Amino-Functionalized Cellulose Nanofiber/Lignosulfonate New Aerogel Adsorbent for the Removal of Dyes and Heavy Metals from Wastewater

Adsorbents prepared from epoxy-based porous materials of microcrystalline cellulose for excellent adsorption of anionic and cationic dyes

It reported a porous material prepared from microcrystalline cellulose (MCC), to achieve rapid preparation of adsorbents. The porous material was characterized by several tools including 1H NMR, FTIR, XPS, and SEM. Two adsorbents were prepared and subjected to adsorption experiments. Dye adsorption experiments show that the adsorption driving is electrostatic interactions and the process is chemisorption. The maximum capacity of Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Tannins (MPT) reached 191.3 (Methylene blue), 123.7 mg g-1 (Rhodamine B), and Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Lysine (MPL) attained 425.8 (Methylene blue), 480.7 mg g-1 (Methyl orange). The results were followed the pseudo-second-order (PSO) and agreed with the Langmuir fit model. Adsorption-desorption cycling experiments further indicate that the adsorbent possesses outstanding reproducibility. At last, epoxidized bio-porous materials are positive in the preparation of dye adsorbents with critical adsorption properties.

Self-Assembled Aminated and TEMPO Cellulose Nanofibers (Am/TEMPO-CNF) Aerogel for Adsorptive Removal of Oxytetracycline and Chloramphenicol Antibiotics from Water

Antibiotics are used for the well-being of human beings and other animals. Detectable levels of antibiotics can be found in pharmaceutical, municipal, and animal effluents. Therefore, the treatment of antibiotic contaminated water is of great concern. In this study, we fabricated a sustainable aminated/TEMPO cellulose nanofiber (Am/TEMPO-CNF) aerogel to remove oxytetracycline (OTC) and chloramphenicol (CAP) from synthetic wastewater. The prepared aerogel was characterized using different analytical techniques such as elemental analysis, FTIR, TGA, SEM-EDS, and N2 adsorption-desorption isotherms. The characterization techniques confirmed the presence and interaction of quaternary amine -[NR3]+ and -COOH groups on Am/TEMPO-CNF with OTC and CAP, which validates the successful modification of Am/TEMPO-CNF. The adsorption process of the pollutants was examined as a function of solution pH, concentrations, reaction time, and temperatures. The maximum adsorption capacity was 153.13 and 150.15 mg/g for OTC and CAP, respectively. The pseudo-second order (PSO-2) was well fitted to both OTC and CAP, confirming the removal is via chemisorption. Hydrogen bonding and electrostatic attraction have been postulated as key factors in facilitating OTC and CAP adsorption according to spectroscopic studies. Energetically, the adsorption was spontaneous and endothermic for both pollutants. In conclusion, the efficient removal rate and excellent reusability of Am/TEMPO-CNF indicate the strong potential of the adsorbent for antibiotics' removal.

Bacterial Cellulose Aerogels Derived from Pineapple Peel Waste for the Adsorption of Dyes

Valorization of pineapple peel waste is an attractive research topic because of the huge quantities of this byproduct generated from pineapple processing industries. In this study, the extract from pineapple waste was collected to produce a hydrogel-like form containing bacterial cellulose fibers with a three-dimensional structure and nanoscale diameter by the Acetobacter xylinum fermentation process. The bacterial cellulose suspension was subsequently activated by freeze-drying, affording lightweight aerogels as potential adsorbents in wastewater treatment, in particular the adsorptive removal of organic dyes. Intensive tests were carried out with the adsorption of methylene blue, a typical cationic dye, to investigate the influence of adsorption conditions (temperature, pH, initial dye concentration, time, and experiment scale) and aerogel-preparation parameters (grinding time and bacterial cellulose concentration). The bacterial cellulose-based aerogels exhibited high adsorption capacity not only for methylene blue but also for other cationic dyes, including malachite green, rhodamine B, and crystal violet (28-49 mg/g). However, its activity was limited for most of the anionic dyes, such as methyl orange, sunset yellow, and quinoline yellow, due to the repulsion of these anionic dyes with the aerogel surface, except for the case of congo red. It is also an anionic dye but has two amine groups providing a strong interaction with the hydroxyl group of the aerogel via hydrogen bonding. Indeed, the aerogel has a substantially large congo red-trapping capacity of 101 mg/g. Notably, the adsorption process exhibited similar performances, upscaling the solution volume to 50 times. The utilization of abundant agricultural waste in the simple aerogel preparation to produce a highly efficient and biodegradable adsorbent is the highlight of this work.

