Amorphous g-C3N4 Research Articles

3D lithiophilic collector coated by amorphous g-C3N4 enabling Ultra-Stable cycling Li metal batteries

Lithium metal batteries (LMB) are thought of the most promising candidates for the next generation of high energy density batteries, but the problems of interface instability and uncontrollable dendrite growth are key constraints to the commercial application. Herein, we constructed an amorphous graphitic carbon nitride (g-C3N4) “outerwear” modified lithiophilic 3D Au/CoO nanoarray matrix (CACM) as a multifunctional dual-layer host, achieving dendrite-free and cycling stabilized Li metal anode. The density functional theory (DFT) calculations show that the reaction between CACM and Li atoms has a strong binding energy and a large amount of charge transfer. The lithiophilic 3D host induces Li metal uniform deposition with a low nucleation barrier within the 3D skeleton. The amorphous g-C3N4 “outerwear” can effectively avoid direct contact between the electrolyte and Li and reduce the irreversible side reaction. Meanwhile, the g-C3N4 layer has abundant Li ion transport channels, which facilitated fast Li+ transfer and modulate the ion concentration over the anode surface. Thus, the half-cell equipped with the CACM electrode has ultra-high cyclic stability, maintaining a CE value of 99.6 % over 230 cycles at 1 mA cm−2 with 1 mAh cm−2. The symmetric-cell can maintain a low overpotential stable run 1300 cycles at 10 mA cm−2. Similarly, the full cell also showed outstanding long-term cycle stability (capacity maintained at 96.3 % after 400 cycles at 1C) and superior rate capability. The in-situ visualization cell test and ex-situ SEM also demonstrated that the multifunctional host inhibits volume expansion and the dendritic growth of Li.

W18O49/crystalline g-C3N4 layered heterostructures with full solar energy harvesting towards efficient H2O2 generation and NO conversion

The photocatalytic performance of graphitic carbon nitride (g-C3N4) heterostructures related to the charge carrier separation and transport efficiency is often governed by the interfaces. Herein, in-situ growth of W18O49 nanobelts is attained on amorphous and crystalline g-C3N4 nanosheets to study the effects of the interfaces on photocatalytic oxidation activities. The horizontal growth of W18O49 on g-C3N4 nanosheets is the key in formation of two dimensional (2D)/2D W18O49/g-C3N4 heterostructures. The growth of W18O49 nanobelts on crystalline g-C3N4 nanosheets shows well-developed interfaces (sample W18O49-CCN) in comparison with heterostructures constructed using amorphous g-C3N4 base (sample W18O49-ACN). Characterizations on the structure, components, and properties of the samples demonstrate that these heterostructures reveal extended photo-absorption in visible to near infrared region, with sample W18O49-CCN showing much higher photogenerated charge carrier separation and transport efficiency. A H2O2 evolution rate of 5550 µMg−1h−1 is observed for sample W18O49-CCN under full solar-spectrum illumination (and 398 µMg−1h−1 observed for pristine crystalline g-C3N4), which is ∼ 2.4 times of that of sample W18O49-ACN prepared using amorphous g-C3N4. In addition, a NO removal rate of 72.1% is observed for sample W18O49-CCN with a NO2 selectivity of 6.2%. These results provide inspiration for construction of g-C3N4 homojunctions for practical photo-redox reaction applications.

Electrostatic Self-Assembled Synthesis of Amorphous/Crystalline g-C3N4 Homo-Junction for Efficient Photocatalytic H2 Production with Simultaneous Antibiotic Degradation.

