Monolayer Coverage Research Articles

Insights into the Moisture Scavenging Properties of Different Types of Starch in Tablets Containing a Moisture-Sensitive Drug.

Starch is a commonly used excipient in the pharmaceutical industry. However, information on the effect of the moisture scavenging properties of starch to protect moisture-sensitive drugs is limited. The interaction between starch and moisture is of particular interest as moisture fugacity can impact drug stability. In this study, the moisture behavior of different starches was examined for an understanding of its role in the degradation of acetylsalicylic acid. The starches were characterized for their dimensional- and moisture-related properties. Stability testing was carried out on tablets containing acetylsalicylic acid and different starches. Although moisture sorption processes were visually comparable for the different starches, quantitative differences were found in their moisture interaction and distribution. From the sorption isotherms, moisture monolayer coverage and area of hysteresis were found to correlate well with the percentage of acetylsalicylic acid degradation. The lowest percentage of acetylsalicylic acid degradation was observed in starch that exhibited high monolayer coverage, large area of hysteresis, and good capacity for internally absorbed moisture. Findings from this study highlighted the value of moisture scavenging excipients when formulating moisture-sensitive drug products. Clearly, the assessment of moisture sorption properties of excipients during the preformulation phase can be an invaluable exercise for identifying the best possible ingredients in formulations where moisture sensitivity is an area of concern.

Entropy in multiple equilibria. Argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous materials

Analysis of multiple equilibria of compounds with different coordination sites is extended to the description of adsorption isotherms with focus on the low relative pressure range. The entropy evolution is described using the particle distribution theory which also holds for adsorbents consisting of materials bearing more than one type of sites and applies for the condition that the adsorptive-adsorbent binding strength is larger than the adsorptive-adsorbate binding strength, so that monolayer coverage is favored. This allows to accurately determine the adsorption enthalpy. No assumption concerning the growth mechanism and specifics regarding the structure of the surface is needed. We find on a rigorous basis that this leads to Langmuir's equation for each site independently, that the total fractional amount of bound adsorptive can be described as a linear combination of individual Langmuir isotherms, and that such a linear combination has never the shape of the original Langmuir isotherms. The results are successfully applied to argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous adsorbents which allows comparing systems for which the properties of the active surface span a large range. We observe that all experimental data can accurately be described by means of a linear combination of two Langmuir isotherms in the low relative pressure range up to a coverage of 60%–95%. This means that the shape of all adsorption isotherms is essentially determined by the entropy decrease with increasing coverage. The two site interactions involved exhibit substantially different adsorption enthalpies. Interestingly the Ar enthalpy of adsorption Δ a d s H 1 ∅ of the sites 1 for the Stöber-type silica and of the three investigated MCM-41 adsorbents (with pore size of 2.7 nm, 4.1 nm, and 4.4 nm) are similar, namely −11 kJ/mol. The situation is analogous for the enthalpy of adsorption Δ a d s H 2 ∅ for the sites 2, which amounts to −8 kJ/mol. A significantly larger enthalpy of adsorption Δ a d s H 1 ∅ for the sites 1, namely −14.3 kJ/mol, and Δ a d s H 2 ∅ = − 11.7 kJ / mol for the sites 2 is measured for potassium zeolite L thus reflecting the more polar nature of this adsorbent. The measured specific surface area for these samples ranges from 14 m 2 /g for the Stöber-type silica up to 1100 m 2 /g for the MCM-41(4.1 nm) adsorbent. The information provided by the lc2-L (linear combination of 2 Langmuir functions) analysis allows calculating the evolution of the coverage of site 1 and of site 2 as a function of increasing pressure. The inflection points of the isotherms, which mark the point where the curvature changes sign, were determined by numerically evaluating the second derivatives which vanish at this point and are compared with values obtained using BET analysis.

