Novel electrochemical method to activate biochar derived from spent coffee grounds for enhanced adsorption of lead (Pb)

Biochar (BC) has received much attention as a promising adsorbent that can be exploited to remove heavy metals in domestic and wastewater. The adsorption capacity of BC is, however, relatively low compared to that of conventional adsorbents, and its performance is inversely proportional to its stability. Various chemical and physical methods have been tried to address these limitations, but BC activation still generates too much acidic or alkaline wastewater. Here we propose a novel electrochemical method and compare its lead (Pb) adsorption capacity to that of acid- and alkaline-based approaches. We found that electrochemical activation significantly increased the number of hydroxyl and carboxylic groups on the BC surface, which led to an increase in Pb absorption from 27 % (pristine BC) to 100 % because the oxygenated-functional groups contributed to the adsorption of Pb. Pb capacity was 1.36, 2.64, 3.31, and 5.00 mg g^-1, corresponding to pristine, acidic, alkaline, and electrochemical activation, respectively. The Pb absorption capacity of electrochemically activated BC was also higher than that of acid- and alkali-activated BC, which we attribute to the observed increases in oxygen ratio and surface area. Moreover, the adsorption rate of BC after electrochemical activation was 190 times faster and its capacity was 2.4 times higher than that of pristine BC. These findings show that the electrochemical activation of BC results in greater adsorption capacity than conventional methods.

Electrochemical reactions of highly active nitroxyl radicals with thiol compounds

Nitroxyl radicals are known to electrochemically oxidize thiols as well as alcohols and amines. In this study, a preliminary investigation of the electrochemical reaction of thiols with 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO), 2-azaadamantane N-oxyl (AZADO), and nortropine N-oxyl (NNO), which are highly active due to their bicyclo structures, for use in electrochemical analysis was performed and the results were compared with those for a typical nitroxyl radical compound, 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO). Mercaptopropane sulfonic acid (MPS) was used as a model compound to investigate the electrochemical response in aqueous solution. In addition, electrochemical detection of glutathione, a biological thiol molecule, was performed.

Study on electrochemical reduction mechanisms of iron oxides in pipe scale in drinking water distribution system

Iron release from pipe scale is an important reason for water quality deterioration in drinking water distribution systems (DWDS) globally. Disruption of pipe scale, release and transformation of iron compounds are hot topics in the field of water supply. The aim of this study is to determine whether and how ferric components in pipe scale be reduced under anoxic condition. In this study, new investigation approaches were applied, which include simplifying the complex scale into electrode pairs, developing novel simulating reactors and conducting tailored electrochemical assays. A galvanic cell reactor with anode of metallic iron (Fe⁰) and various cathode made of certain iron oxide (FeO_x) was firstly developed to simulate the complex niche and components of pipe scale. Electrochemical methods were used to study the reduction characteristics of scale. The results proved that reduction of iron oxide scale did occur under anoxic condition. Electromotive forces between various electrodes match the Nernst Equation quite well. As main components in pipe scale, lepidocrocite (γ-FeOOH) was found to be the most reducible iron oxide but at low rate, while goethite (α-FeOOH) has weak reducibility but can be quickly reduced. As a result of electrochemical reactions, goethite in pipe scale was transformed into magnetite (Fe₃O₄). By these means, electrochemical reaction mechanisms of pipe scale disruption were revealed, which is helpful to restrain pipe corrosion and water deterioration in DWDS.

Ultrasonic-assisted synthesis of porous S-doped carbon nitride ribbons for photocatalytic reduction of CO2

A series of porous S-doped carbon nitride ribbons (PSCN) were prepared by one-pot hydrothermal and sonochemical synthesis techniques. The morphologies and nanostructures of the catalysts were characterized by SEM, XRD and IR, which confirmed the pristine graphitic structures of carbon nitrides retained in the products. Due to sonication treatment, PSCN has porous structures in the thin ribbon and larger specific surface areas (PSCN 43.5 m²/g, SCN 26.6 m²/g and GCN 6.5 m²/g). XPS and elemental mappings verified that sulfur atoms were successfully introduced into the carbon nitride framework. Diffuse reflectance spectroscopy (DRS) results showed S-doping in the carbon nitride reduced the bandgap energy and enhanced their capability of the utilization of visible light, which contributed to higher photo-generated current. Photoluminescence (PL) analysis indicates the recombination of photogenerated carriers was suppressed in PSCN. Moreover, the photocatalytic performance showed that S-doping and porous and thin ribbon nanostructures may effectively boost the CO₂ reduction rate (to as much as 5.8 times of GCN) when illuminated byvisible light (>420 nm) without the need of sacrificial materials. The preliminary mechanisms of the formation of PSCN and its applications in photocatalytic CO₂ reduction are proposed. It highlights the potential of the current technique to produce effective, nonmetal-doped carbon nitride photocatalysts.

