Nitrogen-containing Groups Research Articles

Plasma-induced aging of microplastics and its effect on mercury transport and transformation

Microplastics are known to adsorb heavy metals, with aged microplastics exhibiting greater adsorption capacity. This study investigates the impact of microplastic aging on the transport and transformation of mercury (Hg), a highly toxic heavy metal. Polystyrene (PS) and polyvinyl chloride (PVC) were aged using plasma treatment to simulate environmental conditions. Characterization of virgin and plasma-treated microplastics revealed aging mechanisms induced by plasma treatment. Notably, aged PS, unlike PVC, did not show a decrease in particle size but exhibited a decrease in specific surface area, likely due to chain cleavage and re-polymerization of polystyrene fragments, and thermal effects during plasma treatment. Both aged PS and PVC demonstrated increased hydrophilicity, enhanced negative charge, and a higher presence of nitrogen- and oxygen-containing functional groups. These changes were correlated with a significant increase in Hg adsorption capacity. Density functional theory (DFT) calculations further indicated that the adsorption of Hg2+ by microplastics is promoted by the presence of oxygen- and nitrogen-containing functional groups. The particularly strong influence of nitrogen-containing functional groups on Hg2+ adsorption was confirmed through both experimental and theoretical approaches. Adsorption kinetics and isothermal experiments, along with X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) analyses, were conducted to elucidate the Hg adsorption mechanism of on microplastics before and after aging. The mechanisms involved include pore filling, van der Waals’ forces, electrostatic interactions, hydrophobic interactions, and functional group complexation. The intraparticle diffusion model indicated that adsorption is controlled by multiple steps. Importantly, the surface functional groups of aged microplastics can reduce Hg2+ to Hg+ and adsorb it, suggesting a more complex adsorption process for Hg on aged microplastics. This study provides a scientific basis for understanding microplastic aging and the Hg adsorption mechanism on microplastics, highlighting the complex dynamics of combined microplastic and heavy metal contamination.

Development of a novel bio char for CO2 capture and biogas upgrade: Static and dynamic testing

The optimization of the pyrolysis of the spruce sawdust was conducted based on the yield, textural properties, and static capture capacity of the chars to generate a new micro porous char for biogas upgrade. The nature of the precursor (C: 45.68 %, H: 6.08 %, N: 0.15 %, and 0.34 % ash content) helped to tune the porosity of the char for capturing CO2 from gas streams and biogas. The optimization of the pyrolysis at 700 °C, a heating rate of 10 °C / min and holding time of 1 hour, produced a microporous char with high yield, CO2 capture capacity and CO2/CH4 selectivity. The presence of the oxygen and nitrogen-containing functional groups in the optimum char help in the selective capture of CO2. The static CO2 capture capacity of the optimum char was 1.98 mmol/g at atmospheric pressure and 25 °C (90 % CO2 stream). The CSD (700−10−60) have capture capacity of 1.50 mmol/g (at a feed gas stream of 50 % CO2 and adsorption temperature of 25 °C and 120 kPa) which is equivalent to Norit C and Calgon BPL. Hence, spruce sawdust can be used to produce efficient biochar for biogas upgrade (CO2 capture) owing to high capture capacity and CO2/CH4 selectivity (around 3) and easy regeneration of the biochar for 10 consecutive cycles.

Interactions between nanobiochar and arsenic: Effects of biochar aging methods on arsenic binding capacity and mechanisms

