Boost piezocatalytic activity of BaSO₄ by coupling it with BaTiO₃, Cu:BaTiO₃, Fe:BaTiO₃, S:BaTiO₃ and modify them by sucrose for water purification

Abstract

The purpose of this study is to improve the efficiency of decontamination using BaSO₄ as a piezocatalyst. Three techniques are employed in this study to enhance the piezocatalytic activity of BaSO₄. The first method involves coupling BaSO₄ with BaTiO₃. The acid red 151 and acid blue 113 decontamination rates improved from 56.7% and 60.9% to 61.3% and 64.4%, respectively, as a result of this strategy. Additionally, the composite of BaSO₄ and BaTiO₃ was doped with copper, iron, sulfur, and nitrogen. By doping BaTiO₃, acid red 151 and acid blue 113 achieved 86.7% and 89.2% efficiency, respectively. Finally, the nanostructures were modified with sucrose. These strategies improved degradation efficiency for acid red 151 and acid blue 113 to 92.9% and 93.3%, respectively. The reusability results showed that the piezo-catalytic activity of the m-S–BaSO₄–BaTiO₃ catalyst did not show a significant loss after five recycles for the degradation of AB113.

Introduction

Water containing organic pollutants such as phenolic compounds, dyes, and antibiotics is almost non-biodegradable. Such toxic pollutants create chronic toxicity and sometimes can be carcinogenic. These unwelcome properties cause an enormous challenge to the environmental amendment^1–5. Therefore, it is an urgent demand to treat and neutralize wastewater and constrain the deterioration of water quality to reduce the risks stood to creatures and bio networks⁶. However, conservative treatment approaches such as photocatalysis, photolysis, Fenton Process, and ozonation have some disadvantages such as proper pH/temperature and slow reaction rate^7–9. So far, advanced oxidation technologies (AOT) have been successfully applied to remove toxic materials^10–12. Organic contaminants have been decontaminated and decomposed using semiconductor materials in AOT. During this process, strong oxidizing radicals are generated when visible to ultraviolet wavelength light is illuminated. The free radicals produced by these processes react with toxic pollutants^13,14. In typically advanced oxidation catalysis, the semiconductor should have a vigorous capacity to generate separated electron–hole pairs on the surface by irradiation of photons with energy more than its bandgap. However, the rapid charge carrier’s recombination, a low photon-to-current yield of semiconductor photocatalysts, and low percentages of UV light in the sunlight lead to a low level of photocatalytic efficiency for practical application. Therefore, researchers look for alternative clean and renewable energy to treat wastewater. Piezo-catalytic degradation is a viable alternative to photocatalytic degradation in environmental remediation.

The piezoelectric material can produce electrons and holes by harvesting energy from mechanical vibrations in the surrounding environment. Using these electrons and holes, oxidative free radicals can be produced to decontaminate water^15–18. From an environmental perspective, lead-free piezoelectric materials are of particular interest^19,20. Due to its non-toxic structure and abundance^21,22, BaSO₄ might be an interesting candidate. However, BaSO₄ suffers from low piezoelectricity. By coupling it with doped and non-doped BaTiO₃ and preparing related composites with sucrose, we attempted to improve its piezocatalytic activity. By using dopants, researchers have been able to enhance piezoelectric coefficients. As an example, Shruti B. Seshadri et al. Al. reported a huge enhancement in piezoelectric coefficients and piezoelectricity of lead zirconate titanate by doping 2% of Sm²³. Another report published by H. M. A. Hamid, and Z. Çelik-Butler demonstrated that the piezoelectricity of ZnO could improve by doping with Li-ion²⁴. Doping BaSO₄–BaTiO₃ with a dopant can potentially improve its performance because of the following reasons. First, the dopant could act as a shallow-level acceptor in BaSO₄–BaTiO₃ and can significantly reduce the piezoelectric potential screening effect^25–29. Second, depending on the radius of the dopant, it could create an increased strain while replacing the Ba with the BaSO₄–BaTiO₃ lattice, thus leading to an increase in the piezoelectric coefficient^30–32. Next, dopants could increase electrical resistivity and reduce charge leakage³³.

This research aims to enhance the piezocatalytic activity of BaSO₄ by coupling it with BaTiO₃ (doped and non-doped) and sucrose. One of the most common natural piezoelectric materials is sucrose. BaSO₄, BaSO₄–BaTiO₃, doped BaSO₄–BaTiO₃, and BaSO₄–BaTiO₃-Sucrose composites were used to treat water containing various contaminants. As a mechanical source, ultrasonic vibrations were used to stimulate the piezo material. The results indicate that coupling BaTiO₃ and sucrose has a dramatic effect on its piezocatalytic activity. In terms of solving environmental problems, piezocatalysts appear to be a viable alternative to AOP technology. Additionally, the effects of pulse and power of ultrasonics on the decontamination efficiency of organic pollutants were investigated.

