Hydrogel Catalyst Research Articles

Preparation of a novel lactose-lignin hydrogel catalyst with self-reduction capacity for nitrogenous wastewater treatment

Preparation of a novel lactose-lignin hydrogel catalyst with self-reduction capacity for nitrogenous wastewater treatment

Realizing Direct Uranium Extraction from Seawater Using a Carboxyl-g-C3N4/CdS Hydrogel.

The photocatalytic U(VI) reduction is regarded as an effective strategy for recovering uranium. However, its application in seawater uranium extraction poses challenges due to limited reactivity in the presence of carbonate and under atmospheric conditions. In the present study, a photoactive hydrogel made of carboxyl-functionalized g-C3N4/CdS (CCN/CdS) is designed for extracting uranium. The carboxyl groups on g-C3N4 enhance the affinity toward uranyl ions while CdS facilitates the activation of dissolved oxygen. Under atmospheric conditions, the prepared hydrogel catalyst achieves over 80% reduction rate of 0.1mM U(VI) within 150 min in the presence of carbonate, without the assistance of any electron donors. During the photocatalytic process, U(VI) is reduced to form UO2+x. The hydrogel catalyst exhibits a high uranium extraction capacity of >434.5mgg⁻1 and the products can be effectively eluted using a 0.1M NaCO3 solution. Furthermore, this hydrogel catalyst offers excellent stability, good recyclability, outstanding antifouling activity, and ease of separation, all of which are desirable for seawater uranium extraction. Finally, the test in real seawater demonstrates the successful extraction of uranium from seawater using the prepared hydrogel catalyst.

A dual-thermosensitive hydrogel catalyst with Ag nanoparticles capable of single/tandem/non catalytic switchable ability

Thermosensitive hydrogels are among the most promising class of catalysts for self-controlled tandem catalytic systems. In this study, we developed a bi-layered, molecularly imprinted, thermosensitive hydrogel catalyst that is loaded with silver metal nanoparticles (Ag NPs) and acidic sites. This catalyst is capable of regulating alternating single and tandem reactions, making it a valuable tool for complicated catalytic applications. The catalyst displays two key phase transition temperatures, at 37 °C and 46 °C, by combining positive and negative response temperature-sensitive hydrogel layers together, enabling crossing range responsive ability of the "open" or "closed" state of the substrate channels. Meanwhile, the hydrogel layers can effectively separate the different catalytic sites to prevent active sites and intermediate products from mixing and causing cross-reactions. The opposite thermosensitive characteristics of the hydrogels coupled together produce a swelling-contraction behavior, enabling efficient sequencing of single/tandem/non-catalytic reactions. Overall, this study presents a promising strategy for the development of smart hydrogel catalysts in self-controlling tandem catalytic systems.

Smart hydrogel catalyst with tunable activity for 4-nitrophenol reduction at different temperatures and pH

In this study, a novel method is introduced for preparing the poly (N-isopropylacrylamideco-methacrylic acid) (PNIPAM) hydrogel catalyst (PNMC-Ag) with embedded silver nanoparticles (Ag NPs), by employing in situ reduction of Ag+ in polymeric network. The prepared hydrogel catalyst exhibits both thermal and pH responsiveness, facilitating precise control of catalytic efficiency in reducing pollutants such as 4-nitrophenol (4-NP) under varying environmental conditions. The embedded Ag NPs demonstrate remarkable stability against self-aggregation due to their confinement within the polymeric network, thus maintaining their exceptional catalytic performance over time. Leveraging the dual-responsive nature of the PNMC-Ag catalyst, tunable catalytic activity can be achieved by adjusting the temperature and pH of the reaction environment. Specifically, the Ag NPs-hydrogel catalyst exhibits high catalytic activity (21 min, 98.5%) in low-temperature ([Formula: see text]< 32°C) at neutral pH and alkaline (pH = 9) conditions at room temperature, while its activity is attenuated in high-temperature ([Formula: see text]> 32°C) at neutral pH or acidic (pH [Formula: see text]4) environments at room temperature owing to the hydrogel’s thermal and pH-responsive characteristics. This distinctive feature enables precise control over the catalytic reaction, offering an effective approach for the removal of 4-NP from wastewater using a noble-metal-containing stimuli-responsive hydrogel (SRH) catalyst. Overall, this work represents a significant step towards the development of intelligent catalytic materials with superior environmental remediation capabilities.

