Next Article in Journal
Uncertainty of Postmortem Time Estimation Based on Potassium Ion Determination in Vitreous Humor Using Potentiometric Ion-Selective Electrode and Microwave-Induced Plasma with Optical Emission Spectrometry Methods
Previous Article in Journal
A Validated HPLC-RID Method for Quantification and Optimization of Total Sugars: Fructose, Glucose, Sucrose, and Lactose in Eggless Mayonnaise
Previous Article in Special Issue
Inter-Comparisons of Major Ions and Organic Matter Using Aerodyne Aerosol Mass Spectrometer, Ion Chromatography and Sunset Lab Carbon Analyzer in Aged Aerosols from Okinawa in the Western North Pacific Rim
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effective Removal of Methylene Blue by Mn3O4/NiO Nanocomposite under Visible Light

1
Department of Chemistry, COMSATS University Islamabad, Park Road, Islamabad 45550, Pakistan
2
Department of Electrical Engineering, Sukkur IBA University, Sukkur 65200, Pakistan
3
Department of Chemistry, Lahore Garrison University, DHA Phase VI, Lahore 54792, Pakistan
4
Wet Chemistry Laboratory, Department of Metallurgical Engineering, NED University of Engineering and Technology, University Road, Karachi 75720, Pakistan
5
Institute of Environmental Sciences, University of Sindh Jamshoro, Jamshoro 76080, Pakistan
6
Department of Physics, COMSATS University Islamabad, Park Road, Islamabad 45550, Pakistan
7
Pakistan Council of Scientific and Industrial Research (PCSIR), PCSIR Head Office, 01-Constitution Avenue, Sector G-5/2, Islamabad 44000, Pakistan
8
Department of Basic Science and Humanities, Dawood University of Engineering and Technology, Karachi 74800, Pakistan
9
Department of Basic Health Sciences, Foundation Year, Princess Nourah bint Abdulrahman University, Riyadh 11671, Saudi Arabia
10
Biology Department, College of Science, Princess Nourah bint Abdulrahman University, Riyadh 11671, Saudi Arabia
11
Environment and Biomaterial Unit, Health Sciences Research Center, Princess Nourah bint Abdulrahman University, Riyadh 11671, Saudi Arabia
12
Saudi Society for Applied Science, Princess Nourah bint Abdulrahman University, Riyadh 11671, Saudi Arabia
*
Author to whom correspondence should be addressed.
Separations 2023, 10(3), 200; https://doi.org/10.3390/separations10030200
Submission received: 30 January 2023 / Revised: 3 March 2023 / Accepted: 6 March 2023 / Published: 14 March 2023
(This article belongs to the Special Issue Extraction and Analysis of Emerging Environmental Pollutants)

Abstract

:
Wastewater treatment is indispensable as wastewater can lead to adverse health effects and deteriorate the quality of life on earth. Photocatalysis is a facile methodology to address this issue. In this study, nanocomposites (NCs) of manganese oxide (Mn3O4) and nickel oxide (NiO) were synthesized in different weight ratios via the solid-state reaction route. Structural properties, optical properties, surface morphology, and functional group analysis of the synthesized nanomaterials were conducted using X-ray diffraction (XRD), UV– Vis spectroscopy, scanning electron microscopy (SEM) along with energy-dispersive X-ray (EDX) analysis, and Fourier-transform infrared (FTIR) spectroscopy, respectively. The bandgap of the nanocomposite decreases significantly from 2.35 eV for the Mn3O4 NPs to 1.65 eV for the Mn3O4/NiO nanocomposite (NC). Moreover, adsorption studies followed by the photocatalytic performance of the Mn3O4/NiO NCs were evaluated to determine the removal of methylene blue (MB) dye from wastewater. The photocatalytic performance of the nanocomposite enhances as the ratio of Mn3O4 in the composite increases from one weight percentage to three weight percentage. The photocatalytic degradation efficiency was calculated to be 95%. The results show that the synthesized NCs could play an important role in photocatalytic wastewater purification and environmental remediation.

1. Introduction

Water is vital for life, and its availability in its purest form is crucial to healthy life expectancy on earth. Water pollution, in comparison to other forms of pollution, poses a major threat to living beings since effluents from various dye factories and tanneries contaminate water bodies [1]. The world’s current primary challenge is the unavailability of safe drinking water [2]. An estimation of worldwide population regarding the unavailability of safe drinking water is about 1.2 billion, while the estimation regarding the lack of water accessibility for basic sanitary purpose is approximately 2.6 billion [3]. Asia and Africa are home to the majority of people who face pure water scarcity [4]. Multiple factors contribute to the contamination of clean water at a larger scale, such as climate change, population increase, soil degradation, inadequate sanitation, toxic algae, cleaning products, synthetic fertilizers, insecticides, pesticides, pharmaceuticals, pigment production, personal care products, disinfection byproducts, textile, leather, and dyeing [5,6,7]. According to recent studies, almost 15% of total dyes used in the textile industry remain unreacted, contributing significantly to effluents [1]. Various industries produce pollutants that contaminate water bodies. Statistically, the textile industry produces around 10 tons of fabric daily. Its water consumption is approximately 18 tons per day, while 4 million liters of water is produced as run off. Dye runoffs are hazardous as they contain organic and inorganic salts, acids, alkalis, and heavy metals that are poisonous, neurotoxic, teratogenic, and carcinogenic [5]. Among the various pollutants, some major ones that have gained substantial concerns owing to their serious threats to human health are fluorides, uranium, lead, copper, zinc, iodine, polymers, and a variety of organic pollutants [6]. Their prevalence has a harmful effect on living beings, including humans and animals, resulting in organ damage, skin rashes, nausea, vomiting, gastrointestinal tract irritation, and other problems [7]. Consequently, resolving this issue can improve not only human living conditions but also aquatic life.
Due to a growing concern about the safe removal of water pollutants, a number of advanced water treatment techniques have recently been used. For example, J. Jjagwe et al. worked on the synthesis and application of granular activated carbon from biomass waste materials for water treatment [8]. Granular activated carbon is presently used as a water treatment material to efficiently remove a variety of pollutants, including organic micropollutants, pharmaceuticals, arsenic and carcinogenic compounds, microplastics, heavy metals, as well as color and odor from pollutants [9]. Similarly, G. Gallareta-Olivares et al. used metal-doped carbon dots as robust nanomaterials for the monitoring and degradation of water pollutants [10]. Likewise, S. Jiang et al. used magnetically separable electrospun La-Mn-Fe tri-metal oxide nanofibers as a novel adsorbent for fluoride remediation [11]. Furthermore, J. Wang et al. worked on poly(amidoxime)-modified MOF macroporous membrane for high-efficient uranium extraction from seawater [12]. G. Zhou et al. fabricated Fir sawdust as a low-cost and easily recyclable adsorbent for the efficient removal of Pb (II), Cu (II), and Zn (II) [13]. Additionally, G. Obey et al. prepared biochar derived from non-customized matamba fruit shell as an adsorbent for iodine [2]. Moreover, S. Liu et al. prepared covalent organic frameworks [14] and J. Wang et al. prepared metal-organic framework materials (MOFs) for efficient water treatment with a super-high dye adsorption capacity at a high dye concentration [12].
Amongst the various treatment methods, photocatalysis is a highly attractive technique for the removal of dye pollutants due to its efficient capturing and transporting of light energy, use of visible light, and enhanced charge separation [15,16,17,18]. In this process, a photocatalyst is exposed to light, and if the light has sufficient energy, an electron–hole pair is generated. After the activation of the catalyst, oxygen is reduced, and organic compound is oxidized [19]. The reactant mass transfers to the surface of the photocatalyst, and then adsorption of the reactant occurs on the surface. Photocatalytic reaction takes place in an adsorbed state. The photogenerated charge carriers then move to the catalyst’s surface. The activated catalyst absorbs photon energy equal or greater than the band gap, which transfers an electron from the valence band to the conduction band [20]. Hence, metal oxide semiconductors are extensively used in the process of photocatalysis [21].
Oxide-based semiconductors, such as ZnO, SnO2, and TiO2 MnO2 [22,23,24,25], have played a central role in enhanced photodegradation process occurring at an accelerated rate [26]. However, their efficiency of degradation is still found to be limited. Therefore, the use of co-catalysts is highly needed [27]. There is a vast range of applications of Mn3O4 NPs in various domains, including rechargeable batteries, ion-sieves, chemical sensing devices, catalysts, microelectronics, as well as optoelectronics [28]. Furthermore, Mn3O4 NPs have been reported as an effective photocatalyst for dye degradation [29,30]. NiO has been used as a co-catalyst to enhance the photocatalytic activity of some other metal oxides [31]. Due to the limitations in the photocatalytic performance of pure Mn3O4 NPs, NiO could be used as a co-catalyst to enhance the photocatalytic activity. The p-type semiconductor, NiO, has a significant photocatalytic role because of its larger gap between the conduction and valence bands [32]. NiO NPs have received significant attention because of some particular features, such as a bandgap of 3.6 eV, phase stability, increased magnetic permeability, and electrical conductivity [33]. These features are responsible for NiO NPs being considered ideal for photocatalysis [34]. Only a few reports are available about the synthesis of Mn3O4/NiO nanocomposite for catalytic degradation. Therefore, the present work focuses on the fabrication of an efficient photocatalyst comprising Mn3O4 NPs in conjunction with NiO NPs to form a nanocomposite that can enhance photocatalytic performance and, thus, the removal of pollutants. To the best of our knowledge, the photocatalytic performance of Mn3O4 in conjunction with NiO NPs has not yet been reported in the literature. However, the photodegradation of Mn3O4 and NiO by itself and other nanocomposites, such as V/ Mn3O4, Pb/Mn3O4, Ag/Mn3O4, Fe/NiO and Mn3O4/γ-MnOOH etc., (mentioned in Table 2) have been studied before [35,36,37,38,39,40,41,42,43,44,45,46].

