Cellulose nanomaterials and their hybrid structures in the removal of aqueous micropollutants

Abstract Micropollutants are synthetic or natural organic compounds that are present in the environment at very low concentrations. They end up in nature via industrial and domestic wastewaters, for example, and are suspected of having adverse effects on the environment and biota. Conventional wastewater treatment processes fail to remove them completely and therefore there is an urgent need for new technical solutions that improve the treatment processes at wastewater treatment plants and/or at the point source. Biobased cellulose nanomaterials provide an environmentally friendly option for micropollutant removal from water due to their inherent properties, such as customizability and high reactive surface area. In this work, a urea–lithium chloride (LiCl) deep eutectic solvent (DES)-based pretreatment for the preparation of anionic cellulose nanomaterials was developed. Moreover, three different concepts (batch, precipitation, filtration) were developed where an investigation was made of the suitability of charged cellulosic nanomaterials prepared with DES pretreatments for the removal of ionizable micropollutants (pharmaceutical, dyes), either alone or in combination with natural inorganic materials. According to the results, urea–LiCl DES acted as a non-reactive solvent that swelled the fiber matrix and allowed carboxylation of the fiber surface with succinic anhydride. Based on concept testing, anionic and cationic cellulosic nanomaterials were capable of binding ionizable micropollutants to themselves. Increasing the dose of cellulosic nanomaterial improved the removal of the micropollutant but complicated the separation of the exhausted material from the treated water. The intensity of the interaction was mainly dependent on the pH of the solution, which affected the charge of both the adsorbent and the micropollutant. In addition, combining the cellulosic nanomaterial with natural inorganic particles or materials facilitated the separation of both from the treated water and in some cases, improved the purification result. This work provides new insights into the interaction of organic compounds and cellulose nanoparticles in different removal concepts and demonstrates the suitability of charged cellulosic nanomaterials and their hybrid structures for reducing ionizable micropollutants from aqueous solutions.Tiivistelmä Mikropollutantit ovat synteettisiä tai luonnollisia orgaanisia yhdisteitä, joita esiintyy ympäristössä erittäin alhaisissa pitoisuuksissa. Ne päätyvät luontoon esimerkiksi teollisuuden ja kotitalouksien jätevesien mukana, jossa niiden epäillään aiheuttavan haitallisia vaikutuksia ympäristöön ja eliöstöön. Perinteiset jätevedenpuhdistusprosessit eivät sellaisenaan poista mikropollutantteja tehokkaasti, joten uusien teknologioiden kehitys jätevesien esi- tai jatkokäsittelyä varten on tarpeen. Biopohjaiset selluloosananomateriaalit ovat ympäristöystävällinen vaihtoehto mikropollutanttien poistoon vedestä johtuen niiden luontaisista ominaisuuksista, kuten muokattavuudesta ja suuresta reaktiivisesta pinta-alasta. Tässä työssä kehitettiin ureasta ja litiumkloridista (LiCl) muodostuvaan syväeutektiseen liuottimeen (DES) pohjautuva esikäsittely anionisten selluloosananomateriaalien valmistukseen. Lisäksi työssä kehitettiin kolme eri konseptia (panos, saostus, suodatus), joissa tutkittiin erilaisten DES-esikäsittelyiden avulla valmistettujen varauksellisten selluloosananomateriaalien soveltuvuutta ionisoituvien mikropollutanttien (lääkeaine, väriaineet) poistoon joko yksinään, tai yhdistettynä luonnosta saataviin epäorgaanisiin materiaaleihin. Tulosten perusteella urea–LiCl DES toimi ei-reaktiivisena liuottimena, joka turvotti kuitumatriisia ja mahdollisti kuidun pinnan karboksylaation meripihkahappoanhydridillä. Konseptitestauksien perusteella anioniset ja kationiset selluloosananomateriaalit kykenivät sitomaan ionisoituvia mikropollutantteja itseensä. Selluloosananomateriaalin määrän kasvattaminen paransi mikropollutantin poistumaa, mutta vaikeutti materiaalin erotusta käsitellystä vedestä. Vuorovaikutuksen voimakkuus oli pääsääntöisesti riippuvainen liuoksen pH:sta, joka vaikutti sekä adsorbentin että mikropollutantin varaukseen. Lisäksi havaittiin, että selluloosananomateriaalin yhdistäminen luonnosta saataviin epäorgaanisiin partikkeleihin tai materiaaleihin edesauttoi molempien erotusta käsitellystä vedestä ja jossain tapauksissa paransi puhdistustulosta. Tämä työ tarjoaa uutta tietoa orgaanisten yhdisteiden ja selluloosananopartikkeleiden vuorovaikutuksesta erilaisissa poistokonsepteissa, sekä osoittaa varauksellisten selluloosananomateriaalien ja niiden hybridirakenteiden soveltuvuuden ionisoituvien mikropollutanttien vähentämiseen vesiliuoksista

