Resonance Characterization Research Articles

Fabrication of n-n isotype BiOBr-Bi2WO6 heterojunctions by inserting Bi2WO6 nanosheets onto BiOBr microsphere for the superior photocatalytic degradation of Ciprofloxacin and tetracycline

Fabrication of n-n Isotype BiOBr-Bi 2 WO 6 Heterojunctions by Inserting Bi 2 WO 6 Nanosheets onto BiOBr Microsphere for the Superior Photocatalytic Degradation of Ciprofloxacin and Tetracycline. • Microwave-assisted hydrothermal synthesis of efficient n-n isotype BiOBr-Bi 2 WO 6 . • Novel 2D-3D nanosheet-insertion-microsphere construction boosted catalytic activity. • Strong interfaces between BiOBr and Bi 2 WO 6 enhanced e - /h + separation and transfer. • The BiOBr-Bi 2 WO 6 = 8:1 showed superior degradation of ciprofloxacin and tetracycline. • A detailed Z-scheme mechanism was elucidated based on experimental results. Ciprofloxacin (CIP) and tetracycline (TC) are emerging contaminants which seriously threaten the survival of aquatic life and human health. In this study, we report a facile and energy-efficient one-step hydrothermal strategy for the fabrication of n-n isotype BiOBr-Bi 2 WO 6 heterojunctions with nanosheet-insertion-microsphere morphology. Morphological characterizations indicated that two-dimensional (2D) n-Bi 2 WO 6 nanosheets were inserted or covered upon n-type three-dimensional (3D) BiOBr microspheres which acted as the support successfully restricted the aggregation of Bi 2 WO 6 nanosheets and supplied more active sites. The 2D Bi 2 WO 6 nanosheets enhanced the interfacial contact and improved visible-light absorption efficiency. Photocatalytic degradation experiments revealed that BiOBr-Bi 2 WO 6 = 8:1 exhibited superior CIP and TC degradation (90%and 96%, respectively) within 120 min as compared to that of the pristine BiOBr and Bi 2 WO 6 . Moreover, BiOBr-Bi 2 WO 6 = 8:1 also realized efficient photocatalytic degradation of Rhodamine B (100%) and Methylene blue (94%). Excellent stability and recyclability remained in BiOBr-Bi 2 WO 6 = 8:1 composite after five consecutive cycles. Based on the band structure analyses, and radical trapping and electron spin resonance characterization results, a possible Z-scheme path of charger transfer was proposed to elucidate the enhanced photocatalytic mechanism. This study offers a novel avenue to design efficient n-n isotype heterojunction with superior visible-light response for refractory antibiotics degradation.

Effective activation of peroxymonosulfate with natural manganese-containing minerals through a nonradical pathway and the application for the removal of bisphenols

Synthetic manganese oxides had been widely investigated to activate peroxymonosulfate (PMS) for contaminant removal in recent years. The generation of reactive oxygen species (ROS, e.g., radicals) was believed to be the primary PMS activation pathways. In this work, we report that natural manganese-containing minerals (NMMs) were also effective for PMS activation to degrade bisphenols in water. Moreover, a nonradical pathway different from literatures, was confirmed according to scavenging tests, electron paramagnetic resonance (EPR) characterization, chemical probing, solvent exchange, and Raman and electrochemical analysis. It was verified that PMS complexed with the mineral surface via inner-sphere interaction. This surface interaction improved its reactivity towards the probe compounds, bisphenols. Taking bisphenol AF (BPAF) as an example, its degradation rate was related to surface area and dosages of the mineral. Water constituents such as Cl-, HCO3-, and NOM had negligible impact on BPAF removal. The activity of the mineral was kept in an 80-hour continuous flow test. The PMS/NMM coupled oxidation degraded BPAF through direct electron transfer, and the degradation intermediates further underwent hydroxylation, bond cleavage, H-atom substitution, aromatic ring-opening, and decarboxylation. Consequently, eco-toxicity of BPAF can be reduced during the oxidation.

Effects of oxygen vacancy defect on microwave pyrolysis of biomass to produce high-quality syngas and bio-oil: Microwave absorption and in-situ catalytic.

