Catalytic green synthesis of Tin(IV) oxide nanoparticles for phenolic compounds removal and molecular docking with EGFR tyrosine kinase

In this study, tin dioxide nanoparticles (SnO2 NPs) were successfully synthesized through an eco-friendly method using basil leaves extract. The fabricated SnO2 NPs demonstrated significant adsorption capabilities for phenol (PHE), p-nitrophenol (P-NP), and p-methoxyphenol (P-MP) from water matrices. Optimal conditions for maximum removal efficiency was determined for each phenolic compound, with PHE showing a remarkable 95% removal at a 3 ppm, 0.20 g of SnO2 NPs, pH 8, and 30 min of agitation at 35 °C. Molecular docking studies unveiled a potential anticancer mechanism, indicating the ability of SnO2 NPs to interact with the epidermal growth factor receptor tyrosine kinase domain and inhibit its activity. The adsorption processes followed pseudo-second order kinetics and Temkin isotherm model, revealing spontaneous, exothermic, and chemisorption-controlled mechanisms. This eco-friendly approach utilizing plant extracts was considered as a valuable tool for nano-sorbent production. The SnO2 NPs not only exhibit promise in water treatment and also demonstrate potential applications in cancer therapy. Characterization techniques including scanning electron microscopy, UV–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy (XRD), and energy-dispersive X-ray spectroscopy (EDAX) provided comprehensive insights into the results.


Instrumentation and characterization.
A pH meter (HANNA instruments, HI5521-02, UK) was employed to estimate the pH solutions.The orbital shaker (LAUDA, Germany) was used to shake solution contents.A hot plate (Bibby Scientific HB502, UK) was utilized to raise the temperature of the adsorption system.A UV-vis spectrophotometer (Perkin-Elmer Model lambda 25, USA) was utilized to analyze the residual phenolic compound content employing a 1 cm path length quartz cuvette (Hellma, Germany).The tin oxide (SnO 2 NPs) was monitored by UV-visible spectroscopy (Schimadzu UV-visible spectrophotometer, model UV-1800).More characterization was done using powder XRD-analysis (Advance Powder X-ray diffractometer, Bruker, Germany, model D8), The characterization of peaks for the Fourier transform-infrared spectroscopy (FT-IR) was done using (Alpha TBruker), for the morphological studies for the surface was done by SEM (Hitachi H-7100 using an accelerating voltage of 120 kV).The elemental analysis was studied using EDAX (Bruker, Germany).

Formation of O. Basilicum Leaves Extract
The O. basilicum leaves were washed with tap water to remove any dust particles, then they were rinsed with D.H 2 O and were thoroughly dried in the shade at ambient temperature.To prepare the extract, 20 g of the clean and dry leaves were added into an air-tight container with 200 ml of boiled D.H 2 O for 90 min.After letting the mixture come to ambient temperature and filtering it, centrifugation was performed for 20 min at 4000 rpm.The final greenish-yellow extract was kept at 4 °C for further experiment.

Fabrication of SnO 2 NPs
The target SnO 2 NPs were prepared by mixing 6.25 ml of SnCl 4 .5H 2 O (0.05 M) with 6.25 ml of O. basilicum leaves extract while heating (80 °C) and stirring (250 rpm) continuously for 20 min.The aged gel was thoroughly washed three times using hot D.H 2 O, stirring for 2 min, and letting it settle for sufficient time.The product was centrifuged (20 min at 3000 rpm) and washed again with ethanol.After that, it was calcined at 400 °C for 3 h.The resulting brown crystals were finely crushed into a powder and stored in a polyethylene bottle for subsequent
The batch experiments were performed by mixing fabricated SnO 2 NPs powder and phenolic solutions in different ratios (% w/w) in a 50 mL aqueous media and equilibrated at an orbital shaker for different agitation times at constant shaking speed (240 rpm).After that, all samples were centrifuged, and the absorbent went through a 0.22 μm filter membrane.The phenolic content residue in supernatants was analyzed using a UV-Vis spectrophotometer before and after adsorption.To understand the impact of adsorbent and adsorbate dosage, the adsorbent and phenolic solutions were mixed in different ratios by varying the formed SnO 2 NPs dosage from 0.10 to 0.30 g and phenolic solutions starting concentration from 1 to 10 ppm under optimal conditions.The initial pH of each phenolic solution was rigorously adjusted from 4 to 10 using hydrochloric acid (HCl, 1 M) and sodium Hydroxide (NaOH, 1 M) solutions.Different agitation times from 5 to 60 min were prepared to determine the optimum agitation time between SnO 2 NPs and phenolic solutions.The removal efficiency and adsorption capacity are calculated from Eqs. (1) and ( 2), respectively.Where the starting (C i ) and final (C t ) amounts of phenolic compounds as well as the mass of SnO 2 NPs (M), and the volume of the aqueous media used (V) 22 .All batch adsorption experiments were conducted in triplicate (n = 3), and the average results were provided.

