Study on the degradation performance of novel molecularly imprinted Nd-TiO2 for oxytetracycline hydrochloride

doi:10.21203/rs.3.rs-3943937/v1

Download PDF

Research Article

Study on the degradation performance of novel molecularly imprinted Nd-TiO2 for oxytetracycline hydrochloride

https://doi.org/10.21203/rs.3.rs-3943937/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

The objective of the study was to synthesize a novel photocatalyst, referred to as molecularly imprinted Nd-TiO₂ (MIP-Nd-TiO₂), through the sol-gel method. It rapidly identifies and breaks down oxytetracycline hydrochloride (OTC). By manipulating the doping ratio of Nd, incorporating imprinted molecules, and regulating the calcination conditions, the molar ratio of Ti to Nd was optimized to 100:1.25, the mass of added OTC was maintained at 0.15 g, and MIP-Nd-TiO₂ was synthesized by calcining it for 2 h at 500 had the best degradation performance. Furthermore, the impact of these variables on the photocatalytic efficiency of the MIP-Nd-TiO₂ catalysts was thoroughly investigated by varying the concentrations of pollutants and pH. The materials underwent evaluation employing precise characterization techniques, including, XPS, BET, and FT-IR among others. The findings from the photocatalytic experiments revealed that the degradation rates of OTC by MIP-Nd-TiO₂, Nd-TiO₂, and TiO₂ consisted of 91.97%, 76.47%, and 64.34%, correspondingly, after dark adsorption equilibrium and followed by irradiation with 365 nm UV light for 30 min. Specifically, in just 40 minutes, the MIP-Nd- TiO₂ adsorption-photocatalytic synergy was capable of achieving a 93.14% degradation rate for OTC. Moreover, an investigation was conducted into the photocatalytic and adsorption selectivity of MIP-Nd-TiO₂. To conclude, this study has illustrated the viability of employing photocatalysis and molecular imprinting in tandem, which can be an extremely efficient technique for treating OTC in wastewater.

Molecular imprinting

MIP-Nd-TiO2

Oxytetracycline hydrochloride

Selective degradation

Adsorption-photocatalytic synergistic reaction

Highly efficient treatment

Antibiotics have been widely utilized in recent decades due to their potent bactericidal properties and diverse array of indications. These attributes have significantly contributed to the prevention and treatment of diseases affecting both humans and animals(Boot et al 2022; Dong et al 2021; Wei et al 1994). Oxytetracycline hydrochloride (OTC) is a broad-spectrum and inexpensive antibiotic that has been widely used to prevent and treat disease. However, due to large-scale production and overuse, its release into the aquatic environment has adversely affected human health and the aquatic ecosystem as a whole(Yang et al 2020). Therefore, the degradation of hygromycin hydrochloride is an issue that must be taken seriously, and so far, antibiotic removal methods include adsorption、biological treatment(Zhang and Wang 2022)、membrane treatment(Singh and Sharma 2018)、Fenton process(Zhao et al 2020), and photocatalytic degradation(Wang et al 2023). Photocatalytic degradation is a commonly employed method for breaking down antibiotics due to its distinct benefits, including strong stability, high efficacy, environmental friendliness, and absence of pollution.

TiO₂ is one of the semiconductor photocatalysts that has been utilized extensively in photocatalysis owing to numerous benefits, including affordability, non-toxicity, and ease of preparation(Fujishima et al 2000; Ohno et al 2003). At the same time, because of its degradation effect on various organic and inorganic pollutants, which is incomparable to other conventional water treatment processes, it is often used for the degradation of difficult-to-degrade organic matter(Linsebigler et al 1995). Nevertheless, the utilization of TiO₂ in photocatalytic reactions is impeded by certain specific limitations. TiO₂ has an inherent constraint in its narrow prohibited band widths, rendering it primarily responsive to ultraviolet (UV) light. Furthermore, the generated electron-hole pairs promptly combine, significantly compromising the effectiveness of the photocatalytic process(Irie et al 2003; White et al 2010). As a result, enhancing the photocatalytic ability primarily involves figuring out how to make it more sensitive to visible light and how to make photogenerated electron-hole pairs last longer. Various endeavors have been undertaken to enhance the photocatalytic efficacy of TiO₂, including surface sensitization、noble metal deposition、doping(Peisan et al 2018). One of the most popular techniques for raising the photocatalytic activity of TiO₂ is doping. Bayati et al(Bayati et al 2010) used a sol-gel method to synthesize Nd-doped TiO₂ nanoparticles that degraded methylene blue (MB) by 92% after 45 minutes, while the degradation rate of pure TiO₂ was 86%. Its photocatalytic activity was enhanced. The degradation efficiency might be further improved if selective degradation of the target pollutants could be realized. Molecular imprinting technology (MIT) may be a good solution to this problem. MIT is a molecular recognition technology that selects a certain carrier as the substrate and then adds amount of functional monomers, target ions (molecules), cross-linking agents, and initiators. Their functional groups are connected under the initiating polymerization of the initiator(Sun et al 2022). When the imprinted molecules are eluted, imprinted cavities are presented(Liu et al 2024), and these imprinted cavities produce molecular recognition sites that are well adapted to the shape and size of the template molecule(Villa et al 2021). MIP has significant selectivity for template molecules compared to non-molecularly imprinted polymers (NIP). Zhang et al(Zhang et al 2022) synthesized Pr-doped TiO₂ (Pr-MIP-TMCs), which have been molecularly imprinted with 2-sec-butyl-4,6-dinitrophenol (DNBP) as a template, were able to degrade 90% of DNBP. Comparably, TiO₂ crystallize (TMCs) exhibited a reduced degradation rate of 50%. Pr-MIP-TMCs exhibited superior adsorption capacity and selectivity for DNBP compared to the structural analog phenol, resulting in enhanced photocatalytic performance.

Combining the advantages of rare-earth metal-doped TiO₂ and molecular imprinting. in this study, The sol-gel approach was used to successfully synthesize molecularly imprinted Nd-doped TiO₂ photocatalysts (MIP-Nd-TiO₂) utilizing (Nd(NO₃)₃-6H₂O) the Nd source, and oxytetracycline hydrochloride (OTC) as a molecularly imprinted template. The prepared MIP-Nd-TiO₂ samples exhibited excellent photocatalytic degradation effect on the OTC degradation with excellent photocatalytic degradation, with OTC structural analog TC as a competitor when comparing the selectivity. Through the use of various characterization techniques, including XPS, TEM, and XRD, the impact of material structure evolution on photocatalytic degradation was analyzed. Some ideas are provided for future water treatment to make wastewater treatment more efficient.

