Photochemical Methods Research Articles

The Application of Porphyrins and Their Analogues for Inactivation of Viruses

The problem of treating viral infections is extremely relevant due to both the emergence of new viral diseases and to the low effectiveness of existing approaches to the treatment of known viral infections. This review focuses on the application of porphyrin, chlorin, and phthalocyanine series for combating viral infections by chemical and photochemical inactivation methods. The purpose of this review paper is to summarize the main approaches developed to date in the chemical and photodynamic inactivation of human and animal viruses using porphyrins and their analogues and to analyze and discuss the information on viral targets and antiviral activity of porphyrins, chlorins, of their conjugates with organic/inorganic compounds obtained in the last 10–15 years in order to identify the most promising areas.

Synthesis of Ag2O Coated TiO2 Nanoparticles by Sonochemically Activated Methods for Enhanced Photocatalytic Activities

TiO2 nanoparticles were successfully synthesized by sol-hydrothermal (SH) method using sonochemically activated precursors. Sonochemical activation yields product bearing desirable crystallinity at relatively lower temperature in comparison with conventional SH method. Glycine was used as a mineralizer in the ultrasound activation process which suppress the formation of brookite phase (of TiO2) observed in the sonochemically activated sample. TiO2 sample synthesized in presence of Glycine [SA-SH(GLY)] was further modified by coating Ag2O nanoparticles by sonochemical (SD-Ag) and photochemical (PD–Ag) methods. The deposition by sonochemical method yields product with better crystallinity, high surface area and improved optical properties. Morphological investigations confirm the formation of rounded cube and cube shaped Ag2O particles in the sonochemical and photochemical methods respectively. Photoactivities of the catalysts were investigated in terms of degradation of methyl orange (MO) dye contaminated aquatic waste. Equilibrium of MO photo-degradation was achieved within about 90 min with removal efficiencies of 99.9, 67.1, and 44.4% for SD-Ag, PD–Ag, and SA-SH-(GLY) samples, respectively at 50 mg/L of MO dye concentration. The high photo-catalytic activity of SD-Ag sample was observed for MO photo-degradation, which is attributed to the improved properties like crystallinity, visible light absorption capacity and higher surface area. Advance route of sonochemical activation process for synthesis of Ag2O co-capped TiO2 nanocomplex for MO photo-degradation

Photodegradation kinetics, mechanism and aquatic toxicity of deltamethrin, permethrin and dihaloacetylated heterocyclic pyrethroids

Photochemical methods attracted much research interests for their high-efficiency and low secondary pollution. Decomposition of synthetic pyrethroids, the fourth major group of insecticides in use worldwide, was also of great significance due to their possible environmental risks. The photodegradation of deltamethrin, permethrin and dihaloacetylated heterocyclic pyrethroids in methanol/acetone = 9/1 (by volume) by a 400 W mercury lamp was examined. The t1/2 of tested pyrethroids was less than 25 min, except for cis-permethrin with a t1/2 of up to 50 min. The trans-isomer of permethrin and compound DCA-01 with a smaller t1/2 might be more susceptible to degradation than their cis-isomer. Besides, the photodegradation of pyrethroids was divided into twelve pathways including isomerization, ester hydrolysis, ester bond cleavage, CO bond cleavage, 3,3-dimethylacrylate formation, double bond break, C1-C3 bond cleavage in cyclopropyl, reductive dehalogenation, decarboxylation, nucleophilic reagents attack on lone pair electrons on oxygen atoms in the phenyl ether, cyano hydrolysis, and halogenated hydrocarbon hydrolysis. The ECOSAR program displayed that pyrethroids and most of their photodegradation products were toxic to fish, daphnid, green algae. Particularly, some photodegradation products were more harmful to aquatic organisms than their parents.

