Superabsorbent nanocomposite hydrogels made of carboxylated cellulose nanofibrils and CMC-g-p(AA-co-AM)

Tunicate cellulose nanocrystal reinforced multifunctional hydrogel with super flexible, fatigue resistant, antifouling and self-adhesive capability for effective wound healing

Hydrogels as skin wound dressings have been extensively studied owing to their good flexibility and biocompatibility. Nevertheless, the mechanical performance, adhesive capability, antifouling and antibacterial properties of conventional hydrogels are still unsatisfactory, which hinder the application of hydrogel for cutaneous healing. Here, we developed a novel biocompatible multifunctional hydrogel with super flexible, fatigue resistant, antifouling and self-adhesive capability for effective wound healing, where naturally rigid polymers including quaternized chitosan (QCS) and Tunicate cellulose nanocrystals (TCNCs) are used as bioactive cross-linkers and reinforcers to endow the hydrogel with excellent mechanical and antibacterial property, and the synergistic contributions from the poly(acrylic acid/methacrylate anhydride dopamine/sulfobetaine methacrylate) (poly(AA/DMA/SBMA)) chains and QCS endow the hydrogel with excellent adhesive property, antioxidant, antifouling and pH-responsive sustained drug release capabilities. The optimized hydrogel exhibited high tensile strength (77.69 KPa), large tensile strain (889.9 %), large toughness (307.51KJ.m-3), high adhesive strength (35.57 KPa) and ideal compressive property. The in vivo infected full-thickness skin model demonstrated that the hydrogel with vanvomycin sustained release ability efficiently improved the granulation tissue formation, facilitating collagen deposition and reducing inflammatory expression, thus effectively accelerating wound healing. This superiorly skin-adhesive antibacterial biocompatible hydrogel appears to be a promising candidate for wound therapy.

Biodegradable coating constructed from carboxycellulose nanofibers for high photocatalytic decomposition of ethylene and synergistic antibacterial what of perishable fruits

Postharvest fruits, especially climacteric fruits, are prone to ethylene ripening, browning and aging, microbial growth accelerated decay and other problems in natural environment. Herein, a carboxylated cellulose nanofibers/phytic acid‑titanium dioxide nanoparticles (CPT) biodegradable coating with "photocatalytic antibacterial barrier" structure，was developed by homogeneous dispersion of phytic acid(PA) complexed titanium dioxide nanoparticles (TNPs) in carboxylated cellulose nanofibers(CCNF). The CPT coating achieves effective dispersion and efficient utilization of TNPs through the complexation of PA. The coating ethylene clearance rate of CPT up to 70.89 %. Meanwhile, the coating exhibits excellent antibacterial (99.67 %), UV resistance, gas barrier. It was found that the CPT coating delays fruit ripening caused by ethylene, which effectively maintaining the quality of respiratory climacteric fruits and non- climacteric fruits, extending the shelf life of perishable fruit by up to 9 days. In particular, the coating is virtually biodegradable in soil after 21 days, which offers the possibility of replacing non-biodegradable multifunctional coatings in food packaging.

Rational Design of a Multifunctional Hydrogel Trap for Water and Fertilizer Capture: A Review

Water scarcity and land infertility pose significant challenges to agricultural development, particularly in arid and semiarid regions. Improving soil-water-retention capacity and fertilizer utilization efficiency through the application of soil additives has become a pivotal approach in agricultural practices. Hydrogels exhibit exceptional water absorption and fertilizer retention capabilities, making them extensively utilized in the fields of agriculture, forestry, and desert control. Currently, most reviews primarily focus on the raw materials, classification, synthesis methods, and application prospects of hydrogels, with limited attention given to strategies for enhancing water-retention performance, mechanisms underlying fertilizer absorption, and environmental risks. This review covers the commonly used cross-linking methods in hydrogel synthesis and the structure-activity relationship between hydrogels and water as well as fertilizer. Additionally, a thorough analysis of the ecological benefits and risks associated with hydrogels is presented. Finally, future prospects and challenges are delineated from the perspectives of material design and engineering applications.

Effect of chain structures of monomer on hydroxyethyl cellulose-based superabsorbent properties and improvement of chickpeas plant growth of water deficit-stressed

The aim of this research was evaluation of the influence of distance between zwitterionic monomer ions on the performance of superabsorbents. For this purpose, two zwitterionic monomers 4-(3-aminopropyl) amino-4-oxo-2-butenoic acid (APOB) and 4-(6-aminohexyl) amino-4-oxo-2-butenoic acid (AHOB) were prepared and applied for synthesis of two new superabsorbents through graft copolymerization onto hydroxyethyl cellulose (HEC) in the presence of acrylic acid (AA). In synthesis of superabsorbents factors such as the highest water absorbency capacity, absorbency rate, gel strength, and environmental problems should be resolved or improved. The results demonstrated that the water absorbency capacity and rate parameters (τ) of HEC-g-p(AA-co-APOB) and HEC-g-p(AA-co-AHOB) in distilled water were 986.62, 664.38 g/g, and 98.04, 140.84 min, respectively. The biodegradability of HEC-g-p(AA-co-APOB) was approximately 4 times more than HEC-g-p(AA-co-AHOB). However, based on the rheological analyses (G'/G″) HEC-g-p(AA-co-AHOB) was stronger than the other. Additionally, studies of water retention on soil containing HEC-g-p(AA-co-AHOB) superabsorbent (soil with 0.25 wt% material) showed that the after 30 days has ≤5 % water while soil in the absence of superabsorbent after 10 days completely dried. Studies of the growth of plants in soil demonstrated in the presence of HEC-g-p(AA-co-AHOB) the average length of shoots was 36 cm while without superabsorbent were 25 cm.

