Ecofriendly synthesis and characterization of Ni2+ codoped silica magnesium zirconium copper nanoceramics for wastewater treatment applications

This article investigates the effect of Ni2+ content on structural (XRD, XPS), morphological (TEM), and magnetic behaviors of silica magnesium zirconium copper nanoceramics calcined at 800 °C. The sol–gel route is followed for the silica magnesium zirconium copper/(0.0–0.7) Ni2+ samples preparation. X-ray photoelectron spectroscopy is employed to analyze the chemical states of elements for the samples. The three representative binding energy magnitudes for O, Ni, and Cu reside at 534, 857, and 979 eV, consecutively. The saturation magnetization constricts with the elevation of Ni2+ content, while the magnetic hysteresis loop resembles the superparamagnetic attitude. The optical spectra present the possibility of direct and indirect transitions in the prepared nanoceramics. Energy gap (value and type), refractive index, and real and imaginary dielectric constant were extracted. The energy gap approaches 3.75 eV and 3.71 eV for direct and indirect transitions correspondingly with (0.7) Ni2+. The antimicrobial and the toxicity performance of all inspected nanocomposites were conducted against pathogenic microbes. The attained results evidenced that SMZC-0.7Ni possesses energetic antimicrobial potential against all targeted microbes. The investigated SMZC-0.7Ni nanocomposite functioned to eradicate frequent waterborne pathogens in wastewater at an appropriate dose (100 mg/L), demonstrating that SMZC can be utilized as a competent disinfectant in the municipal wastewater decontamination process. Inherently, SMZC-0.7Ni can be employed as an excellent nano-weapon against multiple dangerous microorganisms.

Water is amongst the necessities of human civilization and other life forms in the universe, as it is utilized in various daily activities. Industrial development significantly contributes to the creation of sewage, which is often dumped untreated into bodies of water, resulting in pollution 1 . Due to rising costs of freshwater resources, increasing population, and a range of climatic and environmental challenges, it is estimated that over 1.1 M people have no access to an appropriate water supply 2 . Likewise, pathogenic microbes encompassing bacteria, viruses, fungi, protozoa, and rickettsia, trigger 80% of the total illnesses in underdeveloped countries, representing a severe hazard to public health and claiming millions of lives each year around the world 3 .
The management of wastewater could be a dormant solution to pollution reduction; yet, typical treatment procedures are insufficient to eliminate new pollutants and meet stringent water quality criteria entirely. The chlorination process is employed to inactivate pathogenic microorganisms in wastewater treatment plant effluents (WWTPs) before the point of discharge. Chlorination and ultraviolet (UV) irradiation are the most frequently applied disinfecting techniques 4 . Nevertheless, the difficulties these two approaches encounter, such as the Silica magnesium zirconium copper doped with Ni 2+ nanoceramics preparation. Silicate Finally, the resultant pure and Ni 2+ doped gels were happened by stirring the sols at 100 °C and then calcined the samples at 800 °C in an electric oven, to give SMZC and Ni 2+ doped nanoceramics before characterization. X-ray photoelectron spectroscopy using a KRATOS-AXIS: (XPS) Ultra-spectrometer fortified with the monochromatic (hm = 1486.71 eV) α-X-ray source. The (CuKα) source, (λ = 0.15406 nm) of X-ray diffraction (XRD: D8-Bruker) Axs-Advance X-ray diffractometer (Bruker Co., Germany) was working for describing manufactured nanoceramic samples. The particle nanosize of the prepared nanoceramics samples was observed by HR-TEM (JEM-model; Jeol, Japan).
Agar diffusion assay. The antimicrobial capabilities of four innovative nanocomposites were investigated using the disc and well diffusion approaches against the microorganisms above. In this experiment, 100 L of each fresh selected microorganisms culture was carefully disseminated on the top layer of Mueller Hinton agar (MHA; Becton Johnston Co., Sparks, MD). Likewise, the autoclaved paper discs were filled with 50 µL of each studied nanocomposites for the disc diffusion assay and deposited into the inoculated agar plates. At the same time, the same volume of each nanocomposite investigated was injected directly into the wells, perforating MHA's profound layer of MHA agar. After 24 h of plate incubation at 37 °C, The clear zones diameters (CZD) formed were estimated in millimeters (mm) 26 .
