Search

As a result of social distancing measures in response to the Covid-Sars 2 pandemic, our school sent chemistry kits to the students’ homes for remote experimentation. This allowed the performance of ∼25 experiments per person in each of the Fall 2020 and Spring 2021 semesters in an elective chemistry course. Students were requested to design some experiments of their own and then have the entire group reproduce them. One such experiment consisted of the anodic indirect electrogeneration of colloidal sulfur by solution acidification to produce thiosulfate disproportionation. This was evidenced by the well-known Rayleigh scattering phenomenon. Here, the trajectory and polarization state of light are modified by its interaction with a medium containing particles of smaller diameter than the wavelengths of incident light. If white light interacts with this medium, the smaller wavelengths (e.g., blue, violet) are radially scattered while the longer wavelengths (e.g., orange, red) pass through the suspension. Such scattering is responsible for beautiful sunsets and blue skies and is produced here by an indirect electrochemical process that generates colloidal sulfur. Students evidence the scattering of light shone from simple cell phone flashlights. The entire procedure is performed in a 2-h class session. Key student outcomes are presented.

Social distancing measures due to the SARS-CoV-2 virus have profoundly challenged the educational experimental work. We have sought to remediate this issue by designing a series of low cost, low risk, quick, and qualitative electrochemistry and corrosion experiments to be performed in the student’s homes at the microscale with a kit provided by the teacher. One such experience is the electroplating of Sn from an aqueous chloride solution using readily available soldering wires (e.g., Sn–Pb alloy, or Sn–Ag–Cu alloy). This process catches students’ attention due to its simplicity and variety of possible applications that include corrosion protection, fabrication of electronic components, plating of cooking utensils, lithium batteries, etc.

Due to social distancing constraints during the COVID-19 pandemic, several experiments were designed in the Fall 2020 and Spring 2021 semesters in our Electrochemistry and Corrosion elective course to demonstrate electrochemical phenomena and applications at the students’ homes with a kit sent by the school. We report here a student-designed experiment focused on water electrolysis, a well-studied phenomenon of great interest to the electrochemical industry. Its main appeal derives from the use of solar energy for the production of hydrogen gas, which is used in fuel cells. Here, the light-to-electricity converting function of light-emitting diodes is exploited to produce an electric current from solar radiation. This current is, in turn, utilized to perform microscale water electrolysis at graphite electrodes with the aid of a magnetic field. Lastly, the electrolysis products are employed to generate a voltage, demonstrating the fuel cell principle.

This paper presents a student-designed one-pot electroless deposition of Bi extracted from a Pepto Bismol® tablet by galvanic displacement of the Zn coating of a galvanized iron nail. This experiment relies on a readily accessible and reasonably safe method and materials and it has been used during the present COVID pandemic as a hands-on activity with higher education students (i.e., Junior and Senior Chemical Engineering students). Its simplicity should allow its use with High School students as well. The entire procedure can be completed in 30–45 min.

This activity allows students to visualize how to obtain different stoichiometries with various techniques in a single experiment. The involvement of three phases adds to the student’s interest. Instructional materials are provided to facilitate the experimental procedures, interpretation of results, and error analysis. The reaction of Li from a Li battery with water inside a syringe allows measurement of the gas evolved, the metal consumed, and the hydroxide produced. Li batteries can be obtained for less than US $1.00. This report describes the development of a 2 h activity that has been tested in whole or in part in various teacher workshops in Mexico, Panama, El Salvador, and Thailand, and it has been implemented and assessed in a general chemistry laboratory.

Various international perspectives from selected regions where substantial work is being done on green and sustainable chemistry education emphasize a systems thinking framework. Common to most of the perspectives is the inclusion of more global paradigms involving economic, environmental, political, and social aspects as fundamental issues in the formerly merely technical and scientific discussions, as well as the development of laboratory experiences, training sessions, written materials, discussion meetings, and conferences. We include bird’s eye views from Europe (the Green Chemistry Centre of Excellence at the University of York, United Kingdom; the University of Cordoba, Spain; and the University of Amsterdam, The Netherlands), Latin America (the Universidad Nacional de Rosario, Argentina, and the Universidad Iberoamericana, Mexico), Africa (the University of Venda, South Africa), and Australia (Monash University).