2.1. Catalyst synthesis steps

Sol-gel synthesis was used to synthesize MIP-Nd-TiO₂ nanoparticles, as shown in Fig. 1. Initially, a solution was prepared by dissolving 10 mL of glacial acetic and 20 mL of Tetra-butyl ortho-titanate (C16H36O4Ti) acid in 40 mL of anhydrous ethanol. Following the addition of a predetermined quantity of oxytetracycline hydrochloride (OTC), the solution underwent 30 minutes of magnetic stirring (called solution A). For the subsequent procedure, a precise quantity of Nd(NO₃)₃-6H₂O was dissolved in 20 mL of anhydrous ethanol, which was called solution B. After 20 minutes of magnetic stirring to ensure complete dissolution, solution B was subsequently introduced drop by drop to solution A. After that, the mixture was mixed for 3h. After 24 h at ambient temperature, the sol underwent a transformation into a moist gel. Then the wet gel was dried in an oven set to 60°C for 24 h, and this made the gel dry. Ultimately, MIP-Nd-TiO₂ was prepared by calcination in a muffle furnace at a temperature of 500°C for a duration of 2 h. MIP-Nd-TiO₂ was prepared without adding Nd(NO₃)₃-6H₂O and OTC to synthesize pure TiO₂. MIP-Nd-TiO₂ was prepared without adding OTC to synthesize Nd-TiO₂.

2.2. Characterize

Transmission electron microscopy (TEM, Talos F200X) was used to observe the material's micro-morphological structure and lattice spacing. Detection of the valence of the element and the form in which it is present in the material by X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi). Phase analysis and crystal composition of materials by X-ray diffractometer (XRD, analytical B.V). A Specific Surface Area and Porosity Analyzer (BET, ASAP 2460) was used to examine the specific surface area and porosity of the material. Analysis of photoluminescence profiles (PL) by fluorescence spectrophotometer (HORIBA, JY Fluorolog3). Using Fourier Transform Infrared Spectrometer (FI-IR, Shimadzu Corporation, Japan) to examine the material's functional groups. The light absorption characteristics of the materials were examined using a solid-state UV-visible spectrophotometer (UV3600I Plus, Shimadzu). A spectrometer (Bruker A300) was used to measure electron spin resonance (ESR) spectra by UV illumination with a dominating wavelength of 365 nm.

2.3. Photocatalytic experiment

Firstly, a volume of 60 mL containing 20 mg/L of OTC solution was transferred into a test tube made of quartz glass, and then 0.012 g of catalyst was weighed with a balance and poured into the test tube. After the catalysts attained adsorption-desorption equilibrium, subsequently, the photocatalytic reaction was conducted using a 400 W ultraviolet (UV) light, with a sampling interval of 5 min, and 6 ml of solution was taken each time. The samples taken at each time were first filtered and then analyzed by UV-visible spectrophotometer at 343 nm, and the rate of change of OTC concentration in the solution was used to figure out the rate of degradation.

2.4. Quenching experiment

Previous investigations have identified ·O₂ ⁻、·OH and h⁺ as the primary oxidized agents during the photocatalytic degradation process(Wang et al 2020). 60 mL of a 20 mg/L OTC solution were added to quartz glass tubes containing 0.012 g of MIP-Nd-TiO₂, then 0.15 mmol/L p-benzoquinone (BQ),1 mL of isopropanol (t-BuOH), and 0.15 mmol/L disodium ethylenediaminetetraacetate (EDTA-2Na) were added, serving as a capturing substance for ·O₂ ⁻, -OH, and h⁺, correspondingly. And 400 W of ultraviolet (UV) light was used to conduct the reaction and sample every 8 minutes. The absorbance change of OTC was measured once to determine what active substances were involved in the photocatalytic reaction process.

3.1. Analyzing the characterization results

3.1.1. XRD, BET, and UV-Vis characterization

XRD was used for examining the three catalysts, TiO₂, Nd-TiO₂, and MIP-Nd-TiO₂, for phase detection. Figure 2(a) illustrates the 2θ values of 25.32°, 37.79°, 48.14°, 54.09°, 62.82°, and 75.12° matched to the diffraction peaks of anatase TiO₂ according to the standard diffraction card (PDF# 21-1272), indicating that materials exhibited pure anatase phase, which facilitates the absorption of light with higher photocatalytic catalytic activity. The XRD patterns did not exhibit any distinct peaks associated with Nd₂O₃. The reason for this is that when Nd³⁺ ions penetrate the TiO₂ crystals, the amount of Nd₂O₃ is very small and highly dispersed in TiO₂. Nd³⁺ may be seen either as an amorphous phase that is adsorbed onto the outside of TiO₂ or as an inclusion inside the TiO₂ lattice(Marcì et al 2001).

All three materials were investigated using the BET test, and the findings are presented in Fig. 2(b). The N2 adsorption-desorption isotherms of the three catalysts exhibit Type IV isotherms with H3-type hysteresis behavior, based on the IUPAC. This behavior is characteristic of mesoporous materials.(Liu et al 2023). The majority of the pore size distributions of the three materials illustrated in Fig. 2(c) range between 0 and 20 nm and the preparation of catalysts with mesoporous characteristics was confirmed by this result. TiO₂, Nd-TiO₂, and MIP-Nd- TiO₂ had specific surface areas of 12.02 m²/g, 65.90 m²/g, and 86.85 m²/g, correspondingly, as displayed in Table 1. As contrasted to TiO₂ and Nd-TiO₂, the specific surface area of MIP-Nd-TiO₂ rose dramatically, and the reaction sites were increased due to the larger specific surface area, which led to the improvement of photocatalytic performance.

