CdS QDs decorated on 3D flower-like Sn₃O₄: a hierarchical photocatalyst with boosted charge separation for hydrogen production

Abstract

Developing novel catalysts with excellent photocatalytic hydrogen evolution activity is crucial for expediting current research on solar-chemical energy conversion. In the present study, unique Sn₃O₄/CdS composites were carefully designed and prepared using a facile hydrothermal method to achieve outstanding photocatalytic H₂ production activity. Various techniques were employed to determine the crystalline structure, chemical composition, microstructure, and optical and electrochemical characteristics of the prepared samples. The experimental results indicate that zero-dimensional (0D) CdS quantum dots were tightly attached to the surface of three-dimensional (3D) Sn₃O₄ nanoflowers. Furthermore, enhanced light-absorbing capacity and accelerated electron–hole separation and transfer were achieved after incorporating CdS quantum dots into Sn₃O₄ nanoflowers. The generation rate of hydrogen using the optimal sample (Sn₃O₄/CdS QDs-2) was about 20.74 μmol g⁻¹ h⁻¹, which was 2.86 and 3.16 times those of pure Sn₃O₄ and CdS, respectively. In addition, the possible photocatalytic H₂ production mechanism of Sn₃O₄/CdS nanocomposites was also revealed. This work is highly desirable to provide valuable inspiration for rational design and preparation of efficient photocatalysts for H₂ evolution.

---

1. Introduction

The progressive exhaustion of conventional fossil fuels and the escalating environmental pollution issues have sparked worldwide concerns.^1,2 In this regard, the use of semiconductors for photocatalytic hydrogen production through water splitting is eagerly awaited, as it can directly convert limitless solar energy into renewable and eco-friendly hydrogen energy.³ To achieve effective hydrogen generation, novel and efficient photocatalysts are crucial. To date, a large number of semiconductor-based photocatalysts (e.g., oxides, sulfides, and polymers) have been synthesized and investigated for the hydrogen evolution reaction (HER).^4–6 Unfortunately, the majority of single-component photocatalysts suffer from low light energy utilization and high carrier combination rates, resulting in poor photocatalytic performance.³ Therefore, expanding the light absorption response range and improving the separation and transportation efficiency of photo-induced electron–holes to construct efficient photocatalysts for the photocatalytic HER are still the key points to be solved.

In recent years, Sn₃O₄, a non-stoichiometric tin-based oxide consisting of Sn²⁺ and Sn⁴⁺, has attracted much attention and been recognized as a potentially excellent photocatalyst due to its natural abundance, nontoxicity, thermodynamic stability, responsiveness to visible light, and favorable band-edge position for hydrogen production.^7,8 However, the pristine Sn₃O₄ material also encounters the disadvantages of fast electron–hole combination, limited visible light absorption range, and poor stability, which exist in most single-component photocatalysts, leading to unsatisfactory performance and seriously affecting its practical applications.^9–11 The construction of heterojunctions provides an idea for the solution of the above issues. To this end, researchers have been successful in constructing a wide variety of photocatalytic hydrogen generation catalysts based on Sn₃O₄. For instance, Zn_0.5Cd_0.5S/Sn₃O₄ (ZCS/SO) composites prepared by Jiang and colleagues using a one-step hydrothermal method exhibited an enhanced hydrogen production rate, which is due to the improved light absorption range and electron–hole separation efficiency.¹⁰ Additionally, Wang's group prepared Sn₃O₄/TiO₂ NT composites through a hydrothermal method and achieved a higher photocatalytic H₂-production rate compared to that of the single component.⁹ Cui et al. synthesized two dimensional (2D)-2D g-C₃N₄/Sn₃O₄ heterojunctions using a calcination strategy. In comparison to g-C₃N₄ and Sn₃O₄, the H₂ evolution rates of the heterojunctions were 5.4 and 3.2 times higher, respectively.¹² From the above successful cases, it is clear that it is possible to develop excellent Sn₃O₄-based photocatalysts by constructing composite structures with wide light absorption and unique photogenerated charge transfer pathways. It should be noted, however, that the construction of composite structures frequently necessitates the selection of semiconductor materials with suitable energy band structures and that a reasonably close contact between the components in the composites is required for the full effect.^3,13–15 Therefore, the task of selecting suitable semiconductor materials that can effectively enhance the photocatalytic H₂-production activity when combined with Sn₃O₄ to create composite materials remains a challenge, and further research in this area is still ongoing.

