Complete Degradation of Polyolefin Plastic Wastes to High-Value Products.

Plastic wastes continuously accumulate, causing critical environmental issues. It is urgent to develop efficient strategies to convert them to valuable products. Very recently, two novel approaches for plastic recycling were reported by Huber et al. (Science, 2023, 381, 660-666) and Liu et al. (Science, 2023, 381, 666-671), where polyethylene (PE) and polypropylene (PP) plastics were converted into potentially valuable products, such as alcohols, aldehydes, surfactants, and detergents. The two processes achieved complete degradation, high selectivity of target products, as well as high values of products, showing economic feasibility for industrial scale-up. These breakthroughs for plastic recycling are highlighted in this article.

Gradient Functional Layer Anode for Carbonate-Superstructured Solid Fuel Cells with Ethane Fuel.

Carbonate-superstructured solid fuel cells (CSSFCs) are an emerging type of fuel cells with high flexibility of fuels. However, using ethane fuel for solid fuel cells is a great challenge due to serious degradation of their anodes. Herein, this critical issue is solved by creating a novel gradient functional layer anode for CSSFCs. First, a finer-scale anode with a larger surface area is demonstrated to provide more active sites for the internal reforming reaction of ethane, achieving a 60% higher ethane conversion rate and 40% lower polarization resistance than conventional anodes. Second, incorporating a gradient functional layer into the anode results in an additional 50% enhancement in the peak power density of CSSFCs to a record high value (up to 241 mW cm-2) with dry ethane fuel at a low temperature of 550 °C, which is even comparable to the power density of conventional solid oxide fuel cells above 700 °C. Furthermore, the CSSFC with the gradient anode exhibits excellent durability for over 200 h. This finding provides a new strategy to develop efficient anodes for hydrocarbon fuels.

Thermo-photo catalytic anode process for carbonate-superstructured solid fuel cells.

Converting hydrocarbons and greenhouse gases (i.e., carbon dioxide, CO2) directly into electricity through fuel cells at intermediate temperatures (450 to 550 °C) remains a significant challenge, primarily due to the sluggish activation of C-H and C=O bonds. Here, we demonstrated a unique strategy to address this issue, in which light illumination was introduced into the thermal catalytic CO2 reforming of ethane in the anode as a unique thermo-photo anode process for carbonate-superstructured solid fuel cells. The light-enhanced fuel activation led to excellent cell performance with a record-high peak power density of 168 mW cm-2 at an intermediate temperature of 550 °C. Furthermore, no degradation was observed during ~50 h operation. Such a successful integration of photo energy into the fuel cell system provides a new direction for the development of efficient fuel cells.

Critical Role of In-Situ-Generated Eutectic Carbonates in Superstructured Solid Fuel Cells.

As a distinct type of fuel cell, a carbonate-superstructured solid fuel cell (CSSFC), which possesses excellent performance and easy fabrication as well as low cost, was recently invented by our group. Herein, we demonstrated the critical role of the in-situ-generated eutectic carbonate phase in CSSFC. Namely, the in-situ generation of eutectic Li2CO3/Na2CO3 system increased the oxygen ionic conductivity of Ce0.8Sm0.2O1.9 solid electrolyte by 20 times (from 3.5 × 10-3 to 7.3 × 10-2 S cm-1), leading to 6 times enhancement of CSSFC peak powder density (up to 206 mW cm-2) with methane fuel at 550 °C. This finding is extremely important for designing efficient CSSFCs.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction.

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Direct Observation of Twin van der Waals Molecular Chains.