Design of reduced graphene oxide coating carbon sub-microspheres hierarchical nanostructure for ultra-stable potassium storage performance

The development of high-performance carbon-based anode materials is still a significant challenge for K-ion storage. In our work, we designed reduced graphene oxide coating carbon sub-microspheres hierarchical nanostructure (CS@RGO) hierarchical nanostructure via a simple freeze-drying and subsequent pyrolysis as anode for K-ion batteries (KIBs), which presented an excellent electrochemical performance for K-ion storage, with a reversible specific capacity of 295 mAh g^-1 after 100 cycles at 100 mAh g^-1. Even at a high current density of 1 A g^-1, our CS@RGO still achieves ultra-stable K-ion storage of 200 mAh g^-1 at 1 A g^-1 after 5000 cycles almost without capacity fade. According to the galvanostatic intermittent titration technique result, the CS@RGO hybrid receives a high average diffusion coefficient of 7.35 × 10^-8 cm² s^-1, contributing to the rapid penetration of K-ion, which facilitates the enhancement of electrochemical performance for KIBs. Besides, we also use Raman spectra to investigate the electrochemical behavior of our CS@RGO hybrid for K-ion storage and confirm the reaction process. We believe that our work will offer the opportunity to enable ultra-stable carbon-based materials by the structure design in the K-ion battery field.

Self-Healing, Self-Adhesive and Stable Organohydrogel-Based Stretchable Oxygen Sensor with High Performance at Room Temperature

With the advent of the 5G era and the rise of the Internet of Things, various sensors have received unprecedented attention, especially wearable and stretchable sensors in the healthcare field. Here, a stretchable, self-healable, self-adhesive, and room-temperature oxygen sensor with excellent repeatability, a full concentration detection range (0-100%), low theoretical limit of detection (5.7 ppm), high sensitivity (0.2%/ppm), good linearity, excellent temperature, and humidity tolerances is fabricated by using polyacrylamide-chitosan (PAM-CS) double network (DN) organohydrogel as a novel transducing material. The PAM-CS DN organohydrogel is transformed from the PAM-CS composite hydrogel using a facile soaking and solvent replacement strategy. Compared with the pristine hydrogel, the DN organohydrogel displays greatly enhanced mechanical strength, moisture retention, freezing resistance, and sensitivity to oxygen. Notably, applying the tensile strain improves both the sensitivity and response speed of the organohydrogel-based oxygen sensor. Furthermore, the response to the same concentration of oxygen before and after self-healing is basically the same. Importantly, we propose an electrochemical reaction mechanism to explain the positive current shift of the oxygen sensor and corroborate this sensing mechanism through rationally designed experiments. The organohydrogel oxygen sensor is used to monitor human respiration in real-time, verifying the feasibility of its practical application. This work provides ideas for fabricating more stretchable, self-healable, self-adhesive, and high-performance gas sensors using ion-conducting organohydrogels.

Role of carbon fiber electrodes and carbonate electrolytes in electrochemical phenol oxidation

In-situ chemical oxidation (ISCO) requires an injection of oxidants into a contaminated site. However, the oxidants decompose and react with contaminants during transport to the contaminated region, which causes oxidant over-consumption. In-situ oxidant generation can solve this problem, and electrochemical methods can be applied to achieve this. Electrochemical oxidation is highly dependent on electrode material type. In this study, we evaluated graphite and carbon fiber as candidates for electrochemical oxidant generation and phenol as the model compound. The carbon fiber anode oxidized the phenol more effectively than graphite, with removal proportional to the applied current. Carbonate electrolytes were more effective at oxidizing phenols than sulfate electrolytes. The faster carbon fiber anode phenol oxidation is due to its large surface area. Carbonate radicals in the carbonate electrolyte contribute to phenol oxidation as well as further intermediate oxidation. The carbon fiber cathode was not an effective phenol oxidizer even though it generated more hydrogen peroxide. This is because there was no catalyst to transform the hydrogen peroxide into hydroxyl radicals. Results indicate that electrochemical oxidation using carbon fiber is an effective method for treating phenol found in groundwater with high concentrations of (bi)carbonate.

