Hydrogel Adsorbent Research Articles

Removal of methylene blue from wastewater using hydrogel nanocomposites: A review

Water pollution by organic dyes continues to pose a serious health and environmental threat to the ecosystem. Although adsorption using biopolymer-based hydrogels has proven to be an ideal technique for the treatment of these dye contaminants from aqueous solutions, these hydrogels suffer from lack of mechanical stability and recovery as compared to synthetic polymers. Herein, we review the low-cost synthesis of hydrogel incorporated with inorganic components mainly focusing on strategies to improve the mechanical stability and separation of the hydrogel in removing methylene blue (MB) dye from aqueous solution. The literature shows that hydrogel nanocomposites are a class of materials that have flourished significant consideration, especially concerning water treatment. In adsorption technology, hydrogel nanocomposites act as absorbents, prominent to enhance their removal efficiency towards contaminants. This review highlights the preparation and use of hydrogel nanocomposites as efficient adsorbents. In-depth discussions on adsorption and diverse synthetic routes of hydrogels have been devoted to applications of these nanocomposites and are compared in this contribution to the removal efficiency of MB dye from wastewater.

Adsorption isotherms and kinetics pertinent to modified composite hydrogel adsorbents adopted for heavy metals removal

ABSTRACT Environmental friendly adsorbents constitute an effective method for heavy metals pollution mitigation. In this work, batch adsorption experiments were conducted for the adsorption of various heavy metals including Cr, Co, Ni and Pb using cost-effective modified adsorbents. These comprise polyacrylate hydrogels prepared using microwave (M) irradiation technique (ACM) or ultrasonic (U) irradiation technique (ACU). Further blends of acrylic acid salts with Egyptian kaolin (AKM and AKU) or zeolite (AZM and AZU) were also investigated. The effect of pH and initial concentration on the performance of the composite hydrogels has been studied. Also, several adsorption isotherm and kinetic models were studied. AKU revealed the highest maximum adsorption capacities among other investigated composites for all the tested heavy metals. The equilibrium adsorption experiments revealed that Langmuir isotherm model is best fitted than other models with maximum adsorption capacities of 84.5, 73.3, 61 and 97 mg/g for Cr, Co, Ni and Pb, respectively and equivalent results were obtained from Tempkin isotherm for all ions except Ni. Adsorption kinetics of Cr, Co, Ni and Pb using all the composite hydrogels were best described with the Pseudo-second order kinetic model.

Graphene oxide-chitosan hydrogel for adsorptive removal of diclofenac from aqueous solution: preparation, characterization, kinetic and thermodynamic modelling.

This work aimed at developing a natural compound-based hydrogel adsorbent to remove diclofenac as a model pharmaceutical from water. First, graphene oxide–chitosan (GO–CTS) and amine graphene oxide–chitosan (AGO–CTS) hydrogel adsorbents were synthesized via a facile mechanical mixing method. The synthesized materials were characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, and thermogravimetric analysis (TGA) techniques. In the second stage, adsorption experiments were conducted to determine the best GO to CTS ratio and find the optimized adsorption parameters, including the initial drug concentration, adsorbent dosage, pH, and temperature. The results showed that the optimal GO to CTS mass ratio is 2 : 5 and thus the same ratio was selected as the AGO to CTS mass ratio to understand the effect of amine-functionalization on removal efficiency. The optimal adsorption parameters were determined to be pH of 5, Ci of 100 ppm and dosage of 1.5 g L−1, where 90.42% and 97.06% removal was achieved for optimal GO–CTS and AGO–CTS hydrogel adsorbents, respectively. Langmuir and Freundlich isotherms models were employed to investigate the adsorption behavior of diclofenac onto the synthesized hydrogels. The results revealed that the adsorption tends to be of the monolayer type and homogeneous, as the results were in better accordance with the Langmuir model than the Freundlich model. The thermodynamics of adsorption demonstrated that the adsorption is exothermic, exhibiting higher removal efficiency at lower temperatures. Furthermore, Gibb's free energy change of adsorption (ΔG) suggested that the adsorption is spontaneous, being more spontaneous for AGO–CTS than GO–CTS hydrogels. Finally, the regeneration ability of the hydrogel adsorbents was studied in five consecutive cycles. The adsorbent maintained its efficiency at a relatively high level for three cycles but a considerable decrease was observed between the third and the fourth cycle, indicating that the hydrogels were recoverable for three cycles.