2. Experimental

2.1. Materials

The reagent-grade chemicals used in this study included extra pure manganese chloride tetrahydrate (MnCl2.4H2O), with a molecular weight of 197.91 g/mol; nickel chloride hexahydrate (NiCl2.6H2O), with a molecular weight of 129.59 g/mol and 98% purity; cetyl tetra butyl ammonium bromide (CTAB), with a molecular weight of 322.37 g/mol and 98% purity; and sodium hydroxide (NaOH). All chemicals were purchased from Sigma Aldrich, Germany. Double distilled (DD) water was used to prepare the molar solutions of these chemicals.

2.2. Synthesis of Pure Mn3O4 Nanoparticles

A simple chemical precipitation method was used to synthesize Mn3O4 NPs at room temperature. A calculated amount of NaOH (0.88 g) was dissolved in 100 mL of distilled water at room temperature for almost ten minutes. To this solution, 2.177 g of MnCl2.4H2O was dissolved with continuous stirring. To suppress the reunion of nanoparticles, 25 mg of cetyl tetra methyl ammonium bromide (CTAB) was added as a surfactant with constant stirring. After 24 h of stirring, a brown-colored precipitate was formed, which indicated the completion of reaction. The resulting precipitate was then filtered, followed by washing with DD water several times and drying overnight in a hot air oven at roughly 80 °C. Next, thermal treatment of the as-prepared sample was performed at 500 °C for 2 h under air at a ramping rate of 5 °C min−1 to remove the surfactant CTAB. As a result of calcination, the brown color of the sample was turned into black. In the Supplementary Materials, Figure S1a–f show the different steps of the preparation of Mn3O4 NPs in the laboratory.

2.3. Synthesis of Pure NiO Nanoparticles

Nickel oxide NPs were synthesized by a simple co-precipitation method. At first, a 0.2 M of nickel chloride hexahydrate solution was prepared in deionized water and magnetically stirred for 40 min at 50 °C. A total of 2 M of NaOH solution was prepared in DI water and added to the above-mentioned solution dropwise at room temperature until the pH became 8. The produced green gel was subjected to centrifugation, and the extracted gel was then rinsed with DD water and ethanol. The gel was dried under vacuum at 60 °C for almost 14 h. The formed nickel hydroxide was subjected to calcination for 2 h at 450 °C in a tube furnace in order to obtain NiO NPs. The sample’s color changed from green to greyish black as a result of the annealing process. Figure S2a–d show the different steps of the preparation of NiO NPs in the laboratory. The following equation shows the overall chemical reaction to synthesize NiO NPs:
N i C l 2 .6 H 2 O + H 2 O + 2 N a O H N i O + 8 H 2 O + 2 N a C l

2.4. Synthesis of Mn3O4/NiO Nanocomposites

The prepared Mn3O4 and NiO NPs were used to synthesize Mn3O4/NiO NCs in different w/w ratios by using a simple solid-state method. In order to synthesize Mn3O4/NiO NC at a ratio of (1:1), equally weighted amounts of Mn3O4 and NiO NPs were grounded for almost one hour, followed by calcination at about 80 °C for two hours in a tube furnace. The temperature of 80 °C was used to adhere the two materials through Van der Waal forces, and the successful formation of the physically prepared composite system was used for an evaluation of the photocatalytic properties of the two different materials together in single physical phase. Mn3O4/NiO NC at a ratio of (3:1) was synthesized by taking 3 times the amount of Mn3O4 to the amount of NiO NPs to make a composite with a 3:1 concentration, following the same procedure mentioned before. The different steps of the preparation of the Mn3O4/NiO nanocomposites in the laboratory are shown in Figure S3a–c. An overview of the whole experimental process is shown in the following schematic illustration (Scheme 1).

