Photocatalytic, antimicrobial and antibiofilm activities of MgFe2O4 magnetic nanoparticles

This study reports the antibacterial and antibiofilm activities of Magnesium ferrite nanoparticles (MgFe2O4) against gram-positive and gram-negative bacteria. The photocatalytic degradation of Carbol Fuchsin (CF) dye (a class of dyestuffs that are resistant to biodegradation) under the influence of UV-light irradiation is also studied. The crystalline magnesium ferrite (MgFe2O4) nanoparticles were synthesized using the co-precipitation method. The morphology of the resulting nanocomposite was examined using scanning electron microscopy (SEM), while transmission electron microscopy (TEM) was employed for further characterization of particle morphology and size. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were utilized to analyze the crystalline structure, chemical composition, and surface area, respectively. Optical properties were evaluated using UV–Vis spectroscopy. The UV-assisted photocatalytic performance of MgFe2O4 nanoparticles was assessed by studying the decolorization of Carbol fuchsin (CF) azo dye. The crystallite size of the MgFe2O4 nanoparticles at the (311) plane, the most prominent peak, was determined to be 28.5 nm. The photocatalytic degradation of 10 ppm CF using 15 mg of MgFe2O4 nanoparticles resulted in a significant 96% reduction after 135 min at ambient temperature (25 °C) and a pH value of 9. Additionally, MgFe2O4 nanoparticles exhibited potent antibacterial activity against E. coli and S. aureus in a dose dependent manner with maximum utilized concentration of 30 µg/ml. Specifically, MgFe2O4 nanoparticles demonstrated substantial antibacterial activity via disk diffusion and microbroth dilution tests with zones of inhibition and minimum inhibitory concentrations (MIC) for E. coli (26.0 mm, 1.25 µg/ml) and S. aureus (23.0 mm, 2.5 µg/ml), respectively. Moreover, 10.0 µg/ml of MgFe2O4 nanoparticles elicited marked percent reduction in biofilm formation by E. coli (89%) followed by S. aureus (78.5%) after treatment. In conclusion, MgFe2O4 nanoparticles demonstrated efficient dye removal capabilities along with significant antimicrobial and antibiofilm activity against gram-positive and gram-negative bacterial strains suggesting their potential as promising antimicrobial and detoxifying agents.

