Black Phosphorus, a Rising Star 2D Nanomaterial in the Post-Graphene Era: Synthesis, Properties, Modifications, and Photocatalysis Applications.

Semiconductor photocatalysis, a sustainable and renewable technology, is deemed to be a new path to resolve environmental pollution and energy shortage. The development of effective photocatalysts, especially the metal-free photocatalysts, is a critical determinant of this technique. The recently emerged 2D material of black phosphorus with distinctive properties of tunable direct bandgap, ultrahigh charge mobility, fortified optical absorption, large specific surface area, and anisotropic structure has captured enormous attention since the first exfoliation of bulk black phosphorus into mono- or few layered phosphorene in 2014. In this article, the state-of-the-art preparation methods are first summarized for bulk black phosphorus, phosphorene, and black phosphorus quantum dot and then the fundamental structure and electronic and optical properties are analyzed to evaluate its feasibility as a metal-free photocatalyst. Various modifications on black phosphorus are also summarized to enhance its photocatalytic performance. Furthermore, the multifarious applications such as solar to energy conversion, organic removal, disinfection, nitrogen fixation, and photodynamic therapy are discussed and some of the future challenges and opportunities for black phosphorus research are proposed. This review reveals that the rising star of black phosphorus will be a multifunctional material in the postgraphene era.

Degradation of naphthalene with magnetic bio-char activate hydrogen peroxide: Synergism of bio-char and Fe-Mn binary oxides.

This study investigated the hydrogen peroxide (H2O2) activation potential of Fe-Mn binary oxides modified bio-char (FeMn/bio-char) for the degradation of naphthalene, the dominant PAHs in drinking water. Results showed that FeMn/bio-char exhibited 80.7- and 2.18-times decomposition rates towards H2O2 than that of pure bio-char and Fe-Mn binary oxides, respectively, and consequently the FeMn/bio-char/H2O2 photo-Fenton system presented highest naphthalene removal efficiency. The enhanced catalytic activity could be ascribed to the synergistic effect of the combination of bio-char and Fe-Mn binary oxides, such as promoting the adsorption capacity towards contaminant, increasing concentration of persistent free radicals (PFRs) and introducing Fe-Mn binary oxides as new activator. According to the batch-scale experiments, FeMn/bio-char/H2O2 photo-Fenton system could degrade naphthalene effectively at a wide pH ranges, and 82.2% of naphthalene was degraded under natural pH of 5.6 within 148 min. Free radicals quenching studies and electron spin resonance (ESR) analyses verified that the dominant free radical within FeMn/bio-char/H2O2 photo-Fenton system was hydroxyl radical (•OH). According to the preliminary analysis, the generation of •OH were ascribed to the activation of H2O2 by Fe (II), Mn (II) and PFRs on the catalyst surface. The mainly degradation intermediates of naphthalene were identified by GC-MS analysis. Consequently, the possible degradation pathways were proposed. Moreover, naphthalene degradation experiments were also conducted in river, tap water, industrial wastewater as well as medical wastewater, and the results indicated that the FeMn/bio-char/H2O2 photo-Fenton system was effective in the treatment of naphthalene in natural waters. This study brings a valuable insight for the potential environmental applications of modified bio-char.

Synthetic strategies and application of gold-based nanocatalysts for nitroaromatics reduction.

With the increasing requirement of efficient organic transformations on the basic concept of Green Sustainable Chemistry, the development of highly efficient catalytic reaction system is greatly desired. In this case, gold (Au)-based nanocatalysts are promising candidates for catalytic reaction, especially for the reduction of nitroaromatics. They have attracted wide attention and well developed in the application of nitroaromatics reduction because of the unique properties compared with that of other conventional metal-based catalysts. With this respect, this review proposes recent trends in the application of Au nanocatalysts for efficient reduction process of nitroaromatics. Some typical approaches are compared and discussed to guide the synthesis of highly efficient Au nanocatalysts. The mechanism on the use of H2 and NaBH4 solution as the source of hydrogen is compared, and that proposed under light irradiation is discussed. The high and unique catalytic activity of some carriers, such as oxides and carbons-based materials, based on different sizes, structures, and shapes of supported Au nanocatalysts for nitroaromatics reduction are described. The catalytic performance of Au combining with other metal nanoparticles by alloy or doping, like multi-metal nanoparticles system, is further discussed. Finally, a short discussion is introduced to compare the catalysis with other metallic nanocatalysts.

Fabrication of novel magnetic MnFe2O4/bio-char composite and heterogeneous photo-Fenton degradation of tetracycline in near neutral pH.

