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Article

Interfacial Engineering of 0D/2D Cu2S/Ti3C2 for Efficient Photocatalytic Synchronous Removal of Tetracycline and Hexavalent Chromium

by
Zengyu Wang
1,
Zhiwei Lv
1,*,
Bowen Zeng
2,
Fafa Wang
2,
Xiaoyu Yang
2 and
Ping Mao
2,*
1
School of Energy and Environmental Engineering, Hebei University of Engineering, Handan 056038, China
2
Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National & Local Joint Engineering Research Center for Mineral Salt Deep Utilization, School of Chemical Engineering, Huaiyin Institute of Technology, Huaian 223003, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(5), 458; https://doi.org/10.3390/catal15050458
Submission received: 14 April 2025 / Revised: 4 May 2025 / Accepted: 5 May 2025 / Published: 7 May 2025
(This article belongs to the Special Issue Synthesis and Catalytic Applications of Advanced Porous Materials)
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Abstract

:
With the advancement of industrialization and urbanization, the arbitrary emission of sewage containing TC-tetracycline and hexavalent chromium (Cr(VI)) possesses a serious threat to both ecological–environment and public health. However, developing a low-toxicity and cost-effective photocatalyst for the simultaneous elimination of these two pollutants remains a formidable task. This study devised a photocatalytic sample (CSMX-X) comprised of Copper(I) sulfide (Cu2S) and Titanium carbide (Ti3C2) through a simple solvothermal method and applied it to remove TC-tetracycline and Cr(VI). The CSMX-X not only increases the specific surface area from 2.7 m2·g−1 for pure Cu2S to 30.65 m2·g−1, but also effectively addresses the problems of insufficient separation efficiency of photogenerated holes and electrons and low carrier density. The photocatalytic efficiency for an individual pollutant (10 mg·L−1 Cr(VI) or 20 mg·L−1 TC-tetracycline) can reach more than 90%, while the removal efficiency for mixed Cr(VI) and TC-tetracycline pollutants only decreases by 12%. Meanwhile, copper leaching levels under different pH conditions (0.032–0.676 mg·L−1) are considerably lower than the 2 mg·L−1 safety standard set by the World Health Organization. This study provides valuable perspectives for constructing Cu2S-based composite photocatalysts to remove multiple contaminants in real aquatic environments.

1. Introduction

In recent years, the excessive reliance on antibiotics (e.g., tetracycline, TC) in the medical field, coupled with the over-discharge of heavy metals (such as Cr(VI)) in industrial production, has presented significant risks to both the ecological environment and human security [1,2]. Cr(VI) is recognized as one of the most hazardous and typical toxic heavy metals in the world [3]. Prolonged exposure to Cr(VI) may result in teratogenicity and mutagenesis [4]. TC is a widely used antibiotic [5], which has been employed to treat infectious diseases and manage animal ailments, accounting for over 60% of antibiotic usage in veterinary medicine [6]. However, its excessive accumulation within the food chain also poses a risk to human health, potentially resulting in endocrine disruption, neurological defects, and renal disease [7]. Efficient removal of TC and Cr(VI) from contaminated water has thus become an urgent necessity.
In contrast to the traditional wastewater processing technologies such as membrane separation, ion exchange, and chemical adsorption, semiconductor photocatalysis offers several advantages: high removal efficiency, cost-effectiveness, no generation of secondary pollutants, and the ability to directly harness natural light [8]. Nevertheless, designing an economical and low-toxicity photocatalyst with high visible-light utilization that can simultaneously remove both Cr(VI) and TC pollutants remains a formidable challenge. Efficient light capture and swift charge transfer are vital to optimizing solar energy and are essential prerequisites for achieving high photocatalytic activity. Metal sulfides with suitable band gaps and extended light absorption range are considered to be ideal candidates [9]. This phenomenon is attributed to the limited energy gap of metal sulfides, where the valence band (VB) is primarily populated by S-3p orbitals, which are situated at a higher energy level than the O-2p orbitals. This arrangement results in reduced formation of positive holes in the VB and an improvement in hole mobility, thus promoting faster charge transfer [10]. Liu et al. enhanced the photocatalytic performance by preparing CdS/Ti3C2 composites, achieving an optimal hydrogen production rate of 2.04 mmol⋅h−1⋅g−1 [11]. However, the carcinogenic nature of CdS severely limits its range of applications [12]. Compared to other metal sulfides, Cu2S has attracted considerable attention due to its p-type conductivity, suitable band gap, low toxicity, unique optical properties, cost-effectiveness, and abundant availability on Earth [13,14,15]. Nonetheless, the practical effectiveness is hindered by the limited adsorption capacity and the elevated recombination rate of photoexcited electron–hole pairs due to coulombic interactions [16,17].
To enhance the photocatalytic activity of Cu2S, researchers have employed various strategies, such as constructing Cu2S/MoS2 heterostructures for efficient separation and transfer of charge carriers [18,19]. However, once the laser energy exceeds the band gap of MoS2, photo-corrosion can occur, even under low irradiation [20]. The electronic structure of Cu2S semiconductors can be modified by adjusting the copper vacancies, thereby enhancing photoelectric performance [21]. However, the increase of copper vacancies can lead to an increase in hole concentration [22], thus hindering the photocatalytic reduction reactions and intensifying photodegradation. In previous research, our group significantly enhanced photocatalytic performance by homogeneous deposition of metal sulfide Cd0.5Zn0.5S onto single-layered Ti3C2, utilizing the exceptional photoelectrochemistry properties of Ti3C2 to promote charge carrier separation and transfer [23]. Ti3C2, an emerging two-dimensional layered MXene, exhibits tremendous potential in the photocatalysis field due to its outstanding metallic conductivity, hydrophilicity, environmental friendliness, and the abundance of titanium on Earth [24,25]. Huang et al. intercalated ZnIn2S4 into multilayer Ti3C2, and made the multilayer Ti3C2 stripped into ultrathin nanosheets, dispersing them in flower-like microspheres, increasing the hydrogen production rate to 0.978 mmol⋅h−1⋅g−1 [26].
Herein, the synthesis of Cu2S/Ti3C2 was discussed from the perspectives of low toxicity and cost-effectiveness, and the characterization of SEM, XRD, and XPS confirmed that Cu2S nanoparticles were successfully loaded on Ti3C2 nanosheets. Cationic and anionic interference and different pH values were used to simulate real aquatic environments, evaluating the photocatalytic activities of samples for removal of Cr(VI) and TC, and to evaluate the safety of samples for practical applications. The mechanism of photocatalysis was also explored. The high photocatalytic efficiency of Cr(VI) reduction and TC degradation provides inspiration for design and application of this method in other photocatalytic functional materials.