Fabrication of Polyamide6/Polyaniline as an Effective Nano-web Membrane for Removal of Cr (VI) from Water and a Black Box Approach in Modeling of Adsorption Process

Chromium (Cr), as a highly toxic heavy metal ion, is still a severe environmental issue, although many research efforts have been put into its removal from water. Polyaniline (PANI), as a conductive polymer, demonstrated great capability in heavy metal adsorption due to its low cost, ease of synthesis, reversible redox behavior, and chemical stability. However, using PANI powder alone in heavy metal removal causes secondary pollution and aggregation in water. The PANI coating on a substrate could tackle this problem. In this study, polyaniline-coated polyamide6 (PA6/PANI) nano-web membrane was used for the removal of Cr(VI) in both adsorption and filtration-adsorption modes. The PA6/PANI nano-web membrane was fabricated via PA6 electrospinning followed by in-situ polymerization of the aniline monomer. The electrospinning condition of PA6 was optimized by the Taguchi method. The PA6/PANI nano-web membrane was characterized by FESEM, N2-adsorption/desorption, FT-IR, contact angle measurement, and tensile test. FT-IR and FESEM results demonstrated the successful synthesis of PA6/PANI nano-web and PANI homogeneous coating on PA6 nanofibers, respectively. The N2 adsorption/desorption results indicated that the pore volume of the PA6/PANI nano-web decreased by 39% compared to PA6 nanofibers. The tensile test and water contact angle studies showed that the coating of PANI on PA6 nanofibers improves the mechanical properties and hydrophilicity of PA6 by 10% and 25%, respectively. The application of PA6/PANI nano-web in the removal of Cr(VI) in batch and filtration modes exhibits excellent removal of 98.4 and 86.7%, respectively. A pseudo first order model well described the adsorption kinetics, and the adsorption isotherm was best fitted by the Langmuir model. A black box modeling approach based on artificial neural networks (ANN) was developed to predict the removal efficiency of the membrane. The superior performance of PA6/PANI in both adsorption and filtration-adsorption systems makes it a potential candidate for the removal of heavy metals from water on an industrial scale.

Application of Unsupervised Machine Learning for the Evaluation of Aerogels’ Efficiency towards Ion Removal—A Principal Component Analysis (PCA) Approach

Water scarcity is a global problem affecting millions of people. It can lead to severe economic, social, and environmental consequences. It can also have several impacts on agriculture, industry, and households, leading to a decrease in human quality of life. To address water scarcity, governments, communities, and individuals must work in synergy for the sake of water resources conservation and the implementation of sustainable water management practices. Following this urge, the enhancement of water treatment processes and the development of novel ones is a must. Here, we have investigated the potential of the applicability of “Green Aerogels” in water treatment’s ion removal section. Three families of aerogels originating from nanocellulose (NC), chitosan (CS), and graphene (G) are investigated. In order to reveal the difference between aerogel samples in-hand, a “Principal Component Analysis” (PCA) has been performed on the physical/chemical properties of aerogels, from one side, and the adsorption features, from another side. Several approaches and data pre-treatments have been considered to overcome any bias of the statistical method. Following the different followed approaches, the aerogel samples were located in the center of the biplot and were surrounded by different physical/chemical and adsorption properties. This would probably indicate a similar efficiency in the ion removal of the aerogels in-hand, whether they were nanocellulose-based, chitosan-based, or even graphene-based. In brief, PCA has shown a similar efficiency of all the investigated aerogels towards ion removal. The advantage of this method is its capacity to engage and seek similarities/dissimilarities between multiple factors, with the elimination of the shortcomings for the tedious and time-consuming bidimensional data visualization.

Synthesis of a Polymer Composite Based on a Modified Aminohumic Acid Tuned to a Sorbed Copper Ion

A composite based on amino-containing humic acid with the immobilization of multi-walled carbon nanotubes preliminarily tuned to a copper ion has been obtained. The synthesis of a composite pre-tuned for sorption by the local arrangement of macromolecular regions was obtained by introducing multi-walled carbon nanotubes and a molecular template into the composition of humic acid, followed by copolycondensation with acrylic acid amide and formaldehyde. The template was removed from the polymer network by acid hydrolysis. As a result of this tuning, the macromolecules of the composite “remember” conformations that are favorable for sorption, i.e., adsorption centers are formed in the polymer network of the composite, capable of repeated, highly specific interaction with the template and the highly selective extraction of target molecules from the solution. The reaction was controlled by the added amine and by the content of oxygen-containing groups. The structure and composition of the resulting composite were proven by physicochemical methods. A study of the sorption properties of the composite showed that after acid hydrolysis, the capacity increased sharply compared to a similar composite without tuning and a composite before hydrolysis. The resulting composite can be used as a selective sorbent in the process of wastewater treatment.