Preparation of biodegradable sodium alginate/carboxymethylchitosan hydrogels for the slow-release of urea fertilizer and their antimicrobial activity

Characterization and slow-release of urea fertilizer of hydrogel composites based on poly(vinyl alcohol)/ sodium alginate/ humic acid/ citric acid

The purpose of this research was to develop a hydrogel-based slow-release fertilizer for wheat cultivation. A new polyvinyl alcohol (PVA)/sodium alginate (SA)/humic acid (HA)/citric acid (CA) (PSHC) hydrogel composite was synthesized, using a liquid-state crosslinking method, with citric acid serving as the crosslinker. Then, the PSHCU-hydrogel was formed by incorporating urea with PSHC-hydrogel. The samples were analyzed using FTIR, FESEM, and EDX, confirming the hydrogel network's formation through ester linkages, and successful urea incorporation. PSHCU-hydrogel's water absorption and retention, biodegradation, and urea release in soil and water were examined. The highest amount of water absorbed by PSHCU-hydrogel after 24 h at pH 10 was 945.16 %. The urea release rate in soil was 80.77 % and 90.84 % for the PSHCU- and PSCU-hydrogels over 30 days, respectively. The PSHCU-hydrogel's effects on wheat plants' development and yield were investigated. Incorporating humic acid improved PSHCU-hydrogel's slow-release characteristics, and enhanced plant growth (p < 0.05) and yielded 4199 kg hm-2. Thus, the PSHCU-hydrogel showed potential to be a valuable fertilizer for wheat cultivation.

Natural polysaccharide and protein-based hydrogels: a novel class of materials for sustainable agricultural development

As global population growth and resource constraints intensify, traditional agriculture relies on high-energy consumption and high-pollution measures that can no longer support the demand for sustainable development. Owing to their biocompatibility, degradability and functional diversity, natural polysaccharide- and protein-based hydrogels have become ideal materials for supporting the sustainable use of agricultural soils. This paper systematically reviews the design and preparation of such hydrogels and their potential for agricultural applications. First, in terms of the raw material properties, the molecular structure of polysaccharides and proteins endows hydrogels with excellent water absorption and retention capacity, stimulus responsiveness and environmental adaptability; second, the mechanical strength, swelling behaviour and degradation rate of hydrogels can be precisely regulated through physical cross-linking or chemical cross-linking. At the application level, natural polysaccharide- and protein-based hydrogels subsequently exhibit multidimensional functions. They act as 'miniature reservoirs' to optimise soil water management and the slow release of fertilisers and pesticides to improve utilisation efficiency; they can repair degraded soils and inhibit salinisation by improving the structure of soil aggregates, increasing the content of organic matter, and adsorbing heavy metal ions; and their degradation products can provide carbon sources for soil microorganisms to synergistically promote crop growth. Finally, this paper summarises the research progress on using natural polysaccharide- and protein-based hydrogels in theiragriculture, proposes a vision for the development of next-generation hydrogels based on their multifunctionality, smart responsiveness and practical applications and provides efficient, adaptive and environmentally compatible solutions for sustainable agriculture.

Sustainable sodium alginate hydrogels incorporating banana leaf activated carbon and organo-clay for enhanced dye removal

New sodium alginate-based hydrogels using activated carbon from banana leaves and organo-modified montmorillonite for water treatment. Activated carbon extracted successfully from banana leaves and montmorillonite clay was surface-modified using cetyltrimethylammonium bromide as a cationic surfactant. Hydrogels were then synthesized using calcium chloride as the cross-linking agent. They were characterized using FTIR, X-ray diffraction, and scanning electronic microscopy. Characterization intimated the incorporation of components successfully. Adsorption performance was determined using pH, adsorbent dosages, initial dye concentration, and contact time. Sodium alginate-based hydrogels demonstrated remarkable efficacy in removing MB and EBT dyes from synthetic solutions, achieving removal efficiencies of up to 80.3% and 84.9% respectively within 90 min at pH 7. The adsorption process corresponded better to the Freundlich isotherm model. The kinetics of EBT dye removal were described by a pseudo-second-order model. Meanwhile, the kinetics of the removal of MB dyes were described by both pseudo-first order and intraparticle diffusion models. We conducted MTT assays to determine the cytotoxicity of our blends. This showed a dose-dependent drop in viability. Sodium alginate-based hydrogels made the cells least cytotoxic. The developed hydrogels can be used as safe and effective agents for water treatment, as indicated by the results.