2. Results and Discussion

2.1. Characterization of All Samples

Microscopic morphologies of multilayer Ti3C2 and single-layer Ti3C2, CS, CSMX-1, CSMX-5, and CSMX-10 were characterized, as shown in Figure 1. The multilayer structure (Figure 1a) presents a tight stack after LiF + HCl etching, which may be attributed to the insertion of water or cations [27]. Layered Ti3C2 was obtained (Figure 1b) after ultrasonic treatment in an ice bath. Due to the high surface free energy and small average size of CS nanoparticles, a phenomenon of agglomeration is observed in the CS photocatalyst, as displayed in Figure 1c. The electronegativity and hydrophilicity of the surface of Ti3C2 can fix Cu2+ in solution, which then reacts with L-cysteine to promote the in situ growth of CS (0D) on Ti3C2 (2D) (Figure 1d–f). The elemental distribution shown in the EDS mapping (Figure 1g) indicates the presence of C, Cu, S, and Ti, demonstrating that CS is evenly coated on the Ti3C2 nanosheets. By comparing CS (Figure 1h) and CSMX-5 (Figure 1i and Figure S1c), it is evident that the doping of Ti3C2 effectively alleviates the agglomeration of CS. Figure 1j shows that the lattice fringe spacings of 0.28 nm and 0.198 nm correspond to the (110) and (220) planes of Ti3C2 and Cu2S, indicating the formation of a Schottky heterojunction and the development of a 0D/2D interface (Figure S1c).
Figure 2a displays the XRD patterns for Ti3C2 and Ti3AlC2. The disappearance of the (104) and (004) crystal plane diffraction peaks of Ti3AlC2 aligns with previous research, indicating that the Al layers had been largely etched away by LiF + HCl [28]. Additionally, the (002) peak shifts to lower angles indicate an expansion of interlayer spacing within Ti3C2, leading to the increase of c-lattice parameter (c-LP), thereby confirming the successful preparation of Ti3C2 [29]. Additionally, the overall peak intensity of Ti3C2 is lower than that of Ti3AlC2 due to the finer-layered structure of Ti3C2 [30]. Figure 2b reveals that all characteristic peaks of CS align with those of Cu2S (JCPDS No. 03-1071), with no other diffraction peaks, confirming the successful preparation of Cu2S. Notably, the XRD patterns of CS and Ti3C2-doped samples do not exhibit any characteristic peaks of Ti3C2, which is attributed to the low content and well dispersion of Ti3C2.
XPS analysis was performed to examine the surface compositions of Ti3C2, CS, and CSMX-5. Figure 2c shows that elements detected in the CS and CSMX-5 samples include C, Ti, Cu, and S, and the satellite peak of Ti in CSMX-5 is obviously weak. Calibration in all XPS spectra was performed, referencing 284.8 eV. In Figure S2a, four satellite peaks at 282.1, 284.8, 286.1, and 289.0 eV are the C 1s spectra of C-Ti, C-C, C-O, and C-F bonds [23]. Figure 2d displays the Ti 2p spectrum of CSMX-5 and Ti3C2, where the peaks at 455.5, 459.5, and 462.0 eV are the Ti-C 2p3/2, Ti-C 2p1/2, and Ti-O 2p1/2 bonds in Ti3C2 [31]. The weakening of the Ti-C bond strength is due to the surface of Ti3C2 being covered by CS, and XPS can only measure the chemical environment of the material’s surface at a depth of a few nanometers [32]. Figure 2e shows that the binding energies at 932.2 and 952.1 eV in the spectrum of CS and CSMX-5 are associated with Cu+ 2p3/2 and Cu+ 2p1/2, respectively. Notably, the peaks at 934.1 and 954.2 eV, associated with Cu2+ 2p3/2 and Cu2+ 2p1/2, likely result from a small amount of oxidation on the surface of CS [33]. The peaks for Cu+ shift to higher binding energies, indicating a close interaction between CS and Ti3C2 [34]. In Figure S2b, the peak at 168.7 eV corresponds to sulfate [35], while the binding energies at 161.6 and 162.8 eV are assigned to S 2p3/2 and S 2p1/2.
Using N2 adsorption–desorption measurements, the specific surface areas of CS, Ti3C2, and CSMX-X were evaluated, with the results shown in Figure 2f. The samples, including CS, CSMX-X, and Ti3C2, exhibit type IV isotherms. The specific surface areas are ranked as follows: CS (2.7 m2·g−1) < CSMX-1 (19.32 m2·g−1) < Ti3C2 (20.53 m2·g−1) < CSMX-5 (30.65 m2·g−1) < CSMX-10 (34.23 m2·g−1). After the formation of the composite heterojunction structures, the specific surface area increases as the Ti3C2 proportion rises, and even exceeds that of pure Ti3C2. This phenomenon may be due to the fact that CS nanostructures tend to aggregate, reducing the available specific surface area. In Figure S2c, the smaller pore volume of CS molecules was due to aggregation. However, after doping with Ti3C2, the pore volume increased, further indicating that Ti3C2 alleviated the aggregation of the molecules and increased the specific surface area. This suggests that the formation of CSMX-X (0D/2D) may create additional active sites, facilitating adsorption and photocatalytic reactions.

