Tailoring morphological and chemical properties of covalent triazine frameworks for dual CO2 and H2 adsorption

The development of functional porous samples suitable as gas-adsorption materials is a key challenge of modern materials chemistry to face with global warming or issues related to renewable energy-storage solutions. Herein, a set of five Covalent Triazine Frameworks (CTFs) featured by high specific surface area (SSA, up to 3201 m² g^?1) and N content as high as 12.2 wt% have been prepared through a rational synthetic strategy and exploited with respect to their gas uptake properties. Among CTFs from this series, CTF-pDCB/DCI^HT (4) combines ideal morphological and chemico-physical properties for CO₂ and H₂ adsorption. Noteworthy, besides ranking among CTFs with the highest CO₂ adsorption capacity reported so far (up to 5.38 mmol g^?1 at 273 K and 1 bar), 4 displays a H₂ excess uptake at 77 K of 2.84 and 5.0 wt% at 1 and 20 bar, respectively, outperforming all CTF materials and 2D Porous Organic Polymers of the state-of-the-art.     

The comparison of two activation techniques to prepare activated carbon from corn cob

We report on the preparation of biomass-based activated carbons by the steam physical activation and KOH chemical activation methods. In addition, we also investigate their adsorption performance. By adjusting the reaction parameters, different carbon materials are prepared from corn residues and characterized using instrumental analyses such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer–Emmett–Teller (BET). It is found that the synthesized activated carbons exhibit high surface area (1600 m² g⁻¹) and large pore volume (2.01 cm³ g⁻¹). Furthermore, the high methylene blue and iodine adsorption value and a considerable CO₂ uptake (exceeding 1.5 mmol g⁻¹) are attained with the activated carbons, showing their potential usage for the CO₂ adsorbent.     

Melamine assisted preparation of nitrogen doped activated carbon from sustainable biomass for H2 and CO2 storage

Activated carbon (AC), as an effective solid adsorbent, is extensively employed in H₂ and CO₂ storage. To enhance its adsorption capability and selectivity, it is necessary to increase its surface area and dope heteroatoms by a simple and environment-friendly method. In this work, nitrogen doped activated carbon (NAC) has been synthesized from sustainable biomass by direct activation with the assistance of melamine. The obtained NAC with 2.1 wt% N dopants possesses a high surface area (2477.27 m²/g) and pore volume (1.93 cm³/g). The NAC displayed enhanced H₂ uptake capacity (2.29 wt% at 77 K, 1 bar and 0.83 wt% at 298 K, 100 bar) and adequate CO₂ uptake capacity (2.85 mmol/g at 298 K, 1 bar and 4.49 mmol/g at 273 K, 1 bar). Activation mechanism with the assistance of melamine was proposed in accordance with the experimental data. The facile method of preparing NAC is potential for large-scaled production.     

Sodium alginate assisted preparation of oxygen-doped microporous carbons with enhanced electrochemical energy storage and hydrogen uptake

Microporous carbons with large oxygen content have been successful synthesized from biomass by the sodium alginate assisted strategy. During the activation process, the Na₂O formed by the decomposition of sodium alginate combines with the activator KOH to undergo a redox reaction in situ with precursor, thereby forming a rich porosity in the samples. The obtained samples possess not only high SSA (2310~3001 m² g^?1) and large pore volume (0.89~1.19 cm³ g^?1) arising almost completely (>90%) from micropores, but also retains a high content of oxygen (21.86~32.47 wt %). As supercapacitor electrodes, the oxygen-doped microporous carbons display a high specific capacitance of 385 F g^?1 at 0.5 A g^?1 with capacity stability of 91.5% after 20 000 cycles at 5 A g^?1. As hydrogen storage materials, the oxygen-doped microporous carbons exhibit enhanced hydrogen storage capacity of 2.84 wt% (77 K, 1 bar) and 0.91 wt% (303 K, 50 bar). Experimental data indicate that this work provides a simple-efficient and universal strategy for preparing oxygen-doped microporous carbon for high-performance energy and hydrogen storage.     

