Journal of Nanotechnology
Volume 2021 (2021), Article ID 5581621, 12 pages
https://doi.org/10.1155/2021/5581621

Research Article

Microwave-Assisted Synthesis of CuO Nanoparticles Using Cordia africana Lam. Leaf Extract for 4-Nitrophenol Reduction

Aklilu Guale Bekru,¹ Osman Ahmed Zelekew,² Dinsefa Mensur Andoshe,² Fedlu Kedir Sabir,¹ and Rajalakshmanan Eswaramoorthy¹

¹Department of Applied Chemistry, Adama Science and Technology University, Adama, Ethiopia
²Department of Materials Science and Engineering, Adama Science and Technology University, Adama, Ethiopia

Correspondence should be addressed to Fedlu Kedir Sabir; fedluked130@gmail.com and Rajalakshmanan Eswaramoorthy; rajalakshmanan.e@gmail.com

Received 21 January 2021; Revised 9 March 2021; Accepted 17 March 2021; Published 30 March 2021

Academic Editor: Brajesh Kumar

Copyright © 2021 Aklilu Guale Bekru et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Copper-oxide-based nanomaterials play an important role as a low-cost alternative to nanoparticles of precious metals for the catalytic reduction of 4-nitrophenols. In this study, CuO nanoparticles were synthesized by a microwave-assisted method using Cordia africana Lam. leaf extract for reduction or stabilization processes. The synthesized CuO nanoparticles (NPs) were characterized using X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The analysis indicated that nanocrystals of the monoclinic CuO phase having a cluster of agglomerated morphology with a crystallite size of about 9 nm were synthesized. We also evaluated the catalytic performance of CuO NPs against 4-nitrophenol (4-NP) reduction. The catalyst has shown excellent performance completing the reaction within 12 min. Furthermore, the performance of CuO NPs synthesized at different pH values was investigated, and results indicated that the one synthesized at pH 7 reduced 4-NP effectively in shorter minutes compared to those obtained at higher pH values. The CuO NPs synthesized using Cordia africana Lam. leaf extract exhibited a better reducing capacity with an activity parameter constant of 75.8 min⁻¹·g⁻¹. Thus, CuO synthesized using Cordia africana Lam. holds a potential application for the catalytic conversion of nitroarene compounds into aminoarene.

1. Introduction

Water is an essential component responsible for the survival of life on Earth [1]. These days, pollution of water has become one of the challenges people are facing because of the continuous rise in the organic, inorganic, and biological pollutants which have industrial and domestic sources [2, 3]. Organic pollutants such as pesticides, synthetic dyes, phenols, and aromatic hydrocarbons are among the major causes of water pollution [4–8]. Among organic water pollutants, 4-nitrophenol (4-NP) and its derivatives have been listed as toxic pollutants by the US Environmental Protection Agency (EPA) [9]. It is known that 4-NP has versatile applications in pesticides, fungicidal agents, dyes, drugs, and leather manufacturing industries as raw materials [10]. 4-NP and its derivatives possess high solubility and stability in aqueous media [9] and pose serious human health complications [2, 3, 11]. Therefore, it is of crucial significance to remove effectively or transform these pollutants into chemicals with low toxicity level.

Over the past decades, a considerable amount of methods have been utilized for the removal of 4-NP pollutant from water including adsorption [12], emulsion liquid membrane [13], bioremediation [14], micellar-enhanced ultrafiltration [15], reverse osmosis [16], photocatalysis [17], catalytic reduction [18], and others [19, 20]. However, the method that is ecofriendly, cost-effective, and efficient is still the biggest challenge that researchers are trying to achieve. While 4-NP is a toxic nitroaromatic compound, its reduced form 4-aminophenol has a low toxicity level and has application in a variety of industries for the synthesis of drugs, dyes, and others. Therefore, the use of catalysts to transform nitroaromatic compounds into economically valuable and less toxic chemicals is highly desirable, and it is a growing area of investigation for environmental remediation.

Owing to their distinctive properties, nanostructured catalysts of metals (Pd, Pt, Ag, and Au) provide a sustainable way in the transformation of organic compounds in an environmentally benign manner in an aqueous medium [21–23]. However, the high cost and high chance of agglomeration of the bare metallic nanoparticles during reactions are serious problems that limited their large-scale application as a catalyst. Coupling metallic NPs with suitable support material is one of the mechanisms employed to overcome limitations due to agglomeration. Several reports pointed out that the dispersibility and stability of metallic nanostructured materials could be improved by coupling metallic NPs with support materials such as graphene [24], bentonite [25], sodium borosilicate [11], graphene oxide/manganese dioxide nanocomposite [26], and magnetic biodegradable microcapsules [27]. Recently, there are increasing interest in using nonnoble metal oxide semiconductor catalysts as a low-cost alternative to the precious-metal-based catalysts for the reduction of 4-NP [28]. Among metal oxides, CuO NPs catalysts have attracted significant attention in the field of catalysis due to the advantages of low cost, versatility, distinct acid-base properties, and redox properties. CuO NPs have applications in photocatalysis [29], as an antimicrobial [30], in biomedical industry [31], as a gas sensor [32], as solar cells [33], and as batteries [34]. Reports have shown that CuO NPs have the capacity of catalyzing the reduction of 4-NP [35–38].