2.2. Photoelectrochemical Characterization Analysis

To evaluate the photochemical performance of the CSMX-X samples and gain insights into the separation and transport of photo-excited charge carriers, a series of characterizations were performed, including photoluminescence (PL) spectroscopy to examine the recombination rate of charge carriers; transient photocurrent response to assess the photo-generated charge mobility; and electrochemical impedance spectroscopy (EIS) to evaluate impedance to charge transfer.
The PL emission spectra are due to the recombination of photo-excited electron–hole pairs. Stronger photoluminescence peak indicates that more electrons (e−) are transitioning from the conduction band (CB) to recombine with h+, resulting in the emission of greater photon energy, which in turn indicates a higher electron–hole recombination efficiency. Thereby, the intensity of the steady-state PL emission peak serves as an indicator of the recombination ratio of photogenerated charge carriers [36]. Figure 3a shows that fluorescence intensity of CS doped with Ti3C2 is clearly lower than that of pure CS, manifesting that the combination of Ti3C2 with CS to form Schottky heterojunction enhances the charge separation [37]. Notably, CSMX-5 exhibits the lowest PL intensity due to the optimal Ti3C2 content. However, excessive doping may introduce recombination sites.
The efficiency of photo-excited electron–hole pairs separation can be directly evaluated through transient photocurrent response and EIS analysis [38]. As displayed in Figure 3b and Figure 4c, CSMX-X exhibits a significantly higher photocurrent intensity compared to CS. Moreover, the Nyquist plots of the EIS spectra reveal a smaller radius for CSMX-X, in which CSMX-5 photocurrent intensity is the highest and impedance is the lowest. This indicates that the close contact between CS and Ti3C2 reduces the interfacial charge transfer resistance, accelerates the transport of the interfacial charge, and inhibits the recombination of photo-excited e− and h+. Furthermore, as displayed in Figure S3a, the overpotential of all CSMX-X samples is lower than that of CS, with CSMX-5 exhibiting the lowest value. This suggests that the introduction of Ti3C2 improves the redox activity of CS.
The photoelectrochemical properties of CSMX-X composites show a clear dependence on Ti3C2 content. CSMX-5 demonstrates optimal performance, exhibiting the highest photocurrent response and lowest charge transfer resistance, which can be attributed to the well-dispersed Cu2S nanoparticles on an appropriate amount of Ti3C2 nanosheets. This ideal distribution enables efficient charge separation through Schottky junction formation. In contrast, both insufficient and excessive Ti3C2 loading result in higher charge transfer resistance and poorer separation efficiency of electron–hole pairs.
Light absorption performance is another crucial factor impacting photocatalytic efficiency. As displayed in Figure 3d and Figure S3b, the UV-DRS spectrum shows that under different testing conditions, the light absorption edge of CS is approximately 560 nm, highlighting its significant absorption capability in the visible light range. However, after doping with Ti3C2, the absorption intensity of the CSMX-5 at 560 nm does not show a noticeable change, which may be attributed to the deep color of CS and its unique narrow bandgap structure coupled with a high absorption coefficient (>104 cm−1) [39]. The optical bandgap energy (Eg) in Figure 3e is derived from the equation αhν = A(hν − Eg)ⁿ, where α denotes the absorbance, h is Planck’s constant, ν is light frequency, and A is a material-related constant [40]. The value of n reflects the type of electronic transition, with CS being a direct bandgap material [41], hence n = 0.5. The Eg values indicate that the bandgap values of CS and CSMX-5 are both 1.5 eV, suggesting that the doping of Ti3C2 does not alter the bandgap. In Figure 3f, CS is identified as a p-type semiconductor (with a negative slope) [14], and the flat band potential (Efb) (intercept) is 0.64 V.
Efb can be transformed to the standard hydrogen electrode potential using the following formula [42]: ENHE = EAg/AgCl + 0.059 × pH + E*Ag/AgCl; where E*Ag/AgCl = 0.197 V, the solution has a pH of 7. Thus, the EVB edge of CS is derived to be 1.25 V. The CB edge (ECB) is −0.25 V (ECB = EVB − Eg). The energy levels of the CB and VB at zero charge point are determined using the following formula [43]: ECB = χ − Ee − 1/2Eg, χ = [χ(A)aχ(B)b]1/(a+b), EVB = ECB + Eg, where χ denotes the semiconductor’s absolute electronegativity (with a and b representing the atomic numbers of the elements). Ee is a reference value in relation to the standard hydrogen electrode (approximately 4.5 eV), and Eg denotes the bandgap energy. Using this formula, ECB is calculated to be −0.26 V, which differs from the previously derived value by only 0.01 V, thus validating the positions of the VB and CB of the photocatalytic sample.