Lignin-based ternary composite hydrogel for slow-release of fertilizer and soil water retention

Slow-release hydrogel can effectively improve nutrient content of soil and reduce evaporation rate of the water. However, petroleum-based hydrogels will cause secondary pollution to soil. Herein, the nitrogen content of aminated lignin reached 7 % by Mannish reaction with microwave heating, and the influence of microwave heating on the aminated process of lignin was investigated. Afterwards, lignin-based ternary composite hydrogel (sodium alginate (SA)/sanxan(SX)/aminating lignin (OLS)) was successfully prepared using all-biomass sources. The slow-release hydrogel with optimal water absorption, water retention and slow-release properties can be obtained by adjusting the ratio of SX and OLS. The maximum water absorption capacity of hydrogel with rich pore structure can be as high as 91.9 g/g and can still reach 88.95 g/g after 8 times of recycling. The addition of SA/SX/OLS into soil increased the maximum water holding capacity and water retention by 27.88 % and 42.66 %, respectively. Besides, the effects of SA/SX/OLS on physical and chemical properties of soil were explored, and the soil improvement mechanism by the ternary composite hydrogel was also proposed. This work offered a novel strategy to enhance soil fertility by adding SA/SX/OLS composite hydrogel to the soil, Making it of great value in the field of sustainable agricultural development.

Coal-bearing kaolinite-based plant growth-promoting fertilizer with integrated slow-release and water-retention properties

The development of ecological fertilizers has become crucial in modern agriculture due to the increasing global population and diminishing arable land resources. Herein, a plant growth-promoting fertilizer (UKS) with dual functions of slow-release and water-retention was prepared by combining liquid-phase intercalation method and crosslinking gel method. The physicochemical properties of UKS were analyzed and its dissolution, slow-release, and water-retention properties were systematically evaluated. The intercalation ratio was able to reach 53.3 % after intercalation for 5 days, exhibiting the slow-release potential of nitrogen fertilizer. The incorporation of sodium alginate improved the mechanical strength of the frame structure and effectively enhanced the water retention and slow-release properties of the fertilizer. Moreover, the cultivation experiments had shown that UKS can promote the growth of crops' leaves and roots, as evidenced by the fact that the length of them reached 9.8 cm and 5.4 cm, representing a respective growth of 16.8 % and 16.9 %, respectively. This strategy delivers a new approach for the development of eco-friendly agricultural fertilizers, and also provides a potential way to use coal-based solid waste for ecological restoration nearby.

Creating ultra-strong and recyclable green plastics from marine-sourced alginate-chitosan nanowhisker nanocomposites for controlled release urea fertilizer

In response to the pressing environmental challenge posed by petroleum-derived plastics, the development of green plastics derived from all-biomass nanocomposites offers promising solutions. However, conventional nanocomposites often prioritize enhanced stiffness at the expense of flexibility. We introduce sodium alginate (SA)/chitosan nanowhisker (CSW) nanocomposites, derived entirely from marine-sourced all-biomass, to create ultra-strong and flexible green plastics. Through the synergistic interaction between SA and CSW, these nanocomposites demonstrate simultaneous stiffening and toughening, overcoming the traditional trade-off. Two key mechanisms contribute: geometric reinforcement from the needle-like structure of CSW and electrostatic reinforcement at the interface between oppositely charged CSW and SA. Compared to control SA, the SA/CSW nanocomposites exhibit remarkable enhancements in tensile modulus, strength, and stretchability, by 49%, 85%, and 55%, respectively (7.6 GPa, 223.3 MPa, 14.7%). Cellulose nanocrystals, serving as a control, only stiffen the nanocomposites, adhering to the typical trade-off. Biodegradability in compost can be tailored based on the type of nanofillers. Due to the water resistance of CSW, SA/CSW nanocomposites are proven effective for the controlled release of urea fertilizer in agricultural applications. With recyclability and superior mechanical properties, these marine-sourced green plastics offer a sustainable alternative to conventional plastics, promising significant impact in the eco-plastic industry.