Inactivation of cell viability. Using the broth dilution assays, the antimicrobial properties performance of each of the evaluated nanocomposites was checked to obtain the minimum inhibitory concentrations (MICs) values. As explained previously, every microbe examined (10 6 CFU/mL) was undergo to various concentrations of each nanocomposite solution (25-100 mg/L) for varying retention times (5-30 min). The numbers of developed colonies (around 30-300 CFU) were calculated to quantify microbial populations before and after treatment to particular nanocomposites 27 . The total number of surviving microbial cells was counted using the platelet count viability technique.
Estimation of released protein. Protein amounts released from damaged microbial cells were measured using the Coomassie blue assay. A hundred μL of the microbial suspension was inserted into two tubes of 50 mL sterile Typricase soy broth. One contains the effective dose and the other, which is considered a negative control, was lacking tested nanocomposites. All tubes were placed at 37 °C with agitating at 200 rpm in a shaking incubator, and samples were obtained every 2 h for 24 h (n = 12 readings) 28,29 .
Kinetic modeling for the mechanism of action. The pseudo-first-order was applied for estimating the kinetic modeling to appraise Ascertaining the speed of the effect of this effective concentration on microbial species and determining the fastest destroyed species with the concentration mentioned above.
Toxicity assay. The ecotoxicity of four aqueous suspension solutions of four nanocomposites was assessed using the luminescent Vibrio fischeri measurement technique. The hypothesis behind this test is that when this marine bacterium is subjected to sample matrices, the intensity of light produced by such bacteria increases or reduces relaying of its metabolic activity. To quantify the toxic level of aqueous solutions, the Microtox 500 analyzer was used to perform, with bioluminescence light output estimates taken after 5, 10, and 15 min as a contact time. For each nanocomposite investigated, EC 50 of bioluminescence inhibition was estimated using the MicrotoxOmni Azur program 30,31 .
Decontamination of wastewater using innovative nanocomposites. Wastewater water samples, which were collected from the clarifier system of the Abu-Rawash wastewater treatment plant, were decontaminated with an appropriate dosage of the investigated CAS antiseptic. Appropriate techniques were applied to estimate the sewage sample's physicochemical features. Waterborne pathogens such as E. coli O157, Salmonella typhimurium, S. aureus, and B. subtilis were checked in water samples before and after decontamination using the diffusion plate approach 32 . Each disinfectant's effective dose (200 ppm) was injected into each flask containing 50 mL of sewage water. After dosage exposure at different varying intervals ranging from 0 to 60 min, a suitable portion (100 µL) was taken from the flask and distributed on the surface of the chromomeric agar medium indicated in previously published articles by Hemdan et al. 21 .

Results and discussion
XPS analysis. To explore the chemical structure of SMZC and (0.0, 0.3, 0.5, 0.7) Ni 2+ -doped nanoceramics, XPS was performed in the binding energy range from 1 to 1100 eV, to obtain their compositional elements (Fig. 1). The obtained atomic concentrations of the elements for pure and doped samples in the lower binding energy are Mg, Si, and Zr at 12, 24.99, and 154 eV, respectively 33,34 . The three characteristic binding energy values for O, Ni, and Cu are at 534, 857, and 979 eV, respectively. The higher peak at 534 eV corresponds to the (O 1s) of the Si-O and Si-O-M (M = Mg, Zr, Cu) in SMZC nanoceramic 34 . The binding energy for Ni 2+ doped samples is notably higher than that in the pure SMZC nanoceramics, supporting the introduction of Ni 2+ effects on the local structure of SMZC crystal structure. This result appears to be the ability of XPS rays penetration for the complex SMZC surface and detectable their compositions through the analysis, where Ni concentration increased with decreasing Si in the SMZC matrix. Further, the varying in silicate compositions under the influence of various species (i.e., Mg, Ca, Fe, and Go) using the XPS analysis has been reported 35,36 . X-ray diffraction analysis. Figure 2 shows the diffraction pattern for the prepared SMZC and Ni 2+ doped nanoceramics, with the indexed diffraction planes, and (B), the Williamson-Hall plot for estimating the crystallite size and the lattice microstrain.