2.3. Photocatalytic Reduction of Cr(VI)

Photocatalytic Reduction Activities

To assess photocatalytic reduction activity, Cr(VI) reduction was investigated for all samples. As illustrated in Figure 4a, all samples attained adsorption equilibrium in dark after 30 min. Given that Ti3C2 possesses no intrinsic photocatalytic activity [44], the Cr(VI) removal efficiency by pure Ti3C2 is consequently quite limited. CS achieves a reduction efficiency of 50%, whereas the CSMX-X samples show higher photocatalytic reduction efficiencies compared to CS. Notably, the reduction efficiency of CSMX-5 reaches to 90%, indicating that the doping of Ti3C2 significantly enhances the photocatalytic reduction efficiency of CS. The layered structure formed between CS and Ti3C2 creates a favorable band alignment, which accelerates the migration of e− and reduces their recombination with h+. However, as the Ti3C2 content increases, the photocatalytic efficiency declines, indicating that excessive addition of Ti3C2 negatively impacts photocatalytic activity. This is primarily because Ti3C2 cannot generate electrons and holes [45]. Excessive doping reduces the generation of these charge carriers, further diminishing the overall photocatalytic activity. The appropriate doping of Ti3C2 nanosheets with the photocatalyst facilitates electron transport and enhances photocatalytic activity.
To precisely compare the photocatalytic activities of CS, CSMX-X, and Ti3C2, the reaction kinetics are fitted using the pseudo-first-order (Equation (1)) and the pseudo-second-order models (Equation (2)):
ln(C0/C) = kt
1/C − 1/C0 = kt
where t and k denote the illumination time, the rate constant. As displayed in Figure S4, the first-order kinetic rate constants of CS, Ti3C2, CSMX-1, CSMX-5, and CSMX-10 are 0.00136 min−1 (R2 = 0.90), 0.000789 min−1 (R2 = 0.95), 0.00547 min−1 (R2 = 0.98), 0.00716 min−1 (R2 = 0.98), and 0.00684 min−1 (R2 = 0.99), respectively, while the second-order kinetic rate constants are 0.000236 L·mg−1·min−1 (R2 = 0.91), 0.000152 L·mg−1·min−1 (R2 = 0.96), 0.00183 L·mg−1·min−1 (R2 = 0.98), 0.00354 L·mg−1·min−1 (R2 = 0.99), and 0.0029 L·mg−1·min−1 (R2 = 0.97). All kinetic models showed excellent correlation coefficients (R2 > 0.90), confirming the appropriateness of the kinetic models. All CSMX-X samples exhibit higher Cr(VI) photocatalytic reduction efficiencies than CS and Ti3C2. CSMX-5 exhibited the highest photocatalytic reduction efficiency, primarily because of its optimal separation efficiency of photo-excited electron–hole pairs involved in Cr(VI) reduction among the CSMX-X samples.
Figure 4b displays the photocatalytic reduction activity of CSMX-5 at different initial Cr(VI) concentrations. The increased initial concentration of Cr(VI) occupies the limited active sites on the sample, delaying the reduction process and causing the reaction to reach saturation [46]. Figure 4c demonstrates that as the pH value increases, both the adsorption capacity and photocatalytic activity of CSMX-5 significantly decrease. Cr(VI) can be found in different forms depending on the pH of the environment: it exists as Cr2O72- in neutral conditions, as HCrO4− in acidic conditions, and as CrO42− in alkaline conditions [47]. In low pH conditions, the high degree of protonation on the photocatalyst surface increases the positive charge, which favors the attraction of the dominant anion HCrO4−. Conversely, at high pH conditions, the heightened negative charge on CSMX-5 surface repels Cr2O72−, thereby lowering photocatalytic performance in Cr(VI). Furthermore, in neutral and alkaline conditions, Cr(III) tends toward forming insoluble Cr(OH)3, which binds to the CSMX-5 surface, obstructing photocatalytic active sites and hindering further photocatalytic reactions [48]. Moreover, one of the reasons for selecting CS as a photocatalyst is the low toxicity of Cu, but it remains a substance that the human body cannot metabolize, and its long-term accumulation will affect health. After the photocatalytic reaction, the solution was allowed to settle to collect the supernatant liquid. Subsequently, a high-speed centrifugation method was employed to further separate any remaining photocatalyst particles from the solution. The liquid was then filtered through a 0.22 μm membrane filter to ensure complete removal of particulate matter. Figure 4d shows the results of Cu concentration in the post-reaction solution, measured by ICP-OES after photocatalytic experiments conducted at different pH values. Even at pH = 3, the release of Cu was only 0.676 mg·L−1, which is well below the World Health Organization (WHO) safety standard of 2 mg·L−1.
To evaluate the practical applicability of the photocatalysts, the impact of anions and cations, present at identical concentrations, on the photocatalytic performance of CSMX-5 was examined. As shown in Figure 4e, SO42−, NO3−, and Cl− anions exert minimal impact on Cr(VI) photocatalytic reduction. However, CO32− anion significantly reduces photocatalytic reduction efficiency due to weak alkalinity of its solution. Figure 4f shows that Na+, Ca2+, and Mg2+ ions slightly reduce photocatalytic efficiency in Cr(VI) reduction, indicating that coexisting cations compete with Cr(VI) for active sites during adsorption. Additionally, these stable and oxidizing cations may utilize some of the photogenerated charge carriers, resulting in a reduction in Cr(VI) reduction efficiency. Conversely, the Al3+ ions significantly enhance photocatalytic Cr(VI) reduction, likely attributable to higher hydrolysis constant of Al3+ (1.4 × 10−5), which consumes OH− ions and results in a decrease in pH.
Compared with other reported photocatalytic reduction properties of metal sulfides on Cr(VI) (Table 1), CSMX-5 displays excellent photocatalytic reduction activity of Cr(VI). Additionally, bismuth (Bi), cadmium, and molybdenum disulfide (MoS2) are toxic and can cause secondary pollution [49,50], while indium (In) and silver (Ag) are not suitable for large-scale applications of precious metals. Zinc sulfide (ZnS) has a large band gap (3.6 eV), leading to poor visible light absorption. In contrast, CSMX-X offers significant advantages in reduction efficiency, cost-effectiveness, low toxicity, and environmental eco-friendliness.
To examine how active species affect the photocatalytic performance of CSMX-5, isopropanol (IPA), ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), and potassium persulfate (K2S2O8) were chosen as quenchers of hydroxyl radicals (▪OH), h+ and e− in photocatalytic systems. Figure 5a shows that adding K2S2O8 lowered Cr(VI) reduction efficiency in CSMX-5 from 80% to 48%, suggesting that e− is the dominant active species. By contrast, the reduction efficiency decreases by only 7% with the addition of IPA, suggesting a negligible role of ▪OH in degradation. However, the addition of EDTA-2Na increases the Cr(VI) reduction efficiency to 92%, which is due to the consumption of h+ and the reduction of its recombination with e−, which once again confirms the importance of e− in Cr(VI) photocatalytic reduction.
Reusability and long-term physicochemical stability are crucial factors to evaluate the practical viability of photocatalysis. As shown in Figure 5b, after 5 cycles, CSMX-5 has always maintained a high Cr(VI) reduction efficiency, indicating that the sample possesses excellent photocatalytic reusability and durability. However, the slight decrease in photocatalytic efficiency observed during the cycling may be related to the adhesion of Cr(III) on the surface of the photocatalyst [59]. The reusability and stability of this photocatalysis give CSMX-X great potential in wastewater remediation applications. The SEM image of CSMX-5 after photocatalytic reaction (Figure S5) shows that the appearance of CSMX-5 does not change. The XRD pattern (Figure S6) further confirms the stability of the crystalline structure. XPS characterization of the photocatalyzed CSMX-5 samples shows peaks at 577.3 eV and 587 eV, which are assigned to Cr3+ 2p3/2 and Cr3+ 2p1/2 in Figure 5c [60]. This confirms that CSMX-5 successfully reduced Cr(VI) to Cr(III) through photocatalytic action. Consequently, the photocatalytic Cr(VI) reduction by CSMX-5 demonstrates excellent reusability and structural stability.