As an n-type semiconductor, CdS has garnered considerable interest due to its abundant earth resources, visible light response, suitable electronic structure, and exceptional catalytic performance.⁴ In recent years, it has been reported that CdS can couple with many semiconductors (ZnO,¹⁶ Co₉S₈,¹⁷etc.) to produce composites with enhanced H₂-production performance.⁴ Given the extremely matched energy band edge positions of CdS and Sn₃O₄, it is promising to accelerate charge separation and migration by carefully designing and constructing Sn₃O₄/CdS composites with a unique energy band arrangement, thus realizing efficient hydrogen production. In addition, a lot of research has also been done on the morphology of heterojunctions because of the remarkable structure–activity relationship in photocatalysis. It is noted that zero-dimensional (0D)/three-dimensional (3D) composites constructed by modifying 3D nanostructures with 0D quantum dots (QDs) not only have good interfacial contacts for accelerated carrier separation, but also optimize multiple light reflection/scattering with the help of the hierarchical structure to improve the light energy utilization.^17–19 However, the attempt of constructing 3D/0D Sn₃O₄/CdS composites for enhanced HER has not been reported so far.

Inspired by the aforementioned analysis, in this study, by confining 0D CdS QDs on 3D Sn₃O₄ nanoflowers using a simple hydrothermal method, novel 3D/0D Sn₃O₄/CdS composites were carefully designed and constructed for the first time. The as-prepared catalysts’ activity under visible light was revealed by photocatalytic HER experiments. It is interesting to find that the coupling of Sn₃O₄ and CdS can dramatically improve the HER activity. By analyzing the optical and electrochemical properties of the composites, the enhanced efficiency of Sn₃O₄/CdS composites is elucidated, and a potential photocatalytic mechanism is suggested. This work opens up ideas for further research on efficient Sn₃O₄-based visible-light-driven photocatalysts with enhanced H₂-evolution activity.

2. Experimental section

2.1. Preparation of CdS quantum dots (CdS QDs)

In a 100 mL beaker, 50 mL of 10 mM cadmium chloride aqueous solution was poured, and then 0.25 mL of thioglycolic acid was added. The pH was adjusted to 11 by adding NaOH aqueous solution (1 M). Afterwards, a solution containing 5 mL (0.1 M) of dehydrated sodium sulfide was added to the previous mixture and agitated for a duration of 4 hours. As a result, CdS QDs were obtained. The reaction was consistently conducted in an atmosphere of nitrogen.

2.2. Preparation of Sn₃O₄ and Sn₃O₄/CdS QD composites

A homogeneous solution was formed by dissolving 5 mmol of SnCl₂·2H₂O and 12.5 mmol of Na₃C₆H₅O₇·2H₂O in 12.5 mL of deionized water, which was then stirred and sonicated for 20 minutes. Subsequently, different amounts of CdS QD solutions were added to the above solution, and the resulting mixture was named solution A. In order to prepare solution B, 0.3 g of NaOH was dissolved in 12.5 mL of distilled water. Solutions A and B were combined and agitated for 30 minutes. Subsequently, the resulting mixture was transferred to a 50 mL autoclave and underwent a 12 hour hydrothermal reaction at 180 °C in an oven. Once the reactor dropped to ambient temperature, the resultant yellow solid was rinsed multiple times with deionized water and ethanol. Finally, the Sn₃O₄/CdS QD composites were obtained by vacuum-drying the above precipitates at 60 °C for 12 hours. The preparation process of Sn₃O₄/CdS QDs is depicted in Fig. 1. Sn₃O₄/CdS QDs-1, Sn₃O₄/CdS QDs-2, Sn₃O₄/CdS QDs-3 and Sn₃O₄/CdS QDs-4 were the final corresponding samples, which are labeled based on the addition of CdS QD solutions of 0.5, 1.0, 1.5 and 2.0 mL, respectively.

Fig. 1 A schematic illustration depicting the preparation process of Sn₃O₄/CdS QD photocatalysts.

The preparation process of pure Sn₃O₄ flower-like structures was the same as that of the Sn₃O₄/CdS QD composites described above, except that the CdS QD solution was not added.

