The progressive development of advanced industrialization and agriculturalization, the explosive growth of the global population, and the continued increase in human needs have led to a dramatic increase in wastewater discharge [[1], [2], [3]]. The contaminants in wastewater are often composed of complex constituents, including soluble aromatic compounds and dye pollutants, insoluble oils and organic solvents, and various pathogenic bacteria, which can result in serious environmental issues and cause health risks to human beings [[4], [5], [6], [7], [8]]. Soluble aromatic compound and dye pollutants, including 4-nitrophenol (4-NP), rhodamine B (RhB), methylene blue (MB), and methyl orange (MO), have toxic properties and are resistant to biodegradation due to the inherent aromatic structures [9]. Insoluble oils and organic solvents discharged from oil leakage and industrial processing can induce significant risks to aquatic species and water quality, further posing potential hazards to human's health [10]. Similarly, pathogenic bacteria are favorable to reproduced in wastewater, which can spread various diseases, further endangering human health. Accordingly, the exploration of wastewater treatment techniques to eliminate diverse contaminants from wastewater is essential for a reliable supply of clean water. With these considerations in mind, enormous endeavors have been made to eliminate intricate pollutants from waterbodies through various approaches based on different materials, such as physical adsorption, membrane filtration, chemical dispersion, coagulation, combustion, degradation, and so on [[11], [12], [13], [14], [15]]. Nevertheless, there are limitations associated with these conventional approaches to wastewater remediation. Most of the approaches suffer from the single-function characteristic, which is invalid for the remediation of complicated wastewater. Hence, it is urgent to explore multifunctional materials that possess the capability of removing soluble aromatic compounds and dye pollutants, disinfecting bacteria, and separating insoluble oils from wastewater.

In previous research, active carbon, graphene, clay, mesoporous silica, and synthetic polymers have been employed as substrates to immobilize functional material for the remediation of complicated wastewater [[16], [17], [18], [19], [20]]. Unfortunately, most of these substrates typically present various shortcomings, including the use of non-environmentally friendly reagents, complex preparation processes, poor recyclability and biocompatibility, and high cost, which severely restricts their practical application in the remediation of complicated wastewater. Recently, there has been considerable focus on substrate materials derived from biological sources due to their environmental friendliness, good biocompatibility, and low cost [[21], [22], [23], [24], [25], [26], [27]]. Therefore, biobased materials have been regarded a promising substrate for wastewater treatment application. Among the biobased substrate materials, hydrogels based on biopolymers are recognized as promising candidates for the fabrication of functional material owing to the individual three-dimensional cross-linked structure and excellent mechanical and biocompatible properties [[28], [29], [30], [31]]. The rich hydration groups contained in the cross-linked polymer chains of the hydrogels, including the hydroxyl, amino, and carboxyl groups, endow the hydrogels with remarkable water absorption and water-retaining capacity [32,33]. Additionally, hydrogels can be employed to coat a variety of substrates to construct anti-oil fouling surfaces, which can prohibit insoluble oil from permeating the hydrogel-coated surfaces, thus achieving oil-water separation [34]. Moreover, despite their ability to achieve oil-water separation, the hydrogel-coated surfaces are susceptible to organic and biological fouling over a long period of use, which ultimately leads to decrease in separation efficiency of oil-water mixtures. Hence, it is advantageous for practical applications to endow hydrogels with the capabilities of self-cleaning.

Additionally, hydrogels are vulnerable to mechanical damage produced by the external stimulus in the process of application, which severely decline the separation efficiency. In recent years, extensive research has been conducted on self-healing hydrogels in order to enhance the durability and prolong the functional lifespan. Self-healing materials are substances that possess the inherent capability to autonomously fix up cracks after sustaining damage without requiring any external stimulus, due to the reversible and dynamic covalent bonds or non-covalent bonds within the molecular network. The covalent bonds involve various types of chemical bonds, including CC bonds, disulfide bonds, imine bonds, phenylboronate ester bonds, acylhydrazone bonds, and so on. In contrast, the non-covalent bond involves hydrogen bonding, electrostatic interactions, ionic bonding, boronate esters, hydrophobic associations, host-guest interactions, and so on [35]. However, there are certain drawbacks associated with these self-healing hydrogels, including intricate chemical modification, non-naturally occurring macromolecular constituents, or slow speeds of self-healing. Given environmental sustainability, the adoption of natural resources for the preparation of self-healing materials is also highly desirable.

