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Article

A Novel P@SiO2 Nano-Composite as Effective Adsorbent to Remove Methylene Blue Dye from Aqueous Media

by
AbdElAziz A. Nayl
1,*,
Ahmed I. Abd-Elhamid
2,
Wael A. A. Arafa
1,
Ismail M. Ahmed
1,
Aref M. E. AbdEl-Rahman
2,
Hesham M. A. Soliman
2,
Mohamed A. Abdelgawad
3,
Hazim M. Ali
1,
Ashraf A. Aly
4 and
Stefan Bräse
5,6,*
1
Department of Chemistry, College of Science, Jouf University, Sakaka 72341, Aljouf, Saudi Arabia
2
Composites and Nanostructured Materials Research Department, Advanced Technology and New Materials Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg Al-Arab 21934, Egypt
3
Department of Pharmaceutical Chemistry, College of Pharmacy, Jouf University, Sakaka 72341, Aljouf, Saudi Arabia
4
Chemistry Department, Faculty of Science, Organic Division, Minia University, El-Minia 61519, Egypt
5
Institute of Organic Chemistry (IOC), Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76133 Karlsruhe, Germany
6
Institute of Biological and Chemical Systems-Functional Molecular Systems (IBCS-FMS), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
*
Authors to whom correspondence should be addressed.
Materials 2023, 16(2), 514; https://doi.org/10.3390/ma16020514
Submission received: 1 December 2022 / Revised: 23 December 2022 / Accepted: 28 December 2022 / Published: 5 January 2023
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Abstract

:
This work aims to prepare a novel phosphate-embedded silica nanoparticles (P@SiO2) nanocomposite as an effective adsorbent through a hydrothermal route. Firstly, a mixed solution of sodium silicate and sodium phosphate was passed through a strong acidic resin to convert it into hydrogen form. After that, the resultant solution was hydrothermally treated to yield P@SiO2 nanocomposite. Using kinetic studies, methylene blue (MB) dye was selected to study the removal behavior of the P@SiO2 nanocomposite. The obtained composite was characterized using several advanced techniques. The experimental results showed rapid kinetic adsorption where the equilibrium was reached within 100 s, and the pseudo-second-order fitted well with experimental data. Moreover, according to Langmuir, one gram of P@SiO2 nanocomposite can remove 76.92 mg of the methylene blue dye. The thermodynamic studies showed that the adsorption process was spontaneous, exothermic, and ordered at the solid/solution interface. Finally, the results indicated that the presence of NaCl did not impact the adsorption behavior of MB dye. Due to the significant efficiency and promising properties of the prepared P@SiO2 nanocomposite, it could be used as an effective adsorbent material to remove various cationic forms of pollutants from aqueous solutions in future works.

1. Introduction

Many hazardous materials, such as heavy metals, dyes, drugs, pesticides, etc., have been discharged into the aquatic environment. This water pollution has become a severe universal subject and attracts attention worldwide from researchers, politicians, and simple people. Dyes are one of the more industrial effluents and are heavily used in several industries, such as food, wood, leather, paper, silk, etc. Discharging dyes in the aquatic sphere, even at low concentrations, will harm all living organisms that live in water, animals, and humans, where it is a toxic, carcinogenic, mutagenic, and non-degradable materials that can stay in the environment for a long time [1]. Methylene blue (MB) dye is the most famous water contaminant that badly impacts health through abdominal disorders, respiratory distress, skin sensitization, and blindness [2,3,4]. Also, methylene blue, with its deep blue color, reduces the penetration of the light for aquatic organisms, which has a bad effect on the environment and disorders the balance of the ecosystem leading to dangerous issues for all forms of living systems and thus threatens their life [1,5,6,7]. Therefore, it is very important to decontaminate this dye from water to prevent its discharge into the environment, especially aquatic bio-systems [1]. So, the remediation of such pollutants has extraordinary value due to the water shortage that many countries face.
Several strategies have been investigated and developed to purify water from such harmful material, including photocatalytic degradation, solvent extraction, coagulation, biodegradation, oxidation, zonation, and adsorption [5,8,9]. Adsorption, among the techniques, is the most powerful, economical, and efficient technique utilized to decontaminate dyes from wastewater at low concentrations due to its simplicity, low cost, and not requiring advanced technology [10,11,12,13]. During this year, novel adsorbent materials have been reported to remove toxic dyes such as methylene blue from wastewater [14,15,16,17,18,19,20,21,22,23,24,25,26,27]. Activated carbon (AC) is one of the most traditional, effective, and extensively utilized adsorbents in adsorption technologies, and it is among the cheapest sorbents in market. However, its failure to regenerate is still considered a major setback [28], and recycling its powdered form from the liquid phase is another intractable issue [29]. Also, some investigated materials’ main shortcomings cause them to be considered undesirable adsorbent materials due to their relatively higher cost and generation of secondary contaminants. Therefore, selecting proper adsorbent materials that produce low secondary contaminants with favorable chemical and thermal stability as well as suitable regeneration operations is the key to adsorption technologies [13]. So, scientists direct their works to investigate other alternative natural materials to treat the colored dyestuff effluents to overcome such disadvantages [30]. Siliceous adsorbents, such as silica, perlite, and glass fibers, are cost-effective and found naturally with good biocompatibility, excellent performance with non-toxicity, and considerable thermal stability in various applications, such as separation [31]. Due to the lower toxicity, easy availability, eco-friendly synthesis processes, cost-effectiveness, and bioactivity of SiO2-NPs, it is safely used in food industries, drug delivery, pharmaceutical, and water treatment systems [9,32]. Also, it has higher efficiency in removing dyes such as MB dye, where silica nanoparticle adsorbents are characterized by high surface area, low toxicity, high stability, and economical preparation that enable them to serve as an efficient adsorbent in the water treatment processes. To enhance the removal capacities of such silica nanoparticles, the surface of the material has been modified by other materials [32]. Therefore, several processes were applied to surface silica particles for water treatments [33], especially in dye removal. The first is a reduction in particle size to nanoscale to obtain a great specific surface area [33]. Surface silica nanoparticles are also hybridized, functionalized, magnetized, and doped with polymers [33,34]. One or more of these processes is carried out to increase the adsorption capacity [34]. The presence of surface (-OH) groups attached to the Si-atom on SiO2NPs is a very important characteristic and are termed silanols [34]. These silanols can interact selectively with dyes and are improved by changing the pH values [34]. Recently, many works have reported a great achievement for the new generation of silica-based nanomaterials, which illustrates outstanding adsorption capacities for several dyes by synthesis, functionalized, and hybrid SiO2NPs [34]. Modifying the silica nanoparticles’ surface will improve the adsorption performance [35]. Also reported in the literature, the surface of the silica nanoparticles was modified with organic chains involved in silane compounds. Jesionowski and Krysztafkiewicz [36] precipitated silica nanoparticles in an acidic solution followed by coupling with hydrophobic/hydrophilic function groups. Lee and Jo [37] prepared silica nanoparticles using the Stöber method and functionalized them with methyltriethoxysilane. Hah and Koo [38] synthesized silica nanoparticles using tetraethyl orthosilicate (TEOS) under a basic environment, and then methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS) were employed for anchoring the surface of the nanoparticles.
In previous studies, the modification of the silica nanoparticles was prepared through discontinuous processes with different steps and required expensive chemicals. Therefore, in our present study, tri-sodium phosphate (Na3PO4), an inexpensive and valuable material, was grafted into silica nanoparticles through a simple and green hydrothermal route. Trisodium phosphate and sodium silicate were dissolved in an aqueous solution, passed through highly acidic resin, and finally, hydrothermally treated to produce a white precipitate (P@SiO2 nanocomposite) which will be used as an effective adsorbent to the methylene blue (MB). The characterization of the fabricated P@SiO2 nanocomposite was obtained with various physicochemical techniques such as scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), elemental dispersive energy (EDX), and Fourier-transform infrared spectroscopy (FTIR). Also, the influences of the adsorption conditions, including P@SiO2 nanocomposite dosage, initial MB dye concentrations, and solution pH, on the removal efficiencies were investigated. Also, the thermodynamic, kinetic and regeneration properties were studied.