3. Results and discussion

3.1. Phase characteristics

The phase composition of Sn₃O₄, CdS QDs and Sn₃O₄/CdS composite samples was determined using X-ray diffraction (XRD). The results are compared in Fig. 2. As can be seen, the diffraction peaks at 24.2°, 27.11°, 31.81°, 32.41°, 33.01°, 37.11°, 40.31°, and 51.71° belong to the (101), (111), (210), (121), (210), (130), (102), and (132) crystal planes of Sn₃O₄ (JCPDS no. 160737), respectively, indicating the successful synthesis of high-purity Sn₃O₄.¹⁰ The XRD pattern of the prepared CdS QDs is consistent with JCPDS no. 750581 (Fig. S1, ESI†).^19,20 The XRD patterns of the Sn₃O₄/CdS composite samples are similar to those of Sn₃O₄, indicating that the introduction of CdS did not affect the lattice of the original component. No obvious characteristic diffraction peaks belonging to CdS are found in the Sn₃O₄/CdS composite samples, possibly because of the low concentration and effective dispersion of CdS QDs within the composites.¹⁹ The average crystallite sizes of pure Sn₃O₄ and Sn₃O₄/CdS QD samples are shown in Table S1 (ESI†), which were calculated by Scherer's formula.²¹

Fig. 2 XRD patterns of pure Sn₃O₄ and Sn₃O₄/CdS QD samples.

3.2. Micromorphological analysis

The samples’ morphological characteristics and microstructure were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fig. S2a (ESI†) depicts the SEM image of pure Sn₃O₄. As illustrated in the figure, the prepared pure Sn₃O₄ sample has a three-dimensional flower-like structure composed of various nanosheets. Fig. 3 shows the SEM images of different Sn₃O₄/CdS QD catalysts. When compared, it is possible to conclude that the flower-like structure of pure Sn₃O₄ is inherited by the composite samples. Therefore, it can be inferred that the Sn₃O₄ sample did not undergo a significant change in morphology upon coupling with CdS QDs, but rather maintained the original structural property.

Fig. 3 SEM images of Sn₃O₄/CdS QDs-1 (a), Sn₃O₄/CdS QDs-2 (b), Sn₃O₄/CdS QDs-3 (c), and Sn₃O₄/CdS QDs-4 (d).

TEM images of pure Sn₃O₄ are shown in Fig. S2b and c (ESI†). These images reveal that a flower-like structure is uniform throughout the material, and demonstrate that the flower-like structure is formed of stacked thin nanosheets. From the TEM image of CdS (Fig. S2d, ESI†), it is clear that the prepared pure CdS QDs are quantum dots with small sizes. Fig. 4a and b depict the TEM images of the Sn₃O₄/CdS QDs-2 composite sample, in which the structural features of the thin nanosheets are clearly visible and are not disrupted after coupling with CdS QDs, confirming the SEM results. Moreover, the high-resolution transmission electron microscopy (HRTEM) image reveals that CdS QDs in the composite sample appeared on the nanosheets of Sn₃O₄ and were uniformly dispersed (Fig. 4c and Fig. S3, ESI†). A favorable contact interface is formed between the two components. The interface promotes the establishment of a pathway for carrier transportation and facilitates the efficient carrier movement. The composite sample exhibits distinct lattice stripes (Fig. 4d). And, a lattice spacing of 0.369 nm corresponds to the (101) crystal plane of Sn₃O₄, confirming the presence of Sn₃O₄ in the prepared catalysts. CdS can be identified in the composite sample because the characteristic lattice spacing of 0.205 nm is consistent with its (220) crystal plane. Furthermore, the nanostructure of Sn₃O₄/CdS QDs can be corroborated by the high-angle annular dark-field (HAADF) image (Fig. 4e) and energy dispersive spectroscopy (EDS) elemental mapping images (Fig. 4f–i and Fig. S4, ESI†), from which it is clear that Sn, O, Cd, and S are all present in the composite structure and are distributed evenly throughout the nanostructure.

Fig. 4 TEM (a) and (b) and HRTEM (c) and (d) images of Sn₃O₄/CdS QDs-2. (e)–(i) HAADF and EDS mapping images of Sn, O, Cd, and S in Sn₃O₄/CdS QDs-2.

