Conversion Routes Research Articles

Interface interaction mediated surface plasmon resonance enhancement promoted visible-light-driven CO2 reduction with water

The conversion of carbon dioxide (CO2) into fuel using solar energy holds significant promise. However, the inefficient use of light and poor production activity have hindered its development. Here, we propose a simple in situ annealing oxidation method by coating a layer of TiO2 outside TiN, a material with a favorable price and localized surface plasmon resonance (LSPR) effect, to create an L-TiNO composite. The yield of CO over L-TiNO (50.8 μmol g−1 h−1) is 56.4 times that over TiO2 (0.9 μmol g−1 h−1) under visible light irradiation in pure aqueous environment, with a selectivity of 95.98%. In-situ Fourier transform infrared (FTIR) measurements reflect the CO2-COOH*-CO conversion route happening on L-TiNO. Characterizations like the Kelvin probe force microscopy (KPFM) technique confirm the generation of built-in electric field, which facilitates efficient carrier separation and migration. Density functional theory (DFT) calculations support that L-TiNO with LSPR effect alters the shape of absorbed CO2 to facilitate generation COOH* via forming hydroxyl end group (Ti-OH) and promotes CO* desorption to CO(g). This work provides valuable insights into the coupling of plasmonic materials with semiconductors to achieve efficient solar energy utilization.

Synthesis of lignin-based carbon/graphene oxide foam and its application as sensors for ammonia gas detection

The present study highlights the integration of lignin with graphene oxide (GO) and its reduced form (rGO) as a significant advancement within the bio-based products industry. Lignin-phenol-formaldehyde (LPF) resin is used as a carbon source in polyurethane foams, with the addition of 1 %, 2 %, and 4 % of GO and rGO to produce carbon structures thus producing carbon foams (CFs). Two conversion routes are assessed: (i) direct addition with rGO solution, and (ii) GO reduction by heat treatment. Carbon foams are characterized by thermal, structural, and morphological analysis, alongside an assessment of their electrochemical behavior. The thermal decomposition of samples with GO is like those having rGO, indicating the effective removal of oxygen groups in GO by carbonization. The addition of GO and rGO significantly improved the electrochemical properties of CF, with the GO2% sensors displaying 39 % and 62 % larger electroactive area than control and rGO2% sensors, respectively. Furthermore, there is a significant electron transfer improvement in GO sensors, demonstrating a promising potential for ammonia detection. Detailed structural and performance analysis highlights the significant enhancement in electrochemical properties, paving the way for the development of advanced sensors for gas detection, particularly ammonia, with the prospective market demands for durable, simple, cost-effective, and efficient devices.

ReaxFF reactive molecular dynamic and density functional theory study on supercritical water gasification of waste hydrofluorocarbons to fuels

Hydrofluorocarbon (HFC) working fluid with high global warming potential are step out of the stage of history due to the intensifying global greenhouse effect. Supercritical water gasification (SCWG), an effective and clean waste disposal method, may have better potential for the conversion of waste HFCs working fluid. ReaxFF reactive molecular dynamic and density functional theory method are used in this work to investigate the SCWG mechanism of HFC-245fa. The results indicate that the main products of HFC-245fa SCWG are high value-added chemicals and fuels such as CO, CO2, H2, and HF. During the gasification process, almost 100 % of the F atoms in HFC-245fa have the potential to become HF, which means that the SCWG method has a strong defluorination effect. The generation of H2 molecules is promoted and the formation of CO molecule is inhibited in the presence of H2O molecules. More importantly, hydrogen bonds are formed between HFC-245fa and H2O molecules, which results in the dissociation of HFC-245fa is improved by the SCWG environment. This work provides an available and environmentally friendly route for the efficient conversion of waste HFCs to fuels.