Experimental

Material

Synthesis of piezocatalyst: For bare BaSO₄–BaTiO₃ without dopant, 1.19 g BaSO₄ was dispersed in 10 mL distilled water. Then 11 mL of an ethanol-based solution of tetraethyl orthotitanate was added to the above solution and stirred for 10 min. Then 2 mL of NaOH 0.5 M was added under stirring. Then the solution was transferred to an autoclave and was heated at 160 °C for 8 h. Finally, the obtained precipitate was washed twice with ethanol and water and calcinated at 750 °C for 2 h.

For doped BaSO₄–BaTiO₃, 1.19 g BaSO₄ was dissolved in 10 mL dispersed water. Afterward, 0. 12 mmol of a dopant was added to the initial solution. Thioacetamide, copper sulfate, iron sulfate, or ammonia was added as a dopant. 11 mL of the ethanol-based solution of tetraethyl orthotitanate (10% V:V) was added to the above solution and stirred for 10 min. Then 2 mL of NaOH 0.5 M was added under stirring. Then the solution was transferred to an autoclave and was heated at 160 °C for 8 h. Finally, the obtained precipitate was washed twice with ethanol and water and calcinated at 750 °C for 2 h.

Preparing doped BaSO₄–BaTiO₃-sucrose

1 g of doped BaSO₄–BaTiO₃ was added to the 20 mL DI water. Then 20 mL of an aqueous solution of sucrose (0.2 M) was added to the above solution and stirred for 12 h. The above solution was centrifuged for 10 min to remove an excess of sucrose.

Piezocatalytic decontamination test

The piezoelectric catalytic performance of the doped and modified BaSO₄–BaTiO₃ was evaluated by their ability to degrade acid red 151 (AR151) as an organic pollutant. In each piezocatalytic experiment, 50 mg of a BaTiO₃-based catalyst was dispersed in a 100 mL beaker containing 50 mL AR151 solution (5 ppm).

Before the degradation process, the mixture was magnetically stirred for 30 min in the dark until adsorption–desorption equilibrium was attained. Then the UV–Vis absorption spectra of the samples were recorded just before turning on ultrasound. The experiment was performed in the darkness to eliminate the interference of light. The piezocatalytic performance of the prepared samples was tested by the degradation of AR151 and acid blue 113 (AB113) under ultrasonic vibration. Here, ultrasonic prob with power of 100 W and ultrasound frequency of 20 kHz was used for 60 min as mechanical source. The mixture was centrifuged and the concentration of AR151 and AB113 was measured from their UV–Vis absorbances. Besides, we studied the effect of vibration pulse and power.

Results and discussion

Here we improved the efficiency of the piezocatalytic activity of BaSO₄–BaTiO₃ as a new class of catalyst for the decontamination of water. This is a promising way to use mechanical waste energy to treat wastewater. Here we doped BaSO₄–BaTiO₃ by Cu, Fe, S, and N and coupled them with sucrose as a natural piezomaterial that was labeled as Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃-sucrose, Fe–BaSO₄–BaTiO₃-sucrose, S–BaSO₄–BaTiO₃-sucrose, and N–BaSO₄–BaTiO₃-sucrose, respectively.

The XRD patterns of BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and m-S–BaSO₄–BaTiO₃ are shown in Fig. 1a–f and Figure S1–S6 (raw patterns). The result indicates reasonable agreement with JCPDS 76–213 for BaSO₄. As a result, it has been crystallized as an orthorhombic crystal. Stars in this pattern indicate diffraction peaks that can be indexed quite well by a tetragonal BaTiO₃ cell with JCPDS 812203. Cu, Fe, S, N, and sucrose did not have a significant effect on the crystal structures. The EDX results confirm their presence in related samples.

Figure 1.

XRD pattern of (a) BaSO₄–BaTiO₃, (b) Cu–BaSO₄–BaTiO₃, (c) Fe–BaSO₄–BaTiO₃, (d) S– BaSO₄–BaTiO₃, (e) N–BaSO₄–BaTiO₃, and (f) m-S–BaSO₄–BaTiO₃.

