Strong alginate/reduced graphene oxide composite hydrogels with enhanced dye adsorption performance

A short review on polysaccharide-based nanocomposite adsorbents for separation and biomedical applications

Polysaccharides such as chitosan, alginate, cellulose, and carrageenan have emerged as promising adsorbents due to their biodegradability, abundant availability, and diverse chemical functionality. These biopolymers exhibit promising performance for adsorption of a wide range of pollutants including heavy metals (e.g., lead, cadmium), organic dyes (e.g., methylene blue, methyl orange), and even pathogenic microorganisms. However, inherent hydrophilicity and poor mechanical properties limit their broader application in environmental and biomedical fields. As an effective way to address the issues, recent advancements have focused on the incorporation of nanoparticles (e.g., metal oxides, carbon nanotubes and clays) into polysaccharides to obtain nanocomposite films. Generally, these nanocomposites offer enhanced surface area, tunable porous network, and improved chemical and mechanical resistances for adsorption and biomedical applications. The current review gives a focused overview of the recent progresses in polysaccharide-based nanocomposites, with particular attention to their fabrication methods, adsorption capacity and mechanism, and diverse applications in water purification, drug delivery, and antimicrobial treatments. Critical challenges such as the optimization of nanoparticle dispersion and the environmental impacts of nanocomposite biodegradation are also discussed to pave the road for the future research in this promising field.

Magnetic carrageenan gum-grafted-polyacrylamide nanocomposite for uptake of cationic dyes from the aquatic systems

Using an ex-situ growth approach, this research fabricated k Carrageenan/Polyacrylamide@magnetite nanocomposites (NCs), (k-Car/PAM@Magnetite NCs). The k-Carrageenan (k-Car) backbone was modified through graft polymerization of acrylamide (PAm) via radical polymerization using ammonium persulfate (APS) as the initiator. N'-N' methylenebisacrylamide (MBAA) was used as the cross-linking agent, and magnetic nanoparticles (MNPs) were incorporated to impart magnetic properties. The successful synthesis of the k-Car/PAM@Magnetite NCs was confirmed through various analyses, including FT-IR, FESEM, EDS, XRD, VSM, BET, TGA, and Zeta. The adsorption effectiveness of the NCs for removing methylene blue (MB) and rhodamine B (RhB) from wastewater was evaluated by optimizing experimental parameters such as pH, adsorbent dosage, agitation time, and initial dye concentration. The NCs demonstrated a maximum adsorption capacity according to the Langmuir Isotherm (Qmax) of 204.082 mg. g-1 for MB and 200 mg.g-1 for RhB using 0.004 g of NCs.The adsorption data fit the Freundlich non-linear isotherm model well, and the kinetic data followed a pseudo-second-order (PSO) model. It is evident from the thermodynamic parameters that adsorption is an endothermic process that is spontaneous and favourable. The k-Car/PAM@Magnetite NCs also exhibited excellent regeneration capabilities, maintaining high adsorption efficiency after three consecutive adsorption-desorption cycles.

Nano-enabled smart and functional materials toward human well-being and sustainable developments

Fabrication and operation on increasingly smaller dimensions have been highly integrated with the development of smart and functional materials, which are key to many technological innovations to meet economic and societal needs. Along with researchers worldwide, the Waterloo Institute for Nanotechnology (WIN) has long realized the synergetic interplays between nanotechnology and functional materials and designated 'Smart & Functional Materials' as one of its four major research themes. Thus far, WIN researchers have utilized the properties of smart polymers, nanoparticles, and nanocomposites to develop active materials, membranes, films, adhesives, coatings, and devices with novel and improved properties and capabilities. In this review article, we aim to highlight some of the recent developments on the subject, including our own research and key research literature, in the context of the UN Sustainability development goals.

Integrating DFT and machine learning for the design and optimization of sodium alginate-based hydrogel adsorbents: Efficient removal of pollutants from wastewater