Electrochemistry has much to offer for a better understanding of natural electron exchange phenomena and multiple environmental remediation schemes. We have designed and tested several laboratory experiments to explore and demonstrate these functions in a teaching lab setting. These include: indirect electrolytic destruction of organic wastes, indirect H2S removal, electrocoagulation of oily wastewater, color removal of simulated wastewater by electrocoagulation-electroflotation, electrokinetic processing of soils, recovery of a soil metal pollutant and its extractant, production of disinfectants (ferrate and ozone), experimental transitions in a potential vs. pH (Pourbaix) diagram, electrolytically-generated activation of a metal surface for CO2 conversion, the indirect generation of colloidal sulfur to demonstrate Rayleigh scattering, a mini-solar cell, and the construction of a solar fuel cell. We have also generated experiments on non-electrodic electron transfer phenomena like simultaneous photocatalysis, removal of metal ions by cementation, destruction of pollutants by Fenton´s reagent, photoreduction of metal ions, production of disinfectants (ClO2, chloramines), water acidification by oxidation of mineral sulfides (acid mine drainage), and the oxidation of Fe(II) ions by molecular dioxygen.

Conducting polymers (CPs), thanks to their unique properties, structures made on-demand, new composite mixtures, and possibility of deposit on a surface by chemical, physical, or electrochemical methodologies, have shown in the last years a renaissance and have been widely used in important fields of chemistry and materials science. Due to the extent of the literature on CPs, this review, after a concise introduction about the interrelationship between electrochemistry and conducting polymers, is focused exclusively on the following applications: energy (energy storage devices and solar cells), use in environmental remediation (anion and cation trapping, electrocatalytic reduction/oxidation of pollutants on CP based electrodes, and adsorption of pollutants) and finally electroanalysis as chemical sensors in solution, gas phase, and chiral molecules. This review is expected to be comprehensive, authoritative, and useful to the chemical community interested in CPs and their applications.

This paper describes the electrochemical behavior of poly-bithiophene (PBTh), poly-ethylene-3,4-dioxythiophene (PEDOT), and poly-3,4-ortho-xylendioxythiophene (PXDOT) in an EtOH/H2O (1:1) mixture using 0.1 M LiClO4 as supporting electrolyte and AcOH/AcONa to buffer pH. PBTh suffers fast degradation, whereas PEDOT and PXDOT show reasonable stability in the EtOH/H2O mixture. A strong interaction between the 3,4-alkoxythiophene polymers and the EtOH/H2O mixture was evidenced by a charge/discharge process limited by ionic movement and slow electron transfer (as signaled by a large ΔEp). Both of these processes were faster in ACN. The stability of the prepared films was studied through 100 charge/discharge cycles in ACN and in the EtOH/H2O mixture. Considerable electroactivity loss for PEDOT and PXDOT was observed in ACN, which may be caused by charge trapping phenomena and oligomer release. This loss diminished substantially in the EtOH/H2O mixture showing a current higher than 75% of the initial value and an electrochemical reversibility (i.e., the Qc/Qa ratio) higher than 90%. Due to the stability of the PEDOT and PXDOT films in the EtOH/H2O mixture, it was possible to use them in modified electrodes for Cu (II) detection using anodic stripping voltammetry, where concentration-dependent current signals were observed.

Electropolymerized polythiophene (PTh) is a conductive polymer with low crystallinity, excellent thermal stability, and good conductivity. Its applications strongly depend on the electrochemical conditions employed during film growth, the nature of the doping counterion, the substituents attached to the thiophene ring, and the reaction medium employed. Electropolymerization of bithiophene (BTh) to produce polybithiophene (PBTh) can be successful both in aqueous and organic media. The objective of the present study was to compare the influence of the electropolymerization conditions on the doping level (δ) of PBTh films. A high doping level was reached using ACN as solvent (% δ = 25.58% ± 0.77), while in water the electropolymerization was strongly inhibited. The study of in-situ conductance during electropolymerization in ACN showed a conductance increase with the number of cycles, while conductance did not increase in water. This electropolymerization inhibition is attributed to a nucleophilic attack by the H2O molecule on the cationic species formed during the oxidation of PBTh.

