An S-type heterojunction NiO / NiS photocatalyst, its preparation method and application

Abstract

This invention discloses an S-type heterojunction flower-like NiO / NiS photocatalyst, its preparation method, and its applications, belonging to the field of photocatalyst preparation technology. Using Ni-MOF as a substrate, this invention constructs a three-dimensional flower-like NiO / NiS photocatalytic material through calcination and in-situ solvothermal sulfidation processes. The material structure is assembled from interwoven, hierarchically stacked two-dimensional ultrathin nanosheets. The surface of the nanosheets is a heterogeneous porous rough interface formed by tightly packed micro-nanoparticles. The micro-nanoparticles exhibit non-uniform high-low contrast in space, and the interior of the flower-like structure contains hierarchical mesoporous channels and a hollow cage-like topological microenvironment. The unique S-type charge migration mechanism of this invention achieves the physical separation of photogenerated carriers in space, retaining the extremely negative reducing electrons in the NiS conduction band and the extremely positive strongly oxidizing holes in the NiO valence band, providing a thermodynamic driving force for the generation of superoxide radicals and achieving efficient destruction of the tetraphenylene skeleton.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst preparation technology, and more specifically to an S-type heterogeneous NiO / NiS photocatalyst, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of the global pharmaceutical industry and the widespread use of antibiotics, the problem of antibiotic pollution in pharmaceutical wastewater, agricultural and livestock wastewater, and medical wastewater has evolved into a global environmental crisis. Among many antibiotics, tetracyclines (such as tetracycline and oxytetracycline) have extremely high chemical stability and bioresistance due to their unique tetraphenyl skeleton, making them difficult to completely eradicate using conventional biodegradation and physical adsorption methods.

[0003] To achieve superior photocatalytic degradation activity, researchers have developed numerous catalytic systems, including metal oxides, sulfides, and carbon-based materials. However, traditional single-phase photocatalysts (such as pure-phase TiO2, BiOBr, or metal sulfides) still face significant bottlenecks in practical applications. On the one hand, while wide-bandgap semiconductors (such as NiO) possess deep valence bands and extremely strong oxidation capabilities, their response range to visible light is narrow, resulting in low solar energy utilization. On the other hand, while narrow-bandgap semiconductors (such as NiS) can effectively capture visible light, their internal photogenerated electron-hole recombination rate is extremely fast, leading to low quantum efficiency. Furthermore, composite materials prepared by traditional hydrothermal or co-precipitation methods often suffer from severe particle agglomeration, small specific surface area, and insufficient exposure of active sites.

[0004] Therefore, how to provide a photocatalyst with high solar energy utilization and high catalytic activity is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention utilizes Ni-MOF as a self-sacrificing template to construct a nickel oxide / nickel sulfide (NiO / NiS) S-type heterojunction composite material with multi-level flower-like morphology through a stepwise in-situ derivation process, which becomes a breakthrough in solving the bottleneck of antibiotic degradation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An S-type heterojunction flower-like NiO / NiS photocatalyst is described, wherein the photocatalyst is a regular three-dimensional multi-level nanoflower-like structure. This structure is assembled from interwoven and hierarchically stacked two-dimensional ultrathin nanosheets. The surface of the nanosheets is a heterogeneous porous rough interface formed by the close packing of microscopic nanoparticles. The microscopic nanoparticles exhibit non-uniform high and low contrast in space. The interior of the nanoflower-like structure contains hierarchical mesoporous channels and hollow cage-like topological microenvironments.

[0008] Preferably, the catalyst contains a face-centered cubic NiO phase and a rhombohedral NiS phase, which form a heterogeneous interface with close contact between the two phases.

[0009] Preferably, the catalyst has micropores, mesopores and macropores, with the pores mainly concentrated in the range of 2-5 nm.

[0010] A method for preparing an S-type heterojunction NiO / NiS photocatalyst includes the following steps: (1) Ni(NO3)2·6H2O and 1,3,5-benzenetricarboxylic acid are dissolved in anhydrous ethanol and then subjected to a solvothermal reaction to obtain Ni-MOF; (2) Take Ni-MOF and heat it to 300~400℃ at 5℃ / min under nitrogen atmosphere and calcine it at a constant temperature for 4~8h to obtain flower-shaped Ni; (3) After the flower-shaped Ni is naturally cooled to room temperature, it is heated again to 300~400℃ at 5℃ / min in air atmosphere and calcined at a constant temperature for 4~8h to obtain flower-shaped NiO; (4) Take flower-shaped NiO and thiourea in a mass ratio of 5:(1~5) and dissolve them in anhydrous ethanol. Then react them at 170℃ for 12~24h. The product is washed and dried to obtain flower-shaped NiO / NiS.

[0011] Preferably, the mass ratio of Ni(NO3)2·6H2O to 1,3,5-benzenetricarboxylic acid in step (1) is 5:(1-4); the temperature of the solvothermal reaction is 150~170℃, and the reaction time is 18~24h.

[0012] Preferably, in step (2), the Ni-MOF is heated to 300°C at 5°C / min and calcined at a constant temperature for 6 hours.

[0013] Preferably, in step (3), the flower-shaped Ni is heated to 300°C at 5°C / min and calcined at a constant temperature for 6 hours.

[0014] Preferably, in step (4), the mass ratio of flower-shaped NiO to thiourea is 5:2~5; Preferably, in step (4), the mass ratio of flower-shaped NiO to thiourea is 5:2~4; Preferably, in step (4), the mass ratio of flower-shaped NiO to thiourea is 5:3~4; Preferably, in step (4), the flower-shaped NiO and thiourea are dissolved in ethanol at a mass ratio of 5:3, and then reacted at 170°C for 16 h; after the solvothermal reaction, the product is centrifuged, washed alternately with anhydrous ethanol and distilled water, and then vacuum dried at 40~60°C for 12~24 h.

