Adsorption of Cationic Basic Fuchsin dye from aqueous solution on Green Synthesized Zinc oxide nanocomposite

doi:10.21203/rs.3.rs-4812940/v1

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Adsorption of Cationic Basic Fuchsin dye from aqueous solution on Green Synthesized Zinc oxide nanocomposite

https://doi.org/10.21203/rs.3.rs-4812940/v1

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The cationic basic fuchsin (BF) dye was removed from wastewater using green synthesized Zinc oxide-reduced graphene oxide nanocomposite (ZnO-rGO NC) derived from Carica papaya leaf extract (CPLE). The nanocomposite was characterized using various techniques: XRD, FT-IR, TEM, EDX, and FE-SEM. Adsorption experiments were conducted to examine the effects of several experimental parameters, including contact time, solution pH, temperature, initial dye concentration, and adsorbent dose. The highest amount BF dye removal was attained at pH 7 at a temperature range of 35 to 50°C, and equilibrium time was reached in 60 minutes. The Langmuir isotherm model provided a good fit for adsorption isotherms. The determination of thermodynamic parameters, including ΔG°, ΔH°, and ΔS°, revealed that spontaneous adsorption took place as evidenced by the negative values of ΔG°. An exothermic reaction was indicated by the values of ΔH°. ZnO-rGO NC was used to remediate basic fuchsin dye (BF) dye-polluted wastewater at 50 mg/L^− 1. The maximum amount of dye adsorbed was found to be approximately 84.08 mg/g, indicating that the predominant adsorption mechanism was cation exchange. Based on the results, ZnO-rGO NC was shown to be a good adsorbent.

Basic fuchsin dye

Zinc oxide

Nanoparticles

Nanocomposite

Carica papaya

One of the biggest global contaminants of water is dyes [1]. Dyes find their way into water and wastewater systems through two main sources: the dye manufacturing sector and the finishing processes used to color various industrial items [2]. Environmental protection is now highly valued in our society, which has led to numerous studies on reducing the causes of pollution and continuous research into more effective depollution methods. Nowadays, large amounts of water are employed for both residential and commercial purposes worldwide, which lead to the contamination of water containing various contaminants. Reused water returns to the natural ecosystem, even though reuse is becoming more and more common. Yet, as water poisoning affects human health and the surrounding natural ecosystem, direct discharges into the environment must be prevented.

Dyes containing varying chemical compositions are used in the food, cosmetics, leather, and textile industries. As a result, these enterprises release "huge" amounts of effluent that is heavily contaminated with dyes into the environment. When such an effluent is discharged into bodies of water, it immediately degrades their aesthetic value. Such a change is detrimental to the ecosystem. Even without taking into account the possibility of restricting the ability of bacteria and water plants to photosynthesize, the intricacy of the problem is apparent. This effect is made worse by these dyes' dissimilar structures and susceptibility to biodegradation. Due to their known carcinogenic potential, these dyes typically have detrimental effects on both human and environmental health [1–4]. Many diseases spread among local people, and pollution results from the massive amounts of dye-containing water that are released into the environment [5–9]. There are numerous methods for cleaning up dye-contaminated water, one of which is adsorption [10–12]. In dying fabrics, leather goods, and silk products, cationic dyes such as basic violet 14—also termed basic fuchsin (BF) dye—are utilized. The ecosystem is contaminated when this dye is dumped into water since it is poisonous and non-biodegradable [13]. Figure 1 depicts the chemical makeup of the BF cationic dye. A variety of non-conventional, low-cost adsorbents have been studied, and the application of inexpensive adsorbents for dye removal has been assessed. In this study, green synthesized zinc oxide nanocomposite from Carica papaya leaf extract was used as an effective extraction method of BF dye from aqueous solution as an inexpensive and effective adsorbent.