CuO nanostructure materials can be synthesized using physical, chemical, and biological methods including flame spray pyrolysis and spin-coating processing [39], hydrothermal [34], microwave-assisted [40], solution combustion [41], precipitation [42], biosynthesis [43], and others. Microwave- (MW-) based techniques as a heating source have advantages of faster rate of reaction, higher reproducibility, better product purity, higher yields, and scalability compared to conventional heating processes [44, 45]. Varieties of CuO nanostructures such as nanosheet [32], nanodiscs [46], nanoflower [32], colloidal [29], and others [40, 47] have been synthesized using MW-assisted methods. In addition to simple and scalable techniques of synthesizing nanostructures, it is desirable to comply with the principles of green chemistry, which requires the use of methods that promote minimum energy consumption, use of low-cost and ecofriendly reagents, and none or minimum waste generation [48]. In this regard, plant extracts are promising alternatives to the harsh chemicals for reduction and stabilization processes [49]. The resulting nanostructured materials are usually ecofriendly, less expensive, and less susceptible to chemical contaminants [31, 50]. Among the various types of nanostructured materials synthesized using plant extracts are metallic [51, 52], metallic-based composites [8, 11, 53–56], metal oxides [57, 58], and metal oxide nanocomposites [59]. CuO NPs have been synthesized using biomolecules of various plants such as Gloriosa superba L. [47], Sapindus mukorossi [60], Murayya koeniggi [37], Sambucus nigra L. [43], Aloe Vera [61], Cynodon dactylon and Cyperus rotundus [62], Catha edulis Forsk [30], Moringa oleifera and Punica grantum [63], Anthemis nobilis [57], and Tamarix gallica [58]. However, synthesis of CuO NPs with the support of Cordia africana Lam. for 4-NP has not been reported elsewhere to the best of our knowledge. According to the literature data, the aqueous extract of Cordia africana Lam. leaf contains phytochemicals with strong reducing power like polyphenols and tannins [64].

Herein, we report the synthesis of CuO NPs employing an effective, low-cost, facile, and fast MW-assisted method using an aqueous extract of Cordia africana Lam. leaf, NaOH, and copper (II) acetate for catalytic reduction of 4-NP. The resulting catalyst was characterized by XRD, FTIR, and SEM techniques. The catalytic performance of CuO NPs was also evaluated against 4-nitrophenol reduction in the presence of NaBH₄ in aqueous media. Besides, the performance of the catalyst synthesized at different pH values was demonstrated.

2. Experimental

2.1. Materials

All of the chemical reagents were of analytic grade: cupric acetate (Cu(CH₃COO)₂. H₂O) (UNI-CHEM, 99%) and sodium hydroxide (NaOH) (Loba, 98%). The leaves of Cordia africana Lam. were collected from the Adama Science and Technology University campus and its surroundings, Adama, Ethiopia. Deionized water (DW) was used throughout the experiment.

2.2. Extract Preparation

The leaves of Cordia africana Lam. were washed thoroughly several times with tap water and DW sequentially to remove dust particles attached to the surface of the plant and then allowed to air dry. Then, the dried leaves were powdered using a grinder. 20 g leaf powder and 200 mL DW were mixed in a 1000 mL conical flask and stirred for 20 min. Then, the mixture was heated up to the boiling point and allowed to boil for 10 min under stirring. After cooling to room temperature, it was stirring continued for 20 min and then filtered to obtain an extract using Whatman filter paper. The resulting extract was stored at about 4°C for further use.

2.3. CuO Synthesis

CuO NPs were prepared by the MW-assisted modified method using Cu(CH₃COO)₂.H₂O and Cordia africana Lam. leaf extract [40]. In a typical procedure, 6.2 g Cu(CH₃COO)₂.H₂O was added to a 1000 mL beaker containing 100 mL DW and then stirred for 20 min. Then, 10 mL of the extract was added to the Cu(CH₃COO)₂.H₂O solution under stirring. To adjust the pH, NaOH aqueous solution was added drop wise while stirring. After 20 min of stirring, the mixture was placed into a domestic microwave (MW) oven with a maximum power of 1000 W, and only 50% power output was used for 9 min. The brown precipitates were collected and washed with DW and ethanol sequentially. Finally, the residue was dried at 80°C for 12 h and then at 100°C for 2 h. The dried powder was powdered using a mortar and pestle. The flow chart of the synthesis of the CuO NPs is shown in Scheme 1.

Scheme 1: Flow chart for CuO NPs synthesis by the MW method.

2.4. Characterization

The crystal structure characterization and phase analysis studies of the as-prepared samples were realized by XRD (Shimadzu XRD-7000) with Cu Kα radiation (λ = 1.5406 Å) sources. FTIR spectra of the samples were recorded on a Spectrum 65 FT-IR (PerkinElmer) with a spectral resolution of 4 cm⁻¹ in the range 4000–400 cm⁻¹ using KBr pellets. The surface morphology and composition of the synthesized sample were characterized by SEM-EDX (COXIEM-30).

2.5. Performance Tests

In order to evaluate the catalytic performance of the CuO NPs, a 4-NP reduction reaction was conducted. Typically, 20 mg NaBH₄ and 100 mL 4-NP (20 ppm) aqueous solutions were transferred to a conical flask. After 2 min shaking, 5 mg of the catalyst was added to the NaBH₄ and 4-NP mixture. The progress of the 4-NP reduction was monitored by using a UV-vis spectrophotometer (SM-1600) at a wavelength around 400 nm at room temperature. From the resulting mixture, 3 mL was taken out every 3 min and transferred to the cuvette for the absorbance measurement. The kinetic analysis was conducted using equations (1) and (2).

For Co and Ct corresponding to the concentration of 4-NP at time 0 and t, respectively,

where Ao and At corresponds to the absorbance of Co and Ct.