2. Materials and Methods

2.1. Materials

Di-sodium silicate (Na2SiO3, Sigma-Aldrich, St. Louis, MO, USA), tri-sodium phosphate (Na3PO4·12H2O, 96%, Sigma-Aldrich), strong acid type of cation exchange resin (Rohm and Haas, Valbonne, France) and methylene blue (Sigma-Aldrich), NaCl (Sigma-Aldrich) were used.

2.2. Characterization and Analysis

The surface morphologies of the nanocomposite were detected using a scanning electron microscope (SEM, JEOL GSM-6610LV. Japan) operating at an acceleration voltage of 20 kV. The surfaces of the specimen were treated with a thin layer of gold before imaging. The dimension of the nanomaterial was measured using Image J software (Copyright 1998-2003 JEOL LDT) from the SEM captures in an original magnification of 30,000× and 50,000×. At least 25 isolated nanoparticles were randomly selected, and their diameters and diameter distributions were measured and averaged. The elemental analysis of the materials before and after the adsorption process was determined by the EDS unit connected with the SEM. The infrared spectrum of the nanoparticles was investigated by Fourier transform infrared spectrometer (FTIR, Shimadzu FTIR-8400 S, Japan) FTIR spectra. The infrared spectra were recorded in the transmission mode using nanomaterials mixed with KBr. The experiments were investigated in the range of 4000–400 cm−1. The crystal structure of the composite was described by X-ray diffraction (XRD, Shimadzu, Japan XRD-7000) with a scanning speed of 12° min−1 from 5 to 100°.

2.3. Preparation of P@SiO2 Nanocomposite

In a typical experiment, 9.0 g of di-sodium silicate and 2.0 g of tri-sodium phosphate were dissolved in 50 mL of double distilled water. After that, the previously prepared solution was loaded on a strong acid type of cation exchange resin column. The acidified solution was recovered from the column by elution. The eluted solution was charged into stainless steel autoclave reactor and placed in a muffle at 150 °C for 24 h. The resulting white powder centrifuge was washed several times with double distilled water and dried at 70 °C for 24 h. Figure S1 (in Supplementary Materials) shows the schematic diagram of the prepared powder.

2.4. Adsorption Studies

A methylene blue (MB) dye stock solution was investigated by stirring 1.0 g of the solid dye in 1.0 L of double distilled water, and the required concentrations were obtained by dilution. Batch removal experiments were prepared by stirring 10–25 mg of nanopowder (NPs) with 10 mL aqueous solution of methylene blue in 50 mL flasks at different concentrations (100–300 mg/L), pH (1.5–11), temperatures (25–80 °C), sodium chloride dose (0–2 g) and adsorbent tests take place at constant stirring speed. The nanopowder was isolated from the MB dye solution by centrifugation. The dye concentration residue was analyzed using UV–vis spectroscopy at λ = 664 nm. The dye removal percent, %R, can be measured by applying the Equation (1):
% R = C o − C e C o × 100
where Cₒ and Ce are the initial and equilibrium concentrations of the liquid phase of the dye (mg/L), respectively.

2.5. Mathematical Modeling

Adsorption kinetic, isotherm, and thermodynamic models investigated in our study are explained in the Supplementary Material file (Sections S1.1–S1.3, respectively).

