Degree Of Protonation Research Articles

Photochemical charge accumulation in a heteroleptic copper(i)-anthraquinone molecular dyad via proton-coupled electron transfer.

Developing efficient photocatalysts that perform multi electron redox reactions is critical to achieving solar energy conversion. One can reach this goal by developing systems which mimic natural photosynthesis and exploit strategies such as proton-coupled electron transfer (PCET) to achieve photochemical charge accumulation. We report herein a heteroleptic Cu(i)bis(phenanthroline) complex, Cu-AnQ, featuring a fused phenazine-anthraquinone moiety that photochemically accumulates two electrons in the anthraquinone unit via PCET. Full spectroscopic and electrochemical analyses allowed us to identify the reduced species and revealed that up to three electrons can be accumulated in the phenazine-anthraquinone ring system under electrochemical conditions. Continuous photolysis of Cu-AnQ in the presence of sacrificial electron donor produced doubly reduced monoprotonated photoproduct confirmed unambiguously by X-ray crystallography. Formation of this photoproduct indicates that a PCET process occurred during illumination and two electrons were accumulated in the system. The role of the heteroleptic Cu(i)bis(phenanthroline) moiety participating in the photochemical charge accumulation as a light absorber was evidenced by comparing the photolysis of Cu-AnQ and the free AnQ ligand with less reductive triethylamine as a sacrificial electron donor, in which photogenerated doubly reduced species was observed with Cu-AnQ, but not with the free ligand. The thermodynamic properties of Cu-AnQ were examined by DFT which mapped the probable reaction pathway for photochemical charge accumulation and the capacity for solar energy stored in the process. This study presents a unique system built on earth-abundant transition metal complex to store electrons, and tune the storage of solar energy by the degree of protonation of the electron acceptor.

Effect of the number of hydroxyl groups of CO2-triggered surfactants on capability and performance in CO2-stimulated response

This paper reports the synthesis and characterization of three CO2-triggered surfactants (S-0, S-2, S-4) containing different number of hydroxyl groups. The impact of the hydroxyl groups on S-0, S-2, and S-4 was investigated by observing the morphological appearance, conductivity, and pH after CO2 bubbling. The surface tension of the three CO2-triggered surfactants decreased from S-0 to S-2 then to S-4, meaning surface tension decreasing with increasing the number of hydroxyl groups. The interfacial tension results showed that surfactants with more hydroxyl groups can better reduce the interfacial tension at a given pH. The pKa and micromorphology results revealed different degree of protonation of the CO2-triggered surfactants by CO2 in water, causing variations in their aggregation patterns. Molecular simulations revealed that increasing the number of hydroxyl groups increases the thickness of the hydration layer. And S-4 with a thicker hydration layer will more likely form a complex network structure than S-0 and S-2 with a thinner hydration layer. The new surfactants utilize a simple and mild approach to synthesis; solving problems such as insolubility and phase separation through the introduction of hydroxyl groups. The study serves as a guide to the application of CO2-trigger surfactant solutions.

Studies of Mercaptosuccinic Acid-Crosslinked Chitosan Hydrogel with Grafted Cinnamaldehyde and Silver Nanoparticles for Antibacterial Biomedical Application

For the effective clinical antibacterial application of biomaterials, such as for wound management and tissue repair, the biomaterials need to show proper antibacterial capability as well as non-cytotoxicity. Furthermore, the material needs to have suitable mechanical characteristics for further medical use. Chitosan hydrogel is a potential candidate for various antibacterial biomedical applications due to its amine functionalities that lead to antimicrobial characteristics. Nevertheless, its antimicrobial capability is dependent upon the degree of protonation of amine groups caused by the pH value. Moreover, its mechanical compressive strength may not be high enough for clinical use if not chemically or physically crosslinked. This study utilized a novel chemical crosslinker, mercaptosuccinic acid, to improve its mechanical characteristics. The natural antibacterial agent, cinnamaldehyde, was grafted onto the crosslinked chitosan to improve its antimicrobial capability. Meanwhile, to take advantage of the thiol functionality in the mercaptosuccinic acid, the bactericidal silver nanoparticles were incorporated through silver-thiol covalent bounding. NMR analyses indicated the chitosan was successfully mercaptosuccinic acid-crosslinked and grafted with cinnamaldehyde at different ratios. Combined the results from the mechanical assessment, swelling experiments, antimicrobial assessment, and cytotoxicity assay, the chitosan hydrogel with the highest crosslinked degree and grafted with cinnamaldehyde and silver nanoparticles is of great promise for further clinical uses.

