Pore size dependent molecular adsorption of cationic dye in biomass derived hierarchically porous carbon

Water Adsorption on Hydrophilic Fibers and Porous and Deliquescent Materials: Cellulose, Polysaccharide, Silica, Inorganic Salt, Sugar Alcohol, and Amino Acid

Water adsorption isotherms are systematically summarized by using celluloses and polysaccharides as hydrophilic crystal/amorphous materials with functional groups, silicas as hydrophilic porous materials, and inorganic salts, sugar alcohols, and amino acids as hygroscopic deliquescent materials. For hydrophilic fibers such as celluloses and polysaccharides, water was adsorbed on amorphous solids, and water clusters were formed around functional groups. For porous materials such as silicas, capillary condensation occurred in the micropores of silicas. For deliquescent materials such as inorganic salts, sugar alcohols, and amino acids, water adsorption rapidly increased stepwise at a specific threshold relative humidity, accompanied with a structure transformation to a liquid state. In addition, the water activity (Aw) of materials used in packed products was able to be estimated from the water adsorption isotherms of the pure component. This indicated that the deliquescent materials have a great effect on the depression of Aw for the suppression of microbial growth at an extremely high water content. The deliquescent materials could be useful to develop new environmentally and sustainable products and technologies with the mediation of water vapor and/or hydration.

Porous chitosan-infused graphitic carbon nitride nanosheets for potential microbicidal and photo-catalytic efficacies

Supply of safe drinking water is a high-risk challenge faced internationally. Hybrid technologies involving nanomaterials can offer possible solutions to this research involving natural biopolymers. Porous chitosan with a high specific surface area has promising properties but its use as a membrane component in water purification is still rarely reported. Graphitic carbon nitride (g-C₃N₄) is a carbon nitride allotrope with a graphene-like layered structure that gifts unfamiliar physicochemical properties due to the presence of s-triazine fragments. It is a metal-free semiconductor with a band gap of ~2.7 eV to ~3.7 eV; which shows better visible light-activated photocatalyst properties. This work aims at synthesizing graphitic carbon nitride-biopolymer composite and exploring its properties in the field of wastewater treatment. The samples were synthesized via a soft chemical process with urea, as the source material. The flake-like morphology is displayed in the microstructural SEM image. The composition of the material was analyzed using EDS. Thermogram shows that the material is stable up to 500 °C and also confirms the formation of graphitic carbon nitride. In XRD spectra the intensity reduction shows the chitosan inclusion at the nitride site. The band gap of the prepared material was identified to be 2.3, 2.4 eV. The structural properties were analyzed using Fourier Transform Infrared Spectrometer and Raman spectroscopy. FTIR spectra and Raman spectra indicate the stretching vibration modes of CN and CN heterocycles and chitosan inclusion in the carbon nitride network. The photocatalytic activity was done in sunlight and a UV lamp with different dyes for doped and undoped g-C₃N₄. The doped (Porous/Non-porous chitosan) g-C₃N₄ showed faster dye degradation in sunlight compared to UV light. A biomolecular interaction study was done using Bovine serum albumin. It shows the material interaction with the BSA protein. The anti-microbial activity was performed on the Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli by disk diffusion method, the chitosan doped g-C₃N₄ showed good inhibitions against bacterial growth. The current work reveals the impact of nanoscale chitosan nanostructures doped on the optical, microstructural, catalytic, and antimicrobial properties of g-C₃N₄ nanosheets. This work provides new research options for nanocomposite-based photocatalytic nanomaterial g-C₃N₄ so that the quality of contaminated water could be improved.