Chitosan xerogel embedded with green synthesized cerium oxide nanoparticle: An effective controlled release fertilizer for improved cabbage growth

With the growing awareness on the adverse effects of conventional fertilizers; the use of sustainable and controlled release fertilizers has garnered much significance. In the present study, we report the synthesis of chitosan-benzaldehyde Schiff base xerogel incorporated with green synthesized cerium oxide nanoparticle using Psidium guajava leaves extract as a sustainable fertilizer. Spherical CeO2 NPs having an average particle size of 15.3 nm and zeta potential of - 39.9 mV was obtained. The urea-loaded nanocomposite xerogel (CsB@U/CeO2) was examined for cabbage growth. The water retention capacity extended for >2 weeks. A controlled release profile for urea was accomplished from CsB@U/CeO2 for a period extending for 30 days. The kinetics assay suggested that presence of CeO2 NPs asserted a greater role in urea-controlled release from the CsB@U/CeO2 nanocomposite hydrogel owing to polymer relaxation. The growth parameters of cabbages such as head height, diameter, fresh head weight, head circumference was enhanced in plants fertilized by CsB@U/CeO2 as compared to urea. Furthermore, the phenolic content, free radical scavenging activity, protein content, sugar and flavonoid content were also found higher in CsB@U/CeO2 fertilized plants. This study puts forth CsB@U/CeO2 xerogel can be potentially harnessed as an alternative to urea in sustainable agriculture.

An update review on biopolymer Xanthan gum: Properties, modifications, nanoagrochemicals, and its versatile applications in sustainable agriculture

During the development of green agriculture and pesticide use, "reducing pesticides use and improving control efficiency" is imperative. To date, new pesticide formulations created by nanotechnology can be expected to overcome the difficulties that cannot be solved by the traditional pesticide processes and make pesticide formulations close to the needs of green agricultural production. As natural polysaccharides, Xanthan gum (XG) charactered by a repeated units and side chain of d-glucose, d-mannose, and d-glucuronic acid, and thereby having the unprecedented features in response to wide practice in various fields. This review introduces the properties of the natural polymer XG and its current status of application in agriculture, focusing on the pesticide adjuvant and preparation of novel pesticide and fertilizer delivery systems (such as core-shell and hydrogel), and combined with the applications in mulch film and soil engineering. Furthermore, the properties of Xantho-oligosaccharides suitable for agriculture were discussed. Finally, the potential of XG for the creation of nanopesticides and its future prospects are highlighted. Taken together, XG's excellent performance endows it with a wide range of applications in the agriculture field, and result in strong stimulating the sustainable development of agriculture and evolution of agricultural industry.

Chitosan/Sodium Alginate Hydrogel for the Release of Berberine as an Algae Suppressant: RSM Optimization and Analysis of Sustained Release Characteristics

In this study, we used chitosan/sodium alginate hydrogel as a carrier to prepare berberine sustained-release capsule materials that can inhibit algae for a long time and safely. The preparation conditions of the material were optimized by the response surface method, and the optimized capsule material was characterized and the sustained release characteristics were analyzed to study the change of the algae inhibition effect of the material within 30 days. The results showed that the optimum preparation parameters of the material were 0.54% chitosan content, 2.46% sodium alginate content and 1.09% anhydrous calcium chloride content by response surface optimization design, which was consistent with the parameters set by each factor at the central point. The algae inhibition rate of the material under this preparation condition was 93.75 ± 1.01%, which was similar to the predicted value. The release characteristics analysis showed that the material continuously released up to 90% of berberine within 24 days, and its release characteristics were sustained release after burst release, with good sustained release effect. The results of material characterization showed that chitosan/sodium alginate hydrogel could effectively load berberine and was beneficial to the loading and release of berberine. The results of algae inhibition experiments showed that low concentration materials could control the outbreak of cyanobacterial blooms in a short time, while under high concentration conditions, the materials could inhibit Microcystis aeruginosa efficiently and for a long time.