3.3. Surface composition analysis

Using X-ray photoelectron spectroscopy (XPS), the chemical composition and state of pure Sn₃O₄, CdS QD, and Sn₃O₄/CdS QDs-2 composites were determined. Fig. 5 depicts the results. The high-resolution spectrum of Sn 3d (shown in Fig. 5a) consists of two distinct asymmetric splitting signals, which are respectively 3d_3/2 and 3d_5/2, suggesting that Sn possesses multiple chemical states in pure Sn₃O₄. Among them, Sn 3d_3/2 can be deconvolved into two peaks, the first of which is Sn⁴⁺ at 495.0 eV, and the second of which is Sn²⁺ at 496.4 eV.^7,8 Meanwhile, the signal of Sn 3d_5/2 can fit into two peaks. The peak centered at 486.6 eV can be attributed to Sn⁴⁺, while the binding energy of 486.1 eV is ascribed to Sn²⁺.^14,22 The peak of O1s of Sn₃O₄ in Fig. 5b can be dissolved into two peaks, one at 531.4 eV (corresponding to O–Sn⁴⁺) and the other at 530.3 eV (belonging to O–Sn²⁺).¹⁰Fig. 5c and d reveals the high-resolution XPS of Cd 3d and S 2p for Sn₃O₄ and Sn₃O₄/CdS QDs-2. As shown in Fig. 5c, two characteristic peaks located at 411.9 and 405.2 eV belong to Cd 3d_3/2 and Cd 3d_5/2, respectively.^10,17 Additionally, the S 2p spectrum shown in Fig. 5d can be dissolved into two peaks, located at 162.6 and 161.4 eV, which is assigned to S 2p_1/2 and S 2p_3/2, respectively.¹⁷ It is noteworthy that the positions of the characteristic peaks corresponding to Sn 3d and O 1s in the Sn₃O₄/CdS QDs-2 composite are slightly shifted toward higher binding energies compared to that of pure Sn₃O₄. And the characteristic peaks corresponding to Cd 3d and S 2p in the composite can be observed to be shifted toward lower binding energy with respect to pure CdS. These phenomena indicate that the coupling of Sn₃O₄ and CdS forms an effective interfacial contact between the two component materials, and strong interactions and charge redistributions occur, which contribute to the separation of charge carriers.^10,19,23

Fig. 5 High-resolution XPS spectra of (a) Sn 3d, (b) O 1s, (c) Cd 3d, and (d) S 2p in Sn₃O₄ and Sn₃O₄/CdS QDs-2.

3.4. Optical absorption properties and energy band structures

In order to reveal the light absorption ability and energy band gap of the resulting samples, the optical properties of Sn₃O₄, CdS QD, and Sn₃O₄/CdS QDs-2 composites were revealed by UV-vis diffuse reflectance spectroscopy (DRS). It can be found that the prepared catalysts can all respond within the wavelength range of 300–800 nm (Fig. 6a), implying that the samples can undergo photocatalytic reactions by absorbing UV light and visible light, respectively. Among them, the strong absorption edges of Sn₃O₄ and CdS QDs are at about 510 nm and 530 nm, respectively. After decorating the surface of Sn₃O₄ with CdS QDs, a slight redshift at the band edge of the Sn₃O₄/CdS QDs-2 composite could be achieved and the light absorption intensity also increased. This suggests that the formation of Sn₃O₄/CdS QD heterostructures can significantly improve the material's utilization efficiency for sunlight, thereby promoting the involvement of more photogenerated carriers in the redox process and boosting the photocatalytic performance. Furthermore, the intrinsic energy gaps (E_g) of Sn₃O₄ and CdS QDs can be derived from the Kubelka–Munk function.^24,25 The Tauc-plots of Sn₃O₄ and CdS QDs are shown in Fig. 6b, and by extrapolating the linear portion of the Sn₃O₄ and CdS QDs curves until their intercepts with the x-axis, the band gaps of Sn₃O₄ and CdS QDs can be determined as 2.6 and 2.4 eV, correspondingly. These values align well with the reported values.^26,27

Fig. 6 (a) DRS of Sn₃O₄, CdS QD, and Sn₃O₄/CdS QDs-2 samples. (b) Tauc and (c) and (d) Mott–Schottky plots of Sn₃O₄ and CdS QDs.