Kinetics, isotherm, thermodynamic analysis
To further understand the mechanism of PHE, P-NP, and P-MP adsorption process progressed, several adsorptive characteristics of fabricated SnO 2 NPs were diagnosed in this study.The kinetic was studied by estimating the adsorption rate upon arrival for equilibrium.The adsorption isotherm mechanism was analyzed using the Langmuir, Freundlich, and Temkin isotherm models to explore the relationship between the SnO 2 NPs capacity and the phenolic concentration in the surrounding solution upon equilibrium.In the thermodynamic context, the . Schematic representation of the fabrication of SnO 2 NPs using the Ocimum basilicum extract.

Molecular docking and protein preparation
The Molecular Operating Environment (MOE) software was employed for the assessment of the binding capabilities of specific SnO 2 NPs obtained from the PubChem database (http:// pubch em.ncbi.nlm.nih.gov).The 3D structure of these NPs was prepared in an SDF (structure-data file) format and selected for subsequent molecular docking studies.Two distinct methods were utilized for the screening of compounds: (a) pharmacophore-based screening and (b) molecular docking.In the pharmacophore-based virtual screening, the Compute option within MOE was used to identify the pharmacophoric features of the co-crystalized ligand.
Following the selection of these ligand features, the software was executed to filter compounds based on the identified features within the co-crystal ligand.The resulting output file containing the selected compounds was then employed for subsequent molecular docking studies 19,23 .
In employing a molecular docking strategy, the ligands, pre-screened based on pharmacophore considerations, were subjected to docking with the 3D structure of the target protein.The investigation focused on determining the most favorable outcome in terms of biological activity, utilizing the crystal structure of the inactive EGFR tyrosine kinase domain in complex with erlotinib (PDB: 4HJO), with a resolution of 2.75 Å 24 .This crystal structure was retrieved from the Protein Data Bank (PDB) and meticulously prepared in the MOE for subsequent docking analyses.To anticipate the active site residues within the binding pocket, several steps were taken, including 3D protonation, energy minimization of the protein, and utilization of a site finder.The preparation of the protein structure involved tasks such as adding missing hydrogen atoms, correcting bond order assignments, adjusting charge states and orientations of various groups, and performing restrained minimizations that allowed hydrogen atoms to be freely optimized 25,26 .

Resources
The study was in accordance with relevant institutional, national, and international guidelines and legislation.

X-ray diffraction (XRD) analysis of SnO 2 NP
To investigate the phase formation and purity of the sample, Xray diffraction technique is used.The X-ray diffraction pattern of synthesized SnO2 nanoparticles was recorded at a scanning rate of 1 0 /min and within scanning angle range of 20-70.
The observation of intense peaks represents the high crystalline nature of the prepared sample with very high purity.Those peaks of the XRD analysis confirmed the type of crystalline SnO 2 which was confirmed in the literature and by other researchers 27 .All the observed peaks are matched with standard JCPDS card No. 41-1445 having tetragonal unit cell.

Fourier transform-infrared spectroscopy
The Fourier Transform Infrared Spectroscopy (FT-IR) of the prepared SnO 2 is shown in Fig. 3.The FTIR shows stannous material with strong vibration in the range of 2600 to 3600 cm −1 that proves the existence of O-H bond

Scanning electron microscope and EDAX
The study of morphological characteristics of SnO 2 NPs was studied using scanning electron microscopy (SEM) and the energy dispersive X ray analysis (EDAX).The SEM indicated the presence of very fine flakes that have very tiny agglomerates 19,27,29 as shown in Fig. 4. The EDAX spectra showed that Sn and O are the most constituents of the SnO 2 NPs as shown in Fig. 5.

