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Ammonia is the main precursor for the production of fertilizers, a hydrogen energy carrier and an emerging clean fuel that plays a crucial role in sustaining life on the globe. Herein, hybrid MoSe2@g-C3N4 micro/nanostructures are described that can serve as photoelectrochemical (PEC) catalysts to fix N2 into NH3 in a basic electrolyte at a low potential (−0.3 V vs. RHE) under ambient conditions. In situ functionalization of the hierarchical micro/nanoflowers of MoSe2 with exfoliated g-C3N4 nanosheets dramatically boosts the faradaic efficiency and yield rate up to 28.91% and 7.72 μmol h−1 cm−2 respectively. The high PEC activity can be attributed to the hierarchical architecture, light-harvesting capability, tunable active sites and formation of heterojunctions, as confirmed by various characterization and density functional theory (DFT) calculations. Therefore, this work not only develops an effective procedure to obtain hierarchical heterojunction catalysts towards a high-efficiency NRR but also provides a deep understanding of artificial N2 fixation at the MoSe2@g-C3N4 interface.

Covalent inorganic–organic hybrid frameworks (CIOFs) composed of inorganic heterocycles covalently linked to organic building blocks are a relatively unexplored and fertile area of research compared to the covalent organic frameworks. Herein, we report the selective light responsive CIOFs prepared by considering energy gaps (Egs) of the inorganic heterocycle (P3N3Cl6) (Eg 5.745 eV), organic building block (4,4-sulfonyldiphenol) (Eg 4.05 eV), and triazine heterocycle (1,3,5-triazine-2,4,6-triamine) (Eg 4.79 eV) under mild reaction conditions (by P–O–C and P–NH–C bond formation). The morphology of CIOF-I (prepared from hexachlorocyclotriphosphazene and 4,4-sulfonyldiphenol) is micro-spherical (diameter, ca. 0.6–1 μm), whereas that of CIOF-II (prepared from hexachlorocyclotriphosphazene and 1,3,5-triazine-2,4,6-triamine) is micro-spherical (diameter, ca. 0.5–1 μm) as well as tubular. The X-ray diffraction (XRD) analysis showed that these CIOFs are amorphous in nature. The luminescence studies of both CIOFs have shown a selective response to different lights; when excited under UV light at a wavelength of 365 nm, the CIOFs showed cyan emission, while under visible region 420 nm and 546 nm excitations, the emission shifts to green and red, respectively. CIOF-I demonstrated maximum emission at 454 nm (Ex. 365 nm), 487 nm (Ex. 420 nm), and 708 nm (Ex. 546 nm), while CIOF-II exhibited maximum emission at 460 nm (Ex. 365 nm), 478 nm (Ex. 420 nm), and 604 nm (Ex. 546 nm). The density functional theory (DFT) studies were performed based on Gaussian 09 (B3LYP/6-311+G (d,p)) for the core structure of CIOFs’ HOMO and LUMO levels (CIOF-I −6.54 eV, −2.62 eV and CIOF-II −6.44 eV, −2.55 eV), and Egs (3.92 eV and 3.84 eV) which are in good agreement with the experimental values. The mechanism behind the demonstration of similar emission colors by two different chemical structures is also underpinned. The selective response towards different lights is ascribed to the aggregation/clustering-induced/triggered emission (AIE/CTE) and restricted rotation emission (RRE) due to the crosslinking of the wider energy gap inorganic heterocycle and organic linkers. This study may grab the attention of researchers to study the inorganic heterocycle centered selective light responsive materials due to their extensive application prospects.

The utilization of solar energy is an epitome towards water splitting for hydrogen generation and environmental remediation. For efficient use of solar energy, photocatalysts capable of light-harvesting, with appropriate band energetics, that are inexpensive, stable, and scalable, are desired. Herein, a prototypical cyclotriphosphazene (P3N3)-based covalent inorganic–organic hybrid framework (CIOF) is designed with highly crosslinked aggregation that can produce hydrogen fuel from photocatalytic water splitting, as well as the degradation of industrial waste-water pollutant (rhodamine B). The P3N3-CIOF was synthesized by the aggregation, self-assembly, and subsequent polycondensation of hexachlorocyclotriphosphazene, tris(4-hydroxyphenyl)ethane and pyridine, in one-pot under ultrasonication. Morphology and structure of the newly synthesized P3N3-CIOF are characterized through scanning electron microscopy, Fourier transform infrared spectroscopy, solid-state 31P and 13C nuclear magnetic resonance spectroscopy, X-ray photoelectron microscopy, UV-visible absorbance, photoluminescence, and micro-spectrophotometry. The P3N3-CIOF shows selective response to the UV-visible light by emitting bright green (Ex. 365 nm), yellow (Ex. 420 nm), and red (Ex. 546 nm) colors. Moreover, the onset bandgap (2.14 eV) and the potential of the conduction band (−0.26 eV) and valence band (+1.88 eV) straddle the potential range for photocatalytic water splitting and dye degradation. The as-synthesized P3N3-CIOF continuously produced hydrogen fuel (24.5 μmol g−1 h−1) during photocatalytic water splitting for a period of 16 h, using Pt (3 wt%) and triethanolamine as the co-catalyst and holes scavenger, respectively. It also showed photodegradation ability to rhodamine B as a proxy dye to industrial waste-water pollutants. The plausible photocatalytic mechanism is also proposed based on the energetics of the photogenerated excitons, and scavenging experiments. These findings exemplify a critical first step towards photocatalytic hydrogen generation and remediation of organic pollutants through P3N3-CIOF, as well as motivation to engineer new materials based on aggregation-induced phenomena.