This paper proposed to use ferric oxide (Fe2O3) and ferroferric oxide (Fe3O4) as catalysts with both microwave absorption and catalytic properties. Carbon dioxide (CO2) was introduced as the reaction atmosphere to further improve the quality of biofuel produced by microwave pyrolysis of food waste (FW). The results showed the bio-gas yield and the syngas concentration (H2+CO) increased to 70.34wt% and 61.50mol%, respectively, using Fe3O4 as the catalyst. The content of aliphatic hydrocarbons in bio-oil produced with the catalyst Fe2O3 increased to 67.48% and the heating value reached 30.45MJ/kg. Compared with Fe2O3 catalyst, Fe3O4 exhibited better microwave absorption properties and catalytic properties. Transmission electron microscopy (TEM) and Electron paramagnetic resonance (EPR) characterizations confirmed that the crystal surface of Fe3O4 formed more oxygen vacancy defects and unpaired electrons. Additionally, according to the X-ray photoelectron spectroscopy (XPS) analysis, the content of lattice oxygen in Fe3O4 was 14.11%, a value that was much lower than Fe2O3 (38.54%). The oxygen vacancy defects not only improved the efficient utilization of microwave energy but also provided the reactive sites for the reaction between the volatile organic compounds (VOCs) and CO2 to generate CO. This paper provides a new perspective for selecting catalysts that have both microwave absorption and catalytic properties during the microwave pyrolysis of biomass.

Vibration Characteristics of Graphene nano resonator as mass sensor

The decrease in the physical dimensions of the devices have sought the attention of research community due to quick response, high sensitivity and sturdiness of the devices. These devices in the form of nano resonators have been extensively used as sensors to detect the entity at submicron level as well as to identify the properties of matter at submicron level. With the process like chemical vapour deposition, lithography technique as well as mechanical exfoliation techniques, it has become possible to produce materials which are 2D in nature. The excellent mechanical and electrical properties of graphene as well as its complete plain geometry advocate it as an ideal material for the development of sensors used for identifying the object at nano level. Here an attempt is made to analyse the vibration characterization of graphene resonator in the form of membrane to understand the shift in the frequency by adsorbing the mass and change in the temperature. The tobacco mosaic virus is considered as a mass adsorbed onto the graphene nano ribbon based membrane. Along with the adsorption of the mass, the effect of variation in temperature is also introduced to observe the shift in the natural frequency of the graphene membrane based resonator.

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure-Melt Stability Relationship.

Phenylethynyl-terminated aromatic polyimides meet requirements of resin transfer molding (RTM) and exhibits high glass transition temperature (Tg) were prepared. Moreover, the relationship between the polyimide backbones structure and their melting stability was investigated. The phenylethynyl-terminated polyimides were based on 4,4′-(hexafluorosiopropylidene)-diphthalic anhydride (6FDA) and different diamines of 3,4′-oxydianiline (3,4′-ODA), m-phenylenediamine (m-PDA) and 2,2′-bis(trifluoromethyl)benzidine (TFDB) were prepared. These oligoimides exhibit excellent melting flowability with wide processing temperature window and low minimum melt viscosities (<1 Pa·s). Two of the oligoimides display good melting stability at 280–290 °C, which meet the requirements of resin transfer molding (RTM) process. After thermally cured, all resins show high glass transition temperatures (Tgs, 363–391 °C) and good tensile strength (51–66 MPa). The cure kinetics studied by the differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR) characterization and density functional theory (DFT) definitely confirmed that the electron-withdrawing ability of oligoimide backbone can tremendously affect the curing reactivity of terminated phenylethynyl groups. The replacement of 3,4′-ODA units by m-PDA or TFDB units increase the electron-withdrawing ability of the backbone, which increase the curing rate of terminated phenylethynyl groups at processing temperatures, hence results in the worse melting stability.

