CO2 Production Rate Research Articles

Ambient Sunlight Driven Photothermal Green Syngas Production at 100 m3 Scale by the Dynamic Structural Reconstruction of Iron Oxides with 38.7% Efficiency

AbstractAmbient sunlight‐driven photothermal green syngas production via reverse water‐gas shift (RWGS) reaction is important for carbon neutrality, which lacks efficient and inexpensive catalysts at low temperatures. This studydemonstrates that the scalable Fe3O4 supported with K atoms modified Ag nanoparticles (AgK/Fe3O4) exhibits a RWGS CO production rate of 1089 mmol g−1 h−1 at 300 °C and 100% CO selectivity through dynamic structural reconstruction, surpassing all reported platinum‐based catalysts. In situ characterization and theoretical simulation indicate that the AgK nanoparticles activate H2 to reduce Fe3O4 as metallic Fe. Subsequently, the metallic Fe spontaneously reacts with CO2 to form CO and Fe3O4, thereby facilitating low‐temperature RWGS. Owing to its superior low‐temperature performance, AgK/Fe3O4 equipped with a homemade photothermal device achieves one sun‐driven photothermal RWGS with a CO production rate of 1925 mmol g−1 h−1 and a 38.7% solar to enthalpy energy conversion efficiency. Furthermore, the enlarged outdoor demonstration yields 100.6 m3day−1 of green syngas with an H2/CO ratio of 3. This work paves the way for designing efficient platinum‐free CO2 hydrogenation catalysts and introduces a new approach for sunlight‐driven scalable green syngas production.

Self-Assembly Synthesis of Oxygen and Sulfur Co-Doped Porous Graphitic Carbon Nitride Nanosheets for Boosting CO2 Photoreduction.

Graphitic carbon nitride (CN) has garnered considerable attention in the field of visible-light CO2 photoreduction, but its efficiency remains limited by the intrinsic π-conjugated skeleton. Here, O and S were co-doped CN (O, S/CN) by a facile "hydrolysis + calcination" approach to modulate the physicochemical and electronic structure. Distinctive from S doped CN (SCN), O, S/CN owned porous layer structure with several nanosheets and less SO4 2- groups on the surface. The amount of heteroatom-doping was achieved by changing the hydrothermal temperature. The optimum O, S/CN-80 achieved moderate CO production rate of 1.29 μmol g-1 h-1, which was 3.79 times as much as SCN (0.34 μmol g-1 h-1). The O and most S atoms were substitutionally doped and the effect of S doped state on the improved efficiency of CO generation in O, S/CN was also explored based on the theoretical calculations. This work provides an inspiration to develop efficient dual-doped CN photocatalysts for photocatalytic CO2 reduction.

Improvement of Photocatalytic CO2 Reduction with Conjugated Organic Polymers by Rational Modulation of Donor, Acceptor and Bonding Method.

The use of metal-free catalysts to convert CO2 into valuable chemicals is very challenging. Here, we synthesized a conjugated organic polymer (TpTf-1) featuring 2,4,6-Triphenyl-1,3,5-Triazine as the acceptor unit, triphenylamine as the donor unit, and vinylidene bond as the linkage. The local structure of donor-acceptor (D-A) forms an intramolecular electric field that can promote the separation of photogenerated electrons and charges, meanwhile, the vinylidene bond can further change the charge distribution to promote exciton dissociation. Without the use of photosensitizers, the TpTf-1 exhibits outstanding selectivity of CO of up to 91.96 %, with a production rate of 45.2 μmol g-1 h-1 at visible light, which is 3.4-fold than TaTf-1 with the same D-A structure but linking in imine bond and is 2.8-fold than TpTf-2 linking in vinylidene bond but with a different donor unit. Moreover, TpTf-1 has a CO production rate of up to 117.3 μmol g-1 h-1 under full wavelength light irradiation.

