Highly dispersed copper cobalt oxide nanoclusters decorated carbon nitride with efficient heterogeneous interfaces for enhanced H2 evolution

Plasma-assisted fabrication of ultra-dispersed copper oxides in and on C-rich carbon nitride as functional composites for the oxygen evolution reaction

Significant efforts have been continuously devoted to the mastering of green catalysts for the oxygen evolution reaction (OER), whose sluggish kinetics prevents a broad market penetration of water splitting as a sustainable route for large-scale hydrogen production. In this extensive scenario, carbon nitride (CN)-based systems are in focus thanks to their favorable characteristics, and, whereas graphitic CN has been largely investigated, the potential of amorphous carbon nitride (a-CNx) systems remains almost entirely unexplored. In this regard, our study presents a novel two-step plasma-assisted route to a-CNx systems comprising ultra-dispersed, i.e. "quasi-atomic" CuxO (x = 1, 2). The target materials were fabricated using an original strategy consisting in the magnetron sputtering of a-CNx on conducting glasses at room temperature, followed by functionalization with low CuxO amounts by radio frequency (RF)-sputtering, and final annealing under an inert atmosphere. The tailoring of the CuxO co-catalyst content and spatial dispersion, as well as the overall composite features as a function of preparative conditions, enabled a direct modulation of the resulting OER performances, rationalized based on the formation of p-n CuxO/a-CNx heterojunctions. The amenable and scalable synthesis approach underscores the practicality of this method to develop (photo)electrocatalysts synergistically integrating the advantages of both constituents, yielding low-cost, green, and stable functional platforms that could contribute to the broader adoption of sustainable energy solutions.

Photodegrading rhodamine B dye with cobalt ferrite-graphitic carbon nitride (CoFe2O4/g-C3N4) composite

The present research utilizes a sol-gel approach to create a CoFe2O4/g-C3N4 nanocomposite (NC) and explored several analytical methods to evaluate physical, chemical and optical based characteristics via XRD, FTIR, UV-vis, SEM/EDS and XPS for the prepared pure CoFe2O4, g-C3N4, and CoFe2O4/g-C3N4 NC. The XRD results show that the prepared g-C3N4, CoFe2O4, exhibits hexagonal and cubic phases respectively, whereas the g-C3N4/CoFe2O4 NC exhibit mixing of two phases. The energy band gaps for pure g-C3N4, CoFe2O4 and g-C3N4/CoFe2O4 NC values are viz., 2.75, 1.3, and 2.4 eV. As photocatalysts, synthesized materials were utilized for the decomposition of Rhodamine-B (RhB) dye. Finally, the CoFe2O4/g-C3N4 NC showed good performance of photocatalysis for RhB dye disintegration under the stimulus of visible light. According to the induced visible light, the rate at which the photocatalytic degradation occurs for the CoFe2O4/g-C3N4 NC was found to be 57% in 120 min and this is greater when compared with pure catalysts like CoFe2O4 (28%) and g-C3N4 (10%). These outcomes suggest that the prepared NC have efficiently worked during the photocatalytic process compared with its pure materials.

Facile synthesis of NiAl2O4/g-C3N4 composite for efficient photocatalytic degradation of tetracycline

Designing high-efficiency photocatalysts responsive to visible light is important for the degradation of antibiotics in water. Heterojunction engineering is undoubtedly an effective strategy to improve the photocatalytic performance. In this work, spinel-type metal oxides (NiAl₂O₄, NAO) are synthesized by a simple sol-gel and calcination process. After compounding graphitic carbon nitride (g-C₃N₄), NAO/g-C₃N₄ heterojunction is obtained, which then is used as the photocatalyst for tetracycline hydrochloride (TC). The effects of photocatalyst dosage, the initial concentration of TC, and solution pH on photodegradation performance are systematically studied. The removal rate of TC on NAO/g-C₃N₄ reach up to ∼90% after visible light irradiation for 2 hr and the degradation rate constant is ∼7 times, and ∼32 times higher than that of pure NAO and g-C₃N₄. The significantly improved photocatalytic activity can be attributed to the synergistic effect between well matched energy levels in NAO/g-C₃N₄ heterojunctions, improvement of interfacial charge transfer, and enhancement of visible light absorption. This study provides a way for the synthesis of efficient photocatalysts and an economic strategy for removing antibiotics contamination in water.

