Studies of sodium humate/polyacrylamide/clay hybrid hydrogels. I. Swelling and rheological properties of hydrogels

A type of novel hybrid hydrogels from sodium humate (SH), polyacrylamide (PAM), and hydrophilic Laponite clay were prepared using potassium persulfate (KPS) as the initiator and N,N′-methylenebisacrylamide (MBA) as the cross-linker. The structures of the hydrogels were characterized by field emission scanning electron microscope and FTIR. Their swelling properties, swelling mechanism and rheological properties were also investigated. Experiments show that the composite is heterogeneous in the PAM/SH hydrogel system, while the clay collaborates with SH and improves the network structure of PAM/SH/clay hydrogel. High water-absorbing capability is shown for both hydrogel systems. Han plot proves that clay and SH are compatible with PAM for PAM/SH/clay hydrogels.     

Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings

This paper reports the synthesis and characterization of polyurethane (PU)-imide/clay hybrid coatings based on two types of polyester (PE) polyols (PE-1 and PE-2). PE-1 was prepared from neopentyl glycol (NPG), adipic acid (AA) and isophathalic acid (IPA), whereas PE-2 contains NPG, AA, IPA and TMP (trimethylol propane) with the same hydroxyl value 280 as PE-1. Cetyl trimethyl ammonium bromide (CTAB) modified montmorillonite (K10) was used as the organoclay for the synthesis of the hybrid coatings. The organoclay particles (3 wt%) were well-dispersed into the PE matrix by ultrasonication method. Then the isocyanate terminated PU prepolymers were synthesized by the reaction of polyester polyols with hard segments such as 2,4-toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI) in different NCO/OH ratios e.g., 1.6:1, 2:1 and 3:1, respectively. Finally the thermally stable imide rings were incorporated into the PU backbone by complete reaction of excess NCO content present in the PU prepolymer with pyromellitic dianhydride (PMDA). The thermogravimetric analysis (TGA) shows a higher thermal stability for the PU-imide hybrid coatings with respect to the corresponding PU-imide films. A higher NCO/OH ratio has resulted in higher thermal stability. The activation energies of degradation were calculated by the Broido and Coats-Redfern methods, respectively. The dynamic mechanical thermal analysis (DMTA) results show an enhancement in the glass transition temperature value (T_g) for the clay containing hybrid coatings. The surface analysis by angle resolved X-ray photoelectron spectroscopy (AR-XPS) showed an enrichment of the soft segment towards the surface, and an enhancement in the hard segment composition in the hybrid coatings, resulted in phase mixing.     

Removal of methylene blue from aqueous solutions using Poly(AA-co-DVB)

Functional cross-linked polymers (Poly(AA-co-DVB)) were synthesized using a one-step method. The properties of Poly(AA-co-DVB) were measured by SEM, FTIR, and TGA. The adsorption capacity of the Poly(AA-co-DVB) was investigated using methylene blue as an adsorbate. The effect of the mole compositions of acrylic acid and divinylbenzene monomers on the adsorption capacity was investigated in detail. The initial pH of solutions and contact time were also studied. The kinetics and isotherms of the adsorption process were also investigated. The result showed that the maximum equilibrium adsorption capacity was 1698.9?mg/g at room temperature and the adsorption kinetic was well fitted by a pseudo-second-order model and the adsorption isotherm agreed well with the Langmuir model.     

Preparation of a novel clay/metal complex hybrid film and its catalytic oxidation to chiral 1,1-binaphthol

