Synthesis of mesoporous silica from geothermal water.

Mesoporous silica was successfully synthesized for the first time using geothermal water from the Onuma Geothermal Power Plant, Akita Prefecture, Japan. Cetyltrimethylammonium bromide (CTAB) was used as an organic template for the synthesis. CTAB with a concentration of 2.4 × 10-4 mol/L was reacted for 30 min with geothermal water at a temperature of 90 °C, which had a total silicic acid concentration of 475 mg/L (SiO2), at pH 7.0, pH 8.2 (raw water) and pH 9.0. By calcination of the resulting precipitate at 550 °C, mesoporous silica with a pore size of about 2.8 nm and a specific surface area of > 800 m2/g was formed. The total silicic acid concentration in the solution after formation of the mesoporous precipitates was reduced to < 280 mg/L, indicating efficient recovery of supersaturated silicic acid from geothermal water. The monosilicic acid in geothermal water plays an important role in the formation of mesoporous silica. Production of mesoporous silica by our method will contribute not only to prevention of silica scale formation in the piping systems of geothermal power plants but also to its use as an industrial resource.

Investigations on Adsorption of Inorganic Ions in Aqueous Solution to Some Metal Oxides, Hydroxides and a Carbonate by the X-Ray Spectroscopic Method.

Why does the adsorption and concentration of inorganic chemical species proceed at aqueous-solid interfaces? In this review paper, we discuss the use of X-ray chemical state analysis to elucidate the intrinsic adsorption mechanism. Based on the chemical states of the species adsorbed to solids as determined by X-ray chemical state analysis, possible adsorption mechanisms are discussed. The driving forces of adsorption are represented by the Gibbs free energy change (ΔGchem = ΔGchem,1 + ΔGchem,2) resulting from the formation of covalent bonds between metal ions (M) in metal oxides or hydroxides and adsorbed species (X) (M-O-X bond, ΔGchem,1) and the formation of new phases consisting of M and X (ΔGchem,2). The concept of ΔGchem,2 is proposed based on the experimental results from chemical state analyses. As examples, the following investigations are discussed in this review paper: the formation of mullite precursors by the adsorption of monosilicic acid to Al(OH)3, the spontaneous reduction of Au(III) to Au(0) by adsorption of Au(III) to Al(OH)3, MnO2 and Ni(OH)2 and the mechanism of concentration of Co2+, Tl+, Pb2+, Pt2+, Au+, and Pd2+ in marine ferromanganese crusts.

A new and practical Se(IV) removal method using Fe3+ type cation exchange resin.

An effective method for removing selenium (Se) from water is required from the viewpoint of environmental preservation. To establish this method, a cation exchange resin that adsorbed ferric ions was applied as an adsorbent. In this study, the adsorption behavior of Se to the adsorbent was examined by both batch and column methods. The batch experiment confirmed that selenite ions (Se(IV)) are effectively adsorbed but selenate ions (Se(VI)) are hardly adsorbed. To elucidate the adsorption mechanism, the Fe in the adsorbent and the Fe in the adsorbent after the adsorption of Se(IV) were characterized by Fe K-edge X-ray absorption spectroscopy and 57Fe Mӧssbauer spectroscopy. The analytical result of Se K-edge EXAFS spectra for the Se(IV) adsorbed on the adsorbent suggests that Se(IV) are adsorbed specifically to the adsorbent through the formation of Fe-O-Se bonds. The breakthrough curve obtained by the column experiment showed that Se(IV) in 3 tons of synthetic solution containing 0.1 ppm Se can be efficiently removed using a column in which 12.8 g (10.4 cm3) of the adsorbent was packed.

Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity.

Decarbonylation of furfural to furan was efficiently catalyzed by ZrO2 -supported Pd clusters in the liquid phase under a N2 atmosphere without additives. Although Pd/C and Pd/Al2 O3 have frequently been used for decarbonylation, Pd/ZrO2 exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO2 . ZrO2 with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al2 O3 despite their high surface areas. The catalytic activity of Pd/ZrO2 was enhanced with a decrease in particle size, and the smallest Pd/ZrO2 was the most active catalyst for decarbonylation. When CeO2 was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO2 with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO2 . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO2 maintained its catalytic activity until its sixth use.