Use of Ultrasound and Ultraviolet Radiation in Hybrid Methods for Water Disinfection

Hybrid photochemical methods are considered for water disinfection in which treatment with ultraviolet (UV) and ultrasonic (US) radiations are combined (US/UV) and applied consecutively or simultaneously; the use of catalysts is also included. The literature survey shows that inactivation of pathogenic microorganisms in aquatic media by high-frequency US (>100 kHz) has not been studied adequately, whereas only low-frequency (<100 kHz) US and low-pressure mercury vapor lamps (254 nm) were used in hybrid US/UV methods. Irradiation with high-frequency US generates reactive oxygen species (primarily hydroxyl radicals) in greater proportions, and a synergistic effect is observed when UV irradiation is included in treatment. Therefore, the use of high-frequency US and mercury-free UV sources in hybrid oxidizing systems, including those based on Fenton-like processes, is promising for intensifying disinfection processes and improving their effectiveness.

The influence of pH and current density on an UV254 photo-assisted electrochemical process generating active chlorine and radicals for efficient and rapid ciprofloxacin mineralization compared to individual techniques

A photo-assisted electrochemical process is herein evaluated with the aim of improving and accelerating the degradation and mineralization of Ciprofloxacin (CIP) in aqueous media, in comparison with single electrochemical or photochemical methods. Active chlorine species are initially electro-generated on a synthesized (Pechini method) Ti/TiO2-RuO2 DSA, and subsequently fragmented homolitically using UVC irradiation under very low fluency rate (3300 μW cm−2, λ = 254 nm) to produce radicals with higher oxidation potentials compared to the original active chlorine. A faster CIP degradation (5 min) and higher mineralization is obtained in the coupled system against the individual techniques. Variations of pH and current density in the UV-assisted electrochemical process reveal that a similar degradation rate is obtained during 60 min for pH 6 and 9 due to the co-existence of HOCl and OCl− species in this range of pH, leading to the possible production of highly reactive radicals (e.g. HOaq•, Claq•, Oaq-•) after chlorine species fragmentation. The highest total organic Carbon (TOC) removal was obtained at pH = 6 (70 % in 60 min), where the highest HOCl concentration is observed, thus, enhancing the HOaq• production. The contaminant degradation and mineralization strongly depend of the radicals formed from the irradiation of chlorine species, which on its turn rely on the redox couples formed as a function of pH: 3 (HOCl + Cl2), 6 and 9 (HOCl + OCl−). Mechanisms are proposed for these homolysis reactions, while the degradation pathway of CIP is rationalized using HPLC analyses during 60 min of electrolysis.

A REVIEW STUDY ON ORGANIC WASTE MANAGEMENT BY GREEN CHEMISTRY

Purpose: The review article discusses the title topic describing mostly authors' work on green chemical, photochemical and electrochemical methods for the treatment of organic wastes present in different matrices. Emphasis is mainly placed on the importance of the matrix, associated compounds and the method's selection.&#x0D; Methodology: Different green methods of treatment for organic waste available are reviewed with an outline of scientific principles. Different case studies, from the authors, work, involving the treatment of organic waste present in different matrices are discussed. Available green chemical, photochemical, and electrochemical methods are reviewed, and results obtained are described and discussed. The rationale behind the choice of method was discussed in detail. Laboratory to plant adoption and the considerations therein are considered.&#x0D; Main findings: The selection of treatment method depends on the nature of the organic waste and the matrix in which it is present. This has been brought out in the study. Advanced oxidation and electrochemical oxidation processes are practically useful methods for waste treatment and discussed with case studies. The optimization of the advanced oxidation process is still an empirical approach. It needs a sound scientific base.&#x0D; Applications of the work: The case studies described in the paper enable the proper choice of treatment method among several available options. The study covers the essential green chemical techniques, viz., photochemical and electrochemical techniques.&#x0D; The novelty of the work: Many of the organic substrates subjected to treatment study were rarely reported in the open literature. Laboratory to plant scale development and the factors involved therein have been brought in many places.