[0015] The beneficial effects of this invention are: This invention prepared a regular flower-like Ni-MOF precursor using 1,3,5-benzenetricarboxylic acid as an organic ligand. Through calcination and in-situ solvothermal sulfidation, a series of NiO / NiS (MNOS) S-type heterojunction photocatalysts with regular multi-level flower-like morphologies were successfully constructed. In this structure, NiO with a wide bandgap is in close contact with NiS with a narrow bandgap. Due to the difference in their Fermi levels, electrons spontaneously rearrange at the interface, thereby inducing a strong built-in electric field in situ. Under visible light irradiation, this built-in electric field selectively drives the directional recombination of electrons with weaker reducing power in the NiO conduction band and holes with weaker oxidizing power in the NiS valence band at the interface. This unique S-type charge transfer mechanism not only achieves the physical separation of photogenerated carriers in space but also perfectly preserves the extremely negative reducing electrons in the NiS conduction band and the extremely positive strongly oxidizing holes in the NiO valence band. This "dual retention" of high redox potential provides a thermodynamic driving force for the system to generate a large number of superoxide radicals, thereby synergistically achieving efficient destruction of the tetraphenyl pyroxene skeleton. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 The images show the morphology of MNOS-3; (a) SEM image of Ni-MOF; (b) SEM image of MNOS-3; (c) EDS image of MNOS-3; (d) low-resolution TEM image of MNOS-3; (e) high-resolution TEM image of MNOS-3; (f) XRD patterns of MNOS-3, NiO, and NiS; (g) adsorption isotherm curve of MNOS-3; and (h) pore size distribution of MNOS-3. Figure 2 The following diagrams show the photoelectric properties and band structure analysis of different materials: (a) UV diffuse reflectance diagrams of MNOS-1 to MNOS-5, NiO, and NiS; (b) band gap diagrams of MNOS-1 to MNOS-5; (c) band gap diagram of NiS; (d) band gap diagram of NiO; (e) Mott-Schottky diagram of NiO; (f) Mott-Schottky diagram of NiS; (g) electrochemical impedance diagrams of different materials; and (h) transient photocurrent diagrams of different materials. Figure 3XPS analysis images of different materials are shown below: (a) O 1s high-resolution spectrum of MNOS-3; (b) Ni 2p high-resolution spectrum of MNOS-3; (c) C 1s high-resolution spectrum of MNOS-3; (d) O 1s high-resolution spectrum of NiO; (e) Ni 2p high-resolution spectrum of NiO; (f) S 2p high-resolution spectrum of MNOS-3; (g) S 2p high-resolution spectrum of NiS; and (h) Ni 2p high-resolution spectrum of NiS. Figure 4 The graphs show the photocatalytic degradation performance of different materials; (a) photokinetic curves of different materials for TC; (b) photokinetic curves of different materials for OTC; (c) degradation amount of different materials for TC; (d) degradation amount of different materials for OTC; (e) linear fitting graphs of different materials for TC; and (f) linear fitting graphs of different materials for OTC. Figure 5 Analysis of MNOS-3 cycling performance and active groups; including (a) recycling of TC; (b) recycling of OTC; (c) capture experiments of TC; and (d) capture experiments of OTC. Figure 6 Possible degradation pathways of TC by MNOS-3; Figure 7 Possible degradation pathways of OTC by MNOS-3; Figure 8 Toxicity analysis of TC and its intermediates during the degradation of TC by MNOS-3 on three aquatic organisms (fish, water fleas, and green algae); including (a) acute toxicity analysis of TC and pathway I intermediates on the three aquatic organisms; (b) chronic toxicity analysis of TC and pathway I intermediates on the three aquatic organisms; (c) acute toxicity analysis of TC and pathway II intermediates on the three aquatic organisms; (d) chronic toxicity analysis of TC and pathway II intermediates on the three aquatic organisms; (e) acute toxicity analysis of TC and pathway III intermediates on the three aquatic organisms; and (f) chronic toxicity analysis of TC and pathway III intermediates on the three aquatic organisms. Figure 9 Toxicity analysis of OTC and its intermediates during the degradation of OTC by MNOS-3 on three aquatic organisms (fish, water fleas, and green algae); including (a) acute toxicity analysis of OTC and intermediates of pathway I on the three aquatic organisms; (b) chronic toxicity analysis of OTC and intermediates of pathway I on the three aquatic organisms; (c) acute toxicity analysis of OTC and intermediates of pathway II on the three aquatic organisms; (d) chronic toxicity analysis of OTC and intermediates of pathway II on the three aquatic organisms; (e) acute toxicity analysis of OTC and intermediates of pathway III on the three aquatic organisms; and (f) chronic toxicity analysis of OTC and intermediates of pathway III on the three aquatic organisms. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] All chemicals used in all embodiments of this invention are analytical reagent grade and can be used without further purification.