In situ carbothermal synthesis of carbonized bacterial cellulose embedded with nano zero-valent iron for removal of Cr(VI)

Carbonized bacterial cellulose embedded with highly dispersed nano zero-valent iron (nZVI), denoted as nZVI@CBC, was prepared through one-step in situ carbothermal treatment of bacterial cellulose adsorbing iron(III) nitrate. The structure characteristics of nZVI@CBC and its performance in removing hexavalent chromium Cr(VI) were investigated. Results showed the formation of nZVI@CBC with a surface area of 409.61 m2/g at 800 °C, with nZVI particles of mean size 28.2 nm well distributed within the fibrous network of CBC. The stability of nZVI was enhanced by its carbon coating, despite some inevitable oxidation of exposed nZVI. Batch experiments demonstrated that nZVI@CBC exhibited superior removal efficiency compared to bare nZVI and CBC. Under optimal conditions, nZVI@CBC exhibited a high Cr(VI) adsorption capacity of up to 372.42 mg/g. Therefore, nZVI@CBC shows promise as an effective adsorbent for remediating Cr(VI) pollution in water.

Superabsorbent carboxymethyl cellulose-based hydrogel fabricated by liquid-metal-induced double crosslinking polymerisation

Herein, we introduced a liquid-metal/polymerisable deep eutectic solvent (LM/PDES) system to the carboxymethyl cellulose (CMC) and acrylic acid solution to prepare a double-cross-linked CMC-polyacrylic acid (PAA)-LM/PDES superabsorbent hydrogel via graft crosslinking polymerisation for 5 min. FTIR and XRD provided evidence for the coordinate crosslinking between Ga3+ and carboxy groups in the CMC-PAA-LM/PDES gel structure and chemical crosslinking between CMC and PAA components. The pore size of the obtained hydrogels gradually decreases with the increase of LM-AA/PDES content. The rigid CMC polysaccharide chains increased the distance between the ionic groups on the flexible PAA molecular chains, resulting in high osmotic pressure. In addition, the synergistic effects of hydrophilic groups, electrostatic repulsion, macroporous structures and double crosslinking on the CMC and PAA structures provided a driving force and space for the gel to absorb electrolyte containing liquid. The absorption capacity of the CMC-PAA-LM/PDES gel for physiological saline reached 97 g/g, which exceeded that of a single cross-linked CMC-PAA gel and a reported superabsorbent material (71 g/g). This work solved the problem of long heating times and insufficient mechanical properties for the preparation of superabsorbent gels, providing a theoretical reference for improving the absorption capacity of superabsorbent materials for electrolyte-containing aqueous solutions.

Seed gum-based polysaccharides hydrogels for sustainable agriculture: A review

Globally, water scarcity in arid and semiarid regions has become one of the critical issues that hinder sustainable agriculture. Agriculture, being a major water consumer, presents several challenges that affect water availability. Hydrogels derived from polysaccharides seed gums are hydrophilic polymers capable of retaining substantial moisture in their three-dimensional network and releasing it back into the soil during drought conditions. Implementation of hydrogels in the agricultural sectors enhances soil health, plant growth, and crop yield. Furthermore, the soil permeability, density, structure, texture, and rate of evaporation and percolation of water are modified by hydrogel. In this review, hydrogels based on natural plant seed gum like guar, fenugreek, Tara and locust beans have been discussed in terms of their occurrence, properties, chemical structure, method of synthesis, and swelling behavior. The focus extends to recent applications of modified seed gum-based natural hydrogels in agriculture, serving as soil conditioners and facilitating nutrient delivery to growing plants. The swelling behavior and inherent structure of these hydrogels can help researchers unravel their maximum possibilities to promote sustainable agriculture and attenuate the obstacles propounded by our dynamic nature. The current review also examines market growth, prospects, and challenges of eco-friendly hydrogels in recent times.

Superabsorbent hydrogels based on natural polysaccharides: Classification, synthesis, physicochemical properties, and agronomic efficacy under abiotic stress conditions: A review

Superabsorbent polymers (SAPs) are a class of polymers that have attracted tremendous interest due to their multifunctional properties and wide range of applications. The importance of this class of polymers is highlighted by the large number of publications, including articles and patents, dealing with the use of SAPs for various applications. Within this framework, this review provides an overview of SAPs and highlights various key aspects, such as their history, classification, and preparation methods, including those related to chemically or physically cross-linked networks, as well as key factors affecting their performance in terms of water absorption and storage. This review also examines the potential use of polysaccharides-based SAPs in agriculture as soil conditioners or slow-release fertilizers. The basic aspects of SAPs, and methods of chemical modification of polysaccharides are presented and guidelines for the preparation of hydrogels are given. The water retention and swelling mechanisms are discussed in light of some mathematical empirical models. The nutrient slow-release kinetics of nutrient-rich SAPs are also examined on the basic of commonly used mathematical models. Some examples illustrating the advantages of using SAPs in agriculture as soil conditioners and agrochemical carriers to improve crop growth and productivity are presented and discussed. This review also attempts to provide an overview of the role of SAPs in mitigating the adverse effects of various abiotic stresses, such as heavy metals, salinity, and drought, and outlines future trends and prospects.