3. Results and Discussion

3.1. Characterizations

Scanning electron microscopy (SEM) was applied to study the surface morphologies of the prepared P@SiO2 nanocomposite. The SEM images of typical phosphate-doped silica (Si-P) nanoparticles are shown in Figure S1a–d. The prepared nanoparticles are spherical and have a diameter range (85–173 nm). The dimensions of the P@SiO2 nanoparticles were determined using image J software from the SEM captures in an original magnification of 30,000× and 50,000×. The average diameters and diameter distributions for 25 randomly selected isolated nanoparticles were measured and averaged, as represented in Figure 1. The data obtained showed that the morphologies of the synthesized P@SiO2 nanocomposite are relatively homogenous.
FTIR spectra of silica and P@SiO2 nanocomposite were investigated to obtain the basic information that illustrates the chemical structures of the prepared adsorbent material, as shown in Figure 2a.
The common bands assigned to various vibrations of SiO2 were observed. A broad band centered at around 3401 cm−1 corresponds to the stretching bands of the H-bonded H2O molecules in the interlayer [35]. The adsorbed water molecules show a bending vibrations band at 1597 cm−1 [35]. Two strong bands appear at 1016 cm−1 and 1136 cm−1 corresponding to the Si-O-Si asymmetric stretching vibrations [33]. Furthermore, the symmetric stretching and the bending mode vibrations of Si-O-Si appear at 738 cm−1 [39] and 405 cm−1, respectively. Upon addition of phosphate to form Si-P, these peaks have a shift (405→467, 738→800, 1016→1066, 1136→1226, 1597→1646, and 3401→3465) [40]. A strong band at 1066 and 956 cm–1, a characteristic of a PO4−3 group, was detected [41]. All of these mentioned spectral data prove that the P@SiO2 nanocomposite was successfully prepared and has many active groups on the prepared P@SiO2 nanocomposite surface that enhance the adsorption processes.
X-ray diffraction patterns were investigated to obtain information about the internal structures of SiO2 and P@SiO2 nanocomposites. The data obtained showed a broad peak at 2θ ≈ 20° and broad peaks due to the amorphous nature of the synthesized P@SiO2 nanocomposite, as represented in Figure 2b [42]. Also, other diffraction peaks were not observed at 2θ = 0.5–10°, due to the exchanges of hydrated protons and cations between the interlayers [35].
EDS measurements of P@SiO2 nanocomposite (Figure 2c), P@SiO2-MB (Figure 2d), and P@SiO2-MB (Figure 2e) in the presence of NaCl (P@SiO2-MB-NaCl) are presented in Figure 2c. The diagram shows that the prepared P@SiO2 powder consists of Si, O, P, and Na, as demonstrated in Figure 2c. After interaction with the MB dye, the introduction of C is detected in the analyzed powder (P@SiO2-MB) (as illustrated in Figure 2c). Moreover, to evaluate the influence of ionic strength on the adsorption of MB dye onto P@SiO2 nanocomposite, the elements of Na and Cl were observed in the powder (P@SiO2-MB-NaCl). This result proves that NaCl does not has any influence on the adsorption process under the investigated conditions

3.2. Adsorption Study

3.2.1. Effect of Contact Time and P@SiO2 Nanocomposite Dose

The effect of contact time on the adsorption percentage (%R) of MB dye was tested using various P@SiO2 nanocomposite adsorbents mixed with a defined concentration of MB dye (10–25 mg/10 mL) at a period of 0.0–400 s. The removal percentages (%R) of the MB dye increased linearly with the time increase to 100 s (Figure 3a). This is an attractive property of the promising P@SiO2 nanocomposite and gives it added value to use as an effective and economical adsorbent material in wastewater treatment processes.
To study the effect of the P@SiO2 nanocomposite dose on the uptake of the MB dye species, various weights of P@SiO2 (10–25 mg/10 mL) were tested at constant other conditions ([MB] = 100 ppm, pH = 7, and T = 25 °C), as shown in Figure 3b. Also, it can be observed that the (%R) increased from 80.2 to 94.8%, with a further increase in the adsorbent dose from 10 to 25 mg, as illustrated in Figure 3b. This is attributed to increasing the number of active sites with an increase in the adsorbent dose, which enhances the removal percentage of MB dye molecules [43]. On the other hand, the increase in the adsorbent dose leads to a reduction in the amount of dye adsorbed to one gram of the adsorbent; this causes a decrease in qe value as the adsorbent dose increase [43], as shown in Figure 3b. Figure S2 represented the relation between qe vs. Ce at different (a) P@SiO2 nanocomposite doses and (b) initial MB concentrations.

3.2.2. Effect of Initial MB Dye Concentration

The effect of the initial MB dye concentrations on the removal percent (%R) and the equilibrium adsorption amount of the MB dye by P@SiO2 nanocomposite from an aqueous solution was investigated (as in Figure 3c) using initial MB dye concentrations ranging from 100 to 300 mg L−1 at adsorbent dose = 25 mg/10 mL, pH = 7, and T = 25 °C. It was observed that the %R increased with the time of the initial concentration to 100 s. After that, the equilibrium state was reached, as shown in Figure 2c. Moreover, the adsorption capacity of MB dye (qe) increases with a further increase in the initial dye concentration in the range (100–300 mg L−1), as presented in Figure 3d. The reason for this may refer to the increase in the MB dye concentrations causing improvement in the concentration gradient’s driving force, which accelerates the MB dye species’ diffusion velocity into the P@SiO2 nanocomposite adsorbent particles [44]. Then, the concentration gradient reduces due to the adsorption of MB molecules on the active sites of the P@SiO2 nanocomposite.
In other words, at higher initial concentrations of MB, the binding sites of P@SiO2 nanocomposite adsorbent were encompassed with many MB species in the solution. Hence, the adsorption capacity of the P@SiO2 nanocomposite was enhanced by increasing the MB concentration, enhancing the adsorption capacity [45].