A tightly regulated expression system for E. coli using supersaturated silicic acid.

OBJECTIVE: To develop a new expression system regulated by a ferric uptake regulator in which silicic acid is used as an inducer. RESULTS: Fur box (binding site for Fur) was substituted for the lac operator to regulate the expression of GFP with the lac promoter. Since the addition of supersaturated silicic acid invokes iron deficiency, supersaturated silicic acids were used as an inducer. GFP expression was dependent on silica concentration, and the expression level without silica was negligible. Basal expression level of this lac-Fur system was extremely low and, hence, lytic enzyme gene E from bacteriophage ϕX174 could be retained in this system. Furthermore, the expression of genes of interest was spontaneously initiated as the cell density increased and the costs of the inducer are considerably less than IPTG. CONCLUSION: The combination of lac promoter and Ferric uptake repressor allowed the protein expression by supersaturated silicic acid as an inducer in an easy and cost-effective way.

Silica-Induced Protein (Sip) in Thermophilic Bacterium Thermus thermophilus Responds to Low Iron Availability.

UNLABELLED: Thermus thermophilus HB8 expresses silica-induced protein (Sip) when cultured in medium containing supersaturated silicic acids. Using genomic information, Sip was identified as a Fe(3+)-binding ABC transporter. Detection of a 1-kb hybridized band in Northern analysis revealed that sip transcription is monocistronic and that sip has its own terminator and promoter. The sequence of the sip promoter showed homology with that of the σ(A)-dependent promoter, which is known as a housekeeping promoter in HB8. Considering that sip is transcribed when supersaturated silicic acids are added, the existence of a repressor is presumed. DNA microarray analysis suggested that supersaturated silicic acids and iron deficiency affect Thermus cells similarly, and enhanced sip transcription was detected under both conditions. This suggested that sip transcription was initiated by iron deficiency and that the ferric uptake regulator (Fur) controlled the transcription. Three Fur gene homologues (TTHA0255, TTHA0344, and TTHA1292) have been annotated in the HB8 genome, and electrophoretic mobility shift assays revealed that the TTHA0344 product interacts with the sip promoter region. In medium containing supersaturated silicic acids, free Fe(3+) levels were decreased due to Fe(3+) immobilization on colloidal silica. This suggests that, because Fe(3+) ions are captured by colloidal silica in geothermal water, Thermus cells are continuously exposed to the risk of iron deficiency. Considering that Sip is involved in iron acquisition, Sip production may be a strategy to survive under conditions of low iron availability in geothermal water. IMPORTANCE: The thermophilic bacterium Thermus thermophilus HB8 produces silica-induced protein (Sip) in the presence of supersaturated silicic acids. Sip has homology with iron-binding ABC transporter; however, the mechanism by which Sip expression is induced by silicic acids remains unexplained. We demonstrate that Sip captures iron and its transcription is regulated by the repressor ferric uptake regulator (Fur). This implies that Sip is expressed with iron deficiency. In addition, it is suggested that negatively charged colloidal silica in supersaturated solution absorbs Fe(3+) ions and decreases iron availability. Considering that geothermal water contains ample silicic acids, it is suggested that thermophilic bacteria are always facing iron starvation. Sip production may be a strategy for surviving under conditions of low iron availability in geothermal water.

Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides.

The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.

¹³C and ²7Al NMR study of complexation between aluminium ion and simple dicarboxylic acids under an acidic condition: new peak assignments of ²7Al NMR spectra of mixed solutions of Al³âº and simple dicarboxylic acids.

Due to a consideration of Al detoxicification by simple carboxylic acid, the interaction between aluminium ion (Al³âº) and three dicarboxylic acids (oxalic acid (OX), malonic acid (MA) and succinic acid (SU)) under an acidic condition was investigated using ¹³C and ²7Al NMR techniques. Based on deconvolution of the ²7Al NMR spectra and quantitative ¹³C NMR spectra, the structure of each complex was elucidated. Especially, we focused on the peak assignments of ²7Al NMR spectra by combining of the results of quantitative ¹³C NMR spectra. In the OX system, the peak at 16 ppm in the ²7Al NMR spectrum originates from Al(OX)3³â» and Al(OX)2⁻, and the ratio of each complex depends on the OX/Al molar ratio. In the MA system, the three complexes (Al(MA)2⁻, Al(MA)3³â» and Al(MA)⁺) are represented in the peak at 2 ppm in the ²7Al NMR spectrum. The assignment of peaks in the ²7Al NMR spectra in this study differs from those described in previous papers.