Lignin‐derived heteroatom‐doped porous carbons for supercapacitor and CO2 capture applications

The present study reports the economic and sustainable syntheses of functional porous carbons for supercapacitor and CO₂ capture applications. Lignin, a byproduct of pulp and paper industry, was successfully converted into a series of heteroatom‐doped porous carbons (LHPCs) through a hydrothermal carbonization followed by a chemical activating treatment. The prepared carbons include in the range of 2.5 to 5.6 wt% nitrogen and 54 wt% oxygen in its structure. All the prepared carbons exhibit micro‐ and mesoporous structures with a high surface area in the range of 1788 to 2957 m² g^?1. As‐prepared LHPCs as an active electrode material and CO₂ adsorbents were investigated for supercapacitor and CO₂ capture applications. Lignin‐derived heteroatom‐doped porous carbon 850 shows an outstanding gravimetric specific capacitance of 372 F g^?1 and excellent cyclic stability over 30,000 cycles in 1 M KOH. Lignin‐derived heteroatom‐doped porous carbon 700 displays a remarkable CO₂ capture capacity of up to 4.8 mmol g^?1 (1 bar and 298 K). This study illustrates the effective transformation of a sustainable waste product into a highly functional carbon material for energy storage and CO₂ separation applications.     

Enhanced methane storage of chemically and physically activated carbide-derived carbon

Carbide-derived carbons (CDCs) produced by chlorination of carbides offer great potential for precise pore size control at the atomic level, making them attractive candidates for energy storage media. CDCs activated with CO₂ or KOH possess distinct improvements in porosity, displaying specific surface areas above 3000 m² g⁻¹ and pore volumes above 1.3 cm³ g⁻¹. These correspond to gravimetric methane uptake of 16 wt% at 35 bar and 25 °C, close to the currently best reported material PCN-14, a metal-organic framework (MOF), at 35 bar and 17 °C or KOH activated anthracite at 35 bar and 25 °C. The best excess gravimetric methane uptake is obtained with a TiC-derived CDC activated with CO₂ at 975 °C for 2 h, namely a very large surface area of 3360 m² g⁻¹ resulting in 18.5 wt% at 25 °C and 60 bar. To obtain realistic volumetric methane capacity, the packing density of completely dried CDC was measured, from which we obtain excess capacity of 145 v(STP) v⁻¹ from CDC activated with CO₂ at 875 °C for 8 h, 81% of the DOE target (180 v(STP) v⁻¹) at 35 bar and 25 °C. From small-angle X-ray scattering (SAXS) measurements, pore radii of gyration (R_g) between 0.5 nm and 1 nm are determined. Temperature-dependent methane isotherms show that the isosteric heat of adsorption reaches 24 kJ mol⁻¹ at the initial stage of low loading.     

Adsorption and compression contributions to hydrogen storage in activated anthracites

We prepared activated carbons (ACs) that are among the best adsorbents for hydrogen storage. These ACs were prepared from anthracites and have surface areas (S_BET) as high as 2772 m² g⁻¹. Anthracites activated with KOH presented the highest adsorption capacities with a maximum of 5.3 wt.% at 77 K and 4 MPa. Non-linearity between hydrogen uptake at 77 K and pore texture was confirmed, as soon as their S_BET exceeded the theoretical limiting value of (geometrical) surface area, i.e., S_BET > 2630 m² g⁻¹. We separated adsorption and compression contributions to total hydrogen storage. The amount of hydrogen stored is significantly increased by adsorption only at moderate pressure: 3 MPa and 0.15 MPa at 298 and 77 K, respectively. Hydrogen adsorption on ACs at high pressure, above 30 MPa at 298 K and 8 MPa at 77 K, has not interest because more gas can be stored by simply compression in the same tank volume.     

H2S removal from biogas for fuelling MCFCs: New adsorbing materials

Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na₂CO₃ solutions were studied as H₂S sorbents for biogas purification for fuelling molten carbonate fuel cells. H₂S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H₂S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h⁻¹) of 8 ppm H₂S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H₂S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H₂S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na₂CO₃ solutions improved the H₂S adsorption properties: AC treated with Na₂CO₃ was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC.     