Phase identification for the X-ray diffractogram was performed. Here, we can index the peaks about JCPDS card no. 01-087-0045 for magnesium copper silicate with the chemical formula of Mg (Mg 0. 56  This is denoted as Williamson-Hall expression for uniform deformation. By plotting a relation on the form of y = mx + c, with βcosθ, being the y-axis and 4sinθ on the x-axis, we can estimate the micro-strain from the linear fit slope, and the crystallite size from the intercept with the y-axis.
The diffraction parameters were calculated and tabulated in Table 1.
Crystallite size was estimated using the Scherrer equation and compared to Williamson-the Hall plot. The strain was calculated directly as well as from the slope of the Williamson-Hall graph. The interplanar distance offered by Bragg's law. The correlation between average crystallite size with HRTEM histogram and Sherrer equation was confirmed.
(1)    Experimentally, (A) can be determined via measuring both (I o ) and (I). The absorption coefficient is wavelength reliant and the plot of (α) as a function with the λ is the spectrum of concern.
The optical constants and related parameters of (SiO 2 /MgO/ZrO 2/ CuO) doped with 0, 0.5, and 0.7 Ni 2+ films have been investigated using UV-Vis-NIR transmittance and reflectance spectrum in the wavelength region of 300-2500 nm. Figure 4a shows the optical transmittance and reflectance spectra of tested films as a function of wavelength.
The general observation shows that the films have strong absorption at short wavelengths and show a transmittance edge at the higher wavelength and these observations indicate the transition of an electron from the valance band to the conduction band. The transmittance edge slightly moves towards a higher wavelength by increasing Ni dopant which can be due to the improvement in crystallinity. Above the transmittance edges, the absorption is negligible and the films become nearly optically transparent. Besides, at low wavelengths, the reflectance of the films shows a sudden decrease and then it reaches a steady state. Moreover, there is a dependence on the Ni content where the transmittance and the corresponding reflectance of the films slightly increase with increasing Ni content which can be due to crystallinity improvement as noted from XRD. With the increase in Ni 2+ containing through the silicate-based nanoceramics, the surrounding system is a complex matrix from MgO/ZrO 2 /CuO/NiO within the SiO 2 matrix, which supports a high-crystallinity magnesium copper silicate phase as observed from XRD.
The absorption coefficient (α) is an important physical parameter that is frequently used to characterize the light wave's penetration inside film layers.
The absorption coefficient of the films was calculated with the following formula: where the film thickness is d.
The absorption coefficient behavior of the films with different Ni content (0, 5, and 7 wt%) is explored in Fig. 4b. The figure indicates that the films have an absorption peak at about 290 nm wavelengths. At higher wavelengths, the absorption is negligible and saturated. Also, the increasing Ni content leads to an increase in the absorption coefficient that may be due to the increase in light trapping 44,45 .
The optical transition type and its value can be extracted from the absorption coefficient dependence on the incident light energy through the use of Tauc's expression 46 : where p, hν, E g , and r represent a transition probability constant, photon energy, optical band gap energy, and an exponent, respectively. The exponent r can take the values of 2, 3, 0.5, and 1.5 which are corresponding to the indirect allowed, indirect forbidden, direct allowed, and directly forbidden transitions, respectively. Figure 5a,b (4) A = logI 0 /I = εLC = αC. The refractive index (n) is calculated with the next formula 21 : where k = αλ/4π, the absorption index, and λ is the light wavelength.
