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Article

Monitoring Lead–Phosphorus Interactions Through 31P-NMR Used as a Sensor in Phosphine Functionalized Silica Gel Adsorbent

by
Jessica Badillo-Camacho
1,2,
José A. Gutiérrez-Ortega
1,*,
Ilya G. Shenderovich
3,
Yenni G. Velázquez-Galván
4 and
Ricardo Manríquez-González
1,2,*
1
Department of Wood, Cellulose and Paper, University of Guadalajara-CUCEI, Km 15.5 of Carretera Guadalajara-Nogales, Zapopan 45020, Jalisco, Mexico
2
Department of Chemistry, Universidad de Guadalajara-CUCEI, Blvd. Marcelino García Barragán #1421, Guadalajara 44430, Jalisco, Mexico
3
Faculty of Chemistry and Pharmacy, University of Regensburg, Universitaetstrasse 31, 93053 Regensburg, Germany
4
Department of Mathematics and Physics, Instituto Tecnológico y de Estudios Superiores de Occidente (ITESO), Periférico Sur Manuel Gómez Morín 8585, Tlaquepaque 45604, Jalisco, Mexico
*
Authors to whom correspondence should be addressed.
Gels 2025, 11(8), 580; https://doi.org/10.3390/gels11080580 (registering DOI)
Submission received: 19 June 2025 / Revised: 22 July 2025 / Accepted: 23 July 2025 / Published: 26 July 2025
(This article belongs to the Special Issue Gel-Based Adsorbent Materials for Environmental Remediation)
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Abstract

A triphenylphosphine-functionalized silica gel material, optimized for lead adsorption, was synthesized via a one-pot sol–gel reaction and characterized using FTIR and solid-state 13C and 29Si NMR and XPS spectroscopy. The interaction between lead cations and phosphine groups was evaluated using the 31P NMR chemical shift tensor as a sensor. Two distinct types of phosphine groups, exhibiting different rotational mobility behaviors, were identified, with their ratio influenced by the presence of lead cations. These results suggest that the adsorption behavior of lead on this functionalized silica gel adsorbent can be directly evaluated by its lead–phosphorus interaction. This association was corroborated by the shifting of the binding energies of phosphorus functional groups after lead uptake in the XPS analysis.

1. Introduction

Heavy metal ions from industrial discharges into natural water systems have become a global environmental concern [1]. Their presence in the water bodies from different industrial processes clearly affects short- and long-term human health due to their proven toxicity and lack of biodegradability. From this group, arsenic, copper, mercury, lead, nickel, cadmium, and zinc are the most toxic to humans [2,3]. Lead (Pb2+) is especially hazardous due to its high toxicity, even at trace concentrations, since this metal ion can be bioaccumulated by chronic exposure [4]. In fact, one of the potential sources of lead exposure in drinking water, not exclusively from industrial wastewater, is old lead-based household water supply infrastructure. The World Health Organization (WHO) determined the lead concentration for drinking water to be 10 µg/L [5]. Several methods have been proposed for the treatment of water polluted with lead and some other heavy metals, including ion exchange, precipitation, flocculation, adsorbent zeolites, activated carbon, functionalized mesoporous materials, metallic oxides, membranes, composites, and biobased materials with chitosan, cellulose, and agriculture or forest crops, among others [6,7,8,9].
One of the most efficient methods for removing heavy metal ions from contaminated water is adsorption using functionalized materials [10,11]. Addressing this challenge, hybrid materials synthesized via the sol–gel process have emerged as highly promising candidates. Their tunable porosity, large surface area, and customizable functionalization make them ideal platforms for incorporating specific binding sites [10,12]. In this regard, several attempts using silica gel hybrid materials for the uptake of lead ions from aqueous solutions have been proposed with outstanding performance and efficiency [9,13,14,15,16]. However, only a few works are committed to exploring a critical step in the development of advanced adsorbents by achieving a molecular-level understanding of the adsorption mechanisms by the direct evaluation of the interactions [17,18,19,20]. On the other hand, solid-state NMR can be applied for the study of noncovalent interactions by the estimation of the chemical shielding anisotropy (CSA). Shenderovich (2013) studied the effect of the phosphorus moieties and lead (II) interactions by 31P NMR chemical shift tensor (CST) of phosphine oxides, phosphinic, phosphonic, and phosphoric acids using density functional theory-gauge including invariant atomic orbitals (DFT-GIAO) approach [21]. This method, based on the change in 31P NMR chemical shift of the phosphorus signal due to the metal association, was successfully used as the P--Pb interaction sensor in the adsorbent functionalized with methyl phosphonate functional groups onto a silica gel matrix [22]. These results demonstrated that phosphorus-based active sites both exhibit excellent adsorption properties and act as molecular sensors, sensitive to interactions with metal ions.
This study focuses on the direct inspection of the molecular interaction between ligands and heavy metal ions in functionalized silica gel materials. Thus, a new hybrid material, silica gel-aminopropyl tris (4-chlorophenyl)phosphine (SG-APT4PP), was synthesized, which features phosphine groups attached to a silica gel matrix through aminopropyl silane. The material was characterized using BET analysis, FTIR, 13C, 29Si, 31P NMR, and XPS spectroscopy. The functional groups were specifically designed to interact with lead ions and act as molecular sensors of their local chemical environment. To investigate this, 31P NMR measurements were conducted on the functionalized material before and after exposure to lead. Changes in the 31P chemical shift tensor provide molecular-level insights into the binding mechanisms involved. Furthermore, this lead–phosphorus interaction in the hybrid material was also corroborated by XPS analysis.

2. Results and Discussion

2.1. Lead Adsorption Test

The maximum lead adsorption capacity of SG-APT4PP was determined to be 50 ± 6 mg of Pb per gram. The material demonstrates a strong affinity for lead, comparable to the performance of silica-based material functionalized with phosphonate groups [22]. Although this functionalized material does not compete with several materials already reported with exceptional performance in lead adsorption [9,13,14,15,16], the information obtained through this adsorption test provides novel insights at the molecular level to determine how lead ions interact with available phosphines. On the other hand, these findings highlight the effectiveness of incorporating phosphorus-containing functional groups as a strategic approach for designing advanced materials for selective interactions, particularly with heavy metals.

