Natural Porous Mineral Research Articles

Nonmetallic Mineral as the Carrier of TiO2 Photocatalyst: A Review

The composite photocatalyst can be constructed by using natural porous minerals with a wide range of sources, low prices and stable chemical properties as the titanium dioxide catalyst carrier, which can not only reduce the cost of catalyst preparation and application, but also effectively improve the dispersion, recyclability and catalytic performance of the catalyst. In recent years, a large number of scientific researchers have conducted a lot of research on the preparation and performance of porous mineral-supported composite catalytic materials. This paper describes the catalytic mechanism of titanium dioxide, as well as the research and application progress of various nonmetallic mineral materials supported by titanium dioxide, and prospects the development trend in the future.

Use of Natural Minerals to Immobilize Bacterial Cells for Remediating Cracks in Cement-Based Materials

Cracks in cement-based materials are one of the main factors affecting the durability of structure. Recent research in the field of concrete materials showed that self-healing in cement-based systems can be achieved by triggering biogenic calcium carbonate (CaCO3) precipitation. The goal of this study is to establish a comparative evaluation of the use of sepiolite, bentonite, and diatomaceous earth (DE) as an immobilization barrier of Sporosarcina pasteurii (S. pasteurii) cells to trigger self-healing in cement-based systems. For the first time in the literature, this study will provide insight into the use of natural minerals, such as bentonite and sepiolite, as protective carriers for vegetative S. pasteurii cells in cement-based materials and present a comparative evaluation of factors influencing crack healing, such as the microstructure and composition of immobilization barriers. A two-phase self-healing bioadditive was obtained by immobilizing vegetative S. pasteurii cell samples on natural porous minerals with or without the use of required nutrients. Then the samples were cracked by a three-point bending test, and the healing process was screened via stereomicroscope imaging and ultrasonic pulse velocity (UPV) testing after subjecting the cracked samples to 28 days of moist curing. Flexural cracks induced in mortar samples were filled with biogenic precipitate. Relatedly, the water absorption capacity of the samples was decreased in mortar samples containing bacterial cells, the nutrients were added in the curing solution. Fourier transform infrared spectroscopy and scanning electron microscopy analyses showed that calcite was the predominant polymorph of CaCO3 sealant in cracks.

Highly selective NO2 chemiresistive gas sensor based on hierarchical In2O3 microflowers grown on clinoptilolite substrates

Hierarchical In2O3 microflowers (HIMF) were prepared via a simple one-step hydrothermal method on the surface of the clinoptilolite substrate (CS). Structural characterizations were investigated by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectric spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the HIMF were comprised of abundant ultrathin two-dimensional nanosheets with a width of about 500 nm and the thickness of approximately 20 nm. The high-yield HIMF with a hexagonal phase were loose and uniformly distributed on the surface of the CS. The CS accompanied with the HIMF was made into a gas sensor to test NO2 sensing properties. It indicated that the gas sensor exhibited excellent NO2 sensing performance of low operating temperature, fast response, high selectivity and good reversibility. The outstanding NO2 sensing properties of the HIMF could be ascribed to its unique hierarchical structure and the synergistic effect of the CS. The possible formation process and sensing mechanism of the HIMF were proposed. The results show a potential prospect for using the natural porous mineral as the substrate to synthesize high-performance sensing material.

The preparation of self-floating Sm/N co-doped TiO2/diatomite hybrid pellet with enhanced visible-light-responsive photoactivity and reusability

Powdery photocatalyst has long been studied, yet its several disadvantages such as light-harvesting and recyclability in suspension system are the bottlenecks for practical application. The recent report on floating photocatalyst provided an alternative method to solve the above problem. In this paper, TiO2 nanoparticles were co-doped by samarium and nitrogen, and then supported onto natural porous mineral diatomite via sol-gel method. The composite powder was granulated to produce self-floating pellet catalyst (Sm/N co-doped TiO2/diatomite hybrid pellet), denoted as SN-TDHP. Its various physicochemical properties such as light absorbance, crystallinity, surface condition as well as morphology were systematically analyzed. The synergy between Sm and N dopants, as well as diatomite and TiO2 were studied. The photoactivity of SN-TDHP was investigated via the degradation towards an antibiotic tetracycline (TC) solution under visible light, and then the optimal co-doping amount and pellet dosage were determined. The optimal pellet catalyst presented its removal rate of TC as 87.2% within 150 min of reaction time. Moreover, self-floating SN-TDHP could simply be filtrated from the surface of water matrix, and presented good reusability after 5 repetitions.