Water pollution has become a global threat to mankind due to accelerated pace of global industrialization 1-3 .According to sustainable development goal (SDG) 6.3, the provision of uncontaminated water and the development of safe and sustainable water purification methods are of paramount importance from environmental, industrial, and societal, and perspectives 4 .It is estimated that poor drinking water quality contributes to 80% of world's diseases and 50% of child deaths 5 .Given the extensive contamination of water resources, there has been increasing endeavors towards developing safe and effective water treatment strategies over the recent decades 6,7 .According to the World Bank estimates, approximately 17-20% of global pollutants can be attributed to the textile industry 8 .The persistent nature of these pollutants stems from the stability of the water-soluble compounds used in textile industry such as dyes, resulting in prolonged environmental impacts.Carbol fuchsin (CF), a cationic organic dye that is used as a biological stain and in addition to other applications 9 .As per the regulations outlined in 29 CFR 1910.1200 by the Occupational Safety and Health Administration (OSHA), CF is categorized as a hazardous substance 10 .Furthermore, Carbol fuchsin has the potential to cause various health hazards, including chemical burns.Considering the available literature highlighting its potential environmental accumulation, especially in water, and its hazardous effects, novel methods for its safe and efficient removal should be considered 11 .
Traditional approaches to water treatment like coagulation, flocculation, sedimentation, and filtration, have been employed 12,13 .However, these methods often fall short in terms of efficiency and cost-effectiveness.Photocatalytic decomposition process is one of the most applicable processes that have been utilized for industrial dyes degradation 14 .The utilization of nanomaterials in wastewater treatment for removal of harmful dyes has been identified as a green and environmentally friendly approach which presents significant opportunities to revolutionize the approach for the removal of toxic dyes, particularly, magnetic nanoparticles [15][16][17][18][19][20][21][22] .Magnetic nanoparticles possess exceptional properties such as high surface area to bulk volume ratios, low toxicity, increased activity, thermal stability, adaptability for surface modifications, and efficient dispersibility 23 .
In recent years, the problem of multidrug-resistance and extensive drug-resistance to antibiotics has surged to a critical level that requires urgent intervention.The World Health Organization (WHO) has alarmingly warned that a "post-antibiotic era" has arrived in which previously treatable infections can become life-threatening due to antimicrobial resistance (AMR).This poses unimaginable risks to human and animal health in the twenty-first century.Additionally, there is decline in the development of new antibiotics due to elevated costs of development coupled with low return on investment 24 .According to a global report on tackling drug-resistant infections, AMR is expected to be the cause of death of one person every three seconds by 2050, if no novel therapeutic modalities were developed to combat AMR 25 .Inorganic nanoparticles with magnetic properties offer a promising solution for fighting antibiotic-resistant bacteria that don't rely on targeted blocking of specific antibiotic resistance pathways.Instead, these nanoparticles rely on antimicrobial mechanisms such as reactive oxygen species (ROS) generation, delivery of metal ions, and magnetic hyperthermia to which the bacteria have not been able to evolve resistance mechanisms 26,27 .
Ferrites are chemical compounds with magnetic characteristics that present as powder or ceramic substances.Their ferrimagnetic characteristics are primarily attributed to iron oxides, specifically Fe 2 O 3 and FeO, which can be partly replaced by other transition metal oxides 28 .Magnesium ferrite (MgFe 2 O 4 ) is one of the most important ferrites.It has a cubic structure of normal spinel-type and is a soft magnetic n-type semiconducting material.It is utilized in various fields such as magnetic technologies, sensors, adsorption, and heterogeneous catalysis 29 .In recent years, nanostructures of magnetic materials have garnered increasing interest because of their exceptional material characteristics, which are particularly different from those of bulk materials 30 .
There is a growing interest in examining the antimicrobial properties of MgFe 2 O 4 nanoparticles (NPs) that is driven by the escalating antimicrobial resistance towards conventional antibiotics and the potentially promising antimicrobial properties of MgFe 2 O 4 magnetic nanoparticles 31,32 .
The current study has two key objectives.The first is to conduct an in-depth analysis of the efficacy of magnesium ferrite nanoparticles in water treatment, with a particular focus on their adsorption capabilities and photocatalytic properties.The second objective is to investigate their antimicrobial and antibiofilm activities against certain gram-positive and gram-negative bacterial strains.Through this comprehensive investigation, we aim to contribute to the development of more effective, sustainable, and safe solutions for water treatment and antimicrobial applications, thereby addressing the pressing global issue of water contamination and antibiotic resistance.

Materials
The materials utilized in this study were ferric chloride hexahydrate (FeCl 3 •6H 2 O) and magnesium chloride hexahydrate (MgCl 2 •6H 2 O).Carbol fuchsin (CF) was obtained from Sigma Aldrich; purity ≤ 100%).All the chemicals were of analytical grade and were utilized without additional refinement.Distilled water was used in nanoparticle preparation experiments.

Synthesis of Mg Fe 2 O 4 NPs
MgFe 2 O 4 NPs were synthesized via the co-precipitation technique 33 .The desired chemical composition is achieved by combining equimolar quantities of magnesium chloride (MgCl 2 •6H 2 O) and anhydrous ferric chloride (FeCl 3 ) dissolved in distilled water.The neutralization process is performed using a 1 M solution of sodium hydroxide (NaOH), with the reaction temperature held at 60 °C.The pH of the solution is maintained at 8 and stirring continues for duration of 2 h.The resulting precipitate is then washed with distilled water until it attains a state devoid of impurities.Subsequently, the product is subjected to drying at 100 °C to remove any remaining water content 34 .

