Abstract
Green synthesis of di-manganese trioxide mesoporous structure (super nano porous) sheets (Mn2O3-rGO-NS), Graphene oxide nano sheets (GO) and Mn2O3-rGO-NS nano sheets composite (Mn2O3-rGO-NS) were prepared via Thermal decomposition, seconds timescale water electrolytic oxidation and sonication method respectively. The prepared samples were characterized via X-ray diffraction, FESEM, TEM , and FTIR. Average crystallite size was found about 38 and 26 nm for Mn2O3-NS and Mn2O3-rGO-NS, respectively. Mn2O3-rGO–NPs morphology reveal nano porous sheets within average 35 nm and 26 nm in pores diameter and thickness respectively. Mn2O3-NS act distributed on and between graphene sheets creating macro and nano pores. The obtained results showed that the characteristics of the α-Mn2O3-rGO-NS sheets were improved by the addition of rGO sheets. Methyl orange (MO) dye adsorption onto Mn2O3-rGO-NS composite was investigated at various adsorption parameters, including pH, adsorbent quantity, and time. It was discovered that the adsorption behavior complies with the intra-particle diffusion model and the Friedendlich isotherm. Methyl orange in aqueous media may be eliminated 99.3% by Mn2O3-rGO-NS composite.
HIGHLIGHTS
Mesoporous graphene-based composite synthesis for dye removal from aqueous media with high efficiency and capacity. According to thermodynamics and kinetics adsorption is favorable, which opens up the possibility for further trials on various types of pollutant removal studies for the industry.
INTRODUCTION
The primary goal of modern nanotechnology research is the environmentally friendly synthesis of nanomaterials. Green synthesis of nanoparticles is a non-toxic, ecologically beneficial, clean, less expensive, and essentially novel method (Verma et al. 2019; Nakum & Bhattacharya 2022). Removal of dyes by adsorption-technology is a particularly important technique, because of its usability, simplicity, high efficiency, and scale-up over a wide range of concentrations (Kurniawan et al. 2012; Al Jebur & Alwan 2022). Nanomaterials are utilized for water treatment due to being eco-friendly, low-cost, high-performance materials that are well positioned for large-scale water treatment and elucidated in many field studies (Hashem 2014; Hairom et al. 2021; Jain et al. 2021). Metal oxides and their composites are commonly utilized in materials for pollution control and removal. Their various oxidation states, huge surfaces, and diverse electronic configurations give them these features (Liu et al. 2023).
Tuning synthesis in broad diversity of manganese oxides (such as MnO, MnO2, Mn2O3, Mn3O4) morphology and type appear unique properties, and receive great scientific interest in various applications such as environmental control, batteries, magnetism, and pollution sensing applications (Ahmed et al. 2022a, 2022b). Mn2O3 (p-type semiconducting material) is regarded as likely candidate material as it is non-toxic, low-cost material, has superior structural flexibility, and is environmentally compatible (stable) (Vignesh et al. 2022). Various processes have been carried out to improve the properties of metal oxide nanoparticles by using different methods of preparation or trying to control the particle size or doping with other materials (Stankic et al. 2016; Pradeev Raj et al. 2018; Chavali & Nikolova 2019; Krstić 2021; Pan et al. 2021; Sharma et al. 2022). Mesoporous oxides have drawn considerable interest due to their attractive physical (surface area) and chemical (reactivity) properties, which promised enormous potential for their neutral effect on the environment and their capability for pollutant trapping (Zhang et al. 2020; Yu et al. 2022). Graphene has a hexagonal two-dimensional layer made up of sp2 carbon atoms. It is well known for having a good electron acceptor, excellent charge transport, and a higher surface area, which has good mechanical, thermal, and electronic properties and can be utilized as nanosorbents, is typically composed of one or more atomically layer carbon atoms and it also has a special two-dimensional structure. The adsorption of dyes on a few-layered graphene nanosheets is made possible by Van der Waals forces and stacking interactions. Reduced graphene oxide nanosheets (rGO-NS) can improve metal oxide performance by first incorporating them into composite materials to change their chemical and physical properties (Sundriyal et al. 2018; Cong et al. 2021; Yeon et al. 2022). Strong intermolecular forces between adsorbates are provided by the broad electronic surfaces and high aspect ratios of both rGO-NS layers and single layers. Graphene performs admirably in terms of