Preparation and characterization of cellulose/N,N’-methylene bisacrylamide/graphene oxide hybrid hydrogels and aerogels

Novel Photothermal Graphene-Based Hydrogels in Biomedical Applications

In the last decade, photothermal therapy (PTT) has attracted tremendous attention because it is non-invasive, shows high efficiency and antibacterial activity, and minimizes drug side effects. Previous studies demonstrated that PTT can effectively inhibit the growth of bacteria and promotes cell proliferation, accelerating wound healing and tissue regeneration. Among different NIR-responsive biomaterials, graphene-based hydrogels with photothermal properties are considered as the best candidates for biomedical applications, due to their excellent properties. This review summarizes the current advances in the development of innovative graphene-based hydrogels for PTT-based biomedical applications. Also, the information about photothermal properties and the potential applications of graphene-based hydrogels in biomedical therapies are provided. These findings provide a great potential for supporting their applications in photothermal biomedicine.

Cellulose Dissolution, Modification, and the Derived Hydrogel: A Review

The cellulose-based hydrogel has occupied a pivotal position in almost all walks of life. However, the native cellulose can not be directly used for preparing hydrogel due to the complex non-covalent interactions. Some literature has discussed the dissolution and modification of cellulose but has yet to address the influence of the pretreatment on the as-prepared hydrogels. Firstly, the "touching" of cellulose by derived and non-derived solvents was introduced, namely, the dissolution of cellulose. Secondly, the "conversion" of functional groups on the cellulose surface by special routes, which is the modification of cellulose. The above-mentioned two parts were intended to explain the changes in physicochemical properties of cellulose by these routes and their influences on the subsequent hydrogel preparation. Finally, the "reinforcement" of cellulose-based hydrogels by physical and chemical techniques was summarized, viz., improving the mechanical properties of cellulose-based hydrogels and the changes in the multi-level structure of the interior of cellulose-based hydrogels.

A Comprehensive Review of Polysaccharide-Based Hydrogels as Promising Biomaterials

Polysaccharides have emerged as a promising material for hydrogel preparation due to their biocompatibility, biodegradability, and low cost. This review focuses on polysaccharide-based hydrogels' synthesis, characterization, and applications. The various synthetic methods used to prepare polysaccharide-based hydrogels are discussed. The characterization techniques are also highlighted to evaluate the physical and chemical properties of polysaccharide-based hydrogels. Finally, the applications of SAPs in various fields are discussed, along with their potential benefits and limitations. Due to environmental concerns, this review shows a growing interest in developing bio-sourced hydrogels made from natural materials such as polysaccharides. SAPs have many beneficial properties, including good mechanical and morphological properties, thermal stability, biocompatibility, biodegradability, non-toxicity, abundance, economic viability, and good swelling ability. However, some challenges remain to be overcome, such as limiting the formulation complexity of some SAPs and establishing a general protocol for calculating their water absorption and retention capacity. Furthermore, the development of SAPs requires a multidisciplinary approach and research should focus on improving their synthesis, modification, and characterization as well as exploring their potential applications. Biocompatibility, biodegradation, and the regulatory approval pathway of SAPs should be carefully evaluated to ensure their safety and efficacy.

Konjac Glucomannan Aerogels Modified by Hydrophilic Isocyanate and Expandable Graphite with Excellent Hydrolysis Resistance, Mechanical Strength, and Flame Retardancy

At present, biomass foamlike materials are a hot research topic, but they need to be improved urgently due to their defects such as large size shrinkage rate, poor mechanical strength, and easy hydrolysis. In this study, the novel konjac glucomannan (KGM) composite aerogels modified with hydrophilic isocyanate and expandable graphite were prepared by a facile vacuum freeze-drying method. Compared with the unmodified KGM aerogel, the volume shrinkage of the KGM composite aerogel (KPU-EG) decreased from 36.36 ± 2.47% to 8.64 ± 1.46%. Additionally, the compressive strength increased by 450%, and the secondary repeated compressive strength increased by 1476%. After soaking in water for 28 days, mass retention after hydrolysis of the KPU-EG aerogel increased from 51.26 ± 2.33% to more than 85%. The UL-94 vertical combustion test showed that the KPU-EG aerogel can achieve a V-0 rating, and the limiting oxygen index (LOI) value of the modified aerogel can reach up to 67.3 ± 1.5%. To sum up, the cross-linking modification of hydrophilic isocyanate can significantly improve the mechanical properties, flame retardancy, and hydrolysis resistance of KGM aerogels. We believe that this work can provide excellent hydrolytic resistance and mechanical properties and has broad application prospects in practical packaging, heat insulation, sewage treatment, and other aspects.

