Application of Synthesized Vanadium–Titanium Oxide Nanocomposite to Eliminate Rhodamine-B Dye from Aqueous Medium

In this study, a V@TiO2 nanocomposite is examined for its ability to eliminate carcinogenic Rhodamine (Rh-B) dye from an aqueous medium. A simple ultrasonic method was used to produce the nanosorbent. In addition, V@TiO2 was characterized using various techniques, including XRD, HRTEM, XPS, and FTIR. Batch mode studies were used to study the removal of Rh-B dye. In the presence of pH 9, the V@TiO2 nanocomposite was able to remove Rh-B dye to its maximum extent. A correlation regression of 0.95 indicated that the Langmuir model was a better fit for dye adsorption. Moreover, the maximum adsorption capacity of the V@TiO2 nanocomposite was determined to be 158.8 mg/g. According to the thermodynamic parameters, dye adsorption followed a pseudo-first-order model. Based on the results of the study, a V@TiO2 nanocomposite can be reused for dye removal using ethanol.


Introduction
Industrial wastewater contains artificial pigments that constitute an environmental risk; thus, toxic dyes should permanently be removed from the aquatic system [1]. Dumping colored wastewater into receiving waterways has become a severe environmental issue worldwide [2]. The release of wool, rug, pulp, sheet, and textile effluents frequently tint the collecting waters for kilometers in the direction of the source [3]. The color is visually unappealing and inhibits the passage of light into the water, lowering the effectiveness of photosynthesis in aquatic plants and negatively affecting their development [4]. The extensive use of dyes in the fabric, publishing, latex, beauty product, plastic, and leather sectors produces a massive volume of colored wastewater [5][6][7]. Rhodamine B has a comprehensive application, encompassing textiles, food, laser technology, biomarkers, molecular probes, sensitizers, electrochemical-luminescence, and solar panels [8]. rhodamine B (Rh-B) dye is considered a skin-irritating agent, neurotoxic, chronically toxic to aquatic organisms, and carcinogenic to humans. [9]. Thus, purifying water bodies from Rhodamine B is an urgent task to protect the environment and human health. One of the most popular cationic water-soluble organic dyes is Rh-B [10]; it is toxic and lethal to aquatic environments [11]. The numerous procedures for decolorization are categorized as chemical, physical, and microbial techniques [12][13][14]. Physical treatments involve sorption, ozonation, and membrane processes [15]. While chemical procedures comprise oxidation, For the V-TiO 2 sorbent, 0.0338 moles of TiO 2 nanoparticles (Sigma Aldrich) were dispersed in 0.12 L isopropanol solvent using an ultrasonic bath for 20.0 min. Then, 0.00165 moles of V 2 O 5 were added to the milky TiO 2 solution, and the mixture was sonicated for a further 40.0 min with vigorous stirring (550 rpm). After the mixtures were blended, they were heated for 20 h at 90 • C in an electric dry oven, and the resulting nanoparticles were ground before being calcined. The greenish-white powders were annealed for 2 h at 145 • C.

Sorbent Characteristics
The structural properties of the as-synthesized sample were investigated by X-ray diffraction (XRD) utilizing a Rigaku diffractometer operated with Cu K radiation ( though these approaches are successful, they have several drawbacks, including increased chemical consumption and sludge formation, and they are expensive [17]. Among all the dye treatment procedures, adsorption is reported to be efficient and economical [18]. Activated carbon is an efficient adsorbent for removing dyes from industrial sewage effluents; nevertheless, its cost limits its usage [19]. Alongside traditional adsorbents, various economical nonconventional adsorbents have been demonstrated to eliminate dyes efficiently [20]. For the removal of dyes, investigations, including the analysis of practical and inexpensive adsorbents produced from available resources, are increasingly relevant [21]. Employing nanotechnology to clean contaminated environments has shown to be advantageous, saving a lot and lowering pollution levels to tolerable levels [22][23][24]. Metallic nanoparticles and nanocomposites are regarded as potential adsorbents with high dye removal capability due to their sensitivity, permeability, and recyclability within each known sorbent [25,26]. Lately, metal-based nanocomposites such as MgO/TeSe, (Y2O3)n-ZnO, GO-TiO2, Fly-Ash@Fe3O4, and Fe2O3-TiO2-graphene have been used to eliminate various dyes from water systems [27][28][29][30][31][32][33]. Several proposals for nanoparticle production have involved mechanical, physiochemical, and biological procedures [34][35][36]. Furthermore, nanostructured and composite materials can be employed to capture or destroy dye contamination in an aqueous environment [37][38][39]. V-TiO2 was utilized as the base material to synthesize triple composites and used mostly as a photocatalyst [40][41][42].
This research aimed to establish a straightforward method for producing V-TiO2 nanomaterial. The synthesized V-TiO2 will be analyzed by physical means and introduced as a practical, environmentally friendly, and inexpensive composite to get rid of the coloring dyes from water.