The use of soluble and highly oxidizing Ag(III) in the form of the tetrahydroxoargentate ion Ag(OH)4− is reported for the oxidation of surrogate organic recalcitrant dyes (i.e., rhodamine 6G (Rh6G) and fluorescein (Fl)). The possible use of Ag(OH)4− for the treatment of these and other refractory compounds is assessed. Such dyes were selected due to their common occurrence, stability, refractory nature, the relatively high toxicity of Rh6G, and their structural similarity to Fl. Several reaction intermediates/products were identified. The results showed that the highly oxidizing tetrahydroxoargentate anion was capable of degrading these recalcitrant dyes. Furthermore, the final degradation products do not represent a higher environmental risk than the original surrogates themselves. In addition, the partial mineralization of the dyes was proven.

This paper focuses on the design and application of a teacher training strategy to promote the inclusive education of students with disabilities in the science classroom, through the creation of ad...

Commercial solutions of paraquat (PQ) herbicide were treated by solar corrosion Fenton processes (SCF). A borosilicate reactor was packed with a coiled filament of annealed iron wire to different reactor volume/filament surface area ratios (Vt/Af). A cylindrical parabolic concentrator was designed to concentrate UV light. The response surface methodology was used to determine the optimal process conditions using a Box-Behnken design in the removal of PQ, COD, and TOC. The independent variables used in this study were: H2O2 concentration (500, 1500, and 2500 mg L−1), hydraulic retention time (HRT) (20, 30, and 40 min), and Vt/Af (3:1, 6:1 and 9:1 cm3: cm2). Solution pH was adjusted to 2.8. The optimal conditions for the removal of PQ were: 2248.7 mg L−1 of H2O2, an HTR of 28 min, and Vt/Af of 3.4:1. These yielded a 99.9 % removal of PQ, 100 % removal of COD, and 96.7 % of TOC. Toxicity was 100 % removed with 700 mg L−1 of H2O2. CFD indicated operating fluid velocity and turbulence contributed to maintaining an adequate Fe2 +.

This study investigated the degradation of the herbicides diquat (DQ) and paraquat (PQ) by a solar photo-Fenton process that is mediated by Fe(III)-oxalate complexes at circumneutral pH = 6.5 in compound parabolic collectors (CPC)-type reactors. The photo-Fenton process operates efficiently at acidic pH, however, circumneutral operation was key to overcome drawbacks, such as acidification and neutralization steps, reagent costs, and the environmental footprint of chemical auxiliaries. This work revealed a remarkable reduction of total organic carbon for PQ (87%) and DQ (80%) after 300 min (at ca. 875 kJ L&minus, 1). Phytotoxicity assays confirmed that the treatment led to a considerable increase in the germination index for DQ (i.e., from 4.7% to 55.8%) and PQ (i.e., from 16.5% to 59.7%) using Cucumis sativus seeds. Importantly, treatment costs (DQ = USD$8.05 and PQ = USD$7.72) and the carbon footprint of the process (DQ = 7.37 and PQ = 6.29 kg CO2-Eqv/m3) were within the ranges that were reported for the treatment of recalcitrant substances at acidic conditions in CPC-type reactors. Life cycle assessment (LCA) evidenced that H2O2 and electricity consumption are the variables with the highest environmental impact because they contribute with ca. 70% of the carbon footprint of the process. Under the studied conditions, a further reduction in H2O2 use is counterproductive, because it could impact process performance and effluent quality. On the other hand, the main drawback of the process (i.e., energy consumption) can be reduced by using renewable energies. The sensitivity study evidenced that carbon footprint is dependent on the energy share of the local electricity mix, therefore, the use of more renewable electrical energy sources, such as wind-power and photovoltaic, can reduce greenhouse gases emissions of the process an average of 26.4% (DQ = 5.57 and PQ = 4.51 kg CO2-Eqv/m3) and 78.4% (DQ = 3.72 and PQ = 2.65 kg CO2-Eqv/m3), respectively. Finally, from the economic and environmental points of view, the experimental results evidenced that photo-assisted treatment at circumneutral pH is an efficient alternative to deal with quaternary bipyridinium compounds.