RETRACTED: The fabrication of floating Fe/N co-doped titania/diatomite granule catalyst with enhanced photocatalytic efficiency under visible light irradiation

Abstract Powdery photocatalyst has long been studied, yet its several disadvantages such as light-harvesting and recyclability in suspension system are the bottlenecks for practical application. The recent report on floating photocatalyst provided an alternative method to solve the above problem. In this work, TiO2 nanoparticles were co-doped by iron and nitrogen, and then dispersed onto natural porous mineral diatomite via sol-gel method. The composite powder was granulated to produce floating granule catalyst (Fe/N co-doped TiO2/diatomite hybrid granule), denoted as FN-TDHG. Its various physicochemical properties such as light absorbance, crystallinity, surface condition as well as morphology were systematically analyzed. The synergy between Fe and N dopants, as well as diatomite and TiO2 were studied. The photoactivity of FN-TDHG was investigated via the degradation towards tetracycline (TC) solution under visible light irradiation, and then the optimal co-doping amount and granule dosage were determined. The optimal granule catalyst presented its removal rate of TC as 96.5% within 150 min. Moreover, floating FN-TDHG could simply be filtrated from the surface of water matrix, and presented good reusability after 5 repetitions. This photocatalytic granule is hopefully considered suitable to be applied in environmental remediation.

RETRACTED: The fabrication of self-floating Ti3+/N co-doped TiO2/diatomite granule catalyst with enhanced photocatalytic performance under visible light irradiation

Abstract Powdery photocatalyst has long been investigated and developed, yet its disadvantages such as low light-harvesting and reuse capability in suspension system have greatly hindered its practical application. The proposal of floating photocatalyst provided an alternative method to overcome the above limitations. In this work, TiO2 nanoparticles were doped by Ti3+ and N, and dispersed onto natural porous mineral diatomite via sol-gel method. The obtained black powder was granulated to produce floating granule catalyst (black Ti3+/N co-doped TiO2/diatomite hybrid granule), denoted as b/N-TDHG. The synergy between Ti3+ and N dopants, as well as diatomite and TiO2 were studied. The photoactivity of b/N-TDHG was investigated via the degradation of antibiotic tetracycline (TC) solution under visible light irradiation, and then the optimal co-doping amount and granule dosage were determined. The optimal granule catalyst presented its removal rate of TC as 92.0% within 150 min, and its rate constant was 0.0144 min−1, while the corresponding powdery sample showed the removal rate of TC as 90.5% during the same period, with its rate constant as 0.0135 min−1. Moreover, floating b/N-TDHG could simply be filtrated from TC solution, and the removal rate slightly dropped to 89.6% after 5 repetitions, presenting good reusability.

Adsorption of volatile organic compounds onto natural porous minerals.

The abundance of natural porous minerals and their low cost make them the potential adsorbents for VOCs (volatile organic compounds). In this paper, three natural minerals (diatomite, stellerite and vitric tuff) and their corresponding acid-treated minerals were used as adsorbents. The adsorption performances of minerals were investigated by the adsorption breakthrough curves of VOCs. The results indicated that the properties of organic compounds such as boiling point and polarity and the surface area and pore volume of minerals had obvious effects on the adsorption of VOCs over minerals. Increasing adsorption temperature and relative humidity would have negative effects on the VOC adsorption of minerals. The adsorption capacity of 2-heptanone over acid stellerite decreased by 7.2% as the temperature rose from 25°C to 45°C. The adsorption capacity of acid stellerite for 2-heptanone reduced by 60.9% when relative humidity increased from 0% to 75%. Minerals were tested for five adsorption-regeneration cycles to study the reusability. Better fittings of Thomas model, pseudo-first order kinetics model, and Freundlich model were showed in fitting the adsorption. Overall, porous minerals with high specific surface area and pore volume have promising prospect in VOCs adsorption.

