Development of a low-cost photocatalytic aerogel based on cellulose, carbon nanotubes, and TiO2 nanoparticles for the degradation of organic dyes

A hybrid ultra-light and porous cellulose aerogel was prepared by extracting cellulose fibers from white paper, alkali/urea as a crosslinker agent, and functionalized with CNTs and pure anatase TiO2 nanoparticles. Since CNTs work as mechanical reinforcement for aerogels, physical and mechanical properties were measured. Besides, since TiO2 acts as a photocatalyst for degrading dyes (rhodamine B and methylene blue), UV-Vis spectroscopy under UV light, visible light, and darkroom was used to evaluate the degradation process. XRD, FTIR, and TGA were employed to characterize the structural and thermal properties of the composite. The nanostructured solid network of aerogels was visualized in SEM microscopy confirming the structural uniformity of cellulose and TiO2-CNTs onto fibers. Moreover, CLSM was used to study the nano-porous network distribution of cellulose fibers and porosity, and the functionalization process in a detailed way. Finally, the photocatalytic activity of aerogels was evaluated by degradation of dye aqueous solutions, with the best photocatalytic removal (>97 %) occurring after 110 min of UV irradiation. In addition, HPLC-MS facilitated the proposed mechanism for the degradation of dyes. These results confirm that cellulose aerogels coupled with nanomaterials enable the creation of economic support to reduce water pollution with higher decontamination rates.

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports

This study explores the use of silica-coated bacterial nanocellulose (BC) scaffolds with bulk macroscopic yet nanometric internal pores/structures as functional supports for high surface area titania aerogel photocatalysts to design flexible, self-standing, porous, and recyclable BC@SiO₂-TiO₂ hybrid organic-inorganic aerogel membranes for effective in-flow photo-assisted removal of organic pollutants. The hybrid aerogels were prepared by sequential sol-gel deposition of the SiO₂ layer over BC, followed by coating of the resulting BC@SiO₂ membranes with a porous titania aerogel overlayer of high surface area using epoxide-driven gelation, hydrothermal crystallization, and subsequent supercritical drying. The silica interlayer between the nanocellulose biopolymer scaffold and the titania photocatalyst was found to greatly influence the structure and composition, particularly the TiO₂ loading, of the prepared hybrid aerogel membranes, allowing the development of photochemically stable aerogel materials with increased surface area/pore volume and higher photocatalytic activity. The optimized BC@SiO₂-TiO₂ hybrid aerogel showed up to 12 times faster in-flow photocatalytic removal of methylene blue dye from aqueous solution in comparison with bare BC/TiO₂ aerogels and outperformed most of the supported-titania materials reported earlier. Moreover, the developed hybrid aerogels were successfully employed to remove sertraline drug, a model emergent contaminant, from aqueous solution, thus further demonstrating their potential for water purification.

Direct Electron Transfer from Upconversion Graphene Quantum Dots to TiO2 Enabling Infrared Light-Driven Overall Water Splitting

Utilization of infrared light in photocatalytic water splitting is highly important yet challenging given its large proportion in sunlight. Although upconversion material may photogenerate electrons with sufficient energy, the electron transfer between upconversion material and semiconductor is inefficient limiting overall photocatalytic performance. In this work, a TiO₂/graphene quantum dot (GQD) hybrid system has been designed with intimate interface, which enables highly efficient transfer of photogenerated electrons from GQDs to TiO₂. The designed hybrid material with high photogenerated electron density displays photocatalytic activity under infrared light (20 mW cm⁻²) for overall water splitting (H₂: 60.4 μmol g_cat.⁻¹ h⁻¹ and O₂: 30.0 μmol g_cat.⁻¹ h⁻¹). With infrared light well harnessed, the system offers a solar-to-hydrogen (STH) efficiency of 0.80% in full solar spectrum. This work provides new insight into harnessing charge transfer between upconversion materials and semiconductor photocatalysts and opens a new avenue for designing photocatalysts toward working under infrared light.

