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In recent years, facing the problem of improving environmental quality, cellulose and cellulose-based (nano) composites have received great attention as adsorbents. In this work, we report the modification and functionalization of cellulose by nitrogen- and sulfur-containing moieties through a three-steps process; native cellulose is first oxidized by potassium periodate (KIO4) to form dialdehyde cellulose (DAC), which then condenses with aminoguanidine and react with phenyl isothiocyanate to form 4-phenyl guanyl thiosemicarbazide dialdehyde cellulose (DAC@GuTSC). The prepared DAC@GuTSC is characterized by a number of techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), elemental analysis (EA), Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA). The prepared DAC@GuTSC adsorbent was used to remove Cu2+ Hg2+ and Pb2+ from aqueous solution and environmental water samples. The influence of various factors on the adsorption efficiency including pH, initial metal concentration, contact time, adsorbent dosage, temperature, and ions interfering with adsorption was investigated. Under optimal adsorption conditions, the adsorption capacity of Cu2+, Hg2+ and Pb2+ was 50, 94 and 55 mg g−1, respectively. The adsorption process is well described by the Langmuir model, and it was found to follow the pseudo-second-order kinetics model. The spontaneous and endothermic adsorption of Cu2+, Hg2+ and Pb2+ was confirmed by the calculated thermodynamic functions. The prepared DAC@GuTSC composite has been successfully applied to remove Cu2+, Hg2+ and Pb2+ from real water samples with recovery greater than 90% and relative standard deviation (RSD) less than 3%. The reasonable Cu2+, Hg2+ and Pb2+adsorption mechanism on the prepared DAC@GuTSC composite has been elucidated. [ABSTRACT FROM AUTHOR]