Enhanced photocatalytic properties of reusable TiO2-loaded natural porous minerals in dye wastewater purification

Diatomite-based recyclable photocatalysts containing single lanthanide doped TiO2 nanoparticles (NPs) were synthesized by using simple sol–gel method. Photocatalytic activities of the prepared Ce- or La- single doped TiO2/diatomite catalysts were estimated by the degradation of Rhodamine B (RhB) under simulated sunlight irradiation. The XRD and Raman spectra shown only anatase phase of TiO2 for the un-doped and Ce-doped samples. The TEM images revealed uniform distribution of TiO2 NPs on the matrix, indicating that diatomite played an important role to prevent the agglomeration of TiO2 NPs. Ce-TiO2/diatomite showed a red shift in UV–visible light absorption edge with enhanced absorption intensity than un-doped sample, whereas La-TiO2/diatomite showed a blue shift. The bandgap energy of 1.5%-Ce doped sample is as low as 2.75eV. The XPS spectra showed the presence of both Ce3+ and Ce4+ oxidation states for Ce dopant. The photoluminescence spectra of the Ce-doped samples showed first decrease in the recombination centers with the maximum decrease for 1.5%-Ce doped sample and then started increase with the increasing Ce in the samples. As compared to the La-doped samples, a desired behavior was observed for the Ce-doped hybrid due to the redox Ce4+/Ce3+ pairs acting as electron scavengers and localized unoccupied Ce 4f level narrowing the band gap. The incorporation with diatomite as support of TiO2 nanoparticles is contributed for the improved reusability and also gives a promising strategy to enable the application of nano-photocatalysts in a real wastewater remediation treatment.

Synthesis of natural porous minerals supported TiO2 nanoparticles and their photocatalytic performance towards Rhodamine B degradation

Natural porous mineral supported (TiO2/diatomite) photocatalyst was prepared via a modified sol–gel method using titanium (IV) butoxide (TBOT) and diatomite. The effect of TBOT dosage on adsorption capacity and photocatalytic activity for Rhodamine B (RhB) solution was investigated. The morphology and elemental distribution were determined by scanning electron microscopy with attached energy-dispersive X-ray detector. The porous and crystalline structures were characterized using nitrogen adsorption–desorption and X-ray diffraction techniques, respectively. The prepared TiO2/diatomite hybrid catalyst has shown relatively even porous structure and dispersion of TiO2 over the surface. This suggests that the diatomite matrix prevented the agglomeration of TiO2 particles. Initially, the surface area and pore volume of the hybrid catalyst were increased by adding TBOT then decreased for dosages higher than 1.0ml. The crystalline size of TiO2 immobilized on diatomite matrix by sol–gel method was around 20nm. When the experiments were carried out in the absence of diatomite, this value was increased to 33.73nm. The use of diatomite also promoted an increase of the transformation temperature of the crystalline phase anatase to rutile for the TiO2. The as-prepared TiO2/diatomite composite exhibited high photocatalytic activity (96.0% for 0.5h UV-light irradiation) for the degradation of RhB from wastewater as a result of its unique porous structure and optimum TiO2 loading. In addition, it can be easily separated from suspension and possess a good durability. This hybrid material holds great promise in the engineering field for the environmental remediation.

Capturing and storage of CO2 by micron-nano minerals: Evidence from the nature

The increase of CO2 in atmosphere is a main factor leading to “greenhouse effect”, which causes more and more serious global environmental problems. The reduction of CO2 is a challenge for the survival of human beings, and it is also a big technical problem. CO2 fluid-rock interaction is a key scientific problem involved in geological storage. The CO2 fluid-rock interaction has a variety of multi-scale changes. Due to great differences in the quantity of surface atoms and surface energy between micron-nano-sized minerals, and ions and crystals, the speed and efficiency of CO2 fluid-rock interaction on a micron-nano scale are much higher than those on other scales. As is known from the natural world, the micron-nano structures of pores and the surface chemical modification of natural porous minerals (zeolite, diatomite, sepiolite, palygorskite, halloysite, etc.) should be further investigated, which can be used as the micron-nano -mineral porous materials with high capacity and high efficiency for capturing CO2. Through simulating the adsorption capacity and process of CO2 by minerals in the natural world, the micron-nano technology is applied to calcium- and magnesium-based minerals (olivine, pyroxene, feldspar, clay, etc.) so as to improve the activity of calcium and magnesium and enlarge the reaction contact area. In this way, the efficiency of capturing and storage of CO2 by calcium- and magnesium-based minerals can be greatly improved. These minerals can also be used as the micron-nano-mineral materials with large capacity and high efficiency for capturing and storing CO2.

