A C3N5 photocatalyst with Janus homogeneity, its preparation method and application

Abstract

Homojunction engineering has demonstrated high performance in photocatalyst applications; however, establishing and regulating effective junction interfaces remains a significant challenge. To address this issue, this invention designs and constructs a novel Janus homostructure photocatalyst by integrating two different forms of triazole carbon nitride (C3N5). In this invention, nitrogen-rich honeycomb C3N5 is epitaxially grown on ultra-large, ultra-thin carbon-rich C3N5 nanosheets, forming a dense and extensive interfacial contact area. This arrangement enhances the built-in electric field (IEF) between the two forms of C3N5, promoting faster directional transfer of photogenerated electrons and improved visible light collection.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic energy conversion, specifically relating to a C3N5 photocatalyst with a Janus homogeneous structure, its preparation method, and its application. Background Technology

[0002] C3N5-based materials, as a novel type of nitrogen-rich carbon nitride, have attracted widespread attention in the field of photocatalytic energy conversion due to their unique electronic and optical properties. However, their overall photocatalytic activity is greatly limited by low charge separation efficiency, small surface area, and lack of active sites. To improve the catalytic performance of C3N5, various strategies have been adopted, including crystallization, heteroatom doping, defect removal, and heterostructure construction. Among these, heterojunction engineering is considered one of the most effective strategies for enhancing carrier separation. However, junctions constructed between different semiconductors are often affected by random lattice mismatch, discontinuities, and defects, which negatively impact carrier transfer.

[0003] Homojunction structures within a single semiconductor have been proposed as a viable strategy to circumvent limitations. Similar compositions on both sides of the junction interface provide better lattice matching and chemical bond continuity. Furthermore, a built-in electric field can be established within the junction region, enhancing carrier separation and driving their migration to active sites. Carbon nitride-based photocatalysts possess unique structural properties, offering great potential for the design and fabrication of novel heterojunction photocatalysts. For example, Cui et al. developed a salt-assisted thermal polymerization method for preparing intermolecular homojunctions in carbon nitride nanosheets. Due to the intermolecular homojunction structure, this method achieves molecular-level contact, thereby enhancing the built-in electric field in carbon nitride (UTMCN). Consequently, the PHE rate of UTMCN was increased by 38.9 times compared to bulk g-C3N4. Other types of homojunctions have been discovered in carbon nitride-based photocatalysts by combining modified carbon nitride with pristine carbon nitride through doping with heteroatoms, structural vacancies, size control, and high crystallinity. However, most reported homojunction-based photocatalysts are synthesized through direct thermal polymerization of two or more monomers or by assembling guest carbon nitride onto host carbon nitride, resulting in random junction structures. This randomness hinders the study of catalytic performance and mechanisms. Therefore, controlling the synthesis of homojunction photocatalysts with well-defined junction structures is crucial.

[0004] Janus heterostructure engineering offers promising methods due to the apparent physical separation of the bonding components and ordered junction interfaces. However, current synthetic approaches face significant challenges in designing, fabricating, and tuning regular Janus homostructures in targeted carbon nitride-based photocatalysts. Recently, additive-mediated strategies have emerged as effective means of shaping carbon nitride-based nanostructures. In these methods, additives can serve both as gaseous templates guiding morphology development and as dopants altering the internal structure. Summary of the Invention

[0005] The first objective of this invention is to provide a C3N5 photocatalyst with a Janus homogeneous structure, wherein the photocatalyst is composed of nitrogen-rich carbon nitride and has a structure combining a honeycomb network and nanosheet morphology, and has stacked pores inside.

[0006] The nitrogen-rich carbon nitride is a nitrogen-rich triazole group.

[0007] The photocatalyst forms a homojunction at the interface between the nanosheet and the cellular network.

[0008] The cellular network is the rough side, and the nanosheet is the smooth side.

[0009] The cellular network is mainly composed of nitrogen-rich and triazole groups, and the nanosheets are mainly composed of carbon-rich and triazole groups.

