Excellent Adsorption of Dyes via MgTiO₃@g-C₃N₄ Nanohybrid: Construction, Description and Adsorption Mechanism

Abstract

This report investigates the elimination of hazardous Rhodamine B dye (RhB) from an aqueous medium utilizing MgTiO₃@g-C₃N₄ nanohybrids manufactured using a facile method. The nanohybrid MgTiO₃@g-C₃N₄ was generated using an ultrasonic approach in the alcoholic solvent. Various techniques, including HRTEM, EDX, XRD, BET, and FTIR, were employed to describe the fabricated MgTiO3@g-C3N4 nanohybrids. RhB elimination was investigated utilizing batch mode studies, and the maximum removal was attained at pH 7.0. The RhB adsorption process is more consistent with the Langmuir isotherm model. The highest adsorption capacity of MgTiO₃@g-C₃N₄ nanohybrids for RhB was determined to be 232 mg/g. The dye adsorption followed a pseudo-second-order model, and the parameters calculated indicated that the kinetic adsorption process was spontaneous. Using ethanol and water, the reusability of the nanomaterial was investigated, and based on the results; it can be concluded that the MgTiO₃@g-C₃N₄ nanohybrids are easily regenerated for dye removal. The removal mechanism for the removal of RhB dye into MgTiO₃@g-C₃N₄ nanohybrids was also investigated.

1. Introduction

The continuous expansion of the industrial sector has resulted in a dramatic increase in wastewater production [1,2]. Dyes are commonly found in effluent due to their extensive usage in the packaging, woven, leather, cosmetics, and food industries [3,4,5]. Synthetic dyes display substantial mutagenic and cancerous consequences [6,7,8]. Rhodamine B (RhB) dye is an artificial colorant frequently utilized to decorate fabrics and food items. It is an organic fluorescent pigment that is brilliant red and is employed as a coloring agent in various sectors, including fabrics, paper, paint, and others. It is a widely utilized pigment in many sectors due to its excellent water solubility and inexpensive cost [9,10,11,12]. However, colors cannot be biodegraded because they have intricate chemical structures. RhB dye is resistant to sunlight, fire, and oxidation like other dyes and is not biodegradable [13,14]. According to several research studies, RhB dye is mutagenic and carcinogenic to humans and animals. It produces biological problems such as rashes on the skin, lung irritation, hemolysis, and deteriorating liver and renal functions [15,16,17]. Since it is employed as a water-monitoring system to measure the flow rates and directions, it is known as a luminous water tracer [18,19]. Cleaning up dyes in wastewater before dumping them into the environment is vital in preventing potential health problems and environmental harm. Many years of research on dye elimination from industrial wastewater have been conducted. Decolorization of water can be accomplished by oxidation, adsorption, or filtration, and different technological processes [20,21]. Removing dye from water by adsorption methods is one of the most successful techniques. Therefore, the alienation of pigments using adsorption onto zeolite, charcoal, sand, agricultural residues, activated carbon, and slag has been studied, and the adsorption isotherm was appropriately examined [22,23]. These adsorption techniques extract pigments from concentrated industrial waste [24,25,26,27]. However, the regeneration of most adsorptive materials is challenging for some of these adsorbents. In addition, the cost of adsorption procedures employing such materials is high. Nowadays, nanotechnology is one of the most remarkable technologies for effectively eliminating dye from sewage with adsorption approaches [28,29]. This technology is useful for dealing with water containing small amounts of organic and inorganic dyes, and it is a low cost compared to other methods. Recently, the most efficient adsorption and photocatalytic agents for entirely removing dyes from sewage are nanoparticles and nanocomposites [30,31]. Notably, the features of oxide nanocrystals such as MgO, TiO₂, ZnO, and CuO are widely employed in pollutant removal due to their unique physicochemical functions, which may also be modified by doping with other materials to meet specific needs and usage [4,32].

