Green synthesis of nitrogen-doped self-assembled porous carbon-metal oxide composite towards energy and environmental applications

Nitrogen-doped biochar (N-doped BC) and iron/nitrogen co-doped biochar (Fe/N co-doped BC) for removal of refractory organic pollutants

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed.

Coupling of Mn2O3 with Heteroatom-Doped Reduced Graphene Oxide Aerogels with Improved Electrochemical Performances for Sodium-Ion Batteries

Currently, efforts to address the energy needs of large-scale power applications have expedited the development of sodium-ion (Na-ion) batteries. Transition-metal oxides, including Mn₂O₃, are promising for low-cost, eco-friendly energy storage/conversion. Due to its high theoretical capacity, Mn₂O₃ is worth exploring as an anode material for Na-ion batteries; however, its actual application is constrained by low electrical conductivity and capacity fading. Herein, we attempt to overcome the problems related to Mn₂O₃ with heteroatom-doped reduced graphene oxide (rGO) aerogels synthesised via the hydrothermal method with a subsequent freeze-drying process. The cubic Mn₂O₃ particles with an average size of 0.5-1.5 µm are distributed to both sides of heteroatom-doped rGO aerogels layers. Results indicate that heteroatom-doped rGO aerogels may serve as an efficient ion transport channel for electrolyte ion transport in Mn₂O₃. After 100 cycles, the electrodes retained their capacities of 242, 325, and 277 mAh g^-1, for Mn₂O₃/rGO, Mn₂O₃/nitrogen-rGO, and Mn₂O₃/nitrogen, sulphur-rGO aerogels, respectively. Doping Mn₂O₃ with heteroatom-doped rGO aerogels increased its electrical conductivity and buffered volume change during charge/discharge, resulting in high capacity and stable cycling performance. The synergistic effects of heteroatom doping and the three-dimensional porous structure network of rGO aerogels are responsible for their excellent electrochemical performances.

Evaluating the Growth of Ceria-Modified N-Doped Carbon-Based Materials and Their Performance in the Oxygen Reduction Reaction

Owning to their distinctive electronic structure, rare-earth-based catalysts exhibit good performance in the oxygen reduction reaction (ORR) and can replace commercial Pt/C. In this study, CeO₂-modified N-doped C-based materials were synthesized using salt template and high-temperature calcination methods, and the synthesis conditions were optimized. The successful synthesis of CeO₂-CN-800 was confirmed through a series of characterization methods and electrochemical tests. The test results show that the material has the peak onset potential of 0.90 V and the half-wave potential of 0.84 V, and has good durability and methanol resistance. The material demonstrates good ORR catalytic performance and can be used in Zn-air batteries. Moreover, it is an excellent catalyst for new energy equipment.

A Comparative Study of Biomimetic Synthesis of EDOT-Pyrrole and EDOT-Aniline Copolymers by Peroxidase-like Catalysts: Towards Tunable Semiconductive Organic Materials

It has been two decades since biomimetic synthesis of conducting polymers were first reported, however, the systematic investigation of how catalysts influence the properties of the conducting polymers has not been reported yet. In this paper, we report a comparative study between peroxidase-like catalyst, dopants, and their effect on the properties of poly (3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). We also investigate the EDOT-Pyrrole and EDOT-Aniline copolymerization by enzymomimetic synthesis using two catalysts (Ferrocene and Hematin). It was found that, chemically, there are no detectable effects, only having small contributions in molar ratios greater than 0.7–0.3. Spectroscopic data provide solid evidence concerning the effect in the variation of the molar fractions, finding that, as the molar fraction of EDOT decreases, changes associated with loss of the conjugation of the structure and the oxidation state of the chains were observed. The electrical conductivity was considerably modified depending on the type of catalyst. Hematin produces conductive homopolymers and copolymers when doped with p-toluene sulfonic acid (TSA), while ferrocene produces low conductive copolymers under the same conditions. The mole fraction affects conductivity significantly, showing that as the EDOT fraction decreases, the conductivity drops drastically for both EDOT-PY and EDOT-ANI copolymers. The type of dopant also notably affects conductivity; the best values were obtained by doping with TSA, while the lowest were obtained when doping with polystyrene sulfonate (PSS). We also draw a biomimetic route to tailor the fundamental properties of conducting homopolymers and copolymers for their design and scaled-up production, as they have recently been found to have use in a broad range of applications.

