Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

A review on g-C3N4-based photocatalysts

The development of new layered materials has experienced an evolution from graphene to metal oxide and metal chalcogenide nanosheets, and more recently to two-dimensional (2D) covalent organic frameworks, such as conjugated carbon nitride nanosheets (CNNs) with a spectral gap in the band structure. The anisotropic 2D geometric morphology, together with the aromatic π-conjugated framework, endows polymeric CNNs with unique properties, such as an enlarged surface area with a highly opened-up flat structure, reduced thickness with enhanced electron mobility and with intrinsic semiconductive features, which support their attractive bandgap- and surface-engineered applications ranging from energy-related topics to other new emerging fields. In this review, recent research advances in the establishment of two synthetic strategies for CNNs are firstly overviewed, namely, the top-down delamination of graphitic carbon nitride (CN) solids and the bottom-up assembly of molecular building blocks in a 2D manner. Efficient approaches aimed at advancing CNNs for target-specific applications, including hybridizing, doping, sensitization, copolymerization and nanorefinement, are also described as possible solutions.

Two-dimensional covalent carbon nitride nanosheets: synthesis, functionalization, and applications

Semiconductor polymeric graphitic carbon nitride (g-C3N4) photocatalysts have attracted dramatically growing attention in the field of the visible-light-induced hydrogen evolution reaction (HER) because of their facile synthesis, easy functionalization, attractive electronic band structure, high physicochemical stability and photocatalytic activity. This review article presents a panorama of the latest advancements in the rational design and development of g-C3N4 and g-C3N4-based composite photocatalysts for HER application. Concretely, the review starts with the development history, synthetic strategy, electronic structure and physicochemical characteristics of g-C3N4 materials, followed by the rational design and engineering of various nanostructured g-C3N4 (e.g. thinner, highly crystalline, doped, and porous g-C3N4) photocatalysts for HER application. Then a series of highly efficient g-C3N4 (e.g., metal/g-C3N4, semiconductor/g-C3N4, metal organic framework/g-C3N4, carbon/g-C3N4, conducting polymer/g-C3N4, sensitizer/g-C3N4) composite photocatalysts are exemplified. Lastly, this review provides a comprehensive summary and outlook on the major challenges, opportunities, and inspiring perspectives for future research in this hot area on the basis of pioneering works. It is believed that the emerging g-C3N4-based photocatalysts will act as the “holy grail” for highly efficient photocatalytic HER under visible-light irradiation.

Semiconductor polymeric graphitic carbon nitride photocatalysts: the “holy grail” for the photocatalytic hydrogen evolution reaction under visible light

Semiconductor photocatalysis is recognized as a promising strategy to simultaneously address energy needs and environmental pollution. Titanium dioxide (TiO2 ) has been investigated for such applications due to its low cost, nontoxicity, and high chemical stability. However, pristine TiO2 still suffers from low utilization of visible light and high photogenerated-charge-carrier recombination rate. Recently, TiO2 photocatalysts modified by dual cocatalysts with different functions have attracted much attention due to the extended light absorption, enhanced reactant adsorption, and promoted charge-carrier-separation efficiency granted by various cocatalysts. Recent progress on the component and structural design of dual cocatalysts in TiO2 photocatalysts is summarized. Depending on their components, dual cocatalysts decorated on TiO2 photocatalysts can be divided into the following categories: bimetallic cocatalysts, metal-metal oxide/sulfide cocatalysts, metal-graphene cocatalysts, and metal oxide/sulfide-graphene cocatalysts. Depending on their architecture, they can be categorized into randomly deposited binary cocatalysts, facet-dependent selective-deposition binary cocatalysts, and core-shell structural binary cocatalysts. Concluding perspectives on the challenges and opportunities for the further exploration of dual cocatalyst-modified TiO2 photocatalysts are presented.

Dual Cocatalysts in TiO 2 Photocatalysis.

The synthesis of a novel In2O3/In2S3 microsphere heterostructures is conducted through a well-designed two-step hydrothermal method. These composites are first applied for efficient fixation of N2 to NH3 under mild conditions without any organic scavengers and precious-metal cocatalysts. Here the In2S3 flakes are in situ generated and uniformly assembled on In2O3 microsphere. The phase structures, morphologies and oxygen vacancies of the samples are systematically characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse-reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL), Raman, electron spin resonance (ESR) spectroscopy and photoelectrochemistry. Meanwhile, the investigation of photocatalytic performance can confirm that the nitrogen fixation rate of In2O3/In2S3 (III) heterostructure is 40.04 μmol g−1 h−1, which is about 4.7 and 6.0 times higher than that of pure In2O3 and In2S3, respectively.