Fabrication of V@TiO2 Sorbent
For the V-TiO2 sorbent, 0.0338 moles of TiO2 nanoparticles (Sigma Aldrich) were dispersed in 0.12 L isopropanol solvent using an ultrasonic bath for 20.0 min. Then, 0.00165 moles of V2O5 were added to the milky TiO2 solution, and the mixture was sonicated for a further 40.0 min with vigorous stirring (550 rpm). After the mixtures were blended, they were heated for 20 h at 90 °C in an electric dry oven, and the resulting nanoparticles were ground before being calcined. The greenish-white powders were annealed for 2 h at 145 °C.

Sorbent Characteristics
The structural properties of the as-synthesized sample were investigated by X-ray diffraction (XRD) utilizing a Rigaku diffractometer operated with Cu K radiation (ʎ = 0.15406 nm) at 40 kV and 40 mA. Fourier transform infrared (FT-IR) spectra were acquired with the KBr pellet (400 to 4000 cm −1 ) on a Thermo Scientific Nicolet 380 Fourier transform spectrometer. Using a JEM-2100 high-resolution transmission electron microscope (TEM), the microscopic characteristics of the materials were studied. X-ray photoelectron spectroscopy (XPS) was utilized to investigate surface chemistry using an RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with Al K radiation (ℎ = 1486.6 eV). ʎ = 0.15406 nm) at 40 kV and 40 mA. Fourier transform infrared (FT-IR) spectra were acquired with the KBr pellet (400 to 4000 cm −1 ) on a Thermo Scientific Nicolet 380 Fourier transform spectrometer. Using a JEM-2100 high-resolution transmission electron microscope (TEM), the microscopic characteristics of the materials were studied. X-ray photoelectron spectroscopy (XPS) was utilized to investigate surface chemistry using an RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with Al K radiation (hv = 1486.6 eV).

Rh-B Sorption Studies
The batch test protocol was employed to investigate the Rh-B dye adsorption onto the V@TiO 2 nanocomposite. In 0.025 L small bottles, 5 to 100 ppm concentrations of Rh-B dye in distilled water were mixed with 10 mg of the nanocomposite. The mixture solution was constantly agitated for 20 h. Following the establishment of equilibrium with the aqueous phase, the nanocomposite was isolated by filtering, and Rh-B dye concentrations were measured using a UV-vis spectrophotometer. The amount of adsorbed Rh-B dye at any given time (in minutes) and adsorption equilibrium magnitudes Q t and Q e (mg/g) were calculated using the same equation (Equation (1)): where V is the volume of the solution in liters; C 0 , C e , and C t are the starting concentration, equilibrium concentration, and concentration of the Rh-B dye in solution, respectively, in milligrams per liter; and m is the mass of the adsorbent (g). The contact times data were used to investigate the Rh-B sorption via the pseudo-first-order, and pseudo-second-order models (PSFOM, PSSOM) as expressed in equations 2 and 3, respectively. Also, the sorption control mechanism was studied utilizing the liquid film and the intraparticle diffusion models (IDM and LDM) presented by Equations (4) and (5) [43]: where q e (mg g −1 ) represents q t at equilibrium and k 1 (min −1 ) and k 2 (g mg −1 min −1 ) are the rate adsorption constants for the PSFO and PSSO models, which have been calculated from the slope and intercept values, respectively. The LFDM and IPDM constants were represented as K IP (mg g −1 min −0.5 ) and K LF (min −1 ), and both were computed from their slope values. C i (mg g −1 ) is a boundary-layer-thickness factor [44].

pH Point of Zero Charges Experiment
In each flask, with a pH ranging from 1 to 12, ten milligrams of V@TiO 2 nanocomposite and ten milliliters of a 0.1 mole/L sodium chloride (NaCl) solution were added. A trace amount of hydrochloric acid or sodium hydroxide was incorporated into the solution in order to bring about a change in the pH. In order to achieve equilibrium, these bottles were left on a multi-stirrer at room temperature for exactly one hour; then, the pH levels of the solutions were measured. The point zero charges were found by comparing the initial and final pH values against the original pH graph.