Effect of Tungsten Nanolayer Coating on Si Electrode in Lithium-ion Battery

Tungsten (W) was coated onto a silicon (Si) anode at the nanoscale via the physical vaporization deposition method (PVD) to enhance its electrochemical properties. The characteristics of the electrode were identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis, and electron probe X-ray microanalysis. With the electrochemical property analysis, the first charge capacities of the W-coated and uncoated electrode cells were 2558 mAh g^- 1 and 1912 mAh g^- 1, respectively. By the 50th cycle, the capacity ratios were 61.1 and 25.5%, respectively. Morphology changes in the W-coated Si anode during cycling were observed using SEM and TEM, and electrochemical characteristics were examined through impedance analysis. Owing to its conductivity and mechanical properties from the atomic W layer coating through PVD, the electrode improved its cyclability and preserved its structure from volumetric demolition.

Research on metallic iron for environmental remediation: Stopping growing sloppy science

Research on using metallic iron (Fe(0)) for environmental remediation has boomed during the passed two decades. Achieved results have established filtration on Fe(0) packed beds as an efficient technology for water treatment at several scales. However, the further development of Fe(0)-based filtration systems is impaired by useless discussion on the mechanism of contaminant removal. However, the whole discussion becomes superfleous while properly considering the difference between a chemical and an electrochemical reaction. This note ends the discussion and suggests practical ways to avoid the further propagation of the mistake.

Optimization of electrochemical reaction for nitrogen removal from biological secondary-treated milking centre wastewater

In order to remove the residual nitrogen from the secondary-treated milking centre wastewater, the electrochemical reaction including NH4-N oxidation and NOx-N reduction has been known as a relatively simple technique. Through the present study, the electrochemical reactor using the Ti-coated IrO2 anode and stainless steel cathode was optimized for practical use on farm. The key operational parameters [electrode area (EA) (cm(2)/L), current density (CD) (A/cm(2)), electrolyte concentration (EC) (mg/L as NaCl), and reaction time (RT) (min)] were selected and their effects were evaluated using response surface methodology for the responses of nitrogen and colour removal efficiencies, and power consumption. The experimental design was followed for the central composite design as a fractional factorial design. As a result of the analysis of variance, the p-values of the second-order polynomial models for three responses were significantly fit to the empirical values. The nitrogen removal was significantly influenced by CD, EC, and RT (p < .05), whereas colour removal was significantly governed by EA, CD, RT, the interaction of EA and EC (p < .05). For higher efficiency of nitrogen removal over 90%, the combination of [EA, 20 cm(2)/L; CD, 0.044 A/cm(2); EC, 3.87 g/L as NaCl; RT, 240 min] was revealed as an optimal operational condition. The investigation on cathodic reduction of NOx-N may be required with respect to nitrite and nitrate separately as a future work.

Technique for Determining Fluids Motion Characteristics in the Vicinity of Ferromagnetic Solids Under Magneto-Chemical Treatment

We report on new technique for determining and visualization of fluids motion in the vicinity of magnetized ferromagnetic surfaces under chemical dissolution and autocatalytic formation of spatiotemporal structures. The proposed method of obtaining data on the motion of fluids does not require the use of additional inclusions and allows to avoid the distortions caused by such inclusions or other changes in the nature of the reaction. The developed technique allows to obtain both the integral dependences and time frequencies distributions of the fluids over the volume of the medium under investigation.

Design, fabrication, and applications of in situ fluid cell TEM

In situ fluid cell TEM is a powerful new tool for understanding dynamic processes during liquid phase chemical reactions, including mineral formation. This technique, which operates in the high vacuum of a TEM chamber, provides information on crystal structure, phase, morphology, size, aggregation/segregation, and crystal growth mechanisms in real time. In situ TEM records both crystal structure and morphology at spatial resolutions down to the atomic level with high temporal resolution of up to 10(-6)s per image, giving it distinct advantages over other in situ techniques such as optical microscopy, AFM, or X-ray scattering or diffraction. This chapter addresses the design, fabrication, and assembly of TEM fluid cells and applications of fluid cell TEM to understanding mechanisms of mineralization.