P-cresol, indole and indole-3-acetic acid (IAA) are catabolites of amino acids, formed by the gut microbiome. Most of these aromatic hydrocarbon derivatives are excreted by the colon before reentering the body to form “exogenous” protein-bound uremic toxins (PBUTs), which aggravate chronic kidney disease (CKD). Removal efficiencies of these PBUT precursors from model phosphate-buffered saline solutions by three different surface-modified nanoporous carbon adsorbents (PCs) were studied. PCs were produced by physicochemical and/or acid base activation of carbonized rice husk waste. Removal rates achieved values of 32–96% within a 3 h contact time. High micro/mesoporosity and surface chemistry of the N- and P-doped biochars were established by N₂ adsorption studies, SEM/EDS analysis, XPS and FT-IR-spectroscopy. The ammoxidized PC-N1 had the highest adsorption capacity (1.97 mmol/g for IAA, 2.43 mmol/g for p-cresol and 2.42 mmol/g for indole), followed by “urea-nitrified” PC-N2, whilst the phosphorylated PC-P demonstrated the lowest adsorption capacity for these solutes. These results do not correlate with the total pore volume values for PC-N2 (0.91 cm³/g) < PC-P (1.56 cm³/g) < PC-N1 (1.84 cm³/g), suggesting that other parameters such as the micropore volume (PC-N1 > PC-N2 > PC-P) and the interaction of surface chemical functional groups with the solutes play key roles in the adsorption mechanism. N-doped PC-N1 and PC-N2 have basic functional groups with higher affinity with acidic IAA and p-cresol. The ion-exchange mechanism of phenolic and indolic compound chemisorption by nanoporous carbon adsorbents, modified with surface N- and P-containing functional groups, has been proposed.

Alginate, as a natural polymer, has been widely used in the removal of pollutants in water due to its renewability, biocompatibility and abundant functional groups. However, it still has some limitations such as low specific surface area, poor mechanical strength and single function. Introducing metal oxides can effectively enhance their adsorption capacity and multi-functionality. Nevertheless, binary composites remain insufficient for treating complex water bodies. Therefore, the construction of structurally stable and functionally diverse ternary composites has become an important research direction. The review is based on alginate/metal oxide binary composites, analyzing their deficiencies in structural stability, nanoparticle dispersion and functional synergy. On this basis, the synthetic strategy and structural characteristics for constructing ternary composites by incorporating inorganic non-metallic frameworks, metal nanoparticles, porous carbon-based materials, and other natural polymers are discussed. The synergistic mechanism and performance enhancements of various components during pollutant removal are primarily summarized. Although the ternary composite system has a promising application prospect, it still faces challenges such as complex synthesis processes, insufficient interfacial stability, limited reusability, and poor adaptability to complex water bodies. Therefore, future efforts should focus on structural optimization, green preparation and resource utilization of waste materials to promote their engineering application and sustainable development in the field of water treatment.

Efficient removal of organic dye pollutants remains challenging owing to the limited adsorption capacity and poor reusability of most conventional adsorbents. Herein, rhombic-dodecahedral zeolitic imidazolate framework-67 (ZIF-67) was successfully fabricated via a facile aqueous strategy. The obtained ZIF-67 exhibited a high BET specific surface area of 1842.31 m² g⁻¹, with a maximum Langmuir adsorption capacity of 156.74 mg g⁻¹ toward methyl orange (MO). The adsorption kinetics successfully followed the pseudo-second-order model, and the material maintained 88.9% dye removal efficiency after six ethanol-regeneration cycles. Common inorganic anions (HCO₃⁻ and SO₄²⁻) presented a distinct inhibitory effect on MO adsorption. Static electrostatic potential calculations and hydrated molecular dynamics simulations were further adopted to reveal the interfacial adsorption behavior on typical ZIF-67 (100) and (110) facets. Based on equilibrated trajectories of 40–50 ps, both facet systems exhibited stable temperature and potential-energy fluctuations. The dominant Co–O(MO) radial distribution distances for (100) and (110) facets were determined to be 5.825 Å and 5.775 Å, respectively, both far beyond conventional short-range Co–O coordination lengths. The stronger radial ordering of the (110) facet suggests facet-sensitive interfacial organization, rather than direct Co–O chemical bonding during MO adsorption.

