As an emerging nitrogen-rich 2D carbon material, graphitic carbon nitride (CN) has drawn much attention for applications ranging from photo-/electrocatalysts to biosensors. Interfacial modification of CN is fundamentally vital but is still in its infancy and remains challenging due to the low reactivity of CN. Here we report that, in conjunction with a π-π stacking interaction, bulk CN could be simultaneously exfoliated via facile mechanical grinding. The obtained CN nanosheets (m-CNNS) not only retained the pristine optoelectronic properties of bulk CN but also enriched a friendly interface for further coupling biomolecules with advanced properties, overcoming the deficiencies of CN in surface science. The m-CNNS were further covalently linked to a DNA probe, and the resultant electrochemiluminescent biosensor for the target DNA exhibited much enhanced sensitivity with respect to that obtained by direct physical absorption of the DNA probe on unmodified CNNS. This noncovalent exfoliation and interfacial modification should greatly expand the scope of potential applications of CN in areas such as biosensing and should also be applicable to other 2D materials in interface modulation.

Pomelo peel, a waste biomass, was used as an all-in-one (carbon source, self-template, and heteroatom) precursor to develop a nanoporous N/C-electrocatalyst for highly selective and energy-saving H2O2 production, in which disordered carbonous defects and five-membered rings (pyrrolic-N) played vital roles.

A heterojunction photocatalyst made up of a single substrate is reported. The heterointerfaces of carbon nitride (CN) are natively compatible due to their very similar chemical and crystalline structures. Moreover, the varieties in the nanostructures of CN led to different energy levels that not only matched well with each other but also enabled a sufficient internal electric field at their interfaces to suppress unwanted recombination of charge carriers in photocatalysis.

A hydrogen bond-driven supramolecular strategy to synthesize multiphase-Fe anchoring on hierarchical N-doped graphitic carbon was proposed. As a result, the as-obtained catalysts showed unusual trifunctional activities in the oxygen reduction reaction, oxygen evolution reaction and hydrogen evolution reaction, even surpassing noble-metal catalysts such as Pt/C and RuO2.

Owing to the well-defined molecular structure and tunable mono-, di- or multinuclearity, Cu–N complexes have recently drawn specific attention as emerging catalysts for sustainable electrocatalytic oxygen reduction reaction (ORR) and other reactions. However, compared to state-of-the-art Pt/C, most of these Cu-based molecular catalysts show low catalytic activity due to the intrinsically limited capability and challenges in electronic structure modulation and sequential electron transfer within a single small molecule. Herein, inspired by structure–property relationships of laccases (a type of macromolecular biological catalyst), we report a facile molecular assembly of Cu(3,3′-diaminobenzidine) polymeric complex on carbon black via Cu–N complexing and π–π interaction as a highly efficient bifunctional electrocatalyst for ORR and hydrazine oxidation reaction (HOR), two half reactions for hydrazine fuel cells. Similar to the function of the Cys–His group in natural laccases, the 3,3′-diaminobenzidine ligand in the proposed polymeric catalyst synergistically adjusted the electronic structure of the Cu–N complex center and mediated a multiple-electron transfer cooperatively with carbon black via a long-range π–π interaction, owing to its electron reservation and π-conjugated properties. This study may provide a new way to design highly efficient biomimetic noble-metal-free electrocatalysts with well-defined and tunable structures.

The development of efficient and low-cost non-precious-metal electrocatalysts such as Fe–N/C for the oxygen reduction reaction (ORR) is crucial for fuel cells and metal–air batteries. Here, we report a class of highly efficient Fe–N/C electrocatalysts derived from versatile imidazolium-based ionic liquids (ILs) with a halogen-coordinated iron anion. Without any supports, templates, or multi-step pyrolysis, the as-prepared Fe–N/C catalysts exhibited superior activity in the ORR to the state-of-the-art Pt/C in alkaline electrolytes by 44 mV in half-wave potential. More interestingly, owing to the versatile configuration of the imidazolium-based IL precursors, a diverse range of catalyst structures was successfully modulated. Based on this, it was clearly revealed that the electrical conductivity, type/amount of N dopants, and “effective porosity” (not the conventional total surface area) jointly determined the electrocatalytic activity. A pivotal radar chart is further proposed to successfully predict activity in the ORR merely from the structures of Fe–N/C catalysts. The proposed ILs platform would provide a valuable toolbox for the molecular design of precursors to tune the structures of Fe–N/C electrocatalysts towards excellent activity in the ORR in a highly flexible manner, and facilitate the long-term challenging study of relationships between processing, structure and activity.

