As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

A review on g-C3N4-based photocatalysts

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties becom...

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

Replacing the rare and precious platinum (Pt) electrocatalysts with earth-abundant materials for promoting the oxygen reduction reaction (ORR) at the cathode of fuel cells is of great interest in developing high-performance sustainable energy devices. However, the challenging issues associated with non-Pt materials are still their low intrinsic catalytic activity, limited active sites, and the poor mass transport properties. Recent advances in material sciences and nanotechnology enable rational design of new earth-abundant materials with optimized composition and fine nanostructure, providing new opportunities for enhancing ORR performance at the molecular level. This Review highlights recent breakthroughs in engineering nanocatalysts based on the earth-abundant materials for boosting ORR.

Earth-Abundant Nanomaterials for Oxygen Reduction.

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.

Dissolution and Liquid Crystals Phase of 2D Polymeric Carbon Nitride

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

Chemical Cleavage of Layered Carbon Nitride with Enhanced Photoluminescent Performances and Photoconduction

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.

Reversible Assembly of Graphitic Carbon Nitride 3D Network for Highly Selective Dyes Absorption and Regeneration

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.

Recent advances of doped carbon as non-precious catalysts for oxygen reduction reaction

A novel porphyrin-based two-dimensional metal–organic framework (MOF) nanodisk with small size and few layers was prepared by coordination chelation between meso-tetra(4-carboxyphenyl)porphine ligand and Zn(II) paddlewheel metal nodes. With 4,4′-biphenyldicarboxylic acid (BPDC) as nucleation modulator, the anisotropic growth of MOF was impeded by the increased steric hindrance, yielding small Zn–TCPP(BP) MOF crystals. The as-prepared MOF nanodisk exhibited good electrocatalytic activity and selectivity towards nitrite due to the independent distribution of the porphyrin molecules in the framework and the sandwich structure of the prepared Zn–TCPP(BP) nanodisk, which increased the accessible active sites.

Anran Liu

Papers

Dissolution and Liquid Crystals Phase of 2D Polymeric Carbon Nitride

Chemical Cleavage of Layered Carbon Nitride with Enhanced Photoluminescent Performances and Photoconduction

Reversible Assembly of Graphitic Carbon Nitride 3D Network for Highly Selective Dyes Absorption and Regeneration

Recent advances of doped carbon as non-precious catalysts for oxygen reduction reaction

Synthesis of porphyrin-based two-dimensional metal–organic framework nanodisk with small size and few layers