[0010] The second objective of this invention is to provide a method for preparing a C3N5 photocatalyst with a Janus homogeneous structure. The aim is to prepare C3N5-based nanomaterials with a Janus structure using NH4Cl as a gas template. By utilizing the rapid pyrolysis of NH4Cl and the copolymerization of 1,2,4-triazol-3-thiol, two oriented g-C3N5 nanomaterials are integrated to form Janus-C3N5. Specifically, the method includes the following steps:

[0011] Step 1: Grind and mix triazole thiol and ammonium chloride to rapidly pyrolyze the ammonium chloride and obtain the photocatalyst precursor;

[0012] Step 2: Transfer the photocatalyst precursor obtained in Step 1 to a covered ceramic crucible for calcination.

[0013] In step one, the triazole thiol used is 1H-1,2,4-triazole-3-thiol (3-ST), and the amount added is 1-5g; ammonium chloride is added at 10-20g, and the grinding time is 20-40min.

[0014] In step two, the calcination conditions include: a heating rate of 1-3℃ min⁻¹, a temperature of 500-600℃, and a calcination time of 1-5 h, preferably 4 h.

[0015] The third objective of this invention is to provide the application of a C3N5 photocatalyst with a Janus homogeneous structure in energy conversion and photocatalysis.

[0016] Beneficial effects

[0017] The photocatalyst Janus-C3N5 of this invention exhibits two distinct morphologies: ultra-large, ultrathin nanosheets (smooth side) and a honeycomb network (rough side). The nanosheets are primarily composed of carbon-rich triazole carbon nitride, while the honeycomb network is primarily composed of nitrogen-rich triazole carbon nitride. This configuration results in an enhanced internal electric field (IEF) between these different structures. Under visible light irradiation, the H2 evolution rate of Janus-C3N5 reaches 1712.4 μmol h⁻¹. 1 g- 1 Compared to blocky C3N5 (306.8 μmol h- 1 g- 1 It is about 5.58 times higher than that of bulk C4N4 (121.2 μmol h⁻¹). 1 g- 1 It is 14.1 times higher. Attached Figure Description

[0018] Figure 1 (a) Schematic diagram of the preparation process of Janus-C3N5; (bc) SEM micrographs; (de) TEM images; (f) dark-field STEM images and their corresponding (gh) elemental mapping (c, N) images; (i) EDS line scan of Janus-C3N5. Yellow dashed rectangles highlight the rough sides, red dashed rectangles represent the smooth sides, white dashed circles mark the pores, and white solid arrows indicate the areas of pore line EDS scanning.

[0019] Figure 2 Proposed reaction pathway for Janus-C3N5 sample formation.

[0020] Figure 3 SEM images of (a) Janus-C3N5-1h, (b) Janus-C3N5-2h, (c) Janus-C3N5-3h and (d) Janus-C3N5 samples.

[0021] Figure 4 XRD patterns of Janus-C3N5-1h, Janus-C3N5-2h, Janus-C3N5-3h and Janus-C3N5 samples.

[0022] Figure 5 (a) XRD patterns of bulk C3N5, bulk C3N5 and Janus-C3N5; (bd) FT-IR spectra; (e) XPS spectra of the C1s core layer of Janus-C3N5 at different etching times and (f) XPS spectra of the N1s core layer; (g) structural model representation of bulk C3N5 and Janus-C3N5 samples and (h) solid-state 13C spectra.

[0023] Figure 6 Static water contact angle measurement of bulk C3N5.

[0024] Figure 7 Static water contact angle measurement of bulk C3N5.

[0025] Figure 8 :(af)Static water contact angle measurement of Janus-C3N5.

[0026] Figure 9 XPS spectral investigation of different Janus-C3N5-1h, Janus-C3N5-2h, Janus-C3N5-3h and Janus-C3N5 samples.

[0027] Figure 10 (a) XPS spectra of the C1s core layer of Janus-C3N5 and bulk-C3N5 samples at different etching times and (b) XPS spectra of the N1s core layer.

[0028] Figure 11 Surface C and N composition of samples (a) Janus-C3N5 and (b) bulk-C3N5 under Ar ion etching processes (0s, 15s and 30s).

[0029] Figure 12 (a) N2 adsorption-desorption isotherms, insert: showing photographs of different samples; (b) Pore size distribution derived from the isotherms; (c) EPR spectra; (d) UV-vis absorption spectra; (e) Schematic diagram of band structure; (f) UPS spectra; (g) Photocurrent response spectra; (h) EIS-Nquist plot; (i) Steady-state PL spectra of bulk-C3N4, bulk-C3N5 and Janus-C3N5.

