Supramolecular Preorganization Research Articles

Recent Advances in g-C3N4 Photocatalysts: A Review of Reaction Parameters, Structure Design and Exfoliation Methods

Graphitized carbon nitride (g-C3N4), as a metal-free, visible-light-responsive photocatalyst, has a very broad application prospect in the fields of solar energy conversion and environmental remediation. The g-C3N4 photocatalyst owns a series of conspicuous characteristics, such as very suitable band structure, strong physicochemical stability, abundant reserves, low cost, etc. Research on the g-C3N4 or g-C3N4-based photocatalysts for real applications has become a competitive hot topic and a frontier area with thousands of publications over the past 17 years. In this paper, we carefully reviewed the recent advances in the synthesis and structural design of g-C3N4 materials for efficient photocatalysts. First, the crucial synthesis parameters of g-C3N4 were fully discussed, including the categories of g-C3N4 precursors, reaction temperature, reaction atmosphere and reaction duration. Second, the construction approaches of various nanostructures were surveyed in detail, such as hard and soft template, supramolecular preorganization and template-free approaches. Third, the characteristics of different exfoliation methods were compared and summarized. At the end, the problems of g-C3N4 materials in photocatalysis and the prospect of further development were disclosed and proposed to provide some key guidance for designing more efficient and applicable g-C3N4 or g-C3N4-based photocatalysts.

Photocatalytic Terminal C-C Coupling Reaction Inside Water Soluble Nanocages.

Developing methods that activate C-H bonds directly with high selectivity for C-C bond formation in complex organic synthesis has been a major chemistry challenge. Recently it has been shown that photoactivation of weakly polarized C-H bonds can be carried out inside a cationic water-soluble nanocage with visible light-mediated host-guest charge transfer (CT) chemistry. Using this novel photoredox activation paradigm, here we demonstrate C-C bond formation to photo-generate 1,3-diynes at room temperature in water from terminal aromatic alkynes for the first time. The formation of cavity-confined alkyne radical cation and the proton-removed neutral radical species highlight the unique C-C coupling step driven by supramolecular preorganization.

Photocatalytic Terminal C−C Coupling Reaction Inside Water Soluble Nanocages

AbstractDeveloping methods that activate C−H bonds directly with high selectivity for C−C bond formation in complex organic synthesis has been a major chemistry challenge. Recently it has been shown that photoactivation of weakly polarized C−H bonds can be carried out inside a cationic water‐soluble nanocage with visible light‐mediated host‐guest charge transfer (CT) chemistry. Using this novel photoredox activation paradigm, here we demonstrate C−C bond formation to photo‐generate 1,3‐diynes at room temperature in water from terminal aromatic alkynes for the first time. The formation of cavity‐confined alkyne radical cation and the proton‐removed neutral radical species highlight the unique C−C coupling step driven by supramolecular preorganization.

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies

AbstractThe facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride‐based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large‐scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies.

The facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride-based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large-scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Structural Analysis of Non-native Peptide-Based Catalysts Using 2D NMR-Guided MD Simulations.

Proteins and enzymes generally achieve their functions by creating well-defined 3D architectures that pre-organize reactive functionalities. Mimicking this approach to supramolecular pre-organization is leading to the development of highly versatile artificial chemical environments, including new biomaterials, medicines, artificial enzymes, and enzyme-like catalysts. The use of β-turn and α-helical motifs is one approach that enables the precise placement of reactive functional groups to enable selective substrate activation and reactivity/selectivity that approaches natural enzymes. Our recent work has demonstrated that helical peptides can serve as scaffolds for pre-organizing two reactive groups to achieve enzyme-like catalysis. In this study, we used CYANA and AmberTools to develop a computational approach for determining how the structure of our peptide catalysts can lead to enhancements in reactivity. These results support our hypothesis that the bifunctional nature of the peptide enables catalysis by pre-organizing the two catalysts in reactive conformations that accelerate catalysis by proximity. We also present evidence that the low reactivity of monofunctional peptides can be attributed to interactions between the peptide-bound catalyst and the helical backbone, which are not observed in the bifunctional peptide.

