Progress and Perspectives on Promising Covalent-Organic Frameworks (COFs) Materials for Energy Storage Capacity.

In recent years, a new class of highly crystalline advanced permeable materials covalent-organic frameworks (COFs) have garnered a great deal of attention thanks to their remarkable properties, such as their large surface area, highly ordered pores and channels, and controllable crystalline structures. The lower physical stability and electrical conductivity, however, prevent them from being widely used in applications like photocatalytic activities and innovative energy storage and conversion devices. For this reason, many studies have focused on finding ways to improve upon these interesting materials while also minimizing their drawbacks. This review article begins with a brief introduction to the history and major milestones of COFs development before moving on to a comprehensive exploration of the various synthesis methods and recent successes and signposts of their potential applications in carbon dioxide (CO2 ) sequestration, supercapacitors (SCs), lithium-ion batteries (LIBs), and hydrogen production (H2 -energy). In conclusion, the difficulties and potential of future developing with highly efficient COFs ideas for photocatalytic as well as electrochemical energy storage applications are highlighted.

Uncovering the Dynamics of Urease and Carbonic Anhydrase Genes in Ureolysis, Carbon Dioxide Hydration, and Calcium Carbonate Precipitation.

The hydration of CO2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO2-fixing carbonic anhydrases (CAs) remarkably accelerate its equilibration by 6 orders of magnitude and are, therefore, "ideal" catalysts. Notably, CA has been detected in ureolytic bacteria, suggesting its potential involvement in microbially induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and CA genes remain poorly understood. Here, through the use of the ureolytic bacteriumSporosarcina pasteurii, we investigate the differing role of Ur and CA in ureolysis, CO2 hydration, and CaCO3 precipitation with increasing CO2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO3-] following the hydration of CO2 to HCO3- by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO3 mineral formed. Understanding the role of CO2 hydration on the performance of ureolysis and CaCO3 precipitation provides essential new insights, required for the development of next-generation biocatalyzed CO2 trapping technologies.

Advances in microalgae-based carbon sequestration: Current status and future perspectives.

The advancement in carbon dioxide (CO2) sequestration technology has received significant attention due to the adverse effects of CO2 on climate. The mitigation of the adverse effects of CO2 can be accomplished through its conversion into useful products or renewable fuels. In this regard, microalgae is a promising candidate due to its high photosynthesis efficiency, sustainability, and eco-friendly nature. Microalgae utilizes CO2 in the process of photosynthesis and generates biomass that can be utilized to produce various valuable products such as supplements, chemicals, cosmetics, biofuels, and other value-added products. However, at present microalgae cultivation is still restricted to producing value-added products due to high cultivation costs and lower CO2 sequestration efficiency of algal strains. Therefore, it is very crucial to develop novel techniques that can be cost-effective and enhance microalgal carbon sequestration efficiency. The main aim of the present manuscript is to explain how to optimize microalgal CO2 sequestration, integrate valuable product generation, and explore novel techniques like genetic manipulations, phytohormones, quantum dots, and AI tools to enhance the efficiency of CO2 sequestration. Additionally, this review provides an overview of the mass flow of different microalgae and their biorefinery, life cycle assessment (LCA) for achieving net-zero CO2 emissions, and the advantages, challenges, and future perspectives of current technologies. All of the reviewed approaches efficiently enhance microalgal CO2 sequestration and integrate value-added compound production, creating a green and economically profitable process.

Exploring the potential of steel slag waste for carbon sequestration through mineral carbonation: A comparative study of blast-furnace slag and ladle slag.