Effects of inorganic nitrogen enrichment on soil CH4 and CO2 production in freshwater and mesohaline marshes across six estuaries in China

Eutrophication is an important environmental stressor in coastal wetlands that alters ecosystem processes including primary production and the carbon cycle. However, how different nitrogen eutrophication scenarios may affect CH4 and CO2 production along a salinity gradient in coastal wetlands is poorly known. We collected the surface soil samples from both tidal freshwater and mesohaline Phragmites australis marshes in six main estuaries in China and conducted inorganic nitrogen enrichment anaerobic incubation experiments. Background soil CH4 and CO2 production rates were strongly correlated with total nitrogen but not salinity. On average, nitrate enrichment decreased soil CH4 and CO2 production rates by ca. 20 % in freshwater marsh and 16–43 % in mesohaline marshes, whereas ammonium enrichment decreased CO2 production by ca. 26–30 % but had no effect on CH4 production. Salinity was not an important mitigating factor in either eutrophication scenario. In most cases, nitrogen addition decreased the extracellular enzyme activities of β-1,4-glucosidase and cellobiohydrolase, but increased the activity of β-N-acetyl glucosaminidase, phenol oxidase and peroxidase. Nitrate addition decreased the mcrA gene abundance on average by 34–35 % but ammonium addition had insignificant effect. Total nitrogen availability was an important driver of CH4 and CO2 production rates in these tidally influenced coastal wetlands. Our results showed that tidal marshes with salinity < 15 ppt had similar soil CH4 production rates, and increasing inorganic nitrogen eutrophication might lower soil microbial carbon gas production in both tidal freshwater and mesohaline marshes.

Interfacial engineering of 0D–2D hierarchical MXene@PEI@AgNC nanohybrids to achieve flame retardant, mechanical and antibacterial properties of ABS nanocomposites

It is an intractable challenge that the hierarchical MXene-based nanohybrid fillers are intended to modify the inherent flammability and easily breeding bacteria property of ABS polymeric materials, thereby facilitating wide applicability of ABS composites. Here, an interface engineering strategy was proposed, wherein polyethyleneimine (PEI)-modified silver nanocubes (AgNCs) was firmly assembled on MXenes via electrostatic interaction to construct 0D–2D hierarchical MXene-based nanohybrids (MXene@PEI@AgNC). The MXene was protected and the interface compatibility between MXene-based nanohybrid and ABS matrix was enhanced. Results revealed that the unique hierarchical structure of the composite promoted enhanced dispersion of MXene@PEI@AgNC in the ABS matrix. Combustion tests showed that 1.0 wt%MXene@PEI@AgNC provided the ABS with effective fire safety. Moreover, ABS-1.0 wt%MXene@PEI@AgNC exhibited a 31.88 % decrease in peak heat release rate, a 39.60 % decrease in peak smoke release rate, a 41.50 % decrease in peak CO2 production rate, and a 50.04 % reduction in the smoke factor. Meanwhile, 1.0 wt%MXene@PEI@AgNC improved the tensile strength of ABS-1.0 %MXene@PEI@AgNC (+18.1 %) without reducing the elongation at break. They also enhanced the antibacterial properties of ABS-1.0 %MXene@PEI@AgNC. This study proposed a novel and feasible approach to address the interfacial stability of MXene and to construct MXene-based hierarchical nanoblends, thereby facilitating the wide practical applications of polymeric nanomaterials in industry.

Pt‐Mo₂N Catalyst Formed by Inverse Sintering for the Reverse Water‐Gas Shift Reaction

AbstractThe reverse water‐gas shift (RWGS) reaction is significant for the resource utilization of CO2. However, this reaction requires high temperatures and metal catalysts are prone to agglomeration, leading to loss of activity. In this work, a Pt catalyst supported on Mo₂N formed via phase transition and metal reverse sintering under a high‐temperature NH₃ atmosphere is developed. This catalyst exhibits excellent RWGS activity, achieving a CO production rate of 294.8 mmolgcat−1 h−1 at 623 K, with CO selectivity maintained at 93%. Moreover, under continuous testing conditions for 100 h, the catalyst's activity shows no significant decline. Notably, further investigation reveals that the surface reaction mechanism at 623 K differs from the previously reported associative mechanism, instead following a redox mechanism in the presence of H₂. This research not only provides a deeper theoretical understanding of the mechanism of CO2 hydrogenation but also offers valuable insights for developing novel and efficient metal catalyst regeneration technologies.