Graphitic carbon nitride (g-C₃N₄), one of the essential double-layered materials, has garnered global interest in multiple disciplines, such as photocatalytic degradation, energy conversion, and ecological environment protection [32,33,34]. There has been much interest in compounds derived from g-C₃N₄ due to their unique qualities, including physicochemical stability, low cost, and low environmental impact [35,36]. The current work aims to develop a low-cost, high-performance g-C₃N₄-based metallic nanocomposite for dye eradication in the aquatic phase. This research contributes significantly to the g-C₃N₄ structural design and property modulation via double doping by MgO and TiO₂.

2. Results and Discussion

2.1. MgTiO₃@g-C₃N₄ Nanohybrids Structure Characteristics

The as-fabricated MgTiO₃@g-C₃N₄ nanohybrid was analyzed by transmission electron microscopy (TEM). As shown in Figure 1a–c, the as-synthesized MgTiO₃@g-C₃N₄ nanohybrids exhibited characteristic 2D nanosheet-like nanoparticle architectures with a corrugated thickness of around 30 nm. The average diameter of the MgO and TiO₃ nanoparticles integrated into the MgTiO₃@g-C₃N₄ nanohybrid composite is less than 20 nm. MgTiO₃ nanoparticles are disseminated well on the surface of g-C₃N₄ which generates an abundance of self-active sites on the surface of MgTiO₃@g-C₃N₄ nanohybrids. The Energy-Dispersive-X-ray Spectroscopy (EDX) image identifies the constituents of the MgTiO₃@g-C₃N₄ sorbent material. Therefore, it is evident from the results of Energy-Dispersive-X-ray Spectroscopy of MgTiO₃@g-C₃N₄ nanohybrids that the surface consists of magnesium (Mg), titanium (Ti), oxygen (O), nitrogen (N), and carbon (C), as the spectrum corresponds to these constituents, which are described in Figure 1d.

The presence of magnesium and titanium can determine the development of the combination of nanohybrid and oxygen in addition to carbon and nitrogen (Figure 2a–f). The EDS elemental mapping (Figure 2) displays the elemental maps of the composite constituents N, C, O, Mg, and Ti along with the appropriate overlay image. In order to ensure even distribution throughout the composite, the contrast between dark and light colors is used.

The XRD spectra of the MgTiO₃@g-C₃N₄ nanohybrids, which can be seen in Figure 3a, exhibit well-defined diffraction peaks with relative broadening and intensity, demonstrating the creation of a well-nanocrystallized phase(s). The identification of the peaks through the use of the High Score algorithm reveals the existence of three phases, specifically MgO, anatase TiO₂, and g-C₃N₄. It would appear that the typical diffraction peaks for g-C₃N₄ are located at 2θ = 12.7° and 27.38°. These peaks appear to match the in-plane structural stacking pattern (100) and the interlayer layering plane (002) of the hexagonal structure (JCPDS card No. 87-1526) [37]. In comparison, the peaks that are placed at 2θ of 25.07°, 37.59°, 47.05°, 53.91°, 61.99°, 69.09°, and 74.53° indicate the characteristic reflections (101), (004), (200), (105), (204), (116), and (220) of the anatase phase TiO₂ (JCPDS card No. 021-1272) [38]. The additional peaks that were detected at 2θ angles of 36.61°, 42.53°, 61.99°, and 78.16° have been ascribed to the (111), (200), (220), and (222) planes of the MgO cubic structure [39].