Steel slag is a by-product of steelmaking which has emerged as a potential CO2 sequestration material due to its high reactivity and abundance. This research investigates the use of steel slag waste for the direct capture of carbon from air and its storage through mineral carbonation. Two abundant wastes, blast-furnace slag (BFS) and ladle slag (LS), were tested for their carbon sequestration potential, and the effects of operational parameters such as reaction time between CO2 and slag waste, temperature, liquid-solid ratio, and pressure on CO2 sequestration were determined. Quantitative and qualitative results reveal that much higher CO2 sequestration was achieved using LS compared to BFS after exposure to CO2 for 1 day at room temperature. By increasing the exposure time to four days, levels of CO2 sequestration increased gradually from 2.71% to 4.19% and 23.46%-28.21% for BFS and LS respectively. Increasing the temperature from 20 ± 2 °C to 90 ± 2 °C positively influenced CO2 sequestration in BFS, resulting in an enhancement from 3.45% to 13.21%. However, the impact on LS was insignificant, with sequestration levels rising from 27.72% to 29.90%. Moreover, better CO2 sequestration was observed for BFS than LS when the liquid-to-solid ratio increased from 3:1 to 4:1, whereupon the sequestration potential reached approximately 15% for BFS and 30% for LS at 90 ± 2 °C. Meanwhile, higher pressure reduced the sequestration potential of slag. The results of this study suggest that there is potential for scaling up the process to industrial applications and contributing to the reduction of CO2 emissions in the steelmaking industry.

Charge-Assisted Hydrogen-Bonded Organic Frameworks with Inorganic Ammonium Regulated Switchable Open Polar Sites.

Surface open polar sites within the voids of porous molecular crystals define the localized physicochemical environment for critical functions such as gas separation and molecular recognition. This study presents a new charge-assisted hydrogen bonding (H-bonding) motif, by exploiting inorganic ammonium (NH4 + ) cations as H-bond donors, to regulate the assembly of C2 -symmetric carboxylic tectons for building robust H-bonded frameworks with permanent ultra-micropores and open oxygen sites. Diverse building blocks are bridged by tetrahedral NH4 + to expand distinctive H-bonded networks with varied pore architectures. Particularly, the open polar oxygen sites can be switched by altering NH4 + sources to tune the deprotonation of carboxyl-containing tectons. The activated porous PTBA·NH4 ·DMF preserves the pore architecture and open polar oxygen sites, exhibiting remarkably selective sorption of CO2 (107.8 cm3 g-1 ,195 K) over N2 (11.2 cm3 g-1 , 77 K) and H2 (1.4 cm3 g-1 , 77 K).

Microalgal upgrading of the fermentative biohydrogen produced from Bacillus coagulans via non-pretreated plant biomass.

BACKGROUND: Hydrogen is a promising source of alternative energy. Fermentative production is more feasible because of its high hydrogen generation rate, simple operating conditions, and utilization of various organic wastes as substrates. The most significant constraint for biohydrogen production is supplying it at a low cost with fewer impurities. RESULTS: Leaf biomass of Calotropis procera was used as a feedstock for a dark fermentative production of hydrogen by Bacillus coagulans AH1 (MN923076). The optimum operation conditions for biohydrogen production were 5.0% substrate concentrationand pH 9.0, at 35 °C. In which the biohydrogen yield was 3.231 mmol H2/g dry biomass without any pretreatments of the biomass. A freshwater microalga Oscillatroia sp was used for upgrading of the produced biohydrogen. It sequestrated 97 and 99% % of CO2 from the gas mixture when it was cultivated in BG11 and BG11-N media, respectively After upgrading process, the residual microalgal cells exhibited 0.21mg/mL of biomass yield,high content of chlorophyll-a (4.8 µg/mL) and carotenoid (11.1 µg/mL). In addition to Oscillatroia sp residual biomass showed a lipid yield (7.5-8.7%) on the tested media. CONCLUSION: Bacillus coagulans AH1 is a promising tool for biohydrogen production avoiding the drawbacks of biomass pretreatment. Oscillatroia sp is encouraged as a potent tool for upgrading and purification of biohydrogen. These findings led to the development of a multiproduct biorefinery with zero waste that is more economically sustainable.

Interpretation and Prediction of the CO2 Sequestration of Steel Slag by Machine Learning.