The UV-visible spectroscopy technique was used to investigate the optical absorption characteristics of the synthesized materials. The optical absorption edge thresholds of TiO₂, Nd-TiO₂, and MIP-Nd- TiO₂ are illustrated in Fig. 2(d), where they are 434 nm, 431 nm, and 430 nm, respectively. Using the empirical equation Eg = 1240/λ(Qi and Wang 2020), the prohibited band widths of the three catalysts were determined to be 2.85 eV, 2.88 eV, and 2.89 eV, correspondingly. In contrast to TiO₂ and Nd-TiO₂, the optical absorption edge of MIP-Nd-TiO₂ shows a very little degree of blueshift, but exhibits an upward shift in the wavelength range of 450–800 nm, indicating an improvement in visible light absorption. This increase in absorption may be attributed to Nd elemental doping and the incorporation of imprinted molecules.

Table 1

Specific surface area (SBET), pore volume (Vp), and average pore size (Dp) of the different catalysts
Catalyst	S_BET(m²/g)	Vp(cm³/g)	Dp(nm)
TiO₂	12.02	0.06	2.82
Nd-TiO₂	65.90	0.12	7.31
MIP-Nd-TiO₂	86.85	0.14	6.21

3.1.2. TEM characterization

To further analyze the surface morphology and microstructure of the synthesized materials, TEM characterization of the samples was carried out. Figure 3(a), (b), and (c) illustrate 100 nm TEM images of the synthesized material. We can observe that the agglomeration phenomenon of pure TiO₂ is more serious, and the agglomeration phenomenon of MIP-Nd-TiO₂ has not been so obvious compared to that of TiO₂ and Nd-TiO₂ with a greater improvement. MIP-Nd-TiO₂ has a smaller particle size, and the particle distribution can be more clearly observed, indicating that doping Nd elements and adding imprinted molecules can effectively reduce the inter-particle aggregation, which may enable it to have a larger specific surface area, and this aligns with the findings shown in Table 1. The introduction of Nd elements and imprinted molecules during the synthesis of modified TiO₂ samples did not significantly change the overall morphology of the catalysts can be observed. Figure 3(d) displays a 5 nm TEM image of MIP-Nd-TiO₂, where a lattice stripe of 0.352 nm can be clearly observed, corresponding to the (101) crystal plane of anatase, which conforms to the XRD characterization results (Fig. 2(a)). In summary, the agglomeration of MIP-Nd-TiO₂ particles was suppressed and the particle size was small, so there were more photocatalytic active sites with higher photocatalytic activity.

3.1.3. XPS characterization

XPS was used to investigate the valence states of the elements in MIP-Nd-TiO₂. The XPS spectra of O, Nd, C, and Ti elements were detected, corresponding to O 1s, Nd 3d, C 1s, and Ti 2p, as depicted in Fig. 4(a). The Ti 2p XPS spectra of MIP-Nd-TiO₂ are displayed in Fig. 4(b). The electronic orbitals of Ti 2p3/2 and Ti 2p1/2 are represented by these peaks, which are situated at 458.45 eV and 464.15 eV of the binding energy. Suggests that the presence of TI is in the form of Ti4 + in MIP-Nd-TiO₂^{(Luo et al 2017)}. Figure 4(c) displays the O 1s XPS spectra of MIP-Nd-TiO₂. Lattice oxygen in TiO₂ contributes to the material's peak at 529.72 eV, whereas the presence of hydroxyl groups (-OH) results in a peak at 532.05 eV (Qin et al 2024). The Nd 3d XPS spectra of MIP-Nd-TiO₂ are illustrated in Fig. 4(d), where two prominent peaks matching the Nd 3d5/2 and Nd 3d3/2 orbitals are located at 974.43 eV and 994.19 eV, respectively, indicating that the sample doped Nd exists in the form of Nd3⁺ (Nithya et al 2018). Overall, the XPS characterization results showed proof of successful doping of Nd, proving that the MIP-Nd-TiO₂ catalyst was successfully synthesized.

3.1.4. FT-IR and PL characterization

FT-IR spectroscopy was used to examine the materials' functional groups. All three catalysts exhibited -OH peaks at 1324 cm^− 1 and 3327 cm^− 1, as illustrated in Fig. 5(a), as a result of the absorption of CO₂ and O₂ from the surrounding air. Among them, Nd doping and the addition of imprinted molecules resulted in larger peaks due to increased ligand bonding and the creation of new bonds, respectively. The O-H stretching vibration peaks of carboxylic acid dimers are 2850 cm^− 1 and 2779 cm^− 1(Zhu et al 2020), where the MIP-Nd-TiO₂ produced new peaks at 2349 cm^− 1, and the strong hydrogen bonding formed may increase its performance in degrading pollutants. It can be clearly observed that no functional groups such as lipid and amide bonds were found for MIP-Nd-TiO₂ at 1680 cm^− 1-1750 cm^− 1, indicating that the imprinted molecules were completely eluted.

Figure 5(b) shows the PL patterns of the three species of catalysts, the PL peaks of MIP-Nd-TiO₂ are conspicuously diminished in comparison to those of Nd-TiO₂ and TiO₂. A decrease in the intensity of the PL peaks of the catalysts corresponds to a reduction in the rate of electron-hole pair complexation. This indicates that the charge transfer effect is enhanced and electron-hole pair recombination is impeded(Ma et al 2024). This phenomenon improves the photocatalytic performance. The lowest spectral peak of MIP-Nd-TiO₂ among the three catalysts represents the better photocatalytic performance of MIP-Nd-TiO2.

3.2. Catalyst degradation performance studies

3.2.1. Influence of catalyst doping ratio on catalyst degradation performance

To achieve the most efficient degradation of OTC by the catalyst, the optimal Nd and Ti doping ratios as well as the optimal doping content for molecular imprinting were explored, and the orthogonal experimental bubble diagrams with different Nd doping ratios and OTC doping are shown in Fig. 6(a). The results of the preexisting experiments show that there is almost no enhancement for n(Nd)/n(Ti) < 1% and m(OTC) < 0.1 g. The poor enhancement effect may be due to the small hindering effect on photogenerated carrier complexation or incomplete formation of imprinted cavities when the doping amount of Nd or molecular imprinting is too small. It is evident from Fig. 6(a) that the bubble volume is highest when n(Nd):n(Ti) = 1.25:100 and m(OTC) = 0.15 g. The highest OTC degradation rate of the synthesized catalyst under these conditions reaches 91.97%, which is a 1.42-fold enhancement compared to that of the pure TiO₂ without any doping, which is 64.34%, for the degradation rate of OTC. It indicates molecular imprinting adding and Nd doping enhanced the photocatalytic capacity of TiO₂.

