Petr Praus

Information retrieval in hydrochemical data using the latent semantic indexing approach

Kwok-wing Chau (corresponding author) Nitin Muttil Department of Civil and Structural Engineering, Hong Kong Polytechnic University, Hung Hom, Hong Kong, China Tel: +852 2766 6014 E-mail: cekwchau@polyu.edu.hk In this study, data mining using box plots and multivariate statistical analysis using factor analysis are employed for a spatio-temporal analysis of coastal water quality data from Tolo Harbour, Hong Kong. The analysis of box plots reveals pronounced spatial heterogeneity of the parameters studied. The spatial analysis clearly shows monitoring station TM2 in the Harbour Subzone to be most susceptible to eutrophication with the highest nutrient and algal biomass concentrations. The factor analysis brings to light dominant parameters to the ecological system under the coastal marine environment. The temporal analysis confirms the considerable decline in nutrient levels in recent years. In spite of this decline, the factor analysis indicates that nutrient processes play an important role even in recent years, suggesting an adequate supply of nutrients. It seems that they are being released from sources other than known point sources, possibly from nutrients accumulated in the sediments, necessitating steps to be undertaken for their control also. This study demonstrates the use of data mining techniques in the ecological system in Tolo Harbour.

CdS nanoparticles deposited on montmorillonite: Preparation, characterization and application for photoreduction of carbon dioxide

CdS nanoparticles were precipitated by the reaction of cadmium acetate with sodium sulphide in the presence of cetyltrimethylammonium (CTA) and deposited on montmorillonite (MMT). The resulting CdS-MMT nanocomposite contained 6 wt.% of CdS and 30 wt.% of CTA. Band-gap energy of CdS was estimated at 2.63±0.09 eV using the Tauc plot. The size of CdS nanoparticles was calculated from the band-gap energy at 5 nm and from the micrographs of transmission electron microscopy (TEM) at 5 nm. Selected area electron diffraction (SAED) recognized the cubic structure of CdS (Hawleite). The dynamic light scattering (DLS) method confirmed that CdS nanoparticles were anchored on the surface of MMT particles. CTA was found to be intercalated into MMT and adsorbed on its external surface. CdS-MMT was used for the photoreduction of carbon dioxide dissolved in NaOH solutions. The yields of originating gas products can be arranged in the order: H(2) ≫ CH(4) > CO. Amounts of these products were 4-8 folds higher then those obtained with TiO(2) Evonic P25. Hydrogen reduced CO(2) to CO and CH(4).

Preparation and characterization of ZnS nanoparticles deposited on montmorillonite.

ZnS nanoparticles were prepared and deposited on montmorillonite (MMT) in the presence of cetyltrimethylammonium (CTA). UV spectrometry and transmission electron microscopy (TEM) proved the formation of nanoparticles with diameters ranging from 3 nm to 5 nm. Selected-area electron diffraction (SAED) patterns revealed the presence of romboedric ZnS. The band gap energy of nanosize ZnS was estimated at 3.89 ± 0.03 eV. Photoluminescence spectra exhibited a strong emission band between 300 nm and 600 nm explained by the vacant ZnS nanostructure. The prepared ZnS-montmorillonite nanocomposite (ZnS-MMT) was used for the photocatalytic reduction of CO(2) providing a considerably high efficiency that exceeded 5-6-fold the results of commercial TiO(2) Degussa P25. The main reaction products were hydrogen and methane. Methanol and carbon oxide were also observed in about 7-fold lower amounts. The stability of ZnS against oxidation was confirmed by the determination of sulphate using capillary isotachophoresis.

Study of silver adsorption on montmorillonite

Neste trabalho foi estudada a adsorcao de Ag+ sobre montmorilonita (MMT) do tipo Wyoming rica em Na+. Os dados de adsorcao foram ajustados de acordo com varias isotermas comuns, mas os melhores parâmetros de regressao foram obtidos pelo modelo de Langmuir, indicando que Ag+ foi adsorvido na superficie de MMT formando monocamadas. A adsorcao de pequenas quantidades de Ag+ promoveu o aumento da area superficial especifica (SSA) de micro (r = 0.4-0.5 nm) a mesoporos (r = 1.5-3 nm). A intercalacao de Ag+ em MMT foi observada por difracao de raios-X (XRD). Com o aumento da concentracao de solucoes de nitrato de prata, a quantidade de Ag+ em MMT tambem aumentou e a estrutura em camadas gradualmente sofreu colapso e esfoliacao. As amostras de MTT saturadas com Ag+ foram tratadas com solucao de boro hidreto de sodio para produzir Ag0. Foi estimado um tamanho medio de L111 = 8.5(1) nm dos cristalitos de Ag0. As nanoparticulas de prata metalica ficaram localizadas na superficie e nas bordas dos cristais de MMT.