A Copper Peroxide Fenton Nanoagent-Hydrogel as an In Situ pH-Responsive Wound Dressing for Effectively Trapping and Eliminating Bacteria

Bacterial infection has been a great threat to wounds due to the abuse of antibiotics and drug resistance. Elaborately constructing an efficient antibacterial strategy for accelerated healing of bacteria-infected wounds is of great importance. Herein, we develop a transferrin-conjugated copper peroxide nanoparticle-hydrogel (denoted as CP@Tf-hy) wound dressing with no toxicity to mammalian cells at a test dosage. When exposed to an initial acidic wound environment, the CP@Tf-hy simultaneously displays in situ self-supplied H₂O₂ and pH-responsive release of Fenton catalytic copper ions accompanied by highly toxic hydroxyl radical (•OH) generation against antibiotic-resistant bacteria. Meanwhile, the positively charged CP@Tf-hy can efficiently trap and restrain negatively charged bacteria to the range of •OH destruction to greatly overcome its intrinsic disadvantages of short life and diffusion distance. Importantly, the CP@Tf-hy consumes the bacterial overexpressed antioxidant glutathione while boosting Fenton catalytic copper(I) ions to generate more •OH. The synergistic effects of the enhanced Fenton reaction, responsive copper ion release, and bacterial trapping can achieve high bacterial elimination efficacy (7 log reduction). In vivo investigations demonstrate that the porous CP@Tf-hy significantly promotes hemostasis, cell proliferation, and migration of the wound, consequently accelerating bacteria-infected wound healing. The safe, low-cost, and all-in-one CP@Tf-hy holds great prospects as an antibacterial dressing for rapid resistant bacteria-infected purulent wound healing.

Facile synthesis of nitrogen-doped porous carbon materials using waste biomass for energy storage applications

A simple, low-cost, and green route for the preparation of lotus carbon (LC) materials using lotus parts including leaves, flowers, fruits (seed pods), and stems as a renewable precursor is reported. Different porous carbons, leaf-carbon (LF-carbon), flower-carbon (FL-carbon), fruit-carbon (FR-carbon), and stem-carbon (ST-carbon) were synthesized from different parts of the lotus plant by simple carbonization method. The as-synthesized LC materials were well-characterized by many techniques such as electron microscopy and spectroscopy techniques, X-ray diffraction, and BET-surface area analysis. These techniques confirmed the porous structure of LC materials and the existence of heteroatoms in the prepared LC materials. The mesoporous structure of LC materials suggested employing it for the supercapacitor applications. The obtained FR-Carbon exhibits a high specific capacitance of 160 F/g in a three-electrode system in an aqueous 1 M H₂SO₄ electrolyte with a high rate performance of 52% retention from 0.5 to 5.0 A/g with good cycling stability of 95%. These results indicate that the porous carbon derived from lotus fruits is a potential electrode material for high-performance supercapacitors.