Quantification method of size distribution of polysilicic acid in supersaturated silicic acid solution.

In order to estimate the absolute size distribution of polysilicic acid particles in geothermal waters, the distribution coefficient (K(av)) of gel permeation chromatography (GPC) for polysilicic acid particles and the hydrodynamic radius for the same polysilicic acid particles from Dynamic Light Scattering (DLS) are combined to quantify the particle size. From the combination, a quantitative relationship between the K(av) from GPC and the hydrodynamic radius for polysilicic acid from DLS was built up. Using this relationship, the change in particle size of polysilicic acid formed during the polymerization of silicic acid at pH 8 and 9 (initial silicic acid concentration: 800 ppm as SiO2) was examined. The result showed that polysilicic acid grew to 500 and 1000 nm by 5 h at pH 9 and 8, respectively. It was found that aluminum affects the growth of polysilicic acid particles, and that the effect depends on the pH. The proposed method in this study has been proved to be valid to measure the size of polysilicic acid during the polymerization of silicic acid in solutions with relatively low silicic acid concentration, such as geothermal water.

Adsorption kinetics of silicic acid on akaganeite.

As part of a series of studies on the interaction between ferric ions and silicic acid in the hydrosphere, the adsorption of silicic acid on akaganeite was investigated kinetically at various pH values. The adsorption of silicic acid increased with increasing pH over an initial pH range of 4-11.5. In the kinetic experiment, the Cl(-) was released from akaganeite much faster than silicic acid was adsorbed. From this result, we concluded that chloride ions bound on the surface of akaganeite are released and Fe-OH or Fe-O(-) sites are formed, which then acts as an adsorption site for silicic acid. The uptake mechanism of silicic acid by akaganeite is significantly different from that by schwertmannite, despite the presence of the same tunnel structure.

Silica deposition induced by isolated aluminum ions bound on chelate resin as a model compound of the surface of microbes.

To elucidate the mechanism of silica biodeposition in hot spring water, which is induced by Al(3+) ions bound to the surface of microbes, a chelate resin (Chelex 100) was used as a model compound of the surface of microbes. No silicic acid was adsorbed on the Na type Chelex 100, whereas silicic acids were significantly adsorbed to the Al type Chelex 100. In the Al type Chelex 100, the Al(3+) ions were present as 1:1 tridentate complex with iminodiacetate (IDA) group. After adsorption of silicic acid to Al type Chelex 100, a IDA-Al-O-Si-(OH)(3) site formed. The site acted as a template for the successive adsorption of silicic acids to form silica sheets around Al type Chelex 100 particles. In conclusion, Al(3+) ions bound to the surface of microbes play a key role as a trigger for the biodeposition of silica in hot spring water.

Interaction of Au(III) and Pt(IV) complex ions with Fe(II) ions as a scavenging and a reducing agent: a basic study on the recovery of Au and Pt by a chemical method.

In order to develop a chemical technique for the recovery of gold (Au) and platinum (Pt) in the metallic state from spent catalysts, e.g., catalysts for environmental protection and automobile and petroleum catalysts, the coprecipitation behaviors of Au(III) and Pt(IV) complex ions with Fe(OH)(2) as a scavenging and reducing agent were investigated. The Au(III) complex ions were found to be stoichiometrically and rapidly reduced to metallic Au due to electron transfer in acidic aqueous solution prior to coprecipitation with Fe(OH)(2). Conversely, Pt(IV) complex ions were reduced only after coprecipitation with Fe(OH)(2) due to electron transfer through a Pt(IV)-O-Fe(II) bond on the solid Fe(OH)(2). Using this chemical technique, Au and Pt can be selectively and effectively recovered in the metallic state.

The inhibition abilities of multifunctional polyelectrolytes for silica scale formation in cooling water systems: role of the nonionic functional group.