Nano-biochar (nanoBC), produced from biochar aging, exhibits significant molecular heterogeneity that may affect the fate and toxicity of co-occurring pollutants. However, the interaction between nanoBC and arsenic (As) remains unclear. Herein, we simulated biochar aging through water erosion, photoaging, and thermal chemical decomposition to generate three types of nanoBC (nUBC, nPBC, and nHBC). We then investigated their distinct binding affinities and interaction mechanisms with arsenite (AsIII) and arsenate (AsV). Complementary analysis using optical spectrophotometer and high-resolution mass spectrometry revealed significant differences in properties and chemical compositions among the three nanoBCs at a size of 100 nm. Specifically, nHBC had higher yield, nPBC had higher aromaticity, and nUBC had more intricate molecular compositions and larger molecular weights. Binding experiments showed that nHBC and nUBC exhibited the highest conditional distribution coefficient (KD) for AsIII and AsV, respectively. In nHBC, a higher proportion of humic-like fluorescent component C3 enhanced its affinity for AsIII, attributed to lignin-like molecules with CHONS formulas where thiol acted as active binding sites. In contrast, the robust AsV binding capacity of nUBC stemmed from its richness in humic-like fluorescent component C1 and tryptophan-like fluorescent component C2. This is facilitated by lipid-like molecules and CHO formulas in C1 and aliphatic/peptide-like molecules and CHON formulas in C2, which provided oxygenic and nitrogen-containing groups for binding. All nanoBC had a significantly higher binding affinity for As than bulk BC. These findings provide a deeper understanding of As-nanoBC binding mechanisms at the molecular level, facilitating more accurate prediction of As fate in biochar-amended soil and associated ecosystem risks.

Effect of puffing on electrochemical properties of sorghum seed based porous carbon materials in supercapacitors

Biomass-based carbon materials are renewable, affordable and environmentally friendly, possessing great potential in electrochemical energy storage as electrode materials in supercapacitors due to their large specific surface area and self-doped heteroatoms. However, the electrochemical properties of these carbon materials may be influenced to some extent by pretreatment procedures of carbon precursors. For this research, a range of porous carbon materials based on unpuffed and puffed sorghum seeds were synthesized under various pre‑carbonization and activation temperatures. Among them, the puffed sorghum seed-based porous carbon (PH-R6A7), prepared through pre‑carbonization at 600 °C and KOH activation at 700 °C, exhibits a higher graphitization degree, increased N and O content, as well as a greater variety of nitrogen-containing groups and significant increasing graphite nitrogen compared to unpuffed sorghum seed-based porous carbon (PC-R6A7) fabricated under similar conditions. These improvements result in enhanced conductivity and wettability of electrode materials, thereby boosting their electrochemical properties. In a three-electrode setup employing a 6 M solution of KOH, PH-R6A7 demonstrates an exceptional specific capacitance of 523.84 F g−1 at 1 A g−1 compared with PC-R6A7 of 366.00 F g−1; even at a high current density of 20 A g−1 it maintains a high level of capacitance at 387.94 F g−1. When employed in a double-electrode configuration at the same current density (i.e., 1 A g−1), PH-R6A7 also achieves higher specific capacitance of 357.83 F g−1 than PC-R6A7 (286.89 F g−1), accompanied by an increased energy density of 12.35 Wh kg−1 and 8.85 Wh kg−1 at a power density of 249.97 W kg−1 and 4.98 kW kg−1, respectively. Furthermore, after undergoing 10,000 cycles at 2 A g−1, PH-R6A7 demonstrates a superior capacitance retention of 99.68 % and coulomb efficiency of 99.91 %. PH-R6A7 fabricated through the combination method of puffing pretreatment and carbonization activation merits acknowledgment as an electrode material of superior performance and notable practical importance.

Pentaerythritol-Based Compound as a Novel Leveler for Super-Conformal Copper Electroplating

Leveler is one of the most important organic additives in copper electroplating for microvia filling. To enhance the microvia filling efficiency and reduce the bath control difficulty, novel levelers with high filling performance and wide application concentration range has long been pursued. Herein, a novel leveler named L1 with four pyrrolidine rings linked by a pentaerythritol backbone is designed and synthesized. Compared with the previously reported leveler TPM-1, L1 shares the same nitrogen-containing group but has an additional pyrrolidine ring. The structure-property relationship of L1 is thoroughly characterized by electrochemical measurements, theoretical calculations, and electroplating experiments. Results show that with one more positively charged ammonium groups, L1 exhibits stronger interactions with Cl− and the accelerator SPS compared to TPM-1. However, due to the variation of the connecting group, its interaction with the suppressor PEG is much weaker. With L1 as the leveler, both good microvia filling performance and high-quality copper deposition was obtained within a wide concentration range. The findings indicate that L1 is a very promising leveler for microvia filling copper electroplating, and both nitrogen-containing groups and linking groups in a leveler significantly influence its properties and performances.

