Non-conventional low-cost adsorbents for dye removal: A review

Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the 'MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a 'MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide 'clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.

Conductive two-dimensional titanium carbide ‘clay’ with high volumetric capacitance

Determination of the Cation Exchange Capacity (CEC) of Clay Minerals Using the Complexes of Copper(II) Ion with Triethylenetetramine and Tetraethylenepentamine

Many problems—from soil research to ceramics—require a reliable characterization of the clay minerals involved. This can be done using four clay-organic reactions: (i) staining tests and dye adsorption; (ii) glycerol and glycol adsorption; (iii) intercalation; (iv) alkylammonium ion exchange. Dye adsorption (staining tests) and glycerol adsorption allow a preliminary identification of the clay mineral groups. Intercalation reactions indicate minute differences between kaolins which cannot be detected by XRD and DTA. Alkylammonium ion exchange provides the best method for characterizing smectites and is sensitive to changes in the layer charge.

Characterization of clays by organic compounds

Kinetics, isotherm and thermodynamic studies of adsorption of Acid Blue 193 from aqueous solutions onto natural sepiolite

The Swelling Behaviour of Clays

Determination of the cation exchange capacity and the surface area of bentonite, illite and kaolinite by methylene blue adsorption

Li (super +) , Na (super +) , Ca (super 2+) , Sr (super 2+) , Cu (super 2+) , or Zn (super 2+) -saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200-700 degrees C. Half of each heated sample was subsequently autoclaved under steam at 200 degrees C ( approximately 1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer. Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li (super +) , Cu (super 2+) , and Zn (super 2+) ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu (super 2+) and Zn (super 2+) -rich samples release 16-23 meq/100 g of Mg (super 2+) from the structure. No Mg (super 2+) release is observed for the Li (super +) -rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu (super 2+) , Zn (super 2+) , and Li (super +) -rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu (super 2+) and Zn (super 2+) -rich smectites show a peak doublet between 480-700 degrees C. For the Li (super +) , Na (super +) , Ca (super 2+) , and Sr (super 2+) -rich montmorillonites, the second peak disappeared and a third peak at approximately 760 degrees C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.

Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic Cis-Vacant Montmorillonites

Nineteen drill core samples of lower Dogger opalinum shale from wells drilled in connection with a tunnel project near Brugg, northern Switzerland, were investigated. The shale is a well known swelling rock that has caused problems in underground construction work. Swelling pressures determined under constant volume conditions to obtain maximum values were 0.7 to 2.2 N/ram 2. The samples contained 37-59% clay-size material and about 35% quartz, 7-18% carbonate minerals, and about 5% feldspar, pyrite, and organic matter. In addition to kaolinite, illite, and chlorite, the clay-size fraction also contained mixed-layer illite/smectite with about 30% swelling layers.The specific surface area of the clay fraction was 135 m2/g. The specific surface charge of the clay (6.7 x 104 esu/cm2), the ion concentration in the pore fluid of the specimen after the swelling test (10 -2 mmole/cm3), the valence of the ions in the double layer of the clay particles (+ 1), and the half distance between the clay plates in the specimen (8- 15/~) allowed the calculation of the swelling pressure for each sample according to the Gouy double layer theory. The mean value of the calculated swelling pressures was found to be of the same order of magnitude as the measured values, indicating that the technique can be used where cylindrical or rectangular spec- imens are not available for direct measurement.

Swelling pressure calculated from mineralogical properties of a jurassic opalinum shale, switzerland

There has been much interest in the rare specimen of beidellite from the Black Jack Mine, Florida Mountain, Idaho. A variety of aluminous clays exists along veins such as the Black Jack vein, in rhyolite and latite flows, and in near-surface ash beds, often containing less than 1.0% MgO and 0.5% Na20. Associated clays include beidellite, illite, kaolinite, 10-A halloysite, dickite, nacrite, rectorite and a tarasovite-like mineral. The predominant clay is mixed-layer illite—beidellite. The beidellites have Al2O3 contents ranging from about 28 to 33%, and predominantly Ca and K as interlayer cations. The typical beidellite dehydroxylation temperatures of about 595 °C readily differentiate the beidellite from montmorillonite, which has a dehydroxylation temperature in the range of 735 °C. A modified differential thermal analysis (DTA) method is given for readily estimating the interlayer cation populations of smectites, including Mg++ and Al+++ cations. Chemical analyses and layer charges of II beidellites from mines around the Black Jack Mine are given. The beidellites have an American Society for Testing and Materials (ASTM) classification of CR, φ value, internal friction angle of about 8° and an expansion pressure of about 9 kgf/cm2 (88.3 kPa), similar to that of nontronite.

Fritz T. Madsen

Papers

The Swelling Behaviour of Clays

Determination of the cation exchange capacity and the surface area of bentonite, illite and kaolinite by methylene blue adsorption

Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic Cis-Vacant Montmorillonites

Swelling pressure calculated from mineralogical properties of a jurassic opalinum shale, switzerland

Beidellite and associated clays from the DeLamar Mine and Florida Mountain area, Idaho