Diverse Hydrogen-Bonded Structural Motifs in 1,4-Diazabicyclo[2.2.2]octane N,N’-Dioxide Salts with Oxoanions

Four new hybrid inorganic–organic salts of 1,4-diazabicyclo[2.2.2]octane N,N’-dioxide (odabco) with the formulae odabco·2HNO3 (1), odabco·HClO4 (2), odabco·H2SO4 (3) and odabco·2H2SO4 (4) were synthesized and characterized by single-crystal x-ray diffraction (XRD), powder XRD and infrared spectroscopy. Compound 1 is based on the isolated (H2odabco)2+ fragments, representing 0D structure. 2 is based on cationic 1D {Hodabco}nn+ hydrogen-bonded chains. Compound 3 comprising a strongly coordinated sulfate anion consists of two-component hydrogen-bonded {-H2odabco-SO4−} fragments forming uncharged 1D helical chains. 4 contains both {-HSO4-}nn– and {-HSO4-H2odabco-HSO4−} hydrogen bonding motifs, resulting in a 3D polymeric network. A comparative structural analysis of both the obtained and the previously reported cognate structures was performed to rationalize the impact of the degree of odabco protonation and the anion donor ability on the structural features and dimensionalities of odabco-based hydrogen-bonded lattices.

Dynamic modulation and epoxy functionalization of protein-mediated enoate ester-based hybrid cryogels

The current work is focused on the preparation of protein-mediated poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) copolymer as a self-template for in situ synthesis of hybrid gels. Gelatin, collagen, biotin, and l-arginine were used to create hybrid materials with adjustable swelling and elastic properties. Hybrid cryogels tended to swell more than hybrid hydrogels due to their porous nature. Collaged-doped cryogels had the highest swelling, whereas gelatin-doped hybrids showed enhanced elastic modulus. All hybrid gels exhibited pH-sensitive swelling to controlled release applications depending on the degree of protonation of NH2 and COOH groups in the side chains. At low pH conditions, hybrid cryogels exhibited a higher swelling tendency compared to hydrogels. Ion-stimulus-response of hybrid gels was studied to evaluate the effect of salt concentration and features of ambient ions on swelling. Depending on the polyelectrolytic or polyampholytic nature, the extent of swelling in NaCl and KCl solutions varied according to the charge distribution in the network chains. Hybrid gels showed excellent adsorption performance for methyl orange by the presence of epoxy, hydroxyl groups, amino and carboxyl groups providing sufficient active sites. Adsorption capacity of hybrid cryogels is higher than that of hydrogels. The removal rate 97/%, reached an equilibrium state in a short period, suggested that collagen-doped hybrid cryogels have a potential application to remove dyestuff from wastewater. In relation to the decrease of methyl orange concentration in solution, adsorption process followed pseudo-second-order kinetic model. Avrami model has provided a better experimental-calculated fit and adsorption thermodynamics analysis indicated that the adsorption was a spontaneous process with a negative standard free energy. The characteristic findings from this research will provide insights into the design and application of enoate-ester and protein-based combinations in the food, biomedical and cosmetic fields.