An ITO electrode modified with a hybrid film of chiral metal complex (Λ-[Os(phen)₃]²⁺) and a clay (montmorillonite) has been prepared for the purpose of chiral sensing. As a first step, a floating monolayer of amphiphilic Os(II) complex, [Os(phen)₂(dC18bpy)](ClO₄)₂ (phen=1,10-phenanthroline, dC18bpy=4,4^′-dioctadecyl-2,2^′-bipyridyl), was formed on an aqueous dispersion of sodium montmorillonite. The monolayer acted as an organic part for the hybridization of clay particles in an aqueous phase. The hybrid film of clay and amphiphilic metal complex was transferred onto an indium tin oxide (ITO) substrate by the vertical dipping method. The next step was to immerse the electrode in chloroform, during which the amphiphilic Os(II) complex was removed from the clay surface. Thereafter the electrode was immersed in an aqueous solution of 0.5 mM Λ-[Os(phen)₃](ClO₄)₂ and rinsed with water. Cyclic voltammetric measurements were performed at each step of the above procedures. When the observed curves were simulated on the basis of a double-layered modified electrode, the electron transfer rate constant (k₁) for Λ-[Os(phen)₃]²⁺/Λ-[Os(phen)₃]³⁺ was determined to be 0.25 s⁻¹. This Os^II/Os^III redox couple was found to mediate the electrochemical oxidation of chiral 1,1^′-2-binaphthol in a stereoselective way: i.e., the S-isomer was oxidized at a 1.4 times higher rate than the R-isomer.     

Localized hydrogels based on cellulose nanofibers and wood pulp for rapid removal of methylene blue

Access to clean water has become increasingly difficult, motivating the need for materials that can efficiently remove pollutants. Hydrogels have been explored for remediation, but they often require long times to reach high levels of adsorption. To overcome this limitation, we developed a rapid, locally formed hydrogel that adsorbs dye during gelation. These hydrogels are derived from cellulose—a renewable, nontoxic, and biodegradable resource. More specifically, we found that sulfated cellulose nanofibers or sulfated wood pulps, when mixed with a water-soluble, cationic cellulose derivative, efficiently remove methylene blue (a cationic dye) within seconds. The maximum adsorption capacity was found to be 340 ± 40 mg methylene blue/g cellulose. As such, these localized hydrogels (and structural analogues) may be useful for remediating other pollutants.     

Removal of Cu(II) and Zn(II) from industrial wastewater by acid-activated montmorillonite-illite type of clay

An acid-activated montmorillonite-illite type of clay collected from the Gulbarga region of Karnataka, India was examined for removing copper and zinc ions from industrial wastewater containing Cu(II), Zn(II) and minor amounts of Pb(II). Langmuir, Freundlich, Brunauer-Emmett-Teller (BET), and competitive Langmuir (two competing ions) isotherms were fitted to experimental data and the goodness of their fit for adsorption was compared. The shapes of isotherms obtained indicated multilayer adsorption of Cu(II) and monolayer adsorption of Zn(II) on the acid-activated clay. Competitive adsorption was found to be significant due to the presence of Cu(II) in the wastewater.     

Removal of methylene blue dye from aqueous solution by semi‐interpenetrating polymer network hybrid hydrogel: Optimization through Taguchi method

In this study, sodium humate/poly(acrylamide‐co‐methacrylic acid)/kaolin semi‐interpenetrating polymer network hybrid hydrogel was synthesized as an effective adsorbent for the removal of methylene blue. The morphological and structural properties, and swelling behavior in distilled water and various environments of hybrid hydrogel were investigated with different analyses and tests. The equilibrium swelling percent of hybrid hydrogel reached to 37,000% in 240 min. The parameters (agitation time, concentration, dose, temperature, and pH) affecting adsorption process for methylene blue were optimized using Taguchi method. The data obtained in optimum conditions were well fitted to Langmuir adsorption isotherm and maximum adsorption capacity was determined as 833. 33 mg/g. In the light of the results, the utilization of hybrid hydrogel with high swelling capacity is foreseen as a favored adsorbent in several separation processes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1070–1078     

Adsorption performance and stability of the modified straws and their extracts of cellulose,lignin, and hemicellulose for Pb2+: pH effect

Adsorption performance and stability of the carboxyl groups modified straws and their extracts of cellulose, lignin, and hemicellulose for Pb²⁺ were investigated, and the optimum pH range for Pb²⁺ adsorption was determined by considering both the stability and capacity of the modified biosorbents for the first time. Results showed that adsorption capacity and stability of the straws and extracts were both improved significantly after modification. Adsorption capacities of the modified straws and extracts followed the order: modified hemicellulose > modified lignin, modified straw > modified cellulose, while stability of them followed the reverse order. In the optimum pH range from 4.0 to 5.0, modified rape and cotton straw showed better stability than the modified maize straw, and total organic carbon (TOC) values determined from the two modified straws and extracts were lower than 5.0 mg L⁻¹ even after adsorption for 30 days, which reached the drinking water standard in China.     