The refractive index change with the wavelength of SMZC: (0, 0.5, 0.7) Ni films are represented in Fig. 6a. from the figure, it is obvious that the values of n are constant with increasing wavelength. It is found that the refractive index of SMZC: (0, 0.5, 0.7)Ni film slightly increases with the increase of Ni content which is referred to as the crystallinity enhancement with the increases of Ni content.
The dielectric real and imaginary parts of the SMZC: (0, 0.5, 0.7)Ni films are extracted by the next formulas: where ε 1 and ε 2 represent the real and imaginary components of the dielectric constant, respectively. The variation of two components of dielectric constant with the photon wavelength of SMZC: (0, 0.5, 0.7)Ni films are represented in Fig. 6b,c, respectively. The figure shows that the real component values are higher than that of the imaginary component. The value of ε 1 shows a constant behavior with increasing the wavelength. As the Ni content increases the real part of the dielectric constant is slightly increased. On the other hand, the imaginary component of dielectric, ε 2 , slowly increases with the increase of incident wavelength for all films. Also, ε 2 increases slightly with an increase in Ni content.

VSM.
The magnetic performance of the prepared SMZC: (0.3, 0.5, 0.7) Ni 2+ nanoceramics was investigated via a vibrating sample magnetometer within the cycled external field of ± 10 kOe, as the resultant magnetic moment with the applied magnetic field. Most of the magnetic specifications are linked with the magnetic domain state and the particle size and shape 48 . The behavior of the produced composites resembles the superparamagnetic material attitude with very tiny remanent and negligible coercivity magnitudes. This superparamagnetic behavior is reported with close values of coercivity earlier 48 . Key magnetic parameters such as (Hc), (M S ), (M r ), and SQ, extracted from the M-H loops (Fig. 7a) are illustrated in Table 2.
The magnetization at its saturation optimum is determined by the upper limit of the magnetization curve, where the coercivity is calculated from the equation where H c right and H c left are the intersection points of the hysteresis loops with the x-axis. A noticeable slight reduction in the saturation magnetization magnitude is remarked in samples by increasing the Ni 2+ concentration (Fig. 7b), which affirms the successful grafting of nonmagnetic particles on the Ni 2+ nanoceramics. Other ε 1 = n 2 − k 2 and ε 2 = 2nk,  An inverse proportional is acquired between the coercivity and the crystallite size, This can be expressed mathematically as 16 : where E and F are constants, a plot between the inverse of crystallite size and the coercivity should result in a linear relation. the demagnetizing factor (N) (i.e. a larger demagnetizing factor is required for higher coercivities) can be obtained using the subsequent formula from Ref. 48 where N is the demagnetizing field which can be calculated by all the pre-estimated other parameters, and µ 0 is the permeability of the vacuum.
The increase in the coercivity (Fig. 7b) value might be attributed to the elevation of the magnetocrystalline anisotropy (H k ) or the demagnetizing field (N) which requires higher values to overcome the energy barrier. Another possible correlation with the reduction of the crystallite size. The acquired magnetic moment per unit formula in Bohr magneton is expressed by 52 :

Effects of studied nanoconjugates interface on tested microbial cell viability. The antimicrobial
effects of the four nanocomposites (SMZC-0.0Ni, SMZC-0.3Ni, SMZC-0.5Ni, and SMZC-0.7Ni) were verified using a qualitative agar diffusion assay and a quantitative total viable cell assay against four species of microorganisms, including (E. coli O157:H7, S. aureus, C. albicans, and A. niger) (Fig. 8). To evaluate the biocidal efficacy of all nanocomposites, the width of the defined clear zone around the discs and the well was determined (Fig. 8).
