Nanocellulose constitutes a sustainable and biobased solution both as an efficient sorbent material for water treatment and as support for other inorganic nanomaterials with sorbent properties. Herein, we report the synthesis of a nanocomposite by deposition of in situ-generated silver nanoparticles (AgNPs) onto TEMPO-oxidized cellulose nanofibers (TOCNFs). Following an in-depth analytical investigation, we unveil for the first time the key role of AgNPs in enhancing the adsorption efficiency of TOCNF toward Cd²⁺ ions, chosen as model heavy metal contaminants. The obtained nanocomposite shows a value of Cd²⁺ sorption capacity at equilibrium from 150 mg L^-1 ion aqueous solutions of ∼116 mg g^-1 against the value of 78 mg g^-1 measured for TOCNF alone. A combination of field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) analyses suggests that Cd²⁺ ions are mainly adsorbed in the neighborhood of AgNPs. However, XPS characterization allows us to conclude that the role of AgNPs relies on increasing the exposure of carboxylic groups with respect to the original TOCNF, suggesting that these groups are still responsible for absorption. In fact, X-ray absorption spectroscopy (XAS) analysis of the Cd-K edge excludes a direct interaction between Ag⁰ and Cd²⁺, supporting the XPS results and confirming the coordination of the latter with carboxyl groups.

This work reports the preliminary results of the development of composite self-assembling membranes obtained by the combination of reduced graphene oxide (rGO) with commercial Degussa P25 titanium dioxide (TiO₂). The purpose is to demonstrate the possibility of combining, in the same self-standing material, the capability to treat wastewater containing both inorganic and organic pollutants by exploiting the established ability of rGO to capture metal ions together with that of TiO₂ to degrade organic substances. Moreover, this study also investigates the potential photocatalytic properties of tionite (TIO), to demonstrate the feasibility of replacing commercial TiO₂ with such waste-derived TiO₂-containing material, fulfilling a circular economy approach. Thus, rGO–TiO₂ and rGO–TIO composite membranes, 1:1 by weight, were prepared and characterized by SEM-EDX, XRD, thermogravimetry, as well as by Raman and UV-Vis spectroscopies to verify the effective and homogeneous integration of the two components. Then, they were tested towards 3-mg L⁻¹ aqueous synthetic solutions of Fe³⁺ and Cu²⁺ ions to evaluate their metal adsorption ability, with values of the order of 0.1–0.2 mmol g_membrane⁻¹, comparable or even slightly higher than those of pristine rGO. Finally, the ability of the composites to degrade a common organic pesticide, i.e., Imidacloprid^®, was assessed in preliminary photocatalysis experiments, in which maximum degradation efficiencies of 25% (after 3 h) for rGO–TiO₂ and of 21% (after 1 h) for rGO–TIO were found. The result of tionite-containing membranes is particularly promising and worthy of further investigation, given that the anatase content of tionite is roughly 1/6 of the one in commercial TiO₂.

Adsorption is one of the simplest and most cost-effective techniques for water decontamination. In this field, biochar has recently emerged as a promising alternative to traditional adsorbents, exhibiting a high surface area and affinity to metal ions, as well as often being waste-derived. Similarly, reduced graphene oxide (rGO) shows an excellent adsorption capacity. Having self-assembling properties, it has already been employed to obtain self-standing heavy-metal-adsorbing membranes. In this research, a novel self-standing membrane of biochar and rGO is presented. It was obtained through an eco-friendly method, consisting of the simple mechanical mixing of the two components, followed by vacuum filtration and mild drying. Vine pruning biochar (VBC) was employed in different rGO/biochar mass ratios, ranging from 1/1 to 1/9. The best compromise between membrane integrity and biochar content was achieved with a 4/6 proportion. This sample was also replicated using chestnut-shell-derived biochar. The composite rGO–biochar membranes were characterized through XRD, FTIR-ATR, TG-DTG, SEM-EDX, BET, ZP, particle dimension, and EPR analyses. Then, they were tested for metal ion adsorption with 10 mM Cu²⁺ and 100 mM Zn²⁺ aqueous solutions. The adsorption capacity of copper and zinc was found to be in the range of 1.51–4.03 mmol_Cu g⁻¹ and 18.16–21.99 mmol_Zn g⁻¹, respectively, at an acidic pH, room temperature, and contact time of 10 min. Interestingly, the composite rGO–biochar membranes exhibited a capture behavior between that of pure rGO and VBC.