Removal of methylene blue by seed-watermelon pulp-based low-cost adsorbent: Study of adsorption isotherms and kinetic models

Based on the abundance of seed-watermelon pulp (SWP) in Xinjiang, China, SWP was employed to prepare low-cost adsorbent toward the removal of methylene blue (MB). The effects of contact time at different initial concentration were studied. The widely used adsorption isotherm models including Langmuir, Freundlich, and Temkin isotherms were employed to depict the adsorption process. The Langmuir isotherm was best fitted to the experimental data. Batch kinetic studies showed that an equilibrium time of 300 minutes was needed for the adsorption. The adsorption properties can be well described by pseudo-second-order kinetic model and the MB uptake was not controlled by intraparticle diffusion mechanism.     

Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota

In present study adsorption capacity of waste materials of Daucus carota plant (carrot stem powder: CSP and carrot leaves powder: CLP) was explored for the removal of methylene blue (MB) malachite green (MG) dye from water. The morphology and functional groups present were investigated by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The operating variables studied were pH, adsorbent dose, ionic strength, initial dye concentration, contact time and temperature. Equilibrium data were analysed using Langmuir and Freundlich isotherm models and monolayer adsorption capacity of adsorbents were calculated. Kinetic data were studied using pseudo-first and pseudo-second order kinetic models and the mechanism of adsorption was described by intraparticle diffusion model.Various thermodynamic parameters such as enthalpy of adsorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. Negative value of ΔH° and negative values of ΔG° showed that the adsorption process was exothermic and spontaneous. Negative value of entropy ΔS° showed the decreased randomness at the solid–liquid interface during the adsorption of MB and MG onto CSP and CLP.     

Hydrolytic degradation of POSS-PEG-lactide hybrid hydrogels

A polyhedral oligomeric silsesquioxane (POSS), functionalized with eight arms of poly(ethylene glycol) (PEG; MW 400) and then acrylated, was incorporated into a hydrogel network based on triblock copolymers of poly(lactide-b-ethylene glycol-b-lactide) diacrylates using a redox-initiated polymerization. The organic-inorganic hybrid hydrogels so prepared contained the inorganic crosslinker POSS from 1 to 28 wt.%. The degradation properties of the hydrogels in a pH 7.4 phosphate-buffered saline solution at 37 °C were studied using measurements of mass loss, cryogenic SEM, and ATR-FTIR spectroscopy. It was found that copolymerization of acrylated 1kPEG-lactide with increasing amounts of POSS created a more porous network which was more resistant to hydrolysis. The ATR-FTIR technique was used to monitor the progress of degradation with exposure time through the changes in the carbonyl and C-H deformation bands of the lactide and the Si-C stretching band of the POSS. Increasing POSS incorporation resulted in decreased rate of degradation due to its hydrophobic nature and inertness to hydrolysis. Conversely, an increase in lactide content increased the degradation rate due to the increased number of hydrolytically-sensitive ester groups in the network.     

Determination of adsorptive properties of clay/water system: methylene blue sorption

In this study, adsorption of methylene blue onto clay was investigated. The effect of adsorption time and temperature on the adsorption process was studied. To reveal the adsorptive characteristics of the clay studied, porosity and BET surface area measurements were made. It was observed that the adsorption capacity decreases with increasing temperature, and adsorption equilibrium was attained within 1 h. It was found that the data fit well to Langmuir, Halsey, Henderson, and Harkins-Jura models but experimental data deviate significantly from BET and Freundlich models at especially high concentrations. Furthermore, isosteric adsorption enthalpy and entropy are calculated as -7.99 kJ mol(-1) and 25.41 JK(-1)mol(-1), respectively.     

