 h (Rabbani et al., 2019). The dark brown crystal products were obtained after washing with distilled water followed by acetone. The resultant product obtained was dried in an oven at 80°C Figure 1 for 2 hrs and saved for further characterization.

Photocatalytic activity
To study the photocatalytic activity of synthesized compounds, 0.2 g of the compound was taken in the beaker containing 100 mL of MB dye. The solution was stirred for 30 min to attain absorption equilibrium the mixture was irradiated in direct sunlight. 5 mL solution was taken out after regular intervals (30 min) and check the absorption at the UV-Vis Spectrophotometer. The proportion degradation of dye in the presence and absence of compounds was calculated by formula (Pouretedal et al., 2009) %D Co − Ct Co × 100

Antimicrobial activity
The antimicrobial activity was examined by using the disc diffusion method against pathogenic bacterial strains (Escherichia coli and Staphylococcus aureus) (Altaf et al., 2020b). For 30 min, nutrient agar containing the following ingredients was placed in the autoclave: peptone 5, beef extract 1, yeast extract 2, sodium chloride 5, and agar 20. With the aid of sterile culture swabs, fresh cultures of each test organism containing 1 of the colony-forming units (CFU)/ml were applied to nutrient agar plates to grow bacteria. Different dilutions (0.25, 0.5, and 1 mg/mL) were then developed to test the susceptibility of the prepared nanocomposites. The negative control utilized was deionized water (DIW). After being soaked in l of these dilutions, discs were placed on agar plates and incubated for 24 h in an aerobic environment at 37 C. Zone of inhibition was evaluated on a meter scale (mm) at various values (Image J software). By doing the experiment three times, the repeatability and reliability of the results were verified.

Instrumentation
The microcrystalline phase information of Mn2Se3Cl2O7 and SnSe3O4Cl was investigated using PAAnlytical Xpert PRO X-ray diffraction (XRD) and Cu Kα radiation (λ~1.5406 Å), yielding data in the 2θ range 5°-80°. Using a FE-SEM (JSM-6460LV) coupled to an EDX analyzer, the morphological properties and composition of the goods were ascertained. Using a Genesys 10S UV-visible spectrophotometer, optical absorption spectra in the 120-1,100 nm range were examined.

Results and discussion
Powder X-Ray diffraction analysis (XRD) The resulting synthesized compound i.e., Mn 2 Se 3 Cl 2 O 7 and SnSe 3 O 4 Cl firstly ground and homogenized and placed on the sample holder of XRD (D8-Discoverer Bruker Germany) and measured 2 o θ from 15-90°for almost 30 min. The search match procedure was done by using XPERT-HIGHSCORE. The result showed that the powder XRD pattern of both compounds did not match with the binary and tertiary compounds of metal oxo chalcogen halides of given elements i.e., Mn and Sn Figure 2 indicated that there must be some new phase present in the compound which makes it novel from other known compounds.

Scanning electron microscopy (SEM)
The result obtained from SEM as shown in Figure 3 showed that the newly formed compound Mn 2 Se 3 Cl 2 O 7 exhibits well-defined Frontiers in Materials frontiersin.org 03 edges and a smooth surface with a rod-like arrangement having a particle size ranging from 0.2-2.5 μm. While the SEM graph of SnSe 3 O 4 Cl shows that this compound has layers arrangement with particle size ranging from 2.0-6.0 μm.
The elemental analysis and their stoichiometry were carried out with the help of an EDX-Spectrometer (EDX, LINK AN10000). The spectrum of Mn 2 Se 3 Cl 2 O 7 confirmed the atom's stoichiometry in the compound and provided the mean compositional analysis of the compound Table 1.Whereas the EDX spectrum of SnSe 3 O 4 Cl insured the presence of all the elements (Sn, Se, O 2 , Cl) in specific ratio.
For the photocatalytic activity of two synthesized compounds against methylene Blue (MB) dye, 100 mL of MB dye was taken in a Petri dish with the addition of 0.2 mg of samples. To achieve absorption-desorption equilibrium between the dye and produced  Frontiers in Materials frontiersin.org chemicals, the reaction mixture was agitated for 30 min in the dark prior to exposure to radiation. These Petri dishes were placed in direct sunlight for irradiation. 5 mL of the sample was taken out at regular intervals (every 30 min) during light irradiation, filtered, and centrifuged to obtain a pure solution (Shanmugam et al., 2015). Then the filtrate is subjected to a UV-Visible spectrometer and photodegradation was calculated by using the equation as follows.
%D Co − Ct Co × 100 (1) Figure 4 shows the dye degradation during the different intervals of time under light irradiation in the presence of two synthesized compounds. As more hydroxyl radicals are generated as a result of increased radiation falling on the catalyst surface, the degradation efficiency rises. So with the passage of time, more and more free radicals of oxygen are formed which are responsible for the degradation of organic dye. The percentage degradation was calculated by Eq. 1 and values are shown in Table 2. The data clearly shows that after 150min of irradiation, almost 75% of the dye was degraded in the presence of Mn compound while 71% degradation was shown by Sn compound. The rate constant for the degradation of dye was calculated by a first-order reaction equation (Kannadasan et al., 2014).
lnCo Ct kt (2) Where k is the rate constant. Figure 5 shows the plot illustrating the linear relationship between time and ln C o /C t and from the slope of the graph, the rate constant is calculated. The value of the rate constant for the SnSe 3 O 4 Cl compound is 0.00378 min -1 whereas the rate constant value of the Mn 2 Se 3 Cl 2 O 7 compound is 0.00447 min -1 which shows that increases in rate constant value increase the efficiency for photodegradation.