Diesel production from lignocellulosic residues: trends, challenges and opportunities

AbstractThis article aims to review the various techniques used to produce diesel from lignocellulosic biomass. Data were collected using the Web of Science database to identify trends, barriers, and prospects associated with the alternative methods used. The analysis reviewed 359 papers published between 2006 and 2021, focusing on three key areas: biomass pretreatment, biomass conversion, and biorefining. Pretreatment technologies require extensive research to reduce excessive energy and reagent consumption, thereby reducing overall costs. Fast pyrolysis and lipid‐producing microorganisms have been shown to be the most promising conversion routes due to their versatility in utilizing different lignocellulosic residues and producing a wide range of marketable co‐products. The most widely used method used for refining is hydroprocessing coupled with catalysts, with the objective of improving bio‐oil quality. Two of the main challenges are the excessive cost of the overall process and the limitations imposed by the technology. These limitations require processing optimization to achieve sustainable production and valuable co‐products. The growth of lignocellulosic diesel production will depend on the integration with other biodiesel and biofuel production processes by the optimization of new processes and the generation of new bioproducts to increase efficiency and reduce costs for commercial viability.

High-Efficiency Rechargeable Fe-CO2 Battery: A Route for Effective CO2 Conversion and Energy Storage.

Because of their high theoretical energy density, metal-CO2 batteries based on Li, Na, or K have attracted increasing attention recently for meeting the growing demands of CO2 recycling and conversion into electrical energy. However, the scarcity of active anode material resources, high cost, as well as safety concerns of Li, Na, and K create obstacles for practical applications. Herein, we demonstrate for the first time a high-efficiency (η = 77.2%) rechargeable Fe-CO2 battery that is composed of iron (Fe) anode and MoS2-catalysts deposited carbon cathode. MoS2 catalysts are crucial to the successful acceleration of reaction kinetics of Fe during charge and discharge with a minimum overpotential of the cell. The Fe-CO2 cell has a higher initial specific capacity of 12,500 mA h g-1 with an average discharge potential of 0.65 V and operates reversibly with a lower overpotential than that of Li-CO2 batteries with a cutoff capacity of 500 mA h g-1. Our Fe-CO2 battery can effectively convert CO2 greenhouse gas into electrical energy by consuming 1 ton of CO2 with usage of 1.23 tons of iron.

Production of sustainable methanol from aquatic biomass via thermal conversion route

Energy security is considered a basic need for the community. The development of a non-competing energy source is necessary to maintain harmony when fulfilling energy and food needs. Aquatic biomass such as algae is a promising sustainable energy source as it can be cultivated in the sea or pond which does not require productive land. By using thermal reaction, algae can be converted into methanol via gasification followed by hydrogenation reactions. The key challenge of algae utilization lies in the high moisture content. This work presents an understanding of the role of moisture on the algae for methanol production. Although moisture content has a negative impact on the syngas quality, the methanol production does not change with increasing moisture content. Under the optimum condition, the algae-to-methanol route converts ∼45% of the total energy input into energy in the form of methanol. The production of one-ton methanol from algae with 10 wt% moisture requires algae (2.7 ton), oxygen (0.9 ton), boiler feed water (1.5 ton), thermal energy (12.1 GJ) and electricity (0.7 MWh). The present work provides a clear understanding of the potential of aquatic biomass for methanol production, leading to further development to achieve a feasible algae-to-methanol route.

Multi-color polymer carbon dots synthesized from waste polyolefins through phenylenediamine-assisted hydrothermal processing

The large accumulation and low recycling rates of polyolefin waste have posed a threat to the environment and human health. The shortage of chemical recycling methods for polyolefins strongly demands the development of new and sustainable treatment technologies for hydrocarbon plastics to improve their waste management. In this study, polyethylene (PE) and polypropylene (PP) were utilized for the preparation of multi-color polymer carbon dots (PCDs) via a two-step hydrothermal (HT) synthesis involving (i) thermo-oxidative degradation of polyolefins to precursors containing plentiful oxygen-based functional groups, and (ii) modification with phenylenediamine (PDA). The fluorescence of PCDs depends on the structure of isomeric PDA and PCDs modified by ortho-, meta-, and para-PDA emit blue, green, and yellow color fluorescence, respectively. The formation mechanism of PCDs, involving dehydrative condensation and amination of PE or PP-derived precursors by PDA, was proposed. The obtained PCDs were utilized for the detection and quantification of Fe3+ ions at ppm concentrations. The proposed strategy here aims to broaden the scope of the chemical recycling methods for polyolefin plastic waste as well as to develop a conversion route of polyolefin to value-added materials.

