David A. Rockstraw

Pecan shell activated carbon: synthesis, characterization, and application for the removal of copper from aqueous solution

Activated carbon with a high adsorption capacity for removal of copper ions from aqueous solution is produced from pecan shells. Air and phosphoric acid are used for the oxidation and the modification or development of oxygen- or phosphorus/oxygen-containing groups on the carbon surface. It was found that the adsorption capacity of the produced carbon is significantly higher than that of the commercial activated carbons that were tested, and comparable to an ion exchange resin designed for copper adsorption. Based on the results obtained from a variety of characterization methods, it has been determined that the surface of the carbon is covered with a considerable concentration of phosphorus, present in the form of various functional groups. It is proposed that the acidic groups detected using the Boehm titration method not only be considered as oxygen-containing acidic groups, but also as oxygen/phosphorus groups. From pH studies, it was observed that adsorption of copper at very low concentrations occurs by ion exchange of 2H+ from the surface with a Cu2+ ion from solution; while at higher concentrations, other forms of ion-exchange and surface complexation with oxygen- and phosphorus-containing functional group sites can be proposed as well.

Copper and strontium adsorption by a novel carbon material manufactured from pecan shells

Abstract A novel carbon material (PS276a) was produced from pecan shells, a waste product of the agricultural industry. Preparation of this material involved the impregnation of the pecan shell feedstock with a phosphoric acid solution. Activation was followed by a water wash and a sodium hydroxide treatment. The carbon produced was characterized by adsorption of N 2 and revealed a pore structure with an average pore diameter of 74.8 A. Equilibrium sorption isotherms prepared for this carbon demonstrate that it has a significantly higher capacity for copper and strontium sorption than that of a commercial material used for comparison. A maximum of 95 mg Cu 2+ and 180 mg Sr 2+ are adsorbed per gram of this carbon at pH 3.6 and 8.5, respectively. Demonstrated process advantages of this carbon material and preparation technique include low temperature manufacture, in-situ regeneration potential, and adsorbate recovery capability.

Silver nanoparticles from ultrasonic spray pyrolysis of aqueous silver nitrate

Silver particles less than 20 nm in diameter were synthesized by pyrolysis of an ultrasonically atomized spray of highly dilute aqueous silver nitrate solution at temperatures above 650°C and below the melting point of silver. Feed solution concentration and ultrasound power applied to the atomizer were found to have a significant impact on the particle size of the silver nanoparticles. Average particle size was found to be controllable in the range of 20 nm to 300 nm by varying the solution concentration and the ultrasound power to the atomizer.

A generating equation for mixing rules and two new mixing rules for interatomic potential energy parameters

A generating equation for the mixing rules of interatomic potential energy parameters is proposed. It is demonstrated that this equation can, indeed, reproduce many popular mixing rules. A weighting matrix is used with the generating equation. This weighting matrix approach is superior to the present status of mixing rule development. A systematic framework is given for devising new mixing rules and/or comparing them. Two new mixing rules, which are more accurate than the available rules in the literature, are proposed. These rules are capable of reproducing the collision diameter and well‐depth parameters for the binary values of noble gases to within their experimental uncertainties.

A systematic study and proposed model of the adsorption of binary metal ion solutes in aqueous solution onto activated carbon produced from pecan shells

Adsorption isotherms of a number of binary solute systems have been obtained. The adsorption behavior of these cations in the presence of other metal ions that display strong or intermediate affinities for adsorption sites has been systematically investigated. In this investigation the following factors have been considered: (1) metal ion site competition; (2) charge accumulation near the carbon surface; and (3) speciation of the metal ions. Two multicomponent adsorption models are proposed, and the results are compared to two models presented in the literature. The performance of these models is evaluated by an analysis of error. It is found that models with three interaction parameters generally provide a better fit of the data. In most cases, the proposed two-parameter model gives acceptable results.

Rapid oxidation of sulfide mine tailings by reaction with potassium ferrate

The chemistry of sulfide mine tailings treated with potassium ferrate (K2FeO4) in aqueous slurry has been investigated. The reaction system is believed to parallel a geochemical oxidation in which ferrate ion replaces oxygen. This chemical system utilized in a pipeline (as a plug flow reactor) may have application eliminating the potential for tailings to leach acid while recovering the metal from the tailings. Elemental analyses were performed using an ICP spectrometer for the aqueous phase extract of the treated tailings; and an SEM-EDX for the tailing solids. Solids were analyzed before and after treatments were applied. ICP shows that as the mass ratio of ferrate ion to tailings increases, the concentration of metals in the extract solution increases; while EDX indicates a corresponding decrease in sulfur content of the tailing solids. The extraction of metal and reduction in sulfide content is significant. The kinetic timeframe is on the order of minutes.

Synthesis of Ru-Ni Core-Shell Nanoparticles for Potential Sensor Applications

Nanoparticles of Ru-Ni with a core-and-shell structure were synthesized as potential sensors in a single-step spray-pyrolysis process at 700-1000. The majority of the core consists of ruthenium, while the shell is predominately composed of nickel. An aqueous precursor containing ruthenium chloride and nickel chloride was nebulized by an ultrasonic atomizer to generate an aerosol. The aerosol droplets were subsequently decomposed to form uniformly distributed Ru-Ni bimetallic nanoparticles. Atomic fractions of precursors, solvent type and process temperature play crucial roles in the formation of core-and-shell structures.