This study presents a novel approach to design and optimize a sodium alginate-based hydrogel (SAH) for efficient adsorption of the model water pollutant methylene blue (MB) dye. Utilizing density functional theory (DFT) calculations, sodium alginate-g-poly (acrylamide-co-itaconic acid) was identified with the lowest adsorption energy (Eads) for MB dye among 14 different clusters. SAHs were prepared using selected monomers and sodium alginate combinations through graft co-polymerization, and swelling studies were conducted to optimize grafting conditions. Advanced characterization techniques, including FTIR, XRD, XPS, SEM, EDS, and TGA, were employed, and the process was optimized using statistical and machine learning tools. Screening tests demonstrated that Eads serves as an effective predicting indicator for adsorption capacity (qe) and MB removal efficiency (RRMB,%), with reasonable agreement between Eads and both responses under given conditions. Process modeling and optimization revealed that 5 mg of selected SAH achieves a maximum qe of 3244 mg g-1 at 84.4% RRMB under pH 8.05, 98.8 min, and MB concentration of 383.3 mg L-1, as identified by the desirability function approach. Moreover, SAH effectively eliminated various contaminants from aqueous solutions, including sulfasalazine (SFZ) and dibenzothiophene (DBT). MB adsorption onto selected SAH was exothermic, spontaneous, and followed the pseudo-first-order and Langmuir-Freundlich isotherm models. The remarkable ability of SAH to adsorb MB is attributed to its well-designed structure predicted through DFT and optimal operational conditions achieved by AI-based parametric optimization. By integrating DFT-based computations and machine-learning tools, this study contributes to the efficient design of adsorbent materials and optimization of adsorption processes, also showcasing the potential of SAH as an efficient adsorbent for the abatement of aqueous pollution.

Enhancing Alginate Hydrogels as Possible Wound-Healing Patches: The Synergistic Impact of Reduced Graphene Oxide and Tannins on Mechanical and Adhesive Properties

Hydrogels are three-dimensional crosslinked materials known for their ability to absorb water, exhibit high flexibility, their biodegradability and biocompatibility, and their ability to mimic properties of different tissues in the body. However, their application is limited by inherent deficiencies in their mechanical properties. To address this issue, reduced graphene oxide (rGO) and tannins (TA) were incorporated into alginate hydrogels (Alg) to evaluate the impact of the concentration of these nanomaterials on mechanical and adhesive, as well as cytotoxicity and wound-healing properties. Tensile mechanical tests demonstrated improvements in tensile strength, elastic modulus, and toughness upon the incorporation of rGO and TA. Additionally, the inclusion of these materials allowed for a greater energy dissipation during continuous charge-discharge cycles. However, the samples did not exhibit self-recovery under environmental conditions. Adhesion was evaluated on pig skin, revealing that higher concentrations of rGO led to enhanced adhesion, while the concentration of TA did not significantly affect this property. Moreover, adhesion remained consistent after 10 adhesion cycles, and the contact time before the separation between the material and the surface did not affect this property. The materials were not cytotoxic and promoted healing in human fibroblast-model cells. Thus, an Alg/rGO/TA hydrogel with enhanced mechanical, adhesive, and wound-healing properties was successfully developed.

Alginate-based composites as novel soil conditioners for sustainable applications in agriculture: A critical review

The development of alginate-based composites in agriculture to combat nutrient loss and drought for sustainable development has drawn increasing attention in the scientific community. Existing studies are however scattered, and the retention and slow-release mechanisms of alginate-based composites are not well understood. This paper systematically reviews the current literature on the preparation, characterization, and agricultural applications of various alginate-based composites. The synthesis methods of alginate-based composites are firstly summarized, followed by a review of available analytical techniques to characterize alginate-based composites for the attainment of their desired performance. Secondly, the performance and controlling factors for agricultural applications of alginate-based composites are discussed, including aquasorb, slow-release fertilizer, soil amendment, microbial inoculants, and controlled release of pesticides for pest management. Finally, suggestions and future perspectives are proposed to expand the applications of alginate-based composites for sustainable agriculture.

A synergistic approach combining Adsorption and Biodegradation for effective treatment of Acid Blue 113 dye by Klebsiella grimontii entrapped Graphene Oxide-Calcium Alginate Hydrogel Beads

This study investigated the degradation of Acid Blue 113 (AB 113) dye using Klebsiella grimontii entrapped Graphene Oxide-Calcium Alginate Hydrogel beads (KG-GO-CA) in a Fluidized Bed Bioreactor (FBBR) under varying inlet loading rates. The minimum fluidization velocity of the KG-GO-CA hydrogel beads in FBBR was found to be 0.15 mm/s. The KG-GO-CA beads showed a maximum removal efficiency of 94.6% at an inlet flow rate of 20 mL/h over 15 days. Reusability studies indicated a removal efficiency of 70.6 ± 2.5% for AB 113 after the 12th cycle. Langmuir adsorption isotherm showed the best fit (R2 = 0.98724) with model parameters of Qm (203.83 mg/g) and Ki (0.0101 L/g). The study also confirmed that treated wastewater was more environmentally safe for domestic and commercial uses than untreated wastewater. The research highlights the potential use of KG-GO-CA hydrogel beads for removing dyes from wastewater.