[0030] Figure 13 Band gap energies of bulk C3N4, bulk C3N5 and Janus-C3N5 samples.

[0031] Figure 14 (a) H2 evolution rate of bulk C3N4, bulk C3N5 and Janus-C3N5; (b) Recyclability of Janus-C3N5 in terms of hydrogen release; (c) Comparison of H2 release rate of Janus-C3N5 with other reported C3N5-based photocatalysts.

[0032] Figure 15 Photocurrent response and time-resolved PL decay spectra of bulk C3N4, bulk C3N5 and Janus-C3N5 samples.

[0033] Figure 16Schematic diagram of charge transport driven by potential difference.

[0034] Figure 17 Charge density difference of CN-C3N5 (yellow and blue represent charge accumulation and loss, respectively).

[0035] Figure 18 Charge density difference of C-C3N5 (yellow and blue represent charge accumulation and loss, respectively).

[0036] Figure 19 (ac) Work function and density of states (df) of carbon-rich C3N5 (c-C3N5), nitrogen-rich C3N5, and composite C3N5. (eg) Schematic diagram showing the internal electric field formation and charge transport mechanism between C-C3N5 and N-C3N5. Detailed Implementation

[0037] Reagents and materials

[0038] 1H-1,2,4-triazol-3-thiol (C2H3N3S, ≥97.0%), melamine (C3H6N6, ≥99.0%), potassium hexachloroplatinate (K2PtCl6, ≥98.0%), ammonium chloride (NH4Cl, ≥99.0%), and triethanolamine (TEOA, C6H 15 NO3 (≥99.0%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. All chemicals were used without further purification.

[0039] Preparation of Janus-C3N5

[0040] C3N5 with a Janus structure was prepared by gas-templated assisted thermal polymerization. In a standard procedure, 3.0 g of 1H-1,2,4-triazol-3-thiol (3-ST) and 15.0 g of ammonium chloride were manually ground for 30 minutes. The mixed precursor was transferred to a covered ceramic crucible (200 mL) and calcined at 550 °C for 4 hours. The resulting product was named Janus-C3N5. Furthermore, comparative samples of Janus-C3N5 with different calcination times (1 h, 2 h, 3 h) were prepared to investigate the synthetic mechanism; these samples were designated Janus-C3N5-1h, Janus-C3N5-2h, and Janus-C3N5-3h, respectively. The preparation of bulk g-C3N4 and bulk g-C3N5 is as follows: 10g of melamine is directly heated to 550℃ for 4 hours in a covered ceramic crucible (200mL) (heating rate, 2.3℃ / min). -1 The resulting products were designated as bulk g-C3N4 and bulk g-C3N5.

[0041] feature

[0042] The morphological structures of samples bulk-C3N4, bulk-C3N5, and Janus-C3N5 were observed using transmission electron microscopy (TEM, JEM-2010EX, 200 kV) and scanning electron microscopy (SEM, S4800, 5 kV, 10 μA). The chemical structures were characterized by powder X-ray diffraction (XRD, Smartlab™ 9 kW, Cu Kα radiation, λ = 0.154178 nm), X-ray photoelectron spectroscopy (XPS, Al Kα X-ray source, ULVAC-PHI), 13C solid-state nuclear magnetic resonance (NMRC, Bruker Avance III 400 MHz), and Fourier transform infrared spectroscopy (FTIR, Nicolet Nexus 470). In-depth analysis of the chemical structures of Janus-C3N5 and bulk-C3N5 was performed using XPS combined with ion beam etching (0 s, 15 s, 30 s). Porosity information for bulk C3N4, bulk C3N5, and Janus-C3N5 was obtained at 77 K using a BELSORP-MINI instrument. The photogenerated charge separation properties of bulk C3N6, bulk C3E5, and Janus-C3N5 were analyzed using steady-state photoluminescence spectroscopy (PL, F-4600FL), time-resolved photoluminescence decay spectroscopy (FLS920), UV-Vis diffuse reflectance spectroscopy (UV-visDRS, Perkin-Elmer Lambda 35 spectrophotometer, 200nm–800nm), and electron paramagnetic resonance spectroscopy (Bruker ESR JESFA200 spectrometer). Defect information was collected using a Bruker ESR JESFA200 spectrometer. Thermogravimetric analysis (TG-DSC) was performed using a Netzsch STA449F3 (Ar flow) spectrometer.