Polymeric carbon nitride (CN) has recently emerged as a novel metal-free semiconductor due to its unique electronic structure, wide availability, and promising applications in photoelectrochemical solar energy conversion. However, few works regarding CN photoelectrode optimization such as by minimization of unwanted grain boundary effects have been reported, which would greatly influence the photoelectrochemcial conversion efficiency. Herein, three general ways of preparing CN photoelectrode are presented and compared, including drop-casting of CN particles, or further blendeding with Nafion or PEDOT–PSS as the binder. In addition, the influences of CN particle sizes (0.5, 1.1, and 3.2 μm) and the film thickness (i.e., the loading amount) to the overall photoelectrochemcial activity were also evaluated in detail. As a result, when PEDOT–PSS acted as binder, CN particles with size of 0.5 μm and an optimal loading amount (2.4 mg/cm2) were adopted; the as-prepared CN photoelectrode had much superior photoelectrochemical activity than all other counterparts. Therefore, this study would pave the way for preparing CN photoelectrode of superior quality so as to promote CN materials to be better applied in solar fuel and sensing applications.Keywords: binder; carbon nitride; drop-casting; grain boundaries effects; photoelectrochemistry; photoelectrode optimization

Chemical structures of two-dimensional (2D) nanosheet can effectively control the properties thus guiding their applications. Herein, we demonstrate that carbon nitride nanosheets (CNNS) with tunable chemical structures can be obtained by exfoliating facile accessible bulk carbon nitride (CN) of different polymerization degree. Interestingly, the electrochemiluminescence (ECL) properties of as-prepared CNNS were significantly modulated. As a result, unusual changes for different CNNS in quenching of ECL because of inner filter effect/electron transfer and enhancement of ECL owing to catalytic effect were observed by adding different metal ions. On the basis of this, by using various CNNS, highly selective ECL sensors for rapid detecting multiple metal-ions such as Cu2+, Ni2+, and Cd2+ were successfully developed without any labeling and masking reagents. Multiple competitive mechanisms were further revealed to account for such enhanced selectivity in the proposed ECL sensors. The strategy of preparing CNNS with tunable chemical structures that facilely modulated the optical properties would open a vista to explore 2D carbon-rich materials for developing a wide range of applications such as sensors with enhanced performances.

Responsive assembly of 2D materials is of great interest for a range of applications. In this work, interfacial functionalized carbon nitride (CN) nanofibers were synthesized by hydrolyzing bulk CN in sodium hydroxide solution. The reversible assemble and disassemble behavior of the as-prepared CN nanofibers was investigated by using CO2 as a trigger to form a hydrogel network at first. Compared to the most widespread absorbent materials such as active carbon, graphene and previously reported supramolecular gel, the proposed CN hydrogel not only exhibited a competitive absorbing capacity (maximum absorbing capacity of methylene blue up to 402 mg/g) but also overcame the typical deficiencies such as poor selectivity and high energy-consuming regeneration. This work would provide a strategy to construct a 3D CN network and open an avenue for developing smart assembly for potential applications ranging from environment to selective extraction.Keywords: carbon dioxide responsive; graphitic carbon nitride; reversible dye adsorption; self-assembly; surface chemistry

Graphite-phase polymeric carbon nitride (GPPCN) has emerged as a promising metal-free material toward optoelectronics and (photo)catalysis. However, the insolubility of GPPCN remains one of the biggest impediments toward its potential applications. Herein, we report that GPPCN could be dissolved in concentrated sulfuric acid, the first feasible solvent so far, due to the synergistic protonation and intercalation. The concentration was up to 300 mg/mL, thousands of time higher than previous reported dispersions. As a result, the first successful liquid-state NMR spectra of GPPCN were obtained, which provides a more feasible method to reveal the finer structure of GPPCN. Moreover, at high concentration, a liquid crystal phase for the carbon nitride family was first observed. The successful dissolution of GPPCN and the formation of highly anisotropic mesophases would greatly pave the potential applications such as GPPCN-based nanocomposites or assembly of marcroscopic, ordered materials.