The Caricaceae family, which includes the C. papaya L. plant, is widely utilized around the world for herbal remedies, especially in tropical and subtropical areas. In Table 1, the plant's taxonomy is presented. In conventional medicine, it treats a wide range of illnesses. The leaf has been extensively used for research of all the parts used for different purposes. Its current use is supplemented by its most recent utilization in the production of nanoparticles [14]. The green synthesis process has several benefits over chemical approaches, some of which include simplicity, energy efficiency, environmental friendliness, and non-toxicity. The ecologically friendly synthesis of ZnO NPs for crucial applications with a restricted particle distribution is becoming more and more popular, thanks to green synthesis.

Table 1

Taxonomy of C. *papaya* Plant
No.	Classification of C. papaya
1	Kingdom	Plantae
2	Division	Magnoliophyta
3	Class	Magnoliopsida
4	Order	Brassicales
5	Family	Caricaceae
5	Genus	Carica
6	Species	Papaya Linn.

ZnO NPs have been synthesized using an extract from coffee powder and the effects on proteinase's secondary structure, enzyme activity, and thermal stability have been studied [15]. Like C. papaya, another green synthesis approach has been adopted in ZnO NPs production using the outer peel of C. paradisiac. Then, to increase their antioxidant activity, these nanoparticles (NPs) were employed as photocatalysts to degrade the dye methylene blue (MB). Notably, they demonstrated 56% degradation effectiveness against MB dye throughout a 6-hour exposure period [16]. However, the extract of Physalis alkekengi L. and Sedum alfredii Hance have been used in the synthesis of crystalline ZnO NPs [17]. Compared to some microbe extracts and other biological extracts, plants or their extracts appear to be the best agents because of their accessibility, ability to produce large quantities of nanoparticles, and environmentally benign waste products [18].

Phyto compounds present in plant extracts, notably C. papaya leaf extract have a variety of safe and adaptable properties, including simultaneous stabilizing and reducing effects [19, 20]. The plant has a variety of chemical components, including fibers, minerals (such as potassium and magnesium), vitamins B (including pantothenic acid), and antioxidant nutrients (like carotene, vitamin C, and flavonoids). Vitamins C and E, alkaloids, carpaine, pseudocarpain, caproside, choline, and dehydrocarpain are all present in papaya leaves. Fruits are rich in biomolecules, including volatile chemicals, alkaloids, glycosides, minerals, vitamins, and carbohydrates, lipids, proteins, and carbs.

During the synthesis process, phytochemicals within the extract function as stabilizing and reducing agents, particularly in the case of ZnO NPs with a unique structure (Fig. 2), which convert the precursors of the metal into NPs. Flavonoids, and alkaloids within the C. papaya leaf extract, for example, can reduce zinc ions. To stabilize the metal ions after reduction by the C. papaya leaf extract, the metal ions would be encapsulated as an organic coating in three steps of the synthesis process. Phase one is known as the activation phase, during which time metal ions reduce and nucleate. The nanoparticle stabilizes during the next phase, which is referred to as the growth phase, and takes on its shape during phase three, which is known as the termination phase [21]. To remove BF dye, the synthesized ZnO NPs and rGO were combined via straightforward ultrasonic-assisted technique giving rise to the production of inexpensive and environmentally friendly adsorbent used to investigate the impacts temperature, pH, contact time, adsorbent dosage, and initial dye concentration on the dye’s removal.

2.1 Materials

Analytical grade reagents and chemicals were all utilized for this study. Zinc acetate dihydrate [CH₃OO]₂ Zn.2H₂O (Fisher Scientific) with purity 99%, Sodium Nitrate [NaNO₃](Fisher Scientific) with purity 99.99%, Sulfuric acid [H₂SO₄] (Somadi) with purity 98.0%, Hydrogen peroxide [H₂O₂] (Somadi) with purity 30.0%, Acetone[(CH₃)₂CO] (Somadi) with purity 99%, Hydrochloric acid [HCl] (Somadi) with purity 99%, Potassium permanganate [KMnO4] (Fisher Scientific) with 98.5%, Sodium hydroxide [NaOH] ](Fisher Scientific) with purity with 99%, Thiourea [NH₂CSNH₂] and Basic Fuchsin dye were used.