Highly efficient and rapid adsorption of methylene blue dye onto vinyl hybrid silica nano-cross-linked nanocomposite hydrogel

Adsorption treatment of dyes from industrial effluent by hydrogel adsorbent has been a research hotspot, but few high-performance hydrogel adsorbents with high adsorption capacity have been reported. Previously reported poly (acrylic acid) PAA-based hydrogel adsorbents show a low swelling ratio due to the unsatisfactory cross-linked structure, which causes a passive impact on the exhibit of adsorptive sites and the penetration of water inside the hydrogel. Herein, we prepared a novel super-adsorbent nanocomposite (NC) hydrogel adsorbent by employing vinyl hybrid silica nanoparticles (VSNPs) with average diameter of 30 nm as crosslinking agent. The introduction of an optimal content of VSNPs effectively forms a well three-dimensional network structure. The structure system of our NC hydrogel effectively promotes the active sites on the polymer chains to be exposed to dye molecules. Thus, the NC hydrogel adsorbent achieved a high adsorption capacity of 1690 mg/g for adsorbing methylene blue and obtain a high removal ratio of 90 % within 40 min. Furthermore, the hydrogel exhibits excellent reusability after 4 repeated cycles of adsorption and desorption. The work confirmed that the VSNPs can build a well covalent hybrid cross-linked system of a PAA-based hydrogel without other organic crosslinkers and further provided a new method to develop novel hydrogel adsorbent with enhanced adsorption capacity for removing organic dyes from industrial wastewater.

Charge balanced anti-adhesive polyacrylamidoxime hydrogel membrane for enhancing uranium extraction from seawater

• A charge balanced adsorbent is fabricated for uranium extraction from seawater. • The adsorbent can resistant both biofouling and abiotic fouling. • The uranium extraction capacity is highly enhanced. • The uranium adsorption ability and anti-adhesive ability are highly reusable. The extraction of uranium from seawater is vital to meet the increase demands of uranium resource for the nuclear energy industry, while it is severe hazarded by the marine fouling, including both the biofouling and abiotic fouling. Previous reports only focused on the control of biofouling and rare attention is paid to the abiotic fouling. However, the abiotic fouling is the fundamental of the biofouling. Herein, a charged balanced hydrogel adsorbent is fabricated by introducing the charge-positive tetraethylenepentamine (TEPA) into the charge-negative polyacrylamidoxime (PAO). The fabricated PAO-CB hydrogel membrane shows high anti-adhesive ability to the marine fouling, including both the biofouling and abiotic fouling, which is due to the decrease of the charge attraction between the adsorbent and the charged contaminants. Benefitting from the reduce of marine fouling, the PAO-CB hydrogel membrane shows a high uranium extraction capacity of 8.59 mg g −1 , which is higher than that of PAO hydrogel membrane by 44.59%. The finding of this study indicates that the construction of charge balanced adsorbent would be an effective strategy to control the complicated marine fouling during uranium extraction from seawater.

A pH-responsive carboxymethyl cellulose/chitosan hydrogel for adsorption and desorption of anionic and cationic dyes

A carboxymethyl cellulose/chitosan interpenetrating network hydrogel was prepared to adsorb and desorb anionic and cationic dyes applying different pH conditions. The three-dimensional network structure of the hydrogel was investigated using Scanning Electron Microscopy (SEM). Fourier Transform Infrared (FT–IR) was used to analyze the bonding mechanism of the hydrogel. The compression modulus of the hydrogel under neutral conditions exhibited an increase in parallel with the increase of carboxymethyl cellulose content. Under alkaline conditions, the swelling properties of hydrogels in water were enhanced with the increase of the carboxymethyl cellulose content. On the other hand, under acidic conditions, the swelling performance of hydrogels in water was decreased with the increase of carboxymethyl cellulose content. The adsorption capacity and desorption ratio of carboxymethyl cellulose/chitosan hydrogel for Acid Orange II were higher than 100 mg/g and 90%, respectively, while for Methylene Blue were higher than 110 mg/g and 95% even after five adsorption/desorption cycles. This study suggests that the carboxymethyl cellulose/chitosan interpenetrating network hydrogel showed different swelling behaviors under different pH values, which could present great potential as carrier materials in the controllable release-based applications.

