Tunable localized surface plasmon resonances in MoO3−-TiO2 nanocomposites with enhanced catalytic activity for CO2 photoreduction under visible light

Plasmon-Switched Kinetics for Formic Acid Dehydrogenation: Selective Adsorption Driven by Local Field and Hot Carriers

Understanding illumination-mediated kinetics is essential for catalyst design in plasmon catalysis. Here we prepare Pd-based plasmonic catalysts with tunable electronic structures to reveal the underlying illumination-enhanced kinetic mechanisms for formic acid (HCOOH) dehydrogenation. We demonstrate a kinetic switch from a competitive Langmuir-Hinshelwood adsorption mode in dark to a non-competitive type under irradiation triggered by local field and hot carriers. Specifically, the electromagnetic field induces a spatial-temporal separation of dehydrogenation-favorable configurations of reactant molecule HCOOH and HCOO- due to their natural different polarities. Meanwhile, the generated energetic carriers can serve as active sites for selective molecular adsorption. The hot electrons act as adsorption sites for HCOOH, while holes prefer to adsorb HCOO-. Such unique non-competitive adsorption kinetics induced by plasmon effects serves as another typical characteristic of plasmonic catalysis that remarkably differs from thermocatalysis. This work unravels unique adsorption transformations and a kinetic switching driven by plasmon nonthermal effects.

Development of defective molybdenum oxides for photocatalysis, thermal catalysis, and photothermal catalysis

The localized surface plasmon resonance (LSPR) of noble metals has been investigated for decades for applications in various catalysis reactions and optical research studies, but its development has been hampered by inefficient light absorption and high costs. In comparison, the creation of less expensive semiconductors (metal oxides) with strong plasmonic absorption is an appealing option, particularly defective molybdenum oxide (H_xMoO_3-y) has received considerable attention and investigation as a promising plasmonic material for a variety of catalytic reactions (photocatalysis, thermocatalysis, photothermal catalysis, etc.).The LSPR effect of H_xMoO_3-y can be tuned throughout a broad spectrum range from visible to near-infrared (NIR) by altering the doping amount by electrochemical control, chemical reduction, or photochemical control. Notably, defects (oxygen vacancies) in H_xMoO_3-y arise in conjunction with the LSPR effect, resulting in the formation of unique and useful active sites in a range of catalytic processes. In this review, we explore the formation mechanism of H_xMoO_3-y with plasmonic features and discuss its applications in photocatalysis, thermocatalysis, and photothermal catalysis.

Review on LSPR assisted photocatalysis: effects of physical fields and opportunities in multifield decoupling

Since nano scale local surface plasmon resonance (LSPR) can broaden the visible absorption region, enhance the local electromagnetic field and produce a thermal effect simultaneously, the appropriate utilization of the LSPR effect is a noteworthy research direction towards visible light driven photocatalysts with high efficiency and low cost. In this study, the influence mechanism of the optical, electric, magnetic, and thermal physical fields on the photocatalytic efficiency of the LSPR system is for the first time reviewed, based on which the research bottlenecks of this method including the accurate predesign and regulation of the photocatalyst, the interpretation of electron movement and energy transfer mechanism, are specifically analyzed. Due to the micro-nano localization of LSPR, auxiliary methods are needed to reflect the micro electromagnetic and temperature field distribution which are otherwise formidable to measure experimentally. Alternatively, numerical methods with decoupling calculations of nano-scale physical fields are necessary to develop. Therefore, the development potential of different numerical simulation methods including mainstream FDTD, FEM and DDA is subsequently expounded, providing opportunities in resolving the bottleneck issues associated with photocatalysis. It is worth mentioning that although many important advances have been achieved in the preparation and application of LSPR assisted photocatalysts, the convincing function mechanism of LSPR is still lacking due to its multifield synergistic enhancement effect.