Kinetics of Ion-Exchange Extraction of Lithium from Aqueous Solutions by Protonated Potassium Polytitanates

In this work, protonated forms of potassium polytitanate were obtained by treating the precursor in HCl solution at pH 2.0, 3.0, 4.0, 5.0, 6.0, or 7.0. The synthesized materials were studied using XRD, FTIR, and XRF. The ion-exchange properties were studied using a LiCl solution with a concentration of C(Li+) = 0.01 mol/L. It was shown that extraction of lithium by potassium polytitanates is dependent on their protonation degree. It has been established that the samples with the highest degree of protonation obtained at pH = 2.0 and 3.0 have the highest efficiency in the ion-exchange extraction of Li+ ions from an aqueous solution. For determination of exchange ion rates and the mechanism of the ion-exchange process, pseudo-first- and pseudo-second-order models as well as the Weber–Morris intraparticle diffusion model, were employed. Experimental data with their participation are in good agreement with the pseudo-second-order kinetic model. The calculated kinetic parameters were qe = 0.47–0.52 mmol/g and k2 = 0.25–0.43, depending on the protonation degree of potassium polytitanate. The obtained experimental and calculated values of the sorption capacity were compared with the cation-exchange capacity of materials studied. According to the kinetics study, the mechanism of lithium adsorption by potassium polytitanates with a higher protonation degree is the ion-exchange chemical reaction. Low-cost protonated potassium polytitanates are promising to extract Li+ ions from aqueous solutions with a low concentration, as confirmed by the analysis of the results.

PSS-doped PANI nanoparticle/Ti3C2Tx composites for conductometric flexible ammonia gas sensors operated at room temperature

The detection of ammonia (NH3) is significant because it can seriously damage human health and atmospheric environment. However, the development of high-performance flexible NH3 gas sensors operated at room temperature is still challenging. Thus, a flexible NH3 film sensor based on poly(4-stryenesulfonate)-doped polyaniline nanoparticle (PANI:PSS)/Ti3C2Tx composite was developed by in-situ polymerization. This optimized PANI:PSS/Ti3C2Tx film displayed the high response of 0.57–1 ppm NH3, which was improved by 1.78-fold in comparison with PANI:PSS film. Besides, the response value of this film to NH3 was 1.46 times higher than to NO2, and this value was much higher than to other interfering gases (NO, toluene, ethanol, and acetone). Additionally, this film sensor possessed excellent mechanical stability and low detection limit (20 ppb) at room temperature. The abundant Schottky heterojunctions formed in PANI:PSS/Ti3C2Tx composite, the numerous -SO3H groups introduced by PSS anion chains, and the improved protonation degree of PANI component are responsible for the enhanced sensing properties. The monitoring experiment of shrimp spoilage has demonstrated the application feasibility of this film sensor. This research provides a novel and practical method for constructing high-performance polymer/MXene based gas sensors.

Photoluminescence Mechanism of Carbon Dots: Triggering Multiple Color Emissions through Controlling the Degree of Protonation.

Carbon dots (CDs) have excellent optical properties, low toxicity and easy preparation, which have led to them being widely used in biomedicine, sensing and optical devices. However, although great progress has been made in the preparation of CDs, the detailed exploration of their photoluminescence (PL) mechanism is still under debate due to their complex structures and surface functionalities. Here, we proposed a single change in the pH of the synthesis condition, which had no effect on the CDs intrinsic core states and avoided the mutual influence of multiple PL origins. The m-phenylenediamine (m–PD) served as a carbon source, whose protonation degree determined the surface state of the resulting CDs and the accompanying fluorescence characteristics. The as-obtained CDs materials can be applied in the chemical sensor and anti-counterfeiting fields in a targeted manner. Therefore, our work not only contributes to the explanation of the CDs PL mechanism, but also obtains a series of CDs materials with controllable PL properties.

