Incorporating photocatalytic nanoparticles with biochar templates can produce biochar-supported photocatalysts (BSPs) and combine the advantages of biochar with catalytic nanoparticles. The obtained composite exhibits excellent surface properties, crystallinity, chemical stability, recoverability, and higher photocatalytic competency than the bare semiconductor photocatalyst. The literature and advances in BSPs based on the combination of low-cost biochar and catalytic nanoparticles are presented in this review. Various synthetic techniques and physicochemical properties of BSPs are summarized. The article then discusses in detail the important role of biochar in influencing the photocatalytic performance of BSPs such as supporting nanoparticles, increasing the surface area and the number of active sites, shuttling electrons, acting as an electron reservoir, increasing charge separation, and reducing band gap energy. Furthermore, the synergistic effects of adsorption and photodegradation of organic pollutants by BSPs are discussed with in-depth mechanistic evidence. Finally, the application of BSPs in various fields and constructive suggestions for their future development are reported.

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Recent progress in biochar-supported photocatalysts: synthesis, role of biochar, and applications

MoS2 is a very attractive material and has been well studied for potential applications in various areas. However, due to the wide variety of factors affecting the molecular and electronic structure of MoS2, several contradictory reports about the adsorptive and photocatalytic properties of such materials have been published. In most of these reports, the effect of the actual phase of the materials on the properties was neglected. Here, different phases of MoS2 nanosheets (1T/2H, 1T/3R and 2H) have been obtained using the hydrothermal method with different Mo : S molar ratios and different autoclave filling ratios. The obtained materials have been thoroughly characterized using Raman, UV-vis, powder XRD, SEM, TEM and XPS measurements in order to accurately identify the existing phases in each material. A comparative study of the photocatalytic organic dye degradation efficiency under white light irradiation has been conducted using methyl orange to correlate the different activity of each material to the respective phase composition. The results indicate a much higher performance of the 1T/2H phase compared to the 2H and 3R phases. Detailed computational studies of the different phases revealed the emergence of mid-gap states upon introducing 1T sites into the 2H lattice. This leads to the improvement of the photocatalytic activity of 1T/2H compared to the other prepared materials.

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A comparative study on the photocatalytic degradation of organic dyes using hybridized 1T/2H, 1T/3R and 2H MoS2 nano-sheets

Multiwalled carbon nanotube (MWCNT)/Bi4O5Br2 materials have been prepared with the Bi4O5Br2 ultrasmall nanosheets in situ strong coupling to MWCNT via the ionic liquid (IL) assisted solvothermal method. The formation mechanism was based on the original formation of strong coupling between the IL and MWCNT, and then the tight junctions between Bi4O5Br2 and MWCNT can be established as the bromine ions in the IL react with bismuth source to in situ produce Bi4O5Br2 during solvothermal process. The structures, morphologies, surface features, optical properties, electronic structures and photocatalytic properties were investigated in detail. The MWCNT/Bi4O5Br2 materials exhibited increased photocatalytic activity than pure Bi4O5Br2 for the degradation of antibiotic agent tetracycline hydrochloride and rhodamine B. Meanwhile, the 0.1 wt% MWCNT/Bi4O5Br2 materials displayed the highest activity. The hole and O2 − were determined to be the main active species during the photodegradation process under visible light irradiation by the electron spin resonance, X-ray photoelectron spectroscopy valence band spectra and active species trapping experiments. After the introduction of MWCNT, the molecular oxygen activation capacity of Bi4O5Br2 greatly improved, which was believed to be responsible for the increased photocatalytic activity.

Bi4O5Br2 ultrasmall nanosheets in situ strong coupling to MWCNT and improved photocatalytic activity for tetracycline hydrochloride degradation

Edge-rich active sites of ultrathin layered molybdenum disulphide (MoS2) nanosheets were synthesized by a hydrothermal method. The effect of pH on the formation of MoS2 nanosheets and their photocatalytic response have been investigated. Structural and elemental analysis confirm the presence of S–Mo–S in the composition. Morphological analysis confirms the presence of ultrathin layered nanosheets with a sheet thickness of 10–28 nm at pH 1. The interplanar spacing of MoS2 layers is in good agreement with the X-ray diffraction and high-resolution transmission electron microscopy results. A comparative study of the photocatalytic performance for the degradation of methylene blue (MB) and rhodamine B (RhB) by ultrathin layered MoS2 under visible light irradiation was performed. The photocatalytic activity of the edge-rich ultrathin layered nanosheets showed a fast response time of 36 min with the degradation rate of 95.3% of MB and 41.1% of RhB. The photocatalytic degradation of MB was superior to that of RhB because of the excellent adsorption of MB than that of RhB. Photogenerated superoxide radicals were the key active species for the decomposition of organic compounds present in water, as evidenced by scavenger studies.

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Ultrathin layered MoS2 nanosheets with rich active sites for enhanced visible light photocatalytic activity

Molybdenum disulfide (MoS2) with unique electronic and physical properties has attracted great interest in the field of next-generation optoelectronic and photonic devices for societal benefits. In...

Multifunctional Few-Layer MoS2 for Photodetection and Surface-Enhanced Raman Spectroscopy Application with Ultrasensitive and Repeatable Detectability

MoS2 nanosheets were for the first time prepared by H2SiO3 exfoliation, i.e., the precursors ((NH4)6Mo7O24·4H2O and thiourea) were embedded inside the hydrogel of H2SiO3 which provides steric hindrance for MoS2 growth. After removal of H2SiO3, MoS2 nanosheets were obtained. The appropriate dosage of hydrogel of silicic acid is the determining factor in preparing homogeneous nanosheets of MoS2. The prepared MoS2 nanosheets possess a high specific surface area of 37.8 m2/g, and present excellent UV–visible-NIR absorbance properties, and the absorption peaks of visible region are much higher than that of ultraviolet region. Therefore, they can be used as excellent catalysts for visible-light-driven degradation of methyl orange (MO). The effect of photo-degradation parameters of MO including pH value, dosage of catalyst and initial concentration was studied. The strongly acidic solution of MO facilitates producing free radicals of OH in this catalytic system. The MoS2 nanosheets can be reused 10 times with little change of degradation rate, indicating that they are stable under visible-light irradiation.

Photo-catalytic degradation of methyl orange under visible light by MoS2 nanosheets produced by H2SiO3 exfoliation

The invention discloses a composite nanotube composed of a molybdenum disulfide-carbon-carbon nanotube and a preparation method thereof. The method comprises the following steps: firstly, orderly dissolving ammonium tetrathiomolybdate and a carbon high-molecular polymer with surface activity into water; then adding a multiwalled carbon nanotube; centrifuging, drying and burning after carrying out ultrasonic dispersing, so as to prepare MoS2-C/CNTs. By using the surface activity of a carbon high-molecular polymer, the molybdenum disulfide is more evenly dispersed on the surface of the carbon nanotube; on the other hand, the conductivity of a compound is improved through the compound of amorphous carbon and molybdenum disulfide left on the surface of the carbon nanotube when a mixture is burnt at high temperature.

Liu Wenhong

Papers

Photo-catalytic degradation of methyl orange under visible light by MoS2 nanosheets produced by H2SiO3 exfoliation

Composite nanotube composed of molybdenum disulfide-carbon-carbon nanotube and preparation method thereof