MOF-5 derived carbon as material for CO2 absorption

In our study we prepared MOF-5 derived carbon to reveal the thermodynamics of CO₂ absorption processes in great detail. Porous carbon material was prepared from a metal–organic framework (MOF-5) via carbonization at 1000 °C. The obtained structure consists only of carbon and exhibits a BET specific surface area, total pore volume and micropore volume of 1884 m² g⁻¹, 1.84 cm³ g⁻¹ and 0.59 cm³ g⁻¹, respectively. Structural analysis allowed the assumption that this material is an ideal candidate for efficient CO₂ absorption. The CO₂ uptake was 2.43 mmol g⁻¹ at 25 °C and 1 bar. Additionally, the absorption over a wide range of temperatures (25, 40, 60, 80 and 100 °C) and pressures (in range of 0–40 bar) was investigated. It is shown that the CO₂ absorption isotherm fits a multitemperature Sips model. The calculated Sips equation parameters allows the isosteric heat of adsorption to be obtained. The isosteric heat of adsorption for CO₂ decreased substantially with an increase in surface coverage by gas molecules. This indicates a negligible intermolecular interaction between CO₂ molecules. A decrease in the isosteric heat of adsorption with surface coverage is a result of the disappearance of favourable adsorption sites.

In our study we prepared MOF-5 derived carbon to reveal the thermodynamics of CO₂ absorption processes in great detail.     

Synthesis of palm sheath derived-porous carbon for selective CO2 adsorption

Biomass-derived porous carbons are regarded as the most preferential adsorbents for CO₂ capture due to their well-developed textural properties, tunable porosity and low cost. Herein, novel porous carbons were facilely prepared by activation of palm sheath for the highly selective separation of CO₂ from gas mixtures. The textural features of carbon materials were characterized by the analysis of surface morphology and N₂ isotherms for textural characterization. The as-prepared carbon adsorbents possess an excellent CO₂ adsorption capacity of 3.48 mmol g⁻¹ (298 K) and 5.28 mmol g⁻¹ (273 K) at 1 bar, and outstanding IAST selectivities of CO₂/N₂, CO₂/CH₄, and CH₄/N₂ up to 32.7, 7.1 and 4.6 at 298 K and 1 bar, respectively. Also, the adsorption evaluation criteria of the vacuum swing adsorption (VSA) process, the breakthrough experiments, and the cyclic experiments have comprehensively demonstrated the palm sheath derived porous carbons as efficient adsorbents for practical applications.

Novel porous carbons were facilely prepared by activation of palm sheath for the highly selective separation of CO₂ from gas mixtures.     

Facilely controlled synthesis of a core-shell structured MOF composite and its derived N-doped hierarchical porous carbon for CO2 adsorption

A new strategy for controlled synthesis of a MOF composite with a core–shell structure, ZIF-8@resorcinol–urea–formaldehyde resin (ZIF@RUF), is reported for the first time through in situ growth of RUF on the surface of ZIF-8 nanoparticles via an organic–organic self-assembly process by using hexamethylenetetramine as a formaldehyde-releasing source to effectively control the formation rate of RUF, providing the best opportunity for RUF to selectively grow around the nucleation seeds ZIF-8. Compared with the widely reported method for MOF composite synthesis, our strategy not only avoids the difficulty of incorporating MOF crystals into small pore sized materials because of pore limitation, but also effectively guarantees the formation of a MOF composite with a MOF as the core. After carbonization, a morphology-retaining N-doped hierarchical porous carbon characterized by its highly developed microporosity in conjunction with ordered mesoporosity was obtained. Thanks to this unique microporous core–mesoporous shell structure and significantly enhanced porosity, simultaneous improvements of CO₂ adsorption capacity and kinetics were achieved. This strategy not only paves a way to the design of other core–shell structured MOF composites, but also provides a promising method to prepare capacity- and kinetics-increased carbon materials for CO₂ capture.

New strategy for controlled synthesis of core–shell structured ZIF-8 composite and hierarchical N-doped carbon via an effective in situ self-assembly process.     