Enhanced hydrogen generation using ZrO2-modified coupled ZnO/TiO2 nanocomposites in the absence of noble metal co-catalyst

Mesoporous ZrO₂-modified coupled ZnO/TiO₂ nanocomposites were prepared by a surfactant assisted sol–gel method. The photocatalytic performance of these materials was investigated for H₂ evolution without noble metal co-catalyst using aqueous methanol media under AM1.5 simulated light. The H₂ evolution was compared with coupled ZnO/TiO₂, TiO₂, ZnO and Degussa P25. The ZrO₂-modified nanocomposites exhibited higher H₂ generation, specifically 0.5 wt.% ZrO₂ loading produced 30.78 mmol H₂ g⁻¹ compared to 3.55 mmol H₂ g⁻¹ obtained with coupled ZnO/TiO₂. A multiple absorbance thresholds at 435 nm and 417 nm were observed with 0.5 wt.% ZrO₂ loading, corresponding to 2.85 eV and 2.97 eV band gap energies. The high surface area, large pore volume, uniform crystallite sizes and enhanced light harvesting observed in ZrO₂-modified nanocomposites were contributing factors for effective charge separation and higher H₂ production. The possible mechanism of H₂ generation from aqueous methanol solution over ZrO₂-modified nanocomposite is presented.     

Posidonia Oceanica and Wood chips activated carbon as interesting materials for hydrogen storage

The goal is to investigate the feasibility to use a local biomass (Posidonia Oceanica and Wood chips), as a raw precursor, to the production of activated carbons (AC) with a high surface area and remarkable hydrogen (H₂) adsorption properties.Biomasses (particle size of 0.3–0.4 mm) were pyrolyzed at 600 °C with a heating rate of 5 °C/min under an argon atmosphere. The biochar obtained from the carbonization step was chemically activated with KOH. The activation methodology induces a considerable improvement of the properties of the porous carbon in terms of carbon content (from 58 to 69 wt% to 93–96 wt%), surface area (from 41 to 425 m²/g to 2810–2835 m²/g) and H₂ adsorption in cryogenic condition (from 0,1 wt% to over 5 wt%).All porous carbons were characterized in terms of elemental analysis (CHNS–O), textural properties and H₂ adsorption measurements.     

Melaleuca bark based porous carbons for hydrogen storage

Typical porous carbons were obtained from waster biomass, melaleuca bark activated by potassium hydroxide (KOH), and characterized by XRD, SEM, TEM, FTIR, XPS and N₂-sorption. The different samples with tunable morphologies and texture were prepared by controlling synthesis reaction parameters. The resulting samples demonstrate both high surface area (up to 3170 m² g⁻¹) and large hydrogen storage capacity (4.08 wt% at 77 K and 10 bar), implying their great potential as hydrogen storage materials.     

Different ratios of carbon sources in the fermentation of cheese whey and glucose as substrates for hydrogen and ethanol production in continuous reactors

The fermentation of glucose, cheese whey and the mixture of glucose and cheese whey were evaluated in this study from two inocula sources (sludge from a UASB reactor for swine wastewater treatment and poultry slaughterhouse) for hydrogen production in continuous anaerobic fluidized bed reactors (AFBR). For all fermentations, a hydraulic retention time (HRT) of 6 h and a substrate concentration of 5 g COD L⁻¹ were used. In glucose fermentation, the maximum hydrogen yield (HY) was 1.37 mmol H₂ g⁻¹ COD. The co-fermentation of the cheese whey and glucose mixture was favorable for the concomitant production of hydrogen and ethanol, with yields of up to 1.7 mmol H₂ g⁻¹ COD and 3.45 mol EtOH g⁻¹ COD in AFBR2. The utilization of cheese whey as a sole substrate resulted in an HY of 1.9 mmol H₂ g⁻¹ COD. Throughout the study, ethanol fermentation was evident.     