[0043] Photocatalytic hydrogen production activity evaluation

[0044] The photocatalytic hydrogen evolution rates (HERs) of different samples were tested in an online testing system (Beijing Perfect Light Technology Co., Ltd., 300W xenon lamp, λ≥420nm). Initially, 0.05g of photocatalyst was dispersed in 100mL of triethanolamine aqueous solution (10 vol%). Then, platinum (3 wt%) was loaded onto the surface of the photocatalyst by photodeposition. After purging with N2 for 30 min, the system was irradiated with a 300W xenon lamp equipped with a 420nm cutoff filter. The HER rate as a function of time was analyzed using an online gas chromatograph (GC 9890A, TCD, argon). The apparent quantum yield (AQY) of H2 evolution at 420nm and 450nm was calculated using the following equation:

[0045]

[0046] DFT calculation

[0047] The entire calculation was performed using a spin-unrestricted DFT framework and implemented via the DMol3 module in the Materials Studio software. In the generalized gradient approximation (GGA), the exchange and correlation models were specified using the Perdew-Burke-Ernzerhof (PBE) function, and the atomic orbitals were described using a dual numerical polarization (DNP) basis set.

[0048] Results Analysis

[0049] The preparation process of Janus-C3N5 is as follows: Figure 1 (a) and Figure 2 As shown, two different reaction pathways can occur during heat treatment: rapid pyrolysis of NH4Cl and thermal copolymerization of 1,2,4-triazole-3-thiol. Gaseous byproducts (NH3 and HCl produced from the decomposition of NH4Cl) serve as a gaseous template, promoting the thermal condensation reaction to form a nitrogen-rich triazole C3N5 structure with a honeycomb structure. Simultaneously, as polymerization proceeds, the gaseous template also mediates another set of thermal condensation reactions, leading to the formation of a carbon-rich triazole C3N5 structure with a nanosheet morphology. Ultimately, an ultrathin nanosheet layer is formed on the honeycomb network. These morphological differences are attributed to the differences in the reaction temperature regions of various reaction chains, which can be demonstrated by SEM and XRD analysis of samples subjected to different heat treatment times. Figure 3 As shown, the coverage of nanosheets on the surface of the honeycomb network increases with increasing heating time, reaching its maximum when the precursor is completely reacted. The precursor is completely converted to C3N5, as... Figure 4 As shown, samples were obtained after 1 hour, 2 hours, 3 hours, and 4 hours. The results yielded a Janus-C3N5 structure characterized by large, ultrathin nanosheets (smooth sides) and a cellular network (rough sides). This Janus structure exhibits a well-defined and ordered junction interface, further confirmed by TEM and HAADF imaging results. Figure 1 (b)-(f)). The cellular network consists of small nanosheets and contains many larger pores. Interestingly, EDX line scan results show that Janus-C3N5 has two distinct structural regions, characterized by carbon-rich and carbon-poor regions, corresponding to two different morphologies.

[0050] The structural features of Janus-C3N5 and bulk-C3N5 were analyzed using XRD and FT-IR. Figure 5As shown in (a), bulk-C3N5 exhibits two distinct diffraction peaks at 13.5° and 27.9°, corresponding to the in-plane repeating unit (100) and the interlayer stacked unit (002), respectively. In contrast, Janus-C3N5 shows a slight shift towards lower angles and wider peaks in the (002) and (100) reflections, indicating a more compact interlayer spacing and an expanded in-plane periodicity. Fourier transform infrared spectroscopy analysis ( Figure 5 (b)-(d) indicate that blocky C3N5 and Janus-C3N5 are at 3000-3500 cm⁻¹ -1 1100-1700cm -1 and 810cm -1 The regions exhibit vibrational peaks similar to those in bulk C3N4. These peaks correspond to the residual -NH2 / -OH groups, the CN heterocycle in the triazine, and the CN heterocycle within the triazine moiety, respectively. Furthermore, in bulk C3N5 and Janus-C3N5, vibrational peaks are observed at 774 cm⁻¹. -1 1348cm -1 and 1618cm -1 The observed new peak at 889 cm⁻¹ indicates the presence of a triazole structure. Notably, the peak at 889 cm⁻¹... -1 The peak intensity decreased to 807 cm⁻¹. -1 The peak value redshifted, indicating that the triazole moiety in C3N5 replaced the triazine moiety. Figure 5 (c) Due to overlapping vibrational modes, vibrations associated with the CN bonds in the triazole moiety are difficult to distinguish. For Janus-C3N5, the intensity of the new peak is reduced compared to bulk-C3N5, indicating partial degradation of the triazole moiety. TEM and SEM analyses show that the rough surface of Janus-C3N5 contains less C (triazole moiety), while the smooth surface contains more C, despite the presence of partial triazole degradation. Figure 1 (a) and (b)). Furthermore, compared to bulk C3N4 and bulk C3N5, Janus-C3N5 showed better performance at 3000-3500 cm⁻¹. -1 The peak value shifts to higher wavenumbers and the intensity increases, indicating enhanced hydrogen bonding, which may positively impact the separation of photogenerated electron-hole pairs. Static water contact angle measurements of Janus-C3N5 at different times further confirm the Janus structure. Figure 6-8 ).