Enhanced stability of sub-nanometric iridium decorated graphitic carbon nitride for H2 production upon hydrous hydrazine decomposition

Stabilizing metal nanoparticles is vital for large scale implementations of supported metal catalysts, particularly for a sustainable transition to clean energy, e.g., H₂ production. In this work, iridium sub-nanometric particles were deposited on commercial graphite and on graphitic carbon nitride by a wet impregnation method to investigate the metal-support interaction during the hydrous hydrazine decomposition reaction. To establish a structure-activity relationship, samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic performance of the synthesized materials was evaluated under mild reaction conditions, i.e. 323 K and ambient pressure. The results showed that graphitic carbon nitride (GCN) enhances the stability of Ir nanoparticles compared to graphite, while maintaining remarkable activity and selectivity. Simulation techniques including Genetic Algorithm geometry screening and electronic structure analyses were employed to provide a valuable atomic level understanding of the metal-support interactions. N anchoring sites of GCN were found to minimise the thermodynamic driving force of coalescence, thus improving the catalyst stability, as well as to lead charge redistributions in the cluster improving the resistance to poisoning by decomposition intermediates.

CuS/Ag2O nanoparticles on ultrathin g-C3N4 nanosheets to achieve high performance solar hydrogen evolution

Ternary heterostructures play a crucial role in improving the separation of charge carriers and fast surface reaction kinetics, which in turn helps in understanding the effective photocatalytic water splitting performance. Herein, CuS/Ag₂O nanoparticles were presented on a graphitic carbon nitride (g-C₃N₄) surface to obtain CuS/Ag₂O/g-C₃N₄ material using facile hydrothermal and precipitation methods. Structural and morphological studies confirmed the presence of ternary nanostructures comprising CuS, Ag₂O, and g-C₃N₄ with nanoparticle and nanosheet morphologies. The as-synthesized CuS/Ag₂O/g-C₃N₄ exhibited a remarkable photocatalytic H₂ production of 1752 µmol.h^-1.g^-1_cat, which is considerably superior than those of CuS and g-C₃N₄. The improved H₂ production performance which is due to the effective interfacial CuS/Ag₂O/g-C₃N₄ heterojunction interface and superior hole (h⁺) trapping capability of the CuS at the CuS/Ag₂O/g-C₃N₄ interface. This can efficiently enhance the lifetime of photoexcited charge carriers and enhance the electron density for the production of H₂. The optimum CuS/Ag₂O/g-C₃N₄ heterostructure remained stable after 8 successive experimental cycles, although with a slight change in the H₂ production rate. Therefore, this study offers a novel approach to exploit the efficacy through the synergetic effect of integrating CuS as the photocatalyst and Ag₂O as the visible sensitizer, thus proposing a viable strategy of using earth-abundant material to enhance the conversion of solar energy to fuel.

Recent advances in Co-based co-catalysts for efficient photocatalytic hydrogen generation

Recent progress in photocatalytic hydrogen generation reaction highlights the critical role of co-catalysts in enhancing the solar-to-fuel conversion efficiency of diverse band-matched semiconductors. Because of the compositional flexibility, adjustable microstructure, tunable crystal phase and facet, cobalt-based co-catalysts have stimulated tremendous attention as they have high potential to promote hydrogen evolution reaction. However, a comprehensive review that specifically focuses on these promising materials has not been reported so far. Therefore, this present review emphasizes the recent progress in the pursuing of highly efficient Co-based co-catalysts for water splitting, and the advances in such materials are summarized through the analysis of structure-activity relationships. The fundamental principles of photocatalytic hydrogen production are profoundly outlined, followed by an elaborate discussion on the crucial parameters influencingthe reaction kinetics. Then, the co-catalytic reactivities of various Co-based materials involving Co, Co oxides, Co hydroxides, Co sulfides, Co phosphides and Co molecular complexes, etc, are thoroughly discussed when they are coupled with host semiconductors, with an insight towards the ultimateobjective of achieving a rationally designed photocatalyst for enhancing water splitting reaction dynamics. Finally, the current challenge and future perspective of Co-based co-catalysts as the promising noble-metal alternative materials for solar hydrogen generation are proposed and discussed.