Hydrogen bonds between the oxygen-containing functional groups of biochar and organic contaminants significantly enhance sorption affinity

Sorption affinity is an essential parameter to immobilize contaminants, but the controlling structures of biochar with strong sorption affinity to organic compounds are unidentified, hindering targeted biochar modification. In the face of multiple types and structures of organic contaminants in the aquatic environment, it is urgent to prepare biochar which can remove a large number of contaminants by targeted biochar modification. This study compared the sorption and desorption of five different type organic contaminants on biochar and graphite to understand sorption affinity and to inform the structural regulation of biochar. The sorption capacity of organics on biochar was 3–7 times higher than graphite, and the desorption ratios of organics on biochar were approximately one-fourth of those on graphite. Hydrophobic areas and aromatic rings were confirmed to be low-energy sorption sites, and most pores were inaccessible. The stronger sorption affinity was thus attributed to the hydrogen bonds between biochar surface functional groups and organics. Furthermore, sorption capacity and desorption ratios correlated positively with calculated sorption thermodynamics and binding energies, aligning with theoretical models based on oxygen- and nitrogen-containing groups. Further verification experiments revealed that functionalized graphite with hydroxyl and carboxyl groups showed the most significantly increased sorption capacity and rate, and decreased desorption ratios, enhancing sorption affinity through hydrogen bonds. These findings offer valuable insights into biochar sorption affinity to organics and guide its structural regulation for organic pollution control in the aquatic environment

Highly-selective and temperature-compensated toluene sensor based on MOF-actuated optical WGM microresonator

This paper reports an optical fiber toluene sensor based on whispering gallery mode (WGM) microbottle resonator. The sensor includes a single-mode fiber (SMF)- no-core fiber (NCF)- SMF offset structure, which can be used as not only a coupler to couple light into the microbottle but also a multimode interferometer. The microbottle is formed by self-assembly of polydimethylsiloxane (PDMS) polymer doped with metal-organic framework (MOF) under the action of surface tension and gravity. The high specific surface area, suitable pore size, nitrogen-containing functional groups of MOF-Fe-PD and nonpolar groups on PDMS impart the high sensitivity and specific response of the sensor to toluene. When toluene is captured by the MOF and PDMS, the refractive index and volume of the cavity change, which affects the mode shift of WGM. According to test results, WGM of the sensor shows a linear sensitivity of 12.44pm/ppm with toluene concentration between 0 ppm and 337 ppm at room temperature, but it is affected by temperature crosstalk. While multimode interference dip is only sensitive to temperature, which can compensate for the mode shift of WGM caused by temperature change. Repeatability experiments show that the response and recovery time of the sensor are less than 70s. The method provides a toluene sensor with high selectivity, stable performance and simple preparation, which has potential environmental benefits and good industrial application prospects.

Developing adjustable micro- and mesopore structured carbon materials from wood via biotechnology for enhanced capacitive deionization

Capacitive deionization (CDI) has attracted significant investigation interest for its potential in low-cost, efficient, and non-selective ion removal. However, achieving high performance in adsorption capacity and efficiency remains challenging, particularly with conventional biomass-derived electrodes. In this study, we developed adjustable, intricately porous, and hydrophilic wood-derived nanocarbon electrodes for electrochemical deionization. Our approach utilized biological pretreatment white-rot fungi, followed by chemical activation, effectively disrupting the rigid crystalline-amorphous structure of wood to create open micro-mesoporous networks. The resulting CDI carbon electrodes featured a predominance of micropores (especially below 0.8 nm) and a pronounced mesoporous arrangement, with a specific surface area of 1788 m2/g and 48 % meso-porosity. Additionally, this process enhanced surface oxidation and nitridation, resulting in surfaces rich in oxygen- and nitrogen-containing functional groups. These characteristics enable the electrodes to achieve a maximum adsorption capacity of 28.78 mg/g within 30 min, outperforming the performance of common biomass-derived electrodes. Moreover, the electrodes demonstrated excellent adsorption capacities for other contaminants, including 29.76 mg/g for NaF, 30.12 mg/g for Cd(NO3)2, and 27.24 mg/g for Pb(NO3)2. This study offers a cost-effective and viable alternative to current CDI electrodes, advancing the field by providing a viable solution to the limitations of existing technologies.