2.2. Surface Textural Properties

Textural characterization of SG, SG-APT4PP, and SG-APT4PP-Pb materials through nitrogen adsorption–desorption isotherms revealed significant structural changes resulting from Pb2+ ion interactions (Figure 1 and Table 1). The resulted isotherms correspond to type IV according to the IUPAC classification, typically associated with mesoporous materials [23]. A distinct hysteresis loop (type H3) was noted, suggesting the presence of mesopores with slit-like or plate-like shapes formed by the aggregation of particles [23,24,25]. The non-functionalized silica gel (SG) exhibited a high BET surface area of 406.09 m2/g, a total pore volume of 0.70 cm3/g, and an average pore diameter of 5.22 nm, confirming its mesoporous nature with a significant fraction of small mesopores. Upon functionalization with APT4PP, a dramatic reduction in surface area was observed from 406.09 m2/g to 21.12 m2/g, indicating extensive coverage of the internal surface by the organic moieties. This modification also led to a notable decrease in pore volume (from 0.70 to 0.41 cm3/g), accompanied by a substantial increase in average pore diameter (from 5.2 to 19.74 nm), suggesting partial pore blocking and preferential suppression of smaller mesopores during the grafting process. A notable decrease in BET specific surface area was evidenced from 21.12 m2/g for SG-APT4PP to 12.78 m2/g for SG-APT4PP-Pb, clearly demonstrating effective lead adsorption within the porous structure. This significant reduction can be directly attributed to the occupation of the available active adsorption sites by Pb2+ ions, effectively blocking nitrogen accessibility to internal surfaces and consequently limiting the available surface area for adsorption. Additionally, pore volume (Vp) showed a moderate decrease from 0.41 cm3/g to 0.38 cm3/g after lead adsorption, reinforcing the hypothesis that adsorption primarily occurs on readily accessible regions rather than completely blocking internal pores. Such a slight reduction in pore volume suggests that lead ions predominantly interact with the pore entrances and external surface areas, causing partial occupancy rather than complete occlusion of internal porous channels. Moreover, an increase in the average pore diameter (Dp) from 19.74 nm to 21.66 nm post-adsorption was observed. This shift in pore size distribution implies selective occupancy and saturation of smaller mesopores by Pb2+ ions, leaving a relatively higher proportion of larger mesopores available. Such a redistribution provides additional confirmation of the preferential adsorption mechanism taking place in smaller and more accessible pores. The pore size distribution analysis (Figure 1a,b) corroborates this interpretation by highlighting specific changes within the 5–40 nm pore range, clearly affected by Pb2+ ion interactions. The comparison with the non-functionalized silica gel (SG) further confirms the transformation of the textural properties across the functionalization and adsorption steps. The disappearance of the intense peak centered at ~5 nm (Figure 1b) in the SG sample and the emergence of a broader distribution centered around 20 nm in the modified materials underscore the structural reorganization and surface tailoring achieved by APT4PP grafting. Collectively, these structural analyses offer comprehensive views into the adsorption mechanism of Pb2+ onto SG-APT4PP, affirming its potential efficacy for selective heavy metal ion removal applications of this functionalized silica gel adsorbent.

2.3. FTIR Analysis

Figure 2 shows the spectrum of the non-functionalized silica gel (SG) material, featuring two characteristic bands of SiO2 at 1045 cm−1 and 800 cm−1, attributed to Si-O-Si stretching and Si-O bending vibrations, respectively. In the case of the spectrum of functionalized silica gel (SG-APT4PP) reveals new signals confirming the presence of the APT4PP ligand. These include the N-H bending vibration at 1581 cm−1 of the amino group, the C=C stretching at 1476 cm−1 from phenyl groups, aliphatic C-H bending vibration at 1388 cm−1 from the propyl chain, as well as the aromatic ring bending at 816 cm−1 and 752 cm−1. Finally, the signal at 588 cm−1 is attributed to the stretching vibration of C-Cl and P-C bonds [26,27].

2.4. NMR Analysis

Figure 3 shows the 13C CP-MAS NMR spectrum of SG-APT4PP. The three signals at 12, 21, and 43 ppm are attributed to the propyl carbon binding chain, and the broad signal, split in three on the top, between 125 and 135 ppm, belongs to all aromatic carbon signals of the T4PP head, confirming the proposed structure [28]. The signal at 165 ppm is possibly attributed to the formation of carbamate from unreacted amino propyl residue (AP) and atmospheric CO2, as was previously reported by Schimming et al. (1999) [29]. Signals with asterisks are due to the spinning side bands of the aromatic carbon signal.
The 29Si MAS NMR spectra (Figure 4a,b) provide valuable insights into the silicon environments present in SG-APT4PP and SG-APT4PP-Pb adsorbents. Both samples exhibit characteristic signals corresponding to Q– and T–silicon species, confirming the formation of the SiO2 matrix and successful surface functionalization. These signals remain largely unchanged after Pb2+ adsorption, suggesting that the functional groups are preserved.
In the SG-APT4PP sample, distinct silicon signals related to the silica gel matrix (Q) and the organic ligand (T) environments are observed at approximately −63.0 ppm (T2, Si (OSi)2 (OH)R), −67.6 ppm (T3, Si (OSi)3R), −90.8 ppm (Q2, Si (OSi)2 (OH)2), −99.5 ppm (Q3, Si (OSi)3OH), and −109.6 ppm (Q4, Si (OSi)4) [30,31,32]. Following Pb2+ adsorption (SG-APT4PP-Pb), these signals exhibit minor shifts and variations in intensity (Table 2). Given the amorphous nature of the material, the observed NMR signals are broad and cannot be narrowed by spectral processing techniques. This results in considerable overlap of the peaks, making it difficult to precisely determine their positions and intensities. Consequently, it remains unclear whether the subtle spectral differences between the two samples reflect genuine surface chemical changes due to Pb2+ adsorption or whether they are artifacts arising from the mathematical deconvolution of the broad, overlapping signals.

