Direct Photoreforming of Real-World Polylactic Acid Plastics into Highly Selective Value-Added Pyruvic Acid under Visible Light.

Although polylactic acid (PLA) represents a pivotal biodegradable polymer, its biodegradability has inadvertently overshadowed the development of effective recycling techniques, leading to the potential wastage of carbon resources. The photoreforming-recycling approach for PLA exhibits significant potential in terms of concepts and methods. However, the reaction faces enormous challenges due to the limited selectivity of organic oxidation products as well as the increased costs and challenging separation of organic products associated with alkali-solution-assisted prehydrolysis. Herein, we report an alkali-free direct-photoreforming pathway for real-world PLA plastics utilizing the Pd-CdS photocatalyst under visible-light illumination, obviating the need for chemical pretreatment of PLA. The devised pathway successfully produces H2 at a rate of 49.8 µmol gcat.-1 h-1, sustained over 100 h, and exhibits remarkable selectivity toward pyruvic acid (95.9% in liquid products). Additionally, experimental findings elucidate that Pd sites not only function as a typical cocatalyst for enhancing the photocatalytic evolution of H2 but also suppress competitive side reactions (e.g., lactic acid coupling or decarboxylation), consequently augmenting the yield and selectivity of pyruvic acid and H2. This investigation provides a straightforward and sustainable direct-photoreforming route capable of simultaneously mitigating and repurposing plastic waste into valuable chemicals, thus offering a promising solution to the current environmental challenges.

Quantifying the Contribution of Hot Electrons in Photothermal Catalysis: A Case Study of Ammonia Synthesis over Carbon-supported Ru Catalyst.

Photothermal catalysis is one of the most promising green catalytic technologies, while distinguishing the effects of hot electrons and local heating remains challenging. Herein, we reported that the actual reaction temperature of photothermal ammonia synthesis over carbon-supported Ru catalyst can be measured based on Le Chatelier's principle, enabling the hot-electron contribution to be quantified. By excluding local heating effects, we established that the activation energy via photothermal catalysis was much lower than that of thermocatalysis (54.9 vs. 126.0 kJ mol-1 ), stemming from hot-electron injection lowering the energy barriers for both N2 dissociation and intermediates hydrogenation. Furthermore, hot-electron injection acted to suppress carbon support methanation, giving the catalyst outstanding operational stability over 1000 h. This work provides new insights into the hot-electron effects in ammonia synthesis, guiding the design of high-performance photothermal catalysts.

Understanding Aerobic Nitrogen Photooxidation on Titania through In Situ Time-Resolved Spectroscopy.

Nitrate is an important raw material for chemical fertilizers, but it is industrially manufactured in multiple steps at high temperature and pressure, urgently motivating the design of a green and sustainable strategy for nitrate production. We report the photosynthesis of nitrate from N2 and O2 on commercial TiO2 in a flow reactor under ambient conditions. The TiO2 photocatalyst offered a high nitrate yield of 1.85 µmol h-1 as well as a solar-to-nitrate energy conversion efficiency up to 0.13 %. We combined reactivity and in situ Fourier transform infrared spectroscopy to elucidate the mechanism of nitrate formation and unveil the special role of O2 in N≡N bond dissociation. The mechanistic insight into charge-involved N2 oxidation was further demonstrated by in situ transient absorption spectroscopy and electron paramagnetic resonance. This work exhibits the mechanistic origin of N2 photooxidation and initiates a potential method for triggering inert catalytic reactions.

Revealing Ammonia Quantification Minefield in Photo/Electrocatalysis.

Photo/electrocatalytic ammonia synthesis has recently developed fast while the ammonia yields over state-of-the-art photo/electrocatalysts are still very moderate. Such low concentration of synthesized NH3 brings about a challenge to the reliable quantification of the product in photo/electrocatalysis. Notably, we found that the quantitative detection of ammonia concentration below 0.2 ppm is error-prone, which is likely the case happening in the majority of photo/electrocatalytic NH3 synthesis, thus arising concerns about the rationality and accuracy for low-concentration ammonia quantification in these processes. Herein, we discuss the methodology used and analyze the reliability of various detection methods for the detection of trace ammonia in aqueous media. The challenges facing the detection of low concentration of ammonia in photo/electrocatalysis can be overcome by integration with multiple detection methods. According to the data presented, we also propose an effective criterion for precise quantification of ammonia, avoiding the unreasonable comparisons in photo/electrocatalytic ammonia synthesis.

