Hydrogel Catalyst Research Articles

Cu(ii)-alginate-based superporous hydrogel catalyst for click chemistry azide-alkyne cycloaddition type reactions in water.

A novel sustainable hydrogel catalyst based on the reaction of sodium alginate naturally extracted from brown algae Laminaria digitata residue with copper(ii) was prepared as spherical beads, namely Cu(ii)-alginate hydrogel (Cu(ii)-AHG). The morphology and structural characteristics of these beads were elucidated by different techniques such as SEM, EDX, BET, FTIR and TGA analysis. Cu(ii)-AHG and its dried form, namely Cu(ii)-alginate (Cu(ii)-AD), are relatively uniform with an average pore ranging from 200 nm to more than 20 μm. These superporous structure beads were employed for the copper catalyzed [3 + 2] cycloaddition reaction of aryl azides and terminal aryl alkynes (CuAAC) via click chemistry at low catalyst loading, using water as a solvent at room temperature and pressure. The catalytic active copper(i) species was generated by the reduction of copper(ii) by terminal alkyne via the oxidative alkyne homocoupling reaction. The prepared catalysts were found to be efficient (85–92%) and regioselective by affording only 1,4-disubstituted-1,2,3-triazoles. They were also recoverable and reused in their dried form for at least four consecutive times without a clear loss of efficiency. A mechanistic study was performed through density functional theory (DFT) calculations in order to explain the regioselectivity outcome of Cu(ii)-alginate in CuAAC reactions. The analysis of the local electrophilicity (ωk) at the electrophilic reagent and the local nucleophilicity (Nk) at the nucleophilic confirms the polar character of CuAAC. This catalyst has the main advantage of being sustainably ligand-free and recyclable.

A highly efficient thermo responsive palladium nanoparticles incorporated guar gum hydrogel for effective catalytic reactions

Hydrogel, especially stimuli responsive hydrogel, has attracted enormous attention due to its unique properties for many applications. Herein, Pd NPs@ CNCs was firstly attained by in situgeneration of Pd NPs onto CNCs, and subsequently incorporated into guar gum-based hydrogel, so that a thermo responsive Pd NPs@ CNCs/ guar gum hydrogel catalytic system was obtained. The sol-gel transition was achieved viaa simple heating/cooling cycle: a sol state was obtained above 70 °C, allowing the catalytic reaction; a gel state was attained below 20 °C, allowing the reuse/ recycling of the Pd NPs. Pd NPs were formed by in situ reduction of PdCl2 in the presence of CNCs so that Pd NPs were loaded onto CNCs surfaces. CNCs acted as stabilizers for the Pd NPs. The TEM image showed that the average size of Pd NPs is ˜3 nm. Subsequently, the Pd NPs@ CNCs composites were loaded into the guar gum hydrogel, based on the boron crosslinking chemistry. The hydrogel exhibited rapid sol-gel transition process upon heating (70 °C) and cooling (20 °C) cycles. The Pd NPs loaded sol-gel transition concept was subsequently applied to the Suzuki coupling reactions between aryl bromides and phenyl boronic acids, and a highly efficient catalytic performance (over 85% yield within 2 h) was obtained. The reuse/recycling of the thermo responsive Pd NPs@ CNCs/guar gum hydrogel catalyst system was investigated. This novel Pd NPs loaded thermo-responsive sol-gel transition concept is a promising new catalytic system.

