Enhanced Photocatalytic CO₂ Reduction via CCH/g-C₃N₄ Heterojunction: Optimizing Charge Carrier Dynamics and Visible-Light Utilization

Abstract

The photocatalytic CO₂ reduction (PCR) into value-added fuels offers a promising solution to energy shortages and the greenhouse effect, thanks to the mild conditions and environmental sustainability. However, the activation of CO₂ is challenging because of the thermodynamic stability and chemical inertness of CO₂ molecules, which significantly restricts the efficiency of PCR. Cobalt carbonate hexahydrate (CCH), known for its excellent CO₂ adsorption and activation properties, faces challenges like poor electron–hole separation and photoresponse. To address these issues, graphitic carbon nitride (CN) as a “pseudo-sensitizer” was introduced into the system by an in situ heterojunction synthesis strategy to produce CCH/CN photocatalyst, where Co–N bonds formed between CCH and CN enhance charge carrier migration and lower interfacial resistance. The CCH/CN catalyst achieved a CO production rate of 19.65 μmol g⁻¹ h⁻¹, outperforming CCH, CN, and a mechanically mixed sample (Mix) by 7.74, 2.31, and 1.77 times, respectively. This work demonstrates an effective strategy for designing heterojunction catalysts to improve visible light utilization and charge transfer for efficient CO₂ reduction.

1. Introduction

With the rapid advancement of the global economy, the widespread exploitation and consumption of fossil fuels have led to a substantial increase in atmospheric CO₂ concentrations, triggering large-scale global warming and severe ecological degradation [1,2,3]. Converting CO₂ into utilizable fossil fuels (such as CO, CH₄) under pollution-free circumstances is one of the most effective approaches to mitigate the greenhouse effect and contributes to alleviating the global energy crisis. Photocatalytic CO₂ reduction (PCR) has drawn extensive attention from researchers because of its merits, like mild reaction conditions, environmental friendliness, and absence of pollution [4,5,6]. Nevertheless, the constraint of PCR lies in the chemical activation of CO₂, which typically demands extremely high energy [7,8]. Hence, lowering the activation energy barrier of CO₂ constitutes the key to making a significant breakthrough in PCR technology [9].

Recently, cobalt carbonate hydroxide (CCH) has emerged as a promising catalyst for PCR to CO species [10,11]. Nevertheless, bare CCH exhibits limited photocatalytic activity, primarily due to its poor electron–hole separation efficiency and the strong electron–hole recombination ability. As depicted in Figure S1a, CCH exhibits a relatively short photoluminescence (PL) lifetime of approximately 2.21 ns, indicating insufficient charge carrier dynamics for photocatalysis. Consequently, photosensitizers, such as [Ru(bpy)₃]Cl₂, are often required to supply additional photogenerated electrons for the photocatalytic reaction [10,11]. However, the high cost and poor stability of these photosensitizers hinder the practical application of CCH in large-scale processes. To overcome this limitation, constructing a heterojunction catalyst structure is a widely adopted strategy. When two or more semiconductors are recombined through van der Waals force, hydrogen bonds, chemical bonds, etc., a heterojunction will be formed among the photocatalysts. The photoinduced carriers can be transferred via the interface charge, thereby enhancing the separation efficiency of carriers [12,13]. Furthermore, the construction of heterojunctions can further enhance the light absorption capacity. Therefore, an effective approach for CCH is to identify an inexpensive material with strong visible light absorption, high charge carrier mobility, and suitable bandgap alignment to act as a “pseudo-sensitizer”. When coupled with CCH, such a material can form a novel composite catalyst that improves overall photocatalytic efficiency while addressing the cost and stability concerns associated with traditional photosensitizers.

