Strategy to improve gold nanoparticles loading efficiency on defect-free high silica ZSM-5 zeolite for the reduction of nitrophenols.

Catalytic reduction of toxic and aqueous stable nitrophenols by gold nanoparticles (Au NPs) is hot issue due to the serious environmental pollution in recent years. But the expensive price and poor recycling performance of Au NPs limit its further application. Defect-free high silica zeolite is suitable support for Au NPs due to its cheaper price, higher stability and stronger adsorbability, but the low alumina content and defect sites usually lead to poor Au NPs loading efficiency. Herein, we reported the improved Au NPs loading efficiency on defect-free high silica ZSM-5 zeolite through the additional surface fluffy structure. The fluffy structure was created through the addition of multi-walled carbon nanotubes (MWCNTs) and ethanol into synthesis gel. Highly dispersed ca. 4 nm Au NPs on zeolite surface are prepared by the green enhanced sol-gel immobilization method. The Au NPs loading efficiency on conventional ZSM-5 zeolite is 10.7%, in contrast, this result can arrive to 82.6% on fluffy structure ZSM-5 zeolite. The fluffy structure ZSM-5 zeolite and Au NPs nanocomposites show higher efficiency than traditional Au/ZSM-5 nanocomposites towards catalytic reduction of nitrophenols. Additionally, the experiments with different affecting factors (MWCNTs dosage, aging time, catalysts dosage, pH, initial 4-NP concentration, storage time and recycling times) were carried out to test general applicability of the nanocomposites. And the degradation of nitrophenols experiment was operated to explore the catalytic performance of the prepared nanocomposites in further environmental application. The detailed possible relationship between zeolite with fluffy structure and Au NPs is also proposed in the paper.

Anchoring single-unit-cell defect-rich bismuth molybdate layers on ultrathin carbon nitride nanosheet with boosted charge transfer for efficient photocatalytic ciprofloxacin degradation.

Photocatalysis technology is regarded as a promising way for environmental remediation, but rationally designing photocatalysis system with high-speed interfacial charge transfer, sufficient photoabsorption and surface reactive sites is still a challenge. In this study, anchoring single-unit-cell defective Bi2MoO6 on ultrathin g-C3N4 to form 2D/2D heterostructure system is a triple-purpose strategy for high-performance photocatalysis. The defect structure broadens photo-responsive range. The large intimate contact interface area between two monomers promotes charges carrier transfer. The enhanced specific surface area exposes more reactive sites for mass transfer and catalytic reaction. As a result, the obtained heterostructure displays excellent photocatalytic performance for ciprofloxacin (CIP) (0.0126 min-1), which is 3.32 and 2.93 folds higher than Bi2MoO6 and g-C3N4. In addition, this heterostructure retains high-performance for actual wastewaters treatment, and it displays strong mineralization ability. And this heterojunction also exhibits excellent photostability based on cyclic experiment. Mechanism exploration reveals that hole, superoxide radical, and hydroxyl radical are chief reactive species toward CIP degradation, thereby a Z-scheme charge carrier transfer channel is proposed. In addition, the intermediates and degradation pathways of CIP are tracked by liquid chromatography-triple quadrupole tandem mass spectrometry (LCMS/MS) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs). This study paves new way to design and construct atomic level 2D/2D heterojunction system for environment remediation.

Electrochemical biosensor for amplified detection of Pb2+ based on perfect match of reduced graphene oxide-gold nanoparticles and single-stranded DNAzyme.

In this study, a sensitive amplification strategy for Pb2+ detection using reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) was proposed. Thiol-modified DNAzyme is specific for Pb2+ self-assembly on RGO-AuNPs-modified electrode surface. Ferrocene labeled single-stranded DNAzyme (Fc-ssDNAzyme) self-hybridizes to form a DNA hairpin structure. The amount of Fc adsorbed on the electrode surface changes after the appearance of Pb2+, leading to a change of electrical signal. This change can be sensitively identified by differential pulse voltammetry (DPV) assisted by ferricyanide ([Fe(CN)6]3-/4-) in the electrolyte. The high conductivity and specific surface area of RGO and the strong chemical bond adsorption effect between DNAzyme and AuNPs are responsible for the amplified detection of Pb2+, which realize a detection range of 0.05-400,000.0 nM and a minimum detection limit of 0.015 nM. Moreover, the selectivity test results indicated that the biosensor had specificity for Pb2+, even if there was interference from other high-concentration metal ions. This simple biosensor also exhibited good responsiveness in actual sample detection, which provides a good application prospect for field detection of Pb2+ in water. Graphical abstract.

Multiple charge-carrier transfer channels of Z-scheme bismuth tungstate-based photocatalyst for tetracycline degradation: Transformation pathways and mechanism.

As a sustainable and cost-efficient technique, photocatalytic technology provides an ideal method for energy utilization and environmental pollution control. The current photocatalyst is commonly based on single charge transfer approach, which cannot meet the demand of rapidly charge transfer to improve the photocatalytic performance. Herein, a novel Ag3PO4/MWCNT/Bi2WO6 Z-scheme heterojunction photocatalyst with multiple charge-carrier transfer channels was successfully prepared by a simple hydrothermal and deposition procedure, which possessed remarkable charge carriers separation efficiency and broad photoabsorption: (i) Z-scheme charge transfer channel was formed by Ag3PO4, Bi2WO6 and Ag; (ii) Ag showed the "electron sink" property and surface plasmon resonance (SPR) effect; (iii) multi-walled carbon nanotube (MWCNT) can act as electron accepter to improve the transfer efficiency of photoinduced electron. Ag3PO4/MWCNT/Bi2WO6 composite shows excellent visible light drive photocatalytic performance for organic pollution degradation. And the degradation pathways of tetracycline (TC) were investigated at length. In addition, the cyclic experiments confirmed that the photocatalytic stability of Ag3PO4/MWCNT/Bi2WO6. The hole (h+) and superoxide radical (O2-) radicals were confirmed that played a key role in the photodegradation system. This work provides inspiration for rational fabrication of excellent photocatalyst with multi-charge carrier transfer channels to meet increasing environmental requirements.

Hierarchical porous carbon material restricted Au catalyst for highly catalytic reduction of nitroaromatics.

In this study, four kinds of porous carbon materials were used as supports to anchor gold nanoparticles (AuNPs) for catalytic reduction of nitroaromatics and 4-nitrophenol (4-NP) was employed as a model material. Results identified that carbon black (CB) restricted-Au catalyst (Au/CB) provided large specific surface area, small AuNPs size, and low cost, which showed highly catalytic activity for 4-NP reduction. Besides, with the increase of Au loadings, the catalytic activity of Au/CB was enhanced and the 1.2 wt% of Au loading exhibited the best catalytic activity with the high rate of 0.8302 min-1 and the turnover frequency of 492.50 h-1. Universality and real water application demonstrated that the as-prepared Au/CB catalyst was promising candidate for other phenols and azo dyes reduction and had great potential for practical application. Furthermore, after ten cycles, Au/CB still retained satisfying stability and activity. These results suggested that the larger specific surface area and smaller particle size attributing to the porosity of CB were conducive to improving the catalytic activity of Au catalysts. This design shows high potential of hierarchical porous carbon materials for highly catalytic reaction in many fields, especially the water purification.

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.