In addition, the Mott–Schottky (M–S) curves provide insight into the catalysts’ semiconductor type and energy band structure. Fig. 6c and d show the M–S curves of Sn₃O₄ and CdS QDs. It can be seen that both exhibit a linear region with a positive slope, indicating that both of them are n-type semiconductors. The flat band potentials of Sn₃O₄ and CdS QDs are −0.61 and −0.88 eV (vs. NHE, pH = 7), respectively, obtained from the tangent intercepts of the M–S curves. In general, the conduction band potential (E_CB) of n-type semiconductors can be considered to be approximately equal to their flat band potentials.^12,13,22 Thus, the E_CB values of Sn₃O₄ and CdS QDs are estimated to be around −0.61 and −0.88 eV (vs. NHE, pH = 7), respectively. Meanwhile, according to the following equation: E_g = E_VB − E_CB, and in combination with the E_g of Sn₃O₄ and CdS QDs in Fig. 6b, the valence band edge positions (E_VB) of Sn₃O₄ and CdS can be calculated as 1.99 and 1.52 eV (vs. NHE, pH = 7), respectively.²⁸

3.5. Photocatalytic performance and interfacial charge transfer

The efficiency of H₂-evolution from water splitting (λ ≥ 420 nm) is a criterion for evaluating the photocatalytic performance of catalysts. In this experiment, to reflect the photocatalytic performance of Sn₃O₄, CdS and Sn₃O₄/CdS composites, the amount of H₂ production of the samples was measured over a period of 4 h and its average hydrogen production rate was calculated. To consume the photogenerated holes, the CH₃OH aqueous solution was used as the sacrificial agent.

Fig. 7a shows the fluctuation curves of hydrogen production over time for different photocatalysts. It can be seen that the photocatalytic activities of both pure Sn₃O₄ and bare CdS QDs are poor under the above conditions, which is due to the rapid recombination of photogenerated carriers. Surprisingly, the coupling of Sn₃O₄ with CdS QDs enhances the hydrogen production performance of all Sn₃O₄/CdS QD composite samples. In order to explain more directly the change in performance after the addition of CdS QDs, the H₂-evolution rates of the corresponding products are shown in Fig. 7b. The comparison of the hydrogen production rates of other Sn₃O₄-based photocatalysts is shown in Table S2 (ESI†). Pure Sn₃O₄ and bare CdS QDs exhibit average hydrogen production rates of 7.25 and 6.55 μmol g⁻¹ h⁻¹, respectively. Among a series of composites, Sn₃O₄/CdS QDs-2 shows the highest H₂ production rate of 20.74 μmol g⁻¹ h⁻¹, surpassing those of pure Sn₃O₄ and CdS by 2.86 and 3.16 times. The hydrogen production rates of the composite samples show the following trend: Sn₃O₄/CdS QDs-2 (20.74 μmol g⁻¹ h⁻¹) > Sn₃O₄/CdS QDs-3 (17.85 μmol g⁻¹ h⁻¹) > Sn₃O₄/CdS QDs-1 (15.87 μmol g⁻¹ h⁻¹) > Sn₃O₄/CdS QDs-4 (14.25 μmol g⁻¹ h⁻¹). It can be seen that more CdS do not always mean higher photocatalytic performance since it might have a negative impact on the catalyst's dispersion, interfacial contact ability, and light absorption capacity at high concentrations. The cyclic stability test (Fig. S5, ESI†) shows that the H₂ production rate of the prepared catalyst does not decrease considerably after four reactions, indicating that the material has good stability. The photocatalytic H₂ evolution curve of Sn₃O₄/CdS QDs-2 with an error bar is shown in Fig. S6 (ESI†), which further proves the reliability and stability of Sn₃O₄/CdS QDs-2. In addition, the XRD and TEM results of Sn₃O₄/CdS QDs-2 after the photocatalytic reaction are shown in Fig. S7 and S8 (ESI†). The results show that the morphology and crystal structure of the sample did not change significantly after the photocatalytic hydrogen production reaction.

Fig. 7 (a) Photocatalytic H₂-production versus time and (b) the rates of H₂ production for different samples.