Figure 3b displays the surface area and pore particle diameter characteristics of the nanohybrid MgTiO₃@g-C₃N₄ as manufactured. The adsorption-desorption graphs of MgTiO₃@g-C₃N₄ nanohybrid suited isotherm type IV and produced a hysteresis loop (H2) at relative pressures between 0.0 and 1.0. (Figure 3b). This result validated the mesoporous nature of the as-prepared MgTiO₃@g-C₃N₄ nanohybrid [40,41,42], which was further corroborated by the pore size distribution map generated using the Barret-Joyner-Halender (BJH) method. The enhanced surface area and porosity of the MgTiO₃@g-C₃N₄ nanohybrid, as revealed by a bigger specific surface area and a higher pore volume, will increase the adsorption capacity due to the presence of additional active sites on the surface [42]. In addition, the MgTiO₃@g-C₃N₄ nanohybrid isotherm exhibits a substantial BET surface area (S_BET) of 107 m².g⁻¹. In addition to its high surface area, the mesoporous structure of MgTiO₃@g-C₃N₄ nanohybrid makes it a promising candidate for metal ion and organic pollutant adsorption by providing a large number of active sites. The pore size distribution plot (Figure 3c) displays a mean pore diameter of 15.75 nm and a cumulative pore volume of 0.254 cm³ g⁻¹ due to BJH adsorption.

2.2. Adsorption Studies

2.2.1. Effect of Initial Concentration and pH Changing

In order to determine the influence of initial dye concentration on adsorption, the beginning concentration was varied from 5.0 to 100.0 mg/L (Figure 4a). The adsorption capacity of RhB increases from 18.5 to 215 mg/g as the initial concentration of RhB increases. With a higher initial dye concentration, the gradient of dye molecules increases, resulting in a greater adsorption capacity of MgTiO₃@g-C₃N₄ nanohybrid. As the concentration of the dye increases, the number of dye molecules in the solution will exceed the number of reactive sites on the composite’s surface. Due to their rising repulsion, the MgTiO₃@g-C₃N₄ nanohybrid will become saturated with dye molecules, decreasing dye adsorption.

Figure 4b depicts the influence of pH on the RhB sorption onto MgTiO₃@g-C₃N₄. Furthermore, the removal effectiveness of MgTiO₃@g-C₃N₄ exceeded 90% of RhB at a pH of 7.0. In addition, it can be noted that in both acidic and alkaline media (pH ≥ 5.0 and pH ≤ 9.0), the removal efficiency decreased dramatically.

Metal oxides are recognized for their amphoteric activity in aqueous solutions; thus, MgO and TiO2 in the nanocomposite may react with either H⁺ or ⁻OH ions [43,44]. The pH drift method was employed to determine the point of zero charge P_ZC of MgTiO₃@g-C₃N₄ nanocomposite. Figure 4c demonstrates that the P_ZC was located at PH = 9.9 where no electrostatic attraction will occur; on the other hand, below this PH the MgTiO3@g-C₃N₄ surface will be positively-charged and favors the sorption of negatively-charged species [45,46].

2.2.2. The Impact of Equilibrium Contacts Time and Adsorption Kinetic Studies

Contact durations up to 120 min were investigated for their influence on RhB adsorption capacity. As shown in Figure 5a, the contact time significantly impacts RhB dye sorption onto MgTiO₃@g-C₃N₄. For all concentrations, adsorption capacity increases progressively with the contact time until 40 min, when it attains equilibrium. Two well-known kinetic models were used to explain the RhB adsorption kinetics on MgTiO₃@g-C₃N₄. The original nonlinearized forms of the pseudo-first-order (Equation (1)) and pseudo-second-order (Equation (2)), and the Elovich (Equation (3)) kinetic models were utilized [47,48].

$${\mathrm{q}}_{\mathrm{t}}={ \mathrm{q}}_{\mathrm{e}}\left(1-{ \exp }^{-{\mathrm{K}}_{1.}\mathrm{t}}\right)$$

(1)

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

(2)

$$\mathrm{qt} =1 \mathsf{\beta } \ln \left(1+ \mathsf{\alpha }\mathsf{\beta }\mathrm{t}\right)$$

(3)

where k₁ (min⁻¹) and k₂ (g mg⁻¹ min⁻¹) are the rate constants of the pseudo-first-order and the pseudo-second-order, accordingly; q_t (mg g⁻¹) is the adsorption capacities displayed by the adsorbent at time t, and q_e is q_t at equilibrium; α (mmol g⁻¹ s⁻¹) is the initial rate sorption, and β (g mmol⁻¹) is the sorption constant. Figure 5b–d demonstrates the pseudo-first-order, pseudo-second-order, and Elovich investigations for the RhB sorption onto MgTiO₃@g-C₃N₄, and the kinetic findings were gathered in

Table 1. Kinetic model parameters for the adsorption of RhB dye by nanocomposite.