Co2+-adsorbed chitosan-grafted-poly(acrylic acid) hydrogel as peroxymonosulfate activator for effective dye degradation

In this work, chitosan-grafted-poly(acrylic acid) (CS-g-PAA) was synthesized for use as a Co2+ adsorbent and circularly utilized as a peroxymonosulfate (PMS) activator in the degradation of rhodamine B (RhB) dye. CS-g-PAA demonstrated 3.7 times higher adsorption capacity toward Co2+ than pristine chitosan. The impact of the adsorption conditions was evaluated. The pseudo-second-order kinetic model and the Langmuir isotherm model best described the adsorption process. Under optimum conditions, the adsorption capacity of CS-g-PAA for Co2+ was 212 mg/g. The Co2+-adsorbed CS-g-PAA hydrogel was further utilized in the RhB degradation process. The effects of catalyst dosage, initial RhB concentration, pH, and the coexistence of anions on the degradation of RhB were studied. The hydrogel catalyst could remove 98 % of RhB within 5 min, at a degradation rate of 0.624 per min. Electron paramagnetic resonance (EPR) analysis and the radical scavenger experiment suggested that SO4•−, HO•, 1O2, and O2•− were involved in the degradation. Furthermore, when tested in various water systems, high degradation efficiencies of 98 % were attained after 20 min. The hydrogel catalyst performed excellent degradation over ten cycles without any chemical recovery processes. Moreover, high degradation efficiencies were observed between 95 % and 98 % when tested with other dyes.

Novel durable and recyclable Cu@MoS2/polyacrylamide/copper alginate hydrogel photo-Fenton-like catalyst with enhanced and self-regenerable adsorption and degradation of high concentration tetracycline

A durable and recyclable Cu@MoS2/polyacrylamide/copper alginate nanocomposite double network (Cu@MoS2/PAAm/CA NCDN) hydrogel photo-Fenton-like catalyst was prepared for efficient removal of high concentration tetracycline (TC) in pharmaceutical wastewater. This hydrogel catalyst exhibits a remarkable synergistic effect between adsorption and catalytic degradation of TC. Consequently, this hydrogel catalyst shows a larger TC adsorption capacity of 122.2 mg g−1 and a higher TC degradation efficiency of 90% (degradation amount = 70.2 mg g−1) at the TC concentration of 200 mg L−1, while the TC degradation efficiency by Cu@MoS2 catalyst is only 19% (degradation amount = 38.2 mg g−1). This hydrogel catalyst can effectively remove high concentration TC under both light and dark conditions. Moreover, the tensile strength of Cu@MoS2/PAAm/CA NCDN hydrogel catalyst reaches an extraordinary 1.46 MPa and maintains 0.68 MPa after 15-day immersion in water, indicating high durability. In addition, the flexible hydrogel catalyst can keep good integrity after being deformed by stretching, bending, and knotting, etc., enabling its easy recovery. This investigation provides an innovative and versatile strategy to develop high-performance hydrogel catalysts for treating antibiotics-polluted water.

Hydrogel-based heterogeneous-acid-catalysts for converting carbohydrates into the platform chemical: 5-hydroxymethylfurfural

