Abstract: Cellulose extracted from corncobs, a bulk agricultural waste product, by a solvent at −12 °C, was composited with carbon nanotubes (CNTs) with excellent light absorption properties to construct CNT/cellulose hydrogel composites. Taking advantage of the superior water retention ability and degradability of cellulose hydrogels, and the high-efficiency solar-thermal conversion performance, excellent mechanical properties and biocompatibility of CNTs, CNT/cellulose hydrogel composites are used in water purification by interfacial solar-powered evaporation. The effects of the addition of CNTs on the solar energy absorption, mechanical properties and interfacial solar-thermal water evaporation efficiency of the composites were investigated. With an optimum CNT content of 0.2 wt.%, the composite had an average evaporation rate of ~1.52 kg m⁻² h⁻¹ and a solar-steam conversion efficiency of about 92%. After continuous evaporation in seawater for 8 h, the evaporation rate of the composite remained at about 1.37 kg m⁻² h⁻¹ without salt precipitation, indicating its strong resistance to salt. The quality of the purified water was superior to the WHO and EPA standards for drinking water. When the composite was used in concentrated acid/alkaline aqueous systems, dye wastewater and heavy metal ion polluted water, the evaporation rates remained in the range 1.30-1.40 kg m⁻² h⁻¹, and the solar-steam conversion efficiencies reached 80-86%. The retention rates for both organic pollutants and salt were as high as 99.9%, confirming the evaporation stability of the composite. This work indicates that an evaporator based on the composite has broad application prospects in the fields of seawater desalination and industrial wastewater purification.