conductivity, flexibility, and chemical inertness. Lately, graphene-based material is of great scientific interest due to its superior mechanical characteristics, thermochemical stability and conductivity, which is predicted to have various uses (Li et al. 2010; Upadhyay et al. 2013; Kalaiselvi & Chandar 2021). Graphene oxide (GO) is a semiconductor material with a bandgap of 2.2 eV that can be decreased through reduction (Konale et al. 2020). The rGO has a bandgap in the range of 1–1.69 eV (Abid et al. 2018). This material previously was used to tune the optical, physico-chemical, adsorption efficiency, mechanical and promoted properties of metal oxides (Loh et al. 2010; Malefane et al. 2019; Ajala et al. 2022; Chi et al. 2022; Stefan et al. 2022). There are numerous methods for creating nanomaterials, the thermal decomposition process is being considered as a ‘green method’ that does not use or produce harmful chemicals or solvents (Dikshit et al. 2021). In addition, the procedure permits the preparation of a vast quantity of samples in a single batch compatible with ethics of COP 27 regulations (Nassar 2013; Nassar et al. 2013; Stanczyk 2022). In an effort to reduce the production of harmful wastes, this work created impacted nanosheets of Mn2O3-NS and Mn2O3-rGO with thickness less than 100 nm simply by thermal decomposition of metal-citric extract and sonication respectively. The composites were described and their adsorption activity was evaluated. There is not much information in the literature about the study of rGO impact on the structural and adsorption properties of Mn2O3. So, synthesis of Mn2O3-rGO-NS by the green method in two-dimensional morphology and the investigation of adsorption isotherm and kinetics of Mn2O3-rGO-NS are the main objectives of this work.
EXPERIMENTAL
Chemicals and reagents
All chemicals were used without any further purification. Manganese (II) acetate tetra hydrate (Acros, 99+ %), citrus peel was obtained from a local market in Hail Region, Saudi Arabia. The fruit peel was removed from the pulp. During this process, aluminum foil was used to protect the samples from light. Sodium hydroxide (Fisher chemical, ≥ 97%) graphite rods (99% extra pure) were obtained from LOBA CHEMIE, India. Hydrochloric acid (HCl) (37%), nitric acid (HNO3), sodium hydroxide (NaOH) powder, sulfuric acid (H2SO4), potassium permanganate (KMnO4) and standard Ni (II) solution were purchased from Sigma Aldrich, USA, while hydrogen peroxide (H2O2) and sodium nitrate (NaNO3) were purchased from PIOCHEM, Egypt and ISO-CHEM, France, respectively.
Synthesis of dimanganese trioxide nanosheets (Mn2O3-NS)
For the green synthesis Mn2O3-rGO-NS mesoporous nanosheets, 8 mM of manganese (II) acetate tetra hydrate (C4H16MnO8) was added to 20 mL of Milli Q water and pH was adjusted to 4 (acidic medium) to obtain a flat two-dimensional sheet is consistent with previous reports (Wahab et al. 2009; Nagyné-Kovács et al. 2020; Xie et al. 2022). Using M acetic acid and M NaOH solution for pH optimization. After that, 90 mL of as-prepared citric extract from citrus peels (Fernandes et al. 2022) was then added to C4H16MnO8 mixture and kept under vigorous magnetic stirring for 5 h at 78–80 °C. The visual color change and precipitate (ppt) were formed. The resulting ppt was centrifuged at 10,000 rpm for 20 min and washed several times with Milli Q water. Finally, ppt powder was dried at 85 °C for 6 h then calcined at 700 °C for 2 h. A dark brown residue of Mn2O3-NS was formed.
Graphene oxide (GO) synthesis
The GO was synthesized using Green method via seconds timescale water electrolytic oxidation (Pei et al. 2018).
Synthesis of Mn2O3-rGO nanocomposites
Mn2O3-rGO nanocomposites were prepared via the sonication method (Mohammadi & Entezari 2018) by mixing the GO and Mn2O3- NS (1:4) in 100 mL DI water, then probe sonicated for 30 min in pulsed mode at 600 W (20 KHz high frequency). Finally, homogeneous solutions of the Mn2O3-rGO nanocomposite were obtained and dried in a vacuum oven at 100 °C for 10 h.
Batch adsorption experiments
The amount of Mn2O3-rGO-NS nanoparticles adsorption trials began with 0.1 g (100 mg) achieving 50% removal and increasing directly proportional to the quantity added reaching the maximum removal of 99.3% at 0.5 g (500 mg). pH varies from 3 to 9, and contact time is the time needed to reach the equilibrium between the adsorbent and dyes. In a time range of 0–120 minutes, the impact of contact time on the removal of the dye by Mn2O3-rGO-NS at pH 4, and the concentration of the dye were all studied using a batch technique. All experiments were performed in triplicate to ensure repeatability and accuracy.
