A novel dual Z-scheme BiOBr/NH 2 -MIL-101(Fe)/g-C 3 N 4 (BNG) heterojunction was constructed via a simple two-step solvothermal process. NH 2 -MIL-101(Fe) nanoparticles and BiOBr microspheres were uniformly deposited on the surface of g-C 3 N 4 . The prepared BNG exhibited significantly enhanced photocatalytic performance for tetracycline (TC) degradation compared to single catalyst. The optimized BNG-19 composite (with 19% NH 2 -MIL-101(Fe)/g-C 3 N 4 ) achieved 92.38% degradation of TC within 75 min under visible light, which was 2.47, 1.78, and 1.84 times higher than that of pure g-C 3 N 4 , NH 2 -MIL-101(Fe), and BiOBr, respectively. Moreover, the composite exhibited excellent stability with 82.4% removal efficiency after five cycles. The enhanced photocatalytic performance was attributed to the synergistic dual Z-scheme charge transfer mechanism, which was directly evidenced by in-situ irradiated XPS showing opposite directional shifts of Bi 4f (positive) and Fe 2p/N 1s (negative). This unique charge transfer pathway effectively promoted the separation of photogenerated carriers, with •OH and •O 2 ⁻ identified as the dominant reactive species. This work provides a new strategy for constructing g-C 3 N 4 -based dual Z-scheme heterostructures with direct mechanistic evidence for efficient environmental remediation.
A dual modification strategy combining MHNT tubular structure and Fe doping is proposed. • MHNT tubular structure offers high surface area and effective charge transport channels. • Fe doping introduces impurity levels to tailor the band structure of g-C 3 N. • Photoelectrode material maintains stable photoelectrochemical response after one-year ambient storage. Dopamine (DA), a key neurotransmitter in the central nervous system, exhibits concentration abnormalities that are closely associated with various neurological disorders. Thus, its accurate and stable detection in biological samples is crucial for early diagnosis. In this study, using melamine as a precursor, hydrochloric acid-modified halloysite nanotubes (MHNT) as a porous support material, and FeCl 3 ·6H 2 O as an iron source, an Fe-doped graphitic carbon nitride/halloysite nanotube (Fe-g-C 3 N 4 /MHNT) composite photoelectrode material was successfully synthesized via a hydrothermal dispersion combined with high-temperature calcination method. A photoelectrochemical sensor was subsequently constructed for dopamine detection. Fe doping effectively modulated the band structure of g-C 3 N 4 , broadening the visible light absorption range and suppressing the recombination of photogenerated charge carriers. Meanwhile, the tubular structure of MHNT provided a high specific surface area and efficient charge transport pathways. Under optimized conditions, the sensor exhibited good linearity in the concentration ranges of 10–200 μM and 200–2300 μM, with a sensitivity of 0.527 μA·μM −1 ·cm −2 and a detection limit as low as 0.28 μM (S/N = 3). Moreover, the sensor demonstrated excellent selectivity for dopamine in the presence of interfering substances in simulated body fluid. Notably, after one year of storage at room temperature, the sensor retained a stable linear photocurrent response with a detection limit of only 0.39 μM (S/N = 3), indicating outstanding long-term storage stability. This work effectively overcomes the intrinsic drawbacks of g-C 3 N 4 , including insufficient active sites and rapid charge carrier recombination, through the synergistic strategy of MHNT incorporation and Fe doping, providing a viable pathway for the development of highly selective and stable photoelectrochemical sensors. Download: Download high-res image (201KB) Download: Download full-size image
Heterogeneous catalysts with ultra-small clusters and atomically dispersed (USCAD) active sites have gained increasing attention in recent years. However, developing USCAD catalysts with high-density metal sites anchored in porous nanomaterials is still challenging. Here, through the template-free S-assisted pyrolysis of low-cost Fe-salts with melamine (MA), porous alveolate Fe/g-C 3 N 4 catalysts with high-density (Fe loading up to 17.7 wt%) and increased USCAD Fe sites were synthesized. The presence of a certain amount of S species in the Fe-salts/MA system plays an important role in the formation of USCAD S-Fe-salt/CN catalysts; the S species act as a “sacrificial carrier” to increase the dispersion of Fe species through Fe-S coordination and generate porous alveolate structure by escaping in the form of SO 2 during pyrolysis . The S-Fe-salt/CN catalysts exhibit greatly promoted activity and reusability for degrading various organic pollutants in advanced oxidation processes compared to the corresponding Fe-salt/CN catalysts, due to the promoted accessibility of USCAD Fe sites by the porous alveolate structure. This S-assisted method exhibits good feasibility in a large variety of S species (thiourea, S powder, and NH 4 SCN) and Fe salts, providing a new avenue for the low-cost and large-scale synthesis of high-density USCAD metal/g-C 3 N 4 catalysts.
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