Zn2+-imprinted porous polymer beads: Synthesis,structure, and selective adsorption behavior for template ion

Zn²⁺-imprinted polymer was synthesized in porous spherical forms via a self-assembled complex between 2,2′-bipyridyl/4-vinylpyridine complexant/functional monomer and Zn²⁺ template ion. Diameters of particles ranged from 250 to 550 μm to enlarge the surface area and thus enhance the adsorption capacity. The presence/absence of the template ion in the preparation of the imprinted polymer was confirmed by EDX spectroscopy, and the physical structure of the particles was investigated using ESEM and BET analysis. The particle and the pore size were controlled by the cross-linker/monomer feed ratio. The adsorption capacity of the imprinted polymers was 210.61 μmol g^?1 for Zn²⁺, while those for Cu²⁺, Ni²⁺, and Pb²⁺, were 37.92 μmol g^?1, 33.02 μmol g^?1, and 9.70 μmol g^?1, respectively. This big discrepancy of the adsorption capacities illustrates the excellent separation selectivity of the imprinted polymers. The adsorption capacity decreased significantly at pH below 4.5, as the polymers are easily protonated. The imprinted particles lost only 10 % of their adsorption ability after 10 repeated uses.     

Characterization of catalysts in their active state by adsorption microcalorimetry: Experimental design and application to sulfated zirconia

A method to characterize the surface sites of catalysts in their active state by adsorption microcalorimetry was developed. A calorimeter cell was used as a flow-type reactor, and the skeletal isomerization of n-butane (1 kPa) at 378 K and atmospheric pressure proceeded at comparable rates and with the same states of induction period, maximum and deactivation phase as in a tubular reactor. The reaction was run for selected times on stream and after the removal of weakly adsorbed species, n-butane or isobutane were adsorbed at 313 K. The surface of activated sulfated zirconia was characterized by at least two different sites for n-butane adsorption, a small group of sites (about 20 μmol g^?1) that yielded heats of 50–60 kJ mol^?1 and sites that were populated at higher pressures (above about 5 hPa n-butane) and yielded heats of about 40 kJ mol^?1. The strongly interacting sites disappear during the induction period and are proposed to be the sites where the isomerization reaction is initiated.     

Uranyl ion-selective optical test strip

A novel, optical sensor, test strip has been developed for the spectrophotometric determination of trace amounts of uranyl ions, UO₂²⁺, based on immobilization of C.I. Mordant Blue 29 (Chromazurol S)/cetyl N,N,N-trimethyl ammonium bromide ion pair on a triacetyl cellulose membrane. Optimization of the sensor for the detection of low levels of uranyl ion is described. The test strip responded linearly to uranyl ions between 3.0 × 10^?7 and 6.0 × 10^?5 mol L^?1; the reproducibility of the sensor at a medium level of UO₂²⁺ activity was ±0.55%. The optical sensor can be regenerated using 0.01 mol L^?1 HCl or 0.01 mol L^?1 NaF solution after 10 min. The developed test strip was used in the determination of UO₂²⁺ in ground water samples.     

Synthesis and adsorption studies of novel hybrid mesoporous copolymer functionalized with protoporphyrin for batch and on-line solid-phase extraction of Cd2+ ions

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol–gel process was evaluated as novel adsorbent for solid-phase extraction of Cd²⁺ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted (R² = 0.9982) to hybrid non-linear Langmuir–Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g^?1. The adsorption kinetics data also corroborated to the isotherm, where the Cd²⁺ ions adsorption followed the pseudo-second-order kinetic (R² = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min^?1 flow rate. The on-line desorption of Cd²⁺ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min^?1 flow rate using 0.8 mol L^?1 HNO₃. Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g^?1. Analytical curve ranged from 0.0 up to 50.0 μg L^?1 (r = 0.997), limit of detection of 0.27 μg L^?1, preconcentration factor of 38.4, sample throughput of 30 h^?1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd²⁺ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.     

Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide

Structurally well ordered, sulfur-doped microporous carbon materials have been successfully prepared by a nanocasting method using zeolite EMC-2 as a hard template. The carbon materials exhibited well-resolved diffraction peaks in powder XRD patterns and ordered micropore channels in TEM images. Adjusting the synthesis conditions, carbons possess a tunable sulfur content in the range of 1.3–6.6 wt.%, a surface area of 729–1627 m² g^?1 and a pore volume of 0.60–0.90 cm³ g^?1. A significant proportion of the porosity in the carbons (up to 82% and 63% for surface area and pore volume, respectively) is contributed by micropores. The sulfur-doped microporous carbons exhibit isosteric heat of hydrogen adsorption up to 9.2 kJ mol^?1 and a high hydrogen uptake density of 14.3 × 10^?3 mmol m^?2 at ?196 °C and 20 bar, one of the highest ever observed for nanoporous carbons. They also show a high CO₂ adsorption energy up to 59 kJ mol^?1 at lower coverages (with 22 kJ mol^?1 at higher CO₂ coverages), the highest ever reported for any porous carbon materials and one of the highest amongst all the porous materials. These findings suggest that S-doped microporous carbons are potential promising adsorbents for hydrogen and CO₂.     

A self-healing polymer network based on reversible covalent bonding

A self-healing polymer network for potential coating applications was designed based on the concept of the reversible Diels–Alder (DA) reaction between a furan functionalized compound and a bismaleimide. The network allows local mobility in a temperature window from ca. 80 °C to 120 °C by shifting the DA equilibrium towards the initial building blocks. Changing the spacer length in the furan functionalized compound leads to tailor-made properties. Elastomeric model systems were chosen to evaluate the kinetic parameters by Fourier transform infrared spectroscopy. For the DA reaction a pre-exponential factor ln(A_DA in kg mol^?1 s^?1) equal to 13.1 ± 0.8 and an activation energy (E_DA) of 55.7 ± 2.3 kJ mol^?1 are found. For the retro-DA reaction, ln(A_rDA) and E_rDA are 25.8 ± 1.8 s^?1 and 94.2 ± 4.8 kJ mol^?1, respectively. The enthalpy and entropy of reaction are calculated as ?38.6 kJ mol^?1 and ?105.3 J mol^?1 K^?1. The kinetic results are validated by micro-calorimetry. Non-isothermal dynamic rheometry provides the gel-point temperature of the reversible network. The sealing capacity is evaluated by atomic force microscopy for micro-meter sized defects. Repeatability of the non-autonomous healing is checked by micro-calorimetry, ruling out side-reactions below 120 °C.     

Thin layer solar drying characteristics of silkworm pupae

Thin layer solar drying experiments of silkworm pupae using a solar tunnel dryer were conducted under the tropical weather conditions of Mahasarakham, Thailand. The dryer consisted of a transparent glass covered flat-plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using a blower. During the experiments, silkworm pupae were dried to the final moisture content of 0.15 kg water kg^?1 dry matter from 4.37 kg water kg^?1 dry matter in 373 min at the corresponding air flow rate of 0.32 kg s^?1. Ten different thin layer drying models were compared according to their coefficient of determination to estimate drying curves. The Midilli–Kucuk model precisely represents the solar tunnel drying behavior with the coefficient of determination (R²) of 0.9982. The maximum drying rate and effective moisture diffusivity were 0.6723 kg water kg^?1 dry matter h^?1 and 2.7696 × 10^?10 m² s^?1, respectively, on the drying air flow rate of 0.32 kg s^?1. A quality assessment shows that the lipid content of the dried silkworm pupae was not affected by the solar tunnel dryer. A slight decrease of polyunsaturated fatty acid (PUFA) was observed.     

A chemiluminescence sensor for determination of epinephrine using graphene oxide–magnetite-molecularly imprinted polymers

A chemiluminescence (CL) sensor for the determination of epinephrine using the system of luminol–NaOH–H₂O₂ based on a graphene oxide–magnetite-molecularly imprinted polymer (GM-MIP) is described. The epinephrine GM-MIP was synthesized using graphene oxide (G) which improved the adsorption capacity, and magnetite nanoparticles which made the polymers easier to use in the sensor. The adsorption performance and properties were characterized. The GM-MIP was used in CL analysis to increase the selectivity and the possible mechanism was also discussed. The CL sensor responded linearly to the concentration of epinephrine over the range 1.04 × 10^?7–7.06 × 10^?3 mol/L with a detection limit of 1.09 × 10^?9 mol/L (3σ). The relative standard deviation for determination was 3.87%. On the basis of speediness and sensitivity, the sensor is reusable and shows a great improvement in selectivity and adsorption capacity over other sensors. The sensor had been used for the determination of epinephrine in drug samples.     