Covalent Organic Framework Stabilized Single CoN4Cl2 Site Boosts Photocatalytic CO2 Reduction into Tunable Syngas

AbstractSolar carbon dioxide (CO2) reduction provides an attractive alternative to producing sustainable chemicals and fuel. However, the construction of a highly active photocatalyst was challenging because of the rapid charge recombination and sluggish surface CO2 reduction. Herein, a unique Co−N4Cl2 single site was fabricated by loading Co species into the 2,2′‐bipyridine and triazine‐containing covalent organic framework (COF) for CO2 conversion into syngas under visible light irradiation. The resulting champion catalyst TPy‐COF‐Co enabled a record‐high CO production rate of 426 mmol g−1 h−1, associated with the unprecedented turnover number (TON) and turnover frequency (TOF) of 2095 and 1607 h−1, respectively. The catalyst also exhibited favorable recycling performance and widely adjustable syngas production (CO/H2 ratio: 1.8 : 1–1 : 16). A systematical investigation including operando synchrotron X‐ray absorption fine structure (XAFS) spectroscopy, in situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS), and theoretical calculation indicated that the triazine‐based COF framework promoted the charge transfer towards the single Co−N4Cl2 sites that greatly promoted the CO2 activation by lowering the energy barrier of *COOH generation, facilitating the CO2 transformation. This work highlights the great potential of the molecular regulation of COF‐derived single‐atom catalysts to boost CO2 photoreduction efficiency.

Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (AuSA), Au clusters (AuC), and a mixed-phase of AuSA and AuC (AuSA+C) on CdS. In addition, we elucidate the synergistic effect of AuSA and AuC in enhancing the photocatalytic performance of CdS substrates for simultaneous CO2 reduction and aryl alcohol oxidation. Specifically, AuSA can effectively lower the energy barrier for the CO2→*COOH conversion, while AuC can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the AuSA and AuC co-loaded CdS show impressive overall photocatalytic CO2 conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g−1 h−1, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of AuSA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.

Unleashing the synergistic potential of 2D-2D nanosheet based S-scheme heterojunction: Cooperative boosting of CO2 reduction to solar fuel and biomass valorization.

Harnessing inexhaustible solar energy for CO2 valorization is substantial step toward achieving carbon-neutral energy cycle. However, CO2 conversion often exhibits slow kinetics, necessitating the utilization of sacrificial agents making the process economically unfeasible. In the ongoing quest for sustainable and economically feasible CO2 valorization, herein the photoreduction of CO2 to CO coupled with biomass-based alcohol oxidation to fine chemicals is reported via Bi2WO6/g-C3N4 (BWO/g-CN) 2D-2D nanosheet based S-scheme heterojunction. Importantly, BWO/g-CN-60 exhibits highest photocatalytic activity with CO production rate of 6.87 mmol g-1 h-1, accompanied by >98% selectivity and selective oxidation of veratryl alcohol to veratraldehyde, with notable yield of 42% in 6 h under simulated solar light. The apparent quantum yield (AQY) of 14.3% is achieved for CO production at the wavelength of 420 nm. Additionally, the formed heterostructure results in enhanced charge separation and accelerated charge transfer kinetics as validated by PL, EIS, and photocurrent studies. EPR, 13CO2 labeling, DFT studies, and various controlled experiments provided deeper insight into the mechanism of underlying photo-redox process. Thus, the current study presents a sustainable paradigm for CO2 mitigation by converting it into solar fuel, while synergistically producing the fine chemicals through effectively harnessing the full potential of charge carriers.