Insight into adsorption process and mechanisms of Cr(III) using carboxymethyl cellulose-g-poly(acrylic acid-co-acrylamide)/attapulgite composite hydrogel

Cr(III) as one of the most concerned potentially toxic elements, is discharged from relevant industries and Cr(VI) reduction. Hydrogel-based adsorption could be one of the promising approaches for Cr(III) removal. Featured with environmental friendliness and low cost, carboxymethyl cellulose (CMC) was employed for the hydrogel synthesis, and attapulgite (APT) could be used to strengthen its stability. However, the adsorption performance and mechanisms need to be examined. In the present study, carboxymethyl cellulose-g-poly(acrylic acid-co-acrylamide)/ attapulgite (CMC-g-p(AA-co-AM)/APT) was synthesised via in situ copolymerisation. Its efficacy for removing Cr(III) from an aqueous solution was investigated using batch adsorption experiments. Results showed that the introduction of APT enhanced the thermal stability but decreased the swelling performance of the hydrogel. The prepared hydrogel could strongly adsorb Cr(III) at a wide pH range of 3.0-7.0. Cr(III) can be efficiently removed by the composite hydrogel within 1-2 h. At low concentration, CMC-g-p(AA-co-AM)/APT could slightly adsorbed more Cr(III) than CMC-g-p(AA-co-AM). The maximum absorption of CMC-g-p(AA-co-AM) and CMC-g-p(AA-co-AM)/APT were 74.8 and 47.7 mg/g at 298 K, respectively. The negative value of ΔHo and ΔGo indicated the adsorption of Cr(III) onto the two studied hydrogels is an exothermic and spontaneous process. Ion exchange and complexation, as implied by EDS, FT-IR and XPS, combining with electrostatic attraction are the possible adsorption mechanisms for Cr(III) onto the prepared hydrogels. All the results above suggests that the composite hydrogel CMC-g-p(AA-co-AM)/APT can be a promising candidate for the removal of Cr(III) from waste water.

Salting-Out Effect Realizing High-Strength and Dendrite-Inhibiting Cellulose Hydrogel Electrolyte for Durable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are limited by poor Zn stripping/plating reversibility. Not only can hydrogel electrolytes address this issue, but also they are suitable for constructing flexible batteries. However, there exists a contradiction between the mechanical strength and the ionic conductivity for hydrogel electrolytes. Herein, high-concentration kosmotropic ions are introduced into the cellulose hydrogel electrolyte to take advantage of the salting-out effect. This can significantly improve both the mechanical strength and ionic conductivity. Additionally, the obtained cellulose hydrogel electrolyte (denoted as Con-CMC) has strong adhesion, a wide electrochemical stability window, and good water retaining ability. The Con-CMC is also found to accelerate the desolvation process, improve Zn deposition kinetics, promote Zn deposition along the (002) plane, and suppress parasitic reactions. Accordingly, the Zn/Zn cell with Con-CMC demonstrates dendrite-free behavior with prolonged lifespan and can endure extremely large areal capacity of 25 mAh cm-2. The Con-CMC also enables a large average Coulombic efficiency of 99.54% over 500 cycles for the Zn/Cu cell. Furthermore, the assembled pouch-type Zn/polyaniline full battery provides great rate capability, superior cyclability (even with limited Zn anode excess), a slow self-discharge rate, and outstanding affordability to external forces. Overall, this work extends our knowledge of the rational design of hydrogel electrolytes.

Study on the Degradation of a Semi-Synthetic Lignin-Acrylic Acid Hydrogel with Common Bacteria Found in Natural Attenuation Processes

In this study, lignin was chemically modified to promote hydrogel degradation as a source of carbon and nitrogen for a bacterial consortium consisting of P. putida F1, B. cereus and, B. paramycoides. A hydrogel was synthesized using acrylic acid (AA), acrylamide (AM), and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and cross-linked with the modified lignin. The structural changes and mass loss in the hydrogel, as well as its final composition, were evaluated as functions of the growth of the selected strains in a culture broth with the powdered hydrogel. The average loss was 18.4% wt. The hydrogel was characterized using FTIR spectroscopy, scanning electronic microscopy (SEM), elemental analysis (EA), and thermogravimetric analysis (TGA) before and after bacterial treatment. FTIR showed that the carboxylic groups present in both the lignin and the acrylic acid of the hydrogel decreased during bacterial growth. The bacteria showed a preference for the biomaterial components of the hydrogel. SEM demonstrated superficial morphological changes in the hydrogel. The results reveal that the hydrogel was assimilated by the bacterial consortium while preserving the water retention capacity of the material and that the microorganisms carried out a partial biodegradation of the hydrogel. The results of the EA and TGA confirm that the bacterial consortium not only degraded the biopolymer (lignin), but also used the synthetic hydrogel as a carbon source to degrade its polymeric chains and modified original properties. This modification with lignin as a crosslinker (which is a waste product of the paper industry) is therefore proposed to promote hydrogel degradation.

Evaluation of Acute Toxicity and Antioxidant Response of Earthworm Exposed to a Lignin-Modified Crosslinked Hydrogel

Hydrogels are polymers of great importance due to their multiple applications, which have led to an exponential increase in their production. However, once they have fulfilled their function, they become waste and their ecotoxicological effects are unknown. The aim of the present study was to evaluate the acute toxicity and total antioxidant capacity of the earthworm (Eisenia fetida) exposed to a terpolymeric hydrogel (acrylic acid, acrylamide, and 2-acrylamido-2-methyl-1-propane-sulfonic acid) crosslinked with modified kraft lignin. Four different amounts of hydrogel per unit area were evaluated (0.0924, 0.1848, 0.9242, and 1.848 mg hydrogel/cm²) plus a control, and three replicates were performed for each group. Starting from the amount of 0.1848 mg hydrogel/cm², the earthworms showed physiological and behavioral alterations; at higher amounts, 0.9242 and 1.848 mg hydrogel/cm², more acute signs were observed with mortality rates of 51.7% and 100%, respectively. On the other hand, the antioxidant activity assay showed that the higher the hydrogel exposure amount, the higher the oxidative stress, as evidenced by lower antioxidant activity (67.09% inhibition of the ABTS^●+ radical). Therefore, we concluded that the lignin-modified hydrogel generated oxidative stress and acute lethal toxic effects in Eisenia fetida.