Ofloxacin exclusion using novel HRP immobilized chitosan cross-link with graphene-oxide nanocomposite

Ofloxacin (OFX) release in aquatic vicinities may execute toxicity and affect the biological hierarchy. Therefore, to save the vital beauty of our earth and water streams, it is essential to remove ofloxacin from aqueous system. In this work, green nano adsorbent was prepared by cross-linking the chitosan (Cs) to graphene oxide (GO) via electrostatic interaction. Additionally, the adsorbent was bio-catalyzed by immobilizing horseradish peroxidase (HRP) onto CsGOn (HRP-CsGOn) through covalent bonding to enhance the mechanical strength of HRP and for industrial application with high reusability and low cost. SEM and FT-IR analysis of CsGOn and HRP-CsGOn confirm cross-linking of chitosan with GO and immobilization of HRP onto CsGOn. The enzyme activity of HRP-CsGOn with the free enzyme was compared at different process conditions such as pH (6,7 and 8), temperature (303, 313 and 323 K), self-life (0–15 days) and reusability (0–5 cycles). HRP-CsGOn demonstrated that better temperature, pH stability, and self-life than free enzyme. Batch ultra-sonication assisted adsorption was performed for removal of OFX using HRP-CsGOn. Kinetic and equilibrium studies presented that the experimental data of OFX were defined by pseudo-second order kinetic with monolayer coverage (Langmuir model) and three-stage of adsorption. Maximum adsorption capacity 378 (mg/g) was obtained at an equilibrium time of 10 min and a temperature of 35 °C. The positive value of thermodynamic parameters ΔH 2939.26 (kJ/mol) and ΔS 10.10 (kJ/mol K) obtained in the present study and negative value of ΔG at temperature (328–333 K) presented that the present system is spontaneous, and endothermic. The reusability studies specified that the HRP-CsGOn can be reused for a minimum of 5 cycles. This study provides a promising HRP-CsGOn green nano adsorbent and can be used for various applications.

Synthesis of stable S- functionalized metal-organic framework using MoS42- and its application for selective and efficient removal of toxic heavy metal ions in wastewater treatment

In this work, a novel sulfur functionalized porous metal-organic framework based on Cu(II) and benzene-1,3,5- tricarboxylic acid (Cu-BTC) was synthesized. Tetrathiomolybdate (MoS42−), inorganic sulfur-containing transition metal compound, was immobilized for the first time on the MOF for selective removal of heavy metal ions of Hg2+, Pb2+, Ni2+, Cd2+, and Zn2+ from wastewaters. The MoS4-MOF sorbent shows high potential with excellent selectivity for the sorption of a variety of soft Lewis acid heavy metal ions by M–S bonding interactions. The crystal phase and morphology of the as-prepared MoS4-MOF were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron spectroscopy, thermal gravimetric and Brunauer-Emmett-Teller (BET) analysis. Sorption isotherm corresponds with the Langmuir model and shows good agreement with monolayer coverage of the heavy metal ions on the MoS4-MOF surface through a chemical sorption process. The sorption kinetic curves for metal ions fitted well with the pseudo-second-order model. The MoS4-MOF displays selectivity order of Hg2+ > Cd2+ ∼ Pb2+ > Zn2+ > Ni2+. The enormous sorption capacities of 714.3–1000.0 mg g-1 and very high distribution coefficients (Kd) of 6.0 × 103-5.5 × 104 mL g-1 (C0 = 100 mg L-1) place the porous MoS4-MOF as a promising sorbent for the removal of polluted water. The synthesized MoS4-MOF showed good chemical stability and recyclability.The first immobilization of (NH4)2MoS4 on Cu-BTC MOFs which enhances the stability of S-functionalized MOFs, simplifies its storage problems & enhanced maximum sorption capacities.

Protein Stabilization and Delivery: A Case Study of Invasion Plasmid Antigen D Adsorbed on Porous Silica.