2.5. XPS Analysis Results

X-ray photoelectron spectroscopy (XPS) analysis was performed on the SG-APT4PP and SG-APT4PP-Pb samples to investigate the surface chemical composition and the interaction between phosphorus (P) and lead (Pb) (Figure 5). In both samples, the signals correspond to C1s, O1s, N1s, Cl2p, Si2p, and P2p. In the SG-APT4PP-Pb sample, clear signals corresponding to both P and Pb were detected, confirming metal adsorption. The Pb 4f core-level spectra revealed characteristic peaks corresponding to Pb (II) species, while the P 2p region showed the presence of phosphine groups [22,33].
The C 1s spectrum of SG-APT4PP (Figure 6a, top) was deconvoluted into three main components ranged at approximately 284.6, 285.5, and 286.4 eV, which were attributed to C–Si, C–C, and C–O/C–P bonds, respectively. These signals are consistent with the expected chemical structure of the silane-grafted phosphine ligand [22,34]. After Pb (II) adsorption, the C 1s spectrum of SG-APT4PP-Pb (Figure 6a, bottom) maintained the same three components with minor shifts of binding energy, indicating that the ligand functional groups remain chemically stable after metal uptake. The O 1s spectrum of SG-APT4PP (Figure 6b, top) was fitted with two primary peaks located at approximately 533.38 eV and 535.15 eV, assigned to O-H/Si–O and C–O bonds, respectively [33,35]. These components indicate the presence of oxygen atoms involved in both siloxane and organic functionalities, such as OH groups from silanols (Si-OH), bridging oxygens in siloxane bonds (Si-O-Si), and C-O bonds from remaining methoxysilane groups (Si-O-CH3). Upon interaction with Pb (II), the O1s spectrum of SG-APT4PP-Pb (Figure 6b, bottom) revealed three resolved components, indicating modifications in the local oxygen environment. A new peak at 530.81 EV was assigned to N-O interactions from nitrate anions (NO3−) present in the Pb (NO3)2 salt. This suggests that lead coordinates with oxygen atoms [36,37,38], supporting the proposed interaction mechanism, in which the phosphorus atom from the phosphine-type group participates in the stabilization process.
The high-resolution XPS spectrum in the P 2p region (Figure 6c) reveals important changes in the chemical environment of phosphorus upon Pb (II) coordination. In the SG-APT4PP spectrum, the P 2p signal (Figure 6c, top) shows two principal peaks attributed to P 2p3/2 and P 2p1/2 components of phosphine-type groups at 132.19 eV and 133.38 eV, respectively. After the interaction with Pb2+, the SG-APT4PP-Pb spectrum (Figure 6c, bottom) shows a shift to 138.70 eV (P 2p3/2) and 139.83 eV (P 2p1/2). The binding energy of P 2p increased by approximately 6.5 eV, indicating that the phosphorous atoms donate electron density to the lead ions during coordination, resulting in a decrease in electron density around phosphorous [39].
The Pb 4f spectrum of SG-APT4PP-Pb (Figure 6d) shows two well-defined peaks at 138.11 eV and 142.87 eV, corresponding to Pb 4f7/2 and Pb 4f5/2, respectively. A binding energy shift of 1.4 eV is observed, which can be ascribed to the coordination of phosphorus groups with Pb2+. This suggests that electron density is transferred from phosphorus to lead ions during the adsorption process [40,41]. The clear separation and intensity of the Pb 4f components support the successful interaction between Pb2+ ions and electron-donating groups, such as phosphine moieties, present in the material. These results are consistent with the shift observed in the P 2p region (Figure 6c) and collectively confirm the coordination of Pb2+ through electron donation from phosphorus-containing groups [21,42].

2.6. Evaluation of Lead Interaction by 31P NMR

Qualitatively, both the MAS and static 31P NMR spectra of SG-APT4PP appear similar before and after lead loading. The MAS spectra show two peaks at −8.8 (II) and −10.7 ppm (I), Figure 7a. The static spectra exhibit a single anisotropic signal, Figure 7b. Line-shape analysis of this static signal shows that it corresponds to the second peak in the MAS spectra, while the −8.8 ppm peak remains isotropic. The only change caused by lead loading is an increase in the relative intensity of the −8.8 ppm (II-Pb) peak compared to the −10.7 ppm peak, shifting the ratio from 3:10 to 7:10.
The most plausible explanation for these findings is the presence of two types of surface phosphine groups. One type exhibits slow rotational diffusion, characterized by an isotropic chemical shift of −10.7 ppm, a span (Ω) of 42 ppm, and a skew (κ) of 0.8. These values are consistent with those of phosphines in the crystalline state [43]. The other type undergoes fast rotational diffusion, which averages out the anisotropy of its CST, yielding an isotropic peak at −8.8 ppm. Similar mobility-driven transitions, induced by thermal or hydration effects on branched organic molecules in sub-monolayer amounts loaded onto mesoporous silica, have been previously reported [44]. The chemical shift difference between these signals cannot be attributed to interactions with lead cations or conversion to phosphine oxide; instead, it reflects variations in the ordering of phenyl rings in the two structures.
The interaction between these functional groups and lead cations is weak, resulting in no measurable changes in chemical shifts. This suggests that the adsorbent can be regenerated. Note that when phosphorus is coordinated to a transition metal center, its isotropic 31P chemical shift can change by more than 100 ppm [45]. However, lead loading increases the number of rotationally mobile functional groups (II-Pb). This implies that the mechanism restricting their rotational diffusion involves mutual interactions among these groups, which are disrupted in the presence of lead cations. This statement could also support the explanation of the increased pore size in the textural surface analysis of the material after lead absorption (SG-APT4PP-Pb). On the other hand, enhancing the interaction with lead cations can be achieved by converting the phosphine groups into phosphine oxide groups [22].
Furthermore, these observations are consistent with the findings obtained by XPS measurements, where changes in binding energies of P from phosphine groups were observed upon Pb2+ binding, supporting the presence of specific P--Pb interactions at the atomic level.
In summary, the present work demonstrated the possibility of investigating the lead uptake affinity, at the molecular level, of the phosphorus functionalized silica gel adsorbents by the direct evaluation of the Pb–P interaction through 31P NMR spectroscopy and corroborated by XPS analysis. Furthermore, this molecular approach represents valuable information for the design of more efficient functionalized adsorbents involving analogous and cost-effective materials.