Modeling substrate particle degradation by Bacillus coagulans biofilm

A mathematical model for solid particle degradation by an aerobic biofilm of Bacillus coagulans is developed. A moving biofilm is assumed to be present on the surface of the solid particle. Oxygen and glucose are assumed to be growth limiting. The depleting glucose concentration in the solid particle is tracked as a function of time and it is found that the time taken for degradation of the particle is a function of particle size. Comparison with the experimental results found in literature on the particle size reduction by the action of Bacillus coagulans (Nandakumar et al., 1996) indicates that the model is able to predict the general trends of experimental data well. It is suggested that the diffusion of the enzyme glucoamylase plays a crucial role and is a more dominant determining factor than the variation of the composition of particles with size as suggested previously (Nandakumar et al., 1996) for the experimental observation that larger particles took more time to degrade than smaller particles. It is hoped that the results obtained will lead to a better understanding of the mechanism of particle degradation by aerobic biofilms and help in better design of biofilm reactors.

Direct Synthesis of Ru-Ni Nanoparticles with Core-and-Shell Structure

Nanoparticles of Ru-Ni with a core-and-shell structure were synthesized as potential catalysts for fuel cells and other applications in a single-step spray-pyrolysis process at 700°–800°C. The majority of the core consists of ruthenium, while the shell is predominately composed of nickel. Bimetallic nanoparticles with a core-and-shell structure are being considered as new and promising catalysts with enhanced catalytic activity, better stability, and higher resistance to contaminants for fuel cells and other applications. An aqueous precursor containing ruthenium chloride and nickel chloride was nebulized by an ultrasonic atomizer to generate an aerosol. Droplets were subsequently decomposed to form uniformly distributed Ru-Ni bimetallic nanoparticles, then deposited on a substrate. Atomic fractions and melting temperatures are expected to play a crucial role in the formation of core-and-shell structures.

Deposition of Ru-Ni-S Nanoparticles on Carbon by Spray-Pyrolysis: Effects of Solvent and other Processing Parameters

Nanoparticles of Ru-Ni-S were synthesized in a single-step spray-pyrolysis process as potential catalysts for fuel cells and other applications. The liquid precursors containing ruthenium, nickel, and sulfur were nebulized by an ultra-sonic atomizer to generate aerosol droplets, which were subsequently decomposed to form uniformly distributed nanoparticles for deposition on a carbon thin film. It was observed that the application of methanol as solvent has a strong effect on the particle morphology, size, and composition. The morphology of the Ru-Ni-S nanoparticles changed from spherical with water as solvent, to dendrites upon increase in the methanol con- centration in the precursor solution. It was also found that the pyrolysis temperature strongly affected the particle morphology when methanol was used as solvent. High temperatures promote dendrite formation. When a water/methanol mixture was used as solvent, crys- talline ternary nanoparticles of Ru-Ni-S on a carbon layer were formed at lower temperatures. A very interesting and unique structure of spherical clusters of crystalline particles attached by a chain of crystalline nanoparticles was synthesized. Elemental analysis obtained with EDS attached to the SEM used for particle characterization has confirmed the existence of all elements of interest, and X-ray map- ping showed all elements were distributed uniformly in the nanoparticles. Spray-pyrolysis processing is a versatile technique for produc- tion of inorganic materials of a wide range of composition, size, and morphology. It typically consists of several steps that may include: precursor preparation, precursor atomization, droplet evaporation, droplet precipitation, droplet drying, droplet coagulation, thermoly- sis, and sintering. An review on spray-pyrolysis processing by Messing et al. (1) has discussed the fundamental process parame- ters enabling the formation of particles with controlled morphology and composition. Among the important process parameters in spray-pyrolysis processing, the effects of precursor properties on particle size, composition, and morphology are probably the least understood. Synthesis of electrocatalysts in a spray-pyrolysis process for different types of fuel cells is a relatively new application of the spray-pyrolysis technique. Tolerance to small amounts of carbon monoxide and sulfur is important for proton exchange membrane fuel cells operating on hydrogen obtained by reforming carbon- based fuels. Conventional nanoparticles (2-5 nm) of platinum-based metal alloys are used as both anode and cathode catalysts for proton exchange membrane fuel cells due to the high activity for both hy- drogen oxidation and oxygen reduction (2). However the platinum- based catalysts used today suffer high polarization losses, reducing performance and fuel efficiency due to particle agglomeration, car- bon monoxide and sulfur poisoning (2, 3). The search for carbon monoxide and/or sulfur-tolerant non-platinum electrocatalysts for fuel cell applications have been a very active research endeavor (4- 10). Only a few researchers have studied the platinum- and ruthe- nium-based nanoparticles for methanol oxidation in fuel cell appli- cations. The binary and ternary crystalline nanoparticles were sup- ported on carbon nanofilm as fuel cell catalysts. Waszczuk et al. (11) studied the methanol adsorption on platinum-ruthenium sur- faces and observed that the decomposition of methanol is quite different at ultra-high vacuum. It was observed that the behavior of simple molecules would be different under ultra-high vacuum. Con- trol of size, morphology, and composition of nanoparticles is im- portant in the synthesis processing of ceramic powders. It was