g-C3N4 has been regarded as a promising photocatalyst for photo-reforming antibiotics for H2 production but still suffers from its high charge recombination, which has been proven to be solvable by constructing a g-C3N4 homo-junction. However, those reported methods based on uncontrollable calcination for preparing a g-C3N4 homo-junction are difficult to reproduce. Herein, an amorphous/crystalline g-C3N4 homo-junction (ACN/CCN) was successfully synthesized via the electrostatic self-assembly attachment of negatively charged crystalline g-C3N4 nanorods (CCN) on positively charged amorphous g-C3N4 sheets (ACN). All the ACN/CCN samples displayed much higher photo-reforming of antibiotics for H2 production ability than that of pristine ACN and CCN. In particular, ACN/CCN-2 with the optimal ratio exhibited the best photocatalytic performance, with a H2 evolution rate of 162.5 μmol·g-1·h-1 and simultaneous consecutive ciprofloxacin (CIP) degradation under light irradiation for 4 h. The UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and electrochemical results revealed that a homo-junction is formed in ACN/CCN due to the difference in the band arrangement of ACN and CCN, which effectively suppressed the charge recombination and then led to those above significantly enhanced photocatalytic activity. Moreover, H2 was generated from the water reduction reaction with a photogenerated electron (e-), and CIP was degraded via a photogenerated hole (h+). ACN/CCN exhibited adequate photostability and reusability for photocatalytic H2 production with simultaneous CIP degradation. This work provides a new idea for rationally designing and preparing homo-junction photocatalysts to achieve the dual purpose of chemical energy production and environmental treatment.

Phase engineering in graphitic carbon nitride with imidazolium sulfonic acid chloride ionic liquid functionalization for photocatalytic side-chain oxidation of toluene

Herein, the phase and photocatalytic property of graphitic carbon nitride (g-C3N4) are modulated with the functionalization of ionic liquid (IL) by post-treatment of g-C3N4 with imidazolium sulfonic acid chloride. The structure, morphology and optoelectronic properties of synthesized catalyst were thoroughly investigated. The functionalization of Ionic liquid has induced polycrystallinity to the amorphous g-C3N4. The g-C3N4 –IL is highly efficient towards photocatalytic side-chain oxidation of toluene using H2O2with toluene conversion of 58% with 97% benzaldehyde selectivity in acetonitrile and toluene conversion of 49% and 96% benzaldehyde selectivity in organic solvent-free conditions. The synergy between g-C3N4 and the IL elevates the visible light absorption and lower photoluminescence intensity. The g-C3N4-IL catalyst efficiently halts over-oxidation to get high selectivity for the desired product. In addition, graphene oxide and reduced graphene oxide were also functionalized with IL to examine their photocatalytic efficiency and considerable efficiencies were observed. The g-C3N4-IL is highly stable and recyclable.

Introduction of crystalline hexagonal-C3N4 into g-C3N4 with enhanced charge separation efficiency

Polymeric carbon nitride is a promising candidate for photocatalytic hydrogen evolution but mostly just shows moderate activity because of its inefficient charge separation and sluggish surface reaction kinetics. Phase-based heterostructures, especially crystal-phase heterostructures that are composed of identical compositions with different crystal phases, can endow nanomaterials with promising properties and efficient photocatalysis applications. In this study, a novel crystalline hexagonal-C3N4/g-C3N4 hetero-phase junction was synthesized using a direct in situ alkali salt template coupled with organic solvents strategy. High hydrophilicity was obtained because of the synergistic effect between alkali salt and organic solvents in the polycondensation process. The greatly increased separation and transfer efficiency of charge carriers and the improved proton absorption in the surface reaction of the photocatalyst were achieved by the constructed phase junctions between the crystalline hexagonal-C3N4 and amorphous g-C3N4 decorated with numerous hydrophilic groups. Thus, the carbon nitride hetero-phase junction exhibited dramatically enhanced photocatalytic performance in hydrogen evolution and excellent cycling stability under visible light irradiation. This work presents a novel insight into phase engineering based on carbon nitride materials with surface functional modification for an efficient photocatalytic activity.

Facile construction of O-doped crystalline / non-crystalline g-C3N4 embedded nano-homojunction for efficiently photocatalytic H2 evolution

Realizing the efficient utilization of photogenerated carriers is a pivotal process to access the efficient transformation of light energy. Herein, we firstly practice a facile template method to synthesize O-doped crystalline/none-crystalline g-C3N4 embedded nano-homojunction photocatalysts (CMCCN-x). This nano-homojunction makes the crystalline phase sufficiently contact with amorphous phase and further facilitates the photoinduced electron transformation. Therefore, the best performance catalyst CMCCN-5 well integrates the advantages of crystal g-C3N4 and amorphous g-C3N4, which exhibits an excellent photogenerated carrier separation ability and abundant photocatalytic hydrogen evolution reaction activity sites. Excellent performance in the separation and use of photogenic carriers endows CMCCN-5 with efficient utilization of photogenerated carriers. Although there is a limited light absorption range (<460 nm), the photocatalytic hydrogen evolution rate of CMCCN-5 is up to 203.66 μmol h−1 under the visible light irradiation, about 86 times higher than pristine g-C3N4. The AQY numbers of CMCCN-5 at 420 nm and 450 nm are up to 26.9% and 14.0%, respectively. Thus, the significant effectiveness is forcefully proved for the facile construction of O-doped g-C3N4 crystalline/none-crystalline nano-homojunction.

