Preparation and Catalytic Performance of Z-Type Heterojunction BiPO₄/g-C₃N₄ Photocatalyst AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY24110005

Chinese Library Classification Number:X703.5

Citation Information:

Organic dye wastewater poses a significant threat to aquatic environments，and traditional treatment methods are often inefficient and costly. Photocatalysis，as one of the advanced oxidation processes （AOPs），has garnered considerable attention for its ability to effectively degrade organic pollutants using semiconductor photocatalysts under sunlight，converting them into non-toxic，harmless small molecules （H₂O，CO₂，etc.）. It is recognized for its high efficiency，rapid action，cost-effectiveness，and environmental friendliness. BiPO₄ is a low-cost，non-toxic photocatalyst widely used in water treatment，but its 3.85 eV band gap limits solar energy utilization，hindering dye wastewater degradation. To enhance its visible light absorption，strategies like doping and heterojunction formation are often used. Graphitic carbon nitride （g-C₃N₄），with a 2.9 eV band gap，absorbs visible light up to 460 nm but suffers from poor electron-hole pair separation. Combining g-C₃N₄ with BiPO₄ forms a heterojunction that broadens light absorption and improves photocatalytic efficiency，making it a key research area. Therefore，in this study，BiPO₄/g-C₃N₄ composite photocatalyst was successfully designed and synthesized using a hydrothermal method. Its crystal structure，microstructure and photoelectric properties were systematically analyzed through characterization techniques，including X-ray diffraction （XRD），scanning electron microscopy （SEM），ultraviolet-visible diffuse reflectance spectroscopy （UV-Vis DRS） and transient photocurrent measurements. XRD analysis revealed g-C₃N₄'s pure phase with a strong （002） diffraction peak at 27.4°，while BiPO₄ displayed a highly crystalline monoclinic phase. In BiPO₄/g-C₃N₄ composite photocatalyst，g-C₃N₄ peaks were weak due to its low content and uniform dispersion. SEM images showed g-C₃N₄'s lamellar structure and BiPO₄'s rod-like morphology. The composite's layered g-C₃N₄ structure improved BiPO₄ dispersion，reducing aggregation and enhancing catalytic activity. Energy dispersive X-ray spectroscopy （EDX） confirmed uniform distribution of C，N，Bi，P，and O，verifying successful composite synthesis. UV-Vis DRS spectroscopy revealed that BiPO₄ absorbed only in UV region （~330 nm），while BiPO₄/g-C₃N₄ composite photocatalyst extended absorption to ~430 nm，shifting into the visible light range. This enhanced absorption was attributed to the formation of a heterojunction structure in BiPO₄/g-C₃N₄ composite photocatalyst，which facilitated charge transfer at the interface，leading to a red shift of the absorption edge. This shift effectively broadened the light absorption range of the catalyst，significantly improving its photocatalytic activity. Kubelka-Munk function analysis revealed that the band gaps of BiPO₄ and g-C₃N₄ were 3.80 and 2.70 eV，respectively，consistent with literature values. BiPO₄/g-C₃N₄ composite photocatalyst exhibited a band gap of 2.90 eV，indicating successful synthesis and excellent visible light responsiveness. The variation in band gap directly influenced the light absorption range，where a smaller band gap corresponded to a wider absorption range，and vice versa. Photocurrent measurements further validated the superior performance of BiPO₄/g-C₃N₄ composite photocatalyst. Under visible light irradiation，the photocurrent intensity of the composite was significantly higher than that of pure BiPO₄ and g-C₃N₄，indicating superior electron-hole separation efficiency and charge transfer ability. This enhanced photocurrent response was attributed to the in situ composite formation of BiPO₄ on g-C₃N₄，which improved the carrier migration efficiency and，consequently，enhanced the photocatalytic performance. A series of catalytic degradation experiments were conducted using methylene blue as the model water pollutant. The results showed that as the illumination time increased，the degradation efficiency of BiPO₄，g-C₃N₄ and BiPO₄/g-C₃N₄ gradually increased. After 120 min of illumination，the degradation rates of BiPO₄，g-C₃N₄ and BiPO₄/g-C₃N₄ were 70%，84%，and 97%，respectively. BiPO₄/g-C₃N₄ composite photocatalyst exhibited the highest catalytic activity among all samples. The combination of g-C₃N₄ and BiPO₄ expanded light absorption，generated more electrons and holes and allowed effective separation of electrons and holes，thereby enhancing the catalytic degradation ability of BiPO₄/g-C₃N₄ composite photocatalyst. Catalytic degradation experiments with different dyes showed significant variations in the degradation activity of BiPO₄，g-C₃N₄ and BiPO₄/g-C₃N₄，indicating that the catalysts exhibited some selectivity during dye degradation. The degradation rates of different dyes，from high to low，were as follows：Rhodamine B，methyl violet，malachite green，methylene blue and methyl orange. Under the same conditions，BiPO₄/g-C₃N₄ composite photocatalyst exhibited better photocatalytic degradation performance compared to g-C₃N₄ and BiPO₄. Cyclic testing results showed that after five cycles，the catalyst still maintained a degradation rate of 86% for methylene blue，demonstrating that BiPO₄/g-C₃N₄ composite photocatalyst had good stability and reusability，with high potential for commercial applications. Radical quenching experiments were conducted using disodium ethylenediaminetetraacetate （EDTA-2Na），isopropyl alcohol （IPA），and benzoquinone （BQ） to detect holes （h⁺），hydroxyl radicals （·OH） and superoxide radicals （·O₂^-）. The results showed that the three scavengers inhibited the methylene blue degradation to different extents. The addition of BQ significantly reduced the catalytic degradation efficiency，indicating that ·O₂^- played a dominant role in the degradation process. The addition of IPA also inhibited degradation，suggesting that h⁺ and ·O₂^- were the main active species in BiPO₄/g-C₃N₄ composite photocatalyst，with ·OH also involved in the degradation of organic pollutants. In summary，this study proposed a novel BiPO₄/g-C₃N₄composite photocatalyst to eliminate secondary pollution and provided a new approach for the rapid and deep treatment of dye wastewater，with broad application prospects.