Ultrasound-assisted fabrication and characterization of a novel UV-light-responsive Er₂Cu₂O₅ semiconductor nanoparticle Photocatalyst

2.1 Sonochemistry fabrication of Er₂Cu₂O₅ nano-products

Er₂Cu₂O₅ nanostructures were synthesized by sonochemical route and TEPA alkaline agent according to previous research (Talebzadeh et al., 2021). Er(NO₃)₃·5H₂O and Cu(NO₃)₂·5H₂O powders were dissolved in deionized H₂O based on stoichiometric ratios (1:1), separately and added together. Subsequently, an ultrasonic probe was dipped in a straight line to the reaction beaker for 30 min. Meanwhile, TEPA alkaline agent was added to previous cationic solution under ultrasonic waves to set the pH = 10. The made samples after centrifuging and drying were annealed at 900 °C for 4 h. To reach boosted photocatalytic routine through erbium cuprate nanostructures with promising dimension and morphology, the efficacy of annealing temperature, time and power sonochemistry reaction were examined (Table 1). Similarly, a blank examination without ultrasonic influences was performed. The concluding nano models were deliberated over various physical characterization routes. The related schematic of sonication synthesis of Er₂Cu₂O₅ nanoparticles was illustrated in Scheme 1. To calculate power output, the solution temperature of the reaction was determined in diverse times during sonochemistry fabrication. According to the equation of Power = (dT/dt) c_p M (Contamine et al., 1995); Where c_p and M are the heat capacity (in J kg⁻¹ K⁻¹) and mass (in kg) of the solvent, the power output is computed 17.3 W for Er₂Cu₂O₅ (sample No. 6) in a water solvent. Also, the energy requirement during ultrasonic preparation was calculated 10,380 j according to the equation of Energy (j) = power (W) * time (s).

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Scheme 1

Schematic model for sonochemistry preparation of ECO nanoparticles in presence of TEPA alkaline and complexing agent.

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2.2 UV-Photo sensitive catalytic examinations

The photo-degradation catalytic tests were done according to previous works (Talebzadeh et al., 2021) in a beaker set comprising 100 mL erythrosine and methyl violet solutions (10 ppm). For every test, 10 mg Er₂Cu₂O₅ nano-ceramics were distributed in contamination result. The final solutions were kept in dark surroundings under magnetic stirring for 30 min. eventually, the reaction beaker was subjected to UVA (λ = 320–400 nm) and UVB (λ = 290–320 nm) waves. Influence of pollutant, scavenger, dye concentration, nano-catalyst loading and pH was checked out. After sampling and separating of nano-catalyst with centrifuging at the specified time, the sample absorbance was recorded by UV–Vis spectrometer. $\mathrm{d}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{e}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}\left(\mathrm{\eta }\right)\%=\frac{\left(A0-At\right)}{A0}\times 100$ equation was utilized to compute the UV sensitive catalyst efficiency Which A₀ and A_t are absorbance in times of start and t min.

3.1 X-ray diffractogram results

X-ray diffractograms (XRD) of Er-Cu-O models fabricated by sonochemistry way in heat treatment of 700 °C for 4 h (ECO1) have been displayed in Fig. 1a. This temperature and time of heat process are not satisfactory for the creation of pure Er₂Cu₂O₅ nanocomponents and sample includes the binary oxides of Er₂O₃ (JCPDS No = 77–0777) and CuO (JCPDS No = 41–0254). By proliferating calcination heat to 900 °C (ECO2) and without ultrasonic irradiation, the mixture of phases are formed consist of Er₂O₃ (JCPDS No = 77–0777), CuO (JCPDS No = 41–0254) and Er₂Cu₂O₅ (JCPDS No = 83–0498) (Fig. 1b). Pure Orthorhombic Er₂Cu₂O₅ structures were created at 900 °C for 4 h in presence of ultrasonic waves that have been described in Fig. 1c (ECO3). It was deduced that ultrasonic irradiation is a crucial tool for the production of pure Er₂Cu₂O₅ nanocrystals. The Er₂Cu₂O₅ structures are containing the key Bragg reflections at 2 theta of 17.9, 21.8, 27.2, 30.7, 31.6, 33.3, 33.8, 34.2, 45.2 and 48.2 related to (2 0 1), (2 0 2), (2 0 3), (1 1 2), (2 1 1), (2 0 4), (0 1 3), (4 0 1), (4 1 2) and (2 1 5) plans. The crystalline dimension of Er-Cu-O nanograins (ECO3) was accounted by way of the Scherer relation (Monshi et al., 2012) about 39 nm. Crystallographic parameters of ECO nanocrystals obtained from XRD patterns have been summarized in Table. 2.