A computational study of adsorption on activated carbons containing basic oxygenated surface groups of two priority organochlorine pesticides from water

In previous work, molecular modeling was used to investigate how acidic and nitrogen-containing surface groups (SG) on an activated carbon (AC) model affect the adsorption of chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH), considering the effects of pH and hydration. Interactions involving acidic SGs at neutral pH indicated chemisorption, while interactions with nitrogen basic SGs suggested physisorption. This study presents a theoretical investigation of the interactions between these pesticides and oxygenated SGs on AC. A coronene molecule with functional groups—specifically pyrone, chromene, or ketone at the edges was used as a simplified model of AC. The Multiple Minima Hypersurface methodology was employed to study the interactions between CLD and β-HCH with SGs on AC using the PM7 semi-empirical Hamiltonian. Further re-optimization of the obtained structures for pesticide-AC complexes was performed using Density Functional Theory. The Quantum Theory of Atoms in Molecules was applied to characterize the interaction types using the Nakanishi criteria. No interactions were observed at acidic pH for both pollutants, whereas dispersive interactions were found at neutral and basic pH, indicating a physisorption process. Molecular dynamics simulations were also conducted to illustrate these findings. Ultimately, our previous studies showed that the adsorption process of CLD and β-HCH on AC is more effectively enhanced with acidic SGs rather than basic SGs. Moreover, MD simulations of β-HCH and CLD pesticides at concentrations higher than their solubilities reveal aggregation in both pure aqueous solutions and those containing AC. Analysis of MD trajectories and RDFs shows that hydrophobic interactions lead to aggregation of these molecules. RDFs indicate that β-HCH aggregates more in the solution due to its lower solubility compared to CLD. This aggregation reduces pesticide adsorption on AC surfaces, with β-HCH showing a more significant decrease in adsorption, dropping by more than half. Similar effects were observed with other biochar models for both pesticides.

Sulfonating and polyhedral oligomeric silsesquioxane crosslinking in one step to build multiple proton pathways for proton exchange membrane fuel cells over a wide temperature range

Developing proton exchange membrane fuel cells (PEMFCs) operating over a wide temperature range can avoid additional internal/external heating or cooling devices for the PEMFCs operating. Polybenzimidazole (PBI) doped with phosphoric acid (PA) exhibits significant potential in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Nevertheless, the traditional PA-PBI membranes are limited to operating within 140∼180 °C. In this work, a sulfonated polyhedral oligomeric silsesquioxane crosslinked polybenzimidazole membrane enriched pyridine and diazafluorene (CSPBI-X) is prepared where the sulfonation and crosslinking are accomplished by one-step heating. The theoretical calculations confirm that PA molecules have strong interactions with sulfonic acid groups and nitrogen-containing groups, enabling the membrane to achieve proton conductivity in a wide temperature range (80–180 °C). Moreover, the cross-linked sulfonated membranes have excellent PA retention ratio as high as 83.8% under 80 °C and 40% relative humidity for 120 h. Remarkably, with the acid doping level of 7.6, the proton conductivity of the CSPBI-20 membrane reaches 0.0491 S cm−1 and 0.145 S cm−1 at 80 °C and 180 °C in dry state, respectively. The highest power density of the CSPBI-20 at 80, 100, 120, 140, 160, and 180 °C is 257.3, 362.9, 485.3, 604.6, 755.3, and 956.1 mW cm−2, respectively.

Synergistic effects of nitrogen-containing functionalized copolymer and silicon-doped DLC for friction and wear reduction

We present a strategy to enhance the tribological performances of diamond-like carbon (DLC) films based on synergistic chemical modifications in the polymer lubricant additives and in the carbon film. Our experiments revealed that the polymer functionalization with nitrogen-containing groups and the DLC doping with silicon atoms result in significant friction and wear reduction under severe boundary lubrication conditions. Atomic Force Microscopy revealed the formation of a lubricious tribofilm. Ab initio calculations highlighted the key role of N-Si interactions in promoting the polymer chemisorption on the film, which represents the first, essential step for the tribofilm formation. Our findings suggest that targeted chemical modifications in lubricants and films can substantially advance the tribological performances of DLC films for various industrial applications.

Highly Selective Recovery of Gold by In Situ Magnetic Field-Assisted Fe/Co-MOF@PDA/NdFeB Double Network Gel.