The utilization of steel slag for CO2 sequestration is an effective way to reduce carbon emissions. The reactivity of steel slag in CO2 sequestration depends mainly on material and process parameters. However, there are many puzzles in regard to practical applications due to the different evaluations of process parameters and the lack of investigation of material parameters. In this study, 318 samples were collected to investigate the interactive influence of 12 factors on the carbonation reactivity of steel slag by machine learning with SHapley Additive exPlanations (SHAP). Multilayer perceptron (MLP), random forest, and support vector regression models were built to predict the slurry-phase CO2 sequestration of steel slag. The MLP model performed well in terms of prediction ability and generalization with comprehensive interpretability. The SHAP results showed that the impact of the process parameters was greater than that of the material parameters. Interestingly, the iron ore phase of steel slag was revealed to have a positive effect on steel slag carbonation by SHAP analysis. Combined with previous literature, the carbonation mechanism of steel slag was proposed. Quantitative analysis based on SHAP indicated that steel slag had good carbonation reactivity when the mass fractions of "CaO + MgO", "SiO2 + Al2O3", "Fe2O3", and "MnO" varied from 50-55%, 10-15%, 30-35%, and <5%, respectively.

Carbonate Coprecipitation for Cd and Zn Treatment and Evaluation of Heavy Metal Stability Under Acidic Conditions.

Mining wastes or combustion ash are materials of high carbon sequestration potential but are also known for their toxicity in terms of heavy metal content. To utilize such waste materials for engineered carbon mineralization purposes, there is a need to investigate the fate and mobility of toxic metals. This is a study of the coprecipitation of metals with calcium carbonate for environmental heavy metal mitigation. The study also examines the stability of precipitated phases under environmentally relevant acid conditions. For a wide range of cadmium (Cd) and zinc (Zn) concentrations (10 to 5000 mg/L), induced coprecipitation led to greater than 99% uptake from water. The calcium carbonate phases were found to contain amounts as high as 9.9 wt % (Cd) and 17 wt % (Zn), as determined by novel synchrotron techniques, including X-ray fluorescence element mapping and three-dimensional (3D) nanotransmission X-ray microscopy (TXM). TXM imaging revealed first-of-a-kind observations of chemical gradients and internal nanoporosity within particles. These observations provided new insights into the mechanisms leading to the retention of coprecipitated heavy metals during the dissolution of calcite in acidic (pH 4) solutions. These observations highlight the feasibility of utilizing carbonate coprecipitation as an engineered approach to the durable sequestration of toxic metals.

CO2 sequestration and biodiesel production from Volvox aureus a newly isolated green microalgal species from industrial wastewater.

Recently, large-scale biofuel production is mainly dependent on third-generation feedstock, especially microalgae. Since most microalgae can sequester carbon dioxide and utilize it for the enhancement of their growth parameter. In the present study, CO2 sequestration and Biodiesel production from Volvox aureus a newly isolated green microalgal species from industrial wastewater. Volvox aureus was isolated from the wastewater sample collected from the sewage treatment plant. The isolated V.aureus was grown in the BBM culture containing excess nutrients along with Artificial CO2 supply to the bioreactor. The addition of an external carbon dioxide source enhanced the total lipid content by up to 27.95%. Further, the lipid was extracted using soxhlet extraction from the isolated microalgal biomass. The extracted lipid was converted into biodiesel using a base catalyst potassium hydroxide. The produced biodiesel was analyzed to test their fuel properties and compared with the diesel standard. This study approach investigated the potential of a future possible environmental pollution reduction and significant potential for a viable biofuel production from microalgae.

Accelerated and natural carbonation of a municipal solid waste incineration (MSWI) fly ash mixture: Basic strategies for higher carbon dioxide sequestration and reliable mass quantification.