The abilities of multifunctional polyelectrolytes to enhance aluminum hydroxide dispersion and inhibit silica scale formation were examined in a pilot cooling water system. The following multifunctional polyelectrolytes were studied: a terpolymer of acrylic acid (AA), 2-acrylamide-2-methyl propane sulfonic acid (SA) and N-vinylpyrrolidone (NVP) (P(AA/SA/NVP)), acrylic acid homopolymer (P(AA)) and a copolymer of AA and SA (P(AA/SA)). The order of inhibition ability was P(AA/SA/NVP)>P(AA/SA)>P(AA), and was consistent with that of the dispersing ability for aluminum hydroxide. Other terpolymers incorporating different nonionic monomers were also examined and factors affecting their inhibition abilities were investigated, based on interaction energies calculated by density functional theory. Based on the correlation between scale inhibition abilities and interaction energies, we elucidated that the effective nonionic monomer of terpolymer for silica scale inhibition had low affinity for aluminum hydroxide and high affinity for H(2)O and Si(OH)(3)O(-). The affinities of nonionic monomer for aluminum hydroxide and H(2)O suggested that there was proper conformation of polyelectrolyte adsorbed for effectively dispersing aluminum hydroxide. Also, high affinity of nonionic monomer for Si(OH)(3)O(-) suggested that interacting Si(OH)(3)O(-) is an important role of inhibition of silica scale formation.

Interaction between Al3+ and acrylic acid and polyacrylic acid in acidic aqueous solution: a model experiment for the behavior of Al3+ in acidified soil solution.

From the viewpoint of the phytotoxicity and mobility of Al(3+) released from soil minerals due to soil acidification, the interaction between Al(3+) and acrylic acid (AA) and polyacrylic acid (PAA) as a model compound of fulvic acid was investigated. The interaction was examined at pH 3 so as to avoid the hydrolysis of Al(3+). The interaction between Al(3+) and AA was weak. However, the interaction between Al(3+) and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (R(P)) of the solution. For the range of 1/R(P), the interaction between Al(3+) and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al(3+) combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al(3+) combines to more than 2 carboxyl groups of other Al-PAA-complexes) in addition to the 1:1 Al-PAA-complex and (3) precipitation of intermolecular complexes. In conclusion, R(P) is an important factor affecting the behavior of Al(3+) in acidic soil solution.

Formation of a silicato complex of zinc in aqueous solution and its accelerating effect on the formation of silica scales in cooling water systems.

This study elucidates the effect of zinc (Zn), which is an anticorrosive water additive, on the formation of silica scales from cooling water. In these experiments, the silica scales were analyzed by EPMA, and the results indicate that Zn is sorbed into the silica scales during formation. Measurements of the solubility of Zn(OH)(2) at various concentrations of silicic acid demonstrate that Zn is present as a silicato complex of Zn (SCZ) in cooling water. From adsorption experiments of the SCZ on silica and alumina, which are major components of the silica scales, it can be concluded that the SCZ accelerates the formation of silica scales from cooling water.

Effects of adsorption conformation on the dispersion of aluminum hydroxide particles by multifunctional polyelectrolytes.

The influence of multifunctional polyelectrolytes on the dispersion of aluminum hydroxide particles was studied, in particular the influence of monomer units acting as functional groups, with respect to particle size and zeta potential. The conformation of polyelectrolytes adsorbed on aluminum hydroxide particles, which affects their dispersion abilities, was investigated via their adsorption isotherms and (1)H NMR spectral analysis. Furthermore, the functions of monomer units were evaluated by the calculation of the interaction energies between each monomer unit and aluminum hydroxide or H(2)O by density functional theory. Three multifunctional polyelectrolytes were compared: a terpolymer of acrylic acid (AA), 2-acrylamide-2-methyl propane sulfonic acid (AMPS), and N-vinylpyrrolidone (NVP) (P(AA/SA/NVP)), acrylic acid homopolymer (P(AA)), and a copolymer of AA and AMPS (P(AA/SA)). The most effective dispersant was P(AA/SA/NVP), which prevented further coagulation among the initial particles and shifted the zeta potential to the most negative value. The conformations of the adsorbed polyelectrolytes exhibited the following order of extended conformation (larger loops and longer tails): P(AA) > P(AA/SA/NVP) > P(AA/SA). From these results, we reasonably concluded that the prominent dispersing capability of P(AA/SA/NVP) was due to its preferred extended conformation on the particle surface due to a subtle balance between the moderate affinity of NVP and the relatively higher affinities of AA and AMPS for aluminum hydroxide in an aqueous solution and the hydrophobicity of the amide groups of AMPS.