Fe-doped g-C3N4 synthesized by supramolecular preorganization for enhanced photo-Fenton activity

The photo-Fenton process, with a synergistic effect of Fenton oxidation and photocatalysis, is a promising technique for the removal of refractory organic pollutants. However, the rapid recombination of photogenerated charge carriers results in less electrons for Fe(III)/Fe(II) cycle and later generation of hydroxyl radicals. In this work, Fe-doped graphite carbon nitride with a thin nanosheet structure (∼5 nm thickness) was prepared using the supramolecular preorganization method (Fe/CNSP), which effectively suppresses the recombination of photogenerated charges compared with that of Fe-doped bulk carbon nitride (Fe/BCN), resulting in an obviously improved photo-Fenton performance by increasing the electron gain at the Fe sites and the speed of the reduction of Fe(III) to Fe(II). The heterogeneous photo-Fenton activity of Fe/CNSP displays a 6.5 times higher kinetic constant for carbamazepine degradation than that of Fe/BCN, and universal effectiveness toward other organic pollutants, namely phenol, sulfamethoxazole, bisphenol A, and 2,4-dichlorophenol, with TOC removals between 37.4% and 91.3% in 150 min. OH, O2−, e−, h+, and 1O2 contribute to the degradation of organic pollutants. Fe/CNSP was proven to be stable and reusable in cyclic experiments. The analysis of the intermediate toxicity demonstrated that the Fe/CNSP photo-Fenton system effectively reduced the toxicity of carbamazepine. This study offers a simple, highly reproducible method for developing efficient heterogeneous photo-Fenton catalysts.

Optimization of hydrothermal pretreatment to prepare g-C3N4 with enhanced catalyst yield and photocatalytic activity for aqueous contaminant removal

Supramolecular preorganization via hydrothermal is regarded as a cost-effective pretreatment to prepare g-C3N4 nanosheets. However, photocatalytic activity has been the primary focus of many g-C3N4 studies while other aspects have often been ignored. In addition to photocatalytic activity that is measured by the photodegradation efficiency of rhodamine B dye, the yield of g-C3N4 material is also selected for process optimization in the present study because of its practical significance. Response surface methodology and characterization tools are utilized to evaluate the individual and combined effects of hydrothermal pretreatment conditions on these responses. Hydrothermal temperature and time played major roles in determining both responses and the photocatalytic activity was 10 times higher than the bulk g-C3N4 when hydrothermal conditions are optimized. However, the optimal conditions for these two responses are contradictory to each other. Yield increases by a factor of two without compromising the photocatalytic activity using the desirability function approach for multiobjective optimization. Our work provides valuable insights into synthesis optimization for real-world applications of g-C3N4 materials.

High-loading Cu single-atom nanozymes supported by carbon nitride with peroxidase-like activity for the colorimetric detection of tannic acid

The design of nanozymes with high metal atom loading is of great significance to improve enzyme activity and is also the key to furthering the construction of highly sensitive colorimetric sensors. In this work, a colorimetric sensor for the quantitative analysis of tannic acid (TA) was developed based on two-dimensional carbon nanosheet carbon nitride (CN)-supported Cu single-atom nanozymes (Cu/CN). Cu/CN was synthesized by supramolecular preorganization and calcination, with an ultrathin nanosheet structure and a high density of Cu active sites, with a Cu loading of up to 14.3 wt%. Benefiting from the above characteristics, Cu/CN exhibits peroxidase-mimicking activity and excellent catalytic performance. Therefore, a colorimetric sensor was constructed for the fast and sensitive quantitative analysis of TA with good linearity in the range of 0.09–3.2 μM and a low detection limit of 30 nM. Furthermore, the sensor was successfully applied to the analysis of TA in tea samples of different varieties. This work sheds new light on the design of nanozymes with a high density of active sites and the analysis of TA in real environments.