There are enormous economic benefits to conveniently increasing the selective recovery capacity of gold. Fe/Co-MOF@PDA/NdFeB double-network organogel (Fe/Co-MOF@PDA NH) is synthesized by aggregation assembly strategy. The package of PDA provides a large number of nitrogen-containing functional groups that can serve as adsorption sites for gold ions, resulting in a 21.8% increase in the ability of the material to recover gold. Fe/Co-MOF@PDA NH possesses high gold recovery capacity (1478.87mg g-1) and excellent gold selectivity (Kd = 5.71mL g-1). With the assistance of an in situ magnetic field, the gold recovery capacity of Fe/Co-MOF@PDA NH is increased from 1217.93 to 1478.87mg g-1, and the recovery rate increased by 24.7%. The above excellent performance is attributed to the efficient reduction of gold by FDC/FC+, Co2+/Co3+ double reducing couple, and the optimization of the reduction reaction by the magnetic field. After the samples are calcined, high-purity gold (95.6%, 22K gold) is recovered by magnetic separation. This study proposes a forward-looking in situ energy field-assisted strategy to enhance precious metal recovery, which has a guiding role in the development of low-carbon industries.

Novel nitrogen-rich hydrogel adsorbent for selective extraction of rare earth elements from wastewater

Efficient recovery of rare earth elements (REEs) from wastewater is crucial for advancing resource utilization and environmental protection. Herein, a novel nitrogen-rich hydrogel adsorbent (PEI-ALG@KLN) was synthesized by modifying coated kaolinite-alginate composite hydrogels with polyethylenimine through polyelectrolyte interactions and Schiff’s base reaction. Various characterizations revealed that the high selective adsorption capacity of Ho (155 mg/g) and Nd (125 mg/g) on PEI-ALG@KLN is due to a combination of REEs (Lewis acids) via coordination interactions with nitrogen-containing functional groups (Lewis bases) and electrostatic interactions; its adsorption capacity remains more than 85 % after five adsorption-desorption cycles. In waste NdFeB magnet hydrometallurgical wastewater, the recovery rate of PEI-ALG@KLN for Nd and Dy can reach more than 93 %, whereas that of Fe is only 5.04 %. Machine learning prediction was used to evaluate adsorbent properties via different predictive models, with the random forest (RF) model showing superior predictive accuracy. The order of significance for adsorption capacity was pH > time > initial concentration > electronegativity > ion radius, as indicated by the RF model feature importance analysis and SHapley Additive exPlanations values. These results confirm that PEI-ALG@KLN has considerable potential in the selective extraction of REEs from wastewater.

Synthesis of mixed-base active material from drilling fluid solid waste and biomass for oil wastewater adsorption and its mechanism

To address the issues of high energy consumption, high cost and the risk of secondary pollution in drilling fluid solid waste treatment methods, this study prepared a mixed-based active material using drilling fluid solid waste and biomass materials as raw materials. The mixed-based active material is characterized by its abundant pore structure and high pore volume, demonstrating excellent adsorption performance for heavy metal ions and residual oil in industrial wastewater. Thermogravimetric and basic physical property analyses indicated a synergistic effect between drilling fluid solid waste and biomass materials, showing that joint pyrolysis of the two can enhance the yield of active materials. The adsorption performance of mixed-base active materials for heavy metal ions and residual oil were was tested. It was found that the removal rate of four heavy metal ions (Cr6+, Mn2+, Cu2+, and Zn2+) from the solution could reached 57.1 %, 96.3 %, 99.0 % and 94.1 %, respectively, at a concentration of 0.5 g/L of mixed-base active materials. Characterization revealed that the mixed-base activated carbon has a well-developed pore structure and numerous types of functional groups. The isothermal adsorption process of heavy metal ions by the active material is consistent with the Langmuir model and belongs to the monomolecular layer adsorption. The adsorption rate model of residual oil in wastewater by active materials conforms to the pseudo-second-order equation. The adsorption performance of mixed-base active materials primarily stems from physical adsorption enabled by their well-developed internal pore structure, along with chemical adsorption facilitated by oxygen- and nitrogen-containing functional groups on the surface.

