Facile Synthesis of β-C₃N₄ and Its Novel MnTeO₃ Nanohybrids for Remediating Water Contaminated by Pharmaceuticals

Abstract

A facile method was adopted to fabricate β-C₃N₄, and it was then doped with manganese and tellurium to obtain novel 10%MnTeO₃@β-C₃N₄ (10%MnTe@β) and 20%MnTeO₃@β-C₃N₄ (20%MnTe@β) nanohybrids. The β-C₃N₄, 10%MnTe@β, and 20%MnTe@β showed surface areas of 85.86, 97.40, and 109.54 m² g⁻¹, respectively. Using ciprofloxacin (CIP) as a pollutant example, 10%MnTe@β and 20%MnTe@β attained equilibrium at 60 and 45 min with q_t values of 48.88 and 77.41 mg g⁻¹, respectively, and both performed better at pH = 6.0. The kinetic studies revealed a better agreement with the pseudo-second-order model for CIP sorption on 10%MnTe@β and 20%MnTe@β, indicating that the sorption was controlled by a liquid film mechanism, which suggests a high affinity of CIP toward 10%MnTe@β and 20%MnTe@β. The sorption equilibria outputs indicated better alignment with the Freundlich and Langmuir models for CIP removal by 10%MnTe@β and 20%MnTe@β, respectively. The thermodynamic analysis revealed that CIP removal by 10%MnTe@β and 20%MnTe@β was exothermic, which turned more spontaneous as the temperature decreased. Applying 20%MnTe@β as the best sorbent to groundwater and seawater spiked with CIP resulted in average efficiencies of 94.8% and 91.08%, respectively. The 20%MnTe@β regeneration–reusability average efficiency was 95.14% within four cycles, which might nominate 20%MnTe@β as an efficient and economically viable sorbent for remediating CIP-contaminated water.

1. Introduction

Rapid industrialization and population growth have led to significant water contamination issues. Vast amounts of toxic elements, plastics, and pharmaceutical and dye effluents are released into rivers and other natural water bodies by various sectors, including pharmaceutical, metallurgy, mining, textile, paint, leather good, paper, and cosmetics industries [1,2]. These contaminants are known to be detrimental to humans, animals, aquatic life, and the entire environment [3]. Since both industrial intermediates and hazardous substances are physiologically carcinogenic, they are the targets of laws. Hence, it is imperative to ensure both environmental sustainability and human health by implementing laws and regulations regarding the disposal of waste effluent [4]. Some of these hazardous chemicals are found in personal care products (PCPs) and essential medications, which is why they are targeted by pollution control authorities [5]. Antibiotics (ANBs) are the most commonly used PCPPs, and a study of 76 nations showed that drug consumption increased by 65% within 15 years, with a 39% increase in ANB consumption. A 200% increase in ANB usage was anticipated for the upcoming half-decade [6]. Large amounts of ANBs and their by-products eventually make their way into the sewage system unaltered, as the majority of the doses are discharged unmetabolized from the body via excretion [7]. These ANBs endanger the ecosystem’s flora and fauna unless they are efficiently broken down or removed from wastewater. Ciprofloxacin (CIP) is a frequently prescribed antibiotic with a broad spectrum of antibacterial activity that was initially introduced to the market in 1987 [8]. It is a second-generation fluoroquinolone (FQ) that functions by inhibiting the cellular replication of bacteria and ultimately hindering their ability to proliferate. CIP is extensively utilized in the fields of medicine, aquaculture, and agriculture; moreover, in 2013, CIP was the second-most-used FQ antibiotic in China (5340 t production), which makes the case of it being chosen as a representative model pollutant ANB in many research studies concerning water remediation [8]. Due to its persistent and ongoing use, CIP has been detected in widespread concentrations in surface water and wastewater. CIP has been identified in effluents from wastewater treatment facilities at a concentration of 5.6 μg L⁻¹ [9]. The CIP contamination levels in 25 wastewater samples from German hospital effluents ranged from 0.7 to 124.5 μg L⁻¹ [10]. The literature indicates that wastewater from drug production can potentially be a significant source of considerably higher CIP concentrations. A survey of adjoining effluent treatment plants in Hyderabad, India, revealed a CIP concentration range from 1.0 to 14.0 mg L⁻¹, whereas it was approximately 6.5 mg L⁻¹ in two nearby lakes [11]. The accumulation of CIP in an organism’s body presents a considerable health risk; therefore, the effective removal of CIP is essential due to its resistance to degradation and potential ecotoxicity [12]. Unless removed by an efficient treatment procedure, CIP is predicted to persist in the environment for a considerable period, with grave adverse effects [13,14]. Numerous strategies have been proposed for the remediation of wastewater contaminated by CIP, including ozonation, advanced oxidation processes, and bioremediation [15,16,17]. However, these methods have concomitant drawbacks, including ineffective removal, intricate processes, and/or significant energy requirements [18]. Because of its low cost, high performance, and versatility, adsorption is favored [19]. Various adsorbents have been investigated for antibiotic adsorption, including carbon-based materials, polymers, resins, metal–organic frameworks, clays, and minerals [20,21]. The use of the adsorption approach in the uptake of CIP from an aqueous medium is a reasonable protocol that requires developing an appropriate sorbent and adjusting the optimum conditions in order to gain the highest benefits it offers. CIP removal from water has been studied using carbon nitride (C₃N₄) and its nanocomposites [22]. β-C₃N₄, a family member of layered materials, is among the oldest synthetic polymers known to scientists [23]. It is a special metal-free organic semiconductor photocatalyst that is active in the visible light spectrum and has adjustable electrical characteristics [24]. Despite the outstanding characteristics of β-C₃N₄, including its layered structure stability, tunable properties, and strong tetrahedral bonding, relatively few studies have investigated it as an adsorbent [25]. Graphene and boron nitride ribbon fibers were combined to create graphene nanoplatelet/Boron nitride, which composed an adsorbent for removing CIP from aqueous solutions [26]. β-C₃N₄ is inexpensive, hard, lightweight, and has a relatively high surface area, exhibiting outstanding stability under ambient conditions [27,28]. Its applications extend to various fields, including energy conversion, water purification, NOx decomposition, and the standardization of materials for identifying sites in oxidation reactions, as well as the development of H₂ and fuel cells [29,30]. Numerous studies have recommended doping with transition metal oxides to enhance the properties and adsorption capabilities of base materials [31,32]. Doping can narrow the band gap, extend visible light absorption, reduce electron–hole recombination, and, most importantly for sorbents, expand the surface area of base substrates [33,34]. Although some studies have investigated manganese compounds, such as Mn/Te and Mn@NiO, in the fields of photocatalysis and antibacterial applications, these materials have not been tested as adsorbent-doping substrates [35,36,37]. Manganese tellurite is characterized by its hexagonal channel crystal structure, which features high remaining electron densities within the channels [37], resulting in partially positive and negative sites on the sorbent surface. This creates the potential for electrostatic attraction between the sorbents and sorbates, thereby enhancing the sorption process. Nevertheless, there is an investigation deficiency regarding MnTeO₃ that is likely attributable to the challenge of synthesizing single-phase MnTeO₃ compounds [38].