Aminophenols formation from nitrophenols using agar biopolymer hydrogel supported CuO nanoparticles catalyst

Abstract In this article, copper (II) oxide (CuO) nanomaterial was synthesized by a quick microwave heating method from the basic pH copper sulfate solution and mixed with agar (AG) biopolymer powder aqueous suspension to make the AG-CuO nanocomposite hydrogel. The mixture was subjected to hydrogel formation by using the thermal treatment at 85 oC followed by cooling to 25 oC. The spontaneous turning of the hot AG-CuO fluid to a soft hydrogel was confirmed. The synthetic steps for the AG-CuO hydrogel were verified by different techniques such as FESEM, EDX, TGA and XRD. The AG-CuO hydrogel was utilized as catalyst in the reduction of three different nitroarenes of 4-nitrophenol (4-NP), 2,6-dinitrophenol (2,6-DNP) and 2-nitrophenol (2-NP) to corresponding aminophenols by using sodium borohydride. The AG-CuO was able to reduce the nitroarenes in the increasing rate order of 4-NP> 2-NP> 2,6-DNP. The AG-CuO hydrogel catalyst showed good and easy recyclability as revealed by five times use in the same reduction reaction while keeping the high catalytic activity. The data provided in this article by using AG-CuO hybrid hydrogel suggest that it could be an efficient material for the other water-based chemical reduction reactions.

A novel composite hydrogel for adsorption and photocatalytic degradation of bisphenol A by visible light irradiation

A novel hydrogel catalyst (P(HEA-co-HAM)-CdS) was synthesized to remove bisphenol A (BPA) from water through adsorption and in-situ photocatalytic degradation. The characterization of P(HEA-co-HAM)-CdS hydrogel through SEM-EDS, TEM, XPS and FT-IR demonstrated heterogeneous structure and chemical combination between CdS and hydrogel. Besides, the optical properties of P(HEA-co-HAM)-CdS hydrogel illustrated enhanced photocatalytic activity under visible light irradiation with efficient separation ability of electron-hole pairs and effective visible light utilization capability. In addition, the ability of hydrogel in adsorption and degradation were observed. BPA adsorption capacity of P(HEA-co-HAM)-CdS hydrogel was 11.26 mg/g, higher than similar adsorbents. The adsorption process fitted in pseudo-second-order rate equation and Langmuir monolayer adsorption. Under 500 W visible light irradiation, BPA degradation rate of P(HEA-co-HAM)-CdS hydrogel reached 92% in 3 h and photocatalytic oxidative radicals detection experiment verified holes (h+) and ·O2− play major role in this system, mineralization rate of BPA was 47%. HPLC-TOF-MS was employed to detect the degradation intermediates, with theoretically Fed2 value calculating results, possible degradation pathway of BPA was proposed. Furthermore, degradation rate remained over 84.4% after recycle. The results indicated that P(HEA-co-HAM)-CdS hydrogel was a promising catalyst material in application.

Adsorption and photocatalytic degradation of sulfamethoxazole by a novel composite hydrogel with visible light irradiation

A novel hydrogel catalyst (p(HEA/NMMA)-CuS) with the function of adsorption and degradation of organic pollutants in water was successfully synthesized using irradiation polymerization and in situ precipitation methods The composite hydrogel catalyst was characterized by SEM-EDS, TEM, swelling kinetics, zeta potential, TGA, XPS, FTIR and XRD. Besides, the effects and mechanisms of adsorption and degradation of sulfamethoxazole(SMX) as the representative pollutant by p(HEA/NMMA)-CuS hydrogel were observed. The results presented that adsorption process of SMX on complex hydrogel fit well to Langmuir monolayer adsorption, and followed a pseudo-second-order rate equation. The decomposition of SMX by p(HEA/NMMA)-CuS hydrogel in aqueous solution under 500w visible light achieved balance in 24h, the removal ratio reached 95.91%, and the SMX was mineralized with 43.56%. Hydroxyl radicals was detected as the reactive species using EPR in the system, degradation intermediates of SMX were further analyzed by LC-TOF-MSMS, a possible pathway for SMX degradation was presented. The degradation mechanism of SMX was also illustrated by theoretical calculations of frontier electron densities. Furthermore, mineralization, stability and regeneration results indicated that the developed hydrogel catalyst, p(HEA/NMMA)-CuS hydrogel, was promising in practical application.