	Pseudo-First-Order Model			Elovich Model
	qe(Cal)b (mg g−1)	K1 × 103 (min−1)	r2	β × 102 (g mg−1)	α	r2
RhB	16.96	4.63	0.5701	0.241	3.79 × 106	0.7310
	Pseudo-Second-Order Model
RhB	qe(Exp)a (mg g−1)	t1/2 (min)	h0 (mg g−1.min−1)	qe(Cal)b (mg g−1)	K2 × 103 (g mg−1 min−1)	r2
	85	2.99	27.48	82.24	4.06	1.000

. The RhB sorption on MgTiO₃@g-C₃N₄ fitted to the pseudo-second-order with an R² value of 1.000, and the computed q_e was almost typical of the experimental one.

2.2.3. Intra-Particle Diffusion Study for Nanohybrid

The intraparticle diffusion model (IPDM) was utilized to investigate the RB sorption mechanism onto the MgTiO₃@g-C₃N₄ nanohybrid. According to Equation (6), the obtained q_t plot against the t^1/2 is monitored in Figure 4.

$$q_t=K_{ip}*t^{\frac{1}{2}}+C_i$$

(4)

K_ip (mg g⁻¹ min^−0.5) represents the rate constant of the IPDM, and C (arbitrary) is a constant proportional to the boundary-layer thickness [49]. Obtaining a C value of zero (i.e., the line pass through the origin point) indicated that IPDM controlled the RB sorption, which is not the case here (

Table 2. Adsorption rate control mechanism parameters for removing RhB by MgTiO₃@g-C₃N₄ nanohybrid.

Intra-Particle Diffusion/Transport Model
kdif(mg.g−1 min−1/2)	C1	r2	kdif(mg g−1 min−1/2)	C2	r2	kdif(mg g−1 min−1/2)	C3	r2
17.5340	5.06	0.9603	0.4543	74.82	0.9940	0.0093	81.66	0.9838

). Thus, Figure 6 revealed three linear regressions, illustrating that the IPDM was participating but not the only mechanism controlling the RhB sorption on the MgTiO₃@g-C₃N₄ nanohybrid [50].

2.2.4. MgTiO₃@g-C₃N₄ Nanohybrids Adsorption Isotherm

In order to provide insight into sorbent-sorbate interactions, the equilibrium data of RhB sorption onto MgTiO₃@g-C₃N₄ at 25 °C was treated via isotherm models. Specifically, the Langmuir (LIM, Equation (5)), Fredulich (FIM, Equation (6)), and Temkin (TIM, Equation (7)) isotherm models were selected to investigate sorption possibilities [34,51,52].

$$\frac{1}{q_e}=\frac{1}{K_l q_m}. \frac{1}{C_e}+\frac{1}{K_l}$$

(5)

$$\ln q_e=\ln K_f+\frac{1}{n} \ln C_e$$

(6)

$$q_e=\frac{RT}{b_T} \ln A_T+\frac{R_T}{b_T} \ln C_e$$

(7)

where q_m (mg g⁻¹) is the computed maximum q_t, K_L (L mg⁻¹) and K_f (L mg⁻¹) are Langmuir and Freundlich constants, respectively, and relate to sorption energy change and sorbent’s capacity, respectively; while n is the Freundlich constant related to sorption’s favorability. A_T (L mg⁻¹) and b_T (J mol⁻¹) are the TIM constant and Temkin constant associated with the heat of sorption. Figure 7 illustrates the linear and nonlinear plots of LIM, FIM, and TIM. The isotherms result (

Table 3. Different equilibrium Isotherms’ constants for RhB dye adsorption by MgTiO₃-g-C₃N₄ nanomaterial.

