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Interactions between organic molecules in aqueous environments, whether in the fluid phase or adsorbed on solids, are often affected by the cations present in the solution. We investigated, at nanometre scale, how surface carboxylate interactions are influenced by dissolved divalent cations: Mg2+, Ca2+, Sr2+ and Ba2+. Self assembled monolayer (SAM) surfaces with exposed terminations of alkyl, -CH3, carboxylate, -COO- or dicarboxylate, -DiCOO-, were deposited on gold coated tips and substrates. We used atomic force microscopy (AFM), in chemical force mapping (CFM) mode, to measure adhesion forces between various combinations of SAMs on the tip and substrate, in solutions of 0.5 M NaCl, that contained 0.012 M of one of the divalent cations. The type of cation, the number of carboxyl groups that interact and their structure on the SAM influenced adhesion between the surfaces. The effect of the reference solution, which only contains Na+ cations, on adhesion force was mainly attributed to van der Waals and hydrophobic forces, explaining lower force in systems that are more hydrophilic, i.e., -COO--COO-, and higher force for more hydrophobic systems. For charged surfaces, i.e., -COO- and -DiCOO-, in divalent cation solutions, results were consistent with ion bridging. The inclusion of a hydrophobic surface, i.e., the -CH3-COO- or -CH3-DiCOO- system, decreased the possibility for strong cation bridging with the charged surface, resulting in lower adhesion. For systems including -COO-, the adhesion force series followed the inverse cation hydrated radius trend (Na+~ Mg2+2+2+2+) whereas -DiCOO- was responsible for lower adhesion force and modified trends, depending on the corresponding surface in the system. Differences in force magnitude between the monolayers were correlated with lower charge availability on the -DiCOO- surface as a result of fewer active sites, probably because of the tendency of exposed malonate surface groups to interact between them, as well as high rigidity, resulting from the molecule structure. The characteristic response of the -DiCOO- surface in solutions of Sr2+ and Ca2+ was correlated with possible malonate complexation modes. Comparison with previous studies suggested that the strong response of a -DiCOO- surface to Sr2+ resulted from bidentate chelation, whereas Ca2+ response was attributed to alpha mode association to malonate.

Interactions between graphene oxide (GO) and organic molecules play a role in processes such as environmental remediation and water treatment. However, little is known about underlying molecular level processes with the presence of ions. In this study, we utilized atomic force microscopy (AFM) in chemical force mapping (CFM) mode to directly probe their adhesion interactions. AFM tips were functionalised to serve as models for nonpolar and polar organic molecules, i.e. with alkyl, –CH3, and carboxyl, –COO(H). For experiments with –COO(H) tips, adhesion between GO and tips decreased in the order: Ba2+ > Ca2+ > Mg2+ > Na+, whereas for the –CH3 tips, ion dependent adhesion was relatively low but followed the same: Ba2+ > Ca2+ > Mg2+ ≈ Na+. Calculations with Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and the Schulze–Hardy rule could not account for the observations. We propose that ion bridging plays a definitive role in adhesion between –COO(H) tips and the GO surface. This is consistent with proposed models with density functional theory (DFT) calculations. Adhesion of –CH3 tips is a response to the hydrophilic interactions and the ion dependent part is suggested to arise from ion bridging between slightly negative charged –CH3 tips and the GO surface. High pH had a notable influence on the adhesion of the –COO(H) tip but a negligible effect on the –CH3 tip. These results offer important insights into interactions between solutions and mineral surfaces with adsorbed organic molecules.

We demonstrate a facile selective synthesis of phase-pure anatase, rutile, and brookite nanocrystal polymorphs of titania (TiO

We demonstrate a facile selective synthesis of phase-pure anatase, rutile, and brookite nanocrystal polymorphs of titania (TiO2) using a benign hydrothermal treatment of an industrial grade TiOSO4 precursor. Acetic acid (CH3COOH) is used for the synthesis of anatase, glycolic acid (HOCH2COOH) is used for rutile, and both glycolic acid and ammonium hydroxide (NH4OH) are used for obtaining brookite. The detailed morphologies of the as-synthesized materials are determined from a combination of powder X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The anatase nanocrystals are terminated by low-energy {101} facets and a small amount of high-energy {001} facets, whereas the rutile nanocrystals are terminated by low-energy {110} facets and a small amount of high-energy {111} facets. The brookite nanocrystals are terminated by low-energy {210} facets and {111} facets, and not the high-energy {101} and {201} facets erroneously reported in the literature. The activities of as-synthesized TiO2 nanocrystals as supports for vanadia-titania catalysts are investigated by measuring the selective catalytic reduction of NO using ammonia (NH3-SCR). The O2-activated samples show similar oxidovanadium(V) bands in their Raman spectra, and the relative activity relation is found to be anatase > brookite > rutile. In addition, the photocatalytic activity is evaluated by measuring the decomposition of Rhodamine B (RhB) under UV-light irradiation, and the relative activity order is found to be P25 > anatase ≈ rutile > brookite.

