Effect of Particle-Substrate Interactions on Colloidal Layer Structure Prepared by Convective Self-Assembly Using Polyelectrolyte-Grafted Silica Particles.

Cationic and anionic polyelectrolytes, poly(vinylbenzyl trimethylammonium chloride) (PVBTA) and poly(sodium styrene sulfate) (PSSS), were grafted on the surface of the silica particles, respectively, and then these two types of polyelectrolyte-grafted silica particles were applied to the colloidal layer preparation by convective self-assembly (CSA) using hydrophilic or hydrophobic glass substrates to investigate the effect of the interactions between the particles and the substrate surface on the resultant layer structures. When the PVBTA-grafted silica particle (PVBTA-Si) was used, the colloidal monolayers with a non-close-packed (NCP) structure were formed on both hydrophilic and hydrophobic glass substrates, where the NCP colloidal layers on the hydrophobic glass substrate have a somewhat more ordered structure than those on the hydrophilic glass substrate. In the case of the PSSS-grafted silica particle (PSSS-Si), on the other hand, stripe patterns with close-packed (CP) colloidal layers were obtained on both types of the glass substrates. The number of layers of the stripes on the hydrophilic glass substrate was less than that on the hydrophobic glass substrate, while the spacing and width of the stripes on both substrates were similar to each other. The difference in the structures of the colloidal layers obtained here indicates that an attractive interaction, such as an electrostatic attraction and a hydrophobic interaction, between the particle and the substrate surface is necessary to achieve the NCP structure by the CSA process using polyelectrolyte-grafted silica particles.

Efficient separation of phycocyanin of Nostoc commune by multistep diafiltration using ultra-filtration membrane modules.

Diafiltration (DF) is a separation method used to separate and concentrate macromolecules, such as polysaccharides and proteins. To obtain high-purity target molecules by DF, appropriate conditions should be used. In this study, a mathematical model was developed to suggest appropriate ultra-filtration (UF) membrane modules for the separation of phycocyanin (PC) by multistep DF. PC is a protein produced by microalgae. The contribution of each UF membrane module to PC productivity and purity at each stage of the multistep DF process was quantified by the proposed model. The parameters required as model inputs (k, Fα1, and Fα2) were experimentally determined by permeating PC-containing solution through UF membrane modules (150, 30, and 10 kDa cutoffs). The resulting analytical solutions and those predicted by the model were in close agreement. The PC purity increased from 0.20 to 0.30 when a 10 kDa UF membrane module was used in two-step DF. An orthogonal table was used to determine the combination of UF membrane modules needed to achieve higher purity of PC. The model predicted that the 30 kDa UF membrane module would have the highest contribution to PC productivity and purity at any position in a three-step DF. The developed model can help identify appropriate conditions for separating macromolecules by DF.

Separation of microalgae using a compacted magnetite-containing gel bed.

Separation of microalgae of various sizes and shapes is an important process that enables subsequent production of useful compounds. Herein, the separation of microalgae was accomplished using a magnetite-containing gel (42 µm) packed into a column. An algal suspension was injected into the top of the gel bed, after which water was passed through the column. The pressure generated during the process caused the lower domain of the gel bed to deform, resulting in narrowed gaps between the gel beads. When a suspension of Nannochloropsis sp. (0.0069-0.69 g L-1) was loaded and water was passed through the column at an applied pressure of 0.01-0.10 MPa, the majority of microalgae were captured within the upper domain of the gel bed, while only 20% were captured within the lower domain. The amount of Nannochloropsis sp. captured was expressed by an ordinary differential equation to determine the capture coefficient, K, and the maximum capture amount, Qmax. As pressure increased, gel gaps narrowed, K increased, and Qmax decreased because of a reduction in the number of effective capture sites upon compaction of the gel. When a mixed suspension of Anabaena sp., Monoraphidium sp., and Desmodesmus sp. (0.069 g L-1 each) was injected into the gel bed at an applied pressure of 0.01 MPa, only Anabaena sp. was captured at the bottom of the gel bed. This device can be applied for the separation of microalgae in rivers and the sea.

Surfactant-Assisted Synthesis of Pt Nanocubes Using Poly(N-isopropylacrylamide) Nanogels.