The carbonation of alkaline wastes is an interesting research field that may offer opportunities for CO2 reduction. However, the literature is mainly devoted to studying different waste sequestration capabilities, with lame attention to the reliability of the data about CO2 reduction, or to the possibilities to increase the amount of absorbed CO2. In this work, for the first time, the limitation of some methods used in literature to quantify the amount of sequestered CO2 is presented, and the advantages of using suitable XRD strategies to evaluate the crystalline calcium carbonate phases are demonstrated. In addition, a zero-waste approach, aiming to stabilize the waste by coupling the use of by-products and the possibility to obtain CO2 sequestration, was considered. In particular, for the first time, the paper investigates the differences in natural and accelerated carbonation (NC and AC) mechanisms, occurring when municipal solid waste incineration (MSWI) fly ash is stabilized by using the bottom ash with the same origin, and other by-products. The stabilization mechanism was attributed to pozzolanic reactions with the formation of calcium silicate hydrates or calcium aluminate hydrate phases that can react with CO2 to produce calcium carbonate phases. The work shows that during the AC, crystalline calcium carbonate was quickly formed by the reaction of Ca(OH)2 and CaClOH with CO2. On the contrary, in NC, carbonation occurred due to reactions also with the amorphous Ca. The sequestration capability of this technology, involving the mixing of waste and by-products, is up to 165 gCO2/Kg MSWI FA, which is higher than the literature data.

Carbon dioxide fixation and lipid storage of Scenedesmus sp. ASK22: A sustainable approach for biofuel production and waste remediation.

In this study, an airlift reactor (ALR) has been employed to evaluate the carbon dioxide fixation rate (Rc) and lipid yield (LY) of unicellular green microalgae Scenedesmus sp. ASK22, using dairy effluent as a biofuel feedstock. Independent process parameters (PPs) such as light intensity, CO2 concentration, and aeration rate and their effect on Rc and LY were revealed. The central composite design (CCD) was used to optimize the PPs. The best-operating conditions were measured as light intensity -6.24 Klux, CO2 concentration -14.03% (v v-1), and aeration rate -1.02 liter per minute (LPM). Under these conditions, LY and Rc were found to be 4.22 gL-1 and 1.27 gL-1d-1 which were 2.24- and 1.94-fold higher than the value obtained in the control experiment (1.88 gL-1 and 0.656 gL-1d-1) at the end of 12th day. The corresponding values for bioremediation of nitrate, phosphate, as well as chemical oxygen demand (COD), remained within 98-100%. The biochemical, CHN, thermogravimetric, and fatty acid analysis of Scenedesmus sp. ASK22 biomass and lipid confirmed their potential as a clean biofuel feedstock. Furthermore, a comprehensive analysis of lipid-extracted microalgae biomass (LEMB) was carried out suggesting that LEMB could be used as a high-quality cattle and fish feed, fertilizers, and a sustainable source for biogas, bioethanol, and bio-oils. In addition to improving the developed system's efficiency, a semi-continuous regime was implemented which resulted in biomass productivity of 1.89 gL-1d-1 which was 2.6-fold higher than the batch cultivation without hampering lipid productivity (0.377 gL-1d-1). The present results suggest that Scenedesmus sp. ASK22 is a potential candidate for CO2 sequestration from atmosphere/flue gas, biofuel production (biodiesel, bioethanol, biogas, biobutanol, etc.), and waste remediation.

Carbon capture technology exploitation for vanadium tailings and assessment of CO2 sequestration potential.

