The surface carboxyl group of carbonaceous microspheres effects on the synthesis and structure of SiOC ceramics

•NaOH etching increases the surface carboxyl group of carbonaceous microspheres.•The hydroxyl increases the oxygen-enriched structural units of SiOC ceramics.•The reaction of carboxyl with Si–OH results in the formation of cristobalite SiO2.•The oxidation resistance of SiOC is superior to that of C and SiO2.