Poly(N-isopropylacrylamide) (PNIPAM) nanogels were prepared by emulsion polymerization using sodium dodecyl sulfate (SDS) and employed as a capping agent in platinum nanoparticle (Pt NP) synthesis by liquid-phase reduction with hydrogen gas. When the PNIPAM nanogels were used without removing SDS, that is, a slight amount of SDS was included in the reaction solution, Pt nanocubes (NCs) were predominantly produced (>80%). The proportion of the resultant Pt NCs was much higher than that obtained using the PNIPAM linear polymer (∼60%). To clarify the effects of the three-dimensional polymer network and SDS, we synthesized Pt NPs using the PNIPAM nanogel without SDS (SDS-free PNIPAM nanogel) and found that Pt NCs are rarely formed, and most NPs obtained have an irregular shape. When only SDS was used as a capping agent, NCs were hardly obtained, but other polyhedral NPs were formed. Furthermore, the use of SDS together with the PNIPAM polymer led to the decrease in the proportion of the Pt NCs compared with that obtained using only the linear polymer. These results indicate that the enhancement of the Pt NC proportion using the PNIPAM nanogel with SDS is attributable to not only the three-dimensional polymer network of the PNIPAM nanogel but also the assist of SDS as a capping agent.

Optimization of an adsorption process for tetrafluoroborate removal by zirconium (IV)-loaded orange waste gel from aqueous solution.

This investigation provides new insights into the effective removal of tetrafluoroborate (BF4-) by means of bio-sorption on waste generated in the orange juice industry. It was undertaken to evaluate the feasibility of zirconium (IV)-loaded saponified orange waste gel for BF4- removal from an aqueous solution. Batch adsorption experiments were carried out to study the influence of various factors such as pH, presence of competing anions, contact time, initial BF4- concentration and temperature on the adsorption of BF4-. The optimum BF4- removal was observed in the equilibrium pH region 2-3. The presence of coexisting anions showed no adverse effect on BF4- removal except SO4(2-). The equilibrium data at different temperatures were reasonably interpreted by the Langmuir adsorption isotherm and the maximum adsorption capacities were evaluated as 2.65, 3.28, 3.87 and 4.77 mmol g(-1) at 293, 298, 303 and 313 K, respectively. Thermodynamic parameters such as deltaGo, deltaHo and deltaSo indicated that the nature of BF4- adsorption is spontaneous and endothermic. The results obtained from this study demonstrate the potential usability of orange waste after juicing as a good BF4- selective adsorbent.

Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: an allosteric regulation of the first metal ion for stepwise extraction of the second ion.

A calix[5]arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5]arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5]arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.

Multiple proton ionizable calixarene derivatives with different ring sizes and complexation ability as efficient ionophores for complexation and solvent extraction of trivalent indium.

The solvent extraction behavior of multiple proton ionizable p-tert-butylcalix[4]arene and [6]arene carboxylic acid derivatives towards indium has been investigated along with an acyclic monomeric analogue from weakly acidic media into chloroform. The extraction mechanism is ion exchange and carboxylic acid groups are adequate ligating sites for extraction. The cyclic structure of calixarene ligands to accommodate the potential guest species and the cooperativity effect of multifunctional groups significantly affect the complexation behavior and calixarene derivatives are found to be excellent extractants over the monomeric analogue. The composition of the extracted complex depends on the solution pH and attempts to determine the composition of the extracted complex for the extraction of indium have been stymied by complications arising from the formation of polynuclear species of indium and bridged polymeric species of calixarene carboxylic acid derivatives. One mole of calix[4]arene derivative extracts 2.5 moles of indium whereas the calix[6]arene derivative tends to extract 4.0 moles of indium. The loaded indium is back extracted with 1 mol dm(-3) hydrochloric acid solution. Though quantitative back extraction of indium was achieved from the fully loaded calix[6]arene derivative, it was only achieved up to 85% in the case of the calix[4]arene derivative.

Recovery of Filtered Particles by Elastic Flat-Sheet Membrane with Cross Flow.

After filtration, filtered residue is recovered by a spoon, during which, the structure of the residue is destroyed, and the activity of the microorganism would be reduced. Thus, a more efficient recovery method of filtered residue is required. This study addressed the recovery method of filtered residue by the restoration of an elastic membrane, followed by cross flow. An elastic membrane composed of a copolymer of poly(ethylene glycol) diacrylate and polyacrylonitrile was prepared by photopolymerization. The pore diameter of the obtained membrane was about 10 µm. Silica particle (1 and 10 µm) and Nannochloropsis sp. (2 µm) suspension was filtered, demonstrating that silica particles of 10 µm were filtered perfectly, whereas the filtration percentage of 1 µm silica particles and Nannochloropsis sp. was lower. After the filtration, the applied pressure was released to restore the elastic membrane which moved the filtered particles up, then the filtered residue was recovered by cross flow above the membrane, demonstrating that 71% of the filtered 10 µm silica particles was recovered. The elastic behavior of the membrane, along with the cross flow, has the potential to be used as a technique for the recovery of the filtered residues. This proposed scheme would be used for the particle recovery of ceramics, cells, and microorganisms from a lab scale to a large-scale plant.

