Editorial for Special Issue “Carbon-Based Materials Applied in Water and Wastewater Treatment”

In the past decade, carbon nanostructures have emerged as one of the most rapidly advancing areas of research [1,2,3]. Novel carbon-based materials—such as activated carbon, carbon nanotubes, fullerenes, and graphene—exhibit superior mechanical, electrical, chemical, and optical properties, making them highly promising candidates for water and wastewater treatment applications [4,5,6,7]. Given that over two billion people worldwide face water scarcity, access to clean water remains one of the most critical global challenges [8,9,10]. At the same time, wastewater, often regarded as spent water, can be viewed as a valuable resource when properly treated and reused [11,12,13]. In addition, carbon-based nanomaterials—including activated carbon, single- and multi-walled carbon nanotubes [14], carbon quantum dots, and graphene or reduced graphene—have recently emerged as promising photocatalysts for removing organic and inorganic pollutants from water, owing to their abundance, high efficiency and selectivity, cost-effectiveness, and recyclability [15,16,17,18]. This Special Issue of C—Journal of Carbon Research compiles and highlights cutting-edge research on the design and application of carbon materials in water and wastewater treatment, emphasizing their remarkable adsorption capacity, high pollutant removal efficiency, multifunctional properties, structural stability, cost-effectiveness, and environmental sustainability. Collectively, these articles present a comprehensive overview of recent progress in developing innovative treatment strategies for aquatic environments through the use of carbon-based materials. The contributions included in this Special Issue are summarized as follows:

• Tasić et al. [19] present a study that highlights the potential of porous cellulose-based carbon fibers as effective adsorbents for chlorpyrifos removal form water.
• Ouyang et al. [20] developed “carbon-magnetic” Ni@SiC/CNF (C/Ni, C/SiC) composites, synthesized by electrostatic spinning, that efficiently degraded methylene blue under microwave radiation.
• An et al. [21] fabricated wood-derived carbon aerogel/Mg(OH)₂ bio-composites that were applied in relation to the adsorption and separation of cadmium ions.
• Guagliano et al. [22] produced chestnut waste-derived Fe-based photocatalysts for diclofenac degradation through a hybrid adsorption/photocatalytic process.
• Vamvuka et al. [23] explored magnesium-, zinc-, or calcium-modified nut residue biochar activated by nitrogen/steam for the adsorption of arsenate from wastewaters.
• Sengupta and Hussain [24] reported a review regarding advancements in graphene-based technologies for removing antibiotics from wastewater between 2016 and 2024.
• Li et al. [25] presented the research progress in relation to graphene-based adsorbents for wastewater treatment. Focus was given to the preparation, adsorption properties, and mechanisms of inorganic and organic pollutants.
• Guo et al. [26] synthesized TiO₂-modified g-C₃N₄ composites using one-pot calcination for the photocatalytic purification of orange-II-dye-polluted wastewater.
• Rahimi et al. [27] developed and fully characterized biomass-derived carbons for the removal of Cu²⁺ and Pb²⁺ from aqueous solutions. The biomass-based carbon adsorbents were produced from olive stones and almond shells using various activating agents including KOH, H₃PO₄, and ZnCl₂.
• Tavukcuoglu et al. [28] demonstrated a monohydrogen phosphate-selective carbon composite membrane electrode for soil water samples. This electrode is developed for on-site and real-time applications using a silver polyglutaraldehyde phosphate and carbon nanotube (CNT) matrix.
• Ledesma et al. [29] investigated the possible reuse of activated carbons used as filters in steam cycle treatment in a nuclear power plant.
• Puente Torres et al. [30] applied an innovative X-Ray absorption technology for the improved monitoring of the degradation and oxidation of granular activated carbon filters used in hospital water treatment systems.

As shown by the published papers contained in this Special Issue, recent advances in graphene synthesis have enabled the development of efficient graphene-based adsorbents for the rapid removal of heavy metals, dyes, pharmaceuticals, and other pollutants from wastewater. Their performance can be further enhanced through functionalization with specific groups or the incorporation of nanomaterials. For instance, functionalized graphene materials, as well as graphene combined with metal oxides or polymers, show improved efficiency in antibiotic removal via adsorption and photocatalytic mechanisms. Moreover, biomass-based carbon adsorbents produced from agricultural waste, i.e., olive stones or chestnut waste and cellulose-based porous carbon fibers, are promising materials for the removal of heavy metals and pharmaceutical substances from waste. Finally, carbon-based materials were applied for the photocatalytic purification of water and wastewater.

We sincerely thank all contributing authors and the reviewers for their excellent efforts and insights. We also extend our appreciation to the editorial team of C for their continuous support. We hope that this Special Issue will serve as a valuable reference for researchers in the fields of carbon-based materials applied in water and wastewater treatment.