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat) from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox) and from similar sunspot conditions (about 1.5 years before the sunspot minimum) providing an excellent set of data to study the MLT and Kp dependence of parameters with high temporal and spatial resolution. All the parameters show a clear MLT variation, which is different for low and high Kp conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for Kp≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity. An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (Kp<3 and Kp≥3). In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to auroral arcs as a result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004) In addition, a part of the anticorrelation may come from polarization effects inside high-conductance regions, e.g. auroral arcs. These observations confirm the speculated effect of small scale electrodynamics, which is not included in most of the global modeling efforts of Joule heating rate

Anionically stabilized cellulose nanofibrils through succinylation pretreatment in urea–lithium chloride deep eutectic solvent

Abstract Deep eutectic solvents (DESs) are green chemicals that have the potential to replace traditional solvents in chemical reactions. In this study, urea–LiCl DES was used successfully as a reaction medium in the anionic functionalization of wood cellulose with succinic anhydride. The effects of reaction temperature and time on the carboxyl content and yield were evaluated. The analyses of the degree of polymerization and crystallinity revealed that the DES was a nondegrading and nondissolving reaction medium. Three samples with the highest carboxyl contents were further nanofibrillated with a microfluidizer to diameters of 2–7 nm, as observed by atomic force microscopy. Samples treated at 70–80 °C for 2 h gave the best outcome and resulted in highly viscose and transparent gels. The sample treated at 90 °C contained larger nanoparticles and larger aggregates owing to the occurrence of possible side reactions but resulted in better thermal stability

Rapid uptake of pharmaceutical salbutamol from aqueous solutions with anionic cellulose nanofibrils:the importance of pH and colloidal stability in the interaction with ionizable pollutants

Abstract Micropollutants escaping conventional wastewater treatment processes pose a threat to biota and the environment. Amongst micropollutants, small and ionizable organic compounds are particularly challenging, since their removal depends significantly on prevailing conditions. In this study, anionic cellulose nanofibrils (CNFs) were shown to perform as promising adsorbents for an ionizable pharmaceutical, salbutamol. The adsorbents were produced from wood cellulose through succinylation pretreatment in urea-LiCl deep eutectic solvent (DES), followed by a nanofibrillation procedure. The impact of pH, contact time, salbutamol concentration, and adsorbent dose on salbutamol uptake were investigated in batch adsorption studies. Based on the results, the chemical modification of cellulose significantly enhanced the adsorption of salbutamol. The adsorption efficiency was mainly dependent on the charge and colloidal stability of the anionic nanofibril suspension rather than the charge of salbutamol, because the adsorption was considerably improved at pH > 7 due to the deprotonation of the cellulose carboxyl groups. The experimental maximum adsorption capacity was 196 mg/g. This study highlights the potential of cellulose nanomaterial adsorbents and the importance of controlling the charge of the adsorbent material when developing solutions for ionizable micropollutant removal

Surface modification of cured inorganic foams with cationic cellulose nanocrystals and their use as reactive filter media for anionic dye removal

Abstract In this work, a surface cationized inorganic–organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H₂O₂ as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5–10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs

Efficient entrapment and separation of anionic pollutants from aqueous solutions by sequential combination of cellulose nanofibrils and halloysite nanotubes

Abstract The synergistic combination of different nanomaterials for improved performance in environmental applications such as the removal of aqueous micropollutants has attracted increasing interest in recent years. This study demonstrates a novel sequential adsorption–aggregation concept that harnesses tubular halloysite nanotubes (HNTs) and flexible cellulose nanofibrils (CNFs) for the removal of a small, anionic dye molecule, chrome azurol S, from water. Hollow HNTs were first allowed to interact with the aqueous dye solution, after which the dye-loaded colloidal nanotubes were aggregated and separated from the water phase with cationized CNFs. The combination of 25 mg CNFs with 1 g HNTs at pH 7 resulted in efficient removal of dye (80%) and turbidity (~100%) and the removal of dye was further promoted in more acidic conditions (within the pH range of 6–8.5) because of the attractive electrostatic interactions. Cationic CNFs not only enabled the separation of dye-loaded clay particles from the water phase through a rapid aggregation but also participated in dye removal through adsorption (~20%). In comparison with nano-sized HNTs, the dye removal performance of micro-sized and chemically similar kaolin was poor (43%). Given the good availability of both HNTs and CNFs and the low consumption of the more expensive component (i.e., CNFs) in the process, the concept is straightforward, readily applicable, environmentally benign, and potentially cost-effective

Features of the Z-scoring method in graphical two-dimensional web surveys: the case of ZEF

Survey, Web survey, Two-dimensionality, Standardization, Comparing,