Dehydration of lactic acid to acrylic acid over lanthanum phosphate catalysts: the role of Lewis acid sites.

Lanthanum phosphate (LaP) nano-rods were synthesized using n-butylamine as a shape-directing agent (SDA). The resulting catalysts were applied in the dehydration of lactic acid to acrylic acid. Aiming to understand the nature of the active sites, the chemical and physical properties of LaP materials were studied using a variety of characterization techniques. This study showed that the SDA not only affected the porosity of the LaP materials but also modified the acid-base properties. Clearly, the modification of the acid-base properties played a more critical role in determining the catalytic performance than porosity. An optimized catalytic performance was obtained on the LaP catalyst with a higher concentration of Lewis acid sites. Basic sites showed negative effects on the stability of the catalysts. Good stability was achieved when the catalyst was prepared using the appropriate SDA/La ratio.

2D/2D Heterojunction of BiOBr/BiOI Nanosheets for In Situ H2 O2 Production and Activation toward Efficient Photocatalytic Wastewater Treatment.

The presence of toxic organic pollutants in aquatic environments poses significant threats to human health and global ecosystems. Photocatalysis that enables in situ production and activation of H2 O2 presents a promising approach for pollutant removal; however, the processes of H2 O2 production and activation potentially compete for active sites and charge carriers on the photocatalyst surface, leading to limited catalytic performance. Herein, a hierarchical 2D/2D heterojunction nanosphere composed of ultrathin BiOBr and BiOI nanosheets (BiOBr/BiOI) is developed by a one-pot microwave-assisted synthesis to achieve in situ H2 O2 production and activation for efficient photocatalytic wastewater treatment. Various experimental and characterization results reveal that the BiOBr/BiOI heterojunction facilitates efficient electron transfer from BiOBr to BiOI, enabling the one-step two-electron O2 reduction for H2 O2 production. Moreover, the ultrathin BiOI provides abundant active sites for H2 O2 adsorption, promoting in situ H2 O2 activation for •O2 - generation. As a result, the BiOBr/BiOI hybrid exhibits excellent activity for pollutant degradation with an apparent rate constant of 0.141 min-1 , which is 3.8 and 47.3 times that of pristine BiOBr and BiOI, respectively. This work expands the range of the materials suitable for in situ H2 O2 production and activation, paving the way toward sustainable environmental remediation using solar energy.

Fe-Co Bimetallic Catalysts for Pyrolysis of Disposable Face Masks and Nitrile Gloves: Synthesis and Characterization of N-Doped Carbon Nanotubes.

The global spread of severe acute respiratory syndrome coronavirus 2 has led to a widespread surge in the use of disposable medical face masks (DFMs) and waste nitrile gloves (WNGs). To address the immense disruption in waste management systems, the catalytic pyrolysis of DFMs and WNGs was undertaken to yield multiwalled carbon nanotubes. Two MgO-supported bimetallic catalysts, Fe-Co and Fe-Ni, were synthesized for catalytic pyrolysis. The MgO-supported Fe and Co catalysts showed a good yield of N-doped CNTs (N-CNTs) above 33 wt %, while the percentage of WNGs did not exceed 20 wt %. The pyrolysis process resulted in the formation of Fe-Co microspinels, which were subsequently encapsulated within N-CNTs, ultimately yielding FeCo-NCNTs. The synthesized FeCo-NCNTs were approximately 25 nm in diameter and were extended over several micrometers in length. Subsequent evaluations included testing several acid-washed FeCo-NCNTs as catalysts for the oxygen reduction reaction. The FeCo-NCNTs exhibited remarkable catalytic performance, with a half-wave potential at 0.831 V (vs RHE) and exceptional resistance to methanol poisoning. These remarkable findings have the potential to contribute to the sustainable recycling of waste generated during the COVID-19 pandemic and to the utilization of waste-derived materials.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis.

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

Integration of Single-Atom Catalyst with Z-Scheme Heterojunction for Cascade Charge Transfer Enabling Highly Efficient Piezo-Photocatalysis.

Piezo-assisted photocatalysis (namely, piezo-photocatalysis), which utilizes mechanical energy to modulate spatial and energy distribution of photogenerated charge carriers, presents a promising strategy for molecule activation and reactive oxygen species (ROS) generation toward applications such as environmental remediation. However, similarly to photocatalysis, piezo-photocatalysis also suffers from inferior charge separation and utilization efficiency. Herein, a Z-scheme heterojunction composed of single Ag atoms-anchored polymeric carbon nitride (Ag-PCN) and SnO2- x is developed for efficient charge carrier transfer/separation both within the catalyst and between the catalyst and surface oxygen molecules (O2 ). As revealed by charge dynamics analysis and theoretical simulations, the synergy between the single Ag atoms and the Z-scheme heterojunction initiates a cascade electron transfer from SnO2- x to Ag-PCN and then to O2 adsorbed on Ag. With ultrasound irradiation, the polarization field generated within the piezoelectric hybrid further accelerates charge transfer and regulates the O2 activation pathway. As a result, the Ag-PCN/SnO2- x catalyst efficiently activates O2 into ·O2 - , ·OH, and H2 O2 under co-excitation of visible light and ultrasound, which are consequently utilized to trigger aerobic degradation of refractory antibiotic pollutants. This work provides a promising strategy to maneuver charge transfer dynamics for efficient piezo-photocatalysis by integrating single-atom catalysts (SACs) with Z-scheme heterojunction.

Modified Bacterial Cellulose for Biomedical Applications.

Bacterial cellulose, or microbial cellulose, had gained tremendous interest as a hydrogel material for biomedical purposes in the recent years. It has many intrinsic physiological properties like fibrous nature, ultrafine 3D nanostructure network, high water holding capacity, excellent mechanical properties, biocompatibility and biodegradability that allow for the use of such purposes, and the lacking properties can be easily supplemented or enhanced by modifications. In this review, some of the biomedical applications that uses bacterial cellulose are discussed. These include wound healing, drug delivery, tissue engineering and tumor cell and cancer therapy. In each section, different modifications of BC are showcased and examined on how they benefit the application. Finally, key takeaways on these modifications are also deliberated.

Kombucha SCOBY Waste as a Catalyst Support.

It is established that food waste can be repurposed to extend its lifecycle and decrease its carbon footprint. In this work, SCOBY (symbiotic culture of bacteria and yeast) waste from kombucha tea production has been repurposed as a catalyst support. Copper nanoparticles (Cu NPs) have been embedded in a piece of treated SCOBY via an in-situ method which enabled the catalyst, inCu/t-SCOBY, to be easily recycled. In addition, inCu/t-SCOBY catalyzed the full reduction of 4-nitrophenol in an excess of sodium borohydride (NaBH4 ) within 20 minutes. After 6 additional catalytic cycles, the catalyst maintained up to 50% of its performance in the first cycle. Characterization of the catalyst has also been done to understand the mechanism of action and interactions occurring between t-SCOBY and Cu NPs. The results of this work clearly present a proof-of-concept in utilizing porous wastes materials such as SCOBY as catalyst supports, allowing metallic NPs to be efficacious and practical heterogenous catalysts.

Solar-Powered Photodegradation of Pollutant Dyes Using Silver-Embedded Porous TiO2 Nanofibers.

Titanium dioxide (TiO2) nanomaterials have been ubiquitously investigated as a photocatalyst for organic contaminant treatment in wastewater due to their exemplary semiconductor properties. However, their huge band gap remains a barrier for visible light absorption, limiting their utility in practical applications. The incorporation of noble metals in the TiO2 scaffold would help mitigate the problem via plasmonic resonance enhancements. Silver (Ag) is the chosen noble metal as it is relatively cheap and has great plasmonic effects. In this study, the use of electrospun Ag-embedded TiO2 nanofibers as a photocatalyst is shown to be effective in decomposing rhodamine B and methyl orange dyes under a solar simulator in 3 h, which is more efficacious as opposed to pristine TiO2 nanofibers. This showcases the potential of a simple and economic wastewater treatment system for the removal of organic pollutants.

Gram-Scale Production of Photothermally Active Tetrahedrite Nanoparticles for Solar-Driven Water Evaporation.

Pristine and substituted tetrahedrite nanoparticles have shown immense potential as low-cost and sustainable materials for energy conversion applications. However, the commonly used synthetic methods for their production are cumbersome and are not easily scalable. In this work, we report a facile colloidal synthetic protocol for the preparation of phase-pure samples of pristine (Cu12 Sb4 S13 ) and Zn-substituted (Cu11 ZnSb4 S13 ) tetrahedrite nanoparticles on the gram scale. Both tetrahedrite compositions were found to be photothermally responsive, enabling their use in solar-driven water evaporation.

Advances in photothermal nanomaterials for biomedical, environmental and energy applications.

Materials that exhibit photothermal effect have attracted enormous research interests due to their ability to strongly absorb light and effectively transform it into heat for a wide range of applications in biomedical, environmental and energy related fields. The past decade has witnessed significant advances in the preparation of a variety of photothermal materials, mainly due to the emergence of many nano-enabled new materials, such as plasmonic metals, stoichiometric/non-stoichiometric semiconductors, and the newly emerging MXenes. These photothermal nanomaterials can be hybridized with other constituents to form functional hybrids or composites for achieving enhanced photothermal performance. In this review, we present the fundamental insight of inorganic photothermal materials, including their photothermal conversion mechanisms/properties as well as their potential applications in various fields. Emphasis is placed on strategic approaches for improving their light harvesting and photothermal conversion capabilities through engineering their nanostructured size, shape, composition, bandgap and so on. Lastly, the underlying challenges and perspectives for future development of photothermal nanomaterials are proposed.

Engineering luminescent pectin-based hydrogel for highly efficient multiple sensing.

Luminescent hydrogels with sensing capabilities have attracted much interest in recent years, especially those responsive to stimuli, making such materials potential for various applications. Pectin is a high-molecular-weight carbohydrate polymer that has the ability to form hydrogel upon heating or mixing with divalent cations. However, intrinsic pectin gels are weak and lack of functionalities. In this study, lanthanide ions and silk fibroin derived carbon dots were incorporated into Pectin/PVA hydrogel (PPH) to form luminescent tough hydrogels. The luminescence of the hydrogel can be tuned by adjusting the ratio of blue emission carbon dots to Eu3+ ions (red emission) and Tb3+ ions (green emission). Such incorporation of emitters only slightly changed the mechanical properties of the tough hydrogel. Notably, the luminescent Pectin/PVA hydrogel (LPPH) showed chromic response to external stimuli, like pH and metal ions. By measuring the ratio of luminescent intensity at 473 nm and 617 nm (I473/I617), the pH response can be quantified in high sensitivity. In addition, the specific detection of Cu2+ and Fe3+ ions using the fabricated hydrogel were demonstrated, the mechanism was also proposed. The different chromic responses to Fe2+ and Fe3+ endow the luminescent tough Pectin/PVA hydrogel potential for multiple sensing applications.

Gold-decorated TiO2 nanofibrous hybrid for improved solar-driven photocatalytic pollutant degradation.

TiO2-based nanomaterials are among the most promising photocatalysts for degrading organic dye pollutants. In this work, Au-TiO2 nanofibers were fabricated by the electrospinning technique, followed by calcination in air at 500 °C. Morphological and structural analyses revealed that the composite consists of TiO2 nanofibers with embedded Au nanoparticles that are extensively distributed throughout the porous fibrous structure of TiO2. The photocatalytic performance of these Au-embedded TiO2 nanofibers was evaluated in the photodegradation of Rhodamine B and methylene blue under solar simulator irradiation. Compared with pristine TiO2 nanofibers, the Au-embedded TiO2 nanofibers displayed far better photocatalytic degradation efficiency. The plasmon resonance absorption of Au nanoparticles in the visible spectral region and the effective charge separation at the heterojunction of the Au-TiO2 hybrid are the key factors that have led to the considerable enhancement of the photocatalytic activity. The results of this study clearly demonstrate the potential of Au-TiO2 electrospun nanofibers as solar-light-responsive photocatalysts for the effective removal of dye contaminants from aquatic environments.

PCL-Based Thermogelling Polymer: Molecular Weight Effects on Its Suitability as Vitreous Tamponade.

Polymeric hydrogels are promising biomaterials to be used as vitreous tamponade in the eye. However, while the clinical need and the required attributes of a vitreous replacement hydrogel are clear, there is a major gap in understanding the various polymer requirements to achieve the "ideal" hydrogel. In this study, we investigated the effect of the polymer molecular weight on polyurethane thermogel properties and found that there is a theoretical minimum number of hydrophobic blocks required for gelation. We then used these polymers as vitreous replacements. We found that there is a preferred molecular weight range, whereby hydrogels with lower molecular weights can cause retinal atrophy and corresponding functional visual loss, while those with higher molecular weights lead to opacity issues. Thermogels in the preferred molecular weight range retained the normal retinal structure and exhibited full visual recovery within 3 months. The effect of the molecular weight was further demonstrated by the effects of postsynthetic autoclaving on the retinal structure and function. The effect of the polymer molecular weight on the functional characteristics of hydrogels demonstrated herein is an important design parameter for polymeric hydrogels for ocular applications.

Reaction discovery using acetylene gas as the chemical feedstock accelerated by the "stop-flow" micro-tubing reactor system.

Acetylene gas has been applied as a feedstock under transition-metal catalysis and photo-redox conditions to produce important chemicals including terminal alkynes, fulvenes, and fluorinated styrene compounds. The reaction discovery process was accelerated through the use of "stop-flow" micro-tubing reactors. This reactor prototype was developed by joining elements from both continuous micro-flow and conventional batch reactors, which was convenient and effective for gas/liquid reaction screening. Notably, the developed transformations were either inefficient or unsuccessful in conventional batch reactors. Its success relies on the unique advantages provided by this "stop-flow" micro-tubing reactor system.