Rapid and efficient adsorption of methylene blue dye from aqueous solution by hierarchically porous, activated starbons®: Mechanism and porosity dependence

Hierarchically porous activated Starbons® derived from starch are found to make excellent adsorbents for methylene blue, even in the presence of other dyes and inorganic salts, highlighting their potential to be used in water purification. The optimal material (S950C90) has a methylene blue adsorption capacity (891 mg g^-1) almost nine times higher than that of unactivated S800 and four times higher than that of commercial activated carbon at 298 K. The adsorption of methylene blue onto optimal materials (S950C90 and S800K4) reaches equilibrium within 5 min. Adsorption data for all the adsorbents show a good fit to the Freundlich isotherm which allows the Gibbs free energies of adsorption to be calculated. The adsorption capacities increase as the pH of the methylene blue solution increases, allowing the dye to be desorbed by treatment with acidic ethanol and the Starbon® materials reused. Porosimetry and SEM-EDX imaging indicate that methylene blue adsorbs throughout the surface and completely fills all the micropores in the Starbon® adsorbent. The methylene blue adsorption capacities show excellent correlations with both the BET surface areas and the micropore volumes of the materials.

Variation in Pore Structure and Associated Fractal Dimensions of Barakar and Barren Measures Carbon-Rich Gas Shales of Jharia Basin, India

The carbon-rich Barakar and Barren Measures shale beds of the Jharia basin were evaluated for variation in pore size, pore structure, and fractal dimensions. The shale core samples were obtained from exploratory boreholes drilled at the Jharia basin. The shale samples were analyzed for organo-inorganic composition by FTIR, pore size, and pore structure using BET low-pressure N₂ adsorption and pore geometry through FE-SEM photographs. The shale samples have significant carbon-rich content and are intercalated-banded in nature. The pore structures were evaluated through N₂ isotherms and validated by SEM images, revealing the mixed contribution of organo-inorganic matter in pore formations controlled by geochemical alteration, diagenesis, and mineral interaction. The rough internal surfaces of the pore were evaluated by categorizing them into fractals D ₁, D ₂, and D ₃. It is observed that the D ₂ type of fractals is in abundance associated with mesopores. The positive trend of fractals with pore size, pore structure, depth, fixed carbon, and TOC suggests the influence of different parameters on the formation of pore internal rugged surfaces in shale beds. The FE-SEM images indicate shallow to deep pores with different pore structures with fair to good pore connectivity. In summary, the shale beds of Jharia have heterogeneous complex pore structures, a rough surface, and sorption mechanisms controlled by weathering/alteration, depositional conditions, and organo-inorganic content. In shale beds, gas storage and transport phenomena are directly related to pore size distribution, pore structure, and associated fractal dimensions. The calculated values using the proposed empirical models for porosity (EPO_f) and permeability (EPE_f) showed excellent linear correlation with the measured porosity (MPOc, R ² = 0.8577) and permeability (MPEc, R ² = 0.8577), which are close to measured values. The curve matching of EPO_f with MPOc and EPE_f with MPEc follows a similar path, validating the results and suitability of the models. Hence, the proposed models may be considered to estimate the porosity and permeability of shale and coal beds.

Downsizing of Block Polymer-Templated Nanopores to One Nanometer via Hyper-Cross-Linking of High χ-Low N Precursors

Synthesizing nanoporous polymer from the block polymer template by selective removal of the sacrificial domain offers straightforward pore size control as a function of the degree of polymerization (N). Downscaling pore size into the microporous regime (<2 nm) has been thermodynamically challenging, because the low N drives the system to disorder and the small-sized pore is prone to collapse. Herein, we report that maximizing cross-linking density of a block polymer precursor with an increased interaction parameter (χ) can help successfully stabilize the structure bearing pore sizes of 1.1 nm. We adopt polymerization-induced microphase separation (PIMS) combined with hyper-cross-linking as a strategy for the preparation of the bicontinuous block polymer precursors with a densely cross-linked framework by copolymerization of vinylbenzyl chloride with divinylbenzene and also Friedel-Crafts alkylation. Incorporating 4-vinylbiphenyl as a higher-χ comonomer to the sacrificial polylactide (PLA) block and optimizing the segregation strength versus cross-linking density allow for further downscaling. Control of pore size by N of PLA is demonstrated in the range of 9.9-1.1 nm. Accessible surface area to fluorescein-tagged dextrans is regulated by the relative size of the pore to the guest, and pore size is controlled. These findings will be useful for designing microporous polymers with tailored pore size for advanced catalytic and separation applications.