Hydrothermal supramolecular preorganization synthesis of multi-morphological g-C3N4/Fe2O3 for photocatalytic removal of indoor formaldehyde under visible light

In this study, multi-morphological g-C3N4/ Fe2O3 were prepared via hydrothermal supramolecular preorganization for the removal of formaldehyde in simulated indoor environments. We synthesized bulk, spherical and tubular g-C3N4 under hydrothermal conditions and subsequently attached Fe2O3 nanoparticles by impregnation method. Tubular g-C3N4/Fe2O3 (27.46 m2/g) and spherical g-C3N4/Fe2O3 (33.50 m2/g) synthesized through hydrothermal supramolecular preorganization method possessed the higher specific surface area than bulk g-C3N4/Fe2O3 (11.05 m2/g). Among three morphologies of g-C3N4/Fe2O3, tubular g-C3N4/Fe2O3 exhibited the best performance (65%) than bulk (41%) and spherical (59%) and possessed favorable stability. In addition, we explored and optimized the effects of different indoor simulation conditions (formaldehyde concentration, relative humidity, light source power) on the photocatalytic removal of formaldehyde. The mechanism was proposed that g-C3N4/Fe2O3 formed Z-type heterojunction to promote the separation of photo-generated electrons and holes, further generating hydroxyl radical and superoxide radical to oxidize formaldehyde.

Supramolecular preorganization synthesis of nitrogen-doped carbon nanotubes functionalized by Brønsted acidic ionic liquid for microwave-assisted production of promising furanic derivatives

Brønsted acidic ionic liquids functionalized nitrogen-doped carbon nanotubes catalysts, [C4SO3HN][OTf]-NCNTs (OTf = SO3CF3), are synthesized by an additive-free supramolecular preorganization-thermal condensation route followed by chemical modification. By controlling the molar composition of carbon–nitrogen based monomers, sequence of the monomers and thermal condensation temperature, the tubular morphology and porosity properties of the catalysts are well-adjusted. The [C4SO3HN][OTf]-NCNTs are successfully applied in the reactions of great relevance to the development of sustainable bio-economy, namely, microwave-assisted production of 5-hydromethylfurfural (HMF) and furfural (FFR) from the dehydration of fructose and xylose, and the important reaction parameters including microwave irradiation temperature and time as well as solvent are considered. Co-operation of strong Brønsted acidity, unique tubular nanostructures and microwave heating approach finally endows [C4SO3HN][OTf]-NCNTs the enhanced dehydration reactivity and selectivity, in which the [C4SO3HN][OTf]-NCNTs800-2 with perfect tubular nanostructures displays the highest HMF yield (82.6%, 15 min in THF media) and FFR yield (56.2%, 45 min in DMSO media). The [C4SO3HN][OTf]-NCNTs also exhibit good catalytic reusability, attributing to covalent bonding of the [C4SO3HN+][OTf−] units onto NCNTs frameworks; meanwhile, the formation of considerable amount of humins at the surface of the catalysts is effectively inhibited by using microwave heating mode.

Stereospecific Formation of the rctt Isomer of Bis-crown-Containing Cyclobutane upon [2 + 2] Photocycloaddition of an (18-Crown-6)stilbene Induced by Self-Assembly via Hydrogen Bonding.

The formation and the spectroscopic and structural properties of 1:1 and 2:1 (ligand-to-dication) complexes of an (18-crown-6)stilbene with ethane-1,2-diammonium diperchlorate in MeCN were studied by UV-vis and NMR spectroscopy and by density functional theory calculations. Prolonged UV irradiation of 2:1 mixtures of the crown stilbene and the diammonium salt led to the formation of two main photoproducts, namely, the single syn-"head-to-head" photodimer of the crown stilbene (rctt cyclobutane) due to supramolecular-assisted [2 + 2] photocycloaddition and a crown ether derivative of phenanthrene due to a photoinduced electrocyclization reaction. The rctt cyclobutane was isolated by preparative photolysis, followed by chromatography. The selectivity of the [2 + 2] photocycloaddition is explained by supramolecular pre-organization of crown stilbene molecules into the 2:1 complexes that have a pseudo-sandwich structure with stacking interactions between the stilbene moieties.