The EDX for BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and S–BaSO₄–BaTiO₃ was demonstrated in Fig. 2a–e. Figure 2a shows the sample containing Ba, S, Ti, and O elements that could be assigned to the BaSO₄–BaTiO₃ composite. By adding CuSO₄ in the synthesis step, the copper element appeared in the EDX. This indicated that Cu successfully doped into the composite (Fig. 2b). Also, the EDX results approved that Cu has been doped into the BaTiO₃ (in BaSO₄–BaTiO₃ composite) structure (Figure S1 in supporting information). As SEM and EDX in Figure S1 show, the smaller particles contain Cu and Ti, Ba, and O while the big particles mainly contain Ba, S and O. Therefore, the big particles could be related to the BaSO₄ and the smaller particles form Cu doped BaTiO₃. Figure 2c demonstrates the EDX of Fe–BaSO₄–BaTiO₃. EDX approved the presence of Ba, Ti, S, O, and Fe. As Figure S2 shows, the same scenario happened and the smaller particles were Fe-doped BaTiO₃ while the bigger particles were BaSO₄ in the BaSO₄–BaTiO₃ composite system. The EDX of N–BaSO₄–BaTiO₃ was shown in Fig. 2d. According to this result, nitrogen does not appear in the related EDX. This could happen because of two reasons. First, nitrogen does not dope into BaTiO₃. Second, the amount of nitrogen is less than 1 W %, therefore it does not appear in EDX. EDX of S–BaSO₄–BaTiO₃ was presented in Fig. 2e. The EDX showed the presence of Ba, Ti, O, and S. In this case, the small particles belong to the BaTiO₃ again. As can be seen, it contains sulfur. It means sulfur is successfully doped in BaTiO₃ in the BaSO₄–BaTiO₃ system (Figure S3).

Figure 2.

EDX for (a) BaSO₄–BaTiO₃, (b) Cu–BaSO₄–BaTiO₃, (c) Fe–BaSO₄–BaTiO₃, (d) N–BaSO₄–BaTiO₃ and (e) S–BaSO₄–BaTiO_3.

Raman spectroscopy is an appropriate method for exploring chemical bonding and the solid-state structure of crystals. Dopants can also be detected using Raman spectroscopy in host-crystal lattices^34–36. Raman spectra of the composite BaSO₄–BaTiO₃, when BaTiO₃ was not doped, are shown in Fig. 3a. Figure 3b illustrates a Raman spectrum of the composite Cu–BaSO₄–BaTiO₃. As a consequence of the doping of Cu in the BaTiO₃ crystal, the peak at 403 cm⁻¹ is associated with the peak at 403 cm⁻¹. Fe doping resulted in the disappearance of the peak at 1138 cm⁻¹ and the appearance of new Raman shifts at 514 cm⁻¹ and 145 cm⁻¹ (Fig. 3c). As a result of the addition of N to BaTiO₃, new Raman shifts are observed around 514 cm⁻¹ and 1171 cm⁻¹ (Fig. 3d). A new Raman shift was observed at 514 cm⁻¹ after BaTiO₃ was doped with S as a dopant (Fig. 3e).

Figure 3.

Raman spectra of (a) BaSO₄–BaTiO₃, (b) Cu–BaSO₄–BaTiO₃, (c) Fe–BaSO₄–BaTiO₃, (d) S– BaSO₄–BaTiO₃, (e) N–BaSO₄–BaTiO₃, and (f) S–BaSO₄–BaTiO₃.

Figure 4a–d shows the EDX of Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and S–BaSO₄–BaTiO₃ modified by sucrose. Figure 4a illustrates the EDX of Cu–BaSO₄–BaTiO₃ modified by sucrose. By comparing Figs. 2b and 4a, we can recognize that sucrose modifies Cu–BaSO₄–BaTiO₃. Besides Ba, Ti, O, S, and Cu, carbon has also appeared in the EDX of Cu–BaSO₄–BaTiO₃ modified by sucrose that could be assigned to the carbon of sucrose. Also, a comparison of Figs. 2c and 4b clarifies the presence of sucrose. The same peak appeared in the EDX of N–BaSO₄–BaTiO₃ and S–BaSO₄–BaTiO₃ modified by sucrose. This indicates that all nanostructures were successfully modified by sucrose (Fig. 4c, d). We applied FT-IR as more evidence.

Figure 4.

EDX of (a) Cu–BaSO₄–BaTiO₃, (b) Fe–BaSO₄–BaTiO₃, (c) N–BaSO₄–BaTiO₃ and (d) S–BaSO₄–BaTiO₃ modified by sucrose.