Graphitic carbon nitride (g-CN) is an exciting material – a semiconductor comprised only of carbon and nitrogen. It is very easy to synthesize and there are many papers on the development of this material in key energy applications such as photoelectrochemical (PEC) conversion of solar energy into chemical fuels. As a promising candidate for sustainable photocathodes, g-CN has advantages such as low cost, visible light sensitivity and high chemical stability. However, to date, the performance of g-CN has been limited, partly because standard synthesis methods produce relatively dense materials with low surface area. To combat this, there are now many examples of hard and soft templating to change the structure and morphology of g-CN and introduce porosity. This review will discuss the key advances and challenges in this interesting new field.

Graphite-phase polymeric carbon nitride (GPPCN) is one kind of new organic semiconductor for photoelectric conversion, photocatalysis and other important catalytic reactions. However, the low surface area of bulk GPPCN limits its potential applications. Here, we report the preparation of porous GPPCN using industrially available calcium carbonate particles as the hard template; these are not only low-cost, but also easily removed by dilute hydrochloric acid. Interestingly, upon engineering the w/w ratio of template to GPPCN precursor along with the template sizes, our approach resulted in increases of about 4 and 7.5 times in the cathodic photocurrent under visible light (λ > 420 nm) irradiation compared with bulk GPPCN when biased at −0.2 V and 0 V (vs. Ag/AgCl), respectively. These photoelectrochemical activities were higher than those of porous GPPCN obtained by all other reported techniques including the common strategy of using silica nanoparticle templates. This study opens a new avenue to explore the fascinating GPPCN materials for solar energy conversion and environmental remediation, especially for large-scale industrial applications.

As an emerging semiconductor, graphite-phase polymeric carbon nitride (GPPCN) has drawn much attention not only in photocatalysis but also in optical sensors such as electrochemiluminescence (ECL) sensing of metal ions. However, when the concentrations of interfering metal ions are several times higher than that of the target metal ion, it is almost impossible to distinguish which metal ion changes the ECL signals in real sample detection. Herein, we report that the dual-ECL signals could be actuated by different ECL reactions merely from GPPCN nanosheets at anodic and cathodic potentials, respectively. Interestingly, the different metal ions exhibited distinct quenching/enhancement of the ECL signal at different driven potentials, presumably ascribed to the diversity of energy-level matches between the metal ions and GPPCN nanosheets and catalytic interactions of the intermediate species in ECL reactions. On this basis, without any labeling and masking reagents, the accuracy and reliability of sensors based on the ECL of GPPCN nanosheets toward metal ions were largely improved; thus, the false-positive result caused by interferential metal ions could be effectively avoided. As an example, the proposed GPPCN ECL sensor with a detection limit of 1.13 nM was successfully applied for the detection of trace Ni2+ ion in tap and lake water.Keywords: carbon nitride nanosheets; dual-signal sensing; electrochemiluminescence; potential resolved; single luminophor

Surface patterns of well-defined nanostructures play important roles in fabrication of optoelectronic devices and applications in catalysis and biology. In this paper, the diporphyrin honeycomb film, composed of titanium dioxide, protoporphyrin IX, and hemin (TiO2/PPIX/Hem), was synthesized using a dewetting technique with the well-defined polystyrene (PS) monolayer as a template. The TiO2/PPIX/Hem honeycomb film exhibited a higher photoelectrochemical response than that of TiO2 or TiO2/PPIX, which implied a high photoelectric conversion efficiency and a synergistic effect between the two kinds of porphyrins. The TiO2/PPIX/Hem honeycomb film was also a good photosensitizer due to its ability to generate singlet oxygen (1O2) under irradiation by visible light. This led to the use of diporphyrin TiO2/PPIX/Hem honeycomb film for the photocatalytic inactivation of bacteria. In addition, the photocatalytic activities of other metal-diporphyrin-based honeycomb films, such as TiO2/MnPPIX/Hem, TiO2/CoPPIX/Hem, TiO2/NiPPIX/Hem, TiO2/CuPPIX/Hem, and TiO2/ZnPPIX/Hem, were investigated. The result demonstrated that the photoelectric properties of diporphyrin-based film could be effectively enhanced by further coupling of porphyrin with metal ions. Such enhanced performance of diporphyrin compounds opened a new way for potential applications in various photoelectrochemical devices and medical fields.Keywords: antibacterial activity; diporphyrin; photoelectrochemistry; singlet oxygen; synergistic effect; template synthesis;