3. Conclusions

A novel functionalized silica gel adsorbent, SG-APT4PP, was successfully synthesized using a one-pot sol–gel reaction through TEOS, APTES, and T4ClPP precursors. Spectroscopic characterizations, including FTIR, 13C and 29Si solid-state NMR, confirmed the presence of active organic phosphine grafted onto the silica gel matrix in the form of T2 and T3 species, as well as the tridimensional silica gel matrix by Q2–Q4 structures.
Lead removal tests revealed adsorption capacity of up to 50 mg g−1, confirming the specific adsorptive affinity of this material toward lead cations. Furthermore, lead presence is also observed in the reduction in the specific surface area of the material up to 60%. 31P NMR CST analysis identified two distinct types of surface phosphine groups exhibiting different rotational diffusion behaviors. For one type, the characteristic rotational reorientation time is much longer than milliseconds (slow diffusion), while for the other, it is significantly shorter (fast diffusion). Although the isotropic chemical shift values of these signals remained unchanged in the presence of lead cations, noncovalent interactions between neighboring phosphine groups are disrupted, leading to a marked increase in the number of groups with high rotational mobility. Furthermore, the P–Pb interaction was corroborated by XPS analysis through changes in the binding energies of the phosphine moieties upon lead uptake.
Finally, while the scope of this work was not related to reporting a competitive functionalized silica gel material for lead sorption, the novel contribution of one-pot synthesis and the molecular-level understanding of the interactions between phosphorus moieties and lead cations highlight the potential of this research to design new materials with selective sorption of heavy metals for environmental applications.

4. Materials and Methods

4.1. Materials

Tetraethyl orthosilicate (TEOS, ≥99%), 3-aminopropyltrimethoxysilane (APTMS) (≥97%), Tris (4-chlorophenyl) phosphine (T4ClPP) (≥95%), triethylamine (TEA, ≥99%), lead nitrate (99.9%), and nitric acid (Ultrex) were purchased from Sigma-Aldrich (Toluca, Mexico). Absolute ethanol and sodium chloride (≥99%) were supplied by Fermont (Monterrey, Mexico). All the reactants were used as received.

4.2. Synthesis of SG-APT4PP

The synthesis route used for SG-APT4PP was adapted from sol–gel methodologies previously developed and optimized by our group for the functionalization of mesoporous silica with organophosphorus ligands [22,46,47]. The experimental conditions were selected to ensure efficient incorporation of the tris (4-chlorophenyl)phosphine moiety into the silica matrix while maintaining structural homogeneity and stability of the hybrid network.
The synthesis of SG-APT4PP was carried out according to the sol–gel procedure illustrated in Figure 8a–f. Initially (Figure 1a), in a one-pot reaction, a mixture of reactants tetraethyl orthosilicate (TEOS, 10 mM), Tris (4-chlorophenyl) phosphine (T4ClPP, 1.1 mM), and (3-aminopropyl) trimethoxysilane (APTMS, 3.3 mM) was prepared in the presence of sodium chloride (NaCl, 1 mM) under nitrogen atmosphere. Triethylamine (TEA, 0.3 mL) was added dropwise as a base catalyst, and the reaction mixture was stirred for 2 h at room temperature to promote precursor hydrolysis and co-condensation. Subsequently, 4.4 mL of a solution of ethanol and deionized water (0.8% v/v) was added to the mixture and stirred for 2 h to ensure the formation of silanol groups and their condensation (Figure 8b). The resulting material was aged for 2 days at room temperature to allow the polymeric network development (Figure 8c). After aging, the gel material was dried at 60 °C for 24 h to remove residual solvents (Figure 8d). The xerogel was then washed thrice using a 1:1 (v/v) ethanol/deionized water mixture to eliminate unreacted precursors and byproducts (Figure 8e), followed by a final drying step at 60 °C for 24 h (Figure 8f). The xerogel corresponds to the hybrid silica gel material functionalized with APTMS and T4ClPP was named SG-APT4PP.

4.3. SG-APT4PP Characterization

The specific surface area (BET) was determined from nitrogen adsorption–desorption isotherms at 77 K using an ASAP 2020 KMP analyzer (Micromeritics, Norcross, GA, USA) in the relative pressure range of 0.05 < P/P0 < 0.35. The analysis was conducted on SG-APT4PP before and after the lead adsorption test. The chemical composition of SG-APT4PP and a control of non-functionalized silica gel (SG) was evaluated by FTIR spectroscopy using a Thermo Fisher Scientific Nicolet iS50 Model equipment, with an ATR device. Samples were acquired with 16 scans using a spectral width range of 500–4000 cm−1 and a resolution of 4 cm−1.
Solid-state NMR measurements of SG-APT4PP samples were performed at ambient temperature on an Infinityplus NMR spectrometer system (Agilent) operated at 7 T (300 MHz), equipped with a 6 mm CP-MAS probe of variable-temperature Chemagnetics-Varian. Samples were packed into 6 mm pencil rotor of ZrO2 and measured with a spinning speed of 7 kHz, with a 90° pulse length of 4.0 μs, a relaxation delay of 3 s. Contact times were set to 3 ms, 10 ms, and 1 ms for 13C {1H}, 29Si{1H}, and 31P{1H} CP NMR, respectively. Further experimental details can be found in [44].
Elemental composition and chemical states of the functionalized silica gel adsorbent before and after lead uptake were studied by a SPECs Flex SP X-Ray Photometry (XPS) using a monochromatic Al Kα source ( h v = 1486.7 eV) and a pass energy of 10 eV. Spectra were analyzed using CasaXPS software version 2.3.24.

