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Indoor volatile formaldehyde is a serious health hazard. The development of low-temperature and efficient nonhomogeneous oxidation catalysts is crucial for protecting human health and the environment but is also quite challenging. Single-atom catalysts (SACs) with active centers and coordination environments that are precisely tunable at the atomic level exhibit excellent catalytic activity in many catalytic fields. Among two-dimensional materials, the nonmagnetic monolayer material g-C3N4 may be a good platform for loading single atoms. In this study, the effect of nitrogen defect formation on the charge distribution of g-C3N4 is discussed in detail using density functional theory (DFT) calculations. The effect of nitrogen defects on the activated molecular oxygen of Pt/C3N4 was systematically revealed by DFT calculations in combination with molecular orbital theory. Two typical reaction mechanisms for the catalytic oxidation of formaldehyde were proposed based on the Eley-Rideal (E-R) mechanism. Pt/C3N4-V3N was more advantageous for path 1, as determined by the activation energy barrier of the rate-determining step and product desorption. Finally, the active centers and chemical structures of Pt/C3N4 and Pt/C3N4-V3N were verified to have good stability at 375 K by determination of the migration energy barriers and ab initio molecular dynamics simulations. Therefore, the formation of N defects can effectively anchor single-atom Pt and provide additional active sites, which in turn activate molecular oxygen to efficiently catalyze the oxidation of formaldehyde. This study provides a better understanding of the mechanism of formaldehyde oxidation by single-atom Pt catalysts and a new idea for the development of Pt as well as other metal-based single-atom oxidation catalysts.

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Graphitic carbon nitrides (g-C3N4) possess various benefits as heterogeneous photocatalysts, including tunable bandgaps, scalability, and chemical robustness. However, their efficacy and ongoing advancement are hindered by challenges like limited charge-carrier separation rates, insufficient driving force for photocatalysis, small specific surface area, and inadequate absorption of visible light. In this study, boron dopants and nitrogen defects synergy are introduced into bulk g-C3N4 through the calcination of a blend of nitrogen-defective g-C3N4 and NaBH4 under inert conditions, resulting in the formation of BCN nanosheets characterized by abundant porosity and increased specific surface area. These BCN nanosheets promote intermolecular single electron transfer to the radical initiator, maintaining radical intermediates at a low concentration for better control of photoinduced atom transfer radical polymerization (photo-ATRP). Consequently, this method yields polymers with low dispersity and tailorable molecular weights under mild blue light illumination, outperforming previous reports on bulk g-C3N4. The heterogeneity of BCN enables easy separation and efficient reuse in subsequent polymerization processes. This study effectively showcases a simple method to alter the electronic and band structures of g-C3N4 with simultaneously introducing dopants and defects, leading to high-performance photo-ATRP and providing valuable insights for designing efficient photocatalytic systems for solar energy harvesting.

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Resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging in metal-sulfur batteries. Motivated by a theoretical prediction, herein, we strategically propose nitrogen-vacancy tantalum nitride (Ta3N5-x) impregnated inside the interconnected nanopores of nitrogen-decorated carbon matrix as a new electrocatalyst for regulating sulfur redox reactions in room-temperature sodium-sulfur batteries. Through a pore-constriction mechanism, the nitrogen vacancies are controllably constructed during the nucleation of Ta3N5-x. The defect manipulation on the local environment enables well-regulated Ta 5d-orbital energy level, not only modulating band structure toward enhanced intrinsic conductivity of Ta-based materials, but also promoting polysulfide stabilization and achieving bifunctional catalytic capability toward completely reversible polysulfide conversion. Moreover, the interconnected continuous Ta3N5-x-in-pore structure facilitates electron and sodium-ion transport and accommodates volume expansion of sulfur species while suppressing their shuttle behavior. Due to these attributes, the as-developed Ta3N5-x-based electrode achieves superior rate capability of 730 mAh g-1 at 3.35 A g-1, long-term cycling stability over 2000 cycles, and high areal capacity over 6 mAh cm-2 under high sulfur loading of 6.2 mg cm-2. This work not only presents a new sulfur electrocatalyst candidate for metal-sulfur batteries, but also sheds light on the controllable material design of defect structure in hopes of inspiring new ideas and directions for future research.

