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Resistance to algae contamination is an important characteristic of insulators used in overhead power distribution in coastal environments. It is therefore important to understand the parameters governing algae adhesion onto polymer insulator materials such as silicone. Flow cell-based shear experiments were conducted in order to characterize the adhesion strength of algae onto polydimethylsiloxane surfaces, comparing fresh polymer substrates with those that have been soaked in water and saline solutions for 1 month. Both freshwater algae and seawater species could withstand considerably less drag force and were therefore more easily removed when the polymer was soaked in salt water. The polymer surface was found to be unaltered in terms of its roughness, contact angle, and lack of water uptake; no macroscopic surface characterization was therefore able to account for the differences in cell adhesion strength resulting from the soaking treatment. Surface-specific nonlinear vibrational spectroscopy, however, revealed subtle differences in the orientation of surface methyl groups that resulted from the water and saline exposure.

The mechanical performances of hydrogels are greatly influenced by the functionality of cross-linkers and their covalent and non-covalent interactions with the polymer chains. Conventional chemical cross-linkers fail to meet the demand of large toughness and high extensibility for their immediate applications as artificial tissues like ligaments, blood vessels, and cardiac muscles in human or animal bodies. Herein, we synthesized a new graphene oxide-based two-dimensional (2D) cross-linker (GOBC) and exploited the functionality of the cross-linker for the enhancement of toughness and stretchability of a poly(acrylic acid) (PAA) hydrogel. The 2D nanosheets of GO were modified in such a way that they could provide multifunctional sites for both physical and chemical bonding with the polymer chains. Carboxylic acid groups at the surfaces of the GO sheets were coupled with the acrylate functional groups for covalent cross-linking, while the other oxygen-containing functional groups are responsible for physical cross-linking with polymers. The GOBC had been successfully incorporated into the PAA hydrogel and the mechanical properties of the GOBC cross-linked PAA hydrogel (PAA-GOBC) were investigated at various compositions of cross-linker. Seven times enhancement in both toughness and elongation at break has been achieved without compromising on the modulus for the as-synthesized PAA-GOBC compared to the conventional N,N′-methylenebis(acrylamide) (MBA) cross-linked PAA hydrogel. This facile and efficient way of GO modification is expected to lead the development of a high-performance nanocomposite for cutting-edge applications in biomedical engineering.

A combination of strong load-bearing capacity and high swelling degree is desired in hydrogels for many applications including drug delivery, tissue engineering, and biomedical engineering. However, a compromising relationship exists between these two most important characteristics of hydrogels. Improving both of these important properties simultaneously in a single hydrogel material is still beyond the satisfactory limit. Herein, we report a novel approach to address this problem by introducing a silica-based bi-functional 3D crosslinker. Our bi-functional silica nanoparticles (BF-Si NPs) possess amine groups that are able to offer pseudo-crosslinking effects induced by inter-cohesive bonding, and acrylate groups that can form conventional covalent crosslinking in the same hydrogel. We fabricated polyacrylic acid (PAc-Si) and polyacrylamide (PAm-Si) hydrogels using our BF-Si NPs via free radical polymerization to demonstrate this concept. Incorporation of the BF-Si crosslinkers into the hydrogels has resulted in a large enhancement in the mechanical properties compared to conventional hydrogel crosslinked with N,N′-methylene bisacrylamide (MBA). For instance, tensile strength and the toughness increased by more than 6 times and 10 times, respectively, upon replacing MBA with BF-Si in polyacrylamide hydrogel. Moreover, the hydrogels crosslinked with BF-Si exhibited a remarkably elevated level of swelling capacity in the aqueous medium. Our facile yet smart strategy of employing the 3D bi-functional crosslinker for combining high swelling degree and strong mechanical properties in the same hydrogels can be extended to the fabrication of many similar acrylate or vinyl polymer hydrogels.

The development of safe and cost-effective methods for the treatment of dye polluted wastewater has been a great concern among researchers. Herein, we developed a nanocomposite (M3D–PAA–CCN) based on polyacrylic acid (PAA) crosslinked with magnetic 3D crosslinkers (M3D) and carboxylated cellulose nanocrystals (CCN), for the removal of cationic dyes from aqueous solutions. Acrylic-functionalized Fe3O4 nanoparticles were covalently linked to the polymer chains via the form of the 3D crosslinker to introduce magnetic properties into the as-synthesized nanocomposite. The addition of highly dispersive CCN reduced the gel-like properties of the nanocomposite and instead incorporated a diffusive nature, which was more desirable for adsorbents. The surface morphology of the nanocomposite was analyzed by FESEM and the size of the nanocomposite particles was found to be in the range of 60–90 nm. The chemical functionalities and compositions were determined by XPS, FTIR, and EDX analyses whereas TGA confirmed the thermal stability of M3D–PAA–CCN. The maximum adsorption capacity of the M3D–PAA–CCN (332 mg g−1) was measured higher than that of M3D–PAA (114 mg g−1) to a cationic methylene blue (MB) dye indicating the significant contribution of CCN. The adsorption capacity of the as-synthesized M3D–PAA–CCN was found to be highly pH-dependent and the adsorption capacity increased with the increase of pH owing to the greater negative charge as indicated by the higher zeta potential. The adsorption kinetics of MB on the composites was found to follow the pseudo-second-order model. The adsorption capacity was also investigated as a function of concentration to figure out the adsorption mechanism using Langmuir and Freundlich isotherm models. The Langmuir model fitted the adsorption process better as suggested by the relatively smaller nonlinear chi-square value obtained from the fitting parameters.

