Reduced graphene oxide (RGO)-supported Pd-CeO2 nanocomposite as a highly active electrocatalyst for facile formic acid oxidation

Stable and efficient electrocatalysts capable of oxidizing formic acid molecule is highly required to realize direct formic acid fuel cells (DFACs) as promising energy conversion sources. Herein, electrocatalytic activity of...

Silicon Binding in Soil Humic Substances

In the present study, an attempt has been made to probe the nature of silicon-humus bonding as it occurs in nature ('untreated') as compared to the samples wherefrom the metalloid ions have been removed ('treated'). Infrared (IR) spectroscopy revealed the role of carboxylic acid groups of Humic acid (HA) in metal complexation. Si-O absorption reduced considerably in treatment to remove metalloid ions, but it remained quite strong in the treated samples indicating a strong Si-O linkage with humus. In XRD analysis, treated samples showed stronger γ-bands. DTA analysis indicated structural strain on the humic molecule induced by complexation with metalloid ions. Treated HAs had higher acidity values compared to the untreated samples. Treatment for removal of metal ions caused an increase in cation exchange capacity while a reduction of E4/E6 ratio. Treated HAs also showed higher molecular weights (Mv) compared to the untreated samples. Removal of metals renders certain groups free which form intermolecular bonds. On the basis of analytical data, it was observed that there is still some silicon bonds within humic acid molecule, even after removal of silicon by forcing conditions. Association of silicon with humus in soils are quantitatively and qualitatively different from other metal ions and it is clear that humic acid molecule possess silicon-humus bond like pure organo-metallic compounds.

Silicon Binding in Soil Humic Substances

In the present study, an attempt has been made to probe the nature of silicon-humus bonding as it occurs in nature ('untreated') as compared to the samples wherefrom the metalloid ions have been removed ('treated'). Infrared (IR) spectroscopy revealed the role of carboxylic acid groups of Humic acid (HA) in metal complexation. Si-O absorption reduced considerably in treatment to remove metalloid ions, but it remained quite strong in the treated samples indicating a strong Si-O linkage with humus. In XRD analysis, treated samples showed stronger γ-bands. DTA analysis indicated structural strain on the humic molecule induced by complexation with metalloid ions. Treated HAs had higher acidity values compared to the untreated samples. Treatment for removal of metal ions caused an increase in cation exchange capacity while a reduction of E4/E6 ratio. Treated HAs also showed higher molecular weights (Mv) compared to the untreated samples. Removal of metals renders certain groups free which form intermolecular bonds. On the basis of analytical data, it was observed that there is still some silicon bonds within humic acid molecule, even after removal of silicon by forcing conditions. Association of silicon with humus in soils are quantitatively and qualitatively different from other metal ions and it is clear that humic acid molecule possess silicon-humus bond like pure organo-metallic compounds.

Selective Enhancement of SERS Spectral Bands of Salicylic Acid Adsorbate on 2D Ti3C2Tx-Based MXene Film

In this research, we have demonstrated that 2D Ti3C2Xn-based MXene (MXene) films are suitable for the design of surface-enhanced Raman spectroscopy (SERS)-based sensors. The enhanced SERS signal was observed for a salicylic acid molecule on Ti3C2Tx-based MXene film. Confirmation of the adsorption of the salicylic acid molecule and the formation of a salicylic acid–MXene complex were determined by experimental SERS-based spectral observations such as greatly enhanced out-of-plane bending modes of salicylic acid at 896 cm−1 and a band doublet at 681 cm−1 and 654 cm−1. Additionally, some other spectral features indicate the adsorption of salicylic acid on the MXene surface, namely, a redshift of vibrational modes and the disappearance of the carboxyl deformation spectral band at 771 cm−1. The determined enhancement factor indicates the value that can be expected for the chemical enhancement mechanism in SERS of 220 for out-of-plane vibrational modes. Theoretical modeling based on density functional theory (DFT) calculations using B3LYP/6311G++ functional were performed to assess the formation of the salicylic acid/MXene complex. Based on the calculations, salicylic acid displays affinity of forming a chemical bond with titanium atom of Ti3C2(OH)2 crystal via oxygen atom in hydroxyl group of salicylic acid. The electron density redistribution of the salicylic acid–MXene complex leads to a charge transfer effect with 2.2 eV (428 nm) and 2.9 eV (564 nm) excitations. The experimentally evaluated enhancement factor can vary from 220 to 60 when different excitation wavelengths are applied.

