Microanalysis of blue pigments from the Ptolemaic temple of Hathor (Thebes), Upper Egypt: a case study

The aim of the present work was to characterize blue pigment samples collected from the Ptolemaic temple of Hathor (Thebes), the western bank of Luxor, Upper Egypt. The characterization of the examined pigments was carried out by means of optical microscopy, scanning electron microscopy equipped with an energy dispersive X‐ray detector, micro X‐ray fluorescence spectrometry and Fourier transform infrared spectroscopy. On the basis of the chemical composition and microstructure of the samples, the blue pigments were identified as Egyptian blue (cuprorivaite, CaCuSi₄O₁₀). Moreover, the micro X‐ray fluorescence analysis revealed significant quantities of lead in the glass phase suggesting that a leaded bronze scrap was used to produce the pigment. The optical examination of the paint layers showed that the pigments were applied on a thin layer consisting of gypsum (CaSO₄?2H₂O) and dolomite (CaMg(CO₃)₂). In addition, some pigment samples showed discoloration mainly in the form of green and black hues. The obtained results helped in improving our knowledge about some painting materials used during the Ptolemaic era of ancient Egypt. Copyright © 2012 John Wiley & Sons, Ltd.     

Nano-silica and SiO2/CaCO3 nanocomposite prepared from semi-burned rice straw ash as modified papermaking fillers

Silica (SiO₂) nanoparticles and silica/calcium carbonate (SiO₂/CaCO₃) core–shell nanocomposites were prepared by sol–gel technique as fillers for papermaking application. Semi-burned rice straw ash (SBRSA), as waste material, was used to prepare the targeted fillers. Preparation of SiO₂ nanoparticles and SiO₂/CaCO₃ nanocomposites was carried out using Na₂SiO₃ solution that was prepared from SBRSA and CaCO₃ nanoparticles of 30–70 nm. The targeted SiO₂/CaCO₃ nanocomposites were prepared with different molar ratio of SiO₂:CaCO₃ 1:15, 1:10 and 1:5. The percentage of silica increased from 62.5% to 82.9% by thermal treatment of SBRSA at 800 °C for 2 h. The prepared SiO₂ nanoparticles and SiO₂/CaCO₃ nanocomposites were characterized by using XRD, XRF, TEM, FT-IR and Zeta potential. The results indicate that a pure semi-crystalline SiO₂ nanoparticle and semi-crystalline shell of SiO₂ coated CaCO₃ core particles were produced. The work extended also to investigate the effect of the prepared fillers on physical, mechanical and optical properties of paper.Application of the prepared SiO₂ nanoparticles and SiO₂/CaCO₃ nanocomposites improved the optical properties of paper (brightness, whiteness and opacity) but it slightly reduced the mechanical properties when compared to commercial precipitated CaCO₃ (PCC) filler.The results showed that the retention of SiO₂ nano-particles was highly increased. The retention of the prepared nanocomposites increased along with increasing of SiO₂:CaCO₃ molar ratio.     

Electrochemical Fabrication of Prussian Blue Nanocube‐decorated Electroreduced Graphene Oxide for Amperometric Sensing of NADH

In this study, Prussian blue (PB) film on the electroreduced graphene oxide (ERGO)‐modified Au electrode surface (ERGO/PB) is easily prepared by means of cyclic voltammetric technique in the mixture of K₃Fe(CN)₆ and FeCl₃. Its electrochemical behaviors for NADH biosensor are studied. The structural and morphological characters of modified electrode material are analyzed with using of XPS, XRD, Raman, EDS, and SEM techniques. ERGO/PB hybrid nanocomposite for NADH biosensor is exhibited to the higher catalytic effect (linear range from 1.0 to 100 μM, detection limit of 0.23 μM at S/N=3) compared to naked Au, ERGO‐modified Au, and PB‐modified Au electrodes. In addition to, ERGO/PB electrode was used to voltammetric and amperometric detection of H₂O₂. ERGO/PB electrodes also showed the same behavior as the NADH sensor. This ERGO/PB‐modified electrode supplied a simple, new, and low‐cost route for amperometric sensing of both NADH and H₂O₂.     