[0020] Example 1 A method for preparing an S-type heterojunction NiO / NiS photocatalyst is as follows: Synthesis of Ni-MOF: 5.09 g Ni(NO3)2·6H2O and 2.05 g 1,3,5-benzenetricarboxylic acid were dissolved in 80 mL anhydrous ethanol, stirred evenly, and then transferred to a reaction vessel. The reaction was carried out at 150 °C for 24 h in a solvothermal environment. After centrifugation and washing, the product was dried under vacuum at 60 °C for 12 h for later use. Preparation of flower-like Ni: 2.0 g of Ni-MOF was placed in a tube furnace and heated to 300 °C at 5 °C / min under a nitrogen atmosphere and calcined at a constant temperature for 6 h. After carbonization and removal of organic ligands, flower-like Ni was obtained. Preparation of flower-shaped NiO: After the flower-shaped Ni was naturally cooled to room temperature, it was placed in a muffle furnace and heated to 300℃ at 5℃ / min under air atmosphere and calcined at a constant temperature for 6h. The skeleton carbon was oxidized and volatilized to remove it, and the nickel was oxidized to obtain flower-shaped NiO. Preparation of NiO / NiS flower-like composite materials: 0.5 g of flower-like NiO was dissolved in 80 mL of ethanol with different masses (0.1, 0.2, 0.3, 0.4, and 0.5 g) of thiourea. After stirring evenly, the mixture was transferred to a reaction vessel and reacted at 170 °C for 16 h. The products were centrifuged, washed alternately with anhydrous ethanol and distilled water, and then vacuum dried at 50 °C for 18 h. They were named MNOS-1 to MNOS-5 according to the amount of thiourea used, from lowest to highest.

[0021] 1. Morphological analysis The geometric topology of sample MNOS-3 was observed across scales using SEM and EDS. Figure 1 As shown in Figure a, Ni-MOF exhibits a highly regular three-dimensional hierarchical nanoflower-like structure, which is assembled from a large number of interwoven, hierarchically stacked two-dimensional ultrathin nanosheets. After calcination and in-situ solvothermal sulfidation treatment ( Figure 1(b) In this study, MNOS-3 fully retains its original hierarchical flower-like framework, but the originally smooth nanosheet surface has evolved into a heterogeneous porous rough interface composed of highly compacted micro-nanoparticles. The micro-particles exhibit a non-uniform, high-low contrast in space, confirming the presence of abundant hierarchical mesoporous channels and hollow cage-like topological microenvironments within the nanoflowers. This hierarchical, loose, and porous geometric advantage not only significantly increases the achievable specific surface area, providing high-flux adsorption and trapping sites for antibiotic molecules, but also facilitates multiple scattering and refraction of incident photons within the porous network, thereby fundamentally enhancing the material's visible light capture efficiency. EDS was used to qualitatively and quantitatively analyze the local elemental distribution of the MNOS-3 nanoflowers. Figure 1 As shown in Figure c, Ni, O, and S elements exhibit highly uniform planar topological overlap throughout the entire three-dimensional hierarchical flower-like framework, with no macroscopic phase separation or regional enrichment observed. This result strongly demonstrates that the sulfidation reaction is not a simple physical mixing, but rather accompanied by a local in-situ phase transformation. The quantitative pie chart inset shows that the contents of Ni, O, and S are 73.2%, 18.2%, and 8.6%, respectively, confirming that MNOS-3 successfully achieved highly dispersed sulfur doping and deep integration of the oxygen and sulfur phases.

[0022] The crystal structure and phase composition of the sample were determined using XRD and TEM. TEM images ( Figure 1 d in Figure 1 In XRD pattern (e), the close contact state of the two-phase interface is clearly revealed at the atomic scale. The lattice spacing is 0.208 nm, corresponding to the (200) crystal plane of the face-centered cubic NiO, while the lattice fringe spacing is 0.297 nm, corresponding to the (110) crystal plane of the rhombohedral NiS. This clearly visible "phase boundary" contact at the nanoscale confirms the successful construction of the NiO / NiS heterogeneous interface at the atomic configuration level. Figure 1In f), pure NiO exhibits sharp diffraction peaks at 2θ = 37.2°, 43.3°, and 62.9°, corresponding to the (111), (200), and (220) crystal planes of face-centered cubic NiO, respectively. Pure NiS exhibits dense diffraction features, with peaks at 2θ = 18.4°, 30.1°, 32.1°, and 35.7°, corresponding to the (110), (111), (300), and (211) crystal planes of NiS, respectively. For the optimized heterojunction sample MNOS-3, its spectrum perfectly preserves the backbone diffraction peaks of NiO, while also introducing characteristic diffraction peaks of NiS. Due to the microscopic interlacing of the grain configuration, the peak intensity exhibits reasonable physical attenuation and local topological coverage, indicating that NiO and NiS phases form a good coexistence state in the composite material. This atomically close-knit heterostructure greatly eliminates the disorder energy barrier of charge transport, providing a solid physical foundation for the spontaneous generation of the built-in electric field at the interface and the efficient extraction of the subsequent S-type heterojunction charge topology pump.

[0023] like Figure 1 As shown in g, the adsorption-desorption curves of this sample exhibit typical type IV isotherm characteristics, accompanied by a significant H3-type hysteresis loop in the high-pressure region of 0.8-1.0 relative pressure. The slight upward movement of the isotherm in the low-pressure region (p / p0 < 0.1) reflects the presence of micropores, while the obvious hysteresis loop in the medium-high pressure region and the sharp increase in adsorption near the relative pressure of 1.0 clearly reveal the multi-level mesoporous and macroporous network system spontaneously evolved from the hierarchical stacking and particle packing of two-dimensional nanosheets in the material. Pore size distribution curve ( Figure 1 The h) in the model further quantified this characteristic, revealing that the phase porosity of MNOS-3 is mainly concentrated in a localized narrow mesoporous region around 2-5 nm, accompanied by a continuous diffuse distribution extending towards macropores. This multi-scale, hierarchical porous geometry, integrating micropores (enriching adsorption sites), mesopores (reducing solid-liquid mass transfer resistance), and macropores (optimizing photon transmission channels), endows MNOS-3 with outstanding physicochemical synergistic catalytic activity, laying an unparalleled structural foundation for its ability to drive the deep mineralization of antibiotic molecules under visible light.