2.2 Methods

2.2.1 Preparation of Carica papaya Leaf

The Carica papaya leaf was boiled for 30 min. in 100 mL of double distilled water after it had been cleaned, slashed into pieces, and dried. 10g of the dried C. papaya was used for boiling. The resultant extract was filtered using Whatman No. 1 before being utilized in synthesizing ZnO NPs.

2.2.2 Synthesis of Zinc Oxide Nanoparticles

A 50 mL of 0.1M of Zinc acetate dihydrate was prepared using double distilled water. At 80 ^oc, 10 mL of Carica papaya leaf extract was carefully added to the solution drop-wise and stirred magnetically for 4 hrs at pH 12. In addition, the mixture underwent a 10 min, 10,000-rpm centrifugation. Afterward, the pellet was centrifuged for 10 min at 5,000 rpm. The washed pellets obtained after centrifugation were dried for 6 hrs and at 50 ^OC in a hot air oven and further Calcined at 450 ^OC before subsequently synthesizing zinc oxide [22, 23].

2.2.3 Synthesis of Reduced Graphene Oxide

A modified version of Hummer's method was employed to oxidize graphite powder [24]. NaNO₃ (1.5 g), H₂SO₄ (115 mL), and pre-oxidized graphite (3 g) were mixed and stirred in an ice bath for 20 minutes. At a constant temperature (> 20 ^OC), 9 g of KMnO₄ was gradually added to the suspension while it was vigorously agitated. The temperature was increased to 35°C, and the solution was continuously stirred for about 12 hrs. 300 mL of double distilled water was added to the precursor solution once it had reached 98°C. 30% weight colorless H₂O₂ was used to extract the residual manganese dioxide and permanganate from the solution and diluted with 1L of distilled water. The mixture's pH was adjusted by filtering and frequently washing with (5% weight) HCl and distilled water, respectively. The pellets was then vacuum-dried for 24 hrs at 40°C to synthesize the final product of GO. The GO obtained was combined with the reducing agent (Thiourea) at 100°C for about 24 hours and stirred continuously and rGO was synthesized [25].

2.2.4 Synthesis of rGO-ZnO Nanocomposite

For 30 mins, 150 mL double distilled water was used to sonicate 1 g of rGO. For ZnO NPs, 0.25 g was placed in 50 mL double distilled water and sonicated for 30 mins separately. Both solutions were mixed and subjected to 45 minutes of sonication. Afterward, the solutions were continuously stirred for 1 hr and dried in the hot-air oven. The ZnO-rGO NC powder was eventually ready for further use [25].

2.6 X-ray Diffraction Studies

CuKα radiation from an X-ray diffractometer was used for ZnO and ZnO-rGO NC XRD studies between 2θ = 5–600. This versatile device can be used for a wide range of X-ray diffraction analyses on powders and other materials. By employing the pre-FIX optical modules, sample platform, and tube rotation functionality, the user can change the system from a high-resolution to a typical Bragg-Brentano line focus configuration or a reflectometry system.

2.2.5 FESEM Spectra

FESEM pictures of ZnO, rGO, and ZnO-rGO nanocomposite were obtained. Accurate, actual nanoscale scale data is delivered by the FESEM-Nova Nano FE-SEM 450 (FEI) with its ultra-high resolution characterization and analysis. Advanced optics and detection, including beam slowing in lens ETD (SE), TLD (custom), lens-attached DBS, and LVD, offer the best information selection and picture optimization.

2.2.6 TEM Spectrum

ZnO nanoparticle TEM pictures were captured. Tecnai G2 20 S-TWIN [FEI] is a 200 Kv TEM that provides imaging with excellent resolution. The apparatus has a 0.24 nm point resolution, 0.14 nm line resolutions, and 1.0 nm STEM resolution.

2.2.7 FTIR Spectrum

FTIR image of ZnO NPs were recorded. The small, easy-to-use, and potent FT-IR Spectrum 2 (Perkin Elmer) instrument measures liquid (in KBr cells) and solid (in KBr pellets) samples in the 4100–400 cm-1 range thanks to its fully integrated, universal sampling mechanism.