Novel self-assembly nano OSA starch micelles controlled by protonation in aqueous media

A new micellization method was applied to produce the nano octenyl succinic anhydride (OSA) modified starch micelles with controllable size. The underlying mechanism was explored by using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), zeta-potential, surface tension, fluorescence spectra and transmission electron microscope (TEM). Due to the new starch modification method, the electrostatic repulsion between the deprotonation carboxyl groups prevented the aggregation of starch chains. With the progress of protonation, the weaken electrostatic repulsion and enhanced hydrophobic interaction driven the self-assembly of micelles. The size of micelles increased gradually with the increase of the protonation degree (PD) and concentration of OSA starch. However, a V-shaped trends were observed in the size as the increase of substitution of degree (DS). Curcuma loading test indicated that micelles had good encapsulated capability and the maximum value was 52.2 μg/mg. The understanding of the self-assembly behavior of OSA starch micelles can facilitate and improve the starch-based carrier designs used to synthesis complex and smart micelle delivery system with good biocompatibility.

PROPERTIES OF POLYMERS BASED ON AROMATIC DIAMINES

This review provides detailed information on the synthesis, structure, properties, methods for studying, and areas of application conductive polymers synthesized on the basis of phenylenediamines. Conductive polymers based on phenylenediamines are cationic salts of highly conjugated polymers and are synthesized by electrochemical or chemical oxidation. Chemical oxidative polymerization has led to the formation of various functional polymers. Depending on the reaction conditions, polyphenylenediamines are produced as powders, colloidal dispersions, thin films, or composites. The close similarity of the chemical structure of polyanilines and polyphenylenediamines endows both groups with some similar properties, such as, for example, redox activity. They act as reductants of noble-metal compounds to the corresponding metals. Due to electrical conductivity and redox activity, as well as the dependence of electrical conductivity on the degree of protonation, it is possible to create various sensors based on polyphenylenediamines. In addition, polyphenylenediamines can be used as one of the components of composite materials, for example, in anticorrosion coatings. In general, some main groups of applications for polyphenylenediamines can be distinguished. The literature indicates a number of areas of their application; they include the corrosion protection of metals, catalysis, electrorheology, sensors, energy-conversion devices, electrochromism, noble-metal recovery, and water treatment. At the same time, polymers of phenylenediamines can be used in medicine, unlike aniline and its oligomers, which have potential toxicity

Species identification of phosphate at the ZrO2/water interface: A combined ATR-FTIR and DFT study

In our work, in-situ attenuated-total-reflection Fourier transformation infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations were used to investigate the interface interactions between phosphate and zirconium oxide surface. The results showed that phosphate mainly forms three inner-sphere complexes, (≡ZrO)2PO2, (≡ZrO)2(HO)PO and (≡ZrO)(HO)2PO, on ZrO2 surface in a wide pH range. At pH 9 and above, no band shift was observed upon replacing light water by deuterium water as the medium, implying a non-protonated bidentate (NB) structure, (≡ZrO)2PO2. At pH 4–7, surface phosphate species have similar structures due to similar spectra, while the band position differences in between the two media suggest that the surface phosphate is protonated. At pH 2, the spectra display remarkable differences in between the two media, suggesting a higher protonation degree of surface phosphate. On the comprehensive analysis, it is reasonable to confirm that the surface phosphate species are in modes of mono-protonated bidentate (MB) at pH 4–7 and bi-protonated monodentate (BM) at pH 2, designated as (≡ZrO)2(HO)PO and (≡ZrO)(HO)2PO, respectively. DFT calculations suggest the stability of these species follows the sequence: MB > NB > BM, and the bidentate structures are corner-sharing.

Best Practices in Constant pH MD Simulations: Accuracy and Sampling.