Design, preparation, and performance of different adsorbents based on carboxymethyl chitosan/sodium alginate hydrogel beads for selective adsorption of Cadmium (II) and Chromium (III) metal ions

Developing cost-effective and efficient adsorbents for heavy metals in multicomponent systems is a challenge that needs to be resolved to meet the challenges of wastewater treatment technology. Two adsorbents were synthesized, characterized, and investigated for the removal of Cd2+ and Cr3+ as model heavy metals in their single and binary solutions. The first adsorbent (ACZ) was a nanocomposite formed of O-Carboxymethyl chitosan, sodium alginate, and zeolite. While, the other (ACL) contained ZnFe layered double hydroxides instead of the zeolite phase. Adsorbents were characterized using XRD, FTIR, SEM, and swelling degree analysis. For single heavy metal adsorption isotherms, data for both adsorbents was best fitted and indicated a multilayer adsorption nature. For binary adsorption, Langmuir model with interacting parameters showed the best results compared to other models for both pollutants. For single system, Avrami model was found to be the best model representing the adsorption kinetics data, which indicates that the mechanism of adsorption follows multiple kinetic orders that may change during duration of adsorption process. Numerous interaction mechanisms can occur between the heavy metals and functional groups in the synthesized hydrogels such as NH2, COOH, and OH groups leading to efficient adsorption of metal ions.

Urea-rich sodium alginate-based hydrogel fertilizer as a water reservoir and slow-release N carrier for tomato cultivation under different water-deficit levels

In this study, a new eco-friendly urea-rich sodium alginate-based hydrogel with a slow-release nitrogen property was prepared, and its effectiveness was evaluated in the cultivation of tomato plants under different water stress levels. The structure and performance of the hydrogel were investigated by FTIR, XRD, TGA, DTG, and SEM. The swelling and release experiments showed that prepared urea-rich hydrogel exhibited a high-water holding capacity (412 ± 4 g/g) and showed a sustained and slow nitrogen release property. A greenhouse pot experiment was conducted using two hydrogel levels (0.1 and 0.5 wt%) under two water deficit levels (30 and 70 % based on required water irrigation). Germination tests indicated that the developed hydrogel fertilizer has no phytotoxicity and has a positive impact on the germination rate even under water deficit conditions. The application of hydrogel fertilizer at 0.5 wt% significantly (p > 0.05) enhanced plant growth parameters such as leaf number, chlorophyll content, stem diameter, and plant length compared to the control treatment. The magnitude of the responses to the hydrogel fertilizer application depended on the concentration of applied hydrogel fertilizer and stress severity with the most positive effects on the growth and yield of tomato observed at a level of 0.5 %. Tomato yield was significantly enhanced by 19.58 %-12.81 %, 18.58 %-22.02 %, and 39.38 %-43.18 % for the plant amended with hydrogel at 0.1-0.5 wt% and grown under water deficit levels of 0, 30, and 70 %, respectively, compared to the control treatment.

Sustained-release nitrogen fertilizer delivery systems based on carboxymethyl cellulose-grafted polyacrylamide: Swelling and release kinetics

Sustained or controlled-release delivery systems can enhance functions such as nutrient usage; minimize soil contamination, and reduce the required fertilizer dose. This paper reports the development of a carboxymethyl cellulose-g-polyacrylamide copolymer (CMC-g-PAM) as a sustained and slow-release fertilizer carrier for urea. The developed copolymer was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and thermo gravimetric analysis (TG). The grafting process increased the activation energy of CMC from 0.1521 to 0.5952 J/mol with a higher loading percentage of 72.140.85% using a 15% urea solution. The swelling ratio is significantly dependent on the pH. The maximum swelling ratio of 1199.58% at pH 9. However, Swelling follows a pseudo-first-order reaction with the maximum swelling ratio in a saline of 349.76%. The CMC-g-PAM copolymer loaded with urea exhibited sustained and slow release, with the maximum cumulative percentage of 69.12% at pH 9 and 38.94% in saline. Urea release from the CMC-g-PAM copolymer followed the first-order, Fickian, and biexponential biphasic release mechanisms. The release of the CMC-g-PAM copolymer loaded with urea is a complicated process governed by diffusion and a biphasic releasing profile.