Tailoring the amorphous Mo sites on layered double hydroxide nanosheets for nitrogen photofixation.

While photocatalytic technology has brought additional opportunities and possibilities for the green conversion and sustainable development of ammonium-based nitrogen fertilizers, the low activation efficiency of the molecular N2 has impeded its further application feasibility. Here to address the concern, we designed an amorphous molybdenum hydroxide anchored on the ultrathin magnesium-aluminum layered double hydroxide (Mo@MgAl-LDH) nanosheets for benefiting the N2 photofixation to NH3. With the aid of the designed amorphous Mo(V) species, the pristine MgAl-LDH exhibited a considerable performance of nitrogen photofixation under visible light irradiation (NH3 production rate of 114.4 µmol g-1 h-1) due to the improved N2 activation efficiency. The work demonstrated a feasible strategy for nitrogen photofixation using amorphous Mo(V) species, which may also deliver a novel inspiration for the development of amorphous photocatalysts toward the photoactivation of molecular N2.

Photothermal recycling of waste polyolefin plastics into liquid fuels with high selectivity under solvent-free conditions.

The widespread use of polyolefin plastics in modern societies generates huge amounts of plastic waste. With a view toward sustainability, researchers are now seeking novel and low-cost strategies for recycling and valorizing polyolefin plastics. Herein, we report the successful development of a photothermal catalytic recycling system for transforming polyolefin plastics into liquid/waxy fuels under concentrated sunlight or xenon lamp irradiation. Photothermal heating of a Ru/TiO2 catalyst to 200-300 °C in the presence of polyolefin plastics results in intimate catalyst-plastic contact and controllable hydrogenolysis of C-C and C-H bonds in the polymer chains (mediated by Ru sites). By optimizing the reaction temperature and pressure, the complete conversion of waste polyolefins into valuable liquid fuels (86% gasoline- and diesel-range hydrocarbons, C5-C21) is possible in short periods (3 h). This work demonstrates a simple and efficient strategy for recycling waste polyolefin plastics using abundant solar energy.

Strain Engineering: A Boosting Strategy for Photocatalysis.

Whilst the photocatalytic technique is considered to be one of the most significant routes to address the energy crisis and global environmental challenges, the solar-to-chemical conversion efficiency is still far from satisfying practical industrial requirements, which can be traced to the suboptimal bandgap and electronic structure of photocatalysts. Strain engineering is a universal scheme that can finely tailor the bandgap and electronic structure of materials, hence supplying a novel avenue to boost their photocatalytic performance. Accordingly, to explore promising directions for certain breakthroughs in strained photocatalysts, an overview on the recent advances of strain engineering from the basics of strain effect, creations of strained materials, as well as characterizations and simulations of strain level is provided. Besides, the potential applications of strain engineering in photocatalysis are summarized, and a vision for the future controllable-electronic-structure photocatalysts by strain engineering is also given. Finally, perspectives on the challenges for future strain-promoted photocatalysis are discussed, placing emphasis on the creation and decoupling of strain effect, and the modification of theoretical frameworks.

Accelerating Electron-Transfer Dynamics by TiO2 -Immobilized Reversible Single-Atom Copper for Enhanced Artificial Photosynthesis of Urea.

Photocatalysis as a sustainable technology is expected to provide a novel sight for the green synthesis of urea directly using N2 , CO2 , and H2 O under mild conditions. However, the fundamental issue of inefficient electron transfer in photocatalysis strongly hinders its feasibility, especially for the above multi-electron-demanding urea synthesis. Herein, an effective strategy of accelerating electron-transfer dynamics is reported by TiO2 -immobilized reversible single-atom copper (denoted as Cu SA-TiO2 ) to enhance the performance for photosynthesis of urea from N2 , CO2 , and H2 O. As revealed by a series of quasi-in-situ characterizations (e.g., electron paramagnetic resonance, and wavelength-resolved and femtosecond time-resolved spectroscopies), the expedited dynamics behaviors originating from reversible single-atom copper in as-designed Cu SA-TiO2 (electron extraction rate: over 30 times faster than the reference photocatalysts) allow the assurance of abundant and continual photogenerated electrons for multi-electron-demanding co-photoactivation of N2 and CO2 , resulting in considerable rates of urea production. The strategy above for improving the photoelectron-extraction ability of photocatalysts will offer a high-efficiency and promising route for artificial urea photosynthesis and other multi-electron-demanding photocatalytic reactions.