M. Olivares-Marín

Modification of carbon screen-printed electrodes by adsorption of chemically synthesized Bi nanoparticles for the voltammetric stripping detection of Zn(II), Cd(II) and Pb(II).

A simple procedure for the chemical synthesis of bismuth nanoparticles and subsequent adsorption on commercial screen-printed carbon electrodes offer reliable quantitation of trace zinc, cadmium and lead by anodic stripping square-wave voltammetry in nondeareated water samples. The influence of two hydrodynamic configurations (convective cell and flow cell) and the effect of various experimental variables upon the stripping signals at the bismuth-coated sensor are explored. The square-wave peak current signal is linear over the low ng mL(-1) range (120 s deposition), with detections limits ranging from 0.9 to 4.9 ng mL(-1) and good precision. Applicability to waste water certified reference material and drinking water samples is demonstrated. The attractive behaviour of the new disposable Bi nanoparticles modified carbon strip electrodes, coupled with the negligible toxicity of bismuth, hold great promise for decentralized heavy metal testing in environmental and industrial effluents waters.

Improving the Performance of Biomass-Derived Carbons in Li-Ion Batteries by Controlling the Lithium Insertion Process

Disordered carbons obtained from cherry stones were tested as electrodes for lithium batteries and their properties were compared with those of short multiwalled carbon nanotubes (s-MWCNT), proposed as candidates for use in these electrochemical devices. Cells were cycled (up to 100 cycles) over a wide range of rates (C/10 to 5C). Previously, their structural, textural, and morphological properties were examined by X-ray diffraction patterns, N 2 adsorption data, and electron microscopy images (scanning electron microscopy and transmission electron microscopy), respectively. All carbons exhibited irreversible capacity (IC) to an extent roughly governed by the H/O content among other variables. The best performing carbons were obtained at low calcination temperatures (500°C). Although these conditions can increase IC, the effect can be offset by limiting the amount of Li inserted in the first charge. Moreover, this method improves capacity retention and rate capabilities. This approach allows one to obtain activated carbons with specific capacities of as high as 200 mAh g -1 at 5C; a high rate indeed. Their performance after as many as 100 cycles over a wide range of charge/discharge rates surpassed that of s-MWCNT and matched that of the best performing carbons reported so far.

The influence of the precursor and synthesis method on the CO2 capture capacity of carpet waste-based sorbents

Adsorption is one of the most promising technologies for reducing CO(2) emissions and at present several different types of sorbents are being investigated. The use of sorbents obtained from low-cost and abundant precursors (i.e. solid wastes) appears an attractive strategy to adopt because it will contribute to a reduction not only in operational costs but also in the amount of waste that is dumped and burned in landfills every year. Following on from previous studies by the authors, in this work several carbon-based adsorbents were developed from different carpet wastes (pre-consumer and post-consumer wastes) by chemical activation with KOH at various activation temperatures (600-900 °C) and KOH:char impregnation ratios (0.5:1 to 4:1). The prepared materials were characterised by chemical analysis and gas adsorption (N(2), -196 °C; CO(2), 0 °C), and tested for CO(2) adsorption at temperatures of 25 and 100 °C. It was found that both the type of precursor and the conditions of activation (i.e. impregnation ratios, and activation temperatures), had a huge influence on the microporosity of the resultant samples and their CO(2) capture capacities. The carbon-based adsorbent that presented the maximum CO(2) capture capacities at 25 and 100 °C (13.8 wt.% and 3.1 wt.%, respectively), was prepared from a pre-consumer carpet waste and was activated at 700 °C using a KOH:char impregnation ratio of 1:1. This sample showed the highest narrow microporosity volume (0.47 cm(3) g(-1)), thus confirming that only pores of less than 1 nm are effective for CO(2) adsorption at atmospheric pressure.

Low-cost disordered carbons for Li/S batteries: A high-performance carbon with dual porosity derived from cherry pits

A micro- and mesoporous carbon obtained from cherry pit waste and activated with H3PO4 acid has been studied as the sulfur host for Li/S batteries. The carbon has a high specific surface area of 1,662 m2·g–1 (SBET) and micropore and mesopore volumes of 0.57 and 0.40 cm3·g–1, respectively. The S/C composite, with a sulfur content of 57% deposited by the disproportionate reaction of a S2O32− solution in an acid medium without an additional heating step above the S melting point, delivers an initial specific capacity of 1,148 mAh·g–1 at a current of C/16. It also has a high capacity retention of 915 mAh·g–1 after 100 cycles and a Coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates and long-term cycling tests. The capacities delivered by the cell after 200 cycles were 707 and 410 mAh·g–1 at C/2 and 1C (1C = 1,675 mA·g–1), respectively, maintaining the high Coulombic efficiency. The overall electrochemical response of this carbon as the sulfur matrix is among the best reported so far among the other biomass-derived carbons, probably because of the micro- and mesopore system formed upon activation.

Suppressing Irreversible Capacity in Low Cost Disordered Carbons for Li-Ion Batteries

In this work, we developed an easy method to suppress the irreversible capacity (IC) observed in disordered carbons acting as electrode materials in lithium batteries by limiting the amount of Li inserted in the first discharge to different nominal capacities. This strategy is quite effective with carbons with a high IC. To suppress IC, the proposed method improves capacity retention and rate capabilities.

Influence of the operation conditions on CO2 capture by CaO-derived sorbents prepared from synthetic CaCO3

In this work, a statistical experimental design is performed in order to prepare CaCO3 materials for use as CaO-based CO2 sorbent precursors. The influence of different operational parameters such as synthesis temperature (ST), stirring rate (SR) and surfactant percent (SP) on CO2 capture is studied by applying Response Surface Methodology (RSM). The samples were characterized using different analytical techniques including X-ray diffraction, N2 adsorption isotherm analysis and Scanning Electron Microscopy-X-ray Energy Dispersive Spectroscopy (SEM-EDX). CO2 capture capacity was determined by means of a thermogravimetric analyzer which recorded the mass uptake of the samples when these were exposed to a gas stream containing diluted (15%) CO2. The statistical approach used in this work provides a rapid way of predicting and optimizing the main preparation variables of CaO-derived sorbents for CO2 sorption. The results obtained clearly indicate that four parameters statistically influence CO2 uptake: SR, the square of SR, its interaction with SP and the square of SP.

Preparation of Micropore-Containing Adsorbents from Kenaf Fibers and Their Use in Mercury Removal from Aqueous Solution

Here, a number of activated carbon fibers (ACFs) prepared from kenaf natural fibers (KNFs) by chemical activation with KOH under different operation conditions have been used as adsorbents for the removal of mercury from aqueous solutions. Samples were characterized by N2 adsorption at 77 K, mercury porosimetry, scanning electronic microscopy (SEM), and FT-IR spectroscopy. The adsorption of mercury at 25°C without pH adjustment from an aqueous solution was evaluated from both kinetic and equilibrium standpoints. It was found that the activation conditions during the preparation of ACFs (i.e., impregnation ratios and activation temperatures) had a strong influence on the porosity of the resultant samples and, therefore, on their mercury adsorption capacity. The sample prepared at 800°C using an impregnation ratio of 3:1 (named K3-800) presented the maximum Langmuir adsorption capacity (10.53 mg/g). This sample showed a specific surface area of 881 m2/g, a micropore volume of 0.60 cm3/g, and the highest total pore volume (2.69 cm3/g).