Synthesis and characterization of well-defined poly(methyl methacrylate)/CaCO3/SiO2 three-component composite particles via reverse atom transfer radical polymerization

The attempt to prepare structurally well-defined polymer/inorganic composite particles, i.e., poly(methyl methacrylate) (PMMA)/CaCO₃/SiO₂ three-component composite particles, via reverse atom transfer radical polymerization (ATRP), using 2-2′-azo-bis-isobutyronitrile as initiator and Cu(II) bromide as catalyst was reported. CaCO₃/SiO₂ two-component composite particles were first obtained through sol–gel method, and their morphology and surface element information were determined by transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. The results indicate that the CaCO₃ was encapsulated by the obtained SiO₂. After being modified by silane coupling agent, the CaCO₃/SiO₂ composite particles copolymerized with methyl methacrylate (MMA) under standard reverse ATRP conditions to produce PMMA/CaCO₃/SiO₂ three-component composite particles. In the case concerned, first-order kinetic plots and linear increase of molecular weight (Mn) vs conversion and narrow molecular weight distribution for the graft polymer samples were observed. Furthermore, the gel permeation chromatography results illustrated that both the free PMMA chains from the solvent and the graft PMMA chains from the surface of CaCO₃/SiO₂ two-component composite particles were growing at the same rate. Characterizations of the PMMA-grafted CaCO₃/SiO₂ composite particles were done by Fourier transform infrared and thermogravimetric analysis. The results showed that the surface of the modified inorganic particles was grafted by the MMA and that the grafting percentage was about 8.7%.     

Efficient catalytic degradation of single and binary azo dyes by a novel triple nanocomposite of Mn3O4/Ag/SiO2

The strategy of structurally integrating noble metal and metal oxides is expected to offer exceptional opportunities toward emerging functions of all. We report the creation of an efficient hetero-structured nanocatalyst consisting of Mn₃O₄ core, SiO₂ shell impregnated with noble Ag nanoparticles. The triple nanocatalyst Mn₃O₄/Ag/SiO₂ was synthesized by using a facile three-step approach to disperse Ag nanoparticles between the surfaces of functionalized Mn₃O₄ and SiO₂. The physicochemical structural characterization was performed by XRD and FTIR. The surface morphologies were observed by SEM and TEM. The EDX measurements confirmed the composition of the composite. The nanocomposite has been used as a catalyst for the degradation of Direct blue 78 in the presence of sodium borohydride (NaBH₄). It has a drastic catalytic effect as compared to Mn₃O₄/Ag and Mn₃O₄. The rate constant of Direct blue 78 reduction followed the order: Mn₃O₄/Ag/SiO₂ (0.25166 min⁻¹) > Mn₃O₄/Ag (0.07971 min⁻¹) > Mn₃O₄ (0.00947 min⁻¹). The effects of different reaction conditions of the catalytic reaction have been determined. The catalytic activity of the as- synthesized nanocomposite was examined for the binary dyes system by incorporation of an additional dye (Sunset yellow). Its influence on the degradation rate and efficiency of Direct blue 78 was investigated. The nanocatalyst exhibited excellent catalytic activity towards the complete degradation of both the Direct blue 78 and Sunset yellow. The degradation percentage for these dyes reached 99.33 and 94.68%, respectively. The recovery and reusability of the Mn₃O₄/Ag/SiO₂ nanocomposite was studied in the reduction reaction of Direct blue 78. Five consecutive recovery reaction cycles were performed. They revealed high stability and constant efficiency of the catalyst for four cycles.     

Electropolymerization of Acid Chrome Blue K on Glassy Carbon Electrode for the Determination of Curcumin

Acid chrome blue K (ACBK) was electropolymerized on the surface of a glassy carbon electrode (GCE) by cyclic voltammetric sweep in the potential range from –0.2 to 0.9 V. The characteristic of poly‐ACBK film was studied by different methods such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. This modified electrode showed excellent electrocatalytic response to curcumin with the increase of the electrochemical responses. Under the optimal conditions a good linear voltammetric response could be obtained over the range of 1.0 × 10^?7‐7.0 × 10^?5 M and the detection limit was got as 4.1 × 10^?8 M (S/N = 3). The method was successfully applied for the determination of curcumin in human urinev samples.     

Reverse Atom Transfer Radical Polymerization of MMA in the Presence of CaCO3/SiO2 Two-Component Composite Particles

Summary: We previously discovered that structurally well-defined polymer/inorganic composite particles, i.e., poly(methyl methacrylate) (PMMA)/CaCO₃/SiO₂ three-component composite particles, can be achieved via reverse atom transfer radical polymerization (ATRP), using 2,2′-azo-bis-isobutyronitrile as initiator and Cu^II bromide as catalyst. In the present study, the influence of the mass ratio of CaCO₃/SiO₂ two-component composite particles to methyl methacrylate (MMA) on the rate and behavior of the polymerization was studied in detail. The results illustrate that increasing the mass ratio of CaCO₃/SiO₂ two-component composite particles will decrease the overall rate of polymerization of MMA under standard reverse ATRP conditions. Thermal properties of the obtained well-defined particles were characterized and determined by thermogravimetric analysis (TGA). The results indicate that well-defined PMMA chains grafted on the surface of CaCO₃/SiO₂ particles were only degraded by random chain scission of C C linkages within the PMMA chain, which is different from the degradation of PMMA chains prepared via traditional radical polymerization. This difference is reasonably ascribed to the difference between the end groups of PMMA prepared via reverse ATRP and that via traditional radical polymerization, which has been confirmed by end group analysis measured by ¹H–NMR spectroscopy.     