An FT-IR spectrum of CuSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and S–BaSO₄–BaTiO₃ modified by sucrose is plotted in Fig. 5. In Figure S4 and Table 1, FT-IR spectra of Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and S–BaSO₄–BaTiO₃ are also shown before the addition of sucrose. These peaks may be attributed to the sulfur–oxygen stretches found in inorganic sulfates³⁷. Based on the FT-IR spectra of Figure S4 and Fig. 5, we can conclude that sucrose modifies nanostructure surfaces. The peak at 979 cm⁻¹ could be associated with ring C–C stretching vibrations. The peak at ~ 1034 cm⁻¹ is caused by the stretching vibration of CH₂–OH in the C–O plane. The peak in 3000–3500 cm⁻¹ could be related to sucrose's OH group.

Figure 5.

FT-IR of (a) Cu-BaSO₄–BaTiO₃, (b) Fe–BaSO₄–BaTiO₃, (c) N–BaSO₄–BaTiO₃ and (d) S–BaSO₄–BaTiO₃ modified by sucrose.

Table 1.

FT-IR peaks assigned to different functional groups.

Peak number	Wavenumber (cm−1)	Functional group
1	979	C–C stretching vibrations
2	1034	Stretching vibration of CH2–OH
3	1434	Asymmetric stretching of the carbonates
4	2921	CH2 groups
5	2854
6	2390
7	3000–3500	Sucrose's OH

Figure 6a–i displays the SEM images of BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, and N–BaSO₄–BaTiO₃. According to Fig. 6a, b, Figure S1, and EDX results, micro-size particles are BaSO₄, while nanostructures form BaTiO₃. It seems BaTiO₃ starts to form rod-like nanostructures. In the case of Cu–BaSO₄–BaTiO₃ flowers like structures and microstructures could be assigned to the Cu–BaTiO₃ and BaSO₄, respectively (Fig. 6c, d, and Figure S1). SEM results presented in Fig. 6e, f indicate Fe–BaSO₄–BaTiO₃ has been assembled and formed flower-like structures. For S–BaSO₄–BaTiO₃, nanorod form S–BaSO₄–BaTiO_3, and microstructures are BaSO₄ (Fig. 6g, h). Figure 6i shows that very uniform flower-like structures formed when ammonia was used in the synthesis of N–BaSO₄–BaTiO_3.

Figure 6.

SEM images of (a, b) BaSO₄–BaTiO₃, (c, d) Cu–BaTiO₃, (e, f) Fe–BaTiO₃, (g, h) S–BaTiO₃, and (i) N–BaTiO_3.

SEM images for as-prepared nanostructures including Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and S–BaSO₄–BaTiO₃ modified by sucrose are summarized in Fig. 7a–d. SEM image of Cu–BaSO₄–BaTiO₃-sucrose is illustrated in Fig. 7a. We can figure out sucrose cover Cu–BaSO₄–BaTiO₃ and stuck particles by comparing it with SEM images of Cu–BaSO₄–BaTiO₃ (Fig. 6c, d). The same conclusion could be made by comparing SEM images of nanostructures before sucrose (Fig. 6e–i) and after modification with sucrose (Fig. 7b–d).

Figure 7.

SEM images for as-prepared nanostructures including (a) Cu–BaSO₄–BaTiO₃, (b) Fe–BaSO₄–BaTiO₃, (c) N–BaSO₄–BaTiO₃ and (d) S–BaSO₄–BaTiO₃ modified by sucrose.

