Photocatalytic degradation of 2,4-dichlorophenoxiacetic acid and 2,4,6-trichlorophenol with ZrO2 and Mn/ZrO2 sol-gel materials

Because of its semiconductor properties, sol-gel zirconia can be used as a photocatalyst. When zirconia is doped with transition metals, its electronic properties are modified. In this work, sol-gel Mn/ZrO₂ and ZrO₂ materials were tested for photocatalytic degradation of 2,4-dichlorophenoxiacetic acid and 2,4,6-trichlorophenol. The powders were characterized by XRD, UV-Vis and Raman spectroscopy. The apparent rate constants were calculated assuming pseudo-first order kinetics. The results reveal that ZrO₂ is effective as a photocatalyst; moreover, its photocatalytic properties improve when it is doped with manganese.     

Chromatographic properties of mesoporous silica gel modified with acetylacetonates of europium and copper

New mesoporous materials prepared from tetraethoxysilane, i.e., sorbents obtained with the use of surfactants, are synthesized. Their chromatographic polarity is assessed quantitatively. Their Kovats retention indices and Rohrschneider polarity coefficients are calculated. Based on physicohemical data, it is demonstrated that modifying supports with metal chelates changes the structure and properties of the initial sorbents: the differential molar Gibbs free energies rise considerably for sorbent modified with copper acetylacetonate with respect to ethanol (?ΔG′ _i = 7.09 kJ/mol) and nitromethane (?ΔG′ _i = 6.75 kJ/mol), relative to the initial silica gel (5.43 and 4.15 kJ/mol, respectively).     

Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace copper(II) determination

This paper described a facile and direct electrochemical method for the determination of ultra-trace Cu²⁺ by employing amino-functionalized mesoporous silica (NH₂-MCM-41) as enhanced sensing platform. NH₂-MCM-41 was prepared by using a post-grafting process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared (FTIR) spectroscopy. NH₂-MCM-41 modified glassy carbon (GC) electrode showed higher sensitivity for anodic stripping voltammetric (ASV) detection of Cu²⁺ than that of MCM-41 modified one. The high sensitivity was attributed to synergistic effect between MCM-41 and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption, and amino-groups are able to chelate copper ions. Some important parameters influencing the sensor response were optimized. Under optimum experimental conditions the sensor linearly responded to Cu²⁺ concentration in the range from 5 to 1000 ng L⁻¹ with a detection limit of 0.9 ng L⁻¹ (S/N = 3). Moreover, the sensor possessed good stability and electrode renewability. In the end, the proposed sensor was applied for determining Cu²⁺ in real samples and the accuracy of the results were comparable to those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) method.     

Ti-containing mesoporous organosilica as a photocatalyst for selective olefin epoxidation

We previously found that Ti-containing mesoporous silica (T-S) with isolated and tetrahedrally coordinated Ti-oxide species, when photoactivated in acetonitrile with molecular oxygen (O(2)), catalyzes highly selective epoxidation of olefins (Chem. Commun. 2005, 5977). The system showed the highest epoxide selectivity among the photocatalytic systems proposed so far, but showed insufficient olefin conversion. In the present work, we have employed Ti-containing mesoporous organosilicas (T-OS), synthesized by a surfactant-templating method with an organosilane precursor, as the photocatalyst and have studied the effects on the olefin conversion and the epoxide selectivity. The T-OS catalysts demonstrate the same high epoxide selectivity as does T-S, but scarcely improve the olefin conversion. Photoluminescence measurement reveals that the T-OS catalysts with high surface hydrophobicity enhance the access of hydrophobic olefins to the photoexcited Ti-oxide species as expected, but destabilize the excited species themselves. ESR analysis demonstrates that the T-OS catalysts also destabilize the active oxygen radical (O(3)(*-)), a crucial oxidant for olefin epoxidation, formed on the excited Ti-oxide species. These destabilizations counteract the enhanced olefin access to the excited species, resulting in almost no improvement in olefin conversion. Through detailed analyses, we have summarized the changes in photocatalytic properties of the Ti-oxide species, associated with the organic modification of the catalyst.     

Sulfonic acid functionalized mesoporous MCM-41 silica as a convenient catalyst for Bisphenol-A synthesis

Sulfonic acid groups anchored to the surface of mesoporous MCM-41 silica have been identified with S K-edge XANES spectra and the material is an efficient catalyst for the liquid phase condensation of phenol with acetone to form Bisphenol-A with high selectivity.     

Adsorption and preconcentration of 2,4-dichlorophenoxyacetic acid on a chemically modified silica gel surface

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), chemically anchored to a silica gel surface, was used to adsorb and preconcentrate the same herbicide from aqueous solutions at room temperature. From a series of adsorption isotherms adjusted to a modified Langmuir equation, the maximum number of moles adsorbed was calculated as 4.67 x 10(-5) mol g(-1), with the highest retention capacity at pH 5. This modified silica gel was used in a column for preconcentrating trace levels of 2,4-D. The preconcentrated herbicide can be directly eluted with methanol with a recovery efficiency higher than 97%. The concentration factor was 8.33.     