3.2.3. Effect of pH

The pH of the aqueous media is a very important factor in the adsorption process. The pH value affects the surface charge of the P@SiO2 nanocomposite adsorbent and the degree of the ionization of the MB dye species. The effect of the pH was studied in the range 1.5–11 (by adjusting the pH with HCl (0.1 N) and NaOH (0.1 N) solutions) ([MB dye] = 150 ppm, [P@SiO2 nanocomposite] = 25 mg/10 mL, T = 25 °C) on the removal percent %R of the MB dye by P@SiO2 nanocomposite was performed in Figure 4a. It was observed that the removal percentages were changed with further variation in the pH values as the following; at pH = 1.5, 3.0, 7.0, 9.0, and 11.0 the %R was 96.6, 67.1, 84.7, 99.7, and 95.3%, respectively. Consequently, the maximum adsorption capacities varied according to the pH values, as shown in Figure 4b.
Therefore, with an increase in the pH value of 3–9, the active groups on the P@SiO2 nanocomposite are deprotonated to carry negative charges, leading to electrostatic interactions with MB molecules increasing the removal percentages. At pH > 9, the removal percentage decreased, and this may be attributed to the –OH-anions of NaOH which can inhibit the electrostatic interactions between P@SiO2 nanocomposite and MB molecules by blocking the positive charges on MB molecules surfaces [46].
The color intensity of the MB dye sample varied according to pH value and is represented in Figure S3.

3.2.4. Effect of Temperature

The influence of the temperature, ranged from 25 to 80 °C, on the %R of the MB dye from aqueous media onto P@SiO2 nanocomposite at pH = 7, [MB] = 150 ppm, [P@SiO2 nanocomposite] = 25 mg/10 mL was investigated and is represented in Figure 4c. It was found that the %R of the MB dye increased with the time the temperature degrees were used overall. Consequently, the removal percentages decreased as the temperature increased, as illustrated in Figure 4c. Furthermore, as the dye solution temperature rose, the adsorbate’s maximum adsorption capacity decreased [47], as plotted in Figure 4d. This can be attributed to the exothermic nature of the adsorption process.

3.2.5. Adsorption Kinetics

The kinetics of the MB dye adsorption on the P@SiO2 nanocomposite for various P@SiO2 nanocomposite doses were tested in contact times ranging from 0.0 to 7.0 min, and the results obtained are illustrated in Figure 5a,b. The calculated kinetic parameters are summarized in Table 1. As shown in Table 1, the correlation coefficient (R2) related to the pseudo-second-order is higher than that obtained for the pseudo-first-order. Moreover, the calculated maximum adsorption capacity for the pseudo-second-order matches well with the experimental data. This indicated that the adsorption kinetics of various P@SiO2 nanocomposite doses were described very well with the pseudo-second-order. For this model, it is suggested that the rate-limiting step might be chemical adsorption for the adsorption of MB dye onto P@SiO2 nanocomposite [23].
The mechanism and kinetics of the removal of MB dye onto P@SiO2 nanocomposite nanoparticles were evaluated by applying the data obtained from the dye concentration experiment using the pseudo-first-order (Equation (S3)) and pseudo-second-order models (Equation (S5)). Moreover, the kinetic parameters obtained from the linear plots (Figure 5c,d) of the two models were calculated and recorded in Table 2. Referring to the values of R2, the experimental data of the adsorption of MB dye on the P@SiO2 nanocomposite showed a better fit with the pseudo-second-order models, which indicates that the dye species was chemically adsorbed and the adsorbent surface is the rate-limiting step [48].
By plotting log (qe–qt) versus t at different pH values of the MB dye solution (Figure 6a,b), the correlation coefficient (R2), the first-order rate constant (k1), and qe were calculated from the slopes and intercepts of the straight lines and listed in Table 3. Similarly, R2, k2, and qe related to the pseudo-second-order were calculated from the linear plot of the t/qt versus t at different pH values of the dye solution and recorded in Table 3. By comparing the values of R2 related to the pseudo-first-order kinetic model with that in the case of the pseudo-second-order kinetic model, it can be observed that the R2 in the pseudo-second-order kinetic model is higher than in the pseudo-first-order kinetic model. Moreover, the calculated qe value obtained from the pseudo-second-order kinetic model is closer to the experimental qe values. This indicates that the pseudo-second-order kinetic model best describes the adsorption kinetics rather than the pseudo-first-order model. To investigate the mechanism of the adsorption of MB dye at various temperatures, the Lagergren pseudo-first-order kinetic and pseudo-second-order kinetic models were applied (Figure 6c,d). The revealing parameters of the two models were evaluated and summarized in Table 4. According to the data obtained, it can be decided that the pseudo-second-order equation is the better-fitting model. This is due to it owning higher R2 values [48]. In addition, the calculated maximum adsorption capacities, qe, from the pseudo-second-order model are close to the values of the experimental ones. This demonstrated that surface control mainly explains the adsorption processes rather than adsorbate diffusion. These results illustrated that chemical bonding or chemisorption between MB dye molecules and the active sites on the surface of P@SiO2 nanocomposite might dominate the adsorption process, and this result agrees with what was reported in the literature [29].

