Latest ArticlesAlthough MoS2 has been proved to be a very ideal cocatalyst in advanced oxidation process (AOPs), the activation process of peroxymonosulfate (PMS) is still inseparable from metal ions which inevitably brings the risk of secondary pollution and it is not conducive to large-scale industrial application. In this study, the commercial MoS2, as a durable and efficient catalyst, was used for directly activating PMS to degrade aromatic organic pollutant. The commercial MoS2/PMS catalytic system demonstrated excellent removal efficiency of phenol and the total organic carbon (TOC) residual rate reach to 25%. The degradation rate was significantly reduced if the used MoS2 was directly carried out the next cycle experiment without any post-treatment. Interestingly, the commercial MoS2 after post-treated with H2O2 can exhibit good stability and recyclability for cyclic degradation of phenol. Furthermore, the mechanism for the activation of PMS had been investigated by density functional theory (DFT) calculation. The renewable Mo4+ exposed on the surface of MoS2 was deduced as the primary active site, which realized the direct activation of PMS and avoided secondary pollution. Taking into account the reaction cost and efficient activity, the development of commercial MoS2 catalytic system is expected to be applied in industrial wastewater.
Due to the relatively sluggish charge carrier separation in metal sulfides, the photocatalytic activity of them is still far lower than expected. Herein, sulfur vacancies and in-plane SnS2/SnO2 heterojunction were successfully introduced into the SnS2 nanosheets through high energy ball-milling. These defective structures were studied by the electron paramagnetic resonance, Raman spectra, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscope analyses. The sulfur vacancies and in-plane heterojunctions strongly accelerate the separation of photoexcited electron-hole pairs, as confirmed by the photoluminescence emission spectra and time-resolved photoluminescence decay spectra. The introduction of sulfur vacancies and in-plane heterojunction in SnS2 nanosheets results in roughly six times higher photodegrading rate for methyl orange and four times higher photocatalytic reduction rate of Cr6+ than those of pure SnS2 nanosheets.
Metal nanoclusters have shown great potential in photocatalysis, while simultaneous removal of both inorganic and organic contaminants by metal nanoclusters under visible light is less explored. Here, we synthesized Agm(SR)n (SR represents 3-mercaptopropyltriethoxysilane ligand) nanoclusters (~1 nm) via a reduction of silver triphenylphosphine under ambient conditions in the presence of 3-mercaptopropyltriethoxysilane. The nanocluster was characterized by UV–vis spectroscopy, high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectrum (FTIR), and X-ray photoelectron spectroscopy (XPS). Under 5 W blue LED, the Agm(SR)n/P25 exhibits enhanced catalytic activity for simultaneous methyl orange (MO) oxidation and Cr(Ⅵ) reduction, and also for synchronous 4-chlorophenol oxidation and Cr(Ⅵ) reduction. Mechanism studies by electrochemical impedance spectroscopy (EIS), photoluminescence (PL), electron spin resonance (ESR) etc. and control experiments reveal that the unique structure of silver nanoclusters with thiolate ligands is vital to the high catalytic performance, and both the photo-generated holes and superoxide radicals are responsible for the decomposition of MO.
In recent years, oil spills caused by human activities have occurred frequently, and the resultant oil pollution has received extensive attention worldwide. In this paper, a total of 50 water samples were collected from the northeastern part of the South China Sea, and total petroleum hydrocarbons (TPHs) and n-alkane content in the samples were analyzed by gas chromatography-flame ionization detector (GC-FID) technology. The petroleum hydrocarbon characteristic indices, such as carbon predominance index (CPI) and terrigenous/aquatic ratio (TAR), were calculated to trace the source of petroleum hydrocarbons. The measured value of TPHs ranged from 121.31–603.02 μg/L. For surface waters, the TPHs in the northern coastal waters and the central waters were higher than that in the far shore. For vertical waters, the TPHs sharply decreased at first, and then increased slowly and finally reached a steady state. The n-alkanes in the water samples were concentrated in C10-C38, and they were mainly from terrestrial higher plant. The waters in the near shore, mid-layer and deep sea showed a strong reducing terrestrial characteristic, while the surface waters in the open sea showed an obvious oxidizing endogenous characteristic.
In this study, various conditions for the removal of polyvinyl alcohol (PVA) by electrocoagulation (EC) coupled catalytic oxidation are systematically studied. The direct oxidation of the anode, the reduction of the cathode, the oxidation of ·OH and ·Cl, and the synergistic effect of flocculation on the degradation of polyvinyl alcohol are investigated. It is observed that the optimum experimental conditions obtained are as follows: Cell voltage 9 V, natural pH 7, NaCl concentration 0.02 mol/L, and interelectrode distance 3.0 cm. The evolution of iron ions is also discussed in the EC process. By contrast, EC had made an outstanding contribution to the removal of PVA, which removes 71.29% of PVA. Free radicals, especially ·OH and ·Cl, are equivalent to the contribution of the electrodes in the degradation of PVA. And the contribution of PVA degradation by anode oxidation and cathode reduction are 12.76% and 8.02%, respectively. Characterization of solution and floc, such as Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), GC–MS and molecular weight, showed that PVA is effectively removed by the EC process, and a possible degradation pathway is proposed.