2.4. Photocatalytic Degradation of TC

2.4.1. Photocatalytic Reduction Mechanism

To understand the photocatalytic degradation performance of CSMX-X, the degradation effects of all samples in water were investigated. As shown in Figure 6a, the adsorption capacities in the dark correlate positively with the specific surface area. After 210 min of irradiation, the removal efficiency of CS and Ti3C2 are about 66% and 46.2%, respectively, while the degradation efficiency of CSMX-X is significantly improved. Among them, CSMX-5 exhibits the highest photocatalytic degradation rate (approximately 93%). This is ascribed to the effective combination of CS and appropriate Ti3C2. The photocatalytic degradation of TC was analyzed using the pseudo-first-order (Equation (1)) and pseudo-second-order (Equation (2)) kinetic models. It can be found from Figure S7 that CSMX-5 has the highest rate constants (0.0098 min−1 for first-order kinetics and 0.0027 L·mg−1·min−1 for second-order kinetics). In addition, CSMX-5 shows the best degradation efficiency and rate, consistent with its photocatalytic reduction of Cr(VI), which may attribute to the favorable distribution of CS on Ti3C2 with moderate amount, resulting in optimal photocatalytic activity.
As depicted in Figure 6b, the degradation efficiency of CSMX-5 is 92% at a TC concentration of 20 mg·L−1. However, when the initial concentration increased to 40 mg·L−1, the efficiency dropped to 54%. This is because when the amount of photocatalyst is fixed, the photocatalytic active substance on its surface also remains unchanged. A rise in TC concentration results in a higher concentration of generated intermediates, which can obstruct the active site [61]. Figure 6c shows the TC degradation of CSMX-5 at different pH values. The pH value with the highest photocatalytic degradation efficiency is 7, indicating that both acidic and alkaline environments hinder TC degradation. This phenomenon can be put down to the alterations in the molecular structure of TC under these conditions. At pH < 3.3, TC primarily exists as cations (TC3+), while at pH 3.3~7.6, TC predominantly exists as zwitterions. At pH ≥ 7.6, TC predominantly takes the form of anions (TC− or TC2−) [62]. Additionally, H⁺ in the aqueous solution can consume reactive species such as ▪O2− [63]. Therefore, the photocatalytic degradation efficiency is lowest at pH = 3.
Figure 6d,e demonstrate the influence of different coexisting anions and cations in the photocatalytic degradation of TC, revealing that SO42−, Cl−, and CO32− anions negatively influence the degradation process, as Cl− reacts with h⁺ in the system to form the weaker oxidizing species ▪Cl [30], while SO42− generates ▪SO4− [64] with h⁺. Additionally, CO32− hydrolyzes in water, resulting in an alkaline solution that adversely affects photocatalytic efficiency. Al3+ hydrolysis influences the pH of the solution [65]. However, Ca2+ and Mg2+ tend to accumulate around the electronegative atoms in the TC molecule, obstructing attacks from h+ and other species on these electronegative sites, thereby inhibiting photocatalytic degradation efficiency [66]. Compared with the previously reported metal sulfide photocatalysts (Table 2), CSMX-5 is competitive due to its excellent degradation efficiency of TC.
Based on the previous analysis, the photocatalytic Cr(VI) reduction by CSMX-X is deduced, with the specific steps outlined as follows:
Cu2S + hv → h+ + e−
h+(Cu2S) + OH− → ▪OH
3e− + Cr(VI) → Cr(III)
In visible light condition, the photocatalyst generates photoexcited e− and h+, of which h⁺ combines with OH− to form ▪OH radicals. The e− reacts with Cr(VI) to produce Cr(III). The CB potential of CS is lower than both φθ(Cr2O72−/Cr3+) (+1.33 V) and φθ(HCrO4−/Cr3+) (+1.35 V), thus providing sufficient negative potential for the photogenerated e− to drive reduction of Cr(VI) to Cr(III).

2.4.2. Photocatalytic Degradation Mechanism

Benzoquinone (BQ), EDTA-2Na, IPA, and N2 were used to quench ▪O2−, h+, ▪OH, and O2, respectively, to analyze the primary active substances for TC degradation. As depicted in Figure 7a, the addition of EDTA-2Na obviously decreases the degradation efficiency of TC. Meanwhile, BQ and N2 also slightly inhibit the photocatalytic degradation. This shows that h+ is instrumental in the TC degradation, followed by ▪O2− and dissolved oxygen. Figure 7b presents the cyclic experiment results of CSMX-5 in the TC degradation. After five cycles, the degradation efficiency decreases to 74%. This decrease in degradation efficiency is primarily attributed to degradation intermediates on the surface of the photocatalyst. These substances occupy some active sites, thereby limiting the effective utilization of the catalytic active sites [77]. Additionally, by comparing XRD pattern (Figure 7c) and SEM image (Figure S8a) of CSMX-5 before and after the reaction, it can be clearly observed that the corresponding XRD pattern and apparent morphology remain unchanged. This phenomenon further confirms the excellent stability and recyclability of the CSMX-5 in photocatalytic reactions, indicating that it can maintain a high photocatalytic activity even after five cycles.
To further explore the photocatalytic degradation of TC by CSMX-5, LC-MS was conducted to identify the intermediates formed during the degradation process, with results illustrated in Table S1. The proposed products of the degradation process are depicted in Figure 8. The N-C bond in the TC molecule is relatively weak, making the two -CH3 groups susceptible to attack by the reactive substance, forming the intermediates T2 (m/z = 372) and T3 (m/z = 416) [67]. Subsequently, through hydroxylation, addition reactions, and deamination reactions, T5 (m/z = 279) and T6 (m/z = 274) are generated. The T1 molecule is formed by the demethylation of the TC molecule [78]. The hydroxyl group attached to the benzene ring possesses reducing properties, rendering it susceptible to oxidation, which produces T4 (m/z = 399). Additionally, the T4 molecule may generate T5 through deamination and addition reactions. These substances subsequently undergo further degradation via carbonylation and ring-opening reactions, yielding T7 (m/z = 150), T8 (m/z = 149), and T9 (m/z = 223). As the degradation process advances, the aforementioned products are progressively mineralized into harmless inorganic compounds under the assault of active substances, effectively dismantling the structure of tetracycline.
Based on the previous analysis, the photocatalytic reduction process of TC by CSMX-X is derived, and the specific process is as follows:
Cu2S + hv → h+ + e−
h+(Cu2S) + OH− → ▪OH
e−(Cu2S) + O2 → ▪O2−
▪O2−/h+ + TC → CO2 + H2O
The CB potential is more negative than O2/▪O2− redox couple (−0.046 eV vs. NHE) [79]. Additionally, the ESR experiments (Figure S8b) further confirmed the generation of ▪O2− radicals during the photocatalytic process. During the photocatalytic degradation of TC, photogenerated e− combines with dissolved O2 to produce highly oxidative ▪O2−, which then reacts with TC in the solution to facilitate its oxidative degradation. Simultaneously, photo-excited h⁺ can also directly degrade TC molecules [80].