Preparation and Characterization of a New Bis-Uracil Chitosan-Based Hydrogel as Efficient Adsorbent for Removal of Anionic Congo Red Dye

A new hydrogel, based on chitosan crosslinked with 2-chlorophenyl-bis(6-amino-1,3-dimethyluracil-5-yl) methane, (2Clph-BU-Cs), has been successfully created. Various instrumental techniques such as elemental analysis, FTIR, SEM, and XRD were used to prove its structure. Its removal efficiency for anionic Congo red (CR) dye under different conditions for industrial wastewater treatment was studied. For optimizing the conditions to maximize CR dye removal, the impacts of temperature, contact time, pH, and initial concentration of the dye on adsorption capacity were investigated. The removal of the dye was pH-dependent, with a much higher value achieved at pH 4 than at pH 7 and 9. The maximum adsorption capacity of the hydrogel was 93.46 mg g^-1. The model of adsorption process was fitted to the pseudo-second-order kinetic model. The intraparticle diffusion demonstrated the multi-step nature of the adsorption process. The thermodynamic results showed that the adsorption process was endothermic because of the positive value of enthalpy (43.70 kJ mol^-1). The process of adsorption at high temperatures was spontaneous, according to the values of ∆G⁰. An increase in randomness was seen in the value of ∆S°. Generally, the investigated hydrogel has the potential to be used as a promising effective reusable adsorbent for industrial wastewater remediation.

Graphene oxide modified κ-carrageenan/sodium alginate double-network hydrogel for effective adsorption of antibiotics in a batch and fixed-bed column system

The treatment of antibiotic wastewater pollution is imminent, the studies of double-network hydrogels as adsorbents have gradually increased, it is quite important to develop a non-toxic hydrogel with excellent properties as adsorbent. In this study, a graphene oxide modified κ-carrageenan/sodium alginate (GO-κ-car/SA) gel was prepared by calcium hardening. The addition of GO nanosheets enhances the mechanical strength and anti-swelling property of the double-network hydrogel, making it possible for the application in the fixed-bed column system. The elastic modulus is twice as much as the hydrogel without GO. The maximum adsorption capacity in the experiments of the GO-κ-car/SA gel for CIP and OFL can reach 272.18 mg g^-1 and 197.39 mg g^-1, respectively. The GO-κ-car/SA gel always remains negatively charged, which means that the adsorption capacity of the gel is better in an acidic environment. In the fixed-bed column system, through Thomas fitting, the maximum adsorption capacity of the simulated OFL wastewater (200 mg L^-1) is 83.99 mg g^-1. The adsorption mechanism of antibiotics by GO-κ-car/SA gel depends on hydrogen bond, functional groups and electrostatic adsorption. The good hydrophilic properties, excellent adsorption capacity and high mechanical strength, which can ensure that the adsorbent is in full contact with the contaminants without major deformation or damage, makes the study more helpful for the further study on hydrogel in the fixed-bed column system.

Evaluation of the Adsorption Efficiency of Graphene Oxide Hydrogels in Wastewater Dye Removal: Application of Principal Component Analysis

Industrial dye wastewater is one of the major water pollution problems. Adsorbent materials are promising strategies for the removal of water dye contaminants. Herein, we provide a statistical and artificial intelligence study to evaluate the adsorption efficiency of graphene oxide-based hydrogels in wastewater dye removal by applying Principal Component Analysis (PCA). This study aims to assess the adsorption quality of 35 different hydrogels. We adopted different approaches and showed the pros and cons of each one of them. PCA showed that alginate graphene oxide-based hydrogel (without polyvinyl alcohol) had better tolerance in a basic medium and provided higher adsorption capacity. Polyvinyl alcohol sulfonated graphene oxide-based hydrogels are suitable when higher adsorbent doses are required. In conclusion, PCA represents a robust way to delineate factors affecting hydrogel selection for pollutant removal from aqueous solutions.