3. Results and Discussion

3.1. XRD Analysis of CuO Nanoparticles

To investigate the crystallinity and phase of the synthesized material, the XRD technique was used. The XRD pattern of the CuO NPs obtained using Cordia africana Lam. leaf extract is displayed in Figure 1. The noticeable peaks positioned at 2θ values of 32.44°, 35.46°, 38.68°,48.7°, 53.50°, 58.0°, 61.49°, 66.14°, 67.86°, 72.38°, and 74.89° correspond to (110), (002), (111), (20–2), (020), (202), (11–3), (31–1), (113), (311), and (004) crystal planes, respectively. These values agree with the monoclinic CuO phase (JCPDS Card number 48–1548, C2/c space group). The absence of peaks matching to Cu(OH)₂ and Cu₂O in the pattern with the appearance of all peaks corresponding to the monoclinic CuO phase signifies the formation of pure crystalline CuO by MW-assisted synthesis method. The crystallite size of the sample was calculated using the Scherrer equation:

where D = crystallite size, λ = the wavelength of the X-ray source applied, β = the width of the peak at half of its height (FWHM), θ = the Bragg angle, and k = the shape constant ≈ 0.9. The average crystallite size of the CuO NPs calculated for the highest peaks at 35.46° and 38.68° was around 9 nm. The resolved sharp peaks with the crystallite size of about 9 nm suggest the formation of the nanocrystalline CuO [65].

Figure 1: XRD pattern of the as-synthesized CuO NPs using Cordia africana Lam. leaf extract.

3.2. FTIR Analysis

The FTIR spectra of the aqueous extract of Cordia africana Lam. leaf and the CuO NPs synthesized using Cordia africana Lam. leaf extract are shown in Figure 2. Several characteristic bands were shown in the spectra of both the Cordia africana Lam. leaf extract (Figure 2(a)) and CuO NPs synthesized using the extract (Figure 2(b)). In both spectra (Figures 2(a) and 2(b)), the bands at 3400 and 2920 cm⁻¹ correspond to the O–H and C-H functional groups stretching vibrational frequencies, respectively. Similarly, the bands at 1603 and 1300 to 1000 cm⁻¹ (Figure 2(a)) belong to the stretching vibrations of the C=C aromatic ring and C–OH [58]. The sharp peaks that appeared at 1555 and 1393 cm⁻¹ (Figure 2(b)) could be attributed to the carboxylate C-O stretching vibrations (asymmetric and symmetric). The bands arising due to the vibrational frequencies of the metal-oxygen (M–O) bond generally appear in the region below 1000 cm⁻¹. Hence, the peaks positioned at 497 and 591 cm⁻¹ belong to characteristic vibrations of Cu–O bond, revealing CuO NPs formation [66]. No infrared active modes from Cu₂O were detected, indicating that, under the conditions stated in the synthesis method, only the CuO phase was selectively produced. A comparison of the extract spectrum with that of CuO NPs shows that the molecules of the extract are found adsorbed on the surface of the CuO NPs. Furthermore, the FTIR results indicate the formation of the CuO phase supporting the XRD result.

Figure 2: FTIR spectrum of (a) leaf extract of Cordia africana Lam. of and (b) as-synthesized CuO NPs.

3.3. Morphology Analysis

Figures 3(a) and 3(b) show the surface analysis of the SEM image of the sample with different magnifications. The SEM image reveals that the CuO nanostructure synthesized using Cordia africana Lam. leaf extract by the MW-assisted method exhibits a uniformly distributed cluster of agglomerated morphology. The image taken at high magnification (1 µm) shows that some particles having spherical-shaped morphology are found separated from the agglomerated clusters. Figure 3(c) demonstrates the energy-dispersive spectroscopy (EDS) analysis of the sample obtained at 20.0 kV HV accelerating voltage. The EDS spectrum of the sample confirmed that the sample is composed of Cu and O elements. Thus, the biomolecules of the extract have taken part in the formation of CuO NPs.

(a)

(b)

(c)

Figure 3: SEM images and of CuO NPs synthesized with Cordia africana Lam. leaf extract with low magnification (a) and high magnification (b); (c) EDS spectrum.

3.4. Catalytic Reduction Reaction

The performance of the as-synthesized CuO NPs as a catalyst was evaluated against 4-NP reduction in the presence of NaBH₄ as a reducing agent. Figure 4 shows the reduction of 4-NP into 4-aminophenol. The UV-vis absorbance of p-NP in the absence of NaBH₄ displayed a peak at around 320 nm. However, the peak at 320 nm disappeared, and a new intense peak at around 400 nm appeared when NaBH₄ was added to the p-NP solution. In alkaline media, a light yellowish p-NP solution changes to an intense yellowish-orange p-nitrophenolate ion with absorbance at around 400 nm (Figure 4(a)). The intense initial spectrum was the UV-vis absorbance of the mixture of p-NP and NaBH₄ without catalysts.

(a)

(b)

(c)

(d)

(e)

Figure 4: (a) Absorption spectra of 4-NP before and after the addition of aqueous NaBH₄ solution, (b) reduction of 4-NP with NaBH₄ but without a catalyst, (c) reduction of 4-NP with CuO but without NaBH4, (d) reduction of 4-NP with NaBH₄ in the presence of a CuO catalyst, and (e) plots of Ct/C₀) versus reaction time (min) for the reduction of 4-NP with and without a CuO catalyst and NBH₄.