2.5. Photocatalytic Removal of Mixed TC and Cr(VI) Pollutants

To further assess the photocatalyst’s potential for removing mixed pollutants, a systematic study on CSMX-5 in mixed solutions of Cr(VI) (10 mg·L−1) and TC (20 mg·L−1) was conducted, as displayed in Figure 6f. Only a slight decline was found in the photocatalytic efficiency of CSMX-5 in Cr(VI) reduction and TC degradation. The decline is primarily attributed to the consumption of the photo-excited e− during Cr(VI) reduction, while TC degradation requires the participation of ▪O2−. Notably, the generation of ▪O2− also depends on the involvement of e−. Therefore, e− is consumed competitively in the process of synchronous photocatalytic removal of Cr(VI) and TC, leading to a slight decrease in photocatalytic degradation efficiency, which does not exceed 12%. This finding indicates that, despite the presence of competitive mechanisms, CSMX-5 still demonstrates strong photocatalytic capability. When the concentration of mixed pollutants increases, it intensifies the competition among active substances, leading to a decrease in removal efficiency.
In summary, the photocatalytic mechanism of TC degradation and Cr(VI) reduction by CSMX-X is shown in Figure 9. Under the excitation of sunlight, photogenerated e− transfers to Ti3C2, thereby inhibiting the recombination of e− with photogenerated h+, which would otherwise result in light emission. The photogenerated e− on Ti3C2 reduces Cr(VI) to Cr(III), and together with the product from the reaction of the e− with O2 and the photogenerated h+, they effectively facilitate the degradation of TC. In the photocatalytic sample, CS serves as the primary photocatalyst, while Ti3C2 acts as a cocatalyst. The e− from the VB of CS is excited to the CB. Since the CB potential of CS (−0.25 V) is more negative than the Fermi level of Ti3C2 (−0.04 V) [23], the e− can transfer from CS to the surface of Ti3C2 through the interface. The e− captured by Ti3C2 cannot return to the CB of CS, thereby reducing charge carrier recombination [81]. The introduction of Ti3C2 enhances the strong interfacial interactions, effectively extending the longevity of photogenerated charge carriers, increasing carrier density and charge transfer efficiency, and minimizing the recombination of photo-excited e− and h+. The prepared photocatalyst not only excels in the removal of individual pollutants but also exhibits excellent adaptability and potential in addressing complex environmental issues. This provides an important theoretical foundation and practical guidance for future applications in water treatment, suggesting a promising outlook for the use of CSMX-5 photocatalysts in environmental remediation.

3. Materials and Methods

Details of regents and photoelectrochemical analysis were in the Supporting Materials.

3.1. Characterization of Photocatalysts

The crystalline phases of the samples were analyzed using an X-ray diffractometer (XRD, D8 Discover, Germany) equipped with a Cu Kα radiation source. The microscopic morphology of the samples was characterized using a scanning electron microscope (SEM, S-3000N, Japan). Transmission electron microscopy (TEM, F200S, USA) was utilized to examine their morphology and interfacial structure. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) measurements were conducted on a UV-visible near-infrared spectrophotometer (UV3600, Japan). Fluorescence spectroscopy (PL, F-7000, Japan) was utilized to investigate the separation dynamics of electron-hole pairs. The photoelectrochemical properties of the samples were analyzed using an electrochemical workstation (CHI660D, China). Additionally, a specific surface area analyzer (BET, TriStar II 3020, USA) was employed to measure the surface area of Ti3C2, CS, and CSMX-X. X-ray photoelectron spectroscopy (XPS, Nexsa G2, USA) was employed to investigate the bonding configurations of surface elements in the samples. Electron spin resonance (ESR, Bruker EMXplus, Germany) was employed to investigate the signals of the radicals captured by DMPO in the samples. The intermediates of photocatalytic degradation of TC were analyzed using a high-performance liquid chromatography-mass spectrometry system (LC-MS, Agilent 1290II-6460, USA) equipped with a Waters BEH-C18 chromatographic column (2.1 × 100 mm, 1.7 µm).

3.2. Preparation of Photocatalysts

Dissolved 800 mg of LiF in 20 mL HCl solution (9 mol·L−1), stirring for 10 min. Gradually added 500 mg of Ti3AlC2 while stirring for another 10 min, then ultrasonic treatment for 10 min and stirred at 40 °C for 48 h. Following this, the sample was washed several times using centrifugation until the pH ≥ 6. After vacuum-drying the sample for 10 h, it was dispersed in deionized water, stirred uniformly, purged with N2 for 10 min, and given ultrasound treatment (800 W) in an ice bath for 60 min. The black suspension was collected by centrifuging at 3500 rpm for 60 min, then freeze-dried for 3 days to obtain a single layer of Ti3C2.
Preparation flowchart of CSMX-X is shown in Figure 10. Added 1 mg, 5 mg, and 10 mg of Ti3C2 to 40 mL of a mixed solution (30% isopropanol (IPA)/70% deionized water), respectively. Dissolved 1 mmol of Cu(NO3)2·3H2O into the above solution, stirred uniformly to allow Cu2+ to adsorb onto the Ti3C2. Introduced 1 mmol of L-cysteine into the mixed solution, followed by 5 min of ultrasonic treatment (800 W), stirring constantly for 60 min. The solution was then placed in a 50 mL hydrothermal reactor and heated at 180 °C for 12 h. After cooling, the mixture underwent centrifugation and was washed repeatedly with deionized water and anhydrous ethanol. Finally, the residue was vacuum-dried overnight. Cu2S was labeled as CS, and the samples were designated with different Ti3C2 amounts as CSMX-X, where X represented the doping weight of Ti3C2.

3.3. Evaluation of the Photocatalytic Activity

The samples were dispersed in Cr(VI) (10 mg·L−1–50 mg·L−1) or TC (20 mg·L−1–50 mg·L−1) solution at a solid–liquid ratio (weight ratio) of 1:4, and magnetic stirring was conducted in the dark to achieve adsorption saturation. After illumination with a 300 W Xenon lamp (λ > 420 nm), about 2mL of mixture was extracted, then filtered to remove the solid sample. The concentration of Cr(VI) was measured following the standard method (GB 7467–1987) [82], while TC concentration was determined using a UV-vis spectrophotometer at 356 nm. The ratio C/C0 indicates the change in removal efficiency of pollutants (Cr(VI) or TC), where C represents the residual concentration at the sampling time, and C0 is the initial concentration. Prior to the next cycle experiment, the used sample needs to be activated through centrifugal washing and vacuum drying.