Photodegradation of an azo dye using immobilized nanoparticles of TiO 2 supported by natural porous mineral

Natural mordenite, replacing the synthetic zeolites, has been employed as the support of TiO 2, and its photocatalytic activity has been examined in methyl orange (MO) aqueous under UV light. AFM, TEM, XRD, FTIR and fluorescence spectra have been used to reveal the loading effects of TiO 2 on mordenite. The results show that the photocatalytic degradation (PCD) reaction rates are sharply increased by natural zeolite supports. Since mordenite is photo-inert, the PCD-enhancement is mostly caused by the bonding effects of Ti–O–Si and Ti–O–Al. Moreover, another two distinct natural zeolites have been employed as the supports of TiO 2, in order to check the universality of PCD-enhancement effect of natural zeolites on TiO 2. And the factors of PCD reaction on TiO 2–zeolite, such as pH and catalyst dose, have been investigated.

Preparation and antimicrobial ability of natural proous antibacterial materials

The liquid ion exchange method, solid salt melt method and dry-wet circulation method were used to prepare natural porous antimicrobial materials with natural minerals, such as zeolite, spilite, palygorskite and montmorillonite, respectively. Atomic absorption spectrum and X-ray diffraction analysis were carried out to investigate the effects of Ag+, Cu2+ and Zn2+ on antimicrobial abilities of natural porous minerals, and the effect of preparation method on ion exchange capacity of antimicrobial material, respectively. The results show that for the ion exchange capacity, clay mineral is higher than fibrous mineral, i. e. both zeolite and montmorillonite are higher; the antimicrobial ability of material with Ag+ is the best; the exchange capacities of materials with Cu2+ or Zn2+ are all higher, but the antimicrobial ability of Cu2+ is better than that of Zn2+.

Factors Affecting the Performances of Sepiolite and Zeolite for the Treatment of Textile Wastewater

In this study, the adsorption mechanism of three reactive azo dyes (Everzol Black B, Everzol Red 3BS, Everzol Yellow 3RS H/C) on natural porous minerals, sepiolite and zeolite, have been examined in order to identify the ability of clay minerals on the removal of colored textile dyes from aqueous solutions. High ion exchange capacity, high surface areas and importantly their relatively cheap prices make them attractive adsorbents. For this purpose, series of batch adsorption tests were carried out as a function of solids concentration, time and dye concentration using natural and modified sepiolites and zeolites. Also, experiments were conducted to determine the amount of solid to be used in adsorption tests. An optimum solids concentration was selected as 0.05 g/mL (5%). Most of the adsorption was found to take place within the first 2 h of mixing, taking into account the extreme changes like pH and concentration, the mixing period was selected as 4 h for further testing. The adsorption results indicate that both natural sepiolite and zeolite have limited adsorption capacities of the reactive dyes but are substantially improved by modifying their surfaces with quaternary amines. The mechanism of adsorption process is elucidated on the basis of experimental data.

Interlayer conductivity of rocks — a fractal model of interface irregularities for calculating interlayer conductivity of natural porous mineral systems

A theory has been developed for calculating interlayer conductivity for natural porous systems, such as sedimentary rocks. As the materials investigated are mainly made up of silica and alumina minerals, an electrical double layer can be presumed, which carries the physical process. A new approach has been attempted by modelling the geometrical conditions. A self-similarity model has been established for describing the porous medium, the parameters of which can be derived from physical measurements. The considerations are based on the fact that the pore wall surface is structured in all orders of magnitude in such a way that the theory of fractal dimensions is applicable. Apart from the geometrical constraints, the electrochemical conditions and limitations are discussed. Experimentally, a set of sedimentary rocks were investigated for nine physical properties. A mean charge density calculated from interlayer conductivity gave a relatively high value close to that from cation-exchange capacity measurements.

Interlayer conductivity of rocks — a fractal model of interface irregularities for calculating interlayer conductivity of natural porous mineral systems

A theory has been developed for calculating interlayer conductivity for natural porous systems, such as sedimentary rocks. As the materials investigated are mainly made up of silica and alumina minerals, an electrical double layer can be presumed, which carries the physical process. A new approach has been attempted by modelling the geometrical conditions. A self-similarity model has been established for describing the porous medium, the parameters of which can be derived from physical measurements. The considerations are based on the fact that the pore wall surface is structured in all orders of magnitude in such a way that the theory of fractal dimensions is applicable. Apart from the geometrical constraints, the electrochemical conditions and limitations are discussed. Experimentally, a set of sedimentary rocks were investigated for nine physical properties. A mean charge density calculated from interlayer conductivity gave a relatively high value close to that from cation-exchange capacity measurements.