Novel Double Cross-Linked Acrylic Acid/Bagasse Cellulose Porous Hydrogel for Controlled Release of Citral and Bacteriostatic Effects

In this study, double cross-linked acrylic acid/bagasse cellulose (AA/BC) porous hydrogels were first prepared using cold plasma (CP) technology instead of chemical initiators. The structure and properties of porous hydrogels, as well as the controlled release and bacteriostatic application as functional carriers, were investigated. Results showed that a novel double cross-linked hydrogel had been successfully synthesized by utilizing ^•OH and H⁺ produced during plasma discharge. The acrylic acid (AA) monomers were successfully grafted onto the main chains of bagasse cellulose (BC), forming a porous three-dimensional network structure. The AA/BC porous hydrogels showed excellent swelling levels and intelligent responses. The release of citral in hydrogel inclusion compounds embedded with citral was controlled by adjusting the pH, and the slow release period was about 2 days. The inclusion compounds presented strong bacteriostatic effects against Escherichia coli and Staphylococcus aureus, extending the shelf life of fruits for about 4 days. Therefore, it can be concluded that CP technology is considered to be an efficient and environmental-friendly initiation technology for preparing hydrogels. The potential application of hydrogel inclusion compounds in the food field is expanded.

Synthesis and property of superabsorbent polymer based on cellulose grafted 2-acrylamido-2-methyl-1-propanesulfonic acid

An eco-friendly superabsorbent polymer (SAP) was prepared by grafting 2-acrylamido-2-methyl-1-propanesulfonic acid onto microcrystalline cellulose in lithium chloride/N, N-dimethylacetamide system. The synthesized SAP (cellulose-g-PAMPS) was characterized by FTIR, TGA, SEM, ¹H NMR, ¹³C NMR and XRD. The water absorption equilibrium of cellulose-g-PAMPS could be achieved within 10 min in distilled water. Moreover, the maximum water absorption capacities of cellulose-g-PAMPS in distilled water, 0.9 wt% NaCl solution and 3.2 wt% Na₂CO₃ solution were 648.9, 298.4 and 207.3 g·g^-1, respectively. The water absorption behavior of cellulose-g-PAMPS was interpreted by the pseudo-second-order model. Furthermore, cellulose-g-PAMPS could be used in some extreme conditions due to its high acid and alkali resistance. The water retention rate of cellulose-g-PAMPS could be maintained above 90 % at 25 °C for 6 h. As a consequence, the synthesized SAP can be applied to increase the plant growth and survival time under drought conditions, even under saline alkali conditions.

Surface analysis and thermal behavior of the functionalized cellulose by glutaric anhydride through a solvent-free and catalyst-free process

According to the 12 principles of green chemistry, surface functionalization was performed using glutaric anhydride under solvent-free and catalyst-free conditions. FTIR spectra and DS analyses demonstrated the functionalization of HCl-hydrolyzed cellulose. The influence of two parameters, i.e., the glutaric anhydride concentration and the reaction time, on the functionalization of HCl-hydrolyzed cellulose was investigated. Protocol efficiency was studied by a degree of substitution (DS). It was found that higher concentrations of glutaric anhydride cause an enhancement of DS to 0.75 and 0.87 for GA3-12 and GA9-12, respectively. In addition, the longer reaction time increased zeta potential from -12.2 ± 1.7 for G9-6 to -34.57 ± 2.2 for GA9-12. Morphology analysis by SEM showed a decrease in fiber length for the functionalized cellulose. DSC profiles confirmed dehydration at a range of 17 to 134 °C. A glass transition was revealed at -30 to -20 °C for all studied samples. The fusion, the depolymerization of cellulose chains, the cleavage of glycosidic linkages, and the decomposition of the crystalline parts of cellulose occur at 195 to 374 °C. Therefore, an efficient and greener process was developed to functionalize the HCl-hydrolyzed cellulose by glutaric anhydride, a safe and non-toxic anhydride, in the absence of the solvent and catalyst.

Synthesis and characterization of silver nanoparticle embedded cellulose-gelatin based hybrid hydrogel and its utilization in dye degradation

The present work describes the synthesis of a cellulose and gelatin based hydrogel by the grafting of poly(acrylic acid) using ammonium persulphate (APS)-glutaraldehyde as the initiator-crosslinker system. The structure of the hydrogel was studied through scanning electron microscopy (SEM) and FTIR. The maximum swelling rate of C-G-g-poly(AA) was found to be 92 g g-1 at pH 10. The size and structure of the prepared silver nanoparticles (AgNPs) were studied through TEM and zeta potential, and it was found that the synthesized AgNPs were spherical and the size range was 11-30 nm. The reduction process followed pseudo 1st order kinetics. EtBr and eosin dye degradation were more than 4 times faster, when AgNPs were used with sodium borohydride. Thus, it can be concluded that the synthesized C-G-g-poly(AA) AgNPs hybrid hydrogel is effective for the reduction and degradation of carcinogenic dyes in wastewater.

Maleic acid as an important monomer in synthesis of stimuli-responsive poly(acrylic acid-co-acrylamide-co-maleic acid) superabsorbent polymer

Poly(acrylic acid-co-acrylamide-co-maleic acid) (p(AA-co-AM-co-MA)) superabsorbent polymer was synthesized from acrylic acid (AA), acrylamide (AM), and maleic acid (MA) via free radical copolymerization. Results showed the presence of maleic acid in structure of superabsorbent has the key and superior role in creating a smart superabsorbent. The structure, morphology, and strength of the superabsorbent were characterized using FT-IR, TGA, SEM, and rheology analysis. The effect of different factors was investigated to determine the ability of water absorbency of the superabsorbent. According to optimized conditions, the water absorbency capacity of the superabsorbent in distilled water (DW) was 1348 g/g and in a solution containing 1.0 wt.% NaCl (SCS) was 106 g/g. The water retention ability of the superabsorbent was also investigated. The kinetic swelling of superabsorbent was identified by Fickian diffusion and Schott's pseudo-second-order model. Furthermore, the reusability of superabsorbent was studied in distilled water and saline solution. The ability of superabsorbent was investigated in simulated urea and glucose solutions, and very good results were obtained. The response ability of the superabsorbent was confirmed by swelling and shrinking behavior against changes of temperature, pH, and ionic strength.