The results showed that SMZC-0.0Ni had no potential biocidal efficacy against all tested microbial species. On the contrary, when compared with SMZC-0.3Ni nanocomposite, simulation results indicated that SMZC-0.5Ni and SMZC-0.7Ni nanocomposites showed significant inhibitory effects against all tested pathogens (E. coli, S. aureus, C. albicans, and A. niger). Using the well diffusion assay, the researchers discovered that the SMZC-0.7Ni nanocomposite presented a cumulative inhibition zone of 25, 19, 17, and 16 mm versus E. coli, S. aureus, C. albicans, and A. niger, in contrast.
On the other hand, data represented in Fig. 8, confirmed that SMZC-0.3Ni nanoceramic had the shortest apparent area width compared to the species mentioned above in both disc assays and well diffusion. In addition, according to the results, when compared to the other tested species, E. coli O157:H7 was more susceptible to all analyzed nanoceramics. Moreover, compared with different bacterial strains, the fungal species were more resistant to all the nanocomposites, which could be due to the rigid cell walls, which protect them from the lethal effects of the investigated nanocomposites.

Determination of minimal inhibitory concentration and surviving cells.
The observed results are illustrated graphically in Figs. 9, 10 and 11, the MIC values and inhibitory effect of all studied nanocomposites (SMZC-0.3Ni, SMZC-0.5Ni, and SMZC-0.7Ni). The lethal dose of SMZC-0.3Ni was 75 mg/L in 10 min for E. coli and 15 min for S. aureus, while data showed that SMZC-0.3Ni could not wholly eliminate fungal species without diminishing log counts (Fig. 9). Results illustrated in Fig. 10 displayed that SMZC-0.5Ni nanocomposite had a more significant deadly dose for the pathogens studied than SMZC-0.3Ni nanocomposite antiseptic). Results obtained exhibited that SMZC-0.7Ni nanocomposite had a superior inhibitory effect and total mortality in overall log counts for all examined species, the levels of the lethal dose of SMZC-0.0Ni towards E. coli, S. aureus were 50 mg/L within 10 min, and for S. aureus and fungal species, 100 mg/L within 10 min for, C. albicans and A. niger (Fig. 11). Interestingly, SMZC-0.5Ni and SMZC-0.7Ni nanocomposites revealed a decrease in the populations of all examined species. Consequently, SMZC-0.3Ni nanocomposites had a greater antimicrobial action than SMZC-0.3Ni and SMZC-0.5Ni nanocomposites. Gram-negative and positive bacterial species (E. coli and S. aureus) were both sensitive to all of the nanocomposites examined, but there was no difference between the two molds and yeast strains whenever it came to the SMZC-0.3Ni nanocomposite.
Although the interpretations are in the same line with the findings of El Nahrawy et al. 10 , who and her coauthors perceived that the Cu-NPs have excellent antimicrobial features. Findings by similar researchers that bacterial species are more susceptible to CuSi NPs than mold and yeast species (C. albicans and A. niger) approved with the results of this investigation. The combined antibacterial effects of Cu and Si NPs are attributed to the disruption of the pathogen's cell membrane, expected due to the presence of OH radicles, as it can penetrate the (18) n B / f .u. = molecular weight × saturation magnetization 5585 . Estimation of released protein. The results are depicted graphically in Fig. 12, demonstrating that the amounts of liberated protein from targeted species before subjecting to examined nanocomposites were low. However, these amounts of produced protein were increased gradually according to the types of species and examined nanocomposites. It's worth noting that all of the microbial pathogens examined revealed a considerable amount of protein after receiving the lethal dose of SMZC-0.7Ni nanocomposites was swiftly increased. The estimated protein liberated from E. coli, S. aureus, C.albicans, and A. niger were recorded as 621, 460, 336, and 349, respectively. Several investigations revealed that the most considerable amount of protein produced indicates the examined nanocomposites' effectiveness in destroying the cell wall, releasing cellular contents outside 10 .