The oxygen reduction reaction (ORR) plays an important role at the cathode of fuel cells in practical applications. Herein, a titanium dioxide/graphene supported hemin (TiO2/Gr/Hem) composite material with a flower-like superstructure was successfully prepared through a two-step solvothermal reaction. By a further heat-treatment at 300–900 °C, the electrocatalytic activity of the as-obtained catalysts was examined, and it was found that the pyrolysis at 700 °C gave rise to the best catalytic activity for the ORR in alkaline media. This heat-treatment temperature was found to be crucial in determining the activity and stability of catalysts, due to the enhanced structural defects, active sites, geometrical complexity, and larger fraction of the pyridinic nitrogen and pyrrolic nitrogen groups. The titanium dioxide/graphene (TiO2/Gr) and graphene/hemin (Gr/Hem) were also studied and compared, and it was revealed that the catalytic activity of TiO2/Gr/Hem catalysts for ORR can be further enhanced. In addition, the chemically bonded element iron in the heat-treated TiO2/Gr/Hem catalysts showed an inhibition effect for ORR and Ti–C–N materials garnered high catalytic activity compared with Ti–C–N–Fe materials in alkaline media. The higher methanol tolerance and durability of the TiO2/Gr/Hem composite materials during ORR were also confirmed. These results reflected the critical influences of the pyrolysis temperature and the chemically bonded element dopants to be the key factor for ORR.

Graphene quantum dots (GQDs) and carbon dots (C-dots) have various alluring properties and potential applications, but they are often limited by unsatisfied optical performance such as low quantum yield, ambiguous fluorescence emission mechanism, and narrow emission wavelength. Herein, we report that bulk polymeric carbon nitride could be utilized as a layered precursor to prepare carbon nitride nanostructures such as nanorods, nanoleaves and quantum dots by chemical tailoring. As doped carbon materials, these carbon nitride nanostructures not only intrinsically emitted UV lights but also well inherited the explicit photoluminescence mechanism of the bulk pristine precursor, both of which were rarely reported for GQDs and C-dots. Especially, carbon nitride quantum dots (CNQDs) had a photoluminescence quantum yield (QY) up to 46%, among the highest QY for metal-free quantum dots so far. As examples, the CNQDs were utilized as a photoluminescence probe for rapid detection of Fe3+ with a detection limit of 1 μM in 2 min and a photoconductor in an all-solid-state device. This work would open up an avenue for doped nanocarbon in developing photoelectrical devices and sensors.Keywords: carbon nitride; photoconduction; photoluminescence; quantum dots; sensors;

Owing to their remarkable catalytic activities, doped nanocarbon materials have been widely employed as efficient noble metal-free catalysts for oxygen reduction reaction (ORR) towards the artificial energy conversion systems, such as fuel cells and a variety of sensors. After several decades of innovative investigation, the substantial controversies still exist ranging from synthesis strategies to actual active sites for doped nanocarbon materials, but greatly pave the development of sustainable ORR electrocatalysts with high efficiency. This review mainly focuses on the newly developed synthesis methods, such as ball milling, co-doping with multi-elements and low temperature preparation with more predictable structures that were reported in the last five years. Particularly, we have also discussed the open controversies and mechanism studies of doped carbon for ORR.

Evaluating the kinetics of biological reaction occurring in confined nanospaces is of great significance in studying the molecular biological processes in vivo. Herein, we developed a nanochannel-based electrochemical reactor and a kinetic model to investigate the immunological reaction in confined nanochannels simply by the electrochemical method. As a result, except for the reaction kinetic constant that was previously studied, more insightful kinetic information such as the moving speed of the antibody and the immunological reaction progress in nanochannels were successfully revealed in a quantitative way for the first time. This study would not only pave the investigation of molecular biological processes in confined nanospaces but also be promising to extend to other fields such as biological detection and clinical diagnosis.