Characterization of MgFe 2 O 4 NPs
The composition of functional groups and surface characteristics of MgFe 2 O 4 NPs were elucidated through FT-IR spectroscopy (JASCO FT-IR 3600 Infrared spectrometer).The samples under study were analyzed using the KBr disc method, with spectra recorded in the range of 400-4000 cm −1 .X-ray diffraction (XRD) analysis was then conducted on the synthesized Mg-F NPs using a Shimadzu XRD-6000 apparatus (SSI, Japan) to evaluate crystallinity, phase composition, crystallite size, and lattice properties.The X-ray diffraction patterns were generated by measuring the intensity of diffracted X-rays as a function of the diffracted angle (2θ).The average crystallite size was determined using the Williamson-Hall (W-H) method, as described by (Eq. 1) 35 .
In this context, the symbol (λ) signifies the wavelength of the employed radiation, whereas (β) and (θ) represent the full width at half-maximum (FWHM) and the angle corresponding to the peak with the highest (1) D = 0.9 /β cos θ intensity, respectively.The dimensions and morphology of the synthesized MgFe 2 O 4 nanoparticles (NPs) were analyzed using a High-Resolution Transmission Electron Microscope (HRTEM, JEM2100, Jeol, Japan).The surface characteristics and grain size of these MgFe 2 O 4 NPs were examined using Scanning Electron Microscopy (SEM, ZEISS, EVO-MA10, Germany).Additionally, an Energy Dispersive X-ray (EDX) analysis was conducted with a BRUKER Nano GmbH instrument (Model D-12489, 410-M, Germany) to determine the elemental composition, purity, and relative proportions of each metal within the structured MgFe 2 O 4 NPs.

Antimicrobial activity testing of MgFe 2 O 4 NPs
For antibacterial activity testing, gram-positive Staphylococcus aureus (ATCC 25923) and gram-negative E. coli (ATCC 25922) were selected as the target organisms to model two etiological agents of various infectious diseases in humans.The antimicrobial efficacy of the prepared Mg Fe 2 O 4 NPs was qualitatively assessed using agar-disc diffusion and quantitatively using microbroth dilution methods [36][37][38] .Bacterial suspensions of 1.5 × 10 8 CFU mL −1 (0.5 McFarland density) obtained from 18 to 24 h bacterial cultures developed on Trypticase Soy agar (TSA) were used.Three Mg Fe 2 O 4 NPs concentrations (10, 20 and 30 mg/ml) were prepared in DMSO and dispensed by sonication.Sterile filter paper discs (6.0-mm) were saturated by the Mg Fe 2 O 4 NPs solution and placed on the culture and incubated at 37 °C for 24 h after which the zones of inhibition were recorded.Sterile filter paper was saturated with DMSO and used as control.For performance comparison, conventional antibiotic disc containing Gentamycin (CN) (Oxoid) at a concentration of 10 μg and with a diameter of 6.0 mm was employed 39 .
For quantitative determination of the minimum inhibitory concentration (MIC) of MgFe 2 O 4 NPs, Macrobroth dilution technique was performed in test tubes containing Muller Hinton broth (MHB) of 2 mL total volume according to previously reported methods 37 .Two bacterial suspensions of gram-positive Staphylococcus aureus (ATCC 25923) and gram-negative E. coli (ATCC 25922) were collected after 24 h culture on Nutrient broth and adjusted to 0.5 McFarland standard turbidity (1.5 × 10 −8 CFU/mL).Different concentrations of Mg Fe 2 O 4 NPs (0.025, 0.05, 0.1 and 0.2) were tested.A positive control tube containing uninoculated broth with nanoparticles and a negative control tube containing inoculated broth without nanoparticles were included.The MIC values were determined by Multi Mode Microplate reader (Hidex Sense) spectrophotometer after 24 h incubation at 36.0 ± 1.0 °C as the lowest concentration at which no visible turbidity could be detected 40 .

Antibiofilm activity testing of MgFe 2 O 4 NPs
A qualitative assessment of the antibiofilm activity of MgFe 2 O 4 NPs was conducted by the tube adherence test according to the method outlined by a previous report 41 .Antibiofilm biofilm activity in the presence and absence of MgFe 2 O 4 NPs at a concentration of 10.0 μg/mL.5 mL of nutrient broth was introduced into both the treated and control tubes followed by the inoculation of the test bacteria (S. aureus, ATCC 25923) and (E.coli, ATCC 25922) at a concentration of 1.5 × 10 8 CFU mL −1 (0.5 McFarland density).Subsequently, tubes were incubated at 37.0 ± 0.5 °C for 24 h.The media in both the control and treated tubes was removed then the tube was filled with Phosphate Buffer Saline (PBS) at pH 7.0.Bacterial cells adhering to the tube walls were dislodged by treating with 5 mL of 3.5% sodium acetate for approximately 20 min, followed by a thorough cleaning with deionized water.Biofilm formed on the inner walls of the tubes was stained with 20 mL of 0.15% Crystal Violet (CV) and subsequently rinsed with deionized water to remove excess CV.For semi-quantitative assessment of antibiofilm activity of NPs, 5 mL of absolute ethanol was introduced to dissolve the stained bacterial biofilm 38 .The optical density (O.D.) of the stained bacterial biofilm was measured using UV-Vis (Biochrom. WPA Biowave III) spectrophotometer at 570.0 nm 39 .The percentage inhibition of bacterial biofilm formation in the presence of MgFe 2 O 4 NPs was calculated using the following equation (Eq.2) 40 :