4. Conclusions

An economical and low-toxicity photocatalyst composed of CS and Ti3C2 was synthesized through a straightforward solvent method. The in situ growth of CS (0D) nanoparticles on single-layered Ti3C2 (2D) effectively mitigates the agglomeration of CS nanoparticles and increases the specific surface area from 2.7 m2·g−1 (pure Cu2S) to 30.65 m2·g−1. Removal efficiency > 90% was achieved for 10 mg·L−1 Cr(VI) and 20 mg·L−1 TC under visible light using CSMX-5 catalyst. This enhancement can benefit from the optimal doping amount of layered Ti3C2, which not only boosts the interaction area with the pollutants but also forms a Schottky barrier that effectively inhibits the recombination of photo-excited e− and h+. Furthermore, the photocatalytic mechanism is thoroughly investigated, revealing that h+ and ▪O2− are the principal active components in TC degradation, while e− is the key active component for Cr(VI) reduction. The repeated stability of the material was examined, and CSMX-5 was able to maintain over 90% of its initial efficiency even after five photocatalytic reactions. Copper leaching (0.032–0.676 mg·L−1) remained well below the WHO safety limit (2 mg·L−1) across pH 3–11. In addition, the efficiency of removing the mixed Cr(VI) and TC contaminants decreased by no more than 12% compared to that of the single contaminant. This study offers valuable insights for constructing Cu2S-based composite photocatalysts to efficiently remove contaminants from real water environments.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15050458/s1. Figure S1: SEM images of (a) CSMX-1, (b) CSMX-10. TEM image of (c) CSMX-5. Figure S2: XPS spectra of Ti3C2, CS, and CSMX-5 samples: (a) C 1s, (b) S 2p. (c) Pore size distributions of CS, CSMX-1 and CSMX-10. Figure S3: (a) linear sweep voltammetry (LSV) curves of the CS and CSMX-X, (b) UV–visible DRS spectra with low concentrations. Figure S4: Photocatalytic Cr(VI) (10 mg·L−1) reduction curves of (a) Pseudo-first-order kinetics, (b) Pseudo-second-order kinetics. Figure S5: SEM image of CSMX-5 after photocatalytic reduction of Cr(VI). Figure S6: XRD patterns of CSMX-5 before and after photocatalytic reduction of Cr(VI). Figure S7: Photocatalytic TC degradation curves of (a) Pseudo-first-order kinetics, (b) Pseudo-second-order kinetics. Figure S8: (a) SEM image of CSMX-5 after photocatalytic degradation of TC. (b) ESR spectra of spin-tripping of DMPO−▪O2− produced by CSMX-5. Table S1: HPLC-MS of the TC intermediates in the degradation process by CSMX-5.

Author Contributions

Z.W.: Writing—original draft, formal analysis, data curation. Z.L.: Writing—review & editing, data curation. B.Z.: Formal analysis, data curation, conceptualization. F.W.: Methodology, investigation, formal analysis. X.Y.: Writing—review & editing, supervision, investigation. P.M.: Writing—review & editing, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (51908240, 12205113), the Natural Science Research of Jiangsu Higher Education Institutions of China (23KJA430005), Qing Lan Project, and the Foundation of Jiangsu Provincial Key Laboratory of Palygorskite Science and Applied Technology (HPZ202001).