To investigate the separation and transfer efficiency of photogenerated carriers in the catalysts, various experiments were performed, including transient photocurrent analysis (I–t curves), electrochemical impedance spectroscopy (EIS), steady-state photoluminescence (PL) spectroscopy, and time-resolved photoluminescence (TR-PL) spectroscopy. In general, the higher the transient photocurrent density, the higher the interfacial carrier separation efficiency of the catalyst, and the better the photocatalytic performance.^29,30Fig. 8a shows the transient photocurrent response plots of CdS QD, Sn₃O₄, and Sn₃O₄/CdS QDs-2 nanocomposites under visible light irradiation for several on–off cycles. The results show that the transient photocurrent response of the Sn₃O₄/CdS QDs-2 composite photocatalyst is significantly enhanced when used as working electrodes compared to pristine Sn₃O₄ or CdS, suggesting that the photogenerated charge separation and transfer of Sn₃O₄/CdS QD nanocomposites is more capable under light irradiation. This conclusion can also be confirmed by the Nyquist plots of the corresponding samples shown in Fig. 8b. For the optimal sample of Sn₃O₄/CdS QDs-2, the radius of a semicircle arc is the smallest compared with that of pristine CdS QDs and Sn₃O₄, respectively. This implies that Sn₃O₄/CdS QDs-2 has the smallest electron-transfer resistance, signifying that it has the fastest electron transfer, which is favorable for the efficient separation and transfer of carriers.³¹ The recombination rate of charge carriers in the catalysts was further assessed by PL. Fig. 8c reveals the fluorescence intensity of Sn₃O₄ and a series of Sn₃O₄/CdS QD nanocomposites. Generally, the low signal of fluorescence peak indicates a low recombination probability of photo-induced electron–hole pairs, thus showing high photocatalytic activity.^32,33 It is not difficult to find that the PL intensity of pure Sn₃O₄ is the highest, and the PL intensity of Sn₃O₄/CdS QDs-2 is the lowest. The results indicate the recombination of photogenerated carriers in the composite material is sufficiently suppressed, which also corroborates with the experimental outcomes of I–t and EIS. Additionally, the lifetime of photoinduced carriers in the photocatalysts was analyzed using TR-PL spectra.³⁴ The average lifetime (τ_av) can be obtained by fitting the decay process with a bi-exponential function: τ_av = (A₁τ₁² + A₂τ₂²)/(A₁τ₁ + A₂τ₂).²⁷ The specific fitting data are summarized and shown in Table S3 (ESI†). From the TR-PL spectra (Fig. 8d), the τ_av values of Sn₃O₄, CdS QD, and Sn₃O₄/CdS QDs-2 composites are 1.78, 1.37 and 2.25 ns, respectively. Apparently, the fluorescence lifetime of the Sn₃O₄/CdS QDs-2 nanocomposite is increased compared with those of Sn₃O₄ and CdS QDs. The increase in the carrier lifetime implies an increase in the utilization of electron–hole pairs during the photocatalytic process and a boost in the activity of photocatalysis.³⁵ This is also consistent with the above findings on photocurrent, EIS, and hydrogen production properties.

Fig. 8 (a) I–t curves, (b) Nyquist plots, (c) PL spectra, and (d) TR-PL spectra.

3.6. Photocatalytic mechanism

Based on the above results and analyses, we propose a possible mechanism for the efficient separation of photogenerated carriers and high H₂ evolution performance in the Sn₃O₄/CdS QD composite system (as shown in Fig. 9). When compared to Sn₃O₄, CdS QDs have more negative conduction band (CB) and valence band (VB) locations. Then, a matched and staggered energy band structure is formed between them. Under visible light irradiation, both CdS and Sn₃O₄ are capable of creating photogenerated carriers when they get excited. Due to the potential difference between CdS and Sn₃O₄, the photogenerated electrons on the CB of CdS migrate quickly to the CB of Sn₃O₄, where they react with the water molecules adsorbed on the catalyst's surface to reduce H₂O to H₂. Conversely, the holes generated on the VB of Sn₃O₄ tend to migrate to the VB of CdS. Subsequently, these holes are consumed by CH₃OH as the sacrificial agent. Such an electron transfer pathway effectively suppresses the combination of photogenerated charges with different electrical properties in the Sn₃O₄/CdS QD heterostructures, thereby extending the lifetime of photoinduced electron–hole pairs and enhancing photocatalytic activity.