Piezocatalytic activity of Pure BaSO₄, BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃, and m-BaTiO₃ was evaluated by degradation of AR151 and AB113 under external mechanical force (ultrasonic vibration). Figure 8a–c and Table 2 present results for the piezocatalytic degradation of AR151 by ultrasonic vibration without catalyst, BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, and N–BaSO₄–BaTiO₃. Also, the degradation efficiency of Pure BaSO₄ for AR1 and AB113 is presented in Figure S5. According to Figure S5, Pure BaSO₄ degrade 56.7% and 60.9% of AR151 and AB113 during 90 min ultrasonic. The red curve in Fig. 8a shows the UV–Vis spectrum of the initial AR151 solution. The black curve represents the spectrum for AR151 when it was vibrated by 100 W ultrasonic without a catalyst. We label it as Blank 2. As can see from Fig. 8 and Table 2, 44.8% of AR151 was degraded during 90 min by bare ultrasonic waves with 2 on:2 off the pulse. When BaSO₄–BaTiO₃ was added, degradation increased to 61.3% for AR151 (green curve). N–BaSO₄–BaTiO₃ and S–BaSO₄–BaTiO₃ degrade 88.5 and 72.6% of AR151, respectively. In the case of AR151, using the S dopant does not show a significant effect on the piezocatalytic activity of BaSO₄–BaTiO₃, while using N, Cu⁺², and Fe⁺³ as dopant significantly improve decontamination yield. Decontamination yields of 85.9% and 83.8% for doped BaTiO₃ with Cu⁺² and Fe⁺³ for AR151 were achieved, respectively. As the results in Fig. 8a–c and Table 2 show, Cu–BaSO₄–BaTiO₃ shows promising degradation efficiency compare to the –BaSO₄–BaTiO₃. It seems to replace A and B cations in perovskite structure with the general formula of ABX₃ shows more effect on the piezocatalytic activity of composite. Besides BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, and N–BaSO₄–BaTiO₃ were applied to treat water containing AB113, Fig. 9a–c and Table 3 reveal related results. Related results show that 48.3% of AB113 was degraded during 90 min ultrasonic vibration without the catalyst. Adding BaSO₄–BaTiO₃ as a piezocatalyst leads to an increased piezocatalytic degradation of AB113 to 64.4%. By changing the piezocatalyst to Cu–BaSO₄–BaTiO₃ degradation efficiency increased to 86.7%. However, by changing the catalyst to Fe–BaSO₄–BaTiO₃ degradation efficiency of 77.6% was achieved. In the case of using the BaSO₄–BaTiO₃ series catalyst, S–BaSO₄–BaTiO₃ shows the highest efficiency. It degrades 89.2% of AB113 during 90 min ultrasonic. Finally, we examine N–BaSO₄–BaTiO₃ as a piezocatalyst in the same operating condition. A decontamination efficiency of 80.9% was achieved. Results approve that dopants could show dramatically effect on piezocatalytic activity. The origin of these improvements could be the following reasons: (I) dopant could act as a shallow level acceptor in BaTiO₃ and can significantly reduce the piezoelectric potential screening effect^25–29,38. (II) Depending on the radius of the dopant, it could create an increased strain while replacing the Ba or Ti in the BaTiO₃ lattice, thus leading to an increase in the piezoelectric coefficient^30–32. (III): dopant could increase electrical resistivity and reduce charge leakage³³.

Figure 8.

(a) The UV–Vis spectrum of initial AR151 (blank 1), AR151 after treat it with bare ultrasonic (blank 2), BaSO₄–BaTiO₃ (bare BaTiO₃), Cu–BaSO₄–BaTiO₃ (Cu–BaTiO₃), Fe–BaSO₄–BaTiO₃ (Fe–BaTiO₃), S–BaSO₄–BaTiO₃ (S–BaTiO₃), and N–BaSO₄–BaTiO₃ (N–BaTiO₃). (b) Degradation efficiency by using bare ultrasonic (blank 2), BaSO₄–BaTiO₃ (bare BaTiO₃), Cu–BaSO₄–BaTiO₃ (Cu–BaTiO₃), Fe–BaSO₄–BaTiO₃ (Fe–BaTiO₃), S–BaSO₄–BaTiO₃ (S–BaTiO₃), and N–BaSO₄–BaTiO₃ (N–BaTiO₃). (c) Show the photo of blank 1, blank 2, Cu––BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃ and S–BaSO₄–BaTiO₃ after 90 min vibration and centrifuge.

Table 2.

Piezoelectric catalytic capability of Pure BaSO₄, BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃ nanostructure for degradation of AR151.

Catalyst	Ultrasonic time (min)	Pulse: on: off (s)	Power (W)	Decontamination efficiency (%)
W/O catalyst (Blank 2)	90	2:2	100	44.8
Pure BaSO4	90	2:2	100	56.7
BaSO4–BaTiO3	90	2:2	100	61.3
N–BaSO4–BaTiO3	90	2:2	100	88.5
S–BaSO4–BaTiO3	90	2:2	100	72.6
Cu–BaSO4–BaTiO3	90	2:2	100	85.9
Fe–BaSO4–BaTiO3	90	2:2	100	83.8

Figure 9.

(a) The UV–Vis spectrum of initial AB113 (blank 1), AB113 after treat it with bare ultrasonic (blank 2), BaSO₄–BaTiO₃ (bare BaTiO₃), Cu–BaSO₄–BaTiO₃ (Cu–BaTiO₃), Fe–BaSO₄–BaTiO₃ (Fe–BaTiO₃), S–BaSO₄–BaTiO₃ (S–BaTiO₃), and N–BaSO₄–BaTiO₃ (N–BaTiO₃). (b) Degradation efficiency by using bare ultrasonic (blank 2), BaSO₄–BaTiO₃ (bare BaTiO₃), Cu–BaSO₄–BaTiO₃ (Cu–BaTiO₃), Fe–BaSO₄–BaTiO₃ (Fe–BaTiO₃), S–BaSO₄–BaTiO₃ (S–BaTiO₃), and N–BaSO₄–BaTiO₃ (N–BaTiO₃). (c) Show the photo of blank 1, blank 2, BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃ and S–BaSO₄–BaTiO₃ after 90 min vibration and centrifuge.

