Abstraction and regeneration potential of temperature-enhanced rice husk montmorillonite combo for oil spill

Chemical modification of montmorillonite though popular may be expensive and environmentally noxious and can result in secondary contamination. Therefore, there is a need for eco-friendly and efficient treatment techniques. The use of thermally enhanced rice husk montmorillonite combo (TRMC) for aqueous crude oil pollution was evaluated. The physical characterization of the sorbate revealed a light crude oil. Scanning electron microscopy of TRMC and untreated montmorillonite (UM) showed efficient utilization of the pores for crude oil sequestration. Temperatures, pH, initial oil concentration, dosage of sorbent, and time were found to be significant in the batch sorption investigation. The heterogeneous surface nature of TRMC was elucidated by the Freundlich and Scatchard model analyses. The Langmuir monolayer maximum sorption capacity was 5.8 and 9.7 g/g for UM and TRMC respectively and the latter was found to be higher than most reported sorbents. The pseudo-first-order model gave better fit than pseudo-second-order, the Bangham, and the Elovich models in kinetics based on regression and chi-square analysis. Thermodynamics showed a spontaneous, feasible, endothermic, and physical sorption processes. Regeneration and reusability studies using n-hexane as eluent showed TRMC as suitable, environmental friendly sorbents for oil spill remediation.http://link.springer.com/journal/113562019-12-01hj2018Chemistr

Calcined Corncob-Kaolinite Combo as New Sorbent for Sequestration of Toxic Metal Ions From Polluted Aqua Media and Desorption

This study investigated a new area of improving the adsorption capacity of clay using corn cob as an alternative means of clay modification to the more expensive and complicated chemical treatment techniques. Kaolinite Clay (KC), Calcined corncob-kaolinite Combo (CCKC), and Corncob (CC) adsorbents were utilized. The adsorbents were characterized by Fourier Transform-Infrared (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM), X-ray fluorescence spectroscopy, and Brunauer-Emmett-Teller (BET) surface area analyzer. Batch adsorption methodology was used to investigate the effect of pH, initial metal concentration, adsorbent dose, and contact time on adsorption of Pb (II) and Cd (II). A slight increase in BET surface area of 29.31 m2/g for CCKC from 14.12 m2/g for raw KC was achieved. The trend of metal adsorption on the adsorbents was in the order CC>CCKC>KC. The Langmuir isotherm was found to present the best fit for the unmodified adsorbents while the Freundlich was applicable for CCKC indicating multilayer heterogeneous surface. The pseudo second order kinetic model was found to be suitable in the kinetic analysis. Thermodynamic studies revealed a spontaneous physical adsorption process of metal ions on CCKC. The combo adsorbent showed highest percentage desorption (>70%) of Cd and Pb ions in both acid and basic media compared to the other adsorbents. The results of the study established the efficiency of calcined corn cob kaolinite combo as suitable adsorbent for metal ions

Waveguide-Based Spectroelectrochemical Characterization of Band Edge Energies in Submonolayers of CdSe Quantum Dots Tethered to Indium–Tin Oxide Electrodes

We present here high sensitivity attenuated total reflectance (ATR) spectroelectrochemical studies of electron injection (reduction) into surface-tethered, submonolayer to monolayer coverages of CdSe quantum dots (QDs) linked to indium–tin oxide (ITO) electrodes using a strong X-type bifunctional phosphonic acid (PA) surface linker, octanediphosphonic acid (ODiPA). Estimates of conduction band energies (ECB) were obtained from the onset of absorbance bleaching as a function of QD diameter (3.2–6.4 nm) and as a function of the supporting electrolyte (LiClO4) concentration. For CdSe QDs created from combinations of moderately strong stearic acid, hexadecylamine, trioctylphosphine oxide, and trioctylphosphine ligands, surface-tethering was accompanied by decreases in QD diameter and loss of up to 25% volume for the largest QDs. For QDs prepared with PA ligands, followed by aggressive (3×) pyridine exchange to produce QDs with weak capping ligands, no size reduction was observed as a result of adsorption to the ODiPA/ITO surface. For both types of tethered CdSe QDs, significant stabilization of the reduction product of the surface-tethered QD was observed with ca. 700 meV lowering of ECB relative to estimates of ECB obtained from our recent in vacuuo UV-photoemission studies of bare CdSe QDs tethered to Au surfaces. A sizeable fraction of that stabilization is proposed to arise from the tethering of these asymmetric QDs to a complex, high dielectric constant interface region. At least 200 meV of the stabilization arises from concentration-dependent charge screening by the solution counter ion (Li+), with no evidence for the incorporation of Li+ as a result of the electron injection process. The overall stabilization in the reduced form of these tethered QDs is larger than seen for previous spectroelectrochemical studies of QD reduction, in solution, tethered at higher coverages to transparent electrodes, or as electrophoretically deposited multilayer QD thin films. This waveguide ATR spectroelectrochemical approach to estimating energetics for QDs tethered to semiconductor or oxide substrates at low surface coverages is likely to be relevant for a wide array of energy conversion and energy storage processes using nanomaterials and may be especially useful for studying the effects of surface coverage, type of surface linker, contacting solvent/electrolytes, and adsorbed molecular reactants