Nanoporous air filtering systems made from renewable sources: benefits and challenges

There is a crucial need for air purification systems due to increasing air contamination, while conventional air-filtering materials face challenges in eliminating gaseous and particulate pollutants. This review examines the development and characteristics of nanoporous polymeric materials developed from renewable resources, which have rapidly advanced in recent years. These materials offer more sustainable alternatives for nanoporous structures made out of conventional polymers and significantly impact the properties of porous polymers. The review explores nanoporous materials' production from renewable sources, filtering mechanisms, physicochemical makeup, and sensing capabilities. The recent advancements in this field aim to enhance production techniques, lower pressure drop, and improve adsorption efficiency. Currently, supporting approaches include using adsorbent layers and binders to immobilize nanoporous materials. Furthermore, the prospects and challenges of nanoporous materials obtained from renewable sources used for air purification are discussed.

Triazine-Based Porous Organic Polymers: Synthesis and Application in Dye Adsorption and Catalysis

The scientific community has been developing promising materials to increase the sustainability and efficiency of production processes and pollutant environmental remediation strategies. Porous organic polymers (POPs) are of special interest, as they are insoluble custom-built materials at the molecular level, endowed with low densities and high stability, surface areas, and porosity. This paper describes the synthesis, characterization, and performance of three triazine-based POPs (T-POPs) in dye adsorption and Henry reaction catalysis. T-POPs were prepared by a polycondensation reaction between melamine and a dialdehyde (terephthalaldehyde (T-POP1) or isophthalaldehyde derivatives with a hydroxyl group (T-POP2) or both a hydroxyl and a carboxyl group (T-POP3)). The crosslinked and mesoporous polyaminal structures, with surface areas between 139.2 and 287.4 m² g^-1, positive charge, and high thermal stability, proved to be excellent methyl orange adsorbents, removing the anionic dye with an efficiency >99% in just 15-20 min. The POPs were also effective for methylene blue cationic dye removal from water, reaching efficiencies up to ca. 99.4%, possibly due to favorable interactions via deprotonation of T-POP3 carboxyl groups. The modification of the most basic polymers, T-POP1 and T-POP2, with copper(II) allowed the best efficiencies in Henry reactions catalysis, leading to excellent conversions (97%) and selectivities (99.9%).

Comparison between nanocellulose-polyethylenimine composites synthesis methods towards multiple water pollutants removal: A review

Nanocellulose/polyethylenimine composites have attracted growing attention due to their versatility as new materials for application in different fields. Water remediation is one of the traditional applications of these composites and their investigation as adsorbents for single water pollutants is well established. However, most water resources such as rivers, lakes, and even oceans contain complex mixtures of pollutants. Despite several recently published reviews on water purification technology, they only focused on these material as single pollutant removers and hardly mentioned their capacity to simultaneously recover multiple pollutants. Therefore, there is still a gap in the archived literature considering nanocellulose/polyethylenimine composites targeting water remediation with multiple water pollutants. In this review, methods for synthesizing such composites are classified and compared according to the mechanism of reactions, such as chemical crosslinking and physical adsorption, while outlining advantages and limitations. Then, the water pollutants mainly targeted by those composites are discussed in detail to expound the relationship between the synthesis method and the type and adsorption capacity. Finally, the last section presents challenges and opportunities of these nanocellulose/polyethylenimine composites as emerging sorbents for sustainable multiple water pollutants purification technologies. This review aims to lay out the basis for future developments of these composites for multiple water pollutants.

Pd-Loaded Cellulose NanoSponge as a Heterogeneous Catalyst for Suzuki-Miyaura Coupling Reactions

The (eco)design and synthesis of durable heterogeneous catalysts starting from renewable sources derived from biomass waste represents an important step for reducing environmental impacts of organic transformations. Herein, we report the efficient loading of Pd(II) ions on an eco-safe cellulose-based organic support (CNS), obtained by thermal cross-linking between TEMPO-oxidized cellulose nanofibers and branched polyethyleneimine in the presence of citric acid. A 22.7% w/w Pd-loading on CNS was determined by the ICP-OES technique, while the metal distribution on the xerogel was evidenced by SEM-EDS analysis. XPS analysis confirmed the direct chelation of Pd(II) ions by means of the high number of amino groups present in the network, so that further functionalization of the support with specific ligands was not necessary. The new composite turned to be an efficient heterogeneous pre-catalyst for promoting Suzuki-Miyaura coupling reactions between aryl halides and phenyl boronic acid in water, obtaining yields higher than 90% in 30 min, by operating in a microwave reactor at 100 °C and with just 2% w/w of CNS-Pd catalyst with respect to aryl halides (4.5‱ for Pd). At the end of first reaction cycle, Pd(II) ions on the support resulted in being reduced to Pd(0) while maintaining the same catalytic efficiency. In fact, no leaching was observed at the end of reactions, and five cycles of recycling and reusing of CNS-Pd catalyst provided excellent results in terms of yields and selectivity in the desired products.