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Enhancing the sensitivity and selectivity of chemiluminescence (CL) sensors for detecting chemical species in complex samples poses a significant challenge in nanoparticle surface engineering. Graphitic carbon nitride (CN) shows promise but suffers from weak CL intensity and unknown luminescence mechanisms. In this study, we propose a nitrogen defect strategy to enhance the CL efficiency of europium-functionalized graphitic carbon nitride (Eu-CNNPs). By controlling the dosage of the europium modification, we can adjust the nitrogen defect content to reduce the energy gap and improve the CL performance. Remarkably, Eu-CNNPs with rich nitrogen defects exhibit strong chemiluminescence emission specifically for singlet oxygen (1O2) without responding to other reactive oxygen species (ROS). Building upon this finding, we developed a direct, selective, and sensitive CL sensing platform for 1O2 in PM2.5 and monitored 1O2 production in photosensitizers without interference from metal ions. Through extensive experiments, we attribute the 1O2-driven CL response to the presence of abundant nitrogen defects in the CN material, accelerating electron transfer and yielding a high generation of 1O2. Furthermore, chemiluminescence resonance energy transfer (CRET) between (1O2)2* (1O2 dimeric aggregate) and Eu-CNNPs contributes to strong CL emission. This work provides insights into enhancing the CL performance of CN and offers new possibilities for advancing the practical analysis of nanomaterials using the intriguing mechanism of nitrogen defects.

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The selective hydrogenation of alkynes is an important reaction; however, the catalytic activity and selectivity in this reaction are generally conflicting. In this study, ultrafine Pd nanoparticles (NPs) loaded on a graphite-like C3 N4 structure with nitrogen defects (Pd/DCN) are synthesized. The resulting Pd/DCN exhibits excellent photocatalytic performance in the transfer hydrogenation of alkynes with ammonia borane. The reaction rate and selectivity of Pd/DCN are superior to those of Pd/BCN (bulk C3 N4 without nitrogen defects) under visible-light irradiation. The characterization results and density functional theory calculations show that the Mott-Schottky effect in Pd/DCN can change the electronic density of the Pd NPs, and thus enhances the hydrogenation selectivity toward phenylacetylene. After 1 h, the hydrogenation selectivity of Pd/DCN reaches 95%, surpassing that of Pd/BCN (83%). Meanwhile, nitrogen defects in the supports improve the visible-light response and accelerate the transfer and separation of photogenerated charges to enhance the catalytic activity of Pd/DCN. Therefore, Pd/DCN exhibits higher efficiency under visible light, with a turnover frequency (TOF) of 2002 min-1 . This TOF is five times that of Pd/DCN under dark conditions and 1.5 times that of Pd/BCN. This study provides new insights into the rational design of high-performance photocatalytic transfer hydrogenation catalysts.

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The realization of solar-light-driven CO2  reduction reactions (CO2 RR) is essential for the commercial development of renewable energy modules and the reduction of global CO2 emissions. Combining experimental measurements and theoretical calculations, to introduce boron dopants and nitrogen defects in graphitic carbon nitride (g-C3 N4 ), sodium borohydride is simply calcined with the mixture of g-C3 N4 (CN), followed by the introduction of ultrathin Co phthalocyanine through phosphate groups. By strengthening H-bonding interactions, the resultant CoPc/P-BNDCN nanocomposite showed excellent photocatalytic CO2 reduction activity, releasing 197.76 and 130.32 µmol h-1  g-1 CO and CH4 , respectively, and conveying an unprecedented 10-26-time improvement under visible-light irradiation. The substantial tuning is performed towards the conduction and valance band locations by B-dopants and N-defects to modulate the band structure for significantly accelerated CO2 RR. Through the use of ultrathin metal phthalocyanine assemblies that have a lot of single-atom sites, this work demonstrates a sustainable approach for achieving effective photocatalytic CO2 activation. More importantly, the excellent photoactivity is attributed to the fast charge separation via Z-scheme transfer mechanism formed by the universally facile strategy of dimension-matched ultrathin (≈4 nm) metal phthalocyanine-assisted nanocomposites.

