Environmental remediation by microporous carbon: An efficient contender for CO2 and methylene blue adsorption

Machine learning and experimentally exploring the controversial role of nitrogen in CO2 uptake by waste-derived nitrogen-containing porous carbons

Waste-derived nitrogen-containing porous carbons were widely accepted as promising carbon capture materials. However, roles of nitrogen in CO2 uptake were highly controversial, posing a challenge in designing high CO2 uptake porous carbons. Herein, nitrogen-containing species was firstly introduced into machine learning (ML) models to uncover the complex relationship of nitrogen, micropore and CO2 uptake by combining ML models, DFT computations and experiments. The results revealed that micropore volume (Vmicro) was the most important property influencing CO2 uptake, but was not the only determinant factor. Nitrogen-containing species (pyrrolic/pyridonic-N (N5) and pyridinic-N (N6)) rather than total nitrogen content, also played an essential role. On the one hand, they can enhanced CO2 adsorption by Lewis acid-base and hydrogen bonding. On the other hand, they promoted development of micropores by participating in activation reactions. The model further indicated that excessive N5 (>1.5 wt%) or N6 (>1.7 wt%) led to restriction on developments of micropores, which was attributed to enlargement of pore size, collapses or blockage of micropores. The double edged-sword effect of N5 and N6 on changes of microporous structures was responsible for the long-standing controversy over nitrogen. The result was further verified by synthesizing eight porous carbons with different textural and chemical properties. This study provided not only a new perspective for resolving the controversy of nitrogen in CO2 uptake, but also a graphical user interface prediction software meaningful for designing porous carbons.

N-rich chitosan-derived porous carbon materials for efficient CO2 adsorption and gas separation

Capturing and separating carbon dioxide, particularly using porous carbon adsorption separation technology, has received considerable research attention due to its advantages such as low cost and ease of regeneration. In this study, we successfully developed a one-step carbonization activation method using freeze-thaw pre-mix treatment to prepare high-nitrogen-content microporous nitrogen-doped carbon materials. These materials hold promise for capturing and separating CO2 from complex gas mixtures, such as biogas. The nitrogen content of the prepared carbon adsorbents reaches as high as 13.08 wt%, and they exhibit excellent CO2 adsorption performance under standard conditions (1 bar, 273 K/298 K), achieving 6.97 mmol/g and 3.77 mmol/g, respectively. Furthermore, according to Ideal Adsorption Solution Theory (IAST) analysis, these materials demonstrate material selectivity for CO2/CH4 (10 v:90 v) and CO2/CH4 (50 v:50 v) of 33.3 and 21.8, respectively, at 1 bar and 298 K. This study provides a promising CO2 adsorption and separation adsorbent that can be used in the efficient purification process for carbon dioxide, potentially reducing greenhouse gas emissions in industrial and energy production, thus offering robust support for addressing climate change and achieving more environmentally friendly energy production and carbon capture goals.

Facile synthesis of a GO-g-C3N4/BaTiO3 ternary nanocomposites for visible-light-driven photocatalytic degradation of rhodamine B

Photogenerated charge carriers can undergo rapid recombination in conventional photocatalyst systems, reducing their photocatalytic efficiency. To address this bottleneck, a g-C3N4/BaTiO3 (CNB) heterojunction composite was decorated with different mass ratios of graphene oxide (GO) to form a novel visible-light responsive ternary GO-g-C3N4/BaTiO3 (GOCNB) nanocomposite using a facile fabrication method. The GOCNB photocatalyst exhibited significantly higher light absorption and greater charge transfer than CNB, g-C3N4, or BaTiO3. The photodegradation performance of GOCNB was optimized with a 2% mass loading of GO, and it achieved a degradation rate constant of 14.9 × 10-3 min-1 for rhodamine B with an efficiency of 94% within 180 min. The rate constant was 8-fold and 6-fold higher than that of bare BaTiO3 and CNB, respectively. The stronger photocatalytic activity was attributed to the synergistic effect of GO, g-C3N4, and BaTiO3, with g-C3N4 and BaTiO3 promoting charge transfer within a wider visible light range and GO promoting electron mobility and the photocatalyst's adsorption capacity. In particular, the proposed system maintained the spatial separation of photogenerated electron-hole pairs, which is vital for high photocatalytic activity. This study provides new insights into semiconductor-based photocatalytic systems and suggests a route for more environmentally sustainable technologies.