Transforming CO2 to valuable feedstocks: Emerging catalytic and technological advances for the reverse water gas shift reaction

Current conditions suggest that to mitigate climate change, carbon neutrality must be achieved. Despite efforts to reduce carbon dioxide emissions, existing strategies remain inadequate. Thus, it is inevitable that carbon dioxide utilization will play a crucial role in the fight against climate change. Among the conversion routes available, the reverse water–gas shift reaction (RWGS) is promising as it allows the conversion of CO2 to CO, which can then be further converted to other valuable feedstocks while utilizing renewable H2. However, this route presents several challenges, as the RWGS reaction requires high energy input and is less favored over the methanation reaction at lower temperatures. Hence, the development of novel catalysts and advanced technologies is necessary to achieve high conversions and selectivity. This review summarizes the most recent progress and advances in heterogenous catalyst systems and emerging technologies explored for the RWGS reaction. Techniques to enhance catalyst performance, alter reaction mechanisms, and improve catalyst stability are discussed. Novel technologies and their recent developments to achieve equilibrium conversions and improve CO yield are also given focus and compared. This review thus provides insight into the possibilities available for improving the RWGS reaction as a practical carbon mitigation route.

Anaerobic propionic acid production via succinate pathway at extremely low pH

Propionic acid, a C-3 platform chemical with applications in a wide variety of industries, is currently produced via petroleum-based pathway. Bio-propionic acid can be a promising alternative to petroleum-based one. However, the bio-production of propionic acid is easily inhibited by low pH (<4.5). Typical vegetable wastes, cabbage and Chinese cabbage were fermented for propionic acid production in leaching bed reactors (LBRs) without pH control. The highest propionic acid production reached up to 12.50 g COD/L in LBR with large-size cabbage, corresponding to cumulative yields of 0.27 g COD/g·VSremoval. Without pH control, pH in this reactor was ∼3.5 during the whole operation period. Extremely low pH regulated the intracellular NADH/NAD+ balance and induced a relatively reductive micro-environment. Adenosine triphosphate (ATP) consumption reactions were triggered to maintain the intracellular proton balance and metabolic activity; thus, the relative abundance of H+-ATPase-related genes was increased to maximize ATP production. The low-pH inducible micro-environment selected Lactobacillus fermentum and Lactobacillus plantarum as dominant species in the microbial community. Succinate pathway was identified as the main fermentative pathway for propionic acid production with both cabbage and Chinese cabbage wastes, which maximized energy generation in propionic acid fermentation. This work unveils a unique propionic acid production pathway from vegetable waste biomass and offers a promising route for waste conversion towards a circular bioeconomy.

Assessment and modeling of mercury adsorption on carbon-based adsorbents prepared from Jacaranda mimosifolia and guava biomass via pyrolysis and hydrothermal carbonization

Abstract The mercury adsorption properties of carbon-based materials prepared from jacaranda (Jacaranda mimosifolia) and guava (Psidium guajava) seed wastes are reported and compared in this paper. These adsorbent samples were obtained via pyrolysis and hydrothermal carbonization. Mercury adsorption equilibrium was studied at pH 4 and 20–40 °C, and the adsorption enthalpy changes were calculated for all adsorbent samples. The results showed that jacaranda-based materials contained a higher amount of acidic functional groups than guava seed-based adsorbents, and consequently, their mercury adsorption properties were better. The surface area of these adsorbents was &amp;lt;10 m2/g thus being classified as low-porosity materials. Elemental analysis indicated that all adsorbents were mainly composed of oxygen (4–25%) and carbon (75–95%). The calculated adsorption capacities at saturation of the best adsorbent were 18.05–30.09 mg/g under the tested experimental conditions. Statistical physics calculations also indicated that the adsorption mechanism of HgCl2 species was multi-molecular and endothermic. Ligand exchange and van der Waals forces were involved in generating the mercury–adsorbent interface. These results highlight the importance of comparing and optimizing biomass thermochemical conversion routes to tailor the surface properties of adsorbents used for water purification.