Study of the degradation in an ultisol of alginate-chitosan complex and its stability and applicability as a soil conditioner

The present work describes the process of degradation of a polyelectrolytic complex (PEC) based on sodium alginate (ALG) and chitosan (CHI), buried for different time intervals, in a clayey soil (ultisol) collected from the municipality of Campos dos Goytacazes, in the northern region of the state of Rio de Janeiro, Brazil. The influence of PEC on soil moisture was also investigated. The results showed that soil moisture increased with the presence of PEC after 7 days of testing, and remained high until the end of the study. FTIR and Raman spectra showed that the breaking of the glycosidic bond (C-O-C) was responsible for the PEC degradation. Thermogravimetry results revealed that alginate was possibly degraded faster than chitosan. Microscopic analysis of the PEC revealed a fragile and fragmented surface of the samples that were buried, in comparison with those not buried. The microbiological assays of the soil confirmed the biodegradation of the polysaccharides. Chemical analysis of soil indicated that PEC did not significantly influence soil fertility. Therefore, we conclude that the PEC (ALG: CHI), formed only by electrostatic interaction, buried in clayey soil, even being biodegraded, can be a promising soil conditioner for agricultural applications.

The water-retaining functional slow-release fertilizer modified by carboxymethyl chitosan

To solve the problem of shortage of agricultural water resources and low utilization rate of fertilizer, a slow-release fertilizer based on chitosan modified water retention function was developed. Solution polymerization and semi-interpenetrating network technology were used to load urea aldehyde into carboxymethyl chitosan superabsorbent resin network. This technology realizes the simultaneous slow release of nutrients and water by using modified chitosan, which has important implications for the application of chitosan in agriculture to regulate the soil water and fertilizer conditions. The optimal preparation conditions were: MBA 0.07 %, KPS 0.8 %, AM to AA mass ratio of 0.3:1, CMC content of 10 %, AA neutralization degree 85 %, UF 20 %, AA+AM mass sum of 10 g, reaction temperature 70 °C and reaction time 2 h. The maximum water absorption rate of the optimized NC reached 172.3 g/g. The cumulative release of nitrogen in 30 days was 83.67 %. The application of NC in sandy soil promoted seed germination and growth. The comprehensive results indicate that NC has broad application prospects in arid areas based on its excellent water retention and nutrient release performance.

Development of a Near-Zero-Waste Valorization Concept for Waste NdFeB Magnets: Production of Antimicrobial Fe Alginate Beads via Adsorption and Recovery of High-Purity Rare-Earth Elements

Nowadays, with the evolution of technology, rare earths are raw materials for a multitude of products, especially in high technological applications. A high amount of REEs is used in the production of permanent magnets, particularly NdFeB. The demand for some of the REEs, including neodymium, praseodymium, and dysprosium, is expected to increase in the coming years. REEs are defined as critical materials due to their high supply risk and economic importance. Recycling secondary raw materials for supplying REEs in the future is one promising option, and one of the best candidates is NdFeB magnets. NdFeB magnets include approximately 30% REEs and 66% of iron. For the near-zero-waste concept, the recovered iron from NdFeB must be evaluated in other applications. In this study, the near-zero-waste valorization concept for EoL-NdFeB magnets is developed, and high-purity REEs are achieved with a two-step process, including leaching and adsorption using alginate beads. Moreover, antimicrobial Fe alginate beads are produced in the leach liquor via adsorption. The antimicrobial activity of the produced Fe alginate beads is evaluated with disc diffusion and broth dilution methods against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The most effective antibacterial Fe alginate beads are against E. coli and S. aureus with inhibitions of 87.21 and 56.25%, respectively.

In situ forming of PEG-NH2/dialdehyde starch Schiff-base hydrogels and their application in slow-release urea

In this study, a biodegradable Schiff-base hydrogel urea, possessing substantial water retention and certain slow-release ability was designed and synthesized. Firstly, dialdehyde starch (DAS) and amine-terminated polyethylene glycol (PEG-(NH2)2) were synthesized using potato starch and polyethylene glycol. Then, a novel Schiff-base hydrogel (SH) was prepared through the in-situ reaction between the aldehyde group of DAS and the amino group of PEG-(NH2)2. Three SH based slow-release urea, designated as SHU1, SHU2, and SHU3 and distinguished by varying urea content, were obtained using SH as the substrate. Several characterizations and tests were conducted to determine the structure, thermal properties, morphology, swelling properties, sustainable use, water retention, and biodegradation properties of SH. Additionally, the slow-release behavior of SHU was studied. SEM results revealed that SH possessed a porous three-dimensional network structure, with a maximum water absorption capacity of 4440 % ± 6.23 %. Compared to pure urea, SHU exhibited better slow-release performance after 30 days of release in soil, with SHU1 having a residual nitrogen content of specifically 36.01 ± 0.57 % of the initial nitrogen content. A pot experiment with pakchoi substantiated the water retention and plant growth promotion properties of SHU. This study demonstrated a straightforward method for the preparation of starch-based Schiff-base hydrogels as fertilizer carriers.