2.5. Evaluation of Adsorption and Photocatalytic Activity of Mn3O4/NiO Nanocomposites

The photocatalysis of the nanocomposites of Mn3O4 and NiO was performed by taking methylene blue as a model pollutant. Methylene blue (C16H18ClN3S) is a potentially hazardous organic cationic dye that is water soluble. The photocatalytic experiment was performed under direct sunlight.
Before studying the photocatalytic activity, an adsorption/batch study was performed in the dark (without light). A stock solution of 998.86 mg/L was first prepared, and, from this solution, further dilute solutions of different mg/L (2, 4, 6, 8, and 10) were obtained. After an analysis of the data from the calibration curve, a batch study was performed in the dark at a concentration of 5.99 mg/L. For the adsorption experiment, the pH of the sample was kept at 7, and the experiment was performed at a concentration of 998.86 mg/L. Various solutions at 10 mL were obtained from this solution. A total of 10 mg of the catalyst was added in all the solutions, and then they were kept for agitation in a shaker bath at different times. After agitation, the samples were centrifuged, filtered, and then examined under UV–Vis spectroscopy.
After the batch study, the next experiment was a pH study which was also performed in the dark. In the pH study, 499.43 mg/L of the stock solution was prepared in 250 mL of deionized water. The same steps were followed as explained earlier in the adsorption study; however, different solutions of 10 mL were prepared at different pH values, i.e., 2, 7 and 11, by using acidic and basic buffer solutions, such as 0.1 M acetate buffer and 0.1 M ammonium hydroxide and ammonium chloride buffer solution, respectively.
The photocatalytic performance of the nanocomposites was investigated by using the organic dye, methylene blue, under natural visible light illumination. The synthesized nanocomposites with different ratios (1:1, 2:1, and 3:1) were transferred into 50 mL of 799.62 mg/L and 399.81 mg/L of MB dye solution. The degradation experiment was accomplished after achieving an adsorption/desorption equilibrium state of the MB dye on the surface of the catalyst. The mixture was then exposed to direct sunlight at different time intervals of 50–350 min. At the end, the degradation of the MB dye was assessed by carefully measuring the residual concentration of the MB dye from the vial with the help of a UV–Visible spectrophotometer. The dye removal percentages for the synthesized nanocomposites were calculated using the following formula:
Dye   removal   % = C o C t C o × 100
where ‘Co’ and ‘Ct’ are the MB dye absorbance before degradation and final absorbance of the dye at regular time intervals ‘t’ under natural light irradiation, respectively.

2.6. Characterization

The X-ray diffraction (XRD) analysis of the synthesized samples was performed with the help of a (STOE, Darmstadt, Germany) Theta-Theta S/N 65022 diffractometer with CuKα radiation. A (JEOL, Akishima, Japan) JSM-6490A electron scanning microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS) was used for the morphological, microstructural, and elemental analyses. The optical analysis of the sample material was performed by using an OPTIZEN Alpha UV/Vis Spectrophotometer (Shang hai, China). For the functional group analysis, a (Perkin Elmer, Waltham, MA, USA) Spectrum 100 Fourier-transform infrared spectrophotometer (FTIR) was employed.

3. Results and Discussion

3.1. Structural Analysis of the Synthesized Mn3O4/NiO NPs and NCs

The XRD spectra for the pure Mn3O4 and NiO NPs and NCs are shown in Figure 1. The pure Mn3O4 NPs show diffraction peaks located at the Bragg angles (2ϴ) ≅ 38.48, 44.61, 64.83, 72.61, and 78.06 parallel to the crystal planes (004), (220), (400), (332), and (325), respectively; these results precisely resemble the values reported by the Joint committee on Powder Diffraction Standards (JCPDS card no. 01-080-0382). The structure formed is highly crystalline and has a tetragonal shape. By using the Debye–Sherrer formula, the average crystallite size was calculated to be 24.94 nm, and the average lattice strain (ε) was found to be 0.0033 [38]. The FWHM and d-spacing values, along with the (hkl) and 2ϴ degrees, are listed in the Supplementary Materials in Table S1. The pure NiO NPs show various diffraction peaks located at the Bragg angles (2ϴ) ≅ 36.6°, 42.7°, 44.6°, 62.5°, and 72.7° parallel to the crystal planes (003), (012), (200), (104), and (311), respectively; these results also precisely resemble the values reported by the Joint Committee on Powder Diffraction Standards (JCPDS card no. 00-022-1189 and 00-047-1049). The average crystallite size was calculated to be 21.51 nm, and the average lattice strain (ε) was found to be 0.0054 [39]. The values for the FWHM and d-spacing values are shown in Table S2.
The nanocomposite Mn3O4/NiO (1:1), as revealed in Figure 1, shows diffraction peaks located at the Bragg angles (2ϴ) ≅ 38.31°, 44.71°, 64.98°, 72.63, and 78.08° parallel to the crystal planes (004), (220), (400), (332), and (325), respectively, which precisely resemble the values reported by the Joint Committee on Powder Diffraction Standards (JCPDS card no. 01-080-0382 and 00-022-1189). By using the Debye–Sherrer formula, the average crystallite size was calculated to be 30.87 nm, and the average lattice strain (ε) was found to be 0.0026. The FWHM values are shown in Table S3. The nanocomposite Mn3O4/NiO (3:1) shows diffraction peaks located at the Bragg angles (2ϴ) ≅ 38.48°, 42.11 °, 44.71°, 72.63°, and 78.23° parallel to the crystal planes (004), (012), (220), (332), and (325), respectively, which also precisely resemble the values reported by the Joint Committee on Powder Diffraction Standards (JCPDS card no. 01-080-0382 and 00-022-1189). Only a small shift in the peak positions distinguishes the diffraction patterns of the pure and modified Mn3O4 with NiO NPs, and the intensity of the pure sample is lower than that of the modified sample. A little shift toward the left indicates the NiO doping in manganese oxide. The average crystallite size was calculated to be 25.93 nm, and the average lattice strain (ε) was found to be 0.00372 for the NC 3:1. The structure formed is highly crystalline in nature. The values for FWHM and d-spacing are listed in Table S4.

3.2. Morphological and Elemental Analyses of Mn3O4/NiO NPs and NCs

The morphological characterization of the synthesized nanoparticles and their composites were performed using scanning electron microscopy along with energy-dispersive X-ray analysis. Figure 2 shows the morphology of the Mn3O4 and NiO NPs and the Mn3O4/NiO NCs (1:1 and 3:1). Spherical aggregated nanoparticles of Mn3O4 with diameters ranging from 20 to 80 nm are observed, as revealed in Figure 2a. Figure 3a–d show the EDX spectra of the Mn3O4 and NiO NPs and the Mn3O4/NiO NCs 1:1 and 3:1, respectively. The peaks corresponding to manganese, nickel, and oxygen are present in the spectra, which further confirms the successful synthesis of the targeted Mn3O4 and NiO NPs and NCs. An unknown peak is also observed in the EDX spectra of the Mn3O4 and NiO NPs, which is suspected to be from the solvent used. The atomic and weight percentage for each element are presented in Table 1. The SEM image of the synthesized NiO nanoparticles at 450 °C is shown in Figure 2b. The SEM image clearly indicates smaller, spherical grains with diameters ranging from 35 to 60 nm. The SEM image of the nanocomposite of Mn3O4 and NiO 1:1 (one part NiO and one part Mn3O4) is shown in Figure 2c, whereas Figure 2d shows the SEM image of the composite 3:1 (three parts Mn3O4 and one part NiO). The particles exhibit a spherical shape and have a non-uniform size distribution because of agglomeration. The pure Mn3O4 has a smooth surface, but clusters are developed with NiO doping and, hence, the grain size has increased, which is also in accordance with the XRD results. The weight percentages of manganese and oxygen in the pure sample are 80.9% and 19.1%, respectively, whereas in the NiO-modified sample, the weight percentage varies according to the doping concentration, as shown in Table 1 [36,40].