Study of adsorption of methylene blue and new methylene blue in liquid-solid interface by slab optical waveguide spectroscopy

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid–solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. Effect of pH on adsorption on MB and NMB was investigated. Binding rate constant analysis showed that both MB and NMB on bare SOWG demonstrates larger association constants than those on ODS-SOWG. Interactions of MB and NMB on bare SOWG and ODS-SOWG were analyzed by molecular mechanics calculation method. The binding energy change was in the following order: E_NMB–bare > E_MB–bare > E_NMB–ODS > E_MB–ODS.     

Polarographic reduction of methylene blue in presence of clay minerals

Clay-Methylene Blue suspensions have been examined polarographically. The degree of binding of the dye on the clay particles has been calculated. The possibility of using the data in estimating the clay content of a sample and identifying the mineral is suggested.     

AlCl3催化玉米秸秆中半纤维素的选择性转化

研究了AlCl₃ 催化剂作用下, 水热体系中玉米秸秆中半纤维素组分在温和条件下的选择性转化. 详细考察了反应温度、反应时间和AlCl₃用量对半纤维素选择性转化的影响. 原料及反应后的固体残渣分别采用化学滴定、X射线衍射和扫描电镜进行表征. 结果表明, 140 ℃下反应1 h可转化玉米秸秆中的大部分半纤维素, 转化率为85.1%;而玉米秸秆中的绝大部分纤维素和木质素组分仍保留在固体残渣中, 此时纤维素和木质素的转化率分别为10.7%和23.9%. 半纤维素转化的主要液体产物为木糖, 同时含有一些乙酸和糠醛. 升高温度, 将滤液进行进一步反应可促进木糖的转化. 在水/四氢呋喃反应体系中, 滤液的进一步反应有利于乙酰丙酸、甲酸和糠醛的生成. 固体酸催化剂γ-Al₂O₃/SO₄^2-的加入可进一步提高糠醛的收率.     

Decontamination of methylene blue from aqueous media using alginate-bonded polyacrylamide/carbon black nanocomposite hydrogel

This work synthesized the novel alginate (Alg) based nanocomposite hydrogel using the free radical polymerization method to remove methylene blue (MB) from the aqueous solution. The successful grafting of acrylamide (AAm) monomer onto the alginate backbone was confirmed by the FTIR test. Different carbon black (CB) nanoparticle levels (0–12.5 wt.%) were embedded in a hydrogel matrix to enhance the removal efficiency, and its optimum value was obtained at 7.5 wt.%. FTIR, TGA, BET, and SEM analyses were performed to characterize synthesized adsorbents. TGA results showed that Alg-g-poly(AAm)/CB nanocomposite hydrogel has a higher thermal stability than Alg-g-poly(AAm) hydrogel. SEM analysis showed that incorporating CB into Alg-g-poly(AAm) considerably enhances roughness and surface area. Also, a higher surface area of Alg-g-poly(AAm)/CB (2.5 m²/g) was confirmed by BET analysis. The removal efficiency of nanocomposite hydrogel at optimum conditions of pH 6, initial concentration 10 mg/L, temperature 25 °C, and contact time 60 min was calculated at 94.63%. The kinetic and isotherm data were best fitted to pseudo-second-order and Langmuir models. The monolayer adsorption capacity for Alg-g-poly(AAm) and Alg-g-poly(AAm)/CB were calculated at 22.77 and 24.56 mg/g, respectively, showing CB's effectiveness in improving MB adsorption. The thermodynamic study showed that the removal process of MB by both adsorbents is spontaneous and exothermic, and entropy decreases. The synthesized adsorbents showed a good performance in textile wastewater treatment. Finally, it can be concluded that the synthesized adsorbents can be successfully applied for wastewater treatment application.     

