90 research outputs found
Irrigated water, polymer application in
In the past decade, water-soluble polyacrylamide (PAM)
was identified as an environmentally safe and highly
effective erosion preventing and infiltration enhancing
polymer when applied in furrow irrigation water at
1 mg L-1 - 10 mg L-1 , i.e., 1 ppm- 10 ppm.[1-9] Various
polymers and biopolymers have long been recognized as
viable soil conditioners because they stabilize soil surface
structure and pore continuity. The new strategy of adding
the conditioner, high molecular weight anionic PAM, to
irrigation water in the first several hours of irrigation
implies a significant costs savings over traditional
application methods, in which hundreds of kilograms per
hectare of soil additives are tilled into the entire (15 cm
deep) soil surface layer. By adding PAM to the irrigation
water, soil structure is improved in the important 1-5 mm
thick layer at the soil/water interface of the 25%-30% of
field surface contacted by flowing water.
In 1995, the U.S. Natural Resource Conservation
Service (NRCS) published a PAM-use conservation
practice standard for PAM-use in irrigation water." 01 A
3-year study[21 applying these standards showed that PAM
at dosage rates of 1 kg ha-1 -2 kg ha-1 per irrigation
eliminated 94% (80%-99% range) of sediment loss in
furrow irrigation runoff, while increasing infiltration
15%-50%. Seasonal application rates using the NRCS
standard typically total 3 kg ha -1 -5 kg ha-1 .
As PAM-use is one of the most effective and
economical technologies for reducing soil-runoff, it has
branched into stabilization of construction sites and road
cuts, with formal statewide application standards set in
Wisconsin and several southern states. Recent studies with
biopolymers such as charged polysaccharides,[11-143
whey," 51 and industrial cellulose derivatives[11.141 introduce
potential biopolymer alternatives to PAM
Structural and Morphological Characterization of Micro and Nanofibers Produced by Electrospinning and Solution Blow Spinning: A Comparative Study
Nonwoven mats of poly(lactic acid) (PLA), poly(ethylene oxide) (PEO), and poly(ε-caprolactone) (PCL) were prepared at a nano- and submicron scale by solution blow spinning (SBS) and electrospinning in order to compare crystalline structure and morphology developed by both processes during fiber formation. Polymer solutions were characterized by rheometry and tensiometry. Spun fibers were characterized by several analytical steps. SEM analyses showed that both solution blow spun and electrospun fibers had similar morphology. Absence of residual solvents and characteristic infrared bands in the solution blow spun fibers for PLA, PCL, and PEO was confirmed by FTIR studies. XRD diffraction patterns for solution blow spun and electrospun mats revealed some differences related to distinct mechanisms of fiber formation developed by each process. Significant differences in thermal behavior by DSC were observed between cast films of PLA, PCL, and PEO and their corresponding spun nanofibers. Furthermore, the average contact angles for spun PLA and PCL were higher than for electrospun mats, whereas it was slightly lower for PEO. When comparing electrospun and solution blow spun fibers, it was possible to verify that fiber morphology and physical properties depended both on the spinning technique and type of polymer
Hydroxyurea electrooxidation at gold electrodes. In situ infrared spectroelectrochemical and DFT characterization of adsorbed intermediates
The oxidation of hydroxyurea (H2NCONHOH, HU) at Au(100), Au(111) and Au(111)–25 nm thin film electrodes is studied spectroelectrochemically in perchloric acid solutions. HU, which in agreement with DFT results interacts weakly with the gold surfaces, oxidizes irreversibly at gold electrodes irrespective of the surface orientation. The in situ infrared external reflection spectra prove the formation of dissolved carbon dioxide and adsorbed cyanate as products of the HU electrooxidation reaction. A band at ca. 2230 cm−1 can be related both to dissolved isocyanic acid coming from the protonation of adsorbed cyanate or to nitrous oxide coming from the oxidation of hydroxylamine, which is formed (together with adsorbed cyanate) upon the chemical decomposition of hydroxyurea. ATR-SEIRAS experiments allow the observation of other adsorbate bands that can be tentatively ascribed to reaction intermediates that conserve the NCN skeleton