Approximately half of all vaccines produced annually are wasted because effectivity is dependent on protein structure and heat exposure disrupts the intermolecular interactions needed to maintain the structure. Thus, most vaccines require a temperature-controlled supply chain to minimize waste. A more sustainable technology was developed via the adsorption of invasion plasmid antigen D (IpaD) onto mesoporous silica, improving the thermal stability of this protein-based therapeutic. Seven silicas were characterized to determine the effects of pore diameter, pore volume, and surface area on protein adsorption. The silica-IpaD complex was then heated above the IpaD denaturing temperature and N,N-dimethyldodecylamine N-oxide was used to remove IpaD from the silica. Circular dichroism confirmed that the adsorbed IpaD after the heat treatment maintained a native secondary structure rich in α-helix content. In contrast, the unprotected IpaD after heat treatment lost its secondary structure. Isotherms using Langmuir, Freundlich, and Temkin models demonstrated that the adsorption of IpaD onto silicas is best fit by the Langmuir model. If pores are less than 15 nm, adsorption is negligible. If the pores are between 15 and 25 nm, then monolayer coverage is achieved and IpaD is protected from thermal denaturing. If pores are larger than 25 nm, the adsorption is a multilayer coverage and it is easier to remove the protein from the silica because of a less-developed hydrogen bond network. This case study provides strong evidence that IpaD is thermally stabilized via adsorption on mesoporous silica with the proper range of pore sizes.

In Situ Study of Molecular Doping of Chlorine on MoS2 Field Effect Transistor Device in Ultrahigh Vacuum Conditions.

We report a precise measurement of the sensor behavior of the field effect transistor (FET) formed with the MoS2 channel when the channel part is exposed to Cl2 gas. The gas exposure and the electrical measurement of the MoS2 FET were executed with in situ ultrahigh-vacuum (UHV) conditions in which the surface analysis techniques were equipped. This makes it possible to detect how much sensitivity the MoS2 FET can provide and understand the surface properties. With the Cl2 gas exposure to the channel, the plot of the drain current versus the gate voltage (Id–Vg curve) shifts monotonically toward the positive direction of Vg, suggesting that the adsorbate acts as an electron acceptor. The Id–Vg shifts are numerically estimated by measuring the onset of Id (threshold voltage, Vth) and the mobility as a function of the dosing amounts of the Cl2 gas. The behaviors of both the Vth shift and the mobility with the Cl2 dosing amount can be fitted with the Langmuir adsorption kinetics, which is typically seen in the uptake curve of molecule adsorption onto well-defined surfaces. This can be accounted for by a model where an impinging molecule occupies an empty site with a certain probability, and each adsorbate receives a certain amount of negative charge from the MoS2 surface up to the monolayer coverage. The charge transfer makes the Vth shifts. In addition, the mobility is reduced by the enhancement of the Coulomb scattering for the electron flow in the MoS2 channel by the accumulated charge. From the thermal desorption spectroscopy (TDS) measurement and density functional theory (DFT) calculations, we concluded that the adsorbate that is responsible for the change of the FET property is the Cl atom that is dissociated from the Cl2 molecule. The monotonic shift of Vth with the coverage suggests that the MoS2 device sensor has a good sensitivity to detect 10–3 monolayers (ML) of adsorption corresponding to the ppb level sensor with an activation time of 1 s.

Natural biodegradable polymeric bioadsorbents for efficient cationic dye encapsulation from wastewater

With increasing the dye contamination scenes reported around the globe, the highly promising materials are needed to clean up the water to safeguard the human health. In this work, we have investigated the naturally available carbohydrate polymeric biodegradable adsorbent of wheat flour (WF) for the encapsulation of cationic Rhodamine B (RB) dye with high sensitivity and selectivity. The adsorbent was characterized to define the functional groups existing for complexation ability to the RB dye molecules. Adsorption studies were evaluated in batch mode with the function of solution acidity, contact time, initial RB concentration, competing ions existing and reusability with using eluent. The solution acidity was exhibited the key role, and the suitable pH 5.50 was selected based on the high adsorption efficiency and sensitivity nature. Moreover, the adsorption data were highly adjacent with the Langmuir adsorption isotherms model with monolayer coverage. The determined maximum adsorption was 142.26 mg/g, which was comparable with the other forms of adsorbents in the cationic dye adsorption operations. The competing ions were not adversely affected in the RB dye adsorption by the WF adsorbent due to the complexation ability. The WF adsorbent was exhibited the high reusability based on the elution and reuses performances. The adsorbed RB dye elution was evaluated using ethanol and then the WF adsorbent was ready to use for RB dye adsorption after washing with water without significant loss in its functionality. Therefore, the biodegradable natural carbohydrate polymeric WF adsorbent will attract the scientific community as suitable bio-adsorbent for efficient cationic dye removal from contaminated water as well as the production of value-added adsorbent for water treatments for safeguarding the public health.

