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• Aerogels can be easily fabricated via cross-linking vermiculite and MXene. • The pore structures and surface compositions of aerogels can be finely tuned. • Monolithic aerogel has excellent CO 2 storing capacity by boosted hydrate formation. • Degree of water saturation plays the most vital role in hydrate formation. Gas hydrate provides an ideal way for CO 2 capture and storage using water by forming cages via an environment-friendly and energy-efficient hydrate formation process. However, the practical utilization and upscaling of hydrate-based gas storage are impeded by the slow formation kinetics of gas hydrate due to the limited multiphase interface for mass transfer and reaction. Herein, we demonstrated a simple strategy to fabricate composite aerogels assembled of natural vermiculite and MXene nanosheets as the ideal substrate for boosting CO 2 hydrate formation. The structure and surface compositions of vermiculite/MXene composite aerogels were analyzed by XRD, FT-IR, SEM, and XPS. It shows that monolithic pore structures and surface functional groups can be finely tuned by controlling the mass ratio of vermiculite and MXene, leading to an outstanding CO 2 storage capacity of 136.9 v/v (corresponding to 0.121 mol CO 2 /mol water) with enhanced hydrate formation kinetics. The degree of water saturation plays the most vital role in controlling formation kinetics and gas storage capacity. This work provides a reliable method to synthesize aerogels for boosting CO 2 storage via enhanced hydrate formation and sheds light on the structure performance relationship of porous materials for enhancing gas hydrate formation. [ABSTRACT FROM AUTHOR]

• Aerogels with tunable surface properties significantly promoted hydrate formation. • C O and –OH were found to dominate nucleation and growth of hydrate. • The finely tuned oxygen-containing groups lead to the enhanced kinetics. • Aerogels exhibit high storage capacity and excellent cycling stability. • Aerogels can be prepared in a large scale for hydrate-based applications. Gas hydrate, composed of water molecule cages, is promising for safe and sustainable gas storage with minor energy consumption. However, the practical utilization of hydrate-based technologies is hindered by the sluggish formation kinetics of gas hydrate. Central to the challenge of utilizing hydrate-based gas storage is developing effective promoters and improving the understanding of the complicated interplay between a promoter's structure and chemical composition. Herein, we reported a simple and scalable strategy to produce pyrolytic composite aerogels assembled from vermiculite nanosheets and sodium alginate as efficient promoters for the methane hydrate formation. Benefiting from the high specific surface area and finely tuned surface functional groups, the as-made aerogels significantly improve methane hydrate formation kinetics with high storage capacity and excellent cycling stability. It is found that the phase change process of water to methane hydrate conversion can be controlled by adjusting the content of carbonyl and hydroxyl groups of the as-made aerogels. Raman spectra were used to elucidate the molecular mechanisms for the enhanced methane hydrate formation due to the interaction between oxygen-containing surface functional groups and water molecules close to used aerogels. This work not only provides an effective way to fabricate aerogel-based promoters for methane hydrate formation but also sheds light on the underlying mechanism of the surface composition dependent performance for improving gas hydrate formation. [ABSTRACT FROM AUTHOR]

• CBCMs significantly improved the hydrate formation kinetics and storage capacity. • Carbonyl groups was identified as the active sites enhancing CH 4 hydrate formation. • Functional groups tuned hydrogen-bonding network results in the enhanced kinetics. The sluggish formation kinetics is a formidable challenge for the practical application of gas hydrate-based technologies for natural gas storage and transportation. Methane hydrates in both nature and labs exclusively form with the assistant of foreign additives via a heterogeneous process. Although the process is common and widely used, it remains unclear what makes a material a good methane hydrate promoter. Additionally, the molecular mechanisms underlying the promoted hydrate formation remain largely unknown. Herein, carbon monoliths (labeled as CBCM) with finely controlled surface functional groups were produced using cellulose as precursors. The oxygen-containing groups have been identified as the active sites enhancing the nucleating ability of methane hydrates. Carbonyl oxygen is pinned down as the most effective functional group in reducing the induction time and enhancing the formation kinetics of methane hydrate. The turned hydrogen bonds between water molecules, which are close to the surface of CBCM, contribute to the enhanced formation kinetics as confirmed by the Raman spectroscopy. The CBCM with optimized carbonyl oxygen significantly improve the methane hydrate formation kinetics and storage capacity with outstanding cycle stability, which are superior than most of the previously reported promoters, particularly in shorter induction time. The finding in this work paves the way for effectively designing promoters and unraveling the underlying mechanism for enhancing gas hydrate formation. [ABSTRACT FROM AUTHOR]