3.2.6. Adsorption Isotherm

The most famous isotherms used to describe the adsorption isotherm are Langmuir, Freundlich, and Tempkin isotherm expressions given by Equations (S6)–(S8), respectively.
Langmuir isotherm supposes a monolayer of the adsorbate adsorbed on homogenously active sites with the same adsorption energies. Moreover, once these sites are occupied, no more adsorption takes place. Langmuir constants Q° and b (Table 5) can be obtained from the slope and intercept of the linear plot of Ce/qe versus Ce as illustrated in Figure 7a.
Dimensionless separation factor (RL) for the MB dye adsorption onto the P@SiO2 nanocomposite surface was determined from Equation (S6). If RL > 1, unfavorable; RL = 1, linear; 0 < RL < 1, favorable; RL = 0, irreversible (Figure 7b). It can be observed that the RL values between 0 and 1 indicate a favorable adsorption process.
The Freundlich isotherm suggested a heterogeneous surface with non-equivalent energetic binding sites. The Freundlich constants can be calculated by plotting ln qe versus ln Ce (Figure 7c and Table 5). From the data in Table 5, 1/n < 1, which suggests a normal Langmuir isotherm.
The adsorption performance of MB dye onto P@SiO2 nanocomposite was assessed by referring to the Tempkin isotherm model (Equation (S8)), and the linear relationship is plotted in Figure 7d. The correlation coefficient (R2 = 0.940) shows the poorest fit to the experimental adsorption equilibrium data, as summarized in Table 5.
The obtained values of the correlation coefficient (R2) (≈0.98) suggesting that the adsorption isotherm data of the adsorption of MB species onto P@SiO2 nanocomposite fits better for both Langmuir and Freundlich isotherm models. Based on the closest values of the experimental and calculated Qmax, the adsorption results of MB species onto P@SiO2 nanocomposite were fitted well with the Langmuir model representing monolayer adsorption on homogeneous surfaces [17,26]. Hence, the MB species sequestration processes occurred at P@SiO2 nanocomposite surfaces via the monolayer adsorption systems [26,47].

3.2.7. Adsorption Thermodynamics

Thermodynamic parameters were determined from the linear plot of Ln Kc vis T−1 (Figure S4) and according to Equations (S8)–(S10) and summarized in Table 6. The negative ∆G° values make it clear that the adsorption of MB dye on P@SiO2 nanocomposite is a spontaneous adsorption process. Moreover, the decrease showed for the ∆G° values with the increasing temperature from 298 to 353 K, demonstrating the adsorption performance is favored at lower temperatures and the adsorption of MB species onto P@SiO2 nanocomposite is a spontaneous process [26,35]. The ∆H° had a negative value confirming the exothermic nature of the adsorption process. The negative value of ∆S° suggests decreasing in the randomness of the solid/solution interfaces [26]. Activation energies, Ea, lower than 42 kJ/mol, suggest a diffusion-controlled mechanism, and higher than that value exhibits chemisorptions behavior. Here, the calculated value of Ea is 45.3 kJ mol−1; this indicates that the adsorption of MB onto P@SiO2 nanocomposite is a chemically controlled process. The data represented in Figure 4b confirms this result. Also, the P@SiO2 nanocomposite illustrates excellent efficiency in adsorbing MB dye molecules from both acidic and alkaline media. Therefore, we can conclude that the P@SiO2 nanocomposite will not be regenerated well. This could be considered an advantage where the MB dye molecules will be restricted from release again into the surrounding environment after adsorption due to the chemical bonding or chemisorption between MB dye molecules and the active groups on the surface of the P@SiO2 nanocomposite.

3.2.8. Effect of Ionic Strength on the Adsorption Percent of MB Dye

In practical application, studying the effect of NaCl dose is very important to evaluate the influence of ionic strength on the adsorption percent of MB dye onto P@SiO2 nanocomposite. Here, we study the effect of NaCl dose in the range 0.00–2.00 g on the removal percent of MB dye, as shown in Figure S5. It was observed that the NaCl dose did not affect the adsorption percent of MB dye in the studied range, as shown in Figures S5 and S6.

3.2.9. Adsorption Mechanism

The P@SiO2 nanocomposite was prepared by combining sodium silicate and sodium phosphate. Hence, the binding sites, which were responsible for the interaction with the MB species, were mainly composed of silanol and phosphate groups. Upon contacting with the positive MB species pollutants in the aqueous media, the negative binding sites P@SiO2 nanocomposite interact with the MB species through ionic bond and oxygen lone pair sharing. The proposed adsorption mechanism is illustrated in Figure 8. The electrostatic attractions between the positive MB species and the negative active sites of P@SiO2 nanocomposite mainly depends on the reaction pH [49,50]. In an acidic environment, the H-atom will convert Si=O into Si-OH which will enhance the activity of these groups towards interaction with the positive MB species. On the other hand, as the pH of the media increases, the ionization of P-O− Na+ groups increase, which will increase the affinity of the P@SiO2 nanocomposite towards the MB species. Also, the H-bonding becomes dominant in the adsorption mechanism and plays a vital role to improve the adsorption capacity [26,50]. P@SiO2 nanocomposite and MB dye have many N-atoms; therefore, the adsorption capacities are enhanced due to the formation of N-H…N bonds between P@SiO2 nanocomposite and MB species.

3.3. Comparison Study

A comparative evaluation of the maximum adsorption capacity of P@SiO2 nanocomposite to adsorb MB dye according to the Langmuir isotherm and other adsorbent materials in the literature is listed in Table 7 [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79]. Referring to the recent literature, equilibrium time and adsorption capacities are the main goals for scientists to investigate and develop many novel adsorbent materials. Comparatively, the prepared P@SiO2 nanocomposite illustrated considerable adsorption capacity compared to many novel materials and modified activated carbon materials. On the other hand, the obtained adsorption capacity of the prepared P@SiO2 nanocomposite was lower than some reported adsorbents; the major advantages of the prepared adsorbent over those reported materials were the rapid adsorption rate and easy recovery from aqueous solution after the adsorption process for reuse. Also, for the prepared P@SiO2 nanocomposite, the equilibrium time was reached rapidly within 100 s with an adsorption capacity of 76.9 mg/g. Therefore, the prepared P@SiO2 nanocomposite is suggested as an available, high-potential, and promising sorbent nanocomposite to remove MB dye from an aqueous media with considerable efficiency. Also, the P@SiO2 nanocomposite can meet commercial needs for water treatment applications.