Since Wang et al. [14] first utilized graphitic carbon nitride (g-C₃N₄, CN) for photocatalytic water splitting in 2009, CN has garnered significant attention in materials science and energy conversion research [15,16,17]. Over the years, CN has been extensively studied as a vital photocatalyst for CO₂ reduction due to its remarkable visible light absorption, large specific surface area, and appropriately tailored bandgap structure [18,19]. Additionally, the layered structure of CN offers exceptional flexibility, enabling it to be bent, twisted, and effectively coated onto the surfaces of other catalysts. This versatility makes CN an excellent platform for constructing advanced PCR systems [20,21]. For example, the presence of CN within the Z-scheme Bi₁₉S₂₇Br₃/CN heterojunction enhances the PCR activity through improved photogenerated charge transfer via an interfacial C-S bond [22]. The protonated ultrathin CN (p-CN) nanosheets of p-CN/InVO₄ are beneficial for the separation of charge carriers and the transfer of photoelectrons from the p-CN to the adsorbed CO₂ molecules, thereby enhancing the photocatalytic activity [23]. Additionally, the type-II heterojunction of CN/TiO₂ enhances the efficiency of spatial charge separation and inhibits charge carrier recombination, thus improving the photocatalytic performance [24]. As illustrated in Figure S1b, CN nanosheets exhibit a PL lifetime of approximately 19.4 ns, indicating stronger electron–hole separation capability than CCH. This property, combined with CN’s structural advantages, makes it an ideal candidate for integration with CCH.

Inspired by the aforementioned analysis, the CCH/CN heterojunction was successfully fabricated using an in situ heterojunction synthesis strategy. This approach facilitated the formation of Co–N bonds at the interface between CCH and CN, which not only enhanced visible-light utilization and charge carrier dynamics but also improved CO₂ adsorption on the catalyst surface. Notably, the CCH/CN heterojunction demonstrated exceptional photocatalytic performance for CO₂ reduction, achieving a CO production rate of 19.65 μmol g⁻¹ h⁻¹. This rate is approximately 7.74, 2.31, and 1.77 times higher than those of CCH (2.54 μmol g⁻¹ h⁻¹), CN (8.52 μmol g⁻¹ h⁻¹), and a mechanically mixed sample (Mix, 11.13 μmol g⁻¹ h⁻¹), respectively. The CCH/CN heterojunction thus represents a highly effective system for photocatalytic CO₂ reduction, combining improved light absorption, efficient charge separation, and enhanced surface CO₂ adsorption into a single, integrated catalyst design. These results underscore the synergistic effects of the heterojunction structure in significantly enhancing the catalytic efficiency of the composite material.

2. Results and Discussion

2.1. Morphological and Structural Characterization

The morphologies of the synthesized materials were characterized by SEM and TEM. As depicted in Figure 1a,e, CCH exhibits a one-dimensional nanowire morphology with a diameter of tens of nanometers and a length of several microns. CN presents a two-dimensional nanosheet topography (Figure 1b,f). When CCH/CN was obtained through the in situ hydrothermal method, CN was uniformly wrapped on the surface of CCH (Figure 1c,g), and the formation of heterojunctions did not compromise the original morphology of the catalyst. In addition, the selected area electron diffraction (SAED) pattern displays two sets of diffraction fringes of CCH and CN (Figure 1h), demonstrating the successful construction of the heterostructure of CCH/CN. In Mix (Figure 1d), CN and CCH are grown separately. The crystallographic property and phase purity of the as-prepared samples were investigated through XRD measurements. As shown in Figure 1i, the X-ray diffraction patterns (XRD) of the CCH samples are highly in accordance with the orthorhombic phase of Co(CO₃)_0.5(OH)·0.11H₂O. The two characteristic diffraction peaks of CN at 12.8° (100) and 27.8° (002) were related to the continuous tri-s-triazine stacking and interlayer stacking reflection, respectively [25,26]. All the XRD diffraction patterns of CCH/CN are inspected, and no new peaks emerged or vanished, indicating that the formation of the CCH/CN heterojunction does not disrupt the crystal structure.

The FTIR spectra were used to verify the interaction of CCO and CN. As shown in Figure 2 and Table S1, the peak at 3432 cm⁻¹ was ascribed to the N–H group stretching mode of C–NH₃ in CN. The peaks located at 1249, 1321, and 1413 cm⁻¹ were assigned to stretching vibration modes of triazine ring for CN [27,28,29]. In CCH, the peak center at 3500 cm⁻¹ was ascribed to the stretching modes of the O–H group of water molecules. The peaks situated at 686 and 968 cm⁻¹ were designated to the in-plane and out-of-plane bending vibrations of CO₃²⁻ [11,30]. Notably, the peaks of triazine ring and CO₃²⁻ in CCH/CN show a shift towards higher wavenumber, implying the strong interaction between CCH and CN. Specifically, the indistinct N–H group stretching peaks of CCH/CN and Mix manifest that the CCH may link with the N atom of N–H in CN.