Influence of nano-sorbent dosage
The impact of SnO 2 NPs dosage on each PHE, P-NP, and P-MP adsorption onto SnO 2 NPs surface was investigated with 50 mL of 10 ppm PHE, P-NP, and P-MP solutions for 30 min at 25 °C by using different nano-sorbent dosages of 0.10, 0.15, 0.20, and 0.30 g are shown in Fig. 6.Adsorption efficiency and capacity were calculated by using Eqs.
(1) and ( 2).As depicted in Fig. 6a, the higher adsorption efficiency of PHE was 16, 46, 75, and 71% with 0.10, 0.15, 0.20, and 0.30 g of SnO 2 NPs, respectively.This trend may be attributed to the active sites on the surface of phenol were initially unsaturated, but after reaching the best adsorption, the accumulation of adsorbents and competing substances causes adsorption impairment 30 .In contrast, with 0.10 g of SnO 2 NPs, the higher adsorption efficiency of P-MP and P-MP were 82 and 71%, respectively.The adsorption efficiency almost remained constant as the nano-sorbent dosage increased, as shown in Fig. 6b, c.This may be due to the fact that the nano-sorbent has high surface areas relative to their very small size, this provides more  space for adsorption even with the use of few dosages.However, increasing the nano-sorbent dosage may cause SnO 2 NPs aggregation, thus impeding adsorption efficiency.In addition, it was observed that the adsorption capacity (amount) for PHE, P-NP, and P-MP were 9.72, 9.63, and 8.28 mg/g, respectively.The adsorption capacity remained constant as the nano-sorbent dosage decreased; this suggests a preference for using NPs as absorbent surfaces of target phenolic compounds 10 .Therefore, the nano-sorbent dosage was taken as 0.20 g of PHE, whereas 0.10 g of P-NP and P-MP in further experiments.

Influence of agitation time
In order to evaluate the effect of agitation time on the adsorption uptake of PHE, P-NP, and P-MP molecules, experiments were carried out under agitation times from 0 to 60 min.Figure 7 illustrates the removal efficiency of PHE, P-NP, and P-MP onto SnO 2 NPs as a function of agitation time.The removal process occurred in two stages: a rapid removal within the first 5 min and a relatively slow adsorption within 5-60 min.The PHE, P-NP, and P-MP adsorption rates reached equilibrium at 30 min with 88, 83, and 91% removal effectiveness, respectively.These results could be attributed to the presence high number of vacant active sites and the appropriate pore size of the nano-sobent surface, which can promote the internal mass transfer and adsorption process progress.However, the adsorption rate decreased progressively within 30-60 min due to accumulated adsorbate on the adsorbent surface and a rise of internal diffusion resistance 28,31 .The results indicate SnO 2 NPs prefer to remove PHE, P-NP, and P-MP molecules.

Influence of starting phenolic solutions concentration
The adsorption of PHE, P-NP, and P-MP onto the SnO 2 NPs surface is highly dependent on the starting concentration of these phenolic solutions.This is related to the abundance of active sites on the nano-sorbent surface.Therefore, the impact of starting concentrations on adsorption quality was studied by varying PHE, P-NP, and P-MP concentrations from 1 to 10 ppm.The experiment was performed under the optimal parameters previously mentioned.The maximum removal efficiencies of each PHE, P-NP, and P-MP were obtained at 3 ppm of PHE, P-NP, and P-MP as a starting concentration, with 91, 88, and 77% removal, respectively.Afterward, adsorption efficiency decreased significantly as the starting concentration of the solution was increased, as depicted in Fig. 8.This phenomenon may attributed to the increased amount of PHE, P-NP, and P-MP ions with limited active sites on the SnO 2 NPs surfaces, thus decreased the removal quality 32 .Moreover, this is a logical trend, as high concentrations of solutions are expected to be accompanied by increased agitation time required to achieve adsorption equilibrium.Our result agrees with previous literature 9,33 .