and are bonded to the metal by the nitrogen atoms at near on-top positions. Bonding to the surface can be either unidentate or bidentate, involving covalent-type bonds or dative bonding through the lone pairs of the N atoms. Some of the signals of the experimental spectra, in particular those appearing around 1800 cm−1, can be assigned to the CO stretch of adsorbed intermediates having a nitrosyl group formed by oxidation of the NOH moiety (namely, adsorbed nitrosoformamide or its deprotonated form). The bands observed around 1650 cm−1 can correspond either to the NO stretching mode of the former species or to the CO stretching modes of adspecies conserving the NOH group.The authors acknowledge the funding by Ministerio de EconomÃa y Competitividad through projectsCTQ2016-76221-P (AIE/FEDER, UE) and CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and by the University of Alicante (VIGROB-263). William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142
On the electrochemical behavior of formamidine disulfide on gold electrodes in acid media
The adsorption and reactivity of formamidine disulfide (FDS) were studied at gold single crystal and thin film electrodes in perchloric acid solutions and the results of cyclic voltammetry and in situ infrared spectroscopy (SNIFTIR and ATR-SEIRAS) experiments compared with those previously obtained with thiourea (TU). In addition, optimized geometries and theoretical harmonic vibrational frequencies were obtained for adsorbed FDS, TU and thioureate from plane-wave DFT calculations using periodic surface models. These results were compared in the case of TU and thioureate to those previously obtained with a model Au cluster surface with (111) orientation. In the case of FDS, weak adsorption takes place with the S–S bond essentially parallel to the metal surface. No specific bands for adsorbed FDS can be identified in the experimental ATR-SEIRA spectra. These latter spectra suggest that adsorbed thioureate species are spontaneously formed upon dissociative adsorption of FDS when dosing this molecule at open circuit. Some of the adsorbed thioureate species undergo reductive protonation giving rise to a mixed adlayer formed by adsorbed thioureate and thiourea in a surface process which is faster when a controlled potential of 0.70 V is applied. In agreement with the observations reported when dosing TU, the ratio between TU and thioureate adsorbates is found to depend on the electrode potential, being higher for potentials close to the hydrogen evolution limit and decreasing for higher potential values.The authors acknowledge the finance by Ministerio de EconomÃa y Competitividad (project CTQ2013-44083-P) and the University of Alicante. William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142
Biopolymer additives to reduce erosion-induced soil losses during irrigation
A series of biopolymers added to irrigation water were tested for their efficacy in reducing shear-induced erosion
in a laboratory-scale mini-furrow. Suspensions of chitosan, starch xanthate, cellulose xanthate, and acid-hydrolyzed
cellulose microfibrils, at concentrations of 20, 80, 80, and 120 ppm, respectively, reduced suspended solids by more
than 80%. None of these biopolymers, however, exhibited the > 90% runoff sediment reduction shown by the present
industry standard, synthetic polyacrylamide polymers, PAM. PAM is effective at concentrations as low as 5 ppm. In
field tests, chitosan solutions were only marginally effective in reducing runoff from the end of a 137 m long furrow,
with indications that results were dependent on the length of the furrow. Sediment runoff of some clay-rich Northern
California soils was reduced by up to 85% by increasing the concentration of exchangeable calcium to > 2.5mM.
Calcium improved the sedimentation of the polyelectrolytic polymers in this study
Polymer additives in irrigation water to reduce erosion and better manage water infiltration
Water-soluble polyacrylamide
(PAM) was identified as an
environmentally safe and highly
effective erosion preventing and
infiltration-enhancing polymer
when applied in furrow irrigation
water at 1-10 g m-3, i.e.
1-10 ppm. The agricultural use of
polyacrylamide, PAM, as an
additive in irrigation water has
grown rapidly since commercial
introduction in 1995 because it
improves water infiltration and
reduces erosion-induced soil
losses up to 97%, saving tons of
topsoil per hectare per year.