Batch adsorption kinetics
Bath adsorption isotherm
The adsorption isotherm, which is based on the homogeneity or heterogeneity of the adsorbent surface and the interaction between absorbed molecules, theoretically depicts the distribution of dye molecules between the adsorbent and liquid phase. To determine the best model for analysis and optimization of adsorption processes, the equilibrium adsorption data were examined using the most popular adsorption isotherms models, including Langmuir, Freundlich, and Temkin. Four hundred mg of Mn2O3-rGO-NS at pH 4 was added to a 1 L solution of various MO-Dye concentrations (10, 20, 30, 40, 50 and 60 ppm), to evaluate the adsorption isotherms.
Langmuir adsorption isotherm
Freundlich adsorption isotherm
Freundlich isotherm offers an empirical isotherm that is used to represent multilayer adsorption and assumes that the adsorption occurs on a heterogeneous surface and layers.
Temkin adsorption isotherm
The B is constant which is equal to RT/bT. AT (L/mg) and BT (J/mol) are the Temkin constants. BT is related to the heat of adsorption and AT is the equilibrium binding constant corresponding to the maximum binding energy. R (8.314 J/mol K) is the universal gas constant in energy unit and T (K) is the absolute temperature. The values of AT and BT are calculated from the linear plots of qe versus ln Ce.
Characterization techniques
The phase composition and crystal structure examined via the X-ray diffraction (XRD), model Malvern Panalytical Empyrean. The TEM images of the samples were determined via transmission electron microscope (TEM), model Joel-JEM-2100, operated at 200 kV. The FTIR spectra were collected using a FTIR spectrometer, model Vertex 70-Bruker, Germany (in the range of 400–4,000 cm−1 with a resolution of 4 cm−1). The UV-vis absorption spectra of the samples were measured using a double beam spectrophotometer (Perkin Elmer Lambda 40).
RESULTS AND DISCUSSION
X-ray diffraction
XRD pattern of graphene oxide (GO), Mn2O3-rGO and Mn2O3-rGO nanoparticles.
The ε and δ values are calculated and tabulated in Table 1.
Crystallite size (D), micro-strain (ε), and dislocation density (δ)
Sample . | D(222) (nm) . | ε(222), ×10−3 . | δ(222), ×1014 (m−2) . |
---|---|---|---|
Mn2O3 | 56 | 2.3 | 3.2 |
Mn2O3-rGO | 43 | 3 | 5.5 |
Sample . | D(222) (nm) . | ε(222), ×10−3 . | δ(222), ×1014 (m−2) . |
---|---|---|---|
Mn2O3 | 56 | 2.3 | 3.2 |
Mn2O3-rGO | 43 | 3 | 5.5 |
As shown, ε and δ values were increased when rGO was inserted in the matrix. This result confirms the compression of the material and consequently the particle size decreases as well (Vignesh et al. 2022).
FESEM-TEM analysis
FESM images of (a, b, e) Mn2O3-NS, TEM images (c, d, g) Mn2O3-NS, FESEM images (h,i,k) of graphene nanosheets and FESEM (l,m,n) Mn2O3/G composite.
FESM images of (a, b, e) Mn2O3-NS, TEM images (c, d, g) Mn2O3-NS, FESEM images (h,i,k) of graphene nanosheets and FESEM (l,m,n) Mn2O3/G composite.
FT-IR analysis
Adsorption study
Batch adsorption was studied along with other parameters such as pH, Mn2O3-NS concentration, Methyl Orange starting concentration, and contact time. While maintaining all other variables constant throughout the study (temperature = 25 °C and stirring power = 300 rpm), the study hinges on modifying the parameter to determine its impact on the adsorption process.
Effects of pH on adsorption
Relation between percent (%) of removed dye and Mn2O3-rGO –NS at diverse parameters, (a) adsorbent (Mn2O3-rGO-NS) weight (mg), (b) pH, (c) Contact Time and (d) different concentration of MO-dye.
Relation between percent (%) of removed dye and Mn2O3-rGO –NS at diverse parameters, (a) adsorbent (Mn2O3-rGO-NS) weight (mg), (b) pH, (c) Contact Time and (d) different concentration of MO-dye.