4. Conclusions and Future Perspectives

Here, we investigated a simple hydrothermal strategy to prepareP@SiO2 nanocomposite to efficiently remove methylene blue dye from an aqueous solution. SEM, EDX, XRD, and FTIR techniques were employed to characterize the prepared nanomaterial. Various parameters that affected the adsorption process were investigated, such as preparing P@SiO2 nanocomposite dose, MB dye concentration, pH, temperature, and NaCl dose in the kinetic study. An increase in the adsorbent dose leads to minimizing the amount of dye adsorbed to one gram of the adsorbent. While the adsorption capacity of MB dye (qe) increases with a further increase in the initial dye concentration. On the other hand, the maximum adsorption capacities of the MB dye have varied according to the pH values. Moreover, increasing the dye solution temperature will lead to a decrease in the maximum adsorption capacity of the adsorbate. Finally, NaCl at various doses does not affect MB adsorption. From the analysis of the experimental results, the pseudo-second-order was an excellent fit for the obtained data. Moreover, according to Langmuir isotherm, the P@SiO2 nanocomposite shows excellent saturation capacity (76.92 mg g−1) which was suitable compared to other adsorbents in the literature. The thermodynamic studies showed that the adsorption process is preferred at low temperatures, exothermic, and ordered at the solid/solution interface. Also, the comparison study showed the promising properties and adsorption efficiency of P@SiO2 nanocomposite compared with other adsorbent materials. Also, P@SiO2 nanocomposite can be recommended as an eco-friendly absorbent material to purify wastewater from various cationic pollutants with significant efficiency in future works.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ma16020514/s1. Figure S1: SEM images of as prepared Si-P nanoparticles; Figure S2: The relation between qe vs. Ce at different (a) P@SiO2 nano-composite doses and (b) initial MB concentrations; Figure S3: The color of MB-dye variation as a function of at time 5–420 s at different pH values; Figure S4: Thermodynamic plots for MB-dye removal from aqueous media by P@SiO2 nano-composite; Figure S5: Effect of NaCl doses on removal percent of MB-dye onto P@SiO2 nanocomposite. ([P@SiO2] = 10–25 mg/10 mL, [MB] = 100 ppm, pH =7, T = 25 °C); Figure S6: Color variation as a function of NaCl doses at intervals 0–420 s. References [80,81] are cited in Supplementary file.

Author Contributions

Conceptualization, A.I.A.-E., A.A.N., A.A.A. and S.B.; methodology, A.I.A.-E. and I.M.A.; software, I.M.A., A.M.E.A.-R., H.M.A.S., A.A.N., H.M.A.S. and A.M.E.A.-R.; validation, M.A.A., W.A.A.A., I.M.A. and S.B.; formal analysis, H.M.A., A.M.E.A.-R. and H.M.A.S.; investigation, H.M.A., W.A.A.A. and A.I.A.-E.; writing—original draft preparation, A.I.A.-E., M.A.A., W.A.A.A., I.M.A. and A.A.A.; writing—review and editing, A.I.A.-E., A.A.A., A.A.N. and S.B.; project administration, A.A.N.; funding acquisition, A.A.N. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Deanship of Scientific Research at Jouf University under grant No. (DSR2022-RG-0130).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Acknowledgments

This work was funded by the Deanship of Scientific Research at Jouf University under grant No. (DSR2022-RG-0130). The authors acknowledge support from the KIT-Publication Fund of the Karlsruhe Institute of Technology. Stefan Bräse is grateful for support from the DFG-funded cluster program “3D Matter Made To Order” under Germany’s Excellence Strategy-2082/1-390761711. The authors acknowledge grants from the Science and Technology Commission of Shanghai Municipality (19440741300).

Conflicts of Interest

The authors declare no conflict of interest.