The van der Waals (vdW) assemblies are the most common structures of materials. However, direct mapping of intermolecular electron clouds of a vdW assembly has never been obtained, even though the intramolecular electron clouds were visualized by atomic-resolution techniques. In this report, we unprecedentedly mapped the intermolecular electron cloud of the assemblies of ethanol molecules via ethyl groups with high-resolution atomic force microscopy and scanning tunneling microscopy at 5 K, leading to the first visualization of vdW molecular chains, in which ethanol molecules assemble into twin vdW molecular chains in a reverse parallel configuration on the Ag(111) plane. Furthermore, spontaneous order-disorder transitions in the chain were dynamically observed, suggesting its unusual properties different from those of 2D vdW materials. These findings provide an "eye" to see the atomic world of vdW materials.

Chemical recycling of plastic wastes with alkaline earth metal oxides: A review.

Plastics have been widely used in daily life and industries due to their low cost and high durability, leading to huge production of plastics and tens of millions of plastic wastes every year. Chemical recycling can recycle contaminated and degraded plastics (that mechanical recycling cannot deal with) to obtain value-added products, which potentially solves the environmental problems caused by plastics and realizes a circular economy. Alkaline earth metal oxides, as a category of cost-effective and multi-functional materials, have been widely used in chemical recycling of common plastics, acting as three roles: catalyst, template, and absorbent. Among five commercial plastics, polyethylene terephthalate is suitable for pyrolysis and solvolysis. Polyethylene and polypropylene, which are ideal precursors for synthesis of carbon nanotubes, could be combined with biomass for co-pyrolysis. Polyvinyl chloride needs to be pretreated to reduce chloride content prior to pyrolysis. Depolymerization of polystyrene into monomers is attractive. This review summarized the chemical recycling approaches of commercial plastics and the strategies with alkaline earth metal oxides for the development of efficient recycling processes. It will aid understanding of the advances and challenges in the field and promote the future research.

Recent progress in removal of heavy metals from wastewater: A comprehensive review.

The heavy metal pollution constitutes a critical environmental issue. This has stimulated intensive efforts to develop treatment techniques for their removal from wastewater, including adsorption, membrane separation, precipitation/electrodeposition, ion exchange, coagulation-flocculation, flotation/electroflotation, solvent extraction, catalysis, and bioremediation. This article provides a comprehensive review on the advances in those techniques with the focus on the recent decade (2013-2023). It shows that the adsorption has attracted the most attention and membrane filtration the second, followed by precipitation and ion exchange. Interests in bioremediation and electrochemical treatments as well as catalysis are expected to increase in the future. Furthermore, the combination of different processes is a promising strategy to develop efficient hybrid technologies.

Structural transition and chemical reactivity of atomic carbon chains.

The sp-hybridized carbon chain (carbyne) is a representative 1D atomic material, whose bonding structure and chemical reactivity have remained a mystery for a century. Here, we report the unexpected alternating bond orders of 1.4 and 2.6 for the most stable carbon chain and the in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) detection of the temperature-dependent reversible change of the bond order alternation. Moreover, we revealed its reactivities with O2, H2, and CO2 at temperatures up to 600 °C and created an end-group-protection strategy to stabilize it. These observations open a new door to the chemistry of atomic materials.

3D graphene: synthesis, properties, and solar cell applications.

Three-dimensional (3D) graphene is one of the most important nanomaterials. This feature article highlights the advancements, with an emphasis on contributions from our group, in the synthesis of 3D graphene-based materials and their utilization in solar cells. Chemistries of graphene oxides, hydrocarbons, and alkali metals are discussed for the synthesis of 3D graphene materials. Their performances in dye-sensitized solar cells and perovskite solar cells (as counter electrodes, photoelectrodes, and electron extracting layers) were correlatively analyzed with their properties/structures (accessible surface area, electrical conductivity, defects, and functional groups). The challenges and prospects for their applications in photovoltaic solar cells are outlined.

Turning dead leaves into an active multifunctional material as evaporator, photocatalyst, and bioplastic.