4.4. Lead Removal Test

Since the scope of this research is oriented to the evaluation of lead–phosphines interaction, neither equilibrium adsorption models nor kinetics were performed. However, in a triplicate experiment, the maximum Pb uptake was measured to evaluate the interaction. Functionalized silica gel adsorbent (SG-APT4PP) was treated with a 3000 mg L−1 stock solution of Pb at pH 3, prepared using lead nitrate and adjusting the pH with 1% HNO3. A total of 100 mg of the adsorbent was placed in a flask containing 25 mL of the lead solution. The flasks were stirred for 24 h on a thermostirrer (Thermo Fisher Scientific, Cincinnati, OH, USA) set to 120 rpm at 303.15 K. Afterward, the solution was filtered, and the initial and final Pb concentrations were measured by an Agilent 240FSAA Atomic Absorption Spectrometer (Agilent Technology, Santa Clara, CA, USA).
Calibration curves were used to construct concentration vs. absorbance using a certified standard of Pb ion solution (Sigma-Aldrich, St. Louis, MO, USA). The lead adsorbed amount on the SG-APT4PP adsorbent was obtained between the initial and final lead concentration (Equation (1)):
q = V C 0 − C f m
where q is the amount of lead adsorbed (in mg g−1); C0 and Cf are lead concentrations (in g L−1) in the initial and final concentrations, respectively; V is the volume of solution with lead ions (L); and m is the amount of adsorbent (g).