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in situ photoelectron spectroscopy. The acid–base properties of the catalyst have been probed by NH₃ adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption q_diff,initial = 57 kJ mol^?1 until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm² at 313 K. The decrease of the heat to q_diff,initial = 40 kJ mol^?1 after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in situ XPS while the catalyst was working applying reaction temperatures between 323 and 693 K, different feed compositions containing 0 mol.% and 40 mol.% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed-bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo⁶⁺ and enrichment in V⁵⁺ sites. In the presence of steam in the feed, the active ensemble for acrylic acid formation appears to consist of V⁵⁺ oxo-species in close vicinity to Te⁴⁺ sites in a Te/V ratio of 1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.     

Development of thermal conductive consolidated activated carbon for adsorption refrigeration

A new type consolidated composite activated carbon (AC) was developed with a host matrix of expanded natural graphite treated with sulfuric acid (ENG-TSA). Samples with different density, different grain size of AC, and different proportion of AC were produced and thermo-physical properties were evaluated. Results show that the highest effective thermal conductivity and thermal diffusivity of consolidated composite AC were 34.2 W m^?1 K^?1 and 3.89 × 10^?5 m² s^?1, which were 150 times and 72 times higher, respectively, than ordinary granular AC. The permeability of adsorbents ranged between 1.24 × 10^?14 and 7.81 × 10^?10 m² while the density ranged between 215 and 448 kg m^?3. The adsorption performance for composite AC and granular AC were evaluated by fitting experimental data with the equilibrium Dubinin–Astakhov (D–A) equations. Results show that the addition of ENG-TSA can improve the performance of adsorption refrigeration machines by increasing the concentration swing.     

Effective Cd2+ chelating fiber based on polyacrylonitrile

A reusable chelating fiber containing polyamino–polycarboxylic acid ligands was prepared via the stepwise modification of polyacrylonitrile fiber with diethylenetriamine and chloroacetic acid. The amination and carboxylmethylation conditions were optimized, and the modified fiber was characterized by elemental analysis, XRD, SEM and FTIR. For Cd²⁺ in water, this chelating fiber has prominent adsorption abilities such as low adsorption limitation (0.001 mg/L), high adsorption capacity (1.34 mmol/g) and fast response speed (half-saturation adsorption time less than 0.5 min based on 1 mg/mL Cd²⁺). The effectiveness of this chelating fiber has been proved by using it to treat actual sewage water, where the concentration of Cd²⁺ was reduced from 0.540 to below 0.001 mg/L. This level easily meets drinking water standards (0.003 mg/L) issued by the World Health Organization. Moreover, this chelating fiber is also very effective at treating other metal ions such as Cu²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Pb²⁺, Ni²⁺, Ag⁺ and Hg²⁺.     

Comparison of the influence of nanomaterials on response properties of copper selective electrodes

Novel Cu²⁺ ion selective electrode in carbon paste matrices based on incorporation of bis(2-hydroxynaphthaldehydene)-1,6-hexanediamine (BHNHDA) has been developed. The influence of variables including sodium tetraphenylborate (NaTPB), ionophore, and amount of multiwalled carbon nanotubes (MWCNT) and Nujol and effect of two new nanoparticles including gold nanoparticles loaded on activated carbon (Au-NP-AC) and zinc sulfide nanoparticles loaded on activated carbon (ZnS-NP-AC) on the electrodes response was studied and optimized. At optimum specified conditions, the proposed electrodes have appropriate advantages such as short response times and suitable reproducibility and applicability for a period of at least 1 month without any significant divergence in slope and response properties. The sensor based on impregnations of MWCNT, Au-NP-AC and ZnS-NP-AC have wide linear range of concentration (6 × 10^?8–1.0 × 10^?1 mol L^?1) and detection limit of lower than 4 × 10^?8 mol L^?1 of Cu²⁺ ion. The electrodes based on incorporation of Au-NP-AC and ZnS-NP-AC have Nernstian response with slope of 29.34 ± 1.41 and 29.78 ± 1.23 mV decade^?1 and response is independent of pH in the range of 2.0–5.0. Finally, these electrodes have been successfully applied for the determination of Cu²⁺ ions content in various real samples. Due to their acceptable selectivity coefficient, they are usable for accurate and successful evaluation of Cu²⁺ ions content in various real sample with complicated matrices.     