Large numbers of leaves fall on the earth each autumn. The current treatments of dead leaves mainly involve completely destroying the biocomponents, which causes considerable energy consumption and environmental issues. It remains a challenge to convert waste leaves into useful materials without breaking down their biocomponents. Here, we turn red maple dead leaves into an active three-component multifunctional material by exploiting the role of whewellite biomineral for binding lignin and cellulose. Owing to its intense optical absorption spanning the full solar spectrum and the heterogeneous architecture for effective charge separation, films of this material show high performance in solar water evaporation, photocatalytic hydrogen production, and photocatalytic degradation of antibiotics. Furthermore, it also acts as a bioplastic with high mechanical strength, high-temperature tolerance, and biodegradable features. These findings pave the way for the efficient utilization of waste biomass and innovations of advanced materials.

Superstructured NiMoO4@CoMoO4 core-shell nanofibers for supercapacitors with ultrahigh areal capacitance.

High areal capacitance for a practical supercapacitor electrode requires both large mass loading and high utilization efficiency of electroactive materials, which presents a great challenge. Herein, we demonstrated the unprecedented synthesis of superstructured NiMoO4@CoMoO4 core-shell nanofiber arrays (NFAs) on a Mo-transition-layer-modified nickel foam (NF) current collector as a new material, achieving the synergistic combination of highly conductive CoMoO4 and electrochemical active NiMoO4. Moreover, this superstructured material exhibited a large gravimetric capacitance of 1,282.2 F/g in 2 M KOH with a mass loading of 7.8 mg/cm2, leading to an ultrahigh areal capacitance of 10.0 F/cm2 that is larger than any reported values of CoMoO4 and NiMoO4 electrodes. This work provides a strategic insight for rational design of electrodes with high areal capacitances for supercapacitors.

Mesoporous MgO enriched in Lewis base sites as effective catalysts for efficient CO2 capture.

Capturing CO2 has become increasingly important. However, wide industrial applications of conventional CO2 capture technologies are limited by their slow CO2 sorption and desorption kinetics. Accordingly, this research is designed to overcome the challenge by synthesizing mesoporous MgO nanoparticles (MgO-NPs) with a new method that uses PEG 1500 as a soft template. MgO surface structure is nonstoichiometric due to its distinctive shape; the abundant Lewis base sites provided by oxygen vacancies promote CO2 capture. Adding 2 wt % MgO-NPs to 20 wt % monoethanolamine (MEA) can increase the breakthrough time (the time with 90% CO2 capturing efficiency) by ∼3000% and can increase the CO2 absorption capacity within the breakthrough time by ∼3660%. The data suggest that MgO-NPs can accelerate the rate and increase CO2 desorption capacity by up to ∼8740% and ∼2290% at 90 °C, respectively. Also, the excellent stability of the system within 50 cycles is verified. These findings demonstrate a new strategy to innovate MEA absorbents currently widely used in commercial post-combustion CO2 capture plants.

3D meso/macroporous carbon from MgO-templated pyrolysis of waste plastic as an efficient electrode for supercapacitors.

Converting waste plastic into valuable carbon materials as the electrode for supercapacitors represents a sustainable way to deal with the severe waste plastic-related environmental issues. However, ideal carbon materials for supercapacitors require not only a large specific surface area but also abundant meso/macropores, which is still challenging for conventional synthesis methods. Herein, MgO-templated pyrolysis with chemical activation was demonstrated as an effective approach to convert waste polyethylene terephthalate (PET) plastic bottles into 3D meso/macroporous carbon (MMPC) with both large total surface area (1863.55 m2/g) and meso/macropore surface area (1478.46 m2/g). Furthermore, it exhibited a high capacitance of 191.4 F/g and an excellent rate capability (86.3% retention from 0.5 to 10 A/g) for supercapacitor. This work provides not only a facile approach to synthesize 3D meso/macroporous carbon materials but also a sustainable way to mitigate plastic-derived pollution.

In Situ Observation of Electron-Beam-Induced NaH Decomposition in Graphene Nanoreactors by Transmission Electron Microscopy.