Recyclable and degradable nonwoven-based double-network composite hydrogel adsorbent for efficient removal of Pb(II) and Ni(II) from aqueous solution

This study reports a novel adsorbent structure and shows the satisfactory removal performance of Pb(II) and Ni(II). The fabric structure increases the strength of the hydrogel. The hydrogel plays a major role in the composite structure as a matrix, while the fabric bears the applied load and protects the structure from mechanical damage. The double-network composite hydrogel is reinforced by plasma grafted polylactic acid melt-blown non-woven fabric and polyethylene glycol dimaleate, and its compressive strength reaches 40.6 kPa at 60% strain. The interface substantially improves the compression strength by 42.9%. Through the adsorption isotherm model, the adsorption capacity of the hydrogel for Pb(II) and Ni(II) reaches 233.12 and 165.06 mg/g, respectively, and the removal rate of heavy metal ions in water at low concentrations exceeds 95%, showing the excellent removal rate of heavy metals. Even after the fifth cycle, the removal efficiency barely declines, indicating the feasibility of repeatedly use. Cost analysis reveals that the adsorbent is relatively low cost, solving the problems of difficult recovery, low strength, and easy damage of hydrogel adsorbents, and promoting the industrial application of hydrogels as adsorbents.

Dichromate and arsenate anion removal by PEI microgel, cryogel, and bulkgel

Among the various metal ions, chromate (Cr(VI)) and arsenate (As(V)) are the two most hazardous toxic ion species and are found in nature in the form of dichromate and arsenate anions. In this investigation, polyethyleneimine (PEI)-based hydrogels were prepared with microgel, cryogel, and bulkgel morphologies employing glycerol diglycidyl ether as a crosslinker. The prepared PEI-based hydrogels were used to remove dichromate and arsenate anions from aqueous media. PEI microgel, cryogel, and bulkgels weighing 50 mg of each adsorbed 84.7 ± 0.8, 76.5 ± 5.2, and 108.9 ± 2.4 mg.g−1 of dichromate anions and 15.9 ± 0.7, 45.4 ± 1.9, and 79.2 ± 11.6 mg.g−1 of arsenate anions in 30, 120, and 240 min, respectively. The dichromate and arsenate anions adsorption of PEI-based hydrogels were found to fit to the pseudo-second-order kinetic, and nonlinear Langmuir isotherm models, respectively with higher R2 values. The highest distribution coefficient (Kd) value of PEI-based hydrogels for dichromate adsorption was obtained on the cryogel forms of PEI as 1.89 ± 0.05. Likewise, the highest Kd value for the arsenate adsorption was calculated on PEI-based bulkgels as 0.46 ± 0.01. The thermodynamic parameters of PEI based hydrogels in the adsorption of dichromate and arsenate anions e.g., ΔG (all negative (except for the arsenate adsorption by PEI microgels), and ΔH that is around 2−10 kJ.mol−1, and ΔS what is around 0.01−0.02 kJ.mol−1. K−1 were calculated. The reusability studies showed that PEI-based hydrogels can be used for at least 5 consecutive adsorption-desorption cycles with almost 70 % anion removal efficiency after the fifth cycle.

Synthesis of carboxymethyl cellulose-chitosan-montmorillonite nanosheets composite hydrogel for dye effluent remediation

MMTNS were introduced into carboxymethyl cellulose-chitosan system to synthesize porous hydrogel adsorbent with stable structure and high dye handling capacity. Al-OH on edge of MMTNS formed hydrogen-bond (-OH···+NH3-) with -NH2 on CS, CS then cooperated with CMC via amidation and chains interleaving, forming three-dimensional hydrogel. Morphology characterization revealed that hydrogel possessed microporous open-framework structure, facilitating free entrance of macromolecular MB dye to react with internal reaction sites in hydrogel. Factor tests indicated that high removal (97%) of MB was achieved via 0.2 g/L hydrogel within 360 min even after 5 adsorption-regeneration cycles. Adsorption process followed Pseudo-first-order, Pseudo-second-order kinetic model and Sips isotherm model, owing to both monolayer physical and chemical adsorption behavior of MB molecules onto homogeneous surface of hydrogel. Adsorption mechanism was attributed to ion-exchange, groups combination of carboxyl and hydroxyl, and Si active sites reaction. Such hydrogel realized promotion of polysaccharide polymers in materials design and wastewater treatment.