[0024] 2. Photoelectric properties and band structure Analysis of the UV-Vis DRS and Tauc plots of MNOS-1~5 revealed that the construction of the NiO / NiS heterojunction significantly altered the optical response characteristics of the material. Figure 2As shown in section a, the absorption edge of pure-phase NiO (the flower-like NiO prepared in Example 1) is mainly concentrated in the ultraviolet region (<400 nm), and its absorption ability in the visible light region is extremely weak. In contrast, pure-phase NiS exhibits strong continuous absorption characteristics throughout the entire visible light range (400-800 nm). With the introduction of NiS, the absorption edge of the composite material (MNOS-1-MNOS-5) shows a significant redshift compared to pure NiO. This means that the construction of the heterojunction effectively reduces the energy barrier of the system, enabling it to respond to lower-energy visible light photons. With the increase of the NiS component ratio, the absorbance of the sample gradually increases in the visible light region (400-800 nm), indicating that the NiS loading compensates for the wide bandgap of NiO and significantly improves the material's utilization of the solar spectrum.

[0025] Band gap data calculated using the Tauc Plot tangent method further confirmed the synergistic effect between components. With increasing vulcanization degree, the band gap of the MNOS series composites gradually decreased from 2.77 eV to 1.72 eV. Figure 2 (b) This continuous tunability of the band gap confirms the formation of a tight interfacial contact between the two phases and the existence of strong electronic coupling, thereby enabling fine-tuning of the energy capture capability through band reconstruction. The construction of the NiO / NiS heterojunction, by introducing the narrow band gap component NiS, successfully extended the response range of NiO from the ultraviolet region to the visible light region. Among them, MNOS-3, as the best-performing catalyst, has a band gap (2.55 eV) that thermodynamically ensures effective capture of visible light while providing sufficient redox overpotential, thus achieving rapid degradation of antibiotic molecules under the S-scheme mechanism.

[0026] To further elucidate the electronic band structures of NiS and NiO, this study performed Mott-Schottky (MS) analysis. Extrapolation analysis of the linear region of the MS curves was conducted... Figure 2 e and Figure 2The flat-band potentials (Efb) of NiS and NiO relative to the saturated calomel electrode (SCE) are determined to be -0.14V and 1.19V, respectively. Using the energy scale conversion formula ENHE = ESCE + 0.2V, converted to the standard hydrogen electrode scale, the flat-band potentials are 0.06eV and 1.39eV (vs. NHE), respectively. Based on the empirical rule in semiconductor physics that the valence band peak (EVB) of p-type semiconductors is typically 0.2V higher than its flat-band potential, the EVB of NiS is estimated to be 0.26V, and that of NiO is 1.59V. Combining the band gap determined by solid-state ultraviolet diffuse reflectance spectroscopy (NiS: 1.6eV, NiO: 2.75eV), the final calculated conduction band potentials are 1.34V for NiS and -1.16V for NiO. This staggered band arrangement provides a thermodynamic basis for constructing high-performance S-shaped heterojunctions, which is beneficial for the spatial separation of photogenerated carriers and the synergistic enhancement of redox capabilities.

[0027] To further reveal the intrinsic mechanism of the enhanced performance of NiO / NiS heterojunctions from the perspective of charge dynamics, the samples were characterized by electrochemical impedance spectroscopy and transient photocurrent response. Figure 2 As shown in g, the interfacial charge transfer resistance of the samples was further investigated using electrochemical impedance spectroscopy. The relatively large arc radii of pure-phase NiO and NiS revealed their slower charge transfer rates. After forming the composite system, the impedance arc radii of all samples decreased to varying degrees. MNOS-3 exhibited a smaller arc radius, indicating superior conductivity and the lowest interfacial charge transport barrier. Furthermore, all samples showed stable and rapid current responses during multiple "on-off" photocycles. Figure 2 While the photocurrent density of pure-phase NiO and NiS is relatively low, indicating a faster recombination rate of photogenerated electron-hole pairs, the MNOS series composites exhibit enhanced photocurrent signals after heterojunction construction. Among them, MNOS-3 has the highest photocurrent density (approximately 7.8 μA / cm³). 2 This value is approximately 3.9 and 17.5 times that of pure NiO and NiS, respectively, and far exceeds that of composite materials with other proportions. The significant increase in photocurrent intensity directly and strongly proves the existence of a built-in electric field at the MNOS-3 interface. This electric field, as a driving force, accelerates the directional spatial migration of charges and significantly suppresses bulk and interfacial recombination of charge carriers. Combining the photocurrent and impedance analysis results, MNOS-3 achieves the highest separation efficiency and the fastest interfacial transport dynamics under photoexcitation. This comprehensive leap in photoelectric properties experimentally confirms the advantage of S-type heterojunctions in effectively separating strongly reducing electrons and strongly oxidizing holes in space, thus providing a sufficient guarantee of active charge carriers for the subsequent efficient degradation of antibiotic molecules.

[0028] 3. XPS Analysis To further investigate the elemental composition and chemical valence state of the NiO / NiS heterojunction, this study characterized the samples using X-ray photoelectron spectroscopy (XPS).