After catalyst addition, the peak at 405 nm was gradually decreasing while the new peak at around 300 nm started growing, representing the conversion of the p-nitrophenolate ion into p-aminophenol, as indicated in Scheme 2 and Figure 4(d). The time taken for the complete conversion of 4-NP was measured based on the disappearance of the absorbance peak at around 400 nm in the presence of the CuO catalyst. It took less than 12 min for the complete conversion of 4-NP into aminophenols when the CuO catalyst was used, while no change was observed in the absence of the catalyst (Figure 4(e)). The pH at which the CuO NPs were synthesized has a significant influence on the reducing capability of the resulting CuO catalysts. As depicted in Figure 5, CuO NPs synthesized at pH 7 performed better than those synthesized at higher pH values. The difference in performance could be due to the variation in morphology of the resulting CuO nanostructures, which significantly affects the rate of the 4-NP catalytic reduction reaction [35].

Scheme 2: Catalytic reduction reaction of 4-NP into 4-aminophenol using CuO NPs [18].

(a)

(b)

(c)

(d)

(e)

Figure 5: Reduction of 4-NP using CuO nanostructures synthesized at different pH values: (a) pH = 12, (b) pH = 10, (c) pH = 7, (d) plots of Ct/C₀ versus reaction time (min), and (e) plots of ln(Ct/C₀) versus reaction time (min).

The kinetics of the 4-NP reduction reaction in the presence of the CuO catalyst synthesized at different pH values is shown in Figure 5(e). Since the concentration of NaBH₄ is much higher than that of 4-NP, the analysis was conducted using the concentration of 4-NP alone [67]. The kinetic analysis results indicated that the data best fit with pseudo-first-order equation (equation (1)). The apparent rate constant (kapp) of the reaction can be obtained from the slop of a plot ln(Ct/Co) vs t. Figure 5(e) shows that the rate of catalytic reduction reaction of 4-NP is the highest for the CuO catalyst synthesized at pH 7 using Cordia africana Lam. leaf extract.

There are different catalytic mechanisms proposed for the reduction reaction of nitroarene compounds into aminoarene. Generally, the mechanism of 4-NP reduction by NaBH₄ using metal-oxide-based catalysts involves transfer of electrons and hydrogen, adsorption and desorption steps [68, 69]. The mixture of NaBH₄ and 4-NP in an aqueous medium produces 4-nitrophenolate and ions. provides both hydrogen and electrons [70]. Besides, in an aqueous environment, water serves as an additional source of hydrogen. Both and 4-nitrophenolate ions adsorb onto the surface of the catalyst. Then, the catalysts assist the transfer of electrons/hydrogen from the ions to the NO₂ group of the 4-nitrophenolate to produce 4-aminophenolate ions. Finally, the 4-nitrophenolate ions desorb from the catalyst surface. The major steps in the catalytic reduction of 4-NP using CuO nanoparticles are shown in Scheme 2.

The catalytic performance of the present nanocatalyst is compared with previously reported CuO-based nanocatalysts for the 4-NP reduction under different the reaction conditions (Table 1). The results indicated that the CuO NPs synthesized using Cordia africana Lam. leaf extract exhibited a better reducing capacity with an activity parameters constant of 75.8 min⁻¹·g⁻¹. This value is higher than that reported for CuO nanoleaves, CuO@C, and CuO/ZnO/Eggshell nanocomposites [71, 74, 75].

Table 1: Comparison of the catalytic activity of CuO NPs with the previously reported CuO-based catalysts for the reduction of 4-NP.

Catalyst
4-NP (x10⁻³ mmol)
NaBH₄ (x10⁻³ mmol)
Catalyst amount (mg)
Time (min)
Rate constant, kapp (min⁻¹)
Ratio constant K, (min⁻¹·g⁻¹)
Ref

CuO nanoleaves
0.36
30
1
15
0.022
22
[71]

CuO flowers
0.25
50
2
4
0.565
282.5
[72]

Pd/CuO NPs
62.5
6250
7
1
3.3
471
[73]

CuO@C
100
2250
50
18
0.36
7.2
[74]

CuO/ZnO/Eggshell
2
1320
20
30
0.2037
6.79
[75]

CuO/Cu₂O nanowires
0.25
50
0.1
4
0.5014
125.35
[76]

CuO NPs
14.38
528
5
12
0.379
75.8
Present work

4. Conclusions

CuO Nps were successfully synthesized using the aqueous extract of Cordia africana Lam. leaf following the MW-assisted method. The XRD result revealed the formation of a monoclinic CuO phase with an average crystallite size of 9 nm. The FTIR spectra confirmed the formation of CuO, NPs supporting the XRD result. Similarly, the EDS spectrum revealed that the synthesized material is composed of Cu and O elements. The SEM micrograph indicated that the obtained CuO NPs were found as agglomerated clusters of spherical-shaped morphology. The resulting NPs showed high catalytic efficiency with a catalyst loading of 5 mg in 12 min towards the reduction of 4-NP. CuO NPs synthesized at pH 7 showed strong catalytic activities compared to those synthesized at pH values 10 and 12. Thus, the CuO NPs synthesized using Cordia africana Lam. leaf extract showed great promise as a potential candidate for the reduction of other nitroarenes and dyes.

Data Availability

The [Excel] data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Authors’ Contributions

Aklilu Guale Bekru conducted the study and wrote the first draft, and the supervision and editing were carried out by Prof. Rajalakshmanan Eswaramoorthy. The co-authors Osman Ahmed Zelekew, Dinsefa Mensur Andoshe, and Fedlu Kedir Sabir participated in analyzing the results and drafting the manuscript.