Influence of the initial pH
The pH of solutions constitutes a significant effect on the adsorption efficiency of phenols from aqueous systems as shown in Fig. 9. Particularly when the phenolic compounds may exist in various forms such as phenolic or phenolate relative to the pH of the solution.Therefore, the initial pH was studied to investigate its effect on the phenolic compounds adsorption at different initial pH values of 4, 6, 8, and 10, and starting phenolic solutions concentration of 3 ppm for 30 min at 25 °C.As illustrated in Fig. 9a, the maximum removal efficiency for PHE, P-NP, and P-MP were obtained at pH values of 8, 8, and 6 with 94, 94, and 83% removal, respectively.This phenomenon may be related to the pH ZPC of SnO 2 NPs, implying that the nano-sorbent surface has a zero charge at a specific pH value 8 .The adsorption efficiencies increased dramatically as the pH values increased.At a pH of lower than pHPzc, the nano-sorbent surface is positively charged.PHE, P-NP, and P-MP act as weak acids in the solutions, and all become phenolate anions, as depicted in Fig. 9b.Thus, the removal happens due to the dipole-dipole interaction at higher pH values.At much lower pH, additional positive protons compete for active binding sites on the nano-sorbent surface; this reduces adsorption efficiency.Conversely, at a pH of higher than  www.nature.com/scientificreports/pH ZPC , the nano-sorbent surface is negatively charged.Adsorption decreases slightly, and this may be due to the electrostatic repulsion interaction between the nano-sorbent and the adsorbate (negative charge holders).The achieved results agree with the previous literature's data 10 .Furthermore, it can be seen that the effectiveness of the adsorption of both PHE and P-NP was greater than that of the adsorption of P-MP.This assessment is supported by the fact that the hydrogen binding capabilities of phenolic compounds are directly proportional to their acidities.The protons transfer to nano-sorbent surface is easier in the case of PHE and P-NP; this allows them to form H-bonds and achieve higher adsorption effectiveness.In the case of P-MP, weak H-bonding interactions are formed; this may be attributed to the steric effect of methoxy groups.Overall, a change in the solution pH predominantly impacts the strength of H-bonding, adsorbent-adsorbate interactions and adsorption efficiency 34    www.nature.com/scientificreports/

Influence of temperature
The impact of temperatures on each PHE, P-NP, and P-MP adsorption was assessed in this study.For this purpose, The adsorption studies were conducted at 25, 35, 45, and 55 °C, and optimized parameters were maintained during the experiment.The results demonstrated that the maximum adsorption effectiveness of P-MP was 94% at 25 °C, and then the adsorption significantly decreased as the temperatures rose to 68% at 55 °C, as shown in Fig. 10.This may refer to the destruction and damage of active binding sites on the SnO 2 NPs surface due to high temperatures.It should be noted that the effectiveness of both PHE and P-NP removal increased significantly by increasing the temperature from 25 to 35 °C, then progressively decreasing as the temperature increased from 35 °C to 55 °C.Accordingly, it was determined that 35 °C is favorable for the PHE and P-NP adsorption onto SnO 2 NPs with 95 and 85% removal, respectively.This result can be justified as it is with the increasing system temperature over 35 °C, the boundary's thickness will gradually drop.This can increase the tendency of PHE and P-NP to escape to the solution phase, decreasing adsorption 35 .

Modelling of adsorption kinetics
The adsorption process of each PHE, P-NP, and P-MP was further characterized using the pseudo-1st order (Eq.3) and pseudo-2nd order (Eq.4) kinetic models and is shown in Fig. 11.The linearized forms of the pseudo-1st order (Fig. 11a,c, e) and pseudo-2nd order kinetic models are depicted in (Fig. 11b,d,f).The removal rate constants of the adsorption process were indicated by k 1 and k 2 , respectively.Also, the adsorption quantity in mg of each PHE, P-NP, and P-MP per g of SnO 2 NPs at both equilibrium (q e ) and different agitation times (q t ) was calculated from the adsorption experimental data.
The coefficient of determination (R 2 ) value indicated that the adsorption of all PHE, P-NP, and P-MP more closely obeyed a pseudo-2nd order model.This model presumes the dominance of chemisorption over the adsorption mechanism of PHE, P-NP, and P-MP onto SnO 2 NPs.This case involves exchanging or sharing electrons between the phenolates and SnO 2 NPs 10,36 .
The experimental and calculated adsorption quantity (qe, mg/g) of PHE, P-NP, and P-MP at equilibrium and all kinetic parameters of pseudo-1st order and pseudo-2nd order models were calculated and presented in Table 1.