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Materials 16 00514 g001 550
Figure 1. Histogram for the particle size distributions of the prepared P@SiO2-nanoparticles.
Figure 1. Histogram for the particle size distributions of the prepared P@SiO2-nanoparticles.
Materials 16 00514 g001
Materials 16 00514 g002 550
Figure 2. (a) FTIR spectrum of SiO2 and P@SiO2 nanoparticles, (b) XRD pattern of SiO2 and P@SiO2 nanoparticles, and EDS analysis of (c) Si-P and (d) P@SiO2-MB and (e) P@SiO2-MB-NaCl powder.
Figure 2. (a) FTIR spectrum of SiO2 and P@SiO2 nanoparticles, (b) XRD pattern of SiO2 and P@SiO2 nanoparticles, and EDS analysis of (c) Si-P and (d) P@SiO2-MB and (e) P@SiO2-MB-NaCl powder.
Materials 16 00514 g002
Materials 16 00514 g003a 550Materials 16 00514 g003b 550
Figure 3. Effect of (a) P@SiO2 nanocomposite doses at the different contact times, (b) effect of P@SiO2 nanocomposite doses on qe values, (c) effect of initial MB concentrations at the different contact time, and (d) its effect on qe values, on the adsorption of MB dye. (P@SiO2 dose ([MB] = 100 mg/L/10 mL, pH = 7, T = 25 °C) and (d) initial MB concentrations ([P@SiO2] = 25 mg/10 mL, pH = 7, T = 25 °C).
Figure 3. Effect of (a) P@SiO2 nanocomposite doses at the different contact times, (b) effect of P@SiO2 nanocomposite doses on qe values, (c) effect of initial MB concentrations at the different contact time, and (d) its effect on qe values, on the adsorption of MB dye. (P@SiO2 dose ([MB] = 100 mg/L/10 mL, pH = 7, T = 25 °C) and (d) initial MB concentrations ([P@SiO2] = 25 mg/10 mL, pH = 7, T = 25 °C).
Materials 16 00514 g003aMaterials 16 00514 g003b
Materials 16 00514 g004 550
Figure 4. Effect of (a) pH, (b) effect of pH on qe values, (c) effect of temperature, and (d) its effect on qe values, on the adsorption of MB dye at different contact times ([P@SiO2] = 25 mg, [MB] = 150 mg/L/10 mL, T = 25 °C) and (d) temperature ([P@SiO2] = 25 mg, [MB] = 150 mg/L/10 mL, pH = 7).
Figure 4. Effect of (a) pH, (b) effect of pH on qe values, (c) effect of temperature, and (d) its effect on qe values, on the adsorption of MB dye at different contact times ([P@SiO2] = 25 mg, [MB] = 150 mg/L/10 mL, T = 25 °C) and (d) temperature ([P@SiO2] = 25 mg, [MB] = 150 mg/L/10 mL, pH = 7).
Materials 16 00514 g004
Materials 16 00514 g005a 550Materials 16 00514 g005b 550
Figure 5. (a) Effect of contact time on removal percent of MB dye, (b) P@SiO2 nanocomposite dose on equilibrium constant, (c) pseudo-first-order plot, (d) pseudo-second-order plot. ([P@SiO2] = 10–25 mg/10 mL, [MB] = 100 ppm, pH = 7, T = 25 °C).
Figure 5. (a) Effect of contact time on removal percent of MB dye, (b) P@SiO2 nanocomposite dose on equilibrium constant, (c) pseudo-first-order plot, (d) pseudo-second-order plot. ([P@SiO2] = 10–25 mg/10 mL, [MB] = 100 ppm, pH = 7, T = 25 °C).
Materials 16 00514 g005aMaterials 16 00514 g005b
Materials 16 00514 g006a 550Materials 16 00514 g006b 550
Figure 6. (a) Effect of contact time on removal percent of MB dye, (b) pH on the equilibrium constant, (c) pseudo-first-order plot, (d) pseudo-second-order plot (pH = 1.5–11, [MB] = 150 ppm, [P@SiO2] = 25 mg/10 mL, T = 25 °C).
Figure 6. (a) Effect of contact time on removal percent of MB dye, (b) pH on the equilibrium constant, (c) pseudo-first-order plot, (d) pseudo-second-order plot (pH = 1.5–11, [MB] = 150 ppm, [P@SiO2] = 25 mg/10 mL, T = 25 °C).
Materials 16 00514 g006aMaterials 16 00514 g006b
Materials 16 00514 g007 550
Figure 7. Adsorption isotherms: (a) Langmuir isotherm plot (b) Freundlich isotherm plot (c) RL (d) Tempkin isotherm plot for removal of MB dye (t = 42. s, ([MB] = 100–300 ppm, [dose] = 25 mg/10 mL, pH = 7, T = 25 °C).
Figure 7. Adsorption isotherms: (a) Langmuir isotherm plot (b) Freundlich isotherm plot (c) RL (d) Tempkin isotherm plot for removal of MB dye (t = 42. s, ([MB] = 100–300 ppm, [dose] = 25 mg/10 mL, pH = 7, T = 25 °C).
Materials 16 00514 g007
Materials 16 00514 g008 550
Figure 8. The proposed adsorption mechanism of MB dye onto P@SiO2 nanocomposite from aqueous media.
Figure 8. The proposed adsorption mechanism of MB dye onto P@SiO2 nanocomposite from aqueous media.
Materials 16 00514 g008
Table
Table 1. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various P@SiO2 nano-composite.
Table 1. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various P@SiO2 nano-composite.
Adsorbent Dose, mgqe exp (mg/g)First-Order Kinetic ParameterSecond-Order Kinetic Parameter
K1 (min−1)qe cal (mg/g)R2K2 (g mg−1 min−1)qe cal (mg/g)R2
10
15
20
25		79.58
58.67
45.81
37.9		−0.31
−0.77
−0.54
−0.77		21.38
17.78
8.79
5.32		0.981
0.938
0.927
0.931		0.069
0.11
0.26
0.35		80.00
55.90
46.10
39.02		0.996
0.970
0.999
0.999
Table
Table 2. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various concentrations of MB dye.
Table 2. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various concentrations of MB dye.
[MB], ppmqe exp (mg/g)First-Order Kinetic ParameterSecond-Order Kinetic Parameter
K1 (min−1)qe cal (mg/g)R2K2 (g mg−1 min−1)qe cal (mg/g)R2
10037.9−0.775.320.8990.3638.460.999
15050.85−0.718.710.9870.3750.510.998
20058.64−1.1418.880.9880.2459.170.998
30073.95−0.7127.540.9930.02875.470.999
Table
Table 3. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various pH values.
Table 3. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model for various pH values.
pHqe exp (mg/g)Pseudo-First-Order Kinetic ParameterPseudo-Second-Order Kinetic Parameter
K1 (min−1)qe cal (mg/g)R2K2 (g mg−1 min−1)qe cal (mg/g)R2
1.558.17−1.459.950.940.4358.48 ± 0.40.999
340.27−0.8813.120.8860.1741.67 ± 1.10.999
750.85−0.718.170.9270.3650 ± 0.70.999
959.800.000.000.000−1.3458.48 ± 1.50.999
1157.15−0.379.550.640.1658.14 ± 1.30.998
Table
Table 4. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model at different temperatures.
Table 4. The calculated parameters of the pseudo-first-order and pseudo-second-order kinetic model at different temperatures.
T, °Cqe exp (mg/g)First-Order Kinetic ParameterSecond-Order Kinetic Parameter
K1 (min−1)qe cal (mg/g)R2K2 (g mg−1 min−1)qe cal (mg/g)R2
2559.800.000.000.000−1.3458.48 ± 0.50.999
4548.41−0.9712.880.7770.2250 ± 0.80.999
6044.74−1.578.510.9700.6045.45 ± 0.30.999
8042.51−2.4214.130.9100.3543.48 ± 0.60.999
Table
Table 5. Calculated equilibrium constants for adsorption of MB.
Table 5. Calculated equilibrium constants for adsorption of MB.
AdsorbentLangmuir Isotherm ModelFreundlich Isotherm ModelTempkin Isotherm Model
Q° (mg/g)b (L/mg)R2nKf (mg/g)R2B (J mol−1)A (L mg−1)R2
MB76.92 ± 0.20.0920.9804.764.140.9804.7011.400.94
Table
Table 6. Thermodynamic parameters for MB dye removal from aqueous media by P@SiO2 nanocomposite.
Table 6. Thermodynamic parameters for MB dye removal from aqueous media by P@SiO2 nanocomposite.
T (K)MB
−ΔG (KJ mol−1)2981.982 ± 0.09
3181.356 ± 0.07
3330.435 ± 0.005
353−0.088 ± 0.001
−ΔH (KJ mol−1)-13.56 ± 0.3
−ΔS (KJ mol−1) 0.04 ± 0.008
Table
Table 7. Comparison of the maximum adsorption capacities of P@SiO2 with recently reported SiO2-based materials to remove MB dye [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79].
Table 7. Comparison of the maximum adsorption capacities of P@SiO2 with recently reported SiO2-based materials to remove MB dye [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79].
AdsorbentT, minAdsorbent doseT, °CpHqe, mg/gRef.
MOFs, MIL-101(Cr)24 h2.5 mg/10 mL25--34.3[49]
Fe3O4@SiO2-CR1030 mg/30 mL251131.44[50]
Mesoporous Fe3O4@SiO251 mg/L25733.12[51]
PLA-PEG/MgSiO3 Membrane--3251079% [MB] = 5.5 ppm[52]
Fe3O4@SiO2-EDA-COOH6020 mg/50 mL251043.15[53]
Monodispersed MSNs65 mg/26 mL25734.23[54]
(FA-DMSN)610 mg/15 mL25790.7[55]
CMMSNs3000.02 g/50 mL25743.03[56]
SNFs-LMw3605 mg/10 mL2510278.8[57]
SNFs-HMw240123.3
MSM@PDA150.37 g251083.8[58]
γ-Fe2O3/SiO22402 g/L257116.09[59]
Fe3O4@[email protected]235 mg/15 mL259163.93[60]
Fe3O4-graphene@mesoporous SiO2 Nanocomposites151040110.98–102.2[61]
Silica Xerogel Synthesized from Volcanic Tuff600.0016 g/mL40551.967[62]
Silica gel derived from Algerian siliceous2401 g/L256.380.45[63]
Cysteine-Functionalized Mesoporous Silica ((MSN-Cys)8010 mg/10 mL258.5140[64]
(MSN)
(MSN-NH2)		300.05 g/25 mL--112.899
1.736		[65]
βCD-SNHS7200.01 g/7 mL2710.560.55[66]
Modified Nano-silica with Bismuth and Iron208 g/L255-69.54[67]
Mesoporous Silicalite-12400.10 wt%/50 mL30 19.04[68]
Silica Nanoparticles (SNPs)600.3 g/L30731[69]
Mesoporous Silica Spheres2015 mg/15 mL305-760[70]
AC-MnFe2O41524 mg/L30477.74[71]
Activated Charcoal from Ficus carica bast900.5 g/100 mL30847.62[72]
Activated Carbon1200.1 g/100 mL30872[73]
AC145 2 g/L 25 928.65 [74]
AC212017.57
AC31200.809
BCC 60 0.1 g/20 mL 25 711.63 [75]
BCAC-1012.71
BCAC-2016.85
DMWTAC3020020853[76]
CNZL Activated Carbon8010050--14.493[77]
GFSF3603 g/L27819.18[78]
Carbon Nanoparticles (TPCNPs)9050 mg/120 mL20598[79]
P@Si100 s25 mg/10 mL25776.92This work
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Nayl, A.A.; Abd-Elhamid, A.I.; Arafa, W.A.A.; Ahmed, I.M.; AbdEl-Rahman, A.M.E.; Soliman, H.M.A.; Abdelgawad, M.A.; Ali, H.M.; Aly, A.A.; Bräse, S. A Novel P@SiO2 Nano-Composite as Effective Adsorbent to Remove Methylene Blue Dye from Aqueous Media. Materials 2023, 16, 514. https://doi.org/10.3390/ma16020514