Techno-economic analysis of biomass processing with dual outputs of energy and activated carbon

Biomass utilization is facing great challenge mainly due to the low profit margin of biomass products. Bio-energy plants using gasification and liquefaction technologies are barely surviving, while biomass to activated carbon (AC) route has been demonstrated economically successful. In this work, spent mushroom substrate was used to produce AC and fuel gas with two different processes using internal flue gas and external air as activation agents, respectively. Experimental work was conducted to produce input data for Aspen Plus simulation including processing temperature, flue gas composition, AC yield, etc. Techno-economic analysis was performed, which reveals a great economic potential of integrating AC production in biomass processing. Air activation has obvious advantage in economic benefits, while the risk of precise temperature control and operation stability needs to be carefully evaluated in large-scale production. Flue gas activation is more reliable and it also generates less CO₂ that is beneficial for the long-term operation.

Removal of Rhodamine B (A Basic Dye) and Acid Yellow 17 (An Acidic Dye) from Aqueous Solutions by Ordered Mesoporous Carbon and Commercial Activated Carbon

In this work, adsorption of rhodamine B (RB) and acid yellow 17 (AY17) was investigated on ordered mesoporous carbon material obtained by soft-templating method with hydrochloric acid (ST-A). For comparison, the adsorption process on commercial activated carbon CWZ-22 was also carried out. The sorbents were characterized by nitrogen adsorption/desorption isotherms and scanning electron microscopy. Langmuir and Freundlich adsorption isotherm models were applied to simulate the equilibrium data of RB and AY17. Adsorption isotherm data could be better described by the Langmuir model than the Freundlich model. The adsorption kinetics of RB and AY17 on studied carbons could be well depicted by using pseudo-second-order kinetic modeling. The adsorption capacity increased with temperature increase in the range of 298–315 K. In the whole diffusion process, the intraparticle diffusion was involved, but not the whole rate-controlling step. The calculated thermodynamic parameters, including Gibbs free energy (∆G), enthalpy (∆H), and entropy (ΔS) suggested that adsorption processes of RB and AY17 on ST-A and CWZ-22 were endothermic and spontaneous.

Hierarchical Porous Carbon Microfibers Derived from Tamarind Seed Coat for High-Energy Supercapacitor Application

The overwhelming interest in supercapacitors has led to the search for various carbonaceous materials, leading to hierarchical porous carbons. Herein, we report a natural biomass (tamarind seed)-based hierarchical porous carbon without any template and activated by a facile scheme. The tamarind seed coat-based hierarchical porous carbon possessed a unique configuration, making the material exhibit superior supercapacitor properties. A single carbon fiber hosting a distinctive micro- and mesoporous structure formed a connecting thread between the pores. This unique structure enabled high surface area and high capacitance. The highest surface area obtained by this method was 1702 m² g^-1, whereas the capacitance was 157 F g^-1 in 6 M KOH. Further, an ionic liquid-based electrolyte revealed 78 F g^-1 at a current density of 0.5 A g^-1. Outstanding capacity retentions of 96 and 93% were obtained over 1000 cycles at a current density of 2 A g^-1 for aqueous (6 M KOH) and ionic liquid (1-butyl 3-methyl imidazoliumbistrifluorosulfonylimide) electrolytes, respectively. The high charge-storage ability of the porous carbon microfibers (PCMFs) can be ascribed to the coexistence of micro- and mesopores. The power characteristics and the cyclic stability of PCMF materials were appealing in both electrolytes. The synthesis process described is amenable for large-scale applications with less complexity.