Self-healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers the design and generic principles of self-healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self-healing materials are summarised, and generic, fundamental material-independent principles and mechanism are discussed and evaluated.

Self‐Healing Materials

Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2: a review

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

Although graphitic carbon nitride (g-C3N4) is an attractive photocatalyst for solar H2 generation, the preparation of g-C3N4 nanosheets via a “green” and simple method as well as the construction of highly-efficient g-C3N4-based photocatalysts are still challenges. In this study, g-C3N4 nanosheets prepared by a simple probe sonication assisted liquid exfoliation method were used to construct 2D-2D MoS2/g-C3N4 photocatalyst for photocatalytic H2 production. The 2D-2D MoS2/g-C3N4 photocatalyst containing 0.75% MoS2 showed the highest H2 evolution rate of 1155 μmol·h−1·g−1 with an apparent quantum yield of 6.8% at 420 nm monochromatic light, which is much higher than that of the optimized 0D-2D Pt/g-C3N4 photocatalyst. The high photocatalytic H2 production activity of 2D-2D MoS2/g-C3N4 photocatalyst can be attributed to the large surface area and the formed 2D interfaces between MoS2 and g-C3N4 nanosheets. As demonstrated by photoluminescence quenching and time-resolved fluorescence decay studies, the 2D interfaces can accelerate the photoinduced charge transfer, resulting in the high photocatalytic H2 production performance. This study provides a new strategy in developing highly-efficient g-C3N4-based photocatalysts for H2 production via using 2D nanojunction as a bridge to promote the photoinduced charge separation and transfer.

Liquid exfoliation of g-C3N4 nanosheets to construct 2D-2D MoS2/g-C3N4 photocatalyst for enhanced photocatalytic H2 production activity

Recently, Fe-based metal–organic frameworks (MOFs) have attracted increasing attention and been widely used. To date, however, it is unknown whether they can be employed to degrade tetracycline, one of the most widely used antibiotics. This work therefore aims to provide such support by comparing the performance of three Fe-based MOFs (namely, Fe-MIL-101, Fe-MIL-100, and Fe-MIL-53) in removing tetracycline. Experimental results showed that Fe-MIL-101 exhibited the best performance in tetracycline removal, with 96.6% of tetracycline being removed (initial tetracycline concentration at 50 mg/L) while Fe-MIL-100 and Fe-MIL-53 removed 57.4% and 40.6% under the same conditions. Additionally, the effects of adding dosage, adsorption time, and initial concentration of tetracycline on degradation efficiency were examined. It was found that the adsorption and photocatalytic degradation effect was better with the increase of time, the optimum dosage of Fe-MIL-101 was 0.5 g/L and the removal efficiency decreased with the increasing of initial tetracycline concentrations. Moreover, the trapping experiments and ESR tests indicated that O2−, OH and h+ were the main active species in photocatalytic degradation process of tetracycline. Due to its high removal efficiency and simple synthesis, it could be used as a potential catalyst for degradation of tetracycline and other antibiotics.

Simultaneously efficient adsorption and photocatalytic degradation of tetracycline by Fe-based MOFs.

NiS and MoS2 nanosheet co-modified graphitic C3N4 ternary heterostructure for high efficient visible light photodegradation of antibiotic

Graphitic C3N4/ultrathin MoS2 (MoS2/g-C3N4) hybrids were synthesized via a facile bathing and ultrasound method. In this process, a well-bonded interface structure was formed between ultrathin MoS2 nanosheets and g-C3N4 through adjusting the amount of MoS2 in the MoS2/g-C3N4 hybrids. The MoS2/g-C3N4 hybrids were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), transmission electron microscopy (TEM) and UV-vis spectroscopy (UV-vis). The MoS2/g-C3N4 photocatalyst showed excellent photocatalytic activity in the photodegradation of organic pollutants. In this work, methyl orange (MO) was used as the simulative pollutant; the highest photodegradation rate (92.4%) was obtained when the amount of MoS2 was 5 wt% in the MoS2/g-C3N4 hybrids (0.05-MC), with a kinetic constant of 0.0189 min−1 after being irradiated under visible light for 2 h. Besides, 0.05-MC also showed excellent recyclability and chemical stability, and a photodegradation rate of 79.93% was reached after being reused 10 times. For practical pollutants, the photocatalytic degradation rates of ciprofloxacin (CIP) and tetracycline hydrochloride (TC) have been increased dramatically under the visible light irradiation. The excellent photocatalytic properties of MoS2/g-C3N4 hybrids can be ascribed to the enhanced separation rate and accelerated mobility of photogenerated charges through ultrathin MoS2 nanosheets’ modification.

Controllable synthesis of graphitic C3N4/ultrathin MoS2 nanosheet hybrid nanostructures with enhanced photocatalytic performance

N, S co-doped-TiO2/fly ash beads composite material and visible light photocatalytic activity

Bi nanoparticles are grown on BiOCl nanosheets via an in situ chemical reduction in a KBH4 aqueous solution. Bi/BiOCl nanosheets with different contents of Bi nanoparticles can be achieved by changing the concentration of the KBH4 solution. The structure, morphology, elemental composition and optical absorption performance are characterized using an X-ray diffraction diffractometer, a scanning electron microscope, a high resolution transmission electron microscope, an X-ray photoelectron spectrometer and a UV-Vis diffuse reflection spectrometer. The photocatalytic activities of the as-prepared photocatalysts are tested using the degradation of methyl orange under both UV light and visible light irradiation. Bi nanoparticles modified on BiOCl nanosheets not only enhance the photocatalytic activity under UV light irradiation, but also achieve visible light photocatalytic activity. The mechanism of the photocatalytic processes, such as optical absorption, charge transfer and surface reactions, for the Bi/BiOCl nanosheets are discussed in detail.

Zhixiang Zheng

Papers

NiS and MoS2 nanosheet co-modified graphitic C3N4 ternary heterostructure for high efficient visible light photodegradation of antibiotic

Controllable synthesis of graphitic C3N4/ultrathin MoS2 nanosheet hybrid nanostructures with enhanced photocatalytic performance

N, S co-doped-TiO2/fly ash beads composite material and visible light photocatalytic activity

Photocatalytic properties of Bi/BiOCl heterojunctions synthesized using an in situ reduction method

Effect of silica on the microstructure and photocatalytic properties of titania