Pyridinium 3-nitrobenzoate–3-nitrobenzoic acid (1/1)

The crystal structure of the product of the neutralization reaction between 3-nitrobenzoic acid and pyridine is reported. The entities that crystallized are a pyridinium cation, a 3-nitrobenzoate anion and a 3-nitrobenzoic acid molecule in a 1:1:1 molar ratio, C5H6N+·C7H4NO4 −·C7H5NO4. Distinct sets of hydrogen bonds link the pyridinium and benzoate ions (N—H...O) and the acid and benzoate moieties (O—H...O). The hydrogen bonding along with π–π stacking between the acid and benzoate moieties accounts for the long-range ordering of the crystal.

Psilacetin derivatives: fumarate salts of the methyl–ethyl, methyl–allyl and diallyl variants of the psilocin prodrug

The solid-state structures of the salts of three psilacetin derivatives, namely, 4-acetoxy-N-ethyl-N-methyltryptammonium (4-AcO-MET) hydrofumarate {systematic name: [2-(4-acetyloxy-1H-indol-3-yl)ethyl](methyl)ethylazanium 3-carboxyprop-2-enoate}, C15H21N2O2 +·C4H3O4 −, 4-acetoxy-N-allyl-N-methyltryptammonium (4-AcO-MALT) hydrofumarate {systematic name: [2-(4-acetyloxy-1H-indol-3-yl)ethyl](methyl)prop-2-enylazanium 3-carboxyprop-2-enoate}, C16H21N2O2 +·C4H3O4 −, and 4-acetoxy-N,N-diallyltryptammonium (4-AcO-DALT) fumarate–fumaric acid (1/1) (systematic name: bis{[2-(4-acetyloxy-1H-indol-3-yl)ethyl]diprop-2-enylazanium} but-2-enedioate–(E)-butenedioic acid (1/1)), 2C18H23N2O2 +·C4H2O4 2−·C4H4O4, are reported. All three salts possess a protonated tryptammonium cation. The 4-AcO-MET and 4-AcO-MALT compounds are charge-balanced by 3-carboxyacrylate (hydrofumarate) anions. The 4-AcO-DALT complex crystallizes as a two-to-one tryptammonium-to-fumarate salt, which co-crystallizes with a fumaric acid molecule. Each structure is consolidated by N—H...O and O—H...O hydrogen bonds.

Interaction of N-acetylneuraminic acid with surface silicon in aqueous solution with carbohydrates

The aim of the work is to study interaction of N-acetylneuraminic acid (NANA) with the surface of ultrafine silica (UFS) with the participation of glucose and sucrose in aqueous solution at the supramolecular level by density functional theory method (exchange-correlation functional B3LYP, basis set of 6-31G (d, p). The adsorption of N-acetylneuraminic acid, as well as individual carbohydrates (glucose and sucrose) on the hydrated surface of UFS in aqueous solution, was considered as a process of replacement of water molecules on the surface of silica by adsorbate molecules. This work considers two schemes of carbohydrate molecule influence on adsorption of N-acetylneuraminic acid. According to the first scheme the interaction of the NANA molecule occurs with the silica-monosaccharide complex, according to the second scheme, the silica cluster interacts with the NANA-monosaccharide complex, where silica binds to the complex through the carbohydrate molecule. The analysis of the calculated geometric and energy characteristics show that adsorption on the surface of silica, with hydration taken into account, is thermodynamically probable for the sucrose. The glucose molecule has a positive value (+9.8 and +2.7 kJ / mol) is an unfavorable process in terms of thermodynamics regardless of the hydrating water cluster size. The N-acetylneuraminic acid molecule has a value of -1.3 kJ / mol for the reaction with five water molecules and +0.9 kJ / mol with eight water molecules. It was found that the presence of sucrose on the silica surface in the aqueous solution weakens the hydration energy (i.e. it is easier to replace the cluster of water with the N-acetylneuraminic acid molecule from the surface of the modified adsorbent), which in turn promotes NANA adsorption on the silica surface. Therefore, scheme 1 is thermodynamically more likely than scheme 2. This indicates that there is a mutual influence of substances in a mixture of NANA with carbohydrates on the interaction with silica in comparison with the interaction of substances with silica alone.