Adsorption of chromate and para-nitrochlorobenzene on inorganic–organic montmorillonite

Batch studies of chromate and para-nitrochlorobenzene (p-NCB) on montmorillonite modified by poly(hydroxo aluminium) ions (Al) and cetyl trimethylammonium bromide (CTMAB) are reported. The amounts adsorbed decreased in the order Al-CTMA-mont > CTMA-mont > Al-mont > montmorillonite. Adsorption of chromate on Al-CTMA-mont reached a maximum at pH = 4 while p-NCB was pH independent. The adsorption kinetics could be described by the pseudo-second-order model. The adsorption rates for chromate and p-NCB were 9.73 and 5.78 mg g^? 1 min^? 1, respectively. The adsorption capacity of chromate and p-NCB on Al-CTMA-mont calculated by the Langmuir model was 2.3 × 10^? 4 and 2.2 × 10^? 4 mol/g, the values of the adsorption energy of the Dubinin-Radushkevitch (D-R) model were 13.9 and 7.8 kJ/mol. These results implied that the chromate adsorption proceeded as chemisorption, mainly by ion exchange whereas p-NCB was bound by van der Waals forces.     

Polystyrene-based carbon spheres as electrode for electrochemical capacitors

A series of carbon spheres with various porous texture parameters were prepared from polystyrene-based macroreticular resin spheres by carbonization and activation. The as-prepared carbon spheres had a maximum specific surface area of 996 m² g^?1, total pore volume of 1.34 cm³ g^?1 and average pore size of 5.39 nm. Moreover, these carbon spheres showed a mesopore size distributed mainly in about 40 nm. A high specific capacitance of 153 F g^?1 for carbon sphere by carbonization, 164 F g^?1 for carbon sphere by activation for 1 h and 182 F g^?1 for carbon sphere by activation for 2 h can be obtained. Moreover, a specific energy between 2.3 and 5.1 Wh kg^?1 for these carbon spheres can be obtained in 6 mol L^?1 KOH electrolyte.     

Comparison of novel sorbents for preconcentration of metal ions prior to their flame atomic absorption spectrometry determination

In the present study, the efficiency and usability of two sorbents including silver nanoparticles loaded on activated carbon and homemade activated carbon for removal and recoveries of heavy metal ions by solid-phase extractant were investigated. These materials characterization was carried out using different techniques such as SEM, XRD, BET and UV–vis. The analytes such as Zn²⁺, Cu²⁺ and Pb²⁺ ions was enriched onto sorbent and subsequent eluted and determined by flame atomic absorption spectroscopy. The influences of the analytical parameters including pH, type and condition of eluent, adsorption capacities and amount of adsorbent, condition of eluent and sample volume on the metal ions recoveries were optimized. The optimum pH value for the separation of metal ions on these new sorbents was 4. The adsorbed metal ions could be completely eluted by using 10.0 mL 4.0 mol L^?1 HNO₃ solution. The loading of 30 mg of ligand onto 0.6 and 0.1 g of AC and Ag-NP-AC, respectively, make possible quantitative sorption of analytes. The accurate and easy determination of analytes in the presence of high limit of matrices constituent is possible without generation of significant problems. The applicability and accuracy of method were tested by its application for analytes quantification in complicated matrices with recoveries more than 91% and relative standard deviation lower than 5%.     