Highly efficient photocatalytic H2 evolution over NiCo2S4/Mn0.5Cd0.5S: Bulk twinned homojunctions and interfacial heterojunctions

A twinned Mn_0.5Cd_0.5S (T-MCS) homojunction, consisting of wurtzite and zinc-blende Mn_0.5Cd_0.5S with different energy band structures, was fabricated using a facile hydrothermal method, resulting in the formation of a type-II bulk phase twinned homojunction. Furthermore, NiCo₂S₄ nanoparticles were deposited on the surface of T-MCS to form a surface heterojunction. The activities of T-MCS and NiCo₂S₄/T-MCS were tested in the photocatalytic H₂ evolution reaction. T-MCS exhibits a superior H₂ evolution rate of 61.4 mmol∙g^-1∙h^-1 under visible light (λ > 420 nm) irradiation owing to faster bulk phase charge separation, which is 8.2 and 1.9 times higher than those of wurtzite and zinc-blende Mn_0.5Cd_0.5S, respectively. Moreover, NiCo₂S₄ can facilitate interfacial electron transfer and can lower the H₂ evolution overpotential; the H₂ evolution rate is boosted to 127.3 mmol∙ g^-1∙h^-1 with an apparent quantum yield (AQY) of 23.4% with irradiation of 2 wt%-NiCo₂S₄/T-MCS under 400 ± 7.5 nm light. This work demonstrates that bulk phase twinned homojunctions and a surface heterojunction can combine to promote bulk and interfacial charge transfer and separation, simultaneously improving the kinetics of photocatalytic H₂ evolution.

5,10,15,20-tetrakis (4-carboxyl phenyl) porphyrin-functionalized urchin-like CuCo2O4 as an excellent artificial nanozyme for determination of dopamine

Urchin-like peroxidase mimics 5,10,15,20-tetrakis (4-carboxyl phenyl) porphyrin-functionalized CuCo2O4 nanospheres (Por-CuCo2O4) has been fabricated as an excellent visual biosensor. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) have been employed to characterize the composition, morphologies, and elemental analysis of the as-synthesized Por-CuCo2O4. The catalytic activity of Por-CuCo2O4 was evaluated by the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) with the aid of H2O2, which exhibited a visual blue change with an absorption maximum at 652 nm for only 10 s. The peroxidase-like behaviors of Por-CuCo2O4 conformed to the Michaelis-Menten equation. Electrochemistry, radical scavenger, and fluorescence probe experiments verified that electron transfer, •O2- radicals, and holes (h+) are the important factors during the catalytic oxidation of TMB. Based on the inhibition of dopamine (DA) on TMB oxidation, the Por-CuCo2O4-based colorimetric biosensor has been successfully constructed for sensitive determination of DA witha detection limit (LOD) of 0.94 μΜ. In addition, colorimetry was validated to detect DA in serum samples with high sensitivity and good selectivity. 5,10,15,20-tetrakis (4-carboxyl phenyl) porphyrin-functionalized urchin-like CuCo2O4 (Por-CuCo2O4) with excellent peroxidase activity, ascribed to the synergistic effect between •O2- radicals and holes (h+). A fast colorimetric sensor on the basis of Por-CuCo2O4 has been constructed to quantitatively determine dopamine concentration in human serums.