Electrochemical Polymerization of Azure Blue H and Its Electro-catalytic Activity toward NADH Oxidation

Poly (azure blue II) (PABII) thin film modified electrode was successfully assembled on the surface of a glassy carbon electrode by means of electrochemical polymerization, which was carried out with cyclic voltammetric sweeping in the potential range of ‐ 0.6 to + 1.3 V (vs. SCE) in Britton‐Robinson buffer solution (pH = 9.8) containing 1.25 ± 10–⁴ mol/L azure blue II. The effect of pH on the polymerization process of azure blue II and the electrochemical characteristics of the polymer‐modified electrodes were studied in detail. The experimental results indicated that the electropolymerization of azure blue II could take place in basic or neutral media. The cyclic voltammograms of poly (azure blue II) thin film modified electrode showed the presence of two couples of redox peaks. The film modified electrode exhibited potent and persistent electrocatalysis for oxidation of dihydronicotiamide adenine dinucleotide (NADH) in phosphate buffer media with a diminution of the overpotential of about 410 mV and an increase in peak current. The presence of some divalent cations in an electrolyte can greatly enhance the electrocatalytic current for oxidation of NADH. The electrocatalytic current increased linearly with NADH concentration from 1.0 ± 10–⁵ to 8.0 ± 10–³ mol/L in the presence of 4.0 ± 10–² mol/L Mg²⁺ cation. The detection limit (3s_b1/S) was 5.0 ± 10–⁶ mol/L, and the relative standard deviation of determination results was 4.2% for six successive determinations of 5.0 ± 10–⁴ mol/L NADH in the presence of Mg²⁺ cation.     

Molecular dynamics simulations of aggregation behavior of sodium dodecyl sulfate on SiO2 and CaCO3 surfaces

Molecular dynamics simulations were carried out to investigate the aggregation behavior of anionic surfactant sodium dodecyl sulfate (SDS) on the surfaces of SiO₂ and CaCO₃. The results indicate that SDS molecules formed a spherical micelle structure near the SiO₂ surface; moreover, there were more head groups near the SiO₂ surface. However, they could form a self‐assemble film on the CaCO₃ surface. The self‐assemble film of SDS on the CaCO₃ surface was more stable than that on the SiO₂ surface. Our simulation results have a certain significance to understand the aggregation behavior of SDS on different surfaces on molecular level.     

Preparation of poly(methyl methacrylate)/CaCO3/SiO2 composite particles via emulsion polymerization

A novel method to prepare organic/inorganic composite particles, i.e. poly(methyl methacrylate)/CaCO₃/SiO₂ three-component composite particles, using emulsion polymerization of methyl methacrylate with sodium lauryl sulfate as a surfactant in an aqueous medium was reported. CaCO₃/SiO₂ two-component inorganic composite particles were obtained firstly by the reaction between Na₂CO₃ and CaCl₂ in porous silica (submicrometer size) aqueous sol and the specific surface area of the particles was measured by the Brunauer–Emmett–Teller (BET) method. The results show that the BET specific surface area of the CaCO₃/SiO₂ composite particle is much smaller than that of the silica particle, indicating that CaCO₃ particles were adsorbed by porous silica and that two-component inorganic composite particles were formed. Before copolymerization with methyl methacrylate, the inorganic composite particles were coated with a modifying agent through covalent attachment. The chemical structures of the poly(methyl methacrylate)/CaCO₃/SiO₂ composite particles obtained were characterized by Fourier transform IR spectroscopy and thermogravimetric analysis. The results show that the surface of the modified inorganic particles is grafted by the methyl methacrylate molecules and that the grafting percentage is about 15.2%.     