3.2.2. Influence of variation of calcination temperatures on the degradation performance of catalysts

Figure 6(b) illustrates the impact of MIP-Nd-TiO₂ on OTC degradation at calcination temperatures of 450, 500, and 550 ℃. As the calcination temperature was raised from 450 ℃ to 500 ℃, the degradation performance of MIP-Nd-TiO₂ increased; As the calcination temperature was raised from 500°C to 550°C, the degradation performance of MIP-Nd-TiO₂ reduced. At 500°C, the MIP-Nd-TiO₂ degrading performance was the best, which indicated that the TiO₂ calcined at 500 ℃ was in the phase of pure anatase, and the photocatalytic effect of MIP-Nd-TiO₂ was the best at this time.

3.2.3. Influence of variation of calcination time on the degradation performance of catalysts

The degrading impact of MIP-Nd-TiO₂ was investigated at calcination temperatures of 500°C and periods ranging from 1 to 4 h, as illustrated in Fig. 6(c). It is evident that increasing the calcination temperature from 1 to 2 h enhanced the MIP-Nd-TiO₂ degrading performance, indicating that the calcination time was too short leading to the incomplete formation of anatase. The degradation performance of MIP-Nd-TiO₂ gradually decreased with the time from 2 h to 4 h, indicating that the calcination time was too long leading to the formation of rutile-phase TiO₂, which was unfavorable to the photocatalytic reaction. When the calcination time is 2 h, the formation of the anatase phase can be better and the photocatalytic performance can be improved, so the optimal calcination time of the catalyst is 2 h. Combined with the above, the optimal calcination conditions of MIP-Nd-TiO₂ were obtained to be calcined at 500 ℃ for 2 h.

3.2.4. Adsorption properties of catalysts

Figure 6(d) shows the pure adsorption diagram of the catalysts. The degradation rates of OTC by TiO₂, Nd-TiO₂, and MIP-Nd-TiO₂ were 3.74%, 9.98%, and 16.21%, respectively, after achieving the adsorption-desorption equilibrium of the three catalysts after 60 minutes of adsorption in the dark. The adsorption rate of pure TiO₂ was negligible at less than 5%. In contrast, doping Nd and adding imprinted molecules enhanced adsorption performance, which might be attributed to an enhancement in the catalyst's specific surface area after doping Nd and adding imprinted molecules (following the results of Table 1), and the incorporation of the molecular imprints provided more selective active sites, which allowed for the adsorption of more pollutants.

3.2.5. Photocatalytic performance of catalysts

Figure 7(a) shows the photocatalytic degradation of the catalysts. It can be clearly found that the photocatalytic performance of MIP-Nd-TiO₂ is much larger than its adsorption performance, which degrades OTC mainly through photocatalytic reaction. The degradation rates of TiO₂, Nd-TiO₂, and MIP-Nd-TiO₂ on OTC were 64.34%, 76.67%, and 91.97%, correspondingly. MIP-Nd-TiO₂ exhibited a 1.42-fold increase in degradation efficiency in comparison to pure TiO₂. It suggests that doping with Nd and adding imprinted molecules improves the photocatalytic activity of pure TiO₂ more than before. The degradation rate of OTC by MIP-Nd-TiO₂ is enhanced by 15.5% compared with that of Nd-TiO₂. It may be due to the formation of imprinted cavities after doped molecules imprinting, which provides recognition sites for OTC and can degrade OTC more efficiently.

3.2.6. Influence of different reaction conditions on the degradation performance of catalysts

(1) Influence of different initial concentrations of OTC catalysts on degradation performance

In daily life, the concentration of pollutants in wastewater can be different due to different production methods, so it is necessary to study the efficiency of the catalyst to degrade different concentrations of degradation. Figure 7(b) investigated the degradation rate of MIP-Nd-TiO₂ for the degradation of different concentrations of OTC. The experimental procedure is the same as the photocatalytic experiment. The degradation rates of MIP-Nd-TiO₂ for 10 mg/L, 20 mg/L, 30 mg/L, and 40 mg/L OTC were 95.50%, 91.97%, 84.03%, and 75.24%, correspondingly. It is evident that the concentration of OTC increased concurrently with a progressive reduction in the MIP-Nd-TiO₂ degradation rate. This may be attributed to the fact that with the gradual increase of OTC concentration, on the one hand, the color of the solution gradually deepens, which reduces the light transmittance, and on the other hand, the light absorption is lower because more OTC molecules in solution are encapsulated on the surface of MIP-Nd-TiO₂. These factors made the degradation performance of MIP-Nd-TiO₂ decline.

(2) Influence of OTC at different pH on the degradation performance of catalysts

The pH of the wastewater may change every moment, so it is necessary to study the degradation rate of MIP-Nd-TiO₂ when degrading OTC at different pH, It is evident from Fig. 7(c) that at pH = 6.65(pH of 20 mg/L OTC), MIP-Nd-TiO₂ had the maximum degrading efficiency of 91.97%., and degradation efficiencies at pH = 3, 5, and 9 respectively were 79.93%, 87.16%, and 83.17%. As the pH of OTC rises, the degrading performance of MIP-Nd-TiO₂ on OTC tends to first rise and then fall, which may be due to the fact that when the pH is lower, there is a strong positive charge in the solution; When the pH is higher, there is a strong negative charge in the solution, and the strong electrostatic repulsion between the charges significantly reduces the photocatalytic performance of the catalysts(Wu et al 2016). When pH = 6.65, the solution is neutral, there are fewer positive and negative charges in the system, and electrostatic repulsion is almost nonexistent(Shen et al 2023). As a result, the photocatalytic performance remains almost unchanged. So it shows higher photocatalytic performance.