3.3. Optical Analysis of Mn3O4/NiO NPs and NC

The UV–Vis spectrum of the Mn3O4 NPs synthesized with the precursor manganese chloride tetrahydrate is shown in Figure 4a. The characteristic peak in the UV–Vis spectrum at 240 nm exhibits a remarkable agreement with the values reported in the literature for Mn3O4 nanoparticles [47]. The band gap energy of the synthesized NPs and NCs were calculated using the Tauc’s equation as given below:
α h ϑ n = A h ϑ E g      
where ‘A’ is a constant; ‘Eg’ is the band gap of the material; ‘α’ is the absorption coefficient; ‘h’ is the incident photon energy; and ‘n’ is the exponent that depends on the kinds of transition. For direct or allowed transition, it is a value of n = 2, and for indirect transition, it is value of n = 1/2. It can also be expressed as follows:
E g = h c / λ
To calculate the direct band gap of the sample material, a graph is plotted between hv(eV) and (αhv)2(eVcm−1)2, which is shown in the inset of Figure 4a. For the Mn3O4 NPs, the bandgap energy was calculated to be 2.35 eV. The UV–Vis absorption spectrum of the NiO NPs is shown in Figure 4b. An absorption peak is discovered in the electromagnetic area of ultraviolet light. The characteristic peak at 230 nm in the UV–Vis spectrum clearly indicates the synthesis of NiO NPs, and the bandgap energy was calculated to be 3.15 eV [48]. The UV–Visible spectrum of the Mn3O4/NiO NC is shown in Figure 4c. Absorption peaks are discovered in the electromagnetic area of ultraviolet light. The characteristic peaks at 230 nm and 370 nm are observed in the UV–Vis spectrum of the Mn3O4/NiO nanocomposite, where a red shift can be observed (a shift toward longer wavelength). This red shift is attributed to the lattice distortion and new localized bands being introduced. On the host matrix, an increase in dopant concentration is the reason that causes the formation of these localized bands. However, the bandgap energy calculated by the Tauc plot was found to be 1.65 eV for Mn3O4/NiO, as shown in the inset of Figure 4c.

3.4. Functional Group Analysis of Mn3O4/NiO NPs and NCs

The FTIR spectra of the synthesized Mn3O4 and NiO NPs and the Mn3O4/NiO NCs are shown in Figure 5. From the corresponding spectra obtained in the wavelength range from 4000 to 400 cm−1, the presence of functional groups and bonds can be inferred. In Figure 5, the black colored plot represents the Mn3O4 spectrum, where the peak at 3421 cm−1 shows the stretching vibration of OH group while the peak at 1632 cm−1 shows the absorption of moisture on the sample surface. The peak at 1020 cm−1 shows the bending vibrations of Mn atoms with –OH groups. The bands at 623 cm−1 and 482 cm−1 indicate the stretching modes of the tetrahedral and octahedral sites in Mn-O [49].
Red color represents the FTIR spectrum of the NiO nanoparticles calcined at 450 °C for two hours. The broad bands, as previously described, correspond to O-H stretching due to the presence of adsorbed water from the atmosphere on the surface of the NiO nanoparticles, whereas the adsorption band in the region of 581 cm−1 corresponds to NiO-stretching vibrations [32].
Figure 5 also shows the FTIR spectra of the 1:1 and 3:1 Mn3O4/NiO nanocomposites in green and blue color, respectively. In both spectra, the band at 3421 cm−1 shows the stretching vibration of OH group, while the peak in the region of 1600 cm−1 shows the absorption of moisture on the sample surface. The bands at 1021 cm−1 and 1016 cm−1 in the nanocomposites with a 1:1 and 3:1 ratio show bending vibrations of Mn atoms with –OH groups. The bands in the region of 600 cm−1, 500 cm−1, and 400 cm−1 indicate the stretching modes of Mn-O and Ni-O. Noticeably, the characteristic peak at 623 cm−1 for the Mn3O4 NPs is observed in the nanocomposites, which further proves the successful synthesis of the Mn3O4/NiO NCs.

3.5. Adsorption Study of MB Dye Using Mn3O4/NiO NCs

Without adding any catalyst, a maximum absorption peak is obtained at 660 nm with a full scan of the adsorption of MB dye for comparison. Figure S4 shows the calibration curve for the stock sample solution. For the adsorption experiment, the pH of the sample was optimized at 7, and the experiment was performed at a concentration of 6 ppm. Figure 6a shows the experimental data of the adsorption of MB dye against contact time for the Mn3O4-based nanomaterial. Figure 6b shows the kinetic study of the adsorption process in the dark. It indicates that the adsorption of MB dye increases linearly with increase in time interval with a fixed adsorbent amount (10 mg) and becomes slow after 60 min. After nearly 80 min of the adsorption experiment, saturation occurs. Initially, the kinetic rate is very high, and as time increases, it becomes slow until it attains equilibrium. Initially, the Mn3O4 NPs have a large number of unoccupied active sites, which decreases after a transition of time. The decrease in the absorbance peak in Figure S5 clearly indicates the adsorption phenomenon. The main aim of conducting the adsorption study was to confirm whether efficient dye removal could be made possible by using the adsorption phenomenon only. However, the results from the adsorption study are not very satisfactory, which suggests a need to opt for photocatalytic activity for efficient dye removal. In order to make the test fair, the adsorption phenomenon was tested further at different pH values (as described in the next section). Here, the results again support the fact that light has a major role in the activation of the catalyst. This evidence supports testing for photocatalytic activity for efficient dye removal.

3.6. Effect of pH on Adsorption of MB Dye

The chemical properties of both the MB dye and the adsorbent (Mn3O4) generally change with the pH of the adsorbate solution MB. Thus, it is important to study the pH effect on the adsorption of MB by the Mn3O4 NCs. The experiment performed for the pH study was also performed in the dark, and the same steps were followed as explained earlier in the adsorption study; the only difference was that those different 10 mL solutions were optimized at different pH, i.e., 2, 7, and 11. Figure 7a–c show the adsorption of MB dye by using the Mn3O4/NiO NCs as a catalyst at a pH of 2, 11, and 7, respectively. Figure 7b shown below indicates that the maximum value of adsorption for MB dye is at a pH of 11, which is a basic medium. The minimum adsorption occurs at a pH of 2, which is an acidic medium. Adsorption is very slow in the acidic medium and gradually increases as it moves toward the basic medium, but it still does not give satisfactory results in terms of considerable dye removal.