Sandwich-like Z-scheme g-C3N4/reduced graphene oxide@TiO2composite for enhanced visible light photoactivity

The sandwich-like Z-scheme g-C3N4/reduced graphene oxide@TiO2 (CN/RGO@T) composite with enhanced photocatalytic performance was successfully synthesized by hydrothermal method followed by a calcination process. It is interesting to note that TiO2 completely enclosed by RGO is presented in a nanoscroll morphology. Photocatalytic performance of the composite was evaluated in the propylene degradation. The results revealed that by introducing RGO as an interfacial mediator, Z-scheme g-C3N4-TiO2 nanocomposites could remarkably speed up the interfacial charge transmission and improve the separation efficiency of photogenerated carriers. Especially, 20%CN/RGO@T composite showed the highest visible light activity up to 21.9% for propylene oxidation. A lower photogenerated electron-hole recombination rate and higher carrier separation efficiency of the ternary complex 20%CN/RGO@T were confirmed by electron spin resonance, photoluminescence spectrum, and photocurrent-time characterization. This is due to the fact that strong π-π interaction between g-C3N4 and RGO leads to a carrier transmission channel between N-O and C-O-C bonds of g-C3N4 and RGO. This newly formed Z-scheme composite is having a possibility to be explored as a versatile photocatalyst to conduct various type photoreactions.

Aqueous Microdroplets Capture Elusive Carbocations

Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.

The alcohol-induced cardiomyopathy: A cardiovascular magnetic resonance characterization

BackgroundAlcoholic cardiomyopathy(ACM) is part of the non-ischaemic dilated cardiomyopathy(NI-DCM) spectrum. Little is known about cardiovascular magnetic resonance(CMR) features in ACM patients. The aim of this study is to describe CMR findings and their prognostic impact in ACM patients. MethodsConsecutive ACM patients evaluated in five referral CMR centres from January 2005 to December 2018 were enrolled. CMR findings and their prognostic value were compared to idiopathic NI-DCM(iNI-DCM) patients. The main outcome was a composite of death/heart transplantation/life-threatening arrhythmias. ResultsOverall 114 patients (52 with ACM and 62 with iNI-DCM) were included. ACM patients were more often males compared to iNI-DCM (90% vs 64%, respectively, p ≤ 0.001) and were characterized by a more pronounced biventricular adverse remodelling than iNI-DCM, i.e. lower LVEF (31 ± 12% vs 38 ± 11% respectively, p = 0.001) and larger left ventricular end-diastolic volume (116 ± 40 ml/m2 vs 67 ± 20 ml/m2 respectively, p < 0.001). Similarly to iNI-DCM, late gadolinium enhancement (LGE), mainly midwall, was present in more than 40% of ACM patients but, conversely, it was not associated with adverse outcome(p = 0.15). LGE localization was prevalently septal (87%) in ACM vs lateral in iNI-DCM(p < 0.05). Over a median follow-up of 42 months [Interquartile Range 24–68], adverse outcomes were similar in both groups(p = 0.67). ConclusionsACM represents a specific phenotype of NI-DCM, with severe morpho-functional features at the onset, but similar long-term outcomes compared to iNI-DCM. Despite the presence and pattern of distribution of LGE was comparable, ACM and iNI-DCM showed a different LGE localization, mostly septal in ACM and lateral in iNI-DCM, with different prognostic impact.

Biosynthesis of Nondigestible Galactose-Containing Hetero-oligosaccharides by Lactobacillus plantarum WCFS1 MelA α-Galactosidase

This work describes the high capacity of MelA α-galactosidase from Lactobacillus plantarum WCFS1 to transfer galactosyl residues from melibiose to the C6-hydroxyl group of disaccharide-acceptors with β-linkages (lactulose, lactose, and cellobiose) or α-linkages (isomaltulose and isomaltose) to produce novel galactose-containing hetero-oligosaccharides (HOS). A comprehensive nuclear magnetic resonance characterization of the transfer products derived from melibiose:lactulose reaction mixtures revealed the biosynthesis of α-d-galactopyranosyl-(1 → 6)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose as the main component as well as the presence of α-d-galactopyranosyl-(1 → 3)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose and α-d-galactopyranosyl-(1 → 6)-α-d-galactopyranosyl-(1 → 6)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose. Melibiose-derived α-galactooligosaccharides (α-GOS), manninotriose and verbascotetraose, were also simultaneously synthesized. An in vitro assessment of the intestinal digestibility of the novel biosynthesized HOS revealed a high resistance of α-galactosides derived from lactulose, lactose, cellobiose, and isomaltulose. According to the evidence gathered for conventional α-GOS and certain disaccharides used as acceptors in this work, these novel nondigestible α-galactosides could be potential candidates to selectively modulate the gut microbiota composition, among other applications, such as low-calorie food ingredients.