Uptake of Ba2+ ions by natural bentonite and CaCO3: A radiotracer, EDXRF and PXRD study

Ba²⁺ uptake by natural bentonite, CaCO₃ in addition to a number of bentonite-CaCO₃ mixtures with variable compositions as a function of pH and Ba²⁺ concentration was studied. Radiotracer method, EDXRF, and PXRD were used. The results of radiotracer experiments showed that the uptake of Ba²⁺ by CaCO₃ was larger than its uptake by natural bentonite samples, particularly at low initial concentrations of Ba²⁺ and higher pH values. This finding was supported by the EDXRF results. According to the sorption data, the apparent DG° values of sorption were in the range -9±1 to -13±3 kJ/mol. The PXRD studies revealed the formation of BaCO₃ upon sorption of Ba²⁺ on pure CaCO₃ and on some of the bentonite-CaCO₃ mixtures.     

Localized quantification of anhydrous calcium carbonate polymorphs using micro-Raman spectroscopy

Micro-Raman spectroscopy is a powerful technique for qualitative and quantitative analysis of different mineral mixtures. In this paper, micro-Raman spectroscopy was used for quantification in local regions (180 × 180 μm area) of ternary mixtures of the synthetic calcium carbonate (CaCO₃) polymorphs (vaterite, aragonite, calcite) as well as CaCO₃ formed during the carbonation of nanolime suspension. The obtained results of localized quantification were in agreement with the detected concentrations obtained from bulk quantitative phase analysis of X-ray powder diffraction patterns. The detection limits were found to be below 0.5 wt.% for each CaCO₃ polymorphs. Through the use of 2D mapping, localized quantification of CaCO₃ polymorphs can be achieved. This information could be potentially useful for conservation of valuable Cultural Heritage objects, as it might influence the consolidation treatment chosen.     

Abrasive Stripping Voltammetry in Room Temperature Ionic Liquids

We report on the abrasive stripping voltammetry (AbrSV) of six different solid compounds of widely different natures in room temperature ionic liquids (RTILs). Copper as a metal representative, Prussian blue as a typical inorganic complex, indigo as an organic dye model, and anthracene, pyrene, and 9,10‐diphenylanthracene as the typical representatives of aromatic hydrocarbons were chosen in this study. They were immobilized on a gold electrode surface by mechanical abrasion and their subsequent voltammetric measurements were carried out in the ionic liquid [C₄mim][NTf₂], 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide. The present work demonstrates that RTILs provide an excellent electrochemical solvent environment for abrasive stripping voltammetric analysis; in particular, the much wider potential windows in RTILs as compared to aqueous media greatly enhance the analytical applicability of the AbrSV technique.     

Electrochemical DNA Biosensor Based on Graphene and TiO2 Nanorods Composite Film for the Detection of Transgenic Soybean Gene Sequence of MON89788

Based on graphene (GR), TiO₂ nanorods, and chitosan (CTS) nanocomposite modified carbon ionic liquid electrode (CILE) as substrate electrode, a new electrochemical DNA biosensor was effectively fabricated for the detection of the transgenic soybean sequence of MON89788. By using methylene blue (MB) as hybridization indicator for monitoring the hybridization with different ssDNA sequences, the differential pulse voltammetric response of MB on DNA modified electrodes were recorded and compared. Due to the synergistic effects of TiO₂ nanorods and GR on the electrode surface, the electrochemical responses of MB were greatly increased. Under optimal conditions the differential pulse voltammetric response of the target ssDNA sequence could be detected in the range from 1.0×10^?12 to 1.0×10^?6 mol/L with a detection limit of 7.21×10^?13 mol/L (3σ). This electrochemical DNA biosensor was further applied to the polymerase chain reaction (PCR) product of transgenic soybeans with satisfactory results.     

The electrochemical determination of ammonium based on the selective inhibition of the low-spin iron(II)/(III) system of Prussian blue

A new method is described for the determination of ammonium in aqueous solutions with electrodes modified by Prussian blue (PB). The specific voltammetric response of PB-modified electrodes to ammonium ions is used for their analytical determination. In the presence of ammonium ions, a concentration-dependent inhibition of the low-spin iron(II/III) system of PB occurs. Only thallium and rubidium ions cause similar inhibition. A useful electrochemical determination method is thus available for detecting ammonium ions in the presence of frequently interfering potassium and sodium ions. Paraffin-impregnated graphite electrodes modified with a mechanically transferred PB layer and bulk-modified PB-composite electrodes are studied. The method is applicable within a concentration range which extends from 4 × 10⁻⁵ mol/l to 10⁻² mol/l NH₄ ⁺. The composite electrode is used in an electrochemical flow-through system in conjunction with the Kjeldahl method. Received: 21 April 1997 / Accepted: 28 May 1997     