Due to great potential in nanobiotechnology, nanomachines, and smart materials, DNA-directed disassembly of gold nanoparticles (AuNPs) has been extensively explored. In a typical system, nonbase-paired regions (e.g., overhangs and gaps in the linker DNA and oligonucleotide spacers between thiol group and hybridization sequence) are indispensable portions in the disassembly of AuNPs based on DNA displacement reaction. Therefore, it is necessary to study the effect of nonbase-paired regions to improve the kinetics of disassembly of AuNPs. Herein, the disassembly rate of AuNPs based on DNA displacement reaction was investigated by using different length spacers and linker DNA containing various lengths of gaps or overhangs. Interestingly, it was revealed that among the gaps in the linker DNA could be most effectively used to improve the disassembly rate of the AuNPs. As a result, when we introduced gaps into linker DNA, the DNA displacement reaction of AuNPs was markedly shortened to less than 50 min, which was much faster than the previous methods. As a proof of the importance of our findings, a rapid AuNP-based colorimetric DNA biosensor has been successfully prepared. In addition, we showed that the signal of the biosensors could be further amplified using exonuclease III, resulting in a much lower detection limit in comparison with previous sensors similarly using AuNP aggregates as probes.

One of the biggest challenges for materials science is to design facile routes to structurally complex materials, which is particularly important for global applications such as fuel cells. Doped nanostructured carbons are targeted as noble metal-free electrocatalysts for this purpose. Their intended widespread use, however, necessitates simple and robust preparation methods that do not compromise on material performance. Here, we demonstrate a versatile one-pot synthesis of nitrogen-doped carbons that exploits the templating ability of biological polymers. Starting with just metal nitrates and gelatin, multiphase C/Fe3C/MgO nanomaterials are formed, which are then etched to produce active carbon electrocatalysts with accessible trimodal porosity. These show remarkable performance in the oxygen reduction reaction – a key process in proton exchange membrane fuel cells. The activity is comparable to commercial platinum catalysts and shows improved stability with reduced crossover effects. This simple method offers a new route to widely applicable porous multicomponent nanocomposites.

A hydrogen bond-driven supramolecular strategy to synthesize multiphase-Fe anchoring on hierarchical N-doped graphitic carbon was proposed. As a result, the as-obtained catalysts showed unusual trifunctional activities in the oxygen reduction reaction, oxygen evolution reaction and hydrogen evolution reaction, even surpassing noble-metal catalysts such as Pt/C and RuO2.

A heterojunction photocatalyst made up of a single substrate is reported. The heterointerfaces of carbon nitride (CN) are natively compatible due to their very similar chemical and crystalline structures. Moreover, the varieties in the nanostructures of CN led to different energy levels that not only matched well with each other but also enabled a sufficient internal electric field at their interfaces to suppress unwanted recombination of charge carriers in photocatalysis.

The development of efficient and low-cost non-precious-metal electrocatalysts such as Fe–N/C for the oxygen reduction reaction (ORR) is crucial for fuel cells and metal–air batteries. Here, we report a class of highly efficient Fe–N/C electrocatalysts derived from versatile imidazolium-based ionic liquids (ILs) with a halogen-coordinated iron anion. Without any supports, templates, or multi-step pyrolysis, the as-prepared Fe–N/C catalysts exhibited superior activity in the ORR to the state-of-the-art Pt/C in alkaline electrolytes by 44 mV in half-wave potential. More interestingly, owing to the versatile configuration of the imidazolium-based IL precursors, a diverse range of catalyst structures was successfully modulated. Based on this, it was clearly revealed that the electrical conductivity, type/amount of N dopants, and “effective porosity” (not the conventional total surface area) jointly determined the electrocatalytic activity. A pivotal radar chart is further proposed to successfully predict activity in the ORR merely from the structures of Fe–N/C catalysts. The proposed ILs platform would provide a valuable toolbox for the molecular design of precursors to tune the structures of Fe–N/C electrocatalysts towards excellent activity in the ORR in a highly flexible manner, and facilitate the long-term challenging study of relationships between processing, structure and activity.