Sodium hydride (NaH) was unprecedently embedded inside graphene nanobubbles via the discovered reaction between NaH and CO. With the graphene nanobubble as a nanoreactor for NaH, we directly observed the electron-beam-induced decomposition process of graphene-covered NaH by in situ high-resolution transmission electron microscopy with energy dispersive spectrometry and electron energy loss spectroscopy, revealing its decomposition mechanism. This can provide guidance for the design of hydrogen storage materials.

Facile and Scalable Synthesis of Metal- and Nitrogen-Doped Carbon Nanotubes for Efficient Electrochemical CO2 Reduction.

Metal- and nitrogen-doped carbon (M-N-C) is a promising material to catalyze electrochemical CO2 reduction reaction (CO2RR). However, most M-N-C catalysts in the literature require complicated synthesis procedures and produce small quantities per batch, limiting the commercialization potential. In this work, we developed a simple and scalable synthesis method to convert metal-impurity-containing commercial carbon nanotubes (CNTs) and nitrogen-containing organic precursors into M-N-C via one-step moderate-temperature (650 °C) pyrolysis without any other treatment nor the need to add metal precursors. Batches of catalysts in varied mass up to 10 g (150 mL in volume) per batch were synthesized, and repeatable catalytic performances were demonstrated. To the best of our knowledge, the 10 g batch is one of the largest batches of CO2RR catalysts synthesized in the literature while requiring minimal synthesis steps. The catalyst possessed single-atomic iron-nitrogen (Fe-N) sites, enabling a high performance of >95% CO product selectivity at a high current density of 400 mA/cm2 and high stability for 45 h at 100 mA/cm2 in a flow cell testing. The catalyst outperformed a benchmark noble-metal nanoparticle catalyst and achieved longer stability than many other reported M-N-C catalysts in the literature. The scalable and cost-effective synthesis developed in this work paves a pathway toward practical CO2RR applications. The direct utilization of metal impurities from raw CNTs for efficient catalyst synthesis with minimal treatment is a green and sustainable engineering approach.

Critical role of tetracycline's self-promotion effects in its visible-light driven photocatalytic degradation over ZnO nanorods.

Zinc oxide (ZnO), which is widely applied for ultraviolet-light driven photocatalysis, has no activity in visible-light photocatalytic process due to its large band gap of ∼3.2 eV. Herein, however, we demonstrated the multiple self-promotion effects of tetracycline as band adjuster, photo-sensitizer, and charge transfer promoter for ZnO nanorods, realizing its visible-light photocatalytic degradation with an excellent removal efficiency up to 91.1% within only 2 h. Besides, the influence of complex realistic factors on this unique process was evaluated together with tests with realistic water matrices. Furthermore, the active species and degradation products were identified. Both acute and developmental toxicities were found to be reduced as the degradation proceeds. These results pave the path for the brand-new self-driven visible-light photocatalysis.

Carbonate-superstructured solid fuel cells with hydrocarbon fuels.

A basic requirement for solid oxide fuel cells (SOFCs) is the sintering of electrolyte into a dense impermeable membrane to prevent the mixing of fuel and oxygen for a sufficiently high open-circuit voltage (OCV). However, herein, we demonstrate a different type of fuel cell, a carbonate-superstructured solid fuel cell (CSSFC), in which in situ generation of superstructured carbonate in the porous samarium-doped ceria layer creates a unique electrolyte with ultrahigh ionic conductivity of 0.17 S⋅cm-1 at 550 °C. The CSSFC achieves unprecedented high OCVs (1.051 V at 500 °C and 1.041 V at 550 °C) with methane fuel. Furthermore, the CSSFC exhibits a high peak power density of 215 mW⋅cm-2 with dry methane fuel at 550 °C, which is higher than all reported values of electrolyte-supported SOFCs. This provides a different approach for the development of efficient solid fuel cells.

Thermo-photo catalysis: a whole greater than the sum of its parts.

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.