The molecular structure information of CCH/CN was studied by Raman spectra (Figure 3 and Table S2). The Raman shifts of CN at 452, 472, 487, 707, 469, 976, 1117, 1154, 1216, and 1234 cm⁻¹ were assigned to vibration modes of CN heterocycles in CN [31,32]. Specifically, the intense peaks at 769 and 1154 cm⁻¹ were assigned to the A₁′ vibrations of the tri-s-triazine ring [33]. The strong diffraction peaks at 707, 1117, and 1234 cm⁻¹ are caused by the different types of ring breathing modes of the tri-s-triazine ring [31]. The Raman peaks of CCH at 691 and 1087 cm⁻¹ belong to carbonate ions. In addition, the Raman modes at 481 cm⁻¹ were attributed to the Co–O vibration modes [11]. Observingly, the exocentric Raman shift of the tri-s-triazine ring and Co–O vibration modes with steady Raman vibration modes of carbonate ions indicate that the CCH may link with CN by Co–N bond in the CCH/CN.

The chemical composition and electron transfer direction of CCH, CN, and CCH/CN were further characterized by XPS. As depicted in Figure 4a, the peaks of Co 2p XPS at 796.9 and 780.7 eV were attributed to the Co 2p_1/2 and 2p_3/2 spin orbits of Co²⁺, respectively [3,34,35]. Compared with CCH, the Co 2p binding energy of CCH/CN slightly shifts to a lower energy level, suggesting that electrons are transferred from CN to CCH. The three peaks at 397.8, 398.4, and 399.9 eV in the N 1s spectrum of CN (Figure 4b) were assigned to the XPS peaks of C–C=N, N–(C)₃, and C–NH₃, respectively [36]. Compared with CN, the N 1s binding energy spectra of CCH/CN shift to a higher energy level, indicating that electrons are transferred from CN to CCH [37,38,39]. The decreased peak area of C–NH₃ in the N 1s XPS peak of CCH/CN (Table S3) from 15.5% to 9.8% compared with CN suggests the reduced content of N–H bonds in CCH/CN, which is mainly due to the bonding of N–H on CN and Co in CCH. Based on the results of FTIR spectra, Raman spectra, and XPS spectra, the bonding mode of CCH and CN might be the (CCH)–Co–N–(CN) chemical bond.

2.2. PCR Performance

The PCR activity of CCH/CN and control samples was evaluated under simulated sunlight without any co-catalysts or sacrificial agents. As shown in Figure 5a,b, the evolution of CO and CH₄ exhibits a linear process with the increase of illumination time. The CO production rate of CCH/CN (Figure 5c) reaches 19.65 μmol g⁻¹ h⁻¹, which is 7.74, 2.31, and 1.77 times higher than that of CCH (2.54 μmol g⁻¹ h⁻¹), CN (8.52 μmol g⁻¹ h⁻¹), and Mix (11.13 μmol g⁻¹ h⁻¹), respectively. The CH₄ production rate of CCH/CN was 0.69 μmol g⁻¹ h⁻¹, which is 4.31, 2.03, and 1.30 times that of CCH (0.16 μmol g⁻¹ h⁻¹), CN (0.34 μmol g⁻¹ h⁻¹), and Mix (0.53 μmol g⁻¹ h⁻¹), respectively. The selectivity of CO generation for CCH, CN, Mix, and CCH/CN is 94.1%, 96.2%, 95.5%, and 96.6%, respectively. By comparing our work with some reported CN-based photocatalysts (Table S4), it is obvious that the PCR activity and selectivity of CCH/CN have distinct advantages, which further verifies that the CCH/CN prepared through an in situ heterojunction synthesis strategy is outstanding for PCR. The apparent quantum yield (AQY) was also measured to illustrate the photon conversion efficiency. The AQY (Figure S2) achieved 0.054% for CCH/CN at 420 nm band-pass filter irradiation. As depicted in Figure S3, the evolution of CO and CH₄ still maintains good activity at 500 nm band-pass filter irradiation, indicating a favorable utilization rate of visible light. As shown in Figure 5d, the activity of CCH/CN remained stable after four cycles (40 h). The SEM (Figure S4a) and XRD (Figure S4b) indicated that the morphology and crystal structure do not undergo significant changes after cycling. In addition, based on the results of the FTIR spectra, the chemical structure of CCH/CN remained stable after the cyclic reaction (Figure S4c), suggesting that CCH/CN is a stable photocatalyst for PCR.