Biomass: A Versatile Resource for Biofuel, Industrial, and Environmental Solution

Biomass, noted for its adaptability, has various applications in biofuel generation, industrial use, and environmental cleaning. This study looks into the multiple roles of biomass as a renewable energy source, with a particular emphasis on its vital contribution to biofuel production. Through a thorough evaluation of different conversion routes—thermal, biological, and physical—the study emphasizes thermochemical processes' efficiency, cost-effectiveness, and adaptability. Notably, technologies like gasification and quick pyrolysis are thoroughly investigated, followed by in-depth discussions of reactor optimization strategies to enhance performance and output. The complex structure of biomass, which is dominated by high-molecular-weight polysaccharides such as cellulose and hemicelluloses, demonstrates its significant potential for energy generation. Furthermore, the study categorizes biomass by content, origin, and conversion processes, resulting in a comprehensive inventory of available resources. Biomass from the agriculture and forestry industries, such as starch, sugar, lignocellulose, and organic wastes, is rigorously analyzed for energy production. Furthermore, various biomass processing techniques, including thermochemical, biochemical, and physicochemical conversions, are carefully tested in real-world applications to ensure their efficacy and viability. Beyond its importance in biofuel production, the article underlines biomass' versatility in satisfying industrial needs and contributing to environmental cleanup initiatives. This study lays the groundwork for informed decision-making and innovative solutions in various industries by providing a thorough understanding of biomass's various benefits and applications, including energy provision, industrial processes, and ecological restoration.

Unprecedented 100% conversion from pyridinic to pyrrolic nitrogen configuration for electrochemically active nitrogen-doped carbon materials

Nitrogen-doped carbons with promising electrochemical performance exhibit a strong dependence on nitrogen configuration. Therefore, accurate control of nitrogen configurations is crucial to clarify their influence. Unfortunately, there is still no well-defined conversion route to finely control nitrogen configuration. Herein, we proposed the concept of 100% conversion from pyridinic to pyrrolic nitrogen in carbon materials through low-temperature pyrolysis and alkali activation of hydroxypyridine-3-halophenol-formaldehyde resins. Their dehalogenation pyrolysis promotes formation of carbon intermediates and conversion of tautomeric pyridone and hydroxypyridine into pyrrolic and pyridinic nitrogen through eliminating carbonyl and hydroxyl functionalities, respectively. Continuous thermal alkali activation introduces hydroxyl groups into carbon materials, converting pyridinic species to intermediate hydroxypyridine and pyridone; subsequently, these configurations transform to pyridinic and pyrrolic nitrogen, respectively, and finally, an excessive alkali ensures 100% conversion from pyridinic to pyrrolic nitrogen. NaOH activation for pyrrolic and pyridinic nitrogen co-doped carbon and KOH activation for model nitrogen-containing compounds including acridine, phenanthridine, and acridone further confirm that alkali activation plays an indispensable role in 100% conversion from pyridinic to pyrrolic units through the tautomeric hydroxypyridine and pyridone intermediates. Low-temperature alkali-induced controllable conversion of nitrogen configuration in carbon materials is suitable modulating nitrogen configurations for almost all nitrogen-doped carbon materials in electrochemical applications.

Divergent Bimetallic Mechanisms in Copper(II)-Mediated C-C, N-N, and O-O Oxidative Coupling Reactions.

Copper-catalyzed aerobic oxidative coupling of diaryl imines provides a route for conversion of ammonia to hydrazine. The present study uses experimental and density functional theory computational methods to investigate the mechanism of N-N bond formation, and the data support a mechanism involving bimolecular coupling of Cu-coordinated iminyl radicals. Computational analysis is extended to CuII-mediated C-C, N-N, and O-O coupling reactions involved in the formation of cyanogen (NC-CN) from HCN, 1,3-butadiyne from ethyne (i.e., Glaser coupling), hydrazine from ammonia, and hydrogen peroxide from water. The results reveal two different mechanistic pathways. Heteroatom ligands with an uncoordinated lone pair (iminyl, NH2, OH) undergo charge transfer to CuII, generating ligand-centered radicals that undergo facile bimolecular radical-radical coupling. Ligands lacking a lone pair (CN and CCH) form bridged binuclear diamond-core structures that undergo C-C coupling. This mechanistic bifurcation is rationalized by analysis of spin densities in key intermediates and transition states, as well as multiconfigurational calculations. Radical-radical coupling is especially favorable for N-N coupling owing to energetically favorable charge transfer in the intermediate and thermodynamically favorable product formation.