Equilibrium Model	Parameters	RhB
Langmuir	qm (mg.g−1)	232.02
	KL (mg.g−1)	0.0047
	RL (L.mg−1)	0.4788
	R2	0.9991
Freundlich	n	2.06
	KF (L.mg−1)	88.64
	R2	96488
Temkin	B (J.mol−1)	60.18
	KT (L.mg−1)	17.65
	R2	0.9816

) indicated that the RhB sorption by MgTiO₃@g-C₃N₄ fitted LIM with an R² of 0.999. In addition, the 1/n value of less than one implied the favorability of RhB sorption on MgTiO₃@g-C₃N₄ [52]. Temkin’s correlation coefficient suggested an essential role for electrostatic interaction in the sorption mechanism [53].

2.2.5. RhB Dye Adsorption Mechanism

To comprehend the adsorption process, FTIR spectra (Figure 8a,b) of MgTiO₃@g-C₃N₄ nanohybrid before and after the adsorption of RhB dye were recorded in the region of 400–3600 cm⁻¹. The FTIR spectrum of the nanohybrid MgTiO₃@g-C₃N₄ is broad between 3000 and 3400 cm⁻¹ due to the stretching modes of the O–H and terminal amino groups. The bands at 1232, 1315, and 1454 cm⁻¹ correspond to aromatic C–N stretching, whereas the peaks at 1574 and 1632 cm⁻¹ correspond to C≡N stretching. The band at 892 cm⁻¹ corresponds to the triazine ring mode peak, which is a typical mode in carbon nitride. As demonstrated in Figure 8a, the FTIR spectrum of MgTiO₃@g-C₃N₄ nanohybrid shifted slightly after RhB dye adsorption. Furthermore, the central peak in the broadband at 3165 cm⁻¹ changed to 3157, revealing that the OH and amino groups of MgTiO₃@g-C₃N₄ nanohybrid were entangled throughout the adsorption process. This observed result could be caused by the interaction between RhB molecules and MgTiO₃@g-C₃N₄ nanohybrid hydrogen bonds. In addition, a vibrational triazine ring mode at 888 cm⁻¹ nearly shifted with the adsorption of RhB dye, which was attributed to the π-π interaction between the electron clouds in the g-C₃N₄ skeleton of MgTiO₃@g-C₃N₄ nanohybrid and the aromatic rings of RhB molecules. Consequently, as depicted in Figure 8b, RhB dye molecules are adsorbed onto the MgTiO₃@g-C₃N₄ nanohybrid. On the nanohybrid, the hydrogen bonds and π-π interactions enhance the adsorption of RhB dyes. The contact time trend (Figure 5a) may be deduced from the surface area reducing after the pores have filled. Furthermore, the agreement of sorption to the FIM may explain the slowdown in the sorption rate after the first hour.

2.3. MgTiO₃@g-C₃N₄ Nanohybrid Regeneration

The regeneration capacity of the hybrid was examined by eliminating the RhB dye from the MgTiO₃@g-C₃N₄ nanohybrid. The ethanol solvent demonstrated the desorption of RhB dye from the MgTiO₃@g-C₃N₄ nanohybrid instantaneous coloring. The freshly generated RhB dye solution’s volume and concentration were then applied to the MgTiO₃@g-C₃N₄ nanohybrid (25 mg/L, 100 mL). Five times this entire cycle was repeated. The removal effectiveness of the RhB dye from MgTiO₃@g-C₃N₄ nanohybrid desorbed by ethanol and distilled water is given in (Figure 9). With each desorption cycle, it was found that the MgTiO₃@g-C₃N₄ nanohybrid’s ability to remove dyes somewhat diminished.