2.3. Study on Photocatalytic Mechanism

Generally, the enhanced photocatalytic activity and selectivity are mainly summarized in three aspects [40]: (1) the electronic structure of the photocatalyst; (2) interfacial characterization of CO₂ on the photocatalyst; and (3) separation efficiency of photogenerated electron–hole pairs. The optical properties of CCH and CN were investigated via UV–Vis DRS. As depicted in Figure 6a, the fabricated CCH demonstrates multiband absorption characteristics with dominant optical absorption in the region below 400 nm. The optical absorption in the visible range around 500 nm might be attributed to the d–d transition of the Co atoms [35,41,42]. The light absorption edge of CN is approximately 450 nm. The Mix demonstrates similar light absorption characteristics to CCH/CN. As shown in Figure 6b, the band gaps of CCH and CN are 2.96 and 2.93 eV, respectively. The Mott–Schottky plots measurement was employed to determine the flat-band potentials (V_fb) of CCH and CN (Figure 6c). The positive slope of the Mott–Schottky plots for the CCH samples indicates the n-type nature. And the V_fb is located just below the bottom of the conduction band (CB) (about 0.1 eV) for an n-type semiconductor [43,44]. Therefore, the CB of CCH and CN are −1.36 and −1.40 V vs. the Ag/AgCl electrode (−0.75 and −0.79 V vs. NHE, pH = 7), respectively. Based on the UV–Vis DRS spectra and Mott–Schottky plots, the band gap structure of the CCH/CN heterojunction was illustrated in Figure 6d. It can be perceived that, under visible light excitation, electrons will transfer from CN to CCH for the reduction of CO₂ to CO and CH₄, while holes will shift from CCH to CN for the oxidation of water to O₂. The mode of electron transfer has also been confirmed by XPS spectra (Figure 4). This transfer approach can spatially separate electron–hole pairs and prevent their recombination, thereby enhancing the PCR performance.

The specific surface area of the prepared samples was investigated via the N₂ adsorption–desorption curve. As depicted in Figure 7a, the largest Bruner–Emmett–Teller (BET) specific surface area (141.28 m² g⁻¹) of CN can be attributed to the peculiarity of 2D nanosheets with a large aperture and a low mass density. In contrast, CCH exhibited the smallest BET specific surface area of 8.55 m² g⁻¹. This is due to the fact that CCH is a nanowire structure, with a large mass density and no obvious aperture on the surface, resulting in a small BET specific surface area determined by mass. Interestingly, the specific surface area of CCH/CN (86.21 m² g⁻¹) is larger than that of Mix (52.14 m² g⁻¹), possibly because CN is uniformly coated on the surface of CCH in CCH/CN, while the two are separated in Mix. The results of the N₂ adsorption–desorption curve indicate that the superior performance of CCH/CN compared to other samples is not only due to the large surface area.

The electron–hole separation capability of the fabricated materials was investigated through EIS and photocurrent curve tests. As shown in Figure 7b, CCH has the largest Nyquist curve radius due to the suppressed electron transfer kinetics. The Nyquist curve radius of Mix decreased significantly, suggesting a remarkable enhancement in the electron migration ability. CCH/CN exhibits the smallest Nyquist curve radius, indicating the highest electron transfer capacity [25,44]. According to the photocurrent curve (Figure 7c), CCH shows the lowest photocurrent response. In contrast, the photocurrent response capacity of CN is significantly increased, signifying that CN has a superior electron–hole transfer capacity compared with CCH. When CCH and CN form a heterojunction, CCH/CN demonstrates the highest photocurrent response, indicating that the separation efficiency of the photogenerated electron–hole pairs in CCH/CN is the highest [35].

The recombination behavior of photocarriers of catalysts was investigated via the PL technique. As depicted in Figure 7d, when excited by light, CN exhibits a strong PL response at 465 nm, which is attributed to the strong recombination ability of photogenic electron–hole pairs. However, the low PL response of CCH at 575 nm is due to poor carrier migration and low optical response, which can be verified by EIS spectra and photocurrent curves. In the CCH/CN heterojunction, the PL signal at 465 nm is conspicuously quenched, while the PL peak intensity at 575 nm is augmented, suggesting that the photogenerated electrons are transferred from CN to CCH. The peak strength of Mix at 465 nm is higher than that of the CCH/CN heterojunction, and the PL strength at 575 nm is lower than that of the CCH/CN heterojunction, indicating that the electron transfer capability of Mix is inferior to that of the CCH/CN heterojunction. Consequently, the PCR capacity is lower than that of the CCH/CN heterojunction.