Preparation of silver-montmorillonite nanocomposites by reduction with formaldehyde and borohydride

Montmorilonita rica em sodio (MMT) foi intercalada com cations prata, os quais foram subsequentemente reduzidos com formaldeido ou boroidreto de sodio. Os nanocompostos prata-montmorilonita foram estudados por espectrometria UV-Vis, microscopia eletronica de transmissao (TEM) e difratometria de raios-X (XRD). A influencia de diferentes agentes redutores na dispersao e no tamanho das particulas de prata depositadas na superficie da montmorilonita foi investigada. A reducao com boroidreto produziu particulas de prata dispersas uniformemente, com tamanhos limitados entre 3 e 13 nm. A reducao com formaldeido gerou particulas dispersas irregularmente com uma distribuicao de tamanho muito maior, variando entre 3 e 100 nm. Alem disso, entre as particulas de prata preparadas por reducao com formaldeido, algumas particulas de Ag 2 O foram obtidas como resultado de reducao incompleta. Os compositos de prata-montmorilonita preparados por reducao com boroidreto e formaldeido contem 2,4% e 5,3% em massa de Ag, respectivamente. Na-rich montmorillonite (MMT) was intercalated with silver cations, which were subsequently reduced with formaldehyde or sodium borohydride. The silver-montmorillonite nanocomposites were studied by UV-visible spectrometry, transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The influence of different reducing agents on the dispersity and size of silver particles deposited on montmorillonite surface was investigated. The reduction with borohydride gives rise to uniformly dispersed silver particles with a narrow particle size distribution from 3 nm to 13 nm. Formaldehyde reduction forms unevenly dispersed particles with a much wider size distribution, ranging from 3 to 100 nm. In addition, some Ag 2 O particles were found among silver particles prepared with formaldehyde, likely as a result of incomplete reduction. Silvermontmorillonite composites prepared by reduction with borohydride and formaldehyde contain 2.4 wt% and 5.3 wt% of Ag, respectively.

Fluorescence of reduced charge montmorillonite complexes with methylene blue: Experiments and molecular modeling

The intensity of fluorescence of montmorillonites fully saturated by methylene blue (MB) is very poor due to energy dissipation in MB aggregates. A series of reduced charge montmorillonites (RCM) were prepared from Na-homoionic SWy and Ca homoionic SAz with the aim to decrease the MB aggregation. Fine tuning MB adsorption degree by charge reduction and MB concentration enabled controlled production of different dye species from aggregates via dimers to monomers. It was shown that the intensity of the fluorescence of low-loaded MB-RCM complexes is enhanced by several orders of magnitude with respect to dye-saturated original montmorillonites. XRD analyses, molecular modeling, and diffuse reflectance spectroscopy revealed that low MB-loaded RCMs are very probably adsorbed mainly on the external montmorillonite surface as isolated dye molecules. Such a state cannot be achieved in the solid state without very careful tailoring of the host-guest interaction.

Precipitation, stabilization and molecular modeling of ZnS nanoparticles in the presence of cetyltrimethylammonium bromide.

ZnS nanoparticles were precipitated in aqueous dispersions of cationic surfactant cetyltrimethylammonium bromide (CTAB). The sphere radii of ZnS nanoparticles calculated by using band-gap energies steeply decreased from 4.5 nm to 2.2 nm within CTAB concentrations of 0.4-1.5 mmol L(-1). Above the concentration of 1.5 mmol L(-1), the radii were stabilized at R=2.0 nm and increased up to R=2.5 nm after 24 h. The hydrodynamic diameters of CTAB-ZnS structures observed by the dynamic light scattering (DLS) method ranged from 130 nm to 23 nm depending on CTAB concentrations of 0.5-1.5 mmol L(-1). The complex structures were observed by transmission electron microscopy (TEM). At the higher CTAB concentrations, ZnS nanoparticles were surrounded by CTA(+) bilayers forming positively charged micelles with the diameter of 10nm. The positive zeta-potentials of the micelles and their agglomerates were from 16 mV to 33 mV. Wurtzite and sphalerite nanoparticles with R=2.0 nm and 2.5 nm covered by CTA(+) were modeled with and without water. Calculated sublimation energies confirmed that a bilayer arrangement of CTA(+) on the ZnS nanoparticles was preferred to a monolayer.