Graphite-phase polymeric carbon nitride (GPPCN) is one kind of new organic semiconductor for photoelectric conversion, photocatalysis and other important catalytic reactions. However, the low surface area of bulk GPPCN limits its potential applications. Here, we report the preparation of porous GPPCN using industrially available calcium carbonate particles as the hard template; these are not only low-cost, but also easily removed by dilute hydrochloric acid. Interestingly, upon engineering the w/w ratio of template to GPPCN precursor along with the template sizes, our approach resulted in increases of about 4 and 7.5 times in the cathodic photocurrent under visible light (λ > 420 nm) irradiation compared with bulk GPPCN when biased at −0.2 V and 0 V (vs. Ag/AgCl), respectively. These photoelectrochemical activities were higher than those of porous GPPCN obtained by all other reported techniques including the common strategy of using silica nanoparticle templates. This study opens a new avenue to explore the fascinating GPPCN materials for solar energy conversion and environmental remediation, especially for large-scale industrial applications.

Owing to their remarkable catalytic activities, doped nanocarbon materials have been widely employed as efficient noble metal-free catalysts for oxygen reduction reaction (ORR) towards the artificial energy conversion systems, such as fuel cells and a variety of sensors. After several decades of innovative investigation, the substantial controversies still exist ranging from synthesis strategies to actual active sites for doped nanocarbon materials, but greatly pave the development of sustainable ORR electrocatalysts with high efficiency. This review mainly focuses on the newly developed synthesis methods, such as ball milling, co-doping with multi-elements and low temperature preparation with more predictable structures that were reported in the last five years. Particularly, we have also discussed the open controversies and mechanism studies of doped carbon for ORR.

One of the biggest challenges for materials science is to design facile routes to structurally complex materials, which is particularly important for global applications such as fuel cells. Doped nanostructured carbons are targeted as noble metal-free electrocatalysts for this purpose. Their intended widespread use, however, necessitates simple and robust preparation methods that do not compromise on material performance. Here, we demonstrate a versatile one-pot synthesis of nitrogen-doped carbons that exploits the templating ability of biological polymers. Starting with just metal nitrates and gelatin, multiphase C/Fe3C/MgO nanomaterials are formed, which are then etched to produce active carbon electrocatalysts with accessible trimodal porosity. These show remarkable performance in the oxygen reduction reaction – a key process in proton exchange membrane fuel cells. The activity is comparable to commercial platinum catalysts and shows improved stability with reduced crossover effects. This simple method offers a new route to widely applicable porous multicomponent nanocomposites.

Due to great potential in nanobiotechnology, nanomachines, and smart materials, DNA-directed disassembly of gold nanoparticles (AuNPs) has been extensively explored. In a typical system, nonbase-paired regions (e.g., overhangs and gaps in the linker DNA and oligonucleotide spacers between thiol group and hybridization sequence) are indispensable portions in the disassembly of AuNPs based on DNA displacement reaction. Therefore, it is necessary to study the effect of nonbase-paired regions to improve the kinetics of disassembly of AuNPs. Herein, the disassembly rate of AuNPs based on DNA displacement reaction was investigated by using different length spacers and linker DNA containing various lengths of gaps or overhangs. Interestingly, it was revealed that among the gaps in the linker DNA could be most effectively used to improve the disassembly rate of the AuNPs. As a result, when we introduced gaps into linker DNA, the DNA displacement reaction of AuNPs was markedly shortened to less than 50 min, which was much faster than the previous methods. As a proof of the importance of our findings, a rapid AuNP-based colorimetric DNA biosensor has been successfully prepared. In addition, we showed that the signal of the biosensors could be further amplified using exonuclease III, resulting in a much lower detection limit in comparison with previous sensors similarly using AuNP aggregates as probes.

Graphitic carbon nitride (g-CN) is an exciting material – a semiconductor comprised only of carbon and nitrogen. It is very easy to synthesize and there are many papers on the development of this material in key energy applications such as photoelectrochemical (PEC) conversion of solar energy into chemical fuels. As a promising candidate for sustainable photocathodes, g-CN has advantages such as low cost, visible light sensitivity and high chemical stability. However, to date, the performance of g-CN has been limited, partly because standard synthesis methods produce relatively dense materials with low surface area. To combat this, there are now many examples of hard and soft templating to change the structure and morphology of g-CN and introduce porosity. This review will discuss the key advances and challenges in this interesting new field.