3.7. Photocatalysis under Visible Irradiation

When light is turned on, photocatalytic reaction begins. The valence band will be breached by the creation of an electron–hole pair because of the transition of electron from the valence band to the conduction band. This will lead to a photogenerated e/h+ pair. This process occurs when light interacts with a material having a wavelength within the bandgap of the semiconductor. This light has an optical energy comparable to the semiconductor’s bandgap. Charge carriers can then travel from the bulk to the surface of the material. If dissolved oxygen is deposited on the photocatalyst’s surface in an aqueous solution, reduction will take place by electrons, resulting in superoxide radical anions, O2·, whereas holes can oxidize both water and hydroxyl anions, resulting in hydroxyl radicals, HO. Furthermore, O2· can form hydroperoxyl radicals, HOO·, by protonation [34].
Mn3O4 + hv → Mn3O4 (e (CB) + h+) (VB)
H2O (ads) + h+ (VB) → OH (ads) + H+ (ads)
OH + h+→ HO
O2 + e (CB) → O2· (ads)
O2· (ads) + H+ → HOO· (ads)
HO/HOO/O2· + Pollutants → (Oxidized Intermediates) → CO2 + H2O
HO· + H+ + e→ H2O
2HOO·(ads) → H2O2+ O2
H2O2(ads) → 2OH (ads)
However, ‘scavenging’ reactions such as charge recombination might occur, thereby lowering the photocatalyst’s effectiveness.
For photocatalytic activity, the pH of the sample was optimized at seven. Figure 8a–c shows the UV–Vis absorbance curves with wavelength for different sample solutions of the Mn3O4/NiO nanocomposites. The maximum absorption peak is obtained at 657 nm with a full scan of the adsorption of MB dye. The graphs show how the absorbance intensity decreases with an increase in the irradiation time. The absorption intensity of MB dye drops progressively with an increase in irradiation time without a change in the wavelength of absorption. This shows that in the presence of the Mn3O4 photocatalyst, considerable dye removal occurs.
Figure 9a shows the kinetic study of the photocatalytic process, which indicates that the adsorption of MB dye increases linearly with an increase in time interval. Initially, the kinetic rate is very high as the time increases. Figure S6 shows the remaining concentration of dye with respect to time. Initially, there is a large number of unoccupied active sites, which decreases with the transition of time, and thus, a descending curve is obtained here. After a definite time interval, the reaction attains an equilibrium state. Figure 9b shows the percentage of dye removal for the three composites at regular intervals. As obvious from the curves in the graphs, the Mn3O4/NiO (3:1) NC shows the best photocatalytic activity, with 95% dye removal efficiency, whereas the Mn3O4/NiO (1:1) NC shows 91% and the Mn3O4/NiO (2:1) NC shows 92% dye removal efficiency [50].
As shown in Figure 10, the pseudo-first order (PFO) kinetic model is most suited to understand the photocatalysis process and the reaction rate during the process, as provided by the following equation:
l n C o C t = k a p p t
where ‘Co’ is the initial dye concentration prior to illumination; ‘Ct’ is the concentration of the dye after each time interval t; and kapp is the apparent rate of the photocatalytic reaction. In Figure 10, ‘qe’ and ‘qt’ represent the amount of dye adsorbed at equilibrium and at any time ‘t’.
Using the equation for the pseudo-first order reaction, the value of the rate constant was calculated to be 0.0014 min−1.
A comparative study of the photocatalytic degradation efficiency of the pure Mn3O4 NPs and Mn3O4/NiO NCs with different existing nanostructures is presented in Table 2. The pure Mn3O4 NPs have less degradation efficiency compared to the Mn3O4/NiO NCs [36]. It can be concluded that the Mn3O4/NiO NCs are a potential candidate for photodegradation of harmful pollutants in comparison to the sole Mn3O4 NPs and can also be used in other related environmental applications.

4. Conclusions

Manganese oxide (Mn3O4) and nickel oxide (NiO) NPs and their composites in three different ratios were synthesized using a solid-state reaction method. Using XRD, the successful and complete formation of Mn3O4 and NiO NPs at 450 °C was observed. The XRD data demonstrated that the material prepared at 450 °C had a larger crystallinity, which is why this sample was chosen for further processing. Using the Scherrer’s formula, the average crystallite size was calculated to be about 0.152 nm for Mn3O4 and 0.168 nm for NiO. The FTIR data further demonstrated the presence of respective functional groups in the synthesized sample. The UV–Vis spectroscopy was used to investigate the absorption spectrum of the Mn3O4 and NiO NPs and NC in the wavelength range from 200 to 800 nm. The calculated bandgap of the synthesized sample from the Tauc plot was 2.35 eV for Mn3O4 and 3.15 eV for NiO, which are very close to the results reported in the literature. Since the results from the adsorption studies were not very satisfactory, photocatalytic activity was opted for efficient dye removal. Several photocatalytic treatments using the composites of synthesized NPs were conducted to determine their efficiency at removing methylene blue dye from water. Methylene blue dye was photodegraded by exposing it to the synthesized NCs in the presence of UV and visible light. Some characteristics of dye degradation, such as concentration of the sample and contact duration, were assessed for their effect on dye disintegration. This study suggests that the prepared material could be effectively used as a photocatalyst for wastewater treatment and other related environmental applications.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/separations10030200/s1, Figure S1. Pictorial description of synthesis steps for Mn3O4 NPs; Figure S2. Pictorial description of synthesis steps for NiO NPs; Figure S3. Pictorial description of Mn3O4/NiO nanocomposite formation; Figure S4. Calibration curve of diluted stock solution; Figure S5. Adsorption capacity of MB dye Vs. time in dark; Figure S6. Remaining concentration of dye Vs. time in-terval; Table S1. XRD measurement of Mn3O4 NPs; Table S2. XRD measurement of NiO NPs; Table S3. XRD measurement of nanocomposite Mn3O4:NiO (1:1) and Table S4. XRD measurement of nanocomposite Mn3O4/NiO (3:1).

Author Contributions

Conceptualization, K.M., S.S.B., M.F. and A.D.C.; Methodology, K.M., S.M., M.A.B. and S.N.U.S.B.; Software, S.M. and A.D.C.; Validation, S.A.K. and M.F.; Formal analysis, S.M., M.A.B. and S.J.G.; Investigation, A.A.S., M.F. and S.N.U.S.B.; Resources, S.A.K., A.A.S., M.A.B. and M.N.B.J.; Data curation, S.A.K., M.F. and S.N.U.S.B.; Writing—original draft, K.M. and M.N.B.J.; Writing—review & editing, J.A., A.A.S., S.S.B. and S.J.G.; Supervision, J.A. and S.S.B.; Project administration, J.A., A.A.S., S.S.B., A.D.C. and S.J.G.; Funding acquisition, S.J.G. and M.N.B.J. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2023R108), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Data Availability Statement

Not Applicable.

