Single-Atom Metal Sites Anchored Hydrogen-Bonded Organic Frameworks for Superior “Two-In-One” Photocatalytic Reaction

Photoredox catalysis is a green solution for organics transformation and CO₂ conversion into valuable fuels, meeting the challenges of sustainable energy and environmental concerns. However, the regulation of single-atomic active sites in organic framework not only influences the photoredox performance, but also limits the understanding of the relationship for photocatalytic selective organic conversion with CO₂ valorization into one reaction system. As a prototype, different single-atomic metal (M) sites (M²⁺ = Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) in hydrogen-bonded organic frameworks (M-HOF) backbone with bridging structure of metal-nitrogen are constructed by a typical “two-in-one” strategy for superior photocatalytic C N coupling reactions integrated with CO₂ valorization. Remarkably, Zn-HOF achieves 100% conversion of benzylamine oxidative coupling reactions, 91% selectivity of N-benzylidenebenzylamine and CO₂ conversion in one photoredox cycle. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to synergic effect of atomically dispersed metal sites and HOF host, decreasing the reaction energy barriers, enhancing CO₂ adsorption and forming benzylcarbamic acid intermediate to promote the redox recycle. This work not only affords the rational design strategy of single-atom active sites in functional HOF, but also facilitates the fundamental insights upon the mechanism of versatile photoredox coupling reaction systems.     

Role of lignin in a biorefinery: separation characterization and valorization

Lignin, a major component of the cell wall of vascular plants, has long been recognized for its negative impact and treated as a by‐product in a biorefinery. This highly abundant by‐product of the biorefinery is undervalued and underdeveloped due to its complex nature. The development of value‐added products from lignin would greatly improve the economics of the biorefinery. The inherent properties of lignin significantly affect the productivity of the biorefinery processes and its potential applications. Although the structure and biosynthetic pathway of lignin have been studied for more than a century, they have not yet been completely elucidated. In this mini‐review, the primary obstacles to elucidating the structure of native lignin, including separation and characterization, are highlighted. Several classical methods for separation and various NMR techniques, especially 2D HSQC NMR, for characterization of lignin are reviewed. Some potential applications of lignin are introduced. It is believed that a knowledge of the method to separate lignin from the cell wall and structural features of the lignin polymer from lignocellulosic materials will help to maximize the exploitation of lignocelluloses for the biorefinery as well as the utilization of lignin for novel materials and chemicals. © 2012 Society of Chemical Industry     

Methane and oxygen from energy-efficient,low temperature in situ resource utilization enables missions to Mars

The United States National Aeronautics and Space Administration's (NASA's) mandate is a human mission to Mars in the 2030s and sustained exploration of Mars requires in situ resource utilization (ISRU). Exploiting the Martian water cycle (alongside perchlorate salts that depress water's freezing point to <213 K) and the available 95 vol.% atmospheric CO₂, we detail an ultra-low temperature (255 K) CO₂–H₂O electrolyzer to produce methane fuel and life-supporting oxygen on Mars. Our polarization model fit experimental Martian brine electrolyzer performance and predicted CO₂ electrolysis occurring at comparatively lower potentials (vs. water electrolysis) on Mars. A hypothetical 10-cell, 100 cm² electrode-area-per-cell electrolyzer produced 0.45 g W⁻¹ day⁻¹ of CH₄ and 3.55 g W⁻¹ day⁻¹ of O₂ at 2 V/cell and 50% electrolyzer faradaic efficiency versus a best-case production of 2.5 g W⁻¹ day⁻¹ of O₂ by the Mars Oxygen in situ Resource Utilization Experiment (MOXIE) from NASA's Mars 2020 mission (MOXIE produces no fuel). Material performance requirements are presented to advance this technology as an energy-efficient complement to MOXIE.     

Integrated chemo- and biocatalytic processes: a new fashion toward renewable chemicals production from lignocellulosic biomass

Concerns over climate change and environmental pollution resulting from petroleum refining has spurred the exploitation of green replacements for producing chemicals and fuels. Valorization of lignocellulosic biomass into chemicals represents a promising alternative to petroleum refining. Biological and chemical catalysis are two leading routes for lignocellulose variolization, but strategies relying simply on biological or chemical conversion have shown limitations. Integrating biocatalysts with chemocatalysts could leverage the inherent strengths of both while circumventing their respective disadvantages, benefiting product yield and selectivity, and reducing cost and waste generation. This review focuses on the coupled chemocatalytic and biocatalytic synthesis of renewable chemicals from polysaccharides and their derived platform chemicals. In addition, strategies for producing value-added products from lignin via integrated chemical depolymerization and biological conversion are highlighted. The techno-economics of integrating chemocatalysts and biocatalysts in producing chemicals in the context of biorefinery are also discussed. Finally, perspectives on designing integrated chemical and biological catalysis for renewable chemicals production are provided. © 2022 Society of Chemical Industry (SCI).     