[0051] Figure 9 The X-ray photoelectron spectroscopy (XPS) measurements confirm that bulk C3N5 and Janus-C3N5 are primarily composed of carbon (C), nitrogen (N), and oxygen (O). High-resolution C1s spectra of bulk C3N5 are also shown. Figure 10The spectrum shows three distinct peaks at 284.6, 286.0, and 287.9 ​​eV, corresponding to the C-C bond, NC=N group, and C-NHx group, respectively. The N1s spectrum of Bulk-C3N5 exhibits peaks at 398.4, 400.0, and 401.1 eV, attributed to the CN=C, N-(C)3, and N-Hx groups, respectively. Notably, compared to bulk C3N4 (287.6 eV), the 287.9 ​​eV peak in bulk C3N5 shows a higher binding energy, while the peaks at 398.4 and 400.0 eV show lower binding energies (398.6 and 399.9 eV, respectively). These variations suggest stronger electronic coupling between the CN or C=N bonds, likely due to the introduction of the triazole moiety, which enhances the electron absorption capacity of the carbon atom by increasing the nitrogen content.

[0052] XPS depth profile of blocky C3N5 ( Figure 10 and Figure 11 The results showed that the surface composition of C and N, as well as the relative percentages and positions of the C1s and N1s peaks, changed very little during Ar ion etching. This stability indicates that bulk-C3N5 maintains a consistent nitrogen-rich triazole carbon nitride structure. In contrast, XPS depth analysis of Janus-C3N5 showed distinct behavior. Three fitted peaks were observed at 284.6, 286.1, and 287.8 eV before etching (0s). The peak at 287.8 eV had a lower binding energy compared to bulk C3N5 (287.9 ​​eV), while the peak at 284.6 eV had a higher relative percentage (20.1% vs. 14.5%). As etching progressed, the relative percentages of C and N at 284.6 eV decreased from 53.1 wt% to 51.4 wt% and from 20.1 at% to 18.1 at%, respectively. Conversely, the relative percentage at 398.4 eV increased from 77.4 atomic% to 78.5 atomic%. These findings are consistent with FT-IR, TEM, and SEM results. Figure 1 and Figure 5 This indicates that with the etching of carbon-rich nanosheets, the C and N contents approach those of bulk C3N5. The carbon-rich properties are attributed to the partial destruction of the triazole moiety, leading to the formation of π-conjugated structures, such as... Figure 5 As shown in (g). Furthermore, the solid-state nuclear magnetic resonance spectra of bulk-C3N5 and Janus-C3N5 ( Figure 5 (h) at 156.7 and 164.6 ppm (attributable to C2N-NH in the Mellem unit) xA distinct peak is observed at 111.9 ppm (attributed to CHN-C(H)=N(δ) in the triazole unit) for both C(α) and C3N(β). A novel peak at 104.3 ppm in Janus-C3N5 corresponds to the carbon-rich motif (γ). The slight shift of the NMR signals of C(α), C(β), and C(δ) to higher fields is due to the increased shielding effect of adjacent C and C groups. These results indicate that Janus-C3N5 exhibits two distinct morphologies: the nanosheet regions are predominantly carbon-rich and triazole-based, while the cellular network is predominantly nitrogen-rich and triazole-based. The Janus structure facilitates the formation of well-defined homojunctions at the interfaces of these different carbon nitride structures.