This study aimed to develop a simplified one-pot route employing guanidine hydrochloride as an unconventional precursor for synthesizing nitrogen-rich β-C₃N₄. The β-C₃N₄ fabricated in this study is modified via MnTeO₃ doping at 10% and 20% ratios. β-C₃N₄ and both nanohybrids are characterized and examined for adsorbing CIP as a contaminant example due to pre-identified justifications. Then, the solution conditions are adjusted to achieve the best possible CIP sorption capacities onto β-C₃N₄ nanohybrids. The CIP sorption order, mechanism, isotherm, and thermodynamics are tested. Moreover, the most effective β-C₃N₄/MnTeO₃ nanohybrid sorbent is utilized to remediate synthetic CIP-contaminated groundwater (GW) and seawater (SW). Furthermore, as a cost-effective part of the survey, the reusability of the selected β-C₃N₄/MnTeO₃ nanohybrid is investigated.

2. Materials and Methods

2.1. Materials

Guanidine hydrochloride (GU-HCl) was obtained from Loba-Chem, Mumbai, India; potassium tellurite and manganese chloride (tetrahydrate) were purchased from Sigma Aldrich, Saint Louis, MO, USA. All the reagents were of analytical grade and used without any further purification.

2.2. Synthesis of β-C₃N₄ Nanoparticles

β-C₃N₄ was prepared by placing 20 g of GU-HCl in a 200 mL covered crucible, and it was then pyrolyzed in a muffle furnace at 500 °C for 2.0 h. The product was then cooled, and the obtained powdered β-C₃N₄ was collected.

2.3. Fabrication of β-C₃N₄MnTeO₃ Nanocomposites

An accurate 4.5 g of β-C₃N₄ was dispersed in 200 mL of distilled water (D-W) in a 400 mL beaker. Totals of 0.4356 g of MnCl₂ · 4H₂O and 0.5579 g of K₂TeO3 were dissolved separately in 50 mL of deionized water (D-W). The last two beakers were poured simultaneously into the β-C₃N₄ beaker with vigorous stirring. The formed suspensions were sonicated for 30 min, filtered under suction, washed with D-W, and then dried at 110 °C for 1.0 h in an oven. They were then calcined at 400 °C in a tubular furnace under a nitrogen flow of 60 mL/min and labeled as (10%MnTe@β). The 20%MnTe@β-C₃N₄ was synthesized similarly, except for using 4.0 g of β-C₃N₄, 0.8712 g of MnCl₂.4H₂O, and 1.158 g of K₂TeO₃, and it was then labeled as (20%MnTe@β).