Assessing of cesium removal from wastewater using functionalized wood cellulosic adsorbent

Sustainable materials are urgently desired for treatment of radioactive cesium (Cs) contaminated water to safe-guard the public health. Apart from the synthetic ligand-based materials, the Mangrove charcoal modified adsorbent was fabricated for assessing of Cs removal from waste sample. The raw charcoal was oxidized using nitrification approach and diverse oxygen containing carboxyl, carbonyl and hydroxyl functional groups were introduced. After modification, the adsorbent characteristics were drastically changed as compared to the charcoal during the measurement of FTIR, N2 adsorption-desorption isotherms and SEM micrographs. The data clarified that charcoal modified adsorbent was exhibited high Cs transport through the inner surface of the adsorbent based on bonding ability. The adsorbent was shown comparatively slow kinetics to Cs ion; however, the adsorption capacity was high as 133.54 mg/g, which was higher than the crown ether based conjugate materials. The adsorption data were followed to the Langmuir adsorption isotherms and the monolayer coverage was possible due to the data presentation. The presence of high amount of Na and K were slightly interfered to the Cs adsorption by the charcoal modified adsorbent, however; the Na and K concentration was 350–600 folds higher than the Cs concentration. Then the proposed adsorbent was selective to Cs for the potential real radioactive Cs contaminated water. The volume reduction was established rather than desorption and reuses advantages. More than 99% volume reduction was measured by burning of Cs adsorbed adsorbent at 500 °C for ensuring the safe storage and disposal of used adsorbent. Therefore, the charcoal modified adsorbent may open the new door to treat the Cs containing wastewater.

Surface-induced dimerization of 2-thiazoline-2-thiol on silver and gold nanoparticles: A surface enhanced Raman scattering (SERS) and density functional theoretical (DFT) study

The adsorption behavior of an anti-thyroid agent, 2-thiazoline-2-thiol (TT) on silver (Ag) and gold (Au) nanoparticles (NPs) was studied using surface enhanced Raman scattering (SERS) and density functional theory (DFT). The tautomers of TT involved in the surface adsorption processes were identified. Raman scattering studies indicated the predominance of the thione form in solid and the thiol tautomer in aqueous solution. SERS studies of TT functionalized Ag (TT-Ag) and Au NPs (TT-Au) showed maximum enhancement for 1 μM concentration, suggesting monolayer coverage. Surface induced dimerization of TT was evident from SERS and DFT. The appearance of prominent peaks at 484 (SS stretch) and 317 (CSS bend) cm−1 for TT-Ag revealed the formation of disulphide dimer, while the emergence of a distinct band at 2124 cm−1 (H-bonded SH stretch) for TT-Au indicated the development of H-bonded dimer. Thus, in the present study, selective formation of disulphide dimer and the H-bonded dimer was observed on the surface of Ag and Au NPs, respectively. In addition, the thiol tautomer was found to be exclusively bound to the metal surface, via the thiazoline ring N atom. In this work, a qualitative relation between the strength of TT-metal charge transfer complex and inter-molecular association of TT on the surface of metal NPs was established. This study, thus paves the way for designing novel metal nanosubstrates that can be exploited for studying interesting surface phenomenon, viz. surface induced dimerization or rearrangement reactions, surface catalysis, etc. as well as for designing valuable drugs suitable for chelation therapy.