In most commercial electrochemical processes, only one of the two sides of the cell produces a desirable reaction, whereas the complementary reaction at the other side simply avoids interference with the target process and/or offers fast kinetics as not to limit it. An overview of several possible paired reaction schemes and their advantages is given, accompanied with specific thermodynamic and kinetic selection criteria, cell and reaction design strategies, and examples from the organic, inorganic, and environmental areas. The unnecessary nomenclature dispersion in this field (e.g., combined, concurrent, conjugate, convergent, coupled, divergent, dual, duet, linear, paired, parallel, simultaneous and synchronous electrochemical processes) is revised and a simple, consistent classification, as well as a homogeneous schematization system, is proposed.

Plaguicide pollution is a major problem in agricultural zones due to their intensive use to attain increased crop yields. In the present work commercial methyl parathion (MP), was electrochemically degraded in a divided H-type cell equipped with two boron doped diamond electrodes, BDDE and a Nafion cation exchange membrane. High removals (i.e., > 90%) of total organic carbon, TOC and of chemical oxygen demand, COD were obtained after 180 min at a current density, j of 5 mA/cm2 with specific energy consumption, Esp of ca. 200 kWh per kg of COD degraded. These results show that the anodic oxidation route may be an efficient alternative for MP degradation in polluted waters.

Water quality assessment typically includes the determination of chemical oxygen demand (COD) by oxidation of organic matter with Cr(VI) in an acidic medium followed by digestion. Unfortunately, the required reagents are harmful and the reaction times are rather long. We investigated earlier the use of H2O2 as a more environmentally friendly oxidizing agent to replace the hazardous chromates. In the present study, we have furthered this possibility by incorporating the use of H2O2 in the presence of UV light. A protocol has been devised and tested with standards and real samples that replaces toxic Cr(VI), halves the amount of silver sulfate required, and greatly reduces the necessary reaction time, thus yielding a faster and more environmentally sound method.

The use of soluble and highly oxidizing Ag(III) in the form of the tetrahydroxoargentate ion Ag(OH)

Scanning electron microscopy (SEM) is employed to monitor the surface morphology of polypyrrole films (PPy) grown on different working electrodes (i.e., vitreous carbon and Au (111)) under diverse experimental conditions (i.e., dynamic vs. static potential protocols) and anion dopants (i.e., I- and F-). The morphology of the electrosynthesized films includes rings (doughnuts) and microcontainers, and depends on the synthesis parameters such as the electropolymerization method, the nature of the substrate, the anion dopant, and the sequence of sandwich composite growth. The formation of well-defined rings and microcontainers is attributed to overoxidation occurring during the formation of F--doped PPy. It is possible to design microcontainers by controlling the overoxidation and degradation of the polymer surface.

A mechanism based on electrochemical, spectrophotometric and scanning electron microscopy (SEM) data in alkaline media is proposed for the generation of Ag(III) in the form of Ag(OH)4−. The formation of Ag(III) from Ag0 is a rather complex multistep process that involves several steps. The presence of soluble Ag(I) species as Ag(OH)2− is of paramount importance for the production of soluble Ag(OH)4−, whose decomposition time is shown to exceed 8 h.

The electrochemical elimination of the herbicide diquat dibromide (DQ) in an undivided electrochemical cell (Condiacell®-type cell) and an H-type cell (a divided electrochemical cell) using boron-doped diamond (BDD) electrodes is reported for the first time. The degradation of essentially 100% of the DQ present was achieved in the undivided electrochemical cell and ca. 92% in the H-type cell. Nearly 80% of the total organic carbon (TOC) and of the chemical oxygen demand (COD) were removed after 5 h of treatment at different current densities (i.e., 0.5, 1.0, and 1.5 mA/cm2 for the undivided cell, and 2.5, 5.0, and 7.5 mA/cm2 for the H-type cell) with a maximum specific energy consumption of approximately 150 kWh kg−1 of COD degraded in the undivided cell, and 300 kWh kg−1 of COD in the H-type cell. Energy consumption of about 0.30 kWh g−1 of TOC occurred in the undivided electrochemical cell and 2.0 in the H-type cell. In spite of obtaining similar percentages of DQ degradation and of COD and TOC removal, a smaller energy usage was required in the undivided cell since smaller current densities were employed. Best results were obtained with the undivided cell, since it required a smaller current density to obtain virtually the same percentage of DQ degradation and removal of COD and TOC. The results obtained herein show that the use of electrochemical advanced oxidation processes may be a good alternative for DQ degradation in polluted water.