Energy saving intermittent electro-Fenton system combined with commercial MoS2 for effective Rhodamine B degradation

Abstract Without external O2 supply and solution pH adjusting, commercial molybdenum sulfide (MoS2) was firstly applied as co-catalyst in intermittent electro-Fenton process for Rhodamine B (RhB) degradation. In this energy saving system, Fe2+/Fe3+ conversion was facilitated and H2O2 activating was accelerated by MoS2. Granular activated carbon wrapped with stainless steel mesh (GACSS) was used as cathode, from which, H2O2 and iron sources were in-situ generated. With 0.1 g/L MoS2, and 50 mA applied current with 10 min on-10 min off power frequency, RhB degradation rate constant in the MoS2 intermittent electro-Fenton was approximately 2.4 times as that without MoS2 system. Quenching experiments, electron spin resonance (ESR) characterization and free radical fluorescence tests demonstrated hydroxyl radicals (·OH) was the dominant reactive species, and the superiority of intermittent electrolysis mode for RhB degradation. During power on, H2O2 was constantly generated on cathode. In electricity interval, Fe2+/Fe3+ conversion was accelerated on the active sites (Mo4+) to activate residual H2O2 and more ·OH was generated to RhB degradation. Additionally, the characterization analysis (XPS, SEM and FT-IR) demonstrated MoS2 and GACSS cathode exhibited excellent catalytic and chemical stability in recyclability. Low-cost multifunctional cathode with a high efficiency co-catalyst was combined in this energy saving electro-Fenton operating system for RhB degradation.

Optical Characterization of Free-space Coupled Microsphere Resonators

Optical Characterization of Free-space Coupled Microsphere Resonators

Nuclear magnetic resonance characterisation of ionic liquids and organic ionic plastic crystals: common approaches and recent advances.

Ionic liquids, and their solid-state equivalents organic ionic plastic crystals, show many useful and tailorable properties that make them interesting for a wide range of applications including as electrolytes for energy storage devices. Nuclear magnetic resonance spectroscopy and related techniques offer a powerful and versatile toolkit for the characterisation of structure, interactions and dynamics in these materials. This article summarises both commonly used methods and some recent advances in this area, including solution- and solid-state methods, dynamic nuclear polarisation, imaging, diffusion and relaxation measurements, and example applications of some less commonly studied nuclei.

Improved CO2/CH4 separation performance of mixed‐matrix membrane by adding ZIF‐7‐NH2 nanocrystals

AbstractMembrane‐based technology is an attractive alternative in terms of CO2 separation. Pebax‐based membranes are regarded as potential candidates for CO2 separation due to the favorable interaction between its poly (ethylene oxide) chains with CO2 molecules and inorganic fillers. However, the separation performance for CO2/CH4 mixture is still suffered from the moderate gas permeability and selectivity. To overcome this problem, in this work, amino‐functionalized zeolite imidazolate framework (ZIF‐7‐NH2) nanocrystals were used as fillers to blend with Pebax 1657 for fabricating mixed‐matrix membranes (MMMs). XRD, Brunauer–Emmett–Teller (BET), scanning electron microscope, and 1H nuclear magnetic resonance characterization indicated that ZIF‐7‐NH2 with the highest crystallinity was synthesized. Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and Young's modulus showed that it has good interfacial interaction. Gas separation test results showed that both the CO2 permeability and CO2/CH4 selectivity of the 31 wt% ZIF‐7‐NH2/Pebax MMMs increased by 80 and 170%, respectively. The improved performance is attributed to the addition of ZIF‐7‐NH2 nanocrystals and the favorable interfacial interactions between the polymer and ZIF‐7‐NH2 nanocrystals. Furthermore, the polyvinylidene fluoride supported hollow fiber composite membranes also exhibit the long‐term stability for CO2/CH4 separation.