Photo- and electro-catalysis evolution of superior thin g-C3N4 nanosheets with their microstructure and Ni[sbnd]Fe oxide composite

Graphitic carbon nitride (g-C3N4) is normally used in photocatalysis under visible light, to realize its' enhanced electrocatalytic hydrogen evolution reaction is still a challenge. In this paper, superior thin g-C3N4 nanosheets with different composition and crystallinity are prepared via theromal polarization process to test their photo- and electro-chemical activities. Interestingly, a crystalline/amorphous g-C3N4 nanosheet homojunctions are successfully prepared via one-step thermal polymerization by adjusting preparation parameters. Crystalline and amorphous phases are homogeneously distributed in thin g-C3N4 nanosheets. Compared with crystalline and amorphous g-C3N4 nanosheets, the homojunction prepared using optimized C/N ratio and crystalline/amorphous phase distribution reveals the quick photodegradation of dyes. NiFe oxides are deposited on g-C3N4 by a further thermal polymerization process. After loading metal oxides, the photo- and electro-catalytic performance of crystalline/amorphous homojunctions is greatly enhanced. Especially, the co-loading of Fe2O3 and NiO drastically enhances the electrochemical performance of g-C3N4 nanosheet homojunctions. Using optimized loading amount, the overpotentials of amorphous g-C3N4 nanosheets, g-C3N4 amorphous/crystalline nanosheet homojunctions, and crystalline g-C3N4 nanosheets are 756, 691 and 672 mV for electrochemical hydrogen evolution reaction with Tafel slope of 101, 79 and 74 mV/dec, respectively.

Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO2 Reduction with Nearly 100% CO Selectivity.

Single metal atom photocatalysts have received widespread attention due to the rational use of metal resources and maximum atom utilization efficiency. In particular, N-rich amorphous g-C3N4 is always used as a support to anchor single metal atoms. However, the enhancement of photocatalytic activity of g-C3N4 by introducing a single atom is limited due to the bulk morphology and the excess defects of amorphous g-C3N4. Here, we report crystalline g-C3N4 nanorod supported copper single atoms by molten salts and the reflux method. The prepared single Cu atoms/crystalline g-C3N4 photocatalyst (Cu-CCN) shows highly selective and efficient photocatalytic reduction of CO2 under the absence of any cocatalyst or sacrificial agent. The introduction of single Cu atoms can be used as the CO2 adsorption site, thus increasing the adsorption capacity of Cu-CCN samples to CO2. Theoretical calculation results show that reducing CO2 to CH4 on Cu-CCN samples is an entropy-increasing process, whereas reducing CO2 to CO is an entropy-decreasing process. As a result, the Cu-CCN samples exhibited enhanced photocatalytic CO2 reduction with nearly 100% selective photocatalytic CO2 to CO conversion. The mechanism of photocatalytic CO2 reduction over Cu-CCN samples was proposed based on in situ Fourier transform infrared spectra, X-ray absorption spectroscopy, and density functional theory calculation. This work provides an in-depth understanding of the design of photocatalysts for enhancing active sites of the reactants.

Photo-chemical property evolution of superior thin g-C3N4 nanosheets with their crystallinity and Pt deposition

The crystallinity and composition of superior thin g-C3N4 nanosheets were adjusted at different temperature settings to study property evolution via a two-step thermal polymerization procedure. g-C3N4 sample prepared at 600 °C shows high N/C ratio and amorphous structure while a crystalline g-C3N4 sample with C/N ratio of nearly 0.75 was obtained at 750 °C. The band gap varies for each type of g-C3N4 sample and photodegradation kinetics were examined to be related to the crystallinity of the g-C3N4 sample. The RhB photocatalytic degradation plots for g-C3N4 nanosheets samples prepared at more than 600 °C are fitted using the pseudo-first-order model while the reaction for bulk g-C3N4 sample prepared at 550 °C follows zero-order kinetics. This phenomenon is ascribed to the varying surface states of the g-C3N4 samples. g-C3N4 nanosheets prepared at 700 °C showed the best photocatalytic performance, in which the sample with both amorphous and crystalline structural features is assumed to be amorphous/crystalline homojunctions. Moreover, Pt deposition confirms that g-C3N4 nanosheets prepared at 700 °C reveal the highest photocatalytic H2 evolution rate of 4892 μmol/hg which is about 21 times high compared with amorphous g-C3N4 nanosheets prepared at 600 °C.

