N-doped carbon fibers in situ prepared by hydrothermal carbonization of Camellia sinensis branches waste for efficient removal of heavy metal ions

Unraveling the promotive mechanism of nitrogen-doped porous carbon from wasted lignin for Cr (VI) removal

Persistent environmental pollution by heavy metals, particularly Cr (VI), poses significant risks to ecosystems and human health due to its high toxicity and bioaccumulation potential. The development of high-performance, cost-effective adsorbents from sustainable materials remains a critical challenge in the field of Cr (VI) remediation. This study investigates the influence of pyrrolic-N (N-5) within nitrogen-doped hierarchical porous carbon (N-HPC) on its adsorption capacity. Results indicate that N-HPC variants with a higher N-5 content exhibit superior adsorption abilities. The optimal sample demonstrated an exceptional adsorption capacity of 386.2 mg/g for Cr (VI). Even after seven regeneration cycles, this N-HPC variant maintained a remarkable 77.8 % removal efficiency for Cr (VI), highlighting its robust stability and selectivity. The relationship between the physicochemical properties of N-5 and N-HPC was thoroughly examined, revealing that N-5 plays a crucial role in the adsorption process. Due to its high electronegativity, nitrogen-doping into the carbon framework generates a dipole moment, enhancing the electronegativity of N-HPC, altering its local electron density and polarity, increasing specific surface area, carbon defect density, and ion exchange capacity. These factors collectively contribute to significant improvements in pore filling, ion exchange efficiency, and electrostatic adsorption by N-HPC. The reduction complexation mechanism emerges as the dominant factor in the adsorption process. N-5 not only provides reducing electrons as an electron donor, facilitating the continuous conversion of Cr (VI) to Cr (III), but also acts as an adsorption active site, complexing Cr to the surface of N-HPC. This synergistic effect strengthens the reduction complexation, enhances adsorption performance, and improves the regeneration cycle and adsorption selectivity for Cr.

Recent advances in environmental and agricultural applications of hydrochars: A review

Hydrochar is a carbonaceous material that is generated through the process of hydrothermal carbonization (HTC) from biomass, which has garnered considerable attention in recent years owing to its potential applications in a diverse range of fields, such as environmental remediation and agriculture. Hydrochar is produced from a diverse range of biomass waste materials and retains exceptional properties, including high carbon content, stability, and surface area, making it an optimal candidate for various enviro-agricultural applications. Moreover, it delves into the production process of hydrochar, with explicit emphasis on the optimization of certain properties during the production of hydrochar from bio-waste. Furthermore, the potential of hydrochar as an adsorbent and catalyst support for heavy metals and dyes was extensively explored, along with a soil remediation potential that can improve the physical, chemical and biological properties of soil. This comprehensive review aims to provide a thorough overview of hydrochar with a particular focus on its production, properties, and prospective applications. The significance of hydrochar is accentuated and the growing need for alternative sources of energy and materials that are environmentally sustainable is highlighted in this paper. Besides, the consequence of hydrochar on soil properties such as water-holding capacity, nutrient retention, and total soil porosity, as well as its influence on soil chemical properties such as cation exchange capacity, electrical conductivity, and surface functionality is scrutinized.

Advances in Micro-/Mesopore Regulation Methods for Plant-Derived Carbon Materials

In recent years, renewable and clean energy has become increasingly important due to energy shortage and environmental pollution. Selecting plants as the carbon precursors to replace costly non-renewable energy sources causing severe pollution is a good choice. In addition, owing to their diverse microstructure and the rich chemical composition, plant-based carbon materials are widely used in many fields. However, some of the plant-based carbon materials have the disadvantage of possessing a large percentage of macroporosity, limiting their functionality. In this paper, we first introduce two characteristics of plant-derived carbon materials: diverse microstructure and rich chemical composition. Then, we propose improvement measures to cope with a high proportion of macropores of plant-derived carbon materials. Emphatically, size regulation methods are summarized for micropores (KOH activation, foam activation, physical activation, freezing treatment, and fungal treatment) and mesopores (H3PO4 activation, enzymolysis, molten salt activation, and template method). Their advantages and disadvantages are also compared and analyzed. Finally, the paper makes suggestions on the pore structure improvement of plant-derived carbon materials.