Waste wool derived nitrogen-doped hierarchical porous carbon for selective CO2 capture

The goal of this research is to develop a low-cost porous carbon adsorbent for selective CO₂ capture. To obtain advanced adsorbents, it is critical to understand the synergetic effect of textural characteristics and surface functionality of the adsorbents for CO₂ capture performance. Herein, we report a sustainable and scalable bio-inspired fabrication of nitrogen-doped hierarchical porous carbon by employing KOH chemical activation of waste wool. The optimal sample possesses a large surface area and a hierarchical porous structure, and exhibits good CO₂ adsorption capacities of 2.78 mmol g⁻¹ and 3.72 mmol g⁻¹ at 25 °C and 0 °C, respectively, under 1 bar. Additionally, this sample also displays a moderate CO₂/N₂ selectivity, an appropriate CO₂ isosteric heat of adsorption and a stable cyclic ability. These multiple advantages combined with the low-cost of the raw material demonstrate that this sample is an excellent candidate as an adsorbent for CO₂ capture.

In this work, N-doped hierarchical porous carbon has been successfully fabricated by KOH activation of waste wool. The optimal sample exhibits good CO₂ adsorption capacity under atmospheric pressure (1 bar), as well as excellent CO₂/N₂ selectivity.     

Promising activated carbon derived from sugarcane tip as electrode material for high-performance supercapacitors

We present a simple, low-cost method for producing activated-carbon materials from sugarcane tips (ST) via two-step pre-carbonization and KOH activation treatment. After optimizing the amount of KOH, the resulting ST-derived activated carbon prepared with a KOH to PC-ST mass ratio of 2 (ACST-2) contained 17.04 wt% oxygen and had a large surface area of 1206.85 m² g⁻¹, which could be attributed to the large number of micropores in ACST-2. In a three-electrode system, the ACST-2 electrode exhibited a high specific capacitance of 259 F g⁻¹ at 0.5 A g⁻¹ and good rate capability with 82.66% retention from 0.5 to 10 A g⁻¹. In addition, it displayed a high capacitance retention of 89.6% after 5000 cycles at a current density of 3 A g⁻¹, demonstrating excellent cycling stability. Furthermore, the ACST-2//ACST-2 symmetric supercapacitor could realize a high specific energy density of 7.93 W h kg⁻¹ at a specific power density of 100 W kg⁻¹ in 6 M KOH electrolyte. These results demonstrate that sugarcane tips, which are inexpensive and easily accessible agricultural waste, can be used to create a novel biomass precursor for the production of low-cost activated carbon materials for high-performance supercapacitors.

The aim of this study is to produce activated-carbon materials from sugarcane tips (ST) via two-step pre-carbonization and evaluate the electrochemical performance.     

Nitrogen doped hierarchical activated carbons derived from polyacrylonitrile fibers for CO2 adsorption and supercapacitor electrodes

Nitrogen doped hierarchical activated carbons with high surface areas and different pore structures are prepared form polyacrylonitrile fibers through KOH activation by two steps. It is found that the specific surface area and porosity of the activated carbons depend strongly on the activation temperatures. The specific surface area increases from 607 m² g⁻¹ to 3797 m² g⁻¹ when the activation temperature increases from 600 °C to 800 °C, and then decreases to 3379 m² g⁻¹ at 900 °C. It shows that the hierarchical activated carbon prepared at a moderate activation temperature of 700 °C exhibits the largest CO₂ capture amount, i.e., 5.25 and 3.63 mmol g⁻¹ at 273 and 298 K, respectively, under the pressure of 1 bar. The excellent CO₂ capture properties are due to the high specific surface area of 2146 m² g⁻¹ and high nitrogen content (5.2 wt%) of the obtained sample. On the other hand, when used as supercapacitor electrodes, the sample with the activation temperature at 800 °C shows the largest specific capacitance of 302 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH aqueous electrolyte, with an excellent rate capability of 231 F g⁻¹ at 10 A g⁻¹. Furthermore, a nearly linear relationship between nitrogen content in the nitrogen doped activated carbons and specific CO₂ uptake as well as the specific capacitance were first established, indicating nitrogen doping was playing key roles in improving CO₂ adsorption and supercapacitor performance. The experimental results indicate that the thus obtained nitrogen doped hierarchical activated carbons are very promising for reducing CO₂ green house gas by adsorption as well as storing energy as utilized in supercapacitors.

Nitrogen doped activated carbons with high surface area up to 3797 m₂ g⁻¹ exhibit specific capacitance of 231 F g⁻¹ at a current density of 10 A g⁻¹.     