Photocatalytic degradation of Carbol fuchsin (CF) using MgFe 2 O 4 NPs
A nanocomposite weighing 10 mg was introduced into a 50 ml aqueous solution containing Carbol fuchsin (CF) with an initial concentration (C 0 ) of 10 mg/L.The mixture was stirred continuously at room temperature (25 °C) for 30 min in the absence of light to establish equilibrium between adsorption and desorption processes.Subsequently, a simulated UV light source, in the form of a UV lamp, was utilized to irradiate the solution containing the photocatalyst and CF.The UV lamp was positioned axially within a quartz immersion tube.At fixed time intervals during irradiation, a syringe equipped with a filter (pore size of 2.5 mm) was employed to extract a 1 ml sample of the CF suspension.The degradation rate of CF was determined by monitoring the change in CF concentration over the irradiation period using a UV-visible spectrophotometer (Agilent Technologies Cary 60 UV-visible) at a wavelength (λmax) of 545 nm.Deionized water served as the reference medium 41 .In Eq. ( 3), (β) denotes the full width at half maximum (FWHM) of the diffraction peak, and K represents the shape factor.The shape factor, K, is approximately 0.9 and is equal to 0.15406, corresponding to the wavelength of CuK X-rays 26 .The crystallite size of the MgFe 2 O 4 nanoparticles at the (311) plane, the most prominent peak, was determined to be 28.5 nm.It is noteworthy that the performance of nano photocatalytic substances is substantially influenced by their particle size.

Morphological analysis of Zn 0.5 Cu 0.5 Fe 2 O 4 NPs
The SEM image of MgFe 2 O 4 nanoparticles, as depicted in Fig. 2a, indicates that the synthesized particles have a spherical morphology and aggregate readily; their grain sizes range between 25 and 35 nm.It is crucial to note that the particle sizes shown in the SEM pictures may not completely reflect the real properties of the sample.The restriction arises from the potential for surface charge of the samples during their interaction with the electron beam.Electrostatic charging may increase, particularly when no atmosphere exists, as the electron beam moves across non-conductive metal oxide surfaces.These conditions can result in a decrease in SEM magnification and level of detail.In contrast, HRTEM showed that the synthesized MgFe 2 O 4 NPs appears as a semi-spherical  www.nature.com/scientificreports/shape and small sizes as shown in Fig. 2b.The detected sizes varied from 20.7 to 30.6 nm and the average particle size was determined to be 27.3 nm.

Fourier transform infrared spectroscopy (FT-IR) analysis of MgFe 2 O 4 NPs
The FT-IR spectrum of the synthesized MgFe 2 O 4 nanoparticles (NPs), illustrated in Fig. 3, was obtained over a frequency range from 500 to 4000 cm −1 .The spectra can be broadly classified into two main regions: the fingerprint region (400-1800 cm −1 ) and the lattice water H-O-H stretching band region (3200-3600 cm −1 ) 31,32 .The characteristic absorption bands observed in the 550 to 700 cm −1 range are associated with the intrinsic vibrations of tetrahedral groups 28 .Furthermore, the absorption band at 1100 cm −1 can be ascribed to the stretching modes of metal-oxygen bonds (M=O), where molecules with a single terminal oxygen atom exhibit absorption 32 .Additionally, the peak observed at 1631 cm -1 corresponds to the bending vibration of O-H bonds in adsorbed water molecules present on the nanoparticle's surface due to moisture adsorption.Furthermore, a peak at 3400 cm -1 is indicative of the stretching mode of adsorbed O-H groups.Several bacterial species of clinical importance are known to develop biofilm that is associated with increased antibiotic resistance 48,49 .Consequently, the design of novel antimicrobial agents that specifically target biofilms is crucial.In the current study, the antibiofilm activity of MgFe 2 O 4 NPs was tested on two specific bacterial strains known for their biofilm-producing capabilities; S. aureus (ATCC 25923) and E. coli (ATCC 25922) by the tube adherence test 50,51 .Both S. aureus and E. coli inoculated in the absence of MgFe 2 O 4 NPs developed a thick whitish yellow biofilm at the air-liquid interface as demonstrated for E. coli in Fig. 6A.This biofilm appeared as a blue ring after CV staining and was adherent to the tube wall (Fig. 6B).After dissolving the CV-stained blue ring with ethanol, a blue suspension was formed (Fig. 6C).Conversely, S. aureus and E. coli that were treated with MgFe 2 O 4 NPs demonstrated marked inhibition of biofilm formation observed before and after CV staining (Fig. 6).The highest inhibition percentage was observed against E. coli (89%) followed by S. aureus (78.5%) after treatment with 10.0 µg/ml of MgFe 2 O 4 nanoparticles (NPs), as shown in (Fig. 6D and Table 1).Elbasuney et al. 52 reported that the addition of 10.0 µg/mL of Ag-HA nanocomposite resulted in the highest inhibition percentages of 96.09% and 95.60% against S. aureus and E. coli, respectively 52 .The differential percentage inhibition of biofilm formation by MgFe 2 O 4 NPs for E. coli versus S. aureus may be due to multiple factors including differential antimicrobial activity, and distinct chemical interactions governing the antibiofilm properties of the nanocomposite on various  www.nature.com/scientificreports/bacterial species 44 .Table 2 listed the antibacterial activity of different nanoparticles against the selected bacterial strains compared to the obtained results from this study.