Large impact of heating time on physical properties and photocatalytic H2 production of g-C3N4 nanosheets synthesized through urea polymerization in Ar atmosphere

The effect of heating time on the polymerization processes of urea into g-C₃N₄ nanosheets was studied in Ar atmosphere. It was found that heating time had a great influence on the crystalline quality, specific surface area (S_BET) and photocatalytic H₂ production of the obtained g-C₃N₄ nanosheets. G-C₃N₄ nanosheets with some degree of disorders in crystal structure were formed within 1 h at 550 °C, and these structural disorders maintained after 4 h, however disorders disappeared after extended heating of 6 h. G-C₃N₄ nanosheets with similar disorders in the crystal structure hold similar S_BET and exhibit comparable H₂ production rates. The highest H₂ production rate of 1.4 mmol h⁻¹ g⁻¹ occurs after 8 h heating, corresponding to 2.6% quantum efficiency at 420 nm.     

The effects of seed sludge and hydraulic retention time on the production of hydrogen from a cassava processing wastewater and glucose mixture in an anaerobic fluidized bed reactor

The potential for co-fermentation of a cassava processing wastewater and glucose mixture was studied in anaerobic fluidized bed reactors. The effects of different hydraulic retention times (HRTs) (10–2 h) and varying sources of inoculum are reported. The sludge from a UASB reactor that had been used to treat poultry slaughterhouse wastewater (SP) resulted in the highest yields of hydrogen (HY) and ethanol (EtOHY) of 1.0 mmol H₂ g⁻¹ COD (10 h) and 3.0 mmol EtOH g⁻¹ COD (6 h). The sludge from a UASB reactor used for the treatment of swine wastewater (SW) resulted in a maximum HY of 0.65 mmol H₂ g⁻¹ COD (6 h) and EtOHY of 2.1 mmol g⁻¹ COD (10 and 8 h). Methane was produced with a maximum production of 9.68 L CH₄ d⁻¹ L⁻¹. Based on phylogenetic analysis of 16S rRNA, bacteria and methanogenic archaea similar to Lactobacillus and Methanobacterium, respectively, were identified.     

Impregnated carbon–ionic liquid as innovative adsorbent for H2/CO2 separation from biohydrogen

Currently, purification is a considerably important technology for biohydrogen (bioH₂) production as a renewable energy resource. Adsorption methods are promising techniques for separation of CO₂ from the H₂/CO₂ mixture of bioH₂. In this study, the adsorbent is synthesized by impregnating activated carbon (AC) with ionic liquid (IL). The ILs were prepared using choline chloride and zinc chloride at different wt% with the AC, i.e., 0.5 wt%–3 wt%. The physical and chemical properties of the synthesized adsorbents, such as surface morphology, porosity, and structures, were investigated and characterized by using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller analysis (BET). To investigate the actual adsorption performances, the effects of different synthesized adsorbent types and feed gas flow rates, i.e., 0.1–1.0 L min⁻¹, were observed. Hence, a commercial gas composed of CO₂ and H₂ mixture with different compositions, i.e., 40, 50, and 60 vol%, was used as synthetic bioH₂ gas. The adsorption capacity of CO₂, i.e., adsorption capacity, were determined using single adsorber column (0.6 L) at a temperature of 300 K and pressure of 1 bar. Results showed that adsorption capacity decreased with the increased feed gas flow rate. Moreover, the carbon impregnated with 1 wt% of IL showed the most excellent adsorption capacity at 84.89 mg of CO₂/g of adsorbent. The present results are the initial findings generated for the bioH₂ separation technology for future high-purity hydrogen production.     

Study of methane and carbon dioxide adsorption capacity by synthetic nanoporous carbon based on pyrogallol-formaldehyde

Nanoporous carbons were synthesized at certain conditions by sol–gel method combined with furnace firing in inert atmosphere from pyrogallol-formaldehyde (PF) mixtures in water using perchloric acid as catalyst. Their morphology was studied experimentally to examine their adsorption capacity for greenhouse gases. The preparation conditions of the nanoporous carbons were explored by changing the pyrolysis temperature. The effect of this factor on determining the pore structures and the adsorption capacities were evaluated. The synthesized xerogels were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that surface areas and nitrogen adsorption capacity are dependent completely on the pyrolysis temperature. Equilibrium and enthalpies studies for the CO₂ and CH₄ adsorption on PF were measured at room temperature and up to 25 bar. The adsorption capacity on PF was highest for CO₂ and then CH₄. The best sample shows maximal adsorption capacities as follows 5.50 mmol g^?1 of CH₄ and 7.62 mmol g^?1 of CO₂ at 25 bar and 30 °C.     