XRD Analysis of V@TiO 2 Nanocomposite
X-ray diffraction (XRD) examination was conducted to verify the produced V@TiO 2 nanocomposite. Figure 1  with JCPDS Card No. 01-0359 [45]. By means of the Debye-Scherer equation [46], the average crystal size of the V@TiO2 nanocomposite was determined to be 33.83 nm, with a dspacing of 3.236 Å .  (Figure 2d). The EDX analysis sheds light on the stoichiometry of oxygen, vanadium, and titanium, as well as the proportions of these elements and the actual integration of V2O5 into the TiO2 lattice. The transmission electron microscope (TEM) gave an estimate of 30-100 nm for the typical particle size of the sorbent. The value, however, was comparable to the crystallite size determined by XRD.   (Figure 2d). The EDX analysis sheds light on the stoichiometry of oxygen, vanadium, and titanium, as well as the proportions of these elements and the actual integration of V 2 O 5 into the TiO 2 lattice. The transmission electron microscope (TEM) gave an estimate of 30-100 nm for the typical particle size of the sorbent. The value, however, was comparable to the crystallite size determined by XRD. with JCPDS Card No. 01-0359 [45]. By means of the Debye-Scherer equation [46], the average crystal size of the V@TiO2 nanocomposite was determined to be 33.83 nm, with a dspacing of 3.236 Å .

Morphological Observations
The TEM images of the V@TiO2 sorbent at different magnifications confirmed the morphology and indicated the elemental distribution, as shown in Figure 2a-c. The semispherical form of the TiO2 nanoparticles is seen clinging to the V2O5 nanomaterials, as shown in the TEM pictures. The elemental distribution of V, Ti, and O in the synthesized nanomaterials is characterized by means of EDX spectra (Figure 2d). The EDX analysis sheds light on the stoichiometry of oxygen, vanadium, and titanium, as well as the proportions of these elements and the actual integration of V2O5 into the TiO2 lattice. The transmission electron microscope (TEM) gave an estimate of 30-100 nm for the typical particle size of the sorbent. The value, however, was comparable to the crystallite size determined by XRD.   [47]. Due to the self-orbital coupling effect, the Ti 2p peak was subdivided into Ti 2p3/2 (458.3 eV) and Ti 2p1/2 (464.1 eV), as shown in Figure 3c. They were symmetrical with a normal Gaussian peak shape, indicating that Ti 4+ was predominantly present in the undoped sample. Due to the influence of the O1s satellite peak, only the V 2p3/2 peak was displayed in the current experiment. The V doped in the TiO 2 nanoparticles (Figure 3d) consisted of two chemical states, V 5+ and V 4+ , with energies of 514.9 and 527.33 eV, respectively. The literature [48] indicates that V dopants can exist in surficial VO 2+ , surficial V 2 O 5 islands, interstitial, and replacement V ions. In light of the XRD and TEM analyses, as well as the fact that V doping can result in the O1s peak shifting, it is plausible to assume that the V ions existed in a substituted form and not as the V 2 O 5 isolated phase, as suggested by the literature [49].
O-Ti) and surface-absorbed hydroxyl groups of Ti-OH ( Figure 3a) [47]. Due to the selforbital coupling effect, the Ti 2p peak was subdivided into Ti 2p3/2 (458.3 eV) and Ti 2p1/2 (464.1 eV), as shown in Figure 3c. They were symmetrical with a normal Gaussian peak shape, indicating that Ti 4+ was predominantly present in the undoped sample. Due to the influence of the O1s satellite peak, only the V 2p3/2 peak was displayed in the current experiment. The V doped in the TiO2 nanoparticles ( Figure 3d) consisted of two chemical states, V 5+ and V 4+ , with energies of 514.9 and 527.33 eV, respectively. The literature [48] indicates that V dopants can exist in surficial VO 2+ , surficial V2O5 islands, interstitial, and replacement V ions. In light of the XRD and TEM analyses, as well as the fact that V doping can result in the O1s peak shifting, it is plausible to assume that the V ions existed in a substituted form and not as the V2O5 isolated phase, as suggested by the literature [49].
Usually, due to the similar radii of V 4+ and Ti 4+ species, V 4+ ions can typically only integrate into the TiO2 lattice by substituting Ti 4+ ions. Therefore, the Ti-O-V bond, which results in oxygen vacancy and a high electron production capability, is formed by sharing the oxygen atoms of the V 4+ ions in the TiO2 lattice. Furthermore, the presence of more V 4+ ions leads to the creation of more O2 radicals, the most powerful oxidizing species in photocatalysis [50,51]. As a result, the existence of V 4+ contributes significantly to the improvement of photocatalytic activity [52].  Usually, due to the similar radii of V 4+ and Ti 4+ species, V 4+ ions can typically only integrate into the TiO 2 lattice by substituting Ti 4+ ions. Therefore, the Ti-O-V bond, which results in oxygen vacancy and a high electron production capability, is formed by sharing the oxygen atoms of the V 4+ ions in the TiO 2 lattice. Furthermore, the presence of more V 4+ ions leads to the creation of more O 2 radicals, the most powerful oxidizing species in photocatalysis [50,51]. As a result, the existence of V 4+ contributes significantly to the improvement of photocatalytic activity [52].

pHzc of V@TiO 2 Nanocomposite
The pH of the point of zero charge (pHzc) of the V@TiO 2 nanocomposite was evaluated using the pH drift method to completely comprehend the pH effect on the adsorptive removal of dye pollution from an aqueous medium. According to the obtained results, the  (Figure 4). The influence of pH on Rh-B dye removal is a significant factor for the adsorption technique, as it modifies not only the active sites on the V@TiO 2 surface of the adsorbent that are capable of Rh-B dye bonding, but also the solubility of Rh-B dye in the aqueous solution.
Molecules 2023, 28, x FOR PEER REVIEW 6 of 15 3.1.3. pHzc of V@TiO2 Nanocomposite The pH of the point of zero charge (pHzc) of the V@TiO2 nanocomposite was evaluated using the pH drift method to completely comprehend the pH effect on the adsorptive removal of dye pollution from an aqueous medium. According to the obtained results, the pHZPC value of the V@TiO2 nanocomposite was 4.2. At this pH (pHzc = 4.2), the surface charge on the V@TiO2 nanocomposite is zero, whereas the surface charge is positive at pH values less than 4.2 and negative at pH values greater than the pHZPC (Figure 4). The influence of pH on Rh-B dye removal is a significant factor for the adsorption technique, as it modifies not only the active sites on the V@TiO2 surface of the adsorbent that are capable of Rh-B dye bonding, but also the solubility of Rh-B dye in the aqueous solution.

Surface Characteristics of the V@TiO2 Nanocomposite
From the surface property investigation, the isotherm and pore size distribution of the manufactured V@TiO2 nanocomposite are depicted in Figure 5a. The resulting isotherm is of class IV with H1 hysteresis loops, which seem to be characteristic of nanostructured and mesoporous materials [53,54]. Figure 5b shows a BET surface area of 16 m 2 /g and a pore volume of 0.018 cc/g, along with a pore size distribution with a median of roughly 27.6 nm.  From the surface property investigation, the isotherm and pore size distribution of the manufactured V@TiO 2 nanocomposite are depicted in Figure 5a. The resulting isotherm is of class IV with H1 hysteresis loops, which seem to be characteristic of nanostructured and mesoporous materials [53,54]. Figure 5b shows a BET surface area of 16 m 2 /g and a pore volume of 0.018 cc/g, along with a pore size distribution with a median of roughly 27.6 nm.

pHzc of V@TiO2 Nanocomposite
The pH of the point of zero charge (pHzc) of the V@TiO2 nanocomposite was evaluated using the pH drift method to completely comprehend the pH effect on the adsorptive removal of dye pollution from an aqueous medium. According to the obtained results, the pHZPC value of the V@TiO2 nanocomposite was 4.2. At this pH (pHzc = 4.2), the surface charge on the V@TiO2 nanocomposite is zero, whereas the surface charge is positive at pH values less than 4.2 and negative at pH values greater than the pHZPC (Figure 4). The influence of pH on Rh-B dye removal is a significant factor for the adsorption technique, as it modifies not only the active sites on the V@TiO2 surface of the adsorbent that are capable of Rh-B dye bonding, but also the solubility of Rh-B dye in the aqueous solution.

Surface Characteristics of the V@TiO2 Nanocomposite
From the surface property investigation, the isotherm and pore size distribution of the manufactured V@TiO2 nanocomposite are depicted in Figure 5a. The resulting isotherm is of class IV with H1 hysteresis loops, which seem to be characteristic of nanostructured and mesoporous materials [53,54]. Figure 5b shows a BET surface area of 16 m 2 /g and a pore volume of 0.018 cc/g, along with a pore size distribution with a median of roughly 27.6 nm.  interaction. In addition, the impact of the concentrations of Rh-B on sorption by V@TiO 2 was tested. Figure 6b illustrates that the q t value increased proportionally up to 75 mg L −1 , after which the inflation occurred, indicating the suitability of a 1:4 sorbent solution ratio up to 75 mg L −1 . Typically, q t values of 133.4 mg g −1 from 100 mg L −1 Rh-B solutions imply the applicability of the V@TiO 2 for treating industrial effluents with high pollutant concentrations. Additionally, the semi-complete Rh-B dye removal by V@TiO 2 from the 10 mg L −1 solutions demonstrates its effectiveness in treating contaminated water resources. Furthermore, the decrease of qt values from the same concentrations as the temperature increased showed the exothermic nature of removing Rh-B dye by a V@TiO 2 sorbent.
mentioning that nearly 95% of these uptakes occurred during the first 60 min of interaction. In addition, the impact of the concentrations of Rh-B on sorption by V@TiO2 was tested. Figure 6b illustrates that the qt value increased proportionally up to 75 mg L −1 , after which the inflation occurred, indicating the suitability of a 1:4 sorbent solution ratio up to 75 mg L −1 . Typically, qt values of 133.4 mg g −1 from 100 mg L −1 Rh-B solutions imply the applicability of the V@TiO2 for treating industrial effluents with high pollutant concentrations. Additionally, the semi-complete Rh-B dye removal by V@TiO2 from the 10 mg L −1 solutions demonstrates its effectiveness in treating contaminated water resources. Furthermore, the decrease of qt values from the same concentrations as the temperature increased showed the exothermic nature of removing Rh-B dye by a V@TiO2 sorbent.
Furthermore, the pH impact on Rh-B adsorption on V@TiO2 was evaluated ( Figure  6c). The obtained results show the suitability of mild alkaline media for removing Rh-B dye. The decrease in sorption capacity for V@TiO2 in strongly acidic media is probably due to the protonation of oxygen atoms in the nanocomposite and/or turning part of the oxides into soluble salts. On the other hand, the hydroxyl groups in strong alkaline media may compete with Rh-B dye for sorbent sites and/or repulse it away from the V@TiO2 surface [55,56].  Furthermore, the pH impact on Rh-B adsorption on V@TiO 2 was evaluated (Figure 6c). The obtained results show the suitability of mild alkaline media for removing Rh-B dye. The decrease in sorption capacity for V@TiO 2 in strongly acidic media is probably due to the protonation of oxygen atoms in the nanocomposite and/or turning part of the oxides into soluble salts. On the other hand, the hydroxyl groups in strong alkaline media may compete with Rh-B dye for sorbent sites and/or repulse it away from the V@TiO 2 surface [55,56].

Adsorption Kinetics
The linear regression plots of the PSFOM, PSSOM, IDM, and LDM for Rh-B dye sorption on V@TiO 2 are illustrated in Figure 7. The k 1 , k 2 , K IDM , and K LDM values gathered in Table 1 were computed utilizing the extracted regression parameters (slope and intercept) [43,57]. The obtained results revealed that Rh-B sorption on V@TiO 2 fit the PSFOM model, which may explain their relatively short-time equilibrium. Further, the investigation of the rate-control step showed that the intraparticle diffusion step controlled the adsorption of Rh-B onto the V@TiO 2 surface. These findings indicate that Rh-B dye has a higher affinity toward the V@TiO 2 surface and imply fast pore-diffusion during the Rh-B dye removal by V@TiO 2 [58].

Adsorption Kinetics
The linear regression plots of the PSFOM, PSSOM, IDM, and LDM for Rh-B dye sorption on V@TiO2 are illustrated in Figure 7. The k1, k2, KIDM, and KLDM values gathered in Table 1 were computed utilizing the extracted regression parameters (slope and intercept) [43,57]. The obtained results revealed that Rh-B sorption on V@TiO2 fit the PSFOM model, which may explain their relatively short-time equilibrium. Further, the investigation of the rate-control step showed that the intraparticle diffusion step controlled the adsorption of Rh-B onto the V@TiO2 surface. These findings indicate that Rh-B dye has a higher affinity toward the V@TiO2 surface and imply fast pore-diffusion during the Rh-B dye removal by V@TiO2 [58].

Adsorption Isotherms
The Langmuir and Freundlich models (LIM and FIM) were the most used isotherm models for describing adsorption processes. Both linearized models (Equations (6) and (7)) were utilized to analyze Rh-B sorption on synthesized V@TiO 2 . q e = K l q m C e 1 + q m C e (6) In these equations, Ce (mg L −1 ) is the equilibrium solution concentration, q m is the computed maximum sorption capacity, 1/n is the Freundlich adsorption intensity, and KL and KF are the LIM and FIM constants, respectively [59]. The linear fits of LIM and FIM studies of Rh-B sorption on synthesized V@TiO 2 are shown in Figure 8. Better fitting to LIM was observed in the data presented in Table 2. The Rh-B sorption showed preferential sorption, as indicated by the 1/n value below unity, which was also consistent with its PFOM agreement [60][61][62].

Adsorption Isotherms
The Langmuir and Freundlich models (LIM and FIM) were the most used isotherm models for describing adsorption processes. Both linearized models (Equations (6) and (7)) were utilized to analyze Rh-B sorption on synthesized V@TiO2.
1 ⁄ In these equations, Ce (mg L −1 ) is the equilibrium solution concentration, qm is the computed maximum sorption capacity, 1/n is the Freundlich adsorption intensity, and KL and KF are the LIM and FIM constants, respectively [59]. The linear fits of LIM and FIM studies of Rh-B sorption on synthesized V@TiO2 are shown in Figure 8. Better fitting to LIM was observed in the data presented in Table 2. The Rh-B sorption showed preferential sorption, as indicated by the 1/n value below unity, which was also consistent with its PFOM agreement [60][61][62].    As shown in Table 2, the performance of the V@TiO 2 nanocomposite in adsorbing Rh-B dye has been further evaluated and compared to that of other adsorbents that have been reported in the literature. First, the equilibrium time for the V@TiO 2 nanocomposite is shorter. These obtained results show that the Rh-B dye leaves the aqueous solution quickly. Further, the V@TiO 2 nanocomposite has a more significant adsorption capacity than the other nanostructures, i.e., 158.8 mg/g compared to 7-161 mg/g, as documented in Table 2.

Adsorption Thermodynamics
The thermodynamics of Rh-B removal by the V@TiO 2 were inspected. The slope and intercept extracted from the plot of Equation (8) (Figure 9) were utilized in computing the enthalpy and entropy (∆S o and ∆H o ). The Gibbs free energy (∆G o ) was obtained by applying the ∆S o and ∆H o values in Equation (9). The ideal gas constant (R) was used as 0.0081345 kJ mol −1 for calculating these parameters, and the findings are summarized in Table 3.
been reported in the literature. First, the equilibrium time for the V@TiO2 nanocomposite is shorter. These obtained results show that the Rh-B dye leaves the aqueous solution quickly. Further, the V@TiO2 nanocomposite has a more significant adsorption capacity than the other nanostructures, i.e., 158.8 mg/g compared to 7-161 mg/g, as documented in Table 2.

Adsorption Thermodynamics
The thermodynamics of Rh-B removal by the V@TiO2 were inspected. The slope and intercept extracted from the plot of Equation (8) (Figure 9) were utilized in computing the enthalpy and entropy (ΔS o and ΔH o ). The Gibbs free energy (ΔG o ) was obtained by applying the ΔS o and ΔH o values in Equation (9). The ideal gas constant (R) was used as 0.0081345 kJ mol −1 for calculating these parameters, and the findings are summarized in Table 3. Table 3 shows that Rh-B sorption possessed negative ΔG o values, indicating the sorption's spontaneity and exothermic nature. Also, the negative ΔH o values corroborate that V@TiO2 removed the Rh-B dye via a physisorption process [73][74][75][76][77].  Table 3. The isotherms and thermodynamic findings for the Rh-B sorption on the V@TiO2 nanocomposite.

Rh-B Dye Adsorption Mechanism
Several variables, such as the functional group of adsorbents, the pH of a solution, the surface charge on the particles, the porosity, and the nature of the adsorbate, can affect the adsorption process. Rh-B dye was adsorbed on the V@TiO 2 nanocomposite surface in this study. Point zero charges (surface charge) and FTIR (functional groups) that existed on the V@TiO 2 sorbent could explain the likely mechanism of the adsorption process. Hydrogen bonding and electrostatic interactions might have contributed to the adsorption of the Rh-B dye (Figure 10a). In Figure 10a of the FTIR spectrum, the absorption peak at 2309 cm −1 due to C-N stretching vibrations that appeared after the adsorption of Rh-B dye demonstrates its role in the adsorption of dye molecules. Due to the presence of C-H and C=C functional groups in the spectra of adsorbed Rh-B dye, the absorption band between 1539.58 and 1448 cm −1 was observed. The narrow peak between 1000 and 900 cm −1 is attributable to the C-H bond, which indicates their participation in the elimination of Rh-B dye. A prominent broad peak at 521 cm −1 , which shifted lower to 472 cm −1 , correlates to V@TiO 2 nanocomposite stretching; FTIR of the dye-loaded V@TiO 2 nanocomposite revealed a considerable drop in the peak, indicating its significance in the elimination of Rh-B dye from an aqueous solution.
the surface charge on the particles, the porosity, and the nature of the adsorbate, can affect the adsorption process. Rh-B dye was adsorbed on the V@TiO2 nanocomposite surface in this study. Point zero charges (surface charge) and FTIR (functional groups) that existed on the V@TiO2 sorbent could explain the likely mechanism of the adsorption process. Hydrogen bonding and electrostatic interactions might have contributed to the adsorption of the Rh-B dye (Figure 10a). In Figure 10a of the FTIR spectrum, the absorption peak at 2309 cm −1 due to C-N stretching vibrations that appeared after the adsorption of Rh-B dye demonstrates its role in the adsorption of dye molecules. Due to the presence of C-H and C=C functional groups in the spectra of adsorbed Rh-B dye, the absorption band between 1539.58 and 1448 cm −1 was observed. The narrow peak between 1000 and 900 cm −1 is attributable to the C-H bond, which indicates their participation in the elimination of Rh-B dye. A prominent broad peak at 521 cm −1 , which shifted lower to 472 cm −1 , correlates to V@TiO2 nanocomposite stretching; FTIR of the dye-loaded V@TiO2 nanocomposite revealed a considerable drop in the peak, indicating its significance in the elimination of Rh-B dye from an aqueous solution.
The pHpzc study determined that the pHpzc exists at a pH of 4.2, above which the surface of V@TiO2 is negatively charged, which may increase the sorption by withdrawing the positive N + -(CH3)2 group on Rh-B ( Figure 10a); this hypothesis indicates high participation of electrostatic attractions in Rh-B removal by V@TiO2. Furthermore, the adsorption of Rh-B dye on the surface of the V@TiO2 sorbent is also the result of interactions involving H-H bonding and dipole-dipole interactions. In addition, the isothermal studies demonstrate that the multilayer adsorption of the Rh-B molecules is physical sorption; this result is in line with the ΔH o values less than 80 kJmol −1 . Figure 10b depicts the subsequent adsorption of Rh-B dye molecules onto the V@TiO2 sorbent. Rh-B dye is attracted to the nanocomposites via hydrogen bonds and electrostatic interactions.  The pHpzc study determined that the pHpzc exists at a pH of 4.2, above which the surface of V@TiO 2 is negatively charged, which may increase the sorption by withdrawing the positive N + -(CH 3 ) 2 group on Rh-B ( Figure 10a); this hypothesis indicates high participation of electrostatic attractions in Rh-B removal by V@TiO 2 . Furthermore, the adsorption of Rh-B dye on the surface of the V@TiO 2 sorbent is also the result of interactions involving H-H bonding and dipole-dipole interactions. In addition, the isothermal studies demonstrate that the multilayer adsorption of the Rh-B molecules is physical sorption; this result is in line with the ∆H o values less than 80 kJmol −1 . Figure 10b depicts the subsequent adsorption of Rh-B dye molecules onto the V@TiO 2 sorbent. Rh-B dye is attracted to the nanocomposites via hydrogen bonds and electrostatic interactions.

V@TiO 2 Nanomaterials Regeneration
The regeneration of V@TiO 2 nanomaterials was studied by removing the Rh-B dye using absolute ethanol. During the regeneration process, ethanol was used as the desorption agent ( Figure 11). The rapid discoloration of absolute ethanol filtrate confirmed Rh-B dye desorption from the V@TiO2 sorbent. The sorbent was re-immersed in a freshly produced Rh-B dye solution with the same concentration and volume (5 mg/L, 75 mL). A total of five repetitions of this step were performed. Figure 11 illustrates the effectiveness of Rh-B dye desorption by ethanol from the V@TiO 2 sorbent. The efficacy of the V@TiO 2 nanocomposite to remove dyes decreased with each desorption cycle.

V@TiO2 Nanomaterials Regeneration
The regeneration of V@TiO2 nanomaterials was studied by removing the Rh-B dye using absolute ethanol. During the regeneration process, ethanol was used as the desorption agent (Figure 11). The rapid discoloration of absolute ethanol filtrate confirmed Rh-B dye desorption from the V@TiO2 sorbent. The sorbent was re-immersed in a freshly produced Rh-B dye solution with the same concentration and volume (5 mg/L, 75 mL). A total of five repetitions of this step were performed. Figure 11 illustrates the effectiveness of Rh-B dye desorption by ethanol from the V@TiO2 sorbent. The efficacy of the V@TiO2 nanocomposite to remove dyes decreased with each desorption cycle.

Conclusions
Nanostructured V@TiO2 is synthesized from metal oxide using ultrasonic synthesis techniques. A study of the adsorption properties of Rh-B dye on V@TiO2 was conducted. According to XRD, the V@TiO2 nanomaterials had a crystal size of 33.83 nm. In aqueous media, the nanosorbent of V@TiO2 was demonstrated to be capable of eliminating Rh-B dye molecules with a maximum adsorption capacity of 158.8 mg/g. Furthermore, the thermodynamic analysis showed that such reactions were highly spontaneous and endothermic. The Langmuir technique emphasized the adsorption monolayer. As a result, the adsorption kinetic could be fitted with a pseudo-first-order reaction model. Additionally, 100% ethanol was chosen as the best selective desorption eluent for reusing the adsorbent. Hence, the regeneration of V@TiO2 sorbent is a cost-effective method for treating effluents from the textile industry.

Conclusions
Nanostructured V@TiO2 is synthesized from metal oxide using ultrasonic synthesis techniques. A study of the adsorption properties of Rh-B dye on V@TiO 2 was conducted. According to XRD, the V@TiO 2 nanomaterials had a crystal size of 33.83 nm. In aqueous media, the nanosorbent of V@TiO 2 was demonstrated to be capable of eliminating Rh-B dye molecules with a maximum adsorption capacity of 158.8 mg/g. Furthermore, the thermodynamic analysis showed that such reactions were highly spontaneous and endothermic. The Langmuir technique emphasized the adsorption monolayer. As a result, the adsorption kinetic could be fitted with a pseudo-first-order reaction model. Additionally, 100% ethanol was chosen as the best selective desorption eluent for reusing the adsorbent. Hence, the regeneration of V@TiO 2 sorbent is a cost-effective method for treating effluents from the textile industry.

Conflicts of Interest:
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.