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

A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .

Alkali-Assisted Synthesis of Nitrogen Deficient Graphitic Carbon Nitride with Tunable Band Structures for Efficient Visible-Light-Driven Hydrogen Evolution.

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, ...

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Efficient utilization of solar energy for clean water is an attractive, renewable, and environment friendly way to solve the long-standing water crisis. For this task, we prepared the long-range vertically aligned graphene sheets membrane (VA-GSM) as the highly efficient solar thermal converter for generation of clean water. The VA-GSM was prepared by the antifreeze-assisted freezing technique we developed, which possessed the run-through channels facilitating the water transport, high light absorption capacity for excellent photothermal transduction, and the extraordinary stability in rigorous conditions. As a result, VA-GSM has achieved average water evaporation rates of 1.62 and 6.25 kg m–2 h–1 under 1 and 4 sun illumination with a superb solar thermal conversion efficiency of up to 86.5% and 94.2%, respectively, better than that of most carbon materials reported previously, which can efficiently produce the clean water from seawater, common wastewater, and even concentrated acid and/or alkali solutions.

Vertically Aligned Graphene Sheets Membrane for Highly Efficient Solar Thermal Generation of Clean Water

Delamination of layer materials into two-dimensional single-atom sheets has induced exceptional physical properties, including large surface area, ultrahigh intrinsic carrier mobility, pronounced changes in the energy band structure, and other properties. Here, atomically thin mesoporous nanomesh of graphitic carbon nitride (g-C3N4) is fabricated by solvothermal exfoliation of mesoporous g-C3N4 bulk made from thermal polymerization of freeze-drying assembled Dicyandiamide nanostructure precursor. With the unique structural advantages for aligned energy levels, electron transfer, light harvesting, and the richly available reaction sites, the as-prepared monolayer of mesoporous g-C3N4 nanomesh exhibits a superior photocatalytic hydrogen evolution rate of 8510 μmol h(-1) g(-1) under λ > 420 nm and an apparent quantum efficiency of 5.1% at 420 nm, the highest of all the metal-free g-C3N4 nanosheets photocatalysts.

Atomically Thin Mesoporous Nanomesh of Graphitic C3N4 for High-Efficiency Photocatalytic Hydrogen Evolution

To achieve high energy and power density simultaneously in miniaturized electronic devices, a zinc-ion micro-supercapacitor (ZmSC) is constructed for the first time by integrating a battery-type zinc micro-anode and a capacitor-type carbon nanotube micro-cathode. In the meantime, an electroplating method is developed to in situ replenish the zinc anode when needed without destroying the configuration of the ZmSC, in which the micro-cathode, micro-anode and electrolyte of the ZmSC function as the working electrode, counter electrode and plating solution in the plating process, respectively. This strategy effectively avoids the irreversible consumption of the zinc anode and the fading of the capacitance and cycle life. As a result, the prepared ZmSC exhibits an excellent electrochemical performance, including a high area capacitance of 83.2 mF cm−2 at 1 mA cm−2, a high energy density of 29.6 μW h cm−2 and a high power density of 8 mW cm−2. After 6000 cycles, the ZmSC shows about 87.4% retention (60.9 mF cm−2) of its initial area capacitance at 5 mA cm−2. Furthermore, a higher capacitance (76 mF cm−2) and a longer cycling life are obtained after re-plating the zinc anode. This method features a simple configuration and easy operation, and holds great promise for use in other long cycle life zinc-based microdevices.

A capacity recoverable zinc-ion micro-supercapacitor

High‐Density Monolith of N‐Doped Holey Graphene for Ultrahigh Volumetric Capacity of Li‐Ion Batteries

An interconnected framework of mesoporous graphitic-C3N4 nanofibers merged with in situ incorporated nitrogen-rich carbon has been prepared. The unique composition and structure of the nanofibers as well as strong coupling between the components endow them with efficient light-harvesting properties, improved charged separation, and a multidimensional electron transport path that enhance the performance of hydrogen production. The as-obtained catalyst exhibits an extremely high hydrogen-evolution rate of 16885 μmol h−1 g−1, and a remarkable apparent quantum efficiency of 14.3 % at 420 nm without any cocatalysts, which is much higher than most reported g-C3N4-based photocatalysts even in the presence of Pt-based cocatalysts.

Graphitic Carbon Nitride/Nitrogen-Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts

Mesoporous materials have attracted considerable interest due to their huge surface areas and numerous active sites that can be effectively exploited in catalysis. Here, 2D mesoporous graphitic-C3N4 nanolayers are rationally assembled on 2D mesoporous graphene sheets (g-CN@G MMs) by in situ selective growth. Benefiting from an abundance of exposed edges and rich defects, fast electron transport, and a multipathway of charge and mass transport from a continuous interconnected mesh network, the mesh-on-mesh g-CN@G MMs hybrid exhibits higher catalytic hydrogen evolution activity and stronger durability than most of the reported nonmetal catalysts and some metal-based catalysts.

Jian Gao

Papers

Atomically Thin Mesoporous Nanomesh of Graphitic C3N4 for High-Efficiency Photocatalytic Hydrogen Evolution

A capacity recoverable zinc-ion micro-supercapacitor

High‐Density Monolith of N‐Doped Holey Graphene for Ultrahigh Volumetric Capacity of Li‐Ion Batteries

Graphitic Carbon Nitride/Nitrogen-Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts

Mesh‐on‐Mesh Graphitic‐C3N4@Graphene for Highly Efficient Hydrogen Evolution