2.2.8 Preparation of Adsorbate

Commercial basic fuchsin was acquired and used to prepare dye wastewater for this work. 100 mg of the dye was dissolved in one liter (1L) of double distilled water to prepare the stock solution with a concentration of (1000 ppm). For the batch tests, different concentrations were prepared from the stock solution by dilution. The concentration of the dye was measured at 546 nm before and after the experiment using the UV-vis spectrophotometer.

2.2.9 Batch Adsorption Studies

Batch experiments were performed for the adsorption of BF dye. The maximum wavelength (λ_max) of 546 nm of the dye was determined using a UV-vis spectrophotometer (UV-1800 Shimadzu, Japan). 20 mL of BF dye solution and 0.7g of ZnO-rGO NC were mixed continuously at 200 rpm, and the absorbance at λ_max was recorded. The calibration curve was obtained and used to determine the final concentrations. Various parameters such as temperature (35, 40, 45 and 50°C), pH (2 to 10), adsorbent dosage (0.3 to 0.7 g), dye concentration (10, 25, 50, 75, and 100 ppm) and time (15 to 90 min) were investigated. To regulate the pH, 0.1M HCl and 0.1M NaOH were used. The percentage removal (%R) of the dye, the amount of dye adsorbed q_e (mg/g), and the amount adsorbed at time t, q_t (mg/g) were calculated using Eq. 1, 2, and 3 respectively, where C_o and C_e represent the initial and equilibrium dye concentrations, V and m is the volume and mass of the solution and adsorbent, while the weight of the adsorbent is indicated by W (g).

Removal % = (𝐶_𝑜− 𝐶_𝑒)/𝐶_𝑜 ×100 (1)

q _𝑒 = (𝐶_𝑜 − 𝐶_𝑒) ×𝑉/𝑊 (2)

q _t = (𝐶_𝑜− 𝐶_t) V/m (3)

3.1. X-ray Diffraction (Both XRD Y axis in

ZnO NPs and ZnO-rGO NC XRD patterns are displayed in (Fig. 3a & b). The distinctive diffraction peaks of the green synthesized ZnO NPs was given at 2θ = 31.74^o, 34.44^o, 36.28^o, 47.68^o, 56.54^o, 62.98^o, and 67.92^o which were assigned to the appropriate planes of (100), (002), (101), (110), (103), and (112). By using the Debye-Scherrer equation [26], Eq. (4) was used to determine the crystalline size.

D = Kλ / βCOSθ (4)

Where λ is the wavelength, β is the full width at half maximum (FWHM), and θ is the Bragg angle. K is a constant (0.94). The average crystallite size of ZnO NPs was 16 nm. ZnO-rGO NC has a substantially higher peak intensity at 2θ = 31.74°, while other peaks have much lower intensity. In (Fig. 3b), the formation of the nanocomposite is shown with reducing peak intensities. The ZnO-rGO NC XRD pattern shows both rGO-related broad peaks and ZnO-related diffraction peaks. The UV–Vis absorption spectra of green synthesized ZnO NPs in an aqueous solution was also displayed (Fig. 3c). At 374 nm, a significant absorption peak from the UV-vis-spectrophotometer is observed. This implies that the nanoparticles can interact through surface changes or chemical or physical adsorption processes with molecules or species in their immediate surroundings to enhance adsorption.

3.2. FESEM Spectra

FESEM images obtained from ZnO, rGO, and ZnO-rGO NC are depicted in Fig. 4. The ZnO (Fig. 4a) shows the formation of evenly organized spherical structures; in Fig. 4b, rGO nanostructures were shown and appeared to form sheets. Furthermore, the ZnO-rGO NC showed a cluster of dispersed pellets across the plates, indicating that the composite was produced in the presence of rGO plates and zinc pellets (Fig. 4c). As a starting point for additional research and understanding of the characteristics and possible uses of the materials under study, the descriptions given for Figs. 4a, 4b, and 4c provide insightful information about the materials' morphology, structure, and composition.

3.3 FTIR ZnO Nanoparticles

In Fig. 5, a peak limited to the region of the spectrum (500–4000 cm–1) was seen in the FTIR spectrum of ZnO NPs. The vibration of OH at 3440 cm-1 is associated with the adsorption of water molecules. A peak at 2949 cm-1 is linked to internal C-H stretching bonds [27]. The peak indicates the C-C bond in the adsorption at 1450 cm-1. 1270 cm-1 stretching bond is attached to C-OH groups.