[0029] Depend on Figure 3 As shown in 'a', MNOS-3 contains C, Ni, O, and S elements, which is consistent with the EDS test results. The fine spectrum of O1s of MNOS-3 can be divided into three independent characteristic peaks. The strong peak at 529.56 eV corresponds to the metal-oxygen bond (Ni-O) in the NiO lattice; the fitting peak at 530.64 eV is attributed to oxygen species at oxygen vacancies or defect sites on the material surface. The presence of these defects usually facilitates the capture and migration of photogenerated carriers; while the peak at 531.70 eV originates from the chemisorbed oxygen of hydroxyl groups (-OH) or water molecules adsorbed on the surface. Figure 3 In the image, b represents the high-resolution spectrum of Ni 2p, which exhibits a distinct spin-orbit bimodal structure. After Gaussian-Lorentz fitting, the characteristic peaks at 853.73 eV and 873.16 eV are attributed to Ni in NiS. 2+ 2p 3 / 2 and 2p 1 / 2 The peak at 855.80 eV corresponds to the Ni-O bond in NiO. Furthermore, the two broad peaks observed at 861.33 eV and 879.65 eV represent Ni 2p orbitals; while the peak at 855.80 eV corresponds to the Ni-O bond in NiO. 3 / 2 and Ni 2p 1 / 2 The excitation peaks confirmed that Ni mainly exists in the +2 valence state in the material. Figure 3 In the high-resolution spectrum of C1s, the strong main peak at 284.81 eV is attributed to the CC / C=C bond, originating from the conjugated benzene ring skeleton and pyrolytic amorphous carbon network in the precursor. The fitting peak at 285.92 eV corresponds to the CO single bond, attributed to the phenolic hydroxyl group, ether bond, or CO-Ni interface bridging bond produced by the incomplete thermal decomposition of the carboxyl group. The characteristic peak at 288.37 eV corresponds to the C=O bond, representing residual incompletely decarboxylated carboxyl groups or surface oxygen-containing unsaturated defects. In the S 2p spectrum ( Figure 3 f), located at 161.80 eV (S 2p). 3 / 2 ) and 162.91 eV (S 2p 1 / 2 The bimodal characteristics of NiS clearly reveal the S content in NiS. 2- The presence of [something]. It is noteworthy that the high binding energy peak at 168.80 eV corresponds to surface sulfate species (SO4). 2- This is attributed to the high surface energy of the nanoflower structure, which causes sulfur to undergo slight natural oxidation in the air.

[0030] like Figure 3 As shown in e, the Ni 2p of pure phase NiO3 / 2 The lattice peak is located at 855.60 eV, while in MNOS-3 ( Figure 3 In (b), the characteristic peak shifted positively by 0.20 eV to 855.80 eV. Simultaneously, the peak position of the NiO lattice oxygen O1s ( Figure 3 In the pure phase, d) also shifted positively by 0.33 eV to 529.56 eV from 529.23 eV. This general increase in binding energy indicates that the electron cloud density inside the NiO component is significantly reduced at the heterojunction interface, exhibiting characteristics of electron loss. For pure phase NiS ( Figure 3 (h in the middle), its Ni2p 3 / 2 The core energy level is located at 853.08 eV, while in MNOS-3 ( Figure 3 In (b), the peak clearly shifts 0.65 eV towards higher energies, reaching 853.73 eV. Meanwhile, S2p... 3 / 2 ( Figure 3 g and Figure 3 In f), a positive shift also occurred from 161.61 eV to 161.80 eV. Notably, both core energy levels in MNOS-3 exhibit a universal positive shift, breaking through the traditional local understanding of heterojunctions as "one rising and one falling," and deeply revealing the microscopic advantages of in-situ topological transformation in Ni-MOFs. Firstly, the delocalized sp2 energy level formed by the pyrolysis of MOF organic ligands... 2 The conjugated carbon network exhibits a strong induced electron-withdrawing effect, performing space charge extraction on both semiconductors through interfacial bonding. Secondly, the in-situ sulfidation process disrupts local electroneutrality, inducing high-density oxygen vacancies and other unsaturated coordination defects on the NiO surface (corresponding to the 530.64 eV peak in O1s), leading to lattice distortion and electron depletion. Although the synergistic electron-withdrawing effect of the carbon network and defects results in an overall positive shift in the spectrum, the positive shift of NiS (0.65 eV) is much greater than that of NiO (0.20 eV). Its significant asymmetry qualitatively confirms that NiS has a stronger tendency to lose electrons. In the dark state, the intrinsic trend of electrons diffused directionally from NiS to NiO strongly confirms the successful incubation of the built-in electric field from NiS to NiO at the phase boundary. Combined with Schottky measurements, it can be seen that the staggered band arrangement of NiS and NiO successfully forms an S-type heterojunction. Therefore, under photoexcitation conditions, the built-in electric field drives the recombination of photogenerated electrons in the NiO conduction band and holes in the NiS valence band at the interface, thus allowing the NiS conduction band to retain its extremely strong reducing power (-1.34 eV) and the NiO valence band to retain its excellent oxidizing power (1.59 eV). This S-shaped charge migration pathway not only effectively suppresses carrier recombination but also provides a continuous source of highly reactive redox species for the degradation of tetracycline antibiotics.

[0031] 4. Analysis of photocatalytic degradation performance and cycle performance To investigate the effect of different component ratios on photocatalytic degradation efficiency, the activity of MNOS catalysts with different composite ratios of NiO / NiS was systematically evaluated through degradation experiments of tetracycline (TC) and oxytetracycline (OTC) using different materials under visible light irradiation. Experimental procedure: 20 mg of photocatalysts with different ratios were placed in 50 mL of TC and OTC solutions (50 mg / L) for photocatalytic evaluation. A 300W xenon lamp (CEL-LB70) was used to simulate sunlight. The experiment began with a 300 min dark reaction to reach adsorption-desorption equilibrium. The photolysis phase lasted 60 min, with samples taken and centrifuged every 15 min. The absorbance of the solution was monitored using a UV-Vis spectrophotometer.

[0032] like Figure 4 a and Figure 4 As shown in d, the dark adsorption phase (30 min before reaction initiation) revealed that the MNOS composite material exhibited stronger adsorption capacity than pure-phase NiO and NiS, with MNOS-3 showing the highest equilibrium adsorption capacity. This is attributed to the nanoflower-like structure providing more abundant active sites and hierarchical pores. After entering the light irradiation phase, the degradation efficiency of each sample showed significant differences. Pure-phase NiO and NiS exhibited slow degradation of both antibiotics, with removal rates of less than 60% at 60 min. In contrast, all MNOS composite materials demonstrated enhanced photocatalytic activity. MNOS-3 showed the best degradation performance, achieving almost complete degradation of TC and OTC within 60 min, with residual concentrations approaching zero.