Boosted Solar Thermochemical Low-Temperature CO2 Splitting On Pt/CeO2 by Interface Catalysis.

Solar thermochemical CO2 splitting using metal oxides is considered as a promising approach to produce solar fuels since it is capable to tap abundant sunlight directly and store solar energy in the renewable fuel. It remains a grand challenge to achieve highly efficient CO2 splitting at low temperature (<800 °C) due to insufficient activation of metal oxides for CO2. Herein, the introduction of a small amount of Pt was found to be able to greatly increase the performance of CO2 splitting with the highest peak CO production rate of about 65 mL min-1 g-1, CO productivity of about 53 mL g-1, nearly 100 % CO2 conversion and long-term stability for 0.5Pt/CeO2, which exceeded most of the state-of-the-art transition metals-based oxides even at lower temperature (700 °C). This could be attributed to the addition of Pt leading to the formation of an interface (Pt0-Ov-Ce3+) after CH4 reduction, which improved CO2 activation and dissociation due to beneficial breakage of C=O bond by the cooperation of Pt0 and oxygen vacancies in the interface.

Biochemical and microbial characterization of a forest litter-based bio-fertilizer produced in batch culture by fermentation under different initial oxygen concentrations.

This work focused on the physico-chemical, biochemical and microbiological characterization of a new organic fertilizer based on fermented forest litter (FFL) mixed with agro-industrial by-products, on the culture realized in airtight glass bottle. Under strict anaerobiosis (0% initial oxygen concentration (IOC)), after a 16-day batch culture, the bottle-headspace analysis showed that the specific CO2 production rate was low (0.014 mL/h.g dry matter) compared to those reached under aerobic conditions (e.g. 0.464 mL/h.g dm at 21% IOC). Moreover, the culture displayed a slight fermented fruity odour, mainly due to ethanol and ethyl acetate detected in the headspace (335 µL and 58.6 µL accumulated, respectively). The FFL organic matter degradation followed by infrared spectroscopy and catabolic potential and diversity characterized by BIOLOG® EcoPlates were poor and pH dropped to 4.54. The microbiome's metabolism was oriented toward lactic fermentation with medium acidification, enrichment in lactic acid bacteria (LAB), depletion in fungi and absence of pathogens. By increasing IOC from 0 to 21%, the respirometric activity, and the catabolic potential and diversity increased. However, some enterobacteria were detected above 5% IOC. Ethanol and ethyl acetate decreased strongly with IOC, and aromatics and proteins contained in the solid matrix remained in the culture. This study showed the importance of oxygen on the final product. A 2% IOC was found to ensure an optimal balance between LAB development, preservation of functional catabolic diversity and bio-product free of microbial pathogens.

Enhanced CO2 Reduction via S-Scheme Heterojunction of Amorphous/Crystalline Metal-free Carbon Nitride Photocatalysts

Metal-free carbon nitride nanosheets (CNs) are promising photocatalysts, but face challenges with severe charge recombination and limited visible light absorption. To overcome these challenges, we have developed a 2D/2D amorphous/crystalline carbon nitride (CNs/CCN) S-scheme heterojunction photocatalyst through electrostatic self-assembly. The built-in electric field in the CNs/CCN heterojunction facilitates an S-scheme transfer of photogenerated electrons from CCN to CNs, effectively enhancing electron-hole separation. Our optimized CNs/CCN-1/3 heterojunction exhibits substantially higher production rates of CO and CH4 compared to its individual components. Notably, CNs/CCN-1/3 maintains excellent CO2 reduction efficiency even under irradiation at wavelengths exceeding 700 nm. This study introduces an innovative strategy for the development of CNs-based photocatalysts with improved charge separation and enhanced visible-light absorption.

