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As one of the most promising photocatalysts for H2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H2 evolution rate of 752.9 µmol g-1 h-1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the SH bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H2 evolution activity.

RESUMEN

In the present work, a cobalt-doped carbon nitride nanotubes (Co-CNt) was synthesized via self-assembly process. Contributed to the narrow band gap, enlarged specific surface area and abundant active sites, Co-CNt has excellent photoelectric properties and superior performance than pristine CN in sulfisoxazole (SIZ) degradation under blue light irradiation, which achieved 100% removal within 40 min. Meanwhile, the system not only exhibited practical applicability by efficiently degrading SIZ, but also generating high levels of H2O2. Moreover, the Co-CNt/visible light system shows superior operability over a wide pH range, micro-concentration contaminants, various anions, water matrices and other sulfonamides with promising catalytic stability and applicability. The contribution of RSs in the degradation process were elucidated based on radical scavenging and spin-trapped tests, clarifying that O2·- and h+ majorly dominated the process. In addition, 4 probable degradation pathways of SIZ were provided and the generated intermediates' toxicity were evaluated. Overall, this study successfully synthesized a self-assembled 1D tubular photocatalyst with Co-doped and demonstrated the potential Co-CNt/visible light system for environmental remediation, providing a promising approach for the development of photocatalysis.

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Carbon nitride is an attractive non-metallic photocatalyst due to its small surface area, rapid electron-hole recombination, and low absorption of visible light. In this study, one-dimensional carbon nitride nanotubes were successfully synthesized by supramolecular self-assembly method for photocatalytic reduction of CO2 under mild conditions. The material demonstrates significantly improved CO2-to-CO activity compared to bulk carbon nitride under visible light irradiation, with a rate of 12.58 µmol g-1h-1, which is 3.37 times higher than that of pristine carbon nitride. This enhanced activity can be attributed to the abundant oxygen defects and nitrogen vacancies in the unique tubular carbon nitride structure, which results in the generation of more active sites and the efficient acceleration of the migration of photogenerated electron-hole pairs. Various characterizations collectively support the presence of these defects and vacancies. Moreover, in situ DRIFTS spectroscopy supported the proposed reaction mechanism for the photoreduction of CO2. This eco-friendly design approach provides novel insights into utilizing solar energy for the production of value-added products.

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The use of easily available solar energy to achieve pollutants efficient degradation and waste carbon resource CO2 utilization under mild conditions is highly desired. Herein, novel carbon vacancies enriched nanotubes graphitic carbon nitride (SCNT-500) has been successfully fabricated via melamine (MA) supramolecular hydrogen-bonded self-assembly in the presence of H2SO4. Pd NPs loaded carbon vacancies enriched carbon nitride nanotubes (Pd/SCNT-500) were used for photocatalytic chlorophenols hydrodechlorination and CO2 cycloaddition with styrene oxide. Up to 6.93 s-1 4-chlorophenol hydrodechlorination TOF and obviously improved CO2 cycloaddition efficiency could be realized with Pd/SCNT-500. The improved photocatalytic efficiency should be related to the morphology and carbon vacancies based Pd coordination environment optimization. Such as, the surface area increased nanotubes structure promoted light harvesting along with photoelectrons and holes generation; the carbon vacancies improved excited electrons capture, photoinduced carriers recombination inhibition along with substrates adsorption with electron rich Pd NPs. Mechanism studies not only demonstrated the important role of atomic hydrogen and Pd coordination environment optimization in the chlorophenols hydrodechlorination, but also confirmed the promotion ability of photogenerated electrons on CO2 cycloaddition.

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The increasingly electromagnetic wave (EMW) pollution has rendered the study and development of new, high-efficiency EMW absorbers a sought-after topic. In this study, graphite carbon nitride nanotubes/cobalt@carbon (GCNNs/Co@C) composites were fabricated using an in-situ synthesis method, which included facile grinding and carbonization pyrolysis. The synthesized GCNNs/Co@C composites exhibited a unique castor-fruit-like structure, that is, GCNNs formed an entwined three-dimensional (3D) network structure on the surface of cobalt@carbon (Co@C), which improved the EMW absorption properties of composites. The obtained GCNNs/Co@C composites exhibited excellent EMW absorption performance. For the fabricated GCNNs/Co@C composites, the minimum reflection loss (RLmin) value reached -63.90 dB at a thickness of 1.96 mm, and the effective absorption bandwidth (EAB, RL ≤  -10 dB) achieved 4.44 GHz at an ultra-thin thickness of 1.51 mm. The EAB covered the entire X and Ku bands (6.96-18.00 GHz) through thickness adjustment from 1.51 to 2.50 mm. Underlying EMW absorption mechanisms were briefly discussed. This study presents a novel design method to prepare light-weight and highly-efficient EMW absorbing absorbers.

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This work for the first time reports bimetallic Ni-Co and monometallic (Ni and Co) nanoparticles (NPs)-engineered carbon nitride nanotubes with nitrogen vacancies (V-CNNTs) for visible-light photocatalytic H2 generation application. The bimetallic Ni-Co NPs have an average size of less than 5 nm and are homogenously dispersed along the nanochannels of V-CNNTs. The composition of the bimetallic NPs plays an essential role to maximize photocatalytic activity. With the optimal Ni/Co atom ratio of 3:1, Ni-Co/V-CNNTs nanohybrids yielded a H2 production rate of 4.19 µmol/h, which is higher than those of monometallic counterparts and V-CNNTs. The intimately loaded Ni-Co NPs and incorporated nitrogen vacancies enhance the photocatalytic performance through extended light absorption, abundant active sites, strong metal-support interaction, and efficient charge carrier transfer along the axial direction. This study presents a stable and highly efficient hybrid as a promising photocatalyst for visible light photocatalytic H2 production through water splitting.

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The independent effect of nanotube surface chemistry and structure on the flow of water under nanoscale confinement is demonstrated in this paper for the first time via the synthesis of novel carbon nitride nanotube (CNNT) membranes. Using a combination of experiments and high-fidelity molecular dynamics (MD) simulations, it is shown here that the hydrophilization of the sp2 carbon structure, induced by the presence of the C-N bonds, decreases the pure water permeance in CNNTs when compared with pristine and turbostratic carbon nanotubes (CNTs). The MD simulations are based on a model true to the chemical structure of the synthesized nanotubes, built from spectroscopy measurements and calibrated potentials using droplet experiments. The effect on permeance is explained in terms of solid-liquid interactions at the nanotube wall with increased water viscosity and decreased surface diffusion near the CNNT wall, when compared to CNTs. A model directly linking the solid-liquid interactions to the water permeance is presented, showing good agreement with both experiments and MD simulations. This work opens the way to tailoring surface chemistry and structure inside nanotube membranes for a wide range of transport and separation processes.