Carboxymethyl starch as a reducing and capping agent in the hydrothermal synthesis of selenium nanostructures for use with three-dimensional-printed hydrogel carriers

The hydrothermal method is a cost-effective and eco-friendly route for preparing various nanomaterials. It can use a capping agent, such as a polysaccharide, to govern and define the nanoparticle morphology. Elemental selenium nanostructures (spheres and rods) were synthesized and stabilized using a tailor-made carboxymethyl starch (CMS, degree of substitution = 0.3) under hydrothermal conditions. CMS is particularly convenient because it acts simultaneously as the capping and reducing agent, as verified by several analytical techniques, while the reaction relies entirely on green solvents. Furthermore, the effect of sodium selenite concentration, reaction time and temperature on the nanoparticle size, morphology, microstructure and chemical composition was investigated to identify the ideal synthesis conditions. A pilot experiment demonstrated the feasibility of implementing the synthesized nanoparticles into vat photopolymerization three-dimensional-printed hydrogel carriers based on 2-hydroxyethyl methacrylate (HEMA). When submersed into the water, the subsequent particle release was confirmed by dynamic light scattering (DLS), promising great potential for use in bio-three-dimensional printing and other biomedical applications.

Preparation of an Aminated Lignin/Fe(III)/Polyvinyl Alcohol Film: A Packaging Material with UV Resistance and Slow-Release Function

To reduce the usage of petroleum-based plastic products, a lignin-based film material named aminated lignin/Fe(III)/PVA was developed. The mixture of 8 g lignin, 12 mL diethylenetriamine, 200 mL NaOH solution (0.4 mol·L^-1), and 8 mL formaldehyde was heated at 85 °C for 4 h; after the aminated lignin was impregnated in the Fe(NO₃)₃ solution, a mixture of 3 g aminated lignin/Fe(III), 7 g PVA, and 200 mL NaOH solution (pH 8) was heated at 85 °C for 60 min; after 2 mL of glycerin was added, the mixture was spread on a glass plate to obtain the aminated lignin/Fe(III)/PVA film. This film demonstrated hydrophobicity, an UV-blocking function, and a good slow-release performance. Due to the formation of hydrogen bonds between the hydroxyl groups of lignin and PVA, the tensile strength, the elongation at break, and the fracture resistance of the film were 9.1%, 107.8%, and 21.9% higher than that of pure PVA film, respectively. The iron content of aminated lignin/Fe(III)/PVA was 1.06 wt%, which mainly existed in a trivalent form. The aminated lignin/Fe(III)/PVA film has the potential to be used as a food packaging material with anti-ultraviolet light function and can also be developed as other packaging materials, such as seedling bowls, pots for transplanting, and coating films during transport.

In situ forming dialdehyde xanthan gum-gelatin Schiff-base hydrogels as potent controlled release fertilizers

Controlled release fertilizer (CRF) hydrogels have blossomed into promising materials in agriculture owing to the sustained release of the fertilizer and also as soil conditioner. Apart from the traditional CRF hydrogels; Schiff-base hydrogels have garnered significant thrust that release nitrogen slowly in addition to reducing the environmental pollution. Herein, we have fabricated Schiff-base CRF hydrogels composed of dialdehyde xanthan gum (DAXG) and gelatin. The formation of the hydrogels was accomplished via the simplistic in situ crosslinking reaction between the aldehyde groups of DAXG and the amino groups of gelatin. The hydrogels acquired a compact network upon increasing the DAXG content in the matrix. The phytotoxic assay on different plants indicated the hydrogels to be nontoxic. The hydrogels demonstrated good water-retention behaviour in soil, along with reusability even after 5 cycles. A controlled release profile for urea was evident from the hydrogels wherein macromolecular relaxation played a crucial role in the release mechanism. Growth assays on Abelmoschus esculentus (Okra) plant presented an intuitive evaluation on the growth and water-holding capacity of the CRF hydrogel. The present work demonstrated a facile preparation of CRF hydrogels to enhance the utilization of urea and retain soil humidity as fertilizer carriers.