Adsorption Behavior and Wettability of Rhodochrosite Surface: Effect of C18 Fatty Acid Unsaturation

Mineral surface wettability and its regulation by the adsorption of collectors have an important influence on the flotation performance. The adsorption behavior of C18 fatty acid with different unsaturation and its effect on rhodochrosite wettability was investigated with surface tension, contact angle, and atomic force microscopy (AFM) measurements. The results indicated that rhodochrosite hydrophobicity increased with the increasing concentration of fatty acid, along with the maximum contact angle (θmax) between hemimicelle concentration (HMC) and critical micelle concentration (CMC). Oleic acid (OA), linoleic acid (LA), and α-linolenic acid (ALA) had a higher θmax than stearic acid (SA), but the value decreased with the increase of C=C bond number. Besides, preferential adsorption of unsaturated fatty acids on the liquid-air interface can be attributed to the molecule’s steric hindrance resulting from C=C double bond, and the θ kept almost invariant with a higher value of ΓLG than ΓSL until HMC. The oriented monolayer and bilayer structure of fatty acids formed gradually on rhodochrosite surface with increasing concentration. However, the θmax may not necessarily correspond to the beginning of bilayer formation. Cylindrical monolayer and bilayer micelles of SA molecules were observed on rhodochrosite surface at HMC and CMC, respectively. While bilayer structures of unsaturated fatty acids formed before complete coverage of monolayer on rhodochrosite surface because of surface heterogeneity. This work provided a good understanding on the adsorption mechanism of fatty acid on rhodochrosite for flotation.

Enhanced heavy metal removal from an aqueous environment using an eco-friendly and sustainable adsorbent

Thiol-lignocellulose sodium bentonite (TLSB) nanocomposites can effectively remove heavy metals from aqueous solutions. TLSB was formed by using –SH group-modified lignocellulose as a raw material, which was intercalated into the interlayers of hierarchical sodium bentonite. Characterization of TLSB was then performed with BET, FTIR, XRD, TGA, PZC, SEM, and TEM analyses. The results indicated that thiol-lignocellulose molecules may have different influences on the physicochemical properties of sodium bentonite, and an intercalated–exfoliated structure was successfully formed. The TLSB nanocomposite was subsequently investigated to validate its adsorption and desorption capacities for the zinc subgroup ions Zn(II), Cd(II) and Hg(II). The optimum adsorption parameters were determined based on the TLSB nanocomposite dosage, concentration of zinc subgroup ions, solution pH, adsorption temperature and adsorption time. The results revealed that the maximum adsorption capacity onto TLSB was 357.29 mg/g for Zn(II), 458.32 mg/g for Cd(II) and 208.12 mg/g for Hg(II). The adsorption kinetics were explained by the pseudo-second-order model, and the adsorption isotherm conformed to the Langmuir model, implying that the dominant chemical adsorption mechanism on TLSB is monolayer coverage. Thermodynamic studies suggested that the adsorption is spontaneous and endothermic. Desorption and regeneration experiments revealed that TLSB could be desorbed with HCl to recover Zn(II) and Cd(II) and with HNO3 to recover Hg(II) after several consecutive adsorption/desorption cycles. The adsorption mechanism was investigated through FTIR, EDX and SEM, which demonstrated that the introduction of thiol groups improved the adsorption capacity. All of these results suggested that TLSB is an eco-friendly and sustainable adsorbent for the extraction of Zn(II), Cd(II) and Hg(II) ions in aqueous media.

Theoretical Study of Transition-Metal-Modified Mo2 CO2 MXene as a Catalyst for the Hydrogen Evolution Reaction.