Fig. 9 Schematic diagram of the photocatalytic H₂ evolution mechanism of Sn₃O₄/CdS QDs.

4. Conclusions

In conclusion, unique 3D/0D Sn₃O₄/CdS QD composite photocatalysts were successfully synthesized by employing a simple hydrothermal method. TEM observations indicated that 0D CdS QDs were closely confined on the 3D Sn₃O₄ nanoflowers forming a close contact interface. The effective formation of the composite contributes to the improvement of the light absorption capacity of the composite sample as well as the charge carrier separation between the components, as evidenced by the DRS analysis and the electrochemical test. As a result, enhanced hydrogen production performance was achieved in Sn₃O₄/CdS QD composites. The optimal hydrogen generation rate of Sn₃O₄/CdS QDs-2 was about 20.74 μmol g⁻¹ h⁻¹, which was 2.86 and 3.16 times those of pure Sn₃O₄ and CdS, respectively. Moreover, the Sn₃O₄/CdS QDs-2 nanocomposite exhibited stable cycling performance. This study provides a feasible new strategy for the design and preparation of efficient Sn₃O₄-based composite photocatalysts for solar-driven hydrogen production from water splitting.

Author contributions

Pengfei Tan: synthesis, data analysis, and writing; Lu Yang: methodology, writing, supervision, and reviewing; Hele Liu, Yi Zhang, and Binhua Zhou: methodology and investigation; Jun Pan: supervision and reviewing.

Conflicts of interest

The authors declare that there are no conflicts of interest.

Acknowledgements

The Natural Science Foundation of Hunan Province (2022JJ40613), the Open Project of Yunnan Precious Metals Laboratory Co., Ltd (no. YPML-2023050264), the National Natural Science Foundation of China (52001335 and 12074435), and the Natural Science Foundation of Yunnan Province (202201AT070259) provided financial support for this work.