Highly conductive and anti-freezing cellulose hydrogel for flexible sensors

Ionic conducting hydrogels (ICHs) are emerging materials for multi-functional sensors in the fields of healthcare monitoring and flexible electronics. However, there is a long-standing dilemma between ionic conductivity and mechanical properties of the ICHs. In this work, ionic conductive, flexible, transparent, and anti-freezing hydrogels are fabricated by dissolving cotton linter pulp in ZnCl2/CaCl2 solution and cross-linking with epichlorohydrin (ECH). The presence of inorganic salt imparts the hydrogel with high ionic conductivity and low-temperature tolerance. While the introduction of ECH as the second network gives the hydrogel with desirable mechanical performance. By tailoring the ECH addition, the tensile strength, compressive strength, elongation at break, and conductivity of the hydrogel could reach 0.82 MPa, 2.80 MPa, 260 %, and 5.48 S m-1, respectively. The prepared ICHs are fabricated into sensors for detecting full-range human body motions, and they demonstrate fast response and durable sensitivity to both tensile strain and compressive deformation. Moreover, flexible sensors can work at subzero temperatures. This work provides a new idea for the preparation of cellulose-based hydrogels with good ionic conductivity and mechanical properties under extreme conditions.

Development of a Xanthan Gum Based Superabsorbent and Water Retaining Composites for Agricultural and Forestry Applications

In this work, bio-based hydrogel composites of xanthan gum and cellulose fibers were developed to be used both as soil conditioners and topsoil covers, to promote plant growth and forest protection. The rheological, morphological, and water absorption properties of produced hydrogels were comprehensively investigated, together with the analysis of the effect of hydrogel addition to the soil. Specifically, the moisture absorption capability of these hydrogels was above 1000%, even after multiple dewatering/rehydration cycles. Moreover, the soil treated with 1.8 wt% of these materials increased the water absorption capacity by approximately 60% and reduced the water evaporation rate, due to the formation of a physical network between the soil, xanthan gum and cellulose fibers. Practical experiments on the growth of herbaceous and tomato plants were also performed, showing that the addition of less than 2 wt% of hydrogels into the soil resulted in higher growth rate values than untreated soil. Furthermore, it has been demonstrated that the use of the produced topsoil covers helped promote plant growth. The exceptional water-regulating properties of the investigated materials could allow for the development of a simple, inexpensive and scalable technology to be extensively applied in forestry and/or agricultural applications, to improve plant resilience and face the challenges related to climate change.

Recent advances in enhanced polymer gels for profile control and water shutoff: A review

Polymer gels have been effectively employed as a water management material for profile control and water shutoff treatments in low-middle temperature and low-middle salinity reservoirs. However, most polymer gel systems have limitations under high temperature and salinity reservoir conditions, such as short gelation time, poor strength, and long-term instability. Therefore, several researchers have developed enhanced polymer gels to satisfy the water control requirements in high temperature and salinity reservoirs. This work reviews the five main types of enhanced polymer gels that have been developed so far: nano silica-enhanced gel systems, cellulose-enhanced gel systems, graphite-enhanced gel systems, oily sludge-enhanced gel systems, and foam-enhanced polymer gel systems. Further, this article investigates the fundamental properties, strengthening and crosslinking mechanisms, reservoir application conditions, and field applications of several enhanced polymer systems. In this paper, it is found that the addition of strengthening materials can increase the bound water content in the gel network and significantly improve the temperature and salt resistance of polymer gel, so as to cope with the application of profile control and water plugging in high temperature and high salt reservoirs. Moreover, it also offers references and future research directions for enhanced polymer gel systems.

Cellulose/nanocellulose superabsorbent hydrogels as a sustainable platform for materials applications: A mini-review and perspective

Superabsorbent hydrogels (SAH) are crosslinked three-dimensional networks distinguished by their super capacity to stabilize a large quantity of water without dissolving. Such behavior enables them to engage in various applications. Cellulose and its derived nanocellulose can become SAHs as an appealing, versatile, and sustainable platform because of abundance, biodegradability, and renewability compared to petroleum-based materials. In this review, a synthetic strategy that reflects starting cellulosic resources to their associated synthons, crosslinking types, and synthetic controlling factors was highlighted. Representative examples of cellulose and nanocellulose SAH and an in-depth discussion of structure-absorption relationships were listed. Finally, various applications of cellulose and nanocellulose SAH, challenges and existing problems, and proposed future research pathways were listed.

Development of a ghatti gum/poly (acrylic acid)/TiO2 hydrogel nanocomposite for malachite green adsorption from aqueous media: Statistical optimization using response surface methodology

The primary goal of this study is to prepare and characterize a ghatti gum/poly(acrylic acid)/TiO₂ (GG/poly(AA)/TiO₂) hydrogel nanocomposite for adsorption of the dye malachite green (MG) from the aqueous phase in a discontinuous system. A variety of approaches were used to investigate the structure, morphology, and thermomechanical characteristics of the synthesized hydrogel nanocomposite. Response surface methodology (RSM) was performed to analyze the impact of three processing parameters, namely adsorbent dosage, dye concentration, contact duration, and their interactions on MG dye adsorption capacity. Analysis of variance was used to assess the experimental findings, which revealed that the quadratic regression model was statistically acceptable. The integration of TiO₂ nanoparticles into the hydrogel matrix improved its thermal stability, mechanical strength, and performance in adsorbing MG dye from water. The kinetics and isotherm were evaluated, and the adsorption process was well fitted with pseudo-second order and Temkin isotherm models, respectively. Using the Langmuir equation, the maximum adsorption capacity at 45 °C within 50 min was calculated to be 2145 mg/g. Thermodynamic analysis at 25-45 °C revealed that the MG dye was spontaneously absorbed by the hydrogel nanocomposite. The prepared hydrogel nanocomposite demonstrated excellent reusability without a noticeable loss in MG dye adsorption capability for 6 cycles.