Background5-hydroxymethylfurfural (5-HMF) is a significant platform chemical with the potential to be converted into hydrocarbon biofuels. Herein, a facile and reusable catalyst was investigated to synthesize 5-HMF from monosaccharides in a green solvent medium following eight green chemistry principles. MethodsA hydrogel-based heterogeneous acid catalyst was synthesized through photoreaction to determine its ability to dehydrate fructose in the invert sugar syrup into 5-HMF. The main structure of the hydrogel catalyst was formed with polyethylene glycol diacrylate (PEGDA), and this backbone structure was modified by 3-sulfopropyl methacrylate potassium salt (3SMP) and further acidified by 3M HCl to form PEGDA-3SMP-H with 32.54 mmole/g of H+ amount on the catalyst. Significant findingsWith the PEGDA-3SMP-H catalyst, fructose conversion of 85.80% with a 5-HMF yield of 46.99% could be attained at 120°C for a 24 h reaction time in an aqueous medium with the co-solvent gamma-butyrolactone (GBL), which is considered a green solvent medium. PEGDA-3SMP-M (M=metal) hydrogel catalyst was synthesized using 8 different metal ions fixed on the 3SMP through ion exchange. The catalytic ability sequence for synthesized hydrogel catalysts followed H+> Cr3+> Cu2+> Al3+> Ni2+> Co2+ > Cu+> Fe3+> Fe2+ for 5-HMF formation. The 5-HMF yield was improved with consecutive cycles of using a regenerated PEGDA-3SMP-H catalyst. In the first cycle, the 5-HMF yield was 36.86%; in the second and third cycles, it was 39.39% and 41.49%, respectively. The prepared heterogeneous catalyst is preferred in terms of industrial applications owing to its facile synthesis, recyclability, stability, simple separation method, low equipment corrosion, and minimization of final product contamination with acid catalysts.

Simple synthesis of copper/MXene/polyacrylamide hydrogel catalyst for 4-nitrophenol reduction

• A non-noble copper/MXene/polyacrylamide hydrogel was designed. • The hydrogel was synthesized by in-situ polymerization and self-reduction methods. • The hydrogel catalyst had superior catalytic activity for 4-nitrophenol reduction. • The hydrogel catalyst with foam-like structure can be simply recycled. Noble metal-based catalysts are often used in industrial catalytic reactions. However, the high price hinders their practical application. Herein, a novel Copper/MXene/polyacrylamide hydrogel catalyst is synthesized via in-situ polymerization and self-reduction method. We use Copper (Cu) as catalytic species, two-dimensional transition metal carbides (MXene) as electron transfer medium, and porous polyacrylamide (PAM) as adsorbent for designing this non-noble hydrogel catalyst. The electron transfer and adsorption capacity are improved by the synergy effects of Cu/MXene/PAM, and thus the composite catalyst for 4-nitrophenol reduction shows high catalytic activity. It is impressive that this foam-like hydrogel catalyst can be easily separated and reused many times, which has potential application for industrial catalysis.

Peroxymonosulfate activation by Mg-introduced Fe-N carbon nanotubes to accelerate sulfamethoxazole degradation: Singlet oxygen-dominated nonradical pathway

Here, Mg-introduced Fe-N carbon nanotube catalysts (FeMg@NCNTs) were prepared for peroxymonosulfate (PMS). Experiments suggested that the introduction of Mg improved the removal of sulfamethoxazole (SMX) and found a transformation from the original radical pathway to a nonradical pathway dominated by singlet oxygen (1O2). XPS characterization demonstrated an enhanced pyridinic N content with the introduction of Mg. SMX degradation was not inhibited by pH, coexisting ions, or humic acid (HA). The free radical scavengers and electron paramagnetic resonance (EPR) indicate that the primary reactive substance was 1O2. Experimentally, 1O2 was proven to have a predominant effect on the degradation of SMX. The concentration of 1O2 increased 6.37 times after the introduction of Mg. Four decomposition pathways and three fragile sites for SMX were proposed by DFT calculations and HPLC-MS. The toxicity estimation software tool (T.E.S.T) analyzed the intermediates with lower ecotoxicity than SMX. The different contaminants (CIP, BPA, TBBPA, TCS, TC and Rh B) had a removal rate of more than 99% at 60 min except TC. The removal rates of SMX in tap water, river water and lake water were 100%, 96.6% and 93.1% in 40 min, respectively. The SMX degradation efficiency remained good after 5 cycles of the experiment. FeMg@NCNTs hydrogel catalyst continuous flow device exceeded 90% within 15 h for SMX removal efficiency and the Rh B is always running at 99% removal rate. In conclusion, this work provides a singlet oxygen-dominated non-radical pathway activating material and provides a new option for antibiotic wastewater degradation and practical applications.