References

1. S. Nishioka, F. E. Osterloh, X. Wang, T. E. Mallouk and K. Maeda, Nat. Rev. Methods Primers, 2023, 3, 1–15.
2. C. Bie, L. Wang and J. Yu, Chem, 2022, 8, 1567–1574.
3. B. Samanta, Á. Morales-García, F. Illas, N. Goga, J. A. Anta, S. Calero, A. Bieberle-Hütter, F. Libisch, A. B. Muñoz-García, M. Pavone and M. C. Toroker, Chem. Soc. Rev., 2022, 51, 3794–3818.
4. L. Cheng, Q. Xiang, Y. Liao and H. Zhang, Energy Environ. Sci., 2018, 11, 1362–1391.
5. L. Hu, H. Yang, S. Wang, J. Gao, H. Hou and W. Yang, J. Mater. Chem. C, 2021, 9, 5343–5348.
6. W. Zhang, Z. Deng, J. Deng, C.-T. Au, Y. Liao, H. Yang and Q. Liu, J. Mater. Chem. A, 2022, 10, 22419–22427.
7. H. Liu, P. Tan, H. Zhai, M. Zhang, J. Chen, R. Ren, Z. Wang and J. Pan, New J. Chem., 2022, 46, 14043–14051.
8. H. Liu, P. Tan, L. Yang, M. Zhang, J. Chen, R. Ren, H. Zhai, T. Qi and J. Pan, Mol. Catal., 2023, 547, 113309.
9. Q. Wang, Y. Zhao, Z. Zhang, S. Liao, Y. Deng, X. Wang, Q. Ye and K. Wang, Ceram. Int., 2023, 49, 5977–5985.
10. X. Zhou, J. Wu, Y. Xiao, Y. Jiang, W. Zhang, Y. Liu, Z. Liu and J. Zhang, Sep. Purif. Technol., 2023, 311, 123243.
11. C. Aruljothi, P. Balaji, E. Vaishnavi, T. Pazhanivel and T. Vasuki, J. Chem. Technol. Biotechnol., 2023, 98, 1908–1917.
12. Y. Zhu, Y. Cui, B. Xiao, J. Ou-yang, H. Li and Z. Chen, Mater. Sci. Semicond. Process., 2021, 129, 105767.
13. Y. Wen, D. Wang, H. Li, W. Jiang, T. Zhou, X. Deng, B. Hu, C. Liu and G. Che, Appl. Surf. Sci., 2021, 567, 150903.
14. L. Chen, C. Hou, Z. Liu, Y. Qu, M. Xie and W. Han, Chem. Commun., 2020, 56, 13884–13887.
15. B. Parasuraman, B. Kandasamy, V. Vasudevan and P. Thangavelu, Environ. Sci. Pollut. Res., 2023, 1–11.
16. Y. Liu, R. Dong, Y. Ma, W. Liu, A. Zhu, P. Tan, Y. Bian, X. Xiong, E. Li and J. Pan, Int. J. Hydrogen Energy, 2019, 44, 25599–25606.
17. P. Tan, Y. Liu, A. Zhu, W. Zeng, H. Cui and J. Pan, ACS Sustainable Chem. Eng., 2018, 6, 10385–10394.
18. X. Hao, D. Xiang and Z. Jin, Dalton Trans., 2021, 50, 10501–10514.
19. Z. Zhu, X. Li, Y. Qu, F. Zhou, Z. Wang, W. Wang, C. Zhao, H. Wang, L. Li, Y. Yao, Q. Zhang and Y. Wu, Nano Res., 2021, 14, 81–90.
20. X. Xiang, B. Zhu, B. Cheng, J. Yu and H. Lv, Small, 2020, 16, 2001024.
21. B. Parasuraman, B. Kandasamy, I. Murugan, M. S. Alsalhi, N. Asemi, P. Thangavelu and S. Perumal, Chemosphere, 2023, 334, 138979.
22. R. Yang, Y. Ji, L. Wang, G. Song, A. Wang, L. Ding, N. Ren, Y. Lv, J. Zhang and X. Yu, ACS Appl. Nano Mater., 2020, 3, 9268–9275.
23. Y. Qiu, Z. Xing, M. Guo, T. Zhao, Y. Wang, P. Chen, Z. Li, K. Pan and W. Zhou, J. Colloid Interface Sci., 2021, 582, 752–763.
24. Z. Dai, J. Lian, Y. Sun, L. Li, H. Zhang, N. Hu and D. Ding, Chem. Eng. J., 2022, 433, 133766.
25. Y. Su, X. Xu, R. Li, X. Luo, H. Yao, S. Fang, K. Peter Homewood, Z. Huang, Y. Gao and X. Chen, Chem. Eng. J., 2022, 429, 132241.
26. L. Li, K. Zhang, W. Jin, W. Xia, J. He and X. Zeng, Int. J. Hydrogen Energy, 2022, 47, 10594–10602.
27. T. Zhao, Z. Xing, Z. Xiu, Z. Li, S. Yang and W. Zhou, ACS Appl. Mater. Interfaces, 2019, 11, 7104–7111.
28. L. Xu, W.-q Chen, S.-q Ke, S.-m Zhang, M. Zhu, Y. Zhang, W.-y Shi, S. Horike and L. Tang, Chem. Eng. J., 2020, 382, 122810.
29. H. Hou, L. Wang, F. Gao, X. Yang and W. Yang, J. Mater. Chem. C, 2019, 7, 7858–7864.
30. Q. Liang, C. Zhang, S. Xu, M. Zhou, Y. Zhou and Z. Li, J. Colloid Interface Sci., 2020, 577, 1–11.
31. H. Miao, H. Zong, X. Zhu, J. Chen, Z. Mo, W. Zhang, Z. Chen and H. Xu, New J. Chem., 2022, 46, 17704–17712.
32. F. Dong, H. Liu, L. Qin, T. Zhang, X. Li and S.-Z. Kang, New J. Chem., 2023, 47, 13177–13185.
33. C. Li, S. Yu, H. Dong, C. Liu, H. Wu, H. Che and G. Chen, Appl. Catal., B, 2018, 238, 284–293.
34. Z. Ren, X. Zhang, X. Shi, D. Yang, M.-H. Yu, W. Zheng and J. Zhang, New J. Chem., 2023, 47, 10506–10513.
35. X. Yu, Z. Zhao, D. Sun, N. Ren, J. Yu, R. Yang and H. Liu, Appl. Catal., B, 2018, 227, 470–476.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3nj03611a

---