2.4. Adsorption Capability of MgTiO₃@g-C₃N₄ Nanohybrids for other Color Contaminants

To test the adsorption capability of MgTiO₃@g-C₃N₄ nanohybrid, various dye solutions with fixed concentrations (50 mg/L) were studied. Extraction tests were conducted by combining the obtained MgTiO₃@g-C₃N₄ nanohybrid sorbent (10 mg) with dyes and an aqueous solution (25 mL), in a 50 mL bottle for 24 h at room temperature with magnetic stirring. After centrifuging the dye solutions for 10 min, 5.0 mL of the supernatant solutions recovered. The capacity of MgTiO₃@g-C₃N₄ nanohybrid to adsorb various colors from an aqueous solution was evaluated. Figure 10 depicts the removal percentage of various dyes by MgTiO₃@g-C₃N₄ nanohybrid adsorbent. The obtained results confirmed that the elimination ability percentages of malachite green (MG), methylene blue (MB), indigo carmine (IC), crystal violet (CV), congo red (CR), and basic fuchsin (BF) were 93, 99, 87, 95, 96, and 87%, respectively. However, the uptake of MB and CR dyes was higher than that of other colors.

Compared to recent literature findings, MgTiO₃@g-C₃N₄ nanohybrid performed competitively under optimized operating conditions in removing RB within 40 min (

Table 4. Recent literature findings compared to the MgTiO₃@g-C₃N₄ fabricated in this study in removing RhB.

Nanomaterial	Adsorption Capacity (mg. g−1)	Reference
MgTiO3@g-C3N4 nanohybrids	223	This study
Carbon microspheres	19.9	[54]
Fe2O4-montmorillonite nanocomposite	209	[55]
Zn–Fe layered double hydroxide-activated carbon nanocomposite	97.0	[56]
Activated carbon	264	[57]
Carbon–cobalt ferrite	94.1	[58]
activated carbon-supported MgO/MnO2	16.2	[59]

). This finding can be attributed to the high surface area of 107 m² g⁻¹ and the mesoporous material nature of this sorbent. In addition to removing toxic metals and organic pollutants, this nanomaterial is also cost-effective.

3. Experimental Section

3.1. Building Up of MgTiO₃@g-C₃N₄ Nanomaterials

The powdered g-C₃N₄ was produced through the decomposition of the urea compound. An amount of 7 g of urea substance was loaded in a covered pot and heated at 550 °C for 2.0 h. The acquired raw, yellow g-C₃N₄ was then allowed to cool, ground, and packed into a bottle. Magnesium oxide (MgO) powder was produced by the thermal degradation of MgCO₃ in a muffle furnace (SNOL-LSF21) at 800 °C for 1.0 h, whereas nanosized TiO₂ was purchased from Sigma Aldrich. Using a standard ultrasonication procedure (Ultrasonic cleaner-100W, Labtech-Co., LTD, Seol, Korea), MgTiO₃@g-C₃N₄ nanomaterial was fabricated. In 125 mL of methanol, 1.84 g of g-C₃N₄ was ultrasonically treated for 15 min. The g-C₃N₄ in methanol solution received 400 mg of MgO and TiO₂ nanopowder, which was then sonicated for an extra 45 min. The resultant yellowish solution was heated at 85 °C for 24.0 h and 180 °C for 1.0 h; then the produced MgTiO₃@g-C₃N₄ nanomaterial was annealed.

3.2. Characterization

The prepared MgTiO₃@g-C₃N₄ nanohybrid was characterized using X-ray Diffraction (XRD) (PAN-alytical X’Pert Pro Multipurpose Diffractometer), Cu-Kα X-ray radiation (λ = 1.5418 Å) at 40 kV and a current 5.0 flow of 40 mA. The structure, surface morphology, and elemental characterization of the MgTiO₃@g-C₃N₄ nanohybrid were determined by using Field emission scanning electron microscope (FESEM) and Energy-dispersive X-ray spectroscopy (EDX) techniques, respectively (FESEM Carl Zeiss Merlin Compact, Oberkochen, Germany). The specific surface area of MgTiO₃@g-C₃N₄ nanohybrid was measured using the BET (Brunauer-Emmett-Teller) analyzer (Micrometrics ASAP 2020, Miami, FL, USA) using the N₂ adsorption-desorption method, where a sample was dried under a constant flow of N₂ at 60 °C for 24 h. TEM images were acquired using FEI Tecnai G2 20 TWIN microscope (Miami, FL, USA) operating at 200 kV. The salt addition method evaluated the point of zero charges (pHpzc). The Fourier Transform Infra-Red (FTIR) spectrum was recorded to determine the existence of functional groups present over the surface of the adsorbent by using FTIR (Shimadzu IR AFFINITY-I, Tokyo, Japan).