Degradation of methylene blue through Fenton-like reaction catalyzed by MoS2-doped sodium alginate/Fe hydrogel

In this study, a low-cost and high-performance MoS2/sodium alginate (SA)/Fe (MSF) hydrogel catalyst was prepared. It was found that the MSF hydrogel could efficiently catalyze the degradation of methylene blue (MB) through the Fenton reaction without the addition of Fe2+. The reaction was initiated by Fe2+ which was derived from the cyclic redox reaction between MoS2 and Fe3+ and produced large quantities of ·OH to degrade the MB. The effect of MoS2 concentration, FeCl3·6H2O concentration, H2O2 dosage, solution pH, and light on the degradation was systematically studied. The MoS2 concentration of 0.5 mg/ mL, FeCl3·6H2O concentration of 0.25 g/mL, 50 μL H2O2, and the pH of 4.0 were the optimized parameters. Moreover, it was found that the MB degraded faster under the infrared radiation. The MB removal rate reached as high as 98% within 15 min in the presence of a low concentration of H2O2 and the procedure could be repeated 5 times. The MSF hydrogel provided an effective and simple strategy for the sustainable degradation of organic pollutants in wastewater.

Graphene-based hydrogel with embedded gold nanoparticles as a recyclable catalyst for the degradation of 4-nitrophenol

Hydrogels have been utilized as a sort of scaffold in catalytic field since they can offer good accommodation for noble metal nanoparticles (NPs) to the preparation of recyclable catalysts. In this work, the poly(4-vinylpyridine) (P4VP) grafted graphene oxide (GO) was firstly synthesized through surface-initiated atom transfer radical polymerization (SI−ATRP). Then, a tough and self-healable composite hydrogel was fabricated by integration of the P4VP-grafted GO into poly(acrylic acid) (PAA) matrix through hierarchically hydrogen-bonding interactions and simultaneous in-situ growth of gold nanoparticles (AuNPs) in the hydrogel scaffold. The as-prepared AuNPs@GO-g-P4VP/PAA composite hydrogel possesses improved mechanical strength and integrity, and exhibits higher catalytic activity in the reductive degradation of 4-nitrophenol into 4-aminophenol than other reported AuNPs-loaded hydrogel catalysts. In addition, the self-healing composite hydrogel catalyst shows ease of separation as well as good reusability without obvious loss of catalytic activity. This work provides an attractive method for the synthesis of robust functional nanoparticle-embedded composite hydrogel for application in various fields.

Facile synthesis of Ag nanoparticles/Ti3C2Tx/polyacrylamide composite hydrogel as efficient catalyst for methylene blue and 4-nitrophenol reduction

Catalytic reduction has been regarded as one of the most efficient strategy for organic pollutants removal from aqueous solution. However, lack of efficient catalyst prevents its practical application. Herein, we design a simple and environmental friendly fabrication strategy for the 3D Ag nanoparticles/Ti3C2Tx/polyacrylamide (Ag/MX/PAM) composite hydrogel as high efficient catalyst. In this composite hydrogel, the Ag nanoparticles, Ti3C2Tx (MXene) and polyacrylamide (PAM) act as active species, efficient electron transfer medium and high-capacity adsorbent respectively. Due to these synergistic effects for the composite hydrogel catalyst, the electron-transferring ability as well as the adsorption capacity are boosted and thus high catalytic activity achieves towards both methylene blue (MB) and 4-nitrophenol (4-NP) reduction. The superior rate constant k of 8.333 min−1 and turnover frequency (TOF) up to 25.17 min−1 for 4-NP reduction are realized over the 12%-Ag/MX/PAM hydrogel. Impressively, this composite hydrogel with a foam-like bulk structure can be reused easily after catalytic reaction, making it a potential catalyst for reduction of organic pollutants in industrialization.