Acknowledgments

This research project was supported by the Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2023R108), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Ibrahim, R.K.; Hayyan, M.; AlSaadi, M.A.; Hayyan, A.; Ibrahim, S. Environmental application of nanotechnology: Air, soil, and water. Environ. Sci. Pollut. Res. 2016, 23, 13754–13788. [Google Scholar] [CrossRef] [PubMed]
  2. Obey, G.; Adelaide, M.; Ramaraj, R. Biochar derived from non-customized matamba fruit shell as an adsorbent for wastewater treatment. J. Bioresour. Bioprod. 2022, 7, 109–115. [Google Scholar] [CrossRef]
  3. Linley, S.; Thomson, N.R. Environmental Applications of Nanotechnology: Nano-enabled Remediation Processes in Water, Soil and Air Treatment. Water Air Soil Pollut. 2021, 232, 1–50. [Google Scholar] [CrossRef]
  4. Tom, A.P. Nanotechnology for sustainable water treatment—A review. Mater. Today Proc. 2021. [Google Scholar] [CrossRef]
  5. Emmanuel, S.S.; Adesibikan, A.A.; Saliu, O.D. Phytogenically bioengineered metal nanoarchitecture for degradation of refractory dye water pollutants: A pragmatic minireview. Appl. Organomet. Chem. 2023, 37, e6946. [Google Scholar] [CrossRef]
  6. Morin, N.; Eric, C.; Guorui, L.; Balaram, V.; Rita, A.; Ribeiro, L. Worldwide cases of water pollution by emerging contaminants: A review. Environ. Chem. Lett. 2022, 20, 2311–2338. [Google Scholar] [CrossRef]
  7. Bhatti, M.A.; Shah, A.A.; Almani, K.F.; Tahira, A.; Chalangar, S.E.; dad Chandio, A.; Nur, O.; Willander, M.; Ibupoto, Z.H. Efficient photo catalysts based on silver doped ZnO nanorods for the photo degradation of methyl orange. Ceram. Int. 2019, 45, 23289–23297. [Google Scholar] [CrossRef]
  8. Jjagwe, J.; Olupot, P.W.; Menya, E.; Kalibbala, H.M. Synthesis and Application of Granular Activated Carbon from Biomass Waste Materials for Water Treatment: A Review. J. Bioresour. Bioprod. 2021, 6, 292–322. [Google Scholar] [CrossRef]
  9. Ziemba, C.; Larivé, O.; Reynaert, E.; Huisman, T.; Morgenroth, E. Linking transformations of organic carbon to post-treatment performance in a biological water recycling system. Sci. Total Environ. 2020, 721, 137489. [Google Scholar] [CrossRef]
  10. Gallareta-Olivares, G.; Rivas-Sanchez, A.; Cruz-Cruz, A.; Hussain, S.M.; González-González, R.B.; Cárdenas-Alcaide, M.F.; Iqbal, H.M.; Parra-Saldívar, R. Metal-doped carbon dots as robust nanomaterials for the monitoring and degradation of water pollutants. Chemosphere 2023, 312, 137190. [Google Scholar] [CrossRef]
  11. Jiang, S.; Yang, W. Template-Free Synthesis of Magnetic La-Mn-Fe Tri-Metal Oxide Nanofibers for Efficient Fluoride Remediation: Kinetics, Isotherms, Thermodynamics and Reusability. Polymers 2022, 14, 5417. [Google Scholar] [CrossRef] [PubMed]
  12. Wang, J.; Sun, Y.; Zhao, X.; Chen, L.; Peng, S.; Ma, C.; Duan, G.; Liu, Z.; Wang, H.; Yuan, Y.; et al. A poly (amidoxime)—Modified MOF macroporous membrane for high—Efficient uranium extraction from seawater. e-Polymers 2022, 22, 399–410. [Google Scholar] [CrossRef]
  13. Zhou, G.; Li, S.; Niu, C.; Wang, Q.; Zhang, X.; Meng, Q.; Li, L. Fir sawdust as a low—Cost and easily recyclable adsorbent: Efficient removal of Pb (II), Cu (II), and Zn (II) contaminants from wastewater. Environ. Sci. Pollut. Res. 2023, 1–15. [Google Scholar] [CrossRef]
  14. Liu, S.; Wang, M.; He, Y.; Cheng, Q.; Qian, T.; Yan, C. Covalent organic frameworks towards photocatalytic applications: Design principles, achievements, and opportunities. Coord. Chem. Rev. 2023, 475, 214882. [Google Scholar] [CrossRef]
  15. Bukhari, S.N.; Shah, A.A.; Bhatti, M.A.; Tahira, A.; Channa, I.A.; Shah, A.K.; Chandio, A.D.; Mahdi, W.A.; Alshehri, S.; Ibhupoto, Z.H.; et al. Psyllium-Husk-Assisted Synthesis of ZnO Microstructures with Improved Photocatalytic Properties for the Degradation of Methylene Blue (MB). Nanomaterials 2022, 12, 3568. [Google Scholar] [CrossRef] [PubMed]
  16. Ujjan, Z.A.; Bhatti, M.A.; Shah, A.A.; Tahira, A.; Shaikh, N.M.; Kumar, S.; Mugheri, A.Q.; Medany, S.S.; Nafady, A.; Alnjiman, F.; et al. Simultaneous doping of sulfur and chloride ions into ZnO nanorods for improved photocatalytic properties towards degradation of methylene blue. Ceram. Int. 2022, 48, 5535–5545. [Google Scholar] [CrossRef]
  17. Shah, A.A.; Bhatti, M.A.; Tahira, A.; Chandio, A.D.; Channa, I.A.; Sahito, A.G.; Chalangar, E.; Willander, M.; Nur, O.; Ibupoto, Z.H. Facile synthesis of copper doped ZnO nanorods for the efficient photo degradation of methylene blue and methyl orange. Ceram. Int. 2020, 46, 9997–10005. [Google Scholar] [CrossRef]
  18. Bhatti, M.A.; Almaani, K.F.; Shah, A.A.; Tahira, A.; Chandio, A.D.; Mugheri, A.Q.; Bhatti, A.L.; Waryani, B.; Medany, S.S.; Nafady, A.; et al. Low Temperature Aqueous Chemical Growth Method for the Doping of W into ZnO Nanostructures and Their Photocatalytic Role in the Degradration of Methylene Blue. J. Clust. Sci. 2022, 33, 1445–1456. [Google Scholar] [CrossRef]
  19. Ouyang, W.-T.; Xiao, F.; Ou, L.-J.; He, W.-M. Green Photocatalytic Syntheses Using Water as Solvent/Hydrogen Source/Oxygen Source. Curr. Opin. Green Sustain. Chem. 2023, 40, 100760. [Google Scholar] [CrossRef]
  20. Khan, S.; Hussain, A.; He, K.; Liu, B.; Imran, Z.; Ambreen, J.; Hassan, S.; Ahmad, M.; Batool, S.S.; Li, C. Tailoring the bandgap of Mn3O4 for visible light driven photocatalysis. J. Environ. Manag. 2021, 293, 112854. [Google Scholar] [CrossRef] [PubMed]
  21. Jian, S.; Tian, Z.; Zhang, K.; Duan, G.; Yang, W.; Jiang, S. Hydrothermal Synthesis of Ce-doped ZnO Heterojunction Supported on Carbon Nanofibers with High Visible Light Photocatalytic Activity. Chem. Res. Chin. Univ. 2021, 37, 565–570. [Google Scholar] [CrossRef]
  22. Nami, M.; Sheibani, S.; Rashchi, F. Photocatalytic performance of coupled semiconductor ZnO–CuO nanocomposite coating prepared by a facile brass anodization process. Mater. Sci. Semicond. Process. 2021, 135, 106083. [Google Scholar] [CrossRef]
  23. Shah, A.A.; Chandio, A.D.; Sheikh, A.A. Boron doped ZnO nanostructures for photo degradation of methylene blue, methyl orange and rhodamine B. J. Nanosci. Nanotechnol. 2021, 21, 2483–2494. [Google Scholar] [CrossRef] [PubMed]