[0053] The effects of the Janus homojunction on the physical structure, visible light absorption, and charge carrier transfer pathway of C3N5 were further investigated. Figure 12 As shown in (a), all samples exhibited a type IV isotherm with an H3 hysteresis loop, indicating the formation of stacked pores within the C3N5 fragments. Among these samples, Janus-C3N5 showed the largest volume expansion and a narrower pore size distribution than bulk-C3N4 and bulk-C3N5. Figure 12 (a) and (b)). This phenomenon is attributed to the unique stacking arrangement of C3N5 fragments, in which a cellular network is dispersed on the surface of the nanosheets. Figure 12 As shown in (b), the EPR signal intensity increases at a g value of 2.004 for bulk-C3N4, bulk-C3N5, and Janus-C3N5, indicating an enhanced presence of unpaired electrons on the sp2 carbon atoms in Janus-C3N5. Figure 12 In (c), bulk-C3N5 and Janus-C3N5 exhibit distinct absorption bands near 500 nm due to n–π* electronic transitions induced by the triazole group. Janus-C3N5 shows a higher absorption intensity at 500 nm, which can be attributed to the enhanced n–π* transitions promoted by the homojunction. The band gap energy (Eg), valence band potential (VB), and conduction band potential (CB) of bulk C3N4, bulk C3N5, and Janus-C3N5 are calculated as follows: Eg values ​​are 2.53 eV, 1.72 eV, and 1.58 eV, respectively (αhν = A(hν - E). g ) 1 / 2 ); VB and CB values ​​are 1.32 eV, 0.83 eV, and 0.79 eV, respectively (E g =CB-VB); the Mott–Schottky spectral values ​​are -1.21eV, -0.89eV and -0.99eV, respectively. Figure 12As shown in (f), the work function of Janus-C3N5 (5.43 eV) is lower than that of bulk C3N5 (5.81 eV), which is attributed to the homojunction effect at the interface between the smooth nanosheet side and the rough honeycomb network side. The photoluminescence (PL) intensity and resistance values ​​obtained from the EIS-Nquist plot follow the order bulk-C3N4 > bulk-C3N5 > Janus-C3N5, while the photocurrent intensity follows the order Janus-C3N5 > bulk-C3N5 > bulk-C3N4. Furthermore, Janus-C3N5 exhibits the longest photogenerated carrier lifetime (1.68 ns). Figure 13 These results demonstrate that the Janus-C3N5 structure significantly improves the efficiency of photogenerated charge separation, indicating its excellent photocatalytic activity. The interaction between the carbon-rich triazole nanosheets and the nitrogen-rich triazole honeycomb network leads to charge transfer due to the difference in Fermi levels, thereby forming an internal electric field (IEF) that promotes efficient charge carrier separation.

[0054] The hydrogen evolution efficiency of bulk C3N4, bulk C3N5, and Janus-C3N5 was evaluated using platinum (3 wt%) as a cocatalyst and triethanolamine (10 vol%) as a sacrificial agent. Figure 14 As shown in (a), the HER of Janus-C3N5 is 1712.4 μmol h⁻¹. 1 g- 1 Approximately bulk C3N5 (306.8 μmol h- 1 g- 1 5.58 times that of bulk C3N4 (121.2 μmol h- 1 g- 1 The apparent quantum yield (AQY) of Janus-C3N5 at 420 nm and 500 nm was calculated to be 14.1 times that of other materials. Figure 14 (b)). These AQY values ​​are consistent with their UV-Vis absorption spectra, indicating that hydrogen production is primarily driven by photogenerated electrons. Furthermore, Janus-C3N5 exhibits superior HER performance under similar illumination conditions compared to most reported C3N5-based photocatalysts. Figure 14 (d) It is worth noting that Janus-C3N5 maintained stable HER activity in four cycles of photocatalysis testing, showing minimal decline in hydrogen production rate.