2.4. Characterization Techneaques

Using standard physical techniques, β-C₃N₄, 10%MnTe@β, and 20%MnTe@β sorbents were characterized. The Rigaku Smart-Lab X-ray diffractometer, equipped with PDXL2 software-2015 (Tokyo, Japan), was employed to match the XRD patterns and compute the lattice parameters. The surface morphologies of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β were surveyed via JSM-IT300-scanning (JEOL Ltd., Tokyo, Japan) electron-energy dispersive X-ray technique (SEM–EDX). The functional groups of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β were explored via a Bruker TENSOR-FTIR spectrophotometer (Berlin, Germany). The β-C₃N₄, 10%MnTe@β, and 20%MnTe@β surface and porosity properties were analyzed by N₂ adsorption–desorption isotherms (ASAP 2020 Micromeritics analyzer, Miami, FL, USA).

2.5. Adsorption Experiments

The contact time study involved preparing a stock solution of 600 mL of 50.0 mg L⁻¹ CIP in distilled water. An amount of 120 mL of CIP solution was stirred separately with 50 mg of each sorbent, and 5 mL of each mixture was withdrawn at serial intervals. Following this, each solution was filtered using a 0.22 μm nylon syringe filter and measured via a UV-Vis spectrophotometer, from which the adsorption capacity (q_t, (mg g⁻¹) was computed via the following Equation (1):

$${\mathrm{Q}}_{\mathrm{t}}=\mathrm{v}\left({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{t}}\right)/\mathrm{m}$$

(1)

where m is the mass of the sorbent (g), v denotes the solution’s volume (L), C₀ is the initial supplied concentration, and C_t is the unabsorbed concentration. The nonlinear pseudo-first-order (NPFO, Equation (2)) and second-order (NPSO, Equation (3)) models were used to investigate CIP sorption rates onto 10%MnTe@β and 20%MnTe@β nanocomposites. Additionally, Equations (4) and (5) were utilized to elucidate the adsorption control mechanisms via the liquid film and intraparticle diffusion models (LFM and IPM). These equations are shown as follows:

$${\mathrm{q}}_{\mathrm{t}}={\mathrm{q}}_{\mathrm{e}}(1-{\mathrm{e}\mathrm{x}\mathrm{p}}^{-{\mathrm{k}}_{1.}\mathrm{t}})$$

(2)

$${\mathrm{q}}_{\mathrm{t}}={\displaystyle \frac{{\mathrm{k}}_2{.\mathrm{q}}_{\mathrm{e}}^2.\mathrm{t}}{1+{\mathrm{k}}_{2.}{\mathrm{q}}_{\mathrm{e}}.\mathrm{t}}}$$

(3)

$${\mathrm{q}}_{\mathrm{t}}={\mathrm{K}}_{\mathrm{I}\mathrm{P}}\ast {\mathrm{t}}^{{\displaystyle \frac{1}{2}}}+{\mathrm{C}}_{\mathrm{i}}$$

(4)

$$\mathrm{l}\mathrm{n}(1-\mathrm{F})=-{\mathrm{K}}_{\mathrm{L}\mathrm{F}}\ast \mathrm{t}$$

(5)

where C_i represents the boundary layer factor, while k₁ (min⁻¹), k₂ (g mg⁻¹ min⁻¹), K_IP (mg g⁻¹ min^−1/2), and K_LF (min⁻¹) denote the constants for NPFO, NPSO, LFM, and IPM, respectively.

The initial CIP feed concentration impact was tested utilizing 10, 20, 30, and 50 mg L⁻¹ solutions, and temperature impact was examined in a range of 293–323 K.

To enhance the understanding of CIP sorption onto 10%MnTe@β and 20%MnTe@β, the concentration study outputs were used to investigate the isotherms. The Langmuir (LIM, Equation (6)) and Freundlich (FIM, Equation (7)) isotherm models were utilized to examine the hypothesis of single-layered CIP sorption and the potential for multilayer sorption, as follows:

$$q_e= \left({\displaystyle \frac{K_l{q}_m{C}_e}{1+q_m{C}_e }}\right)$$

(6)

$$q_e=K_F.C_e^{{\displaystyle \frac{1}{n}}}$$

(7)

where C_e (mg L⁻¹) represents the CIP concentration; q_m denotes the maximum q_t; K_L (L mg⁻¹) is the LIM constant; K_F (L g⁻¹) and 1/n are the FIM constant and favorability factor, respectively [39].