Adsorption of Cu2+, Cd2+ and Pb2+ in wastewater by modified chitosan hydrogel

ABSTRACT Heavy metal pollution is extraordinary critical, so it is urgent to develop an effective adsorbent to dispose of such pollution. Modified chitosan was combined with polyacrylic acid to form N-carboxymethyl chitosan hydrogel (NCS-hydrogel) adsorbent. The morphology and structure of NCS-hydrogel were analyzed and identified by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and other characterization methods. NCS-hydrogel adsorption was used to treat water pollution of Cu, Cd and Pb ions, and the influencing factors of adsorption performance were studied. The intrinsic mechanism of adsorption process was discussed by thermodynamic, kinetic and isotherm models. The results show that the adsorption process of metal ions by NCS-hydrogel meets the spontaneous monolayer chemisorption, and the adsorption process is accompanied by heat release.

Hydrogel adsorbent in industrial wastewater treatment and ecological environment protection

With the gradual deterioration of the ecological environment and the shortage of water resources, the resource-based treatment of industrial wastewater has become the focus of scientific research. At present, there are many research results on industrial wastewater resource treatment, such as ammonia desulfurization technology, ion exchange membrane technology, chemical precipitation technology, etc., but these technologies have the disadvantages of complex process, secondary pollution and so on In order to improve the efficiency of industrial waste water treatment, solve the water resource crisis and realize the coordinated development of ecological environment, based on the characteristics of hydrogel materials, a new hydrogel adsorbent was prepared, and its adsorption properties and effects on heavy metal ions were analyzed. The results showed that the maximum adsorption capacity of the hydrogel adsorbent to Pb could reach 170.31 mg/g, and the adsorption capacity was best when the adsorption time was 8 h and the temperature was controlled at 25 C. The adsorption regeneration experiment also confirmed that the hydrogel adsorbent could maintain good adsorption capacity and recycle 4 times. All these indicate that the hydrogel adsorbent has a very significant effect on the treatment of industrial waste water and the protection of ecological environment.

Low-cost hydrogel derived from agro-waste for veterinary antibiotic removal: Optimization, kinetics, and toxicity evaluation

Abstract A green hydrogel from biochar and chitosan (BC) was synthesized as an adsorbent to remove ciprofloxacin (CIP) and enrofloxacin (ENR) from aqueous solution. BC hydrogel was prepared through an eco-friendly and inexpensive approach, using chitosan extracted from shrimp shells and biochar produced from rice husk. The physicochemical characteristics of BC were determined by SEM, FTIR, and pH PZC . A Taguchi method was employed to determine the optimal conditions for adsorption of CIP and ENR, and these were found to be 1.0 and 1.5 g/L of BC adsorbent for 300 and 450 min at pH=7, respectively. Adsorption kinetics of CIP and ENR were found to follow a pseudo-second-order model. Langmuir, Freundlich, and Temkin adsorption isotherms were applied to illustrate the adsorption equilibrium of veterinary antibiotics. The results indicate that CIP and ENR fit the Langmuir isotherm well with maximum adsorption capacities of 106.038 and 100.433 mg/g, respectively. Also, the BC hydrogel adsorption mechanism were combined with electrostatic π – π interactions and hydrogen bonds. Furthermore, a toxicity survey of microalgae Chlorella sp. for 72 h confirmed that the BC hydrogel is non-toxic for the environment.