Correction: Preparation of magnesium silicate/carbon composite for adsorption of rhodamine B

Correction for ‘Preparation of magnesium silicate/carbon composite for adsorption of rhodamine B’ by Zhiwei Sun et al., RSC Adv., 2018, 8, 7873–7882.

Optimisation of Cu+ impregnation of MOF-74 to improve CO/N2 and CO/CO2 separations

Carbon monoxide (CO) purification from syngas impurities is a highly energy and cost intensive process. Adsorption separation using metal–organic frameworks (MOFs) is being explored as an alternative technology for CO/nitrogen (N₂) and CO/carbon dioxide (CO₂) separation. Currently, MOFs'' uptake and selectivity levels do not justify displacement of the current commercially available technologies. Herein, we have impregnated a leading MOF candidate for CO purification, i.e. M-MOF-74 (M = Co or Ni), with Cu⁺ sites. Cu⁺ allows strong π-complexation from the 3d electrons with CO, potentially enhancing the separation performance. We have optimised the Cu loading procedure and confirmed the presence of the Cu⁺ sites using X-ray absorption fine structure analysis (XAFS). In situ XAFS and diffuse reflectance infrared Fourier Transform spectroscopy analyses have demonstrated Cu⁺–CO binding. The dynamic breakthrough measurements showed an improvement in CO/N₂ and CO/CO₂ separations upon Cu impregnation. This is because Cu sites do not block the MOF metal sites but rather increase the number of sites available for interactions with CO, and decrease the surface area/porosity available for adsorption of the lighter component.

We present an in situ study of CO adsorption on Cu impregnated MOF-74 and study the competitive adsorption of CO vs. CO₂ and N₂.     

Alkali modified P25 with enhanced CO2 adsorption for CO2 photoreduction

To improve the CO₂ adsorption on the photocatalyst, which is an essential step for CO₂ photoreduction, solid solutions were fabricated using a facile calcination treatment at 900 °C. Using various alkalis, namely NaOH, Na₂CO₃, KOH, K₂CO₃, the resulted samples presented a much higher CO₂ adsorption capacity, which was measured with the pulse injection of CO₂ on the temperature programmed desorption workstation, compared to the pristine Evonik P25. As a result, all of the fabricated solid solutions produced higer yield of CO under UV light irradiation due to the increased basicity of the solid solutions even though they possessed only the rutile polymorph of TiO₂. The highest CO₂ adsorption capacity under UV irradiation was observed in the sample treated with NaOH, which contained the highest amount of isolated hydroxyls, as shown in the FTIR studies.

Enhanced CO₂ adsorption capability and photocurrent with alkali modified P25 for CO₂ photoreduction.     

Biomass derived hierarchical porous carbon for high-performance O2/N2 adsorption; a new green self-activation approach

Biomass-derived porous carbons are the most common adsorbent materials for O₂/N₂ adsorption because of their excellent textural properties, high surface area, and low expense. A new synthesis method based on a self-activation technique was developed for a new green porous carbon adsorbent. This ecofriendly system was used for the synthesis of hierarchical porous carbons from walnut-shell precursors. The sorbent was successfully synthesized by facile one-step carbonization, with the activating reagents being gases released during the activation. The sample morphology and structure were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray powder diffraction, thermogravimetric, and differential thermal analysis. The optimal porous carbons were synthesized at 1000 °C, providing a surface area as high as 2042.4 (m² g⁻¹) and micropore volume of about 0.499 (m³ g⁻¹). At 298 °K under 9.5 bar pressure, the potential for O₂/N₂ separation using porous carbon samples was studied, and the sips isotherms with the highest adsorption potential were determined to be 2.94 (mmol g⁻¹) and 2.67 (mmol g⁻¹), respectively. The sample exhibited stable O₂/N₂ separation over ten cycles, showing high reusability for air separation. Finally, the technology described presents a promising strategy for producing eco-friendly porous carbon from a variety of biomass on an industrial scale.

Green porous carbon was synthesized by self-activation methodology with facile one-step carbonization from a walnut-shell precursor for air separation. The adsorption process behavior was surveyed using isotherm, kinetic and thermodynamic models.     