3.4. TEM Spectra of ZnO Nanoparticles

As can be seen in (Fig. 6a & b), ZnO is found to consist of clumped, flake-like nanoparticles that range in size from 50 to 100 nm. The enlarged TEM spectra below show resolved lattice fringes of individual ZnO crystallites. Smaller nanoparticles frequently have larger surface area-to-volume ratios. This larger surface area can be useful in situations where surface interactions are important, such as in catalysis. ZnO's reactivity can rise in a range of chemical processes.

3.5. EDX Spectrum of ZnO-rGO NC

At 50.1, 35.16, and 9.56 weight percent, respectively, the presence of C, O, and Zn was verified by the EDX image. Furthermore, as seen in Fig. 7, the EDX spectrum showed no additional peaks, indicating the purity of the green synthesized nanocomposite. The presence and purity of C, O, and Zn in the nanocomposite, as inferred from the EDX analysis, indicate that the material is appropriate for adsorption applications. A high surface area is implied by high carbon content, and the lack of contaminants guarantees that the adsorption capacity is not diminished. These elements working together suggest that the green synthesized nanocomposite has great promise as an adsorbent.

3.6 Energy Bandgap

The energy bandgap of ZnO NPs was ascertained using the Tau Plot since a semiconductor's bandgap significantly affects both its electrical and optical capabilities. Understanding the bandgap of ZnO NPs is crucial to understanding how they behave under different circumstances. The band gap was found to be 3.085 eV (Fig. 8); the nanoparticles provide useful information for their applications in a variety of domains. The measured bandgap is in agreement with green synthesized ZnO NPs that were previously used in a related experiment [28].

3.7 Effect of Contact Time on BF Dye Removal

Using a series of batch studies with fixed dosages of 0.7 g, pH values of 7, and dye concentrations of 50 ppm, the effect of time on BF dye removal efficacy was investigated. Figure 9 displayed the time-dependent graph. The findings showed that the percentage of the dye removed increased as the dye exposure to adsorbent increased over a longer time period. For ZnO-rGO NC, the highest percentage of dye removed at 60 minutes was 82.72%. There was no discernible improvement in dye removal efficiency after 60 minutes. This could have occurred from prolonged dye and adsorbent exposure as well as the absence of active sites.

3.8. Percent removal of BF dye from aqueous Solution

At different time interval, ZnO NPs, rGO NPs and ZnO-rGO NC's adsorption efficiencies were studied (Fig. 10). The highest level of adsorption was reached in 60 minutes. ZnO-rGO NC removed the highest percentage of BF dye (82.72%), whereas ZnO NPs recorded the lowest percentage (55.5%) and rGO NPs removed (64.3%). Given that nanoparticles tend to clump together, the high value observed for ZnO-rGO NC in comparison to ZnO NPs and rGO NPs may have resulted from these nanoparticles' lower surface areas. Indeed, the results suggest that this may have been the case. The formation of bigger clusters as a result of the aggregation may have restricted the accessibility of the active areas on the nanoparticle surfaces.

As opposed to agglomerating nanoparticles, ZnO-rGO NC has a high surface area, is evenly distributed throughout the solution, and increases the number of active adsorption sites. No more notable adsorption was seen after the maximum adsorption was reached at 60 minutes in most instances [29]. The FESEM image (Fig. 11a) shows that before adsorption, the ZnO-rGO nanocomposite has a relatively smooth and well-defined surface morphology. Following basic Fuchsin (BF) dye adsorption, the surface morphology was altered by the presence of dye molecules, adsorption-induced particle aggregation occurred, and the surface texture was altered (Fig. 11b).