With the rapid development of agriculture, controlling phosphorus emissions is a pressing challenge for preventing water eutrophication. A graphite-promoted cyclopentane (CP) hydrate-based desalination was proposed to remove K 3 PO 4 from effluents. It was found via the in situ optical microscopy that the reaction temperature and the concentration of feeding K 3 PO 4 solution significantly affect the morphologies and amount of the as-produced CP hydrate crystals. The lower reaction temperature produces more crystals with irregular shapes, while fewer crystals formed in K 3 PO 4 solution with higher concentration. The reaction temperature, time and feeding concentration-dependent desalination and salt enrichment performances were studied. It was found that desalination efficiency linearly increases with the elevated reaction temperature ranging from − 2 °C to 3 °C; however, water recovery declines with temperature. The temperature-dependent water recovery is due to the strong driving force for hydrate formation at low temperatures. The time-dependent water recovery shows a three-stage feature, including exponential growth, linear increase, and stable stages, owing to the interaction between the driving force of supercooling and the increasing K 3 PO 4 concentration during the reaction processes. The desalination efficiency shows an inverted volcanic shape with the increased concentration of feeding K 3 PO 4 solution. The pre-melting effect plays a critical role in improving desalination efficiency at high K 3 PO 4 concentrations. A maximum desalination efficiency of 85.0% was reached for treating an artificial solution with salinity as high as 42452 mg/L. Both desalted water and concentrated phosphorus-containing solution can be recovered by this method, which is attractive for producing freshwater with potential for recovery of resources. [Display omitted] • A method using cyclopentane hydrate formation was proposed to extract freshwater and enrich K 3 PO 4. • An impressive water recovery over 50% can be obtained in 2 h. • This method can treat an artificial solution with salinity as high as 42452 mg/L. [ABSTRACT FROM AUTHOR]

Gas hydrate-based CO 2 storage, using only water cages, provides an environmentally friendly and energy-efficient solution to reduce greenhouse gas emissions. However, the sluggish formation kinetics of gas hydrate is hindered by the limited reaction interfaces, thereby impeding the practical utilization of hydrate-based greenhouse gas storage. Herein, we reported a novel strategy to fabricate natural vermiculite and tannic acid composite aerogels as the effective substrates for boosting CO 2 hydrate formation. The results show that the formation kinetics of CO 2 hydrate in the aerogels exhibits composition dependence and an outstanding CO 2 storage capacity of 130.1 v/v (corresponding to 0.114 mol CO 2 /mol water). Inverse gas chromatography was used to analyze the surface energy and its components of the aerogels. Raman spectra and nuclear magnetic resonance were used to unravel the water molecule assembly and states. The CO 2 uptake capacity can be further improved by compressing the aerogel to 75 % of the original volume, showing an impressive storage capacity of 146.8 v/v. The as-made aerogels demonstrated outstanding cycle stability and short induction time for CO 2 hydrate formation. The results of this study pave the way for designing effective CO 2 hydrate promoters and facilitating promising CO 2 capture and storage technologies via gas hydrate. [Display omitted] • Monolithic aerogel can be easily fabricated by cross-linking vermiculite nanosheets. • The surface compositions and pore structures of aerogels can be finely tuned. • Aerogels have excellent CO 2 storing capacity by boosting hydrate formation. • Hydrogen bond arrangement plays the most vital role in hydrate formation. [ABSTRACT FROM AUTHOR]

Natural gas hydrates are a potential future energy modality with the advantages of clean burning and large resource reserves and have attracted worldwide attention. Natural gas hydrates formation and dissociation impact the skeletal structure and mechanical properties of porous media sediments. In addition, there is a synergistic effect between the migration of fine clay particles in porous media and hydrate behavior. In this study, methane hydrate was examined in-situ using a low-field nuclear magnetic resonance system in the presence of two suspensions of clay particles with different stability. The results showed that clay particles impacted methane hydrate formation and dissociation and the pore structure of porous media. Hydrate nucleated preferentially in large pores, causing them to split into smaller pores; the presence of clay particles, especially illite, improved the water conversion rate. The results indicated that water content in large pores increased after hydrate dissociation but was discontinuous among different pores. When illite was present, the distribution was more continuous; when montmorillonite was present, the water distribution of the large pores was similar to that of the original state. This work increases our understanding of the kinetics, water migration, and pore structure alteration of methane hydrate formation and dissociation in sediments with clay particles and provides support for the safe and efficient development of natural gas hydrates. • Clay particles impacted methane hydrate formation and dissociation • Hydrate nucleated preferentially in large pores • Clay particles, especially illite, improved the water conversion rate • Water content in large pores increased after hydrate dissociation but was discontinuous among different pores [ABSTRACT FROM AUTHOR]

Abstract Desalination via hydrate processes is promising in producing freshwater at low energy cost. However, it is a great challenge to instantaneously produce and form large amount of hydrates in short time, particularly with salts presence. In this study, we used cheap and easily separated graphite particles to promote hydrate based desalination. The added graphite can promote the formation of hydrate, greatly shortening the induction time. The desalination efficiency was also enhanced due to the introduced graphite. Combined graphite and stirring, both the desalination efficiency and water conversion ratio were boosted. The impact of particle sizes of graphite on hydrate formation was found to be different at static state and stirring. The proposed hydrate based desalination is almost independent on treated volume. Additionally, this method can use the nature chilling, which is potential in further reducing the energy cost of desalination via hydrate. The findings in this study would help rationally choose and design promoting agents and hydrate processes for facilitating hydrate formation and desalination via hydrates. Highlights • Introduction of graphite boosted the hydrate formation rate. • Graphite increased desalination efficiency and water conversion ratio. • The particle size of graphite played critical roles in enhancing desalination via hydrate process. [ABSTRACT FROM AUTHOR]