The molecular origin of overcharging at mineral oxide surfaces remains a cause of contention within the geochemistry, physics, and colloidal chemistry communities owing to competing “chemical” vs “physical” interpretations. Here, we combine vibrational sum frequency spectroscopy and streaming potential measurements to obtain molecular and macroscopic insights into the pH-dependent interactions of calcium ions with a fused silica surface. In 100 mM CaCl2 electrolyte, we observe evidence of charge neutralization at pH~10.5, as deducted from a minimum in the interfacial water signal. Concurrently, adsorption of calcium hydroxide cations is inferred from the appearance of a spectral feature at ~3610 cm-1. However, the interfacial water signal increases at higher pH, while adsorbed calcium hydroxide appears to remain constant, indicating that overcharging results from hydrated Ca2+ ions present within the Stern layer. These findings suggest that both specific adsorption of hydrolyzed ions and ion-ion correlations of hydrated ions govern silica overcharging with increasing pH.

Paper and paper products are widely used without any antimicrobial efficacy in our everyday lives and thus can act as potential transporters of many diseases. Herein, we introduce antimicrobial activity to cellulose paper by presenting a tailored mussel-inspired strategy for the sustainable immobilization of silver nanoparticles (AgNPs), which are well-known for the effectiveness in preventing annexation and proliferation of microbes on materials surfaces. First, we functionalized the cellulose paper with succinic acid that eventually reacted with dopamine to give dopamine-modified paper. The dopamine molecules possess excellent adhesion and strong coordination with metal substrates through catechol groups offering a potentially robust interface between AgNPs and the organic structure of the paper. Next, AgNPs were deposited onto the paper by simply immersing dopamine-modified paper in a silver salt solution to accomplish the antimicrobial properties. Field emission scanning electron microscopic study of ...

The structure of water adjacent to silica is sensitive to the degree of deprotonation of surface silanol groups. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. We have used nonlinear vibrational spectroscopy of the water O–H stretching band over a temperature range of 10–75 °C to account for the increase in surface potential from deprotonation. We demonstrate that the behavior at the silica surface is a balance between increasing surface charge and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, we use our data to report the changes in enthalpy and entropy for deprotonation at each site. This is the first experimental determination of these thermodynamic parameters for hydrated silanol groups at the silica surface, critical to a wide range of geochemical and technological applications.

Here, we report a novel fabrication of a magnetic carbon nanotube-reduced graphene oxide-silver nanocomposite for the adsorption and simultaneous catalytic reduction of two environmental pollutants. Fe3O4 nanoparticles were grown and anchored onto the multi-walled carbon nanotube (CNT) first to generate magnetic CNT (MCNT), which was further coated with polydopamine to enhance the stability of the Fe3O4 particles and introduce new functionalities on the surface. Hydrothermal treatment of the polydopamine-coated MCNT (PD-MCNT) with graphene oxide (GO) produced a highly carbonaceous reduced GO-PD-MCNT (rGO-PD-MCNT), which by itself exhibited very high adsorption capability. The catalytic property was integrated by depositing silver nanoparticles (AgNPs) on the rGO-PD-MCNT by reducing Ag(I) ions. High catalytic efficacy besides fast and efficient adsorption of the as-synthesized nanocomposites was demonstrated at variable pH during the removal of a toxic model dye, methylene blue (MB), and an aromatic nitro compound, 4-nitrophenol (4-NP). The nanocomposites were found to be magnetically separable, easily regenerable through desorption using water and ethanol, and thus highly recyclable (more than 15 cycles). The rare combination of all these properties in a single scaffold makes this nanocomposite potentially useful in a wide range of engineering and environmental applications.