3.9 Effect of initial BF dye concentration

The outcomes of batch studies that were conducted to ascertain how much dye concentration affected the efficacy of removing BF dye are shown (Fig. 12). The batch experiments were conducted with different dye concentrations (10, 25, 50, 75, and 100 mg/L) under constant circumstances (pH: 7, dosage: 0.7g, time: 60 minutes at room temperature). ZnO-rGO NC adsorbent resulted to 81% removal efficiency, according to the data. When the initial dye concentration increased, so does the competition for the active sites in the adsorbent. The removal percentage (Re %) is lowered as dye molecules build up in the active sites.

3.10 Effect of adsorbent dose on BF dye Adsorption

To find the dye removal efficiency, the experiment was conducted using a pH of 7 at room temperature, 50 ppm of BF dye, and a 60 minute equilibrium time. The impact of adsorbent dosage on BF dye removal was investigated from 0.3 to 0.7 g/L (Fig. 13). It was evident that the maximum dye removal at 0.7g was 77%. Similar studies in the literature highlighted the primary cause of dye removal attributed to the increased dosage of the adsorbent, which subsequently resulted led to the enhancement in active sites and improved dye removal [30].

3.11 Effect of pH on BF dye Adsorption

The pH sensitivity of ZnO-rGO NC adsorbent in removing BF dye at room temperature, 0.7g dose, 60 min of equilibrium time, and dye concentration of 50 ppm, respectively, was determined from the studies. Figure 14 displayed the dye removal efficiency results at different pH values (3 to 8). The findings showed that pH 7 was the point at which the maximum removal BF dye occurred. The ZnO-rGO NC adsorbent's dye removal efficacy was found to be 55% in an acidic environment (pH 3). At pH 7, BF dye removal effectiveness increased to 85%, and at pH 8, there was a minute decrease in the dye’s removal from 85 to 80% when the solution's pH was alkaline. This result is supported by findings on malachite green under similar conditions reported in the literature. Ionization potential of the functional groups of the adsorbent decreases with increasing pH of the solution and the rise in pH (alkaline) enhanced the removal efficacy of malachite green at a reduced level from 96–76% [31].

3.12 Adsorption Isotherms

The dispersion of the adsorbate amongst the adsorbent and solution at equilibrium circumstances, or the dynamic balancing between the adsorbate concentrations at the interface and bulk solution, must be examined in order to comprehend the workings of the adsorption process. The adsorption capacity and a few constants whose values represent the surface characteristics and affinity of a sorbent can be found using the data from the sorption equilibrium. The analysis of the equilibrium adsorption data in this investigation was carried out using the isotherm parameters proposed by Langmuir and Freundlich.

3.12.1 Langmuir Isotherm

According to the Langmuir isotherm [32] there are no contacts or transmigrations of adsorbed molecules on the adsorption surface, and mono-layer adsorption takes place at binding sites with homogenous energy levels. Eq. (5) is the linear Langmuir equation.

q _e = q_mK_LC_e / 1 + K_LC_e (5)

From the above equation, the equilibrium concentration of BF dye is C_e (mg L^− 1), the quantity of BF dye adsorbed per unit mass of adsorbent is q_e (mg g − 1), and the Langmuir constants for adsorption capacity and rate of adsorption are q_m (mg g^− 1) which is compared to other natural or modified adsorbents in literature (Table 2) and K_L (L mg^− 1), respectively. Plotting Ce/qe against C_e yields a straight line with a slope of 1/q_m and intercept of 1/q_mK_L (Fig. 15). A dimensionless separation factor, R_L, which is defined (Eq. 6), can be used to express the main features of the Langmuir equation.

R _L= 1/1 + K_L C₀ (6)

In the aforementioned equation, C₀ is the initial concentration of BF dye. The value of R_L indicates whether the adsorption is Unfavorable, if: R_L>1; Linear, if: R_L= 1; Favorable, if: 0 < R_L< 1; Irreversible, if: R_L= 0.