For a better understanding of CIP removal by 10%MnTe@β and 20%MnTe@β, the thermodynamics were examined utilizing the concentration–temperature study outputs. The entropy (ΔS°) and enthalpy (ΔH°) were computed via Equation (8). The Gibbs free energy (ΔG°) was then derived by introducing their values into Equation (9).

$$\mathrm{l}\mathrm{n} K_c= {\displaystyle \frac{\Delta H^o}{RT}} + {\displaystyle \frac{\Delta S^o}{R}}$$

(8)

$$\Delta G^o=\Delta H^o-T\Delta S^o$$

(9)

where R stands for the ideal gas constant (0.008314 kJ mol⁻¹), T stands for temperature (K), and K_c stands for the CIP sorption distribution coefficient.

Furthermore, the pH influence was surveyed between pH 3.0 and 10.0 to optimize the parameters for CIP sorption on 10%MnTe@β and 20%MnTe@β. Portions of 50 mg L⁻¹ CIP solution were adjusted at the desired value (pH = 3 to 10) via adding HCl and/or NaOH. In order to prevent any potential errors arising from the alteration of CIP chromophore by the specific pH, an adequate quantity of 50 mg L⁻¹ CIP solution was adjusted to utilize each extra solution as a standard for its typical pH sample. Moreover, the optimized parameters were applied to GW and SW as natural samples after being spiked to achieve 5 and 10 mg CIP pollution levels. Furthermore, the reusability of the two sorbents was examined through four consecutive cycles.

3. Results and Discussions

3.1. Yield Percentage of β-C₃N₄

Calcining 20.0 g of GU-HCl at 500 °C produced a pale yellow product mass of 12.3 g β-C₃N₄, indicating a 61.5% yield of utilizing this precursor via the suggested method parameters. Such a relatively high yield suggests that GU-HCl is a suitable precursor for a facile one-pot synthesis method compared to the other studied precursors.

3.2. Characterization

Figure 1a illustrates the stacked plot of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β diffraction patterns. The Rigaku Smart-Lab PDXL2 (2015) software was employed to match the obtained patterns with reference JCPDS cards. The two distinctive β-C₃N₄ peaks of 2θ°= 13.79° and 27.56° allocated to (100) and (110) β-C₃N₄ crystal planes [40], in addition to other weak and broad peaks at 44.65 (300) and 57.08 (220) JCPDS -00-087-1526), confirming the successful fabrication of β-C₃N₄ from GU-HCl [41,42]. The presence of pre-identified peaks in the 10%MnTe@β and 20%MnTe@β patterns indicated the existence of β-C₃N₄ without chemical alteration. Moreover, the 10%MnTe@β and 20%MnTe@β peaks at 2θ° of 18.25 (112), 21.22 (101), 25.73 (020), 32.75 (002), (37.95 (220), 42.10 (022), 43.21 (202), 52.10 (103), and 56.57 (400) align with the centered cubic MnTeO₃ pattern JCPDS 00-078-1713) [43]. Hence, these data confirmed the incorporation of MnTeO₃ within the β-C₃N₄ nanosheets and further indicated the excellent purity of the synthesized nanohybrids, as no foreign peak was observed. The XRD lattice parameters β-C₃N₄, 10%MnTe@β, and 20%MnTe@β are illustrated in

Table 1. The lattice parameters of the β-C₃N₄, 10%MnTe@β, and 20%MnTe@β nanomaterials.

Phase Name	D (nm)	A (Å)	B (Å)	C (Å)	α (deg)	β (deg)	γ (deg)
β-C3N4	0.65	7.343	7.343	2.9	90.00	90.00	120.00
MnTeO3 of 10%MnTe@β	19.0	13.92	10.23	11.78	90.00	92.9	90.00
β-C3N4 of 10%MnTe@β	9.07	4.459	4.459	6.470	90.00	90.00	120.00
MnTeO3 of 20%MnTe@β	8.0	6.42	7.55	4.683	90.00	90.00	90.00
β-C3N4 of 20%MnTe@β	3.28	6.165	6.165	2.694	90.00	90.00	120.00

.

The FT-IR analysis was employed to elucidate the functional groups of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β (Figure 1b and

Table 2. The FT-IR results of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β nanomaterials.