[0033] To further quantify catalytic activity, this study compiled a graph showing the degradation rates of the target pollutant for each sample. Experimental data indicate that ( Figure 4 b and Figure 4 As the proportion of NiS component is adjusted, the catalytic performance exhibits a "volcano-like" trend of first increasing and then decreasing. MNOS-3 shows the best catalytic capacity, with degradation rates of 47.9 mg / g for TC and 47.5 mg / g for OTC. Compared to the pure phase NiS, which has a TC degradation rate of 22.5 mg / g, the performance of MNOS-3 is improved by more than 100%. This trend indicates that a moderate heterostructure helps to form a tight interfacial contact and an optimal charge transport path, while excessive NiS may inhibit activity due to the shielding effect or by becoming a carrier recombination center. The degradation process was linearly fitted using the pseudo-first-order kinetic model ln(Ct / C0)=kt. Figure 4 c and Figure 4 The results (f) showed that MNOS-3 had the highest apparent rate constant for TC and OTC. Specifically, the k-value for MNOS-3 degradation of TC and OTC reached 3.85 × 10⁻⁶. -2 min -1 and 3.61×10-2 min -1 They are pure phase NiO (6.31 × 10⁻⁶) -3 min -1 and 3.6×10 -3 min -1 ) and NiS (5.13×10 -3 min -1 and 3.13×10 -3 min -1 The efficiency was 6.10, 7.50, 10, and 11.5 times that of NiO and NiS. The results indicate that the composite of NiO and NiS produced a significant synergistic effect, greatly improving visible light utilization. The significant increase in efficiency confirms the successful construction of the S heterojunction mechanism.

[0034] The degradation stability and reusability of the optimized NiS / NiO heterojunction material (MNOS-3) were evaluated through five consecutive cyclic degradation tests. The test results showed that ( Figure 5 a and Figure 5 (b) The optimized heterojunction material exhibits excellent degradation persistence. After 5 cycles, the degradation rates of tetracycline and oxytetracycline by MNOS-3 remained above 94.3% and 93.5%, respectively, with the slight decrease from the first cycle not exceeding 1.6%. This maintenance of high degradation efficiency close to the initial state clearly demonstrates that the MNOS-3 composite material possesses extremely strong structural stability, degradation stability, and reusability. These excellent performance indicators provide strong scientific evidence and technical support for further applying this material to practical, long-term photocatalytic degradation of antibiotic pollution.

[0035] 5. Capture experiment and analysis of the degradation mechanism of antibiotics by MNOS-3 To elucidate the mechanism by which the optimized heterojunction material (MNOS-3) efficiently degrades antibiotics under visible light, free radical capture experiments were conducted. Tetracycline and oxytetracycline were used as target pollutants, and superoxide radicals (·O2) were evaluated by adding BQ, IPA, and EDTA-2Na, respectively. - ), hydroxyl radicals (·OH) and photogenerated holes (h + The contribution of ) in the degradation process. After adding different scavenging agents ( Figure 5 c and Figure 5In step d), the degradation effects on tetracycline and oxytetracycline showed a consistent effect. After adding BQ, the degradation rates of tetracycline and oxytetracycline decreased significantly to 30.2% and 27.5%, respectively. The addition of IPA and EDTA-2Na also led to a decrease in degradation rates, to 51.6%, 47.30%, 40.10%, and 35.20%, respectively. Comprehensive analysis shows that in the MNOS-3 catalytic system, the contributions of these three ROS to antibiotic degradation have a clear hierarchy of relative importance: ·O2 - h + Superoxide radicals were identified as the main active group for MNOS-3 degradation of antibiotic molecules, exhibiting the strongest inhibitory effect on the degradation of both tetracycline and oxytetracycline, while photogenerated holes and hydroxyl radicals played important auxiliary roles.

[0036] To further investigate the photocatalytic degradation mechanism of tetracycline and oxytetracycline by MNOS-3, this study used liquid chromatography-mass spectrometry (LC-MS) to identify the intermediate products in the reaction process. Figure 6 As shown, the degradation process of TC (m / z = 445) mainly unfolds through three parallel pathways. Pathway I focuses on defunctionalization and early ring-opening processes. TC is first converted into intermediate P1 ($m / z = 433), followed by a drastic breakage of the parent skeleton, degrading into bicyclic product P2 (m / z = 228) and chain organic compound P3 (m / z = 130). Pathway II is centered on deamination and skeleton fragmentation. TC undergoes initial transformation to generate P4 (m / z = 429), followed by the crucial removal of the N,N-dimethylamino group to generate P5 (m / z = 386), marking the loss of the core toxic site of the antibiotic, and further cleavage into P6 (m / z = 260). Pathway III involves a continuous collapse caused by multi-site oxidation. P7 (m / z = 426) undergoes deep fragmentation, evolving into P8 (m / z = 302) and P9 (m / z = 238). In the later stages of the reaction, the intermediates generated by the above pathway are further transformed into small molecule organic acids or alcohols such as P10 (m / z = 116), P11 (m / z = 74) and P12 (m / z = 89) under the continuous attack of the generated strong oxidizing free radicals. These fragments are eventually completely mineralized into CO2 and H2O.