Cellulose for the Production of Air-Filtering Systems: A Critical Review

The control of airborne contaminants is of great interest in improving air quality, which has deteriorated more and more in recent years due to strong industrial growth. In the last decades, cellulose has been largely proposed as suitable feedstock to build up eco-friendly materials for a wide range of applications. Herein, the issue regarding the use of cellulose to develop air-filtering systems is addressed. The review covers different cellulose-based solutions, ranging from aerogels and foams to membranes and films, and to composites, considering either particulate filtration (PM₁₀, PM_2.5, and PM_0.3) or gas and water permeation. The proposed solutions were evaluated on the bases of their quality factor (QF), whose high value (at least of 0.01 Pa^-1 referred to commercial HEPA (high-efficiency particulate air) filters) guarantees the best compromise between high filtration efficiency (>99%) and low pressure drop (<1 kPa/g). To face this aspect, we first analyzed the different morphological aspects which can improve the final filtration performance, outlining the importance on using nanofibers not only to increase surface area and to modulate porosity in final solutions, but also as reinforcement of filters made of different materials. Besides the description of technological approaches to improve the mechanical filtration, selected examples show the importance of the chemical interaction, promoted by the introduction of active functional groups on cellulose (nano)fibers backbone, to improve filtration efficiency without reducing filter porosity.

Zinc- and Copper-Loaded Nanosponges from Cellulose Nanofibers Hydrogels: New Heterogeneous Catalysts for the Synthesis of Aromatic Acetals

Herein we report the synthesis of cellulose-based metal-loaded nano-sponges and their application as heterogeneous catalysts in organic synthesis. First, the combination in water solution of TEMPO-oxidized cellulose nanofibers (TOCNF) with branched polyethyleneimine (bPEI) and citric acid (CA), and the thermal treatment of the resulting hydrogel, leads to the synthesis of an eco-safe micro- and nano-porous cellulose nano-sponge (CNS). Subsequently, by exploiting the metal chelation characteristics of CNS, already extensively investigated in the field of environmental decontamination, this material is successfully loaded with Cu (II) or Zn (II) metal ions. Efficiency and homogeneity of metal-loading is confirmed by scanning electron microscopy (SEM) analysis with an energy dispersive X-ray spectroscopy (EDS) detector and by inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis. The resulting materials perform superbly as heterogeneous catalysts for promoting the reaction between aromatic aldehydes and alcohols in the synthesis of aromatic acetals, which play a fundamental role as intermediates in organic synthesis. Optimized conditions allow one to obtain conversions higher than 90% and almost complete selectivity toward acetal products, minimizing, and in some cases eliminating, the formation of carboxylic acid by-products. ICP-OES analysis of the reaction medium allows one to exclude any possible metal-ion release, confirming that catalysis undergoes under heterogeneous conditions. The new metal-loaded CNS can be re-used and recycled five times without losing their catalytic activity.

Synthesis and Application of Cellulose-Polyethyleneimine Composites and Nanocomposites: A Concise Review

Cellulose/polyethyleneimine composites have increasingly attracted the attention of scientific community, devoted to the design and development of new synthetic strategies and materials for different application fields. In this review, after introducing the main characteristics of the two polymeric components, we provide in the second section a critical overview on the main protocols for the synthesis of these composites, considering both the several cellulose sources and forms, and the different cross-linkers and cross-linking procedures developed for this purpose, outlining advantages and limits for the reported approaches. The last section analyses the principal results obtained in different application fields. A wide discussion is dedicated to the principal use of cellulose/polyethyleneimine composites as sorbents for water remediation from heavy metal ions and organic contaminants. Subsequently, we introduce the literature describing the use of these composites, functionalized appropriately, where necessary, as drug delivery systems, sensors, and heterogeneous catalysts for organic reactions. Finally, after a brief description of other random applications, we furnish a personal analysis of actual limits and potentialities for these systems.