Joe B. Dixon

Bio: Joe B. Dixon is an academic researcher from Texas A&M University. The author has contributed to research in topics: Clay minerals & Birnessite. The author has an hindex of 35, co-authored 84 publications receiving 3523 citations. Previous affiliations of Joe B. Dixon include King Saud University & Stephen F. Austin State University.

Ion exchange, thermal transformations, and oxidizing properties of birnessite

Abstract: Synthetic sodium bimessite, having a cation-exchange capacity (CEC) of 240 meq/100 g (cmol/kg) was transformed into Li, K, Mg, Ca, Sr, Ni, and Mn2+ cationic forms by ion exchange in an aqueous medium. Competitive adsorption studies of Ni and Ba vs. Mg showed a strong preference for Ni and Ba by bimessite. The product of Mg2+-exchange was buserite, which showed a basal spacing of 9.6 A (22°C, relative humidity (RH) = 54%), which on drying at 105°C under vacuum collapsed to 7 A. Of the cation- saturated bimessites with 7-A basal spacing, only Li-, Na-, Mg-, and Ca-bimessites showed cation exchange. Heating bimessite saturated with cations other than K produced a disordered phase between 200° and 400°C, which transformed to well-crystallized phases at 600°C. K-exchanged bimessite did not transform to a disordered phase; rather a topotactic transformation to cryptomelane was observed. Generally the larger cations, K, Ba, and Sr, gave rise to hollandite-type structures. Mn- and Ni-bimessite transformed to bixbyite-type products, and Mg-bimessite (buserite) transformed to a hausmannite-type product. Li-bimessite transformed to cryptomelane and at higher temperature converted to hausmannite. The hollandite-type products retained the morphology of the parent bimessite. The mineralogy of final products were controlled by the saturating cation. Products obtained by heating natural bimessite were similar to those obtained by heating bimessite saturated with transition elements.

Quantitative determination of clinoptilolite in soils by a cation-exchange capacity method

Abstract: A cation-exchange capacity (CEC) method based on ion-sieving properties was developed for the quantitative determination of clinoptilolite in soils. In this method, both zeolitic and non-zeolitic exchange sites in the soil sample are saturated with Na t. The CEC of the non-zeolitic exchange sites is determined by replacing the Na- in these sites with tert-butylammonium ions. The tert-butylammonium ion cannot be exchanged into the zeolitic exchange sites because it is too large to pass through the channels in the clinoptilolite structure. The sample is next washed with NH4OAc to replace the Na + in the zeolitic exchange sites. The amount of soil zeolite is then estimated by comparing the CEC of zeolitic exchange sites to the total zeolite CEC ( 175 meq/100 g for pure clinoptilolite). Prior to the CEC analyses, carbonates and organic matter must be removed to minimize interference with the exchange process. A high cor- relation (r-' = .96) was observed between the abundance of clinoptilolite estimated using the CEC method and the abundance estimated by semiquantitative X-ray powder diffraction analysis. The CEC procedure was used to quantify clinoptilolite in an Aridic Calciustoll soil from south Texas. About 2-5% clinoptilolite occurs in the A and B horizons, and concentrations progressively increase with soil depth to as much as 20% in the CBk2 horizon.

Synthesis of Todorokite

Abstract: Todorokite of chemical composition (Mg0.77Na0.03)(Mg0.18Mn2+0.60Mn4+5.2222) O12·3.07 H2O was synthesized by a two-step procedure. First, sodium birnessite was synthesized and magnesium was exchanged for sodium to form magnesium birnessite, which was autoclaved under a saturated steam pressure at 155°C for 8 hours to form well-crystallized todorokite. Synthesized todorokite particles consisted of fibers extending from a central plate. The plate itself was made of twinned fibers forming a trilling pattern. The infrared spectra and x-ray diffraction patterns were similar to those of natural todorokite samples. Calcium birnessite and nickel birnessite, when autoclaved under conditions similar to those for magnesium birnessite, yielded a todorokite structure. However, the formation of todorokite from calcium and nickel birnessite was less extensive.

Oxidation of Chromium(III) to (VI) by Manganese Oxides

Abstract: Manganese oxides in soils oxidize Cr from a stable form to a more toxic mobile form. The influence of Mn oxide diversity on Cr oxidation is the subject of this report. Oxidation of Cr(III) to Cr(VI) by coarse clay-size natural Mn oxides, birnessite, todorokite, and lithiophorite was studied at pH 4 and 7, and at 200 and 400 μM initial Cr(III) concentrations. The oxidation rate obeyed the first-order rate law at the 400 μM Cr(III) initial concentration; the 200 μM concentration was too low and reverse reactions may have interfered. Rate law is valid only far from equilibrium. The rate of oxidation was greater for todorokite and birnessite that contained the most quadrivalent Mn and least for lithiophorite that contained a greater proportion of trivalent Mn determined by x-ray photoelectron spectroscopy (XPS). The deviation of Mn oxidation state from the frequently assumed quadrivalent form in Mn oxides suggests the need for a thorough assessment of the ion species of Mn in Mn oxides that occur in soils. At 400 μM Cr(III), the rate of Cr oxidation by the pyrolusite sample was intermediate between birnessite and todorokite suggesting that the sample was not pure pyrolusite. Apparently, the synthesis process did not reach equilibrium with pyrolusite. The sample used as a chemical standard was apparently more soluble and more effective in oxidizing Cr(III) than would be expected for the natural mineral pyrolusite.

Intercalation and delamination of layered carbides and carbonitrides

Abstract: Intercalation and delamination of two-dimensional solids in many cases is a requisite step for exploiting their unique properties. Herein we report on the intercalation of two-dimensional Ti3C2, Ti3CN and TiNbC-so called MXenes. Intercalation of hydrazine, and its co-intercalation with N,N-dimethylformamide, resulted in increases of the c-lattice parameters of surface functionalized f-Ti3C2, from 19.5 to 25.48 and 26.8 A, respectively. Urea is also intercalated into f-Ti3C2. Molecular dynamics simulations suggest that a hydrazine monolayer intercalates between f-Ti3C2 layers. Hydrazine is also intercalated into f-Ti3CN and f-TiNbC. When dimethyl sulphoxide is intercalated into f-Ti3C2, followed by sonication in water, the f-Ti3C2 is delaminated forming a stable colloidal solution that is in turn filtered to produce MXene 'paper'. The latter shows excellent Li-ion capacity at extremely high charging rates.

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

Abstract: Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.