ABSTRACT
Nitrates level in water is a worldwide problem that represents a risk to the environment and people's health; efforts are currently devoted to the development and implementation of new biomaterials for their removal. In this study, chitosan (Ch) from shrimp waste and the related epichlorohydrin-modified crossover chitosan (Ch-EPI) were used to remove nitrates from aqueous solutions. The mechanism of selective nitrate removal was elucidated and validated by theoretical calculations. The physicochemical performance of Ch and Ch-EPI was investigated through the main parameters pH, adsorption capacity, contact time, initial nitrate concentration, coexisting anions, and temperature. The experimental data were fitted to widely used adsorption kinetic models and adsorption isotherms. The maximum percentage of nitrate adsorption was reached at an equilibrium pH of 4.0 at an adsorbent dose of 2.0 g/L after a contact time of 50 min. Competing anion experiments show that chloride and sulfate ions have minimal and maximal effects on nitrate adsorption by Ch-EPI. Experimental adsorption data are best fitted to pseudo-second-order kinetic and isothermal Langmuir models. The maximum adsorption capacities of Ch and Ch-EPI for nitrate removal were 12.0 mg/g and 38 mg/g, respectively.
Subject(s)
Chitosan , Water Pollutants, Chemical , Humans , Nitrates , Epichlorohydrin , Anions , Water , Adsorption , Kinetics , Models, Theoretical , Hydrogen-Ion ConcentrationABSTRACT
The effect of the nature of the catalyst on the performance and mechanism of the hydrogen oxidation reaction (HOR) is discussed for the first time in this work. HOR is an anodic reaction that takes place in anionic exchange membrane fuel cells (AEMFCs) and hydrogen pumps (HPs). Among the investigated catalysts, Pt exhibited the best performance in the HOR. However, the cost and the availability limit the usage. Co is incorporated as a co-catalyst due to its oxophylic nature. Five different PtCo catalysts with different Pt loading values were synthesized in order to decrease Pt loading. The catalytic activities and the reaction mechanism were studied via electrochemical techniques, and it was found that both features are a function of Pt loading; low-Pt-loading catalysts (Pt loading < 2.7%) led to a high half-wave potential in the hydrogen oxidation reaction, which is related to higher activation energy and an intermediate Tafel slope value, related to a mixed HOR mechanism. However, catalysts with moderate Pt loading (Pt loading > 3.1%) exhibited lower E1/2 than the other catalysts and exhibited a mechanism similar to that of commercial Pt catalysts. Our results demonstrate that Co plays an active role in the HOR, facilitating Hads desorption, which is the rate-determining step (RDS) in the mechanism of the HOR.
ABSTRACT
In the present work, chemically modified graphene oxide (GO) was incorporated as a crosslinking agent into thin-film composite (TFC) nanofiltration (NF) membranes for water desalination applications, which were prepared by the interfacial polymerization (IP) method, where the monomers were piperazine (PIP) and trimesoyl chloride (TMC). GO was functionalized with monomer-containing groups to promote covalent interactions with the polymeric film. The composite GO/polyamide (PA) was prepared by incorporating amine and acyl chloride groups into the structure of GO and then adding these chemical modified nanomaterial during IP. The effect of functionalized GO on membrane properties and performance was investigated. Chemical composition and surface morphology of the prepared GO and membranes were analyzed by thermogravimetric analysis (TGA), Raman spectroscopy, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The fabricated composite membranes exhibited a significant increase in permeance (from 1.12 to 1.93 L m-2 h-1 bar-1) and salt rejection for Na2SO4 (from 95.9 to 98.9%) and NaCl (from 46.2 to 61.7%) at 2000 ppm, when compared to non-modified membranes. The amine- and acyl chloride-functionalized GO showed improved dispersibility in the respective phase.
ABSTRACT
Nowadays, infectious diseases caused by drug-resistant bacteria have become especially important. Linezolid is an antibacterial drug active against clinically important Gram positive strains; however, resistance showed by these bacteria has been reported. Nanotechnology has improved a broad area of science, such as medicine, developing new drug delivery and transport systems. In this work, several covalently bounded conjugated nanomaterials were synthesized from multiwalled carbon nanotubes (MWCNTs), a different length oligoethylene chain (S n ), and two linezolid precursors (4 and 7), and they were evaluated in antibacterial assays. Interestingly, due to the intrinsic antibacterial activity of the amino-oligoethylene linezolid analogues, these conjugated nanomaterials showed significant antibacterial activity against various tested bacterial strains in a radial diffusion assay and microdilution method, including Gram negative strains as Escherichia coli (11 mm, 6.25 µg mL-1) and Salmonella typhi (14 mm, ≤0.78 µg mL-1), which are not inhibited by linezolid. The results show a significant effect of the oligoethylene chain length over the antibacterial activity. Molecular docking of amino-oligoethylene linezolid analogs shows a more favorable interaction of the S 2-7 analog in the PTC of E. coli.
ABSTRACT
UNLABELLED: Since 2000, the city of Chihuahua had a distribution system of treated wastewater for irrigation of green areas and has replaced this water for processes that do not require the consumption of drinking water. This replacement was necessary in order to meet the growing demand for potable water which has exceeded the current supply of 700 L (184,88 gallons) per second. Nowadays it is necessary to identify and assess the risks to public health and the environment due to the substitution of drinking water by treated wastewater in the last 10yr. Treated wastewater contains compounds whose effects have not been evaluated when used for irrigation in public green areas. Therefore, it is not known whether there is a danger to the health of park visitors due to exposure and/or inhalation of the emitted gases, accidental ingestion of water, or impact to the environment. The purpose of the research, using an experimental prototype, is to identify the changes from nitrogen present in the treated wastewater to nitrous oxide. The research objective is the generation of data to simulate a regional scale at this stage, which will be analyzed and statistically validated using Minitab and Origin software. The experiment was performed using three different samples to compare water quality: drinking water treated wastewater, and water with nitrogen-based fertilizer (urea). Prototypes were filled with two types of soil: sand and clay Each type of water was sprinkled on the prototype, grass was planted in it, and the prototype was equipped with samplers to capture the gas in the root zone. The authors found high emissions of nitrous oxide in the clay-filled lysimeters, and climate and growing conditions of vegetation were the most important factors for producing nitrous oxide. IMPLICATIONS: Major problems in the ecosystem arise from solutions that are not based on environmental public policy research or experimentation. For example, before application a specific policy or regulation, research should be performed to evaluate long term effects to the ecosystem and this can be done through close monitoring. This study raises awareness about the public policy of substituting potable water with treated wastewater for irrigation of green areas in Chihuahua City. The present study was performed during a sufficient period of time in order to assess the impact to the environment.