Table 2

Comparison between ZnO-rGO NC's adsorption capability and other known natural and modified adsorbents reported in Literature.
Adsorbent	Dye	Adsorption capacity(mg g^− 1)	Reference
Eggshell Membrane	Basic Fuchsin	48	[33]
Graphene-Fe₃O₄	Basic Fuchsin	85	[34]
Prunus Cerasefera (LPC)	Basic Fuchsin	158.73	[35]
ZrO₂-MgMn₂O₄/MgO₄	Basic Fuchsin	239.81	[36]
Biochar	Basic Fuchsin	283.3	[37]
Mussel Shell Biomass Waste	Basic Fuchsin	156.67	[38]
Local natural clay	Basic Fuchsin	149.1	[39]
ZnO-rGO NC	Basic Fuchsin	84.08	This Study

Table 3. Langmuir and Freundlich isotherms on the adsorption of BF dye onto ZnO-rGO NC adsorbent.

Adsorbent

Isotherms

ZnO-rGO nanocomposite

Langmuir

Q_max

K_L

R²

84.08

0.789

0.973

Freundlich

K_f

1/n

R²

13.5325

0.53

0.897

3.12.2 Freundlich Isotherm

A surface that is heterogeneous or supports sites with different affinities is the basis of the Freundlich model [40], an empirical equation. The subsequent equation (Eq. 7) provides the logarithmic form of Freundlich:

log(q _e ) = log(K _f ) + 1/n log(C _e ) (7)

Where n is the heterogeneity factor, K_f (mg g − 1)(L g − 1)1/n is the Freundlich constant associated with adsorption capacity, and q_e is the equilibrium dye concentration on the biosorbent (mg g − 1). The intercept and slope of the straight line plotting log (q_e) against log (C_e) (Fig. 16) are used to compute K_f and 1/n. The Freundlich and Langmuir models were used to characterize the equilibrium data gathered at different temperatures during this experiment. The results are shown in Table 3.

The slope and intercept of the plot between Ce/qe and Ce were used to compute the Langmuir isotherm constants, K_L and q_m. Table 3 illustrates how well the isotherm fits the experimental data. At 308 K, ZnO-rGO NC's maximum dye adsorption capacity was determined to be 84.08 mg g − 1. As the temperature rose to 323K, the values of K_L decreased, suggesting that a lower maximum adsorption capacity was caused by the rising temperature.

Based on the intercept and slope of the straight line in the plot of log (qe) vs. log (Ce), the Freundlich constants K_f and 1/n were determined. Table 3 demonstrates how the temperature increased while the adsorption capacity of K_f dropped. The favorability of adsorption is measured by the magnitude of n. Adsorption that is advantageous is represented by values of n between 1 and 10 (1/n smaller than 1). The value of n for this investigation was 0.53, showing a favorable adsorption.

The adsorption of Basic Fuchsin onto ZnO-rGO NC was found to have the best fit to the Langmuir isotherm equation based on the data gathered. The binding energy may have been uniform throughout the entire surface of the adsorbent by the fit of the adsorption data to the Langmuir isotherm. Furthermore, it further signifies that the dye molecules that were adsorbed formed a monolayer and did not interact or compete with one another.

3.13 Adsorption Thermodynamic

The essential thermodynamic factors dictate the spontaneity of the adsorption reaction. The following equations can be used to determine the conventional Gibbs free energy changes (ΔG◦), entropy changes (ΔS◦), and enthalpy changes (ΔH◦):

ΔG^◦ = ̶̶ RT Ln (K_L) (8)

Ln (K_L) = ΔS^◦/R ̶̶ ΔH^◦/RT (9)

Where K₀ is the thermodynamic equilibrium constant, T is the absolute temperature (K), R is the universal gas constant (8.314 J mol1K1), and ΔG^◦ is the free energy change (kJ mol1). By extrapolating to zero, values of K₀ can be computed using the relation Ln (qe/Ce) vs. qe at various temperatures.