Author Contributions

J.B.-C.: Methodology, investigation, formal analysis, validation. J.A.G.-O.: Formal analysis, data curation, writing—original draft preparation, visualization. I.G.S.: Formal analysis, data curation, writing—review and editing. Y.G.V.-G.: Formal analysis, visualization, data curation. R.M.-G.: Conceptualization, data curation, writing—review and editing, supervision, project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors thank the National Council of Humanities, Science, and Technology (Now SECIHTI) in Mexico for the postdoctoral grant of J.A.G.-O. (grant number: I1200/311/2023).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Mushak, P. A Brief Early History of Lead as an Evolving Global Pollutant and Toxicant. Trace Met. Other Contam. Environ. 2011, 10, 23–39. [Google Scholar] [CrossRef]
  2. Fu, F.; Wang, Q. Removal of Heavy Metal Ions from Wastewaters: A Review. J. Environ. Manag. 2011, 92, 407–418. [Google Scholar] [CrossRef]
  3. Costa-Böddeker, S.; Hoelzmann, P.; Thuyên, L.X.; Huy, H.D.; Nguyen, H.A.; Richter, O.; Schwalb, A. Ecological Risk Assessment of a Coastal Zone in Southern Vietnam: Spatial Distribution and Content of Heavy Metals in Water and Surface Sediments of the Thi Vai Estuary and Can Gio Mangrove Forest. Mar. Pollut. Bull. 2017, 114, 1141–1151. [Google Scholar] [CrossRef]
  4. Collin, M.S.; Venkatraman, S.K.; Vijayakumar, N.; Kanimozhi, V.; Arbaaz, S.M.; Stacey, R.G.S.; Anusha, J.; Choudhary, R.; Lvov, V.; Tovar, G.I.; et al. Bioaccumulation of Lead (Pb) and Its Effects on Human: A Review. J. Hazard. Mater. Adv. 2022, 7, 100094. [Google Scholar] [CrossRef]
  5. Strandberg, J. Lead in Drinking-Water, Health Risks, Monitoring and Corrective Actions—Technical Brief; World Health Organization: Geneva, Switzerland, 2022. [Google Scholar]
  6. Qasem, N.A.A.; Mohammed, R.H.; Lawal, D.U. Removal of Heavy Metal Ions from Wastewater: A Comprehensive and Critical Review. NPJ Clean Water 2021, 4, 36. [Google Scholar] [CrossRef]
  7. Gahrouei, A.E.; Rezapour, A.; Pirooz, M.; Pourebrahimi, S. From Classic to Cutting-Edge Solutions: A Comprehensive Review of Materials and Methods for Heavy Metal Removal from Water Environments. Desalin. Water Treat. 2024, 319, 100446. [Google Scholar] [CrossRef]
  8. Lupa, L.; Cocheci, L. Heavy Metals Removal from Water and Wastewater. In Heavy Metals—Recent Advances; Almayyahi, B.A., Ed.; IntechOpen: Rijeka, Croatia, 2023; ISBN 978-1-83768-515-8. [Google Scholar]
  9. Chowdhury, I.R.; Chowdhury, S.; Mazumder, M.A.J.; Al-Ahmed, A. Removal of Lead Ions (Pb2+) from Water and Wastewater: A Review on the Low-Cost Adsorbents. Appl. Water Sci. 2022, 12, 185. [Google Scholar] [CrossRef]
  10. Wieszczycka, K.; Staszak, K.; Woźniak-Budych, M.J.; Litowczenko, J.; Maciejewska, B.M.; Jurga, S. Surface Functionalization—The Way for Advanced Applications of Smart Materials. Coord. Chem. Rev. 2021, 436, 213846. [Google Scholar] [CrossRef]
  11. Kumar, V.; Dwivedi, S.K.; Oh, S. A Critical Review on Lead Removal from Industrial Wastewater: Recent Advances and Future Outlook. J. Water Process Eng. 2022, 45, 102518. [Google Scholar] [CrossRef]
  12. Rigoletto, M.; Calza, P.; Gaggero, E.; Laurenti, E. Hybrid Materials for the Removal of Emerging Pollutants in Water: Classification, Synthesis, and Properties. Chem. Eng. J. Adv. 2022, 10, 100252. [Google Scholar] [CrossRef]
  13. Quirarte-Escalante, C.A.; Soto, V.; De La Cruz, W.; Porras, G.R.; Manríquez, R.; Gomez-Salazar, S. Synthesis of Hybrid Adsorbents Combining Sol-Gel Processing and Molecular Imprinting Applied to Lead Removal from Aqueous Streams. Chem. Mater. 2009, 21, 1439–1450. [Google Scholar] [CrossRef]
  14. Bakry, A.M.; Amri, N.; Adly, M.S.; Alamri, A.A.; Salama, R.S.; Jabbari, A.M.; El-Shall, M.S.; Awad, F.S. Remediation of Water Containing Lead(II) Using (3-Iminodiacetic Acid) Propyltriethoxysilane Graphene Oxide. Sci. Rep. 2024, 14, 18848. [Google Scholar] [CrossRef]
  15. Liu, B.; Azmatullah, K.; Ki-Hyun, K.; Deepak, K.; Zhang, M. The Adsorptive Removal of Lead Ions in Aquatic Media: Performance Comparison between Advanced Functional Materials and Conventional Materials. Crit. Rev. Environ. Sci. Technol. 2020, 50, 2441–2483. [Google Scholar] [CrossRef]
  16. Samuel, M.S.; Shang, M.; Klimchuk, S.; Niu, J. Novel Regenerative Hybrid Composite Adsorbent with Improved Removal Capacity for Lead Ions in Water. Ind. Eng. Chem. Res. 2021, 60, 5124–5132. [Google Scholar] [CrossRef]
  17. Blair, S.M.; Brodbelt, J.S.; Marchand, A.P.; Kumar, K.A.; Chong, H.-S. Evaluation of Binding Selectivities of Caged Crown Ligands toward Heavy Metals by Electrospray Ionization/Quadrupole Ion Trap Mass Spectrometry. Anal. Chem. 2000, 72, 2433–2445. [Google Scholar] [CrossRef]
  18. Deblonde, G.J.-P.; Lohrey, T.D.; An, D.D.; Abergel, R.J. Toxic Heavy Metal—Pb, Cd, Sn—Complexation by the Octadentate Hydroxypyridinonate Ligand Archetype 3,4,3-LI(1,2-HOPO). N. J. Chem. 2018, 42, 7649–7658. [Google Scholar] [CrossRef]
  19. Deng, H.; Tian, C.; Li, L.; Liang, Y.; Yan, S.; Hu, M.; Xu, W.; Lin, Z.; Chai, L. Microinteraction Analysis between Heavy Metals and Coexisting Phases in Heavy Metal Containing Solid Wastes. ACS EST Eng. 2022, 2, 547–563. [Google Scholar] [CrossRef]
  20. Aztatzi-Pluma, D.; Castrejón-González, E.O.; Almendarez-Camarillo, A.; Alvarado, J.F.J.; Durán-Morales, Y. Study of the Molecular Interactions between Functionalized Carbon Nanotubes and Chitosan. J. Phys. Chem. C 2016, 120, 2371–2378. [Google Scholar] [CrossRef]
  21. Shenderovich, I.G. Effect of Noncovalent Interactions on the 31P Chemical Shift Tensor of Phosphine Oxides, Phosphinic, Phosphonic, and Phosphoric Acids, and Their Complexes with Lead(II). J. Phys. Chem. C 2013, 117, 26689–26702. [Google Scholar] [CrossRef]
  22. Gutiérrez-Ortega, J.A.; Gómez-Salazar, S.; Shenderovich, I.G.; Manríquez-González, R. Efficiency and Lead Uptake Mechanism of a Phosphonate Functionalized Mesoporous Silica through P/Pb Association Ratio. Mater. Chem. Phys. 2020, 239, 122037. [Google Scholar] [CrossRef]
  23. Thommes, M.; Kaneko, K.; Neimark, A.V.; Olivier, J.P.; Rodriguez-reinoso, F.; Rouquerol, J.; Sing, K.S.W. Physisorption of Gases, with Special Reference to the Evaluation of Surface Area and Pore Size Distribution (IUPAC Technical Report). Pure Appl. Chem. 2015, 87, 1051–1069. [Google Scholar] [CrossRef]
  24. Landers, J.; Gor, G.Y.; Neimark, A.V. Density Functional Theory Methods for Characterization of Porous Materials. Colloids Surf. A Physicochem. Eng. Asp. 2013, 437, 3–32. [Google Scholar] [CrossRef]
  25. Lowell, S.; Shields, J.E.; Thomas, M.A.; Thommes, M. Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density; Springer: Berlin/Heidelberg, Germany, 2006; Volume 16. [Google Scholar]
  26. Niu, F.; Tao, L.-M.; Deng, Y.-C.; Wang, Q.-H.; Song, W.-G. Phosphorus Doped Graphene Nanosheets for Room Temperature NH3 Sensing. N. J. Chem. 2014, 38, 2269–2272. [Google Scholar] [CrossRef]
  27. Peng, K.-H.; Yang, S.-H.; Wu, Z.-Y.; Hsu, H.-C. Synthesis of Red Cesium Lead Bromoiodide Nanocrystals Chelating Phenylated Phosphine Ligands with Enhanced Stability. ACS Omega 2021, 6, 10437–10446. [Google Scholar] [CrossRef]
  28. Aziz, I.; Sirajuddin, M.; Nadeem, S.; Tirmizi, S.; Sajjad, W. Synthesis, Spectral Characterization and Evaluation of Biological Properties of Pd(II) Tris-4-Cholorophenyl Phosphine Complexes of Thioureas and Heterocyclic Thiones. J. Chem. Soc. Pak. 2018, 40, 171–181. [Google Scholar]