Performance evaluation of different nitrogenous biomass pyrolysis chars: Physicochemical properties and ibuprofen adsorption

The preparation of high-performance porous carbons (HPPCs) using biomass as adsorbent is a viable strategy for the treatment of ibuprofen (IB) in water. In the present study, pyrolyzed carbon was prepared from duckweed (DW) and rice straw (SW) at 400, 500, and 600 °C, and subsequently mixed pyrolysis with KOH to prepare the HPPCs. The HPPCs were used for the treatment of ibuprofen (IB) in water to evaluate their absorption performance. The physicochemical properties of biochar and HPPCs were investigated using scanning electron microscopy, X-ray electron microscopy, Raman microscopy, and the Brunauer-Emmett-Taylor method. In IB adsorption experiments, adsorption equilibrium was evaluated using Langmuir and Freundlich isotherm models. The maximum adsorption capacities of DW and SW were 0.952 and 0484 g/g, respectively, at an IB concentration of 0.5 g/L. The adsorption capacity of HPPCs for IB is influenced by a multifactorial combination of the specific surface area, nitrogen content, and nitrogen-containing functional groups on the surface. Generally, the HPPCs showed great potential for the removal of the IB pharmaceutical contaminants from aqueous solutions.

Polypyrrole functionalized cellulose/polypropylene composite membrane with zinc inducing and dendrite resistance for robust zinc-ion batteries

Dendrite growth and subsequent membrane puncture stemming from uneven deposition of zinc ions pose a significant challenge for aqueous zinc ion batteries (AZIBs). Herein a polypyrrole functionalized cellulose/polypropylene (PPy-cellulose/PP) composite membrane with promising zinc inducing and dendrite resistance was rationally designed through an in-situ polymerization strategy to enable robust zinc-ion batteries. Experimental data and theoretical simulations reveal that a continuous conducting network, constructed by PPy nanoparticles, could homogenize the electric field and reduce the interfacial resistance of zinc anode. Moreover, the zincophilic nitrogen-containing functional groups in PPy induced the migration and deposition of zinc ions uniformly. The combination of polypropylene laminate enhanced the puncture resistance and mechanical strength of the composite membranes. Consequently, Zn||Zn symmetric cell assembled with the PPy-cellulose/PP composite membrane exhibited stable cycling performance over 2000 h at 0.5 mA cm−2/0.5 mAh cm−2. Further verification was conducted on the practical application of PPy-cellulose/PP membranes in Zn||MnO2 full cells and Zn||AC capacitors. Notably, a high capacity retention of 89.6 % was achieved for the Zn||AC capacitor after 10,000 cycles at 1 A g−1. The new design of PPy functionalized cellulose/polypropylene membranes provides a valuable protocol to stabilize zinc anodes for zinc-ion batteries.

Supermolecule-opitimized defect engineering of rich nitrogen-doped porous carbons for advanced zinc-ion hybrid capacitors.

Pitch-based porous carbons with adjustable surface chemical property and controllable pore structure are regarded as promising cathode materials for aqueous zinc-ion hybrid capacitors (ZIHCs), while its disordered carbon matrix and microstructure as well as insufficient surface defects often result in low Zn2+-storage capacity and poor rate capability of ZIHCs. Herein, a synergetic strategy of self-assembled supermolecule and enriched defective carbon engineering was developed to achieve ultrahigh edge-nitrogen doping for ZIHCs. The crystallite defects and surface structure of porous carbon could be effectively achieved through grafting electronegative oxygen-containing small molecules and high-level nitrogen-containing functional groups between modified polycyclic aromatic hydrocarbon and supermolecule framework. The optimized three-dimensional carbon structure delivered high capacity of 218 mAh g-1 at 0.2 A g-1, fast charge/discharge capability, enhanced energy density (165.4 Wh kg-1) and superior cycling stability (95% retention after 10000 cycles as cathode of ZIHCs). This provided new insight into the controllable synthesis of carbon cathodes for ZIHCs and expects to prepare functional porous carbon by supermolecules and special precursors.