Use of micellar extraction and cloud point preconcentration for valorization of saponins from sisal (Agave sisalana) waste

Sisal (Agave sisalana) is the main hard fiber produced worldwide, with an estimated generation of 400 thousands t in 2011. From its leaves, only the hard fibers, which represent 3–5% of their weight, are removed. The remaining 95–97% is referred to as sisal waste and contains steroidal saponins that can be potentially used in foods, cosmetics and pharmaceuticals formulations, as well as for soil bioremediation. The present work aimed at to evaluate strategies for the extraction and concentration of saponins from sisal waste, focused on the use of clean solvents, such as water and ethanol. For this purpose, it was firstly performed a central composite rotatable design for the optimization of the extraction conditions followed by a comparison of this strategy with other methods (Soxhlet, ultrasound-assisted extraction and micellar extraction). Cloud point preconcentration was then tested, using several types and concentrations of salts. The use of orbital shaker extraction (200 rpm) with an ethanolic solution (30%, v/v) at 50 °C, a mass/volume ratio sisal/solvent of 0.17 (g/mL) for 4 h allowed a recovery of 38.6% of the saponins. When a micellar extraction strategy using 7.5% (v/v) of Triton X-100, under the above-mentioned conditions was performed, saponins recovery raised to 98.4%. In a subsequent step, the addition of 20% (m/v) sodium carbonate led to a preconcentration factor of 20.3. The best adsorbent for Triton removal from the preconcentrated solution was Amberlite FPX-66. The process strategy proposed in the present study showed to be efficient for saponins extraction and preconcentration from a low-cost, highly available agricultural waste.     

Microstructural development and electrical behavior during crystalization of iron-rich glass-ceramics obtained from mill scale

Mill scale is one of the most hazardous waste generated from the steelmaking industry. In 2014, around 16.4–32.8 million t of mill scale was generated all over the world. In this paper, we present recent results about the effect of the structure and microstructure of iron-rich glass-ceramics obtained from mill scale on their electrical behavior. Five iron-rich glass compositions were investigated. The crystalline phases of the crystallized (glass-ceramic) materials were identified by X-ray diffractometry, and phase content quantifications were performed by the Rietveld method. The crystallinity and porosity were also related to the electrical behavior of the glass-ceramics, which was determined by impedance spectroscopy, and the hardness, measured by the Vickers indentation method. Albite, andradite, anorthite, clinopyroxene, franklinite, nepheline, and spinel were shown to be the main crystalline phases present in the investigated compositions. The conductivity showed an increasing trend with the degree of crystallinity. This behavior was attributed to a decrease in porosity, an increase in the concentration of charge carriers in the glass phase (iron, Li⁺, and Na⁺), and an increase in the number of conduction paths through the glassy phase/crystalline phase interfaces. The relationship between hardness and crystallinity could not be verified due to the structural complexity of the glass-ceramics studied. However, a nearly linear relationship was found between the effect of porosity and hardness. The G2Z composition exhibited a hardness of 6.1 ± 0.5 GPa at 850 °C, which is a value in very good agreement with other iron-rich glass-ceramics studied.     

Strategies of valorization of sludge from wastewater treatment

Sludge is regarded as a potential source to achieve valorization via strategies such as resource recovery, sludge based adsorbents preparation, bioflucculants production, sludge manufacturing construction materials preparation, sludge composting and thermal valorization, which are currently common and effective strategies. Appropriate treatment strategies of sludge are of great importance worldwide for the fast growing population and rapidly increasing waste. This mini review summarized some widely used and effective strategies to achieve sludge valorization based on whether the strategy would utilize or reuse the potential of sludge to obtain valuable product and eliminate secondary pollution. Anaerobic digestion of sludge is perceived as a potentially cost‐effective method to achieve sludge reduction and resource recovery including carbon, nitrogen, phosphorus resource recovery coupled with other technologies. Utilizing sludge as raw material for preparation of valuable products including sludge based adsorbents, bioflocculants and construction materials is another aspect to achieve sludge valorization. Sludge composting and thermal valorization are also introduced in the mini review since the two strategies could also achieve sludge valorization. In addition, the strategies mentioned were discussed and analyzed in the mini review from environmental and economic aspects. © 2017 Society of Chemical Industry     

Structural performance of alkali/acid-ultrasound modified Agave fibers during the melt mixing process with polyvinyl alcohol

This study aims to investigate changes in the structural properties of alkali/acid-ultrasound modified Agave fibers and their performance immersed on a polyvinyl alcohol (PVA) matrix with plasticizer during melt mixing processing. Structural analysis revealed that ultrasound enhances the effectiveness of the conventional alkaline/acid treatments to modify fibers since the simultaneous treatment increased the partial removal of lignocellulosic components, water molecules, and amorphous regions which improved their processability on a PVA matrix. Specific energy consumption values indicated that during melt mixing the modified fibers required more energy to expose the chains of cellulose fraction to function as an interaction site for PVA chains. Once the mixture was homogenized, the fiber-matrix interactions promoted high viscosity, friction, and mechanical stress in the chamber. Therefore, the modified fibers restricted the interaction between plasticizer and PVA in the obtained films, resulting in a highly structured, and reinforced network, increasing the storage modulus as dynamic mechanical analysis indicated. These findings highlight a feasible way to valorize Agave fibers and allow the understanding of the matrix-fiber interactions during melt mixing processing, useful to predict the structural and mechanical properties of the films.