[0055] The relationship between the electronic and chemical structures of C3N5 variants was investigated using density functional theory (DFT). In carbon-rich C3N5 (C-C3N5), nitrogen-rich C3N5, and their complex (CN-C3N5), the bottom of the conduction band and the top of the valence band are predominantly occupied by carbon and nitrogen, respectively. C-C3N5 exhibits impurity levels near the bottom of the conduction band, leading to differences in band potentials between samples. Compared to N-C3N5, C-C3N5 has a higher calculated work function (Φ) and Fermi level (Ef), indicating that Φ and Ef values ​​are balanced. Variations in band position and Φ contribute to the formation of a built-in electric field in CN-C3N5. Figure 15 As shown, the charge generated in N-C3N5 (lower Φ) migrates to the C-C3N5 region with higher Φ under the drive of the inherent potential difference until equilibrium is reached. This results in a built-in field (BIF) between C-C3N5 and N-C3N5. Differential charge density analysis ( Figure 16-18 This confirms the charge redistribution at the homojunction interface, consistent with the observed work function difference. Therefore, the construction of C3N5 and CN-C3N5 homojunctions leads to efficient charge separation and redistribution, which is crucial for improving photocatalytic activity.

[0056] Based on the analysis of characterization, photocatalytic activity, and DFT calculation results, a charge transfer process between the homojunctions of C-C3N5 and N-C3N5 is proposed. Figure 19 (g) When C-C3N5 and N-C3N5 are in close contact, charges in C-C3N5 spontaneously transfer to N-C3N5 at the interface until their Fermi levels reach equilibrium. This charge rearrangement creates a built-in electric field from C-C3N5 to N-C3N5, causing the energy band of C-C3N5 to bend upwards (due to electron loss) and the energy band of N-C3N5 to bend downwards (due to electron accumulation). Thus, a CN-C3N5 homojunction is successfully constructed. These properties enable CN-C3N5 to promote faster and more efficient directional transfer of photogenerated electrons, significantly improving its photocatalytic performance.

[0057] In summary, a novel Janus homojunction C3N5 was constructed using a gas template-mediated strategy. Extensive experimental and theoretical analyses revealed that the optimized catalyst Janus-C3N5 exhibits two distinct morphologies: ultra-large, ultrathin nanosheets (smooth side) and a honeycomb network (rough side). The nanosheets are primarily composed of carbon-rich triazole carbon nitride, while the honeycomb network is mainly composed of nitrogen-rich triazole carbon nitride. This configuration leads to an enhanced internal electric field (IEF) between these different structures. Under visible light irradiation, the H2 evolution rate of Janus-C3N5 reaches 1712.4 μmol h⁻¹. 1 g- 1 Compared to blocky C3N5 (306.8 μmol h- 1g- 1 It is about 5.58 times higher than that of bulk C3N4 (121.2 μmol h- 1 g- 1 It is 14.1 times higher. The AQY estimates for Janus-C3N5 at 420 nm and 500 nm are 2.8% and 0.5%, respectively.

Claims

1. A C3N5 photocatalyst with a Janus homogeneous structure, characterized in that, The photocatalyst has a structure combining a honeycomb network and nanosheets, with stacked pores inside; the honeycomb network is mainly composed of nitrogen-rich triazole carbon nitride, and the nanosheets are mainly composed of carbon-rich triazole carbon nitride; and a homogeneous junction is formed at the interface between the nanosheets and the honeycomb network.

2. The C3N5 photocatalyst with a Janus homogeneous structure according to claim 1, characterized in that, The cellular network is the rough side, and the nanosheet is the smooth side.

3. The method for preparing the C3N5 photocatalyst with a Janus homogeneous structure as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: Grind and mix triazole thiol and ammonium chloride, and rapidly pyrolyze the ammonium chloride to obtain the photocatalyst precursor; Step 2: Transfer the photocatalyst precursor obtained in Step 1 to a covered ceramic crucible for calcination.

4. The method for preparing the C3N5 photocatalyst with a Janus homogeneous structure according to claim 3, characterized in that, In step one, the triazole thiol used is 1H-1,2,4-triazole-3-thiol, and the amount added is 1-5g; ammonium chloride is added at 10-20g, and the grinding time is 20-40min.

5. The method for preparing the C3N5 photocatalyst with a Janus homogeneous structure according to claim 3, characterized in that, In step two, the calcination conditions include: a heating rate of 1-3℃ / min, a temperature of 500-600℃, and a calcination time of 1-5h.

6. The application of the C3N5 photocatalyst with Janus homogeneity as described in claim 1 or 2 in energy conversion and photocatalysis.

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