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Metal nitride complexes have recently been proposed as an efficient noble-metal-free catalyst for ammonia synthesis utilizing a dual active site concept. However, their high sensitivity to air and moisture has restricted potential applications. We report that their chemical sensitivity can be improved by introducing Al into the LaN lattice, thereby forming La-Al metallic bonds (La-Al-N). The catalytic activity and mechanism of the resulting TM/La-Al-N (TM=Ni, Co) are comparable to the previously reported TM/LaN catalyst. Notably, the catalytic activity did not degrade after exposure to air and moisture. Kinetic analysis and isotopic experiment showed that La-Al-N is responsible for N2 absorption and activation despite substantial Al being introduced into its lattice because the local coordination of the lattice N remained largely unchanged. These findings show the effectiveness of metallic bond formation, which can support the chemical stability of rare-earth nitrides with retention of catalytic functionality.

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Post thermal treatment of bulk graphitic carbon nitride (g-C3N4) by ammonia gas acts as a significant structure regulation approach, while pure ammonia-assisted g-C3N4 synthesis from precursors like melamine is rarely investigated. Here we prove the synthesis of N-defects abundant carbon nitride nanosheets (ACN) through a one-pot thermal polymerization of melamine in pure ammonia gas, for photocatalytic organic pollutant removal in water and H2 evolution applications. Compared to bulk g-C3N4 (BCN), ACN-550 (ACN prepared at 550 °C) exhibited thin-layered porous morphology with higher surface area and abundant N defects, resulting in wider distribution of active sites. Moreover, the abundant N defects in the heptazine heterocycle structure could change the electronic structure of g-C3N4, leading to more efficient transport of photogenerated charge carriers and enhanced photoreduction potential, which gives rise to notable improvement activities in photocatalytic reaction. With superoxide ion radical and photoinduced holes as the predominant reactive species, ACN-550 realized efficient photocatalytic bisphenol A (BPA) degradation, which is 1.6- and 4.7-fold high over commercial TiO2 (P25) and BCN, respectively. ACN-550 exhibited excellent reusability and stability in five consecutive photocatalytic BPA degradation tests. In photo-reductive H2 production system by ACN-550, 761.8 ± 4.3 µmol/h/g H2 was produced, which was 11.6-fold as high as that by BCN.

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In this study, with thiourea and 3-aminopyridazine as precursors, the graphite-phase carbon nitride (ACN-x) with nitrogen defects and sponge structure is prepared via the introduction of the benzene-like ring structure of pyridazine replacing a "melem" group through hydrothermal procedure combined with calcination. It is made possible by the attraction of three hydrogen bond receptors for 3-aminopyrazine to lone pair electrons on the "melem" molecule. The remarkable extensively photocatalytic activity can be attributed to three effects of the introduction of 3-aminopyridazine: (i)formation of nitrogen defects between adjacent tri-s-triazine groups; (ii)formation of effective charge transfer channels within the tri-s-triazine group; (iii)the spongy structure exposed abundant amino groups(-NH3) at edge sites, combining with the internal amino group and as hole stabilizer to prolong the excited state life of photocatalyst. The photogenerated carrier migration and separation efficiency improved effectively through the tuning synergy. As a result, ACN-x exhibits excellent photocatalytic activity, with hydrogen production efficiency of up to 11331.74 µmol g-1 h-1, which is approximately 94.5 times that of the pristine g-C3N4 (119.88 µmol g-1 h-1). The degradation constants of TC and RhB are 0.0498min-1 and 0.129min-1, which are 3.32 and 6.35 times of the pristine g-C3N4, respectively. The TC degradation in different initial concentrations, pH, dissolved organic matter concentrations, and water sources is conducted to prove the environmental adaptability of the ACN-x system. The mechanism of the system indicates that ·O2- plays an important role, and the ·OH and h+ play a minor role in the TC photocatalytic degradation. Finally, the TC degradation possible pathway is proposed.