Proposed mechanism of the antimicrobial effect of the synthesized MgFe 2 O 4 NPs
An in-depth investigation is required to fully comprehend the antibacterial mechanism demonstrated by the synthesized MgFe 2 O 4 NPs. Figure 7 demonstrates a visual representation of the hypothesized antimicrobial action.It is understood that the activity of the synthesized MgFe 2 O 4 NPs commences through their wrapping and adherence to the outer surface of microbial cells, resulting in membrane destruction and alteration of the transport potential.The MgFe 2 O 4 NPs are posited to initiate contact by enclosing the outer layer of the microbial cells, leading to the breakdown of the cell membrane and alteration of the electrochemical gradient 60 .Following this initial interaction, the nanoparticles disseminate throughout the cell leading to cellular damage affecting bacterial genome, plasmid DNA, and other crucial organelles, primarily due to oxidative stress from reactive oxygen species (ROS) production.In the final stages, the nanocomposite impedes ion exchange with the across bacterial membranes 26 .However, morphological and topological features like shape, size, porosity, and surface roughness of NPs play a vital role in governing NP dissolution and antimicrobial efficacy 61 .Vishal Chaudhary et al. have proven that the size-dependent mechanism is the primary regulating element for the antibacterial efficacy and toxicity of AgNPs with diameters ranging from 1 to 10 nm 62 .Within this size range, Ag-NPs exhibit a higher dissolution rate than larger NPs.This is attributed to their increased surface-to-volume ratio, which aligns with the overall pattern of quantum size effects.Ag-NPs larger than 10 nm exhibit both ion-only and synergistic ion-particle processes, which ultimately act in a manner similar to their larger-scale counterparts.Furthermore, the structure of NPs also plays a crucial role in determining their antibacterial and dissolving performance.NPs with higher surface energy, such as nanoplates, dissolve faster than nanospheres.This is due to their smaller size and high-energy crystallographic aspects 26 .