Adsorption of perchlorate onto raw and oxidized carbon nanotubes in aqueous solution

Perchlorate (ClO₄^?) is an emerging trace contaminant. The adsorption of ClO₄^? on raw and oxidized carbon nanotubes (CNTs) was investigated to elucidate the affinity mechanism of CNTs with anion pollutants. The adsorption of ClO₄^? into different CNTs increased in the order multi-walled CNTs < single-walled CNTs < double-walled CNTs (DWCNTs). Co-existing anions (SO₄^2?, NO₃^?, Cl^?) significantly weakened ClO₄^? adsorption, while the co-existence of Fe³⁺ and cetyltrimethylammonium cations increased ClO₄^? adsorption 2- to 3-fold. ClO₄^? adsorption was promoted by oxidized DWCNTs due to the introduction of more oxygen-containing functional groups, which served as additional adsorption sites. The pH values significantly affected the zeta potential of raw and oxidized DWCNTs and thus ClO₄^? adsorption. The pH-dependent curves of ClO₄^? adsorption on CNTs were distinct from those of conventional sorbents (e.g., activated carbon and resin). Maximum ClO₄^? adsorption occurred at pH = the isoelectric point (pH_IEP) + 0.85 rather than at pH < pH_IEP, which cannot be explained by electrostatic interactions alone. Hydrogen bonding is proposed to be a dominant mechanism at neutral pH for the interaction of ClO₄^? with CNTs, and variations of ClO₄^? affinity with CNTs in different pH ranges are illustrated.     

Adsorption Behavior of Rhodamine B on UiO-66

The adsorption characteristics of UiO-66 (a Zr-containing metal–organic framework formed by terephthalate) for Rhodamine B (RhB), such as isotherms, kinetics and thermodynamics, were investigated systematically. The batch adsorption data conform well to the Langmuir and Freundlich isotherms. The adsorption kinetics of UiO-66 for RhB can be well described by the pseudo first-order model, and the adsorption thermodynamic parameters ΔG₀, ΔH₀ and ΔS₀ at 273 K are − 6.282 kJ·mol^− 1, 15.096 kJ·mol^− 1 and 78.052 J·mol^− 1·K^− 1, respectively. The thermodynamic analyses show that the adsorption process of RhB on UiO-66 is more favorable at higher temperatures. UiO-66 can be regenerated by desorbing in DMF solution with ultrasonic for 1 h. UiO-66 can keep good performance for at least six cycles of sorption/desorption.     

Kinetic and thermodynamic studies on the removal of Cu(II) ions from aqueous solutions by adsorption on modified sand

Studies on the removal of copper by adsorption on modified sand have been investigated. The adsorbent was characterized by XRD, FTIR and SEM. Removal of Cu was carried out in batch mode. The values of thermodynamic parameters namely ΔG⁰, ΔH⁰ and ΔS⁰ at 25 °C were found to be −0.230 kcal⁻¹ mol⁻¹, +4.73 kcal⁻¹ mol⁻¹ and +16.646 cal K⁻¹ mol⁻¹, respectively. The process of removal was governed by pseudo second order rate equation and value of k₂ was found to be 0.122 g mg⁻¹ min⁻¹ at 25 °C. The resultant data can serve as baseline data for designing treatment plants at industrial scale.     

Removal of lead,copper, nickel,cobalt, and zinc from water by a cancrinite-type zeolite synthesized from fly ash

As a low Si/Al ratio zeolite, cancrinite received very scant study in previous studies on the adsorption removal of heavy metals from water. In this study, a cancrinite-type zeolite (ZFA) was synthesized from Class C fly ash via the molten-salt method. Adsorption equilibriums of Pb²⁺, Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺ on ZFA were studied in aqueous solutions and were well represented by Langmuir isotherms. The increase of pH levels during the adsorption process suggests that the uptake of heavy metals on ZFA was subjected to an ion exchange mechanism. It is found that the maximum exchange level (MEL) follows the order: Pb²⁺ (2.530 mmol g^?1) > Cu²⁺ (2.081 mmol g^?1) > Zn²⁺ (1.532 mmol g^?1) > Co²⁺ (1.242 mmol g^?1) > Zn²⁺ (1.154 mmol g^?1). Comparison with previous studies shows that the MEL of ZFA is higher than the commonly used natural zeolites; and it is also comparable to (or higher than) several synthetic zeolites and ion exchange resins. The high MEL of heavy metals on ZFA is attributed to the high cation exchange capacity (CEC) and proper pore size of cancrinite. The pseudo-first-order kinetics suggests that the ion exchange processes were diffusion-controlled.