Table 4

List of Thermodynamic Parameters of BF dye adsorption onto ZnO-rGO NC
Adsorbent	Temp. (K)	K_L	ΔG^o (KJmol^− 1)	ΔH^o (KJmol^− 1)	ΔS^o (KJ^− 1 mol^− 1)	R²
ZnO-rGO nanocomposite	308	2.201	−2020.17592	−7.30	−30.26	0.9996
	313	2.304	−2171.986195
	318	2.404	−2319.012524
	323	2.514	−2475.623702

Table 4 contains a list of thermodynamic variables. The BF dye adsorption process onto ZnO-rGO NC is spontaneous and feasible by the negative ΔG◦ values (− 2020.17592 kJ mol − 1 to − 2475.623702 kJ mol − 1). When the temperature was elevated from 308 to 323 K, the ΔG◦ values increased, indicating that the adsorption was chemical in nature. Subsequently, ΔH^◦ and ΔS^◦ were calculated using Eq. (9) and the slope and intercept of LnK_L against 1/T plot (Fig. 17). In Table 4, the data are displayed. The sorption process is exothermic, as indicated by the negative value of ΔH^◦ (-7.30 kJ mol − 1), and the solid-solution interface appears to be more random, as indicated by the negative value of ΔS^◦ (-30.26 J mol − 1K − 1). Also, it validates the enhanced randomness during adsorption at the solid-liquid interface. The phenomena of chemical adsorption, which is brought about by electrostatic interactions, naturally lead to this outcome.

This study looks at the contaminating effects of dyes, especially those from industrial sources, in water bodies. With a focus on basic fuchsin, a cationic dye that is extensively utilized in many industries, adsorption is suggested as an efficient technique. Carica papaya leaf extract was used to synthesize zinc oxide nanoparticles (ZnO NPs), a green technique. Subsequently, the effects of variables such as temperature, pH, contact time, adsorbent dosage, and initial concentration of the dye on the removal of BF dye were examined by batch adsorption tests. The adsorption equilibrium data were analyzed using the Langmuir and Freundlich isotherm models. ZnO-rGO NC had good adsorption effectiveness at pH 7 for the elimination of BF dye. The adsorption data best fit the Langmuir isotherm model, which suggested monolayer adsorption. The Freundlich model demonstrated favorable adsorption properties. The nanocomposite exhibited great prospects as an adsorbent for cationic dye removal from wastewater. Therefore, it may be worthwhile to investigate this eco-friendly adsorbent further for real-world uses in wastewater treatment procedures in subsequent research.

Authorship Contribution Statement

Flomo L. Gbawoquiya: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. Km. Rachna: Writing – original draft, Validation, Methodology, Supervision. Fredrick K. Saah: Writing – review & editing. Pramod K. Singh: Supervision, editing and Validation. Shiv Shankar: Supervision, Review & editing of final draft. I.M. Noor: Supervision & editing. M. Z. A. Yahya: Validation, review & editing.

Funding Declaration

There is no funding source available for this research

Conflict of Interest

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

Data availability

Data will be made available on request.

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Adsorption of Cationic Basic Fuchsin dye from aqueous solution on Green Synthesized Zinc oxide nanocomposite

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Abstract

Figures

1. Introduction

2. Experiments

2.1 Materials

2.2 Methods

2.2.1 Preparation of Carica papaya Leaf

2.2.2 Synthesis of Zinc Oxide Nanoparticles

2.2.3 Synthesis of Reduced Graphene Oxide

2.2.4 Synthesis of rGO-ZnO Nanocomposite

2.6 X-ray Diffraction Studies

2.2.5 FESEM Spectra

2.2.6 TEM Spectrum

2.2.7 FTIR Spectrum

2.2.8 Preparation of Adsorbate

2.2.9 Batch Adsorption Studies

3. Results and Discussions

3.1. X-ray Diffraction (Both XRD Y axis in

3.2. FESEM Spectra

3.3 FTIR ZnO Nanoparticles

3.4. TEM Spectra of ZnO Nanoparticles

3.5. EDX Spectrum of ZnO-rGO NC

3.6 Energy Bandgap

3.7 Effect of Contact Time on BF Dye Removal

3.8. Percent removal of BF dye from aqueous Solution

3.9 Effect of initial BF dye concentration

3.10 Effect of adsorbent dose on BF dye Adsorption

3.11 Effect of pH on BF dye Adsorption

3.12 Adsorption Isotherms

3.12.1 Langmuir Isotherm

3.12.2 Freundlich Isotherm

3.13 Adsorption Thermodynamic

4. Conclusion

Declarations

References

Additional Declarations

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