Rapid visible light catalytic reduction of Cr(VI) over amorphous g-C3N4 modified palygorskite composite via a charge-transfer-surface complex-mediated pathway

A simple method of high-temperature calcination was used to construct palygorskite/g-C3N4 composite photocatalysts. The as-prepared composites were characterized by X-ray diffractions, Fourier transform infrared spectrum, UV–vis diffused reflection spectra, specific surface area, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activities were evaluated by Cr(VI) reduction efficiency in the presence of tartaric acid under visible light illumination. The results showed that the PAL/g-C3N4-4 sample exhibited enhanced visible light photocatalytic performance, which is due to increased light absorption, specific surface areas and close interfacial contact between g-C3N4 and PAL. Charge-transfer-surface complex-mediated pathway was proposed for the Tar-induced photocatalytic reduction mechanism of Cr(VI). Because of the existence of N vacancies, the surface of prepared PAL/g-C3N4-4 composite is positive charged. The endogenous positive charge surface of PAL/g-C3N4-4 sample is not only conducive to the formation of charge-transfer-surface complex, but also conducive to wide pH range application. Additionally, the reusability and stability of PAL/g-C3N4-4 sample were measured by successive recycling tests and XRD analysis, respectively.

Fabricating Amorphous g-C3N4/ZrO2 Photocatalysts by One-Step Pyrolysis for Solar-Driven Ambient Ammonia Synthesis.

Solar-driven nitrogen fixation remains a significant challenge. Graphitic carbon nitride (g-C3N4) is considered as a promising visible light photocatalyst. However, the photocatalytic performance of g-C3N4 is unsatisfactory because of the random transfer of charge carriers in the plane and the low activation efficiency of the reactants. Herein, amorphous ZrO2 was used as a robust cocatalyst of g-C3N4 to increase the NH3 production activity. The g-C3N4/ZrO2 lamellar composites were constructed by a simple one-step pyrolysis of the deep eutectic solvent ZrOCl2·8H2O/urea. The optimum NH4+ yield could reach as high as 1446 μmol·L-1·h-1 at 30 wt % ZrO2 in the g-C3N4/ZrO2 composites, with an apparent quantum efficiency over 2.14% at 400 nm. It is 7.9 times that of pristine g-C3N4 and 27.5 times that of ZrO2. The introduction of amorphous ZrO2 restrained the hydrogen generation, and the amorphous ZrO2 and g-C3N4 together contribute to the rapid photoproduced electron transfer of less electron-hole pair recombination.

Crystallinity and phase controlling of g-C3N4 /CdS hetrostructures towards high efficient photocatalytic H2 generation

The heterostructures of graphitic carbon nitride (g-C3N4) and CdS were synthesized by controlling the crystalline degree of g-C3N4 and the phase composition of CdS. A thermal polycondensation process of N precursors was adjusted to get amorphous and crystalline g-C3N4. A multistep adsorption method was used to deposit CdS nanoparticles on g-C3N4. An annealed process was used to adjust the phase composition of CdS from cubic to hexagonal. The morphology of CdS was changed to rod. Amorphous g-C3N4/CdS heterostructures revealed enhanced photocatalytic activity because the amorphous g-C3N4 has a lower crystallinity, it is easier to form a heterojunction with the CdS. Further, an annealing process resulted in the phase transfer and morphology change of CdS. The high stability and rod morphology of CdS make the heterostructures with high H2 generation rate to 5440 μmol h-1 g-1 which is ~5 times high compared with g-C3N4.

Boosting Photocatalytic Hydrogen Production by Modulating Recombination Modes and Proton Adsorption Energy.