[0037] like Figure 7As shown, the degradation of OTC (m / z = 461) mainly proceeds through three parallel pathways, involving defunctionalization, skeleton ring opening, and the final mineralization stage. This process fully reflects the multi-site synergistic attack of active radicals generated by the heterojunction on antibiotic molecules. Pathway I is the defunctionalization process: OTC (m / z=461) undergoes dehydration and deamidation to generate P2 (m / z=355) under the attack of active species, and then is converted into P3 (m / z=341) through successive demethylation, which rapidly destroys the polar groups of the molecule. Pathway II is the core step of skeleton collapse. Due to the low bond energy of C-N bond, the dimethylamino group is preferentially removed to generate P4 (m / z=381). Then, photogenerated charges induce ring opening and fragmentation of ring A and ring B to generate bicyclic intermediate P5 (m / z=208) and monocyclic derivative P6 (m / z=135), marking the complete collapse of the tetracene skeleton. Pathway III represents deep oxidative degradation 43, generating fragment P7 (m / z=333) through multi-site attack, and then evolving into P8 (m / z=191) and monocyclic product P9 (m / z=123) via dehydrogenation and oxygenation. In the late stage of the reaction, the products of each pathway are further degraded into small molecular fragments such as benzaldehyde (P10), toluene derivatives (P11) and furans (P12), and these small molecular fragments are then completely mineralized into CO2 and H2O.

[0038] 6. Toxicity analysis of degradation products to aquatic organisms To comprehensively evaluate the ecological safety of NiO / NiS photocatalyst MNOS-3 during the degradation of tetracycline (TC) and oxytetracycline (OTC), this study used the ECOSAR program in EPISuite software developed by U.S. EPA to conduct quantitative aquatic biotoxicity assessment on the parent compounds of TC and OTC and 12 main intermediates (P1-P12) involved in their degradation pathways. The assessment covered three key trophic levels of the aquatic ecosystem: Fish, Daphnid and Green Algae. By calculating the logarithm values of acute toxicity (half-lethal concentration logLC50 and half-effect concentration logEC50) and chronic toxicity (ChV), the toxicity is divided into four grades: extremely toxic (log<0), toxic (0<log<1), harmful (1<log<2) and harmless (log>2).

[0039] The toxicity evolution during TC degradation presents non-linear fluctuation characteristics, such as Figure 8As shown in a~f, in pathway I (P1-P3), the toxicity index fluctuates slightly with dehydration and functional group modification, but remains within the high-risk range. Pathways II and III are the stages with the most dramatic changes in toxicity: intermediates P4-P9 (such as dedimethylamine or products with preliminary ring-opening of the skeleton) exhibit obvious "toxicity jumps," entering the "highly toxic" region. However, with further attack from strong oxidizing free radicals, all pathways achieve elimination of toxicity after complete skeleton fragmentation. The logLC50 and logEC50 values ​​of the terminal products P10-P12 both jump significantly to above 3.0, even reaching around 5.0 (corresponding to the area turning from red to dark blue in the heatmap), and are judged to be "harmless." This proves that the system can not only efficiently degrade TC molecules, but also overcome the high toxicity barrier of intermediates, mineralizing them into eco-friendly small molecules.

[0040] ECOSAR assessment shows that ( Figure 9 (a~f) The OTC parent compound exhibits significant toxicity to aquatic organisms, and the degradation process is not a linear attenuation of toxicity. In pathways II and III, intermediates P4 and P7 exhibit transient "toxicity jumps," even reaching highly toxic levels, due to changes in hydrophobicity or enhancement of specific activities caused by functional group stripping. However, these high-risk fragments only exist briefly and are rapidly further broken down by strong oxidizing free radicals, transforming into harmless terminal small molecules P10-P12. Ultimately, all pathway intermediates achieve complete mineralization, crossing the toxicity threshold.

[0041] The photocatalyst prepared in this invention significantly disrupts the tetracyclic core framework of TC and OTC through multi-pathway synergistic action. This not only achieves efficient destruction of the tetraphenylene skeleton but also demonstrates, from an ecotoxicological perspective, its excellent safety and environmental remediation potential in treating antibiotic wastewater.

[0042] Furthermore, this invention, through deep dynamic mechanisms and electron transfer behavior analysis, confirms that the Fermi level recombination induced by the two-phase contact constructs a built-in electric field at the asymmetric interface, driving the system to excite a stepped charge topology pump path with the characteristic of "abandoning weak and retaining strong" carriers. Under the physical constraints of the built-in electric field and band bending, NiO conduction band electrons and NiS valence band holes undergo directional nonradiative recombination sacrifice. This mechanism completely blocks the topological recombination of highly active carriers in space, thus preserving the NiS conduction band electron flow with an ultra-negative reduction potential (-1.34 V) and the NiO valence band hole flow with an ultra-positive oxidation potential (+1.59 V). The generated ROS attacks antibiotic molecules, driving and causing deep multi-path fragmentation (P1-P12) of the tetraphenyl framework, ultimately achieving safe mineralization and detoxification. This fully demonstrates the enormous application potential of multiphase hierarchical interface engineering and band engineering co-design in the deep green remediation of complex industrial antibiotic wastewater.

[0043] Example 2 In the preparation of the flower-like Ni in Example 1, the temperature was raised to 400°C and calcined at that temperature for 4 hours. Although the temperature was slightly increased, the holding time was short, so the three-dimensional flower-like structure and the crystal structure were not destroyed.

[0044] Example 3 The temperature was raised to 350°C during the preparation of the flower-like NiO in Example 1, and then calcined at that temperature for 4 hours. Scanning electron microscopy showed that its flower-like morphology was intact, and XRD showed that its crystal structure was consistent with MNOS-3.

[0045] Example 4 In the preparation of the flower-like NiO in Example 1, the temperature was raised to 400℃ and calcined at a constant temperature for 3 hours. The outer two-dimensional nanosheets became thinner, and the three-dimensional flower-like structure shrank slightly, but the difference was not significant compared to calcining at 300℃ for 6 hours.

