фізична хімія, физическая химия, physical chemistry ; бромування ; каталіз, катализ
Проведено бромування вуглецевого волокна та отримано активні бромвмісні прекурсори, в яких бром здатний заміщуватися на сірковмісні функціональні групи. Досліджено хімічні та термодесорбційні властивості отриманих зразків. Показано, що синтезовані матеріали, що містять в поверхневому шарі сульфогрупи, мають значну термічну стійкість і можуть бути використані як кислотно-основні каталізатори.
Проведено бромирование углеродного волокна и получены активные бромсодержащие прекурсоры, в которых бром способен замещаться на серодержащие функциональные группы. Исследованы химические и термодесорбционные свойства полученных образцов. Показано, что синтезированные образцы, содержащие в поверхностном слое сульфогруппы, имеют достаточно высокую термическую устойчивость и могут быть использованы как кислотно-основные катализаторы.
Bromination of PAN-based carbon fibres (CFs) was carried out and active precursors, in which bromine is capable to be substituted by Scontaining functional groups, were obtained. The properties of the synthesized samples were studied by chemical and thermogravimetric analyses as well as thermodesorption with mass-spectrometry registration of the escaped particles. Bromination of carbon fibres both with liquid bromine and aqueous solution of Br2·KBr complex provides obtaining samples with up to 0.4-0.5 mmol/g of bromine in the surface layer. CFs with grafted bromine are sufficiently stable and do not hydrolyze being kept in air or water for a long time. Short-term boiling in pure water does not ruin the brominated fibres, but hydrolysis occurs under treatment with alkali, especially when heated.
It is shown that CFs bromination is accompanied by surface oxidation. The TG data and changes in mass spectra (shapes and relative intensities of signals that are assigned to carbon oxides) confirm this parallel process.
The treatment of brominated fibres with aqueous solutions of sodium sulfide or sodium mercaptoacetate provides replacement of surface bromine by S-containing functional groups. Further oxidation of obtained samples by hydrogen peroxide leads to formation of strong acidic SO3Hgroups in the surface layer. According to the data obtained, concentration of acidic groups in the synthesized samples does not depend on bromination method, but treatment with sodium sulfide provides higher concentration of these groups compared to sodium mercaptoacetate.
The catalytic activity of CFs samples containing strong acidic groups was investigated in model reaction of gas phase dehydration of isopropanol. It is shown that fibres modified with SO3H-groups groups have significantly higher catalytic activity compared to initial ones: conversion of isopropanol to propylene is increased from 5-20% to 100%. Temperature of 100% conversion was chosen to compare catalytic activity of CFs with acidic SO3H-groups. The highest catalytic activity of the modified CFs is observed for samples that are obtained from brominated precursors treated with sodium sulfide. The lowest activity is observed for samples modified with S-containing compounds without pre-bromination. In accordance to their catalytic activity all CFs samples are arranged in sequence that fully correlates with the concentration of surface SO3H-groups.