Lycopene was extraction, isolation and purification using recrystallization, column chromatography, and preparative thin layer chromatography (TLC) methods as well as degradation kinetics of lycopene were studied at refrigerated temperature and room temperature for 3 wk from watermelon. Higher lycopene degradation was observed at refrigerated temperature as compared to ambient temperature throughout the storage periods. The highest amount of lycopene retained in recrystallization (101.69 μg/g) followed by column chromatography (18.20 μg/g) and preparative TLC (15.57 μg/g). Color parameters, half-life time (t1/2 ), and color retention (%R) were dependent on extraction, isolation, and purification methods and storage life. Recrystallization and preparative TLC were followed by first order reaction model. Preparative TLC exhibited higher activation energy than did the recrystallization and column chromatography. Therefore, the result shows that recrystallization method could apply to extract and purify lycopene from watermelon that would also be used as a natural colorant as well as value-added product.

This study reports the antimicrobial activity and improved dyeing performance of cotton knitted fabric by depositing silver nanoparticles on the surface. The cotton fabric is first treated with caustic soda (NaOH) of three different concentrations to activate the hydroxyl groups on the cellulose surface and then the nanoparticles are introduced on fabric surface by direct reduction of silver nitrate salt using ascorbic acid. The presence of silver nanoparticles on the fabric surface is clearly observed by scanning electron micrograph. The elementary analysis is done by energy dispersive spectroscopy and the chemical interaction of cotton fibre with nano silver is characterized by Fourier transform infrared spectrum. In this work, the antimicrobial activity on Ag deposited sample is investigated by quantitative analysis against both Gram positive (S. aureus) and Gram negative (E. coli) bacteria. Results shows a significant antimicrobial activity such as more than 90% bacterial reduction of both Gram positive and Gram negative bacteria are inhibited. The fabric sample is dyed with 2% direct dye and consequently the result shows very good performance in dye exhaustion, colour strength and fastness property. For instance, the incorporation of Ag nanoparticles increases 7% of dyestuff exhaustion and 15% of colour strength of the fabric. However, Ag nanoparticles deposited fabric loses its strength slightly due to the pretreatment using NaOH for the functionalization of cotton.

A polyacrylic acid (PAA) functionalized magnetic Fe3O4 nanoparticle-graphene oxide nanocomposite (PAA/MGO) was synthesized by a facile method. The structure and surface properties of MGO and PAA/MGO composites were characterized by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and zeta potential measurements. The adsorption of a model dye pollutant, methylene blue (MB), on MGO and PAA/MGO was investigated in batch tests. The functionalization of PAA to MGO significantly enhances the maximum adsorption capacity of MB (at pH = 7) from ∼70 mg g−1 (on MGO) to ∼291 mg g−1 (PAA/MGO). The adsorption of MB on MGO and PAA/MGO was mainly driven by the electrostatic attraction between positively charged MB molecules and negatively charged nanocomposite surfaces, and the higher adsorption capacity of PAA/MGO is mainly attributed to the functionalization of PAA and its higher content of charged carboxyl groups than MGO. The adsorption capacity of MB on both MGO and PAA/MGO adsorbents also increases with increasing solution pH from 3 to 11, due to enhanced electrostatic attraction at high pH conditions. The limited adsorption capacity of MB on MGO and PAA/MGO at pH 3, when electrostatic attraction is almost negligible, indicates that π–π interaction between the GO surface and MB also plays a role in the adsorption process. The PAA/MGO shows a rapid adsorption rate and high adsorption capacity of MB with magnetic properties for easy separation and excellent recyclability, which endows the nanocomposite with great potential for the removal of cationic organic pollutants in wastewater treatment.

We have monitored the interactions of DNA strands immobilized on silica at the buried solid/liquid interface using vibrational sum frequency generation. We find that the nucleobases exhibit net order even prior to hybridization for immobilized single strands. Moreover, varying the temperature of the hybridized samples leads to spectral changes from the thymine nucleobases that are consistent with duplex dissociation.

Using second harmonic generation and sum frequency generation spectroscopy, we monitor the influence of sodium and potassium halides on acid–base processes at the negatively charged silica/aqueous electrolyte interface. We find that the two types of acidic silanols at the surface are very sensitive to the presence of halides in the aqueous phase. As the halide size increases, the pH at which half the more acidic sites are deprotonated (pH0.5) shifts to lower pH. Conversely, the pH0.5 of the less acidic sites shifts to higher pH with increasing halide size. We also observe titration curves of increasing sharpness as the halide size increases, indicative of positive cooperativity. Using a simple cooperative model, we find that the cooperative unit for the dissociation of more acidic surface sites is ∼1, 2, and 3 for the chloride, bromide, and iodide electrolytes, respectively, which reveals that the larger anions promote deprotonation among the more acidic silanol groups. We also find that the fraction of m...