A facile approach to cellulose/multi-walled carbon nanotube gels-Structure, formation process and adsorption to methylene blue

In view of the deficiencies in the preparation of cellulose gels, such as, cumbersome process, harsh conditions, high consumption of chemicals, secondary pollution caused by side reactions, this work reports a facile approach to make cellulose/multi-walled carbon nanotube (MWCNTs) hydrogels and aerogels via mixing cellulose with N,N'-methylene bisacrylamide (MBA) and MWCNTs in NaOH/urea/H₂O aqueous solution. The gels were revealed to be formed by an addition reaction between the double bonds of MBA and the hydroxyl groups of cellulose and the intermolecular interactions between cellulose and MWCNTs. The preparation process can be realized at room temperature and atmospheric pressure without the intervention of ultrasonic dispersion, catalyst and initiator. The gelation time, puncture strength and water retention ability of the hydrogels were investigated. Results showed that, compared with pure cellulose hydrogel, cellulose/MWNCTs hydrogels have obviously shorter sol-gel transition time (124-129.2 min), higher puncture strength (29.6022-34.2854 KPa) and water retention ability (274.2619-301.7291 g/g). Cellulose/MWCNTs aerogels possessed three dimensional network with macroporous structure (about 500 μm), low density (0.00546-0.00557 g/cm³), high porosity (99.6360-99.6426 %), good thermal stability (242 °C) and certain absorbency to methylene blue (233.2901-242.1122 mg/g).

Machine Learning of Microscopic Ingredients for Graphene Oxide/Cellulose Interaction

Understanding the role of microscopic attributes in nanocomposites allows one to control and, therefore, accelerate experimental system designs. In this work, we extracted the relevant parameters controlling the graphene oxide binding strength to cellulose by combining first-principles calculations and machine learning algorithms. We were able to classify the systems among two classes with higher and lower binding energies, which are well defined based on the isolated graphene oxide features. Using theoretical X-ray photoelectron spectroscopy analysis, we show the extraction of these relevant features. In addition, we demonstrate the possibility of refined control within a machine learning regression between the binding energy values and the system's characteristics. Our work presents a guiding map to control graphene oxide/cellulose interaction.

Converting Complex Sewage Containing Oil, Silt, and Bacteria into Clean Water by a 3D Printed Multiscale and Multifunctional Filter

The exacerbating water pollution and water resource shortage pose a great danger to human health and make it imperative to recycle and treat the sewage. In this study, a direct-writing three-dimensional (3D) printing technology was adopted to prepare a 3D sodium alginate (SA)/graphene oxide (GO)/Ag nanoparticle (AgNP) aerogel (SGA), aiming to turn the complex sewage containing oil, silt, and bacteria into clean water depending only on gravity separation. The physicochemical properties and surface structure of the synthesized SGA were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The swelling rate, mechanical properties, antibacterial properties, oil and water separation effect, and durable stability of the filter membrane were also investigated to verify the versatility of the SGA filter. The results showed that GO helped improve the mechanical properties of the printed filter to withstand water impact during the filtration process. The printed filter had a well-designed and multiscale gradient pore structure, which can effectively intercept particles with different sizes to separate the silt from water, and the turbidity of the filtered water can be reduced from 60 to 1 nephelometric turbidity unit (NTU). The presence of SA endowed the printed filter with hydrophilic and oleophobic behaviors, which can effectively separate various kinds of oils from water. The uniform distribution of AgNPs in the filter produced via a facile and green reduction of SA facilitated the efficient bactericidal ability of the printed filter during the filtration process; meanwhile, the lower release concentration of Ag ions ensured drinking safety. What is more, the filter can be easily produced on a large scale and used for different sewage treatment situations with a durable stability of over 30 days. Taken together, the printed SGA filter has a broad application prospect in complex sewage treatment, providing a special solution for sewage treatment in poverty areas.