Various approaches have been proposed to include the effect of pH in molecular dynamics (MD) simulations. Among these, the λ-dynamics approach proposed by Brooks and co-workers [Kong, X.; Brooks III, C. L. J. Chem. Phys.1996, 105, 2414−2423] can be performed with little computational overhead and hfor each typeence be used to routinely perform MD simulations at microsecond time scales, as shown in the accompanying paper [Aho, N. et al. J. Chem. Theory Comput.2022, DOI: 10.1021/acs.jctc.2c00516]. At such time scales, however, the accuracy of the molecular mechanics force field and the parametrization becomes critical. Here, we address these issues and provide the community with guidelines on how to set up and perform long time scale constant pH MD simulations. We found that barriers associated with the torsions of side chains in the CHARMM36m force field are too high for reaching convergence in constant pH MD simulations on microsecond time scales. To avoid the high computational cost of extending the sampling, we propose small modifications to the force field to selectively reduce the torsional barriers. We demonstrate that with such modifications we obtain converged distributions of both protonation and torsional degrees of freedom and hence consistent pKa estimates, while the sampling of the overall configurational space accessible to proteins is unaffected as compared to normal MD simulations. We also show that the results of constant pH MD depend on the accuracy of the correction potentials. While these potentials are typically obtained by fitting a low-order polynomial to calculated free energy profiles, we find that higher order fits are essential to provide accurate and consistent results. By resolving problems in accuracy and sampling, the work described in this and the accompanying paper paves the way to the widespread application of constant pH MD beyond pKa prediction.

Behaviors of Organic Ligands and Phosphate during Biochar-Driven Nitrate Adsorption in the Presence of Low-Molecular-Weight Organic Acids.

A batch experiment was conducted to examine the behavior of nitrate, organic ligands, and phosphate in the co-presence of biochar and three common low-molecular-weight organic acids (LMWOAs). The results show that citrate, oxalate, and malate ions competed with nitrate ion for the available adsorption sites on the biochar surfaces. The removal rate of LMWOA ligands by the biochar via adsorption grew with increasing solution pH. The adsorbed divalent organic ligands created negatively charged sites to allow binding of cationic metal nitrate complexes. A higher degree of biochar surface protonation does not necessarily enhance nitrate adsorption. More acidic conditions formed under a higher dose of LMWOAs tended to make organic ligands predominantly in monovalent forms and failed to create negatively charged sites to bind cationic metal nitrate complexes. This could adversely affect nitrate removal efficiency in the investigated systems. LMWOAs caused significant release of phosphate from the biochar. The phosphate in the malic acid treatment tended to decrease over time, while the opposite was observed in the citric- and oxalic-acid treatments. This was caused by re-immobilization of phosphate in the former due to the marked increase in solution pH over time.

Cation Protonation Degree Influence on the Formation of Anion⋅⋅⋅Anion and Other Non‐Valent Interactions in Guaninium Perrhenates and Pertechnetate

AbstractH2Gua(ReO4)2, HGuaReO4 and HGuaTcO4 were first obtained and structurally characterized. Two types of anionic interactions were found in the structure with the twice protonated cation. One type of the rare double‐lock interaction of perrhenate anions was found in the case of the singly protonated guanine salt. Singly charged cations are linked by hydrogen bonds into layer. π‐Stacking interactions between these layers form 3‐dimensional frame. Multiple and relatively abundant anion‐π interactions are formed in H2Gua(ReO4)2 as compared to HGuaReO4 and HGuaTcO4. Different types of crystal packing are formed in the compounds under research. Hirshfeld surface analysis has given evidence that the main contribution to intermolecular interactions for the cations is made by hydrogen bonds of the O⋅⋅⋅H/H⋅⋅⋅O type in all structures, O⋅⋅⋅C/C⋅⋅⋅O and O⋅⋅⋅N/N⋅⋅⋅O interactions in H2Gua(ReO4)2, N⋅⋅⋅H/H⋅⋅⋅N and H⋅⋅⋅H interactions in HGuaReO4 and HGuaTcO4.

Conducting and magnetic hybrid polyaniline/nickel composites

Hybrid organic/inorganic polyaniline/nickel composites were prepared by the in-situ oxidation of aniline hydrochloride with ammonium peroxydisulfate in the presence of various portions of nickel microparticles. Electron microscopies demonstrated the coating of nickel with polyaniline. FTIR and Raman spectroscopies indicated the reduced degree of polyaniline protonation. As a consequence, the composites containing 7.2–58.8 wt% of nickel had the conductivity of the order of 10−3–10−2 S cm−1, i.e. several order of magnitude lower than the conductivity of polyaniline or nickel. The conductivity as a function of applied pressure is also reported. Relatively low conductivity of composites is explained by the partial reduction of polyaniline with hydrogen gas evolved during the synthesis and consequent hydrogenation of polyaniline catalysed by nickel. The accompanying partial dissolution of nickel manifests itself by the reduced composite yield. The reason why hydrogen is generated mainly after the synthesis of polyaniline is discussed. The magnetic properties afforded by nickel are also reported. The composites dispersed in thermoplastic polyurethane matrix providing mechanical properties have been tested for electromagnetic interference shielding.