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Precisely tailoring the nitrogen defects has been verified to be a promising approach for promoting the photocatalytic efficiency of C3N4. Herein, two-coordinated-N vacancies are selectively introduced into the C3N4 framework by a facile Cl- modification method, whereas its concentration can be facilely tuned by varying Cl- usage in the process of thermal polymerization. Impressively, the optimal defective C3N4 (20 mg) exhibited superior hydrogen and oxygen evolution rates of 48.2 and 21.8 µmol h-1, respectively, in photocatalytic overall water splitting and an apparent quantum efficiency of 6.9% at 420 nm, the highest of reported single-component C3N4 photocatalysts for overall water splitting. Systematic studies including XPS, DFT simulations, and NEXAFS reveal that Cl- modification preferentially facilitates the introduction of two-coordinated-N vacancies through tuning the formation energy and promotes charge carrier separation efficiency, thereby greatly enhancing the photocatalytic efficiency. This work allows for a viable approach to rationally designing defective C3N4 for efficient photocatalysis.

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The promising solar irradiated photocatalyst by pairing of bismuth oxide quantum dots (BQDs) doped TiO2 with nitrogen doped graphene oxide (NGO) nanocomposite (NGO/BQDs-TiO2) was fabricated. It was used for degradation of organic pollutants like 2,4-dichlorophenol (2,4-DCP) and stable dyes, i.e. Rhodamine B and Congo Red. X-ray diffraction (XRD) profile of NGO showed reduction in oxygenic functional groups and restoring of graphitic crystal structure. The characteristic diffraction peaks of TiO2 and its composites showed crystalline anatase TiO2. Morphological images represent spherical shaped TiO2 evenly covered with BQDs spread on NGO sheet. The surface linkages of NO-O-Ti, C-O-Ti, Bi-O-Ti and vibrational modes are observed by Fourier transform infrared spectroscopy (FTIR) and Raman studies. BQDs and NGO modified TiO2 results into red shifting in visible region as studied in diffused reflectance spectroscopy (DRS). NGO and BQDs in TiO2 are linked with defect centers which reduced the recombination of free charge carriers by quenching of photoluminescence (PL) intensities. X-ray photoelectron spectroscopy (XPS) shows that no peak related to C-O in NGO/BQDs-TiO2 is observed. This indicated that doping of nitrogen into GO has reduced some oxygen functional groups. Nitrogen functionalities in NGO and photosensitizing effect of BQDs in ternary composite have improved photocatalytic activity against organic pollutants. Intermediate byproducts during photo degradation process of 2,4-DCP were studied through high performance liquid chromatography (HPLC). Study of radical scavengers indicated that O2·- has significant role for degradation of 2,4-DCP. Our investigations propose that fabricated nanohybrid architecture has potential for degradation of environmental pollutions.

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Hexagonal boron nitride (h-BN) has lately received great attention in the oxidative dehydrogenation (ODH) reaction of propane to propylene for its extraordinary olefin selectivity in contrast to metal oxides. However, high crystallinity of commercial h-BN and elusive cognition of active sites hindered the enhancement of utilization efficiency. Herein, four kinds of plasmas (N2 , O2 , H2 , Ar) were accordingly employed to regulate the local chemical environment of h-BN. N2 -treated BN exhibited a remarkable activity, i.e., 26.0 % propane conversion with 89.4 % selectivity toward olefins at 520 °C. Spectroscopy demonstrated that "three-boron center" N-defects in the catalyst played a pivotal role in facilitating the conversion of propane. While the sintering effect of the "BOx " species in O2 -treated BN, led to the suppressed catalytic performance (12.4 % conversion at 520 °C).