The Absorbing Group	β-C3N4	10%MnTe@β	20%MnTe@β
Adsorbed moisture O-H	-	~3444 cm−1	~3444 cm−1
N—H stretching	3080–3280 cm−1	3130–3308 cm−1	3120–3334 cm−1
C-H stretching	2933 cm−1	2933 cm−1	2933 cm−1
C≡N stretching,	2368 cm−1	2374 cm−1	2364 cm−1
C—N stretching	1234–1642 cm−1	1234–1642 cm−1	1234–1642 cm−1
Out-of-plane bending of the triazine ring	803–812 cm−1	803–812 cm−1	803–812 cm−1
Te—O stretching	-	755 cm−1	760 cm−1
Mn—O stretching	-	584 cm−1	575 cm−1

). Stretching vibrations of the moisture O-H and the primary and secondary amine bonds appeared at 3000–3500 cm⁻¹, while the weak band of 2933 cm⁻¹ may be allocated to traces of C-H bond stretching. In 10%MnTe@β and 20%MnTe@β spectra, it is possible to attribute the two shallow peaks at 2374 and 2364 cm⁻¹ to the C≡N stretching, while the stretching mode of heterocycles of C–N is attributed to the peaks at 1200 and 1600 cm⁻¹ [44]. The out-of-plane bending vibration of the triazine ring is responsible for the steep peak at 809 cm−1, confirming the presence of β-C₃N₄ in the composite framework. Additionally, the 592 and 589 cm⁻¹ bands are ascribed to the Mn–O and Te–O bonds, showing that MnTeO₃ was incorporated efficiently [45]. These findings support the XRD indications of the successful synthesis of β-C₃N₄ and its MnTeO₃ nanocomposites via the simple procedure adopted in this work.

The size and morphology of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β nanomaterials were obtained using SEM imaging (Figure 2a–c). This revealed the appearance of the pristine β-C₃N₄ as irregularly folded sheets, particles, and plates, as illustrated in Figure 2a. Both 10%MnTe@β and 20%MnTe@β revealed that the prepared materials are composed of fine MnTeO₃ nanoparticles dispersed on the surface and/or impeded within the β-C₃N₄ plates. The nanoparticles of manganese tellurite were dispersed on the surface of the base material as clusters of spherical particles. The 10%MnTe@β and 20%MnTe@β average particle sizes obtained from SEM images were 32.08 ± 5.8 and 40.40 ± 6.6 nm, respectively.

The EDX spectrum of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β, shown in Figure 2d–f, confirms the presence of the expected elements in each sorbent. The homogeneity of elements constituting β-C₃N₄, 10%MnTe@β, and 20%MnTe@β was tested via EDX mappings shown in Figure 3a, b, and c, respectively. The contrast between the dark and light colors ensures an even distribution of C, N, Mn, Te, and O atoms among the entire tested area of the nanohybrids.

The surface properties of β-C₃N₄, 10%MnTe@β, and 20%MnTe@β nanomaterials were examined using the N₂ adsorption–desorption technique. Figure 4a–c illustrates that N₂ adsorption was negligible at low pressures in type IV isotherms, which increased significantly with increasing gas pressure. The figures show that the three products exhibit type IV isotherm curves with H3 hysteresis loops, which are characteristic of mesoporous constructions with more likely slit-shaped pores [45,46].

Table 3. The surface characteristics β-C₃N₄, 10%MnTe@β, and 20%MnTe@β.

Sorbent	SA (m2 g−1)	PD (Å)	PV (cm3 g−1)
β-C3N4	85.86	12.61	0.29
10%MnTe@β	97.40	13.99	0.22
20%MnTe@β	109.54	10.42	0.37

gathers the BET surface area (SA), average pore diameter (PD), and pore volume (PV). The 20%MnTe@β demonstrates the largest surface area (109.54 m² g⁻¹), suggesting that it is the most effective adsorbent among the three sorbents. The elevated pore volume of 0.365 cm³ g⁻¹ of this sorbent supports this hypothesis.

3.3. Contact Time and Effect of pH

The produced β-C₃N₄, 10%MnTe@β, and 20%MnTe@β nanocomposites were tested for adsorbing CIP from aqueous solutions. A diagrammatic representation of the time impact on the adsorption of CIP is presented in Figure 5a. After sixty minutes, the β-C₃N₄ and 10%MnTe@β sorbent systems achieved a state of equilibrium, displaying q_t values of 27.30 and 48.88 mg g⁻¹, respectively; on the other hand, 20%MnTe@β attained equilibrium at min 45 with a q_t of 77.41 mg g⁻¹, which positioned 20%MnTe@β among the effective CIP adsorbing materials (Table 4). Notably, within the first two minutes, 20%MnTe@β exhibited a rapid adsorption rate, collecting 75% of its total q_t value, which can be attributed to the availability of binding sites resulting from the exterior surface and wider pores of 20%MnTe@β. The observed increase in q_t in the 20%MnTe@β composite is most likely attributed to the substantial presence of MnTeO₃ nanoparticles, which have the potential to enhance the adsorption of CIP on the material. Additionally, the impediment of ionically bonded Mn, Te, and O (MnTeO₃) within and between the β-C₃N₄ layers created electrostatic diversity via the partially positive Mn and Te sites and the partially negative O sites. Such polarization might lead to the electrostatic attraction force becoming more involved in the sorption process onto 20%MnTe@β, especially given the even distribution revealed by the EDX mapping. The proportional increase in the qt value as the MnTeO₃ concentration increased indicated the possibility of achieving a higher q_t by further increasing the MnTeO₃ doping dose.