Insights into Photothermocatalytic Dry Reforming of Methane on Ru/La‐Al2O3 using Carbonate Species and Reactive Oxygen Species to Enhance the Fuel Production Rates and Completely Prevent Coking

AbstractPhotothermocatalytic dry reforming of methane (DRM) offers a promising strategy for converting solar energy into fuel. However, the high light intensity required for high fuel production rates and thermodynamically more favorable coking side reactions limit this strategy. Herein, a nanocomposite of La‐doped Al2O3 supporting Ru nanoparticles (NPs) (Ru/La‐Al2O3) is synthesized. At relatively low light intensity (80.2 kW m−2), Ru/La‐Al2O3 obtains high production rates of CO and H2 per gram of Ru (rRu, CO and rRu, H2, 8410.19 and 7181.94 mmol gRu−1 min−1) with light‐to‐fuel efficiency (η, 26.6%), and completely prohibits coking. In striking contrast, the reference catalyst without La doping (Ru/Al2O3) exhibits lower rRu, CO, rRu, H2, η and produces large amounts of coke. The improved photothermocatalytic performance stems from the fact that reactive oxygen species and carbonate species are involved in the oxidation of carbon species (rate‐determining steps of DRM) through two different reaction pathways, which significantly increases catalytic activity and prevents the carbon species from polymerizing into coke. Additionally, light not only enhances the DRM on Ru NPs and the oxidation reaction between carbonate species and carbon species but also promotes the dissociation of CH4 and desorption of H2, which improves the catalytic activity and product selectivity of Ru/La‐Al2O3.

Anion Effect in Electrochemical CO2 Reduction: From Spectators to Orchestrators.

The electrochemical CO2 reduction reaction (eCO2RR) offers a pathway to produce valuable chemical fuels from CO2. However, its efficiency in aqueous electrolytes is hindered by the concurrent H2 evolution reaction (HER), which takes place at similar potentials. While the influence of cations on this process has been extensively studied, the influence of anions remains largely unexplored. In this work, we study how eCO2RR selectivity and activity on a gold catalyst are affected by a wide range of inorganic and carboxylate anions. We utilize in situ differential electrochemical mass spectrometry (DEMS) for real-time product monitoring coupled with molecular dynamics (MD) simulations. We show that anions significantly impact eCO2RR kinetics and eCO2RR selectivity. MD simulations reveal a new descriptor─free energy of anion physisorption─where weakly adsorbing anions enable favorable CO2 reduction kinetics, despite the negative charge carried by the electrode surface. By leveraging these fundamental insights, we identify propionate as the most promising anion, achieving nearly 100% Faradaic efficiency while showing high CO production rates that are comparable to those in bicarbonate. These insights underscore the vital role of anion selection in achieving a highly efficient eCO2RR in aqueous electrolytes.

Functionalized LDH via intercalation of gluconate anion and surface assembly of ultrafine copper hydroxide for improving mechanical properties and the fire safety of epoxy resin

To impart epoxy resin (EP) with outstanding mechanical properties and fire safety, LDH was systematically functionalized through gluconate anion (GA) intercalation followed by surface assembly of ultrafine Cu(OH)2, resulting in the LDH-GA@Cu(OH)2 hybrid. Comprehensive characterizations confirmed the successful synthesis of the desired product, with a uniform distribution of ultrafine Cu(OH)2 nanoparticles on the GA-intercalated LDH surface. The findings revealed that LDH-GA@Cu(OH)2 improved the mechanical properties of EP due to the increased LDH layer spacing, facilitating EP chain insertion, and the hydrogen bonding between the –OH of GA and the EP matrix. Fire retardancy tests indicated that the EP composite containing 7.5 wt% LDH-GA@Cu(OH)2 achieved a limiting oxygen index (LOI) of 30.1%. Furthermore, compared to pure EP, the composite demonstrated significant reductions in the peak heat release rate (PHRR) and peak CO production rate (PCOP) by 47.4% and 60.5%, respectively, underscoring its superior flame-retardant and toxic smoke suppression capabilities. Mechanistic studies further indicated that ultrafine Cu(OH)2 enhanced char formation through catalytic charring at the interface, which promoted compact and cohesive char layers. Overall, this work proposes a promising functionalization strategy for LDH to endow EP with excellent comprehensive performance.