One-pot synthesis of indoles and aniline derivatives from nitroarenes under hydrogenation condition with supported gold nanoparticles.

One-pot sequences of hydrogenation/hydroamination to form indoles from (2-nitroaryl)alkynes and hydrogenation/reductive amination to form aniline derivatives from nitroarenes and aldehydes were catalyzed by Au nanoparticles supported on Fe(2)O(3). Nitro group selective hydrogenations and successive reactions were efficiently catalyzed under the conditions.

Formation conditions and stability of a toxic tridecameric Al polymer under a soil environment.

It is important to study the formation conditions and the stability of the tridecameric Al polymer (Keggin-type Al(13) polycation, [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+), known as Al(13)) due to its strong toxicity to living organisms of a soil environment. In order to examine the pH range where toxic Al(13) can exist in aqueous solution, (27)Al NMR spectra for sample solutions containing Al(3+) ions with various pH (pH 3.5-6.1) were measured. The results show that the peak due to Al(13) (peak due to 4-coordinated Al around 63 ppm) appeared at pH 3.6-5.7 and the peak intensity was relatively high at pH 4.1-4.8, suggesting that Al(13) can be formed at pH 3.6-5.7, while it can exist dominantly at pH 4.1-4.8. It was also found that Al(13) can stably adsorb onto a chelate resin, Chelex 100, by weak electrostatic interaction. The Chelex 100, with iminodiacetate groups, served as a model compound for surfaces of microbes covered with carboxyl groups and for surfaces of soil particles covered with humic substances having many carboxyl groups. Additionally, decomposition of Al(13) did not occur even after adsorption, and its pH stability range was wide compared to that in aqueous solution.

Effect of aluminum on the deposition of silica scales in cooling water systems.

The mechanism of formation of silica scales from cooling water was studied by chemical analyses of the cooling water and silica scales, characterization of the aluminum in the silica scales by 27Al magic angle spinning NMR, the relationship between size distribution of particles in the cooling water and their Al/Si atomic ratios and zeta potentials, and the adsorption properties of the particles on the surface of silica gel powder as a mimic of silica scale. From our results, we determined that aluminum is concentrated from the cooling water into silica scales during their formation, 6-coordinate aluminum is preferentially adsorbed on the surface of the solid, and various particles with differing sizes, surface charges, and Al/Si atomic ratios are formed in the cooling water after addition of polyaluminum chloride. The formation mechanism for silica scales in the cooling water system is proposed based on the electrostatic interaction. The formation of aluminum hydroxide particles smaller than 0.2 microm with positive charges, consisting of 6-coordinate aluminum, and their subsequent adsorption on the surface of the solid are the most important factors contributing to the formation of silica scales.

Stimulation of expression of a silica-induced protein (Sip) in Thermus thermophilus by supersaturated silicic acid.

The effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan, were examined at 75 degrees C. At concentrations higher than the solubility of amorphous silica (400 to 700 ppm SiO(2)), a silica-induced protein (Sip) was isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the molecular mass and pI of Sip to be about 35 kDa and 9.5, respectively. Induction of Sip expression occurred within 1 h after the addition of a supersaturating concentration of silicic acid to TM broth. Expression of Sip-like proteins was also observed in other thermophiles, including T. thermophilus HB8 and Thermus aquaticus YT-1. The amino acid sequence of Sip was similar to that of the predicted solute-binding protein of the Fe(3+) ABC transporter in T. thermophilus HB8 (locus tag, TTHA1628; GenBank accession no. NC_006461; GeneID, 3169376). The sip gene (987-bp) product showed 87% identity with the TTHA1628 product and the presumed Fe(3+)-binding protein of T. thermophilus HB27 (locus tag TTC1264; GenBank accession no. NC_005835; GeneID, 2774619). Within the genome, sip is situated as a component of the Fbp-type ABC transporter operon, which contains a palindromic structure immediately downstream of sip. This structure is conserved in other T. thermophilus genomes and may function as a terminator that causes definitive Sip expression in response to silica stress.