In-situ formed Cyclodextrin-functionalized graphene oxide / poly (N-isopropylacrylamide) nanocomposite hydrogel as an recovery adsorbent for phenol and microfluidic valve

Phenolic compounds are important industrial raw materials for various industrial applications, but phenol-containing wastewater creates significant environmental and biological hazards. To address these issues, a three-dimensional network graphene oxide-cyanoethyltriethoxysilane-β-cyclodextrin/poly (N-isopropylacrylamide) (GO-CTES-β-CD/PNIPAM) nanocomposite hydrogel as a phenol recovery adsorbent is prepared herein by in-situ polymerization. Double graft modification on the graphene oxide (GO) via the silane coupling agent 2-cyanoethyltriethoxysilane (CTES) and single (6-tetraethylenepentamine-6-deoxy)-β-cyclodextrin (NH-β-CD) compensated the loss of the active sites on both GO and N-isopropylacrylamide (NIPAM), and the hydrogel shows excellent mechanical properties as the chemical crosslinking and physical entanglement of the two components. Consequently, the composite hydrogel achieved an adsorption capacity of 131.64 mg·g^-1 for the common environmental toxin 4-NP. After five repeated adsorption-desorption cycles, the hydrogel retained 74% of the initial 4-NP removal ratio. The adsorption results followed pseudo-first-order kinetics, corresponding to heterogeneous multilayer adsorption, which was regulated by a combination of surface adsorption and intra-particle diffusion mechanisms. In general, the nanocomposite hydrogel shows promising application in the field of recycling phenols from wastewater. Also, high photothermal conversion and temperature-sensitive properties are also demonstrated, which makes the hydrogel possessing great potential to be applied in smart microvalves.

Graphene Integrated Hydrogels Based Biomaterials in Photothermal Biomedicine

Recently, photothermal therapy (PTT) has emerged as one of the most promising biomedical strategies for different areas in the biomedical field owing to its superior advantages, such as being noninvasive, target-specific and having fewer side effects. Graphene-based hydrogels (GGels), which have excellent mechanical and optical properties, high light-to-heat conversion efficiency and good biocompatibility, have been intensively exploited as potential photothermal conversion materials. This comprehensive review summarizes the current development of graphene-integrated hydrogel composites and their application in photothermal biomedicine. The latest advances in the synthesis strategies, unique properties and potential applications of photothermal-responsive GGel nanocomposites in biomedical fields are introduced in detail. This review aims to provide a better understanding of the current progress in GGel material fabrication, photothermal properties and potential PTT-based biomedical applications, thereby aiding in more research efforts to facilitate the further advancement of photothermal biomedicine.

A facile synthesis of graphene oxide/locust bean gum hybrid aerogel for water purification

Graphene oxide/locust bean gum (GO/LBG) aerogels, synthesized in an ice crystal template without using any chemical modifiers, were used for the treatment of water pollution. Various characterization results showed that GO/LBG aerogel exhibited a network-like three-dimensional (3D) structure with large specific surface area. The adsorption data revealed that GO/LBG aerogels with GO/LBG mass ratio of 1:4 (GO/LBG-1 aerogels) exhibited more prominent adsorption properties for Rhodamine-B (RhB, 514.5 mgg^-1) than Indigo Carmine (IC, 134.6 mgg^-1). Simultaneously, GO/LBG-1 aerogels could selectively remove RhB from a binary mixed solution of RhB-IC dyes. Furthermore, GO/LBG-1 aerogels also displayed excellent reusability and could still reach 92.4 % after ten cycles. Based on the above results, GO/LBG-1 aerogel could be considered as an ideal adsorbent with potential application value for removing water-soluble RhB from wastewater.

Flexible Underwater Oleophobic Cellulose Aerogels for Efficient Oil/Water Separation

Hybrid cellulose/N,N'-methylene bisacrylamide/graphene oxide (GO) aerogels with high flexibility and underwater oleophobicity were fabricated via the NaOH/urea solvent system. The as-prepared aerogels demonstrated low density, high porosity, and good flexibility. Underwater oleophobicity is attributed to the abundant hydrophilic groups in the aerogel skeleton, rough surface, and homogeneous distribution of GO. The samples were shaped into the membrane and filtered for oil/water separation by gravity. The separation efficiency over membrane-shaped CG₁ was 99.8% with a permeate flux of 22,900 L/(m²·h). Moreover, excellent reusability and durability were observed under long-term tests and corrosive conditions.