3. Experimental

3.1. Synthesis of Catalysts

Synthesis of CCH nanowire photocatalyst. In a typical procedure, 300 mg of Co(NO₃)₂·6H₂O (Aladdin Industrial Corporation, Shanghai, China), 50 mg of NH₄F (Aladdin Industrial Corporation, Shanghai, China), and 210 mg of urea (Sinopharm Chemical Reagent Corporation, Shanghai, China) were dissolved in 70 mL of deionized water. Ultrasonic treatment was conducted for 30 min to ensure complete dissolution. Subsequently, the solution was transferred into a 100 mL Teflon-lined stainless steel autoclave. This configuration was then subjected to heat treatment in an oven maintained at 120 °C for 12 h. After the reaction, the synthesized material was acquired through centrifugation and subsequently washed thoroughly with deionized water for at least three times. The final step involved drying the product in an oven set at 70 °C for 12 h to obtain the desired photocatalyst.

Synthesis of CN photocatalyst: 1.0 g of melamine was placed in an alumina crucible and heated to 550 °C at a rate of 2.3 °C min⁻¹ for 4 h. A total of 0.1 g of the sample was ground into powder and ultrasonically dispersed in 70 mL of water, then transferred to a 100 mL Teflon-lined stainless steel autoclave and reacted in an oven at 120 °C for 12 h. After the temperature cooled naturally, the resulting product was centrifuged and collected, washed with distilled water at least three times, and ultimately dried in the oven at 70 °C for 12 h.

Synthesis of CCH/CN heterojunction photocatalysts: 0.1 g of the CN sample was ground into powder and then ultrasonically dispersed in 70 mL of water. A total of 300 mg of Co(NO₃)₂·6H₂O, 50 mg of NH₄F, and 210 mg of urea were dissolved in the aforementioned solution and stirred for 30 min. Subsequently, the prepared mixture was transferred to a 100 mL Teflon-lined stainless steel autoclave and underwent a thermal treatment in an oven kept at 120 °C for 12 h. The obtained product was separated by centrifugal separation, thoroughly washed with deionized water for no less than three times and later dehydrated in the oven at 70 °C for 12 h.

Synthesis of the Mix photocatalyst: the ratio of CN to CCH was determined by the disparity between the mass of the synthesized heterojunction and the mass of CN in the hydrothermal process. The mass of CN is 0.1 g, and the mass of CCH/CN is approximately 0.2 g. For a physically mixed sample, 0.1 g of the prepared CCH and 0.1 g of CN were fully ground in an agate mortar to obtain Mix.

3.2. Characterization Studies

The structure and composition of the synthesized samples were meticulously examined through a suite of advanced analytical techniques. Specifically, the external and internal morphologies were scrutinized by SEM (utilizing the Hitachi SU8200 model from Tokyo, Japan) and TEM with the Talox F200X from the Thermo Fisher Scientific, Waltham, MA, USA. For the assessment of crystalline structures, XRD (employing the TTR–III apparatus from Rigaku, Tokyo, Japan), making use of a Cu Kα radiation source, was adopted. The surface chemical compositions were elucidated via XPS with the ESCA Lab MKII from the VG Scientific Ltd., London, UK, activated by Mg Kα X-rays. Additionally, FTIR (employing the Nicolet 8700 instrument, Madison, WI, USA) was utilized to explore the chemical bonds and functional groups. Raman spectroscopy, performed with a confocal Raman microscope (LabRam HR from Horiba, Kyoto, Japan) and excited by a He/Ne laser at 532 nm, provided insights into the vibrational modes. The optical properties were characterized by UV–Vis DRS with the SOLID 3700 from Shimadzu, Kyoto, Japan. The PL characteristics were quantified under ambient conditions using an F–4600 PL spectrophotometer (Hitachi Ltd., Tokyo, Japan), with an excitation wavelength of 345 nm and a slit width of 5.0 nm. Furthermore, time-resolved PL measurements were acquired by a time-corrected single-photon counting system (Fluorohub, Horiba Scientific, Kyoto, Japan), also at room temperature, with an excitation wavelength set at 370 nm.