Acknowledgments

The authors are thankful to Adama Science and Technology University, Adama, Ethiopia, and Wachemo University, Hossana, Ethiopia, for financially supporting of this study.

References

F. Westall and A. Brack, “The importance of water for life,” Space Science Reviews, vol. 214, p. 50, 2018.

P. K. Boruah, P. Borthakur, and M. R. Das, Magnetic Metal/metal Oxide Nanoparticles and Nanocomposite Materials for Water Purification, in Nanoscale Materials in Water Purification, Elsevier, Amsterdam, Netherlands, 2018.

S. Ramanathan, S. P. Selvin, A. Obadiah et al., “Synthesis of reduced graphene oxide/ZnO nanocomposites using grape fruit extract and Eichhornia crassipes leaf extract and a comparative study of their photocatalytic property in degrading Rhodamine B dye,” Journal of Environmental Health Science and Engineering, vol. 17, no. 1, pp. 195–207, 2019.

K. Zhang, J. M. Suh, J.-W. Choi, H. W. Jang, M. Shokouhimehr, and R. S. Varma, “Recent advances in the nanocatalyst-assisted NaBH₄ reduction of nitroaromatics in water,” ACS Omega, vol. 4, no. 1, pp. 483–495, 2019.

B. M. Teklu, A. Hailu, D. A. Wiegant, B. S. Scholten, and P. J. Van den Brink, “Impacts of nutrients and pesticides from small- and large-scale agriculture on the water quality of Lake Ziway, Ethiopia,” Environmental Science and Pollution Research, vol. 25, no. 14, pp. 13207–13216, 2018.

F. M. Drumond Chequer, G. A. R. de Oliveira, E. R. Anastacio Ferraz, J. Carvalho, M. V. Boldrin Zanoni, and D. P. de Oliveir, Textile Dyes: Dyeing Process and Environmental Impact, in Eco-Friendly Textile Dyeing and Finishing, InTech, Rijeka, Croatia, 2013.

H. Zeghioud, N. Khellaf, H. Djelal, A. Amrane, and M. Bouhelassa, “Photocatalytic reactors dedicated to the degradation of hazardous organic pollutants: kinetics, mechanistic aspects, and design - a review,” Chemical Engineering Communications, vol. 203, no. 11, pp. 1415–1431, 2016.

B. Khodadadi, M. Bordbar, and M. Nasrollahzadeh, “Achillea millefolium L. extract mediated green synthesis of waste peach kernel shell supported silver nanoparticles: application of the nanoparticles for catalytic reduction of a variety of dyes in water,” Journal of Colloid and Interface Science, vol. 493, pp. 85–93, 2017.

W. Pan, G. Zhang, T. Zheng, and P. Wang, “Degradation of p-nitrophenol using CuO/Al2O3 as a Fenton-like catalyst under microwave irradiation,” RSC Advances, vol. 5, no. 34, pp. 27043–27051, 2015.

M. Abdollahi and A. Mohammadirad, Nitrophenol 4- in Encyclopedia of Toxicology, Elsevier, Amsterdam, Netherlands, 3rd edition, 2014.

M. Nasrollahzadeh, M. Sajjadi, M. Maham, S. M. Sajadi, and A. A. Barzinjy, “Biosynthesis of the palladium/sodium borosilicate nanocomposite using euphorbia milii extract and evaluation of its catalytic activity in the reduction of chromium (VI), nitro compounds and organic dyes,” Materials Research Bulletin, vol. 102, pp. 24–35, 2018.

Y.-X. Yao, H.-B. Li, J.-Y. Liu, X.-L. Tan, J.-G. Yu, and Z.-G. Peng, “Removal and adsorption of p-nitrophenol from aqueous solutions using carbon nanotubes and their composites,” Journal of Nanomaterials, vol. 2014, pp. 1–9, 2014.

Q. Al-Obaidi, M. Alabdulmuhsin, A. Tolstik, J. G. Trautman, and M. Al-Dahhan, “Removal of hydrocarbons of 4-nitrophenol by emulsion liquid membrane (ELM) using magnetic Fe₂O₃ nanoparticles and ionic liquid,” Journal of Water Process Engineering, vol. 39, Article ID 101729, 2021.

M. S. Samuel, A. Sivaramakrishna, and A. Mehta, “Bioremediation of p-nitrophenol by Pseudomonas putida 1274 strain,” Journal of Environmental Health Science and Engineering, vol. 12, p. 53, 2014.

A. Ankita, “A brief review of micellar enhanced ultrafiltration (MEUF) techniques for treatment of wastewater in India,” Journal of Water Resource Engineering and Management, vol. 1, pp. 14–30, 2020.

A. M. Hidalgo, G. León, M. Gómez, M. D. Murcia, E. Gómez, and C. Giner, “Behaviour of RO90 membrane on the removal of 4-nitrophenol and 4-nitroaniline by low pressure reverse osmosis,” Journal of Water Process Engineering, vol. 7, pp. 169–175, 2015.

Y. Zhang, Y. Kuwahara, K. Mori, and H. Yamashita, “Construction of hybrid MoS2 phase coupled with SiC heterojunctions with promoted photocatalytic activity for 4-nitrophenol degradation,” Langmuir, vol. 36, no. 5, pp. 1174–1182, 2020.

H. Sun, O. A. Zelekew, X. Chen et al., “A noble bimetal oxysulfide CuVOS catalyst for highly efficient catalytic reduction of 4-nitrophenol and organic dyes,” RSC Advances, vol. 9, no. 55, pp. 31828–31839, 2019.