Processing and modification of hydrogel and its application in emerging contaminant adsorption and in catalyst immobilization: a review

Due to the wonderful property of hydrogels, they can provide a platform for a wide range of applications. Recently, there is a growing research interest in the development of potential hydrogel adsorbents in wastewater treatment due to their adsorption ability toward aqueous pollutants. It is important to prepare such a hydrogel that possesses appropriate robustness, adsorption capacity, and adsorption efficiency to meet the need of water treatment. In order to improve the property of hydrogels, much effort has been made by researchers to modify hydrogels, among which incorporating inorganic components into the polymeric networks is the most common method, which can reduce the product cost and simplify the preparation procedure. Not only can hydrogel be applied as adsorbent, but it also can be used as matrix for catalyst immobilization. In this review, the key advancement on the preparation and modification of hydrogels is discussed, with special emphasis on the introduction of inorganic materials into polymeric networks and consequential changes in the properties of mechanical strength, swelling, and adsorption. Besides, hydrogels used as adsorbents for removal of dyes and inorganic pollutants have been widely explored, but their use for adsorbing emerging contaminants from aqueous solution has not received much attention. Thus, this review is mainly focused on hydrogels' application in removing emerging contaminants by adsorption. Furthermore, hydrogels can be also applied in immobilizing catalysts, such as enzyme and photocatalyst, to remove pollutants completely and avoid secondary pollution, so their progress as catalyst matrix is overviewed.

Sulfo-functional 3D porous cellulose/graphene oxide composites for highly efficient removal of methylene blue and tetracycline from water

Cellulose/graphene oxide (CG) porous composites with 3D network structure were prepared via a solution mixing-regeneration and freeze-drying process. The CG aerogels were functionalized with 1,4-butane sultone under mild reaction conditions to achieve sulfated composite aerogels (SCGs), in which the sulfo groups were simultaneously introduced onto GO and cellulose components. The adsorption ability of SCG aerogel was greatly enhanced compared with CG aerogels. The fitting results of adsorption models suggested the monolayer adsorption and chemisorptive characteristics with the maximal uptake capacity as high as 421.9 mg/g for methylene blue (MB) and 163.4 mg/g for tetracycline (TC). The adsorption mechanism was also studied in detail. For the simulated wastewater containing MB and TC, the novel SCG adsorbent exhibited a removal efficiency of 99%. Furthermore, its adsorption capacity was not apparently deteriorated after seven cycles for MB and ten cycles for TC while the original structural integrity was almost maintained. Herein, this recyclable and reusable adsorbent exhibited the potential application on the removal of MB and TC from water.

Preparation and Characterization of High Amylose Corn Starch⁻Microcrystalline Cellulose Aerogel with High Absorption

Microcrystalline cellulose (MCC) aerogels were synthesized, blendingwith high amylose corn starch of different contents based on a NaOH–urea solution, and following by vacuum freeze-drying technology. The microstructure of the aerogel was observed by scanning electron microscopy (SEM) as an interconnected, porous three-dimensional structure, while X-ray diffractogram (XRD) measurements showed that the crystalline form was converted from cellulose I to cellulose II during dissolution and regeneration. Thermogravimetric analysis (TGA) showed that the content of starch had little effect on the thermal stability of the aerogel, whereas the content of starch had great influences on absorption and viscoelastic properties. When the ratio of starch was 10% and 15%, the prepared aerogels presented a low density and abundant pores, which endowed the aerogels, not only with the highest absorption ratio of pump oil and linseed oil (10.63 and 11.44 g/g, respectively), but also with better dynamic viscoelastic properties.

Insights into the phosphate adsorption behavior onto 3D self-assembled cellulose/graphene hybrid nanomaterials embedded with bimetallic hydroxides

3D self-assembled cellulose/graphene hybrids (3D cell/GO hybrids) were used as the host for encapsulating the Zr and La hydroxides, forming the Zr/La-cell/GO hybrids. After phosphate adsorption, the crystallization peaks of LaPO₄·xH₂O in saturated Zr/La-cell/GO hybrids were observed and they were reduced with the increase in pHs. Especially, a low crystallization was observed at pH 10.0 as compared with those at pH 3.0 and 6.0; this also corresponded well to the varied adsorption capacity as a function of pHs. The increased humic acid (HA) amounts (150 mg/L) only resulted in a low capacity loss (16.3%) in phosphate uptake from 25.3 to 21.2 mg/g. A noticeable La leach (2.1 mg/L) was observed at the HA level of 150 mg/L but no Zr leach was detected, and therefore, complexation of La with HA seemed a potential explanation for the increased La leaching. The interference of different coexisting anions on phosphate uptake followed the order as F^- > SiO₃^2- > HCO₃^- > SO₄^2- > NO₃^- > Cl^-. Phosphate uptake by Zr/La-cell/GO hybrids was significantly reduced at the co-existing fluoride partially due to the stronger electro-negativity of fluoride to combine with the protonated Zr/La hydroxides. In addition, Ca²⁺ laden on the Zr/La-cell/GO hybrids significantly enhanced the adsorption of phosphate by Zr/La-cell/GG hybrids due to the formation of calcium phosphate precipitation in framework of Zr/La-cell/GG hybrids.