In recent years, the global warming trend is still increasing due to CO2 emissions from various sources, such as electricity, heat production, industry, and transportation. In the vanadium industry, the vanadium bearing shale is of low grade, and the extraction of the required elemental vanadium produces large quantities of vanadium tailings (VTs). Both the roasting pretreatment of vanadium shale during vanadium extraction and the high-temperature calcination process for the preparation of vanadium products generate large amounts of CO2 gas. Therefore, it is particularly important to find an effective and environmentally friendly method for the treatment of vanadium tailings and CO2 generated by the vanadium industry. In this study, a potential method for the indirect carbonation of low calcium VTs under atmospheric pressure conditions was investigated. The carbonation reaction was investigated for different ammonia addition factors and different introduced CO2 concentrations and temperatures. The carbonation experiments showed that under the conditions of coefficient of ammonia addition of 1.4, reaction time of 60 min and reaction temperature of 60 °C, the utilization rate of calcium in VTs reached 97.9% and the CO2 uptake of VTs at 0.073 g-CO2/g, indicating that the carbonation of vanadium with low-calcium VTs was effective. The carbonation product was analyzed and measured using TG, XRD, and SEM-EDS, and it was discovered to be CaCO3, confirming the feasibility of carbonation reaction with vanadium tailings. Furthermore, the characterization of the carbonation product confirmed the mechanism and safety of the carbonation reaction, laying the groundwork for future applications.

Converting industrial waste into a value-added cement material through ambient pressure carbonation.

Converting industrial wastes into value-added building products in an environmental management strategy is a challenging yet vital component of the industrial process. Steel slag (SS), an industrial waste by-product from the steel-making process, is typically disposed of in landfill which consumes land resources and pollutes the environment. This paper explores the possibility of a closed-loop system to convert steel slag into a cement material through carbonation activation, thereby significantly reducing the amount of steel slag waste sent to landfills across Canada. The production of this cementing material can occur next to the steel mill, utilizing steel slag and carbon dioxide collected on-site to fabricate carbon-negative products. To save energy and allow production to be feasible on an industrial scale, ambient pressure (AP) carbonation is developed to reduce carbon emissions while improving their performance. High pressure (HP) carbonation curing and normal hydration (NH) references were also implemented at the same time to justify the application of AP carbonation in reducing CO2 emission. The results of this study found AP carbonation-activated SS compacts have comparable CO2 uptake (about 7.5 tons CO2/100 tons slag) and mechanically compressive strength values as those subjected to HP carbonation, suggesting that AP could be used to replace HP in carbonation curing to ensure a lower energy input. Additionally, AP seemed to possess as effective carbonation as HP. The studies investigated by multiple techniques including X-ray diffractometer (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopic analysis, and scanning electron microscopy (SEM) aim to identify the microstructure development of carbonated SS paste to assess carbonation results. Developed with life cycle assessment (LCA), environmental impact evaluation shows that AP presents a smaller global warming potential (GWP) value than HP. The comparable CO2 sequestration, satisfactory engineering properties, enhanced microstructure and lesser environmental impact in AP carbonation confirm the feasibility of replacing high pressure with extremely low pressure to cure concrete products. The use of AP carbonation for cement material created using steel slag reduces carbon emissions, energy usage, and natural resource consumption.

Development of a bench-scale photobioreactor with a novel recirculation system for continuous cultivation of microalgae.

Microalgae cultivation can be used to increase the sustainability of carbon emitting processes, converting the CO2 from exhaust gases into fuels, food and chemicals. Many of the carbon emitting industries operate in a continuous manner, for periods that can span days or months, resulting in a continuous stream of gas emissions. Biogenic CO2 from industrial microbiological processes is one example, since in many cases it becomes unsustainable to stop these processes on a daily or weekly basis. To correctly sequester these emissions, microalgae systems must be operated under continuous constant conditions, requiring photobioreactors (PBRs) that can act as chemostats for long periods of time. However, in order to optimize culture parameters or study metabolic responses, bench-scale setups are necessary. Currently there is a lack of studies and design alternatives using chemostat, since most works focus on batch assays or semi-continuous cultures. Therefore, this work focused on the development of a continuous bench-scale PBR, which combines a retention vessel, a photocollector and a degasser, with an innovative recirculation system, that allows it to operate as an autotrophic chemostat, to study carbon sequestration from a biogenic CO2-rich constant air stream. To assess its applicability, the PBR was used to cultivate the green microalga Haematococcus pluvialis using as sole carbon source the CO2 produced by a coupled heterotrophic bacterial chemostat. An air stream containing ≈0.35 vol% of CO2, was fed to the system, and it was evaluated in terms of stability, carbon fixation and biomass productivity, for dilution rates ranging from 0.1 to 0.5 d-1. The PBR was able to operate under chemostat conditions for more than 100 days, producing a stable culture that generated proportional responses to the stimuli it was subjected to, attaining a maximum biomass productivity of 183 mg/L/d with a carbon fixation efficiency of ≈39% at 0.3 d-1. These results reinforce the effectiveness of the developed PBR system, making it suitable for laboratory-scale studies of continuous photoautotrophic microalgae cultivation.