RELEASING HYDROGEN FROM NABH4 VIA HYDROGEL BASED CoF2 CATALYST

In this paper, the dehydrogenation reaction of NaBH4 was performed in the presence of Co-ion loaded hydrogel catalyst. The reactions took place within 27, 18 and 9 hours at 25, 35 and 45 °C, respectively. In addition, the relation between the initial concentration of NaBH4 and released hydrogen was investigated at 45°C. A linear relationship between initial borohydride concentration and produced H2 was determined. Also, differential method was used to determine reaction rate constants and rate order. Hence, first-order-kinetics was proved by using experimental data. After that, the activation energy was found as 58.26 kJ/mol by means of the slope of the graph of lnk versus 1/T for the dehydrogenation reaction. This value is nearly equal to 50kJ/mol, which was expected in literature for the studies of the catalytic dehydrogenation. As the hydrophilic and macroporous structure of the prepared poly(acrylamide-co-acrylic acid) (p(AAm-co-AAc)-Co) hydrogel catalyst allowed inlet of NaBH4 solution up to its interior and release of produced H2, effect of pore diffusion limitation was neglected. Dehydrogenation index of NaBH4 was calculated as 2526.31 mL H2/g NaBH4 according to the amount of NaBH4 in the aqueous solution

Carboxylcellulose hydrogel confined-Fe3O4 nanoparticles catalyst for Fenton-like degradation of Rhodamine B

Facile preparation of functional hydrogel materials for environmental catalysis is a hot research topic of soft materials science and green catalysis. In this study, a carboxylcellulose hydrogel confined Fe3O4 nanoparticles composite catalyst (Fe3O4@CHC) with magnetic recyclability has been synthesized by taking the advantages of the newly developed cellulose solution in tetramethyl guanidine/DMSO/CO2 through in situ acylation using mixed cyclic anhydrides and ion exchange reaction. The achieved Fe3O4@CHC hydrogel catalyst was shown to be an more efficient and better Fenton-like catalyst for decomposition of the organic dye rhodamine B (RhB) in the presence of hydrogen peroxide, with almost complete decomposition occurring within 180 min, in comparison with Fe3O4@cellulose hydrogel (CH) with excellent recyclability. This work provided a facile strategy for the preparation of hydrogel-based functional composite green catalytic materials, which has potential applications in green catalysis.

Application of Redox-Responsive Hydrogels Based on 2,2,6,6-Tetramethyl-1-Piperidinyloxy Methacrylate and Oligo(Ethyleneglycol) Methacrylate in Controlled Release and Catalysis.

Hydrogels have reached momentum due to their potential application in a variety of fields including their ability to deliver active molecules upon application of a specific chemical or physical stimulus and to act as easily recyclable catalysts in a green chemistry approach. In this paper, we demonstrate that the same redox-responsive hydrogels based on polymer networks containing 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) stable nitroxide radicals and oligoethylene glycol methyl ether methacrylate (OEGMA) can be successfully used either for the electrochemically triggered release of aspirin or as catalysts for the oxidation of primary alcohols into aldehydes. For the first application, we take the opportunity of the positive charges present on the oxoammonium groups of oxidized TEMPO to encapsulate negatively charged aspirin molecules. The further electrochemical reduction of oxoammonium groups into nitroxide radicals triggers the release of aspirin molecules. For the second application, our hydrogels are swelled with benzylic alcohol and tert-butyl nitrite as co-catalyst and the temperature is raised to 50 °C to start the oxidation reaction. Interestingly enough, benzaldehyde is not miscible with our hydrogels and phase-separate on top of them allowing the easy recovery of the reaction product and the recyclability of the hydrogel catalyst.