An efficient bioinspired functional micellar nanoreactor for dephosphorylation reactions

An efficient bioinspired catalytic system for dephosphorylation reactions should combine imidazole reaction sites with a hydrophobic region that favors intimate interaction with the substrate. In this work, we show that the catalytic activity of long-chain alkylimidazoles such as 1-tetradecylimidazole (ImR) that are poorly soluble in aqueous medium is greatly improved by the use of mixed micelles of ImR with cetyltrimethylammonium bromide (CTAB). The size, zeta potential, degree of protonation of ImR and the catalytic activity in dephosphorylation of diethyl 2,4-dinitrophenyl phosphate (DEDNPP) were found to be functions of the CTAB/ImR ratio and the pH of the medium, with optimal catalytic activity at pH 6 and at low CTAB/ImR ratios (3/1 and 2/1). For 3/1 CTAB/ImR, the ImR-catalyzed dephosphorylation of DEDNPP was 9x106-fold faster than the spontaneous hydrolysis of DEDNPP and ca. 102-fold faster than the reaction catalyzed by free imidazole. The same 3/1 CTAB/ImR mixed micelles were also shown to accelerate the dephosphorylation of the pesticide Paraoxon (diethyl 4-nitrophenylphosphate). The relative structural simplicity of the components of these mixed micellar aggregates, combined with the ability to promote significant accelerations of the rates of dephosphorylation reactions, point to mixed micellar aggregates of this type as prototypes for the design of efficient nanoreactors for performing alkylimidazole-catalyzed dephosphorylation reactions.

Free-energy landscapes and insertion pathways for peptides in membrane environment.

Free-energy landscapes for short peptides-specifically for variants of the pH low insertion peptide (pHLIP)-in the heterogeneous environment of a lipid bilayer or cell membrane are constructed, taking into account a set of dominant interactions and the conformational preferences of the peptide backbone. Our methodology interprets broken internal H-bonds along the backbone of a polypeptide as statistically interacting quasiparticles, activated from the helix reference state. The favored conformation depends on the local environment (ranging from polar to nonpolar), specifically on the availability of external H-bonds (with H_{2}O molecules or lipid headgroups) to replace internal H-bonds. The dominant side-chain contribution is accounted for by residue-specific transfer free energies between polar and nonpolar environments. The free-energy landscape is sensitive to the level of pH in the aqueous environment surrounding the membrane. For high pH, we identify pathways of descending free energy that suggest a coexistence of membrane-adsorbed peptides with peptides in solution. A drop in pH raises the degree of protonation of negatively charged residues and thus increases the hydrophobicity of peptide segments near the C terminus. For low pH, we identify insertion pathways between the membrane-adsorbed state and a stable trans-membrane state with the C terminus having crossed the membrane.

Protonated amines mediated CO2 mineralization of coal fly ash and polymorph selection of CaCO3