Adsorption isotherms
The removal isotherm mechanism was studied to provide information about the attitude of mono-layer adsorption and multi-layer adsorption, in addition to suggesting the nature of the adsorption surface and interactions between the nano-sorbent and the adsorbate 37 and are shown in Fig. 12.Therefore, the Langmuir (Fig. 12a,d,g), Freundlich (Fig. 12b,e,h), and Temkin isotherm models (Fig. 12c,f,i) were identified by examining the adsorptive capacity of SnO 2 NPs, and they are expressed by (Eq.5), (Eq.6) and (Eq.7) and are shown in Fig. 12a-i, respectively.
(3) ln q e − q t = lnq e − k 1 t (4) t q t = 1 k 2 q 2 e + t q e (5)  where the q max represents maximum mono-layer adsorption capacity (mg of phenolic compounds per g of SnO 2 NPs).R L is the separation factor, and n is the surface heterogeneity index, whereas K L K F , and B T are the Langmuir constant (L/mg), the Freundlich constant (mg 1/n g −1 L −1/n ), and the Temkin constant (J/mol).
As illustrated in Fig. 12, the R 2 values were lower in the Langmer and Ferndlich models plots than in the Temkin model.Therefore, all PHE, P-NP, and P-MP adsorption processes were fitted well to Temkin isoherm model.The adsorption isotherm results of PHE, P-NP, and P-MP indicate that multi-layer adsorption occurred.Furthermore, with an increase in nano-sorbent surface coverage, the heat of the adsorption system (all molecules) in the layer decreases linearly rather than logarithmically 38 .
According to Temkin isoherm, higher B T values refer to stronger adsorption binding between the adsorbent and adsorbate; thus, the phenolates are more strongly attracted to the SnO 2 NPs surface.Meanwhile, higher K T values refer to a higher concentration of phenolic molecules on the SnO 2 NPs surface, confirming a favorability www.nature.com/scientificreports/extent of adsorption.Overall, these results indicate that the uniform distribution of phenolate groups on the adsorbate and SnO 2 NPs surfaces may cause a uniform distribution of binding energies 39,40 .
All isotherm parameters of the Langmuir, Freundlich and Temkin models were provided in Table 2.

Adsorption thermodynamics
Thermodynamic adsorption was studied to calculate the amount of energy and heat changing during the PHE, P-NP, and P-MP adsorption processes and to determine these processes' spontaneity as shown in Fig. 13.So, the dissociation coefficient (K d ) and standard Gibbs free energy (ΔG 0 ) were calculated at a specific temperature employing Eqs. ( 8), (9), and plots of ln K d vs. 1/T were produced as depicted in Fig. 13.In addition, the standard enthalpy changes (ΔH 0 ), and standard entropy changes (ΔS 0 ) were calculated from van't Hoff plot and Eq.(10).Regarding the data in Table 3, the ∆G o negative values suggest the PHE (Fig. 13a), P-NP (Fig. 13b) and P-MP(Fig.13c) adsorption processes were spontaneous and favorable.This corresponds to the fact that adsorption decreases with high temperatures.A negative ΔH 0 value indicates an exothermic nature for all PHE, P-NP and P-MP adsorption processes.Moreover, the negative ΔS 0 (randomness index in adsorption system) value in PHE adsorption indicates that the system is becoming more ordered.In contrast, in P-NP and P-MP adsorption thermodynamics, the positive value of ΔS 0 indicates the processes favored to be less ordered.This may be justified by the fact that the degree of the freedom of solvent molecules decreases as the number or size (8)  www.nature.com/scientificreports/ of surrounding molecules increases, imposing less ordered adsorption 41 .In general, further understanding of thermodynamic parameters can help to promote the adsorption process for several applications.