Preparation of PdNPs doped chitosan-based composite hydrogels as highly efficient catalysts for reduction of 4-nitrophenol

The development of functional hydrogel materials for applications in catalysis has attracted great research interest, especially in aqueous phase catalysis. However, preparation of new structural hydrogel catalysts with enhanced catalytic activity still remains a challenge. In this study, a series of Pd nanoparticles (PdNPs) doped chitosan (CS)-based composite hydrogels were successfully prepared by adding graphene oxide (GO), carbon nanotubes (CNTs) and layered double hydrotalcites (LDHs) to CS hydrogel with glutaraldehyde as a cross-linking agent and in situ growing PdNPs. The structure and morphology analysis indicated that chitosan-based composite hydrogels could be used as carriers to load PdNPs and effectively prevent the agglomeration of PdNPs. Subsequently, 4-nitrophenol (4-NP) catalytic reaction was used as a typical model to evaluate catalytic performances of chitosan (CS)-based composite hydrogel catalysts. The obtained chitosan-based composite hydrogel catalysts exhibited better catalytic activity than that of PdNPs doped CS hydrogel catalyst (CS-PdNPs) and reusability for the reduction of 4-nitrophenol in water. The catalytic process conformed to the pseudo-first-order kinetic equation. Moreover, chitosan-based composite hydrogel catalysts containing CNTs had the best catalytic performance since the particle size of PdNPs was the smallest among three kinds of chitosan-based composite hydrogel catalysts. This work provides new ideas for the preparation of stable and efficient precious metal nanoparticle catalysts for applications in aqueous phase catalysis.

A computational model for the catalytic hydrogel membrane reactor

The catalytic hydrogel membrane reactor (CHMR) is a promising new technology for hydrogenation of aqueous contaminants in drinking water. It offers numerous benefits over conventional three-phase reactors, including immobilization of nano-catalysts, high reactivity, and control over the hydrogen (H2) supply concentration. In this study, a computational model of the CHMR was developed using AQUASIM and calibrated with 32 experimental datasets for a nitrite (NO2−)-reducing CHMR using palladium (Pd) nano-catalysts (~4.6 nm). The model was then used to identify key factors impacting the behavior of the CHMR, including hydrogel catalyst density, H2 supply pressure, influent and bulk NO2− concentrations, and hydrogel thickness. Based on the model calibration, the reaction rate constants for the NO2− steady-state adsorption Hinshelwood reaction equation, k1 and k2, were 0.0039 m3 mole-Pd−1 s−1 and 0.027 (mole-H2 m3)1/2 mole-Pd−1 s−1, respectively. The reactant flux, which is the overall NO2− removal rate for the CHMR, is affected by the NO2− reduction rate at each catalyst site, which is in turn controlled by the available NO2− and H2 concentrations that are regulated by their mass transport behavior. Reactant transport in the CHMR is counter-diffusional. So for thick hydrogels, the concurrent concentrations of NO2− and H2 are limiting in the middle region along the x-y plane of the hydrogel, which results in a low overall NO2− removal rate (i.e., flux). Thinner hydrogels provide higher concurrent reactant concentrations throughout the hydrogel, resulting in higher fluxes. However, if the hydrogel is too thin, the flux becomes limited by the amount of Pd that can be loaded, and unused H2 can diffuse into the bulk and promote biofilm growth. The hydrogel thickness that maximized the NO2− flux ranged between 30 and 150 μm for the conditions tested. The computational model is the first to describe CHMR behavior, and it is an important tool for the further development of the CHMR. It also can be adapted to assess CHMR behavior for other contaminants or catalysts or used for other types of interfacial catalytic membrane reactors.

Palladium nano-catalyst supported on cationic nanocellulose–alginate hydrogel for effective catalytic reactions