Solar-driven production of renewable energy (e.g., H2) has been investigated for decades. To date, the applications are limited by low efficiency due to rapid charge recombination (both radiative and nonradiative modes) and slow reaction rates. Tremendous efforts have been focused on reducing the radiative recombination and enhancing the interfacial charge transfer by engineering the geometric and electronic structure of the photocatalysts. However, fine-tuning of nonradiative recombination processes and optimization of target reaction paths still lack effective control. Here we show that minimizing the nonradiative relaxation and the adsorption energy of photogenerated surface-adsorbed hydrogen atoms are essential to achieve a longer lifetime of the charge carriers and a faster reaction rate, respectively. Such control results in a 16-fold enhancement in photocatalytic H2 evolution and a 15-fold increase in photocurrent of the crystalline g-C3N4 compared to that of the amorphous g-C3N4.

Atomically dispersed Mo atoms on amorphous g-C3N4 promotes visible-light absorption and charge carriers transfer

Atomically dispersed atom catalysts with atomically distributed active metal centers have attracted great attention owing to the maximum atom efficiency and excellent selectivity. Herein, for the first time, we found atomically dispersed Mo atoms can be formed on g-C3N4, and induce its amorphous transformation. This amorphous transformation leads to the formation of strong band tails with remarkably enhancing the absorbance edge of Mo-C3N4 up to 750 nm, resulting in almost whole visible-light range absorption. The formation of new Mo-C and Mo-N bonds due to strong interfacial interaction between atomically dispersed Mo atoms and g-C3N4 provide new electron and hole transport pathways to accelerate the separation of charge carriers. As a result, amorphous Mo/C3N4 (a-Mo/C3N4) reveals excellent photoreduction of CO2, yielding CO and H2 productions of 18 and 37 μmol g−1 h−1 under visible-light illumination (λ > 420 nm), which manifest a remarkable 10.6- and 4-folds enhancement of that over crystalline g-C3N4. This finding provides a conceptually different approach to fabricate high-efficient photocatalyst through the strong interfacial interaction between atomically dispersed metal atoms and host.

Interactions between ZnO nanoparticles and amorphous g-C3N4 nanosheets in thermal formation of g-C3N4/ZnO composite materials: The annealing temperature effect

In this study, C3N4/ZnO composite materials were prepared at various annealing temperatures and systematically characterized to investigate the role of ZnO in the thermal formation of graphitic C3N4 (g-C3N4), and to understand effect of annealing temperatures on the interaction between g-C3N4 and ZnO in the composite materials. ZnO nanoparticles in the composite materials facilitated the thermal formation of the g-C3N4 structure due to the strong interaction between g-C3N4 and ZnO nanoparticles, resulting in a decrease in thermal polymeric condensation temperatures. Moreover, the morphological structure of g-C3N4 was significantly influenced by the presence of ZnO nanoparticles with an amorphous g-C3N4 nanosheet structure in the composite materials and a crystalline interlayered g-C3N4 structure in g-C3N4 only. The higher annealing temperatures for composite materials induced the stronger interaction between ZnO nanoparticles and g-C3N4 nanosheets. The strong interaction in a core-shell g-C3N4/ZnO structure not only gradually decreased the electronic density of ZnO nanoparticles but also proportionally inhibited the recombination of photo-generated electron-hole pairs in the composite materials, with increasing the annealing temperature. The g-C3N4/ZnO composite material prepared at 500 °C exhibited the highest photocatalytic reaction rate constant for photocatalytic degradation of methylene blue, which might be caused by the slowest recombination rate.

Synthesis and luminescence mechanism of multicolor-emitting g-C3N4 nanopowders by low temperature thermal condensation of melamine

Graphite like C3N4 (g-C3N4) was synthesized facilely via the low temperature thermal condensation of melamine between 300–650°C. The results showed that the products maintained as melamine when the temperature is below 300°C. With the increase of temperature, the products were transformed into carbon nitride and amorphous g-C3N4 successively. The morphology of products was changed from spherical nanoparticles of melamine into layer carbon nitride and g-C3N4 with the increase of temperature. The photoluminescence spectra showed that the carbon nitride products have continuous tunable photoluminescence properties in the visible region with increasing temperature. With the help of steady state, transient state time-resolved photoluminescence spectra and Raman microstructural characterization, a novel tunable photoluminescence mechanism was founded systematically, which is mainly related to the two dimensional π-conjugated polymeric network and the lone pair of the carbon nitride.