Figure 5b illustrates that the adsorption of CIP onto 10%MnTe@β and 20%MnTe@β increased from a pH value of 3 to 6, followed by a slight decrease from pH 7 to pH 8, while notable reductions in q_t are observed with further increases in pH. The highest q_t value was obtained at pH 5.0 for β-C₃N₄, while pH 6 was most favorable for the 10%MnTe@β and 20%MnTe@β sorbents. The adsorption behavior of CIP is attributable to the electrostatic interaction between the CIP form in solution and the surface charge of 10%MnTe@β and 20%MnTe@β, with CIP present in the mono-cationic form at pH levels below 6. CIP exists as a zwitterion within the pH range of 6 to 9, while, above pH 9, CIP may adopt an anionic form due to carboxylic group ionization and/or repulsion with the surrounding -OH groups on the sorbents [47,48,49].

Table 4. Comparing the performance of sorbents found in the literature with the prepared 10%MnTe@β and 20%MnTe@β in removing ciprofloxacine from water.

Sorbent	qt (mg g−1)	Reference
10%MnTe@β	48.88	This study
20%MnTe@β	77.41	This study
Carbon nanoparticles (CNPs) derived from sunflower seed waste	103.6	[50]
Carbon Nanoparticles prepared from coffee skin waste	142.6	[51]
Carbon nanotubes synthesized from commercial gasoline	95.5	[39]
Aluminous oxide	13.6	[52]
Magnetite	12.73	[53]
Activated carbon derived from pomegranate peel waste	2.353	[54]
Zeolites	5.79	[55]
Activated carbon	1.86	[56]
Modified montmorillonite	1.67	[56]
Alumina	1.15	[56]

Table 4. Comparing the performance of sorbents found in the literature with the prepared 10%MnTe@β and 20%MnTe@β in removing ciprofloxacine from water.

Sorbent	qt (mg g−1)	Reference
10%MnTe@β	48.88	This study
20%MnTe@β	77.41	This study
Carbon nanoparticles (CNPs) derived from sunflower seed waste	103.6	[50]
Carbon Nanoparticles prepared from coffee skin waste	142.6	[51]
Carbon nanotubes synthesized from commercial gasoline	95.5	[39]
Aluminous oxide	13.6	[52]
Magnetite	12.73	[53]
Activated carbon derived from pomegranate peel waste	2.353	[54]
Zeolites	5.79	[55]
Activated carbon	1.86	[56]
Modified montmorillonite	1.67	[56]
Alumina	1.15	[56]

3.4. Adsorption Kinetics

The k₁ and k₂ values shown in

Table 5. Kinetic results of CIP sorption onto 10%MnTe@β and 20%MnTe@β nanocomposites.

Adsorption Rate Order
Sorbent	qmax exp (mg. g−1)	NPFO					NPSO
		qe (mg. g−1)	K1	R2	X2	RSS	qe (mg. g−1)	K2	R2	X2	RSS
10%MnTe@β	48.89	45.158	0.6555	0.9682	8.63182	60.42273	47.8555	0.67344	0.9919	2.19657	15.376
20%MnTe@β	77.41	74.192	0.5117	0.9729	19.09689	133.67823	77.2766	1.2512	0.9944	3.9636	27.745
Adsorption rate mechanism
Sorbent	IPM							LFM
	KIP (mg. g−1 min1/2)		C (mg. g−1)		R2	RSS		KLF (min−1)	R2	RSS
10%MnTe@β	2.666		29.185		0.845	42.64233		0.06747	0.850	2.2715
20%MnTe@β	2.97888		57.3552		0.834	57.76773		0.0725	0.953	0.74024