3.3. RhB Dye Removal Experiments

Dye adsorption tests were conducted in Erlenmeyer flasks in batch mode; an adsorbent dosage of 0.01 g of MgTiO₃@g-C₃N₄ nanohybrid was used to remove RhB dye from 25 mL solutions containing 25 to 100 mg/L of the dye. To attain the required dye concentrations, the dye stock solutions (1000 mg/L) were diluted with three times as much distilled water for all adsorption studies. All studies were conducted in the dark using an orbital shaker at 272 °C and 180 rpm shaking speed. Adjusting the pH of the dye solution with (0.1 M) HCl and (0.1 M) NaOH solution. Utilizing a UV-VIS spectrophotometer, the concentration of the dye solutions was measured (UV-1800 Spectrophotometer Shimadzu). A duration of 15 min was used to remove the MgTiO₃@g-C₃N₄ nanohybrid from the dye solution using centrifugation at 5000× g rpm. The absorbance values of the supernatant were measured to determine the remaining RhB dye concentration at a wavelength (λ max) of 550 nm. Employing the following expression, the adsorption capacity of the MgTiO₃@g-C₃N₄ nanohybrid for the removal of RhB dye and the removal % was calculated:

$$Q_e=w\times \frac{\left(C_0-C_e\right)}{V}$$

(8)

$$RhB removal (\%)=100\times \frac{\left(C_0-C_e\right)}{C_0}$$

(9)

3.4. Regeneration Experiments

Methanol and distilled water have been investigated as desorbing solutions for MgTiO₃@g-C₃N₄ nanohybrid regeneration investigations for RhB dye. Under ideal conditions, 25 mg/L concentrations of the RhB dye in 100 mL volumes were initially adsorbed onto the MgTiO₃@g-C₃N₄ nanohybrid. After that, centrifugation was used to remove the solution from the used MgTiO₃@g-C₃N₄ nanohybrid. Next, the separated MgTiO₃@g-C₃N₄ nanohybrid was submerged in 50 mL of methanol and 50 mL of distilled water, each for 60 min, in an orbital shaker. The MgTiO₃@g-C₃N₄ nanohybrid was then washed three times with deionized water and oven dried to assess their reusability. Using ethanol and distilled water solution, the MgTiO₃@g-C₃N₄ nanohybrid’s efficiency for reuse in up to five cycles was calculated.

4. Conclusions

In this study, MgTiO₃@g-C₃N₄ nanohybrids were used as adsorbents to remove the hazardous RhB dye. By combining MgO, TiO₂, and g-C₃N₄ nanosheets, MgTiO₃@g-C₃N₄ nanohybrids were fabricated. The synthesized composite possessed adsorption capabilities of 232 mg/g and a strong correlation coefficient. RhB adsorption was well represented by the Langmuir isotherm model and followed pseudo-second-order kinetics. The relevance of electrostatic interaction, hydrogen bonding, and π-π interaction between the dye molecules and MgTiO₃@g-C₃N₄ nanohybrids was proposed by FTIR analyses of the adsorption mechanism. In addition to having a broader range of applications, the composite was successful in removing other dyes. Thus, the present work demonstrates that MgTiO₃@g-C₃N₄ nanohybrids, with their excellent adsorption efficiencies, are highly important for eliminating polluted colors.