Kinetics and Thermodynamics Study of Methylene Blue Adsorption to Sucrose- and Urea-Derived Nitrogen-Enriched, Hierarchically Porous Carbon Activated by KOH and H3PO4

Hierarchically porous nitrogen-enriched carbon materials synthesized by polymerization of sucrose and urea (SU) were activated by KOH and H₃PO₄ (SU-KOH and SU-H₃PO₄, respectively). Characterization was undertaken and the synthesized materials were tested for their ability to adsorb methylene blue (MB). Scanning electron microscopic images along with the Brunauer-Emmett-Teller (BET) surface area analysis revealed the presence of a hierarchically porous system. X-ray photoelectron spectroscopy (XPS) confirms the surface oxidation of SU upon activation with KOH and H₃PO₄. The best conditions for removing dyes utilizing both activated adsorbents were determined by varying the pH, contact time, adsorbent dosage, and dye concentration. Adsorption kinetics were evaluated, and the adsorption of MB followed second-order kinetics, suggesting the chemisorption of MB to both SU-KOH and SU-H₃PO₄. Times taken to reach the equilibrium by SU-KOH and SU-H₃PO₄ were 180 and 30 min, respectively. The adsorption isotherm data were fitted to the Langmuir, Freundlich, Temkin, and Dubinin models. Data were best described by the Temkin isotherm model for SU-KOH and the Freundlich isotherm model for SU-H₃PO₄. Thermodynamics of the adsorption of MB to the adsorbent was determined by varying the temperature in the range of 25-55 °C. Adsorption of MB increased with increasing temperature, suggesting that the adsorption process is endothermic. The highest adsorption capacities of SU-KOH and SU-H₃PO₄ (1268 and 897 mg g^-1, respectively) were obtained at 55 °C. Synthesized adsorbents were effective in removing MB for five cycles with some loss in activity. The results of this study show that SU activated by KOH and H₃PO₄ are environmentally benign, favorable, and effective adsorbents for MB adsorption.

Development of Low-Cost Porous Carbons through Alkali Activation of Crop Waste for CO2 Capture

To achieve the "double carbon" (carbon peak and carbon neutrality) target, low-cost CO₂ capture at large CO₂ emission points is of great importance, during which the development of low-cost CO₂ sorbents will play a key role. Here, we chose peanut shells (P) from crop waste as the raw material and KOH and K₂CO₃ as activators to prepare porous carbons by a simple one-step activation method. Interestingly, the porous carbon showed a good adsorption capacity of 2.41 mmol/g for 15% CO₂ when the mass ratio of K₂CO₃ to P and the activation time were only 0.5 and 0.5 h, respectively, and the adsorption capacity remained at 98.76% after 10 adsorption-desorption cycle regenerations. The characterization results suggested that the activated peanut shell-based porous carbons were mainly microporous and partly mesoporous, and hydroxyl (O-H), ether (C-O), and pyrrolic nitrogen (N-5) functional groups that promoted CO₂ adsorption were formed during activation. In conclusion, KOH- and K₂CO₃-activated P, especially K₂CO₃-activated P, showed good CO₂ adsorption and regeneration performance. In addition, not only the use of a small amount of the activator but also the raw material of crop waste reduces the sorbent preparation costs and CO₂ capture costs.

Facile synthesis of ternary dual Z-scheme g-C3N4/Bi2MoO6/CeO2 photocatalyst with enhanced 4-chlorophenol removal: Degradation pathways and mechanism

The design of visible-light-driven photocatalysts has been rapidly developed due to the great application potential in environmental pollution remediation. The present work focused on the construction of a novel ternary g-C₃N₄/Bi₂MoO₆/CeO₂ nanocomposite and the application for photocatalytic removal of 4-CP under irradiation. The g-C₃N₄/Bi₂MoO₆/CeO₂ photocatalysts were successfully synthesized by a facile solid-state thermolysis assisted ultrasonic dispersion to introduce g-C₃N₄ nanosheets into Bi₂MoO₆/CeO₂ composite. Morphology characterization revealed that the Bi₂MoO₆/CeO₂ spherical structure uniformly dispersed on the g-C₃N₄ nanosheets and the close interface contact induced the generation of dual Z-scheme heterojunction. The as-prepared photocatalysts shown enhanced catalytic activity in comparison with binary Bi₂MoO₆/CeO₂ composites and the optimal CBC-20% exhibited the highest degradation efficiency of 99.1% for 4-CP under 80 min illumination, which was attributed to the efficient separation of photogenerated e^--h⁺ pairs under the dual Z-scheme charges transfer mode. Additionally, combined with trapping experiments and EPR analysis, 4-CP was decomposed mainly by the active species ^•O₂^- and h⁺ with a marginal assistance of ^•OH during the photocatalytic process. The intermediates for 4-CP degradation were analyzed and a reasonable degradation pathway was proposed.