Enhanced sequestration of CO2 from simulated electrolytic aluminum flue gas by modified red mud.

The aluminum industry is facing severe economic and environmental problems due to increasing carbon emissions and growing stockpiles of red mud (RM). RM is a strongly alkaline, high-emission solid waste from the alumina industry with potential for CO2 sequestration. However, the effectiveness of RM carbon sequestration is poor, and the mechanism behind it is not well understood. In this study, the effect of microwave and tube furnace activation of RM on CO2 sequestration in alumina was first investigated at different temperatures. The result showed that the CO2 sequestration capacity of unmodified RM (URM) was only 14.35 mg/g at ambient temperature and pressure, and the CO2 sequestration capacity could be increased to 52.89 mg/g after high-temperature activation and modification. Besides, high-temperature activation and modification will effectively improve the carbon sequestration capacity of RM. The carbonized RM was characterized by FT-IR, SEM, XRD, laser particle size, TG-DSC, and pH measurements. In addition, the mechanism of RM capturing CO2 was also proposed, which shows that CO2 was finally sequestered in the RM as CaCO3. The change in particle size distribution and the mineral phase in the RM indicated that high-temperature activation modification positively affects the application of RM to the sequestration of CO2. This study can provide a promising technology for the low-carbon and green development of the aluminum industry, as well as achieving the waste treatment and utilization objective.

Inclusive greenhouse gas budget assessment in turfs: From turf production to disposal of grass clippings.

Globally, greenhouse gas (GHG) reduction is a serious concern. To evaluate whether turfs serve as a GHG sink or source, GHG budget assessments for life cycle are required. However, previous studies have only focused on the use of turfs. To bridge these gaps in literature, this study investigated GHG (CO2, N2O, and CH4) emissions from the disposal of grass clippings and soil GHG fluxes in turfs. Additionally, GHG budgets in the turf production phase were assessed. Finally, inclusive GHG budgets from turf production to disposal of grass clippings for four turf uses (soccer stadium, golf course, office, and urban park) were assessed. Grass clippings were disposed in three forms (incineration, leaving as-is, and biochar). We found that GHG emissions from incineration and leaving 1 t-fresh weight (FW) of grass clippings were 0.711 and 0.207 t-CO2e, respectively. Contrastingly, the GHG emissions from the biochar yield from 1 t-FW of grass clippings were -0.200 t-CO2e. Further, annual soil GHG fluxes in newly established Zoysia and Kentucky bluegrass turfs were calculated at 0.067 and 0.040 tCO2eï½¥ha-1ï½¥yr-1, respectively. As the turf grass in production fields sequester large amounts of CO2, GHG budgets in turf production phase were estimated at approximately -20 t-CO2eï½¥ha-1ï½¥yr-1. Inclusive GHG budget assessment from turf production to disposal of grass clippings showed that turfs only in the urban parks served as a GHG sink and this ability was comparable to CO2 sequestration in forests. To enhance the ability of GHG sinks and to promote changes from a GHG source to GHG sink, our study revealed the importance of reduction of GHG emissions from energy and resource uses (especially fertilizers and gasoline) for turf management.

A Highly Compatible Phototrophic Community for Carbon-Negative Biosynthesis.

