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A sequential treatment involving HNO3 delignification in liquid phase and NO2-induced cellulose oxidation in gas phase was applied to raw jute fibers. The structure, chemical compositions, morphology and surface properties of the treated materials in each step were systematically characterized. First, delignification of jute fibers could occur at a mild HNO3 condition (30%, 25 °C, 6 h), capable of removing a significant portion of lignin without changing the native cellulose I structure. Subsequently, gas-phase NO2 treatment can oxidize partially delignified jute fibers and produce high concentrations of carboxyl groups (1.31–1.45 mmol/g) on the material surface, comparable to TEMPO-mediated oxidation. The resultant material is effective in removing positively charged contaminants, such as Thallium(I) ions from water (the removal efficiency >80%). The mixed liquid-gas phase nitro-oxidation process (NOP) provides better control of cellulose oxidation for fabrication of water remediation adsorbents from lignocellulose biomass and further reduces the energy and water consumption since there is no requirement for washing the oxidized cellulose after gas-phase NO2 treatment.