Iron-based magnetic materials are deemed to be promising catalysts for various catalytic reactions and can be recovered conveniently by an external magnetic field. MnFe2O4 nanoparticle and MnFe2O4/bio-char composite with different bio-char contents were prepared to activate hydrogen peroxide for the degradation of tetracycline (TC). The catalysts were characterized by SEM, BET, XRD, FTIR, VSM and XPS. The results indicated that MnFe2O4 had a spherical shape and was successfully loaded onto the surface of bio-char. The introduction of bio-char effectively suppressed the aggregation of MnFe2O4 and drastically increased the specific surface area. Both MnFe2O4 and MnFe2O4/bio-char composite can be separated easily by an external magnetic field. Using 1:2 composite as heterogeneous photo-Fenton catalyst obtained a degradation of 95% through visible light irradiation of 40 mg L-1solution at natural pH (pH = 5.5) in the presence of 100 mmol L-1 H2O2 for 2 h. Free radical quenching experiment and the ESR results confirm that hydroxyl radicals play the main role for TC degradation. XPS measurements show that both Fe and Mn ions simultaneously participate in the activation of H2O2. The bio-char not only restrains the aggregation of MnFe2O4 leading to the improved removal efficiency of TC, but also has side effects by consuming hydroxyl radicals. By cyclic degradation experiments, the performance of MnFe2O4/bio-char composite is stable and almost unchanged, and the leaching metal ions of both Fe and Mn are neglectful (both below 0.2 mg L-1). Besides, steady performance of MnFe2O4/bio-char catalyst to remove TC from tap water and river water has been certified.

Electrochemical Aptasensor Based on Sulfur-Nitrogen Codoped Ordered Mesoporous Carbon and Thymine-Hg2+-Thymine Mismatch Structure for Hg2+ Detection.

A renewable electrochemical aptasensor was proposed for super-sensitive determination of Hg2+. The novel aptasensor, based on sulfur-nitrogen codoped ordered mesoporous carbon (SN-OMC) and thymine-Hg2+-thymine (T-Hg2+-T) mismatch structure, used ferrocene as signal molecules to achieve the conversion of current signals. In the absence of Hg2+, the thiol-modified T-rich probe 1 spontaneously formed a hairpin structure by base pairing. After being hybridized with the ferrocene-labeled probe 2 in the presence of Hg2+, the hairpin structure of probe 1 was opened due to the preferential formation of the T-Hg2+-T mismatch structure, and the ferrocene signal molecules approached the modified electrode surface. SN-OMC with high specific surface area and ample active sites acted as a signal amplification element in electrochemical sensing. The sensitive determination of Hg2+ can be actualized by analyzing the relationship between the change of oxidation current caused by ferrocene signal molecules and the Hg2+ concentrations. The aptasensor had a fine linear correlation in the range of 0.001-1000 nM with a detection limit of 0.45 pM. The aptasensor also displayed a good response in real sample detection and provided a promising possibility for in situ detection.

Facile Hydrothermal Synthesis of Z-Scheme Bi2Fe4O9/Bi2WO6 Heterojunction Photocatalyst with Enhanced Visible Light Photocatalytic Activity.

An efficient binary Bi2Fe4O9/Bi2WO6 Z-scheme heterojunction was fabricated through a facile hydrothermal route. The obtained Bi2Fe4O9/Bi2WO6 displays high catalytic activity for rhodamine B (RhB) photodegradation, and 100% of RhB was photodegraded by Bi2Fe4O9 (7%)/Bi2WO6 within 90 min, which is much better than that by pure Bi2Fe4O9 and Bi2WO6. The effective photoinduced carrier separation, the broadened photoabsorption range, high oxidation capacity of hole, and the high reduction power of electron are in charge of the elevated catalytic activity because of the formed Z-scheme system. In addition, the effects such as pollutant concentration, pH, inorganic anions, and water sources exerted on photocatalytic performance were also investigated, and the results suggest that Bi2Fe4O9/Bi2WO6 still possesses a high photocatalytic performance. The free-radical trapping experiments and electron spin resonance spin-trapping technology disclose that hole (h+), hydroxy radical (•OH), and superoxide radical (•O2-) are cardinal active radicals in the catalytic system. In terms of the above experimental analysis, a possible photodegradation mechanism of the as-fabricated photocatalyst is thoroughly elucidated. In addition, the possible RhB photodegradation pathway is also raised in the light of the analysis of liquid chromatography-mass/mass spectrometry. In addition, Bi2Fe4O9/Bi2WO6 composite does not display dramatic reduction of the catalytic performance after five recycles. Thus, this study reveals that the as-obtained Bi2Fe4O9/Bi2WO6 catalyst has a great prospect for the environmental purification.