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) SEM image of multilayer Ti3C2. (b) SEM image of layered Ti3C2. (c) SEM image of CS. (d–f) SEM image of CSMX-5. (g) EDS mappings of Cu, S, C, and Ti elements. (h) TEM image of CS. (i) TEM image of CSMX-5. (j) HRTEM image of CSMX-5.
Figure 1. (a) SEM image of multilayer Ti3C2. (b) SEM image of layered Ti3C2. (c) SEM image of CS. (d–f) SEM image of CSMX-5. (g) EDS mappings of Cu, S, C, and Ti elements. (h) TEM image of CS. (i) TEM image of CSMX-5. (j) HRTEM image of CSMX-5.
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Figure 2. XRD patterns of (a) Ti3C2 and Ti3AlC2; (b) CS and CSMX-X. XPS spectra of Ti3C2, CS, and CSMX-5 samples: (c) survey; (d) Ti 2p; (e) Cu 2p. (f) Nitrogen adsorption–desorption isotherms of Ti3C2, CS, and CSMX-X.
Figure 2. XRD patterns of (a) Ti3C2 and Ti3AlC2; (b) CS and CSMX-X. XPS spectra of Ti3C2, CS, and CSMX-5 samples: (c) survey; (d) Ti 2p; (e) Cu 2p. (f) Nitrogen adsorption–desorption isotherms of Ti3C2, CS, and CSMX-X.
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Figure 3. (a) PL spectra. (b) Transient photocurrent response curves. (c) Electrochemical impedance spectra. (d) UV–visible DRS spectra. (e) Kubelka–Munk transformed reflectance spectra. (f) Measurement of Mott–Schottky diagram at multiple frequencies.
Figure 3. (a) PL spectra. (b) Transient photocurrent response curves. (c) Electrochemical impedance spectra. (d) UV–visible DRS spectra. (e) Kubelka–Munk transformed reflectance spectra. (f) Measurement of Mott–Schottky diagram at multiple frequencies.
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Figure 4. (a) Photocatalytic reduction of Cr(VI) (10 mg·L−1) under visible light irradiation. (b) Effects of initial Cr(VI) concentrations for photocatalytic reduction of Cr(VI) by CSMX-5. (c) Photocatalytic reduction of Cr(VI) (30 mg·L−1) by CSMX-5 at different pH values. (d) Residual concentration of Cu in the solution after experiments at different pH values. (e) Influence of coexisting anions (sodium salts) and (f) coexisting cations (chloride salts) on the photocatalytic reduction of Cr(VI) (10 mg·L−1) by CSMX-5.
Figure 4. (a) Photocatalytic reduction of Cr(VI) (10 mg·L−1) under visible light irradiation. (b) Effects of initial Cr(VI) concentrations for photocatalytic reduction of Cr(VI) by CSMX-5. (c) Photocatalytic reduction of Cr(VI) (30 mg·L−1) by CSMX-5 at different pH values. (d) Residual concentration of Cu in the solution after experiments at different pH values. (e) Influence of coexisting anions (sodium salts) and (f) coexisting cations (chloride salts) on the photocatalytic reduction of Cr(VI) (10 mg·L−1) by CSMX-5.
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Figure 5. (a) Trapping experiment of active species of Cr(VI). (b) Cyclic experiments on the photocatalytic reduction of Cr(VI) by CSMX-5. (c) XPS spectra of CSMX-5 after photocatalytic reduction of Cr (VI) assigned to Cr 2p.
Figure 5. (a) Trapping experiment of active species of Cr(VI). (b) Cyclic experiments on the photocatalytic reduction of Cr(VI) by CSMX-5. (c) XPS spectra of CSMX-5 after photocatalytic reduction of Cr (VI) assigned to Cr 2p.
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Figure 6. (a) Photocatalytic degradation of TC (20 mg·L−1) by CS, Ti3C2, and CSMX-X. (b) Effects of initial TC concentrations for photocatalytic reaction by CSMX-5. (c) Photocatalytic degradation of TC (20 mg·L−1) by CSMX-5 at different pH values. (d) Impact of coexisting anions (sodium salts) and (e) impact of coexisting cations (nitrates) on the photocatalytic degradation of TC (20 mg·L−1) by CSMX-5. (f) Effect of CSMX-5 on the removal of mixed pollutants TC and Cr(VI).
Figure 6. (a) Photocatalytic degradation of TC (20 mg·L−1) by CS, Ti3C2, and CSMX-X. (b) Effects of initial TC concentrations for photocatalytic reaction by CSMX-5. (c) Photocatalytic degradation of TC (20 mg·L−1) by CSMX-5 at different pH values. (d) Impact of coexisting anions (sodium salts) and (e) impact of coexisting cations (nitrates) on the photocatalytic degradation of TC (20 mg·L−1) by CSMX-5. (f) Effect of CSMX-5 on the removal of mixed pollutants TC and Cr(VI).
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Figure 7. (a) Trapping experiment of active species of TC. (b) Cyclic experiment of CSMX-5 in the photocatalytic degradation of TC. (c) XRD patterns of CSMX-5 before and after photocatalysis.
Figure 7. (a) Trapping experiment of active species of TC. (b) Cyclic experiment of CSMX-5 in the photocatalytic degradation of TC. (c) XRD patterns of CSMX-5 before and after photocatalysis.
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Figure 8. Potential intermediates during the TC degradation.
Figure 8. Potential intermediates during the TC degradation.
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Figure 9. Photocatalytic Mechanism Diagram.
Figure 9. Photocatalytic Mechanism Diagram.
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Figure 10. Preparation flowchart of CSMX-X.
Figure 10. Preparation flowchart of CSMX-X.
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Table 1. Comparing Cr(VI) removal performance of different metal sulfide photocatalysts.
Table 1. Comparing Cr(VI) removal performance of different metal sulfide photocatalysts.
PhotocatalystLight SourceAmount
(mg)		Concentration (mg·L−1)Solid-Liquid RatioLight Time (min)EfficiencyRef.
CSMX-5300 W10101:424090%This work
2-Cu2S-MoS2500 W10101:424080%[19]
Bi2S3 nanospheres500 W20401:2120100%[51]
1%CuS-Bi2WO6/CNFsXenon lamp80101:1180100%[52]
Cd0.5Zn0.5S@ZIF-8300 W40201:130100%[53]
Ag@C-TiO2/Cd0.5Zn0.5S500 W5051:212098%[54]
ZnS500 W40401:118053%[55]
Bi2WO6/CuS500 W100152:59095%[56]
Cu-Cu2−xS/C300 W20101:218090%[57]
Cu2S@CT500 W14507:1512019.24%[58]
Table 2. Comparing the degradation efficiencies of TC by different metal sulfide photocatalysts.
Table 2. Comparing the degradation efficiencies of TC by different metal sulfide photocatalysts.
PhotcatalystLight SourceAmount
(mg)		Antibiotics
(mg·L−1)		Solid-Liquid RatioLight Time (min)EfficiencyRef
CSMX-5300 W20TC (20)1:418092%This work
PANI/Cd0.5Zn0.5S300 W20TC (15)1:312084.9%[67]
CdS@CoTiO3500 W30TC (10)3:58091.8%[68]
Zn3In2S6/Bi-MOFXenon lamp10TC (60)1:56060%[69]
Zn1−xCdxS300 W50TC (50)1:212091%[70]
Ag-ZnS/rGO300 W125TC (10)1.25:111086.78%[71]
ZnS/PILED light25TC (20)1:224084%[72]
Cu2O/Cu2S300 W10TC (50)1:1012084.8%[73]
In2S3/Cu2S300 W20TC (120)2:515078.38%[74]
BiOBr/Cu2S1000 W50TC (10)1:26088.5%[75]
Cu2S/PSDLED light10TC (20)1:59093.9%[76]
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Wang, Z.; Lv, Z.; Zeng, B.; Wang, F.; Yang, X.; Mao, P. Interfacial Engineering of 0D/2D Cu2S/Ti3C2 for Efficient Photocatalytic Synchronous Removal of Tetracycline and Hexavalent Chromium. Catalysts 2025, 15, 458. https://doi.org/10.3390/catal15050458

AMA Style

Wang Z, Lv Z, Zeng B, Wang F, Yang X, Mao P. Interfacial Engineering of 0D/2D Cu2S/Ti3C2 for Efficient Photocatalytic Synchronous Removal of Tetracycline and Hexavalent Chromium. Catalysts. 2025; 15(5):458. https://doi.org/10.3390/catal15050458

Chicago/Turabian Style

Wang, Zengyu, Zhiwei Lv, Bowen Zeng, Fafa Wang, Xiaoyu Yang, and Ping Mao. 2025. "Interfacial Engineering of 0D/2D Cu2S/Ti3C2 for Efficient Photocatalytic Synchronous Removal of Tetracycline and Hexavalent Chromium" Catalysts 15, no. 5: 458. https://doi.org/10.3390/catal15050458

APA Style

Wang, Z., Lv, Z., Zeng, B., Wang, F., Yang, X., & Mao, P. (2025). Interfacial Engineering of 0D/2D Cu2S/Ti3C2 for Efficient Photocatalytic Synchronous Removal of Tetracycline and Hexavalent Chromium. Catalysts, 15(5), 458. https://doi.org/10.3390/catal15050458

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