The kinetic modeling of the killing rate of the tested microbes. The findings of kinetics modeling employing pseudo-first-order were depicted in Fig. 13; it was established that E. coli O157:H7 seemed to have the fastest destruction frequency of all constructed nanocomposites, whereas the filamentous fungi would have the shortest frequency. Interestingly, the fabricated SMZC-0.7Ni nanocomposite's effective dose was the only one that could significantly limit the growth of microorganisms in a faster manner than those of other nanocomposites. It was necessary to keep in mind that the species of A. niger investigated were being destroyed over a significant period.
Toxicity performance testing. Nanocomposites are broadly applied in various bio-applications, but notwithstanding nanobiotechnology's rapid advancement and early acceptability, the occurrence of negative health implications from prolonged exposure at various concentration ranges in humans and the environment has yet to be determined. The influence on the environment of NPs, on the other hand, is expected to increase in the future. The capacity of NPs to organize around protein content is influenced by particle diameter, curve, form, surface composition, charge, bifunctional moieties, and renewable power 56 . The average EC50 value of all the tested nanocomposites was 214 for SMZC-0.3Ni, 198 for SMZC-0.3Ni, 208 for SMZC-0.5Ni, and 173 for SMZC-0.7Ni after 30 min of incubation (Table 3).  www.nature.com/scientificreports/ This is attributed to the fact that the nanocomposites examined are harmless and have no deleterious impacts; consequently, they may be used in various fields, encompassing ecological applications such as water decontamination, food packaging, and the textiles sector. The findings are following El Nahrawy et al. 57 , who found that copper is non-toxic when mixed with nanoceramic materials. The study also revealed that while Zr NPs are harmful, their toxicity has been reduced in this nanoceramic. As a result of its effectiveness, it could be administered as a powerful antibacterial without even being poisonous or environmentally destructive 58 .  www.nature.com/scientificreports/ Wastewater decontamination using innovative nanocomposites. Based on the above experimental results, it could be considered the SMZC-0.7Ni the best choice to apply as an alternative disinfecting agent for the wastewater disinfection process. Figure 14, illustrates the disinfection efficiency of SMZC-0.7Ni as a promising deactivator for some waterborne pathogens. Results displayed that the effective dose of SMZC-0.7Ni could wholly deactivate all estimated waterborne pathogens. The different interaction time (25 and 30 min) for eliminating the growth of E. coli, S. enterica, and P. aeruginosa was recorded. While S. aureus, L. monocytogenes,  www.nature.com/scientificreports/ and E. faecalis required a prolonged interaction time (40 and 50 min) to be completely inactivated. Likewise, Xu et al. 59 revealed that 99% of log 5 of the bacterial populations of some respective waterborne pathogens such as E. coli, Pseudomonas aeruginosa, Acinetobacter, and Bacillus have been reduced after disinfecting with some nanocomposites.

Conclusion
High-crystallinity Ni 2+ doped silicate-based nanoceramics have been grown utilizing a controlled sol-gel process and calcined at 800 °C. XPS, XRD, and TEM analyses reveal that the SMZC and doped nanoceramics consist of a crystalline SMZC matrix containing Ni 2+ in the crystalline structures. Optical analysis shows that the samples except both direct and indirect transition with values of 3.66, 3.70, and 3.75 eV (direct case), and 3.54, 3.62, and 3.71 eV (indirect case), for SMZC: (0, 0.5, and 0.7)Ni +2 , respectively. The refractive index is constant with increasing wavelength and slightly increases with increasing Ni content. The magnetic results reveal that the existence of a higher magnetization depends on the SMZC compositions, as they exhibited a smooth hysteresis loop, with a slight reduction in their saturation magnetization magnitude with increasing the Ni 2+ concentration. The antimicrobial activities results exhibited that SMZC-0.7Ni has outstanding antimicrobial properties, particularly against the investigated positive and negative bacterial species, as well as fungal strains. Consequently, the SMZC-0.7Ni nanocomposites exhibit exceptional inhibitory properties and may be applied for decontaminating wastewater by eradicating all harmful waterborne microorganisms.

Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.