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Fig. 1

XRD patterns of Er₂Cu₂O₅ samples No (a) 1, (b) 2 and (c) 3.

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3.2 Morphology examination (SEM & TEM)

In order to consider the impact of ultrasonic reaction time on shape, dimension and particle distribution of Er₂Cu₂O₅ products, the reaction was carried out at different times of 10, 20 and 30 min and FESEM images of nano-products prepared have been displayed in Fig. 2a-f. As observed in Fig. 2, when precursors are exposed to ultrasonic waves for 10 min, particles with the wide size distribution of 30–200 nm are created. In times of 20 and 30 min, agglomerated products were appeared. The physical and chemical events are initiated during the cavitation bubble collapse of ultrasonic waves. A shock wave of implosive collapse of bubbles can propagate out into the precursor solution and speed up suspended solid particles. Inter-particle collisions can change particle size distributions and their shapes. On the other hand, pursuant to the Ostwald development, when the sonication period rises, the ultrasonic waves’ shock can be lead to particle evolution in the primary step. With boosts of the ultrasonic time of up to 20 and 30 min, the bulky shapes of particles are prearranged. Though, by growing the duration of ultrasound emission from a definite limit, the concentration of bubbles formed in the solution rises. This phenomenon acts as a barrier to the publication of ultrasound waves, and agglomerated products are formed. The ideal particle size was attained within 10 min of the wave transmission.

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Fig. 2

FESEM images of Er₂Cu₂O₅ nano-samples fabricated via ultrasonic waves in various times of (a, b) 30, (c, d) 20 and (e, f) 10 min.

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Ultrasonic wave power can affect the size, uniformity and shape of prepared nano-products (Hinman and Suslick, 2017) that SEM images of Er₂Cu₂O₅ nanostructures in different powers of 60 and 45 W have been presented in Fig. 3a-d, correspondingly. The medium power of 60 W is ideal power for the fabrication of uniform small structures of Er₂Cu₂O₅ because with creation of suitable bubble concentration in solution medium and finally active groups of radical help to obtain fine particles.

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Fig. 3

FESEM images of Er₂Cu₂O₅ nanostructures fabricated via ultrasonic waves in various powers of (a, b) 60 and (c, d) 45 W.

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FESEM images of Er₂Cu₂O₅ structures prepared without ultrasonic waves have been displayed in Fig. 4a, b. agglomerated structures with irregular size and shape were formed in the precipitation route. Fig. 5a-e illustrate particle scale dispensation charts of samples created in dissimilar times and powers of ultrasonic irradiation (sample Nos. 3–7), respectively. As shown in Fig. 5a-e, Er₂Cu₂O₅ nanoparticles synthesized through 10 min and 60 w ultrasonic waves (sample No. 6) have ideal particle size distribution.

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Fig. 4

FESEM images of Er₂Cu₂O₅ sample fabricated without ultrasonic irradiation (sample No. 2).

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Fig. 5

Particle size distribution charts of sample No of (a) 3, (b) 4, (c) 5, (d) 6 and (e) 7.

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Fig. 6 depicts transmission microscopic pictures of improved Er₂Cu₂O₅ nano model made-up via the sonochemistry route (ECO6). Ellipsoidal-shaped nano samples have scale of approximately 10–50 nm.

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Fig. 6

TEM images of optimized nano Er₂Cu₂O₅ product (ECO6).

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3.3 Mechanism of sonochemistry synthesis

Optimal designed nano Er₂Cu₂O₅ materials are shaped with the ultrasonic treatment together with TEPA as both alkaline and covering agents. Pursuant to hot-spot principle, extreme pressure and temperature cause the formation of oxidizing components that help to rapid manufacture of optimized erbium cuprate nanoparticles (Gedanken, 2004). Water is pyrolyzed to H and OH radicals in presence of ultrasonic waves. The created radicals help to release of hydroxyl ions from TEPA. Then, Er(OH)₃ and Cu(OH)₂ precursors produced in an alkaline medium are calcined at 900 °C for 4 h and final product with optimal properties is synthesized. The reactions performed in the aquatic environment by ultrasound waves are described below:. H₂O → H^• + OH H^• + H^• → H₂ OH^• + OH^• → H₂O₂ TEPA + H₂O + H^• → TEPA-H⁺ + OH Er³⁺ + OH^– → Er(OH)₃ Cu²⁺ + OH^– → Cu(OH)₂ Er(OH)₃ + 2 Cu(OH)₂ → Er₂Cu₂O₅ nanoparticles + 5 H₂O

3.4 EDX and FT-IR spectra analysis

The result of EDX spectrum of pure Er₂Cu₂O₅ nanoparticles (ECO6) has been represented in Fig. 7a. In Fig. 7a, the entity of Er, Cu and O lines corroborate construction of net Er₂Cu₂O₅ nanomaterial.