Removal Organic Matter and of Phosphates Using Photochemical and Biological Methods for the Treatment of Municipal Wastewater in Peru

In this work, the percentage of removal of organic matter and phosphates from municipal wastewater of the Wastewater Treatment Plant (WWTP) Puca Puca, Ayacucho Region, Peru was determined by applying the combined method of photochemical water treatment and biological, which consists of coupling the photolysis process and the microalgae culture technique using Chlorella sp. The experience was carried out at the laboratory level using a photoreactor with an ultraviolet (UV) lamp for the photolysis process and a set of bioreactors that were illuminated with a light emitting diode (LED) lamp and continuously injected with CO2 from the air and a pure gas system during the biological process. Finally, with the application of the integrated photochemical and biological method, it was possible to reduce the organic matter of the municipal wastewater of the Puca Puca WWTP from 226 to 102.6 mg/L (54.60%) and from 93 to 55.17 mg/L (40.68%) for chemical and biochemical oxygen demand respectively; and phosphates from 6.8 to 4.1 mg/L (33.82%). A similar performance was observed in the cultivation of microalgae with wastewater without prior treatment with Photolysis. In this case, the decrease in chemical and biochemical oxygen demand was from 226 to 90.9 mg/L (59.78%) and from 93 to 48.78 mg/L (47.55%) respectively, and phosphates from 6.8 to 4 mg/L (41.18%).

Oxidation of styrene oxide via chemical and photochemical methods using TiO2-CeO2-V2O5 catalysts

This work reports the preparation of the TiO2-CeO2 (TiCe) catalytic support of V2O5 catalysts, which was tested in the oxidation process of styrene oxide via chemical and photochemical methods. The TiCe-V2O5 catalytic support was prepared by the co-precipitated method from the individual metal oxides, varying the amount of vanadium oxide by 3, 6, and 10 % mol with respect to the support. The obtained catalysts were characterized by different spectroscopies, as well as by the N2 adsorption-desorption technique. The catalytic reaction test was carried out in the liquid phase during 120 min with/without ultraviolet light irradiation at 50 °C. There was no V2O5 effect on the surface area, pore volume, and pore diameter since all catalysts had similar textural values. In all samples the structures identified by X-ray diffraction were the Anatase phase and CeO2 in the cubic phase. XPS results revealed the formation of surface carbonate species, which were also identified by infrared spectroscopy. The conversion rate was better when employing ultraviolet light, and the rate increased as the V2O5 amount rose. The main reaction products were 2-phenylethanol and 1-phenylethanol. However, a low amount of benzaldehyde was detected. The selectivity to the desirable product (2-phenylethanol) increased when the reaction was irradiated with UV light and the catalyst contained a higher amount of vanadium. It was observed that the effect of UV radiation on the electric mobility produces an acceleration of the reaction to 2-phenylethanol, avoiding the 1-phenylethanol formation. The bandgap value decreased as the vanadium oxide amount increased, boosting the electric mobility.

Electron Transfer in Nitrogenase.

Nitrogenase is the only enzyme capable of reducing N2 to NH3. This challenging reaction requires the coordinated transfer of multiple electrons from the reductase, Fe-protein, to the catalytic component, MoFe-protein, in an ATP-dependent fashion. In the last two decades, there have been significant advances in our understanding of how nitrogenase orchestrates electron transfer (ET) from the Fe-protein to the catalytic site of MoFe-protein and how energy from ATP hydrolysis transduces the ET processes. In this review, we summarize these advances, with focus on the structural and thermodynamic redox properties of nitrogenase component proteins and their complexes, as well as on new insights regarding the mechanism of ET reactions during catalysis and how they are coupled to ATP hydrolysis. We also discuss recently developed chemical, photochemical, and electrochemical methods for uncoupling substrate reduction from ATP hydrolysis, which may provide new avenues for studying the catalytic mechanism of nitrogenase.

Synthesis and characterization of nanoparticles using egg shell

Nano particles (NPs) have been the subject of great interest for the researcher topic of their interesting properties (e.g., size and shape depending optical, antimicrobial, and electrical properties). There are various variety of preparation techniques have accounted for the synthesis of NPs; which include, laser ablation, gamma irradiation, electron irradiation, chemical reduction, photochemical methods, microwave processing, and biological synthetic methods etc. As a part of research, we tried to work on the biochemical product composite like the egg shell powder and the titanium dioxide nano particle synthesis and studying the particle size. The composition of both the components and their physicochemical properties were studied at nano particle level. The salinity of the water was reduced using the column studies with the immobilized beads with the egg shell nano particles. The analysis of the particles with the help of analyzing instruments like the scanning electron microscope (SEM), Tunneling electron microscope (TEM), Fourier transform (FTIR), XRD. With the help of these analyzing methods the nano particle size was characterized and the properties were studied.