Gradient Supramolecular Preorganization Endows the Derived N/P Dual-Doped Carbon Nanosheets with Tunable Storage Performance toward Sodium-Ion Batteries

Gradient Supramolecular Preorganization Endows the Derived N/P Dual-Doped Carbon Nanosheets with Tunable Storage Performance toward Sodium-Ion Batteries

Loofah-like carbon nitride sponge towards the highly-efficient photocatalytic transfer hydrogenation of nitrophenols with water as the hydrogen source

The vigorous development of photocatalytic water splitting technology has laid the foundation for the photocatalytic transfer hydrogenation of organic substrates to produce the high value-added chemicals using water as hydrogen source. Nevertheless, the high dissociation energy of the O–H bond impedes its academic progress and the practical applications. Herein, we synthesize a 3D hierarchical porous loofah-like carbon nitride sponge (LCN) with ultrathin thickness via the supramolecular pre-organization coupling with the oxidation etching process, in which the heterogeneous oxygen atoms and the nitrogen vacancies are in-situ engineered. On top of the adorable photocatalytic H2 evolution (4812 μmol h−1 g−1), LCN associated with Pt cocatalyst reveals a conversion rate of 96.5 % towards the hydrogenation of 4-nitrophenol, substantially superior to the reference experiment (8.3 %). Further based on the isotope-labeling tests and the density functional theory calculations, the photo-generated H0 from water is clarified to be the direct reducing agent, tactfully skipping the hydrogen extraction step in the traditional path. This work provides a green and sustainable methodology to transfer the solar energy to the valuable fine chemicals, as well as highlights the importance of the 3D hierarchical porous structure to the catalytic activity.

One-step supramolecular preorganization constructed crinkly graphitic carbon nitride nanosheets with enhanced photocatalytic activity

• Crinkly graphitic carbon nitride nanosheets are prepared by a one-step polycondensation process using urea and melamine as the precursors. • The conversion of urea to cyanuric acid during polycondensation enables the formation of melamine-cyanuric acid. • The obtained crinkly graphitic carbon nitride nanosheets exhibit much better optoelectronic properties compared to its bulk counterpart. • The photocatalytic hydrogen production rate of crinkly graphitic carbon nitride nanosheets is increased by 7 times. Here we report a new one-step thermal polycondensation process to form crinkly graphitic carbon nitride nanosheets (CGCNNs) via supramolecular preorganization, using a mixture of urea and melamine as the starting material. Systematical studies reveal that the newly developed CGCNNs significantly strengthen the optical absorption, widen the bandgap, and increase the Hall mobility and carrier density compared to that of its bulk counterpart, regardless of the similar chemical composition and structure. As a result, the photocatalytic hydrogen production rate is improved by 7 times. Moreover, Na doping of CGCNNs can further promote its photocatalytic activity, leading to an excellent photocatalytic hydrogen production rate of 250.9 µmol h –1 , which is approximately 10.5 times higher than its bulk counterpart. Moreover, an impressive apparent quantum efficiency of 19.12% is achieved at 420 nm. This study provides a facile strategy for the design of efficient low-cost carbon-nitride-based photocatalysts for solar fuel production.

Supramolecular Preorganization Synthesis of Nitrogen-Doped Carbon Nanotubes Functionalized by Brønsted Acidic Ionic Liquid for Microwave-Assisted Production of Promising Furanic Derivatives

Supramolecular Preorganization Synthesis of Nitrogen-Doped Carbon Nanotubes Functionalized by Brønsted Acidic Ionic Liquid for Microwave-Assisted Production of Promising Furanic Derivatives

Phenyl-Modified Carbon Nitride Quantum Nanoflakes for Ultra-Highly Selective Sensing of Formic Acid: A Combined Experimental by QCM and Density Functional Theory Study

Formic acid (HCOOH) is an important intermediate in chemical synthesis, pharmaceuticals, the food industry, and leather tanning and is considered to be an effective hydrogen storage molecule. Direct contact with its vapor and its inhalation lead to burns, nerve injury, and dermatosis. Thus, it is critical to establish efficient sensing materials and devices for the rapid detection of HCOOH. In the present study, we introduce a chemical sensor based on a quartz crystal microbalance (QCM) sensor capable of detecting trace amounts of HCOOH. This sensor is composed of colloidal phenyl-terminated carbon nitride (Ph-g-C3N4) quantum nanoflakes prepared using a facile solid-state method involving the supramolecular preorganization technology. In contrast to other synthetic methods of modified carbon nitride materials, this approach requires no hard templates, hazardous chemicals, or hydrothermal treatments. Comprehensive characterization and density functional theory (DFT) calculations revealed that the QCM sensor designed and prepared here exhibits enhanced detection sensitivity and selectivity for volatile HCOOH, which originates from chemical and hydrogen-bonding interactions between HCOOH and the surface of Ph-g-C3N4. According to DFT results, HCOOH is located close to the cavity of the Ph-g-C3N4 unit, with bonding to graphitic carbon and pyridinic nitrogen atoms of the nanoflake. The sensitivity of the Ph-g-C3N4-nanoflake-based QCM sensor was found to be the highest (128.99 Hz ppm-1) of the substances studied, with a limit of detection (LOD) of HCOOH down to a sub-ppm level of 80 ppb. This sensing technology based on phenyl-terminated attached-g-C3N4 nanoflakes establishes a simple, low-cost solution to improve the performance of QCM sensors for the effective discrimination of HCOOH, HCHO, and CH3COOH vapors using smart electronic noses.