Development of a novel three-dimensional magnetic polymer aerogel as an efficient adsorbent for malachite green removal

A novel three-dimensional (3D) magnetic bacterial cellulose nanofiber/graphene oxide polymer aerogel (MBCNF/GOPA) composed of bacterial cellulose nanofibers (BCNFs), Fe₃O₄ nanoparticles, graphene oxide (GO) nano-sheets, and polyvinyl alcohol (PVA) was developed by combining a facile filler-loaded networks method with a vacuum freeze-drying process for the removal of malachite green (MG) dye from aqueous solution. The influence of various factors on adsorption, including initial dye concentration, adsorbent dosage, contact time, temperature, and pH of dye solution, was then investigated. The adsorbent preserved a high adsorption capacity over a wide range of pH conditions. Moreover, the adsorption isotherms data fitted well with the Langmuir isotherm model with a maximum adsorption capacity of 270.27 mg g^-1. Adsorption kinetics followed the pseudo-second-order model, and the thermodynamic parameters showed that the adsorption of MG dye was feasible and endothermic in nature and occurred spontaneously. Therefore, owing to its demonstrated properties such as 3D interconnected porous structure, lightweight, large specific surface area, superparamagnetic behavior at room temperature, excellent adsorbent efficiency (93% removal) and also its simple and eco-friendly synthesis process, MBCNF/GOPA could be considered a promising candidate for removing cationic dye pollutants from aqueous solution, which can easily be collected from aqueous solution by a small magnet. MBCNF/GOPA also showed favorable reusability for MG removal in wastewater treatment, and its application in different water samples for the removal of MG dye molecules from "real" samples was successfully performed.

Facile synthesis of hierarchical CNF/SnO2/Ni nanostructures via self-assembly process as anode materials for lithium ion batteries

Hierarchical carbon nanofibre (CNF)/SnO₂/Ni nanostructures of graphitized carbon nanofibres and SnO₂ nanocrystallines and Ni nanocrystallines have been prepared via divalent tin-alginate assembly on polyacrylonitrile (PAN) fibres, controlled pyrolysis and ball milling. Fabrication is implemented in three steps: (1) formation of a tin-alginate layer on PAN fibres by coating sodium alginate on PAN in a water medium followed by polycondensation in SnCl₂ solution; (2) heat treatment at 450°C in a nitrogen atmosphere; (3) ball milling the mixture of CNF/SnO₂ fibres and Ni powder. The CNF/SnO₂/Ni nanocomposite exhibits good lithium ion storage capacity and cyclability, providing a facile and low-cost approach for the large-scale preparation of anode materials for lithium ion batteries.

Probing the Effects of Templating on the UV and Visible Light Photocatalytic Activity of Porous Nitrogen-Modified Titania Monoliths for Dye Removal

Porous nitrogen-modified titania (N-titania) monoliths with tailored morphologies were prepared using phase separation and agarose gel templating techniques. The doping and templating process were simultaneously carried out in a one-pot step using alcohol amine-assisted sol-gel chemistry. The amount of polymer used in the monoliths that were prepared using phase separation was shown to affect both the physical and optical properties: higher poly(ethylene glycol) content increased the specific surface area, porosity, and visible light absorption of the final materials. For the agarose-templated monoliths, the infiltration conditions affected the monolith morphology. A porous monolith with high surface area and the least shrinkage was obtained when the N containing alkoxide precursor was infiltrated into the agarose scaffolds at 60 °C. The effect of the diverse porous morphologies on the photocatalytic activity of N-titania was studied for the decomposition of methylene blue (MB) under visible and UV light irradiation. The highest visible light activity was achieved by the agarose-templated N-titania monolith, in part due to higher N incorporation. This sample also showed better UV activity, partly because of the higher specific surface area (up to 112 m(2) g(-1)) compared to the phase separation-induced monoliths (up to 103 m(2) g(-1)). Overall, agarose-templated, porous N-titania monoliths provided better features for effectively removing the MB contaminant.

Preparation of monolithic titania aerogels with high surface area by a sol–gel process combined surface modification

Monolithic titania (TiO₂) aerogels with high surface area were successfully synthesized by the sol–gel process combined surface modification, followed by ambient pressure drying.