A mixed oxide of cobalt (Co) and nickel (Ni) with an approximate composition of Co 0.4 Ni 0.4 O 0.2 was prepared chemically by precipitating from the corresponding metal carbonates and heating the mixture of carbonates at 650 °C under ambient atmosphere. The mixed (Co–Ni) oxide thus prepared was characterized by IR, SEM and XRD methods. The composition of the mixed metal oxide was obtained by EDX analysis. The surface behavior of the Co–Ni mixed oxide matrix was tested by adsorption studies and pH pzc measurement. The Co–Ni mixed oxide matrix behaves as a charged adsorbent at the pH media higher and lower than its pH pzc value (9.50) and thus found to be capable of anchoring the oppositely charged species onto its surface. Removal of cationic and anionic dyestuffs, viz ., methylene blue (MB) and procion red (PR), respectively, was attempted using the mixed oxide surface as adsorbent. Although both the dyes can be removed by the mixed oxide, the extent of PR removal (∼70%) seems to be much higher than that of MB (∼20%) demonstrating the superior performance of the Co–Ni mixed oxide for its use as adsorbent in removing the anionic PR dyestuff from water.

Using nonresonant second harmonic generation spectroscopy, we have monitored the change in surface charge density of the silica/water interface over a broad pH range in the presence of different alkali chlorides. Planar silica is known to possess two types of surface sites with pKa values of ∼4 and ∼9, which are attributed to different solvation environments of the silanols. We report that varying the alkali chloride electrolyte significantly changes the effective acid dissociation constant (pKa(eff)) for the less acidic silanol groups, with the silica/NaClaq and silica/CsClaq interfaces exhibiting the lowest and highest pKa(eff) values of 8.3(1) and 10.8(1), respectively. Additionally, the relative populations of the two silanol groups are also very sensitive to the electrolyte identity. The greatest percentage of acidic silanol groups was 60(2)% for the silica/LiClaq interface in contrast to the lowest value of 20(2)% for the silica/NaClaq interface. We attribute these changes in the bimodal behavior to the influence of alkali ions on the interfacial water structure and its corresponding effect on surface acidity.

The immobilization of oligonucleotide sequences onto glass supports is central to the field of biodiagnostics and molecular biology with the widespread use of DNA microarrays. However, the influence of confinement on the behavior of DNA immobilized on silica is not well understood owing to the difficulties associated with monitoring this buried interface. Second harmonic generation (SHG) is an inherently surface specific technique making it well suited to observe processes at insulator interfaces like silica. Using a universal 3-nitropyrolle nucleotide as an SHG-active label, we monitored the hybridization rate and thermal dissociation of a 15-mer of DNA immobilized at the silica/aqueous interface. The immobilized DNA exhibits hybridization rates on the minute time scale, which is much slower than hybridization kinetics in solution but on par with hybridization behavior observed at electrochemical interfaces. In contrast, the thermal dissociation temperature of the DNA immobilized on silica is on average 12 °C lower than the analogous duplex in solution, which is more significant than that observed on other surfaces like gold. We attribute the destabilizing affect of silica to its negatively charged surface at neutral pH that repels the hybridizing complementary DNA.

We report the synthesis and self-assembly of azide and amine trimethoxysilanes that result in mixed monolayers on silica. The amine and azide functional groups can be independently reacted with acid chlorides and terminal alkynes, respectively. Consequently, these orthogonally reactive monolayers represent a general starting point for making bifunctional surfaces. Using X-ray photoelectron spectroscopy, we determined the azide/amine surface ratio as well as the reactivity of the azide and amine functional groups in the mixed self-assembled monolayer (SAM). Significantly, the surface azide/amine ratio was much lower than the azide/amine ratio in the self-assembly mixture. After determining the self-assembly mixture composition that would afford 1:1 azide−amine mixed monolayers, we demonstrated their subsequent functionalization. The resulting bifunctional surface has a similar functional group ratio to the azide/amine precursor SAM demonstrating the generality of this approach.

Mn 3 O 4 nanoparticles with diameter ca. 10 nm were synthesized by the forced hydrolysis of Mn(II) acetate at 80 °C. The X-ray diffraction (XRD), Fourier transform infra red (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were employed to study structural features and chemical composition of the nanoparticles. The unique oxidative activity of the Mn 3 O 4 nanoparticles was demonstrated in the polymerization and dye degradation reactions. On adding Mn 3 O 4 suspension to an acidic solution of aniline, yielded immediately green sediment of polyaniline (PANI). The organic dyes, viz ., methylene blue (MB) and procion red (PR) were found to be completely decolorized from their aqueous solution on treating the dyes with Mn 3 O 4 suspension in acidic media. The Mn 3 O 4 nanoparticles also showed a clear antibacterial activity against the Vibrio cholerae , Shigella sp ., Salmonella sp ., and Escherichi coli bacteria that cause cholera, dysentery, typhoid, and diarrhea diseases, respectively.