Efficient CO2 photoreduction enabled by the one-dimensional (1D) porous structured NiTiO3 nanorods

In this study, porous, and hollow nanorods of NiTiO3 (NiTiO3 NRs-p: 2–3 μm in length and 400 nm in diameter) are successfully prepared using an ethylene glycol-mediated approach at room temperature (25 °C), followed by calcination at 700 °C in air environment. Their rough surfaces and accumulated holes are advantageous for adsorption and subsequent photoreduction of carbon dioxide (CO2) under UV–vis irradiation. The NiTiO3 NRs-p exhibit superior performance in terms of photoconversion of CO2 (purity 99.999 %, 100 mL/min) into gaseous CO (57.833 μmolg−1 h−1) and CH4 (24.33 μmolg−1 h−1) with an overall CO2 selectivity (SCO2) of 89 %. In contrast, the solid NiTiO3 nanorods (NiTiO3 NRs) exhibit moderate performance in CO2 reduction, producing CO (30.33 μmolg−1 h−1) and CH4 (11.50 μmolg−1 h−1) with a CO2 selectivity of SCO2 = 60 %. NiTiO3 NRs-p exhibits superior photocatalytic activity against CO2 over other NiTiO3 morphologies with similar physical and chemical properties (such as nanoparticles (NPs) and nanofibers (NFs). This enhancement in photocatalytic activity can be attributed to the porous texture and hollow rod-like structure of NiTiO3 NRs-p, which provides a larger number of active sites to promote rapid mass transport. This unique one-dimensional (1D) structure also facilitates the separation of photogenerated electron-hole pairs, as demonstrated experimentally. This study opens a new room for a simple and facile routes for the photocatalytic conversion of CO2 into solar fuels.

Recent Advancements in Pyrolysis of Halogen-Containing Plastics for Resource Recovery and Halogen Upcycling: A State-of-the-Art Review.

Plastic waste has emerged as a serious issue due to its impact on environmental degradation and resource scarcity. Plastic recycling, especially of halogen-containing plastics, presents challenges due to potential secondary pollution and lower-value implementations. Chemical recycling via pyrolysis is the most versatile and robust approach for combating plastic waste. In this Review, we present recent advancements in halogen-plastic pyrolysis for resource utilization and the potential pathways from "reducing to recycling to upcycling" halogens. We emphasize the advanced management of halogen-plastics through copyrolysis with solid wastes (waste polymers, biomass, coal, etc.), which is an efficient method for dealing with mixed wastes to obtain high-value products while reducing undesirable substances. Innovations in catalyst design and reaction configurations for catalytic pyrolysis are comprehensively evaluated. In particular, a tandem catalysis system is a promising route for halogen removal and selective conversion of targeted products. Furthermore, we propose novel insights regarding the utilization and upcycling of halogens from halogen-plastics. This includes the preparation of halogen-based sorbents for elemental mercury removal, the halogenation-vaporization process for metal recovery, and the development of halogen-doped functional materials for new materials and energy applications. The reutilization of halogens facilitates the upcycling of halogen-plastics, but many efforts are needed for mutually beneficial outcomes. Overall, future investigations in the development of copyrolysis and catalyst-driven technologies for upcycling halogen-plastics are highlighted.

Facile synthesis of β-Ga2O3 based high-performance electronic devices via direct oxidation of solution-processed transition metal dichalcogenides