Fabrication of In2O3/In2S3 microsphere heterostructures for efficient and stable photocatalytic nitrogen fixation

A new visible light responsive ZnO–ZnS/C photocatalysts have been successfully synthesized by a simple heat-treating procedure using ZnSO4 as single precursor for the first time. The resultant samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and BET surface area measurement. The results showed that the ZnO–ZnS/C catalysts were directly formed by thermal decomposition of ZnSO4 impregnated on the activated carbon at high temperature under open atmospheric conditions. Here, a possible growth mechanism of the coupled ZnO–ZnS/C photocatalysts was proposed. Activated carbon played both reducing agent and support role in formation of ZnO–ZnS/C catalysts. The photocatalytic activities of catalysts were investigated by degrading reactive brilliant blue K-3R under visible light irradiation. The synthesized catalysts showed excellent photocatalytic activity compared with ZnO/C and pure ZnO, which is ascribed to the formation of ZnO–ZnS heterojunctions in catalysts. Furthermore, influences of preparation conditions on photocatalytic activity of the catalysts have been investigated.

Synthesis of visible light responsive ZnO–ZnS/C photocatalyst by simple carbothermal reduction

Sunlight-driven dinitrogen fixation can lead to a novel concept for the production of ammonia under mild conditions. However, the efficient artificial photosynthesis of ammonia from ordinary air (instead of high pure N2) has never been implemented. Here, we report for the first time the intrinsic catalytic activity of Bi2MoO6 catalyst for direct ammonia synthesis under light irradiation. The edge-exposed coordinatively unsaturated Mo atoms in an Mo−O coordination polyhedron can act as activation centers to achieve the chemisorption, activation, and photoreduction of dinitrogen efficiently. Using that insight as a starting point, through rational structure and defect engineering, the optimized Bi2MoO6 sunlight-driven nitrogen fixation system, which simultaneously possesses robust nitrogen activation ability, excellent light-harvesting performance, and efficient charge transmission was successfully constructed. As a surprising achievement, this photocatalytic system demonstrated for the first time ultra-efficient (1.3 mmol g−1 h−1) and stable sunlight-driven nitrogen fixation from air in the absence of any organic scavengers.

Hydrogenated Bismuth Molybdate Nanoframe for Efficient Sunlight-Driven Nitrogen Fixation from Air.

Photocatalysis is intensely employed to remove refractory organic pollutants in water but suffers from low efficiency due to the rapid recombination of photogenerated electrons and holes. Here, car...

Graphitic Carbon Nitride with Carbon Vacancies for Photocatalytic Degradation of Bisphenol A

Over the past few years, the direct assembly of co-catalyst/modification materials into mesoporous photocatalysts has been considered a great challenge. Additionally, for photooxidation, the simultaneous achievement of fast charge separation, broad spectrum photocatalytic activity and higher carrier utilization efficiency (generating more active oxidizing groups) is quite necessary but has never been studied. To this end, for the first time, using sub-3 nm GQDs as co-catalyst, we have successfully achieved uniform modification for a mesoporous photocatalyst (mesoporous Bi2MoO6) using a novel electrostatic self-assembly method. The sub-3 nm GQDs, which were prepared from graphene nanosheets by a modified chemical oxide method, exhibit many unique physical and chemical properties, such as small size, electronic capture, up-conversion, and in particular, peroxidase-like activity. After the GQDs were modified, the resulting mesoporous hybrid photocatalyst (GQDs–BM) exhibited excellent charge separation efficiency and broad spectrum photocatalytic activity from UV to NIR light. More importantly, we found that a certain amount of H2O2 was produced through a photoreduction effect during the photocatalytic process. Unfavorably, for bare Bi2MoO6, the continuously-accumulating H2O2 could not efficiently convert into ·OH by a one-photoelectron reduction, which results in the indirect waste of photo-excited electrons. However, the chemical co-catalysis of GQDs could make this process (H2O2 → ·OH) more quick and efficient and moreover, did not need any additional photoelectrons, which means the effective enhancement of the utilization efficiency of photo-excited electrons (generating more ·OH). Additionally, for the as-prepared GQDs–BM, a sharp increase in photo-degradation activity for different target pollutants, such as BPA, MB, TC, CIP and phenol further confirmed that the simultaneous physical and chemical co-catalysis of GQDs can efficiently enhance the photocatalytic activity of mesoporous Bi2MoO6.

Controllable electrostatic self-assembly of sub-3 nm graphene quantum dots incorporated into mesoporous Bi2MoO6 frameworks: efficient physical and chemical simultaneous co-catalysis for photocatalytic oxidation

Hongchao Ma

Papers

Fabrication of In2O3/In2S3 microsphere heterostructures for efficient and stable photocatalytic nitrogen fixation

Synthesis of visible light responsive ZnO–ZnS/C photocatalyst by simple carbothermal reduction

Hydrogenated Bismuth Molybdate Nanoframe for Efficient Sunlight-Driven Nitrogen Fixation from Air.

Graphitic Carbon Nitride with Carbon Vacancies for Photocatalytic Degradation of Bisphenol A

Controllable electrostatic self-assembly of sub-3 nm graphene quantum dots incorporated into mesoporous Bi2MoO6 frameworks: efficient physical and chemical simultaneous co-catalysis for photocatalytic oxidation