Table 3.

Piezoelectric catalytic capability of Pure BaSO₄, BaSO₄–BaTiO₃, Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, N–BaSO₄–BaTiO₃ nanostructure for degradation of AB113.

Catalyst	Ultrasonic time (min)	Pulse: on: off (s)	Power (W)	Decontamination efficiency (%)
W/O catalyst (Blank 2)	90	2:2	100	48.3
Pure BaSO4	90	2:2	100	60.9
BaSO4–BaTiO3	90	2:2	100	64.4
N–BaSO4–BaTiO3	90	2:2	100	80.9
S–BaSO4–BaTiO3	90	2:2	100	89.2
Cu–BaSO4–BaTiO3	90	2:2	100	86.7
Fe–BaSO4–BaTiO3	90	2:2	100	77.6

In another strategy, we modified doped BaTiO₃ (in the BaSO₄–BaTiO₃ system) with sucrose to improve its piezocatlytic activity. Sucrose is a natural piezocatalytic material, therefore it could improve piezocatlytic activity^37,39.

Figure 10a–c and Table 4 show the effect of sucrose on the piezocatalytic activity of doped BaSO₄–BaTiO₃ to degrade AR151. We labeled the modified samples as follows: m-Cu–BaSO₄–BaTiO₃ (for Cu doped BaTiO₃ modified by sucrose), m-Fe–BaSO₄–BaTiO₃ (for Fe doped BaTiO₃ modified by sucrose), m-S–BaSO₄–BaTiO₃ (for S doped BaTiO₃ modified by sucrose), and m-N–BaSO₄–BaTiO₃ (for N doped BaTiO₃ modified by sucrose). M-Cu–BaSO₄–BaTiO₃ degraded 85.9% of AR151 during 90 min ultrasonic vibration, while Cu–BaTiO₃ degraded 86.7% of AR151 in the same vibration time. Fe-doped BaSO₄–BaTiO₃ and m-Fe–BaSO₄–BaTiO₃ almost showed the same degradation efficiency, Fe–BaSO₄–BaTiO₃ and m-Fe–BaSO₄–BaTiO₃ degraded 83.8 and 82.1% of AR151, respectively. S-doped BaSO₄–BaTiO₃ modified by sucrose showed better performance compare to the S-BaSO₄–BaTiO₃. S-BaSO₄–BaTiO₃ showed 72.6% degradation efficiency, while m-S–BaSO₄–BaTiO₃ degraded 81.7% of AR151. Finally, N-doped BaSO₄–BaTiO₃ was modified by sucrose. As can be seen, m-N–BaSO₄–BaTiO₃ shows higher degradation efficiency. M-N–BaSO₄–BaTiO₃ degraded 92.9% of AR151 which was much higher than the degradation yield for N–BaSO₄–BaTiO₃ (88.5%).

Figure 10.

Effect of sucrose on piezocatalytic activity of doped BaTiO₃ to degrade AR151. (A) related UV–Vis spectra, (b) related degradation efficiency, and (c) compare degradation for sucrose and without sucrose.

Table 4.

Effect of sucrose on piezocatalytic activity of doped BaTiO₃ to degrade AR151.

Catalyst	Ultrasonic time (min)	Pulse: on: off (s)	Power (W)	Decontamination efficiency (%)
m-N–BaSO4–BaTiO3	90	2:2	100	92.9
m-S–BaSO4–BaTiO3	90	2:2	100	81.7
m-Cu–BaSO4–BaTiO3	90	2:2	100	85.9
m-Fe–BaSO4–BaTiO3	90	2:2	100	82.1