Adsorption performance and mechanism of cationic and anionic dyes by KOH activated biochar derived from medical waste pyrolysis

The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R² ≥ 0.996) and pseudo-second-order kinetics (R² ≥ 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg⋅g^-1. The thermodynamics study of both dyes showed a positive change in enthalpy (ΔH°) and entropy (ΔS°), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Salt sealing induced in situ N-doped porous carbon derived from wheat bran for the removal of doxycycline from aqueous solution

In situ N-doped porous carbon (NPC) derived from wheat bran via a convenient salt sealing and air-assisted strategy was prepared for the removal of doxycycline (DOX) from aqueous solution. The NPC was precisely characterized by SEM, FTIR, XPS and BET analysis. Additionally, the experimental variables including contact time, adsorbent dosage of NPC and pH were optimized by using Box-Behnken design (BBD) under response surface methodology (RSM). The predicted adsorption capacity of DOX was found to be 291.14 mg g-1 under optimalizing experimental conditions of 196 min contact time, 0.2 g L-1 adsorbent dosage and pH 5.78. The adsorption experimental data fitted Langmuir, Koble-Corrigan and Redlich-Peterson models well, and the pseudo-second-order model perfectly described the DOX adsorption process onto NPC. Thermodynamic parameters of DOX adsorbed onto NPC indicated that the adsorption process was spontaneous and endothermic. Moreover, the adsorption of DOX on NPC was mostly controlled by electrostatic interaction, π-π electron-donator-acceptor (EDA) interaction, hydrogen-bonding and Lewis acid-base effect. Besides, the N element of NPC also played a role in capturing DOX. The maximum monolayer adsorption capacity of DOX was turn out to be 333.23 mg g-1 at 298 K, which suggested that the NPC could be a prospectively adsorbent for the removal of DOX from wastewater.

The development of activated carbon from corncob for CO2 capture

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO2.

Biogenic and biocompatible silver nanoparticles for an apoptotic anti-ovarian activity and as polydopamine-functionalized antibiotic carrier for an augmented antibiofilm activity

Silver nanoparticles (AgNPs) could be employed in the combat against COVID-19, yet are associated with toxicities. In this study, biogenic and biocompatible AgNPs using the agro-waste, non-edible Hibiscus sabdariffa stem were synthesized. Under optimized reaction conditions, synthesized green AgNPs were crystalline, face cubic centered, spherical with a diameter of around 17 nm and a surface charge of -20 mV. Their murine lethal dose 50 (LD50) was 4 folds higher than the chemical AgNPs. Furthermore, they were more murine hepato- and nephro-tolerated than chemical counterparts due to activation of Nrf-2 and HO-1 pathway. They exerted an apoptotic anti-ovarian cancer activity with IC50 value 6 times more than the normal cell line. Being functionalized with polydopamine and conjugated to either moxifloxacin or gatifloxacin, the conjugates exerted an augmented antibiofilm activity against Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii biofilms that was significantly higher than antibiotic alone or functionalized AgNPs suggesting a synergistic activity. In conclusion, this study introduced a facile one-pot synthesis of biogenic and biocompatible AgNPs with preferential anti-cancer activity and could be utilized as antibiotic delivery system for a successful eradication of Gram-negative biofilms.

Development of Boron-Doped Mesoporous Carbon Materials for Use in CO2 Capture and Electrochemical Generation of H2O2

Mesoporous carbon materials have been increasingly studied due to their large specific surface area and good chemical stability. Optimizing their functionality through a doping modification can broaden their application in many fields. Herein, a series of B-doped mesoporous carbon materials are prepared by a convenient hydrothermal synthesis using F127 as the template and boric acid as the boron source. The whole material preparation process meets the requirements of green chemistry. Notably, the prepared carbon materials not only exhibit good electrocatalytic oxygen reduction to hydrogen peroxide in alkaline media but also have an excellent CO2 adsorption capacity (up to 121.34 mg/g) at 303 K and atmospheric pressure. These results show that the prepared samples can be utilized as multifunctional materials for handling a variety of environmental issues.

Continuous Synthesis of Nanodroplet-Templated, N-Doped Microporous Carbon Spheres in Microfluidic System for CO2 Capture

Microporous carbon has been widely known as a probable material to capture greenhouse gases. This work provides a facile synthesis of monodisperse biomass-derived microporous carbon spheres (CSs) for effective CO₂ capture. The spheres were synthesized by a novel continuous microfluidic strategy from oil-in-water-in-oil ((O₁/W₂)/O₂) emulsions. O₁ nanodroplets could be self-assembled into the cores of micelles, which were formed by chitosan and surfactant F127 in the W₂ phase through high-speed liquid-phase shearing. The obtained O₁/W₂ emulsion can be further sheared into a sphere by the O₂ phase. After carbonization, nanodroplet-templated pores shrank to micropores and ultramicropores. The optimal sample showed the developed pore structure with a Brunauer-Emmett-Teller (BET) surface area of 576 m²/g and microporous volume of 0.22 cm³/g. Compared with O₁ free CS, the dynamic adsorption capacity of CO₂ was improved to 1.20 mmol/g from 0.42 mmol/g. The CO₂ capture capacity, cycling stability, isosteric heats, and mass diffusion coefficient of CSs were evaluated as well. The results demonstrate that microporous CSs are promising candidates for CO₂ capture with low cost and a green synthesis route, which was achieved via continuous microfluidic strategy using sustainable biomass chitosan as a carbon precursor and droplets as templates.