Electrochemical degradation of phenol (PhOH) with simultaneous reduction of O2(g) to H2O2 in acidic media was performed in an H-type divided cell (500 mL), separated with a cationic membrane (Nafion 424). Boron-doped diamond (BDD) electrodes were used as anode and cathode. The study was divided into three stages: (a) Electroanalytical study of the oxygen reduction reaction (ORR) to H2O2 by hydrodynamic linear-sweep voltammetry with a BDD-RDE in acidic and alkaline solutions; (b) galvanostatic ORR to H2O2 at BDD electrode in acidic solution (unpaired system); (c) pairing the anodic PhOH degradation with the H2O2 cathodic production at BDD electrodes. The best production of H2O2 under our conditions with the unpaired system was 250.1 mg L−1 at 1.5 mA cm−2 after 540 min of electrolysis, the highest reported to date for BDD electrode in acidic media. Total mineralization of 100 mg L−1 of PhOH in the paired system required a higher current density (i.e., 2.5 mA cm−2); in spite of this, the process is one order of magnitude faster than any electrochemical process previously reported. © 2013 The Electrochemical Society. [DOI: 10.1149/2.027307jes] All rights reserved.

The aim of the present work was to characterize and treat a mature landfill leachate using a coagulation/flocculation process followed by a photo-Fenton oxidation treatment. The leachate was obtained from a landfill in Tetlama, Morelos (Mexico) during the drought season and was characterized in terms of its major pollutants. Considerable levels of chemical oxygen demand (COD), total carbon (TC) and NH4+ were identified, as well as high concentrations of Hg, Pb, and As. Other heavy metals such as Ni, Co, Zn, Cd, and Mn were detected at trace levels. The lethal concentration (LC50) of the leachate, evaluated on Artemia salina, was 12,161±11 mg/L of COD, demonstrating an antagonistic interaction among the leachate's components. The treatment of this effluent consisted of a coagulation-flocculation process using an optimal dose of FeCl3 · 6H2O of 300 mg/L. The supernatant was treated using a photo-Fenton process mediated with FeCl2 · 4H2O and H2O2 in a compound parabolic concentrator (CPC) photo-reactor operating in batch mode using an R ratio (R=[H2O2]/[Fe2+]) of 114. The global removal efficiencies after treatment were 56% for the COD, 95% for TC, and 64% for NH4+. The removal efficiencies for As, Hg, and Pb were 46%, 9%, and 85%, respectively.

Las ventajas y posibilidades de la Química en Microescala en México han sido presentadas por muchas personas en diversos foros y publicaciones. De los intentos tempranos para implementarla, sobresale el de la Universidad Nacional Autónoma de México en la década de los setenta. Por razones cuyo análisis queda fuera del alcance del presente artículo, ningún intento sobrevivió por mucho tiempo, excepto el de la Escuela Nacional Preparatoria-UNAM (uno de cuyos maestros —Miguel García Guerrero— ha impartido talleres a más de un millar de profesores).

Muchos contaminantes pueden convertirse en especies menos peligrosas mediante una transferencia de electrones. Estas transferencias pueden llevarse a cabo en interfases electrificadas (electrodos), ser directas o indirectas, oxidaciones o reducciones, usarse para tratar líquidos, gases, suelos, etc. En este artículo discutimos algunas aplicaciones y experimentos.

The paired production of ClO2 by reduction of ClO3- and oxidation of ClO2- is achieved in a divided cell. The highly acidic nature of the catholyte and the neutral conditions at the anolyte require an intermediate compartment to prevent their interaction, since passage of H3O+ from the former to the later would chemically produce ClO2. An anionic exchange membrane, AEM/fritted glass/AEM set up was effective in preventing proton migration. The production of ClO2 was spectroelectrochemically monitored in situ and in real time at its characteristic absorption wavelength (359 nm) by adapting a normal rectangular spectrophotometer quartz cell as the electrolytic cell inside a spectrophotometer. The corresponding yields are highly dependent on the applied potential: the cathodic production is favored as the potential approaches the rest potential of the catholyte, whereas the anodic production behaves the opposite. The highest overall yield after 30 min of reaction was ca. 10%.