A physico-chemical study of the cationic surfactants adsorption on montmorillonite

O objetivo deste trabalho e o estudo da adsorcao de brometo de cetiltilmetilamonio (CTA) e de cloreto de cetilpiridinio (CP) em argilas do tipo montorilonita (MMT) ricas em sodio. Um metodo isotacoforetico (ITP) especifico foi desenvolvido visando a determinacao rapida e simultânea dos surfatantes cationicos (CS) adsorvidos. A fim de reduzir os limites de deteccao, o metodo isotacoforetico foi conjugado com a tecnica de eletroforese capilar. Para determinar o arranjo dos surfatantes cationicos (CS) adsorvidos na superficie das argilas foi efetuada a avaliacao do balanco molar entre os surfatantes e os cations metalicos juntamente com as isotermas de adsorcao. A maior adsorcao do CP comparada a do CTA pode ser entendida nao so pela acao das forcas eletrostaticas, mas tambem por outras interacoes, tais como, interacao hidrofobica cauda-cauda e/ou interacoes entre aneis piridinicos formando bicamadas incompletas e/ou monocamadas condensadas, respectivamente. The adsorption of cetyltrimethylammonium (CTA) bromide and cetylpyridinium (CP) chloride on Na + -rich montmorillonite (MMT) was studied. An ad hoc isotachophoretic (ITP) method was developed for the simultaneous and rapid determination of the cationic surfactants (CSs) adsorbed. In order to decrease the detection limits, ITP was on-line coupled with capillary zone electrophoresis. Adsorption data were analysed by their fitting with adsorption isotherms. The adsorption of CP is well described by the Langmuir isotherm. It indicates the monolayer arrangement of CP on the MMT surface. In case of the CTA data, the best fitting LangmuirFreundlich model with the power constant r<1 was found. It can be explained by the CTA interactions because of its intercalation into the MMT interlayer space.

SVD-based principal component analysis of geochemical data

Principal Component Analysis (PCA) was used for the mapping of geochemical data. A testing data matrix was prepared from the chemical and physical analyses of the coals altered by thermal and oxidation effects. PCA based on Singular Value Decomposition (SVD) of the standardized (centered and scaled by the standard deviation) data matrix revealed three principal components explaining 85.2% of the variance. Combining the scatter and components weights plots with knowledge of the composition of tested samples, the coal samples were divided into seven groups depending on the degree of their oxidation and thermal alteration.The PCA findings were verified by other multivariate methods. The relationships among geochemical variables were successfully confirmed by Factor Analysis (FA). The data structure was also described by the Average Group dendrogram using Euclidean distance. The found sample clusters were not defined so clearly as in the case of PCA. It can be explained by the PCA filtration of the data noise.

Photocatalytic decomposition of phenol by nanocomposite of ZnS nanoparticles and montmorillonite

The nanocomposite of ZnS nanoparticles stabilized by cetyltrimethylammonium ions (ZnS-CTA) and montmorillonite (ZnS-CTA-MMT) was prepared and used as a catalyst for the photodecomposition of phenol under UV irradiation of a medium pressure Hg lamp. The content of ZnS in ZnS-CTA-MMT was about 7 wt.%. For comparison, the photodecomposition was also performed with ZnS-CTA, montmorillonite and with no catalyst, i.e., using only UV irradiation. The photodecomposition efficiency decreased in the order: UV + ZnS-CTA-MMT ≈ UV + ZnS-CTA > UV > UV + MMT. The photodecomposition in the presence of ZnS-CTA-MMT and ZnS-CTA proceeded according to the pseudo-first order reaction kinetics. In other cases, the photodecomposition corresponded to the pseudo-second order reaction of phenol and hydroxyl radicals. Hydroxyl radicals were produced by reactions of dissolved oxygen and electrons released from the ZnS nanoparticles and excited phenol molecules. MMT decreased the photodecomposition reaction rate and no MMT catalytic activity was observed.