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Fig. 7

(a) EDS analysis, (b) FT-IR spectrum and (c) M−H curve of ECO6 nanoparticles.

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FT-IR study of optimal designed nano Er₂Cu₂O₅ materials (ECO6) has been performed in Fig. 7b. The platy sorption within 3430 cm⁻¹ and a slight summit at 1632 cm⁻¹ are allocated to shaking of O-H connections of water. All frequency attractions nearby 400–700 cm⁻¹ and 1158 cm⁻¹ can be correlated to Cu-O and Er-O connection (Gaafar et al., 2009; Erdoğan and Güllü, 2010). The FT-IR outcomes approve that a miniature amount of TEPA alkaline and covering mediator is appended to the Er₂Cu₂O₅ product and following that preventing nanoparticles agglomeration.

3.5 Magnetic and porosity features

The magnetic properties of pure Er₂Cu₂O₅ nanoparticles explored with VSM have been revealed in Fig. 7c. Ferromagnetic behavior was concluded from the hysteresis loop according to the earlier study (Garcia-Munoz et al., 1995). The vital magnetic parameters including coercivity, residue magnetization and supreme saturation magnetization of ideal Er₂Cu₂O₅ product have been listed in Fig. 7c.

The BET analysis to specify important factors in porosity of pure Er₂Cu₂O₅ nanoparticles surface have been exhibited in Fig. 8a, b. The reached erbium cuprate nanoparticles are assorted in IV group and H4 type which qualified to accumulated units with macro and mesoholes (Leofanti et al., 1998). As exposed in Fig. 8b, the accomplished nanostructures have a wide-ranging pore dimension. The particular surface area, hole volume and average hole dimension for the Er₂Cu₂O₅ sample are 2.59 m² g⁻¹, 0.59 cm³ g⁻¹ and 12.74 nm, correspondingly. From the presented data, it was realized that Er₂Cu₂O₅ nanoparticles have satisfactory porosity for UV-sensitive catalytic act.

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Fig. 8

(a, b) N₂ adsorption/desorption isotherm and pore size distribution, (c, d) UV–Vis diffuse absorption spectrum and linear portion of plots of (αhν)^1/2 against (hν) of optimized Er₂Cu₂O₅ nanoparticles (ECO6).

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3.6 Electronic structures

To distinguish optical energy structure and bandgap of Er₂Cu₂O₅ nano semiconductor, UV–Vis absorption spectroscopy was carried out that exposed in Fig. 8c, d. The characteristic absorption area is about 200–400 nm. The bandgap of Er₂Cu₂O₅ nano specimen was tested by Tauc’s relation (Tauc et al., 1966; Paul et al., 2019; Ranjeh et al., 2020; Ghanbari and Salavati-Niasari, 2021; Selvamani et al., 2021; Al-Nayili et al., 2021; Kadhem and Al-Nayili, 2021; Al-Nayili and Albdiry, 2021) about 3.2 eV.

3.7 UV-sensitive catalytic efficacy

Due to the Er₂Cu₂O₅ sample being in semiconductors group, the activity of ECO6 nanocatalyst was assessed subjecting UV wave for converting of water pollutants to harmless materials. The elements of contamination type, Er₂Cu₂O₅ nanocatalyst dosage and different trappers were examined to realize the maximum degradation proportion. Fig. 9 indicates the UV-catalytic performance of ECO6 nanoparticles arranged using ultrasonication radiation for removing of various pollutants of thymol blue, erythrosine, acid red, methyl orange and eriochrome black T after 120 min. As illustrated in Fig. 9, degradation efficiency of erythrosine dye as drinking water pollutant is more than other dyes. Degradation percentage of erythrosine dye by ECO6 was obtained 99.3 % after 120 min. Also, to consider kinetic behaviors of samples according to Langmuir–Hinshelwood mechanism, the promising reaction rate coefficients can be expanded from Eq. (2):.

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Fig. 9

(a) Photocatalytic efficiency and (b) plots of ln(C/C₀) vs time of Er₂Cu₂O₅ nanocatalysts for removal different dyes under UV light.