Response Surface Optimization of Graphene Oxide-Reinforced Dual-Crosslinked Alginate/Poly(Vinyl Alcohol) Hydrogel Beads for Methylene Blue Adsorption

Response surface methodology (RSM) was used to determine the optimal blend of alginate (ALG), poly (vinyl alcohol) (PVA) and graphene oxide (GO), as well as glutaraldehyde (GA) crosslinking solution concentration for the synthesis of dual-crosslinked ALG/PVA/GO nanocomposite hydrogel adsorbent beads for methylene blue (MB) removal. Statistical analyses show that PVA concentration contributes the largest effect to the adsorption capacity response, attributed to improved accessibility of MB molecules to adsorption sites. The optimal blend was determined to be 3% polymer with 50% PVA, 383.8384 ppm GO, crosslinked in 1% CaCl2 and 5% GA. These results were validated, and the experimental value of the adsorption capacity deviated by only 1.702% from the RSM model prediction, suggesting good model predictability. Adsorption isotherm models were tested to provide a description of the adsorption process. The Sips isotherm model, suggesting monolayer adsorption over heterogeneous surface with action of cooperative adsorbate-adsorbate interactions, was the best fit to the experimental equilibrium data, with an R2 of 0.9782. Furthermore, the ALG/PVA/GO beads demonstrated a maximum monolayer adsorption capacity of 1081.62 mg/g, showing superior performance compared to known biosorbents of MB.

Polydopamine/montmorillonite-embedded pullulan hydrogels as efficient adsorbents for removing crystal violet

Both secondary pollution and the low mechanical strength of adsorbents have severely impeded the practical application of adsorption methods in the dye wastewater treatment. In this work, we innovatively synthesized a composite hydrogel adsorbent by incorporating polydopamine (PDA) and montmorillonite (MMT) into the pullulan hydrogel matrix for dye adsorption. First, the successful formation of the resultant adsorbents was verified by Fourier-transform infrared spectroscopy and scanning electron microscope elemental mapping analysis. Then, several physicochemical properties (such as thermal and swelling properties, microarchitecture, and mechanical strength) of the five prepared adsorbents (PM1–PM5) were investigated. These results demonstrated the adsorbents had tunable properties, which can be achieved by adjusting the PDA/MMT mass ratio. Next, the dye adsorption performance was systematically explored. The resultant adsorbent (PM3) had a maximum adsorption capacity of 112.45 mg/g and its adsorption data was best described by a Langmuir isotherm and pseudo-second-order kinetic. Finally, the adsorption mechanisms and potential commercial practicability of the adsorbent were studied. Altogether, the designed adsorbent could effectively avoid generating the secondary pollution typical of adsorbents and it displayed excellent mechanical strength, thus opening up a new horizon in mitigating environmental pollution from textile industries.

Agar/κ-carrageenan composite hydrogel adsorbent for the removal of Methylene Blue from water

Water pollution caused by dyes is a significant global problem. Adsorption technique is successfully applied for the removal of dyes from water. In this technique, the use of effective adsorbents is very important. Here, agar/κ-carrageenan composite hydrogel adsorbent prepared through free radical cross-linking reaction in the presence of tri (ethylene glycol) divinyl ether as a cross-linker and characterized by using FTIR, SEM and TGA measurements was used to remove Methylene Blue from water. FTIR results exhibited that electrostatic interaction and hydrogen bonding formation were the main interactions in the adsorptive removal of Methylene Blue by agar/κ-carrageenan hydrogel. Pseudo second order and Langmuir models were found to be the most suitable kinetic and isotherm models, respectively. Maximum dye adsorption capacity of 242.3 mg·g−1 was obtained at 35 °C and pH 7. Thermodynamic parameters were calculated to understand the nature of adsorption process. Different solvents were applied for the regeneration of dye adsorbed-agar/κ-carrageenan hydrogel and the most suitable solvent was determined as ethyl alcohol. The results demonstrated that agar/κ-carrageenan hydrogel is a promising adsorbent for the removal of cationic dyes from water.

N-Aminorhodanine modified chitosan hydrogel for antibacterial and copper ions removal from aqueous solutions

A novel adsorbent based on N-Aminorhodanine modified chitosan hydrogel was synthesized and evaluated for antibacterial and copper ions removal from aqueous systems. N-Aminorhodanine was reacted with glutaraldehyde to yield Schiff base followed by reaction with chitosan to obtain the new hydrogel adsorbent. The new adsorbent was analyzed using FTIR, 1H NMR, XRD, TGA, HR-SEM and EDX in addition to the swelling behavior. The maximum adsorption capacities of chitosan and modified chitosan for copper ions were 38 and 62.5 mg/g respectively. The adsorption isotherm belongs Freundlich model and pseudo second order kinetics regime. The adsorption was reach to maximum within 15 min for modified chitosan hydrogel while take about 360 min for chitosan. Regeneration of adsorbent showed only 23% decline after 6 cycles which indicate the stability of the new adsorbent and it can be reused several times with good efficiency. N-Aminorhodanine modified chitosan hydrogel showed good activity towards gram positive bacteria.