  29. Schimming, V.; Hoelger, C.-G.; Buntkowsky, G.; Sack, I.; Fuhrhop, J.-H.; Rocchetti, S.; Limbach, H.-H. Evidence by 15N CPMAS and 15N−13C REDOR NMR for Fixation of Atmospheric CO2 by Amino Groups of Biopolymers in the Solid State. J. Am. Chem. Soc. 1999, 121, 4892–4893. [Google Scholar] [CrossRef]
  30. Mauder, D.; Akcakayiran, D.; Lesnichin, S.B.; Findenegg, G.H.; Shenderovich, I.G. Acidity of Sulfonic and Phosphonic Acid-Functionalized SBA-15 under Almost Water-Free Conditions. J. Phys. Chem. C 2009, 113, 19185–19192. [Google Scholar] [CrossRef]
  31. Ek, S.; Iiskola, E.I.; Niinistö, L.; Vaittinen, J.; Pakkanen, T.T.; Root, A. A 29Si and 13C CP/MAS NMR Study on the Surface Species of Gas-Phase-Deposited γ-Aminopropylalkoxysilanes on Heat-Treated Silica. J. Phys. Chem. B 2004, 108, 11454–11463. [Google Scholar] [CrossRef]
  32. Casserly, T.B.; Gleason, K.K. Density Functional Theory Calculation of 29Si NMR Chemical Shifts of Organosiloxanes. J. Phys. Chem. B 2005, 109, 13605–13610. [Google Scholar] [CrossRef]
  33. Brückner, R.; Chun, H.-U.; Goretzki, H.; Sammet, M. XPS Measurements and Structural Aspects of Silicate and Phosphate Glasses. J. Non-Cryst. Solids 1980, 42, 49–60. [Google Scholar] [CrossRef]
  34. Chen, D.A.; Ratliff, J.S.; Hu, X.; Gordon, W.O.; Senanayake, S.D.; Mullins, D.R. Surface Science Dimethyl Methylphosphonate Decomposition on Fully Oxidized and Partially Reduced Ceria Thin Films. Surf. Sci. 2010, 604, 574–587. [Google Scholar] [CrossRef]
  35. Tosatti, S.; Michel, R.; Textor, M.; Spencer, N.D. Self-Assembled Monolayers of Dodecyl and Hydroxy-Dodecyl Phosphates on Both Smooth and Rough Titanium and Titanium Oxide Surfaces. Langmuir 2002, 18, 3537–3548. [Google Scholar] [CrossRef]
  36. Melhi, S.; Alosaimi, E.H.; El-Gammal, B.; Alshahrani, W.A.; El-Aryan, Y.F.; Al-Shamiri, H.A.; Elhouichet, H. Novel Porous Organic Polymer for High-Performance Pb(II) Adsorption from Water: Synthesis, Characterization, Kinetic, and Isotherm Studies. Crystals 2023, 13, 956. [Google Scholar] [CrossRef]
  37. Zhou, X.; Liu, Y.; Jin, C.; Wu, G.; Liu, G.; Kong, Z. Efficient and Selective Removal of Pb(Ii) from Aqueous Solution by a Thioether-Functionalized Lignin-Based Magnetic Adsorbent. RSC Adv. 2022, 12, 1130–1140. [Google Scholar] [CrossRef]
  38. Baltrusaitis, J.; Chen, H.; Rubasinghege, G.; Grassian, V.H. Heterogeneous Atmospheric Chemistry of Lead Oxide Particles with Nitrogen Dioxide Increases Lead Solubility: Environmental and Health Implications. Environ. Sci. Technol. 2012, 46, 12806–12813. [Google Scholar] [CrossRef]
  39. Aliev, V.S.; Badmaeva, I.A.; Pokrovsky, L.D. Lead Phthalocyanine Films Deposited by ECR Plasma-Induced Sublimation. J. Phys. D Appl. Phys. 2012, 45, 305202. [Google Scholar] [CrossRef]
  40. Wakiya, N.; Kuroyanagi, K.; Xuan, Y.; Shinozaki, K.; Mizutani, N. An XPS Study of the Nucleation and Growth Behavior of an Epitaxial Pb(Zr,Ti)O3/MgO(100) Thin Film Prepared by MOCVD. Thin Solid Film. 2000, 372, 156–162. [Google Scholar] [CrossRef]
  41. Ai, S.; Huang, Y.; Xie, T.; Zhang, X.; Huang, C. Fabrication of Composites with Ultra-Low Chitosan Loadings and the Adsorption Mechanism for Lead Ions. Environ. Sci. Pollut. Res. 2020, 27, 37927–37937. [Google Scholar] [CrossRef]
  42. Aklil, A.; Mouflih, M.; Sebti, S. Removal of Heavy Metal Ions from Water by Using Calcined Phosphate as a New Adsorbent. J. Hazard. Mater. 2004, 112, 183–190. [Google Scholar] [CrossRef]
  43. Shenderovich, I.G. Experimentally Established Benchmark Calculations of 31P NMR Quantities. Chem.–Methods 2021, 1, 61–70. [Google Scholar] [CrossRef]
  44. Shenderovich, I.G. For Whom a Puddle Is the Sea? Adsorption of Organic Guests on Hydrated MCM-41 Silica. Langmuir 2020, 36, 11383–11392. [Google Scholar] [CrossRef]
  45. Shenderovich, I.G. 1,3,5-Triaza-7-Phosphaadamantane (PTA) as a 31P NMR Probe for Organometallic Transition Metal Complexes in Solution. Molecules 2021, 26, 1390. [Google Scholar] [CrossRef]
  46. Ransing, A.A.; Dhavale, R.P.; Parale, V.G.; Bangi, U.K.H.; Choi, H.; Lee, W.; Kim, J.; Wang, Q.; Phadtare, V.D.; Kim, T.; et al. One-Pot Sol–Gel Synthesis of Highly Insulative Hybrid P(AAm-CO-AAc)-Silica Aerogels with Improved Mechanical and Thermal Properties. Gels 2023, 9, 651. [Google Scholar] [CrossRef]
  47. Moran-Salazar, R.G.; Carbajal-Arizaga, G.G.; Gutierréz-Ortega, J.A.; Badillo-Camacho, J.; Manríquez-González, R.; Shenderovich, I.G.; Gómez-Salazar, S. As(V) Removal from Aqueous Media Using an Environmentally Friendly Zwitterion L-Cysteine Functionalized Silica Adsorbent. Chem. Eng. Sci. 2023, 278, 118879. [Google Scholar] [CrossRef]
Gels 11 00580 g001
Figure 1. (a) Nitrogen adsorption–desorption isotherms, and (b) BJH pore size distribution of SG-APT4PP (black line) and SG-APT4PP-Pb (red line).
Figure 1. (a) Nitrogen adsorption–desorption isotherms, and (b) BJH pore size distribution of SG-APT4PP (black line) and SG-APT4PP-Pb (red line).
Gels 11 00580 g001
Gels 11 00580 g002
Figure 2. FTIR spectra: (a) silica gel (SG) and (b) SG-APT4PP.
Figure 2. FTIR spectra: (a) silica gel (SG) and (b) SG-APT4PP.
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Gels 11 00580 g003
Figure 3. 13C CP-MAS NMR spectrum of SG-APT4PP and its carbon chemical shift assignment. Spinning side bands of the aromatic signals (*).
Figure 3. 13C CP-MAS NMR spectrum of SG-APT4PP and its carbon chemical shift assignment. Spinning side bands of the aromatic signals (*).
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Gels 11 00580 g004
Figure 4. 29Si MAS NMR spectra of (a) SG-APT4PP and (b) SG-APT4PP-Pb adsorbents.
Figure 4. 29Si MAS NMR spectra of (a) SG-APT4PP and (b) SG-APT4PP-Pb adsorbents.
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Gels 11 00580 g005
Figure 5. Wide-scan XPS spectra of SG-APT4PP and SG-APT4PP-Pb.
Figure 5. Wide-scan XPS spectra of SG-APT4PP and SG-APT4PP-Pb.
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Gels 11 00580 g006
Figure 6. XPS spectra of SG-APT4PP and SG-APT4PP -Pb samples: (a) C 1s, (b) O 1s, (c) P 2p, and (d) Pb 4f.
Figure 6. XPS spectra of SG-APT4PP and SG-APT4PP -Pb samples: (a) C 1s, (b) O 1s, (c) P 2p, and (d) Pb 4f.
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Gels 11 00580 g007
Figure 7. (a) MAS and (b) static 31P{1H} CP NMR spectra of SG-APT4PP (black) and SG-APT4PP-Pb (red).
Figure 7. (a) MAS and (b) static 31P{1H} CP NMR spectra of SG-APT4PP (black) and SG-APT4PP-Pb (red).
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Gels 11 00580 g008
Figure 8. One-pot synthesis (a–c) and the cleaning steps (d–f) of SG-APT4PP.
Figure 8. One-pot synthesis (a–c) and the cleaning steps (d–f) of SG-APT4PP.
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Table 1. Structural parameters of adsorbents (Vp = pore volume, Dp = mean pore diameter).
Table 1. Structural parameters of adsorbents (Vp = pore volume, Dp = mean pore diameter).
SampleBET Surface AreaVpDp
SBET (m2g−1)cm3g−1nm
SG406.090.705.22
SG-APT4PP21.120.4119.74
SG-APT4PP-Pb12.780.3821.66
Table 2. 29Si CP-MAS NMR chemical shifts for different silicon species in SG-APT4PP and SG-APT4PP-Pb samples.
Table 2. 29Si CP-MAS NMR chemical shifts for different silicon species in SG-APT4PP and SG-APT4PP-Pb samples.
SampleChemical Shift (ppm)Q/T
T2T3Q2Q3Q4
SG-APT4PP−63.0
(2.7, 13%) a		−67.6
(1.9, 9%) a		−90.8
(0.8, 4%) a		−99.5
(6.4, 30%) a		−109.6
(9.4, 44%) a		3.6
SG-APT4PP-Pb−61.9
(1.2, 6%) a		−67.1
(2.8, 14%) a		−93.2
(1.3, 6%) a		−99.1
(4.5, 23%) a		−109.1
(10.1, 51%) a		3.9
a Peak areas and percentages are provided in parentheses.
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MDPI and ACS Style