3.2.7. Adsorption-photocatalytic synergistic reaction

In practical engineering, wastewater treatment often pursues the highest possible degradation efficiency. Through our study, we found that the efficiency of OTC degradation by MIP-Nd-TiO₂ was higher under the adsorption-photocatalytic synergistic reaction. Figure 7(d) shows the degradation of OTC by three catalysts under the adsorption-photocatalytic synergistic reaction of MIP-Nd-TiO₂, it can be seen that after 40 min of reaction, the degradation of OTC by pure TiO₂, Nd-TiO₂, and MIP-Nd-TiO₂ degradation of OTC after 40 min of reaction were:64.44%, 77.19%, and 93.14%, correspondingly. This phenomenon occurs owing to the concomitant operation of adsorption and photocatalysis: catalysts containing adsorbed cavities have a greater propensity to absorb photons, thereby enhancing the movement of photogenerated electrons and subsequently augmenting their photocatalytic efficiency(Chen et al 2022). Compared with dark adsorption followed by photocatalytic reaction, the reaction time was 50 min less while achieving a better degradation effect and improving the efficiency of MIP-Nd-TiO₂ in degrading OTC.

3.3. Molecularly imprinted Nd-TiO₂ degradation selectivity studies

3.3.1. Adsorption selectivity

To investigate the selectivity of MIP-Nd-TiO₂, tetracycline (TC), a structural analog of oxytetracycline hydrochloride (OTC), was selected as a competitive degradation pollutant for selectivity experiments. The adsorption selectivity of MIP-Nd-TiO₂ was briefly investigated because of its much weaker adsorption performance compared to the photocatalytic ability. A 100 mL conical flask holding 50 mL of 20 mg/L OTC solution was filled with 0.01 g of MIP-Nd-TiO₂, and the conical flask was placed into a thermostatic oscillator to oscillate for 3 h under dark conditions to test the final OTC concentration. The distribution coefficient K_D and adsorption selectivity coefficient α1 were used to evaluate the adsorption selectivity of MIP-Nd-TiO₂. Calculate the adsorption selectivity factor by listing the formula:

$${K}_{D}=\frac{{Q}_{e}}{{C}_{e}}$$

$${\alpha }_{1}=\frac{{K}_{D1}}{{K}_{D2}}$$

Where the competitor's and template's distributed factors are denoted by K_D1 and K_D2, accordingly.

α₁ is the adsorption selectivity coefficient(Qi and Wang 2020).

Table 2

exhibits the fitting coefficient values. The adsorption selectivity coefficient of MIP-Nd-TiO₂ and Nd-TiO₂ for OTC are 1.392 and 0.895, correspondingly, in contrast to the adsorption selectivity coefficient of MIP-Nd-TiO₂ for OTC, which are 1.55 times more than those of Nd-TiO₂. It is demonstrated that MIP-Nd-TiO₂ has superior adsorption ability for OTC compared to TC, indicating the selective adsorption of MIP-Nd-TiO₂ on OTC.
Catalyst	Contaminants	Qe	Ce	K_D	α₁
MIP-Nd-TiO₂	OTC	0.811	16.755	0.048	1.392
MIP-Nd-TiO₂	TC	0.610	17.550	0.034	1.392
Nd-TiO₂	OTC	0.499	18.003	0.027	0.895
Nd-TiO₂	TC	0.550	17.790	0.031	0.895

Table 2 Adsorption selectivity and distribution coefficients of MIP-Nd-TiO₂ and Nd-TiO₂ for OTC

3.2.2. Photocatalytic selectivity

Figure 8(a) shows the degradation of OTC and TC by MIP-Nd-TiO₂ and Nd-TiO₂, respectively, and it can be clearly seen that both catalysts degraded OTC better than TC, but due to the blotting molecules doped in MIP-Nd-TiO₂, the degradation of OTC by MIP-Nd-TiO₂ was significantly superior to that of degradation of TC, whereas the degradation of OTC and TC by Nd-TiO₂ degradation effects were very similar. Figure 8(b) shows the fitting of the photocatalytic reaction kinetics. it can be observed that the reaction kinetic constants, K, for the degradation of OTC and TC by MIP-Nd-TiO_2, are 0.7756 and 0.4458, respectively, which is a very large difference, whereas there is a very small difference between the reaction kinetic constants, K, for the degradation of OTC and TC by Nd-TiO₂. Furthermore, the photocatalytic selectivity of MIP-Nd-TiO₂ for OTC was assessed using photocatalytic selection factors and selection coefficients. The kinetic constants of the two catalysts' photocatalytic processes are displayed in Table 3, the photocatalytic selectivity factors α₂(Sharabi and Paz 2010), and the selectivity coefficient of R(Gadzekpo and Christian 1984). Where R and α₂ are calculated as:

$$R=\frac{{K}_{1}}{{K}_{2}}$$

$${\alpha }_{2}=\frac{{R}_{1}}{{R}_{2}}$$

The higher selectivity factor represents the better selective degradation of OTC by the catalyst, and the selectivity factor of MIP-Nd-TiO₂ for OTC is higher than that of Nd-TiO₂, which is 1.653 times higher in comparison. It indicates that the doping of imprinted molecules improved the selectivity of the catalyst.

Table 3

Comparison of the main reaction kinetic parameters of photocatalyst
Catalyst	Contaminants	k/min^− 1	R	α₂
MIP-Nd-TiO₂	OTC	0.077	1.974	1.653
MIP-Nd-TiO₂	TC	0.039	1.974
Nd-TiO₂	OTC	0.043	1.194
Nd-TiO₂	TC	0.036	1.194

Figure 8 (a) Photocatalytic degradation of OTC and TC with different catalysts, (b) Reaction kinetic fitting

3.4. Analysis of photocatalytic degradation mechanism·

Quenching experiments were performed to investigate the contribution of ·O₂⁻, ·OH, and H⁺ to the photocatalytic reactions, with 0.15 mmol/L BQ, 1 mL t-BuOH, and 0.15 mmol/L EDTA-2Na as the trapping agents of ·O₂⁻, ·OH, and h⁺, and Fig. 9(a) displays the outcomes of the quenching studies. It can be obviously seen that all three capture agents have some inhibition effect on the photocatalytic reaction, indicating that all three active substances play a role in the photocatalytic reaction, in which the inhibition of photocatalytic reaction is most obvious after the addition of BQ, compared with the degradation rate without any capture agent was reduced by 70.85%, which indicates that the ·O₂ ⁻ plays a major role in the photocatalytic reaction. Figures 9(b), (c), and (d) illustrate the pattern obtained from the study using the electron spin resonance (ESR) technique, which can be associated with seeing that ·OH, ·O₂ ⁻ and h⁺ all exhibited signals at 2 min of the reaction. This aligns with the findings of the quenching experiments, suggesting that all three active components contribute to the photocatalytic process.