One-step synthesis of methyl methacrylate from methyl propionate and methanol under mild condition

In recent years, coal-based one-step synthesis of methyl methacrylate (MMA) stimulated researchers’ interest due to the over-capacity of coal chemical industry. However, the high reaction temperature, low yield and selectivity, catalyst deactivation due to carbon deposition, and volatilization and polymerization of formaldehyde have been the challenging problems in this field. In this work, the cascade reactions of methanol dehydrogenation to formaldehyde, aldol condensation between formaldehyde and methyl propionate, and O2-inteerrupted hydrogenation of MMA were resolved via construction of mild and efficient cobalt complex catalyzed interrupted hydrogen borrowing system. Thus, one-step synthesis of MMA from methyl propionate and methanol in liquid phase at 80 °C with yield and selectivity of 25.7% and 92.6% was realized. The cobalt complex activation and methanol dehydrogenation mechanisms were investigated with nuclear magnetic resonance (NMR) characterization, and the C–H bond activation and breakage of methanol was identified as the rate-controlling step through kinetic isotopic effect experiments, which provided new research direction for coal-based synthesis of MMA.

Characterization of photonic band resonators for DNP NMR of thin film samples at 7 T magnetic field

Polarization of nuclear spins via Dynamic Nuclear Polarization (DNP) relies on generating sufficiently high mm-wave B1e fields over the sample, which could be achieved by developing suitable resonance structures. Recently, we have introduced one-dimensional photonic band gap (1D PBG) resonators for DNP and reported on prototype devices operating at ca. 200 GHz electron resonance frequency. Here we systematically compare the performance of five (5) PBG resonators constructed from various alternating dielectric layers by monitoring the DNP effect on natural-abundance 13C spins in synthetic diamond microparticles embedded into a commercial polyester-based lapping film of just 3 mil (76 μm) thickness. An odd-numbered configuration of dielectric layers for 1D PBG resonator was introduced to achieve further B1e enhancements. Among the PBG configurations tested, combinations of high-ε perovskite LiTaO3 together with AlN as well as AlN with optical quartz wafers have resulted in ca. 40 to over 50- fold gains in the average mm-wave power over the sample vs. the mirror-only configuration. The results are rationalized in terms of the electromagnetic energy distribution inside the resonators obtained analytically and from COMSOL simulations. It was found that average of B1e2 over the sample strongly depends on the arrangement of the dielectric layers that are the closest to the sample, which favors odd-numbered PBG resonator configurations for their use in DNP.

High-Q titanium dioxide micro-ring resonators for integrated nonlinear photonics.

We report on the nonlinear characterizations of the titanium dioxide micro-ring resonators (TiO2 MRRs). By utilizing optimized fabrication processes, high quality factors (Q∼1.4 × 105) doubling that of the previous work are achieved here for TiO2 MRRs with high-confinement TiO2 waveguides. The four-wave mixing (FWM) experiment results with low and high signal power demonstrate that, the fabricated TiO2 MRRs can perform broadband (∼40 nm) wavelength conversion and cascaded FWMs. These achievements pave the way for key nonlinear photonic applications with TiO2 waveguides and provide an efficient platform for various integrated photonic devices.

Vacancies boosting strategy enabling enhanced oxygen evolution activity in a library of novel amorphous selenite electrocatalysts

Transition metal selenites are promising in catalytic field, but their oxygen evolution reaction (OER) performance and the corresponding catalysis mechanism has rarely been reported. Here, we report a vacancy-boosting strategy to realize enhanced activity in a library of novel selenite electrocatalysts. Unexpectedly, we found that all Fe-based sample of this series delivers amorphous structure with rich oxygen/selenium vacancies compared to their crystalline counterparts. Consequently, the amorphous Ni1Fe1SeO sample displays outstanding OER activity with an overpotential of 257 mV at 10 mA cm−2, low Tafel slop of 34 mV·dec−1 and excellent stability. X-ray absorption near edge structure (XANES), electron paramagnetic resonance (EPR) characterizations and density functional theory (DFT) calculation reveal the amorphous structure with abundant oxygen/selenium vacancies drastically decreases the energy barrier during the OER process. Our study provides a library of novel OER electrocatalysts from amorphous metal selenites with superior activity through the vacancy-boosting strategy.