Efficient generation of singlet oxygen (1O2) by an excitonic energy transfer process is highly desired on a semiconductor photocatalyst for selective oxidation of methyl phenyl sulfide (MPS). Herein, it is demonstrated that a large amount of 1O2 is produced on pristine graphitic carbon nitride (CN) nanosheet compared with bismuth oxybromide (BiOBr) and commercial P25 titanium dioxide (TiO2). This leads to a certain photoactivity of CN for MPS oxidation. The observed ~77% selectivity for CN depends on the competitive results of excitonic energy transfer for 1O2 formation and charge carrier separation for superoxide radical (O2·-) production, which are based on the phosphorescence spectra and electron paramagnetic resonance signals, respectively. Moreover, ultrathin CN nanosheets are synthesized by thermal treatment with the cyanuric acid-melamine hydrogen bonded aggregates as precursors. It is confirmed that the amount of produced 1O2 could be increased by decreasing the thickness of resultant CN nanosheets. The optimized ultrathin CN nanosheet (~4 nm) exhibits excellent photoactivity with high selectivity (~99%). It is suggested that the excitonic energy transfer for 1O2 formation is close related to the intrinsic exciton binding energy and the two-dimensional quantum confinement effect. This work establishes a basic mechanistic understanding on the excitonic processes in CN, and develops a feasible route to design CN-based photocatalysts for efficient 1O2 generation.
In this work, we report Co3O4@PPy hybrid structured electrode materials for overall water splitting. The as-synthesized Co3O4/PPy-120 samples present excellent electrocatalytic performances for OER and HER and long durability. It only requires an operating potential of 1.67 V to deliver a current density of 10 mA/cm2 with a remarkable durability for 28 h. The superior electrocatalytic performances mainly can be attributed to the unique heterostructures and the synergistic effects between PPy and Co3O4 electrode materials.
Alloy and small size nanostructures are favorable to catalytical performance, but not to surface-enhanced Raman spectroscopy (SERS) applications. Integrating SERS and catalytic activity into the nanocrystals with both alloy and small size structures is of great interest in fabrication of SERS platform to in situ monitor catalytical reaction. Herein, we report a facile method to synthesize Au@AgPd trimetallic nanoflowers (Au@AgPd NFs) with both SERS and catalytic activities, through simultaneous selective growth of Ag and Pd on Au core to form highly-branched alloy shell. These nanocrystals have the properties of small sizes, defects abundance, and highly-dispersed alloy shell which offer superior catalytic activity, while the merits of monodisperse, excellent stability, and highly-branched shell and core/alloy-shell structure promise the enhanced SERS activity. We further studied their growth mechanisms, and found that the ratio of Ag to Pd, sizes of Au core, and surfactant cetyltrimethylammonium bromide together determine this special structure. Using this as-synthesized nanocrystals, a monolayer bifunctional platform with both SERS and catalytical activity was fabricated through selfassembly at air/water interface, and applied to in situ SERS monitoring the reaction process of Pd-catalyzed hydrogenation of 4-nitrothiophenol to 4-aminothiophenol.
In the past ten years, perovskite solar cells were rapidly developed, but the intrinsic unbalanced charge carrier diffusion lengths within perovskite materials were not fully addressed by either a planar heterojunction or meso-superstructured perovskite solar cells. In this study, we report bulk heterojunction perovskite solar cells, where perovskite materials CH3NH3PbI3 is blended with solution-processed n-type TiOx nanoparticles as the photoactive layer. Studies indicate that one-step solution-processed CH3NH3PbI3:TiOx bulk-heterojunction thin film possesses enhanced and balanced charge carrier mobilities, superior film morphology with enlarged crystal sizes, and suppressed trapinduced charge recombination. Thus, bulk heterojunction perovskite solar cells by CH3NH3PbI3 mixed with 5 wt% of TiOx, which is processed by one-step method rather than typical two-step method, show a short-circuit current density of 20.93 mA/cm2, an open-circuit voltage of 0.90 V, a fill factor of 80% and with a corresponding power conversion efficiency of 14.91%, which is more than 30% enhancement as compared with that of perovskite solar cells with a planar heterojunction device structure. Moreover, bulk heterojunction perovskite solar cells possess enhanced device stability. All these results demonstrate that perovskite solar cells with a bulk heterojunction device structure are one of apparent approaches to boost device performance.
Potassium-ion capacitors (KICs) emerge as a promising substitute for the well-developed lithium-ion capacitors (LICs), however, the energy density of KICs is below expectations because of lacking a suitable electrical double-layer positive electrode. Using chemical activation of the Aldol reaction product of acetone with KOH, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 2947 m2/g and a narrow pore size distribution ranging from 1 nm to 3 nm. Half-cell (versus potassium metal) test demonstrates that this porous carbon has high capacitive performance in K+ based organic electrolytes. Furthermore, a novel KIC fabricated by this porous carbon as the cathode, yields high values of energy density and power density. The processes used to make this porous carbon are readily low-cost to fabricate metal-ion capacitors.
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