Rice husk (RH) is a renewable siliceous lignocellulosic waste providing a unique, greener and less toxic alternative to conventional synthetic polymeric precursors in the production of carbon-based materials for biomedical applications. In this work we studied the porous structure of RH-lignin-based activated carbon produced in the form of honeycomb carbon monoliths and assessed their potential as hemoadsorbents for blood purification in the treatment of patients with serious medical conditions, such as kidney failure and sepsis. To determine their clinical suitability for such an application, the hemocompatibility and cytotoxicity of the monoliths were investigated using the standard ISO guidelines. The monoliths did not cause any changes in the cell viability or cell lysis. High micro/mesoporosity and surface chemistry of the initial monolith-C, N- and P-doped nanostructured carbon honeycomb monoliths were established by low-temperature nitrogen adsorption (LTNA) studies, mercury porosimetry data (MIP), SEM/EDS analysis and FT-IR spectroscopy. The micro-mesoporous, activated carbon-based filtration/adsorbent prototype devices, in the form of three-dimensional (3D) carbon matrix, functionalized with ion-exchange amino- and phosphate groups and encased in polyolefin heat shrink cable sleeve, have been developed with the capacity to remove protein-bound uremic toxins (PBUTs), such us PCS and IS, as well as inflammatory cytokines (IL-6 and IL-8) from human plasma in a flowing model system. The ammoxidized monolith-N, derived from the monolith-C, had the highest removal efficiency (40.05% for PCS, and 28.4% for IL-6). By contrast, phosphorylated monolith-P demonstrated the highest removal efficiency (54.62% for IS, and 54.4% for IL-8), whilst the monolith-C has the lowest removal efficiency for these adsorbates. These results do not correlate with the LTNA and MIP study results, suggesting that the interaction of surface chemical functional groups with the solutes play key roles in the adsorption mechanism. The ion-exchange mechanism of PBUTs and inflammatory cytokine chemisorption by the monoliths, modified with surface N- and P-containing functional groups, has been proposed.

Microplastics (MPs) are pervasive emerging contaminants in freshwater and drinking-water systems, and conventional treatment processes may achieve insufficient removal of smaller MP fractions. Membrane filtration provides an effective barrier to MPs; however, commercial ceramic membranes can be relatively expensive. In this work, low-cost porous ceramic membranes were fabricated by extrusion-based three-dimensional (3D) printing of a kaolin–rice husk paste, followed by sintering at 1200 °C. The removal of model spherical polyethylene (PE) and irregularly shaped polyethylene terephthalate (PET) MPs across different particle-size fractions was evaluated using dead-end filtration and benchmarked against a commercial ceramic membrane. The 3D-printed membrane removed 58.3 ± 3.6% of 1–10 µm PE particles, while complete removal was achieved for the 75–90, 300–355, and 600–710 µm PE fractions. For PET, removal efficiencies of 80.8 ± 0.9%, 94.9 ± 1.8%, and 100% were obtained for the 10–45, 45–75, and 75–150 µm fractions, respectively. By comparison, the commercial membrane achieved 100% removal across all PE and PET fractions tested. The fabricated membrane had a modal pore size of 0.80 µm and an estimated cost of USD 2.98, compared with USD 54.45 for the commercial 0.45 µm membrane. Thus, the 3D-printed membrane effectively removed medium and large MP fractions, while its estimated fabrication cost was approximately 94.5% lower than the purchase cost of the commercial membrane used for comparison. Although its larger pore size resulted in incomplete removal of the smallest MP fractions, the combination of effective removal of larger MPs and substantially lower estimated fabrication cost demonstrates the potential of extrusion-based 3D printing as an alternative approach for producing ceramic membranes for MP removal.

Three-dimensional (3D) printing has emerged as an alternative fabrication approach for membrane development, offering increased flexibility in membrane geometry, architecture, and material integration. Conventional membrane fabrication methods enable large-scale production but suffer from limited tunability of internal architecture, constraints on material combinations, and challenges in reproducibility. In contrast, 3D printing enables precise layer-by-layer construction, customizable pore morphologies, and the incorporation of functional fillers, thereby expanding the design space for high-performance membranes. Polymeric membranes produced by fused deposition modeling, direct ink writing, digital light processing, and electrohydrodynamic techniques have demonstrated enhanced permeability and shape-defined porosity. Hybrid membranes integrating polymers with nanoparticles, ceramics, and catalytic materials exhibit improved mechanical stability, antifouling behavior, and multifunctionality. Ceramic membranes fabricated through 3D printing show advances in structural precision, high-temperature stability, and the integration of catalytic and photocatalytic functionalities for the removal of micropollutants, pharmaceuticals, and oil-in-water emulsions. Despite rapid progress, challenges remain, including the optimization of printing inks and rheology, multi-material co-printing, scale-up, and long-term fouling resistance. This review highlights opportunities for future development, particularly in hybrid catalytic systems, bio-derived raw materials, and digitally designed architectures. Overall, 3D printing represents a rapidly evolving fabrication approach that provides new opportunities for controlling membrane architecture and integrating functional materials for water treatment applications.