Synthesis and characterization of Ni doped TiO2 nanoparticles and its application for the degradation of malathion

Nanoparticles have been the subject of wide research with interesting properties like size and shape depending optical and electrical properties. Varieties of preparation techniques have accounted for the synthesis of nanoparticles including laser treatments, chemical reduction, photochemical methods and biologically related synthetic methods, electron irradiation. As a part of the research, the size of the nano particles was analyzed using various methodologies. The analysis of the particles with the help of analyzing instruments like the scanning electron microscope (SEM), Tunneling electron microscope (TEM), Fourier transform (FTIR), XRD. With the help of these analyzing methods the nanoparticle size was characterized and the properties were studied. The work presents the methodology of the removal of malathion, a compound which is a toxic pesticide. The degradation of malathion using Ni/TiO2 nano particle, catalyzed malathion by photocatalysis and reduces its toxicity.

Photochemical methods in metathesis reactions.

Metathesis reactions are one of the most reliable and prevalent ways of creating a C-C bond in synthesis. Photochemical variants exist, and they have proven extremely useful for the construction of complex molecules, from natural products to Möbius rings. A variety of starting materials can undergo photometathesis reactions, including alkenes, alkynes, carbonyls, thiocarbonyls, and ketenes. While many of these reactions proceed with UV light and require harsh conditions, a handful of new techniques for visible-light photometathesis reactions have appeared recently. Given the current developments in visible-light photocatalysis, we believe that many more visible light photometathesis reactions await discovery. In this first review on the subject of photometathesis, we have gathered the relevant literature to give the reader an in-depth understanding of the field, and to inspire further development and synthetic application of these fascinating reactions.

Радиационные и фотохимические методы дехлорирования полихлорбифенилов (Обзор)

В обзоре анализируются результаты исследований и разработок, посвященных применению радиационно-химических и фотохимических методов для дехлорирования опасных химических соединений - полихлорированных бифенилов (ПХБ). ПХБ широко выпускались ранее для применения в качестве диэлектрических жидкостей в трансформаторах и конденсаторах или в качестве присадок к трансформаторным маслам, которые до сих пор продолжают использоваться. В настоящее время ПХБ признаны стойкими органическими загрязнителями и, согласно Стокгольмской конвенции, должны быть обезврежены, а их запасы подлежат утилизации. В обзоре обобщена информация об исследованиях, в которых с помощью радиации и фотохимического воздействия выполняется очистка от ПХБ трансформаторных масел, гидравлических масел и некоторых видов жидких отходов. Рассмотрено воздействие на полихлорбифенилы различных видов ионизирующего излучения и ультрафиолетового излучения, в том числе в присутствии растворителей, щелочи и различных окисляющих добавок. Приведены энергетические выходы разложения, рассмотрены механизмы и скорости реакций деградации, степени разложения, продукты реакций. Сделанные выводы могут быть использованы в качестве практических рекомендаций по обезвреживанию систем, содержащих ПХБ, указанными методами. The review examines research and development progress referring to application of radiation-chemical and photochemical methods for dechlorination of hazardous chemical compounds - polychlorinated biphenyls (PCBs). PCBs have been widely produced previously as dielectric fluids used in transformers and condensers, or as additives for transformer oils, which are still being in use. Currently, PCBs have been recognized as persistent organic pollutants and, according to the Stockholm Convention on POPs, are required detoxification and disposal of their stockpiles. The review summarizes studies applying radiation and photochemical procedures for degradation of PCBs which are contained in transformer oils, hydraulic oils, and some types of liquid wastes. An effect of ionizing radiation and ultraviolet radiation on polychlorinated biphenyls is considered, including degradation protocols involving the presence of solvents, alkali and various kinds of oxidizing agents. The values of degradation energy yields, supposed mechanisms, calculated rates of degradation reactions, degrees of decomposition, and dechlorination products are considered. The conclusions drawn can be used as practical recommendations for disposal of PCB-based systems with the help of the methods indicated above.