Direct nanocomposite of crystalline TiO2 particles and mesoporous silica as a molecular selective and highly active photocatalyst

Well-crystallised TiO2 particles (P-25, 20-30 nm in diameter) were directly incorporated into surfactant-templated mesoporous silica particles (pore diameter: 2.7 nm), and the composite material with a high TiO2 content (60 wt%) showed molecular selective and enhanced photocatalysis for decomposition of 4-nonylphenol.     

Synthesis of mesoporous silica materials with ascorbic acid as template via sol-gel process

Mesoporous silica materials with pore diameters of 2-5 nm have been prepared using ascorbic acid as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethylorthosilicate,followed by removing the ascorbic acid compound by extraction with ethanol.Characterization results from nitrogen sorption isotherm,powder X-ray diffraction and transmission electron microscopy indicate that the materials have large specific surface areas (e.g.1000 m2/g) and pore volumes (e.g.0.8 cm3/g).The rnesoporosity is arisen from interconnecting disordered wormlike channels and pores with relatively broad size distributions.As the ascorbic acid concentration is increased,the pore diameters and pore volumes of the materials increase.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

Iron modified mesoporous carbon and silica catalysts for methanol decomposition

Iron modified silica and carbon mesoporous materials with similar textural characteristics are compared in methanol decomposition to H₂, CO and CH₄. The influence of the support on the phase composition and reductive properties of the catalysts is studied by M?ssbauer spectroscopy and TPR with hydrogen. This revised version was published online in June 2006 with corrections to the Cover Date.     

1-Allyl-3-propylthiourea modified mesoporous silica for mercury removal

1-Allyl-3-propylthiourea modified mesoporous silica has high adsorption capacity for mercury ions and its regeneration can be accomplished by washing with 10% thiourea in aqueous 0.05 M HCl.     

An application of transparent mesoporous bulk silica to a titanium dioxide photocatalyst with adsorption and decomposition functions

Mesoporous bulk silica with optical transparency and high porosity can be prepared using a gel-templating method. This unique material has potentially wide-ranging applications as containers of specific molecules, smart deliverers of target molecules, and photonic devices. Among the potential applications, the use of silica as a photocatalyst is explored in this paper; the photocatalyst was prepared by loading titanium dioxide (titania) from the titania precursor solution into the mesoporous structure of silica with a controlled pore size. Even after crystallization, the titania-loaded silica remained highly mesoporous with uniform pore size and optical transparency. The ability of the adsorption and decomposition of acetaldehyde gas was evaluated by measuring the concentration change of the gas with and without the irradiation of ultraviolet rays. As a result, the specific surface area, the amount of titania and the calcination temperature were essential in determining the adsorption ability as well as the decomposition ability.     

Synthesis of transparent and ordered mesoporous silica monolithic films embedded with monomeric zinc phthalocyanine dye

Monolithic transparent mesoporous silica films embedded with zinc phthalocyanine (ZnPc) have been synthesized and it is shown that the encapsulated ZnPc dye molecules exist predominantly in monomeric form.     

Hydroxyapatite modified with silica used for sorption of copper(II)

This paper aims to increase the sorption capacity of hydroxyapatite and to find the best apatite-based material for metal ions sorption. The sorption process of copper ions from water solutions by HAP and structurally modified HAP was carried out in this work. Structural modifications of HAP were realized in the preparation phase by an addition of sodium silica into the reaction medium. The prepared materials were characterized by physical-chemical methods: IR, electron-microscopy and X-ray diffraction. The composites characterized were tested in kinetic studies regarding ion exchange and adsorption of Cu²⁺. It was revealed that the silica content, particle size and initial copper ion concentration influence the process rate. Presented at the 8th Conference on Solid State Chemistry, Bratislava, Slovakia, 6–11 July 2008.     

Non-surfactant synthesis of mesoporous silica with dye as template

A novel non-suffactant method was described to synthesize mesoporous silica using dye basic fuchsin as template.Chemical reactions were introduced into the formation of mesopores rather than the weak electrostatic or hydrogen-bonding interactions in the traditional surfactant routes.The reactant composition was found to be crucial to the pore structure of objective product.The formation mechanism of mesopore was also proved.     

Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests

Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests.     

Synthesis of ZnO photocatalyst modified with activated carbon for a perfect degradation of ciprofloxacin and its secondary pollutants

The proposed research, presents the synthesis, characterization, and photocatalytic accomplishment of ZnO nanoplate (ZnOs) modified with activated carbon derived from Konar bark. The obtained nanocomposite (photocatalyst) was characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). First, the ZnO photocatalyst and activated carbon (AC) were prepared separately; then, the ZnO photocatalyst was modified with activated carbon. Various parameters namely pH, degradation time, and photocatalyst dose were optimized and studied in multivariate method by design expert7 software. The synergic efficiency of ZnO‐AC (adsorbent/photocatalyst) exhibited a good rate of ciprofloxacin (CIP) removal under visible irradiation. In addition, first pseudo order kinetic and isotherms equations were calculated. Moreover, the identification of degradation products was performed by ultra performance liquid chromatography‐tandem mass spectrometer (UPLC‐MS/MS). It is for the first time that a ZnO photocatalyst modified with activated carbon (ZnO‐AC) applied for CIP degradation.