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.

Environmentally friendly hydrogel: A review of classification, preparation and application in agriculture

Superabsorbent hydrogel (SH) is three-dimensional (3D) cross-linked hydrophilic polymer that can absorb and retain large quantities of water or other aqueous solutions. SH is made of water-affinity monomers and is widely used in biomedicine, wastewater treatment, hygiene and slow-release fertilizers (SRFs). This article focused on the preparation methods of SH, superabsorbent hydrogel composite and the application of SH in agriculture. By selecting various synthetic technologies and cross-linking agents, a series of chemical cross-linking or physical networks can be designed and tailored to meet specific applications. In view of the excellent characteristics of water absorption, biodegradability, water retention and slow-release capacity, SH occupies a dominant position in the SRFs market. In this work, the agricultural application of SH in double coated SRFs and nutrients carriers is also discussed. Some mechanisms related to the nutrient release were analyzed by mathematical models. In addition, some agronomic benefits of using superabsorbent hydrogels in improving water absorption, water holding capacity and increasing crop yields were also discussed. Although SH has certain shortcomings, from the perspective of long-term development, it will further show great potential in sustainable agriculture.

Macroalgal-Derived Alginate Soil Amendments for Water Retention, Nutrient Release Rate Reduction, and Soil pH Control

There is a need to develop sustainably sourced products that can address the needs for improved water retention in soils, slow the release rate of fertilizers (to prevent leaching and downstream eutrophication), and control soil pH for use in agriculture. This article investigates the use of industrial kelp solid waste extracted alginate (IW) slurries to produce soil amendment beads, potentially improving soil water retention, acting as slow-release fertilizers (SRFs), and combined with limestone controls soil pH levels. Alginate extracted from the IW was determined to have a lower guluronic (G) to mannuronic (M) acid ratio than pure laboratory-grade (LG) alginate (0.36 vs. 0.53). Hydrogels produced from the IW alginate achieved significantly higher equilibrium swelling ratios (1 wt% IW = 1.80) than LG hydrogels with similar concentrations (1 wt% LG = 0.61). Hydrogel beads were impregnated with ammonium nitrate and potassium chloride to produce potential SRFs. The release rates of K⁺ and NO₃⁻ nutrients from the produced SRFs into deionised water were decreased by one order of magnitude compared to pure salts. The nutrient release rates of the IW-based SRFs were shown to be similar to SRFs produced from LG alginate. Hydrogel beads were impregnated with limestone, and it was determined that the alginate-based hydrogels could significantly decrease the nutrient release rate. Using industrial kelp solid waste extracted alginate slurries shows potential for soil amendments production. This report emphasises, for the first time, the use of a crude alginate product in soil amendment formation. Further, it demonstrates slower release rates and soil pH control.

Development of hydrogel based on Carboxymethyl cellulose/poly(4-vinylpyridine) for controlled releasing of fertilizers

A novel Carboxymethyl cellulose (CMC) and poly (4-vinylpyridine) (P4VP) hydrogel system is synthesized with different ratios, in the presence of cross-linker N, N,- methylene bis-acrylamide (MBA). The hydrogel is characterized via FTIR spectroscopy, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The FTIR results showed a strong interaction between both CMC, P4VP and the loaded fertilizer. The water uptake of the hydrogel was evaluated by swelling tests under variations in pH, biodegradability was investigated in soil to simulate real-world conditions. To determine the best release behavior of urea and calcium nitrate from the hydrogel, fertilizers were loaded with different ratios onto the hydrogel during its formation. Fertilizers release was followed by Atomic absorption spectroscopy to study the release of calcium nitrate and urea. Release kinetic parameters were obtained based on different mathematical models as Zero order, First order, Korsmeyer-Peppas and Higuchi models. The suitable proportionality between the mathematical models used and the fertilizers release was determined based on the correlation coefficients (R2). According to Zero order model urea release showed independent concentration. Based on Korsmeyer-Pappas and Higuchi models with high n value and R2 equals to 0.97. Compared to urea, Ca2+, Zero order and Higuchi have been ignored due to their poor correlation coefficients values as proportion with Ca2+ fertilizer release.