The 2D MXenes have attracted great recent attention as the electrocatalytic materials for hydrogen evolution reaction (HER). However, the activity and the modification strategy of the catalytic properties have not been firmly established yet. In this study, we performed density functional theory (DFT) calculations to investigate the stability and HER performance of functionalized Mo2 C MXene. The Pourbaix diagram indicates the fully oxidized surface is the most stable state. The oxidized Mo2 CO2 is electrically conductive, yet the surface HER activity is unsatisfactory owing to the strong first H adsorption. The doping of transition metals (TM) into the Mo lattice, however, leads to much more enhanced H adsorption and deteriorates the activity. Alternatively, the H binding can be effectively weakened and flexibly tuned by anchoring the TM atoms over the surface with appropriate coverage, and Mn/Fe decoration at 12.5 % ML (monolayer) coverage is identified as the promising candidates with close to zero Gibbs free energy of H adsorption (ΔGH* ) for the first H adsorption. The weakening effect arises from charge transfer from TM to surface O, resulting in increased occupancy and weakened O-H bonds. Furthermore, contrary to the weakening effect, the tensile strain leads to enhanced O-H binding by the up-shifted Op electronic states, which can further modulate the HER performance of TM-modified Mo2 CO2 . The synergistic effect between TM modification and strain engineering offers beneficial advantages for the realization of efficient electrochemical HER, which can be applied to other MXenes for electronic and catalytic applications.

Application of macroalgal biomass derived biochar and bioelectrochemical system with Shewanella for the adsorptive removal and biodegradation of toxic azo dye

The present study aimed towards adsorptive removal of the toxic azo dye onto biochar derived from Eucheuma spinosum biomass. Characterization of the produced biochar was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). Eucheuma spinosum biochar (ES-BC) produced at 600 °C revealed a maximum adsorption capacity of 331.97 mg/g towards reactive red 120 dye. The adsorption data fitted best to the pseudo-second order kinetics (R2 > 0.99) and Langmuir isotherm (R2 > 0.98) models. These adsorption models signified the chemisorption mechanism with monolayer coverage of the adsorbent surface with dye molecules. Furthermore, the adsorption process was mainly governed by electrostatic interaction, ion exchange, metal complexation, and hydrogen bonding as supported by the solution pH, FTIR, XPS, and XRD investigation. Nevertheless, alone adsorption technology could not offer a complete solution for eliminating the noxious dyes. Therefore, the bioelectrochemical system (BES) equipped with previously isolated marine Shewanella marisflavi BBL25 was intended for the complete remediation of azo dye. The BES II demonstrated highest dye decolorization (97.06%) within 48 h at biocathode where the reductive cleavage of the azo bond occurred. Cyclic voltammetry (CV) studies of the BES revealed perfect redox reactions taking place where the redox mediators shuttled the electrons to the dye molecule to accelerate the dye decolorization. Besides, the GC-MS analysis revealed biotransformation of the dye into less toxic metabolites as tested using a phyto and cytogenotoxicity.

A monolayer of Pd on ZrC(0 0 1) speeds up O2 dissociation: An ab initio study

We propose the Pd monolayer (ML) on ZrC(001) surface as an effective catalyst for the dissociation of oxygen by density functional theory calculations. We find that the coverage of Pd has a conspicuous impact on the adsorption and dissociation of O2. The strong interaction between the Pd atoms and the ZrC(001) support enhances the reactivity and stability of the electrocatalyst. By comparing the binding energies of Pd-Pd and Pd-C, we conclude that the Pd adatoms do not aggregate to form a cluster and prefer to form a monolayer when the coverage is low. With a monolayer of coverage, the C sites are fully saturated by adsorbed Pd atoms, which prevent the oxidation of the ZrC(001) surface. The dissociation activity of O2 on PdML/ZrC(001) is predicted to be a rival of or even surpass Pt(111). In addition, the high mobility of the dissociated oxygen atoms on PdML/ZrC(001) also benefits the later reaction step for ORR.