Double-Stranded DNA Matrix for Photosensitization Switching

Photosensitization, originated from the activation of triplet states, is the basis of many photodynamic applications, but often competes with a series of nonradiative processes. Herein, we communic...

Fabrication of Fe-doped cobalt zeolitic imidazolate framework derived from Co(OH)2 for degradation of tetracycline via peroxymonosulfate activation

The exploration of transforming insoluble solid hydroxide as a metal source into metal organic frameworks (MOFs) has attracted much attention in recent years. Herein, Fe-doped cobalt zeolitic imidazolate framework (Co-ZIF-(Fe)x, x meant the different adding amount of Fe3+) were successfully synthesized by using radical cobalt layered double hydroxide (Co(OH)2) as a cobalt ion source. The catalytic performance of samples was evaluated by activating peroxymonosulfate (PMS) to degrade tetracycline hydrochloride (TC) from aqueous solution. Remarkably, the Co-ZIF-(Fe)0.5 demonstrated the highest catalytic activity that the removal efficiency of TC could reach up to 96.71% within 5 min, which was 1.136 times higher than Co-ZIF. The Co-ZIF-(Fe)0.5 have a larger surface area (268.97 m2 g−1) and pore volume (0.25 cm3 g−1), which can be contributed to a large number of accessible active sites. The possible TC degradation pathways were investigated on basis of the intermediates. According to the classical radical-quenching test and electron paramagnetic resonance (EPR) characterization, manifested that the degradation of TC was accomplished by the free radical (SO4−) and the non-radical (1O2) pathways. Moreover, the Co-ZIF-(Fe)0.5/PMS system exhibited a high activity in a wide pH range (4–10) and less influenced by organic and inorganic ions. The effect of actual water (medical wastewater, river water and tap water) was discussed in detail, and the reusability was also be considered. Therefore, this study provided a reference for the fabricating of MOF-based catalysts for wastewater treatment.

Fabricating iron-cobalt layered double hydroxide derived from metal-organic framework for the activation of peroxymonosulfate towards tetracycline degradation

Herein, iron-cobalt layered double hydroxide (FeCo-LDH) was synthesized by sacrificing Co-containing zeolite imidazolate framework materials (ZIF-67) in iron ethanolic solution at room temperature. The catalytic performances of catalysts were investigated by activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. Experimental results were demonstrated that FeCo-LDH with molar ratios of Fe and Co was 1.5 (FeCo-LDH-1.5) exhibited the highest catalytic activity, in which the TC degradation efficiency was reached to 92% within 5 ​min. The system of FeCo-LDH-1.5/PMS exhibited high stability and high efficiency in the influencing factor experiments including TC concentrations, initial pH, coexisting anions (Na+, Cl-, SO42−) and humic acid (HA). Results of quenching experiments and electron paramagnetic resonance (EPR) characterization showed that O2•- and SO4•- radicals were the foremost reactive species for TC degradation. Liquid chromatograph - mass spectrometer (LC-MS) and three-dimensional excitation emission matrix fluorescence spectro photometer (3D EEMs) were conducted to investigate the degradation intermediate and possible degradation pathway. Moreover, high degradation efficiency was implemented in actual wastewater by the FeCo-LDH-1.5/PMS system. Compared to Fe3+/PMS and Co2+/PMS homogeneous system, the FeCo-LDH-1.5/PMS system was exhibited advantages in catalytic activity and high reusability. This study provided a convenient method to synthesis advanced hydrotalcite-like catalysts, which showed remarkable performance in actual wastewater treatment.