Defect-induced charge redistribution of MoO3-x nanometric wires for photocatalytic ammonia synthesis

MoO3 with the Synergistic Effect of Sulfur Doping and Oxygen Vacancies: The Influence of S Doping on the Structure, Morphology, and Optoelectronic Properties

Molybdenum trioxide (MoO3) is an attractive semiconductor. Thus, bandgap engineering toward photoelectronic applications is appealing yet not well studied. Here, we report the incorporation of sulfur atoms into MoO3, using sulfur powder as a source of sulfur, via a self-developed hydrothermal synthesis approach. The formation of Mo-S bonds in the MoO3 material with the synergistic effect of sulfur doping and oxygen vacancies (designated as S-MoO3-x) is confirmed using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The bandgap is tuned from 2.68 eV to 2.57 eV upon sulfur doping, as confirmed by UV-VIS DRS spectra. Some MoS2 phase is identified with sulfur doping by referring to the photoluminescence (PL) spectra and electrochemical impedance spectroscopy (EIS), allowing significantly improved charge carrier separation and electron transfer efficiency. Therefore, the as-prepared S-MoO3-x delivers a sensitive photocurrent response and splendid cycling stability. This study on the synergistic effect of sulfur doping and oxygen vacancies provides key insights into the impact of doping strategies on MoO3 performance, paving new pathways for its optimization and development in relevant fields.

Multienzyme cascades analysis of α-glucosidase by oxygen deficient MoO3-x

BACKGROUND

Recently, the enzymatic cascade reactions during the cellular process are widely used for fabricating robust biosensors and they have attracted extensive attention in analyzing various clinical biomarkers. The enzymatic cascades analysis is commonly based on the peroxidase (POD)/oxidase coupled system. However, the requirement of harsh acidic environment, poor stability and interference from the oxidase further limit their analytical practicability. Herein, novel chromogenic nanomaterials with H2O2 sensitive features are urgently required to replace the POD nanozyme in enzymatic cascades based bioanalysis.

RESULTS

Herein, oxygen deficient MoO3-x with H2O2 sensitive features and near-infrared (NIR) absorption band have been ultra-fast synthesized and utilized for the enzymatic cascades analysis of α-Glucosidase's activity, and inhibitors screening. With the addition of 4-nitrophenyl-α-d-glucopyranoside, the simultaneous presence of α-Glucosidase and glucose oxidase (GOx) would fade their dark blue color and decrease the NIR absorption. The α-Glucosidase's activity can be analyzed by the absorption at 770 nm, and their limit of detection is 8 × 10-5 U/mL, indicating the superior performance of the proposed colorimetric assay. Moreover, this proposed α-Glucosidase assay is further utilized for inhibitors screening. Moreover, the activity of α-Glucosidase can also be analyzed by the smartphone and microplate reader through the agarose-based colorimetric portable kit.

SIGNIFICANCE

This MoO3-x involved enzymatic cascades assay would facilitate for the development of bio-analysis related to H2O2 generation or consumption. Moreover, this bio-analysis strategy will contribute to the development of other H2O2 sensitive chromogenic nanomaterials for the analysis of certain biomolecules and biological enzymes.

Fabrication of Ultrafine Cu2 O Nanoparticles on W18 O49 Ultra-Thin Nanowires by In-Situ Reduction for Highly Efficient Photocatalytic Nitrogen Fixation

Photocatalytic ammonia synthesis technology is one of the important methods to achieve green ammonia synthesis. Herein, two samples of Cu ion-doped W18 O49 with different morphologies, ultra-thin nanowires (Cu-W18 O49 -x UTNW) and sea urchin-like microspheres (Cu-W18 O49 -x SUMS), are synthesized by a simple solvothermal method. Subsequently, Cu2 O-W18 O49 -x UTNW/SUMS is synthesized by in situ reduction, where the NH3 production rate of Cu2 O-W18 O49 -30 UTNW is 252.4 µmol g-1  h-1 without sacrificial reagents, which is 11.8 times higher than that of the pristine W18 O49 UTNW. The Cu2 O-W18 O49 -30 UTNW sample is rich in oxygen vacancies, which promotes the chemisorption and activation of N2 molecules and makes the N≡N bond easier to dissociate by proton coupling. In addition, the in situ reduction-generated Cu2 O nanoparticles exhibit ideal S-scheme heterojunctions with W18 O49 UTNW, which enhances the internal electric field strength and improves the separation and transfer efficiency of the photogenerated carriers. Therefore, this study provides a new idea for the design of efficient nitrogen fixation photocatalysis.