Biopolymeric Nanocarriers for Nutrient Delivery and Crop Biofortification

Driven by the possibility of precise transformational change in nutrient-enrichment technology to meet global food demand, advanced nutrient delivery strategies have emerged to pave the path toward success for nutrient enrichment in edible parts of crops through bioderived nanocarriers with increased productivity. Slow and controlled release of nutrient carrier materials influences the nutrient delivery rate in soil and in the edible parts of crops with a sluggish nutrient delivery to enhance their availability in roots by minimizing nutrient loss. With a limited understanding of the nutrient delivery mechanism in soil and the edible parts of crops, it is envisaged to introduce nutrient-enrichment technology for nutrient delivery that minimizes environmental impact due to its biodegradable nature. This article attempts to analyze the possible role of the cellulose matrix for nutrient release and the role of cellulose nanocomposites and nanofibers. We have proposed a few cellulose derived biofortificant materials as nutrient carriers, such as (1) nanofibers, (2) polymer-nanocellulose-clay composites, (3) silk-fibroin derived nanocarriers, and (4) carboxymethyl cellulose. An effort is undertaken to describe the research need by linking a biopolymer derived nanocarrier for crop growth regulation and experimental nitrogen release analysis. We have finally provided a perspective on cellulose nanofibers (CNFs) for microcage based nutrient loading ability. This article aims to explain why biopolymer derived nutrient carriers are the alternative candidate for alleviating nutrient deficiency challenges which are involved in focusing the nutrient delivery profile of biopolymers and promising biofortification of crops.

A Multifunctional Microspheric Soil Conditioner Based on Chitosan-Grafted Poly(acrylamide-co-acrylic acid)/Biochar

A multifunctional microspheric soil conditioner based on chitosan-grafted poly(acrylamide-co-acrylic acid)/biochar [CS-g-P(AM-co-AA)/BC] was prepared. First, the P(AM-co-AA) was synthesized and successfully grafted onto CS, and the three-dimensional network structure of microspheres was formed with N,N-methylenebis(acrylamide) as the cross-linking agent according to the inverse suspension polymerization method. Meanwhile, BC and urea were encapsulated into the body of microspheres during the polymerization. The structure of the microspheres was analyzed by Fourier transform infrared spectroscopy, polarized optical microscopy, and scanning electron microscopy, and the mechanism of adsorption of Cu²⁺ on the microspheres was investigated by X-ray photoelectron spectroscopy. Furthermore, the experimental results demonstrated the excellent water absorption and retention capabilities of microspheres, and the release rate of urea was dramatically reduced. Importantly, the introduction of BC significantly enhanced the adsorption performance of the microspheres with respect to heavy metal ions. Consequently, the multifunctional soil conditioner held promise for use in soil improvement and agricultural production.

Sugarcane cellulose-based composite hydrogel enhanced by g-C3N4 nanosheet for selective removal of organic dyes from water

The effective removal of toxic dyes from aqueous solution is of great significance for environmental protection. Herein, an eco-friendly sugarcane cellulose (SBC)/sodium carboxymethylcellulose (CMC-Na) adsorbent reinforced with carbon nitride (g-C₃N₄) was successfully prepared via a facile sol-gel method. The resulting gel-like adsorbent or composite hydrogel was comprehensively characterized with FTIR, SEM, EDS, TGA analysis. The adsorption behaviors of the adsorbent in the removal of methylene blue (MB) were systematically investigated. Results showed the pseudo-second-order kinetic model and Langmuir model described adsorption process accurately with the maximum adsorption capacity of 362.3 mg g^-1, indicating that adsorption behavior is a monolayer chemical adsorption. Moreover, the composited hydrogel displayed excellent adsorption selectivity on MB/MO or MB/RhB mixed dyes. In addition, adsorbent showed great stability and reusability with almost no loss in adsorption capacity after 7 cycles. Due to the facile preparation process and outstanding mechanical properties, as well as high recyclability, g-C₃N₄@SBC/CMC has great potential in wastewater treatment.

Construction of nickel ferrite nanoparticle-loaded on carboxymethyl cellulose-derived porous carbon for efficient pseudocapacitive energy storage

The preparation of biomass-derived carbon electrode materials with abundant active sites is suitable for development of energy-storage systems with high energy and power densities. Herein, a hybrid material consisting of highly-dispersed nickel ferrite nanoparticle on 3D hierarchical carboxymethyl cellulose-derived porous carbon (NiFe₂O₄/CPC) was prepared by simple annealing treatment. The synergistic effects of NiFe₂O₄ species with multiple oxidation states and 3D porous carbon with a large specific surface area offered abundant active centers, fast electron/ion transport, and robust structural stability, thereby showing the excellent performance of the electrochemical capacitor. The best performing sample (NiFe₂O₄/CPC-800) exhibited a superior capacitance of 2894F g^-1 at a current density of 0.5 A g^-1. Encouragingly, an asymmetric supercapacitor with NiFe₂O₄/CPC-800 as a positive electrode and activated carbon as a negative electrode delivered a high energy density of 135.2 W h kg^-1 along with an improved power density of 10.04 kW kg^-1. Meanwhile, the superior cycling stability of 90.2% over 10,000 cycles at 5 A g^-1 was achieved. Overall, the presented work offers a guideline for the design and preparation of advanced electrode materials for energy-storage systems.