The extensive consumption of acid and alkaline reagents is the most critical challenge hindering the development of the pH-swing process for CO2 mineralization. To deal with the problem, the present paper demonstrates the feasibility of using protonated amine as the reagent in coal fly ash (CFA) based leaching-mineralization process. The protonated amine could leach Ca2+ from CFA and be converted into free amine. The free amine was supposed to be in-situ regenerated into protonated amine by grab protons released from the CaCO3 precipitation reaction. 13 typical amines with varying amino types, pKa values, and side-chain length, were selected to systematically investigate the effects of amino groups on Ca2+ leaching performance from CFA, carbonation performance, CaCO3 nucleation, and crystal growth, as well as the process mechanism. Results indicated that effective Ca leaching, CaCO3 precipitation, and protonated amine regeneration were achieved. There was a linear relationship between the Ca utilization efficiency and pKa values of different amines. TEA obtained the highest CaCO3 yield and Ca utilization efficiency of 56.8 % and 16.8 %, respectively. In addition, amines provided excellent control of the size, polymorph, and morphology of the CaCO3 product. The primary amino group had a more pronounced effect on vaterite stabilization than secondary and tertiary ones. Introducing a side chain could promote the vaterite transforming to calcite and increasing chain length could decrease the vaterite particle size. Moreover, the maximal utilization efficiency in MEA was 15.9 % at conditions: 160 g/L solid to liquid ratio, 58 % degree of protonation, and 2.0 mol/L MEA concentration.

Early Warning of Coal Spontaneous Combustion: A Study of CO Response Mechanism Based on PANI/Ti3AlC2 Composite Gas Sensing Film**

AbstractFire accidents caused by coal spontaneous combustion seriously affect the production safety of coal mines. Carbon monoxide (CO) is an important gas indicator used for monitoring and early warning detection of coal spontaneous combustion. Therefore, the development of CO sensors with low cost, low power consumption, and environmental protection is highly desirable. This can be achieved through deep optimization of semiconductor CO sensors as alternatives to infrared detection and electrochemical sensors. In this paper, Ti3AlC2 (MXenes)/polyaniline (PANI) composite were studied as semiconductor CO sensors. The optimal added amount of Ti3AlC2 was determined by testing at gas concentrations of 100 ppm and 150 ppm CO. The morphology, structure, and chemical characteristics of each composite were analyzed by field emission transmission electron microscopy (SEM‐EDS), Fourier infrared spectrometry, UV‐visible near infrared spectrophotometer, X‐ray photoelectron spectroscopy (XPS), and thermogravimetric techniques. Compared to pure PANI material, the SEM‐EDS experimental results showed Ti3AlC2 with an increased number of PANI flake structures, generating more CO gas adsorption sites. The XPS results showed Ti3AlC2 was able of improving the protonation and oxidation degree of PANI, thereby improving its gas sensing performance. Accordingly, a sensing mechanism model was proposed, revealing the excellent sensing performance originating from the gas sensing enhancement effect of heterojunction. In sum, this study provided a scientific basis for the design and development of CO sensors with low cost, low power consumption, and future environmental protection.

Molecular models of hematite, goethite, kaolinite, and quartz: Surface terminations, ionic interactions, nano topography, and water coordination

In light of the modern needs in mineral processing and extractive metallurgy, advanced knowledge about the surface chemistry of minerals is essential, especially their interactions with water. These interactions are intimately related to several processes in mineral technology, such as flotation, wet grinding, dewatering, and leaching. Hematite, goethite, quartz, and kaolinite are the main minerals in iron ore processing circuits. Thus, understanding their differences is fundamental to making lower-grade iron ores processing worthwhile. In this work, we studied the surface physical chemistry of these minerals by molecular modeling and simulation, focusing on surface terminations, protonation degrees, ionic interactions, nano topography, and water coordination. We demonstrate that fundamental differences exist between the terminations of the same mineral, particularly for quartz (100) and hematite (001) surfaces. Iron minerals exhibit strong interactions with water, mainly due to the coordination of surface iron atoms by aquo ligands and their relatively low molecular-scale roughness, in most cases. Such characteristics help explain the behavior of adsorption of reagents and the difficulties in dewatering and drying iron ore. In contrast, the silicate minerals present lower water structuring. We also show how neutral surfaces behave towards ions, cases of both attraction and repulsion were observed and attributed to the surfaces' topmost atomic layering. This work provides novel insights which can connect the fundamentals of surface phenomena with process engineering. Additionally, we provide molecular models to help in related computational studies.