EFFECTIVE ADSORPTION OF TETRACYCLINE WITH Co3O4/Fe3O4 BIMETALLIC NANOPARTICLES

In the present study cobalt oxide/iron oxide bimetallic nanoparticles (Co3O4/Fe3O4 NPs) were synthesized by chemical coprecipitation method. The synthesized Co3O4/Fe3O4 NPs were characterized by SEM and XRD analysis. The synthesized nanoparticles were used as an adsorbent for the removal of a kind of antibiotic as Tetracycline (TC) from aqueous solutions. According to characterization results, small plate-like structures and agglomerated irregular spherical nanosized particles (101.85 ± 15.04 nm) were formed. The XRD data confirmed the structure of synthesized adsorbent was Co3O4/Fe3O4. The optimum tetracycline adsorption conditions were determined as the initial pH of solution 9.0, temperature 55°C, and adsorbent concentration 3.0 g/L. A linear increase was observed in equilibrium uptakes of TC with the increasing the initial antibiotic concentrations. The experimental equilibrium data was modelled with Langmuir and Freundlich isotherm models. The experimental equilibrium data was the best agreement to the Langmuir isotherm model. The maximum monolayer coverage capacity of Co3O4/Fe3O4 NPs for TC adsorption was found to be 149.26 mg/g at 55°C optimum temperature. The experimental kinetic adsorption data were defined as the best agreement with the pseudo-second-order kinetic model. Weber Morris mass transfer modelling results showed that both the film (boundary layer) and intra-particle diffusion were effective in the adsorption process. The thermodynamic studies suggested that the adsorption process was endothermic, spontaneous and the positive ΔS value indicated increased disorder at the solid-solution interface during the adsorption. Moreover, the synthesized adsorbent showed high adsorption efficiencies at the end of seven sequence usages.

Grain-boundary phosphorus segregation in highly neutron-irradiated reactor pressure vessel steels and its effect on irradiation embrittlement

Reactor pressure vessel (RPV) steels for pressurized water reactors (PWRs) with bulk P contents ranging from 0.007 to 0.012wt.% were subjected to neutron irradiation at fluences ranging from 0.3 to 1.2 × 1020 n/cm2 (E > 1 MeV) in PWRs or a materials testing reactor (MTR). Grain-boundary P segregation, which was analyzed using Auger electron spectroscopy (AES) on intergranular facets, increased with increasing neutron fluence. A rate theory model based on four diffusion-reaction equations for substitutional P atoms, octahedral interstitial P atoms, vacancies, and self-interstitial atoms was also used to simulate the increase in grain-boundary P segregation for RPV steels with a bulk P content up to 0.020wt.%, using parameters optimized by the present AES data. The increase in grain-boundary P segregation in RPV steel with a bulk P content of 0.015wt.%, which is the maximum P concentration in RPV steels used in Japanese nuclear power plants intended for restart, was estimated to be less than 0.1 in monolayer coverage at 1 × 1020 n/cm2 (E > 1 MeV). A comparison of the PWR data with the MTR data, including that from the literature, showed that neutron flux had no effect upon grain-boundary P segregation for A533B steels. The relationships of the ductile-brittle transition temperature (DBTT) shifts to grain-boundary P segregation and to yield strength were also discussed. A linear relationship between the yield strength and the DBTT shift with a slope of 0.63 was obtained for RPV steels with a bulk P content up to 0.026wt.%, which is higher than that of most U.S. A533B steels. It is concluded that the intergranular embrittlement is unlikely to occur for RPV steels irradiated in PWRs.

Low-cost and high-wet-strength paper-based lignocellulosic adsorbents for the removal of heavy metal ions