  24. Bhatti, M.A.; Gilani, S.J.; Shah, A.A.; Channa, I.A.; Almani, K.F.; Chandio, A.D.; Halepoto, I.A.; Tahira, A.; Bin Jumah, M.N.; Ibupoto, Z.H. Effective removal of methylene blue by surface alteration of TiO2 with Ficus Carica leaf extract under visible light. Nanomaterials 2022, 12, 2766. [Google Scholar] [CrossRef] [PubMed]
  25. Osgouei, M.S.; Kamrani, N.; Fazli-Shokouhi, S.; Khatamian, M. Improved performance of Mn3O4-based nanocomposites in photocatalytic removal of methylene blue. J. Alloys Compd. 2022, 902, 163729. [Google Scholar] [CrossRef]
  26. Shaikh, B.; Bhatti, M.A.; Shah, A.A.; Tahira, A.; Shah, A.K.; Usto, A.; Aftab, U.; Bukhari, S.I.; Alshehri, S.; Shah Bukhari, S.N.U.; et al. Mn3O4 @ ZnO Hybrid Material: An Excellent Photocatalyst for the Degradation of Synthetic Dyes including Methylene Blue, Methyl Orange and Malachite Green. Nanomaterials 2022, 12, 3754. [Google Scholar] [CrossRef] [PubMed]
  27. Wu, S.; Lin, Y.; Hu, Y.H. Strategies of tuning catalysts for efficient photodegradation of antibiotics in water environments: A review. J. Mater. Chem. A 2021, 9, 2592–2611. [Google Scholar] [CrossRef]
  28. Tholkappiyan, R.; Naveen, A.N.; Vishista, K.; Hamed, F. Investigation on the electrochemical performance of hausmannite Mn3O4 nanoparticles by ultrasonic irradiation assisted co-precipitation method for supercapacitor electrodes. J. Taibah Univ. Sci. 2018, 12, 669–677. [Google Scholar] [CrossRef] [Green Version]
  29. Chen, R.; Yu, J.; Xiao, W. Hierarchically porous MnO2 microspheres with enhanced adsorption performance. J. Mater. Chem. A 2013, 1, 11682–11690. [Google Scholar] [CrossRef]
  30. Sukhdev, A.; Challa, M.; Narayani, L.; Manjunatha, A.S.; Deepthi, P.R.; Angadi, J.V.; Kumar, P.M.; Pasha, M. Synthesis, phase transformation, and morphology of hausmannite Mn3O4 nanoparticles: Photocatalytic and antibacterial investigations. Heliyon 2020, 6, e03245. [Google Scholar] [CrossRef] [Green Version]
  31. Mannaa, M.A.; Qasim, K.F.; Alshorifi, F.T.; El-Bahy, S.M.; Salama, R.S. Role of NiO Nanoparticles in Enhancing Structure Properties of TiO2 and Its Applications in Photodegradation and Hydrogen Evolution. ACS Omega 2021, 6, 30386–30400. [Google Scholar] [CrossRef]
  32. Kannan, K.; Radhika, D.; Nikolova, M.P.; Sadasivuni, K.K.; Mahdizadeh, H.; Verma, U. Structural studies of bio-mediated NiO nanoparticles for photocatalytic and antibacterial activities. Inorg. Chem. Commun. 2020, 113, 107755. [Google Scholar] [CrossRef]
  33. Kumar, V.P.; Pradeep, C.; Sha, M.M.R.; Radhakrishnan, P.; Mujeeb, A. Band-gap dependence of three-photon absorption in NiO nanoparticles synthesized at different calcination temperatures. Opt. Laser Technol. 2023, 158, 108809. [Google Scholar] [CrossRef]
  34. Bhat, S.A.; Zafar, F.; Mondal, A.H.; Kareem, A.; Mirza, A.U.; Khan, S.; Mohammad, A.; Haq, Q.M.R.; Nishat, N. Photocatalytic degradation of carcinogenic Congo red dye in aqueous solution, antioxidant activity and bactericidal effect of NiO nanoparticles. J. Iran. Chem. Soc. 2020, 17, 215–227. [Google Scholar] [CrossRef]
  35. Şahin, B.; Aydin, R.; Cetin, H. Tuning the morphological, structural, optical and dielectric properties of hausmannite (Mn3O4) films by doping heavy metal lead. Superlattices Microstruct. 2020, 143, 106546. [Google Scholar] [CrossRef]
  36. Ramezanpour, S.; Sheikhshoaie, I.; Khatamian, M. Synthesis, characterization and photocatalytic properties of V-doped Mn3O4 nanoparticles as a visible light-activated photocatalyst. J. Mol. Liq. 2017, 231, 64–71. [Google Scholar] [CrossRef]
  37. Koe, W.S.; Lee, J.W.; Chong, W.C.; Pang, Y.L.; Sim, L.C. An overview of photocatalytic degradation: Photocatalysts, mechanisms, and development of photocatalytic membrane. Environ. Sci. Pollut. Res. 2020, 27, 2522–2565. [Google Scholar] [CrossRef] [PubMed]
  38. Raj, B.G.S.; Asiri, A.M.; Wu, J.J.; Anandan, S. Synthesis of Mn3O4 nanoparticles via chemical precipitation approach for supercapacitor application. J. Alloys Compd. 2015, 636, 234–240. [Google Scholar] [CrossRef]
  39. Bonomo, M. Synthesis and characterization of NiO nanostructures: A review. J. Nanopart 2018, 20, 222. [Google Scholar] [CrossRef]
  40. Raj, R.A.; AlSalhi, M.S.; Devanesan, S. Microwave-assisted synthesis of nickel oxide nanoparticles using Coriandrum sativum leaf extract and their structural-magnetic catalytic properties. Materials 2017, 10, 460. [Google Scholar] [CrossRef] [Green Version]
  41. Zhang, Y.; Fu, F.; Li, Y.; Zhang, D.; Chen, Y. One-step synthesis of Ag@TiO2 nanoparticles for enhanced photocatalytic performance. Nanomaterials 2018, 8, 1032. [Google Scholar] [CrossRef] [Green Version]
  42. Ashraf, M.A.; Liu, Z.; Peng, W.X.; Jermsittiparsert, K.; Hosseinzadeh, G.; Hosseinzadeh, R. Combination of sonochemical and freeze-drying methods for synthesis of graphene/Ag-doped TiO2 nanocomposite: A strategy to boost the photocatalytic performance via well distribution of nanoparticles between graphene sheets. Ceram. Int. 2020, 46, 7446–7452. [Google Scholar] [CrossRef]
  43. Onkani, S.P.; Diagboya, P.N.; Mtunzi, F.M.; Klink, M.J.; Olu-Owolabi, B.I.; Pakade, V. Comparative study of the photocatalytic degradation of 2–chlorophenol under UV irradiation using pristine and Ag-doped species of TiO2, ZnO and ZnS photocatalysts. J. Environ. Manag. 2020, 260, 110145. [Google Scholar] [CrossRef] [PubMed]
  44. Khatri, A.; Rana, P.S. Visible light assisted photocatalysis of Methylene Blue and Rose Bengal dyes by iron doped NiO nanoparticles prepared via chemical co-precipitation. Phys. B Condens. Matter 2020, 579, 411905. [Google Scholar] [CrossRef]
  45. Jdidi, R.; Krifa, I.; Saadaoui, K.; Selma, H.B.; Krifa, H. Métastase méningée révélatrice d’un cancer du sein. Neurochirurgie 2020, 66, 325. [Google Scholar] [CrossRef]
  46. Li, N.; He, M.; Lu, X.; Liang, L.; Li, R.; Yan, B.; Chen, G. Enhanced norfloxacin degradation by visible-light-driven Mn3O4/γ-MnOOH photocatalysis under weak magnetic field. Sci. Total Environ. 2021, 761, 143268. [Google Scholar] [CrossRef] [PubMed]