Dewatering of algal suspension using microfiltration with cross flow in the presence of magnetite as a filter aid.

Dewatering algal suspensions is an important step in the extraction of oil and other useful substances from algae. In this study, spherical Nannochloropsis sp. and ellipsoidal Monoraphidium sp. suspensions were dewatered in the presence of different amounts of 350-nm magnetite particles using a microfiltration membrane with 360-nm pores in cross-flow mode. Magnetite functions as a filter aid by reducing the deformation of the cake of filtered algae on the membrane and providing paths for water to flow through the filtration cake of algae. In the case of Nannochloropsis sp., the highest dewatering rate was obtained when the number ratio, defined based on the size and ideal density, between Nannochloropsis sp. and magnetite was 1:12.5, but the addition of magnetite had no observable effect on the filtration of ellipsoidal Monoraphidium sp. suspensions through the membrane. After dewatering, magnetite was effectively separated from the concentrated algal suspension by the application of a magnetic field in an open flow system. Magnetite has the potential to enhance dewatering performance using a cross-flow membrane system.

Filtration of Elastic Polymers and Spherical Gels through a Silica-Deposited Layer on a Porous Membrane.

A 120-nm silica suspension was permeated through a porous polyethylene (PE) hollow-fiber membrane, as was a solution of deformable elastic particles of poly(N-isopropylacrylamide) (PNIPAM) gel and dextran. The amount adsorbed and flux of permeation were analyzed with ordinary differential equations to obtain adsorption coefficients, maximum amounts adsorbed, and pore-narrowing factors. The thickness of the "silica-deposited layer" on the membrane was 1 µm. In a batch adsorption mode, 5.0 mg of PNIPAM gel and 30 mg of dextran were adsorbed on the PE membrane, with no adsorption on the silica. The PE membrane pores were narrowed by a secondary layer of adsorbed PNIPAM gel. When filtered through the silica-deposited layer, PNIPAM gel occupies gaps, resulting in a reduced permeation flux. Dextran passed through the silica-deposited layer and was partially adsorbed on the PE membrane. The modified membrane can control adsorption, filtration, and flux permeation, which leads to dynamic membrane separations.

Dynamic rejection of colloidal particles with generating dextran by enzymatic reaction.

Dextransucrase forms a complex with dextran during an enzymatic reaction with sucrose. Using its enzymatic character, we performed a continuous and dynamic rejection of colloidal particles by generating dextran with dextransucrase immobilized in an inorganic porous membrane. Inorganic membranes having 1.9 and 3.0 U/g of immobilized dextransucrase, and 4.1 and 9.4 mg/g of generated dextran, respectively, had constant rejection percentages for 55 and 100 nm colloidal particles in permeating solutions. On the other hand, permeating sucrose solutions containing colloidal particles through a dextran-immobilized membrane dynamically increased the rejection percentages of the colloidal particles owing to dextran generation via enzymatic reaction. The dynamic increase was due to the gradually generating dextran dynamically occupying the membrane pore with its steric volume.

Grape waste as a biosorbent for removing Cr(VI) from aqueous solution.

Grape waste generated in wine production is a cellulosic material rich in polyphenolic compounds which exhibits a high affinity for heavy metal ions. An adsorption gel was prepared from grape waste by cross-linking with concentrated sulfuric acid. It was characterized and utilized for the removal of Cr(VI) from synthetic aqueous solution. Adsorption tests were conducted in batch mode to study the effects of pH, contact time and adsorption isotherm of Cr(VI), which followed the Langmuir type adsorption and exhibited a maximum loading capacity of 1.91 mol/kg at pH 4. The adsorption of different metal ions like Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at different pH values 1-5 has also been investigated. The cross-linked grape waste gel was found to selectively adsorb Cr(VI) over other metal ions tested. The results suggest that cross-linked grape waste gel has high possibility to be used as effective adsorbent for Cr(VI) removal.