Figure 10 illustrates the reaction pathway of the photocatalytic degradation of OTC using MIP-Nd-TiO₂. MIP-Nd-TiO₂ has visible light responsiveness, and after absorbing the light energy, it excites valence band electrons into the conduction band. At this time, the electron valence band jumps, getting a free electron (e⁻). The electron that is exiting the valence band will produce a "hole" (h⁺). The formation of electrons and holes occurs almost simultaneously, and together they form electron-hole pairs. However, to carry out an effective photocatalytic reaction, the electrons, and holes need to be separated to prevent them from compounding rapidly. h⁺ can directly oxidize the OTC molecules adsorbed on the surface of MIP-Nd-TiO₂ or react with water to form ·OH, and in the meanwhile, reactive oxides like ·O₂⁻ can be created when e-reacts with oxygen molecules in solution or other oxidizing agents. Quenching experiments have proved that ·O₂⁻ is the main active species for photocatalysis. These ·O₂⁻ have strong oxidizing ability and can degrade the hygromycin molecule from the following two pathways: in the first pathway, the OTC molecule is deamidated and demethylated, followed by further oxidation, ─H═CO releases and opens the double bond, and then C═O will be oxidized and demethylated, and finally the double bond is broken to obtain P1-5. In the second pathway, the OTC molecule is stripped of H₂O first to produce P2-1, the decarbonylation reaction produces P2-2, and further dehydration produces P2-3(Gao et al 2022). These two pathways eventually continue to break down into other small molecule compounds and eventually mineralize into CO₂ and H₂O.

3.5. Repeatable experiments

The treatment cost is a necessary consideration in practical applications, and the reuse of catalysts can reduce the cost to a large extent, therefore, the reuse rate of catalysts is an important index to examine the catalysts. To elucidate the impact on the deterioration of OTC when MIP-Nd-TiO₂ is reused, four cycles experiments of MIP-Nd-TiO₂ for OTC degradation under the same conditions were set up, the experiments were adsorption-photocatalytic synergistic reaction (same as above), and the degradation rate of OTC was tested for 40 min in each experiment. Before each cycle, the catalyst from the previous cycle is recovered, rinsed, and dried. The outcomes of four cycles are exhibited ed in Fig. 11. The degradation performance for OTC is weakened a little bit after each cycle experiment, which may be due to the fact that the catalyst cannot completely wash away the OTC molecules adhered to the surface of MIP-Nd-TiO₂ during each cleaning, which not only the reactive sites of MIP-Nd-TiO₂ is reduced but also the light absorption of MIP-Nd-TiO₂ is reduced and thus the degradation rate of MIP-Nd-TiO₂ to OTC decreases. It can be observed that after four cycles, the degradation rate of MIP-Nd-TiO₂ on OTC is 82.1%, which is only 11.04% less than that of the first cycle, which indicates that MIP-Nd-TiO₂ can be reused at a higher rate.

In this work, the best degradation of OTC was achieved by MIP-Nd-TiO₂ at n(Nd):n(Ti) = 1.25:100, m(OTC) = 0.15 g, calcination temperature of 500 ℃, calcination time of 2 h. After adsorption equilibrium, the degradation rate of MIP-Nd-TiO₂ for OTC was 91.97% at 30 min, and the degradation rates of TiO₂ and Nd-TiO₂ for OTC were 64.34% and 76.67%, respectively.MIP-Nd-TiO₂ has various improvements in degrading OTC, including the addition of imprinted molecules to increase the selectivity, more surface-active sites due to enhanced specific surface area, and electron-hole pair complexation is inhibited because of Nd doping. These effects together resulted in a 1.42-fold increase in the degradation efficiency of MIP-Nd-TiO₂ compared to TiO₂. MIP-Nd-TiO₂ was more effective in the adsorption-photocatalytic synergistic reaction compared to the adsorption equilibrium followed by photocatalytic degradation of OTC, which resulted in a better degradation rate with a reduction in time by 50 min. Due to the addition of imprinted molecules to increase the selective active sites, MIP-Nd-TiO₂ showed better adsorption selectivity and photocatalytic selectivity for the degradation of OTC compared to Nd-TiO₂. During the degradation process, the ·O₂⁻ actives play a major role. In conclusion, this research presents a technique for increasing the efficiency of OTC degradation and a recommendation for treating additional contaminants in wastewater.

Author contribution ZhongWei Huang: conceptualization, software, validation, investigation, data curation, writing—review and editing. Bei Liu: validation, BoHai Wang: validation. Hang Yu: validation. Xian Liu: validation Lei Zhu: visualization, supervision. Xun Wang: visualization, supervision.

Funding This work is supported by the National Natural Science Foundation of China (51672196)

Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request

Ethics approval There are no ethical issues in this article.

Consent to participate All the authors agree to participate in this paper.

Consent for publication All the authors agree to the publication of this paper.

Competing interests The authors declare no competing interests.