3.3. Photoelectrochemical Testing

Electrochemical measurements were carried out by a CH Instruments (Austin, TX, USA) 660E electrochemical workstation in a three-electrode cell using platinum wire, fluorine-doped tin oxide (FTO) coated with catalysts, and Ag/AgCl as the counter electrode, working electrode, and reference electrode, respectively. A total of 0.5 M Na₂SO₄ was saturated by Ar in room temperature (25 °C) as the electrolyte at the −0.5 V bias potential vs. Ag/AgCl electrode. The light source was provided by a 300 W xenon lamp (PLS–SXE 300, Beijing Perfectlight, Beijing, China) for transient photocurrent responses and electrochemical impedance spectra. In consideration of the divergent character of the xenon lamp, it is requisite to calculate the average light intensity of the xenon lamp by Equation (1) [45]:

$$\overline{I}={\displaystyle \frac{2}{3}}{\overline{I}}_{edge}+{\displaystyle \frac{1}{3}}{\overline{I}}_{center}$$

(1)

where $\overline{I}$_edge and $\overline{I}$_center are the average value of light intensity at edge and centre region, respectively, as shown in Figure S5. The average value of light intensity ($\overline{I}$) is 20.4 mW cm⁻² detected by photometer (ST-85, Beijing Normal University Photoelectric Technology Co., Ltd., Beijing, China).

The characteristics of the working electrodes are depicted as follows: A quantity of 5 mg of the catalyst was uniformly dispersed in a mixture composed of 1 mL of anhydrous ethanol and 5 μL of Nafion solution by means of ultrasonic treatment. Subsequently, a volume of 10 μL from this resultant suspension was drop-coated onto FTO (fluorine-doped tin oxide) glass substrates, each with a size of 1 cm × 1 cm. Before utilization, these FTO glass substrates with catalysts were subjected to a drying process at 80 °C for 24 h in a vacuum oven, with the purpose of eliminating any volatile organic compounds.

3.4. Catalytic Activity

The PCR experiments were carried out in an all-glass automatic on-line trace gas analysis system (Labsolar-6A, Beijing Perfectlight, Beijing, China) with a 450 mL top-irradiated glass reactor chamber connected to a water bath, maintaining the reactor temperature at a constant 25 °C by circulating condensed water. Typically, 25 mg of photocatalysts was dispersed in 10 mL of deionized water under ultrasonication for 30 min. The suspension was then deposited onto a quartz sheet with a diameter of 65 mm and allowed to dry naturally at ambient temperature. Subsequently, the quartz sheet was positioned in the center of the reactor using a tripod. To scavenge the holes created in the photocatalytic reaction and provide protons, 100 mL of water was added to the bottom of the reactor as a source of water vapor, effectively moderating the temperature within the reactor and preventing excessive internal temperatures. The reaction vessel was evacuated and then purged with high-purity CO₂ gas (≥99.999%). The light source for the photocatalytic test is identical to photoelectrochemical measurement. Gas chromatography equipped with a TDX–01 packed column (Techcomp GC–7900) was employed for the determination of CO and CH₄ production; CO was subsequently converted by methanation into CH₄ and analyzed using flame ionization detection (FID).

4. Conclusions

In summary, the synthesis of the CCH/CN heterojunction photocatalyst was achieved through an in situ heterojunction assembling strategy, successfully bonding CCH and CN via Co–N chemical bonds. The results indicate that CCH/CN demonstrates type II heterojunction electron transfer properties, which significantly improve the mobility of photogenerated electron–hole pairs and reduce interfacial migration resistance. As a result, CCH/CN exhibited exceptional photocatalytic activity for CO₂ reduction, with a CO yield of 19.65 μmol g⁻¹ h⁻¹ under pure water conditions, about 7.74-fold, 2.31-fold, and 1.77-fold higher than that of CCH, CN, and Mix, respectively. Additionally, the selectivity of CO for CCH, CN, Mix, and CCH/CN was recorded at 94.1%, 96.2%, 95.5%, and 96.6%, respectively. This study provides a straightforward yet effective design approach for developing photocatalytic materials aimed at enhancing visible light utilization and facilitating photogenerated electron transfer.