Guar gum, an outstanding biopolymer for hydrogel formation, has drawn extensive attention owing to its abundant active sites for further modification, its environmental friendliness with sustainability and biocompatibility, and its low cost in comparison with other synthetic polymers [[36], [37], [38]]. A great many hydroxyl groups along the chain enable the guar gum to be miscible with water at room temperature. In aqueous solution, the chains in the molecular of guar gum easily form hydrogels with the addition of cross-linking agents. For example, sodium periodate (NaIO4) can oxidize hydroxyl groups into aldehyde groups, resulting in the generation of self-healing hydrogels [39,40]. Borax can also be used as a cross-linker for the generation of guar gum hydrogel with self-healing capabilities owing to the inherent dynamic nature of boronate ester linkages [41]. Self-healable guar gum hydrogels could spontaneously recover their functionality after destruction by external forces, which can extend the service life and reduce the economic cost during practical application.

However, the guar gum hydrogel itself cannot fulfill the removal of soluble pollutants and the disinfection of pathogenic bacteria. Hence, it is desirable to impart the guar gum hydrogel with the capacity of removing soluble pollutants, eliminating bacteria as well as separating oil-water mixtures. Recently, hydrogels incorporated with silver nanoparticles (Ag NPs) have drawn enormous attention in versatile applications [[42], [43], [44]]. The unique physicochemical properties of Ag NPs arise from their small particle size, tunable morphologies, large specific surface areas, and plentiful reactive sites in comparison to their bulk counterparts. Ag NPs have significant applications in the field of catalysts and biological medicine, which is related to their extensive properties for the reduction of organic pollutants and their strong capacity to inhibit bacterial growth. However, the nanostructured Ag particles exhibit a significant tendency for aggregation, which in turn declines the activity. To disperse and stabilize Ag NPs, different methods have been applied including the employment of organic surfactants, ligands, and inorganic or polymeric substrates [[45], [46], [47], [48]]. Nevertheless, it has been documented that organic surfactants and ligands might affect the activity of Ag NPs. Inorganic substrates without modification usually suffer from a weak binding force with Ag NPs, leading to the peeling of Ag NPs from inorganic substrates. Moreover, the fabrication procedure of Ag NPs involves toxic and harmful materials, which can cause secondary environmental pollution. With this in mind, great efforts should be dedicated to develop feasible, efficient, and environmentally friendly approaches for preparing high-active Ag NPs. To address these issues, polymeric hydrogels would be an ideal alternative option for stabilization and immobilization of Ag NPs [[49], [50], [51]]. The hydrogels with cross-linked three-dimensional network structures can prohibit aggregation and affect the size distribution of Ag NPs, which is beneficial to maintaining the high activity of Ag NPs [52]. Combining of Ag NPs with the guar gum hydrogels can provide the hydrogels with new functions. Additionally, the Ag NP-immobilized guar gum hydrogels can be obtained by a facile one-step method, during which the generation of Ag NPs and the gelation of guar gum occur simultaneously and complete in a very short time [53].

In this research, we illustrate a facile approach for the fabrication of multifunctional Ag/guar gum hydrogels, during which natural guar gum, silver nitrate (AgNO3), and sodium borohydride (NaBH4) were applied as raw material. A redox reaction occurred between AgNO3 (oxidizing agent) and NaBH4 (reducing agent), and Ag NPs were formed in situ. In the meantime, the sodium metaborate (NaBO2), an oxidative product of NaBH4, played as a crosslinking agent for the gelation of guar gum. The whole procedure was exceptionally quick and easy, which was accomplished within a few minutes. The presence of Ag NPs endows the Ag/guar gum hydrogels with high catalytic reduction for aromatic compounds and dye pollutants, and extensive antibacterial performance. The prominent self-healing property of the guar gum hydrogels is capable of providing the Ag/guar gum hydrogels with excellent recyclability. On the other hand, the Ag NPs/guar gum hydrogels were applied to construct oil/water separation interfaces for insoluble oils/organic solvent disposal. The Ag NPs/guar gum hydrogels exhibited exceptional superhydrophilicity/underwater superoleophobicity and ultralow oil adhesion performance, making them feasible for the efficient separation of oil-water mixtures. Considering the easy preparation procedure as well as the multiple functionalities of AgNPs/guar gum hydrogels, the present research aims to introduce novel insight into the fields of wastewater treatment.