Bayati M R, Molaei R, Zargar H R, Kajbafvala A, Zanganeh S (2010) A facile method to grow V-doped TiO₂ hydrophilic layers with nano-sheet morphology. Materials Letters 64(22): 2498-2501.https://doi.org/10.1016/j.matlet.2010.08.037
Boot W, Foster A L, Guillaume O, Eglin D, Schmid T, D'Este M, Zeiter S, Richards R G, Moriarty T F (2022) An Antibiotic-Loaded Hydrogel Demonstrates Efficacy as Prophylaxis and Treatment in a Large Animal Model of Orthopaedic Device-Related Infection. Front Cell Infect Microbiol 12: 826392.https://doi.org/10.3389/fcimb.2022.826392
Chen X, Liu X, Zhu L, Tao X, Wang X (2022) One-step fabrication of novel MIL-53(Fe, Al) for synergistic adsorption-photocatalytic degradation of tetracycline. Chemosphere 291: 133032.https://doi.org/10.1016/j.chemosphere.2021.133032
Dong S, Zhao Y, Yang J, Liu X, Li W, Zhang L, Wu Y, Sun J, Feng J, Zhu Y (2021) Visible-light responsive PDI/rGO composite film for the photothermal catalytic degradation of antibiotic wastewater and interfacial water evaporation. Applied Catalysis B: Environmental 291: 120127.https://doi.org/10.1016/j.apcatb.2021.120127
Fujishima A, Rao T N, Tryk D A (2000) Titanium dioxide photocatalysis. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 1(1): 1-21.https://doi.org/10.1016/S1389-5567(00)00002-2
Gadzekpo V P Y, Christian G D (1984) Determination of selectivity coefficients of ion-selective electrodes by a matched-potential method. Analytica Chimica Acta 164: 279-282.https://doi.org/10.1016/S0003-2670(00)85640-8
Gao S, Wang Z, Wang H, Jia Y, Xu N, Wang X, Wang J, Zhang C, Tian T, Shen W (2022) Peroxydisulfate activation using B-doped biochar for the degradation of oxytetracycline in water. Applied Surface Science 599: 153917.https://doi.org/10.1016/j.apsusc.2022.153917
Irie H, Watanabe Y, Hashimoto K (2003) Carbon-doped Anatase TiO₂ Powders as a Visible-light Sensitive Photocatalyst. Chemistry Letters 32(8): 772-773.https://doi.org/10.1246/cl.2003.772
Linsebigler A L, Lu G, Yates J T, Jr. (1995) Photocatalysis on TiO₂ Surfaces: Principles, Mechanisms, and Selected Results. Chemical Reviews 95(3): 735-758.https://doi.org/10.1021/cr00035a013
Liu R, Han X, Liu R, Qi Z, Ren B, Sun Y (2024) Molecularly imprinted Fe₃O₄/g-C₃N₄/TiO₂ catalyst for selective photodegradation of chlorotetracycline. Colloids and Surfaces A: Physicochemical and Engineering Aspects 680: 132691.https://doi.org/10.1016/j.colsurfa.2023.132691
Liu Y, Tian L, Wang Z, Fu Y, Zhao D (2023) Citric acid enhanced oxytetracycline degradation by Fe(Ⅲ)/peracetic acid: Performance, mechanism and influence factors. Journal of Environmental Chemical Engineering 11(5): 110723.https://doi.org/10.1016/j.jece.2023.110723
Luo X, Zhu S, Wang J, Wang C, Wu M (2017) Characterization and Computation of Yb/TiO₂ and Its Photocatalytic Degradation with Benzohydroxamic Acid. International Journal of Environmental Research and Public Health 14(12): 1471.https://doi.org/10.3390/ijerph14121471
Ma Z, Song X, Ren Y, Li Z, Liu W, Hou X, Wang J (2024) Monodispersed Ag nanoparticles deposited on Ni-based coordination polymer composite with enhanced photocatalytic degradation for bisphenol A. Colloids and Surfaces A: Physicochemical and Engineering Aspects 681: 132821.https://doi.org/10.1016/j.colsurfa.2023.132821
Marcì G, Augugliaro V, López-Muñoz M J, Martín C, Palmisano L, Rives V, Schiavello M, Tilley R J D, Venezia A M (2001) Preparation Characterization and Photocatalytic Activity of Polycrystalline ZnO/TiO₂ Systems. 1. Surface and Bulk Characterization. The Journal of Physical Chemistry B.https://doi.org/10.1021/jp003172r
Nithya N, Bhoopathi G, Magesh G, Kumar C D N (2018) Neodymium doped TiO₂ nanoparticles by sol-gel method for antibacterial and photocatalytic activity. Materials Science in Semiconductor Processing 83: 70-82.https://doi.org/10.1016/j.mssp.2018.04.011
Ohno T, Mitsui T, Matsumura M (2003) Photocatalytic Activity of S-doped TiO<SUB>₂</SUB> Photocatalyst under Visible Light. Chemistry Letters 32(4): 364-365.https://doi.org/10.1246/cl.2003.364
Peisan W, Chunxia Q, Pengchao W, Luyuan H, Xin X, Simeon A (2018) Synthesis of Si, N co-Doped Nano-Sized TiO₂ with High Thermal Stability and Photocatalytic Activity by Mechanochemical Method. Nanomaterials 8(5): 294-.https://doi.org/10.3390/nano8050294
Qi H-P, Wang H-L (2020) Facile synthesis of Pr-doped molecularly imprinted TiO₂ mesocrystals with high preferential photocatalytic degradation performance. Applied Surface Science 511: 145607.https://doi.org/10.1016/j.apsusc.2020.145607
Qin X, Ji L, Zhu A (2024) Construction of rutile/anatase Ohmic heterojunction of TiO₂/Ti₃C₂ with robust built-in electric field for boosting photocatalytic organic pollutant and hydrogen evolution. Applied Surface Science 652: 159338.https://doi.org/10.1016/j.apsusc.2024.159338
Sharabi D, Paz Y (2010) Preferential photodegradation of contaminants by molecular imprinting on titanium dioxide. Applied Catalysis B: Environmental 95(1): 169-178.https://doi.org/10.1016/j.apcatb.2009.12.024
Shen Y, Xu H, Zheng Y, Wang Y, Zhang L, Zhang Z, Zhong L, He Z (2023) Fabrication of Bi/BiOCOOH/PVDF with improved photocatalytic activity for the degradation of ciprofloxacin. Surfaces and Interfaces 42: 103483.https://doi.org/10.1016/j.surfin.2023.103483
Singh S, Sharma R (2018) Bi₂O₃/Ni-Bi₂O₃ system obtained via Ni-doping for enhanced PEC and photocatalytic activity supported by DFT and experimental study. Solar Energy Materials and Solar Cells 186: 208-216.https://doi.org/10.1016/j.solmat.2018.06.049
Sun Y, Bai L, Han C, Lv X, Sun X, Wang T (2022) Hybrid amino-functionalized TiO₂/sodium lignosulfonate surface molecularly imprinted polymer for effective scavenging of methylene blue from wastewater. Journal of Cleaner Production 337: 130457.https://doi.org/10.1016/j.jclepro.2022.130457
Villa C C, Sánchez L T, Valencia G A, Ahmed S, Gutiérrez T J (2021) Molecularly imprinted polymers for food applications: A review. Trends in Food Science & Technology 111: 642-669.https://doi.org/10.1016/j.tifs.2021.03.003
Wang W, Niu Q, Zeng G, Zhang C, Huang D, Shao B, Zhou C, Yang Y, Liu Y, Guo H, Xiong W, Lei L, Liu S, Yi H, Chen S, Tang X (2020) 1D porous tubular g-C3N4 capture black phosphorus quantum dots as 1D/0D metal-free photocatalysts for oxytetracycline hydrochloride degradation and hexavalent chromium reduction. Applied Catalysis B: Environmental 273: 119051.https://doi.org/10.1016/j.apcatb.2020.119051
Wang Y, Zhou H, Kong J, Shen M (2023) Self-assembled composite heterojunction material PDIsm/BiOCOOH promotes photocatalytic degradation of levofloxacin. Journal of Alloys and Compounds: 173314.https://doi.org/10.1016/j.jallcom.2023.173314
Wei C, Lin W Y, Zainal Z, Williams N E, Zhu K, Kruzic A P, Smith R L, Rajeshwar K (1994) Bactericidal Activity of TiO₂ Photocatalyst in Aqueous Media: Toward a Solar-Assisted Water Disinfection System. Environmental Science & Technology 28(5): 934-938.https://doi.org/10.1021/es00054a027
White, Powell, Holland, Worley (2010) The effect of TiO2 and Fe₂O₃ on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃. Journal of Metamorphic Geology 18(5).https://doi.org/10.1046/j.1525-1314.2000.00269.x
Wu Y, Dong Y, Xia X, Liu X, Li H (2016) Facile synthesis of N–F codoped and molecularly imprinted TiO₂ for enhancing photocatalytic degradation of target contaminants. Applied Surface Science 364: 829-836.https://doi.org/10.1016/j.apsusc.2015.12.230
Yang Y, Zeng G, Huang D, Zhang C, He D, Zhou C, Wang W, Xiong W, Song B, Yi H, Ye S, Ren X (2020) In Situ Grown Single-Atom Cobalt on Polymeric Carbon Nitride with Bidentate Ligand for Efficient Photocatalytic Degradation of Refractory Antibiotics. Small 16(29): e2001634.https://doi.org/10.1002/smll.202001634
Zhang S, Wang J (2022) Biodegradation of chlortetracycline by Bacillus cereus LZ01: Performance, degradative pathway and possible genes involved. Journal of Hazardous Materials 434: 128941.https://doi.org/10.1016/j.jhazmat.2022.128941
Zhang Z, Yi G, Li P, Wang X, Wang X, Zhang C, Zhang Y, Sun Q (2022) Eu/GO/PbO₂ composite based anode for highly efficient electrochemical oxidation of hydroquinone. Colloids and Surfaces A: Physicochemical and Engineering Aspects 642: 128632.https://doi.org/10.1016/j.colsurfa.2022.128632
Zhao J, Ji M, Di J, Zhang Y, He M, Li H, Xia J (2020) Novel Z-scheme heterogeneous photo-Fenton-like g-C₃N₄/FeOCl for the pollutants degradation under visible light irradiation. Journal of Photochemistry and Photobiology A: Chemistry 391: 112343.https://doi.org/10.1016/j.jphotochem.2019.112343
Zhu L, Liu X, Wang X, Meng X (2020) Evaluation of photocatalytic selectivity of Ag/Zn modified molecularly imprinted TiO₂ by multiwavelength measurement. Science of The Total Environment 703: 134732.https://doi.org/10.1016/j.scitotenv.2019.134732