Direct oxidation borohydride fuel cells are very attractive energy conversion devices. Silver has been reported as one of the few materials which can catalyze an 8-electron oxidation. Potential step amperometric pulse techniques to synthesize nanostructured silver material on flat glassy carbon electrodes is reported and significant differences with bulk silver deposit have been observed. The oxidation of borohydride ion on the silver particles occurs at -0.025 V vs. SCE and the potential decreases towards negative values at longer cycle times. The oxidation current also decreases with the number of cycles, suggesting that the silver active sites become partially blocked by oxidation products of borohydride. The electroactive area per unit electrode area of silver was relatively low for particles deposited using potential step amperometric techniques on glassy carbon (0.002 cm2 per cm-2) compared with the area found at a polycrystalline silver electrode (0.103 cm2 per cm-2).

A voltammetric characterization of a dental amalgam and simple solid metal amalgams and their applications for detecting low concentrations of Cu(II) ions in solution is presented. Dental amalgams display a series of oxidation peaks characteristic of the different metal phases present. A reaction between deposited copper and γ2-Sn7-8Hg phase which transforms into a η'-Cu6Sn5 phase has been proposed to explain the well defined oxidation peaks in the potential range of-0.2 to 0.1 V vs. SCE. Dental amalgams were not found suitable for detecting Cu(II) ions in solution, due to the interference between the γ2-Sn7-8Hg oxidation peak and the copper stripping peak. Instead of a dental amalgam a silver amalgam, i.e, Ag-Hg, is recommended as a better option for detecting Cu(II) ions in solution at low concentrations. It yields a well defined oxidation peaks for copper stripping without having interfering oxidation peaks for the amalgam phase oxidation.

A critical review is offered concerning the different sources, effects, concentrations, removal methods, speciation, and analysis of metals (e.g., Al, Ca, Cd, Cu, Fe, Pb, Mg, Mn, Ni, K, Na, and Zn) present in a wide variety of alcoholic beverages.

The selective recovery of Cd from simulated spent nickel–cadmium battery solutions was achieved using a Cd working electrode in a laboratory cell with a three-electrode arrangement in hydrochloric, nitric, and sulfuric acids. The latter was selected for further study of the recovery step. Nitrate media were found to be unsuitable for Cd recovery since nitrates are reduced at the required deposition potentials. Cd(II) deposition on Cd electrodes is favored in sulfate or chloride media since it occurs at a potential some 200 mV less negative than that of Ni(II). A good percent Cd recovery (>90%) with high selectivity (approximately 0% Ni) and a reasonably high current efficiency (>80%) can be achieved under appropriate conditions. The irreversible nature of Ni(II) reduction provides the necessary framework to achieve such a selective separation.

Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8e9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl2 gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given. 2008 Elsevier Ltd. All rights reserved.

A method for assaying a flowing gas mixture for SO2(g) and SO3(g) is described. The proof-of-concept for this method presented here uses the quantitative reaction of SO3(g) with CaC2O4(s) at 325 °C to produce CO2(g). The gas mixture is passed first through a plug of CaC2O4 and then through a series of two optical cells. SO2(g) is measured directly at one cell by UV spectrometry, and SO3(g) is measured indirectly as CO2(g) at the second cell by IR spectrometry. Good correlation coefficients were found for both analytes. Potential interference by SO2 on the IR response of CO2 can be neglected within a 1% error marginexcept when the ratio CO2/SO2 is very small. A summary of key analytical methods for the analysis of sulfur oxides is given.

Concentrations of metals such as copper in alcoholic beverages must be strictly regulated due to negative effects ranging from beverage spoilage and hazing, to sensorial and health consequences. In this paper, a voltammetric alternative is presented for the analysis of copper in tequila, a Mexican spirituous alcoholic beverage. Anodic Stripping Voltammetry is applied and the standard addition method is used to quantify copper in this beverage at concentrations commonly present in tequila (

This paper reports the capacity of polypyrrole to reduce toxic hexavalent chromium (Cr(VI)). The influence of using different electrolytes during the polymer's synthesis has been studied. To improve the reduction of Cr(VI), the parameters considered were the polypyrrole morphology and the amount of conducting polymer. Polypyrrole obtained by cyclic voltammetry at a low sweep rate using KBr as supporting electrolyte showed better performance for Cr(VI) reduction compared to coatings obtained by constant potential or cyclic voltammetry at high sweep rates.