T. Liu, N. Chen, Y. Deng, F. Chen, and C. Feng, “Degradation of p-nitrophenol by nano-pyrite catalyzed Fenton reaction with enhanced peroxide utilization,” RSC Advances, vol. 10, no. 27, pp. 15901–15912, 2020.

J.-P. Zou, Y. Chen, S.-S. Liu et al., “Electrochemical oxidation and advanced oxidation processes using a 3D hexagonal Co₃O₄ array anode for 4-nitrophenol decomposition coupled with simultaneous CO₂ conversion to liquid fuels via a flower-like CuO cathode,” Water Research, vol. 150, pp. 330–339, 2019.

C. Gadipelly and L. K. Mannepalli, “Nano-metal oxides for organic transformations,” Current Opinion in Green and Sustainable Chemistry, vol. 15, pp. 20–26, 2019.

M. F. Salas Orozco, N. Niño-Martínez, G. A. Martínez-Castañón, F. T. Méndez, and F. Ruiz, “Molecular mechanisms of bacterial resistance to metal and metal oxide nanoparticles,” International Journal of Molecular Sciences, vol. 20, p. 2808, 2019.

M. Nasrollahzadeh, N. Shafiei, M. Eslamipanah et al., “Preparation of Au nanoparticles by Q switched laser ablation and their application in 4-nitrophenol reduction,” Clean Technologies and Environmental Policy, vol. 22, no. 8, pp. 1715–1724, 2020.

M. Nasrollahzadeh, Z. Nezafat, M. G. Gorab, and M. Sajjadi, “Recent progresses in graphene-based (photo)catalysts for reduction of nitro compounds,” Molecular Catalysis, vol. 484, Article ID 110758, 2020.

M. Nasrollahzadeh, S. M. Sajadi, M. Maham, and I. Kohsari, “Biosynthesis, characterization and catalytic activity of the Pd/bentonite nanocomposite for base- and ligand-free oxidative hydroxylation of phenylboronic acid and reduction of chromium (VI) and nitro compounds,” Microporous and Mesoporous Materials, vol. 271, pp. 128–137, 2018.

S. Naghdi, M. Sajjadi, M. Nasrollahzadeh, K. Y. Rhee, S. M. Sajadi, and B. Jaleh, “Cuscuta reflexa leaf extract mediated green synthesis of the Cu nanoparticles on graphene oxide/manganese dioxide nanocomposite and its catalytic activity toward reduction of nitroarenes and organic dyes,” Journal of the Taiwan Institute of Chemical Engineers, vol. 86, pp. 158–173, 2018.

T. Baran and M. Nasrollahzadeh, “Facile synthesis of palladium nanoparticles immobilized on magnetic biodegradable microcapsules used as effective and recyclable catalyst in Suzuki-Miyaura reaction and p-nitrophenol reduction,” Carbohydrate Polymers, vol. 222, Article ID 115029, 2019.

G. Wu, X. Liang, L. Zhang et al., “Fabrication of highly stable metal oxide hollow nanospheres and their catalytic activity toward 4-nitrophenol reduction,” ACS Applied Materials & Interfaces, vol. 9, no. 21, pp. 18207–18214, 2017.

S. V. Kumar, A. P. Bafana, P. Pawar et al., “Optimized production of antibacterial copper oxide nanoparticles in a microwave-assisted synthesis reaction using response surface methodology,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 573, pp. 170–178, 2019.

K. Gebremedhn, M. Hagos Kahsay, and M. Aklilu, “Green synthesis of cuo nanoparticles using leaf extract of catha edulis and its antibacterial activity,” Journal of Pharmacy and Pharmacology, vol. 7, pp. 327–342, 2019.

M. Grigore, E. Biscu, A. Holban, M. Gestal, and A. Grumezescu, “Methods of synthesis, properties and biomedical applications of CuO nanoparticles,” Pharmaceuticals, vol. 9, no. 4, p. 75, 2016.

C. Yang, F. Xiao, J. Wang, and X. Su, “3D flower- and 2D sheet-like CuO nanostructures: microwave-assisted synthesis and application in gas sensors,” Sensors and Actuators B: Chemical, vol. 207, pp. 177–185, 2015.

J. K. Sharma, M. S. Akhtar, S. Ameen, P. Srivastava, and G. Singh, “Green synthesis of CuO nanoparticles with leaf extract of calotropis gigantea and its dye-sensitized solar cells applications,” Journal of Alloys and Compounds, vol. 632, pp. 321–325, 2015.

P. C. Rath, J. Patra, D. Saikia et al., “Comparative study on the morphology-dependent performance of various CuO nanostructures as anode materials for sodium-ion batteries,” ACS Sustainable Chemistry & Engineering, vol. 6, no. 8, pp. 10876–10885, 2018.

W. Che, Y. Ni, Y. Zhang, and Y. Ma, “Morphology-controllable synthesis of CuO nanostructures and their catalytic activity for the reduction of 4-nitrophenol,” Journal of Physics and Chemistry of Solids, vol. 77, pp. 1–7, 2015.

K. Sahu, J. Singh, and S. Mohapatra, “Catalytic reduction of 4-nitrophenol and photocatalytic degradation of organic pollutants in water by copper oxide nanosheets,” Optical Materials, vol. 93, pp. 58–69, 2019.

M. Shamsuddin and N. Raja Nordin, “Biosynthesis of copper (II) oxide nanoparticles using Murayya koeniggi aqueous leaf extract and its catalytic activity in 4-nitrophenol reduction,” Malaysian Journal of Fundamental and Applied Sciences, vol. 15, no. 2, pp. 218–224, 2019.