Covalent [2]Catenane and [2]Rotaxane Synthesis via a δ-Amino Acid Template.

Despite the advances in the synthesis of mechanically interlocked molecules, a generally applicable approach to interlocked natural products, such as lasso peptides, is yet to be formulated. While amino acid sequences have been introduced into several rotaxanes, the key structural components have always been dictated by the method used for supramolecular preorganization. In this work, we report the use of an ester-functionalized, aromatic δ-amino acid as the central covalent templating unit in the synthesis of both a [2]catenane and a [2]rotaxane from the same multimacrocyclic intermediate. This represents a key step toward future synthetic peptide-based interlocked products.

Engineering of graphitic carbon nitride with simultaneous potassium doping sites and nitrogen defects for notably enhanced photocatalytic oxidation performance

Graphitic carbon nitride (g-C3N4) offers exciting opportunities for sustainable photocatalytic oxidation of organic pollutants but suffers from drawbacks of insufficient oxidation driving force and low quantum efficiency. To over the drawbacks, here a simple and effective strategy was developed to engineer g-C3N4 with simultaneous interstitially embedded potassium dopant and nitrogen defects, and the process included supramolecular preorganization followed by KOH-assisted thermal polycondensation. In the prepared DN-K-CN catalysts, potassium doping level and the amount of nitrogen defects were both controllable. With the increment of potassium doping level, the bandgap of the DN-K-CN became narrow, along with continuously downshifted valence band position. The DN-K-CN showed greatly enhanced visible-light photocatalytic oxidation performance with respect to g-C3N4 in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben; meanwhile, the oxidation performance of DN-K-CN depended on potassium doping level and the amount of nitrogen defects. Combination of experimental findings and theory calculations it is confirmed that the enhanced photocatalytic oxidation performance of DN-K-CN was attributed to the synergistic effect of potassium dopant and nitrogen defects, which resulted in the generation of plentiful active oxygen species and the improvement of oxidation driving force of valence holes. The influence of potassium dopant and nitrogen defects on the electronic and band structures of g-C3N4 was revealed; simultaneously, mechanism of the enhanced photocatalytic oxidation performance of g-C3N4 after the introduction of potassium dopant and nitrogen defects was studied. The present work provided new insights into the electronic and band structure tuning for the improvement of the photocatalytic oxidation performance of g-C3N4.

Guanidine carbonate assisted supramolecular self-assembly for synthesizing porous g-C3N4 for enhanced photocatalytic hydrogen evolution

Graphitic carbon nitride (g-C3N4) is taken as one of the most promising polymer semiconductor photocatalysts for energy conversion. However, the photocatalytic activity of g-C3N4 is usually impeded by the low light absorption and fast recombination of photogenerated carriers. Herein, three-dimensional porous g-C3N4 with controllable morphology are synthesized by thermal polycondensation of supramolecular preorganization assembly of melamine, cyanuric acid and guanidine carbonate (1:1:x, x means the ratio of guanidine carbonate). By adjusting the amount of guanidine carbonate in the assembly, the precursors’ morphology can be changed from microrods to polyhedrons, which affects the g-C3N4 structure accordingly. The optimized hollow porous polyhedral g-C3N4 shows the enhanced light absorption and improved photogenerated carriers separation efficiency, thus exhibiting a 7.7-fold hydrogen evolution activity and 9-fold apparent quantum efficiency (AQE) higher than microtube without addition of guanidine carbonate. This work paves a complementary way towards synthesizing highly efficient photocatalysts through the guanidine carbonate-assisted supramolecular assembly.