Fabrication of graphitic carbon Nitride/Nonstoichiometric molybdenum oxide nanorod composite with the nonmetal plasma enhanced photocatalytic hydrogen evolution activity

The extended light absorption and the prevented charge recombination are crucial for the graphitic carbon nitride (g-C₃N₄) based photocatalytic materials. Herein, nonstoichiometric molybdenum oxide (MoO_3-x) nanorods with oxygen vacancies were synthesized by a hydrothermal method with trace amount of oleylamine, and the Z-scheme two-dimentional (2D)/one-dimentional (1D) g-C₃N₄/MoO_3-x composites were prepared by a facile electrostatic assembling approach. The blue MoO_3-x nanorods with oxygen vacancies are loaded uniformly on the g-C₃N₄ nanosheets. The g-C₃N₄/MoO_3-x composite materials exhibit strong absorption in the visible and near-infrared light regions, and the improved charge separation efficiency through the Z-scheme charge transfer mechanism. The g-C₃N₄/MoO_3-x composite presents a significantly improved photocatalytic hydrogen generation activity with good cycling stability compared with sonicated g-C₃N₄ nanosheets. The best hydrogen generation activity of 209.2 μmol·h^-1 under solar light irradiation and the highest apparent quantum efficiency of 4.4% irradiated at 365 nm are obtained by the g-C₃N₄/MoO_3-x composite with a mass percent of 27.5%, which is 2.63 times of g-C₃N₄. The weight ratios and the content of oxygen vacancies in the small-size MoO_3-x nanorods have a significant influence on the photocatalytic hydrogen performance. Moreover, effective photocatalytic overall water splitting can be achieved with the H₂ and O₂ evolution rates of 0.755 and 0.368 μmol∙h^-1 by the g-C₃N₄/MoO_3-x composite. The novel g-C₃N₄/MoO_3-x composite will have broad prospects in the field of photocatalytic applications.

Environmental management of industrial decarbonization with focus on chemical sectors: A review

A considerable portion of fossil CO₂ emissions comes from the energy sector for production of heat and electricity. The industrial sector has the second order in emission in which the main parts are released from energy-intensive industries, namely metallurgy, building materials, chemicals, and manufacturing. The decarbonization of industrial wastes contemplates the classic decarbonization through optimization of conventional processes as well as utilization of renewable energy and resources. The upgrading of existing processes and integration of the methodologies with a focus on efficiency improvement and reduction of energy consumption and the environment is the main focus of this review. The implementation of renewable energy and feedstocks, green electrification, energy conversion methodologies, carbon capture, and utilization, and storage are also covered. The main objectives of this review are towards chemical industries by introducing the potential technology enhancement at different subsectors. For this purpose, state-of-the-art roadmaps and pathways from the literature findings are presented. Both common and innovative renewable attempts are needed to reach out both short- and long-term deep decarbonization targets. Even though all of the innovative solutions are not economically viable at the industrial scale, they play a crucial role during and after the energy transition interval.

C. SS, Bajiri MA, Drmosh QAQ, Krishnappagowda LN, Ananda S. Rational design of 2D TiO2-MoO3 Step-scheme heterostructure for boosted photocatalytic overall water splitting

Designing of step-scheme (S-scheme) heterostructure photocatalyst is a promising strategy for the high utilization of photogenerated charge carriers. Herein, a novel S-scheme two-dimensional (2D) TiO2-MoO3 heterojunction photocatalyst is fabricated by...

Photo-thermo catalytic selective oxidation of cyclohexane by In-situ prepared nonstoichiometric Molybdenum oxide and Silver-palladium alloy composite

The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is one of the most challenging issues in the chemical industry. However, the difficulty in attaining high selectivity and high conversion rate in parallel for the existing catalysts limits its practical application. In this paper, a novel photo-thermo synergistic catalyst was reported for the aerobic oxidation of cyclohexane. The uniform blue MoO_3-x nanowires with small diameter stabilized by polyvinyl pyrrolidone (PVP) were synthesized by a hydrothermal method, and a series of MoO_3-x-AgPd composite materials of different proportions were prepared by an in-situ reduction process. The morphology, crystalline structure, surface chemical bonding, photoelectrochemical properties of MoO_3-x-AgPd composites are thoroughly characterized. The MoO_3-x-AgPd composites present significantly increased catalytic performance than MoO_3-x nanowires in the photo-thermo synergistic catalytic oxidation of cyclohexane under dry air. The high conversion rate of 11.3% with the KA oil selectivity of 99.0% was achieved by the MoO_3-x-Ag₂₀Pd₂₀ composites under photo-thermo catalytic process at 120 ℃, which is 1.5 times of that by MoO_3-x nanowires. Under photo-thermo catalytic process, a high cyclohexane conversion rate similar to that of higher temperature thermal catalysis can be obtained at lower reaction temperature, and more cyclohexanol can be produced with a ketone to alcohol (K/A) ratio of 0.254. The significantly enhanced catalytic activity can be attributed to the effective charge transfer in the AgPd alloy nanoparticles, the optimized band gap structure, the suppressed charge recombination, and the promoted photo-thermo synergetic catalytic effect. This work provides a new reference scheme for the design and preparation of high-efficiency photo-thermo catalysts for the selective oxidation of cyclohexane.

Molybdenum Trioxide Quantum Dot-Encapsulated Nanogels for Virus Detection by Surface-Enhanced Raman Scattering on a 2D Substrate

The use of nanogels (NGs) to modulate surface-enhanced Raman scattering (SERS) activities is introduced as an innovative strategy to address certain critical issues with SERS-based immunoassays. This includes the chemical deformation of SERS nanotags, as well as their nonspecific interactions and effective "hotspots" formation. Herein, the polymeric cocoon and stimuli-responsive properties of NGs were used to encapsulate SERS nanotags containing plasmonic molybdenum trioxide quantum dots (MoO₃-QDs). The pH-controlled release of the encapsulated nanotags and their subsequent localization by maleimide-functionalized magnetic nanoparticles facilitated the creation of "hotspots" regions with catalyzed SERS activities. This approach resulted in developing a biosensing platform for the ultrasensitive immunoassays of hepatitis E virus (HEV) or norovirus (NoV). The immunoassays were optimized using the corresponding virus-like particles to attain limits of detection of 6.5 and 8.2 fg/mL for HEV-LPs and NoV-LPs, respectively. The SERS-based technique achieved a signal enhancement factor of up to ∼10⁸ due to the combined electromagnetic and chemical mechanisms of the employed dual-SERS substrate of MoO₃-QDs/2D hexagonal boron nitride nanosheets. The highlight and validation of the developed SERS-based immunoassays was the detection of NoV in infected patients' fecal specimen and clinical HEV G7 subtype. Importantly, this system can be used to maintain the stability of SERS nanotags and improve their reliability in immunoassays.

Molybdenum Trioxide Nanocubes Aligned on a Graphene Oxide Substrate for the Detection of Norovirus by Surface-Enhanced Raman Scattering

A novel biosensing system based on graphene-mediated surface-enhanced Raman scattering (G-SERS) using plasmonic/magnetic molybdenum trioxide nanocubes (mag-MoO₃ NCs) has been designed to detect norovirus (NoV) via a dual SERS nanotag/substrate platform. A novel magnetic derivative of MoO₃ NCs served as the SERS nanotag and the immunomagnetic separation material of the biosensor. Single-layer graphene oxide (SLGO) was adopted as the 2D SERS substrate/capture platform and acted as the signal reporter, with the ability to accommodate an additional Raman molecule as a coreporter. The developed SERS-based immunoassay achieved a signal amplification of up to ∼10⁹-fold resulting from the combined electromagnetic and chemical mechanisms of the dual SERS nanotag/substrate system. The developed biosensor was employed for the detection of NoV in human fecal samples collected from infected patients by capturing the virus with the aid of NoV-specific antibody-functionalized magnetic MoO₃ NCs. This approach enabled rapid signal amplification for NoV detection with this biosensing technology. The biosensor was tested and optimized using NoV-like particles within a broad linear range from 10 fg/mL to 100 ng/mL and a limit of detection (LOD) of ∼5.2 fg/mL. The practical applicability of the developed biosensor to detect clinical NoV subtypes in human fecal samples was demonstrated by effective detection with an LOD of ∼60 RNA copies/mL, which is ∼10³-fold lower than that of a commercial enzyme-linked immunosorbent assay kit for NoV.