Effect of weight of Mn2O3-rGO nanoparticles
To evaluate the impact of Mn2O3 -rGO quantities and the removal of MO, interval amounts of 100–500 mg of Mn2O3-rGO at 25 °C and pH 4 were added to 1 L (50 ppm) of MO-dye solutions. The outcomes demonstrate that the Mn2O3-rGO-NS concentration rises, the elimination of MO-dye also rises; 99.3% of the maximum removal was attained with 0.4 g of Mn2O3. The abundance of low energy active sites contributes to the gradual increase in removal efficiency. The remaining active sites will then have more energy, which will lead to a decrease in adsorption capacity that is associated to the development of stacking layers and unequal distribution (Chen et al. 2023).
Effect of contact time
In a time range of 0–120 minutes, the impact of contact time on the removal of the dye by Mn2O3-rGO-NS at pH 4 was examined. Figure 4(c) of the results showed that removal rises with increasing time until it achieves constant adsorption after 40 min. The active sites on the surface of Mn2O3-rGO-NS are predicted to become saturated with the dye after 40 minutes, at which point there will be no active sites left for adsorption.
Effect of the initial concentration of dye
A batch method of dye concentrations (30, 50, 60, 70, 80, and 90 mg/L) was used to study adsorption isotherms and influence of initial on the removal efficiency. The remaining dye in solution can be measured spectrophotometrically at 464 nm. The influence of initial dye concentrations concentration on the removal efficiency of MO-dye was studied as shown in Figure 3(d) using the same weight of Mn2O3-rGO-NS (0.4 gm) at pH 4, keeping all other factors constant. As can be seen in Figure 3(d), the percentage removal of the dye was found to decrease with the increase in initial dye concentration up to 50 mg/L. This suggests that according to active size availability, adsorption energy need, and competition between solvent and dye molecules with adsorbate and one another, saturation occurs.
Adsorption kinetics
Experimental and calculated parameters of kinetics models of adsorption of MO-dyes
. | Pseudo first order . | Pseudo second order . | Intra-particle diffusion . | ||||||
---|---|---|---|---|---|---|---|---|---|
qe (exp) . | qe (cal.) . | k1 . | R2 . | qe (cal.) . | k2 . | R2 . | C . | k1 . | R2 . |
99.3 | 215.17 | 0.194 | 0.89 | 181.34 | 2.7 × 10−4 | 0.913 | –17.03 | 22.2 | 0.99 |
. | Pseudo first order . | Pseudo second order . | Intra-particle diffusion . | ||||||
---|---|---|---|---|---|---|---|---|---|
qe (exp) . | qe (cal.) . | k1 . | R2 . | qe (cal.) . | k2 . | R2 . | C . | k1 . | R2 . |
99.3 | 215.17 | 0.194 | 0.89 | 181.34 | 2.7 × 10−4 | 0.913 | –17.03 | 22.2 | 0.99 |
Kinetic models of MO-dye adsorption on Mn2O3-rGO-NS. (a) The pseudo-first-order model, (b) The pseudo-second-order model, (c) The intra-particle diffusion model.
Kinetic models of MO-dye adsorption on Mn2O3-rGO-NS. (a) The pseudo-first-order model, (b) The pseudo-second-order model, (c) The intra-particle diffusion model.
Adsorption isotherm
Adsorption isotherm for MO-dyes over Mn2O3-rGO-NS. (a) Freundlich isotherm, (b) Langmuir isotherm, (c) Temkin isotherm.
Adsorption isotherm for MO-dyes over Mn2O3-rGO-NS. (a) Freundlich isotherm, (b) Langmuir isotherm, (c) Temkin isotherm.
CONCLUSIONS
This work opens a green synthesis gate for super nanoporous benign metal oxide (mesoporous structure of α-Mn2O3) with a thickness of less than 26 nm and graphene sheets using thermal decomposition of metal- citrus peels extracts complex and second timescale electrolytic oxidation respectively. Following that, a composite was formed via utilizing ultrasonic radiation. The obtained results showed that the characteristics of the Mn2O3-rGO-NS sheets were improved by the addition of rGO sheets. In comparison to the literature, Mn2O3-rGO-NS adsorption capacity exhibits a high adsorption capacity of 210 mg/g to MO dye when compared to the literature at various adsorption parameters, including pH, adsorbent quantity, and time. It was discovered that the adsorption behavior complies with the intra-particle diffusion model and the Freundlich isotherm and the Langmuir isotherm model with a lower regression coefficient. This technique exhibits good practice for the synthesis of eco-friendly composite materials for the large-scale removal of dye from aqueous systems.
FUNDING
No funding for this research.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.