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

Influence of the Silver Nanocrystal Shape on the Luminous Efficiency of Blue-Emitting Polymer Light-Emitting Diodes.

Truncated silver nanodecahedrons (TAgNDs) and truncated silver nanoplates (TAgNPs) fabricated via chemical reduction and photochemical methods were added to poly[3,4-ethylenedioxythiophene]:poly[styrenesulfonate] (PEDOT:PSS) as dopants to promote the luminous efficiency of blue-emitting polymer light-emitting diodes (PLEDs). The differences in shape between TAgNDs and TAgNPs result in better dispersion of TAgNDs in PEDOT:PSS. Therefore, at an optimal doping concentration (the distributed density in the light-emitting region is 6.88 μg cm-2 for TAgNDs and 5.16 μg cm-2 for TAgNPs), the average current efficacy and maximum electroluminescence intensity enhancement factor for TAgND-doped PLEDs were 4.18 cd A-1 and 420%, respectively, which are much higher than those for TAgNP-doped PLEDs (1.83 cd A-1 and 200%) at a luminescence wavelength of 440 nm.

Photochemical Thiolation of Carbon Particles with Mercaptoproyltrimethoxysilane

ABSTRACTSurface modification of carbon black (CB) is an important tool to refashion properties of its composites. CB surface modification is usually practiced through thermal procedures. However, environmental concerns have provided the base to rethink for alternate methods, particularly photochemical methods that are considered comparatively eco-friendly due to reduced chemical and thermal waste. Present investigation is based on a photochemical method for CB surface modification that has effectively modified particle surface with alkoxysilane. This method carries the active centers, generated by photoinitiator, to the shaded areas which otherwise are not possible to reach. Hence, this reaction scheme has prevailed over huge activation barrier without thermal support. A photo-thermal modification method has also been utilized for comparative analysis. Effectiveness of photochemical modification method to alter the surface of CB has been confirmed through different instrumental techniques, including XPS, TGA, FTIR, Raman and SEM.

Synthesis of α,β-dibromo ketones by photolysis of α-bromo ketones with N-bromosuccinimide: Photoinduced β-bromination of α-bromo ketones

Irradiation of α-bromopropiophenones in the presence of NBS results in the formation of α,β-dibromopropiophenones, which can be viewed as β-bromination of α-bromopropiophenones. The reaction is believed to go through a series of reactions; photoinduced C–Br bond cleavage, elimination of HBr to give α,β-unsaturated ketone intermediates, and addition of Br2, which are formed by the reaction between HBr and NBS. From mechanistic studies of the reaction, we have also found a very convenient method for α-debromination of the α,β-dibromopropiophenones which is by simple irradiation of the dibromo ketones in acetone or 2-propanol without the use of any additives. Our results demonstrate that bromine can be added into or eliminated from the alpha, beta, or both positions to the carbonyl group by photochemical methods, which make synthetic options of bromine containing carbonyl compounds versatile.

Effect of (Ag, Pd) doping on structural, and optical properties of ZnO nanoparticales: As a model of photocatalytic activity for water pollution treatment

This study presents a favorable application to use (Ag, Pd) co-doped Zinc oxide nanoparticles as nanocatalysts in photocatalytic degradation of maxilon blue (GRL) dye. Un-doped ZnO nanoparticles were prepared by hydrothermal method and Ag, Pd and (Ag, Pd) co-doped ZnO nanoparticles by photochemical methods for photocatalytic application. XRD results revealed that ZnO has a hexagonal wurtzite phase with (1 0 1) plane preferred orientation. FE-SEM results demonstrated that the samples with a high agglomeration except at pH11 that have a rod-like shape. FT-IR absorption peak at ~520 cm−1, revealed a slight shift which observed after the doping between (520 and 450) cm−1. Diffuse reflectance shows the band gab of doped ZnO nanoparticles is at 2.61 eV. PL results indicate that (Ag, Pd)/ZnO has a lower recombination rate when compared with Ag or Pd doped ZnO nanoparticles. Novel photocatalytic high activity were observed for (Ag, Pd) co-doped ZnO which is about 95.67% at pH9.

