ABSTRACT
With the increasing concern about climate change and the energy crisis, the use of reverse electrodialysis (RED) to utilize salinity gradient power (SGP) has drawn attention as one of the promising renewable energy sources. However, one of the critical issues in RED processes is membrane fouling and channel blockage, which lead to a decrease in the power density. Thus, this study aims to improve our understanding of SGP generation by using RED by investigating the effect of pretreatment on the RED performance. Experiments were conducted by using a laboratory-scale experimental setup for RED. The low-salinity and high-salinity feed solutions were brackish water reverse osmosis (BWRO) brine from a wastewater reclamation plant, and a NaCl solution simulating seawater desalination brine. Several pretreatments were applied to the RED process, such as cartridge filter (CF), microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), activated filter media (AFM), and granular activated carbon (GAC). The results indicate that the open-circuit voltage (OCV) and the power density were similar, except for in the NF pretreatment, which removed the dissolved ions to increase the net SGP. However, the pressure in the RED stack was significantly affected by the pretreatment types. The excitation-emission matrix (EEM) fluorescence spectroscopy and the parallel factor analysis (PARAFAC) quantified the organic compounds that are related to the stack pressure. These results suggest that the removal of both colloidal and organic matters by pretreatments is crucial for improving the RED performance by reducing the pressure that is increased in the RED stack.
ABSTRACT
High-quality and reproducible perovskite layer fabrication routes are essential for the implementation of efficient planar solar cells. Here, we introduce a sequential vapor-processing route based on physical vacuum evaporation of a PbCl2 layer followed by chemical reaction with methyl-ammonium iodide vapor. The demonstrated vapor-grown perovskite layers show compact, pinhole-free, and uniform microstructure with the average grain size of ~ 320 nm. Planar heterojunction perovskite solar cells are fabricated using TiO2 and spiro-OMeTAD charge transporting layers in regular n-i-p form. The devices exhibit the best efficiency of 11.5% with small deviation indicating the high uniformity and reproducibility of the perovskite layers formed by this route.
ABSTRACT
The study of heterogeneous catalytic reactions remains a major challenge because it involves a complex network of reaction steps with various intermediates. If the vibrational spectra of individual molecules could be monitored in real time, one could characterize the structures of the intermediates and the time scales of reaction steps without ensemble averaging. Surface-enhanced Raman scattering (SERS) spectroscopy does provide vibrational spectra with single-molecule sensitivity, but typical single-molecule SERS signals exhibit spatial heterogeneities and temporal fluctuations, making them difficult to be used in single-molecule kinetics studies. Here we show that SERS can monitor the single-molecule catalytic reactions in real time. The surface-immobilized reactants placed at the junctions of well-defined nanoparticle-thin film structures produce time-resolved SERS spectra with discrete, step-transitions of photoproducts. We interpret that such SERS-steps correspond to the reaction events of individual molecules occurring at the SERS hotspot. The analyses of the yield, dynamics, and the magnitude of such SERS steps, along with the associated spectral characteristics, fully support our claim. In addition, a model that is based on plasmonic field enhancement and surface photochemistry reproduces the key features of experimental observation. Overall, the result demonstrates that it is possible, under well-controlled conditions, to differentiate the chemical and physical processes contributing to the single-molecule SERS signals, and thus shows the use of single-molecule SERS as a tool for studying the metal-catalyzed organic reactions.
ABSTRACT
BACKGROUND: Affordable water disinfection is key to reducing the waterborne disease experienced worldwide where resources are limited. A simple electrochemical system that can generate chlorine as a disinfectant from the electrolysis of sodium chloride is an appropriate technology to produce clean water, particularly if driven by solar energy. This study examined the affordability of an electrochemical chlorine generation system using solar energy and developed the necessary design information for its implementation. METHOD: A two-electrode batch reactor, equipped with commercial IrO(2)-coated electrodes and a solar panel (approximate area 0.2 m(2)), was used to produce chlorine from a 35g/L solution of NaCl. RESULTS: Within 1 h, sufficient chlorine (0.8 g) was generated to produce clean drinking water for about 80 people for 1 day (target microorganism: Escherichia coli; daily drinking water requirement: 2 L per person; chlorine demand: 4 mg/L; solar power: 650 W/m(2) in Seoul, Korea. Small household batteries were demonstrated to be a suitable alternative power source when there is insufficient solar irradiation. Using a 1 m(2) solar panel, the reactor would take only 15 min in Seoul, Korea, or 7 min in the tropics (solar power 1300 W/m(2)), to generate 1 g of chlorine. CONCLUSION: The solar-powered electrochemical chlorine generation system for which design information is provided here is a simple and affordable way to produce chlorine with which to convert contaminated water into clean drinking water.