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Which C₀ and C_t are dye concentration in times of start and t min and k is the pseudo-1st-order rate coefficient (min⁻¹). According to linear dependences of ln(C₀/C_t) versus time, the 1st-order rate constant k has been reached. As observed in Fig. 9b, the rate constant of k for erythrosine dye (k = 0.04816 min⁻¹) is more than other pollutants that confirm catalytic degradation of erythrosine dye in presence of ECO nanoparticles is carried out with higher speed.

Fig. 10a-f unveil the consequences of UV-elimination of ECO6 nanocatalyst in dissimilar quantities of 0.03, 0.05 and 0.07 g in various pollutant concentrations of 10, 15 and 20 ppm. It is noticeable that degradation percentage of all examples is above of 90 %. Also, kinetic studies of ECO6 nanocatalyst in diverse pollutant dosages have been illustrated in Fig. 10 b, d and f.

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Fig. 10

(a), (c), (e) Photocatalytic efficiency and (b), (d) and (f) plots of ln(C/C₀) vs time in diverse dosages of Er₂Cu₂O₅ nanocatalysts of 0.03, 0.05 and 0.07 g.

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In Fig. 11a, photocatalytic performance of Er₂Cu₂O₅ nanocatalysts in different pH of acidic (pH = 4), neutral (pH = 8) and alkaline (pH = 10) was studied for removal erythrosine dye under UV light. According to Fig. 11a, photocatalytic efficiency of ECO nanoparticles was obtained 95.04, 85.12 and 60.22% at pH of 4, 8 and 10. According to Fig. 11b, the optimum medium for performing photocatalytic tests is acidic circumstances with kinetic constant of 0.03639 min⁻¹.

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Fig. 11

Photocatalytic efficiency and plots of ln(C/C₀) vs time of Er₂Cu₂O₅ nanocatalysts (a, b) in different pH and (c, d) in presence of three types of scavenger for removal erythrosine dye under UV light.

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Fig. 11c, d displays the UV-degradation measurement and plots of ln(C/C₀) vs time of ECO6 nanocatalyst in attendance of diverse trappers to ensnare of h⁺, ^•OH and ^•O₂^– active radicals (Paul et al., 2019; Ranjeh et al., 2020; Ghanbari and Salavati-Niasari, 2021; Selvamani et al., 2021; Al-Nayili et al., 2021; Kadhem and Al-Nayili, 2021; Al-Nayili and Albdiry, 2021). As illustrated, UV-degradation proficiency of erythrosine pollutant by Er₂Cu₂O₅ nano-catalyst has prominently diminished with benzoquinone as a ^•O₂^– trapper. It is derived that ^•O₂^– radical element has the greatest influence in deletion water impurity. The erythrosine removal process with details via optimized Er₂Cu₂O₅ by ^•O₂^– trapper has been shortened in follows:. ECO nano-catalyst + hν → ECO nano-catalyst* (e^-_CB + h⁺_VB) O₂ + e^- → ^•O₂ ^•O₂^– + e^- + 2H⁺ → H₂O₂ H₂O₂ + e^- → OH^– + ^•OH h⁺ + H₂O → ^•OH + 2H⁺ Erythrosine dye + (^•O₂^– + ^•OH active agents) → product + H₂O + CO₂

Fig. 12a, b display the photocatalytic efficiency and plots of ln(C/C₀) vs time of Er₂Cu₂O₅ nanocatalysts for removal phenol dye under UV light. The catalytic yield of nanoparticles is about 90 % and speed constant is 0.00150 min⁻¹. As presented in Fig. 13, after 5 times recycling photocatalytic activity, degradation efficiency fell gradually from 99.3 to 86.2%.

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Fig. 12

Photocatalytic efficiency and plots of ln(C/C₀) vs time of Er₂Cu₂O₅ nanocatalysts for removal phenol dye under UV light.

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Fig. 13

Recycling results of ECO nanoparticles after 5 cycles photocatalytic activity.

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In Table 3, photocatalytic performance of Er₂Cu₂O₅ nanoparticles was linked with other nanocatalysts (Ranjeh et al., 2020; Ghanbari and Salavati-Niasari, 2021; Selvamani et al., 2021). In this work, photo-degradation proficiency of Er₂Cu₂O₅ nanoparticles was deliberate for the first period and concluded that ECO nanoparticles have promising photocatalytic activity among nanomaterials. The schematic design of photo-degradation mechanism of ECO6 has been illustrated in Scheme. 2.

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Scheme 2

Photo-degradation mechanism of Er₂Cu₂O₅ nano products.

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