were computed from the slope values of the NPFO and NPSO graphs depicted in Figure 6a,b. The correlation coefficient (R²), in conjunction with the residual sum of squares and the reduced Chi-square, served as the primary criterion for selecting the model that provided the optimal fit [57]. The CIP sorption by 10%MnTe@β and 20%MnTe@β fitted NPSO for CIP, yielding R² values of 0.992 and 0.994, respectively. The q_t values derived from Equation 3 were closely aligned with the experimental values, the k₂ values were similarly comparable, and the lower RSS and X² values with the higher R² values verified fitting the NPSO, indicating that CIP uptakes by 10%MnTe@β and 20%MnTe@β are contingent upon the availability of CIP and the active sites on the 10%MnTe@β and 20%MnTe@β surfaces [58,59]. Figure 6c,d, along with the results presented in Table 4, demonstrate the outcomes of the CIP sorption control mechanism. CIP diffusion toward 10%MnTe@β and penetration through the interior layers of 10%MnTe@β both contributed to controlling CIP sorption, as indicated by the R² values for LFD and IPD, which are nearly typical. The results gathered in Table 4 demonstrate that LFM regulates CIP sorption onto the 20%MnTe@β nanocomposite. This indicates that the diffusion of CIP toward the 20%MnTe@β activate sites was slower compared to CIP penetration into 20%MnTe@β interior shells, demonstrating the high affinity of CIP toward the 20%MnTe@β nanocomposite [60].

3.5. Sorption Equilibria

The impact of CIP concentration on its sorption by 10%MnTe@β and 20%MnTe@β was investigated (Figure 7a,b). The q_t increased proportionally as the concentration rose from 10 to 50 mg L⁻¹, where the line showed significant inflation, indicating the sorbent’s unsuitability to treat more than 30 mg L⁻¹ with such a solution-sorbent ratio (12:5). Raising the CIP solution temperature from 293 to 323K decreased the sorption efficiency significantly, demonstrating that CIP adsorption by 10%MnTe@β and 20%MnTe@β was exothermic.

Figure 7c,d illustrate the collective nonlinear plots of LIM and FIM regarding CIP adsorption on 10%MnTe@β and 20%MnTe@β, and their results are presented in

Table 6. Isotherms and thermodynamic outputs of CIP sorption by 10%MnTe@β and 20%MnTe@β.

Adsorption Isotherms
Isotherm model	Langmuir			Freundlich
Sorbent	R2	KL	qm	R2	Kf	1/n
10%MnTe@β	0.99397	0.01606	136.007	0.99603	3.16823	0.77782
20%MnTe@β	0.9779	3.1375 × 105	71715.2	0.96835	1.6375	1.10947
Thermodynamic results 10%MnTe@β
Conc. (mg L−1)	ΔH°	ΔS°	ΔG°(293 K)	ΔG°-303 K	ΔG°-313 K	ΔG°-323 K	R2
10.0	−7.698	−0.025	−0.479	−0.232	0.014	0.014	0.999
20.0	−9.455	−0.032	0.057	0.382	0.706	1.031	0.859
30.0	−8.939	−0.032	0.375	0.693	1.011	1.329	0.603
50.0	−11.770	−0.044	1.013	1.449	1.885	2.322	0.995
Thermodynamic results 20%MnTe@β
Conc. (mg L−1)	ΔH°	ΔS°	ΔG°(293 K)	ΔG°-303 K	ΔG°-313 K	ΔG°-323 K	R2
10.0	−9.840	−0.032	−0.428	−0.107	0.214	0.214	0.853
20.0	−9.782	−0.034	0.192	0.532	0.873	1.21	0.872
30.0	−12.206	−0.044	0.632	1.070	1.508	1.946	0.952
50.0	−3.323	−0.016	1.221	1.376	1.531	1.686	0.937

. The outputs from the fitting indicated that the sorption of CIP onto 10%MnTe@β was more in line with FIM; hence, the process of CIP adsorption onto this sorbent was characterized by multilayer adsorption. Additionally, adsorption was favorable, as the 1/n values fell within the range from 0.0 to 1.0. Conversely, the LIM model was shown to be the most appropriate for CIP adsorption onto 20%MnTe@β, and it predicted that 1.0 g of it could uptake 136.0 mg CIP. In addition, the fact that 1/n was above one suggested the unfavorability of multilayered CIP sorption onto 20%MnTe@β [61].

Figure 7e,f present the thermodynamic plot for 10%MnTe@β and 20%MnTe@β, and the computed parameters are shown in Table 6. The negative ΔH° and rising ΔG° values as the temperature increased indicated exothermic CIP sorption on 10%MnTe@β and 20%MnTe@β, which tended towards spontaneity as the temperature decreases. The increase in ΔG° values with a decreasing starting concentration is encouraging for the application of both 10%MnTe@β and 20%MnTe@β in water treatment, particularly in scenarios with low pollutant concentrations, with a preference for 20%MnTe@β. Moreover, the ΔG° values of less than 40.0 kJ mol⁻¹ indicated that the CIP was eliminated by 10%MnTe@β and 20%MnTe@β via physisorption process.