Comparison with other sorbent to removal of phenolic pollutants
The performance of various adsorbents for phenolic pollutants removal was compared and summarized in Table 4.As can be seen, the removal efficiency of phenolic compounds on SnO 2 NPs was higher than other adsorbents previously reported in the literature.The SnO 2 NPs in this study were superior to other adsorbents in terms of large adsorption surface area, adsorption rate, and chemical saving, thereby promoting adsorption capacity in SnO 2 NPs.

Molecular docking studies
Molecular docking studies of synthesized nanomaterials revealed their possible interactions with active site residues of given protein targets 40 .The SnO 2 NPs demonstrated moderate binding energies against the crystal structure of the inactive EGFR tyrosine kinase domain in complex with erlotinib (PDB: 4HJO) showing their critical interaction with key amino acids.Docked complexes obtained for SnO 2 showed two conventional hydrogen bonds with ARG817 (2.3 Å) and LYS721(2.0Å) with a binding score of − 6.619 kcal/mol.The negative and low docking score value indicate that the compounds underwent strong and favorable binding interactions.
Our findings are compatible with those found in the literature 43 , and RMSD refine 1.1985 Å is less than 2 Å, i.e., a good result, as depicted in Fig. 14.While in silico investigations have exhibited encouraging outcomes concerning the capability of SnO 2 NPs to impede the EGFR tyrosine kinase pathway, additional inquiries are imperative to ascertain their therapeutic effectiveness in clinical applications.This research holds the potential to advance the development of efficacious cancer therapies, underscoring the necessity for comprehensive investigations to validate the therapeutic utility of these NPs as anticancer agents targeting the EGFR tyrosine kinase pathway 44 .

Conclusion
In summary, we report here the green synthesis of the SnO 2 NPs using O. basilicum leaves extracts.Fabricated SnO 2 NPs showed superior PHE, P-NP, and P-MP removal from the aqueous system.The influence of five key variables on all PHE, P-NP, and P-MP adsorption by fabricated SnO 2 NPs, including pH, starting PHE, P-NP, and P-MP concentrations, nano-sorbent dose, agitation time, and temperature was also investigated and enhanced.According to the data, the maximum removal effectiveness of PHE, P-NP, and P-MP were 95%, 85%, and 94%, respectively.Based on the Kinetic experiments, the PHE, P-NP, and P-MP adsorption data demonstrated the best fit by the pseudo-2nd order kinetic model, and all mechanisms are controlled by chemisorption.In equilibrium studies, adsorption processes are described by Temkin isotherm model.The Thermodynamic results show that the PHE, P-NP, and P-MP adsorption processes onto fabricated SnO 2 NPs have a spontaneous and exothermic nature.
Based on the overall analysis, it can be indicated that the eco-friendly approach serves as an invaluable tool for the production of nano-sorbents mediated by plant extracts.Moreover, our nano-sorbent's ultra-effective adsorption of phenolic pollutants may be attributed mainly to the availability of active adsorption sites regardless of their extremely small size.Our molecular docking studies revealed the potential of SnO 2 NPs to interact with the EGFR tyrosine kinase domain and inhibit its activity, suggesting a novel anticancer mechanism of action.However, we need more research and progress into nanoscale adsorbents and their development for real applications.

Figure 6 .
Figure 6.Impact of the nano-sorbent dosage on both adsorption capacity and removal efficiency for (a) PHE at pH = 8, (b) P-NP at pH = 8, and (c) P-MP at pH = 6 (Conditions: agitation time, 30 min; starting phenolic solution concentration, 10 ppm; at room temperature).

Figure 14 .
Figure 14.2D and 3D view of the binding interaction of SnO 2 NPs within active sites of the EGFR receptor (PDB: 4HJO).

Table 1 .
Calculated kinetic parameters for PHE, P-NP, and P-MP adsorption.

Table 2 .
Calculated isotherm parameters for PHE, P-NP, and P-MP adsorption.Where the R is ideal gas constant, and T represents temperature in the Kelvin scale.

Table 4 .
Comparison of the phenolic compounds removal by SnO 2 NPs with other sorbents.