  47. Shaik, M.R.; Syed, R.; Adil, S.F.; Kuniyil, M.; Khan, M.; Alqahtani, M.S.; Shaik, J.P.; Siddiqui, M.R.H.; Al-Warthan, A.; Sharaf, M.A.; et al. Mn3O4 nanoparticles: Synthesis, characterization and their antimicrobial and anticancer activity against A549 and MCF-7 cell lines. Saudi J. Biol. Sci. 2021, 28, 1196–1202. [Google Scholar] [CrossRef]
  48. Alagiri, M.; Ponnusamy, S.; Muthamizhchelvan, C. Synthesis and characterization of NiO nanoparticles by sol-gel method. J. Mater. Sci. Mater. Electron. 2012, 23, 728–732. [Google Scholar] [CrossRef]
  49. Shaik, D.P.M.D.; Rosaiah, P.; Hussain, O.M. Supercapacitive properties of Mn3O4 nanoparticles synthesized by hydrothermal method. Mater. Today Proc. 2016, 3, 64–73. [Google Scholar] [CrossRef]
  50. Ristig, S.; Cibura, N.; Strunk, J. Manganese Oxides in Heterogeneous (Photo)Catalysis: Possibilities and Challenges. Green 2015, 5, 23–41. [Google Scholar] [CrossRef]
Scheme 1. Schematic illustration of the experimental process for the synthesis of Mn3O4 NPs, NiO NPs, and Mn3O4/NiO NCs.
Scheme 1. Schematic illustration of the experimental process for the synthesis of Mn3O4 NPs, NiO NPs, and Mn3O4/NiO NCs.
Separations 10 00200 sch001
Figure 1. XRD spectra of the Mn3O4 NPs, the NiO NPs, and the Mn3O4/NiO NCs in different ratios.
Figure 1. XRD spectra of the Mn3O4 NPs, the NiO NPs, and the Mn3O4/NiO NCs in different ratios.
Separations 10 00200 g001
Figure 2. SEM images of (a) Mn3O4 NPs, (b) NiO NPs, (c) 1:1 Mn3O4/NiO NC, and (d) 3:1 Mn3O4/NiO NC.
Figure 2. SEM images of (a) Mn3O4 NPs, (b) NiO NPs, (c) 1:1 Mn3O4/NiO NC, and (d) 3:1 Mn3O4/NiO NC.
Separations 10 00200 g002
Figure 3. (a) EDX image of pure Mn3O4 NPs, (b) EDX image of pure NiO NPs, (c) EDX image of Mn3O4/NiO NC (1:1), and (d) EDX image of Mn3O4/NiO NC (3:1).
Figure 3. (a) EDX image of pure Mn3O4 NPs, (b) EDX image of pure NiO NPs, (c) EDX image of Mn3O4/NiO NC (1:1), and (d) EDX image of Mn3O4/NiO NC (3:1).
Separations 10 00200 g003
Figure 4. UV–Vis spectra of (a) Mn3O4 NPs, (b) NiO NPs, and (c) Mn3O4/NiO NC 1:1 with bandgap energy.
Figure 4. UV–Vis spectra of (a) Mn3O4 NPs, (b) NiO NPs, and (c) Mn3O4/NiO NC 1:1 with bandgap energy.
Separations 10 00200 g004
Figure 5. FTIR spectra of pure Mn3O4 NPs, NiO NPs, and Mn3O4/NiO NCs (1:1) and (3:1).
Figure 5. FTIR spectra of pure Mn3O4 NPs, NiO NPs, and Mn3O4/NiO NCs (1:1) and (3:1).
Separations 10 00200 g005
Figure 6. (a) Adsorption of MB dye in the presence of Mn3O4-based nanomaterials, and (b) kinetic study of the adsorption process in the dark.
Figure 6. (a) Adsorption of MB dye in the presence of Mn3O4-based nanomaterials, and (b) kinetic study of the adsorption process in the dark.
Separations 10 00200 g006
Figure 7. MB dye adsorption in the presence of the Mn3O4/NiO NC (a) at pH of 2, (b) at pH of 11, (c) at pH of 7.
Figure 7. MB dye adsorption in the presence of the Mn3O4/NiO NC (a) at pH of 2, (b) at pH of 11, (c) at pH of 7.
Separations 10 00200 g007
Figure 8. UV–Visible absorption spectra of the (a) NC Mn3O4/NiO (1:1), (b) NC Mn3O4/NiO (2:1), and (c) NC Mn3O4/NiO (3:1) under visible light at 657 nm.
Figure 8. UV–Visible absorption spectra of the (a) NC Mn3O4/NiO (1:1), (b) NC Mn3O4/NiO (2:1), and (c) NC Mn3O4/NiO (3:1) under visible light at 657 nm.
Separations 10 00200 g008
Figure 9. (a) Kinetic study of the photocatalytic process for the Mn3O4/NiO nanocomposites, and (b) dye removal percentage at different time intervals.
Figure 9. (a) Kinetic study of the photocatalytic process for the Mn3O4/NiO nanocomposites, and (b) dye removal percentage at different time intervals.
Separations 10 00200 g009
Figure 10. Pseudo-first order kinetic model for photocatalytic activity.
Figure 10. Pseudo-first order kinetic model for photocatalytic activity.
Separations 10 00200 g010
Table 1. Weight and atomic % of the Mn3O4 NPs, the NiO NPs, and the Mn3O4/NiO (1:1) and (3:1) NCs.
Table 1. Weight and atomic % of the Mn3O4 NPs, the NiO NPs, and the Mn3O4/NiO (1:1) and (3:1) NCs.
MaterialsElementWeight %Atomic %
Mn3O4 NPsO K19.144.7
Mn K80.955.3
NiO NPsO K23.146.0
Na K14.520.1
Ni K62.533.9
Mn3O4/NiO NC 1:1O K22.548.3
Na K5.27.8
Mn K37.523.5
Ni K34.820.4
Mn3O4/NiO NC 3:1O K27.650.7
Na K16.621.2
Mn K39. 121.5
Ni K16.76.6
Table 2. Comparative study of the photodegradation efficiency of the proposed catalysts against reported photocatalysts in the literature.
Table 2. Comparative study of the photodegradation efficiency of the proposed catalysts against reported photocatalysts in the literature.
CatalystStructure of CatalystDye DegradedDye Removal PercentRate Constant (min−1)References
Mn3O4NanoparticlesMethylene blue 68% (UV)0.003[36]
Ag-TiO2NanoparticlesMethyl orange 72.48% (UV)
48.08 (Visible)
0.00395[41]
Graphene/Ag/TiO2NanocompositeYellow 2-0.022[42]
Ce/ZnONanocompositeMethylene blue96%0.007[21]
Ag/ZnONanoparticlesChlorophenol57% (UV)-[43]
Fe-NiONanoparticlesMethylene blue85% (UV)0.031[44]
Ag/Mn3O4NanoparticlesCongo red 89% (UV + Visible)-[45]
Ag/Mn3O4NanoparticlesMethylene blue90% (Visible)0.024[20]
Mn3O4/γ-MnOOHNanocompositeNorfloxacin-0.0720[46]
Mn3O4/NiONanocompositeMethylene blue 95%0.0014 Present
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Majeed, K.; Ambreen, J.; Khan, S.A.; Muhammad, S.; Shah, A.A.; Bhatti, M.A.; Batool, S.S.; Farooq, M.; Shah Bukhari, S.N.U.; Chandio, A.D.; et al. Effective Removal of Methylene Blue by Mn3O4/NiO Nanocomposite under Visible Light. Separations 2023, 10, 200. https://doi.org/10.3390/separations10030200

AMA Style

Majeed K, Ambreen J, Khan SA, Muhammad S, Shah AA, Bhatti MA, Batool SS, Farooq M, Shah Bukhari SNU, Chandio AD, et al. Effective Removal of Methylene Blue by Mn3O4/NiO Nanocomposite under Visible Light. Separations. 2023; 10(3):200. https://doi.org/10.3390/separations10030200

Chicago/Turabian Style

Majeed, Komal, Jaweria Ambreen, Saeed Ahmed Khan, Saz Muhammad, Aqeel Ahmed Shah, Muhammad Ali Bhatti, Syeda Sitwat Batool, Muhammad Farooq, Syed Nizam Uddin Shah Bukhari, Ali Dad Chandio, and et al. 2023. "Effective Removal of Methylene Blue by Mn3O4/NiO Nanocomposite under Visible Light" Separations 10, no. 3: 200. https://doi.org/10.3390/separations10030200

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop