Pyrolytic Depolymerization of Polyolefins Catalyzed by Zirconium-based UiO-66 Metal-Organic Frameworks.

Polyolefins such as polyethylenes and polypropylenes are the most-produced plastic waste globally, yet are difficult to convert into useful products due to their unreactivity. Pyrolysis is a practical method for large-scale treatment of mixed, contaminated plastic, allowing for their conversion into industrially-relevant petrochemicals. Metal-organic frameworks (MOFs), despite their tremendous utility in heterogenous catalysis, have been overlooked for polyolefin depolymerization due to their perceived thermal instabilities and inability of polyethylenes and polypropylenes to penetrate their pores. Herein, we demonstrate the viability of UiO-66 MOFs containing coordinatively-unsaturated zirconia nodes, as effective catalysts for pyrolysis that significantly enhances the yields of valuable liquid and gas hydrocarbons, whilst halving the amounts of residual solids produced. Reactions occur on the Lewis-acidic UiO-66 zirconia nodes, without the need for noble metals, and yields aliphatic product distributions distinctly different from the aromatic-rich hydrocarbons from zeolite catalysis. We also demonstrate the first unambiguous characterization of polyolefin penetration into UiO-66 pores at pyrolytic temperatures, allowing access to the abundant Zr-oxo nodes within the MOF interior for efficient C-C cleavage. Our work highlights the potential of MOFs as highly-designable heterogeneous catalysts for depolymerization of plastics which can complement conventional catalysts in reactivity.

Contact-electro-catalytic CO2 reduction from ambient air.

Traditional catalytic techniques often encounter obstacles in the search for sustainable solutions for converting CO2 into value-added products because of their high energy consumption and expensive catalysts. Here, we introduce a contact-electro-catalysis approach for CO2 reduction reaction, achieving a CO Faradaic efficiency of 96.24%. The contact-electro-catalysis is driven by a triboelectric nanogenerator consisting of electrospun polyvinylidene fluoride loaded with single Cu atoms-anchored polymeric carbon nitride (Cu-PCN) catalysts and quaternized cellulose nanofibers (CNF). Mechanistic investigation reveals that the single Cu atoms on Cu-PCN can effectively enrich electrons during contact electrification, facilitating electron transfer upon their contact with CO2 adsorbed on quaternized CNF. Furthermore, the strong adsorption of CO2 on quaternized CNF allows efficient CO2 capture at low concentrations, thus enabling the CO2 reduction reaction in the ambient air. Compared to the state-of-the-art air-based CO2 reduction technologies, contact-electro-catalysis achieves a superior CO yield of 33 µmol g-1 h-1. This technique provides a solution for reducing airborne CO2 emissions while advancing chemical sustainability strategy.

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.

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.