Synergistic effect and role of light for efficient photothermocatalytic CO2 reduction by CH4 on Pd/Co-Al1Mg3Ox

Photothermocatalytic CO2 reduction by CH4 converts greenhouse gases into valuable syngas, but limited by high light intensity and carbon deposition. Here, we designed a nanocomposite supporting low content of Pd nanoparticles on Co and Al doped MgO (Pd/Co-Al1Mg3Ox), achieving high production rates of H2 (rH2, 73.04 mmol min−1 g−1) and CO (rCO, 84.80 mmol min−1 g−1) with light-to-fuel efficiency (η, 25.3 %) at relatively low light intensity (81.1 kW m−2). Compared to Pd/Al1Mg3Ox, Pd/Co-Al1Mg3Ox demonstrates improvements of rH2, rCO and η by 6.5, 6.2 and 6.7 times respectively with great durability of 48 hours. This originates from a synergetic effect between Pd and Co-Al1Mg3Ox that the participation of active oxygen from Co-Al1Mg3Ox greatly accelerates carbon species (C*) oxidation. Interestingly, light plays unique roles on Pd/Co-Al1Mg3Ox which not only expedites C* oxidation, activates the oxygen connected to Pd and Co-Al1Mg3Ox, but also reverses rapid thermocatalytic deactivation by boosting CO desorption.

A multifunctional epoxy composites based on cellulose nanofiber/carbon nanotube aerogels: Simultaneously enhancing fire-safety, thermal conductive and photothermal performance

As 5G technology develops and electronic power density increases, preparing epoxy resin (EP) composites with excellent fire-safety, thermostability, and thermal conductivity remains challenging. Herein, hexaphenoxy cyclotriphosphazene and poly(piperazine methylphosphonic acid pentaerythritol ester) were used as synergistic flame retardants (FR) for EP. The cellulose nanofiber/carboxylated multiwalled carbon nanotubes aerogels (CCA80) were prepared and immersed into the EP and FR mixture to obtain EP/CCA80/FR composites. Compared with neat EP, the limiting oxygen index of EP/CCA80/6 wt% FR increased by 38.9 %, the total heat release and CO2 production rate decreased by 30.61 % and 39.47 %, respectively, achieving the UL-94 V-0 rating. Moreover, its thermal conductivity was 1.06 W · m−1·K−1, 457.9 % higher than neat EP, while maintaining excellent electrical insulation. Its surface temperature maintained at 94.5 °C under 1.0 kW·m−2 irradiation for 2 h, exhibiting good photothermal conversion capability and photobleaching resistance. A novel fabrication methodology of multifunctional EP composites for high-performance electronic component was proposed.

Alkyl-linked TiO2@COF heterostructure facilitating photocatalytic CO2 reduction by targeted electron transport

Targeted electron transfer to catalytically active site for CO2 reduction is promising for enhancing the efficiency of artificial photosynthesis. Here, we demonstrate a design of an alkyl-linked heterostructure composing of TiO2 and a Cu-porphyrin-based covalent organic framework (TiO2@CuPorTT-COF) for the photoreduction of CO2 with H2O. Through specific coordination effect, the alkyl chain bridges TiO2 and Cu moiety in COF. Upon light illumination, the photoinduced electrons in TiO2 can be directionally transported across the interface along the alkyl chain to the Cu active sites to reduce adsorbed CO2, while the left holes are consumed by the H2O oxidation, enhancing the spatial separation and utilization of electron-hole pairs. Accordingly, the TiO2@CuPorTT-COF enables remarkably superior catalytic activities over the counterpart without the alkyl bridge for electron transfer with 5 times of CO production rate. An apparent quantum efficiency of 0.455% at 380 nm was achieved. Moreover, a dynamic evolution of Cu active site for CO2 reduction is revealed, which can be promoted by the targeting electron transport approach. This work provides a targeted electron transport strategy for constructing photocatalysts.

