pH Dependence of Photochemical Kinetics of Thioxanthen-9-one from Nanosecond Time-resolved Laser Flash Photolysis

pH dependent uorescence emission of a thioxanthone-based probe has been re-ported recently.The potential deter-minant factors of pH dependence may provide important clues to design novel thioxanthone-based probes in the fu-ture.pH dependence of photochemical kinetics of thioxanthone itself was inves-tigated in this work using nanosecond time-resolved laser ash photolysis.The nanosecond time-resolved transient absorption spectra and kinetics of TX in aqueous acetonitrile were recorded,as well as for a model reaction system including TX with diphenylamine(DPA)as a co-initiator.Besides the well-known absorption peak of ^(3)TX*,other peaks at 417,518,673 and 780 nm,have been reliably attributed to major intermediates in the overall reaction between TX and DPA with photolysis,which has been con rmed to occur along a multistep process.In the strong acidic solution(pH≈3.0),TX and protonated TX ions(TXH^(+))coexist due to protonated equilibrium.Consequently,high proton concentration promotes the predominant decay pathway after photolysis from electron transfer to proton affnity.Subsequently,the di erent primary products,^(3)TXH^(+*)or TX^(·-),proceed di erent secondary reaction channels.In addition,within the wide pH range from weak acid(pH=5.0)to alkaline solution(pH=13.0),the overall reaction mechanism and rates do not show visible changes.

pH-Induced selective electrocatalytic hydrogenation of furfural on Cu electrodes

The efficient and selective electrocatalytic hydrogenation(ECH)of furfural is considered a green strategy for achieving biomass-derived high-value chemicals.Regulating an aqueous electrolytic environment,a green hydrogen energy source of water,is significant for improving the selectivity of products and reducing energy consumption.In this study,we systematically investigated the mechanism of pH dependence of product selectivity in the ECH of furfural on Cu electrodes.Under acidic conditions,the oxygen atom dissociated directly from hydrogenated furfural-derived alkoxyl intermediates,followed by stepwise hydrogenation until H_(2)O formation via a thermodynamically favorable proton-coupled electron transfer process,thereby inducing a high proportion of the hydrogenolysis product(2-methylfuran).However,under partial alkaline conditions,furfural could be directly hydrogenated to furfuryl alcohol(selectivity~98%)due to the high-energy barrier of the deoxidation process via a surface hydride(Had)transfer.Our results highlight the vital role of the electrolytic environment in furfural selective conversion and broaden our fundamental understanding of hydrodeoxygenation reactions in ECH.

Adsorption Behavior of a Water-soluble Porphyrin at the Glass-water Interface as Studied by Synchronous Total Internal Reflection Fluorescence Spectroscopy

Total internal reflection fluorescence spectroscopy (TIRF) and synchronous scanning technique were combined to study the adsorption behavior of the meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) at the glass-water interface without any surfactant. The pH dependence of synchronous fluorescence signal at the interface was analyzed. Both unprotonated (TPPS4-) and diprotonated (H2TPPS2-) forms of TPPS were observed at the interface. But the interface favored the adsorption of. The apparent estimated pKa2 value shifted from 5.00 in the bulk solution to 2.7 at the interface. STIRF provides a good technique to study multi-component systems at the interface.

Controllable Biosynthesis and Properties of Gold Nanoplates Using Yeast Extract

Biosynthesis of gold nanostructures has drawn increasing concerns because of its green and sustainable synthetic process. However, biosynthesis of gold nanoplates is still a challenge because of the expensive source and difficulties of controllable formation of morphology and size. Herein, one-pot biosynthesis of gold nanoplates is proposed, in which cheap yeast was extracted as a green precursor. The morphologies and sizes of the gold nanostructures can be controlled via varying the pH value of the biomedium. In acid condition, gold nanoplates with side length from 1300 ± 200 to 300 ± 100 nm and height from 18 to 15 nm were obtained by increasing the pH value. Whereas, in neutral or basic condition, only gold nanoflowers and nanoparticles were obtained. It was determined that organic molecules, such as succinic acid, lactic acid, malic acid, and glutathione, which are generated in metabolism process, played important role in the reduction of gold ions. Besides, it was found that the gold nanoplates exhibited plasmonic property with prominent dipole infrared resonance in near-infrared region, indicating their potential in surface plasmon-enhanced applications, such as bioimaging and photothermal therapy.

DILUTE SOLUTION BEHAVIOR OF CHITOSAN IN DIFFERENT ACID SOLVENTS

Dilute solution behavior of chitosan was studied in formic acid, acetic acid, lactic acid andhydrochloric acid aqueous solution under different pH values. The reduced viscosities, η_(sp)/C,ofchitosan solutions were dependent on the properties of acid and pH value of solvents. For a givenchitosan concentration, η^(sp)/C decreased with the increase of acid concentration, or decreasing pHof solvent, indicating shielding effect of excessive acid similar to adding salt into solution. Thestabilities of dilute chitosan solution in formic acid and lactic acid were better than that in acetic acid and hvdrochloric acid.