Water pollution is one of the most concerning issues of our times, requiring the development of effective decontamination technologies, as remarked in UN Sustainable Development Goal 6. Photocatalysis represents a promising and sustainable strategy for water decontamination. Photocatalytic materials are able to mineralize organic pollutants and, compared to sorbent materials, offer the advantages of being reusable multiple times and being effective toward a broad range of contaminants. Titanium dioxide (TiO₂) is the most studied and used photocatalyst. However, its practical application is still restricted for two main reasons: i) TiO₂ large energy gap of ∼3.2 eV requires UV light for photocatalysis, implying a significant energy consumption, ii) TiO₂ is mostly used in the form of nanoparticles, which are hardly recoverable from water and tend to agglomerate, reducing their photocatalytic activity. Coupling TiO₂ with reduced graphene oxide (rGO) has already been proved as an effective strategy to obtain photoactive materials with lower bandgap. Nevertheless, as TiO₂, rGO/TiO₂ composites are mainly studied as slurries. In this research, we developed a green and facile methodology to immobilize TiO₂ in rGO/TiO₂ membranes and coatings, exploiting the self-assembling properties of rGO. Briefly, we obtained a rGO/TiO₂ aqueous dispersion by mixing TiO₂ nanopowder with a GO commercial dispersion, after controlled reduction with L-Ascorbic Acid at ambient temperature and pressure. Membranes were produced by vacuum filtration of the dispersion onto a PVDF filter, obtaining, to the best of our knowledge, the first self-standing rGO/TiO₂ membrane reported in the literature [1]. The same dispersion was also employed as coating for 3D porous structures. The deposition method consisted in dip-coating followed by mild drying. Polyurethane flexible foams of 10 PPI, 20 PPI and 30 PPI were used as supports. For both membranes and coatings, rGO:TiO₂ mass ratios of 1:1, 1:2 and 1:3 were considered. A higher content of TiO₂ was found to compromise rGO self-assembling properties and, consequently, membranes integrity. Membranes and coated foams were also tested for photodegradation of organic molecules in water. The pesticide Imidacloprid and the drug paracetamol were selected as representative organic pollutants. Degradation tests were performed in dynamic conditions, under UV-A and simulated solar light. Adsorption experiments in dark were also carried out. Preliminary results indicated a pollutants degradation of approximately 20%, obtained with the rGO/TiO₂ 1:1 membrane after 5 h under UV-A light. Despite being limited, this photocatalytic activity is notable, considering the low amount of TiO₂ contained in the sample. We may reach a higher photodegradation level with membranes containing a double or triple quantity of TiO₂. Coated foams appear particularly promising for their geometry, as it allows to maximize the interaction surface between water, light and photocatalyst, and to minimize shaded areas. [1] A. Basso Peressut et al., “Reduced Graphene Oxide/Waste-Derived TiO₂ Composite Membranes: Preliminary Study of a New Material for Hybrid Wastewater Treatment,” Nanomaterials, vol. 13, no. 6, Mar. 2023, doi: 10.3390/nano13061043.

Titanium dioxide (TiO₂) photocatalysis is a promising sustainable solution for water decontamination; however, the industrial application of TiO₂ is hindered by its wide band gap and high handling and recovery costs. This work proposes to overcome these issues by developing a composite coating of nanopowder TiO₂ and reduced graphene oxide (rGO) applied onto commercial polyurethane (PU) foams by means of a simple, low-energy dip-coating process designed to enhance pollutant adsorption and photocatalytic activity. The rGO-TiO₂ coating was optimized by exploring different surface pre-treatments of the PU foams, the deposition of rGO-TiO₂ multilayers, and the variation in the rGO-TiO₂ mass ratio (1:3, 1:4, and 1:5). The prepared materials were characterized by optical microscopy, SEM-EDX, DSC, and thermogravimetry, while the stability of the coating was preliminarily evaluated through ultrasonic tests. The water decontamination capability of the coated foams was investigated by adsorption and UV-Vis photodegradation tests using a 3 mg/L aqueous solution of Rhodamine B (RhB) as a model contaminant. The results demonstrated that the rGO-TiO₂ 1:3-coated samples achieved complete RhB photodegradation within 90 min, with a pseudo-first-order kinetic constant of 0.0446 1/min. Moreover, pre-treating the foam with a 3 M NaOH solution improved coating adhesion onto the PU substrate while maintaining comparable decontamination efficiency.