Methods for integrating the production of carboxylated CNCs and carboxylated CNFs from cellulose are provided. Carboxylated CNCs, carboxylated cellulosic solid residues (CSRs) in the form of cellulose fibers (CF) and/or cellulose microfibrils (CMFs), and carboxylated CNFs fabricated using the methods are also provided. The methods are based on the acid hydrolysis of a cellulosic material using weak solid organic acids to produce carboxylated CNCs and CNFs with thermal stabilities that are higher than the thermal stabilities of the cellulosic materials from which they are derived.