Thermoeconomic modeling of new energy system based on biogas upgrading to multigenerational purpose

The following article outlines an integrated approach toward the valorization of biogas for energy, chilled water, hot water, freshwater, and liquid carbon dioxide production. The suggested system includes a biogas upgrading unit with a biomethane-fueled burner, a Kalian cycle, an LNG regasification process, and a multi-effect desalination unit that can provide CO2, electricity, cooling, and heating. The new ideas in the proposed system include a cryogenic biogas upgrading process that can be used in many industrial settings, the production of liquid carbon dioxide through biogas upgrading, and the use of biomethane in the integrated combustion process. Furthermore, the grey wolf optimization technique is applied in various multi-objective optimization contexts to achieve optimal operating conditions and preferred performance outcomes. In this simulation, the generation of electricity reaches a value of 755 kW. Attached to it is a cooling load of about 5102 kW, with a heating load of 4725 kW, freshwater capacity about 1.33 kg/s, production rate of liquid CO2 at 0.58 kg/s, and natural gas at 3.1 kg/s. Thermodynamic results reveal that the proposed multigeneration performance scheme providently enhances energy and exergy efficiencies up to 59.82 % and 5.74 %, respectively, compared to the condition of a single product. The performed exergy analysis shows that the overall irreversibility of the suggested configuration is equal to 18,047 kW while about 42.6 % of this value is contributed from the heat exchanger E-104. Moreover, the CO2 emission intensity of the process can be kept as 0.35 kg/kWh. Cryogenic separation can obtain about 88 % of CO2 in biogas and turn it into its liquid phase. The performed economic assessment has resulted in the following total cost rate as well as cost per unit exergy: 321.38 $/h and 83.06 $/GJ, respectively. Under optimal conditions, an exergy efficiency of 13.40 % and a net power output of 2034.39 kW are attained.

Bismuth-based photocatalysts enhanced by sulfur/oxygen vacancies for the selective reduction of carbon dioxide into methane

Reducing carbon dioxide (CO2) into methane (CH4) through photocatalysis technology can effectively decrease carbon emissions and ease the energy crisis. However, the low photocatalytic efficiency and high electron-hole recombination rates still hinder the large-scale utilization of photocatalysis. Vacancy engineering can reduce electron-hole pair complexation, however, the effects of oxygen (O) and sulfur (S) vacancies on the CO2 reduction properties of bismuth (Bi)-based photocatalysts are unclear. This study prepared different Bi-based photocatalysts, including α-Bi2O3, α-Bi2O3-X, Bi2S3, and Bi2S3-X. The introduction of vacancies was found to greatly increase the specific surface areas, effectively reduce electron-hole recombination, decrease charge transfer resistance, and enhance electron transfer, leading to enhanced CH4 production. Comparatively, Bi2S3-X has substantially demonstrated a superior efficiency in the photocatalytic conversion of CO2 to CH4 compared to Bi2S3, while α-Bi2O3-X exhibited slightly higher than α-Bi2O3. There are more S vacancies in Bi2S3-X (x=0.581) than O vacancies in α-Bi2O3-X (x=0.329), leading to its superior photocatalytic activity, with CO and CH4 production rates of 3.706 μmol·g−1·h−1 and 7.697 μmol·g−1·h−1, respectively. Moreover, the CH4 selectivity of Bi2S3-X reaches 67.50 %, which is 1.67 times that of α-Bi2O3-X. Therefore, Bi2S3-X holds great promise as a photocatalyst for CO2 reduction. This work proves that in Bi-based photocatalyst, S vacancy is more effective than O vacancy in enhancing the selective reduction of CO2 to CH4, offering a pathway for achieving selective CO2 reduction to CH4.