[0046] Example 5 The temperature in the preparation process of the NiO / NiS flower-like composite material in Example 1 was modified to 200℃ and the time was modified to 12h.

[0047] Example 6 In Example 1, the temperature was maintained at 170°C and the preparation time was modified to 24 hours.

[0048] Comparative Example 1 In Example 1, the tube furnace used for preparing the flower-like Ni was replaced with a muffle furnace. The temperature was increased to 300°C at a rate of 5°C / min and then calcined at this temperature for 6 hours in an air atmosphere. Because the calcination was carried out in an air atmosphere, the carbon elements in the original framework were oxidized and volatilized, causing the three-dimensional structure to collapse and preventing the formation of a three-dimensional flower-like structure.

[0049] Comparative Example 2 In Example 1, the calcination temperature during the preparation of the flower-like Ni was adjusted to 200°C. Due to the low temperature, the organic matter in the Ni-MOF could not be completely carbonized, resulting in a larger thickness of the two-dimensional nanosheets and a larger size of the assembled three-dimensional nanoflowers. XRD results showed that the crystal structure changed.

[0050] Comparative Example 3 In Example 1, the calcination temperature for preparing the flower-like NiO was adjusted to 200℃, and the calcination time was modified to 12h. Due to the low temperature, although the time was extended, it was still impossible to carbonize the residual organic matter and the residual framework carbon. As a result, the three-dimensional nanoflowers were larger in size and the pore structure distribution was worse.

[0051] Comparative Example 4 In Example 1, the calcination temperature during the preparation of the flower-like NiO was adjusted to 500℃, 600℃, or 700℃, and the calcination time was modified to 3 hours. This caused the thickness of the outer two-dimensional nanosheets to shrink, resulting in a slight collapse of the three-dimensional nanoflowers.

[0052] Comparative Example 5 Increasing the amount of thiourea added in Example 1 to 2 grams will result in the formation of Ni3S2 due to excessive addition.

[0053] Comparative Example 6 The preparation temperature of the NiO / NiS flower-like composite material in Example 1 was changed to 150℃. Because of the lower temperature, the rate of thiourea decomposition to generate active S species slows down, hindering the reaction kinetics between NiO and S, and significantly reducing the overall degree of sulfidation.

[0054] Comparative Example 7 The preparation temperature of the NiO / NiS flower-like composite material in Example 1 was changed to 200℃. Because the temperature is too high, other products, such as NiS2, will be generated.

[0055] Comparative Example 8 The reaction time for preparing the NiO / NiS flower-like composite material in Example 1 was modified to 10 hours. Due to the short reaction time, the S produced by thiourea decomposition was not completely converted into NiS, resulting in a low degree of sulfidation.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An S-type heterogeneous NiO / NiS photocatalyst, characterized in that, The photocatalyst is a regular three-dimensional multi-level nanoflower structure, which is assembled from interwoven and stacked two-dimensional ultrathin nanosheets. The surface of the nanosheets is a heterogeneous porous rough interface formed by the close packing of micro-nanoparticles. The micro-nanoparticles exhibit non-uniform high and low contrast in space. The nanoflower structure contains hierarchical mesoporous channels and hollow cage-like topological microenvironments.

2. The S-type heterogeneous NiO / NiS photocatalyst according to claim 1, characterized in that, The face-centered cubic NiO and rhombohedral NiS phases form a heterogeneous interface, and the two phases are in close contact.

3. The S-type heterogeneous NiO / NiS photocatalyst according to claim 1, characterized in that, The catalyst has micropores, mesopores, and macropores.

4. A method for preparing an S-type heterojunction NiO / NiS photocatalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Ni(NO3)2·6H2O and 1,3,5-benzenetricarboxylic acid are dissolved in anhydrous ethanol and then subjected to a solvothermal reaction to obtain Ni-MOF; (2) Take Ni-MOF and heat it to 300~400℃ at 5℃ / min under nitrogen atmosphere and calcine it at a constant temperature for 4~8h to obtain flower-shaped Ni; (3) After the flower-shaped Ni is naturally cooled to room temperature, it is heated again to 300~400℃ at 5℃ / min in air atmosphere and calcined at a constant temperature for 4~8h to obtain flower-shaped NiO; (4) Take flower-shaped NiO and thiourea in a mass ratio of 5:(1~5) and dissolve them in anhydrous ethanol. Then react them at 170℃ for 12~24h. The product is washed and dried to obtain flower-shaped NiO / NiS.

5. The preparation method according to claim 4, characterized in that, In step (1), the mass ratio of Ni(NO3)2·6H2O to 1,3,5-benzenetricarboxylic acid is 5:(1-4); the temperature of the solvothermal reaction is 150~170℃, and the reaction time is 18~24h.

6. The preparation method according to claim 4, characterized in that, In step (2), the Ni-MOF is heated to 300℃ at 5℃ / min and calcined at a constant temperature for 6h.

7. The preparation method according to claim 4, characterized in that, In step (3), the flower-shaped Ni is heated to 300℃ at 5℃ / min and calcined at a constant temperature for 6 hours.

8. The preparation method according to claim 4, characterized in that, In step (4), the flower-shaped NiO and thiourea are dissolved in ethanol at a mass ratio of 5:3 and then reacted at 170℃ for 16h. After the solvothermal reaction, the product is centrifuged, washed alternately with anhydrous ethanol and distilled water, and then vacuum dried at 40~60℃ for 12~24h.

9. The use of the photocatalyst according to any one of claims 1 to 3 in the degradation of antibiotics.

10. The application according to claim 9, characterized in that, The antibiotic in question is a tetracycline antibiotic.

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