Photocatalytic degradation of Carbol fuchsin (CF) using MgFe 2 O 4 NPs
The removal of CF was monitored spectrophotometrically at its maximum absorbance wavelength, λmax = 545 nm 63 .Figure 8A   The pH value at the Point of Zero Charge (PZC) was determined by plotting the final pH against the initial pH, as illustrated in Fig. 9b.The PZC pH was identified at pH = 6.9,where no significant difference existed between the final and initial pH values.This finding indicates that the surface charge of the MgFe 2 O 4 NP photocatalyst is positive when the pH is below the PZC pH and negative when the pH exceeds the PZC threshold.Moreover, at the PZC pH, the surface charge of the photocatalyst becomes neutral, leading to minimal electrostatic interactions with ions such as CF ions.The calculated PZC pH value for MgFe 2 O 4 NPs was found to be 6.9.The effective photocatalytic degradation of CF at pH 9.0, as shown in Fig. 9a, can be attributed to the negative net surface charge of MgFe 2 O 4 NPs at this pH.This negative charge results in attraction between the negatively charged NPs and the positively charged CF, enhancing the degradation process.Conversely, the degradation of CF begins to decrease at pH 5.0, where the net surface charge of MgFe 2 O 4 NPs becomes positive, leading to repulsion forces between the positive charge of CF and the positively charged surface of the NPs.We investigated the impact of varying the initial concentration of CF on its removal by MgFe 2 O 4 nanoparticles (NPs) while maintaining constant reaction conditions.Figure 10a illustrates the variation in CF removal percentage over time for different initial CF concentrations (5.0, 10.0, and 15.0 mg/L).The findings indicate that as the initial CF concentration decreased from 5 to 15 mg/L, the removal efficiency increased.This suggests that even at low initial concentrations, CF can be effectively removed when exposed to UV light in the presence of the synthesized nanocomposite.This result could be explained by the Beer-Lambert Law, which states that an increment in initial dye concentration lowers the path length of photons exiting a solution.This reduces photon absorption by photocatalyst particles, drastically reducing the photocatalytic reaction rate 64 .

Effect of MgFe 2 O 4 NPs dose on Carbol fuchsin (CF) degradation efficiency
The effect of varying doses of MgFe 2 O 4 nanocomposite on the efficacy of CF removal under UV-light was studied by adjusting the quantity of the photocatalyst from 5 to 20 mg, with the CF concentration held constant at 10 mg/L, as illustrated in Fig. 10b.The results showed that the removal efficiency increased as the photocatalyst dose increased from 5 to 20 mg.The enhancement in removal efficiency with increasing photocatalyst quantity in the reaction could be attributed to the increased active area or active sites of the photocatalyst relative to the volume ratio of the CF solution 65 .Gao et al. reported similar behavior in dye degradation by using the cubic SrTiO 3 66 .

Kinetic studies
The CF removal rate can be computed using the following equation (Eq.4): Here, C t and C o denote the remaining and initial concentrations of CF, respectively, while t represents the removal time, and k represents the removal rate constant.Figure 11 illustrates the relationship between -ln(C t / C o ) and t.The findings indicated that the removal kinetics of the reaction adhered to pseudo-first-order rate kinetics.An increase in the initial concentration of CF led to a rise in the apparent pseudo-first-order rate constants, as seen in Fig. 11.The correlation between reaction rate constants and CF concentration is consistent with previous studies 67 .

Mechanism of photocatalysis of Carbol fuchsin (CF)
As reported in multiple studies [68][69][70] , the potential mechanism can be elucidated as follows: photodegradation mechanisms are influenced by variations in pH levels and involve the participation of hydroxyl radicals, oxidation via positive holes in the valence band, and reduction by electrons in the conduction band.Photocatalytic degradation is expected to happen in the presence of MgFe 2 O 4 NPs when UV light promotes the formation of electron-hole pairs on the surface of MgFe 2 O 4 NPs 71,72 .These holes can either react with -OH groups to produce hydroxyl radicals or oxidize the reactive CF to create a degradation product due to their oxidative potential 73,74 .Equations (5-8) summarize the reactions between CF and the photocatalyst used.Figure 12 illustrates the suggested mechanism of the interaction between the produced MgFe 2 O 4 nanoparticles and CF.When MgFe 2 O 4 NPs are subjected to UV light, the excitation process generates charge carriers, initiating redox reactions.Consequently, the resultant free radicals, including OH• and O2• − , participate in the degradation of CF, resulting in the formation of smaller organic compounds.It is noteworthy that, as of the current juncture, A few reports have been published regarding the degradation products of CF.Therefore, further investigations employing analytical techniques such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) are imperative for a more comprehensive analysis of CF degradation products.Table 3 listed the photocatalytic degradation activities of the different nanoparticles compared to the obtained results from this study.

Figure 6 .
Figure 6.Antibiofilm activity of MgFe 2 O 4 NPs E. coli using the tube adherence method.(A) Growth of bacterial cells and biofilm formation (rings) without treatment with MgFe 2 O 4 NPs (left) and the inhibition of bacterial growth after treatment with MgFe 2 O 4 NPs (right).(B) Staining of the adherent bacterial cells with crystal violet.(C) Removing and dissolving the adherent bacterial cells by ethanol for determination of quantitative biofilm inhibition (%).(D) Quantitative analysis of antibiofilm activity of MgFe 2 O 4 NPs.The optical density (OD) of both the control sample (without MgFe 2 O 4 ) and of the treated samples with 10ug/ml MgFe 2 O 4 was measured at a wave length of 570 nm.