Materials diversity of hydrogel: Synthesis, polymerization process and soil conditioning properties in agricultural field

BACKGROUND

The cumulative influence of global warming, climate abrupt changes, growing population, topsoil erosion is becoming a threatening alarm for facing food challenges and upcoming global water issues. It ultimately affects the production of food in a water-stressed environment and slows down the production with more consumption of fertilizers by plants. The superabsorbent hydrogels (SAHs) have extensive applications in the agricultural field and proved very beneficial for plant growth and soil health. These polymeric materials are remarkably distinct from hygroscopic materials owing to their multidimensional network structure. It retains a lot of water in its 3D network and releases it slowly along with nutrients to plant in stressed environment.

AIM OF REVIEW

A soil conditioner boosts up the topology, compactness, and mechanical properties (swelling, water retention, and slow nutrient release) of soil. The superabsorbent hydrogel plays an astonishing role in preventing the loss of nutrients during the heavy flow of rainwater from the upper surface of soil because these SAHs absorb water and get swollen to keep water for longer time. The SAHs facilitate the growth of plants with limited use of water and fertilizers. Beyond, it improves the soil health and makes it fertile in horticulture and drought areas.

KEY SCIENTIFIC CONCEPT OF REVIEW

The SAHs can be synthesized through grafting and cross-linking polymerization to introduce value-added features and extended network structure. The structure of superabsorbent hydrogel entirely based on cross-linking that prompts its use in the agricultural field as a soil conditioner. The properties of a SAHs vary due to its nature of constituents, polymerization process (grafting or cross-linking), and other parameters. The use of SAHs in agricultural field comparatively enhances the swelling rate up to 60-80%, maximum water retaining, and slowly nutrient release to plants for a longer time.

Core-Shell Structured Magnetic Carboxymethyl Cellulose-Based Hydrogel Nanosorbents for Effective Adsorption of Methylene Blue from Aqueous Solution

This article reports effective removal of methylene blue (MB) dyes from aqueous solutions using a novel magnetic polymer nanocomposite. The core-shell structured nanosorbents was fabricated via coating Fe₃O₄ nanoparticles with a layer of hydrogel material, that synthesized by carboxymethyl cellulose cross-linked with poly(acrylic acid-co-acrylamide). Some physico-chemical properties of the nanosorbents were characterized by various testing methods. The nanosorbent could be easily separated from aqueous solutions by an external magnetic field and the mass fraction of outer hydrogel shell was 20.3 wt%. The adsorption performance was investigated as the effects of solution pH, adsorbent content, initial dye concentration, and contact time. The maximum adsorption capacity was obtained at neutral pH of 7 with a sorbent dose of 1.5 g L⁻¹. The experimental data of MB adsorption were fit to Langmuir isotherm model and Pseudo-second-order kinetic model with maximum adsorption of 34.3 mg g⁻¹. XPS technique was applied to study the mechanism of adsorption, electrostatic attraction and physically adsorption may control the adsorption behavior of the composite nanosorbents. In addition, a good reusability of 83.5% MB recovering with adsorption capacity decreasing by 16.5% over five cycles of sorption/desorption was observed.

Hotspots, Frontiers, and Emerging Trends of Superabsorbent Polymer Research: A Comprehensive Review

Superabsorbent polymer (SAP) is a kind of functional macromolecule with super-high water absorption and retention properties, which attracts extensive research and has wide application, especially in the areas of hygiene and agriculture. With reference to the Web of Science database, the SAP research literature from 2000 to 2019 is reviewed both quantitatively and qualitatively. By examining research hotspots, top research clusters, the most influential works, the representative frontier literature, and key emerging research trends, a visual panorama of the continuously and significantly increasing SAP research over the past 2 decades was presented, and issues behind the sharp increase in the literature were discovered. The findings are as follows. The top ten keywords/hotspots headed by hydrogel highlight the academic attention on SAP properties and composites. The top ten research themes headed by clay-based composites which boast the longest duration and the strongest impact have revealed the academic preference for application rather than theoretical study. Academically influential scholars and research studies have been acknowledged, and the Wu group was at the forefront of the research; however, more statistically significant works have been less detected in the last 10 years despite the sharper increase in publications. Hydrogel, internal curing, and aerogel are both current advances and future directions.

Synthesis of a slow-release fertilizer composite derived from waste straw that improves water retention and agricultural yield

To enhance waste straw utilization and improve fertilizer efficiency, a novel semi-interpenetrating polymer network fertilizer (CMCK-g-PAA/PDMUP) was prepared from straw cellulose and linear polymer by solution polymerization. Polydihydroxymethyl-urea potassium phosphate (PDMUP) was included to supply nitrogen, phosphorus, and potassium nutrients. Characterization of CMCK-g-PAA/PDMUP with FTIR, XPS, XRD, and SEM techniques provided evidence for semi-interpenetrating polymer networks (semi-IPNs) and component interactions. The prepared product exhibited excellent water absorbency (681.3 g/g) and enhanced the soil's water-retention capacity. Cumulative release of N, P, and K was 56.1%, 64.3%, and 74.1%, respectively, after 40 days-meeting a Committee of European Normalization (CEN) standard. Agricultural application of CMCK-g-PAA/PDMUP promoted wheat growth. Desirable water retention, slow-release properties, and wheat growth effects highlight the product's potential for improving agriculture.

Biodegradable gelatin composite hydrogels filled with cellulose for chromium (VI) adsorption from contaminated water

Biopolymers are promising materials for water treatment applications due to their abundance, low cost, expandability, and chemical structure. In this work, gelatin hydrogels filled with cellulose in the form of pristine eucalyptus residues (PER) or treated eucalyptus residues (TER) were prepared for adsorption and chromium removal in contaminated water. PER is a lignocellulosic compound, with cellulose, hemicellulose, and lignin, while TER has cellulose as a major component. FT-Raman Spectroscopy and FTIR analysis confirmed the crosslink reaction with glutaraldehyde and indicated that fillers altered the gelatin molecular vibrations and formed new hydrogen bonds, impacting the hydrogels' crystalline structure. The hydrogen bond energy was altered by the cellulosic fillers' addition and resulted in higher thermal stability (~10 °C). Hydrogels presented a Fickian diffusion, where gelatin hydrogel showed the highest swelling ability (466%), and composites showed lower values with the filler content increase. The chromium adsorption capacity presented values between 12 and 13 mg/g, i.e., featuring an excellent removal capacity which is related with hydrogel crosslinked structure and fibers surface hydroxyl groups, highlighting gelatin hydrogel TER 5% with better removal capacity. The developed hydrogels were produced from biomacromolecules with low-cost and potential application in contaminated water.