Functionalization effect of Fe-type MOF for methylene blue adsorption

Water pollutant such as dyes had danger the water quality. Todays, porous materials are great potential for dye adsorption from water bodies. In this study, the iron-based metal–organic framework (MOF-Fe) of MIL-101 is synthesized through a facile solvothermal method. The amine-functionalization effect of the MOF-Fe (amine-MOF-Fe) is evaluated for the adsorptive removal of methylene blue (MB) from aqueous solution. The adsorption behaviour had shown a rapid MB adsorption within the first hour of the process due to the pore-filling mechanism of the porous MOF-Fe structure. The electrostatic interaction between the amino group of amine-MOF-Fe and MB had contributed to the high adsorption capacity. The amine-functionalization effect also found the amine-MOF-Fe is having two times higher adsorption capacity when used with the loading two times lower than non-functionalized MOF-Fe. The maximum equilibrium adsorption capacities were measured at 149.25 and 312.5 mg/g with optimum MOFs loading of 0.8 and 0.4 g/L for MOF-Fe and amine-MOF-Fe, respectively. The adsorption mechanism proposed includes the electrostatic interaction, pore filling, hydrogen bonding, and π–π stacking. The regeneration study showed the MOFs could be recycled without interfering with the removal efficiency. Hence, the results indicate that the MOFs had desirable reusability for the practical adsorption of cationic dyes with its features of fast adsorption and high capacity.     

Electrocatalytic evaluation of liquid phase deposited methylene blue/TiO2 hybrid films

Methylene blue (MB)/TiO₂ hybrid thin films were prepared on glassy carbon (GC) electrode surface by the liquid phase deposition (LPD) process. The electrochemical measurements indicated that MB retained its electrochemical activity in the hybrid films. The linear dependence of the reduction peak current for MB upon the scan rate and linear relationship between the middle point potential of MB and pH revealed the surface-confined two-proton two-electron electrochemical characteristics of MB entrapped in hybrid LPD films. Although the electron transfer of K₃[Fe(CN)₆] on GC surface was inhibited by TiO₂ film, the catalytic reduction of K₃[Fe(CN)₆] by MB was observed on the MB/TiO₂ hybrid films. The electrocatalytic activity of hybrid films was also demonstrated as an “artificial peroxidase” for the catalytic reduction of H₂O₂.     

Cyclodextrin/silica hybrid adsorbent for removal of methylene blue in aqueous media

Functionalization of a silica surface using cyclodextrin was performed using citric acid as a bonding agent. The material obtained was characterized using spectroscopic, X-ray, and thermogravimetric analyses. The effectiveness of the product for removal of dyes from aqueous media was evaluated using methylene blue as a model molecule, for which the best adsorption was achieved at pH values higher than 3.5. The correlation coefficients obtained using the Langmuir isotherm enabled elucidation of the adsorption mechanism. The maximum capacity of the nano-adsorbent for adsorption of the dye was 212 mg g^?1. Thermodynamic tests performed at 25, 35, and 45 °C showed that the mechanism was spontaneous and temperature-dependent, with adsorption following the pseudo-second order kinetic model and being fastest during the early stages, with equilibrium achieved after around 3 h. The results showed that hybrid materials based on cyclodextrin can be used for removal of dyes from aqueous media, and could therefore substitute other more expensive adsorbents. Advantages of these new materials include ease of preparation, relatively low cost, and good adsorption properties.     

Preparation and characterization of sodium carboxymethylcellulose/poly(N-isopropylacrylamide)/clay semi-IPN nanocomposite hydrogels

A new kind of pH-/temperature-responsive semi-interpenetrating polymer network hydrogels based on linear sodium carboxymethylcellulose (CMC) and poly(N-isopropylacrylamide) (PNIPA) cross-linked by inorganic clay (CMC/PNIPA/Clay hydrogel) was prepared. The temperature- and pH-responsive behaviors, the mechanical properties of these hydrogels were investigated. The CMC/PNIPA/Clay hydrogels exhibited a volume phase transition temperature around 32 °C with no significant deviation from the conventional PNIPA hydrogels. The swelling ratio of the CMC/PNIPA/Clay hydrogels gradually decreased with increasing the contents of clay. The influence of pH value on swelling behaviors showed that there is a maximum swelling ratio at pH 5.9. Moreover, the CMC/PNIPA/Clay hydrogels exhibited excellent mechanical properties with high tensile stress and elongation at break in excess of 1200%.