Effect of temperature on activated carbon nanotubes for hydrogen storage behaviors

In this work, activated multi-walled carbon nanotubes (Acti-MWNTs) with well-developed pore structures, a highly specific surface area, and higher hydrogen adsorption capacities due to CO₂ activation were prepared. The activation was performed at activation temperatures in the range of 500–1100 °C. The microstructure and crystallinity of the Acti-MWNTs were evaluated with a transmission electron microscope (TEM) and an FT-Raman spectrometer, respectively. The textural properties of the Acti-MWNTs were investigated by using a nitrogen gas sorption analyzer at 77 K. The hydrogen storage capacities of the Acti-MWNTs were investigated by BEL-HP at 298 K/100 bar. The hydrogen storage capacities of the Acti-MWNTs were enhanced to 0.78 wt.% by increasing activation temperatures to 900 °C, which resulted in the formation of a defective structure in the Acti-MWNTs. This result indicated that the CO₂ activation was one of the most effective methods to develop the textural properties, as well as to enhance the hydrogen storage capacities of MWNTs.     

Hydrogen adsorption characteristics of magnesium combustion derived graphene at 77 and 293 K

Bulk graphene was prepared by the method of magnesium combustion in a CO₂ atmosphere, producing large quantities of material which had a different morphology and importantly, a more ordered carbon lattice than reduced graphene oxide and other bulk graphene synthetic methodologies. Despite a low surface area of 235.5 m²/g and ca 9 at.% of magnesium and its oxides which do not contribute to hydrogen adsorption, we observe 0.85 wt.% of H₂ at 65 bar and 77 K, and 0.9 wt.% of H₂ at 300 bar and 293 K. As this methodology readily produces many-gram quantities with cheap starting materials, we anticipate that with further enhancements to the synthetic methodology, improving both surface area and reducing reaction by-products, this material will provide a robust platform for further H₂ adsorption investigations.     

NiS2 Co-catalyst decoration on CdLa2S4 nanocrystals for efficient photocatalytic hydrogen generation under visible light irradiation

NiS₂ nanoparticles as noble metal-free co-catalysts were deposited onto the CdLa₂S₄ nanocrystals through a hydrothermal process. The loading of NiS₂ co-catalyst resulted in remarkable enhancement for H₂ production over the CdLa₂S₄ photocatalyst under visible light irradiation. The optimal hybrid photocatalyst with 2 wt% NiS₂ loading exhibited a H₂ production rate of 2.5 mmol h⁻¹ g⁻¹, which was more than 3 times higher than that of the pristine CdLa₂S₄ photocatalyst. The promoted photocatalytic H₂ production by NiS₂-loading is attributed to the enhanced separation of photogenerated electrons and holes as well as the activation effect of NiS₂ for H₂ evolution.     

Y2O3-promoted NiO/SBA-15 catalysts highly active for CO2/CH4 reforming

A series of Y₂O₃-promoted NiO/SBA-15 (9 wt% Ni) catalysts (Ni:Y weight ratio = 9:0, 3:1, 3:2, 1:1) were prepared using a sol–gel method. The fresh as well as the catalysts used in CO₂ reforming of methane were characterized using N₂-physisorption, XRD, FT-IR, XPS, UV, HRTEM, H₂-TPR, O₂-TPD and TG techniques. The results indicate that upon Y₂O₃ promotion, the Ni nanoparticles are highly dispersed on the mesoporous walls of SBA-15 via strong interaction between metal ions and the HO–Si-groups of SBA-15. The catalytic performance of the catalysts were evaluated at 700 °C during CH₄/CO₂ reforming at a gas hourly space velocity of 24 L g_cat⁻¹ h⁻¹(at 25 ^°C and 1 atm) and CH₄/CO₂molar ratio of 1. The presence of Y₂O₃ in NiO/SBA-15 results in enhancement of initial catalytic activity. It was observed that the 9 wt% Y–NiO/SBA-15 catalyst performs the best, exhibiting excellent catalytic activity, superior stability and low carbon deposition in a time on stream of 50 h.