Paper-based lignocellulosic adsorbents with high wet strength, high adsorption capacity and good separation and recycling performance were prepared from polar chemimechanical pulp by simple papermaking and one-step dip coating. Green crosslinking agent of citric acid, which can react with the hydroxyl groups of cellulose under the catalysis of sodium hypophosphite, was used to increase the wet strength as well as the carboxyl content of the paper-based adsorbents. Both the wet strength and carboxyl content increase upon increasing the beating degree and the dosage of citric acid. The wet strengths reach 40∼50 % of their dry strengths and the carboxyl contents are tuned in the range of 0.07∼ 0.66 mmol/g. Pseudo-second-order equation was found to fit the kinetics data best, indicating the adsorption is chemisorption process. The good agreement of equilibrium data with Langmuir model confirm the monolayer coverage of Cu(II) and Pb(II) onto adsorbents. The maximum adsorption capacities of Cu(II) and Pb(II) are high up to 61.96 and 138.11 mg/g, respectively. Good regeneration stability and more than 90% of its initial adsorption capacity are achieved even after four adsorption-regeneration cycles, and the adsorbents are basically unaffected during the desorption process. In addition, the paper-based adsorbents with micron pores are able to effectively separate particles with the size larger than 50 μm. Combined with the filtration device, the paper-based adsorbents are easy to realize the continuous adsorption process and can be simply recycled from water without separation difficulty. The synthetic strategy of multifunctional paper-based adsorbents from polar chemimechanical pulp provides new ideas and methods for the full and high-value utilization of lignocellulose.

Photocatalytic Decolorization and Biocidal Applications of Nonmetal Doped TiO2: Isotherm, Kinetic Modeling and In Silico Molecular Docking Studies.

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO2 against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO2 with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO2. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m2 g−1 specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g−1 with Kads of 0.113 mg−1. The LH model yielded a higher coefficient KC (1.15 mg L−1 h−1) compared to the adsorption constant KLH (0.3084 L mg−1). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol−1) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Adsorption Kinetics, Isotherms, and Thermodynamics of Removal of Anionic Surfactant from Aqueous Solution Using Fly Ash

Surfactants are organic compounds which can be used in several applications. However, they can contaminate world water resources causing detrimental effects to human beings, aquatic life, and animals. This paper investigates the adsorption kinetics, isotherms, and thermodynamic properties for the removal of an anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), using fly ash. Characteristics of fly ash such as surface area and pore size analysis and the point of zero charge (PZC) were determined. The effects of parameters such as pH, surfactant concentration, and temperature and the adsorption kinetics, isotherms, and thermodynamic properties and adsorption mechanism were determined. Fly ash is a mesoporous material having surface area and pore size of 1.079 m2/g and 9.813 nm and PZC at pH 6.58. pH 2 and the temperature 25 °C were optimum for adsorbing SDBS onto fly ash. The adsorption capacity and removal efficiency increased by increasing the concentration of SDBS from 100 to 2000 mg/L, indicating that the increase of surfactant concentration could not saturate the surface of fly ash. The pseudo-second-order and the Langmuir isotherm models showed best fit to the adsorption data and the thermodynamic properties described adsorption as an exothermic, barrierless, non-spontaneous, and entropy-reducing reaction which is more feasible at a lower temperature of 25 °C. This indicated that the adsorption occurs by both physisorption and chemisorption with monolayer coverage of SDBS on the surface of fly ash. SDBS surfactant adsorbed onto fly ash mainly through electrostatic interactions between oppositely charged SDBS and fly ash.

Theory-Guided Machine Learning Finds Geometric Structure-Property Relationships for Chemisorption on Subsurface Alloys

Summary Developing physically transparent and quantitatively accurate models that relate the chemical interaction (chemisorption strength) between an adsorbate and a solid surface to the adsorption site's geometry is critical for our understanding of catalysis, corrosion, and electrochemistry. We develop a theory-guided machine-learning (ML) approach, which uses an interpretable class of ML models called generalized additive models (iGAM models), to discover predictive structure-property models that can quantify and explain the link between the geometric structure of an adsorption site and the chemisorption strength. We demonstrate the approach through several case studies, where we analyze the chemisorption strength of chemically distinct adsorbates (O, OH, S, and Cl) on subsurface metal alloy surfaces subjected to various strain- and ligand-induced changes in the local geometric structure. By comparing the ML-derived chemisorption models to previously established electronic-structure models, we clarify the critical physical parameters that control the chemisorption process on metal surfaces.