Download PDF

Reviewers agreed at journal
29 Mar, 2024
Reviewers invited by journal
29 Mar, 2024
Editor invited by journal
29 Feb, 2024
Editor assigned by journal
20 Feb, 2024
First submitted to journal
13 Feb, 2024

You are reading this latest preprint version

Study on the degradation performance of novel molecularly imprinted Nd-TiO2 for oxytetracycline hydrochloride

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental part

2.1. Catalyst synthesis steps

2.2. Characterize

2.3. Photocatalytic experiment

2.4. Quenching experiment

3. Results and discussion

3.1. Analyzing the characterization results

3.1.1. XRD, BET, and UV-Vis characterization

3.1.2. TEM characterization

3.1.3. XPS characterization

3.1.4. FT-IR and PL characterization

3.2. Catalyst degradation performance studies

3.2.1. Influence of catalyst doping ratio on catalyst degradation performance

3.2.2. Influence of variation of calcination temperatures on the degradation performance of catalysts

3.2.3. Influence of variation of calcination time on the degradation performance of catalysts

3.2.4. Adsorption properties of catalysts

3.2.5. Photocatalytic performance of catalysts

3.2.6. Influence of different reaction conditions on the degradation performance of catalysts

3.2.7. Adsorption-photocatalytic synergistic reaction

3.3. Molecularly imprinted Nd-TiO₂ degradation selectivity studies

3.3.1. Adsorption selectivity

3.2.2. Photocatalytic selectivity

3.4. Analysis of photocatalytic degradation mechanism·

3.5. Repeatable experiments

4. Conclusions

Declarations

References

Status:

Version 1

Study on the degradation performance of novel molecularly imprinted Nd-TiO2 for oxytetracycline hydrochloride

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental part

2.1. Catalyst synthesis steps

2.2. Characterize

2.3. Photocatalytic experiment

2.4. Quenching experiment

3. Results and discussion

3.1. Analyzing the characterization results

3.1.1. XRD, BET, and UV-Vis characterization

3.1.2. TEM characterization

3.1.3. XPS characterization

3.1.4. FT-IR and PL characterization

3.2. Catalyst degradation performance studies

3.2.1. Influence of catalyst doping ratio on catalyst degradation performance

3.2.2. Influence of variation of calcination temperatures on the degradation performance of catalysts

3.2.3. Influence of variation of calcination time on the degradation performance of catalysts

3.2.4. Adsorption properties of catalysts

3.2.5. Photocatalytic performance of catalysts

3.2.6. Influence of different reaction conditions on the degradation performance of catalysts

3.2.7. Adsorption-photocatalytic synergistic reaction

3.3. Molecularly imprinted Nd-TiO2 degradation selectivity studies

3.3.1. Adsorption selectivity

3.2.2. Photocatalytic selectivity

3.4. Analysis of photocatalytic degradation mechanism·

3.5. Repeatable experiments

4. Conclusions

Declarations

References

Status:

Version 1

3.3. Molecularly imprinted Nd-TiO₂ degradation selectivity studies