R. Chowdhury, A. Khan, and M. H. Rashid, “Green synthesis of CuO nanoparticles using Lantana camara flower extract and their potential catalytic activity towards the aza-Michael reaction,” RSC Advances, vol. 10, no. 24, pp. 14374–14385, 2020.

C.-Y. Chiang, K. Aroh, and S. H. Ehrman, “Copper oxide nanoparticle made by flame spray pyrolysis for photoelectrochemical water splitting-part I. CuO nanoparticle preparation,” International Journal of Hydrogen Energy, vol. 37, no. 6, pp. 4871–4879, 2012.

N. M. Shaalan, M. Rashad, and M. A. Abdel-Rahim, “CuO nanoparticles synthesized by microwave-assisted method for methane sensing,” Optical and Quantum Electronics, vol. 48, p. 531, 2016.

C. Dong, X. Xiao, G. Chen, H. Guan, and Y. Wang, “Morphology control of porous CuO by surfactant using combustion method,” Applied Surface Science, vol. 349, pp. 844–848, 2015.

K. Phiwdang, S. Suphankij, W. Mekprasart, and W. Pecharapa, “Synthesis of CuO nanoparticles by precipitation method using different precursors,” Energy Procedia, vol. 34, pp. 740–745, 2013.

H. Dadashi and R. Hajinasiri, “Biosynthesis of Cu and CuO nanoparticles using aqueous leaves extract of Sambucus nigra L.,” International Journal of Nano Dimension, vol. 11, pp. 405–411, 2020.

M. B. Schütz, L. Xiao, T. Lehnen, T. Fischer, and S. Mathur, “Microwave-assisted synthesis of nanocrystalline binary and ternary metal oxides,” International Materials Reviews, vol. 63, no. 6, pp. 341–374, 2018.

A. Kumar, Y. Kuang, Z. Liang, and X. Sun, “Microwave chemistry, recent advancements, and eco-friendly microwave-assisted synthesis of nanoarchitectures and their applications: a review,” Materials Today Nano, vol. 11, Article ID 100076, 2020.

M. S. Jagadeesan, K. Movlaee, T. Krishnakumar, S. G. Leonardi, and G. Neri, “One-step microwave-assisted synthesis and characterization of novel CuO nanodisks for non-enzymatic glucose sensing,” Journal of Electroanalytical Chemistry, vol. 835, pp. 161–168, 2019.

M. R. Quirino, G. L. Lucena, J. A. Medeiros, I. M. G. dos Santos, and M. J. C. de Oliveira, “CuO rapid synthesis with different morphologies by the microwave hydrothermal method,” Materials Research, vol. 21, 2018.

M. Paristiowati, Z. Zulmanelis, and M. F. Nurhadi, “Green chemistry-based experiments as the implementation of sustainable development values,” JTK (Jurnal Tadris Kimiya), vol. 4, no. 1, pp. 11–20, 2019.

M. Nasrollahzadeh, M. Atarod, M. Sajjadi, S. M. Sajadi, and Z. Issaabadi, Plant-mediated Green Synthesis of Nanostructures: Mechanisms, Characterization, and Applications, in Interface Science and Technology, Elsevier, Amsterdam, Netherlands, 2019.

I. Hussain, N. B. Singh, A. Singh, H. Singh, and S. C. Singh, “Green synthesis of nanoparticles and its potential application,” Biotechnology Letters, vol. 38, no. 4, pp. 545–560, 2016.

M. Nasrollahzadeh and S. M. Sajadi, “Preparation of Au nanoparticles by Anthemis xylopoda flowers aqueous extract and their application for alkyne/aldehyde/amine A3-type coupling reactions,” RSC Advances, vol. 5, no. 57, pp. 46240–46246, 2015.

M. Nasrollahzadeh and S. M. Sajadi, “Green synthesis of Pd nanoparticles mediated by Euphorbia thymifolia L. leaf extract: catalytic activity for cyanation of aryl iodides under ligand-free conditions,” Journal of Colloid and Interface Science, vol. 469, pp. 191–195, 2016.

A. Hatamifard, M. Nasrollahzadeh, and J. Lipkowski, “Green synthesis of a natrolite zeolite/palladium nanocomposite and its application as a reusable catalyst for the reduction of organic dyes in a very short time,” RSC Advances, vol. 5, no. 111, pp. 91372–91381, 2015.

M. Nasrollahzadeh and S. M. Sajadi, “Preparation of Pd/Fe₃ O₄ nanoparticles by use of Euphorbia stracheyi Boiss root extract: a magnetically recoverable catalyst for one-pot reductive amination of aldehydes at room temperature,” Journal of Colloid and Interface Science, vol. 464, pp. 147–152, 2016.

M. Tajbakhsh, H. Alinezhad, M. Nasrollahzadeh, and T. A. Kamali, “Green synthesis of the Ag/HZSM-5 nanocomposite by using Euphorbia heterophylla leaf extract: a recoverable catalyst for reduction of organic dyes,” Journal of Alloys and Compounds, vol. 685, pp. 258–265, 2016.

B. Khodadadi, M. Bordbar, A. Yeganeh-Faal, and M. Nasrollahzadeh, “Green synthesis of Ag nanoparticles/clinoptilolite using vaccinium macrocarpon fruit extract and its excellent catalytic activity for reduction of organic dyes,” Journal of Alloys and Compounds, vol. 719, pp. 82–88, 2017.