The Possible Mechanism for Photocatalytic Degradation
During light irradiation, some electrons from the valance band make a quantum jump to the conduction band and move to the   surface for surface reaction. These electrons from the surface react with the absorbed oxygen to form oxygen radicals. The concentration of oxygen is responsible for the efficiency of photo-degradation. And the holes in the valance band form during the excitation and react with water molecules to produce hydroxyl radicals. The two oxygen radicals and hydroxyl radicals are accountable for the oxidative photodegradation of methylene blue. The Possible Mechanism for Photocatalytic Degradation is shown in Figure 6.

Antibacterial and antifungal activity
The disc diffusion method was used to analyze the bacterial sensitivity against the synthesized compounds as shown in Figure 7. The zone inhibition was measured against Gram-positive and Gram-negative bacteria ranging from 0 mm to 32.4 mm in diameter. The outcomes show an additive effect of nanocomposites' concentrations and inhibition zones (mm). For the nanocomposite

FIGURE 5
Degradation ratio Vs. time.

FIGURE 6
Mechanism for photocatalytic activity.
Frontiers in Materials frontiersin.org 06  On the other hand, the Mn compound significantly reduced the mycelial growth of Aspergillus flavus and Candida albicans ( Table 3). The increase in the concentration of compounds shows a decrease in the concentration of bacterial colonies due to the formation of reactive oxygen species. Particle size, shape, and surface-to-mass ratio of nanocomposites, which are crucial for antibacterial activity, are some of the variables that affect oxidative stress (Panáček et al., 2006;Ruparelia et al., 2008;Ruparelia et al., 2008;Hans et al., 2014). Reactive oxygen species (ROS) that damage bacterial membranes and promote the ejection of cytoplasmic contents and bacterial growth are produced effectively by nano-sized composites (Haider et al., 2019). This oxidative stress kills the bacterial DNA and inhibits the enzyme activity which is necessary for the growth of cells (Elkhoshkhany et al., 2017). The charge on the bacterial cell wall is negative while the overall charge on the metallic compound is positive (Tang and Lv, 2014). The cationic interaction of metal ions (Mn 2+ and Sn 4+ ) with negatively charged bacterial cell walls is another possible mechanism for the death of bacteria . The bacterial and fungal cell wall layer consists of a network of covalently cross-linked peptide and glycan chains and is a proven target for antimicrobial agents that can provide great mechanical strength through osmotic lysis. There are two families of enzymes that play an important role in forming this layer, including transglycosylases and transpeptidases. At pH above 7, this peptide chain is negatively charged. These metal complexes can bind to peptide substrates in the peptidoglycan layer, preventing them from reacting with enzymes. However, the net effect is very similar, with reduced peptidoglycan cross-linking and consequent weakening of the cell wall (Schneider and Sahl, 2010;Ahmad et al., 2019;Wu et al., 2019).

Conclusion
In the present research, Mn 2 Se 3 Cl 2 O 7 a dark brown crystalline material, and SnSe 3 O 4 Cl have been synthesized by a solid-state reaction. The synthesized nanocomposite has been characterized by various spectroscopic techniques. After the successful formation of desired product, the composite has been tested to estimate the efficiency of the synthesized sample for dye degradation and antimicrobial activity. The presence of all the elements (Mn, Se, O, and Cl) was confirmed by the EDX spectrum. The result obtained by XRD proved that there must be a new phase present in it. The dye degradation efficiency was found to be 75% in the presence of Mn 2 Se 3 Cl 2 O 7 having the rate constant value of 0.00447 min -1. Similarly, 71% of the dye is degraded in the presence of SnSe 3 O 4 Cl having the rate constant value of 0.00378 min -1. The Mn 2 Se 3 Cl 2 O 7 showed the maximum antimicrobial activity against Gram-positive bacteria i.e., 32.5 mm while 26.4 mm against Gram-negative bacteria. In the same way, the SnSe 3 O 4 Cl showed the maximum antimicrobial activity against Gram-positive bacteria at 22 mm while 26 mm was against Gram-negative bacteria. These two newly synthesized compounds can be used as photo-catalysts and antimicrobial agents for the removal of organic pollutants from industrial effluents especially from the textile and food industry due to their proven efficiency against methylene blue dye and pathogens.

Data availability statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.