Green/sustainable catalyst system is highly desirable, and to this end, biopolymer based functional hydrogel has received much attention due to its various unique properties. Herein, a palladium nanoparticle catalyst supported by natural polymer-based hydrogel, consisting of cationic nanocellulose and alginate (Pd NPs@CNCC–AHB) was prepared and its efficient catalytic applications were demonstrated for dye removal and Suzuki coupling reaction. Cationic nanocellulose was prepared based on (1) periodate oxidation, (2) Schiff base reaction, then the hydrogels were synthesized based on the ionic interaction (Ca2+) and electrostatic interactions of cationic nanocellulose and anionic alginate. Subsequently, Pd NPs formed in situ within the hydrogel based on green synthesis, consisting of PdCl2 adsorption into the CNCC–AHB hydrogel, and carbonyl-induced reduction of Pd2+ to Pd0 at 80 °C (carbonyl groups of nanocellulose as a result of periodate oxidation). CNCC here acted as the support/stabilizer and reducing agent for the preparation of Pd NPs. The TEM image shows the average diameter of Pd NPs is ~ 9 nm inside the CNCC–AHB hydrogel matrices. The as-prepared Pd NPs@CNCC–AHB hydrogel bead catalyst showed excellent performance for methylene blue in both batch and continuous systems. Also, a high catalytic performance (as high as 99% yield after 2 h) for the Suzuki reaction was obtained. The recyclability of the hydrogel catalyst was investigated. The palladium nanoparticle loaded cationic nanocellulose–alginate hydrogel (Pd NPs@CNCC–AHB) catalyst system has great potential for catalytic applications.

Catalytic Application of Silver Nanoparticles in Chitosan Hydrogel Prepared by a Facile Method

In this research work, a simple method of silver nanoparticles’ self-synthesis in chitosan (CH) biopolymer hydrogels without utilizing a reducing agent is shown. The synthesized material was used as a catalyst in different reduction reactions. For this purpose, different amounts of CH powder were dissolved in acidic aqueous solutions and then crosslinked it with the formaldehyde solution to make a CH biopolymer hydrogel. Among all the prepared samples, a CH hydrogel prepared from a dense solution was found to be suitable for this study because of good mechanical stability. For the self-synthesis of silver nanoparticles inside hydrogel, it was immersed in an aqueous solution of AgNO3 (10 mM) for 3 days at room temperature. The color of the chitosan hydrogel changed to brown from transparent which indicated the successful formation of silver nanoparticles on CH hydrogel (Ag-CH). No reducing agent for conversion of the Ag1+ ions to nanoparticles in this whole synthesis method. Instrumental techniques such as FESEM, XRD and EDX analysis confirmed the successful preparation of Ag-CH. The Ag-CH was checked as a catalyst in the 2-nitrophenol (2-NP) and acridine orange (ArO) reduction reactions. Both reactions were carried out at high rate constants (2-NP = 0.260 min−1, ArO = 0.253 min−1) by using the Ag-CH hydrogel catalyst. In addition, we discussed the mechanism of action of the reducing agent, the effect of kapp on the two reduction reactions of Ag-CH and the recyclability.

Highly porous egg white/polyethyleneimine hydrogel for rapid removal of heavy metal ions and catalysis in wastewater

The water pollution caused by the heavy metal ions have raised potent damages to the water ecosystem and human health. It is thus important to develop materials that can capture the heavy metal ions effectively and efficiently in the wastewater to resolve this issue. Herein, a highly porous functional hydrogel from the egg white (EW) integrated with polyethyleneimine (PEI) was prepared and examined for the adsorptive removal of the Cu2+, Pb2+ and Cd2+ ions in aqueous solutions. A systematic study was performed to illustrate the EW/PEI hydrogel's excellent affinity to the metallic ions in both the mono- and competitive adsorption systems. The maximum adsorption capacities for the Cu2+, Pb2+ and Cd2+ ions in the mono-adsorption system were determined to be 7.494, 2.194 and 3.705 mmol g−1, respectively with the adsorption rates and isotherms complying with the pseudo-second order kinetics and Langmuir isotherm model, respectively. Furthermore, in situ reduction turned the adsorbed Cu2+ ions into uniformly distributed Cu nanoparticles (NPs) in the EW/PEI hydrogel. This material can serve as an excellent catalyst as confirmed by a ~98% conversion of 4-nitrophenol (20 mmol) to 4-aminophenol in 10 min at the ambient temperature. The EW/PEI hydrogel and the Cu NPs-decorated EW/PEI hydrogel catalyst can be regenerated easily as proved by the consecutive adsorption/desorption and catalysis experiments for several repetitions, respectively. Therefore, the current study highlights the application of the EW/PEI hydrogel as an effective and practical approach for capturing and recycling/utilizing the toxic metal ions in the wastewater.