Stably suspended SiO2-supported CdS photocatalyst for a promising organic pollutant degradation in the absence of mechanical stirring

Even with solar-activatable photocatalyst, incommensurable energy input for stirring is still required to overcome the transport limitations in powder-photocatalysis. To counter this, a novel concept of auto-suspending photocatalyst based on SiO2/CdS was proposed to enable promising photo-activity even under stirring-free condition. Functionally-speaking, CdS would act as photoreaction-driver while SiO2 endows sufficient buoyance for suspension-stabilization during stirring-free photocatalysis. In photoreactions degrading methylene blue for theoretical demonstration, SiO2/CdS_0.3 promises only 4.57% activity reduction in non-stirred photoreaction, enabling 15.26% of methylene blue decolorization comparing to 15.99% of stirred-photoreaction under visible light irradiation. This could be ascribed to the slow settling tendency of SiO2/CdS_0.3, evading severe light-shielding under stacked condition. Also, its rightly-exposed SiO2 surface permits 'adsorb-and-degrade' mechanism, thereby overcoming the sluggish surface transport across thick boundary layer. Contrarily, photocatalyst with quintuple CdS content (SiO2/CdS_1.5) exhibits largest activity reduction (31.47%), reasoned by its quick-settling tendency. Overall, current study provides new perspectives to photocatalysis-community. The success elimination of mechanical stirring from photocatalysis promises significant energy-saving (19.1-136 kW/m3), thus consenting better practicality for solar energy-harvesting and environmental protection.

In-situ construction of WS2/ZIF-8 composites with an electron-rich interface for enhancing nitrogen photofixation

Photocatalytic nitrogen reduction reaction (PNRR) is an environmentally friendly synthesis method. It has been regarded as a promising approach for future NH3 preparation, which can reduce the natural fuel consumption and pollution of the Haber Bosch process. Nevertheless, this method exists poor activity for mass production, so it is urgent but challenging to explore highly efficient catalysts. Here, the novel WS2/ZIF-8 composites are reported, DFT and XPS indicate the transfer direction of electrons is from ZIF-8 to WS2, forming an electron-rich interface between WS2 and ZIF-8, thus it endows the more powerful photocatalytic nitrogen reduction ability for 2-WS2/ZIF-8 than monomer material. Meanwhile, 2-WS2/ZIF-8 exhibits admirable photocatalytic nitrogen reduction performance under real and simulated sunlight or in tap water, further attesting its excellent stability and practicability.

Constructing CoAl-LDO/MoO3-x S-scheme heterojunctions for enhanced photocatalytic CO2 reduction

Converting CO2 into chemicals and fuels by solar energy can alleviate global warming and solve the energy crisis. In this work, CoAl-LDO/MoO3-x (LDO/MO) composites were successfully prepared and achieved efficient CO2 reduction under visible light. The CoAl-layered double oxides (CoAl-LDO) evolved from CoAl-layered double hydroxide (CoAl-LDH) exhibited a more robust structure, broader light absorption, and improved CO2 adsorption ability. The local surface plasmon resonance (LSPR) effect excited by nonstoichiometric MoO3-x broadened the photo-response range of CoAl-LDO/MoO3-x. In addition, constructing step-scheme (S-scheme) heterojunctions could simultaneously optimize the migration mechanism of photogenerated electrons and holes, and retain carriers with strong redox ability. Therefore, the production rates of CO and CH4 on the optimal LDO/MO composite were 7 and 9 times higher than the pristine CoAl-LDH, respectively. This work hybridizes oxidation photocatalysts and LDO-based materials to optimize the charge separation and migration mechanisms, which guides the modification of LDO-based materials.

Controllable Synthesis, Photocatalytic Property, and Mechanism of a Novel POM-Based Direct Z-Scheme Nano-Heterojunction α-Fe2O3/P2Mo18

In order to improve photocatalytic activity and maximize solar energy use, a new composite material Fe2O3/P2Mo18 was prepared by combining polyoxometalates (P2Mo18) with Fe2O3 nanosheets. FT-IR, XRD, XPS, SEM, TEM, UV-vis, EIS, and PL were used to characterize the composite material, and nano-Fe2O3 of different sizes and morphologies with a controllable absorption range was prepared by adjusting the reaction time, and, when combined with P2Mo18, a composite photocatalyst with efficient visible light response and photocatalytic activity was constructed. The EIS, Bode, and PL spectra analysis results show that the Fe2O3/P2Mo18 composite material has outstanding interfacial charge transfer efficiency and potential photocatalytic application possibilities. Model reactions of methylene blue (MB) and Cr (VI) photodegradation were used to evaluate the redox activity of Fe2O3/P2Mo18 composites under simulated visible light. The photocatalytic degradation rate was as high as 98.98% for MB and 96.86% for Cr (VI) when the composite ratio was Fe2O3/P2Mo18-5%. This research opens up a new avenue for the development of high-performance photocatalysts.