Synergy between Interconnected Porous Carbon-Sulfur Cathode and Metallic MgB2 Interlayer as a Lithium Polysulfide Immobilizer for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are the potential candidates for developing high-energy-density electric vehicles. However, poor electrical conductivity of sulfur/discharged products, low active material utilization, shuttle mechanism, and poor cycle life remain the major challenges for the development of Li-S batteries. Herein, we report the nitrogen-doped highly porous carbon (NC) with interconnected pores as the sulfur host (NC-S), which is synthesized by a facile one-step process without using any template and activation agents. The highly interconnected porous structure of NC can accommodate a high amount of sulfur loading and provide space for sulfur volume expansion during redox reactions. Besides, to mitigate the lithium polysulfide dissolution and shuttle mechanism, metallic and polar magnesium diboride (MgB₂) is used as an interlayer. Consequently, the NC-S/MgB₂ cathode delivers higher specific capacity, rate capability, and excellent cyclic stability than the NC-S cathode and bulk sulfur cathode with MgB₂ interlayer. The lithium polysulfide (LPS) adsorption test shows that MgB₂ has strong chemisorption toward lithium polysulfides, which can inhibit the dissolution of LPS into the electrolyte and minimizes the shuttle effect. The dynamic electrochemical impedance spectroscopy analysis investigates the electrochemical reaction kinetics of the NC-S/MgB₂ cathode during the charging and discharging processes. Overall, this work demonstrates that the synergy between the nitrogen-doped porous carbon-sulfur host and polar metallic MgB₂ improves the performance of the Li-S battery, which is beneficial for the development of high-energy-density batteries for the future.

Nitrogen/Carbon-Coated Zero-Valent Copper as Highly Efficient Co-catalysts for TiO2 Applied in Photocatalytic and Photoelectrocatalytic Hydrogen Production

Zero-valent copper (Cu⁰) is a promising co-catalyst in semiconductor-based photocatalysis as it is inexpensive and exhibits electronic properties similar to those of Ag and Au. However, its practical application in photocatalytic hydrogen production is limited by its susceptibility to oxidation, forming less active Cu species. Herein, we have carried out in situ encapsulation of Cu⁰ nanoparticles with N-graphitic carbon layers (14.4% N) to stabilize Cu⁰ nanoparticles (N/C-coated Cu) and improve the electronic communication with a TiO₂ photocatalyst. A facile solvothermal procedure is used to coat the Cu⁰ nanoparticles at 200 °C, while graphitization is achieved by calcination at 550 °C under an inert atmosphere. The resultant N/C-coated Cu/TiO₂ composites outperform the uncoated Cu counterparts, exhibiting a 27-fold enhancement of the hydrogen evolution rate compared to TiO₂ and achieving a rate of 19.03 mmol g^-1 h^-1 under UV-vis irradiation. Likewise, the N/C-coated Cu co-catalyst exhibits a less negative onset potential of -0.05 V toward hydrogen evolution compared to uncoated Cu (ca. -0.30 V). This superior activity is attributed to coating Cu⁰ with N/C, which enhances the stability, electronic communication with TiO₂, conductivity, and interfacial charge transfer processes. The reported synthetic approach is simple and scalable, yielding an efficient and affordable Cu⁰ co-catalyst for TiO₂.

One-step dry synthesis of an iron based nano-biocomposite for controlled release of drugs

Bio-based drug carriers have gained significant importance in Control Drug Delivery Systems (CDDS). In the present work, a new iron-based magnetic nano bio-composite (nano-Fe-CNB) is developed in a one-step dry calcination process (solventless) using a seaweed-based biopolymer. The detailed analysis of the developed nano Fe-CNB is carried out using FE-SEM, HR-TEM, P-XRD, XPS, Raman spectroscopy, FTIR etc. and shows that nano-Fe-CNB consists of nanoparticles of 5–10 nm decorated on 7–8 nm thick 2-D graphitic carbon material. The impregnation of nano-Fe-CNB into the calcium alginate (CA) hydrogel beads is found to have good drug loading capacity as well as pH responsive control release behavior which is demonstrated using doxorubicin (DOX) as a model cancer drug. The drug loading experiments exhibit ∼94% loading of DOX and release shows ∼38% and ∼8% release of DOX at pH 5.4 and 7.4 respectively. The developed nano Fe-CNB facilitates strong electrostatic interactions with cationic DOX molecules at pH 7.4 and thereby restricts the release of the drug at physiological pH. However, at cancer cell pH (5.4), the interaction between the drug and nano-Fe-CNB reduces which facilitates more drug release at pH 5.4. Thus, the developed nano-biocomposite has the potential to reduce the undesired side effects associated with faster release of drugs.

Schematics for synthesis and application of magnetic nano-biocomposite for control release of DOX.