M. Nasrollahzadeh, S. Mohammad Sajadi, and A. Rostami-Vartooni, “Green synthesis of CuO nanoparticles by aqueous extract of Anthemis nobilis flowers and their catalytic activity for the A3 coupling reaction,” Journal of Colloid and Interface Science, vol. 459, pp. 183–188, 2015.

M. Nasrollahzadeh, S. M. Sajadi, and M. Maham, “Tamarix gallica leaf extract mediated novel route for green synthesis of CuO nanoparticles and their application for N-arylation of nitrogen-containing heterocycles under ligand-free conditions,” RSC Advances, vol. 5, no. 51, pp. 40628–40635, 2015.

M. Bordbar, N. Negahdar, and M. Nasrollahzadeh, “Melissa Officinalis L. leaf extract assisted green synthesis of CuO/ZnO nanocomposite for the reduction of 4-nitrophenol and Rhodamine B,” Separation and Purification Technology, vol. 191, pp. 295–300, 2018.

S. Sundar, G. Venkatachalam, and S. Kwon, “Biosynthesis of copper oxide (CuO) nanowires and their use for the electrochemical sensing of dopamine,” Nanomaterials, vol. 8, no. 10, p. 823, 2018.

T. shima, M. Kharaziha, and S. Ahmadi, “Green synthesis and morphology dependent antibacterial activity of copper oxide nanoparticles,” Journal of Nanostructure, vol. 9, pp. 163–171, 2019.

S. Suresh, R. Ilakiya, G. Kalaiyan et al., “Green Synthesis of copper oxide nanostructures using cynodon dactylon and cyperus rotundus grass extracts for antibacterial applications,” Ceramics International, vol. 46, no. 8, pp. 12525–12537, 2020.

G. Theophil Anand, S. John Sundaram, K. Kanimozhi, R. Nithiyavathi, and K. Kaviyarasu, “Microwave assisted green synthesis of CuO NPs was done using fruit extract of materials chemistry and physics,” Materials Today: Proceedings, vol. 8, pp. 214–222, 2020.

A. Geyid, D. Abebe, A. Debella et al., “Screening of some medicinal plants of Ethiopia for their anti-microbial properties and chemical profiles,” Journal of Ethnopharmacology, vol. 97, no. 3, pp. 421–427, 2005.

M. Ahamed, H. A. Alhadlaq, M. A. M. Khan, P. Karuppiah, and N. A. Al-Dhabi, “Synthesis, characterization, and antimicrobial activity of copper oxide nanoparticles,” Journal of Nanomaterials, vol. 2014, Article ID 637858, 4 pages, 2014.

F. Buazar, S. Sweidi, M. Badri, and F. Kroushawi, “Biofabrication of highly pure copper oxide nanoparticles using wheat seed extract and their catalytic activity: a mechanistic approach,” Green Processing and Synthesis, vol. 8, no. 1, pp. 691–702, 2019.

A. N. Imangaliyeva, Y. Mastai, and G. A. Seilkhanova, “In situ synthesis and catalytic properties of Cu₂O nanoparticles based on clay materials and polyethylene glycol,” J. Nanoparticle Res., vol. 21, p. 97, 2019.

L. R. Shultz, B. McCullough, W. J. Newsome et al., “A combined mechanochemical and calcination route to mixed cobalt oxides for the selective catalytic reduction of nitrophenols,” Molecules, vol. 25, p. 89, 2020.

R. K. Sharma and R. Ghose, “Synthesis of nanocrystalline CuO-ZnO mixed metal oxide powder by a homogeneous precipitation method,” Ceramics International, vol. 40, no. 7, pp. 10919–10926, 2014.

Y. Zhao, R. Li, P. Jiang, K. Zhang, Y. Dong, and W. Xie, “Mechanistic study of catalytic hydride reduction of −NO₂ to −NH₂ using isotopic solvent and reducer: the real hydrogen source,” The Journal of Physical Chemistry C, vol. 123, no. 25, pp. 15582–15588, 2019.

A. Bhattacharjee and M. Ahmaruzzaman, “Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of p-nitrophenol,” Materials Letters, vol. 161, pp. 79–82, 2015.

K. Sahu, R. Singhal, and S. Mohapatra, “Morphology controlled CuO nanostructures for efficient catalytic reduction of 4-nitrophenol,” Catalysis Letters, vol. 150, no. 2, pp. 471–481, 2020.

M. Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, and M. Bagherzadeh, “Green synthesis of Pd/CuO nanoparticles by Theobroma cacao L. seeds extract and their catalytic performance for the reduction of 4-nitrophenol and phosphine-free heck coupling reaction under aerobic conditions,” Journal of Colloid and Interface Science, vol. 448, pp. 106–113, 2015.

A. A. Kassem, H. N. Abdelhamid, D. M. Fouad, and S. A. Ibrahim, “Catalytic reduction of 4-nitrophenol using copper terephthalate frameworks and CuO@C composite,” Journal of Environmental Chemical Engineering, vol. 9, no. 1, Article ID 104401, 2021.

X. Zhang, X. He, Z. Kang, M. Cui, D.-P. Yang, and R. Luque, “Waste eggshell-derived dual-functional CuO/ZnO/eggshell nanocomposites: (Photo)catalytic reduction and bacterial inactivation,” ACS Sustainable Chemistry & Engineering, vol. 7, no. 18, pp. 15762–15771, 2019.

K. Sahu, B. Satpati, R. Singhal, and S. Mohapatra, “Enhanced catalytic activity of CuO/Cu₂O hybrid nanowires for reduction of 4-nitrophenol in water,” Journal of Physics and Chemistry of Solids, vol. 136, Article ID 109143, 2020.