AMA Style

Nayl AA, Abd-Elhamid AI, Arafa WAA, Ahmed IM, AbdEl-Rahman AME, Soliman HMA, Abdelgawad MA, Ali HM, Aly AA, Bräse S. A Novel P@SiO2 Nano-Composite as Effective Adsorbent to Remove Methylene Blue Dye from Aqueous Media. Materials. 2023; 16(2):514. https://doi.org/10.3390/ma16020514

Chicago/Turabian Style

Nayl, AbdElAziz A., Ahmed I. Abd-Elhamid, Wael A. A. Arafa, Ismail M. Ahmed, Aref M. E. AbdEl-Rahman, Hesham M. A. Soliman, Mohamed A. Abdelgawad, Hazim M. Ali, Ashraf A. Aly, and Stefan Bräse. 2023. "A Novel P@SiO2 Nano-Composite as Effective Adsorbent to Remove Methylene Blue Dye from Aqueous Media" Materials 16, no. 2: 514. https://doi.org/10.3390/ma16020514

APA Style

Nayl, A. A., Abd-Elhamid, A. I., Arafa, W. A. A., Ahmed, I. M., AbdEl-Rahman, A. M. E., Soliman, H. M. A., Abdelgawad, M. A., Ali, H. M., Aly, A. A., & Bräse, S. (2023). A Novel P@SiO2 Nano-Composite as Effective Adsorbent to Remove Methylene Blue Dye from Aqueous Media. Materials, 16(2), 514. https://doi.org/10.3390/ma16020514

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