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Constructing bulk defects and doping are feasible ways to essentially narrow the band gap and improve the light absorption of photocatalysts. Herein, inspired by bread foaming, the foaming agent azoformamide or azodicarbonamide (AC) was introduced during the thermal polymerization of urea. In the polymerization process, a large number of bubbles produced by AC decomposition seriously interfered with the polymerization of urea, resulting in the breaking of the hydrogen bonds and van der Waals interaction in carbon nitride, distortion of its structure, and partial oxidation, thus forming a series of porous carbon nitrides U/ACx (x is the ratio of AC to urea; where x = 0.25, 0.5, and 1) with bulk N defects and O doping. Its band gap was reduced to 1.91 eV and the absorption band edge was greatly extended to 650 nm. The optimal U/AC0.5 exhibits the highest visible light photocatalytic hydrogen production rate of about 44.7 µmol·h-1 (10 mg catalysts) and shows superior photocatalytic performance for the oxidation of diphenylhydrazine to azobenzene, with conversion and selectivity of almost 100%, and is one of the most active defective carbon nitrides, especially under long-wavelength (λ ≥ 550 nm) light irradiation. It paves the way for the design of highly efficient and wide-spectral-response photocatalysts.

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Defects are significant for graphitic carbon nitride (g-C3N4, CN) in photocatalytic applications. Defective CN not only accelerate charge separation but also extend spectral response. Engineering carbon or nitrogen defects in CN has been achieved by variety of strategies, but it is still a long-term interest to develop a simple and controllable route for engineering defects in CN. Herein, we present tuning the nitrogen defects in CN by either changing the heating rate or prolonging the pyrolysis time during polymerization melamine sulfate. It was found that either lower heating rate or longer pyrolysis time lead to the formation of more N vacancies and suspended terminal amino. As a result, an optimal photocatalytic H2 yield rate (λ > 420 nm) of 905 µmol g-1 h-1 was reached, which was 2 times higher than that of CN prepared with a heating rate of 1 °C/min and pyrolysis at 600 °C for 4 h.

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Graphitic carbon nitride (CN) is considered as a promising photocatalyst for solar energy conversion. However, low specific surface area and fast electrons and holes recombination restrict the photocatalytic applications of CN material. Herein, a nitrogen defect-rich and highly porous CN nanostructure (CN-LT) was prepared by combining two strategies, i.e., LiOH treatment and heat etching. The as-prepared nitrogen defect-rich porous CN-LT not only has a larger specific surface area, as compared with pristine CN, but also the photogenerated electron-hole separation was boosted remarkably. Using Pt as a co-catalyst and lactic acid aqueous solutions as sacrificial reagent under visible light irradiation (λ > 400 nm), the hydrogen evolution reaction (HER) rate for CN-LT (1.54 mmol h-1 g-1) was 19.25 times higher than that for pristine CN (0.08 mmol h-1 g-1). While subjecting pristine CN to heat etching under the same experimental conditions, excepting the use of LiOH (CN-T), an increase in HER rate of 7.5 times was obtained. Our current study may shed more light on the enhancement of the photocatalytic activity of bulk CN materials by altering their microstructure.

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A porous g-C3N4 nanosheet containing nitrogen defects (D-g-C3N4) was synthesized by using a one-step polymerization process in an atmosphere produced via the decomposition of ammonium persulfate. The photocatalytic removal rate of D3-g-C3N4 for meropenem (MER) is 7.45-fold higher than the one of a conventional g-C3N4 sample. The sample mineralization increases from 27% to 52% when the defects are generated. The position of the N defects was inferred via XPS, element analysis and ESR. The introduction of the N2C defects leads to the formation of a midgap state that suppresses the photoexcited carrier recombination. In addition, several environmental factors were simulated during the MER degradation including the initial concentration of MER, of humic acid (HA), and of the common anions and cations. The analysis of the Fukui function combined with LC-Q-TOF-MS predicted the probable degradation path of MER. Its main channel includes the breaking of the ß-lactam ring and of the C-S bond, and the shedding of the carboxyl group and the amino group. Moreover, the toxicity of the intermediates was acquired via USEPA.