Various polymers and biopolymers
have long been recognized as
viable soil conditioners because
they stabilize soil surface structure
and pore continuity. The new
strategy of adding the conditioner,
high molecular weight anionic
PAM, to the irrigation water in the
first several hours of irrigation
enables a significant costs savings
over traditional application
methods of tilling soil conditoner
into the entire (15 cm deep) soil
surface layer. By adding PAM to
the irrigation water, soil structure is
Unproved in the all-important
1-5 mm thick layer at the
soil/water interface of the 25 to
30% of field surface contacted by
flowing water. Recent studies with
biopolymers such as chitosan,
charged polysaccharides, whey,
and industrial cellulose derivatives
show potential as biopolymer
alternatives to PAM. Their success
will depend on production
economics
Squaric acid adsorption and oxidation at gold and platinum electrodes
The adsorption and oxidation of squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione, H2C4O4, SQA) at platinum and gold electrodes were studied spectroelectrochemically in perchloric acid solutions. Voltammetric experiments demonstrate that reversible adsorption takes place at gold electrodes in the double-layer region. As a difference with platinum electrodes, no dissociative adsorption processes leading to the blocking of the electrode surface are detected. ATR-SEIRAS experiments show potential-dependent adsorbate bands at potentials below 1.20 V vs RHE that, according to DFT calculations, can be assigned to adsorbed squarate. For platinum electrodes, the potential-dependent adsorption of squarate anions is coupled with the oxidative stripping of adsorbed carbon monoxide, which is formed upon dissociative SQA adsorption. Bonding of squarate species to the platinum and gold surfaces involves two oxygen atoms in a bidentate configuration, with the molecular plane perpendicular to the metal surface. The ATR-SEIRA spectra obtained for gold electrodes in the SQA oxidation region show bands for adsorbed bicarbonate anions formed from dissolved carbon dioxide molecules. In the case of platinum, distinct bands are observed for adsorbed oxidation products which probably are formed upon opening of the SQA ring.The authors acknowledge the funding by Ministerio de EconomÃa y Competitividad (through projects CTQ2016-76221-P (AIE/FEDER, UE) and CTQ2016-76231-C2-2-R (AEI/FEDER, UE)) and by the University of Alicante (VIGROB-263 project)
Spectroelectrochemical detection of specifically adsorbed cyanurate anions at gold electrodes with (111) orientation in contact with cyanate and cyanuric acid neutral solutions
The adsorption and reactivity of cyanate at Au(111) single crystal and Au(111)-25 nm thin film electrodes is studied spectroelectrochemically in sodium perchlorate solutions and compared to those of cyanuric acid (C3N3O3H3). From the Surface Enhanced Infrared Reflection Absorption spectra obtained under Attenuated Total Reflection conditions (ATR-SEIRAS) it can be concluded that adsorbed cyanate species predominate at the electrode surface for low cyanate concentrations. However, for cyanate concentrations above 1 mM, the similarity of the ATR-SEIRA spectra with those obtained in cyanuric acid containing solutions indicates that some species coming from cyanuric acid is formed and adsorbed at the (111) gold surface sites as the result of an electroless trimerization reaction. Taking into account the results of Density Functional Theory (DFT) calculations, the experimental voltammetric and ATR-SEIRAS results agree with the formation of adlayers of specifically adsorbed triketo-monocyanurate species that adsorb perpendicular to the electrode surface.The authors acknowledge the funding by Ministerio de EconomÃa y Competitividad (projects CTQ2016-76221-P and CTQ2016-76231-C2-2-R) and the University of Alicante (VIGROB-044 and VIGROB-263). William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142
DFT and spectroelectrochemical study of cyanate adsorption on gold single crystal electrodes in neutral medium
The adsorption of cyanate anions at Au(111) and Au(100) single crystal electrodes has been studied spectroelectrochemically in neutral solutions. Potential-dependent in situ InfraRed Reflection Absorption spectra obtained below the onset of cyanate oxidation were compared with previously published data and analyzed on the basis of periodical Density Functional Theory (DFT) calculations. The calculated adsorption energies for cyanate and related species suggest that cyanic and isocyanic acid adsorb weakly at the studied gold surfaces and, thus, seems not to be at the origin of any of the adsorbate bands in the experimental infrared spectra collected in the cyanate-containing solutions. The latter features can be clearly ascribed to the asymmetric OCN stretching of N-bonded cyanate species. The observation of absorption bands in a wide spectral region, including features above 2200 cm− 1, agrees with the coexistence of N-bonded cyanate species with different adsorption sites and tilting angles. DFT calculations have revealed that although these adspecies can have significantly different frequencies, their adsorption energies are rather close. In addition, the existence of collective in-phase vibrations at relatively high cyanate coverages also contributes to the widening of the absorption bands.The authors acknowledge the funding by the Ministerio de EconomÃa y Competitividad (project CTQ2013-44083-P) and the University of Alicante (VIGROB-263). William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142
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