Hierarchically porous N-doped carbon derived from supramolecular assembled polypyrrole as a high performance supercapacitor electrode material

Rationally designed precursors of N-doped carbon are crucial for high performance carbon materials of supercapacitor electrodes. Herein, we report a scalable preparation of hierarchically structured N-doped carbon of micro/meso porous nanofiber morphology by using a supramolecular assembled polypyrrole as the precursor. The influences of the dose of supramolecular dopant on final products after carbonization and sequential chemical activation were investigated. The interconnected nanofiber backbone allows better electron transport and the optimized hierarchically porous structure of the material exhibits a large specific surface area of 2113.2 m² g⁻¹. The N content of the carbon is as high as 6.49 atom%, which is favorable to improve the supercapacitive performance via additional reversible redox reaction over pure carbon. The hierarchically porous N-doped carbon electrode delivered an outstanding specific capacitance of 435.6 F g⁻¹ at 0.5 A g⁻¹, significantly higher than that of the control sample derived from undoped polypyrrole samples. Moreover, the capacitance retention is as high as 96.1% after 5000 cycles. This precursor''s structural control route is readily applicable to various conducting polymers, and provides a methodology to design carbon materials with advanced structure for developing high-performance supercapacitor electrode materials.

Hierarchically porous N-doped carbon with optimized morphology exhibits an enhanced specific capacitance of 435.6 F g⁻¹ at 0.5 A g⁻¹ and 96.1% capacitance retention after 5000 cycles in 1 M H₂SO₄.     

Synthesis of zeolitic material from basalt rock and its adsorption properties for carbon dioxide

A zeolitic 4A type material was successfully prepared from natural basalt rock by applying an alkali fusion process and hydrothermal synthesis. In particular, the optimum synthetic conditions were examined at different crystallization times. Several methods such as XRD, SEM, EDX, and N₂ and CO₂ adsorption analysis were used to characterize the synthesized 4A type zeolite. In addition, CO₂ adsorption equilibrium capacities for this basalt base zeolite were measured over temperature ranges from 283 to 303 K and pressure ranges from 0.1 to 1500 kPa in a volumetric adsorption apparatus. Then the results were compared to those of commercial zeolite. Moreover, to further investigate the surface energetic heterogeneity of the prepared zeolite, the isosteric heat of adsorption and adsorption energy distribution was determined. We found that basalt based zeolite 4A shows a CO₂ adsorption equilibrium capacity of 5.9 mmol g⁻¹ (at 293 K and 1500 kPa) which is much higher than the 3.6 mmol g⁻¹ of the commercial zeolite as its micro-pore surface area, micro-pore volume and surface heterogeneity indicate.

A zeolitic 4A type material was successfully prepared from natural basalt rock by applying an alkali fusion process and hydrothermal synthesis.     

Synthesis of porous carbon material based on biomass derived from hibiscus sabdariffa fruits as active electrodes for high-performance symmetric supercapacitors

Carbon-based materials are manufactured as high-performance electrodes using biomass waste in the renewable energy storage field. Herein, four types of hierarchical porous activated carbon using hibiscus sabdariffa fruits (HBFs) as a low-cost biomass precursor are synthesized through carbonization and activation. NH₄Cl is used as a chemical blowing agent to form carbon nanosheets, which are the first types of hibiscus sabdariffa fruit-based carbon (HBFC-1) sample, and KOH also forms a significant bond in the activation process. The prepared HBFC-1 is chosen to manufacture the symmetric supercapacitor due to its rough surface and high surface area (1720.46 m² g⁻¹), making it show a high specific capacity of 194.50 F g⁻¹ at a current density of 0.5 A g⁻¹ in a three-electrode system. Moreover, the HBFC-1 based symmetric supercapacitor devices display a high energy density of 13.10 W h kg⁻¹ at a power density of 225.00 W kg⁻¹, and a high specific capacity of 29 F g⁻¹ at 0.5 A g⁻¹. Additionally, excellent cycle life is observed (about 96% of capacitance retained after 5000 cycles). Therefore, biomass waste, especially hibiscus sabdariffa fruit based porous carbon, can be used as the electrode for high-performance supercapacitor devices.

Carbon-based materials are manufactured as high-performance electrodes using biomass waste in the renewable energy storage field.     

Correction: The β-cyclodextrin-modified nanosized ZSM-5 zeolite as a carrier for curcumin

Correction for ‘The β-cyclodextrin-modified nanosized ZSM-5 zeolite as a carrier for curcumin’ by Shahin Amani et al., RSC Adv., 2019, 9, 32348–32356, DOI: 10.1039/C9RA04739E.