Leaching of phosphorus from incinerated sewage sludge ash by means of acid extraction followed by adsorption on orange waste gel.

Ashes from sewage sludge incineration have a high phosphorus content, approximately 8% (W/W), which indicates a potential resource of the limiting nutrient. Incineration of sewage sludge with subsequent recovery of phosphorus is a relatively new sludge treatment technique. In this article, the leaching of phosphorus by using sulfuric acid as well as hydrochloric acid by means of several batch experiments was presented. At the same time a selective recovery of phosphorus by adsorption was also discussed. The effects of acid concentration, temperature and time on extraction were studied. The phosphorus leaching increased with the increase in acid concentration and temperature. Kinetic studies showed that the complete leaching of phosphorus took place in less than 4 h. Selective adsorption of phosphorus by using orange waste gel provided a hint for recovery of this natural resource, which eventually could meet the ever-increasing requirement for phosphorus. The overall results indicated that the incinerated sewage sludge ash can be treated with acid to efficiently recover phosphorus and thus can be considered a potentially renewable source of phosphorus.

Hydrothermal preparation of a platinum-loaded sulphated nanozirconia catalyst for the effective conversion of waste low density polyethylene into gasoline-range hydrocarbons.

A platinum-loaded sulphated nanozirconia (Pt/nano ZrO2-SO4) bifunctional metal-acid catalyst was synthesized using a hydrothermal process. The nano ZrO2-SO4 was initially prepared by dispersing the nano ZrO2 in H2SO4, followed by wet impregnation via heating in an aqueous PtCl4 solution. This material was subsequently calcined and reduced under hydrogen gas to produce the catalyst. The Pt/nano ZrO2-SO4 was found to be a highly active, selective and stable solid acid catalyst for the conversion of waste low density polyethylene (LDPE) to high value hydrocarbons. The catalytic activity and stability of this material were evaluated during the hydrocracking of waste LDPE while optimizing the reaction temperature, time and catalyst-to-feed ratio. The activity of catalyst prepared by hydrothermal was attributed to highly dispersion of Pt species interacting with the support and inhibition of the agglomeration process. The impregnation method of hydrothermal generated highly active and selective catalyst with Pt loads of 1 wt%. The hydrocracking of waste LDPE over Pt/nanoZrO2-SO4 at 250 °C for 60 min with a catalyst-to-feed proportion of 1 wt% gave the largest gasoline fraction.

Novel carbonyl-group-containing dextran synthesis by pyranose-2-oxidase and dextransucrase.

The carbonyl polysaccharide, keto-dextran, was synthesized by the regioselective oxidation of sucrose and by the subsequent transfer reaction of the oxidized sucrose. The regioselective oxidation of sucrose was performed by bioconversion with pyranose-2-oxidase (EC 1.1.3.10). After 24h, the conversion percentage of sucrose into keto-sucrose was 100% as determined by a colorimetric method with dinitrophenylhydrazine. Converted keto-sucrose was polymerized to keto-dextran by dextransucrase (EC 2.4.1.5). Polymerization of keto-dextran was confirmed by the increase in molecular weight and amount of keto-dextran produced. The amount of keto-dextran produced decreased to 80% of the amount of dextran produced owing to the substrate recognition of DSase. From a Lineweaver-Burk reciprocal plot, the Michaelis constants for sucrose and keto-sucrose were 4.6 mmol L(-1) and 14.0 mmol L(-1), respectively. The keto-dextran had a carbonyl group in all glucose units.

Removal and recovery of phosphorus from water by means of adsorption onto orange waste gel loaded with zirconium.

Orange waste, an available biomass, was immobilized with zirconium(IV) to investigate its feasibility for phosphate removal from an aquatic environment. Kinetics, effects of pH and foreign anions, and the adsorption isotherm for phosphate have been examined. The adsorption capacity has been compared to that of two commercially available adsorbents such as zirconium ferrite and MUROMAC XMC 3614. The prepared gel was an effective adsorption gel for phosphate removal with a reasonably high sorption capacity of 57mg-P/g, which was four times higher than that of zirconium ferrite. The highest removal of phosphate was observed at low pH, whereas higher pH suppressed phosphate removal, but even up to pH 9 more than 85% phosphate removal was observed. Adsorbed phosphate was eluted by NaOH solution. Fixed bed column-mode experiments confirmed the complete adsorption of phosphate in continuous-mode operation. Throughout the operating conditions, zirconium was not leaked.

