SnO₂ nanosheet with N-doped graphene layer coating as a highly sensitive material to formaldehyde gas at ppb level

The tin dioxide nanosheet coated by N-doped graphene (SnO₂@NGO) as a formaldehyde sensing material is prepared by a hydrothermal method. The coating of NGO thin layer on SnO₂ forms a porous coating-nanosheet structure composite with a remarkable large heterogeneous interface. It promotes gas adsorption, carrier transport, and the final sensing performances significantly. The as-prepared SnO₂@NGO shows a linear response to formaldehyde at ppb level concentration. The response value to 500 ppb formaldehyde is 9.8, which is about 7 times that of ethanol, ammonia and acetone. Such excellent selectivity and sensitivity are attributed to the following aspects: (i) active adsorption of oxygen by (110) oriented SnO₂; (ii) selective adsorption of formaldehyde by the porous NGO layer; (iii) catalytic effect on redox reactions between HCHO and O₂⁻ by the pyridinic-N structure; (iv) efficient carrier transport through the spacious heterogeneous interfaces. The coating strategy provides a new insight into designing ultra-sensitive heterogeneous materials.