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The porous graphitic carbon nitride (g-C3N4) with nitrogen defects and cobalt-nitrogen (CoN) bonds (g-C3N4-Co-K) is prepared by controllable copolymerization of melamine with KOH and Co(NO3)2·6H2O. The method not only provides g-C3N4 with porous structure and CoN bonds that accelerate photoexcited carrier transfer and endow numerous active sites, but also redshifts the g-C3N4 absorption edge into near-infrared (NIR) light region through the introduction of nitrogen defects and thus is suitable for H2 evolution. The g-C3N4-Co-K exhibits significantly superior photocatalytic hydrogen generation performance (808 µmol h-1 g-1) under simulated solar light irradiation, about 15.5 times higher than pure g-C3N4, about 5.2 times higher than g-C3N4 with CoN bonds (g-C3N4-Co), and about 2.1 times higher than g-C3N4 with nitrogen defects (g-C3N4-K). Interestingly, it is for the first time revealed that the synergistic effect of nitrogen defects and CoN bonds result in enhanced H2 generation activity (470 µmol h-1 g-1) under NIR light irradiation.

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Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C3 N4 ) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C3 N4 . The resultant boron-doped and nitrogen-deficient g-C3 N4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h-1 g-1 , much higher than previously reported g-C3 N4 . It is well evidenced that with conduction and valence band positions substantially and continuously tuned by the simultaneous introduction of boron dopants and nitrogen defects into g-C3 N4 , the band structures are exceptionally modulated for both effective optical absorption in visible light and much increased driving force for water oxidation. Moreover, the engineered electronic structure creates abundant unsaturated sites and induces strong interlayer C-N interaction, leading to efficient electron excitation and accelerated charge transport. In the present work, a facile approach is successfully demonstrated to engineer the electronic structures and the band structures of g-C3 N4 with simultaneous introduction of dopants and defects for high-performance photocatalytic oxygen evolution, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.

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Graphitic carbon nitride with nitrogen defects (g-C3N4-x) is prepared by a facile and effective solid-state chemical reduction technique at mild temperature conditions. The cyano groups and nitrogen vacancies, as evidenced by electron paramagnetic resonance (EPR), X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectra (FTIR) and Solid-state 13C MAS NMR spectra, are controllable via adjusting chemical reduction temperature. Comparing to the pristine g-C3N4, the as-prepared g-C3N4-x shows much enhanced photocatalytic H2 evolution activity under visible-light irradiation. The maximum H2 evolution rate of 3068 µmol·g-1·h-1 is achieved with g-C3N4-x after chemical reduction treatment at 400 °C for 1 h, which is 4.85 times that of the pristine g-C3N4. Moreover, excellent reusability and storage stability have been shown by this photocatalyst as well. It is discovered that nitrogen defects can result in both the up-shift of the valance band and the down-shift of the conduction band, which benefit the absorption of longer wavelength photons and trapping of the photoinduced electrons, therefore reducing the recombination losses of the generated carriers. It is because of this improved visible-light absorption and charge carrier separation, g-C3N4-x displays better visible-light photocatalytic activity compared to the pristine g-C3N4. It is then concluded that the synthetic strategy presented here represents a straightforward and efficient way to synergistically optimize the chemical composition, optical response, and photocatalytic characteristics of g-C3N4-based photocatalysts.

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Holey defective g-C3 N4 photocatalysts, which are easily prepared via a novel photoassisted heating process, are reported. The photoassisted treatment not only helps to create abundant holes, endowing g-C3 N4 with more exposed catalytic active sites and crossplane diffusion channels to shorten the diffusion distance of both reactants from the surface to bulk and charge carriers from the bulk to surface, but also introduces nitrogen vacancies in the tri-s-triazine repeating units of g-C3 N4 , inducing the narrowing of intrinsic bandgap and the formation of defect states within bandgap to extend the visible-light absorption range and suppress the radiative electron-hole recombination. As a result, the holey defective g-C3 N4 photocatalysts show much higher photocatalytic activity for H2 O2 production with optimized enhancement up to ten times higher than pristine bulk g-C3 N4 . The newly developed synthetic strategy adopted here enables the sufficient utilization of solar energy and shows rather promising for the modification of other materials for efficient energy-related applications.