Heavy metal removal from contaminated scallop waste for feed and fertilizer application.

The present work elucidates environmental friendly removal process of heavy metals by using biomass waste and natural product. The process consists of the following three steps: (1) leaching of all metals including heavy metals by dilute sulfuric acid, (2) removal of turbid organic materials from the leach liquor by means of coagulation using astringent persimmon extract enriched with persimmon tannin leaving all heavy metal ions in the leach liquor and (3) adsorptive removal of heavy metals by means of adsorption onto the gel prepared from apple waste. The operational conditions at these three steps were discussed in detail, among which the pH adjustment is the key factor; i.e. the lower the pHs the higher the efficiency of the leaching, while reverse was the case for the adsorption.

Pre-concentration and separation of heavy metal ions by chemically modified waste paper gel.

Iminodiacetic acid was immobilized on waste paper by chemical modification in order to develop a new type of adsorption gel for heavy metal ions. Adsorption behavior of the gel was investigated for a number of metal ions, specifically Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. From batch adsorption tests, the order of selectivity was found to be as follows: Cu(II)>>Fe(III)>Pb(II)>Ni(II)>>Co(II)>Cd(II). Column tests were carried out for pairs of metal ions to understand the separation and pre-concentration behavior of the gel. It was found that mutual separation of Ni(II) from Co(II) and that of Pb(II) from Cd(II) can be achieved at pH 3. Similarly, selective separation of Cu(II) from Cu(II)-Fe(III) and Cu(II)-Pb(II) mixtures at pH 1.5 and 2, respectively, was observed by using this new adsorption gel. In all cases, almost complete recovery of the adsorbed metal was confirmed by elution tests with HCl.

Adsorptive removal of As(V) and As(III) from water by a Zr(IV)-loaded orange waste gel.

Orange waste, produced during juicing has been loaded with zirconium(IV) so as to examine its adsorption behavior for both As(V) and As(III) from an aquatic environment. Immobilization of zirconium onto the orange waste creates a very good adsorbent for arsenic. Adsorption kinetics of As(V) at different concentrations are well described in terms of pseudo-second-order rate equation with respect to adsorption capacity and correlation coefficients. Arsenate was strongly adsorbed in the pH range from 2 to 6, while arsenite was strongly adsorbed between pH 9 and 10. Moreover, equimolar (0.27 mM) addition of other anionic species such as chloride, carbonate, and sulfate had no influence on the adsorption of arsenate and arsenite. The maximum adsorption capacity of the Zr(IV)-loaded SOW gel was evaluated as 88 mg/g and 130 mg/g for As(V) and As(III), respectively. Column adsorption tests suggested that complete removal of arsenic was achievable at up to 120 Bed Volumes (BV) for As(V) and 8 0BV for As(III). Elution of both arsenate and arsenite was accomplished using 1 M NaOH without any leakage of the loaded zirconium. Thus this efficient and abundant bio-waste could be successfully employed for the remediation of an aquatic environment polluted with arsenic.

Comparison of interfacial behavior and silver extraction kinetics with various types calix[4]arene derivatives at heterogeneous liquid-liquid interfaces.

Various p-tert-octylcalix[4]arene derivatives as hydrophobic extractants have been prepared to investigate Ag(I) extraction efficiency in a batch-wise process in nitric acid media. The influence of the functional groups of the hydrophobic extractants on the interfacial behavior and Ag(I) extraction efficiency in nitric acid media has been investigated using the drop-volume method. Fitting of the interfacial tension isotherms to the Gibbs and Szyszkowski equations has provided parameters characterizing the interfacial activity of the extractants, in particular the Gibbs free energy of adsorption at the interface, the interface excess on saturation (Г∞) and the average area per the adsorbed extractant molecule (Amin). The amido-type p-tert-octylcalix[4]arene derivatives have strong interfacial activity and fast extraction rates. The interface excess at saturation (Г∞) increased with the type of functional groups in the following order: methyl ketonic < phenyl ketonic < dibenzyl amido < diethyl amido < quinolyl < pyridyl. The relationship between the interfacial activity and the dependence of the Ag(I) extraction efficiency on the different functional groups is discussed. The interfacial behavior of the extractants affected both the solvent extraction equilibrium and the kinetics and the overall results are consistent with a mass transfer mechanism at the heterogeneous liquid-liquid interfaces.