Defect Induced Polarization Loss in Multi-Shelled Spinel Hollow Spheres for Electromagnetic Wave Absorption Application

Defect engineering is an effective approach to manipulate electromagnetic (EM) parameters and enhance absorption ability, but defect induced dielectric loss dominant mechanism has not been completely clarified. Here the defect induced dielectric loss dominant mechanism in virtue of multi-shelled spinel hollow sphere for the first time is demonstrated. The unique but identical morphology design as well as suitable composition modulation for serial spinels can exclude the disturbance of EM wave dissipation from dipolar/interfacial polarization and conduction loss. In temperature-regulated defect in NiCo2O4 serial materials, two kinds of defects, defect in spinel structure and oxygen vacancy are detected. Defect in spinel structure played more profound role on determining materials' EM wave dissipation than that of oxygen vacancy. When evaluated serial Co-based materials as absorbers, defect induced polarization loss is responsible for the superior absorption performance of NiCo2O4-based material due to its more defect sites in spinel structure. It is discovered that electron spin resonance test may be adopted as a novel approach to directly probe EM wave absorption capacities of materials. This work not only provides a strategy to prepare lightweight, efficient EM wave absorber but also illustrates the importance of defect engineering on regulation of materials' dielectric loss capacity.

Plasmonic quaternary heteronanostructures (HNSs) for improved solar light utilization, spatial charge separation, and stability in photocatalytic hydrogen production

Recently, the frenetic development of stable quaternary material with a wide range of solar energy absorption and separation of charge carrier has emerged as a favorable material for the solar-to-hydrogen conversion. In this work, quaternary CuS-AgVO₃/Ag-TNR heteronanostructures (HNSs) synthesized by an ultra-sonication method for stabilized solar light photocatalytic hydrogen production in glycerol-water mixture. Among the prepared photocatalysts, the 1 wt% CuS-AgVO₃/Ag-TNR HNS produced the highest H₂ activity (756 µmol/g), approximately 84 times greater than the TNR due to higher charge separation, excellent conductivity, plasmonic resonance effect, and electron-storing capacity. Interestingly, the accelerated charge transfer pathway through the Schottky junction between the AgVO₃ and Ag to the conduction band of the TNR and thereafter to the electron acceptor of CuS for the reduction of H⁺ ions to H₂. Additionally, a possible photocatalytic mechanism of CuS-AgVO₃/Ag-TNR HNS for improved H₂ production was proposed based on the results obtained by various characterization techniques. Therefore, present research work explores the new insights to design high-performance CuS-AgVO₃/Ag-TNR HNS material for the conversion of clean renewable H₂ energy for the futuristic transport applications.

Enhancement of the photocatalytic synchronous removal of Cr(vi) and RhB over RP-modified flower-like SnS2

Although photocatalysis is frequently employed to remove various pollutants in water, it still suffers from low efficiency due to the rapid recombination of photogenerated electrons and holes. In this study, a red phosphorus/tin disulfide (RP/SnS₂) composite photocatalyst is fabricated by loading nano-sized RP on flower-like SnS₂ films with a facile hydrothermal method. It is noteworthy that the 2D heterojunction formed between SnS₂ and RP provided channels for the rapid transfer of photon-generated carriers and their effective separation. Furthermore, the separated electrons can react with absorbed O₂ for the generation of superoxide radicals (˙O₂ ^-), thereby impacting the photocatalytic degradation oxidation reaction. The application of photocatalytic synchronous removal of Cr(vi) and RhB over RP/SnS₂ was implemented first. Compared with pristine SnS₂, the photocatalytic degradation activity of Cr(vi) and RhB over the RP/SnS₂ composite was significantly enhanced and the kinetic rate constant reached 8.2, which is 10.8 times that of pristine SnS₂. Moreover, the hybrid photocatalysts exhibited prominent reusability and stability. Therefore, a photocatalytic degradation mechanism and pathway of carriers are proposed in the study. Furthermore, it is considered that the present study is a promising method in the treatment of wastewater by photocatalysis.