Poly(acrylic acid)/poly(acrylamide) hydrogel adsorbent for removing methylene blue

AbstractCationic dye can cause severe damage to the environment due to their refractory degradation, complex composition and strong stability. Hydrogels as adsorbents have been widely used to treatment the wastewater with dyestuff for their low prices, simple operations, and high efficiency. This work uses poly(acrylic acid) (PAA)/poly(acrylamide)(PAM)/calcium hydroxide nanoparticles (CHN) polymeric hydrogel absorbent to eliminate methylene blue (MB) dye. First, PAM/PAA/CHN hydrogel is produced through copolymerization of acrylic acid monomer and acrylamide monomer using inorganic CHN as cross‐linker. And then, the adsorption performance of such PAM/PAA/CHN hydrogel adsorbent for adsorbing MB dye is explored at different conditions including pH, contacting time, adsorbent dosage, initial concentration of MB, and temperature. A maximum adsorption capability for adsorbing MB reaches 1,056 mg/g. Furthermore, the pseudo‐first‐order mode and Langmuir isotherm model can well describe adsorption behavior of MB dye onto such PAA/PAM/CHN hydrogel adsorbent. Thereby, as‐prepared PAA/PAM/CHN hydrogel could be a potential adsorbent for eliminating organic dyes from wastewater.

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

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

Development and assessment of adsorptive hydrogel: Process engineering and economic considerations

AbstractThis article addresses the production of an adsorbing hydrogel to be used for removal of heavy metals. A review of literature on hydrogel adsorption of heavy metals is highlighted. The adopted process is briefly described and typical adsorption results as compared to reported work are presented. The technical specifications of an industrial scale plant of appropriate capacity of 3000 ton/year are detailed. The total capital investment and the production cost have been estimated to be about $M 10.6 and 6.5, respectively. Financial analysis determined the effect of variation of selling price within the reported international range on financial indicators. Furthermore, analysis of the effect of variation by 10% increase/decrease of capital investment and annual operating cost has been also estimated. Indicators include net present value (NPV $M), internal rate of return (IRR%), and average simple return of return (Average. SRR%), which have been estimated as 24%, 18%, and 19%, respectively. The project proves to be techno‐economically viable under the estimated conditions for wider application.

Polymer hydrogel cross‐linked by inorganic nanoparticles for removing trace metal ions

AbstractHydrogels for absorbing metal ions in wastewater have attracted more attentions in the environmental field especially for recent years. The removal efficiency of hydrogel adsorbents for eliminating metal ions is highly related with the effective contact between adsorbents and adsorbates. However, poor water absorption capacity of the hydrogel adsorbents would restrict on the expose of adsorption sites to the targeted subjects, causing undesirable removal ratio (RR) especially for metal ions at trace level. Thereby, the reported hydrogel adsorbents mainly focus on the removal of high content but not the trace level of metal ions so far. In this work, poly(acrylamide) (PAM)/poly(acrylic acid) (PAA)/Ca(OH)2 composite hydrogel is applied to adsorb trace metal ions. Swelling ratio of such PAM/PAA/Ca(OH)2 gel reaches 2,530 g/g, resulting in effective exposure of active sites and further expected RR for trace metal ions. The RRs of such adsorbent for Cu2+ (initial concentration C0 = 0.064 mg/L), Al3+ (C0 = 0.27 mg/L), Co2+ (C0 = 0.59 mg/L), Cr6+ (C0 = 0.52 mg/L), Mn2+ (C0 = 0.55 mg/L), Ni2+ (C0 = 0.59 mg/L), Zn2+ (C0 = 0.65 mg/L), Ag+ (C0 = 1.08 mg/L), and La3+ (C0 = 1.39 mg/L) are 56.6, 80.8, 41.3, 29.3, 34.6, 44.6, 55.9, 45.8, and 35.5%, respectively. This work broadens the application of hydrogel adsorbent for eliminating trace metal ions from polluted water.