We repeated these tests for degradation of AB113 and summarized results in Fig. 11a–c and Table 5. Cu–BaSO₄–BaTiO₃ degrades 86.7% of AB113 under ultrasonic waves with 100 W in power for 90 min. By displacing Cu ions with Ba in the BaTiO₃ lattice, the smaller ionic radius results in the Cu–O bonds rotating more easily in the direction of the applied field. Thus, produces a larger piezoelectric effect and enhances the electromechanical responses. The smaller ionic radius of Cu can also result in a smaller defensive force between the ions and produces a larger displacement of Cu under stress. Therefore, when the same amount of mechanical force was applied, the dipole moment induced in Cu–BaSO₄–BaTiO₃ would be larger and a higher piezoelectric constant would be obtained^40–42. By modifying it with sucrose the degradation efficiency for AB113 was increased to 90.7%. M-Fe–BaSO₄–BaTiO₃ decontaminates about 90.1% of AB113, while Fe–BaSO₄–BaTiO₃ degrades about 77.6% of AB113. Comparing the decomposition efficiency of S-doped BaSO₄–BaTiO₃ and S-doped BaSO₄–BaTiO₃ modified by sucrose showed higher decomposition efficiency for S-doped BaSO₄–BaTiO₃ modified by sucrose (degradation efficiency of 89.2 and 93.3% was achieved, respectively). N–BaSO₄–BaTiO₃ and m-N–BaSO₄–BaTiO₃ degraded 80.9 and 87.3% of AB113, respectively. Results showed that both dopants type and pollutants affect degradation efficiency. For example in the decontamination of AR151, Cu–BaSO₄–BaTiO₃ showed the highest piezocatalytic activity, while S–BaTiO₃ showed the highest performance in decontamination AB113. Results also showed that sucrose generally could improve the piezocatalytic activity of BaSO₄–BaTiO_3.

Figure 11.

Effect of sucrose on piezocatalytic activity of doped BaTiO₃ to degrade AB113. (A) related UV–Vis spectra, (b) compare degradation for sucrose and without sucrose, and (c) related degradation efficiency with sucrose.

Table 5.

Effect of sucrose on piezocatalytic activity of doped BaTiO₃ to degrade AB113.

Catalyst	Ultrasonic time (min)	Pulse: on: off (s)	Power (W)	Decontamination efficiency (%)
m-N–BaSO4–BaTiO3	90	2:2	100	87.3
m-S–BaSO4–BaTiO3	90	2:2	100	93.3
m-Cu–BaSO4–BaTiO3	90	2:2	100	90.7
m-Fe–BaSO4–BaTiO3	90	2:2	100	90.1

Study the effect of ultrasonic power and pulse on piezocatalytic degradation efficiency of AB113

As a piezocatalyst, S–BaSO₄–BaTiO₃ was used to study the effects of ultrasonic power and pulse. Three power levels, including 100, 150, and 200 W, and three pulse rates, including 1:5, 2:2, and 5:1 s on–off, were chosen. The related spectra are shown in Fig. 12a, and the related decontamination efficiency is shown in Fig. 12b. According to the results, a pulse with 2 s on and 2 s off showed the highest decontamination efficiency for all ultrasonic powers. To produce more active radicals and exhibit piezoelectricity again, piezocatalysts need time to return to the ground state. As the ground state, we define it as the state in which positive and negative charges are symmetrically dispersed. The Piezocatalyst has enough time to return to the ground state when the pulse is 2:2 (on–off). Thus, can produce more radicals in the next vibration pulse and shows a higher degradation efficiency. As a result of increasing the power, degradation efficiency decreased. As the ultrasonic power increases, the temperature of the reaction will also rise. Our previous study showed that increasing temperature resulted in a decrease in decontamination yield because dye degradation by piezo is exothermic⁴³.

Figure 12.

Effect of ultrasonic pulse and power on decontamination of AB113. S–BaSO₄–BaTiO₃ was used as the piezocatalyst: (a) related spectrum and (b) degradation results.

Piezocatalytic Mechanism

To recognize a possible active species in piezocatalytic degradation of pollutants EDTA, isopropanol, and L-methionine were used as the hole (h⁺), hydroxyl radical (·OH), and peroxide radicals (O₂·⁻) scavengers, respectively. Results are summarized in Fig. 13a–c. Based on the results EDTA, isopropanol, and L-methionine significantly suppressed the piezoelectric decontamination process. By adding EDTA, L-methionine, and IPA, the decontamination efficiencies were decreased from 89.2% to 30.1%, 56.6%, and 23.1.0%, respectively. Radical trapping evaluation indicated that the piezo-generated O₂·⁻ and holes (h⁺) played the main role in the piezoelectric decontamination of AB113^44–47. According to Fig. 13c, by applying mechanical force (ultrasonic waves) the centers of symmetry of the charges move apart. They no longer coincide and give rise to the net charge on the surface. These positive and negative charges react with oxygen and water and produce active radical species that could degrade organic pollutants. Based on the results, the degradation process model could be as follow:

$${\text{BaSO}}_{{\text{4 - BaTiO}}_3}\text{composite}+\text{Vibration}\to {\text{BaSO}}_{{\text{4 - BaTiO}}_3}\text{composite}({\text{e}}^{-}+{\text{h}}^{+})$$ 1

$${\text{e}}^{-}+{\text{O}}_2\to {\text{O}}_2^{-}$$ 2

$${\text{h}}^{+}+{\text{H}}_2\text{O}\to {\text{H}}^{+}{+}^{·}\text{OH}$$ 3

$${}^{·}{\text{O}}_2^{-}+\text{dye}\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{by-products}$$ 4

$${\text{h}}^{+}+\text{dye}\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{by-products}$$ 5

$${}^{·}\text{OH}+\text{dye}\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{by-products}$$ 6

Figure 13.

Possible mechanism for decontamination of AB113 by using a piezocatalyst. EDTA, IPA, and L-methionine as the hole (h⁺), hydroxyl radical (·OH), and peroxide radical (O2·⁻²) scavengers, respectively. (a) Related spectrum, (b) related degradation efficiency, and (c) schematic for piezo degradation.

Reusability of piezo-catalyst

In addition to piezo-catalytic efficiency, the reusability of a piezo-catalyst is an important factor for practical applications. Five successive piezo-catalytic experimental runs were conducted to evaluate the stability of as-prepared piezo-catalysts in operation conditions by adding recycled m-S–BaSO₄–BaTiO₃ nanomaterial to fresh AB113 solutions without changing the overall concentration of the catalyst under ultrasonic irradiation. Results provided in Fig. 14 show that the piezo-catalytic activity of the m-S–BaSO₄–BaTiO₃ sample does not show a significant loss after five recycles for the degradation of AB113.

Figure 14.

Reusability of the m-S–BaSO₄–BaTiO₃ in five successive experimental runs for the piezocatalytic degradation of AB113 in aqueous solution under ultrasonic irradiation.

Conclusion

In this research, the piezocatalytic activity of barium sulfate (a very cheap mineral) improved by coupling it with BaTiO₃ and doped BaTiO₃ (Cu–BaTiO₃, Fe–BaTiO₃, S–BaTiO₃, and N–BaTiO₃) in the BaSO₄–BaTiO₃ composite. Cu–BaSO₄–BaTiO₃, Fe–BaSO₄–BaTiO₃, S–BaSO₄–BaTiO₃, and N–BaSO₄–BaTiO₃ were modified by sucrose as a natural piezo-material to achieve more improvement.

SEM and EDX results show that BaSO₄ appeared as micro-size particles, while BaTiO₃ and Cu–BaTiO₃, Fe–BaTiO₃, S–BaTiO₃, and N–BaTiO₃ appeared as nano-sized structures. Ba source for preparing BaTiO₃ came from initial BaSO₄. XRD and EDX do not support doping N into BaTiO₃, this could be happening because it does not dop into BaTiO₃ or a very low amount of it is doped into BaTiO₃. Piezocatalytic activity of BaSO₄, BaSO₄–BaTiO₃, X-BaSO₄–BaTiO₃ (X: Cu, Fe, S, and N), and X-BaSO₄–BaTiO₃ modified by sucrose were studied by the degradation of AR151 and AB113. Ultrasonic irradiation was used as a mechanical force. Results approve that the piezocatalytic activity of BaSO₄ sufficiently improved by coupling it with BaTiO₃, X-BaTiO₃, and their modification by sucrose. For instance, BaSO₄ degrade 56.7% of AR151 and 60.9% of AB113 during 90 min ultrasonic vibration. By coupling it with BaTiO₃, degradation efficiency increased to 61.3% and 64.4%, respectively. Doping BaTiO₃ with copper improves the degradation efficiency of AR151 to 86.7%. Doping BaTiO₃ with S improves the decontamination efficiency of AB113 to 89.2% which shows a huge enhancement. Modify BaSO₄–S–BaTiO₃ with sucrose lead to achieve a degradation efficiency of 93.3% for AB113. Besides, a possible mechanism was disused by using radical trapping experimental.

Author contributions

O.A designed and conceived the idea and wrote the paper. G.A., Ch. B., and H. H. prepared the catalyst, performed most of the experiments, and collected and analyzed the data. A.A. helped to measure and analyze the SEM. M. S helped to wrote the paper. M. J. edited the manuscript. All the authors contributed to discussing and commenting on the manuscript.

Data availability

All data generated or analysed during this study are included in this published article (and its Supplementary Information files).

Competing interests

The authors declare no competing interests.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-022-24992-y.