CO2 sequestration engineering is promising for carbon-negative biosynthesis, and artificial communities can solve more complex problems than monocultures. However, obtaining an ideal photosynthetic community is still a great challenge. Herein, we describe the development of a highly compatible photosynthetic community (HCPC) by integrating a sucrose-producing CO2 sequestration module and a super-coupled module. The cyanobacteria CO2 sequestration module was obtained using stepwise metabolic engineering and then coupled with the efficient sucrose utilization module Vibrio natriegens. Integrated omics analysis indicated that enhanced photosynthetic electron transport and extracellular vesicles promote intercellular communication. Additionally, the HCPC was used to channel CO2 into valuable chemicals, enabling the overall release of -22.27 to -606.59 kgCO2 e kg-1 in the end products. This novel light-driven community could facilitate circular economic implementation in the future.

Engineering Photosynthetic Microbial Consortia for Carbon-Negative Biosynthesis.

Microbial consortia consisting of phototrophs and heterotrophs have raised extensive attention due to their potential in sustainable biotechnology. The challenge remains in the selection of appropriate partners since most heterotrophic microorganisms cannot naturally use the intermediate carbohydrates secreted by autotrophic partners. In a recent study, the Ni Lab has developed a highly compatible autotrophic-heterotrophic symbiotic system comprising Synechococcus elongatus and Vibrio natriegens. V. natriegens (the sucrose utilization module) shows a high degree of nutritional complementarity and culturing compatibility with the engineered S. elongatus (the CO2 sequestration module). The combination of both species channels CO2 into various valuable chemicals, enabling carbon-negative biosynthesis.

Bioelectrocatalytic CO2 Reduction by Mo-Dependent Formylmethanofuran Dehydrogenase.

Massive efforts are invested in developing innovative CO2 -sequestration strategies to counter climate change and transform CO2 into higher-value products. CO2 -capture by reduction is a chemical challenge, and attention is turned toward biological systems that selectively and efficiently catalyse this reaction under mild conditions and in aqueous solvents. While a few reports have evaluated the effectiveness of isolated bacterial formate dehydrogenases as catalysts for the reversible electrochemical reduction of CO2 , it is imperative to explore other enzymes among the natural reservoir of potential models that might exhibit higher turnover rates or preferential directionality for the reductive reaction. Here, we present electroenzymatic catalysis of formylmethanofuran dehydrogenase, a CO2 -reducing-and-fixing biomachinery isolated from a thermophilic methanogen, which was deposited on a graphite rod electrode to enable direct electron transfer for electroenzymatic CO2 reduction. The gas is reduced with a high Faradaic efficiency (109±1 %), where a low affinity for formate prevents its electrochemical reoxidation and favours formate accumulation. These properties make the enzyme an excellent tool for electroenzymatic CO2 -fixation and inspiration for protein engineering that would be beneficial for biotechnological purposes to convert the greenhouse gas into stable formate that can subsequently be safely stored, transported, and used for power generation without energy loss.

Microbial CO2 fixation and biotechnology in reducing industrial CO2 emissions.

The rapid acceleration in emissions of inevitably generated CO2 due to numerous activities mainly anthropogenic have devastating environmental effects leading to climatic concerns. Hence, significant, sustainable approaches should be developed for reduction of CO2 emission targets, balancing the existing needs of the current population. Biological carbon acquisition, storage and usage are considered crucial alternative strategies in assimilating inorganic carbon, manifested by diverse variety of microorganisms. Furthermore, central biochemical routes along with associated enzymes serve as considerable factors for understanding molecular microbial CO2 assimilation. Microorganisms exhibit an impeccable capability to facilitate evolved mechanisms in sequestering inorganic carbon at higher pace to produce biomaterials like biofuels, bioplastics etc. This review endorses the importance of microorganisms in reducing the concomitant release of CO2 by providing supervision in biotechnological applications (such as genetic engineering, microbial electrosynthesis, gas fermentation and protein engineering) to mitigate CO2 at an industrial scale.