新型球形纳米空心SiO2的模板合成方法研究

以纳米碳酸钙颗粒为新颖的无机模板剂, 硅酸钠为无机硅源, 通过溶胶-凝胶法形成CaCO₃/SiO₂的核壳结构; 随后通过高温煅烧、酸溶和干燥处理, 合成出了具有高比表面积的球形纳米空心二氧化硅粒子. 然后, 分别采用TEM, SEM, EDS, XRD, FTIR和TG等测试手段对样品进行了分析和表征, 并考察了不同合成条件, 如反应温度、反应pH值、煅烧温度和包覆反应时SiO₂/CaCO₃的配比对纳米空心二氧化硅粒子的比表面积变化. 实验结果表明: 较高的反应温度如60～80 ℃, pH值9左右、SiO₂包覆量为碳酸钙质量的10%, 以及煅烧温度为700 ℃, 有利于形成空心形貌较好、比表面较大的球形纳米空心二氧化硅.     

以碳酸钙为模板制备不同形貌的SiO_2中空粒子

以粒径1μm左右的球形和斜方碳酸钙为模板,制备了不同形貌的SiO2中空粒子。通过SEM,TEM,XRD,BET,TGA等对模板和中空粒子的结构和性能进行了表征,对包覆机理进行了探讨。结果表明:由于碳酸钙对壳层具有良好的物理支撑作用和化学亲和作用,SiO2中空粒子不仅结构完整,孔径分布良好,而且准确地复制了模板表面的细微结构。该方法操作简便,成本低廉,适合于工业化生产。     

Electrochemical DNA biosensor for the detection of short DNA species of Chronic Myelogenous Leukemia by using methylene blue

A novel assay for the voltammetric detection of 18-bases DNA sequences relating to Chronic Myelogenous Leukemia (CML, Type b3a2) using methylene blue (MB) as the hybridization indicator was reported. DNA was covalently attached onto a glassy carbon electrode (GCE) through amines of the DNA bases using N-hydroxysulfosuccinimide (NHS) and N-(3-dimethylamion)propyl-N′-ethyl carbodiimidehydrochloride (EDC). The covalently immobilized single-stranded DNA (ssDNA) could selectively hybridize with its complementary DNA (cDNA) in solution to form double-stranded DNA (dsDNA) on the surface. A significant increase of the peak current for methylene blue upon the hybridization of immobilized ssDNA with cDNA in the solution was observed. This peak current change was used to monitor the recognition of CML DNA sequence. This electrochemical approach is sequence specific as indicated by the control experiments in which no peak current change was observed if a non-complementary DNA sequence was used. Factors, such as DNA target concentration and hybridization conditions determining the sensitivity of the electrochemical assay were investigated. Under optimal conditions, this sensor has a good calibration range between 1.25 × 10⁻⁷ and 6.75 × 10⁻⁷ M, with CML DNA sequence detection limit of 5.9 × 10⁻⁸ M.     

Enhancement of the Electrochemical Performance of Prussian Blue Modified Electrode via Ionic Liquid Treatment

This article first reports the preparation of a Prussian blue (PB) modified electrode with improved electrochemical properties at the functionalized glass carbon electrode (GC) by imidazolium based ionic liquid. The molecular ionic liquid film on the GC electrode has been found to influence the electrodeposition of PB by a way of enhancement of voltammetric currents, suggesting efficient electrodepositon. Such efficient electrodeposition was caused by the static electric effect which existed between the positively charged imidazolium group on the electrode surface and the negative ferric‐ferricyanide in solution. Compared with the PB/GC electrode, the PB/[Bmim][Cl]/GC electrode showed much better electrochemical stability after successive potential cycling for 250 cycles. A comparative study on amperometric responses of both electrodes to reduce H₂O₂ was also investigated. PB/[Bmim][Cl]/GC electrode showed a better electrocatalytic performance to H₂O₂ with wider linear detection range and higher sensitivity than that at the electrode without [Bmim][Cl]. Furthermore, the kinetics for both electrodes was discussed. The PB/[Bmim][Cl]/GC electrode possessed a greater diffusion coefficient.     

Blue phase stability of n-OCB homologue chiral nematic liquid crystal mixtures

Blue phase (BP) stability of a chiral nematic liquid crystal (LC) mixture is dependent upon chemical structure as well as physical properties. In this study, the blue phase temperature range dependent on alkyl chain length was investigated in order to evaluate the relationship between blue phase stability and the molecular structures of four kinds of 4-n-alkyloxy-4'-cyanobiphenyl (n-OCB) homologue chiral nematic LC mixtures composed of rod-like nematic LCs. It was confirmed that the blue phase temperature range was strongly dependent upon the molecular parity, K ₃₃/K ₁₁ and the helical twist power of the n-OCB homologues chiral nematic LC mixtures.