Catalytic dehydrogenation of calcium borohydride by using hydrogel catalyst

The aim of this study was to investigate dehydrogenation of calcium borohydride (Ca(BH4)2) in the presence of a catalyst. Co ion-loaded poly(acrylamide-co-acrylic acid) (p(AAm-co-AAc)-Co) hydrogel was taken as a catalyst for this dehydrogenation procedure. Dehydrogenation reactions were performed under three different reaction temperatures, so the rate order and activation energy of the reaction were determined by using experimental results. The amount of hydrogen production increased with temperature and yields of the dehydrogenation reactions were determined as 46.5, 76.0 and 98.5% for 25, 35 and 45 °C, respectively. The activation energy of the dehydrogenation of Ca(BH4)2 was found as 71.39 kJ/mol according to zero order reaction kinetic. In addition, in order to determine reusability of p(AAm-co-AAc)-Co hydrogel, the same catalyst system was used in ten consecutive runs for the hydrolysis of Ca(BH4)2. This catalyst system was used ten times without any structural defect of the catalyst. On the other hand, the conversion ratio decreased from 98.5% to 83.5%.

Efficient Degradation of Cellulose in Its Homogeneously Aqueous Solution over 3D Metal-Organic Framework/Graphene Hydrogel Catalyst

Catalytic degradation of cellulose to chemicals is an attracting topic today for the conversion of biomass, and the development of novel catalysts is a key point. Since metal-organic frameworks (MOFs) possess uniform, continuous, and permeable channels, they are valuable candidate as catalysts. Here, a new 3D MOF/graphene catalyst was prepared by in situ growth of the zeolitic imidazolate frameworks (ZIF-8) nanoparticles inside the pore of an as-formed 3D reduced graphene oxide (rGO) hydrogel. The ZIF-8/rGO nanocomposite owns both micropores and mesopores with large specific surface area and plenty of acids sites, which is an idea catalyst for biomass degradation. Cellulose was dissolved in alkaline aqueous solution at first, and then it was degraded efficiently over the new catalyst under hydrothermal condition. The conversion reaches 100% while the main products are formic acid with a maximum yield of 93.66%. In addition, the catalyst can be reused with high activity.

Synthesis of Borohydride and Catalytic Dehydrogenation by Hydrogel Based Catalyst

This paper deals with the synthesis of calcium borohydride (Ca(BH4)2) as hydrogen storage material. Calcium chloride salt (CaCl2), magnesium hydride (MgH2), and boron oxide (B2O3) were used as reactants in the mechanochemical synthesis of Ca(BH4)2. The mechanochemical reaction was carried out by means of Spex type ball milling without applying high pressure and temperature. Parametric studies have been established at different reaction times and for different amounts of reactants at a constant ball to powder ratio (BPR) 4:1. The best combination was determined by Fourier Transform Infrared (FT-IR) analysis. According to the FT-IR analysis, reaction time, the first reaction parameter, was found as 1600 min. After the reaction time was fixed at 1600 min, the difference of the B-H peak areas was dependent on the amount of reactant MgH2 that was investigated. The amount of the reactant (MgH2), the second reaction parameter, was measured to be 2.85 times more than the stoichiometric amount of MgH2. According to our previous studies, BPR was selected as 4:1 for all experiments. Samples were prepared in a glove box under argon atmosphere but the time that elapsed for FT-IR analysis highly affected B-H bonds. B-H peak areas clearly decreased with time because of negative effect of ambient atmosphere. A catalyst was prepared by absorbing cobalt fluoride (CoF2) in poly (acrylamide-co-acrylic acid) hydrogel matrices type and its catalytic dehydrogenation performance that has been characterized by the catalytic reaction of sodium borohydride's known hydrogen capacity in an alkaline medium. The metal amount of hydrogel catalyst was determined as 135.82 mg Co by Atomic Absorption Spectroscopy (AAS). The specific dehydrogenation capacity of the Co active compound in the catalyst thanks to catalytic dehydrogenation of commercial sodium borohydride was measured as 1.66 mL H2/mg Co.