Synthesis and application of eco-friendly superabsorbent composites based on xanthan gum and semi-coke

An eco-friendly superabsorbent composites of xanthan gum-g-polyacrylic acid/semi-coke (XG-g-PAA/SC) were fabricated via grafting of polyacrylic acid onto the XG in the presence of SC. The obtained products were characterized in combination with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The result indicated that the SC interacted with the polymeric network by hydrogen bond or electrostatic interaction. The swelling ratio of the best sample XG-g-PAA/SC (15 wt%) in distilled water and 0.9 wt% NaCl solution was 410.8 and 61.5 g/g by optimizing the polymerization conditions. In addition, compared with the blank sample (only containing soil), it can be found that adding a certain amount of XG-g-PAA/SC can significantly improve the soil water retention efficiency, which can be further proved by the results of plant pot experiment. Based on the above excellent swelling capacity, water holding capacity and plant growth promoting performance, it can be inferred that the XG-g-PAA/SC is expected to become a water retaining agent or soil regulator for plant growth.

Environmentally friendly superabsorbent fibers based on electrospun cellulose nanofibers extracted from wheat straw

Superabsorbent polymers currently used in health and agricultural sectors are based on petroleum-based materials which led to serious concerns in the society. Here, superabsorbent fibers (SAFs) based on electrospun cellulose nanofibers (ECNFs) were prepared. Firstly, cellulose was removed from wheat straw, pre-treated with the TEMPO-mediated oxidation and subsequently dissolved into Trifluoroacetic acid for production of ECNFs through the electrospinning approach. The maximum swelling ratios of 225 g/g and 208 g/g in distilled water and 0.9 wt% NaCl solution were measured for ESAFs composed of oxidized ECNFs containing 15 % poly (sodium acrylate), respectively. The ESAFs were characterized using Fourier transform infrared spectroscopy and field emission scanning electron microscopy analysis. The FESEM showed that ESAFs formed high strength three-dimensional architecture networks. Also, the results showed that the ionic sensitivity of this ECNFs were low. The prepared ESAFs are attractive renewable alternatives for different applications, contributing to a reduction of plastic microspheres.

Valorization of Colombian fique (Furcraea bedinghausii) for production of cellulose nanofibers and its application in hydrogels

Cellulose nanofibers were obtained from the Colombian fique (Furcraea bedinghausii) and Acrylic hydrogels (H) and reinforced acrylic hydrogels with fique nanofibres (HRFN) were synthesized, using the solution polymerization method. The extraction was carried out using a combined extraction method (chemical procedures and ultrasound radiation). The raw material (NAT-F), bleached fibers (B-F), hydrolyzed fibers and fibers treated with ultrasound (US-F) were characterized by infrared spectroscopy (FTIR) and thermal stability analysis; also, in order to have a comparison criterion, a commercial microcrystalline cellulose sample (CC) was analyzed, which demonstrated the extraction of fique cellulose. The surface morphology of the NAT-F and the B-F was determined by scanning electron microscopy and the average particle size of the nanofibers was made through transmission electron microscopy. In H y HRFN the strain percent and compression resistance (Rc) were measured. The fique nanofibers showed diameter and length averages of 25.2 ± 6.2 nm and 483.8 ± 283.2 nm respectively. Maximum degradation temperature was 317 °C. HRFN presented higher compression resistance (16.39 ± 4.30 kPa) and this resistance was 2.5 greater than the resistance of H (6.49 ± 2.48 kPa). The results indicate that fique lignocellulosic matrix has potential application for obtaining polymeric type composite materials.

Bottom-up assembly of nanocellulose structures

Nanocelluloses, both cellulose nanofibrils and cellulose nanocrystals, are gaining research traction due to their viability as key components in commercial applications and industrial processes. Significant efforts have been made to understand both the potential of assembling nanocelluloses, and the limits and prospectives of the resulting structures. This Review focuses on bottom-up techniques used to prepare nanocellulose-only structures, and details the intermolecular and surface forces driving their assembly. Additionally, the interactions that contribute to their structural integrity are discussed along with alternate pathways and suggestions for improved properties. Six categories of nanocellulose structures are presented: (1) powders, beads, and droplets; (2) capsules; (3) continuous fibres; (4) films; (5) hydrogels; and (6) aerogels and dried foams. Although research on nanocellulose assembly often focuses on fundamental science, this Review also provides insight on the potential utilization of such structures in a wide array of applications.

Simple One Pot Preparation of Chemical Hydrogels from Cellulose Dissolved in Cold LiOH/Urea

In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) and chemically cross-linked with methylenebisacrylamide (MBA) to form a robust hydrogel with superior water absorption properties. Different cellulose concentrations (i.e., 2, 3 and 4 wt%) and MBA/glucose molar ratios (i.e., 0.26, 0.53 and 1.05) were tested. The cellulose hydrogel cured at 60 °C for 30 min, with a MBA/glucose molar ratio of 1.05, exhibited the highest water swelling capacity absorbing ca. 220 g H2O/g dry hydrogel. Moreover, the data suggest that the cross-linking occurs via a basic Michael addition mechanism. This innovative procedure based on the direct dissolution of unmodified cellulose in LiOH/urea followed by MBA cross-linking provides a simple and fast approach to prepare chemically cross-linked non-derivatized high-molecular-weight cellulose hydrogels with superior water uptake capacity.