The properties and behavior of the interface between mineral surfaces, adsorbed organic compounds, and water are important for oil recovery. Low-salinity (LS) water flooding releases more oil from sandstone reservoirs than conventional flooding with seawater or formation water. However, the role of strongly adsorbed organic material, as an anchor for oil molecules, is not yet completely understood. Here, we mimic reservoir pore surfaces using graphene oxide sheets deposited on flat silicon wafers. The LS response was quantified using atomic force microscopy (AFM) in chemical force mapping mode to directly measure the adhesion force. AFM tips were functionalized to serve as models for hydrophobic and polar oil molecules, i.e., with alkyl, −CH3, and carboxyl, −COO(H). Adhesion force, measured with −CH3 tips, was 18% lower in LS (∼1500 ppm) than high-salinity (HS, ∼35 600 ppm) solutions, while for −COO(H) tips, adhesion force was 13% lower in LS than HS solutions. The Dejarguin–Landau–Verwey–Overbeek theory ...

The unambiguous determination of the chemical functionality over graphene oxide (GO) is important to unleash its potential applications. However, the mapping of oxygen functionalities distribution remains to be unequivocally determined because of highly inhomogeneous non-stoichiometric structures and ultra-thin layers of GO. In this study, we report an experimental observation of the spatial distribution of oxygen functional groups on monolayer and multilayer GO using AFM-IR, atomic force microscopy coupled with infrared spectroscopy. Overcoming conventional IR diffraction limit for several micrometers, the novel AFM-IR reaches high spatial resolution ∼20 nm and could detect IR absorption on ∼1 nm thickness of monolayer GO. With nanoscale chemical mapping, the distribution of different oxygen functional groups is distinguished with AFM-IR over the GO surface. It allows us to observe that these oxygen functional groups prefer to sit on the fold areas, in discrete domains and on the edges of GO, which gave more insights into its chemical nature. The determination of the position of functional groups through precise imaging contributes to our understanding of GO structure-properties relations and paves the way for targeted tethering of polymers, biomaterials, and other nanostructures.

Three new carboxylic-acid substituted oligo-phenylenevinylenes (OPVs) with electron-donating substituents in the central ring were synthesized in high yield by the Mizoroki–Heck reaction. The linkers were optically characterized by UV–vis absorption spectrophotometry, fluorescence spectroscopy in solution and the solid state, and measurement of the emission quantum yield. A comparison of substituted and unsubstituted OPVs shows that the electron-donating groups significantly affect the luminescent properties of the linkers. As the electron-donating strength of the substituent increases, the absorption bands strengthen, the emission wavelength shifts bathochromically, and the emission quantum yield increases. Moreover, fluorescence analysis of the OPVs in the solid state shows that the nature of the substituent significantly affects the inter-chromophore interactions. These results suggest that the new linkers have potential for electro-optic applications in which high emission efficiency is required, such as chemical sensing.

Interactions between mineral surfaces and organic molecules are fundamental to life processes. The presence of cations in natural environments can change the behavior of organic compounds and thus alter the mineral–organic interfaces. We investigated the influence of Na+, Mg2+, Ca2+, Sr2+, and Ba2+ on the interaction between two models, self-assembled monolayers, that were tailored to have hydrophobic −CH3 or hydrophilic −COO(H) terminations. Atomic force microscopy in chemical force mapping mode, where the tips were functionalized with the same terminations, was used to measure adhesion forces between the tip and substrate surfaces, to gather fundamental information about the role of these cations in the behavior of organic compounds and the surfaces where they adsorb. Adhesion force between hydrophobic surfaces in 0.5 M NaCl solutions that contained 0.012 M divalent cations did not change, regardless of the ionic potential, that is, the charge per unit radius, of the cation. For systems where one or the...