Figure 7 .
Figure 7.A model depicting the four main mechanisms underlying the antibacterial potential of the synthesized MgFe 2 O 4 NPs.(I) MgFe 2 O 4 NPs nanoparticles attach to and enfold the microbial cell surface, potentially via electrostatic interactions.(II) MgFe 2 O 4 NPs penetrate the microbial cells and interact with cellular machinery components such as plasmid DNA, ribosomes, chromosomal DNA, and mesosomes, affecting their function.(III) MgFe 2 O 4 induces the release and accumulation of ROS, leading to cellular damage.(IV) MgFe 2 O 4 NPs modulate the cellular signal system and causing cell death.(V) Ultimately, the Mg-F nanoparticle composite impedes the bidirectional flow of ions across the microbial membrane.

Figure 8 .
Figure 8. Photocatalytic degradation of Carbol fuchsin (CF) using MgFe 2 O 4 NPs (a) Uv-Vis spectrum of CF after 15 min time interval using 10 mg of MgFe 2 O 4 NPs under UV radiation.(b) Calibration curve of different concentrations of CF.(c) Percentage removal of CF photolysis is indicated by the black line, adsorption in dark by the red line, and UV photocatalysis by the blue line.

Figure 9
presents a graphical representation depicting the removal of CF over time at different pH values (3.0, 5.0, 7.0, and 9.0).Notably, the maximum CF removal at equilibrium was observed at pH 9.0 as illustrated in Fig. 9a.To determine the point of zero charge (PZC) of the MgFe 2 O 4 nanocomposite, 0.01 g of MgFe 2 O 4 NPs.was introduced into 50 mL of a 0.01 M NaCl solution.The pH of the solutions was adjusted using HCl or NaOH to achieve pH values of 2, 4, 6, 8, 10, and 12. Subsequently, the samples were stirred at 200 rpm for 48 h, and pH measurements were conducted after the magnetic separation of MgFe 2 O 4 NPs.

Figure 9 .
Figure 9.Effect of pH on removal of Carbol fuchsin (CF) by MgFe 2 O 4 NPs.(a) Percentage removal of CF at different solution pH (5.0, 7.0 and 9.0).(b) Point of zero charge (PZC) of MgFe 2 O 4 NPs at different pH values.

Figure 10 .
Figure 10.(a) The variation of percent removal as a function of contact time at different initial CF concentration (5, 10 and 15 ppm) at pH 9.0 and 10.0 mg MgFe 2 O 4 NPs, (b) Effect of the photocatalyst dose on the Removal efficiency of CF (50 ml CF solution (10 mg/l), Temp.= 25 0C and pH 9.0).

( 4 )Figure 11 .
Figure 11.A linear fit, pseudo-first-order model data are reported in kinetic form for CF degradation under UV irradiation with beginning CF concentrations of 5, 10, and 15 ppm.

MgFe 2 O 4
NPs were successfully synthesized through a co-precipitation methodology and subjected to comprehensive structural and optical characterization.The photocatalytic performance of the resultant MgFe 2 O 4 nanocatalyst was evaluated using CF dye as the target pollutant.Additionally, a thorough exploration of various factors affecting the degradation efficacy, including pH levels during CF degradation, initial CF concentration, and the dosage of MgFe 2 O 4 NPs as photocatalysts, was conducted.The MgFe 2 O 4 NPs demonstrated notable photocatalytic efficiency in the removal of CF from aqueous solutions.Remarkably, under conditions of pH 9 and utilizing 15 mg of MgFe 2 O 4 NPs, approximately 96% of a 10 ppm CF solution was effectively photodegraded after 135 min.In vitro assessments further corroborated the antimicrobial potential of MgFe 2 O 4 NPs, as evidenced by zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) results.Specifically, MgFe 2 O 4 NPs (6) h + VB + MgFe 2 O 4 NPs → MgFe 2 O 4 NPs + oxidation of the compound (7) h + VB + OH − → OH (8) OH .+ CF → Degradation products

Table 1 .
Antimicrobial activity assays of MgFe 2 O 4NPs by disk diffusion and macrobroth dilution methods.MIC (Minimum inhibitory concentration).