Cu2O nanocubes with mixed oxidation-state facets for (photo)catalytic hydrogenation of carbon dioxide

Cuprous oxide (Cu2O), an earth-abundant, low-cost metal-oxide semiconductor, has received enormous attention for its CO2 reduction ability in aqueous media by photochemical, photoelectrochemical and electrochemical methods. An unresolved problem with all of these approaches, however, is the instability of the Cu2O caused by its tendency to undergo an irreversible redox disproportionation reaction. Here, we report a way to circumvent this troublesome behaviour of Cu2O by driving the CO2 reduction in the gas-phase via heterogeneous photocatalytic hydrogenation. To this end, Cu2O nanocubes with surfaces comprising mixed oxidation-state copper Cu(0,I,II) sites, oxygen vacancies [O] and hydroxyl OH groups were synthesized. These surfaces enable heterolysis of H2 and adsorption of CO2 under mild conditions; they facilitate the reverse water–gas shift reaction, while rendering the redox disproportionation reaction reversible. This synergism provides Cu2O nanocubes with high photocatalytic activity and stability. Cu2O is a promising photocatalyst, although its stability is compromised by a disproportionation reaction that leads to the formation of Cu and CuO. Now, a method is reported to stabilize Cu2O nanocubes, rendering them highly active and stable for the photocatalytic reverse water–gas shift reaction.

Performance Comparison of the Electrolytic Cells Having Different Configurations for the Production of HCl and NaOH from Brine

CO2 capture and utilization (CCU) researches are being actively pursued to suppress its global warming effects and to utilize CO2 as a feedstock for producing useful organic and inorganic substances such as methanol, formic acid, and carbonates through biological, thermal, photochemical and electrochemical methods. This study focuses on the development of compact continuous-flow electrochemical cells for energy-efficient splitting of brine (aqueous NaCl) to produce alkali (NaOH) and hydrochloric acid (HCl) that would be used to convert carbon dioxide into carbonate minerals at a subsequent stage. For this purpose, bipolar membrane cells are usually used, that are composed of three types of membranes, an anion, a cation and a bipolar membrane in a cell. Recently a new type of electrolytic cell was proposed which greatly reduce the working voltage by supplying hydrogen into the anode side of the cell. In this study two types of cell designs, namely one-membrane cell and two-membrane cell, are investigated and compared for their performances under various operating conditions. The one-membrane cell consisted of a membrane sandwiched between an anode and a cathode. A feedstock comprising of a NaCl solution and H2 gas was supplied to the anode side while a pure water or a dilute NaOH solution was supplied to the cathode side. Upon applying a voltage of 1.5V across the two electrodes, the electrolytic reactions proceeds to produce HCl at the anode and NaOH and H2 at the cathode. In the case of two-membrane cells, two membranes were used and a middle plate was placed between the two membranes, and a NaCl solution was fed to the middle plate while H2 gas was fed to the anode and a dilute NaOH solution to the cathode. The one-membrane cell employing platinum-based electrodes shows initial reaction rate as high as 500 mA/cm2 at an applied voltage of 1.5V. The reaction rate, however, drops rapidly due to the degradation of the anode Pt-catalyst by hydrochloric acid that is produced at the anode side during the reaction. On the other hand, the two-membranes cell shows very stable performance over 300 hours though its reaction rate is kept below 100mA/cm2 at an applied voltage of 1.5V. The one-membrane cell has a simple reactor configuration and displays a high reaction rate because of a low internal resistance, but it suffers from a poor stability and a low caustic efficiency below 10%. On the other hand, the two membrane cell exhibits a high caustic efficiency over 50% and a good stability, but its cell configuration is complicated and the reaction rate is below 100 mA/cm2. Various materials have been tested to improve the reaction rate as well as the caustic efficiency and stability. Through optimization of the cell components, we have achieved a very reasonable caustic efficiency over 50% and a reaction rate over 200 mA/cm2 on a one-membrane cell. Detailed comparison is presented on the performances of the cells under various operating conditions and an optimal combination of the cell components is suggested.