The authors regret that the names of the authors were listed incorrectly in the original article. The corrected author list is as shown above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Preparation of a MoS2/carbon nanotube composite as an electrode material for high-performance supercapacitors

MoS₂ and MoS₂/carbon allotrope (MoS₂/C) composites for use as anodes in supercapacitors were prepared via a facile hydrothermal method. In this study, we report the effects of various carbon-based materials (2D graphene nanosheet (GNS), 1D carbon nanotube (CNT), and 0D nano carbon (NC)) on the electrochemical performances. Among all nanocomposites studied, MoS₂/CNT exhibited the best electrochemical performance. Specifically, the MoS₂/CNT composite exhibits remarkable performances with a high specific capacitance of 402 F g⁻¹ at a current density of 1 A g⁻¹ and an outstanding cycling stability with 81.9% capacitance retention after 10 000 continuous charge–discharge cycles at a high current density of 1 A g⁻¹, making it adaptive for high-performance supercapacitors. The superiority of MoS₂/CNT was investigated by field emission scanning electron microscopy and transmission electron microscopy, which showed that MoS₂ nanosheets were uniformly loaded into the three-dimensional interconnected network of nanotubes, providing an excellent three dimensional charge transfer network and electrolyte diffusion channels while effectively buffering the collapse and aggregation of active materials during charge–discharge processes. Overall, the MoS₂/CNT nanocomposite synthesized by a simple hydrothermal process presents a new and promising candidate for high-performance anodes for supercapacitors.

The effect of carbon supports on the electrochemical performance of MoS₂ nanosheets for supercapacitor applications was investigated.     

Porous carbon material derived from fungal hyphae and its application for the removal of dye

In this work, fungal hyphae (FH, Irpex lacteus) was used as the carbon resource for the preparation of porous carbon materials (PCFH) using mixed alkali as the activator. The SEM, N₂ adsorption/desorption, FT-IR, XRD, Raman, and XPS were used to characterize the structure and surface properties of PCFH. The results showed that the PCFH not only has a huge Brunauer–Emmett–Teller (BET) surface area (2480 m² g⁻¹), but also has abundant functional groups containing carbon, oxygen, and nitrogen. Rhodamine B (RhB) was selected to evaluate the adsorption properties of the PCFH prepared under different conditions in dyeing wastewater. A fast adsorption rate was observed, and an uptake capacity of 765 mg g⁻¹ was achieved in the initial 5 min. The maximum adsorption capacity of PCFH to RhB reached 1912 mg g⁻¹ at the pH value of 9, which could efficiently remove RhB from the aqueous solution. The adsorption process was fitted better by a pseudo-second order model, and the adsorption isotherm for the RhB was well fitted by the Freundlich model. Moreover, the probable mechanism of adsorption was analyzed. In short, the good adsorption performance of PCFH indicated that it has a broad application prospect for dye water pollution control.

A highly porous carbon material based on fungal hyphae was prepared using mixed alkali and its application for removal of dye investigated.     

Correction: Synthesis of high surface area porous carbon from anaerobic digestate and it’s electrochemical study as an electrode material for ultracapacitors

Correction for ‘Synthesis of high surface area porous carbon from anaerobic digestate and it’s electrochemical study as an electrode material for ultracapacitors’ by Vikash Chaturvedi et al., RSC Adv., 2019, 9, 36343–36350.

The authors regret that the name of one of the authors (Saurabh Usgaonkar) was shown incorrectly in the original article. The corrected author list is as shown above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Nitrogen-doped mesoporous carbon supported CuSb for electroreduction of CO2

The construction of an efficient catalyst for electrocatalytic reduction of CO₂ to high value-added fuels has received extensive attention. Herein, nitrogen-doped mesoporous carbon (NMC) was used to support CuSb to prepare a series of materials for electrocatalytic reduction of CO₂ to CH₄. The catalytic activity of the composites was significantly improved compared with that of Cu/NMC. In addition, the Cu content also influenced the activity of electrocatalytic CO₂ reduction reaction. Among the materials used, the CuSb/NMC-2 (Cu: 5.9 wt%, Sb: 0.49 wt%) catalyst exhibited the best performance for electrocatalytic CO₂ reduction, and the faradaic efficiency of CH₄ reached 35%, and the total faradaic efficiency of C1–C2 products reached 67%.

CuSb anchored onto nitrogen-doped mesoporous carbon (CuSb/NMC) were prepared for electroreduction of CO₂ to CH₄, C₂H₄ and CO.