Gallium oxide (Ga2O3) is a promising wide bandgap semiconductor that is viewed as a contender for the next generation of high-power electronics due to its high theoretical breakdown electric field and large Baliga’s figure of merit. Here, we report a facile route of synthesizing β-Ga2O3 via direct oxidation conversion using solution-processed two-dimensional (2D) GaS semiconducting nanomaterial. Higher order of crystallinity in x-ray diffraction patterns and full surface coverage formation in scanning electron microscopy images after annealing were achieved. A direct and wide bandgap of 5 eV was calculated, and the synthesized β-Ga2O3 was fabricated as thin film transistors (TFT). The β-Ga2O3 TFT fabricated exhibits remarkable electron mobility (1.28 cm2 Vs−1) and a good current ratio (I on/I off) of 2.06 × 105. To further boost the electrical performance and solve the structural imperfections resulting from the exfoliation process of the 2D nanoflakes, we also introduced and doped graphene in β-Ga2O3 TFT devices, increasing the electrical device mobility by ∼8-fold and thereby promoting percolation pathways for the charge transport. We found that electron mobility and conductivity increase directly with the graphene doping concentration. From these results, it can be proved that the β-Ga2O3 networks have excellent carrier transport properties. The facile and convenient synthesis method successfully developed in this paper makes an outstanding contribution to applying 2D oxide materials in different and emerging optoelectronic applications.

Recent advances in organolead halide crystalline materials for photocatalytic H2 evolution and CO2 reduction applications.

The photocatalytic technique has been widely recognized as a feasible technological route for sustainable energy conversion of solar energy into chemical energy. Photocatalysts play a vital role in the whole catalytic process. In particular, organolead halide perovskites have become emerging photocatalysts, owing to their precisely tunable light absorption range, high carrier diffusion mobility, and longer carrier lifetime and diffusion length. Nevertheless, their intrinsic structural instability and high carrier recombination rate are the major bottlenecks for further development in photocatalytic applications. This Frontier is focused on the recent research about the instability mechanism of organolead halide perovskites. Then, we summarize the recently developed strategies to improve the structural stability and photocatalytic activity of organolead halide materials, with an emphasis on the construction of organolead halide crystalline catalysts with high intrinsic structural stability. Finally, an outlook and challenges of organometal halide photocatalysts are presented, demonstrating the irreplaceable role of this class of emergent materials in the field of photo-energy conversion.

Photocatalytic CO2 reduction to CO catalysed by lanthanide complexes.

Here we demonstrate the efficient CO2 reduction to CO catalysed by lanthanide-based complexes under light irradiation, by which the highest CO evolution rate can reach 78 ± 8 μmol g-1 h-1 in 4 h. This work provides an economic and environmentally friendly route for CO2 conversion.

Transition metal chalcogenide nanoparticle embedded metal–organic framework nanosheets for high-performance H2O2 electrosynthesis

Through a partial conversion route using NiFe-MOF nanosheets as precursors, a transition-metal chalcogenide@metal–organic framework (TMC@MOF) composite was fabricated as an efficient 2e-ORR electrocatalyst.

Selective conversion of methane to methanol facilitated by molecular metal-methoxy complexes via a self-correcting chemical cycle.

The controlled oxidation of methane to methanol has been an area of intense research over the past decades. Despite the efforts, the identification of an efficient catalyst with high selectivity is still elusive. Here we propose a thoroughly different strategy employing catalysts containing a metal methoxy unit. This family of catalysts has been used for the activation of C-H bonds but this is the first systematic investigation for the conversion of methane to methanol highlighting the advantages over the typically used metal oxides. Specifically, we start our investigation with an Fe(III) center coordinated by four ammonia ligands, (NH3)4FeOCH32+. Structures and energetics are reported for two mechanisms ([2+2] and proton coupled electrons transfer) and for different spin multiplicities via density functional theory, multi-reference, and coupled cluster quantum chemical calculations. The excited low-spin doublet state of this model system exhibits the best performance in terms of activation barriers and selectivity. Therefore, we then switched to the corresponding Ru(III) complex, which has a doublet ground state and manifests better performance than the doublet state of Fe(III). For both systems the activation barrier for methanol is larger than that of methane due to the interaction of the OH group of methanol with the coordinated NH3 ligands (hydrogen bonding) and/or the metal center. This observation suggests that the activation of methanol is slower, hindering its oxidation. In addition, we show that the metal-methoxy family of catalysts offers a potential mechanism that can prevent the oxidation of an activated methanol molecule (self-correcting chemical loop). This work aspires to induce experimental interest and pave the road for the development of high-performance high-selectivity methane to methanol direct conversion routes under mild conditions.