Badillo-Camacho, J.; Gutiérrez-Ortega, J.A.; Shenderovich, I.G.; Velázquez-Galván, Y.G.; Manríquez-González, R. Monitoring Lead–Phosphorus Interactions Through 31P-NMR Used as a Sensor in Phosphine Functionalized Silica Gel Adsorbent. Gels 2025, 11, 580. https://doi.org/10.3390/gels11080580

AMA Style

Badillo-Camacho J, Gutiérrez-Ortega JA, Shenderovich IG, Velázquez-Galván YG, Manríquez-González R. Monitoring Lead–Phosphorus Interactions Through 31P-NMR Used as a Sensor in Phosphine Functionalized Silica Gel Adsorbent. Gels. 2025; 11(8):580. https://doi.org/10.3390/gels11080580

Chicago/Turabian Style

Badillo-Camacho, Jessica, José A. Gutiérrez-Ortega, Ilya G. Shenderovich, Yenni G. Velázquez-Galván, and Ricardo Manríquez-González. 2025. "Monitoring Lead–Phosphorus Interactions Through 31P-NMR Used as a Sensor in Phosphine Functionalized Silica Gel Adsorbent" Gels 11, no. 8: 580. https://doi.org/10.3390/gels11080580

APA Style

Badillo-Camacho, J., Gutiérrez-Ortega, J. A., Shenderovich, I. G., Velázquez-Galván, Y. G., & Manríquez-González, R. (2025). Monitoring Lead–Phosphorus Interactions Through 31P-NMR Used as a Sensor in Phosphine Functionalized Silica Gel Adsorbent. Gels, 11(8), 580. https://doi.org/10.3390/gels11080580

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