Alginate-based nano-adsorbent materials - Bioinspired solution to mitigate hazardous environmental pollutants

Population growth and industrialization is associated with the elevation of hazardous pollutants, including heavy metals, biomedical wastes, personal-care products, endocrine-disrupters, pharmaceutically active compounds, and colorants in the environment. The scientific focus has been devoted to developing novel adsorbents to mitigate hazardous pollutants by constructing hybrids of different polymers and nano-structured materials for improved workability and physicochemical attributes. Recently, much attention has been devoted to nanomaterials in environmental remediation, owning to their exceptional characteristics including novel electrical/chemical features, quantum size effects, tunable functionalization, high scalability, and surface-area-to-volume ratio. Target-specific designing of nanocomposites impart high functionality. The cost-effective and eco-friendly synthesis of bioadsorbent materials is increasing for the removal of hazardous pollutants. Due to biocompatible, biodegradable, and eco-friendly nature, sodium alginate has been widely reported for the preparation of bioadsorbent materials to remove different inorganic/organic pollutants. In this review, the potentialities of alginate-based nanocomposites have been described for environmental remediation purposes. Different nanomaterials, including silica, metallic oxide, graphene oxide, hybrid inorganic-organic, non-magnetic-magnetic, carbon nanorods, nanotubes, polymeric nanocarriers, and several other materials have been described in combination with alginate biopolymer for environmental remediation.

Modulation of Conductivity of Alginate Hydrogels Containing Reduced Graphene Oxide through the Addition of Proteins

Modifying hydrogels in order to enhance their conductivity is an exciting field with applications in cardio and neuro-regenerative medicine. Therefore, we have designed hybrid alginate hydrogels containing uncoated and protein-coated reduced graphene oxide (rGO). We specifically studied the adsorption of three different proteins, BSA, elastin, and collagen, and the outcomes when these protein-coated rGO nanocomposites are embedded within the hydrogels. Our results demonstrate that BSA, elastin, and collagen are adsorbed onto the rGO surface, through a non-spontaneous phenomenon that fits Langmuir and pseudo-second-order adsorption models. Protein-coated rGOs are able to preclude further adsorption of erythropoietin, but not insulin. Collagen showed better adsorption capacity than BSA and elastin due to its hydrophobic nature, although requiring more energy. Moreover, collagen-coated rGO hybrid alginate hydrogels showed an enhancement in conductivity, showing that it could be a promising conductive scaffold for regenerative medicine.

Silk Fibroin Enhances Cytocompatibilty and Dimensional Stability of Alginate Hydrogels for Light-Based Three-Dimensional Bioprinting

Three-dimensional (3D) bioprinting is a technology under active study for use in tissue engineering and regenerative medicine. Bioink comprises cells and polymers and is the essential material for 3D bioprinting. The characteristics of the bioink affect its printability, gelation behavior, and cell compatibility. In this study, alginate derivatives were synthesized to induce rapid gelation, and a bioink was prepared by mixing these alginate derivatives with silk fibroin to enhance cell compatibility. A low-concentration (3 wt %) alginate/silk fibroin (Alg/SF) bioink was pregelated by the ionic cross-linking of Alg to increase the viscosity for 3D printing. The rheological and mechanical properties were analyzed using a rheometer and a texture meter, respectively. Analysis of cell viability and proliferation using fibroblasts (NIH-3T3) in the bioinks showed that the Alg/SF bioink has improved cytocompatibility compared to that of conventional Alg bioinks, making it a promising material for tissue engineering.

Hydrothermally Reduced Graphene Hydrogel Intercalated with Divalent Ions for Dye Adsorption Studies

Fundamental studies involving divalent ion intercalated graphene-based hydrogel are still lacking in terms of their adsorption behavior towards dye pollutants. In this study, we prepared a self-assembled Mg2+ and Ca2+ intercalated reduced graphene hydrogel (rGH) using hydrothermal treatment to evaluate the intercalation impact on the adsorption capability towards cationic dyes, methylene blue and rhodamine B. The morphological, structural, thermal, and textural properties of the divalent ion intercalated reduced graphene hydrogels were studied using Fourier transform infrared spectrometer, thermogravimetric analysis, Raman spectroscopy, scanning electron microscope-energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area analysis, and X-ray diffraction. The increased adsorption capacity of the divalent ion intercalated reduced graphene-based hydrogels towards the dye molecules resulted from the increase in the specific surface area and pore volume due to the Mg2+ and Ca2+ bridging that formed spaces between the graphene sheets framework. Adsorption kinetics and the equilibrium adsorption isotherm were fitted by a pseudo-second-order alongside intraparticle diffusion kinetic models and Langmuir isotherm respectively. In addition, the divalent ion intercalated reduced graphene hydrogel showed good generation after three cycles of simultaneous adsorption.