3.6. Application of 20%MnTe@β to Remediate Natural Water

As suggested by the contact time outcome, 20%MnTe@β was selected for this test. The total dissolved solids (TDS) for the natural samples (GW and SW) were 1.59 and 33.62 g L⁻¹, with pH values of 7.8 and 8.1, respectively. Thermodynamic data indicated a preferred CIP removal as the temperature was reduced; hence, incorporating a heating phase to enhance sorption was not required. The pH of GW and SW was set at the optimal pH level (6.0). Figure 8a presents the outcomes of the 20%MnTe@β effective eradication of CIP as a model pollutant from GW and SW. The removal percentages of CIP from GW and SW were 96.93% and 92.78% for 5 mg L⁻¹ spiked samples and 92.64% and 89.38% for 10 mg L⁻¹ concentration, indicating that no significant alterations occurred due to the presence of other natural water constituents. The relative reduction in CIP removal percentage in SW compared to GW may be attributed to the higher salt content in SW, which potentially obstructs specific active sorption sites on 20%MnTe@β and/or hinders the diffusion of the CIP solution to the surface of 20%MnTe@β.

3.7. Regeneration and Reusability

The reusability of 20%MnTe@β was investigated using 50 mL of the 5.0 mg L⁻¹ CIP concentration. Following the initial cycle, further adsorption experiments were conducted using the regenerated 20%MnTe@β adsorbent. The preparation of the 20%MnTe@β nanocomposite for reuse involved washing with 10 mL of 0.2 M NaOH, followed by two washes with 10 mL of ethanol each, and then drying at 80 °C for 2.0 h to be applied in the next round. Figure 8 illustrates the 20%MnTe@β reusability outcomes in removing CIP; the effectiveness of the 20%MnTe@β nanocomposite in the fourth cycle was 92.8%, which represents a slight decrease in the CIP adsorption percentage. These findings suggest that the 20%MnTe@β nanocomposites can be regenerated and subjected to multiple uses with suitable reuse, at least four times, without significant loss in performance. Although tellurite salts were known to be sparingly soluble in ethanol and/or cold water, it is possible to attribute the slight decrease in the 20%MnTe@β to a partial loss of doping material.

4. Conclusions

The present investigation employed a straightforward pyrolysis technique to produce β-C₃N₄ from guanidine hydrochloride, subsequently doped with manganese tellurite, resulting in the creation of the novel nanohybrids 10%MnTe@β and 20%MnTe@β. The XRD patterns confirmed the β-C₃N₄ phase and the success of incorporating MnTeO₃ into β-C₃N₄. SEM pictures showed particle sizes of 27.97 nm, 32.08 nm, and 40.40 nm for β-C₃N₄, 10%MnTe@β, and 20%MnTe@β, respectively. The surface areas were 85.86, 97.40, and 109.54 m² g⁻¹, respectively. This size–surface area contradiction for 10%MnTe@β and 20%MnTe@β could be attributed to the 20%MnTe@β particles being sufficiently large enough to separate the β-C₃N₄ layers, exposing additional plate surfaces. In adsorbing CIP from aqueous solutions, β-C₃N₄ and 10%MnTe@β reached equilibrium at 60 min, while 20%MnTe@β required 45 min, with q_t values of 27.30, 48.88, and 77.41 mg g⁻¹, respectively. It is worth noting that, with a pH of 6.0, 10%MnTe@β and 20%MnTe@β worked more effectively. In the kinetic studies, more agreement was found with the NPSO for CIP sorption on 10%MnTe@β and 20%MnTe@β. Moreover, the LFM controlled CIP sorption onto 20%MnTe@β, indicating a strong affinity towards CIP; on the other hand, both LFM and IPD participated in influencing CIP sorption onto 10%MnTe@β. The sorption equilibria outputs suggested a superior alignment with the Freundlich and Langmuir models for eliminating CIP by 10%MnTe@β and 20%MnTe@β, respectively. The multilayered sorption mechanism might explain the higher qt value of 20%MnTe@β. The thermodynamic results demonstrated that CIP sorption by 10%MnTe@β and 20%MnTe@β was exothermic and became more spontaneous as the temperature in the system dropped. Applying 20%MnTe@β as the most effective sorbent to natural GW and SW spiked by 5 and 10 mg L⁻¹ CIP, and average efficiencies of 94.8 and 91.08 were obtained. Throughout four cycles, the average efficiency of the 20%MnTe@β regeneration–reusability process was 95.14%. These outcomes of the 20%MnTe@β performance, with no need for heating, may nominate 20%MnTe@β as a practical and feasible sorbent for remedying CIP-contaminated water.