We report the use of a derivative method to estimate the rate of ozone, oxygen and hydrogen production at a Pt anode/graphite cathode laboratory system as a function of the gas volumes produced, using the ideal gas law with the corresponding pressure corrections. The rates were evaluated at different applied potentials and sulfuric acid concentrations.

A method for establishing the kinetics and products of the electrochemical degradation of hexachlorobenzene (HCB) is described. One plausible way of reducing HCB´s toxicity is through cathodic dehalogenation. The characterization of products formed during the electrochemical reduction and the reaction kinetics are both reported. Pentachlorobenzene (PCB), tetrachlorobenzene (TCB) and trichlorobenzene (TriCB) were identified among the degradation products by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The kinetics is analyzed under different electrolysis conditions.

The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with reticulated vitreous carbon (RVC) electrodes;this reduction can be accomplished by the application of relatively small potentials. Treatment of synthetic samples and field samples (from an electrodeposition plant) results in final Cr(VI) concentrations of 0.1 mg/L (i.e., the detection limit of the UV-vis characterization technique used here) in 25 and 43 min, respectively. Such concentrations comply with typical environmental legislation for wastewaters that regulate industrial effluents (at presenttime = 0.5 mg/L for discharges). The results show the influence of the applied potential, pH, electrode porosity, volumetric flow, and solution concentration on the Cr(VI) reduction percentage and on the required electrolysis time. Values for the mass transfer coefficient and current efficiencies are also obtained. Although current efficiencies are not high, the fast kinetics observed make this proposed treatment an appealing alternative. The lower current efficiency obtained in the case of a field sample is attributed to electrochemical activation of impurities. The required times for the reduction of Cr(VI) are significantly lower than those reported elsewhere.

Paired (simultaneous) electrochemical processes can increase energy savings in selected cases by using the reactions at both electrodes of an electrochemical cell to perform a desired process, as is the case in the commercially successful chlor-alkali process. In the demonstration described herein, simultaneous blue electrochemiluminescence (ECL) is obtained with luminol in a basic medium in a divided electrochemical cell. ECL is obtained in the anolyte through the direct oxidation of luminol, the reaction products of which interact with H2O2 in the vicinity of the electrode to yield an excited emitting species. ECL is also obtained in the catholyte through an indirect, mediated process involving the initial reduction of ClO2– to ClO–, which then reacts with luminol and H2O2 to produce the excited emitting species. The co-reactant (H2O2) is needed to complete the reaction sequences in both compartments of the cell. This ECL phenomenon is visible to the naked eye in a darkened room at a distance of up to 5 m.

We present a demonstration involving the oxidative photobleaching of a raspberry juice dye under visible laser light irradiation using the semiconductor titanium dioxide. A plausible interpretation of the phenomenon is discussed that aids in the understanding of semiconductor energetics and the nature of light.

Many soils throughout the world are contaminated with metal salts of diverse toxicity. We have developed an experiment to demonstrate the removal of a metal from an insoluble surrogate soil pollutant, CuCO3·Cu(OH)2, by complexation followed by the simultaneous electrochemical recovery of the ligand (i.e., EDTA) and of the metal in its elemental form (i.e., Cu0). We have calculated speciation diagrams to predict appropriate conditions and to interpret the results.

Copper(I) oxide photoresponsive layers are prepared on copper surfaces (e.g., U.S. pre-1982 pennies) by simple thermal, chemical, and electrochemical procedures. An easily measurable photovoltage (up to 100 mV) is obtained in each case under visible light illumination.

The existence of solvated electrons has been known for a long time. Key methods for their production (i.e., photoionization of reducing ions, water radiolysis, and the reaction between H· and OH−) are unsuitable for most school laboratories. We describe a simple experiment to produce liquid ammonia and solvated electrons using materials commonly available, without the dangers associated with the use of solid Na or K metal.