Urea-modified hazelnut shell biochar (N-HSB) for efficient Cr(VI) removal: Performance and mechanism insights

Composite with a high specific surface area of 224.62 m2 g−1 was prepared by adding urea as a nitrogen source to hazelnut shell biochar (HSB). Nitrogen doping significantly enhanced the ability of biochar for Cr(VI) elimination, achieving twice the removal efficiency of unmodified biochar. The impacts of varying the pH and initial concentrations on Cr(VI) removal by urea-modified biochar (N-HSB) were investigated. The Cr(VI) removal by N-HSB was better described by intra particle diffusion model and pseudo-second order kinetic model under optimal conditions. Furthermore, XPS, FTIR, SEM, and BET analyses were used to verify the pivotal roles of oxygen- and nitrogen-containing functional groups. Electrostatic attraction, redox reaction, and complexation constituted the principal mechanisms facilitating Cr(VI) elimination by N-HSB. This study demonstrated that the modification of biochar with urea as a nitrogen source represented a promising strategy for enhancing the removal capacity of biochar for Cr(VI) in aqueous environments.

Bio-efficacy of Essential Oil Extracted from Locally Available Orange (Citrus sinensis) Peels from Nepal

Essential oils from various plants are valued for their therapeutic, aromatic, antimicrobial, and antioxidant properties. The majority of them are employed in cleaning procedures, aromatherapy, stress reduction, food flavouring and preservation, and beauty products. The present investigation focuses on elucidating the chemical composition along with the antimicrobial and antioxidant properties of essential oil extracted from locally available orange (Citrus sinensis) peels, mainly exploring its bio-efficacy. The antibacterial property was studied against the gram-negative bacterium Escherichia coli and the gram-positive bacterium Bacillus subtilis. The analysis results revealed significant antimicrobial activity with zones of inhibition of 4 mm and 5.5 mm, respectively. The antifungal property was studied against the opportunistic pathogenic yeast Candida albicans, which showed positive activity, producing 4.5 mm of zone of inhibition. The antioxidant activity of the oil was determined using DPPH free radical scavenging assay, which showed an IC50 value of 1.3532 µL/mL. Qualitative phytochemical screening of the essential oil as determined using some standard colour-developing methods showed the presence of alkaloids, flavonoids, terpenoids, phenols, cardiac glycosides, and saponins. The above results were validated by FT-IR and GC/MS analysis. The FT-IR analysis revealed the presence of nitrogen-containing and oxygen-containing functional groups. The GC/MS analysis showed the presence of limonene, d-limonene, 1S-α-Pinene, 1R-α-Pinene, β-myrcene, linalool, α-humulene, α-terpineol, etc. These findings demonstrated that orange peels from Nepal that are readily available locally could be a source of compounds with antibacterial, antifungal, and antioxidant properties.

Preparation of lignin-based porous carbon through thermochemical activation and nitrogen doping for CO2 selective adsorption

Preparing CO2 adsorbents from biomass feedstock has garnered considerable attention due to its potential for fostering sustainable, economic, and eco-friendly development. Introduction of nitrogen-containing functional groups can enhance the affinity for CO2 of biochar but also inevitably affect the pore structure. The challenge lies in ascertaining and regulating the effect of N-doping on the pore structure. In this work, lignin was activated using KOH, and then followed by urea N-doping through pyrolysis or hydrothermal methods. At small dosages of KOH (the mass ratio of KOH/lignin = 0.25), in addition to introducing nitrogen-containing functional groups, urea modification boosted pore volume of <1 nm favorable for CO2 adsorption through etching carbon skeleton, while the small dosage of KOH reduced its inherent corrosive hazards. Correlation analysis showed that the dominant influencing factor for CO2 adsorption at ambient temperature and pressure was the pore volume with pore size of 0.6–0.8 nm, whereas nitrogen content (especially N-5 content) was the main influencing factor at high temperatures (50 °C) and low pressures (0.15 bar). The peak enhancement of the C–N bond under the CO2 adsorption at 50 °C by in situ diffuse reflectance infrared Fourier transform test indicated that the nitrogen-containing functional groups have a chemisorption effect on CO2. The adsorbent PK-0.25-HU exhibited adsorption capacity of 4.46 mmol/g (25 °C, 1 bar), 2.97 mmol/g (50 °C, 1 bar). Dynamic separation coefficient of CO2/N2 reached 93.82 in a gas mixture of CO2/N2 = 15 %/85 %.